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zchandran
Apr 28, 2009, 4:19 PM
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This would pertain to setting up a quad as a toprope anchor for use with two horizontally even bolts. Long's book states that using 2 biners at the master point is solid, 3 are absolutely bomber. I'm using 3 biners since they are non-locking ovals.
So if the strands are like this:
Do I just clip one biner each to 1, 2, 3, and leave 4 alone, or do I clip (1,2), (2,3), (3,4) as pairs? I can't make out in the picture from the book exactly how the biners are clipped in.
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theguy
Apr 28, 2009, 4:31 PM
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Picture on p. 172 is fairly clear: clip 1,2,3 as a unit
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fresh
Apr 28, 2009, 4:34 PM
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long says that you clip either (2, 3, 4) or just (3, 4). last sentence of the second-to-last paragraph on page 171.
I love the quad personally.
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theguy
Apr 28, 2009, 4:42 PM
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P.S. This is a question for lab:
The text on p.172 claims that "clipping just two strands at the power point gives you twice the strength ever needed".
However, this doesn't seem to reconcile with info on:
- p.158: "a looped leg of high-tensile cord still fails at 5,000 pounds, not 10,000 as you would expect", unless a knotted high-tensile cord behaves differently from a looped cord
- p. 190: "tests on the quad revealed numbers virtually identical to the equalette"
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thepuddlestore
May 1, 2009, 9:47 PM
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theguy wrote: Picture on p. 172 is fairly clear: clip 1,2,3 as a unit
clip any three, and if you leave your quad tied, make sure you don't consistently leave one strand out.
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no_email_entered
May 1, 2009, 10:37 PM
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theguy wrote: P.S. This is a question for lab: The text on p.172 claims that "clipping just two strands at the power point gives you twice the strength ever needed". However, this doesn't seem to reconcile with info on: - p.158: "a looped leg of high-tensile cord still fails at 5,000 pounds, not 10,000 as you would expect", unless a knotted high-tensile cord behaves differently from a looped cord - p. 190: "tests on the quad revealed numbers virtually identical to the equalette"
one looped leg is still one piece of cord, running over a biner. the quad [or other rig] separates strands so you are doubling or tripling---
----but you probably figured that out by now
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no_email_entered
May 1, 2009, 10:41 PM
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thepuddlestore wrote: theguy wrote: Picture on p. 172 is fairly clear: clip 1,2,3 as a unit quoted for truth clip any three, and if you leave your quad tied, make sure you don't consistently leave one strand out.
i think you mean don't consistently leave the 'same' strand out---
---but even doing so would make very little difference to rig integrity, even over time
---unless i'm missing sumpin'
---and who leaves a cordy in a quad ad infinitum anywho?
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thepuddlestore
May 2, 2009, 2:43 AM
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no_email_entered wrote: thepuddlestore wrote: theguy wrote: Picture on p. 172 is fairly clear: clip 1,2,3 as a unit quoted for truth clip any three, and if you leave your quad tied, make sure you don't consistently leave one strand out. i think you mean don't consistently leave the 'same' strand out--- ---but even doing so would make very little difference to rig integrity, even over time ---unless i'm missing sumpin' ---and who leaves a cordy in a quad ad infinitum anywho?
you are correct in your assumption, i should have been more clear i think i was talking about quads built out of dyneema runners; some of my friends leave their quads tied, one of whom always left the same strand out, then i used it and clipped the "one" which by that time was much shorter than the others and thus took more of the load. It never posed danger, but some people might infer that the same strand should always be left out. how about some clarifications? well maybe not
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fresh
May 4, 2009, 2:50 PM
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no_email_entered wrote: theguy wrote: P.S. This is a question for lab: The text on p.172 claims that "clipping just two strands at the power point gives you twice the strength ever needed". However, this doesn't seem to reconcile with info on: - p.158: "a looped leg of high-tensile cord still fails at 5,000 pounds, not 10,000 as you would expect", unless a knotted high-tensile cord behaves differently from a looped cord - p. 190: "tests on the quad revealed numbers virtually identical to the equalette" one looped leg is still one piece of cord, running over a biner. the quad [or other rig] separates strands so you are doubling or tripling--- ----but you probably figured that out by now
the next question would be: isn't this a general property for all materials, not just high-tensile cord? does a looped length of rope have twice the strength as one strand? I can't imagine that it does.
it just seems peculiar that he'd point out this property specifically for high-tensile cord if it's indeed a general property.
