Biocidal antifouling paints are hazardous mixtures that function by preventing the build-up of marine organisms on the hulls of commercial
ships and pleasure craft of all sizes. Antifouling paints work largely by releasing biocides into the water, thus preventing organisms from attaching themselves to the bottom of boats.
Whilst antifouling does a great job of keeping our hulls clean, and even has some environmental benefits such as improving fuel efficiency and preventing the spread of invasive non-native species, it is toxic to aquatic life. Since the banning of TBT in 1987, most antifouls are now copper or zinc based. Some of the compounds found in these antifouls can accumulate in marine organisms, and can find their way into marine wildlife further up the food chain.
The majority of copper in antifouling enters the marine environment through leaching. However concentrated amounts do enter the marine environment during the removal of antifouling paint, which occurs mostly by water blasting or mechanical scraping, and can form concentrated deposits in the sediments around marinas and in river beds.
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.
Following the Protect, Collect, Dispose method you can ensure that any debris or paint drips are captured by laying down a ground sheet before work begins.
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.
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.
Coatings such as Copper Coat 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 water1, 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.
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 Copper Coat, 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.
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.