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MARINE TERMINAL DESIGN PRACTICESGANGWAYS FOR SHIP / SHORE ACCESS Section

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1 of 17EXXONENGINEERING PROPRIETARY INFORMATION - For Authorized Company Use Only

DateDecember, 1999

EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.

CONTENTSSection Page

SCOPE ............................................................................................................................................................ 3

REFERENCES ................................................................................................................................................ 3

INTRODUCTION ............................................................................................................................................. 3

TYPES OF SHORE BASED GANGWAYS ..................................................................................................... 3MOBILE GANGWAY SYSTEMS............................................................................................................. 3

Conventional ........................................................................................................................................ 3Platform Mounted................................................................................................................................. 3Carriage Mounted ................................................................................................................................ 3

STATIONARY GANGWAY SYSTEMS ................................................................................................... 3Column Mounted.................................................................................................................................. 3Tower Mounted .................................................................................................................................... 4Shore Accommodation Ladder............................................................................................................. 4

SELECTION OF A GANGWAY SYSTEM..................................................................................................... 12GENERAL CONSIDERATIONS............................................................................................................ 12DESIGN OPERATING ENVELOPE...................................................................................................... 12

DESIGN CRITERIA....................................................................................................................................... 15GENERAL DESIGN REQUIREMENTS ................................................................................................ 15LOAD CONDITIONS............................................................................................................................. 15

Self-Weight Load................................................................................................................................ 15Live Load ........................................................................................................................................... 15Wind Load.......................................................................................................................................... 15Earthquake Load................................................................................................................................ 16

MATERIALS.......................................................................................................................................... 16

MANEUVERING AND CONTROL SYSTEMS .............................................................................................. 16

ELECTRICAL ISOLATION ........................................................................................................................... 17

DESIGN PRACTICES MARINE TERMINALSection

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2 of 17GANGWAYS FOR SHIP / SHORE ACCESS

DateDecember, 1999 PROPRIETARY INFORMATION - For Authorized Company Use Only

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TABLESTable 1 Types Of Gangway Systems ...........................................................................................4Table 2 Types of Gangway Loads..............................................................................................15

FIGURESFigure 1 Conventional Gangway ...................................................................................................5Figure 2 Platform Mounted Mobile Gangway.................................................................................6Figure 3 Carriage Mounted Mobile Gangway With Track Parallel To Pier Face............................7Figure 4 Carriage Mounted Mobile Gangway With Track Perpendicular To Pier Face..................8Figure 5 Side-Mounted, Shore Accommodation Ladder................................................................9Figure 6 Front-Mounted Shore Accommodation Ladder................................................................9Figure 7 Column Mounted Gangway ...........................................................................................10Figure 8 Tower Mounted Gangway..............................................................................................11Figure 9 Basic Gangway Operating Envelope.............................................................................13Figure 10 Design Operating Envelope Data ..................................................................................14

Revision Memo

12/99 Original Issue of Design Practice XXXI-N


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SCOPEThis design practice covers shore based gangway systems for use at conventional marine piers and sea islands to allowpersonnel to safely and efficiently pass between moored vessels and shore side facilities. Procedures are provided forcalculating the required operating envelope for gangways serving various sized vessels and discusses the necessaryrequirements that should be included in a gangway Design Basis Memorandum or Design Specification. This design practicedoes not cover detailed gangway design, fabrication, or installation.

REFERENCESEE.10TT.78, Shore Based Gangway Systems, June, 1978International Safety Guide for Oil Tankers & Terminals (ISGOTT), 4th Ed., 1996

INTRODUCTIONMarine terminal operations require that shore personnel periodically board vessels at their terminal. For example, after thevessel first moors, the berth operator or another appropriate shore representative boards the vessel to complete a ship/shoresafety checklist and to conduct a pre-cargo transfer conference. While the vessel is at the berth, shore personnel will periodicallyboard the vessel to recheck certain items on the ship/shore safety checklist. Shore personnel also are typically involved inmeasuring and sampling the vessel's cargo tanks at certain times in the cargo transfer procedure.

Either a ship mounted or shore based gangway can be used to provide a means for personnel to pass between a moored shipand the deck of a conventional pier or sea island. Every ship will have some form of gangway. Larger vessels, normally thoseabove 10,000 dwt, will have a permanently mounted, power operated gangway. Smaller vessels and barges may only carry amanual gangway.

