Understanding the basics of antifouling paint can go a long way in protecting your investment while delivering long-term service. I always recommend checking with the boatyard hired to do the bottom job, but an informed skipper can aid the process by knowing more than just the color options.
For starters, be there at the haul out to see how well the last bottom job performed. I spend a fair amount of time inspecting the bottom, running gear and every submerged thru-hull fitting after a thorough pressure cleaning. If there was improper preparation before the last coat of antifouling paint was applied, I may see peeling, cracking or flaking sections. On the other hand, if I am satisfied with the results, I generally request the same paint for the next recoating.
Bottom paints have come a long way. Today’s antifoulant paints cover two basic categories: seasonal and multiseasonal. Ingredients and formulas include a myriad of biocides to repel marine growth. Those biocides are mixed into a petroleum- or water-based substrate with environmental protections built in.
Multiseasonal paints are popular with experienced mariners, and are the usual choice for new boats. These coatings, called ablative paints, are designed to wear away gradually from the friction of the boat’s surface coursing through the water. Ablative paints constantly erode and expose fresh biocide, and work best when the boat is used regularly. If the boat sits at the dock, slime may develop, although subsequent boat rides will likely wipe it away.
The other advantage with ablative paints is that the boat may require just a waterline touch-up, instead of a fresh coat, at the next launch. You can tell what’s needed if the ablative paint has been applied in thin coats, with the first coat in a color different from the top coats. The idea is that when the first color begins to show, it is time for a fresh top coat or two. Ablative coatings also help avoid the constant buildup of single-season paints that eventually must be removed with sanding, chemicals or soda blasting.
Seasonal paint lasts for several months, with the biocide protecting against fouling via a constant release throughout the layer of paint. When the boat is removed from the water for winter storage, however, the paint is likely to require a fresh top coat. I have cheated this process with smaller outboard boats, sneaking a second season from the old paint, but doing so often meant jumping overboard during the summer to remove growths.
Single-season bottom paint, often formulated with a copper biocide additive, is heavier than ablative formulas. A constant buildup and subsequent layers eventually add weight to the coating, causing it to flake off in chunks or sheets. If the bottom paint is applied in damp weather, moisture can collect under each layer and bubble.
Removing bottom paint is a miserable job, at best, and boatyards typically do not allow customers to do any bottom work, for environmental and other safety reasons. Water-based bottom paints are a cleaner, faster way to get the job done safely and economically. These low-odor coatings repel marine life and require nothing more than soap and water to clean up.
Biocides can also lean more eco-friendly, but be sure that the coating you select is compatible with the existing paint on the hull when you are top-coating. Some paints may require only a cleaning, while others recommend a light or more thorough sanding before applying a new coat. It is imperative to read the instructions, especially since many paint companies are providing choices in new colors that can give the boat a unique look and style.
And, consider adding a coating that’s specialized for running gear and hardware, and that chemically bonds to the metal. It can significantly reduce the adhesion ability of marine life for an enjoyable cruising season.
One final tip: Always be sure that any underwater hardware, including raw-water intakes, is completely free of barnacles or other obstructions. Inspect the condition and age of hoses that supply the water to these systems. If barnacles or shells are inside any of the fittings, then the hoses are likely similarly affected.
This article was originally published in the January/February 2023 issue.
