Stray current at the dock

[finatic]

I searched but couldn't find anything so I'll ask. An 85' motor yacht that is more or less abandoned rubbed through its 100Amp cord against the dock and chine and almost melted through the aluminum hull! Now everyone has zinc issues! Is there a way to test for stray current?

[Captain Ralph]

Connect a DVM lead to a dry bonding contact point of your hull.
Dip the other lead into the water. a difference in readings on the two sides of your boat will tell in what direction the stray currents are coming/going from.
Were talking micro volts so the old Simpson may not work.

Proper techs have long (real long) zero resistivity leads with a silver ball on the wet lead.
For any legal issues, one of these proper techs will need to be hired.

I would hope the cable is unplugged at both ends and not still stuck (welded) onto the alloy hull.
If the boat no longer is green wire tied to the power pole, then she will have a different potential thru the water.
In what direction,, I would be guessing.

I would recommend to get the marina to re-connect at least the fault current lead (green wire) back to the boat. This way most boats (not all) will be at the same potential and reduce the straw currents thru the water.

I would further recomend the marina get a tech and have their wires tested. A shorting jolt as you described may have damaged or cooked some dock side connections. White and green connects come to mind. Higher resistance here would impead any reduction of potential thru the green wire connect between all the other boats.

[finatic]

Connect a DVM lead to a dry bonding contact point of your hull.
Dip the other lead into the water. a difference in readings on the two sides of your boat will tell in what direction the stray currents are coming/going from.
Were talking micro volts so the old Simpson may not work.

Proper techs have long (real long) zero resistivity leads with a silver ball on the wet lead.
For any legal issues, one of these proper techs will need to be hired.

I would hope the cable is unplugged at both ends and not still stuck (welded) onto the alloy hull.
If the boat no longer is green wire tied to the power pole, then she will have a different potential thru the water.
In what direction,, I would be guessing.

I would recommend to get the marina to re-connect at least the fault current lead (green wire) back to the boat. This way most boats (not all) will be at the same potential and reduce the straw currents thru the water.

I would further recomend the marina get a tech and have their wires tested. A shorting jolt as you described may have damaged or cooked some dock side connections. White and green connects come to mind. Higher resistance here would impead any reduction of potential thru the green wire connect between all the other boats.

The power was killed to the whole facility and boat in question was unplugged as soon as the issue was discovered. Not sure how long it was going on. Didn't trip any breakers that I am aware of!!??

[jim rosenthal]

You might try to find a copy of Nigel Warren's book, "Metal Corrosion in Boats" May be out of print, but there is always eBay. Not for the acute emergency here, but very good reading, believe it or not.

[Captain Ralph]

The power was killed to the whole facility and boat in question was unplugged as soon as the issue was discovered. Not sure how long it was going on. Didn't trip any breakers that I am aware of!!??

If the whole dock was down, some breaker tripped or that cable was really doing some welding. ZZZZZZZAAAAAAPPPPPPPPPPP.
Further re-enforces my thought that green wires up & down the dock may have cooked for a second or or two. Cooked wires or connections (alloy squeeze lugs & copper wire) may have picked up some resistance. Automatic differences in potential between some boats.
Now, your comment, the boat was unplugged, was the boat end of the cable unplugged? If the questioned boat's wires are welded together, and still on the hull, I can easily picture a super conductor (alloy hull boat) out there either drawing or giving galvanic currents thru the water.

Jim recommends a book that may explain way better than I, how this stuff really works.
Maybe other better reading than mine. I always lead to caution, I have seen enough to know it's not good, still can not describe all the science behind it.