However, ship gangway systems can be operationally limited due to design, damage, equipment malfunction, or space limitationson the berth deck to land the gangway. In addition, local tidal conditions or the overall pier layout may restrict the use of theship's gangway. For these reasons, new Exxon terminals should include a shore-based gangway as part of the design basis.

TYPES OF SHORE BASED GANGWAYS

Shore gangway systems can generally fall into one of two categories depending on how the onshore end of the gangway is fixedto the berth: "mobile systems" and "stationary gangway systems". Brief descriptions of each type of system are given below.

MOBILE GANGWAY SYSTEMS

Conventional

The simplest type of gangway system, consisting of a fixed length walkway with handrails and wheels or a roller on the shore endwith wheels or gunwale clips at the ship end. Moved about manually or with the assistance of a shore crane.

Platform Mounted

A gangway attached to a tower that is mounted on a platform supported by wheels. The wheels of the platform may be powered,or the structure may be pulled about the pier deck by a small, motorized vehicle. The gangway is normally controlled by ahydraulic piston between the tower and the underside of the gangway.

Carriage Mounted

Consists of a conventional type gangway with the shore end attached to a carriage, which moves on tracks either parallel orperpendicular to the pier face. Normally positioned with the assistance of a shore crane.

STATIONARY GANGWAY SYSTEMS

Column Mounted

The most versatile type of gangway system, consisting of a telescopic gangway with it onshore end connected to the top of acolumn fixed to the pier deck. Column mounted gangways are usually provided with self-leveling steps which allow safe accessfor gangway inclinations up to 50 - 55 degrees.


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TYPES OF SHORE BASED GANGWAYS (Cont)

Tower Mounted

The most sophisticated and expensive type of gangway system, consisting of a fixed length or telescopic gangway connected toa carriage mounted on vertical tracks secured to the face of a tower. The gangway can be raised or lowered to any stage (floor)of the tower to minimize the gangway angle with the vessel deck.

Shore Accommodation Ladder

Basically a ship's accommodation ladder permanently mounted on the pier deck. Provides a good solution for providing accessto small vessel decks that are always below the pier deck elevation. The gangway is raised and lowered by its own motorizedderrick. This system is unique in that the ship end does not actually sit on the vessel deck. Rather it is held alongside the vesselat the proper elevation by the gangway derrick. The operator must be periodically reposition the gangway as the vessel changesdraft or the tide changes the vessel deck elevation relative to the pier deck.Table 1 lists the various types of gangway systems, the range of vessel sizes they can typical accommodate, and theiradvantages and disadvantages. A more detailed description of each type of gangway system can be found in ER&E Report,EE.10TT.78, Shore Based Gangway Systems, June 1978.

TABLE 1TYPES OF GANGWAY SYSTEMS

TYPE ILLUSTRATION TYPICAL RANGE OFSHIP SIZE(1) ADVANTAGE DISADVANTAGE

Conventional (MobileSystem)

Figure 1 0.5 kdwt - 1 kdwt1 kdwt - 5 kdwt

5 kdwt - 20 kdwt20 kdwt -50 kdwt

Low cost, easymaneuverability, andMinimal Maintenance

Long lengths required forvessels with high freeboardrelative to pier deck.Not practical when vesseldeck below pier deck

Platform Mounted(Mobile System)

Figure 2 10 kdwt - 50 kdwt50 kdwt - 100 kdwt

Easily positioned to avoidvessel deck obstructions ifsufficient pier spaceavailable to maneuvergangway

Requires very large pier deckarea for operation andstowage

Carriage Mounted withTrack Parallel to PierFace (Mobile System)


Easily positioned to avoidvessel deck obstructions

May interfere with cargotransfer equipment

Carriage Mounted withTrack Perpendicular toPier Face, Attached toSide of Pier (Mobilesystem)


No pier deck space requiredfor operation and stowage

Allowable slew motions maybe limited when vessel deckbelow pier deck

Shore AccommodationLadder (StationarySystem)

Figure 5 0.5 kdwt - 1 kdwt1 kdwt - 5 kdwt

Simple to operate, quicklypositioned, and avoidsobstructions on vessel deck

Limited to small vessels withdecks below the pier deck.Must be periodicallyrepositioned

