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Old 25-09-2015, 09:08   #16
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Re: Dangerous Voltage No Swimming signs at marina

This may answer most questions about electric shock drowning:
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Old 25-09-2015, 09:18   #17
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Re: Dangerous Voltage No Swimming signs at marina

We recently left our Marina at Clear Lake in TX. The voltage had got so bad that I was changing zincs on our Catalina every 3 months. Some of the problem was from wiring just getting a little old but I think more from so many boats not properly taken care of and literally just sitting there falling apart. The marina did not seem to care so we left. We had about 1.4 volts at the old Marina, our new one only shows about .25-.4 volts. At our old Marina my next door neighbor had a fairly new model Hunter 386. He literally had the blades fall off the propeller one morning. When we inspected the prop you could easily see all the pink spotting that indicates galvanic corrosion in bronze. I have one bronze through hole fitting that was corroding pretty badly after we moved in . When we switched marinas I cleaned it up with a wire brush and some corrosion X and none of the blue corrosion has come back since. I was always kind of amazed at how many boats just sat around at the marina and that people actually must have continued to pay rent there. I have really learned a lesson, I would never move into a Marina again with alot of derilect boats kept there.
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Old 25-09-2015, 09:24   #18
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Re: Dangerous Voltage No Swimming signs at marina

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At our old Marina my next door neighbor had a fairly new model Hunter 386. He literally had the blades fall off the propeller on morning. When we inspected the prop you could easily see all the pink spotting that indicates galvanic corrosion in bronze.
You are talking about electrolytic corrosion (also known as stray current corrosion), not galvanic corrosion. Galvanic corrosion is caused by two dissimilar metals being in contact with one another while immersed in an electrolyte. The pink color that you mentioned is caused by dezincification of the metal, where (in the absence of zinc anode protection) the zinc component of the bronze is given up instead, making the metal much more brittle.

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Old 25-09-2015, 10:11   #19
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Re: Dangerous Voltage No Swimming signs at marina

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Originally Posted by jlrubin83 View Post
We recently left our Marina at Clear Lake in TX. The voltage had got so bad that I was changing zincs on our Catalina every 3 months. Some of the problem was from wiring just getting a little old but I think more from so many boats not properly taken care of and literally just sitting there falling apart. The marina did not seem to care so we left. We had about 1.4 volts at the old Marina, our new one only shows about .25-.4 volts. At our old Marina my next door neighbor had a fairly new model Hunter 386. He literally had the blades fall off the propeller one morning. When we inspected the prop you could easily see all the pink spotting that indicates galvanic corrosion in bronze. I have one bronze through hole fitting that was corroding pretty badly after we moved in . When we switched marinas I cleaned it up with a wire brush and some corrosion X and none of the blue corrosion has come back since. I was always kind of amazed at how many boats just sat around at the marina and that people actually must have continued to pay rent there. I have really learned a lesson, I would never move into a Marina again with alot of derilect boats kept there.
How do you actually test the water for voltage?
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Old 25-09-2015, 10:12   #20
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Re: Dangerous Voltage No Swimming signs at marina

This doesn't address the electrified water issue , but, as far as protecting your boat from other boats plugged into the same circuit on the docks goes. When a bunch of boats are on the same circuit, electrically speaking you are all one piece of metal. You want to keep your a.c. ground to protect from shock but you want to break the d.c. loop to isolate your boat from others. Install a galvanic isolator, which is a couple of 50 amp blocking diodes in your A.
C. system . That will solve that part of the problem. Your zincs will thank you. Hope this helps.
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Old 25-09-2015, 11:06   #21
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Re: Dangerous Voltage No Swimming signs at marina

Just take an ohm meter and set it on a low voltage scale. Put the positive end in the water and the ground or black wire to something grounded on your boat.
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Old 25-09-2015, 11:16   #22
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Re: Dangerous Voltage No Swimming signs at marina

If there is submarine cable near by ther could be stray voltage from the nuetral wires that are wrapped around the phase wire .These area the frost to corroad.The minimum voltage would be 7200 volts . Solarsam
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Old 25-09-2015, 11:26   #23
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Re: Dangerous Voltage No Swimming signs at marina

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Just take an ohm meter and set it on a low voltage scale. Put the positive end in the water and the ground or black wire to something grounded on your boat.
Can you stick the ground end in the ground hole in the a/c outlet on the dock?
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Old 25-09-2015, 13:03   #24
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Re: Dangerous Voltage No Swimming signs at marina

There is no need, all the stantions on our boat are grounded. I'm not sure I go putting the ohm meter in an outlet directly
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Old 28-09-2015, 09:53   #25
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Re: Dangerous Voltage No Swimming signs at marina

You want your meter on Volts, NOT ohms.
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Old 28-09-2015, 10:05   #26
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Re: Dangerous Voltage No Swimming signs at marina

IMHO the most meaningful measurement would be using the AC volts mode of the meter with one of the probes connected to the green safety wire in the dock outlet (or inside the boat, provided there is no iso transformer or galvanic isolator) and the other probe connected to the water via a long wire with some "electrode" at the end ( I use a copper pipe). As you move the electrode you may see a change in reading that tells you which way the gradient goes.


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Old 28-09-2015, 10:27   #27
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Re: Dangerous Voltage No Swimming signs at marina

I agree, the one reading I'm most concerned about is the prop shaft vs water voltage. The zincs should be connected to the boats DC grounding system, and at the same voltage.
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Old 28-09-2015, 13:17   #28
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Re: Dangerous Voltage No Swimming signs at marina

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I agree, the one reading I'm most concerned about is the prop shaft vs water voltage. The zincs should be connected to the boats DC grounding system, and at the same voltage.
The prop shaft is in the water, hence at same potential as water near the boat. That does not eliminate the danger caused by water at potential different than earth in places close to AC leaks into water.

This is because a boat with a proper installation will have chassis of appliances, etc connected to the non-current carrying (hence zero drop) green wire that takes potential from a ground rod somewhere. If the water is at a different potential than the green wire then there is unnecessary risk.

I trust this explains why the relevant measure to detect AC leaks into water is delta voltage between water and green wire/ground rod.

The ABYC electric shock drowning guru has a good video on this.





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Old 28-09-2015, 13:24   #29
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Re: Dangerous Voltage No Swimming signs at marina

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There is no need, all the stantions on our boat are grounded. I'm not sure I go putting the ohm meter in an outlet directly
They are "grounded" but not necessarily to the potential you want, which is earth as in a ground rod next to the transformer. There has been plenty of science and engineering (and death statistics) used in the development of electrical safety best practices.

On a related matter, you should not use an ohm meter for this. You want a voltage meter. An ohm meter will get fried by AC.
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