Bonded vs Unbonded Boats

[Shack]

Wotname - Check PM.
Thanks

[s/v Jedi]

Okay, I can understand the part where the resistance in the aircraft dissipator limits the current but it's still enough to discharge the fuselage (it still matches the build-up caused by friction with air molecules). However, I think the dissipater will discharge (bleed off) the static charge without any sparking... that's why it needs the sharp point (ions can go from the point to surrounding air).

My current way of thinking is that maybe the resistance is there to limit damage during a lightning strike... i.e. it doesn't strike the dissipater or exit from the dissipater.

ciao!
Nick.

[Wotname]

Originally Posted by Wotname

<snip>At the risk of further thread drift, it is impossible to create a spark with a PD of 12 or 24 volts, for those who don't believe this, PM me for the explanation or I can start another thread about this (if anyone is interested) rather than drift this thread any further . Hint, you can use 12 volts to create a very large voltage which will create a spark.

If interested, see http://www.cruisersforum.com/forums/...uff-25069.html

[Wotname]

Originally Posted by s/v Jedi

<snip>

My current way of thinking is that maybe the resistance is there to limit damage during a lightning strike... i.e. it doesn't strike the dissipater or exit from the dissipater.

ciao!
Nick.

Aircraft lighting strikes are a completly different matter. Static wicks have nothing (repeat - nothing) to do with them. Lighting does NOT strike an aircraft because it has a static build up or because of its electrical potential; strikes occur in aircraft because the aircraft has got in the way of a large electrical charge between two clouds or a cloud and ground. The aircraft just becomes part of the circuit.

Inspection of the airframe after a strike almost always shows an entry point and an exit point of the strike. Providing all the metal parts between the two points are well bonded, the current flows into the airframe and out of the airframe normally leaving only burn marks, pitting and melted skin at the actual points. Some times it can enter a prop tip, go through an engine and out a wing tip or whatever. And yes, sometimes does cause big damage.

In fact, any resistance in the circuit actually makes matters worse, current flow a resistance creates heat and melts stuff.

Hope this helps .

[s/v Jedi]

Wotname: Why do you put words in my mouth that aren't there? You are too focused on the "nothing to do with lightning" aspects of the wicks; I don't dispute that at all. Many things can be protected against lightning while they themselves have nothing to do with lightning (like the use of lightning arrestors etc.) Putting a resistance into these wicks would protect them against damage from lightning strikes. This is the only use of the resistance that I can think of... until someone educates me otherwise ;-)
Also, your experience with entry and exit damage of strikes seem to confirm that the wicks are spared.

cheers,
Nick.

[Wotname]

Well Nick I apologise if you felt I was putting words in your mouth, that wasn't my intention. My point was simply that the resistance factor is, IMO, unrelated to any lightning mitagation aspects of either the airframe or the wicks themselves. I would think that the resistance might even make them more susceptible but I have not put any depth of thought into this aspect so I could be way off the mark.

FWIW, I am enjoying your discussion points on this subject. It makes one think clearly about accepted wisdoms.

[s/v Jedi]

Okay, I guess we'll never know until someone shows up here who can tell us the function of the resistance in series with the wicks.

ciao!
Nick.

[Wotname]

Try this, while it doesn't go into deep theory, it does explain some more about wicks.
http://www.flightsafety.org/amb/amb_jul-aug92.pdf

[s/v Jedi]

Wotname: good document! It confirms that the resistance is partly there to reduce damage during lightning strikes. If that happens, the charge prefers to jump to the outer-sleeve and discharging from there instead of traveling through the resistance of the inner part.

The second reason is to limit RFI during normal operation. I'm a bit confused here but it says that the resistance LIMITS the discharge so that RFI is minimized for clearer readio communications. This would only be needed when the build-up of charge is NOT gradual. The rest of the document seems to confirm this: the build-up changes substantially depending on conditions like flying through clouds, dry snow, rain etc. The added resistance bleeds the charge off slowly, keeping RFI as small as possible.

