Ship Construction( PART 3 )

 

                       Ship Construction Part 3

Transom floor

The floor which connects the rudder port or floor is fitted at abaft and higher of stern frame to support the body part of the rudder.

Torsional

When a twisting or a torque moment occurs on the ships hull the ship is said to be in torsion. usually happens when taking waves at 45 degree. it happens max where the width of ship is larger as well as it has large openings .ex container ship in empty condition torsion is max. to overcome this condition ships are provided with torsion boxes.

Dry docking stress

Its the distortion of side shell plating and it develops along length of the ship.

Types of framing

Longitudinal framing

Transverse framing

Combined framing

 

Longitudinal framing

For ships 100m or more in length stiffeners are used in longitudinal direction. stiffeners are either bulb, angle or T section placed vertically to bulkhead and 760 mm apart.

Frame – on side plating, running vertically up and down

Beam – under deck , runs transversely 

Floors – found only in double bottom runs transversely

Stringer – on side plating and longitudinal bulkheads runs horizontally fore and aft.

Longitudinal  - found on longitudinal frame ships runs fore and aft.

Girder – found under decks and on bottom plating ,runs fore and aft

Longitudinal frame – The system is designed to withstand longitudinal bending moments ,which are pronounced in long vessels . the main feature of strengthening in this system is the longitudinal an L shaped stiffener. Which is fitted under the decks on the side plating ,on the bottom plating ,under the tank top on the longitudinal bulkheads as well. The longitudinal runs the full length of t vessel from fwd to aft providing longitudinal strength.

 

Transverse framing

Used in ships of less than 120 m .because of less BM in longitudinal direction

Stiffeners are in transverse direction

Stiffeners are bulb angle or T section

Transverse frames are joined with deck beams with knee brackets

Deep frames or web frames are used in machinery spaces.

Under decks, deck beams are fitted at every frame space. A frame space is the distance between one frame on side plating to the next frame.

Deck beams are connected to the frames on side by means of beam knees . the beam knees are very efficient connections joining the beam directly to the frame. The bottom structure usually consists of a cellular double bottom above the outer bottom plating , an inner bottom is fitted called the tank top .the space between outer bottom plating and inner bottom plating is called double bottom.

 

Combined framing

This framing system came for intermediate length ships ,mainly bulk carriers ,large general cargo ships ,container ships and some medium sized tankers .

Under the decks and on bottom plating ,the vessel is longitudinally framed

 

Collision bulkhead

Must have 12% thicker plating than other bulkhead. Positioned between 0.05Length and 0.08Length from the forward end of the load waterline.

 

Aft peak bulkhead

Which encloses the stern tube and rudder trunk in a water tight compartment.  

 

Functions of stern frame

To support the rudder bearing

To support propeller and shaft

To reduce vibration stresses

To enable the keel to be connected to the structure satisfactorily.

Types of floors

Water tight / oil tight floors

Solid plate floors

Bracket floors.

 Frame Numbering

 

·        Frame numbering starts from rudder stock ( frame number 0 ) and counted towards stem/bow .

·        Rudder stock is not the aftermost part , there are frames behind no zero. They are counted as negative numbers.

·        Frames are spaced at a distance of 600 mm to 950 mm

 

 

Shell plating numbering

 

·        We need to count plates in two dimensions

·        One is athwartship position and other being along the length,.

·        Keel strake is on the centre line.

·        Next to keel strake is garboard strake

·        Garboard strake is known as plate A and above A is B

·        Plates are counted from Aft to Forward in numbers

·        Each plate is therefore indicated by a letter to show its level and a number to show its position.

 

 

Shell Expansion Plan

 

·        Its’ a ships plan giving details of shell plating

·        It’s a two dimension drawing of a three dimensional surface of the ships hull form.

·        Shows shell plating , framing , seams and butts.

 

 

Bottom shell Plating ( thickness)

 

·        Through out the length of the ship the width and thickness of the keel plate remains constant.

·        A flat plate keel is fitted , it’s thickness is not less than that the adjoining bottom plating

·        Keel strake is on the centre line

·        Strakes of bottom plating to the bilges have their greatest thickness over 40% of ships length amid ship where bending stresses are higher.

·        Bottom plating tapers to a lesser thickness at the ends apart from pounding regions which requires increased thickness .

 

 

Side Shell plating

 

·        The greatest thickness of side shell plating maintained within 40% of the vessel . length amid ship and tapers its thickness at ends

·        Thickness increased where high vertical stresses occur.

·        Usually in transverse bulkhead , at stern frame connection , way of hawse pipe .

·        Shell plate thickness increases at panting region.

 

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