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A hydrofoil is a boat with wing-like foils mounted on struts below the hull. As the craft increases its speed the hydrofoils develop enough lift for the boat to become foilborne - i.e. to raise the hull up and out of the water. This results in a great reduction in drag and a corresponding increase in speed. A sailing hydrofoil or hydrosail is a sailboat with wing-like foils mounted under the hull. As the craft increases its speed the hydrofoils lift the hull up and out of the water, greatly reducing wetted area, resulting in decreased drag and increased speed. A sailing hydrofoil can achieve speeds exceeding two times the wind speed.
Early hydrofoils used U-shape foils.Hydrofoils of this type are known as surface-piercing since portions of the U-shape hydrofoils will rise above the water surface when foilborne. Modern hydrofoils use T-shape foils which are fully submerged. Fully submerged hydrofoils are less subject to the effects of wave action, and are therefore more stable at sea and are more comfortable for the crew and passengers. This type of configuration, however, is not self-stabilizing. The angle of attack on the hydrofoils needs to be adjusted continuously in accordance to the changing conditions, a control process that is performed by computers. Failure to make the proper adjustments will result in the foilborne hull dropping violently back into the sea. The term "hydrofoil" is also used to refer to the foil itself, especially when the airfoil profile has been specifically designed for use in water (such as for a propeller blade). Hydrofoils are now being applied in multiple marine applications. Surfers have surfboards with hydrofoils, better suited for big waves further out to sea. Since air and water are basically the same at the fluid level, albeit with different levels of viscosity, the hydrofoil and airfoil create lift in identical ways (see Foil (fluid mechanics)). The foil is shaped to move smoothly through the water while displacing some water downwards, creating an upwards force on the foil. This upward force lifts the body of the vessel, decreasing drag and increasing speed. The lifting force eventually balances with the weight of the craft, reaching a point where the hydrofoil no longer lifts out of the water, but remains in equilibrium. Since the force of the waves acts over a smaller area of the hydrofoil, there is a marked decrease in turbulence drag. History
A March 1906 Scientific American article by American hydrofoil pioneer William E. Meacham explained the basic principle of hydrofoils. Alexander Graham Bell considered the invention of the hydroplane a very significant achievement. After reading this article Bell began to sketch concepts of what is now called a hydrofoil boat. With Casey Baldwin, he began hydrofoil experimentation in the summer of 1908. Baldwin studied the work of the Italian inventor Enrico Forlanini and began testing models based on his designs. This led him and Bell to the development of hydrofoil watercraft. During Bell's world tour of 1910-1911 he and Baldwin met with Forlanini in Italy. They had rides in the Forlanini hydrofoil boat over Lake Maggiore. Baldwin described it as being as smooth as flying. On returning to Baddeck a number of designs were tried culminating in the HD-4. Using Renault engines a top speed of 87 km/h (54 mph) was achieved, accelerating rapidly, taking wave without difficulty, steering well and showing good stability. Bell's report to the United States Navy permitted him to obtain two 260 kW (350 horsepower) engines. On September 9, 1919 the HD-4 set a world marine speed record of 114 km/h (70.86 mph). This record stood for ten years. Between 1899 and 1901, the British boat designer John I Thornycroft worked on a series of models with a stepped hull and single bow foil. In 1909 his company built a full scale 22 foot long boat, Miranda III, driven by 60 hp engine that rode on a bowfoil and flat stern. The subsequent Miranda IV was credited with 35 knots. [1]. Baron von Schertel worked on hydrofoils prior to and during World War II in Germany. After the war Schertel's team was captured by the Russians. Schertel himself went to Switzerland, where he established the Supramar company. In 1952, Supramar launched the first commercial hydrofoil, PT10, in Lake Maggiore, between Switzerland and Italy. The PT10 is of surface-piercing type, it can carry 32 passengers and travel at 35 knots. In 1968, the financier Hussain Najadi acquired the Supramar AG and