# Gross tonnage

Gross tonnage (often abbreviated as 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, along with net tonnage, was defined by The International Convention on Tonnage Measurement of Ships, 1969, adopted by the International Maritime Organization in 1969, and came into force on July 18, 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.

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.

## 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 July 18, 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 meters (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 meters and log-meters, have no physical significance, but were rather chosen for historical convenience.

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

${\displaystyle V={\frac {50\times \ln 10\times GT}{W(500,000,000,000\times \ln 10\times GT)}}}$

where ln is the natural logarithm and 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 (about 2.83 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

Batillus-class supertanker

The Batillus-class supertankers was a class of supertanker ships built in France at the end of the 1970s. Four such ships were built between 1976 and 1979—serving until the final one was scrapped in 2003. They were built in the Bassin C dock of the Chantiers de l'Atlantique shipyards at Saint Nazaire, France. Measured by gross tonnage, these were, at the time, the largest ships of any type ever constructed.

Bellamya

Bellamya was a supertanker, built in 1976 by Chantiers de l'Atlantique at Saint-Nazaire for the French branch of Shell Oil. She was the second Batillus class supertanker. Bellamya, together with her sister ships Batillus, Pierre Guillaumat and Prairial, was one of the biggest ships in the world, surpassed in size only by Seawise Giant (later Jahre Viking, Happy Giant and Knock Nevis) built in 1976, and extended in 1981, although the four ships of the Batillus class had a larger gross tonnage. If size is indicated by gross tonnage—a measure of volume--Bellamya was the largest ship ever built.

Compensated gross tonnage

Compensated Gross Tonnage (CGT) is an indicator of the amount of work that is necessary to build a given ship and is calculated by multiplying the tonnage of a ship by a coefficient, which is determined according to type and size of a particular ship.

The standard CGT system was developed in 1977 by the OECD so that inter-country shipbuilding output could be reasonably compared, as different types of ships require a greater or lesser degree of work relative to their gross tonnage. For example, passenger ferry of a given size would require substantially more work to build than a bulk carrier of the same size due to the differing design requirements, internal structure, and required level of detail, but simply comparing the gross tonnage or deadweight of each ship would incorrectly show that they took the same amount of work. When expanded on a national scale, this difference could greatly mislead people as to the actual maritime production capacity of a given country.

The formula to calculate CGT was revised by the OECD in 2007.

Costa Cruises

Costa Crociere S.p.A. (Italian pronunciation: [ˈkɔsta kroˈtʃɛːre]), operating as Costa Cruises (Italian: Costa Crociere), is an Italian cruise line, based in Genoa, Italy, owned by Carnival Corporation & plc.Founded in 1854, the company originally operated cargo ships, in order to carry olive oils and textiles from Sardinia to Liguria. In 1924 the company passed to founder's sons (Federico, Eugenio and Enrico) that started commercial activities, buying the ship Ravenna. Commercial activities continued until the introduction of passenger services in 1947, with regular services between Italy and South America. The company later converted its entire fleet to full-time cruising, and as an independent company became one of the largest cruise operators in Europe. Acquired by Carnival Corporation in 2000, Costa Cruises is now one of ten brands operated by Carnival and accounts for approximately 16% of its revenue.Today, as Costa Cruises Group, the company is one of the main operating companies in the Carnival group, with executive control of the group's activities in Europe. The company is responsible for operation of Costa Cruises in Italy, and AIDA Cruises in Germany and was formerly responsible for the operation of Ibero Cruises in Spain. AIDA was previously a subsidiary of P&O Princess Cruises, being transferred to Costa following the merger of Carnival Corporation and P&O Princess in 2002. Ibero Cruises is a new brand, created in 2007 as a joint venture between Carnival Corporation and Orizonia Group.

The Costa Cruises brand currently operates fourteen cruise ships, which all sail under the Italian flag and provide cruise holidays in the Mediterranean, Northern Europe, the Caribbean, the Indian Ocean, the Middle East, South East Asia and South America.

The company gained international attention on January 13, 2012 when one of its cruise ships, the Costa Concordia, ran aground and capsized off the coast of Italy, because Captain Francesco Schettino wanted to 'salute' the Italian island of Giglio off Tuscany with a close sail past at night. The captain was one of the crew to leave the sinking ship early while many passengers were still on board. The ship was left lying on its starboard side in shallow water. Thirty-two people died. Six weeks later the company made headlines again when a fire on Costa Allegra left it drifting without power for 13 hours in waters near Somalia frequented by pirates, before the ship was taken under tow.

