Wikipedia

# 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.[1] Neither gross tonnage nor gross register tonnage should be confused with measures of mass or weight such as deadweight tonnage or displacement.

Gross tonnage is calculated by measuring a ship's volume (from keel to funnel, to the outside of the hull framing) and applying a mathematical formula.

Gross tonnage, along with net tonnage, was defined by the International Convention on Tonnage Measurement of Ships, 1969, adopted by the International Maritime Organization (IMO) in 1969, and came into force on 18 July 1982. These two measurements replaced gross register tonnage (GRT) and net register tonnage (NRT). Gross tonnage is calculated based on "the moulded volume of all enclosed spaces of the ship" and is used to determine things such as a ship's manning regulations, safety rules, registration fees, and port dues, whereas the older gross register tonnage is a measure of the volume of only certain enclosed spaces.

## History

The International Convention on Tonnage Measurement of Ships, 1969 was adopted by IMO in 1969.[2] The Convention mandated a transition from the former measurements of gross register tonnage (grt) and net register tonnage (nrt) to gross tonnage (GT) and net tonnage (NT).[2] It was the first successful attempt to introduce a universal tonnage measurement system.[2]

Various methods were previously used to calculate merchant ship tonnage, but they differed significantly and one single international system was needed.[2] Previous methods traced back to George Moorsom of Great Britain's Board of Trade who devised one such method in 1854.[2]

The tonnage determination rules apply to all ships built on or after 18 July 1982.[2] Ships built before that date were given 12 years to migrate from their existing gross register tonnage (GRT) to use of GT and NT.[2] The phase-in period was provided to allow ships time to adjust economically, since tonnage is the basis for satisfying manning regulations and safety rules.[2] Tonnage is also the basis for calculating registration fees and port dues.[2] One of the convention's goals was to ensure that the new calculated tonnages "did not differ too greatly" from the traditional gross and net register tonnages.[2]

Both GT and NT are obtained by measuring ship's volume and then applying a mathematical formula.[2] Gross tonnage is based on "the moulded volume of all enclosed spaces of the ship" whereas net tonnage is based on "the moulded volume of all cargo spaces of the ship".[2] In addition, a ship's net tonnage is constrained to be no less than 30% of her gross tonnage.[2]

## Calculation

The gross tonnage calculation is defined in Regulation 3 of Annex 1 of The International Convention on Tonnage Measurement of Ships, 1969.[3] It is based on two variables, and is ultimately an increasing one-to-one function of ship volume:

• V, the ship's total volume in cubic metres (m3), and
• K, a multiplier based on the ship volume.

The value of the multiplier K varies in accordance with a ship's total volume (in cubic metres) and is applied as an amplification factor in determining the gross tonnage value. For smaller ships, K is smaller, for larger ships, K is larger. K is calculated with a formula which uses the common or base-10 logarithm:

${\displaystyle K=0.2+0.02\times \log _{10}(V)\,}$

Once V and K are known, gross tonnage is calculated using the formula, whereby GT is a function of V:

${\displaystyle GT=V\times K\,}$

which by substitution is:

${\displaystyle GT=V\times (0.2+0.02\times \log _{10}(V))}$

Note that the units of gross tonnage, which involve both cubic metres and log-metres, have no physical significance, but were rather chosen for historical convenience.

The inverse, on the other hand, is not as simple. A root-finding algorithm may be used for obtaining an approximation to a ship's volume given its gross tonnage. The exact formula is:

${\displaystyle V={\frac {50\times \ln 10\times GT}{W(5\times 10^{11}\times \ln 10\times GT)}}}$

where ${\displaystyle ln}$  is the natural logarithm and ${\displaystyle W}$  is the Lambert W function.

Gross tonnage Volume (m3) Ratio (1/K)
0.2 1 5
2.2 10 4.545
24 100 4.167
260 1,000 3.846
2800 10,000 3.571
30000 100,000 3.333
320000 1,000,000 3.125

## Notes

1. ^ The gross register ton (GRT) is a unit of volume defined as 100 cubic feet (2.8 m3).
2. International Maritime Organization, 1982.
3. ^ "International Convention on Tonnage Measurement of Ships, 1969". Admiralty and Maritime Law Guide. London. 23 June 1969.

## References

• "International Convention on Tonnage Measurement of Ships, 1969". 1969-06-23. Retrieved 2008-03-23.
• International Maritime Organization (1982). "International Convention on Tonnage Measurement of Ships, 1969". International Maritime Organization. Retrieved 2018-08-19.
• Hayler, William B. (2003). American Merchant Seaman's Manual. Cornell Maritime Press. ISBN 0-87033-549-9.
• Turpin, Edward A.; McEwen, William A. (1980). Merchant Marine Officers' Handbook (4th ed.). Centreville, MD: Cornell Maritime Press. ISBN 978-0-87033-056-8.

