Abstract: An adjustable fin for use on a surfboard, the adjustable fin comprising: a base which comprises a mounting means for mounting the adjustable fin to a surfboard, and a member extending in a direction contrary to the mounting means. The adjustable fin further comprises a fin section comprising two outer fin surfaces which meet at a leading edge and a trailing edge; an underside surface comprising an opening to an internal cavity, the internal cavity configured to house the member and enable slidable movement of the member in a direction towards the leading edge or the trailing edge; and a locking means that is manipulate and which projects into the internal cavity, wherein the locking means can releasably couple to the member at one of two or more locking positions thereby preventing slidable movement of the member.

Abstract: A planing-type hull has a keel which projects downwardly from a disk which is mounted in the bottom of the hull for limited rotational movement about a vertical axis located rearwardly of the center of the keel. In a second embodiment the keel projects downwardly from a sector or generally pie-shaped member, which is pivotal in the bottom of the hull between two limit positions. A spring-loaded detent may be employed to return the keel to a centered position.

Abstract: A sealing lip assembly for surfboards or sailboats, which closes the underwater side of the opening of the centerboard case or fin case in a virtually flow-tight and non-vortical manner in every position of the centerboard, and including two sealing lips, with each lip defined by a sealing area capable of flexing along the longitudinal axis of the assembly, a resilient area perpendicular to the longitudinal axis, and a mounting portion.

Abstract: A novel fin for surfboards and watercraft that includes a pivoting rudder-like section that swings out when a turn is commenced, enhancing the maneuvrability of the surfboard by reducing the resistance of the fin as it moves sidewards through the water in a turn and by redirecting the water flow through the pivoting rudder section in the direction of the turn. A fixed blade attaches to the surfboard and a separate pivoting fin section is joined to the fixed blade by two pivot pins. Protruding from a vertical hole in the top of the pivoting fin section is a spring loaded pin which presses into a channel in the underside of a foil integrated into the underside of the fixed blade mounting section. The channel is deepest in the center of the foil thus the spring loaded pin in travelling back and forth along the channel seeks the deepest portion which tends to align the two fin blade sections.

Abstract: A sailboat pivotally carries a pair of weighted complementary shaped keels for independent rotation about a common longitudinally directed medial hinge axis for influencing the roll, moment of inertia and draft of the boat. The keels are independently supported at variable angles with respect to the vertical by lines directed upward along opposite sides of the boat. The upper ends of the lines are attached to a winch mechanism within the boat which includes one rotatable drum for varying the angle between the keels while maintaining the orientation of the angle bisector substantially constant and another rotatable drum for varying the orientation of the angle bisector while maintaining the angle between the keels substantially constant. A bolt carried slideably by the keels selectively locks the keels together for rotation as a unit. The bolt is remotely operated from within the boat via a controlling cable.