Device for the gradual displacement and fixing of the mast foot of a rig in the longitudinal direction on a windsurfing board

A device for the gradual displacement and fixing of the mast foot of a rig in the longitudinal direction on a windsurfing board (2) has a mast-foot rail (1) to be mounted in the windsurfing board, a mast-foot housing (5) which can be adjusted and fixed along the mast-foot rail, and a shaft (22) mounted in the mast-foot rail (1) in such a way that it can be rotated to a limited extent. The shaft (22) can be adjusted back and forth between three rotary positions, which can be alternatively and firmly set, and has three areas axially one behind the other which are in each case designed differently for the release or fixing of the mast-foot housing (5) and are allocated to the three rotary positions. A locking means (41) which can be disenaged only by the further area in the additional rotary position is provided on the mast-foot housing (5), and allocated to the locking means (41) on the mast-foot rail (1) is a counter-locking means (11') securing the centre position.