I have a NE Dory lug rig with the default white (not red) sail. It has a lable with "Douglas Fowler sail maker" on it. I bought the kit about three years ago.
Packing up the boat this autumn I noticed a quantity of bird cr@p on it.
What material is used on these sails and what can I do about cleaning them up before packing them away for the winter?
Warm water and maybe a soft brush is a good place to start. Maybe add a little mild dish soap to the mix if some of the spots are stubborn. The cloth would be some sort of polyester (dacron) with a stiffish finish calendered in for stability and to seal the fibers. In my experience, anything short of mildew should come out with a bit of gentle scrubbing. Be careful around the threads; you don't want to damage those.
.....Michael
FWIW: I recently bought a Skerry that needs lots of TLC, and the sail, a Fowler, also was left outside under trees for a few months, by the kids of the person I purchased it from.
I cleaned a trash can, put the sail in and filled it with water. I added OXYclean powder to it. It took three days of soaking and stirring once in a while, but all the mildew and brown and dark spots came out. The sail is white, again and no damage to threads or otherwise. Good luck!
I second the Oxyclean. I soak my sails at the end of every season.