Lightning

[Sumner]

I suspect the metal keel on the Ventures would be fine....useless on my generation of powersailor of course (FG)

Im rethinking that. You need good connections on these systems or else the lightning reaches the point of resistance and then just blows a hole whereever it jumps - in this case the bottom of your boat.

How would you make sure your keelboat has a low IMP connection to your keel??

All this points back to Rich's post that to do this right costs MegaBucks.

I agree that the pivot bolt on a swing keel might not be a very good choice.

I'll have to disagree with the "costs MegaBuck" . If you feel that the StrikeShield.....

http://www.strikeshield.com/Lightning%2 ... 20Products

....system has some merit you could buy it or replicate it for not all that much. We have a lot of money in 3 good anchors of different types and lots of good rode and shorelines and since we are anchored out every night spending a couple hundred (making my own parts) might be a good choice for us, maybe not everyone.

The system they have is not rocket science, but is made of parts that aren't that hard to duplicate. If we had a large boat with an inboard, propeller shaft, ovens and lots of other larger metal objects then I would agree that things get a lot more complicated. On an S our outboard is out of the water and our primary goal as I see it is directing the charge from the mast (where from most of what I read is where it is going to go) off the side of the boat and into the water.

Since lightning is so unpredictable it is still a crap shoot what might work or not. It just boils down to doing what you feel comfortable with, which might be nothing, and living or not living with the results.

This has been a good thread and made me re-read some of the things I've read before and hopefully understand them better.

c ya,

Sum

Our Trips to..

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[Catigale]

Strikeshield comes in at 600-800 bucks depending on options. If you are in a t-storm infested area that might make sense indeed.

[flynfol]

When we were struck in the tail(corporate jet), the seven #10 screws that held the aluminum tailcone on were GONE.....vaporized. There were seven half inch holes in their place, including one through the glass lens! (300 exit holes on airframe...mostly at rivets) I know to get the resistance on your connections down to thousandths of an ohm, you need a megger. Then you have to seal the connection to prevent corrosion. At millions of volts, you don't need much of a resistance to create a significant voltage drop. We had all kinds of static issues afterward, and needed to have static sweeps done.(plane placed on rubber pads and charged) IMHO a direct strike is going to cause major if not catastrophic damage. You can mitigate electronic damage with some sort of bonding/dissipation system, but avoidance is your best bet. Some composite airplanes actually put a metallic screen layer between layups for bonding. I like the faraday cage idea for a storm shelter

J

[Catigale]

Realistically, I have to be Rich's sock puppet on this. How many of us are going to check the resistance on our grounds and metal plates on a monthly basis? In aviation, this will be done routinely if its part of the protocol. Pleasure boaters can be guaranteed to skip this step if American Idol reruns are on. (Ok, that last line was a little harsh)

[Hamin' X]

Connection to the iron keel would have to be through a flexible bonding cable, that at no time describes a radius of less than 12 inches. The ends need to be permanently bonded to both the cable and the keel using the Cadweld, or similar process. Anything less is asking for failure under load (lightning strike). Milliohms of resistance will create a significant voltage drop under load and force the further failure of the connection and result in the current finding alternate paths. In addition, all shrouds must be similarly bonded to both the mast and chainplates. All adjusters and thimbles must be jumpered by bonded cables. This is due to the propensity of lightning striking sideways from the main stroke and possibly striking the shrouds, instead of the mast.

Most of my knowledge has been gain from the communications industry, but I'm sure that you can see the similarity between a mountain top tower with multiple guy wire sets and a sailboat. I have seen many failures of commercial installations due to poor, or missed bonds.

Once you decide to not avoid the lightning by beginning the grounding process, you MUST complete the rest of these steps, as you are attracting lightning, rather than avoiding it and you must be prepared to handle the result. As I have stated before, most of us do not have the funds, or expertise to do this correctly and for my amateur radio repeater experience, I prefer the avoidance method, by using dissipators and so far over thirty years, my record is perfect, while the commercial installations around me is less so.

