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Key Considerations When Choosing a Biofouling Boat Bottom Paint

Sep. 23 2021 Maintenance By Yankee Boating Center

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Boat bottom paint covers the area below a boat’s waterline. Paint in this area usually contains a preventive antifouling agent, a type of biocide or algaecide,  that works against the growth of barnacles, weeds and marine slime. Marine growth disturbs flow, reducing travel efficiency. It’s also a liability. Extensive buildup can hamper maneuverability, making the boat less safe in the water. The following guide contains key points to consider when you’re choosing a bottom paint. To learn more, contact the helpful staff at Yankee Boating Center, located in Lake George, New York, and serving Clayton, New York.

Antifouling Paint Types

You’ll have different paint options based on such considerations as environment, type of use, purpose and paint and boat-hull composition.

  • Hard Bottom – Hard bottom paints are good for only one season and will accumulate over time, eventually requiring expensive removal. Biocide in a hard boat bottom paint continually leeches, losing effectiveness. Exposure to air also neutralizes the antifouling effect, so a hard paint is best for boats that stay in the water. These paints are also best for racing boats as hard paints will burnish with increased speed.
  • Ablative – The opposite of hard paints, ablative boat bottom paint wears away gradually with flow, regularly exposing fresh biocide and making it best for frequently active boats. There are both single and multi-season formulas as well as water or solvent-based paints and copper–free and copper-based formulas.
  • Copolymer Self-Polishing Ablative – This all-season ablative antifouling paint not only refreshes biocide layers but also contains a copper copolymer formula with controlled-release action that self polishes in either active or anchored conditions.
  • Hybrid Copolymer Ablative – A hybrid boat bottom paint has all the above properties of a self-polishing copolymer. It will, however, also burnish for speed and smoothness.

Which Formula Is Best?

Different formulas work for different situations. The following addresses some key questions:

  • Copper-free or copper-based paint – While a higher copper content is more effective against shells, the environment might prohibit its use. There are copper-free, eco-friendly alternatives that work handily against mussels and barnacles.
  • Solvent or water-based – The high level of volatile organic compounds, or VOCs, in solvent-based boat bottom paints may not meet local environmental restrictions. Low-VOC water-based paints are an effective alternative that, once cured, will hold up in wet conditions.
  • The amount of paint to use depends on the coating thickness and the size of the boat. When to paint depends on a number of factors, including boating conditions and paint type.  While multi-season paints do exist, it’s best to check once per year to decide.

What to Know Before Painting

There are some essential questions to answer before making an informed decision about which paint to use:

  • Type of existing paint – Paint compatibility is important. New layers can peel if they aren't compatible with existing coats, so knowing the original paint formula is critical. In absence of knowing, it’s best to simply remove and restart. And while there are general compatibility guidelines for the industry, the best option is to refer to manufacturer recommendations.
  • Boat material – Boat bottom paint typically contains a copper biocide, which is fine for wooden or fiberglass hulls. Copper and aluminum hulls will, however, result in destructive galvanic corrosion. Aluminum hulls will require copper-free paints.
  • Salt or freshwater – While boats in both salt and freshwater environments deal with algae and slime, only boats in saltwater will hassle barnacles. Boats in freshwater can save costs by using freshwater-specific algaecides that cost less.
  • Location – The level of fouling depends greatly on the local water environment. More fouling tends to happen in still and warm waters while less occurs in colder waters with unrestricted flow.
  • Frequency of use – Ablative boat bottom paint works best for active boats. Self-polishing copolymers are best suited to boats frequently at anchor. A hard ablative is a good choice for boats that scuff easily. Multi-season paints work best for longer boating seasons while single-season paints are better for shorter seasons.
  • Racing boats – High-speed boats do best with hard modified epoxy formulas, thin-film boat bottom paint or a hybrid formula that will burnish.

There are multiple considerations that should be properly addressed to find out which paint is best for your boat and the type of boating you do. Whatever your situation, the knowledgeable team at Yankee Boating Center can answer your questions. Come visit us. We’re located in Lake George, New York, also serving the community of Clayton, New York.