expanded its operations into Japan, Hong Kong, Singapore, UK, Norway and USA. General Dynamics of the United States became its licensee, and the Pentagon awarded its first R&D naval research project in the field of supercavitation. Hitachi Shipbuilding of Osaka, Japan, was another licensee of Supramar, as well as many leading ship owners and shipyards in the OECD countries. From 1952 to 1971, Supramar designed many models of hydrofoils: PT20, PT50, PT75, PT100 and PT150. Except the PT150, all are of surface-piercing type. Over 200 of Supramar's design were built, most of them by Rodriquez in Italy. The Canadian Navy built and tested a high-speed anti-submarine hydrofoil, the HMCS Bras d'Or, in the late 1960s, but the program was cancelled due to a shift away from ASW by the Canadian Navy. The Bras d'Or was a surface-piercing type which performed well during her trials, reaching a maximum speed of 63 knots. The Soviet Union experimented extensively with hydrofoils, constructing hydrofoil river boats and ferries with streamlined designs, especially during the 1970s and 1980s. Such vessels include the Raketa (1957) type, followed by the larger Meteor type and the smaller Voskhod type. The U.S. Navy operated combat hydrofoils, such as the Pegasus class, from 1977 through 1993. These hydrofoils were fast and well armed, and were capable of sinking all but the largest surface vessels. In their narcotics interdiction role, they were a nightmare for drug runners, being very fast, and having missiles and guns to stop anything they could not catch, as well as the ability to call in air support. The Italian Navy has used 6 hydrofoils of the Nibbio class from the late 1970s. These were armed with a 76 mm gun, two missiles and were capable of speed up to 50 knots. The French experimental sail powered hydrofoil Hydroptère is the result of a research project that involves advanced engineering skills and technologies. In January 2007, the Hydroptère has reached a top speed of 47.2 knots. The SeaWorld San Diego (California) Adventure Park began hydrofoil operations soon after the park opened. Visitors could take a 10-minute, 4-mile round trip into Mission Bay aboard a small fleet of surface-piercing hydrofoils. This popular attraction was halted in the mid-1980s, due to concerns about increasing personal watercraft traffic in the Bay. A new kayak design, called Flyak, has hydrofoils that lift the kayak enough to significantly reduce drag, allowing speeds of up to 27 km/h. Current operation
Some operators of hydrofoil include:
Gallery
See also
External links  Wikimedia Commons has media related to:
A sailing hydrofoil or hydrosail is a sailboat with wing-like foils mounted under the hull. As the craft increases its speed the hydrofoils lift the hull up and out of the water, greatly reducing wetted area, resulting in decreased drag and increased speed. A sailing hydrofoil can achieve speeds exceeding two times the wind speed. Both monohull and multihull sailboats can be retrofitted with hydrofoils, although greater stability can be achieved by using the wider planform of a catamaran or trimaran.
Typical configurationsSome multihulls use three foils; two main forward foils provide lift so that the boat "flies" while while a horizontal foil on the rudder is trimmed to drive and control attitude. On catamarans, a single main foil can be attached between the hulls just in front of the center of gravity and at 2 degrees of incidence, spanning the tunnel with supporting struts. Hydrofoil catamarans are also called foilcats. Multihull sailboats can also employ hydrofoils only to assist performance. Just as daggerboards and rudders are foils that enhance the control of a boat, assisting hydrofoils provide lift to the hull to reduce the wetted area without actually lifting the boat completely out of the water. Monohull boats typically employ a "ladder" arrangement of hydrofoils splayed out with a dihedral angle of 50 degrees, with a stabilizing rudder foil. One of the earliest examples is the Monitor boat from 1957. This design offers the advantages of maximum lifting foil area at slow speeds and less at higher speeds, with rolling resistance arising from the dihedral support of the outboard ladder foils. Production designs
Experimental designs
Many non-production experimental designs have been built. Some examples of notable designs are:
See alsoReferences
External links
This article is licensed under the GNU Free Documentation License. It uses material from Wikipedia Encyclopedia article "Hydrofoil" |
