# Lightning and safety at sea



## LuckyMon (Apr 16, 2009)

During a recent sailing trip in the Bahamas, we got to dodge numerous lightening storms. While I understand that my Bavaria 37 Crusier is "grounded" for lightning strikes, we naturally try to avoid lighting storm situations if possible.

Once, while anchored, and had the choice to stay and wait out a storm, or get underway to our next destination.

Question: Are you more likely to get a lightning hit while sailing or at anchor? Or does it matter?

Thanks


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## CaptainForce (Jan 1, 2006)

It seems that the only variable would be if you were to have an all chain rode and if the metal gypsy on the windlass were bonded. Then, the question is if you are offering a path of less resistance that would facilitate a strike; however, if the chain increases the ability of the charge to exit your vessel without damage, that is an advantage. What puzzles me is the ability to dodge these electrical storms by moving about in a sailboat. I don't think that's effective. 'take care and joy, Aythya crew


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## LarryandSusanMacDonald (Apr 3, 2005)

I have heard that more boats are struck by lightning at anchor or at the dock than while sailing. That would, of course, make it seem as if you are safer sailing. However, it is also a fact that boats spend more time at anchor and the dock than they do sailing. (Therefore always be skeptical of statistics.)

Also, try to avoid people who make posts and say absolutely nothing. Like this one.


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## SeanConnett (Apr 20, 2007)

LuckyMon said:


> Question: Are you more likely to get a lightning hit while sailing or at anchor? Or does it matter?
> Thanks


I have heard so many debates on this subject and the conclusion I have come with is that it's no one really knows the answer to it. With that in mind, I tend to not leave the dock when lightning is known to be in the area. If however I'm out on the water and front comes through, bringing lightning with it, I just hunker down, avoid holding onto the rig and hope for the best.

When I was bringing my boat back from Abaco Bahamas, sailing across the Bahama Bank, we got stuck in a very active lightning storm. There was one strike that the back of my hairs tell me hit ten feet off our stern. Luckily the electricity didn't travel through the shaft and into our wiring. Of course, my boat is bonded and theoretically protected from lighting strikes but I know very well that does not mean my boat is not going to get hit one day. I live and boat in South Florida so I am pretty certain that a lightning strike is inevitable.

The bottom line is that we can do everything we can to protect our boats systems and ourselves from the effect of a lightning strike but we can never predict when one will happen.

Lucky Mon - Moored or Underway? It doesn't matter.


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## ottos (Aug 12, 2008)

LuckyMon said:


> Once, while anchored, and had the choice to stay and wait out a storm, or get underway to our next destination.
> Thanks


I would think that getting under way during or just before a storm would have more issues than just concerns over lightning.


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## Boasun (Feb 10, 2007)

LarryandSusanMacDonald said:


> I have heard that more boats are struck by lightning at anchor or at the dock than while sailing. That would, of course, make it seem as if you are safer sailing. However, it is also a fact that boats spend more time at anchor and the dock than they do sailing. (Therefore always be skeptical of statistics.)
> 
> Also, try to avoid people who make posts and say absolutely nothing. Like this one.


Of course!! At anchor or at the dock you are an easy sitting target... And while underway you are a moving target and harder to hit.. 
But what really matters is; Did you turk off the big guy up in the sky? Did you?


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## Bene505 (Jul 31, 2008)

CaptainForce said:


> ... What puzzles me is the ability to dodge these electrical storms by moving about in a sailboat. I don't think that's effective. 'take care and joy, Aythya crew


Maybe since you are heeling, you've lowered the height of the mast. Just saying...


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## Joesaila (May 19, 2007)

*Never ending story!*

About the best advice, and most useless that I've seen goes like this- "When lightning is taking place, stay away from the mast" :laugher So the remedy is to get in the dinghy??? I know I let go of my metal wheel upon a flash :laugher We were at anchor on Nantucket when a nasty thunderstorm came through at about midnight and our only consolation was the multitude of taller masts around us. I'm very happy that we don't read a lot about direct hits on sailboats!


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## Boasun (Feb 10, 2007)

Joesaila said:


> About the best advice, and most useless that I've seen goes like this- "When lightning is taking place, stay away from the mast" :laugher So the remedy is to get in the dinghy??? I know I let go of my metal wheel upon a flash :laugher We were at anchor on Nantucket when a nasty thunderstorm came through at about midnight and our only consolation was the multitude of taller masts around us. I'm very happy that we don't read a lot about direct hits on sailboats!


When you see the flash it is already to late to let go of that wheel.


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## barby (Feb 19, 2011)

*lightning at sea*



LuckyMon said:


> During a recent sailing trip in the Bahamas, we got to dodge numerous lightening storms. While I understand that my Bavaria 37 Crusier is "grounded" for lightning strikes, we naturally try to avoid lighting storm situations if possible.
> 
> Once, while anchored, and had the choice to stay and wait out a storm, or get underway to our next destination.
> 
> ...


Hi Mon.
Tell me please. Did you recieve any answers of any value at all?
The only answer that made any useful sense to me was Joesalia and his taller masts. That's gotta help.
Cheers
barby


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## aeventyr60 (Jun 29, 2011)

Luck of the draw...Lots of Boats in Asia getting struck, at anchor, in the marina, at sea too. Most electronics getting fried as well. Bonded or not bonded. Lightning packs a mean punch!


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## barby (Feb 19, 2011)

*lightning at sea*



CaptainForce said:


> It seems that the only variable would be if you were to have an all chain rode and if the metal gypsy on the windlass were bonded. Then, the question is if you are offering a path of less resistance that would facilitate a strike; however, if the chain increases the ability of the charge to exit your vessel without damage, that is an advantage. What puzzles me is the ability to dodge these electrical storms by moving about in a sailboat. I don't think that's effective. 'take care and joy, Aythya crew


CaptainForce. Quite a fancy name. So can you tell me two things, please CF?
What exactly does "bonded" mean? and 2 about dodging electrical storms. What alternative would you suggest?
Cheers
barby


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## barby (Feb 19, 2011)

*lightning at sea*



LarryandSusanMacDonald said:


> I have heard that more boats are struck by lightning at anchor or at the dock than while sailing. That would, of course, make it seem as if you are safer sailing. However, it is also a fact that boats spend more time at anchor and the dock than they do sailing. (Therefore always be skeptical of statistics.)
> 
> Also, try to avoid people who make posts and say absolutely nothing. Like this one.


Hi LaSMD.
HEAR, HEAR!
Carry on regardless.
CHEERS
barby


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## aeventyr60 (Jun 29, 2011)

sail away from the big black ugly cloud/storm fronts.....if you can


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## barby (Feb 19, 2011)

*lightning at sea*



aeventyr60 said:


> sail away from the big black ugly cloud/storm fronts.....if you can


Hi aeventyr. (Is that adventure in danish or norwegian?)
Exactly my thought. What else can you do? We can but try.
Cheers
barby


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## barby (Feb 19, 2011)

*lightning at sea*

Hi all,
Further to the discussion on "lightning and safety at sea" it would be a good idea perhaps if we were all more or less on the same level. A level as scientific as possible. It's not that I don't appreciate your opinions but they don't do much to promote "safety at sea". Do they??
So why not try to lift the game a wee bit and make it more interesting and beneficial for us all.
My first contribution is found at SGEB-17/SG071: Lightning & Sailboats.
See what you guys think.
Cheers
barby


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## eddie nelson (Jul 8, 2011)

Very interesting read B! Thanks


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## CaptainForce (Jan 1, 2006)

barby said:


> CaptainForce. Quite a fancy name. So can you tell me two things, please CF?
> What exactly does "bonded" mean? and 2 about dodging electrical storms. What alternative would you suggest?
> Cheers
> barby


