The terms "Tonnage" and "Ton" have different meanings and are often confused.
Tonnage is a measure of the size or
cargoCargo is goods or produce transported, generally for commercial gain, by ship, aircraft, train, van or truck. In modern times, containers are used in most intermodal long-haul cargo transport.- Marine Cargo Types :...
capacity of a
shipA ship is a large vessel that floats on water. Ships are generally distinguished from boats based on size and passenger capacity. Ships may be found on lakes, seas, and rivers and they allow for a variety of activities, such as the transport of people or goods, fishing, entertainment, public...
. 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
feeA fee is the price one pays as remuneration for services, especially the honorarium paid to a doctor, lawyer, consultant, or other member of a learned profession...
s on
commercialCommerce is a division of trade or production which deals with the exchange of goods and services from producer to final consumer. It comprises the trading of something of economic value such as goods, services, information, or money between two or more entities...
shippingShipping has multiple meanings. It can be a physical process of transporting goods and cargo, by land, air, and sea. It also can describe the movement of objects by ship.Land or "ground" shipping can be by train or by truck...
.
Gross Register TonnageGross register tonnage represents the total internal volume of a vessel, with some exemptions for non-productive spaces. A register ton is equal to a volume of 100 cubic feet...
(
GRT) represents the total internal
volumeThe volume of any solid, liquid, gas, plasma, theoretical object, or vacuum is how much three-dimensional space it occupies, often quantified numerically. One-dimensional figures and two-dimensional shapes are assigned zero volume in the three-dimensional space...
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 feetThe cubic foot is an imperial and US customary unit of volume, used in the United States, Canada and the United Kingdom. It is defined as the volume of a cube with sides of one foot in length.- Symbols :...
(2.83
m³The cubic metre is the SI derived unit of volume. It is the volume of a cube with edges one metre in length. An alternative name, which allowed a different usage with metric prefixes, was the stère...
), which volume, if filled with fresh water, would weigh around 2,800 kg or 2.8
tonneA tonne or metric ton , also referred to as a metric tonne, is a measurement of mass equal to , or approximately the mass of one cubic metre of water. It is not an SI unit but is accepted for use with the SI...
s.
The terms "Tonnage" and "Ton" have different meanings and are often confused.
Tonnage is a measure of the size or
cargoCargo is goods or produce transported, generally for commercial gain, by ship, aircraft, train, van or truck. In modern times, containers are used in most intermodal long-haul cargo transport.- Marine Cargo Types :...
capacity of a
shipA ship is a large vessel that floats on water. Ships are generally distinguished from boats based on size and passenger capacity. Ships may be found on lakes, seas, and rivers and they allow for a variety of activities, such as the transport of people or goods, fishing, entertainment, public...
. 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
feeA fee is the price one pays as remuneration for services, especially the honorarium paid to a doctor, lawyer, consultant, or other member of a learned profession...
s on
commercialCommerce is a division of trade or production which deals with the exchange of goods and services from producer to final consumer. It comprises the trading of something of economic value such as goods, services, information, or money between two or more entities...
shippingShipping has multiple meanings. It can be a physical process of transporting goods and cargo, by land, air, and sea. It also can describe the movement of objects by ship.Land or "ground" shipping can be by train or by truck...
.
Tonnage measurements
Gross Register TonnageGross register tonnage represents the total internal volume of a vessel, with some exemptions for non-productive spaces. A register ton is equal to a volume of 100 cubic feet...
(
GRT) represents the total internal
volumeThe volume of any solid, liquid, gas, plasma, theoretical object, or vacuum is how much three-dimensional space it occupies, often quantified numerically. One-dimensional figures and two-dimensional shapes are assigned zero volume in the three-dimensional space...
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 feetThe cubic foot is an imperial and US customary unit of volume, used in the United States, Canada and the United Kingdom. It is defined as the volume of a cube with sides of one foot in length.- Symbols :...
(2.83
m³The cubic metre is the SI derived unit of volume. It is the volume of a cube with edges one metre in length. An alternative name, which allowed a different usage with metric prefixes, was the stère...
