Ship Structural Components

Ship Structural Components For Ship Construction Subject

1. Ship’s Structural Components
1pt.wikipedia.org

2. LongitudinalLongitudinal Structural ComponentsStructural Components
Keel
- Large center-plane girder
- Runs longitudinally along the bottom of the ship
• Longitudinals
- Girders running parallel to the keel along the bottom
- It provides longitudinal strength
2

3. Longitudinal Structural Components (cont’d)
• Deck Girder
- Longitudinal member of the deck frame (deck longitudinal)
• Stringer
- Girders running along the sides of the ship
- Typically smaller than a longitudinal
- Provides longitudinal strength
….Primary role of longitudinal members :
Resist the longitudinal bending stress due to sagging and
hogging
3

4. Transverse Structural Components
• Floor
- Deep frame running from the keel to the turn of the bilge
• Frame
- A transverse member running from keel to deck
- Resists hydrostatic pressure, waves, impact, etc.
- Frames may be attached to the floors (Frame would be the
part above the floor)
• Deck Beams
- Transverse member of the deck frame
•Primary role of transverse members : to resist the hydrostatic loads
4

5. • Plating
- Thin pieces closing in the top, bottom and side of structure
- Contributes significantly to longitudinal hull strength
- Resists the hydrostatic pressure load (or side impact)
5

6. LONGITUDINAL
MEMBERS
TRANSVERSE
MEMBERS
FLOOR
LONGITUDINAL
DECK BEAM
F
R
A
M
E
STRINGERS
DECK
GIRDERS
DECK PLATING
PLATING
KEEL
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7. LONGITUDINAL
MEMBERS
TRANSVERSE
MEMBERS
FLOOR
LONGITUDINAL
DECK BEAM
F
R
A
M
E
STRINGERS
DECK
GIRDERS
DECK PLATING
PLATING
KEEL
7

8. The ship’s strength can be increased by:
- Adding more members
- increasing the size & thickness of plating and structural pieces
All this will increase cost, reduce space utilization, and
allow less mission equipment to be added
Optimization
• Longitudinal Framing System
• Transverse Framing System
• Combination of Framing System
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9. Shell Plating details:
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(Longitudinal) Rows of plating are called “strakes”
Welded horizontal joints between strakes are called seams
Welded vertical joints between plates in a given strake are
called butts
Strakes that do not run the entire ship length (as the hull
surface area decreases at the ends) are drop strakes
Bilge (“F”) Strake
“G” Strake
“H” Strake drop 
“J” Strake Through 
“K” Strake Sheer Strake
Strakes running stem to stern are called through strakes
An oversized plate merging a drop & through strake is a stealer
plate
The strake at the deck edge is the sheer strake and is heavier
than typical side shell plating

10. Shell & Deck Construction
Seam or ‘Edge Laps’ are joints which runs fore and aft, along the
longer edges of plates
Butts or ‘End Laps’ are joints which run athwartships, or vertically,
along the shorter edges of plates.
Sheer strakes are the upper strakes (continuous, fore and aft, lines
of plates) of shell plating on either side, next to upper deck.
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11. Shell & Deck Construction
Welded plating is more liable to crack under hogging and sagging
stresses, especially in the region of sheer strake and the bilge.
The upper edges of sheer strake should be ground -off smooth,
whilst other parts should not be welded to it, if avoidable
Any openings in the shell plating must have special arrangements
to preserve strength and their corners must be rounded.
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12. Shell & Deck Construction
The corners of the openings must be rounded
and special arrangement to preserve strength
When large openings, such as cargo doors, are
cut in the plating, they are usually framed in by a
face bar.
Web frames are often placed on either side of
the opening and insert plates are fitted above
and below it, or right around it.
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13. Openings in shell plating must:
* have rounded corners
* be reinforced to make up for missing material
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portholes
Watertight doors
Hatch openings
below decks
… and on weather deck -- COAMINGS

14. Shell & Deck Construction
14

15. Transverse Framing System
Stiffening the shell plating, prevents buckling and
resists distortion of vessel due to racking
The frames support ends of deck beams
Frames are closely spaced where loading is higher
especially at ends of ships
Provide transverse strength.
15