Please! 'nothing fancy....Captain just comes commonly referrenced with the master's license and Force is my family surname. Seriously, not my purpose to be fancy or pretencious. By "bonded" I mean secured with metal conductive material to other metalic components like the mast in order to provide a pathway for a lightning strike, not unlike a ground plate present on many vessels that would only function with it's bonded connection to the rigging. I'm not expecting that a chain would be nearly as good a pathway to the water as a ground plate, but then, I personally don't have or desire to offer an easy pathway for a lightning strike. Many people, myself included, believe that by offering an easier path, you are increasing your chance of a strike. I don't think that it is effective to attempt to "dodge" an electrical storm with the movements of a sailboat. This would seem similar to worms trying to outrun birds. If a storm becomes apparent and you did not see it before, then it is approaching and running from it in a sailboat doesn't seem wise unless you have prior knowledge by forecast or long rang radar. I would also caution people not to move away from the "cone of protection" offered by their rigging and escape to a dinghy. It is best not to be touching the rigging or metal helm during the electrical storm. This is another reason to favor anchoring. If you are within the area spanned by your mast and rigging and not part of this big potential circuit, you are safer than outside this field. Take care and joy, Aythay crew


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## barby (Feb 19, 2011)

*lightning at sea*



eddie nelson said:


> Very interesting read B! Thanks


You are very welcome Eddie


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## barby (Feb 19, 2011)

*lightning at sea*



CaptainForce said:


> Please! 'nothing fancy....Captain just comes commonly referrenced with the master's license and Force is my family surname. Seriously, not my purpose to be fancy or pretencious. By "bonded" I mean secured with metal conductive material to other metalic components like the mast in order to provide a pathway for a lightning strike, not unlike a ground plate present on many vessels that would only function with it's bonded connection to the rigging. I'm not expecting that a chain would be nearly as good a pathway to the water as a ground plate, but then, I personally don't have or desire to offer an easy pathway for a lightning strike. Many people, myself included, believe that by offering an easier path, you are increasing your chance of a strike. I don't think that it is effective to attempt to "dodge" an electrical storm with the movements of a sailboat. This would seem similar to worms trying to outrun birds. If a storm becomes apparent and you did not see it before, then it is approaching and running from it in a sailboat doesn't seem wise unless you have prior knowledge by forecast or long rang radar. I would also caution people not to move away from the "cone of protection" offered by their rigging and escape to a dinghy. It is best not to be touching the rigging or metal helm during the electrical storm. This is another reason to favor anchoring. If you are within the area spanned by your mast and rigging and not part of this big potential circuit, you are safer than outside this field. Take care and joy, Aythay crew


Thanks CF. Sorry about the "fancy" bit. Your name really seems quite natural after all. However, about running away from danger, I don't think the worms agree.
Cheers
barby


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## Bene505 (Jul 31, 2008)

A friend boat got struck a few days ago, at anchor. His Catalina 38 was 200 feet from our Beneteau 50. We have the taller mast. I'm anchor using chain, he was anchored using nylon line.

Note that one data point does not make a trend, only an anecdote.

Regards,
Brad


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## barby (Feb 19, 2011)

*lightning at sea*



Bene505 said:


> A friend boat got struck a few days ago, at anchor. His Catalina 38 was 200 feet from our Beneteau 50. We have the taller mast. I'm anchor using chain, he was anchored using nylon line.
> 
> Note that one data point does not make a trend, only an anecdote.
> 
> ...


Thanks Brad. As they say 'there are more ways than one to skin a cat'.
This subject of lightning at sea is very complex indeed. I have found an article from SGEB-17/SG071: Lightning & Sailboats that is quite illuminating, if I can put it that way. It's a good read and if you are interested feel free to go to this website of University of Florida.
Cheers barby


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## aeventyr60 (Jun 29, 2011)

We were offshore Sailing around Borneo last year and there isn't any early warnings except the old "MKII EYEBALL", So, yes, we ran as quickly as we could AWAY from the big, black ugly MOFO's that packed not only a lot of wind, but torrents of rain and lots of electrical strikes, so if you've got sea room, and are not preoccupied with your chart plotters,radars, AIS, sat radio etc, then run, run, run away, saved my bacon more then a few time...same thing in the So. Pacific too...


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## aeventyr60 (Jun 29, 2011)

Hi aeventyr. (Is that adventure in danish or norwegian?)

Yes, can also mean fairy tale. So we are in year 12 of a fairy tale adventure...


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## LarryandSusanMacDonald (Apr 3, 2005)

Your boat's best protection against lightning? A good insurance policy.

Cone of protection? Research I did for the "Lightning and Your Boat" page on our website "The Frugal Mariner" indicates that the Cone of Protection (though taught by many reputable boating organizations, including US Power Squadron) is a myth.

Our quote in the Frugal Mariner: "The very famous and totally unsubstantiated "Cone of Protection." (claiming an angle of 60 degrees - 99 percent protection; or 45 degrees - 99.9 percent protection from the tip of a well grounded lightning rod.) These numbers are made up - there is no scientific theory upon which to base it. The earliest reference I can find is from a British lightning rod trade group - in the year 1874.
See this from the  National Lightning Safety Institute


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## CaptainForce (Jan 1, 2006)

Interesting thoughts about the "cone of protection" myth,- and it might be mythical, but the Nat'l Lightning Safety Inst's graphic is referrenced to a mast like a flag pole on the ground and not a sailboat mast with all the rigging forming the "cone" which is not necessarily 45 degrees and not the same "cone". Considering that the Faraday Cage is not a myth; then, what about the protection offered by being within the "cage" of rigging. I'm not taking a firm stand here, but I would not equate the position of crew on a sailboat with standing next to a flag pole or a tree in lightning. At this time and with the current data, I would favor being within my rigging "cage", not touching the rigging, rather than off in a dinghy away from the sailboat! Of course, I have 19 stainless steel shrouds on my old ketch rig. By my take it would be less safe on a Freedom with no stays! Take care and joy, Aythya crew


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## zeehag (Nov 16, 2008)

dont have anything fancy to say ..just sailed thru it a lot for a year with an old man in gulf of mexico. was scary as hell, but we didnt get hit at all. the only ones i know of hit that year were at docks. we caught a lot of high winds, as thunderstorms pack a wind quite worthy of sailing. i would be able to sail in it again, but wouldnt make me the happiest soul in the sea.
the mast height was 55 ft and aluminum.
my boat has 48 ft mast as a main mast and my mizzen. both wood. i am living in lightning hell right now in mazatlan with my boat--waiting out named storm season--hoping and praying that we dont suffer a strike.
lightning is totally random. doesnt matter if you have alleged protection-- the boat that was hit that i knew is owned by a NASA engineer and was so protected he was hit 2 times in 4 yrs at same dock behind his home.. 
i think i will continue with my crocs, which do not attract anything, my feline, as there is no report recorded in history of a feline being struck by lightning, my rubber suit and gloves and rubber hat. makes as much sense as putting lightning attracting items on boat. i want lightning to not see me. i carry jumper cables just for need--i have 2 pair. cli[p onto shrouds and pray. so far i havent used em.


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## LarryandSusanMacDonald (Apr 3, 2005)

Faraday cage protection is indeed a fact. Airplanes get hit frequently and are unhurt. Occasionally a car will get hit and nobody's hurt. And you can build one to store your electronics in (if you have time to unmount them) and they will be protected.

