Lightning on masts

[ted655]

There are "supposedly photos of ground to sky bolts. It's NOT accepted by most scientists &and (your right) it hasn't been explained. For my own health I will continue to follow those practices which have been tried & proven to work. I'm a sky to ground devotee.
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Putting metal in an insulator does not prevent it from becoming a path to ground. Just ask those with fried electronics as a result of not unplugging them. Better yet, think of trees, surrounded by a non conductor layer of wood. They STILL become "The fastest, nost direct path to ground because they are internally wet". Remain the less desirable path to ground on the boat and sail confidently on.
Back to the "masts", they are chaise #1 for a strike. Do what you need to do & make damn certain the bolt follows it all the way to ground (straight path to a wet keel). The danger is, leading the strike down the mast, THEN slowing , bending or blocking the path. That is when it gets impatiens & starts jumping off, trying to find a quicker, wider path.
It's ALL about "path" guys, don't deny it a suitable path!

[TerryKing]

Originally Posted by Fanie

If lightning does pose a serious thread, why doesn't they glass metal sheets or strands in the cabins and hulls to divert the lightning ?

Fanie, the reason this is not done is that it would likely result in lots of damage and probably a fire. Lightning current rises from zero to 100,000 amps or more in a few millions of a second. That makes it effectively "high frequency" and much of the current flows in the outer portion of the conductor (wire). Therefore there is much more instantaneous heating than would be expected, even in a large wire.

Lightning conducted down through steel rebar in a concrete column may result in an internal explosion and significant damage to the column with a lightning strike. Wires inside a fibreglass laminate would probably cause similar damage.

High Radio/TV towers (200 to 350 feet) I had installed for broadcast stations always had the bottom of the tower (or it's base insulator if used) sitting on a concrete pillar. We always ran four copper straps about 4 inches wide and .062" thick from the tower base down the four sides of the concrete column, to a hefty ground system, to conduct lightning currents OUTSIDE the concrete.

This is a lot like the modern recommendations to have external shrouds, railings etc. on a boat connected to the water at the outer edges of the hull, not only down through the mast.

Take a look at:
http://boatdesign.net/forums/showthr...ight=lightning

for more discussion.

[Ike]

You need first a basic understanding of lightning. I like to use the anology of a carbon arc lamp, with two carbon electrodes. As the electrodes approach each other they finally get close enough that the potential energy overcomes the resistance of the air gap and the spark jumps the gap, from both directions! I have actually seen this happen. It's pretty much the same with lightning. The clouds have a high negative charge. The earth is of course positive in relationship to the clouds, but with think of it as "ground" potential. As the current begins to find a low resistance path to ground through the air (that's why in photos of lightning it looks jagged) it follows the path toward ground. As soon as it gets close enough to ground to overcome the resistance of the air gap between it and ground a spark jumps FROM THE GROUND to the point in the air where the electric current is. So lightning appears to the human eye to come down because the last part happens so fast we can't see it, but high speed cameras have recorded it. So your boat is actually getting the part that goes up. You boat is the low resistance path for current to flow. But if you present an even lower resistance path, a very large cable from the top of the mast to a large metal mass under water, then in theory it takes that path.

By the way, experiments have shown that a mast or lightning rod with a dull rounded head works better than the traditional sharp pointed lightning rod.

The flaw in all of this is the simple fact that the current flow is so huge that it jumps to anything conductive that is near it's path to ground, thus frying your electronics.

I once had the tuner in my tv get fried. It didn't touch anything else, but the lightning hit the tree in my back yard, and enough current leaked down through my roof antenna that it fried my tuner. I assume that when that happened the tunner stopped conducting, in effect acting as a circuit breaker. When I replaced the tuner the tv worked fine. Can't do that with these solid state TVs.

Anyway, so lightning actually goes both ways, and researchers have actually recorded bolts strictly from the ground up to low lying clouds. I think the one that sticks in my mind is a video of a rocket being launched. They use rockets trailing a long thin wire to attempt to induce the lightning to start. The rocket takes off and litterally trails a large bolt of lightning behind it as it rises which is met by one from the clouds. Very dramatic. All this happens in a few seconds but they use high speed cameras to record it.

Oh I forgot to add. interposing dielectric material (an insulator) between the lightning and the interior of the boat doesn't work simply because the lightning is so powerful that it just blows a hole through the insulator. It would require insulation so thick that it wouldn't be practical to use on a boat.

