Lightning Question

[Ross]

Lightning like so many things in this world comes in all strengths and sizes. The strike that hit our house was relatively mild. I have seen large trees blown into kindling wood, seen six inch wide strips of bark torn off from top to bottom of oak trees. Sometimes a strike will just crackle and another strike will sound like a bomb blast. The cloud to cloud strikes boom and rumble but the cloud to ground strikes bang like dynamite.

 

[walt]

Check out the video "wet or dry, does it help" - its I believe the forth one down..

http://www.struckbylightning.org/

Interesting that this says you might be safer if your clothes are soaking wet.

 

[T37 Phil]

My brother is an electrician Ross and we all find it particularly ironic/funny that he has some bizzarre gremlin issue with his house. He hasn't had direct strikes, so far as I know, but he has had many "ball lightning" events. I suspect that may also be what MS experienced given his description of total electronics catastrophe and zero structural damage. My brother has constant problems losing TV cable signal, phone interference and modem failure (dialup, DSL and cable). All the problems are focused in one corner of the house where most of the electronics reside, of course. It must be some geological phenomenon, who knows. As you say, lightning comes in many varieties.

 

[zeehag]

in denver there was a phenomenon known as ball lightning--i experienced that when i was 3 yrs old, within a foot of my face. scared the beegeeziz outta me--in the 1980s, there was a team of alleged scientists who debated the existence of ball lightning phenomnon --they said it does note xist--those of us who have experienced it first hand are familiar with its properties and patterns of behavior. scary stuff follows you...fills air pockets and dances in front of you then after you run away, disappears. seems to me that lightning that is trapped in an airpocket and dancing in front of you will do same damage as a regular bolt of the zappy stuff....i donot take lightning lightly--is serious stuff.
whenyou are sailing i believe the target isnt stationary. i prefer to be a moving target, even for the gods and their bolts from hell than choose to sit still and call it to me...i will not protect my boats from it as that seems to attract it more--see the neighbor of nne who has been hit twice in 4 yrs despite protection and now has a 1 -1 1/2 yr yard bill to cover...maybe tow a catalina 20 with full lightning protection behi8nd the unprotected boat??? sacrificial catalina 20??? just to save your good boat?? i dont know---all i know is the only thing i was n wearing in the rain and lightning out at sea--where would YOU go in deep 220 ft water and 100 mi from shore--lol----just keep sailing--get out in your own time and make sure the crocs are on your feets and the kat is sleeping in a berth....i wear sailing gloves-gil is a good kind--they go on sale frequently enough for me to have 2 pairs!!!
no sox, as the feets are spozed to contact the rubber of the shoes for emotional comfort----what to do !! what to do !!!!--just keep on keeping on, is what to do ---we didnt try to outrun the storm, we just sailed thru it as it was in the way....and came after we got there---many will dissipate before you get into them--but many will not--those are the scary ones.
could it be that the water passing under the hull breaks the static electricity and makes the boat less attractive to the lightning??? if that is the case, then continuing on your way is the very very best idea anyone could come up with. why stop and increase chances of being hit??

as for the corner of the house--does he get the same problem if he disperses his tronix over a wider area and uses a different electrical outlet?? mebbe places a lightning rod down that corner of his house?? eliminate the outlet in that corner and place one elsewhere out of that corner?? makes sense to me--but , has he tried that? if not, it might work----seems that may just be a place where the lightning finds an easy pathway..interrupt that path and should make life easier for him??

 

[Don12364]

Sailed Right Round One

Long time ago. Was at anchor when mother of a summer storm cell came up over the horizon from the south and directly towards us. Scary.
Generally wind was light before the cell arrived. Got under way just as skies clouded over completely so we lost sight of the storm's true position but could still see the lightning.
Knowing the winds always blow inwards towards the centre of a thunder head I set course on a close reach to the south towards the storm but a little to the west.
Did not touch the sails and kept the same heading to the apparent wind.
Gradually our course changed from SW to S and then to SE and eventually to east - which, fortuitously, was our way home.
My wife couldn't understand why we set off SW when we needed to go E.
The storm cell was broad on our port beam the whole time until it went ashore and we saw no more of it. No lightning strikes within a mile of us throughout.

I was particularly pleased because everything turned out exactly as I hoped - a rare event for us.
May have been just beginner's luck!

BTW: When thunder storms arrive when we are in port I always put the navigation laptop in the microwave. I guess one day I will forget and fry it!