However, I don't believe that the rigging on a sailboat could be considered a Faraday cage. I understand Faraday Cages can be made of wire mesh, or even chicken wire (not verified). Solid metal, grounded, is best. It not only conducts the electricity around it, but also conducts the electromagnetic pulse - which is what fries much of today's electronics. Integrated circuits operate on extremely small voltages, tenths, or even hundredths of a volt - the voltage induced by a very strong electromagnetic pulse can ruin them even without a direct hit. This is why some boats have electronics damage when the lightning strike was only near, not a direct hit.

Like I said earlier, your only protection is a good insurance policy. 

Bonded or unbonded doesn't seem to make a difference. I have yet to find anyone who has taken a large enough survey to establish one way or the other. 

And offering lightning a 'path of least resistance' does not insure that the lightning will travel only down this path. The path of least resistance is all paths. If you were to make common 10 conductive paths to a ground, each of which has a different amount of resistance and apply a current to that circuit, voltage would be present across all of the paths in inverse proportion to their resistance. If this were, say, household current of 120 volts, most of it will go down a path containing 1 ohm resistance as opposed to others which have a higher resistance, but there would still be voltage along each path. 

Now substitute a 200 million volt lightning strike for your 120 volts of household current. if 99% went down one, your intended, conductor, that still leaves 2 million to travel all of the other paths. On a sailboat, that's your shrouds, all your electric wires, your bonding system and your thru-hulls. 

Admittedly, this is subjective and certainly arguable, but it is for this reason that we do not bond our boat. (Electrolosys is much slower than lightning, and I have time to respond to it.) Our mast sets firmly on our keel. During lightning storms, we stay away from the mast(s) and don't position ourselves near any large conductors - or between any. Lightning, having just jumped possibly several miles through the air, will laugh at the distance between a shroud and that massive rudder post just a few feet away. 

We have been fortunate and have never been hit in our 14 years of living aboard, but we know many who have. Protect yourself first. Let the insurance cover the boat. 

My opinion.


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## CaptainForce (Jan 1, 2006)

LarryandSusanMacDonald said:


> ....................We have been fortunate and have never been hit in our 14 years of living aboard, but we know many who have. Protect yourself first. Let the insurance cover the boat.
> 
> My opinion.


I'm not bonded either and I don't offer a path of less resistance via a ground plate. We too, have never been struck by lightning during our forty years of living aboard, mostly in Florida, and we also know many who have been struck. So, you say "protect yourself first". What does that mean? I trust you're not rowing away from you sailboat in a dinghy whenever a lightning storm is near! The insurance is totally irrelevant to your personal safety. What do you mean by "protect yourself first"? Take care and joy, Aythya crew


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## zeehag (Nov 16, 2008)

protecting self sounds a heckuvalot like what i do....wear rubber shoes, as crocs attract nothing, sleep UNDER the cat, as felines havent ever in recorded history ever been hit by a bolt , and i also wear gloves for sailing. and a rubber hat. and remain away from mast and shrouds and metal rails.....that stuff.


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## CaptainForce (Jan 1, 2006)

So, when you're not sleeping you wear a cat on your head? Zeehag, your interpretations of cause and effect relationships are a constant entertainment and your knowledge of the historical relationship between cats and lighting is phenomenal. I wish I had your confidence in footwear and cats. If Larry and Susan MacDonald tell me they sleep under cats too, I'm going to search for a cat surrogate! I'm allergic to cats,- am I doomed to cruise without safety? Take care and joy, Aythya crew


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## aeventyr60 (Jun 29, 2011)

Speaking of rubber, always carry a few spare "french postcards" as well.


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## zeehag (Nov 16, 2008)

captforce---lol--i am afraid of lightning since age 3 yrs old when i was damnear hit by a lightning ball in denver colorado. skeereded me white, blue, gurlee, and done ...i know lightning--is my enemy i have to keep it close. there is no way to predict it. there is no prevention from it. there is no life after it burns my boat to waterline. and kills me and kat. is malo. muy malo. i sit with kat on my lap wearing crocs. yes. have to.
crocs attract nothing. absolutely nothing. coool. i can dig that. 
is fact...there is no recorded history of a feline ever being struck by lightning. is ok--he sits on my lap or lies on my chest in storms. guarding me
---truth. cats are smarter than we are-- they go underground and hide in dark places low and cool. underground. the ferals outside go into holes in the ground. under cars so not wet and not in the way of streaming water. smarter than humans who sail in the stuff..idiots we are all.... laughable... i love sailing --i will sail in a storm, but when i am at helm in a lightning storm i will wear crocs, i will wear rubber and gloves and rubber hat--sou'ester..amd i willhug neither mast... havent got hit yet.... not that i am trying.....but i know the boat that was hit twice in 4 yrs in slidell--i sailed out of the place across the canal from him for a year.

i prefer avoidance to prevention...hard to do .


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## LarryandSusanMacDonald (Apr 3, 2005)

I didn't know that about cats. I, too, am allergic to cats. But how about mounting a cat at the top of the mast? Finally - a practical use for a cat.

By protect yourself first, I mean staying away from the metal stuff - and particularly stay away from areas between two large hunks of metal - like the rudder shaft and the shrouds, the mast(s) and the engine, the antenna downlead and your golf clubs. 

This just gives you better odds, it's no guarantee. With voltages in the millions, ionization can turn anything into a conductor. 

I don't know what the incidence of boaters killed by lightning is, compared to the number of boats hit, but I'd bet it's a very small percentage. 

I would also think that a boat with a metal deck and hull (probably not aluminum, though) would make an excellent Faraday cage - just like a car or a plane. 

I'd like to find significant statistical studies on lightning hits on boats. What I have found, according to Boat U.S. "The feature reports that in any one year the odds of your boat being struck by lightning is about 1.2 in 1,000, with 33% of all lightning claims coming from the sunshine state, Florida. The second most struck area in the country was the Chesapeake Bay region (29%), while on the opposite side, 13 states had no lightning-related claims, including states such as Idaho and Nebraska."

The odds are, of course, higher on a sailboat, and for some reason, higher still for a multihull sailboat. 

Of these, I wonder, how many people (or cats) were injured or killed.


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## zeehag (Nov 16, 2008)

as my boat has little metal topside, including masts and rudder, i am prolly in a decent position .... i cant brag as bragging yields contempt of the gods of the sea.....there is one good thing about owning a boat like a formosa--- they are made in a more traditional more wood oriented manner, with a fiberglass hull, where it counts.
is very scary sailing a sloop with a tall aluminum mast in lightning storms day after day wondering when the gods will stop the foolishnesss and strike ye with a bolt for the helluvit.


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## dnf777 (Jun 23, 2007)

Interesting thread, especially the posts that admittedly say nothing, to which I'll add this. ;-)

Karma aside, my general rule in my chosen profession, is when credible sources cite examples at opposite ends of the debate, some very well supported by scientific method......its usually means we don't know where the hell the truth is! Also, trying to study and analyze relatively rare events, makes statistical significance VERY difficult to obtain, and stratify risk.

Now, back to anecdotals.....after reading about someone finding consolation in being surrounded by taller masts, or faraday shielding....my buddy in Houston who was a harbor policeman at the time, told me of two unfortunate gents who were found dead in a 20' aluminum fishing boat (with aluminum wheelhouse) next to a marina with sailboats at anchor. You guessed it.....lightening strike. Sometimes your number is up.


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## zeehag (Nov 16, 2008)

i do not believe in any thing that states anything but randomness to lightning strikes, as that is my btdt observation. there is NO way to prevent lightning if it wants to hit you. good luck and believe what you will---i will continue to experience sailing under various weather skies until i am dead.


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## LarryandSusanMacDonald (Apr 3, 2005)

(More anecdotals)
As far as taller masts are concerned...
Friend of mine had a wooden boat - at the dock. Wooden mast. On both sides of his boat were fiberglass boats with much taller masts. Also, on his mast one of those Forespar Static Dissapater thinghies grounded directly to the keel with stranded 4 gauge wire.

