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Old 25-11-2014, 06:36   #46
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Re: Hit by lightning this afternoon in Botany Bay

Ha ha! It sounds like the consensus on lightning protection is much the same as the consensus on anchors :-)

I'm finding it particularly interesting to hear from those of you who have been hit and who didn't have any grounding and are still OK. I have been hit once, on a boat with a wooden mast and am pretty sure the large copper grounding strip saved us. The consensus among civil engineers is also pretty much that grounding is a good thing. Some large buildings get hit several times a year. They're all well grounded and they seem to come out fine. So, i think i'll do something......... maybe a plate of some sort.
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Old 25-11-2014, 07:04   #47
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Re: Hit by lightning this afternoon in Botany Bay

We were hit while sitting aground about a mile north of the Chub Cay, Bahamas marina. The aground part is a different story.
I remember looking at the large steel structures just a half mile away on the cay as a line of thunderstorms approached from the east. At least we're not the the tallest structure around, I thought. Surely the lightning will hit that radio tower way before it would hit us. That thing is certainly grounded.
Wrong. We were sitting at the galley table, with the steel compression post down through the middle, bolted to the mast above. Felt like the universe got whacked with a bat or something. Big physical whack. My hand got tingled, her hand and foot got mild shocks, and one of her ears rang for about 36 hours. Immediate smoke from bad wiring behind VHF. More smoke from battery monitor wiring in one engine room. Primary point of contact on mast was 3 ft. metal VHF whip, which vaporized. Took out a lot of the 12v equipment, including everything on the mast. Solar chargers. Alternators. SSB. VHF. Radar, Lights, etc. I'm still finding things that are failing and I can sometimes see where a big spike might have shortened some life spans. The previous owners-added wiring on this boat is pretty bad, and has been since we bought it. One long term effect is that the batteries all died within a year of the strike, and they were only two and a half year old lead acids. I think the shock of the strike knocked all the gunk off the plates and it settled to the bottom and built up or something. I don't know. They seemed to short and boil away really quickly after that.

Here's a question: I've been using the replacement whip antenna clamped to a rail, as I haven't gotten around to climbing the mast yet. Bwock bwock bwock. It will be a pain to pull the big coax cable and replace it. It's the large diameter, low loss stuff. I forget the number at the moment. I'm not on the boat right now. What would be the chances that the existing VHF antenna cable would still be useful if I clean up and reterminate the top end with a new connector? I am hoping that the lightning bolt jumped to ground up at the antenna mounting bracket, and didn't continue on down the longer path through the jacketed coax. So the end is blasted, but not the rest of it, perhaps.
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Old 25-11-2014, 07:38   #48
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Re: Hit by lightning this afternoon in Botany Bay

Quote:
Originally Posted by Canibul View Post
We were hit while sitting aground about a mile north of the Chub Cay, Bahamas marina. The aground part is a different story.
I remember looking at the large steel structures just a half mile away on the cay as a line of thunderstorms approached from the east. At least we're not the the tallest structure around, I thought. Surely the lightning will hit that radio tower way before it would hit us. That thing is certainly grounded.
Wrong. We were sitting at the galley table, with the steel compression post down through the middle, bolted to the mast above. Felt like the universe got whacked with a bat or something. Big physical whack. My hand got tingled, her hand and foot got mild shocks, and one of her ears rang for about 36 hours. Immediate smoke from bad wiring behind VHF. More smoke from battery monitor wiring in one engine room. Primary point of contact on mast was 3 ft. metal VHF whip, which vaporized. Took out a lot of the 12v equipment, including everything on the mast. Solar chargers. Alternators. SSB. VHF. Radar, Lights, etc. I'm still finding things that are failing and I can sometimes see where a big spike might have shortened some life spans. The previous owners-added wiring on this boat is pretty bad, and has been since we bought it. One long term effect is that the batteries all died within a year of the strike, and they were only two and a half year old lead acids. I think the shock of the strike knocked all the gunk off the plates and it settled to the bottom and built up or something. I don't know. They seemed to short and boil away really quickly after that.

Here's a question: I've been using the replacement whip antenna clamped to a rail, as I haven't gotten around to climbing the mast yet. Bwock bwock bwock. It will be a pain to pull the big coax cable and replace it. It's the large diameter, low loss stuff. I forget the number at the moment. I'm not on the boat right now. What would be the chances that the existing VHF antenna cable would still be useful if I clean up and reterminate the top end with a new connector? I am hoping that the lightning bolt jumped to ground up at the antenna mounting bracket, and didn't continue on down the longer path through the jacketed coax. So the end is blasted, but not the rest of it, perhaps.
Lightening just doesn't seem to follow logic, at least as we perceive it. My house is in the lowest spot in my neighborhood with much higher spots and tall trees starting 50 yards away and getting higher as you move away. I had three lightening strikes on trees in my yard over a 5 year period. All causing extensive damage to electronics in the house and twice exploded the main water line at the meter.

