Rudder

{{short description|Control surface for fluid-dynamic steering in the yaw axis}} {{about|the navigational instrument|other meanings|Rudder (disambiguation)|mythological meaning|Gubernaculum (classical)}} [[File:Brosen propelersterntychy.jpg|thumb|Modern ship rudder (the tall red rectangle behind the [[propeller (marine)|propeller]])]] [[File:Olympic stern and rudder.jpg|thumbnail|right|{{RMS|Olympic}}'s rudder turned]]

A '''rudder''' is a primary control surface used to steer a [[ship]], [[boat]], [[submarine]], [[hovercraft]], [[airship]], or other vehicle that moves through a [[fluid]] medium (usually [[aircraft|air]] or [[watercraft|water]]). On an [[airplane]], 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 (watercraft)|hull]] or [[fuselage]], thus imparting a turning or [[yaw (rotation)|yaw]]ing motion to the craft. In basic form, a rudder is a flat plane or sheet of material attached with [[hinge]]s to the craft's [[stern]], tail, or afterend. Often rudders are shaped to minimize [[Drag (physics)|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 turned by a [[helmsman]]. In larger vessels, cables, [[pushrod]]s, or hydraulics may link rudders to steering wheels. In typical aircraft, the rudder is operated by pedals via mechanical linkages or hydraulics.

==History of the rudder==

Generally, a rudder is "part of the steering apparatus of a boat or ship that is fastened outside the hull, " denoting all types of oars, paddles, and rudders.<ref name="rudder.Encyclopædia Britannica">rudder.Encyclopædia Britannica. Retrieved August 8, 2008, from [[Encyclopædia Britannica 2006 Ultimate Reference Suite DVD]]</ref> More specifically, 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 where the rudder was mounted. Stern-mounted rudders are uniformly suspended at the back of the ship in a central position.<ref name="William F. Edgerton 255-265">William F. Edgerton: “Ancient Egyptian Steering Gear”, ''The American Journal of Semitic Languages and Literatures'', Vol. 43, No. 4. (1927), pp. 255-265</ref><ref name="R. O. Faulkner 3-9">R. O. Faulkner: ''Egyptian Seagoing Ships'', ''The Journal of Egyptian Archaeology'', Vol. 26. (1941), pp. 3-9</ref>

