The purpose of this article is to provide information on today’s anti fouling paints as they apply to boaters in California. To create this article I have drawn from 16 years maintaining hulls, talking to our clients and research via the Internet, much of which pertains to the east coast. Fouling conditions vary widely depending on your location, my personal experience relates to where I operate: Channel Islands Harbor which is located approximately 60 miles north of Los Angeles.

Getting The Most From Your Anti Fouling Bottom Paint

Which type of paint is better, hard or soft?

From this divers perspective, the short answer is the modified epoxy, or "hard" paints. This opinion is backed by the various studies that have been conducted. Established Best Management Practices encourage avoiding soft paints in favor of hard paints and cleaning more frequently in a gentler manner. Sea Grant - Selecting Hull Paint

The build up of hard paint on a hull is commonly considered a "disadvantage" as compared with no build up on hulls painted with soft paint. The average length of time between needing to strip built up paint is 15 years for hard paint. When hard paint is stripped in a yard it can be properly disposed of.

Not needing to strip soft paint (unless changing paint types) is commonly considered an "advantage". I wouldn't consider it an advantage for the water. Hull cleaners are encouraged not to create a "cloud" when cleaning a hull, yet that cloud is the ablative paint doing exactly what it is specifically designed to do.

Best Management Practices

Pettit - maker of Trinidad, Z-Spar, Ultima and Vivid lines of marine coatings in their maintenance guide has the following recommendations; No antifouling paint can be effective under all conditions of exposure. Man made pollution and natural occurrences can adversely affect antifouling paint performance. Extreme hot and cold water temperatures, silt, dirt, oil, brackish water and even electrolysis can ruin an antifouling paint. Therefore, we strongly suggest that the bottom of the boat be checked regularly to make sure it is clean and that no growth is occurring. Lightly scrub the bottom with a soft brush to remove anything from the antifouling paint surface. Scrubbing is particularly important with boats that are idle for extended periods of time. The coating is most effective when the boat is used periodically.

There are several main types of anti fouling paints, modified epoxy or "Hard" bottom paint, Vinyl and Ablative. To understand which will provide the best return on your investment we should examine what makes anti fouling paint work. Both types of paint typically contain varying amounts of Cuprous Oxide. This copper oxide, also used in pigments and fungicides has for the most part replaced the highly toxic tin based Tributyltin or TBT. There are now concerns about increasing levels of dissolved copper being found in the boat basins and harbors of southern California. In response, the state of California has enacted stricter regulations regarding the amount of copper content allowed in anti fouling paints being sold and used in the state. In addition local communities are enacting their own measures to reduce or eliminate copper use in anti fouling. These environmental concerns are encouraging the research and development of new booster biocides that work alongside copper and non toxic alternatives to copper based paints.

Copper, or Cuprous oxide is primarily effective against hard shelled marine animals such as barnacles and keel worms. Biocide boosters such as Irgarol, zinc pyrithione and zinc omidine block photosynthesis near the water's surface restricting the growth of algae. Introduced in 2007, Econea TM is a non-metal alternative to cuprous oxide.

Hulls painted with hard epoxy “contact leaching” paints will last longer but steadily decline in effectiveness. The reason for the decline in effectiveness is in how the paint releases its antifouling biocides. When hard paint dries it creates a porous film. The biocides held in the pours then dissolve when they come in contact with water. Over time less biocide is released from the hard paint. Hard epoxy paints should not be out of the water for more than a couple of weeks else it should be lightly sanded or repainted prior to being put back in the water.

Thin-film Vinyl paints with Teflon such as Petit SR-21 and Interlux VC 17 are commonly used by performance-orientated sailors. The primary advantage of these paints is their extremely smooth and "slippery" finish, giving a very low drag hull surface. The paints use an extremely aggressive solvent, and can lift other non-vinyl paints. They are also very thin coatings, and the substrate condition will govern the smoothness of the final surface. For these reasons, this paint is commonly applied over either gel-coat or a barrier coat that has been sanded to a 150-grit finish. The anti-fouling protection is only moderate, and the paint has a typical lifespan of only one year.

If you plan to haul out, do not allow algae and other growth to dry on the hull. It will likely never be the same again. Have your diver clean the hull just prior to haul out or have it pressure washed. Keep in mind that pressure washing can blow paint chips free of the hull. Hard paints should not be applied over ablative paints without first stripping away the old paint.

Copolymer ablative paints are partially soluble, meaning they wear down as they move through the water. Ablative paints work in the same way as the copolymer ablative with one exception; they loose their effectiveness after being dry for 30 days. Ablative paints contain less copper than hard paints but release them in a more controlled manner over longer periods of time by shedding the paint itself. Similar to how a bar of soap becomes gradually smaller, ablative paints will wear thin and need to be reapplied sooner.

Although coverage may not last as long as harder paints, there is minimal build up on the hull over time. Another point to consider is when these paints begin to wear through, the growth becomes difficult to remove and the very act of removing the growth from the exposed area increases the rate at which that area enlarges. The longevity of these paints is directly related to the number of coats applied. Boats with copolymer paints can be hauled out for extended periods of time and should be the paint of choice if kept on or often put on a trailer. This type of paint can be painted over hard paints.

Here in Channel Islands and Ventura Harbors one should expect 2 – 3 years of “effective” life from quality bottom paint with proper and professional maintenance. This holds true even with ablative paints so long as they have sufficient coats applied. Professionalism from your dive service is key.

When it comes to bottom paint, ask ten people the same question and you’ll get eleven opinions. My bottom paint opinions are based on years of personally cleaning hulls, by hand and in the past with hydraulic rotary brushes also. Boat yard operators are very knowledgeable about the paints they prefer and are a reliable source of information but they do not hand clean bottom paints underwater, 5 and 6 days a week. When they observe the boats they haul out, they cannot always know for certain how well that boat was taken care of. As an example, a new client of mine was being told by his previous dive service that the bottom paint on his sailboat was in poor condition and that he needed to haul out and apply new paint. My initial service was two hours of intensive scrubbing to bring about a professionally cleaned hull. That would appear to bear out the claims of the other dive service but I knew better and predicted as much. I could tell from the look and feel and coverage of the paint that it would be much easier to keep clean from that point on and it is. The previous service was simply padding the top layer of algae away, allowing build up to occur that becomes very difficult to remove while reducing or even halting the antifouling properties of the paint altogether. So yes, the hull was in poor condition but not because of the bottom paint!

Effective longevity

The truth to getting effective longevity from any bottom paint is to keep it fairly clean of growth. When bottom paint becomes covered in slime and algae, the biocides in the paint are no longer able to inhibit new growth from forming on top. The longer growth adheres, the thicker the layer becomes and the firmer the removal technique required. A light buildup of growth equals a light touch to remove. These points are at the heart of accepted Best Management Practices concerning in water hull cleaning.

Comparing the copper content of various paints

Hard paints have a high copper load, up to 70 percent due to the delivery system of the paint. After an initial high release the amount of copper steadily declines thus the effectiveness as well. Expect 2 years of effectiveness.
Soft paints have a lower copper load, typically 40 percent. The delivery system for this category of paint allows for a steady, predictable release of copper for as long as there is paint on the hull. Standard practice in the Ventura County California area is two coats on the hull, three on the water line, leading area of the bow and the rudder. Expect 2 years of effective coverage.

Antifouling Compatibility Charts


Interlux Compatibility Chart


Petit Compatibility Chart