Stray current experts?

[MikeP]

With my increasing zinc use lately - zincs in 2-3 months instead of 6 as previously, I did a stray current check today with equipment I borrowed from the marina.

I followed all the directions and found .543 VDC; this is very high - the instructions state that anything over 1100Mv indicates a problem. Per the instructions I disconnected the shore power cable and then started turning off each breaker, to find if I had a current leak on my boat and, if so, where it was. But even with all the breakers off, there was no change in the reading. I did the same with the AC breakers. THe instructions stated that turning off the breaker(s) that served the leaking circuits would drop the voltage. But there was no drop regardless. I reconnected the shore cable and reactivated all ac and dc breakers and there was, again, no change in the voltage reading.

If I read the instructions correctly, this indicates that the problem is not on my boat but caused by stray current in the marina.

Can anyone verify if I am understanding this correctly or, if not, how to proceed.

 

[saltshaker]

Unless you have something wired directly to the batteries, it would seem like you have a problem with a neighboring boat. Try the same test but away from your slip. Look for any wires that may be touching any through hulls or fasteners that penetrate the hull.

 

[Canuck Dennis]

Go from battery negative to bonding system, I believe that would show if there is a dc positive leak to the bonding system and then check from there. That can be done with a high quality ohm meter

 

[OBXTucker]

I would have to agree with Jack. Any new neighbors nearby?
You can probably just walk around the docks testing the water periodically. Kind of the the games we played as kids, "you're cold...you're getting warmer....you're burning up".

 

[Vincentc]

Mike,
Wish I could offer some advice, but I do have a request.
Could you desribe the equipment and procedure you used to check for stray current?
My zincs do not last as long as yours.
Thanks

 

[MikeP]

FIRST, let me make it perfectly clear that I don't know anything about stray current.

I used a Corrosion Reference Electrode from BoatZincs.com, http://www.boatzincs.com/corrosion-reference-electrode-specs.html lent to me by the Marina's manager. It has complete instructions and all I did was follow them.

Basically you connect the silver anode to the Positive input on a multimeter set to measure DC voltage and another cable from the boat's bonding circuit to the neg terminal of the multimeter. You disconnect the shore power cable and drop the anode in the water "within several feet of the running gear."

Then you just read the voltage. The instructions show what you should be reading and what steps to take if the reading is outside the correct range. The correct range is different depending on what metal you have in the water - Bronze, SS, etc.

The key item for me was the statement that voltages over 1150mV can be caused by stray currents. You check this on your own boat by disconnecting successive DC loads until one/some of them drop the level to the correct range - then you have found the offending circuit(s). But nothing on my boat caused the voltage to change at all.

One thing I did not do, and will tomorrow, is to actually disconnect the battery neg cables from the banks. I just shut off switches/breakers so it's possible that perhaps a main cable is causing a problem.

But again, according to instructions I should have had around 1100 Mv but had .5V (5000Mv).

 

[Kim Beatley]

What about zincs in your engine coolers? Just replaced mine yesterday. They seem to last only two months or so. Does that time span sound right for most engines?

 

[Colwyn D]

Mike, when carrying out cp (cathodic protection) measurements in seawater the reading for a protected structure would be around the 850-1100 range as your instructions suggest. The equipment we use is a hand held device carrying a silver/silver chloride half cell within it, a voltage display and a pointed end to make contact with the material being tested so you would appear to have the right information and equipment. However, unless solid contact is made between the meter and the structure you will have all sorts of readings. This would probably be difficult to obtain through the various connections in your bonding system and a crocodile clip. The batteries I would think should be completely disconnected when trying to measure 800mv of potential.
Hopefully someone who has more knowledge about this will jump in.

 

[MikeP]

Disconnected all batts at the terminals and shore power cable - readings are exactly the same - .54 VDC.

One piece of info from a dock neighbor who once had a problem with electrolysis from an adjacent boat - the damage was on the side of the boat closest to the "bad" boat. In my case, all zincs showed the same level of erosion. Based on his info it would seem unlikely that an adjacent boat is the issue unless both had the same level of stray leakage.

Everything seems to check out that there is no problem yet the voltage is 5X what the instructions claim it should be and the zincs seem to be eroding faster than they used to.

Maybe I should just forget about it; I hang a guppy over the side for the winter so I'm not really worried that there will be any damage since that adds considerable zinc to the mix. I install shaft/rudder zincs in May and again in Sep.

Re engine zincs - They seemed to last quite a long time in comparison. Of course, when the boat is not running, the HE zincs in our 871TIs are not in water; the level of raw water in the HE ends up below the zincs. Over the years I have gone back and forth on using zincs in the main engines and currently I don't use any at all. The NL genny does not have zincs from the factory and has no fittings for them and no mention of any need for them in the manual.

