A hydrofoil ferry 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 of the ferry.
Early hydrofoil ferries used U-shape foils. Hydrofoil ferries of this type are known as surface-piercing since portions of the U-shape hydrofoils will rise above the water surface when foilborne.
Modern hydrofoil ferries use T-shape foils which are fully-submerged. Fully submerged hydrofoil ferries are less subjected to the effects of waves, they 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 hydrofoil ferry needs to be adjusted continuously in accordance to the changing conditions, a control process that is performed by computers.
The Soviet Union experimented extensively with hydrofoils, constructing hydrofoil ferries with streamlined designs, especially during the 1970s and 1980s. Such vessels include the Meteor type
(above) and the smaller Voskhod type; these vessels have inspired people in the former Soviet Union to continue tinkering with hydrofoils and selling them to hydrofoil ferry operators.
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