Larry wrote:
Stephen Trapani wrote in news:Fyt1o.18052
:

I lost a zinc on my prop shaft very quickly. My boat is moored with
only
one other boat within miles. The only possible source on my boat (I
think) is the bilge switch in my bilge because it is the only thing
on.
The connection to the switch is out of the bilge water, so it can only
be coming from the switch itself. I have a voltmeter. Is there any
easy
way to test to see if the switch is leaking current?


The negative terminal of the battery and battery charger are hooked to
the engine block.....and the zinc on the shaft, probably......

Drag the dock cord dock end into the boat with the cord plugged into the
boat and measure resistance between the ground pin on the dock plug and
the engine block. I, personally, think there should be NO connection
between the dock ground pin and the engine block through the battery
charger. That will start an interminable argument about safety, but I'm
willing to stick my neck out in the name of zinc survival. The battery
charger's DC circuit shouldn't be connected to dock ground because that
will form a huge battery because the dock ground is GROUNDED! You now
have a shorted battery formed between the bottom of the ocean the dock
ground is connected to and the prop shaft with the ocean as
electrolyte....eating the zinc. If the engine block is NOT connected to
the dock ground pin, current cannot flow through it eating the zinc.
The only current, then, would be the battery formed by the shaft/prop
steel/brass/potmetal and the zinc, a much, much smaller battery current
eating the zinc.

So since I have no shore power, could the bilge switch itself be eating
up a whole zinc within six months? There seems to be an unexplained
drain of the batteries also.

The other important test uses the ammeter of the digital voltmeter or
analog VOM. Leave the dock cord unplugged from the dock, but plugged
into the boat. plug one lead from the DC ammeter into the dock socket
GROUND socket. If you're not absolutly sure which that is...DO NOT DO
THIS TEST. TOUCHING THE HOT AC POWER MAY CAUSE PERSONAL INJURY. Turn
off the dock breakers before doing this test, anyways, as it doesn't
unconnect ground.

Now, with the DC milliameter connected to the dock ground, touch the
other lead to the boat ground. The current should be ZERO DC CURRENT.
If you see a measurable DC current flowing to/from the dock ground,
there's your zinc problem....the zinc is protecting the entire
electrical system of the local power company all the way back to the
generator house! This is NOT good.....

Sometimes the ONLY cure is an isolation transformer that completely DC
isolates the boat from the dock electrical system, the best solution for
cruisers going overseas. The little diode isolators work ONLY if there
is no leaking AC power in the system. If you've ever looked under a
marina dock, you know the chance of that is damned near Zero. Those
half-eaten conduits drooping into the seawater, flooded to the core,
will never get fixed unless it blows the main breakers or makes a dock
transformer explode in the night.

Thanks for the help Larry, but what if I have no shore power?

Stephen