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Stern-mounted steering oar of an Egyptian riverboat depicted in the Tomb of Menna (c. 1422-1411 BC)
Stern-mounted steering oar of a Roman boat, 1st century AD (RG-Museum, Cologne).

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

Terminology

Generally, the steering gear of ancient vessels can be classified into side-rudders and stern-mounted rudders, depending on their location on the ship. A third term, steering oar, can denote both types. In a Mediterranean context, side-rudders are more specifically called quarter-rudders as the later term designates more exactly the place where the rudder was mounted. Stern-mounted rudders are uniformly suspended at the back of the ship in a central position, but the term has historically been found wanting because it does not take into account that the stern rudders were attached to the ship hull in quite a different way: While the European pintle-and-gudgeon rudder was attached to the sternpost by pivoting iron fastenings, the Arabs used instead a system of lashings. Chinese stern rudders also featured tackles, but, unlike their medieval and Arab counterparts, had no sternpost to which to attach them. Roman and particularly ancient Egyptian stern rudders featured again a different method of fastening where the stock, having a single point of contact with the stern, was additionally secured to the ship body by an upright rudderpost or braced ropes.

Ancient Egypt

Rowing oars set aside for steering appeared on large Egyptian vessels long before the time of Menes (3100 BC). In the Old Kingdom (2686 BC-2134 BC) as much as five steering oars are found on each side of passenger boats. The tiller, at first a small pin run through the stock of the steering oar, can be traced to the fifth dynasty (2504–2347 BC). Both the tiller and the introduction of an upright steering post abaft reduced the usual number of necessary steering oars to one each side. Apart from side-rudders, single rudders put on the stern can be found in a number of tomb models of the time, particularly during the Middle Kingdom when tomb reliefs suggests them commonly employed in Nile navigation. The first literary reference appears in the works of the Greek historian Herodot (484-424 BC), who had spent several month in Egypt: "They make one rudder, and this is thrust through the keel", probably meaning the crotch at the end of the keel (see right pic "Tomb of Menna").

In Iran, oars mounted on the side of ships for steering are documented from the 3rd millennium BCE in artwork, wooden models, and even remnants of actual boats.

Ancient Rome

Roman navigation used primarily quarter rudders which went in the Mediterranean through a long period of constant refinement and improvement, so that by Roman times ancient vessels reached extraordinary sizes. The strength of quarter rudder lay in its combiantion of effectiveness, adaptability and simpleness. Roman quarter rudder mounting systems survived mostly intact through the medieval period.

By the first half of the 1st century AD, rudders mounted on the stern were also quite common in Roman river and harbour craft as proved from reliefs and archaeological finds (Zwammderdam, Woerden 7). A tomb plaque of Hadrianic age shows a harbour tug boat in Ostia with a long stern-mounted oar for better leverage. Interestingly, the boat already featured a spritsail, adding to the mobility of the harbour vessel. Further attested Roman uses of stern-mounted rudders includes barges under tow, transport ships for wine casks, and diverse other ship types. Also, the well-known Zwammerdam find, a large river barge at the mouth of the Rhine, featured a large rudder mounted on the stern. According to new research, the advanced Nemi ships, the palace barges of emperor Caligula (37-41 AD), may have featured 14 m long stern-mounted rudders.

China

One of oldest known depiction of a stern-mounted rudder in China can be seen on a 2 ft. long tomb pottery model of a 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.

Chinese rudders were not supported by pintle-and-gudgeon as in the Western tradition; rather, they were attached to the hull by means of wooden jaws or sockets, while typically larger ones were suspended from above by a rope tackle system so that they could be raised or lowered into the water. 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.

Middle Ages

The pintle-and-gudgeon attachment system on European medieval ships. The iron hinge system made a vital contribution to the navigation achievements of the age of discovery and thereafter.

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. While stern-mounted rudders were found in Europe on a wide range of vessels since Roman times, including light war galleys in Mediterranean, the oldest known depiction of a pintle-and-gudgeon rudder can be found on church carvings dating to around 1180.

Historically, the radical concept of the medieval pintle-and-gudgeon rudder did not come as a single invention into being. It presented rather a combination of ideas which each had been long around before: rudders mounted on the stern, iron hinges and the straight sternpost of northern European ships. While earlier rudders were mounted on the stern by the way of rudderposts or tackles, the iron hinges allowed for the first time to attach the rudder to the entire length of the sternpost in a really permanent fashion. However, its full potential could only to be realized after the introduction of the vertical sternpost and the full-rigged ship in the 14th century. From the age of discovery onwards, European ships with pintle-and-gudgeon rudders sailed successfully on all seven seas.

Contrary to an older hypothesis, all evidence indicates that the European hinged 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.

Arabs

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

The tail of a Martin B-57E with rudder deflected to starboard.

On an aircraft, the rudder is called a "control surface" along with the rudder-like elevator (attached to horizontal tail structure) and ailerons (attached to the wings) that control pitch and roll. The rudder is usually attached to the fin (or vertical stabilizer) which allows the pilot to control yaw in the vertical axis, i.e. change the horizontal direction in which the nose is pointing. The rudder's direction is manipulated with the movement of foot pedals by the pilot.

