Abstract: A pivotal fin system, for use with an aquafoil, such as surfboards, body boards, wave skis, sail boards, wake boards and the like, comprising a pot (3) and a fin (2), having a tab (18) extending from the base (17) of the fin (2). The pot (3) has a central slot (11) and is mounted in the board (23) with the opening of the central slot (11) flush with the board (23). The slot (11) has a releasable locking means (6 & 7) therein, and the tab (18) has a connection means (21 & 22), which is releasably engaged by locking means (6 & 7). Preferably the releasable locking means (6 & 7) is a substantially c-shaped clamp, and the connection means (21 & 22) has a recess or recesses (22) behind a bulbous extension (21), which is engaged in the c-shaped clamp, with arms (5) of the c-shaped clamp engaging in the recess or recesses (22).