wrote in message
...
On Aug 21, 10:30 am, wrote:
On Aug 21, 10:09 am, "Eisboch" wrote:



"Richard Casady" wrote in message

.. .

You evidently think a lightning rod will somehow increase the danger,
but such has been proven by long experience not to be the case. BS in
other words. The lightning rod doesn't know or care what is under it.
It prevents strikes in a 90 degree cone under it. Works equally well
for buildings, boats, and powerlines.

Casady

I think we are talking two different concepts here.

A lightning rod is designed to be "the" point of strike, should one
occur
and equipped with sufficiently sized conductors to discharge the strike
to
ground.
.
I am talking about making the building, boat, or whatever less
favorable to
the strike.

It has to do with the positive column .... based on the static charge
that
builds on the ground point.

Eisboch

Wiki has a good discussion of Lightning rods and basically the theory
of preventing a strike by dissipating charge from the ground is very
controversial. Like Eisboch, I have some familiarity with HV and
large electrical sparks, My graduate work was on electrical particle
charging by very high electric fields to improve electrostatic
precipitators. My experience with this is that things like so-called
lightning dissipators tend to increase the likelyhood of attracting a
spark. I am not certain this experience can be generalized to
lightning but such dissipators do not seem to work well in practice
any better than conventional lightning rods.
The safe approach would seem to be to have a very good conducting path
with few bends going to a large grounded conductor.
I do not think that those sintered metal plates used to ground radios
will work to replace a large area conductor for lightning. The
electric fields inside the pores of those plates will essentially be
zero so that the actual area for the purpose of dissipating a
lightning strike will basicall be the outside surface area that is
fairly small.

My reasoning on why the so-called dissipators do not work (these
things often look like a brush atop a mast) is that the actual static
charge that would need to be dissipated is enormous. Basically, you
are trying to dissipate a charge from many meters around your boat (or
other object) and in these kinds of E fields, everything conducts.
So, if you do end up dissipating this charge, you ionize the air above
the dissipator causing a strike. In general, these systems are well
grounded so they then act like a conventional lightning rod.

Indeed, they are controversial, but the theory is supported by many in the
"field" so to speak.
My understanding is that they act in a similar manner to a dark space shield
around the back side and edges of a sputtering target. When the target or
cathode is energize with enough voltage to ionize the partial pressure
within the vacuum chamber, the small space (1/4 inch or so, depending on
pressure and voltage) between the cathode and the grounded dark space shield
does not have sufficient ions to sustain current flow, so there is no
plasma. Move the dark space shield *away* from the cathode (increasing
the space) and a discharge current will start. I am sure you are familiar
with the Faraday Column and the voltage division nature of a plasma (or
lightning) discharge.

One explanation of the workings of the static charge dissipaters is similar.
There simply are not enough ions around each of the thousands of points so
sustain current flow.

In the case of my boat that has one .... I figure it can't do any harm, even
if the theory is wrong.

Eisboch