Program of Ship Salvage Engineering POSSE Introduction

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

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• 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.).

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• Keel - Longitudinal center plane girder along
  bottom of the ship
• The ships 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)

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• 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.

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• 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.

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• 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

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• 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

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• 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

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• 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

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• 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

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• Structural Drawings
• Midships Section
• Deep Frame, Scantlings

175,000 DWT TankerLWL 1027 ftB 158 ftD
83.75 ftT 54.25 ft
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• Structural Drawings
• Midships Section
• Deep Frame, Scantlings

105,000 DWT BulkerLWL 818.3 ftB 124.7 ftD
69 ftT 50.75 ft
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• 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