Os e406_2010 04(Free Fall Lifeboats)

OFFSHORE STANDARD

DET NORSKE VERITAS

DNV-OS-E406

DESIGN OF FREE FALL LIFEBOATS

APRIL 2010

FOREWORDDET NORSKE VERITAS (DNV) is an autonomous and independent foundation with the objectives of safeguarding life, prop-erty and the environment, at sea and onshore. DNV undertakes classification, certification, and other verification and consultancyservices relating to quality of ships, offshore units and installations, and onshore industries worldwide, and carries out researchin relation to these functions.DNV Offshore Codes consist of a three level hierarchy of documents:— Offshore Service Specifications. Provide principles and procedures of DNV classification, certification, verification and con-

sultancy services.— Offshore Standards. Provide technical provisions and acceptance criteria for general use by the offshore industry as well as

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Offshore Service Specifications and Offshore Standards.DNV Offshore Codes are offered within the following areas:A) Qualification, Quality and Safety MethodologyB) Materials TechnologyC) StructuresD) SystemsE) Special FacilitiesF) Pipelines and RisersG) Asset OperationH) Marine OperationsJ) Cleaner EnergyO) Subsea Systems

Amendments and Corrections This document is valid until superseded by a new revision. Minor amendments and corrections will be published in a separatedocument normally updated twice per year (April and October). For a complete listing of the changes, see the “Amendments and Corrections” document located at: http://webshop.dnv.com/global/, under category “Offshore Codes”.The electronic web-versions of the DNV Offshore Codes will be regularly updated to include these amendments and corrections.

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Offshore Standard DNV-OS-E406, April 2010Changes – Page 3

AcknowledgmentsThe development of this Offshore Standard was commissionedby Norsk Hydro and StatoilHydro, who both acted on behalf ofthe Norwegian Oil Industry Association OLF. This support isgratefully acknowledged. Likewise, Prof. S. Chakrabarti,Mr. J. Kalis, TU Delft, FiReCo AS and Marintek are gratefullyacknowledged for their permissions to use proprietary materialfor illustration purposes.

Main changes

— Correction of errors detected since the first issue of thestandard in April 2009.

— Updating to comply with requirements and recommenda-tions in DNV-OS-C501 and DNV-RP-C205.

— Following the detection of a serious error in the require-ment to the material factor for short term loading of com-posites, a total reassessment of the material factorrequirements for composites has been worked out and hasbeen implemented in Sec.6.

— Unintended requirements to secondary means of launch-ing have been removed from Sec.6 A800 and from Sec.11A200 and A700.

— A requirement to account for dynamic amplification in thedesign of release hooks has been added to Sec.6 A800.

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Offshore Standard DNV-OS-E406, April 2010 Page 4 – Changes

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Offshore Standard DNV-OS-E406, April 2010 Contents – Page 5

CONTENTS

Sec. 1 Introduction........................................................... 9

A. General....................................................................................9A 100 General.............................................................................. 9A 200 Objectives ......................................................................... 9A 300 Scope and application ....................................................... 9A 400 Quality assurance.............................................................. 9A 500 Other codes ..................................................................... 10A 600 Equivalence and future developments ............................ 10

B. References ............................................................................10B 100 General............................................................................ 10

C. Definitions ............................................................................11C 100 Verbal forms ................................................................... 11C 200 Terms .............................................................................. 11

D. Abbreviations and Symbols..................................................14D 100 Abbreviations.................................................................. 14D 200 Symbols .......................................................................... 14

Sec. 2 Safety Philosophy and Design Principles.......... 17

A. General..................................................................................17A 100 Objective......................................................................... 17A 200 Application...................................................................... 17

B. Safety Philosophy .................................................................17B 100 General............................................................................ 17B 200 Safety objective............................................................... 17B 300 Systematic review........................................................... 17B 400 Safety class methodology ............................................... 17B 500 Target Safety................................................................... 17

C. Design Principles and Design Conditions ............................18C 100 Methods for structural design ......................................... 18C 200 Aim of the design............................................................ 18C 300 Design conditions ........................................................... 18

D. Limit States...........................................................................18D 100 General............................................................................ 18

E. Design by the Partial Safety Factor Method.........................19E 100 General............................................................................ 19E 200 The partial safety factor format ...................................... 19E 300 Characteristic load effect ................................................ 20E 400 Characteristic resistance ................................................. 21E 500 Load and resistance factors ............................................ 21

F. Design Assisted by Testing ..................................................21F 100 General............................................................................ 21F 200 Full-scale testing and observation of performance of

existing lifeboat structures .............................................. 21

G. Probability-Based Design .....................................................21G 100 Definition ........................................................................ 21G 200 Structural reliability analysis .......................................... 21

Sec. 3 Environmental Conditions................................. 23

A. General..................................................................................23A 100 General............................................................................ 23

B. Wind Conditions...................................................................23B 100 Introduction..................................................................... 23B 200 Wind parameters ............................................................. 23B 300 Wind data........................................................................ 24B 400 Wind modelling .............................................................. 24B 500 Wind speed profiles ........................................................ 25B 600 Turbulence ...................................................................... 25B 700 Wind spectra ................................................................... 25

C. Wave Conditions ..................................................................26C 100 Wave parameters............................................................. 26C 200 Wave data ....................................................................... 26C 300 Wave modelling.............................................................. 27C 400 Wave theories and wave kinematics............................... 28

D. Current ..................................................................................29D 100 Current parameters.......................................................... 29D 200 Current data .................................................................... 29D 300 Current modelling........................................................... 29

E. Water Level ..........................................................................30E 100 Water level parameters ................................................... 30E 200 Water level data .............................................................. 30

F. Other Environmental Conditions..........................................30F 100 Snow and ice accumulation ............................................ 30F 200 Salinity............................................................................ 30F 300 Temperature.................................................................... 30F 400 Air density ...................................................................... 30F 500 Ultraviolet light............................................................... 30

Sec. 4 Loads and Load Effects ..................................... 31

A. General..................................................................................31A 100 General............................................................................ 31

B. Basis for Selection of Characteristic Loads..........................31B 100 General............................................................................ 31B 200 Characteristic loads during launch of lifeboat ................ 32B 300 Characteristic loads during stowage of lifeboat.............. 33

C. Permanent Loads (G)............................................................33C 100 General............................................................................ 33

D. Variable Functional Loads (Q) .............................................33D 100 General............................................................................ 33D 200 Tank pressures ................................................................ 34D 300 Miscellaneous loads........................................................ 34

E. Environmental Loads (E)......................................................34E 100 General............................................................................ 34E 200 Trajectory in air .............................................................. 34E 300 Trajectory through water ................................................ 37E 400 Sailing phase................................................................... 41E 500 Load cases for the ULS................................................... 41E 600 Slamming loads .............................................................. 42E 700 Inertia loads .................................................................... 43E 800 Load distributions ........................................................... 43E 900 Fatigue loads................................................................... 47

F. Accidental Loads (A)............................................................47F 100 General............................................................................ 47

G. Deformation Loads (D).........................................................48G 100 General............................................................................ 48G 200 Temperature loads .......................................................... 48

H. Load Effect Analysis ............................................................48H 100 General............................................................................ 48H 200 Global motion analysis ................................................... 48H 300 Load effects in structures ............................................... 48

I. Stowage Loads......................................................................48I 100 General............................................................................ 48I 200 Snow and ice loads ......................................................... 48

J. Load Factors for Design .......................................................49J 100 Load factors for the ULS, launching .............................. 49J 200 Load factors for the ULS, stowage ................................. 49J 300 Load factor for the ALS.................................................. 49J 400 Load factors for design of hooks and attachments ......... 49

Sec. 5 Materials.............................................................. 50

A. General..................................................................................50A 100 Scope............................................................................... 50A 200 Temperatures for selection of material ........................... 50A 300 Fire.................................................................................. 50A 400 Inspections ...................................................................... 50

B. Structural Categorization ......................................................50B 100 Structural categories ....................................................... 50

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Offshore Standard DNV-OS-E406, April 2010 Page 6 – Contents

B 200 Inspection categories.......................................................51

C. Steel ...................................................................................... 51C 100 General ............................................................................51C 200 Structural steel designations............................................51

D. Aluminium............................................................................ 53D 100 Material designations ......................................................53

E. Composite Materials............................................................. 56E 100 Introduction.....................................................................56E 200 Laminate specification ....................................................56E 300 Laminate strength and stiffness.......................................57E 400 Qualification of material .................................................58E 500 Glass fibres......................................................................58E 600 Carbon reinforcement .....................................................58E 700 Aramid reinforcement .....................................................58E 800 Polyester and vinylester products ...................................59E 900 Production .......................................................................60E 1000 Inspection ........................................................................61

F. Sandwich Materials .............................................................. 61F 100 Introduction.....................................................................61F 200 Sandwich specification ...................................................61F 300 Strength and stiffness ......................................................61F 400 Qualification of material .................................................61F 500 Sandwich core materials .................................................61F 600 Core material in areas exposed to slamming ..................63F 700 Sandwich adhesives ........................................................63F 800 Adhesives ........................................................................64F 900 Production and inspection...............................................65

Sec. 6 Structural Design................................................ 66

A. General Principles................................................................. 66A 100 Application......................................................................66A 200 Phases..............................................................................66A 300 Functional requirements..................................................66A 400 Premises for structural design .........................................66A 500 Structural design principles.............................................66A 600 Design loads ....................................................................67A 700 Structural analysis ...........................................................68A 800 Launching system ..........................................................68A 900 Fire ..................................................................................69A 1000 Ice accretion ....................................................................69

B. Metallic Structures................................................................ 69B 100 General ............................................................................69B 200 Ductility ..........................................................................69B 300 Yield check .....................................................................70B 400 Buckling check ...............................................................70B 500 Flat-plated structures and stiffened panels......................70B 600 Shell structures ................................................................70B 700 Special provisions for plating and stiffeners...................70B 800 Special provisions for web frames, girders and girder

systems ............................................................................71B 900 Welded connections ........................................................72

C. Composite Structures: Single-Skin and Sandwich Constructions ....................................................... 76

C 100 Application .....................................................................76C 200 Design principles.............................................................76C 300 Structural calculations.....................................................77C 400 Laminate rupture .............................................................78C 500 Core shear fracture .........................................................79C 600 Face wrinkling.................................................................79C 700 Fracture of bonded joints ................................................79C 800 Bolted connections ..........................................................79C 900 Long term performance...................................................80C 1000 Material factors ...............................................................80

Sec. 7 Operational Requirements ................................ 81

A. General.................................................................................. 81A 100 General ............................................................................81

B. Mustering and Boarding ....................................................... 81B 100 Muster area .....................................................................81B 200 Boarding .........................................................................81

C. Launch ..................................................................................81C 100 Release function..............................................................81C 200 Rudder.............................................................................81C 300 Start of engine .................................................................81

D. Water Entry and Resurfacing................................................81D 100 General ............................................................................81D 200 Position and headway......................................................82D 300 Stability ...........................................................................82

E. Sailing Phase.........................................................................82E 100 General ............................................................................82E 200 Buoyancy and stability....................................................82E 300 Thrust and rudder ............................................................83E 400 Engine .............................................................................83E 500 Access .............................................................................83E 600 Retrieval of occupants from lifeboat at sea.....................83

F. Miscellaneous .......................................................................84F 100 Operational manual .........................................................84F 200 Training of personnel ......................................................84F 300 Maintenance ....................................................................84

Sec. 8 Occupant Safety and Comfort ......................... 85

A. General..................................................................................85A 100 General ............................................................................85

B. Occupant Safety....................................................................85B 100 General ............................................................................85B 200 Occupant properties .......................................................85B 300 Acceleration measures ....................................................85B 400 Other human load measures............................................86B 500 Characteristic values .......................................................87B 600 Injury classification.........................................................88B 700 Acceptance criteria for occupant acceleration loads.......88B 800 Seats and harnesses ........................................................89B 900 Pre-injured occupants......................................................89

C. Occupant Comfort ................................................................90C 100 General ............................................................................90C 200 Occupant seating ............................................................90C 300 Cabin temperature and fresh air quality .........................90C 400 Lighting ..........................................................................91C 500 Sanitary conditions..........................................................91

D. Miscellaneous .......................................................................91D 100 Fire ..................................................................................91D 200 External colour................................................................91

Sec. 9 Model Scale Testing and Full Scale Testing .... 92

A. General..................................................................................92A 100 Introduction.....................................................................92A 200 General guidance.............................................................92A 300 Extrapolation of test results.............................................92

B. Model Scale Testing .............................................................92B 100 Introduction.....................................................................92B 200 General requirements and simplifications.......................92B 300 Recommended test execution..........................................93B 400 Minimum level of testing................................................95B 500 Correlation and validation...............................................96

C. Full Scale Prototype Testing.................................................96C 100 Introduction.....................................................................96C 200 General requirements and simplifications.......................96C 300 Test execution .................................................................96C 400 Minimum level of prototype testing................................97C 500 Correlation and validation for prototype testing .............97C 600 Fire test............................................................................97C 700 Test of water spray system..............................................98

D. Full Scale Acceptance Testing..............................................98D 100 Introduction.....................................................................98D 200 Minimum level of acceptance testing .............................98D 300 Test of release system .....................................................98D 400 Lifeboat system testing ...................................................98D 500 Manoeuvring tests ...........................................................98

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Offshore Standard DNV-OS-E406, April 2010 Contents – Page 7

Sec. 10 Installation........................................................... 99

A. General..................................................................................99A 100 General............................................................................ 99A 200 Maintenance.................................................................... 99

Sec. 11 Equipment ......................................................... 100

A. General................................................................................100A 100 General.......................................................................... 100A 200 Launching and recovery appliances.............................. 100A 300 Primary means of launching ......................................... 100A 400 Release mechanism for the primary means of

launching....................................................................... 100A 500 Means of launch testing by simulation ......................... 100A 600 Secondary means of launching ..................................... 100A 700 Release mechanism for the secondary means of

launching....................................................................... 101A 800 Means of retrieval ......................................................... 101A 900 Fire protection systems ................................................. 101A 1000 Water spray system....................................................... 101A 1100 Engine ........................................................................... 101A 1200 Fuel tank ....................................................................... 101A 1300 Air intake ...................................................................... 101A 1400 Electrical equipment ..................................................... 101A 1500 Manoeuvring positions and instrument panel............... 102A 1600 Maintenance of equipment............................................ 102A 1700 Miscellaneous ............................................................... 102

Sec. 12 Qualification of New Lifeboat Concepts......... 104

A. General................................................................................104A 100 General.......................................................................... 104A 200 System analysis............................................................. 104A 300 Methodology................................................................. 104A 400 Design processes........................................................... 104

B. Qualification Procedure......................................................106B 100 General.......................................................................... 106

C. Methods for System Analysis.............................................106C 100 General.......................................................................... 106C 200 Hazard identification analysis (HAZID)....................... 106C 300 Hazard and operability study (HAZOP) ....................... 106C 400 Failure mode, effects and criticality analysis

(FMEA/FMECA).......................................................... 107C 500 Fault tree analysis ......................................................... 107C 600 Quantitative risk analysis (QRA).................................. 108C 700 Reliability, availability and maintainability analysis

(RAM)........................................................................... 109

D. Application of System Analysis to Free Fall Lifeboats......110D 100 General.......................................................................... 110D 200 Areas of concern ........................................................... 110

App. A Interpretation of Probability Distribution and Characteristic Value from Model Tests.................. 115

A. General................................................................................115A 100 General.......................................................................... 115A 200 Methodology................................................................. 115A 300 Example ........................................................................ 116A 400 Commentary.................................................................. 116

B. Miscellaneous .....................................................................118B 100 Long-term distribution of metocean parameters........... 118B 200 Fitting of parametric distribution functions to

empirical distributions .................................................. 118

App. B Manufacturing of FRP Structures .................. 119

A. Introduction ........................................................................119A 100 General.......................................................................... 119

B. Storage ................................................................................119B 100 General.......................................................................... 119

C. Manufacturing Premises and Conditions............................119C 100 Manufacturing premises ............................................... 119C 200 Manufacturing conditions............................................. 119

D. Production Procedures and Workmanship..........................120D 100 Production procedures .................................................. 120D 200 Workmanship................................................................ 120

E. Manual Lamination.............................................................120E 100 General.......................................................................... 120

F. Vacuum Assisted Resin Transfer Moulding (VARTM) and Vacuum-Bagging................................................................121

F 100 General.......................................................................... 121

G. Curing .................................................................................121G 100 General.......................................................................... 121

H. Secondary Bonding.............................................................121H 100 General.......................................................................... 121

I. Adhesive Bonding ..............................................................121I 100 General.......................................................................... 121

J. Quality Assurance...............................................................121J 100 General.......................................................................... 121J 200 Quality control .............................................................. 121

App. C Structural Analysis and Calculations by the Finite Element Method ........................................ 122

A. Introduction.........................................................................122A 100 General.......................................................................... 122

B. Types of Analysis ...............................................................122B 100 General.......................................................................... 122B 200 Static analysis ............................................................... 122B 300 Frequency analysis........................................................ 122B 400 Dynamic analysis.......................................................... 122B 500 Stability/buckling analysis............................................ 122B 600 Thermal analysis ........................................................... 123B 700 Global and local analysis .............................................. 123B 800 Material levels – composite/sandwich materials .......... 124B 900 Nonlinear analysis ........................................................ 124

C. Modelling............................................................................124C 100 General.......................................................................... 124C 200 Input data ...................................................................... 124C 300 Model idealization ........................................................ 124C 400 Coordinate systems....................................................... 125C 500 Material models and properties .................................... 125C 600 Element types and elements.......................................... 126C 700 Combinations................................................................ 126C 800 Element size and distribution of elements .................... 127C 900 Element quality............................................................. 128C 1000 Boundary conditions..................................................... 129C 1100 Types of restraints......................................................... 129C 1200 Symmetry and antimetry............................................... 129C 1300 Loads............................................................................. 130

D. Documentation....................................................................130D 100 Model............................................................................ 130D 200 Geometry control .......................................................... 130D 300 Mass – volume – centre of gravity ............................... 130D 400 Material......................................................................... 130D 500 Element type ................................................................. 130D 600 Local coordinate system ............................................... 130D 700 Loads and boundary conditions .................................... 130D 800 Reactions....................................................................... 130D 900 Mesh refinement ........................................................... 130D 1000 Results........................................................................... 130

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Offshore Standard DNV-OS-E406, April 2010 Page 8 – Contents

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Offshore Standard DNV-OS-E406, April 2010 Sec.1 – Page 9

SECTION 1INTRODUCTION

A. General

A 100 General101 This Offshore Standard provides principles, technicalrequirements and guidance for design, construction, stowageand operation of free fall lifeboats for use for emergency evac-uation from offshore structures.102 The standard has been written for general world-wideapplication with the limitation that free fall lifeboats for useunder arctic conditions are not covered. National and govern-mental regulations may include requirements in excess of theprovisions given by this standard. 103 The standard shall be used for design of free fall life-boats for use from offshore structures and for design of skidsand other parts of the arrangements required to launch the life-boats from these structures. The standard can be used as astand-alone document.104 The standard shall be used for design of free fall life-boats with a specified design lifetime.105 Lifeboats designed according to this standard can be usedin an emergency event for evacuation of personnel from offshorestructures, which have been designed to high safety class.106 Lifeboats designed according to this standard are meantto be used for only one emergency evacuation at the most.Reuse of a lifeboat which has been used for an evacuationrequires requalification of the lifeboat. The requalification canbe carried out based on this standard.107 Lifeboats designed according to this standard can alsobe used for emergency evacuation from offshore structureswhich do not meet the requirements to design to high safetyclass, such as jack-up platforms and other rigs used in tempo-rary phases during exploration and drilling. However, for useof lifeboats for emergency evacuation of personnel from suchstructures, it is a prerequisite that personnel on the offshorestructure in question are evacuated from the structure when-ever there is a weather forecast for severe storms. Which levelof forecast storm intensity shall initiate such a precautiousevacuation of personnel shall be established on a case-to-casebasis, depending on a site-specific risk evaluation.

A 200 Objectives201 The standard specifies general principles, requirementsand guidelines for site-specific design of free fall lifeboats andtheir launching appliances such as skids, davits and releaseunits. In this respect, the standard has three main areas offocus, viz.

— structural safety, i.e. safety of hull and canopy againststructural failure

— human safety, i.e. limitation of accelerations of the humanbody

— headway, i.e. sufficient forward speed after launch.

Guidance note:Site-specific design implies design for the particular conditionsprevailing at the location of the offshore facility on which thelifeboat is to be installed and used. These conditions include, butare not limited to, the site-specific metocean conditions as wellas the drop height implied by the geometry of the host facility andthe physical location of the lifeboat on the facility.

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202 The objectives of this standard are to:

— provide an internationally acceptable standard of safetyfor free fall lifeboats by defining minimum requirementsfor the design, materials, fabrication, testing, operation,repair and requalification of free fall lifeboats

— specify requirements to lifeboat stations and launchingappliances to the extent necessary for the design of freefall lifeboats

— serve as a technical reference document in contractualmatters between purchaser and contractor

— serve as a guideline for designers, purchasers, contractorsand regulators.

A 300 Scope and application301 This standard applies to free fall lifeboat systems andtheir launching appliances. 302 The standard applies to the design, materials, fabrica-tion, testing, operation, repair and requalification of free falllifeboats and their launching appliances.303 This standard is not applicable to design of an evacua-tion system as a whole. This limitation reflects that free falllifeboats and their launching appliances constitute only partsof an evacuation system. Lifeboats and their launching appli-ances must be compatible with and have interface to escaperoutes, muster stations, communication systems, power supplysystems, lighting and other features of the host facility whichare not covered by this standard.304 This standard is not applicable to design of davit-launched lifeboats.

Guidance note:This limitation reflects the difference between free fall lifeboatsand davit-launched lifeboats, e.g. when it comes to loads andmodes of operation.


305 This standard is not applicable to design of lifeboats onhost facilities located in waters where sea ice or sea floes occur.

A 400 Quality assurance401 The safety format used in this standard requires thatgross errors, such as human errors and organizational errors,shall be handled by requirements to organization of the work,competence of the personnel performing the work, verificationof the design, and quality assurance during all relevant phases. 402 For the purpose of this standard, it is assumed that theowner of a lifeboat or a lifeboat system has established a qual-ity objective. In all quality-related aspects, the owner shallseek to achieve the quality level of products and servicesintended by the quality objective. Further, the owner shall pro-vide assurance that intended quality is being, or will be,achieved.403 A quality system shall be applied to facilitate compli-ance with the requirements of this standard.

Guidance note:ISO 9000 provides guidance on the selection and use of qualitysystems.


404 It is a prerequisite for design of free fall lifeboats accord-ing to this standard that an efficient quality assurance system isin place, covering all critical production processes involved inthe manufacturing of a lifeboat.

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Offshore Standard DNV-OS-E406, April 2010 Page 10 – Sec.1

A 500 Other codes501 In case of conflict between requirements of this standardand a reference document, the requirements of this standardshall prevail.502 Wherever reference is made to other codes, the latestrevision of the code in question shall be applied, unless other-wise specified.503 When code checks are performed according to othercodes than DNV codes, the partial safety factors as specified inthe codes in question shall be used.504 The provision for using non-DNV codes is that the samesafety level as the one resulting for designs according to thisstandard is achieved.

A 600 Equivalence and future developments601 This code specifies requirements to the design of freefall lifeboats intended to ensure a safety level that is deemedacceptable for lifeboats on offshore installations. Some ofthese requirements imply certain constraints on lifeboatdesigns that reflect the current practice in the industry andestablished principles of design and construction of free falllifeboats. Alternative designs and arrangements that deviatefrom these requirements may be accepted provided that it isdocumented by a sound engineering analysis that the level ofsafety is at least as high as that implied by the requirements ofthis code. Basic premises for such analyses should be that theavailability on demand of the lifeboat exceeds 99% and that allcost effective risk control options have been implemented.

Guidance note:A recommended method for identifying risk control options anddocumenting the safety of alternative designs and arrangementscan be found in DNV-RP-A203.Risk acceptance criteria may be taken according to IMO MSC/Circ.1023−MEPC/Circ.392 “Guidelines for Formal SafetyAssessment”. An updated consolidated version may be found inMSC83/INF.2.


602 The specific requirements of this standard reflect whatwas deemed cost effective means of managing the risks asso-ciated with lifeboats on offshore installations at the time ofissue of this standard. Technology developments after thatpoint in time may provide new means of cost effective riskreduction. Should relevant cost benefit assessment show thatuse of such new technology would provide cost effective riskreduction, such new technology shall be implemented on newlifeboats where it fits.

B. References

B 100 General101 The DNV documents listed in Tables B1 and B2 and therecognized codes and standards in Table B3 are referred to inthis standard.102 The latest valid revision of each of the DNV referencedocuments in Tables B1 and B2 applies.

Table B1 DNV Offshore Standards, Rules for Classification and Rules for Certification Reference TitleDNV-OS-B101 Metallic MaterialsDNV-OS-C101 Design of Offshore Steel Structures, General

(LRFD Method)DNV-OS-C401 Fabrication and Testing of Offshore StructuresDNV-OS-C501 Composite Components

DNV-OS-D301 Fire ProtectionStandard for Cer-tification No. 2.20

Lifeboats and Rescue Boats

Standard for Cer-tification No. 2.22

Lifting Appliances

Rules for Classification of High Speed, Light Craft and Naval Surface Craft

Table B2 DNV Recommended Practices and Classification NotesReference TitleDNV-RP-A203 Qualification Procedures for New Technology

DNV-RP-C201 Buckling Strength of Plated StructuresDNV-RP-C202 Buckling Strength of Shells

DNV-RP-C203 Fatigue Strength Analysis of Offshore Steel Structures

DNV-RP-C205 Environmental Conditions and Environmental Loads

DNV-RP-C206 Fatigue Methodology of Offshore Ships

DNV-RP-H101 Risk Management in Marine and Subsea Operations

Classification Notes 30.1

Buckling Strength Analysis


Structural Reliability Analysis of Marine Structures


Fatigue Assessments of Ship Structures

Table B3 Other referencesReference TitleAISC LRFD Manual of Steel ConstructionAPI RP 2A LRFD Planning, Designing, and Constructing Fixed

Offshore Platforms – Load and Resistance Factor Design

ASTM C297 Standard Test Method for Flatwise Tensile Strength of Sandwich Constructions

ASTM D1002 Standard Test Method for Apparent Shear Strength of Single-Lap-Joint Adhesively Bonded Metal Specimens by Tension Loading (Metal-to-Metal)

ASTM D3163 Standard Test Method for Determining Strength of Adhesively Bonded Rigid Plastic Lap-Shear Joints in Shear by Tension Loading

ASTM D3528 Standard Test Method for Strength Properties of Double Lap Shear Adhesive Joints by Ten-sion Loading

BS 7910 Guide on methods for assessing the accepta-bility of flaws in fusion welded structures

EN 1993-1-1 Eurocode 3: Design of Steel Structures, Part 1-1: General Rules and Rules for Buildings

EN 1999-1-1 Eurocode 9: Design of Aluminium Structures, Part 1-1: General – Common Rules

EN 10204 Metallic products – types of inspection docu-ments

EN 10025-2 Hot rolled products of structural steel. Techni-cal delivery conditions for non-alloy struc-tural steels.

EN 10025-3 Hot rolled products of structural steels. Tech-nical delivery conditions for normalized/nor-malized rolled weldable fine grain structural steels.

Table B1 DNV Offshore Standards, Rules for Classification and Rules for Certification (Continued) Reference Title

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C. DefinitionsC 100 Verbal forms101 Shall: Indicates a mandatory requirement to be followedfor fulfilment or compliance with the present standard. Devia-tions are not permitted unless formally and rigorously justified,and accepted by all relevant contracting parties.102 Should: Indicates a recommendation that a certaincourse of action is preferred or is particularly suitable. Alterna-tive courses of action are allowable under the standard where

agreed between contracting parties, but shall be justified anddocumented.103 May: Indicates a permission, or an option, which is per-mitted as part of conformance with the standard.104 Can: Requirements with can are conditional and indi-cate a possibility to the user of the standard.105 Agreement, or by agreement: Unless otherwise indi-cated, agreed in writing between contractor and purchaser.

C 200 Terms201 Accidental Limit States (ALS): Excessive structuraldamage as a consequence of accidents, such as collisions,grounding, explosion and fire, which affect the safety of thestructure, environment and personnel. Design against the ALSshall ensure that the structure resists accidental loads andmaintain integrity and performance of the structure due to localdamage or flooding.202 ALARP: As low as reasonably practicable; notation usedfor risk.203 Cathodic protection: A technique to prevent corrosionof a steel surface by making the surface to be the cathode of anelectrochemical cell.204 Characteristic load: The reference value of a load to beused in the determination of the design load. The characteristicload is normally defined as a specific quantile in the upper tailof the distribution function for load. The quantile is specifiedby specifying the corresponding probability of exceedance inthe distribution; for example, the 99% quantile is specified byhaving 1% (= 10–2) probability of exceedance. It is importantnot to confuse this probability of exceedance with any failureprobability.205 Characteristic load effect: The reference value of a loadeffect to be used in the determination of the design load effect.The characteristic load effect is normally defined as a specificquantile in the upper tail of the distribution function for loadeffect.206 Characteristic material strength: The nominal value ofa material strength to be used in the determination of the designstrength. The characteristic material strength is normallydefined as a specific quantile in the lower tail of the distribu-tion function for material strength.207 Characteristic resistance: The reference value of astructural strength to be used in the determination of the designresistance. The characteristic resistance is normally defined asa specific quantile in the lower tail of the distribution functionfor resistance. 208 Characteristic value: A representative value of a loadvariable or a resistance variable. For a load variable, it is a highbut measurable value with a prescribed probability of not beingunfavourably exceeded during some reference period. For aresistance variable it is a low but measurable value with a pre-scribed probability of being favourably exceeded. 209 Classification Notes: The classification notes coverproven technology and solutions which are found to representgood practice by DNV, and which represent one alternative forsatisfying the requirements stipulated in the DNV Rules orother codes and standards cited by DNV. The classificationnotes will in the same manner be applicable for fulfilling therequirements in the DNV Offshore Standards.210 Coating: Metallic, inorganic or organic material appliedto material surfaces for prevention of corrosion or other degra-dation or both.211 Contractor: A party contractually appointed by the pur-chaser to fulfil all, or any of, the activities associated with fab-rication and testing.212 Corrosion allowance: Extra steel thickness that may rustaway during the design lifetime.

ENV 1090-1 Execution of steel structures ¾ Part 1: General rules and rules for buildings

ENV 1090-5 Execution of steel structures – Part 5: Supple-mentary rules for bridges

IEC 60079 Explosive atmospheresIEC 60529 Degrees of protection provided by enclosures

(IP code)IEC 60812 Analysis techniques for system reliability –

Procedure for Failure Mode and Effects Anal-ysis (FMEA)

IEC 61508-1 Functional Safety of Electrical/Electronic/Programmable Electronic Safety-Related Sys-tems – Part 1: General Requirements

IEC 61882 Hazard and operability studies (HAZOP stud-ies) – Application Guide

IMO MSC83/Inf.2 Formal Safety AssessmentIMO MSC/Circ.1023−MEPC/Circ.392

Guidelines for Formal Safety Assessment

IMO MSC1206 Measures to prevent accidents with lifeboatsIMO Resolution MSC.48 (66)

International Life-Saving Appliance Code

IMO Resolution MSC.81(70)

Revised Recommendation on Testing of Life-Saving Appliances

ISO 1922-81 Cellular Plastics – Determination of Shear Strength of Rigid Materials

ISO 9000 Quality management systems – Fundamentals and vocabulary

ISO 12100-1 Safety of machinery – Basic concepts, general principles for design – Part 1: Basic terminology, methodology

ISO 12100-2 Safety of machinery – Basic concepts, general principles for design – Part 2: Technical prin-ciples

ISO 14119 Safety of machinery – Interlocking devices associated with guards – Principles for design and selection

ISO 17776 Guidelines on tools and techniques for hazard identification and risk assessment

MIL-STD-1629 A Military Standards: Procedures for performing a Failure Mode, Effects, and Criticality Analysis

NAFEMS Benchmark Tests (several volumes)NORSOK N-004 Design of Steel StructuresNORSOK R-002 Lifting EquipmentNORSOK S-001 Technical SafetyNORSOK S-002 Working EnvironmentOLF Guidelines No. 2

Guidelines for Safety and Emergency Train-ing

OLF LBP2-R001 Minimal Strength Test Procedure for Free Fall Lifeboat Seats

SAE J211 Recommended Practice: Instrumentation for impact tests

Table B3 Other references (Continued)Reference Title

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213 Current: A flow of water past a fixed point and usuallyrepresented by a velocity and a direction.214 Design brief: An agreed document where owners’requirements in excess of this standard should be given.215 Design life, design lifetime: The period of time overwhich the lifeboat is designed to provide at least an acceptableminimum level of safety, i.e. the period of time over which thelifeboat is designed to meet the requirements set forth in thestandard.216 Design temperature: The design temperature for a unitis the reference temperature to be used for assessment of areaswhere the unit can be transported, installed, stored and oper-ated. The design temperature shall be lower than or equal to thelowest daily mean temperature in air for the relevant areas.217 Design value: The value to be used in the deterministicdesign procedure, i.e. characteristic value modified by theresistance factor or the load factor, whichever is applicable.218 Driving voltage: The difference between closed circuitanode potential and protection potential.219 Effective clearance: A horizontal distance, whichreflects the ability of the free fall lifeboat to move away fromthe facility after a free fall launch without using its engine.220 Empty lifeboat: Lifeboat with crew of three persons.221 Environmental state: Short term condition of typically10 minutes, 1 hour or 3 hours duration during which the inten-sities of environmental processes such as wave and wind proc-esses can be assumed to be constant, i.e. the processesthemselves are stationary.222 Evacuation system: A system for evacuation from a hostfacility by means of a free fall lifeboat.223 Expected loads and response history: Expected load andresponse history for a specified time period, taking intoaccount the number of load cycles and the resulting load levelsand response for each cycle.224 Failure probability: Probability of failure or probabilityof malperformance, e.g. probability of load exceeding capac-ity.225 Fatigue: Degradation of the material caused by cyclicloading.226 Fatigue critical: Structure with predicted fatigue lifenear the design fatigue life.227 Fatigue Limit States (FLS): Fatigue crack growth andassociated failure of structural details due to stress concentra-tion and damage accumulation under the action of repeatedloading. 228 Free fall acceleration: Rate of change of velocity expe-rienced by the occupants during the launch of a free fall life-boat.229 Free fall height: The launch height, measured verticallyfrom the mean water level (MWL) to the lowest point on thelifeboat when the lifeboat is in the launch position on a skid orin a davit on the host facility.230 Free fall lifeboat: Lifeboat, which is launched by a freefall from some height above the sea level. Free fall lifeboats areusually used for emergency evacuation of personnel from off-shore facilities and from ships.231 Guidance note: Information in the standard in order toenhance the understanding of the requirements.232 Highest astronomical tide: Level of high tide when allharmonic components causing the tide are in phase.233 Hindcast: A method using registered meteorologicaldata to reproduce environmental parameters. Mostly used forreproduction of wave data and wave parameters.234 Host facility: Fixed or floating offshore structure on

which the lifeboat is permanently located and for which itserves as a means for emergency evacuation.235 Hybrid III: Standard crash test dummy used for frontalimpact testing. The Hybrid III median male (50-percentilemale) is 168 cm tall and has a mass of 77 kg. 236 Independent organizations: Accredited or nationallyapproved certification bodies.237 Inspection: Activities such as measuring, examination,testing, gauging one or more characteristics of an object orservice and comparing the results with specified requirementsto determine conformity.238 Launching ramp angle: The angle between the horizon-tal and the launch rail of the lifeboat in its launching positionwith the offshore facility, on which it is used, on even keel.239 Launching ramp length: The distance between the sternof the lifeboat and the lower end of the launching ramp.240 Lifeboat system: A structural system consisting of a life-boat and its supports in storage and use, including release unitand skids or davits for launching. 241 Light waterline: The waterline of a vessel without cargo.242 Limit State: A state beyond which a structure or struc-tural component ceases to fulfil its intended function. The fol-lowing categories of limit states are of relevance for structures:ULS = ultimate limit state; FLS = fatigue limit state;ALS = accidental limit state; SLS = serviceability limit state.243 List: Sideways tilt, inclination, deviation from the verti-cal.244 Load effect: Effect of a single design load or combina-tion of loads on the equipment or system, such as stress, strain,deformation, displacement, motion, etc.245 Lowest astronomical tide (LAT): Level of low tide whenall harmonic components causing the tide are in phase.246 Lowest mean daily temperature: The lowest value, overthe year, of the mean daily temperature for the area in question.For seasonally restricted service the lowest value within thetime of operation applies.247 Lowest waterline: Typical light ballast waterline forships, transit waterline or inspection waterline for other typesof units. 248 Mean daily average temperature: The long-term meanvalue of the daily average temperature for a specific calendarday.

— Mean: Statistical mean based on a number of years ofobservations.

— Average: Average during one day and night (24 hours).

249 Mean: Statistical mean over observation period.250 Mean water level (MWL): Mean still water level,defined as mean level between highest astronomical tide andlowest astronomical tide. 251 Mean zero-upcrossing period: Average period betweentwo consecutive zero-upcrossings of ocean waves in a seastate.252 Means of launch testing by simulation: A system fortesting the release mechanism of the primary means of launch-ing without free fall.253 Means of retrieval: A lifting appliance designed forretrieval of the lifeboat from sea to its stowed position on thehost facility.254 Metocean: Abbreviation of meteorological and oceano-graphic.255 Nondestructive testing (NDT): Structural tests andinspection of welds by visual inspection, radiographic testing,ultrasonic testing, magnetic particle testing, penetrant testing

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and other nondestructive methods for revealing defects andirregularities.256 Offshore Standard: The DNV Offshore Standards aredocuments which presents the principles and technical require-ments for design of offshore structures. The standards areoffered as DNV’s interpretation of engineering practice forgeneral use by the offshore industry for achieving safe struc-tures.257 Omnidirectional: Wind or waves acting in all directions.258 Partial Safety Factor Method: Method for design whereuncertainties in loads are represented with a load factor anduncertainties in strengths are represented with a material fac-tor.259 Pilot: The person designated to steer the lifeboat, alsoreferred to as helmsman.260 Potential: The voltage between a submerged metal sur-face and a reference electrode.261 Primary means of launching: The main lifeboat launch-ing system, normally based on gravity free fall or skiddingcombined with free fall.262 Purchaser: The owner or another party acting on hisbehalf, who is responsible for procuring materials, componentsor services intended for the design, construction or modifica-tion of a structure.263 Qualification: Confirmation by examination and provi-sion of evidence that a piece of technology meets the specifiedrequirements for the intended use.264 Recommended Practice (RP): The recommended prac-tice publications cover proven technology and solutions whichhave been found by DNV to represent good practice, andwhich represent one alternative for satisfy the requirementsstipulated in the DNV Offshore Standards or other codes andstandards cited by DNV.265 Redundancy: The ability of a component or system tomaintain or restore its function when a failure of a member orconnection has occurred. Redundancy can be achieved forinstance by strengthening or introducing alternative load paths.266 Reference electrode: Electrode with stable open-circuitpotential used as reference for potential measurements.267 Refraction: Process by which wave energy is redistrib-uted as a result of changes in the wave propagation velocitycaused by variations in the water depth.268 Reliability: The ability of a component or a system toperform its required function without failure during a specifiedtime interval.269 Requalification: Term used for evaluation of the fitnessof a structure following an event which has exposed the struc-ture to significant loading, to make sure that all assumptionsmade in the original design of the structure are still valid andhave not suffered from the loading experienced during theevent. An example is the requalification of a lifeboat, origi-nally designed according to this standard, after it has been usedfor an emergency evacuation. The requalification then impliesa verification that the lifeboat after the emergency evacuationstill fulfils the requirements of this standard.270 Residual currents: All other components of a currentthan tidal current.271 RID3D: Crash test dummy. Originally a rear impactdummy (RID) used to evaluate the risk of whiplash injuries incar crashes. Its predecessor RID2 has been transformed to awhiplash dummy for rear, frontal and oblique whiplash evalu-ations, hence denoted RID3D. 272 Risk: The qualitative or quantitative likelihood of anaccidental or unplanned event occurring considered in con-junction with the potential consequences of such a failure. Inquantitative terms, risk is the quantified probability of a

defined failure mode times its quantified consequence.273 Secondary means of launching: An alternative lifeboatlaunching system, normally based on gravity lowering orpower lowering by a lifting appliance.274 Service temperature: The service temperature is a refer-ence temperature for various structural parts of the lifeboat,used as a criterion for material selection, such as selection ofsteel grades.275 Serviceability Limit States (SLS): Disruption of normaloperations due to deterioration or loss of routine functionality.The SLS imply deformations in excess of tolerance withoutexceeding the load-carrying capacity, i.e., they correspond totolerance criteria applicable to normal use or durability. Unac-ceptable deformations and excessive vibrations are typicalexamples of the SLS.276 Shakedown: A linear elastic structural behaviour isestablished after yielding of the material has occurred.277 Slamming load: Impact load with high pressure peaksduring impact between a body and water.278 Specified Minimum Yield Strength (SMYS): The mini-mum yield strength prescribed by the specification or standardunder which the material is purchased.279 Specified value: Minimum or maximum value duringthe period considered. This value may take into account oper-ational requirements, limitations and measures taken such thatthe required safety level is obtained.280 Splash zone: The external region of a unit which is mostfrequently exposed to wave action.281 Submerged zone: The part of a unit which is below thesplash zone, including buried parts.282 Survival condition: A condition during which a unit maybe subjected to the most severe environmental loadings forwhich the unit is designed. Drilling or similar operations mayhave been discontinued due to the severity of the environmen-tal loadings. The unit may be either afloat or supported on thesea bed, as applicable.283 Target safety level: A nominal acceptable probability ofstructural failure.284 Temporary conditions: An operational condition thatmay be a design condition, for example the mating, transit orinstallation phases.285 Tensile strength: Minimum stress level where strainhardening is at maximum or at rupture.286 Tidal range: Distance between highest and lowest astro-nomical tide.287 Tide: Regular and predictable movements of the seagenerated by astronomical forces.288 Transit conditions: All unit movements from one geo-graphical location to another.289 Trim: Adjustment of the angle of the lifeboat to waterwhen it is in the launch position. Also used as a term todescribe the angle or position of a floating host facility withrespect to the horizontal.290 Ultimate Limit States (ULS): Collapse of all or part ofstructure due to loss of structural stiffness or exceedance ofload-carrying capacity. Overturning, capsizing, yielding andbuckling are typical examples of the ULS.291 Unidirectional: Wind and/or waves acting in one singledirection.292 Verification: Examination to confirm that an activity, aproduct or a service is in accordance with specified require-ments.293 Water-entry angle: The angle between the horizontaland the launch rail of the lifeboat when it first enters the water.

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D. Abbreviations and SymbolsD 100 Abbreviations101 Abbreviations as shown in Table D1 are used in thisstandard.

D 200 Symbols201 Latin characters

Table D1 AbbreviationsAbbreviation In fullAIS Abbreviated Injury ScaleALARP As Low As Reasonably PracticableALS Accidental Limit StateAPI American Petroleum InstituteBEM Boundary Element MethodBS British Standard (issued by British

Standard Institute)CAR Combined Acceleration RatioCFD Computational Fluid DynamicsCN Classification NotesCOG Centre Of GravityCSM Chopped Strand MatCTOD Crack Tip Opening DisplacementDB Double Bias fibre arrangementDBL Double Bias Longitudinal fibre arrangementDCPD DicyclopentadieneDDF Deep Draught FloatersDFF Design Fatigue FactorDNV Det Norske VeritasDOF Degree Of FreedomEHS Extra High StrengthFAT Full-scale Acceptance TestFEA Finite Element AnalysisFEM Finite Element MethodFLS Fatigue Limit StateFORM First Order Reliability MethodFPF First Ply FailureFPSO Floating Production, Storage and Offloading vesselFRP Fibre Reinforced PlasticsGBS Gravity Based StructureGRP Glass fibre Reinforced PolyesterHAT Highest Astronomical TideHAZ Heat-Affected ZoneHIC Head Injury CriterionHISC Hydrogen Induced Stress CrackingHLL Human Load LevelHS High Strength IMO International Maritime OrganizationIP Ingress ProtectionISO International Organization for StandardizationLAT Lowest Astronomical TideLED Light Emitting DiodeLHS Left Hand SideLSA Life Saving AppliancesMTTF Mean Time To FailureMTTR Mean Time To RepairMWL Mean Water LevelNACE National Association of Corrosion EngineersNDT Nondestructive Testing NS Normal StrengthODE Ordinary Differential EquationPER Project External ReviewPPM Parts Per Million

QRA Quantitative Risk AnalysisRAM Reliability, Availability and Maintainability analysisRHS Rectangular Hollow SectionRHS Right Hand SideRP Recommended PracticeRPM Revolutions Per MinuteSAE Society of Automotive EngineersSCE Saturated Calomel ElectrodeSCF Stress Concentration FactorSLS Serviceability Limit StateSMYS Specified Minimum Yield StressSOLAS Safety Of Life At SeaSPH Smoothed Particle HydrodynamicsSRB Sulphate Reducing BacteriaSWL Still Water LevelTLP Tension Leg PlatformULS Ultimate Limit StateVARTM Vacuum Assisted Resin Transfer MouldingVHF Very High FrequencyVOF Volume Of FluidWF Wave FrequencyWR Woven RovingWSD Working Stress Design

a0 connection areaas acceleration of launch skidb full breadth of plate flangebe effective plate flange widthc detail shape factorc wave celerityd bolt diameterd water depthf frequencyf load distribution factorfn natural frequency of structurefr strength ratiofu nominal lowest ultimate tensile strengthfub ultimate tensile strength of boltfw strength ratiofy specified minimum yield stressg acceleration of gravityh heighth water depthh0 reference depth for wind-generated currenthD drop height, launch heighthL drop height, launch heighthpc vertical distance from the load point to the position of

max filling heightk wave numberka correction factor for aspect ratio of plate fieldkm bending moment factorkpp fixation parameter for platekps fixation parameter for stiffenerskr correction factor for curvature perpendicular to the

stiffeners

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202 Greek characters

ks hole clearance factorkt shear force factorl stiffener spanlo distance between points of zero bending momentsmean arithmetic mean of test resultsmsv manufacturer’s specified minimum valuemsmv manufacturer’s specified valuen numberp pressurepd design pressurep0 valve opening pressurer root facerc radius of curvatures distance between stiffenerssdev standard deviation of test resultst thickness of laminatet0 net thickness of platetk corrosion additiontw throat thicknessvtide0 tidal current at still water levelvwind0 wind-driven current at still water levelz vertical distance from still water level, positive

upwardsz0 terrain roughness parameterA scale parameter in logarithmic wind speed profileAC Charnock’s constantAC wave crest heightAT wave trough depthAW wave amplitudeC weld factorCD drag coefficientCM mass coefficientCS slamming coefficientCe factor for effective plate flangeD deformation loadE modulus of elasticityE environmental loadE luminous emittanceE[⋅] mean valueF cumulative distribution functionF force, loadFd design loadFk characteristic loadFpd design preloading force in boltG permanent loadH wave heightH reference height for wind speedHC wave crest heightHD drop height, launch heightHmax maximum wave heightH0 wave height in deep watersHS significant wave heightL length of lifeboatLgo sliding distanceLra length of guide railM structural mass of lifeboat and occupants

M momentMp plastic moment resistanceMy elastic moment resistanceN fatigue life, i.e. number of cycles to failureNp number of supported stiffeners on the girder spanNs number of stiffeners between considered section

and nearest supportP loadPpd average design point load from stiffenersQ variable functional loadR radiusR resistanceR ratio between minimum stress and maximum stressRd design resistanceRk characteristic resistanceS girder span as if simply supportedS power spectral densitySA response spectral accelerationSD response spectral displacementSV response spectral velocitySd design load effectSk characteristic load effectSx x-projected exposed wind area of the lifeboatT wave periodTP peak periodTR return periodTS sea state durationTZ zero-upcrossing periodU10 10-minute mean wind speedU10,hub 10-minute mean wind speed at hub heightW steel with improved weldabilityZ steel grade with proven through thickness properties

with respect to lamellar tearing.

α angle between the stiffener web plane and the plane perpendicular to the plating

α exponent in power-law model for wind speed profileα coefficient in representation of wave loads according

to diffraction theoryβw correlation factorδ deflectionΔσ stress rangeφ resistance factorγ spectral peak enhancement factorγf load factorγM material factorγMw material factor for weldsη ratio of fatigue utilization, cumulative fatigue damage

ratioκ Von Karman’s constantλ wavelengthλ reduced slendernessθ rotation angleμ friction coefficientν Poisson’s ratioν spectral width parameter

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ρ densityσd design stressσe elastic buckling stressσfw characteristic yield stress of weld depositσjd equivalent design stress for global in-plane mem-

brane stressσpd1 design bending stressσpd2 design bending stressσU standard deviation of wind speedτd design shear stressω angular frequencyξ coefficient in representation of wave loads according

to diffraction theoryΦ cumulative distribution functionΘ launch skid angle.

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SECTION 2SAFETY PHILOSOPHY AND DESIGN PRINCIPLES

A. General

A 100 Objective101 The purpose of this section is to present the safety phi-losophy and the corresponding design principles applied in thisstandard.

A 200 Application201 This section applies to all free fall lifeboats which are tobe built in accordance with this standard.

B. Safety Philosophy

B 100 General101 The integrity of a lifeboat or lifeboat system constructedto this standard is ensured through a safety philosophy inte-grating different parts as illustrated in Figure 1.

Figure 1 Safety philosophy structure

B 200 Safety objective201 An overall safety objective shall be established, plannedand implemented, covering all phases from conceptual devel-opment until decommissioning.

Guidance note:Most manufacturers, owners and operators have a policy regard-ing human aspects, environmental issues and financial issues.Such policies are typically formulated on an overall level, butthey might be supplemented by more detailed objectives andrequirements within specific areas. These policies, when availa-ble, should be used as a basis for defining the safety objective fora specific lifeboat or lifeboat system. They typically includestatements such as- the impact on the environment shall be reduced to as low as

reasonably practicable- there shall be no serious accidents and no loss of life.If no policy is available, or if it is difficult to define the safetyobjective, it is recommended to get started by carrying out a riskanalysis. The risk analysis can be used to identify all hazards andtheir consequences, and it can then enable back-extrapolation todefine acceptance criteria and areas that need a close follow-up.It is recommended that the overall safety objective be followedup by giving specific measurable requirements.


B 300 Systematic review301 As far as practical, all work associated with the design,construction and operation of a free fall lifeboat shall be suchas to ensure that no single failure will lead to life-threateningsituations for any person or to unacceptable damage to thefacilities or the environment.302 A systematic review or analysis shall be carried out forall phases during the design, construction and operation of alifeboat to identify and evaluate the consequences of singlefailures and series of failures in the lifeboat or lifeboat system,such that necessary remedial measures can be taken. Theextent of the review or analysis shall reflect the criticality ofthe lifeboat system, the criticality of planned operations andprevious experience with similar lifeboat systems and theiroperations.

Guidance note:Quantitative risk analysis (QRA) is an accepted methodology forexecution of a systematic review. A QRA may provide an esti-mation of the overall risk to human health and safety, to the envi-ronment and to assets. A QRA comprises:- hazard identification- assessment of probabilities of failure events- assessment of accident developments- consequence and risk assessment.Other methodologies for identification of potential hazards areFailure Mode, Effect and Criticality Analysis (FMECA) andHazard and Operability studies (HAZOP).A QRA is sensitive to the reliability and possible weaknesses ofthe data that it is based on. A Project External Review (PER) bypeople with a wide and deep knowledge within the field of inter-est may form an alternative to the QRA. Another alternative is tocarry out a PER of the QRA.


B 400 Safety class methodology401 In this standard, structural safety is ensured by use of asafety class methodology. The structure to be designed is clas-sified into a safety class based on the failure consequences.The classification is normally determined by the purpose of thestructure. For each safety class, a target safety level can bedefined in terms of an annual probability of failure or in termsof a probability of failure per operational event.402 Three safety classes are defined. Low safety class isused for structures, whose failures imply low risk for personalinjuries and pollution, low risk for economical consequencesand negligible risk to human life. Normal safety class is usedfor structures, whose failures imply some risk for personalinjuries and significant economic consequences. High safetyclass is used for structures, whose failures imply large possibil-ities for personal injuries or fatalities, for significant environ-mental pollution or major societal losses, or very largeeconomic consequences.403 Free fall lifeboats shall be designed to high safety class.

B 500 Target Safety501 The target safety level for structural design of free falllifeboats can be expressed in terms of a target probability offailure per launch event.

Guidance note:The target failure probability can be determined by a cost-benefitanalysis. In this context, the cost is the cost involved with rein-forcement of a lifeboat structure whereas the benefit is thenumber of fatalities averted by this reinforcement of the struc-ture. The principle is to invest in safety by reinforcement of the

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structure until the marginal benefit from the reinforcementbecomes too small for additional investments to serve any rea-sonably practicable purpose. There is proportionality betweenthe reduction in failure probability and the number of fatalitiesaverted by the reinforcement of the structure, such that the targetfailure probability can be solved as the failure probability whichcomes out at the limit between where further investments willserve a purpose and where they will not.For details of how to determine the target failure probability, refer-ence is made to IMO Guidelines for Formal Safety Assessment.


502 In addition to the requirement to safety given in terms ofthe target probability of failure per launch event, there is arequirement to the failure probability conditioned on a launchin an extreme sea state. This requirement is based on safetyequivalency principles for life-saving appliances and is set to10–2. The conditioning extreme sea state is taken as the 3-hourstationary sea state whose significant wave height has a returnperiod of 100 years. 503 The requirements to safety levels given in 501 and 502and the principles behind their derivation apply not only tostructural design, but also to design against large accelerationscausing human injury in the launch phase and to design againstcollision with the host facility in the subsequent sailing phase.

Guidance note:The requirement to safety during launch at an arbitrary point intime, given in 501, governs the design against large accelera-tions, whereas the requirement to safety during launch in the 100-year sea state, given in 502, governs the design against collisionwith the host facility. The requirement given in 501 further gov-erns the structural design of lifeboats which become fully sub-merged during the launch, whereas the requirement given in 502governs the structural design of lifeboats which only becomepartly submerged during the launch.


504 The target safety level is the same, regardless of whichdesign philosophy is applied.

Guidance note:A design of a structural component which is based on an assump-tion of inspections and possible maintenance and repair through-out its design life may benefit from a reduced structuraldimension, e.g. a reduced cross-sectional area, compared to thatof a design without such an inspection and maintenance plan, inorder to arrive at the same safety level for the two designs.This refers in particular to designs which are governed by theFLS or the SLS. It may be difficult to apply this to designs whichare governed by the ULS or the ALS, although also for suchdesigns this may be of relevance, for example for lifeboats whichare subject to wear, tear and degradation from wind and sunlightduring storage.


C. Design Principles and Design ConditionsC 100 Methods for structural design101 The following design principles and design methods forlimit state design of lifeboats are applied in this standard:

— design by partial safety factor method— design by direct simulation of combined load effect of

simultaneous load processes— design assisted by testing— probability-based design.

102 General design considerations regardless of designmethod are also given in C301. 103 This standard is based on the partial safety factormethod, which is based on separate assessment of the load

effect in the structure due to each applied load process. Thestandard allows for design by direct simulation of the com-bined load effect of simultaneously applied load processes,which is useful in cases where it is not feasible to carry out sep-arate assessments of the different individual process-specificload effects.104 As an alternative or as a supplement to analytical meth-ods, determination of load effects or resistance may in somecases be based either on testing or on observation of structuralperformance of models or full-scale structures.105 Structural reliability analysis methods for direct proba-bility-based design are mainly considered as applicable to spe-cial case design problems, to calibrate the load and resistancefactors to be used in the partial safety factor method, and todesign for conditions where limited experience exists.

C 200 Aim of the design201 Structures and structural elements shall be designed to:

— sustain loads liable to occur during all temporary, operat-ing and damaged conditions if required

— ensure acceptable safety of structure during the design lifeof the structure

— maintain acceptable safety for personnel and environment— have adequate durability against deterioration during the

design life of the structure.

C 300 Design conditions301 The design of a structural system, its components anddetails shall, as far as possible, satisfy the following require-ments:

— resistance against relevant mechanical, physical andchemical deterioration is achieved

— fabrication and construction comply with relevant, recog-nized techniques and practice

— inspection, maintenance and repair are possible.

Structures and structural components shall possess ductilebehaviour unless the specified purpose requires otherwise.302 Structural connections are, in general, to be designedwith the aim to minimize stress concentrations and reducecomplex stress flow patterns.303 As far as possible, transmission of high tensile stressesthrough the thickness of plates during welding, block assemblyand operation shall be avoided. In cases where transmission ofhigh tensile stresses through the thickness occurs, structuralmaterial with proven through-thickness properties shall beused. 304 Structural elements in steel structures and in aluminiumstructures may be manufactured according to the requirementsgiven in DNV-OS-C401.305 Structural FRP elements may be manufactured accord-ing to Appendix B.

D. Limit StatesD 100 General101 A limit state is a condition beyond which a structure orstructural component will no longer satisfy the design require-ments. 102 The following limit states are considered in this stand-ard:Ultimate limit states (ULS) correspond to the maximum load-carrying resistance.Fatigue limit states (FLS) correspond to failure due to theeffect of cyclic loading.

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Accidental limit states (ALS) correspond to (1) maximum load-carrying resistance for (rare) accidental loads or (2) post-acci-dent integrity for damaged structures.Serviceability limit states (SLS) correspond to tolerance crite-ria applicable to intended use or durability.103 Examples of limit states within each category:Ultimate limit states (ULS)

— loss of structural resistance (excessive yielding and buck-ling)

— failure of components due to brittle fracture— loss of static equilibrium of the structure, or of a part of the

structure, considered as a rigid body, e.g. overturning orcapsizing

— failure of critical components of the structure caused byexceeding the ultimate resistance (which in some cases isreduced due to repetitive loading) or the ultimate deforma-tion of the components

— excessive deformations caused by ultimate loads— transformation of the structure into a mechanism (collapse

or excessive deformation).

Fatigue limit states (FLS)

— cumulative damage due to repeated loads.

Accidental limit states (ALS)

— structural damage caused by accidental loads (ALS type 1)— ultimate resistance of damaged structures (ALS type 2)— loss of structural integrity after local damage or flooding

(ALS type 2).

Serviceability limit states (SLS)

— excessive vibrations producing discomfort or affectingnonstructural components

— deformations that exceed the limitation of equipment(induced by load and/or temperature)

— deflections that may alter the effect of the acting forces ordeformations that may change the distribution of loadsbetween supported rigid objects and the supporting struc-ture unless these are explicitly accounted for in the ULScheck.

Guidance note:For conventional offshore structures, excessive motions andexcessive deformations are usually referred to as serviceabilitylimit states (SLS). However, for free fall lifeboats, excessivemotions and excessive deformations can both lead to fatalitiesand therefore in many cases have to be referred to as ultimatelimit states (ULS).


E. Design by the Partial Safety Factor MethodE 100 General101 The partial safety factor method is a design method bywhich the target safety level is obtained as closely as possibleby applying load and resistance factors to characteristic valuesof the governing variables and subsequently fulfilling a speci-fied design criterion expressed in terms of these factors andthese characteristic values. The governing variables consist of

— loads acting on the structure or load effects in the structure— resistance of the structure or strength of the materials in

the structure.

102 The characteristic values of loads and resistance, or ofload effects and material strengths, are chosen as specific

quantiles in their respective probability distributions. Therequirements to the load and resistance factors are set such thatpossible unfavourable realizations of loads and resistance, aswell as their possible simultaneous occurrences, are accountedfor to an extent which ensures that a satisfactory safety level isachieved.

E 200 The partial safety factor format201 The safety level of a structure or a structural componentis considered to be satisfactory when the design load effect Sddoes not exceed the design resistance Rd:

This is the design criterion. The design criterion is also knownas the design inequality. The corresponding equation Sd = Rdforms the design equation.

Guidance note:The load effect S can be any load effect such as an external orinternal force, an internal stress in a cross section, or a deforma-tion, and the resistance R against S is the corresponding resist-ance such a capacity, a yield stress or a critical deformation.


202 There are two approaches to establish the design loadeffect Sdi associated with a particular load Fi:(1) The design load effect Sdi is obtained by multiplication ofthe characteristic load effect Ski by a specified load factor γfi

where the characteristic load effect Ski is determined in a struc-tural analysis for the characteristic load Fki.(2) The design load Sdi is obtained from a structural analysisfor the design load Fdi, where the design load Fdi is obtained bymultiplication of the characteristic load Fki by a specified loadfactor γfi

Approach (1) shall be used to determine the design load effectwhen a proper representation of the dynamic response is theprime concern, whereas Approach (2) shall be used if a properrepresentation of nonlinear material behaviour or geometricalnonlinearities or both are the prime concern.203 The design load effect Sd is the most unfavourable com-bined load effect resulting from the simultaneous occurrenceof n loads Fi, i = 1,...n. It may be expressed as

where f denotes a functional relationship.According to the partial safety factor format, the design com-bined load effect Sd resulting from the occurrence of n inde-pendent loads Fi, i = 1,...n, can be taken as

where Sdi(Fki) denotes the design load effect corresponding tothe characteristic load Fki.When there is a linear relationship between the load Fi actingon the structure and its associated load effect Si in the structure,the design combined load effect Sd resulting from the simulta-neous occurrence of n loads Fi, i = 1,...n, can be achieved as

When there is a linear relationship between the load Fi and itsload effect Si, the characteristic combined load effect Sk result-ing from the simultaneous occurrence of n loads Fi, i = 1,...n,

dd RS ≤

kifidi SS γ=

kifidi FF γ=

),...( 1 dndd FFfS =

∑=

=n

ikidid FSS

1

)(

∑=

=n

ikifid SS

1

γ

DET NORSKE VERITAS


can be achieved as

204 Characteristic load effect values Ski are obtained as spe-cific quantiles in the distributions of the respective load effectsSi. In the same manner, characteristic load values Fki areobtained as specific quantiles in the distributions of the respec-tive loads Fi.

