Lightning Protection, pros and cons

[a64pilot]

Originally Posted by noelex 77

The other issue is that epoxy resins start to lose strength at relatively low temperatures. I used to fly high performance gliders and these were always painted white for this reason. There was even concern about small amounts of orange that were sometimes added to wingtips and the rear of rudders. The idea of the colour was to provide a contrast and thereby reduce the chance of midair collisions. All white gliders disappear against a background of white cloud and midair collisions are unfortunately reasonably common, nevertheless even in small areas anything other than white was outlawed by many manufacturers.

And yet almost all Military helicopter rotor blades are composite, painted flat black and sit in Deserts, and that was thirty years ago.
Composite resins have come a long way.

[Wotname]

Originally Posted by Texlan

........

And lightning likes big low impedance conductors (lightning is effectively RF energy) like masts, not small high impedance conductors like shrouds.

.........

The lightning arc generates RF energy but it isn't created by or consists of RF energy. It is a static discharge.

Originally Posted by thunderhoof

A carbon fiber mast is just as attractive to lightning as one that is aluminum. The top of the mast is pointy and high off the water so that initially it accumulates static charge via low current flow, so the material resistance is not an issue. When the ionized channel in the air is formed just before the strike it makes much higher current flow possible. When the strike occurs the flow is a matter (more of less) of Ohms Law at work. The current into the Earth will be divided among the available paths... mast, rigging, wiring... in inverse proportion to the resistance of each path. Lower resistance, higher current. In all cases the mast is the lowest resistance and will carry the large bulk of the current. Problems of carbon composite are that it has a significantly higher volume resistivity (think 50:1) and lower damage temperature (250 vs 1000 deg F) compared to aluminum.

A strike on a carbon mast causes localized heating that punches a burned hole in the material. Aircraft deal with this by using a lightweight copper mesh in the high strike probability areas (wing and tail tips) to distribute the current over an area as it is "launched" into the carbon, reducing the heating effect.
I have thought that applying this material to the top and bottom 2 feet of a composite mast might limit catastrophic damage. Generally there is cosmetic damage and some mesh must be replaced after a strike.

Thank you thunderhoof, an accurate factual analysis of lighting - so often missing in these lightning threads.

[kev_rm]

Originally Posted by noelex 77

The risk of a sailboat boat being hit by lightning is around 0.5-1% per year.

So one in 100-200 sailboats are hit every year? So like 5 or 6 per decent size marina per year? I think not.

[Texlan]

Originally Posted by Wotname

The lightning arc generates RF energy but it isn't created by or consists of RF energy. It is a static discharge.


Thank you thunderhoof, an accurate factual analysis of lighting - so often missing in these lightning threads.

Lightning current amplitude rises and falls many times per strike, and does so at such a speed as to be effectively at radio frequency. This radio frequency energy that travels along a conductor (the ionization path through air, your mast, etc) during a strike, and just like any other unbalanced conductor (otherwise known as an antenna), emits electromagnetic radiation (what you are talking about, but not what I am talking about) but the current pulses are still at radio frequency -- ie, a frequency high enough to emit electromagnetic radiation. It is not direct current and should not be treated as such, even if the net charge movement is in one direction. It's the rise and fall of the current amplitude that is defined as rf, not to be confused with AC.

It's the different behavior of RF energy with respect to the DC or low frequency AC we are familiar with that I was trying to point out we should be concerned with. And the factual analysis you speak of actually isn't.. lightning seeks the low impedance paths, not the low resistance paths -- again, because it is at radio frequency, and is not direct current.

Anyways to get some actual real data on how to deal with lightning and keep your electronics from smoking, look at how commercial and amateur radio operators deal with it on our 300 foot towers topped with antennas on the tops of 7000 foot mountain peaks. They get hit all the time.. The magical fuzzy devices people put on the top of their masts hoping somehow to "dissipate" the massive hundreds of kiloamp charge potential of the earth/seawater that their boat is sitting in seem to be missing on them..

