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Old 11-07-2012, 15:28   #76
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Re: Lightning Strikes

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OK!

My conscience is clear....

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Old 21-07-2012, 17:34   #77
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Re: Lightning Strikes

For many years I made a living in the telecommunications outside plant area--and I can assure anyone who thinks lightning protection a waste of time should consider that public utilities consider it mandatory and for very good reasons--it saves them lotsa dough!

Whenever I have examined any unprotected structure which received a moderate discharge the total destruction of all of the equipment and usually the structure itself is so badly damaged it requires replacement.

A full lightning discharge involves many thousands of amps, or even megamps, flowing for up to a few seconds. This produces tremendous heat and a magnetic pulse, as has already been explained. The heating effect is the square of the current multiplied by the resistance of the structure--and no boat afloat will survive a major strike, nor will its crew.

Effective lightning conductors do two major things quite well. They conduct to earth minor residual discharges, and they reduce the charge potential on the air surrounding the collection point of the protection.

One of the problems involved in explaining how lightning conductors work is the way tiny-tots versions of transient events which are very complex get explained. These explanations are full of holes because it is not a simple situation whi8ch produces a discharge and it varies constantly as the storm or disturbance continues.

There are a few ideas one might consider.

The air is not a conductor unless ionized. Ionized gasses are conductors.
Ionization requires a high charge potential. If this charge potential can be collected and safely conducted to earth, atmospheric ionization is reduced in the area surrounding the structure which is protected.

This reduction in the conductivity of the atmosphere does reduce the potential for a "strike", either because there will now be some other structure elsewhere which will be a better conductor, or the atmosohere will not permit a discharge at the present electrostatic potential of the charged storm clouds and surrounding air. This charge emanates from the friction of the jet stream on the slower moving air beneath, is always present, and a strorm situation provides additional turbulence which can provide an ionized discharge path to earth. Once this pathway is established, a current will flow further ionizing the air and reducing its "resistance" to the flow of electrons.

Once this path is established, rapid reduction in the electrostatic potential of one portion of the atmosphere can lead to other charges areas discharging into the same pathway--and the "strike" can be prolonged. Sometimes electrons may flow backwards and forwards along the path initially established.

I have heard the phenomena explained as the air being a dielectric between two plates of a capacitor, one plate being the earth and the other the charged upper layers of atmosphere. It is not that simple. Capacitance is an electrostatic effect in its ability to hold charge--and a charged atmosphere could be an electrostatic charge--but it is NOT a static system, and many factors apply.

The jury is still out on some aspects of the reasons lightning strikes occur--but somethings we do know from practical experience and we can take a bit of an educated guess at others.

Lightning protection properly fitted will reduce the severity of a discharge, and may well prevent most discharges from occurring. Once a discharge does occur, the severity of it will depend on whether or not the charged area from which the discharge emanated is not re-supplied with charge by some other area of higher charge potential. One can see lighning flashes from one part of the sky to another--so this is not an uncommon thing.

Photographs of lightning running from the sky to the top of a lightning conductor show small to medium discharges. There is no lightning conductor made which can conduct the high currents of a major strike without vaporizing. I once searched for a mahor fault inn a lead-sheathed multiconductor copper wired cable which had simply vanished after an unprotected terminal was damaged by a discharge I would class as of medium intensity. There were four hundred pairs of 0.9mm copper star quad cable, but there was no cable remaining. The entire cable had vanished, diffused into the surrounding soil. Copper, lead, steel armour--the lot had simply boiled away, staining the surrounding dried out earth with small particles of condensed metal droplets.

Before a strike the air must become ionized--or it is not a conductor. Moisture is partially responsible--but it is the ionized gasses that carry the current--as in a neon tube. Streamers of illumination sometimes appear as the ionization takes place--the St Elmo's fire reported by sailors in the rigging of ships.

I would rig my own lightning protection using the methods for protecting power pylons. I would buy a Mu metal cabinet in which to lock away vital navigation equipment top protect it from electromagnetic forces. If you can not buy a Mu metal cabinet second hand, a soft iron or even a steel box is a poorer substitute but better than nothing.
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Old 22-07-2012, 07:14   #78
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Re: Lightning Strikes

mike, excellent post. we sailed with little wire whiskers at the top of our masts connected down to copper grounds. thought they might dissipate charges before they built up. dont know if it worked, but never had a strike in 40 years of sailing. lot of itcz sailing(well, sitting around mostly). we also created a "faraday cage" out of simple heavy gauge copper wire. again dont know if it would work but gave us comfort that some electronic items might survive a strike. again, your right on about a major strike. that will vaporize a voyage quickly. had a crew once who got righteously drunk during big lightening storms. that also might help. we were more afraid of sudden down bursts ripping apart the masts, but that is another issue.
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Old 22-07-2012, 07:37   #79
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Re: Lightning strikes

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I can underscore this statement with an example:

Yesterday in our current anchorage here in Panama, a powerboat took a direct strike. The powerboat was anchored with large sailboats all around it and was the lowest point by a good 40'. None of the sailboats were hit. And the powerboat had an extensive lightning protection system that consisted of multiple down-conductors connected to multiple thruhull electrodes around the waterline.

