Fullscreen HTML5Med Res (??MB)HTML4

Ultrasonic Anti-Fouling Unit for Boats, MkII By Leo Simpson & John Clarke Part 2: building it and fitting it to your boat If you own a boat which spends its time in the water, you’ll know what a (costly!) bane marine growth can be. Last month we introduced our new, improved Ultrasonic Anti-Fouling Unit which can significantly reduce the amount of growth on your hull – and increase the interval between slipping and cleaning. U ltrasonic anti-fouling won’t completely eliminate marine growth but it can minimise it. As we explained last month, the tiny organisms which like to attach to your hull will be actively discouraged from, well, attaching. And the larger marine plants which feed on them will go elsewhere. That’s the theory – and using our previous Ultrasonic Anti-Fouling Unit (Sept, Nov 2010) as a yardstick, the theory is well borne-out in practice. Growth-cleaning intervals can easily be doubled and even then there is less growth into the bargain, as our photos last month showed. There are only a few hull types which aren’t suitable (which we covered last month) and, somewhat surprising to us, ultrasonic anti-fouling is effective in fresh water as well as salt. We confidently expect this new, higher performance Ultrasonic Anti-Fouling Unit to be even more effective than the previous model and well worth the investment in money and time to build it and fit it to your boat. area of the circuit diagram (published last month) shaded yellow. Similarly, the component overlay diagram of Fig.5 is shaded yellow to show the extra parts for the second transducer. So if you are going to build a one-transducer version, ignore any discussion of these particular parts in the construction procedure. Assembly can begin by installing the resistors and optional PC stakes. Table 1 shows the resistor colour codes but you should also check each resistor using a digital multimeter (DMM). Note that the 220kΩ and 130kΩ resistors near the neon lamps are first covered in a 10mm length of 3mm diameter heatshrink tubing before being fitted to the PCB, to reduce the chance of electric shock if you make accidental contact with these leads. Use a hot air gun to shrink the tubing after the resistors have been soldered in place. PC stakes can then be installed for TP1 & TP2 and the Construction The Ultrasonic Anti-fouling MkII circuitry is built on a double-sided, plated through PCB coded 04104171 and measuring 158.5 x 110.5mm. This is mounted inside an IP56 sealed polycarbonate enclosure with a clear lid, measuring 171 x 121 x 55mm. Use the PCB overlay diagram, Fig.5, as a guide during construction. You can build the unit to drive one or two transducers. For the single transducer version, CON2, T2, Q3, Q4, ZD3, ZD4, D3, D4, D6 and all associated resistors and the 1nF 2kV capacitor are not required. All parts for the second transducer are depicted on the 66  Silicon Chip Unlike the earlier design, which required the ultrasonic transducer to be “potted”, the MkII version uses the Soanar YS-5606 (from Jaycar) which comes already potted. siliconchip.com.au The Ultrasonic Anti-Fouling Unit can be built to drive one or (as shown here) two ultrasonic transducers. If your craft is less than 8m long, you should be able to get away with one – in which case, the majority of components on the bottom right of this photo are not installed (see below). two TP GND points. Following these, mount the diodes, which must be orientated as shown in Fig.5. Note that there are several different diode types: 1N5819s for D1-D4 and D10; UF4007 for D5 and D6; 1N4004 for D7; BAT46 for D8 and D9; and 5.1V zener diodes for ZD1-ZD4. As with the resistors, diodes D5 and D6 should be covered in 3mm heatshrink tubing before installation. Next, install the 18-pin socket for IC1, taking care to orient it correctly. Leave IC1 out for the time being. Q1-Q5 can be fitted next. These mount horizontally onto the PCB and are secured with a 6-10mm M3 screw, star washer and nut. Bend the leads at right angles so they can be inserted into the allocated holes. Secure the tab of each Mosfet before soldering its leads. You can then fit regulator REG1, again orientated as 5819 10k 1N5819 5819 1N5819 IC1 20MHz D3* 470 ZD3 * 5.1V 2200 F 25V low ESR T1 + + + C 2017 REV.B 47k 130k S2 F1 K Q3* STP60 N F06L STP60NF06L Q4 * + 04104171 ULTRASONIC ANTIFOULING II K LED3 A FAULT 5.1V L1 470 H 5A * K LED2 A LOW BATTERY 10 5.1V * 10 5.1V 10k 100nF 5.1V ZD4* 5.1V LED1 A POWER 100nF PIC16F88 5819 Q1 S2 F1 470 22pF D4 * S1 F2 1N5819 470 22pF ZD1 10 10k 1nF S1 F2 STP60NF06L STP60NF06L 5819 3.0 D10 10k Q2 X1 1 STP60NF06L 10 F BAT46 Q5 10 5.1V BAT46 F1 3A ZD2 5.1V D1 10k 5819 12k TP2 47k D9 VR1 5k VR2 5k TP1 TPGND