Lightning?

[ssullivan]

True, true... I should have known to be more precise. A full metal enclosure is the only way to keep the E and M fields out. Should dig out my old Electrodynamics books - ahh... to peruse Maxwell's Equations again...

[Princewig]

I just came across this web page from another sailor about a lightning strike while under way http://www.longpassages.org/lightning.htm

This story would be the number one reason why I would want to have my back ups in a protected box.
The information is priceless as usual.
Christopher

[soul searcher]

Rick,
Would an old surplus ammo can work?

[GordMay]

1. A Farraday Cage must be grounded.
2. Don’t waste you’re money on a “dissipater”.
3. When deliberating the alternative strategies of bonding & grounding vs isolating, consider the difficulties of achieving an effective isolation. Remember, the lightning bolt , that strikes a boat, may have traveled miles through air.

[bvimatelot]

I've not yet been hit - but I suppose its "statistically inevitable". During electrical storms, I put a hand held gps in the oven sort of thinking that this might work as a Faraday Cage......Am I wasting my time or will the oven work?

Tony

[rleslie]

Do microwave ovens protect electronics? While underway I always put my handheld GPS and VHF radio in our micro.

[Rick]

Yes, a steel ammo box should work well for electronics protection. A microwave oven will work partially because although the enclosure is usually constructed of steel, I don't believe that the front door screen is made from ferrous material. Regardless, it would be a good compromise and certainly convenient.

The principle behind the Faraday cage is that no matter what is the charge on the outside of the cage the voltge gradient INSIDE will be zero. Grounding or isolating the cage will not change that phenomenon.

[hellosailor]

Soul Searcher- An ammo case sounds good until you remember there's a big insulator under the lid, the waterproof seal. Might defeat the purpose.

Gord-
"1. A Farraday Cage must be grounded." And, how does that gibe with the concept that aircraft in flight, with metal bodies, pass lightning strikes without frying the occupants? Isn't the same Farraday Cage concept supposed to be working there? I don't doubt a ground helps, but I thought the cage kept the charge on the exterior (the skin) rather than letting it flow through the contents, regardless of ground. No?

Sean, you know the saying about "you can lead a horse to water but you can't make him drink" ? Same thing with lightning, you can take practial steps to direct a strike on a boat, but you can't force that bolt to follow your path all the time. It's still worth "encouraging" it to take a direct route off the boat though.<G>

[Rick]

Because uniform static voltage gradient lightning discharges occuring through symmetrical conductor structures generate arcs which are fairly easy to predict, whenever arc paths are taken that appear to be unpredictable (like a discharge arc taking a circuituous route where an obvious direct low conductance preferential one exists through a conductor) we may tend to feel that lightning is truly capricious. What we cannot easily observe are the secondary effects caused by the primary flow of electrons and positive charges. Such effects force both positive and negative charges around conductors. Charge shifts induce voltages in other conductors (or even poor conductors) and so on. Each charge movement results in a magnetic field causing other effects. Charges, currents, and non-uniform heating of the ionized air cause widly varying paths of an arc to occur.

So, when an ionization path begins (invisible) the path may be immediatly warped to other directions, before, and after, visible arcing occurs, by adjacent charged particle movement and currents induced in conductors that generate other magnetic fields. Think of this in four-space with time-lapsing being the fourth dimension. Include all of the various items inside and outside a boat and you have a very complex picture to resolve concerning any predictive capabilities regarding safety. This is why lightning appears to be so capricious.

[Pblais]

Think of this in four-space with time-lapsing being the fourth dimension. Include all of the various items inside and outside a boat and you have a very complex picture to resolve concerning any predictive capabilities regarding safety.

Capricious! Somehow the word falls short of the explanation.

I've a scant few encounters with the stuff and every time was an amazement as what really could explain why it was so destructive.

Seems like it could be worse. I could get hit by lightning next week and actually be here right now.

[GordMay]

Originally Posted by hellosailor

...
Gord-
"1. A Farraday Cage must be grounded." And, how does that gibe with the concept that aircraft in flight, with metal bodies, pass lightning strikes without frying the occupants? Isn't the same Farraday Cage concept supposed to be working there? I don't doubt a ground helps, but I thought the cage kept the charge on the exterior (the skin) rather than letting it flow through the contents, regardless of ground. No? ...