Although some{{efn|Lawrence Mott in his comprehensive treatment of the history of the rudder,<ref name="Lawrence V. Mott 2f., 92">{{Cite web |url=http://nautarch.tamu.edu/pdf-files/Mott-MA1991.pdf |title=Lawrence V. Mott, ''The Development of the Rudder, A.D. 100-1600: A Technological Tale'', Thesis May 1991, Texas A&M University, p.2f., 92 |access-date=2006-11-05 |archive-date=2017-11-06 |archive-url=https://web.archive.org/web/20171106082642/http://nautarch.tamu.edu/pdf-files/Mott-MA1991.pdf |url-status=dead }}</ref> Timothy Runyan,<ref>Timothy J. Runyan: “Review of The Development of the Rudder: A Technological Tale“, ''Speculum'', Vol. 74, No. 4, (1999), pp. 1096-1098 (1098)</ref> the [[Encyclopædia Britannica]],<ref name="rudder.Encyclopædia Britannica"/> and The Concise [[Oxford Dictionary of English Etymology]]<ref>[http://www.encyclopedia.com/doc/1O27-rudder.html The Concise Oxford Dictionary of English Etymology]</ref>}} classify a [[steering oar]] as a rudder, others{{efn|[[Joseph Needham]], [[Richard Lefebvre des Noëttes|Lefèbre des Noëttes]], K.S. Tom, Chung Chee Kit, S.A.M. Adshead, John K. Fairbank, Merle Goldman, Frank Ross, and Leo Block.<ref name="tom 1989 103 104"/><ref name="Needham volume 4 part 3 649 650"/><ref name="Adshead 156">Adshead, Samuel Adrian Miles. (2000). ''China in World History''. London: MacMillan Press Ltd. New York: St. Martin's Press. {{ISBN|0-312-22565-2}}. Page 156.</ref>}} argue that the steering oar used in ancient Egypt and Rome was not a true rudder and define only the stern-mounted rudder used in ancient [[History of the Han dynasty|Han dynasty China]] as a true rudder. The steering oar can interfere with the handling of the sails (limiting any potential for long ocean-going voyages) while it was fit more for small vessels on narrow, rapid-water transport; the rudder did not disturb the handling of the sails, took less energy to operate by its [[helmsman]], was better fit for larger vessels on ocean-going travel, and first appeared in [[History of China|ancient China]] during the 1st century AD.<ref name="tom 1989 103 104">Tom, K.S. (1989). ''Echoes from Old China: Life, Legends, and Lore of the Middle Kingdom''. Honolulu: The Hawaii Chinese History Center of the University of Hawaii Press. {{ISBN|0-8248-1285-9}}. Page 103–104.</ref><ref name="adshead 156">Adshead, Samuel Adrian Miles. (2000). ''China in World History''. London: MacMillan Press Ltd. New York: St. Martin's Press. {{ISBN|0-312-22565-2}}. Page 156.</ref><ref name="Needham volume 4 part 3 627 628">Needham, Joseph. (1986). ''Science and Civilization in China: Volume 4, Physics and Physical Technology, Part 3, Civil Engineering and Nautics''. Taipei: Caves Books Ltd. Pages 627–628.</ref><ref>Fairbank, John K. and Merle Goldman. (1998). ''China: A New History, Enlarged Edition''. Cambridge: Harvard University Press. {{ISBN|0-674-11673-9}}. Page 93.</ref><ref>Block, Leo. (2003). ''To Harness the Wind: A Short History of the Development of Sails''. Annapolis: Naval Institute Press. {{ISBN|1-55750-209-9}}. Page 123.</ref> In regards to the ancient [[Phoenicia]]n (1550–300 BC) use of the steering oar without a rudder [[History of the Mediterranean region|in the Mediterranean]], Leo Block (2003) writes:

<blockquote>A single sail tends to turn a vessel in an upwind or downwind direction, and rudder action is required to steer a straight course. A steering oar was used at this time because the rudder had not yet been invented. With a single sail, frequent movement of the steering oar was required to steer a straight course; this slowed down the vessel because a steering oar (or rudder) course correction acts as a brake. The second sail, located forward, could be trimmed to offset the turning tendency of the mainsail and minimize the need for course corrections by the steering oar, which would have substantially improved sail performance.<ref>Block, Leo. (2003). ''To Harness the Wind: A Short History of the Development of Sails''. Annapolis: Naval Institute Press. {{ISBN|1-55750-209-9}}. 8–9.</ref></blockquote>

Before the invention of the rudder, oversized oars called steering oars, or boards called steering boards, were used to control the direction of a ship or other watercraft. These are normally attached to the starboard side in larger vessels, though in smaller ones it is rarely if ever, attached.

