Types of Ships

Home PR Center Ship Story Types of Ships

  • Types of Ships
  • Size of Ships
  • Categolization of Tons

Categorization of Tons

Tonnage is used to describe sizes of ships and used as weight or capacity unit as well. Gross tonnage or net tonnage are used to denote ship capacity, deadweight tonnage to the weight of cargoes a ship can carry, displacement tonnage to the weight of a ship, and compensated gross tonnage to provide a common yardstick for different ship types.

Gross Tonnage GT,Net Tonnage:NT

GT and NT are official measurement units for ships. They are officially used tons, and are used as criteria for registering ships or for various levies, including tax.

GT
GT is a measure of the total internal capacity of the ship, and represents the total volume in cubic feet divided by 100.
NT

NT is a measure of the capacity available for the carriage of cargo and passengers, once crew accommodation, safety and storage spaces, engine room, and water ballast tanks have been deducted. The resulting volume in cubic feet is divided by 100.

NT refers to the space that is used for direct sales activities, and is a standard for port duty, ton duty, canal passage rate, lighthouse usage fee, and port facility usage fee.

NT is generally around 65% of GT.

Why GT and NT are units for volume
When the concept of tonnage was first introduced, the most important cargo was wine. Wine was transported in oak barrels. The number of barrels that one ship could carry determined the size of the ship, and this was decided by not the weight of the barrel, but by the amount of space each barrel required. This is why official tonnage is based on volume rather than weight.

Deadweight Tonnage: DWT, and Displacement Tonnage

DWT

DWT is the maximum load volume of a ship.
The actual cargo tonnage is DWT minus tonnage for passengers, crew, fuel, ballast, food, and ship supplies.

DWT
Full Load Displacement Full Load Displacement is the weight of a ship that is fully loaded with cargo
and passengers, as scheduled
FLight Ship Displacement The weight of the ship alone.
Displacement Tonnage
This is the weight of water displaced by the ship. It is equal to the weight of the water whose volume is the same as that of the water under the sea surface.
Light ship displacement refers to displacement before loading the cargo. Deadweight tonnage refers to the water that the ship displaces when the cargo is loaded to the full draft load line.
Deadweight tonnage is typically used to distinguish the size of a battleship, and light ship displacement is used to estimate how much scrap iron would be generated if a ship were to be dismantled.

CGT Compensated  Gross Tonnage

CGT is an integrated measure that includes standards not feeding into GT, such as workload, production capacity, and ship prices to provide a common yardstick to reflect the relative output of shipbuilding activities.