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Old 24-09-2015, 22:29   #1
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Dangerous Voltage No Swimming signs at marina

When we parked our boat at our own dock and had our water tested for stray current I didn't worry much about galvanic corrosion. Several years ago, however, we moved to a downtown marina and I'm embarrassed to say that I only recently noticed warning signs around the dock saying ""Dangerous Voltage" no swimming within 100 yards of the dock" It doesn't say High voltage but nonetheless I begin to think this might be a very bad situation for our boat. We're on a fresh water river but what questions should I be asking and who should I be asking them to?
Jean9
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Old 24-09-2015, 22:38   #2
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Re: Dangerous Voltage No Swimming signs at marina

Maybe I'm not reading the post correctly... it's been a long day - but where is the question? In any marina, faulty wiring or grounding could leak electrical current into the surrounding water. It happens quite frequently, and fresh water means riskier business because of how current carries in a desalinated environment (which sounds counter-intuitive, but it's true). ELCIs (electrical leakage circuit interrupters) are on the newer boats, but as you know, most marinas have their share of older boats.

Some marinas have detection and warning systems in place; the siren light goes off when a current is detected, then the marina staff locate the source(s) and try to resolve the problem. Other than that, I'm not sure what you can hope for, other than avoiding fresh water marinas.
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Old 24-09-2015, 23:02   #3
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Re: Dangerous Voltage No Swimming signs at marina

I have no idea why GFCIs are not used at all marinas to avoid zapping swimmers.

But as NorthernSeaWolf points out, stray current is much more dangerous in fresh water than salt. Simplest explanation is that fresh water is a poorer conductor than a human. Salt is a better conductor than a person. Therefore the same current in fresh water kills you where in salt it wouldn't.

Betcha the signs are lawyer-recommended because of that fact. One little wiring problem and zaaaaap goes the swimmer.

Ask the marina management about why, where, and how much that 'dangerous voltage' is coming from. Also have the correct protective anodes for your water type on your boat and inspect them often. If you're burning through a zinc (not really zinc in fresh water) in a month or so, you have a problem.
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Old 24-09-2015, 23:04   #4
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Re: Dangerous Voltage No Swimming signs at marina

lots of people have been killed swimming near boats in fresh water.


I doubt there is constant voltage in the water. but it only takes a sec for a wire to break and short against a through hull. would hate to be in the water during that exact time... I would never swim near a marina in fresh water no mater how good or how often it is tested.


and leaking ac (which kills people) doesn't cause corrosion. leaking DC does. so it's 2 different issues anyways.
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Old 25-09-2015, 05:17   #5
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Re: Dangerous Voltage No Swimming signs at marina

Greetings and welcome aboard the CF, Jean.
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Old 25-09-2015, 06:01   #6
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Re: Dangerous Voltage No Swimming signs at marina

There has been a swimmer killed in the water from electrical current in our area. Our marina is installing new wiring that is meant to prevent it. One of the docks has been rewired already. I probably can't explain it properly but my understanding that if there is leakage it shuts the power down to the whole dock. The power kept going off when my friend moved his Cape Dory 33 to the dock. He can't hook up to shore power on that dock without taking everyone down.
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Old 25-09-2015, 06:06   #7
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Re: Dangerous Voltage No Swimming signs at marina

Apparently it only requires millivolts to cause a diaphram spasm. Very little water enters the lungs. Not a medical person, but have been involved in a number of marine incidents whilst in the fire service.
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Old 25-09-2015, 06:13   #8
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Re: Dangerous Voltage No Swimming signs at marina

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Originally Posted by smac999 View Post
lots of people have been killed swimming near boats in fresh water.


I doubt there is constant voltage in the water. but it only takes a sec for a wire to break and short against a through hull. would hate to be in the water during that exact time... I would never swim near a marina in fresh water no mater how good or how often it is tested.


and leaking ac (which kills people) doesn't cause corrosion. leaking DC does. so it's 2 different issues anyways.
Man I have spent the last 25 years on a fresh water lake and when I was a kid we used to swim off the boat yard docks all the time. We also don't have any anodes on our boat at all, nor does 99% of the boats i've seen dry docked in the winter. I think the only ones that do are boats that moved there from the ocean.
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Old 25-09-2015, 06:16   #9
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Re: Dangerous Voltage No Swimming signs at marina

When I was a teenager, we took a trip down the Dismal Swamp Canal to Elizabeth City, NC. After we docked, I jumped in for a swim. Wow, did I get a surprise! I could feel a strong tingling all over my body--well, more than tingling--it was almost shocking. I made it back to the ladder, luckily. Never tried that again!
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Old 25-09-2015, 06:41   #10
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Re: Dangerous Voltage No Swimming signs at marina

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I have no idea why GFCIs are not used at all marinas to avoid zapping swimmers.
I have the answer for you. The US is a wonderful country but unfortunately it has a very "democratic" process of developing codes (such as NEC) that gives lots of weight to the opinion of people who do not know what they are talking about, just because they have political power or represent those who do.