[Man Overboard]

These electrodes were meant to run through the hull, and according to Marine Lightning Protection Inc. They won't melt when the boat is struck by lightning I believe the insulator is Marelon.

http://marinelightning.com/

[Frosty]

Its difficult to estimate the power of lightening. Im not an expert in this field but if you've been within 100 yds of a strike it will all become clear. There is no explaining it.

You would not want that under your fibre glass.

I notice that many people say they live in a lightening prone area. Well Singapore is pretty good, they say that with a roll of film in a storm and you keep clicking you will photograph a strike.

Any way I have seen a small keel yacht get hit whilst on the hard sitting in a cradle. It looked to have done nothing untill I looked at it closer . A portion the size of a large hand had been de laminated--not blown out, but seriously damaged as the power tried to get out through to the cradle and into the ground.

I cant think of anything more silly than through hull lightening electrodes. How do they test them? I dont believe there is such a thing as lightening insulation, the power will build up untill it blows it apart.


I also believe that there is different kinds of lightening storms . Theres the very quick thin type that has a crack like a whip. Or theres the longer arc type that burns for enough time to see it ,maybe 1/4 of a second and has a thick arc maybe 6 feet across its width.
Motoring along at 4 am with no wind and torrential rain and a mast sticking into the sky during a storm like that is a humbling experience. You start to think defferently about --everything.

[PAR]

I've inspected vessels after lightening strikes and it can do a lot of damage, including blowing holes right through a hull. A lightening bolt can vary in intensity, from a few million volts to several tens of million. The Tampa Bay area is the lightening capital of the world, with the general central Florida region being nearly equal in frequency of strikes. Several places around the world also have their share of unusually high strike activity. The unprotected strike I mentioned earlier, was at the mouth of Tampa Bay.

I've seen space shuttle video of lightening going up from clouds, literally into space.

You can protect your boat and several companies offer packages that work.

[FAST FRED]

Any ideas on keeping a boat with electronic injection diesel engine running after a strike?

Only two "solutions " I've heard so far is have a metal boat and 6 spare computer packs and pray.

FF

[Frosty]

Even then the computer packs rely on various senders for feed back of information.

A complete wiring loom, computer pack, and every sender on the engine.

And you'lle still need to pray.

I really don't know what these engine manufacturers are thinking of. They may be more economical but whats the point when fuel goes up every year.

[tom28571]

Originally Posted by PAR

You can protect your boat and several companies offer packages that work.

Which packages and which companies? Some are just feel good stuff. How would you suggest protection for a sailboat without a metal keel? Not trying to put you on the spot.

[Fanie]

Here's what I think.

The risk of getting hit by lightning is not neccessary higher because you're on a yacht, unless you're right in the direct place the bolt would discharge. I don't think this risk is any higher than lightning hitting your house. I've seen a house's brick awning knocked off and a concrete wall right between two buildings disintegrated on seperate occasions. Why not hit the houses which were beside it...

You ever stood on a high building looking down ? You're not even close to the clouds where the discharge would take place, yet the objects protruding upwards looks insignificant. So why on earth would lightning specifically pick your little mast to discharge through ? It's like you looking down to your lawn and wants to focus on the ant that sits on a grass stem. Truth, you don't even see the ant.

Besides, lightning is good (if it's somewhere else ), it creates many tonnes of ozone killing bac and teria and generates plenty of oxygen.

Getting hit is merely a matter of unfotunately happening to be just in the right spot at the wrong time. One advantage is that us humans are not very conductive, so unless you drink a LOT of sea water, you could consider yourself pretty safe.

So I don't think we get picked on more than is probably needed, and some people needs a bit of lightning every now and again eh !

[TerryKing]

Originally Posted by FAST FRED

Any ideas on keeping a boat with electronic injection diesel engine running after a strike?

Fred, that's an interesting area to try to figure out.

One of the significant parts of the problem is, like Frosty just said, "Even then the computer packs rely on various senders for feed back of information. A complete wiring loom, computer pack, and every sender on the engine."

Two unfortunate realities:

1. All the wiring for the many sensors, monitoring NMEA signals, engine alarms etc etc. act as ANTENNAS when there is lots of electromagnetic energy around.

2. Lightning currents rise so quickly that the discharges are effectively huge radio transmitters.

Ike had the experience: " I once had the tuner in my tv get fried. It didn't touch anything else, but the lightning hit the tree in my back yard, and enough current leaked down through my roof antenna that it fried my tuner."

I think, in Ike's case, that the huge instantaneous magnetic field caused by the nearby lightning strike was coupled (like in a transformer) to his home antenna wire, and was powerful enough to damage his tuner. This is a well-known effect in Lightning damage.

