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Alan Ward
Alan Ward

Posted: Mon Jun 09, 2014 5:28pm

Post Subject: Sea Otter aluminium corrosion

Hi - we have a sea otter boat built in 2006 and have been told that we don't have to worry about corrosion. I have never been convinced and now it turns out we have a serious problem as we have a hole in our fuel tank under the water and much of the cosmetic blacking is peeling off to reveal pitting and signs of corrosion. Sea otters are fitted with galvanic isolation - I have tested the device and it seems to be working OK (readings of 0.933 & 0.912 volts). However, something is wrong and I need to know how best I can prevent future corrosion. I have asked my marina to make the repair but not to re-black the boat until we understand the problem and can stop it from re-occurring. They have suggested fitting an isolator but if the problem is not galvanic corrosion caused by the shore line connection we may be paying a lot of money without sorting the problem. Other options may be a special coatings or even anodes. At the moment we are urgently trying to contact Sea Otter for guidance but without any joy so far

Sea Otter aluminium corrosion

Posted: Mon Jun 09, 2014 5:44pm

Post Subject: Sea Otter aluminium corrosion

I suspect the problems in contacting SeaOtter may be related to reports I have seen about problems there. Galvanic isolators are not all they are cracked up to be. They can only prevent the effects of a voltage of between 1.2 and 2.1 depending upon their design. This means that if the cumulative voltage on the earth line exceeds this valve the isolator will conduct, despite any spot checks you make. This applies to the sum of any voltages for all the shore powered boats in your vicinity so a fault on any boat and the effects of radios suppression on switched mode equipment can soon add up to this value. I note that you only have 0.3 of a volt headroom before your isolator is likely to conduct. I am not convinced anodes will be very effective as Vetus sell aluminium ones. Personally I would fit an isolation transformer that can never be effected by other boats but make sure it is installed and tested by someone qualified and very experienced in doing such things. It is also possible that if you are moored close to a boat with a fault on it the fault current may be flowing through the water to your boat hull and then onto another boat without an isolator. I think that you need to find a good marine electrician and have them check the boat and advise. Try asking on the Canal World Web Forum for recommendations and advice. Tony Brooks

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