[Rhodes22-list] Lighting Rod

[James Nichols]

There is something else that is shorting out the route between the mast and
the water, not the length of the mast.  High power lines run at 120kV and
only have a meter or two of glass insulating them from the 50 meter steel
tower that the lines are attached to.  The lines and the tower are vastly
larger than the glass insulators so there is no possibility that the 3+
meters (circumference because the lightning will try and travel on the skin
of the material first) of fiberglass on the boat is more than enough to
insulate the mast from the water.

The problem is most likely related to the metal fittings that pierce the
skin of the hull from the mast hull and allow the lightning to get to the
core.  Which if it is like my boat, my core is saturated with water from a
poor repair job on the forward hatch.  That linked with other imperfections
in the hull could lead to lightning finding a path through the boat, however
a well maintained boat that has not had water penetrate into the core would
most likely not have any problems insulating the mast from the water
sufficiently.

Which on a side note, the '71 Rhodes has a balsa core and not a plywood core
like I had originally thought.  I've got most of inside fiberglass skin
peeled off the forward deck on my boat and I'm getting ready to go back with
some nice waterproof ply and oak strips to frame and reinforce the forward
deck.  I'll upload pictures on my previous thread when I get a little
further along.

James

-----Original Message-----
From: rhodes22-list-bounces at rhodes22.org
[mailto:rhodes22-list-bounces at rhodes22.org] On Behalf Of Ron Lipton
Sent: Monday, March 10, 2014 10:33 PM
To: The Rhodes 22 Email List
Subject: Re: [Rhodes22-list] Lighting Rod

I got interested in this because I know that lightning will punch through
fiberglass hulls. The dielectric strength (breakdown voltage) of dry air is
about 3000 V/mm. The dielectric strength that I could find for fiberglass is
about 20000 V/mm.  So fiberglass (at least the stuff used in PC boards) is
only about a factor six or seven better than air.  Humidity actually appears
to increase the breakdown voltage a bit. As a rough estimate I would guess
that a 10 meter mast "shorts out" the equivalent of 1 meter of fiberglass,
much thicker than the hull (the number seems too large to me-I will check
some more). So if given the choice the lightning will proceed through the
mast and fiberglass rather than the air. That explains why lightning will
often punch a hole in the fiberglass on the bottom of a boat, sinking it,
rather than find a path outside. 

I am pretty sure fields generated by the motor have no effect. 

Ron

> On Mar 10, 2014, at 21:42, "James Nichols" <jfn302 at yahoo.com> wrote:
> 
> Typically Lightning will not strike anything that does not give it a 
> clear path to ground, so running a wire from the mast to the water is 
> only inviting lightning to strike the boat more often.  Lightning, 
> like water, always looks for the easiest path to ground.  Fiberglass 
> is an awesome insulator,  so the mast doesn't typically attract 
> lightning.  Also, while lake and sea water conduct electricity (sea 
> water is a much better conductor because of the salt) Lightning on a 
> lake setting will more likely hit a tree on the shoreline because the 
> path through the tree into the earth is much easier than the path 
> through the boat, through the water, then into the ground.  Also, 
> while most lightning happens during a storm, so the fiberglass on the 
> boat will be wet, the amount of water clinging to the deck doesn't 
> usually offer enough of an electrical pathway from the mast to the 
> main body of water  that the lightning would choose to strike the boat
over striking the water directly.
> 
> All these statements aside though, as Ron said, stay away from large 
> metal objects on the boat during a storm, and you should be fine.
> 
> As a side note about the quote about deaths of boaters but not sailboats.
> The boats that have deaths are because they are running motorboats 
> that have large engines that create large electro-magnetic fields to 
> drive the motor, and they tend to run them all out, so the 
> electro-magnetic field is as large as it can get, and as they are 
> screaming across the water, what they don't realize is they are screaming,
"STRIKE ME!!"  And nature says, "Ok."
>