Guidance note:Which quantiles are specified as characteristic values maydepend on which limit state is considered. Which quantiles arespecified as characteristic values may also vary from one speci-fied combination of load effects to another among the load com-binations that are specified to be investigated in order to obtain acharacteristic combined load effect Sk equal to a particular quan-tile in the distribution of the true combined load effect S.


205 In this standard, design in the ULS is either based on acharacteristic combined load effect Sk defined as the 99%quantile in the long-term distribution of the combined peakenvironmental load effect during a launch at an arbitrary pointin time, or on a characteristic load Fk defined as the 99% quan-tile in the long-term distribution of the combined peak environ-mental load during a launch at an arbitrary point in time.

Guidance note:When n load processes occur simultaneously during a launch, thestandard specifies more than one set of characteristic load effects(Sk1,...Skn) to be considered in order for the characteristic com-bined load effect Sk to come out as close as possible to the 99%quantile. For each specified set (Sk1,...Skn), the correspondingdesign combined load effect is determined according to Clause203. For use in design, the design combined load effect Sd isselected as the most unfavourable value among the design com-bined load effects that result for these specified sets of character-istic load effects.


206 The resistance R against a particular load effect S is, ingeneral, a function of parameters such as geometry, materialproperties, environment, and load effects themselves, the latterthrough interaction effects such as degradation.There are two approaches to establish the design resistance Rdof the structure or structural component:(1) The design resistance Rd is obtained by dividing the char-acteristic resistance Rk by a specified material factor γm:

(2) The design resistance Rd is obtained from the design mate-rial strength σd by a capacity analysis

in which R denotes the functional relationship between mate-rial strength and resistance and in which the design materialstrength σd is obtained by dividing the characteristic materialstrength σk by a material factor γm,

Which of the two approaches applies depends on the design sit-uation. In this standard, the approach to be applied is specifiedfrom case to case.207 The characteristic resistance Rk is obtained as a specificquantile in the distribution of the resistance. It may be obtainedby testing, or it may be calculated from the characteristic val-ues of the parameters that govern the resistance. In the lattercase, the functional relationship between the resistance and thegoverning parameters is applied. Likewise, the characteristic

material strength σk is obtained as a specific quantile in theprobability distribution of the material strength and may beobtained by testing.208 Load factors account for:

— possible unfavourable deviations of the loads from theircharacteristic values

— the limited probability that different loads exceed theirrespective characteristic values simultaneously

— uncertainties in the model and analysis used for determi-nation of load effects.

209 Material factors account for:

— possible unfavourable deviations in the resistance of mate-rials from the characteristic value

— uncertainties in the model and analysis used for determi-nation of resistance

— a possibly lower characteristic resistance of the materialsin the structure, as a whole, as compared with the charac-teristic values interpreted from test specimens.

E 300 Characteristic load effect301 For operational design conditions, the characteristicvalue Sk of the load effect resulting from an applied load com-bination is defined as follows, depending on the limit state:

— For load combinations relevant for design against theULS, the characteristic value of the resulting load effect isdefined as the 99% quantile in the long-term distributionof the peak value of the combined load effect during alaunch at an arbitrary point in time.

— For load combinations relevant for design against the FLS,the characteristic load effect history is defined as theexpected load effect history.

— For load combinations relevant for design against the SLS,the characteristic load effect is a specified value, depend-ent on operational requirements.

— For load combinations relevant for design against theALS, the characteristic load effect is a specified value,dependent on operational requirements.

Guidance note:The characteristic value of a load effect is a representative valueof the load effect variable. In general, for a load effect variable,the characteristic value is defined as a high but measurable valuewith a prescribed probability of not being unfavourably exceededduring some reference period.For a load effect that governs the design of a free fall lifeboatagainst the ULS during a launch at an arbitrary point in time, thereference period of interest is the duration of the launch, and theload effect variable of interest is the peak value of the load effectduring this reference period. The characteristic value of the load effect is defined as the valueof the load effect whose probability of being exceeded during thelaunch is 1%. This is recognized as the 99% quantile in the long-term probability distribution of the peak load effect during thelaunch. This probability distribution comes about if a repeatednumber of launches at arbitrary points in time are conducted andthe peak load effect is recorded during each launch.A free fall lifeboat is exposed to the loading from wind andwaves, which governs its design, only during the duration of thelaunch. This is in contrast to a permanent offshore structure, suchas the host facility, which is continuously exposed year-round tothe loading from wind and waves, which governs its design.Referring to this difference in exposure, using the 99% quantilein the long-term distribution of the peak load effect as character-istic load effect value for a free fall lifeboat is consistent with andanalogous to using the 99% quantile in the distribution of theannual maximum load effect as characteristic load effect valuefor a permanent offshore structure which is common practice inoffshore design codes. This 99% quantile in the distribution ofthe annual maximum load effect is recognized by its more popu-lar term, the 100-year load effect.

∑=

=n

ikik SS

1

m

kd

RR

γ=

)( dd RR σ=

m

kd γ

σσ =

DET NORSKE VERITAS


No 100-year load effect can be associated with the launch of afree fall lifeboat. If the lifeboat had been continuously exposed toenvironmental loading year-round, a 100-year load effect couldhave been established in line with the definition of the character-istic load effect in offshore design codes. The adopted characteristic load effect, defined as the 99% quan-tile in the long-term distribution of the peak load effect during alaunch at an arbitrary point in time, is a smaller load effect valuethan such a 100-year load effect under continuous exposurewould be. The consequence of this difference is that the requiredload factors to be used with the adopted definition of character-istic load effect in design are somewhat higher than those com-monly required for use with 100-year load effects in offshoredesign codes.Appendix A provides guidance for how to determine the long-term probability distribution of a quantity such as a resulting loadeffect and how to determine the 99% quantile in this distribution,e.g. when measurements of the quantity are available from tests.


302 For temporary design conditions, the characteristicvalue Sk of the load effect resulting from an applied load com-bination is a specified value, which shall be selected dependenton the measures taken to achieve the required safety level. Thevalue shall be specified with due attention to the actual loca-tion, the season of the year, the duration of the temporary con-dition, the weather forecast, and the consequences of failure.

Guidance note:For a free fall lifeboat, temporary conditions include transporta-tion of the lifeboat to site and installation of the lifeboat on thehost facility. The launch of the lifeboat, however, is referred to asan operational condition and is not to be handled as a temporarycondition.


303 In some cases the load effect is a deformation. Fordesign against deformations, no particular characteristic defor-mation is defined. In stead, a design deformation for direct usein the design checks for deformations is defined as theexpected deformation conditional on the characteristic loadsfactored by the load factor, for example determined by calcu-lations in an FEM analysis.

E 400 Characteristic resistance401 For metallic materials the characteristic resistance isdefined as the 5% quantile in the distribution of the resistancein question, e.g. resistance against buckling or resistanceagainst yield.402 For composite materials the characteristic resistance isdefined as the 2.5% quantile in the distribution of the resist-ance in question, e.g. resistance against buckling or resistanceagainst rupture.

E 500 Load and resistance factors 501 Load and resistance factors for the various limit statesare given in Sec.4 and Sec.6.

F. Design Assisted by TestingF 100 General101 Design by testing or observation of performance shall ingeneral be supported by analytical or numerical design meth-ods. 102 Load effects, structural resistance and resistance againstmaterial degradation may be established by means of testing orobservation of the actual performance of full-scale lifeboatstructures.103 To the extent that testing is used for design, the testingshall be verifiable.

F 200 Full-scale testing and observation of performance of existing lifeboat structures201 Full-scale tests and monitoring of existing lifeboat struc-tures may be used to give information about response and loadeffects. This information can be utilized in calibration andupdating of the safety level of the lifeboat structure. The safetylevel of the lifeboat structure can also be updated whenimproved methods become available.

Guidance note:Updating of the safety level can be useful for free fall lifeboatswhich have been used for emergency evacuation and are to berequalified. Methods for updating of safety level can be found inClassification Notes No. 30.6.


G. Probability-Based DesignG 100 Definition101 The structural reliability, or the structural safety, isdefined as the probability that failure will not occur, or that aspecified failure criterion will not be met, within a specifiedperiod of time.

G 200 Structural reliability analysis201 As an alternative to design by the partial safety factormethod specified in this standard, a full probability-baseddesign by means of a structural reliability analysis may be car-ried out. This requires that a recognized structural reliabilitymethod be used.202 This subsection gives requirements to be met for struc-tural reliability analyses that are undertaken in order to docu-ment compliance with the standard.203 Acceptable procedures for structural reliability analysesare documented in Classification Notes No. 30.6.204 Reliability analyses shall be based on Level 3 reliabilitymethods. These methods utilize probability of failure as ameasure of safety and require representation of the probabilitydistributions of all governing load and resistance variables.205 In this standard, Level 3 reliability methods are mainlyconsidered applicable to:

— calibration of a Level 1 method to account for improvedknowledge

— special case design problems— novel designs for which limited or no experience exists.

Guidance note:Level 1 methods are deterministic analysis methods that use onlyone characteristic value to describe each uncertain variable, i.e.the partial safety factor method applied in this standard.


206 Reliability analysis may be updated by utilization ofnew information. Wherever such updating indicates that theassumptions upon which the original analysis was based arenot valid, and the result of such non-validation is deemed to beessential to safety, the subject approval may be revoked.207 Target reliabilities shall be commensurate with the con-sequence of failure. The method of establishing such targetreliabilities, and the values of the target reliabilities them-selves, should be agreed in each separate case. To the extentpossible, the minimum target reliabilities shall be based onestablished cases that are known to have adequate safety,cf. B400 and B500.208 Where well established cases do not exist, e.g. in thecase of novel and unique design solutions; the minimum target

DET NORSKE VERITAS


reliability values shall be based upon one or more of the fol-lowing approaches:

— transferable target reliabilities for similar existing designsolutions, i.e. acceptable past practice

— internationally recognized codes and standards

— Classification Notes No. 30.6.

209 Suitably competent and qualified personnel shall carryout the structural reliability analysis. Extension into new areasof application shall be subject to technical verification.

DET NORSKE VERITAS


SECTION 3ENVIRONMENTAL CONDITIONS

A. General

A 100 General101 Environmental conditions consist of all site-specificconditions which may influence the design of a lifeboat bygoverning its loading, its capacity or both. 102 Environmental conditions cover virtually all environ-mental conditions on the site, including but not limited tometeorological conditions, oceanographic conditions, soilconditions, seismicity, biology, and various human activities.The environmental conditions of most importance for free falllifeboats are dealt with in this section.

Guidance note:The meteorological and oceanographic conditions which mayinfluence the design of a lifeboat and its lifeboat station andrelease system consist of phenomena such as wind, waves, cur-rent and water level. These phenomena may be mutually depend-ent and for the three first of them the respective directions arepart of the conditions that may govern the design.


103 Wind, waves, current and water level influence the tra-jectory during the launch of a lifeboat and thereby govern theenvironmental loads on the lifeboat. Wind, rain, snow, hail andice may all produce stowage loads when the lifeboat is stowedin the lifeboat station between emergency operations. Humid-ity, salinity and sunlight will not necessarily imply any loadingof the lifeboat, but may over time cause degradation of thematerial strengths and the structural capacity of the lifeboat.104 Environmental conditions, first of all in terms of thewave climate, form the basis for the environmental loads thata lifeboat will experience during a launch. The wave climate isusually represented by the significant wave height HS and thepeak period TP, which can be assumed as constants in short-term sea states of 3-hour or 6-hour durations, and which can berepresented by their joint probability distribution in the longterm. The joint site-specific long-term distribution of (HS, TP)may be needed in order to establish the long-term distributionsof the loads on canopy and hull that govern the design of thelifeboat and to interpret the corresponding characteristic loadsfrom these distributions.

Guidance note:When a load on the lifeboat is given in terms of the probabilitydistribution of this load conditioned on the sea state parameters(HS, TP), e.g. as determined from model tests in irregular sea inthe laboratory, the joint long-term distribution of (HS, TP) isneeded to allow for integration over all sea states to establish theunconditional long-term distribution of the considered load in alaunch of the lifeboat at an arbitrary point in time.


105 Other environmental conditions that may govern theenvironmental loads that the lifeboat will experience include,but are not limited to, wind, current and water level. The windclimate is usually represented by the 10-minute mean windspeed U10 and the standard deviation σU of the wind speed.These properties can be assumed as constants in short-term 10-minute periods and can be represented by their joint probabil-ity distribution in the long term. The current climate can berepresented by a current speed with a long-term probabilitydistribution. The water level consists of a tidal component anda storm surge component and can be represented by its long-term probability distribution.

Guidance note:It may be relevant to use different averaging periods for wind inthe free fall phase and in the sailing phase.


106 For lifeboats which are launched from a fixed offshore hoststructure, the trajectory shall be predicted based on the assump-tion that the water level is located at LAT. If the differencebetween LAT and HAT is large, two trajectories should be pre-dicted for water levels located at LAT and HAT, respectively.

Guidance note:The water level, and in particular tidal effects, influences the freefall height. The water level needs to be accounted for separately,if its variation has not been accounted for in establishing thelong-term distribution for the load, for example if this long-termdistribution has been established based on model tests in irregu-lar sea in the laboratory, where the still water level has been keptconstant equal to the MWL.There may be cases where the water level at HAT could be morecritical than at LAT, for example with respect to headway afterthe free fall.In assessing the water level and its effects, the effects of subsid-ence of the seabed need to be addressed.


B. Wind ConditionsB 100 Introduction101 Wind speed varies with time. It also varies with theheight above the ground or the height above the sea surface.For these reasons, the averaging time for wind speeds and thereference height must always be specified.102 A commonly used reference height is H = 10 m. Com-monly used averaging times are 1 minute, 10 minutes and 1hour.103 Wind speed averaged over 1 minute is often referred toas sustained wind speed.104 For details of representation of wind conditions, refer-ence is made to DNV-RP-C205.

B 200 Wind parameters201 The wind climate can be represented by the 10-minutemean wind speed U10 at height 10 m and the standard deviationσU of the wind speed at height 10 m. In the short term, i.e. overa 10-minute period, stationary wind conditions with constantU10 and constant σU can be assumed to prevail. This wind cli-mate representation is not intended to cover wind conditionsexperienced in tropical storms such as hurricanes, cyclonesand typhoons. It is neither intended to cover wind conditionsexperienced during small-scale events such as fast propagatingarctic low pressures of limited extension.

Guidance note:The 10-minute mean wind speed U10 is a measure of the intensityof the wind. The standard deviation σU is a measure of the vari-ability of the wind speed about the mean. When special condi-tions are present, such as when hurricanes, cyclones andtyphoons occur, a representation of the wind climate in terms ofU10 and σU may be insufficient.


202 The instantaneous wind speed at an arbitrary point intime during 10-minute stationary conditions follows a proba-

DET NORSKE VERITAS


bility distribution whose mean value is U10 and whose stand-ard deviation is σU. 203 The turbulence intensity is defined as the ratio σU/U10.204 The short term 10-minute stationary wind climate maybe represented by a wind spectrum, i.e. the power spectral den-sity of the wind speed process, S(f). S(f) is a function of U10and σU and expresses how the energy of the wind speed is dis-tributed between various frequencies.

B 300 Wind data301 Wind speed statistics are to be used as a basis for repre-sentation of the long-term and short-term wind conditions.Long-term wind conditions typically refer to 10 years or more,short-term conditions to 10 minutes. The 10-minute meanwind speed at 10 m height above the ground or the still waterlevel is to be used as the basic wind parameter to describe thelong-term wind climate and the short-term wind speed fluctu-ations. Empirical statistical data used as a basis for design mustcover a sufficiently long period of time.

Guidance note:Site-specific measured wind data over sufficiently long periodswith minimum or no gaps are to be sought. For design, the windclimate data base should preferably cover a 10-year period ormore of continuous data with a time resolution of 6 hours or bet-ter.


302 Wind speed data are height-dependent. The mean windspeed at 10 m height is often used as a reference. When windspeed data for other heights than the reference height are notavailable, the wind speeds for the other heights can be calcu-lated from the wind speeds in the reference height in conjunc-tion with a wind speed profile above the ground or above thestill water level. 303 The long-term distributions of U10 and σU should pref-erably be based on statistical data for the same averagingperiod for the wind speed as the averaging period which is usedfor the determination of loads. If a different averaging periodthan 10 minutes is used for the determination of loads, the winddata may be converted by application of appropriate gust fac-tors. The short-term distribution of the instantaneous windspeed itself is conditional on U10 and σU.

Guidance note:An appropriate gust factor to convert wind statistics from otheraveraging periods than 10 minutes depends on the frequencylocation of a spectral gap, when such a gap is present. Applica-tion of a fixed gust factor, which is independent of the frequencylocation of a spectral gap, can lead to erroneous results. A spec-tral gap separates large-scale motions from turbulent scalemotions and refers to those spatial and temporal scales that showlittle variation in wind speed.The latest insights for wind profiles above water should be con-sidered for conversion of wind speed data between different ref-erence heights or different averaging periods.Unless data indicate otherwise, the conversions may be carriedout by means of the expressions given in 504 and 505.


304 The wind velocity climate at the location of the hostfacility shall be established on the basis of previous measure-ments at the actual location and adjacent locations, hindcastpredictions as well as theoretical models and other meteoro-logical information. If the wind velocity is of significantimportance to the design and existing wind data are scarce anduncertain, wind velocity measurements should be carried out atthe location in question.

B 400 Wind modelling401 The long-term probability distributions for the wind cli-mate parameters U10 and σU that are derived from available

data can be represented in terms of generic distributions or interms of scatter diagrams. An example of a generic distributionrepresentation consists of a Weibull distribution for the arbi-trary 10-minute mean wind speed U10 in conjunction with alognormal distribution of σU conditional on U10. A scatter dia-gram provides the frequency of occurrence of given pairs (U10,σU) in a given discretization of the (U10, σU) space.402 Unless data indicate otherwise, a Weibull distributioncan be assumed for the arbitrary 10-minute mean wind speedU10 in a given height z above the ground or above the sea waterlevel,

in which the scale parameter A and the shape parameter k aresite- and height-dependent.

Guidance note:In areas where hurricanes occur, the Weibull distribution asdetermined from available 10-minute wind speed records maynot provide an adequate representation of the upper tail of thetrue distribution of U10. In such areas, the upper tail of the distri-bution of U10 needs to be determined on the basis of hurricanedata.


403 In areas where hurricanes do not occur, the distributionof the annual maximum 10-minute mean wind speed U10,maxcan be approximated by

where N = 52 560 is the number of stationary 10-minute peri-ods in one year. Note that N = 52 595 when leap years are takeninto account.

Guidance note:The quoted power-law approximation to the distribution of theannual maximum 10-minute mean wind speed is a good approx-imation to the upper tail of this distribution. Usually only quan-tiles in the upper tail of the distribution are of interest, viz. the98% quantile which defines the 50-year mean wind speed or the99% quantile which defines the 100-year mean wind speed. Theupper tail of the distribution can be well approximated by a Gum-bel distribution, whose expression may be more practical to usethan the quoted power-law expression.


404 The annual maximum of the 10-minute mean windspeed U10,max can often be assumed to follow a Gumbel distri-bution,

in which a and b are site- and height-dependent distributionparameters.

Guidance note:Experience shows that in many cases the Gumbel distributionwill provide a better representation of the distribution of thesquare of the annual maximum of the 10-minute mean windspeed than of the distribution of the annual maximum of themean wind speed itself.


405 The 10-minute mean wind speed with return period TRin units of years is defined as the (1–1/TR) quantile in the dis-tribution of the annual maximum 10-minute mean wind speed,i.e. it is the 10-minute mean wind speed whose probability ofexceedance in one year is 1/TR. It is denoted U10,TR and isexpressed as

))(exp(1)(10

kU A

uuF −−=

NUU uFuF ))(()(

10max,10 year 1, =

)))(exp(exp()(year 1,max,10buauFU −−−=

)11(1year 1,,10 max,10

RUT T

FUR

−= − ; TR>1 year

DET NORSKE VERITAS


in which FU10,max,1 year denotes the cumulative distributionfunction of the annual maximum of the 10-minute mean windspeed.

Guidance note:The 50-year 10-minute mean wind speed becomesU10,50 = FU10,max,1 year

–1(0.98) and the 100-year 10-minutemean wind speed becomes U10,100 = FU10,max,1 year

–1(0.99).Note that these values, calculated as specified, are to be consid-ered as central estimates of the respective 10-minute wind speedswhen the underlying distribution function FU10,max is deter-mined from limited data and is encumbered with statisticaluncertainty.


B 500 Wind speed profiles501 The wind speed profile represents the variation of themean wind speed with height above the ground or above thestill water level, whichever is applicable. When terrain condi-tions and atmospheric stability conditions are not complex, thewind speed profile may be represented by an idealized modelprofile. The most commonly applied wind profile models arethe logarithmic profile model, the power law model and theFrøya model, which are presented in 502 through 505.502 A logarithmic wind speed profile may be assumed forneutral atmospheric conditions and can be expressed as

where U is the mean wind speed, z is the height, H = 10 m isthe reference height, and z0 is a terrain roughness parameter,which is also known as the roughness length. For offshorelocations z0 depends on the wind speed, the upstream distanceto land, the water depth and the wave field. For open sea with-out waves z0 = 0.0001 m will be a typical value, whereas foropen sea with waves, values up to z = 0.01 m are seen. DNV-RP-C205 provides further guidance about the terrain rough-ness parameter.503 As an alternative to the logarithmic wind speed profile apower law profile may be assumed

where the exponent α depends on the terrain roughness. Val-ues for the exponent α at offshore locations are typically in therange 0.12 to 0.14.504 The following expression can be used for calculation ofthe mean wind speed U with averaging period T at height zabove sea level

where H = 10 m and T10 = 10 minutes, and where U10 is the10-minute mean wind speed at height H. This expression con-verts mean wind speeds between different averaging periods.When T < T10, the expression provides the most likely largestmean wind speed over the specified averaging period T, giventhe original 10-minute averaging period with stationary condi-tions and given the specified 10-minute mean wind speed U10.The conversion does not preserve the return period associatedwith U10.505 For offshore locations, the Frøya wind profile model isrecommended unless data indicate otherwise. For extrememean wind speeds corresponding to specified return periods inexcess of about 50 years, the Frøya model implies that the fol-lowing expression can be used for conversion of the one-hour

mean wind speed U0 at height H above sea level to the meanwind speed U with averaging period T at height z above sealevel

where H = 10 m, T0 = 1 hour and T < T0, where and, and where

U will have the same return period as U0.Guidance note:The Frøya wind speed profile includes a gust factor which allowsfor conversion of mean wind speeds between different averagingperiods.The Frøya wind speed profile is a special case of the logarithmicwind speed profile. The Frøya wind speed profile is the best doc-umented wind speed profile for offshore locations and maritimeconditions. Over open sea, the coefficient C may tend to be about 10%smaller than the value that results from the quoted expression. Incoastal zones, somewhat higher values for the coefficient Cshould be used, viz. 15% higher for U0 = 10 m/s and 30% higherfor U0 = 40 m/s.


B 600 Turbulence601 The natural variability of the wind speed about the meanwind speed U10 in a 10-minute period is known as turbulenceand is characterized by the standard deviation σU. For givenvalue of U10, the standard deviation σU of the wind speedexhibits a natural variability from one 10-minute period toanother. Measurements from several locations show that σUconditioned on U10 can often be well represented by a lognor-mal distribution

in which Φ () denotes the standard Gaussian cumulative distri-bution function. The coefficients b0 and b1 are site-dependentcoefficients dependent on U10. 602 The coefficient b0 can be interpreted as the mean valueof lnσU, and b1 as the standard deviation of lnσU. The follow-ing relationships can be used to calculate the mean value E[σU]and the standard deviation D[σU] of σU from the values of b0and b1,

Guidance note:E[σU] and D[σU] will, in addition to their dependency on U10,also depend on local conditions, first of all the terrain roughnessz0, which is also known as the roughness length.


603 For details about turbulence and turbulence modelling,reference is made to DNV-RP-C205.

B 700 Wind spectra701 Short-term stationary wind conditions may be describedby a wind spectrum, i.e. the power spectral density of the wind

⎟⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜⎜

⎝

⎛

⎟⎟⎠

⎞⎜⎜⎝

⎛

⎟⎠⎞

⎜⎝⎛

+⋅=

0

ln

ln1)()(

zHHz

HUzU

α

⎟⎠⎞

⎜⎝⎛=

HzHuzu )()(

)ln047.0ln137.01(),(10

10 TT

HzUzTU −+⋅=

⎭⎬⎫

⎩⎨⎧

⋅⋅−⋅⎭⎬⎫

⎩⎨⎧ ⋅+⋅=

00 ln)(41.01ln1),(

TTzI

HzCUzTU U

02 148.011073.5 UC +⋅= −

22.00 )()043.01(06.0 −⋅+⋅=

HzUIU

)ln

()(1

0| 10 b

bF UU

−Φ=

σσσ

[ ] )21exp( 2

10 bbE U +=σ

[ ] [ ] 1)exp( 21 −= bED UU σσ

DET NORSKE VERITAS


speed. Site-specific spectral densities of the wind speed proc-ess can be determined from available measured wind data.702 When site-specific spectral densities based on measureddata are used, the following requirement to the energy contentin the high frequency range should be fulfilled, unless dataindicate otherwise: The spectral density SU(f) shall asymptoti-cally approach the following form as the frequency f in thehigh frequency range increases

in which Lu is the integral length scale of the wind speed proc-ess.703 Unless data indicate otherwise, the spectral density ofthe wind speed process may be represented by a model spec-trum. Several model spectra exist. They generally agree in thehigh frequency range, whereas large differences exist in thelow frequency range. Most available model spectra are cali-brated to wind data obtained over land. Only a few are cali-brated to wind data obtained over water. Model spectra areoften expressed in terms of the integral length scale of the windspeed process. The most commonly used model spectra withlength scales are presented in DNV-RP-C205.

Guidance note:Caution should be exercised when model spectra are used. In par-ticular, it is important to beware that the true integral length scaleof the wind speed process may deviate significantly from theintegral length scale of the model spectrum.


704 For wind over water, the Frøya model spectral density isrecommended

where

and n = 0.468, U0 is the 1-hour mean wind speed at 10 m heightin units of m/s, and z is the height above sea level in units of m.The Frøya spectrum is originally developed for neutral condi-tions over water in the Norwegian Sea. Use of the Frøya spec-trum can therefore not necessarily be recommended in regimeswhere stability effects are important. A frequency of 1/2400 Hzdefines the lower bound for the range of application of the Frøyaspectrum. Whenever it is important to estimate the energy in thelow frequency range of the wind spectrum over water, the Frøyaspectrum is considerably better than the Davenport, Kaimal andHarris spectra, which are all based on studies of wind over land,and it should therefore be applied in preference to these spectra.

C. Wave Conditions

C 100 Wave parameters101 The wave climate is represented by the significant waveheight HS and the spectral peak period TP. In the short term, i.e.over a 3-hour or 6-hour period, stationary wave conditionswith constant HS and constant TP are assumed to prevail.

Guidance note:The significant wave height HS is defined as four times the stand-ard deviation of the sea elevation process. The significant wave

height is a measure of the intensity of the wave climate as well asof the variability in the arbitrary wave heights.


102 The wave height H of a wave cycle is the differencebetween the highest crest and the deepest trough between twosuccessive zero-upcrossings of the sea elevation process. Thearbitrary wave height H under stationary 3- or 6-hour condi-tions in the short term follows a probability distribution whichis a function of the significant wave height HS. 103 The wave period is defined as the time between two suc-cessive zero-upcrossings of the sea elevation process. Thearbitrary wave period T under stationary 3- or 6-hour condi-tions in the short term follows a probability distribution, whichis a function of HS, TP and H.104 The wave crest height HC is the height of the highestcrest between two successive zero-upcrossings of the sea ele-vation process. The wave crest height is measured from theSWL. The arbitrary wave crest height HC under stationary 3-or 6-hour conditions in the short term follows a probability dis-tribution which is a function of the water depth, the significantwave height HS and the zero-upcrossing period TZ.105 The short term 3- or 6-hour sea state may be representedby a wave spectrum, i.e. the power spectral density function ofthe sea elevation process, S(f). S(f) is a function of HS and TPand expresses how the energy of the sea elevation is distributedbetween various frequencies.

C 200 Wave data201 Wave statistics are to be used as a basis for representa-tion of the long-term and short-term wave conditions. Empiri-cal statistical data used as a basis for design must cover asufficiently long period of time.

Guidance note:Wave data obtained on site are to be preferred over wave dataobserved at an adjacent location. Measured wave data are to bepreferred over visually observed wave data. Continuous recordsof data are to be preferred over records with gaps. Longer periodsof observation are to be preferred over shorter periods. When no site-specific wave data are available and data fromadjacent locations are to be capitalized on in stead, proper trans-formation of such other data shall be performed to account forpossible differences due to different water depths and differentseabed topographies. Such transformation shall take effects ofshoaling and refraction into account.Hindcast of wave data may be used to extend measured timeseries, or to interpolate to places where measured data have notbeen collected. If hindcast is used, the hindcast model shall becalibrated against measured data to ensure that the hindcastresults comply with available measured data.


202 The long-term distributions of HS and TP should prefer-ably be based on statistical data for the same averaging periodfor the waves as the averaging period which is used for thedetermination of loads. If a different averaging period than 3 or6 hours is used for the determination of loads, the wave datamay be converted by application of appropriate adjustmentfactors. 203 Wave climate and wind climate are correlated, becausewaves are usually wind-generated. The correlation betweenwave data and wind data shall be accounted for in design.

Guidance note:Simultaneous observations of wave and wind data in terms ofsimultaneous values of HS and U10 should be obtained. It is rec-ommended that directionality of wind and waves is recorded.Extreme waves may not always come from the same direction asextreme winds. This may in particular be so when the fetch in thedirection of the extreme winds is short.

353

2

10

214.0)(−

−

⎟⎟⎠

⎞⎜⎜⎝

⎛⋅= f

UL

fS uUU σ

nnU

f

zU

fS35

45.020

)~

1(

)10

()10

(320)(

+⋅=

75.0032 )10

()10

(172~ −⋅⋅⋅=

Uzff

DET NORSKE VERITAS


Within a period of stationary wind and wave climates, individualwind speeds and wave heights can be assumed independent anduncorrelated.


C 300 Wave modelling301 Site-specific spectral densities of the sea elevation proc-ess can be determined from available wave data.302 Unless data indicate otherwise, the spectral density ofthe sea elevation process may be represented by the JON-SWAP spectrum,

where

f = wave frequency, ω = 1/TT = wave periodfp = spectral peak frequency, fp = 1/TpTp = peak periodg = acceleration of gravityα = generalized Phillips’ constant

= 5 ⋅ (HS2fp

4/g2) ⋅ (1–0.287 ⋅ lnγ)σ = spectral width parameter; σ = 0.07 for f ≤ fp

and σ = 0.09 for f > fpγ = peak-enhancement factor.

The zero-upcrossing period TZ depends on the peak period Tpthrough the following approximate relationship,

An alternative approximate relationship between TZ and Tpcan be found in DNV-RP-C205, 3.5.5.4.The peak-enhancement factor is

where Tp is in seconds and HS is in metres.When γ = 1 the JONSWAP spectrum reduces to the Pierson-Moskowitz spectrum.303 The long-term probability distributions for the wave cli-mate parameters HS and TP that are interpreted from availabledata can be represented in terms of generic distributions or interms of scatter diagrams. A typical generic distribution repre-sentation consists of a Weibull distribution for the significantwave height HS in conjunction with a lognormal distribution ofTP conditional on HS. A scatter diagram gives the frequency ofoccurrence of given pairs (HS,TP) in a given discretization ofthe (HS,TP) space.304 Unless data indicate otherwise, a Weibull distributioncan be assumed for the significant wave height,

Guidance note:The quoted Weibull distribution is recognized as the long-termdistribution of the significant wave height and represents the dis-tribution of the significant wave height at an arbitrary point intime.


305 When FHs(h) denotes the distribution of the significantwave height in an arbitrary t-hour sea state, the distribution ofthe annual maximum significant wave height HSmax can betaken as

where N is the number of t-hour sea states in one year. Fort = 3 hours, N = 2 920.

Guidance note:The quoted power-law approximation to the distribution of theannual maximum significant wave height is a good approxima-tion to the upper tail of this distribution. Usually only quantilesin the upper tail of the distribution are of interest, in particular the99% quantile which defines the 100-year significant waveheight. The upper tail of the distribution can be well approxi-mated by a Gumbel distribution, whose expression is more oper-ational than the quoted power-law expression.


306 The significant wave height with return period TR inunits of years is defined as the (1–1/TR) quantile in the distri-bution of the annual maximum significant wave height, i.e. itis the significant wave height whose probability of exceedancein one year is 1/TR. It is denoted HS,TR and is expressed as

The significant wave height with return period one year isdefined as the mode of the distribution function of the annualmaximum of the significant wave height.

Guidance note:The 50-year significant wave height becomes HS,50 = FHs,max,1 year

–1(0.98) and the 100-year significant waveheight becomes HS,100 = FHs,max,1 year

–1(0.99). Note that thesevalues, calculated as specified, are to be considered as central esti-mates of the respective significant wave heights when the under-lying distribution function FHs,max is determined from limited dataand is encumbered with statistical uncertainty.


307 In deep waters, the short-term probability distribution ofthe arbitrary wave height H can be assumed to follow aRayleigh distribution when the significant wave height HS isgiven,

where FH|Hs denotes the cumulative distribution function andν is a spectral width parameter whose value is ν = 0.0 for a nar-row-banded sea elevation process and ν ≈ 0.37 when the peak-enhancement factor is γ = 3.3. For further details, reference ismade to DNV-RP-C205, 3.5.9.2.The maximum wave height Hmax in a 3-hour sea state charac-terized by a significant wave height HS can be calculated as aconstant factor times HS.

Guidance note:The maximum wave height in a sea state can be estimated by themean of the highest wave height in the record of waves that occurduring the sea state, or by the most probable highest wave heightin the record. The most probable highest wave height is alsoknown as the mode of the highest wave height. Both of these esti-mates for the maximum wave height in a sea state depend on thenumber of waves, N, in the record. N can be defined as the ratio

⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛

⎟⎟⎠

⎞⎜⎜⎝

⎛

⋅

−−−

−

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

⎟⎟⎠

⎞⎜⎜⎝

⎛−=

2

5.0exp4

54

2

45exp

)2()( p

p

fff

pfffgfS

σγ

πα

γγ

++

=115

pZ TT

⎪⎪⎪⎪

⎩

⎪⎪⎪⎪

⎨

⎧

<

≤<−

≤

=

S

p

S

p

S

p

S

p

H

Tfor

H

Tfor

H

TH

Tfor

51

56.3)15.175.5exp(

6.35

γ

))(exp(1)( β

αchhF

SH−

−−=

NHH hFhF

SS))(()(year 1,max,

=

)11(1year 1,, max,

RHTS T

FHSR

−= − ; TR > 1 year

))1(

2exp(1)( 22

2

|

S

HH HhhF

S ν−−−=

DET NORSKE VERITAS


between the duration TS of the sea state and the mean zero-upcrossing period TZ of the waves. For a narrow-banded sea ele-vation process, the appropriate expression for the mean of thehighest wave height Hmax reads

while the expression for the mode of the highest wave heightreads

For a sea state of duration TS = 3 hours and a mean zero-upcross-ing period TZ of about 10.8 sec, N = 1 000 results. For this exam-ple, the mean of the highest wave height becomesHmax ≈ 1.94HS, while the mode of the highest wave heightbecomes Hmax ≈ 1.86HS. For shorter mean zero-upcrossing peri-ods than the assumed 10.8 sec, N becomes larger, and so does thefactor on HS. Table C1 gives the ratio Hmax/HS for various valuesof N.

Other ratios than those quoted in Table C1 apply for waves inshallow waters and in cases where the sea elevation process is notnarrow-banded.It is common to base the estimation of Hmax on the results for themode rather than on the results for the mean.Table C1 is valid for HS/d < 0.2, where d denotes water depth.


308 In shallow waters, the wave heights will be limited bythe water depth. Unless data indicate otherwise, the maximumpossible wave height can be taken as 78% of the water depth.The Rayleigh distribution of the wave heights will become dis-torted in the upper tail to approach this limit asymptotically.Use of the unmodified Rayleigh distribution for representationof the distribution of wave heights in shallow waters maytherefore be on the conservative side.309 The long-term probability distribution of the arbitrarywave height H can be found by integration over all significantwave heights

where

in which fHsTp(hs,t) is the joint probability density of the sig-

nificant wave height HS and the peak period TP and ν0(hs,t) isthe zero-upcrossing rate of the sea elevation process for givencombination of HS and TP. FH|HsTp(h) denotes the short-termcumulative distribution function for the wave height H condi-tioned on HS and TP.310 When FH(h) denotes the distribution of the arbitrarywave height H, the distribution of the annual maximum waveheight Hmax can be taken as

where NW is the number of wave heights in one year.311 The wave crest height HC can roughly be assumed to be0.65 times the associated arbitrary wave height H. For moredetailed modelling of wave crest heights, reference is made toDNV-RP-C205.312 The wave height with return period TR in units of yearsis defined as the (1–1/TR) quantile in the distribution of theannual maximum wave height, i.e. it is the wave height whoseprobability of exceedance in one year is 1/TR. It is denotedHTR and is expressed as; TR > 1 year

The wave height with return period one year is defined as themode of the distribution function of the annual maximum ofthe wave height.

Guidance note:The 50-year wave height becomes H50 = FHmax,1 year

–1(0.98) andthe 100-year wave height becomes H100 = FHs,max,1 year

–1(0.99).Note that these values, calculated as specified, are to be consid-ered as central estimates of the respective wave heights when theunderlying distribution function FHmax is determined from lim-ited data and is encumbered with statistical uncertainty. Note also that the 100-year wave height H100 is always greaterthan the mode of the maximum wave height Hmax in the 3-hoursea state whose return period is 100 years and whose significantwave height is denoted HS,100. This implies that in deep watersH100 will take on a value greater than Hmax ≈ 1.86HS,100. Valuesof H100 equal to about 2.0 times HS,100 are not uncommon indeep waters.


313 Directionality of waves shall be considered for determi-nation of wave height distributions and wave heights withspecified return periods when such directionality has an impacton the design of a lifeboat.

C 400 Wave theories and wave kinematics401 The kinematics of regular waves may be represented byanalytical or numerical wave theories, which are listed below:

— linear wave theory (Airy theory) for small-amplitude deepwater waves; by this theory the wave profile is representedby a sine function

— Stokes wave theories for high waves— stream function theory, based on numerical methods and

accurately representing the wave kinematics over a broadrange of water depths

— Boussinesq higher-order theory for shallow water waves— solitary wave theory for waves in particularly shallow

water.

The ranges of validity for different wave theories are outlinedin Figure 1.

Table C1 Ratio for deep water waves in narrow-banded sea elevation process

No. of wavesN = TS/TZ

Ratio Hmax/HSmode mean

500 1.763 1.8451 000 1.858 1.9361 500 1.912 1.9882 000 1.949 2.0232 500 1.978 2.0515 000 2.064 2.134

smean HN

NH⎥⎥⎦

⎤

⎢⎢⎣

⎡+=

ln22886.0ln

21

max,

sHNH⎥⎥⎦

⎤

⎢⎢⎣

⎡= ln

21

modemax,

Nln21

NN

ln22886.0ln

21

+

∫ ∫ ⋅⋅=S

PSPSh

SSTHTHHSt

H dtdhthfhFthhF ),()(),(1)( |00

νν

∫ ∫ ⋅=S

PSh t

SSTHS dtdhthfth ),(),(00 νν

WNHH hFhF ))(()(year 1,max

=

)11(1year 1,max

RHT T

FHR

−= −

DET NORSKE VERITAS


Figure 1 Ranges of validity for wave theories (d = water depth, H = wave height, T = wave period)

402 The wave length λ in water depth d is given implicitlyby the dispersion relation

in which T is the wave period and g is the acceleration of grav-ity. The dispersion relation results from linear wave theory andis not valid for higher-order Stokes theory and stream functiontheory, which are the relevant wave theories for waves in shal-low water.403 For details about wave theories and wave kinematics,reference is made to DNV-RP-C205.

D. Current

D 100 Current parameters101 The current typically consists of a wind-generated cur-rent and a tidal current, and a density current when relevant. 102 The current is represented by the wind-generated currentvelocity vwind0 at the still water level and the tidal currentvelocity vtide0 at the still water level.103 Other current components than wind-generated currents,tidal currents and density currents may exist. Examples of suchcurrent components are

— subsurface currents generated by storm surge and atmos-pheric pressure variations

— near-shore, wave-induced surf currents running parallel tothe coast.

D 200 Current data201 Current statistics shall be used as a basis for representa-tion of the long-term and short-term current conditions. Empir-ical statistical data used as a basis for design must cover asufficiently long period of time.

Guidance note:Current data obtained on site are to be preferred over current dataobserved at an adjacent location. Measured current data are to bepreferred over visually observed current data. Continuousrecords of data are to be preferred over records with gaps. Longerperiods of observation are to be preferred over shorter periods.


202 The variation of the current with the water depth shall beconsidered when relevant.203 In regions where bottom material is likely to erode, spe-cial studies of current conditions near the sea bottom may berequired.

D 300 Current modelling301 When detailed field measurements are not available, thevariation in current velocity with depth may be taken as

λπ

πλ dTg 2tanh

22=

)()()( zvzvzv windtide +=

DET NORSKE VERITAS


where

and

in which

v(z) = total current velocity at level zz = distance from still water level, positive upwardsvtide0 = tidal current at still water levelvwind0 = wind-generated current at still water levelh = water depth from still water level (taken as positive)h0 = reference depth for wind-generated current;

h0 = 50 m.302 The variation in current profile with variation in waterdepth due to wave action shall be accounted for. In such cases,the current profile may be stretched or compressed vertically,such that the current velocity at any proportion of the instanta-neous depth is kept constant. By this approach, the surface cur-rent component remains constant, regardless of the seaelevation during the wave action.303 Unless data indicate otherwise, the wind-generated cur-rent at still water level may be estimated as

where

k = 0.015 to 0.03U0 = 1-hour mean wind speed at 10 m height

E. Water LevelE 100 Water level parameters101 The water level consists of a mean water level in con-junction with tidal water and a wind- and pressure-inducedstorm surge. The tidal range is defined as the range between thehighest astronomical tide (HAT) and the lowest astronomicaltide (LAT), see Figure 2.

Figure 2 Definition of water levels

E 200 Water level data201 Water level statistics shall be used as a basis for repre-sentation of the long-term and short-term water level condi-tions. Empirical statistical data used as a basis for design mustcover a sufficiently long period of time.

Guidance note:Water level data obtained on site are to be preferred over waterlevel data observed at an adjacent location. Measured water leveldata are to be preferred over visually observed water level data.Continuous records of data are to be preferred over records withgaps. Longer periods of observation are to be preferred overshorter periods.


F. Other Environmental ConditionsF 100 Snow and ice accumulation101 When the lifeboat is to be located and stowed in an areawhere ice may develop, ice conditions shall be properly con-sidered. 102 Ice accretion from sea spray, fog, snow and rain andfrom air humidity shall be considered wherever relevant. Thisapplies to the lifeboat and its release system and also to the life-boat station with skids, hooks and launching arrangements.

F 200 Salinity201 The salinity of seawater shall be addressed with a viewto its potential influence with respect to corrosion.

Guidance note:The salinity of seawater may contribute to a corrosive environ-ment for the lifeboat during stowage.


F 300 Temperature301 Extreme values of high and low temperatures shall beexpressed in terms of the most probable highest and most prob-able lowest value with the return period in question. 302 For complete representation of the temperature environ-ment, both air and seawater temperatures shall be considered.

F 400 Air density401 Air density shall be addressed since it affects the struc-tural design through wind loading.

F 500 Ultraviolet light501 Ultraviolet light shall be addressed with a view to itspotential for material degradation during stowage of the life-boat.

71

0)( ⎟⎠⎞

⎜⎝⎛ +

⋅=h

zhvzv tidetide for z ≤ 0

⎟⎟⎠

⎞⎜⎜⎝

⎛ +⋅=

0

00)(

hzh

vzv windwind for –h0 ≤ z ≤ 0

00 Ukvwind ⋅=

DET NORSKE VERITAS


SECTION 4LOADS AND LOAD EFFECTS

A. GeneralA 100 General101 In this section, loads, load components and load combi-nations to be considered in the overall strength analysis fordesign of lifeboats and lifeboat systems are specified. Require-ments to the representation of these loads and their combina-tions are given.102 For representation of site-specific sea state wave param-eters and wind and current climate, which form an importantbasis for prediction of hydrodynamic loads, reference is madeto DNV-RP-C205.

B. Basis for Selection of Characteristic LoadsB 100 General101 Unless specific exceptions apply, as documented withinthis standard, characteristic load effects as specified in TableB1 shall apply to design for temporary conditions, characteris-

tic load effects as specified in Table B2 shall apply to designfor operational conditions, and characteristic load effects asspecified in Table B3 shall apply to design for stowage condi-tions.

Guidance note:Temporary design conditions cover design conditions duringtransport, assembly, maintenance, repair and decommissioningof the lifeboat and lifeboat system.Operational design conditions cover design conditions during thelaunch of the lifeboat.Stowage design conditions cover design conditions during stow-age of the lifeboat in the lifeboat station.


102 Wherever environmental and accidental loads might actsimultaneously, the characteristic load effects may be deter-mined based on their joint probability distribution.103 Characteristic values of environmental load effects shallbe estimated by their central estimates.

Table B1 Basis for selection of characteristic load effects for temporary design conditionsLimit states – temporary design conditions

Load category ULS FLS ALS SLSIntact structure Damaged structure

Permanent (G) Expected valueVariable (Q) Specified valueEnvironmental (E) Specified value Expected load

effect historySpecified value Specified value Specified value

Accidental (A) Specified value

Deformation (D) Expected extreme value

Table B2 Basis for selection of characteristic load effects for operational design conditionsLimit states – operational design conditions


Permanent (G) Expected valueVariable (Q) Specified valueEnvironmental (E) 99% quantile in long-

term distribution of peak load effect dur-ing launch at arbitrary

point in time (†)

Expected load effect history

Not applicable 99% quantile in long-term distribution of

peak load effect during launch at arbitrary point in time (†)

Specified value

Accidental (A) Specified value(*)

Deformation (D) Expected extreme value(*) In the case of accidental environmental load during launch: 99.99% quantile in long-term distribution of peak load effect during launch at arbitrary point in time.

(†) Load effect value with 1% probability of being exceeded during a launch at an arbitrary point in time.

DET NORSKE VERITAS


B 200 Characteristic loads during launch of lifeboat201 The basis for definition of the characteristic value of aparticular load associated with the launch of a lifeboat is thepeak value of this load during the entire launch operation con-sisting of release, free fall, immersion and resurfacing of thelifeboat.

Guidance note:An example of a load associated with the launch of a lifeboat isthe water pressure in a specified position of the canopy, and thepeak value of this water pressure during the launch operation isthen considered. Another example is the slamming pressureagainst the hull when the lifeboat impacts the water surface.


202 For design against the ULS, the characteristic value of aparticular load associated with the launch of the lifeboat isdefined as the 99% quantile in the long term distribution of theassociated peak load during a launch initiated at an arbitrarypoint in time.

Guidance note:The lifeboat is in principle to be used in an emergency situationonly once at the most. Without limitations in the weather condi-tions for which the lifeboat can be used, and without correlationbetween the weather conditions and the launch event, it is thevalue of the peak load during a launch operation initiated at anarbitrary point in time which is of interest. The peak load duringa launch initiated at an arbitrary point in time is represented bythe long-term distribution of the peak load. The long term distribution of the peak load can be establishedfrom the short term distribution of the peak load conditioned onsea state parameters such as the significant wave height HS andthe peak period TP. This requires integration of the short term dis-tribution over all realizations of the sea state parameters,weighted according to the joint long term distribution of the seastate parameters. The peak load during a launch in a sea statecharacterized by a particular set of sea state parameters (HS, TP)will exhibit variability from one launch to another and have aprobability distribution, because there will be variability in theheight and period of the wave that the lifeboat hits when it entersinto the water and because there will be variability in the positionon the wave where the lifeboat enters.Other parameters than HS and TP which may be needed for char-acterization of a sea state when the long-term distribution of thepeak load during launch is to be established are current speed,water level, and wind. The choice of the characteristic value of the peak load as a highquantile in the long-term distribution of the peak load reflects adesire to account for the natural variability in the peak load byusing an unfavourable value in design. It also reflects a desire tocapture the loads that are associated with a launch into the mostunfavourable water entry point on the profile of the wave thatpasses when the launch is carried out. For loads on the hull, water entry in following sea with the life-boat about parallel to the wave surface is usually most unfavour-able. For loads on the canopy, water entry in head sea with the

lifeboat about perpendicular to the wave surface is usually mostunfavourable.


203 For design against the ULS, the characteristic ULS load,defined as the 99% quantile in the long-term distribution for aparticular load, shall be estimated for every conceivable condi-tion for the lifeboat and its host structure during the launch.The most unfavourable characteristic load value among thoseestimated shall be used in design. Conditions to be assumed fordesign of the lifeboat against the ULS include, but are not nec-essarily limited to,

— fully loaded lifeboat (full complement of occupants)— empty lifeboat (3 occupants including the pilot).

For lifeboats on floating host facilities additional conditions tobe assumed for design of the lifeboat against the ULS include

— launch from damaged host floater with trim and list.

Trim and list in damaged condition for floating host facilitydepend on the stability of the host facility and are the results ofloss of buoyancy in one or more supporting buoyant compart-ments. The trim and the list for the damaged host facility shallbe set to ±17° unless other host facility specific values areknown.

Guidance note:For lifeboats on floating host facilities, the requirement in thisclause implies that a characteristic ULS load, as given inTable B2, shall be estimated under the assumption that the hostfacility has a permanent trim and list of ±17° (or a permanent trimand list equal to the host facility specific trim and list when appli-cable) in all emergency evacuation situations. This characteristicULS load shall be used in design, if it is unfavourable relative tocharacteristic ULS loads estimated under other assumptions.Since only a fraction of the emergency evacuation situations fora floating host facility is associated with trim and list, the require-ment to assume trim and list in all situations may seem too con-servative. Such conservatism can be circumvented by followinga probabilistic design approach as outlined in Sec.2 G instead ofthe deterministic design approach based on characteristic loads.


204 For design against the ALS, the characteristic value of aparticular load associated with the launch of the lifeboat isdefined as the mode in the distribution whose cumulative dis-tribution function is

in which F(x) denotes the long term distribution of the consid-ered peak load during a launch initiated at an arbitrary point intime. Trim and list in damaged condition for floating host facilitydepend on the stability of the host facility and are the results ofloss of buoyancy in one or more supporting buoyant compart-

Table B3 Basis for selection of characteristic load effects for stowage design conditionsLimit states – stowage design conditions


Permanent (G) Expected valueVariable (Q) Specified valueEnvironmental (E) 99% quantile in distri-

bution of annual max-imum load effect

Expected load effect history

Not applicable Load effect with return period not less than 1

year

Specified value

Accidental (A) Specified value(*)Deformation (D) Expected extreme value* In the case of accidental environmental load during stowage: 99.99% quantile in distribution of annual maximum load or load effect, e.g. 10 000-year

wind load effect, or 10 000-year slamming load effect from waves.

10000max )()( xFxF =

DET NORSKE VERITAS


ments. The trim and the list for the damaged host facility shallbe set to ±17° unless other host facility specific values areknown. This applies to ULS checks of damaged lifeboat struc-ture against environmental loads as well as to design of intactlifeboat structure against accidental loads.

Guidance note:The mode in the distribution Fmax(x) can be approximated wellby the 99.99% quantile in the distribution F(x).


Figure 1 Launching from host structure in damaged condition

B 300 Characteristic loads during stowage of lifeboat301 For design against the ULS, the characteristic value of aparticular environmental load is defined as the 99% quantile inthe distribution of the annual maximum of the load in question,i.e. the 100-year value of the load.

Guidance note:During stowage of the lifeboat in the lifeboat station on the hostfacility, the prime environmental loading expected stems fromwind. The characteristic wind load is the wind load whose returnperiod is 100 years.


302 For design against the ALS, the characteristic value of aparticular environmental load is defined as the 99.99% quan-tile in the distribution of the annual maximum of the load inquestion, i.e. the 10 000-year value of the load.

C. Permanent Loads (G)

C 100 General101 Permanent loads are loads that will not vary in magni-tude or position during the period considered. Examples are:

— mass of structure— mass of permanent ballast and equipment— external and internal hydrostatic pressure of a permanent

nature— reactions to the above.

102 The characteristic value of a permanent load is definedas the expected value of the load based on accurate data for thestructure, the mass of the material and the volume in question.

Guidance note:The expected value of a permanent load may be calculated fromthe nominal dimensions and the mean values of the material den-sities.


D. Variable Functional Loads (Q)D 100 General101 Variable functional loads are loads which may vary dur-ing the period under consideration, and which are related tostorage and operation of the structure. Examples are:

— weight of occupants and their personal supplies (clothes,survival suits)

— loads from fenders— loads from variable ballast and equipment— stored materials, equipment, gas, fluids and fluid pressure.

102 Loads on access platforms and internal structures areused only for local design of these structures and do thereforeusually not appear in any load combination for design of pri-mary lifeboat structures.103 The characteristic value of a variable functional load isthe maximum (or minimum) specified value, whichever pro-duces the most unfavourable load effects in the structure underconsideration.

Guidance note:For each load or load effect to be considered in any point of thelifeboat structure, the most unfavourable number, weight anddistribution of occupants need to be assumed when the character-istic load or load effect is to be established. Situations may wellexist for which the highest load or load effect in a point resultsfrom a partly occupied lifeboat with an uneven distribution of theoccupants, e.g. all occupants in a half-full lifeboat are seated upfront. B203 specifies a minimum number of relevant load condi-tions to be considered.


104 The specified value shall be determined on the basis ofrelevant specifications. An expected load history or load effecthistory shall be used in the FLS.105 Unless data indicate otherwise, the mass of an occupantincluding clothes and survival suit can be set equal to 100 kg.

Guidance note:For the condition with 100% loaded lifeboat, a low weight ofoccupants with survival suits rather than a high weight will beconservative with respect to accelerations, whereas a high weightrather than a low weight will be conservative with respect tomaximum submersion and possibly also headway after resurfac-ing. In general, assumption of a high weight of occupants is rec-

DET NORSKE VERITAS


ommended, in particular with a view to the difficulty insatisfying the requirements to headway.


D 200 Tank pressures201 Requirements to hydrostatic pressures in tanks are givenin DNV-OS-C101.

D 300 Miscellaneous loads301 Railing shall be designed for a horizontal line load equalto 1.5 kN/m, applied to the top of the railing.302 Ladders shall be designed for a concentrated load of 2.5 kN.

E. Environmental Loads (E)E 100 General101 Environmental loads are loads which may vary in mag-nitude, position and direction during the period under consid-eration, and which are related to operations and normal use ofa lifeboat. Examples are:

— hydrodynamic loads induced by waves and current,including drag forces, inertia forces and slamming forces

— wind loads — water level.

102 According to this standard, characteristic environmentalloads and load effects shall be determined as quantiles withspecified probabilities of exceedance. The statistical analysis ofmeasured data or simulated data should make use of differentstatistical methods to evaluate the sensitivity of the result. Thevalidation of distributions with respect to data should be testedby means of recognized methods. The analysis of the data shallbe based on the longest possible time period for the relevantarea. In the case of short time series, statistical uncertainty shallbe accounted for when characteristic values are determined.103 The environmental loads acting on the lifeboat duringlaunch can be referred to three motion phases

— motion in air— submerged or partially submerged motion phase (trajec-

tory through water)— sailing motion phase.

The three motion phases are further dealt with in 200, 300 and400, respectively, with emphasis on prediction of the trajectoryof the lifeboat through air and water.

E 200 Trajectory in air201 The trajectory of the lifeboat through the air during alaunch operation governs the environmental loads that the life-boat structure becomes exposed to during the launch operation. 202 The trajectory in air shall be predicted to form part of thebasis for load calculations.203 A free fall lifeboat can be launched from a skid or it canbe dropped vertically from a hook. The launch of the lifeboatfrom a skid is composed of three phases:

— sliding phase along the launch skid— constrained rotation phase— free-fall phase.

204 The sliding phase is the phase when the lifeboat slidesalong the launch skid. In still water, the motion of the lifeboatdown the launch skid can be taken as purely translational. Inwaves, the effect of the motion of the launch skid should betaken into account. In general the launch skid will have a time-dependent velocity and acceleration during launch.

205 The main parameters determining the motion during thesliding phase is the launch skid angle Θ, the coefficient of fric-tion μ between launch skid and guide rail on the lifeboat, andthe acceleration of the launch skid due to wave induced motionof the host structure. A strong head wind may reduce the accel-eration during sliding and the resulting translational velocity atthe start of the rotation phase.

Guidance note:In the sliding phase, the motion of the lifeboat is governed by thefollowing parameters (Figure 2)

In the sliding and constrained rotation phases the motion of the life-boat can be modelled as a three degree of freedom system, specifiedby coordinates (x,z) of the centre of gravity (COG) and the rota-tional angle θ of the axis of the lifeboat relative to the horizontal. The forces acting on the lifeboat during the sliding phase are thegravity force Mg, the reaction force normal to the guide rail Fnand the friction force parallel to the guide rail μFn and in theopposite direction of the motion. When the lifeboat is launchedin a strong head (or following) wind, the wind drag force shall betaken into account.The equations of motion in the sliding phase are given by

where are the accelerations of COG, and Fwx(t) is theinstantaneous horizontal wind induced drag force given by

when a strong wind has effect on the motion of the lifeboat,, which is assumed in the equations of motion above.

During the sliding phase the lifeboat axis coincides with thedirection of the launch skid, θ = Θ. For a fixed host structure orin the case of still water for a floating host structure motion, thereaction force is given by

Note that for head wind, Fwx < 0. The exit horizontal and verticalvelocities of COG at the end of the launch skid is obtained byintegration of the equations of motion and are given by


Guidance note:In the case of wave generated motion of a floating host structurewith acceleration as = (ax,az) of the launch skid, inertia forces –Max and –Maz should be added to the RHS of the equations oftranslational motion given above. ax is the horizontal accelera-tion and az is the vertical acceleration. The reaction force normal to the launch skid is given by


M = structural mass of lifeboat and occupantsg = acceleration of gravity (9.81 m/s2)μ = coefficient of friction Θ = launch skid angle Lgo = sliding distanceLra = length of guide railUw(t) = instantaneous wind speed in the launch direction ρa = mass density of airCDx = aerodynamic drag coefficientSx = x-projected exposed wind area of the lifeboatas = acceleration of launch skid as = (ax, az)

MgFMzMtFFMxM

nz

wxnx

−+==+−==

)sin(cos)()cos(sin

θμθβθμθβ

&&

&&

),( zx &&&&

wwxDxawx UUSCtF ρ21)( =

xU w &>>

Θ−Θ= sincos wxn FMgF

Θ== cos2 00 gx Lxu β&

Θ−== sin2 00 gz Lzw β&

Θ−+Θ+= sin)(cos)( wxxzn FMaagMF

DET NORSKE VERITAS


Figure 2 Launching parameters of a free fall lifeboat. Sliding phase.

206 The coefficient of friction for the material applied incontact areas between guide rail on lifeboat and launch skidshall be determined by testing. The coefficient of friction issensitive to surface wetting, material combination, surface fin-ish and contaminations. The possible change of coefficient offriction due to such effects and degradation of material withtime shall be assessed. It should be noted that sliding frictionalresistance is normally different from the static frictional resist-ance.

Guidance note:The coefficient of friction may typically vary between μ = 0.05for lubricated surfaces to μ = 0.40 for dry surfaces. Nylon blocksmay be used for contact between guide rail and launch skid.Coefficient of friction for relative motion between dry nylon sur-face and another dry nylon surface may vary between 0.15 and0.25.


207 If the launch skid is in a rotated position during launch,due to extensive heel or list of the platform, the effective coef-ficient of friction may be different than in the designed posi-tion, due to contact between different materials and change innormal force. The effect of this change of coefficient of fric-tion should be considered.208 The pure sliding phase ends when the centre of gravity(COG) of the lifeboat passes the lower end (point O in Figure2) of the launch skid, and the lifeboat begins to rotate. In theconstrained rotation phase the rate of rotation of the lifeboatincreases until the lifeboat is no longer in contact with thelaunch skid.

Guidance note:In the rotation phase, the motion of the lifeboat is governed bythe following additional parameters (Figure 3),

It should be noted that the mass of the lifeboat as well as theradius of gyration depends on the loading condition (number ofoccupants on board and the positions of the occupants).The rotation of the lifeboat is determined by a moment from aforce couple produced by the weight of the body and the reactionforce on the guide rail. The governing equations for the transla-tional motion of the centre of gravity are the same as for the slid-ing phase given in 205. For launch in a strong head (or following)wind the resulting moment due to wind drag should be taken intoaccount. The equation of motion for the rotation of the lifeboatduring this phase is

where Fn is the reaction force normal to the guide rail and Mwy(t)is the instantaneous wind induced pitch moment. During rotationthe following geometrical restraint condition holds

where h is the distance between the lower surface of the guide railand the centre of gravity (COG) of the boat. During rotation of the lifeboat the normal force Fn changes withtime. An explicit expression for Fn can be obtained by differen-tiating the restraint condition above and eliminating the transla-tional and rotational accelerations from the equations of motion,

where

SWL

HD

hθ

COG

Lra

Lgo

Sliding distance

Length of guide rail

Guide rail

O

z

x

Θ

Launch skid

Lifeboat

I = Mr2 = rotational pitch moment of inertia of lifeboat including occupants

r = radius of gyration of lifeboath = distance from guide rail to centre of gravity

d = distance along guide rail from end of launch skid to centre of gravity

Mw(t) = instantaneous drag induced moment from the wind

[ ] )(sincos( tMhzxFI wyn ++−= μθθθ&&

hzx =+ θθ cossin

),,(),,;,,(

θθθ

zxRzxzxPFn

&&&=

[ ][ ]2)sincos(2)/(

sin)/(cos),,;,,(θθθθ

θθθθ&&&&

&&&

hzxIdMMIMFgMIzxzxP

wy

wx

−−+−−=

)(),,( hdMdIzxR μθ ++=

DET NORSKE VERITAS


The distance along the guide rail from end of launch skid to cen-tre of gravity is given by

At the start of the rotation phase, d = –μh, , Mwyd/I is verysmall and can be neglected. Hence, the expression for the reac-tion force reduces to the expression for the reaction force in thesliding phase given in 205. The rotation phase continues as long as the normal reaction forceis nonzero (Fn > 0). The duration of the rotation at the end of thelaunch skid is determined by the length of the guide rail, Lra.Selection of a very small Lra results in a negligible rotation at theedge of the skid.


