[Rhodes22-list] lightning protection
Roger Pihlaja
cen09402@centurytel.net
Thu, 21 Nov 2002 08:29:15 -0500
Brad,
You're right, the ASCE lightning database is based upon land based
structures. I haven't seen any good data re structures on water fresh or
saltwater. I suspect an industry like offshore oil drilling would be quite
knowledgeable in lightening strikes on the water. Companies like Shell Oil
& British Petroleum probably have extensive databases on the subject, but
may also regard it as proprietary & don't publish. But, if you're going to
do a search, you might look in the technical periodicals that cater to the
oil industry.
Many large companies are also self-insured, so the insurance industry won't
have good data. For example, I once sat next to an engineer from BP on a
transatlantic flight. This fellow was involved with BP's offshore oil
drilling program in the North Sea. At the time, these offshore oil
platforms cost about one billion dollars each. They were built in Scotland
or the Netherlands & towed into position into the North Sea. BP had setup
their financing & self-insurance on these projects such that a 25% loss rate
on these platforms during towing & installation was acceptable!
When I say a tree's roots on the shoreline extend quite a distance out into
the water, I'm referring to a distance comparable to the size of the tree's
leaf canopy or maybe a little larger. If you were anchored, say 50 yards,
offshore in a cove from such a tree & it got struck, you would get the
living daylights scared out of you from the flash & the simultaneous
deafening kaboom! You might even have some damage to the on-board
electronics from the EMP. But, even, if the lightening caused a steam
explosion in the underwater root system, your boat would just get a violent
shaking. So, if you can't find a cove that's at least 100 yards across,
then that's probably too small to be a good place to hole up during a storm.
My family has had two close encounters with lightning. The 1st involved a
lightning strike on a big oak tree behind our garage, which jumped to the
roof of our garage, got into the garage's electrical system, & set fire to
the circuit breaker box in the garage. It also caused some electrical surge
damage to our refrigerator & television set in the house. The strike
happened in the middle of the night, but fortunately, we were home at the
time. I put out the fire in the circuit breaker box myself with a fire
extinguisher in the garage even before the fire dept arrived. Amazingly,
the oak tree survived the lightning strike, although the scars are very
visible even to this day.
The 2nd close lightning encounter occurred at the marina on Kelly's Island
in Western Lake Erie. We were docked right up against the wharf right
across from the Marina store. The enclosed link is a photo of Dynamic
Equilibrium at the dock the day after this incident:
http://www.rhodes22.org/rhodes/pics/BiminiTop4.jpg
The building in the background behind our boat is the marina store. Anyway,
at about 03:00, the night before, Daniel, Gary, & I were awakened by a
deafening kaboom & painfully bright flash, even inside Dynamic Equilibrium's
cabin. I was sleeping on the main cabin settee & I jumped up to look out
the starboard side window on the pop top enclosure. All the yard lights in
the marina had been knocked out by the strike & everything was pitch black.
But, gradually, my night vision returned & I could make out the fading dull
red outline of the top of a sailboat's mast about 5 slips down. Then, there
was a cloud-to-cloud lightning flash that illuminated the scene sufficiently
that I could see the boat's mast was melted & bent above the spreader! The
EMP or power surge had triggered the alarm in the marina store, so that was
ringing loudly thru the entire incident. The boys & I quickly threw on some
clothes, went over to the stricken boat, & boarded her. There was nobody on
board. There was no fire on board & the boat didn't seem to be taking on
water. So we left & went & stood in the front entrance of the marina store,
despite the noise from the alarm. The owner of the store lived nearby.
After a few more minutes, he arrived & shut off the alarm. We watched the
rest of the storm pass thru the area from inside the store along with about
20 other boaters. The following morning, the owner of the boat arrived. I
went over & introduced myself. We talked about the events of the night
before & I told him I'd boarded his boat to search for any injured, fire,
&/or leaks. Besides the mast, all the electronics on board the boat were
fried.
But, I digress...
Although the existing data on lightening strikes is based upon land-based
data which may not be perfectly representative of the situation on the
water, it's still the only trustworthy data I've seen. The lightning
phenomena is too chaotic & complex to believe the theory & computer models
without a lot of back-up data. So, with due respect for your learned
professors, until they can show me their data, I take everything they say
with a grain of salt. Until someone can show me different, I'm going to
follow the lessons from the ASCE database & not ground my mast.
