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Title: Hydrofoils  
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Subject: Aquatic locomotion
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The term "hydrofoil" can have one of two basic meanings.

Firstly, a hydrofoil is a foil which operates in water. They are similar in appearance and purpose to airfoils.[1]

Second, the term "hydrofoil" is often used to refer to boats using hydrofoil technology. Most of this article is about this meaning of hydrofoil.

Hydrofoil, as lifting surface

Hydrofoils can be artificial, such as the rudder or keel on a boat, the diving planes on a submarine, a surfboard fin, or occur naturally, as with fish fins, the flippers of aquatic mammals, the wings of swimming seabirds, or other creatures like the sand dollar.

The term "hydrofoil" is commonly used for the wing-like structure mounted on struts below the hull, or across the keels of a catamaran in a variety of boats (see illustration), which lifts the boat out of the water during forward motion, in order to reduce hull drag; as such,

Hydrofoil as foil supported craft

As a hydrofoil-equipped watercraft increases in speed, the hydrofoil elements below the hull(s) develop enough lift to raise the hull up and out of the water. This results in a great reduction in hull drag, and a further corresponding increase in speed and efficiency in operation in terms of fuel consumption.

A wider adoption of the technical innovations of hydrofoils is prevented by the increased complexity of building and maintaining them. Hydrofoils are generally prohibitively more expensive than conventional watercraft. However, the design is simple enough that there are many human-powered hydrofoil designs. Amateur experimentation and development of the concept is popular.[2]

A boat equipped with hydrofoils is also called a hydroplane (boat).[3]

Hydrofoils configurations

Since air and water are governed by similar fluid equations, albeit with vastly 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 causing the flow to be deflected downward which according to Newton's Third Law of Motion exerts an upward force on the foil. This turning of the water causes higher pressure on the bottom and reduced pressure on the top of the foil. This pressure difference is accompanied by a velocity difference, via Bernoulli's principle, so the resulting flowfield 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 (physics) on the hull are eliminated as the hull is lifted clear, turbulence and drag act only on the much smaller surface area of the hydrofoil and there is 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 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.



Italian inventor Enrico Forlanini began working on hydrofoils in 1898, and used a “ladder” foils system. Forlanini obtained patents in Britain and the United States for his ideas and designs.[4][5]

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 22-foot (6.7 m) long boat, Miranda III. Driven by a 60 hp (45 kW) engine, it rode on a bowfoil and flat stern. The subsequent Miranda IV was credited with a speed of 35 knots (65 km/h).[6]

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 his designs, which led them 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 87 km/h (54 mph) 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 260 kW (350 horsepower) engines. On 9 September 1919 the HD-4 set a world marine speed record of 114 km/h (70.86 mph), a record which stood for two decades. A full-scale replica of Bell's 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 a hydrofoil water craft called the White Hawk that was jet powered in an attempt to beat the absolute water speed record.[7] But in tests the White Hawk could barely top the record breaking speed of Bell's 1919 HD-4. The designers had come up against an engineering phenomenon that limits the top speed of even today's modern hydrofoils. Cavitation similar to high speed prop cavitation of the foils that breaks the lift created by the foils as they move through the water at speed above 70 m.p.h. which bends the lifting foil and, basically causes the stall characteristics of fixed wing aircraft when they are moving too slow in flight, only in reverse.[8]

First passenger boats

German engineer Hanns 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 35 knots (65 km/h). In 1968, Hussain Najadi the Bahraini born banker, 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 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".[9] 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.[10]


Military applications

Canada - During World War II, Baldwin worked on an experimental smoke laying hydrofoil (later called the Comox Torpedo) 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 (e.g. Baddeck and two vessels named Bras d'Or), 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 63 knots (117 km/h).

The USSR introduced several hydrofoil-based fast attack craft into their navy, principally:

  • the Sarancha class missile boat, a unique vessel built in the 1970s
  • the Turya class torpedo boat, which was introduced in 1972 and still remains in service today
  • the Matka class missile boat, which was introduced in the 1980s and still remains in service today
  • the Muravey class patrol boat, which was introduced in the 1980s and still remains in service today

The U.S. Navy began experiments with hydrofoils in the mid-1950s by funding a sailing vessel that used hydrofoils to reach speeds in the 30 mph range.[11][12] After a few minor experiments using sailing vessels the US Navy implemented a small number of 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 illegal drug runners, as they were very fast and had the ability to stop anything they could not catch, as well as the ability to call in air support.

