# lightning



## frankbarbehenn

I read that there are conflicting views about how to deal with lightning: to protect and ground to water or not. It seems to me that there must have been some real physics research on this question since it is so important for sailors. Does anyone know where to look for a real scientific answer???


----------



## GordMay

Some excellent on-line resources on 'Lightning & Boats' - Goto:
http://CruisersForum.com - Power Equipment & Electricity - Lightning Information
http://cruisersforum.com/showthread.php?s=&postid=10366#post10366
including:
"Lightning And Sailboats" - by Ewen M Thomson, Univ. Fla. 1992. Sea Grant Publication 
[size]The best basic lightning primer for boaters[/size]
http://www.thomson.ece.ufl.edu/lightning/
and more
HTH,
Gord May


----------



## tondelayo29

I just read a great article this morning but it is far to large (20,000 characters) to post here....<I tried)
It is from 
Bruce A. Kaiser
President
Lightning Master Corporation
09/26/90


----------



## sailphoto

Lightning scares the bejeebes out of me and I have spent many nights anchored out among other boats hoping that if lightning strikes it would find the radio tower across the harbor or a taller mast ( without any ill will towards others) on a grounded boat around me more attractive than my own. When I first bought my boat which is a 1980 Dockrell 27 cutter and read the survey it revealed that my little ship is not grounded and this prompted me to do a little research on the matter. What I found out after exhausting the resources on the web is the following: In rough numbers a boat that is grounded is twice as likely to be hit by lightning than one that isn't. On the flip side, a boat that isn't grounded and is hit by lighning is twice as likely to catastrophic damage i.e. have a hole blown in the hull and sink and/or kill the crew. None of the sites I visited gave me any absolute statistics except for the ones selling products which in my sceptical way always assume are skewed. It seems also that grounding a boat doesn't provide absolute protection to the crew, especially on smaller boats where you cannot physically get away from the path the lightning wants to take to the ground, down the mast and out through the grounding cable and line.
I don't really love any of these odds. What I have done to date is *not* ground my boat and to further reduce the likelyhood of being struck I have installed a stainless brush at the mast top designed to "bleed off" negative ions thereby reducing the potential of the boat. Experts disagree as to the effectiveness of this system. As I write this though I am again wondering if I shouldn't ground my boat. The following link discusses the brush system in greater detail http://www.oceanpix.co.uk/Seamanship/Lightning-at-sea-2.htm


----------



## sailingdog

Sailphoto-

If I understand the theory behind the lightning dissipators, then the boat needs to be grounded for them to work. Adding one to a boat that is not properly grounded does nothing. The brush can not bleed off the massive static charge potential if it is not ground.


----------



## Cruisingdad

Photo, et all,

I believe SD is right. Not going to help a lot with the dissipator if the boat is not grounded.

My personal opinion (AND IT IS A PERSONAL OPINION): If you are primarily coastal and do NOT need a SSB, do NOT ground.

If you either want an SSB or are going to be doing a fair amount of offshore: Ground the crap out of the boat and put a dissipator on top. 

Either way, you take your chances... but you also take your chances everytime you hop in your car and get on the highway. Do your best, then don't let it consume you (no pun intended).


----------



## sailingdog

I'd second CruisingDad's recommendation to not ground if primarily coastal or inland, and ground well if going offshore or need an SSB. BTW, why would you have an SSB if you're not going offshore???

BTW, I'll take my chances with sailing...far fewer idiots out on the ocean than on the local streets.


----------



## sailphoto

sailingdog said:


> Sailphoto-
> 
> If I understand the theory behind the lightning dissipators, then the boat needs to be grounded for them to work. Adding one to a boat that is not properly grounded does nothing. The brush can not bleed off the massive static charge potential if it is not ground.


The problem with using an ionic dissipator on a grounded boat is that you then are trying to disipate the negative charge of the entire ocean through this little stainless steel brush. It just isn't going to be able to do it.


----------



## Cruisingdad

Photo,

Buy a bigger brush... HAHA!! Just kidding.


----------



## sailingdog

sailphoto said:


> The problem with using an ionic dissipator on a grounded boat is that you then are trying to disipate the negative charge of the entire ocean through this little stainless steel brush. It just isn't going to be able to do it.