Regarding your antennae cable, I would hesitate to short change my VHF system and just ran new coax up my mast (of course my mast is down so was a relatively easy job once I got the PVC conduit installed which wasn't so easy). If you want to give it a go I would first cut off the bad ends and take a look. If you can cut back to nice clean wire, insulation looks good, braid good, etc then I would be encouraged. Next test is to test resistance between the braid and center wire to see if there are any shorts somewhere up the cable. If both of those look good then might be worth a try.
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Old 25-11-2014, 09:52   #49
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Re: Hit by lightning this afternoon in Botany Bay

One other thing you might want to look at, is your water line. To be sure that the lightning did not blow small holes in your fiberglass at the water line, trying to escape to ground.
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Old 25-11-2014, 10:08   #50
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Re: Hit by lightning this afternoon in Botany Bay

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One other thing you might want to look at, is your water line. To be sure that the lightning did not blow small holes in your fiberglass at the water line, trying to escape to ground.
Yes, happened to a friend. Didn't leave a hole but melted the glass and resin at a couple of spots leaving a clear hole covered with a very thin layer of melted boat hull. No water but you could clearly see light through the round holes it made. About 1/2" diameter.
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Old 25-11-2014, 11:04   #51
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Re: Hit by lightning this afternoon in Botany Bay

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Yes, happened to a friend. Didn't leave a hole but melted the glass and resin at a couple of spots leaving a clear hole covered with a very thin layer of melted boat hull. No water but you could clearly see light through the round holes it made. About 1/2" diameter.
Is the copper bottom paint what's going on?
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Old 25-11-2014, 11:20   #52
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Re: Hit by lightning this afternoon in Botany Bay

Lots of pin holes at the waterline, put a copper strap around the boat at the waterline and tie all the stays to the copper strap. Current coming down the stays will cause opposing EMPs that could protect electronics. Electromagnetic pulse acronym is EMP
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Old 25-11-2014, 11:23   #53
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Re: Hit by lightning this afternoon in Botany Bay

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Originally Posted by westwinds View Post
Lots of pin holes at the waterline, put a copper strap around the boat at the waterline and tie all the stays to the copper strap. Current coming down the stays will cause opposing EMPs that could protect electronics.
I hope that was in gest?
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Old 25-11-2014, 11:50   #54
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Re: Hit by lightning this afternoon in Botany Bay

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I hope that was in gest?
Not in jest, lighting does not follow Ohm's law for direct current. A lightning pulse is of such sort duration that we are dealing with radio frequencies around 200,000 Hertz where surface effect for conductors happens. That is why you have pin holes at the waterline.
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Old 25-11-2014, 11:57   #55
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Re: Hit by lightning this afternoon in Botany Bay

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Is the copper bottom paint what's going on?
Don't think so in this case. His little window (DIY glass bottom boat anyone?) was just above the waterline and bottom paint as the boat sat at rest at the dock.
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Old 25-11-2014, 13:20   #56
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Re: Hit by lightning this afternoon in Botany Bay

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Originally Posted by westwinds View Post
Not in jest, lighting does not follow Ohm's law for direct current. A lightning pulse is of such sort duration that we are dealing with radio frequencies around 200,000 Hertz where surface effect for conductors happens. That is why you have pin holes at the waterline.
I was referring to rapping a copper strip around the water line. Sounded highly impractical.

A good sold ground to a grounding plate makes more sense. the OP's idea about keel bolts encased in a fiberglass keel, makes no sense.

I have no idea what lightning seeks. I'm assuming the shortest path to ground. It is conventional thinking. I'm not convinced sticking a grounded rod up in the air is sensible.

I've had both ground and ungrounded masts. I think it's a crap shoot. I had my pickup truck hit while driving down the road. Why? Wrong place at the wrong time? I didn't feel a thing. Guess I'm just a lucky SOB.
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Old 25-11-2014, 13:44   #57
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Re: Hit by lightning this afternoon in Botany Bay

I think trying to influence the path of a thunderbolt is like trying to influence the path of a steel rifle bullet by placing a magnet near it's path!
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Old 25-11-2014, 13:52   #58
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Re: Hit by lightning this afternoon in Botany Bay

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I think trying to influence the path of a thunderbolt is like trying to influence the path of a steel rifle bullet by placing a magnet near it's path!
I think it is a little better than that. Consider that once lightning has reached the top of the mast, the probability is very high that it continues down the mast rather than jumping out sideways all around and finding other paths to take. The mast is working to influence its path to ground.

It is not a giant leap to imagine that once lightning has gone down the mast, one can have some influence as to how it exits the last couple of feet to ground.

If the above wasn't true, then all buildings, communications towers, etc would never be useable.

Unless you actually are talking about thunderbolts - those require anechoic ducting to influence…

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Old 25-11-2014, 14:05   #59
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Re: Hit by lightning this afternoon in Botany Bay

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I think it is a little better than that. Consider that once lightning has reached the top of the mast, the probability is very high that it continues down the mast rather than jumping out sideways all around and finding other paths to take. The mast is working to influence its path to ground.

It is not a giant leap to imagine that once lightning has gone down the mast, one can have some influence as to how it exits the last couple of feet to ground.

If the above wasn't true, then all buildings, communications towers, etc would never be useable.

Unless you actually are talking about thunderbolts - those require anechoic ducting to influence…

Mark
One big difference is towers and steel framed buildings have a lot more steel IE path to ground and are also very well grounded so power goes easily and directly to ground. Sailboats have a much smaller and usually more convoluted path to ground hence the random nature of the results. I have read reports of boats bonded and grounded that the current did not follow the direct path to ground and boats unbounded that had the strike mostly exit the through hulls.

I also seem to recall some very negative reports about what can happen with ground plates in a lightening strike but cannot recall the issue. Any comments on this?
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Old 25-11-2014, 14:19   #60
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Re: Hit by lightning this afternoon in Botany Bay

What about side flashes? There was that boat off Florida with a young man that sunk where it was believed he was knocked unconscious or killed due to a side flash. Can't find the thread now, but how can one prevent that? A rubber suit? Placing yourself wherever in the hull is furthest away from the mast (presumably the quarterberth)?
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