On July 27, 2014, after tugboats had slowly towed the wreck of the Costa Concordia 200 miles (320 kilometers) north from the island of Giglio over a period of five days, the Costa Concordia arrived in its home port of Genoa, Italy, for eventual scrapping. The total cost of the disaster is estimated to be over $2 billion, including$500 million for the loss of the ship and \$1.5 billion for the salvage and recovery operations. On February 11, 2015, Captain Francesco Schettino was found guilty by an Italian court of multiple manslaughter, causing the shipwreck, and abandoning his passengers and was sentenced to 16 years in prison. An Italian appeals court on May 31, 2016 upheld the 16-year prison sentence. He will be released in 2031.

In February 2018, Costa announced its partnership with football club Juventus - “The Italian Champion at Sea, The Glorious League.”

Costa neoRomantica

Costa neoRomantica (formerly Costa Romantica) is a cruise ship for Costa Crociere completed 1993 as a sister ship to Costa neoClassica and was refurbished in 2003. Her public rooms are decorated with rare woods, Carrara marble, and millions of dollars in original works of art. There is also a full luxury spa aboard. Her decks are named for well-known European cities: Monte Carlo, Madrid, Vienna, Verona, Paris, London, Copenhagen and Amsterdam. In November 2011, Costa Romantica underwent a €90 million refurbishing. Two new half decks were added as a part of the refurbishment. This increased the gross tonnage of the ship from 53,000 to 56,769 tons. After the refurbishing, the ship was renamed neoRomantica and started her first journey with the new name on March 2012.In spring 2017, Costa neoRomantica arrived in Hong Kong to operate cruises in the Asia market.In February 2018, Costa neoRomantica served as The J Winter Fashion Show 2018 setting in Hong Kong.

Destiny-class cruise ship

The Destiny class is a class of cruise ships owned by Carnival Cruise Line. The class was modified after the lead ship, Carnival Destiny, was launched. This is reflected in both Carnival Triumph and Carnival Victory.

Displacement (ship)

The displacement or displacement tonnage of a ship is its weight based on the amount of water its hull displaces at varying loads. It is measured indirectly using Archimedes' principle by first calculating the volume of water displaced by the ship then converting that value into weight displaced. Traditionally, various measurement rules have been in use, giving various measures in long tons. Today, metric tonnes are more used.

Ship displacement varies by a vessel's degree of load, from its empty weight as designed (known as "Lightweight tonnage") to its maximum load. Numerous specific terms are used to describe varying levels of load and trim, detailed below.

Ship displacement should not be confused with measurements of volume or capacity typically used for commercial vessels, such as net tonnage, gross tonnage, or deadweight tonnage.

K-class ferry

The K-class ferries (often referred to as 'K-barges', due to their hull type and size) are a group of similarly designed ferries operated by both BC Ferries and TransLink in British Columbia, Canada.

With the exception of MV Kuper, all of the listed K-class vessels were built for service in British Columbia's Ministry of Highways salt water inter-island ferry fleet which was absorbed by BC Ferries in 1985.

List of largest cruise ships

Cruise ships can carry up to thousands of passengers in a single trip, and are some of the largest ships in the world by internal volume, bigger than many cargo ships. The following is a list of cruise ships with a gross tonnage larger than 120,000. Ships are ranked by gross tonnage, and divided into ships that are in service, under construction, and out of service.

List of largest ships by gross tonnage

This is a list of some of the world's largest ships by gross tonnage. Gross tonnage is a monotonic and 1-to-1 function of the ship's internal structural volume, and does not include removable objects placed outside the deck or superstructure, like the shipping containers of a container ship.

MS Freedom of the Seas

MS Freedom of the Seas is a cruise ship operated by Royal Caribbean International. It is the namesake of Royal Caribbean's Freedom class, and can accommodate 3,634 passengers and 1,300 crew on fifteen passenger decks. Freedom of the Seas was the largest passenger ship ever built (by gross tonnage) from 2006 until construction of the Royal Caribbean International's Oasis-class ships in late 2009. As of November 2018, she is the 13th largest passenger ship in the world by gross tonnage, at 155,889 GT.

Since May 2018, the ship is home-ported in San Juan, Puerto Rico and sails to the Caribbean. Although the ship is registered in Nassau, The Bahamas, it was homeported in Barcelona, Spain until October 2017, when it moved to Port Everglades, near Fort Lauderdale.

