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 by releasing toxic biocides at a controlled rate. Copper compounds (cuprous oxide or cuprous thiocyanate) are most popular; and conventional thinking is that the higher the copper content, the more effective the antifouling paint.
Choosing an antifouling paint is regional, as boaters in the Great Lakes, Pacific Coast, Southeast, Gulf Coast and other regions tend to choose similarly to their neighbors in the local marina. Your choice also depends on how you use your boat and the type of paint you applied in the past (since there can be compatibility problems between some types and others). In general, softer paints can be applied over harder paints but not vice-versa. There are exceptions however, so it's always best to consult a compatibility chart. Interlux and Pettit each make a full line of excellent bottom paints, including five primary types of antifouling paints. Let's review each type.
Copolymer/Ablative Paints [back to overview]
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 haulout at the end of the season. In the spring, the paint is reactivated with a scrubbing or light sanding and you're ready for another season. This is a huge time-saver for those living in northern climates. While the percentage of copper in the paint is important for evaluating its effectiveness, copper content is not the only consideration. Controlled polishing, the technology that controls how quickly the paint wears away, is another way we measure the effectiveness in a copolymer ablative paint.
Copolymer paints, such as West Marine PCA Gold, Interlux MicronCSC and Micron Extra, 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. Pettit Hydrocoat offers the added benefit of being a water-based product with no solvents, an environmental plus, so there are fewer fumes to protect yourself from and easier clean-up using only water.
White Copper for Bright Colors [back to overview]
Two copolymer paints, Pettit Vivid and Interlux Trilux 33, use a different biocide compound, cuprous thiocyanate or white copper, that produces the brightest colors, whitest whites and blackest blacks. White copper also requires 50% less content than the heavy, dark copper used in conventional antifouling paints. Like most other paints, these types can be applied to fiberglass, wood or properly primed steel, and they are the only copper-based paints that are compatible with aluminum. Since copper and aluminum are dissimilar metals, applying a traditional copper paint directly on an aluminum hull would be disastrous. Galvanic corrosion would begin immediately and the hull would quickly deteriorate. For best results, aluminum boat owners should still prime their hull with an appropriate zinc-chromate or strontium chromate primer such as Pettit AlumaProtect before applying either Vivid or Trilux 33.
Modified Epoxy[back to overview]
If you keep your boat in the water year round you are most likely a candidate for a high-copper-content 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. Since these types of paints do not wear away, build-up will occur with each new coat and eventually your hull will need to have the coating stripped.
We have used blue Pettit Trinidad SR on our 30' Newport sailboat, kept in a year-round marina and have had great results since the last haul-out in June 2007. It's got 67% copper, and we expect at least another year of service in our moderate-fouling environment, with light scrubbing by a diver every two months (along with a check on our underwater zinc anodes). Interlux Ultra is a similar high-copper paint.
Modified epoxy paints are the economy single-season choice if you're in the Northeast or other regions where you dry-store your boat each winter. Two affordable and popular modified epoxies are West Marine BottomShield and Interlux Fiberglass Bottomkote Classic, which are budget choices compared to more sophisticated ablative paints or high-copper modified epoxies. They offer hard, durable finishes with between 28% and 35% copper content.
Composite Copper Technology (CCT) [back to overview]
Replace the core of traditional cuprous oxide in a modified epoxy paint 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. Our new West Marine BottomShield features Composite Copper Technology, which is also environmentally beneficial, releasing 25% less copper metal into the environment.
Thin-film Paints
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Freshwater locations like the Great Lakes are plagued primarily by algae, and thin film paints such as VC 17M Extra and are a good choice for these environments. They offer a super-slick Teflon® finish to keep growth from attaching to the hull, in addition to one or more biocides. These paints dry almost instantly, so you can rapidly apply several coats and launch almost immediately. Because they are so thin, they must be applied with either a solvent-resistant foam roller head cover or by spray with an airless sprayer.