(This post was edited by fresh on May 4, 2009, 2:51 PM)
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patto
May 4, 2009, 3:28 PM
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fresh wrote: does a looped length of rope have twice the strength as one strand? I can't imagine that it does.
Of course it does! How could it not!?
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fresh
May 4, 2009, 3:34 PM
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as NEE said:
"one looped leg is still one piece of cord, running over a biner."
if that is the logic used to explain why a looped strand of high-tensile cord doesn't have double the strength, then it should apply to all other materials. a looped strand of rope still has one strand running over the carabiner.
I mean I expect that the dynamic nature of climbing rope somehow reduces this effect, because JL singles out high-tensile cord. I'm just curious as to why.
(This post was edited by fresh on May 4, 2009, 3:37 PM)
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no_email_entered
May 4, 2009, 3:57 PM
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think about how they test climbing ropes, dropping a 60kg weight over a steel bar. at the point of stress, you basically have a 'looped leg'---
---twice the strength? or do you figure that it's all in the application?
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patto
May 4, 2009, 3:59 PM
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fresh wrote: as NEE said: "one looped leg is still one piece of cord, running over a biner." if that is the logic used to explain why a looped strand of high-tensile cord doesn't have double the strength, then it should apply to all other materials. a looped strand of rope still has one strand running over the carabiner.
NEE's 'logic' is wrong. A looped strand has double the strength.
I can hang of cotton thread around a biner if you wrap enough loops.
EDIT:
no_email_entered wrote: think about how they test climbing ropes, dropping a 60kg weight over a steel bar. at the point of stress, you basically have a 'looped leg'---?
No you don't have a looped leg. You have one strand.
(This post was edited by patto on May 4, 2009, 4:12 PM)
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fresh
May 4, 2009, 4:17 PM
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patto wrote: fresh wrote: as NEE said: "one looped leg is still one piece of cord, running over a biner." if that is the logic used to explain why a looped strand of high-tensile cord doesn't have double the strength, then it should apply to all other materials. a looped strand of rope still has one strand running over the carabiner. NEE's 'logic' is wrong. A looped strand has double the strength.
to be clear: I'm wondering if this is also the case for climbing rope, and why.
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patto
May 4, 2009, 4:29 PM
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fresh wrote: when it comes to high-tensile cord, this is not so, according to JL. to be clear: I'm wondering if this is also the case for climbing rope, and why.
I suspect you are misinterpreting this. Either way regardless what any book you have read has said a loop of cord is twice as strong as a single strand.
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no_email_entered
May 4, 2009, 4:29 PM
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depends on what you're referring to. a fig 8 on a bight on one biner is one strand. a clove? like i said, it's in the application and i took it to an extreme---
---regardless, you really need to step back now and again [way the frick back in many cases] and see the whole picture. is the quad (equalette, cordelette, rope rig) 'good enough' [to quote mr. Long]? meaning, what is it attached to? bomber pieces? questionable pieces? a mix? for me it all really boils down to [safe] efficiency---
---case in point, i did a five pitch [trad] route yesterday and had my cordy tied in a quad [left over from a day of dip & clip during the week]. on the wall at 10am:
---the first belay: two bolts w/chain, on goes the quad
---2nd belay: coming up behind slow party. they is hoggin' the two bolts so i builds a quick anchor. needed the cordy to sling a tree. rope rig for anchor
---3rd belay: two bolts again. straight up sliding X with double runner
---4th belay: traditional cordy on three pieces
---5th belay: two bolts, sliding x again
---rapped off
---had an early lunch
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no_email_entered
May 4, 2009, 4:32 PM
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oh and to add, i actually had a very nice talk with JL last saturday---
---and rigging was the last f'ing thing i would ever talk to him about
---Gaines was roaming around, too
---and, uh, ditto
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rocknice2
May 4, 2009, 11:26 PM
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patto wrote: I suspect you are misinterpreting this. Either way regardless what any book you have read has said a loop of cord is twice as strong as a single strand.
