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Old 29-05-2013, 18:15   #1
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Zinc fish attachment point

I want to hang a zinc fish, but don't have anything to clamp it to on the back of the boat that is electrically bonded. Inside the lazerette area, there is a green/yellow wire attached to the fuel filler neck that I believe goes back to the engine block.
-I plan to simply attach a wire at that point on the filler neck to a screw on the city water connection "thru-hull" point at the back of the boat and use that for the zinc fish clamp. Any issues with that plan?
-I don't have solar yet and leave the boat plugged in...I don't fully understand the "why" yet, but I've read here that this accelerates the zinc depletion...Can I flip the dock breaker off or do I need to physically disconnect the plugs?
Thanks for the help!
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Old 29-05-2013, 19:52   #2
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Re: Zinc fish attachment point

Your plan to use the filler connection bonding wire sounds like a good one. On my boat there is a hatch over the rudder post. I run the ground wire through that hatch and connect to the bonding wire on the rudder post.

Staying connected to dock power can deplete your zincs. If an adjacent boat has an internal fault where DC is leaking to ground, that voltage can follow the green ground wire on the AC system back up to the marina's power system and back down to your boat. The DC voltage on the ground will quickly eat up zincs.

Tripping the breaker won't help, because the green wire will still be connected. You have to physically disconnect the power cord.

There are two other solutions: install a galvanic isolator on your boat (good) or install an isolation transformer (best).

David
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Old 30-05-2013, 10:15   #3
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Re: Zinc fish attachment point

Adding a fish is just feeding the monster. You need to determine why your zincs are being depleted or what is causing the electrolysis.

If you are on shore power, the first line of defense is a galvanic isolator in the ground lead. Turning off the breaker won't help, it doesn't disconnect the ground lead. Unplugging the shore power cable would break the circuit but that is inconvenient.

You can get a 50 amp Galvanic Isolator for under $100 that will pay for itself in saved zincs.
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Old 30-05-2013, 10:24   #4
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Re: Zinc fish attachment point

I have both a galvanic isolator and an isolation transformer, but still use a zinc fish. My neighbor is a 100' steel yacht built in the 1930's, and I suspect that it's going to be a hot dock as long as he's afloat.

I clip my fish to the chainplates, which are bonded, but I can't image that being helpful info for someone with a Mainship.
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Old 04-06-2013, 08:58   #5
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Re: Zinc fish attachment point

All, Thanks for the advice. I put on a fresh prop zinc and wired/hung the fish as planned. I'll see what the depletion rate looks like before I take the next step and install an isolator.

On a side note, this boat seem remarkably 'zinc free' as compared to what I read from others on this forum and what my trawler/powerboat neighbors seem to have. I have only a zinc on the prop and on the thruster. There aren't any anywhere else, not even the engine (4jh4-te) as far as I am able to determine.
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