Abstract: An adjusting fin for a watercraft consisting of a fin removably attached to a spindle that is held within a fin box. The spindle is rotatable within the fin box such that the fin can pivot with action of water against the fin as the watercraft moves through the water. Adjustable stops act against cams on the spindle to limit the range of rotation available, thus allowing the adjusting fin to be set up to suit the prevailing conditions and the expertise of the user. An optional biasing means biases the fin towards a neutral position which is perpendicular to an underside of the watercraft.