Damfino's mainmast is unstayed, round and rotating. The sail is boomless and furls/reefs on the spar. The mast is rotated by a furling line that rolls up on a composite spool just above the deck where the mast is about 6" in diameter. The furler line is run through a fairlead block to a dedicated winch on the house top. It all works much like a jib furler except that there is no housing around the spool to keep the furling line in order. Like a jib furler, when the sail is not reefed and there's no tension needed on the furler line, the mast rotates as the sail pulls one way or another and so it gives or takes a few inches of furler line on alternate tacks.
As an alternative to a housing around the spool, I'm trying to think of a tensioning device for the furler line. It needs to permit the line to be let out or cranked in (The total travel is about 12 feet.), keep a couple of pounds of tension on the line and want to take back the last few inches of travel. The furler line is currently 3/8" Sta-Set-X, and i'm thinking of changing it to something lower stretch.
Anybody got any ideas?