Hal used this opportunity to inspect the ship's bottom for evidence of the presence of the teredo worm, which in these warm waters could eat away the bottom timbers of a ship. At times these creatures grew as long as a man's arm and as thick as his thumb ... A ship so afflicted could have the bottom drop out of her in heavy seas. - From Monsoon, a novel of high-seas adventure by South African writer Wilbur Smith.
Today's fiberglass-boat owners need not worry about the teredo worm, a creature worse than a termite that plagued 17th-century sailboats. Early captains coated their hulls with tar and canvas to deter the boring beasts. At other times, mariners bolted sheets of copper to the wood, trying to eliminate everything from barnacles to slime.
Many years later, copper remains the antifouling weapon of choice. Blended with resins in bottom paints, copper keeps boat hulls relatively free of barnacles, algae and grass. And that keeps hulls afloat, decreases drag in the water and increases fuel efficiency.
That explanation seems simple enough. But when boaters head to a marine supply store to purchase paint, things get complicated. The choice becomes more than a matter of color. Paints can contain 20 to 76 percent copper. They can release copper by passive leaching or by wearing away to expose new layers. Some paints oxidize out of the water, becoming ineffective if the boat is kept in dry storage. Some work well in colder climates, but can't beat back the horde of organisms swarming in tropical waters.
Boaters also may see noncopper, "biocide-free" paints sold and advertised. Many of these products work, but not without definitive drawbacks. Copper-based antifouling paints - though they are registered pesticides - remain the industry standard.
To demystify these choices, help boaters understand the effects and limitations of antifouling paint, and explore the options beyond copper, I asked the two major paint companies - Interlux and Pettit - for help. I also talked with Leigh Taylor Johnson, marine adviser for the University of California Sea Grant Extension Program. Forgoing the chemistry lesson, we'll look at this systematically.
The invasive saltwater trio is shell, slime and weed, says Interlux marketing manager Bob Donat. "Weed is long, stringy growth. Slime is a thin film of green or brown algae that won't allow a bottom paint to leach the biocide [copper]," he says. And shell includes barnacles and other animals that attach to hard surfaces.
Warm tropical waters incite these enemies. Waters from Virginia south along the East Coast would present the greatest "fouling challenges," Donat says. "Picture a canal or backwater way up into [Fort] Lauderdale, where there's not much water movement. Or consider the Bahamas - anywhere they've got nice, warm salt water. That's where you get the most fouling." That warm-water rule of thumb remains true - unless you live in Boston. "We consider Boston Harbor to be one of the highest fouling areas in the country," says John Ludgate, vice president of sales and marketing for Pettit. "That's because of the high sewage discharge that's adding so many nutrients of all sorts."
Where fouling growth can literally be noticed in a matter of hours - i.e., Florida - high-copper paints sell well. "The more copper, the more effective the paint is against fouling," Ludgate says. "Paints in Florida have between 55 and 70 percent copper in them. In the Northeast, they need 35 to 55 percent copper. Unfortunately, copper is the expensive part."
While copper or, more correctly, cuprous oxide may be the most important biocide in antifouling paint, the copper percentage is only one factor in determining how well the paint will work, Donat says. The paint must release the copper so it can attack the growth; the way it releases that biocide determines the product's effectiveness. Some paints with lower copper percentages may work as well or better than those with higher numbers.
California could be considered a separate country with respect to antifouling coatings. The state requires companies to abide by more stringent pollution standards than the EPA sets, Ludgate says. That gives Californians fewer choices in bottom paints.
Most Californians leave their vessels in the water all year. And while Pacific water commonly measures 20 or more degrees cooler than that of the Atlantic or Gulf off Florida, fouling continues to be a major concern. Californians prefer hard paints, Ludgate says, because they hire diving contractors to scrub their hulls underwater.
Leaching or Sloughing
Antifouling paints work in two primary ways. "Hard" paints form a coating on the hull through which copper can leach to the surface. These paints work until no more copper is left.
