Antifoulant Paints – How They Work
Antifouling paint keeps marine growth such as barnacles, mussels and sometimes oysters, and plant
growth from attaching to your sailboat, trawler or motor yacht. Most antifouling paints use the dispersion of metals within the paint to halt these foul critters from bonding. Copper (cuprous oxide) and tributyl tin are 2 metals that have proven to be successful as biocides, but tin, banned worldwide on ship hulls in 2009, was so poisonous that it eradicated whole marine ecosystems.
Copper compounds are now universally acknowledged, but the price of the copper raw material has risen considerably. In addition, high copper concentrations have dissolved in the water in several places in the USA setting limitations on the practical application of copper-based paints.
Paint manufacturers continue to develop a number of new antifouling technologies that tackle these and other problems.
New Paint Products
Composite Copper: Substitutes the traditional cuprous oxide with silica, lowering the copper content by up to 40%. The consequence is a copper based biocide that gives superior protection for your boat, with a base that is made from elements found in the sea.
Water-Based ablatives: Water substitutes the solvents found in standard bottom paints. Low-odor formula allows painting inside. Practical application is trouble free and clean up involves only soap and water.
White copper: Clean and white in color, white copper (cuprous thiocyanate) necessitates 50% less content than the dark copper used in conventional antifouling paint.
Econea: Paint manufacturers believe that, a metal-free biocide developed by the pharmaceutical industry, is the future of antifouling paint. Advantages include protection at low usage levels, they degrade rapidly and are biodegradable. Unlike some metal-based antifouling agents, ECONEA can be used to easily develop lighter and brighter paints, resulting in bright colors with better uniformity. Because it is a metal-free compound, ECONEA will not cause galvanic corrosion on aluminum hulls. This rules out the trouble and cost of thick barrier coats. ECONEA-based paints also add less weight to a yacht when applied at the same film thickness as metal-containing paints.
Antifouling Paint Choices
Copolymer paints are typically used on slow watercraft such as trawlers and sailboats and release biocide at a steady controlled pace all through their lives, wearing off or “ablating” a great deal like a bar of soap. Paint wears off faster in higher drag areas on the hull and appendages. These paints work well in high-growth areas and continue to be efficient after haul-out and relaunch. Copolymer paints offer true multi-season protection, lasting as long as there is an satisfactory coating thickness. Because they expose new biocide until the coating is worn totally away, additional coats add to their length of service. We recommend a covering of two coats on each new bottom job. Copolymer paints with anti-slime additives are best for nutrient-rich, heavy fouling regions.
Modified epoxy paints are best if you own a fast planning hull boat. Contact leaching paint releases the biocide at a steadily decreasing rate, leaving the hard coating of the original thickness at season’s end. Higher copper content, rather than the type of paint binder as with ablative paints, generally means greater effective performance in this paint type. Modified epoxy paints stick to most surfaces, and can be applied over most types of paints. On the down side, they lose effectiveness when the boat is stored out of water. In addition, after several coats of paint, the existing paint will begin to build up requiring removal.
Dual Biocides
Paint suppliers often add a second biocide to some versions of their applications, normally in the final coat, using formulas such as Biolux, Irgarol and zinc pyrithione and zinc omidine. These additives further limit the growth of algae.
Aluminum Hulls and Underwater Metals
Aluminum hulls, outdrives and props need paints such as Vivid, Trilux 33, Trilux Prop and Drive Paint and Alumaspray that do not contain cuprous oxide, which reacts in a hostile way with the aluminum. Copper-based paints are safe for use on properly primed stainless and bronze.
Zinc anodes should be left unpainted to retain their effectiveness.
Conclusion
Good preparation and priming are the groundwork for any paint
job and antifouling paints are no different. Solid prep ensures acceptable adhesion and better performance over time. Remember that most bottom paint changes color when exposed to air or water, so do not estimate the color of your bottom paint on dry land. It will show its true color after a couple weeks of submersion in the water.
Don’t be too alarmed by a greenish tint of bottom paint near the waterline due to the paint’s reaction with oxygen. It does not affect the effectiveness of the paint.