 

[MikeP]

Just came across this quote re bonding:

"In the old days, the technique of bonding everything together worked okay. In its defense, the "bond everything together" approach makes your boat less sensitive to electrolytic corrosion that can result from faulty wiring on your own boat. The problem is, the "bond everything" approach leaves your boat totally defenseless to wiring errors in nearby boats and nearby industry, that cause stray DC currents to run through the water."

THat quote is from here:

http://www.sailmail.com/grounds.htm

 

[rsmith]

Just came across this quote re bonding:

"In the old days, the technique of bonding everything together worked okay. In its defense, the "bond everything together" approach makes your boat less sensitive to electrolytic corrosion that can result from faulty wiring on your own boat. The problem is, the "bond everything" approach leaves your boat totally defenseless to wiring errors in nearby boats and nearby industry, that cause stray DC currents to run through the water."

THat quote is from here:

http://www.sailmail.com/grounds.htm

Sounds right to me. Disconect your bonding system and your zinks will last much longer. BAHAHAHAHA. Mr Ward of Wards Marine electric told me (back when he was the guy that came to the boat and his wife answered the phone) that 99.9% of electrolisis problems are DC related and can come from a bad dc motor to corrosion on a terminal strip to the battery tops having enough boiled out electrolyte on top to be conductive. Anything that can cause a slightly conductive path. Your only talking about a milivolt current to cause problems.

 

[Canuck Dennis]

Stray current can also come from anywhere on land and track a path across the water to your marina.

 

[Boatnut]

For what it is worth. If it were me I would try the meter on another boat. It wouldn't be the first time a meter was defective or way off.

bought a meter from another member on this forum, and it was junk, I hope he never used it foir anything serious.

 

[saltshaker]

For what it is worth. If it were me I would try the meter on another boat. It wouldn't be the first time a meter was defective or way off.

bought a meter from another member on this forum, and it was junk, I hope he never used it foir anything serious.

Excellent point. Measurements as small as a millivolt won't leave much room for error on an inaccurate meter.

 

[eze2bme]

Maybe it's not the boats on either side of you ... do you have a boat directly infront/behind you at the slip?

 

[SeaEric]

As I have suggested here before - I think it was determined some time back that the dial tone voltage from the phone wires on your dock were the cause of the stray current problem. Did you happen to notice how fuzzy and orange all of the wooden dock pilings were, (not to mention the exploding tops) before they encased them in PVC pipe?

 

[MikeP]

Eric - yes, thanks, I recall. But I'm having trouble figuring out what has changed this year as opposed to last year when the zincs seemed to last longer. I wouldn't think the phone line issue would have changed.

I'm going to report the readings to Joe (Marina Manager for those of you not here) and go from there. Several other G dockers have said they would be glad to share the cost to have a real stray current expert check the dock. I'm told that a few years ago there was 7kUSD of damage to a stabilizer on a Hatt caused by stray current/faulty system on the boat next to it. A stray current person did an eval and allegedly that boat's owner had the necessary repairs made. Maybe it's something similar.

HOWEVER, I just found on another website re stray current that .5 volts is a proper reading. SO either it's way to high or it's just right...

WTF? Go Figure....

 

[SeaEric]

The only stabilizer issue that I recall was on a Chris Craft with Aluminum Sea Brace fins. I believe that boat's damage was self-inflicted, and FWIW the fins were never repaired.

G dock has been hot for well over a decade. It made me nuts when I owned a slip on that dock and kept my Classic wooden boat there. My Capac Monitor got a workout. The readings were always right on the very edge of acceptable.

Figuring out the source of the current will be quite a task. Solving the problem once identified may be even more daunting.

 

[MikeP]

Well, I said I didn't really want to learn more about this subject but after much research and many articles/ papers I found information that indicates if boats have too much zinc, the zincs will then create higher voltage and the higher voltage will then cause zincs to erode faster - sort of a self-destructing scenario. I wish I had bookmarked that particular paper so anyone interested could look at it. But it's interesting because I have been dropping a guppy in the water when I'm not here. I never did that before. Now my propshaft/rudder zincs don't last as long as they used to... hmmm.

Essentially, the article says that the more zinc you put on (beyond the amount required), the higher the voltage and the faster the zincs erode due to the higher voltage. So the thing to try would be to dive the boat, REMOVE some of the zincs, and see what the voltage does. Frankly, although it would be interesting, I doubt that I'll do it until next spring but since I'll be here another month I guess I could...

 

[rsmith]

I've heard the same story about puting 2 zinks in the HE causing issues. I used to have a friend that ran large steel gas and underground utilities. They would bury a large zink ingot and tie it to the underground runs. He used to give me one every year and I would drop it to the bottom and connect it to the boat. I've continued to do that with the largest zink plate I can buy. I have had times the plate was gone and didnt notice any difference in the zink usage. I do notice a big difference between brands. I started using Zinmars and they last almost 5 months vs the 3 I get out of the Camps.