Hydrofoil
A hydrofoil is a lifting surface, or foil, that operates in water. It is similar in appearance and purpose to aerofoils used by airplanes. Boats that use hydrofoil technology are also simply termed hydrofoils. As a craft gains speed, the hydrofoils lift the boat's hull out of the water, decreasing drag and allowing greater speeds.
Description
The hydrofoil usually consists of a winglike structure mounted on struts below the hull, or across the keels of a catamaran in a variety of boats. As a hydrofoil-equipped watercraft increases in speed, the hydrofoil elements below the hull develop enough lift to raise the hull out of the water, which greatly reduces hull drag. This provides a corresponding increase in speed and fuel efficiency.Wider adoption of hydrofoils is prevented by the increased complexity of building and maintaining them. Hydrofoils are generally prohibitively more expensive than conventional watercraft above a certain displacement, so most hydrofoil craft are relatively small, and are mainly used as high-speed passenger ferries, where the relatively high passenger fees can offset the high cost of the craft itself. However, the design is simple enough that there are many human-powered hydrofoil designs. Amateur experimentation and development of the concept is popular.
Hydrodynamic mechanics
Since air and water are governed by similar fluid equations—albeit with different levels of viscosity, density, and compressibility—the hydrofoil and airfoil create lift in identical ways. The foil shape moves smoothly through the water, deflecting the flow downward, which, following the Euler equations, exerts an upward force on the foil. This turning of the water creates higher pressure on the bottom of the foil and reduced pressure on the top. This pressure difference is accompanied by a velocity difference, via Bernoulli's principle, so the resulting flow field about the foil has a higher average velocity on one side than the other.When used as a lifting element on a hydrofoil boat, 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 wave resistance and other impeding forces such as various types of drag on the hull are eliminated as the hull lifts clear, turbulence and drag act increasingly on the much smaller surface area of the hydrofoil, and decreasingly on the hull, creating a marked increase in speed.
Foil configurations
Early hydrofoils used V-shaped foils. Hydrofoils of this type are known as "surface-piercing" since portions of the V-shape hydrofoils rise above the water surface when foilborne. Some modern hydrofoils use fully submerged inverted T-shape foils. Fully submerged hydrofoils are less subject to the effects of wave action, and, therefore, more stable at sea and more comfortable for crew and passengers. This type of configuration, however, is not self-stabilizing. The angle of attack on the hydrofoils must be adjusted continuously to changing conditions, a control process performed by sensors, a computer, and active surfaces.History
Prototypes
The first evidence of a hydrofoil on a vessel appears on a British patent granted in 1869 to Emmanuel Denis Farcot, a Parisian. He claimed that "adapting to the sides and bottom of the vessel a series or inclined planes or wedge formed pieces, which as the vessel is driven forward will have the effect of lifting it in the water and reducing the draught.". Italian inventor Enrico Forlanini began work on hydrofoils in 1898 and used a "ladder" foil system. Forlanini obtained patents in Britain and the United States for his ideas and designs.Between 1899 and 1901, British boat designer John Thornycroft worked on a series of models with a stepped hull and single bow foil. In 1909 his company built the full scale long boat, Miranda III. Driven by a engine, it rode on a bowfoil and flat stern. The subsequent Miranda IV was credited with a speed of.
Image:Bell HD-4.jpg|thumb|Alexander Graham Bell's HD-4 on a test run, c. 1919
In May 1904 a hydrofoil boat was described being tested on the River Seine "in the neighbourhood of Paris". This boat was designed by Comte de Lambert. This had 5 variable pitch fins on the hull beneath the water so inclined that when the boat begins to move "the boat rises and the planes come to the surface" with the result that "it skims over the surface with little but the propellers beneath the surface". The boat had twin hulls 18-foot long connected by a single deck 9-foot wide, and was fitted with a 14HP De Dion-Bouton motor, the boat was reported to have reached 20 mph. It was stated that "The boat running practically on its fins resembles an aeroplane".