Column Mounted(Stationary System)

Figure 6 10 kdwt - 50 kdwt50 kdwt - 100 kdwt100 kdwt - 500 kdwt

Simple to operate, quicklypositioned, and easy toavoid obstructions onvessel deck

Relatively high foundationloads, personnel must alwaysclimb to top of column, evenwhen vessel deck elevation isbelow pier deck

Tower Mounted(Stationary System)

Figure 7 100 kdwt - 500 kdwt Simple to operate, quicklypositioned, and easy toavoid obstructions onvessel deck.Gangway inclinations canbe kept to a minimum byraising or lowing carriage ontower

High cost.Most maintenance intensiveoption

Note: (1) Different size or length of gangway required for each ship range


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FIGURE 1CONVENTIONAL GANGWAY

Steps Or Walkway

PLAN

ELEVATION

Offshore End

GunwaleClips OrRollers/ WheelsOnshore End

Rollers/Wheels

Handrails

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FIGURE 2PLATFORM MOUNTED MOBILE GANGWAY

Bulwark Ladder

Fixed-Length Gangway

Hydraulic Luffing Ram

Hydraulic Slewing Mechanism Control Unit

Stairway

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FIGURE 3CARRIAGE MOUNTED MOBILE GANGWAY WITH TRACK PARALLEL TO PIER FACE

Access Ladder

Fender

Tracks

Pier FaceFender

ShipDeck

PLAN

Ship Railing

Ship Deck Bulwark Ladder

Fender Fender

Fore & Aft Travel of Carriage-Gangway Unit

TrackPierDeck

Carriage

Ship High andLow Deck LevelsFixed-Length Gangway

PierDeck

Fender

PierFace

SIDE

FRONT

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FIGURE 4CARRIAGE MOUNTED MOBILE GANGWAY WITH TRACK PERPENDICULAR TO PIER FACE

ShipRailing

Ship SidePierSide

AccessStairway

Fender

Carriage

Ship

Pier

PLAN

Ship Deck

Shore Crane

Bulwark Ladder

Fixed-Length Gangway Max. Ship Deck Level

Min. Ship Deck Level

ShipRailing Track

Fender Drift

Pier Side

Carriage

Fender Deflection

SIDE

BreastingLine

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FIGURE 5SIDE-MOUNTED, SHORE ACCOMMODATION LADDER

FIGURE 6FRONT-MOUNTED SHORE ACCOMMODATION LADDER


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FIGURE 7COLUMN MOUNTED GANGWAY

Fender

Min. ShipDeck Level

Access Stairway

Telescopic Gangway

Max. ShipDeck Level

Pier Deck

Fixed Column

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FIGURE 8TOWER MOUNTED GANGWAY

Ship Railing

Ship Side

Ship Deck

Tower Stairway

Gangway ControlUnit

Turntable

Fender

PLAN

Pier Deck

Pier

Tower FixedTo Pier Deck

BreastingLine

Min. ShipDeck Level

Max. ShipDeck Level

Bulwark Ladder

VerticalTracks

ShipRailing

Fixed-Length or TelescopicGangway

Gangway Control Unit

Carriage

CraneFire Fighting

Equipment

FenderDrift Off

SIDE DP31NF08


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SELECTION OF A GANGWAY SYSTEM

GENERAL CONSIDERATIONSBecause of the wide variety of gangways available, and the specialty nature of gangway design, it is normal practice to prepare agangway "Duty Specification" and allow a number of vendors to propose the design that they believe will best meet the facilityneeds. For a new facility for 10 kdwt vessels and larger, the column mounted gangway will often end up being the system ofchoice. Experience has shown that this type of gangway is highly reliable, can easily accommodate a large operating envelope,and can be used with a wide variety of vessel types and sizes.Ship/shore access for smaller vessels can be more complex, sometimes requiring that two separate gangways be provided, onefor use when the vessel deck is below the pier deck, and one for use when the vessel deck is above the pier deck. In this case, aconventional gangway may be specified for use when the vessel deck is at or above the pier deck, and a shore accommodationtype gangway installed for use when the vessel deck is below the pier deck. For locations where there is negligible tidal range(an infrequent occurrence), a small column mounted gangway can be used for vessels less than 10 kdwt.When selecting a gangway for existing facilities, the space available and the load carrying capacity of the pier deck are the mostsignificant factors effecting the choice of gangway. Detailed drawings of the pier should be provided to the vendor illustrating theopen areas on the pier for locating a shore-based gangway. A vendor may be able to use existing structures and equipment onthe pier deck, such as a hose tower or shore crane, in the gangway design. The dimensions, locations on the pier, and designload capacities of such structures and equipment should be given to the vendor. The use of existing structures or equipmentmay lower the total investment cost for a gangway. However, checks must be made to insure that the existing structures orequipment have adequate capacity for the additional loads imposed by the gangway.

