stray current testing

[warby1212]

Hi,

Our steel boat is in the water and last time it was out there was electrolysis in spots. How can I now test for stray current. I have a digital multi meter only.

Here's hoping

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[Alex_Blackwood]

Hi, I would suggest that a DMM is about as much use as a chocolate teapot in this case. IMHO your only sure answer is to consult a firm of cathodic protection engineers and have a proper survey of the vessel carried out. Cathodic protection of steel hulls can vary from maintaining a good hull coating through to automatic impressed current injection equipment. The need for protection will also vary from where you are on the globe, what sort of jetty or mooring you use and the salinity of the water. (In a tidal estuary it will change with the ebb and flow of the tide).
With a DMM you may measure something, if you tie one lead to the hull and stick the other lead in the water you will get a reading on the millivolt and probably the milliamp scales. Unfortunately these readings are virtually meaningless. A Cathodic Protecion engineer will use special annodes and reference electrodes to determine the required protection levels.
It should also be remembered that indiscriminate use of sacrificial annodes can, if used in the wrong place and amount, lead to over protection. This can prove worse than no protection at all.
Hope the above makes some sense!
Good luck.

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[warby1212]

I always worried about those chocolate teapots my brother gave me, he said they were the NEXT BIG THING. Thanks for your advice Alex, I shall continue my quest. We have just arrived in this area and sorting things out Thanks again Stephen

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[Ships_Cat]

Hi Stephen

You only got one response and that from Alex. In my opinion he gave you the very best advice possible.

I do know a very good professional guy who I believe is still working in Townsville and who I could possibly track down if that is not too far away for you. Whoever you use, if you use anyone, make sure that they are the ones that the best commercial operators use and not some marina myth maker. May cost a bit but is the best way to avoid tears in the long run.

Good luck

John

<hr width=100% size=1>I am the cat but I am only 6.

 

[Coppershield]

Hi,
You have been given sound advise above. Here is my two cents.
As it has been stated above, what you're requesting is very difficult
to diagnose from afar, generally there are two different corrosion's
involving marine vessels. Galvanic corrosion which in itself is Long
subject.

However electrolysis is slightly different, in that usually involves
leaking current from shore power.
If you are suspecting the later, until you can carry out advise from
previous posters. I will advise disconnecting shore power connections.

There's also the possibility of current leaking from the DC electrical
system.
Regards
Muzaffer
Ps: by the way I am practicing writing English, please let me know
on the scale of 1 to 10 how I did?


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[warby1212]

Thanks for that. I am in a marina presently and am disconnectiong the batteries before charging, boring but I'm playing safe. In reference to your request for language check I ahve added a couple of words in quotes "" for your consideration.

Hi,
You have been given sound advise above. Here is my two cents.
As it has been stated above, what you're requesting is very difficult
to diagnose from afar, generally there are two different corrosion's
involving marine vessels. Galvanic corrosion which in itself is "a" Long
subject.

However electrolysis is slightly different, in that "it" usually involves
leaking current from shore power.
If you are suspecting the later, until you can carry out advise from
previous posters. I "would" will advise disconnecting shore power connections.

"if you hadn't mentioned it I wouldn't have noticed anything /forums/images/graemlins/smile.gif cheers Stephen"

 

[Anonymous]

[ QUOTE ]
Ps: by the way I am practicing writing English, please let me know<br>on the scale of 1 to 10 how I did?

[/ QUOTE ]10/10. Almost perfect text-book English and 100% understandable.

I thought your reply was good, also. I can't see why detecting 'stray currents' is shrouded in all this mystery - anyone would think it's like looking for ectoplasm after a seance! It's time someone wrote a good technical article on the subject for the benefit of yachtspeople (in PC mood this am /forums/images/graemlins/grin.gif) David