Wooden ship bottoms were sheathed in copper to ward off worms, barnacles, and other growth. In modern times, especially since the invention of fibreglass, we haven’t been worried about worms, but we’ve been using bottom paint infused with high concentrations of copper to keep fouling at bay. There are antifouling paints that combine copper with biocides and other antifouling agents (see How to choose antifouling paint), and a few that use other compounds and metals, like zinc, but copper is still the most widely used antifouling material. It’s simple, and it works.
Unfortunately, there are downsides to copper paint, and antifouling paint in general. If it’s a hard paint, eventually it flakes and has to be stripped away. If it’s an ablative (sloughing) paint, it can still flake if the application isn’t ideal, and it eventually releases large amounts of copper and other chemicals into the water. There are plenty of national and local regulations restricting the use of copper bottom paints.
And now the paint is getting expensive – very expensive. A gallon of premium-quality copper bottom paint can cost £200 or more, and even most “multi-season” paints are only as effective as application, locale, and boat usage permit. Some are effective for three years, some for only one.
There’s an alternative called Coppercoat, which is in many ways a return to the old concept of copper sheathing. Instead of hammered-on sheets of pure copper, it consists of a high concentration of copper powder stirred into an epoxy matrix at the time of application. It’s rolled on in multiple layers to a substantial thickness, usually about 12mm, and ends up forming, essentially, a shell on the bottom of the boat. It’s sanded before being put in the water, and that abrasion exposes a fixed layer of copper to the surrounding water.
Coppercoat has been around for over 15 years, but until relatively recently has been known mostly in the domain of larger yachts and commercial vessels. Application is not a standard do-it-yourself bottom-painting job. The bottom has to be completely stripped of old paint, either by chemical stripper or soda or nutshell blasting, and carefully prepared for the Coppercoat. The epoxy-copper is rolled on, wet-on-tacky, usually in four applications, all in one day. Temperature, time, and available manpower are important considerations. An amateur skilled in both marine paints and epoxy coatings, and who can provide the right conditions for application, can do the work and save the yard fees, but most people will prefer to have it done by a professional marine paint shop. (The Coppercoat shown in these photos was applied by Dutch Wharf Boatyard in Branford, CT.)
Because the copper does not slough away, Coppercoat acts more like a hard, smooth racing paint. Applied and maintained correctly it can reduce drag and increase speed. As with hard paints, if you want it to stay completely slick and free of slime, it will pay to sponge it off occasionally during the season.
When a Coppercoat bottom is hauled out and dried, it has a coppery-green look of bright to dull metal powder and verdigris, somewhat mottled from the original sanding. In other words, it looks like an old copper-sheathed ship bottom. If you prefer the look of red, blue, green, or black bottom paint, the Coppercoat patina may not appeal.
The upsides to Coppercoat are many. Properly applied, it can last for 10 seasons or more. Because it’s epoxy, there is no need for a separate barrier coat next to the gelcoat. It’s effective, tough, easy to maintain, and easy to repair if scratched or dinged. Over the long haul, it becomes increasingly cost-effective. And it’s probably the most environmentally friendly antifouling alternative on the market.
Coppercoat costs £66.50 for a 1-litre kit, which contains the two-part epoxy mix and a a bag of fine copper powder. The website provides a handy calculator to determine the approximate materials cost (exclusive of rollers, gloves, tape, etc). For example, a displacement or semi-displacement powerboat with a beam of 10 feet, a draft of three feet, and a waterline length of 30 feet, would need 15 kits to achieve the four coats. Add in boatyard labour rates, and it’s not a project to be taken lightly. On the other hand, the same boat would require at least two gallons of bottom paint for the usual two coats, and at today’s (and tomorrow’s) price per litre for a two-season premium ablative, the Coppercoat catches up after only four or five years. After that it draws ahead.
That’s for materials cost only. In terms of labour, for those who have suffered under more boat bottoms than they can count, the idea of a light sanding and a launch, rather than sweating for hours again with brushes, rollers, and solvent fumes… may be very compelling.
Consider Coppercoat if…
- You’re in a locale that restricts or bans copper antifouling paint, especially ablative paint.
- Your antifouling paint is old and flaky and you need to strip or soda-blast it off down to the gelcoat.
- Your underwater gelcoat needs epoxy barrier coating.
- You’re buying a new boat with an unpainted bottom and have your choice of how to cover it.
- You’re not concerned with an old-fashioned copper-verdigris look on the bottom.
- You’re planning to hold on to your boat for more than 4-5 years.
- You’re concerned about the release of too much copper and solvents into the water.
- You don’t mind an occasional swim with a mask and sponge to wipe off slime during the season.
- You’re simply tired of the hassle and expense of bottom-painting every year or so.
For more information, visit Coppercoat. For more on making the right antifouling choices, see How to choose antifouling paint and for application tips see How to prepare and apply antifouling.