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Cover your bottom: Antifouling Do's and Don'ts

by Lyman-Morse Boatbuilding 4 Apr 09:33 UTC

Antifouling paint. It's a coating that's applied to the bottom of a boat. It keeps the barnacles and slime off. Simple, right?

Not exactly. In 21st-century boat maintenance, matching the right antifouling paint to the right boat can be surprisingly tricky.

"There's no one perfect paint that will work in every situation," explains Kevin O'Donnell, marine coatings manager at Lyman-Morse in Thomaston, Maine. "It is all about finding the paint that works for that particular boat."

Many factors come into play budget, paint compatibility, environmental regulations, and changing technologies but O'Donnell sums up the complexities of matching the right anti-fouling finish to the right application in two simple questions:

How often is a boat used, and is it used in fresh or saltwater?

For light use: The harder, the better

O'Donnell, who estimates he and his crew paint or finish about 55 boats per year, has found boats that leave the dock or mooring less than once a week cannot rely on the scrubbing action of the water to keep marine growth at bay. Instead, they require harder finishes that carry a spectrum of biocides that limit the growth of barnacles and seaweeds.

There are three major manufacturers of hard biocidal marine coatings: Pettit, SeaHawk, and Interlux. Each has a full line of products carefully engineered to safely release their biocides over time.

These harder biocides usually rely on cuprous oxide or other copper compounds to ward off marine growth. They almost always require careful preparation, including a deep bottom cleaning, sandblasting, bottom fairing and repairs, and a stable base coat. The goal is to prevent water from seeping in between various layers of finishes and creating blisters.

Specifications vary, but O'Donnell suggests that epoxy basecoats should be at least 10 millimeters thick. And he finds that four coats of antifouling finish, of between 3 to 4 millimeters each, perform the best. Lyman-Morse coatings crew members check the thickness of various layers with measuring devices prescribed by the manufacturer.

If budget is an issue, O'Donnell says most major manufacturers offer lower-priced options, including Pettit's Hybrid Reactive Technology brand. It can run about one-third the cost of higher-priced options.

For heavier use: A soft touch

Where serious anti-fouling efficiencies start is when boats are lucky enough to be used at least several times each week. Here, softer antifouling coatings can do the same work as harder biocides.

These softer, so-called ablative paints physically slough off as the boat moves through the water. According to paint manufacturers, these sloughed-off particles are relatively harmless and they do the work of carrying away marine growth.

Softer ablative finishes open up several intriguing application options. Softer finishes can be laid down in various coats of contrasting colors, hardness, and thicknesses to improve performance. First coats can be in a thicker coat of darker blue, while top coats can be in a thinner coat of a lighter hue, or even white.

"That way, as the top white layers scrub off, you can see the blue layer and know right away where your finish needs re-touching," says O'Donnell.

Again, if budget is an issue, all major manufacturers offer high-quality ablative paints at good prices. O'Donnell recommends Interlux ACT, a reasonably priced ablative coating that comes in a full range of formulations and colors.

Right home port

Once the family of hard or soft antifouling finishes is chosen, the next step is matching the formulation to the salinity of the water. Freshwater vs. saltwater can drastically affect the performance of antifouling finishes, O'Donnell says.

While the vast majority of paints that Lyman-Morse applies are for saltwater, O'Donnell finds Interlux's VC-17m is a high-quality example of freshwater antifouling paint.

The environmental debate

Lyman-Morse takes the considerations about the environmental impact of antifouling finishes seriously. All antifouling finish work done at Lyman-Morse follows best-practices for application and remediation. All procedures occur in carefully controlled environments, where workers wear full protective clothing, groundwater is protected, and paint particles are filtered and disposed of properly.

Changing regulations are also part of O'Donnell's job. He monitors new rules in California that are moving away from copper-based marine finishes. And he's keeping a close eye on a new family of silicone-based antifouling systems like Seacoat Technologies and Elkem. These coatings are currently seeing test duty in the military and some commercial vessels. They promise 10-year lifespans and utilize much more stable environmentally safe compounds.

"We do a lot of testing panels to experiment with new formulations, "says O'Donnell. "There are new finishes on the market. We look for what's appropriate for our customers."

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