 To furl the mainsail, the boom is unlocked, and then rotated to take up the desired amount of mainsail, and then locked in place.More advanced boom furling systems will wrap the furling mechanism in a slotted cover, so the sail furls inside the cover; this also makes sheeting easier, since the sheet may be attached to the outer portion of the boom.These systems use either a line, a hand-operated crank, or a hydraulic or electric powered furler.