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When we hauled the boat out of the water on Tuesday I checkked out the zincs. Despite only being in the water for just over a week, I noticed that one of the 5 inch pancakes on the rudder was already being eaten. About half the surface area was roughed up while the other half was still smooth. Is that normal? I have no bonding system yet. Most of it was removed during my attempt at restoration. Most of the wires were already broken so I just cut most of it out. The bonding system Will be at the top of the To Finish list I guess. I do have one of those Newman galvanic isolators but have no clue at this point how to properly utilize it. Kevin

Kevin,

Sound like you are the victim of stray currents, either from your own boat, a neighbor, or the marina itself. This is something I have been forced to learn a lot about recently.

To check out your boat and it's zincs, you will need a Silver/Silver-Chloride Reference Rlectrode and a good quality digital multimeter. You dangle the electrode over the side and read DC voltages.



When conducting this test, a vessel’s bonding system should have with a DC voltage between -900 mV and -1100 mV (relative to a silver/silver-chloride electrode) to properly protect underwater metals from galvanic corrosion. Readings less than -900 mV indicate the cathodic protection system (zincs) is weak and/or failing. Readings higher than -1150 mV indicate overprotection (over-zinked), a situation that could damage underwater steel, aluminum alloys and and wooden thru-hull backer plates.

Start with nothing connected to the boat (no shore power) and everything OFF. Voltage readings changing dramatically as you turn electrical circuits on or off indicate a problem with that particular circuit leaking out current into the water. You shold check each AC and DC circuit and appliance, one at a time.

Since you don't have the bonding system intact, and you are losing rudder zincs, I would attach the multimeter to that rudder and perform the tests. If you're throwing a current you'll find out this way, and which circuit it's coming from.

Don't forget to check with your engines running too. An alternator that does not have an independent ground wire back to the battery can throw big stray currents.

If your boat comes out clean then it's either because you've got no bonding system or there are stray currents. That's very fast to loose a zinc regardless of no bonding, and I bet there are stray currents at work.

The most common stray current path is from your shore power ground. Test your galvanic isolator to see if it is doing it's job. There will probably be a small voltage (less than 1.0 V) across it, but any current running through it means it's not working.

Oh yeah- shiny half-eaten zincs, or deep pits in them and the insides of the pits are shiny- are from stray currents.

Sean,
There are no boats around with cords in the water. Since you mentioned it, my engines are hooked up independantly to each battery. No switches yet due to my time crunch. No parallel or ground from engine to engine. Just enough wire to power/run the engines. I think the alternator charges battery through the harness, no field disconnects or anything like that. It was dark out when I looked at the zincs so a good inspection was not done. Did not even have time to rinse all the salt of the whole boat. But the red flag went up since it had only been nine days. Most of the time my shoe power was not hooked up either. Just hooked it up for a few days to run power tools at the dock. I wonder how long it can take to destroy parts of the running gear. Kinda nevous about this since my boat is surrounded hundreds of other boats at the show. Hopefully the electrolosis gods will be nice to me this week. Kevin

Sean,
That's impressive to say the least. This is why I love the sand box....people that know stuff that I need to know.

I will be wiring my boat from the bonding system up. I've already saved your "article" for future reference...keep it coming.

Thanks,
Scot

Kevin...

Grounding, bonding, electrolysis and galvanic corrosion are complicated subjects.. I suggest you get a book or two on the subject.. plus Nigel Calder's book "Boatowner's Mechanical and Electrical Manual" is a must for your library.

What most people don't understand is that in a marina even if your neighbors don't have wires in the water and there are no obvious paths for electricity to get into the water you can suffer from other boat's lack of protection or problems.. if you have a live 120 volt system in your boat you are already electrically connected to every other boat in the marina that has 120 volt service, unless you have some type of isolation device.. because 1 - you all are in the water, which we all know is a conducting medium, and 2 - what most of us don't realize is that we are also connected together electrically so current can travel from boat to boat because we all share a common ground between our boat and every other boat through the 120 volt ground. Electrical problems in a neighbor's boat can cause zincs to disappear on your boat!

I am not an expert in this to be sure.. I probably understand only enough to be dangerous.. but I do try to maintain my bonding and grounding system, and I will seriously consider an isolation device to seperate me from my neighbor's problems if I find problems appearing in my boat.

Thanks guys. I think I will have to buy the book. It's either that or buy the farm. As usual you guys come through with some pretty good information. I want have that multimeter test done. Maybe 5" pancake zincs on rudders and tabs is too much! Thanks again, Kevin

Sean,
Great info, do you know of a supplier that handles that silver/silver-chloride electrode

While I've taken C.P. readings before--- there interpetation was unknown.
Thanks
Ray

Ray,

In the original message the colored text is a link to a supplier, just click on it.

I believe We$t Marine and Boater's World have them too

We$t Marine...very fitting.

I like Worst Marine or BoatUSless.

Dang that thing will set you back 100 bucks. anyone interested in renting theirs out. haha

I bought one today from We$t. $79.99 less 10%- free shipping......
Like they say in Mexico "almost free". I ain't renting it out but I think I might wrangle a few free drinks out of it.;)
Ray