Tonnage is a measure of the

cargo Cargo consists of bulk goods conveyed by water, air, or land. In economics, freight is cargo that is transported at a freight rate for commercial gain. ''Cargo'' was originally a shipload but now covers all types of freight, including tra ...

-carrying capacity of a

ship A ship is a large watercraft that travels the world's oceans and other sufficiently deep waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research, and fishing. Ships are generally distinguished ...

, and is commonly used to assess fees on commercial

shipping Freight transport, also referred as ''Freight Forwarding'', is the physical process of transporting commodities and merchandise goods and cargo. The term shipping originally referred to transport by sea but in American English, it has been ...

. The term derives from the taxation paid on ''

tun TUN or tun may refer to: Biology * Tun shells, large sea snails of the family '' Tonnidae'' * Tun, a tardigrade in its cryptobiotic state * Tun or Toon, common name for trees of the genus '' Toona'' Places * Tun, Sweden, a locality in Västra ...

s'' or casks of wine. In modern maritime usage, "tonnage" specifically refers to a calculation of the volume or cargo volume of a ship. Although tonnage (volume) should not be confused with displacement (the actual weight of the vessel), the long ton (or imperial ton) of 2,240 lb is derived from the fact that a "

" of wine typically weighed that much.

Tonnage measurements

Tonnage measurements are governed by an IMO Convention (International Convention on Tonnage Measurement of Ships, 1969 (London-Rules)), which initially applied to all ships built after July 1982, and to older ships from July 1994.''International Convention on Tonnage Measurement of Ships, 1969''
, International Maritime Organisation. Retrieved May 10, 2006. Gross tonnage (GT) is a function of the volume of all of a ship's enclosed spaces (from

keel The keel is the bottom-most longitudinal structural element on a vessel. On some sailboats, it may have a hydrodynamic and counterbalancing purpose, as well. As the laying down of the keel is the initial step in the construction of a ship, in Br ...

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 of ''gross register tonnage (GRT).'' 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 it derives from the volumetric capacity in cubic metres. 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 Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). ...

of a vessel, where one register ton is equal to a volume of ; a volume that, if filled with fresh water, would weigh around 2.83

tonne The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United State ...

s. 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). Gross register tonnage was replaced by ''gross tonnage'' in 1982 under the Tonnage Measurement convention of 1969, with all ships measured in GRT either scrapped or re-measured in GT by 1994. 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

(e.g.,

engine An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power ...

compartment, helm station, and crew spaces, again with differences depending on which

port A port is a maritime facility comprising one or more wharves or loading areas, where ships load and discharge cargo and passengers. Although usually situated on a sea coast or estuary, ports can also be found far inland, such as H ...

country A country is a distinct part of the world, such as a state, nation, or other political entity. It may be a sovereign state or make up one part of a larger state. For example, the country of Japan is an independent, sovereign state, whi ...

does the calculations). It represents the volume of the ship available for transporting freight or

passenger A passenger (also abbreviated as pax) is a person who travels in a vehicle, but does not bear any responsibility for the tasks required for that vehicle to arrive at its destination or otherwise operate the vehicle, and is not a steward. Th ...

s. 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 The Panama Canal ( es, Canal de Panamá, link=no) is an artificial waterway in Panama that connects the Atlantic Ocean with the Pacific Ocean and divides North and South America. The canal cuts across the Isthmus of Panama and is a condui ...

purposes. PC/UMS is based on a mathematical formula to calculate a vessel's total volume; one PC/UMS net ton is equivalent to 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 (TM) is another volumetric system, generally used for small vessels such as

yacht A yacht is a sailing or power vessel used for pleasure, cruising, or racing. There is no standard definition, though the term generally applies to vessels with a cabin intended for overnight use. To be termed a , as opposed to a , such a pleasu ...

s; it uses a formula based on the vessel's length and beam.

Non-maritime usage of the term ''tonnage''

Tonnage can refer to the quantity of a mineral or the mineral ore extracted from a mine. It may refer to the production of any commodity that is normally expressed in tons or tonnes. The term can also apply to the total weight drawn by a railway locomotive, or the total weight of freight passing over a railway line or road. The tonnage may be expressed as , or . The largest difference between these is about 11% which for some applications is negligible.

Origins

Historically, tonnage was the tax on ''

s'' ( casks) of

wine Wine is an alcoholic drink typically made from Fermentation in winemaking, fermented grapes. Yeast in winemaking, Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different ...

King Edward I Edward I (17/18 June 1239 – 7 July 1307), also known as Edward Longshanks and the Hammer of the Scots, was King of England and Lord of Ireland from 1272 to 1307. Concurrently, he ruled the duchies of Aquitaine and Gascony as a vassal o ...

that held of wine and weighed . This suggests that the unit of weight measurement, the long ton (1,016 kg or 2,240 lb), and tonnage share the same etymology. The confusion between weight-based terms ( deadweight and displacement) stems from this common source and the eventual decision to assess dues based on a ship's deadweight rather than counting the tuns of wine. In 1720 the

Builder's Old Measurement Builder's Old Measurement (BOM, bm, OM, and o.m.) is the method used in England from approximately 1650 to 1849 for calculating the cargo capacity of a ship. It is a volumetric measurement of cubic capacity. It estimated the tonnage of a ship ba ...

Rule was adopted in England to estimate deadweight from the length of

and maximum breadth or beam of a ship. This overly simplistic system was replaced by the Moorsom System in 1854 and calculated internal volume, not weight. This system evolved into the current set of internationally accepted rules and regulations. Harbour dues are based on tonnage. In order to prevent steamships operating at a disadvantage, various tonnage calculations were established to minimize the disadvantage presented by the extra space requirements of steamships. Rather than charging by length, displacement, or the like, charges were calculated based on the viable cargo space. As commercial cargo sailing ships are now largely extinct, gross tonnage is becoming the universal method of calculating ships' dues, and is also a more straightforward and transparent method of assessment.

Notes

References

* ''The Oxford Companion To Ships & The Sea'', by I. C. B. Dear and Peter Kemp. Oxford University Press, 1979. * ''Ship Design and Construction, Volume II''; Thomas Lamb, Editor. Society of Naval Architects and Marine Engineers, 2004. {{Authority control Volume Mass Nautical terminology Ship measurements

Tonnage measurements

Non-maritime usage of the term ''tonnage''

Origins

See also

Notes

References