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Go Back   SailNet Community > General Interest > General Discussion (sailing related) > Lightning protection- precision 18
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Topic Review (Newest First)
10-24-2013 03:56 PM
smurphny
Re: Lightning protection- precision 18

Quote:
Originally Posted by manatee View Post
Why a temporary Faraday cage? Back in ham radio days, our entire rig lived inside one. Why not make one out of wire mesh to protect your electrics all the time? If lightning approaches, unplug antennae & power, you're done. Nothing to search for, assemble, install, disassemble and store. Maybe make it big enough to store at least some of your portables, too.

Just a thought, your mileage may vary.
As mentioned above, I do disconnect everything: antennas, power supplies, grounds and the copper foil ground plane of the SSB. I'm thinking more along the lines of individual containments for pieces of equipment. For my small h/h gps and my h/h vhf, I've just cut empty food cans that telescope inside one another. By cutting two cans and crimping the end of one, I've been able to create really tight tubes, the smaller fits inside the slightly larger. Wrapping the elec. device in 6 mil poly in the smaller tube and wrpping it in 6 mil poly, creates two insulated layers. The can setup is easy to open and close and should provide Faraday protection. For my EPIRB, small computer, plotter, and Pactor, I just found an old heavy duty steel Milwaukee drill case (drill died long ago)which I've fitted with padding to fit the devices. With the devices in plastic bags, it should at least provide one layer of protection. I have to believe the heavy steel case is better than aluminum. As for the SSB, it's too darned big to be lifting into some sort of shielding every time a storm gets near so I think I'll make a 1/2" hardware cloth enclosure for it. The antenna tuner is really not in a very accessible place, so attempting to protect the SSB is probably futile. Hope I never have to test the theory but it's worth experimenting.
10-24-2013 11:42 AM
fallard
Re: Lightning protection- precision 18

Quote:
Originally Posted by Maine Sail View Post
You'd be amazed at the number of folks who swear by paper as a back up but I then discover their steering compass compensators were tossed off in the strike. Paper won't do much good if your compass is toast and this very often happens in a good strike..

It's not just the electric field that is intense during a strike, but the magnetic field as well (they are associated). As others have said, lots of strange things can happen in a strike. After our last strike, during the initialization of our autopilot/flux gate compass, we discovered a significant offset that eventually was traced to magnetization of the steel tubing in beach chairs that were stored in close proximity (<2') to the new flux gate compass. Our Ritchie pedestal compass (~6-7' away) appeared to be unaffected.

So, even if your liquid-filled compass survived, there may be external factors affecting its accuracy.

You can check for extraneous magnetic fields in your boat with a handheld compass. You might do this near your installed electronics to make sure you are not seeing magnetic interferences. A permanent magnet speaker from a VHF, for example, might be a problem if it is too close to a compass--whether electronic or liquid-filled. I had this problem a number of years ago in a smaller boat and ended up removing the installed speaker and placing a remote speaker about 4' away.

BTW, aluminum doesn't attenuate magnetic fields. Your compass will still work inside an aluminum foil "faraday cage".
10-24-2013 11:12 AM
manatee
Re: Lightning protection- precision 18

Quote:
Originally Posted by smurphny View Post
I would really like to further investigate the Faraday Cage theory. Aluminum foil and microwave shielding sound like reasonable ideas but I wonder whether there have been any studies into the best designs/shape of portable, temporary Faraday gizmos.
Why a temporary Faraday cage? Back in ham radio days, our entire rig lived inside one. Why not make one out of wire mesh to protect your electrics all the time? If lightning approaches, unplug antennae & power, you're done. Nothing to search for, assemble, install, disassemble and store. Maybe make it big enough to store at least some of your portables, too.

Just a thought, your mileage may vary.
10-24-2013 10:56 AM
smurphny
Re: Lightning protection- precision 18

Quote:
Originally Posted by boatpoker View Post
I've taken courses from several well respected marine electrical experts, a couple of whom are also recognized "lightning" experts (court recognized).

One word that is used repeatedly in these courses and the same word is used in all scholarly publications on the issue ...... "theory"

I've come to believe that most published information on the subject is at best either guess work or theoretical. I was involved in one case several years where a sailboat was hit twice within ten minutes (over 200 witnesses) and the same boat had been hit twice before. With the odd history of this boat and some curious issues regarding its location at time of hits and even odder damage, we could not get any of the recognized experts to testify.

So I will stick to my mantra .. 60,000,000volts, 60,000amps, hotter than the surface of the sun at near the speed of light .. get to hell out of the way
There is only one explanation for the boat hit multiple times: Someone pissed off Zeus!
10-24-2013 10:51 AM
smurphny
Re: Lightning protection- precision 18

In doing a little research, it seems that wrapping something in aluminum foil can be effective in blocking electromagnetic waves but the aluminum (or the inside of a microwave/oven) cannot be in contact with the device. A plastic bag or some sort of insulator needs to be between the device and the Faraday shield. Even better is to do this in more than one layer:insulator-metal-insulator-metal. I think I'm going to keep my little old Garmin GPS12 handheld in such an arrangement from now on and maybe even make up a more substantial box from some aluminum sheeting. One of my computers, a Dell Mini, would also be easy to shield like this as would the EPIRB. The EPIRB and small GPS usually reside in my ditch bag, so making shields for these should be pretty easy. It's worth a try anyway. If even one device survived a hit, it might make a big difference. Anyway, don't abandon paper and DR! :-)
10-24-2013 10:28 AM
gbgreen59
Re: Lightning protection- precision 18

Aren't airplanes designed successfully to take lightning hits without destroying electronics and damaging structure?

