Ship Construction - Definitions and Drawings:

Ship Construction

Definitions and Drawings:

The below definitions are very important and need to know thoroughly. Pls, refer the diagram while learning the definitions, so that you don’t forget easily.

Reference System

In order to locate a point on a ship three-dimensional references are used as follows:

       Since the vessels are made symmetrical about the center plane, the centerline is used as reference line for all athwart distances

For longitudinal distances either Amidships or aft perpendicular is used

For vertical distances the base line is used

After Perpendicular (A.P.): 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 center line of the rudder stock.

Forward Perpendicular (F.P.): A perpendicular drawn to the waterline at the point where the foreside of the stem meets the summer load line.

Length Between Perpendicular (L.B.P.): The length between the forward and the aft perpendiculars measured along the summer load line.
👉 Used for stability conditions

Length Overall (L.O.A.): Length of the vessel taken over all extremities.
👉Used during maneuvering, berthing operations, to calculate swinging circle, etc..

Amidships: A point midway between the after and forward perpendiculars

Base line: A horizontal line drawn at the top of the keel plate. All vertical moulded dimensions are measured relative to this line

Deck Line: The deck line is a horizontal line marked amidships on each side of the ship. Deck line is line from where freeboard is measured and is drawn at a point on midship where deck plate meets the side shell plate.

Moulded beam: Measured at the midship section, is the maximum moulded breadth of the ship

Moulded Draft/ Draught: The distance from the bottom of the keel to the waterline. The load draft is the maximum draft to which a vessel may be loaded.

Moulded Depth: Measured from the base line to the heel of the upper deck beam at the ship’s side amidships.

Sheer: Curvature of decks in the longitudinal direction. Measured as the height of deck at side at any point above the height of deck at a amidships.
👉 It adds buoyancy,
👉 It quickly drains the water from deck.

Camber / Round of Beam: Curvature of decks in the transverse direction. Measured as the height of deck above the height of deck at side

👉 It quickly drains water from deck.

Rise of floor / Deadrise: The rise of the bottom shell plating line above the base line. This rise is measured at the line of moulded beam.

👉 It drains the liquid to the center line.

Half sliding of keel: The horizontal flat portion of the bottom shell measured to port or starboard of the ship’s longitudinal center line. This is useful dimension to know when dry-docking.

Tumble home: The inward curvature of the side shell above the summer load line.

Freeboard: the vertical distance measured from the waterline to the top of the deck plating at the side of the deck amidships. Normally exposed to weather and sea.

Flare: The outward curvature of the side shell above the waterline. It promotes dryness and is therefore associated with the fore end of ship.
👉 Increases reserve buoyance forward
👉 Temporary buoyancy while pitching
👉 Protects shell from anchoring
👉 Provides lift while pitching
👉 Keep forward dry
👉 Absorbs shock load in case of head-on collision.

Rake of Stem / Stem rake: Inclination of stem line from the vertical.

Rake of Keel / Keel rake: Inclination of stem line from the horizontal.

Extreme Beam: The maximum beam taken over all extremities.

Extreme Depth: Depth of vessel at ship’s side from upper deck to lowest point of keel.

Parallel middle body: The length over which midship section remain constant.

Entrance: The immersed body of the vessel “ Forward of parallel middle body”.

Run: The immersed body of the vessel “ Aft of the parallel middle body”.

Light displacement  is the weight of the hull, engines, spare parts, and with Water in the boilers and condensers to working level.

Load displacement is the weight of the hull and everything on board when floating at the designed summer draught.

Deadweight carrying capacity is the difference between the light and Loaded displacements and is the weight of cargo, stores, ballast, fresh water, fuel oil, Crew, passengers and effects on board.

Statutory freeboard is the distance from the upper edge of the summer load Line to the upper edge of the deck line.

Reserve buoyancy is virtually the (available) watertight volume above the waterline.