Deadweight

Deadweight (DWT) is the total mass in metric tonnes that a vessel can carry when loaded to its maximum permitted summer load line, encompassing cargo, fuel oil, fresh water, ballast water, lubricating oil, provisions, stores, crew, and their effects. It is the most commercially important measure of a vessel's carrying capacity, used in charter party negotiations, freight rate calculations, and fleet comparisons. Deadweight is derived by subtracting the vessel's light ship displacement from its full-load displacement at summer draught. SOLAS Chapter V and the Load Line Convention define the draught to which a vessel may be loaded, thereby fixing the maximum deadweight for each load line zone. The chief mate uses the deadweight constantly during cargo planning: the sum of all cargo weights, bunkers, fresh water, and other consumables must not exceed the DWT at the applicable load line zone. In practice, the available cargo deadweight is calculated by subtracting anticipated fuel, water, and constant weights from the total DWT. Miscalculating deadweight—for example by loading cargo without deducting accurately for bunkers already on board—can cause the vessel to exceed its permitted draught, constituting a violation of the International Load Line Convention and a direct safety hazard in heavy seas.