*Actually, the idea is that you're reducing the charge local to the boat, just a slight amount...and thereby reducing the potential of a lightning strike in that specific location.* You aren't trying to dissipate the entire negative charge...that would be almost impossible, given how large the forces involved are.


----------



## Cruisingdad

Now SD, don't get technical. 

The point of a dissipator is the following: Out in the ocean, the lightning finds an easier path away from you... likely one of those mountainous swells.

In the marina: The lightning strikes your buddies boat - you know, the whole cone of uncertainty!!

Which is why, whenever I am in a new anchorage and a storm approaches, I find the lonely Sea Ray, drop his anchor in the water, and raise his VHF Antennae. Does it work...? I will never tell.


----------



## hellosailor

"Does anyone know where to look for a real scientific answer???"

Sure. Any plasma physicist can tell you that when there's a kajillion volts and amps flowing around, it is going to go anywhere it damn well pleases. You can influence the path, sometimes change the odds a little, but for hard answers and guarantees? Uh-uh!

Short of that, "modern" science still doesn't have definite answers for how to keep lightning away. That's why NASA, with their lightning rod on the launch tower, still went exploring to see what might have fried when the lightning rod "took" a big strike this weekend. They just don't know. The final decision was based on a very low-tech inspection routine: The techs SMELLED something burnt.

All the high tech science, and the Mark1Nose was still what they chose.<G>


----------



## marinedtcomRob

*After two strikes I'll keep my grounding systems*

OK, so I've been hit twice so far. Once on my grounded Little Harbor 38 and once on my Grady White 23 motorboat which I grounded to beat the band because I'm paranoid. The sailboat got hit at Three Mile Inlet (Long Island) and the Grady got hit at Cape Lookout, NC. The Grady was nestled in among about 15 sailboats with much taller masts than my 20' outriggers. So, if I had no grounding might I have not been hit? I'd guess that would be likely. On the other hand, a few weeks before the Grady got hit an ungrounded sailboat got hit. The strike went down the shrouds to the chain plates, then blew holes out the bottom of the boat below / near the water line. The boat sunk quickly. So after two strikes, while I hope the third is NOT the one that kills me, I'll still take my chances being grounded. At least I have an idea the of the path the lightning will take. In neither of our strikes did we experience any significant damage. I had disconnected all the electronics I could and lost only a small electronic module on the Grady engine and a Heart Pathmaker on the sailboat.


----------



## Cruisingdad

There are inexpensive ways to ground your boat. A very, very accomplished sailor-friend of mine grew up in the islands. In all honesty, they would wrap the anchor chain around the shrouds and let it drape just off the boat. 

Thus, if you are really that worried about it, you can just do that. Is it worth it... well, that is a question we each must answer...

I have read about the dissipators and the science seems logical. Of course, I am a biochemist, not a physicist. However, it is not 100%. When I said earlier that you keep your boat from being hit so it hits your buddies boat... well, that is not far from the truth. And the trick about lightning, as MANY OF US HAVE SEEN: IT DOES NOT HAVE TO HIT YOUR BOAT. If it hits anywhere close to you, you can kiss your electronics goodbye. Thus, here is a good reason to: ALWAYS CARRY HANDHELD BACKUPS. They are not that expensive, and might just save your life.


----------



## hellosailor

As undertand it, the problem with grounding everything on the boat is that while grounding provides a more direct path for lightning to "come down", and in theory come down directly without flashing over into everything including the crew, that same grounsing also ensures that if there is a charge building up in your area---you are now elevating that charge and putting the ionic path higher into the air, so it is closer to the cloud charge and more likely to be hit. Oopsie.

I'd still rather have the direct path for the strike to come burning down (or up, since ground to cloud strikes are also normal) than have it take a random walk all over the boat.

