The invention relates to a device (10) at a cleat (1) for a sailing boat in order to provide detachable locking of the line (3) to a sail, a rig or the like, where the line (3) runs over a sheave (2) on an elevated level and having cleat (1) for locking the line (3) situated at a distance from the deck of the boat. According to the invention, the line (3) is arranged to run over a sheave (2), which is provided with ratchet back stop (5). The line (3) is in that connection arranged to directly co-operate with a movably actuatable mechanism (14), which is arranged to activate the ratchet back stop (5). The mechanism (14) is formed of at least one pivotably mounted main arm (4), and said mechanism (14) is arranged to activate the ratchet back stop (5), the mechanism (14) being arranged to, upon fixed load of the line (3, 3A), which goes down to deck and by means of which the sail (9) is hoisted, actuate the main arm (4) to connect ratchet back stop function (5) on the sheave (2) and in that connection prevent the pulling backwards (7) of the line toward the sail (9).