Trends in Antifouling

Antifouling paints are like anchors: as voyagers, we all agree we need them, but we can’t seem to agree on which is best.

Any object left in seawater for an extended time will accumulate biomass from biofouling – the unwanted growth of marine organisms. If the object happens to be a boat, bad things start to happen: the boat slows down due to increased drag, propellers and rudders cease to perform their requisite tasks, and finally, the hull itself is attacked and its integrity is ultimately compromised.

The way to prevent fouling is to use biotoxins. Copper predominates as the biotoxin of choice in antifouling paints. Up to 15 pounds of cuprous oxide may be found in a single gallon of modern bottom paint. Other copper-based compounds in common use include metallic copper, copper thiocyanate and copper pyrithione. Each has specific properties (including cost) that indicate its use in a particular paint formulation.

Copper-based antifouling paints slowly release ionic, unbound copper into the water. Although metallic copper is safely used in everyday products like water pipes, electric wires and coins, cupric ions are poisonous to most marine organisms – especially animals – and as a result these organisms cannot live on the painted surface.

Copper-based paints are presently the most cost-effective antifouling solution for recreational boats that spend a lot of time in the water. Since biofouling is destructive to both boat and marina, it seems logical that these paints would be heralded. Yet countries like Sweden and Denmark currently regulate the use of copper-based bottom paints for recreational craft. San Diego Bay authorities are considering the same thing. Water quality pilot studies have been conducted in the Chesapeake and San Francisco Bays as well.

Why? Basically, it’s too much of a good thing. Copper is poisonous to marine organisms. If its toxicity were confined only to those critters trying to attach to your hull, that would be okay. But as more boats concentrate in one area, so too does the copper leaching from bottom paints. In coastal waters that don’t experience good tidal flushing, copper stays in the bottom sediments. When the dissolved copper level is sufficiently high, it is harmful to the food web; shellfish, crustaceans, even phytoplankton are affected.

So with apparently compelling arguments both for and against copper-based paints, where is the industry going? Not surprisingly, agreement is lacking.

Toxic vs. non-toxic

Antifouling paints can be categorized as toxic or non-toxic. Toxic paints prevent fouling with a paint film poisonous to marine life. These paints include those with (now banned) tributyltin (TBT), copper-based compounds or hydrogen-peroxide-generating compounds. Non-toxic paints attempt to thwart marine life by presenting a surface they simply can’t (or won’t) stick to. These paints have chemicals like silicone, Teflon, lanolin or even cayenne pepper in them.

Non-toxic paints occupy a very thin segment of the bottom-paint market. To date, they have simply been more costly and thus less favored than antifouls. Interlux introduced biocide-free Veridian 13 years ago. Although the same paint is very successful in the commercial marine market, it was not accepted in the recreational market because it was more expensive and required higher maintenance or more time underway than conventional toxic paints.

Anecdotes aside, non-toxic paints are for the most part restricted to specialty formulae aimed primarily at consumers in low-fouling applications like dry storage or racing hulls.

Toxic antifouling paints have four basic elements: solvent, pigments, biocide, and binder or resin to hold everything together. Since the solvents go away and the pigments are just there for good looks, it is the combination of binder/resin and biocide that determines the working attributes of the paint.

Copper toxins

Historically, copper has been the choice toxin. Later developments brought about copolymer binders, which allowed the exhausted surface paint to wear away over time, thus keeping fresh biocide exposed to the water and preventing paint buildup. Concurrently, tributyltin became popular since superior paint properties were discovered using organotins with copolymers.

Tributyltin fell from favor when it was discovered accumulating in marine sediments and having an ecologically detrimental effect. Interestingly, though the International Maritime Organization (IMO) first started efforts to ban it in 1988, it was not until 2003 that world consensus agreed. Today, TBT is still manufactured in the United States and is still for sale for recreational boats in isolated parts of the world.

With the demise of tributyltin, manufacturers returned to experimenting with copper compounds. Today, major manufacturers like Interlux believe that they have formulated copper-based paints which now surpass the qualities once available in TBT-based paints.

Significantly, it is not simply the quantity of copper per gallon that determines the effectiveness or durability of a particular formulation. Rather, it is the complex interaction of the binder and biocide that determines a paint’s efficacy as an antifouling coating. And it is here that Interlux applies considerable research and development efforts – as shown by its extensive product range.

Paint manufacturers also understand that many product-purchase decisions are economically driven. Thus, they attempt to have a broad spectrum of price points for consumers. Consider that copper prices are up 30 to 35 percent since August 2005, and more than 200 percent in the past 18 months. That translates directly (though with some delay) into higher paint prices. If new chemistry can reduce copper content, the savings can be passed on to the consumer.

Today, a great deal of the copper used in bottom paints is recycled from common household goods like plumbing pipe and electrical wire. Bob Donat, Interlux marketing manager for North America, pointed out that, “You don’t need very high copper content. Basically, it is how it’s bound into the resin and paint film that matters. We want to use enough to keep the boat clean, but that’s it.”