Guidance note:In the case of wave generated motion of a floating host structurewith acceleration as = (ax,az) of the launch skid, gcosθ shall bereplaced by (g+az)cosθ +axsinθ in the expression for the reactionforce Fn normal to the launch skid.


Figure 3 Launching parameters of a free fall lifeboat. Constrained rotationphase

209 The free fall phase starts when the lifeboat is no longerin contact with the launch skid (Fn = 0) and ends when the bowfirst contacts the water surface. During the free fall, the forcesacting on the lifeboat are the gravity force and the wind forceand moment, taking into account the relative motion betweenlifeboat and air.

Guidance note:The equations of motion during the free fall phase are

where Fwx(t) and Fwz(t) are the instantaneous drag forces in thex- and z-direction respectively and Mw(t) is the instantaneousdrag induced moment from the wind. It should be noted that thelifeboat will rotate during the free fall with a rate of rotationapproximately equal to the rate of rotation ω0 when the boatleaves the edge of the launch skid. The change of rotation angle

during the free fall is given by Δ θ = ω0τ, where τ is the durationof the free fall. The influence of wind drag is significant only forlarge free fall height and high wind speed (storm conditions).


210 The possibility of enhanced wind velocity in the launcharea due to geometric constrictions shall be considered. Reduc-tion of wind velocity due to possible shielding effects shall notbe taken into account in the analysis.

Figure 4 Launching parameters of a free fall lifeboat. Free fall phase

Guidance note:The complete trajectory of the lifeboat in air is found by numer-ically integrating the equations of motions for x(t), z(t) and θ(t)in each of the three phases as given in 205, 208 and 209. Theswitch in forcing functions on the right hand side when goingfrom one phase to the next is determined by - when going from pure sliding to constrained

rotation phase on the skid- Fn = 0 when going from constrained rotation phase to free fall

phase.The equations of motion in the three phases defined above (slid-ing, constrained rotation, free fall) can be solved numerically byrewriting the equations as a system of first order ordinary differ-ential equations (ODEs),

where Xs,r,f , Zs,r,f and Θs,r,f are the respective forcing functions(right hand sides) as defined in 205, 208 and 209.


θθθ sincos),,( zxzxdd −==0=θ&

)(

)()(

tMI

tFMgzMtFxM

wy

wz

wx

=

+−==

θ&&&&

&&

z

x Θ

Launch skid

θ

0=+ hd μ

⎟⎟⎟⎟⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜⎜⎜⎜⎜

⎝

⎛

Θ

=

⎟⎟⎟⎟⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜⎜⎜⎜⎜

⎝

⎛

frs

frs

frs

ZX

zx

zx

zx

dtd

,,

,,

,,

θ

θ

θ &&

&

&&

&

DET NORSKE VERITAS


Figure 5 Free fall lifeboat launched from hook

211 When the lifeboat is launched from a floating host struc-ture, the wave induced motion of the host structure shall betaken into account for calculation of lifeboat trajectory throughair after launching. The wave induced acceleration as of thelaunch skid or hook shall be included in the equations ofmotion for the lifeboat as described in 205 and 208. The waveinduced velocity vs of the launch skid or hook shall be added

to the initial velocity for the free fall phase through air.Guidance note:The wave induced motion of the floater in a given sea-state canbe calculated from the motion transfer functions Hi(ω) for sixdegrees of freedom i = 1,...6 and a wave spectrum S(ω,θ) charac-terizing the sea state. ω is the angular frequency and θ is the meanpropagation direction of the waves. Methods for calculating themotion transfer function and the resulting motion of a given loca-tion (i.e. the launch skid) on the floater is described in DNV-RP-C205.


212 When predicting the free fall phase in air, the duration ofthe free fall phase shall be modified by taking into account thevertical position of the wave surface z = ζ at the point ofimpact.

Guidance note:The duration τ of the free fall phase in air is given by the equation

where w0 is the vertical velocity at the start of the free fall, H’ isthe vertical distance from still water level to the lower end of thelaunch skid, is the vertical wave induced motion at end ofthe launch skid at the start of the free fall and is thewave surface elevation at the position of impact x(t) at time t = τ.In the absence of wind, the angle θ between horizontal axis andlifeboat axis at water impact is given by θ0+ω0τ where θ0 is therotation angle at the end of the constrained rotation phase at theend of the skid.An example of the wave surface elevation is given in Figure 6.


Figure 6 Wave surface elevation (solid line), horizontal water particle velocity (dash-dotted line), and vertical water particle velocity (dotted) atwave surface for a 5th order Stokes wave with H = 17.2 m, T = 10.6 s. AC = 9.92 m, AT = 7.28 m, umax = 6.7 m/s, wmax = 4.7 m/s.

E 300 Trajectory through water301 The trajectory through water for a given lifeboat geom-etry depends on the translational and rotational velocity at startof water entry, the total mass and its mass distribution, and thelocal wave properties at the impact position. The wave proper-ties include wave surface elevation and slope, as well as fluid

particle kinematics (velocity and acceleration) beneath thewave surface. The mass distribution shall reflect how the occu-pants are distributed in the cabin. A possible current will influ-ence the trajectory through the water.302 The trajectory through water shall be predicted to formpart of the basis for load calculations.

HD

COG

HD

)),(()0('21

302 ττζξττ xHwg −+=+

)0(3ξ)),(( ττζ x

DET NORSKE VERITAS


303 Depending on the initial conditions at start of waterentry the following four motion patterns may occur:

I) The lifeboat pitches significantly at maximum submer-gence and ascent so that it surfaces with positive (forward)velocity.

II) The lifeboat pitches significantly at maximum submer-gence and ascent but the forward velocity is reduced tozero and it surfaces with negative (backward) velocity.

III) After reaching the maximum depth in water, the lifeboatmoves backwards keeping almost the same angular posi-tion, then exits from the water surface with a negative

(backward) velocity and after slamming on to the watersurface, moves backward with low velocity.

IV) As a special case of III) the lifeboat exits from the watersurface at an almost vertical angle, vaulting into the air,and drops down on to the water surface with great impactand with a resulting motion in an arbitrary direction.

These motion patterns are depicted in Figure 7.304 For a given lifeboat of length L launched from a launchskid, the motion patterns I)-IV) can be related to the parame-ters HD/L and Lgo/L where HD is the drop height and Lgo is thesliding distance along launch skid. This is shown in Figure 8.

Motion pattern I Motion pattern II

Motion pattern III Motion pattern IV

Figure 7 Motion patterns for a free fall lifeboat

1

2

3

4

5

1

2

3

4

5

1

2

3

4

5

1

2

3

4

5

DET NORSKE VERITAS


Figure 8 Typical relationship between launching parameters drop height HD, sliding distance Lgo, length of lifeboat L and resulting motion pat-terns of type I, II, III and IV.

305 The lifeboat geometry, the lifeboat mass and its distribu-tion, and the lifeboat launch system shall be designed so thatmotion pattern I) is achieved in all conditions. This motion pat-tern is desired since the lifeboat in still water will move awayfrom the platform even if the engine of the lifeboat does notstart. Motion pattern II) may occur during water entry in wavesrequiring use of the lifeboat engine to move away from theplatform. Motion patterns III) and IV) shall be avoided.

Guidance note:The hydrodynamic forces on the lifeboat during water impact area function of the relative velocity between the falling lifeboat andthe water particle velocities in the wave. In high sea states whenthe wave kinematics will have an effect on the trajectory throughwater, the wave length can be assumed much longer than thecharacteristic dimension of the lifeboat so that the wave kinemat-ics can be taken as constant during this phase. The maximum horizontal water particle velocity occurs at top ofthe crest and can for an undisturbed wave be taken as

The minimum horizontal water particle velocity occurs at thebottom of the trough and can be taken as

The maximum vertical water particle velocity occurs close to thestill water level crossing and can be taken as

The variation of velocity with depth in deep water is given by thefactor fw = exp(kz) where k is the local wave number given by

and whereH = wave heigth [m]

T = wave period [s]g = acceleration of gravity = 9.81 m/s2

The horizontal and vertical water particle velocity close to a largevolume host structure will be larger than in an undisturbed wavedue to wave diffraction effects. Guidance on diffracted wave kin-ematics is given in DNV-RP-C205.


306 For numerical assessment of the effect of wave surfaceand wave kinematics on the trajectory through water whenlaunching in a sea state (Hs,Tp), a regular wave with waveheight H shall be defined as the expected value in the shortterm wave height distribution.

Guidance note:The expected wave height in a sea state (Hs,Tp) can be takenas from the Rayleigh distribution with spectralwidth parameter ν = 0.37 as given in Subsection 3 C. The corre-sponding wave period T can be taken as the period of a regularStokes wave where H/λ = 1/10 and the wave length λ is relatedto T by the dispersion relation

valid for large water depth d > λ/2. The dispersion relation formoderate and shallow water is given in Subsection 3 C. A large wave is by nature asymmetric with higher crest height ACthan trough depth AT. The wave height is the sum H = AC + AT.See Figure 9. The asymmetry increases with steepness of thewave. For deep water locations the asymmetry factor AC/H canbe approximated by the formula

For moderate water depth d the asymmetry factor can be foundfrom Stokes 5th order wave theory for given parameters H,Tand d.


Type IV

Type III

Type II

Type I

(H/L)

(Lgo/L)

HD/L

Acceptablemotion pattern

Not acceptablemotion pattern

⎟⎟⎠

⎞⎜⎜⎝

⎛= 2

2

max2expgT

HTHu ππ

THu π

=min

THw π

=max

2

24gT

k π=

HsHH 59.0=

πλ

2

2gT=

2

750.0gT

HHAC +=

DET NORSKE VERITAS


Figure 9 Nonlinear regular wave

307 The wave diffraction effect caused by the submergedpart of the host structure shall be taken into account. The wavesurface elevation and wave kinematics at the position of life-boat water entry shall be used for assessment of lifeboat trajec-tory and loads.

Guidance note:The wave diffraction effect depends on how transparent the sub-merged part of the host structure is. For a jacket structure wherethe substructure consists of slender tubular structures, the wavediffraction effect can be neglected. For large volume host struc-tures like semisubmersibles, TLPs, Spars and FPSOs a wave dif-fraction analysis should be carried out. Guidance on wavediffraction is given in DNV-RP-C205.


308 The trajectory through water can be divided into 4 dif-ferent phases:

— water entry phase— ventilation phase— maximum submersion phase— ascent phase.

The four phases are further described in 309 through 312.309 The water entry phase is characterized by large slam-ming forces. The start of this phase is defined as the timeinstant of first contact between lifeboat and water surface andends when the section of maximum cross-sectional dimensioncrosses the still water level. During this phase, the vertical andhorizontal motion is retarded and the angular velocity of thelifeboat is reversed.

Guidance note:The retardation of the lifeboat motion and change of angularvelocity affect strongly the acceleration induced loads on occu-pants and should therefore be minimized. For water entry on awave surface the slamming force is governed by the relativevelocity between lifeboat (including rotational motion) and thewater particle velocity at the point of entry. During the waterentry phase the water particle velocity in the wave can be consid-ered constant in space and time.


310 The ventilation phase is characterized by the generationof an air cavity behind and above the lifeboat. The size of thecavity depends on the lifeboat stern geometry. During thisphase parts of the lifeboat are not in contact with water, leadingto a buoyancy force that is not vertical. The direction of thetotal force on the lifeboat is opposed to the velocity of the life-boat, leading to large retardation.

Guidance note:Generation of an air cavity contributes to stronger retardation andshould therefore be minimized. The cavity is eventually pinchedoff from the free surface. For a short duration a closed air cavity(bubble) stays attached to the stern of the lifeboat and oscillates.At pinch-off, the air cavity splits in two, one part at the free sur-face being open to the atmosphere, and one closed part (bubble)attached to the stern/canopy of the lifeboat. Just after pinch-off

the pressure in the closed cavity oscillates leading to an oscilla-tory pressure on the lifeboat and resulting unsteady (oscillatory)retardation of the boat and pressure on the stern.


311 The maximum submersion phase is characterized byapproximately constant forward velocity and small verticalcomponent of velocity of COG. The maximum submersiondepth is defined as the depth of the position at which the verti-cal component of the velocity of the COG becomes zero. Atmaximum depth the hydrostatic pressure takes on its maxi-mum value.

Guidance note:It is conceivable that the maximum depth of the bow couldbecome the maximum depth of the COG plus up to about half thelength of the lifeboat.


312 The ascent phase is characterized by an upwards verticalvelocity of COG. This phase ends when the lifeboat exits fromthe water and becomes freely floating.313 It is recommended to calculate a range of possible trajec-tories, thereby to reflect the variability in governing parame-ters as defined in 205 and 208.

Guidance note:The trajectory shall usually be determined for a set of differentsituations, including launching from intact structure and launch-ing from damaged structure. When the trajectory is to be deter-mined for a lifeboat which is to be launched from a floatingstructure in a damaged condition, the drop height and the launchangle may be different from the drop height and the launch anglein the intact condition, owing to list and trim associated with thedamaged condition.


314 Basically, the trajectory trough water can be predictedby four different methods, viz.

— simple analytical expressions for depth of maximum sub-mersion

— simplified numerical models for the different phases oftrajectory trough water

— Computational Fluid Dynamics (CFD) methods— model tests.

The four methods are further described in 315 to 317.315 An approximation for the maximum submersion depth ofthe lifeboat can be obtained by simple energy considerations.The maximum submersion can be approximated by the for-mula

where

AC

AT

u

w

dmax = maximum submersion depth [m]HD* = = modified drop height [m]ΗD = drop height [m]Θ = skid launch angle [rad]Lgo = sliding distance [m]

= = rate of change of vertical added mass at

start of water surface entry [kg/m]L = length of lifeboat [m]M = mass of lifeboat [kg]

MVH

VLdAMHd D

D −

+−=

ρ

φρ*10,33

*max

2cos'

ΘΘ− cossingoD LH

0,33'A0

33

=DdDdA

DET NORSKE VERITAS


Guidance note:The rate of change of vertical added mass may be estimated bycalculating the high frequency limit of the added mass by a sink−source potential flow method at increasing submersion depth.Reference is made to Figure 10.


Figure 10 Position of lifeboat bow during water entry for calculation of rateof change of added mass

316 A simplified numerical method for predicting the trajec-tory through water is based on specifying position and velocitydependent forces and moment acting on the lifeboat and solv-ing the equations of motion by time integration. For an arbi-trary launch and wave propagation direction, a six degree offreedom model should be applied allowing for motion of thelifeboat centre of gravity in 3 spatial directions and for rotationabout 3 axes.

Guidance note:During the partly submerged phase and the fully submergedphase, the lifeboat is acted upon by hydrostatic and hydrody-namic forces. The hydrodynamic forces are functions of fluidpressure and velocities which depend on the motion of the life-boat. Hence the hydrodynamic problem and the equations ofmotion of the lifeboat must be solved as a coupled problem ateach time step. For long and slender lifeboat geometries, thehydrodynamic problem may under certain conditions be simpli-fied to a set of two-dimensional problems (strip theory).


317 Computational Fluid Dynamics (CFD) can be used tocalculate the pressure distribution and the global force andmoment on a lifeboat during its travel through air and water.The exact fluid dynamic equations are solved with respect tothe pressure distribution, the global force and moment, and themotion of the lifeboat. The CFD method used should allow formodelling of two-phase flow, break-up of water particles andtopological changes of the water volume. When applyingCFD, convergence tests shall be carried out to ensure that thefluid cells are sufficiently small. The computational domainshall be large enough to avoid reflections from boundaries ofthe domain. Numerical results based on CFD should be vali-dated with benchmark model test results.

Guidance note:Numerical methods suitable for modelling the violent fluid flowduring lifeboat impact are the Volume-of-Fluid (VOF) methodand Smoothed Particle Hydrodynamics (SPH) method. The VOFmethod requires generation of a volume mesh around the life-boat. The SPH method only needs a surface description of thelifeboat.


318 A minimum clearance between the lowermost point ofthe lifeboat and the seafloor shall be demonstrated at any point

in time during the lifeboat’s travel through the water during thelaunch operation. The minimum clearance shall be 10% of thewater depth and not less than 5 m. This requirement shall bemet in every conceivable condition for the lifeboat, cf. B203.

E 400 Sailing phase401 In the sailing phase the lifeboat is in a stable freely float-ing position responding to forces from wave, wind and current.In the absence of any propulsive force wave forces will cause anoscillatory motion of the lifeboat superimposed a steady driftmotion in the main propagation direction of the wave. Wind andcurrent forces will act in the respective directions of wind andcurrent. The forces and corresponding motion from waves, windand current can be assumed to be independent and added.402 The forward thrust force from the propulsion systemshall be large enough to overcome forces from wind, wave andcurrent when these all act together in a direction towards thehost facility, cf. Sec.7.

Guidance note:The resistance forces against the forward motion of the lifeboatincludes the following components- wind force- current force- wave generating resistance- added resistance due to waves- frictional resistance.


403 In severe weather conditions, the hull and canopy of thelifeboat may become exposed to large breaking wave impactforces and resulting green water loads of similar magnitude asthe impact forces experienced during the launch phase ofpartly submerged lifeboats. Guidance for calculation of waveimpact pressures is given in DNV-RP-C205. Alternatively theloading scenario can be calculated from green water theory,cf. DNV-OS-C102.

E 500 Load cases for the ULS501 For investigation of the behaviour of the lifeboat anddetermination of the loads on the lifeboat during the launchoperation, the following four phases from water entry onwardsshall be considered:

— water entry phase— ventilation phase— maximum submersion phase— ascent phase.

During each phase, the stresses and deformations of relevancefor all possible governing load cases shall be calculated for usein the design rules that shall be fulfilled during the design.502 A set of five load cases to be considered for structuraldesign and for assessment of accelerations causing humanloads is specified. The five load cases are to be considered as aminimum set of load cases to be investigated. Other load casesmay exist which may govern the design. All relevant loadcases shall be investigated. The minimum set of five load casesconsists of:

— slamming pressure on hull from water entry until maxi-mum acceleration is reached

— inertia forces on boat during maximum acceleration— local effects during ventilation phase— pressures at maximum submersion— suction on sides during ascent, related to pressure distribu-

tion from relative velocity squared.

The five load cases are further described in 503 through 507.For each load case, pressures in particular points as well as dif-ferential pressures shall be considered, whichever is criticalwith respect to structural design and human accelerations.

d1 = depth where rate of change of added mass is zero [m]φ = impact angle with free surface [rad]V = volume of lifeboat in fully submerged condition [m3]ρ = mass density of water [kg/m3]

DET NORSKE VERITAS


Guidance note:Differential pressures occur and behave in a different mannerthan other pressures such as pressures on the canopy and maygovern which failure modes are critical.


503 The slamming pressure on the hull from the time ofwater entry until maximum acceleration is reached shall beinvestigated.

Guidance note:Loads on the hull at the water entry and shortly afterwards willtypically evolve from a very high local slamming pressure ini-tially to a high dynamic pressure over a larger part of the hull inthe ventilation phase. The upward force acting on the hull in thisphase will be equal to the upward component of the pressuresintegrated over the wet hull area. The highest total upward forcewill coincide in time with the highest boat accelerations. The hullresponse from water entry until maximum acceleration is usuallydynamic and can be determined by a dynamic analysis of thehull.


504 The inertia forces on the boat during maximum acceler-ation shall be investigated.

Guidance note:This load case takes place during the ventilation phase at the timeof the maximum upward force. The load case is concerned withthe inertia forces that act on the structure when the mass of itsstructural members are subjected to the maximum acceleration.This load case can be investigated as part of a dynamic analysisof the hull. This load case is expected to be more important fordrop-launched boats than for skid-launched boats, since largeraccelerations and smaller submersion are expected for the drop-launched boats.


505 During the typically turbulent phase of downwardsmotion after water entry, various local dynamic effects shall beinvestigated as relevant.

Guidance note:On a skid-launched boat, the front of the wheelhouse will oftenbe exposed to slamming.The shape of the lifeboat may imply that an air pocket becomescreated behind the boat when the boat enters the water andbecomes submerged. When this air pocket subsequentlyimplodes, dynamic water pressures will develop behind the boatand will – depending on the launching arrangement, the shape ofthe boat and the resulting boat trajectory – act on the aft wall, thewheelhouse or the roof. Model tests can be used to determinewhich areas of the boat will be exposed to dynamic water pres-sures from imploding air pockets and load cases can be specifiedaccordingly.


506 At the point of maximum submersion, the pressure fieldaround the lifeboat due to hydrodynamic pressure at maximumacceleration governs the load on the hull and the canopy. Theload case resulting from this pressure distribution shall beinvestigated.

Guidance note:At the point of maximum submersion, the vertical component ofthe acceleration will reach its maximum value. This will give apressure distribution over the hull and the canopy which can leadto large differential pressures. This pressure distribution can insimplified manner be represented by linear potential theory,which gives pressures terms equal to ρ ⋅ ∂φ /∂t, where ρ denotes

mass density of water, φ denotes the velocity potential and tdenotes time.


507 After maximum submersion, the lifeboat will accelerateupwards until it reaches the surface. During this ascent, thepressure distribution over the lifeboat hull and canopy attrib-uted to effects of relative velocity squared governs the load onthe hull and the canopy. The load case resulting from this pres-sure distribution at the point of maximum upward speed shallbe investigated.

Guidance note:This load case can be investigated by applying the relevanthydrostatic pressure, corrected by a negative pressure on thesides of the boat and by an overpressure on the roof, caused bythe upward speed.


508 In assessing the loads on the lifeboat in the differentphases during and after a launch, the effects of asymmetryshould be considered, e.g. asymmetry due to waves propagat-ing at an angle, unsymmetrical load, skewed ascent, and poordirectional stability.

E 600 Slamming loads601 A general description of slamming pressures and slam-ming loads can be found in DNV-RP-C205. 602 Determination of slamming loads on a lifeboat duringimpact is considered complex and difficult to describe withsimple expressions, or simulations. This applies to the use ofgeneral slamming simulation software or Computational FluidDynamics (CFD) codes. In particular, the complexity in anal-yses increases significantly when including waves. Conse-quently the design of the hull, canopy and wheelhouse willhave to rely on model testing and/or full scale testing for deter-mination and calibration of slamming pressures and distribu-tions. 603 Results from general slamming simulation software orCFD codes shall be validated by model tests or full scale tests.

Guidance note:CFD can become a suitable tool for determination of the slam-ming pressures on a lifeboat. One suitable method for simulationis the Volume-of-Fluid (VoF) method which allows for break-upof fluid particles and changed topology of fluid domain. A fullynonlinear Boundary Element Method (BEM) may also be usedwith special boundary conditions at intersection points. 3-D anal-ysis is required and convergence tests must be performed toensure that fluid cells are sufficiently small. Further, the compu-tational domain should be large enough to avoid reflections fromthe boundaries.


604 The importance of carefully conducted model and fullscale testing in relation to determination of slamming pres-sures and distributions is emphasized. This implies that a suf-ficient number of pressure sensors are installed, enablingsubsequent use of data from these sensors in structural analy-ses of hull, canopy and wheelhouse. See further details inSec.9.605 The parameters characterizing slamming on a rigid bodywith a small deadrise angle β (see definition in Figure 11) arethe position and actual value of the maximum pressure, thetime duration and the spatial extent of high slamming pres-sures. Figure 11 presents a schematic view of water entry of atwo dimensional body onto a calm water surface. Duringimpact the free surface is deformed resulting in spray and theformation of a jet.

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Figure 11 Schematic view of water entry of a body onto a calm free surface

606 The complexity with respect to determination of slam-ming pressures increases significantly when taking intoaccount waves from an arbitrary direction during launch of alifeboat. This implies that there will be an asymmetric (3-D)distribution of pressures around the lifeboat and, for example,2-D type simulations will fail to describe the actual pressuredistribution adequately. A similar type of considerationsapplies when damaged conditions (floater heel/trim) are to besimulated.

Guidance note:For 2-D slamming problems (e.g. symmetric wedges impactinga flat water surface) software is available which can represent asymmetric pressure distribution. However with 3-D effectspresent, adjustments have to be made and these adjustments maybe difficult to validate. Slamming pressures predicted by a 2-Danalysis can be assumed to be conservative.


607 It is assumed that the deadrise angle, β, will be largerthan 30 to 40 degrees for free fall lifeboats hence no spaceaveraging of slamming pressures will be required. If, for somereason, the deadrise angle will be less than 30 degrees, specialconsiderations may have to be made. Reference is made to Fig-ure 14.608 Slamming loads will cause structural deformations orvibrations of the lifeboat during impact. The hydrodynamicloading will hence be affected since the slamming pressure isa function of the structural deformations. In general it is con-sidered conservative to neglect such hydroelastic effects.

E 700 Inertia loads701 The lifeboat can be exposed to high accelerations duringthe launch. These accelerations can introduce high reactionloads on different parts of the external and internal structure ofthe lifeboat. Acceleration levels shall be evaluated at differentpositions on the lifeboat wherever inertia loads due to localmass concentrations can occur.

E 800 Load distributions801 The distribution of the hydrodynamic pressure loadsover the wetted surface of the lifeboat causes structural defor-mation and is important for assessment of structural integrityof the lifeboat. When multiple choices of load distributions arerelevant the most conservative distribution shall be selectedbased on structural knowledge of the lifeboat hull. 802 The load distributions related to the different launchphases shall be specified. The distributions shall be specifiedboth related to cross sections (transverse frame related) and tothe longitudinal direction of the lifeboat (fore-and-aft related).

Guidance note:Critical load distributions for the lifeboat structure given as rela-tive pressure distributions in calm water shall be scaled to char-acteristic pressures in waves, cf. 814. All load distributionsrelated to the different launch phases in calm water shall beinvestigated with respect to structural responses. But only themost critical launch phases for the different load distributions arerelevant for scaling to characteristic ULS level. Care should betaken when selecting method for calculating characteristic pres-sure distributions since different methods will give different dis-tribution functions. The most critical load distribution should beestablished for calm water. Sufficient information of the pressuredifference on the hull, the canopy roof, and the sides or as a dif-ferential pressure between side and roof or two longitudinal posi-tions must be maintained in the characteristic value estimates.


803 Different load distributions shall be given depending onthe degree of submergence of the lifeboat during its travelalong its trajectory in water, i.e. depending on whether it ispartly submerged or fully submerged. The degree of submer-gence shall be defined based on conditions prevailing duringlaunch into calm water from the nominal drop height. 804 The lifeboat is referred to as fully submerged when thevertical distance dmax from the still water level to the roof ofthe lifeboat at the time of maximum submergence is larger thanthe height HL of the lifeboat. The distances dmax and HL shallbe measured from the top of the roof at the longitudinal centreof the lifeboat.805 The lifeboat is referred to as partly submerged when thevertical distance dmax from the still water level to the roof ofthe lifeboat is smaller than the height HL of the lifeboat. Thedistances dmax and HL shall be measured from the top of theroof at the longitudinal centre of the lifeboat.

Figure 12 Definition of maximum submergence

806 The load distribution for a lifeboat which is fully sub-merged at maximum depth shall be specified for each of thefollowing launch phases:

— the water entry phase— the ventilation phase— the maximum submergence phase — the ascent phase— the sailing phase.

Guidance note:The ventilation phase is a transient phase which comes aboutwhen the lifeboat enters the water and creates an air pocketbehind the stern. The ventilation phase is also known as the cav-ity transition phase.


Disturbed free surface

Local deadrise angle Jet

Spray root

Pressure

Water entry velocity

Mean free surface

HL

dmax

L/2

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Figure 13 Ventilation phase. Development of air pocket behind stern.

807 The load distribution for a lifeboat which is partly sub-merged at maximum depth is more complex and it is difficultto separate between well defined phases. The following phasescan however be used when load distributions are to be speci-fied:

— the water entry phase— the partly submerged horizontal acceleration phase— the sailing phase.

808 The water entry phase both for partly and fully sub-merged lifeboats is dominated by slamming loads in the bowhull section or slamming in the aft ship hull section or both. Itis required to document maximum slamming pressures in thebow, amidships and in the stern hull region. A two-dimen-sional cross-sectional analysis is considered sufficient for thecrosswise distribution of the slamming pressure. The longitu-dinal distribution, if important, can be assumed to vary linearlybetween the bow and the stern. The cross-sectional distributionof the slamming pressure, ps, is related to the relative velocitybetween the lifeboat and the water surface during impact andis normally expressed as:

Guidance note:It is common to use experimental results from model tests of two-dimensional wedges with different wedge angles, β, for slam-ming evaluations and calculations. Figure 14 shows a typical setup with results. Note that for β > 40 degrees a fairly homogenouspressure over the wetted surface has been measured. Further, therun-up along the wedge implies a larger wetted (typically 60%larger) area than what is submerged below z = 0. It should beemphasized that the results given in Figure 14 are only to be usedfor initial design phases as a means to estimate slamming pres-sures on the lifeboat bow and bottom in calm water conditions,i.e. with no waves.


Figure 14 Pressure (p) distribution during water entry of a rigid wedge withconstant vertical velocity V. pa = atmospheric pressure, β = dead-rise angle. See DNV-RP-C205 for further details.

809 For fully submerged lifeboats the time varying pressureon the hull and the side of the lifeboat in the different phasescan typically be exemplified as shown in the bottom part ofFigure 15. The corresponding deformations due to cross flowload distribution are shown in the upper part of Figure 15.

2v21

Ps Cp ρ=

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Figure 15 Example of typical pressure measurements (bottom) and deformation measurements (top) for a fully submerged lifeboat. Pressuresare indicated at the same cross section amidships at two vertical positions, viz. the canopy roof top and the canopy side. Numbers 1 to4 indicate [1] end of slamming phase with build-up of pressure on roof, [2] ventilation phase with oscillating pressure on roof and roofdeformation upwards, [3] at maximum submergence where there is negligible roof deformation and [4] ascent phase with large differ-ential pressure and maximum roof deformation downwards.

810 The pressure distribution for a fully submerged lifeboatin the ventilation phase is governed by local oscillating pres-sures. These oscillations do not usually represent globaldimensioning loads except for the local shock wave effect onlocal surface appendices like the wheelhouse, the stern, and thehatches. In general, the local fluid flow and hydrodynamicloading in this phase are so complex that the global distributionof pressure loads on the lifeboat side hull and the roof can onlybe provided by detailed CFD analyses or model test experi-ments.

Guidance note:The highly oscillatory behaviour of the pressure is usually fil-tered by the structural response. If the canopy is susceptible toupward deformation, this phase should be carefully investigatedby imposing the actual time histories of pressures as input to astructural analysis in the time domain. A straight forward scalingto characteristic pressure levels in waves is recommendedalthough the frequency level of the pressure spectrum can bequite different in wave conditions than in calm water.


811 The cross-sectional pressure distribution for a fully sub-merged lifeboat in the ventilation phase is usually dominatedby hydrostatic pressure. However, in some cases accelerationdependent pressures can be of importance. It is recommendedto specify a hydrostatic pressure distribution in this phase andimposing the acceleration pressure as well. For calculation ofacceleration pressure distributions in calm water one can usethe methods described in 812 to 817. Since there is no roofdeformation at the end of the ventilation phase (Figure 15), thismeans that the hydrostatic pressure is to be counteracted byacceleration dependent pressure. The longitudinal distributioncan be simplified by assuming half of the structure exposed toa longitudinally uniform distribution. 812 The pressure distribution in the ascent phase can bespecified as a combination of hydrostatic and hydrodynamicpressure. Usually the hydrodynamic pressure is governed byvelocity effects in this phase but acceleration can also beimportant.

Guidance note:As input to the velocity part of a hydrodynamic pressure the fol-lowing formula for the maximum vertical velocity may beapplied:

where

Alternatively, this quantity can be calculated more accurately bynumerical prediction of the lifeboat trajectory either by CFD or asimplified numerical model.A simplified formulation based on cross-sectional flow past a cir-cular cylinder, see Figure 16, is given below. An equivalenthydrodynamic diameter must be defined. This simplification isonly relevant for cross sections which are close to a circular crosssection. The pressure distribution as a function of the polar coordinatesReqv and θ describing the cross section at the lifeboat geometricalcentre position based on potential flow assumption is

where

A correction due to viscosity (Reynolds dependent) can be intro-duced, see Figure 17.Maximum velocity vc and maximum accelerations ac do usuallynot occur at the same time instant. The most conservativeassumption with respect to structural integrity shall be applied.

1

Hullpressure

Roof deformation

2

3

4

Roof pressure

Side pressure

= is the lifeboat submerged displacementM = total mass of lifeboat CD,L = drag coefficient related to the x-y

exposed characteristic area L = lifeboat total lengthB = lifeboat maximum breadth

LBC

Mgv

LDc

,

)(2ρ

−∇=

∇

θρθρθ cos221sin),( 2

ceqvpceqvavseqv aRcvgRpppRp ++=++=

θ2sin41−=pc

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Figure 16 Average pressure distribution illustrated.

Figure 17 Average pressure distribution around a smooth cylinder in steady incident flow dependent on Reynolds number.

For general noncircular cross-sections, the pressure distributioncan be calculated by numerical methods either by a potential flowmethod (sink-source) or by Computational Fluid Dynamicsincluding viscous effects. The potential flow pressure distribu-tion using a sink-source formulation can be found by using highand low frequency limit solutions. Examples of the numericallycalculated distribution against hydrostatic distribution can befound in Figure 18. Note the negative pressure peak. The totalpressure is obtained by adding atmospheric pressure. The possi-bility of underpressure leading to cavitation must be investigated.

Conservative longitudinal distributions must be specified in theascent phase. The most conservative distribution is usually uni-form longitudinally. This should be investigated. Other possiblelongitudinal distributions are also relevant if either measure-ments or numerical calculation can give additional information.


813 Asymmetric pressure distributions shall be considered forcross sea wave headings. Such asymmetric distributions canresult from, for example, asymmetry due to waves propagatingat an angle, asymmetrical load, skewed ascent, and poor direc-tional stability. The differential pressure between both sidewalls should be measured, cf. Sec.9 B303, for correction of thesymmetrical pressure distributions as indicated in Figure 16. 814 All pressures measured during a launch in calm water, infull scale tests as well as in model tests, shall be scaled to ULScharacteristic level, cf. Sec.9. The characteristic pressure isdefined as the 99% quantile in the long term distribution of themaximum peak pressure during a launch initiated at an arbi-trary point in time. If differential pressures measured in wavesfrom model tests will be used to modify the still water pressuredistributions, cf. Sec.9, then the maximum differential pressureshall be scaled to a characteristic differential pressure based onthe 99% quantile in the long term distribution of the maximumdifferential peak pressure during a launch initiated at an arbi-trary point in time.815 The pressure on front top and back of wheelhouse forfully submerged lifeboats cannot be obtained by analytic ornumerical methods as long as the shock effect from ventilationis not properly accounted for in the numerical method. Basedon experimental data the following estimations may beapplied:

— wheelhouse front: 200% of maximum pressure on the roofaft part

— wheelhouse top: 75% of maximum pressure on the roof aftpart

— wheelhouse aft: 75% of maximum pressure on the roof aftpart.

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Figure 18 Example of numerical pressure distribution from potential theory for a given vertical cross flow velocity. “Tot_theo” denotes pressurerelated to a simplified circular cross section. “Total p” denotes numerically calculated pressure for a given cross section. “Static p” ishydrostatic pressure. The horizontal axis is pressure while vertical axis is z-position below free surface.

816 The pressure on other appendices related to the roofstructure of fully submerged lifeboats shall be estimated basedon geometrical considerations. If the appendices are not shel-tered but potentially exposed by the cavity shock wave, theincrease in pressure in the vicinity of the appendix is a factorof two times the maximum pressure at the roof aft of appendi-ces.817 The pressure distribution for a partly submerged lifeboatin the partly submerged horizontal acceleration phase is com-plex and is difficult to relate to time instances. Therefore thefollowing distributions are recommended and shall be evalu-ated in order to impose the most conservative distribution forthe lifeboat structure:

— Slamming loads on the canopy structure: This is in the ini-tial phase of contact between the hull of the lifeboat andwater. The canopy is still dry. The load in this phase isconsidered very little sensitive to the wave conditions. Theload is assumed to act vertically (perpendicular to the keelline).

— Homogenous pressure distribution around the cross sec-tion of the lifeboat. It is assumed that the load acts simul-taneously over the full length.

— A vertical, acceleration-dependent pressure on the canopy.The pressure distribution will be proportional to the cosinebetween the slope of the canopy and the horizontal plane.

— Hydrostatic pressure distribution along the side of the can-opy.

Guidance note:All recommended pressure distributions models must be given asinput to the structural analysis required in Sec.6 A600. The valid-ity of design pressure load models must always be judged againststructural assumptions such as the flexibility in the canopy versusthe flexibility in the hull. The process of defining the design pres-sure distribution is thus iterative and will require that all criticalpressure distributions are thoroughly evaluated as requiredthroughout E800. Alternatively, recognized CFD tools can beused to establish the indicated theoretical pressure distributions.The CFD tools must be validated against full scale or model scalemeasurements.


E 900 Fatigue loads901 For design against failure in the fatigue limit state the

expected load effect history of mean stress, stress range andnumber of stress cycles at each stress level shall be applied.This load effect history includes, but is not limited to, effectsfrom one emergency launch of the lifeboat at an arbitrary pointin time and effects from several operational test launches incalm water and water with relaxed wave conditions. 902 For requalification of a lifeboat, which has been used forone or more emergency launches in the past, sufficient safetyagainst failure in the fatigue limit state shall be ensured withdue account for the load effect history from the previous use ofthe lifeboat.

F. Accidental Loads (A)F 100 General101 Accidental loads are loads related to abnormal opera-tions or technical failure. Examples of accidental loads areloads caused by:

— impact from dropped objects — impact when launched on objects— collision impact (impact from ship collisions, or from col-

lision with host facility)— explosions— fire, including burning sea surface— breaking waves in the sailing phase— accidental impact from vessel, helicopter or other objects— unintended change in ballast distribution— unintended distribution of occupants, in particular unsym-

metrical distribution of occupants— unintended loads from damaged skid and their possible

unfavourable effects on the trajectory.

102 Sufficient robustness during stowage to resist minorimpacts e.g. from dropped tools is normally ensured by therequirements to minimum scantlings given in Sec.6. Suchimpacts are considered part of normal use and are not consid-ered accidents. Hence, there is no need to explicitly defineaccidental loads to represent such scenarios.103 An assumption of this standard is that the lifeboat stationis protected from the hazard areas of the host facility to ensurethat the lifeboat will not be exposed to severe blasts from explo-sions or high temperatures or heat fluxes from a fire. Hence blast

5 -

4 -

3 -

2 -

-60 -40 -20 0 20 40 60 80 Pressurel [kPa]

Total pStatic pTot_theo

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and fire loads when stowed need not be considered.104 Sufficient robustness to resist the impact from strikingminor floating objects in the impact-phase of a launch is nor-mally ensured by the requirements to minimum scantlings ofSec.6. For free-fall lifeboats, it is not considered feasible todevelop a hull structural design that protects the occupantsfrom a collision with a major floating object, such as e.g.another lifeboat or a large piece of floating debris, in theimpact phase of a launch. 105 Sufficient robustness to resist minor impacts that mayoccur during the use of the lifeboat, e.g. from helicopter rescueoperations, is normally ensured by the requirements to mini-mum scantlings of Sec.6. Such impacts are considered part ofnormal use and are not considered accidents. Hence, there is noneed to explicitly define accidental loads to represent such sce-narios.106 Free fall lifeboats are not normally designed to survivecollisions with other ships or the host facility. The key designtarget is to avoid such collisions. However, the inherent robust-ness of structures designed to this code provides some collisionsurvivability and the buoyancy requirements provide somesurvival capability in case the hull is flooded due to a collision.

G. Deformation Loads (D)G 100 General101 Deformation loads are loads caused by inflicted defor-mations such as:

— temperature loads— built-in deformations.

G 200 Temperature loads201 Structures shall be designed for the most extreme tem-perature differences they may be exposed to. 202 The ambient sea or air temperature shall be calculated asthe extreme value whose return period is 100 years.203 Structures shall be designed for a solar radiation inten-sity of 1 000 W/m2.

H. Load Effect AnalysisH 100 General101 Load effects, in terms of motions, displacements, andinternal forces and stresses in the structure, shall be determinedwith due consideration of:

— their spatial and temporal nature including:

— possible nonlinearities of the load— dynamic character of the response

— the relevant limit states for design checks— the desired accuracy in the relevant design phase.

102 Permanent loads, functional loads, deformation loads,and fire loads can generally be treated by static methods ofanalysis. Environmental loads (by wind, waves, current, ice,water level and earthquake) and certain accidental loads (byimpacts and explosions) may require dynamic analysis. Inertiaand damping forces are important when the periods of steady-state loads are close to natural periods or when transient loadsoccur.103 Uncertainties in the analysis model are expected to betaken care of by the load and resistance factors. For accelera-

tion loads in the human body, for which load and resistancefactors are not used, such model uncertainties are expected tobe taken care of by the requirements which are set to theacceptable threshold values. If uncertainties are particularlyhigh, conservative assumptions shall be made.104 If analytical models are particularly uncertain, the sensi-tivity of the models and the parameters utilized in the modelsshall be examined. If geometric deviations or imperfectionshave a significant effect on load effects, conservative geomet-ric parameters shall be used in the calculation. 105 In the final design stage theoretical methods for predic-tion of important responses of any novel system should be ver-ified by appropriate model tests. Full scale tests may also beappropriate.

H 200 Global motion analysis201 The purpose of a motion analysis is to determine dis-placements, accelerations, velocities and hydrodynamic pres-sures relevant for the loading on the lifeboat structure.Excitation by waves, current and wind should be considered.

H 300 Load effects in structures 301 Displacements, forces and stresses in the structure shallbe determined for relevant combinations of loads by means ofrecognized methods, which take adequate account of the vari-ation of loads in time and space, the motions of the structureand the limit state which shall be verified. Characteristic val-ues of the load effects shall be determined.302 Nonlinear and dynamic effects associated with loads andstructural response shall be accounted for whenever relevant.303 The stochastic nature of environmental loads shall beadequately accounted for.

I. Stowage Loads

I 100 General101 During stowage in the lifeboat station, the lifeboat willbe subject to loads from the davit arrangement, the hook sys-tem and the skid system as well as loads associated with theself weight of the lifeboat. The lifeboat shall be designedagainst these loads.102 Wind loads may act on the lifeboat during its stowage inthe lifeboat station and shall be accounted for in design.103 The performance of a lifeboat in a given emergency sit-uation may depend on accumulated loads during stowage andon accidental loads from the launch system. Such loads shallbe identified and analysed. 104 If waves are allowed to act on the stowage position orthere is a potential for run-up in the stowage position, which isnot usually accepted, relevant slamming loads from waves onthe lifeboat shall be investigated.

I 200 Snow and ice loads201 Loads from snow and ice shall be considered.202 Snow and ice loads due to snow and ice accumulationmay be reduced or neglected if a snow and ice removal proce-dure is established.203 Possible increases of cross-sectional areas and changesin surface roughness caused by icing shall be considered wher-ever relevant. This is particularly important whenever windloads and hydrodynamic loads are to be determined and alsowhen the friction between lifeboat and skid is to be assessedfor skid-launched lifeboats.

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J. Load Factors for DesignJ 100 Load factors for the ULS, launching101 For design against failure in the ULS during launching,one set of load combinations shall be considered as specifiedin Table J1. Table J1 specifies the requirements to the load fac-tors.

The load factor γfE for environmental loads is given in 102 and103.102 For environmental loads during launching, the load fac-tor γfE for design in the ULS is formed as a product of two par-tial safety factors,

γfE = γSC ⋅ γC,where γSC is a safety class factor and γC is a condition factor.103 The requirements to γSC and γC in design depend on theconditions during the launch, i.e. whether the lifeboat becomesfully submerged for some time during the launch or whether itdoes not. Table J2 provides values of γSC and γC which shallbe used in design against the ULS. The resulting load factorshall be used in ULS analyses for design as a factor on thecharacteristic environmental load or load effect, defined as the99% quantile in the long-term distribution of the load or loadeffect, whichever is applicable.

Guidance note:The safety class factor γSC is meant to ensure that the overallsafety requirements for design to high safety class is met and theproduct of the safety class factor γSC and the condition factor γCis meant to ensure that an adequate safety is achieved also in therare event that an evacuation is carried out during an extreme seastate such as the sea state whose significant wave height has areturn period of 100 years.


J 200 Load factors for the ULS, stowage201 For design against failure in the ULS during stowage,

two sets of load combinations shall be considered as specifiedin Table J3. Table J3 specifies the requirements to the load fac-tors. The load factor for environmental load shall be used inULS analyses for design as a factor on the characteristic envi-ronmental load or load effect, defined as the 99% quantile inthe distribution of the annual maximum load or load effect,whichever is applicable.

Guidance note:Contrary to environmental loads during launching, which arisefrom a brief exposure to the environment at an arbitrary point intime, environmental loads during stowage arise from continuousexposure to the environment over a longer period of time. This isreflected in different definitions of characteristic environmentalload and in different requirements to the load factor, cf. the dif-ference between Tables J1 and J3. During stowage in the lifeboatstation, environmental loads are expected to arise mainly fromwind and maybe from snow and ice, but not from waves, sincethe lifeboat station is presumed located at a level with sufficientair gap to prevent any waves from reaching the lifeboat. The 3-second gust with return period 100 years can be used as abasis for calculation of the 99% quantile in the distribution of theannual maximum wind load or wind load effect.


J 300 Load factor for the ALS301 The load factor γf in the ALS is 1.0.

J 400 Load factors for design of hooks and attachments401 For design of hooks and attachments for the launchingsystem, two load combinations shall be considered as specifiedin Table J4. Table J4 specifies the requirements to the load fac-tors for each combination. The requirements to the load factorsapply to design during stowage as well as to design duringlaunching prior to the release of the lifeboat.

Table J1 Load factors γf for the ULS, launchingLoad factors Load categories

G Q E Dγf 1.3 1.3 γfE 1.0

Table J2 Load factors for environmental loads in the ULS, launching

Launch conditionLoad factor γfE = γSC ⋅ γC

Safety class factor γSC

Condition factor γC

Partly submerged lifeboat 2.1 1.5

Fully submerged lifeboat 1.8 1.0

Table J3 Load factors γf for the ULS, stowageLoad com-bination

Load categoriesG Q E D

(a) 1.3 1.3 0.7 1.0(b) 1.0 1.0 1.3 1.0

Table J4 Load factors γf for design of hooks and attachmentsLoad com-bination

Load categoriesG Q E D

(a) 1.3 1.3 0.7 1.0(b) 1.0 1.0 1.3 1.0

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SECTION 5MATERIALS

A. GeneralA 100 Scope101 Strength and deformation properties of materials shallbe documented. This section provides criteria for structuralcategorization and corresponding selection of materials forlifeboat structures. Depending on material type and category,requirements to strength and deformation properties of materi-als are given. Inspection principles to be applied in design andconstruction of lifeboat structures are also given. The follow-ing materials are covered:

— steel— aluminium— Fibre Reinforced Plastics (FRP), also known as composite

materials— sandwich materials.

A 200 Temperatures for selection of material201 The design temperature for a structural component is thereference temperature used as a criterion for the selection ofmaterial quality. For structural components constructed fromsteel or aluminium, the design temperature shall be equal to orlower than the lowest daily mean temperature in air in the areaswhere the lifeboat is to be transported, installed, stored andoperated. For structural components constructed from compos-ite or sandwich materials two design temperatures shall apply.The design minimum temperature shall be equal to the designtemperature defined for steel and aluminium. The design max-imum temperature shall be equal to 80°C in areas exposed todirect sunlight. Otherwise the maximum daily temperature canbe used. Materials in the neighbourhood of machinery partsetc. shall be able to withstand the local temperatures.

Guidance note:For steel and aluminium, a low temperature is critical for design,since a too low temperature may lead to brittle material behav-iour. For composites, a high temperature is critical for design,since a too high temperature will lead to soft material behaviour.However, for composites a low temperature can also be criticalin some cases.


202 The service temperatures for different components ofthe lifeboat structure apply as a basis for selection of materialquality. 203 Steel and aluminium components shall be designed for aservice temperature not higher than the design temperature forthe areas where the lifeboat is to transported, installed, storedand operated. In case two or more service temperatures applyto such a structural component, the lower specified value shallbe applied in design.204 Composite components shall be designed for both aminimum service temperature and a maximum service temper-ature. The minimum service temperature shall not be higherthan the design minimum temperature. The maximum servicetemperature shall not be taken lower than the design maximumtemperature. 205 Internal structures in permanently heated rooms neednot be designed for service temperatures lower than 0°C.

A 300 Fire301 The fire resistance of the selected materials shall be suf-ficient to meet the requirement given in Sec.8 D101. Fulfil-ment of this requirement shall be documented by testing in

accordance with specifications given in Sec.9 C601.

A 400 Inspections401 Regardless of material type, inspections by means ofnondestructive testing (NDT) can be used to monitor materialsand document that their properties meet the requirements.Nondestructive testing can be used for inspection of materialsduring manufacturing as well as for periodic inspections dur-ing the service life of the lifeboat.

B. Structural CategorizationB 100 Structural categories101 Structural categories are assigned to both metallic mate-rials and composite components. The category shall beselected based on the criticality of the component. The require-ments to characterization and quality assurance of a materialwill depend on the structural category of the component inwhich the material is used. 102 Components are classified into structural categoriesaccording to the following criteria:

— significance of component in terms of consequence of failure — stress condition at the considered detail that together with

possible weld defects or fatigue cracks may provoke brittlefracture.

Guidance note:The consequence of failure may be quantified in terms of residualstrength of the structure when considering failure of the actualcomponent.


103 The structural category for selection of materials shallbe determined according to principles given in Table B1.

Guidance note:According to the definition of structural categories in Table B1,structural components may exist that qualify both as primarystructures and secondary structures. A stiffener, for example, willbe “secondary” with respect to overloading from fluid pressureswhereas it will be “primary” with respect to overloading fromglobal bending of the hull beam. Structural components thatqualify for more than one structural category according to TableB1 shall always be considered according to the stricter category.

Table B1 Structural categories for selection of materials Structural category Principles for determination of structural category

Special Structural parts where failure will have substantial consequences for the lifeboat and its passengers and which are subject to a stress condition that may increase the probability of a brittle fracture in the life-boat and/or are constructed such that brittle failure is the dominant failure mode.1)

Primary Structural parts where failure will have substantial consequences for the lifeboat and its passengers.

Secondary Structural parts where failure will be without signifi-cant consequence for the lifeboat and its passengers.

1) In complex joints a triaxial or biaxial stress pattern will be present. This may give conditions for brittle fracture where tensile stresses are present in addition to presence of defects and material with low fracture toughness. Particular laminate lay-ups in FRP components combined with certain stress conditions, e.g. through thickness, may exhibit a brittle failure mode.

DET NORSKE VERITAS


The term “secondary structures” is often used to mean entireobjects like railings, masts and even small deckhouses that do notform a part of the main hull structure and canopy of the lifeboat.


104 Requirements and guidance for manufacturing of steeland aluminium materials are given in DNV-OS-C401. Supple-mentary guidance for manufacturing of steel materials can befound in ENV 1090-1 and ENV 1090-5. Steel and aluminiumproducts shall be delivered with inspection documents asdefined in EN 10204 or in an equivalent standard. Unless oth-erwise specified, material certificates according to Table B2shall be presented for metallic materials.

105 Requirements and guidance for manufacturing of com-posite materials are given in DNV-OS-C501. Compliance withthe requirements shall be documented according to Table B3.

B 200 Inspection categories201 Requirements for type and extent of inspection of weldsare given in DNV-OS-C401 depending on assigned inspectioncategory for the welds. The requirements are based on the con-sideration of fatigue damage and assessment of general fabri-cation quality. 202 The inspection category is by default related to the struc-tural category according to Table B4.

203 The weld connection between two components shall beassigned an inspection category according to the highest cate-gory of the joined components. For stiffened plates, the weldconnection between stiffener and stringer and girder web to theplate may be inspected according to inspection Category III.204 If the fabrication quality is assessed by testing, or if it isof a well known quality based on previous experience, theextent of inspection required for elements within structural cat-egory primary may be reduced, but the extent must not be lessthan that for inspection Category III.205 Fatigue-critical details within structural category pri-mary and secondary shall be inspected according to require-ments given for Category I.206 Welds in fatigue-critical areas not accessible for inspec-tion and repair during operation shall be inspected according torequirements in Category I during construction.

C. SteelC 100 General101 For steel materials, the assignment of structural categoryserves the purpose of assuring an adequate level of inspectionin addition to assuring adequate material quality. Conditionsthat may result in brittle fracture shall be avoided.

Guidance note:Brittle fracture may occur under a combination of:- presence of sharp defects such as cracks- high tensile stress in direction normal to planar defect(s)- material with low fracture toughness.Sharp cracks resulting from fabrication may be detected byinspection and can subsequently be repaired. Fatigue cracks mayalso be discovered during service life by inspection.High stresses in a component may occur due to welding. A com-plex connection is likely to provide more restraint and largerresidual stress than a simple one. This residual stress may bepartly removed by post weld heat treatment if necessary. Also, acomplex connection exhibits a more three-dimensional stressstate due to external loading than simple connections. This stressstate may provide basis for a cleavage fracture.The fracture toughness is dependent on temperature and materialthickness. These parameters are accounted for separately inselection of material. The resulting fracture toughness in theweld and the heat affected zone is also dependent on the fabrica-tion method.Thus, to avoid brittle fracture, first a material with suitable frac-ture toughness for the actual design temperature and thickness isselected. Then a proper fabrication method is used. In specialcases post weld heat treatment may be performed to reduce crackdriving stresses, see DNV-OS-C401. A suitable inspection pro-gram is applied to detect defects and allow for removal of planardefects larger than those considered acceptable. Steel qualitieswith appropriate fracture toughness and inspection programs toavoid unacceptable defects are achieved by assigning differentstructural categories and different inspection categories to differ-ent types of structural connections, see Tables B1 and B4.


C 200 Structural steel designations201 Wherever the subsequent requirements for steel gradesare dependent on plate thickness, these requirements are basedon the nominal thickness as built.202 The requirements in this subsection deal with the selec-

Table B2 Material certificates for metallic materials

Certification processMaterial

certificate (EN10204)

Structural category

Test certificateAs work certificate, inspection and tests witnessed and signed by an independent third party body

3.2 Special

Work certificateTest results of all specified tests from samples taken from the prod-ucts supplied. Inspection and tests witnessed and signed by QA department

3.1 Primary

Test reportConfirmation by the manufacturer that the supplied products fulfil the purchase specification, and test data from regular production, not necessarily from products sup-plied

2.2 Secondary

Table B3 Material certificates for composite materials and sandwich materialsCertification process Structural category

Test certificateEvaluation and inspection of production process. Inspection and tests witnessed and signed by an independent third party body

Special

Work certificateEvaluation of production process. Inspec-tion and tests results signed by QA depart-ment.

Primary

Test reportConfirmation by the manufacturer that the supplied products fulfil the purchase speci-fication, and test data from regular produc-tion, not necessarily from products supplied

Secondary

Table B4 Inspection categories Inspection category Structural category

I SpecialII PrimaryIII Secondary

DET NORSKE VERITAS


tion of various structural steel grades in compliance with therequirements given in DNV-OS-B101. Where other codes orstandards have been agreed on and utilized in the specificationof steels, the application of such steel grades within the struc-ture shall be specially considered.203 The steel grades selected for structural components shallbe related to calculated stresses and requirements to toughnessproperties. Requirements for toughness properties are in gen-eral based on the Charpy V-notch test and are dependent ondesign temperature, structural category and thickness of thecomponent in question. 204 The material toughness may also be evaluated by frac-ture mechanics testing in special cases.205 In structural cross-joints where high tensile stresses areacting perpendicular to the plane of the plate, the plate materialshall be tested to prove the ability to resist lamellar tearing, Z-quality, see 212.206 Requirements for forgings and castings are given inDNV-OS-B101.207 Material designations for steel are given in terms of astrength group and a specified minimum yield stress accordingto steel grade definitions given in DNV-OS-B101 Ch.2 Sec.1.The steel grades are referred to as NV grades. Structural steeldesignations for various strength groups are referred to asgiven in Table C1.

208 Each strength group consists of two parallel series ofsteel grades:

— steels of normal weldability— steels of improved weldability.

The two series are intended for the same applications. How-ever, the improved weldability grades have, in addition toleaner chemistry and better weldability, extra margins toaccount for reduced toughness after welding. These grades arealso limited to a specified minimum yield stress of 500 N/mm2. 209 Regardless of strength group, the modulus of elasticityfor structural steel shall be taken as ES = 2.1⋅105 N/mm2.210 Conversions between NV grades as used in Table C1and steel grades used in the EN10025-2 standard are used forthe sole purpose of determining plate thicknesses and are givenin Table C2. The number of one-to-one conversions between

NV grades and EN10025-2 grades given in Table C2 is lim-ited, because the E-qualities of the NV grades are not definedin EN10025-2 and because no qualities with specified mini-mum yield stress fy greater than 355 MPa are given inEN10025-2.

Guidance note:Important notes to the conversions between NV grades andEN10025-2 grades in Table C2:NV grades are, in general, better steel qualities than comparableEN10025-2 grades. For example, all NV grades except NV A andNV B are fully killed and fine grain treated. This is the case onlyfor the J2G3 and K2G3 grades in EN10025-2.The delivery condition is specified as a function of thickness forall NV grades, while this is either optional or at the manufac-turer’s discretion in EN10025-2. The steel manufacturing process is also at the manufacturer’soption in EN10025-2, while only the electric process or one ofthe basic oxygen processes is generally allowed according to theDNV standard.For the grades NV A, NV B and NV D, an averaged impactenergy of minimum 27 Joule is specified for thicknesses up toand including 50 mm. For larger thicknesses, higher energyrequirements are specified. EN10025-2 requires an averagedimpact energy of minimum 27 Joule regardless of thickness.Concerning NV A36 and NV D36, minimum 34 Joule averagedimpact energy is required for thicknesses below 50 mm, 41 Joulefor thicknesses between 50 and 70 mm, and 50 Joule for thick-nesses above 70 mm. EN10025-2 specifies 27 Joule averagedimpact energy for the S355J0 and S355J2G3 grades and 40 Joulefor the S355K2G3 grade.In EN10025-2, minimum specified mechanical properties (yieldstress, tensile strength range and elongation) are thicknessdependent. The corresponding properties for NV grades are spec-ified independently of thickness.


211 Conversions between NV grades as used in Table C1and steel grades used in the EN10025-3 standard are used forthe sole purpose of determining plate thicknesses and are givenin Table C3.

Table C1 Material designations

Designation Strength group Specified minimum yield stress fy (N/mm2)1)

NV Normal strength steel (NS) 235

NV-27High strength

steel (HS)

265NV-32 315NV-36 355NV-40 390NV-420

Extra high strength steel

(EHS)

420NV-460 460NV-500 500NV-550 550NV-620 620NV-690 6901) For steels of improved weldability the required specified minimum

yield stress is reduced for increasing material thickness, see DNV-OS-B101.

Table C2 Steel grade conversionsNV grade EN10025-2NVANVBNVDNVE

S235JR+NS235J0

S235J2+N–

NV A27NV D27NV E27

S275J0S275J2+N

–NV A32NV D32NV E32

–––

NV A36NV D36NV E36

S355J0S355K2+N and S355J2+N

–NV A40NV D40NV E40NV D420NV E420NV F420NV D460NV E460

––––––––

NV F460 –

DET NORSKE VERITAS


Guidance note:Important notes to the conversions between NV grades andEN10025-3 grades in Table C3:The conversions are based on comparable requirements tostrength and toughness.Because EN10025-3 specifies requirements to fine grain treat-ment, the EN10025-3 grades are in general better grades thancorresponding grades listed in EN10025-2 and can be consideredequivalent with the corresponding NV grades.


212 Within each defined strength group, different steelgrades are given, depending on the required impact toughnessproperties. The grades are referred to as A, B, D, E, and F fornormal weldability grades and AW, BW, DW, and EW forimproved weldability grades as defined in Table C4.Additional symbol:

213 The grade of steel to be used shall in general be selectedaccording to the design temperature and the thickness for the

applicable structural category as specified in Table C5. Thesteel grades in Table C5 are NV grade designations. Nationalregulations may provide additional criteria for selection of thegrade of steel.

Guidance note:Norwegian governmental regulations exclude the use of Grade Asteels on facilities in Norwegian waters, including lifeboats onthese facilities.


214 Selection of a better steel grade than minimum requiredin design shall not lead to more stringent requirements in fab-rication. 215 The grade of steel to be used for thickness less than 10mm or design temperature above 0°C or both shall be speciallyconsidered in each case. 216 Welded steel plates and sections of thickness exceedingthe upper limits for the actual steel grade as given in Table C5shall be evaluated in each individual case with respect to thefitness for purpose of the weldments. The evaluation should bebased on fracture mechanics testing and analysis, e.g. inaccordance with BS 7910.217 For regions subjected to only compressive or only lowtensile stresses or both, consideration may be given to the useof lower steel grades than stated in Table C5.

D. AluminiumD 100 Material designations101 Wherever the subsequent requirements for aluminium

Table C3 Steel grade conversionsNV grade EN10025-3 gradeNVANVBNVDNVE

––––

NV A27NV D27NV E27

–S275N

S275NLNV A32NV D32NV E32

–––

NV A36NV D36NV E36

–S355N

S355NLNV A40NV D40NV E40NV D420NV E420NV F420NV D460NV E460

–––

S420NL––

S460NS460NL

NV F460 –

Z = steel grade of proven through-thickness properties. This symbol is omitted for steels of improved weldability although improved through-thickness properties are required.