Safest thing to do is just sink the boat, and dry it out afterwards. Probably almost as good to careen it way over, but for some reason, not very popular. <G>


----------



## sailingdog

Cruisingdad said:


> There are inexpensive ways to ground your boat. A very, very accomplished sailor-friend of mine grew up in the islands. In all honesty, they would wrap the anchor chain around the shrouds and let it drape just off the boat.
> 
> Thus, if you are really that worried about it, you can just do that. Is it worth it... well, that is a question we each must answer...
> 
> I have read about the dissipators and the science seems logical. Of course, I am a biochemist, not a physicist. However, it is not 100%. When I said earlier that you keep your boat from being hit so it hits your buddies boat... well, that is not far from the truth. And the trick about lightning, as MANY OF US HAVE SEEN: IT DOES NOT HAVE TO HIT YOUR BOAT. If it hits anywhere close to you, you can kiss your electronics goodbye. Thus, here is a good reason to: ALWAYS CARRY HANDHELD BACKUPS. They are not that expensive, and might just save your life.


A couple of points...wrapping anchor chain around the shrouds and then dropping it into the water doesn't really help as the lightning will often take the straightest path into the water...at the voltage it is at, the slight resistance caused by an inch or so of fiberglass is not really a problem.

Also, handheld backups of electronics will also get fried on a boat that is hit by lightning unless you store them in a faraday cage. Best simple way to do this is drop them into the unused pressure cooker and seal the top. That way any EMP from the lightning bolt won't fry the handhelds...


----------



## sailingdog

I just had one more question...*Why is this in the HerSailNet forum???*


----------



## Cruisingdad

SD,

Why is this in the sailnet forum? I cannot say.

I agree, you have to protect the handhelds or they will get fried too. I have heard the pressure cooker thing. I always kept mine in a glass jar with clamp lid. I have not done a full scientific research to determine the valididty of whether this will truly work in a lightning strike... but I did live aboard in S Florida (lightning capitol of the country) and they always worked. As far as they pressure cooker, Fooogeettaabbouuut iittt! Love my wife. She is the best and loves boating more than me. However, you really think she would remember to always put those things back in the pressure cooker after dinner?? I don't think so. I would sometimes question whether she would remember to even take them out first!!

As far as the anchor/shrouds - I cannot attest to whether it works. Lightning/electricity will take the easiest path to ground. If the resistance is less going down the shrouds, chain, then water... well, it would seem logical that it would take that path. Fiberglass is not a good conductor (thus the damage via lightning). Now, if your boat WAS grounded, it would seem that tossing over the anchor chain would not make a lot of difference. 

You are right though, a gap in the chain could very well change its path. I did not say I did it... but he did and a lot of the locals.


----------



## hellosailor

CD-
A glass jar won't help. A Faraday cage (all metal enclosure with no gaps or breaks) works by carrying the electrical charge on the outer skin and not allowing it to enter the "cage". Metal screening can work, if the mesh it tight enough, but solid sheet metal is recommended for high power like lightning. That isn't always enough thought, there is some question of whether *magnetic* eddy currents can still be induced into any circuitry inside the cage (like a transformer) causing the contents to get disrupted anyway. Still, the Faraday cage is your best bet and protects against significant problems.

It is OLD technology, but still state of the art for protecting facilities from EMP associated with nuclear attacks. Yes, they do whole rooms and bunkers with all metal seals on everything. (Steel yacht anyone?<G>)

The pressure cooker would *not* make a good Faraday cage unless you replaced the rubber lid gasket with something like metal mesh, or there was a good metal-to-metal contact between the lid and the pot. Any break in the metal-to-metal, and the cage doesn't work.

Folks have also suggested using an oven (which can be a problem if you forget to take the goodies OUT, no joke) or a breadbox, or any cabinet or locker (preferably small) fully lined with metal mesh or metal window screening, copper roof flashing, etc.

If your ToDo list is short enough, or you're in lightning country, those might be things to think about.

The mason jar will certainly help keep your VHF dry and floating if the blast sinks the boat though.<G>


----------



## Cruisingdad

My old man mentioned another thought to me to protect it: He said wrap it in lead foil??

I thought about that... now why wouldn't that work?? Course, I asked him where I am supposed to get lead foil. He suggested an electronics store. I never know if he is pulling my leg or not. 