Oh, but Fred asked for ideas! I've been thinking about this in the context of the Onboard Computer project I'm working on. (Discussion- Multi-purpose Onboard Computers if you're interested).

I have a couple of ideas:

1. Adopt a boat mast/rigging/lightning protection conductor approach that creates multiple lightning paths around and outside the center of the boat where the humans and systems are. There is a whole discussion on this here:
http://boatdesign.net/forums/showthr...ight=lightning
where Fred started a major discussion on this. See the posts / information on this concept.

2. Don't use any wires (AKA Antennae) for sensors, alarms, system monitoring etc. Connect them with FibreOptic lines, or Wireless (Wireless USB, ZigBee, or others).

AND, do some serious lightning protection design work on the individual electronics boxes like Onboard Computers, Electronic Engine Controls, AutoPilot, Power control systems, etc. This is non-trivial work!

I am asking some questions of this guy who designs electronics with lots of sensors, microcomputers, etc., and then puts hundreds of them up on mountains with high metal towers and wires running down the tower. The installations look like this:


This looks a lot like a big sailboat, asking for Lightning Trouble!

There's two parts to this:

1. Encase the electronics system in a sturdy metal box

2. Filter and protect ALL wires going in and out of the box against Over-voltage and Over-Current.

Quite a lot is known about such protection and appropriate devices. I did a lot of that, building broadcast transmitter sites, back in the day. And the Engineering Manager at nrgsystems.com who makes those towers with sensors has sent me a few samples of what they use.

But I'm really thinking that the best approach is: No Wires!

[Fanie]

Of course a non-metalic mast and lines would be ideal. The sailing boat have another problem, there is no-where you can earth anything like in EARTing it, so the boat's metal parts are floating , as the boat is floating on the water. You could drop the achor on a metal cable, but this may rather invite lightning to take short cut to ground.

[ted655]

The risk of getting hit by lightning is not neccessary higher because you're on a yacht, unless you're right in the direct place the bolt would discharge. I don't think this risk is any higher than lightning hitting your house. I
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I disagree. Lightning looks for the tallest object to provide a path. That is why water & golf courses, soccer fields, etc. are more often sites of people being struck.
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For my part, OK...., so lightning hit my boat! It traveled down my mast & blew (or burned or whatever) a hole around my thru hull. It may even have toasted my engine & fried my radio. The sound made me pee my pants & gave me minor shell shock, BUT, I'm OK. I'll live to repair or replace whatever I need to. I can even read the latest opinions & theory's of source and behavior of lightning. WHY? Because I gave the one bolt that picked me, A BETTER PATH than my body to ground (or sky).
For me, the rest is purely academic, because I'm alive!

[Ike]

Lightning simply takes the least resistance path to ground. If that path is you, well, it's been nice to know you. Although some people have survived lightning strikes. But if your mast is metal, it is a much lower resistance path to ground than the air surrounding it. So when you are out on the water, the lowest resistance path around happens to be your mast.

I was out on a Lake in Utah with lightning all around but my mast was wood. Fortunately none of the lightning struck close enough to do any damage, although my son made the mistake of touching the wire shrouds and got a nasty static discharge. So most lighnting protection systems are based on the simple idea that if you provide a lower resistance path to ground, it will take that instead of you or the hull under you.

I had some nasty experiences with lightning in Utah, Talk about another place with a high lightning frequency. Geez. I was convinced it was out to get me.

[tuks]

So I thought I lived in a lightning prone area, I guess I was wrong.

From Usatoday.com

The spot with the most lightning lies deep in the mountains of eastern Democratic Republic of the Congo near the small village of Kifuka (elevation 3200 feet, 970 m). Thunderbolts pelt this land.

Strikes averaged from April 1995 to February 2003 - Note that over the oceans and desert "white" means no lightning.
Courtesy of NASA's Lightning Imaging Sensor (LIS) Instrument Team and the Global Hydrology Resource Center (GHRC). .
The black dot (in the middle of the largest white area in Central Africa) marks the spot — near the tiny town of Kifuka in the Democratic Republic of the Congo — where the greatest lightning activity in the world occurs. The color code at the top of the image shows the number of flashes per square kilometer during the year. Note that over the oceans and desert "white" means no lightning.

In a year, 158 bolts occur over each square kilometer (10 city-blocks square), says atmospheric physicist Steve Goodman of NASA's Global Hydrology and Climate Center (GHCC) in Huntsville, Alabama.

Say out of the red patches and you should be ok.