A sister ship is 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 ...

of the same

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differentl ...

or of virtually identical design to another ship. Such vessels share a nearly identical hull and superstructure layout, similar size, and roughly comparable features and equipment. They often share a common naming theme, either being named after the same type of thing or person (places, constellations, heads of state) or with some kind of alliteration. Typically the ship class is named for the first ship of that class. Often, sisters become more differentiated during their service as their equipment (in the case of naval vessels, their armament) are separately altered. For instance, the U.S.

warship A warship or combatant ship is a naval ship that is built and primarily intended for naval warfare. Usually they belong to the armed forces of a state. As well as being armed, warships are designed to withstand damage and are usually faster a ...

s , , , and are all sister ships, each being an . Perhaps the most famous sister ships were the

White Star Line The White Star Line was a British shipping company. Founded out of the remains of a defunct packet company, it gradually rose up to become one of the most prominent shipping lines in the world, providing passenger and cargo services between t ...

's s, consisting of , and . As with some other liners, the sisters worked as running mates. Other sister ships include the

Royal Caribbean International Royal Caribbean International (RCI), also formerly known as Royal Caribbean Cruise Line (RCCL), is a cruise line brand founded in 1968 in Norway and organised as a wholly owned subsidiary of Royal Caribbean Group since 1997. Based in Miami, Flo ...

's and . ''Half-sister'' refers to a ship of the same class but with some significant differences. One example of half-sisters are the First World War-era British s where the first two ships had four guns, but the last ship, , had two guns instead. All three were converted into aircraft carriers, with ''Furious'' again differing from her half-sisters by initially being flush-decked and later by having a much smaller island. Another example is the American s of the

Second World War World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

that came in "long-hull" and "short-hull" versions. Notable

airships An airship or dirigible balloon is a type of aerostat or lighter-than-air aircraft that can navigate through the air under its own power. Aerostats gain their lift from a lifting gas that is less dense than the surrounding air. In early ...

include the American sister ships and , and the German 's '' Hindenburg'' and ''

Graf Zeppelin II The ''Graf Zeppelin'' (; Registration: D-LZ 130) was the last of the German rigid airships built by Zeppelin Luftschiffbau during the period between the World Wars, the second and final ship of the ''Hindenburg'' class, and the second zeppe ...

''. The generally accepted commercial distinctions of a "sister ship" are the following: * Type: Identical main type (bulk, tank, RoRo, etc.) *

Dry weight Vehicle weight is a measurement of wheeled motor vehicles; either an actual measured weight of the vehicle under defined conditions or a gross weight rating for its weight carrying capacity. Curb or kerb weight Curb weight (U.S. English) or kerb ...

(DWT): ± 10% on the DWT (If the ship is 100,000 DWT, 90,000 to 110,000 DWT) * Builder: Identical shipbuilding company name (not the ship yard location or the country of build) The critical overriding criterion is having the same hull design. For example, the popular TESS-57 standard design built by Tsunishi Shipbuilding are built in Japan, China, and the Philippines. All the ships of this design are classed as sister ships. The International Maritime Organization defined ''sister ship'' in IMO resolution MSC/Circ.1158 in 2006. Criteria included these: * A sister ship is a ship built by the same yard from the same plans. * The acceptable deviation of lightship displacement should be between 1 and 2% of the lightship displacement of the lead ship, depending on the length of the ship.

References

{{Reflist Ships Ship classes

See also

References