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Old 11-08-2012, 16:08   #61
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Re: Lightning Strike Damage Details Needed

Thanks for looking that up, Paul. So apparently the rounded tip is designed to survive strikes, while the traditional pointed tip is designed to *prevent* them by more effectively bleeding off an ionic charge.

Which bring us back to "Where does an eight hundred million volt gorilla strike? Anywhere he damn well pleases."

Or as they say in Florida, lightning is God's way of saying "Go play golf somewhere else!"
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Old 12-08-2012, 05:43   #62
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Re: Lightning Strike Damage Details Needed

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Originally Posted by hellosailor View Post
Thanks for looking that up, Paul. So apparently the rounded tip is designed to survive strikes, while the traditional pointed tip is designed to *prevent* them by more effectively bleeding off an ionic charge ...
Not exactly.

Recent studies have determined that the old sharp-pointed rod is not as effective as a rounded-tipped 1/2 inch to 3/4 inch diameter rod.

“... In field tests, rods with rounded tips have been found to be better strike receptors than were nearby sharp-tipped rods ...”

The Case for Using Blunt-Tipped Lightning Rods as Strike Receptors
http://www.lightning.org/sites/www.l...Blunt_Tips.pdf
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Old 12-08-2012, 07:37   #63
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Re: Lightning Strike Damage Details Needed

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Originally Posted by GordMay View Post
Not exactly.

Recent studies have determined that the old sharp-pointed rod is not as effective as a rounded-tipped 1/2 inch to 3/4 inch diameter rod.

“... In field tests, rods with rounded tips have been found to be better strike receptors than were nearby sharp-tipped rods ...”

The Case for Using Blunt-Tipped Lightning Rods as Strike Receptors
http://www.lightning.org/sites/www.l...Blunt_Tips.pdf
New Mexico Institute of Mining and Technology, Sucorro, New Mexico, Journal of Applied Meteorology, February 3, 2003 publication states on a mountaintop near their lightning laboratory, no sharp pointed lightning rod has been struck in 48 years. The round pointed rods 40 meters (131 feet) from the sharp rods were struck. The article goes on to describe laboratory experiments about round and pointed rods. So if you have a pointed lightning rod on your mast and your neighbor has a rounded end on their lightning rod, you neighbor will be the one struck if water behaves the same way as a mountain top.

In The Art and Science of Lightning Protection by Martin A Uman there is a chapter on devices that are intended to prevent lightning strikes by cloud charge draining. The bottlebrush dischargers do not work. Other devices are also discussed such as radioactive devices that create ions, but these also do not work. The only thing that does work are rockets trailing wires shot into a storm cloud. In another chapter Uman does mention the phenomenon of pointed lightning rod not being struck.
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Old 12-08-2012, 07:38   #64
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Re: Lightning Strike Damage Details Needed

As I am the world's leading expert on lighting strikes, I would would recommend reading the Boat US article in their last newsletter. Basically, they concluded that it is all voodoo. Seriously...voodoo. Take appropriate saftey actions but when lighting strikes, there is no predicting what will happen. Sometimes the damage will be minimal, sometimes it will be severe. I have taken appropriate measures and will let King Neptune or Karma determine what will happen.
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Old 12-08-2012, 17:52   #65
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Re: Lightning Strike Damage Details Needed

Gord, its gonna take some aspirin to read through that paper. While they may conclude round is better, I got as far as
"A comparison of the responses of the sharp- and blunt-tipped rods to the same electric field strength was not possible. An ambient field strength of 100 kV m was not sufficient for the initiation of discharges from the hemispherically tipped rod; field strengths in excess of 200 kV m 21 were required for the onset of avalanches.
On the other hand, as the Van de Graaff generator belt speed was increased to the maximum possible, the emissions from the sharp-tipped rod increased to about 4 mA and negated all of the charge being carried by the belt without a significant increase in the generator potential.
Hence, fields stronger than 100 kV m 21 could not be developed by the generator when it was exposed to a nearby sharp rod."

Which sure as ~hit seems to say that the pointy rods were doing a better job, does it? Or is that just a better job at the uselss job of discharging, rather than shunting to groun?