16. Transverse Framing System
• Ships shorter than 300ft and submersibles
•Transverse Framing System:
- Longitudinals are spaced widely but deep.
- Frames are spaced closely and continuously

•Transverse members: frame, floor, deck beam,
platings
•Primary role of transverse members : to resist the hydrostatic loads
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17. Transverse Framing:
•Deck Beams tie upper
ends of frames
•Fewer, deeper & more
widely spaced
Longitudinals …
•Support Inner Bottom
& give longitudinal
strength
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Longitudinals
supporting Decks are called
(Deck) Girders
Additional Decks (supported by
Beams & Girders) increase
Transverse & Longitudinal strength
Many, closely-spaced Frames
Transverse Bulkheads provide watertight boundaries, contribute significantly to
transverse strength, and provide vertical support for Decks

18. Transverse Framing:
•Advantages
•Open, nearly rectangular interior space
•Ideal for stowing large, irregular, break-bulk items, or
•Vehicles (Ro-Ro’s)
•Disadvantages
•Vertical support for decks requires more closely spaced transverse
bulkheads (hence smaller compartments) or
•Pillars (stanchions) or
•Longitudinal bulkheads
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Many, closely-spaced Frames

19. Transverse Framing System
19

20. Longitudinal Framing System
On ship sides, longitudinals extend from one transverse
bulkhead to another.
Frames supported at intervals by vertical web frames
(heavy plate frame) spaced about 4m apart.
Provide longitudinal strength
The size of the longitudinals ( usually bulb plates)
depends on the spacing, span between bulkhead, length
of ship and distance from the deck
20

21. Longitudinal Framing System
• A typical wave length in the ocean is 300 ft. Ships of this length
or greater are likely to experience considerable longitudinal
bending stress
• Ship that are longer than 300ft (long ship) tend to have a
greater number of longitudinal members than transverse
members
Longitudinal Framing System :
- Longitudinals spaced frequently but shallower
- Frames are spaced widely
Primary role of longitudinal members : to resist the
longitudinal bending stress due to sagging and hogging
21

22. Longitudinal Framing:
•Few & widely
spaced
•Smaller, closely-
spaced
Longitud-nals
support shell
plating
•Side shell
longitudinals
call stringers
22
Deep (Web) Transverse Frames
Inner Bottom gives
additional longitudinal &
transverse strength
Girders in high-stress areas:
Double bottom spaces and …
Under main deck

23. Longitudinal Framing:
•Advantages
•Widely spaced transverse bulkheads allow for large (i.e., long) continuous
cargo spaces (“tanks”)
•Ideal for stowing liquids (reduced free surface effects)
•Disadvantages
•No large, open interior spaces
•Difficult to load or unload break-bulk items
•Difficult to stow large, irregular shaped items
23
Deep (Web) Transverse Frames

24. Longitudinal Framing System
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25. Longitudinally framed hull (tanker)
The longitudinal framing is much better able to resist buckling
when the hull is hogging
Source:
www.marineengineering.org.uk
25

26. Source: www.marineengineering.org.uk
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27. Source:
www.marineengineering.org.uk
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28. Source:
www.marineengineering.org.uk
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29. Longitudinal framing (Dry Cargo)
Source: www.marineengineering.org.uk 29

30. Source:
www.marineengineering.org.uk
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31. Source:
www.marineengineering.org.uk
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32. Source:
www.marineengineering.org.uk
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33. 33

34. Combination Framing System
Introduced to overcome the disadvantage of longitudinal system in
dry cargo ships.
The longitudinal frames are retained at the bottom and under the
strength deck to give longitudinal strength.
Transverse frames are fitted on ship’s sides where longitudinal
stresses are smaller
Plate floors and heavy transverse beams are fitted at intervals to
give transverse strength and support the longitudinals
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35. Framing Systems:Framing Systems:
•Typically, most ships have some combination of transverse &
longitudinal framing
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T

T

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T

T
T

T

T

T

T

T
T

T

T

T

T

T
CL CL
SECTION
VIEW
PLAN VIEW
Typical
Transverse
Frames
Web Frame
L L L L L L L L L L
FLOOR
UPPER TWEEN DECK
LOWER TWEEN DECK
(LOWER) HOLD
Bulkhead STIFFENERS
Stringer

