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 Catalina/Capri 25/250 Sailor's Forums
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 OT - Measuring stray current		  New Topic  Topic Locked
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glivs
Admiral

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USA
836 Posts
Initially Posted - 05/02/2011 :  16:30:37  Show Profile
I was talking with a friend last week about some issues he is having with steel and aluminum hulled boats (tugs, work-boats) at his workplace over the past year (freshwater). They are discovering extensive pitting, and in one case, in a period of only two months. He suspects there is stray current in their boat basin but as they have only just discovered this they have not yet brought in an engineering firm to verify or perform measurements. Just curious, how do you measure stray current in open water or begin to trace its source?

Henk, your thread rekindled my thoughts but did not want to pirate it....
Gerry Livingston, Malletts Bay, VT
"Great Escape" 1989 C-25 SR/WK #5972
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OJ
Master Marine Consultant

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USA
4382 Posts
Response Posted - 05/03/2011 :  04:44:54  Show Profile
Never hurts to repost this - especially for newbies:

http://sailboatfamily.blogspot.com/2009/07/dont-swim-at-marina-electrocution.html
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Stinkpotter
Master Marine Consultant

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Djibouti
9080 Posts
Response Posted - 05/03/2011 :  06:24:26  Show Profile
That's important advice--even more so in fresh water, which dissipates stray current much less efficiently, making your salty circulatory system an attractive conductor. And I think I read that something like .03 amps can cause fibrillation as well as momentary paralysis. A friend experienced it in a swimming pool that had a faulty underwater light--he survived, but the paralysis was frightening!

I've read some things about finding stray current in marinas, both from boats and from other sources. It's a complex process that (at least some) marine electricians and surveyors are trained and equipped to perform. Besides pitting metal on boats, it can <i>kill people</i>. (Let's say the friend fell off his boat and was trying to swim to the dock, and <i>couldn't</i>.) Evidence of this problem should be checked out by a professional.
Edited by - Stinkpotter on 05/03/2011 06:27:56
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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts
Response Posted - 05/03/2011 :  06:43:53  Show Profile
It could simply be galvanic corrosion caused by contact of dissimilar metals. I purchased a rather top of the line tonneau cover for my truck that has steel bolts and aluminum quick clamps. The clamps are now starting to look like old zincs on an outdrive.
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OJ
Master Marine Consultant

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USA
4382 Posts
Response Posted - 08/31/2011 :  17:49:07  Show Profile
And away from the marina . . .

http://www.cbsnews.com/video/watch/?id=7379271n&tag=contentMain;contentBody
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Stu Jackson C34
Admiral

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844 Posts
Response Posted - 09/02/2011 :  19:48:22  Show Profile
Calder's <i>Boatowners Manual for Mechanical & Electrical Systems </i>has a very good description of how to do this.
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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.