[Rhodes22-list] lightning protection

Bill Effros bill@effros.com
Tue, 19 Nov 2002 12:52:34 -0500


Todd,

The image of lightning "jumping gaps" is somewhat misleading.  Rather than
rehash everything that has been said previously, let me post a few of the
responses that meant the most to me from previous discussions:

Here is how Razz put it:

Rummy,

If your electrical thrills are the result of electrostatic charge
building up, grounding the rigging won't eliminate the problem as it
is already acting as ground. The charge most likely is building up on
your butt as you slide across the seats. Much like crossing a wool
carpet and getting shocked when you touch the door knob.

Proper grounding for lightning protection involves installing a
lightning rod at the top of the mast and grounding that to a metal
surface of significant area below the water. Boats with exposed lead
or iron keels can use the keel as a grounding surface. Reuel Parker
uses a
2'x2' copper plate laminated into the bottom of his centerboard boat
designs. The cable connecting the lightning rod to the ground plate
should be very heavy guage and insulated
from the mast and rigging. No other metal on the boat, nor any part of
your electrical system should be grounded to this lightning protection
system. The theory is to provide a
clear alternate path to ground for any potential charge buildup. This
does not attract lightning as it serves to dissipate most charges
before they build up to dangerous levels. If  a strike occurs, the
lightning ground provides a cone of protection for the boat and its
occupants equal to the height of the mast. So as long as you aren't
touching metal you are not likely to be injured. One of Parker's 50'
centerboard schooners took a direct hit that blew a hole in the hull
where his ground plate was attached, but no one on board was injured
and the boat did not sink as his designs have water tight bulkheads
between compartments.

Very few lightning strikes actually occur on inland lakes or on any
body of water where land is nearby. Despite the fact that the earth's
surface is 2/3rds water, 94% of all cloud to earth lightning strikes
occur on land. This is due to the fact that large bodies of water
usually carry a positive ionic charge which is the same polarity as
the positive charge build up in thunderstorms and therefore do not
represent a good ground potential compared to the negative charge of
land surfaces. Earth ground really does mean solid ground. A boat is
more likely to be struck sitting in the marina or anchored near land
than out sailing and then only if it is the tallest object around.

RAZZ


Here is what Fred Lange had to say:

West Marine will send you a free packet of articles about lightning.

Included in the material are some interesting statistical studies about
how lightning damages boats.  In summary, sailboats are more likely to
be hit than power boats.  Boats near shore or docked are more likely to
be hit than boats on the open water.  Boats on salt water are more
likely to be hit than boats on fresh water.

The physics of it is that if your boat is in a lower voltage area
between sky and earth surface, the likelihood of getting struck is
higher.

Boats with lightning protection on open salt water suffer only slightly
less damage  from lightning strikes than boats without lightning
protection, but the people aboard fare better.  Boats on open fresh
water pretty much always get sunk when they are hit, but here again
lightning protection helps the people.

I had a sailboat boat hit at the dock in brackish water.  I know because
I had an anchor chain shackled to a stay and the fiberglass next to the
chain was charred.  No other damage.

Since I'm mainly a fresh water sailor, I have extended my experience
with the chain to try and protect the people in the boat if I get hit.
I have 5 battery cables for clamping to the two back stays, the fore
stay and to the port and starboard sides of the mast.  I hope the cables
with their frayed ends will ground most of the strike into the water
leaving the crew untouched.  However, I expect there is till the
likelihood that much of the strike will jump from the base of the mast,
though the cabin and out of the bottom of the hull, filling the Rhodes
with water.

Fred

Here is Roger's 2 cents worth:

Thena,

Yes, the Beneteau 40 footer had one of the tallest masts in the marina that
night.  But, it wasn't the biggest sailboat & there were other boats around
it that had comparably tall masts.  Mast height is an important factor; but,
predicting a lightening strike isn't that simple.  From what I've read, up
to about 50 feet of mast height, an ungrounded mast has about the same
probability of being hit by lightening as the water in the same area.  It
just depends if the boat happens to be unlucky enough to inside the area
where the charge separation is building up.  I subscribe to the principle of
purposely NOT grounding the mast.  I've been out in a number of
thunderstorms in my sailing career & I haven't been hit yet.  Of course, I
may get clobbered tomorrow!

Roger Pihlaja
S/V Dynamic Equilibrium

Here is Michael:

I sail on salt water, it's my view unless I am ready to do the full job and
the
best job I would be asking for trouble that a jury rig system would be able
to
handle. I rather not ask for trouble then wimp out went it comes, but like
everything else in life "You pay your money and take your chances"

MJM

Another dime's worth from Roger:

Everybody seems to be assuming lightening is a bigger hazard to sailboats on
salt water than on fresh water.  I suppose this is because it's well known
that salt water is a better conductor of electricity than fresh water.

