Rudder
Overview
 
A rudder is a device used to steer a ship
Ship
Since the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...

, boat
Boat
A boat is a watercraft of any size designed to float or plane, to provide passage across water. Usually this water will be inland or in protected coastal areas. However, boats such as the whaleboat were designed to be operated from a ship in an offshore environment. In naval terms, a boat is a...

, submarine
Submarine
A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...

, hovercraft
Hovercraft
A hovercraft is a craft capable of traveling over surfaces while supported by a cushion of slow moving, high-pressure air which is ejected against the surface below and contained within a "skirt." Although supported by air, a hovercraft is not considered an aircraft.Hovercraft are used throughout...

, aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

 or other conveyance that moves through a medium (generally air or water). On an aircraft the rudder is used primarily to counter adverse yaw
Adverse yaw
Adverse yaw is a yaw moment on an aircraft which results from an aileron deflection and a roll rate, such as when entering or exiting a turn. It is called "adverse" because it acts opposite to the yaw moment needed to execute the desired turn. Adverse yaw has three mechanisms, listed below in...

 and p-factor
P-factor
P-factor, also known as asymmetric blade effect and asymmetric disc effect, is an aerodynamic phenomenon experienced by a moving propeller, that is responsible for asymmetrical relocation of the propeller's center of thrust when aircraft is at a high angle of attack.- Causes :When an aircraft is in...

 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 hinge
Hinge
A hinge is a type of bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation. Hinges may be made of flexible material or of moving components...

s to the craft's stern, tail or after end.
Encyclopedia
A rudder is a device used to steer a ship
Ship
Since the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...

, boat
Boat
A boat is a watercraft of any size designed to float or plane, to provide passage across water. Usually this water will be inland or in protected coastal areas. However, boats such as the whaleboat were designed to be operated from a ship in an offshore environment. In naval terms, a boat is a...

, submarine
Submarine
A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...

, hovercraft
Hovercraft
A hovercraft is a craft capable of traveling over surfaces while supported by a cushion of slow moving, high-pressure air which is ejected against the surface below and contained within a "skirt." Although supported by air, a hovercraft is not considered an aircraft.Hovercraft are used throughout...

, aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

 or other conveyance that moves through a medium (generally air or water). On an aircraft the rudder is used primarily to counter adverse yaw
Adverse yaw
Adverse yaw is a yaw moment on an aircraft which results from an aileron deflection and a roll rate, such as when entering or exiting a turn. It is called "adverse" because it acts opposite to the yaw moment needed to execute the desired turn. Adverse yaw has three mechanisms, listed below in...

 and p-factor
P-factor
P-factor, also known as asymmetric blade effect and asymmetric disc effect, is an aerodynamic phenomenon experienced by a moving propeller, that is responsible for asymmetrical relocation of the propeller's center of thrust when aircraft is at a high angle of attack.- Causes :When an aircraft is in...

 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 hinge
Hinge
A hinge is a type of bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation. Hinges may be made of flexible material or of moving components...

s 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
Tiller
A tiller or till is a lever attached to a rudder post or rudder stock of a boat that provides leverage for the helmsman to turn the rudder...

 -- 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
Helmsman
A helmsman is a person who steers a ship, sailboat, submarine, or other type of maritime vessel. On small vessels, particularly privately-owned noncommercial vessels, the functions of skipper and helmsman may be combined in one person. On larger vessels, there is a separate officer of the watch,...

. In larger vessels, cables, pushrods, or hydraulics may be used to link rudders to steering wheels. In typical aircraft, the rudder is operated by pedals via mechanical linkages or hydraulics.

Terminology

Generally, a rudder is "part of the steering apparatus of a boat or ship that is fastened outside the hull", that is denoting all different types of oars, paddles and rudders. 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
Steering oar
The steering oar or steering board is an oversized oar or board to control the direction of a ship or other watercraft prior to the invention of the rudder....

, 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
Hull (watercraft)
A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...

 in quite a different way: While the Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

an pintle-and-gudgeon rudder was attached to the sternpost by pivoting iron fastenings, the Arab
Arab
Arab people, also known as Arabs , are a panethnicity primarily living in the Arab world, which is located in Western Asia and North Africa. They are identified as such on one or more of genealogical, linguistic, or cultural grounds, with tribal affiliations, and intra-tribal relationships playing...

s used instead a system of lashings. Chinese
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

 stern rudders also featured tackles
Block and tackle
A block and tackle is a system of two or more pulleys with a rope or cable threaded between them, usually used to lift or pull heavy loads.The pulleys are assembled together to form blocks so that one is fixed and one moves with the load...