BAT46 22 130k 100k 470 F BAT46 D2 100nF REG1 D8 TPGND 4004 20k 4.7k 1k LP2950ACZ-5.0 1N4004 D7 100nF 100nF 2x1N5819 10 F shown in Fig.5. Bend its leads to fit the PCB pads and solder it in place. Then proceed to mount the capacitors. The electrolytic types must be oriented with the polarity shown. Make sure the 1nF MKT capacitor is placed in the position just above and to the left of ZD1. The remaining MKT capacitors are 100nF. The 1nF 2kV capacitors are installed near T1 and T2. The screw terminals can go in next. The 3-way terminals * 2200 F 25V low ESR T2 * 1nF 2kV = HIGH VOLTAGE REGION F3 D6 * * To Ultrasonic Transducer 2 S3 * 130k 130k NEON1 220k UF4007 D5 To Ultrasonic Transducer 1 S3 220k F3 UF4007 SWITCH +12V 0V 17140140 CON2 CON1 CON3 * NEON2* 1nF * 2kV * Required for second transducer Fig.5: component overlay for the two transducer version of the Ultrasonic Anti-Fouling Unit, MkII. To build the single transducer version, simply leave out all components in the light yellow section of the PCB – Q3, Q4, ZD3, ZD4, D3, D4, D6, NEON2, T2, CON2 and associated resistors/capacitors. Note the area of the PCB with a dashed red border/light pink background has high voltages on both the tracks and component leads when operating. siliconchip.com.au June 2017  67 Here’s what the PCB looks like mounted inside the waterproof polycarbonate box with external connections made . . . for CON1 and CON2 are modified to remove the centre terminal, to increase the voltage rating between the two outer contacts. Fully unscrew the centre screw and prise it out of the plastic connector. The central contact will slide out of the housing. The screw terminals are installed with the lead STEPBYSTEP FITTING GUIDE IN PICS entry toward the lower edge of the PCB. CON3 is made up of two 2-way screw terminals dovetailed together. Install it with the lead entry also toward the lower edge of the PCB. Insert the leads of inductor L1 into the PCB and secure it in place with a cable tie that wraps around the lower part A A: Roughen the bottom of the 50mm flanged nut with some coarse sandpaper. This is to give a good “key” for the adhesive to ensure it won’t vibrate loose when fixed to the boat hull. 68  Silicon Chip B B: It’s important that glue doesn’t get into the thread, where it would clog it up. Smear a good coating of Vaseline right around the threads – make sure it doesn’t get on the bottom of the flange. siliconchip.com.au . . . and here it is with the lid fitted, with the front panel label mounted inside for protection from the marine environment. of the toroid and through the two holes in the PCB. Once secured, solder the leads in place. The fuseholder for F1 can then be fitted. This requires good solder joints so use a hot soldering iron and pre-heat the fuse holder terminals. When applying solder, make sure it has adhered to both the terminals and the PCB pads. C C: Move the empty flange around the hull to determine the best transducer mounting position. When you’re happy with your choice, roughen the surface as you did the black flange – for the same reason. siliconchip.com.au Crystal X1 can be installed next, followed by trimpots VR1 and VR2. Orient the adjustment screws as shown so that clockwise rotation will give a rising voltage adjustment. The LEDs are fitted next. The green LED (LED1) is for Power indication and the two red LEDs for Low Battery and Fault indication (LED2 and LED3). The anodes are the D D: We’re recommending J-B Weld to secure the flange to the hull. It’s not that easy to buy (but Jaycar stores do stock it – Cat NA1518) and it’s not real cheap – but it sticks like the proverbial. June 2017  69 longer of the two leads and these are inserted in the LED holes marked “A” on the PCB. We positioned our LEDs so the tops were 20mm above the PCB for better visibility. You could place these higher if you wish, up to 40mm above the PCB (assuming the leads are long enough). Fit the neon indicators after slipping 5mm lengths of 6mm diameter heatshrink tubing over the leads for insulation. and voltage across the 2200µF capacitors should rise up to around 12V after a few seconds. You can adjust VR1 for the required low battery voltage setting. This is done by monitoring the voltage between TP1 and TP GND for 1/10th the required voltage. If you aren’t sure, adjust for 1.15V (a cut-out voltage of 11.5V). Then set the hysteresis by adjusting VR2 and monitoring the voltage between TP2 and TP GND. If unsure, set this to 0.5V. You can check the operation of the low battery cut-out feature now if you have access to an adjustable supply. After power up, wait about 30 seconds until the power LED flashes on and off. This indicates that Mosfets Q1-Q4 are now being driven. Slowly