At fisrt glance this makes sense until you really examine it.
Say we have a looped sling.
Clip 2 biners into it.
Clip one into a bolt and hang a 10kilos on the other.
Each side of the loop takes 5kg.
But where they meet at the biner the force is 10kg
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patto
May 5, 2009, 12:42 AM
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fresh wrote: I'm excited to learn what other interpretation you can offer.
LOOPING CORD DOUBLES THE LOAD BEARING CAPABILITY
Naturally this works for slings too. How do you think those skinny slings can hold 22kN? Simple because they are double. Of course with cord you often have a knot and as you should know knot weaken cord so a tied cord is closers to 70% of the doubled strength.
fresh wrote: what NEE offered made sense, but I'm still not convinced it shouldn't apply to climbing rope as well. really I'm just curious.
No it doesn't make sense and it is false. A loop shares the load across each strand thus a loop can hold twice the weight.
If you hang a 10kg of a single strand then the strand has 10kg of tension. If you hang 10kg off a looped strand then each strand has 5kg. The tension throughout the strand is 5kg. If you think the tension somehow is additive at the biner then you are wrong.
Similarly if two people tull of either end of a 5m rope with 30kg of force then the total tension in the rope is 30kg NOT 60kg. If one person pulled 60kg and the other 30kg then the total tension is 60kg (with the 30kg puller accelating forward).
Try the experiment with cotton thread if you must. If one strand breaks at 1kg a looped thread will break closer to 2kg.
fresh wrote: yeah this discussion is pretty far from what we need to know to climb safely.
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patto
May 5, 2009, 12:47 AM
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rocknice2 wrote: patto wrote: I suspect you are misinterpreting this. Either way regardless what any book you have read has said a loop of cord is twice as strong as a single strand. At fisrt glance this makes sense until you really examine it. Say we have a looped sling. Clip 2 biners into it. Clip one into a bolt and hang a 10kilos on the other. Each side of the loop takes 5kg. But where they meet at the biner the force is 10kg
No, as I wrote above this is NOT the case.
If you put a spring scale there it would read 5kg.
EDIT
Similarly if you hang your body weight of 80kg on climbing rope off a bolt then you are pulling down 80kg on the rope and the bolt is pulling up 80kg on the rope. This doesn't mean the rope is feeling 160kg. Tension in the rope is only 80kg.
(This post was edited by patto on May 5, 2009, 1:00 AM)
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no_email_entered
May 5, 2009, 1:38 AM
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patto wrote: rocknice2 wrote: patto wrote: I suspect you are misinterpreting this. Either way regardless what any book you have read has said a loop of cord is twice as strong as a single strand. At fisrt glance this makes sense until you really examine it. Say we have a looped sling. Clip 2 biners into it. Clip one into a bolt and hang a 10kilos on the other. Each side of the loop takes 5kg. But where they meet at the biner the force is 10kg No, as I wrote above this is NOT the case. If you put a spring scale there it would read 5kg. EDIT Similarly if you hang your body weight of 80kg on climbing rope off a bolt then you are pulling down 80kg on the rope and the bolt is pulling up 80kg on the rope. This doesn't mean the rope is feeling 160kg. Tension in the rope is only 80kg.
that only applies if you're hanging upside down---
---wait, what are we arguing about?
---all this makes me laugh
---laugh with me now! [hahahahaha]
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fresh
May 5, 2009, 1:35 PM
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patto,
the point I was making is that there is no room for interpretation of JL's quote--it's either correct or incorrect. you're contradicting the statement, which isn't necessarily bad, but it's fairly bold. usually people do that after they've run tests and such.
if you have two cords attached to a mass, naturally they each share half the weight. however, for each cord, there is a separate attachment point. in a looped cord, there is one attachment point--where the loop meets the carabiner.
can you please address why you should not take into account that fact? it's rather intuitive that this should be the point of weakness.
and kg is a unit of mass, not force.
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