Ship Structural Components i211g

EN358 Ship Structures

Ship Structural Components

CDR Jeffrey W. Stettler, USN, PhD Assistant Professor, Permanent Military Professor

Ship 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 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 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 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 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 Components

 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

Ship Structural Components

 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

Ship Structural Components

 Types of framing systems  Combination Framing    

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

Ship Structural Components

 Single Bottom Construction  Usually found on tankers & small ships  Bottom transverse frames are known as “floors”  Floors are vertical structural !  Floors bottom plating - transfer the load to keel (& keelsons) and side frames

 Can be used with any framing system

Ship Structural Components

 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

Ship Structural Components

 Structural Drawings  Midships Section  Deep Frame, Scantlings

175,000 DWT Tanker LWL = 1027 ft B = 158 ft D = 83.75 ft T = 54.25 ft

Ship Structural Components

 Structural Drawings  Midships Section  Deep Frame, Scantlings

105,000 DWT Bulker LWL = 818.3 ft B = 124.7 ft D = 69 ft T = 50.75 ft

Ship Structural Components

 Structural Drawings

20.4# plate = 1/2 inch thick

 Midships Section

Deck Stringer

Sheer Strake

 Scantlings

Weld Seam Symbol

DD-963 Simplified midship section showing shell plate straking plan

Bilge Strake

Garboard Strake