Some information about bottom paints and how they work.
Antifouling paint keeps marine organisms, taking the forms of shell (animal fouling from barnacles and zebra mussels), weed (plant growth) and slime (single-celled algae) from attaching themselves to your boat. Most antifoulings use the dissipation of metal (on the hull's surface and in the water) to prevent these nasty critters from adhering. Copper (cuprous oxide) and tributyl tin are two metals that have proven effective as biocides, but tin (finally banned worldwide on ship hulls only last year) was so poisonous that it decimated underwater ecosystems. Copper compounds are now most popular, but the price of the metal raw material has skyrocketed. Additionally, high copper concentrations dissolved in the water of harbors in California and elsewhere have created environmental problems and restrictions on application of cuprous oxide-based paints. Paint suppliers have developed several new antifouling technologies that address these and other problems. Here are some of the most important:
New Composite Copper Technology: Replace the core of traditional cuprous oxide with environmentally friendly silica, reducing the copper footprint by up to 40%. The result is a copper biocide surface that provides superior protection for your boat, with a core that is made from materials found in the ocean
Water-Based ablatives: Water replaces the solvents found in conventional bottom paints in water-based Pettit Hydrocoat. Low-odor formula allows painting indoors. Application is trouble free and clean up requires only soap and water.
White copper: Clean white in color and used in Pettit's Vivid and Interlux Trilux 33, white copper (cuprous thiocyanate) requires 50% less content than the heavy, dark copper used in conventional antifouling paint. Produces the brightest colors, whitest whites and blackest blacks.
Paint manufacturers believe that ECONEA, a metal-free antifouling agent developed by a pharmaceutical company, is the future of antifouling paint. ECONEA-based paints, for example, Interlux's Pacifica Plus and Pettit's Vivid Eco, are due to be released in the near future. We are still learning about this new biocide, and will provide further data and results from independent testing in the future. ECONEA's proponenants say it provides the following advantages:
Effective at low usage levels: ECONEA provides effective antifouling protection at low usage levels. It's more effective than copper-based paints containing cuprous thiocyanate, and just as effective as those containing cuprous oxide.
Biodegradable: ECONEA degrades rapidly and its degradation products are biodegradable.
Adjustable release rate: The ECONEA release rate from an antifouling paint can be tuned easily, thereby providing a consistent and long-lasting antifouling protection.
Better color selection and stability: Unlike some metal-based antifouling agents, ECONEA can be used to easily formulate light and bright paints, resulting in brilliant colors with better consistency. ECONEA does not cause discoloration in the presence of sulfides, as do metal-based paints.
Compatible with underwater metals: Because it is a metal-free compound, ECONEA will not cause galvanic corrosion on aluminum hulls. This eliminates the trouble and expense of thick barrier coats.
Enables weight reduction: ECONEA-based paints add less weight to a boat when applied at the same film thickness as metal-containing paints.
Antifouling Paint Choices (Copolymer/Ablative Paints)
Copolymer paints release biocide at a constant controlled rate throughout their lives, wearing away or "ablating" much like a bar of soap. Paint wears off faster in higher drag areas on the hull and appendages. These paints work well in high-growth areas and continue to be effective after haul-out and relaunch. Copolymer paints offer true multi-season protection, lasting as long as there is a reasonable coating thickness. Because they expose new biocide until the coating is worn completely away, additional coats add to their longevity. We recommend a covering of two or three coats on the first application. Copolymer paints with anti-slime additives are best for heavy fouling areas.
Ablative paints (of the non-polymer type) work in a similar way and minimize the annual ritual of sanding when applying a fresh coat. Best use: Boats that are used often, but are not serviced by a diver. Not recommended when you want a super-smooth bottom finish and have a diver maintain it, since scrubbing removes paint and reduces longevity. Must be repainted if the boat is pulled out of the water for winter storage. All ablatives of both varieties share the advantages that they can be applied over most other types of antifouling paints and do not create a paint buildup.
Hard "Contact Leaching" Paints
If you keep your boat in the water year round you are most likely a candidate for a modified epoxy paint that prevents growth by leaching biocides upon contact with water. Contact leaching paint releases the biocide at a steadily decreasing rate, leaving the hard coating of the original thickness at season's end. Higher copper content, rather than the type of paint binder as with ablative paints, generally means greater effective performance in this paint type. Modified epoxy paints adhere tenaciously to most surfaces, and can be applied over most types of paints. On the down side, they lose effectiveness when the boat is stored out of water.
Best use: Range of products from inexpensive single season coverage up to top quality multi-season protection in high-fouling environments (Ideal for sailboats and fast powerboats, due to its ability to resist abrasion and be burnished to a smooth surface. Avoid when you don't want paint to build up from annual paint jobs.
Paint suppliers add a second biocide to some versions of their coatings, using formulas such as Biolux, Irgarol and zinc pyrithione and zinc omidine. These additives block photosynthesis near the water's surface and restrict the growth of algae.
Aluminum Hulls and Underwater Metals
Aluminum hulls, outdrives and props require paints that do not contain cuprous oxide, which reacts destructively with the aluminum. Copper-based paints are safe for use on properly primed stainless and bronze. Zinc anodes should be left unpainted to retain their effectiveness.
Application and Prep Choices
If the old paint is known and in good shape: Remove old loose paint, dirt, grease, and marine growth with a power washer, brush or scraper. Wipe down with thinner/dewaxer or solvent wash. Sand with 80 grit paper. Exercise caution to avoid sanding through a barrier coat, if your boat has one. Repeat solvent wash. Clean with the thinner recommended by your paint manufacturer.
If the old paint is unknown and in good shape: Clean, remove loose paint, sand (80 grit paper) and rinse with water. Apply a tie coat primer to ensure optimum paint adhesion. Then simply apply the antifouling of your choice. Some slippery may need to be removed before applying a noncompatible paint.
If the old paint is unknown and in bad shape: Remove the old coats of antifouling paint. If the hull does not have an epoxy barrier coat this is a good time to consider applying this protection. Then proceed with painting.
Good preparation and priming are the basis for any paint job and antifouling paints are no different. Solid prep ensures good adhesion and better performance over time. Remember that most bottom paint changes color when exposed to air or water, so do not judge the color of your bottom paint on dry land. It will show its true color after a couple weeks of immersion. Don't be too alarmed by a greenish hue of bottom paint near the waterline, due to the paint's reaction with oxygen. It does not affect the effectiveness of the paint. If the look troubles you, paint the waterline with a hard antifouling paint and scrub it regularly.