Basic Ship Construction Terminologies

 

Length Between Perpendiculars (LBP):

Aft Perpendicular:

        A perpendicular drawn to the waterline at the point where the aft side of the rudder post meets the Summer load line. Where no rudder post is fitted it is taken as the centre line of the rudder stock.

Forward Perpendicular:

        A perpendicular drawn to the waterline at the point where the foreside of the stem meets the Summer load line.

       LBP is the length between the forward and aft perpendicular measured along the Summer load line.

Amidships:

        It is a point midway between the forward and aft perpendiculars. 

 

Baseline:

• It is a horizontal line drawn at the top of the keel plate.
• All vertical moulded dimensions are measured relative to this line.

 

Moulded Dimensions:

Breadth Moulded (B. Mld):

       It is the greatest breadth of the ship, measured to the inside of the inner strakes of the shell plating.

 

Depth Moulded (D. Mld):

       It is the depth measured from the top of the keel to the uppermost continuous deck at the ship's side amidships.

 

Draught Moulded (d. Mld):

      It is the vertical distance between the top of the keel to the summer load line, usually measured at the ship's midship plane.

 

Extreme Dimensions:

Breadth Extreme (B. Ext):

        It is the greatest breadth of the ship, measured to the outside of the shell plating.

 

Depth Extreme (D. Ext):

       It is the depth of the ship measured at the ship's side from the underside of the keel to the top of the uppermost continuous decks amidships.

 

Draught Extreme (d.Ext):

        It is the vertical distance from the bottom of the keel to the summer load line.  

 

Sheer: 

• The curvature of the deck in a fore and aft direction, rising from amidships to a maximum at the ends.   
• Sheer forward is usually twice that of the sheer aft
• Sheer on exposed decks makes a ship more seaworthy by raising the deck at the fore and aft end.
• It further reduces the volume of water coming on the deck.  

   

Camber:

• The transverse curvature of the deck from the centreline down to the sides  
• The Camber is used on exposed decks to drive water to the sides of the ships.       

 

Rise of Floor (or) Deadrise:   

• It is defined as the Rise of the bottom shell plating line above the baseline.
• This rise is measured at the line of moulded breadth.

 

Tumblehome:

        It is the inward curvature of the side shell above the summer load line. It improves the appearance of the ship.

 

Flare:

• It is the outboard curvature of the side shell above the waterline.
• It promotes dryness and is therefore associated with the fore-end of the ship.

    

Freeboard:    

• It is the vertical distance measured at the ship's side between the summer load line and the freeboard deck.         

Freeboard deck - It is normally the uppermost continuous deck exposed to weather and sea which has permanent means of closing all openings, and below which all openings in the ship's side have watertight openings.

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Reference:    Ship Construction By D.J, Eyres

                      Ship Construction for Marine Students By E.A.Stokoe