Flank speed is an American nautical term referring to 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 ...

's true maximum speed but it is not equivalent to the term ''full speed ahead''. Usually, flank speed is reserved for situations in which a ship finds itself in imminent danger, such as coming under attack by aircraft. Flank speed is very demanding of fuel and often unsustainable because of propulsion system limitations. The related term emergency may not be any faster than flank but it indicates that the ship should be brought up to maximum speed in the shortest possible time. Other speeds include ''one-third'', ''two-thirds'', ''standard'' and ''full''. One-third and two-thirds are the respective fractions of standard speed. Full is greater than standard but not as great as flank. In surface ship

nuclear marine propulsion Nuclear marine propulsion is propulsion of a ship or submarine with heat provided by a nuclear reactor. The power plant heats water to produce steam for a turbine used to turn the ship's propeller through a gearbox or through an electric generato ...

, the difference between full speed and flank speed is of lesser significance, because vessels can be run at or very near their true maximum speed for a long time with little regard for fuel expended, an important consideration for oil-fueled ships. "Flank speed" is exclusively an American phrase and as such is unknown in

Commonwealth A commonwealth is a traditional English term for a political community founded for the common good. Historically, it has been synonymous with "republic". The noun "commonwealth", meaning "public welfare, general good or advantage", dates from the ...

("White Ensign") navies. The Commonwealth navies use the following telegraph commands: * ''Slow ahead/astern'', the number of revolutions is standardized for the individual ship and is unstated * ''Half ahead/astern'', accompanied by an order for a power setting (e.g., "half ahead both engines, revolutions 1,500") * ''Full speed ahead/astern''. This is reserved for emergencies and as such the word "speed" is included to distinguish it from the other commands mentioned. No power setting is expressed, it being implicit that maximum power is required The term's origin is difficult to verify but likely comes from simplifying the term "Flanking speed" in which naval vessels would attempt to get around the sides or "flanks" of another vessel's vulnerable locations.

References

Nautical terminology {{Water-transport-stub

See also

References