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.