reduce the supply voltage until the power LED switches off and the low battery LED flashes and note the voltage. Battery voltage readings are averaged over about 10 seconds and so you need to wait this long each time after dropping the supply voltage. Once low battery shut-down has occurred, assuming it’s at the expected supply voltage, increase the supply until the circuit restarts with the power LED lit, as before, waiting 10 seconds between each adjustment. Readjust VR1 and VR2 if needed. Note that during low-battery shut-down (and while ever the fault indicator is showing), VR1 and VR2 are powered down and so these cannot be set correctly. You can only successfully set VR1 and VR2 during normal startup, when the power LED is continuously lit, or during normal operation when the power LED is flashing. Initial testing Finishing construction Before installing the transformers, do some tests on the PCB. It is safer to work on the PCB without the transformers installed, since high voltages are not being produced. Initially, adjust VR1 fully clockwise by rotating the adjustment screw by 10 turns. This sets the low battery shut-down at its highest voltage. Insert the fuse and place a short length of wire between the switch terminals for CON3. Make sure IC1 is not in its socket and connect 12V across the 0V and +12V terminals of CON3. Check that the voltage between pins 5 and 14 of the IC1 socket is close to 5V (4.975-5.025V). Switch it off, insert IC1, then re-apply power. The power LED should be lit Now switch off power and wait until the power LED goes out. Then wait for the low battery LED to stop flashing. This can take up to 30 seconds. Now check voltage across one of the 2200µF low-ESR capacitors. Only install the transformers when the capacitor voltage has dropped to below 1V. Note that the primary side of the transformer has seven pins and the secondary side has six pins, so it can only go in one way. That completes the PCB assembly. The front panel label can be downloaded from our website as a portable document file (PDF). You can print it out onto plain paper or photo paper. The panel label can also be used as a template for drilling a hole for the power switch. The label is positioned in the upper left corner of You’ll need each of these to mount the transducers in your boat: some Vaseline (petroleum jelly), some Fix-a-tap waterproof lubricant (available at plumbing suppliers) and some J-B Weld two-part epoxy (available at Jaycar stores). We do not recommend any other epoxy glues – J-B Weld really holds on even with a boat hull’s vibration and stress! E E: Apply a good layer of mixed glue all over the roughened base of the flange, again making sure you don’t get any on the thread. You have quite a while before it starts to cure so take your time! 70  Silicon Chip F F: It’s almost inevitable that there will be some J-B Weld oozing out from under the flange. The secret: apply only as much pressure as is really needed to ensure the glue spreads right around, then wipe any excess off before it sets. siliconchip.com.au the lid and goes inside the lid so it is protected from water. It can be attached with a mist of spray glue, with clear tape or with a clear silicone sealant covering the top of the label. The hole for switch S1 is cut out of the panel label using a sharp hobby knife. Holes are required in one side of the box for the power lead cable gland and for the sockets for connection to the ultrasonic transducers. Secure the PCB into the box with M3 x 6mm screws before mounting the sockets and cable gland for the power lead. Wire up the sockets, switch and supply leads as shown in Fig.5 and the internal photos. Use 70-80mm lengths of mains-rated wire from CON1/CON2 to the panel-mount sockets. Insulate the connections at the socket end with heatshrink tubing. Attach the switch to CON3 and wire a suitable length of power cable that will go to the battery, to CON3. When fitting the lid, use the neoprene seal and four stainless screws which came with it. Installation in the boat For installation, you need a few extra parts, including a 50mm BSP flanged back-nut for each transducer. This is secured to the hull using J-B Weld 2-part epoxy (Jaycar NA1518), providing an anchor for the transducer that screws into the flanged back-nut Additionally, “Fix-A-Tap” waterproof lubricant is required. The back-nut and lubricant are available from plumbing suppliers. You will also need a tub or tube of Vaseline (aka petroleum jelly). The Ultrasonic Anti-fouling MkII case needs to be mounted on a bulkhead or other position where it is not likely to be splashed or immersed in any water which may be in the bilge. The encapsulated transducer or transducers must be