Anyways, peace.
Sean
WK7R

[dfelsent]

Originally Posted by a64pilot

Lightning protecting composites
https://www.compositesworld.com/arti...ite-structures

I have been biting my tongue hard through this whole discussion. a64pilot thanks for that article.
I have skin in this game. My grandfather started Dexmet, mentioned in your link as a supplier of material for protection of composites.
My father was hit by lightning near St Augustine while single handing his sailboat. He is not sure whether his muscle soreness was from being thrown by the strike or from having to haul up 150 feet of all chain rode by hand after the strike.
I’ve spent time as an engineer working with high voltage high energy pulse power systems. Nothing big but up to 250 kV and 100 kA.
I’ve never had a direct lightning hit but two within 20-50 feet. Loud.
I’ve been sailing in light air and heard that scary hissing sound of corona as a cloud passes overhead.
There is no serious mystery about where and why lightning does what it does when you get a masthead hit. RF impedance (a whole complex thing in itself) and breakdown voltage really tell you where the current will flow.
It’s the current combined with the relatively short rise times that generate the large magnetic fields that induce large voltages in adjacent conductors. That’s what blows stuff up.
Masthead hit?
I can guess for my current boat with a keel stepped mast on a bronze mast step welded to a bronze centerboard trunk the current will go right there. Electronics? It will all go away.
Two boats ago? Deck stepped mast. No tie rod to the keel. Long curved #8 bonding wires from shrouds to keel bolts. Likely a real mess. Lots of enclosed area in the ground wire to sea loop. High inductance. High RF impedance. I expect the the shrouds might have been the short path (maybe) til they blew up then mast base wiring turning into plasma to the keel.
Hard to say without serious modeling I’m not going to do.
Electronics? Still all going to go away.

It is possible but not cost effective to protect against all this. You will still have the same strike risk, but the consequences might be less.

[Frankly]

Was going to stay out of this, but some people just can't help theirselves (I used to design lightning protection systems for buildings).

1. Unlike gravity there are no absolutes when it comes to lightning. Improve the probability of good outcomes but there will be exceptions.

2. The single overriding consideration of a strike is relative altitude compared to surrounding objects (conductive or otherwise).

3. There is no evidence to date that grounding the mast will increase the probability of being hit. But grounding the mast will improve the chances of a good outcome (nobody hurt and yacht still floating).

4. Once the lightning stroke has attached to the yacht it pretty well follows the laws/ physics of electricity and it is a high enough frequency that conductor surface effect are in play.

5. Although the peak currents are very large, the duration is quite short so reasonable conductors can safely handle the current flow (aluminum is always a lot better conductor than SS, but not as good as copper).

That recent horrendous strike in Boston represents about as bad as it gets, but there are lesser direct strikes and EM coupling from nearby strikes that typically cause most of the damage.

On my personal yacht (located in Florida) there is a copper ground plate connected to the mast with parallel #4 conductors. A disconnect/ selector switch on the VHF antenna, equipotential bonding conductor from the 12v negative to the plate, gas discharge tube on the TV antenna, home made surge protectors on the mast lighting, mast wind sensor, and probably 6 or 8 scattered around the yacht at various locations on the 12v distribution system.

Not likely to survive a Boston type strike, but no problem sleeping at night knowing I made a reasonable attempt at protecting one of my favorite toys.


Frankly

[Texlan]

On my personal yacht (located in Florida) there is a copper ground plate connected to the mast with parallel #4 conductors. A disconnect/ selector switch on the VHF antenna, equipotential bonding conductor from the 12v negative to the plate, gas discharge tube on the TV antenna, home made surge protectors on the mast lighting, mast wind sensor, and probably 6 or 8 scattered around the yacht at various locations on the 12v distribution system.

Not likely to survive a Boston type strike, but no problem sleeping at night knowing I made a reasonable attempt at protecting one of my favorite toys.


Frankly

Great posts guys..

Sean
WK7R

[Cpt Pat]

Originally Posted by GRIT

0.5% to 1% seems high. Can you put up a link to this information?

Here is one such map for the US: https://www.vaisala.com/en/products/...data-sets/nldn

Those of us on the west coast don't think much about lightning. One look at the map will explain why.

