It is a surface-effect ship, not a "hovercraft." Basically, they are a catamaran with rubber skirts fore and aft. Air ducts lift the narrow twin hulls. At rest, they need 6' of water, with the air ducts on, the boat rises until only 3' of the hulls are in the water. This radically reduces their wetted surface (friction). The pressurized air between the hulls dampens wave shock to almost nil, allowing it to go twice as fast as vessels in its size class in the same sea states.