), which volume, if filled with fresh water, would weigh around 2,800 kg or 2.8
tonneA tonne or metric ton , also referred to as a metric tonne, is a measurement of mass equal to , or approximately the mass of one cubic metre of water. It is not an SI unit but is accepted for use with the SI...
s. Calculation of GRT is complex; a hold can, for instance, be assessed for
bulk grainBulk cargo is commodity cargo that is transported unpackaged in large quantities. These cargos are usually dropped or poured, with a spout or shovel bucket, as a liquid or as a mass of relatively small solids , into a bulk carrier ship's hold, railroad car, or tanker truck/trailer/semi-trailer body...
(accounting for all the air space in the hold) or for
bale-Places:* Bale , a small town in Croatia* Bale Province, Ethiopia, a former province in Ethiopia* Bale Zone in Oromia, Ethiopia* Bale, Norfolk in England* Bale, Poland* Balé Province, Burkina Faso* Basel, the Swiss city, for which the French name is Bâle...
s (omitting the spaces into which bulk, but not baled cargo would spill). 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
cargoCargo is goods or produce transported, generally for commercial gain, by ship, aircraft, train, van or truck. In modern times, containers are used in most intermodal long-haul cargo transport.- Marine Cargo Types :...
(e.g.
engineAn engine is a machine that produces mechanical force and motion from another form of energy . It is also referred to as a prime mover. An automobile makes use of several motors to start the car and drive the car's various pumps – but the power plant that propels the car is called an engine...
compartment,
helmThe wheel of a ship is the modern method of adjusting the angle of the rudder, in turn changing the direction of the boat or ship. It is also called the helm, together with the rest of the steering mechanism....
station,
crewA crew is a body or a class of people who work at a common activity, generally in a structured or hierarchical organization. A location in which a crew works is called a crewyard or a workyard...
spaces, etc., again with differences depending on which
port||-||-||-||-||-||-||-||-|}A port is a facility for receiving ships and/or transferring cargo. It is usually found at the edge of an ocean, sea, river, or lake. The best ports have deep water in channels or berths, and protection from the wind and waves...
or
countryIn geography, a country is a geographical region. The term is often applied to a political division or the territory of a state, or to a smaller, or former, political division of a geographical region...
is doing the calculations). It represents the volume of the ship available for transporting freight or
passengerA passenger is a term broadly used to describe any person who travels in a vehicle, but bears little or no responsibility for the tasks required for that vehicle to arrive at its destination.There are two common contexts in which the term is used:...
s. It was replaced by
net tonnage in 1994, under the Tonnage Measurement convention of 1969.
Gross TonnageGross tonnage is a unitless index related to a ship's overall internal volume. Gross Tonnage is different from Gross Register Tonnage...
(
GT) is a function of the volume of all ship's enclosed spaces (from
keelIn boats and ships, keel can refer to either of two parts: a structural element, or a hydrodynamic element. These parts overlap. As the laying down of the keel is the initial step in construction of a ship, the construction is dated from this event, with only the ship's launching considered more...
to
funnelA funnel is a pipe with a wide, often conical mouth and a narrow stem. It is used to channel liquid or fine-grained substances into containers with a small opening. Without a funnel,spillage would occur....
) 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
m³The cubic metre is the SI derived unit of volume. It is the volume of a cube with edges one metre in length. An alternative name, which allowed a different usage with metric prefixes, was the stère...
; 200 GT = 274 GRT = 775
m³The cubic metre is the SI derived unit of volume. It is the volume of a cube with edges one metre in length. An alternative name, which allowed a different usage with metric prefixes, was the stère...
; 500 GT = 665 GRT = 1,883
m³The cubic metre is the SI derived unit of volume. It is the volume of a cube with edges one metre in length. An alternative name, which allowed a different usage with metric prefixes, was the stère...
; 3,000 GT = 3,776 GRT = 10,692
m³The cubic metre is the SI derived unit of volume. It is the volume of a cube with edges one metre in length. An alternative name, which allowed a different usage with metric prefixes, was the stère...
), 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.
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 : , 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 : ), so that, for a ship of 10,000
m³The cubic metre is the SI derived unit of volume. It is the volume of a cube with edges one metre in length. An alternative name, which allowed a different usage with metric prefixes, was the stère...