Naturally, his was the boat that was hit. 

Down in Ft. Pierce Florida at the city marina there are a number of head boats. One of them had been hit numerous times (about a decade ago when we were there). Lots of taller things around it.


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## zeehag (Nov 16, 2008)

lightning is random ...unless you are protected, then it is attracted to ye, seems...the only boats i am in personal knowledge of having been hit had alleged protection. i protect meself with silly things like my gato , and crocs.....


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## barby (Feb 19, 2011)

zeehag said:


> lightning is random ...unless you are protected, then it is attracted to ye, seems...the only boats i am in personal knowledge of having been hit had alleged protection. i protect meself with silly things like my gato , and crocs.....


Hi zeehag. Please read this article and particularly 'Conclusions'.
Intersting point about "protection".
See what you think.
cheers
b

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Publication #SGEB-17

Topics: Thomson, Ewen M | Sea Grant | Recreational Boating

Lightning & Sailboats1

Ewen M. Thomson2

Figure 9.

Introduction

The sight of a jagged lightning bolt licking the not-too-distant horizon undoubtedly gives rise to concerned thoughts in the minds of many sailors. Few actually act on their thoughts. And very few understand the phenomenon well enough to act confidently.

Questions abound: "What do I do if a lightning storm is approaching or on me? What happens when lightning strikes a boat? Does a lightning protection system help? But if I do install a lightning protection system, won't it attract lightning? How do I install a protection system anyway?" Other questions relate to lightning itself: "Does lightning go up or down? Do the light and thunder originate at the same time? What causes thunder? Why does lightning sometimes flicker? What dictates whether lightning will strike an object on the ground or water?"

In this Bulletin and in the Sea Grant video "Lightning and Sailboats" we attempt to answer these questions. We describe the physics of lightning at a layman's level, discuss how a lightning protection system is supposed to work, and explain some of the technical details necessary for the correct installation of a protection system. A more technically oriented paper is published in the technical literature.

A VHS copy is available for $15 from: Florida Sea Grant, University of Florida, P.O.Box 110409, Gainesville, FL32611

Make checks payable to the University of Florida.

E.M.Thomson, A Critical Assessment of the U.S. Code for Lightning Protection of Boats, Institute of Electrical and Electronic Engineers Transactions on Electromagnetic Compatibility, Volume 33, Number 2, pp. 132-138,1991. Available online: Page not found. The copyright is owned by IEEE. It deals with some problems in the code for lightning protection of boats that existed at that time and suggests corrections.

Thunderstorms

From the sailor's point of view, thunderstorms are best avoided. There are several techniques that can be employed to recognize a growing storm and track one that is moving in your direction. The thunderstorm, or cumulonimbus cloud, is best recognized in its forming stages by its tightly packed "cotton wool" appearance. This occurs because a tremendous amount of energy is being released to produce powerful convection inside and around the cloud. Of course, if the thunderstorm is forming directly overhead the cotton wool appearance will not be visible, only a gray overcast that slowly darkens and eventually produces torrential rain, lightning and strong winds. The first few flashes of lightning in a thunderstorm typically do not reach the ground and may be completely invisible during daytime.

One way to determine what is going on in the area is with a cheap AM radio. (Note: FM radios do not work nearly as well for lightning detection.) The characteristic crackle that we call "static" on an AM radio is caused by lightning. A common problem in summer is that there are too many storms within radio range, which may be hundreds of miles. In order to lower the sensitivity of your radio to distant storms, tune it to a local radio station, or, if the signal is too strong, slightly off tune. Any loud static can then be interpreted as a warning that things are charging up.

Once a thunderstorm starts to produce lightning that hits the ground or "ground flashes", these can be used to locate a thunderstorm. One method is to track a collision course using a hand bearing compass: if the bearing to the lightning does not change, on average, the storm is heading your way and it is time to adjust your course. Another method that works once the thunder can be heard is to count the time between the light and the thunder. Since the light arrives almost instantaneously and the thunder travels at a speed of 1/5 mile/second, this time divided by five gives the distance to the lightning. For example, if the thunder starts 30 seconds after the lightning, the flash is 6 miles away. See Figure 1.

Figure 1. 
Thunderstorms ranging using time to thunder.

Note that the thunderstorm is about 10 miles across and that ground flashes originate anywhere inside the storm at a height of about 5 miles. Further, lightning channels usually slant away from vertical and can even emerge from the side of the storm (the classical "bolt from the blue"). The danger to the boat is obvious. That boaters frequently underestimate this danger is borne out by those whose boats have been struck by lightning, a typical comment being that there were no thunderstorms in the area just before their boats were struck.

Others signs of imminent lightning are even more obvious. St. Elmo's fire and buzzing sounds off radio antennas arise when a boat is in the large electric field directly below an electrified cloud. Although lightning may not yet have begun, its occurrence in the immediate vicinity is exceedingly probable when these electrical phenomena are observed. Act as if your boat is about to be hit by lightning, as described below.

Lightning

The only type of lightning that need concern sailors is the ground flash, since lightning that does not reach the ground does not damage boats. Ground flashes can be expected to hit from 4-20% of moored sailboats per year in Florida. Cruising sailboats typically get hit at least once in their lifetimes. The standing records for the total number of strikes to a single boat is five (in Sarasota, Florida) and the highest strike repetition rate is twice within ten seconds (in the Indian Ocean).

The typical ground flash starts at a height of about 5 miles above water, inside a region of the thunderstorm that is charged negatively. The path, or channel, that eventually connects this negative charge to ground begins here. As the channel extends towards ground during the "stepped leader" phase, negative charge is funneled from the cloud into a spark channel. When the tip of the stepped leader is about 30-100 yards above ground level, another spark, this time positively charged, is launched from the ground. A massive amount of power is generated when this positively charged attachment spark and the negatively charged stepped leader connect. At this time the peak lightning current is generated, during the "return stroke". Although cresting at ten thousand to hundreds of thousands of amps, it only lasts for about a millionth of a second. Longer lasting currents of a few hundred to a few thousand amperes may persist for much longer times (on the short time scale of the lightning) during a "continuing current". These long-lasting continuing currents are responsible for large heating effects and are thought to be responsible for forest fire ignition. After a short pause, subsequent leaders may reenergize the channel, followed by more return strokes and, on occasion, continuing currents. A typical ground flash has about three leader/return stroke sequences. Lightning frequently appears to flicker because each return stroke lights up the channel, and the time between them is sufficiently long enough to be seen by the human eye.

The return stroke heats up the lightning channel to a temperature about six times as hot as the sun. This causes the surrounding air literally to explode. We hear this explosion as thunder that appears to last for much longer than the lightning, which is all over in less than a second, because the lightning channel network covers several miles. The speed of sound is only about 600 knots and so thunder from more distant parts of the cloud arrives later than thunder from closer parts. The important thing is that the light and sound are generated at the same time since they are both caused by the return stroke.

Lightning Interaction with a Sailboat

Attachment

As the negatively-charged stepped leader moves downwards, it induces a positive charge on the ground below. When the tip of the leader is about 30-100 yards above ground level, the induced positive charge becomes so concentrated that a new spark forms at the ground, as shown in Figure 2. This positively charged spark is the crucial process as far as the attachment to a boat is concerned. If it starts at the tip of a boat mast, then lightning strikes the mast. Unfortunately, there is no scientifically accepted technique to prevent this spark from forming. Even if a device were effective in diverting the attachment spark, it would not be a good idea to mount it on the masthead as the attachment spark may start elsewhere on the boat or crew. The likelihood of lightning attaching to the masthead is a safety feature as far as the crew is concerned.

