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Old 09-07-2019, 10:24   #76
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Re: Lightning Protection, pros and cons

Cat boats are the hardest to protect since the lightning has to make two right angle turns to reach the water. If I had a catamaran, I'd find a way to provide a direct path from the mast base to the water.

The three rules are: grounding, bonding, and suppression. Grounding of course is a relative thing on a boat (you usually avoid contacting the ground in any way). The advice from others above is all good.[/QUOTE]

Maybe something like this?[/QUOTE]

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Old 09-07-2019, 15:07   #77
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Lightning Protection, pros and cons

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Were the aircraft tie-downs made of chain? Was the plane refueling, with the ground strap connected? Was the plane connected to an external power source? Was the boarding ramp down touching the ground? Were airstairs up against the airframe?


The Faraday Effect only applies to insulated containers. Electrically connected to ground, there's no Faraday Effect protection.


Having three inches of rubber separating you from the ground if your struck by a bolt that jumped literally miles of air gap, that 3” may not do much.
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Old 09-07-2019, 16:37   #78
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Re: Lightning Protection, pros and cons

If you have an encapsulated lead keel that you are grounded too, do you really need an external plate? My fiberglass hull on the side of the keel is maybe 3/8". I used too have an external plate, but a pot caught on it. Now there is just a couple of small holes with epoxy in them. Seems like a bolt would just go out anywhere it wanted or does there need to be continuity?
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Old 09-07-2019, 19:09   #79
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Re: Lightning Protection, pros and cons

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Having three inches of rubber separating you from the ground if your struck by a bolt that jumped literally miles of air gap, that 3” may not do much.
If a hit does occur, skin effect will cause nearly all of the current to travel on the outer surface of the vehicle/aircraft -- if its outer surface is conductive. For a fiberglass boat, all bets are off. And boats with carbon fiber out surfaces may experience very unpleasant effects.

Lightning is RF, as explained in this thread. Even at very low frequencies, skin effect comes into play. Ordinary AC power is affected. At 60 Hertz, there's a point of diminishing returns at a radius greater than 8.5mm (about 2/3 inch diameter) because with a larger conductor decreasingly less current will flow down the middle of the wire. It's common in broadcast transmitters to use hollow tubes for conductors because any metal in the middle only wastes materials.

At 156.8 MHz, VHF channel 16, most of the RF current is only being passed in the outer 5 micrometers of the conductor. A good reason not to let your antennas get rusty.

If you're really concerned about lightning safety, get a boat with a metal hull and deck.
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Old 09-07-2019, 19:50   #80
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Re: Lightning Protection, pros and cons

This is the image that comes to mind when I imagine what could happen when an unprotected carbon fiber hull gets hit by lightning. Viking Funeral!


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Old 09-07-2019, 19:53   #81
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Re: Lightning Protection, pros and cons

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If you have an encapsulated lead keel that you are grounded too, do you really need an external plate? My fiberglass hull on the side of the keel is maybe 3/8". I used too have an external plate, but a pot caught on it. Now there is just a couple of small holes with epoxy in them. Seems like a bolt would just go out anywhere it wanted or does there need to be continuity?

Yes. Provided you mind having holes punched in the keel encapsulation.
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Old 09-07-2019, 22:20   #82
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Re: Lightning Protection, pros and cons

There probably is not a 100% agreement--but there never is--and the bigger the sample the more dopes one encounters.

My opinion, having worked in telecommunications outdoor plant as well as in construction,
is that not using it is insanity and a complete disregard for the safety of one's crew.
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Old 09-07-2019, 22:26   #83
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Re: Lightning Protection, pros and cons

The skin effect pertains to alternating current. Lightning does alternate, but not always. When it does the frequency at which it does alternate is insufficient to cause any appreciable skin effect.

The effect many people imagine is a skin effect is the surface burn that occurs when salt or other conductive impurities encrust an otherwise non-conductive material.

The reason that lightning sometimes passes over the surface of metal objects is to do with the Faraday effect, which is the absence of an electrical field inside a hollow conductor. It is somewhat akin to the lack of a magnetic field inside a hollow soft magnetic enclosure.
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Old 10-07-2019, 07:56   #84
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Re: Lightning Protection, pros and cons

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The skin effect pertains to alternating current. Lightning does alternate, but not always. When it does the frequency at which it does alternate is insufficient to cause any appreciable skin effect.

