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Начало » Сделай кайт » Самодельщики » Тесты: почему стропы лучше зашивать, чем вязать узлы
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| Re: Тесты: почему стропы лучше зашивать, чем вязать узлы [сообщение #18892 является ответом на сообщение #13549] |
Sun, 05 September 2010 12:08   |
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Счел целесообразным привести стаью полностью:
| Цитата: |
Date: Thu, 1 Jun 1995 13:32:35 -1000
From: daveculp@bdt.com (Dave Culp)
Message-Id: <daveculp-0106951632480001@daveculp.dial-up.bdt.com>
Organization: Beckemeyer Development, Oakland CA
Subject: Breaking Lines (was Re: The Bowline Knot)
I hadda try to put an end to all this. I spent a couple of hours last nite
making, and breaking, knots and splices in 800 lb Spectra. I used a
hydraulic jack set-up with carefully designed turning blocks and polished
cylinders so as not to abrade any of the samples. Though I didn't have a
strain guage to measure actual breaking strains, the relative resistance
of the jack handle should serve. I broke 2-4 samples of each type.
I learned the following:
1) The bowline does indeed suck, at least in Spectra (Dyneema). In every
instance, the knot slipped *long* before anything broke. without a stopper
knot in the end of the line, it just slipped off the end. With a stopper
knot, it slipped until the loop was closed and then broke at the knot.
2) With a properly sleeved and stopper-knotted overhand-on-the-bight (a
perfectly normal kite knot) the knot held (did not slip), but always broke
at the knot. Using the actual breaking of the bare spectra as a guide,
this broke at about half to two-thirds of the line's strength.
3) no-knot loops (splices) are *very* strong, in each case the line broke
outside (but near) the splice. (*Big* bang when full strength line/splices
break!)
4) Nop Velthuizen's sewn back loops (sleeved as normal, then simply folded
back and sewn together with zig-zag stitch) was *every bit* as strong as
splices. The line always broke first. I think I've tied my last splice!
Couple of caveats: Use good quality nylon thread, ordinary sewing thread
broke about as easily as knots. I tried sewn lengths from 2" to 6" (25 to
75 line diameters). It made no difference. Even the very short sewn loops
outperformed the line itself. I made 3 passes of the sewing machine on
each sample.
The absolute strongest sample I tried was some old Kevlar rated at 500
pounds, with spliced loops. It's actually the same diameter as the 800
pound (rated) Spectra, and easily 4-5 times the cross-sectional area of
some 300 pound (rated) Kevlar I use. I'm sure it was under-rated; I was
worried that it would break the 2000 pound rated jack. *BIG* bang!
In every sample which did not break at the knot, the line broke near the
splice/loop. Don't know if this was coincidence, test specific, or what.
Conclusions: Stop tying knots, folks, move down one-third in your line
sizes and just sew the loops in. Nop has been doing this all along, and
he's right.
Dave Culp
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Date: Tue, 6 Jun 1995 06:23:22 -1000
From: bchilders@aol.com (BChilders)
Message-Id: <3r1vdq$7r5@newsbf02.news.aol.com>
Organization: America Online, Inc. (1-800-827-6364)
Subject: Re: Breaking Lines (was Re: The Bowline Knot)
Dave posted:
>
...[lots of good stuff deleted]...
>
>Conclusions: Stop tying knots, folks, move down one-third in your line
>sizes and just sew the loops in. Nop has been doing this all along, and
>he's right.
>
>Dave Culp
>
OK,
I thought I'd try this sewn splice loop and had a couple of
observations and questions.
First, the obligatory ASCII drawing:
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I'm trying this on 150lb and 300lb lines (spectra) with sleeve (20" dac).
I used a good quality (strong) nylon thread.
Observations:
1) The sleeved line is side by side as it goes under the foot of the
sewing machine. The zigs go through sleeve and line on one side and
the zags through sleeve and line on the other (as the zig-zag stitch
is
made.)
2) It may be best to sew only one end loop of the lines first (with
regular knotted loops at the other end) and fly the lines a while
until
they are properly stretched and can be equalized.
3) Continue to overhand the bitter end of the line with sleeve. I marked
the sleeve during the final equalization process and didn't want it
moving relative to the line.
