I have worked with ultrasonic technology for the last 20 years, and in my opinion, this is in the same category as those magnets that supposedly give you extra mileage.
We supply clamp-on transducers to mount on the outside of pipes, to measure flow, as well as ultrasonic level and sonic velocity analysers.
There are basically two ways to pass sound waves through or into say a boat hull, either you "inject" it like you see on those depth
transducers that can be mounted on the inside of a solid hull (no soft cores), or you can get the whole area around the transducer to resonate.
The "injection" method limits the area where the ultrasound penetrates, so no good for this application.
To get a part of boat hull to resonate, you need to find the resonant frequency, which is farly easy given todays technology.
To get the complete hull to resonate is impossible at the energy levels they operate at, and the different frequencies required.
First, hulls have reinforcements, stringers, different layups in different areas, engine
mounts, bulkheads. The resonant frequency around all these areas is different, and varies with the distance from the reinforcement.
If the hull doesn´t resonate, it will not move, if the hull doesn't move, the water
around it doesn't either, so their claim is not valid.
Our experience with fibre glass pipes shows even small air inclusions in the layup
really attenuate the signal and spoil it.
Secondly, we have had transducers, more powerful than these, mounted on big (up to >2 meter diameter) cooling
water pipes for power stations, using the lamb wave technology/ resonance system.
These are steel
pipes with a rubber lining to cut down algae and barnacle etc. growth. Lots of power is needed to get those thick hard rubber liners resonating!
They need to send divers in there at least once a year, to clean out the area around the transducers, even with the more malleable rubber lining!
Thirdly, if this worked, all the big steel
ships would be using it, as new figures show an increase in hull resistance of around 0.1% per week! So if you are burning 100 tons of fuel
per day, after a few weeks, the payback time would make this the smartest investment around.
We have used and tested ultrasonic cleaning systems for on-line sensors that need to stay clean to ensure operation. Never had a really good succes, be it soft or hard growth.
Ultrasonic cleaning of gasses on the other hand does work, but that's a completely different story...
So the old adage of "If it's too good to be true, it probably is" still holds true..
P.S. I noticed that the UK website still reccomends that you use your normal antifouling