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Ship Structural ComponentsShip Structural Components
EN358EN358
Ship StructuresShip Structures
CDR Jeffrey W. Stettler, USN, PhDCDR Jeffrey W. Stettler, USN, PhDAssistant Professor, Permanent Military ProfessorAssistant Professor, Permanent Military Professor
Ship Structural ComponentsShip Structural Components
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?
Ship Structural ComponentsShip Structural Components
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.).
Ship Structural ComponentsShip Structural Components
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)
Ship Structural ComponentsShip Structural Components
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.
Ship Structural ComponentsShip Structural Components
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.
Ship Structural ComponentsShip Structural Components
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
Ship Structural ComponentsShip Structural Components
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
Ship Structural ComponentsShip Structural Components
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
Ship Structural ComponentsShip Structural Components
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 frames
Can be used with any framing systemCan be used with any framing system
Ship Structural ComponentsShip Structural Components
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
Ship Structural ComponentsShip Structural Components
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
Ship Structural ComponentsShip Structural Components
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
Ship Structural ComponentsShip Structural Components
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