General Information on Tonnage

 

Displacement:

        The displacement of the ship is defined as the total weight of a volume of water, the ship displaces when it is waterborne.

Lightweight:

        It is the weight of the ship including all framing, machinery, deck etc. and excluding the weight of Cargo, Water, Fuel, Stores etc. 

Deadweight:

• It is the mass of Cargo, Fuel, Water, Stores etc. that the ship carries.
• It is the difference between the displacement of the ship and the Lightweight of the ship.

 DISPLACEMENT = DEADWEIGHT + LIGHTWEIGHT

Gross Tonnage:

• It measures the overall size of a ship determined in accordance with the provision of the present Convention. 
• The Gross Tonnage (GT) of a ship shall be determined by the following formula:

 

Net Tonnage:

        It is the measure of useful capacity of the ship determined in accordance with the provision of the present Convention. 

        The Net Tonnage (NT) of a ship shall be determined by the following formula:

        It will be noted that vessels with high freeboards, (i.e.) low draft to depth (d/D) ratios will have low net tonnages. Squaring this ratio can result in excessively low net tonnages hence the limiting value of 0.30 GT. 

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