Getting a shock in the water.

[HerschelKeller]

Hey there. We have a 1992 Hydra Sports 22' center console with an Mercury 225 or 250 hp 2 stroke. If you are in saltwater near the boat and the batters are on, and you touch anything metal on the boat or even the anchor line, you get a pretty good shock. Any tips on running this down?

 

[alldodge]

Are you floating by your self or are you at or near a dock?

If your near a dock then don't go back in until the fault is found. Actually its best to never swim where a dock has electrical power. Docks/Marinas need to be wired and protected according to the National Electrical code.

 

[HerschelKeller]

Thanks for the quick reply. This is when we are out on a sandbar or near a beach, so it is not related to shore wiring issues.

 

[alldodge]

In that case I would be interested to asking the about the location. If its near a populated area (probably is) then there is a possibility that power lines may run under the water nearby.

I'm not seeing 12V causing this kind of an issue unless you have something like inverter running 120VAC powering equipment onboard. What kind of equipment is on the boat?

 

[HerschelKeller]

It has dual batteries, dual VHF radios, an LC chart plotter, a fish finder, and a stereo. I first notices it when I was setting kicker anchor on a beach. It was like a good 9 volt shock to my hands and arms when I was waist deep in water. We are also seeing some electrolysis damage on the lower unit and metal wrapping the motor mount area. No 120 on board. I think we have a bad ground or a short somewhere and it is dumping 12 volt into the salt water.

 

[alldodge]

Your probably right, I was thinking about your pretty good shock comment so thinking it was a real attention getter.

If you have a mercathode attached check it, if not I'm not sure what would cause it.

Hey dingbat have any ideas?

 

[rallyart]

Is it a static charge? Most metal on your boat is connected only to fibreglass and not the battery in anyway. There is no possibility that a 12V power source will travel through the glass or even a wet surface.

Okay, just read your last comment so probably not static.

Follow the positive line to the starter and see if it contacts something that could be in contact with the water. If there is you might get a shock when you touch something grounded in the boat.

 

[HerschelKeller]

Don't have a mercathode. It does have a through the whole bronze grounding plate. I will check the positive lead to the starter, but I am thinking something else is shorted and leaking 12 volt to the system and it is entering the water through the grounding plate or the motor (or both).

Really appreciate you guys jumping right in to help a newbie to the forum.

 

[dingbat]

Don't have a mercathode. It does have a through the whole bronze grounding plate. I will check the positive lead to the starter, but I am thinking something else is shorted and leaking 12 volt to the system and it is entering the water through the grounding plate or the motor (or both).

Really appreciate you guys jumping right in to help a newbie to the forum.

If your actually “shorting” 12v to earth your batteries would be dead in no time.

A more likely scenario is a voltage leak in a component. The biggest offenders here are electric motors, with bilge pumps being the most common offenders.

I suspect you have a grounding, or should I say a lack of an “earth” ground issue.

Electric takes the path of least resistance to earth. If the grounding system on the boat is compromised in some manner, the route of least resistance is through you

Both battery negatives tied together at a common point then run to engine ground?

Have you checked and cleaned the ground (-) connections at both batteries and the motor?

Put a meter (ohms) between each battery ground and ground on the engine block. Should read 0

If it turns out not to be the ground side, you need to try and isolated the source.

Lift the positive cable from each battery (separately) to see if the problem changes or goes away.

 

[H20Rat]

12v isn't going to travel far, and a DC shock is different than a AC shock. What you are describing certainly sounds like AC. You said batteries on, but how about engine? Engine running at the time?

 

[HerschelKeller]

No, engine off. I think, but my memory is not great, that it stopped when my son turned off the batteries.

 

[Texasmark]

Hey there. We have a 1992 Hydra Sports 22' center console with an Mercury 225 or 250 hp 2 stroke. If you are in saltwater near the boat and the batters are on, and you touch anything metal on the boat or even the anchor line, you get a pretty good shock. Any tips on running this down?

Don't know it this helps or not: Was waiting to launch in salt water one day and noticed a guy off to the side with engine start problems. In short, his battery was dead (poor prior planning) and he got the one out of his truck. The boat is anchored and he is standing waist deep in the water. Upon trying to connect the battery, he connected the negative terminal first....which was tied to the engine, which was in the water, vertical on the transom, as was he.....in the water. He grabs the positive cable and upon placing it on the battery, lets go and jerks his hand up......obviously getting shocked.

Had he reversed the process he wouldn't have had a problem. So, moral of the story is that there is a power loop somewhere around what you are doing. 12v won't feel like much if anything with a dry hand, but wet things down with salt water and the rules change.

 

[Captain Caveman]

Great reminder to all wanna-be electricians. Always connect the positive terminal first, THEN the negative terminal. Disconnecting is the reverse order: take off the negative terminal first and THEN the positive. Live long and prosper.

 

[Fed]

I can't say I've ever been able to feel 12V dc even with wet hands.
A 9V battery on your tongue, yes.
Half wave from a battery charger with wet hands, yes.
Texasmark connecting a battery like shakey the mohel could give rise to a spike from back emf.
HerschelKeller this is one that should be tracked down.
I'd go through the process of elimination by disconnecting things until I found it.
Hope you let us know the end result.

 

[Texasmark]

I can't say I've ever been able to feel 12V dc even with wet hands.
A 9V battery on your tongue, yes.
Half wave from a battery charger with wet hands, yes.
Texasmark connecting a battery like shakey the mohel could give rise to a spike from back emf.
HerschelKeller this is one that should be tracked down.
I'd go through the process of elimination by disconnecting things until I found it.
Hope you let us know the end result.

Yes and sparks attest to that. The only problem I have with that is V (of the "back EMF) comes from L di/dt. I can see the di/dt part making and breaking connections, but with everything off, where's the "L"? Only L of any sort would be in the starter and if he's hooking up the battery, the starter circuit isn't closed, even if he left the ignition switch on. He just had a simple fishing boat, maybe 15' with an outboard, before the days of all the fancy gadgets. Over the years I've felt a 12v tingle on occasions. All dependsup on the resistance of your body "circuit" at the time.

 

[HerschelKeller]

Thanks guys. I just need to travel 5 hours to saltwater to start tracking it down.

 

[gm280]

I don't see how a mere 12 or even 24 volt setup can give you a shock that you could possible feel... It takes a lot more for you to have any sensation to it. I have to watch this thread to see what is causing that.