 

[Bill Roosa]

Latest research agrees with physics

The insurance companies have noted that boats that get hit by lightning have an unusually high incidence of burn holes at or near the water line.
If you are familiar with induced charge and skin depth you know that the skin depth for an induced charge in salt water is less than a foot. So discharging to the keel is discharging into a ground that basically has no potential. Discharging is a misnomer as the charge is actually going upward so you are collecting the charge from a source that has not potential. The lightning will collect on the water surface and jump to the boat by the shortest route. That would not normally be to go downward to the keel then up the mast. It would be to collect near a metal part near the water line then burn through the fiberglass and then jump to the mast or shrouds.
It never made any sense to me to bring lightning into the cabin in the first place which is why I always put a line off the shrouds and over the toe rail to the water. I believe the electrical standards for a house direct you to treat it that way also. Replacing a ground rod for the water surface of course.
FWIW

 

[T37 Phil]

zeehag - I think he's tried everything, that's why we've concluded it's gremlins. It's not like a haunted house where these bizzarro events are always occurring. Things work and then they don't, and the failure rate seems too high for coincidence or bad luck. I'm sure he has a proper lightning rod, though I haven't actually seen it. He's pretty thorough, I'd say.

Donalex - I like your post. That kind of an awareness of weather is something everyone should strive to develop. Perhaps the catamaran I was describing earlier would have done better had they stopped to think about how conditions would evolve.

Bill - I'm not sure I follow. Induced charge can occur about any dielectric, but something does force the charge onto the surface. That means there is a potential. The separation of charge across the dielectric is related to that potential and its change. Furthermore, though the seawater may be considered to be at zero potential, that's a relative term. Potential difference is what gets current flowing. Seawater is definitely full of charge/sources, so being at zero potential isn't relevant if a different potential exists from inside the boat. Perhaps what you're saying is that the reactance of the hull/keel is more than the resistance of 'jumping' paths, and therefore rigging a conductor as you do gives current a place to flow other then through the bottom of your boat. Is that essentially what you're saying?

 

[richk]

take the short course at http://www.srh.weather.gov/jetstream/lightning/lightning_intro.htm

 

[Bill Roosa]

lightning 101

A cloud builds up a static charge. No body knows why or how just take it on faith.
When that cloud moves over ground or water it induces an opposite charge on the SURFACE. If it induced a charge through out the body current would flow till it reached something to stop it. In water it is the water surface. The charge is distributed in a very thin layer at the surface. Your keel "ground" is many times deeper in the water than the surface induced charge. As the cloud increases in potential a point is reached where the air breaks down and ionizes The leader of the lightning strike tries to get to the induced surface charge. If your boat is located in between it gets to participate in the completing the air gap.
So your boat is sitting between the surface charge(negative BTW) and the cloud charge (positive charge). The electrons on the water surface will not down go into the water to complete the circuit via your keel, they will jump in odd and random ways but always toward higher (talking electrons here) electrical potential. That is what the insurance companies are noting. A high incidence of hull burns/holes at the water line. The burn/hole usually has a metal part behind it that concentrated the charge because it was connected electrically to the mast or shrouds/stays.
So grounding to your keel is not a bright idea as your keel is at 0 volts but the water surface is at much higher negative potential. But since it is an induced charge it has no desire to "short to ground" as the whole boat is immersed in the electric field producing the induced charge.

 

[Maine Sail]

Interestingly enough...

1 - My boat did NOT suffer a direct hit. We can only roughly extrapolate from this that my mast was not sending up magical fairy dust to connect to the lightning in the sky so the lightning was more attracted to the water next to my boat than my mast. This to me is a good thing as a direct hit would have literally melted all the wiring in my boat. I have seen this before and it is not pretty.

2- My boat suffered EMI/EMP as even stuff that was not connected such as my hand held VHF, iPod, Magellan HH GPS & a Garmin HH GPS, was still fried. I don't believe for a second that you can protect stuff like radomes or equipment permanently mounted like plotters or wind/depth/speed from these pulses. If lightning likes your boat or even close to it they will get toasted. You can probably protect small devices with a GOOD Farrady cage. Tinfoil DOES NOT work as a Farraday cage as I was once told it would by a very well respected, seasoned sailor and EE who swore by it.

3- My boat took a hit through the ground side of my system as well as EMP/EMI. The ONLY grounds on my boat are well over 1 foot below the surface. The ONLY ground path to my electronics is through my engine ground so that is where it had to come from. My mast & shrouds are grounded to the keel. According to Bill's theory this can't happen but somehow it did? There is also no visible damage to the hull at or near the waterline nor down by the keel and all the bottom paint looks great.



Three years ago a guy right behind me was hit really hard and a guy 300 yards away and much further away than me lost all his brand new TackTick stuff, I lost nothing. The guy hit hard had just spent a few thousand dollars on the latest and greatest lightning protection for his vessel.... The guy with the TackTick stuff only lost that and nothing else. Lighting is fickle. I still did not have a direct hit so am quite happy about my level of protection even though I know I can and may eventually still see a direct hit at some point. Replacing electronics is MUCH less expensive than hundreds of hours or re-wiring which I am ecstatic about.