Sloughing and Vinyl Paints [back to overview]
There are two other types of paints we'll mention. Neither is as popular as today's modified epoxies and ablatives, but you should still know about them, especially if you happen to buy a boat with either type on the hull. Soft or "sloughing" paints used to be very popular among cruising sailors in northerly climates because they are very economical and last for a little longer than a season. Like Ablative paints, old-style sloughing antifoulings wear away as the boat moves, so the more often the boat is used and the faster it goes, the quicker the paint wears off. Sloughing paints are very soft, so few paints can be applied over them.
Vinyl-based paints are slick, hard paints that can be burnished to provide a smooth surface preferred by owners of performance boats. Unlike thin-film Teflon paints, vinyl paints like VC Offshore can be used in salt-water, although their antifouling effectiveness is inferior to the better quality modified epoxies and ablatives. Vinyl based paints are the least compatible, as they cannot be applied over any paints other than an existing vinyl paint. Very thorough sanding is required to achieve a good bond when painting over vinyl coatings with other types.
Paint for Underwater Metal [back to overview]
Aerosol antifouling paints, our final type, are sprayed onto underwater metal such as outdrives and props, which require an alternative to cuprous oxide as the antifouling agent to avoid galvanic corrosion from metal-to-metal incompatibility. Surfaces need to be primed before the paint is applied. Interlux Prop and Drive and Pettit Alumaspray use different biocides, but both offer good protection from fouling. Alumaspray is also only available in black, but Prop and Drive is offered in three different colors plus clear.
"Boosted" with Slime-fighters [back to overview]
Today's paints often contain a second "booster" biocide that prevents algae-related slime from growing at your boat's waterline. These "slimacides" act like sunblock for your hull, screening out the UV radiation that lets slime grow. Look for slimacides on your favorite paints by their trade names of Biolux or Irgarol.
The Future: Non-Copper Paint [back to overview]
Take a look at our West Advisor on Selecting Antifouling Paint for a preview of what the future might look like. Paint manufacturers believe that ECONEA, a metal-free antifouling agent developed by a pharmaceutical company, may be 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. The product appears to offer many advantages over today's copper-based paints.
Blister Repair and Barrier Coats [back to overview]
Now is the best time to consider applying an epoxy barrier coat, and examining your fiberglass hull for blisters is a regular part of the haulout. If your boat was not built with this protection and you keep your boat in the water year round, especially if it is in a warm-water area, or if other boats of the same manufacturer or model have a history of blister problems, barrier coating makes sense as a preventative measure. One thing is certain; it is far easier to apply a barrier coat to an intact hull than to clean out and fix blisters first, and then roll on the epoxy. A barrier coat will also increase the resale value of your boat. For more details on how and why to apply a barrier coat, see our full West Advisor: Blisters and Barrier Coats.
Bottom Prep [back to overview]
If you decided to tackle the barrier coat project, a light sanding with 120-grit sandpaper after the final coat is all that is necessary to prep the boat for paint. If you are painting a new boat for the first time, wipe down the entire bottom with a good solvent wash such as Interlux 202 or Pettit Dewaxer to get rid of all mold release agents from the factory. To avoid just spreading the mold release agent over the hull, turn your cloth frequently and replace often with a clean cloth. You can then lightly sand the hull with 120-grit sandpaper or use a no sand primer instead, such as Interlux Fiberglass No-Sand Primer or Pettit Sandless Primer. However, since most of us will be recoating over a previously painted bottom, we will need to make sure the surface is prepped for another coat.
Cleaning a Dirty Hull
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Power-washing works great to remove any remaining dirt or light fouling. For heavier fouling, use a strong acid-based bottom cleaner such as MaryKate's "On-Off". Be sure to wear eye protection, a good respirator and rubber gloves, as the cleaner is very caustic.
