sailboat boom / furling mast
A chain drive gearbox controls the raising, reefing, and lowering of the mainsail. It is operated by three control lines (the halyard, a furling line, and a ratchet lock release line). The sail is raised in a traditional fashion by the halyard. The furling line is rolled into the rope drive while the sail is being raised (like a head sail furler). An internal ratchet provides tension on the luff at all times. The sail is furled and reefed by withdrawing the furling line.