Zinc Coat Barnacle Barrier
"Zinc Coat Barnacle Barrier 1792 provides easy to use aerosol spray protection for bare metals including steel, stainless steel, cast iron, copper, bronze, galvanized steel, and lead. It forms an excellent bond to underwater metals and running gear, and inhibits corrosion on these surfaces. Zinc Coat Barnacle Barrier’s smooth, hard surface will self-clean in service, and can be used above or below the waterline. The dried film of Zinc Coat contains 93% pure zinc."
I have been using the above on my prop (SS), shaft (SS), and strut (bronze) for several years now with very good results except one season when the water temp were well above the average plus we didnt use the boat much during the month of August. The above is self cleaning when the boat is in service, I doubt anything will work well if you dont use the boat often, often meaning at least once a week.
I have used vaseline on my spped paddle wheel with great result, using a Q tip to apply. Some have mentioned using a sharpie also works well? Dunno