All sails today come equipped with leech and foot lines that enable sailors to stop that annoying flutter up the entire leech or along the foot of your genoa. This flutter usually gets more pronounced as the wind increases.
In the days of Dacron sails, adjusting the leech line was a matter of eliminating a nuisance, nothing more. With laminate sails there is a new importance on properly adjusting the leech line to prevent damage to the sail.
At the edge of the sail there are folded Dacron tapes that enclose the leech and foot lines. When the leech flutters, the laminate bends or hinges just inside these tapes. This frequency of fluttering can amount to hundreds of times per minute in a stiff breeze.
To get an idea of what this is doing to the laminate, straighten out a paper clip and flex it back and forth a couple of times. The result is obvious. Of course the metal in a paper clip isn’t nearly as flexible as a sail laminate, but Mylar film and some high modulus yarns used in racing sails do break down rather quickly when flexed.
Adjusting the leech and foot lines is easy. Just snug them enough to stop the flutter. When the wind dies, you may see a hook in the leech or foot. In that case, ease the leech or foot line until the sail flutters and then put just enough tension on the line to stop the flutter.