The Italian Navy has used six hydrofoils of the Sparviero class since the late 1970s. These were armed with a 76 mm gun and two missiles, and were capable of speeds up to 50 knots (93 km/h). 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 set new sailcraft world speed records in the 500 m category, with a speed of 51.36 knots (95.12 km/h) and in the one nautical mile (1.9 km) category with a speed of 50.17 knots (92.91 km/h).[13][14]

Another trimaran sailboat is the Windrider Rave.[15] The Rave is a commercially available 17-foot (5.2 m), two person, hydrofoil trimaran, capable of reaching speeds of 40 kn (74 km/h). The boat was designed by Jim Brown.

The Moth dinghy has evolved into some radical foil configurations.

Hobie Sailboats once produced a production foiling trimaran. It was and is the fastest production sailboat in history. It is called the Hobie Trifoiler. Trifoilers have clocked speeds upward of thirty knots.

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 (17 mph). Some surfers have developed surfboards with hydrofoils called foilboards, specifically aimed at surfing big waves further out to sea.[16]

Modern passenger boats

Soviet Union built Voskhods are one of the most successful passenger hydrofoil designs. It was developed in the Soviet Union and manufactured in Russia and Ukraine. 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.[19]

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

Current operation

Some operators of hydrofoil include:

  • 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. Since 2012 replaced by a catamaran 'Mercury'.
  • 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. In 2011 the service reopened between Varna, Nesebar, Burgas and Sozopol by Bulgarian Hydrofoils Ltd.
  • 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:
  • In 2012, Agriculture, Fisheries and Conservation Department (AFCD) in Hong Kong leased a 12 meter HAWC - Hydrofoil Assisted Water Craft - a catamaran to patrol the Geo Park, a Unesco Sanctioned Marine Park in the Sai Kung areas off Hong Kong


Hydrofoils had their peak in popularity in the 1960s and 70s. Since then there has been a steady decline in their use and popularity for leisure, military and commercial passenger transport use. There are a number of reasons for this:

  • Hydrofoils are sensitive to impacts with floating objects and marine animals. If the hydrofoils hit something the boat will fall off the foils and this often creates a perception of increased danger. However, hydrofoils operating in Hong Kong, reportedly some of the most littered waters, operate relatively trouble free. The Hong Kong Marine department maintains online records of all accidents in its waters.
  • Hydrofoils have sharp edges that reside in the water while in operation. These edges can fatally injure marine mammals (e.g. whales) they hit.
  • Hydrofoils are expensive to build. A vessel like the Boeing Jetfoil currently costs about 3 times the price of an equivalent catamaran passenger ferry. The increased costs are not always economically justifiable by consumers. Simpler designs such as those of Russian design and those by Rodriquez in Italy are more competitive in price and are still being produced today for operation on ferry routes.
  • It is a very conservative industry. Hydrofoils are still considered exotic by many commercial operators of high-speed craft and many will not take the risk of trying such exotic vessels when they have no experience operating them. Those that do have found benefit in their operation. For example the largest ferry operator in the world, TurboJET (Hong Kong), still operates 20+ year old Boeing Jetfoils because they remain the industry benchmark for passenger comfort in rough seas.
  • They are technically complex and require high maintenance, which has killed most military hydrofoil projects. The US Navy for example developed some of the most technically advanced hydrofoils around but they could never get them to be reliable due to the complex propulsion systems and ride control required. This eventually led to the suspension of their hydrofoil projects. Most other Navy developments followed the same fate. The Russian Navy still operates very large hydrofoils and have been successful in their design, largely because they have opted for simpler systems that might not have the same performance as the US designs but are much more robust and reliable. In Hong Kong, the increasing maintenance cost of keeping the old Jetfoils running is resulting in these vessels slowly being phased out.

See also



External links

  • Limitations of hydrofoils
  • The International Hydrofoil Society
  • Fast CC Hydrofoil design by Prof. KG Hoppe, inventor of HYSUCAT technology patented by University of Stellenbosch, S.A.
  • Hydrofoil Assisted Water Craft employing HYSUCAT and HYSUWAC patents in their projects and vessels currently in operation
  • Hysucat Design, South African originators of Hydrofoil Supported Catamaran technology
  • Swiss experimental hydrofoils
  • HyRaii - Hydrofoil Sailboat, Student Project ETH Zurich

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