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Electrocution in marinas

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michaelj
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132 Posts

Initially Posted - 04/26/2010 : 05:17:51

I got to thinking about this in the vein of lower gudgeon replacement which pretty much requires you getting in the water. Be VERY CAREFUL about doing this when your boat is in a marina. There have been several incidents of shore power (110-120 V) shorting into the boat's 12 V system and then grounding out through the propeller or through something else in the water which creates an electric field around the boat. This will not be a problem unless you are in it and then you touch a ground--like a dock ladder. Then it will be a BIG problem Boat US's Seaworthy magazine recently reported the electrocution death of a young man in Oregon which happened pretty much the way I have described. It's better to work from a dinghy or kayak.

Edited by - on

JohnP
Master Marine Consultant

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1520 Posts

Response Posted - 04/26/2010 : 05:32:38

I think I'll stick a VOM probe into the water off my marina in a few spots to see if somebody has a short circuit. About half of the boats use shore power continuouly.

It's good to avoid fatal mistakes.

(OT - The woodchucks who live in the woods next to my veggie garden would love to take revenge for my shocking their wet little noses with my electric fence's 1000V sparks. I intend on giving them no such pleasure.)

Edited by - on

andypavo
1st Mate

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USA
51 Posts

Response Posted - 04/26/2010 : 05:54:09

Never woulda thunk it. Thanks for the warning! I'm too poor to have a slip at a marina anyway.

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andypavo
1st Mate

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51 Posts

Response Posted - 04/26/2010 : 05:55:25

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by JohnP
 I think I'll stick a VOM probe into the water off my marina in a few spots to see if somebody has a short circuit. About half of the boats use shore power continuouly.

It's good to avoid fatal mistakes.

(OT - The woodchucks who live in the woods next to my veggie garden would love to take revenge for my shocking their wet little noses with my electric fence's 1000V sparks. I intend on giving them no such pleasure.)
<hr height="1" noshade id="quote"></blockquote id="quote">

How many vegatables can a wood chuck chuck before it gets zapped? :-0

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JohnP
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Response Posted - 04/26/2010 : 06:59:15

"How much wood would a woodchuck chuck
If a woodchuck could chuck wood", you ask?

They ate 12 big broccoli plants one morning last spring. Then we bought the hot wire fence.

Edited by - on

OJ
Master Marine Consultant

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USA
4382 Posts

Response Posted - 04/29/2010 : 08:28:56

This very topic is discussed in the most recent copy of Clipper Snips - only I believe the victim had not yet touched anything. Turns out some hot wires got crossed inside a boat connected to shore power - melted through the insulation which resulted in AC current being introduced into the water. Interesting, yet sad, article.

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Stinkpotter
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Djibouti
9074 Posts

Response Posted - 04/29/2010 : 12:11:55

It's especially a hazard in fresh water--apparently salt water conducts the electricity to ground more directly and efficiently. I don't remember where I recently read an article (maybe BoatUS) about a young boy being killed as he swam near his boat in a marina. His mother jumped in and pulled him out, but the boy's heart had stopped, and they couldn't revive him. They didn't suspect electricity until later when the mother reported feeling "tingly all over" in the water.

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glen
Captain

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359 Posts

Response Posted - 04/29/2010 : 12:52:15

Back when I was a muck diver. (A nasty little job) That’s a diver that is hired to find jewelry, glasses or what ever that has fallen off some ones boat. The number 1 rule was they had to completely disconnect there shore power. If possible I would also disconnect the adjacent boats

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michaelj
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132 Posts

Response Posted - 04/29/2010 : 13:30:40

Dave: That was the article I was referring to. I think it might have been in "Seaworthy" which is a BoatUS publication that has great information about various wrecks, hazards, etc. and is well worth the subscription price.

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JohnP
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1520 Posts

Response Posted - 05/02/2010 : 17:59:09

I checked my marina the other day. The current in the water was 0.0 mA grounding to my boat's genoa track.

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Stinkpotter
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Djibouti
9074 Posts

Response Posted - 05/02/2010 : 18:53:09

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by JohnP
 I checked my marina the other day. The current in the water was 0.0 mA grounding to my boat's genoa track.
<hr height="1" noshade id="quote"></blockquote id="quote">I don't think that's the right test--your genoa track is presumably isolated from everything. You want to test between the water and the ground wire for your marina's shore power circuit, which should be the lowest-resistance path to true ground. If you read current from the water to that, there is indeed stray current in the water. If it kicks out the GFI on the shore power outlet, that's big trouble.

BTW, I'll repeat what I've read: This is a much more dangerous issue in fresh water (coincidentally where the boy was killed), because salt water readily conducts stray current directly to ground while fresh water is a poor conductor. The danger in salt water is more the corrosion of underwater metal, especially if it's grounded via the boat's shore power system.

Edited by - Stinkpotter on 05/02/2010 19:01:01

Bortiquai
1st Mate

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88 Posts

Response Posted - 05/07/2010 : 08:16:54

I just read this post, and it's good timing.