 

[seadaddler]

Direct hit

While I was in Greenport,NY the boat next to me got a direct hit while out sailing and he told me his whole family was on the boat with him when it happen but the top of the mast got a direct hit and every piece of electronics got destroyed but they were all OK a side from getting scared to deth and the insurancepaid most of the replacement.
They did pull the boat out of the water and every thing was checked,they also pulled the mast to have it tested and checked,few months later he was out sailing with all new up graded Raymarine electronics on his 42 Saber.
Nick

 

[walt]

MS, Im not sure how you know for sure your boat didn't take a direct hit? You are in salt water and I "understand" (but am not sure) that a solid connection between the mast and the keel can dissipate a lightning strike without a flash over - IF you are in salty water. In this case, if the main energy path was directly down the mast - and then directly to the keel through a hefty low impedance, it would not have melted anything. A typical 30KA strike will not damage 4 gauge wire - so not sure why you think your wiring would have melted. If the main path between the mast and the keel did contain the current, the rest of the wiring would have transients created by the EMP but this also would not melt wiring. If you did take a direct strike, I "understand" (again not sure) that your keel would show some evidence of dissipating the charge into the water. Ie, you would have some patterns or marks on your keel underwater.

If you want the reference on 4 gauge wire not melting, read the stuff around figure 3 in this paper http://www.kp44.org/ftp/A_CriticalAssessment_of_the_US_Code_forLightningProtection_of_Boats_IEEE.pdf

FYI, it would appear that a grounded underwater keel can dissipate a lightning strike in salt water (and there is nothing wrong with grounding a keel ). This is because salt water is maybe 1000 times more resistive than fresh water - and also, the "surface charge time" of salt water is also about 1000 times faster than fresh water. But in fresh water, the underwater keel would appear to not be able to compete with the water surface dissipation so that is where the charge goes - by a side flash to the closest water surface.

 

[walt]

Here is my magical fairy dust theory - cant give a reference..

If you look at the references on the typical cloud charging, the upper levels of the cloud are positive and lower levels are negative.

The cloud lower level negative charge induces a positive charge at the water surface. Some more fun reading on how this works here http://www.lightningsafety.com/nlsi_lhm/Radials.pdf

The water surface gets charged positively by electrons on surface atoms getting driven down into the bulk of the water.

At some point, the electric field gets large enough that a negative streamer heads down from the cloud towards the water.

This negitive downwards streamer has its most intense electric field at its propagating end. As the streamer gets closer to the water surface, the electric field builds - and further charges the water surface. Water itself is very difficult to ionize (both dielectric constant and density in water are MUCH higher than air making water significantly harder to ionize). However, the air just above the water now sees a very intense electric field and this can ionize creating a conductive path for an upwards "positive" streamer to flow. If your mast is in the vaciniity of where this ionization occurs, your mast will get used as the lowest impedance path to follow. The positive streamer then heads up (using your mast) to meet the downwards negitive streamer from the cloud and then bang.. Once again, the "positive" upwards streamer is actually electrons moving in the opposite direction. Note that this whole mechanism had nothing to do with the keel being grouded or not (ie, I dont think grounding has any effect on your chances of getting struck).

One interesting thing from the radials paper is that the surface charging time is inversely proportional to the number of charge carriers disolved in water. Salt water has about 1000 times the number of carriers so charges about 1000 times faster than fresh water. Salt water surface charging takes nano seconds, fresh water is in the 10's of micro seconds. The much longer surface charging time of fresh water is (I beleive, could be wrong) why the surface radial patters are so much longer for fresh water compared to salt water.

 

[Maine Sail]

MS, Im not sure how you know for sure your boat didn't take a direct hit?

Walt,

I have seen the results of many direct hits over many years on the Maine & New England coast. On one boat the antenna blew apart so bad that it rained shrapnel down onto the boat and molten metal burned through the dodger, sail cover and sails. The boat was totaled due to cost of repairs exceeding coverage of the vessel. One boat that was at RRBY had the mast head sheaves get so hot they melted the halyards it also blew apart everything at the mast head including a TV antenna. One boat blew a seacock near the base of the mast clean off the thru-hull and the boat began taking on water. In all these strikes the keel was grounded to the mast with heavy wire and on all three of these boats a decent portion of the wiring had the jacket melted clean off. The common denominator was that all these boats were bonded so the mast strike went to the vessel ground too.

