A hydrofoil is a winglike structure or foil, attached to the hull of a boat that raises all or part of the hull out of the water when the boat is moving forward, thus reducing drag.

The term "hydrofoil" is also sometimes used to refer to the hydrofoil ship itself. 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.

Hydrodynamics

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 (see foil (fluid mechanics)). The foil is shaped to move smoothly through the water with faster flow over the top face of the foil, creating a pressure drop and consequently an upward 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.

Foil configurations

Early hydrofoils used V-shape foils. Hydrofoils of this type are known as surface-piercing since portions of the V-shape hydrofoils will rise above the water surface when foilborne. Some modern hydrofoils use inverted 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 sensors, computer and active surfaces.

History

Prototypes

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 long boat, Miranda III, driven by engine that rode on a bowfoil and flat stern. The subsequent Miranda IV was credited with .

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. A full-scale replica of the HD-4 can be seen in the museum on the Alexander Graham Bell National Historic Site in Baddeck.

First passenger boats

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. As Germany was not authorized to build fast boats, Schertel himself went to Switzerland, where he established the Supramar company. In 1952, Supramar launched the first commercial hydrofoil, PT10 "Freccia d'Oro" (Golden Arrow), in Lake Maggiore, between Switzerland and Italy. The PT10 is of surface-piercing type, it can carry 32 passengers and travel at . In 1968, Hussain Najadi the Bahraini born banker, 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. 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 in Italy.

During the same period the Soviet Union experimented extensively with hydrofoils, constructing hydrofoil river boats and ferries with streamlined designs during the cold war period and into the 1980s. Such vessels include the Raketa (1957) 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 1950's era high speed hydrofoil designs. Later, circa 1970's, Alexeyev combined his hydrofoil experience with the surface effect principle to create the Ekranoplan.

In 1961, SRI International issued a study on "The Economic Feasibility of Passenger Hydrofoil Craft in U.S. Domestic and Foreign Commerce". Commercial use of hydrofoils in the U.S. 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 applications

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 .

The Soviets introduced several hydrofoil-based fast attack craft into their navy

• The Turya class torpedo boat was introduced in 1972 and some are still in service

• The Matka class missile boat introduced in the 1980's and still in service

• The Muravey class patrol boat introduced in the 1980's and still in service

• The Sarancha class missile boat a unique vessel built in the 1970's

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 . Three similar boats were built for the Japan Maritime Self-Defense Force

Sailing and sports

The French experimental sail powered hydrofoil Hydroptère is the result of a research project that involves advanced engineering skills and technologies. In september 2009, the Hydroptère provisionally set a new sailcraft world speed records in the 500 m category, with a speed of and a new 1000 m (1 Km) record of . Both of these new records need ratification by the WSSRC before becoming official.

Another trimaran sailboat is the Windrider Rave. The Rave is a commercially available 17 foot, two person, hydrofoil trimaran, capable of reaching speads of 40 knots. The boat was designed by Jim Brown.

The Moth dinghy has evolved into some radical foil configurations.

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. Some surfers have developed surfboards with hydrofoils, specifically aimed at surfing big waves further out to sea.

Passenger boats today

Ukrainian built Voskhods are one of the most successful passenger hydrofoil designs. Currently, they are in service in more than 20 countries. The most recent model Voskhod-2M FFF, also known as Eurofoil, was built in Feodosiya, Ukraine, for the Dutch public transport operator Connexxion.

The Boeing 929 is widely used in Asia for passenger services between the many islands of Japan, in China and on the Korean peninsula.

Current operation

Some operators of hydrofoil include:

• TurboJET service, which speeds passengers across the Pearl River Delta between Hong Kong and Macau in less than an hour, with an average speed of 45 knots (83km/h), mainly using Boeing's Jetfoil. Also services Shenzhen, Guangzhou and Kowloon. Operated by Shun Tak-China Travel Ship Management Limited.

• Cometa service between Nijneangarsk and Irkutsk on the Lake Baikal.

• Cometa service between Vladivostok and Slavyanka.

• Meteor service between Saint Petersburg, Russia and the Peterhof, a summer palace of Russian tsars.

