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Old 23-08-2008, 18:56   #46
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Wheels,

I would expect frequency varies with what you are trying to achieve. If it is cavitation then have to go to ultrasonic ranges. That might work best for cell wall destruction of certain species. I would expect the attempt at lower frequencies first to conserve energy and help with the propagation of the sound vibration. That would be targeting cell resonation. They both could work but might not be as effective on certain species.

Not sure what is on the boat bottom. Likely some amount of dead cells. Claims to be easy to hose off. Could be live algae too but have to take the word of the author that it isn't.

Don't think vendors care audible or inaudible. Marine mammals can hear well up to 120khz, More likely reapplication for what has worked in ponds to sea growth. I agree more testing required as frequencies may need to sweep to cover a wider spectrum of buggers.

Probably use sonic system in the marina, although expect whales to hear navy boat from long way off. Todays problems may be too much noise in the water. Sad about the accident.

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Old 23-08-2008, 20:00   #47
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Hmmm... All depth finder transducers are ultrasonic, right? Some boats have transducers that shoot through their hulls. So, If this really works then why do boats with glued in hull sonar transducers still require bottom paint?

...Confused and scratching my head....
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Old 24-08-2008, 02:54   #48
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Hmmm... All depth finder transducers are ultrasonic, right? Some boats have transducers that shoot through their hulls. So, If this really works then why do boats with glued in hull sonar transducers still require bottom paint?
...Confused and scratching my head....
I don’t endorse the efficacy of Ultrasonic antifouling on boats. I think it’s bunkum.

At least some of the scientific literature on Ultrasonic Algae control suggests that “For the same input power (120 W), a lower frequency (28 kHz) was found to be more effective in decreasing the photosynthetic activity of BGA than a higher frequency (100 kHz).”

Depth Sounder Transducers for recreational and light commercial boats usually operate on frequencies between about 25 and 400 KHz, with 50 and 200 KHz being the two most common.

Depth Sounder Transducer power outputs generally range from 200 to 1,000 watts, whereas the “Boat Sure” & “Boatsonic” devices specify a Power Consumption of 20 W, or 45-50W for larger units..

I don't know, and the manufacturers don't say, how they get hulls of differing characteristics to resonate at the precise frequency (which they don't disclose) required to kill algae.

Accordingly, perhaps the Depth Sounder Transducers are too powerful, and operate at too high a frequency to be effective antifoulants.
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Old 24-08-2008, 09:44   #49
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Accordingly, perhaps the Depth Sounder Transducers are too powerful, and operate at too high a frequency to be effective antifoulants.
Considering how much crap I find growing on depth sounder transducers, I'd have to agree.
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Old 24-08-2008, 10:50   #50
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I remember in the not so distant past there was a company that used low freq. (20 hz or so) to prevent growth. I do not know if this is still around.

The high freq stuff would appear to make more sense but can one put enough energy in the hull to be effective?
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Old 24-08-2008, 13:54   #51
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that used low freq. (20 hz or so) to prevent growth.
Then we may as well just turn up the stereo and have a range of frequencies and enjoy the experience.
Hmmm, can that be an excuse to noise control officers. No it's not the stereo officer, it's my hull cleaning system.
It was briefly suggested once again somewhere above. My very first post that didn't, went into some info. I won't go back into the depth I did initially so as I keep the post short. But in essence, Ultrasonic cleaning requires a lot of power in a defined area. To make a hull "vibrate" to create bubbles would require an enormous amount of power. Not to mention the fatigue placed on materials and people. The vibration would be easily noticeable. Just put you hand on or in a sonic cleaning bath. All sounds create standing waves and Nulls. All materials that vibrate create their own resonant frequencies which add to the vibrations. Simply creating a sonic vibration (Oooh reminds me of the electric toothbrush add) is not so straight forward. Creating a sonic vibration capable of deterring marine animal growth maybe possible, but I doubt it. There are enough vibrations in hulls now from engines and growth doesn't just fall of. Plant growth I would say even less successful in deterring.
Gord, you commented on power above. Another one of those full of holes area's. Many of the sounder/fishfinders out there are using power figures that are just plain misleading. Peak to peak ratings and even worse. The ability of producing 1000WRMS of high freq energy is impossible in our everyday consumer boat budgets. 40WRMS is closer to reality. It doesn't sound like much, but the energy in sound increases with frequency. Simply put, there are more cycles per second. A cycle is energy. So the energy in 20Khz is 20,000 times "ruffly" more than the energy in only 20Hz. Energy produced means energy consumed. So even though the over all power seems low, the actual energy is very high.
And lastly, the higher the freq, the more directional the sound becomes. In fact high freq sound can be considered similar to the light output from an LED. The energy is very focused and you step outside of the "beam" quickly.
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Old 24-08-2008, 14:37   #52
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This ultra sonic anti-foul thing has all the hallmarks of being invented in Nigeria. Even the name Boat-Sure has a decidedly scammy feel to it.

