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Old 26-01-2012, 01:34   #1
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Help to Fight Electrolysis

We have a 2007 Catalina Morgan 440 which we are sailing in the east coast of America for half the year. We leave the yacht on the hard other times and return home to Australia.

On our maiden voyage we discovered that both air-conditioning units had totally failed due to Electrolysis. Our very helpful air-conditioning technician pointed out that the galvantic isolator was not probably connected.

We have since had a marine electrician on the yacht who has probably fitted the isolator but other work on the propeller shaft has exposed electrolysis to the shaft resulting in it having to be replaced.

While I can't for the life of me understand how electrolysis effects shafts, I am a complete marine electrical acolyte, I am interested in other cruisers experience and solutions for this insidious problem. From my readings it appear that it is the ban of modern cruisers with our love of electrical gadgetry, my husband has to have his iPad and iPhone surgically removed from each hand now as they have become part of his appendages.

I know the Pardeys advocated mechanical, hydraulic and portable systems, but I am a modern woman also in love with what electric's provide on a yacht. Any suggestions on trouble shooting, prevention, and repair would be appreciated.

'Dreadnaught'
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Old 26-01-2012, 02:04   #2
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Re: Help to fight ELECTROLYSIS

We had a little thread drift on a thread about inverters and were talking about the electrolysis problem: Best Inverter for the Buck So you can pick up a bit there.

Basically the source of your problem is probably that the 120V AC safety ground (green wire) from the shore power cord is connected on the boat to the 12V DC ground. The DC ground is connected to the engine which in turn is connected to the shaft and prop. If the shore's ground is at an elevated voltage then you will have electroysis on the prop. A galvanic isolator prevents voltages below about 1.2V from passing; this should prevent damage caused by dissimilar metals (galvanic corrosion). If there is a problem with the marina wiring or on a nearby boat the ground can be elevated more than 1.2V and current can pass the isolator; this will cause stray current corrosion. The bulletproof way of preventing most electrical problems from outside the boat causing harm is to use an isolation transformer. Of course there could be an electrical problem on your boat that is causing current to leak from line to ground and having the same effect. This would also be a safety issue. If you have GFCIs (5ma trip RCD) for all outlets and an ELCI (30ma trip RCD) for the panel then at least such leakage is less likely to get to hazardous levels, but any level will cause electrolysis.

Keep asking questions if you need help.
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Old 26-01-2012, 05:12   #3
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Re: Help to Fight ELECTROLYSIS

Greetings and welcome aboard the CF, Dreadnaught.
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Old 26-01-2012, 05:31   #4
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Re: Help to Fight ELECTROLYSIS

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Originally Posted by Dreadnaught View Post

We have since had a marine electrician on the yacht who has probably fitted the isolator but other work on the propeller shaft has exposed electrolysis to the shaft resulting in it having to be replaced.



'Dreadnaught'
did he probably fit it, or properly fit it? sorry couldnt resist
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Old 26-01-2012, 05:50   #5
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Re: Help to Fight ELECTROLYSIS

Trying to figure out whether the problem is in your boat or your marina. When the boat is in the water, did it spend most of its time in a marina plugged into the dock power, or do you spend most of the time anchored out? Was it based in one particular marina, or did you wander around for the time you were on the boat? How long have you had the boat, and do you think that the electrolysis damage occurred before or after you bought it?
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Old 26-01-2012, 20:46   #6
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Re: Help to fight ELECTROLYSIS

Dear CarinaPDX, thanks, I think I understood some of your "knee bone is connected to the hip bone explanation." I guess my first question is how quickly does this happen. Since buying the yacht in April 2011, she was on the hard until late September, in the water for one month as we cruised approximately 1000 nm, then up on the stand since November 2011. Does it happen that quickly? Does it happen when the yacht is out of the water and nothing is on?

What's an isolation transformer? Is that the zinc thingy on a wire on a cleat hung in the water near the prop?