Table C4 Applicable steel gradesStrength group

Grade Test temperature (°C)Normal

weldabilityImproved weldability

NS A ⎯ Not testedB 1) BW 0D DW –20E EW –40

HS AH AHW 0DH DHW –20EH EHW –40FH ⎯ –60

EHS AEH ⎯ 0DEH DEHW –20EEH EEHW –40FEH ⎯ –60

1) Charpy V-notch tests are required for thickness above 25 mm but is subject to agreement between the contracting parties for thickness of 25 mm or less.

Table C5 Thickness limitations (mm) of structural steels for different structural categories and design temperatures (ºC)Structural Category

Grade ≥ 10 0 –10 –20

Secondary

AB/BWD/DWE/EWAH/AHWDH/DHWEH/EHWFHAEHDEH/DEHWEEH/EEHWFEH

3060

15015050

10015015060

150150150

3060

15015050

10015015060

150150150

2550

1001504080

15015050

100150150

20408015030601501504080150150

Primary

AB/BWD/DWE/EWAH/AHWDH/DHWEH/EHWFHAEHDEH/DEHWEEH/EEHWFEH

304060

1502550

1001503060

150150

203060

1502550

1001503060

150150

102550

100204080

1502550

100150

N.A.204080153060150204080150

Special

D/DWE/EWAH/AHWDH/DHWEH/EHWFHAEHDEH/DEHWEEH/EEHWFEH

3560102550

100153060

150

3060102550

100153060

150

2550

N.A.204080102550

100

2040

N.A.153060

N.A.204080

N.A. = No Application

DET NORSKE VERITAS


grades are dependent on plate thickness, these requirementsare based on the nominal thickness as built.102 The requirements in this subsection deal with the selec-tion of various structural aluminium grades in compliance withthe requirements given in DNV-OS-B101. Where other codesor standards have been agreed on and utilized in the specifica-tion of aluminium, the application of such aluminium gradeswithin the structure shall be specially considered.103 Requirements for forgings and castings are given inDNV-OS-B101.104 Aluminium alloys are classified into grades according tochemical composition and into temper according to hardeningmethod. The alloy grades are listed in Table D1. Temper des-ignations are given in Table D2. The numerical designations(grades) of aluminium alloys are based on those of the Alumin-ium Association. The designations are applicable to wroughtaluminium products within the thickness range of 3 mm to50 mm.105 In this standard, a distinction is made between alloyswhich are capable of being strain hardened and alloys whichare capable of being age hardened. 5000 series alloys are alloys

capable of being strain hardened and are listed in Tables D3and D4. 6000 series alloys are alloys capable of being agehardened and are listed in Table D4.106 The prime alloy selection for main structural compo-nents should be alloy 5083 for plates and alloy 6005 or 6082for profiles. The other alloys listed should be used for second-ary applications. For weld filler material alloy 5183 should bethe prime selection. The use of 6000 series aluminium alloysin direct contact with seawater may be restricted depending onapplication and corrosion protection system.107 Mechanical properties in terms of yield strength and ten-sile strength are given in Tables D3 and D4 as functions ofgrade and temper. The modulus of elasticity for aluminium isgiven as function of grade in Table D5.108 Requirements and guidance for manufacturing of alu-minium materials are given in DNV-OS-C401. Aluminiummaterials and products shall be delivered with inspection doc-uments as defined in EN 10204 or in an equivalent standard.Unless otherwise specified, material certificates according toTable B2 shall be presented.

Table D1 Chemical composition limits 1) for wrought aluminium alloys

Grade Si Fe Cu Mn Mg Cr Zn TiOther elements 2)

Each TotalNV-5052 0.25 0.4 0.1 0.1 2.2-2.8 0.15-0.35 0.1 - 0.05 0.15NV-5154A 0.5 0.5 0.1 0.5 3.1-3.9 0.25 0.2 0.2 0.05 0.15NV-5754 0.4 0.4 0.1 0.5 3) 2.6-3.6 0.3 3) 0.2 0.15 0.05 0.15NV-5454 0.25 0.4 0.1 0.50-1.0 2.4-3.0 0.05-0.20 0.25 0.2 0.05 0.15NV-5086 0.4 0.5 0.1 0.20-0.7 3.5-4.5 0.05-0.25 0.25 0.15 0.05 0.15NV-5083 0.4 0.4 0.1 0.40-1.0 4.0-4.9 0.05-0.25 0.25 0.15 0.05 0.15NV-5383 0.25 0.25 0.2 0.7-1.0 4.0-5.2 0.25 0.4 0.15 0.05 4) 0.15 4)

NV-5059 0.45 0.5 0.25 0.6-1.2 5.0-6.0 0.25 0.40-0.9 0.2 0.05 5) 0.15 5)

NV-6060 0.30-0.6 0.10-0.30 0.1 0.1 0.35-0.6 0.05 0.15 0.1 0.05 0.15NV-6061 0.40-0.8 0.7 0.15-0.40 0.15 0.8-1.2 0.04-0.35 0.25 0.15 0.05 0.15NV-6063 0.20-0.6 0.35 0.1 0.1 0.45-0.9 0.1 0.1 0.1 0.05 0.15NV-6005A 0.50-0.9 0.35 0.3 0.5 6) 0.40-0.7 0.3 6) 0.2 0.1 0.05 0.15NV-6082 0.7-1.3 0.5 0.1 0.40-1.0 0.6-1.2 25 0.2 0.1 0.05 0.151) Composition in percentage mass by mass maximum unless shown as a range or as a minimum.2) Includes Ni, Ga, V and listed elements for which no specific limit is shown. Regular analysis need not be made.3) Mn + Cr: 0.10-0.60.4) Zr: maximum 0.20. The total for other elements does not include zirconium.5) Zr: 0.05-0.25. The total for other elements does not include zirconium.6) Mn + Cr: 0.12-0.50

DET NORSKE VERITAS


Table D2 Temper descriptions and designationsTemper description Temper

Tempers achieved by fabrica-tion, annealing, cold working, or cold working plus partial annealing or stabilization

As fabricated, cold worked without specified mechanical property limits FAnnealed, soft 0Strain hardened to specified strength 1/8 hard

1/4 hard1/2 hard

H11H12H14

Strain hardened and partially annealed (p.a.) to specified strength 1/8 hard, p.a.1/4 hard, p.a.1/2 hard, p.a.

H21H22H24

Strain hardened and stabilized to specified strength 1/4 hard1/2 hard

H32H34

Special tempers- Less strain hardened than H11, e.g. by straightening or stretching - No controlled strain hardening, but there are mechanical property limits - Treatment against exfoliation corrosion - Strain hardened less than required for a controlled H32 temper

H111H112H116H321

Heat treated tempers

Unstable condition after solution heat treatment WSolution heat treated, naturally aged T4Cooled from an elevated temperature shaping process, artificially aged T5Solution heat treated, artificially aged T6Solution heat treated, artificially overaged T7

Table D3 Mechanical properties for rolled aluminium alloys

Grade Temper Yield strength Rp0.2 minimum (N/mm2)

Tensile Strength Rm minimum or range

(N/mm2)

Elongation 1)

A50 mm minimum (%) A5d minimum (%)

NV-5052 0 or H111 65 165-215 19 18H32 130 210-260 12 2) 12H34 150 230-280 9 3) 9

NV-5154A 0 or H111 85 215-275 17 16H32 180 250-305 10 4) 9H34 200 270-325 8 7

NV-5754 0 or H111 80 190-240 18 17H32 130 220-270 10 9H34 160 240-280 10 4) 8

NV-5454 0 or H111 85 215-285 17 16H32 180 250-305 10 4) 9H34 200 270-325 8 7

NV-5086 0 or H111 100 240-310 17 16H112 125 5) 250 5) 8 9

H32 or H321 185 275-335 10 4) 9H34 220 300-360 8 7

NV-5083 0 or H111 125 275-350 16 15H112 125 275 12 10H116 215 305 12 2) 10

H32 or H321 215 305-380 10 4) 9NV-5383 0 or H111 145 290 17

H116 or H321 220 305 10NV-5059 0 or H111 160 330 24

H116 or H321 270 6) 370 6) 101) Elongations in 50 mm column apply to thicknesses up to and including 12.5 mm and in 5d column to thicknesses in excess of 12.5 mm.2) 10% for thicknesses up to and including 6.0 mm.3) 7% for thicknesses up to and including 6.0 mm.4) 8% for thicknesses up to and including 6.0 mm.5) Yield strength minimum 105 N/mm2 and tensile strength minimum 240 N/mm2 for thicknesses in excess of 12.5 mm.6) Yield strength minimum 260 N/mm2 and tensile strength minimum 360 N/mm2 for thicknesses in excess of 20 mm.

DET NORSKE VERITAS


E. Composite Materials

E 100 Introduction101 Composite materials are produced in specific ways bycombining fibres and resin to a laminate. Laminates used in alifeboat shall be clearly specified and all materials shall betraceable. 102 Methods described in DNV-OS-C501 may be used tocalculate and document laminate properties.

E 200 Laminate specification201 A minimum set of process parameters and constituentmaterial characterizations is given in Table E1. All these items

shall be specified.

Table D4 Mechanical properties for extruded aluminium alloys

Grade Temper Yield strength Rp0.2 min-imum (N/mm2)

Tensile Strength Rm mini-mum or range (N/mm2)

Elongation 1)

A50 mm minimum (%) A5d minimum (%)

Openprofiles

NV-5083 0 or H111 110 270 12 10H112 125 270 12 10

NV-5086 0 or H111 95 240-320 18 15H112 95 240 12 10

NV-5383 0 or H111 145 290 17H112 190 310 13

NV-5059 H112 200 330 10NV-6060 T4 60 120 16 14

T5 100 140 8 6T6 140 170 8 6

NV-6061 T4 110 180 15 13T5 205 240 6 7T6 240 260 10 8

NV-6063 T4 65 130 14 12T5 110 150 8 7T6 170 205 10 9

NV-6005A T4 90 180 15 13T5 or T6 215 260 8 6

NV-6082 T4 110 205 14 12T5 2) 230 270 8 -T6 2) 250 290 8 -T6 3) 260 310 10 8

Closed profiles

NV-6060 T5 135 175 5NV-6061 T5 or T6 205 245 4

NV-6005A T5 or T6 215 250 5NV-6082 T5 or T6 240 290 5

1) Elongations in 50 mm column apply to thicknesses up to and including 12.5 mm and in 5d column to thicknesses in excess of 12.5 mm.2) Property limits apply for thicknesses up to and including 5.0 mm.3) Property limits apply for thicknesses in excess of 5.0 mm.

Table D5 Modulus of elasticity for aluminium alloysGrade E [MPa]NV-5052 70 000NV-5083 71 000NV-5086 71 000NV-5154A 70 500NV-5454 70 500NV-5754 70 500NV-6060 69 500NV-6061 70 000NV-6063 69 500NV-6082 70 000

Table E1 Basic information to identify a laminateConstituent materials:Generic Fibre typeType of weaveGeneric resin type (e.g. epoxy, polyester)Specific resin type (trade name)Process parameters:Processing methodProcessing temperatureProcessing pressureProcess atmosphere (e.g. vacuum)Post curing (temperature and time)Control of fibre orientationFibre volume fractionVoid contentConditioning parameters:TemperatureWater content of the laminate (wet, dry)Chemical environmentLoading rateFor each parameter:Measured valuesGuaranteed minimum valuesEstimated standard deviation, based on testsNumber of specimens tested

DET NORSKE VERITAS


202 A laminate is made of a sequence of plies. All materialsand the stacking sequence of the plies shall be clearly identi-fied. The orientation of nonhomogenous or anisotropic materi-als shall be clearly specified on the materials level and on thestructural level.203 The type of fabric shall be clearly specified for each ply,i.e. specification of fibre, weight of reinforcement per unitarea. In addition, the fabrication method shall be specified, forexample manual lamination and vacuum assisted resin transfermoulding.

E 300 Laminate strength and stiffness301 Strength and stiffness shall be represented in terms ofcharacteristic values. 302 For laminates, characteristic values usually have to beestablished based on measurements on test specimens. Forestimation of characteristic values from test data, the followingstatistical properties are needed:

— Sample mean

— Sample standard deviation

— Sample coefficient of variation .

Here, xi, i = 1,...n, are the n observations of the material prop-erty to be estimated, obtained from tests.303 The characteristic value of strength is defined as a low2.5% quantile in the distribution of the arbitrary strength.When characteristic values of strength are estimated from data,the estimate shall be given with confidence. Characteristic val-ues of strength for use in design shall be estimated with 95%confidence. Characteristic values can be estimated with confi-dence in accordance with Table E2.

304 The characteristic value of material stiffness used forstrength calculations is defined as the mean value. The charac-teristic value of material stiffness used for deflection calcula-tions is also defined as the mean value. The characteristic valueof material stiffness can be estimated by the sample mean ofstiffness data from tests. The characteristic value of structuralstiffness can be calculated from the characteristic value of

material stiffness in conjunction with geometry data.305 As a minimum, strength and stiffness shall be docu-mented in all main fibre directions of a laminate. This can bedone by calculations using classical laminate theory. Testingmay be necessary when representative material properties arenot available. 306 Laminate properties shall be documented for the maxi-mum and minimum use temperature. In most cases propertiesdo not change much with temperature as long as the tempera-ture remains 20°C below the glass transition temperature Tg. Ifthe service temperature remains within the non-change condi-tions, testing at room temperature is sufficient.307 For general plate calculations for thin plates, throughthickness stresses are small and can be ignored as long as thegeneral performance requirements for the laminate are met.Through thickness laminate properties need not be measured.If through thickness stresses are needed in the design calcula-tions, their properties have to be based on measured values onthe actual laminates.308 Characteristic values for use in design are needed in thedesign phase before the production phase is initiated. Prior tothe production phase, samples from the actual material usedfor the construction of the lifeboat are not available to allow fordetermination of material properties from tests on such sam-ples, and other means to establish the characteristic valuesmust be resorted to. The characteristic values for the materialproperties can be determined based on experience from similarmaterials. They can also be determined from tests on speci-mens obtained from laminate made in advance, in which caseat least five tests shall be carried out. In determination of char-acteristic values, an extra margin as deemed fitting may beincluded. Such a margin may be necessary to meet the require-ment to verification during production in 309.

Guidance note:The coefficient of variation used for design should be assumedwith care. It is advisable to assume a conservative, large value,maybe even higher than a recommended minimum assumptionof 7%, thereby to make sure that the resulting sample coefficientof variation of the material during production will not come outlarger than the value assumed for design.


309 In the production phase, the characteristic values ofstrength and stiffness used in design shall be confirmed. Thisshall be accomplished by means of tests of cut-outs taken fromsurplus material from the construction of the actual lifeboat. Aplan for the tests of the cut-out specimens shall be providedalready in the design phase. The estimates of the characteristicvalues based on results from these tests shall be establishedwith 50% confidence. This can be done according to themethod specified in 302 and 303. It shall be verified that theseestimates do not fall short of the characteristic values used indesign. Reference is made to Sec.6 C200.

Guidance note:The prime purpose of the verification tests in the productionphase is to detect possible gross errors during the production ofthe laminate structure.


310 For secondary structures representative material valuesmay be used instead of values from testing. In this case thecharacteristic strength shall be taken as 80% of the representa-tive value.

Guidance note:Representative material values are values for material propertiesavailable from data sheets or textbooks.


311 If the material is exposed to long term static loads stress

Table E2 Characteristic value2.5% quantile estimated with confidence

No. of measurements, nc(n)

Confidence 50% Confidence 95%

3 2.3 9.04 2.2 6.05 2.1 4.96 2.1 4.37 2.1 4.08 2.1 3.79 2.0 3.510 2.0 3.412 2.0 3.215 2.0 3.020 2.0 2.825 2.0 2.730 2.0 2.640 2.0 2.550 2.0 2.4∞ 2.0 2.0

∑=

=n

iix

nx

1

1

∑=

−−

=n

ii xx

ns

1

2)(1

1

xsVOC =ˆ

sncxxC ⋅−= )(

DET NORSKE VERITAS


rupture or creep may be relevant. Values of representativematerial properties for long term behaviour can be used instructural calculations. 312 Matrix cracking is an acceptable failure mechanism in alifeboat. However, if such cracks are considered to be presentthe laminate stiffness shall be reduced to reflect the presenceof these cracks. 313 Fatigue properties may be ignored, as long as the life-boat is designed and intended to be used for emergency evac-uation only once.

E 400 Qualification of material401 The laminate shall be suitable for use in a marine envi-ronment. In order to achieve this, the requirements given in500 through 800 shall be fulfilled.

E 500 Glass fibres501 The glass is to be of E-quality where the sum of Na2Oand K2O is to be less than 1%. A certificate showing chemicalcomposition is to be presented, or a chemical analysis is to becarried out showing that the requirements to E glass have been

met (SiO2 52-56%, CaO 16-25%, Al2O3 12-16%, B2O3 6-12%, Na2O + K2O 0-1% and MgO 0-6%).502 Fibres made of other glass qualities may be used subjectto special agreement and provided that their mechanical prop-erties and hydrolytic resistance are equally good or better.503 Coupling agents of silane compound or complex chro-mium compound are to be used.504 The glass fibres shall be produced as continuous fibres.When the glass fibres are to be tested for determination of theirproperties, the tests shall be carried out on samples of the glassfibre product which are in the same particular form as the glassfibre product which is to be used for lifeboat manufacturing inthe yard. 505 For roving that will be applied by spraying, a demonstra-tion shall be performed to show that the roving is suitable forthis form of application. A report from this demonstration shallbe provided.506 Requirements for glass fibre products are given inTable E3.

E 600 Carbon reinforcement601 To avoid brittle behaviour end defects sensitivity, car-bon fibre for use in load-bearing structures should have a strainto failure in excess of 1%.602 The carbon fibres should have a sizing (coupling agenttreatment) that is suitable for the resin material to be used.

Guidance note:Most carbon fibre sizing are optimized for epoxy resins. To workproperly with polyester and vinylester resins a specially formu-lated sizing normally need to be used.


603 When the carbon fibres are to be tested for determinationof their properties, the tests shall be carried out on samples ofthe carbon fibre product which are in the same particular formas the carbon fibre product that is to be used for lifeboat man-ufacturing in the yard. The laminate quality in terms of resincontent, void content, fibre alignment and fibre straightness ofthe test specimens shall be representative of the intended ship-yard production. The use of measured properties from a lami-nate with resin content lower than that expected in the shipyardproduction is not permitted.

Guidance note:Properties of carbon laminate do not necessarily improve withdecreasing resin content.


E 700 Aramid reinforcement701 All Aramid reinforcements are to comply with therequirements given in Table E4.702 The laminate to be tested in interlaminar shear is to beaccording to 708 to 712. The test specimen is to be oriented ina direction parallel to the majority of the fibres when possible,or in the main direction of the reinforcement.703 The laminate to be tested is to be produced according to707 to 710, and is to have a thickness between 3 and 8 mm. 704 The tensile and compressive capacity of the Aramidreinforcement can be determined by testing according toTable E5.705 The laminate to be tested is to be according to 707 to712, and the tensile tests are to be performed in the main fibredirections of a fabric/weave.

Table E3 Glass fibre reinforcements Property Test method1) Required values for approval testing Moisture content ISO 3344-1997 Maximum 0.2% on delivery. * Loss on ignition ISO 1887-1995 Within the manufacturer’s nominal value ± 5%. * Weight per unit length or area Roving:

ISO 1889-1997Mats:ISO 3374-1990 2)Woven fabrics:ISO 4605-1978 2)

The arithmetic mean ± 2 standard deviation is to be within the manufacturer’s value ± 10%.

*

Tensile strength ISO 527-4,5-1997 msmv * Tensile elongation msmv * 1) Other standards may be used if agreed upon with the certifying body prior to testing. 2) ISO 3374 pending. The standard has status as DIS at the time of issue of this standard. * Parameters normally required tested and documented for product certification by the certifying body.

Table E4 Requirements for Aramid reinforcements Reference Property Test standard1) Acceptance criteria B100A Moisture content ISO 3344-77 Manufacturer’s specified value * B100B Mass per unit area ISO 3374-90 2)

ISO 4605-78 2) Mean ± 2 sdev within manufacturer’s nominal value ± 10%

*

B100C Interlaminar shear strength ISO 4585-89 Mean –2 sdev > 25 MPa * 1) Other standards may be used if agreed upon with the certifying body prior to testing. 2) ISO 3374 pending. The standard has status as DIS at the time of issue of this standard. * Parameters normally required tested and documented for product certification by the certifying body.

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706 The fatigue capacity of the Aramid reinforcement can bedetermined by testing according to Table E6. The laminate tobe tested is to be according to 707 to 712. The tests are to berun in load control in tension–compression, with R = −1. Thestatic strength, σstatic, is the manufacturer's specified minimumvalue, tensile or compressive whichever is lesser. If therequirement is not fulfilled, the static strength values have tobe reduced until the fatigue condition is fulfilled.

707 The laminate is to be made with a marine grade polyes-ter, vinylester, or epoxy. The manufacturer may elect type ofresin, but the testing will only be valid for the type of resinused, as well as resins with higher tensile strength and higherelongation at failure.708 It is recommended that the laminate be cured at roomtemperature and atmospheric pressure. However, another cur-ing cycle may be chosen by the manufacturer. It is recom-mended to select a curing cycle which is feasible to accomplishin the yard.709 The laminate shall have a fibre volume fraction as spec-ified by the manufacturer of the reinforcement. It is recom-mended to select a fibre volume fraction which is obtainable inthe yard.710 When laminated, the fibre reinforcement is to have amoisture content at the maximum specified by the manufac-turer, see 701.711 In general, all layers of fabrics/weaves are to be orientedin the same direction in the laminate. Exceptions can be madeif symmetric laminates are needed for testing. Such cases areto be discussed with the certifying body.712 Test specimens are to be wide enough to cover at leastfour repeats of the structure of the weave/fabric.

E 800 Polyester and vinylester products801 For polyester and vinylester, a distinction is madebetween the following quality grades:

— resin grade 1: quality with good water resistance— resin grade 2: quality with normal water resistance— fire retardant resin— gelcoat and topcoat— fire retardant gelcoat and topcoat.

Guidance note:Resin Grade 2 is usually not used for free fall lifeboats.


802 The polyester and the vinylester shall be suitable forlamination by hand lay-up, spraying, resin transfer moulding,and vacuum bagging method. They shall have good wettingproperties and shall cure satisfactorily at normal room temper-ature, or at other specified curing condition. Polyester andvinylester intended for other production methods may beapproved after special consideration.803 Requirements to production of the resin and to qualitycontrol are given in Table E7. As an alternative to the require-ments in Table E7, equivalent requirements in a recognizedstandard may be applied.804 Requirements for cured resin are given in Table E8.Comments: Unless anything else is specified by the manufac-turer, the following curing procedure is to be used:

— Standard MEKP (active oxygen 9.0 to 9.2%)— curing: 24 hours at 23°C— post curing: 24 hours at 50°C.

Curing systems requiring high temperature may be approvedafter special consideration.805 Resins containing waxes and other substances, such asDCPD resins and blends of DCPD, which might lower theexternal adhesive capacity, are to be subjected to the delamina-tion test according to Table E9. For this purpose, the prepara-tion of the test piece shall follow the following procedure:

— A primary laminate consisting of five (5) layers of 450 g/m2emulsion/powder bounded mat with excess polyester in theupper surface. Curing procedure: 48 h at 23°C. The laminatesurface is not to be covered.

— A secondary laminate consisting of five (5) layers of450 g/m2 emulsion/powder bounded mat is built on thefirst without any form of upper surface treatment.

— Curing procedure as selected in 704. The fibre weight frac-tion is to be 50% ± 5%.

806 The preparation of the reference piece shall satisfy

— A laminate consisting of ten (10) layers of 450 g/m2 emul-sion/powder bounded mat. Curing procedure as selected in804.

807 Polyester and vinylester can be approved as fire retard-ant qualities provided they are in compliance with the follow-ing: The hull and canopy material shall be flame tested todetermine its fire-retarding characteristics by placing a testspecimen in a flame. After removal from the flame the burningtime and burning distance shall be measured and shall be to thesatisfaction of the certifying body. 808 The finished resin, including all fillers, shall fulfil therequirements for liquid resin in Table E7, and cured resin inTable E8, grade 2 and the requirements to combustibility inTable E10. 809 A finished resin with water absorption of 100 to 150 mgper test sample may be approved after special consideration.(This shall be evaluated by means of a blistering test and a testof laminate properties after aging at elevated temperature.) 810 Gelcoat and topcoat are to be produced of base polyesterthat fulfils the requirements in 801, Grade 1 and Table E11. 811 Fire retardant gelcoat and topcoat shall be produced ofbase resin that fulfils the requirements to fire retardant resinsin 707 and shall be able to withstand long term exposure toweathering without any visible signs of crazing, outwash ofmatter or dramatic colour change.

Table E5 Tensile and compressive testing

Reference Property Test standard1) Acceptance criteria

B300A

Tensile

ISO 527-4,5-1997

— strength msmv or m –2 sdev — modulus msv

— elongationmsmv or m –2 sdev

Unidirectional: > 1.2%Stitched: > 1.1%

Woven roving: > 0.9%

B300B

Compressive ISO 527-4,5-1997

— with buckling preven-

tion

— strength msmv or m –2 sdev — modulus msv

— elongationmsmv or m –2 sdev

Unidirectional: > 0.2%Stitched: > 0.2%

Woven roving: > 0.2% 1) Other standards may be used if agreed upon with the certifying body

prior to testing.

Table E6 Fatigue testing Reference Property Test standard1) Acceptance criteria B400 Fatigue ISO 527-4,5-1997 N > 105

at 0.45 σstatic 1) Other standards may be used if agreed upon with the certifying body

prior to testing.

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E 900 Production901 Critical process parameters and their tolerances shall beidentified for materials used in primary and special structural

applications. The fabrication requirements given in DNV-OS-C501 shall be followed.

Table E7 Manufacturer’s quality control for polyester and vinylester in liquid condition (Tolerances for base resin and each variant) Control on Test method 1) Acceptance criteria Viscosity ISO 2555 (1989) 2)

(Brookfield) or ISO 2884 (1974) (Cone/plate) msv ± 250 mPas *

Monomer content ISO 3251(1993) msv ± 2% Mineral content DIN 16945 (1989), item 4.10 msv ± 1% * Gel time 3)

ISO 2535 (1997)

For curing time at room temperature:

— < 60 minutes: msv ± 5 minutes — 120 to 60 minutes: msv ± 10 minutes — > 120 minutes: msv ± 15 minutes

1) Other standards may be used if agreed upon with the certifying body prior to testing. 2) For polyester and vinylester, the following parameters are to be used; Viscometer type A, rotational frequency 10, temperature 23°C. Viscosity can

be accepted with msv ± 20%. 3) Specify activator and initiator and % of each. * Parameters normally required tested and documented for product certification by the certifying body.

Table E8 Polyester and vinylester products, cured un-reinforced resin (Parameters normally required to be tested and documented for product certification by the certifying body) Property Test method1) Requirements for approval testing / Data format

Grade 1 Grade 2 Density ISO 1675 (1985) msv (g/cm3) msv (g/cm3) Volumetric curing shrinkage ISO 3521 (1997) msv (%) msv (%) Ultimate tensile strength 2) ISO 527-1,2 (1993) msmv minimum 55 MPa msmv minimum 45 MPa * Tensile modulus ISO 527-1,2 (1993) msv minimum 3 000 MPa msv minimum 3 000 MPa * Fracture elongation ISO 527-1,2 (1993) msmv minimum 2.5% msmv minimum 1.5% * Ultimate flexural strength ISO 178 (1993) msmv minimum 100 MPa msmv minimum 80 MPa Flexural modulus ISO 178 (1993) msv minimum 2 700 MPa msv minimum 2 700 MPa Barcol hardness 3) EN 59 (1990)

ASTM D 2583 (1995) msv minimum 35 msv minimum 35 *

Heat deflection temperature ISO 75-2 (1993) msmv minimum 70°C msmv minimum 60°C Water absorption 4) ISO 62 (1980) msmv maximum 80 mg msmv maximum 100 mg 1) Other standards may be used if agreed upon with the certifying body prior to testing. 2) Test samples for tensile testing ISO 527-2/1A/50; test specimen 1A and test speed 50 mm/minute. 3) Resin may deviate from these values, provided a minimum value of 30 is met and the manufacturer can demonstrate adequate cure. 4) Test sample 50 × 50 × 4 mm (± 1 × 1 × 0.2). Distilled water. Exposure time 28 days at 23°C. Resin may deviate from these values, provided the water

ageing properties are documented.msv Manufacturer’s Specified Value, verified to be within ± 10% of mean of type test results.msmv Manufacturer's Specified Minimum Value, verified to be below m –2 sdev (mean –2 standard deviations) of type test results.

* Parameters normally required tested and documented for product certification by the certifying body. Barcol hardness is to be measured on each spec-imen and is to comply with manufacturer's specified value.

Table E9 Interlaminar strength of LSE resins, double cantilever beam test Property Test method1) Requirements for approval testing Interlaminar fracture toughness, DCB

ASTM D 5528 (1994), Mode 1 2)

Minimum 80% of mean strength in reference pieceThe fracture is not to be a typical brittle fracture with smooth surfaces

*

1) Other standards may be used if agreed upon with the certifying body prior to testing. 2) Double cantilever beam test with high loading rate. * Parameters normally required tested and documented for product certification by the certifying body.

Table E10 Combustibility testing of fire retardant resins Property Test method Requirements for approval testing Combustibility ASTM D 2863 (1995) Oxygen index minimum 23 * * Parameters normally required tested and documented for product certification by the certifying body

Table E11 Properties of gelcoat/topcoat Property Test method 1) Requirements for approval testing Fracture elongation 2) ISO 527-1,2 (1993) 3) Minimum 2.0% Covering Complete covering is to be achieved within a thickness of

maximum 400 μm of cured resin 1) Other standards may be used if agreed upon with the certifying body prior to testing. 2) Test of elongation has to be carried out only for gelcoat/topcoats containing more than 15% minerals and other filling compounds. 3) A test sample is to be made of base resin covered with 400 μm cured gelcoat on each side and cured according to the procedure in 804.

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E 1000 Inspection1001 All structures shall be inspected visually. Inspectionshall be an integral part of the QA system of the builder.

F. Sandwich Materials

F 100 Introduction101 A sandwich structure is considered here as a light weightcore embedded between two faces (or skins). Faces are typi-cally made of FRP laminates. The properties of laminates aredescribed in Section E. This section concentrates on propertiesof cores and the core skin interface.102 Methods described in DNV-OS-C501 may be used tocalculate and document core and interface properties.

F 200 Sandwich specification201 Laminate, core materials and adhesives used in a sand-wich component shall be clearly specified and all materialsshall be traceable. Laminate specification shall be given asdescribed in Section E. 202 For the core material and the adhesive, a minimum set ofprocess parameters and constituent material characterizationsis given in Table F1 and Table F2. All these items shall bespecified.

203 The orientation of nonhomogenous or anisotropic mate-rials shall be clearly specified on the materials level and thestructural level.204 The thickness of laminates and cores shall be specified.205 A core layer is defined as a volume element with threeaxes of symmetry with respect to mechanical properties. Typ-ically, there are two possible microstructure alignments:

— 0/90 cell alignment found in orthotropic cores. Cells runparallel to each other within the same plane. The 3 maindirections to which material properties are referred are;width (W), length (L) and transverse (T) or x-, y- and z-direction. Typical cores are honeycomb, balsa wood andother corrugated core.

— Random cell alignment in quasi-isotropic core. Cells arerandomly oriented without any preferred direction. A typ-ical reinforcement type of this class is cellular foam core.

206 For cellular cores, i.e. wood and foam, material behav-iour and mechanical properties are considered at macroscopicscale, i.e. material properties shall be taken from standard testspecimens of a suitable size. 207 The measured material properties shall be measured ona scale that is compatible with the scale of general structuralanalyses. In regions of high local stress concentrations, theeffects of local material behaviour at geometrical discontinui-ties shall be accounted for by component tests.

F 300 Strength and stiffness301 Strength and stiffness shall be represented in terms ofcharacteristic values. 302 The characteristic value of strength is defined as s a low2.5% quantile in the distribution of the arbitrary strength. Thisis equivalent to the 97.5% tolerance. When characteristic val-ues of strength are estimated from data, the estimate shall begiven with 95% confidence. Characteristic values can be esti-mated with confidence in accordance with Table E2. In estab-lishing the characteristic strength of sandwich materials withbalsa cores, the thickness effect on the strength of the balsacore shall be accounted for. For standard test methods, refer-ence is made to DNV-OS-C501.303 The characteristic value of material stiffness used forstrength calculations is defined as the mean value. The charac-teristic value of material stiffness used for deflection calcula-tions is also defined as the mean value. The characteristic valueof material stiffness can be estimated by the sample mean ofstiffness data from tests. The characteristic value of structuralstiffness can be calculated from the characteristic value ofmaterial stiffness in conjunction with geometry data.304 As a minimum, the out-of-plane shear strength and theshear modulus of sandwich core materials shall be docu-mented. To allow for analysis of core crushing at out-of-planejoints, the through-thickness compression strength shall alsobe documented. For details of standard test methods, referenceis made to DNV-OS-C501.

F 400 Qualification of material401 The sandwich material shall be suitable for use in amarine environment. In order to achieve this, the requirementsgiven in 500 through 900 shall be fulfilled.

F 500 Sandwich core materials501 Core materials are to have stable long-term properties;continuous chemical processes, diffusion, etc. are not to affectthe physical properties of the material. If considered necessary,documentation may be required.502 On delivery the surface of the material is normally to besuch that no further machining or grinding is required to obtainproper bonding onto the material. If, however, surface treat-

Table F1 Core specifications, process parameters and conditioning parametersConstituent core material(s):Generic core type (e.g. foam, honeycomb, balsa etc.)Core trade name (e.g. xyz123)Type of core (e.g. linear foam)Type/ characteristics of microstructureCore manufacturerBatch numberProcess parameters:Laminator (company)Processing methodProcessing temperatureProcessing pressureProcess atmosphere (e.g. vacuum)Curing temperaturePost curing (temperature and time)Density of the core materialGlass transition temperatureConditioning parameters:TemperatureWater content of the core (wet, dry)Chemical environmentLoading rateNumber of specimens tested

Table F2 Adhesive specifications, process parameters and conditioning parametersConstituent adhesive material(s):Generic adhesive type (e.g. epoxy, polyester)Specific adhesive type trade nameSpecific adhesive type batch numberCatalyst (trade name and batch number)Accelerator (trade name and batch number)Fillers (trade name and batch number)Additives (trade name and batch number)Pre-treatment of the core before bonding

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ment is required, this is to be stated by the manufacturer.503 The test methods described consider most grades ofclosed cell polymeric foams and end grain balsa core. For corematerials of particular composition or structure, e.g. honey-combs, other requirements or additional requirements may beintroduced.504 Core materials are normally to be compatible with resinsbased on polyester, vinylester and epoxy. Core materials witha limited compatibility may be accepted upon special consid-eration. Limitations are to be stated by the manufacturer.505 The qualification of the material shall refer to a set ofphysical properties, which will be stated in the material certif-icate. The minimum properties are to be specified by the man-ufacturer and verified by testing. The requirements applicablefor all core materials are stated below and in Table F3. 506 Density: The manufacturer is to specify a “Manufac-turer’s Specified Minimum Value” (msmv) which is con-firmed by the test results.507 Water absorption: The two sides of the cube that facethe laminate skins are to be sealed with resin. The manufac-turer is to specify a “Manufacturer’s Specified MinimumValue” (msmv) which is confirmed by the test results.508 Tensile properties: The tensile tests are to be performedin the through thickness direction of the core. For very aniso-tropic materials, the certifying body may require additionaltests in other directions. The core material is to be laminatedwith:

— a standard ortho polyester, and/or— a resin with better adhesion properties than standard ortho

polyester. In such cases, the use of the core material willbe limited to the resin type used and resins with betteradhesion properties. If the selected resin is temperaturesensitive, e.g. rubberized, testing at +50°C and −10°C maybe needed in addition.

The resin type used is to be stated in the test report. The laminated core may then be glued or laminated to the testfixtures. Testing rate: Maximum speed of deformation, in mm/minute is to be 10% of the value of the measured initial thick-ness. The tensile properties are to be taken as the measuredvalue irrespective of whether the failure is in the core or in thecore resin interface. Elongation shall be measured with exten-someter on the core and secant modulus to be established. The manufacturer is to specify a “Manufacturer’s SpecifiedMinimum Value” (msmv) which is confirmed by the testresults.509 Compression testing: The compression tests are to beperformed in the through thickness direction of the core. Forvery anisotropic materials the certifying body may requireadditional tests in other directions.The cell walls at the loaded surfaces are to be stabilized with asuitable resin. Testing rate: Maximum speed of deformation, inmm/minute is to be 10% of the value of the measured initialthickness. Compression shall be measured with extensometerand secant modulus to be established.The manufacturer is to specify a “Manufacturer’s SpecifiedMinimum Value” (msmv) which is confirmed by the testresults.510 Block shear testing: The shear strength, modulus andelongation of ductile core materials are to be determined byblock shear testing according to ISO 1922-81.The shear strength, modulus and elongation are to be deter-mined by the following method:

— The shear strength of each specimen, τfail (i). is defined asthe maximum shear stress measured and is to be deter-

mined for each specimen.— The manufacturer’s specified minimum shear strength,

τmsmv, is to be specified by the manufacturer, and is to bebelow the calculated value: mean –2 standard deviationsof the individual values of the τfail (i).

— For the purpose of determining the design shear modulus,the design shear strength, τdesign., is defined as 0.3 τmsmv.

— The “0.3 shear elongation”, γ 0.3 τ design(i), is defined as theelongation corresponding to τdesign, and is to be takenfrom the measured stress-strain curve for each specimen.

— The “average 0.3 shear elongation”, γ 0.3 τ design (average), isdefined as the mean of the individual γ 0.3 τ design (i) values.

— The design shear modulus is defined as:

511 Four point bend shear testing of sandwich with ductilecore material: In order to ensure that the tensile strength of thecore and of the core/skin interface is proportionate to the shearstrength, the core variant with the highest density within eachgrade is to be tested in four point bend according to ASTMC393-88.Scored core material of the highest density variant and greatestthickness delivered, is to be laminated with the following lay-up:

— 200 g/m2 CSM at the core skin interface— subsequent layers of 800/100 g/m2 WR/CSM combimat or

200 g/m2 CSM.

The total thickness of each skin laminate is not to exceed 10%of the core thickness. The fibre weight fraction is to be 50%± 5%. The manufacturer may elect to use:

— a standard ortho polyester, and/or— a resin with better adhesion properties than standard ortho

polyester. In such cases, the use of the core material willbe limited to the resin type used and resins with betteradhesion properties. If the selected resin is temperaturesensitive, e.g. rubberized, testing at +50°C and −10°C maybe needed in addition.

The resin type used is to be stated in the test report. The manufacturer may elect to fill the scores with resin, or asandwich adhesive. In this case, filling of the scores will be acondition of use. The shear strength obtained from the four point bend test, cal-culated according to 510, is to confirm the data from the blockshear testing. If the shear strength value obtained from the four point bendtest is lower than the value obtained from the block shear test-ing, the manufacturer may elect to:

— retest with another resin, or — the obtained value will be used. The shear modulus calcu-

lated according to 510 is to be based on the new shearstrength. In such cases, the core variant with the next larg-est density is to be tested in the same manner.

512 Four point bend shear testing of sandwich with brittlecore material: The shear strength of brittle core materials shallbe obtained from four point bend tests. The design shearstrength shall be established for the core thickness to be used.Unless testing is performed for each core thickness intendedused the shear strength of end grain balsa shall be corrected forthe effect of thickness by multiplying the shear strength

)(3.0 averagedesign

designdesignG

τγτ

×

=

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obtained for a thickness of 50 mm by the factor fc:

where c is the core thickness of the actual panel being analysed(mm). The shear strength shall be corrected for the effect ofpanel size by multiplying the shear strength obtained asdescribed above by the factor fib

where a is the smaller of the panel dimensions (m) and fib shallbe equal to 1.0 for a ≤ 1.6 m. 513 Heat resistance temperature is defined as the tempera-ture at which either:

— shear strength or— shear modulus

has decreased by 20%.The heat resistance temperature is to be specified by the man-ufacturer, and is to be greater than +45°C. The heat resistancetemperature is to be confirmed by four point bend testing thehighest density core at the specified temperature according to511, where the shear strength and modulus are to be > 80% ofthe results obtained in 510.514 Water resistance is defined as the loss of shear strengthand stiffness after conditioning in salt water (DIN 50905) at40°C for four weeks. The loss of water resistance is to be confirmed by four pointbend testing the highest and lowest density variant accordingto 511, where the shear strength and modulus are to be > 80%of the results obtained in 511.

F 600 Core material in areas exposed to slamming601 The requirements applicable to core material to be usedin areas exposed to slamming are given in 602 to 607. It shallbe stated in the material certificate whether the material prop-erties with respect to slamming have been determined or not.602 Scored core material of the lowest and highest densityvariant and greatest thickness delivered is to be tested in fourpoint bend according to ASTM C393-88, at a high loading (i.e.slamming) rate.603 The sandwich beam is to include a longitudinal adhesivejoint between two core material planks. The qualification ofthe material is valid for the adhesive used, and for adhesiveswith greater shear elongation at 0°C. The adhesive type used isto be stated in the test report.604 The core material is to be laminated with the followinglay-up:

— 200 g/m2 CSM at the core skin interface— subsequent layers of 800/100 g/m2 WR/CSM combimat or

200 g/m2 CSM.

The total thickness of each skin laminate is not to exceed 10%of the core thickness. The fibre weight fraction is to be

50% + 5%. The manufacturer may elect to use:

— standard ortho polyester, and/or— a resin with better adhesion properties. In such cases, the use

of the core material will be limited to the resin type used andresins with better adhesion properties. If the selected resin istemperature sensitive, e.g. rubberized, testing at +50°C and−10°C may be needed in addition.

The resin type used is to be stated in the test report.605 The manufacturer may elect to fill the scores with resin,or a sandwich adhesive. In this case this is to be stated.606 The beam is to be loaded at a rate of dτ/dt = 65 MPa s–1.607 The shear strength obtained from the four point bend testat slamming rate, is to confirm the data from the block sheartesting determined in 510.

F 700 Sandwich adhesives701 For sandwich adhesives, a distinction is made betweentwo different quality grades: Grade 1: Required quality of sandwich adhesives for hullstructures.Grade 2: Required quality of sandwich adhesives for less crit-

27.050⎟⎠⎞

⎜⎝⎛=

cfc

25.06.1⎟⎠⎞

⎜⎝⎛=

afib

Table F3 General requirements for all core materials Reference Property Test method 1) Acceptance criteria

507 Density for materials with sdev/mean < 5%

ISO 845-88 msmv in kg/m3 *

Density for materials with sdev/mean > 5%

508 Water absorption ISO 2896-87Duration: 1 week in salt water (DIN 50905) at 40°C

1.5 kg/m2

509 Tensile - strength

ASTM C-297 - 94 m –2 sdev > 1.6 msmv shear strength in MPa

Tensile - modulus mean > 1.7 msv shear modulus in MPa

510 Compressive - strength

ISO 844-78 m –2 sdev > 1.0 msmv shear strength in MPa

Compressive - modulus mean > 2.5 msv shear modulus in MPa 511 Block shear - strength

ISO 1922-81 msmv > 0.4 MPa *

Block shear - modulus msv > 9 MPa * Block shear - elongation msv of γ0,3 t design (average) * 512 Four point bend shear - strength ASTM C393-88 ± 10% of msmv shear strength 513 Heat resistance - strength Conditioned to heat resistance temperature,

then ASTM C393-88 all values > 80% of msmv shear strength

Heat resistance - modulus mean > 80% of msv shear modulus 514 Water resistance - strength Conditioning: 4 weeks in salt water (DIN

50905) at 40°C, then ASTM C393-88 all values > 80% of msmv shear strength

Water resistance - modulus mean > 80% of msv shear modulus 1) Other standards may be used if agreed upon with the certifying body prior to testing. * Parameters normally required tested and documented for product certification by the certifying body.

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ical applications than hull structures.Guidance note:Grade 1 is used for structures and components categorized as pri-mary. Grade 2 is used for structures and components categorizedas secondary.


702 The qualification of the material will refer to a set ofphysical properties. The minimum properties shall be specifiedby the manufacturer and verified by testing. The properties tobe documented in the test report are given in Tables F4 and F5together with acceptance criteria. 703 Requirements for production of the adhesive and qualitycontrol are given in Table F4.704 Requirements for cured material in the joint are given inTable F5.705 Curing conditions are to be according to the manufac-turer’s specifications, preferably at temperatures obtainable ina yard. Detailed description of surface treatment and applica-tion procedure is required.706 The heat resistance temperature is defined as the temper-

ature at which the flatwise tensile strength has decreased to80% of the room temperature strength.The heat resistance temperature is to be specified by the man-ufacturer and is to be greater than + 45°C.The heat resistance temperature is to be confirmed by testingaccording to flatwise tensile testing at the specified tempera-ture, where the flatwise tensile strength is to be > 80% of theresults obtained at room temperature.For testing of shear and flatwise tension, the test samples are tobe made of two pieces of high density core material (preferablyPVC foam) with the sandwich adhesive located in the mid-plane parallel to the steel supports. The adhesive layer is tobe > 1 mm thick.

F 800 Adhesives801 Stress patterns in adhesive joints are highly sensitive tojoint geometry, and the performance of an adhesive is thushighly dependent on the type of joint. General requirements forthe adhesive, valid for all joint geometries can therefore not begiven.802 The requirements in this subsection provide:

— the acceptance criteria for allowable degradation whenloaded in a marine environment

— a method for determining basic mechanical performancedata.

803 The design of each joint is to be evaluated duringapproval of classed objects.804 If one of the adherends is glass subject to sunlight, aceramic coating is to be applied to effectively block the UVradiation. If a joint is loaded in fatigue, impact, etc. further test-ing may be required.

805 Information regarding incompatibility of the adhesive’scuring system with other curing systems or chemicals, andpossible lack of chemical resistance of the cured adhesive, tooils, detergents, etc. is to be submitted by the adhesive manu-facturer.806 The following properties shall be considered when test-ing and applying adhesives to lifeboat structures:

— mixing ratio— pot life/open time— range of temperature— range of humidity— range of temperature over dew point— range of maximum and minimum thickness of adhesive

joint.

807 The adhesive shall be tested with each adherend that it isto join. The tests shall be carried out according to the test meth-ods stated in Table F6, with each adherend it is to join. Alumin-

Table F4 Quality control for sandwich adhesives Property Test method Acceptance

criteria Density ISO 3521-1990

ISO 1675 (1985) msv ± 10%

Viscosity ASTM D 1084-1988, method B (for free-flowing adhesives)

msv ± 20%

Table F5 Sandwich adhesives Property Test standard 1) Acceptance criteria

Grade 1 Grade 2 Overall volume shrinkage ISO 3521-1990 2) msv msv

Flatwise tensile strength

ASTM C 297-1994, (Specimen: 5 × 5 cm, speed: 1 mm/minute) 3)At 23°C: At heat resistance temperature

msmv minimum 1.0 (MPa) All values > 80%

of msmv at 23°C

msmv minimum 1.0 (MPa) All values > 80%

of msmvat 23°C

Heat resistance Conditioned to heat resistance temperature, then flatwise tensile testing according to ASTM C 297-1994

minimum 45°CAll values > 80% of

msmv at 23°C

minimum 45°CAll values > 80% of

msmv at 23°C

Tensile strength ISO 527-1997 (Specimen thickness 4 mm)At −10°C, 23°C and at heat resistance temperature

msmv (MPa) msmv (MPa) *

Fracture elonga-tion

msmvat 23°C: minimum 3.5%

at −10°C: minimum 2.0%

msmvat 23°C: minimum 2.0%

at −10°C: minimum 1.0%

*

Shear strength ISO 1922-1981 (23°C) 3) msmv minimum 0.4 (MPa)

msmv minimum 0.4 (MPa)

Water resistance 4 weeks immersion in salt water (DIN 50905) at 40°C.Flatwise tensile testing according to ASTM C 297-1994 (Specimen: 5 × 5 cm, speed: 1 mm/minute, minimum 23°C).

minimum 80% retained strength after immersion

minimum 80% retained strength after immersion

Approval may be refused for materials considered having a too low fracture elongation. 1) Other standards may be used if agreed upon with the certifying body prior to testing. 2) Curing shrinkage is relevant only for gap filling fillers. 3) The test samples are to be made of two pieces of high density core material (preferably PVC foam) with the sandwich adhesive located in the mid

plane parallel to the steel supports. The adhesive layer is to be > 1 mm thick.* Parameters normally required to be tested and documented for product certification by the certifying body.

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ium of different series is to be tested if applicable.

808 Lap-shear strength: The manufacturer is to specify a“Manufacturer’s Specified Minimum Value” (msmv) for the lap-shear strength, measured according to the applicable standard,which are to be confirmed by the test results. The manufacturercan choose to specify a msmv value less than “mean –2 sdev”.809 Fracture strength in cleavage: The manufacturer is tospecify a msmv for the fracture strength in cleavage measuredaccording to ASTM D 3433-93, which is to be confirmed bythe test results.810 Glass transition temperature: The glass transition tem-perature (Tg.) of the adhesive is to be determined according toASTM D 1356-91.811 Minimum toughness: The toughness of the adhesive sys-tem (including the adherends and their surface treatment) shall

be sufficient to prevent undue sensitivity to unforeseen localpeel stresses or other unfavourable modes of loading. This maybe deemed fulfilled if the fracture toughness of the adhesivesystem established according to Table F6 exceeds the mini-mum value specified there. The specimens shall be preparedwith ad her ends of the materials intended to be bonded withsufficient stiffness and strength to produce fracture of thebondline (see guidance given in E805) and with the surfaces tobe bonded prepared under realistic conditions according to thesurface preparation process used at the shipyard.

F 900 Production and inspection901 The same issues as for laminates shall be addressed (seeSubsection E).

Table F6 AdhesivesReference Property Test method 1) Acceptance criteria, data format, and unit808 Lap-shear

a) controlASTM D 1002 - 94, orASTM D 3163 - 92

"m –2 sdev" > "msmv" in MPa *

Lap-shear − loaded and weatheredfor:a) 28 daysb) 56 days

Specimen according 201-a, loadedto "msmv" according to ASTMD 2919 - 95, while weathered accordingto ASTM D 1183 - 92 (D,4 and 8 times), and then tested todestruction

"m –2 sdev" > 90% of "mean" of 201-a results, in MPa"m –2 sdev" > 95% of "mean" of 201-b results, in MPa

809 Fracture strength in cleav-agea) control

ASTM D 3433 - 93 "m –2 sdev" > "msmv" in MPa *

Fracture strength in cleav-age – weathered for:a) 28 daysb) 56 days

Specimen according 202-a, loadedto "msmv" (3 minutes), thenweathered according to ASTM D1183 - 92 (D, 4 times and 8 times),and then tested to destruction

"m –2 sdev" > 90% of "mean" of 202-a results, in MPa"m –2 sdev" > 95% of "mean" of 202-b results, in MPa

810 Glass transition tempera-ture (Tg)

ASTM E 1356 - 91 °C *

811 Fracture toughness ASTM D 5528 (1994), Mode 1 "m" > 50 J/m2 (initiation value)1) Other standards may be used if agreed upon with the certifying body prior to testing.* Parameters normally required tested and documented for product certification by the certifying body.

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SECTION 6STRUCTURAL DESIGN

A. General PrinciplesA 100 Application101 This section gives provisions for checking of ultimateand serviceability limit states for the structure of free fall life-boats and their launching systems.

A 200 Phases201 The design life shall be divided into phases, i.e. welldefined periods within the life span of the lifeboat. All phasesthat could have an influence on the design of the product shallbe considered.202 Normally, the following phases should be considered:

— construction — installation— stowage— exercise launches and retrieval— launch— sailing— rescue.

A decommissioning phase may be specified. It may be conven-ient to split the design life into more detailed phases, includingmaintenance phases.

A 300 Functional requirements301 The structure of the lifeboat and its arrangements shallsatisfy the functional requirements given in 302 to 311.302 The hull structure of the lifeboat shall comprise a water-tight barrier between the exterior of the lifeboat and its occu-pants and maintain the watertight integrity throughout allphases. In maintaining the watertight integrity, this barriermust reliably resist the external pressures that act on it through-out all phases. Failure to meet this functional requirement shallbe regarded an ultimate limit state (ULS).303 The response of the structure shall not cause injuries orfatalities among the occupants. Hence, deflections must bewithin specified limits such that the deformed structure doesnot strike the occupants, noise levels and pressure changesfrom the dynamic deformations, e.g. local buckling or snap-through, must be within acceptable levels that do not causehearing injuries. Failure to meet this functional requirementshall be regarded an ultimate limit state (ULS).

Guidance note:Noise is not normally a problem for lifeboats of conventionalhull form and construction, but may need special considerationfor lifeboats of unusual construction, e.g. lifeboats with veryflexible areas in the hull and lifeboats of unusual hull form.


304 The response of the structure shall not destroy compo-nents that are needed to maintain the safe use and operation ofthe lifeboat or hinder their intended use. Hence, maximumdeflections must be within specified limits such that thedeformed structure does not strike such components, e.g. punc-ture buoyancy elements or open doors or hatches, and any per-manent deformations shall not hinder the operation of doors,hatches or any other safety-critical onboard system. Failure tomeet this functional requirement shall be regarded an ultimatelimit state (ULS).305 The structure shall be so designed as to maintain thespecified level of safety at least for the specified service life ofthe lifeboat considering the intended use of the lifeboat and the

anticipated environmental exposure. Failure to meet this func-tional requirement shall be regarded an ultimate limit state(ULS).306 The response of the structure shall not destroy compo-nents that are needed to maintain the comfort on board or thatwill require repair afterwards, such as nonstructural bulkheadsor other internal structure not contributing to the integrity ofthe hull. Failure to meet this functional requirement shall beregarded a serviceability limit state (SLS). 307 Arrangements shall be provided in the hull structure toallow safe and efficient entry for occupants into the lifeboataccording to the requirements of Sec.7 B200.308 Arrangements shall be provided in the hull structure toallow safe rescue of occupants from the lifeboat as set out inSec.7 E600. 309 Arrangements shall be provided in the hull structure toprovide support for onboard systems and equipment. For theseats of the occupants, reference is made to Sec.8 B808.310 The structure of the launching system shall provide forsafe launching of the lifeboat in all conditions, observing Sec.7C100 and specific requirements in A800. 311 It shall be possible to lock hatches in the open position.

A 400 Premises for structural design401 It is a basic premise for the structural design require-ments provided in this section that the structure has a goodresistance to the propagation of fractures in the governing loadcases.402 Ductility is a mechanism that contributes to the fractureresistance in metals. Hence, ductility of the metallic materialsis important for the safety of metallic structures. 403 Composites have good fracture resistance without muchductility because the inhomogeneous fibrous character of com-posites inherently provides a high fracture resistance across thefibres. The keys to translate this fracture resistance to fractureresistance of the built-up laminates and the entire structure areto properly arrange the directions of fibre reinforcement con-sidering the relevant stress states and otherwise to follow theprinciples of good composite design practice.404 The fracture resistance in composite structures is aninherent property of well designed fibrous composite lami-nates. Hence, for composite structures requirements to fractureresistance are given in terms of requirements that ensure aproper arrangement of fibre reinforcement and load-carryingmembers. These requirements are given in Sec.6 C.405 The ductility of metallic structures, which are designedaccording to this standard and which satisfy all local designcriteria, allows for consideration of secondary stresses sepa-rately from primary stresses in the ULS assessment becausethe effect of excess secondary stress would only be a limitedinelastic deformation that would not threaten the overall integ-rity of the structure. For composite structures, however, thelack of ductility implies that the ULS assessment must includeconsideration of a combination of primary and secondarystresses. This difference between metallic structures and com-posite structures is reflected in the detailed requirements givenin the respective relevant subsections for these two types ofstructures.

A 500 Structural design principles501 The watertight barrier normally consists of monolithicplates of metallic or composite material or sandwich panels.

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All apertures shall be sealed during operation by watertightdoors, hatch covers or windows.502 The plating forming the watertight barrier must beappropriately supported by internal structure.503 Except for sandwich constructions, the hull and decksthat contribute to longitudinal strength are normally to be lon-gitudinally stiffened. The sides may be longitudinally or verti-cally stiffened or both. In lifeboats constructed from sandwichmaterial other framing arrangement may be used provided thatthe strength criteria for the frames are complied with.504 Longitudinal girders are to be carried continuouslythrough bulkheads. Bottom panels shall be supported by longi-tudinal girders unless effective support is demonstrated to beprovided by other members. 505 Longitudinal stiffeners are to be supported by bulkheadsor web frames or both as shown in Figure 1.

Figure 1 Support of longitudinal stiffeners

506 A system of continuous transverse frames is to be fittedwhich, together with other support members, supports theentire hull cross section (including the roof). Discontinuity canbe accepted in a frame at location(s) where the frame is effi-ciently supported in the transverse, vertical and longitudinaldirections of the coordinate system of the vessel. If intermedi-ate bottom frames are fitted, their ends should be well taperedor connected to local panel stiffening.507 Thrust bearings and supports should be strengthened totake the local loads.508 A centre girder is to be fitted to provide a strong supportif the external keel or bottom shape does not provide sufficientstrength and stiffness.509 Openings shall, wherever necessary, be compensated toproperly counteract the effects of shear loadings.510 Main engines are to be supported by longitudinal girderswith suitable local reinforcement to support the engine and thegearbox mounting structure.

A 600 Design loads601 The assessment of the hull structure shall be performedby subjecting a theoretical model of the hull structure to aseries of load cases which are representative of the loads thatmay occur in all phases during the intended life of the lifeboatand which govern the design of the structure. These load casesshall be used to produce reliable predictions of the governingload effects occurring in the structure.602 Depending on the lifeboat design, the pressure distribu-tions can be established by simple theoretical models, numeri-

cal simulations, model tests, full scale tests or a combination ofthese according to Sec.4.603 One approach is to establish the pressure distribution onthe hull as a function of time for all relevant scenarios and per-form stepwise load effect analyses for each scenario. 604 Instead of this comprehensive approach, a limitednumber of idealized loading cases may be defined that aredeemed representative of the critical loadings with respect toeach structural element of the hull. The number of load casesneeded would depend on the accuracy that is required. Con-servative assumptions are normally required unless a largenumber of loading cases is specified. The load cases shall con-sider all the relevant phases of the drops in all relevant condi-tions according to the provisions of Sec.4 and reflect anadjustment deemed necessary from sound engineering judg-ment based on the results of model and full scale tests accord-ing to Sec.9.605 Local structural elements such as plates, secondary stiff-eners and sandwich panels shall be designed to resist extremelocal pressures occurring during the penetration of the lifeboatthrough the sea surface. If these local pressures decay quicklycompared to the build-up of other external pressures, theselocal loads need not be combined with other loads.606 Windows, doors and hatch covers shall be designed toresist the local pressures acting on them. The collapse of theventilation behind the lifeboat shall in particular be consideredin the design of entry doors located astern. If windows, doorsor hatches are supported on a protrusion from the hull, such asa deckhouse, the pressure from the protrusion entering the seasurface and from the passage of a ventilation boundary shall beconsidered. The design of supports for windows, doors andhatch covers shall consider the loading acting on the supportsand be designed to adequately support the windows, doors andhatch covers as well as transmitting this loading to the sur-rounding structure. 607 Transverse frames will respond to the pressure as dis-tributed around the circumference of the hull at the sectionwhere the frame is located. The design load cases should rep-resent the most unfavourable pressure distribution. This distri-bution may differ between different parts of the frame.Furthermore, the variation of pressure around the circumfer-ence combined with the predominantly compressive loading itproduces in the frame may challenge the buckling resistance ofthe frames, cause geometrically nonlinear response and pro-duce snap-through effects particularly in the roof. To assessthis, the difference in pressure from the sides to the roof shouldbe explicitly represented and the sequence of building up pres-sure in different areas should be accounted for.608 If transverse frames are supported by longitudinal gird-ers, full or partial bulkheads or other supporting elements, thecombined response of the supports and adjacent frames need tobe considered. In that case, the longitudinal distribution of thepressures along the hull needs to be reliably represented by thedesign load cases considered. 609 Supports for heavy items such as engine foundations andseat attachments shall be designed for the maximum accelera-tions occurring during drops. These accelerations shall con-sider all the relevant phases of drops in all relevant conditionsaccording to the provisions of Sec.4 and reflect any adjustmentdeemed necessary from sound engineering judgement basedon the results of model and full scale tests carried out accord-ing to Sec.9. Normally the highest accelerations occur in thewater entry phase where the slamming pressures cause highvertical and rotational accelerations of the hull. The highestaccelerations can also occur at maximum submersion. Toobtain a robust design that is not sensitive to deviations fromthe drop conditions assumed in tests and simulations, it is rec-ommended that supports are designed for the maximum accel-erations occurring in any direction rather than using differentacceleration levels in the different coordinate directions.

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A 700 Structural analysis701 The ultimate strength capacity at material level (metalyield, FRP rupture, core fracture) and at structural level (buck-ling, collapse) shall be assessed for all structural elementsusing a rational and justifiable engineering approach. FEM canbe used for this purpose. Guidance for execution of FEM anal-yses is given in Appendix C.702 Other calculation methods than FEM can be used pro-vided the underlying assumptions are in accordance with gen-erally accepted practice, or in accordance with sufficientlycomprehensive experience or tests. However, due to the typi-cal geometry of lifeboats, the structural capacity normallyneeds to be checked in the relevant load cases using general 3Dstructural analyses.703 The structural analysis may be carried out as linear elas-tic analysis provided it is documented that significant geomet-rically nonlinear effects do not occur. However, due to thepredominantly compressive response in the hull shell andframing system, the typical cross sectional geometries of life-boats and the typical non-uniform pressure distributions, ageometrically nonlinear analysis will normally be needed. Inall cases, the structural detailing with respect to strength andductility requirements shall conform to the assumption madefor the analysis. 704 The structural analysis should take account of inertiaeffects (shell vibrations) that significantly affect stresses ordeformations of the structure. In assessing whether inertiaeffects in the structure are significant, considerations should begiven to the duration of the transient loading, the area overwhich it acts and the natural vibration frequencies of the partsof the structure that would be excited by the loading considered(plates, stiffeners, frames, hull girder etc.).

