Principle SHIP DIMENSIONS By Dr. Oladokun Sulaiman Olanrewaju
Length between perpendicular (LBP) Length on waterline (LWL) Length overall (LOA) freeboard Amidships Aft perpendicular Fwd perpendicular Sheer aft Sheer fwd Summer load line SHIP DIMENSIONS Camber Tumble home Depth Moulded beam Rise of floor Half siding of keel Base line Draft flare
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 centre 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.P.P. / L.B.P.) : The length between the forward and the aft perpendiculars measured along the summer load line.
Amidships : A point midway between the after and forward perpendiculars
Length Overall (L.O.A.) : Length of the vessel taken over all extremities.
Base line : A horizontal line drawn at the top of the keel plate. All vertical moulded dimensions are measured relative to this line
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 side amidships
Camber / Round of Beam : Curvature of decks in the transverse direction. Measured as the height of deck above the height of deck at side
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
Half sliding of keel : The horizontal flat portion of the bottom shell measured to port or starboard of the ship’s longitudinal centre 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
This is often referred to when the size of the vessel is discussed, and the gross tonnage is quoted from Lloyd’s register.
Tonnage is a measure of the enclosed internal volume of the vessel, 100 cubic feet representing one ton
Its normally divided into categories as follow:-
1. Displacement Tonnage
A ship’s displacement is the sum of the ship’s actual weight (lightweight) and it’s contents (deadweight).
The metric unit of measurement is 1 tonne (= 1000 Kg).
The displacement represents the amount of water displaced by the ship expressed in tonnes.
The weight of water displaced therefore equals the weight of the ship
2. Lightweight Tonnage (lwt)
The lightweight is the weight of the ship as built (hull, machinery) including boiler water, lubricating oil and the cooling water system.
Lightweight like displacement is expressed in units of tonnes.
It assumes importance in a commercial sense only when considering the value of the vessel which is to be broken up for scrape.
3. Deadweight tonnage (dwt)
Deadweight is the weight of the cargo which a ship carries plus weights of fuel, stores, water ballast, fresh water, crew and passengers and baggage.
It is the difference between the loaded ship displacement and the lightweight.
4. Gross Tonnage (gt)
Measurement of total internal volume of a vessel and includes all under deck tonnage and all enclosed spaces above tonnage deck.
100 cubic feet of space being considered as 1 ton
5. Nett Tonnage (nt)
Ship measurement derived from gross tonnage by deducting spaces allowed for crew and propelling power.
100 cubic feet of space being reckoned as 1 ton
Ship side markings
Load line mark
consists of a ring 300 mm in outside diameter and 25 mm thick which is
intersected by a horizontal line 450 mm in length and 25 mm thick, the upper edge of which passes
through the centre of the ring. The centre of the ring is placed amidships and at a distance equal to the assigned summer freeboard measured vertically below the upper edge of the deck line.