"Russell" wrote in news:1150267403.137578.163050
@p79g2000cwp.googlegroups.com:

Any ideas on what could be going on, why this is an issue and what to
do to correct it?



That's easy. The marina's power system is hooked to ground in a hundred
places, as well as dangling in the seawater under the docks.

There is a complete circuit for your electrolysis hooked to all these
wonderful grounds and underwater conduits because some idiot grounded
your AC power ground to your underwater fittings and outdrive. So, YOUR
zincs, and when they're gone, YOUR OUTDRIVE is protecting the marina's
electrical system from corrosion, like it does to EVERY metal thing it is
hooked to...

Now, where is the issue. First place to look is your battery charger,
the common point to both battery DC systems, the negative terminal of
which is hooked to the engine/outdrive, and the AC power system's ground.
It's supposed to be isolated....Let's test it.

Drag the power cord from the dock post down into the boat so we can get
to the AC ground pin on the dock plug of your boat any ol' place we
want.....

Do you have an ohmmeter and know how to use it?

If yes, measure the resistance from the ground pin on the plug to the
engine block. It SHOULD be open...no connected...infinity resistance.
If it's connected together and shows a low resistance, unplug the battery
charger from the AC power supply, breaking its ground from the AC system,
and measure from the AC ground pin to the engine block, again. If it
opened up, the charger is where they are connected. If it's still
connected, we'll have to start tearing into the power panel to find out
where some idiot interconnected them....probably after reading some of
the posts on this newsgroup where it all gets bonded together to satisfy
some old wives tale that has screwed up many a zinc and prop.

Other places the AC power line can ground the engine block a

**hot water heaters with both AC and engine cooling system heating...
**a jumper wire added to the inside of the power panel from the AC ground
connection to the DC negative bus by some idiot.
**any place else where the systems come together....including seawater-
cooled air conditioners, another electrolysis problem altogether.

The case of the air condition is grounded to the AC line ground....
The case of the air conditioner is also hooked to the seawater by the
seawater passing through its seawater-cooled heat exchanger. There might
as well be a wire hanging over the side and no way of changing it. The
only way I know of to isolate them is feed the AC line through a galvanic
isolator or big isolation transformer like the big yachts use.

Good luck. I can hear your new zincs fizzing away clear over here!

Until you fix it....UNPLUG THE BOAT!