===Steering oar/gear=== ==== Ancient Egypt ==== [[File:Maler der Grabkammer des Menna 013.jpg|thumb|left|Stern-mounted steering oar of an Egyptian riverboat depicted in the Tomb of Menna (c. 1422–1411 BC)]] Rowing oars set aside for steering appeared on large Egyptian vessels long before the time of [[Menes]] (3100 BC).<ref name="William F. Edgerton, 255">William F. Edgerton: "Ancient Egyptian Steering Gear", ''The American Journal of Semitic Languages and Literatures'', Vol. 43, No. 4. (1927), pp. 255</ref> In the [[Old Kingdom]] (2686–2134 BC) as many as five steering oars are found on each side of passenger boats.<ref name="William F. Edgerton, 255"/> 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).<ref name="William F. Edgerton, 257">William F. Edgerton: "Ancient Egyptian Steering Gear", ''The American Journal of Semitic Languages and Literatures'', Vol. 43, No. 4. (1927), pp. 257</ref> Both the tiller and the introduction of an upright steering post [[abaft]] reduced the usual number of necessary steering oars to one each side.<ref name="William F. Edgerton, 260">William F. Edgerton: "Ancient Egyptian Steering Gear", ''The American Journal of Semitic Languages and Literatures'', Vol. 43, No. 4. (1927), pp. 260</ref> Single steering oars put on the stern can be found in several tomb models of the time,<ref>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.</ref> particularly during the [[Middle Kingdom of Egypt|Middle Kingdom]] when tomb reliefs suggest them commonly employed in [[Nile]] navigation.<ref>Mohamed Ata: “Egypt from Past to Present. Through the Eyes of an Egyptian”, Cairo 2007, p. 68</ref> The first literary reference appears in the works of the [[Ancient Greece|Greek]] historian [[Herodotus]] (484–424 BC), who had spent several months in [[Egypt]]: "They make one rudder, and this is thrust through the [[keel]]", probably meaning the crotch at the end of the keel (as depicted in the "Tomb of Menna").<ref>[[Herodot]]: [[Histories (Herodotus)|Histories]], 2.96</ref><ref>William F. Edgerton: “Ancient Egyptian Steering Gear”, ''The American Journal of Semitic Languages and Literatures'', Vol. 43, No. 4. (1927), pp. 263</ref>

==== Ancient Iran ==== 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{{Citation needed|date=June 2026}}.

==== Ancient Rome ==== [[File:Rudder of a Roman Boat (RG Museum Koeln, Germany).JPG|thumb|Steering oar of a Roman boat, 1st century AD (RG-Museum, Cologne)]]

Roman navigation used sexillie quarter steering oars that went in the Mediterranean through a long period of constant refinement and improvement so that by Roman times ancient vessels reached extraordinary sizes.<ref name="Lawrence Mott, p.1">Lawrence V. Mott, The Development of the Rudder, A.D. 100–1600: A Technological Tale, Thesis May 1991, Texas A&M University, p.1</ref> The strength of the steering oar lay in its combination of effectiveness, adaptability and simpleness.<ref name="Lawrence Mott, p.1"/> Roman quarter steering oar mounting systems survived mostly intact through the medieval period.<ref name="Lawrence Mott, p.1"/>

By the first half of the 1st century AD, steering gear mounted on the stern were also quite common in [[Roman Empire|Roman]] river and harbour craft as proved from [[relief]]s and archaeological finds ([[Zwammerdam]], [[Woerden]] 7). A tomb plaque of [[Hadrian]]ic age shows a harbour tug boat in [[Ostia Antica|Ostia]] with a long stern-mounted oar for better leverage.<ref name="Lionel Casson (1965) plate 1">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)</ref> The boat already featured a [[spritsail]], adding to the mobility of the harbour vessel.<ref>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)</ref> Further attested Roman uses of stern-mounted steering oars includes barges under tow, transport ships for wine casks, and diverse other ship types.<ref name="Lawrence V. Mott 84, 95f.">Lawrence V. Mott, The Development of the Rudder, A.D. 100–1600: A Technological Tale, Thesis May 1991, Texas A&M University, p.84, 95f.</ref><ref name="Lionel Casson S.XXVIII, 336f.; Fig.193">Lionel Casson: “Ships and Seamanship in the Ancient World”, {{ISBN|0-8018-5130-0}}, S.XXVIII, 336f.; Fig.193</ref><ref name="Tilmann Bechert p.183, 203 (Fig.266)">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)</ref> A large river barge found at the mouth of the Rhine near [[Zwammerdam]] featured a large steering gear mounted on the stern.<ref name="M. D. de Weerd 15ff.">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.</ref><ref name="M. D. de Weerd 187ff.">M. D. de Weerd: Römerzeitliche Transportschiffe und Einbäume aus Nigrum Pullum / Zwammerdam, in: Studien zu den Militärgrenzen Roms II (1977), 187ff.</ref> According to new research, the advanced [[Nemi ships]], the palace barges of emperor [[Caligula]] (37–41 AD), may have featured 14-m-long rudders.<ref>[http://www.dradio.de/dlf/sendungen/forschak/515375/ Deutschlandfunk: Römische Schiffsversuchsanstalt in den Albaner Bergen]</ref>

