Electric shock...

[trooper]

Just had my p32 lifted for anti foul etc.. when examining prop I got an electric shock. Happens on both props and shafts.
Anyone come across this issue?

[tilo]

I hope you're talking about static electricity, and not full shore power type electric shock. If you're wearing a merino wool sweater and rubbing up against the fiberglass hull I would have an explanation. Grounding the hull should help.

[Trevor]

Hello trooper,

Was the vessel plugged inot mains power at the time or was it just sitting on the hard stand without a power lead plugged in?

Regards,

Trevor

[trooper]

I'm plugged into the mains on the hard at the moment. I don't think it could be a mains voltage shock as I'm still standing, so maybe something to do with the 12v circuit. Very strange though?

[trooper]

Mar 25, 2019 21:26:30 GMT tilo said:

I hope you're talking about static electricity, and not full shore power type electric shock. If you're wearing a merino wool sweater and rubbing up against the fiberglass hull I would have an explanation. Grounding the hull should help.

Don't know what the shock is from but it can't be mains as I'm still standing, but it also felt to powerful for static. What do you mean "Grounding the hull"?

[sitara]

Get it checked out by a sparkie, water and electricity are a bad mix. If the day was dry and you had good insulating shoes on then a mains voltage shock would not be too bad, but if the insulation was not good ...

[Trevor]

Hi trooper,

I agree with sitara. Please get it checked while on the hard. The reason is that the mains ground connection will be bonded to 12 volt negative inside the boat. That ground will ideally be the potential of the shaft and propeller.

If you received a tingle, the mains ground may be damaged on your vessel or on the dock. The ground to mains must be somewhat lacking for enough voltage to develop that it gives you a shock, even a mild one.

The propeller should be at the same potential as mains ground. Any other outcome is bad. It is a safety issue to check this but importantly any voltage potential on the running gear may cause leakage current corrosion. Leakage current corrosion is many times worse than Galvanic corrosion because the voltage causing the current is many times greater than the voltage developed by a galvanic reaction. If the boat were to be lowered into the water in its current state the voltage that gave you a tingle would presumably find a path to ground through the salt water.

Your observations are important and should be investigated as the lack of a safety ground is dangerous and the presence of leakage currents on your running gear can be very expensive if corrosion is the result.

I hope this helps,

Trevor

[tilo]

Mar 26, 2019 0:51:36 GMT trooper said:

Mar 25, 2019 21:26:30 GMT tilo said:

I hope you're talking about static electricity, and not full shore power type electric shock. If you're wearing a merino wool sweater and rubbing up against the fiberglass hull I would have an explanation. Grounding the hull should help.

Don't know what the shock is from but it can't be mains as I'm still standing, but it also felt to powerful for static. What do you mean "Grounding the hull"?

I was thinking of a grounding strap to prevent static build-up, but that's pretty trivial stuff. More importantly, I would follow up on what Trevor and sitara are suggesting.

[trooper]

Mar 26, 2019 11:28:52 GMT Trevor said:

Hi trooper,

I agree with sitara. Please get it checked while on the hard. The reason is that the mains ground connection will be bonded to 12 volt negative inside the boat. That ground will ideally be the potential of the shaft and propeller.

If you received a tingle, the mains ground may be damaged on your vessel or on the dock. The ground to mains must be somewhat lacking for enough voltage to develop that it gives you a shock, even a mild one.

The propeller should be at the same potential as mains ground. Any other outcome is bad. It is a safety issue to check this but importantly any voltage potential on the running gear may cause leakage current corrosion. Leakage current corrosion is many times worse than Galvanic corrosion because the voltage causing the current is many times greater than the voltage developed by a galvanic reaction. If the boat were to be lowered into the water in its current state the voltage that gave you a tingle would presumably find a path to ground through the salt water.

Your observations are important and should be investigated as the lack of a safety ground is dangerous and the presence of leakage currents on your running gear can be very expensive if corrosion is the result.

I hope this helps,

Trevor

Thanks for that Trevor - This answers few questions and makes things a bit clearer. When I bought the boat last year the surveyor noted that the Props were suffering from (Dezinctification) they were quite pink....and were replaced. I'm wondering if this fault could have been the cause?
Would you happen to know where i should be looking to check the condition of "ground to mains" cable? 

[Trevor]

Hi trooper,

Try to establish exactly why you received the tingle off the props. If you plug a mains lead into a power point somewhere on or near the hardstand and simply check with a multimeter between the ground connection on the power lead and the props. Check on the AC voltage scale. How much voltage is present on those props?

If you do have any significant AC voltage it may be best to get an electrician to check it out and explain why you are concerned.

Leakage current through the running gear on the boat can cause serious corrosion problems so it is worth satisfying yourself that the props are not at a voltage potential that can cause those currents.

Regards,

Trevor

[trooper]

Thanks for that Trevor - on the basis of the feedback I've had, the electrician is booked !