Electrical Systems And Aluminum Boats

All of the yachts I have sailed over the last 20 years have been simple boats with fairly minimal electrical equipment. Not one of them (even up to 80ft) had an autopilot—sail training vessels often don’t, as they are set up to be sailed “handraulically” as we say over here.

So when we approached the planning for Pèlerin, we were mindful of our desire to have a simple boat, yet at the same time capable of meeting our wish for self-sufficiency at sea or in harbour. Another factor also nagged away in the back of our minds—the risks of electrolysis with aluminum, a subject upon which we’d heard a great deal of negative comment.

There is no doubt that there are risks inherent when mixing electricity and a material like aluminum, but we reasoned that Alubat have built thousands of OVNIs over the last 30 years, and we’ve never heard of one disappearing! So we did our homework, and made a few changes, and trusted the builders to do the rest. Now that we have her afloat and working, we can make some initial comments on what we have found.

The first thing is that the wiring installation has been done with great care at the factory. OVNIs, like most alloy yachts, have a two wire insulated wiring system, which means that there is no earth to the engine or hull as in a more conventional GRP boat. Each wire goes out and returns to the positive and negative sides of the battery bank. As a result, extra care has to be taken to ensure that there can be no grounding to the structure of the boat that would set up a galvanic circuit. Every OVNI is fitted with a leak meter, which can be used to make a daily check that no stray currents are making their way to ground and thus compromising the boat. If when tested there is any sign of a leak from either the positive or the negative side, it should be possible to identify which circuit is at fault by working through every switch on the panel in turn to identify the circuit, and then setting about finding the leak itself wherever it is in the wiring.

This was very useful when it came to wiring up the new electronics such as the autopilot and the radar, as after each item was fitted the leak test could be conducted to ensure that no fault existed as a result. All electronic units had to be isolated from the hull structure during installation, once again to avoid any chance of leaks to the boat’s structure. We did, in fact, have a small problem during installation, which was traced back to a faulty AIS unit and rectified, so the leak meter is a vital component on this type of boat.

Another area which we approached with caution was the shore power circuit. Having heard of (and seen) the effects of galvanic corrosion on boats kept in some marinas, we were particularly aware that this was an area for concern for us. Not that we intend to base Pèlerin in a marina, but who knows where we may decide to overwinter her at times. We finally opted to fit an isolation transformer, a device that is virtually unknown in Britain, at least, but by all accounts is common in the USA, and should be fitted to all metal boats, not just aluminum. Of course, we may never know just how effective the transformer is—if it’s working then we should see no problems, and I don’t suppose we shall turn it off to find out otherwise! It is a heavy and costly item, though, so we hope that it will prove its worth.

So far we are well pleased with our new home. Not that we haven’t had our share of glitches, but these have been overcome with support from the Agents. We have had her out in a maximum of 30 knots of wind so far, when she was stable, comfortable and easy to handle, so we’re looking forward to our first decent passage in her very soon, when we’ll be able to report back in far greater detail on our impressions.

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Meet the Author

Colin Speedie

Colin, European Correspondent here at AAC, is a deeply experienced offshore sailor who holds a Yachtmaster licence, and a gifted photographer and talented writer who has added a whole new dimension to Attainable Adventure Cruising. In addition, since Colin and Louise are from England and had their OVNI 435, Pèlerin built in France, they bring a European perspective to our site. You can read more about Colin and Louise and their business at their website.

53 comments… add one
  • Chris A. Jan 15, 2011, 7:56 pm

    We have a Garcia 48 with an isolation transformer and a leak meter to check for stray current. This is our first aluminum boat and we are proceeding with caution to avoid the potential problems you outlined above. I came across a system called Electro-guard cathodic protection system. It appears to have a reference anode and then a separate plate to impress a current to cancel the potential detected at the reference anode…I think that is right, I am not an engineer. Sounds like noise canceling earphones for stray current and potential created by dissimilar metals.

    Anybody looked at this in detail? Using it? Don’t trust it?

    Chris A.

    • Colin Speedie Apr 12, 2011, 9:29 am

      Hi Chris

      Sorry I missed this earlier.