Usually, I'm the sort of dill who would waste a pile of cash on that sort of crap. This thread has saved me a heap. Thank you all.

11 years ago, I tried lanolin, rubbed it all over the fresh anti foul after the local distributer advertised that a prawn trawler in Cooktown, FNQ had been "using it for years". So after finding out the hard way that barnacles just love the stuff, I can only surmise that the boys on the trawler had been using Lanolin for something other than anti-foul.
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Old 24-08-2008, 17:25   #53
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Ultrasound is a form of energy and depending on the frequency and form of delivery it can be detrimental to life forms(algae and crustaceans). I used this modality for medical diagnosis and occasionally for treatment of deep ligament,tendon ans muscle problems( the energy can build up localized heat by increasing molecular and atom motion as in microwave oven. Its hard for me to imagine how transducers are going to cover entire hull and how enough energy is to be delivered to kill or dissuade growth even with hull in water medium. Only a controlled scientific study can determine value and safety of system. I suspect some information is available but would take some research to find. Maybe practical sailor will take on the project if there is enough interest?
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Old 25-08-2008, 03:37   #54
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... Simply creating a sonic vibration (Oooh reminds me of the electric toothbrush add) is not so straight forward. Creating a sonic vibration capable of deterring marine animal growth maybe possible, but I doubt it. There are enough vibrations in hulls now from engines and growth doesn't just fall of. Plant growth I would say even less successful in deterring.
Gord, you commented on power above. Another one of those full of holes area's. Many of the sounder/fishfinders out there are using power figures that are just plain misleading. Peak to peak ratings and even worse. The ability of producing 1000WRMS of high freq energy is impossible in our everyday consumer boat budgets. 40WRMS is closer to reality. It doesn't sound like much, but the energy in sound increases with frequency. Simply put, there are more cycles per second. A cycle is energy. So the energy in 20Khz is 20,000 times "ruffly" more than the energy in only 20Hz. Energy produced means energy consumed. So even though the over all power seems low, the actual energy is very high ...
I was hoping Alan would chime in with some of his expertise.
My post was intended to spoof the manufacturer’s “technical” description.
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Old 30-09-2008, 19:40   #55
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Well - to all the disbelievers - "critters must have ears" because it works. Its been 6 weeks since fitting the unit and there is already appears to be a noticeable reduction in growth on the undersides. I will be slipping on the 17th and will post photos however at this stage - looking good. My only issue remains whether one unit is adequate for the length of vessel.

There is growth around the waterline but that is easily wiped away with a sponge.

The one added benefit that I hadnt expected is that the fish love it. At any point in time we have upwards of a dozen reasonable sized fish around the area where the ultrasound is fitted - snapper, bream ......which should make for a good bbq on days out. Might turn it off when swimming though - not sure about the sharks!

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Old 30-09-2008, 21:48   #56
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nmit5903, Good one for a change, I get very dissappointed when you pay for junk!Keep us in touch. I guess you sail the harbour? Lovely place so's the Hawksbury. Store beach, Cobblers' is nice on a hot day! Natureboy
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Old 30-09-2008, 22:00   #57
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nmit5903, yes please keep us posted, with an aluminium hull I have issues with any of the available antifouling paints, high price and not much longevity. As Nola and Reg say it is nice to hear a positive for a change.
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Old 01-10-2008, 12:51   #58
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Well if you normally get growth in 6 weeks, that is fast. Wow. Personally I think that is way to soon to come to any conclusion, but keep us posted.
I wonder if the fish attraction part is like a noise in the water like a feeding freenzy. Snapper and Breem are attracted to those kind of noises. Just a thought.
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Old 01-10-2008, 15:30   #59
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Might turn it off when swimming though - not sure about the sharks!
I wouldn't worry to much about the sharks as they'll all be busy elsewhere now, looking for someone else to sell ultrasonic algae scarers too .
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Old 01-10-2008, 16:54   #60
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Ho ho Midland One. Thanks for the reassurance.

Alan - the boat was anitifouled 12 months ago so its not so much the build up (you're right - couldnt possibly tell in just 6 weeks) but that the algae and growth that has built up over the winter when the boat has had little use is falling off in sheets of dead brown algae.

I was a sceptic and remain cautious until the boat is slipped later in Oct however the research I came up with indicated that using ultrasound to kill algae in dams and water storage is not new. It can also be used in diesel tanks. I understand that the device works on 6 frequencies that have been tested on various organisms and that research into other frequencies is ongoing. As they become available the device can be updated by the local supplier.

We keep the boat on the mooring in Pittwater. I was concerned about power usage. We have an 80W solar panel on the deck which tops up the batteries. After 6 weeks the house batteries were showing 13.1V - not bad.

All round - at this stage I'm reasonably comfortable with the 4k that it cost. More news to come after the 17th!
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