Last weekend we were about 9 miles out from our marina when one of the "straps" that holds the pintle to the rudder popped - not the bolt - the strap itself. Wind was about 18 knots and seas were very choppy with about 4-5 foot swells. It took about 30 seconds to twist the top pintle off, and we had to pull the rudder on board. I just replaced both pintles about 7 months ago. I think there had to have been a defect in that one.

Steering/motoring with the 8hp outboard was not my idea of a nice day sailing, but at least we got home.

So now I am going to replace both gudeons and pintles brand new from CD. I intended on borrowing my friend's little zodiac to do the job. While i've got it, i figured i'd give a light sand and wax buffing to the topsides as well. Any precautions I should take? or should I be ok in the dingy?

To think - I was most concerned about how nasty the marina water is. Not electrocution.

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Voyager
Master Marine Consultant

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USA
5348 Posts

Response Posted - 05/07/2010 : 11:44:12

JohnP
Careful about measuring amps with a digital multi-meter or VOM. The currents in the water are generally a result of ungrounded or incorrectly grounded 120V-AC meaning that a DC ampere reading will give you an average current of ZERO. AC amperes can kill just as effectively, but won't be indicated on your DC ammeter!

Better to measure AC voltages in the water referenced to local 120 VAC ground.

Edited by - on

Dave Bristle
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Djibouti
10005 Posts

Response Posted - 02/08/2012 : 21:25:28

Stray current in marinas is way too common--usually due to faults on boats. The first evidence is rapidly deteriorating sacrificial zinc anodes. Next is corrosion of any metal that is connected to the water by metal. Last (hopefully) is electrocution of somebody who goes into the water around the docks--for example, to clean a bottom. The current subtly paralyzes the person, and they drown for no apparent reason.

I believe marinas should test for leakage, at least annually when boats are in the slips. The safety of customers and workers, as well as the longevity of boats, should be worth a few hours of an electrician's time. If leakage is found, it'll be more time to find it... and it'll be even more worth it. Ask your marina manager. Meanwhile stay out of the water in a marina--and never let kids go in!

Edited by - Dave Bristle on 02/08/2012 21:31:25

cat25
Navigator

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USA
140 Posts

Response Posted - 02/09/2012 : 05:33:26

There is supposed to be a ground wire from 12v dcnegative to the green grounding wire on the boats shore power switch. Most of the old boats dont have them. All new boats have this connection. My boat a 1990 cat 25 did not have the connection. I installed it. Its a step in the right direction.

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waterbaby
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USA
168 Posts

Response Posted - 02/09/2012 : 18:31:05

Michael, thanks for the warning. My husband was thinking of going under the boat last summer to scrape the bottom but decided against it. Now I'm really glad. It has occurred to me that the water at the marina might not be the healthiest but I had never considered electrical current as an issue.

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OJ
Master Marine Consultant

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4382 Posts

Response Posted - 02/09/2012 : 18:42:41

. . . and not just at the marina

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

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redviking
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1771 Posts

Response Posted - 02/10/2012 : 08:18:18

I am at a marina which is located next to an emergency powerplant. There were stray current issues in the past, although my zincs last well over a year. But divers go in daily to clean bottoms. Never seen any of them test before going in. Could be prudent, but I respect the pro's who do bottoms for a living and think that while this topic is helpful info, the actual risk is really minimal.

But we have a tradition of paranoia around here...

sten

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OJ
Master Marine Consultant

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4382 Posts

Response Posted - 02/13/2012 : 15:21:22

Statistics!

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Stinkpotter
Master Marine Consultant

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Djibouti
9074 Posts

Response Posted - 02/13/2012 : 19:50:42

Various sources I've read say the statistics are way off because most cases are recorded merely as drownings. The current paralyzes the person in the water, or causes heart fibrillation. An examination only finds that the person drowned, but typically doesn't determine why. According to Nigel Calder, 50 milliamps can be enough to do it.

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glivs
Admiral

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USA
836 Posts

Response Posted - 02/14/2012 : 04:55:00

By chance I was reading Charlie Wings book on boat electrical systems last evening. I did not realize how common electrical leakage is.

OT - Electrical leaks are not always easily located. My brother works on the St Lawrence and his work area has all the symptoms of an electrical leakage but despite their own engineers and contractual engineers specializing in this issue, they have yet found the source. The standing hypothesis at the moment is that it is a buried conduit (3-phase) that is communicating through the ground water to the river. Symptoms they are dealing with include rapid (<2 yrs) corrosion of small aluminum work boats (the rivets are simply disappearing), steel hulled tug boat, steel anchors holding retaining walls, ...

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Stinkpotter
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Djibouti
9074 Posts

Response Posted - 02/14/2012 : 06:54:06

It could be a street lamp, or a something like faulty appliance in a nearby building sending current to its ground wire. A GFI (GFCI) detects this and turns off a circuit. But most circuits don't have them.

Edited by - Stinkpotter on 02/14/2012 06:54:46

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