Bruce foil

A Bruce foil is a variant of the leeboard, consisting of a foil typically mounted on an outrigger and always set at an angle to provide both lateral and vertical force. It was invented by Edmond Bruce in the early 1960s, and first published in the Amateur Yacht Research Society publication in April 1965. Theory Nearly all methods that increase resistance to sideways movement also cause heeling, the leaning produced by the imbalance of the forces on the sails, high above the waterline, and the sideways resistance, generated by the centerboard or other foil below the waterline. The resulting torque causes the hull to heel until the buoyancy of the hull provides sufficient torque to balance the heeling force. The limited buoyancy of the hull therefore limits the amount of force that the sail can effectively produce. One solution to dealing with this limit is to bring the forces generated by the sail and the underwater foil into alignment, canceling as much of the torque as possible and thus reducing the amount of heeling. Two approaches to this have surfaced one being the inclined rig, and the other the Bruce foil. Implementation A Bruce foil reduces torque by moving the foil far out from the centerline of the hull, and angling it so that a perpendicular line through the center of the underwater portion of the foil will intersect the center of pressure of the sails. Like a traditional centerboard, the Bruce foil is generally a symmetric design, such as the NACA 00xx series, which relies on the leeward slip of the hull to provide the angle of attack needed to generate lift. When mounted on the lee side, the Bruce foil generates an upwards lift in addition to lateral force, and when mounted on the windward side, it generates a downwards force.