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 tonnageNet tonnage is a calculated representation of a the internal volume of a ship's cargo holds. It is expressed in "tons", which are units of volume defined as 100 cubic feet . The "ton" as a unit of volume should not be confused with the far more common "ton" as a unit of weight or mass...
(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 feetThe cubic foot is an imperial and US customary unit of volume, used in the United States, Canada and the United Kingdom. It is defined as the volume of a cube with sides of one foot in length.- Symbols :...
of capacity.
The
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 tonnageThames Measurement, also known as Thames Tonnage, is a system for measuring ships and boats. It was created by the Thames Yacht Club, and was designed for small vessels, such as yachts. It was originally used for calculating the port dues for yachts; the formula was also used in some early...
is another volumetric system, generally used for small vessels such as
yachtA yacht is a high end recreational boat. It designates two rather different classes of watercraft, sailing and power boats. Yachts are different from working ships mainly by their leisure purpose. It was not until the rise of the steamboat and other types of powerboat that sailing vessels in...
s; it uses a formula based on the vessel's length and beam.
Weight measurements
While not "tonnage" in the proper sense, the following methods of ship measurement are often incorrectly referred to as such:
DisplacementA ship's displacement is its mass at any given time, generally expressed in metric tons or long tons. The term is often used to mean the ship's mass when it is loaded to its maximum capacity. A number of synonymous terms exist for this maximum mass, such as loaded displacement, full load...
is the actual total weight of the vessel. It is often expressed in
long tonLong ton is the name for the unit called the "ton" in the avoirdupois or Imperial system of measurements, as used in the United Kingdom and several other Commonwealth countries. It has been mostly replaced by the tonne, and in the USA by the short ton. It is equal to or of salt water with a...
s or in
metric tonA tonne or metric ton , also referred to as a metric tonne, is a measurement of mass equal to , or approximately the mass of one cubic metre of water. It is not an SI unit but is accepted for use with the SI...
s, and is calculated simply by multiplying the volume of the
hullA hull is the watertight body of a ship or boat. Above the hull comes the superstructure and deckhouse. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...
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 feetThe cubic foot is an imperial and US customary unit of volume, used in the United States, Canada and the United Kingdom. It is defined as the volume of a cube with sides of one foot in length.- Symbols :...
. 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 tonLong ton is the name for the unit called the "ton" in the avoirdupois or Imperial system of measurements, as used in the United Kingdom and several other Commonwealth countries. It has been mostly replaced by the tonne, and in the USA by the short ton. It is equal to or of salt water with a...
s. Using the
SISi, si, or SI may refer to :- Places :* Mount Si, a mountain in state of Washington* Si County, county in Anhui, China* Si River, a river in China* Slovenia, a European nation Si, si, or SI may refer to (all SI unless otherwise stated):- Places :* Mount Si, a mountain in state of Washington* 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
ArchimedesArchimedes of Syracuse was a Greek mathematician, physicist, engineer, inventor, and astronomer. Although few details of his life are known, he is regarded as one of the leading scientists in classical antiquity...
, 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
fuelFuel is any material that is burned or altered to obtain energy and to heat or to move object. Fuel releases its energy either through a chemical reaction means, such as combustion, or nuclear means, such as nuclear fission or nuclear fusion...
, passengers,
cargoCargo is goods or produce transported, generally for commercial gain, by ship, aircraft, train, van or truck. In modern times, containers are used in most intermodal long-haul cargo transport.- Marine Cargo Types :...
, water, etc. on board.
Deadweight tonnageDeadweight tonnage is a measure of how much weight a ship is carrying or can safely carry. It is the sum of the weights of cargo, fuel, fresh water, ballast water, provisions, passengers, and crew...
(often abbreviated as
DWT for deadweight tonnes) is the displacement at any loaded condition minus the lightship weight. It includes the crew, passengers, cargo,
fuelFuel is any material that is burned or altered to obtain energy and to heat or to move object. Fuel releases its energy either through a chemical reaction means, such as combustion, or nuclear means, such as nuclear fission or nuclear fusion...
, water, and stores. Like Displacement, it is often expressed in long tons or in metric tons.
