Join Date: Apr 2006
Thanked 173 Times in 170 Posts
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Life expectancy of a sail: 48 hours if left flogging in high winds and strong sunlight. Less if you're a diehard "sail of the day" racer. Or about 10 years for the casual sailor.
A lot depends on how much you expect from the sail, because it will lose shape and power way faster than the cloth wears out. Most are coated with a plastic resin when new, to help keep their shape (locks the fibers in place) and block UV. They'll be stiff and hard on your hands at that point, too.
Once the resin is gone...the shape will be lost faster. That's where it gets subjective, but I'd say ten years is probably time to splurge and get a new one, unless you plan to do the repair yourself and "just want to sail" without fussing over how blown out the sail may be.
If you can see daylight at any of the stitching, from the threads wearing and cutting into the sail. Or if threads have worn and broken. Or if the cloth bears any resemblance to your favorite flannel shirt. Time to do the deed and replace it.
You may be able to have it cut down and recycle it into a storm trysail, so it may not all be wasted. If part of it is in good enough condition...the shape of a storm trysail really isn't important, but using it allows you to keep your good mainsail out of heavy winds.