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  #31  
Old 10-24-2013
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Re: Lightning protection- precision 18

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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".
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  #32  
Old 10-24-2013
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Re: Lightning protection- precision 18

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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.
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Last edited by smurphny; 10-24-2013 at 03:00 PM.
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