Rudder
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. 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 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 afterend. Often rudders are shaped 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 turned by a helmsman. In larger vessels, cables, pushrods, 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. 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.Although some classify a steering oar as a rudder, others 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 Han dynasty China as a true rudder. The steering oar can interfere with the handling of the sails 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 ancient China during the 1st century AD. In regards to the ancient Phoenician use of the steering oar without a rudder in the Mediterranean, Leo Block 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, frequent movement of the steering oar was required to steer a straight course; this slowed down the vessel because a steering oar 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.
The steering oar or steering board is an oversized oar or board to control the direction of a ship or other watercraft before the invention of the rudder. It is normally attached to the starboard side in larger vessels, though in smaller ones it is rarely if ever, attached.
Steering oar/gear
Ancient Egypt
Rowing oars set aside for steering appeared on large Egyptian vessels long before the time of Menes. In the Old Kingdom as many 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. Both the tiller and the introduction of an upright steering post abaft reduced the usual number of necessary steering oars to one each side. Single steering oars put on the stern can be found in several tomb models of the time, particularly during the Middle Kingdom when tomb reliefs suggest them commonly employed in Nile navigation. The first literary reference appears in the works of the Greek historian Herodotus, 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.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 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. The strength of the steering oar lay in its combination of effectiveness, adaptability and simpleness. Roman quarter steering oar mounting systems survived mostly intact through the medieval period.By the first half of the 1st century AD, steering gear mounted on the stern were also quite common in Roman river and harbour craft as proved from reliefs and archaeological finds. A tomb plaque of Hadrianic age shows a harbour tug boat in Ostia with a long stern-mounted oar for better leverage. The boat already featured a spritsail, adding to the mobility of the harbour vessel. Further attested Roman uses of stern-mounted steering oars includes barges under tow, transport ships for wine casks, and diverse other ship types. A large river barge found at the mouth of the Rhine near Zwammerdam featured a large steering gear mounted on the stern. According to new research, the advanced Nemi ships, the palace barges of emperor Caligula, may have featured 14-m-long rudders.
Sternpost-mounted rudder
Ancient China
The world's oldest known depiction of a sternpost-mounted rudder can be seen on a pottery model of a Chinese junk dating from the 1st century AD during the Han dynasty, predating their appearance in the West by a thousand years. In China, miniature models of ships that feature steering oars have been dated to the Warring States period. Sternpost-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 practical use for inland rapid-river travel. One of oldest known depictions of the Chinese stern-mounted rudder can be seen on a pottery model of a junk dating from the 1st century AD, during the Han dynasty. It was discovered in Guangzhou in an archaeological excavation carried out by the Guangdong Provincial Museum and Academia Sinica of Taiwan 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 are 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". 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 and the 17th-century European traveler Louis Lecomte wrote 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" sternpost-mounted rudder, and that such a kind of rudder preceded the pintle-and-gudgeon rudder found in the West by roughly a millennium.
Ancient India
A Chandraketugarh seal dated between the 1st and 3rd centuries AD depicts a steering mechanism on a ship namedMedieval Near East
ships also used a sternpost-mounted rudder. 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 written by al-Muqaddasi in 985:Medieval Europe
Oars mounted on the side of ships evolved into quarter steering oars, 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 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, the oldest known depiction of a pintle-and-gudgeon rudder can be found on church carvings of Zedelgem and Winchester dating to around 1180.File:RudderBereFerrersBenchEnd.jpg|right|thumb|A ship's rudder carved in oak, 15th century, Bere Ferrers church, Devon. Heraldic 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. 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.
Historian Joseph Needham holds that the stern-mounted rudder was transferred from China to Europe and the Islamic world during the Middle Ages.