Ablative (also called copolymer) paints "wear away like a bar of soap," Donat says. "Dead paint wears off, exposing new paint beneath." Ablative paints can contain less copper because of the way the copper combines with the resin, he says.
Hard paints lose their antifouling properties if exposed too long to air. Because most boats in the Northeast overwinter in dry storage, hard-painted hulls must be repainted every year. Paint layers build up over time, and eventually hulls must be scraped clean and repainted.
"Hard paints have tended to be a little cheaper," Ludgate says. "But with new technology out, there's not that much difference anymore."
Paint companies have altered their products in recent years as the EPA began restricting the use of tributyl tin, a substance that aided the dissolution of resin and proved quite deadly to marine organisms. TBT hasn't been used in bottom paints for boats under 82 feet since the late 1980s, but over time, companies created better processes for releasing biocides. Interlux also introduced a "boosting technology" called Biolux? in 1998. Biolux? is a slime blocker found in Interlux's premium brands.
Whether you choose hard or ablative coatings, high or low copper content, the average lifespan of a bottom paint ranges from 12 to 18 months. If you put two coats of paint on the hull, you might get 12 to 24 months, Ludgate says. "That's a very broad rule of thumb. A lot has to do with how much you use the boat. Also, hard coatings tend more toward the 12-month spectrum and ablatives toward 24 months."
By definition, antifouling paints are supposed to kill things. Unfortunately, that can sometimes mean marine organisms other than barnacles. But finding an effective method to keep a hull clean without using copper has proved challenging.
Leigh Taylor Johnson, from California's Sea Grant program, has been conducting a yearlong series of educational field demonstrations to raise awareness of nontoxic bottom coatings. She and her colleagues also published a nine-page brochure, "What You Need to Know About Nontoxic Antifouling Strategies For Boats," in October 2002.
"I was asked in 1999 by the San Diego Regional Water Quality Control Board to do field demonstrations for nontoxic bottom paints," says Johnson. The board and the EPA had measured dissolved copper levels in boat basins of San Diego and Newport bays and found wildly ranging readings from 2.6 up to 29 parts per billion. Federal and state regulatory standards allow a level of 3.1 ppb. Excessive copper levels have been shown to adversely affect mussels, oysters, scallops, sea urchins and crustaceans.
"Nontoxic strategies involve a totally different paradigm. That's why we call it ?strategies' and not 'paints,'" she says. "Nontoxic paints alone don't stop the growth. Nontoxics need more work. There's no magic bullet."
Some of the nontoxic alternatives Johnson has reviewed include Adsil, a slick, hard coating made by combining silicone and oxygen. Adsil retards the attachment of organisms, but the hull surface must be cleaned and sanded before application, and the product costs $240 for three pints, which will cover 200 square feet. Most copper-based bottom paints cost less than $200 a gallon.
Other categories of nontoxic strategies and coatings include silicone, epoxy, ceramic-epoxy, fiber-epoxy, polymer, water-based urethane interpolymer dispersion, bottom wax, slip liners, boat lifts and mechanical cleaning. "There are a variety of approaches coming out on the market. Some have a chemical active in them. We don't know yet if there will be environmental problems with them," Johnson says. "Scientists are also looking at plant extracts that repel rather than kill."
Epoxy coatings have proven durable but require frequent and aggressive cleaning. Silicone coatings can be easily nicked or abraded, but fouling growth tends to slide off of them when boats exceed certain speeds.
Johnson will wrap up her one-year study this fall and publish a brochure of her findings next year. (Visit seagrant.ucdavis.edu to review the results and her report on the economics of nontoxic paints.) The U.S. Navy is also testing a variety of low-copper or copper-free coatings. And industry leaders Interlux and Pettit continue their own in-house research.
"Everybody's looking for a more environmentally preferred paint," Ludgate says. "We have nonstick coatings. But the average boat owner isn't willing to put in the maintenance, which means an almost weekly wipe down of your hull. [A transition] probably isn't going to happen until legislation forces the other products out of the market."