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rrrADAM
Jul 15, 2004, 8:07 PM
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I can hang my Pathfinder from 4,000 lbs, so it's hella strong for even simul-raps. :wink:
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carbo
Jul 15, 2004, 8:21 PM
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I think the figure eight on a bite should be prone to rolling more than the EDK.
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sarcat
Jul 15, 2004, 9:05 PM
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So IF I've decided that I'm only going to use a dbl. fishermans why would I question it?
What's wrong with it that you'd use an EDK or flat fishermans over the DF?
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tradmanclimbs
Jul 15, 2004, 9:12 PM
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double fishermans hard to untie after weighted. also hard to tie with gloves and cold fingers etc. EDK is easier to tie but people have died with the EDK as well. LONG tails ar a must w/ the EDK
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knudenoggin
Jul 15, 2004, 9:36 PM
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In reply to: 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.
This can occur because of the slippage of rope from the knotted side,
causing that side to slacken/elongate, and making thus movement at
the pin!? --what the testers mused in the Lyon report when they didn't
get a break at the knot for the Grapevine. And i.p. the Offset (not "flat",
pulllleeze :o) Grapevine (a Bachmann idea) & Offset Fig.8 are going to
yield a lot of material. BUT, at what force did this rupture occur? (One
might consider that more of the load was borne by the unknotted side.)
Can you simply tie TWO knots, one on each side of the loop? (And,
that way, when one breaks, you have the survivor at a near-break point
to examine--desk ornamentation.)
In reply to: 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).
arrange that the upper strand ran down, the lower up--like reversing legs
when doing the splits. This is an aspect to test, to see what effect it has
(i.e., the orientation of the knot initially). (In the image, the upper strand
initially makes a full loop around the ends, outermost; the lower makes a
sort of *forward arc* and nips the ends to the inside: reverse this and
see what changes.)
In reply to: 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.
which is why it broke first. In a laid rope, thus, one would not expect to
have so much apparent tail-feed!?
In reply to: We also tested the [Offset] Figure 8 and [Offset] Double Fisherman's. Unfortunately, these failed at the link rather than the knot. However, they pulled at most one inch of tail.
feed of material (well, partly: material out of the knot body can still be
considerable, even w/o tails slipping)!? At what forces did the break occur
for these knots?
Good job!
(-;
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gunkiemike
Jul 16, 2004, 12:28 AM
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In reply to: double fishermans hard to untie after weighted. also hard to tie with gloves and cold fingers etc. EDK is easier to tie but people have died with the EDK as well. LONG tails ar a must w/ the EDK
I have read that no one has ever died with the EDK - can you provide some details? Who died and when, where?
The "offset Fig 8" OTOH was judged to be the cause of that death in (IIRC) Zion a year or two ago.
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korporal
Jul 16, 2004, 2:35 AM
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Does anybody know a link to a site that shows how to tie the "flat" double fishermans?
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dirtineye
Jul 16, 2004, 2:44 AM
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HAHAHA that's funny!
but there is a link in some rappel rope joining knot thread to a test of three knots dome by some germans... maybe since I'm bored I'll look for it.
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korporal
Jul 16, 2004, 3:17 AM
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Looks a bit complicated to tie when you are tired and hungry.
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dirtineye
Jul 16, 2004, 3:24 AM
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Found it finally.
http://jost.gudelius.bei.t-online.de/spst.htm
http://www.xmission.com/~tmoyer/testing/EDK.html
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beesty511
Jul 16, 2004, 3:51 AM
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In reply to: I have read that no one has ever died with the EDK - can you provide some details?
...then you are not very well read.
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tradmanclimbs
Jul 16, 2004, 4:11 AM
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I could be wrong but I thought I read an accident report in one of the glossy raggs were the verdict was the tails on an EDK were too short??? I did see a sherrifs dept test that had the edk inverting between 800 and 1100 lbs. they also had cool video of them cutting loose a stokes litter with 200 lbs in it to show how much force it put on the back up anchor. You do not want to be the rescue victim when somthing like that happens :shock: personaly one of my fav. stories is the Largo story about the SAR guys that were drowning in a river while training in WV and had to be rescued by Kayakers.
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rgold
Jul 16, 2004, 4:11 AM
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Since people are now starting to repeat that the knot failed at 4000 pounds, it is worth emphasizing that the 4,000 pound load was shared equally by the two strands and so the knot failed at about 2,000 pounds. Moreover, if the tails started shortening at a few hundred pounds, the force needed to start the tails moving is half that figure.
What I've read about knot strength is that the radius of bend in the rope is an important factor in the knot strength. Fibers along the outer radius have to stretch more than those on the inner radius, and when the radius is sharp there is high stress at the outer part as well as crushing at the inner part. In your situation, this also applies to the links you are using. A bigger radius for the pieces holding the rope ought to eliminate breakage before knot failure.
