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Old 06-04-2009, 11:37   #121
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Originally Posted by Wotname View Post
As to dissipating the surface charge into the air, I just don't see it that way. To me, saying that is like adding a third potential "point" into the circuit. Please correct me if I am wrong but I see any static build up as a electrical potential difference between two points.
But that part is exactly the same as how the wicks do it. I think I posted something on this before, incl. the name of the phenomena. Read Forespar: Marine Products that Perform for a good explanation. I think the experiment that Franklin did was to charge a piece of amber and pointing a rod with a sharp point to it, which discharged the amber without any obvious physical reaction during the discharge. He thought he could discharge storm clouds with these rods.

The surface charge is opposite to the cloud charge, so normally negative. It is created because the positive charge attracts the negative so the ions on the surface concentrate under the cloud.

It doesn't really matter if we understand the surface charge and the discharge by using a sharp point as these are clear and sound principles of nature and demonstrated to be correct just like Ohms law etc.

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These charges only exist because of the electrical nature of electrons and protons and the charges can only be dissipated by the function of a transfer of charged particles from one charged region to another oppositely charged region. I am unaware of any other method to dissipate an electrical charge but if there is one, I am already to learn.
Again, read the link. The principle is called the "point-discharge principle".

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I understand your point that we only have to reduce the charge a little bit so that some other "point" wins the race but given the charges involved, even that "little" bit has to be pretty big IMO.
Well, if you are presented with 2 stacks of quarters and can choose which one you want to take for free, you select the highest one every time. Lightning is like that and this is why scientists can attract a strike by firing a rocket that lifts a wire with close to 100% certainty (they study the fulgurites). A very good page for info is this: Lightning - Wikipedia, the free encyclopedia

cheers,
Nick.
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Old 07-04-2009, 06:19   #122
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Leaders and streamers and other mythical words

Well Nick, its looks its only me and you left in the ring .

The Forespar link is well written and mainly correct in my view; however the stuff about leaders and streamers aren't exactly science and at the worst, is just sales pitch - good pitch should at least 95% fact and this link is at least that IMO.

Seriously what is a leader or a streamer in terms of accepted physics. Are they particles (atoms etc), forces, can they be measured, can laws be ascribed to them. If not, then they may well be meaningless.

However being generous, I am willing to accept that they do exist (and act as described in the link) and they are part of the process of ionization of a gas (in this case air).

The are still some holes in the brush argument IMO. I have pasted some excerpts form the above link to argue against.

<When the intervening air breaks down, the strike itself begins with the propagation of stepped leaders. Stepped leaders originate within the cloud charge. ..... When the stepped leaders reach to within several hundred feet of the ground, the rapidly building electrical field on the ground causes objects on the ground to break down electrically and respond by emitting streamers to jump upward. When a stepped leader and a streamer meet, the ionized channel becomes the path for the main lightning discharge.....When the ionized path is completed, the current discharge occurs. Although a lightning strike appears to be a single flash, it is actually a series of flashes>

This appears to be a description of the ionization process of a gas. I don't believe an object on the ground "breaks down and emits streamers". No description of any object I have ever heard about states it contains "streamers" which can be emitted when influenced by large electrical fields. I can believe that ions are formed in the gas near the objects that are highly charged and such ions will be attracted to oppositely charged ions in the "leader". And when they meet, a low resistance current path is established and current flows by means of charged ions moving towards oppositely charged objects. This current will continue to flow until the charges are equalized (or dissipated).

<These points will also be the points from which streamers tend to originate on your boat. Various objects on your boat exhibit different behavior in forming streamers, and you can use that to your advantage. Streamer formation can be explained by examining the debate over the relative value of a blunt versus a pointed lightning rod. A blunt rod will tend not to break down into ionization until under a relatively high potential, i.e. it is difficult for the cloud charge to ions off the blunt point. However, under the high potential of an approaching stepped leader, the blunt rod, when it finally breaks down, emits a relatively long streamer upward towards the approaching stepped leaders. A pointed rod, on the other hand, breaks down into ionization under a relatively lower potential, i.e. it is easy for the cloud charge to pull ions off the sharp point.>

For the sake of the argument, let's accept this as true. If I understand the point correctly, it says a sharp point will ionize at a lower potential and therefore the streamer will be shorter. This would seem to indicate that the sharp point would be struck more often given that ionization has to occur for the low resistance current path (strike) to be established.

<The ionization, or corona, around the sharp point does not allow a streamer to extend very far upward. Thus a sharply pointed rod is less likely to be struck.>

Yet here, it is suggested that the ionized gases stop a "streamer". What is happening here, earlier we had a streamer meeting up with a leader and an ionized channel becoming a path for the strike. Now we have ionization occuring before the streamer meets the leader and effectivly preventing the two meeting to develope an ionized channel. This sounds like a "Catch 22" - you have to have ionization occuring to prevent ionization occuring.

