NavList:

-------------- Original message --------------

> 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
> &! gt; 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 o! n 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 a! lmost
> > 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 effe! ct, 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
> > > concent! rated 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 other! s
> > > 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 l! aws 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. Thi! s 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 gradie! nt. 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 th! e 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