Consequently, lightning protection means minimizing the damage caused by lightning in the event of a strike, rather than preventing a lightning strike. In general terms, a protected boat is one in which there is a continuous conducting path from the water to the mast tip. The current needed to feed the attachment spark is conducted through the protection system from the water. That is, the path that the lightning takes in the boat is forced to be that of the conductors in the protection system. If this conducting path is not continuous, for example, in a boat which is not well grounded, there is little difference as far as the top of the mast is concerned. The attachment spark still begins there as this is where the positive charges have concentrated. The difference is what happens where the conducting path, the mast, ends. Since current cannot flow from the ground to feed the growing attachment spark, a negative charge accumulates at the base of the mast and eventually arcs across in the general direction of the water or a nearby conductor. (For this exercise, crew members are conductors!) The result is an unharnessed electrical discharge between the bottom of the mast and the water.

Figure 2. 
Lightning attachment to a sailboat.

According to the above argument, the likelihood that lightning will strike a boat does not depend on whether the boat is well grounded or not. There is some support for this in the experiences of marine surveyors. Nine marine surveyors in Florida, each of whom had surveyed more than 200 sailboats in their career, reported that between 2% and 67% (on average 34%) of the boats they surveyed for any reason had a lightning protection system. Of the boats that they surveyed because of a lightning strike, they reported that between 0% and 67% (on average 29%) had a protection system. While the individual estimates varied widely between surveyors, 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.

Sideflashes

Figure 3. 
Proportion of boats struck by lightning suffering hull damage of varying degrees.

Data obtained from sailors whose boats have been struck by lightning are consistent with the above scenario: boats that do not have a protection system do indeed suffer more damage. The type of water, whether salt or fresh, is also important. Damage is much more extensive for boats struck by lightning in fresh water than for boats struck in salt water because fresh water is a worse conductor. Consequently, it is much more difficult to design an adequate protection system for boats in fresh water than for boats in salt water. Figure 3 summarizes these data for a sample of 71 boats that were struck by lightning. The bars show the percentages of boats in each category that received various magnitudes of hull damage. The four categories were boats with/without protection systems in salt/fresh water. The damage indices indicate the severity of hull damage as shown in Table 1.

Table 1. 
Severity of hull damage.

Hull Damage

Index

Type of hull damage

0

No hull damage

1

Small non-leaking cracks

or burns

2

Small holes that did not

leak seriously

3

Holes larger than ¼ inch

diameter above waterline

4

Holes larger than ¼ inch

diameter below waterline

In boats with a hull damage of 2 or higher the lightning had formed its own path(s) through the boat hull. If a lightning protection system was present it malfunctioned. As the statistics show, malfunctioning protection systems are very common in fresh water: 40% of protected boats in fresh water experienced this effect. The most likely way that this happened was through the formation of "sideflashes". These are sparks that form between the lightning protection system and ungrounded conductors or the water. Basically, in order to dissipate a lightning current in fresh water a much more extensive underwater grounding system is needed than that usually found in "protected" boats. This is described in more detail below.

Technical Aspects of the Lightning Protection System

Overview

Although lightning protection needs to be designed on a boat-by-boat basis and ideally installed during manufacture, there are three major considerations in a good protection system: (a) grounding, (b) bonding, and; (e) electronics protection. The grounding system is intended to provide an adequate conducting path from the point of lightning attachment, usually the masthead, to a system of conductors in the water, without producing sideflashes. The bonding system protects the crew and consists of conductors that short out large metal fittings so that large voltages cannot develop between them. Electronics protection limits power supply and transducer voltages through a combination of transient protection devices and careful wiring techniques.

Grounding

Figure 4. 
Possible effects of a lightning strike to an ungrounded boat.

The idea of the grounding system is to divert the lightning current through a predetermined path so that it does not make its own explosive path through fiberglass, teak, crew members, etc. Figure 4 shows what can happen when lightning strikes an ungrounded fiberglass boat with an aluminum mast. The lightning charges all of the rigging but no conducting path exists to channel the charge into the water. The result is destructive sparks between the lower parts of the rigging, such as the mast base and chainplates, and the water. Wherever these sparks travel through bad conductors (fiberglass hull, teak bulkheads, through-hulls, porta-potties, etc.) sufficient heat is generated to explode the impeding material into a nicely conducting plasma that is hotter than the surface of the sun.

The components of the grounding system are: (i) an air terminal at the top of the mast; (ii) downconductors, and; (iii) grounding conductors that are immersed underwater ("ground strips" or "ground plates"). The air terminal is the point where the lightning is supposed to attach, the down-conductors conduct the current from the air terminal to below the water, and the grounding conductors dissipate the current into the water without forming any sideflashes. Usually the aluminum mast is connected in as part of the down-conductor network.

On a sailboat with a VHF radio, the masthead VHF antenna usually serves as a sacrificial air terminal. In fact, one of the first signs that lightning has struck a boat is typically that shards of antenna material are scattered around the deck. The presence of a VHF antenna or other expensive masthead transducers makes a separate air terminal highly desirable, although this will degrade the performance of the VBF. The top of the air terminal should be sufficiently high that the angle from it to any other masthead object is less than 45 degrees. That is, the air terminal provides a "cone of protection" that attracts lightning (or, more accurately, launches an attachment spark) preferentially to any other object that is below a conical surface whose apex is on the top of the air terminal and that has a 90-degree apex angle.

An aluminum mast is the preferred down conductor, being a much better conductor than stainless stays. If the mast base is on top of the cabin, a downconductor is needed to connect the mast base to the ground strips. Use at least #4 gauge copper with preferably bimetallic copper/stainless connections to prevent galvanic corrosion. Alternatively, make a strong mechanical connection and additionally braze or solder, to improve the electrical contact and lessen the chance of contact corrosion, then paint with an insulating coating. A keel-stepped mast similarly needs to be connected to the keelbolts with at least #4 gauge copper.

The ground strips in contact with the water should be connected to the down-conductors with care to avoid galvanic corrosion. In salt water a single grounding conductor of a square foot or more in area is usually enough. In this respect, a lead keel connected to the down-conductor via the keel bolts is adequate. If the lead is either painted or encapsulated in fiberglass, minor repairs may be needed after a lightning strike. However, the paint or fiberglass does not seriously compromise the ballast lead as a lightning ground. Note that this system does not work in river mouths where there may be a less dense layer of fresh water riding on top of a salt water "wedge". The situation in fresh water is much more complicated as the voltages involved during a lightning strike are about a thousand times larger than those that occur on a boat in salt water. A good start is to lay a flat or "D" cross section strip of 3/4" x 1/8" stainless or brass along the outside of the stem of the boat. Connect this to the forestay, mast base, and backstay with #4 gauge vertical copper down-conductors. However, this is not usually enough. In addition, extra ground strips are needed just outside the hull close to metal fittings such as gas tanks, metal-cored plumbing pipes, wiring, etc. Connect these to the grounding system using near vertical down-conductors. Under no event should these down-conductors run close to the hull except where they penetrate the hull to connect to the grounding strip: otherwise the conductor may cause a sideflash through the hull. The engine, propeller shaft, and propeller should be regarded as part of the grounding system and tied in appropriately.

The manner in which a correctly grounded boat reacts to a lightning strike is illustrated in Figure 5. The lightning charge that flows onto the rigging does not accumulate to the point where it forms destructive sparks, as was the case for an ungrounded boat. Instead, it is discharged into the water over a wide region. The more evenly the charge can be discharged into the water, the less likely it is that a sideflash will occur through the boat hull.

