I use COASTAL COPPER 450 that I get from zincsforboats.com Every year I just lightly sand the bad spots, little primer and repaint just the bad spots. Been doing it for over 10 years now and it works great. The paint is only about 100 bucks a gallon which is a good deal for this type of paint. It is an ablative paint which means as it kills the algae it sacrifices a little of its self. They have an online store and sell on ebay also. A gallon lasts me about 3 years doing it this way. I have a 27 foot Bayliner.