DESIGN OPERATING ENVELOPEThe operating envelope of a gangway significantly influences the type and design of gangway that might be proposed by avendor. A shore-based gangway operating envelope is defined as that volume in space within which the ship's end of thegangway must be able to operate. At all positions within the envelope, the gangway must clear the ship's rail. The operatingenvelope takes into consideration the maximum and minimum freeboard of the maximum and minimum sized ship (based on tidalvariations and changes in ship draft), as well as a safety allowance for ship surge along the pier face and drift away from the pier.A basic gangway operating envelope is shown in Figure 9. The specific information that defines the operating envelope is shownin Figure 10. If a shore accommodation ladder, as shown in Figure 5, is used, only the upper and lower bounds of the envelopeneed be considered, as this type of gangway does not actually cross over the ship's rail.


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SELECTION OF A GANGWAY SYSTEM (Cont)

FIGURE 9BASIC GANGWAY OPERATING ENVELOPE

CL

DriftEnvelope

Working Envelope

CL

PlanView

Gangway

Berth

ElevationView

Working Envelope

DriftEnvelope

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SurgeAllowance


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SELECTION OF A GANGWAY SYSTEM (Cont)

FIGURE 10DESIGN OPERATING ENVELOPE DATA

2

34

5

1

Beth Platform

OperatingEnvelope

Shore Gangway

Largest Ship'sMain Deck

L.L.W.

H.H.W.

1. Height of Plaform Deck Above low Water (LLW)2. Maximum Height of Vessel Deck (Largest Vessel) above High High Water (HHW)3. Minimum Height of Vessel Deck (Smallest Vessel) above Low Low Water (LLW)4. Fender Depth (Vessel Standoff from Berth Face)5. Height of Ship's Rail6. Gangway Operating Allowance7. Gangway Drift Allowance DP31Nf10

6 7

Smallest Ship'sMain Deck


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SELECTION OF A GANGWAY SYSTEM (Cont)The height of the berth platform deck above low, low water, fender depth, and water level elevations should be readily availablefrom the berth elevation drawings or can be requested directly from the operating affiliate. The height of the ship's rail is normallytaken as 1.2 meters and is not normally a function of ship size. Gangway drift allowance is normally taken as 3 m (10 ft) in alldirections (off the berth and both forward and aft surge along the berth).The gangway operating allowance is dependent on the size of the vessel and can vary significantly from one vessel size toanother. It is important to discuss this variable with the operating affiliate and the operating affiliate's marine depart. Ifinternational ships are to use the berth, discussions should also be held with Standard Marine Services, Ltd., Exxon's Marine SkillCenter in Southampton, U.K. For U.S.A. terminals, discussions should be held with SeaRiver Maritime, Inc., Exxon's U.S. basedshipping company.

DESIGN CRITERIA

GENERAL DESIGN REQUIREMENTSGangways must provide safe footing at all operating inclinations. Generally, gangways should not be used at angles ofinclination greater than 35 degrees. At sites that require a greater angle of inclination than 35 degrees, a powered gangway with"self-leveling steps" should be provided.All gangways should meet the following general design criteria:a. Minimum walkway width of 2 ft (0.6 m) for gangways less than 13 ft (4 m) in length and 3.2 ft (1 m) width for longer

gangwaysb. Continuous handrail height of 3.9 ft (1.2 m), including the "step-down" from the gangway walkway to the vessel deck (if

provided)c. Store behind deflected fender faced. Designed for a specified operating envelope

LOAD CONDITIONSThere are four load sources that must be considered in the design of a marine gangway as listed in Table 2. The basis for theselection of these loads must be developed during the design basis memorandum or design specification preparation phase of aproject.