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, and after reading the article began to sketch concepts of what is now called a hydrofoil boat. With his chief engineer Casey Baldwin, Bell began hydrofoil experiments in the summer of 1908. Baldwin studied the work of the Italian inventor Enrico Forlanini and began testing models based on those designs, which led to the development of hydrofoil watercraft. During Bell's world tour of 1910–1911, Bell and Baldwin met with Forlanini in Italy, where they rode in his hydrofoil boat over Lake Maggiore. Baldwin described it as being as smooth as flying.
On returning to Bell's large laboratory at his Beinn Bhreagh estate near Baddeck, Nova Scotia, they experimented with a number of designs, culminating in Bell's HD-4. Using Renault engines, a top speed of was achieved, accelerating rapidly, taking waves without difficulty, steering well and showing good stability. Bell's report to the United States Navy permitted him to obtain two engines. On 9 September 1919 the HD-4 set a world marine speed record of, which stood for two decades. A full-scale replica of the HD-4 is viewable at the Alexander Graham Bell National Historic Site museum in Baddeck, Nova Scotia.
In the early 1950s an English couple built the White Hawk, a jet-powered hydrofoil water craft, in an attempt to beat the absolute water speed record. However, in tests, White Hawk could barely top the record breaking speed of the 1919 HD-4. The designers had faced an engineering phenomenon that limits the top speed of even modern hydrofoils: cavitation disturbs the lift created by the foils as they move through the water at speed above, bending the lifting foil.
First passenger boats
German engineer Hanns von Schertel worked on hydrofoils prior to and during World War II in Germany. After the war, the Russians captured Schertel's team. As Germany was not authorized to build fast boats, Schertel went to Switzerland, where he established Together with his business partner and chief designer Karl Johann Büller the Supramar company. In 1952, Supramar launched the first commercial hydrofoil, PT10 "Freccia d'Oro", in Lake Maggiore, between Switzerland and Italy. The PT10 is of surface-piercing type, it can carry 32 passengers and travel at. In 1968, the Bahraini born banker Hussain Najadi acquired the Supramar AG and expanded its operations into Japan, Hong Kong, Singapore, the UK, Norway and the US. 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. All are of surface-piercing type, except the PT150 combining a surface-piercing foil forward with a fully submerged foil in the aft location. Over 200 of Supramar's design were built, most of them by Rodriquez type, followed by the larger Meteor type and the smaller Voskhod type. One of the most successful Soviet designer/inventor in this area was Rostislav Alexeyev, who some consider the 'father' of the modern hydrofoil due to his 1950s era high speed hydrofoil designs. Later, circa 1970s, Alexeyev combined his hydrofoil experience with the surface effect principle to create the Ekranoplan. Extensive investment in this type of technology in the USSR resulted in the largest civil hydrofoil fleet in the world and the making of the Meteor type, the most successful hydrofoil in history, with more than 400 units built.
In 1961, SRI International issued a study on "The Economic Feasibility of Passenger Hydrofoil Craft in US Domestic and Foreign Commerce". Commercial use of hydrofoils in the US first appeared in 1961 when two commuter vessels were commissioned by Harry Gale Nye, Jr.'s North American Hydrofoils to service the route from Atlantic Highlands, New Jersey to the financial district of Lower Manhattan.
Military usage
Germany
A 17-ton German craft VS-6 Hydrofoil was designed and constructed in 1940, completed in 1941 for use as a mine layer; it was tested in the Baltic Sea, producing speeds of 47 knots. Tested against a standard E-boat over the next three years it performed well but was not brought into production. Being faster it could carry a higher payload and was capable of travelling over minefields but was prone to damage and noisier.Canada
In Canada during World War II, Baldwin worked on an experimental smoke laying hydrofoil that was later superseded by other smoke-laying technology and an experimental target-towing hydrofoil. The forward two foil assemblies of what is believed to be the latter hydrofoil were salvaged in the mid-1960s from a derelict hulk in Baddeck, Nova Scotia by Colin MacGregor Stevens. These were donated to the Maritime Museum in Halifax, Nova Scotia.The Canadian Armed Forces built and tested a number of hydrofoils, which culminated in the high-speed anti-submarine hydrofoil HMCS Bras d'Or in the late 1960s. However, the program was cancelled in the early 1970s due to a shift away from anti-submarine warfare by the Canadian military. The Bras d'Or was a surface-piercing type that performed well during her trials, reaching a maximum speed of.