• Meteor service between Saint Petersburg, Russia and the Kronstadt, a strongly fortified Russian seaport town, located on Kotlin Island, near the head of the Gulf of Finland. It lies thirty kilometers west of Saint Petersburg.

• Meteor, Raketa and Voskhod hydrofoil types operate all over Volga, Don and Kama Rivers in Russia. Also the Lena River and Amur River.

• Meteor hydrofoils are operated by a number of tour operators in Croatia, mostly for packaged tours, but there are also some scheduled services to islands in Adriatic.

• Hydrofoils are regularly operated on the three major Italian Lakes by branches of Ministry Of Transportation: Navigazione Lago Maggiore services routes on the Lake Maggiore between Locarno and Arona, Navigazione Lago di Como services routes on the Lake Como and Navigazione Lago di Garda services routes on the Lake Garda. Three units of the Rodriquez RHS150 type operate on each lake, for a total of nine hydrofoils. Navigazione Lago di Como still operates the last Rodriquez RHS70 in active service in Italy.

• Former Russian hydrofoils are used in southern Italy for connection with islands of Lazio and Campania. SNAV has 5 RHS200, RHS160 and RHS150 used in the connections between Naples and the islands of Capri and Ischia.

• Regular hydrofoil service from Istanbul to Yalova.

• Fast Flying Ferries operated by Connexxion, provides a regular public transport service over the North Sea Canal between Amsterdam Central Station and Velsen-Zuid in The Netherlands, using Voskhod 2M hydrofoils.

• Hellenic Seaways operate their Flying Dolphins service over many routes in the Aegean, between the Cycladic islands, Saronic Gulf islands such as Aegina and Poros and Athens.

• Meteor (2), Polesye (4) and Voskhod (3) hydrofoil types operate in Hungary. MAHART PassNave Ltd. operates scheduled hydrofoil liners between Budapest, Bratislava and Vienna, inland liners between Budapest and the Danube Bend, and theme cruises to Komárom, Solt, Kalocsa and Mohács.

• Russian hydrofoils of the Kometa type operated on the Bulgarian Black Sea Coast connecting Varna, Nesebar, Burgas, Sozopol, Primorsko, and Tsarevo, and Raketa and Meteor models served the Bulgarian Danube ports between Rousse and Vidin. Both services were discontinued in the 1990s but may be reopened.

• Vietnamese Greenline Company operates hourly shuttle service between Ho Chi Minh city, Vung Tau and Con Dao island. Hydrofoil lines using the Russian-built Meteor type also connect Hai Phong, Ha Long and Mong Cai in North Vietnam, Phan Thiet and Phu Quy Island and between Rach Gia and Phu Quoc Island in the South.

• The service between Busan, South Korea and Fukuoka, Japan is operated by the two companies. Japanese JR Kyūshū Jet Ferry operates Beetle five times a day. Korean Miraejet operates Kobee three to four times a day. All of their fleets are Boeing 929.

• As of February 2008, all of the commercial lines in Japan use Boeing 929. The routes include:

• *Sado Kisen operates the route between Sado and Niigata.

• *Tōkai Kisen operates Seven Island, running between Tokyo and Izu Islands, via Tateyama or Yokosuka. The destinations include Izu Ōshima, Toshima, Niijima, Shikinejima, and Kōzushima. The same ship also liks Atami and Izu Ōshima.

• *Kyūshū Yūsen operates the route between Fukuoka, Iki, and the two ports of Tsushima.

• *Kyūshū Shōsen operates the route between Nagasaki and the two of Gotō Islands, namely Fukuejima and Nakadōrijima.

• *Kagoshima Shōsen and Cosmo Line operate the various routes between Kagoshima and Tanegashima or Yakushima.

See also

• Voskhod (hydrofoil)

• Raketa (hydrofoil)

• Boeing hydrofoils

• Riverboat

• Hydroplaning

• Sailing hydrofoil

• Sit-down hydrofoil

• Flyak: hydrofoil kayak

• Disco Volante (ship)

• The Hydrofoil Mystery (historical fiction)

• Trampofoil, a one-person man powered hydrofoil