What is deadweight (DWT)?

Deadweight is the total weight a vessel can carry at a given draft: cargo plus fuel, fresh water, ballast, stores, crew, and constant. It is the difference between loaded displacement and lightship weight, read from the hydrostatic tables at the sailing draft.

What is the vessel constant?

The constant is the difference between the calculated lightship weight and the actual measured displacement when empty. It captures stores, spares, crew effects, mud, rust, and unpumpable liquids, and is typically 100 to 400 tonnes. It must be deducted from deadweight before cargo can be loaded.

How is maximum cargo intake calculated?

Cargo intake equals deadweight at the sailing draft minus all deductibles: fuel oil, diesel oil, fresh water, ballast retained, and the constant. Whatever deadweight remains after these is available for cargo.

What is a good deadweight utilisation?

DWT utilisation is cargo intake divided by total deadweight. On a full cargo with minimal bunkers a bulk carrier can exceed 90 percent. Long voyages requiring large bunker quantities, or draft restrictions in port, reduce utilisation and therefore voyage revenue.

Why does draft limit cargo intake?

Port and canal draft restrictions cap the displacement you can reach, which caps deadweight. If the deadweight available at the permitted draft is less than the cargo plus required bunkers, you must reduce cargo or bunkers. Always use the deadweight at the most restrictive draft on the voyage.

Vessel Deadweight Utilisation Calculator

The chartering question on every voyage is simple: how much cargo can this ship actually lift? This calculator starts from deadweight at the sailing draft and deducts bunkers, fresh water, ballast, and the vessel constant to give the maximum cargo intake and the percentage of deadweight that cargo represents.

How it works

Cargo is whatever deadweight remains after the non-cargo weights are removed:

deductibles  = fuel oil + diesel oil + fresh water + ballast + constant
cargo intake = deadweight − deductibles
utilisation% = cargo intake / deadweight × 100

Deadweight itself is fixed by the displacement at the permitted draft, so on a draft-restricted port the cargo you can lift is whatever is left after the required bunkers and constant are subtracted from that limited deadweight.

Example and tips

A vessel with 52,000 DWT at her sailing draft carrying 1,400 t fuel oil, 120 t diesel, 250 t fresh water, 0 t ballast retained, and a 250 t constant has 2,020 t of deductibles, leaving 49,980 t cargo intake at 96.1 percent utilisation. On a long voyage requiring 2,500 t of bunkers, intake would fall to about 48,880 t. Always run the calculation at the most restrictive draft on the route, because that draft, not the design summer deadweight, sets the real cargo limit.