===Sternpost-mounted rudder===

==== Ancient China ==== {{further|Science and technology of the Han dynasty}} [[File:Eastern Han pottery boat.JPG|thumb|left|An [[Han dynasty|Eastern Han]] (25–220 AD) Chinese pottery boat fit for riverine and maritime sea travel, with an anchor at the bow, a steering rudder at the stern, roofed compartments with windows and doors, and miniature sailors]] [[File:Guo Zhongshu-Traveling on the River in Snow.jpg|thumb|right|An early [[Song dynasty]] (960–1279) painting on silk of two [[Junk (ship)|Chinese cargo ships]] accompanied by a [[Sampan|smaller boat]], by Guo Zhongshu (c. 910–977 AD); notice the large sternpost-mounted rudder on the ship shown in the foreground]]

The world's oldest known depiction of a sternpost-mounted rudder can be seen on a pottery model of a Chinese [[junk (ship)|junk]] dating from the 1st century AD during the [[Han dynasty]], predating their appearance in the West by a thousand years.<ref name="tom 1989 103 104"/><ref name="Needham volume 4 part 3 627 628" /><ref name="johnstone mcgrail 191"/> In China, miniature models of ships that feature steering oars have been dated to the [[Warring States period]] (c. 475–221 BC).<ref name="tom 1989 103 104"/> Sternpost-mounted rudders started to appear on Chinese ship models starting in the 1st century AD.<ref name="tom 1989 103 104"/> However, the Chinese continued to use the steering oar long after they invented the rudder, since the steering oar still had practical use for inland rapid-river travel.<ref name="Needham volume 4 part 3 627 628" /> One of oldest known depictions of the Chinese stern-mounted rudder (''duò'' {{lang|zh|舵}}) can be seen on a {{convert|2|ft|cm|adj=on}} pottery model of a [[Junk (ship)|junk]] dating from the 1st century AD, during the [[Han dynasty]] (202 BC{{snd}}220 AD).<ref name="Needham volume 4 part 3 649 650">Needham, Volume 4, Part 3, 649-650.</ref><ref name="fairbank 192">Fairbank, 192.</ref> It was discovered in [[Guangzhou]] in an archaeological excavation carried out by the [[Guangdong Provincial Museum]] and [[Academia Sinica]] of [[Taiwan]] in 1958.<ref name="Needham volume 4 part 3 649 650"/><ref name="fairbank 192"/> Within decades, several other Han dynasty ship models featuring rudders were found in archaeological excavations.<ref>Deng, Gang. (1997). ''Chinese Maritime Activities and Socioeconomic Development, c. 2100 B.C.-1900 A.D''. Westport: Greenwood Press. {{ISBN|0-313-29212-4}}. Page 42.</ref> The first solid written reference to the use of a rudder without a steering oar dates to the 5th century.<ref name="johnstone mcgrail 191">Johnstone, Paul and Sean McGrail. (1988). ''The Sea-craft of Prehistory''. New York: Routledge. {{ISBN|0-415-02635-0}}. Page 191.</ref>