TABLE 2 - TYPES OF GANGWAY LOADS

TYPE OF LOAD ABBREVIATION

Self-Weight Load DLLive Load LLWind Load WL

Earthquake Load EL

Self-Weight Load

Self-Weight Load is the gravity loading acting on the mass of the individual components and members that make up the completegangway. For gangways to be installed in locations that experience ambient temperatures below freezing, the self weight load shouldinclude a specified ice build up (ice specific gravity = 0.80) of at least I inch (2.5 mm). For arms to be installed in areas ofespecially severe cold weather conditions, additional ice build up may be specified after consultation with the operating affiliate orlocal project team.

Live Load

Live loading (personnel using the gangway) only applies to the operating load condition. All gangway walkways should bedesigned for a minimum operating load of 50 psf (2.4 kN/m2). Handrails should be designed for a load of 25 psf (1.2 kN/m2).

Wind Load

Wind load is the air pressure due to wind acting on the surface of the gangway (including any ice build-up). The wind pressuresshould be based on the calculation procedures in IP 4-1-5, Wind Design Loads, and ASCE 7, Minimum Design Loads forBuildings and Other Structures.


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DESIGN CRITERIA (Cont)Wind loading is based on the design wind (fastest mile wind speed) which has been established for the site. The magnitude ofthe wind pressure also depends on the surface roughness and topography of the site, and the geometric shape and height of thegangway. A listing of design wind speeds for worldwide locations is provided in Section XXIX-A. These design wind speeds areapplicable only when the gangway is in the stored position.The selection of the maximum wind speed for the gangway in the operating condition (maneuvering or resting on the ship's deck)is usually set by the operating affiliate. Often this value is taken as 56 mph (25 m/sec). However, In all cases the operating windspeed should be higher than the mooring system wind limit to insure the safety of shore personnel who may need to board thevessel to disconnect loading arms or hoses in high wind conditions.The velocity exposure coefficient, Kz used in ASCE 7 takes into account changes in wind speed with height above ground andwith the nature of the surroundings (types of terrain). The wind speed varies with height because of ground friction, and theamount of friction varies with ground roughness. Marine terminal facilities are generally considered to be located in areas havingsurface roughness characteristic similar to one of two ASCE 7 Exposure categories:

1. Exposure D Flat, unobstructed areas directly exposed to wind flowing over large bodies of water (greater than 1mile wide); and extending inland 1500 ft (457 m) from the shoreline.

2. Exposure C Flat, open terrain with scattered obstructions having heights generally less than 30 ft (9 m).The majority of marine terminals are located in Exposure D terrain. Exposure C should only be used for those sites that aresurrounded on all sides by the appropriate terrain conditions such as a river terminal located some considerable distance inlandfrom the sea.A wind pressure, height variation formula must be included in the gangway design specification to allow the manufacturer tocalculate the wind pressure at various elevation of the gangway. Depending on the exposure category selected, one of thefollowing equations should be specified:

Exposure D PZ = P33 (0.696) (Z)2/10 0.86 P33

Exposure C PZ = P33 (0.369) (Z)2/7 0.8 P33where: PZ = wind pressure at Z ft above lowest low water, psf (Pa)

Z = height above lowest low water, ft (m)

Earthquake Load

Earthquake Load is the load generated due to rapid horizontal motions of the gangway structure base of the due to groundmovement in an earthquake. The magnitude of earthquake for which the gangway must be designed is described in terms of aSeismic Coefficient. Offsites Design Practice XXIX-J, Seismic Design should be consulted to determine the appropriateSeismic Coefficient to specify in the marine loading arm design specification

MATERIALSGangways may be constructed in steel, aluminum, or a combination of steel and aluminum. Usual practice is to constructmanual gangways entirely from aluminum. Aluminum manual gangways designed for small vessels are often light enough to behandled by one or two men. Manual gangways constructed in steel are acceptable, but are usually too heavy to be moved byhand, and therefore often require a crane to maneuver them onto or off of a vessel.Powered gangway support structures are usually constructed in steel, with the walkway from the support structure to the shipconstructed in aluminum to minimize the gravity loading applied to the support structure and the size of the hydraulic controlsystem required to maneuver the walkway to and from the vessel. Where steel and aluminum is used in combination, specialcare must be taken at the interface of the two materials to avoid the potential for "galvanic" corrosion.