Sort of.
See my item 3, regarding the difficulties of isolating against lightning. The aircraft is effectively grounded.
Some references:
http://www.lightningtech.com/d~ta/faq1.html
http://www.sae.org/aeromag/features/aircraftlightning/

[alaskadog]

My boat was struck by lightning this past Sept. 22 and I made a post in this forum to that effect in which I posed some questions. The mast was struck at the very top. My wife saw the strike out the back window of our condo. The lightning hit the boat approx. 20 yards behind the building instead of the four story building which with the roof stands a little higher than the mast which tops out approx. 50 feet above the water. I have one of the little ionic dissapator gizmos at the top which apparently did little or nothing to ward off this strike. The electrical circuits in the boat are grounded to one of those bronze dynaplates that is on the hull. There were three other sailboats located about 100 yards away in finger piers with similar but slightly lower mast heights than on Sun Dog but they were spared. Although one of those boats was struck last year while mine was spared. When we noticed the storm coming I attached an additional grounding gizmo near the base of the mast. It was a knockoff I made of one commercially available from a Canadian company that I had read about in a question-answer section of Sail Magazine in which Nigel Calder was responding to a question about lightning protection. I also had a battery jumper cable aligator clipped to each of the upper shrouds and tossed overboard. The "gizmo" is a 6" x 8" copper plate, bent in the curvature of the mast to insure good contact with and strapped to the mast. A 10 ft. length of #2 marine grade, rubber coated cable is soldered to the copper plate and on the other end of the cable is soldered a 1 1/2in. by 2 ft. copper pipe. This is tossed overboard and the pipe lay well grounded in the mud. Inspection of the mast at the attachment point of the grounding gizmo revealed a scortch and a penny size nick of aluminum blown off the mast. The inside of the copper plate was scortched as well. Repairs are not yet complete. What has been replaced so far or has been diagnosed as bad is as follows: GPS, VHF antenna (which was blown in two pieces) VHF radio, SSB radio, AM-FM Stereo and CD changer, TV antenna, TV set, tricolor masthead nav light and anchor light(the anchor light was completely blown apart and a hole blown in the high density plastic globe/lens of the nav light.) radar, GPS antenna, chartplotter, autopilot electronics including the fluxgate compass, Heart interface battery monitor, electronic control for the air conditioner as well as one of the circuit boards controlling the air conditioner operation, electronic controls for the refrigerator, the circuit breaker/control panel for all circuits located by the nav table, various fuses that service the hard wiring for some of the circuits inside the boat such as the circuit to the windless and interior lightning. There is some more damage regarding shorts in some of the hard wiring that the technicans are presently trying to trace. The boat was plugged into 50 amp shore power at the time and their was indication of schotching on one of the two 30 amp cables as well as the 50 to 30 amp Marinco adaptor that they may have been damaged so the adjuster called them bad also, though I suspect that they might have been usable. Not damaged was my 402 EPIRB that is mounted inside the boat or a handheld GPS and handheld VHF that were stored in soft pouches in a locker. The boat will have to be hauled out to replace the depth sounder/water temperature transducer. That could happen this week. What would have happened or how much more damage would have occurred had I not had the "gizmo" can only be guessed at. It is obvious that a great amount of electricity was diverted off the mast before it entered the boat. Ironically some of the damage looks as it might have entered certain circuits through the ground wire as opposed to the positive connections. I have also read in similar discussions that the better an object is grounded the more likely it may be to attract the lightning in the first place. Kind of like one is screwed either way . This is the second time my boat has suffered from the effects of a lightning strike. About 3 or so years ago I had damage as a result of a strike to a boat 60 or 70 yards away. It was in another slip in this same marina. At that time all nearby boats including power boats incurred some kind of damages to electronics or electrical circuit boards on their boats. That about sums up my direct experience with lightning strikes. I have known several other people who have had their boats hit.

[alaskadog]

