Changing paint

From Ocean Navigator #58
January/February 1994
In past few years, legislation on both the Federal and state level has radically changed the mix of compounds allowed in antifoulant paints. One of these is the 1988 Organotin Antifoulant Paint Control Act (OAPCA) that prohibits the use of tin-based bottom paints on all boats less than 25 meters long, except those with aluminum hulls. The other is southern California’s strict air pollution regulations that limit the amount of solvents allowed in paints, since these solvents are the source of volatile organic compounds (VOCs) that release hydrocarbons into the air and cause smog.

As expected, California has tightened its regulations even further, and by 1994, solvent in marine antifoulants cannot exceed 150 grams per liter. “That’ll knock out all solvent-based bottom paints from the market there, since they contain up to 400 to 550 grams per liter,” notes Jim McCarthy of Petit Paints.

The VOC regulations (which have already driven many antifoulants, most notably hard vinyls, off the market in California) spurred the paint industry to develop new “high-solids” and water-borne paints.

The paint industry had high hopes for the low-solvent, high-solids paints. Unfortunately, high-solids technology didn’t work for bottom paints, which, due to heavy copper concentrations, have a high solids content to begin with. In addition, users of high-solids paints complained of difficult application, slow drying times, and poor paint performance.

Instead, paint manufacturers have concentrated upon perfecting water-borne bottom paints, replacing the solvents with a special water soluble binder to emulsify the paint solids. According to McCarthy, new water-borne paints, which contain about 119 grams of solvent per liter, meet or exceed everybody’s air quality management regulations. Whereas a year and a half ago, fledgling water-based antifoulants were new on the market and reportedly difficult to apply, McCarthy asserts that these problems have been surmounted. “We’ve made big changes in these paints during the last year,” he states. Furthermore, soap and water clean-up saves additional solvents – an added boon for California boat yards which must report all solvent used to the air quality management district.

Manufacturers’ representatives also maintain that water-borne antifoulants perform as well or better than their solvent-based counterparts. “Because the paint has a slight sloughing action,” McCarthy notes, "it is as effective as solvent-based antifoulants containing more copper." Petit even recommends its Aqua-Coat, which contains 58 to 60 per cent cuprous oxide, for use in the tropics.

A side advantage of the new water-borne antifoulants is that they can be applied over (and overcoated with) any other type of bottom paint, even ablative copolymers. “Incompatibility among different antifoulants resulted from the different solvents used,” McCarthy explains. “Without the solvents, there are no compatibility problems.”

One drawback, he admits, of water-borne bottom paints is the long dry times: Four to six hours, ideally overnight, between coats and before the boat is returned to the water. “This inhibits the customary touching up before the boat goes in the water.”

McCarthy envisions that water-borne paints will eventually replace all types of solvent-based coatings. “Already, there are water-borne clear finishes on the market. Soon, we’ll be seeing this technology extend to topside paints, such as urethanes.”Good news for aluminum boats

Until recently, the only bottom paint available for aluminum boats was tributyltin (TBT), because cuprous oxide, the biocide in most antifoulants, causes galvanic corrosion when it comes in contact with aluminum. Also, because OAPCA restricts, even for aluminum boats, the sale and application of TBT paint to trained and certified professionals, the cost of an annual bottom painting has risen.

Last year, the Interlux company introduced a new paint formulated specifically for aluminum outdrives and hulls. Instead of cuprous oxide, this paint utilizes copper thiocyanate, which, according to Linda Lindquist of Interlux, is safe for use on aluminum. The paint is available over the counter and is legal for anyone to apply. “Also,” Lindquist adds, “the white color of the compound allows us to make the paint in light colors such as gray and white.”

However, despite the laws, despite the new technology, TBT-based paint is still out there, according to Mike Rexrode of the Environmental Protection Agency (EPA).

The EPA recently published the results of its Environmental Monitoring and Assessment Program (EMAP) that sampled the sediment layers in 10 areas of the U.S., including Galveston Bay, Lake Erie, Narragansett Bay in Rhode Island, and Puget Sound in Washington. In all 10 sites, TBT concentrations of one part per billion (ppb) or more were found in the marine sediment.

“This is an alarming revelation,” states Rexrode, who notes that concentrations higher than .02 ppb can damage marine life. “We’d expected that TBT would, as it did in Europe, disappear by now.”

“We don’t know why the TBT is here or where it comes from,” adds Rexrode, who doubts the source is large ships. He conjectures that boat owners could be obtaining TBT antifoulants illegally (perhaps from stockpiled sources) or from outside of the U.S. But the source of the contamination remains a mystery. Follow-up for EMAP, known as REMAP, is the responsibility of local agencies.

“No further studies are being done,” says Rexrode. “There just hasn’t been the money or governmental interest.” But Rexrode hopes that concern about the marine environment will change this. “During the last 12 years we’ve seen a lot of leeway towards business at the expense of environmental issues. Hopefully, with the new administration, that focus will change.”The search continues.

Meanwhile, the paint industry is still seeking a toxicant that will be as effective as tributyltin without the harmful environmental side effects. Rexrode notes that certain companies are looking at zinc as a possible base for antifouling, but is uncertain whether this could be the next miracle compound. “There is concern,” he notes, “about the side effects of large amounts of zinc upon the marine environment.”

Another avenue being explored, according to U.S. Navy marine environmental scientist Peter Seligman, is to add growth-inhibiting enzymes to bottom paints.

A new approach to marine antifoulants that held promise was the low surface energy technology – super-slick polymers such as Teflon (registered trademark of DuPont) and silicon – to which no organisms can stick. Five years ago, Interlux acquired a small Swedish company, Extensor, that had developed a Teflon antifoulant which it adapted from a mold release agent used in the rubber industry. Unfortunately, Teflon did not prove to be the great bottom growth inhibitor. “In severe fouling conditions, Teflon does not do the trick,” admits Bob Donat of Interlux. However, the very smooth surface reduces the drag coefficient and increases hull speed, thus making Teflon paints popular among racers.

Katherine Knight is a freelance writer who is currently voyaging in the Caribbean.

By Ocean Navigator