The water is wonderful, but the air is steamy.
Earlier this week, after enjoying a nice sail, I decided to anchor for a bit in the falling breeze, to eat lunch and eventually do some paddling along the coast. The first thing I did was rig an awning, which was a life saver.
I made it up 10 months ago out of a blue nylon tarp I had. Itis attached to the mast and topping lift, with straps around the shrouds and posts fitted to the stern pulpit. I didn't set the back corners correctly for this image (I forgot where they went), but you get the idea. The white paint is nothing more than a single coat of Behr from Home Depot, casually slapped on; I learned from another boat that white really drops the temperature.
Which brings us to sails. Every self-respecting furling genoa has a sacrificial UV strip, usually Pacific Blue Sunbrella (which the sailmakers call "everybody blue"). It lasts until the stitching fails, generally about 5-8 years. You can either restitch it for another 5 years, or have it replaced for $400-$800. It's heavy but durable. Some folks use sail cloth or self-adhesive Insignia Cloth from Bainbridge; a waste if you ask me, since they only last 3-4 years.
You won't see me sewing a UV strip on it. Stitching a Mylar sail is like adding a tear-here perforation.
This jib suffered a 5-foot tear right along the stitch line. The cover was post-factory and the sailmaker that added the cover was an idiot (you need to insert a special scrim or layer of polyester before stitching Mylar).
We also know that paint can stick to sails. This is for advertising, not UV (mostly--it must help), but it does last a year.
Can paint provide a serviceable, light, and economical alternative to Sunbrella UV covers? Maybe it won't last as long, but on an older sail, does that really matter? Perhaps the $600 you save is more wisely earmarked for a new sail in 4-5 years.
I'm lining up some test paints. I think you will see a paint UV cover on my reacher in a few months. We don't leave it up much, so I'm sure it will be enough. I doubt the UV cover will ever fail on our Mylar genoa--the sail will explode first. Would I use paint in place of Sunbella on a new polyester genoa? Probably not, but perhaps for an old dog. On a Mylar jib? Yes, I'm thinking it might be the better value, if I can find the right paint. I already know that stitching a cover onto Mylar is questionable at best.