This totally makes sense as the build-up is always there during normal operation. This is the difference with a boat. The document also confirms that no resistance make the dissipator work better for dissipating the charge and that is why the outer sleeve is added for dealing with big charges like during lightning strikes. It says that even when these sleeves evaporate during a strike, the dissipator itself still works afterwards in many cases.

The document also confirms that the static wicks play an important role during lightning strikes as they become the point of exit instead of rivets, wingtips etc. They give some (but substantial) level of control over the discharge process during strikes. It says that the sleeves enable it to dissipate "massive charges".

The use of carbon is for both adding resistance plus the crystals have many sharp points, acting like the sharp points as used in the "brushes".

When you translate this to the dissipaters as used on boats, it all makes sense. On boats, one only cares about their function during lightning storms as that's the only time a static charge is build up. RFI is ignored for boats as this only happens during those storms and not continuously like with aircraft.

So, you better buy the brushes ;-)

ciao!
Nick.

[GordMay]

This has been (will continue to be) another excellent discussion!

[s/v Jedi] ... So, you better buy the brushes ;-)[/quote]

Some contrary opinions, representing the informed view:

A CRITICAL REVIEW OF NONCONVENTIONAL APPROACHES TO LIGHTNING
PROTECTION ~ BY M. A. UMAN AND V. A. RAKOV
MARTIN A. UMAN, Distinguished Professor: ECE-UF Dr. Martin Uman
http://www.lightningsafety.com/nlsi_lhm/Uman_Rakov.pdf

WAR OF THE LIGHTNING RODS ~ By Abdul M. Mousa, (Ph.D., P.Eng., Fellow IEEE)
http://www.lightningsafetyalliance.c...htning_war.pdf

There Is No Magic To Lightning Protection:
Charge Transfer Systems Do Not Prevent Lightning Strikes ~ William Rison
(Professor of Electrical Engineering, New Mexico Institute of Mining and Technology)
”... The principles of traditional lightning protection are basic — 1) provide preferential strikes point for lightning (an array of conductors higher than the objects being protected), a good grounding system, and conductors between the two to conduct the damaging current from a lightning discharge away from the structure to be protected; and 2) provide appropriate transient protection on power and signal wires entering the structure to protect equipment and personnel from the effects of induced lightning currents ..."
http://www.lightningsafety.com/nlsi_lhm/magic.pdf

Charge Transfer System is Wishful Thinking, Not Science ~ Charles B. Moore*
(Professor Emeritus, Atmospheric Physics, New Mexico Institute of Mining and Technology)
Charge Transfer System is Wishful Thinking, Not Science - National Lightning Safety Institute

*Charles B. Moore is internationally known for his research on the electrical aspects of thunderstorms and volcanoes. He is an expert in many different areas of atmospheric research, including the scientific and political aspects of weather modification, the scientific and practical issues of lightning protection, and the efficacy of different kinds of lightning rods:
Lightning and Thunderstorm Research - Langmuir Laboratory
http://infohost.nmt.edu/mainpage/news/2005/7feb02.html


Fundamentals of Lightning Protection ~ By Richard Kithil, President & CEO, NLSI*
*National Lightning Institute
http://www.lightningsafety.com/nlsi_lhm/lpts.html

Evaluation of Early Streamer Emission Air Terminals ~ By Scott D. McIvor, Roy B. Carpenter, Jr., Mark M. Drabkin, Ph.D.
...”CONCLUSIONS: There is limited test data on ESE performance, and no available data substantiates the suppliers’ claims; conversely, the data collected by independent researchers prove otherwise. That is, the ESE performs no better than the conventional Franklin rod.
2. The physics related to the situation, as provided by the atmospherics physics community, demonstrate that the claims made for all of these ESE are wildly exaggerated ...”
http://www.ees-group.co.uk/downloads/ESE%20paper.PDF

See also, some (of many) earlier CF discussions:

http://www.cruisersforum.com/forums/...on-8705-3.html

http://www.cruisersforum.com/forums/...-not-1362.html

http://www.cruisersforum.com/forums/...orms-9286.html

http://www.cruisersforum.com/forums/...ran-11542.html

[Wotname]

Hmm.... Nick,
I think it might be better if we discussed this over a (insert drink of choice) as I took a radically different meaning from the article. Maybe this is a case of only seeing the evidence which substantiates one' views (applying to both of us).

