ablative Ablative coatings wear away as the boat moves through the water, exposing fresh anti-fouling. This reduces maintenance and preparation when it is time to apply additional coats. The major anti-fouling ingredient in ablative bottom paint is cuprous oxide (copper), with typical percentages ranging from 25 to 76 percent. Ablative coatings are affected more by water temperature, salinity and alkalinity than are controlled depletion polymers (CDPs), and generally wear away faster. They are less expensive than CDPs and provide excellent anti-fouling protection.
biocide The active compounds that repel fouling. The most common biocides are copper compounds such as cuprous oxide or metal copper.
Biolux Organic biocide booster from Interlux that controls slime. Slime and algae feed on sunlight, and anti-foulings that use Biolux prevent growth by acting like sunscreen, according to Interlux.
CDP (controlled depletion polymers) or CSC (controlled solubility copolymers) Jim Seidel of Interlux describes these types of anti-fouling as partially soluble, which means that as water passes across the surface of the coating, it wears down much like a bar of soap would wear away. The physical action of the water over the surface steadily reduces the thickness of the paint at a controlled rate, which results in fresh biocide throughout the season. For this reason these coatings can be used in areas of highest fouling. Since biocides are chemically bound to controlled solubility copolymers, boats with this type of coating can be hauled and relaunched without repainting as the longevity of the paint is related to its thickness.
hard Also referred to as contact leaching paints, these coatings dry to a porous film that is parted with biocides, which leach out on contact with water to prevent fouling. The leaching is chemically designed to release biocide throughout the season, but the amount will steadily decrease until there isn’t enough to maintain protection. Once the biocide is exhausted, the hard paint film remains. Hard bottom paints don’t retain their anti-fouling ability out of the water, so boats with this type of coating cannot be hauled and relaunched without repainting. One of the main benefits of hard anti-fouling is its resistance to abrasion and rubbing. This makes it ideal for fast powerboats, racing sailboats or boats whose bottoms are scrubbed regularly.
Irgarol An organic booster made by Ciba Specialty Chemicals Corp. used to control slime.
modified epoxy One-part epoxy resin coatings cure by evaporation and dry to a tough, hard, reasonably smooth finish. Their less-volatile solvent concentrations keep these paints from attacking old coatings, so they can be applied over existing paint. They are durable and resist abrasion, adhere tenaciously to bare hulls and other finishes, and contain the highest biocide levels of any anti-fouling. However, they are moderately difficult to remove when worn out, gradually lose effectiveness out of water, and aren’t as smooth or quick-drying as other types of paint.
pigment Provides the color and thickness of the coating.
resin A binder that gives dried paint its mechanical properties and controls the release of the copper or other biocide. This will dictate the type of anti-fouling performance achieved.
SPC (self-polishing copolymers) These coatings work because of a controlled chemical reaction between the copolymer resin and the salt in salt water. The chemical reaction controls and sustains the release of biocides throughout the lifetime of the paint without decline, and takes place at the same rate whether the boat is under way or sitting at the dock. This type of technology previously was available only in tin-based copolymer coatings, which are restricted to boats larger than 82 feet. This new, patented type of Interlux coating is available for professional application on boats of all sizes. Not recommended for use in fresh water.
soft sloughing These paints provide dependable, lower-cost protection for cruising boats or other boats with displacement or non-planing hulls. They wear away as the boat passes through the water, and are easy to clean and remove at haulout, which prevents paint buildup. Boats with these types of coatings must be launched within 48 hours of application to retain maximum effectiveness.
solvent Holds the solids in suspension while the paint is being applied and while it is drying. Different solvents will affect the coating flow during application and drying speed.
Price list and Q&A follow..
FAQ on paint, prep and compatibility
Q: I’m moving my boat from New England to Florida. Should I change my bottom paint?
A: It depends on what you’re currently using, but if you’re using a hard paint, you might want to use one with a higher amount of copper. Northern boaters can get away with an ablative coat they can just paint over every season, but sloughing paints used in the warm water of the year-round Southern boating season will require repainting more often than with other choices. With the relatively frequent repainting required in Southern waters, removing the buildup of hard layers may make a copolymer a better choice. Snowbirds should note that the worst time for fouling in Florida typically is from December to April, due to increased oxygen in the cooler water.
Q: How many years can I get out of two or three coats of bottom paint?
A: A copolymer in New England, Long Island Sound or New Jersey should last two or three seasons depending on boat use. Chesapeake Bay-area boaters should expect two seasons. Southern boaters in the Carolinas and Florida might get 15 months of fouling protection. Some Northern boaters like to put a freshener coat on each year, but this is more for cosmetic reasons and really isn’t necessary. Ablative paints are increasingly affected by water temperature the farther south you go. The annual haulout for boats north of the Carolinas requires a fresh coat of hard paint each year. Southern boaters may get 15 to 24 months from a coat of hard paint.
