I'm Shocked!!

[Captsomer]

OK. Here’s my story… I live on my fiberglass trawler. Today it was raining pretty good. Everything outside was good and soaked. The rain dropped off to a fine mist and I decided to use this opportunity to move my boat to another spot in our marina. I pulled into my slip, tied up and shut down the engine. I walked out on deck to put the canvas back on the windshield. (Hang on. Its about to get interesting…) As I reached down to connect the snaps. I leaned one hand on the bare aluminum window frame and the other hand on the metal arm of the windshield wiper and felt a mild tingling sensation. No pain, but not nice. I’ve been hit by 110 AC several times and it was nowhere near that bad. I ran inside and got my voltmeter. I didn’t know if it was AC or DC so I measured on both scales. I got 50 volts on the AC and 4.3 volts on the DC. I am so confused…

Here are some more details. The windshield wiper runs on 12 VDC and it was off at the breaker. To my knowledge, there are no other power wires anywhere near the area, AC or DC. The boat was disconnected from shore power but the inverter was on. I connected the shore power cord to the boat and shut down the inverter and switched over to shore power. I checked the voltages as before and got the same readings. Just for kicks, I tried to light up an LED by connecting it like I did my voltmeter, no luck. There must not be much amperage there. (?)

Does anyone have any ideas? What do you make of the different readings on the AC and DC scale. (Just for reference, when I test my 110AC wall outlet, I get 115 on the AC scale and about 7.5 on the DC scale I expected this.) Do you think this is an AC or DC leak? You guys always come up with some good input and I was wondering what you had for me on this one.

Thanks.

[brak]

it is probably some kind of AC, that's why LED won't work and DC shows lower voltage. what if you shut down both shore power and inverter? is that still happening?

[Valiente]

That would be my next question: if the boat is electrically "dead" with no circuits open, is there still that much stray current? Also, move the boat off the dock and out of that basin/marina. Still happening?

It's either inside or outside the boat. Either way, I wouldn't want to be an anode until you source the "leak".

[Rockter]

It will absolutely fry an aluminium boat, and fry it quickly.... you are fortunate to be fibreglass.

If you were switched off at the breaker, then I suspect that your ship's ground has become live with 110 V AC.

Do all the AC loads work OK? Do you just see this symptom on the wiper motor ground?

Isolate the wiper... pull the wires out of it... and see if the window frame is still live. Check your through-hulls in the same way.

Don't go swimming around that boat in the meantime.

I really would avoid AC loads until it is sorted.

[sailingdog]

You've got a serious problem...

The suggestion that you take the boat away from your marina and then check it is a good one, since that will tell you whether it is your boat or something at the marina. If you take your boat away from the marina and then don't get the AC current running through the window frame—and you should check for AC current with the inverter both off and on—then the problem is at the marina—either their shorepower setup is leaking into the water or another boat has a serious problem. You'll want this fixed rather quickly or it'll eat the zinc and the underwater metal parts of your boat rather quickly.

Have you or the marina recently changed any electrical wiring or the setup of any of the electrical system? Has a new boat come into a slip near yours? Has a boat near yours had any electrical work done to it recently??

Staying out of the water until this problem is fixed at your marina is a really good idea.

[Captsomer]

It got pretty late last night so I didn't get to work on this problem much. I'll get to it today though. The dock is steel. Nobody has done any electric work anywhere that I know of. Everything on my boat has been running fine, even my AC system. When I noticed the problem I was not even plugged into shore power, I was running on my inverter. Does this rule out stray current from the marina?

I'll do some more checking today. Thanks guys.


PS The water temp here is around 35 F and the current is ripping very fast. (I'm on the Ohio River) If I fall in, I'd probably want to die and get it over with .

[Captsomer]

One more thing! How is the window frame part of a complete circuit? It is mounted into a non-conductive fiberglass boat with no other wireing around it. I think that is whats got me stumped more than anything. Could it be the wet decks thats carrying the current back to ground?

[Jeff_H]

It sounds like the Marina has the polarity reversed or a live ground and its back feeding through your bonding system. Everyone has given you good advise but I'd start by going one step at a time, such as starting by disconnecting your shore cable and the shut one system down at a time.

Good hunting,
Jeff

[sailingdog]

You said you had a wiper motor that ran off of 12 VDC. If the motor housing is grounded, and the electricity is on the ground circuit, it could come up the ground wire to the motor and then via the motor housing to the frame, if the wiper motor is mounted to the frame.

Originally Posted by Captsomer

One more thing! How is the window frame part of a complete circuit? It is mounted into a non-conductive fiberglass boat with no other wireing around it. I think that is whats got me stumped more than anything. Could it be the wet decks thats carrying the current back to ground?

[thekeip]

The most useful thing to do is to invest in a 'reverse-polarity' indicator, the kind that you plug into any shore power outlet, and keep it plugged in. It only costs $5 or so and tells you a lot. Your problem sounds more like a missing ground than a reverse, but no matter, it IS serious.
You might need to find a marine electrician who'll make house calls to have a look at it.
Howard Keiper
Sea Quest
Berkeley