, but, unlike their medieval and Arab counterparts, had no sternpost to which to attach them. Roman
Ancient Rome
Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world....

 and particularly ancient Egypt
Ancient Egypt
Ancient Egypt was an ancient civilization of Northeastern Africa, concentrated along the lower reaches of the Nile River in what is now the modern country of Egypt. Egyptian civilization coalesced around 3150 BC with the political unification of Upper and Lower Egypt under the first pharaoh...

ian 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.

Although Lawrence Mott in his comprehensive treatment of the history of the rudder, Timothy Runyan, the Propyläen History of Technology, the Encyclopædia Britannica
Encyclopædia Britannica
The Encyclopædia Britannica , published by Encyclopædia Britannica, Inc., is a general knowledge English-language encyclopaedia that is available in print, as a DVD, and on the Internet. It is written and continuously updated by about 100 full-time editors and more than 4,000 expert...

, and The Concise Oxford Dictionary of English Etymology classify a steering oar as a rudder, Joseph Needham
Joseph Needham
Noel Joseph Terence Montgomery Needham, CH, FRS, FBA , also known as Li Yuese , was a British scientist, historian and sinologist known for his scientific research and writing on the history of Chinese science. He was elected a fellow of the Royal Society in 1941, and as a fellow of the British...

, Lefèbre des Noëttes
Richard Lefebvre des Noëttes
Richard Lefebvre des Noëttes was a French officer and early historian of technology.After his early retirement from the French army in 1901, Lefebvre devoted his time to technological studies, then quite a new field, becoming a main proponent of the negative impact of slavery on technological...

, K.S. Tom, Chung Chee Kit, S.A.M. Adshead, John K. Fairbank, Merle Goldman, Frank Ross, and Leo Block state that the steering oar used in ancient Egypt and Rome (and even ancient China) was not a true rudder; the steering oar has the capacity to interfere with 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
Helmsman
A helmsman is a person who steers a ship, sailboat, submarine, or other type of maritime vessel. On small vessels, particularly privately-owned noncommercial vessels, the functions of skipper and helmsman may be combined in one person. On larger vessels, there is a separate officer of the watch,...

, was better fit for larger vessels on ocean-going travel, and first appeared in ancient China
History of China
Chinese civilization originated in various regional centers along both the Yellow River and the Yangtze River valleys in the Neolithic era, but the Yellow River is said to be the Cradle of Chinese Civilization. With thousands of years of continuous history, China is one of the world's oldest...

 during the 1st century AD. In regards to the ancient Phoenicia
Phoenicia
Phoenicia , was an ancient civilization in Canaan which covered most of the western, coastal part of the Fertile Crescent. Several major Phoenician cities were built on the coastline of the Mediterranean. It was an enterprising maritime trading culture that spread across the Mediterranean from 1550...

n (1550–300 BC) use of the steering oar without a rudder in the Mediterranean
History of the Mediterranean region
The history of the Mediterranean region is the history of the interaction of the cultures and people of the lands surrounding the Mediterranean Sea —the central superhighway of transport, trade and cultural exchange between diverse peoples...

, Leo Block (2003) writes:

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, a 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 like a brake. The second sail, located forward, could be trimmed to offset the turning tendency of the main sail and minimize the need for course corrections by the steering oar, which would have substantially improved sail performance.



Ancient Egypt

Rowing oars set aside for steering appeared on large Egyptian vessels long before the time of Menes
Menes
Menes was an ancient Egyptian pharaoh of the early dynastic period, credited by classical tradition with having united Upper and Lower Egypt, and as the founder of the first dynasty ....

 (3100 BC). In the Old Kingdom
Old Kingdom
Old Kingdom is the name given to the period in the 3rd millennium BC when Egypt attained its first continuous peak of civilization in complexity and achievement – the first of three so-called "Kingdom" periods, which mark the high points of civilization in the lower Nile Valley .The term itself was...

 (2686 BC-2134 BC) as much as five steering oars are found on each side of passenger boats. The tiller
Tiller
A tiller or till is a lever attached to a rudder post or rudder stock of a boat that provides leverage for the helmsman to turn the rudder...