So, not even a well-protected boat underneath much taller conductive structures is safe from a direct strike.

Mark
So if lightening wants to take the past of least resistance doesnt it make sense that the boat with the best grounding system is most likely to get hit?
In this case it was the powerboat
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Old 22-07-2012, 08:38   #80
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Last Thursday we had a ground strike at work. This effected our network switches that are linked by conduit 3 feet plus below ground. Trashed some of the fire alarm boards. A few network switches that were several jumps and no where near the strike lost clusters. This was a ground strike probably 200 feet from the conduit. Some of the damaged network was 2 floors up and 500 feet from the strike. I found patch cables at devices 300 feet away from ground zero to have burnt rj 45 terminals . Pretty amazing. Having a good ground does not increase your. Janice of a hit.
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Old 22-07-2012, 08:49   #81
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Re: Lightning Strikes

friend out in the anchorage in a storm the other day was hit--he is unprotected, and as a result the damage was only an inch sized burn in electrical panel.
funny how the protected boats have much more extensive damage, as far as i have seen. i would still rather enter a storm unprotected than as a guide system for the electrical bits....at least the bolts dont see me as a lightning rod.
btw--none of his electronix were touched by this event, nor was his autopilot. was a simple gotcha of the slightest variety. i would hate to think what would have happened out in that anchorage if he had had protection and bonding.....he coulda ended up like that boat in slidell that was hit 2 times in 4 yrs and became a submarine both times....
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Old 22-07-2012, 09:00   #82
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Makes no sense zee. They have some protection. The mast is sitting on a step that most likely is on a keel. That's very good unplanned protection. I saw a boat that had encased keel and it was hit " no added protection. . The glass had multiple bluster burns and blew out the swing keel glass all electronics etc... . Your friend should dive his boat. If your deck stepped you run a significant risk of side flash. Best is good ground to keel or big.copper ground strip. Especially if your deck stepped gord has provided great links for a proper set up
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Old 22-07-2012, 09:29   #83
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Re: Lightning Strikes

Lightning strikes are too variable to draw any conclusions from the results of a few boats.
The science, however is clear and unequivocal.

Grounding reduces the damage to to a boat and its occupants, usually considerably.
Grounding (slightly) reduces the chance of being hit.

If someone can present a view, from a credible expert, that contradicts these simple statements, present it. I am all ears.
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Old 22-07-2012, 09:33   #84
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Re: Lightning Strikes

The greatest con ever pulled on the general public was the Lighting Rod..if there are trees taller than your house would not that suffice as opposed to directing it to your house?!..DVC
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Old 22-07-2012, 09:41   #85
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Re: Lightning Strikes

my friend does dive his boat, as he is actively cruising at present--he found nothing but the electrical panel damage --he does not believe in attracting it with protection devices that seem to attract rather than dissipate the lightning's power. we are of similar thought. he was anchored when hit, not underway. seems while underway is less chance of being hit, in our situations and per experience..knocking wood as i typo
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Old 22-07-2012, 09:51   #86
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Okay so is the mast deck stepped or keel stepped.suggesting having no protection which I take is no direct ground path is bad advice,
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Old 22-07-2012, 09:53   #87
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Quote:
Originally Posted by tropicalescape
The greatest con ever pulled on the general public was the Lighting Rod..if there are trees taller than your house would not that suffice as opposed to directing it to your house?!..DVC
In the 1800s possibly, as the ability to truly redirect the current/voltage/amps did not exist. Today the science favors the prepared.

A "taller" tree is unlikely the path of least resistance as it lacks all the nice copper plumbing, grounds, etc, our homes have in place.
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Old 22-07-2012, 10:04   #88
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Cone of protection google it.
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Old 22-07-2012, 10:07   #89
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Cone of protection google it.
Meant to add the cone picture
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Old 22-07-2012, 10:10   #90
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Re: Lightning Strikes

Yesterday, looking at chainplates on another boat ... I suddenly realized that our mast is grounded too (!!!) - the forestay attaches to the fore chainplate which extends at least 3 feet below the waterline! (it forms a protection to the leading edge of our keel).

Why not have some of the external chainplates on some boats extended so that they form a natural path to the water/ground?

And will this sort of 'grounding' work?

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