My boat was struck by lightning this past Sept. 22 and I made a post in this forum to that effect in which I posed some questions. The mast was struck at the very top. My wife saw the strike out the back window of our condo. The lightning hit the boat approx. 20 yards behind the building instead of the four story building which with the roof stands a little higher than the mast which tops out approx. 50 feet above the water. I have one of the little ionic dissapator gizmos at the top which apparently did little or nothing to ward off this strike. The electrical circuits in the boat are grounded to one of those bronze dynaplates that is on the hull. There were three other sailboats located about 100 yards away in finger piers with similar but slightly lower mast heights than on Sun Dog but they were spared. Although one of those boats was struck last year while mine was spared. When we noticed the storm coming I attached an additional grounding gizmo near the base of the mast. It was a knockoff I made of one commercially available from a Canadian company that I had read about in a question-answer section of Sail Magazine in which Nigel Calder was responding to a question about lightning protection. I also had a battery jumper cable aligator clipped to each of the upper shrouds and tossed overboard. The "gizmo" is a 6" x 8" copper plate, bent in the curvature of the mast to insure good contact with and strapped to the mast. A 10 ft. length of #2 marine grade, rubber coated cable is soldered to the copper plate and on the other end of the cable is soldered a 1 1/2in. by 2 ft. copper pipe. This is tossed overboard and the pipe lay well grounded in the mud. Inspection of the mast at the attachment point of the grounding gizmo revealed a scortch and a penny size nick of aluminum blown off the mast. The inside of the copper plate was scortched as well. Repairs are not yet complete. What has been replaced so far or has been diagnosed as bad is as follows: GPS, VHF antenna (which was blown in two pieces) VHF radio, SSB radio, AM-FM Stereo and CD changer, TV antenna, TV set, tricolor masthead nav light and anchor light(the anchor light was completely blown apart and a hole blown in the high density plastic globe/lens of the nav light.) radar, GPS antenna, chartplotter, autopilot electronics including the fluxgate compass, Heart interface battery monitor, electronic control for the air conditioner as well as one of the circuit boards controlling the air conditioner operation, electronic controls for the refrigerator, the circuit breaker/control panel for all circuits located by the nav table, various fuses that service the hard wiring for some of the circuits inside the boat such as the circuit to the windless and interior lightning. There is some more damage regarding shorts in some of the hard wiring that the technicans are presently trying to trace. The boat was plugged into 50 amp shore power at the time and their was indication of schotching on one of the two 30 amp cables as well as the 50 to 30 amp Marinco adaptor that they may have been damaged so the adjuster called them bad also, though I suspect that they might have been usable. Not damaged was my 402 EPIRB that is mounted inside the boat or a handheld GPS and handheld VHF that were stored in soft pouches in a locker. The boat will have to be hauled out to replace the depth sounder/water temperature transducer. That could happen this week. What would have happened or how much more damage would have occurred had I not had the "gizmo" can only be guessed at. It is obvious that a great amount of electricity was diverted off the mast before it entered the boat. Ironically some of the damage looks as it might have entered certain circuits through the ground wire as opposed to the positive connections. I have also read in similar discussions that the better an object is grounded the more likely it may be to attract the lightning in the first place. Kind of like one is screwed either way . This is the second time my boat has suffered from the effects of a lightning strike. About 3 or so years ago I had damage as a result of a strike to a boat 60 or 70 yards away. It was in another slip in this same marina. At that time all nearby boats including power boats incurred some kind of damages to electronics or electrical circuit boards on their boats. That about sums up my direct experience with lightning strikes. I have known several other people who have had their boats hit.

[Paul L]

Joe, "What would have happened or how much more damage would have occurred had I not had the "gizmo" can only be guessed at." That's exactly what I was thinking. It seems like you did about all a reasonable person could do and a lot more than would normally be done while on passage or in some remote anchorage. After reading your description, I was back on the thought that it doesn't matter what you do. It is capricious and having some decent backup skills is all that is worth doing. Thanks for posting your event. Paul L

[Alan Wheeler]

Everytime this subject comes up, we here every story under the sun. Why? because I think Lightning has every affect under the sun. There is some very excellent info in here and I am not detracting from one single bit of it.
But here are some answers to some of the questions and comments posed.
Firstly, Rick, yes the Microwave front screen is metal and the holes in it are a certain size so as to stop the energy radiating through. The are a short to the frequency length of the microwave. Thus I am not sure how this would pose to a DC with all sorts of frequency spikes radiating through it from a LStrike. But I guess it is better than nothing.
there are many theories and each year, more and more understanding of what takes place is coming to light. One thing now known is that a strike follows the same rules of physics that any electrical potential does. The reason why we don't or haven't "seen" that is only due to the huge electrical pressure involved. Think of it this way. Voltage is trying to flow from one source to another. It can only do that once an path has been established it can flow via. The ability for it to "meet" thuis path is due to its huge pressure that can cause it to "leap" a huge gap. Once this pressure has met the path to ground, it's emmense preesure overwems the path due to resistance. If lightening were to flow through a pure path of no resistance eg. a super conductor, it would flow and dissapate with no additonal side flashes. Because the path is not a super conductor, the voltage potential can not disapate to earth fast enough and the "back flow" of voltage pressure, now closer to other earths, jumps the shorter distances and side flashes accurr.
The diffuser is a difficult one to describe if it is effective or not. A "leader" is a charge that leads from ground up into the air. This is the initial path a high pressure voltage potential follows on it's way to ground. These very fine charged filaments can reach high into the atmosphere froma single point. but if it is difused, it is suggested that the filamnets don't reach so high. So the idea of having this "brush" on top of a high point ie Mast, it so as these leaders are disapated in every direction and hopefull not up as high as a single leader off another high point. the big issue is that this has not been truely proven as of yet.
The next important point is back to the law of physics. The better earth, the shortest path to earth will be the most likely path a voltage potential is going to take.
Now put that in context with the boat at anchor. The anchor is stuck in the mud(earth) and you are providing a metal path from ocean floor to boat to mast top. This path is less resistance than the water provides, so you have a greater chance of becoming a target. However, if you have the anchor up, and you still get hit, then the high pressure does not have a good clear path to ground, so it can do much more damage as it disapates into the water via your boat. So it is a case of damned if you do, damned if you don't.
And finaly, a Farrady cage will work best if it can be grounded as Gord has stated. However, it will still be better than nothing. y the way, many aircraft have been struck with no issue. But there a few stories that suggest one or two aircraft may have gone down due to strikes, so it is not always clear cut.