AskDefine | Define rudder

Dictionary Definition



1 a hinged vertical airfoil mounted at the tail of an aircraft and used to make horizontal course changes
2 (nautical) steering mechanism consisting of a hinged vertical plate mounted at the stern of a vessel

User Contributed Dictionary






  1. An underwater vane used to steer a vessel. The rudder is controlled by means of a wheel, tiller or other apparatus (modern vessels can be controlled even with a joystick or an autopilot).
  2. A control surface on the vertical stabilizer of a fixed-wing aircraft or an autogyro. On some craft, the entire vertical stabilizer comprises the rudder. The rudder is controlled by foot-operated control pedals.


underwater vane used to steer a vessel
  • Arabic: (sukkān) , (dáffa)
  • Catalan: timó
  • Chinese: (duò)
  • Czech: kormidlo
  • Finnish: peräsin
  • French: gouvernail
  • Georgian: საჭე (sač‘e)
  • German: Steuerruder
  • Hungarian: kormánylapát
  • Italian: timone
  • Japanese: 舵
  • Korean: (ki)
  • Latin: gubernaculum
  • Portuguese: leme
  • Russian: руль (rul’)
  • Spanish: timón
  • Swedish: roder
  • Thai: (hăang sĕua)
control surface of an aircraft

See also

Extensive Definition

A rudder is a device used to steer a ship, boat, submarine, hovercraft, or other conveyance that move through a fluid (generally air or water). On an aircraft the rudder is used primarily to counter adverse yaw and p-factor and is not the primary control used to turn the airplane. A rudder operates by redirecting the fluid past the hull or fuselage, thus imparting a turning or yawing motion to the craft. In basic form, a rudder is a flat plane or sheet of material attached with hinges to the craft's stern, tail or after end. Often rudders are shaped so as to minimize hydrodynamic or aerodynamic drag. On simple watercraft, a tiller -- essentially, a stick or pole acting as a lever arm -- may be attached to the top of the rudder to allow it to be steered by a helmsman. In larger vessels, cables, pushrods and hydraulics may be used to link rudders to steering wheels. In typical aircraft, pedals operate rudders via mechanical linkages.

History of the rudder

Early history

Oars mounted on the side of ships for steering are documented from the 3rd millennium BCE in Persia and in artwork, wooden models, and even remnants of actual boats. An early example of an oar mounted on the stern is found in the Egyptian tomb of Men (1422-1411 BC). Stern-mounted oars were also quite common in Roman river navigation as proved from relief depictions more than a millennium later.


One of the world's oldest known depiction of a stern-mounted rudder can be seen on a 2 ft. long tomb pottery model of a Chinese junk dating from the 1st century CE, during the Han Dynasty (202 BC-220 AD). It was discovered in Guangzhou in an archeological excavation carried out by the Guangdong Provincial Museum and Academia Sinica of Taiwan in 1958. Also, many junks incorporated "fenestrated rudders" (rudders with holes in them, allowing for better control), an innovation adopted in the West in 1901 to increase the manoeuvrability of torpedo boats. Detailed descriptions of Chinese junks during the Middle Ages are known from various travellers to China, such as Ibn Battuta of Tangier, Morocco and Marco Polo of Venice, Italy. Even the later Chinese encyclopedist Song Yingxing (1587-1666) and the 17th century European traveler Louis Lecomte would write of the junk design and its use of the rudder with enthusiasm and admiration.


Oars mounted on the side of ships evolved into quarter rudders, which were used from antiquity until the end of the Middle Ages in Europe. As the size of ships and the height of the freeboards increased, quarter-rudders became unwieldy and were replaced by the more sturdy stern-mounted rudders with pintle and gudgeon attachment. The West's oldest known depiction of a stern-mounted rudder can be found on church carvings dating to around 1180.
All evidence indicates that the European stern-mounted rudder, whose technical specifications considerably differ from the Chinese one, was invented independently:
''The only actual concept which can be claimed to have been transmitted from the Chinese is the idea of a stern-mounted rudder, and not its method of attachment nor the manner in which it was controlled. Since that idea of putting a rudder on the stern can be traced back to the models found in Egyptian tombs, the need to have the concept brought into the Middle East is questionable at best. There is no evidence to support the contention that the sternpost-mounted rudder came from China, and no need to call on exterior sources for its introduction into the Mediterranean.'' jo


The Arabs also used a sternpost-mounted rudder which differed technically from both its European and Chinese counterparts. On their ships "the rudder is controlled by two lines, each attached to a crosspiece mounted on the rudder head perpendicular to the plane of the rudder blade." The earliest evidence comes from the Ahsan al-Taqasim fi Marifat al-Aqalim ('The Best Divisions for the Classification of Regions') written by al-Muqaddasi in 985:
''The captain from the crow's nest carefully observes the sea. When a rock is espied, he shouts: "Starboard!" or 'Port!" Two youths, posted there, repeat the cry. The helmsman, with two ropes in his hand, when he hears the calls tugs one or the other to the right or left. If great care is not taken, the ship strikes the rocks and is wrecked.''

Technical details

Boat rudders may be either outboard or inboard. Outboard rudders are hung on the stern or transom. Inboard rudders are hung from a keel or skeg and are thus fully submerged beneath the hull, connected to the steering mechanism by a rudder post which comes up through the hull to deck level, often into a cockpit.
Some sailors use rudder post and mast placement to define the difference between a ketch and a yawl, similar two-masted vessels. Yawls are defined as having the mizzen mast abaft (ie. "aft of") the rudder post; ketches are defined as having the mizzen mast forward of the rudder post.
Small boat rudders that can be steered more or less perpendicular to the hull's longitudinal axis make effective brakes when pushed "hard over." However, terms such as "hard over," "hard to starboard," etc. signify a maximum-rate turn for larger vessels.

Aircraft rudders

Conventional ship and boat rudders

rudder in Arabic: دفة
rudder in Czech: Kormidlo
rudder in Danish: Ror
rudder in German: Ruder
rudder in Spanish: Timón (Dispositivo)
rudder in French: Gouvernail
rudder in Galician: Temón
rudder in Indonesian: Kemudi
rudder in Italian: Timone
rudder in Hungarian: Oldalkormány
rudder in Dutch: Roer (schip)
rudder in Japanese: 舵
rudder in Norwegian: Ror
rudder in Polish: Ster
rudder in Portuguese: Leme (navegação)
rudder in Simple English: Rudder
rudder in Finnish: Peräsin
rudder in Swedish: Roder
rudder in Turkish: Dümen (havacılık)
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