Abstract: A watercraft having a hull, a mast with sail, an aft rudder and a hydrofoil projecting below the bottom of the hull. The hydrofoil is pivotly connected to the hull enabling the hydrofoil to pitch on a pivot axis which is essentially perpendicular to the longitudinal axis of the hull. The hydrofoils have a vertical part which produces lateral forces to accelerate the boat in turns and resist lateral forces from the sail, and a vertical portion which curves into the horizontal portion which produces vertical lift. The angle of incidence of the hydrofoil is controlled by a sensor arm carrying a trailing sensor.