4) I don't think I would try this with much amaller line. Stretched 80
or
100lb line is a pretty small target. (Dave, I'm not sure what 25 to
75
line diameters means.)
Questions:
1) Is observation 1 the same way Nop and Dave did it?
2) What risk is there that I'm weakening the spectra by cutting fibers
with the needle as I sew?
3) How much stitching is needed to be secure with, say, a 300lb line?
(Dave, I'm not sure what 25 to 75 line diameters means.) I think
I ended up with about a 4 inches passed over 3 times. Is there such a
thing as too much.
Buck Childers bchilders@aol.com
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Date: Tue, 6 Jun 1995 13:08:10 -1000
From: nop@euronet.nl (Nop_Velthuizen)
Message-Id: <nop.39.0017238A@euronet.nl>
Organization: Euronet Internet
Subject: Re: Breaking Lines (was Re: The Bowline Knot)
Buck Chiders post's:
>First, the obligatory ASCII drawing:
>
> // \\
> || ||
> || ||
> || ||
> \\ //
> |||
> |X|
> |X|
> |X|
> |X|
> |X|
> |X|
> |||
> ||\\
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> ||
>
>I'm trying this on 150lb and 300lb lines (spectra) with sleeve (20" dac).
>I used a good quality (strong) nylon thread.
>Observations:
> 1) The sleeved line is side by side as it goes under the foot of the
> sewing machine. The zigs go through sleeve and line on one side and
> the zags through sleeve and line on the other (as the zig-zag stitch
>is
> made.)
> 2) It may be best to sew only one end loop of the lines first (with
> regular knotted loops at the other end) and fly the lines a while
>until
> they are properly stretched and can be equalized.
> 3) Continue to overhand the bitter end of the line with sleeve. I marked
> the sleeve during the final equalization process and didn't want it
> moving relative to the line.
> 4) I don't think I would try this with much amaller line. Stretched 80
>or
> 100lb line is a pretty small target. (Dave, I'm not sure what 25 to
>75
> line diameters means.)
>Questions:
> 1) Is observation 1 the same way Nop and Dave did it?
YES it is.
> 2) What risk is there that I'm weakening the spectra by cutting fibers
> with the needle as I sew?
I have not seen the results under a microscope, but the test-results show that
any damage that might occur is minimal.
> 3) How much stitching is needed to be secure with, say, a 300lb line?
In fact his is the most difficult question. it depends on two main variables:
a) Strength of sewing thread.
b) Number of stitches per inch
Some other points of influance could be the braid of the Spectra. Is it 8, 12
or 16 strands? How many braids per Inch etc.
For a 150 to 300 lb line I would use 3 inches of Zig Zag stich (only passing
over the line twice).
MAZZEL NOP
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Date: Wed, 7 Jun 1995 11:45:05 -1000
From: Dave Culp <daveculp@bdt.com>
Message-Id: <3r56l1$14c@bdt.bdt.com>
Organization: Beckemeyer Development, Oakland CA
Subject: Re: Breaking Lines (was Re: The Bowline Knot)
Buck Childers writes:
>1) The sleeved line is side by side as it goes under the foot of the
> sewing machine. The zigs go through sleeve and line on one side and
> the zags through sleeve and line on the other (as the zig-zag stitch
>is made.)
I stacked the line so each stitch went through both sides (difficult to keep
stacked, probably results in strongest (and thus shortest) set-up)
> (Dave, I'm not sure what 25 to 75 line diameters means.)
If line is 2 mm in diameter (the 800 lb), for instance, 25-75 line diameters
means the sewn length is 50-150 mm long (2-6")
> 2) What risk is there that I'm weakening the spectra by cutting fibers
> with the needle as I sew?
I think minimal, too, but suggest using "ball point" needle, which has
miniture round point; supposed not to snag regular fabric (says my wife), and
thus not to cut fibers. I don't think any puny sewing machine needle could
cut spectra, anyways...
> 3) How much stitching is needed to be secure with, say, a 300lb line?
> (Dave, I'm not sure what 25 to 75 line diameters means.) I think
> I ended up with about a 4 inches passed over 3 times. Is there such a
> thing as too much.
I did same as you, Nop suggests less. I think he's right.
Dave Culp
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