Choosing Bottom Paint

By Carolyn Shearlock © 2015 • all rights reserved

What's the best bottom paint? How do you decide? What factors are important?“What bottom paint should I use?”

“What’s the best bottom paint?”

When I posted about painting the bottom of our boat, I got several questions along these lines.

It’s a big decision – at about $200 a gallon (plus the cost of a haul out and possibly labor to do the prep and painting), making a bad choice is an expensive mistake. And there are lots of paints to choose from.

Unfortunately, there’s no one best paint. The reason that there are so many is because each is good in particular conditions.

What I can tell you is how we chose ours and the questions we asked.

1. Aluminum hull or outdrive? If you’re painting aluminum, you can’t use a paint that contains copper because of the galvanic reaction that it sets up. You must use a paint formulated for aluminum.

2. Salt water vs. fresh water vs. both. Some paints are good only for one or the other and some can go back and forth. We were going to be on the Okeechobee Waterway (fresh water) when we first launched, then hit salt water 40 miles away. “Loopers” going around the eastern half of the US on rivers (fresh) and the Intracoastal Waterway (salt) face the same concern.

Interlux Micron 66 is a popular choice in the Florida Keys, but is for use in salt water only. I’ve been told that it totally loses its effectiveness when put into fresh water, even just for the one day that it would take us to get down the Okeechobee Waterway to salt water. So we quickly ruled it out!

IMPORTANT: Carefully read product information on points such as this. While the Interlux site specifically states that Micron 66 is for salt water only, West Marine’s product information could easily mislead you – in the quick reference bullet points, it says for use in “all fouling waters” although the full text does say not to use in fresh water.

3. Will it be out of the water part of the year? Do you want to re-launch without having to repaint? If you’re a part-year cruiser or keep your boat on a hoist or trailer, this is an important question. In general, ablative paints will retain their effectiveness when out of the water but hard ones won’t. Read the specs on specific paints if this is an issue for you.

4. What was the last paint used? Assuming you’re not going to remove all the previous paint, check the paint compatibility charts to see what paints can go over what. The question is really what will adhere to the old paint. In general, you can’t use hard paints over ablative, and any paint with Teflon is hard to paint over. We go by the general rules to narrow down the paint choices to a few, then check each one’s compatibility chart to make sure it’s okay with the previous paint.

If you’ve got a new-to-you boat, knowing what’s already on the boat can be tough. Sometimes you’re lucky and the previous owner tells you or you can call him/her and ask. Sometimes you can find an old paint can in a locker. Sometimes, like us, you have no clue (the previous owner only owned the boat six months and didn’t know what the owner previous to him had used). In that case, I suggest you contact one or more paint company’s advice lines (we did and their recommendation was to use a “tie” coat between the old and the new but check with them regarding your specifics; don’t simply do what we did).

5. Is slime a problem? Slime can prevent the copper and other biocides in the paint from doing their work, so if you’re in an area with slime (a sort of mossy growth), it’s helpful to use a paint that is also effective against slime, usually designated with “SR” for “slime reducing.”

6. Long term, what will it take to recoat? Hard paints build up over time. At first, you can get by with just sanding and repainting, but eventually it’ll be so thick that the paint will start flaking off and have to be removed, either through sand/soda blasting, scraping or sanding. It’s expensive to have someone else do it, and back-breaking to do yourself (we did it . . . once). Ablative paints wear away and can generally be painted over with just a light sanding.

7. Does the boat sit or is it used frequently? Ablative paints rely on the boat moving through the water to wear away the outer layer of paint and expose new. Strong current will do the same thing. If there’s no water moving against the hull, the ablative paint won’t be “rejuvenated” and its performance will be sub-optimal. That is, the bottom is going to have to be cleaned frequently.

8. Will the bottom have to be cleaned? If the boat is not moving or simply is in a high-growth area (such as when we were in the Sea of Cortez with very warm water and nutrient-rich water from fertilizer runoff and inadequate waste treatment), good bottom paint will simply lengthen the time between bottom cleanings, but won’t eliminate the need. If the bottom is going to be cleaned frequently, hard paint will last much longer than ablative unless the diver is very careful to clean the ablative paint gently so as not to remove much. If you hire a professional diver, they may not be as careful as you wish and/or may charge a substantial premium for the extra work and time involved.

9. DIY or professional application? Some paints require professional application while others can be applied by amateurs with no special equipment. In general, water-based paints are much easier for DIY-ers – no nasty fumes and easier clean up.

10. Cost. It’s easy to be swayed by cost per gallon for the paint, but you need to factor in how long the paint will last, how often you’ll have have it cleaned (or clean it yourself), the cost of supplies and so on. Often the paint that costs the most per gallon isn’t the most expensive in the long run.

11. What’s available? Every area of the world has different paints available. In Mexico, we had our choice of four or five different paints; in the US it’s over 20 – but not some of those we could get in Mexico. Friends in the South Pacific have reported that in some places there’s only one or two paints to choose between.

12. Recommendations from others in your area. No one paint in good everywhere. Paints that work well in New England aren’t necessarily good in the Chesapeake, and those that worked well for us in Mexico get less-than-stellar reviews in Florida, even though both are warm tropical waters. See what other people are using and liking in your area, but keep the points above in mind – your boat and usage may be very different from theirs.

13. Color? We consider this almost a non-issue. I know, some people are set on having a particular color and will only consider paints that offer that color. For Dave and I, effectiveness trumps color every time. We want paint that works.