Originally Posted by s/v Jedi

Wotname: good document! It confirms that the resistance is partly there to reduce damage during lightning strikes. If that happens, the charge prefers to jump to the outer-sleeve and discharging from there instead of traveling through the resistance of the inner part.

I take this to mean they incorporate outer sleeve so that the inner part isn't destoryed by lightning. The airframe does not enjoy increased protection due to the outer sleeve, only the inner part of the wick is protected. Likewise the "boatframe" won't be protected by the brush!

Originally Posted by s/v Jedi

The second reason is to limit RFI during normal operation. I'm a bit confused here but it says that the resistance LIMITS the discharge so that RFI is minimized for clearer readio communications. This would only be needed when the build-up of charge is NOT gradual. The rest of the document seems to confirm this: the build-up changes substantially depending on conditions like flying through clouds, dry snow, rain etc. The added resistance bleeds the charge off slowly, keeping RFI as small as possible.

Maybe it's my RF background but this seems straightforward. It doesn't matter whether the build up is gradual or not; it is what happens after the build up reaches a sufficent voltage level to arc off that matters. Without a wick, the build up will arc off at say X volts and the arc will discharge that portion off the airframe at Y amps causing Z amount of RFI. With a wick, the charge will still have to reach X volts before it will arc off, but this time the current will < Y amps (much less) due to the resistance, therefore the RFI will also be much less tha Z.

Originally Posted by s/v Jedi

This totally makes sense as the build-up is always there during normal operation. This is the difference with a boat. The document also confirms that no resistance make the dissipator work better for dissipating the charge and that is why the outer sleeve is added for dealing with big charges like during lightning strikes.

Well yes, if you mean that the outer sleeve will discharge more current quicker that the the resistive section but again we are talking about a situation where the lightning has already struck the airframe, not bleeding off a charge to prevent the strike.

Originally Posted by s/v Jedi

It says that even when these sleeves evaporate during a strike, the dissipator itself still works afterwards in many cases.

To me, this shows the low resistance element (outer sleeve) protects the inner section but it doesn't say anything about its ability to protect an airframe from receiving the strike in the first place. Correct me if I am wrong but I understand your position is that a short circuit static wick (mast head S/S brush) will assist in preventing a lightning strike to mast/boat. I can't see anything in the article that supports the view that a aircraft static wick decreases the likiehood of a lightning strike.

Originally Posted by s/v Jedi

The document also confirms that the static wicks play an important role during lightning strikes as they become the point of exit instead of rivets, wingtips etc. They give some (but substantial) level of control over the discharge process during strikes. It says that the sleeves enable it to dissipate "massive charges".

IMO, not relevant as the exit point on a boat will always be the waterline or below.

Originally Posted by s/v Jedi

When you translate this to the dissipaters as used on boats, it all makes sense. On boats, one only cares about their function during lightning storms as that's the only time a static charge is build up. RFI is ignored for boats as this only happens during those storms and not continuously like with aircraft.

So, you better buy the brushes ;-)

ciao!
Nick.

I think we need to remember scale here, I don't really know how much charge can be built up on an airframe (without dissipaters) until it starts arcing off (and causing RFI) and how fast it can be replaced but I reckon it would be very very very small to what is built up in a thundercloud that is about to discharge through one's mast. The airframe resistive dissipater allows a smallish build up to be bleed off in a controlled fashion. I don't think the grounded mast head brush will allow a huge build up in the clouds to be safely discharged through the boat to the ground.

[senormechanico]

Wotname,
I believe you have nailed it exactly re the resistive elements, discharge characteristics and RFI.

Steve B.

[s/v Jedi]

Originally Posted by Wotname

I take this to mean they incorporate outer sleeve so that the inner part isn't destoryed by lightning. The airframe does not enjoy increased protection due to the outer sleeve, only the inner part of the wick is protected. Likewise the "boatframe" won't be protected by the brush!