installed inside the hull. For a single transducer, mount it near the running gear (ie, propellers and rudders). Where two transducers are used, one is placed near the running gear and the other toward the bow of the boat. Catamarans will require one transducer per hull, both placed near the running gear. First, you must find a suitable flat section of the hull and on many boats – this will not be easy. Try temporarily positioning the flanged back-nut in a number of positions to get the best spot. G G: Once set (24 hours +), the transducer assembly is screwed into position with a good big dollop of Fix-A-Tap lubricant on the face. But before doing so, wind it anticlockwise a number of turns. siliconchip.com.au Radio, TV & Hobbies April 1939-March 1965 The complete archive on DVD: every article to enjoyonce again  Every issue individually archived by month and year  Complete with index for each year – a must-have for anyone interested in electronics. This remarkable archival collection spans nearly three decades of Australia’s own Radio & Hobbies and Radio, TV & Hobbies magazines,from April 1939 right through to the final issue in March 1965. Every article is scanned into PDF format ready to read and reread at your leisure on your home computer (obviously, a computer with a DVD-ROM is required, along with Acrobat Reader 6 or later (Acrobat Reader is a free download from Adobe). For history buffs, it’s worth its weight in gold. For anyone with even the vaguest interest in Australia’s radio and television history (and much more) what could be better? For students, this archive gives an extraordinary ILICON HIP insight into the amazing breakthroughs in radio NB: requires a computer and electronics following the war years (and with DVD reader to view speaking of the war, R&H had some of the best – will not play on a propaganda you’re ever likely to see!) standard audio/Video This is one DVD which you must have in your DVD player. collection! ONLY $ 00 62 plus P&P Only available from S C ORDER ONLINE NOW AT WWW.SILICONCHIP.COM.AU Having found a good position, roughen the face of the flanged back-nut using coarse sandpaper and a sanding block, as shown in photo A. You want a good “key” for the epoxy resin. Also use the sandpaper and sanding block to thoroughly scour the hull position where the flange is to be mounted. Photo C shows the flanged back-nut temporarily in position on the hull after it has been sanded. It is essential that the mounting area for the flange is clean and dry, and free from dust and grease. Also, there should be no possibility of exposure to bilge water while the epoxy resin is curing. When ready, mix a quantity of the J-B Weld High-Temperature 2-part epoxy resin. Do not H H: The location for the driver unit is just as important as the transducer. It must be one which can NEVER interfere with any boat operation and one which won’t be stepped on if you need to get into the area. June 2017  71 SILICON CHIP use Araldite or any other epoxies. We want to be Power www.siliconchip.com.au sure of a reliable long-term bond to the hull which Low Battery won’t let go with constant ultrasonic, engine and propeller vibration. (see Fault Photo E below). Power Apply a liberal coating of petroleum jelly (or Vaseline) to the thread of the flanged back-nut, as in pic B. We don’t want any epoxy resin to adhere to the threads, otherwise, the flange will not be usable. Apply the mixed epoxy resin to the roughened surface of the flange, as in photo E. Then press it down onto the previously prepared section of the hull. Leave it to set for 24 hours, or longer in cold temperatures. Refer Driver 2 Driver 1 to the instructions supplied with the J-B Weld Same-size front panel artwork. You can copy this or download it from siliconchip.com.au (as a PDF), print it and then secure it to the underside of the case clear lid, to protect it from adhesive. Some adhesive will moisture and damage. A mist of spray glue (available at stationery stores) will secure this to probably ooze out from the lid. The only hole required is that for the power switch – cut this with a sharp knife. under the flange. This doesn’t matter too much, apart from aesthetics. Inside, between the engine compartment and the lazarette. It is though, it should be carefully cleaned away without getmost important that the ultrasonic driver unit is mounted ting it on the thread of the flanged back-nut. That’s so that above any likely spray or splashes from water in the bilge. the transducer (when fitted) will not sit proud of the hull. On no account should you drill holes in the hull to mount the ultrasonic driver. Photo I overleaf shows the ultrasonic Installing the driver unit driver being mounted in