Structural members of ship

⚡SHIP HULL AND STRUCTURAL TERMS

BY: VIPIN DEVARAJ DEPT OF SHIP TECHNOLOGY,

TRAINEE,INTERNATIONAL SHIPPING BUREAU, KAKKANAD ,KOCHI

© VIPIN DEVARAJ, DEPARTMENT OF SHIP TECHNOLOGY,CUSAT

⚡ SHIPS 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.).

⚡ SHIPS STRUCTURAL COMPONENTS


STRUCTURAL MEMBERS TO BE DISCUSSED ARE AS FOLLOWS:

• KEEL• PLATING• FRAMES• FLOORS• DECK BEAMS• LONGITUDNALS• DECK GIRDERS

⚡ KEEL


At the centre line of the bottom structure is located the keel, which is often said to form the backbone of the ship. This contributes substantially to the longitudinal strength and effectively distributes local loading caused when docking the ship. The commonest form of keel is that known as the ‘flat plate’ keel, and this is fitted in the majority of ocean-going and other vessels.A form of keel found on smaller vessels is the bar keel.The bar keel may be fitted in trawlers, tugs, etc., and is also found in smaller ferries.

⚡ 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)

The shell plating forms the watertight skin of the ship and at the same time,in merchant ship construction, contributes to the longitudinal strength andresists vertical shear forces. Internal strengthening of the shell plating maybe both transverse and longitudinal and is designed to prevent collapse ofthe plating under the various loads to which it is subject.

⚡ FLOORS


The transverse vertical plates dividing these tanks into sections are called floors. Vertical transverse plate floors are provided both where the bottom is transversely and longitudinally framed. At the ends of bottom tank spaces and under the main bulkheads, watertight or oil tight plate floors are provided. ‘solid plate floors’ are fitted to strengthen the bottom transversely and support the inner bottom. These run transversely from the continuous center girder to the bilge, and manholes provided for access through the tanks and lightening holes are cut in each solid plate floor. The spacing of the solid plate floors varies according to the loads supported and local stresses experienced. At intermediate frame spaces between the solid plate floors, 'bracket floors’ are fitted. The bracket floor consists simply of short transverse plate brackets fitted in way of the centre girder and tank sides

⚡ OTHER STRUCTURAL MEMBERS


Stringers are large beams or angles fitted in various parts of the vessel to give added strength. Depending upon their locations, stringers are known as bilge stringers, side stringers, hold stringers, etc

Bulkheads (longitudinal & transverse) :-Bulkheads are large partitions made of plates riveted or welded together and stiffened with angle bars, tee bars, etc. Depending on the type of ship there are transverse, longitudinal and side bulkheads. They divide the ship into compartments fore-and-aft, or from port to starboard, and they may run between two or more decks

Frames – Girders which run transversely from keel to main deck. Used to transversely stiffen the outer plating.

⚡ OTHER STRUCTURAL MEMBERS


• MIDSHIP SECTION VIEW SHOWING STRUCTURAL MEMBERS

⚡ FRAMING


• TYPES OF FRAMING SYSTEMS

• 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.

1. Transverse Framing

Primary role of transverse members is to resist the hydrostatic loads.Usually used in ship with length less than 100m

⚡ FRAMING


• TRANSVERSLY FRAMED BOTTOM STRUCTURE

⚡ FRAMING


2.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

Primary role of longitudinal members is to resist the longitudinal bending stress due to sagging and hogging

⚡ FRAMING


• Longitudinally Framed ship

⚡ FRAMING


3.Combination Framing• For combating combined loads • More longitudinal members near top and bottom structure• Side structure is primarily transverse• Most Navy surface ships are of this type

• Ship using combined framing with transverse framing on sides and longitudinally framed bottom.

⚡ TYPES OF BOTTOM CONSTRUCTIONS


1. Single Bottom Construction• Usually found on tankers & small ships• Bottom transverse frames are known as “floors”

1. Floors are vertical structural members.2. Floors support bottom plating - transfer the load to keel (& keelsons)

and side frames• Can be used with any framing system.



Double Bottom Construction

1. Advantages • Construction Stronger -

provides more longitudinal material.

• Provides volume in which to store liquids without taking up cargo space

• Provides damage resistance in the bottom

2. Disadvantages• More expensive to

construct, higher maintenance costs

• Moves neutral axis of the ship down - causing higher stresses in the deck

• Types of Double Bottom Construction



• Double Bottom Construction

⚡

THANK YOU


Engineering

Structural members of ship