Electricians? Stray current- Conclusion

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pdecat

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I seem to have a stray current problem. New paint was removed in two months from props and shafts and the hull area near the shafts.
The problem could be on the boat or dock. How do I measure for stray current in the dock wires and boat? I realize that the 240V 4 wire system green wire should be earth ground but how would I measure for any voltage on a grounded wire??
I am particularly interested in positively identifying the cause before doing the usual clean everything routine.
 
Bruce, a pic of my stray current problem I had a year ago. Had to replace all my thru hulls.
Turned out to be on the 12v side of my boat, just a bad 12v ground.
Since not making the electrical loop , the current went looking for ground. Which it found going thru my engine block and into the bonding wires and out the thru hulls ,down the shaft etc. I now have a good size ground cable connected to both engines, if I ever have a bad ground connection again on a battery it will ground off the other side, I hope.

AnchorinGig-03.jpg
 
Thanks I;ll check those too. How did you find it?? And how can you be certain it is fixed? I have been thinking AC but..........
 
I was stuck on AC also, I ended up hiring a marine electrician who found it after going through a process of elimination.
He also had a DVM with about a 20 foot neg cord with a zinc half cell that was lowered about a foot into the water. He then took the pos side and placed it on my thru hulls, shafts, engine block, bond wire etc and measured. After checking the AC by shutting it all down , plus removing the cord from the Shore power Kiosk we still had voltage.
That told him to look at 12volt side. We then shut down the 12v stuff one at a time including main breaker and it was still there. So he began to take the neg cable off the batteries, it was then found.
I have since purchased a good DVM and the 20 foot or so Neg half cell cord and have made up a longer pos cord for doing my own testing. I probably test about every three months , just for the sake of it. I am stll paranoid I guess.
His bill was relatively cheap, 2 hours labor. I think I paid him less then 2 hundred bucks if I recall.

PS, I have heard of bilge pump wiring running direct to batteries can cause issues if water is left in bilge and a break in the wiring also.

Original reason for concern:
I could probably ratlle on for another 15 minutes on this because I was PO'd my diver was not checking things closer when I belly ached about my zincs eating up so fast.
I finally talked to him one on one and told him of my concerns to look closer at why my zincs were not lasting.
I think the damage you see to my prop took about 6 months or so. I believe I had around 2.5 volts at the time going thru my engine block and bond wire.
If you recall many of my posts have to do with the problems on my port motor.
Boost/gauge-Stop solonoid etc. Just possible it all started with the stray current?
 
Bruce,
From this month's Boating magazine, page 80. Like most Boating articles, the actual helpful part is very minimal, but maybe it will be some help.

CurrentLeaks2.jpg
 
Thanks Joe, there is at least a clue with the meter instructions. Since the engine block is connected to the bonding system i didn’t think there would be any voltage but it wont hurt to check.
 
AC setting will detect either the 12v or 110v where as the 12 v setting will not detect the AC. Sorry I forgot to mention this.

You might pick this book up at some time also, very good one . Easy read , has diagrams.
Also a section on corrosion /bonding/grounds
It is called:
Boatowners Illustrated Handbook of Wiring
by Charlie Wing
 
Pdecat,
Remember to disconnect and clean your engine ground wire, (battery cable) from the block. Even if there is no evidence of corrosion from looking at it, there is alot less voltage drop once cleaned. I like to secure the connection, than paint it with black paint to seal from moisture.
 
A while back there was a post from a guy with jet drives that were pretty much ruined by stray current from somewhere, there was a lot of usefull info in that post on how to find and detect strays, might be worth looking at it again, there was a lot of info on meter usage as well.....D.......
 
Some years back I was vacationing in Tahiti, the island of Moorea. I flew there, but I was staying on Cook's bay which is the popular hangout spot for the cruisers, most of whom are waiting for repair parts to be shipped from where ever they called home.

One of the more interesting situations was a ~45 sail boat that had lost its rudder a couple hundred miles from Tahiti. They were sailing along fine and all of the sudden the rudder just falls off!

They made it to Tahiti using drouges to steer then got a tow into the bay.

Turns out that the problem was an electrical failure in their compass! The compass light essentially lost ground, so the current was seeking an alternate path. That path was down through the steering, through the rudder, across the wet joint to the stuffing box to the ground bonding system.

The 12 volt current slowly ate away at the rudder shaft until it broke.
 
pogybait

I did not make the DVM, I made up a longer positive test lead cord.
I bought the negative half cell test lead cord along with the DVM at last years Seattle boat show.
The reason I went with a DVM is I can can now use it for multiple problems. If you still would like a pix for a visual of the cord i use and the DVM i can certainly take one and post it here. I just need to make a run to the boat with my camera.
 
Bruce,

How are you measuring or determining that you have a leak now?

A suggestion - if you have one it needs to through either the AC circuits, the DC circuits or possibly both. I suggest start simple -- shut down the AC and disconnect all shore power cords, and disconnect all battery negatives. There should now be no leak. Then add back the DC and check again. If no leak, add the AC and check. This will narrow the hunt in the minimum amount of time. If you are clean on DC only but adding AC returns the stray leak, test again with AC connected but All DC disconnected - watch out for battery chargers and the like.

Once you know which side to isolate it should be a matter of isolating the circuit or ground path. An ammeter in line might also be helpful.
 
pogybait
Here is the unit for testing, see pic of the zinc that you lower into water. Then use the positive to probe metal components The leads are now long enough to reach about anywhere on the boat.
DVMandshaftbrushes-3.jpg
a close up pix of the zinc half cell that is put into water
DVMandshaftbrushes-2.jpg
 
The voltmeter with a half-cell is a standard electrochemical set-up, just like a pH meter (I'm an electrochemist). The challenge is that if there is continuity, there will always be a reading. The problem is what the reading should be. There are some general reference numbers, but the actual reading will depend upon where you put it in the water, the conductivity of the water, etc. Even a zero reading doesn't mean zero current. If you change the reference half-cell, the reading will change.

The challenge is to find the current path. Basically, it is just like looking for a short circuit in an automobile, except you need to include the AC system and shore power connections.
 
yup , he found the current path with this set up (except he had a fluke meter) . It worked , he solved my problem. Of course he did not flip it in the water and say there it is, he had to go through all the motions with AC and DC trouble shooting methods. The reference cell is made by electroguard.
 
Marinco also has a reference cell - part number 2435, listed for $84 at West. As an electrochemist, I would prefer a silver/silver chloride ref to zinc. If you're in salt water you could also use a clean silver wire.

Calder has a good, systematic "Comprehensive Grounding and Test Procedure" in his Boatowners Mechanical and Electrical Manual. Parts of the test make use of a reference electrode in the water.

Just like troubleshooting a short in a car, it takes time and patience -- much more so far a boat.
 
After checking every socket and wire for improper continuity and voltages, I started checking the DC connections as navman suggested. I found a voltage 0.6 on the shafts with everything off. It seems that I have a galvanic problem not stray current as a resistance has developed in the shaft coupling. The engine measures 0.2V while the shaft is higher. This does explain the sudden increase in shaft zinc action. I am going to install shaft brushes.
 
What's the reference point for those voltages ? You found 0.20V on the engine - relative to what?
 
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