Dow Chemical Company, where I work, is the world's largest manufacturer of
chlorine & caustic soda.  Chlorine & caustic soda are made by sending
electricity thru a brine solution inside of a specially designed cell which
is designed to collect the two products.  The process is carried out on a
huge scale because chlorine & caustic soda are used in enormous quantities
in the industrial world.  I know a little bit about the behavior of water &
salt water when carrying very high electrical currents.  Basically, at the
kind of voltage & current we are talking about in a lightening bolt, both
fresh water & salt water behave like very poor conductors of electricity.  I
would expect the electrical resistance in either liquid to dissipate the
electrical energy to heat within a few meters of the impact point.  Since we
are talking about a huge amount of energy in a very short period of time,
this heat would cause the water to flash into steam, maybe even superheated
steam!  I wonder if a lot of the damaging effects of a lightening strike
aren't really blast & thermal effects from a "steam explosion" in the water
under the boat.  Of course, the hole in the hull the lightening had to make
to get to the water isn't much fun either!  In any case, since salt water is
a little more electrically conductive than fresh water, the zone of heating
should extend a little farther away from the point of impact than in fresh
water.  This would spread the energy out over a bigger volume resulting in a
less violent event.  But, this is probably splitting hairs, I doubt there is
very much difference between a lightening strike on fresh vs. salt water.

Roger Pihlaja
S/V Dynamic Equilibrium

Fred again:

Roger,

It is not splitting hairs when you said that salt water will "spread the
energy out over a bigger volume resulting in a less violent event."
Lightning strikes to boats on salt water tend to cause less damage and
injury.  While less frequent, strikes to boats on fresh water are much
more damaging.


Regards,

Fred

Tommy Thompson:

His point about not making it a target is "basically" sound,  particularly
when
one considers all the other mechanics that are at work, rain etc....  Like a
car in the rain, it is grounded, it is a question of how good the ground is,
and hence "bonding" comes into play.

The advantage of any grounding scheme design is to "encourage" the discharge
path away from electronics and/or people.   Which is easy  to conceive on
land.  For example,  if you use a grounded pole or wire overhead it creates
a120 degree umbrella of protection from the top looking down.

On a boat however, especially a small boat, you are still close the
discharge
path itself.   There is always that inherent feeling when you have all the
proper "bonding" done and cabling in place that now you are the best source
for
creating "trailers".  Particularly for the surrounding area in your
immediate
vicinity.  The advantage is only to keep the strike as far away from your
crew
as possible.  On a small boat, we are talking some feet.

Seems more like a coin toss for personal preferences as some argument can be
made either way, considering "added value" to a small boat.

Tommy

Ron Lipton:

This is a good reference:

http://www.thomson.ece.ufl.edu/lightning/

The bottom line is that there is no consensus on whether grounding the
boat
increases the probability of a strike.  Lightning protection is intended
to divert
the current of the strike through a good conductor rather than through
the hull
of your boat (or through you) and not to lessen the probability of a
strike.  Due
to the large currents involved it is difficult to do a proper job
without substantial
conductors.

According to Thomson's study the probability of a strike can
be approximated by drawing an "attractive area" cone with an apex angle
of
132 degrees at the top of the mast.  (This is an rough estimate based on
lighting
strike data and not a calculated angle).  This gives the effective area
of the
Rhodes 22 for lighting strike purposes as about 10,000 square feet.  So
it is roughly equal to the probability of lightning striking a house or
yard.

Given the difficulty in protection and the low probability of a strike I
would not
do anything unless I expect to be traveling in a stormy area.  I would
stay away
from metal parts of the boat if caught in a sudden storm and take
comfort in
the foam flotation in the Rhodes.

Ron Lipton

And the last word from Rummy:

There have been many discussions on this site about lightning. The final
conclusion agreed to by the group is that it is a personal choice whether or
not to ground your mast and shrouds. I don't know of a any Rhodes 22's that
are grounded with a plate or whatever. Salt water conducts electricity a lot
better than fresh water.

My personal choice was not to make my boat a target. It has no grounding
straps. It has been moored on a bouy for many years and tied up at a dock
lately without being a target. By choice, whenever lightning becomes an
issue, I leave the boat and head home.

Rummy



I'm done with this topic for now.

