On my 39 foot Beneteau 393, I have a zinc fish connected to engine
ground via a stud I installed in my cockpit.

When I place an analog meter between the fish and the boat's ground, I
read 50 mA with most of my electrics off (except Link20, galvanic
isolator monitors, bilge pumps), 70mA with some DC power on, and 100mA
if I also connect to shore power (I have galvanic isolators, unsure
why the current should change)

Where is a reference I can go to, to learn is this is acceptable ?
E.g. where do I cross the line between this providing evidence I am
getting intended galvanic protection vs. evidence there is a problem ?

Thank,

b393capt wrote:
On my 39 foot Beneteau 393, I have a zinc fish connected to engine
ground via a stud I installed in my cockpit.

When I place an analog meter between the fish and the boat's ground, I
read 50 mA with most of my electrics off (except Link20, galvanic
isolator monitors, bilge pumps), 70mA with some DC power on, and 100mA
if I also connect to shore power (I have galvanic isolators, unsure
why the current should change)

Where is a reference I can go to, to learn is this is acceptable ?
E.g. where do I cross the line between this providing evidence I am
getting intended galvanic protection vs. evidence there is a problem ?

Thank,


Several things come to mind. First, is
the fish your only zinc anode?

Assuming it is, and assuming you are
measuring DC milliamperes (not AC), then
50 mA is probably high, depending on the
surface areas, distance from the fish,
and composition of the underwater metals
you are protecting. A direct current of
50 mA will typically consume a pound of
zinc in about 3 months.

I also assume you are in sal****er.

Applying DC power to various appliances
should not change the current through
the fish. The only thing that I can
think of to explain what you are seeing
is if the switches are switching both
positive and negative wires. Of maybe
something is wired "backwards" and sets
up a galvanic cell.

You should see no significant difference
with AC power connected if your isolator
is working properly. It is not clear how
this would be related to the increased
fish current when DC appliances are
switched on.

I'm having trouble imagining what could
cause all the symptoms you have
reported. And coincidental multiple
problems are usually suspect.

The best references are probably the two
12 Volt Doctor books by Edgar J. Beyn.
Remarkably lucid and useful.

BTW, when measuring the current, was the
negative lead connected to the zinc or
the engine stud? And was your reading +
or - 50 mA?

Good luck.

Chuck


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b393capt wrote:
On my 39 foot Beneteau 393, I have a zinc fish connected to engine
ground via a stud I installed in my cockpit.

When I place an analog meter between the fish and the boat's ground, I
read 50 mA with most of my electrics off (except Link20, galvanic
isolator monitors, bilge pumps), 70mA with some DC power on, and 100mA
if I also connect to shore power (I have galvanic isolators, unsure
why the current should change)

Where is a reference I can go to, to learn is this is acceptable ?
E.g. where do I cross the line between this providing evidence I am
getting intended galvanic protection vs. evidence there is a problem ?

Thank,


One last thought: the Beneteau 393 is
not one of those boats built with
galvanically isolated underwater metals,
is it?

Chuck

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On May 14, 10:02 am, Chuck wrote:
b393capt wrote:
On my 39 foot Beneteau 393, I have a zinc fish connected to engine
ground via a stud I installed in my cockpit.

When I place an analog meter between the fish and the boat's ground, I
read 50 mA with most of my electrics off (except Link20, galvanic
isolator monitors, bilge pumps), 70mA with some DC power on, and 100mA
if I also connect to shore power (I have galvanic isolators, unsure
why the current should change)

Where is a reference I can go to, to learn is this is acceptable ?
E.g. where do I cross the line between this providing evidence I am
getting intended galvanic protection vs. evidence there is a problem ?

Thank,

Several things come to mind. First, is
the fish your only zinc anode?

Assuming it is, and assuming you are
measuring DC milliamperes (not AC), then
50 mA is probably high, depending on the
surface areas, distance from the fish,
and composition of the underwater metals
you are protecting. A direct current of
50 mA will typically consume a pound of
zinc in about 3 months.

I also assume you are in sal****er.

Applying DC power to various appliances
should not change the current through
the fish. The only thing that I can
think of to explain what you are seeing
is if the switches are switching both
positive and negative wires. Of maybe
something is wired "backwards" and sets
up a galvanic cell.

You should see no significant difference
with AC power connected if your isolator
is working properly. It is not clear how
this would be related to the increased
fish current when DC appliances are
switched on.

I'm having trouble imagining what could
cause all the symptoms you have
reported. And coincidental multiple
problems are usually suspect.

The best references are probably the two
12 Volt Doctor books by Edgar J. Beyn.
Remarkably lucid and useful.

BTW, when measuring the current, was the
negative lead connected to the zinc or
the engine stud? And was your reading +
or - 50 mA?

Good luck.

Chuck

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- Show quoted text -

Chuck,

On my 39 foot Beneteau 393, I have a zinc fish connected to engine
ground via a stud I installed in my cockpit.

When I place an analog meter between the fish and the boat's ground, I
read 50 mA with most of my electrics off (except Link20, galvanic
isolator monitors, bilge pumps), 70mA with some DC power on, and 100mA
if I also connect to shore power (I have galvanic isolators, unsure
why the current should change)

Where is a reference I can go to, to learn is this is acceptable ?
E.g. where do I cross the line between this providing evidence I am
getting intended galvanic protection vs. evidence there is a problem ?

