Posted by Fred NC on July 11, 19103 at 18:18:40:
In Reply to: Re: external hull grounding plates posted by ken on July 10, 19103 at 06:18:38:
Sacrificial metals, like ZINC, are great
because they slowly or fastly - "dissolve"
away - when stray electrolysis currents
are present and come into contact with
your boat or motor's metal fittings.
There is some true controversy about "grounding
plates" installed in one's boat hull. This
is documented in several of the major
"mechanical/electrical" marine books. Many
marinas have POOR grounds or no AC grounds for
their dock & piers. Then when they
offer AC shore power connections - often
a boater's hull or metal boat items, becomes
the AC (110 vac) GROUND path for the dock!!! Kind of scarey. They have actually documented deaths of kids swimming in marina areas - killed by these stray AC current loops. The "loop" is
like from your boat's shore power system,
out some metal boat fitting, and back to
the marina dock poorly grounded AC connections!
The "stray AC current" is established between
the missing ground on the AC dock and
marina equipment, thru the water, and into &
thru or via your boat!
It has been suggested that it is a bad
practice, as they do in many older sailboats,
to "ground everything in the boat, all the
sea cocks, etc." - for then for sure you
are all set for the introduction of those
stray errant marina AC currents. Ask you
local marina, when they checked their dock's
AC grounds lately!
It only takes milliamps to kill. Also
"grounding plates" WILL NOT stop or in
any way deter lightning strikes. Nothing
will do that. Possibly one can eliminate
some stray charges from building up on
masts, etc. SSB radio is helped a lot
by these bronze grounding plates (on
outer skin of boat's hull). If anything,
grounding plates - may make it easier
for lightning to find your boat! :)
FYI - retired EE engineer
Fred :) We are building a Double Eagle in timber. The Glen L instructions calls for a 1 sq.ft copper external grounding plate. can any one explain to me what its purpose is and why here in Australia, no fibre glass boats ( the Double Eagle is sheathed in fibre glass ), are fitted with such grounding plates.
: That plate they speak of is used for 'bonding' the fittings in the hull. It helps to prevent electrolysis corrosion of metal parts in the hull.
: A good question would be why has sacrificial zincs become more popular than this system?