Were you swearing at me with your GFCIS and ELCIs or are they electric do ad's? Thanks
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Old 26-01-2012, 20:51   #7
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Re: Help to fight ELECTROLYSIS

Hi Donradcliffe, Yes is looking like a previous problem because we have only had her in the water for about 4 weeks between Sept and October last year. Prior to that she was on the hard and is now on the hard. We travelled 1000 nm, stayed mostly in marina's when we weren't doing overnighters and the longest we were in a marina would of been six nights. We mostly used shore power. What do you think?
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Old 26-01-2012, 21:29   #8
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Re: Help to Fight ELECTROLYSIS

From what you have said, it sounds like either the corrosion was present when you bought the boat and wasn't caught by the survey, or you have a serious problem on board (or both). It is possible to do visible damage in a month but that would require a significant leakage, and since you didn't spend much time in one place that points the finger to a problem on your boat (assuming it wasn't pre-existing damage). You should have had a zinc on the shaft or prop in order to protect both; if so, it would have dissolved instead of the shaft. A zinc hanging in the water from a cleat won't do any good unless it is connected by wire to the boat's ground, but it would suggest that the previous owner was experiencing a problem. To answer your question, this corrosion does not happen out of the water.

An isolation transformer is in a box about 8"x8"x10", weighing 60 lbs, and located between the power connection for shore power and the power distribution panel. If you have a galvanic isolator then you don't have one - it is one or the other, not both. They can be purchased that can handle either 110V or 220V on input and output (independently) so if you are planning to take the boat back to Oz it might make sense to get the multi-voltage version.

As for GFCIs and ELCIs I wasn't swearing but I appreciate that the jargon may have you swearing. In the US a GFCI is a duplex outlet that shuts off if electricity leaks out of the circuit to ground at a rate of 5ma or greater. Most people only encounter them in their bathrooms, as they have been required in the building codes for awhile now. In that application, they mostly protect against the electrical device (e.g. hair dryer) falling into the water in the bathtub or something similar. An ELCI accomplishes the same thing for your entire AC system, and trips at 30ma (just below the current levels that are lethal). Installing both protects the crew from unsafe levels of leakage, not always the boat from electrolysis. However, if the leakage is enough to trigger one of these then you will most likely be having an electrolysis problem.

Personally, I would be looking at the air conditioning units to make sure that there is no corrosion near the electrical components. Just a hunch. But check all electrical systems for corrosion, which could be a sign of leakage.
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Old 26-01-2012, 22:44   #9
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Re: Help to Fight ELECTROLYSIS

One of the really nice things about the cruiser's forum is that you are not the first ones to have had most problems, and you can search the archives to find similar problems which have been solved. Use the search function, but use the Google custom search, not the 'Search Forums'

For example, searching for propeller shaft electrolysis came up with this thread, which has a lot of good information Power Leaking and Electrolysis...

It sounds like your boat has some current leakage due to defective wiring or appliance(s). Sometimes these are not easy to find, as the leakage can come from either the DC systems or AC systems, and the more complex electrical system you have (inverters/gensets/solar panels) the more things you have to check.

I kind of like EngNate's posts on checking out your electrical system when you go back into the water. To summarize, get a digital multimeter and a pencil zinc. Make a sealed connection to the zinc with a piece of insulated wire. Connect the black wire of the multimeter to the wire from the zinc and suspend the zinc in the water. Connect the red wire from the multimeter to the prop shaft.

Now read both DC and AC volts on the meter. Ac volts should always be zero, and DC should be less than 0.5 volts. Start with the boat UNPLUGGED (not just dockpower turned off) and all batteries disconnected at the positive terminals, solar panels disconnected at the panel. Then connect the batteries one by one and retest, then turn on DC circuits one by one and watch for changes. If you have solar panels, connect them back up. Start the engine and see if anything changes as the alternator starts charging the batteries. Finally plug the dockpower in and retest, then turn on the dockpower circuits one by one. If the Aircon units are also suffering from electrolysis, put the red wire of the meter on whatever metal parts are going away and repeat the tests. If your boat has a bonding system which ties all the thru-hulls together, test that also.