      This is a new one on me. It sounds, though, as if your Garcia (great boat!) has the best standard for these boats, i.e. a galvanic isolator and leak meter – basically the same set-up that we have, and has worked fine for us so far.

      Given that many of the problems occur with boats left in marinas, or where the anodes haven’t been checked and/or replaced on a regular basis, that’s an area we watch carefully. Also, if we leave the boat for any extended period we switch everything off, disconnect from the shore, and put out a suspended wire anode fore and aft, both bolted to the boat’s structure to ensure they are in proper contact to be able to do their job.

      When aboard, we check the leak meter daily. On two occasions we have discovered very minor leaks (faulty AIS unit casing), so it has done exactly what we had hoped from it.

      I’m not an engineer either, but the system you mention sounds very complicated, which (personally) wouldn’t endear it to me – but I may be wrong. Anybody out there with more knowledge?

      Kind regards


    • John Apr 12, 2011, 7:29 pm

      Hi Chris A,

      What you are writing about is an impress system. This is a unit that forces the boat’s potential (voltage) when measured against the surrounding water to safe levels for aluminum often using current from the boat’s batteries.

      Big aluminum boats use impress systems since otherwise they would need pounds and pounds of zincs. However the danger with these systems is that if anything goes wrong they have the potential to do a huge amount of damage in a very short time (days). Plus these systems, as Colin so rightly says, represent an unnecessary level of complication for a sailboat. We do not recommend them.

      Also, the system that Colin has is for testing for stray current corrosion caused by a leak from the boat’s own electrical system, not electrolysis (they are two different things). The latter is prevented by having proper zincs and making sure that all dissimilar metals immersed in salt water are isolated from the hull. To test for the latter, you need a silver/silver anode and an accurate and sensitive volt meter. Here is some more detailed information.

      And here is a source for a silver/silver reference anode.

      • Colin Speedie Apr 13, 2011, 9:04 am

        John is absolutely right regarding our leak meter – it is simply for stray current issues.

        And I made a mistake regarding our mains installation – we have an isolation transformer, not a galvanic isolator – a far more effective solution.

        Best wishes


        • George Woodward Jul 5, 2012, 4:15 am


          ” we have an isolation transformer, not a galvanic isolator – a far more effective solution.”

          So which is better for my Ovni 32?


          • Colin Speedie Jul 5, 2012, 5:36 am

            Hi George

            An isolation transformer, but it’s a big old lump to install in a 32ft boat (around 30kg).

            Much of it depends on where you keep and how you sail your boat. If she’s kept in a marina on shore power most of the time, or you tend to visit marinas, then an isolation transformer will be best.

            If you keep her on a mooring and then to anchor when you’re on the move then a galvanic isolator might do.

            Kindest regards


  • Ben Apr 10, 2011, 9:00 am

    Hi Colin and all,

    I’m starting to wonder if some of the paint detachment on Snow Petrel might be slightly stray current related. It is probably more just old epoxy and a million layers of poorly prepared antifouling, but I would like to find out more about detecting stray currents just to be sure.

    I am interested in your leak detector system, do you know who makes it. How does it work, and could a multimeter be used the same way?



    • Colin Speedie Apr 12, 2011, 9:38 am

      Hi Ben

      Paint and metal boats – what a pain. Keeping any paint attached is an endless task, and one of the few real nuisance factors involved. We’re part way through a big touch-up session, and hope (!) that we’ll do a much better job this time, as we’re in southern Portugal, where it’s (a) warm and (b) dry even in spring, a marked difference from the last few years in northern France and Cornwall.

      I’m not sure about the maker of the leak meter (VDO I think), as I’m away from the boat, but it’s a very simple unit, that detects any stray current (either + or -) down to 0.75 milliamps (according to Alubat) going to ground (i.e. the boat’s structure). Of course, it’s possible to use a multimeter, but the beauty of the leak meter is that it is there for use daily – which is how it should be.

      I’ll be back at the boat next week, and will reply again with more detail, and some photos.

