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Know Your Boat: Anti-fouling - What's the difference between self-polishing & hard paint?

Why does my boat need anti-fouling?

Anything that is left in the water will start to have growth of slimy algae and then attract other things like barnacles, seaweed, etc. This is called biofouling. How fast this biofouling grows depends on several things such as how often you use your boat and what the hull is composed of. The Caribbean and other tropical areas are known to be “high fouling” areas because we have a lot of nutrients and light filtering into the water here.

Once things start to grow on your hull, this can cause problems for the safe and efficient operation of your boat for the following reasons:

  • A rough surface creates drag, making your boat slower, less maneuverable and less fuel efficient.

  • If biofouling grows in hull openings or moving parts, blockages can cause engine problems such as overheating.

  • Biofouling can cause your anodes not to function.

What is anti-fouling?

Anti-fouling paint is a chemical treatment that is specifically designed to prevent biofouling. Most types of anti-fouling contain a biocide. A biocide is a substance that prevents growth by destroying or deterring organisms on a surface. It is applied to the hull of a boat to make it a difficult place for things to grow.

How often does my boat need fresh anti-fouling?

Anti-fouling should be on any boat that is in the water for any length of time. Depending on how often you use your boat and how you take care of it, the general recommendation is every 6 to 15 months. If you leave your boat for too long without anti-fouling and allow growth to accumulate, you are risking potential engine problems, higher fuel expenses, gel coat damage (osmosis), and much more work to prepare your hull for its next anti-fouling application.

What are the two main types of anti-fouling?

Ablative (aka sloughing, eroding, polishing, self-polishing)

How does it work? This type of anti-fouling paint works to keep your boat hull clean because it ablates (wears off) slowly so that growth does not accumulate and so that a new layer of biocide is exposed.

Self-polishing co-polymer anti-foulings are a newer type of ablative paint. They have a more complex chemistry and offer controlled release of biocide and erosion level. They are called self-polishing because they become smoother over time.

Recommendations: Bonaire Marine Center recommends using high quality anti-fouling paint such as Seajet Platinum Advanced Self Polishing Copolymer (SPC) to be applied in two coats with an extra coat on the waterline and leading edges. Prior to painting, the hull may need to be prepared with cleaning, power cleaning (if you’ve left it too long), degreasing, sanding or application of a primer but this will depend upon the condition and composition of your boat. The expert technicians of BMC can make that determination for you, just ask us for a quotation.

This type of anti-fouling paint is the best option for trailerable boats.

Re-application interval will depend upon usage and care, but normally lasts a full season or as per manufacturers guidelines.


How does it work?

Hard anti-fouling works by releasing biocide from the surface of the coating to prevent growth.


This type of anti-fouling paint is recommended for high-speed boats. It needs to be cleaned periodically. It is not recommended for boats that will be trailered or stored out of the water for any length of time because after 72 hours of exposure to air, hard anti-fouling paints will oxidize and lose their anti-fouling properties, which will require re-applying the paint.

Re-application interval will depend upon usage and care, but normally lasts a full season or as per manufacturers guidelines.

Environmental Concerns : Copper based antifouling paints are banned or restricted in some parts of the world due to environmental concerns. However, a ban was removed in the Netherlands after the European Union's Scientific Committee on Health and Environmental Risks concluded that the ban did not “provide sufficient sound scientific evidence to show that the use of copper-based antifouling paints in leisure boats presents significant environmental risk."

Other types of biocidal antifouling paint that were previously popular such as Tin (aka Tributyltin, TBT) are extremely bad for the environment and are banned by many international agencies.

Recommendation: To reduce the environmental impact of anti-fouling paint, it is recommended that boats be hauled out and cleaned in a location where the paint will not re-enter the water.

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