GT - TRB

A lo que parece las Ton de TRB y de GT miden lo mismo: 2,83 m-cúbicos

http://en.wikipedia.org/wiki/Ship_measurements

Ton - The unit of measure often used in specifying the size of a ship. There are three completely unrelated definitions for the word. One of them refers to weight, while the others refer to volume.

Measurement Ton or Ship Ton Calculated as 40 cubic feet of cargo space. (Abbreviated M/T). See Bale Cubic - example, a vessel having capacity of 10,000 M/T has a bale cubic of 400,000 cubic ft.

Register Ton - A measurement of cargo carrying capacity in cubic feet. One register ton is equivalent to 100 cubic feet of cargo space.

Weight Ton - Calculated as a long ton (2,240 pounds) (abbreviated W/T)

Tonnage - A measurement of the cargo-carrying capacity of merchant vessels. It depends on not on weight, but on the volume available for carrying cargo. The basic units of measure are the Register Ton, equivalent to 100 cubic feet, and the Measurement Ton, equivalent to 40 cubic feet. The calculation of tonnage is complicated by many technical factors.

Gross Tons - The entire internal cubic capacity of the ship expressed in tons of 100 cubic feet to the ton, except certain spaces with are exempted such as: peak and other tanks for water ballast, open forecastle bridge and poop, access of hatchways, certain light and air spaces, domes of skylights, condenser, anchor gear, steering gear, wheel house, galley and cabin for passengers.

Net Tons - Obtained from the gross tonnage by deducting crew and navigating spaces and allowances for propulsion machinery.