Cargo Tonnage: is either "weight" or "measurement." The weight ton in the United States and in British
countries is the English long or gross ton of 2,240 pounds. In France
and other countries having the metric system a weight ton is 2,204.6 pounds. A "measurement" ton is usually 40 cubic feet,
but in some instances a larger number of cubic feet is taken for a ton. Most ocean package freight is taken at weight or measurement
(W/M) ship's option.
Gross Tonnage: applies to vessels, not to cargo. It is determined by dividing by 100 the contents, in
cubic feet, of the vessel's closed-in spaces. A vessel ton is 100 cubic feet. The register of a vessel states both gross and
Net Tonnage: is a vessel's gross tonnage minus deductions of space occupied by accommodations for crew,
by machinery, for navigation, by the engine room and fuel. A vessel's net tonnage expresses the space available for the accommodation
of passengers and the stowage of cargo. A ton of cargo
in most instances occupies less than 100 cubic feet; hence the vessel's cargo tonnage may exceed its net tonnage, and, indeed,
the tonnage of cargo carried is usually greater than the gross tonnage.
Displacement: of a vessel is the weight, in tons of 2,240 pounds, of the vessel and its contents. Displacement
"light" is the weight of the vessel without stores, bunker fuel, or cargo. Displacement "loaded" is the weight of the vessel
plus cargo, fuel, and stores.
For a modern freight steamer the following relative tonnage figures would ordinarily be approximately correct:
- Net tonnage 4,000
- Gross tonnage 6,000
- Deadweight carrying capacity 10,000
- Displacement, loaded, about 13,350
A vessel's registered tonnage, whether gross or net, is practically the same under the American rules and the British rules.
When measured according to the Panama or Suez tonnage rules most vessels have larger gross and net tonnages than when measured
by British or American national rules.
Source: Article appearing in the American Export Lines, Passenger List from June 28, 1932.