MANEUVERING AND CONTROL SYSTEMSPowered gangways may be maneuvered by a variety of means. Both column mounted gangways and tower mounted gangwaysare classified as stationary systems. Only the actual walkway to the ship is maneuvered. The walkway of a column mountedgangway is normally maneuvered with large diameter hydraulic pistons. The walkway of a tower mounted gangway uses asystem of winches and lifting cables. The winches are often electrically driven, but may be hydraulic or air driven.Mobile gangway systems, such as a platform mounted gangway, normally have less sophisticated maneuvering and controlsystems. A typical platform mounted gangway is moved about the berth deck by a small, motorized vehicle such as a "fort lift"truck. Alternatively, platform mounted gangways have been provided with electrically driven wheels.


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MANEUVERING AND CONTROL SYSTEMS (Cont)Control systems for powered gangways may be either electro-hydraulic or totally hydraulic. Electro-hydraulic systems are moreexpensive but provide more reliability and less maintenance. Typically, selection of powered gangway operating systems is leftto the vendor to propose as part of the bid documentation.Powered gangways should provide for control of all motions of the gangway (luffing, slewing, telescoping, and transversing). Toprovide an adequate factor of safety, the hydraulic components of the gangway maneuvering and control system should be sizedtaking into account accelerative loads and 110% of the operating design wind load.

ELECTRICAL ISOLATIONThe underside of aluminum gangways should be protected with a hard plastic or wooden strip to prevent the gangway frombecoming an electrical path between the ship and shore. If wheels are fitted at one end of the gangway, they should be made ofa non-conductive material such as hard rubber.Aluminum is an excellent conductor of electricity. It is important to prevent an electrical path through the gangway to avoidpotential sparking when setting or removing the gangway from the ship. An electrical connection between the ship and the shorecan also cause a large drain on the terminal's cathodic protection system. Electrical isolation, including the design of gangwaysto avoid creating an electrical path between the ship and shore, is discussed in more detail in Section XXXI-J, Ship-To-ShoreElectrical Isolation.In addition to the above, aluminum equipment dragged or rubbed across rusty steel may leave a smear. If a dropped steelobject, such as a tool for example, strikes this smear, an incendive spark can be generated.

DP MANUALS INDEXMARINE TERMINAL DPs INDEXSCOPEREFERENCESINTRODUCTIONTYPES OF SHORE BASED GANGWAYSMOBILE GANGWAY SYSTEMSConventionalPlatform MountedCarriage Mounted

STATIONARY GANGWAY SYSTEMSColumn MountedTower MountedShore Accommodation Ladder

SELECTION OF A GANGWAY SYSTEMGENERAL CONSIDERATIONSDESIGN OPERATING ENVELOPE

DESIGN CRITERIAGENERAL DESIGN REQUIREMENTSLOAD CONDITIONSSelf-Weight LoadLive LoadWind LoadEarthquake Load

MATERIALS

MANEUVERING AND CONTROL SYSTEMSELECTRICAL ISOLATIONTABLESTABLE 1TYPES OF GANGWAY SYSTEMSTABLE 2 - TYPES OF GANGWAY LOADS

FIGURESFIGURE 1CONVENTIONAL GANGWAYFIGURE 2PLATFORM MOUNTED MOBILE GANGWAYFIGURE 3CARRIAGE MOUNTED MOBILE GANGWAY WITH TRACK PARALLEL TO PIER FACEFIGURE 4CARRIAGE MOUNTED MOBILE GANGWAY WITH TRACK PERPENDICULAR TO PIER FACEFIGURE 5SIDE-MOUNTED, SHORE ACCOMMODATION LADDERFIGURE 6FRONT-MOUNTED SHORE ACCOMMODATION LADDERFIGURE 7COLUMN MOUNTED GANGWAYFIGURE 8TOWER MOUNTED GANGWAYFIGURE 9BASIC GANGWAY OPERATING ENVELOPEFIGURE 10DESIGN OPERATING ENVELOPE DATA

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