MY Raven

The MY Raven is a passenger vessel operating for Ullswater 'Steamers' on the lake of Ullswater in the English Lake District, where she has spent her entire working life. She was built in 1889 as a steam vessel, but converted to diesel power in 1934. She is a member of the National Historic Fleet.The Raven has a length of 111.93 feet (34.12 m), a beam of 14.98 feet (4.57 m) and a draught of 2.85 feet (0.87 m). Her gross tonnage is 63, and she can carry 150 passengers. She is the largest vessel in the Ullswater 'Steamers' fleet.

Net register tonnage

Net register tonnage (NRT, nrt, n.r.t.) is a ship's cargo volume capacity expressed in "register tons", one of which equals to a volume of 100 cubic feet (2.83 m3). It is calculated by subtracting non-revenue-earning spaces i.e. spaces not available for carrying cargo, for example engine rooms, fuel tanks and crew quarters, from the ship's gross register tonnage. Net tonnage is thus used in situations where a vessel's earning capacity is important, rather than its mere size. Net register tonnage is not a measure of the weight of the ship or its cargo, and should not be confused with terms such as deadweight tonnage or displacement.

Gross and net register tonnages were replaced by gross tonnage and net tonnage, respectively, when the International Maritime Organization (IMO) adopted The International Convention on Tonnage Measurement of Ships on 23 June 1969. The new tonnage regulations entered into force for all new ships on 18 July 1982, but existing vessels were given a migration period of 12 years to ensure that ships were given reasonable economic safeguards, since port and other dues are charged according to ship's tonnage. Since 18 July 1994 the gross and net tonnages, dimensionless indices calculated from the total moulded volume of the ship and its cargo spaces by mathematical formulae, have been the only official measures of the ship's tonnage. However, the gross and net register tonnages are still widely used in describing older ships.

Net tonnage

Net tonnage (often abbreviated as NT, N.T. or nt) is a dimensionless index calculated from the total moulded volume of the ship's cargo spaces by using a mathematical formula. Defined in The International Convention on Tonnage Measurement of Ships that was adopted by the International Maritime Organization in 1969, the net tonnage replaced the earlier net register tonnage (NRT) which denoted the volume of the ship's revenue-earning spaces in "register tons", units of volume equal to 100 cubic feet (2.83 m3). Net tonnage is used to calculate the port duties and should not be taken as less than 30 per cent of the ship's gross tonnage.Net tonnage is not a measure of the weight of the ship or its cargo, and should not be confused with terms such as deadweight tonnage or displacement. Also, unlike the net register tonnage, the net tonnage is unitless and thus can not be defined as "tons" or "net tons".

Royal Caribbean International

Royal Caribbean International (RCI), also known by its former name Royal Caribbean Cruise Line, is a cruise line brand founded in Norway and based in Miami, Florida, United States. It was founded in 1968 in Norway, and has been organised as a wholly owned subsidiary of Royal Caribbean Cruises Ltd. since 1997. It is one of the largest cruise lines in the world; in 2018, Royal Caribbean International controlled 19.2% of the worldwide cruise market by passengers and 14.0% by revenue. It also operates many of the world's largest ships; as of May 2018, the line operates twenty-five ships, including the four largest ships in the world, and has five additional ships on order.

SS Aleppo

SS Aleppo was a British passenger cargo vessel, launched on 1 November 1864, measuring 292.5 feet by 38.2 feet, 2,057 gross tonnage, built in Glasgow by J & G Thomson Govan. Its first North Atlantic voyage from Liverpool to Halifax to New York City launched on 15 September 1865. The Aleppo contained accommodations for 46 first class and 593 third class passengers. The ship was commissioned for the British and North American Royal Mail Steam Packet Co, Liverpool and transferred to the Cunard Line on 7 September 1878.

In 1880, the ship was fitted with compound engines and in 1890, the SS Aleppo was re-engined with triple-expansion engines by J. Howden & Co. The ship made its last North Atlantic voyage from Liverpool to Boston on 24 March 1892. In 1905, the SS Aleppo was broken up at Preston by Thos W Ward.

Symphony of the Seas

Symphony of the Seas is an Oasis-class cruise ship owned and operated by Royal Caribbean International. As of 22 January 2019, she is the largest passenger ship in the world by gross tonnage, at 228,021 GT, surpassing her sister Harmony of the Seas.Symphony of the Seas was built in the Chantiers de l'Atlantique shipyard in Saint Nazaire, France. She is the fourth ship in its Oasis-class series.

Timeline of largest passenger ships

This is a timeline list of the world's largest passenger ship, ranked by gross tonnage.

Tonnage

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. 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. Tonnage is commonly used to assess fees on commercial shipping.

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