Guidance note:For typical designs of stiffened aluminium, steel or compositematerials or composite sandwich materials, the natural vibrationperiods of plating, stiffeners and frames are normally short com-pared to the duration of the slamming pulses making a quasi-static analysis appropriate. For long and slender hull-forms, glo-bal hull vibrations may need to be considered. For particularlyflexible designs, consideration may need to be given to dynamicsin the response of the structure. When this is the case, special careshould be exercised in accounting properly for the added mass ofthe surrounding sea water.


705 The structural analysis should take account of any sig-nificant effect of the deformations of the structure on the mag-nitude of sea pressures acting on the hull (fluid structureinteraction).

Guidance note:For typical designs of stiffened aluminium, steel or compositematerials or composite sandwich materials, stiffness is normallysufficient to prevent structural deformations from significantlyaltering the sea pressures making it unnecessary to explicitlyaccount for fluid structure interaction. For particularly flexibledesigns, consideration may need to be given to the effect thatstructural deformations would have on the external pressures.


706 Outfitting and attachment of items in the passengercabin shall be so designed as to ensure that no fixed items comeloose from their supports considering the accelerations thatmay occur at that position. For each potential failure mode ofthe attachments, accelerations in the most unfavourable direc-tions shall be considered. Bonded joints in composite struc-tures shall satisfy C700. Bolted joints in composite structuresshall satisfy C800 as applicable.707 The deflections of the structure shall nowhere cause thefree clearance to seated passengers and crew to fall below

10 cm horizontally and 20 cm vertically. The person size shallaccording to Sec.8 be assumed as follows:

Any inclinations of the seat vertical axis relative to the lifeboatvertical axis should be accounted for as illustrated in Figure 2.

Figure 2 Seat orientation relative to lifeboat

A 800 Launching system 801 The structural strength and stiffness of any skid and itssupports shall be sufficient to prevent the lifeboat from derail-ing considering all relevant trim and list angles and accelera-tions of the host as well as wind forces acting on the lifeboat. 802 It shall be demonstrated that the launch release mecha-nism for the primary and secondary means of launching can beoperated effectively when subject to the load combination ofTable A1. It shall also be demonstrated that the launch releasemechanism for the primary and secondary means of launchingcan be operated effectively when subject to the requirementsgiven in NORSOK R-002 Annex A.

803 The structural strength of the primary means of launch-ing shall be designed for the load combinations given inTable J4 in Sec.4 and for requirements given in NORSOKR-002 Annex A. Additional load effects resulting from thetrim and list angles and accelerations of the host facility, aswell as wind forces acting on the lifeboat, shall be taken intoconsideration.804 The structural strength of the secondary means oflaunching and the means of retrieval shall be designed for theload combinations given in Table J4 in Sec.4 and for therequirements given in NORSOK R-002 Annex A. Additionalload effects resulting from hoisting and lowering movements,offlead and sidelead angles, as well as wind forces acting onthe lifeboat, shall be taken into consideration.805 The structural strength of the release system and themeans of retrieval, including the release hook and the connec-tion to the lifeboat (e.g. a bonded or bolted joint), shall bedesigned for the load combinations of Table J4 of Sec.4

Height from seat pan to top of head: 108 cmShoulder width (50% on each side of centre line): 53 cm

Table A1 Load factors γf for assessment of the release function of the release system (stowage)

Load combinationLoad categories

G Q E D(a) 2.0 2.0 0.0 0.0

108 cm

d

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according to

where S is the design load effect occurring in the release mech-anism (e.g. tension), Rc is the corresponding characteristiccapacity from tests and γm is the material factor according toB500, B600, B911 or C1000, as applicable. The characteristiccapacity Rc shall be determined from tests according to theprinciples given in Sec.5 E302. The design load effect S shallinclude possible dynamic amplifications. For determination ofa relevant dynamic amplification factor for this purpose, refer-ence is made to NORSOK R-002.As an alternative, the characteristic capacity Rc of the releasemechanism including its connection to the lifeboat may be estab-lished from a single test or theoretically from the strength of thematerials used in the release mechanism provided that a reliableengineering method is used. In this case the material factor γmshall be taken as 6.0. This requirement to the material factor isconsidered to account for any long term effects on capacity andshall be used in conjunction with a load factor γf = 1.0.

Guidance note:For secondary means of loading, dynamic amplifications willmost likely be dominated by reaction forces at emergency braking.For means of retrieval, dynamic amplifications due to pick-upfrom sea are relevant and need to be considered. Methods usedfor offshore cranes lifting cargo from the moveable deck on serv-ice vessels can be applied for this purpose.


A 900 Fire901 The lifeboat structure shall be protected against fire tosuch an extent that the criterion given in Sec.8 D101 can be met.

Guidance note:For metallic structures, development of excessive temperaturesinside is the main problem, such that proper insulation of the life-boat structure becomes a major issue. For composite structures,the fire resistance of the composite materials is a major issue.Reference is made to DNV-OS-D301 and DNV-OS-C501.


A 1000 Ice accretion1001 For lifeboats to be operated from host facilities whereice accretion may occur, special consideration shall be given toproviding robustness to allow removal of ice from the lifeboatwithout causing degradation of the hull’s integrity.

B. Metallic StructuresB 100 General101 This subsection gives provisions for checking of ulti-mate limit states for typical structural elements used in metalliccomponents of free fall lifeboats. 102 For steel structures, gross scantlings may be used in thecalculation of the structural strength of the hull. A corrosionprotection system in accordance with DNV-OS-C101 Sec.10shall be installed and maintained.103 Corrosion of aluminium structures leading to loss ofstructural strength is not permitted, and shall be prevented byselection of appropriate corrosion-resistant alloys and corro-sion protection. (This limits the choice of alloys for lifeboats to5xxx and 6xxx series, as indicated in Sec.5.) Thus gross scant-lings shall be used in calculation of structural strength.104 For welded aluminium structures reduction of strengthin the heat-affected zone (HAZ) shall be taken into account inthe calculation of structural strength.

105 When plastic or elastic-plastic analyses are used checksshall be carried out to verify that plastic deformations will notaccumulate in repeated drops in such a way that the structuralreliability becomes less than the structural reliability requiredin the ULS for single loads. The number of drops consideredshall be in accordance with the intended use of the lifeboataccounting for possible evacuations, training, tests etc.106 If plastic or elastic-plastic structural analyses are usedfor determining the sectional stress resultants, limitations tothe width thickness ratios apply. Relevant width thicknessratios are found in the relevant codes used for capacity checks.107 Cross sections of beams are divided into different typesdependent on their ability to develop plastic hinges. A methodfor determination of cross sectional types for steel structures isgiven in DNV-OS-C101 App.A. Corresponding informationfor aluminium structures is given in Eurocode 9, Part 1-1.108 When plastic analysis and/or plastic capacity checks areused (cross section types I and II, according to DNV-OS-C101App.A for steel, or classes 1 and 2 according to Eurocode 9Part 1-1 for aluminium), the structural members shall be capa-ble of forming plastic hinges with sufficient rotation capacityto enable the required redistribution of bending moments todevelop. It shall also be checked that the load pattern will notbe changed due to the deformations.

Guidance note:The ductility in welds and HAZ of aluminium varies and cannotnormally be assumed to provide sufficient rotation capacity toenable the required redistribution of bending moments todevelop. It is therefore not recommended to use plastic capacitychecks for welded aluminium structures unless the rotationcapacity of the specific details is documented.


B 200 Ductility201 It is a fundamental requirement for metallic primarystructures of free-fall lifeboats that all failure modes are suffi-ciently ductile such that the structural behaviour will be inaccordance with the anticipated model used for determinationof the responses. In general all design procedures, regardless ofanalysis method, will not capture the true structural behaviour.Ductile failure modes will allow the structure to redistributeforces in accordance with the presupposed static model. Duc-tile failure modes also ensure that the structure does notbecome unduly sensitive to unforeseen deviations of the load-ing conditions from those assumed in design. Brittle failuremodes shall therefore be avoided.202 The following sources for brittle structural behaviourshall be considered for a steel or aluminium structure:

— unstable fracture caused by a combination of the followingfactors: brittle material, low temperature in the material, adesign resulting in high local stresses and the possibilitiesfor weld defects

— structural details where ultimate resistance is reached withplastic deformations only in limited areas, making the glo-bal behaviour brittle

— shell buckling— buckling where interaction between local and global buck-

ling modes occurs.

Deflections causing the structure to strike occupants shall betreated as a brittle failure mode.

Guidance note:For welded steel structures, the requirements in B800 preventlocalization of plasticity to the welds. The reduction of strength inthe heat-affected zone (HAZ) of welded aluminium structurestends to lead to localization of plastic deformations in limitedareas, thereby leading to unacceptable brittle structural behaviour.


m

cRS

γ<

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B 300 Yield check301 Structural members, for which excessive yielding is apossible mode of failure, shall be investigated for yielding.302 Individual design stress components and the von Misesequivalent design stress for plated structures shall not exceedthe design resistance (Sec.2 E200).

Guidance note:For plated structures the von Mises equivalent design stress isdefined as follows:

where σxd and σyd are design membrane stresses in x- and y-direction respectively, τd is design shear stress in the x-y plane(i.e. local bending stresses in plate thickness is not included). In case local plate bending stresses are of importance for theyield check, e.g. for laterally loaded plates, the yield check maybe performed according to DNV-RP-C201 Sec.5.


303 Local peak stresses from linear elastic analysis in areaswith pronounced geometrical changes may exceed the yieldstress provided the adjacent structural parts have capacities towithstand the redistributed stresses.

Guidance note:Areas mobilized beyond yield as determined by a linear finiteelement method analysis may give an indication of the actualarea of plastification. Otherwise, a nonlinear finite elementmethod analysis may need to be carried out in order to trace thefull extent of the plasticized zone. The yield checks do not refer to local stress concentrations in thestructure or to local modelling deficiencies in the finite elementmodel.


304 For yield check of welded connections, see B800.

B 400 Buckling check 401 Elements of cross sections that do not fulfil the require-ments to cross section type III (steel) or class 3 (aluminium)shall be checked for local buckling.Steel cross section type III is defined in DNV-OS-C101App.A. Aluminium cross section class 3 is defined in Euroc-ode 9 Part 1-1.402 Buckling analysis shall be based on the characteristicbuckling resistance for the most unfavourable buckling mode.403 The characteristic buckling strength shall be based onthe 5th percentile of test results.404 Initial imperfections and residual stresses in structuralmembers shall be accounted for.405 It shall be ensured that there is conformity between theinitial imperfections in the buckling resistance formulas andthe tolerances in the applied fabrication standard.

Guidance note:If buckling resistance of steel structures is calculated in accord-ance with DNV-RP-C201 for plated structures and in accordancewith Classification Note 30.1 for bars and frames, the tolerancerequirements given in DNV-OS-C401 should not be exceeded,unless specifically documented.


B 500 Flat-plated structures and stiffened panels501 The material factor γM for plated structures is 1.15. 502 Yield check of plating and stiffeners may be performedas given in 700.503 Yield check of girders may be performed as given in800.

504 The buckling stability of plated steel structures may bechecked according to DNV-RP-C201.505 In case the stiffened panel is checked for buckling as astiffener with effective plate width, the plate between the stiff-eners need not be checked separately.506 Stiffeners and girders may be designed according to pro-visions for beams in recognized standards such as Eurocode 3(steel), Eurocode 9 (aluminium) or AISC LRFD Manual ofSteel Construction.507 Material factors when using Eurocode 3 and Eurocode 9are given in Table B1.

Guidance note:The principles and effects of cross section types are included inthe AISC LRFD Manual of Steel Construction.


508 Plates, stiffeners and girders may be designed accordingto NORSOK N-004.

B 600 Shell structures601 The buckling stability of cylindrical and un-stiffenedconical shell structures made of steel, including interactionbetween shell buckling and column buckling, may be checkedaccording to DNV-RP-C202.602 If DNV-RP-C202 is applied, the material factor forshells shall be in accordance with Table B2.

603 The buckling stability of stiffened and unstiffenedaxisymmetric shell structures (cylindrical, conical or spheri-cal) made of aluminium may be checked according to Euroc-ode 9, Part 1-5.604 If Eurocode 9, Part 1-5 is applied, the material factor γM1shall be taken as 1.15.

B 700 Special provisions for plating and stiffeners701 The requirements in B700 will normally give minimumscantlings to plates and stiffened panels with respect to yield.Dimensions and further references with respect to bucklingcapacity are given in B500. The buckling stability of plates

222 3 dydxdydxdjd τσσσσσ +−+=

Table B1 Material factors used with Eurocode 3 or Eurocode 9Type of calculation Material factor 1) ValueResistance of Class 1, 2 or 3 cross sections

γM0 1.15

Resistance of Class 4 cross sections

γM1 1.15

Resistance of members to buckling

γM1 1.15

Symbols according to Eurocode 3 and Eurocode 9.

Table B2 Material factors γ M for bucklingType of structure λ ≤ 0.5 0.5 < λ < 1.0 λ ≥ 1.0Girder, beams stiffeners on shells 1.15 1.15 1.15

Shells of single curvature (cylindrical shells, coni-cal shells)

1.15 0.85 + 0.60 λ 1.45

Note that the slenderness is based on the buckling mode under con-sideration.λ = reduced slenderness parameter

=

fy = specified minimum yield stressσe = elastic buckling stress for the buckling mode under

consideration.

fys e-----

DET NORSKE VERITAS


may be checked according to DNV-RP-C201.702 Plating shall have sufficient thickness to ensure welda-bility and adequate resistance to local contact forces that mayarise during fabrication, transport, storage and use.703 Plating, longitudinals, beams, frames and other stiffen-ers subjected to loading resulting from lateral pressure shall bedesigned accordingly. For steel structures DNV-OS-C101 maybe used for this purpose. For aluminium structures Eurocode 9Part 1-1 may be used.

B 800 Special provisions for web frames, girders and girder systems801 The requirements in B800 give minimum scantlings tosimple web frame elements and girders with respect to yield.Further procedures for the calculations of complex girder sys-tems are indicated.802 Dimensions and further references with respect to buck-ling capacity are given in B500. 803 The thickness of web and flange plating is not to be lessthan given in B700. 804 In bending and shear, the requirements for section mod-ulus and web area are applicable to simple girders supportingstiffeners and to other girders exposed to linearly distributedlateral pressures. It is assumed that the girder satisfies the basicassumptions of simple beam theory and that the supportedmembers are approximately evenly spaced and have similarsupport conditions at both ends. Other loads will have to bespecially considered.805 When boundary conditions for individual girders are notpredictable due to dependence on adjacent structures, directcalculations according to the procedures given in 813 to 818will be required.806 The section modulus and web area of the girder shall betaken in accordance with particulars as given in 809 to 812 orin 813 to 818. Structural modelling in connection with directstress analysis shall be based on the same particulars whenapplicable. 807 The effective plate flange area is defined as the crosssectional area of plating within the effective flange width. Thecross section area of continuous stiffeners within the effectiveflange may be included. The effective flange width be is deter-mined by the following formula:

Figure 3 Graphs for the effective flange parameter C

808 Holes in girders will generally be accepted provided theshear stress level is acceptable and the buckling capacity andfatigue life are documented to be sufficient.809 Simple girders which are subjected to lateral pressureand whose capacities are not contributing to the overallstrength of the structure, shall comply with the following min-imum requirements:

— net section modulus according to 810— net web area according to 811.

810 Section modulus:

811 Net web area:

Ce = as given in Figure 3 for various numbers of evenly spaced point loads (Np) on the span

b = full breadth of plate flange e.g. span of the stiffen-ers supported by the girder with effective flange be, see also 810.

l0 = distance between points of zero bending moments (m)

= S for simply supported girders= 0.6 S for girders fixed at both ends

S = girder span as if simply supported, see also 810.

bCb ee ⋅=

S = girder span (m). The web height of in-plane girders may be deducted. When brackets are fitted at the ends, the girder span S may be reduced by two thirds of the bracket arm length, provided the girder ends may be assumed clamped and provided the section modulus at the bracketed ends is satisfac-tory

b = breadth of load area (m) (plate flange) b may be determined as:

= 0.5 (l1 + l2) (m), l1 and l2 are the spans of the sup-ported stiffeners, or distance between girders

km = bending moment factor km-values in accordance with Table B2 may be applied

σpd2 = design bending stress= fyd − σjd

σjd = equivalent design stress for global in-plane mem-brane stress.

kτ = shear force factor kτ may be in accordance with 812 Ns = number of stiffeners between considered section

and nearest supportThe Ns value is in no case to be taken greater than (Np+1)/4.

Np = number of supported stiffeners on the girder spanPpd = average design point load (kN) from stiffeners

between considered section and nearest supportτp = 0.5 ⋅ fyd (N/mm2)

)(mm 10 36

2

2

⋅=pdm

dg k

bpSZ

σ

)(mm 10 23⋅−

=p

pdSdtW

PNSbpkA

τ

DET NORSKE VERITAS


812 The km and kτ values referred to in 810 and 811 may becalculated according to general beam theory. In Table B3, kmand kτ values are given for some defined load and boundaryconditions. Note that the smallest km value shall be applied tosimple girders. For girders where brackets are fitted or theflange area has been partly increased due to large bendingmoment, a larger km value may be used outside the strength-ened region.813 For girders that are parts of a complex 2- or 3-dimen-sional structural system, a complete structural analysis shall becarried out.814 Calculation methods or computer programs appliedshall take into account the effects of bending, shear, axial andtorsional deformation.

815 The calculations of complex girder systems shall reflectthe structural response of the 2- or 3-dimensional structureconsidered, with due attention to boundary conditions.816 For complex girder systems consisting of slender gird-ers, calculations based on beam theory (frame work analysis)may be applied, with due attention to:

— shear area variation, e.g. cut-outs— moment of inertia variation— effective flange— lateral buckling of girder flanges.

817 The most unfavourable loading conditions among thosegiven in Sec.4 shall be applied.818 For girders whose capacities contribute to the overallstrength of the structure, stresses due to the design pressuresgiven in Sec.4 shall be combined with relevant overall stresses.

B 900 Welded connections901 The requirements of B900 apply to both steel and alu-minium welded structures unless otherwise stated.

902 All types of butt joints should be welded from bothsides, with appropriate weld preparation. Before welding iscarried out from the second side, unsound weld metal shall beremoved at the root by a suitable method.903 The connection of a plate abutting on another plate in atee joint or a cross joint may be made as indicated in Figure 4.904 The throat thickness of the weld in a tee joint or a crossjoint is always to be measured as the normal to the weld sur-face, as indicated in Figure 4d.

Figure 4 Tee and cross joints

905 The type of connection in a tee joint or a cross jointshould be adopted as follows:

906 Double continuous welds are required in the followingconnections, irrespective of the stress level:

— oil-tight, watertight and weather-tight connections— connections at supports and ends of girders, stiffeners,

Table B3 Values of km and kτLoad and boundary conditions Bending moment and shear force

factorsPositions 1

km1kτ1

2km2

-

3km3kτ3

1Support

2Field

3Support

120.5

24 120.5

0.38

14.2 8

0.63

0.5

8

0.5

15

0.3

23.3 10

0.7

0.2

16.8 7.5

0.8

0.33

7.8

0.67

a) Full penetration weldImportant cross connections in structures exposed to high stress, especially dynamic, e.g. for special areas and fatigue utilized primary structure. All external welds in way of opening to open sea e.g. pipes, sea-chests or tee-joints as applicable.

b) Partial penetration weldConnections where the static stress level is high. Acceptable also for dynamically stressed connections, provided the equivalent stress is acceptable.

c) Fillet weldConnections where stresses in the weld are mainly shear stresses or where direct stresses are moderate and mainly static, or where dynamic stresses in the abutting plate are small.

DET NORSKE VERITAS


cross-ties and pillars— connections in foundations and supporting structures for

machinery— connections in rudders, except where access difficulties

necessitate slot welds— for aluminium structures, all connections close to the pro-

peller.

907 Intermittent fillet welds may be used in the connectionof girder and stiffener webs to plate and girder flange plate,respectively, where the connection is moderately stressed.With reference to Figure 5, the various types of intermittentwelds are as follows:

— chain weld— staggered weld— scallop weld (closed).

908 Where intermittent welds are accepted, scallop weldsshall be used in tanks for water ballast or fresh water. Chainand staggered welds may be used in dry spaces and tanksarranged for fuel oil only.

Figure 5 Intermittent welds

909 In steel structures, slot welds, see Figure 6, may be usedfor connection of plating to internal webs, where access forwelding is not practicable, e.g. rudders. The length of slots anddistance between slots shall be considered in view of therequired size of welding.910 Lap joints as indicated in Figure 7 may be used in endconnections of stiffeners in steel structures. Lap joints shouldbe avoided in connections with dynamic stresses.

Figure 6 Slot welds

Figure 7 Lap joint

911 The material factors γMw for welded connections in steeland aluminium structures are given in Table B4.

912 In the design of welded joints in aluminium structuresadjacent to the weld, consideration shall be given to both thestrength of the welds and the strength of the HAZ. For the fol-lowing alloys a reduction of yield strength in the HAZ shall betaken into account:

— heat-treatable alloys (6xxx series) in temper T4 and above— nonheat-treatable alloys (5xxx series) in any work-hard-

ened condition.

The severity and size of the HAZ depend on the weldingmethod. Guidance may be obtained from Eurocode 9 Part 1-1.913 For steel structures, if the yield stress of the weld depositis higher than that of the base metal, the size of ordinary filletweld connections may be reduced as indicated in 915. The yield stress of the weld deposit is in no case to be less thangiven in DNV-OS-C401.914 Welding consumables used for welding of normal steeland some high strength steels are assumed to give weld depos-its with characteristic yield stress σfw as indicated in Table B5.If welding consumables with deposits of lower yield stressthan specified in Table B5 are used, the applied yield strengthshall be clearly informed on drawings and in design reports.915 In steel structures the size of some weld connectionsmay be reduced:

— corresponding to the strength of the weld metal, fw:

or— corresponding to the strength ratio value fr, base metal to

weld metal:

minimum 0.75.

Ordinary values for fw and fr for normal strength and high-strength steels are given in Table B5. When deep penetratingwelding processes are applied, the required throat thicknessesmay be reduced by 15% provided that sufficient weld penetra-tion is demonstrated.

Table B4 Material factors γMw for welded connections Limit states Material factor

ULS 1.3ALS 1.0

fy = characteristic yield stress of base material, abutting plate (N/mm2)

σfw = characteristic yield stress of weld deposit (N/mm2).

75.0

235 ⎟⎟⎠

⎞⎜⎜⎝

⎛= fw

wfσ

75.0

⎟⎟⎠

⎞⎜⎜⎝

⎛=

fw

yr

ff

σ

DET NORSKE VERITAS


916 Conversions between NV grades as used in Table B5and steel grades used in the EN10025 standard are given inSec.5.917 In aluminium structures the strength of the weld metal isusually lower than the strength of the base metal except for thestrength in the HAZ. Characteristic yield strengths for weldmetal can be found in Eurocode 9 Part 1-1, Section 8.6. Yieldstrengths are also given in DNV Rules for Classification ofHigh Speed, Light Craft and Naval Surface Craft, Part 2, Chap-ter 3, Sec.2.918 Where the connection of girder and stiffener webs andplate panel or girder flange plate, respectively, are mainlyshear stressed, fillet welds as specified in 919 to 921 should beadopted.919 Unless otherwise established, the throat thickness ofdouble continuous fillet welds should not be less than:

920 The throat thickness of intermittent welds may be asrequired in 819 for double continuous welds provided thewelded length is not less than:

— 80% of total length in the slamming area forward of amid-ships

— 50% of total length for connections in tanks (60% for alu-minium)

— 35% of total length for connections elsewhere (45% foraluminium).

Double continuous welds shall be adopted at stiffener endswhen necessary due to bracketed end connections.921 For intermittent welds in steel structures, the throatthickness is not to exceed:

— for chain welds and scallop welds:

— for staggered welds:

If the calculated throat thickness exceeds that given in one ofthe equations above, the considered weld length shall beincreased correspondingly.922 In structural parts where dynamic stresses or high statictensile stresses act through an intermediate plate, see Figure 4,penetration welds or increased fillet welds shall be used.923 When the abutting plate carries tensile stresses higherthan 120 N/mm2, the throat thickness of a double continuousweld in a steel structure is not to be less than:

924 For aluminium structures, in structural parts where ten-sile stresses are higher than 50 N/mm2, the throat thickness ofa double continuous weld is not to be taken less than:

where the symbols have the same meanings as in 923.925 Stiffeners may be connected to the web plate of girdersin the following ways:

— welded directly to the web plate on one or both sides of thestiffener

— connected by single- or double-sided lugs— with stiffener or bracket welded on top of frame— a combination of the ways listed above.

In locations where large shear forces are transferred from thestiffener to the girder web plate, a double-sided connection orstiffening should be required. A double-sided connection maybe taken into account when calculating the effective web area.926 Various standard types of connections between stiffen-ers and girders are shown in Figure 8.

Table B5 Strength ratios, fw and frBase metal Weld deposit Strength ratiosStrength group Designation

NV gradeYield stressσfw(N/mm2)

Weld metal Base metal/weld metal

Normal strength steels NV NS 355 1.36 0.75High strength steels NV27

NV32 NV36 NV40

375 375 375 390

1.42 1.42 1.42 1.46

0.75 0.88 0.96 1.00

75.0

235 ⎟⎟⎠

⎞⎜⎜⎝

⎛= fw

wfσ

75.075.0

≥⎟⎟⎠

⎞⎜⎜⎝

⎛=

fw

yr

ff

σ

fr = strength ratio as defined in 915 t0 = net thickness (mm) of abutting plate.

For stiffeners and for girders within 60% of the middle of span, t0 should not be taken greater than 11 mm, however, in no case less than 0.5 times the net thickness of the web.

t0 = net thickness abutting plate.

mm 3 minimum (mm), 43.0 0tft rw =

(mm) 6.0 0tft rw =

fw = strength ratio as defined in 915 σd = calculated maximum design tensile stress

in abutting plate (N/mm2)r = root face (mm), see Figure 4bt0 = net thickness (mm) of abutting plate.

(mm) 75.0 0tft rw =

minimum 3 mm .0

0

25.0320

2.036.1 ttr

ft d

ww ⎥

⎦

⎤⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛−+=

σ (mm),

(mm)155

35.0 00

ttrt d

w ⎟⎟⎠

⎞⎜⎜⎝

⎛−+=

σ

DET NORSKE VERITAS


Figure 8 Connections of stiffeners

927 Connection lugs should have a thickness not less thanthe web plate thickness.928 The total connection area (parent material) at supports ofstiffeners should not to be less than:

The total weld area a is not to be less than:

The throat thickness is not to exceed the maximum for scallopwelds given in 921.929 The weld connection between stiffener end and bracketis principally to be designed such that the design shear stressesof the connection correspond to the design resistance.930 The weld area of brackets to stiffeners which are carry-ing longitudinal stresses or which are taking part in thestrength of heavy girders etc., is not to be less than the sectionalarea of the longitudinal. 931 Brackets shall be connected to bulkhead by a doublecontinuous weld, for heavily stressed connections by a partlyor full penetration weld.932 The weld connection area of bracket to adjoining girdersor other structural parts shall be based on the calculated normaland shear stresses. Double continuous welding shall be used.Where large tensile stresses are expected, design according to922 and 923 shall be applied.933 The end connections of simple girders shall satisfy therequirements for section modulus given for the girder in ques-tion.Wherever the shear design stresses in a web plate of a steelstructure exceed 90 N/mm2, or those in an aluminium structureexceed 35 fw, double continuous boundary fillet welds shouldhave throat thickness not less than:

934 The distribution of forces in a welded connection may becalculated directly based on an assumption of either elastic orplastic behaviour.935 Residual stresses and stresses not participating in thetransfer of load need not be included when checking the resist-ance of a weld. This applies specifically to the normal stressparallel to the axis of a weld.936 Welded connections shall be designed to have adequatedeformation capacity.937 In joints where plastic hinges may form, the welds shallbe designed to provide at least the same design resistance asthe weakest of the connected parts.938 In other joints where deformation capacity for joint rota-tion is required due to the possibility of excessive straining, thewelds require sufficient strength not to rupture before generalyielding in the adjacent parent material.

Guidance note:In general this will be satisfied if the design resistance of the weldis not less than 80% of the design resistance of the weakest of theconnected parts.


939 The design resistance of fillet welds is adequate if, atevery point in its length, the resultant of all the forces per unitlength transmitted by the weld does not exceed its designresistance.940 The design resistance of the fillet weld will be sufficientif both the following conditions are satisfied:

c = detail shape factor as given in Table B6fyd = minimum yield design stress (for weld metal in

case of aluminium) (N/mm2)l = span of stiffener (m)s = distance between stiffeners (m)pd = design pressure (kN/m2).

Table B6 Detail shape factor cType of connec-

tion (see Figure 8)

IWeb to web

connection only

IIStiffener or bracket on top of stiffener

Single-sided Double-sidedabc

1.000.900.80

1.251.151.00

1.000.900.80

fr = strength ratio as defined in 915 a0 = connection area (mm2) as given in 928.

)(mm )5.0(103 230 d

yd

psslfca ⋅⋅⋅−⋅⋅⋅=

0afa r= (mm2)

C = 260 for steel, 80 for aluminiumτd = design shear stress in web plate (N/mm2)fw = strength ratio for weld as defined in 915t0 = net thickness (mm) of web plate.

(mm) 0tfCt

w

dw ⋅

⋅=

τ

Mww

udd

fγβ

ττσ ≤++ ⊥⊥ )(3 22||d

2

DET NORSKE VERITAS


and

Figure 9 Stresses in fillet weld

C. Composite Structures: Single-Skin and Sandwich Constructions

C 100 Application 101 The requirements in this subsection apply to structuresof FRP single skin constructions and to structures of sandwichconstruction. The plastics used in such applications shall be ofa type that has documented good durability performance in themaritime environment.102 A single skin construction is considered to be a structureconsisting of an FRP shell laminate supported and stiffenedlocally by a system of closely spaced FRP stiffeners.103 A sandwich construction is considered to be a structuralelement consisting of three components: an FRP skin laminateon each side of a low density core. The properties and the pro-

portions of the component materials shall be such that when asandwich panel is exposed to a lateral load the bendingmoments are carried mainly by the skins and the shear forcesmainly by the core.104 Appendix B contains a recommended set of require-ments to be followed during manufacturing of FRP structures.

C 200 Design principles201 It is a fundamental requirement for FRP primary struc-tures of free-fall lifeboats that the structure has a good damagetolerance and resistance to the propagation of fracture in thegoverning load cases. The fracture resistance in compositestructures is an inherent property of well designed fibrouscomposite laminates and does not require that the materialexhibits a ductile behaviour. Hence, while metallic structuresneed to fulfil requirements to ductility, composite structuresneed to meet requirements that ensure a proper arrangement offibre reinforcement and load-carrying members. Theserequirements are given in this subsection.202 The lifeboat shall be designed such that the loads are car-ried mainly by the fibres. The fibres shall therefore be alignedclose to the direction or directions of the largest principal stressin the governing load conditions.203 Failure governed by the polymeric matrix shall be inhib-ited by alignment of the fibres according to 202 and by use ofa ply stacking sequence without clustering of plies with thesame fibre direction. Note that matrix cracking caused by load-ing carried by fibres aligned in appropriate directions and oftenreferred to as first ply failure FPF is not considered a structuralfailure and thus need not be accounted for in the design.204 In order to maintain the specified level of safety at leastfor the specified service life of the lifeboat considering theintended use of the lifeboat and the anticipated environmentalexposure, and to provide the robustness needed to sustainimpact and abrasive loading as would be expected when oper-ated as intended, the following requirements to minimumscantlings shall be complied with unless equivalent robustnessis documented for an alternative arrangement.The reinforcement of laminates is to contain at least 25% con-tinuous fibres by volume. The mechanical properties of thecore material of structural sandwich panels are to comply withthe minimum requirements given in Table C1.

The amount of reinforcement (g/m2) in skin laminates in struc-tural sandwich panels shall normally not be less than given inTable C2.

The amount of reinforcement (g/m2) of single skin laminatesfabricated from glass shall normally not be less than given inTable C3.

σ⊥d = normal design stress perpendicular to the throat (including load factors)

τ⊥d = shear design stress (in plane of the throat) per-pendicular to the axis of the weld

τ ||d = shear design stress (in plane of the throat) paral-lel to the axis of the weld, see Figure 9

fu = nominal lowest ultimate tensile strength of the weaker part joined or of the weld metal, which-ever is smaller

βw = appropriate correlation factor, see Table B7 for steels. βw = 1 for aluminium.

γMw = material factor for welds

Table B7 The correlation factor βw for steels

Steel grade Lowest ultimate tensile strengthfu

Correlation factor βw

NV NS 400 0.83NV 27 400 0.83NV 32 440 0.86NV 36 490 0.89NV 40 510 0.9

NV 420 530 1.0NV 460 570 1.0

Mw

ud

fγ

σ ≤⊥

Table C1 Minimum core material propertiesStructural member Core properties (N/mm2)

Shear strength Compression strength Hull structure 0.8 0.9 Internal structure 0.5 0.6

Table C2 Minimum requirements for amount of reinforcement W0 (g/m2)

Glass Carbon/Aramid

Skins facing the outside of the hull including the deckhouse

2 400 1 600

Decks, underside skin 750 500 Structural bulkheads and top face of struc-tural decks*

1 200 800

Inside void spaces without normal access 750 500 * if adequately protected by a deck covering.

DET NORSKE VERITAS


205 Suitable local reinforcement and higher-strength corematerials shall be applied in all through-bolt connections ingirders that support the engine and the gear and in other placeswhere large through-thickness compression loads occur.206 Joints within or connecting primary structural elementsshall be designed so that the joint itself does not govern thecapacity of the structural elements in their primary load-bear-ing functions. This includes, but is not limited to, the followingtwo examples:

— For frames and stiffeners, whose primary load-bearingfunction is to transmit bending moments and shear forcesas a beam to the support points, a joint between the hullplating acting as the flange and the web shall be designedwith a shear capacity that is not smaller than that of theweb itself.

— A joint connecting the superstructure to the hull, on whichthe hull girder depends for its bending and shear capacity,shall be designed with a shear capacity that is not smallerthan that of the adjoining laminates of the hull and thesuperstructure.

207 The connection of the skin laminates shall be arrangedin such a manner that laminate peeling is effectively arrested.208 Out-of-plane joints shall be so designed as to primarilybe loaded in compression and shear. The overlap laminatesshould have sufficient width and thickness to transmit theshear forces from the respective adjoining panel to the support-ing panel. If the local compressive stresses in the core exceedthe compression capacity of the core material, strong coreinserts should be used. Local bending at the joint should beconsidered if the adjoining panel forms a tank boundary orwould otherwise support a transverse load during operation ofthe lifeboat. The performance of the joints should be docu-mented with component tests unless solutions are used thathave a documented good service track record. 209 To limit peel and defect sensitivity and to provide ade-quate load-bearing capacity, the overlap length should be atleast

where lmin is the minimum overlap, t is the thickness of thethinnest laminate adherend, σu is the ultimate capacity of thatlaminate in the direction of the loading to be transmitted by thebonded joint and τp is the ultimate plastic shear capacity of theadhesive measured according to a recognized standard such ase.g. ASTM D1002, D3163 or D3528.

Guidance note:This condition is necessary but not sufficient to provide reliablebonded joints; note also the requirement to load-bearing capacityof the joint in C700.


210 The design of the vessel is to be based on mechanicalproperties that are representative for the raw materials, produc-tion method(s), workshop conditions, lay-up sequence etc. thatare used and for the material quality that is expected over timefrom continuous production by the contracted builder as set outin Sec.5 E303 to 308. 211 This shall be confirmed by production testing duringproduction according to Sec.5 E309. The purpose of produc-tion testing is to verify that a consistent level of quality is main-tained throughout production, i.e. that gross errors have notoccurred in production. The production testing shall be carriedout according to a production test plan, which shall be pro-vided in the design phase. The test plan shall be designed toefficiently detect gross errors that can potentially occur in pro-duction considering the manufacturing methods and assemblyprocedures adopted and the raw materials used.212 The production test plan shall as a minimum address thefollowing items:

— mechanical strength of sandwich skin laminates, singleskin laminates, flanges (caps) of stringers and girders

— bond strength between core and skin laminates in sand-wich panels

— mechanical strength of major attachments and joints— acceptance criteria.

213 The test methods specified in Sec.5 shall be used.Through-thickness tests shall be carried out according toASTM C297. For details considered critical with respect tocompressive loads consideration shall be given to the need forperforming compression tests instead of or in addition to thetensile tests. 214 The test samples shall be taken from cut-outs in the hulland main deck. All such cut-outs shall be identified by markingand stored until used for testing purposes or until completionof the vessel. If adequate cut-outs are not possible to obtain,spare laminate for testing shall be made in parallel with themain production.

C 300 Structural calculations301 The governing load effects shall be established fromstructural calculations performed according to establishedengineering methods for composite materials. The need toaccount for out-of-plane deformations in sandwich and singleskin structures shall be considered. Simplified hand calcula-tions can only be used provided that the accuracy of themethod has been documented and all the underlying assump-tions have been complied with.

Guidance note:FEA will normally be required for lifeboats.


302 The effective panel flange area is defined as the cross-sectional area of the panel within the effective flange width.For sandwich panels only the skin laminate at which the beamis fitted shall be considered as effective flange unless the con-tribution from the opposite side is documented for the relevantcase. The effective flange for a uniformly loaded beam, con-sidering only contribution from one face, is found fromFigure 10.

Table C3 Minimum amount of glass reinforcement Structural member W0 (g/m2) Laminates facing the outside of the hull including the deckhouse

4 200

Stem and keel to 0.01 L from centreline 7 500 Chine and transom corners to 0.01 L from chine edge 5 800 Internal decks 2 900 Internal bulkheads 2 500

p

utlτσ

⋅⋅= 5.1min

DET NORSKE VERITAS


Figure 10 Effective flange

The length to be used with the diagram in Figure10 is thelength between the moment inflection points, i.e. between zerobending moments. The breadth b is to be taken as c/c distancebetween the stiffeners or girders. For a beam with fixed ends,the length between inflection points is 0.58 l. For beams withfixed ends, the effective flange outside the inflexion points (i.e.at the ends) is to be taken as 0.67 times the effective flange cal-culated above.

Guidance note:For top hat stiffeners with UD tabbing underneath, and the tab-bing width is less than two times the width of the top hat base, thefull width of the tabbing may be used.


Laminates with E/G ratios above 3.3 are to be corrected forincreased shear lag effect in the flange. Effective flange is thento be taken as:

303 The total stresses combining the contributions fromlocal response of plates and stiffeners, response of the framingsystem and the global response of the hull shall be used in thecapacity checks of fibre-reinforced composite materials. Ifstresses at the various levels are calculated separately, the indi-vidual stress components shall be combined to produce an esti-mate of the total stress.

Guidance note:As a conservative approach, the individual stresses can simply beadded. Information about the phasing between the individualstresses may be used to document a lower combined stress.


304 Further detailed guidance on finite element analysis canbe found in Appendix C.

C 400 Laminate rupture401 Fibre failure is defined here as the failure of a ply byfracture of the reinforcing fibres. Failure shall be checked atthe ply level, not at the laminate level. The maximum straincriterion can be used to check fibre failures.

Other design criteria may be used if it can be shown that theyare equal or conservative compared to the maximum strain cri-terion given here.402 For laminates with a lay-up with fibre orientation seenthrough the entire thickness that are more than 45o apart,matrix cracking or deformation due to in-plane ply shearstresses (not considered failure in itself) may trigger progres-sive damage accumulation that could lead to rupture of thelaminate. To prevent this, it should be documented that matrixcracks or deformations can be tolerated by the laminate underthe relevant loading conditions by use of a suitable laminatefailure criterion. The maximum fibre strain criterion is not suit-able for documenting this. Failure of such laminates may beassessed using the Tsai-Wu laminate failure criterion:

with

, , , , ,

,

where

n the coordinate system is the ply coordinate system: nrefers to the directions 1, 2, and 12.

σn characteristic value of the local load effect of the struc-ture (stress) in the direction n

characteristic tensile strength in the direction n

characteristic compressive strength in the direction n

characteristic shear strength in the direction nk

γm partial resistance factor (material factor).The interaction parameter H12

* can be taken by default as avalue between –0.5 and 0 or it can be determined experimen-tally for the actual material. 403 The strength properties shall be taken as describedbelow. Characteristic strengths as described in Sec.5 E300shall always be used.

beff = effective breadth of flange b = panel breadth between beams E = E modulus of flange laminate G = shear modulus of flange laminate l = length of beam

2

3.31

1

⎟⎠⎞

⎜⎝⎛⋅⋅+

=

lb

GEb

beff

tensile ply strength in fibre direction, as defined in Sec.5.

compressive ply strength in fibre direction, as defined in Sec.5.

modified in-plane tensile ply strength transverse to the fibres.

modified in-plane compressive ply strength trans-verse to the fibres.

In-plane shear strength, as defined in Sec.5.

m

fiberk

nk γε

ε <

( ) ( ) 12 2211211221212

2222

2111

2 <+⋅++++⋅ σσσσσσσ FFRHFFFR

mR γ=ct

F11

11 ˆˆ1σσ

=ct

F22

22 ˆˆ1σσ

= 212

12 ˆ1

σ=F

ct

F11

1 ˆ1

ˆ1

σσ−=

ct

F22

2 ˆ1

ˆ1

σσ−= 2211

*1212 FFHH ⋅=

ntσ̂

ncσ̂

nkσ̂

t1σ̂

c1σ̂

tt EE

11

22 ˆˆ σσ =

cc EE

11

22 ˆˆ σσ =

12σ̂

DET NORSKE VERITAS


C 500 Core shear fracture 501 Core shear fracture shall be assumed to occur if the shearstress predicted in the core in response to the design loadexceeds the characteristic shear strength of the core materialestablished according to Sec.5:

where τ is the maximum shear stress occurring in the core andτc is the characteristic shear strength of the core according toSec.5.

C 600 Face wrinkling601 The critical local buckling stress for skin laminatesexposed to compression is given by

where E denotes Young's modulus, G shear modulus, index crefers to the core and f to the face sheets (skins). The modulusfor the face laminate Ef used in this expression shall be takenas the flexural bending modulus measured directly from a bendtest of a laminate with the actual lay-up or estimated from plyproperties and lay-up using laminate theory.

C 700 Fracture of bonded joints701 The capacity of joint designs for which a successfulservice track record is lacking should be established by com-ponent tests for the critical modes of loading. The tested char-acteristic capacity in each relevant mode of loading shall beverified to exceed the maximum load effect that occurs:

where is the load effect component considered (e.g. bend-ing, shear, tension, compression), is the correspondingcharacteristic capacity from tests calculated according to themethod given in Sec.5 E303 and is the material factor.This safety factor may need to be increased for joint designswhere the resistance to combined loads can be expected to beless than the resistance to the load components consideredindividually. 702 Successful service track record for a specific joint can beconsidered to apply to bonded joints with the same overallgeometry, the same materials and the same bonding proce-dures and with adherend laminates whose strengths are equalto or less than the strengths of the adherend laminates of thejoint for which the experience was recorded.

C 800 Bolted connections801 This paragraph provides general requirements forstrength of the following types of bolted connections:

— bolted connections for transfer of in-plane loads (shearconnections)

— bolted connections for transfer of out-of-plane loads— bolt inserts and similar attachments (not participating in

the structural strength of the hull and superstructure).

The definition of in-plane and out-of-plane loads refers to theload components on each individual bolt. The thickness of the laminates may have to be increased toaccommodate the localized loads from a bolted connection.Definitions are given in Figure 11 which refers to the followingsymbols:

Figure 11 Direction of load on bolt hole

802 Bolted shear connections are only accepted in laminateswith reinforcement placed in at least two directions. The small-est angle between at least two reinforcement directions shallnot be smaller than 35° (does not apply to pure CSM lami-nates). CSM plies in a combined laminate shall not be includedin the calculation of the capacity of the connection.803 The surface of the part of the bolt inside the laminateshall be smooth. No threads are allowed in this area.804 A washer with an outer diameter not smaller than 3 dshall be used under the bolt head and the nut. The washer shallhave adequate stiffness such that the bolt pretension is distrib-ute under the area of the washer. Only flat-face bolts shall beused. Countersunk and tapered bolt heads are not accepted dueto the risk for splitting the laminate by the wedge effect of thebolt head.805 The bolt shall be tightened with such a force that singleskin laminates connected by bolting are subjected to a nominalcompressive stress under the washers, exceeding 15 MPa butnot exceeding 30 MPa. The nominal stress is calculated ascompressive load in the bolt divided by the surface area of thewasher. Due to the creep (and thus stress relaxation) that canbe expected in the laminate, bolts should be re-torqued after aperiod of time not shorter than 2 weeks.806 The pitch transverse to the direction of the load shall sat-isfy p1 ≥ 5 d.The pitch in the direction of the load shall satisfy p2 ≥ 4 d.The edge distance transverse to the direction of the load shallsatisfy e1 ≥ 3 d.The edge distance in the direction of the load shall satisfy thefollowing requirement: e2 ≥ 4 d.807 The nominal bearing stress shall satisfy the followingrequirement:

d = bolt diameter e1 = edge distance transverse to the direction of the load

m

c

γττ <

m

fcc EGEγ

σ35.0

<

m

ci

iR

Sγ

<

iSicR

mγ

e2 = edge distance in the direction of the load p1 = bolt pitch transverse to the direction of the load p2 = bolt pitch in the direction of the load.

σbear = shear load divided by d · t t = thickness of structural laminate γ = 3.0 for holes with a difference between bolt

and hole diameter less than 0.1 mm γ = 4.8 for holes with a difference between bolt

and hole diameter less than 1.0 mm

γσ bear

bearR

=

DET NORSKE VERITAS


The default values of the bearing stress capacity Rbear given inTable C4 can be used.

Higher bearing stress capacity can be used based on represent-ative test results. For hybrid laminates Rbear can be found by linear interpolationbased on the volume fraction of the respective types of fibre.

Guidance note:The requirements are such that it is highly probable that the fail-ure mode will be that the bearing stress will exceed the capacityaround the edge of the hole.


808 A connection for out-of-plane loads shall be boltedthrough the panel, in sandwich panels through both skins.809 Washers or plates shall be provided on both sides of thepanel to distribute the load from bolt heads and nuts. Thesewashers or plates may be fabricated from metallic materials orfrom fibre reinforced thermosets.810 Their bending stiffness shall be large enough to ensure adistribution of the load from each bolt over a sufficiently largearea to prevent compressive overloading of the panel in-between the washers or plates. The combined compressivestress under the washer or plates, resulting from the pretensionof the bolt and the out-of-plane loading, shall not anywhereexceed 30% of the compressive strength of the skin and thecore, respectively.811 The global effect of the out-of-plane load on the panel(in-plane bending moments and through thickness shear) shallbe calculated according to recognized methods for the calcula-tion of load effects in panels subjected to concentrated loads.The stress levels in laminates, skins and core shall satisfy thelimit states of this section.812 Other arrangements may be accepted based on compo-nent test results. Such testing shall be carried out on connec-tions with representative design on representative panelssubjected to representative loads including all in-plane andout-of-plane components. The tested characteristic capacity ineach relevant mode of loading shall be verified to exceed themaximum load effect that occurs:

where is the load effect component considered (e.g. bend-ing, shear, tension, compression), is the correspondingcharacteristic capacity from tests calculated according to themethod given in Sec.5 E303 and is the material factor.This safety factor may need to be increased for joint designswhere the resistance to combined loads can be expected to beless than the resistance to the load components consideredindividually.

813 Inserts and attachments may be used for transferring in-plane and out-of-plane loads for connections not participatingin the structural strength of the hull and superstructure.814 Where adequate, the methods for design describedabove may be used.

C 900 Long term performance901 It is not required to explicitly assess low-cycle fatiguedue to repeated drops for lifeboats of composite materials.902 Degradation or failure due to creep or sustained stressesshall be assessed for details exposed to long term static loads.This is of particular relevance for the release mechanism andits attachment to the lifeboat and any details being subject toconsiderable static loads from the supports during stowage.For release mechanisms qualified according to the simplifiedmethod using a material factor of 6, assessment of long termbehaviour is not required.

C 1000 Material factors1001 The material factor γm is to be taken as the product of ashort term material factor γms and a long term material factor γml.1002 The short term material factor γms is intended toaccount for the variability in the capacity from instance toinstance due to variability in raw materials, manufacturingconditions and workmanship as well as for the uncertainty inthe short term capacity after exposure to the service environ-ment. For material strengths with a coefficient of variation lessthan 10%, the short term material factor γms shall be takenaccording to Table C5. 1003 The long term material factor γml is intended to accountfor the uncertainty in the long term capacity caused by thecharacteristic capacity being estimated from short term tests. Ifraw materials and manufacturing procedures are used that havea proven track record from service in the maritime environ-ment, the long term material factor γml can be taken accordingto Table C5. Otherwise, the long term performance must beassessed based on separate documentation of the long termperformance for the particular material and design. When thereare no long term static load effects, such as for the short termloads that occur only during a launch of the lifeboat, the longterm material factor γml shall be taken as 1.0.

Table C4 Default values of the bearing stress capacity Type of reinforcement Nominal bearing stress strength,

Rbear (MPa) Glass, woven roving 200 (Vf/0.33) Glass, multiaxial laminates 250 (Vf/0.33) Glass, CSM 75 (Vf/0.33) Carbon, woven roving 275 (Vf/0.50) Carbon, multiaxial laminates 325 (Vf/0.50) Aramid, woven roving According to test Aramid, multiaxial laminates According to test Vf = volume fraction of reinforcement in laminates excluding

CSM layers in laminates with layers of continuous fibres.

m

ci

iR

Sγ

<

iSicR

mγ

Table C5 Short-term and long-term material factors γms and γml for typical materials and details of lifeboats

γms γml

Fibre-dominated laminates *) 1.5 2.0Stiffness-dominated failure mechanisms (e.g. buckling, wrinkling)

1.5 1.0

Matrix-dominated laminates *), –0.5 ≤ H12* ≤ 0 1.75 2.7 **

Matrix-dominated laminates *), H12*, determined

experimentally for specific material1.5 2.7 **

Ductile core materials 1.35 2.7Other core materials 1.5 2.7Overlap joints predominately transferring loading by shear across the bondline (e.g. simple overlap joints loaded in tension or in-plane shear, T-joints where adjoining panel is loaded in in-plane shear)

1.5 1.5

Complex joints also transferring loading by tension across the bondline (peel, cleavage) (e.g. T-joints where adjoining panel is loaded in bending or tension, ref. C208)

1.75 2.0

* Fibre-dominated laminates are laminates with continuous fibres withfibre orientation seen through the entire thickness that are not more than45° apart and laminates with predominantly uniaxial stress state (i.e.flange laminates) with fibres oriented in the principal stress direction.Matrix-dominated laminates are all other laminates.

** It is generally recommended to use fibre-dominated laminates in areasexposed to long term loads.

DET NORSKE VERITAS


SECTION 7OPERATIONAL REQUIREMENTS

A. GeneralA 100 General101 This section provides operational requirements to freefall lifeboats during various phases of operation which includemustering, boarding, release, free fall, resurfacing and sailingto safe area. 102 A main purpose of the operational requirements is toensure sufficient headway away from the host facility once thelifeboat has been launched and to ensure safe operation in thesubsequent sailing phase until retrieval of the occupants takesplace.

B. Mustering and BoardingB 100 Muster area 101 The muster area shall meet the requirements set forth inNORSOK S-001.

B 200 Boarding 201 The access to the lifeboat from the muster area shall beefficient. Once the occupants are inside the lifeboat the accessto each individual seat shall also be efficient. Without anyinjured personnel to be brought onboard the lifeboat, the max-imum time for boarding, measured from boarding begins untilthe lifeboat is ready for launching, shall be 3 minutes.

Guidance note:The fastest and most efficient boarding will usually be achievedif the occupants enter the lifeboat in the middle of the boat, pref-erably through two doors, one on either side of the boat, and ifthe occupants disperse from the middle of the boat in both direc-tions, resulting in approximately symmetrical loading of theboat. Fulfilment of the requirement of 3 minutes maximum time forboarding will be facilitated by ensuring easy access to the indi-vidual seats and by ensuring user-friendly harness arrangementsin each seat.Fulfilment of requirements to boarding time can be verified byembarkation trials with time registrations.


202 Provisions must be made for safe and ergonomic entryof the lifeboat in all conditions, including conditions of dam-aged host facility. For damaged host floaters it shall be demon-strated that it is possible to enter the lifeboat and all lifeboatseats safely when the floater is subject to trim and list. Trimand list depend on the stability of the host facility and the pos-sible loss of buoyancy in one or more supporting buoyant com-partments. The trim and the list for the damaged host facilityshall be set to ± 17° unless other host facility specific valuesare known.203 The crew shall see to it that the occupants disperse them-selves as symmetrically as possible around the middle of theboat, and as uniformly as possible between the bow and thestern, such that the loading of the boat becomes approximatelysymmetrical.

C. LaunchC 100 Release function101 The lifeboat shall be equipped with two independent

activation systems for the release mechanisms. The releasesystems shall be designed such that the lifeboat can only bereleased from inside the lifeboat. Each activation system shallbe so designed that release of the lifeboat requires simultane-ous operation by two crew members.

Guidance note:Only one activation system is normally used to release the life-boat. The requirement of two independent activation systemsrepresents a requirement of redundancy. The requirement of twocrew members to simultaneously operate the activation system isgiven for safety reasons.


102 To allow for installation tests despite the lifeboat canonly be released from inside the lifeboat, a system for hangingoff the lifeboat in the lifeboat station shall be implemented.

C 200 Rudder201 The rudder shall be set in the middle position prior to thedrop in order to avoid that the rudder becomes knocked askewduring the drop and to avoid that an off-middle rudder positioncauses the lifeboat to deviate from its straightforward courseduring its submerged phase. The lifeboat shall be furnishedwith a rudder indicator.

Guidance note:To ease the duties of the pilot, the requirement to set the rudderin the middle position can be met by implementing a rudder sys-tem which returns to neutral when the steering wheel is released,i.e. a follow-up system with return to neutral.


C 300 Start of engine301 The engine shall be started prior to the release of the life-boat from the lifeboat station, provided that the transmission isnot engaged. The transmission shall be engaged as soon as pos-sible after water entry. 302 The requirement to start the engine prior to the release ofthe lifeboat may be waived in an emergency situation wheregas is present and the lifeboat is to be launched into followingwind.

Guidance note:When gas is present, the gas may blow towards the lifeboat sta-tion and become ignited by sparks from the running engine of thelifeboat if the lifeboat is to be launched into following wind.


303 The requirement that the transmission shall not beengaged until after water entry may be waived when it can bedocumented that the propeller will not suffer damage if thetransmission is engaged prior to and during water entry.

D. Water Entry and ResurfacingD 100 General101 The pilot shall take control of the rudder as soon as pos-sible after water entry.

Guidance note:Use of autopilot is recommended, provided a robust technicalsolution is available.


DET NORSKE VERITAS


D 200 Position and headway201 The lifeboat shall possess and be able to maintain direc-tional stability after water entry and resurfacing and shall notlose its course in this phase. With thrust engaged and the rud-der fixed in the middle position, the lifeboat shall be able tohead straight on.

Guidance note:To possess and maintain directional stability, the lifeboat mustachieve and maintain positive mean headway relative to the hostfacility, from water entry onwards. The time at which the engineand transmission are engaged after water entry becomes veryimportant in this context. Mean headway refers to speed aver-aged over a time span of several wave periods.To ensure adequate headway in the phase immediately afterwater entry and resurfacing, the propeller must be engagedimmediately after water entry and, if possible, automaticallywithout action from the pilot, and a sufficient propulsion forcemust be provided immediately by the propeller. The lifeboatmust have a documented directional stability with the rudderfixed in the middle position, and the pilot must not be engaged inother activities before he takes control of the rudder. An additional propulsion system in front will improve the direc-tional stability of the lifeboat relative to a propulsion system inthe aft only.Course refers to direction averaged over a time span of severalwave periods.


202 It shall be possible to keep the lifeboat on a stable diag-onal course relative to wind and waves, i.e. the thrust momentinduced from the hydrodynamic lift force on the rudder mustbe large enough to counteract the wave-, current- and wind-induced moments.

Guidance note:It is a necessary condition for a lifeboat to move forward on a sta-ble course in wind and waves that there is equilibrium betweenmoments induced by the propulsive forces, hydrodynamic forceson hull and rudder, and wind forces on the lifeboat hull and can-opy. The rudder must be large enough and be designed so that itcan provide sufficient lift forces in a specific position to counter-act moments induced by the wave and wind forces for all operat-ing speeds.


203 The lifeboat shall not collide with the host facility. Thisno-collision requirement can be fulfilled by meeting a require-ment to distance.

Guidance note:At any point in time, the horizontal distance between the lifeboatand the host facility is defined as the shortest distance betweenthe two. The no-collision requirement is considered fulfilledwhen the horizontal distance between the lifeboat and the hostfacility, at the time of resurfacing and in the situation with calmwater and no wind, is demonstrated to be no less than 40 m. The time of resurfacing shall be taken as the point in time whenthe trajectory of the COG of the lifeboat with its full load of occu-pants passes up through the SWL after water entry.The substitute requirement to 40 m distance in the situation withcalm water and no wind has been set such that requirements tothe safety against collision are met during a launch at an arbitrarypoint in time as well as during a launch in a 100-year sea state.The requirement to distance accounts for effects of- wind action during the free fall- movement towards the host facility by wave action- wind-induced current and wind-induced drift- the time it takes to engage the transmission and gain speed

after resurfacing.To the extent that the distance between the lifeboat and the hostfacility at the time of resurfacing, in the situation with calm waterand no wind, exhibits variability from one launch to another, itsuffices to apply the expected value of the distance in order todocument that the requirement is fulfilled.

The no-collision requirement can be met in other ways than byfulfilling the 40 m requirement to distance, as long as it is docu-mented that the safety against collision meets the requirementsset forth in Sec.2 B500.


D 300 Stability301 Lifeboats that become fully submerged after water entryshall be stable and have a positive righting moment for the fol-lowing two load cases when the lifeboat is in the fully sub-merged condition:

— fully loaded lifeboat (full complement of occupants)— empty lifeboat (3 occupants including the pilot).

For either load case, the submerged stability can be docu-mented by calculating the immersed transversal position ofcentre of buoyancy and making sure that it is located above thetransversal position of centre of gravity.

E. Sailing PhaseE 100 General101 Two positions for manoeuvring the lifeboat shall be pro-vided with redundancy of rudder control, engine control andmain instruments. The two positions shall be used by the pilotand another crew member. The two positions for manoeuvringthe lifeboat shall be so arranged that the occupants in these twomanoeuvring positions need not change seats after water entryand resurfacing.

Guidance note:The pilot and the other crew member in the two manoeuvringpositions shall independently be able to control the lifeboat fromtheir respective seat positions. This will ensure a safer operationof the lifeboat in case of pilot injuries during water entry andresurfacing. It will save valuable time when the pilot can remain in his seatafter the free fall and manoeuvre the lifeboat from the same seatas the seat he is in during the free fall. Time will then not bewasted to unbuckle the harnesses and move to another seat totake control of the lifeboat after water entry and resurfacing. Theposition and orientation of the seat need not be the same duringthe free fall and in the sailing phase, and a mechanical device canbe used to bring the seat from the position and orientation duringthe free fall to the manoeuvring position needed in the sailingphase.


102 In the sailing phase, the pilot shall to the extent possibleonly be occupied with the manoeuvring of the lifeboat. Othercrew members should therefore operate the VHF radio andother equipment which needs attention or handling during thesailing phase. The operator of the VHF radio shall use a head-set. The headset shall be connected to the radio prior to thelaunch of the lifeboat, so it is ready for use from the beginningof the sailing phase. 103 Two conditions for harsh weather are considered, viz.

— a characteristic sea state defined in terms of the 99% quan-tile in the long term distribution of the significant waveheight HS

— a 100-year sea state defined in terms of the 100-year valueof HS.

E 200 Buoyancy and stability201 The lifeboat shall have inherent buoyancy or shall be fit-ted with inherently buoyant material, which shall not beadversely affected by seawater, oil or oil products, sufficient tokeep the lifeboat afloat with all its equipment onboard whenthe lifeboat is flooded and the hatch is open to the sea. When

DET NORSKE VERITAS


the lifeboat is in the stable flooded condition, the water levelinside the lifeboat, measured along the seat back, shall not bemore than 500 mm above the seat pan at any occupant seatingposition. Additional inherently buoyant material, equal to 280N of buoyant force per person, shall be provided for thenumber of persons that the lifeboat is designed to accommo-date. Buoyant material provided according to this item shallnot be installed external to the hull of the lifeboat.202 The lifeboat shall be stable and have a positive metacen-tric height when it is loaded with 50% of the number of occu-pants that it is designed to accommodate, placed in theirnormal positions to one side of the centreline of the lifeboat. Inthis loading condition, the heel of the lifeboat shall not exceedan angle of 20 degrees, and the lifeboat shall have a freeboard,measured from the waterline to the lowest opening throughwhich the lifeboat may become flooded, equal to at least 1.5%of the length of the lifeboat and not less than 100 mm. The free-board shall be documented by freeboard tests.203 The lifeboat shall have self-righting ability in the surfacecondition after resurfacing. The self-righting ability can bedocumented by tests.

Guidance note:The stability and the self-righting ability are dependent on thecomplement of occupants being strapped in their seats. If theweight distribution in the lifeboat changes, these characteristicsmay suffer or even disappear.


E 300 Thrust and rudder301 In calm water, the thrust and rudder capacity shall besufficient to maintain a mean direction and a mean headwayspeed equal to or greater than 3 m/s. When the lifeboat is tow-ing an identical lifeboat in calm water, the thrust and ruddercapacity shall be sufficient to maintain a mean headway speedequal to or greater than 1 m/s.

Guidance note:Adequate shaping of the stern can facilitate the fulfilment of theheadway requirements and so can increasing the size of the pro-peller and increasing the engine power.


302 In the characteristic sea state defined in 103, the thrustand rudder capacity shall be sufficient to maintain a meandirection and a mean headway speed equal to or greater than2.5 m/s.

