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Tonnage is a measure of the cargo-carrying capacity of a ship. The term derives from the taxation paid on ''tuns'' or casks of wine, and was later used in reference to the weight of a ship's cargo; however, in modern maritime usage, "tonnage" specifically refers to a calculation of the volume or cargo volume of a ship. Tonnage should not be confused with displacement, which refers to the actual weight of the vessel. Measurement of tonnage can be complicated, not least because it is used to assess fees on commercial shipping. == Tonnage measurements == Gross tonnage (GT) is a function of the volume of all of a ship's enclosed spaces (from keel to funnel) measured to the outside of the hull framing. The numerical value for a ship's GT is always smaller than the numerical values for both its ''gross register tonnage'' and the GRT value expressed equivalently in cubic meters rather than cubic feet (for example, 0.5919 GT = 1 GRT = 2.8316 m3; 200 GT = 274 GRT = 775,88 m3; 500 GT = 665 GRT = 1,883.07 m3; 3,000 GT = 3,776 GRT = 10,692.44 m3), though by how much depends on the vessel's design (volume). There is a sliding-scale factor. Gross tonnage is therefore a kind of capacity-derived index that is used to rank a ship for purposes of determining manning, safety, and other statutory requirements and is expressed simply as GT, which is a unitless entity, even though its derivation is tied to the cubic meter unit of volumetric capacity. Tonnage measurements are now governed by an IMO Convention (International Convention on Tonnage Measurement of Ships, 1969 (London-Rules)), which applies to all ships built after July 1982. In accordance with the convention, the correct term is now GT, which is a function of the moulded volume of all enclosed spaces of the ship. GT is calculated by using the formula : , where ''V'' = total volume in m3 and ''K'' = a figure from 0.22 to 0.32, depending on the ship's size (calculated by : ). For a ship with a total volume of 10,000 m3, the gross tonnage would be 0.28 × 10,000 = 2,800 GT. GT is consequently a measure of the overall size of the ship. For a ship with a total volume of 80,000 m3,the gross tonnage would be 0.2980617 × 80,000 = 23,844.94 GT. Net tonnage (NT) is based on a calculation of the volume of all cargo spaces of the ship. It indicates a vessel's earning space and is a function of the moulded volume of all cargo spaces of the ship. A commonly defined measurement system is important, since a ship's registration fee, harbour dues, safety and manning rules, and the like may be based on its gross tonnage (GT) or net tonnage (NT). Gross register tonnage (GRT) represents the total internal volume of a vessel, where one register ton is equal to a volume of 100 cubic feet (2.83168 m3), a volume that, if filled with fresh water, would weigh around 2,800 kg or 2.8 tonnes. The definition (and calculation) of the internal volume is complex; for instance, a ship's hold may be assessed for bulk grain (accounting for all the air space in the hold) or for bales (omitting the spaces into which bulk, but not baled cargo, would spill). If ''V'' stands for the total internal volume in m3, then the GRT equals ''V'' / 2.83168, so for a ship of 10,000 m3 total internal volume, the gross register tonnage is 10,000 / 2.83168 = 3531.47 GRT. Gross register tonnage was replaced by ''gross tonnage'' in 1994 under the Tonnage Measurement convention of 1969, and is no longer a widely used term in the industry.〔(''CWP Handbook of Fishery Statistical Standards'' ). Retrieved May 10, 2006.〕〔(''International Convention on Tonnage Measurement of Ships, 1969'' ), International Maritime Organisation. Retrieved May 10, 2006.〕 Net register tonnage (NRT) is the volume of cargo the vessel can carry—that is, the gross register tonnage less the volume of spaces that do not hold cargo (e.g., engine compartment, helm station, and crew spaces, again with differences depending on which port or country does the calculations). It represents the volume of the ship available for transporting freight or passengers. It was replaced by ''net tonnage'' in 1994, under the Tonnage Measurement convention of 1969. The Panama Canal/Universal Measurement System (PC/UMS) is based on ''net tonnage'', modified for Panama Canal purposes. PC/UMS is based on a mathematical formula to calculate a vessel's total volume; one PC/UMS net ton is equivalent to 100 cubic feet of capacity.〔(''Panama Canal Tolls'' ), from the Panama Canal Authority. Retrieved May 10, 2006.〕 Suez Canal Net Tonnage (SCNT) is derived with a number of modifications from the former net register tonnage of the Moorsom System and was established by the International Commission of Constantinople in its Protocol of 18 December 1873. It is still in use, as amended by the ''Rules of Navigation'' of the Suez Canal Authority, and is registered in the Suez Canal Tonnage Certificate. Thames measurement tonnage is another volumetric system, generally used for small vessels such as yachts; it uses a formula based on the vessel's length and beam. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tonnage」の詳細全文を読む スポンサード リンク
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