By the way, when the telephones and cell phones go down, call an amateur radio operator and they will get the message through. any wonder? Your mileage may vary (YMMV). With the temporary connections of the strikeshield system and the SS screws into aluminum, not to mention the failure to bond the rest of the standing rigging, I would not waste my money.

~Rich

[walt]

Hope you don’t mind if I join this discussion, I disagree with many things HaminX is posting here. I could be wrong of course.

For disclosure fairness, I am an electrical engineer and am involved with a company who has a patent related to sailboat lightning protection.

What do some of the experts say on the static dissipaters?

http://www.marinelightning.com/AirTerminals.htm#DAS

“In his paper, Dr. Mousa concludes that “Natural downward lightning flashes cannot be prevented.” His phraseology “natural downward lightning” is carefully chosen, but does cover the case of a sailboat mast. Perhaps the reason why these devices are still popular is the rave review they get from the telecommunications industry. When a dissipater is at the top of a telecommunication tower on a mountain it does appear to lower the incidence of lightning strikes that originate at the tower, that is upward lightning. Unfortunately, this is only applicable to this type of lightning, which is not the type the predominantly strikes boats, or other structures on a flat earth. “


What does Don Casey say about the dissipaters?

http://www.sailnet.com/forums/gear-main ... tions.html

The theory is that the point or points of these devices—called static dissipaters—bleed off the charge from the grounded mast, thus lowering the voltage differential below what is required to "spark" lightning. Dissipaters probably do bleed off static charges, but trying to bleed the ocean's charge into the air with a dissipater on your mast is like trying to lower the ocean's level with a soda straw.

My note – I think Don Casey is on the mark here – we can discuss this more. Before a strike, a dissipater can deal with the charge buildup (caused by electric fields from charge in the clouds – not charge coming up from the water). Some what like using a bucket to collect the water from a very small flow in a gutter. But as the lightning strike is coming down with enormously high and fast changing electric fields, the dissipater is still like having a bucket but now you are trying to fight off a large ocean wave – your efforts are not going to make any difference.


Haminx wrote “Ever wonder why the old dead snag is the one that gets struck in the middle of a healthy forest? The leaves and needles of the live trees are acting as dissipaters. The old dead snag is radiating the charge from just a few points. Fewer points, same amount of charge. It's like waving a flag at the clouds and saying, "Here I am, kick me".

I come to a slightly different conclusion here (from seeing dead trees which were hit by lightning) – the lightning strike killed the tree.


Hammin wrote “Sorry, the charge is coming from the water and crawling up the outside of your hull to start with.”

Not correct, the hull of a sailboat is an insulator. The charging experienced on a sailboat mast and shrouds is due to the electric fields present because of charge in the clouds. It is NOT due to charge coming up from the water.

Does grounding increase your chances of getting a strike (as Hammin X says it does)


http://edis.ifas.ufl.edu/sg071 (Dr. Ewen Thomson)

there is no support for the argument presented by some sailors that they should not ground their sailboat since it will increase the chances of it being struck by lightning.

Also,

http://www.marinelightning.com/catamara ... oatUSStats

The info here shows that Catamarans have twice the claims for lightning strikes compared to monohuls. What is interesting about this is that most monohulls do have grounding through a keel but Catamarans do not have heavy metal keels or the grounding.

If you are drawing wild conclusion from this, it would be that NOT grounding increases your chance of getting struck. This is likely an incorrect conclusion but it does say that other factors are likely more important than grounding or not.

I also don’t agree that if you ground, you have to ground everything. This conclusion would be based on grounding increasing your chances of getting struck. I don’t believe this is true. If its not true, them simply grounding your mast only gives you maybe 75% of the benefits of grounding. Adding the shrouds increases this even more.

[Russ]

Once you decide to not avoid the lightning by beginning the grounding process, you MUST complete the rest of these steps

How do you avoid the lightning?