Also look for streaks of rust on fiberglass, wood, or wire insulation.

Happy hunting.
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Old 26-01-2012, 22:57   #10
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Re: Help to Fight ELECTROLYSIS

"Help to Fight ELECTROLYSIS" This should be on a T-shirt. As a steel boat owner, I'd buy one or two. The hirsute may object however.

Good info here. It's alchemy. Best of luck tracking it down Dreadnaught.
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Old 26-01-2012, 23:18   #11
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Re: Help to Fight ELECTROLYSIS

I like the process using the multimeter. However, I would recommend doing a quick test with the meter and zinc hooked up as described before disconnecting anything. If you can find AC voltage at that point then there is leakage from the AC system. If there is greater than 0.5V or so DC then something is happening through the DC system. At the minimum, you will have something to compare to the results with everything disconnected.
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Old 27-01-2012, 07:13   #12
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Re: Help to Fight ELECTROLYSIS

Corrosion Maxims:
1. Galvanic corrosion occurs when two dissimilar metals are electrically connected and immersed in the same electrolyte.
2. Galvanic corrosion is the wasting of the anode (most active on the Galvanic Scale) and the protection of any connected metal less active on the Galvanic Scale than the anode.
3. Galvanic corrosion is a slow process. Months, if not years.
4. Galvanic cells (the two connected dissimilar metals above) produce milliamps of direct current at less than 1 volt.
5. For galvanic protection to function properly, all electrical connections in the system; e.g., sacrificial anode ("zinc") to shaft connection, must have a resistance less than 1 ohm. (See #4 above.)
6. Stray current corrosion is corrosion induced by a DC positive source (B+) in contact with an underwater metal component thus causing ion current in the electrolyte away from the contacted underwater metal component taking chunks of the metal component with it. Example: a "hot" (B+ potential) 12V conductor draped in the bilge chafes through where it contacts a through hull and the conductor makes contact with the through hull. The through hull will be quickly destroyed.
7. Stray current corrosion is very, very fast. Hours, days, maybe a couple of weeks at most depending on the electrical contact.
8. Leaking AC is dangerous. It rarely, if ever, causes stray current corrosion.
9. "Electrolysis" is the dissociation of molecules into their constituent parts by passing an electrical current through the electrolyte. Electrolysis of water will break the water molecule down to hydrogen and oxygen. "Electrolysis" is incorrectly used to describe corrosion in a marine environment.
10. Galvanic isolators are placed in the shore power safety green wire and will prevent galvanic current (milliamps) at less than about 1.2VDC from leaving your vessel (saves your anodes from protecting another vessel) or from coming aboard your vessel.
11. Galvanic isolators will have no effect on stray current produced on your vessel.
12. Galvanic isolators will have little or no effect on stray current on the safety ground wire coming from another vessel because the stray current is generally near battery potential (see #6 above).

Charlie
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Old 27-01-2012, 08:59   #13
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Re: Help to Fight ELECTROLYSIS

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9. "Electrolysis" is the dissociation of molecules into their constituent parts by passing an electrical current through the electrolyte. Electrolysis of water will break the water molecule down to hydrogen and oxygen. "Electrolysis" is incorrectly used to describe corrosion in a marine environment.
THANK YOU!

The misuse of that term has been a pet peeve of mine for many years.
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Old 27-01-2012, 11:16   #14
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Re: Help to Fight ELECTROLYSIS

So if I understand correctly, DC is the cause of stray current corrosion, and NOT or rarely AC ??
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Old 27-01-2012, 12:28   #15
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Re: Help to Fight ELECTROLYSIS

When I was a kid, electrolysis was always about unwanted hair removal.
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