I have an alum. row boat, kept in salt water most of the year. I have used (needed to ) non copper bottom paint on it for about 4 years, I have not needed to re paint the bottom in 4 yrs !! just hose it off when I pull it out for winter' it seems great , no slim ,no barnacles. the boat is only rowed, not towed. I keep my Mainship in the same marina, I have used interlux copper for years, seems to work OK .I don't use my boat much ,so it doesn't wear off much. Last year I used a water base copper bottom paint, I still had some barnacles & slim. I use zinc spray on my running gear , jury still out on that one. The row boat still has almost no growth after 4years !! My question is has anyone used non copper paint ? solvent or water base & can it be put right over old copper paint ?. And how well does it work on a power boat ?