, 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
Middle Kingdom of Egypt
The Middle Kingdom of Egypt is the period in the history of ancient Egypt stretching from the establishment of the Eleventh Dynasty to the end of the Fourteenth Dynasty, between 2055 BC and 1650 BC, although some writers include the Thirteenth and Fourteenth dynasties in the Second Intermediate...

 when tomb reliefs suggests them commonly employed in Nile
Nile
The Nile is a major north-flowing river in North Africa, generally regarded as the longest river in the world. It is long. It runs through the ten countries of Sudan, South Sudan, Burundi, Rwanda, Democratic Republic of the Congo, Tanzania, Kenya, Ethiopia, Uganda and Egypt.The Nile has two major...

 navigation. The first literary reference appears in the works of the Greek
Ancient Greece
Ancient Greece is a civilization belonging to a period of Greek history that lasted from the Archaic period of the 8th to 6th centuries BC to the end of antiquity. Immediately following this period was the beginning of the Early Middle Ages and the Byzantine era. Included in Ancient Greece is the...

 historian Herodot (484-424 BC), who had spent several months in Egypt
Egypt
Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...

: "They make one rudder, and this is thrust through the keel
Keel
In boats and ships, keel can refer to either of two parts: a structural element, or a hydrodynamic element. These parts overlap. As the laying down of the keel is the initial step in construction of a ship, in British and American shipbuilding traditions the construction is dated from this event...

", probably meaning the crotch at the end of the keel (see right pic "Tomb of Menna").

In Iran
Iran
Iran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia...

, 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.

China

In China, miniature models of ships that feature steering oars have been dated to the Zhou Dynasty
Zhou Dynasty
The Zhou Dynasty was a Chinese dynasty that followed the Shang Dynasty and preceded the Qin Dynasty. Although the Zhou Dynasty lasted longer than any other dynasty in Chinese history, the actual political and military control of China by the Ji family lasted only until 771 BC, a period known as...

 (c. 1050 BC – 256 BC). Stern mounted rudders started to appear on Chinese ship models starting in the 1st century AD. However, the Chinese continued to use the steering oar long after they invented the rudder, since the steering oar still had limited practical use for inland rapid-river travel. One of oldest known depiction of a stern-mounted rudder in China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

 can be seen on a 2 ft. long tomb pottery
Pottery
Pottery is the material from which the potteryware is made, of which major types include earthenware, stoneware and porcelain. The place where such wares are made is also called a pottery . Pottery also refers to the art or craft of the potter or the manufacture of pottery...

 model of a junk
Junk (ship)
A junk is an ancient Chinese sailing vessel design still in use today. Junks were developed during the Han Dynasty and were used as sea-going vessels as early as the 2nd century AD. They evolved in the later dynasties, and were used throughout Asia for extensive ocean voyages...

 dating from the 1st century AD, during the Han Dynasty
Han Dynasty
The Han Dynasty was the second imperial dynasty of China, preceded by the Qin Dynasty and succeeded by the Three Kingdoms . It was founded by the rebel leader Liu Bang, known posthumously as Emperor Gaozu of Han. It was briefly interrupted by the Xin Dynasty of the former regent Wang Mang...

 (202 BC-220 AD). It was discovered in Guangzhou
Guangzhou
Guangzhou , known historically as Canton or Kwangchow, is the capital and largest city of the Guangdong province in the People's Republic of China. Located in southern China on the Pearl River, about north-northwest of Hong Kong, Guangzhou is a key national transportation hub and trading port...

 in an archaeological excavation carried out by the Guangdong Provincial Museum
Guangdong Provincial Museum
Guangdong Province Museum is located on 215 Wenming Rd., Guangzhou, Guangdong Province of China , on what was the original site of Zhongshan University. It is a provincial general museum, founded in 1959 and with a land area of 43,000 square meters...

 and Academia Sinica
Academia Sinica
The Academia Sinica , headquartered in the Nangang District of Taipei, is the national academy of Taiwan. It supports research activities in a wide variety of disciplines, ranging from mathematical and physical sciences, to life sciences, and to humanities and social sciences.Academia Sinica has...

 of Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...

 in 1958. Within decades, several other Han Dynasty ship models featuring rudders were found in archaeological excavations. The first solid written reference to the use of a rudder without a steering oar dates to the 5th century.

