Ship Construction( PART 2 )

 

                   Ship Construction Part 2

1)              Water tight Bulkhead

In general all ships must have

·         A collision or forepeak bulkhead positioned between 0.05Length and 0.08Length from the forward end of the load water line.

·         An aft peak bulkhead which encloses the stern tube and rudder trunk in a watertight compartment.

·         The collision bulkhead must have plating 12% thicker than other watertight bulkheads.

·         Watertight bulkheads have large areas .they are formed of several strakes of plating. The plating strakes are horizontal and the stiffening is vertical.

·         Water pressure in a tank increases with depth and watertight bulkhead must withstand such loading.

·         Bulkhead must have increasingly greater strength towards the base . This is achieved by increasing the thickness of the horizontal strakes of plating towards bottom.

·         Plating of aft peak bulkhead around the stern tube must be doubled up or increased in thickness to reduce vibration.

 

2)      Stern frames

·         Found beneath the stern of the ship in way of the propeller

·         Stern frame supports the propeller shaft , propeller and rudder

·         The bottom portion of the stern frame extends out aft to form the sole piece which supports the bottom bearing of the rudder.

·         The upper end of the stern frame supports the upper bearing of the rudder.

 

3)      Solid floors

In ships less then 120 m in length the bottom shell and tank top supported at intervals of not more than 3m by transverse plates known as solid floors.

 

4)      Double bottom

Which extends from the forepeak bulkhead almost to the aft peak bulkhead. This provides a form of protection in the event of damage to the bottom shell, Increases the longitudinal strength ,used for carriage of oil fuel, fresh water and water ballast .

 

5)      Static forces

Are due to difference in weight and buoyancy which occur at various points along the length of the ship.

 

6)      Dynamic forces

Dynamic forces results from ship motion and action of wind and waves.

 

7)      Static loading

Consider a ship floating in still water weight of ship act downward vertical and buoyancy of ship act vertically upward. In total the two forces exactly equal and balances one another such that the ship floats at particular draft.

 

8)      Shearing force

Shearing force at any point on a structure is defined as the algebraic sum of all the vertical forces acting on the structure to one side of that point.

 

9)      Bending moment

Bending moment at any point on a structure is the algebraic sum of all the moment of forces about that point acting on the structure to one side of that point.

 

10  Racking stress

When the ship is rolling ,it is accelerated and decelerated ,resulting in forces in the structure tending to distort it . this condition is known as racking . greater when ship is light and ballast condition. It is controlled by beams , frames , brackets or beam knees and tank side brackets.

 

11   Forepeak Construction

·         Inner bottom longitudinal are welded to the bottom plating

·         Wash plate is a longitudinal bulkhead divide forepeak tank gives strength

·         Side longitudinal are welded on ships side acts as ribs

·         Stringer is a bottom platform

·         Painting stringers are extra strengthened longitudinal

·         Painting beams are transverse parallel beams welded on painting stringers

·         First stringer is the first platform below the tank top

·         Chain locker

·         Tank top is a watertight plate on the forepeak tank and above this is the deck store

·         Deck head longitudinals are welded underneath tank top for strengthening

·          

12   Deck line

Is the freeboard line issued by the classification society plimsole line below deck line. 

 

13   Weather tight doors

In any sea condition water will not penetrate into the ship .They are situated above waterline . they are weather proof from outside.

 

14   Water tight doors

In any sea condition water will not penetrate from compartment into compartment. They are tested under certain pressure for their integrity . they are water tight from both sides.

 

15)   Sheer Strake

Topmost strake of side shell which connects the deck plating to side shell.

 

16   Bilge Strake

The lower most strake of side shell which connects the side shell plating to bottom shell.

 

17   Stringer strake

The side most strake of deck plating present at side connects to sheer strake.

 

18   Garboard Strake

The strake next to the keel.

 

19   Stealer Plate

The first plate where two strakes of plate join into a single strake. The thickness of the strakes reduce at the bow to compensate with this stealer plate is used.

 

20   Coffin Plate

The plate which connects flat keel to stern frame.

 

21   Shoe Plate

The plate which connects the keel plate to the stem

 

22   Bilge Keel

Dampens the rolling movement , provides longitudinal strength .

A flat bar is attached to the turn of bilge . An offset bulb plate is attached to flat plate bar.

Function of flat plate bar = If the offset bulb breaks then it will break from flat plate box and it won’t damage the outer shell plating.

Bilge keel extends ½ length of ship either side from mid ship and bilge keel tapers towards the end.

 

23   Six degree of freedom a ship is free to move

Three rotational = pitching , rolling, yawning

Three Linear      = Swaying , Surging , Heaving

 

24   Global stress of ship

Longitudinal ( SF and BM)

Transverse ( Dry docking ,water pressure , racking , torsonal )

 

25   Bilge block

Is used in dry dock to support bottom plating of the ship near the bilge.

Will

Revert With Ship construction Part 3 Shortly

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