--Russ

[walt]

I believe the answer is there is not much you can do (other than get the heck out of there - a luxury Power Sailors have but not us with conventional sailboats).

Here is my take on the only method I know of which is "supposed to reduce chances" (static dissipates) and why most experts don't believe they do much (and why boats with them on still get struck).

As mentioned, the charge in the cloud will create an electric field between the sky and the water. An important concept for this explanation is that a conductor in an electric field with take on the voltage potential of its midpoint. So two conductors with different mid point heights - take on different voltage potentials - and you can have a spark go between the two conductors because they are at different potentials. This is the "charging" of the mast, etc which occurs when charged clouds are present. Its why you can get shocked touching shrouds or the mast when charged clouds are around.

There is no doubt that the dissipates can transfer charge to the air and likely the charge which is removed is enough to "discharge" the mast so that it will no longer spark to other metal objects on the boat. But looking at this in terms of the amount of charge that needs to be removed, it is very small - because all that is happening is that the dissipator needs to discharge the capacitance between the mast and other metal objects. And this capacitance is very small - I am guessing but its probably less than 100 pf. Not much charge needs to be removed to discharge this value of cap.

Up in the sky, the forming lightning strike is looking down at the surface and probably does look for significant pooling of positive charge. If we think of the pooling charge as light spots, the charge up in the sky see's a lot of "lights" and probably doesn't even notice the sailboat mast but if it did, it might be similar to looking out the window of an airplane at night and tyring to notice one house where the light was dimmed a little - ie, pretty much not noticeable.

Once the lightning strike has formed and is heading downwards, the leading edge of the bolt is now producing a very intense electric field and its traveling maybe at 130 thousand miles per hour. The electric field travels ahead at the speed of light and its big and very rapidly increasing. Now this is the electric field which would be important for the dissipator to deal with .. but as Don Casey said, it would be like trying to drain the ocean with a straw.

A sailboat mast grounded or not present an electric field shortcut for the lightning. However, how far in advance the lightning picks out this sort of detail, don't know. It may only be 30 to 100 yards (about the same distance where an upward streamer is met).

What creates an upward streamer on the water? Here is an interesting paper http://www.lightningsafety.com/nlsi_lhm/Radials.pdf

One key point in the paper is that the water surface will charge because of the electric field. The water surface charges positive by electrons being driven into the body of the water. Interesting to note in the paper that the time for the water surface to charge is dependent on the number of charge carriers in the water - ie, how much salt. Salt water will have very fast surface charging, fresh water not so fast.

This is my own theory now (and could be wrong) but water is much more difficult to ionize than air (dialectric constant of water is 80 times that of air and its much more dense). So when the water surface charge gets high enough, it could ionize the air just above the water and create conductive paths for an upwards heading leader to meet the downwards coming lightning strike. Note that once again, a mast is a nice electric field short cut for the charge to take - and the mast does NOT need to be grounded for this mechanism to work. In fact, it would make almost no difference if the mast were grounded or not.

[Hamin' X]

Walt, you are certainly welome to the discussion, as this is a forum for the open exchange of ideas and information. I have no more formal education in electronics than being an Extra Class ham and having worked in and around the communications field for 40 years. I am just a truck driver by trade. But, here is my take on it and perhaps you can shed some light on it.

I notice that the Florida reference that is selling the video agrees with me, in that the lightning strikes damage is done when the positive charge from the ground reaches the negative charge from the cloud. The charge from the boat only travels 30 feet, while the charge from the cloud travels up to 5 miles. From the point they meet, the massive cloud charge then re-travels the positive charges path to it's origin. If we can eliminate, or at least reduce this positive charge at it's origin, the negative charge from the cloud will try and find a path with less resistance and hopefully continue to the ground.