Or did I just stop caffienating too early today? "Is there a doctor of literate letters in the audience?!"
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Old 12-08-2012, 18:54   #66
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Re: Lightning Strike Damage Details Needed

Lightning creates a strong electromagnetic pulse that behaves like a radio wave, but with a frequency so low that an ordinary Faraday cage of a conductive material such as copper will not protect electronics. This is for frequencies below 100,000 Hertz. The Faraday cage has to be made of steel or preferably of high magnetic permeability metal alloys such as Permalloy and Mu-metal; however, it looks like steel will do the job. I assume the following mentioned oven is a microwave, but if an ordinary oven does the job and is not even designed as a Faraday cage, well that’s very nice also. My microwave door has a steel plate with little holes in it, and the rest of the box is steel. If a box with materials found in a microwave were formed around electronic equipment and protected from current surges from power supply, and if there is an antenna, the coax connector is also protected from surges, it appears that the equipment would be protected. The thickness of the steel required to protect electronics is dependent on the frequency, the lower the thicker required. On the second post, note that the lightning did not strike the mast, but the water near the boat.

Here is a post I pasted from Cruisersforum.com that shows the importance of a Faraday shield:
Lightning Brings Abrupt End to Journey . . .
#4
14-08-2010, 17:41
By annk
One tip( we have been hit twice), put handheld gps, vhf, phone, computer in the oven. It acts like a faraday cage and has saved our equipment twice now when everything else was fried!


Here is another: note items not plugged in that were destroyed.
Lightning strikes, any real experience?
#3
19-12-2011, 20:07
By Maine Sail
Boat: CS-36T - Cupecoy

We took a hit on our mooring in August 2010. Neighbor said the lightning hit the water right at our stern quarter. It did not come down the mast. The strike came in through the ground side of the system and took out nearly everything. Even the PSS seal had carbon blown all over the engine bay. It survived but it gave me the creeps... The only things to survive were a couple of pumps, macerator and shower sump.. We also lost a bunch of devices not even plugged in to anything. Lost the EPIRB, iPod, Laptop wifi and other features (laptop turned on but was severely compromised), three hand held GPS devices including one that was in a ditch bag wrapped in tinfoil & stored in a ziploc with desiccant.. None of these devices were even plugged in but were still toasted.

On the AC/DC panel some breakers survived and some did not. All volt gauges, tach, temp, etc. were also fried. Alternator VR was fried. All lighting aboard was LED and all was 100% toast except for one in the v-berth that still works, very odd. Engine starter survived but the solenoid died six months later no-doubt due to the lightning strike. Radar, wind, depth, speed, AP, two plotters, Garmin network hub, VHF, TV, stereo, cell phone amplifier and much more were all fried too..

The only wires damaged were very small NEMA type comms wires. All wiring survived just fine. Not one fuse was blown during the strike and the battery switch was off when it happened.
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Old 12-08-2012, 19:09   #67
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Re: Lightning Strike Damage Details Needed

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Gord, its gonna take some aspirin to read through that paper. While they may conclude round is better, I got as far as
"A comparison of the responses of the sharp- and blunt-tipped rods to the same electric field strength was not possible. An ambient field strength of 100 kV m was not sufficient for the initiation of discharges from the hemispherically tipped rod; field strengths in excess of 200 kV m 21 were required for the onset of avalanches.
On the other hand, as the Van de Graaff generator belt speed was increased to the maximum possible, the emissions from the sharp-tipped rod increased to about 4 mA and negated all of the charge being carried by the belt without a significant increase in the generator potential.
Hence, fields stronger than 100 kV m 21 could not be developed by the generator when it was exposed to a nearby sharp rod."

Which sure as ~hit seems to say that the pointy rods were doing a better job, does it? Or is that just a better job at the uselss job of discharging, rather than shunting to groun?


Or did I just stop caffienating too early today? "Is there a doctor of literate letters in the audience?!"
Do not look at me, I could not finish the article either. Generally engineers are not the greatest at using language.
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Old 12-08-2012, 20:06   #68
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Re: Lightning Strike Damage Details Needed

" We also lost a bunch of devices not even plugged in to anything. "
There are inductive effects, magnetic effects, direct flashover...many very diffrent ways for damage to get passed around. I've even personally had fuses blown in my car by a nearby strike--with no other damage.
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Old 12-08-2012, 23:46   #69
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Re: Lightning Strike Damage Details Needed

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Originally Posted by hellosailor View Post
" We also lost a bunch of devices not even plugged in to anything. "
There are inductive effects, magnetic effects, direct flashover...many very diffrent ways for damage to get passed around. I've even personally had fuses blown in my car by a nearby strike--with no other damage.
The PSS shaft seal was blown all over the engine compartment. I would say at least some of the lightning strike came in by way of the propeller and shaft. Water has electrical resistance so the forward part of the boat would see a different potential than the propeller shaft and this would cause the current flow. There was most likely grounding wiring to a grounding plate and probably to through hulls. Someone holding on to an engine control with one hand and a boom with the other, or maybe a pulpet tied into the mast and its ground perhaps could receive a lethal shock. For the devices not hooked to any power, the electromagnetic pulse had to have induced voltages in the integrated circuits that destroyed them.

