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Old 06-04-2009, 19:47   #1
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Power lines and mast?

Getting ready to bring home our new purchase to North Carolina and was wondering - what is to close when it comes to mast height and high voltage power lines? Our mast is at 70' and power lines are stated to be 78'. Have not seen anything in the books. Just want to make it home safe.
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Old 06-04-2009, 19:56   #2
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In 1995 I was in the New River in Fort Lauderdale. It was a very damp day with misty rain......Just up the river where it turn left the power lines span the New River.

The Captain and I saw a sailboat go by.....as he made the turn.....PHOOOOMMMMM!!!! The power arced from the line to his mast.....I got a call from our electronics guy to come over and take a look......Every piece of electronics and electrical stuff was blown out......His Clearance? about 10 feet.

The high humidity/mist probably added to the problem/incident
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Old 06-04-2009, 19:59   #3
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I wouldn't worry about an 8' clearance, assuming the charts and tides are correct. I doubt the power from the lines would arc over even a small air gap and not short without actual contact.

If you are concerned check local knowledge to verify the 78' clearance is accurate. Just in case when passing under the wires I would make sure none of the crew is touching any of the rigging, mast, etc and away from any major wiring or electric panels. Might even step back from the wheel for a second as well.
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Old 06-04-2009, 20:01   #4
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Well I just read the post from Chief Engineer and guess I will eat my words. I have been under that same wire with less than 10' clearance and lived to tell the tale.

Hey CE, do you know if that boat's mast was bonded/grounded for lightening protection?
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Old 06-04-2009, 20:01   #5
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You might want to check with the power company. In theory, depending on humidity, the potential difference between the voltage in the cable (which we don't know) and ground (which your mast will be at) could be enough for the power to arc over across a large air gap. I would think 8' of air gap is "safe" but that's a relative concept. I'm sure two feet isn't safe and six feet I've heard called dangerous, but I'm sure the power company will give you a reasonable answer--they really really don't like paying out wereguild.
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Old 06-04-2009, 20:03   #6
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Quote:
Originally Posted by Surf City View Post
Getting ready to bring home our new purchase to North Carolina and was wondering - what is to close when it comes to mast height and high voltage power lines? Our mast is at 70' and power lines are stated to be 78'. Have not seen anything in the books. Just want to make it home safe.
It depends on the voltage. The greater the voltage the greater distance that electricity can arc.

Look at the length of the insulators on the towers. If they are the really long ones...look out. Your asking for trouble if the distance between your mast and the wire is less than the length of those insulators. Some of those wires can be up to 380,000 volts. I would not risk it if the two distances are anywhere near to being close.

I would not bet on 8 feet of air gap being safe if the insulators appear to look 12 feet long.

Problem is, I have no idea how your going to measure the length of those insulators nor how to measure the wires exact height above the water.

As was already mentioned, call the power company first.
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Old 06-04-2009, 20:14   #7
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Is it a tidal waterway? In Aus, cable and bridge clearances are measured at high water springs. Going at low tide would give greater clearance.
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Old 06-04-2009, 20:22   #8
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Is it a tidal waterway? In Aus, cable and bridge clearances are measured at high water springs. Going at low tide would give greater clearance.
Cables also lengthen (lower) as temperatures rise. I wouldn't guess...call the power company. Why bet your life needing to be being correct with four variables?.... the tide, height, voltage and temperature.
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Old 06-04-2009, 21:09   #9
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I will make the call. The height is is measured at MHW. I will make sure I have all the variables in my favor when we skirt under the lines. There is no rush to curl what hair I have left.
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Old 07-04-2009, 09:10   #10
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Or, go at HIGH water, and get a free battery equalization charge while you're there? (VBG)
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Old 07-04-2009, 11:01   #11
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accept delivery...

on the other side of those powerlines.
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Old 07-04-2009, 12:35   #12
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Just had a lecture from a weather guy so this is fresh in my mind... in dry air, you need a potential difference (if that's the right terminology) of about 15,000 volts to jump a one inch gap. Which is why, as he demonstrated, you can safely put your finger right on the outside of a power socket.

OTOH, higher voltage and wetter air probably make a difference.

And we all know what lightning can do (which was the point he was trying to make).


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Old 07-04-2009, 14:28   #13
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Problem is, I have no idea how your going to measure the length of those insulators nor how to measure the wires exact height above the water.
Got a radar and a sextant?
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Old 07-04-2009, 15:07   #14
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I don't recall if it was well bonded

I think the high humidity and mist created a "perfect electrical storm"

Quote:
Originally Posted by skipmac View Post
Well I just read the post from Chief Engineer and guess I will eat my words. I have been under that same wire with less than 10' clearance and lived to tell the tale.

Hey CE, do you know if that boat's mast was bonded/grounded for lightening protection?
BTW are they still running that cruiseboat/faux sternwheeler up the river?

You could tell when it was 10:00....the canned music would start playin "I've been workin on the raiload.....+ EVERY NIGHT when they came to the rail bridge......That and the Steel Drum Music nearly drove me off my rocker......
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Old 07-04-2009, 15:17   #15
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You can always increase your clearance by raising the sails. With the right wind of course.
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