I have also been to the top of my mast since the hit and there is no evidence of direct hits like I have seen before where the mast head is charred and stuff blown apart like a bomb went off. There is also zero evidence up there of any damage except for the LED anchor light which is blown, but every LED on the boat was blown so that is no big surprise. No under water damage that I can see with a mask and none up top only electronics and no wiring except for a couple of NEMA wire that was melted in the nav station. The ones burnt were all connected to ground.

Also most of the really "fried" stuff, as in charred, was closest to the engine. The Seinsibulb I showed was just feet from it. All the others are just blown not burned. This location is the shortest path from the engine ground. The stereo was totally fried and is closest to the main ground conductor wire length wise.

It may have been a direct hit but the insurance surveyor had just come from a direct hit on a boat Downeast and his statement was "wow you got lucky." Lots of melted wiring on the boat he had just seen. The idea that wiring does not melt in a strike, is just that, an idea, cause I've seen it too many times for it to just be a coincidence..

Fairly certain this was not a direct hit but anything with lightning is possible.

 

[walt]

Thanks.. must have been awful close and a powerful one.

Odd that in Colorado I have seen very little lightning this year which is unusual. Now I know where it all went.

Just one note on the wire burning up - I have to believe that a good solid piece of wire (like 4 gauge) will survive a strike - and have heard enough from other places to back this up. But any sort of connection of the wire which has any impedance at all will get blown up or melt.

 

[Maine Sail]

Thanks.. must have been awful close and a powerful one.

Odd that in Colorado I have seen very little lightning this year which is unusual. Now I know where it all went.

You can have it back now... Usually it goes over the lakes region then up through the mid coast but for some reason this summer they've been rolling though here with some regularity. Last Wed we actually had a tornadoes touch down and that's when I got hit, Wed night...

Just one note on the wire burning up - I have to believe that a good solid piece of wire (like 4 gauge) will survive a strike - and have heard enough from other places to back this up. But any sort of connection of the wire which has any impedance at all will get blown up or melt.

What you may not be considering is that many boats are bonded connecting the mast to the seacocks to the engine etc. which is also connected to the house and then off to MUCH smaller circuits with wire gauges of 12-14 even 16 & 18+ for instrument communication not 4GA. From what I've witnessed it is usually the smaller wires that get toasted the big ones just help it get to the smaller ones...

 

[jibes138]

Maine Sail,
This is exactly the reason why I've been saying all along you need to move down south where you can enjoy your boat all year round. Lightning, tornadoes, pea soup fog, freezing cold water, two month summers, frankly I don't get the attraction. My aunt lives in Ogunquit near Perkins Cove and when I've visited her in late May all the stores are boarded up and the place is deserted. Mid May is mid summer here. I really think it best that you pack up and get out as soon as you can.
Oh yeah and I saw a couple movies where axe murderers live in the lighthouses up there too.

 

[T37 Phil]

A cloud builds up a static charge. No body knows why or how just take it on faith.

Ah, now I gotchya. Cloud to sea, not outside hull surface/inside hull surface. In that case your boat is a speck in a much larger volume, as you point out. As current flows from cloud to surface, there is no reason to presume that the path jumping from the surface through the air(??) or along the exterior of your boat is any more favorable than through the keel. If there is no metal fitting at the water line, then it would still be a capacitive current going straight through the hull. If the path through the water down to and through the keel has less overall reactance, then it's a possibility. With big metal parts in bilges, say big metal rods connecting big metal motors to propellers, it's reasonable to consider the bottom of the boat as a danger zone. What you are telling us, on the other hand, is that insurance companies are collecting data to the contrary. My boat in fact had been hit by lightning in NJ long before I bought her. The prop shaft was melted and the Awlgrip was blasted off at the thru-hull. The damage to electronics was not quite as complete as in MS's case. So I guess I'd agree that lightning does find paths at or above the water line, but I'd also say that it definitely finds paths below the waterline as too.

 

[Ross]

I know of one case where lightning followed a path through one tree from the ground to about two thirds of its height and jumped to an adjacent tree about 15-20 feet away and continued to the top. The damage to the bark is evidence of the path. I don't know if the direction was from ground to sky or from sky to ground or some of each. I am glad that I wasn't leaning against the tree when it struck.

 

[Bill Roosa]

Induced charge and capacitive discharge

I suspect that IF MS did not get a direct hit then he suffered from the following situation.
A large potential builds up overhead near his boat.
A equally large potential builds up in the water that his boat is sitting in.
The boat participates in the large potential buildup but no appreciable current get moving.
The lightning hits nearby dissipating all the potential and induced potential very rapidly
MS boat is now charged like a capacitor and discharges through the most convenient ground (keel, prop).
The large currents in this discharge would be in all the circuits as they all "felt" the induced potential from the cloud.

Thoughts?

I'd note that an ungrounded boat would not have as much of a problem (with this scenario) as a well grounded boat. FWIW