      Kindest regards


  • Alan Teale Oct 17, 2011, 4:09 pm

    Hi Colin, Is your leak monitor indeed a VDO instrument, and if so could you advise the part no.? I haven’t been successful in tracking one down. Best, Alan

    • Colin Oct 18, 2011, 9:21 am

      Hi Alan

      It is indeed a VDO instrument, part of their Logic series, I believe. Unfortunately it doesn’t have a part number on it, so I can’t help you there, but I think it’s one of their custom OEM range, so maybe if you contacted them direct and asked for such a unit as supplied to Alubat, that might help.

      An alternative thought from a clever electrician friend was to install an audible alarm, that would go off whenever any electrical short took place. He reckoned such an installation would be simple.

      Best wishes


    • John Oct 18, 2011, 11:20 am

      Hi Alan and Colin,

      Colin, your friend is indeed right. I made my own with a couple of LEDs and a multi-throw switch. I connect the positive 12 volt buss to the hull through the switch and LED. If that glows then the negative side is shorted to the hull. I then connect the negative buss to the hull through the switch and LED and if that one glows the positive side is shorted to the hull.

      On damp days with high humidity the bulbs do tend to glow a little since LEDs require so little current, but one soon gets used to recognizing the difference between that and a real short.

      I don’t think I would bother with a buzzer since that would only go off in a dead short situation, whereas my system, being more sensitive, has helped us find several higher resistance shorts.

  • Alan Teale Oct 18, 2011, 12:48 pm

    Hi Colin and John, Many thanks to both of you for your respective inputs. Colin, if I have any success with VDO I will post again. That said, John’s LED system has many attractions and I suspect it may be more sensitive than the VDO metering. Kind regards to Both. Alan

  • Petter Dec 12, 2011, 11:11 am

    For those wishing to keep the electrons flowing in only the right places, here are two sources for hull isolation control instruments:

    http://electrospot.eu/hull-isolation-control-p-1769.html (mastervolt)
    [Second link is no longer available. Ed.]

    …. and as owner of an alu vessel, I will probably fit one myself in the not too distant future.

    • John Dec 12, 2011, 11:41 am

      Hi Petter,
      Great stuff, thank you. To clarify for others, on the second link you will get a multi-page PDF and need to scroll down to page 7 to find the short-to-hull warning device that Petter has found. I might even get one of these to replace my home-brewed device.

      • Giancarlo Jan 3, 2012, 12:07 pm

        Hi Alan,
        you might find also interesting
        I have experienced the Reya ,the only one avalaible in Trinidad,with good result.They all work on the same basic principle so i guess they are all pretty much the same,but with different prices ,may be depending on the numbers and colors of l e d !!

    • Alan Teale Jan 3, 2012, 8:35 am

      Dear All, Petter provided (12 December) two very useful links to proprietary twin bulb insulation monitors. Does anyone have any experience of, or any insights into these two particular products on which a rational choice could be based? Alan

      • Petter Jan 3, 2012, 10:48 am

        I do not have direct experience with these devices, as my vessel currently sorely lack them. However, this is a http://electrospot.eu/hull-isolation-control-p-1769.html Mastervolt device, and as far as brand goes I trust that they make good quality products. Another good brand is Victron Energy, but so far I have not found anything this device in their range of products.
        Here is the link to the documentation of this relatively simple device

        • Alan Teale Jan 3, 2012, 2:07 pm

          Thank you Petter and Giancarlo. I think the VDO meter on the Tyboat site must be the one that Colin has, and which I have so far been unable to source in the UK. It is clearly more costly than the simple two bulb instruments, but possibly more informative. On the one hand I feel it may be a little too informative, but without having any experience of them I wonder if the two bulb systems are similarly quantitative in use. John’s earlier post suggests they may be.

          • Colin Jan 3, 2012, 3:34 pm

            Hi Petter

            Giancarlo has achieved the impossible! I haven’t been able to find the VDO meter either, and that is the same unit we have, so well done to him.

