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! 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 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

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

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

DD-963 Simplified midship section showing shell plate straking plan Structural Drawings Midships Section Scantlings 20.4# plate = 1/2 inch thick Deck Stringer Sheer Strake Weld Seam Symbol DD-963 Simplified midship section showing shell plate straking plan Bilge Strake Garboard Strake