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EN358 Ship Structures. Ship Structural Components. CDR Jeffrey W. Stettler, USN, PhD Assistant Professor, Permanent Military Professor. Ship’s Structures are unique for a variety of reasons. For example: Ships are very BIG structures!

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EN358Ship Structures

Ship Structural Components

CDR Jeffrey W. Stettler, USN, PhD

Assistant 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 systems
    • Transverse Framing
      • For combating primarily hydrostatic and side impact loads
      • Closely spaced continuous frames with widely spaced longitudinals
      • Used primarily for
        • Short ships (lengths less than typical ocean waves: ~ 300ft)
        • Submarines
      • Thick side plating is required
      • Longitudinal strength is relatively low
Types of framing systems
    • Longitudinal Framing
      • For combating primarily longitudinal bending (flexure) loads
      • Closely spaced longitudinals and more widely spaced (deep web) frames
      • Side plating is comparably thin …primarily designed to keep the water out
Types of framing systems
    • Combination Framing
      • For combating combined loads
      • More longitudinal members near top and bottom structure
      • Side structure is primarily transverse WHY?
      • Most Navy surface ships are of this type
Single Bottom Construction
    • Usually found on tankers & small ships
    • Bottom transverse frames are known as “floors”
      • Floors are vertical structural members!
      • Floors support bottom plating - transfer the load to keel (& keelsons) and side frames
    • Can be used with any framing system
Double Bottom Construction
    • Advantages over Single Bottom Construction
      • Stronger - provides more longitudinal material
      • Provides volume in which to store liquids without taking up cargo space
      • Provides damage resistance in the bottom
    • Disadvantages
      • More expensive to construct, higher maintenance costs
      • Moves neutral axis of the ship down - causing higher stresses in the deck
Structural Drawings
    • Midships Section
      • Deep Frame, Scantlings

175,000 DWTTankerLWL = 1027 ftB = 158 ftD = 83.75 ftT = 54.25 ft

Structural Drawings
    • Midships Section
      • Deep Frame, Scantlings

105,000 DWTBulkerLWL = 818.3 ftB = 124.7 ftD = 69 ftT = 50.75 ft

Structural Drawings
    • Midships Section
      • Scantlings

20.4# plate = 1/2 inch thick

Deck Stringer

Sheer Strake

Weld Seam Symbol

DD-963Simplified midship section showing shell plate straking plan

Bilge Strake

Garboard Strake