What is the Difference between gross tonnage and net tonnage ?
Gross Tonnage(GT)– It is the total volume of all ship’s enclosed spaces.
A ship’s GT numerical value is always smaller than ship’s GT numerical value of gross register tonnage (GRT).
It is a common measurement of the total internal volume of a holds , tanks , stores , Engine room ,bridge etc
One ton=2,83 m3
Net Tonnage(NT)– It is total volume of all the spaces of the ship,that is used to carry cargo.
As the cargo is loaded in this space it also indicates a ship’s earning or useful space.
Ship’s registration fee, harbour dues, safety and manning rules are calculated on the bases of its gross tonnage (GT) or net tonnage (NT).
N.T = GT – Crew accommodation , Engine room , Bridge.Ballast tanks,void spaces etc.
Its the space available for loading cargo & space for passengers
Registration fees, cargo dues ,tonnage dues etc are calculated on the basis of ship’s tonnage certificate.
Commercial ships need to hold International Tonnage Certificate, which is issued by flag states, in accordance with the IMO International Convention on Tonnage Measurement of Ships 1969 (ITC).
All the calculations are performed by the vessel’s classification society before the delivery of the vessel, the classification society issues the certificate on behalf of the flag state.
There is no expiry date on the certificate, but needs to be amended in case of any conversion to the vessel.
Gross and net tonnage
“Gross registered tonnage” and “net registered tonnage” are replaced by “Gross tonnage” (GT) and “net tonnage” (NT) , when the IMO adopted the ITC, So after 1994 the GT and NT are the official indices to measures ships’ tonnage.
Panama Canal Universal Measurement System (PCUMS) is used to collect Panama Canal tolls , it is based on the international standard of vessel measurement established by the ITC (not applicable for container vessels, they pay in accordance with TEU container-carrying capacity).
Panama Canal Tonnage Certificate is therefore identical to ITC certificates.
Suez Canal tonnage
The Suez Canal, has a different system to calculate the NRT, therefore a term Suez Canal Net Registered Tonnage (SCNRT) is used, SCNRT is used to calculate the passage dues. SCNRT certificate are therefore different from those in ITC certificates.
Weight measurement of ships
It is the volume of water which ship displaces when it is floating, displacement is measured in cubic metres (m3),
It is the weight of the water that a ship displaces when it is floating free with its fuel tanks full and all stores on board
Displacement tonnage is measured in metric tons (MT, equivalent to 1,000 Kg).
It is the actual weight of the ship, as floating object displaces its own weight in water.
It is the actual weight of the ship without passengers, cargo, bunkers, lube oil, ballast, fresh water, stores, etc., on board vessel.
It is the weight of the ship loaded down to its load line marks, that is, loaded to its maximum capacity with passengers, cargo, bunkers, lube oil, ballast, fresh water, stores, etc., on board vessel.
loaded displacement tonnage of the ship – the lightweight of the ship=x mt (metric tons).
Related Read :International maritime dangerous goods code IMDG Code
Related Read : Biggest shipping company in the world