b393capt wrote:
Chuck,

{From Prior thread}
Here are two quick tests you can make:

1) Measure the voltage between the fish
and the engine stud, noting the
polarity. This may confirm that
something is adding to the galvanic
couple set up by the zinc and the prop.



-- With the engine connected to the black wire, and the fish on the
red wire, I got -127mV


2. Disconnect the battery positive
terminal wire and see if your symptoms
change. If you have a breaker at the
battery, or a switch, or a fuse, then
there is no need to remove the wire, as
long as absolutely nothing is connected
to the battery terminal. That includes
bilge pumps, etc. Be careful working
around the battery.


-- No change, between the case of batteries disconnected and running
minimal DC. Both had - 42 mA; However, when I increased the number
of
devices I had in use I saw a change to -21 mA. I realize these
readings are different then yesterday, I used better equipment and
measurement process (see other thread)

-- You made an earlier point, summarized here, that you don't expect
to see any potential if there are two zincs in close proximity both
connected to boat ground (the prop and the fish). That makes a lot of
sense to me, does that statement still make sense to you ?


-- Please look at the new thread and comment





I think 50mA is excessive under the
circumstances, and the 127 mV is not the
right potential difference between a
bronze (i.e., copper) prop and a zinc.

If I understand correctly, you have
connected the fish with a copper cable?

That's OK as long as the copper is not
submerged in sal****er. The zinc fishes
are normally supplied with a stainless
cable, both to support the weight, and
to discourage creation of a galvanic
cell consisting of the wire and the zinc
fish.

Try pulling the fish, hosing the
connection to the copper with fresh
water and submerging without the copper
touching the water. Yeah, I know. Can't
really be done. One thing that will work
in a hurry is a stainless welding rod of
three feet or so between the fish and
the copper cable. Ideally, I guess you
would silver solder the copper to the
stainless, but an alligator clip will do
the job long enough for a measurement.
I'd also attach a rope to the fish to
prevent losing it.

I still don't see how this would explain
your other symptoms, but it could
explain the 50mA.

Chuck

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