1. EN358 Ship 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
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. 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 = ft T = ft

13. 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 = ft B = ft D = 69 ft T = ft

14. 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