Chinese rudders were not supported by pintle
Pintle
A pintle is a pin or bolt, usually inserted into a gudgeon, which is used as part of a pivot or hinge.A pintle/gudgeon set is used in many spheres, for example: in sailing to hold the rudder onto the boat; in transportation a pincer-type device clamps through a lunette ring on the tongue of a...

-and-gudgeon
Gudgeon
A gudgeon is a circular fitting, often made of metal, which is affixed to a surface. It allows for the pivoting of another fixture. It is generally used with a pintle, which is a pin which pivots in the hole in the gudgeon. As such, a gudgeon is a simple bearing.-Winged gudgeons:A winged 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
Block and tackle
A block and tackle is a system of two or more pulleys with a rope or cable threaded between them, usually used to lift or pull heavy loads.The pulleys are assembled together to form blocks so that one is fixed and one moves with the load...

 system so that they could be raised or lowered into the water. 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
Middle Ages
The Middle Ages is a periodization of European history from the 5th century to the 15th century. The Middle Ages follows the fall of the Western Roman Empire in 476 and precedes the Early Modern Era. It is the middle period of a three-period division of Western history: Classic, Medieval and Modern...

 are known from various travellers to China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

, such as Ibn Battuta
Ibn Battuta
Abu Abdullah Muhammad Ibn Battuta , or simply Ibn Battuta, also known as Shams ad–Din , was a Muslim Moroccan Berber explorer, known for his extensive travels published in the Rihla...

 of Tangier
Tangier
Tangier, also Tangiers is a city in northern Morocco with a population of about 700,000 . It lies on the North African coast at the western entrance to the Strait of Gibraltar where the Mediterranean meets the Atlantic Ocean off Cape Spartel...

, Morocco
Morocco
Morocco , officially the Kingdom of Morocco , is a country located in North Africa. It has a population of more than 32 million and an area of 710,850 km², and also primarily administers the disputed region of the Western Sahara...

 and Marco Polo
Marco Polo
Marco Polo was a Venetian merchant traveler from the Venetian Republic whose travels are recorded in Il Milione, a book which did much to introduce Europeans to Central Asia and China. He learned about trading whilst his father and uncle, Niccolò and Maffeo, travelled through Asia and apparently...

 of Venice
Venice
Venice is a city in northern Italy which is renowned for the beauty of its setting, its architecture and its artworks. It is the capital of the Veneto region...

, Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

. The later Chinese encyclopedist Song Yingxing
Song Yingxing
Song Yingxing , born in Yichun of Jiangxi, was a Chinese scientist and encyclopedist who lived during the late Ming Dynasty . He was the author of an encyclopedia that covered a wide variety of technical subjects, including the use of gunpowder weapons...

 (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.

Paul Johnstone and Sean McGrail state that the Chinese invented the "median, vertical and axial" stern-mounted rudder, and that such a kind of rudder preceded the pintle-and-gudgeon rudder found in the West by roughly a millennium. However, Mott points out that the Chinese rudder worked by a very different suspension system, and that it was not permanently attached to a sternpost, leaving little point in comparing two such different types of rudder. The method of mounting steering gear from the stern was well known in Mediterranean navigation by the time the practice appeared in Chinese ships.

Ancient Rome

Roman navigation used sexillie 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 combination 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
Roman Empire
The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....

 river and harbour craft as proved from relief
Relief
Relief is a sculptural technique. The term relief is from the Latin verb levo, to raise. To create a sculpture in relief is thus to give the impression that the sculpted material has been raised above the background plane...

s and archaeological finds (Zwammderdam, Woerden 7). A tomb plaque of Hadrian
Hadrian
Hadrian , was Roman Emperor from 117 to 138. He is best known for building Hadrian's Wall, which marked the northern limit of Roman Britain. In Rome, he re-built the Pantheon and constructed the Temple of Venus and Roma. In addition to being emperor, Hadrian was a humanist and was philhellene in...

ic age shows a harbour tug boat in Ostia
Ostia Antica
Ostia Antica is a large archeological site, close to the modern suburb of Ostia , that was the location of the harbour city of ancient Rome, which is approximately 30 km to the northeast. "Ostia" in Latin means "mouth". At the mouth of the River Tiber, Ostia was Rome's seaport, but, due to...

 with a long stern-mounted oar for better leverage. Interestingly, the boat already featured a spritsail
Spritsail
The spritsail is a form of three or four-sided, fore-aft sail and its rig. Unlike the gaff where the head hangs from a spar along its edge, this rig supports the leech of the sail by means of a spar or spars named a sprit...