We choose the paint first, then pick the color from those available. In Mexico, we couldn’t always get the color paint we’d like, even if was made in the paint we chose . . . we learned not to be picky. Once we had to use three different colors – we just made sure that we had the same color at the waterline all the way around. It was more important to have the best paint for our style of cruising than to have any particular color.

With ablative paint, it’s good to use a different color under the desired top coat so that you can tell when the top layer(s) has worn away.

So what paint are we using? We chose Pettit Hydrocoat SR. It’s a multi-season paint that will survive spending the summer on the hard. It’s water based and was very easy to apply and clean up ourselves. Hydrocoat is ablative, so we’ll never have to scrape all the years of paint off the boat again. And it gets good marks for effectiveness in the Florida Keys . . . and won’t be hurt by being in fresh water when we’re on the Okeechobee.

We’ve only been in the water a little over a month so far, so it’s way too soon to say how well it’s working. But I hope to have a great report in a year!

UPDATE 4/27/16 (second year of use, 6 months since repainting with 2+ coats): Our experience with the Hydrocoat SR hasn’t been horrible, but it hasn’t been stellar, either. We’ve had to clean it every month, starting just a month after we went in the water. Admittedly, we are in a very high growth area with warm water and lots of fertilizer runoff. Since we were hauled out for the summer, we put two more coats on before we relaunched last fall. We were surprised at how much had worn away in just 6 months of use — it’s one of the softest ablatives we’ve seen. We aren’t horribly unhappy with it, but think that there probably is a better choice, particularly if we’re (a) not going to be back in fresh water at all and (b) are using the boat year-around.

FURTHER UPDATE 8/15/16: After 9-1/2 months on this second painting with Hydrocoat SR, I am not happy with its performance. Nine and a half month old paint (2+ coats) and less than three weeks since I last cleaned the bottom. Very little hard growth but thick soft growth that is very hard to get off.

Inside of starboard hull

Inside of starboard hull



Inside of port hull

Inside of port hull

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  1. Found out by chance that our favorite bottom paint for a dinghy is Rustoleum Bottom Paint. A Qrt came on our big boat when we bought it. We applied to a couple of our first dinghies and loved it. Then we tried a few other brands over the years and nothing stood up as well as the cheapo Rustoleum.

  2. Good information, won’t be too much L&A Niger before we will be doing our bottom paint

  3. Bill Dixon says:

    we have always used Trinidad hard paint, but we used to leave the boat in year round. This year went with an ablative ACT sr. Working well so far, real test will be next fall when we launch after summer on the hard.

  4. Here in the Philippines the selection of anti-foul paints is very limited – but large hardware stores sell a bag of copper powder to mix into a gallon of paint when applying. Each bag costs P1000 or about $20 – not sure if it works but seems like a cheap addition if it is effective. Anyone ever done this?

  5. Well written article! We chose Coppercoat for our boat. Primarily because we plan on keeping the boat until our soon-to-be 6-yr old goes to college, so we won’t have to do another bottom job until well after that:

  6. Charlotte caldwell says:

    Can you give your opinion on single season versus multi season paint?

    • It really depends on your haul out frequency and where you are. We’ve always cruised in very high-growth areas and have needed new paint every year — those labeled as multi-season just didn’t have enough left after the first year. But if you’re not planning to haul for more than a year and are in lower growth areas so that is realistic, I’d certainly try a multiseason.

  7. What are your thoughts on coppercoat?

  8. I’m very happy with coppercoat. 5 years. Inspected 2 days ago.

  9. Ouch – what about Interlux Micron CSC ?

  10. Used Pettit Trinidad two years ago this October. Bottom still great. Used in the past a number of times on other boats and always pleased.

  11. Where is that

  12. Dave McCottery thought the timing of this post was relevant.

  13. Thanks for that share!

  14. Is the vessel moving at least once a week?

  15. How much work is that stuff to remove? Will it come off with a scrubber while you are snorkeling or using a snooba? Or is it too thick and stuck on?

  16. Ugh, forgot my swim ladder was Down. Pulled it up after ten days, omg took me 2 hours. Bottom now?!

  17. Seahawk paints

    • Have you used them in the Keys and Bahamas?

    • The Boat Galley – No, we are in the northern tropics of Australia on the Great Barrier Reef where the marine growth is extremely aggressive with water temps around high 20’s to 30deg most of the year. So far Sea hawk antifoul has been outstanding against others I have used on the market.

  18. Thanks for sharing the truth

  19. Interesting, we used hydrocoat eco in April, as of today absolutely no growth on the coated surface, but on boot strap.

  20. Go Kiwi go Altex.

  21. We found that the location of the boat makes a huge difference. We spent a lot of time in St. Martin last year, and are having a different kind of paint applied this year. We got tons of barnacles.

  22. SeaHawk BioCop TF… Simply amazing stuff.

  23. Hemples never let me down

  24. Our friends had the same problem. Debra Bryan? Here are their pics:

  25. Cruising BVI and St. Martin. Used Seahawk Islands 44 and it was as clean as it was going in after seven months. Spent a grand total of 20 min doing the waterline one day. Expensive — $325 a gallon.

  26. PPG Ameron ABC3 works as well as any for $130/gal!

  27. Oh poo!!

  28. Oh my! So sorry to see this. Thank you for sharing.

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