Ein Containerschiff liegt vor den Kränen eines Seehafens.

Anzeige

Understanding deadweight (DWT)

Deadweight (DWT) refers to a mass, not a measure of volume. Under SOLAS, it is the difference between the displacement at the draught corresponding to the assigned summer freeboard and the lightweight. The stated DWT value therefore refers to a defined condition of the ship.

Loaded ship minus lightweight

Lightweight is the fully equipped ship excluding the variable loads excluded from the SOLAS definition. These include, among other things, cargo, fuel, lubricating oil, ballast water and fresh water, stores, passengers, crew, and their effects. To calculate the figures for a particular condition, the ship’s lightweight is subtracted from its displacement in that condition. This gives the actual deadweight on board for that loading condition and draught.

A simplified mass budget illustrates the calculation: if a ship has a lightweight of, for example, 3,000 tonnes and a displacement of 3,500 tonnes in the condition being considered, its actual deadweight is 500 tonnes. The stated SOLAS DWT, by contrast, uses the displacement at the assigned summer freeboard. The reference condition is therefore part of the metric: actual deadweight describes a calculation for a particular condition, whereas the stated DWT refers to the defined summer freeboard condition.

DWT is not a measure of volume

Gross and net tonnage (GT and NT) measure something different. GT is calculated from the volume of enclosed spaces; NT is based on a separate formula that includes cargo hold volume. DWT, by contrast, indicates additional mass. A tonne of DWT therefore says nothing about interior space or passenger capacity. The IMO explains GT and NT as separate measurement figures.

Photo: Alesia Belaya