Bill Effros


----- Original Message -----
From: "Todd Tavares" <sprocket80@mail.com>
To: <rhodes22-list@rhodes22.org>
Sent: Tuesday, November 19, 2002 12:13 PM
Subject: Re: [Rhodes22-list] lightning protection


Bill,

     I am by no means an expert, and even the "experts" disagree but, it
seems to me, that if there is a big enough difference of potential for
lightning to "jump the gap" from the clouds to the water, then the 3 to 4
feet of air and fiberglass in your R22 would do little to stop lightning
from shooting a hole right through your boat........or that theory. IMHO

Todd


----- Original Message -----
From: "Bill Effros" <bill@effros.com>
Date: Tue, 19 Nov 2002 10:21:28 -0500
To: "The Rhodes 22 mail list" <rhodes22-list@rhodes22.org>
Subject: Re: [Rhodes22-list] lightning protection


> Brad,
>
> We have this discussion roughly once a year.  When all is said and done,
its
> clear that this is a poorly understood phenomenon.  People selling things
> will scare the shit out of you with horror stories.  They provide
"experts"
> who you have never heard of before, propounding disproven theories as
facts.
>
> None of the theories relate directly to the construction of our boats.
Most
> of the strikes occur on sailboats where there is a direct electrical path
> from the top of the mast to the bottom of the keel, frying electrical
> circuits as they go.  Our masts are, what, 3-4 feet from the water?  They
> are mounted on non-conducting fiberglass, with wooden support, and a lot
of
> air between the bottom of the mast and the water.
>
> Now the first thing you are told about lightning is to not touch the mast
> anytime you are concerned about it.  But your approach would involve
running
> to find an excellent conductor, carrying it on the deck, attaching it to
the
> mast while the other end is still in your hand, and leading it overboard
in
> such it way that it does not foul.  Every time I find myself in a
potential
> lightning situation I reaffirm the fact that I would not even consider
this
> approach at a time I was concerned that lightning might strike at any
> moment.
>
> We know that some lightning starts in the sky and goes down to earth while
> other lightning starts in the earth and goes to the sky.  Our boats are
not
> susceptible to the earth to sky lightning because there is no direct path
> from the earth to our masts--unless we attach a conductor to the mast and
> drape it over the side and into the water.
>
> There is a school that suggests that these lightning protection devices
> generate more strikes on the boats they are supposed to protect.
>
> I don't know, but I do know that I have never heard of an R-22 being
> structurally damaged by lightning.  And I always go back to my main motto:
> "If it ain't broke, don't fix it."
>
> Bill Effros
>
> PS -- Sorry to hear about your headache.  Maybe it was the fumes from your
> generator?
>
>
>
>
> ----- Original Message -----
> From: "brad haslett" <flybrad@yahoo.com>
> To: "The Rhodes 22 mail list" <rhodes22-list@rhodes22.org>
> Sent: Tuesday, November 19, 2002 9:38 AM
> Subject: Re: [Rhodes22-list] lightning protection
>
>
> Bill, several sources I've read indicate that is a
> mis-conception.  The statistical data for boats at
> moorings don't indicate a higher mast being more
> likely to be struck than a lower one. Brad.
> --- Bill Effros <bill@effros.com> wrote:
> > Sail or dock near a boat with a 30' mast.
> >
> > Bill Effros
> >
> >
> > ----- Original Message -----
> > From: "brad haslett" <flybrad@yahoo.com>
> > To: <rhodes22-list@rhodes22.org>
> > Sent: Tuesday, November 19, 2002 7:58 AM
> > Subject: [Rhodes22-list] lightning protection
> >
> >
> > This all got started while doing research on
> > installing a mast antennae.  Several vendors lightly
> > addressed surge protection from lightning strikes to
> > the mast and I thought, "who cares about electronic
> > euqipment? I want the boat to survive!"  Yesterday I
> > spent eight plus hours on the net researching the
> > issue and downloaded a 3" binders worth of material
> > including the R-22 site info.  My conclusion is
> > this;
> > sailboats take more lightning strikes than one would
> > think, freshwater boats without grounding don't fare
> > well, and, protection is not that difficult.  While
> > there are many different opinions and several "old
> > wives tales" the general concensus among the experts
> > is that having a protection system on board does not
> > make one more likely to be struck.  All protection
> > systems pretty much do the same thing, they provide
> > a
> > path from the mast to the water.  While at dock its
> > a
> > simple matter of attaching a #4 cable or flat
> > conductor to a 1' square or bigger conductor in the
> > water.  The straighter the path and the fewer the
> > bends the better (lightning doesn't like to turn
> > corners).  Under sail is a different story.  No one
> > wants to sail with cables on the foredeck and plates
> > dangling in the water.  Therefore, a portable and
> > quickly attachable system is needed (battery cables
> > get knocked off at the moment of strike).  The
> > StrikeShield system is perfect but expensive.  I am
> > presently researching a "homemade", ie, Home Depot
> > approach that will do the same thing for far less
> > money. Most boat manufacturers don't address the
> > issue, probably for liability reasons.  Catalina
> > issues a bulliten from the ABYC on the subject and
> > basically tells you "you're on your own".  Over the
> > past fifteen years I have been caught at least three
> > times in thunderstorms in powerboats and once in a
> > canoe.  Now that my boat has a 26ft tall lightning
> > rod
> > I'd like to better my chances.  Ideas?
> >
> > Brad Haslett
> > "CoraShen"
> >
> > __________________________________________________
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> >
> >
> >
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