Shock Drowning - Electrical current from Boats kills swimmers?

It's prevented by ensuring that the dockside wiring is good. Of particular concern is the ground wire and proper grounding stakes set well into the earth. Code is generally for 8' long stakes bonded with heavy gauge wire direct to the grounding bus at each load panel. That's hard for a slip holder to do, it's the marina's responsibility. The other half of the equation is the AC wiring on the boat. Generally, if you do not have an electrolysis problem, your boat should be ok.

Use of the generator is highly unlikely to induce electrical currents in the water and therefore create hazards to swimmers.

Best regards,
Frank
 
Pietro said:
Scary...especially in salt water...
Click to expand...

Actually, it's a bit counter-intuitive- but the issue is for freshwater- not salt.

Salt water, as we know, is an excellent conductor of electricity- better than the human body as the salt content is higher. That means any current leakage into the water can be dispersed, or find an easy path to ground. Far as I know, there have been no electric shock deaths in saltwater.

Freshwater doesn't conduct electricity- but people do. So, any stray voltage is going to seek a path to ground through the swimmer.

Never go swimming around the boat in a freshwater marina...
 
tobnpr said:
Actually, it's a bit counter-intuitive- but the issue is for freshwater- not salt.

Salt water, as we know, is an excellent conductor of electricity- better than the human body as the salt content is higher. That means any current leakage into the water can be dispersed, or find an easy path to ground. Far as I know, there have been no electric shock deaths in saltwater.

Freshwater doesn't conduct electricity- but people do. So, any stray voltage is going to seek a path to ground through the swimmer.

Never go swimming around the boat in a freshwater marina...
Click to expand...

NOT TRUE! Fresh water conducts electricity (but not as well as saltwater)
 
We had two drownings across the lake from our house a few years ago. The water levels were high and an old dock with a light on it had bad wiring and a metal conduit that was under water. A person dove in the water off the dock and got into trouble. The sherrif boat was going by at the time and an officer dove in the water to save the swimmer. Both died. We put a new dock in after that and made certain the electrical was up to snuff. Everything is properly grounded, GFIs and the conduit is nonconductive tubing. What we learned from this tradegy is poorly constructed docks can move alot due to wakes and the wiring in metal conduits can chaff and rub the insulation off the wiring creating a dangerous situation.
 
tobnpr said:
Actually, it's a bit counter-intuitive- but the issue is for freshwater- not salt.

Salt water, as we know, is an excellent conductor of electricity- better than the human body as the salt content is higher. That means any current leakage into the water can be dispersed, or find an easy path to ground. Far as I know, there have been no electric shock deaths in saltwater.

Freshwater doesn't conduct electricity- but people do. So, any stray voltage is going to seek a path to ground through the swimmer.

Never go swimming around the boat in a freshwater marina...
Click to expand...

mmmmh, good point Mike!!! Thank you for the explanation... I feel better now as I never boat or swim in freshwater!!! I just have to beware of damn jellyfish!!!
 
fc3 said:
It's prevented by ensuring that the dockside wiring is good. Of particular concern is the ground wire and proper grounding stakes set well into the earth. Code is generally for 8' long stakes bonded with heavy gauge wire direct to the grounding bus at each load panel. That's hard for a slip holder to do, it's the marina's responsibility. The other half of the equation is the AC wiring on the boat. Generally, if you do not have an electrolysis problem, your boat should be ok.

Use of the generator is highly unlikely to induce electrical currents in the water and therefore create hazards to swimmers.

Best regards,
Frank
Click to expand...

Hi Frank I noticed this article. Do you think it was bad wiring perhaps on these boats that caused the death of these people? I had read something in the Sea Ray manual once about running the genny with ppl swimming near the boat. I tried to find it but could not find it again. We run the genny all the time while anchored with the kids swimming around the boat.

http://www.huffingtonpost.com/terry-gardner/esd-hidden-danger-in-fres_b_693454.html
 
http://www.todaysthv.com/news/PDF/electric_shock_drowning_incidents.pdf

The above is a link to numerous episodes of electrocution drowning. We do not swim at or near any marinas (my kids hate that rule). We also only swim from private docks that we assume to be in good working order.

From my understanding one of the big problems with boats electrical services is grounding the AC side into the DC side of wiring.

John
 
I don't know exactly, it's not my field. However the problem is current leakage. Some basics and you can figure the rest out yourself. I'm going to grossly simplify this and with any luck, it'll be understandable.