Once the surface has dried completely, we are ready to sand. Sanding is necessary to give the old surface some "tooth" to allow the fresh paint to mechanically adhere. Bottom paints are toxic by nature and most are solvent based, so you should always try to cover exposed skin, shield your eyes and wear a respirator to avoid breathing toxic fumes. We recommend outfitting yourself with a disposable coverall suit, gloves, high quality goggles and a dual-cartridge respirator. Now get to work!
First, lay out a large tarp or dropcloth to cover the entire work area. Knock off any loose paint with a scraper and, using either a sanding block or a dustless DA sander, lightly sand the entire bottom with 80-grit sandpaper. Spend a little extra time on any high or uneven areas. Try to achieve as smooth of a surface as possible to minimize underwater drag. Work around transducers, prop shaft struts and outdrives. When you have finished sanding, wipe down the surface with a rag and some solvent wash.
Masking Off Borders [back to overview]
Next, select a masking tape that's right for the job. Some things to keep in mind when selecting a tape: General purpose tapes are only designed to be left on a surface for 24 hours or less, unless you want a lengthy job of trying to remove the tape! Select a "long-mask" tape for bottom painting, especially when you'll be applying multiple coats. 3M's 2090 "Scotch Blue Painter's Tape" is a good choice, because it's UV-stable and can be left on for up to 60 days.
Try to tape as close to the existing bootstripe as possible. Start from a natural break point in the line and draw the tape every 1.5' to 2' for a smooth, even border. Be sure to tape around transducers, prop shaft struts, through-hulls and any other metal parts, as the copper in the paint will react with the other metals and cause galvanic corrosion. 3M's Fineline tape is the best choice for when you are ready to re-paint the bootstripe (or for any other painting task where you want the cleanest possible paint line).
Applying the Paint [back to overview]
You're now ready to start painting. Select the right paint accessories to match the type of paint you are applying. Rolling works best for most bottom paint applications, and a 3/8" nap solvent-resistant roller cover is the best match for most bottom paints. Don't be tempted to try and use household-variety roller covers, brushes, or tray liners. Solvents used in bottom paints are much "hotter" than latex or oil-based household paints and will likely dissolve these applicators. (We've tried this and can speak from messy experience here!)
Thin-film paints such as VC-17M are too runny for such a heavy nap and are applied best either by rolling using a solvent-resistant foam roller cover or by spray with an airless sprayer. Make sure to get a few sizes of chip brushes to cut out around the masked areas and at the waterline. Have the paint shaken just prior to application. This will make stirring the copper back into solution much easier, because it will settle into a thick mass at the bottom of the can, making stirring a real chore. After thoroughly stirring the paint, pour into the paint tray and roll the paint evenly from one end of the boat to the other. Recoat following manufacturer recommendations regarding overcoating times, which can vary based on paint type and temperature. Most also have a maximum out-of-water time prior to launch, so be sure to consider it in your work schedule.
Once the paint is dry, remove all masking tape and clean up the area. Be sure to properly dispose of the old paint and any solvents used for clean up. If your boat is on jackstands or a cradle, painting under pads can be tricky. Depending on the drying time for the paint, you may be able to paint under the pads or bunks when the boat is on the Travel-lift for launch. Check with your yard. Some paints will dry adequately in the short time it's "in the air".
Final Thoughts [back to overview]
Completing each of the key steps for painting your boat's bottom is easy with the right knowledge base. We hope this Advisor and our companion video have helped answer your questions and helped you find the best products to do the job right the first time. Finally, for next year, consider this thought: spring weather can be unpredictable, and haul-out schedules in the yard are crowded. At season's end, when you haul out for the winter, paint the hull bottom so you'll be ready to launch in the spring, whatever the weather. Note that this only applies if you use a multi-season ablative type paint. Good luck!
If you haul your boat out for the winter, applying several coats of antifouling paint is one of the rituals of Spring Commissioning. Most boaters find bottom painting messy and tedious, but it's one of the key preventative maintenance jobs that keep your boat performing its best. A clean hull is safe, fast and efficient, and a fouled bottom cuts your top speed, damages maneuverability and lowers your fuel economy.
