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An older style hydrofoil

A hydrofoil is a wing-like structure mounted on struts below the hull of a boat, which lifts the boat partially out of the water during forward motion, in order to reduce drag. Colloquially, the term "hydrofoil" is often used to refer to any boat that utilizes hydrofoil technology.

Hydrofoils are similar in appearance and purpose to airfoils.[1] As the craft increases its speed, the hydrofoils develop enough lift to raise the hull up and out of the water. This results in a great reduction in drag, and a corresponding increase in speed.

Contents

Hydrodynamics

The two types of hydrofoils.

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-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.

History

Forlanini hydrofoil over Lake Maggiore, 1910.
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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 22-foot (6.7 m) long boat, Miranda III, driven by 60 hp (45 kW) engine that rode on a bowfoil and flat stern. The subsequent Miranda IV was credited with 35 knots (65 km/h).[2]

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.

The image indicates how a self-stabilizing system for fully submerged hydrofoils functions. The computer gathers data from electrical engine (boom position) and current water level and determines position for flaps.

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 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, 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.[citation needed] 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".[3] 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.[4]

Uses

A Project 206M "Shtorm" (NATO - Turya class) patrol fast attack craft hydrofoil of the Cuban Navy
USS Aquila, a military hydrofoil. The T-shaped foils are visible just below the water.

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 63 knots (117 km/h).

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

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[citation needed], 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 (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 category with a speed of 50.17 knots (92.91 km/h).[5][6]

Another trimaran sailboat is the Windrider Rave.[7] 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.[citation needed]

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, specifically aimed at surfing big waves further out to sea.

Ukrainian built Voskhod Eurofoil boat operated on the North Sea Canal, Netherland.
TurboJET's Urzela JetFoil
TurboJET's Barca Foilcat

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.[8]

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:

See also

Notes

External links


Simple English

File:20091105-TurboJET
A Boeing Jetfoil

A hydrofoil is a type of boat that can lift it's hull out of the water with a pair of special wings underwater. These wings are like the wings of an airplane.

How it works

When a hydrofoil moves quickly, it's wings allow it to fly. When this happens the boat is said to be in foilborne. The result of flying means less of the boat is touching the water and can make the boat have less drag which allows it to move faster (drag slows a boat down).

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