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Phil,

What exactly are you recommending be done to a cuising sailboat
regarding the equipment sold by the two companies referenced, please ?

Appreciatively,
Courtney



wrote:

> George's ramblings are pretty much right on based on what I have
> learned.  I'd like to share some of my comments to his comments.
>
>
>
>      > Because lighning strikes so randomly, it's hard to study it
>     scientifically.
>      > So there's still a lot of folk-wisdom and superstition,
>
>     Actually lightning has been studied extensively and the knowledge
>     base is huge and all information points to that one can not predict
>     nor prevent it.
>
>      > Don't consider me to be a pundit: in this field, there
>      > are none! Commonsense is what counts.
>      >
>
>     Besides being crew on a racing sailboat (20 + yrs incl. Navigator) I
>     am also a licensed Amateur Radio Operator.  I have four tall towers
>     with mulitple antennas at my home and am well versed and protected
>     against both direct strikes (rare) and induced voltages from nearby
>     strikes (very common).  If one wants to learn more, I'd suggest the
>     following two websites.  Polyphaser and ICE make the lightning and
>     grounding equipment that some of us hams and commercial stations use
>     to protect their gear.  Remember that the police and fire dept, AM &
>     FM & TV stations don't disconnect in a storm.  They systems must be
>     able to take the voltage and keep on working.  Lot's of this info
>     can be applied to boating; you're surrounded by the perfect ground
>     and that's all lightning or induced voltage wants to do, is to get
>     to ground as fast as possible.
>
>
>
>     http://www.polyphaser.com/
>
>
>
>     http://www.arraysolutions.com/Products/ice/
>
>
>      >>
>      > The feeling you get when there's lightning about, and there's
>     just your
>      > sharp metal mast protruding above the sea with nothing else
>     about, is that
>      > if it's going to strike anywhere, it's going to strike that mast. It
>      > doesn't seem to work like that, though. We have frequently seen
>     strikes
>      > that have chosen to go straight down into the sea, perhaps no
>     more than 40
>      > metres away, rather than go for our mast. Being a devout atheist,
>     I can
>      > hardly attribute it to divine intervention on my special behalf!
>
>
>
>     No not divine intervention it's just that your mast is probably well
>     connected to ground and therefore your constantly bleeding off
>     static charge.  Believe it or not, there's also a lightning bolt
>     that jumps up from ground to meet the sky bolt coming down.  If your
>     "system" is bleeding off that charge buildup, then the another area,
>     maybe on the surface of the water, will have a higher potential to
>     ground than your mast and lightning will prefer that.  Things get
>     real fuzzy on this subject but experience has proven it to be true.
>
>
>      >
>      > But if it's going to hit your boat anywhere, it's almost
>     certainly going to
>      > be the top of the mast.
>
>     No necessarily, see above.
>
>     If your mast is in Jove's sights, there's nothing
>      > you can do to stop it. The current will pass through your boat on
>     its way
>      > to the water. All you can do is to provide a path that will
>     create least
>      > damage.
>      >
>      > True, true.  My towers are setup to constantly bleed off charge
>     but if they do take a direct hit, that energy will be shunted right
>     into the ground and away from my house and equipment.
>
>     And within the metal cabin, there's no
>      > personal danger at all, except perhaps from cabling to the
>     masthead and
>      > pulpit.
>      >
>
>     That's called the Faraday Shield effect, like staying inside your
>     car in a lightning storm.
>
>
>      > A fibreglass or wooden vessel is in quite a different category.
>     If we
>      > assume a metal mast, that's likely to be able to carry the
>     current from any
>      > lightning-strike without being damaged. But what happens at the
>     foot of the
>      > mast? If it's stepped at deck level, the current has to somehow
>     find a way
>      > across the insulating deck, and down the insulating hull-sides,
>     to the
>      > water .
>
>      On the other hand, there's an inviting path from the masthead, down
>     the
>      > rigging-wires, and down the wet hull-sides, which bypasses the
>     insulation
>      > of the deck. The steel shrouds are likely to be burned out by the
>      > concentrated current flowing through a thin wire (just like the
>     element of
>      > an electric fire being subject to an overvoltage) if they carry
>     the whole
>      > current of a strike.
>      >
>
>     All the boats I've sailed on have had the mast and/or the rigging
>     connections wired to the metal keel or the grounding plate built
>     into the hull of the boat.  Don't all boats have this plate?  An
>     alternate could be grounded to the prop shaft.
>
>
>      > My strategy is to encourage current-flow down the mast instead. I
>     do this,
>      > in an electrical storm under way or at anchor, by taking some
>     surplus
>      > length of anchor chain and draping it round the foot of the mast
>     and over
>      > the side into the water, in a number of loops. I have heard others
>      > pooh-pooh this idea, on the grounds that the many oxide-coated
>     surfaces
>      > between the links make a chain a rotten conducor. So they would,
>     indeed, if
