Issue: March 2011
The Bottom Line: Bottom Painting


by Gary Caputi

Not long after man first launched a dugout canoe in a saltmarsh, he was introduced to destructive effects of barnacles, algae and marine worms. A few thousand years later, boaters are still dealing with these same bottom-fouling organisms, which are not just unsightly, but can severely hamper performance and fuel efficiency.

Until recently the most common way to combat these troublesome critters was to use a bottom paint containing some form of metal-based biocide and for many years the biocide found in most antifouling paints was tributyltin (TBT)--which was extremely effective in combating slime (algae) and "hard" fouling agents such as barnacles. However, this tin-based compound was eventually found to be harmful to the environment. In harbors containing large numbers of boats, TBT accumulated in the water and bottom sediments to the point where it killed marine vegetation and animals. Its use was phased out in the United States and Europe, and banned outright in 2008. By then paint manufacturers had already begun introducing other biocides, eventually settling on copper derivatives as a more benign active ingredient.

Copper Concerns
It's only been two years since the ban on TBT took effect, but concern is already growing over the effects of excess copper on marine life. In San Diego, where large numbers of private and commercial vessels are berthed, the Port Authority has initiated a program to replace copper-based bottom paints with alternative formulations. The goal is to achieve a 50-percent reduction in copper antifouling paints by the end of 2009, and their total elimination by 2017. If the ban on copper-based biocides takes hold in California, it will likely spread to other states--so  marine paint manufacturers have been wisely developing new types of antifouling bottom paints based on more environmentally benign formulas. Let's take a look at some of these new products.

The three major marine-paint companies--Interlux, Pettit and Sea Hawk--now offer eco-friendlier products that fall into three general categories: low copper, copper-free and biocide-free. Jim Seidel, product manager for Interlux, says his company's research and development has taken it in several directions. Since copper is still the most effective and popular biocide for such hard-fouling organisms as barnacles, Interlux developed new delivery systems--the way in which the biocide is released from the paint--that require considerably less copper to be effective. "Many older formulations consisted of up to fifty percent copper," Seidel said, "but we currently offer products containing as little as twenty-two percent. We boost performance by adding a small percentage of zinc pyrithione, [which] inhibits algae growth." Interlux's new Bottomkote Pro has the lowest copper content [22 percent by weight] of any paint the company has ever offered, while its popular Micron 66 and Micron Extra paints contain about 30 percent copper in a slow-release matrix that reduces the overall amount entering the water over time.

Interlux has also partnered with Janssen PMP, a Belgian division of Johnson & Johnson, to develop a new metal-free and biodegradable antifouling agent, a compound marketed under the trade name Econea. Interlux became the first paint manufacturer to offer it to the public, using its line of Pacifica Plus products. According to Janssen, Econea is highly effective at preventing hard fouling, and its chemical biocides are released at lower levels than copper-based antifouling agents. Better still, the biocides degrade rapidly in the environment. Econea also weighs less than copper-based paints, which can help reduce fuel consumption on larger vessels. In Pacifica products, Econea is combined with slime-fighting zinc pyrithione (ZPT, which, by the way, is the active ingredient in most dandruff shampoos.)

Interlux has also introduced a completely biocide-free product called Intersleek 900. This fluoropolymer paint is so slippery that barnacles and algae have great difficulty adhering to its "low surface energy" finish. It has the added benefit of reducing friction on a boat's wetted surface, resulting in higher top speeds and the reduction of fuel consumption. 

Pettit's environmentally friendly antifouling paints are marketed under the Green Marine brand. John Ludgate, Pettit's general manager, says the com-pany "has developed additives and formulations that leave greatly reduced chemical footprints." In its Vivid brand ablative paints, Pettit now uses a "composite copper" formula that replaces 40 percent of the copper oxide with silica. By using only 25 percent copper thiocyanate, the company says, the product releases much less copper than traditional paints while continuing to serve as an effective barrier against hard fouling organisms. To inhibit algae growth, Vivid low-copper paints also contain three percent ZPT.

Pettit too has introduced an Econea-based antifouling paint, called Vivid Free, as its entry in the copper-free category. By using Econea to replace the traditional copper biocide and adding a zinc-based slime inhibitor, Pettit is able to offer an ablative paint that it says performs as well, if not better, than copper-based paints.

Pettit does not currently make a biocide-free bottom paint, but it does offer PropKoat, a biocide-free, "foul-releasing" product for use on running gear, I/Os and outboard lower units.

Sea Hawk
In the low-copper category, Sea Hawk's Biocop TF contains 38 percent biocides in a blend of copper oxide and zinc omadine held in an ablative, self-polishing paint with a slow release rate. This allows for longer periods between reapplication and results in lower levels of copper entering the water over the life of the coating. "The level of copper in a bottom paint is impacted by the quality of the copper additive used, and Sea Hawk uses ninety-seven-percent pure copper oxide," says Sea Hawk's marketing manager, Jason Revie. "Our antifouling paint with the lowest amount of copper is AF33, also a multiseason product, which contains thirty-three percent."

Sea Hawk's new Smart Solution is unique in the copper-free category, as it contains no metal-based biocides, not even zinc. The primary active ingredient is Econea for fighting barnacles and other hard-fouling organisms, but instead of using zinc omadine or zinc pyrithione, the paint inhibits algae growth by forming a nontoxic, water-soluble skin, which is worn away when the boat is under way and reestablishes itself when the vessel is at rest. Sea Hawk's biocide-free paint is called Hawk Speed. It's a clear, friction-reducing coating containing silicone made for running gear. It prevents the adherence of barnacles and is claimed to increase vessel performance.

So what's right for your boat this spring? Will it be bottom paint with lower copper levels, no copper or a super-slippery substitute? The choice is yours, which is more than we can say for our boating ancestors. For more information on these antifouling products, visit the company websites,, and 

Gary Caputi is a boating and fishing writer based in New Jersey.