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sync
Jul 16, 2004, 12:39 PM
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In reply to: Since people are now starting to repeat that the knot failed at 4000 pounds, it is worth emphasizing that the 4,000 pound load was shared equally by the two strands and so the knot failed at about 2,000 pounds. Moreover, if the tails started shortening at a few hundred pounds, the force needed to start the tails moving is half that figure. What I've read about knot strength is that the radius of bend in the rope is an important factor in the knot strength. Fibers along the outer radius have to stretch more than those on the inner radius, and when the radius is sharp there is high stress at the outer part as well as crushing at the inner part. In your situation, this also applies to the links you are using. A bigger radius for the pieces holding the rope ought to eliminate breakage before knot failure.
Yes, I believe you are correct here, and my numbers should be halved. And yes, I think the reason the rope broke at the link is due to the sharp bend there. We're looking into getting some type of pully shaped device to hold the rope with a more moderate bend so that it won't break there.
Keep in mind everybody that we didn't go into this with a full scientifically thought out experimental procedure. We're just a few curious climbers who had access to the engineering lab. We learned a lot in our first attempt, so maybe when we go back with a new setup we can be a bit more scientific about it all.
I do have the force versus elongation spreadsheets. I will make up a couple of plots and post them here soon.
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pawilkes
Jul 16, 2004, 1:22 PM
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its good to see that equipment put to good use. as far as i can tell its the same room and equipment we use for our ME 307 Mechanics of Materials lab. not a horrible class but this is probably some of the ore useful information that those machines have put out (for me at least)
phil
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knudenoggin
Jul 19, 2004, 11:34 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.
overall production of such things to be produced to such standards that ensure
consistent quality.
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forbin
Jul 20, 2004, 9:56 PM
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In reply to: I have read that no one has ever died with the EDK - can you provide some details? Who died and when, where?
http://www.geocities.com/danielzimmerlin/pages/stories/knot.html
This link is to a Grand Teton Ranger's report of a 30' fall caused by the failure of a Flat (or is it "Offset"?) Overhand aka EDK. However, I assume this fall was not fatal, since the report, nor the page that linked to it, doesn't indicate that it was. The Ranger, Mark Magnuson, goes on to note that his research found that the only reason it is referred to as an EDK is because of it's origin and the initial "no way!" reaction that it causes. I do admit I still kinda have that "you gotta be sh!tting me!" response to it's use even though, with a backup, it seems to be the best thing going. Has anyone used the Flat (or is it "Offset"?) Double Fisherman's? That seems like it could be the knot to put this debate to rest. Damn, one less weekly thread.
forbin
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charlie.elverson
Sep 24, 2009, 8:08 PM
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I've read that backing up an EDK with another EDK on the tails is a pretty good setup. It's definitely easy to tie, but I'm curious how easily the knot gets stuck. Up till now I've almost always rappelled on a figure eight follow through (Is that the right name? I can never keep it straight. I'm referring to tying a figure eight in one rope and then retracing it with the other rope kind of like when you tie in) and have not really had any issues with it getting stuck.
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shoo
Sep 24, 2009, 8:19 PM
Post #46 of 66
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charlie.elverson wrote: I've read that backing up an EDK with another EDK on the tails is a pretty good setup. It's definitely easy to tie, but I'm curious how easily the knot gets stuck. Up till now I've almost always rappelled on a figure eight follow through (Is that the right name? I can never keep it straight. I'm referring to tying a figure eight in one rope and then retracing it with the other rope kind of like when you tie in) and have not really had any issues with it getting stuck.
charlie.elverson wrote: I've read that backing up an EDK with another EDK on the tails is a pretty good setup. It's definitely easy to tie, but I'm curious how easily the knot gets stuck. Up till now I've almost always rappelled on a figure eight follow through (Is that the right name? I can never keep it straight. I'm referring to tying a figure eight in one rope and then retracing it with the other rope kind of like when you tie in) and have not really had any issues with it getting stuck.
Putting a second EDK on the first one partially defeats the purpose of using the EDK in the first place. It creates an edge on which things can be caught.
Also, I generally refer to that version of the figure 8 rethread as a figure 8 fisherman's knot. I am not sure where I got the name from, nor if this is the accepted name.
PS Nice thread revival.
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adatesman
Sep 24, 2009, 8:30 PM
Post #48 of 66
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binrat
Sep 24, 2009, 8:36 PM
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adatesman wrote: Joining ropes with a fig-8 such that the long parts of the rope come out the same side of the knot (like a EDK) is a very bad idea, as it rolls even easier than a EDK does.
binrat
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shoo
Sep 24, 2009, 8:40 PM
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adatesman wrote: shoo wrote: Also, I generally refer to that version of the figure 8 rethread as a figure 8 fisherman's knot. I am not sure where I got the name from, nor if this is the accepted name. If you're talking about this: [image]http://upload.wikimedia.org/wikipedia/commons/thumb/1/1e/Doppelter_Achtknoten_gesteckt.jpg/300px-Doppelter_Achtknoten_gesteckt.jpg[/image] its proper name is a Flemish Bend. Joining ropes with a fig-8 such that the long parts of the rope come out the same side of the knot (like a EDK) is a very bad idea, as it rolls even easier than a EDK does.
Awesome. I learned something today. Flemish Bend is such a cool name.
And yes. I seem to remember an accident in the last couple of years where a joined rappel line failed, most likely due to the use of a figure 8 on a bight which rolled off the end of the rope. I might have to look that up.
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