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Old 26-08-2015, 08:49   #16
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Re: Zinc murderer.

Receptacle ......spellcheck did it......honest!

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Old 26-08-2015, 09:19   #17
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Re: Zinc murderer.

Another thing to check is your bonding system. Are your thru-hulls bonded? If so and there's any kind of poor connection you could be creating a battery between thru hull(s) and the prop/zincs. From previous research, it's a toss up whether or not to have a bonding system in most cases (most european boats do not while most north american boats do). However, if you do then vigilance is required to make sure the system is spotless. If there's any resistance in the system (corrosion) then in salt water you're inadvertently creating a battery which would run between the underwater metals.

Originally Posted by korrigan View Post
The galvanic isolator is a capacitive coupling designed to allow AC currents of about 60Hz to pass while blocking DC currents. The reason for this is that the water is still your ground for fault currents.

120V AC can kill you and that's why there's a third wire. The third wire is supposed to carry any current that might kill you down the wire to ground. Presumably the ground path through this wire is going have a lower impedance than you and most of the current will flow that way.

But remember this is AC current not DC current. It's an error to refer to 'serious current'. AC current of any magnitude should flow through the isolator but it's not supposed to be doing that. If it is there's a fault in your AC equipment.

Electrolysis is a DC phenomena and that's why there's an isolator. You are trying to break any DC link between the AC system ground and the water/boat ground. It's possible that for various reasons there could be a potential difference between your AC ground and the water/boat. Even a small difference will result in current flowing which will plate or deplete below the water line metals depending on which way the current is flowing.

This isn't my area of expertise but I have put some thought and reading into it and it's my opinion that it's not a simple phenomena and that what most people have to say about the subject is anecdotal. If I had to guess I would guess that less actual science has been done on this subject than people would expect.

Presumably if you have the isolator you should be Ok to remain plugged into shore power. It should be difficult to mess up your wiring. You would have to have below the waterline metal at some potential other than that of the surround water.

In the case I experienced last year I believe my issue was caused by a nearby boat who had some 'professional' wire up their bowthruster backwards (couldn't possibly do that on a metal boat!). I believe that it was proximity through the water that ruined my propeller last year not anything to do with the shore power. But I still wonder and it's all too complicated to be able to go to that guy and force him to cover my propeller even though I never had an electrolysis problem before. How do you prove it? Hire another 'professional'?
My theory was simply that the poor connections at the buss bar were allowing current which wanted to get back to the DC negative at the battery to instead follow the engine ground and finally out the prop/zincs. My isolator is spliced into the AC ground before the main breaker, so I'm assuming that any DC stray current inside the boat would not be effected by it's existence.

There may be flaws in this theory though, and I hope I'm not adding to the confusion!

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