Abstract: Self locking apparatus for quick and convenient tensioning of the luff of a sail of a sailboard. In a first embodiment, the tack of the sail is attached to the mastbase close to the hull of the sailboard and the head of the sail is attached to the apparatus of the invention. The invention includes a cap for placement over and receiving the top of the sailboard mast, a lever pivotally engaging the cap; and an adjustment strap connecting the head of the sail to a cross bar on the lever. The lever brings the strap in a self locking position over center for tensioning the luff of the sail. In a second embodiment, the head of the sail is attached in conventional manner to the top of the mast and the lever is positioned by means of a sleeve to the bottom of the mast. Once again, the lever rotates to an over-center self-locking position for tensioning the luff of the sail.