Most sailors are familiar with how roller furling jibs work. They make setting and furling the jib easy and safe because the headstay foil is firm and rigid. When the drum at the base of the headstay is turned, the foil turns unwrapping or wrapping the sail.
The top-down furler applies that same roller furling principle to asymmetrical spinnakers and racing Code Zeros ...but with a twist. Whereas the jib is attached to the headstay foil its entire length, a spinnaker is only attached at the head and the tack. With the development of anti-torsion cable, a bendable but un-twistable rope, setting and dousing spinnakers is now easier and safer than ever!
When you turn the drum on the deck, it twists the anti-torsion cable just like it would a headstay foil. That twisting is transferred to the top of the cable where it’s attached to the sail. The head of the sail begins to twist, to furl, around the cable. The sail furls from the wide head down and furls the foot of the spinnaker last.