I first installed a twin-transponder Ultra 20 system from Ultrasonic Antifouling Ltd. on my Tanton 39 cutter Lunacy in late August of 2010 (“The Ultrasonic Alternative,” February 2011). I’d been wrestling with the problem of antifouling for some time prior to this, as I don’t like to use copper-based paint on Lunacy’s aluminum hull. I had tried E-Paint ZO, a zinc-based ablative paint, for a couple of seasons but was disappointed with the results. For a boat like mine that spends a lot of time idle on a mooring, ZO worked poorly and without frequent scrubbings, Lunacy’s hull would get so foul it could barely move under power or sail.

When Ultrasonic Antifouling, based in the U.K., asked SAIL if we’d give their system a try, I immediately volunteered Lunacy as a test boat. The system, I found, was easy to install. Plastic rings are glued to solid hull surfaces inside the boat below the waterline; into these are threaded special transponders the faces of which must seat flush against the hull. When activated, the transponders transmit digital ultrasound signals that travel along the hull and disrupt the cell walls of simple organisms, such as algae, that are the base component of underwater ecosystems.

At the time I installed the Ultra 20 system, I also had Lunacy hauled (this was not required for the installation) and repainted her bottom with another zinc-based antifouling paint, Pettit’s Vivid Free. The boat thus spent the last two months of the 2010 sailing season with both a fresh coat of bottom paint and the Ultra 20 system running whenever she was idle. The results, when I hauled her for the winter two months later, were spectacular. Except for one tiny patch of green weed growth on the back of the rudder and two small bits of very light barnacle growth on the bow and rudder, the boat’s bottom was immaculate and free of slime. Considering that Lunacy’s mooring in Portland, Maine, is in a high-growth area where boat bottoms tend to get foul very quickly, I found this quite encouraging.

The big question, of course, was how well the system would work over the course of an entire season. On relaunching Lunacy in the spring of 2011, I did nothing to her bottom paint and again ran the Ultra 20 system whenever I wasn’t using her, which (alas) was most of the time. During the season, after the first couple of months had passed, I noticed that tufts of green weed were again growing on the trailing edge of her transom-hung rudder. If left alone these would quickly increase in size, but it was easy enough to reach down and pull them off by hand. Otherwise, I saw no growth at all along Lunacy’s waterline and when using the boat noticed no diminution of performance under either sail or power.

The acid test came when the boat was hauled again in early November 2011, after a full six months in the water. During that time, aside from pulling random tufts of weed off the back of the rudder, I put no effort into keeping the bottom clean and did not once have the hull scrubbed. (In prior seasons, without the Ultra 20 installed, I had to have the bottom scrubbed by a diver two or three times during the year in order to keep the boat’s performance at an acceptable level.)

Unfortunately, I wasn’t able to attend Lunacy’s haul-out last fall, but the crew at Maine Yacht Center, where I store the boat, did a good job of snapping photos before giving her a pressure wash. I had hoped, of course, that the Ultra 20 would prove a silver bullet and that the boat’s bottom would be as clean as it had been the season before. As you can see from the photos, however, this was hardly the case.

Obviously there were certain areas of the hull that experienced significant growth. All in all, however, I am pleased with these results. I spent no money on divers, yet growth was moderate enough that I never really noticed any decrease in performance, even at the very end of the season. I was especially happy to see that both the keel’s vertical surfaces and the propeller blades were clean, and I do believe there would have been much more growth without the ultrasonic system running.

I should note that Lunacy did experience an unusually high amount of zinc wastage during the season. By the time she came out her propeller shaft zinc had disappeared entirely, her prop hub zinc was almost gone, and her two large hull zincs were about 40 percent depleted. The folks at Ultrasonic assure me their system has no corrosive effects, and I really can’t think of any reason why it should. I have to assume, therefore, that the zinc wastage is due to some change in the electrical dynamic of Portland Harbor, which is quite industrialized.

I should note, too, that the Ultra 20’s electrical consumption was within advertised parameters. The two ultrasonic transponders fixed to Lunacy’s hull consumed on average about 25 amps a day, and the boat’s two solar panels and one wind turbine had no trouble feeding this demand.

This season I’ll be renewing the bottom paint and switching to Pettit’s Ultimate Eco, an Econea-based paint I’m hoping will be more effective than the zinc paints I’ve used before. Hopefully, with a stronger paint to help it out, my Ultra 20 unit will keep the boat’s bottom even cleaner this year. The worst-case scenario, I figure, is that I may have to get the bottom scrubbed once during the year in order to keep it spotless.

Ultrasonic Antifouling Ltd, +44 120 260 6185

Photos by Maine Yacht Center