# Dictionary Definition

tonnage n : a tax imposed on ships that enter the
US; based on the tonnage of the ship [syn: tunnage, tonnage
duty]

# User Contributed Dictionary

## English

### Pronunciation

- ˈtɐnɪdʒ
- "tVnIdZ

### Noun

tonnage# Extensive Definition

Tonnage is a measure of the size or cargo capacity of a ship. The term derives from the
taxation paid on tuns 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. The term is still sometimes incorrectly
used to refer to the weight of a loaded or empty vessel.

Measurement of tonnage can be less than
straightforward, not least because it is used to assess fees on commercial shipping.

## Tonnage measurements

Gross Register Tonnage (GRT) represents the total
internal volume of a
vessel, with some exemptions for non-productive spaces such as crew
quarters; 1 gross register ton is equal to a volume of 100 cubic feet
(2.83 m³), which
volume, if filled with water, would weigh around 2,800 kg or 2.8
tonnes. -It- is always
smaller than volume measured in m³. This
calculation is complex; a hold can, for instance, be assessed for
grain (accounting for all
the air space in the hold) or for bales (exempting the spaces between
structural frames). Gross register tonnage was replaced by gross
tonnage in 1994 under the Tonnage Measurement convention of 1969,
but is still a widely used term in the industry.

Net Register Tonnage (NRT) is the volume of cargo
the vessel can carry; ie. the Gross Register Tonnage less the
volume of spaces that will not hold cargo (e.g. engine compartment, helm
station, crew spaces, etc.,
again with differences depending on which port or country is doing 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.

Gross Tonnage (GT) is a function of the volume of
all 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 her gross register
tonnage and the GRT value expressed equivalently in cubic meters
rather than cubic feet, for example: 0.5919 GT = 1 GRT = 2.83
m³;
200 GT = 274 GRT = 775 m³; 500 GT =
665 GRT = 1,883 m³; 3,000 GT
= 3,776 GRT = 10,692 m³), though
by how much depends on the vessel design (volume). There is a
sliding scale factor. So GT is a kind of capacity-derived index
that is used 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.

However, this "less than" so-called relationship
between the values of a ship's GT and GRT is of no consequence or
significance, since the approaches used for determining tonnage
under each scheme are not directly comparable. "Noses are always
smaller than the faces they are attached to" ! True enough
statement, but of no significance. So don't confuse Gross Register
Tons (the volume unit) with Gross Register Tonnage (the
standardized scheme for including / excluding various parts of a
ship to factor in). A ship of 10,000 cub.meters derived under GT
formulation rules has a GT of 2,800 GT. However, you cannot simply
convert the 10,000 cub.meter value into an equivalent number (
divide by 2.83 = 3,533 GRTons) of hundreds of cub.feet (a gross
register ton) and simply relate this back to the GT. That is
because, this converted value of 3,533 GRTons is not truly
reflective of the ship's ACTUAL Gross Register Tonnage, as
determined by another approach and set of measurement rules. GT and
GRT are indicators of different though related things (volume).
Both concepts involve ship volume, and all volumes can be expressed
equivalently in feet or meters cubed.

Furthermore, according to the UN, "The two
tonnage conventions produce very different tonnage values. Although
GT measurement is higher than GRT, there is no simple correlation
between the two units (GT is often double the GRT, but sometimes as
much as four times the GRT)."

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 to
use now is GT, which is a function of the moulded volume of all
enclosed spaces of the ship.

It is calculated by using the formula : GT = K
\cdot V , where V = total volume in m³ and K = a figure from 0.22
up to 0.32, depending on the ship’s size (calculated by : K = 0.2 +
0.02 \cdot\log_V ), so that, for a ship of 10,000 m³ total
volume, the gross tonnage would be 0.28 x 10,000 = 2,800 GT. GT is
consequently a measure of the overall size of the ship.

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 etc, are based on its gross tonnage, GT, or net
tonnage, NT.

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; a PC/UMS net ton is equivalent to 100
cubic
feet of capacity.

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.