Q: I’m changing my bottom paint this year and am concerned about compatibility. How do I know if I can paint over my old paint?
A: If you know what the old paint is, there are compatibility charts available from most marine paint manufacturers. If you’re not sure what the old paint is, there are paints that can be applied over nearly any other paint. If in doubt, a primer coat applied before the new paint will solve the problem. Generally speaking, applying an incompatible paint over an old coat will result in cracking, like the bottom of a dry lake, but the anti-foulant will still be effective. With vinyl anti-fouling paints, all bets are off. Vinyl paints contain ketones, very aggressive solvents that will attack the bottom coat beneath it. If vinyl paint is applied over a non-vinyl bottom coat, the entire sandwich of paints likely will lift off in sheets, in which case the vinyl coat serves as a very expensive paint remover.
Q: What kind of paint can be used on aluminum outdrives?
A: Brush and aerosol paints are available, but preparation and a good primer should be the first steps. Metal surfaces should first be cleaned with a degreaser, then sanded with 80-grit sandpaper or coarse emery cloth. A preprimer wash should follow. Primer will help minimize electrolysis on any metal drive, and is necessary for anti-fouling to adhere to aluminum. An effective, though costlier, application method is to use a brush to apply a heavy coat of anti-fouling, then use an aerosol to get at the nooks and crannies that the brush misses.
Q: Can I paint my transducer?
A: Aerosol paints specifically designed for transducers are available, but most anti-foulings can be applied. Check for warranty issues first, but most manuals from marine electronics manufacturers indicate any type of antifouling can be used, with the exception of vinyl coats, which contain ketones. The solvents used in all other anti-fouling paints aren’t aggressive toward the synthetic transducer housing. Metal transducers require a primer application before painting.
Q: Is there anything I need to do to a new hull before applying anti-fouling?
A: The most important first step is to clean the hull exceptionally well to remove the mold-release wax and any other contaminants. The next step would be to apply a primer coat. Without primer, the hull needs to be sanded with 80-grit paper, which may void the boatbuilder’s warranty.
Q: What’s the best way to apply bottom paint?
A: A fairly heavy nap (3/5-inch) solvent-resistant roller will apply a good, thick coat faster than a wide brush (5 inches or so). But beyond speed, a mistake made by boat owners looking for a smooth final coat is to use a thin roller. The result is they often don’t apply enough anti-fouling. One compromise solution is to apply paint with a heavy roller in 3-by-3-foot sections (2-by-2-foot sections may work better on breezy or hot days), then go over the section gently with a brush to smooth out the roller stipple. Few yards allow spray application of bottom coat these days.
Q: How long before launch day should I apply anti-fouling?
A: Times vary, but the clock basically is ticking as soon as a bottom coat is applied. For hard paints, 60 days maximum is normal. Bottoms coated with copolymer or ablative paints also have a 60-day maximum, but because of the way they work they can be reactivated by using a hose and scrubbing. Hulls coated with soft sloughing or rosin-based coatings should be launched within 48 to 72 hours maximum. With the exception of soft sloughing or rosin-based coatings, optimally the paint would be applied on a weekend and launched the following weekend.
Q: Should anti-fouling to be thinnedbefore application?
A: Most paints should be used straight from the can. If applied on a particularly breezy or hot day, thinning (10 percent) may be necessary to combat rapid drying. When applied to bare wood the same 10-percent thinning will help carry the copper down into the wood.
Jim Seidel, assistant marketing manager at Interlux, contributed to this Q&A.
Fiberglass Bottomkote: $99.99
Fiberglass Bottomkote ACT: $109.99
Fiberglass Bottomkote Aqua: $119.75
Micron 66: $304.99
Micron Extra: $199.99
Micron CSC: $174.99
Super Epoxycop Ablative: $109
Trilux 33: $194.99
VC Performance Epoxy: $139.99
VC 17m Extra: $44.99 (quart)
VC Offshore: $189.99
Not sold retail.
Check with boatyard for pricing.
Horizons: $34.88 (quart)
SR-21: $39.99 (quart)
Trinidad SR: $179.99
Ultima SR: $184.99
Unepoxy Plus: $114.44
West Marine CPP Plus: $89.99
West Marine PCA: $144.99
West Marine Bottom Pro Gold: $139.99
West Marine Bottom Shield: $69.99
Sources: westmarine.com, boatus.com, jamestowndistributors.com, defender.com,
boatersworld.com, and others.