Bonding

Figure 5. 
Effects of lightning strike to a grounded boat.

The difference between the grounding system and the bonding system is only one of degree since both are interconnected and both will conduct current during a lightning strike. Whereas the grounding system is designed to handle the full lightning current, the bonding system consists of mainly horizontal connections between metal fittings to short out any voltages that might otherwise develop. Bonding is a measure that is intended to protect the crew and enable them to work the boat without getting shocks. This can occur from nearby lightning as well as from direct strikes. Smaller gauge conductors than the grounding system are adequate in the bonding system, down to #8 gauge copper. As with the grounding down-conductor connections, all bonding connections should be made to minimize galvanic corrosion. Metallic fittings that should be bonded to the grounding system, using horizontal connections as much as possible and avoiding the hull, are toe rails, chain plates, steering wheels, motor controls, bow and stern pulpits, antenna bases, the ground wire for the electronics, etc.

Figure 6. 
Lightning effects on an unbonded boat.

Figure 7. 
Lightning effects on a bonded boat. Note: Being in contact with a wheel or tiller during a lightning strike is extremely hazardous, even in a grounded, bonded boat.

The illustrations in Figure 6 and 7 show what happens on board a bonded (Figure 7) and unbonded (Figure 6) boat during a lightning strike. On the unbonded boat large voltages develop between the mast, chainplates, forestay, backstay, wheel, rudder post, toe rails, electronics, wiring, metal reinforcing in plumbing fixtures, engine, etc. These make working the boat extremely hazardous, even if lightning is not striking the boat directly. On the bonded boat these voltages are shorted out by bonding conductors. Note, however, that the large magnetic fields associated with a direct lightning strike make the concept of an electrical "short" a misnomer. Appreciable voltages can develop between the ends of long conductors even if the conductors are connected together at their other end. The helm is a particularly dangerous place owing to its proximity to the engine controls, boom, rudder post and backstay. The helmsman in Figure 7 would not be smiling if he had one hand on the tiller and the other on the engine controls, for example. (Note that he is steering with one hand in his pocket to minimize the risk of making a connection between two conductors at different voltages. This is not as safe as throwing over the anchor and going below!) For stations such as the helm that are usually manned, it is crucial that the bonding conductors should be kept as short and straight as possible.

Electronics

Electronics-killing overvoltages may be introduced through the DC power wires, antenna input, or any other external connection such as a lead to a transducer. Electronics on a small sailboat that are struck by lightning are particularly difficult to protect since it is impossible to divert the lightning current any appreciable distance away from the electronics. This difficulty, and the pervasive nature of electronics damage, is illustrated in Figure 8 that shows the percentages of boats with electronics damage of different magnitudes.

Figure 8. 
Proportion of boats struck by lightning suffering electronics damage of varying degrees.

In this case there is less of a distinction between boats struck in fresh water versus salt water as there was for hull damage, but the same trend is evident: boats with protection systems in salt water fare best and boats with no protection systems in fresh water fare worst. More notably, 96% of all boats sustained damage to at least some electronics items. Apparently a lightning protection system, as installed on the boats in the survey, does not necessarily save the electronics. Note that for these boats "lightning protection" merely meant that the boat was grounded, not necessarily bonded with transient protection devices, as explained below.

In order to protect electronics, more is needed than merely diverting the current to ground (water) without its blowing a hole in the hull. Due to the low voltages typically used in modern marine electronics, just a few extra volts is enough to cause extensive damage. However, techniques that are used to protect computers, cable TV and radio equipment on land can also be used in shipboard DC and AC equipment. Some devices are readily available from electronics stores. Radio antennas can be protected using lightning arrestor hardware designed for cable TV. Connect the "ground" connection to the lightning grounding network. AC transient protection outlets or plug-in metal oxide varistors (MOV) work also on boats but need to have their ground connections connected to the shore ground wire. Ideally this ground should also be connected to the lightning protection ground but this circuit arrangement can cause ground current problems in marinas. As for protection of DC electronics, which are probably the most important, transient protection devices are available to clamp voltages at the point where each piece of equipment is connected to the DC supply. These are available from companies such as General Electric or from mail order electronics distributors. They can be found under the generic name "Transient Suppressors" and are of various types: metal oxide varistor, silicon avalanche diode, and surge suppressor zener diode. It is important to locate this protection device immediately next to the equipment and each piece of equipment should have its own device. The overvoltages that appear at DC inputs can be reduced by using twisted-pair wiring in wiring harnesses, ideally with a conducting sheath that is connected to the bonding system. The overall philosophy here is to minimize the spacing between positive and negative DC lines. If a main control center exists, surround it with a conducting enclosure that is connected to the bonding system. Through-hull transducers are especially vulnerable. Due to the typically vertical alignment of the cables connecting these to their main electronics, they should be regarded as being part of the lightning grounding system. Since the wires used in these cables are of an insufficient thickness to withstand a lightning strike, a #4 gauge copper wire should be placed parallel to any cable that leads to a through-hull transducer. The top of this copper wire should be reconnected to the lightning grounding system and the bottom to a ground strip close to the underwater transducer on the outside of the hull.

As with all aspects of lightning protection, 100% effectiveness cannot be guaranteed, even if all the above measures are taken for electronics systems. Disconnecting equipment in advance of a storm helps isolate it from voltages induced by lightning, and the larger the lead separation the better. Use disconnects in preference to knife switches, and these in preference to switch panels.

Personal Safety

Consider the worst case scenario for a lightning strike to a sailboat - a small boat in fresh water. If the boat has been provided with a well-built protection system it is still an exceedingly hazardous situation. If lightning protection does not exist, the situation is life threatening. In both cases, the areas to avoid are close to the waterline and close to large metal fitting. In the unprotected boat, an additional danger zone is beneath the mast or boom. Even in the unprotected boat, it is unwise to get in the water, as electrocution is highly probable if lightning strikes nearby. In fact, there is no safe place on an unprotected small sailboat, and in a protected boat only places of relative safety. There is, however, one place that is more hazardous than a small unprotected sailboat, that is a small unprotected boat without a mast. Every year there are multiple deaths of boaters in open boats caused by lightning strikes, but very few reports of sailors in sailboats killed by lightning.

The above general rules also apply to larger sailboats. These are generally safer, if protected, since it is possible to get away from the waterline and large metal objects, and yet still stay dry inside the cabin. As far as unharnessed electricity is concerned, a dry human body is much less attractive than a wet one.

Conclusions

Lightning protection on a sailboat means diverting the lightning current into the water without its causing any hull damage, personal injury, or electronics damage. This involves providing a continuous, mainly vertical, conducting path from above any vulnerable masthead transducers to grounding conductors immersed in the water (the grounding system) and a network of mainly horizontal interconnected conductors attached to large metal fittings, including the grounding system (the bonding system). Transient suppressors are needed on each piece of electronics equipment, and wiring should all be twisted pair for protection of electronics.

Figure 10.

Sea Grant Project No. R/MI-10 Grant No. NA89AA-D-SG053

Florida Sea Grant College Program Bldg. 803 - University of Florida, Gainesville, Florida 32611

Figure 11.

This publication was supported by the National Sea Grant College Program of the U.S. Department of Commerce's National Oceanic and Atmospheric Administration (NOAA), Grant No. NA89AA-D-SG053. The views expressed are those of the authors and do not necessarily reflect the view of these organizations. Additional copies are available by contacting Florida Sea Grant, University of Florida, PO Box 110409, Gainesville, FL, 32611-0409, (352) 392.2801, Florida Sea Grant.

Footnotes

1.