, 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
Zwammerdam
Zwammerdam is a town in the Dutch province of South Holland. It is a part of the municipality of Alphen aan den Rijn, and lies about 6 km southeast of Alphen aan de Rijn.In 2001, the town of Zwammerdam had 1709 inhabitants...

 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
Nemi ships
The Nemi Ships were ships built by the Roman emperor Caligula in the 1st century AD at Lake Nemi. Although the purpose of the ships is only speculated on, the larger ship was essentially an elaborate floating palace, which contained quantities of marble, mosaic floors, heating and plumbing such as...

, the palace barges of emperor Caligula
Caligula
Caligula , also known as Gaius, was Roman Emperor from 37 AD to 41 AD. Caligula was a member of the house of rulers conventionally known as the Julio-Claudian dynasty. Caligula's father Germanicus, the nephew and adopted son of Emperor Tiberius, was a very successful general and one of Rome's most...

 (37-41 AD), may have featured 14 m long stern-mounted rudders.

Medieval Near East

Arab
Arab
Arab people, also known as Arabs , are a panethnicity primarily living in the Arab world, which is located in Western Asia and North Africa. They are identified as such on one or more of genealogical, linguistic, or cultural grounds, with tribal affiliations, and intra-tribal relationships playing...

 ships also used a sternpost-mounted rudder, but which differed technically from both its European and Chinese counterparts, indicating an independent invention. 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
Al-Muqaddasi
Muhammad ibn Ahmad Shams al-Din Al-Muqaddasi , also transliterated as Al-Maqdisi and el-Mukaddasi, was a medieval Arab geographer, author of Ahsan at-Taqasim fi Ma`rifat il-Aqalim .-Biography:Al-Muqaddasi, "the Hierosolomite" was born in Jerusalem in 946 AD...

 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.


Arab
Arab
Arab people, also known as Arabs , are a panethnicity primarily living in the Arab world, which is located in Western Asia and North Africa. They are identified as such on one or more of genealogical, linguistic, or cultural grounds, with tribal affiliations, and intra-tribal relationships playing...

s used instead a system of lashings. Chinese
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

 stern rudders also featured tackles
Block and tackle
A block and tackle is a system of two or more pulleys with a rope or cable threaded between them, usually used to lift or pull heavy loads.The pulleys are assembled together to form blocks so that one is fixed and one moves with the load...

, but, unlike their medieval and Arab counterparts, had no sternpost to which to attach them. According to Lawrence V. Mott, the "idea of attaching the rudder to the sternpost in a relatively permanent fashion, therefore, must have been an Arab invention independent of the Chinese."

Medieval Europe

Oars mounted on the side of ships evolved into quarter rudders, which were used from antiquity
Classical antiquity
Classical antiquity is a broad term for a long period of cultural history centered on the Mediterranean Sea, comprising the interlocking civilizations of ancient Greece and ancient Rome, collectively known as the Greco-Roman world...

 until the end of the Middle Ages
Middle Ages
The Middle Ages is a periodization of European history from the 5th century to the 15th century. The Middle Ages follows the fall of the Western Roman Empire in 476 and precedes the Early Modern Era. It is the middle period of a three-period division of Western history: Classic, Medieval and Modern...

 in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

. 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
Pintle
A pintle is a pin or bolt, usually inserted into a gudgeon, which is used as part of a pivot or hinge.A pintle/gudgeon set is used in many spheres, for example: in sailing to hold the rudder onto the boat; in transportation a pincer-type device clamps through a lunette ring on the tongue of a...

 and gudgeon
Gudgeon
A gudgeon is a circular fitting, often made of metal, which is affixed to a surface. It allows for the pivoting of another fixture. It is generally used with a pintle, which is a pin which pivots in the hole in the gudgeon. As such, a gudgeon is a simple bearing.-Winged gudgeons:A winged 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 of Zedelgem
Zedelgem
Zedelgem is a municipality located in the Belgian province of West Flanders. The municipality comprises the villages of Aartrijke, Loppem, Veldegem and Zedelgem proper. On January 1, 2006 Zedelgem had a total population of 21,835...

 and Winchester
Winchester
Winchester is a historic cathedral city and former capital city of England. It is the county town of Hampshire, in South East England. The city lies at the heart of the wider City of Winchester, a local government district, and is located at the western end of the South Downs, along the course of...