            It is a quantitative device (although limited to 50mA + or -) and in that sense is more versatile – we like it, and VDO has a good name, so I’m glad someone has tracked it down – although why VDO should choose to hide their light under a bushel by not listing in the UK is beyond me.

            Best wishes


          • Petter Jan 3, 2012, 4:46 pm

            ….. my thinking would be that a switch (mastervolt etc) is better, i.e. no connection between battery and hull unless one flips the switch to test either pluss or minus side for leaks. If that is done at every new install and in addition daily, the rest of the time the system is electrically dead. Without knowing, it looks to me like the VDO is continously connected – and of signals immediately as a benefit.

        • John Jan 3, 2012, 7:45 pm

          Hi All,

          The the VDO gauge would be the one I would select. In fact, I just emailed Tyboat.com to see if they will send me one here in North America. I hear Petter on the worry that the VDO could be passing some current, albeit a very small amount, but that can be solved with the addition of a two pole switch.

          The Mastervolt looks to me as if it is just a simple incandescent indicator light which will show you a dead short, but won’t warn you of a high resistance leak which can be quite damaging over time. Even if the Mastervolt uses an LED, I still like the idea of the VDO’s graduated warning.

          I have been using a home brewed system for years that uses several LED’s to indicate the amount of leakage and it has caught at least four situations that an incandescent light would have missed.

          • Giancarlo Jan 3, 2012, 8:37 pm

            Ciao ,
            you are right John the VDO and the Reya seem to give a more accurate reading,i was just trying to make a joke with colors , led and $$$…..

            The Reya had some current passing even in stand by mode so i installed a switch as John suggested

            For John: if Tyboat does not ship it USA ,if you wish, i can order and ship it to you

          • John Jan 3, 2012, 9:28 pm

            Hi Giancarlo,

            Yes, got the joke, I was addressing Petter’s comment.

            That is very kind, and much appreciated. If they don’t get back to me I will take you up on it. My home built unit works, but elegant it is not!

          • Alan Teale Jan 4, 2012, 12:27 pm

            I think the Philippi monitor uses LEDs, but even so I am with John on this. The VDO stands out from the rather small crowd. Futher enquiries here in the UK lead me to conclude that it is effectively a French product. Apparently the different VDO operations around the world are closely related species rather than a single species. And seemingly they don’t talk to each other, let alone interbreed. This inevitably leads to local adaptations, and the leak meter seems to be one of them.

  • Petter Dec 27, 2011, 9:04 pm

    Hello Colin,
    As a fresh owner of an alu vessel (koopmans 43 pilothouse) I read this “blog” with great interest and appetite.
    Above you write ” Also, if we leave the boat for any period… …. and put out a suspended wire anode fore and aft, both bolted to the boat’s structure to ensure they are in proper contact to be able to do their job.”
    would you care to enlighten me – and the other readers – as to how exactely you do this; my spesific questions are; do you wire the anode to the stainless rigging or the the hull itself? If to the hull how do you attach the anode? I would expext that a copper clamp or copper wire attached to the hull would maybe cause corrosion at the attachment point??

    • Colin Dec 28, 2011, 9:05 am

      Hi Petter

      We bolt the eye on the inboard end of the wire to the boat with mild steel bolts. At the bow we attach this to the stem head fitting via a spare eye, and at the stern to our aft anchor roller. We have suffered no corrosion at either attachment point.

      We use anodes specifically designed and fabricated for the job – not cast-offs attached to wire. These anodes have a mild steel eye at the inboard end, the wire is galvanised (not stainless) and is moulded into the anode itself. The whole idea is to maximise conductivity so that the anodes can function properly.

      One word of caution – some designers have concerns about adding extra anodes (which might cause over-zincing) so it’s best to check with them before going down this route.

      Best wishes


  • Giancarlo Dec 28, 2011, 1:01 pm

    Hi Collin,
    a good instrument for testing if your hull is over protected(over zinced) is
    i made it portable to avoid the Silver chloride through hull complication.i did test it by adding extra suspended anodes and it immediatly reed the differece.
    Of course the same instruments warns you if your hull is protected or corroding.
    For leakage i started with an home made led-buzzer solution ;and later i did use Reya bargraph with good result,again i test it connecting an allmost discharged 1,5v disposable battery to the hull and the bargraph responded with the warning light.
    One curiosity , Garcia did not put ANY anodes on the hull, K&M the Ducht builder ALOT.Black magic!