I have to admit, I did well in physics in college, but it never was my favorite subject. No good looking teachers. In fact, I think the whole floor was devoid of human life. Damn I should have been a business major. Oh well. Point being, I am fairly uneducated in it and should read-up.

Lead foil anyone?? Is that made by Reynolds Wrap??


----------



## sailingdog

My pressure cooker has a stiff enough gasket that the two pieces are in firm contact, especially if the cooker is locked. If it is a really bad storm, I'll wrap the gear in aluminum foil first, and then drop them in the pressure cooker.


----------



## hellosailor

Lead foil would work, it is used in radiology and other labs to shield things during x-ray procedures. You'd have to overlap the edges and french lap them, i.e. like blue jean seams, but then it would just be another Faraday cage. Aluminum fouil would work just as well. Mu metal, which is used as magnetic shielding in speakers and monitors, would also dampen magnetic pulses--which lead and aluminum wouldn't. Don't have ANY ideas where you can buy that.<G>

You can buy lead, tin, aluminum, and copper 'flashing' at any place that sells commercial roofing supplies. Military surplus ammunition cans might be a simpler idea, they're also waterproof and sturdy. Complete with a handle on top.<G>


----------



## sailingfool

*Scientific Answer*



frankbarbehenn said:


> I read that there are conflicting views about how to deal with lightning: to protect and ground to water or not. It seems to me that there must have been some real physics research on this question since it is so important for sailors. Does anyone know where to look for a real scientific answer???


You can find the marine equivalent of a scientific answer at http://www.abycinc.org/standards/purpose.cfm#E4 As I expect most of us won't want to pay to get a copy of the ABYC standard you can read an interesting commentary on it at http://www.kastenmarine.com/Lightning.htm

Conscientious builders and surveyors use this standard to design or evaluate lightning protection. I am unsure whether any builders actually build to this standard, I've never noticed any such claims.

FWIW Upgrading my boat to the full ABYC standard was a recent insurance surveyor's recommendation. My yard quoted this work at $3-5,000. I told the insurance company I did not feel the benefit of meeting the full standard to be worth the cost, and they accepted that position.


----------



## Dewey Benson

marinedtcomRob said:


> I'll still take my chances being grounded. At least I have an idea the of the path the lightning will take.


Have to agree. I know where my grounding plates are located, I can access the area from the interior quickly and carry pads that can be wedged over the areas in extremis.

Was 15 yards away when a lancer 28 sailboat's mast was struck. Very loud boom! The guy on board didn't remember hearing anything. He was down below washing dishes when the minimal electronics he had shot across the cabin in a fireball. He was shook up, dazed and shaking like a kitten. Other than that, completly unhurt. The boat was ungrounded.

The following day he sailed his trailerboat (the lancer 28) around a short point from the marina to the ramp where he hauled it out. The insurance surveyor took a pencil from his pocket as he noted some wrinked areas amidship below the waterline. He probed the area with the eraser end and the pencil passed straight through the hull. EEK!

Dewey


----------



## sailingdog

Dewey Benson said:


> The following day he sailed his trailerboat (the lancer 28) around a short point from the marina to the ramp where he hauled it out. The insurance surveyor took a pencil from his pocket as he noted some wrinked areas amidship below the waterline. He probed the area with the eraser end and the pencil passed straight through the hull. EEK!
> 
> Dewey


Sounds like it was a bit more than wrinkled...


----------



## TSOJOURNER

my method to avoid lightening strikes is constant trembling fervent prayer, which comes pretty easily, even to a non-christian, during a florida summer lightening storm


----------



## Cruisingdad

My opinions:

THe bottle brush in your pic has to be the highest point on the mast. Your VHF antennae is higher, defeating the purpose. As I recall, they suggest 6 inches over the everything.

Dissipators, such as your bottlebrush, have had marginal effects. Many now opt instead for a lightning rod with a very sharp tip on top. The current theory (highly debated) is that by grounding your boat, you decrease your chances of being struck because you can bleed off the potential. I personally find this difficult to believe - but that is the saying.

