Abstract: A retractable boat line for mooring a boat is wound about a payoff reel contained within a stationary housing, which my be mounted beneath the exterior surfaces of the boat, for example within the hull, transom or gunnel. The invention provides a locking mechanism that latches into a guide wall of the payoff reel at a point remote from the edges of the guide wall to rotationally lock the payoff reel relative to the housing. The mooring line can thus be selectively extended to a desired length and remains locked to the selected length until the locking mechanism is disengaged.