Galvanic corrosion from nearby boats? - SailNet Community

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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
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Old 06-23-2011
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Galvanic corrosion from nearby boats?

I am docked near a large motor trawler that seems to run more powered devices then an aircraft carrier. I am not connected to shore power and rely on my solar panels for power. I have a prop shaft zinc and would say I am about 4 feet or so from the trawler in my slip. Can his massive consumption of shorepower increase galvanic corrosion on my prop etc? Am contemplating moving just cause motor trawlers are so ugly to begin with but this would add urgency to the idea...
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Old 06-25-2011
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The size of the boat and the number of electrical items he has don't have much to do with galvanic corrosion as long as everything is done properly. A small boat with a DC or AC leak can be a larger problem.
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Old 06-25-2011
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Galvanic corrosion is caused when two dissimilar metals are in electrical contact with each other while immersed in an electrolyte, such as seawater. This is not likely to be an issue in your scenario. Electrolytic corrosion is an absolute possibility, however. The amount of electrical power your neighbor uses is not the determing factor though. But if he has electrical problems aboard, you could be sharing them. Or rather, you could be sharing the results of his electrical problems.
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Old 06-25-2011
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Quote:
Originally Posted by Fstbttms View Post
Galvanic corrosion is caused when two dissimilar metals are in electrical contact with each other while immersed in an electrolyte, such as seawater. This is not likely to be an issue in your scenario. Electrolytic corrosion is an absolute possibility, however. The amount of electrical power your neighbor uses is not the determing factor though. But if he has electrical problems aboard, you could be sharing them. Or rather, you could be sharing the results of his electrical problems.
+1

We left a "Hot" dock in Newport Beach that would destroy a prop zinc in a month. Also ruined the engine to prop shaft coupling and numerous other parts and fittings on the boat. We have an electrician on our current dock who is diligent about checking for stray current and our zincs are lasting +6mo.
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Old 07-03-2011
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Since you stated that you are not connected to shore power you have no need to be concerned. Stray current from neighboring boats arrives on your boat via the ground wire on the shore power system. A galvanic isolator solves the problem by creating a threshold voltage for the shore power ground system. Obviously not connecting to it would also do the trick.
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Old 07-04-2011
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So your saying that if his boat is producing stray current it would not manifest itself as say a current in the water itself? Wouldn't his whole boat become a large galvanic cell if he had potential differences in places under water from his various through hulls/ fittings/ prop etc? Wouldn't electrons flow from one part to another causing pitting and well electrolytic corrosion? I would think boats with currents flowing through them would have associated magnetic fields and there would be currents in the surrounding water that could affect nearby metal. Am not sure I understand why stray current would only arrive through a ground wire and there would be none in the water itself.
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Old 07-04-2011
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If he had a DC fault on his own boat there could be a problem. If there was a fault on the other boat leaking current (either AC or DC) there could be an issue as well.

Current thinking is against bonding of through hulls. They are composed of one metal and if isolated there is virtually no risk to them. If they are bonded they will become part of any "battery" created by a fault. A fault could be as simple as a bilge pump connector not sealed properly and in water or a faulty float switch.
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SJ34 do you know what was causing your dock to be 'hot'? Was it electrical issues in neighboring boats or something to do with the way the marina wired their shore power units or something else? I am noticing an unbelievable rate of bottom fouling at this slip my dingy has like 3 inches of growth after a couple of weeks of being in the water can that be an indicator of current? Is there some way to test for stray current other than diving down and looking for pitting and the zinc?
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Old 07-04-2011
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Could be caused by current, but not stray current.

Water flowing and not stagnant along with sun will cause a lot of growth in a short while. Notice the change a few weeks after the nice days of spring.
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