Q&A: Which Antifouling Paint Should I Use On An Aluminum Boat?

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.

Update, 2007

We decided to stick with ePaint, but with some adaptations.

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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.

25 comments… add one
  • John Sep 24, 2006, 11:09 am

    Steve Dashew reports that they’ve had really good luck with an industrial system supplied by Ameron, both primers and copper bottom paint. It is possible that you have to start with bare metal, but Steve reports that the bottom paint is better than anything they’ve ever used. Apparently this system has been used on aluminum crew boats for years without problems.

  • John Oct 24, 2006, 11:10 am

    In the end, after a long and informative telephone conversation with the people at ePaint, we applied ePaint ZO. It turns out that the SN-1 product, that we had poor results with, is too hard for a sailboat and is really designed for fast moving motor boat hulls. The ZO product ablates better at sailboat speeds. This difference between the products is not made clear on the ePaint web site, which seems to imply that the SN-1 is a more powerful industrial strength product, when compared to the ZO.

  • John May 24, 2009, 11:11 am

    See this post for tips on using ePaint.

  • Neil McCubbin Sep 14, 2010, 5:35 pm

    We were fairly happy with ePaint, but our needs are not demanding. We sail about 6 months, moving a lot, then put Milvina up on the hard for about 6 months.
    For our first year in Europe, we had ePaint on board, and it worked very well.
    This summer, we applied Hempel Alusafe, which has no copper. We can see some grass on the rudder after 6 months in Scotland, but will be hauling in a few weeks so can live with it.
    Many aluminium boats here use Trilux, but I run scared of ANY copper on the hull.

    • John Sep 14, 2010, 6:00 pm

      I’m with you, Neil, no copper on “Morgan’s Cloud”.

      Who knows, some copper based paints might be OK on aluminum boats, but I don’t want to be the one to find out that they are not!

  • steve Aug 17, 2011, 2:17 am

    I was not aware that Trilux 33 has any copper in it (worry!). I have used it for the last 2 seasons after having poor results with Trilux. I do have to scrub slime and barnacles every 3 or 4 months, more often if the boat isn’t being used. I would wish for TBT to come back as I believe the French have done a more recent study on its affect on sea life and found that the previous study had overstated the harmful effects, and were supposedly reconsidering the ban. Won’t help down here in NZ though.

  • carsten Jun 4, 2012, 11:38 am

    Hi, i have a 44 feet alu boat also and just bought . it is 20 years old and allways used copped based antifouling w/o any problem. so i stick to it. it has a epoxy coat plus vinyl and i use now ecoship / relies Basf a commercial grade AF. Let see … Last year i tried Seajet but poor result against barnacles.

  • Pat Carriere Jul 14, 2012, 11:02 am

    I’m using Trilux II since many years without problems on my Aluminium boat (AG4) builded in 1974. Each years I inspect the hull and until now, no sign of electolysis. (I have initially applied 3 layers of InterProtect 2000e on the hull)

  • Mark Anderson Jan 19, 2014, 10:48 pm

    I have x 2 aluminium pontoon boats that I use for hire/drive – have been using Lanolin for some years to help protect hulls – looking seriously at anti-fouling both boats for longer protection in salt water – I am a bit “gun shy” about reports I have read on antifouling – does anyone have any experience using a suitable anti foul.

  • Mike Shaw Mar 26, 2014, 4:30 pm

    Mark, I also have a pontoon boat which I just purchased new, I am confused as to which product to use. I will be keeping the boat in salt water in Delaware, any advice would be appreciated.

  • Joey Aug 30, 2014, 11:40 am

    Pettit Marine paint offers two copper-free antifouling options: Hydrocoat Eco (water based) and Ultima Eco. Both are copper free and feature a dual biocide for multi-season performance. Here are the links:

    Worth looking at!

    • John Aug 31, 2014, 9:26 am

      Hi Joey,

      Thanks for the tip. A friend of ours is trying out the water based Pettit option. If it works out well for him, we will try a test patch on “Morgan’s Cloud” next time we haul.

  • Mark Anderson Aug 31, 2014, 1:40 am

    Thanks Joey – I will try to contact this firm –

  • Joey Aug 31, 2014, 11:02 am

    No problem. We just put it on our Catalina 445 this spring. We’re in fresh water (Great Lakes). However, we tooled around the Trent Severn Waterway and the Hudson River this summer (still fresh water), and there was no growth (slime or other organisms). Very happy so far. Application was a breeze too. It goes on very smooth and evenly and no harsh odors to contend with. Roughly 1.25 gallons per coat on a 45ft boat with 5ft of draft and a 13.5ft beam.

    If you would like to connect with someone within Pettit, I can direct you to two individuals who I worked very closely with when we were looking at new options earlier this year.

    • John Sep 1, 2014, 8:04 am

      Hi Joey,

      Thanks for the real world information.

      The key will be how the Petit products do in salt water at periods over a year. We are currently getting 18 months from e-Paint ZO so that’t the target to beat.

  • steve Sep 1, 2014, 1:26 pm

    Hi John,
    We will be doing the bottom on our Boreal for the first time this winter. The boat is in Panama so we can use tin based bottom paint. I believe Boreal only put one coat of epoxy on before using the bottom paint they put on the boat. The epoxy paint has come off in many places do you recommend two coats of epoxy before applying bottom paint. Are there any draw backs to using a paint called Seahawk tin based bottom paint on our aluminum hull?