This document is SGEB-17, one of a series of the Sea Grant Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date July 1992. Reviewed March 2009. Visit the EDIS Web site at EDIS - Electronic Data Information Source - UF/IFAS Extension.

2.

retired associate professor, now president of Marine Lightning Protection Inc., 3215 NW 17th Street, Gainesville, Florida 32605 (352) 373-3485

--------------------------------------------------------------------------------

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Millie Ferrer-Chancy, Interim Dean.

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## zeehag (Nov 16, 2008)

when a NASA engineer has only boat that has been protected in an are of many strikes has the ONLY tow hits in 4 years, his is the only boat "protected", his boat was twice injured to the point of requiring out of water repairs for over 6 months first time, and over a year and a half second time, brand new hunter 45,second time the lightning destroyed even the power cord from the house to the boat......he had all the fancy spark attractors on the masthead and divertors and grounding plates and whatever the magic anti lightning inventions are-- when he is only one hit AND he was hit twice, then i must wonder about the efficacy of lightning protection. 
THERE IS NO SUCH THING is my conclusion. the writings mean nothing. in practice, in reality, is where the facts are, not in theory nor on paper nor as lightning rod creation in a boat. 
i cannot afford to have my boat, which is my home, hit by lightning. i cannot take a chance to place alleged protection --err, attraction devices, onto my boat so it becomes the next great lightning rod in my neighborhood.
as i have already stated, the ONLY boats i know to have been hit by lightning were allegedly protected with fancy systems and set ups to prevent lightning hits. and hit TWICE.
lightning is totally random. taller masts do not help. the example for that being a power boat hit in an area infested with tall masts. why didnt the lightning go to one of those---lightning is RANDOM. it is not predictable nor is it going to go to some ones boat that hasnt protection when there is a path of least resistance to ground--the protected boat.
i would rather be sailing in a lightning storm than sitting in a dock as a sitting duck.
i would rather not have a pathway of least resistance for the bolt of lightning to follow--a protected mast with a grounding device---i would rather have no protection, as that is the best protection against something big and electrical coming at me with its force and intensity. 
lightning protection is not something that can be studied in a reality theater. lightning is way too random. there are certain patterns-- and there are its basic needs -- but it goes to path of least resistance--via lightning rod to ground, both of which are presented by the protected boat.


yes i read the article, and these were my conclusions regarding the conclusions i read in that article, as well as my own observations after having sailed thru the stuff for a year off florida and in gulf of mexico


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## barby (Feb 19, 2011)

Dear zeehag. I love the passion of your convictions. Atta girl. I.e. if you are a girl?
Thank you for your courtesy in reading the article. I found it quite interesting.
It revealed to me at least one important point about protection.
I does not mean lightning strike prevention any more than insurance means preventing an event from happening. No, it's all about mopping up the leftovers. The better the protection the more leftovers!!
Also: "lightning is random ...unless you are protected, then it is attracted to ye, seems..."
Your words from a few days ago. Remember? 
The Macquarie Dictionary says: random 1. going, made, occuring, etc,; without definite aim, purpose, or reason. 2. not according to a pattern or method. 4. at random, in a haphazard way; without definite aim, purpose, or method. ( from OF rushing movement, disorder). 
So logically then if lightning is random it can hit any one anywhere any time no matter whether we have protection or not. Otherwise it is not random but acts according to a certain pattern. So which is it?? Random I believe from study and observation. Not logical but disordely.
One set of circumstances can by definition not be more random than another set of circumstances. So we can't really say that "lightning is random ...unless you are protected, then it is attracted to ye, seems...". Can we??
So perhaps we can agree on the fact the lightning strike protection does not mean lightning strike prevention.
Good
cheers barby


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## zeehag (Nov 16, 2008)

lightning is random it hits wherever it wants to . it can be guided it seems but alleged protection that seems to attract bolts as they happen.
things can be more than one way. nothing is absolute


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## barby (Feb 19, 2011)

zeehag said:


> lightning is random it hits wherever it wants to . it can be guided it seems but alleged protection that seems to attract bolts as they happen.
> things can be more than one way. nothing is absolute


If it is random then it cannot be guided. If it can be guided then it is not random. Please make up your mind.


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## zeehag (Nov 16, 2008)

absolutes have no place in science, are you into science or trolling.


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## barby (Feb 19, 2011)

zeehag said:


> absolutes have no place in science, are you into science or trolling.


Dear zeehag thank you. I think i have all I need now.
By the way: I am into truth. And guess what: truth is absolute.


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## ramonex1 (Jun 9, 2013)

This weekend we got caught in a thunder storm sailing in the Mediterranean on a Benetaeau Cyclades 39 and we got hit by lighting, it stroke the tip of the mast first, burning everything up there, then came down and fried all the instruments board and switches, it then went through the wiring back towards the stern and blew the GPS antenna which was right behind the stardboard wheel and me, triggering on the EPRB wich was on it's base fastened to the railing. Luckily there were no injuries onboard but we were really shocked. It burned out all of our electronics, including plotter and auto pilot, even the engine RPM gauge. Our engine was on at the time of the impact and it kept on running, but the alternator had its share. 
Now my question for an expert on this issues; if we had all the instruments off at the time of the strike would they had been saved or they get fried no matter what? 
And “do you have any idea why the EPRB lighted on by itself”
By the way 5 minutes latter the Spanish coast guard called us to make sure we were alright (they got the EPRB distress signal and that made us feel a little bit safer out there)
Thanks


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## desert rat (Feb 14, 2013)

Proper ground seperation, spark gaps, high curent zener diodes, and old fashion knife switches, just might help your electronics. Maybe.


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## Frogwatch (Jan 22, 2011)

I do have a substantial background in this sort of thing as my graduate physics work was on fine particle charging by very high voltage discharges and since then have been involved in some of the biggest HV discharge machines around for nuke weapons effects testing.
So, does rigging provide a "Cone of Protection"? I'd say, statistically "yes" as a discharge path approaching ground is more likely to attach to your mast top than to you sitting next to it.
Does your rigging act as a "Faraday Cage"? Ya gotta know why a faraday cage works. One of the most basic electromagnetic laws is that a static E field will not penetrate a hollow conductor because all the relevant charges will be on its surface. WHAT DOES THIS MEAN IN REAL LIFE?
Lightning is a very fast pulse made up of a sum of many sin waves of different frequencies and intensities (the Fourier Transform for all you geeks). Waves that are long in relation to the spacing between your rigging will see your rigging as a closed shell. Waves that are short will not see it as a closed shell. Thus, the rigging acts as a partial Faraday Cage allowing the High freq stuff to get thru but reduces the low freq stuff. As the low freq stuff is less significant in a fast pulse, I do not expect rigging to make much of a Faraday cage. Consequently, the safety comes from your mast being more likely to get hit than you sitting near it.

Another question I hear a lot is "Should one go into a forest during a lightning storm or stay in an open field because we all hear not to go under a tree in such a storm"?
The answer": Do not go under an isolated tree (or just a few trees) because they are likely to get hit. However, being in a open field, you are more likely to get hit than if you are in a forest where the tops of the trees look like a ground plane. Try not to stand near the highest tree. This is similar to a lone sailboat vs a small sailboat being among many other boats with higher masts. You are better off in a grouping of many boats and have a shorter mast than to be a lone boat


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## TropicCat (Oct 14, 2008)

ramonex1 said:


> ...
> Now my question for an expert on this issues; if we had all the instruments off at the time of the strike would they had been saved or they get fried no matter what? ...


