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| Messages 1 - 18 of total 18 in this topic |
wallyvirginia
Trad climber
Stockholm, Sweden
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Topic Author's Original Post - Mar 6, 2015 - 01:21pm PT
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Hi Supertopo!
I wonder if anyone has some knowledge about load limiting knots? I.e. a knot in the climbing rope that would act like a make shift screamer, a shock absorber, in a high fall factor scenario.
I've heard that a false butterfly knot would have this effect. It could be tied just above the tie in knot on a lead climber. Or in the middle of a loop of rope (a prussik) used as a runner. Or near the anchor in a rope solo lead..
Now, before you fry me, I'm a competent climber, I know I'm going to die and I'm mostly theoretically interested in this question.. 😁
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rgold
Trad climber
Poughkeepsie, NY
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Wally, yer gonna be fried regardless, they're heatin' up the oil as we speak.
Here's some gentle warming to get the process started. I'd suggest you call such knots load-reducing rather than load-limiting, because the former description is accurate and the latter is not.
It is by now well-known that the tightening tie-in knots, (I think all tests have used the figure-eight) has a measureable load-reducing effect. That being the case, you can presumably get more effect by adding more knots. The question is whether the gains are significant enough to bother, and my guess is the answer is no.
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Ksolem
Trad climber
Monrovia, California
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It is important to retie your tie in knot after a fall. A normally tied knot limits the load by compressing (tightening.) Once this has happened it cannot happen again unless it is restored to it's normal tightness.
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Prod
Trad climber
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Why not tie into a screamer?
Prod.
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NutAgain!
Trad climber
South Pasadena, CA
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Or use two separate ropes of smaller diameter with greater elasticity?
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wallyvirginia
Trad climber
Stockholm, Sweden
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Topic Author's Reply - Mar 6, 2015 - 02:53pm PT
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Thanks for your input.
If the idea is for the knot to absorb force only by tightening itself, and not coming completely undone, then I guess a loosely tied figure eight knot above the tie in figure eight would suffice?
I picture the false butterfly coming completely undone and unwrapping itself more like a real screamer than just a knot tightening. Maybe I'm completely wrong? It would be really cool to test it to see if it works and if so how much reduction one could get.
Where's the fun in that, Prod? 😁
@Nutagain Two ropes with greater elasticity individually still has the same elasticity as a pair as one thicker rope does, right? Generally speaking. I mean, half ropes are great, I'm just wondering if the knot works, is all.
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healyje
Trad climber
Portland, Oregon
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wallyvirginia, probably better knot to try and reinvent or improve on what has been worked out over years and works so well...
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Splater
climber
Grey Matter
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My guess is that if the knot absorbed significant energy, it would be converted into frictional heat in the rope, which would damage it. You could fairly easily calculate this effect.
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B.Warne
Trad climber
The flip side
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Agreed with the above post. You could use a prussik bypass that would absorb energy before the knot engaged.
But why?
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wallyvirginia
Trad climber
Stockholm, Sweden
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Topic Author's Reply - Mar 6, 2015 - 03:35pm PT
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Yeah, I guess frictional heat could be an issue if you're intentionally looking to create movement in the knot.
Does a prussik bypass reduce the peak load significantly?
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Kalimon
Social climber
Ridgway, CO
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I think it is called a "noose".
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rgold
Trad climber
Poughkeepsie, NY
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Some of the older folks around here may remember the Tarbuck knot, at least if you knew a little about climbing in the UK. It was devised and promoted as an energy-absorbing knot for climbers in the days of nylon laid ropes, but faded from sight when kernmantle ropes superceded laid ropes.
See, for example, http://knots-guide.blogspot.com/2008/04/t.html
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Flip Flop
Trad climber
Truckee, CA
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Wrap it around your waist 6 times. That will reduce the force on the rope.
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apogee
climber
Technically expert, safe belayer, can lead if easy
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Can someone provide examples of catastrophic failure of a properly used tie-in knot?
The perspective could be invaluable.
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Blakey
Trad climber
Sierra Vista
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I recall the Tarbuck knot, it was still described in climbing and
instructional manuals in my youth. Never saw one in use though!
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Gnome Ofthe Diabase
climber
Out Of Bed
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I think. Dano (Osman(d?) tried various knots at his giant rope swings/free falls, eventually
working to reduce the 'snap' by extending the distance from the anchor point At take off?
As well as other mechanical works?
Who was the Supertopian who played that game as well?
It is not my place to say.
This is the sort of weird question that needs more info before any answers.
What are you doing ? Why ?
Don't try to rethink the great minds and lives that have proven the good working systems!
Silent partner !, Full body harness ! ,WHAT FILP FLOP SAID
As to rope tricks:
Mechanics of nylon friction Welding
Yes tie ten figure8's from your waist, ten feet up the rope, count to three and jump!
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wallyvirginia
Trad climber
Stockholm, Sweden
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Topic Author's Reply - Mar 8, 2015 - 12:51pm PT
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This is the sort of weird question that needs more info before any answers. What are you doing ? Why ?
A guy at work (I work at heights in construction) mentioned it the other day. It caught my attention since I'd never heard of it in thirteen years of climbing obsession.
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