Here is what you need. Buy a couple of these and just keep them on the boat and you will always have a dry towel.
http://www.swimoutlet.com/product_p/1851.htm You can get other brands and sizes but keeping some type of chamois towels on the boat is the ticket. Unless it is chilly, that is all we ever use and even when it gets a little cold, we will still dry off with the chamois to keep the big towels dry so we can use them to keep warm.