Chinese rudders are attached to the hull by means of wooden jaws or sockets,<ref name="Needham volume 4 part 3 632"/> while typically larger ones were suspended from above by a rope [[block and tackle|tackle]] system so that they could be raised or lowered into the water.<ref name="Needham volume 4 part 3 632">Needham, Volume 4, Part 3, 362.</ref> Also, many junks incorporated "fenestrated rudders" (rudders with holes in them, supposedly allowing for better control). 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]]. The later Chinese encyclopedist [[Song Yingxing]] (1587–1666) and the 17th-century European traveler Louis Lecomte wrote of the junk design and its use of the rudder with enthusiasm and admiration.<ref name="Needham volume 4 part 3 634">Needham, Volume 4, Par634.</ref> [[File:Pottery boat from Eastern Han Dynasty showing rudder.jpg|thumb|Pottery boat from [[Eastern Han dynasty]] showing the earliest known representation of a rudder]] Paul Johnstone and Sean McGrail state that the Chinese invented the "median, vertical and axial" sternpost-mounted rudder, and that such a kind of rudder preceded the pintle-and-gudgeon rudder found in the West by roughly a millennium.<ref name="johnstone mcgrail 191"/>

==== Ancient India ==== A [[Chandraketugarh]] (West Bengal) seal dated between the 1st and 3rd centuries AD depicts a steering mechanism on a ship named <nowiki>''</nowiki>Indra of the Ocean<nowiki>''</nowiki> (Jaladhisakra), which indicates that it was a sea-bound vessel.<ref>{{Cite book|last1=Barnes|first1=Ruth|url=https://books.google.com/books?id=wXhACwAAQBAJ&q=Angavijja+ship&pg=PT35|title=Ships and the Development of Maritime Technology on the Indian Ocean|last2=Parkin|first2=David|date=2015-12-22|publisher=Routledge|isbn=978-1-317-79342-7|language=en}}</ref><ref>{{Cite journal|last=Guy|first=John|date=1999|title=A Boat Model and State Ritual in Eastern India|journal=Bulletin de l'École française d'Extrême-Orient|volume=86|pages=105–126|doi=10.3406/befeo.1999.3407|jstor=43732572|issn=0336-1519}}</ref>

====Medieval Near East==== [[Arab]] ships also used a sternpost-mounted rudder.<ref name=Mott-93/> 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."<ref name=Mott-93>Lawrence V. Mott, p.93</ref> 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.''<ref>Lawrence V. Mott, p.92f.</ref>

====Medieval Europe==== [[File:Adler von Lübeck. Model ship 05.jpg|left|thumb|[[Pintle]]-and-[[gudgeon]] rudder of the [[Hanseatic league]] flagship ''[[Adler von Lübeck]]'' (1567–1581), the largest ship in the world at its time]]

Oars mounted on the side of ships evolved into quarter steering oars, which were used from [[Classical antiquity|antiquity]] until the end of the [[Middle Ages]] in [[Europe]]. As the size of ships and the height of the freeboards increased, quarter steering oars became unwieldy and were replaced by the more sturdy rudders with [[pintle]] and [[gudgeon]] attachment. While steering oars were found in Europe on a wide range of vessels since Roman times, including light war galleys in Mediterranean,<ref name="adshead 156"/><ref name="johnstone mcgrail 191"/> the oldest known depiction of a pintle-and-gudgeon rudder can be found on church carvings of [[Zedelgem]] and [[Winchester]] dating to around 1180.<ref name="adshead 156"/><ref name="johnstone mcgrail 191"/>

[[File:RudderBereFerrersBenchEnd.jpg|right|thumb|A ship's rudder carved in oak, 15th century, [[Bere Ferrers]] church, Devon. Heraldic [[Badge (heraldry)|badge]] of Cheyne and Willoughby families.]]

