What to Look for In Boat Bottom Paint

Tips for buying the right anti-fouling paint for your boat.

So you’re looking to protect your boat’s bottom from biological growth, known as fouling. (We’d have to assume so, otherwise why are you reading an article about paint?) Basically, in selecting bottom paint for your boat, you have to ask yourself the following questions, at a minimum. In what part of the country are you doing your boating? Do you haul your boat for the winter or leave it in year-round? Does your boat already have an old coat of bottom paint or are you starting from scratch? Depending on how you answer each of these questions, there’s an anti-fouling bottom paint that’s right for you.

The How

Bottom paint works by releasing a small amount of biocide over time that keeps any algae, plants or animals from adhering to the hull. Usually, but not always, this is accomplished with a metal-based biocide, most commonly copper, but where you live and how you boat will determine what you should use as much as anything. (Washington had passed a ban but has since lifted the restriction.) Beyond that, you will likely be choosing between a single or multi-season “ablative” paint or a hard modified-epoxy paint. With ablative paint, the entire application will wear down over time, while the hard paint will retain its thickness as it sheds biocide. Multi-season ablative paints will still work if you pull a boat for winter storage and relaunch it next season, while single-season ablatives need to be applied every year. Modified-epoxy paints lose their effectiveness when pulled from the water for any length of time.

The Where

Do you boat in salt water or fresh? Paints designed to prevent barnacles in salt water might not be effective in preventing freshwater algae or slime growth, or in deterring zebra mussels. If you boat in the Great Lakes or other freshwater areas where slime is a problem, consider a paint that contains an agent called Irgorol 1051, which works to block photosynthesis in algae and other plant-based hitchhikers. Check out Petit Trinidad SR Antifouling Paint with Irgirol or Interlux Mircon CF with Slime Blocking Technology (not Irgorol but a different agent).

If you boat in salt water, a paint like Interlux Micron 66, which uses a copper-based cuprous-oxide biocide as well as slime-controlling Biolux, is an excellent choice for deterring barnacle growth. Or choose one of Interlux’s Micron CF (Copper Free) paint to do the job.

The When

If you haul your boat in the offseason, you’re going to want to use an ablative paint that will retain its effectiveness if left out of the water for long stretches and relaunched, such as Pettit’s Odyssey HD. If you keep your boat in the water year-round, particularly if you live in areas with heavy fouling issues, look for a hard bottom paint with a higher biocide concentration, such as Petit Trinidad HD or Interlux Ultra with Biolux.

Repeat Performance

If your boat already has bottom paint, it’s best to go with the same type of paint when it’s time to reapply. Some soft ablatives will work over hard modified epoxies, but check with the paint company for compatibility. If worse comes to worse, you’ll have to sand off the entire old coat and start the process again. Fortunately, we have an article to help guide you through it. Go to boatingmag.com/recoat.

Copper Free

For people who want to use an alternative to heavy metals, consider a copper-free paint such as Pettit ECO HRT, which works on fiberglass and aluminum hulls, or Interlux Pacifica Plus, an ablative paint that uses the more environmentally friendly Econea to fight barnacles as well as Biolux to combat slime. Both Pettit and Interlux also offer of water-based products, as opposed to the solvent-based “norm” of anti-fouling coatings. Finally, copper-free paints can safely be applied to underwater metals.

Specialty Antifouling

Some paints, like Interlux VC Offshore, can enhance speed and efficiency. These provide a super smooth, or super slick finish and can often be polished, (“burnished.”) to a fine sheen for delivering utmost efficiency. And, while most antifoulants are dull, some can provide bright colors, like Interlux Vivid. Still other formulations are best for protecting underwater metals. These are usually copper-free to prevent creating a galvanic circuit with aluminum.