Abstract: The invention refers to a variable geometry hydrofoil boat, equipped for this purpose with secant foils supported by articulated arms operated automatically or manually. The invention makes it possible to obtain a craft which, depending on operational requirements, may function either in the "totally submerged foil" mode or in the "secant foil" mode, that is to say with a variable foil surface. The secant foils supported by arms articulated to the hull may, in a variant of the embodiment, also be applied to fast-moving and streamlined naval units of the semi-planing type, for the purpose of damping their rolling and pitching movements.