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sync
Jul 15, 2004, 3:26 PM
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Recently, I was discussing the various rappel knots with another member of the UW Hoofers and another member mentioned that he had access to a machine in the engineering building that would allow us to test some knots. It could stretch a sample, increasing the force on it, and give us a measurement of the force versus elongation. So, we decided to test a few knots.
Unfortunately our test setup wasn't ideal and in most trials we had the rope fail at the position where it was held before it failed at the knot. We will be coming up with a new setup soon and will retry the experiments.
For now, though, I show some pictures of the European Death Knot test that we did. Because the rope stretched so much, we had to set up the rope in this manner, with a small loop. The rope is held at top and bottom over links (this is where the rope failed most of the time - we need to use something that makes for a more gradual bend in the rope) which are pulled apart by the machine - to a maximum of 10,000 pounds of force. Note that this is a gradual increase of the force and most likely does not represent the same effects as shock loading the knot. Note also that this is an old, well-used rope.
Image 1: The starting position (this is not the same loop as the ones shown in the next two photos but it gives you the idea of the setup).
http://img78.photobucket.com/...esting/IMG_3404b.jpg
Image 2: After failure of the rope at the knot - this occurred at about 4000 pounds of force. Several of the threads in the core broke and we could hear a sharp snapping sound as they did.
http://img78.photobucket.com/...esting/IMG_3415b.jpg
Image 3: The rope and knot afterwards.
http://img78.photobucket.com/...esting/IMG_3424b.jpg
The most interesting thing to note in this experiment is that we measured the tails on the knot before and after the testing and they were five inches shorter after the test. And the tails were pulling through at a fairly low load (a couple hundred pounds). So, when using the EDK, make sure to put long tails on it.
We also tested the Flat Figure 8 and Flat Double Fisherman's. Unfortunately, these failed at the link rather than the knot. However, they pulled at most one inch of tail.
When we get a new setup and retest, I'll post more pictures and analysis.
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tradmanclimbs
Jul 15, 2004, 3:50 PM
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Really supprised that you got the rope to fail with an EDK. In all my tests the tails simply pulled through quite easily.
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sarcat
Jul 15, 2004, 3:57 PM
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Hey great stuff. I'll continue to use double fisherman's knots.
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sync
Jul 15, 2004, 4:02 PM
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In reply to: Really supprised that you got the rope to fail with an EDK. In all my tests the tails simply pulled through quite easily.
Well, I don't want to interpret it too much until we try again with a new setup. But it looks like what happened was that the knot constricted enough to stop the pull through of the tails and then caused the rope to break at the severe turn caused by the tight knot.
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timstich
Jul 15, 2004, 4:03 PM
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A much better test was performed that tested the overhand knot that allowed for various sloppy dressings and tail lengths as I recall. All resulted in successive capsizing and eventual breaking of the rope at obscenely high loads. I can't find the link to the results, but they certainly supported the contention that the overhand is an excellent knot for setting up rappels.
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shakylegs
Jul 15, 2004, 4:18 PM
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Possible hypothesis: your test is set up with the force at 180 degrees, i.e. infinite force on each strand (thing American triangle).
Were the strands parallel, it might have taken more weight for failure to occur.
That's my guess.
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carbo
Jul 15, 2004, 4:53 PM
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Some test have been done on this already:
http://www.xmission.com/~tmoyer/testing/EDK.html
http://jost.gudelius.bei.t-online.de/spst.htm
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dingus
Jul 15, 2004, 4:56 PM
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In reply to: Possible hypothesis: your test is set up with the force at 180 degrees, i.e. infinite force on each strand (thing American triangle). Were the strands parallel, it might have taken more weight for failure to occur. That's my guess.
In rappel configuration the strands come out of the knot and depart at 180 degrees, just as configured in this test. The infinite load thing happens when you pull down from the center like pulling on the bottom of the letter T. That is not what happens to a rappel rope as there is no 'triangle.'
Cheers
DMT
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sync
Jul 15, 2004, 5:10 PM
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In reply to: Some test have been done on this already: http://www.xmission.com/~tmoyer/testing/EDK.html http://jost.gudelius.bei.t-online.de/spst.htm
Yeah, it was the latter web page and its "flat double fisherman's" that prompted our desire to test the knot.
Even though tests have been done before, it was still really cool for us to do it ourselves. 8^)
Also, because we had it set up in a loop configuration, the failure force is probably half of what I said, so about 2000 pounds, which is more consistent with the tmoyer tests in the first link you gave.
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carbo
Jul 15, 2004, 5:33 PM
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I guess its always a tradeoff between the possibility of having the double fisherman snag on something or trusting the EDK (with really long tails)
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shakylegs
Jul 15, 2004, 5:37 PM
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dingus, point taken. I added the AT as a quick explanation of the 180 degree force factor.
But yeah, I guess you're right, the strands while rappelling would be close to 180. So don't mind me.
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gds
Jul 15, 2004, 5:41 PM
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OK so what am I missing. This happened at 4000 lbs- do I read that right. The EDK is for rapping not for holding leader falls. How would you get anywhere near 4000 lbs on a rap? I mean that's like 25 -30 people. Am I missing something here?
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bandycoot
Jul 15, 2004, 5:45 PM
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Good stuff. I gave a friend some pieces of rope to test similarly once.
