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|ANTI-FOULING FILES: 3. Ultrasonic Installation|
|Wednesday, 29 September 2010 13:49|
One nice perk of this boat scribe game is that manufacturers are often willing to loan you kit to test on your boat. Sometimes you aren't really interested in the gear, but agree to test it anyway just to be polite. Other times you are dying to get your hands on it, as you are convinced it not only may solve some intractable boat conundrum, but will also mow your lawn, wax your car, and walk your dog as part of the bargain.
The latter accurately describes my reaction to the news that Ultrasonic Antifouling Ltd. of the UK was willing to send me some of their gear to try out on Lunacy. The timing was most propitious. Even as I was scheduling a haul-out so that I could at last (hopefully) resolve at least some of Lunacy's intractable bottom-paint problems, there came word from my print comic SAIL that they were hunting for a boat that could serve as a sonic anti-fouling guinea pig. I at once raised my hand, jumped up and down like the smartest kid in class, and volunteered Lunacy for the job.
Boats belonging to other SAIL editors, I learned, had been ruled out due to the electrical demands of the Ultrasonic system, which are not inconsiderable. According to Ultrasonic's managing director David Sothcott, the company's Ultra 10 unit, with one sonic transponder (appropriate for boats with waterline lengths up to 10 meters), will consume roughly 20 amps of power a day at 12 volts, while the Ultra 20 unit, with two transponders (for waterlines up to 20 meters), will consume about 24 amps.
This is no biggie if your boat is on a dock hooked up to shorepower. But if you're on a mooring it can be a killer UNLESS, like Lunacy, your boat is equipped with some serious alternative power capacity. Thanks to her 150-watt solar array and her Air-X wind turbine, my problem with Lunacy historically has been that her wet-cell batteries tend to get a tad too much juice when she is idle. Consequently, I often have to worry about being sure to top up the electrolyte before too much of it boils off in fruitless agitation.
Two birds, one stone!!! (I thought to myself.) With an Ultrasonic system onboard my batteries, at least, would have something do when I wasn't on the boat and maybe, just maybe, all my anti-fouling problems would also be magically solved.
How the Heck Does It Work?
A critical question, of course. Noodle around on the Internet for a while and you'll find all kinds of speculation as to how and whether ultrasonic anti-fouling really works. Sonic cleaning technology has been around for a while and is used in various applications. In what is probably the most common variation, things like jewelry and industrial parts are cleaned in special boxes filled with fluid brought to something like a cavitational boil by ultrasonic transducers. Such cavitation cleaning, however, requires too much power to be useful over a large area.
In another variation, ultrasonic energy can be pitched to disrupt the microscopic cell walls of simple single-cell organisms, such as algae, that are the base component of underwater eco-systems. The sound effectively bursts the cells, killing existing organisms and creating an environment hostile to new ones. Such technology has been successfully used to combat algae growth in large irrigation, water treatment, aquaculture, and other systems.
So why not do something like this on boats? In the past there were in fact a few attempts to market sonic marine anti-fouling systems, but none really gained any traction. What's different about Ultrasonic's new system, first introduced about four years ago, is that it is digital. It not only purportedly consumes 40% less power than older analogue systems, but is also allegedly more effective, as the digital ultrasound signals are clearer and can be transmitted on a greater range of frequencies.
According to Ultrasonic's sales manager, Nick Griffin, their transponders transmit on frequencies from 20 to 140 kHz while drawing power at rates between .2 to 1.1 amps. The frequency of 50 kHz is intentionally omitted, so that the signals won't interfere with certain high-tech 50-kHz depthsounders. The unit also obviously won't bother more garden-variety sounders that transmit on 200 kHz.
Because Ultrasonic's system does not cause any vibration or cavitation, Griffin also insists it poses no threat to any hull's laminate or paint system.
Installing the Sucker
…is actually quite easy. Well within the capacities of even ambivalent DIY boat-owners. But installation, according to the folks at Ultrasonic, is also very critical to the system's effectiveness, which is why they like to consult closely with users. Currently they are working to create a series of authorized installation centers around the world.
The two critical factors are: 1) transducer placement, as in they must be sited properly; and 2) transducer seating, as in the working face of the transducer must be completely in contact with the surface of the hull.
Because Lunacy's waterline length is almost exactly 10 meters, and because she has a large fin keel and deep rudder and keg, Dave Sothcott recommended I install an Ultra 20 unit with two transponders. At a minimum you want one transducer as close to your propeller and shaft as possible, which on Lunacy is quite easy, as they sprout directly from the back of the keel. The other transducer we decided to mount just a few inches forward of the keel. On some boats, depending on the positioning of integral bulkheads and other features, you may actually need more than two transducers.
To achieve full contact between the transducer face and the hull, the transducer must be mounted someplace where the hull's inner surface is perfectly flat. (Note, too, it must be mounted below the waterline!) On many modern fiberglass boats it will be possible to site transducers right on the centerline, which is ideal. In Lunacy's case, however, as she is a hard-chined aluminum boat with a chine seam right on her centerline, we had to offset the transducers. The aft one was set slightly to port of the centerline, the forward one to starboard.
The transducer face must also be in contact with clean solid hull material. Any paint or surface coatings must be removed, and if the hull is cored, the core in the area where the transducer will be mounted must also be removed. (Note that the system cannot be used on wood boats, as wood is not resonant enough for the sound to carry properly.)
To actually mount the transducer, all you need do is glue its mounting ring to the inside of your hull. The adhesive used must set up perfectly hard, not soft (as is the case with adhesive sealants like Sikaflex or 3M 5200). We decided to use Plexus, a methacrylite adhesive, as we did our install after Lunacy was launched and weren't sure that epoxy would set up properly with the hull immersed in cold water.
The one thing you really must watch out for when gluing the rings in place is that you don't leave any little beads of hardened glue on the inside of the ring. The surface must be perfectly fair to ensure complete contact between the hull and transducer face.
Once your glue has set, all you need do is smear the transducer face with some ultrasonic gel, screw in the transducer, run its wire and plug it into the control box (which can be mounted on any convenient vertical surface), and then wire the box in turn to your electrical panel.
Bingo. You're good to go. Below you see Lunacy's panel with its newly labelled anti-fouling switch in the "on" position. You'll note in this instance we still have about half an amp of surplus output from the panels and wind turbine (this on a vaguely overcast, not very windy day) with the Ultrasonic unit running.
When active the transponders do make a faintly audible clicking noise that some sensitive sorts might find bothersome. My plan, in any event, is to run the unit only when the boat is idle. When we're aboard and sailing around to different places, we'll keep it switched off. Both because we'll want the power it uses for ourselves, and because fouling is much less of a problem when a boat is actually moving.
Meanwhile, I'm keeping my fingers crossed that this thing actually works!
PS: For those concerned about my journalistic integrity, please don't fret. My deal with Ultrasonic is that I shall return the unit if I don't like it (minus the mounting rings, which are now permanently affixed to my bilge) and shall purchase it from them if I do at the full MSRP. (Which is not negligible, by the by. My Ultra 20 unit retails for about 1,500 British pounds; the Ultra 10 is about 800.)