Roger Pihlaja
S/V Dynamic Equilibrium
----- Original Message -----
From: "brad haslett" <flybrad@yahoo.com>
To: "The Rhodes 22 mail list" <rhodes22-list@rhodes22.org>
Sent: Wednesday, November 20, 2002 9:04 PM
Subject: RE: [Rhodes22-list] lightning protection
> Roger,
>
> Thanks for the input. My problem with your data is
> that its based on land based structures. I haven't
> found any statistical data on water based structures
> (ie. boats). The marine insurance industry data
> indicates that 10% of all cruising deaths are by
> lightning strikes. While that may not be a problem
> for Rhodes 22 owners, since we don't make long
> passages, it still leaves some room for doubt about
> overnighting on fresh water lakes. If you anchor in a
> cove you've already violated your suggestion to stay
> away from trees. If you're in the middle of the body
> of water (unlikely for most of us) you ARE the tallest
> structure. Which brings us back to the original
> dilemma, what's the data on that? In my part of the
> South you will give up half the sailing season if you
> stay home any time "a chance of isolated
> thunderstorms" appears in the forcast. I think the
> bottom line on this issue is that there have only been
> a few studies done and most of the articles written on
> the subject keep citing the same sources. I'm anxious
> to read the ABYC and National Fire Code resources on
> the subject but I suspect it will just be a re-hash of
> the same insufficient data.
>
> Brad Haslett
> "CoraShen"
> --- Al Miller <al.shell@verizon.net> wrote:
> > Roger,
> >
> > I like the way your explanation fits what I hoped
> > was true! I suppose
> > my only ground problem will come from installing a
> > ham rig in the boat.
> >
> > Al-Mishka
> >
> >
> > -----Original Message-----
> > From: rhodes22-list-bounces@rhodes22.org
> > [mailto:rhodes22-list-bounces@rhodes22.org] On
> > Behalf Of Roger Pihlaja
> > Sent: Tuesday, November 19, 2002 6:39 PM
> > To: The Rhodes 22 mail list
> > Subject: Re: [Rhodes22-list] lightning protection
> >
> >
> > Guys,
> >
> > I've been involved in the design & construction of
> > several fairly tall
> > structures over the course of my engineering career.
> > Some of these
> > structures were distillation towers, which were 200
> > - 300 feet tall &
> > were handling large quantities of flammable,
> > reactive chemicals. So, we
> > paid quite a lot of attention to lightning
> > protection in these designs!
> >
> > The American Society of Civil Engineers (ASCE) has
> > done quite a bit of
> > research into the effects of the height of a
> > structure & grounding vs.
> > the probability of it being struck by lightning. We
> > always used the
> > ASCE design database.
> >
> > Since I was downsized from my job at the Dow
> > Chemical Co., I no longer
> > have access to this database. However, my
> > recollection is that up to
> > about 50 feet tall, the probability of a well
> > grounded structure being
> > stuck by lightening was statistically no different
> > than level ground
> > nearby. Above 50 feet, the probablity of being
> > struck increases
> > exponentially to the point where very tall
> > structures, like the Empire
> > State Building, are struck at least once annually.
> >
> > The ASCE data indicates that being poorly grounded
> > tends to slightly
> > decrease the probablity of being struck.
> >
> > My take on all of this data is that our R-22's with
> > deck stepped masts
> > are poorly grounded. Since the probability of the
> > 28 foot tall masthead
> > being struck is statistically no different than
> > water level even if it
> > were grounded, my answer is, "Do nothing to ground
> > the boat." The
> > difference in my likelyhood of being struck is
> > probably statisically
> > insignificant, but intentionally not grounding the
> > mast should tend to
> > shift the probability slightly in my favor. Plus,
> > it's easier to do
> > nothing.
> >
> > One thing I do is disconnect the masthead VHF
> > antenna at the base of the
> > mast & turn off the on-board electronics during a
> > thunderstorm.
> >
> > My other advice is, stay away from tall structures
> > like bigger sailboats
> > & trees on hillsides. Many trees on the shoreline
> > have extensive root
> > systems which extend quite a distance out into the
> > water. The roots are
> > a rather poor conductor of electricity & lightening
> > will tend to heat
> > them instantly to incredible temperatures,
> > potentially causing a steam
> > explosion right underneath the boat! This could
> > ruin your whole day.
> > Likewise, you don't want to be nearby a taller
> > structure like a bigger
> > sailboat. A lightning strike puts out an incredible
> > amount of EMP. A
> > nearby strike could inductively fry every piece of
> > electronics on board
> > your boat.
> >
> > Trees, sailboats, the ground, & the water get struck
> > everyday. Use
> > common sense & get off the water when lightning
> > starts flashing if
> > that's at all feasible. But, if you're caught out
> > on the water during a
> > thunderstorm, just realise it's an act of God &
> > there is very little you
> > or I can do to prevent it. Quit worrying about it.
> > It happens, but the
> > odds of it happening to you are slim.
> >
> > Roger Pihlaja
> > S/V Dynamic Equilibrium
> >
> > ----- Original Message -----
> > From: "Rik Sandberg" <racerrik@rea-alp.com>
> > To: "The Rhodes 22 mail list"
> > <rhodes22-list@rhodes22.org>
> > Sent: Tuesday, November 19, 2002 5:36 PM
> > Subject: Re: [Rhodes22-list] lightning protection
> >
> >
> >
> > <snip>
> >
> > >
> >
> >
> > _________________________________________________
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>
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