Mechanism for hoisting and reefing a sail on a sailing vessel wherein the foot of the sail is connected along its length to a roller boom, and wherein the hoisting and reefing of the said sail is effected by halyard means passing over a pulley at an upper portion of a mast associated with the said roller boom and connected at one of its ends to a hoisting drum and connected at the other end to a reefing drum, and is also connected to the peak of the sail, and wherein the said reefing drum is connected to the said roller boom whereby the boom is rotatable with the said reefing drum, characterized in that there are provided: (a) rotatable clutch (25) means for selectively rotating the said hoisting drum (8) and the said reefing drum (4)(b) selective engaging and locking means (9, 9a, 26, 28) for selectively engaging the said clutch to the said hoisting drum or the said reefing drum, and automatically to lock the said hoisting drum with the said reefing drum at the end of a hoisting operation, and to unlock the said drums at the start of a reefing operation, and (c) brake means (12, 13) for providing a braking force on the hoisting drum during a reefing operation whereby free fall of the sail during reefing is prevented.