Unfortunately they dress the thing up in technical terms and publicize BS such as that a 30mA RCD that trips in 100 miliseconds is not enough to protect human life.

There is no excuse for marina pedestals not to have a 30mA residual current device (call it RCD or whatever) that trips when a boat with defective wiring is plugged in. Everything else is OK for the third world but an embarassment for a powerful nation such as the US.
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Old 25-09-2015, 07:31   #11
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Re: Dangerous Voltage No Swimming signs at marina

The signs are probably a little CYA on advice of their legal staff. Also serves to alert swimmers that a bunch of electrified boats in fresh water situation are a possible hazard to your health.

In salt water a little electrical leakage is hazardous to your underwater metals, in fresh water also a hazard to your health.

ELCI breakers will eventually show up on all marina pedestals will just take a little time. A few accidents could speed up the timetable. A two year old floating face down behind a boat might get some attention.

Blue Sea is selling an ELCI Main replacement breaker. Takes up three spaces on the panel, but rewiring is minimal. Probably good investment for us all. Uncover a lot of sloppy boat electrical systems.
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Old 25-09-2015, 08:18   #12
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Re: Dangerous Voltage No Swimming signs at marina

Stray voltage can and does kill, especially in fresh water. I have come across boats just dumping juice in to the water. We wired a new Sheriff boat a few years ago and they came back and complained about stray current, saying it was our "faulty wiring job". I went out to the docks and found a 45' power boat was leaking current badly. All I had to do was put my clampon ammeter on the AC shore power cords of all the boats along the dock. You should get zero amps on an AC cable because the alternating current should be exactly balanced. If not then some of the current is going in to the ground system on the boat and then in to the water. The marina pulled the plug on the boat and contacted the owner who had to get an electrician to come down to fix it before they would allow them to plug in again.

Our marina management tests all the cords in our 400+ boat marina monthly or so. But it only takes one boat that has had new work done, or a failure of older equipment/wiring, whatever to cause a problem. But bottom cleaning divers go in all the time too. But they get tingled and shocked at times and look for it and won't work in any water where they feel it. This is in salt water.

I'm not an industrial electrician and the transformers and wiring for docks are under that category. We just had a new transformer put in on our dock (one of 6) that is massive. A recent power outage caused a surge and blew the old one out. I don't know that there exists an RCD that works on millivolts that could protect an entire dock. So it would have to be at each power pylon for each boat. I have not seen those anywhere yet and don't know if it is technically, let alone financially, feasible. And, if I was a marina manager I would think it is gross mismanagement to allow swimming around a dock with boats coming in and out every day. They are not looking out for swimmers and there isn't any margin for error in tight quarters in alleys. I think that is a more serious risk than the electricity myself. But even a well-maintained boat can start dumping current at any time.
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Old 25-09-2015, 08:35   #13
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Re: Dangerous Voltage No Swimming signs at marina

The technology is there, but marinas are far behind in implementing it.

A lot of power plugs I have seen in marinas looked like they dated from ww2, and many weren't even wired correctly.

The safest thing to do, is don't swim around plugged in boats.

And especially around marinas where the wiring is old, or damaged by storms. (But then that is probably why they have the sign).
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Old 25-09-2015, 09:02   #14
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Re: Dangerous Voltage No Swimming signs at marina

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Stray voltage can and does kill, especially in fresh water.
In saltwater, electricity does not cause ESD (Electric Shock Drowning); saltwater is more conductive than the human body.

Raising Awareness About Electric Shock Drowning - Seaworthy Magazine - BoatUS
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Old 25-09-2015, 09:04   #15
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Re: Dangerous Voltage No Swimming signs at marina

Thank You very much for the great info. I think I have a better grasp of the situation now.
Jean9
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