Gross Register Tonnage or Gross Tonnage (GRT / GT)

  • The gross tonnage is relevant for manning regulations, safety rules and registration fees, as well as for the calculation of port dues;
  • Ships volume in cubic meters below the main deck and enclosed spaces above the main deck; this volume is multiplied by a coefficient which results in a non- dimensional number( no values of t or m3 should be placed after the number) ;

Net Register Tonnage

  • Also a non- dimensional number which describes the volume of the cargo space;
  • Derived from the GT by extracting the volume allocated for the crew, navigation equipment, propulsion equipment, workshops and ballast;
  • May not be less than 30% of the GT and is also relevant for the calculation of the port dues.

Underwater volume or carene ( m3)

Represents the moulded underwater volume of a ship; it is calculated as the displacement( m3) minus the contribution of the shell plating, propeller and rudder;

Displacement ( m3)

The volume of the immersed hull including shell plating, propeller and rudder;

Displacement D or ∆ (ton)

The weight of the volume of the water displaced by the vessel; it equals the total mass of the ship;

Lightship weight ( ton)

The weight of the vessel including the regular inventory( anchors, lifesaving appliances, lubricating oil, paint etc. ) without taking into consideration cargo, fuel or crew;

Deadweight ( ton)

  • The weight a vessel can load until it reaches the maximum allowed immersion( summer load line);
  • Fixed value, unique for each vessel;

Cargo capacity ( ton)        

  • The total weight of cargo a ship is designed to carry at a certain time; it depends on the draught of a vessel and necessary amount of fuel, provisions, drinking water etc.
  • Cargo capacity( tons) = deadweight( tons) – ballast, fuel, provisions( tons)