36. Combined Framing System
• Combination of longitudinal and transverse framing system
• Typical combination :
- Longitudinals and stringers with shallow frame
- Deep frame every 3
rd
or 4
th
frame
Optimization of the structural arrangement for the expected
loading to minimize the cost
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37. Combined Framing System
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38. Double Bottom Tank:
An inner bottom (or tank top) may be provided at a minimum
height above the bottom shell, and maintained watertight to the bilges.
This provides a considerable margin of safety, since in the event of
bottom shell damage only the double bottom space may be flooded.
The space is not wasted but utilised to carry oil fuel and fresh
water required for the ship, as well as providing ballast capacity.
It may be deeper to give the required capacities of oil fuel, fresh water,
and water ballast to be carried in the bottom. Water ballast bottom
tanks are commonly provided right forward and aft for trimming purposes
and if necessary the depth of the double bottom may be increased in
these regions.

In way of the machinery spaces the double bottom depth is also
increased to provide appreciable capacities of lubricating oil and fuel oil.
The increase in height of the inner bottom is always by a gradual
taper in the longitudinal direction, no sudden discontinuities in the
structure being tolerated.

39. Double bottoms may be framed longitudinally or
transversely , but where the ship’s length exceeds
120m it is considered desirable to adopt longitudinal
framing. The explanation of this is that on longer ship
tests and experience have shown that there is a
tendency for the inner bottom and bottom shell to
buckle if welded transverse framing is adopted.
This buckling occurs as a result of the longitudinal
bending of the hull, and may be avoided by having
the plating longitudinally stiffened

40. Source:
www.marineengineering.org.uk

42. Transversally
stiffened

43. Double Bottom details:Double Bottom details:
43
Rider
Plate
Inner Bottom
(Tank Top)
Air-
hole
Margin
Plate
Center
Vertical Keel
Keel
Plate
Outer
Bottom
Lightening
hole
Limber
hole
Longitudinal
Bilge
Frame
“SOLID” FLOOR
Reverse Frame “OPEN” FLOOR
Frame Longitudinal Strut
Bilge
well

44. Shell Plating details:Shell Plating details:
44
Keel
Strake
Garboard Strake
(“A” strake)
“B”
Strake
“C”
Strake
“D”
Strake
“E”
Strake
“G”
Strake
“F” Strake
(Bilge Strake)
(Longitudinal) Rows of plating are called “strakes”
The Keel Plates form the “Keel strake”
The strakes outboard (P&S) of the Keel are the “A” Strakes
or “Garboard Strakes”
Strakes are consecutively lettered moving outboard and up
the side shell

45. Double Bottoms
• Resists:
- Upward pressure
- bending stresses
- bottom damage by grounding and underwater shock

• The double bottom provides a space for storing:
- fuel oil
- ballast water & fresh water

• Smooth inner bottom which make it easier to arrange cargo &
equipment and clean the cargo hold
Two watertight bottoms with a void space
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46. Deck Plating
Deck plating is supported by pillars which ‘tie in’ the deck and
connect with the bottom structure.
The pillars also transmit deck loads to the bottom structure, where
there are distributed into the floors
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47. Discontinuities- Hatchways
Coamings height on freeboard deck : 600 mm and abaft ¼ of
length on exposed superstructure deck from stem : 450 mm
Squared corners not allowed.
Openings may be elliptical or parabolic, or the corners may be
rounded-off
The radius at the corners must be at least 1/24 th of breadth of
opening, but not less than 300mm
Doubling plates not allowed in welded decks, so insert plates must
be fitted at the hatch corners.
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48. Hatch Corners
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49. Openings in the shell – Suction and Discharge
Fittings
If discharges comes from below freeboard deck, they must be fitted
with non-return valves except for discharges from manned E/R
 A scupper passes through the shell plating at a distance of more than
450 mm below freeboard deck or less than 600 mm above the load
waterline, it must have an automatic non-return valve fitted at the shell
A scupper from deck below freeboard deck must lead down to the
bilges or fitted with SDNR valve
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50. Any Question?
Thank you.
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