Many people in many countries, including those
professional people working in maritime industries for many years
or even in their lifetime, often confuse "Tonnage" and "Ton".
Please note that "Tonnage" refers to the unit of a ship's volume in
measurement for registration and "Ton" refers to the unit of
weight. They are totally different in concept.

## Weight measurements

While not "tonnage" in the proper sense, the
following methods of ship measurement are often incorrectly
referred to as such:

Displacement
is the actual total weight of the vessel. It is often expressed in
long
tons or in metric
tons, and is calculated simply by multiplying the volume of the
hull
below the waterline (ie. the volume of water it is displacing) by
the density of the water. (Note that the density will depend on
whether the vessel is in fresh or salt water, or is in the tropics,
where water is warmer and hence less dense.) For example, in sea
water, first determine the volume of the submerged portion of the
hull as follows: Multiply its length by its breadth and the draft,
all in feet. Then multiply the product thereby obtained by the
block
coefficient of the hull to get the hull volume in cubic feet.
Then multiply this figure by 64 (the weight of one cubic foot of
seawater) to get the weight of the ship in pounds; or divide by 35
to calculate the weight in long tons. Using
the SI or metric
system : displacement (in tonnes) is volume (in m³) multiplied by
the specific gravity of sea water (1.025 nominally).

The word "displacement" arises from the basic
physical law, discovered by Archimedes, that
the weight of a floating object equates exactly to that of the
water which would otherwise occupy the "hole in the water"
displaced by the ship.

Lightship or Lightweight measures the actual
weight of the ship with no fuel, passengers, cargo, water, etc. on board.

Deadweight (often abbreviated as DWT for
deadweight tonnes) is the displacement at any loaded condition
minus the lightship weight. It includes the crew, passengers,
cargo, fuel, water, and
stores. Like
Displacement, it is often expressed in long tons or in metric
tons.

## Origins

Historically, tonnage was the tax on tuns
(casks) of wine that held approximately 252
gallons of wine and weighed approximately 2,240 pounds. This
suggests that the unit of weight measurement, long tons (also
2,240 lb) and tonnage both 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 Rule was adopted to estimate deadweight from
the length of keel 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.

When steamships came into being, they could carry
less cargo, size for size, than sailing ships. As well as spaces
taken up by boilers and steam engines, steamships carried extra
fresh water for the boilers as well as coal for the engines. Thus,
to move the same volume of cargo as a sailing ship, a steamship
would be considerably larger than a sailing ship.

"Harbour Dues" are based on tonnage. In order to
prevent steamships operating at a disadvantage, various tonnage
calculations were established to minimise the disadvantage that the
extra space requirements of steamships presented. Rather than
charging by length or displacement etc, charges were calculated 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 straight-forward 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. ISBN 0-19-860616-8
- Ship Design and Construction, Volume II; Thomas Lamb, Editor. Society of Naval Architects and Marine Engineers, 2004. ISBN 99909-0-620-3

tonnage in Danish: Tonnage

tonnage in German: Schiffsmaße

tonnage in Modern Greek (1453-): Χωρητικότητα
πλοίου

tonnage in Finnish: Vetoisuus

tonnage in French: Tonnage

tonnage in Hebrew: תפוסה

tonnage in Croatian: Registarska tona

tonnage in Italian: Stazza

tonnage in Japanese: トン数

tonnage in Dutch: Tonnenmaat

tonnage in Polish: Tonaż

tonnage in Russian: Водоизмещение

tonnage in Slovak: BRT

tonnage in Slovenian: Registrska tona

tonnage in Swedish: Tonnage

tonnage in Chinese: 标准排水量

# Synonyms, Antonyms and Related Words

accommodation, argosy, avoirdupois, beef, beefiness, bottoms, burden, capacity, carriage, cartage, content, cordage, deadweight, drayage, expressage, fatness, fleet, flotilla, freight, freightage, gravity, gross weight, haulage, heaviness, heft, heftiness, limit, line, liveweight, measure, merchant fleet,
merchant navy, navy, neat
weight, net, net weight,
overbalance,
overweight, ponderability, ponderosity, ponderousness, poundage, quantity, room, shipping, ships, space, stowage, underweight, volume, weight, weightiness, whaling
fleet