Abstract: A boat hull keel is disclosed which retracts into the boat hull on a fixed pivot. The pivot location is placed above the keel/hull bottom intersection, rearward of the major axis of the fully lowered keel and rearward of the keel trailing edge at the keel/hull intersection. The placement distances are large in terms of the maximum keel chord length. (measured at the keel/hull intersection.) This amounts to a novel location. The location of the pivot allows the keel rotation to create a change in the attitude of the boat hull.

Abstract: A convertible sailboat/motorboat is disclosed which has capability for displacement movement under maximum speeds typical of the maximum for displacement boats as a function of their size, capability for semi-planing of the hull under sail propulsion, and capability for planing of the hull under motorboat propulsion. The key features are an extremely light hull weight, an engine located approximately amidships, and a deep retractable keel with an upper trim tab which upon retraction into the hull creates a large shift of center-of-gravity rearward for the boat. The keel is hinged at a point above and to the rear of the keel which imparts a large rear movement of the keel weight for motorboat operation upon its retraction. Performance under displacement sailing is uniquely enhanced with the combination of a low-weight, deep keel and the keel trim tab in the upper portion of the keel where slip reaction is generated with the addition of a minimum of extra heeling moment to that generated by the sails.