Antifouling Paints

Four types of bottom paint that discourage foul growth
Antifouling paint discourages the growth of barnacles, weed, and other water life on the submersed hull of your boat. If your boat is wooden, it prevents marine borers from eating it for lunch. I use the word discourages advisedly because there is no acceptable antifouling agent that will stop growth altogether. So if your boat remains in the water year-round, you’ll have to scrape the bottom and recoat it with antifouling paint at least every couple of years.Copper, in one form or another, is the most favored biocide. Tin, in the form of tributyltin, or TBT, was found to be more effective, but its harmful effects on shellfish led to its banning for most marine applications by the U.S. Congress in 1988. It may still be used on aluminum hulls that would react adversely with copper antifouling. The four most common types of antifouling paint are as follows.Ablative. An ablative paint gradually and constantly wears away to reveal a new surface of copper biocide. It wears from both the chemical reaction with the water and the scouring action of water on the hull. If your boat covers large distances at fast speeds, you can expect to lose a lot of ablative bottom paint.It has two big advantages: as long as the paint remains, it’s 100 percent effective, and it retains its biocidal properties no matter how long it’s out of the water.Most ablative paints are expensive because they need a minimum of two coats, preferably three.Sloughing. Sloughing paint is similar to ablative paint in that it wears away constantly. However, it comes from a less refined branch of the family because it seems to slough off in coarse flakes rather than disappear discreetly. It uses a softer binder than ablative paint does, and softer translates to less costly. It also loses its potency quickly if it’s exposed to air.Modified epoxy. With modifiedepoxy antifouling paint, it’s the copper that wears away, not the paint. Copper particles in the epoxy gradually dissolve and allow the water to penetrate deeper and deeper until all the copper biocide is used up. You can scrub epoxy to reinvigorate it, but if you leave it out of the water, it will gradually lose its potency. Although the paint film builds up over the years and occasionally must be removed—an arduous and messy job—epoxy antifouling is a good choice for boats left in the water year-round.Vinyl. Similar in action to epoxy, vinyl antifouling paint develops a hard smooth finish that you can burnish if you race your boat. Like epoxy, it is non-ablative and it loses efficiency out of the water. You must be careful when applying it because its powerful solvents can soften other undercoats, causing them to bubble. Carefully follow the manufacturer’s instructions.See also Bottom Painting.