Deadweight tonnage (also known as deadweight; abbreviated to DWT, D.W.T., d.w.t., or dwt) or tons deadweight (DWT) is a measure of how much
weight
In science and engineering, the weight of an object is a quantity associated with the gravitational force exerted on the object by other objects in its environment, although there is some variation and debate as to the exact definition.
Some sta ...
a ship can carry.
It is the sum of the weights of
cargo
In transportation, cargo refers to goods transported by land, water or air, while freight refers to its conveyance. In economics, freight refers to goods transported at a freight rate for commercial gain. The term cargo is also used in cas ...
, fuel,
fresh water
Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salt (chemistry), salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include ...
,
ballast water
Ballast is weight placed low in ships to lower their centre of gravity, which increases stability (more technically, to provide a righting moment (physics), moment to resist any Heeling (sailing), heeling moment on the Hull (watercraft), hull). I ...
, provisions, passengers, and
crew
A crew is a body or a group of people who work at a common activity, generally in a structured or hierarchy, hierarchical organization. A location in which a crew works is called a crewyard or a workyard. The word has nautical resonances: the ta ...
.
DWT is often used to specify a ship's maximum permissible deadweight (i.e. when it is fully loaded so that its
Plimsoll line
The load line, also known as Plimsoll line, indicates the legal limit to which a ship may be loaded for specific water types and temperatures in order to safely maintain buoyancy, particularly with regard to the hazard of Wind wave, waves. The l ...
is at water level), although it may also denote the actual DWT of a ship not loaded to capacity.
Definition
Deadweight tonnage is a measure of a vessel's weight carrying capacity, not including the empty weight of the ship. It is distinct from the
displacement
Displacement may refer to:
Physical sciences
Mathematics and physics
*Displacement (geometry), is the difference between the final and initial position of a point trajectory (for instance, the center of mass of a moving object). The actual path ...
(weight of water displaced), which includes the ship's own weight, or the volumetric measures of
gross tonnage
Gross tonnage (GT, G.T. or gt) is a nonlinear measure of a ship's overall internal volume. Gross tonnage is different from gross register tonnage. Neither gross tonnage nor gross register tonnage should be confused with measures of mass or weig ...
or
net tonnage
Net tonnage (NT, N.T. or nt) is a dimensionless index calculated from the total moulded volume of the ship's cargo spaces by using a mathematical formula. Defined in ''The International Convention on Tonnage Measurement of Ships'' that was adopte ...
(and the legacy measures
gross register tonnage and
net register tonnage
Net register tonnage (NRT, nrt, n.r.t.) is a ship's cargo volume capacity expressed in "register tons", one of which equals to a volume of . It is calculated by subtracting non-revenue-earning spaces i.e. spaces not available for carrying cargo, ...
).
Deadweight tonnage was historically expressed in
long ton
The long ton, also known as the imperial ton, displacement ton,Dictionary.com - ''"a unit for measuring the displacement of a vessel, equal to a long ton of 2240 pounds (about 1016 kg) or 35 cu. ft. (1 cu. m) of seawater."'' or British ton, is a ...
s, but is now usually given internationally in
tonne
The tonne ( or ; symbol: t) is a unit of mass equal to 1,000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton in the United States to distinguish it from the non-metric units of the s ...
s (metric tons). In modern international shipping conventions such as the
International Convention for the Safety of Life at Sea
The International Convention for the Safety of Life at Sea (SOLAS) is an international maritime treaty which sets out minimum safety standards in the construction, equipment and operation of merchant ships. The International Maritime Organiza ...
and the
, deadweight is explicitly defined as the difference in tonnes between the displacement of a ship in water of a
specific gravity
Relative density, also called specific gravity, is a dimensionless quantity defined as the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for solids and liquids is nea ...
of 1.025 (corresponding to average density of
sea water
Seawater, or sea water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has approximate ...
of ) at the
draft
Draft, the draft, or draught may refer to:
Watercraft dimensions
* Draft (hull), the distance from waterline to keel of a vessel
* Draft (sail), degree of curvature in a sail
* Air draft, distance from waterline to the highest point on a v ...
corresponding to the assigned
summer freeboard and the
light displacement
The displacement or displacement tonnage of a ship is its weight. As the term indicates, it is measured indirectly, using Archimedes' principle, by first calculating the volume of water displaced by the ship, then converting that value into weig ...
(lightweight) of the ship.
See also
*
*
TK Bremen
''TK Bremen'' was a Maltese-flagged cargo ship that ran aground on December 16, 2011, at Erdeven, on the coast of southern Brittany in France, generating extensive media coverage and much controversy. Built in 1982 at a shipyard in Busan, South Ko ...
Notes
References
{{DEFAULTSORT:Deadweight Tonnage
Nautical terminology
Ship measurements
Shipbuilding