This is a common sight in marinas and mooring fields after some heavy weather blows through. Conscientious sailors either don’t have time to strip their sails off their boats, or they figure the weather won’t really be that bad. So they furl their headsails and take a few extra wraps around the clew to make sure the sail is secure. All is safe, they figure. But when they return they find their headsail somehow managed to shred itself anyway.
How the hell does this happen? You’ll notice when it does it is almost always the part of the sail north of the clew that somehow managed to get loose and beat itself up in the breeze. This is because most headsails are cut with an asymmetric shape–the leech above the clew is much longer than the foot beneath it. Thus, when the sail rolls up on a furling rod, the leech, because of all the extra material in it, furls much more loosely. The foot, meanwhile, is nicely tensioned and furls quite tightly.
We confront this same problem, of course, every time we roller-reef a headsail with an asymmetric shape. In this context, most sailors know that to maintain proper headsail shape they must move the sheet lead forward as the sail is reefed so the leech and foot are evenly tensioned.
And here’s your lightbulb revelation: you have to do the same thing when you furl the sail entirely if you want the whole sail to roll up neat and tight.
(Or you can fly a high-cut yankee-type headsail, with a leech and foot that are more or less the same length, and not be bothered with any of this. Though, of course, you’ll miss the extra sail area when the wind is light.)
So next time the forecast is especially grim, even if you don’t have time to take your headsail down, you should at least take the time to furl it properly.