Small Boat underdeck furling units are ideal for sportboats and daysailers from 4.8m to 9m (16 to 30 ft). The drum is located beneath the deck, lowering the tack height for maximized sail area and the upper swivel is included. The single through-deck ball joint provides a low-profile, nearly watertight system that aligns the spool to the headstay. Like all Harken Small Boat furlers, the underdeck furler is for furling only, not reefing. An optional hoistable ball bearing halyard swivel can be installed on your headstay so you can raise or lower the sail without removing the headstay. Swivels are independent of the headstay, allowing you to tension the luff separately from the mast rake. A tack adaptor tang is available to adapt headstay pin diameter to the furling system pin size.