 dating to around 1180. The invention of the rudder in Medieval Europe is attributed to Somerled
Somerled
Somerled was a military and political leader of the Scottish Isles in the 12th century who was known in Gaelic as rí Innse Gall . His father was Gillebride...

 in 1156, when it was the decisive factor in his defeat of Godred Olafsson during the formation of the Lordship of the Isles
Lord of the Isles
The designation Lord of the Isles is today a title of Scottish nobility with historical roots that go back beyond the Kingdom of Scotland. It emerged from a series of hybrid Viking/Gaelic rulers of the west coast and islands of Scotland in the Middle Ages, who wielded sea-power with fleets of...

.
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
Cog (ship)
A cog is a type of ship that first appeared in the 10th century, and was widely used from around the 12th century on. Cogs were generally built of oak, which was an abundant timber in the Baltic region of Prussia. This vessel was fitted with a single mast and a square-rigged single sail...

. 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
Age of Discovery
The Age of Discovery, also known as the Age of Exploration and the Great Navigations , was a period in history starting in the early 15th century and continuing into the early 17th century during which Europeans engaged in intensive exploration of the world, establishing direct contacts with...

 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.

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 which 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 handleing 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.

There is also the barrel type rudder where the ships screw is enclosed and can swiveled to steer the vessel. Designers claim that this type of rudder on a smaller vessel will answer the helm faster.

Aircraft rudders

On an aircraft, the rudder is a directional control surface
Control surface
In the domain of digital audio, a control surface is a human interface device which allows the user to control a digital audio workstation or other digital audio application. Generally, a control surface will contain one or more controls that can be assigned to parameters in the software,...

 along with the rudder-like elevator
Elevator (aircraft)
Elevators are flight control surfaces, usually at the rear of an aircraft, which control the aircraft's orientation by changing the pitch of the aircraft, and so also the angle of attack of the wing. In simplified terms, they make the aircraft nose-up or nose-down...

 (usually attached to horizontal tail structure, if not a slab elevator ) and ailerons (attached to the wings) that control pitch and roll. The rudder is usually attached to the fin
Fin
A fin is a surface used for stability and/or to produce lift and thrust or to steer while traveling in water, air, or other fluid media, . The first use of the word was for the limbs of fish, but has been extended to include other animal limbs and man-made devices...

 (or vertical stabilizer
Vertical stabilizer
The vertical stabilizers, vertical stabilisers, or fins, of aircraft, missiles or bombs are typically found on the aft end of the fuselage or body, and are intended to reduce aerodynamic side slip. It is analogical to a skeg on boats and ships.On aircraft, vertical stabilizers generally point upwards...

) which allows the pilot to control yaw
Flight dynamics
Flight dynamics is the science of air vehicle orientation and control in three dimensions. The three critical flight dynamics parameters are the angles of rotation in three dimensions about the vehicle's center of mass, known as pitch, roll and yaw .Aerospace engineers develop control systems for...

 in the vertical axis, i.e. change the horizontal direction in which the nose is pointing. The rudder's direction in aircraft since the "Golden Age" of flight between the two World Wars into the 21st century has been manipulated with the movement of a pair of foot pedals by the pilot, while during the pre-1919 era rudder control was most often operated with by a center-pivoted, solid "rudder bar" which usually had pedal and/or stirrup-like hardware on its ends to allow the pilot's feet to stay close to the ends of the bar's rear surface.

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
Adverse yaw is a yaw moment on an aircraft which results from an aileron deflection and a roll rate, such as when entering or exiting a turn. It is called "adverse" because it acts opposite to the yaw moment needed to execute the desired turn. Adverse yaw has three mechanisms, listed below in...

. 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 slip
Slip (aerodynamic)
A slip is an aerodynamic state where an aircraft is moving somewhat sideways as well as forward relative to the oncoming airflow. In other words, for a conventional aircraft, the nose will not be pointing directly into the relative wind .A slip is also a piloting maneuver where the pilot...

ping (under-ruddered), nor skidding (over-ruddered). Improperly ruddered turns at low speed can precipitate a spin
Spin (flight)
In aviation, a spin is an aggravated stall resulting in autorotation about the spin axis wherein the aircraft follows a corkscrew downward path. Spins can be entered intentionally or unintentionally, from any flight attitude and from practically any airspeed—all that is required is sufficient yaw...