    • Colin Dec 30, 2011, 9:57 am

      Hi Giancarlo

      Thanks for the useful link – This looks like a practical option.

      As for the number of anodes that different builders require, whilst I can appreciate that much of that will depend on the amount and placement of any dissimilar metals, I’d have to agree with you – it seems like a black art. Going back to the designer and builder seems to be about the only practical solution as far as I can see.

      Best wishes


  • petter Dec 29, 2011, 6:45 am

    Thanks for the quick response Colin,
    Would it be possible for you to provide a pointer as to who supplies you purpose built anodes?
    In ref to the Ciancaro´s post I may mention that the vessel is Dutch built and has two massive zinc disk attached to the rear of the hull – but nothing on the propeller or the axel. A configuration that leaves me somewhat puzzled. She has been in the brackish Ieselmeer (NL) for some years, but have now commenced on the next face of her life in salt water. Hence I now wonder whether I have to add anodes to these two under water parts.

    • Colin Dec 30, 2011, 9:54 am

      Hi Petter

      There are a number of suppliers, but one of the brands most easily found (at least in France) is Supermarine available via many big chandlers.

      Most anode manufacturers seem to make them, though, so depending on where you are it may pay you to check with your local supplier.

      Best wishes


    • Petter Jan 3, 2012, 7:30 pm

      Readers seeking anodes and hanging anodes, may find useful information and advice here:

      at the most favourable price I could locate in the uk is GBP 43.00:

      // p

    • John Jan 3, 2012, 7:57 pm

      Hi All,

      One point on zinc anodes: They are not all created equal, as understand it, quality and purity is really important.

      Having said that, since MC has custom anodes and I have only gone through one set in 20 years, I don’t know a lot about which manufactures make good anodes and which do not.

      I did have a nice chat at the London boat show with the folks at Martyr. They seemed very well informed and committed to making a quality anode, either off-the-shelf, or custom. They also do magnesium for fresh water as well as zinc.

  • John Dec 30, 2011, 11:27 am

    Hi All,

    On the issue of how much zinc to use. It really is not “black magic” although I would certainly agree that it seems that way.

    To accurately determine the correct amount of zinc you need an accurate digital volt meter and a silver/silver reference anode. You then measure the voltage of the hull and keep adding zinc until that voltage reaches .8 to 1.050 for aluminum.

    You can also do the same for the shaft and prop, which should be isolated from the hull. The protected voltage for bronze is .5 to .7.

    By the way, with zinc, more is not better. If you over zinc your boat you will blow patches of paint and actually cause corrosion.

    One other thing. If you are in brackish or fresh water, you need magnesium anodes, not zinc.

  • Giancarlo Dec 31, 2011, 7:32 am

    you are absolutely right,i did add anodes on the Garcia after checking with the Silver /silver portable meter i mention above,on the 2 rudders i could not add the anodes without welding,not very attractive with a just splashed brand new boat ,so i connected them with a wire to the hull.The saildrive was allready protected
    My ”black magic ,,was more referred to different shipyards with different truth.
    In reality i ve seen too many aluminium hulls badly corroded,eventhugh i still spend all my money on the ”floating can,,

    • John Dec 31, 2011, 12:00 pm

      Hi Giancarlo,

      Clearly you have really done zincs right!

      I really like your point “different shipyards with different truth”. The sad thing is proper anodes is just one more incidence in the boating world where good science based best practices exist, but the “professionals” have not bothered to do their home work and insist on spreading “wisdom” that is, frankly, rubbish.

      For those that want accurate information I would strongly recommend “The Boat Owner’s Guide To Corrosion” by Everett Collier.

      Like you, on “Morgan’s Cloud” we have connected the rudder post to the hull with a piece of wire so that the hull zincs protect the rudder too.

