I maintain a couple of white boats. Once I cut n polish or wash them it seems the sparrows enjoy sitting and ****ting from the lower wire lifelines. The stains they leave will not remove even with more cut n polish. I have tried just about everything.
The only way to remove it is just leaving it and with in a few weeks the sun removes the stains like magic.
cleaning sails has always been a problem. I have always thought about a mobile sail cleaning service but have always thought that might be to much work.