Found this:
According to statistics published by the Royal Canadian Air Force, a plane can be struck by lightning on average every 1,000 to 3,000 flight hours. For commercial aircraft, that’s equivalent to one strike per aircraft per year. Although The Boeing Co. (Chicago, Ill.) has reported that the probability of a worst-case strike could be as infrequent as once every 10 to 15 years, aircraft designs must be able to withstand such a strike.
10-24-2013 09:43 AM
Maine Sail
Re: Lightning protection- precision 18

Quote:
Originally Posted by smurphny View Post
I would really like to further investigate the Faraday Cage theory. Aluminum foil and microwave shielding sound like reasonable ideas but I wonder whether there have been any studies into the best designs/shape of portable, temporary Faraday gizmos. I always completely disconnect the SSB and VHF as a minimal action when I see a storm approaching but if some kind of temporary "tent" for components could be designed, it might be worth trying to construct something like this for individual units. Apparently, just the electrical field created by a near-miss is enough to fry semiconductors. If circuits could be somehow shielded, even minimally it might save some of the electronics, especially those needed to call for help after a strike.

Has anyone here had EPIRB damage in a strike? I would think they are just as susceptible as everything else.
Our ditch bag GPS was completely encased in aluminum foil & unplugged, it was fried.

Our laptop was on top of the nav-desk unplugged, it was fried

Our iPod was inside the nav-desk unplugged, it was fried

Our EPIRB was in its holder on the bulkhead unplugged, it was fried

Our GPS MAP 176 was in the nav-desk unplugged, it was fried

Our GPS 76 was in the nav-desk unplugged, it was fried

Our Ritchie steering compass on the pedestal was hit so hard it was off by a dangerous level, on all points



You'd be amazed at the number of folks who swear by paper as a back up but I then discover their steering compass compensators were tossed off in the strike. Paper won't do much good if your compass is toast and this very often happens in a good strike.. This is one major area that insurance surveyors miss almost every time.

New compensators are not in-expensive and neither is having it professionally re-swung. I wound up ordering a new compensator set for ours and then having it professionally swung. "Theory" is they will eventually get back to where they were before the strike but how are you to know when they are done getting back to normal? We now keep two hand held compasses in an Army issue metal ammunition ditch box along with other stuff we don't want fried in a strike. The "theory" being that metal works much better as a Faraday cage than aluminum does. I hope not to test that theory cause there is a lot that won't fit in there.......

We had a major strike but the mast is bonded to the keel with 2/0 wire and we suffered zero hull damage. Our thru-hulls are not bonded.
10-24-2013 09:13 AM
smurphny
Re: Lightning protection- precision 18

I would really like to further investigate the Faraday Cage theory. Aluminum foil and microwave shielding sound like reasonable ideas but I wonder whether there have been any studies into the best designs/shape of portable, temporary Faraday gizmos. I always completely disconnect the SSB and VHF as a minimal action when I see a storm approaching but if some kind of temporary "tent" for components could be designed, it might be worth trying to construct something like this for individual units. Apparently, just the electrical field created by a near-miss is enough to fry semiconductors. If circuits could be somehow shielded, even minimally it might save some of the electronics, especially those needed to call for help after a strike.

Has anyone here had EPIRB damage in a strike? I would think they are just as susceptible as everything else.
10-24-2013 12:54 AM
fallard
Re: Lightning protection- precision 18

Agree with Maine Sail that there are no iron clad guarantees with lighting. That would include through-hull grounds and aluminum foil wrapped electronics. Nonetheless, you improve your chances with these techniques.

That said, my in-water grounding plates are much smaller than desired by folks like Dr. Thomson, but they obviously were somewhat effective. I would agree that an aluminum foil wrap and your oven are far from ideal faraday cages for several reasons, but haven't seen evidence that they do not provide some protection--even if minimal.
10-23-2013 11:43 PM
Maine Sail
Re: Lightning protection- precision 18

Quote:
Originally Posted by boatpoker View Post
I've taken courses from several well respected marine electrical experts, a couple of whom are also recognized "lightning" experts (court recognized).

One word that is used repeatedly in these courses and the same word is used in all scholarly publications on the issue ...... "theory"
Amen! This is why I wish we could get the insurance companies to track strikes and collect better data as to what the boat had for systems, damage etc...

Interestingly in our strike the GPS that was in my ditch bag was wrapped in aluminum foil then inserted into a ZipLock bag with a bag of desicant to keep it dry. The "aluminum foil theory" that was purported to me to never fail, FAILED.........

As I always say lightning simply does what it wants. We can only try to minimize the damage..
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