The stepped leader concept of lightning is very important in understanding. It will only travel +-150 feet before changing direction. Why, I don't know, but it seems to look for a better path at that point. This is why it is important to either bond your shrouds, or insulate them. The catamaran picture is intriguing, but easily explainable by the fact that the dissipater [sic] was doing it's job and the lightning struck a shroud from a sideways strike from one of these steps and grounded through the hull on that side. This could have been verified by checking for arcing at the thimbles between the mast and shrouds, or shrouds and chain plates. No mention of this, so I assume that this was not done. This is a check that we do with towers that have been struck. If the dissipator had been struck, most of it would have been vaporized, as the fine wires would not carry the current.

Of the sailboats that have been struck while using dissipators, no mention was made of whether they were installed correctly. As I mentioned in an earlier post, some shops are selling the dissipators as part of a grounding system. A self defeating practice at best and dangerous in the worst case.

As for the fiberglass being an insulator, this is only true to a partial degree. I think that most folks would think that rubber soled shoes are insulators, until they scuff their feet across a carpet and touch a doorknob on a wooden door (another insulator). There is indeed impedance to current flow. but the higher the voltage and lower the the current, the less effective it becomes.

I totally disagree that the positive charge on the ground, water, boat, or whatever comes from the cloud and not the ground. Accepted theory has been, that the negative charge in the cloud draws the positive charge from the ground to the surface and up objects that are in contact with, or near to it. This could have been changed of course, as theories change all the time, due to empirical results. The same is true for electrical codes. Although some code changes are made due to advancement in technology, most are made due to the failure of the old code. In other words, it didn't always work.

The installation of dissipators is a highly misunderstood field and needs to be done with the understanding that you are avoiding the lightning and not trying to control it. You are not trying to bucket the entire charge of the earth into the air, but only the charge that has accumulated on the higher points of your boat. This is a very low current process that can be handled by the dissipators. This means that nothing in the immediate field that is connected to the object that you are trying to protect should be grounded. To say that the grounding of an object will not attract lightning is in my opinion, ludicrous, as without the opposite charge for the lightning to travel to, it would not exist except as a potential. Properly installed lightning rods have worked for centuries and attracted lightning to a point that was desired, then to ground. Thank you Ben Franklin.

There is no sure way that I know of to avoid, or control lightning, only minimize your chances, or minimize the damage. With my method, if you are unlucky to be in the best direct path as the next step leader comes down on top of you, you will probably have enough residual positive charge to be struck. It is avoidance, not evasion.

Looking forward to discussing it with you and others and furthering my understanding.

~Rich

[SkiDeep2001]

What Rich said, from one of the peanut gallery. Rob

[Catigale]

I wasnt too impressed with the 'statistics' in the links. No sample sizes. no info on sampling, and jumping to conclusions without good backup.

They assert that the strike probability of a catamaran in about 1 in 100....and is 2x that of a regular sailboat. 'Double that in Florida"

>> Are catamarans more likely to be sailed in areas with thunderstorms perhaps?

[dca81]

Hmmm...Just a thought from a non technical and ignorant accountant...but I just painted my boat with VC17 which I believe has a copper content. Does this increase my chances of a lightening strike by decreasing the insulator effect of the fiberglass/gelcoat ??

[Sumner]

First I really appreciate the input from everyone, especially Rich and Walt.

I look at this whole deal kind of like the air bag and seat belts in my car. I could drive around and trust the air bag and not put on the seat belts and probably have good protection, but what if the air bag didn't work or I was in an accident where it wasn't effective? For those reasons I put on the seat belts and if I could only have one or the other it would be the seat belts.

I've read more negative reports about the effectiveness of the diffuser and more positive reports about some type of grounding system working. Still with the grounding system you have all different levels of application and degrees of perceived or real effectiveness. I'm not sold enough on the diffuser and since Rich doesn't recommend using both at the same time we will go with a grounding approach as suggested by Walt.