There is a myth that there is nothing one can do to reduce the damage from a direct hit. Benjamin Franklin, who invented the lightning rod (that's what the whole thing with the kite and the key was about), encountered this myth - that it was "God's will alone" that determined what got hit and destroyed. Ironically, you'll often see his lightning rods most prominently on churches today. Hum... They often have a glass ball in the middle, which is intended to shatter from a direct hit, prompting a close inspection of the system.

I was a broadcast engineer at transmitter sites for many years, and we'd get direct hits several times during each storm. Except for the loud noises and the occasional smell of ozone, nothing untoward happened. Handled properly, there's a lot you can do to diminish the danger.

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.

[Cpt Pat]

Originally Posted by a64pilot

And yet almost all Military helicopter rotor blades are composite, painted flat black and sit in Deserts, and that was thirty years ago.
Composite resins have come a long way.

As a commercial helicopter pilot who's read every helicopter accident report in the past 30 years, I can say that helicopters seldom get hit in the air. No more often than airplanes, which is almost never. It's got to do with the Faraday effect and lightning being deflected around a conductive enclosure that is insulated by surrounding air: counter electromotive force deflects the lightning. (The same effect applies to metal-bodied cars - the best place to take cover in a lightning storm).

And on the ground, it's the metallic rotor hub that gets hit.

[Wotname]

Originally Posted by Cpt Pat

As a commercial helicopter pilot who's read every helicopter accident report in the past 30 years, I can say that helicopters seldom get hit in the air. No more often than airplanes, which is almost never. It's got to do with the Faraday effect and lightning being deflected around a conductive enclosure that is insulated by surrounding air: counter electromotive force deflects the lightning. (The same effect applies to metal-bodied cars - the best place to take cover in a lightning storm).

And on the ground, it's the metallic rotor hub that gets hit.

I'm not sure why you think that airplanes are almost never struck by lightning.

I have personally inspected maybe 10 in the last 25 years. There must be hundreds of thousands of other aviation engineers/mechanics in the world. Even if only 1% have seen as many as I have, that means tens of thousands of hits but likely it is many more.

[GordMay]

... Also true in the electrical world that electricity will take the easiest path to ground. - Usually! ...

Electricity will take ALL paths to ground, in approximately inverse proportion to the impedance of each path.
This is why a proper lightning mitigation system provides a highly conductive continuous path from an elevated air terminal to the water (gnd).

Pray tell - what does one do with this 3/16” rod you speak of? Where do I place it? What do I attach it to? Do I ground this rod? How do I ground it?
Is it a dissapator? A conductor?

The lightning air terminal (rod) is fixed at the mast top, which is grounded to a submerged ground terminal (metal keel, gnd strip, SiedarcTM , etc), with minimum #6 AWG cable.
It’s not a dissipator.

[bglad]

[/QUOTE]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?

[Wotname]

Originally Posted by Texlan

Lightning current amplitude rises and falls many times per strike, and does so at such a speed as to be effectively at radio frequency. This radio frequency energy that travels along a conductor (the ionization path through air, your mast, etc) during a strike, and just like any other unbalanced conductor (otherwise known as an antenna), emits electromagnetic radiation (what you are talking about, but not what I am talking about) but the current pulses are still at radio frequency -- ie, a frequency high enough to emit electromagnetic radiation. It is not direct current and should not be treated as such, even if the net charge movement is in one direction. It's the rise and fall of the current amplitude that is defined as rf, not to be confused with AC.

It's the different behavior of RF energy with respect to the DC or low frequency AC we are familiar with that I was trying to point out we should be concerned with. And the factual analysis you speak of actually isn't.. lightning seeks the low impedance paths, not the low resistance paths -- again, because it is at radio frequency, and is not direct current.

Anyways to get some actual real data on how to deal with lightning and keep your electronics from smoking, look at how commercial and amateur radio operators deal with it on our 300 foot towers topped with antennas on the tops of 7000 foot mountain peaks. They get hit all the time.. The magical fuzzy devices people put on the top of their masts hoping somehow to "dissipate" the massive hundreds of kiloamp charge potential of the earth/seawater that their boat is sitting in seem to be missing on them..

