Forums, Everything Else, Ultrasonic Antifouling

Penfold at 25/09/2009 21:53:35
Has anybody had practical experience of Ultrasonic Antifouling which I understand was launched at last years Southampton Boat Show and that there are 500 users.
Sunmaid is due to have her second dose of drying out and epoxy this winter and we were wondering if Ultrasonic is a viable system of antifouling to use on her ‘new’ clean bottom.

Richard Ritchie at 19/11/2009 17:25:18
I have always wondered what the dolphins feel about this: we give them enough of a headache already with our motors. Do the manufacturers address this?
I have been very impressed so far with my coppercoat. Seems a good solution. But only 12 months so far.

NickVBaker at 31/12/2009 16:37:58
I worked on ultrasound in the 70s when it was being investigated as a safe alternative to x-rays. We tried it out on all kinds of living materials including bacteria, plant cells, human white cells, and except at very high intensities, it had no effect genetically nor on viability. Which was very good news.
The intensity needed to get an effect in the 20- 100khz range, was around 10 – 20 watts/cm2. This lead to cavitation, – the growth and subsequent collapse of micro-bubbles during the negative and positive pressure cycle. The collapsing bubble did generate very violent mechanical action and this is used in ultrasonic cleaners. If you translate this intensity to the 11m2 of an immersed yacht, you would need about a megawatt! Even if this were for a very short pulse, it would be very difficult to achieve.
So, questions I would want to ask before spending a grand, would be (1) why does it work at such low intensities? (2) how is the energy propogated over the surface of the hull from a single transducer? (3) why do barnacles grow on my echo-sounder?
I have asked the manufacturer for references to scientific tests with proper controls on immersed surfaces, but they have not given me any. They just referred to sterilization of liquids using high intensity. I shall continue to badger them, but my advice now would be to not proceed on evidence that they have presented (on their website) so far.
So, I guess its back to the curry powder (used extensively on the East Coast!)
Nick Baker, French Herring