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Old 24-06-2018, 15:18   #1
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How much will braided line length shrink with buried wire?

I have a 30 foot length of 9mm dynex dux Id like to embed a 14awg wire within. The 14awg wire is about 1/8" diameter.

Does anyone have any idea how much the length of this 30' section will shrink when i expand the braid to insert the wire? Ive tried to do calculations with adding volumes and whatnot but Im not sure my calculations make any sense. I keep ending up with about 3 feet of shrinkage, which is quite a bit more than I would have expected.
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Old 24-06-2018, 15:39   #2
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Re: How much will braided line length shrink with buried wire?

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Originally Posted by redpointist View Post
I have a 30 foot length of 9mm dynex dux Id like to embed a 14awg wire within. The 14awg wire is about 1/8" diameter.

Does anyone have any idea how much the length of this 30' section will shrink when i expand the braid to insert the wire? Ive tried to do calculations with adding volumes and whatnot but Im not sure my calculations make any sense. I keep ending up with about 3 feet of shrinkage, which is quite a bit more than I would have expected.

no, sorry, but what is the finished length you require? Is this a backstay antenna?


(Also - I'm curious - will you be doing this by hand, feeding the wire in bit-by-bit, and inchworming the rope down over it?)


I suppose that you could mark off 2 ft on the rope, then thread some wire in, then measure to that 2 ft mark, and that will give you "shrinkage" over 2 ft... multiply by 15, and you have an estimate for 30 ft.


Of course tension and use will stretch it back out some.
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Old 24-06-2018, 16:06   #3
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Re: How much will braided line length shrink with buried wire?

Yes, its a backstay. The turnbuckles are contracted to maximum pull, and can extend a good 8" I'd think, so I was hoping the shrinkage would be somewhere in that range. I'm going to have to milk the braid over the wire bit by bit.

If its really going to be 3' of shrinkage I'm going to have to try a combination of a few things...maybe only bury only a portion, use a smaller gauge wire, or get extension connectors.
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Old 24-06-2018, 17:17   #4
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Re: How much will braided line length shrink with buried wire?

Whether that 14AWG wire is bare, or heavily insulated, can make a huge difference in the total diameter. Since you are dealing with RF...a bare or enameled wire might do. If you're aiming at safety against RF burns....eh, the good stuff is going to be way fatter.
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Old 25-06-2018, 09:48   #5
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Re: How much will braided line length shrink with buried wire?

If I get you right you are trying to set up an SSB aerial by burying 14g copper inside a synthetic back stay right? I tried something very similar and hit to problems. One was that it is incredibly difficult to thread a lone wire inside any rope. Two, if you do manage it the movement in the rope will at some point try to stretch the wire and it beaks. My solution was to use a separate low stretch multi-plat running through a block at the masthead and cleated at the mast foot. I wove the wire back and forth in a stitching action. Excellent transmission and it means you can easily adjust the tension or lower it to check and repair the wire. Also may be that if the mast comes down you can salvage the aerial and drape it over something to send an emergency message!!
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Old 25-06-2018, 10:03   #6
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Re: How much will braided line length shrink with buried wire?

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Two, if you do manage it the movement in the rope will at some point try to stretch the wire and it beaks.
Did you actually experience the wire breaking inside a synthetic backstay? It seems bizzare that a backstay would move enough to cause this, and is surprising because I've heard this is a fairly common technique. Is there something those that are having success with this are doing to mitigate that?
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Old 25-06-2018, 11:44   #7
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Re: How much will braided line length shrink with buried wire?

Don't know how you came up with 3' of shrinkage but I'm not to surprised. I fatten my Spectra single braid life lines with short pieces 1/8 line to shorten them up after the turnbuckles have run out of thread. A 2' length of line fed inside the lifeline is often enough, or even too much sometimes. It's easy to adjust by pulling some back out.
We don't use lifeline gates and climb over the them instead, so they stretch.
I would be a little concerned about how well you taper the ends and the exit of the wire. That could be the spot the stay fails if it's not proper.
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Old 26-06-2018, 06:50   #8
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Re: How much will braided line length shrink with buried wire?

you might consider using mil spec Teflon insulated wire, it should be easier to insert.
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Old 27-06-2018, 01:09   #9
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Re: How much will braided line length shrink with buried wire?

Like you, assuming constant volumes, then the length changes with the square of the change in diameter. So 10% change in diameter, 20% in length. Or in your case going from 9mm up to 12 is 30% on diameter, almost 80% in length! So 17' left from 30. If you get more fresh air in there then the difference will not be as much but still impressive..
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