Convertible sailboat/motorboat

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. The very light weight hull and all its appointments permit a high keel/boat weight ratio, a low boatweight/waterline length ratio and a high engine horsepower/boat weight ratio. The hull has flat planes aft. The lightweight hull is made possible by (1) construction of the hull wall of plastic foam sandwiched between two layers of unidirectional fiberglass skins and (2) designing for only 6 psi water pressure during planing.