Modern hydrofoil ships have evolved in response to the need for a fast reliable means of sea transportation which is capable of operating in all sea conditions. It is the purpose of this paper to describe how the application of modern stabilization and navigation technology to hydrofoil ships has contributed to the achievement of these goals.

First, consider the subject of stability. In particular, consider the source of roll stability in three types of ships: a displacement ship; a surface piercing hydrofoil and a submerged-foil hydrofoil. A roll disturbance of each of the ships is depicted in Fig. 1. In both the displacement ship and in the surface piercing hydrofoil, the righting moment is produced entirely by the change in attitude of the ship relative to the water surface. In the case of the displacement ship, the righting moment is due to the shift of the centre of buoyancy. For the surface piercing hydrofoil, the moment occurs due to the shift of the hydrodynamic pressure centre of the foils. However, for the submerged-foil hydrofoil, no righting moment is produced by the change of the relative position of the water surface. The righting moment for this ship must be produced by underwater control surfaces in response to the change of ship attitude relative to inertial space, as sensed by a vertical gyro. It is this transfer of stability reference from the water surface to an inertial reference that leads to the superior seakeeping capabilities of the submerged foil hydrofoil.