Galvanic corrosion is caused by dissimilar metals below the water line.
Zincs are bandaids, they do not correct the problem. You should be worried,
because your throughhull bronze fittings will fail. It is just a matter of
time and from your description of your zincs, it won't be long. Bonding your
throughhull fittings will even make the corrosion rate faster. I suggest you
locate the cause of the galvanic current and eliminate the problem. I would
not be surprised if you find that the throughull fittings are the cause of
the problem, not the effect. For instance, there is no reason not to replace
the fittings with plastic fittings. You already run the fire risk anyway, as
your hull is plastic. The use of metal throughulls adds no additional value.
There are some exceptional high quality plastic ball valves used in the
corrosive chemical industry, which would make the entire problem go away.
Steve

"cvj" wrote in message
...
I recently had to install a Galvanic Isolator in order to reduce zinc loss
on my boat. I have zinc anodes both on the propellor shaft (3 small zincs
on a Volvo Sail Drive) as well as a large separate zinc wired to the
engine. Prior to the installation of the Galvanic Isolator, the propellor
zincs would be "gone" after only 1 1/2 month.

But now I am concerned that the bronze seacocks (4 years old) may also
have been subject to some galvanic erosion - and I am wondering how you
check the integrity of the bronze seacocks without hauling the boat out of
water? Is this something that can be done by a diver?

And in general - how "paranoid" should one be about the possibility of a
bronze seacock failing without prior warning? I have purchased the
recommended soft wood plugs....but that still does not abate the worry....

Any thoughts.....

Clus

Hello Steve,

Isn't it likely he already solved "the problem" when he installed the
galvanic isolator?

Unbonded, the bronze thru-hulls will be subject only to "self-corrosion"
which is something like 0.0002 inches or less of surface loss per year
for a high-quality bronze in seawater. Hardly a reason for concern.

You are correct that bonding could make matters worse. Galvanic
corrosion can ONLY occur if there is an electrical path (like a bonding
wire) connecting the dissimilar metals.

But the suggestion that unbonded bronze thru-hulls caused accelerated
zinc loss in the presence of stray currents in the 120 vac marina ground
wire is outside my understanding of electrochemistry. A much more likely
culprit is a nearby, unprotected or underprotected boat that is using
the green wire to complete a galvanic cell.

In a hundred years or so, when the current bronze thru-hulls begin to
look bad, maybe plastic would be an attractive replacement.

Chuck






Steve Lusardi wrote:
Galvanic corrosion is caused by dissimilar metals below the water line.
Zincs are bandaids, they do not correct the problem. You should be worried,
because your throughhull bronze fittings will fail. It is just a matter of
time and from your description of your zincs, it won't be long. Bonding your
throughhull fittings will even make the corrosion rate faster. I suggest you
locate the cause of the galvanic current and eliminate the problem. I would
not be surprised if you find that the throughull fittings are the cause of
the problem, not the effect. For instance, there is no reason not to replace
the fittings with plastic fittings. You already run the fire risk anyway, as
your hull is plastic. The use of metal throughulls adds no additional value.
There are some exceptional high quality plastic ball valves used in the
corrosive chemical industry, which would make the entire problem go away.
Steve

"cvj" wrote in message
...

I recently had to install a Galvanic Isolator in order to reduce zinc loss
on my boat. I have zinc anodes both on the propellor shaft (3 small zincs
on a Volvo Sail Drive) as well as a large separate zinc wired to the
engine. Prior to the installation of the Galvanic Isolator, the propellor
zincs would be "gone" after only 1 1/2 month.

But now I am concerned that the bronze seacocks (4 years old) may also
have been subject to some galvanic erosion - and I am wondering how you
check the integrity of the bronze seacocks without hauling the boat out of
water? Is this something that can be done by a diver?

And in general - how "paranoid" should one be about the possibility of a
bronze seacock failing without prior warning? I have purchased the
recommended soft wood plugs....but that still does not abate the worry....

Any thoughts.....

Clus

"chuck" wrote in message
nk.net...
Hello Steve,

But the suggestion that unbonded bronze thru-hulls caused accelerated zinc
loss in the presence of stray currents in the 120 vac marina ground wire
is outside my understanding of electrochemistry. A much more likely
culprit is a nearby, unprotected or underprotected boat that is using the
green wire to complete a galvanic cell.


Chuck, just to add further information to the discussion, I had the marina's
electrician measure the stray currents after the Galvanic Isolator was
installed. He stated that the boat now was protected from the stray currents
in the slip. However, he measured the boat in the next slip, which is
basically in totally run-down condition...boat is never used and not
maintained...and it appeared that this boat was the culprit (confirming your
statement above).

