Question: I bought an aluminum 40ft Roberts from the original owner and am in the process of many changes. One area which seems very gray these days is what bottom paint to use. An epoxy barrier coat is there but I do not want any copper impregnated paint anywhere near my boat. Could you please let me know what you’ve found that works.
Answer: Antifouling paint for aluminum boats has been a problem ever since tin based paints were banned. For some ten years we have used the ZO and SN-1 products from ePaint. However, performance has been inconsistent; some years it has worked well lasting up to a year with almost no slime and some years it has grown slime in just a few months. On two occasions it failed completely after just four months, and this in cold water with the boat constantly on the move. The first time this happened epaint replaced the paint but did not cover the cost of recoating. The second time was last year and we did not approach them about it.
As it happens, as I write this we are removing all the paint off the bottom of the boat down to the barrier coat and so are faced with the same difficult decision you are.
The only other option I know of is Trilux® 33 from Interlux. This is a copper based paint but it is copper thiocyanate, which Interlux say is safe for properly barrier coated aluminum boats. We tried the original Trilux product before switching to ePaint and found it pretty poor. Interlux say that they have substantially improved Trilux from the original product that we tried.
The plot gets even more ambiguous: Interlux sells Trilux® 33 in the USA but not in Canada and Trilux II in Canada but not in the USA. Practical Sailor’s tests would seem to indicate that the Canadian product is better than the US product, but when I asked the Interlux technical department, they said the opposite. (I’m a bit skeptical about the Practical Sailor tests since their test rig does not move, which I think may change everything.) At least you can overcoat Trilux® 33 with Trilux II, according to Interlux technical support.
We decided to stick with ePaint, but with some adaptations.