Guidance note:In harsh weather conditions ocean surface waves are muchlonger than the dimensions of the lifeboat which means that thelifeboat will more or less follow the wave surface and move upand down with an amplitude similar to the amplitude of the wave.Without forward thrust the lifeboat will also move back and forthwith this amplitude since the water particles in the wave move inapproximately circular orbits. A mean drift (Stokes drift) of thelifeboat in the propagation direction of the wave will be superim-posed on this motion. In addition there will be a drift caused bythe wind force on the lifeboat. With thrust from the propeller, thenet forward force will part of the time be positive, when the life-boat is in a wave trough, and part of the time negative, when thelifeboat is close to a wave crest. A positive mean headway speedis ensured if the forward distance covered by the lifeboat whenthe net force is positive is larger than the backward distance whenthe net force is negative.


303 Fulfilment of the headway speed requirements in 301and 302 shall be demonstrated by full scale offshore tests of thelifeboat in relevant sea states, i.e. in calm water and in the char-acteristic sea state as defined in 103.304 A weather condition is defined which consists of thecharacteristic sea state given in 103 in combination with the

largest possible average wave steepness and a concurrent 10-minute mean wind speed equal to the 99% quantile in the long-term distribution of the 10-minute mean wind speed. In thisweather condition, the thrust and rudder capacity shall be suf-ficient to maintain a mean direction and a mean headway speedequal to or greater than 2.5 m/s. Fulfilment of this requirementshall be demonstrated by means of a numerical simulatorwhich is capable of extrapolating full scale test results obtainedin more relaxed sea states.

Guidance note:The average wave steepness of a sea state (HS, TP) is defined as

where HS denotes the significant wave height and TP is the peakperiod. The largest average wave steepness Sp can be taken as 1/15for TP < 8 s and 1/25 for TP > 15 s and can be interpolated linearlybetween these two limits. For a given value of HS, the solution ofthe largest average steepness Sp and the corresponding peak periodTP from the quoted equation may require an iterative procedure.


305 In the 100-year sea state, the thrust and rudder capacityshall be sufficient to maintain a mean direction and a meanheadway speed equal to or greater than 1 m/s. Fulfilment ofthis requirement shall be demonstrated by means of a numeri-cal simulator which is capable of extrapolating full scale testresults obtained in more relaxed sea states. For this purpose, asimultaneous constant head wind equal to the 99% quantile inthe long term distribution of the 10-minute mean wind speedshall be assumed. Collinearity between wind and waves shallbe assumed.306 The lifeboat shall have sufficient thrust and ruddercapacity to allow the pilot to maintain control of the lifeboat inthe 100-year sea state. Fulfilment of this requirement shall bedemonstrated by means of a simulator which is capable ofextrapolating full scale test results obtained in more relaxedsea states. For this purpose, a simultaneous constant head windequal to the 99% quantile in the long term distribution of the10-minute mean wind speed shall be assumed. Collinearitybetween wind and waves shall be assumed.

E 400 Engine401 The engine shall keep running in the situation that thelifeboat is subject to excessive rolling as well as in the situationthat the lifeboat is turned upside down. 402 The engine shall be operative when the lifeboat isflooded up to the centreline of the crank shaft.

E 500 Access501 The lifeboat shall have a boarding ladder that can beused at any boarding entrance of the lifeboat to enable personsin the water to board the lifeboat. The lowest step of the laddershall not be less than 0.4 m below the lifeboat’s light waterline. 502 The lifeboat shall be so arranged that injured or uncon-scious people can be brought onboard either from the sea or onstretchers.

E 600 Retrieval of occupants from lifeboat at sea601 The lifeboat shall be designed in such a manner that itshall be possible to transfer occupants from the lifeboat to ahelicopter or to a larger rescue vessel.

Guidance note:A hatch on top of the canopy and a platform adjacent to this hatchwill allow for transfer of passengers in the sailing phase. Thehatch and the platform do not have to be located on top of thecanopy. The hatch and the platform can also be located in the aft.If the lifeboat is held up against the sea, the aft of the lifeboat willbe the position on the lifeboat with the least motion.

2

2

P

Sp T

Hg

S ⋅=π

DET NORSKE VERITAS


Transfer of injured occupants at sea, in particular in bad weather,may influence which solutions for rescue and retrieval will befeasible. The time it takes before medical treatment can be pro-vided may govern the design of the lifeboat in this respect andmay set operational limitations. The time it takes before medicaltreatment can be provided may, in turn, depend on the availabil-ity of larger rescue vessels and standby vessels with equipmentfor retrieval of occupants.


602 For transfer of occupants from the lifeboat in the sailingphase to a larger rescue vessel, the lifeboat shall be compatiblewith the most recent generation standby vessels that havedocking systems for lifeboats. 603 To allow for transfer of occupants to a standby vessel,the lifeboat shall be equipped with a towline, which can bethrown on the sea surface and which can be picked up by thestandby vessel. Manual as well as automated heave out of thetowline shall be possible. The system of the towline and its fas-tening in the bow of the lifeboat shall be designed in such amanner that it can withstand the loading from pulling the life-boat to dock in the standby vessel.

F. MiscellaneousF 100 Operational manual101 An operational manual for the lifeboat shall be prepared.

The operational manual shall address all assumptions whichhave been made regarding environment, release function,crew, occupants, manoeuvring, headway, and other opera-tional aspects. The operational manual shall also address howretrieval of the lifeboat by lifting appliances shall be carriedout.

F 200 Training of personnel201 Key safety personnel shall undergo training for opera-tion of the lifeboat at regular intervals.

Guidance note:Regular training of key safety personnel under realistic condi-tions with respect to weather and sea state will allow for assess-ment of the physical fitness of personnel for various dutiesonboard the lifeboat, including but not limited to the duties aspilot and pumpman. Use of simulators for training of key safetypersonnel can be considered. Training of key safety personnelshould follow OLF Guidelines No. 002: Guidelines for Safetyand Emergency Training.


F 300 Maintenance301 In order to ensure that the lifeboat functions as intendedin the event of an emergency evacuation, the lifeboat shall besubject to periodic maintenance. For this purpose a mainte-nance plan shall be worked out. The plan shall as a minimumcontain the same elements as the procedure for maintenancegiven in IMO MSC1206.

DET NORSKE VERITAS


SECTION 8OCCUPANT SAFETY AND COMFORT

A. General

A 100 General101 This section provides requirements to free fall lifeboatsduring the various phases of operation as regards the occupantsafety and comfort.

B. Occupant Safety

B 100 General101 To ensure that no occupants will experience harmfulacceleration-induced loads the lifeboat designer must focus onthe complex combination of many coincident relations, such asdifferent body sizes and physical conditions, seating and har-ness, etc.

102 A crucial aspect regarding the safety of personnel duringlaunching is the ability of seat and harness to ensure that a per-son is “very well locked to the seat”, and in particular that therelative motion between the occupant head/neck and the upperpart of the body is minimized. It shall be specified and docu-mented which suits and clothing the combination of seat andharness is valid for.

B 200 Occupant properties 201 The lifeboat occupants will vary with respect to weight,length and body form, as well as with respect to medical andphysical condition. As for the medical and physical conditionit can be assumed that all occupants have valid medical certif-icates allowing them to be offshore. The great majority of theoccupants are not (pre-)injured when entering the lifeboat. Thelifeboat and the seats shall be designed for a range of personswithin the minimum and maximum characteristic values givenin Table B1. The body measures in Table B1 refer to Figure 1.

Figure 1 Occupant properties

Guidance note:Today’s medical/health examination that any offshore workerhas to pass in order to get a new or renewed offshore certificatedoes not take into account relevant medical issues such as mus-cular and skeleton-related issues which vary from one individualto another. This will have an influence on probability and classi-fication of injuries due to occupant acceleration loads.The characteristic occupant properties given in Table B1 areexclusive of clothing, such that in design the effects of clothingshould be added to the quoted minimum and maximum proper-ties. In this respect the effects of clothing should be taken asthose pertaining to the clothing that the combination of seat andharness in the lifeboat is valid for.


B 300 Acceleration measures301 The basis for evaluation of acceleration induced loadson the human body during the launch of a lifeboat consists ofthe acceleration components in relevant directions. The accel-eration components ax, ay and az refer to the seat coordinatesystem given in Figure 2.

Table B1 Characteristic occupant propertiesMinimum Maximum

Weight 50 kg 150 kg# Body measures [mm] [mm]2 Stature 1 400 2 10015 Shoulder height sitting 490 73517 Sitting height 770 1 08022 Shoulder breadth (bi-deltoid) 330 53025 Hip breadth sitting 280 48033 Buttock-knee depth 470 72034 Buttock-foot length 835 1 30041 Foot length 210 320

DET NORSKE VERITAS


Figure 2 The local (seat) coordinate system

302 Various measures of acceleration are used as a basis forcriteria for acceptance of occupant accelerations. The Com-bined Acceleration Ratio CAR, the Head Injury Criterion HICand G are three such measures. Definitions are given in 303 to307. Other human load measures used in acceptance criteriafor human loads are defined in 400.303 The CAR index is the maximum value of the time seriesof the SRSS (Square Root Sum of Squares) of the normalizedx, y and z accelerations.

in which 18 g, 7 g and 7 g are normalization constants for theaccelerations ax, ay and az, respectively. The accelerations ax,ay and az refer to the coordinate system given in Figure 2.Two values of CAR are used, viz.

— CAR1 for out-of-seat acceleration, calculated from posi-tive values of the ax time series only

— CAR2 for in-to-seat acceleration, calculated from negativevalues of the ax time series only.

Guidance note:For calculation of CAR2 for in-to-seat acceleration it is recom-mended to use the expression for CAR as quoted. For calculationof CAR1 for out-of-seat acceleration, it is recommended toreduce the normalization constant for ax by 50% from 18g to 9gto reflect the immature state-of-the-art regarding how to treat theeffects of out-of-seat acceleration on the human body at the timeof issue of this standard. Hence, use of

is recommended.---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---

304 For interpretation of CAR1 and CAR2 from accelerationtime series, acceleration data shall be filtered with no less thanthe equivalent of a 20 Hz low-pass filter. For filtering of accel-eration data, a Butterworth fourth-order filter shall be usedwhere the frequency domain transfer function |H(f)| for the fil-ter can be described by the equation:

where is an arbitrary frequency in Hz (1/s). 305 The HIC36 index refers to an acceleration time seriesover a 36 ms long time interval and is defined as

where and .

306 Both the CAR index and the HIC36 index exhibit varia-bility from one launch of the lifeboat to the next. The charac-teristic value of the CAR index shall be taken as the 99%quantile in the long-term distribution of the CAR index in alaunch at an arbitrary point in time. The characteristic value ofthe HIC36 index shall be taken as the 99% quantile in the long-term distribution of the HIC36 index in a launch at an arbitrarypoint in time.307 Gx, Gy and Gz are the maximum absolute values of thetime series of the acceleration components ax, ay and az,respectively. Characteristic values are the defined as the 99%quantiles in the respective long-term distributions in a launchat an arbitrary point in time.

B 400 Other human load measures401 In addition to the acceleration measures a number ofother human load measures are used as a basis for criteria foracceptance of occupant loads. These other measures are basedon forces in various parts of the human body. Definitions aregiven in 402 to 405. Reference is made to Figure 3.Human load measures as defined in 402 to 405 are usuallymeasured in cadaver tests or in advanced instrumented dummytests on the basis of applied representative acceleration timeseries, usually consisting of a pulse of duration 0.1 to 0.2 s. Foraccurate interpretation of these human load measures fromsuch tests, a sampling frequency equal to 20 000 Hz is recom-mended. For use of filters, reference is made to SAE J211.

+az (eyeballs down)

+ay (eyeballs right)

+ax (eyeballs in)

−ay (eyeballs left) −az (eyeballs up)

−ax (eyeballs out)

222

7718max ⎟⎟

⎠

⎞⎜⎜⎝

⎛+⎟⎟

⎠

⎞⎜⎜⎝

⎛+⎟⎟

⎠

⎞⎜⎜⎝

⎛=

ga

ga

ga

CAR zyx

222

1 779max ⎟⎟

⎠

⎞⎜⎜⎝

⎛+⎟⎟

⎠

⎞⎜⎜⎝

⎛+⎟⎟

⎠

⎞⎜⎜⎝

⎛=

ga

ga

ga

CAR zyx

42

201

1)(

⎟⎠⎞

⎜⎝⎛+

=f

fH

f

⎪⎭

⎪⎬⎫

⎪⎩

⎪⎨⎧

−⋅⎥⎥⎦

⎤

⎢⎢⎣

⎡⋅

−= ∫ )(1

12

5.2

1236

2

1

ttdtatt

HICt

t

222zyx aaaa ++= mstt 3612 +=

DET NORSKE VERITAS


Figure 3 Anatomical terms for the human body

Guidance note:Cadaver tests and tests on volunteers are used for development oflimiting values for human load measures and for correlation ofthese limiting values with particular responses in specific instru-mented test dummies.


402 For loading of the neck by moderate to severe frontalimpacts, a set of four nondimensional neck injury parameters,denoted Nij, are defined. The four components of the set are

— NTE: tension-extension— NTF: tension-flexion— NCE: compression-extension— NCF: compression-flexion

and each component is calculated according to the followingformula

in which

Fz = upper neck axial force measured in z directionFzc = critical force, 6 806 N in tension and –6 160 N in

compression for a Hybrid III median maleMOCy = My –D ⋅ Fx = total momentMyc = critical moment, 310 Nm in flexion and –135 Nm

in extension for a Hybrid III median maleMy = upper neck moment measured about y axisFx = upper neck shear force as measured in x directionD = distance between the force sensor axis and the occipi-

tal condyle axis (D = 0.01778 m for the upper neckload cell of Hybrid III median male, as used in RID3D).

403 For loading of the neck by low-speed impacts, a set offour nondimensional neck injury parameters, denoted Nkm, aredefined. The four components of the set are

— NFA: flexion-anterior

— NEA: extension-anterior— NFP: flexion-posterior— NEP: extension-posterior

and each component is calculated according to the followingformula

in which

Fx = upper neck shear force measured in x directionFzc = critical force, 845 N in both directions, dummy

independent MOCy = My–D ⋅ Fx = total momentMyc = critical moment, 88.1 Nm in flexion and –47.5 Nm

in extension for a Hybrid III median maleMy = upper neck moment measured about y axisFx = upper neck shear force as measured in x directionD = distance between the force axis and the occipital con-

dyle axis (D = 0.01778 m for the upper neck load cellof the Hybrid III median male as used in RID3D).

404 For loading of the abdomen and the thorax the resultingacceleration in the twelfth vertebrae is used as a parameter forassessment of the potential for injury.405 For loading of the thoracic spine, the axial force Fz in thetwelfth vertebrae (thoracal level 12; T12) is used as a parame-ter for assessment of the potential for injury.

B 500 Characteristic values501 The characteristic value of the Combined AccelerationRatio CAR shall be taken as the 99% quantile in the long-termprobability distribution of CAR in a launch at an arbitrarypoint in time. One probability distribution refers to the out-of-seat parameter CAR1 and one probability distribution to the in-to-seat parameter CAR2. Accordingly, there is one characteris-tic value for CAR1 and one for CAR2. Likewise, for any other

yc

OCy

zc

zij M

MFFN +=

intint MM

FFN OCyx

km +=

DET NORSKE VERITAS


measure of human load, the characteristic value of that meas-ure shall be taken as the 99% quantile in the long-term proba-bility distribution of the measure in a launch at an arbitrarypoint in time.

Guidance note:Appendix A provides guidance for how to determine the long-term probability distribution of a quantity and how to determinethe 99% quantile in this distribution, e.g. when measurements ofthe quantity are available from tests.


B 600 Injury classification601 Injuries are classified on the Abbreviated Injury Scale(AIS). There are seven AIS codes according to the classifica-tion on this scale, ranging from AIS0 to AIS6, see Table B2.

Guidance note:The AIS scale is the most widely used injury scale in traumaresearch. It is an anatomically based nonlinear severity scoringsystem, which can be used for every body region. The character-istics indicated in Table B2 refer to application to the brain andto the skeleton.


B 700 Acceptance criteria for occupant acceleration loads701 Each free fall lifeboat shall be so constructed that nooccupants will experience harmful loads or accelerations dur-ing any phase for any dimensioning or characteristic launchingcondition.

Guidance note:With the aim to limit the accelerations that the occupants willexperience during a launch, it will be beneficial to design the hullof the lifeboat in a manner that will minimize the rotation (pitch)of the lifeboat when it penetrates the sea surface. Retardation ofthe lifeboat without significant change of direction is expected tocreate a pleasant acceleration regime with respect to harmfulloads.


702 To ensure that no occupants will experience harmfulloads or accelerations the free fall lifeboat designer must focuson the combination of seating, seat layout, harness and safetybelt arrangements, and dress code and clothing. The physicaland medical conditions of the occupants shall be taken intoconsideration when the loads and accelerations are assessed.703 Out-of-seat accelerations shall be minimized and shallpreferably be eliminated.

Guidance note:The orientation of the seats in the cabin is a key parameter whenthis requirement is to be met.


704 In an early phase of a cabin design project, the potentialfor human injury shall be investigated. A simplified methodfor indication of the occupant acceleration load based on theCAR1 and CAR2 indices shall be applied for this purpose. It isa prerequisite for use of CAR1 and CAR2 in this context thatan optimal seat and harness arrangement is in place as requiredin B800.705 The characteristic value of CAR1 for out-of-seat accel-eration shall be less than 1.0.

Guidance note:In establishing the characteristic value of CAR1 prior to verifyingthe fulfilment of this criterion, it is recommended to use a halved

normalization constant for ax in all calculations of CAR1, cf. therecommendation given in 303.


706 The characteristic value of CAR2 for in-to-seat acceler-ation shall be less than 1.0.707 The requirements in 705 and 706 shall be fulfilled forevery seat in the cabin.708 In final cabin design, a detailed investigation of theacceleration loads based on tests on advanced instrumenteddummies shall be executed. Principles and details of these testsand the premises for them are given in 709 to 713. Acceptancecriteria are given in Table B3.709 A weather condition is defined which consists of a seastate with significant wave height equal to the 99% quantile inthe long-term distribution of the significant wave height, com-bined with the largest possible average wave steepness and aconcurrent 10-minute mean wind speed equal to the 99% quan-tile in the long-term distribution of the 10-minute mean windspeed.

Guidance note:The average steepness of a sea state (HS, TP) is defined as

where HS denotes the significant wave height and TP is the peakperiod. The largest average wave steepness Sp can be taken as 1/15for TP < 8 s and 1/25 for TP > 15 s and can be interpolated linearlybetween these two limits. For a given value of HS, the solution ofthe largest average steepness Sp and the corresponding peak periodTP from the quoted equation may require an iterative procedure.


710 Advanced instrumented dummy tests are based on accel-eration time series, which may be determined from represent-ative model scale tests. With a view to reducing the number oftests necessary to arrive at characteristic values of the varioushuman load measures, which are used in acceptance criteria foracceleration loads, to a practicable level, it is recommended toapply a characteristic acceleration time series with three com-ponents ax, ay and az, determined by means of model scale testsor by means of a numerical simulator, for the situation that thelifeboat is launched in the weather condition defined in 709.

Table B2 Abbreviated Injury ScaleAIS Code

Injury Examples of characteristics and indicationsBrain/head injuries Skeletal injuries

0 Non-injured1 Minor Headache Bruise or minor fracture2 Moderate Loss of consciousness for less than 1 hour Moderate fractures, for example 2 rib fractures 3 Serious Loss of consciousness between 1 and 6 hours Not life-threatening, such as a crushed foot4 Severe Loss of consciousness between 6 and 24 hours 4 or more rib fractures on one side, 2 to 3 rib fractures

with hemothorax or pneumothorax5 Critical Fatal in the short term, such as caused by a broken neck6 Untreatable Unsurvivable Immediate death, such as caused by decapitation

2

2

P

Sp T

Hg

S ⋅=π

DET NORSKE VERITAS


711 The characteristic values of the human load measureslisted in 400 may be estimated by the values of the respectiveload measures that result from an advanced instrumenteddummy test carried out on a median male dummy on the basisof the characteristic acceleration time series which is achievedas specified in 710.712 Injury acceptance criteria are given for various parts ofthe human body. Criteria for the following body parts aregiven:

— pelvis and whole body impact (not including head andneck)

— abdomen, thorax and thoracic spine— head— neck.

713 Requirements to human load measures in various bodyparts are given in Table B3. For each measure listed, the char-acteristic value as defined in 501 and as determined for amedian male dummy shall not exceed the limit specified TableB3. The requirements given in Table B3 shall be fulfilled forevery seat in the cabin.

Guidance note:The intention with the requirements set forth to the varioushuman load measures in Table B3 is to satisfy the safety require-ments given in Sec.2 B500 with respect to injuries at a level cor-responding to AIS2 to AIS3 in such a manner that the relativelylarge variability in capacity from one occupant to another isaccounted for. The requirements specified in Table B3 reflect thestate-of-the-art at the time of issue of this standard when it comesto assessing the effects on the human body of the accelerationsthat occur during the launch of a free fall lifeboat.


714 The requirements to human load measures given inTable B3 are requirements applicable during launching in anemergency situation based on AIS2 to AIS3 as the criticalinjury level. For launching in a training situation it is commonto apply stricter requirements than those given in Table B3.715 Although a crash test dummy often has a similarresponse to the human body along the vertical axis, this is notalways the case for responses in other degrees of freedom suchas neck bending moments. For any response quantity in ques-tion, it therefore needs to be demonstrated that the dummy andthe computational model used in the tests are capable of gen-erating an appropriate representative response.

B 800 Seats and harnesses 801 The lifeboat shall be designed in such a way that anyout-of-the-seat accelerations are minimized and preferablyeliminated. The seat orientation shall be designed to allow foran into-the-seat force. The rotation of the lifeboat, affecting theoccupants in the aft part of the boat, must be kept in mind dur-ing the design of the seat orientation.

Guidance note:In order to reduce or minimize the accelerations that the occu-pants will be exposed to during a launch, the designer shouldattempt to design the hull of the lifeboat in a manner that willminimize the rotation (pitch) of the lifeboat when it penetratesthe sea surface, i.e. the change of direction of the lifeboat whenit penetrates the sea surface shall be as small as possible.


802 The seats and harnesses shall be fit for use for the rangeof people as defined in B200 and Table B1.803 The harness shall be easily mounted, locked and regu-lated to fit all variations of body shapes, with particular focuson rapid mustering and personnel wearing survival suits, stillproviding safe fixation of the occupant. Reference is made tothe body measures given in Table B1.

Guidance note:Use of harness belts with take-up reels or other simple solutions,which allow for fast buckling and fixation to the seat and whichprevent loose belts and tangles that may delay the evacuation, isrecommended.


804 The seats and harnesses shall provide adequate sidewaysfixation, to safeguard the personnel in situations where side-ways accelerations occur.

Guidance note:Based on recent studies and tests, it is suggested that the seatsshould be equipped with a 5- or 6-point harness (1 or 2 crouchstraps, 2 shoulder straps and 2 pelvis straps). It is essential for theintended function of the harness that the crouch belt, the shoulderbelts and the lap belt can be tightened. It is important that theposition of the lap belt is not dependent on how the shoulder har-ness is adjusted. A correct lap belt should always grab below theiliac wings of the pelvis. The shoulder and lap belts can be com-bined into one, if the combined belt can easily slide through thebuckle. It is also strongly recommended that the shoulder beltsare height adjustable, allowing for the entire population in ques-tion to have belts tightly enveloping their shoulders. Other fixation systems than the classical 5- and 6-point har-nesses, which are based on existing equipment without largemodifications, can be foreseen as adequate solutions to meet therequirements to fixation.Spacing is described in C200.


805 The harness must be configured in such a manner thatthe occupant will not be at risk of slipping out underneath it. 806 The designer shall describe what kind of clothing,including survival suits, the seats and harness are authorizedfor. 807 To facilitate easy identification of belts and buckles andthereby to facilitate a fast fixation to the seat, contrasting col-ours for harnesses and suits shall be selected.808 The strength of seat and restraint systems shall be testedaccording to OLF LBP2-R001.

B 900 Pre-injured occupants901 Space as well as provision for ergonomic and safe han-dling of injured personnel shall be included in design. Eachlifeboat shall, as a minimum, allow for 1 injured occupant per20 seats to be catered for. Each lifeboat shall in addition pro-vide space for at least one injured occupant stretched out at full

Table B3 Requirements to human load measures in various body parts in median male dummyBody part Human load measure Requirement

to characteristic value of human load measure

Pelvis / whole body impact (exclusive of head and neck)

Pelvis +Gx (eyeballs in) 25Pelvis –Gx (eyeballs out) 18

Pelvis ±Gy (eyeballs right) 7Pelvis +Gz (eyeballs down) 12

Pelvis –Gz (eyeballs up) 7Abdomen, thorax and thoracic spine

T12_3ms (acceleration resultant)

60 G

T12 Fz-c 6 700 NHead HIC36 650Neck NFx_a/p 845 N

NFz_c –1 112 NNMy_e –57 NmNMy_f 190 Nm

Nij 1.0Nkm5 1.0

DET NORSKE VERITAS


length.Guidance note:A description of the handling of injured personnel with docu-mentation of transport, securing, fastening of the stretchers (orother means of transportation of patients) should be prepared. In working out this description, it is important to consider severaltopics and challenges such as the maximum weight of seats orstretchers for transportation of injured personnel, the number ofpeople necessary for lifting the seat or stretcher, and the abilityof the seat or stretcher to float should it accidentally be droppedinto the sea.


902 Seats for injured occupants shall have a different colourthan the colour of ordinary seats and shall be clearly marked“Seat for injured person” or an equivalent text.903 The seat module and the space around it shall be inaccordance with requirements in C200 for free fall lifeboatseats and shall in addition have necessary space for out-stretched legs of an injured person. Solutions for space forinjured persons need not be limited to seats in the traditionalsense, as long as they serve the purpose, such as stretchers.904 The strength of the seats shall meet the requirements forseats in free fall lifeboats as given in B807.905 Every seat shall be equipped with suitable locking har-nesses capable of quick release under tension to restrain thehead/neck, the body and the feet during launching.

Guidance note:It is not evident that restraining the head will be required in prac-tice, but the requirement in this clause ensures that restraining ofthe head will be possible, should the need be there.


906 It shall be possible to easily transport the seats from atemporary refuge or from the muster area into the lifeboat andsecure them by a simple locking mechanism.907 It shall be possible to easily release the seats from theirplace in the lifeboat for safe transfer by helicopter or by othermeans for retrieval of occupants. It shall be possible to lift theseats by means of a helicopter.908 The seating arrangement shall be designed with atten-tion to easy access for rescue personnel during transfer ofinjured occupants in to and out from the lifeboat.

C. Occupant ComfortC 100 General101 The lifeboat shall be designed bearing in mind that theoccupants may have to stay onboard for several hours beforethey can be rescued. The comfort of the occupants while theyare staying inside the cabin is therefore an important issue.102 This subsection deals with the comfort of the occupantsin the standby phase and in the sailing phase. The standbyphase is reckoned from mustering is completed until the life-boat is launched, and the sailing phase is reckoned from thetime that launch has taken place. 103 The mustering phase is reckoned from mustering is ini-tiated until mustering is completed. The mustering phase thusprecedes the standby phase.Some lifeboats are used as muster area. Even for lifeboatswhich are used as muster area, the mustering phase shall not bereckoned as part of the standby phase. Requirements to musterarea are given in Sec.7 B100 and apply regardless of whethermustering takes place outside or inside the lifeboat.104 The requirements given in this subsection serve to meet

the needs of the occupants after mustering has taken place, i.e.in the standby phase and in the sailing phase. The comfort ofthe occupants in the mustering phase is dealt with throughrequirements given to muster area in Sec.7 B100 and is notcovered in this subsection.105 The interior of the cabin shall be of a colour which doesnot cause discomfort to the occupants.

C 200 Occupant seating 201 For design of occupant seating, the distance from seatpan to top of head measured along the z axis of the local seatcoordinate system shall not be taken less than 108 cm. Theshoulder width shall not be taken less than 53 cm. The shoulderwidth shall be assumed distributed with 50% on either side ofthe centre line of the seat.202 At any point in time during the launch of the lifeboat,there shall be a minimum clearance of 20 cm between everyoccupant and the ceiling of the cabin. In verifying that thisrequirement is met, deformations of the ceiling as establishedfrom structural analysis carried out for structural design shallbe taken into account, cf. Sec.6 A707. 203 At any point in time during the launch of the lifeboat nobody part shall hit a hard object. Thus the clearance betweenevery occupant and any structure or object other than the ceil-ing of the cabin shall be minimum 10 cm in all relevant phasesand conditions. The distance toward neighbouring persons toeach side is exempt from this requirement. In verifying that therequirement is met, deformations of the wall as establishedfrom structural analysis carried out for structural design shallbe taken into account, cf. Sec.6 A707.

Guidance note:To ensure that the requirement in 203 is met for different parts ofthe human body, the maximum body measures given in Table B1can be assumed.


204 With 10 cm allowance for the effect of clothes, therequirement to shoulder width in 201 implies a requirement tothe centre-to-centre distance between two adjacent seats ofminimum 63 cm.205 A robust mock-up seating arrangement shall be builtearly, constituted by, as a minimum, 6 seats arranged in tworows, 3 seats in each row, with intended spacing. The mock-upshall be tested using the full range of body dimensions as givenin B200. For floating host facilities the test shall be carried outfor the host facility in the intact condition as well as in the dam-aged condition with trim and list. The purpose of this mock-uptest is to demonstrate that:

— the seat and harness arrangements are ergonomicallysound

— quick boarding can be ensured— quick, ergonomic and reliable fixation to the seat is

ensured— spacing is adequate.

C 300 Cabin temperature and fresh air quality 301 Both in the standby phase and in the sailing phase thefresh air quality inside the cabin must be acceptable.302 The fresh air supply shall be minimum 80 litres per minper person (total capacity). This requirement applies to thestandby phase and to the sailing phase. In addition it shall bedocumented that the level of CO2 never exceeds 3 000 ppminside the cabin.

Guidance note:CO2 is not directly injurious to health, but the concentration levelwill give indications about the quality of the indoor air. A highCO2 level in excess of 3 000 ppm indicates that the air supply isinsufficient related to number of persons inside.

DET NORSKE VERITAS


When the lifeboat is in the stowed position in the lifeboat stationon the host facility, the air can be assumed to be supplied fromthe host facility. When the lifeboat has been launched and is inthe sailing phase, the required air supply can be achieved bydrawing air through the cabin by means of the running engine.


303 To allow occupants to stand by in the lifeboat for aperiod of time before a launch, a system for temperature con-trol in the cabin shall be implemented. This system need not beinstalled in the lifeboat itself, but can be a part of the host facil-ity. The temperature control system shall be capable of keep-ing the inside temperature between 16 and 22°C. The requirement to implement a system for temperature con-trol can be waived when the lifeboat is not used as muster areaor when the lifeboat is stowed within a temperature-controlledarea. The requirements in this clause apply when the lifeboat isin the stowed position in the lifeboat station and cabin air issupplied by the host facility.

C 400 Lighting 401 The lifeboat shall have two separate systems for light-ing, denoted as System A and System B. When used prior to alaunch, i.e. for standby, both systems shall be powered by theemergency source of power of the host facility. 402 Both systems shall have battery capacity capable of con-tinuous operation for a period of at least 12 hours.

Guidance note:To minimize the need of battery capacity, use of new energy effi-cient technology such as LEDs is recommended.


403 System A shall be designed with respect to giving thelifeboat crew optimal working conditions. 404 System B shall be designed with respect to giving allpersons inside the lifeboat optimal conditions with respect tocomfort and psychological effects.

Guidance note:For occupants to be comfortable, warm colours should be usedfor System B.


405 The illuminance level is measured in terms of luminousemittance. System B shall provide a luminous emittance of 75lux 1.0 m above the floor. The uniformity of the illuminanceshall be equal to or better than Emin/Emean = 0.5, where Emindenotes the minimum luminous emittance and Emean denotesthe average luminous emittance.

Guidance note:To minimize the margin of error when measuring the illuminancelevel, the illuminance level should be measured a distance mini-mum 0.5 m from the wall of the lifeboat.


406 A manually controlled interior light shall be fitted insidethe lifeboat capable of continuous operation for a period of atleast 12 h. It shall produce an arithmetic mean luminous inten-sity of not less than 0.5 cd when measured over the entire upperhemisphere to permit reading of survival and equipmentinstructions.

Guidance note:Candela (cd) is the SI unit of luminous intensity: The candela isthe luminous intensity, in a given direction, of a source that emitsmonochromatic radiation of frequency 540 ⋅ 1012 Hz and that hasa radiant intensity in that direction of 1/683 watt per steradian.Lumen is the SI unit of luminous flux: Luminous flux emitted inunit solid angle (steradian) by a uniform point source having aluminous intensity of 1 candela.

Lux is the SI unit of illuminance: Illuminance produced on a sur-face of area 1.0 m2 by a luminous flux of 1 lumen uniformly dis-tributed over that surface.


C 500 Sanitary conditions501 During standby and in the sailing phase, personal needsfor vomiting and toilet visits shall be planned for during thedesign of the lifeboat.502 Each seat in the lifeboat shall be equipped with sick bagswithin a reachable distance for each occupant when strapped tothe seat and ready for free fall evacuation. The sick bags shallnot be transparent.503 The sick bags shall be so designed that they can besealed airtight after use.504 Containers for collection of sick bags shall be placed at dif-ferent easily accessible locations in the lifeboat cabin. The con-tainers shall be designed with watertight cover and shall bedimensioned for impact during the free fall launch of the lifeboat. 505 Each container shall have a total capacity of one sick bagper person onboard.506 The lifeboat shall be equipped with a toilet arrangementprimarily for use during the sailing phase.For use during mustering and in a standby phase, toilet facili-ties located outside, but near the lifeboat shall be available. Allneeds for toilet visits in the standby phase shall be approved bythe lifeboat pilot and logged in the list of occupants for contin-uously updating.

Guidance note:The toilet arrangement in the lifeboat may be of a simple type.


507 The sanitary arrangements shall have an easily accessi-ble location and shall be screened or shielded from free accessby a curtain or the equivalent.508 The toilet container/tank shall be designed with a water-tight cover which can easily be used without leakage in any seastate occurring.509 In heavy weather condition with risk for injuries to theoccupants when moving around in the lifeboat, such move-ment is up to the pilot’s decision.

D. MiscellaneousD 100 Fire101 A fire-protected lifeboat, when waterborne, shall becapable of protecting the number of persons it is designed toaccommodate when subjected to a continuous oil fire thatenvelops the lifeboat for a period of not less than 10 minutes.Fulfilment of this requirement shall be documented by testing,see Sec.9.

Guidance note:The requirement can usually be met by fitting the lifeboat with awater spray system. A water spray system with sufficient coolingcapacity will allow for use of standard composite materials andwill limit the need for insulation of steel materials in the lifeboatstructure.


D 200 External colour201 The lifeboat shall be of international or vivid reddishorange, or a comparably highly visible colour, on all parts wherethis will assist detection at sea. The lifeboat shall be fitted withretroreflective materials where it will assist in detection.

DET NORSKE VERITAS


SECTION 9MODEL SCALE TESTING AND FULL SCALE TESTING

A. GeneralA 100 Introduction101 This section outlines the general requirements for modeltesting and full scale testing of free fall lifeboats.102 For lifeboat systems, where use of theoretical modelsand analysis tools offers challenges with respect to predictionof responses in a free fall launch, model scale testing is vital ina design process. Carefully executed model tests at an appro-priate scale are therefore required for design of free fall life-boats.103 Full scale tests of free fall lifeboats are carried out withthe following two objectives:

— Prototype testing, where several tests are executed in orderto document the design of a lifeboat type.

— Acceptance testing which usually is limited to one dropper each individual lifeboat. Acceptance testing is typi-cally performed when installing the lifeboat on site, butcan also be executed at an inshore or coastal location.

Guidance note:Execution of acceptance tests on site allows for test of the entirelifeboat system, including the release arrangement and the skid.Execution of acceptance tests inshore will facilitate inspection ofthe lifeboat after the test.


A 200 General guidance201 DNV-RP-C205, Environmental Conditions and Envi-ronmental Loads, describes hydrodynamic model testing ingeneral and is used as a reference for this section.202 Structural Finite Element Analyses (FEA) of the lifeboatshould be performed prior to testing such that critical areas onthe hull and the canopy can be identified and subsequentlyhighlighted in the tests.

A 300 Extrapolation of test results301 It is not always feasible to carry out model scale testsand full scale tests for the entire range of sea states of interest,e.g. because of limitations of the test facility that prevent themost severe wave conditions from being covered by the modeltests. To the extent that results are needed for wave conditionsnot covered by the tests, extrapolation of results obtained inmore relaxed wave conditions will be necessary. Numericalsimulations can be used for this purpose provided that an ade-quate numerical simulator is available.

Guidance note:Appendix A provides guidance on how results from tests in lesssevere sea states can be parameterized and how interpreted math-ematical relationships can be used to extrapolate to more severesea states.


B. Model Scale TestingB 100 Introduction101 Model testing can provide input to numerical analysis,e.g. in terms of hydrodynamic coefficients, and can assist inverification of numerical analysis.102 The model tests are meant to assist in establishing the

characteristic loads, the characteristic accelerations and thecharacteristic pressures for use in design of the lifeboat.103 The model tests will also be used to document theobtained forward speed until water entry and after resurfacingto assess the required propulsion to ensure sufficient headway.

B 200 General requirements and simplifications201 A model test specification shall be established giving alldetails about test objectives, requirements and testing details.202 Model testing of free fall lifeboats should be carried outwith as large a model as possible and with a minimum lengthof the lifeboat model of about 1 m. Multiple models or scalesor both may be chosen depending on the focus area, e.g. trajec-tories, pressures, accelerations, loads, manoeuvrability andforward speed until water entry and immediately after resur-facing. The launching appliance used in the model tests shallbe a model to scale of the launching appliance which isdesigned for the full scale lifeboat.

Guidance note:The minimum length of about 1 m of the lifeboat model reflectsthe required space for instrumentation and the need to reduceinfluence from scale effects. A smaller model may be applied ifit can be documented that the instrumentation and instrumenta-tion cables do not affect the motion behaviour and the pressuredistribution on the model. Typical model scales are in the range1:10 to 1:15, which usually allow for meeting the minimumrequirement to the length of the model.


203 Testing shall include regular waves and irregular seaconditions as well as calm sea.204 The main bulk of testing should be performed with long-crested waves. For areas where a high degree of multidirec-tional sea may occur, tests with short crested waves should beevaluated. Typically this should be evaluated with basis in themetocean specification for the actual site. 205 The model testing should include regular and irregularwaves and wave approach headings of 0o, 45o, 90o, 135o and180o where 0o is waves head on the launch direction (bow oflifeboat). This high number of headings is a basis for initialscreening and once more knowledge about which headings arecritical, the number of headings can be reduced in subsequenttests.206 Influence from current can in general be neglectedbecause current velocities are usually small relative to dropvelocities and wave particle velocities. The only exceptionsfrom this are headway tests and manoeuvring tests, for whichwind-generated current cannot be neglected.

Guidance note:The potential influence of current on the wave profile, i.e.,altered wave steepness and wave height due to the current, canusually be neglected, hence allowing for separate tests of wavesand current.


207 Wind tunnel tests to determine wind coefficients,defined in DNV-RP-C205 and used to calculate wind loads,may be required if it is not possible to determine these coeffi-cients otherwise. If wind coefficients are determined by Com-putational Fluid Dynamics such calculations shall be validatedby wind tunnel tests. These coefficients are to be used as inputto analytical models for calculation of lifeboat trajectorythrough air and as input to the model test facility. It is assumedthat the model test facility has the ability to generate wind by

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use of fans and that wind forces can be monitored and control-led.

Guidance note:Wind forces and moments obtained during model drop testsshould be checked with forces and moments obtained in windtunnel tests. This can be done either directly by use of a 6 com-ponent force transducer or implicitly by measuring the effect onthe air trajectory and the rotational position of the lifeboat atwater impact. Improved correspondence can be obtained byadjusting the wind speed or making minor geometrical changeson the lifeboat model.For determination of wind coefficients to be used for lifeboatsthat are launched from floating host facilities, it is recommendedto carry out the wind tunnel tests for a range of skid anglesdefined by the angle in the untilted condition ± 17°.


208 Test with simultaneous waves and wind shall be per-formed since wind will influence on the relative hit anglebetween water surface and lifeboat. Other means of obtainingchanges in angle might be applied, but it must then be docu-mented that these means do not influence other results unduly.209 Steady wind should be included in the drop testing,whereas dynamic wind effects can be neglected due to theshort drop time. The wind velocity may be taken as the relevant10-minute mean wind speed at a height equal to half the launchheight.

Guidance note:The wind conditions at impact are in general best represented bythe wind speed in a height equal to half the drop height. If localwind speeds prevailing at the skid, owing to effects of a shelterand other (local) geometrical effects, influence the speed of thelifeboat when it leaves the skid, then these local wind speedsneed to be accounted for.


210 Wind directions should be collinear with wave direc-tions. For wave directions 0o, 45o and 90o all tests should beperformed including wind. For wave directions 135o and 180owind can be neglected. Direction 0o is defined as waves headon in the launch direction (bow of lifeboat).

Guidance note:The recommendation of using collinear wind and wave direc-tions reflects that it is most likely that wind and wind-drivenwaves act collinearly. However, it should be kept in mind that itcan sometimes be more critical that the wind acts on the lifeboatin a direction different from the wave direction, because a skewwater entry may generate lateral accelerations.


211 Initially, deep water can be assumed in tests; howeverthe actual water depth at a site shall be taken into account if thishas an effect on the wave kinematics and the wave shapes. 212 For lifeboats to be used from host facilities in shallowwaters, the tests shall be carried out for the actual water depthat the location in question.

Guidance note:Shallow water is usually defined as waters where the water-depth-to-wave-length ratio is less than 0.05.


213 Free fall lifeboats can be used for evacuation from fixedhost facilities as well as floating host facilities, and model testsof lifeboats shall be executed with due consideration of theeffects of the actual type of host facility.

Guidance note:There are basically two main types of host facilities which haveto be considered, i.e. fixed structures and floating structures. Themain types of fixed structures consist of GBS, jackets and jack-ups. The main types of floating structures consist of FPSOs,Semis, TLPs and Spar units. The TLP is restrained in heave, roll

and pitch, but may have surge, sway and yaw motions at the samelevel as the other named floaters. Regarding turret mooredFPSOs their weather vaning capability should be noted. Special types of host facilities like guyed towers and articulatedtowers should be treated like a TLP if wave frequency horizontaldeck/topside motions/accelerations are at the same level as thoseof a TLP.


214 For lifeboats on fixed offshore structures, the motion ofthe lifeboat station due to environmental loading can beneglected in relation to model testing.215 For lifeboats on floating structures the influence offloater motions shall be taken into consideration in the modeltesting either by adjusting the drop height or by varying theheel and trim skid angles, or both.

Guidance note:Evaluations regarding the effect of wave induced floater velocityand acceleration on the lifeboat impact angle and relative veloc-ity between lifeboat and water particles in the wave may be ben-eficial. For large semi submersibles, the effect of low frequencypitch and roll motion in harsh weather should also be evaluated.If deemed important, model tests including at least wave fre-quency motions of floater (and thereby of the lifeboat station)should be performed. If not deemed important the height adjust-ments and/or angle variations can be kept static throughout eachtest. No dynamic motion of the lifeboat station is then to be sim-ulated.


B 300 Recommended test execution301 Typical model scales for offshore structures are in therange 1:30 to 1:100. Model testing of free fall lifeboats shouldbe carried out with as large a model as possible and with a min-imum length of the lifeboat model of about 1 m. For free falllifeboats, it is therefore expected that a scale in the range 1:10to 1:15 is necessary. The model scale selection will typicallybe a trade off between the absolute size of the model, instru-mentation and which wave conditions are to be simulated. Forfurther details about scaling and scaling effects, see DNV-RP-C205 Sec.10.9. In general it is assumed that Froude’s law ofscaling applies.

Guidance note:An air cavity usually develops behind the stern of the lifeboat asthe lifeboat dives into the water. As long as this cavity is open tofree air, i.e. a situation with ventilation prevails, it can beassumed that conventional Froude scaling applies, and thebehaviour of the cavity will be approximately as in full scale.However, when the cavity closes, the behaviour of the cavity inmodel scale will be different from the behaviour in full scale. Forthe closed cavity, the natural frequency of the cavity is propor-tional to the model scale and not to the square root of the modelscale as it should have been according to Froude’s law.


302 The actual model shall be made of sufficiently strongmaterial and should reflect the full scale lifeboat with respectto global stiffness as much as possible. Non-significant detailsmay be omitted; however, details which may have an impacton hydrodynamic behaviour need to be included. Examplesare: flanges, boat skids, rudder, and nozzle systems. The modelshall reflect the true COG position and inertias of the lifeboatand shall have opportunities to alter the longitudinal and trans-verse mass distribution due to variable loading such as thatcaused by variable manning. Deviations from true propertiesand true details of the full scale lifeboat, which are necessarywhen the model is constructed, shall be documented withrespect to their effects and consequences.

Guidance note:It is difficult to obtain a lifeboat model which fully reflects theglobal stiffness of the full scale lifeboat. In practice, typically, the

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external hull geometry is fully reflected, but not the girder sys-tem, such that a completely rigid model is used.


303 Typical instrumentation which will be needed for thesetypes of testing is:

— slamming/force panels (typical diameter: 40-60 mm)— pressure cells (typical diameter: 2-6 mm)— accelerometers (6 DOF) for registration of vibrations and

rigid body motions in at least two positions along length oflifeboat

— camera/optical tracking (above and under water).

Guidance note:Relative wave probes fixed to the model are usually not used,because they tend to influence too much on the test results.It is recommended to use at least three pressure cells or probesalong the circumference of one typical cross section at a criticalstructural point. The difference pressure must be provided in thetime domain such that the maximum of the combined time seriescan be further analysed as required in Sec.4 E809 to E814.


304 A set of regular waves and irregular sea conditions willhave to be calibrated for use in the tests. Post calibration maybe needed to check repeatability in the test basin. The follow-ing requirements apply to wave modelling:

— Wave probes to be installed for control of wave parame-ters and phasing during testing

— Regular waves shall be calibrated to be within 1% and 5%of specified values for wave period and wave heightrespectively. For details, see DNV-RP-C205 10.3.2.2.

— Tolerance levels for irregular waves shall be ± 5% for HSand Tp. The shape of the measured wave spectra shouldmatch the target wave spectra. For details, see DNV-RP-C205 10.3.2.3.

— Requirements to extreme waves (Hmax) and crest eleva-tions in realizations will be other check points in a wavecalibration effort. No specific requirements to tolerancesare given. It is, however, assumed that these parameterswill be monitored during wave calibration and the actualtesting.

305 The following are considered important with respect towind modelling:

— Wind coefficients shall be determined either from windtunnel testing, numerical analysis or from available data.

— Simulating correct wind forces and moments acting on thelifeboat are the key aspects. Wind velocities during thetests are therefore of less importance. Wind moments areof importance since these moments will influence theimpact angle between the lifeboat and the water surface.

— Initially it is assumed that wind fans will have to beapplied and care should be taken to ensure a reasonablyhomogenous wind field with a reasonably correct verticaldistribution of horizontal wind velocity.

306 The actual test preparations and execution should as aminimum follow the below stated requirements. All theserequirements are assumed to be given in the model test speci-fication.

— The calibration of sensors should be performed in condi-tions similar to actual test execution. Uncertainties,including original accuracy of sensors (95% confidencevalues) should be quantified. Reference is made to e.g.ANSI/ASME PTC 19.1-1985 Part I, 1986 with respect tomeasurement uncertainty.

— Calibration and measurement should be carried out withthe same data acquisition setup including probes, wires,amplifier, possible filters and analogue to digital converter

or sampling unit. If this is not the case, uncertainties dueto a change in system components should be quantified.

— Caution should be exercised to avoid unnecessary influ-ence from instrumentation cables. Effect of instrumenta-tion cables should be documented.

— Calibration of the waves in the basin should be done afterthe wave measurement equipment is carefully calibrated.

— The wave conditions need to be continuously measuredduring testing.

— Irregular wave testing shall be performed with a minimumof 30 drops at random positions in the wave train. Whenthe aim is to establish a probability distribution of a varia-ble in question, a minimum of 50 drops at random posi-tions are required.

— Alternatively, testing with conditioned drops, i.e. pre-selected drop points could be used if substantiated that thisis conservative for the sought characteristic response val-ues.

— Characteristics of model to be within given accuracy limitsfor centre of gravity, weight, geometry, and radii of gyra-tion.

Guidance note:The following accuracy limits for characteristics of the lifeboatmodel are recommended:- longitudinal centre of gravity (LCG): 0.1% of Lpp- vertical centre of gravity (VCG): 1% of Lpp- weight of lifeboat: 0.5%- geometry: maximum value of 1% or 1 mm in model scale- radii of gyration: 0.5% of Lppwhere Lpp is the length (between perpendiculars) of lifeboat.


307 The data acquisition, signal processing and analysisshould as a minimum follow the below given recommenda-tions.

a) All measurements and data should be presented in full-scale values based on Froude scaling.

b) Lower limits for sampling rates should typically be:

— accelerometers – 200 Hz full-scale— accelerometers for vibrations – 1 000 Hz full-scale— pressure sensors and slamming panels – 1 000 Hz full-

scale— wave measurements at 100 Hz. Assumed sufficient

for model-scale.

c) For accelerometers, the sampling rate should not be lessthan 2 000 Hz when the acceleration data (time series) areto be used as input to numerical analyses and advancedinstrumented dummy tests.

d) Filtering frequencies and types of filters. Typically ana-logue Butterworth filters of order 4 can be used. Theapplied filters and cut-off frequencies must be docu-mented and evaluated.

e) Calculate values from measured accelerations accordingto specification in Sec.4 and Appendix A (CAR or othervalue). This specification should include filter frequenciesand filter types. Obviously, the Nyquist frequency willlimit filtered signals to below half the sampling frequency,depending on the filter characteristics including the transi-tion band.

f) The acceleration values should be calculated for the rele-vant seating arrangement (positions and angles). Usuallycalculations for the pilot seat, the foremost and rearmostseats will be sufficient. Interpolation between these seatsis acceptable under assumptions of rigid body lifeboatmotion.

g) All estimated values should be presented with an intervalshowing the 95% confidence limits. This includes derived

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values and applies mainly to data from many tests in irreg-ular sea. Bias errors due to limited accuracy of transducersand data acquisition system should be included.

h) Statistical post-processing should be done according torecognized methods

i) Model tests results in calm water should be compared withsimilar results from full-scale testing. This can be used toassess possible scale effects due to e.g. ventilation, cavita-tion or flow separation.

B 400 Minimum level of testing401 In general it is recommended that a high number of droptests are performed in order to determine the governing char-acteristic loads, accelerations and pressures acting on the life-boat during and after water entry. This is mainly related totesting in waves where a large number of wave conditions willhave to be tested.

Guidance note:A wave condition is characterized by the significant wave heightHS, the peak period Tp, the wave spectrum, the mean wave prop-agation direction Θm and the directional spread (for short-crestedsea). Details are given in Sec.3.


402 A platform emergency evacuation via lifeboat shall besafe also in severe weather conditions and from intact as wellas damaged host platform. In this context, damage of the hostplatform refers to heel or tilt or both and is considered relevantfor floaters only, not for fixed platforms.403 Variations in drop height, heel and trim angles of hostfacility shall be included in the test program when the hostfacility is a floater. Motions of floaters and accidental condi-tions like heel and trim can be taken into account by varyingthe launch height and the heel and trim. The most probable val-ues of wave frequency floater motions shall be used as basisfor determination of the adjusted launch height and heel/trimfor intact floater as well as for damaged floater. It is possibleto take into account actual phasing of wave frequency motionsrelative to the wave profile. Trim and heel for damaged hostfacility shall be set to ± 17 degrees unless other host facilityspecific values are known.

Guidance note:The most probable floater motion amplitudes within a specifiedshort term wave condition can be found by assuming the motionamplitudes to be Rayleigh distributed.


404 Model test conditions shall cover representative envi-ronmental conditions ranging from calm water to severe sea.This applies to both intact host facility and damaged host facil-ity. If possible within the capabilities of the model test facility,the most extreme model test conditions should be those of a seastate well beyond the characteristic sea state, but not necessar-ily as severe as the 100-year sea state. In analogy with the char-acteristic ULS load being defined as the 99% quantile in thelong-term distribution of the load during launch at an arbitrarypoint in time, the characteristic sea state may be defined as thesea state whose significant wave height HS is the 99% quantilein the long-term distribution of the significant wave height. Forsome North Sea locations this characteristic significant waveheight is approximately 8 m.

Guidance note:The long-term distribution of the significant wave height HS sig-nifies the distribution of HS at an arbitrary point in time. This isthe distribution that will result if HS is observed at regular inter-vals over a long period of time. The 99% quantile in this distri-bution is the value of HS which is exceeded 1% of the time andcan be estimated by the value of HS which is exceeded by 1% ofthe observed values of HS. Appendix A provides an example ofhow the 99% quantile of a random variable can be interpreted.


405 Table B1 provides a recommendation for a minimumlevel of drop testing in waves for a floating host facility. TableB2 provides a recommendation for a minimum level of droptesting in waves for a fixed host facility. The actual number ofrepetitions of the tests specified in Tables B1 and B2 will haveto be judged based on repeatability and scatter in results, how-ever, as a minimum, 3 repetitions are recommended for calmsea tests whereas minimum 5 repetitions are recommended forthe regular wave tests. For tests with specified hit points in reg-ular waves, a minimum of 3 repetitions for each of four hitpoints are recommended, giving a total minimum of 12 tests.In order to establish probability distribution functions for loadsand pressures in irregular wave tests with reasonable confi-dence, approximately 50 to 100 repetitions will be needed.

Guidance note:The amount of testing indicated in Tables B1 and B2 is very largeand needs thorough screening from case to case to reduce theamount of testing to a practicable level. Tables B1 and B2 inprinciple contain full matrices of recommended tests. Dependingon the response of interest some of the indicated variable combi-nations and associated tests will not be relevant and can be leftout.The number of different wave headings to be considered may bereduced based on an initial heading screening with sensitivitychecks. For test of sufficient headway it is not necessary to con-sider following sea. For lifeboats on weather-vaning FPSOs,fewer wave directions need consideration than for lifeboats onother host floaters. If there are redundant lifeboat stations, thenumber of relevant wave directions can also be reduced. The test matrices in Tables B1 and B2 provide a systematic out-line of recommended minimum requirements to model testingand can be optimized during the execution of the tests as the test-ing proceeds.Tables B1 and B2 provide recommended minimum extents oftest programs for model testing of free fall lifeboats in both reg-ular and irregular waves. In practice, the need for inclusion oftests in both regular waves and irregular waves in the same testprogram will vary from case to case and will be much dependenton what the purpose of the testing is. When the purpose is todetermine “worst case” loads through a controlled launch withwater entry at the most unfavourable hit point in a wave, a testprogram consisting of tests in regular waves only may seem nat-ural, and tests in irregular waves can be left out. When the pur-pose is to determine probability distributions of one or morequantities of interest in connection with lifeboat launches, and inturn estimate characteristic values of these properties as requiredthroughout this standard, then a test program with tests in irreg-ular waves needs to be set up. Tests in regular waves can be usedfor wave direction screening before the irregular wave tests.The number of tests specified in the model test matrices in TablesB1 and B2 can be reduced when model test data are available forthe same lifeboat qualified for another location with correspond-ing, but not necessarily identical environmental conditions. Thenumber of tests can also be reduced when a numerical simulatoris available for prediction of the behaviour of the lifeboat.


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Guidance note:It is recommended to select M (in Table B1 set to 3), the numberof regular waves (H,T), by varying H linearly from (j/M)Hmax toHmax with j = 1,..M and the corresponding period T given by thesteepest regular Stokes wave T = (14πH/g)½. Hmax should betaken as the maximum possible regular wave height attainable inthe test facility.It is recommended to select N (in Table B1 set to 5), the numberof 3-hour irregular wave conditions (HS, Tp), by varying Hs lin-early from (j/N)HS,max to HS,max with j = 1,..N, and determine thecorresponding Tp by assuming the average steepness Sp to haveits maximum value. The average steepness Sp for a short termwave condition and the limiting values are given in DNV-RP-C205. HS,max should be taken as the 99% quantile in the long-term distribution of the significant wave height or as the maxi-mum possible significant wave height attainable in the test facil-ity. It is recommended to select the two wave directions in theirregular wave tests based on the results of the regular wave tests.


Guidance note:100% load condition refers to lifeboat fully loaded with occu-pants. 0% refers to minimum crew required in order to launch thelifeboat, typically this signifies three persons.


406 Test with simultaneous waves and current can generallybe neglected, see 206. When considering headway andmanoeuvring capabilities, results from current only tests andwave only tests may be superimposed.407 Test with simultaneous waves and wind shall be per-formed, see 207 to 210.

B 500 Correlation and validation501 After completion of the model tests, the model testresults shall be validated by comparison of the results withresults from relevant analytical calculations or simulations orboth. The validation work should include an attempt to explainkey differences in results and should provide advice regardingwhich parts of the model test results can be used in the designof the lifeboat. The validation work should also provide adviceon possible additional testing or supplemental analytical workor both. A reference to and correlation with relevant full scale

testing should also be made.

C. Full Scale Prototype TestingC 100 Introduction101 Full scale testing shall be executed and is considered avital validation of analytical work and model scale testing. Thelevel of such testing has to be decided based on the level andextent of analytical work and model scale testing.102 For full scale prototype testing, several tests are neededin order to document that the lifeboat is properly designed andfabricated, see Table C1.103 Full scale drop testing will, in this context, be offshoretesting with relaxed environment, or inshore or coastal testingin calm or benign environments. In order to compare full scaletests to model tests or analytical solutions it is preferable to testin calm environment.

C 200 General requirements and simplifications201 If full scale drop testing on site is considered unsafe, dif-ficult or impractical, full scale tests can alternatively be exe-cuted inshore. Two types of test sites may be considered forsuch inshore testing:

— inshore, in protected (calm) waters— coastal location where tests may be executed with expo-

sure to higher waves.

202 The actual wind, waves and current present during test-ing must be documented. As a minimum the wind velocitiesand directions, the current velocities and directions as well aswave heights and directions must be continuously recorded,e.g. by means of wave buoys or wave radars.203 The prototype testing shall employ the actual drop/skidarrangements, as a minimum with respect to heights, anglesand launch speeds. Also the lifeboat loading conditions whichmight be encountered in a real situation should be tested. 204 In order to avoid human injuries it is required that fullscale prototype testing is performed with no manning. Use ofremote control is recommended. Dummy weights shall be usedto simulate the effects of different manning levels and weightdistributions.205 In order to verify simulations and calculations, proto-type tests shall be carried out with instrumented crash testdummies.

C 300 Test execution301 The prototype should reflect the actual global stiffnessand mass distribution inclusive COG and moments of inertia asintended to be experienced in a real evacuation situation off-shore, such that the actual hydrostatics including metacentricheights are captured. 302 Wherever possible, the location of instrumentation andmeasurements in the model scale tests should be taken into

Table B1 Recommended Minimum Level of Drop Testing in Waves, Floating host facilityTest setup Waves

Launch height Load condition Trim Heel Calm water

Regular Irregular(H, T) Dir (Hs, Tp) Dir

hL 0%+100% - - 1 3 5 5 2hL ±ΔhD 0%+100% - - 1 3 5 5 2hL ±ΔhA 0%+100% 2 - 1hL ±ΔhA 0%+100% - 2 1

hL launch height above SWL for floating host platformsΔhD changes in launch height based on most probable values of wave frequency motions ΔhA changes in launch height due to accidental trim and heel angles.

Table B2 Recommended Minimum Level of Drop Testing in Waves, Fixed host facilityTest setup WavesLaunch height

Load condition Calm water

Regular IrregularH, T Dir HS, Tp Dir

hL 0%+100% 1 3 5 5 2The recommended numbers of tests for bottom-fixed platforms are given for drop testing for a specific launch height hL. Due to varia-bility in the water level about MWL due to tide, different launch heights may have to be considered for testing. To reduce the total number of tests needed, it is recommended to carry out tests for one launch height only, which should then be taken as the launch height above LAT rather than the launch height above MWL.

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account when planning the instrumentation of the full scaletesting. This applies especially to locations of pressure panelsand accelerometers. Findings from finite element analysis orfrom other analytical or numerical tools can also give guidancefor planning of location of instrumentation.303 The prototype lifeboat used for the full scale test shouldas a minimum be equipped with the following instrumentation:

— System for registration of rigid body motions and veloci-ties (6 DOF) of the lifeboat during launch, impact and upto free float condition.

— System for registration and calculation of accelerations atcritical locations in the lifeboat.

— Instrumented slamming panels placed in critical areas asobtained from finite element analysis.

— System for measuring strain and stresses at critical areas.— System for measuring deflections of the hull and the canopy.— Forward motion (video). — For advanced instrumented dummy tests, high-speed

video of the dummy kinematics is needed. 1 000 framesper second are usually sufficient.

304 The following issues regarding instrumentation, sam-pling, signal processing and analyses of the full scale testingshould be addressed:

— Accelerometers – same as for model tests – at least three3-axes accelerometers at three longitudinal positions.Sampling rate 200 Hz.

— For accelerometers, the sampling rate should not be lessthan 2 000 Hz when the acceleration data (time series) areto be used as input to numerical analyses and advancedinstrumented dummy tests.

— Gyros for rotational motions (pitch and roll). Sampling200 Hz.

— Additional measurements of deformations with similarsampling 200 Hz.

— Strain gauges at 1 000 Hz.— Slamming panels with 1 000 Hz sampling rate.— Use digital video cameras to document the drop.— Possibly include systems to monitor engine, autopilot,

rudder etc.— The wind, waves and current should be measured / esti-

mated during testing. — The use of filters should be according to the specification

of the estimation of characteristic values.— Mounting of sensors should be carefully performed in

order to limit structural vibrations.

C 400 Minimum level of prototype testing401 Prototype testing consists of one or more drop tests of aprototype lifeboat, where the lifeboat is subject to a launch.The main bulk of prototype testing is assumed to be performedin calm water.402 A minimum amount of prototype testing shall be carriedout. The minimum amount of prototype testing consists of testswith test setups specified in Table C1. Table C1 applies to life-boats on floating host facilities; hence for lifeboats on fixedhost facilities, tests with variable launch heights and heel/trimconditions as specified in Table C1 can be omitted.

