Abstract: The three-degree of freedom fin apparatus and method described herein is for use on a watercraft (such as a surfboard) and allows adjustment of up to three degrees of freedom, including a translational degree of freedom along a longitudinal axis of the fin structure in the fore and aft direction (longitudinal translation or pitch), a first rotational degree of freedom about the longitudinal axis (roll), and a second rotational degree of freedom about a vertical axis centered at a point on the fin (yaw). Pitch adjustment is made by sliding a base plate and fin assembly along the longitudinal axis. Yaw adjustment is made by moving a front portion of the fin assembly about a yaw pivot point and the rear portion along a yaw track in the base plate. A roll adjustment is made by rotating a fin unit of the fin assembly about the longitudinal axis.

Abstract: A fin assembly for securing a fin to a water craft in a desired angular position relative to a longitudinally oriented axis of the water craft, i.e. the roll angle, is provided in the form of a fin mounting mechanism incorporated in the bottom surface of the water craft and a detachable fin. The attachment mechanism includes a fin mounting box with an elongated channel defined in part by a pair of spaced longitudinal extending side walls. A rotating bar is inserted within the elongated channel of the mounting box and two end caps are affixed to the fin mounting box to hold the rotating bar into the fin mounting box. The end caps when loosened allow the rotating bar to rotate freely and when tightened hold the rotating bar fixedly in place. In this way the detachable fin's roll angle can be easily and accurately selected, fixed and adjusted.