place. You must use AS316-grade The next step is to install the ultrasonic driver unit. Its stainless steel screws; anything else will quickly corrode. IP65 plastic case has internal provision for four mounting Having mounted the ultrasonic driver in place, you are screws, near the screws which attach the lid. To fit them, you ready to install the encapsulated transducer or transducneed to remove the transparent lid of the case and position ers to their flanged back-nut the unit in the spot where it is to be mounted. Preferably, it Inevitably, this will involve running cable through parts should be on a vertical bulkhead above the waterline, say of the boat structure. ULTRASONIC ANTI-FOULING UNIT Mk II I J I: Use the case itself (with the lid off!) as a template to mark your drilling positions, then move the case and drill the holes to mount the driver electronics. J: Use good quality marine stainless steel screws for securing the case to its mounting position. A power screwdriver is a good idea here: we didn’t have the right bit and screwing into the fibreglass was really tough going. 72  Silicon Chip siliconchip.com.au If you can run the cable next to existing cable, so much the better. Lace or tie the cable into position where possible. It should not be allowed to flap about or hang in loose loops. Again, remember that boats experience severe vibration and we don’t want the cable to fail in the long term; see photo K below. You may have to drill holes in bulkheads to run the transducer cable through. If so, smooth off rough edges and fit suitable grommets to protect the cable from chafing. When the J-B Weld has cured, we can return to the transducer mounting. First, liberally coat the face of the encapsulated transducer with a non-hardening grease. We suggest “Fix-A-Tap” waterproof lubricant which can be readily obtained from hardware stores. This is applied to fill any voids when the transducer housing is screwed down into the flange. Before screwing in the transducer, twist it anti-clockwise for the same number of turns as it takes to screw it in so that when the transducer is installed, the cable is in its natural (untwisted) position. Do not over-tighten it but make sure that it is tight enough that it is not likely to shake loose over time. Then make sure that the transducer cable is neatly routed and cannot possibly interfere with the operation of any moveable parts such as the rudder gear. Finally, you need to make the supply connections to the house battery. Again, lace and anchor the supply cable securely. There is no need for an in-line fuse since there is already a 3A fuse within the Ultrasonic Anti-fouling MkII unit. Must nots The electrical systems of boats are not nice places for electronic devices. Very high spike voltages can be generated by solenoids, electric winches, starter motors and particularly from bow and stern thrusters which pull very high currents. With this in mind, you must connect to the ultrasonic anti-fouling unit directly to the terminals of the house battery and not somewhere else in the harness where it might be subjected to spike voltages from anchor winches, solenoids or any other nasties. We know of one user who connected the previous version of the ultrasonic anti-fouling K unit across the starter motor terminals – it did not live long! More importantly, don’t even think about running your ultrasonic anti-fouling unit from the batteries for your bow and stern thrusters. On our own prototype unit, our trusty boat electrician thought he was doing us a favour by connecting the anti-fouling unit to the much larger battery for the stern thruster. We don’t know how long it lasted before the supply input components failed. Don’t do it! Note that since the unit is intended to run continuously, the battery needs to be kept charged. Preferably, a 3-state charger should be used powered via mains power (if shore power is available), solar panels or a wind turbine. When power is applied to the Anti-fouling unit, the green power LED should light. After about 30 seconds, this LED should flash and the neon indicators will flash in unison, to indicate that the transducer(s) are being driven. Where do you get a kit of parts? K: after mounting, connect to an appropriate battery (one that receives shore power or solar panel charging). Dress the leads so that they can’t move around (remember that there is severe vibration present). siliconchip.com.au The Ultrasonic Anti-fouling Unit MkII has been developed in conjunction with Jaycar Electronics and will not be available from any other suppliers. Kits should be available from all Jaycar stores and some resellers from this month. Pricing is as follows: SINGLE TRANSDUCER KIT: (Cat