Guidance note:The launch height required in the prototype drop tests specifiedin Table C1 is 100% of the site-specific launch height hL withadjustment for floater motions when the host facility is a floater. It is recommended to carry out one prototype drop test withlaunch height equal to 130% of the site-specific launch height hL.Such an excess height test will allow for useful benchmarkingagainst experience with lifeboats designed in the past, since thesehave traditionally been subjected to comparable excess heighttests as part of a type approval scheme. The recommended excessheight test will also be a prerequisite for issuance of a SOLAS

certificate for the lifeboat in accordance with IMO ResolutionMSC.48 (66), the International Life Saving Appliances Code.


403 For each test setup, the drop tests should be repeated atleast once in order to indicate the variability of measurements.404 In relation to prototype testing the following additionalitems should be considered.

— Lifeboat course keeping capability after resurfacing.— Manoeuvring / thrust capability— Embarkation tests, i.e. time period from first person enters

the lifeboat until ready for launch— Structural inspections after each prototype launch— Human load level tests by means of crash test dummies.

C 500 Correlation and validation for prototype testing501 A correlation and validation report which combines theresults from the analytical work, the small scale testing and theprototype testing shall be prepared.

C 600 Fire test601 The lifeboat shall be tested in water with burning oil onthe sea surface. For this purpose, the lifeboat shall be mooredin the centre of an area which is not less than five times themaximum projected plan area of the lifeboat. Sufficient kero-sene shall be floated on the water within the area so that whenignited it will sustain a fire which completely envelops the life-boat for a period of time equal to 10 minutes. The boundary ofthe area shall be capable of completely retaining the fuel. The engine shall be run at full speed; however, the propellerneed not be turning. Gas- and fire-protective systems shall bein operation throughout the fire test.The kerosene shall be ignited. It shall continue to burn andenvelop the lifeboat for 10 minutes.During the fire test, the temperature shall be measured andrecorded as a minimum at the following locations:

— at not less than 10 positions on the inside surface of thelifeboat

— at not less than five positions inside the lifeboat at loca-tions normally taken by occupants and away from theinside surface; and

— on the external surface of the lifeboat.

The method of temperature measurement shall allow the max-imum temperature to be recorded.The temperature in the cabin shall not exceed 35°C at any pointin time during the fire test.The atmosphere inside the lifeboat shall be continuously sam-pled and representative retained samples shall be analysed forthe presence and quantity of essential, toxic, and injurious

Table C1 Minimum Level of Prototype TestingTest setup Minimum

number of testsLaunch

height Load condition Trim Heel

hL 0%+100% - - 1hL +ΔhD 0%+100% - - 1hL +ΔhD 0%+100% most

probable*- 1

hL +ΔhD 0%+100% - most probable*

1

hL launch height above LAT for bottom-fixed host platforms and above SWL for floating host platforms

ΔhD change in launch height based on most probable values of wave fre-quency floater motions

* the sign of the selected trim or heel angle should correspond to an increase in launch height.

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gases and substances. The analysis shall cover the range ofanticipated gases and substances that may be produced andwhich can vary according to the materials and fabrication tech-niques used to manufacture the lifeboat. The analysis shallindicate that there is sufficient oxygen and no dangerous levelsof toxic or injurious gases and substances.The pressure inside the lifeboat shall be continuously recordedto confirm that a positive pressure is being maintained insidethe lifeboat.At the conclusion of the fire test, the condition of the lifeboatshall be such that it could continue to be used in the fullyloaded condition.602 The fire test outlined in 601 may be waived for anytotally enclosed free fall lifeboat which is identical in construc-tion to another lifeboat which has successfully completed thistest, provided the lifeboat differs only in size and retains essen-tially the same form. The protective system shall be as effec-tive as that of the lifeboat tested. The water delivery rate andthe film thickness at various locations around the hull and can-opy shall be equal to or exceed the measurements made on thelifeboat originally fire tested.

C 700 Test of water spray system701 The water spray system shall be subject to periodic test-ing for verification of its maintained functionality and for iden-tification of the need for maintenance. The water spray systemshall be tested at least once per year.

D. Full Scale Acceptance TestingD 100 Introduction101 Acceptance testing shall be carried out for each manu-factured lifeboat. The main purposes of the acceptance testingare:

— to document that the actual lifeboat does not have anystructural deficiencies which could be detrimental in a reallaunch situation.

— to test that the release systems installed on the host plat-forms are functioning properly

— to ensure that all systems within the lifeboat are function-ing properly.

102 For full scale acceptance tests (FAT), a minimum of onedrop test per lifeboat shall be carried out. The loading condi-tion shall be 100%.103 For the acceptance testing, the same type of drop/skid

arrangement shall be applied as the one which the lifeboat is tobe used with when installed in the lifeboat station. The launchheight shall be the same as the launch height that applies whenthe lifeboat is launched from its permanent position in the life-boat station.104 In order to avoid human injuries it is required that thetest is performed with no manning. Use of remote control isrecommended. Dummy weights shall be used to simulate the100% load condition.105 If full scale testing on site is considered unsafe, difficultor impractical, full scale tests can alternatively be executedinshore. Two types of test sites may be considered for suchinshore testing:

— inshore, in protected (calm) waters— coastal location where tests may be executed with expo-

sure to higher waves.

D 200 Minimum level of acceptance testing201 The level of instrumentation for acceptance testing maybe limited to registration of accelerations during the launch andwater entry. However, it is recommended also to monitor thedeformations of the canopy and the hull. 202 After the test the lifeboat shall be subjected to a carefulvisual inspection. The inspection shall include outside, inside,the inside of all enclosed spaces and foundations for machin-ery, equipment etc. No visual damages, deformations or mate-rial failures are acceptable. FRP structures shall in addition besubjected to inspection by coin-tapping (or other equivalenttechnique) for detection of possible delaminations. Delamina-tions are not acceptable. Minor delaminations may be acceptedbased on special consideration.203 The measured accelerations shall be within the designenvelope.

D 300 Test of release system301 Acceptance testing shall be performed in relation to thelifeboat release system. This applies to all lifeboat release sta-tions on the host facility. For this test a 10% lifeboat weightoverload shall be incorporated in the test.

D 400 Lifeboat system testing401 Full scale acceptance testing shall include testing of allvital systems within each lifeboat on the host facility.

D 500 Manoeuvring tests501 Requirements to manoeuvring tests are given inSec.7 E300.

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SECTION 10INSTALLATION

A. GeneralA 100 General101 The lifeboat can be installed in the lifeboat station bymeans of any capable lifting appliance such as a crane or awinch with a hook. Such lifting appliance can be brought outtemporarily for the sole purpose of the installation of the life-boat or it can be installed as a permanent piece of equipment inthe lifeboat station. 102 The lifeboat station shall be equipped with means ofretrieval. The means of retrieval shall allow for retrieval of thelifeboat after test launches from the host facility and for rein-stallation of the lifeboat upon completion of maintenance ses-sions ashore. The means of retrieval may be combined with thesecondary means of launching, thereby to allow for davitlaunching of the lifeboat, rather than free fall launching, whenthe lifeboat is to be brought ashore for maintenance.

103 The means of retrieval shall be capable of lifting theempty lifeboat from the sea surface to its stowed position in thelifeboat station. 104 After launch testing by simulation, the means ofretrieval shall be capable of bringing the lifeboat back to itsoriginal stowed position, ready for use in an emergency situa-tion, without causing any damage to the lifeboat.105 For details about design of lifting appliances and meansof retrieval, reference is made to NORSOK R-002, Annex A,and to DNV Rules for Certification of Lifting Appliances.

A 200 Maintenance201 A maintenance plan shall be worked out for any liftingappliances and means of retrieval installed in the lifeboat sta-tion to ensure adequate periodic maintenance. For details, ref-erence is made to NORSOK R-002 and IMO MSC1206.

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SECTION 11EQUIPMENT

A. GeneralA 100 General101 This section provides requirements to equipment whichis part of the lifeboat system or which is installed in a free falllifeboat.102 All pieces of equipment which are to be mounted in thelifeboat shall be mounted in such a manner that they do notcome loose due to vibrations.

A 200 Launching and recovery appliances201 Each lifeboat shall be arranged with a primary and a sec-ondary means of launching. In addition, means of retrievalshall be provided for recovery of the lifeboat from the water tothe host facility. 202 Launching and recovery appliances for lifeboats shallcomply with NORSOK R-002, Revision 2, Annex A. 203 Launching and recovery appliances shall be designed forsimplicity and fail-safe operation, to reduce the risk of humanerrors during maintenance, during drills and in an emergency.204 Launching and recovery appliances shall be so designedand constructed that only a minimum amount of routine main-tenance is necessary. All parts requiring regular maintenanceby the platform crew shall be readily accessible and easilymaintained.205 Launching and recovery appliances and their attach-ments shall be of sufficient strength to withstand a static proofload in test of not less than 2.2 times the maximum workingload, where the maximum working load shall be taken as theexpected load from fully equipped lifeboat plus the expectedload from the number of occupants associated with the loadconditions, which are specified in 301 and 801 for primarymeans of launching and recovery appliances, respectively.Secondary means of launching is not meant for emergencyevacuation of personnel and is therefore exempt from fulfil-ment of this requirement.206 Launching and recovery appliances shall remain effec-tive in a marine atmosphere, under temperature variations andunder conditions of icing.207 The launching appliances shall be arranged so as to pre-clude accidental release of the lifeboat in its unattended stowedposition. If the means provided to secure the lifeboat cannot bereleased from inside the lifeboat, these means shall be soarranged as to preclude boarding of the lifeboat without firstreleasing them.

A 300 Primary means of launching301 The primary means of launching shall not depend on anymeans other than gravity or stored mechanical power, which isindependent of the host facility’s power supplies, to launch thelifeboat in either of the following two loading conditions:

— fully loaded lifeboat (full complement of occupants)— empty lifeboat (crew of three persons).

302 On floating host facilities, the launching appliances shallbe so arranged that the lifeboat can be launched when the hostfloater in damaged condition is subject to a trim and a list andwhen the host floater in intact condition is subject to accelera-tions and motions in the 100-year sea conditions. Trim and listin the damaged condition for the host floater depend on the sta-bility of the host facility and the possible loss of buoyancy inone or more supporting buoyant compartments. The trim andthe list for the damaged host facility shall be set to ± 17° unless

other host facility specific values are known.

A 400 Release mechanism for the primary means of launching401 The operation of the launch release mechanism shall bechecked according to Sec.6 A802. 402 The load-bearing capacity of the release mechanismincluding its connection to the lifeboat structure shall beaccording to Sec.6 A804. 403 The design of the release mechanism for the primarymeans of launching shall be in accordance with ISO 12100-1and ISO 12100-2.404 The primary means of launching shall facilitate means tokeep the lifeboat secured in the stowed position when it is notused and during training and maintenance. The securingarrangement shall be designed to avoid accidental release, cf.ISO 12100-1, ISO 12100-2 and ISO 14119.405 It shall be feasible to test the release function withoutexposing the crew that is in charge of performing the test torisk. Execution of a realistic functional test that physically con-firms that the release mechanism is functional must be possi-ble.

A 500 Means of launch testing by simulation501 The primary means of launching shall have means oflaunch testing by simulation. The means of launch testing bysimulation shall include facilities to perform a simulatedrelease of a fully loaded lifeboat. It shall be feasible to test therelease mechanism (simulation) without exposing the crewthat is in charge of performing the test to risk. A realistic func-tional test which physically confirms that the release mecha-nism is functional shall be described.

A 600 Secondary means of launching601 Each launching appliance shall be provided with a sec-ondary means of launching for replacement and maintenancepurposes. The secondary means of launching shall be equippedwith at least one single off-load capability to release the life-boat. The system shall facilitate controlled lowering of the life-boat to sea, instead of free fall launching, when the lifeboat isto be replaced or brought ashore for maintenance. 602 The secondary means of launching shall be based ongravity or power lowering using the host facility’s power sup-plies, to launch the lifeboat in the following loading condition:

— empty lifeboat (crew of three persons).

603 The secondary means of launching shall facilitate meansto keep the lifeboat secured in the stowed position when it isnot used, and during training, testing of the release mechanismand maintenance. The securing arrangement shall be designedto avoid accidental release, ref. ISO 12100-1, ISO 12100-2 andISO 14119. 604 The secondary means of launching may be combinedwith the means of retrieval.605 The secondary means of launching cannot be used forlaunch of the lifeboat for emergency evacuation without reser-vation, because such use would imply that the lifeboat is beingused as a davit-launched lifeboat. This is a use of the lifeboatwhich is beyond the scope of this standard, cf. Sec.1 A304. To allow for use of the secondary means of launching forlaunch of the lifeboat for emergency evacuation would requirethat the lifeboat meets the requirements of an adequate stand-

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ard for design of davit-launched lifeboats in addition to meet-ing the requirements of this standard. Owing to unresolved safety issues associated with emergencyevacuation by means of davit-launched lifeboats, use of thesecondary means of launching for launch of the lifeboat foremergency evacuation is in general not recommended.

A 700 Release mechanism for the secondary means of launching701 The release mechanism of the secondary means oflaunching shall be designed in accordance with ISO 12100-1,ISO 12100-2 and ISO 14119.702 It shall be feasible to test the release mechanism whenthe lifeboat is secured in its stowed position, without exposingthe crew to risk. Execution of a realistic functional test whichphysically confirms that the release mechanism is functionalmust be possible.

A 800 Means of retrieval801 Each launching appliance shall be equipped with meansof retrieval. The means of retrieval shall be capable to operateafter test launches and maintenance sessions of the lifeboatsashore. The following loading condition shall be considered:

— empty lifeboat (crew of three persons).

802 The means of retrieval may be combined with the sec-ondary means of launching.

A 900 Fire protection systems901 The external equipment including the engine exhaustsystem shall not act as ignition sources. 902 Fire protection systems shall not prevent easy access tothe lifeboat.

A 1000 Water spray system1001 The lifeboat shall be fitted with a water spray system.1002 Water for the system shall be drawn from the sea by aself-priming motor pump. It shall be possible to turn on andturn off the flow of water over the exterior of the lifeboat.1003 The seawater intake shall be so arranged as to preventthe intake of flammable liquids from the sea surface.1004 The system shall be arranged for flushing with freshwater and allowing complete drainage.

A 1100 Engine1101 The engine shall be designed in such a manner that itwill not become damaged if the lifeboat is turned upside downand causes the propeller to be exposed to open air. The engineshall also be designed in such a manner that it will never drawair from the cabin, in particular not in the situation that theengine is turned upside down. 1102 The engine shall be protected against overspeed whenoperated in the water entry phase due to a high probability ofair ventilation. The engine shall be capable of operating with-out damage in 5 minutes without water cooling and with thepropulsion system exposed to air. 1103 Sufficient additional oxygen, e.g. supplied by air bot-tles, shall be provided for the lifeboat engine to be operated in10 minutes without external air access. 1104 All engines shall be fitted with a speed governor soadjusted that the engine speed cannot continuously exceed therated speed by more than 10%. 1105 A separate overspeed device is required. The over-speed protective device may be substituted by an extra speedgovernor that is completely independent of the first governorand acting without delay.

1106 Activation of the overspeed device shall ensure limita-tion of rpm. The overspeed device shall not be dependent onexternal energy sources. 1107 The overspeed device shall be adjusted to ensure thatthe engine speed cannot exceed the maximum permissiblespeed as determined by the design, but not beyond 120% of therated speed except for diesel engines driving generators forwhich 115% of the rated speed applies.1108 For engines operating in areas defined as gas hazardouszones, an additional device that automatically shuts off the airinlet in case of overspeed shall be installed. This shuttingdevice shall be activated at the same speed level as that usedfor the overspeed device required in 1105. For engines withturbochargers that can suffer overspeed due to a sudden inter-ruption of the air intake, the shutting device should be installedbetween the turbocharger and the engine.1109 The engine shall be equipped with a spark arrestor.1110 Stored energy for power starting of the engine may besupplied by batteries. Each battery shall have its own charger.An alarm transmitted to a manned control station should beinstalled for use in case charging fails.1111 It shall be possible to hook up the engine to a coolingsystem while the lifeboat is in its stowed position in the life-boat station, thereby to allow for racing the engine (not justidling) as part of periodic maintenance.1112 It shall be possible to start the engine in an ambienttemperature of –15°C within 2 minutes of commencing thestart procedure.1113 The engine and its accessories shall be designed tolimit electromagnetic emissions. 1114 The exhaust pipe shall be so arranged as to preventwater from entering the engine in normal operation.1115 The engine, the transmission and the engine accesso-ries shall be enclosed in a fire retardant casing or other suitablearrangements providing similar protection.1116 Air cooled engines shall have a duct system to take incooling air from, and exhaust it to, the outside of the lifeboat.Manually operated dampers shall be provided to enable cool-ing air to be taken in from, and exhausted to, the interior of thelifeboat.

A 1200 Fuel tank1201 The fuel tank shall have a capacity which is sufficientto provide enough fuel to run the lifeboat at maximum speedfor half an hour and to run it at 60% of maximum speed for 23hours and a half.1202 The fuel tank shall always be full when the lifeboat isin its stowed position in the lifeboat station. 1203 The fuel tank shall be equipped with shutoff valves.The fuel tank shall be so arranged that it allows for samplingof the fuel in accordance with NORSOK S-002.

A 1300 Air intake1301 To achieve an adequate air circulation in the lifeboat,the air intake for the engine and the air intake for the cabin airshall be located as far as possible from one another.

A 1400 Electrical equipment1401 Electrical equipment which is located externally shallbe provided with an enclosure which meets a weatherproof rat-ing of at least IP67 and which shall be EX certified for Zone 1.Electrical equipment which is located inside the lifeboat shallbe provided with an enclosure which meets a weatherproof rat-ing of at least IP56. Nominal input voltage to electrical equip-ment shall not be greater than 230V.

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Guidance note:Details about weatherproof rating in terms of ingress protection(IP) rating are given in IEC60529. Details about explosive pro-tection (EX) certification and hazardous zones are given inIEC60079.


A 1500 Manoeuvring positions and instrument panel1501 Two positions for manoeuvring the lifeboat shall beprovided. All instruments and warning lamps shall be easilyobservable from both positions. It shall be possible to operatethe VHF radio from both positions.1502 The two positions for manoeuvring the lifeboat shall belocated side by side, one on the starboard side and one on theport side, with a common instrument panel between them.When the seats of the manoeuvring positions have one positionfor the free fall and another for the sailing phase, it will be ben-eficial that the instrument panel follows the seats when they arebrought from the one position to the other. A commonmanoeuvring handspike for engine and transmission, manoeu-vrable from both manoeuvring positions and located betweenthem, should be aimed at. 1503 The order in which the instrumentation is arranged onthe instrument panel should reflect size and design in such amanner that easy observation and handling of the instrumenta-tion are facilitated.1504 Table A1 gives a list of instrumentation and manoeu-vring tools which as a minimum should be included at the twomanoeuvring positions and in the instrument panel betweenthe two manoeuvring positions.

1505 Adequate visibility from the manoeuvring positionsshall be provided for.

Guidance note:It is recommended to provide for a windshield height of at least40 cm. It is also recommended to avoid blind sectors as far as

possible, thereby to allow for 360° visibility from each manoeu-vring position.


A 1600 Maintenance of equipment1601 A maintenance plan shall be worked out for the equip-ment installed in the lifeboat to ensure adequate periodic main-tenance. The maintenance plan shall address the issue of easyaccess for normal service of the engine such as change of oiland oil filter. The maintenance plan shall also address the issueof easy access to engine fuel tank for cleaning and drainage.The plan shall as a minimum contain the same elements as theprocedure for maintenance given in IMO MSC1206.1602 Periodic maintenance of the fuel tank shall be carriedout, including sampling of the fuel to verify adequate fuel qual-ity and including replenishment of fuel.1603 Periodic maintenance of any freshwater tanks shall becarried out, including sampling of the water to verify adequatewater quality and including replenishment of water.1604 Periodic maintenance of the means of launchingincluding the release mechanism shall be carried out. Thismaintenance shall include inspection for rust and corrosion aswell as execution of associated repair.

A 1700 Miscellaneous1701 For layout at the launching and recovery appliances,for outfitting of the lifeboat station, for access for boarding,and for visibility and lighting in the lifeboat station, therequirements set forth in NORSOK S-001 shall be fulfilled.Noise in the lifeboat station shall meet requirements to noiseset forth in NORSOK S-002. 1702 Emergency power should be provided for charging oflifeboat batteries during stowage in the lifeboat station on thehost facility. The disconnection point should be in the vicinityof the lifeboat and disconnection shall be automatic whendropping or lowering the lifeboat.1703 Cabinet housing should be arranged for winches andconsoles.1704 A heater should be provided for electric motors forwinches in the lifeboat station. An optimal placement of theheater should be considered with a view to conditions prevail-ing during icing. 1705 At each seat a pocket shall be provided within reacha-ble distance with space for personal belongings such as glassesand sick bags.1706 A simple nitrogen-filled GPS shall be installed to pro-vide the pilot with position and direction of the lifeboat imme-diately after the lifeboat has been launched. 1707 The windscreen on the wheelhouse should be suppliedwith a windscreen wiper or equivalent equipment that can con-tribute to improve the visibility for the pilot. 1708 The lifeboat shall be fitted with sufficient watertightlockers or compartments to provide for storage of small itemsof equipment, water and food supplies. 1709 The antenna for the VHF radio shall be provided witharrangements for siting and securing the antenna effectively inits operating position. 1710 A manually controlled exterior light shall be fitted. Thelight shall be white and be capable of operating continuouslyfor at least 12 hours with a luminous intensity of not less than4.3 candela in all directions of the upper hemisphere. How-ever, if the light is a flashing light, it shall flash at a rate of notless than 50 flashes and not more than 70 flashes per minute forthe 12 hour operating period with an equivalent effective lumi-nous intensity.1711 The lifeboat shall, where applicable, be provided with

Table A1 Minimum recommended instrumentation and manoeuvring tools and their placementStarboard side

Centre Port side

Manoeuvring position 1

Over-/under-pressure gauge for cabin Manoeuvring

position 2Engine revolution counterEngine oil pressure gauge

Steering wheel

Engine temperature gauge Steering wheel

Dynamo for recharge lightHandling of air bottlesSwitch panel for light etc.

By-pass valves for two independent release sys-tems

Engine Start/Stop Hydraulic pumps for two independent release systems

Common VHF RadioCommon manoeuvring handspike for engine and transmissionController for activation of release mechanismRudder indicatorGPS / digital or magnetic compassValve for activation and shut-off of water spray systemHandle for activation of heave-out mechanism for towlineFuel tank gauge

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electrical short-circuit protection to prevent damage or injury.1712 The lifeboat shall be equipped with adequate propellerprotection. The purpose of the protection is to attend to thesafety of persons in the water and to the possibility of damageto the propulsion system by floating debris.1713 The lifeboat shall be equipped with devices to assist indetecting the lifeboat at sea. Such devices include, but are notlimited to:

— rocket parachute flares— hand flares

— buoyant smoke signals— waterproof electric torches— daylight signalling mirrors— whistle or equivalent sound signal.

1714 Equipment and appliances, which are installed in thelifeboat and which are subject to deterioration with age, shallbe marked with a means for determining their age or the dateby which they must be replaced, e.g. based on certificates forthe equipment.

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SECTION 12QUALIFICATION OF NEW LIFEBOAT CONCEPTS

A. General

A 100 General101 This section provides requirements to qualification offree fall lifeboats and their lifeboat stations and release sys-tems. Requirements to the qualification procedure are speci-fied together with guidance and recommendations for systemanalysis methods which are useful tools in the execution of aqualification.102 A qualification shall be carried out in the design phasefor all novel lifeboat concepts, for all lifeboat concepts thatcontain one or more novel components, and for all skid andrelease arrangements with one or more novel components.

Guidance note:Wherever components of a concept are new, the degree of imma-turity of those components can be identified through the Tech-nology Classification procedure given in DNV-RP-A203.Appropriate risk identification procedures such as HAZID andFMECA can then be applied to assess the risks associated withthe new components.


103 A qualification is not required for existing lifeboat con-cepts and existing skid and release arrangements concepts.

A 200 System analysis201 The overall approach of a system analysis is based on thefollowing elements

— definition of system— definition of risk acceptance criteria— definition of safety functions— allocation of reliability requirements to the safety func-

tions.

The system analysis itself then deals with the assessment of thereliabilities of the safety functions and the verification that thereliability requirements are met. The methods which are usedfor the system analysis also allow for assessment of severity ofpossible consequences and assessment of possible remedialactions and they allow for identification of areas of concern.

Guidance note:The system will typically consist of the lifeboat, the lifeboat sta-tion and the release system.The overall safety function for a free fall lifeboat can be definedas the successful evacuation from the time the occupants are intheir seats in the lifeboat prior to the launch and till the time theyare rescued from the lifeboat after the completion of the launch.This safety function may then be broken down into a number ofsubordinate safety functions, see 302.


202 System analysis forms an important tool for qualifica-tion of new lifeboat concepts. Risk identification with identifi-cation of hazards, failures and unavailability forms part of sucha system analysis. 203 The purpose of a risk identification analysis is to elimi-nate possible design weaknesses and possible operationalweaknesses as early as possible in the design phase.

A 300 Methodology301 The most commonly used analysis methods for identifi-cation of hazards, failures and unavailability are presented inSubsection C together with guidance for selection of analysismethods under various circumstances. Details of these meth-ods are given in IEC61508-1.

Guidance note:The analysis methods given in Subsection C first of all serve asanalysis tools which are useful in order to meet the particularrequirement for execution of analysis for identification of haz-ards, failures and unavailability when a free fall lifeboat and itslifeboat station and release system are subject to design. How-ever, these methods are generally applicable to this kind of anal-ysis for the entire lifeboat evacuation system consisting ofpossibly more than one lifeboat and covering the entire evacua-tion of personnel all the way from the host structure to a com-pleted rescue to a safe area.


302 For execution of analyses for hazard identification, fail-ure identification and unavailability identification it is usefulto systematically break down the free fall lifeboat evacuationsystem into a hierarchy of components or safety functions thatcan pose hazards, cause failure or make the system unavaila-ble. Such a systematical breakdown forms the basis for carry-ing out a technology classification. An example of such asystematic breakdown of a generic free fall lifeboat system isgiven in Figure 1. The methodology is further described inDNV-RP-A203.

Guidance note:An example of a component which can pose hazards or make asystem unavailable is the buoyancy tanks of a lifeboat. A buoy-ancy tank is a secondary structure which may act as a longitudi-nal bearing element (girder) and which may thereby alter orobstruct the intended mode of operation of the main girder sys-tem of the lifeboat.


A 400 Design processes401 The process – for example in terms of a project – thatleads to the design of a lifeboat is denoted as a design process.Four types of design processes are associated with the designof a free fall lifeboat, viz.

— design— design modifications— specification modifications— maintenance projects.

The first three types of design processes are aimed at achievingdesign integrity, whereas the fourth is aimed at maintainingtechnical integrity. For a free fall lifeboat, maintenanceprojects serve to re-establish required integrity or to preventfurther degradation or both. Furthermore, maintenance mayinclude tests required to verify the function of the system. Itshall be ensured that repeated testing does not impose a risk forfatigue of the lifeboat and its auxiliaries.

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Figure 1 Free Fall Lifeboat Evacuation System

Figure 2 Project Governance Process

402 The execution of design projects should follow a ProjectGovernance Process (PGP) as shown in Figure 2. The ProjectGovernance Process forms a useful tool for representation of adesign process when analyses for hazard identification, failureidentification and unavailability identification are to be carriedout. The Project Governance Process consists of 6 main assetintegrity activities and 5 decision gates. The asset integrityactivities should continuously be aligned with a risk registercontaining analysis results from the risk management process.The risk register will typically provide information regardinganomalies with corresponding reduction measures and infor-mation about the responsible person or unit. Generally the early process steps incorporate few and ratherinaccurate analyses, typically qualitative analyses. As theproject evolves into more mature phases, more informationbecome available and the need for more comprehensive analysiswork become evident. At the same time, the results from theanalyses become more accurate as more detailed input informa-tion is available. This project evolution is illustrated in Figure 3.

Figure 3 Relation between analysis volume and accuracy during asset integrity activities

Guidance note:When the design project is a project for design of a free fall life-boat, then the focus in the project governance process is on themain activities around decision gate DG2 in Figure 2, i.e. conceptselection and preparation for execution. There is relatively little

Free Fall Lifeboat Evacuation System

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DG1 DG2 DG3 DG4

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value associated with putting efforts on the initial activitiesregarding business opportunity and feasibility study, since theneed for a life-saving appliance is there and the decision to builda lifeboat has already been made (at decision gate DG1).For design modification projects whose value is less than somelimiting value, some of the steps in the project governance proc-ess in 402 may be combined and the contents between every twodecision gates can then be simplified. Other than this, the con-tents and asset integrity issues should be as given in 402 fordesign projects.Specification modifications do not change the functionality ofthe lifeboat and the lifeboat system, but may be introduced toimprove performance. Specification modifications are thereforeusually not subject to organization according to project govern-ance processes.Maintenance projects are projects during which the basic design,the process layout and the capacities remain unchanged. Mainte-nance projects are driven by ageing of components and systemsand by old or obsolete systems for which spare parts are unavail-able. In principle, a maintenance project implies a replacementmeasure for measure, but in most cases new technology can beintroduced, such that some degree of upgrade can be expected.The maintenance work is usually denoted as a project due to itssize and the number of personnel and the equipment involved.


B. Qualification ProcedureB 100 General101 For qualification of a free fall lifeboat concept asrequired in A102, a risk-based procedure shall be followedwhich is based on recognized methods for risk identificationand system analysis and which shall contain the following ele-ments in the order listed:

— establishing a design basis for lifeboat (functional specifi-cation)

— breaking down the lifeboat system into components— technology classification of components— execution of an FMECA— proposing system modification, if applicable and necessary— selection of qualification methods— verification that all uncertainties are covered— execution of HAZID/HAZOP to verify operability of

design— optional execution of a QRA to assess risks.

102 For details of the qualification procedure, reference ismade to DNV-RP-A203.103 Details of methods used in the execution of the qualifi-cation procedure are given in Subsection C.

C. Methods for System AnalysisC 100 General101 This subsection presents methods which can be used forsystem analysis of lifeboats and their lifeboat stations andrelease systems.

Guidance note:The methods presented are applicable to system analysis at dif-ferent levels, ranging from the overall system associated with theprime safety function of the lifeboat, viz. successful evacuationfrom boarding of lifeboat to rescue of passengers, to subsystemssuch as utility systems and survival systems, including propul-sion, battery, ventilation etc.


C 200 Hazard identification analysis (HAZID)201 Hazard identification analysis (HAZID) is a generalterm used for any hazard identification analysis. A HAZID hasin general fewer rules associated with it than the more specificHAZOP (C300) and FMECA (C400) techniques. Yet, it is astructured review for identification of significant risks associ-ated with a particular design or operation. HAZIDs are widelyused to establish an overall risk picture and are applicable forboth new and existing lifeboat concepts for which access toinformation is limited. New lifeboat concepts can benefit fromthe methodology at a conceptual stage. Existing lifeboat con-cepts can benefit from the methodology wherever some levelof prioritization is needed. A HAZID is frequently used priorto more detailed analysis. A HAZID carried out at an earlystage in a design project may assist in selection of the mostadvantageous design.202 The first step of a HAZID aims at listing all potentialhazards. This is done by considering characteristics such asmaterials processed, operating environment, inventories andlifeboat layout. When a list of all potential hazards has beenestablished, each hazard is assessed in order to determinewhether it is relevant or not. This implies a first step in a qual-itative estimation of the likelihood of occurrence of each haz-ard.

Guidance note:An approach often adopted in the execution of a HAZID is firstto identify all possible undesirable consequences and second, foreach of them, to identify hazards which, when realized, wouldcause that consequence.


203 Following the identification and description of the haz-ards, an identification of consequences and probabilities is per-formed based on best judgment and historical records.Supported by the severity of the individual hazards as based onthe outcome from this identification, a qualitative risk rankingis produced, usually presented in the form of a risk matrix,which assigns risk levels and ranks them from highest to low-est. 204 If existing safeguarding actions are identified during theHAZID sessions, these safeguarding actions are to berecorded. If existing safeguarding actions are found to be inad-equate, recommendations for improvements and further workneeded shall be formulated.205 Personnel with significant experience from structures orsystems similar to the one which is subject to a HAZID shallparticipate in the HAZID.206 For further details about HAZID, reference is made toDNV-RP-H101.

C 300 Hazard and operability study (HAZOP)301 HAZOP is a systematic approach to identify potentialhazards and operability deviations. In addition to identify haz-ards, this methodology can be used for analysis of operatinginstructions and analysis of procedures for identification ofsources of human error. It can also be used to review a processfor a particular system.302 The HAZOP is performed in group sessions where per-sonnel with subject matter proficiency are contributing, guidedby a HAZOP expert. During a session, each potential hazard isassessed using specific guidewords to simulate abnormal situ-ations, ensuring a consistent approach. The consequences ofthe hazard and existing safeguards are also evaluated, and theneed for follow up is documented for critical hazards. 303 HAZOPs can be used at practically any stage during adesign process. However, HAZOPs require more detailedinformation than for example a HAZID and are therefore moreuseful the later in the design phase they are applied. For a newdesign, the most complete result is therefore achieved when

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the HAZOP is carried out as late as possible. Within existingfacilities it can be used at any time.304 Successful HAZOPs are very dependent on the availa-bility of a list of good guide words.305 For further details about HAZOP, reference is made toDNV-OS-H101, IEC61882 and ISO17776.

C 400 Failure mode, effects and criticality analysis (FMEA/FMECA)401 A failure mode and effects analysis (FMEA) is a struc-tured review technique with the purpose of identifying andanalysing all significant failure modes and effects associatedwith a particular system under consideration. A failure mode,effects and criticality analysis (FMECA) is an FMEA wherealso criticality is assessed.402 FMEA and FMECA are qualitative analytical tech-niques used to identify failure modes and associated effectswhich – without adequate precautions – will give rise to a haz-ardous event. 403 The input to an FMEA or an FMECA is a detailed sys-tem description together with operational procedures. Thedetailed system description typically consists of specifications,general arrangement drawings etc.404 The objective of an FMECA is to prevent failures fromoccurring in the future, so an FMECA should preferably becarried out in the design phase. FMEA and FMECA are recom-mended for analysis of any safety system. 405 The analysis includes examination of each individualcomponent of a system in question for determination of possi-

ble failure modes and identification of their effects on the sys-tem. The analysis is based on a worksheet that systematicallylists all components in the system, and for each componentincludes:

— component name— function of component— possible failure modes— causes of failure— how failures are detected— effects of failure on primary system function— effects of failure on other components— necessary preventative/repair actions.

Guidance note:FMEA and FMECA work sheets may be used directly as part ofa project risk register.


406 It is an important part of the analysis to represent the sys-tem in terms of a hierarchy of its subsystems and components.The quality of an FMECA is dependent on a good startingpoint in terms of a list of components which is as complete aspossible.407 The criticality analysis of an FMECA is a procedure thatrates the failure modes according to their frequency or proba-bility of occurrence and according to their consequences. Theassigned ratings can be used to rank the components withrespect to their criticality for the safety of the system. Anexample of a worksheet is given in Table C1.

408 As an FMEA or an FMECA can be conducted at variouslevels, it is important to decide before commencing what levelwill be adopted as otherwise some areas may be examined ingreat detail while others will be examined at the system levelonly without examination of the individual components. Ifconducted at a very detailed level, the analysis can be time-consuming and tedious, but will allow for great understandingof the system. 409 The FMECA is primarily a risk management tool. It is astronghold of the failure mode and effect analysis that, if car-ried out correctly, it identifies safety-critical componentswhere a single failure would be critical for the system. Itshould be noted that the outcome of an FMECA may dependon the experience of the analyst and that it cannot be applied tocover multiple failures.

Guidance note:It is a weakness of the FMECA that it cannot easily be applied tocover multiple failures. For the success of any FMECA, it isimportant that qualified experts are involved in the analysis ses-sions. The FMECA is then a very efficient technique for review-ing a design or a modification of a design.


410 For details about FMEA and FMECA, reference is madeto MIL-STD-1629A and IEC60812.

C 500 Fault tree analysis501 A fault tree is a logical representation of the many eventsand component failures that may combine to cause one criticalevent such as a system failure. It uses “logic gates” (mainly

AND and OR gates) to show how “basic events” may combineto cause a critical “top event”.502 A fault tree is a useful tool to represent complex designsconsisting of several subsystems where a sequence of eventswill lead to a hazard.503 A fault tree analysis uses a top-down approach to breakdown a critical event into contributing components, providedthat these components can be identified as discrete, specific anddefinable. The critical event is the top event of the fault tree.504 A fault tree analysis has several potential uses for safetysystems:

— In a frequency analysis, it is commonly used to quantifythe probability of the top event occurring, based on esti-mates of the failure rates of each component. The topevent may be an individual failure case, or a branch prob-ability in an event tree.

— In a risk presentation, it may be used to show how the var-ious risk contributors combine to produce the overall risk.

— In a hazard identification, it may be used qualitatively to iden-tify combinations of basic events that are sufficient to causethe top event. Such combinations are known as “cut sets”.

505 Construction of a fault tree usually starts with the topevent, and works down towards the basic events. For eachevent, it considers what conditions are necessary to producethe event, and represents these as events at the next level down.If any one of several events may cause the higher event, theyare joined with an OR gate. If two or more events must occurin combination, they are joined with an AND gate.

Table C1 Example of FMECA worksheetActivity No.

Equipment/ component name/ operation

Function Id. No.

Fail-ure mode

Failure effect – local

Failure effect – end effect

Failure detection

Alternative provisions/ redundancy

Frequency rating

Severity rating

Risk = fre-quency× severity

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Guidance note:Various standards for symbols are used − typical ones are shownin Figure 4. An example fault tree is shown in Figure 5.


506 When quantification of the fault tree is the objective,downward development should stop once all branches havebeen reduced to events that can be quantified in terms of prob-abilities or frequencies of occurrence.

Figure 4 Fault Tree Symbols

507 Some types of events, for example a fire or power fail-ure, may affect many components in the system at once. Theseare known as “common-cause failures”, and may be repre-sented by having the same basic event occurring at each appro-priate place in the fault tree.508 Both frequencies and probabilities can be combined in afault tree, providing the rules in Table B1 are followed.

509 Cut sets are combinations of events that are sufficient tocause the top event. Minimal cut sets contain the minimum setsof events necessary to cause the top event, after eliminatingany events that occur more than once in the fault tree. For sim-ple fault trees with each basic event only occurring once, the

minimal cut sets can be identified by inspection. For morecomplex trees, formal methods such as Boolean analysis arerequired. More commonly, computer programs are used toidentify minimal cut sets.510 The minimal cut sets can be used in hazard identificationto describe combinations of events necessary to cause the topevent.511 The minimal cut sets can also be used to rank and screenhazards according to the number of events that must occursimultaneously. In principle, single event cut sets are of con-cern because only one failure can lead to the top event. In real-ity, larger cut sets may have a higher frequency of occurrence.Nevertheless, the method can be useful for hazard screening,and for suggesting where additional safeguards may beneeded.

Guidance note:A minimum cut set is a set of primary events or underdevelopedfaults, which results in the top event, but which in itself does notcontain another cut set.


512 Simple fault trees may be analysed using a gate-by-gateapproach to determine the top event probability, provided thatall events are independent and there are no common-cause fail-ures. This gate-by-gate approach is useful for quantitative riskanalysis, because it quantifies all intermediate events in thefault tree and provides a good insight into the main contribu-tors to the top event and the effectiveness of safeguards repre-sented in the tree. However, because it cannot representrepeated events or dependencies correctly, it is not usuallyused for formal reliability analysis. Reliability analysis ofmore complex fault trees requires minimal cut set analysis toremove repeated events.513 Preparation and execution of a fault tree analysis isadvantageous in the sense that the analysis forces the lifeboatdesigner to systematically examine the safety system of hislifeboat or lifeboat system. When probabilities can be assignedto events, the fault tree methodology can be applied to assessthe overall reliability of the safety system. It can also be usedto determine which events and which parts of the safety systemare most critical.

Guidance note:It is often hard to assess whether a fault tree analysis has beencarried out properly. Fault tree analyses may be complicated,time-consuming and difficult to follow for large systems, and itmay be easy to overlook failure modes and common cause fail-ures. It should be noted that the diagrammatic format may dis-courage analysts from stating explicitly the assumptions andconditional probabilities for each gate. This can be overcome bycareful back-up text documentation. It may also be a limitationthat all events are assumed to be independent. Fault tree analysesmay lose their clarity when applied to systems that do not fall intosimple failed or working states such as human error and adverseweather.


514 For details about fault tree analysis, reference is made toIEC61025.

C 600 Quantitative risk analysis (QRA)601 QRA is a method for addressing and documenting risksin a quantitative manner. QRA is a method of making system-atic analysis of the risks from hazardous activities by a systemapproach and forming a rational evaluation of the significanceof the risks, thereby to provide input to a decision-makingprocess.

Table B1 Rules for Combining Frequencies and ProbabilitiesGate Inputs OutputsOR Probability + Probability ProbabilityAND Frequency + Frequency Frequency

Frequency + Probability Not permittedProbability × Probability ProbabilityFrequency × Frequency Not permittedFrequency × Probability Frequency

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Figure 5 Example Fault Tree

602 The main characteristic elements of a QRA are:

— a system approach, the system in the case of a lifeboat con-sisting of the lifeboat, the lifeboat station, the release sys-tem and the occupants

— a hazard identification by one of several hazard identifica-tion methods such as HAZID, HAZOP and FMECA

— an assessment of the probability of occurrence associatedwith each hazard

— different consequence categories, in the case of a lifeboatmainly restricted to health (injury) and life (fatality)

— a calculation of risk as probability times consequence— identification of risk reducing measures, which are associ-

ated with costs and which need to be prioritized— an integration of the above characteristic elements into a

risk model, where the objective is to recommend the mostcost effective risk reducing measure. A cost-benefit anal-ysis forms part of this.

603 The QRA approach is normally used for risk evaluationsrather than for hazard identification only. A preliminary QRAcan be useful also at the identification stage provided that ade-quate input data are available.604 Within the field of maritime code and rule development,the QRA technique is known as Formal Safety Assessment(FSA).605 For details of QRA, reference is made to IMO MSC/Circ.1023−MEPC/Circ.392.

C 700 Reliability, availability and maintainability anal-ysis (RAM)701 A reliability, availability and maintainability analysis

(RAM) is a technique used to predict system availability andidentify ways to improve system availability by consideringboth equipment failures and maintenance factors. 702 The RAM technique refers to three aspects of systemperformance:

— reliability, in this context expressed as the time betweenequipment failures under given operating conditions

— maintainability, in this context expressed as the timeneeded to return failed or shutdown equipment back tonormal service. Working conditions, organization ofwork, procedures and resources are influencing factors.

— availability, in this context expressed as the fraction oftime the equipment is able to perform its intended functionunder given operating conditions. Availability is a func-tion of reliability and maintainability.

703 In general, the time to failure and the time to repair arestochastic variables with probability distributions, and so istherefore also the availability. The mean values of the time tofailure and the time to repair are used to define the averageavailability as

in which MTTF denotes the mean time to failure, and MTTRdenotes the mean time to repair, i.e. the average time to returna failed item to service.

Guidance note:The average availability can be increased by increasing the meantime to failure or by reducing the mean time to return a faileditem to service. However, improving reliability and maintainabil-ity can reduce the profitability of a project if the additional cost

MTTRMTTFMTTFA

+=

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associated with the improvements is higher than the increasedbenefit. Hence, a RAM analysis can be used to optimize a systembased on a cost-benefit approach.


704 The main elements of a RAM analysis consist of

— Analysis requirements. Identification of the overall pur-poses of the analysis and further definition of the decisivesystem characteristics to be analysed.

— System definition. Familiarization with the system designand the planned operation, maintenance and testingregime. This will include identification of system bounda-ries, system features, physical build-up of system, systemcapacities and limitations, and built-in redundancy.

— Functional breakdown of system. Breaking down the sys-tem into smaller entities for identification of potential con-tributors to loss in the intended function of the system.

— RAM modelling. Establishment of a RAM model, whichtakes into account operational aspects and reliability per-formance of system entities, and which may make use oftechniques such as FMECA and fault tree analysis.

— RAM assessment and recommendations. Assessment ofreliability, maintainability and availability and provisionof recommendations for how the defined system can beoptimized. Features important to the RAM characteristicsof the system shall be identified, including main contribu-tors to system unavailability. Assumptions made shouldbe discussed and recommendations should be givenregarding how the system performance can be improvedand optimized from a cost-benefit point of view.

— Technical reporting with presentation of analysis andresults. The results shall be traceable.

Figure 6 shows a flow chart for the RAM analysis.

D. Application of System Analysis to Free Fall Lifeboats

D 100 General101 This subsection presents a recommended approach toidentify areas of concern and their associated consequences.The approach is based on utilization of a breakdown as indi-cated in Figure 1 and on the methodologies given in subsectionC and in DNV-RP-A203.

D 200 Areas of concern201 The areas of concern shall be identified in a systematicmanner. HAZID may serve as a useful tool for this. HAZIDscan be applied both to technical systems and to operations in asystematic manner. Details are given in C200.202 Table D1 lists potential hazards identified by a HAZIDfor a skid-launched free fall lifeboat of contemporary design.Each hazard represents an area of concern, and associatedcauses, failure modes and failure consequences are listed in the

table. Table D1 represents an example, which may serve asguidance whenever areas of concern for a novel free fall life-boat design are to be identified. For such a novel design, theareas of concern are not necessarily limited to those listed inTable D1.203 Areas of concern identified by a HAZID and docu-mented on the format used in Table D1 shall be systematicallyfollowed up during the design and qualification of the lifeboat.The table shall be updated whenever additional areas of con-cern are identified throughout the execution of the designproject. The areas of concern can be ranked according to theirrisks based on a qualitative approach. An FMECA worksheetas exemplified in C400 can be used for this.

Figure 6 Flow chart for RAM analysis with loop for use in cost-benefitbased system optimization

Element 1Analysis Requirements

Element 2System Definition

Element 3Functional Break Down

Element 4RAM Modelling

Element 5RAM Assessment and

Recommendations

Element 6Technical Reporting

Optimisation based on Cost/ Benefit Evaluations

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Table D1 Areas of concernItem/ Function Failure mode Failure mechanism or

causeConsequences Comments

HullThe lifeboat shall resist all loads occurring during launch

Crack in hull Insufficient Quality Assur-ance (QA) during produc-tion process

Excess buoyancy should keep the boat afloat even if hull cracks

A QA program must be in force during the produc-tion of the lifeboat

The lifeboat shall resist all loads occurring during launch

Crack in hull Impairment and decompo-sition of gelcoat

Ingress of water to lami-nate leading to delamina-tion

Specification of gelcoat must be confirmed and fol-lowed up during produc-tion


Crack in bow Poorly designed bow geometry

Excess buoyancy should keep the boat afloat even if hull cracks

Production follow-up for the bow geometry is important


Collision damages when multiple lifeboats are posi-tioned close to each other

Interference with other free fall lifeboats during or after the launch

Loss of lifeboat or/and fatalities

A coordination control system for the launches of the individual boats may have to be applied


Insufficient buoyancy Leaking of gas below water surface reduces effective water density and hence buoyancy of life-boat

The lifeboat becomes partly submerged or even sinks

It is assumed that the launch zone will be cleared for gas prior to the launch. Still it will be val-uable to know which level of gas content will cause reduced buoyancy to become a problem.


Insufficient water spray (fire resistance) system

Burning oil on sea surface Fire exposure of hull. High temperature inside life-boat.

It must be verified that the SOLAS requirements for fire prevention are suffi-cient.

Lifeboat accelerations shall be within acceptable limits tolerated by passen-gers

Excessive accelerations Skew landing due toerroneous understanding of environmental loads

Passenger fatalities

Lifeboat accelerations shall be within acceptable limits tolerated by passen-gers

Collapse of hull andexcessive accelerations

Ice on the water Passenger fatalities The likelihood for ice on the water during the launch should be investi-gated for the specified location

The lifeboat shall have positive headway after dropThe lifeboat shall be sea-worthy after drop

Air intake in submerged position below water sur-face

Excessive rolling leading to air intake in submerged position

Insufficient breathing air for passengers.Water in cabin.Collapse of hull.

Sufficient breathable air supply must be ensured for all operating conditions. Water in the cabin should be minimized which may dictate the position of the air intake. However, if a check valve or vent is used to prevent water from being sucked into the cabin, the hull must be checked for collapse.

Guide rails on lifeboatInteraction between guide rails on lifeboat and guide rails on davit

- Jam- Fall through- Derailment

Dynamic motions on skid or davit

- Inability to launch

- Lifeboat fallsthrough launch skid

Situations that can lead to jamming or fall through of the lifeboat should be investigated.

The stiffness of the davit as well as the tolerance between the lifeboat and the davit shall be checked.

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Ensure sufficient launch speed for lifeboat

Minimize/limit friction

- High friction- Excessive rotation

- Dirt or contamination on skid- Broken friction pads(on guide rail)- Angle duringdamaged condition

Too low speed as the boat leaves the launch skid may cause the lifeboat to rotate excessively and hit the water surface upside down

An assessment of the expected friction for the materials in use should be performed. Laboratory friction tests are straight-forward to carry out and will give reliable data.

The condition of the fric-tion pads should be included in the inspection routines.

Canopy and roof- Resist loads from drop and be seaworthy after fall

Collapse or deflection of canopy

Assumption that maxi-mum pressure is limited to some threshold for the div-ing depth.

Deflecting canopy hitting the heads of the occupants.

Sensitivity of wave steep-ness with respect to maxi-mum pressure should be performed.

- Resist loads from drop and wave impact loads after drop and be seaworthy after fall

Crack or damage Rough sea Damage to lifeboat machinery

An assessment of impact forces (e.g. slamming, fall-ing sideways from a crest) when sailing in rough sea until passengers are res-cued from the lifeboat

Windshield360° visibility Poor visibility Windshield covered by oil

or salt.Erroneous navigation A mechanism to remove

contamination (wash noz-zle, wiper, etc.) on the window would improve the conditions.

360° degree visibility Poor visibility Dew Erroneous navigation A mechanism to remove dew on the inside of the windshield should be pro-vided.

360° degree visibility Cracks in windshield pos-sibly leading to collapse

Hydrodynamic pressure Leakage Design of windshield as well as its attachment mechanism will be impor-tant to prevent any leakage into the cabin.

HatchHatch for boarding of passengers designed to keep water out

Leakage or unintentional opening

Open hatch Cabin filling up with water during launch

Design verification should include the hatch closure mechanism.

Air intake for engine- Supply air for engine- Ventilation for cabin

Sufficient breathable air supply must be ensured for all operating conditions. Must avoid that air for engine is supplied from cabin air.

Propulsion machineryProvide forward thrust Stalled engine Insufficient maintenance

requirements - Drifting towards installa-tion after drop- Inability to manoeuvre lifeboat

Maintenance requirements for machinery must be specified.

Provide forward thrust Engine stops - Lost lubrication.- Air in hp fuel system- Water in fuel

Loss of propulsion, sized pistons in cylinders

The specification requires the engine to run during rolling. This means that the engine must be able to run upside down. Appro-priate qualification test to be performed in this condi-tion.

Provide forward thrust Ventilating propeller Propeller above water leading to reduced resist-ance

Engine overload An RPM limitation or equivalent should be investigated to reduce the chance of engine over-speed. The supplier should advise if this is needed and provide if possible.

Table D1 Areas of concern (Continued)Item/ Function Failure mode Failure mechanism or


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Provide forward thrust Jammed or galled propel-ler shaft

Water lubricated bearing on shaft

Hard to test propeller dur-ing maintenance

How can the propeller shaft be tested safely (without galling) during maintenance when it is water lubricated? Alterna-tive designs could be con-sidered.

Provide forward thrust Insufficient power Design failure Cannot move forward in extreme wind

Reference is made to requirement of minimum mean forward speed as given in Sec.6.

Provide forward thrust Fuel leaking into passen-ger cabin, or water in the fuel

Erroneous design of fuel tank ventilation arrange-ment

Intoxication/fire Hard tanks require ventila-tion from outside the boat or from inside cabin while a soft tank may not require ventilation.

Rudder (heading mechanism)Heading control Hard to keep steady course Gear ratio between steer-

ing wheel and rudderToo many turns on steer-ing wheel back and forth to control heading (experi-enced during test)

Lesser turns on steering wheel are preferred by test personnel. A rudder indi-cator is preferred to tell when the wheel is in the mid position.The rudder deflection must be limited in order not to reduce positive heading.The physical arrangement of the pilot's position must be designed for steering in heavy sea.

Heading control Incorrect heading Anything that can result in incorrect heading before the pilot takes control.

Engagement of transmis-sion with incorrect head-ing

The requirement that the lifeboat shall keep a mini-mum distance from the installation after the launch may be hard to meet if the lifeboat is turned 180 degrees after the drop.

AutopilotKeep an automatic head-ing for the lifeboat

Inability to keep correct heading

Autopilot reaction time in heavy sea

Loosing control over the boat

If an autopilot system is selected for the lifeboats, the reaction time must be checked in heavy sea. Is a feasible system available? Maintenance will also be important for a potential autopilot system.

Instrumentation General note on instrumentation in general:As little as possible instrumentation for the pilot is recommended, as full focus is needed on manoeuvring the boat in heavy sea. A magnetic compass is of little use because of motions in heavy sea, so a navigation system based on GPS may be a better idea.A study must be carried out to determine which types of instrumentation are needed for: - an emergency situation (pilot)- maintenanceSeatsSeats shall be designed to protect occupants during drop

Incorrect design Missing requirements Fatal injuries Boarding time shall be less than 3 minutes

Seats shall be designed to protect occupants during drop

Pilot reaction time after drop

Pilot seat design Inability to gain control over the lifeboat in time

Seat design for pilot is regarded as important with respect to headway requirement.

Safety belts- Keep passengers in place

- Individual fastening is required

Incorrect design Improper/missing require-ments

Mortal injury CAR < 1 may lead to haz-ardous situations because of the lifeboat boat rota-tion during impact.



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Fire prevention systemPrevent ignition while life-boat is running through fire on sea surface

Note regarding fire pre-vention system:Active - systemPassive - fire retardant material

Retrieval arrangement (on lifeboat)Retrieve lifeboat back to platform

Overload of lifting arrangement

Jerk in wire because of dynamic effects (due to waves)

Loss of lifeboat Safety factor for the life-boat lifting arrangement must be decided and veri-fied

Retrieve lifeboat back to platform

Man overboard Climbing on top of life-boat while connecting lift-ing hook

Rescue operation Safety for personnel that will be performing drop testing must be examined when system and proce-dures are in place

Release mechanism (e.g. hook)- Release of hook initiates drop- Boat shall be kept safely in sk-id at full loads in a dynamics condition until time of release

Review the redundancy of the release mechanism.

- Release of hookinitiates drop

Malfunction of release mechanism

Change in design Failure to release lifeboat when intended

The changes to the design of the releasing hook must be evaluated to prevent unforeseen effects

Skid- Ensure sufficient launch speed for lifeboat- Minimize/limit friction

A sensitivity study for fric-tion should be performed (both numerical and fric-tion testing)

Interaction between guide rails on lifeboat and guide rails on davit

Overload of the skid caus-ing damages to skid and boat

Launching while the skid is tilting sideways

Plastic yield and breakage (critical at end of the skid right before boat is leaving the skid)

This is a load case for The skid design which nor-mally is overlooked. It will likely not prevent the launch. But the conse-quence of this load case must be considered both in design and during full scale testing.

Retrieval arrangement (on davit)Retrieve lifeboat back to platform

The retrieval arrangement is not necessarily required to be designed for lifting occupants

OccupantsAvoiding fatalities Loss of life Problems in entering the

lifeboat from the sea and to leave the lifeboat for res-cue in extreme sea states

Loss of lives The best practical solu-tions for retrieval of occu-pants from lifeboat or from sea and transferring occu-pants to helicopter or res-cue vessel should be identified and incorpo-rated



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Offshore Standard DNV-OS-E406, April 2010 App.A – Page 115

APPENDIX A INTERPRETATION OF PROBABILITY DISTRIBUTION AND CHARACTERISTIC VALUE FROM MODEL TESTS

A. GeneralA 100 General101 In this appendix the methodology for interpretation ofprobability distributions from repeated model tests is outlinedand an example of application of the methodology is givenbased on existing test data for a lifeboat model. The methodol-ogy is outlined in 200 and the example is given in 300.102 The methodology is equally applicable when similardata are available from other sources such as numerical simu-lations.

A 200 Methodology201 The basis for interpretation of the long-term probabilitydistribution of a considered quantity X in a launch, which iscarried out at an arbitrary point in time, consists of observa-tions of that quantity from model tests in irregular waves. 202 Tests are assumed to be carried out in a number of dif-ferent sea states. Each sea state can be characterized by param-eters such as the significant wave height and the peak period.For simplicity in the following, it is assumed that each sea stateis characterized by one parameter only, viz. the significantwave height HS. 203 For each considered HS, there is a set of n observationsof the quantity X, obtained from n model tests where the life-boat has been launched into a sea of irregular waves character-ized by this particular HS. When the n observations of X arearranged in increasing order, they form an empirical distribu-tion of X conditional on HS. To obtain a good grip on the dis-tribution of X conditional on HS, the number of tests n shouldbe at least 50.204 A parametric distribution function should be fitted to theempirical distribution of X conditional on HS. Which paramet-ric distribution function forms the best fit to the empirical dis-tribution depends on what kind of quantity X is, for examplepeak pressure (defined as the maximum pressure throughoutthe duration of a drop test). Weibull, Gumbel and lognormaldistributions are among the generic distribution types thatshould be tried out in the search for an adequate parametric dis-tribution function to fit to the empirical distribution. If a goodfit cannot be obtained to the entire empirical distribution, itshould be attempted to obtain a good fit to the upper tail of theempirical distribution. The fit of a parametric distributionfunction to match the observed empirical distribution impliesthat the distribution parameters of the parametric distributionfunction are determined.205 Tests with observations of the quantity X should be exe-cuted for a number of different HS values. The empirical dis-tribution of X conditional on HS shall be established for eachHS value and a parametric distribution function shall be fittedto the distribution or to its upper tail. The distribution parame-ters of the fitted distribution function can then be expressed asmathematical functions of the significant wave height HS. To

get a good grip on these mathematical functions, tests for asmany different HS values as possible should be carried out, stillmeeting the recommended minimum number of tests per HSvalue. It is not recommended to limit the number of differentHS values to less than three.206 Once a parametric distribution function has been fittedto the empirical distribution of X conditional on HS, FX|Hs(x),then the sought-after unconditional long-term distribution of Xcan be established by integration over all outcomes of the sig-nificant wave height HS according to the long-term distribu-tion of HS,

in which

is the probability density function for HS. Figure 1 shows an example of the probability density functionand the cumulative distribution function for HS. As an exam-ple, the 99% quantile of HS is also shown. This is the value ofthe significant wave height which is exceeded 1% of the time.In Figure 1, the exceedance probability of 1% can be identifiedas an area under the curve that represents the probability den-sity function.

Figure 1 Probability density function and cumulative distribution functionfor HS

∫∞

⋅⋅=0

| )()()( dhhfxFxFSS HHXX

dhhdF

hf S

S

HH

)()( =

FHs

fHs

HS,99%

HS

1%

HS

HS,99%

0

0.99

0

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Offshore Standard DNV-OS-E406, April 2010 Page 116 – App.A

Figure 2 shows a visualization of the conditional distributionsof X, conditional on HS, for various values of HS.

Figure 2 Probability density functions for X conditional on HS

Figure 3 shows the resulting unconditional long-term distribu-tion of X.

Figure 3 Unconditional long-term distribution of X

207 The integration to determine FX(x) can be carried outnumerically, or alternatively FX(x) can be established from theunderlying distributions by Monte Carlo simulation. The char-acteristic value of X can be found as the 99% quantile in theunconditional long-term distribution FX(x) of X. An exampleis given in Figure 3.

A 300 Example301 P is the peak pressure in a position on the canopy of afree fall drop-launched lifeboat model, which has been testedin the laboratory. Measurements of P are available from testsin irregular sea for two different significant wave heights andalso from tests in calm water, i.e. a total of three different HSvalues, viz. HS = 0.0 m, HS = 6.8 m and HS = 9.8 m. The resultsindicate that the short-term distribution of the peak pressureconditioned on the significant wave height is well representedby a Weibull distribution in the body and the upper tail. Let Xdenote the peak pressure on the canopy normalized by thelong-term mean value μP of the peak pressure, P. The short-

term distribution of X = P/μP can then be represented by

where the scale parameter a and shape parameter b are foundto be

302 These functional expressions for the parameters of theWeibull distribution have been obtained by interpretation ofresults from Weibull fits to the bodies and upper tails of thecumulative distribution functions of the peak pressure condi-tional on the significant wave height HS, see Figure 4.303 A particular Norwegian Sea location is consideredwhere the long-term distribution of the significant wave heightis well represented by a Weibull distribution

and where the scale and shape parameters are α = 2.66 m andβ = 1.407. For this location, as a by-product of the integrationin 206 and 207, the long-term mean value of the peak pressureon the canopy becomes μP = 5 730.06.304 The long term distribution of X, FX(x), can be estab-lished by integration of the short-term distribution of X over allrealizations of HS according to the long term distribution ofHS,

The result is shown in Figure 5. The 99% quantile is x99 = 2.00which gives a 99% quantile for the peak pressureP99 = 5 730 × 2.00 = 11 460.

A 400 Commentary401 The example is based on data from tests for only threedifferent values of the significant wave height HS. The data forHS = 0 m (calm water) are rather limited, much less than thepreferred minimum of 50 data points, and the fitting of astraight line on Weibull scale to the upper tail of the condi-tional distribution of X is somewhat ambiguous. For each ofthe two non-zero values of HS, there are 50 data points or more,and a visual inspection of the empirical distribution plots onWeibull scale indicates that the body and upper tail follow astraight line, such that a Weibull distribution is an appropriatedistribution model. However, with as few as only three HS values and with thesomewhat uncertain fit (not particularly well-defined) of aWeibull distribution to the upper tail of the empirical short-term distribution for HS = 0, in particular the interpreted func-tional relationship between the shape parameter b of the short-term Weibull distribution and the significant wave height HSmay be questioned. An improved support for the interpretationof this relationship could have been obtained by tests for moreHS values than the three values investigated or by more modeltests in calm water or both.