So, based on all the valuable information in this thread, I am going to have
a diver inspect the zincs and the seacocks within the next month...and in
addition, I plan to have the seacocks inspected and serviced on the next
scheduled haul-out in the Spring.

In the meantime, I will try to control my paranoia and or guilt or
whatever... :-)

Claus

cvj wrote:

...and in
addition, I plan to have the seacocks inspected and serviced on the next
scheduled haul-out in the Spring.

This is a fairly easy task you may carry out yourself, if desired, that
will give more comfort & familiarity in dealing with potential problems
that can arise afloat.

cvj wrote:

"chuck" wrote in message
nk.net...

Hello Steve,

But the suggestion that unbonded bronze thru-hulls caused accelerated zinc
loss in the presence of stray currents in the 120 vac marina ground wire
is outside my understanding of electrochemistry. A much more likely
culprit is a nearby, unprotected or underprotected boat that is using the
green wire to complete a galvanic cell.



Chuck, just to add further information to the discussion, I had the marina's
electrician measure the stray currents after the Galvanic Isolator was
installed. He stated that the boat now was protected from the stray currents
in the slip. However, he measured the boat in the next slip, which is
basically in totally run-down condition...boat is never used and not
maintained...and it appeared that this boat was the culprit (confirming your
statement above).

So, based on all the valuable information in this thread, I am going to have
a diver inspect the zincs and the seacocks within the next month...and in
addition, I plan to have the seacocks inspected and serviced on the next
scheduled haul-out in the Spring.

In the meantime, I will try to control my paranoia and or guilt or
whatever... :-)

Claus



Bonding and monitoring of metal fittings to zincs is the prime mover
that drives at least part of any electrochemical galvanic corrosion.
The presence of current in a meter monitoring the activity will see
current through the fitting only in the presence of a sacrificial
zinc. Snake oil to cure the healthy, quackery, indeed.

In the event I am wrong, then some other dissimilar metal will be
causing the current (the test probe?) and it too, will be bonded.
Tee hee. Only then is a zinc required, to protect the commoner metal
if the bond cannot be avoided or disconnected, removed. Their
effect is localised. The fact that they erode is proof only that
there is some other metal, bonded close enough to help cause a
reaction, not neccessarily the three required, if you wanted to
remove the zinc without stopping all of the activity.

Is any of this getting through?

Why not gild the through hull, shaft and propellor? I'd do the radio
signal ground test reference resistive sea connection, and the
lightning ground plate, too. Gilt is probably cheaper than zinc
longterm.

Externally imposed electroplating donation / theft of your precious
metal bits cannot happen unless somebody has connected the power
line to the water, for the second time. Find him. Dissasemble the
connection. By the way, one of the two conductor connections
required to complete the circuit, the earth ground connection,
neutral centre balance main power connector, impersonator of a safe,
neccessary, common, free (for them), universal power connection, is
provided (co-opted, liberated, stolen from everybody, actually) by
the hydro company to save money, and it is which alone enables,
attracts, causes "live" wire current to flow in that scenario to
begin with.

It's a form of electrical pollution by big industry. Deadly
murderous pollution, a man trap with every foolish inefficiency
removed from it. One tiny eror and it is garaunteed to get even
you, wherever you are. Everything to make ready has been done. The
earth itself has been energized. Only one small slip is required.

Even the worms aren't safe!

Don't get me started again.

Paranoia? Who could sell anything with paranioa?

Subliminal what?

Terry K

Steve Lusardi wrote:

Bonding your
throughhull fittings will even make the corrosion rate faster.

Steve, omitting all the boats that are bonded or unbonded & various
circumstances & results, I am wondering if it is std practice to
calculate & size anodic protection in terms of current & exposed metal
areas as in commercial practice? (apart from any other considerations
of galvanic currents from neighboring boats/docks/power grounds/etc.)

The use of metal throughulls adds no additional value.
There are some exceptional high quality plastic ball valves used in the
corrosive chemical industry, which would make the entire problem go away.

Would seem wise & even moreso if ball valves are to be used. The
disadvantages of a bronze through-hull combined with those of a
bronze-bodied SS ball valve seem counterproductive all the way around.

In article ,
"Steve Lusardi" wrote:

For instance, there is no reason not to replace the fittings with
plastic fittings.

There are MANY reasons not to use plastic below the waterline. You might
be able to make a case for the fiberglass-enhanced ones, but they're
really not that much less expensive in the long run. I definitely
wouldn't trust a PVC fitting underwater.

Then again, most transducers are some sort of plastic.... and I'm
nervous enough about mine that I inspect them each time I board and
leave the boat.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/