My wife Raine and I have used Micron Extra – an Interlux and International Paint product – on our J40, Gryphon, for years. We would typically get 18 excellent months of antifouling properties in warm tropical waters, and we occasionally stretched this to 24 months. Now we use Micron Extra with Biolux and are pleased with the results.

Non-copper toxin

There is one very interesting copper-toxin alternative available in bottom paint today. E Paint Company produces paints that use hydrogen peroxide (H2O2) as the primary biocide.

Hydrogen peroxide by itself does not bind with resins; instead, a chemical that produces hydrogen peroxide when exposed to light is bound into the paint film. This photo-reactive compound generates H2O2 when exposed to visible light and that chemical then forms a surface that is inhospitable to marine growth. As the hydrogen peroxide leaches out of the paint film, it quickly breaks down into water and oxygen. There is no harmful residue and no build up of poisons in the waters or sediments.

Since the paint’s primary biocide is activated by exposure to light, brighter colors are favored with the E Paint system when compared to traditional bottom paints.

E Paint’s technical service manager Shane Sargent explained, “When dark pigments are added to tint the coating, it slows down the reaction the paint has with oxygenated water and visible light. Vessels that are going to be operating in colder waters or low-fouling areas will do fine with darker colors. If you have a vessel operating in a high-fouling region with warm or tropical waters, E Paint recommends the customer choose a lighter colored E Paint; white and gray are the best performers for those types of waters. Without heavy pigments to block the photo receptors in the coating, the paint is free to react and ablate at a sufficient rate to repel the most aggressive growth.”

E Paint has been in business for 12 years and has focused on government applications for half of its corporate life. E Paint provides paints to the U.S. Navy, Army Corps of Engineers, National Park Service, NOAA, and has recently been specified for use on certain U.S. Coast Guard aids to navigation and response vessels.

Voyagers Scott and Wendy Bannerot have been using E Paint’s EP2000 on Elan, their aluminum-hulled Ovni since 2003 (and another E Paint product prior to that). Aluminum hulls demand special care in application of bottom paints, since an electrolytic reaction could result if copper were to come in direct contact with the metal hull.

The Bannerots find EP2000 to be “quite an effective antifouling, definitely superior €¦ to the last of the TBT products we’d applied when they were still available,” and they plan to use it again. “On the next round I will simply pressure clean, sand and go with EP2000 again,” Bannerot said. “I definitely would not be interested in any other bottom paint.”

Another user of E Paint’s unique system is Bruce Schwab on OceanPlanet, the first American finisher in the Vendee Globe. He said it’s perfect for his application. “Not only is it environmentally safe, the coating is really hard, smooth and fast,” Schwab said. “Another side benefit is the light weight compared to copper-based paints. We saved around 100 pounds by switching to EP2000 from a conventional antifouling.”

E Paint will soon be releasing a new product based on the same technology for inflatables and transducers.

Other additives

Copper, while an effective toxin against organisms like barnacles, is less effective against softer growth such as algae. Also, as release rates decline over time, copper concentrations become low enough that diatomaceous and animal fouling increases.

Variously called anti-slime agents, additives or boosters, paint manufacturers now include additional biocides to broaden the effective toxicity spectrum of copper alone. Licensed for use in the United States are organic biocides such as zinc pyrithione (Zinc Omadine, Arch Chemicals), Irgarol (Ciba), Sea-Nine 211 (Rohm and Haas) or Biolux (Interlux).

Most of these chemicals are in common use in agriculture as herbicides, bactericides and fungicides – and even in anti-dandruff shampoos. Needless to say, these chemicals have an “additive” effect on the paint’s cost.

The future of antifouling paints

The paint industry is heavily regulated by international, state and U.S. agencies. Paint manufacturers must register each formulation they sell (including each color) with federal agencies and with each state in which it is sold.

While new technologies are constantly being sought in research labs and by independent companies, actually getting product into your hands and onto your boat is a time-consuming task. As a result, sudden changes in the industry are unlikely.

But environmental pressures will be felt as the popularity of recreational boating continues to grow, concentrating more boats – and potentially more pollutants – in confined waters. We are now realizing, too, that the oceans are not the infinite waste sinks we once thought them to be, as shown by effects like mercury buildup in pelagic fish species.

Still, even if government authorities start to restrict or ban copper-based products, it is unlikely the effect will be felt broadly for some number of years. Consider the nearly 20 years it has taken for organotin products to be eliminated from the market.

In the mean time, watch for incremental improvements in the efficacy of existing paint lines – greater durability, more effective antifouling properties, lower cost and more vivid colors. And watch the horizon for new technologies offering environmental advantages while still retaining the power to prevent fouling. n

Jeff Williams and his wife Raine completed a six-year circumnavigation aboard their J/40 Gryphon (

By Ocean Navigator