X

HS

mean value, E[X|HS]

conditional distributions

0.99

0 X

X99%

FX

0

))(exp(1)(|b

HX axxF

S−−=

PSHa μ/)0003446.0779.8exp( 0384.3⋅−=

)1405.0exp(0459.4 SHb −⋅=

))(exp(1)( β

αhhF

SH −−=

dhdh

hdFxFxF S

S

HHXX ∫

∞

⋅=0

|

)()()(

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Offshore Standard DNV-OS-E406, April 2010 App.A – Page 117

Figure 4 Distribution of peak pressure on canopy conditional on significant wave height HS, Weibull probability scale

Figure 5 Long-term distribution of peak pressure on canopy

402 The example shows estimation of characteristic valuefor a quantity for which a high realization of that quantity isunfavourable in design and for which the characteristic valuecorrespondingly is defined as a high quantile, viz. the 99%quantile in the long-term distribution of the variable. Such highquantiles used for definition of characteristic values are com-mon for quantities such as loads and accelerations. For quanti-

ties for which a low realization of the quantity is unfavourablein design, a low quantile is usually used for definition of char-acteristic value, viz. the 1% quantile in the long-term distribu-tion of the variable. An example of such a variable, where lowrealizations of the variable is unfavourable in design, is the dis-tance between the lifeboat and the host facility when the life-boat has been launched and has hit the water and resurfaced.

Cumulative distribution function, pressure on canopy, tail fits

-6

-5

-4

-3

-2

-1

0

1

2

6 6.5 7 7.5 8 8.5 9 9.5 10

lnP

ln(-l

n(1-

CDF

))

CalmHs=6.8 mHs=9.8 mCalm tail fit6.8 m tail fit9.8 m tail fit

Long-term distribution of peak pressure on canopy

0

0.2

0.4

0.6

0.8

1

1.2

0.0 0.5 1.0 1.5 2.0 2.5 3.0

X

CDF

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Offshore Standard DNV-OS-E406, April 2010 Page 118 – App.A

B. Miscellaneous

B 100 Long-term distribution of metocean parameters101 Metocean data are often given in condensed form interms of significant wave height HS and 10-minute mean windspeed U10 with specific return periods such as 10, 100 and1 000 years. The long-term distributions of HS and U10 can bederived from such condensed metocean data provided thegeneric distribution types for these distributions are known.102 The long-term distribution of the significant wave heightHS is often a Weibull distribution,

Provided the Weibull distribution is the correct generic distri-bution type for HS, the distribution parameters α and β can besolved by solution of two equation with two unknowns, α andβ. The two equations can be established from two different HSvalues with specified different return periods as given in thecondensed metocean data, e.g. the HS values associated withreturn periods of 10 and 100 years. For each value h of HS withassociated return period TR, given in units of years, the cumu-lative probability is

where N = 2 922 is the number of 3-hour stationary sea statesin one year. When equated to 1–exp(–(h/α)β) this probabilityforms an equation in α and β. With two such equations estab-lished based on the two different HS values and their respectivereturn periods, α and β can be solved. The Weibull distributionassumption can be verified if HS values for three or morereturn periods are available and the corresponding three ormore points (lnHS, ln(–ln(1–FHs(HS)))) plot on a straight line.103 The long-term distribution of the 10-minute mean windspeed U10 is often a Weibull distribution,

Provided the Weibull distribution is the correct generic distri-bution type for U10, the distribution parameters α and β can besolved by solution of two equation with two unknowns, α andβ, in the same manner as outlined in detail for HS. The cumu-lative probability associated with a value of U10 whose returnperiod is TR is

where N = 52 596 is the number of 10-minute periods in oneyear.104 The same principles as those outlined above can beapplied to establish the long-term distributions for HS and U10when the condensed metocean data support another distribu-tion type than the Weibull distribution assumed in 102 and103. This requires that the appropriate expression for thecumulative distribution function is substituted for the Weibulldistribution function in the expressions for FHs and FU10 in 102and 103.

B 200 Fitting of parametric distribution functions to empirical distributions201 When selecting a generic distribution type and fitting itsparametric distribution function to the empirical distribution ofX conditional on HS, or to its upper tail, a number of trial distri-

bution types should be considered, including but not limited to:

— Weibull distribution— Gumbel distribution— Normal distribution— Lognormal distribution.

A visual inspection will often suffice to determine whether aparticular distribution type will be an adequate model for anempirical distribution on hand. 202 The empirical distribution of X conditional on HS isgiven in terms of n data pairs (xi,F(xi)), i = 1,...n, where the xi’sare the n observed values of X, e.g. obtained from n model testsin the laboratory. The xi’s are sorted in increasing order andF(xi) denotes the associated empirical cumulative probability.For calculation of F(xi), it is recommended to use the followingexpression when the Weibull distribution or the Gumbel distri-bution is considered as a distribution model to match the data:

For calculation of F(xi), it is recommended to use the followingexpression when the normal distribution or the lognormal distri-bution is considered as a distribution model to match the data:

203 The cumulative distribution function for the Weibulldistribution reads

where a and b are distribution parameters.If the data pairs (xi,F(xi)) of the empirical distribution form astraight line in an (lnx,ln(–ln(1–F(x)))) diagram, then theWeibull distribution will be an appropriate distribution model.204 The cumulative distribution function for the Gumbeldistribution reads

where a and b are distribution parameters.If the data pairs (xi,F(xi)) of the empirical distribution form astraight line in an (x,ln(–ln(F(x)))) diagram, then the Gumbeldistribution will be an appropriate distribution model.205 The cumulative distribution function for the normal dis-tribution reads

where Φ denotes the standard Gaussian cumulative distribu-tion function and where μ and σ are distribution parameters.If the data pairs (xi,F(xi)) of the empirical distribution form astraight line in an (x, Φ–1(F(x))) diagram, then the normal dis-tribution will be an appropriate distribution model.206 The cumulative distribution function for the lognormaldistribution reads

where Φ denotes the standard Gaussian cumulative distribu-tion function and where μ and σ are distribution parameters.If the data pairs (xi,F(xi)) of the empirical distribution form astraight line in an (lnx, Φ–1(F(x))) diagram, then the lognormaldistribution will be an appropriate distribution model.

))(exp(1)( β

αhhF

SH −−=

RH TN

hFS ⋅

−=11)(

))(exp(1)(10

β

αuuFU −−=

RU TN

uF⋅

−=11)(

10

12.044.0)(

+−

=nixF i

25.0375.0)(

+−

=nixF i

))(exp(1)( b

axxF −−=

)))(exp(exp()( bxaxF −−−=

)()(σ

μ−Φ=

xxF

)ln()(σ

μ−Φ=

xxF

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Offshore Standard DNV-OS-E406, April 2010 App.B – Page 119

APPENDIX B MANUFACTURING OF FRP STRUCTURES

A. IntroductionA 100 General101 This appendix contains a recommended set of require-ments to be followed during manufacturing of FRP structures.102 There are limited or no means available for nondestruc-tive examination of structural components constructed fromcomposite materials and sandwich materials. Therefore, thesafety targets specified in this standard can only be met if boththe design is carried out according to the prescriptions of thisstandard and a rigorous control of all steps of the fabrication ismade to ascertain that the finished product complies with thespecifications.103 The quality assurance system to be implemented at themanufacturer as required in Sec.1 A404 should be formalizedin the form of a quality handbook or a similar documentincluding, but not limited to, the following main subjects:

— organization of all quality related activities— identification of key personnel and their responsibilities — procedures for documentation — qualification of personnel — manufacturing conditions including recording of tempera-

ture and humidity — receipt and storage of raw materials — working procedures and instructions — formulation of resins — lamination records — procedures for quality control and inspection or testing — repair procedures — defect acceptance criteria.

B. StorageB 100 General101 Storage premises are to be so equipped and arranged thatthe material supplier's directions for storage and handling ofthe raw materials can be followed.102 Storage premises for reinforcement materials are to bekept dry and clean so that the raw material is not contaminated.The materials shall be stored in unbroken original packagingbefore being used. Materials on which the original packaginghas been broken shall be adequately protected against contam-ination when stored again after use.103 Reinforcement materials shall normally be stored at thesame temperature and humidity as the workshop in which theyare going to be used. If the storage temperature is not the samethe material shall be acclimatized at the workshop temperatureand humidity prior to being deployed. The time of acclimatiza-tion shall be adequate for the amount of reinforcement: forunbroken packages the acclimatization shall have duration ofat least two days.104 Resins, gelcoat, hardeners, additives etc. shall be storedaccording to the manufacturer’s recommendations as regardstemperature, shelf life etc. Raw materials which are stored attemperatures lower than +18°C shall be acclimatized to thetemperature of the workshop prior to being used. Tanks for res-ins etc. are to be handled during storage according to the man-ufacturer’s recommendations and equipped and arrangedaccordingly.105 Core materials are to be stored dry and protected againstcontamination and mechanical damage. Core materials shall

normally be stored at the same temperature as the workshop inwhich they are going to be used. If the storage temperature isnot the same the material shall be acclimatized at the workshoptemperature and humidity prior to being deployed.106 Core materials shall be stored in such a way that outgas-sing of the material is ensured prior to being used. Outgassingshall be carried out according to the manufacturer’s recom-mendations. When new free surfaces are created in the mate-rial, e.g. by sanding, cutting or machining, proper outgassingshall be ensured again.107 Pre-pregs shall be stored according to the manufacturer'srecommendation. For pre-pregs stored in refrigerated condi-tions a log shall be carried for each package showing the timeand at which temperature the package has been stored or usedoutside of its normal storage conditions.

C. Manufacturing Premises and ConditionsC 100 Manufacturing premises101 Manufacturing premises are to be so equipped andarranged that the material supplier's directions for handling thematerials, the laminating process and curing conditions can befollowed. 102 The manufacturing premises shall be free from dust andother contamination that may in any way impair the quality ofthe end product.

C 200 Manufacturing conditions201 The air temperature in the moulding shops is not to beless than +18°C. The stipulated minimum temperature is to beattained at least 24 hours before commencement of lamination,and is to be maintainable regardless of the outdoor air temper-ature. The temperature in the moulding shop is not to varymore than ± 5°C. This limit can be exceeded provided it has nodetrimental effect on the product and provided there is no riskfor condensation of humidity.202 The relative humidity of the air is to be kept so constantthat condensation is avoided and is not to exceed 80%. Ahigher relative humidity can be accepted on a case by casebasis provided an adequate margin against the risk for conden-sation of humidity is provided. In areas where spray mouldingis taking place, the air humidity is not to be less than 40%. Thestipulated air humidity is to be maintainable regardless of out-door air temperature and humidity. More stringent require-ments to humidity shall be adhered to if recommended by themanufacturer.203 Other manufacturing conditions may be acceptable pro-vided it is documented that condensation of humidity can besafely avoided.204 Air temperature and relative humidity are to be recordedregularly and the records filed for a period of at least two years.In larger shops there is to be at least one thermohydrograph foreach 1 500 m2 where lamination is carried out. The location ofthe instruments shall be such as to give representative meas-urement results.205 Draught through doors, windows etc. and direct sunlightis not acceptable in places where lamination and curing are inprogress.206 The ventilation plant is to be so arranged that the curingprocess is not negatively affected.207 Sufficient scaffoldings are to be arranged so that all lami-

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Offshore Standard DNV-OS-E406, April 2010 Page 120 – App.B

nation work can be carried out without operators standing on thecore or on surfaces on which lamination work is taking place.208 During lamination of larger constructions the tempera-ture should be recorded at least at two levels vertically in theworkshop and the curing system should be adjusted to com-pensate for possible temperature differences.209 Prefabrication of panels and other components is to becarried out on tables, fixtures etc. above the shop floor level.No fabrication shall be carried out on the shop floor.

D. Production Procedures and WorkmanshipD 100 Production procedures101 The supplier’s directions for application of the materialsare to be followed.102 Specified procedures shall be implemented for all taskswith significance to the quality of the end product. Where neces-sary to exercise a satisfactory control of the quality, these proce-dures shall be documented in writing in controlled documents.

D 200 Workmanship201 The reference direction of reinforcement shall afterbeing laid not deviate from the specified by more than ± 5°.202 Adjacent sheets of reinforcement shall in the normalcase overlap to give structural continuity. The overlap lengthshall be such that the shear capacity of the overlap is notsmaller than the tensile strength (perpendicular to the overlap)of the overlapping plies. The shear strength of the matrix shallnot be assumed larger than 8 MPa. A higher shear strength canbe assumed subject to the approval of the certifying body. (Forexample, for a 0/90° 1 000 g/m2 type glass reinforcement theoverlap shall not be smaller than 30 mm.) In areas of low utili-zation, overlaps may be omitted subject to the approval of thecertifying body. Overlaps shall be staggered through the thick-ness of the laminate. The distance between two overlaps inadjacent plies shall not be smaller than 100 mm.203 Thickness changes in a laminate should be tapered overa minimum distance equal to 10 times the difference in thick-ness.204 Thickness changes in core materials should be taperedover a minimum distance equal to 2 times the difference inthickness. A larger distance may be required to maintain struc-tural continuity of the skins.205 Sandwich constructions can be fabricated either by lam-ination on the core, application of the core against a wet lami-nate, by bonding the core against a cured skin laminate using acore adhesive, by resin transfer, or by resin transfer mouldingof the core together with one or both of the skin laminates.206 An efficient bond is to be obtained between the skin lam-inates and the core and between the individual core elements.The bond strength shall not be smaller than the tensile andshear strength of the core. The application of a light CSMbetween core and skin laminate may be advantageous in thisrespect.207 Approved tools for cutting, grinding etc. of varioustypes of core material shall be specified in the production pro-cedure.208 All joints between skin laminates and core and betweenthe individual core elements are to be completely filled withresin, adhesive or filler material. The joint gap between coreblocks should generally not be larger than 3 mm. Larger gapsmay be accepted if necessary, based on the characteristics ofthe adhesive or filler (e.g. its viscosity) and the thickness of thecore. For slamming exposed areas a larger gap width shouldalso be reflected in the qualification testing of the core materialand the adhesive, i.e. during slamming testing, cf. Sec.5 F600.

209 Core materials with open cells in the surface, shouldnormally be impregnated with resin before it is applied to a wetlaminate or before lamination on the core is commenced.210 When the core is applied manually to a wet laminate thesurface shall be reinforced with a chopped strand mat of 450 g/m2 in plane surface and 600 g/m2 in curved surfaces. If vac-uum is applied for core bonding the surface mats may be omit-ted, provided it is demonstrated in the qualification tests that anefficient bond between core and skin laminate is obtained.211 If the core is built up by two or more layers of core andany form of resin transfer is used, arrangements shall be madeto ensure proper resin transfer and filling between the coreblocks. This should be achieved by scoring or holing the coreblocks and by placing a reinforcement fabric between the coreblocks to facilitate resin distribution.212 Frameworks for core build up shall give the core suffi-cient support to ensure stable geometrical shape of the con-struction and a rigid basis for the lamination work.213 When a prefabricated skin laminate is bonded to a sand-wich core measures are to be taken to evacuate air from the sur-face between skin and core.214 The core material is to be free from dust and other con-tamination before the skin laminates are applied or core ele-ments are glued together. The moisture content shall besufficiently low not to have any adverse effect on curing. Theacceptable moisture content shall be specified by the manufac-turer of the core material.215 When vacuum-bagging or similar processes are used itshall be ensured that curing in the core adhesive has not beeninitiated before vacuum is applied.

E. Manual LaminationE 100 General101 The reinforcement material is to be applied in thesequence stated on the approved plan(s).102 When the laminate is applied in a mould, a choppedstrand mat of maximum 450 g/m2 is to be applied next to thegelcoat. The mat can be omitted provided a satisfactory resist-ance against water can be ensured.103 The resin is to be applied on each layer of reinforcement.Gas and air pockets are to be worked out of the laminate beforethe next layer is applied. Rolling of the layers is to be madecarefully, paying special attention to sharp corners and transi-tions. The viscosity and gel-time of the resin shall be adequateto prevent drain-out of resin on vertical and inclined surfaces.The tools and methods used when working the laminate shallnot damage the fibres.104 The time interval between applications of each layer ofreinforcement is to be within the limits specified by the resinsupplier. For thicker laminates care is to be taken to ensure a timeinterval sufficiently large to avoid excessive heat generation.105 Curing systems are to be selected with due regard to thereactivity of the resin and in accordance with the supplier's rec-ommendations. Heat release during curing is to be kept at asafe level in accordance with the material manufacturer's rec-ommendations. The quantity of curing agents is to be keptwithin the limits specified by the supplier.106 After completion of lamination, polyester laminates areto cure for at least 48 hours at an air temperature of minimum+ 18°C. Curing at a higher temperature and a shorter curingtime may be accepted on the basis of control of the curing rate.For other types of resins curing shall be carried out accordingto the specified cure cycle and according to the resin manufac-turer's recommendations.

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Offshore Standard DNV-OS-E406, April 2010 App.B – Page 121

F. Vacuum Assisted Resin Transfer Moulding (VARTM) and Vacuum-Bagging

F 100 General101 Points of resin injection shall be located and opened andclosed in a sequence such that complete filling of the mouldwithout any air being trapped is ensured.102 The resin shall be formulated, based on the resin manu-facturer’s recommendations, such that an adequate viscosityand gel-time is obtained to enable filling of the completemould and such that the maximum temperature during cure iskept within acceptable limits, e.g. with respect to the tempera-ture sensitivity of core materials.103 The pressure level (vacuum) in the mould shall be spec-ified prior to infusion. The pressure shall be adequate to ensureadequate consolidation of the laminate and that the specifiedmechanical properties are reached and that the mould is prop-erly filled. The pressure shall be maintained throughout themould during the cure cycle of the laminate, at least past thepoint of maximum temperature in the laminate, and the speci-fied hold time. The vacuum shall be monitored by the use ofpressure gauges distributed throughout the mould such that areliable indication of the pressure distribution is obtained. Thismeans that pressure gauges shall be placed far away from vac-uum suction points. Adequate means to locate and repair leak-age shall be deployed.

G. Curing

G 100 General101 Cure cycles shall be documented by temperaturerecords.102 For cure taking place at room temperature in the work-shop the registrations made in the workshop are sufficient todocument the cure cycle.103 For cure at elevated temperature, fans with ample capac-ity shall be operated in the compartment in which the cure iscarried out to ensure an even distribution of temperature. Con-tinuous records of temperature throughout the complete curecycle shall be provided. Recording points shall be distributedthroughout out the length, width and height of the cure com-partment to the extent necessary to verify that the temperaturedistribution is even.

H. Secondary Bonding

H 100 General101 A secondary bonding is defined as any bond betweentwo FRP structures which is made after one or both of the indi-vidual structures has effectively cured.102 The surface ply of a laminate subject to secondary bond-ing and the first ply of the bonding laminate is normally to beof chopped strand mat. This mat can be dispensed with pro-vided the necessary bond strength is reached.103 Surfaces in way of secondary bonding are to be cleanand free from dust and other forms of contamination.104 Laminates on which secondary bonds are to be carriedout shall have an adequate surface preparation, normallyincluding grinding.105 If «peel strips» are used in the bonding surface therequired surface treatment may be dispensed with providedthat adequate bond strength is documented.

I. Adhesive BondingI 100 General101 Adhesive bonds shall be carried out according to thesame procedure(s) as on which the design and qualificationtesting has been based, ref. Sec.8 and according to the recom-mendations from the manufacturer of the adhesive. The proce-dure(s) shall give clear requirements to all factors that canaffect the quality of the bond. As a minimum the followingshall be covered: working conditions, surface preparation,application, clamp-up, curing cycle, etc.

J. Quality AssuranceJ 100 General101 The manufacturer is to have implemented an efficientsystem for quality assurance to ensure that the finished productmeets the specified requirements. The person or departmentresponsible for the quality assurance shall have clearly estab-lished authority and responsibility and be independent of theproduction departments.102 The system should be formalized through a qualityhandbook or similar document at least containing the follow-ing main objects:

— organization of all quality related activities— identification of key personnel and their responsibilities— procedures for documentation— qualification of personnel— manufacturing conditions including recording of tempera-

ture and humidity— receipt and storage of raw materials— working procedures and instructions— formulation of resins— lamination records— procedures for quality control and inspection or testing— repair procedures— defect acceptance criteria.

103 The quality handbook shall be made available to the sur-veyor.

J 200 Quality control201 A written quality plan shall be established for the produc-tion of each hull and superstructure. The quality plan shall befully implemented prior to commencement of the production.202 The quality plan shall address at least the followingitems:

— relevant specifications, rules, statutory requirements etc. — drawings— list of raw materials— procedures for handling of raw materials— manufacturing procedures and instructions— procedure for keeping and filing of lamination records— procedure for keeping and filing of cure logs: temperature

and vacuum (for VARTM)— procedures for quality control and inspection or testing— inspection points— witness points by independent surveyor as appropriate— production testing of laminates, joints and panels in

accordance with Sec.5 E— procedures for corrective actions when deficiencies are

identified.

203 The quality plan may contain copies of all the necessarydocumentation or may refer to documents in the quality hand-book or other controlled documentation. The relevant draw-ings may e.g. be identified by a list of drawings.

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Offshore Standard DNV-OS-E406, April 2010 Page 122 – App.C

APPENDIX C STRUCTURAL ANALYSIS AND CALCULATIONS

BY THE FINITE ELEMENT METHOD

A. IntroductionA 100 General101 The objective of this appendix is to provide methods andrecommendations for calculation of the response (with empha-sis on the finite element method (FEM)) of free fall lifeboatsfor specified loads, surrounding environments and boundaryconditions.102 The aim of a structural analysis is to obtain the stresses,strains and displacements (denoted load effects in the follow-ing) in the structure as a result of loads and environmental con-ditions. The load effects are subsequently evaluated againstfailure criteria, see Sec.6. The following procedures are typi-cally involved in such an analysis:

— procedure to calculate load effects in the structure basedon the loads

— procedure to check for global or local failure.

103 If simple calculations cannot be performed to documentthe strength and stiffness of a structural component, a FiniteElement analysis should be carried out.104 Since a FEM analysis is normally used when simple cal-culations are insufficient or impossible, care must be taken toensure that the model and analysis reflect the physical reality.This must be done by means of carrying out a careful evalua-tion of the input to as well as the results from the analysis. 105 FEM analysis tasks should be carried out by qualifiedengineers under the supervision of an experienced senior engi-neer.106 The analysis should be performed according to a plan,which has been defined prior to the analysis, and the approachshould be documented.

B. Types of AnalysisB 100 General101 Analytical and/or numerical calculations may be used inthe structural analysis. The finite element method (FEM) ispresently the most commonly used numerical method forstructural analysis, but other methods, such as finite differenceor finite series methods may also be applied.

Guidance note:While the FE method is applicable for a wide range of problems,analytical solutions and the finite series approach often put toomany restrictions on laminate lay-up, geometry etc. for compos-ite and sandwich types of structures and may thus be insufficientin design.


102 Though different types of analyses can be performed bymeans of FEM analysis, most analyses take the form of staticanalyses for determination of the strength and stiffness ofstructures or structural components.103 Only recognized FEM programs should be used. Otherprograms shall be verified by comparison with analytical solu-tions of relevant problems, recognized FEM codes and/orexperimental testing.104 Laminate analysis is an additional type of analysis thatis applied to layered composites in order to derive the proper-

ties of a laminate from the properties of its constituent plies.105 The structural analysis should be performed for allphases over the entire lifetime of the structure. Initial anddegraded material properties should be considered if relevant.106 It is of primary importance to the analysis of free falllifeboats to assess linear and nonlinear structural behaviour,structural strength and stiffness, as well as global and localbuckling.

B 200 Static analysis201 In a static analysis, structural parts are commonly exam-ined with respect to determining which extreme loads governthe extreme stress, strain and deflection responses.

B 300 Frequency analysis301 Frequency analysis is used to determine the eigenfre-quencies and normal modes of a structure or structural part. 302 The FEM program will normally perform an analysis onthe basis of the lowest frequencies. However, by specifying ashift value, it is possible to obtain results also for a set of higherfrequencies around a user-defined frequency.

Guidance note:The normal modes resulting from a frequency analysis only rep-resent the shape of the deflection profiles, not the actual deflec-tions.


B 400 Dynamic analysis401 Dynamic analysis should generally be performed whenloads are time-dependent and/or when other effects such asinertia (and added mass) and damping forces are significant.402 In a dynamic analysis one may be interested in the tran-sient response of a structure due to prescribed, time-dependentloads or the “eigenvalues” (natural or resonance frequencies)of the structure.403 In order to obtain an accurate transient analysis adetailed structural model and small time steps should be used,in particular for rapidly varying loads.404 For slowly varying loads a quasi-static analysis may beapplied. In such an analysis inertia and damping forces areneglected, and the corresponding static problem is solved for aseries of time steps.405 Dynamic analysis should be carried out in such a mannerthat findings from model scale testing and corresponding load-ing scenarios are properly reflected.

B 500 Stability/buckling analysis501 Stability/buckling analysis is relevant for slender struc-tural parts or sub-parts. This is due to the fact that the loadscausing local or global buckling may be lower than the loadscausing strength problems.502 The analysis is normally performed by applying a set ofstatic loads. Hereafter, the factor by which this set of loads hasto be multiplied for stability problems to occur is determinedby the analysis program.503 The need for special buckling analysis should beassessed carefully in every case. In particular the followingaspects should be considered in making this assessment:

— presence of axial compressive stresses in beam or column

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Offshore Standard DNV-OS-E406, April 2010 App.C – Page 123

type members or structural elements — presence of in-plane compressive stresses or shear stresses

in flat, plate-like elements — presence of in-plane compressive stresses or shear stresses

in shell like elements.

504 Two alternative approaches may be used in analysingbuckling problems:

— analysis of isolated components of standard type, such asbeams, plates and shells of simple shape

— analysis of an entire structure (or of an entire, complexstructural component).

505 Buckling analysis of more complex elements or entirestructures should be carried out with the aid of verified finiteelement software or equivalent.506 Initially an “eigenvalue” buckling analysis should beperformed assuming initial (nondegraded) elastic propertiesfor the laminates and, for sandwich structures, for the core.This should be repeated with alternative, finer meshes, untilthe lowest “eigenvalues” and corresponding “eigenmodes” arenot significantly affected by further refinement. The main pur-poses of this analysis are to clarify the relevant buckling modeshapes and to establish the required mesh density for subse-quent analysis.507 Careful attention should be paid to correct modelling ofboundary conditions.508 If the applied load exceeds, or is close to, the calculatedelastic critical load, the design should be modified to improvethe buckling strength before proceeding further.509 When geometrically nonlinear analyses are carried out,the results must be checked to assess buckling. To calculate thegeometrical nonlinearities accurately in the analysis, it isimportant that the material stiffness specified as input to theanalysis is representative and that the structural shape includ-ing curvatures, eccentricities etc. is represented by the model. For the assessment of the buckling and for calculating other loadeffects (deflections, stresses and strains), the design load effectsmay for simplicity be taken as the load effects of the design load,where the design load is determined as the characteristic loadscaled by the load factor as specified in this standard. For assessment of utilization of the material, a failure criterionappropriate for the respective material shall be used using thematerial factors and the characteristic values of the materialstrength parameters as specified in this standard. Linear buckling calculations for complex structures must beused with great care and can hardly be justified as a method forverification. The only safe method to assess geometric effectsin structures with complex geometries and mainly compressiveforces is to apply nonlinear static analysis.

B 600 Thermal analysis601 By thermal analysis, the temperature distribution instructural parts is determined, based on the initial temperature,heat input/output, convection, etc. This is normally a time-dependent analysis; however, it is usually not very time-con-suming as only one degree of freedom is present at each mod-elled node.

B 700 Global and local analysis701 The global response of the structure is defined as theresponse (displacement and stability) of the structure as awhole.

702 The local response of the structure is defined as thestresses and strains (and deformations) in every local part ofthe structure.703 The response of the structure should be calculated on aglobal or local level depending on the failure mechanism beingchecked and its associated failure criterion.

Guidance note:The failure of the structure should generally be checked on thebasis of the local response of the structure by the use of failurecriteria for each failure mechanism as described in Sec.6. Buck-ling is generally checked on larger parts of the structure andbased on average stresses over large areas. Under such condi-tions a coarser analysis may be sufficient. However, if the FEmethod is used to calculate buckling stresses, a very local analy-sis of the structure may be needed.


704 The advantage of an independent local model (or a sub-model) is that the analysis is carried out separately on the localmodel, requiring less computer resources and enabling a con-trolled step by step analysis procedure to be carried out. 705 The various mesh models must be compatible, i.e. thecoarse mesh model (global model) should produce deforma-tions and/or forces which are applicable as boundary condi-tions for the finer mesh model (sub-model). If super-elementtechniques are available, the model for local stress analysismay be applied at lower level super-elements in the globalmodel.706 Sub-models (fine mesh models) may be solved sepa-rately by use of the boundary deformations, boundary forcesand local internal loads from the coarse model. Load data canbe transferred from the coarse model to the local model eithermanually or, if sub-modelling facilities are available, automat-ically by the computer program.707 For global models based on composite or sandwichmaterial, the actual detail geometry of each part as well asimportant structural details from joining of the different partsare crucial in order to get the correct global deformations andto account for any local or global effects of stiffness, as well asstrength and resulting stress peaks.708 Examples of global and local models of a free fall life-boat are given in Figures 1 and 2.

Figure 1 Global model of free fall lifeboat

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Figure 2 Model for detail analysis of wheelhouse

B 800 Material levels – composite/sandwich materials801 The local response of the structure can in principle beanalysed at the following different material levels:

— the “constituent level” corresponding to the fibre, matrixand core, separately

— the “ply level” corresponding to the individual layers in alaminate or the faces of a sandwich structure

— the “laminate level” corresponding to the whole laminateor sandwich structure.

802 Each failure mechanism can in principle be checked atany material level. However, due to the lack of theoreticalknowledge or for practical reasons, it is not always possible tocheck a given failure mechanism at all material levels.803 The local response of the structure should be analysed ata material level consistent with the failure criteria used in thefailure analysis as described in Sec.6.

B 900 Nonlinear analysis901 Static nonlinear analysis should be performed when geo-metrical and/or material nonlinearity are present and when lin-ear and nonlinear analysis results are expected to differ.902 Geometrical nonlinearity is associated with, e.g., largedisplacements and/or large strains, boundary conditions vary-ing according to deformations, nonsymmetric geometry ofstructure and buckling.903 Nonlinear material behaviour is associated with thestress–strain relation. Following damage in the material, i.e.matrix cracking or yield, stress–strain relationships usuallybecome nonlinear. 904 Structures of composite (FRP) or sandwich materialhave smaller stiffness and generally exhibit a nonlinear behav-iour at a lower load level than steel structures, thus indicatinga stronger need for nonlinear analysis.905 Structures with nonlinear materials should be checkedeither against early failure mechanisms, e.g. matrix cracking oryield, or against ultimate failure, or both.906 A decision between using a progressive, nonlinear fail-ure analysis and using a simplified (linear) failure analysisshould be based on the failure modes of the structure or struc-tural component in question and the failure mechanisms inves-tigated.907 For nonlinear problems, the following special consider-ations should be taken into account:

— the analyst should make several trial runs in order to dis-cover and remove any mistakes

— the solution strategy should be guided by what is learnedfrom the previous attempts

— the analyst should start with a simple model, possibly thelinear form of the problem, and then add the nonlinearitiesone by one.

C. ModellingC 100 General101 The FEM analysis model needs to reflect the actualmethods used for lifeboat fabrication, for interconnection ofthe structural parts of the lifeboat, and for interaction of thestructural component with the rest of the structure.102 The complexity and material application of present freefall lifeboat solutions normally requires a detailed FEM basedon composite material and laminate theory.103 Model behaviour should be checked against the behav-iour of the structure. The following modelling aspects shouldbe treated carefully:

— loads— boundary conditions— static, quasi-static or dynamic problem— damping— possibility of buckling— isotropic or anisotropic material— temperature or strain rate dependent material properties— nonlinearity (due to geometrical and material properties)

membrane effects.

C 200 Input data201 Environmental conditions should be converted intoloads based on guidance to be found in Sections 3 and 4, sup-ported by relevant standards or guidelines.202 The boundary conditions should be selected carefully inorder to represent the nature of the problem in the best possibleway. It should be demonstrated that the chosen boundary con-ditions lead to a realistic or conservative analysis of the struc-ture.203 Thermal stresses that result from the production processand from the in service loading should be considered in allanalysis. 204 Stresses due to swelling from absorbed fluids should beincluded if relevant. 205 The elastic properties of the materials constituting acomposite structure should be taken according to DNV-OS-C501, Sec.4. In particular, time dependent stiffness propertiesbased on the expected degradation due to environmental load-ing conditions should be considered. Local variations of theseconditions should also be considered. 206 As an alternative to elastic constants, the stiffness matrixfor orthotropic plies may be used.207 It should be demonstrated that the estimated stiffnessgives conservative results with respect to load effects. Thechoice of stiffness values may be different in the cases ofstrength and stiffness limited design.

C 300 Model idealization301 The full vessel extent should be included in the globalmodel. 302 The global analysis is intended to provide a reliable rep-resentation of the overall stiffness and global stress distribu-tion in the primary members.303 The global model should contain a primary structure that

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is easily identified with a clear load path which is not very sen-sitive to pressure variations.304 The global analysis may be carried out with a relativelycoarse mesh. Stiffened panels may be modelled by means oflayered (sandwich) elements or anisotropic elements. Alterna-tively, a combination of plate and beam elements may be used.Modelling shall provide a good representation of the overallmembrane panel stiffness in the longitudinal/transverse andshear directions.305 The global model may be used to calculate nominal glo-bal (longitudinal) stresses away from areas with significantstress concentrations. The following features will induce sig-nificant stress concentrations:

— termination of girder and bulkheads— large penetrations, doors, windows, hatches— sharp corners or abrupt transitions.

306 Small penetrations are normally disregarded in the glo-bal model. For consideration of local stresses in web frames,girders and other areas, fine mesh areas may be modelleddirectly into the coarse mesh model by means of suitable ele-ment transitions. However, an integrated fine and coarse meshapproach implies that a large set of simultaneous equationsmust be solved.307 For local analysis, a local mesh refinement must be used.In such an analysis, the original mesh is stiffer than the refinedmesh. When the portion of the mesh that contains the refinedmesh is analysed separately, a correction shall be made so theboundary displacements to be imposed on the local mesh areconsistent with the mesh refinement.308 If sub-models are used, these should be checked toensure that the deformations and/or boundary forces are simi-lar to those obtained from the coarse mesh model. Further-more, the sub-model should be sufficiently large that itsboundaries are positioned at areas where the deformation andstresses in the coarse mesh model are regarded as accurate.Within the coarse model, deformations at web frames andbulkheads are usually accurate, whereas deformations in themiddle of a stiffener span (with fewer elements) are not suffi-ciently accurate. 309 The sub-model mesh should be finer than that the meshof the coarse model; for example a small bracket is normallyincluded in a local model, but not in the global model. 310 All main longitudinal and transverse geometries of thehull should be modelled. Structural components not contribut-ing to the global strength of the lifeboat may be disregarded inthe global model. The mass of disregarded elements shall beincluded in the model. 311 Structural components not contributing to the globalstiffness can lead to local or global stress concentrations and itshould be checked that omission of these parts does not lead tononconservative results. Similarly, the omission of minorstructures may be acceptable provided that such omission doesnot significantly change the deformation of the structure orgive nonconservative results, i.e. too low stress.312 Continuous stiffeners should be included using any ofthe following options:

— lumping of stiffeners to the nearest mesh line— inclusion of stiffeners in layered elements (sandwich ele-

ments), using 6- and 8-node shell elements for triangularand quadrilateral elements respectively

— inclusion of stiffeners as material properties (anisotropicmaterial properties).

313 Joints should be modelled carefully. Joints may haveless stiffness than inherited in a simple model, which may leadto incorrect predictions of global model stiffness. Individualmodelling of joints is usually not appropriate unless the joint

itself is the object of the study.314 The analyst should beware the following aspects:

— for vibrations, buckling or nonlinear analysis, symmetricgeometry and loads should be used with care since in suchproblems symmetric response is not guaranteed. Unlesssymmetry is known to prevail, symmetry should not beimposed by choice of boundary conditions.

— for crack analysis, a quarter point element can be too largeor too small, thereby possibly making results from meshrefinement worse

— the wrong choice of elements may lead to results thatexhibit a dependence on Poisson’s ratio in problemswhose solutions are known to be independent of Poisson’sratio

— if plane elements are warped, so that the nodes of the ele-ments are not coplanar, results may be erratic and verysensitive to changes in the mesh

— imperfections of load, geometry, supports and mesh maybe far more important in a buckling problem than in prob-lems involving only linear response.

C 400 Coordinate systems401 Different coordinate systems may be used to define themodel and the boundary conditions. Hence the coordinate sys-tem valid for the elements and boundary conditions should bechecked, e.g. by plots. This is particularly important for beamelements given that it is not always logical which axes are usedto define the sectional properties.402 Regarding laminate elements, the default coordinatesystem often constitutes an element coordinate system, whichmay have as a consequence that the fibre directions are distrib-uted randomly across a model.403 Extreme care shall be taken when working with differentrelevant coordinate systems, i.e. global, ply based, laminatebased, element based and stiffener based systems.

C 500 Material models and properties501 Several different material properties may be used acrossa model, and plots should be made and checked to verify thatthe material is distributed correctly.502 Drawings are often made by means of using units of mmto obtain appropriate values. When the model is transferred tothe FEM program, the dimensions are maintained. In this casecare should be taken in setting the material properties and loadscorrectly, as kg-mm-N-s is not a consistent set of units. It isadvisable to use SI-units (kg-m-N-s).503 The material model used is usually a model for isotropicmaterial, i.e. the same properties prevail in all directions. Note,however, that for composite materials an orthotropic materialmodel has to be used to reflect the different material propertiesin the different directions. For this model, material propertiesare defined for three orthogonal directions. By definition ofthis material, the choice of coordinate system for the elementshas to be made carefully.504 Composite material, elastic constants: each laminateshall be described with the suitable set of elastic constants.505 Sandwich structures: core materials are generally ortho-tropic and are described by more than two elastic constants.However, most FEM codes can only describe isotropic corematerials. If the elements applied in the FEM analysis do notallow values for all three parameters to be specified, oneshould generally use the measured values for G and ν, and letthe E value be calculated by the program. In that case the shearresponse of the core will be described accurately. However, inparticular applications, in which core shear effects are negligi-ble and axial stresses/strains are crucial, correct E values mustbe applied.

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Guidance note:For many core materials, experimentally measured values of E,G and ν are not in agreement with the isotropic formula:


C 600 Element types and elements601 Element types should be chosen on the basis of the phys-ics of the problem.602 For a specific structural part, several different elementtypes and element distributions may be relevant depending onthe type of analysis to be carried out. Usually, one particularelement type is used for the creation of a FEM model. How-ever, different element types may be combined within thesame FEM model. For such a combination special considera-tions may be necessary.603 1D elements consist of beam elements. Models withbeam elements are quite simple to create and provide goodresults for framework structures. One difficulty may be that thesectional properties are not visible. Hence, the input should bechecked carefully for the direction of the section and thenumerical values of the sectional properties. Some FEM pro-grams can generate 3D views showing the dimensions of thesections. This facility should be used, if present. Naturally, thestresses in the connections cannot be calculated accurately bythe use of beam elements only.604 2D elements consist of shell and plate elements. Shelland plate elements should be used for parts consisting of platesor constant thickness sub-parts. As shell elements suitable forthick plates exist, the wall thickness does not need to be verythin to obtain a good representation by such elements. Theseelements include the desired behaviour through the thicknessof the plate. The same problems as for beam elements arepresent for shell elements as the thickness of the plates is notshown. The thickness can, however, for most FEM programsbe shown by means of colour codes, and for some programs thethickness can be shown by 3D views. The stresses at connec-tions such as welds cannot be found directly by these elementseither.605 3D elements consist of solid elements. 606 A decision to use 2-D or 3-D analysis methods shouldgenerally be made depending on the level of significance of thethrough thickness stresses. If these stresses can be neglected,in-plane 2-D analysis may be applied. Additionally, the analy-sis of certain laminate and sandwich structures may be simpli-fied by a through thickness (cross section) 2-D approach, inwhich plane strain condition is assumed to prevail.

Guidance note:In-plane 2-D analysis is generally preferred when analysing rel-atively large and complex structures, in which through thicknessstresses can be neglected. However, structural details with signif-icant through thickness stresses, such as joints, require a moreaccurate analysis. In these cases 3-D or through thickness 2-D(for components possessing plane strain conditions) approachesshould be applied.


607 In the context of finite element analysis (FEM analysis)of laminate structures one or both of the following elementtypes should be applied:

— layered shell elements with orthotropic material propertiesfor each layer

— solid elements with orthotropic material properties.

Guidance note:There are two options for the solid elements: The modelling maybe performed with (at least) two solid elements through the thick-ness of each ply. Alternatively, one may apply layered solid ele-ments where the thickness of a single element includes two ormore plies.


608 In the context of FEM analysis of sandwich structuresone of the following element types or combinations should beapplied:

— a single layer of layered shell elements through the thick-ness of the entire sandwich material

— (layered) shell elements for the faces and solid elementsfor the core. In this case compensation may be desirablefor the change in stiffness, or alternatively, in order toavoid overlapping areas, shell elements can be positionedadequately without the need for modifying the materialproperties by using the eccentricity property of the ele-ment. Depending on the commercial package used, thisoption is not always available.

— solid elements for both faces and core.

609 For the analysis of sandwich structures, special consid-erations should be taken into account, such as:

— elements including core shear deformation shall beselected

— for honeycomb cores one should account for materialorthotropy, since honeycomb has different shear modulusin different directions

— local load introductions, corners and joints, should bechecked

— curved panels with small radii of curvature should be ana-lysed in 2-D (through thickness direction) or 3-D toaccount for the transverse normal stresses not included inshell elements.

610 By the use of solid elements the correct geometry can bemodelled to the degree of detail wanted. However, this mayimply that the model will include a very large number of nodesand elements, and hence the solution time will be very long.Furthermore, as most solid element types only have threedegrees of freedom at each node, the mesh for a solid modelmay need to be denser than for a beam or shell element model.

C 700 Combinations701 The three types of elements may be combined, however,as the elements may not have the same number of degrees offreedom (DOF) at each node, care should be taken not to createunintended hinges in the model.702 Beam elements have six degrees of freedom in eachnode – three translations and three rotations, while solid ele-ments normally only have three – the three translations. Shellelements normally have five degrees of freedom – the rotationaround the surface normal is missing. However, these elementsmay have six degrees of freedom, while the stiffness for thelast rotation is fictive.703 The connection of beam or shell elements to solid ele-ments in a point, respectively a line, introduces a hinge. Thisproblem may be solved by adding additional ‘dummy’ ele-ments to get the correct connection. Alternatively, constraintsmay be set up between the surrounding nodal displacementsand rotations. Some FEM programs can set up such constraintsautomatically.704 Buckling analysis of stiffened plates and shells: Whenstiffened plate or shell structures are analysed for buckling,special attention shall be paid to the following failure modes:

)1(2 ν+=

EG

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— local buckling of laminate (plate) between stiffeners— possible local buckling of individual plate-like elements in

the stiffeners themselves— overall buckling of the stiffened plate or shell, in which

case separation (debonding) of the stiffener from the plateor the shell laminate must be explicitly considered.

705 The finite element model shall be able to reproduce allrelevant failure modes. Stiffener debonding shall be evaluatedby the insertion of appropriate elements at the interface tomonitor the tensile and shear forces that are transmitted acrossthe bond, together with an appropriate criterion based on testsor relevant published data.706 Buckling analysis for sandwich structures: Sandwichstructures may be exposed to highly localized buckling modessuch as wrinkling and dimpling, in addition to more globalmodes. For simple stress states these local modes may often bechecked using standard formulae.707 The wavelengths for wrinkling are normally very short(often of the order of the sandwich thickness). If a direct FEManalysis of wrinkling is carried out it is essential that a suffi-ciently fine mesh be used in the skin laminates, such that themode shape is well represented. If each skin laminate is mod-elled using shell elements, the element size should not nor-mally be greater than λ/12, where λ is the bucklingwavelength. The core shall be modelled with solid elements ofsimilar size. The required element size shall be establishedusing iterative calculations.708 In performing FEM analysis of wrinkling it is not nor-mally necessary to model a large area of the structure, providedthe in-plane stress state in the skin is well represented. A por-tion of the panel extending over a few wavelengths is normallysufficient. The result is not normally sensitive to the size of thepanel selected for modelling.709 In the absence of detailed information about geometricalimperfections and their consequences, these may be allowedfor by reducing the critical wrinkling stress by 40%. The facewrinkling stress in some text book formulas may alreadyinclude such allowance.710 Wrinkling of skin laminates may be accompanied byyielding of the core if the core is made of a ductile material.This may in turn lead to a reduction in the tangent stiffness ofthe core and a lowering of the critical stress for wrinkling. Thisis mainly a problem at points of load application and at joints,where the core experiences local loading, and may be avoidedby adequate thickening of the skin laminate, insertion of higherstrength core material locally or by other local design features.The adequacy shall be proved by testing or analysis unless pre-vious experience shows the solution is adequate.

C 800 Element size and distribution of elements801 The size, number and distribution of elements requiredin an actual FEM model depend on the type of analysis to beperformed, on the type of elements used and on the type ofmaterial applied.802 The choice of the mesh should be based on a systematiciterative process, which includes mesh refinements in areaswith large stress/strain gradients.803 Generally, as beam and shell elements have five or sixdegrees of freedom in each node, good results can be obtainedwith a small number of elements. As solid elements only havethree degrees of freedom in each node, they tend to be stiffer;hence, more elements are needed.804 The shape and order of the elements influence therequired number of elements. Triangular elements are stifferthan quadrilateral elements, and first-order elements are stifferthan second-order elements.

Guidance note:The required number of elements and its dependency on the elementshape are illustrated in an example, in which a cantilever is modelledby beam, membrane, shell and solid elements, see Figure 3.


Figure 3 Cantilever

Guidance note:Table C1 gives the required number of elements as a function ofthe element type applied, and the corresponding analysis resultsin terms of displacements and stresses are also given.


805 The performance of the model is closely linked to thetype of elements and the mesh topology that is used. The fol-lowing guidance on mesh size etc. assumes the use of 4-nodeshell or membrane elements in combination with 2-node beamor truss elements. The stiffness representation of 3-node mem-brane or shell elements is relatively poor and their use shouldbe limited as far as practical. 806 The shape of 4-node elements should be as rectangularas possible, particularly where in-plane shear deformation isimportant. Skew elements will lead to inaccurate element stiff-ness properties.807 Element formulation of the 4-node elements can requireall four nodes to be in the same plane. Unintended fixation ofa node can occur if it is “out of plane” compared to the otherthree nodes. The fixation will be seen as locally high stressesin the actual elements. Double curved surfaces should there-fore be modelled with 3-node elements instead of 4-node ele-ments. However, some structural analysis programs adjust theelement formulation such that "out of plane" elements does notnecessary create significant errors in the structural analysis.808 Provided that 4-node element formulations include lin-ear in-plane shear and bending stress functions, the same ele-ment size may be used for both 4-node shell elements and 8-node shell elements.809 The use of higher level elements such as 8-node or 6-node shell or membrane elements will not normally lead toreduced model size. 8-node elements are, however, less sensi-tive to element skewness than 4-node elements, and have no“out of plane” restrictions. In addition, 6-node elements pro-vide significantly better stiffness representation than 3-nodeelements. The use of 6-node and 8-node elements is preferred. 810 The mesh size should be decided considering properstiffness representation and load distribution of sea pressure onshell elements or membrane elements.811 The following guideline can be used for the elementselection and distribution for the present design of a free falllifeboat in composite or sandwich type of material:

— Laminate skins: can be modelled using shell elements.This is relevant for the inner and outer laminate in the can-opy and for the outer laminate in the bottom. The shell ele-ments should be layered and have different orthotropicmaterial properties for each layer.

— Core material: (e.g. structured foam, balsa wood or syntacticfoam) can be modelled using solid elements with orthotropicmaterial properties. Also buoyancy foam can be modelledusing solid elements. Limited shear strength or crushing

100 N

10 mm

100 mm

E = 2.1⋅105 N/mm2

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resistance should be included in a nonlinear analysis.— Sandwich structured composites: can be made using shell ele-

ments for the laminated skins and solid elements for the core. — Girders and stiffeners can be modelled using beam elements.

— Brackets can normally be omitted in a global analysis.

One example of suitable element mesh with suitable elementsizes is shown in Figure 4.

812 The aspect ratio is the ratio between the side lengths ofthe element. The aspect ratio should ideally be equal to 1, butaspect ratios of up to 3 to 5 do usually not influence the resultsand are thus acceptable.813 Element shapes should be kept compact and regular toperform optimally. Different element types have different sen-sitivities to shape distortion. Element compatibility shall bekept satisfactory to avoid locally poor results, such as artificialdiscontinuities. Mesh should be graded rather than piecewiseuniform, thereby avoiding great discrepancy in size between

adjacent elements.814 The eccentricity of beam elements should be included. Ifthe program does not support eccentricity of profiles, the mod-elled bending properties of the beams should include theattached total plate flange.815 By applying composite material rather than steel, thestructural ability to redistribute the stresses becomes signifi-cantly reduced; hence the attention to the details and the needsfor a finer mesh must be enhanced.

Figure 4 Global finite element model of lifeboat (symmetric half of lifeboat)

C 900 Element quality901 The results achieved by a certain type and number of ele-ments depend on the quality of the elements. Several measures

for the quality of elements can be used; however, the mostcommonly used are aspect ratio and element warping.902 Element warping is the term used for nonflatness or

Table C1 Analysis of cantilever with different types of elementsElement type Description Number of

elementsuy

[mm]σx,node

[N/mm2]σx,element[N/mm2]

Analytical result - 1.9048 600 600BEAM2D Beam element, 2 nodes per element, 3 DOF per node,

ux, uy and θz10 1.9048 600 6001 1.9048 600 600

PLANE2D Membrane element, 4 nodes per element, 2 DOF per node, ux and uy

10 x 1 1.9124 570 0

TRIANG Membrane element, 3 nodes per element, 2 DOF per node, ux and uy

10 x 1 x 2 0.4402 141 14120 x 2 x 2 1.0316 333 33340 x 4 x 2 1.5750 510 510

SHELL3 Shell element, 3 nodes per element, 6 DOF per node 20 x 2 x 2 1.7658 578 405SOLID Solid element, 8 nodes per element, 3 DOF per node

ux, uy and uz10 x 1 1.8980 570 570

TETRA4 Solid element, 4 nodes per element, 3 DOF per node ux, uy and uz

10 x 1 x 1 0.0792 26.7 26.720 x 2 x 1 0.6326 239 23940 x 4 x 1 1.6011 558 558

TETRA4R Solid element, 4 nodes per element, 6 DOF per node 20 x 2 x 1 1.7903 653 487

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twist of the elements. Even a slight warping of the elementsmay influence the results significantly.903 Most available FEM programs can perform checks ofthe element quality, and they may even try to improve the ele-ment quality by redistribution of the nodes.904 The quality of the elements should always be checkedfor an automatically generated mesh, in particular, for theinternal nodes and elements. It is usually possible to generategood quality elements for a manually generated mesh.905 With regard to automatically generated high-order ele-ments, care should be taken to check that the nodes on the ele-ment sides are placed on the surface of the model and not juston the linear connection between the corner nodes. This prob-lem often arises when linear elements are used in the initial cal-culations, and the elements are then changed into higher-orderelements for a final calculation.906 Benchmark tests to check the element quality for differ-ent element distributions and load cases are given byNAFEMS. These tests deal with beam, shell and solid ele-ments, as well as static and dynamic loads.907 The following requirements should be satisfied in orderto avoid ill-conditioning, locking and instability:

— a stiff element shall not be supported by a flexible element,but rigid-body constraints should be imposed on the stiffelement

— for plane strain and solid problems, the analyst shall not letthe Poisson’s ratio approach 0.5, unless a special formula-tion is used

— 3-D elements, Mindlin plate or shell elements shall not beallowed to be extremely thin

— the analyst shall not use reduced integration rule withoutbeing aware of possible mechanisms (e.g. “hourglassnodes”).

Guidance note:Some of the difficulties associated with ill-conditioning, lockingand instability can be detected by error tests in the coding, suchas a test for the condition number of the structure stiffness matrixor a test for diagonal decay during equation solving. Such testsare usually made posteriorly rather than priorly.


C 1000 Boundary conditions1001 The boundary conditions applied to the model shouldbe as realistic as possible. This may require that the FEMmodel becomes extended to include element models of struc-tural parts other than the particular one to be investigated. Onesituation where this comes about is when the true supports of aconsidered structure have stiffness properties which cannot bewell-defined unless they are modelled by means of elementsthat are included in the FEM model. When such an extended FEM model is adopted, deviationsfrom the true stiffness at the boundary of the structural part inquestion may then become minor only. As a consequence ofthis, the nonrealistic effects due to inadequately modelledboundary conditions, become transferred further away to theneighbouring structural parts or sub-parts, which are now rep-resented by elements in the extended FEM model.1002 The boundary conditions for the global structuralmodel should reflect simple supports that will avoid built-instresses. A three-two-one fixation, as shown in Figure 5, can beapplied. Other boundary conditions may be used if desirable.The fixation points should be located away from areas of inter-est, as the loads transferred from the hydrodynamic load anal-ysis otherwise may lead to imbalance in the model. Fixationpoints are often applied at the centreline close to the aft and theforward ends of the vessel.

Figure 5 Example showing suggested boundary conditions

C 1100 Types of restraints1101 The types of restraints normally used are constrained orfree displacements/rotations or supporting springs. Other typesof restraints may be a fixed non-zero displacement or rotationor a so-called contact, i.e. the displacement is restrained in onedirection but not in the opposite direction.1102 The way a FEM program handles the fixed boundarycondition may vary from one program to another. Oneapproach is to remove the actual degree of freedom from themodel; another is to apply a spring with a large stiffness at theactual degree of freedom. The latter approach may lead to sin-gularities if the stiffness of the spring is much larger than thestiffness of the element model. Evidently, the stiffness can betoo small, which may also result in singularities. An appropri-

ate value for the stiffness of such a stiff spring may be approx-imately 106 times the largest stiffness of the model.1103 As the program must first identify whether the dis-placement has to be constrained or free, the contact boundarycondition requires a nonlinear calculation.1104 Support conditions shall be treated with care. Appar-ently minor changes in support can substantially affect results.In FE models, supports are typically idealized as completelyrigid, or as ideally hinged, whereas actual supports often liesomewhere in between. In-plane restraints shall also be care-fully treated.

C 1200 Symmetry and antimetry1201 Other types of boundary conditions are symmetric and

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antimetric conditions, which may be applied if the model andthe loads possess some kind of symmetry. Taking such sym-metry into account may reduce the size of the FEM model sig-nificantly.1202 The two types of symmetry that are most frequentlyused are planar and rotational symmetries. The boundary con-ditions for these types of symmetry can normally be defined inan easy manner in most FEM programs by using appropriatecoordinate systems.1203 The loads for a symmetric model may be a combinationof a symmetric and an antimetric load. This can be consideredby calculating the response from the symmetric loads for amodel with symmetric boundary conditions, and adding theresponse from the antimetric loads for a model with antimetricboundary conditions.1204 If both model and loads have rotational symmetry, asectional model is sufficient for calculating the response.1205 Some FEM programs offer the possibility to calculatethe response of a model with rotational symmetry by a sec-tional model, even if the load is not rotational-symmetric, asthe program can model the load in terms of Fourier series.

C 1300 Loads1301 The loads applied for the FEM calculation are usuallystructural loads, however, temperature loads may also be rele-vant.1302 Structural loads consist of nodal forces and momentsand of surface pressure. Nodal forces and moments are easilyapplied, but may result in unrealistic results locally. This is dueto the fact that no true loads act in a single point. Thus, appli-cation of loads as pressure loads will in most cases form themost realistic way of load application.

D. DocumentationD 100 Model101 The results of a FEM analysis are normally documentedby plots and printouts of selected extreme response values.However, as the structural FEM model used can be very com-plex, it is important also to document the model itself. Evenminor deviations from the intention may give results that donot reflect reality properly.102 The input for a FEM model must be documented thor-oughly by relevant printouts and plots. The printed data shouldpreferably be stored or supplied as files on a CD-ROM103 The results of a FEM analysis can be documented by alarge number of plots and printouts, which can make it an over-whelming task to find out what has actually been calculatedand how the calculations have been carried out.104 The documentation for the analysis should clearly docu-ment which model is considered, and the relevant resultsshould be documented by plots and printouts.105 The model aspects listed in 200 through 700 can andshould be checked prior to execution of the FEM analysis.

D 200 Geometry control201 A verification of the geometric model by a check of thedimensions is an important and often rather simple task. Thissimple check may reveal if numbers have unintentionally beenentered in an incorrect manner.

D 300 Mass – volume – centre of gravity301 The mass and volume of the model should always bechecked. Similarly, the centre of gravity should correspondwith the expected value.

D 400 Material401 Several different materials can be used in the same FEMmodel. Some of these may be fictitious. This should bechecked on the basis of plots showing which material isassigned to each element, and by listing the material proper-ties. Here, care should be taken to check that the material prop-erties are given according to a consistent set of units.402 Plots should be made and checked in order to verify thatmaterial properties, material types and plate thicknesses aredistributed correctly.

D 500 Element type501 Several different element types can be used, and hereplots and listing of the element types should also be presented.

D 600 Local coordinate system601 With regard to beam and composite elements, the localcoordinate systems should be checked, preferably, by plottingthe element coordinate systems.602 Verification whether the many different relevant co-ordinate systems have been applied correctly shall be consid-ered.

D 700 Loads and boundary conditions701 The loads and boundary conditions should be plotted tocheck the directions of these, and the actual numbers should bechecked from listings. To be able to check the correspondencebetween plots and listings, documentation of node/elementnumbers and coordinates may be required.

D 800 Reactions801 The reaction forces and moments are normally calcu-lated by the FEM programs and should be properly checked.As a minimum, it should be checked that the total reaction cor-responds with the applied loads. This is especially relevantwhen loads are applied to areas and volumes, and not merelyas discrete point loads. For some programs it is possible to plotthe nodal reactions, which can be very illustrative.802 A major reason for choosing a FEM analysis as the anal-ysis tool for a structure or structural part is that no simple cal-culation can be applied for the purpose. This implies that thereis no simple way to check the results. Instead checks can becarried out to make probable that the results from the FEManalysis are correct.

D 900 Mesh refinement901 The simplest way of establishing whether the presentmodel or mesh is dense enough is to re-mesh the model with amore dense mesh, and then calculate the differences betweenanalysis results from use of the two meshes. As several meshesmay have to be created and tried out, this procedure can, how-ever, be very time-consuming. Moreover, as modelling simpli-fication can induce unrealistic behaviour locally, thisprocedure may in some cases also result in too dense meshes.Instead, an indication of whether the model or mesh is suffi-cient would be preferable.902 Need for mesh refinement is usually indicated by visualinspection of stress discontinuities in the stress bands. Analo-gous numerical indices are also coded.

D 1000 Results1001 Initially, the results should be checked to see if theyappear to be realistic. A simple check is made on the basis ofan evaluation of the deflection of the component, whichshould, naturally, reflect the load and boundary conditionsapplied as well as the stiffness of the component. Also, thestresses on a free surface should be zero.1002 Most commercial FEM programs have some means forcalculation of error estimates. Such estimates can be defined in

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several ways. One of the most commonly used estimates is anestimate of the error in the stress. The estimated ‘correct’ stressis found by interpolating the stresses by the same interpolationfunctions as are used for displacements in defining the elementstiffness properties. Another way of getting an indication of stress errors is givenby means of comparison of the nodal stresses calculated at anode for each of the elements that are connected to that node.Large variations indicate that the mesh should be denser.1003 If the results of the analysis are established as linearcombinations of the results from single load cases, the loadcombination factors used should be clearly stated. 1004 The global deflection of the structure should be plottedwith appropriately scaled deflections. For further evaluation,deflection components could be plotted as contour plots to seethe absolute deflections.For models with rotational symmetry, a plot of the deflectionrelative to a polar coordinate system may be more relevant forevaluation of the results.1005 Stresses and strains may be evaluated in nodal points orGauss points. Gauss point evaluation is generally most accu-rate, in particular for layered composites, in which the distribu-tion of stresses is discontinuous, and should therefore beapplied when possible.

Guidance note:The analyst should beware that Gauss point results are calculatedin local (element or ply based) coordinates and must be trans-formed (which is automatically performed in most FE codes) inorder to represent global results. Thus, Gauss point evaluation ismore time-consuming than nodal point calculations.


1006 All components of the stresses are calculated, and it

should be possible to plot each component separately to eval-uate the calculated stress distribution.1007 The principal stresses should be plotted with an indica-tion of the direction of the stress component, and these direc-tions should be evaluated in relation to the expecteddistribution.1008 As for the evaluation of the resulting stresses, also thecomponents of the resulting strains and the principal strainshould be plotted in an evaluation of the results from the anal-ysis.1009 Computed results shall be checked for self-consistencyand compared with, for example, approximate analyticalresults, experimental data, textbook and handbook cases, pre-ceding numerical analysis of similar problems and results pre-dicted for the same problem by another program. Ifdisagreements appear, then the reason for the discrepancy shallbe sought, and the amount of disagreement adequately clari-fied.1010 Analysis results shall be presented in a clear and con-cise way using appropriate post-processing options. The use ofgraphics is highly recommended, i.e. contour plots, (amplified)displacement plots, time histories, stress and strain distribu-tions etc.1011 The results shall be documented in a way to help thedesigner in assessing the adequacy of the structure, identifyingweaknesses and ways of correcting them and, where desired,optimizing the structure.1012 FEM analysis results shall be verified by comparingagainst relevant analytical results, experimental data and/orresults from previous similar analysis.1013 Results shall be checked against the objectives of theanalysis.

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