KC5535) – $249.00* SECOND TRANSDUCER KIT: (Cat KC5536) – $169.00** * Single transducer kits contain only those components necessary to build a single transducer unit. This includes the waterproof case and one transducer. They DO NOT include J-B Weld, Vaseline or waterproof lubricant **Second transducer kits contain the second transducer plus Q3, Q4, ZD3, ZD4, D3, D4, D6, NEON 2, T2, CON2 and associated resistors/capacitors, as shown on the circuit and PCB. June 2017  73 Ultrasonic Anti-fouling FAQs Q: How big a boat can the unit handle? A: The single transducer design and driver presented here is suitable for boats up to 8 metres long. Longer boats, say up to 14 metres, will require two transducers. Boats bigger than 15 metres, say up to 20 metres, will require at least three and maybe four transducers and drivers. Catamarans up to 10 metres long will require a separate transducer and driver unit for each hull. Q: Do I need to cut a hole in the hull for the transducer? A: You must not do this or do anything else to prejudice the integrity of the boat’s hull. This is particularly important for boats with fibreglass or composite (sandwich) construction. The encapsulated transducer is mounted on a flat surface inside the hull. For a boat up to 8 metres, the transducer should be mounted near the running gear (ie, propellers & rudders) so that it offers maximum protection from marine growth. For longer boats, fit one transduder near the running gear and the other closer to the bow. Q: Is ultrasonic anti-fouling suitable for all boats? A: No. Ultrasonic anti-fouling relies on one or more transducers mounted inside the hull to excite it at various frequencies in order to disrupt the cell structure of algae. It works well with metal hulls such as aluminium and with fibreglass hulls. It does not work with timber hulls as the timber is not a good conductor of ultrasonic energy. The same comment applies to ferro-cement or fibreglass hulls with a balsa sandwich or other composite construction (eg, closed-cell PVC foam). Q: Is it necessary for the boat’s hull to be cleaned of marine growth and conventionally anti-fouled before the ultrasonic antifouling system is installed? A: Yes. Ultrasonic anti-fouling is unlikely to kill shell fish or molluscs already attached to the hull. Nor will it cause them to detach from the hull. Hence, there is no alternative to having the hull water-blasted to clean off all existing marine growth. And if it is already on the slips for such cleaning and other maintenance such as servicing outboard legs and replacing sacrificial anodes, it makes sense to have conventional anti-fouling paint applied, al74  Silicon Chip though this may be regarded as optional. We should also emphasise that, no matter how effective ultrasonic anti-fouling may be in keeping the hull clean of marine growth, it will still be necessary to do regular maintenance such as the servicing of outboard legs (in case of boats with inboard/outboard motors) and replacing sacrificial anodes. Q: Does the ultrasonic anti-fouling unit present a risk of electric shock? A: No. As stated in the circuit description, the ultrasonic transducer is driven with peak voltages up to 800V. If you make direct contact with the circuit or the ultrasonic transducer there is a very high probability that you will receive a severe electric shock. That is why the transducer itself must be completely encapsulated in a plastic fitting. This prevents anyone from getting a shock from the system. Q: Will ultrasonic anti-fouling keep propellers, rudders and other “running gear” free of marine growth or is it still necessary to use anti-fouling compounds such as PropSpeed? A: Ultrasonic anti-fouling will help keep props and rudders free of marine growth but it won’t necessarily be the complete answer. Our experience is that PropSpeed is still worthwhile. Q: Does ultrasonic anti-fouling cause increased electrolytic leakage currents (electrolysis) and thereby increase corrosion on boats? A: No. The ultrasonic transducer and driver unit are installed entirely within the hull of the boat and the ultrasonic transducer itself is transformer driven and is completely encapsulated to provide a high degree of insulation. There should be no leakage currents at all. Q: Is ultrasonic anti-fouling equipment likely to cause damage to the hull of a boat, especially those of fibreglass construction? Will it cause osmosis or de-lamination? A: We know of no research into this topic and while it could be suggested that the continuous, albeit very lowpower, ultrasonic vibration of the hull could lead to delamination, such ultrasonic vibration is extremely low in amplitude compared with the severe hull vibration caused by propellers