I was talking about the wicks on airplanes with what I wrote in post #110 in my mind. The resistance protects the wick against lightning damage.

Maybe it's my RF background but this seems straightforward. It doesn't matter whether the build up is gradual or not; it is what happens after the build up reaches a sufficent voltage level to arc off that matters.

Well, I didn't think about RFI at all even though my background is RF too ;-) But the part on gradual buildup: if it would be gradual/constant, you don't need the resistance to limit dissipating it. You could dissipate it full throttle without limiting it. But it's a moot point as the buildup isn't gradual/constant obviously.

Well yes, if you mean that the outer sleeve will discharge more current quicker that the the resistive section but again we are talking about a situation where the lightning has already struck the airframe, not bleeding off a charge to prevent the strike.

The difference is just the amount of charge. A wick without resistance will dissipate any charge it can handle without burning up quicker than a wick with resistance. If it wasn't for all the RFI that comes with that scenario, there wouldn't be a reason for adding the resistance.

To me, this shows the low resistance element (outer sleeve) protects the inner section but it doesn't say anything about its ability to protect an airframe from receiving the strike in the first place. Correct me if I am wrong but I understand your position is that a short circuit static wick (mast head S/S brush) will assist in preventing a lightning strike to mast/boat. I can't see anything in the article that supports the view that a aircraft static wick decreases the likiehood of a lightning strike.

The wicks don't prevent lightning from striking an airplane, I agree. But they are part of damage control during a strike, like preventing it from exiting the air frame from more vulnerable points like rivets.
I also fully agree that the brush isn't a device that prevents a lightning strike on a boat for every scenario. But the fact is that during most lightning storms we are at anchor, berthed etc. with many other objects around us. All of these are candidates for the strike. If the brush just manages to bleed of some of the charge, other objects might win the contest. It's a form of camouflage, not certainty. But like I wrote before: I never encountered a boat equipped with correctly installed brush(es) that was hit at the masthead. I encountered many boats that were hit in the masthead without the brushes, incl. Jedi twice.

IMO, not relevant as the exit point on a boat will always be the waterline or below.

I was just talking about the wicks on airplanes. The document shows that they do play a role during a strike and this is part of what they are engineered for... but it's a secondary role. Someone (was it you?) wrote before that they have nothing to do with lightning at all, which was my reason for the remark.

I think we need to remember scale here, I don't really know how much charge can be built up on an airframe (without dissipaters) until it starts arcing off (and causing RFI) and how fast it can be replaced but I reckon it would be very very very small to what is built up in a thundercloud that is about to discharge through one's mast. The airframe resistive dissipater allows a smallish build up to be bleed off in a controlled fashion. I don't think the grounded mast head brush will allow a huge build up in the clouds to be safely discharged through the boat to the ground.

Ahh but that's not what they do at all!! It's the other way around, they dissipate the static charge that travels on the earth SURFACE under the cloud into the air! And I agree they are only able to dissipate a small part of it but remember that when there are other objects around you, the charge is divided over all those objects and (mostly) only one object is going to win the race for the highest charge and forms the winning upward leader to which the stepped leader from the cloud connects! Again: the brush only needs to work enough so that another object wins that race.

cheers,
Nick.

[s/v Jedi]

Originally Posted by GordMay

This has been (will continue to be) another excellent discussion!

Some contrary opinions, representing the informed view:

Gord: I read all those papers and they are not about the brushes on boats. They are all about systems that use the same principles but used for buildings ashore. What they conclude (and I agree) is:

1. no dissipater will prevent a lightning strike. What they mean is that the strike will come out of the cloud no matter what you do. You only find that when you read it all. So it doesn't say that the dissipater doesn't help preventing a strike on the object it is trying to protect, just that the strike will happen anyway, striking the object that formed the best/biggest/highest upward leader. For static objects like buildings, this means that all of them need the basic path-to-ground protection because the strike is going to strike one of them. I don't even start to argue about that, of course the strike will occur; I just want it to strike something else than my boat.
2. If they are struck, they work like a regular rod but the regular rod is cheaper.
3. the reduction in damage as reported is mostly due to secondary measures like lightning arrestors in antenna cables etc... which also work with a regular rod.
4. no independent research has been done on strike prevention devices.
5. static dissipators do dissipate a static charge. The principles are sound.

