Voltage between positive and keel bolts?

[The Other Woman]

[Note from Nigel: topic split from "Protecting your VP Saildrive from Stray Currents" (different engine)]

I am having trouble with my cast iron keel which gives me a reading of 12.7v when I connect [a multimeter] negative to the keel bolts and positive to the battery, this is with the lightening earth disconnected and no other connection to the keel, but when I remove the neutral from the block the voltage drops to 7v.

The boat is on the hard.
Mick

[The Other Woman]

[Nigel replied in the original thread that the MD22 is isolated from battery negative]

Thanks Nigel

That very near gave me heart attack But as my engine is the MD2030c the wiring is different just checked again on bluemoment.com. Have you any ex plaintion on my other problem regarding the voltage between positive and keel bolts?

Thanks Mick

[Nigel]

The first thing to check is if this is a real connection; I suspect not.

Put a 12V or 24V light bulb (technically called a lamp), across the meter terminals and repeat the measurements. Don't use an LED or a small indicator lamp, 5W or more is needed.

The lamp will cause a higher current to flow, which will drop the voltage if the resistance is high. If the lamp stays lit, there is a connection. This is always a good method to use when checking stray voltages.

To stop you worrying, note that my keel is also connected to negative, via the VHF, through the antenna bracket, the mast, then the lightning strap. Took me ages to figure this out. I'm considering making a proper connection, as there isn't much I can do about it.

[The Other Woman]

Hi Nigel

Thanks for that I have tried the bulb test and there is no light or glimmer so maybe I am gust panicking but my keel does get a lot of pitting even though I have epoxied the dam thing. 
My vhf antenna is mounted on a plastic bracket which came with the antenna
It took me awhile to find the download page that you mentioned in your first reply as there is no link that I could see so I had to search it with google, or maybe I couldn't see the wood for the trees.

Thanks Again your doing a Great Job.
Mick

[Nigel]

The Download page is reached from the site entry page http://bavariayacht.info

[tckearney]

Can anybody tell me where the large cable connection from the keel bolts actually connects to.  I have found the keel end but assume the other is for lightening and connects to the mast.  I can not see a connection anywhere under the mast.  The resistance between the mast and Keel is in the meg ohms. 

[The Other Woman]

Hi

The heavy cable that is connected to the keel is for if the mast is hit by lightening it is connected through the deck at the base of the mast on my 36 there is a inspection cover at the basethe connection is via a bolt.
The mast is not supposed to be any potential as all lights are insulated from the mast.

Hope this helps
Mick