It is a boat with wing-like foils mounted on struts under the hull. As the craft put into its speed the hydrofoils make better enough lift for the boat to become foil borne - i.e. to raise the hull up and out of the water. This consequence has a great decrease in drag and a corresponding increase in speed.
Early hydrofoils worn U-shape foils. Hydrofoils of this type are recognized as surface-piercing since portions of the U-shape hydrofoils will rise over the water surface when foil borne. Modern hydrofoils make use of T-shape foils which are fully submerged. Fully submerged hydrofoils are fewer subjected to the effects of wave action, and are therefore steadier at sea and are more relaxed for the crew and passengers. This type of pattern, however, is not self-stabilizing. The angle of attack on the hydrofoils wants to be adjusted endlessly in accordance to the changing conditions, a control process that is performed by computers. Failure to make the proper adjustments will result in the foil borne hull dipping aggressively back into the sea.