I don't have a degree in fine particle charging but have been struck by lightning while sailing. To answer the question hung out there, if all your electric/electronic items were switched off, it would have made no difference at all. The high voltage discharge was following the boat wiring. Anything connected gets fried. Exceptions are battery operated devices not connected to the boat, which in my case survived the event.(cell phones, cameras, hand held GPS)

As to your engine ... it's a diesel, no electricity required to run it. I have 2 diesels both running at the time of the lightning strike and neither engine missed a beat. However, my port engine alternator and starter never worked again and had to be replaced.

Lastly I believe there is a cone of safety within the metal stays supporting the mast. I was at the helm, soaking wet and bare footed and did not feel anything at all when lightning hit us. Nothing...Nada...zilch... A loud crack and watched my tri color mast head light hit the water off my starboard stern and then felt the molten metal fragments in my hair.

I've tried real hard to stay away from strong storms cells since that day, but unfortunately that day ended my admirals interest in our boat.


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## chef2sail (Nov 27, 2007)

Glad to here you are all ok

We got struck ( side struck) by lightening moored in Annapolis Harbor surrounded by 1100 other sailboats. We also have a diffuser at the mast top as well as bonded. The lightening traveled through the water up the shaft, we had a bright flash in the boat and it went up the mast and jumped to the boat moored next to us and went down his mast ( he also had a diffuser)

All our electronics was off,,,,and most of it got fried as did the Yanmar engine panel (motor was off). The light was indiscriminate what it took out as it didn't affect everything.

Personally and I am not a degreed electrical anything is its hard to diffuse or contain something which is 1,000,000 volt discharge with a rod or cone of protection. If it makes you feel better go ahead and get it. 

Didn't seem to help us or our neighbor.


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## ramonex1 (Jun 9, 2013)

Thaks Thread
I have a colleague down in florida who delivers boats al over the place, who always stores a GPS inside the oven when a thunder storm approaches. He says the oven plates protect it.
I would think if the GPS is not connected to the boat's DC network, it should not suffer any demage from a lighting strike. Besides you might end up having a broiled GPS with your chcken fricasse.


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## boatpoker (Jul 21, 2008)

Professional Boatbuilder Magazine runs a podcast with experts in various fields. The have one scheduled in "Updated Lightning Protection Methods" coming up soon.


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## ramonex1 (Jun 9, 2013)

thanks boatpoker!!


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## Frogwatch (Jan 22, 2011)

Because I know a lot about High voltage discharges, I tend to be fearful of them and am terrified of lightning.
However, in spite of people thinking it to be random, it really does act in an understandable manner. The problem is that we simply cannot measure everyhting before a strike to be able to predict exactly where a strike will or will not happen. The best we can do is to minimize the probability of a strike and to minimize the damage from one. 
In general, other than placement of ones boat near better conductors to ground and staying out of thunderstorms, one cannot do much to minimize the probability of being struck. However, one can minimize damage.
To prevent damage to yourself, do not provide a current path. Sit or stand with legs together and hands in your pockets. That way there is no potential difference across you. In a lightning storm, I went so far as to stand on one foot and lightning struck two meters away and I felt nothing (somehow, I actually knew it would strike. I was so certain of it that I climbed onto a dry wooden table under shelter and crouched on one foot).
Further to minimize damage, one should provide a good path to ground from your mast. We have had discussions here of lightning grounds.
I find it interesting when walking thru woods in Florida to look for pine trees that have been split down the middle or split in a spiral fashion, an almost certain sign of a lightning strike.


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## Frogwatch (Jan 22, 2011)

On a flat open plain with a single tree, what is the best strategy to minimize personal damage from lightning? Remember, the plain is flat, no dips to lay in. So, if one lies down, he provides a path for current to flow if a strike happens nearby. If one stands under the tree, the tree has a high likelyhood of being hit. However, if one crouches down one one foot with hands on his knees near the tree (say half its height from it) one minimizes your chance of being hit directly (it will more likely hit the tree) and minimizes damage to yourself from conduction. THIS IS THE SAME AS GETTING PROTECTION FORM YOUR MAST. This is entirely diff from simply taking refuge under a lone tree while taking no other precautions. This is also not a good strategy for a group of people or boats.


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## Sal Paradise (Sep 14, 2012)

Surprised no one has mentioned this - I searched the thread and it wasn't here. 

I was told by an old sailor that for lighting - you wrap a length of heavy chain around the base of the mast at the deck and drag both ends in the water. Luckily I have never needed to use it, but it makes sense to me.


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## El Rubio (Mar 31, 2013)

Frogwatch said:


> On a flat open plain with a single tree, what is the best strategy to minimize personal damage from lightning? Remember, the plain is flat, no dips to lay in. So, if one lies down, he provides a path for current to flow if a strike happens nearby. If one stands under the tree, the tree has a high likelyhood of being hit. * However, if one crouches down one one foot with hands on his knees near the tree (say half its height from it) one minimizes your chance of being hit directly (it will more likely hit the tree) and minimizes damage to yourself from conduction.* THIS IS THE SAME AS GETTING PROTECTION FORM YOUR MAST. This is entirely diff from simply taking refuge under a lone tree while taking no other precautions. This is also not a good strategy for a group of people or boats.


This is a good way to get yourself killed, but I agree with much of what you've posted on this subject otherwise.

I would skip the diffusers and ionizers, or whatever they're calling the metal toilet bowl cleaners that people put on top of their masts and spend the money on bonding as much metal on the boat to ground. The theory behind the diffuser design is that as a thunderstorm passes overhead, the positive charged cloud is pulling streams of electrons from every object on the ground. Supposedly a dome of electrons builds over an object and eventually the stream reaches the cloud and completes the circuit. Sharply pointed objects tend to be the focal point for that stream. The diffuser supposedly creates thousands of streams that aren't focused on any single point. Some people, usually the folks who sell them, will claim Nikola Tesla proved the effectiveness of this in an experiment. I'm not a Tesla expert, but have read some about his work and this was never mentioned. The best thing you can do is safely route the surge to ground. Ideally, this means bonding every significant piece of metal to ground.

The electricity in a direct strike is going to take every path to ground, just like any electronic circuit. To the surge, the wiring, electronics, and even you, are all paths to ground. These paths have varying impedance and the lowest paths are going to take the most current. This is where bonding things like the mast to the keel become important. You want a low impedance path to ground that will take most of the surge. If there is no low impedance path, it will still go to ground, but it may be through you, the fiberglass hull, wiring, etc.

It was mentioned that someone puts a GPS in the oven to protect it. That isn't so much about direct strikes, but nearby strikes that create large magnetic fields as it travels to ground. As a magnetic field builds and decays, voltage is produced on wires and other conductors within the magnetic field. Many electronic components can be destroyed by even small induced voltages. As a matter of fact, this is the most common damage associated with lightning. It's also, possibly the easiest to protect against. This is what surge protectors are designed to protect from.


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## ottos (Aug 12, 2008)

El Rubio said:


> ...It was mentioned that someone puts a GPS in the oven to protect it. That isn't so much about direct strikes, but nearby strikes that create large magnetic fields as it travels to ground. As a magnetic field builds and decays, voltage is produced on wires and other conductors within the magnetic field. Many electronic components can be destroyed by even small induced voltages. As a matter of fact, this is the most common damage associated with lightning. It's also, possibly the easiest to protect against. This is what surge protectors are designed to protect from.


High impedance circuits will be more vulnerable...but that includes most electronics these days. People have mentioned that ovens do well because they are Faraday cages. One other thing that might come in handy as a Faraday cage (if you have access to someone who has to these).... Circuit cards and other electronic items (like PC cards) often come in translucent grey plastic bags for static shielding. I would imagine that these would do well to protect electronics on a boat. (Note: My theory only...NOT TESTED!!! YMMV) If you know an engineer or technician, you can get some of the large bags....which they are usually throwing out anyway.

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