Difference among deadweight, gross and net tonnage
Deadweight tonnage, gross tonnage, and net tonnage are terms used in the maritime industry to describe various measures of a ship’s size or capacity. Each serves a different purpose:
- Deadweight Tonnage (DWT):
- Definition: This represents the maximum weight that a ship can safely carry when fully loaded. It includes the weight of the cargo, fuel, freshwater, ballast water, provisions, passengers, and crew.
- Purpose: To measure the cargo-carrying capacity of a vessel.
- Calculation: DWT is calculated by subtracting the ship’s lightweight (weight of the ship with no cargo, fuel, etc.) from its displacement (the weight of the ship when fully loaded).
- Gross Tonnage (GT):
- Definition: Gross tonnage is a measure of the overall internal volume of a ship, where one ton is equivalent to 100 cubic feet or 2.83 cubic meters. It encompasses all the enclosed spaces within a ship.
- Purpose: To provide a broad overview of the ship’s size and, in some cases, to calculate port dues or other fees.
- Calculation: GT is based on the total volume of all the ship’s enclosed spaces. The specifics of the calculation can be complex and are standardized by international conventions.
- Net Tonnage (NT):
- Definition: Net tonnage measures the volume of the cargo spaces in a ship, taking into account the spaces that are essential for the operation and safety of the ship (like the engine room).
- Purpose: To provide an understanding of the ship’s profit-generating potential since it measures the volume available for cargo or passengers.
- Calculation: NT is derived by subtracting non-revenue-generating spaces (like machinery spaces) from the gross tonnage. Like GT, the exact calculation is determined by international conventions.
In summary, while DWT measures the weight-carrying capacity of a vessel, GT and NT measure the internal volume of the vessel in different ways. Gross tonnage takes into account all enclosed spaces, while net tonnage focuses on the volume of spaces that can generate revenue.