The National Fire Protection Association has standards for protecting humans on boats and physical damage to boats that requires grounding of engine, through hulls, grounding plate, shrouds, all metal parts larger than a toaster I would guess. I think these standards are hazardous to humans considering what happened to the above sailboat. http://www.nfpa.org/onlinepreview/on...t.asp?id=78011#
NFPA780-2011, Chapter 10. The American Boat and Yacht Council (ABYC) Standard ABYC TE-4 has how been reduced to a new advisory document E-4 although some insurance companies still require the boat owner to meet an ABYC standard.
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Old 13-08-2012, 07:00   #70
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Re: Lightning Strike Damage Details Needed

"Radar, wind, depth, speed, AP, two plotters, Garmin network hub, VHF, TV, stereo, cell phone amplifier and much more were all fried too.."
Anything with a speaker coil, transformer, any type of coil in it, would pick up the flow of electricity past it, and induct power from it. Resulting in a surge even if there was complete physical isolation. With the right coils you could recharge the house batteries, too.
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Old 13-08-2012, 07:20   #71
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Re: Lightning Strike Damage Details Needed

When the lightning strike enters the water, say from a one square foot plate attached to the underside of the sailboat, voltage is going to be very high falling off linearly, depending on the lightning strike current and resistance per meter of the water. This voltage is likely to be higher than the voltage difference in the boat wiring if there are multiple grounds for the boat, such as propeller, through hulls, grounding plate, the fiber glass shell of the boat. This voltage drop off seen in the water would attach to the multiple grounds causing high voltage differences from one end of the boat to the other. Uman has formulas for this, but I am not sure if I can interpret them.
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Old 13-08-2012, 09:47   #72
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Re: Lightning Strike Damage Details Needed

I am convinced they do facilitate lightening strikes by ionizing the air around them and that metal rods when your struck help carry it to ground.

As some posters have said it is a crap shoot whether your struck or not.
So many variables of electrical potentials from cloud to cloud to ground, totally unpredictable. So your odds of being sturck are likely higher with than without, but if your struck better to have them than not.

Lightning rod - Wikipedia, the free encyclopedia

Quote:
Nikola Tesla's U.S. Patent 1,266,175 was an improvement in lightning protectors. The patent was granted due to a fault in Franklin's original theory of operation; the pointed lightning rod actually ionizes the air around itself, rendering the air conductive, which in turn raises the probability of a strike. Many years after receiving his patent, in 1919 Dr. Tesla wrote an article for The Electrical Experimenter entitled "Famous Scientific Illusions", in which he explains the logic of Franklin's pointed lightning rod and discloses his improved method and apparatus.
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Old 13-08-2012, 10:09   #73
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Re: Lightning Strike Damage Details Needed

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I am convinced they do facilitate lightening strikes by ionizing the air around them and that metal rods when your struck help carry it to ground.

As some posters have said it is a crap shoot whether your struck or not.
So many variables of electrical potentials from cloud to cloud to ground, totally unpredictable. So your odds of being sturck are likely higher with than without, but if your struck better to have them than not.......
That may be true in a test/lab environment, but the vast majority of sail boats have metal stuff pointing up from the mast head, even without air terminals/lightening rods. Most have a VHF antenna, some two. Most have wind instruments plus lights and a windex. Something is going to get hit.
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Old 13-08-2012, 11:09   #74
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Re: Lightning Strike Damage Details Needed

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That may be true in a test/lab environment, but the vast majority of sail boats have metal stuff pointing up from the mast head, even without air terminals/lightening rods. Most have a VHF antenna, some two. Most have wind instruments plus lights and a windex. Something is going to get hit.
True, but these pointy things on top of the mast are rarely wired to a highly conductive copper plate on the hull. Most of this is beyond me, but to the extent there's evidence that use of a lightening rod may attract (I understand that if done right it can protect), would the rod being wired/grounded make any diff in attracting lightening?
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Old 13-08-2012, 11:20   #75
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Re: Lightning Strike Damage Details Needed

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True, but these pointy things on top of the mast are rarely wired to a highly conductive copper plate on the hull. Most of this is beyond me, but to the extent there's evidence that use of a lightening rod may attract (I understand that if done right it can protect), would the rod being wired/grounded make any diff in attracting lightening?
There is typically a ground connection to most of the electrical on the mast head. Also, the Windex might be connected to the AL mast.
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