  • Colin Dec 9, 2013, 3:50 pm

    John and Colin (or others)

    We’re looking at a 7-year old French aluminum center boarder built by a well-known yard (would love a Boreal, but we’ve decided to just get out there…). The boat appears well maintained, including the electrical system. There’s a DC leak detector, of course. One thing – the boat has no isolation transformer or galvanic isolator. The shore power connects directly to the battery charger. The builder equips the boat this way and says it presents no problem. There are no other AC systems.

    The present owners cruised for two years, almost entirely on the hook, and then for the last six months they’ve been in a marina. The marina appears well maintained, the 110V systems are nowhere near the water, and neighboring boats are the opposite of derelict. However, my understanding is that while the boat’s DC system is floating, the shore power connection to the battery charger will be grounded to the boat, completing a pathway for galvanic corrosion via nearby boats.

    So, a question. Can I be reasonably comfortable buying such a boat, all else being equal, assuming the zincs and hull appear good on the survey? Or should I be wary on principle? Warm regards, Colin Farrar, [I]Mufasa[/I] Brooklin, ME

    • John Dec 10, 2013, 1:35 pm

      Hi Colin,

      As to buying this particular boat, I think that you should be fine, with a the caveat that she should be very carefully surveyed with particular attention to looking for evidence of stray current corrosion. But there is one issue: I would insist that the propeller shaft and rudder are removed during the survey to examine the state of the prop shaft tunnel and rudder shaft tube. Also, if the boat has a centre board, I would remove that and check the state of the case interior.

      I know that this recommendation will be a huge pain in the neck and expensive to implement, but stray current corrosion could easily have damaged these areas, particularly the shaft tunnel and said damage could both sink the boat and/or be very expensive to fix.

  • Colin Farrar Dec 9, 2013, 6:12 pm

    Addition to the above question: I just learned from an aluminum boat owner whom I respect that it’s common for European aluminum boats to be set up with the shore power directly to the battery charger, which is not grounded to the boat. I’ll check. This would allay my concerns. I was also advised I can get a hull thickness ultrasound during the survey.

    • John Dec 10, 2013, 1:25 pm

      Hi Colin,

      I would agree with Petter, although it is indeed common for aluminium boats built in Europe not to be fitted with an isolation transformer, it is extremely poor practice since all it takes is a week or two in a badly wired marina to do a huge amount of damage. The silly thing is that the reasons for fitting an isolation transformer are very simple and can be shown in about five minutes with a simple diagram to anyone, even those with no electrical knowledge. Therefor anyone who says they are not required on a metal boat with shore power has simply not thought about it.

      • Colin Speedie Dec 10, 2013, 3:35 pm

        Hi Colin, John

        I’d agree with John’s comments. Plenty of people do have aluminium boats in Europe without isolation transformers but that doesn’t mean they aren’t at risk. An isolation transformer, correctly installed is well worth having.

        One word of advice, though, would be to ensure that if you do fit one, the electrician knows how they should be installed, as there are differing views. A very sound French electrician checked our system and explained to me that in some cases the earth wire is still connected, in which case (he said) you might as well not bother installing the isolation transformer as its benefits are negated. In his view the earth wire should not be connected to the shore power, which means that there is no differential between the shore earth value and the boat.

        But the wiring diagram me that came with ours was contradictory, and we had quite a game getting a definitive answer (as I am NOT an electrician). So before making the decision, do check and get a definitive answer.

        As far as the boat you are looking at is concerned, judging from the use the boat has had little time in the marina, and so may well be OK, but John has (of course?) correctly identified the spots to look at.

        Best wishes


  • Petter Dec 10, 2013, 7:15 am

    @Collin Farrar: the response surprises me at bit, even though I am hardly even an electrical amateur. The reason being that while searching Europe for an alu sailing vessel a few years back, I happened to see a few. Not one of these were without an islolation transformer connected to the shore power. Also having talked the issue over with yards, I would not consider being without an isolaiton transformer on a metal vessel.

    Howerver, if the vessel to be bought is sound (not based on assumption, but rigerous checking), I would consult a ship electrician and ask what it would take to retro-fit one. If doable, the price should not be prohibitive if the vessel itself is OK.
    Hope this was of some use.

