Ship Structural Components

Ship Structural ComponentsShip Structural Components

EN358EN358Ship StructuresShip Structures

CDR Jeffrey W. Stettler, USN, PhDCDR Jeffrey W. Stettler, USN, PhDAssistant Professor, Permanent Military ProfessorAssistant Professor, Permanent Military Professor


Ship’s Structures are unique for a variety of reasons. For example:

Ships are very BIG structures!

The shape of a ship is optimized for reasons other than just structural strength. What else is it optimized for?

Navy ships operate in a wide variety of environments and see a variety of static as well as dynamic/random loads. What kinds of loads?


A ship structure consists of a network of welded together cross-stiffened plates (sometimes referred to as a “grillage”). Plates are stiffened by welded girders (I-beams, T-beams, etc.).


Keel - Longitudinal center plane girder along bottom of the ship The ship’s “backbone”

Plating – Thin pieces closing in the top, bottom, and sides of structure. Outer plating (side shell and bottom plating)

Strakes = longitudinal rows of outer plating (e.g. garboard, sheer, deck strakes) Deck plating, inner bottom plating Bulkheads (longitudinal & transverse)


Longitudinals – Stiffeners which run longitudinally (parallel to the keel) along the bottom of the ship. Used to longitudinally stiffen the outer bottom plating.

Stringers – Stiffeners which run longitudinally along the sides of the ship. Used to stiffen and strengthen the outer side shell plating.

Deck Girders – Stiffeners which run longitudinally under decks. Used to stiffen and strengthen deck plating.


Frames – Stiffeners which run transversely from keel to main deck. Used to transversely stiffen and strengthen the outer plating.

Floors – Larger portion of the frames which run from the keel to the turn of the bilge. Used also as foundations for inner bottom plating.

Deck beams – Stiffeners which run transversely under decks. Used to stiffen and strengthen deck plating.


Types of framing systemsTypes of framing systemsTransverse Framing

For combating primarily hydrostatic and side impact loadsClosely spaced continuous frames with widely spaced longitudinals Used primarily for

– Short ships (lengths less than typical ocean waves: ~ 300ft) – Submarines

Thick side plating is requiredLongitudinal strength is relatively low


Types of framing systemsTypes of framing systemsLongitudinal Framing

For combating primarily longitudinal bending (flexure) loadsClosely spaced longitudinals and more widely spaced (deep

web) frames Side plating is comparably thin …primarily designed to keep

the water out


Types of framing systemsTypes of framing systemsCombination Framing

For combating combined loads More longitudinal members near top and bottom structureSide structure is primarily transverse WHY?Most Navy surface ships are of this type


Single Bottom ConstructionSingle Bottom ConstructionUsually found on tankers & small shipsUsually found on tankers & small shipsBottom transverse frames are known as “floors”Bottom transverse frames are known as “floors”

Floors are vertical structural members!Floors are vertical structural members! Floors support bottom plating - transfer the load to keel (& Floors support bottom plating - transfer the load to keel (&

keelsons) and side frameskeelsons) and side framesCan be used with any framing systemCan be used with any framing system


Double Bottom ConstructionDouble Bottom ConstructionAdvantages over Single Bottom ConstructionAdvantages over Single Bottom Construction

Stronger - provides more longitudinal materialStronger - provides more longitudinal material Provides volume in which to store liquids without taking up cargo Provides volume in which to store liquids without taking up cargo

spacespace Provides damage resistance in the bottomProvides damage resistance in the bottom

DisadvantagesDisadvantages More expensive to construct, higher maintenance costs More expensive to construct, higher maintenance costs Moves neutral axis of the ship down - causing higher stresses in Moves neutral axis of the ship down - causing higher stresses in

the deckthe deck


Structural Structural DrawingsDrawingsMidships Section Midships Section

Deep Frame, Deep Frame, ScantlingsScantlings

175,000 DWT Tanker

LWL = 1027 ftB = 158 ft

D = 83.75 ftT = 54.25 ft


Structural Structural DrawingsDrawingsMidships Midships

SectionSectionDeep Frame, Deep Frame,

ScantlingsScantlings

105,000 DWT

BulkerLWL = 818.3 ftB = 124.7 ft

D = 69 ftT = 50.75 ft


Structural Structural DrawingsDrawingsMidships Midships

SectionSectionScantlingsScantlings

DD-963Simplified midship

section showing shell plate straking plan

20.4# plate = 1/2 inch thick

Garboard Strake

Bilge Strake

Sheer Strake

Deck Stringer

Weld Seam Symbol

Ship Structural Components

Documents

ship structural components

strengthen deck plating

outer plating

bottom plating

run transversely

run longitudinally

usedto stiffen

ship