Bronze Seacock Paranoia?
 

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

First question: are the bronze seacocks connected electrically (i.e., by
wire) to your engine ground? If not, you have nothing at all to worry
about. If they are grounded by wire, is there a reason? There are many
different bronzes, of course, but in the old days, they would last the
life of the boat. Were they replaced 4 years ago because of corrosion or
failure?

I believe a reasonably knowledgeable diver would be able to detect
energetic corrosion of the seacocks, as well as any other underwater
metals, like the ruddershaft. I gather you used a diver to inspect your
prop shaft zincs after you installed the isolator but you didn't check
the seacocks at the time?

Good luck, and hopefully, suspend the paranoia.

Chuck



cvj wrote:
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

Hi Chuck,

Thanks for setting my mind at ease.

First question: are the bronze seacocks connected electrically (i.e., by
wire) to your engine ground? If not, you have nothing at all to worry
about.
No, they are not.

If they are grounded by wire, is there a reason? There are many
different bronzes, of course, but in the old days, they would last the
life of the boat. Were they replaced 4 years ago because of corrosion or
failure?

No, that's when the boat was built.

I believe a reasonably knowledgeable diver would be able to detect
energetic corrosion of the seacocks, as well as any other underwater
metals, like the ruddershaft. I gather you used a diver to inspect your
prop shaft zincs after you installed the isolator but you didn't check the
seacocks at the time?

No, I replaced the prop shaft zincs when the boat was hauled out in May.


Good luck, and hopefully, suspend the paranoia.

Suspended now...with thanks.

Claus

cvj wrote:
Hi Chuck,

Thanks for setting my mind at ease.

First question: are the bronze seacocks connected electrically (i.e., by
wire) to your engine ground? If not, you have nothing at all to worry
about.
No, they are not.

It is good & common practice to bond all bronze through-hulls together
on a nonconductive hull to spread/equalize galvanic currents (and
reduce localized problems).

If they are grounded by wire, is there a reason? There are many
different bronzes, of course, but in the old days, they would last the
life of the boat. Were they replaced 4 years ago because of corrosion or
failure?

No, that's when the boat was built.

I believe a reasonably knowledgeable diver would be able to detect
energetic corrosion of the seacocks, as well as any other underwater
metals, like the ruddershaft. I gather you used a diver to inspect your
prop shaft zincs after you installed the isolator but you didn't check the
seacocks at the time?

No, I replaced the prop shaft zincs when the boat was hauled out in May.

Why didn't you do normal through-hull & seacock inspection &
maintenance at the same time? FWIW real seacocks (meaning the tapered
bronze plug variety & not ball valves) often show pitting on their
explosed closed-position side of the plug, which may be rotated 180 for
more life before regrinding. You're supposed to
pull/inspect/clean/lube/repack & otherwise care for seacocks at every
reasonable opportunity, esp when doing the rest of antigalvanic things.
You should also be viewing any signs of excessive through-hull fitting
wastage for yourself.

Good luck, and hopefully, suspend the paranoia.

It is guilt, not paranoia. ;-)

Frank
Hates ball valve seacocks & other expensive, dumass, hard-to-maintain
things people put on boats.

Hello Frank,

Interesting comments.

My experience has been that it is not necessarily good or common
practice to bond all bronze through-hulls. It is rarely done in Europe,
and the ABYC makes clear that electrically isolated through-hull
fittings need not be bonded. While it is true that stray currents inside
the hull may cause corrosion of through-hulls, bonding through-hulls ".
.. . causes corrosion due to stray currents outside the hull".
(Boatowner's Illustrated Handbook of Wiring by Charlie Wing)

Certain types of bronze may need cathodic protection, but they are not
often found in through-hulls.

As I see it, there may be any number of problems with the original
poster's through-hulls. They may be made of junk, may have been attached
with dissimilar fasteners, may be inadvertently carrying stray current
from a wiring problem in the bilge, etc. But the issue, I believe, is
whether an isolated, submerged, marine bronze component can be assumed
to be at risk of corrosion solely by virtue of not being bonded to the
boat's ground system. My understanding is that it cannot.