Anyways, peace.
Sean
WK7R

First let me emphasis I'm not a professional fulminologist or even a serious amateur one however what you write is news to me - I would like to see some reference for the claim that current amplitude rises and falls many times per strike at an RF rate.

Rather it is my understanding of the transient current in negative cloud to ground (CG) discharges (which are 95+% of CG discharges) is a DC surge (or pulse) with a leading edge rise time of ~5 microseconds and a trailing edge of ~100 microseconds. Usually there is a lull of ~50 milliseconds before the next DC pulse (re-strike) and this continues for another 2 or 3 times. Peak current flow for the common negative CG discharge is 30 to 100 kA.

Note I am not referring to the much rarer positive CG discharge which can have peak currents in excess 400kA and over a much longer time period. Nor am I considering the very weak current flows in the preceding formation of the leaders - these are insignificant when compared to the main discharge.

I agree the proper term should be impedance and if I used resistance, then it was sloppy writing on my part. However I do prefer to use the term DC as really there is only DC or AC. Varying DC and pulses of DC remain DC although it useful to think of a varying DC as a constant value of DC with an overlaying AC. The generation of EMR is simply a function of the rise and fall time components of a DC pulse(s).

As an aside for the aviation aspects I and others have posted, it must be remembered most (all?) in air plane strikes are from the far more numerous cloud to cloud (CC) or intracloud (IA) types of lightning.

[GordMay]

Originally Posted by Wotname

First let me emphasis I'm not a professional fulminologist or even a serious amateur one however what you write is news to me - I would like to see some reference for the claim that current amplitude rises and falls many times per strike at an RF rate ...

“The electromagnetic radiation from lightning at microwave frequencies and below is generally referred to as the “radio frequency” or “RF” portion of the spectrum. Radiation from lightning in this portion of the spectrum is important both for scientific investigations of lightning and for engineering assessments of the interference environment during thunderstorms. Measurements have been reported from frequencies below a kilohertz to frequencies above a gigahertz...”
NASA Technical Memorandum 87788
"Review of Measurements of the RF Spectrum of Radiation from Lightning” ~ by David M. Le Vine
➥ https://ntrs.nasa.gov/archive/nasa/c...9870001225.pdf

“Comparison of the RF Frequency Spectra of HEMP and Lightning” ~ by Martin A Uman
➥ https://apps.dtic.mil/dtic/tr/fulltext/u2/a234306.pdf

“ELECTROMAGNETIC SIGNATURES OF LIGHTNING NEAR THE HF FREQUENCY BAND” ~ by JAKKE MÄKELÄ
➥ https://helda.helsinki.fi/bitstream/...=1&isAllowed=y

[Wotname]

Originally Posted by GordMay

“The electromagnetic radiation from lightning at microwave frequencies and below is generally referred to as the “radio frequency” or “RF” portion of the spectrum. Radiation from lightning in this portion of the spectrum is important both for scientific investigations of lightning and for engineering assessments of the interference environment during thunderstorms. Measurements have been reported from frequencies below a kilohertz to frequencies above a gigahertz...”
NASA Technical Memorandum 87788
"Review of Measurements of the RF Spectrum of Radiation from Lightning” ~ by David M. Le Vine
➥ https://ntrs.nasa.gov/archive/nasa/c...9870001225.pdf

“Comparison of the RF Frequency Spectra of HEMP and Lightning” ~ by Martin A Uman
➥ https://apps.dtic.mil/dtic/tr/fulltext/u2/a234306.pdf

“ELECTROMAGNETIC SIGNATURES OF LIGHTNING NEAR THE HF FREQUENCY BAND” ~ by JAKKE MÄKELÄ
➥ https://helda.helsinki.fi/bitstream/...=1&isAllowed=y

Thanks Gord and I understand how lightning generates EMR at RF but I don't see any claim the discharge current (in the arc) is resonating at an RF rate.
In the same manner, a capacitor discharge spark is simply a pulse of DC and not moving back and forth at an RF rate. The same spark generates EMR in the RF spectrum