Now I am in a position to answer my own question (or maybe not), thanks to an article in this month's Yachting Monthly.
The ultrasonic device tested was the Ultra 10
. It sells in the UK for £949.00 incl. 17.5% VAT. The unit, according to the manufacturers, has a power consumption of 0.7 amps maximum @ 12vdc (and probably minimum too), which corresponds to the article's claim of "12A every 24 hours", which is a rather strange way of expressing power consumption.
The test, performed on one boat only, came to the conclusion that, "there was a clear reduction of slime around her hull, rudder, prop shaft and bow compared with the previous year". However, as I see it, the test results are not valid as not only was the Ultra 10 used but the boat was also anti-fouled and anti-fouled with a different anti-fouling than previously. All-in-all, a very inconclusive and unscientific test. One should also take into account the fact that the test was carried out in the English Channel rather than in really high-growth areas, i.e. warmer waters with strong sunlight.
Finally, the article states that Ultrasonic Antifouling's director, David Sothcott, says: "Traditional antifoul is still a good idea". So, why do we need this product if we still have the glorious job of anti-fouling, power-washing and scraping?
Aye // Stephen