While earlier rudders were mounted on the stern by the way of rudderposts or tackles, the iron hinges allowed the rudder to be attached to the entire length of the sternpost in a permanent fashion.<ref>{{Cite web |url=http://nautarch.tamu.edu/pdf-files/Mott-MA1991.pdf |title=Lawrence V. Mott, ''The Development of the Rudder, A.D. 100-1600: A Technological Tale'', Thesis May 1991, Texas A&M University, S.2, 92f. |access-date=2006-11-05 |archive-date=2017-11-06 |archive-url=https://web.archive.org/web/20171106082642/http://nautarch.tamu.edu/pdf-files/Mott-MA1991.pdf |url-status=dead }}</ref> 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.<ref name="Lawrence Mott, 118f."/> From the [[Age of Discovery]] onwards, European ships with pintle-and-gudgeon rudders sailed successfully on all seven seas.<ref name="Lawrence Mott, 118f.">{{Cite web |url=http://nautarch.tamu.edu/pdf-files/Mott-MA1991.pdf |title=Lawrence V. Mott, ''The Development of the Rudder, A.D. 100-1600: A Technological Tale'', Thesis May 1991, Texas A&M University, S.118f. |access-date=2006-11-05 |archive-date=2017-11-06 |archive-url=https://web.archive.org/web/20171106082642/http://nautarch.tamu.edu/pdf-files/Mott-MA1991.pdf |url-status=dead }}</ref>

Historian [[Joseph Needham]] holds that the stern-mounted rudder was transferred from China to Europe and the Islamic world during the Middle Ages.<ref name="tom 1989 103 104"/><ref name="Needham volume 4 part 3 649 650"/><ref name="johnstone mcgrail 191"/>

====Modern rudders==== Conventional rudders have been essentially unchanged since [[Isambard Kingdom Brunel]] introduced the [[balanced rudder]] on the [[SS Great Britain|SS ''Great Britain'']] in 1843<ref>{{cite book |last1= Vaughan|first1= Adrian |title= Isambard Kingdom Brunel |edition=2nd |year=1991 |orig-year=1991 |publisher=John Murray |location=London |isbn= 0-7195-4636-2|page=160 }}</ref> and the [[steering engine]] in the [[SS Great Eastern|SS ''Great Eastern'']] in 1866.<ref name="google">{{cite book|title=A History of Control Engineering, 1800-1930|author=Bennett, S.|date=1986|publisher=Peregrinus|isbn=9780863410475|url=https://books.google.com/books?id=1gfKkqB_fTcC|page=98|access-date=2015-01-10}}</ref> If a vessel requires extra maneuverability at low speeds, the rudder may be supplemented by a [[manoeuvring thruster]] in the bow,<ref>[http://www.osmotech.co.uk/boat-building/bow-thrusters/39/ Osmotech UK on Uses and advantages of bow thrusters] {{webarchive |url=https://web.archive.org/web/20130726031611/http://www.osmotech.co.uk/boat-building/bow-thrusters/39/ |date=July 26, 2013 }}</ref> or be replaced entirely by [[azimuth thruster]]s.

==Boat rudders 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 that comes up through the hull to deck level, often into a cockpit. Inboard keel hung rudders (which are a continuation of the aft trailing edge of the full keel) are traditionally deemed the most damage resistant rudders for off shore sailing. Better performance with faster handling characteristics can be provided by skeg hung rudders on boats with smaller fin keels.

Rudder post and mast placement defines the difference between a ketch and a yawl, as these two-masted vessels are similar. Yawls are defined as having the mizzen mast abaft (i.e. "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. Transom hung rudders or far aft mounted fin rudders generate greater moment and faster turning than more forward mounted keel hung rudders. Rudders on smaller craft can be operated by means of a tiller that fits into the rudder stock that also forms the fixings to the rudder foil. Craft where the length of the tiller could impede movement of the helm can be split with a rubber universal joint and the part adjoined the tiller termed a tiller extension. Tillers can further be extended by means of adjustable telescopic twist locking extension.

There is also the barrel type rudder, where the ship's screw is enclosed and can be swiveled to steer the vessel. Designers claim that this type of rudder on a smaller vessel will answer the helm faster.<ref>[https://books.google.com/books?id=xd8DAAAAMBAJ&dq=%22Popular+Mechanics%22+Jan+1935+floating&pg=PA495 "Barrel Type Rudder Makes Quicker Turns"] ''Popular Mechanics'', October 1934, bottom-right pg.495</ref>