Even if we enhance our chances of being hit, which I don't believe we will, we will have something in place to hopefully handle the hit so that we will escape alive. If we are hit the main goal for us of using a grounding system is first to keep the strike away from us in the cabin and second to try to keep the strike from holing the boat. For that reason I don't believe we need to try a real elaborate (read also expensive) approach to a grounding system as we will strive to mainly protect the cabin area of the boat. Nothing is perfect, especially when dealing with lightning, and everyone has to make a choice they can live with and we have made up our minds what we want to try and feel comfortable with the decision and feel more comfortable than going out on the water for extended periods again without anything other than hoping we won't get hit.

c ya,

Sum

Our Trips to ..

Our Mac Pages

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[walt]

Rich, of course.. many things in your last post I don't agree with.. and that's OK, its a forum discussion.

But.. here is one which is fairly interesting to examine

To say that the grounding of an object will not attract lightning is in my opinion, ludicrous, as without the opposite charge for the lightning to travel to, it would not exist except as a potential

.

I would generally agree with your statement - if we were talking about communication towers. But when we are talking about water, and especially with fresh water, what really is "grounding" anyhow.

I took the unmodified picture below of a little simulated sailboat floating on fresh water. The spark at the top is created with a lab instrument capable of generating just under 20KV.



What you see in the picture is the spark leaving the instrument at the top of the picture and it chooses the path of the mast - because this is the lowest impedance (or an "electric field short cut"). The spark re-ionizes at the bottom of the mast and then jumps to another conductor over a spark gap- once again because this is the lowest impedance path. Note that the bottom conductor does NOT contact the water. There is re-ionizatin again at the bottom of the second conductor and the spark goes to the water surface where something very interesting happens.

Because this is fresh water, there is not much conductivity. You are probably familiar with a parameter called "dielectric constant" and water has a dielectric constant which is 80 times higher than air (water would make a great capacitor dielectric except that it would be very leaky). The dielectric constant of 80 in water means that electric fields will be MUCH smaller in water. So the water does not ionize under the existing conditions and apparently ionized air at the water surface is still the lowest impedance path for the charge to take.

I mentioned this paper before http://www.lightningsafety.com/nlsi_lhm/Radials.pdf (very technical) but what apparently happens is that the mechanism for the charge to go into the water involves the charge getting spread over a large distance by the ionized fingers and at some point the positive water surface charge referenced in the paper becomes sufficient to finally discharge the ionization into the water.

This next picture shows the same setup with very salty water:


The charge goes into the water similar to fresh water (no contact of the bottom conductor to the water as before) however, the surface over which the charge spreads is much smaller. There are likely two reasons for this. One is that the resistance is simply lower for the salt water. The other reason is that from the paper I referenced, the surface charging time is inversely proportional to salt content - ie, the surface charging happens MUCH faster for salt water. Between the two pictures, the surface charging time in the bottom picture may be on the order of 1000 times faster than in the upper picture.

The point Im making is that the discharge of the ionized current to the water surface was aided by the fact that conductors where present - but whether the bottom conductor was in the water or not would not have affected how the charge is actually conducted to the water (through surface charging). This is basically why I also don't think grounding or not grounding makes much difference - ON WATER. You have to consider that it is water we are discharging into and not some large conductor. In fact for fresh water, the surface charge dissipation is about the only way to get the charge dissipated into the water without having a huge underwater conductor.

You can see this same radial pattern discharge at the water surface in many references.

[Catigale]

There is a lot of pseudo-science in the discussion of lightning. Using electrostatic concepts like dielectric constants for phenomenon like lightning, which has 10E-6 time dynamics, and MegaV potentials, is probably not a good way to understand it except in a coarse way. At the very least, you need the time-dependent dielectric constant of the material - those calcs will quickly get you into light reading tomes like Jacksons 'ElectroDynamics

It is 'generally accepted' that strikes originate when negative leaders find positive leaders from the ground (someone posted a nice graphic above)

On the question of whether Cu paint changes the dynamic, I sincerely doubt it. Kinda like the folks who think sneakers will stop them from strikes.