Help to Fight Electrolysis

[sailcruiser]

Originally Posted by bob_77903

So if I understand correctly, DC is the cause of stray current corrosion, and NOT or rarely AC ??

From what I've been told by trusted resources, correct. I'm in the middle of this same process myself. SC

[mitiempo]

Originally Posted by bob_77903

So if I understand correctly, DC is the cause of stray current corrosion, and NOT or rarely AC ??

Yes, but the AC ground is often the route as the AC ground most often is (and should be) connected to the DC negative bus.

A galvanic isolator or in a larger boat an isolation transformer is the solution.

A good explanation here Electrolysis

[CharlieJ]

Always receptive to enlightenment, I followed the link here:

A good explanation here Electrolysis

...to this

The current will be removing metal from one of the metal pieces = "electrolysis".

GOOD GRIEF!!! THE ACTION DESCRIBED IS NOT ELECTROLYSIS!!!

If you do not believe me, here is the dictionary definition:

electrolysis |ilekˈträləsis; ˌēlek-|
noun
1 Chemistry chemical decomposition produced by passing an electric current through a liquid or solution containing ions.

Sheesh.
Charlie

[fstbttms]

Originally Posted by CharlieJ

GOOD GRIEF!!! THE ACTION DESCRIBED IS NOT ELECTROLYSIS!!!

The correct term is "electrolytic corrosion." But just as there are boaters who will always call fenders "bumpers" or shrouds "side stays", there will always be those that incorrectly use the term "electrolysis" to describe the corrosion of their underwater metals. Frequently all corrosion of their underwater metals, even though there are several forms of corrosion.

[Matt Johnson]

Warning: Basic question ahead. Even after reading Casey's book on this, I'm still confused about corrosion on a boat.

If I'm never connected to shore power, but use an inverter to make 110v, do I still have the possibility of galvanic corrosion? Do I only have to worry about stray current corrosion from my DC system?

My chainplates, thru hulls, keel bolts and mast are all bonded together. Should I leave them bonded or unbond each one? We are currently in fresh water on a mooring, but will be moving to saltwater and living on the hook.

[CharlieJ]

If I'm never connected to shore power, but use an inverter to make 110v, do I still have the possibility of galvanic corrosion?

Yes. See Post #12, Item 1.

Do I only have to worry about stray current corrosion from my DC system?

Yes. See Post #12, Items 6, 7 and 8.

My chainplates, thru hulls, keel bolts and mast are all bonded together. Should I leave them bonded or unbond each one?

My recommendation to my clients is, it is electrically safer to have a bonded boat IF (a big IF) they are willing to maintain the bonding system to ensure its functionality. See Post 12, Item 5 above. As an example, in a properly bonded vessel, the specter of stray current corrosion is virtually eliminated as all of the bonded components are at the same potential. Same potential = no current flow. No current flow = no ion flow. No ion flow = no wastage of metal.

We are currently in fresh water on a mooring, but will be moving to saltwater and living on the hook.

As a side note, what type of sacrificial anodes do you currently have installed; zinc, aluminum or magnesium? Zinc or aluminum anodes are for salt water use, magnesium anodes are for fresh water use. If you have Mg anodes, they will have to be changed before getting into salt water.

Hope this helps.
Charlie

[Dreadnaught]

Hi Carina, thanks again for your interest in helping to educate me around marine electrics. Yes the air conditioners were the first things we noticed, they both failed due to the electrolysis. This has been a very expensive lesson for us. Ironies of ironies is that the previous owner is an electrical engineer!!!! From everyone's helpful posts I believe the problem was on the yacht prior to us buying it. Monitoring for electrolysis will be at the top of my maintenance action list from now on.

There is currently another relevant thread going about galvanic isolators that is very helpful on this topic also.

Dreadnaught

[Dreadnaught]

Originally Posted by donradcliffe

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 http://www.cruisersforum.com/forums/...ysis-3664.html

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.

