[Rhodes22-list] Lighting Rod

Tue Mar 11 11:22:14 EDT 2014

Hi James,

    I meant that 10 meters of air is roughly equivalent in spark 
resistance to 1 meter of fiberglass.
We actually have about a centimeter of fiberglass, which corresponds to 
about 200kV, certainly
something that a lightning bolt can develop.  On the other hand, on the 
Rhodes the current is more
likely to follow the shrouds and spark over the sides rather than 
through the bottom. Puncture
of the bottom is much more likely with a keel-stepped mast.
There is more then enough current to be dangerous and kill all 
electronics. Water on the
surface of the boat can increase surface conduction and is an alternate 
path. It will be rapidly
vaporized by the kiloamp currents developed by lightning, but may leave 
an ionized conducting
path to sustain the spark.

   About transmission lines.  They use ceramic or glass insulators which 
are designed as
stacked mushrooms to increase surface path length and shed water. A 
meter of air
corresponds to about 300kV, so an uninsulated transmission line can hold 
off at least that
much.

   I am not an expert, but I do have some experience with high voltage 
systems (long ago).
Back then you painted it with "corona dope" until it stopped sparking.

Ron

On 3/10/14, 11:28 PM, James Nichols wrote:
> Just a little math to show what I am referring to.
>
> Air is about 3000V/mm or about 3,000,000V/M.  Assuming 10 meters of aluminum
> mast is perfect conduction just for ease, but in reality aluminum is only a
> reasonable conductor used mostly for its durability rather than its ability
> to conduct.  That means the lightning can bypass 30,000,000 volts worth of
> air passage.  However, once it reaches the fiberglass hull, 1 meter of
> fiberglass is requires 20,000,000 V to transverse, and with the hull's
> circumference to the waterline being about 9 feet (or 3 meters) that means
> there is 60,000,000 V increased requirements to pass through the hull.
>
> If the direct line distance from the tip of the mast to the water line is 12
> meters, we're talking about 36,000,000 V to traverse that leap.
> The same distance through the mast and then hull requires the lightning to
> use 60,000,000 V.
>
> So it just makes sense that the lightning won't pass through the hull unless
> there is something wrong with the integrity of the hull.
>
> A more likely scenario for a boat in well maintained condition would be that
> the lightning might use the mast to bypass 10 meters of air, then make a
> leap into the air again at the base of the mast around the side of the boat
> to the water, saving a net of 7 meters of air passage.  I could see the mast
> being seriously damaged in that situation and probably the connection to the
> hull at the foot of the mast as well.
>
> -----Original Message-----
> From: rhodes22-list-bounces at rhodes22.org
> [mailto:rhodes22-list-bounces at rhodes22.org] On Behalf Of James Nichols
> Sent: Monday, March 10, 2014 10:55 PM
> To: 'The Rhodes 22 Email List'
> Subject: Re: [Rhodes22-list] Lighting Rod
>
> 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."
>
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