Thanks,

Chuck,

1) I have an anode on my prop, the boat was just splashed two weeks
ago, so hopefully it's still there! Last year it dissapeared
completely.
2) Has to be DC mA, when I am not connected to shore power.
3) Yes, Salt water environment
4) Battery switch is positive wire only. I have a starter and a house
battery, both turn on/off simulateously.
5) I believe the negative meter leed was connected to my engine, but
will recheck tonight.

Dan

Dan, you aren't parked next to a big,
metal-hulled vessel or steel bridge or
dock pilings by any chance, are you?

Metal-hulled vessels (and sometimes
bridge pilings) usually use impressed
current protection and they create
rather strong electric fields in the
vicinity of the hull. If your boat is in
that field, that would explain a lot of
your symptoms.

BTW, if your prop anode was gone in less
than a year, either there is a problem
or it is too small. But you knew that. ;-)

Has the boat always gone through zincs
that fast or is this a new development?

Chuck

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b393capt wrote in
ups.com:

70mA with some DC power on

There's a leak into the water from "something", probably through a
through-hull fitting and its water path....water pump is a place. Watch
the current and switch them on one at a time to see what's leaking.
Whatever's leaking will cause the meter to increase when 12VDC is applied
to the leaker.

As to shore power, that's another ballgame. One of your neighbor's is
leaking. Galvanic isolators breakdown at some preset voltage so you
still have a ground potential in the boat for AC power faults. If any of
your neighbors is applying over that breakdown voltage to the galvanic
isolator, even on the other end of the marina, your current will
increase, your fish will be consumed faster. The only way to stop it is
total isolation, an isolation transformer WITHOUT connecting boat ground
to marina ground, which is where the problem is. You may also be reading
DC current caused by AC leakage of some appliance in the boat, such as a
battery charger that has the battery ground hooked to the marina ground,
which is stupid. The DC circuits in the boat should NOT be connected to
the AC ground as there is no reason to do it...isolators or not.



Larry
--
Grade School Physics Factoid:
A building cannot freefall into its own footprint without
skilled demolition.

Nope, I am not parked next to metal hull vessel or bridge.
Boat is one year old, don't know yet whats normal for the prop zinc.
Would it help if, without the zinc fish, I measure current from just
placing my vom meter probe in the water ?

b393capt wrote:
Nope, I am not parked next to metal hull vessel or bridge.
Boat is one year old, don't know yet whats normal for the prop zinc.
Would it help if, without the zinc fish, I measure current from just
placing my vom meter probe in the water ?


Dan, since you have a zinc on the prop,
the fish should have almost no effect at
all, because it is much farther away
from the prop than the prop zinc. So
there is clearly a problem.

When you disconnected the shore power,
did you actually unplug the cable or did
you just turn off the AC breaker? If you
unplugged it, that pretty much rules out
problems with shore power. With the
cable unplugged, it doesn't matter
whether your galvanic isolator is
working or not.

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.

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.

I'm still leaning toward the idea that
one of your 12 volt appliances is
causing +12 volts (more or less) to be
set up between the engine/prop and
something like a through-hull. It could
be a short or incorrect wiring to the
appliance. The effect would be to
accelerate the corrosion of the zinc.

If all of the underwater metals are
bonded together then this problem
couldn't occur, of course, but usually
they are not.

Chuck





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Chuck wrote in news:1179189498_23605
@sp12lax.superfeed.net:

I'm still leaning toward the idea that
one of your 12 volt appliances is
causing +12 volts (more or less) to be
set up between the engine/prop and
something like a through-hull. It could
be a short or incorrect wiring to the
appliance. The effect would be to
accelerate the corrosion of the zinc.


We had one eating zincs something awful on an adjacent dock. That was
eating everyone's zincs from the stray currents in the supercharged
water. I had a hand in it after someone mentioned it to me. Noone had
switched off one breaker at a time on the DC panel because everyone was
blaming the marina's AC power system, which was in plastic conduit under
the docks.

We used some Family Radio walkies and setup some meters monitoring zinc
currents to some boats and dock post grounds. It was hilarious when I
flipped off the offending boat's water pump. Everyone keyed their radios
at once to report the current just stopped.

What was wrong was the fresh water pump was plumbed to a metal
(stainless?) water tank in a wet bilge that had contact somehow to the
boat's lead keel...into the ocean. Closer inspection showed there was
12VDC on the old metal diaphram pump's frame when the breaker was on!
One of the brushes was contacting the ungrounded case of the motor, which
was bolted to the metal housing of the old pump's parts.....which hooked
it to the fresh water. I supposed the fresh water had to conduct the
current down the plastic pipes into the metal tankage....to the keel.

Putting +12V, or something less, on a big metal keel weight didn't trip
the breaker (nothing down there was grounded to the battery (-) post,
including the motor's frame). The breaker, of course, was 20 amps so the
current leakage was much less than that trip point. If the pump frame
had been grounded, it would have shorted the 12V and tripped the breaker.

I forget the pump name but it's that one that has a little cog belt
driving a concentric that moves a metal pushrod up and down on a rubber
diaphram that pumps the water. Its name escapes me after midnight. He
got a new plastic pump from Jabsco and everyone's zincs quit fizzing
away. I don't think galvanic isolators can stand a good 12V house
battery's potential.

Larry
--
Grade School Physics Factoid:
A building cannot freefall into its own footprint without
skilled demolition.

Larry wrote:

SNIP

Exactly.

And also on the physics!

Chuck

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