Helllo guys,
in the moment I don´t have my own boat, but I´m busy with plans, architect and shipyard. One of the points I focused is the antifouling and the options to make this on a cost efficient way without need to slip the boat every few months and refresh the antifouling. But I guess the ultrasonic system is a fraud. The history of this system is based on the experiences from the submarines times at WW2. They find out that around all the sonar sensors was not so much fouling than around the complete hull of the submarine. Later few companies gone that way and build some supersonic antifouling. The funny thing is that every company explained the working of there system on different ways. So they have had no idea how it really works. The German federal environment department (Bundesumweltamt) published last year a study about supersonic antifouling systems.
You can read here:
"The use and benefits of ultrasound systems as an anti-fouling technology are still controversial. Even among the companies that offer these systems, the way they work is inconsistent. Some companies explain that they work by generating cavitation, while other providers want to avoid this because cavitation could cause damage to the hull. There are currently around 10 providers of ultrasound systems on the German and European market. A precise description of how they work, the frequencies used, energy, etc. is usually not provided.
It is now known that the cleaning effect of ultrasound systems is based on the induction of cavitation. The effect is achieved by generating microbubbles that are created when a sufficiently high, negative pressure is exerted on a liquid. Compression and decompression waves pass through the liquid very quickly. If the waves are strong enough, they can break the attractive forces in the existing molecules and create gas bubbles. When ultrasound energy flows through a liquid, the gas bubbles generated grow to a certain critical size, at which point they collapse and implode. The resulting shock energy generates the sono-chemical reactions. According to the "hot-spot theory", the collapse of the gas bubbles produces a rapid and extreme increase in temperature up to 4000 C° and a high increase in pressure, both of which cause the generation of free radicals with strong oxidative properties. Thus, at low frequencies, the physical phenomena are said to predominate, and at high frequencies, the chemical phenomena."
They tested with 4 different boats.
Hallberg Rassy 38
sailboat Hanse 350, build up 2007
saailboat Sun Odyssey 409
sailboat Hanse 445
All boats was in private use and they was protected with different antifouling coat. The result was in all cases that the ultrasonic system was not very good working. It was more easy to clean the boat hull with high pressure water later than it without the ultrasonic system. But the hull was almost covered with seagrass, vegetation, shellfish and barnacles like it was with paint only. Nobody from the 4 boat owners wanna hold the systems.
Here the German language link to this study:
www.umweltbundesamt.de
Other studies I found show that there is an effect, but you can´t protect a complete boat hull. It´s not useless, but it's not good working.