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

Tonnage measurement 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.

Sailing ship