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Old 23-10-2018, 03:38   #1
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Location: Minnesota / Florida
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Through Hull Electrolysis & Bonding

just need a little help understanding this (i know enough to be dangerous). i visited a boat last weekend that seems to have some electrolysis issues i.e. it states that it has had a new prop and prop shaft, and the new-ish zinks were the correct shape but crumbled when touched. so guessing they were fitted with the new shaft and prop and slowly in the dock disintegrated the softer parts and leaving a matrix. i also noted that none of the seacocks worked or the handles were turning loosely. The boat had water up to just under the floor boards (boards were rotten). none of the seacocks were bonded, i didn't see much evidence of bonding at all. so my understanding of the electrolysis in boats is that the stray current needs to conduct through something to ground. would the standing water in the boat do this, i.e. loose wire in the bilge, through the standing water through the through hull and to ground causing damage? the boat was plugged in and the charger active. bilge pumps were switched off.

needless to say a walked away from the boat but it was a very expensive exercise.
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Old 23-10-2018, 04:49   #2
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Re: Through Hull Electrolysis & Bonding

To your specific question, it could, most certainly, particularly if it was salt water.

As to whether to bond your boat or not there are two schools of thought on this. I've heard experienced marine mechanics with decades of observations make credible arguments on both sides.

In the boat you looked at it's impossible to tell what's going on without more information. How old were the zincs? If very recent, sitting at a marina, the culprit could have been stray current from another boat or the dock electric. You'd need to get to work with a multimeter to determine what was really going on.

The water in the bilge could have been from leaks through the deck. I see you're in Minnesota so could be wood rotting fresh water from either above or below. If the boat were in salt water rotting wood would point to a fresh water leak of some sort.
"Having a yacht is reason for being more cheerful than most." -Kurt Vonnegut
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Old 23-10-2018, 10:13   #3
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Re: Through Hull Electrolysis & Bonding

Suijin the Boat was in salt water, i never tested the bilge water it was a bit too brown and smelly. i'm not too sure how long the zinks had been on there just that the prop and shaft had been changed. i was just wondering if the circuit from... shore power-->charger-->12v circuit-->water-->through hull-->ground was feasible. there were no other zinks on the boat just the prop shaft.
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Old 23-10-2018, 10:27   #4
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Re: Through Hull Electrolysis & Bonding

If this was a boat that you were looking at to buy, walk away. If it is a boat owned by a friend I would suggest replacing all of the seacocks with plastic like Marelon. Rotten floorboards means that it has been sitting that way for some time. Smelly brown water may mean other issues like leaking head hoses or holding tank.
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electrolysis, hull

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