    I am the current owner of a dutch made alu sailing vessel and it has always

  • Colin Farrar Dec 10, 2013, 5:14 pm

    Thanks everyone for the clear insights and helpful suggestions, framed as always with great humility. I’ll let you know how things turn out. – Colin

  • Svein Lamark Jan 17, 2015, 9:40 am

    Hi Colin,
    In your first post on Ovni boats “Choosing a suitable boat-New versus old” I have given a more general critic of this boat. We were a group of boat owners that had a look of 10 different Ovnis as potentially buyers. Our conclusion was negative on this boat also on the electric system: No one of the boats had a main switch on the electric system (or on the fuel system). This is normal in most boats and one of the first things an inspector from a classification company will ask when checking a ship: How do you switch down the systems? This has to do with safety and I believe it is important.
    All the 10 boats had an isolation transformer of good quality, but it was installed wrong. The primary side of the transformer was connected to the hull which makes the transformer useless. It is the secondary side of the Victron transformer that is to bee connected to the hull. All 10 VHF antennas where wrongly installed and connected to the hull. In my opinion this is rather careless on an alum boat, but I do not know if all boats where built like that. Another interesting question is what happens in the long run on such a boat? We saw some corrosion around the stanchions. This corrosion can stop, but it can also increase and become a serious damage.

    • John Jan 17, 2015, 1:17 pm

      Hi Svein,

      Pretty disturbing stuff. It’s amazing how many times you see isolation transformers installed incorrectly in this way, completely negating their efficacy.

      For those that are not aware, there is a quick way to check for proper isolation transformer installation:

      1). Disconnect the shore power.
      2). Connect one probe of an ohm meter to the hull.
      3). Touch the other probe to each of the contacts on the boat’s shore power connector: Line, Neutral, Ground (Earth). All should read infinity. Any continuity indicates a screw up like the one you mention.

      I do this test on our boat every three months to check that the insulation in the isolation transformer has not failed.

      I should add that the above test only verifies correct installation on the primary (shore) side. Correct installation on the secondary side in which the Neutral and Case Ground of the transformer are connected to a common point on the hull, together with the case grounds of all shore power gear, is vital for safety.

      I wish I could say “when in doubt consult a marine electrical technician” but the sad fact is that many, perhaps most, of these “professionals” at least in North America don’t understand this stuff. Therefore the best bet I have found is to make absolutely sure that your boat is wired to ABYC specification for isolated ground systems—that’s what I did on our boat when we bought her.

      • Marc Dacey Jan 19, 2015, 1:36 pm

        John, thanks for this. You are correct that the intricacies of isolation transformers (and galvanic corrosion in general) are not as well understood as they might be. As a fellow metal boat owner, I would like to know what iso transformer you use on Morgan’s Cloud and your rationale for selecting it. I have had the Yandina model (http://www.yandina.com/galvanicIsolator.htm) in mind as I have had it recommended…but I confess some ignorance on the topic.

    • Colin Speedie Jan 23, 2015, 11:58 am

      Hi Svein
      I’m a little puzzled by your comments, but if I’m correct in understanding what you’re saying it sounds like our boat may have some differences to those you viewed.
      We have isolator switches on all of our 12v controls, and there’s an isolator box for the shore circuit in the port cockpit locker. There are shut off valves on each fuel tank, although the standard ones are not great, and I’ve fitted better ones.
      The question of the isolation transformer is interesting, and as others have noted these are often not installed correctly. I had ours fitted after delivery to be sure of correct wiring. As far as I’m aware, Ovni’s were not fitted with isolation transforms as standard (although they should be), but maybe they were for some markets?
      Again, all aftermarket electrical systems on our boat were fitted by us or chosen technicians after delivery and have worked fine.
      I’m surprised to hear of the problems you’ve had, as generally speaking the wiring is well done (at least on our boat).
      A lot better than the paintwork, anyway!
      Kind regards

