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Ship Structural Components

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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Ship Structural Components

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  1. EN358Ship Structures Ship Structural Components CDR Jeffrey W. Stettler, USN, PhD Assistant Professor, Permanent Military Professor

  2. 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?

  3. 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.).

  4. 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)

  5. 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.

  6. 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.

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. Structural Drawings • Midships Section • Deep Frame, Scantlings 175,000 DWTTankerLWL = 1027 ftB = 158 ftD = 83.75 ftT = 54.25 ft

  13. Structural Drawings • Midships Section • Deep Frame, Scantlings 105,000 DWTBulkerLWL = 818.3 ftB = 124.7 ftD = 69 ftT = 50.75 ft

  14. 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

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