There was piece with a "soft spot"
There was a piece that I marked well with a sharpie
There was one piece that seemed OK
Unfortunately the flakey guy never tested them.... It's fun to do the tests yourself and see how well this stuff works.
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bandycoot
Jul 15, 2004, 5:48 PM
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gds: You're missing nothing. Information for the sake of information! Appreciate it! Many people doubt the EDK's strength. This might calm their fears.
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trenchdigger
Jul 15, 2004, 5:50 PM
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gds wrote:
In reply to: OK so what am I missing. This happened at 4000 lbs- do I read that right. The EDK is for rapping not for holding leader falls. How would you get anywhere near 4000 lbs on a rap? I mean that's like 25 -30 people. Am I missing something here?
Yes, the point is that if you want to rap your car off the top of a climb, you'll need to use the flat double fishermans rather than the EDK. :roll:
I think it's been proven many times (and here again) that both knots are safe. It's also been proven that tails must be kept long for the EDK to be a safe knot.
Sync:
If you can, it would be interesting to see a plot of capsizing/tail slippage vs load. If the machine you're using also calculates strain, that should be relatively simple. With a loop of rope that small, you should be able to safely assume zero stretch in the rope. Either that or set up an experiment to calculate rope stretch and subtract that out.
~Adam~
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gds
Jul 15, 2004, 5:58 PM
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In reply to: gds: You're missing nothing. Information for the sake of information! Appreciate it! Many people doubt the EDK's strength. This might calm their fears.
Ah! data for the sake of data. That's OK I was once an academic.
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tradmanclimbs
Jul 15, 2004, 6:03 PM
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My tests were not scientific but they were pretty fun. Tie rope to tree and pull to failure with a VW syncro van 4X4 the EDK reversed and pulled apart without hardly slowing the van down at all. The in line eight that i use bunjied the van 30ft back up a slight hill an average of 3 times before the rope broke at the knott. I saw some sherrifs dept tests from either Vegas or LA? (can't rember which) which had the EDK reversing at loads arround 1,000lbs. I simply don't buy the theory that the EDK is less likely to snagg. A doubble fischermans is hard to untie and does seem to be snagg prone. An in line eight is easy to untie, completely redundant and wont snagg unless you do somthing stupid. the EDK will snagg with the best of them if you let it get in a crack. When the rope monster wants your rope it just eats that sucker up regardless of weather on not it even has a knott in it.
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sync
Jul 15, 2004, 6:26 PM
Post #18 of 66
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In reply to: I guess its always a tradeoff between the possibility of having the double fisherman snag on something or trusting the EDK (with really long tails)
That's why we're curious about the Flat Double Fisherman's:
http://img78.photobucket.com/...esting/IMG_3421b.jpg
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tradmanclimbs
Jul 15, 2004, 6:29 PM
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Note how cheap hardware store quick links that some folks don't trust as top anchors are strong enough to break rope.
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beesty511
Jul 15, 2004, 6:42 PM
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In reply to: Yes, the point is that if you want to rap your car off the top of a climb, you'll need to use the flat double fishermans rather than the EDK. I think it's been proven many times (and here again) that both knots are safe.
The only test on the flat double fisherman's knot I've read about is the Edelrid test. Can you point me to other tests on the flat df?
sync,
I'm interested in seeing your results with the flat df tests. Can you get enough spacing on the machine to tie figure eights on a bight and clip those into the quick links with the test knot in the middle?
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trenchdigger
Jul 15, 2004, 6:56 PM
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beesty511 wrote:
In reply to: The only test on the flat double fisherman's knot I've read about is the Edelrid test. Can you point me to other tests on the flat df?
For the flat DF I think I've seen stories of 2 "tests". Edited to correct/add: (the SAR test I previously mentioned was another site I found ISO info about the beer knot, not the EDK/DF knots.) Anyway, the other DF info (other than the Eldrid test) I found was on a site mentioned earlier in this thread http://www.xmission.com/...yer/testing/EDK.html. Scroll to the bottom of the page for the data.
~Adam~
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sync
Jul 15, 2004, 7:26 PM
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In reply to: Can you get enough spacing on the machine to tie figure eights on a bight and clip those into the quick links with the test knot in the middle?
No, we didn't have enough room for that. We first tried that but the figure eights stretched too much. That's why we switched to the small loop.
Like I said though, we're going to redesign our setup.
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robmcc
Jul 15, 2004, 7:28 PM
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In reply to: Note how cheap hardware store quick links that some folks don't trust as top anchors are strong enough to break rope.
Those things are way bigger than any I've ever seen climbing.
Rob
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beesty511
Jul 15, 2004, 7:29 PM
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In reply to: Anyway, the other DF info (other than the Eldrid test) I found was on a site mentioned earlier in this thread http://www.xmission.com/~tmoyer/testing/EDK.html.
The only thing I found was this:
In reply to: The last three tests (#18, #19, and #20) are on double fisherman's knots - pretty much the gold standard for comparison.
I think you are confused. sync wanted to test a flat double fisherman's knot, and those are the test results I am interested in. The flat df is a new rappel knot proposed by Edelrid as a superior knot than the EDK.
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trenchdigger
Jul 15, 2004, 7:40 PM
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In reply to: I think you are confused. sync wanted to test a flat double fisherman's knot, and those are the test results I am interested in. The flat df is a new rappel knot proposed by Edelrid as a superior knot than the EDK.
~Adam~
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