and diesel or petrol motors when boats are operating at high power, especially when “on the plane”. siliconchip.com.au Since we published our first Ultrasonic Anti-fouling unit in 2010, we have had a great deal of feedback and lots of questions. Here are the answers. Furthermore, hulls are placed under very high stresses when boats are being pounded by heavy seas or are repeatedly slammed though waves or hitting wakes of other boats at speed. Many older fibreglass boats, say more than 25 years old, can be subject to osmosis and de-lamination. Repairs are routine but expensive to carry out and the boat must be out of the water for many months to ensure that any water trapped in hull laminations is removed. If a boat was fitted with ultrasonic anti-fouling and after years of use, there is subsequent evidence of hull osmosis or de-lamination, it would be impossible to determine if it were caused by normal wear and tear or other causes. Ultrasonic anti-fouling is routinely fitted to brand new boats but anyone contemplating such an installation would be wise to check that hull warranties are not invalidated. We make no warranties that ultrasonic antifouling does not cause hull damage. Q: Does ultrasonic anti-fouling harm fish or marine mammals? A: This system causes no harm to fish or to marine mammals. Fish cannot hear it and while marine mammals certainly can perceive and respond to ultrasonic signals, they are not harmed in any way by the relatively low power levels which are likely to be radiated by the hull of the boat. Furthermore, the signal levels are much lower than those directly radiated by depth sounders and fish finders. Q: Will my boat batteries be damaged by the ultrasonic driver unit? A: No. The ultrasonic driver circuitry described last month incorporates battery protection. If the battery is discharged to 11.5V, the circuit is disabled and will not resume operation until the battery is recharged. However, since the ultrasonic anti-fouling driver is designed to operate continuously, the battery supplying it will need to be on permanent float charge. This will require 230VAC shore power if you are fortunate enough to have your boat in a pen or marina berth. If your boat is on a swing mooring or is otherwise without shore power, then a solar panel and suitable charger will be needed to keep the battery up to charge. Q: How big a solar panel will be required to keep the battery sufficiently charged? A: The continuous power drain of the ultrasonic driver is about 5W or less for one transducer and less and 9W siliconchip.com.au for a 2-transducer version, depending on the actual supply (the peak powers applied to the transducers are much higher, at around 40W or more). To provide this level of power on a continuous basis, you will need a solar panel installation of at least 20W. Many boats on swing moorings would already have such a solar panel but it would need to be augmented by at least another 20W to be sure that the battery is fully charged during periods of bad weather or in winter when there are less hours of sunlight. Q: Will I be able to hear the ultrasonic anti-fouling unit in operation, especially at night when the water is very still? A: Probably not. Unless you are a bat(!), you cannot hear ultrasonic frequencies directly. However, the transducers and the driving transformers do emit high frequencies and clicks at low levels. These are actually sub-harmonics of the ultrasonic signals and are most evident as the frequencies are continuously shifted up and down over the operating spectrum. However, once the unit is installed, you will only be able to hear these sounds, if at all, by placing your ear directly over the ultrasonic driver or over the transducer. You might also be able to feel some slight vibration of the transducer itself. On the other hand, divers underneath boats fitted with ultrasonic antifouling often report unpleasant pressure sensations in the ears. So if you have a diver underneath the boat for any reason, turn off the anti-fouling unit. Just remember to turn it back on when the job is finished! Q: Will the ultrasonic anti-fouling cause interference to radio operation on my boat? A: If you place a portable AM radio on top of the ultrasonic anti-fouling driver unit, you should be able to hear evidence of its operation as a continuously shifting squeal. However, at even small distances away from the driver, such interference should be negligible. No interference will be caused to marine radio communications or to broadcast FM or TV reception, or to digital TV or DAB+ reception. Q: Will the ultrasonic anti-fouling unit interfere with the operation of depth sounders or fish finders? A: No. SC JJune une 2017  75 2017  75