electrical shock from backstay

[Bobg]

last fall, I was in my dinghy which had a wet floor, grabbed the backstay to get out and got a good jolt, any ideas why?  I was plugged into shore power.  I took my volt meter and could detect current from the back stay, I connected one end to the backstay and dropped the other into the water, the needle moved slightly. I check other boats around me, and one other boat showed the same symptom. some boats did not move the needle on the volt meter.  Last summer the boat 4 slips down got hit by lightning, the same lightning took out my battery charger.  I changed it and was back in business. I havn't noticed anything wrong with the boat except for that puzzeling current from the back stay to the water.  Any Ideas on what to check?  Thanks, the boat is on the hard right now in Bayfield WI.  Bob

[Jon Schneider]

The real issue is why there was juice in the backstay, not that the saltwater ground did it's job.  Could you tell if it was a 120 AC or 12 DC shock?  ;)  I suspect you must have a short in your mast wiring.  It's likely that your anchor light is connected via a pigtail; the butt connectors could have shed their insulation. 

[Craig Illman]

Bob - I wouldn't think you'd feel 12V. I'd be worried about some sort of ground fault on the 120V AC side. Do you have a galvanic isolator?

Craig

[Jon Schneider]

Bob - I wouldn't think you'd feel 12V.

Try it... I was kidding about knowing the difference between 12v and 120v, although actually I suppose there is one, but you'll definitely feel a jolt from 12v, especially if you weren't expecting it as you grabbed a stay.  (Don't ask how I know this.)  I just can't understand how the AC system could connect with a stay.  The only nexus point is the charger and that is grounded off the metro grid or if not, it would still be delivering 12v. 

[Ron Hill]

Bob : What you need to do is check that stray voltage with the shorepower plugged in and then unplugged.  Keep trying items like battery charger ON and then OFF.  Check the other stays etc. Hopefully you'll eventually isolate it and find the cause.
As far as a shock from 12V DC or 110V AC, just don't wear rings or metal watch bands when screwing around with hot wires. AC/DC makes no difference as you could tear off a finger from a "knee jerk reaction" when you get zapped!!   

[DougP]

Had a similar issue in that I'd get a mild shock when grounding between the faucet and the chain plates. Then I noticed the same small shock when grounding between the pushpit and the wheel. It wasn't strong or constant, and I spent a huge amount of time trying to trace it issue. Started by replacing the old charger and kept going. Nothing helped.

Finally I just connected the multi tester to the wheel and started touching things with the other probe. Finally isolated it when I disconnected the lifeline gates and found current between the pushpit rails and the wheel, or between the pushpit and any other ground.

In the end it turned out that a washer on a bolt for the pushpit had been installed over the wire for the aft reading light in the aft berth. Over the year the compressed insulation finally gave way, and the push pit would get charged, but only if the cabin lights were on.

It's always the littlest things that cause the biggest issues...

[sailingdream]

A few things to try.

1. Disconnect the shore power, i mean remove the power cable totally.
A. See if your getting the shock still, if so then leave it disconnected.

2. Turn your 12v system totally off.
B. Still getting it? Make sure your 120v inverter is not connected as well.
I really can't see 12V system giving you a jolt unless you have mega amps coming out of those batteries.

If you where to leave the shore power connected, but turn off the power at the fuse(on the dock) that would still leave you connected to the ground system for the marina and I would take a wild guess your getting stray juice from a boat near by with faulty wiring.

[Jim Price]

Since marina wiring is not always perfect, you could try same testing routines suggested but by moving your boat (when you get back in water) to differnt slip, preferably one not anywhere near your current slip or neighbors boats or on same dock if possible.  You could have faulty service at your slip / dock.

[Bobg]

Thank you all, those are all good ideas, my boat is on the hard in a different marina at Lake superior, right now, maybe I can check a few things before putting it back in the water.  It sure felt like a 110 jolt, I have done a little wiring in my time and have been bit.  It also felt like I grabbed a spark plug on my car.  But I doubt if there is anything on the boat that could provide that many volts.  Not clear what a pushpit is Doug, I do know one thing, I don't want to feel the shock again, am going to relie on my volt tester.  Thanks guys, 3 months till summer launch.   Bob

[Stu Jackson]

The pushpit is the rear pulpit, the stainless rails enclosing the cockpit.

[Ron Hill]

Bob : It's imperative that you trace down your stray voltage as it can have damaging effects.  Here are two of the real world C34 examples:
1.  A early MKI had pod mounted instruments mounted on the Edson pedestal.  One of the instruments had a wire with worn insulation that was touching the inside mounting bracket.  The current went from the bracket, to the pedestal, to the steering cables, to the stainless rudder column and finally out to the water.  The result was the rudder column where it comes out of the layup had pin holes in it and was severely erroded.  It required an new rudder.
2.  When a MKII was having its deck mated to the hull at the factory, they pinched a 110v AC wire in that joint just where a stanchion was mounted.  After the insulation on the pinched wire finally deteriorated the C34 owner found to he had an "electric fence" not a life line!!  That was fixed by rewiring past the pinched wire.

Don't get mixed up between stray voltage and static electricity.  They both can give you a jolt.  I forget and will rub my shirt on the winter or summer cover and get "reminder-zap"
A few thoughts.