Power that's delivered to your home or marina at 120 or 240 volts. Some of that power is delivered by wires and some passes though the earth, which is why we call one of the leads "ground." So the earth or ground is part of the circuit. Now normally, we don't send any power to ground. On a 240 volt appliance, power is on the two "line" wires. (They call the "hot" wires "line") On a 120 volt appliance, power is on the "line" wire and the other wire is neutral. It's supposed to be at ground potential. A good appliance for the boat does not connect neutral to the case, chassis or ground lead. They're separate. These appliances are called "double insulated" since the neutral wire, as well as the line wire is insulated from the case and the user. So if everything is setup okay, power stays on the wires. If something happens, a short or whatever, power is passed though to ground as a safety.

On the boat, each line wire, the neutral wires, and the ground wires are all kept separate. The ground wire is connected to the boat's bonding system. This is for safety so that the ground wire is grounded both though the shore power connector and also the bonding system (zincs) on the boat. So far, so good, right?

if you introduce a non-double insulated device that has a ground lead onto the boat, the device is now cross-connecting neutral and ground. Lets say you brought you three pronged car battery charger from home and plugged it in. If you have any resistance in your boat's neutral circuit, or the marina does, then some current will flow though the ground circuit. That ground circuit includes not only the green wire, but also the boat's bonding system! That could induce current into the water. Also, since it's a home charger, the negative wire on the charger might be connected to the chassis. So even if it isn't a three prong plug, it still gets connected to the bonding system, since the negative DC wire on a boat is connected to the engine block and thus the bonding system. That battery charger, for example, could cause a problem.

Also, say the marina's grounding stake is bad. It's missing, corroded, or whatever. Code has the neutral and ground circuits bonded to earth. But if the stake is missing, disconnected, the connections corroded, then neutral might be floating (have voltage) above ground. That power is going to want to go somewhere to get to ground. That might be though your or other boat's green wire and bonding circuit and into the water.

So what caused it? Bad wires on the boat? Bad wiring in the marina? An inappropriate appliance? No clue. You have to be careful. Only use double insulated things on the boat. Don't bring things like battery chargers from home. When possible, use marine stuff. Oh yeah, #1 think.

Best regards,
Frank
 
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Frank,

Wouldn't the galvanic isolater prevent bad ground feedback into the water, or is the current too low to trip the isolater?

In any event, this also sounds like one of the best reasons to not install a 'shore power' system on the cheap for use while the boat is in the water.

Henry
 
jmunro123 said:
I had read something in the Sea Ray manual once about running the genny with ppl swimming near the boat. I tried to find it but could not find it again. We run the genny all the time while anchored with the kids swimming around the boat.
Click to expand...

That note in the manual was probably referring to the possible danger from the C02 off the Genny settling on the surface of the water in calm areas with little or no breeze. My manual has a similiar warning.
 
Four Suns said:
C02 is dangerous? I've never seen a C02 warning on anything or any boat... I doubt your manual has such a warning... The only C02 warnings come from greenhouse gas idiots...
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Aha- you got me Gary. It is getting too close to the weekend and trapped inside till 5! :smt021

Carbon Monoxide!
 
Let's understand what a galvanic isolator is and what it's supposed to do. In some cases, it's entirely possible for very tiny voltage imbalances to be present on the ground wire. These voltages, a few hundredths or maybe even a few tenths of a volt aren't a safety issue. But the flow of current would erode the underwater metals. So in order to stop these very small current, an isolator is used that prevents the current flow of small voltages, but allows higher mismatches to flow.

Most simply, a galvanic isolator is comprised of two silicon rectifiers connected in the green wire with one rectifier connected such that the cathode is towards the boat's panel and the other connected parallel to the first but with it's cathode connected towards the shore power connector. Rectifiers only pass current in one direction so connecting them in opposite directions allows current to flow either way. Good thing on AC circuits! A characteristic of silicon rectifiers is that they don't conduct even when forward biased until their breakdown voltage is reached, which is about 0.7 volts. Below that, it looks like an open circuit, so galvanic voltages won't pass. Above that threshold, they'll conduct up to their max current rating.

So in the case of bad or defective wiring, incorrect appliances, or some other problem, the voltage appearing on the green wire very likely will exceed the 0.7 volt breakdown voltage allowing the isolator to conduct the current.

The galvanic isolator is only there to protect the underwater metal. Not people in the water. An isolation transformer would work to protect swimmers since the boat's electrical system is completely isolated by the transformer, except for faults in the marina's grounding system. Those still require a different system.

Best regards,
Frank
 
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