Q&A: Should I Apply Antifouling Paint To An Aluminum Boat?

Question: I’m thinking of leaving the bottom of my aluminum boat unpainted since I’m afraid of electrolysis caused, or at least made worse, by antifouling paint, particularly if the bottom is scratched. The boat is in fresh water, so she will not foul much.

Answer: There is no reason why properly applied antifouling paint that is intended for aluminum boats should cause or aggravate electrolysis. The key to preventing electrolysis is an isolated ground electrical system, good zinc anodes (or magnesium in fresh water) and an isolation transformer to prevent damage from other boats that are improperly wired when plugged into shore power.

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Meet the Author


John was born and brought up in Bermuda and started sailing as a child, racing locally and offshore before turning to cruising. He has sailed over 100,000 miles, most of it on his McCurdy & Rhodes 56, Morgan's Cloud, including eight ocean races to Bermuda, culminating in winning his class twice in the Newport Bermuda Race. He has skippered a series of voyages in the North Atlantic, the majority of which have been to the high latitudes. John has been helping others go voyaging by sharing his experience for twenty years, first in yachting magazines and, for the last 12 years, as co-editor/publisher of AAC.

8 comments… add one
  • rene blei Jan 11, 2016, 1:44 am

    My alloy boat has presently an anti-fouling paint applied.
    Its slip is on fresh water, Lake Union, Seattle and frequently go out on salt water. Am told whatever grows on in fresh water comes off in salt and visa versa. So what is the point of painting an alloy hull as it doesn´t corrode to begin with. Maybe a stupid question.

    • John Jan 11, 2016, 1:40 pm

      Hi Rene,

      Interesting thought but I’m not sure that the effects of fresh and salts on the respective organism are that drastic. I f it were me, I would paint the bottom and then enjoy the longer period between hauls.

  • Rene Jan 11, 2016, 2:27 pm

    Thanks John,
    My experience with fresh and salt water combination hasn´t been long enough and my question is more or less based on what I was told by locals. When on saltwater, we are on the move, and little time for barnacles to attach??

    • John Jan 12, 2016, 9:13 am

      Hi Rene,

      No, even if you are constantly moving in salt water, marine growth will still attach to surfaces that are not anti-fouled. We grew a good crop of barnacles on out transom overhang during a 17 day trans-Atlantic.

  • Rene Mar 10, 2016, 12:28 am

    Have a follow up question, regarding ultrasonic growth preventer kit I noticed at the latest boatshow. The manufacturer claimed a pay-back within one year in Florida waters.
    If it really works, then sailboat owners should have a lot of feedback…………..I hope.
    Many thanks.

    • John Mar 10, 2016, 8:37 am

      Hi Rene,

      Charlie Doane, over at WaveTrain tried one some years ago on his aluminium boat with mixed results.

      • Joshua Thompson Jun 26, 2019, 3:50 pm

        Check out these two posts on a homemade ultrasonic antifouling device on an aluminum sailboat:



        • John Jun 27, 2019, 8:03 am

          Hi Joshua,

          I have been reading about these things for about 20 years. Lot’s of variable results and opinions. Those two articles are definitely the best on the subject. For me the take away is that it’s worth considering for those that cruise in warm water all year where diving to scrub is practical since it keeps the shell away, but probably not worth the agro for people like us that haul every year anyway.

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