  • Svein Lamark Jan 26, 2015, 12:53 pm

    Hi Colin!
    It looks like you have solved the electrical problems in your boat and that is good. I found several problems and I guess it must be different dealers that can be the explanation of the difference in equipment and installation.
    One interesting detail that learned me a lesson was the VHF antenna. The cable had a coax metal layer that was connected to the mast top. This way the case of the VHF (that had a negative load) was connected to the mast top. It is not healthy to the hull and it took me a while to find out. It is easy to fix when you know of it and if the mast is down, just remove the coax from the antenna plug. In boats in other materials this is standard installation. John has a nice post on this matter called “Double pool brakers?”
    By the way I find aluminium easy to paint and maintain. I have myself painted several alu boats with problem free results. I first wash them in acetone, then sand them like wood, then 3 layers of epoxy primer and 3 layers of epoxy paint. 20-30 years later it is still only soap and water. On one boat I had a 50 years old ice skin of alu 2mm thick and 100 M2. After 50 years the paint was ok, no corrosion, but some plates where destroyed by too hard sailing in ice. The steel construction of the wood hull and the oak hull were also ok, well protected by the alu skin. A few of the plates were getting too thin. Aluminium is a good stuff for boats.

  • Stephen Kavanagh Jun 5, 2018, 1:20 am

    I noticed that this article, originally published in 2008 was “updated” on April 1, 2018…and I’m assuming that wasn’t an “April fools joke”. However, I don’t see any comments more recent than January, 2015. There is a lot of back-and-forth about various leak detection systems, most prominently from VDO. It appears, from the comments, only the French are able to get these locally. Has anyone had any more recent luck in finding a US-Based source for a leak detection system such as the VDO? I have a Kanter 63 and I am having the shore power system replaced here in the USA this summer. This will include new isolation transformers (one for the 50 Amp and one for the 30 Amp connection), new inverters, chargers, AC electrical panel, etc. It would be a great time to have a leak monitoring system installed for the DC circuits as well. Any recent considerations or recommendations from others experienced with Aluminum boats would be appreciated. In the meantime, I am reading voraciously to come up to speed. Thanks

    • John Jun 5, 2018, 8:54 am

      Hi Stephen,

      The updated date only shows any changes we make, not comments.

      And no, I have not heard of anyone in North America stocking the VDO gauge, but the firm that sells them in France is very helpful and will ship you one. That’s what we did.

      As far as advice on Aluminium boats, we have a complete series starting with the chapter: https://www.morganscloud.com/2017/11/11/22-aluminum-boat-care-tips-part-1/

  • Dave Sep 17, 2018, 9:44 pm

    Hi Colin, we have an Ovni 435 and have tracked down a voltage regulator issue to the earth isolation solenoid on the Yanmar. It appears the solenoid relay connects the battery negative to the engine block when the ignition is on. Do you know why Alubat installs these, as from what I can see there are no glow plugs, sensors or other electrical connections that use the engine block for a return path? Thanks

    • John Sep 18, 2018, 8:03 am

      Hi Dave,

      Colin probably won’t answer, see https://www.morganscloud.com/2013/11/10/aac-comment-guide-lines/ #3

      However, I think I can help.

      The probable reason is that they have not fitted an isolated ground starter motor and/or alternator, and they have not isolated the engine from the hull and shaft. Therefore, without the solenoid the electrical system negative would be connected to the hull at all times. (As it is, it is still connected whenever the engine is running.)

      This is a bit of a kluge, but still quite common. A better solution is to isolate the engine from the hull and use all duel wire stuff on the engine.

      For more see three chapters starting here: https://www.morganscloud.com/2017/11/11/22-aluminum-boat-care-tips-part-1/

      • Dave Sep 28, 2018, 7:59 am

        Thanks John, #3 is fair enough. You are right, turns out the starter uses the engine block, but the good news is that is it, so the electrical system is isolated from the engine and hull other than when the starter is active. The alternators etc all have their own return, and are isolated from the engine.

        • John Sep 28, 2018, 9:04 am

          Hi Dave,

          Sounds good. We do the same thing with our windlass and that works fine.

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