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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 1 Neither gross tonnage nor gross register tonnage should be confused with measures of mass or weight such as deadweight tonnage or displacement Gross tonnage is calculated by measuring a ship s volume from keel to funnel to the outside of the hull framing and applying a mathematical formula Gross tonnage along with net tonnage was defined by the International Convention on Tonnage Measurement of Ships 1969 adopted by the International Maritime Organization IMO in 1969 and came into force on 18 July 1982 These two measurements replaced gross register tonnage GRT and net register tonnage NRT Gross tonnage is calculated based on the moulded volume of all enclosed spaces of the ship and is used to determine things such as a ship s manning regulations safety rules registration fees and port dues whereas the older gross register tonnage is a measure of the volume of only certain enclosed spaces Contents 1 History 2 Calculation 3 See also 4 Notes 5 ReferencesHistory EditThe International Convention on Tonnage Measurement of Ships 1969 was adopted by IMO in 1969 2 The Convention mandated a transition from the former measurements of gross register tonnage grt and net register tonnage nrt to gross tonnage GT and net tonnage NT 2 It was the first successful attempt to introduce a universal tonnage measurement system 2 Various methods were previously used to calculate merchant ship tonnage but they differed significantly and one single international system was needed 2 Previous methods traced back to George Moorsom of Great Britain s Board of Trade who devised one such method in 1854 2 The tonnage determination rules apply to all ships built on or after 18 July 1982 2 Ships built before that date were given 12 years to migrate from their existing gross register tonnage GRT to use of GT and NT 2 The phase in period was provided to allow ships time to adjust economically since tonnage is the basis for satisfying manning regulations and safety rules 2 Tonnage is also the basis for calculating registration fees and port dues 2 One of the convention s goals was to ensure that the new calculated tonnages did not differ too greatly from the traditional gross and net register tonnages 2 Both GT and NT are obtained by measuring ship s volume and then applying a mathematical formula 2 Gross tonnage is based on the moulded volume of all enclosed spaces of the ship whereas net tonnage is based on the moulded volume of all cargo spaces of the ship 2 In addition a ship s net tonnage is constrained to be no less than 30 of her gross tonnage 2 Calculation EditThe gross tonnage calculation is defined in Regulation 3 of Annex 1 of The International Convention on Tonnage Measurement of Ships 1969 3 It is based on two variables and is ultimately an increasing one to one function of ship volume V the ship s total volume in cubic metres m3 and K a multiplier based on the ship volume The value of the multiplier K varies in accordance with a ship s total volume in cubic metres and is applied as an amplification factor in determining the gross tonnage value For smaller ships K is smaller for larger ships K is larger K is calculated with a formula which uses the common or base 10 logarithm K 0 2 0 02 log 10 V displaystyle K 0 2 0 02 times log 10 V Once V and K are known gross tonnage is calculated using the formula whereby GT is a function of V G T V K displaystyle GT V times K which by substitution is G T V 0 2 0 02 log 10 V displaystyle GT V times 0 2 0 02 times log 10 V Note that the units of gross tonnage which involve both cubic metres and log metres have no physical significance but were rather chosen for historical convenience The inverse on the other hand is not as simple A root finding algorithm may be used for obtaining an approximation to a ship s volume given its gross tonnage The exact formula is V 50 ln 10 G T W 5 10 11 ln 10 G T displaystyle V frac 50 times ln 10 times GT W 5 times 10 11 times ln 10 times GT where l n displaystyle ln is the natural logarithm and W displaystyle W is the Lambert W function Gross tonnage Volume m3 Ratio 1 K 0 2 1 52 2 10 4 54524 100 4 167260 1 000 3 8462800 10 000 3 57130000 100 000 3 333320000 1 000 000 3 125See also Edit Transport portalCompensated gross tonnage List of world s largest ships by gross tonnage Ton TonnageNotes Edit The gross register ton GRT is a unit of volume defined as 100 cubic feet 2 8 m3 a b c d e f g h i j k l m International Maritime Organization 1982 International Convention on Tonnage Measurement of Ships 1969 Admiralty and Maritime Law Guide London 23 June 1969 References Edit International Convention on Tonnage Measurement of Ships 1969 1969 06 23 Retrieved 2008 03 23 International Maritime Organization 1982 International Convention on Tonnage Measurement of Ships 1969 International Maritime Organization Retrieved 2018 08 19 Hayler William B 2003 American Merchant Seaman s Manual Cornell Maritime Press ISBN 0 87033 549 9 Turpin Edward A McEwen William A 1980 Merchant Marine Officers Handbook 4th ed Centreville MD Cornell Maritime Press ISBN 978 0 87033 056 8 Retrieved from https en wikipedia org w index php title Gross tonnage amp oldid 1125972305, wikipedia, wiki, book, books, library,