In practice, both aileron and rudder control input are used together to turn an aircraft, the ailerons imparting roll, the rudder imparting yaw, and also compensating for a phenomenon called adverse yaw. Adverse yaw is readily seen if the most simple type of ailerons alone are used for a turn. The downward moving aileron acts like a flap, generating more lift for one wing, and therefore more drag (though since the 1930s, many aircraft have used frise ailerons or differential ailerons, which compensate for the adverse yaw and require little or no rudder input in regular turns). Initially, this drag yaws the aircraft in the direction opposite to the desired course. A rudder alone will turn a conventional fixed wing aircraft, but much more slowly than if ailerons are also used in conjunction. Use of rudder and ailerons together produces co-ordinated turns, in which the longitudinal axis of the aircraft is in line with the arc of the turn, neither slipping (under-ruddered), nor skidding (over-ruddered). Improperly ruddered turns at low speed can precipitate a spin which can be dangerous at low altitudes.

Sometimes pilots may intentionally operate the rudder and ailerons in opposite directions in a maneuver called a forward slip. This may be done to overcome crosswinds and keep the fuselage in line with the runway, or to more rapidly lose altitude by increasing drag, or both.

Footnotes

  1. Lawrence V. Mott, p.2f.
  2. William F. Edgerton: “Ancient Egyptian Steering Gear”, The American Journal of Semitic Languages and Literatures, Vol. 43, No. 4. (1927), pp. 255-265
  3. R. O. Faulkner: Egyptian Seagoing Ships, The Journal of Egyptian Archaeology, Vol. 26. (1941), pp. 3-9
  4. ^ William F. Edgerton: "Ancient Egyptian Steering Gear", The American Journal of Semitic Languages and Literatures, Vol. 43, No. 4. (1927), pp. 255
  5. William F. Edgerton: "Ancient Egyptian Steering Gear", The American Journal of Semitic Languages and Literatures, Vol. 43, No. 4. (1927), pp. 257
  6. William F. Edgerton: "Ancient Egyptian Steering Gear", The American Journal of Semitic Languages and Literatures, Vol. 43, No. 4. (1927), pp. 260
  7. Lawrence V. Mott, The Development of the Rudder, A.D. 100-1337: A Technological Tale, Thesis May 1991, Texas A&M University, p.84, 92
  8. Francesco Tiradritti (ed.): “The Treasures of the Egyptian Museum”, The American University in Cairo Press, Cairo 1999, ISBN 978 977 424 504 6, p.92f.
  9. Mohamed Ata: “Egypt from Past to Present. Through the Eyes of an Egyptian”, Cairo 2007, p.68
  10. Herodot: Histories, 2.96
  11. William F. Edgerton: “Ancient Egyptian Steering Gear”, The American Journal of Semitic Languages and Literatures, Vol. 43, No. 4. (1927), pp. 263
  12. ^ Lawrence V. Mott, The Development of the Rudder, A.D. 100-1337: A Technological Tale, Thesis May 1991, Texas A&M University, p.1
  13. Lionel Casson: Harbour and River Boats of Ancient Rome, The Journal of Roman Studies, Vol. 55, No. 1/2, Parts 1 and 2 (1965), pp. 31-39 (plate 1)
  14. Lionel Casson, Harbour and River Boats of Ancient Rome, The Journal of Roman Studies, Vol. 55, No. ½, Parts 1 and 2. (1965), pp. 35 (Pl. I); 36, Fn.43 (Pl.II,1)
  15. Lawrence V. Mott, The Development of the Rudder, A.D. 100-1337: A Technological Tale, Thesis May 1991, Texas A&M University, p.84, 95f.
  16. Lionel Casson: “Ships and Seamanship in the Ancient World”, ISBN 0801851300, S.XXVIII, 336f.; Fig.193
  17. Tilmann Bechert: Römisches Germanien zwischen Rhein und Maas. Die Provinz Germania inferior, Hirmer, München 1982, ISBN 3-7774-3440-X, p.183, 203 (Fig.266)
  18. M. D. de Weerd: Ships of the Roman Period at Zwammerdam / Nigrum Pullum, Germania Inferior, in: Roman Shipping and Trade: Britain and the Rhine Provinces. (The Council for) British Archaeology, Research Report 24, 1978, 15ff.
  19. M. D. de Weerd: Römerzeitliche Transportschiffe und Einbäume aus Nigrum Pullum / Zwammerdam, in: Studien zu den Militärgrenzen Roms II (1977), 187ff.
  20. Deutschlandfunk: Römische Schiffsversuchsanstalt in den Albaner Bergen
  21. ^ Needham, Volume 4, Part 3, 649-650.
  22. ^ Fairbank, 192.
  23. ^ Needham, Volume 4, Part 3, 362.
  24. Needham, Volume 4, Par634.
  25. Lawrence V. Mott, The Development of the Rudder, A.D. 100-1337: A Technological Tale, Thesis May 1991, Texas A&M University, S.2, 95f.
  26. ^ Lawrence V. Mott, The Development of the Rudder, A.D. 100-1337: A Technological Tale, Thesis May 1991, Texas A&M University, S.118f.
  27. Lawrence V. Mott, The Development of the Rudder, A.D. 100-1337: A Technological Tale, Thesis May 1991, Texas A&M University, S.2, 92f.
  28. Lawrence V. Mott, p.92
  29. Lawrence V. Mott, p.93
  30. Lawrence V. Mott, p.92f.

References

See also

Conventional ship and boat rudders

Specialist ship and boat rudders


Parts of a sailing ship
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