    • John Sep 2, 2014, 8:53 am

      Hi Steve,

      If the epoxy is coming off that would indicate to me a bonding problem. The bottom line is that epoxy does not stick well to aluminium unless the surface is very carefully acid washed and primed first, so adding coats won’t help. The only way I have got paint to reliably stick to aluminium is:

      • Burnish surface and clean.
      • Acid wash.
      • Spray apply a good two part zinc cromate acid wash primer (the yellow stuff).
      • Spray apply a good epoxy barrier coat primer.
      • Paint with antifouling.
      • It is absolutely critical that the instructions for timing and film thickness requirements are followed to the letter. For example, if you wait too long after acid washing to spray the primer, all is lost.

        Sorry, I know this is not good news. You can probably get by for a while with doing the above to the bare bits, but in the end the only answer to getting a good bond and solving the problem for good is to go down to bare metal and do the above.

        You can also get by with brushing, but the spraying is the right way because you get a better film thickness that way.

        This is the way MC is done and we have not had any paint adhesion problems in 25 years.

  • Neil McCubbin Sep 1, 2014, 2:32 pm

    I have not used Seahawk, but in 2004 had to write a strong complaint letter for owners of two 60 foot french aluminium boats who had used it and were VERY dissatisfied, but did not speak english well enoiugh to write.
    We put 2 coats of hi-build epoxy on our Garcia Passoa 47 in 2003, after sandblasting, Alumaprep 33 and Alodine. It is still in excellent shape.
    We also painted a blue stripe near the gunwhale after sandblasting but no alumprep or Alodine. It has required repainting twice since 2003

  • steve Sep 1, 2014, 7:27 pm

    Thank you Neil for your reply. Do you know the problem those two complaints were about? Was the paint not effective keeping growth off the hull or did the paint not hold up on the bottom? Also did they use the tin booster additive? In Panama we have little choice of paint but Seahawk is available and I do not have to ship it there. And thank you for the tip on Alumaprep 33 and Alodine I will look into it.

  • steve Sep 2, 2014, 10:51 pm

    Thank you John for your expertise on proper bottom application. Being new to aluminum boats your website is very helpful . I think we will wait for the complete bottom job until we get somewhere where we will have the time and the ability to do it right.
    Thanks again

    Steve and Tracy

  • Neil McCubbin Sep 3, 2014, 5:59 am

    Problem with the Seahawk was poor growth protection, and failure of company to respond to questions.
    That was 10 years ago

  • George Woodward Mar 14, 2015, 3:55 pm

    Has anyone experience of using a cold galvanizing base coat on aluminium?
    I had great success with this on a steel boat (http://www.zinga-uk.com) -tensile pull-off values of around 600 – 700 psi,) and I am considering using this on an aluminium hull before anti fouling. Some French yards do this-Meta who built for Moitessier. He did not anti foul but relied on a scrub when hauled out and free diving between to remove barnacles!
    Effectively a large anode.

    • John Mar 15, 2015, 8:19 am

      Hi George,

      Hum, I simply don’t know. However, although Moitessier may have survived without anti-foul, I think it would be a tough life with a lot of diving and scrubbing. So given that you will have to paint and that will require undercoating anyway, it would seem to me that a further coating would be superfluous expense.

      Further, given that aluminium does not suffer from the corrosion problems of steal, I simply wouldn’t bother to pioneer something new unless you can find really compelling real world experience that shows that said coating works on aluminium.

  • Slawomir Jan 14, 2018, 8:32 am

    Dear John,
    Within a few days (I’m in a hurry), I should make an important decision related to how should I prepare the bottom of the hull of my GRP boat for the next seasons.
    The boat’s history is following:
    One and half year ago I have bought the Beneteau Oceanis 40, the construction year 2007. Upon buying the hull was thoroughly checked for osmosis and it was OK. I’ve decided for the anti osmosis check because around 5 years earlier the boat had a major hull repair as a result of hitting an object. After buying the boat, their hull was painted with any International ablative antifouling paint. You can see the hull before painting in 2016 at the enclosed pictures (their names start with 2016 – first 4 ones) https://www.dropbox.com/sh/48you4r1wwveilt/AAB7yr_PSzyLnc5hJ9CVj2Lka?dl=0.
    During last 18 months, most of the time the boat was moored close to Athens at the Aegean Sea. Recently the boat was hauled out and after pressure washing, I’ve found many patches have appeared as a result of peeling off the paint. You can see the recent pictures of the hull enclosed (their names start with 2017 – last 6 ones).
    For the next few years, I plan to keep the boat as long as possible on water mostly on a permanent mooring with no more than 150 hours of sailing during the year.

    What results should I expect after I choose any of the following options:
    • Priming and painting with another layer of ablative paint?
    • Remove all the layers and prepare the hull from scratch?
    • Does it make any sense if I arrange painting for two seasons International Micron 350 antifouling paint without removing all old layers?
    • Could Coppercoat be a solution for long-term cost effective solution for the yacht which will be most of the time on a mooring?

    • John Jan 14, 2018, 12:42 pm

      Hi Slawomir,

      I’m not an expert on paint systems by any stretch of the imagination. That said, it looks to me from the photos like there is no primer on the hull and the paint was applied directly to the gelcoat, probably without good preparation. If that’s so, and given that you want to leave the boat in the water for long periods, I think it would be best to remove all the remaining paint and apply a barrier coat primer before repainting. Most bottom paint manufacturers have a complete system of primer(s) and antifouling coatings that are designed to work together.

      As always the key to the success of this project will be following the paint manufacturer’s instructions to the letter.

      As to Coppercoat, I have no experience with it but I have heard that it requires regular scrubbing to remain clean, so unless you are willing to get in the water and do that, or pay a diver, I would not go that route.

      As to picking the best paint system, Practical Sailor is by far the best resource for that, with many tests documented in their archives, which you can access as soon as you join. I think think they may even have done a test on Coppercoat. https://www.practical-sailor.com/landing/subscribe100416.html

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