===Rudder control=== {{Anchor|Rudder control}} {{Missing information|section|other types of steering gear, such as rotary type steering gear|date=June 2021}} Large ships (over 10,000 ton gross tonnage) have requirements on rudder turnover time. To comply with this, high torque rudder controls are employed.<ref>{{Cite book|last=Molland|first=Anthony F.|url=https://books.google.com/books?id=59XvXKbyvZIC&q=ram+type+steering+gear&pg=PA458|title=The Maritime Engineering Reference Book: A Guide to Ship Design, Construction and Operation|date=2011-10-13|publisher=Elsevier|isbn=978-0-08-056009-0|language=en}}</ref> One commonly used system is the ram type steering gear. It employs four hydraulic rams to rotate the rudder stock (rotation axis), in turn rotating the rudder.<ref>{{Cite web|date=2019-02-20|title=Understanding Steering Gear in Ships|url=https://www.marineinsight.com/naval-architecture/understanding-steering-gear-ships/|access-date=2021-06-03|website=Marine Insight|language=en-US}}</ref>

== Aircraft rudders ==  {{further|Vertical stabilizer}} [[File:Aileron yaw.gif|thumb|Movement caused by the use of rudder]] [[File:MM00756-4.jpg|thumb|The rudder is controlled through [[rudder pedals]] on the bottom rear of the yoke in this photo of a Boeing 727 cockpit.]] On an aircraft, a rudder is one of three directional [[Flight control surfaces|control surfaces]], along with the rudder-like [[elevator (aircraft)|elevator]] (usually attached to the horizontal tail structure, if not a slab elevator) and [[ailerons]] (attached to the wings), which control pitch and roll, respectively. The rudder is usually attached to the [[fin]] (or [[vertical stabilizer]]), which allows the pilot to control [[Flight dynamics|yaw]] about the vertical axis, i.e., change the horizontal direction in which the nose is pointing.

Unlike a ship, both [[aileron]] and rudder controls are used together to turn an aircraft, with the ailerons imparting roll and the rudder imparting yaw and also compensating for a phenomenon called [[adverse yaw]]. A rudder alone will turn a conventional fixed-wing aircraft, but much more slowly than if ailerons are also used in conjunction. Sometimes pilots may intentionally operate the rudder and ailerons in opposite directions in a maneuver called a [[Slip (aerodynamic)|slip]] or sideslip. This may be done to overcome crosswinds and keep the fuselage in line with the runway, or to lose altitude by increasing drag, or both.

Another technique for yaw control, used on some [[tailless aircraft]] and [[flying wing]]s, is to add one or more drag-creating surfaces, such as split ailerons, on the outer wing section. Operating one of these surfaces creates drag on the wing, causing the plane to yaw in that direction. These surfaces are often referred to as drag rudders.

Rudders are typically controlled with [[Rudder pedal|pedals]].

==See also== {{Wiktionary}} *{{annotated link|Ship's wheel}} *{{annotated link|Azipod}} *{{annotated link|Kitchen rudder}} *{{annotated link|Pleuger rudder}} *{{annotated link|Schilling rudder}} *{{annotated link|Cyclorotor|Voith Schneider propeller}}

==Notes== {{notelist}}

==Footnotes== {{reflist|2}}

==References== * [http://nautarch.tamu.edu/pdf-files/Mott-MA1991.pdf Lawrence V. Mott, ''The Development of the Rudder, A.D. 100-1600: A Technological Tale'', Thesis May 1991, Texas A&M University] {{Webarchive|url=https://web.archive.org/web/20171106082642/http://nautarch.tamu.edu/pdf-files/Mott-MA1991.pdf |date=2017-11-06 }} *Fairbank, John King and Merle Goldman (1992). ''China: A New History; Second Enlarged Edition'' (2006). Cambridge: MA; London: The Belknap Press of Harvard University Press. {{ISBN|0-674-01828-1}} *Needham, Joseph (1986). ''Science and Civilization in China: Volume 4, Physics and Physical Technology, Part 3, Civil Engineering and Nautics''. Taipei: Caves Books Ltd.

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