electric shock from the stern tube?

[tonyc]

Help and advice needed please. Launched last week and found a small leak aft of the stern gland where a rubber tube connects the gland to the hull - the tube is held in place by jubilee clips. To my astonishment I got a small electric shock from the jubilee clips when the batteries were turned on. Do I have a problem with the electrical circuits or with the earthing of the engine?

 

[AndrewB]

Could it be mains?

Do you have a mains circuit installed? Are you plugged in?

The stern tube is sometimes used to provide an earth for an on-board mains circuit. If so, either you have a short somewhere - or one of the yachts close to you does.

 

[oldharry]

Re: PROCEED WITH CAUTION!

If you have mains on board, and are getting even slight shocks from on board metal work, GET ASHORE FAST! the next one could be the full 240volts, and be the last thing you ever do on your boat.... Unplug the boat from the mains NOW, and dont re-connect until you have had it checked by a qualified electrician.

You do use an RCD on your supply of course? - yes? I knew you weren't that stupid.

If no mains on board, then the voltage is coming from the batteries, and indicates a possible fault or incorrect wiring. A simple test is to get a Digital voltmeter (because they register with far smaller currents than the analog ones), connect one end to the battery negative terminal, then poke around your engine compartment finding out where you get voltage readings. As long as you have a normal wiring configuration where all metal parts are at negative battery potential, there should not be readings from any metal part with the battery switched on. If there is, there is a serious risk of galvanic damage, and the wiring needs checking either for a mistake, or faults. If unsure how to proceed, there are a number of good books such as the 12volt Bible about boat electrics. Work on the premise that voltage should not be present where you got the shock, and try and find out how the it got there.

Or get a marine electrical expert to check it out.

 

[tonyc]

Re: PROCEED WITH CAUTION!

Thanks to Old harry and andrew B - not connected to mains - so life not endangered - your advice much appreciated