>      > you measured it with a resistance meter. But the voltages in
>     lighting are
>      > so great that they will (in my estimation) break down and
>     spark-over such
>      > interfaces, and provide a useful current path.
>
>     Yes, bad idea.  Lightning will follow the path of least resistance
>     and the chain sounds like a high resistance path.  Some energy will
>     leak this way but most "may" find another path to ground.
>
>
>
>     Such a chain, under such
>      > high voltages, will not be following Ohm's law!
>      >
>      >
>
>     Captain, you can't changes the laws of Nature!!!  Ohms Law will
>     still be valid, period.
>
>      >
>      > "I know of some sailors that will carry heavy duty automotive
>     jumper cables,
>      > and attached one end to the rigging? and let the other end drag
>     in the water
>      > when electric storms come up. Any feeling of whether this is
>      > safe/practical, or would help?"
>      >
>
>     This sounds a little better than the chain.
>
>
>      > I think this would be a useful thing to do, probably better than
>     my chain,
>      > but not quite as Bill suggests, when he says "attach one end to the
>      > rigging". That's exactly what you are trying to avoid, providing
>     an easy
>      > path down the rigging wires. Attach it well, to the metal MAST.
>      >
>      > >>
>      > What about a keel-stepped metal mast on an insulating vessel?
>     That might be
>      > a bit of a worry, in my view, unless you have a metal keel, which is
>      > electrically bonded, through the hull, to the mast. It would seem
>     unwise,
>      > in my view, to make this bond via a keel-bolt, in that the last
>     thing you
>      > would want is to damage a structural keel-bolt. Unless you have
>     such a
>      > bond, then there's a great concentration of electrical stress at
>     the mast
>      > step, and it's easy to imagine how a severe strike could puncture
>     a hull
>      > there.
>      >
>
>
>
>
>      > ==========
>      >
>      > Protecting electrics.
>      >
>      > I doubt if there's any way to protect your masthead electrics in
>     the event
>      > of a strike. What about the rest?
>      >
>      > Just think about the negative 12-volt line that runs around the
>     boat,
>      > starting at the battery, linking one unit to another by a "ground"
>      > connection. Usually, that will be a heavy connector, with no easy
>     way to
>      > deliberately break or disconnect it. Consider (for example) the VHF
>      > antenna. The coax downlead has a a heavy outer conductor, which
>     may or may
>      > not be linked electrically to the metal masthead itself, but is
>     unlikely to
>      > be carefully insulated from it. When a strike occurs, it's likely
>     to reaise
>      > that coax to the transient voltage at the masthead, which could
>     be many
>      > kilovolts. This is fed down to the VHF transceiver, then through
>     its power
>      > supply to the battery negative, perhaps! the engine block,
>     propshaft,
>      > propellor, anode to the sea. Or perhaps to the sea via the
>     echosounder
>      > sensor, or the through-hull log, where the insulation is locally
>     weak.
>      >
>      > >
>
>     What about the grounding plate built into the hull?  I always
>     thought all boats had these.  Good discussion though.  One could use
>     some of those arrestors made by the companies (and there are other
>     companies I'm sure) mentioned in the web links above.
>
>
>      > Is it worth bothering, in an electrical storm? If you're near
>     home, losing
>      > your electrics may not be too serious; you just have to replace
>     it. On
>      > ocean passage, it could be another matter.
>      >
>      > >
>
>     Isn't this why we all carry our sextant with us or at least a kamal
>     and timepiece 'cause one never knows when the electronics may fail!
>
>
>      > Many years ago, I was launching a dinghy from a ramp, when there
>     was a
>      > lightning strike into the water, perhaps 50 metres away. I was
>     holding the
>      > dinghy's rigging at the time, and felt enough of an electrical
>     shock to
>      > make me jump. Presumably, the low cloud base formed one plate of a
>      > capacitor, the land-and-water another, and the lightning had
>     instantly
>      > discharged that capacitor, to some extent. The rigging was
>     picking up some
>      > fraction of the sudden step in voltage gradient. It made me
>     think: if that
>      > rigging had been some sort of antenna for a receiver, that
>     voltage step, if
>      > it could more-than-tickle me, could easily destroy the input
>     stage of an
>      > amplifier. So perhaps it's not necessary for the boat to be
>     struck to
>      > suffer damage; a nearby strike may do the trick.
>      >
>      >
>
>     Induced current and voltage from a nearby strike is a big problem
>     and the one that should be guarded against.  It's what I worry about
>     in the ham radio towers and antennas.  A strike a mile away can
>     induce enough voltage to zap out electronics.  Personally lightning
>     hit and blew up a neighbor's tree.  It induced over 30 amps of
>     current in the electrical wiring in my barn, located 300 ft away
>     (Blew a hole in the side of the 30 amp fuse protecting that
>     circuit.)  My towers and antennas, as close as 200 ft. away, kept on
>     ticking without a scratch.  Just my two cents.  Phil Camera,
>     Lockport, IL
>
>
>


--
s/v Mutiny
Rhodes Bounty II
lying Oriental, NC
WDB5619

   

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