<The same effect explains the operation of a static dissipater. Since a dissipater employs a multiplicity of very sharp points, it retards the formation of upward streamers. The sharper the points employed, the greater the effect>

There is no logic here, it makes a case for something to be true when the premise is (at the best) suspect and not proven. If there is only a slightly different view taken then the argument is reversed i.e. A sharp point "breaks down" at a lower potential and therfore is more likely for an strike to occur at the sharp point.

FWIW, This description of a how a static dissipater works is not given in any reference I have read regarding airframe static dissipaters.


Nick, we might have to agree to disagree on this one but I have enjoyed the discussion.
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Old 07-04-2009, 12:38   #123
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You know, I'm a strange guy... I think I should have been a scientist instead of a cruiser because I really study these things for no other purpose than my need to know how it works. This often makes me skip details in my posts and they still end up very long posts ;-)

So, here we go; I'll be blunt sometimes but be assured that it isn't personal... it's how engineers talk to each other ;-)

Quote:
Seriously what is a leader or a streamer in terms of accepted physics. Are they particles (atoms etc), forces, can they be measured, can laws be ascribed to them. If not, then they may well be meaningless.
Both leader and streamer are fully understood and documented. They have recorded them with high speed filming and you can do experiments yourself with a Van De Graaff (Dutchman of course ;-) generator, where the streamers form from your fingertips and the leader from the generator. They are indeed ionization of air, plasma. The plasma is conductive and this forms the electrical path for the lightning strike.

So, when you look at lightning you often see many many leaders coming down (branching) from the sky, like the roots of a plant. Only one or sometimes two reach the earth. The ones that don't reach the earth are the leaders and the top part of the ones that do reach the earth are the leaders. The bottom part of these are the streamers. You see the leaders that don't reach the earth because they discharge into the path that connects to earth first... they supply power to it just like the cloud. The leaders and streamers are visible when filmed with high speed film as a purple glow... just like St Elmo's fire... you actually see plasma.

As the leaders work their way down while ionizing the air, their presence (they are highly charged) triggers the streamers to form from earth upwards. These are the ones that form from high and sharp points and that can be a brush, carbon-crystal but even tips from leaves on a tree. It is all about the moment when a streamer meets and connects with a leader (they attract each other because they have opposite charges)... now there is that conductive path from cloud to ground and the strike occurs. Many strikes through that same path follow, sometimes so quick you see it as one strike or maybe two or some flickering (there's dozens in reality). The nice thing is that the leaders that didn't make it only flash with the initial strike as they discharge themselves into the path to earth. I have actually seen a single plasma path used over and over for minutes with pauses of up to 20 seconds or so. All the repeat flashes are just the single channel without branches.

To read up on this there is Wikipedia but I also like the "How Stuff Works" site. Here is the page starting with the ionization process... the next pages describe the leaders and streamers etc.: HowStuffWorks "Ionization"

So, there are no questions about if this is what really happens with lightning. The unknown part is how exactly the cloud gets charged because there are multiple theories that make sense. I think the ice-crystals (they melt and freeze over and over) moving up and down in the cloud create it but there are much juicier theories too.

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This appears to be a description of the ionization process of a gas. I don't believe an object on the ground "breaks down and emits streamers". No description of any object I have ever heard about states it contains "streamers" which can be emitted when influenced by large electrical fields.
Blunt mode on: it isn't relevant if you believe this, it's how it is regardless of what you believe ;-) When you see St Elmo's fire in the rigging you are watching the rigging and surrounding air breaking down. Don't think the steel wire is breaking apart, "breaking down" must be read as in how an magnetic field can break down, i.e. it gets ionized. It is not about metal or air breaking apart.

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If I understand the point correctly, it says a sharp point will ionize at a lower potential and therefore the streamer will be shorter. This would seem to indicate that the sharp point would be struck more often given that ionization has to occur for the low resistance current path (strike) to be established.
We're getting very close now ;-) Indeed, a sharp point starts ionizing surrounding air sooner (at a lower level of charge which is earlier in time) than a blunt point. But that doesn't mean it gets struck more often. This is exactly why they started making lightning rods with blunt points or even balls on top. The sharp point starts sooner, when the charge isn't high enough for a large leader to form yet. As the point starts ionizing, it bleeds the charge off, while other objects only build up at that same moment in time. Now, when the charge gets high enough it's time to start the race for who can form the highest leader and the sharp point looses because blunt objects have "saved their charge" earlier.