Dear Donradcliffe, thanks for that maintenance tip. I will endeavour to apply my new found knowledge with your practical application. At the very least I will feel like I know what I am doing. As they say..."if you can't do the job, then dress as if you can"

Dreadnaught

[Dreadnaught]

Originally Posted by CarinaPDX

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.

Originally Posted by donradcliffe

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 http://www.cruisersforum.com/forums/...ysis-3664.html

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.

Originally Posted by CharlieJ

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

Hi Charlie. Excellent summary, but a bit overwhelming. What is the solution again?

Dreadnaught.

[sailcruiser]

Originally Posted by Dreadnaught

Hi Charlie. Excellent summary, but a bit overwhelming. What is the solution again?

Dreadnaught.

Dreadnaught,

I think Charlie gave you a great list there. Since we aren't sure what is happening specifically you got a shotgun blast type answer. I'm in the midst of this myself.

Basically Charlie said electrolysis is not the correct term and gave correct terms and what they mean. I would guess you have either or both of the following: plugged into shore power at a marina that had some stray DC current traveling over the ground wire. The solution for this is either a galvanic isolator or isolation transformer. I am doing the latter. Secondly something in your DC system may be leaking through maybe a broken or chafed wire or perhaps an incorrect ground which from my reading and conversations with knowledgeable people tends to happen often.

The reason I chose an isolation transformer is because of the limits of the galvanic isolator. It can only manage a up to a certain amount of electrical current but not above. I have an aluminum saildrive that gets attacked when my anodes deplete so I'm in the process of digging through my DC system, installing the isolation transformer hen diving into my neighbors boat who thinks he may have an issue as well

Also make sure you're using the correct anode material for your location. Magnesium for fresh water, zinc or aluminum for salt. I'm in fresh water currently and of the 20 or so folks I asked all were using zinc which won't help much in fresh water. The fact I'm using the correct one might be part of my issue! SC

[CarinaPDX]

CharlieJ: Thanks for the correction on "electrolysis". It is always helpful to get back to standard terms. Also good info for DC vs AC effects. I have a correction, or perhaps more accurately, elaboration of your comments about bonding, but I don't think going there will be helpful to the OP. Perhaps we should start working on the wiki...

Dreadnought: Another approach to the problem of corrosion of the shaft and prop is to isolate them. To explain (here we go with more thigh-bone etc): the engine block is connected to the DC common ground point (the ground connection for the starter and often the alternator is through the block). The engine is connected to the transmission, in turned connected to the shaft and finally prop. These are usually metal-to-metal (conductive) connections. On many (most?) boats this is the "seawater interface" - i.e. the path for any current between the DC ground and the sea, and thus the means for holding the DC ground at the same potential as the sea. This is an important function, but one that can lead to corrosion. Ensuring that there is a zinc attached is essential for protecting the shaft and prop. If there is any stray current then zincs can dissolve quite rapidly, leaving the shaft and prop unprotected.

One solution is to isolate the shaft from the transmission using a plastic (insulating) disc called a drivesaver (Globe Composite Solutions > Application Design Center > Products > Marine). (The drivesaver will also help protect the transmission from small mis-alignment of the transmission to the shaft.) This should protect your shaft and prop from stray current corrosion. However, you still need a seawater interface for the DC gound, usually a ground plate. In this case, if there is any corrosion it happens to an inexpensive copper or bronze plate (which can still be protected by a zinc) rather than the expensive shaft and propeller. Something to consider...

[Andina Marie]

Originally Posted by Dreadnaught

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.
'Dreadnaught'

I fail to see how an electrolysis problem would kill your air-condioning units. To reach the heat exchangers the electrolysis would have to travel in the water past the through hull and plumbing to reach the critical parts. That is just not going to happen and a galvnic isolator is not going to solve that problem.

If electrolysis killed AC units it was internal electrolysis unrelated to the exterior or shore power. Many pumps and water cooled condensing units have local "pencil" zincs inside them that need to be checked and replaced every year or two. Look for hex head fittings on the heat exchanger tank area that you can remove. You will find they have an internal thread on the liquid side where you can screw in replacement zincs.