Choosing the Best Anti-Fouling Paint

The earliest anti-fouling systems consisted of two elements. The first was a metal scraper and the second was the lowest ranking sailor on the vessel. But seriously, the buildup of biological matter on the submerged hull is a huge problem for the material and for the efficiency of the vessel. The task of manually scraping bottoms was made much easier when sheet copper was fastened to the bottom of wooden hulled ships. Eventually the technology advanced to produce paint that held copper compounds and slowly released them into the environment. The next major breakthrough was tributyltin which worked very well but it was so toxic to the environment that it was banned three decades later. Improved copper based paints and non-copper alternatives are now available. In fact there are so many specialized paints it’s difficult to leave the copper behind to try something else. Why change? Well in some areas we are already seeing the signs that point to widespread bans. Northern Europe and the West Coast of the U.S. are phasing in bans in some areas and more will follow. Types of Anti-Fouling Paints Ablative Anti-Fouling Anti-fouling paints take different strategies to meet the goal of eliminating plant, animal, and algae growth on the wet parts of the hull. There are three common types of anti-foul available. The most common is ablative paint which wears away like a bar of soap. This soap analogy is very old but really works well for this type of paint. If you use your vessel regularly there should be no problem wearing away the growth. Seasonal boats that have long periods of disuse will not benefit as much of the cleaning takes place while underway. This paint works well since animals like the zebra mussel have difficulty finding a firm hold. They are generally pulled off as the vessel moves through the water. A moderate amount of maintenance is required for this coating since it must be applied to last until the next haul out. Large vessels that cannot be hauled should use a more durable paint. Copolymer Anti-Fouling Copolymers are much tougher than ablatives and don’t have some of the disadvantages of hard paints. They can be exposed to air during maintenance and not lose potency. There is also little chance of paint build up since copolymers are designed to ablate at a much slower rate than a true ablative paint. Unless you have a specific need for an ablative or hard paint this is often the best choice. It is also the safe option if a location has unknown conditions. Some people refer to these as slow polishing paints. Hard Anti-Fouling When a vessel gets to a certain size you no longer want the expense of dry dock or haul out. This is where hard coatings shine. The most common base for these paints is epoxy or some other tough polymer. It releases biocide constantly by allowing the poison to migrate to the surface of the paint and leaches fewer toxins away in the process. This is durable stuff and it does not come off in harsh conditions. In fact it must be removed mechanically by blasting or sanding. Because of the pollution potential of the runoff or dust from these processes produce toxic wastes that have significant costs of disposal. The cost of these paints is generally higher due to specialized application processes. For a smooth finish these paints should be sprayed while the others can be applied by roller and brush. Since this is a low maintenance solution most large commercial vessels use this type of paint. The Biocides Biocides are the toxic element in the paint which deters life from attaching to the hull. There are several types and sometimes combinations in the same product. Cuprous Oxide – This is the most common biocide by far. It is also the target of environmental regulators because it is building up in harbors. This is not necessarily because the bottom paint is leaching too much copper. The problem is thought to be caused by the power washing, scrubbing and sanding done on thousands of recreational vessels.Almost all of this runoff has a short trip from the bottom of the boat to the water it was almost never collected in the past. New regulations are now requiring marinas to collect this waste and dispose of it properly. This will increase the overall cost of maintenance and some services may no longer be available. Cuprous Thiocyanate – Similar in behavior to cuprous oxide but stronger biocides make it useful for high foul areas or low use vessels. Composite Copper – This is still copper but in a better package. The copper is encapsulated in another material that makes it less likely to leach beyond the needed rate. Silica is currently being used as a matrix but this is a rapidly advancing technology. Pyrithione Zinc – One of the best copper alternatives. Alternatives to copper are increasing as bans become inevitable. This biocide is not generally recommended for high fouling areas like the tropics. Non-Metalic Biocides – These are fairly new to the market and are composed of organic molecules most likely modeled from compounds found on a living creature. Anti-Foulings of the Future The future is super slippery and we have been promised something that is more of a thin film than paint. The first of these products have come to market and are best for low-fouling areas. They hold a lot of promise since they have no biocide and may last for the life of the vessel when fully developed. Imagine the days when a coating goes on at the shipyard and never needs replacement and at the same time improves efficiency. Until then somebody go get the scraper. Nanoparticles also hold some promise for the future of low friction coatings of all types.