Can you elaborate on the mechanism by which you believe spreading and
equalizing galvanic currents will protect the through-hulls? Or did you
mean that the through-hulls would help protect the prop thereby?

Regards,

Chuck

wrote:
cvj wrote:

Hi Chuck,

Thanks for setting my mind at ease.


First question: are the bronze seacocks connected electrically (i.e., by
wire) to your engine ground? If not, you have nothing at all to worry
about.

No, they are not.


It is good & common practice to bond all bronze through-hulls together
on a nonconductive hull to spread/equalize galvanic currents (and
reduce localized problems).


If they are grounded by wire, is there a reason? There are many

different bronzes, of course, but in the old days, they would last the
life of the boat. Were they replaced 4 years ago because of corrosion or
failure?

No, that's when the boat was built.

I believe a reasonably knowledgeable diver would be able to detect
energetic corrosion of the seacocks, as well as any other underwater
metals, like the ruddershaft. I gather you used a diver to inspect your
prop shaft zincs after you installed the isolator but you didn't check the
seacocks at the time?

No, I replaced the prop shaft zincs when the boat was hauled out in May.


Why didn't you do normal through-hull & seacock inspection &
maintenance at the same time? FWIW real seacocks (meaning the tapered
bronze plug variety & not ball valves) often show pitting on their
explosed closed-position side of the plug, which may be rotated 180 for
more life before regrinding. You're supposed to
pull/inspect/clean/lube/repack & otherwise care for seacocks at every
reasonable opportunity, esp when doing the rest of antigalvanic things.
You should also be viewing any signs of excessive through-hull fitting
wastage for yourself.


Good luck, and hopefully, suspend the paranoia.


It is guilt, not paranoia. ;-)

Frank
Hates ball valve seacocks & other expensive, dumass, hard-to-maintain
things people put on boats.

chuck wrote:
Hello Frank,

Interesting comments.

My experience has been that it is not necessarily good or common
practice to bond all bronze through-hulls. It is rarely done in Europe,
and the ABYC makes clear that electrically isolated through-hull
fittings need not be bonded. While it is true that stray currents inside
the hull may cause corrosion of through-hulls, bonding through-hulls ".
. . causes corrosion due to stray currents outside the hull".
(Boatowner's Illustrated Handbook of Wiring by Charlie Wing)

To be honest I have no strong opinion either way, but I thought the
ABYC standard was unequivocal. In my 1998 copy they say:

"H-27.7.5.2 Metallic thru-hull fittings and drain plugs, installed
below the normal accumulation of bilge water, shall be bonded to the
boat's common ground point to minimize stray current corrosion."

Has their thinking changed since then?

Hello Jeff,

Thanks for the comment.

I don't have my copy handy, but I believe the section you quoted is a
special case: fittings installed below the normal accumulation of bilge
water. Fortunately, that is not the usual location for thru-hulls.
ABYC's reasoning is probably that should a hot wire come in contact with
the bilge water near the thru-hull, a corrosion circuit could be formed.
Of course, the wire itself would probably quickly corrode to nothing and
the problem would be self-correcting. More or less. At least there is an
identifiable benefit to bonding in this case.

Regards,

Chuck







Jeff wrote:
chuck wrote:

Hello Frank,

Interesting comments.

My experience has been that it is not necessarily good or common
practice to bond all bronze through-hulls. It is rarely done in
Europe, and the ABYC makes clear that electrically isolated
through-hull fittings need not be bonded. While it is true that stray
currents inside the hull may cause corrosion of through-hulls, bonding
through-hulls ". . . causes corrosion due to stray currents outside
the hull". (Boatowner's Illustrated Handbook of Wiring by Charlie Wing)


To be honest I have no strong opinion either way, but I thought the ABYC
standard was unequivocal. In my 1998 copy they say:

"H-27.7.5.2 Metallic thru-hull fittings and drain plugs, installed
below the normal accumulation of bilge water, shall be bonded to the
boat's common ground point to minimize stray current corrosion."

Has their thinking changed since then?

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