 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. The pilots of Air Canada Flight 143 used a similar technique to land the plane as it was too high above the glideslope.

Any aircraft rudder is subject to considerable forces that determine its position via a force or torque balance equation. In extreme cases these forces can lead to loss of rudder control or even destruction of the rudder. (The same principles also apply to water vessels, of course, but it is more important for aircraft because they have lower engineering margins.) The largest achievable angle of a rudder in flight is called its blowdown limit; it is achieved when the force from the air or blowdown equals the maximum available hydraulic pressure.

Trim tab

Trim tabs are small surfaces connected to the trailing edge of a larger control surface
Control surface
In the domain of digital audio, a control surface is a human interface device which allows the user to control a digital audio workstation or other digital audio application. Generally, a control surface will contain one or more controls that can be assigned to parameters in the software,...

, such as a rudder, on a boat
Boat
A boat is a watercraft of any size designed to float or plane, to provide passage across water. Usually this water will be inland or in protected coastal areas. However, boats such as the whaleboat were designed to be operated from a ship in an offshore environment. In naval terms, a boat is a...

 or aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

, used to control the trim of the controls, i.e. to counteract hydro- or aero-dynamic forces and stabilise the boat or aircraft in a particular desired attitude without the need for the operator to constantly apply a control force. This is done by adjusting the angle of the tab relative to the larger surface.

Changing the setting of a trim tab adjusts the neutral or resting position of a control surface (such as an elevator
Elevator (aircraft)
Elevators are flight control surfaces, usually at the rear of an aircraft, which control the aircraft's orientation by changing the pitch of the aircraft, and so also the angle of attack of the wing. In simplified terms, they make the aircraft nose-up or nose-down...

 or rudder). As the desired position of a control surface changes (corresponding mainly to different speeds), an adjustable trim tab will allow the operator to reduce the manual force required to maintain that position—to zero, if used correctly. Thus the trim tab acts as a servo tab
Servo tab
A servo tab is a small hinged device installed on an aircraft control surface to assist the movement of the control surface.-Servo tabs:...

. Because the center of pressure
Center of pressure
The center of pressure is the point on a body where the total sum of a pressure field acts, causing a force and no moment about that point. The total force vector acting at the center of pressure is the value of the integrated vectorial pressure field. The resultant force and center of pressure...

 of the trim tab is further away from the axis of rotation of the control surface than the center of pressure of the control surface, the movement generated by the tab can match the movement generated by the control surface. The position of the control surface on its axis will change until the movements from the control surface and the trim surface balance each other.

Conventional ship and boat rudders

  • Common Dinghy Rudders at Puddle Duck Racer - The Easiest Boat To Build
  • Balanced rudder
    Balanced rudder
    The balanced rudder was an innovation in warship construction used as early as 1862 in the USS Monitor, one of the Union's first ironclads during the American Civil War...


Specialist ship and boat rudders

  • Azipod
    Azipod
    Azipod is the registered brand name of the ABB Group for their azimuth thruster. Originally developed in Finland jointly by Kvaerner Masa-Yards dockyards and ABB, these are marine propulsion units consisting of electrically driven propellers mounted on a steerable pod.The pod's propeller usually...

  • Azimuth thruster
    Azimuth thruster
    An azimuth thruster is a configuration of ship propellers placed in pods that can be rotated in any horizontal direction, making a rudder unnecessary...

  • Kitchen rudder
    Kitchen rudder
    The Kitchen Rudder is the familiar name for "Kitchen's Patent Reversing Rudders", a combination rudder and directional propulsion delivery system for relatively slow speed displacement boats which was invented in the early 20th century by John G.A.Kitchen of Lancashire, England...

  • Pleuger rudder
    Pleuger rudder
    The Pleuger rudder is a power assisted ship's rudder. It creates a flow of water in the direction the rudder points powered by an auxiliary electric motor. This aids maneuverability at low speeds greatly, since it operates on a similar principle to a thruster....

  • Schilling Rudder
    Schilling Rudder
    A Schilling Rudder is a specific type of profiled rudder used on certain boats and ships. See Rudder-The Schilling Concept:The Schilling Profile is designed to improve the effective lift generated by the rudder and hence improve the maneuverability of the craft, especially at slow speeds...

  • Voith Schneider Propeller (a combination propulsion and steering unit)
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