Beat the Barnacles
Do you antifoul your propeller? Looking around the yard where we keep our project boat, Ostara, the consensus seemed to be “no”. Most propellers showed the telltale signs of barnacle infestation, as indeed did our three-bladed Gori folding prop. Barnacles aren‘t just unsightly, they’ll affect your propeller’s performance.
A coat of bottom paint is one way to thwart the marine critters that like to attach themselves to your propeller blades. Usually you’ll have to rough up the blades with sandpaper to provide a key for the paint to stick to, and give the blades a coat of Primocon or similar primer. If you have a saildrive, you’ll have to use a copper-free antifouling paint to minimize the chances of galvanic corrosion.
Many owners just polish their props to a mirror shine in the hope that the barnacles will fail to gain a foothold; others smear on some kind of grease (diaper rash cream is popular) as a deterrent. In warmer waters it’s no big deal to dive on your prop every so often and scrape the barnacles off, but up in frigid New England waters that’s not so appealing.
Of the various proprietary anti-barnacle compounds on the market, Pettit’s Zinc Coat Barnacle Barrier is inexpensive and has a good reputation. Forespar has a new goop called Lanocote Prop & Bottom Foul Release, based on its popular Lanocote anti-seize compound, which in turn is derived from sheep wool.
And then there is PropSpeed, a silicon-based coating from New Zealand that defies barnacles and other critters to get a toehold on its slick surface. It’s not cheap, but it has an excellent reputation. The makers aren’t saying what’s in PropSpeed, but it’s non-toxic and as green as such products can be. It was certainly worth a try, I thought.
1. The trick to getting a non-stick coating to stick to metal lies in careful preparation.
First, I had to thoroughly roughen the propeller with 60 grit sandpaper to provide a key for the ensuing coatings. It hurt to scuff up such a beautiful piece of bronze, but it’ll be easy enough to bring it back to a polish down the road. I wiped the sanding dust off with MEK and let it dry.
2. Next step is to apply the PropPrep surface cleaner—basically, this is phosphoric acid. Suitably gloved up and wearing safety goggles to protect the peepers from stray acid droplets, I brushed the product on, and then, following the instructions, wiped it off with a clean rag before it had a chance to dry. If you don’t want to splash out $99 for a half liter of this at West Marine, you can use acetone instead.
3. The etching primer is a two-part compound that needs careful mixing. It took me five minutes to stir all the settled sediment—the active ingredients—into solution, then I shook the can thoroughly to ensure it was well mixed. I then mixed it with the hardener in a 4:1 proportion. Because I only had one prop to coat and there is enough primer for two or three, I used a separate mixing container and saved the remainder.
4. I brushed the yellow etching primer mix onto the prop. It looks blotchy, but this is apparently usual. The goal is to get a thin, uniform coat over the entire prop.
5. You must brush on the clearcoat as soon as the etching primer starts to dry; as soon as you can touch the primer without it coming off on your finger, start painting on the clearcoat. This dries to a soft finish unlike any paint I’ve used.
6. The finished product. The clearcoat has dried to a soft, slightly sticky coating unlike any paint I’ve used before. I’m looking forward to seeing how it holds up to a season in the frigid New England waters.
PropSpeed comes in various sizes—the 200ml kit I used retails for $199 and was enough to coat a pair of props the size of the folding three-bladed Gori on our project boat. You can use it on propshafts, through-hulls and any other bare underwater metal.