"High frequencies also give rise to what is known as the skin effect, which is simply a consequence of self-inductance. This effect, which opposes the flow of current, is most pronounced along the center-line of a conductor and is caused by proximity to adjacent current flow. It is the region of greatest impedance, which manifests as a gradient that diminishes toward the surface of the conductor. For this reason, the surface or skin of the wire is more conductive. There is nothing mysterious about the skin effect, " .. "Lightning, with a waveform that has a very fast rise time, resembles high-frequency electrical energy. So it is essential to mitigate the skin effect in a conductor meant to conduct during a lightning strike." - https://www.testandmeasurementtips.c...g-skin-effect/


" Vehicles and Lightning - What happens when lightning strikes a vehicle?" ... "Electrically speaking, at lightning's higher frequencies, currents are carried mostly on the outside of conducting objects. A thick copper wire or a hollow-wall metal pipe will carry most of the lightning on outer surfaces. This phenomenon is called "skin effect." The same holds true for lightning when it strikes metal vehicles: the outer surface carries most of the electricity. The persons inside this steel box can be likened to protected by a partial Faraday cage..." - National Lightning Safety Institute Vehicles and Lightning - National Lightning Safety Institute

Skin effect occurs in lightning due to the high frequency nature of the rise and fall of lightning pulses. Skin effect does not only occur in alternating current. It occurs in any electrical current flow that substantially changes amplitude at high frequency .

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Old 10-07-2019, 12:27   #85
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Re: Lightning Protection, pros and cons

[QUOTE=Mike Banks;2927587]The skin effect pertains to alternating current. Lightning does alternate, but not always. When it does the frequency at which it does alternate is insufficient to cause any appreciable skin effect.
/QUOTE]


Please see:

https://ntrs.nasa.gov/archive/nasa/c...9870001225.pdf
or
https://link.springer.com/article/10.1007/BF01042441
or
https://agupubs.onlinelibrary.wiley....D095iD12p20367


As I pointed out above, even ordinary household 50/60 hertz power is affected by skin effect.
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Old 10-07-2019, 17:42   #86
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Re: Lightning Protection, pros and cons

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" Skin effect does not only occur in alternating current. It occurs in any electrical current flow that substantially changes amplitude at high frequency .

Sean
WK7R

Excellent point! Skin effect would also occur in a DC circuit wherever there are fluctuations in current.


And I think most people would agree that lightning "fluctuates."


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Old 12-07-2019, 10:30   #87
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Re: Lightning Protection, pros and cons

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That was on the ground, we had a helicopter hit on the ground in Germany and the Army refused to “total” it, which as the Maintenance officer I was against, I believed it should have gone back to Depot at least, every piece of steel in that aircraft was magnetized.

If they are hit when airborne, they seem to suffer little damage.

The helicopter was chained to the ground, four chains right in front of the tail wheel and two on the main landing gear. The lightning struck the FM antenna on the tail. I assume the lightning would have gone to ground through those four 5/16” chains by the tail and I’m sure a lot of it did, but when inspecting the aircraft, I found that both pitot covers had holes burned in them where the lightning obviously exited the pitot tubes, which were on the wings, well forward of those chains.
Interestingly all the electronics worked, even I believe the FM radio that was connected to the antenna that was struck.
That unpredictability seems to be the most predictable thing about lightning strikes. I worked for a power company one summer and we spent a lot of time repairing lightning damage. Apparently, the power companies have tried everything in the world to stop lightning strikes on power lines and accessories, with little success.
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Old 12-07-2019, 10:56   #88
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Re: Lightning Protection, pros and cons

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Apparently, the power companies have tried everything in the world to stop lightning strikes on power lines and accessories, with little success.
This is repeated point of confusion.

Consumers imagine lightning protection systems will protect against the risk of being hit by lightning. In practice even the best systems have very little effect on the chance of strike.

Lightning protection systems are designed to reduce the chance of damage, especially catastrophic damage, if a strike occurs. They have very little effect (if any) on the risk of experiencing a strike.
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Old 12-07-2019, 12:22   #89
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Re: Lightning Protection, pros and cons

There is a reason the ground conductor is usually on top (transmission/ distribution). Lighting arrestor installed and connected to a ground wire at any pole with equipment, and the ground/ground rod installed at your house meter.

Usually works but not always.


For those floating without a ground rod you need a ground plate and good insurance (rabit's foot dangling from tiller is reported to help).


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Old 12-07-2019, 17:44   #90
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Re: Lightning Protection, pros and cons

More on above by noelex 77 and Frankly:


If you take a look at one of those big three-phase distribution lines on high metal towers, you'll see a thinner conductor at the very top that has no insulators. That's called the "lightning leader" line. The hope, usually fulfilled, is that lightning will strike that line instead. It creates a "zone of protection" around the active lines below.


There's still debate on whether or not a lightning rod actually reduces the risk of a strike. It's there mostly to provide a less destructive path for lightning to follow. A "sacrificial" conductor. On a sailboat, that's often your mast-mounted VHF antenna. If that thought bothers you (it bothers me), there are surge suppressors available: https://www.dxengineering.com/search...rder=Ascending
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