T&T: Green bonding wires and wood boat deterioriation

[Robin Brueckner]

I recently posted the following on the Hatteras owners website...this is
informational and primarily for wood boat owners .......A search should
turn up prior posts on this subject. Delignification of wood simply means
that when even small electrical currents pass through wet wood, the ion
flow destroys some of the wood..lignin.... which leaves a weakened,
leaky,mushy,soft mash of remaining wood components. Most susceptible are
thru hulls where the interior is out of bilge water...shaft log wood
mountings are often susceptible for this reason.

Stray currents (leaking from improper wiring or poor insulation and
called "electrolysis" or stray current corrosion) and especially dc leaks
are SERIOUS and should be corrected promptly. AC leaks should be fixed as
well, but do not ruin metal and wood nearly as fast for comparable
current flows..

Another source of unwanted electrical currents through wet wood is zinc
protection: it can protect underwater metals and destroy wood at the same
time. Too much zinc: wood damage!!!! One solution is to reduce zincs
until just the minimum voltage is present to protect metals...usually
about 500 mv (1/2 volt) for common marine bronze relative to a
silver/silver chloride reference. Once delignification begins that likely
won't be enough to stop further wood damage: it's best to disconnect
bonding from isolated marine silicion bronze thru hulls...they will last
virtually forever. Beware older foreign alloys.

If zincs deterioriate and fall off, galvanic corrosion (current flow due
to different metals being immersed in an electrolyte (salt water)) can
commence and may also further deterioriate wood. A bonding system without
zincs is positively worse than no bonding system. No bonding wires is the
best protection for wood.

Another negative aspect to bonding: if there is stray current present in
the water, say from a poorly insulated dock electric line, the thru hulls
connected via bonding act as a big antenna and pick up the
voltage...current flows into the thru hulls and ashore via
ground....further deterioriating wet wood. If no bonding, no current flow
thru any thru hull and they are safe. Another potential effect of bonding
wires: a lightning strike may be directed to a thru hull and it literally
blows up from a strike...boat sinks...!!!!

Note that in general fiberglass boat bottoms are rather impervious to
normal galvanic current flows...not so wood.
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