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Marine Galvanic Isolator Troubles

960 Views 4 Replies 5 Participants Last post by  macmikeman
I’m a master Electrician well experienced in diagnosing residential wiring issues. I’m now living on a boat and the marina dock is plagued by zincs eroding in a very short time ( 2-3 months). most boats, including mine have galvanic isolators installed. I’m trying to tap into some fellow sparkies who have experience in these waters, so to speak.
Wouldn’t a ( assuming it's still functioning) G.I. Prevent the issue of Accelerated Zinc depletion?
My boat arrived at the marina in January 1st with mostly intact Zincs. Now they’re mostly gone.
In conversations with others on the dock it seems to be in one area so it Suggests it is miswiring on a single boat. Does that make sense?
Some of my neighbors have resorted to hanging the larger anodes over the side when tied up at the marina. ( one fellow sheepishly told me after being here a few month he had forgot about it and went out for a day sail and it almost got fouled in his prop)
Seems to me this is a bandage approach.. if there’s a way to identify the sorcery great. But if there’s a way to fully protect mt boat that’s ideal!
Any thoughts?
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· Sparks fly from my finger
2,526 Posts
Easiest thing to check for would be current on the grounding conductors in the dock electrical in both Ac and Dc. Another issue could be a chemical in the water in that area.

You could check the usage rate on the anodes if you measures the current from the anode to your boat. You could also check the voltage impressed on the boat by the galvanic system. I don’t know what the ideal voltage is for whatever metal your boat is but steel should be lower than -.8 volts to a half cell.

Oh and the depletion of the zinc anode is what provides your cathodic protection. Galvanic isolation is a coating that prevents erosion from galvanic currents not anodes.

· Registered
Retired EC and Fuel distribution contractor
4,622 Posts
Man, it's been a while since I've looked at this. From what I remember, most often this is a "hot" boat (miswired).

When you say galvanic isolator, are talking about one of those devices you install on your shore power input to block DC?

If the whole marina is suffering, then I might look for some stray current in the water. Have you checked for current on the grounds feeding the power centers?

How about a step voltage check in the water?

Did you check for voltage from the ground conductor to the water without the boat plugged in? I've always had a concern with the PoCo service using the waterway (ICW around here) as a parallel path for current back to the substation. If they have a deteriorating neutral connection in their system, I can envision current flowing through the ground system into the boat and then into the water on it's way back to the substation.

If you dive into this, may I recommend you have a written log of your findings because you will get into so much information it will be difficult to recall it all accurately.

I hope you will share your findings with us as you move through this.

· Senile Member
I make all the electrons line up for their Flu shots
37,001 Posts
She'll be fine just as soon as you get her down to Grenada..............
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