Quote:
Yet here, it is suggested that the ionized gases stop a "streamer". What is happening here, earlier we had a streamer meeting up with a leader and an ionized channel becoming a path for the strike. Now we have ionization occuring before the streamer meets the leader and effectivly preventing the two meeting to develope an ionized channel. This sounds like a "Catch 22" - you have to have ionization occuring to prevent ionization occuring.
No, it doesn't stop the sharp object from forming a streamer. But the streamers from the sharp objects are smaller as they lost part of their charge earlier. The moment in time they ionize while blunt objects don't do that yet is the same as the wicks on aircraft even though that charge is from a different source. Also, a sharp point doesn't "bleed ions" better or in a bigger volume compared to blunt objects... they start doing it earlier at a lower level of charge at an earlier moment in time... and while doing so, they loose part of their charge while blunt objects save it all for later.

Quote:
There is no logic here, it makes a case for something to be true when the premise is (at the best) suspect and not proven. If there is only a slightly different view taken then the argument is reversed i.e. A sharp point "breaks down" at a lower potential and therfore is more likely for an strike to occur at the sharp point.
The logic becomes obvious when you realize that the charge builds up as the cloud moves closer. The sharp point starts ionizing at a time that the leaders aren't close enough or far enough down yet to connect to it's little leader.

The whole thing makes sense and it will really works... the question is if it will work good enough, i.e. if the little brush really makes a difference. In a really violent lightning storm I think all bets are off. We have seen some horrific stuff like a horizontal lightning bolt that passed under the boom, striking the water hundreds of yards further on. Try to explain that... we didn't even had the brushes yet at that time. Our neighbors here had a lightning storm so bad that the husband was hiding under the salon table and the wife saw Elmo's fire coming down the mast and traveling over the boom right in her face! She yelled so loud for help on the VHF that the coastguard copied them 125 miles out from California... but that's more for the max. VHF range thread ;-)

So, does it work enough to make a difference? I think they do, statistics will tell us. I challenge anyone to come up with an incident where lightning struck the masthead of a boat that had a static dissipater which was installed correctly (bonded to ground). Every example I received over the last 4 years turned out to be an incorrect installation... even dissipaters screwed onto a wooden mast, like it was some kind of magic wand. Start asking around and check details and you will collect a significant amount of data over the years like I did, so you can form the same opinion... or not... let me know ;-)

It's time people stop thinking of these as magic wands because their enthusiastic stories have nothing to do with it and confuse others who prefer a more scientific approach. It puts many people off when they hear about the magic and they discard them, calling them snake oil as the result. It might te true that they don't work well enough, my personal statistics gathering is too small for any form of conclusive evidence, and I don't record it professionally anyway, but the brushes will really "bleed ions" before any other part of the boat does so with all that I wrote above as the result... only the quantity and if that is enough is what I am not sure of.

ciao!
Nick.
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Old 07-04-2009, 17:29   #124
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Well Nick, its looks its only me and you left in the ring .
Lots of Spectators in the seat though. 2499 views.
Don't feel you're alone.
We're with ya, and with interest.

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Old 07-04-2009, 17:57   #125
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You guys have about as much of a chance of figuring this out as gettin' struck by lightning! Sorry, just had to say that...
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Old 07-04-2009, 18:07   #126
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Quick aside: not much chance of getting struck by lightning if I stay at my keyboard posting about the stuff rather than being out on the water looking up at thunderclouds and my mast top brush
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Old 07-04-2009, 18:27   #127
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C'mon guys! Everyone knows the best way to protect any sailboat is to simply fasten a one iron at mast top. Even God cant hit a one iron!
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Old 08-04-2009, 02:40   #128
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... Even God cant hit a one iron!
I might not take lightning protection advice from Lee Trevino, who was actually struck by lightning at the 1975 Western Open golf tournament. Afterwards, Trevino was asked by a reporter what he would do if he were out on the course and it began to storm again. Trevino answered he would take out his 1 iron and point it to the sky, "because not even God can hit the 1 iron."
One of my all-time favourite sports quotes!

Lee Trevino lies near the 13th hole after being struck by lightning during the second round of the Western Open at the Butler National Golf Club in Oakbrook, Ill., on June 28, 1975.
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Old 08-04-2009, 05:30   #129
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Originally Posted by s/v Jedi View Post
You know, I'm a strange guy... I think I should have been a scientist instead of a cruiser because I really study these things for no other purpose than my need to know how it works. This often makes me skip details in my posts and they still end up very long posts ;-)

So, here we go; I'll be blunt sometimes but be assured that it isn't personal... it's how engineers talk to each other ;-)
<snip>
We might be related .

No offence taken, we are only challenging each other's thoughts on "how stuff works" not the worth of each other.

