SUBSIM Radio Room Forums - View Single Post - Lightning can strike twice in the same place

Etienne · 12-19-05, 06:32 PM

Damn. My long and researched reply was just eaten up by IE. Grrr.

Anyhow.

Ok, sorry about the farraday thing, I got myself confused with the car.

I do have it here, in my electricity textbook, that a sailboat mast will act as a lightning rod, protecting a cone around it from lightning strikes. The mast must establish a continuous electrical link with the water, either through grounding plates (Non-conducting hulls) or through the hull itself (Well, the sacrificial anodes, if you want to be precise).

I cannot find any reference here to the grounding or non grounding of radio antenna, except for a yachting manual advising to disconnect and ground all antennas in case of thunderstorm. I know that on commercial vessel, this is not done. I am under the impression that some time of antenna require grounding, but I can't find a reference to back that up at the moment.

I assume the periscope would be properly grounded for just this eventuality. I don't see why the electricity would go scope-hull-crew-hull-anode-water and not just scope-hull-anode-water. If it hit a crewmember directly, then yes, he's toast. Otherwise, since the boat is wired to be as conductive to lightning as possible, essentially, it's not that dangerous. I'd stay away from the scope and the aerials, that's it. Staying away from any electrical object and turning off the electrical are two impossible concept : The very floor you're standing on is metal, and you need electricity anyway.

Do keep in mind that the boat's electrical system is completly independent of the outside world ; there are no power wires on a pole outside to bring in a surge, and the electrical system isn't grounded to the boat itself - You can stick a finger in a socket aboard a ship, and you won't feel a thing, since the circuit will not close. (Unless there's a ground fault) So a lightning going through the hull wouldn't be directly connected to the electrical system.

I don't know, either, if ships are hit by lightning that routinely. Surprisingly, I spent something like two months in stormy weather last winter and never really noticed it happening, that I can remember... I'll ask around about that.

Anyway, I'll do some research on the antenna grounding thing, you've got me curious

.

'tienne

P.S. The jumper cable trick is only useful when your mast isn't already grounded. I don't think boats are still launched with that set-up, except day cruisers, maybe.

12-19-05, 06:32 PM	#7
Etienne Seasoned Skipper Join Date: Jan 2002 Location: Canada Posts: 695 Downloads: 1 Uploads: 0	Damn. My long and researched reply was just eaten up by IE. Grrr. Anyhow. Ok, sorry about the farraday thing, I got myself confused with the car. I do have it here, in my electricity textbook, that a sailboat mast will act as a lightning rod, protecting a cone around it from lightning strikes. The mast must establish a continuous electrical link with the water, either through grounding plates (Non-conducting hulls) or through the hull itself (Well, the sacrificial anodes, if you want to be precise). I cannot find any reference here to the grounding or non grounding of radio antenna, except for a yachting manual advising to disconnect and ground all antennas in case of thunderstorm. I know that on commercial vessel, this is not done. I am under the impression that some time of antenna require grounding, but I can't find a reference to back that up at the moment. I assume the periscope would be properly grounded for just this eventuality. I don't see why the electricity would go scope-hull-crew-hull-anode-water and not just scope-hull-anode-water. If it hit a crewmember directly, then yes, he's toast. Otherwise, since the boat is wired to be as conductive to lightning as possible, essentially, it's not that dangerous. I'd stay away from the scope and the aerials, that's it. Staying away from any electrical object and turning off the electrical are two impossible concept : The very floor you're standing on is metal, and you need electricity anyway. Do keep in mind that the boat's electrical system is completly independent of the outside world ; there are no power wires on a pole outside to bring in a surge, and the electrical system isn't grounded to the boat itself - You can stick a finger in a socket aboard a ship, and you won't feel a thing, since the circuit will not close. (Unless there's a ground fault) So a lightning going through the hull wouldn't be directly connected to the electrical system. I don't know, either, if ships are hit by lightning that routinely. Surprisingly, I spent something like two months in stormy weather last winter and never really noticed it happening, that I can remember... I'll ask around about that. Anyway, I'll do some research on the antenna grounding thing, you've got me curious . 'tienne P.S. The jumper cable trick is only useful when your mast isn't already grounded. I don't think boats are still launched with that set-up, except day cruisers, maybe.