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