Grounding a boat or not grounding is a serious consideration. I feel that a poorly gounded boat poses more of a danger than a boat that is not grounded at all. Either do it, and do it all the way... or do not do it at all. All metal must be grounded, including toe rails, tie rods, and especially your steering mecahnisms. #8 was once recommended, but now that has been chaged to #4 (IIRC) for a straight run from the mast. DO not use your keel as a grounding plane and FOR GOD's SAKES DONT USE A DYNOPLATE*** unless you plan on swimming afterwards. The more surface area exposed to the saltwater, the better. Special plates have been developed to do this. They should not be painted. A seperate lead, #8-#4, should be run to ground the diesel/prop. It should be independent of the main run, preferably running perpendicular with its own lead and outside of the remainder of the boat grounding (stanchions, etc). The third leads can all be tied together and run to a similair ground plate.

The reality of doing a correct and proper job on grounding a vessel has been severly overlooked by most sailors & manufactureres (and especially motorboaters). It is very involved and moderately expensive. As the odds of being struck are very small, it may be the best money you have ever wasted. However, for anyone in very electrical prone areas such as South Florida, the islands, or the Northern part of South America, it should be highly considered. Those travelling offshore should also strongly consider it. 

Just my opinions.

- CD

*** A bronze dynoplate is porous. That poricity gives it more surface area which makes an very good ground for "low voltage" items such as SSB. However, in a lightning strike, the very high energy causes the water inside those pores to rapidly heat up, then boil. That boiling water creates steam and pressure, which often cannot be released from the pores quickly enough. THus, the plate will explode - often taking a chunk of the hull with it. You will sink quickly. Dynoplates are dangerous lightning grounds and should not in any way be connected with your lightning grounding system in my opinion. Still, I am amazed when I see "offshore" boats whose lightning ground is a dynoplate.


----------



## Cruisingdad

Here is a nice writeup I found on the subject, for those interested:

Lightning Attenuation Onboard

Marine Lightning Protection Inc.

NASD: Boating-Lightning Protection


----------



## SimonV

I too have seen the old jumper cables clipped to the shrouds and thrown over the side, the owner swore by them ( he had never had a strike) and I always put as much as I can in the Microwave.


----------



## hellosailor

I've read the old jumper cables will be better than nothing. But, because they require a right angle turn in the conductor path, and they are not a very good (not low resistance, not wide surface area, just "knife edge" contacts on the jumper clips) contact, they're not a replacement for a proper direct ground path.


----------



## TSOJOURNER

If you go back and read between the lines of each post and think about what you already know, there's only one conclusion.
Lightening strikes when it wants to and where it wants no matter what you do.
It will usually follow a conductor, but know matter how big, it will fry it. There IS no containing a million plus volts.

Maintain good insurance and peace with your god.


----------



## sailaway21

And that's the story on that one.


----------



## TSOJOURNER

Ok - this is from memory, and I don't have any sources I can quote. 

Blowing wind can place a charge on your antennas and then actually attract the lightning. One point of grounding is to take that charge back to zero. I believe the brush is designed to dissipate some of the charge from the air immediately around your boat. So, I'd agree the brush doesn't have to be at the highest point. 
A highly charged boat will be worse than a tall masted boat, which may explain the issue with the frequency of powerboats being hit.


----------



## sailingdog

pluscard said:


> Ok - this is from memory, and I don't have any sources I can quote.
> 
> Blowing wind can place a charge on your antennas and then actually attract the lightning. One point of grounding is to take that charge back to zero. I believe the brush is designed to dissipate some of the charge from the air immediately around your boat. So, I'd agree the brush doesn't have to be at the highest point.
> A highly charged boat will be worse than a tall masted boat, which may explain the issue with the frequency of powerboats being hit.


While this may be true if you had a mast made of non-conductive materials, I doubt it is the case with an aluminum mast and stainless steel shrouds and stays. While airplanes and helicopters can generate a serious static charge, the velocity of the air involved is much higher than what any sailboat will ever safely experience. Also, airplanes and helicopters are surrounded by a fairly good insulator-air, where boats are surrounded by a fairly good conductor-salt water.

Have you ever tried to generate a static charge on a piece of metal... doesn't really work all that well, since the electrons are free to move about relatively speaking. A common way to generate static electricity is to rub wool or silk over plastic... Try generating a static charge on a large piece of plastic ... and you'll get a pretty good one built up...