Origins
Historically, tonnage was the tax on
tuns (
caskPeripheral plasma membrane protein CASK is a protein that in humans is encoded by the CASK gene. This gene is also known by several other names: CMG 2 , calcium/calmodulin-dependent serine protein kinase 3 and membrane-associated guanylate kinase 2.-Genomics:This gene is located on the short arm of...
s) of
wineWine is an alcoholic beverage typically made of fermented grape juice. The natural chemical balance of grapes is such that they can ferment without the addition of sugars, acids, enzymes or other nutrients. Wine is produced by fermenting crushed grapes using various types of yeast. Yeast consumes...
that held approximately 252 gallons of wine and weighed approximately 2,240
poundsThe pound or pound-mass is a unit of mass used in the imperial, United States customary and other systems of measurement...
. This suggests that the unit of weight measurement,
long tonLong ton is the name for the unit called the "ton" in the avoirdupois or Imperial system of measurements, as used in the United Kingdom and several other Commonwealth countries. It has been mostly replaced by the tonne, and in the USA by the short ton. It is equal to or of salt water with a...
s (also 2,240 lb) and tonnage both share the same etymology. The confusion between weight based terms (
deadweightThe term deadweight or dead weight may refer to:*The economics concept deadweight loss.*Deadweight tonnage is an expression of a ship's carrying capacity, including the weight of the crew, passengers, cargo, fuel, ballast, drinking water, and stores....
and
displacementIn fluid mechanics, displacement occurs when an object is immersed in a fluid, pushing it out of the way and taking its place. The volume of the fluid displaced can then be measured, as in the illustration, and from this the volume of the immersed object can be deduced .An object that sinks...
) stems from this common source and the eventual decision to assess dues based on a ship's
deadweightThe term deadweight or dead weight may refer to:*The economics concept deadweight loss.*Deadweight tonnage is an expression of a ship's carrying capacity, including the weight of the crew, passengers, cargo, fuel, ballast, drinking water, and stores....
rather than counting the tuns of wine. In 1720 the
Builder's Old MeasurementBuilder's Old Measurement is the method of calculating the size or cargo capacity of a ship used in England from approximately 1720 to 1849. The BOM estimated the tonnage of a ship based on length and maximum beam...
Rule was adopted to estimate deadweight from the length of
keelIn boats and ships, keel can refer to either of two parts: a structural element, or a hydrodynamic element. These parts overlap. As the laying down of the keel is the initial step in construction of a ship, the construction is dated from this event, with only the ship's launching considered more...
and maximum breadth or
beamThe beam of a ship is its width at the widest point. Generally speaking, the wider the beam of a ship , the more initial stability it has, at expense of reserve stability in the event of a capsize, where more energy is required to right the vessel from its inverted position...
of a ship. This overly simplistic system was replaced by the
Moorsom SystemThe Moorsom System is a method created in Great Britain of calculating the tonnage or cargo capacity of sailing ships as a basis for assessing harbour and other vessel fees...
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.
See also
- Displacement (fluid)
In fluid mechanics, displacement occurs when an object is immersed in a fluid, pushing it out of the way and taking its place. The volume of the fluid displaced can then be measured, as in the illustration, and from this the volume of the immersed object can be deduced .An object that sinks...
- Ton
The term ton or tonne generally refers to a unit of mass. However, there exists more than one measure of mass that are named "ton", so one has to be specific when using the term. While they do vary considerably, a ton is generally one of the heaviest units of mass referred to in colloquial speech...
- Short ton
The short ton is a unit of weight equal to . In the United States it is often called simply ton without distinguishing it from the metric ton or the long ton ; rather, the other two are specifically noted. There are, however, some U.S...
- List of world's largest ships by gross tonnage
- Long ton
Long ton is the name for the unit called the "ton" in the avoirdupois or Imperial system of measurements, as used in the United Kingdom and several other Commonwealth countries. It has been mostly replaced by the tonne, and in the USA by the short ton. It is equal to or of salt water with a...
- Metric tonne
- Measures of ship displacement
- Builder's Old Measurement
Builder's Old Measurement is the method of calculating the size or cargo capacity of a ship used in England from approximately 1720 to 1849. The BOM estimated the tonnage of a ship based on length and maximum beam...