So, all these docs don't show anything contrary. They never even did a proper research on them. And most buildings are very different from boats. They don't have devices and wires on the roofs like we have in our masts (it's all cable TV now etc.) so the damage when a house is struck on it's regular rod protection is minimal and that protection is good enough.

On a boat it's different. A strike in the mast mostly always leads to expensive damage to lots of systems aboard so it makes a lot of sense to find a higher level of protection in addition to the standard path-to-ground protection. That is actually the reason they installed these systems on airport traffic control towers etc. as they have lotsa stuff on the roof. It turned out that the best improvement for these were the secondary measures like lightning arrestors. But they are also the highest building in the area so it's really hard for a dissipater to dissipate enough to reduce the chances of strikes enough.

The hypothetical but interesting scenario would be two exact same towers right next to each other and only one with the dissipaters. There is nothing in all the papers you link to support the view that the chance for each tower would be 50%. One papers actually states that dissipaters reduce the probability that the object with dissipaters will be struck. If you follow that scenario, the resulting conclusion is that if the object with dissipater is struck, this is a case of bad luck as normally the more favorable object wins every time.

So what's favorable: lower resistance, higher, bigger charge. Not many cruisers understand this: they think that not grounding an aluminium mast means the lightning will not strike it (high resistance) but it is about the resistance per distance. Lightning will be happy for the free travel down the mast and ionize some small gap from the foot of the mast to ground or another object so grounding the mast is much much better and safer. Also, some think a wooden mast is safe but they don't see that it has much less resistance than air. Higher is an easy one but the static charge is not. I just found out that even Wotname thought the brush tries to guide the charge from the cloud to ground which is not it's intended mode of operation even though this is what Franklin hoped to accomplish ;-) Other researchers died when they repeated his experiments... struck in the head even. But less charge than other objects means the lightning strike will go somewhere else.

I think that maybe your mind is so made up on the issue that you read what I write in this thread without processing it deep enough... could you tell me the reason that the brushes don't work or any proof of that? These papers can't, they don't support the view that brushes on boats don't work because they never touch that scenario.

ciao!
Nick.

[Wotname]

Nick,
Nice post (#118), I THINK you and I are almost on the same page regarding wicks, the differences can probably be put down to slightly different ways of explaining complex issues via an internet forum and at least for me, a lack of writing skill .

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. A static charge really only exists between two points that is separated by an insulator. Without the insulator, the charge does not build up, rather the + & - ions just move around and cancel each other out. As in the principle of anti-static bags and suchlike for the protection of static sensitive components.

A quick aside: why don't we just wrap the boat up in a anti-static wrapper

So the mechanical movement of the clouds etc causes a positive charge to exist on some clouds and a negative charge on others. How a charge developes on the surface under clouds I am not sure but at this stage I am happy to assume the boffins are correct. I could guess that that potentials in the thunderstorms etc could induce surface potentials.

But IMO, to "discharge" such potentials into an insulator separating the charges goes against the grain of electrical behaviour. I could accept the discharge of the potential into a mass that has the opposite potential IF one could demonstate the process of charge transfer. i.e. free electron flow (or its opposite - positive hole flow) in metals and semi conductors or ion transfer in fluids.

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.

Therefore to remove some of the ground surface charge via a brush, then we have to demostrate the method of charge transfer. Again I believe the only method to move any amount of the surface charge is for the brush tips to ionize the surrounding air to such an extent that there is an ion transfer (via the ionized air - O & O3 molecules) from the water's surface to a region of opposite charge. Basicly sparks flying off the brush or al least "St Elmo" fire. Until that happens, I can't see any way for the charge transfer to take place.

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.

But I am not an expert (that might be obvious) and when a boffin can explain how the brush might work, I will have more faith in mine.