How a furler works...
The furler has a foil (flat piece of metal or plastic) with a center opening that runs the length of it for the forestay and two slots (one on either edge of the foil) that you slide the luff of the head sail into. On a CDI furler, a line runs up one of the slots, around a sheave a the top and then backdown the other side to the drum. On other furlers, the foil is topped by a swivel that offsets the regulard jib halyard. At the base the foil attaches to a drum that has a coil for the furling line. With the sail furled (rolled up) the line is fully depleted from the drum. As you roll the sail out the line fills the drum and vice versa. You need to replace the hanks on most head sails with a luff tape of the approriate size to fit the slots in the foil