Another great post to which I plan to respond; but it have to wait until after Easter as I will away from the computer for the Easter break - hope you can wait .
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Old 14-04-2009, 06:43   #130
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<snip>Both leader and streamer are fully understood and documented. They have recorded them with high speed filming and you can do experiments yourself with a Van De Graaff (Dutchman of course ;-) generator, where the streamers form from your fingertips and the leader from the generator. They are indeed ionization of air, plasma. The plasma is conductive and this forms the electrical path for the lightning strike.
It still would seem by the explanation of leaders and streamers that no current flows until the circuit is completed (leader and streamer join up) thus allowing current flow. Until current flow is achieved, there is no mechanism for reduction of the charge (EMF). After current flow (strike) is achieved, it is too late .

From the how stuff works link you posted is the following "After the step leader and the streamer meet, the ionized air (plasma) has completed its journey to the earth, leaving a conductive path from the cloud to the earth. With this path complete, current flows between the earth and the cloud. This discharge of current is nature's way of trying to neutralize the charge separation."

Let's say there is a highly charged object with a sharp point and it is "streaming", i.e. creating ionization plasma (St Elmo's fire). It there any science telling up what is happening to the charge at this time.

From my reading (and very limited understanding), it would seem that the charge is not dissipating at all. In fact, it is creating a low resistance path around itself (the ionized field) that is just making it easier for current flow to occur. The reduction in charge occurs when the the current path is established; not before. If so, then the "brush" would more likely allow a strike rather than prevent one.

Again IMO, the static wick process confirms that the charge is only dissipated when the tips arc off, not because they are "streaming"

Just to say that "ions bleed off" the sharp point doesn't make sense electrically (once more IMO).

Although I will concede some energy is needed to create anything therefore some energy is required to create the "streamer" and the most obvious source of energy is the electricly charged object. Perhaps the energy is transformed from the EMF into the streamer. The sum total (of object and streamer) remains constant until the streamer and leader hook up and charge is transferred and equalized.



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It's time people stop thinking of these as magic wands because their enthusiastic stories have nothing to do with it and confuse others who prefer a more scientific approach. It puts many people off when they hear about the magic and they discard them, calling them snake oil as the result. It might te true that they don't work well enough, my personal statistics gathering is too small for any form of conclusive evidence, and I don't record it professionally anyway, but the brushes will really "bleed ions" before any other part of the boat does so with all that I wrote above as the result... only the quantity and if that is enough is what I am not sure of.

ciao!
Nick.
Gotta agree here (except for the "bleed ions" bit - I will keep an open mind on that aspect ).

Once again, nice discussion - thanks Mr Jedi.
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Old 16-06-2009, 07:26   #131
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I've revisited this thread as it seems to have a life of it's own and keeps going and going. I think this post best reflects both my experience and most of the guys I know who sail in Florida - Bahama waters. This sailing area is the superbowl of lighting damage.

To reiterate my experience

Repairing Lightning Damage on My Boat

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1. no dissipater will prevent a lightning strike.
Recently at a get together of 10 sailors who've been hit..while sailing-- boats were struck regardless of whether a dissipator was installed.

Although damage to electrical systems was extensive, All boats had inboard diesels, and no hull damage was evident in any of the incidents.

2 boats were bonded, and 8 were not. There did not seem to be any difference in observed boat damage.

Granted, this is not a scientific survey. Granted all boats were in different locations when struck. Yet it can't be coincidence that the observation and conclusions were so similar.
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Old 16-06-2009, 18:15   #132
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Lightning damage

Tropic Cat,
Nice post. A friend of ours got hit a couple years ago and their damage followed the same pattern. Fried most all of the DC equipment and apparently exited the prop shaft to ground.

How did your insurance experience go for you?


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Old 16-06-2009, 18:52   #133
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I did not file an insurance claim
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Old 17-06-2009, 05:08   #134
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... Recently at a get together of 10 sailors who've been hit..while sailing-- boats were struck regardless of whether a dissipator was installed.

Although damage to electrical systems was extensive, All boats had inboard diesels, and no hull damage was evident in any of the incidents.

2 boats were bonded, and 8 were not. There did not seem to be any difference in observed boat damage.

Granted, this is not a scientific survey. Granted all boats were in different locations when struck. Yet it can't be coincidence that the observation and conclusions were so similar.
Ewen Thomson conducted an extensive survey on this issue and concluded that grounding a sailboat mast does not increase strike risk, and does reduce damage in the event of a strike.

See also Ewen Thomson’s interesting article from the October 2007 edition of BoatUS's “Exchange”:

A New Concept for Lightning Protection of Boats
Protect a Boat like a Building

http://www.marinelightning.com/EXCHANGEOct2007Final.pdf

and:
Grounding concepts
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Old 17-06-2009, 05:26   #135
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Gord his study seems to conflict with our little unofficial survey. One thing our little group could not determine is if the boats were struck directly or by a side flash. As I recall none of the guys were staring at their mast at the time the boat was struck as we all were rather busy.
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