Choosing an Antifoul


Many traditional antifouling paints use zinc or copper to prevent a build-up of marine organisms on the hulls of our boats. The metals from the antifoul paint can, however, make their way into the ecosystem through leaching and when applied to and removed from boats, where they are highly toxic to aquatic life. For more information on the problems caused by antifoul and how to use it in the safest way, see our Antifouling page.

Fortunately, there are a wide range of modern antifoul options which are less toxic to the environment than antifouling paints, and new options are being developed all the time.


Ablative / Self-polishing Biocidal Coatings

As mentioned above, most antifouls currently applied contain biocides. They are generally applied annually in the form of a soft coating that “ablates”, i.e. slowly falls off, in order to reveal further layers of the biocide. Thus much of the coating finds its way into the water during the year. If the remaining layer is then jet washed in preparation for over coating without using a bunded washdown facility, then the more of the paint will be lost into the water during maintenance.

One clear advantage of biocidal coatings to boaters is the relatively low annual cost, and the ability to take a DIY approach, although proper protective clothing including suitable masks should be worn and care taken not to allow the material to find its way into the water. If DIY antifouling then follow the environmental best practice in the Protect, Collect, Dispose Guide, which includes ensuring a ground sheet is used to capture any drips, spills and antifoul paint debris.

A person applying antifoul paint to the hull of a boat

Hard Coatings

Hard antifouls are used mostly for racing boats. They require more preparation for annual re-coating (i.e. sanding down as well as cleaning) and are designed to give a smooth finish. In other respects they are similar to ablative coatings in terms of their biocidal effects, and the measures that need to be taken to ensure that the material doesn’t enter the water.

Long-life Coatings

Coatings such as Coppercoat are still biocides, but they are not designed to ablate or to be annually over-coated. They are usually a suspension of copper in an epoxy resin, so can last upwards of 10 years. The slow release over that time hugely reduces pollution and the impact on marine organisms. It is recommended that the hull is lightly sanded annually to reveal a clean layer of the material, though speaking to boaters who have used Copper Coat, some do not do this and are still happy with the result. While the coating prevents significant growth, slime will build up and can be removed with a soft cloth while in the water [1], or by lifting and washing.

It is recommended that these coatings are applied professionally. The application conditions need to be right for the coating to last. While it is possible to seal any existing antifoul layers, it is recommended that the hull be grit blasted back to the original substrate and applied from there.

There is a high up-front cost, but over a 10 year period the costs are comparable to soft coatings.

[1] The RYA worked successfully with Defra and British Marine in 2019-20 to obtain a “derogation” from the outright ban on in-water cleaning of hulls that was in place until then. Boaters can use a soft cloth or 1200 grit wet & dry sandpaper to remove any slime while in the water. More vigorous cleaning methods are still banned, to prevent further pollution from antifoul paints and other contaminants.

Foul Release Coatings

These coatings, such as Silicone, are designed to be slippery rather than poisonous. Any growth falls off if the boat is moving at more than 7-8 knots, or can be wiped off with a soft cloth. The coating is soft, and care needs to be taken not to damage it. People who have used this material report good results, particularly on high speed craft. Particular care is needed when lifting or slipping the boat as the surface is vulnerable and, being slippery, it is difficult to get repairs to stick!

The coating is harmless to marine life, though if it is damaged it is possible that what is, in effect, a plastic, will remain in the environment for a considerable time.

As with Coppercoat, foul release coatings should be applied professionally.  While it is possible to seal any existing antifoul layers, it is recommended that the hull be grit blasted back to the original substrate and applied from there.

Again, up-front costs are higher than for ablative coatings, but the longevity of the coating mitigates the initial cost.


The use of ultrasound to deter growth has been well established in the large ship sector. Products are also available for small vessels. It is important to have a system professionally specified as, while the transmission of ultrasound waves through steel is well understood, successful use with softer materials such as wood and fibreglass requires careful design.

A key point is that, while it is low power, you will require a constant power supply for this to be effective, and manufacturers usually recommend its use in conjunction with a hard antifoul coating.

The jury is out as to whether the sound waves will cause any wider issues for marine organisms, although the low power of the system suggests it will not transmit far from the hull.

Biomimetic Approach

Biomimicry is growing in popularity in a number of fields. The main product in this category is Finsulate. It is designed to mimic the surface of sea urchin shells, which don’t suffer from algal growth. The material comes in the form of sheets that are glued to the hull, and the resulting surface is like a short-cropped nylon carpet. The manufacturer claims that the fibres will not fall off into the water, and we are following test installations in real-life conditions with interest.


Recently, we have seen an increase in the number of new products coming to the market. Some are from the existing main players, but others are looking to disrupt with new technologies and approaches. It is difficult for us to make recommendations without seeing independently verified tests of both toxicity and effectiveness, alongside some real world reports from early adopters.

Two recent / up-coming arrivals that are of note are:

  • Hull Defender. This uses a combination of a foul release approach with a hard base, to improve longevity. The manufacturer claims that the product is completely non-toxic and can be applied by anyone. Their objective is to “hide” the surface, so that marine organisms don’t see a surface to which they can attach but just “see” water.
  • A new product likely to appear later this year or in early 2023 is of particular interest. It is a combination of a ceramic with a pharmaceutical material and comes from the biomedical sector. The developers of the product come from the medical sector, and realised that coatings used in, for example, replacement heart valves, are designed not to allow anything to stick to them, so should have good antifouling properties. They are also, clearly, non-toxic, at least to humans, and the developers state that volumes required would be low (2 litres for a 40’ boat). Static plate tests are on-going.

Boaters need to balance the different factors for their particular application. We strongly recommend a move away from biocidal coatings as our waters are increasingly polluted. Low impact products are already available that represent good value over their lifetime but with high up-front costs. New products are appearing that will likely offer low toxicity combined with similar costs to ablative coatings and ease of application for annual use.




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