----------



## Cruisingdad

Honestly Rick, I dissagree (nicely).

It just does not make sense to me otherwise. Now I have only had about 2 years of physics in college, so I am not the expert in any of this... far from it. But I cannot see how having it at a level lower than another close conductive source in the same proximity will benefit it. In fact, I think it will be a detriment.

Since the bottle brush basic method of operation is to dissipate the charge which will accumulate on the easiest path to ground (ie, typically the highest point), having it below the easiest path to ground would not benefit it. Though on a large strike it may still have some benefit as the entire top of the mast will be gettting charged, it would be better suited by placing it higher than any corresponding conducturs/charge accumulators. I can see, as they wrote up in their web site, that you could place it too high... ie, ten feet or higher where there is a conductive loss between the easiest point to ground and the dissipator - which would decrease the dissipators effectiveness. However, on a sailboat where everything is in very close proximity, that does not make sense.

As far as the 6 inches, I meant for a lightning rod. My typo and mistake. It would not hurt for a bottlebrush too, but that was in the instructions I had for my lightning rod.

In general, using a faraday cage, I would see the top of the VHF antenae as the top of your cone. Given the buildup of the charge on top of your mast and the fact that the dissipator is lower, I would see the top of your VHF antenae as the top of your cage and the point where the strike would occur. If I were you, I would lower the antennae and add a lightning rod instead. THere seems to be some debate whether it shoud be very sharp or blunt... who knows?? But that is what I would do. I looked at the Forspar and other sites and they also reccomend the disspator being the highest point. Sailnet also sails it and says the same thing. Lightning Master is the only site that says it does not HAVE to be at the top - but there statement is based upon observation and not scientific, proven experiments. I also think (THINK) that they are being a little sarcastic when they say it may have a detrimental effect, "... when mounted too high..." as in a height well above what would be practical in a marine application... especially a sailboat.

The whole science behind disspiating a charge is pretty debated. I think a disspator of one type or another is a benefit, but I think the prudent sailor should be even more concerned with finding a clear and direct path to ground where the boat and its occupants would not be injured. A dissipator, in theory, only lowers the chance of a strike. It does not remove it. 

Just my opinions, Rick. 

- CD


----------



## Idiens

RickBowman said:


> Can this be a partial explanation as to why mobile homes are tornado magnets?


No that's a sub-prime effect.


----------



## hellosailor

Mobile homes, being such cheap flimsy construction, often erected on bare lots with no shelter around them, don't need to be "magnets" to make spectacular targets.

I've seen old (40-50 year old) mobile home parks in areas hit by Wilma, with mature heavy-rooted trees reaching up 30-50 feet sheltering the homes, and they took less damage than the exposed small homes (what I'd call bungalows) around them.

Building homes--or boats--"to code" helps make sure they can weather the environment with less damage. Won't do squat if the environment sits up one day and says "I'll take that one!"


----------



## TSOJOURNER

Ok, this is OT, creepy and sad...

But my dog just got hit by lightning, after I posted on this thread early this morning. He was on a dog tieout in his dog house. The tieout was between two large oak trees - I think it must have hit one of the trees, then traveled down the tieout to his metal collar.

His name was Grunt, and he was a large dog.


----------



## Insails

First we must understand how lightning works..so from my blog here I will post this:
Lightning is a series of several strokes the first being a stepped leader stroke which develops a path from the cloud to the ground sometimes the channels lead nowhere which explains why lightning forks ,eventually a path is developed from the cloud to the ground and lightning happens..
Once the stepped leader stroke develops a conducting channel to the ground or you get the "Return Streamer" which is a discharge of electricity from the ground to the cloud. This stroke is more brilliant than the leader stroke and is the observed stroke we see..an average of three leader strokes and three return stokes occur in one conducting channel..

So now we have a boat floating in the worlds best GROUND, water)

Now as I see it the brush is designed to disrupt the strokes within the conducting channel...does it work ??it could because even wind can disrupt the channels and change the path.....


----------



## TSOJOURNER

Thanks Rick - well spoke.


----------

