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rocke
Feb 8, 2005, 1:43 PM
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This question pertains to steep ice. Is it safe to use double ropes as twins (clipping both ropes into one piece of protection)? Can you alternate by clipping both ropes into one piece of protection then clipping only one rope into the next piece?
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cantbuymefriends
Feb 8, 2005, 2:49 PM
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"Is it safe?" What is safe in iceclimbing, anyway? :wink:
But really. If you fall with the ropes clipped as twins, you will get a higher impact force, increasing the probability of pulling out your protection. And since ice protection is marginal at best anyway... Well, you know what they say: "Stack the odds in your favor."
About alternating clips. I think it's quite common to clip the first or two pieces of pro as twins (regardless of what I said above) and then separate the ropes. But letting the ropes go back together again after clipping them separately is NOT good:
1. Different lengths of rope out will mean different stretch if you fall. So the ropes may rub together and heat/burn (the same reason why not to thread the rope through a sling.)
2. The ropes coming to a biner from different directions, you'll get tri-axis loading of the biner.
We discussed this a while back. There was some other reasons as well that I can't remember.
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mtnbkrxtrordnair
Feb 8, 2005, 3:01 PM
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You can use doubles as twins. If you do, clip both ropes into all the pro with one biner from start to finish. If you use double rope technique, and you want to clip both ropes to the same piece of pro, use a separate biner for each rope. The idea with twins is that both ropes are used as one rope and if you fall they move more or less together so that they won't saw across each other. If you clipped your doubles to separate pieces, then higher up you clipped both to one piece with one biner, during a fall both ropes could move through the same biner at different rates which is bad, creating rope on rope friction.
Comprende?
Edited to add: I will let someone else address the issues of impact force when doing this, or can you spell s-c-r-e-a-m-e-r.
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lambone
Feb 8, 2005, 6:59 PM
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In reply to: This question pertains to steep ice. Is it safe to use double ropes as twins (clipping both ropes into one piece of protection)? Can you alternate by clipping both ropes into one piece of protection then clipping only one rope into the next piece?
no, it's not safe. Half ropes (doubles...whatever) were designed to be clipped in seperately. Clipping both into the peice doubles the impact force, amking it much higher then if you were just using one 10 or 11 mil rope.
don't do it, if you want more security place two screws.
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sspssp
Feb 8, 2005, 7:30 PM
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There are some ropes that are marketed as both double and twins. Using them as twins ups the impact force some, but not near as much as you might think.
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sspssp
Feb 8, 2005, 7:30 PM
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There are some ropes that are marketed as both double and twins. Using them as twins ups the impact force some, but not near as much as you might think.
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scrapedape
Feb 8, 2005, 7:35 PM
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In reply to: There are some ropes that are marketed as both double and twins. Using them as twins ups the impact force some, but not near as much as you might think.
I would think that it doubles the impact force. How is this not so?
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phaedrus409
Feb 8, 2005, 7:42 PM
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In reply to: In reply to: This question pertains to steep ice. Is it safe to use double ropes as twins (clipping both ropes into one piece of protection)? Can you alternate by clipping both ropes into one piece of protection then clipping only one rope into the next piece? no, it's not safe. Half ropes (doubles...whatever) were designed to be clipped in seperately. Clipping both into the peice doubles the impact force, amking it much higher then if you were just using one 10 or 11 mil rope. don't do it, if you want more security place two screws.
I'm a bit confused... How is the force much higher with two double ropes into one piece, as opposed to a 10 or 11mm rope? I'm not really grasping the physics of it all.
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dingus
Feb 8, 2005, 7:55 PM
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In reply to: In reply to: There are some ropes that are marketed as both double and twins. Using them as twins ups the impact force some, but not near as much as you might think. I would think that it doubles the impact force. How is this not so?
Double of WHAT???
A single rope in a double rope config should not be expected to incur the full force of a leader fall. According to the math / theory I saw articulated on wreck.climbing a few years ago, the first rope of a double will stretch until the 2nd rope begins to absorb part of the fall as well. Thus impact force will be higher than falling onto just that one rope (which isn't designed to absorb the full force of a leader fall more than once or twice to begin with).
The doubles I use were definitely marketed as dual use... double or twin. They were designed and rated for that dual usage. And I have almost ALWAYS clipped them as twins. Never pulled any pro in a fall, nor did I scramble my innards. But then again, I haven't fallen on them ALL that many times, and never on ice, so maybe I'm just lucky.
Say you are using doubles as doubles. You are ice climbing. You go up 30 feet and place a screw. You clip one rope. Now you climb 15 more feet and as you begin to place your second screw, you fall. That is not an ideal scenario, falling on one rope like that.
The thought of an ice climbing 30 footer onto an 8.1 with only 45 feet of rope out makes my skin crawl and my asshole pucker up like the end of a hotdog. I would pretty much always clip both ropes to that first screw, though some would counsel using two draws to accomplish the deed.
And if you are going to clip that first piece that way... why not continue? If impact forces are your sole concern (as opposed to rope drag), they will become more favorable as you get more rope in the system. You've already passed the highest impact force point at the first piece. Which you have to do anyway?
That's my thinking, subject to correction by those who actually know what they are talking about, hehe.
DMT
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tradklime
Feb 8, 2005, 8:42 PM
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In reply to: And if you are going to clip that first piece that way... why not continue? If impact forces are your sole concern (as opposed to rope drag), they will become more favorable as you get more rope in the system. You've already passed the highest impact force point at the first piece. Which you have to do anyway?
The reasons to clip the two together early, and then start alternating higher up, would be if the impact force on the early pieces was less of a concern than pieces higher up, ie. the first couple of pieces are bomber and the higher pieces are suspect (or the route starts wandering). In this case, early in the climb, you'd have to be less concerned with the placement quality and more concerned with forces imparted on a single strand of a double rope system.
That said, you really nailed it when you stated that you usually use your ropes as twin anyways. That's what I have found that I prefer as well. As a former diehard double rope user, I realized that I only really benefitted from doubles when it came to to rappel. I've gone to twins so that I can have a light two rope system that is designed to be clipped together and offer low impact forces. I never liked hanging it out there above a single line that isn't designed to catch the full force of the fall itself.
If I need, or want, low impact forces I use load limiters.
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lambone
Feb 8, 2005, 9:10 PM
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In reply to: In reply to: In reply to: This question pertains to steep ice. Is it safe to use double ropes as twins (clipping both ropes into one piece of protection)? Can you alternate by clipping both ropes into one piece of protection then clipping only one rope into the next piece? no, it's not safe. Half ropes (doubles...whatever) were designed to be clipped in seperately. Clipping both into the peice doubles the impact force, amking it much higher then if you were just using one 10 or 11 mil rope. don't do it, if you want more security place two screws. I'm a bit confused... How is the force much higher with two double ropes into one piece, as opposed to a 10 or 11mm rope? I'm not really grasping the physics of it all.
the logic is simple, two 8 or 9 mil ropes = more impact foce then 1 10 or 11. I don't know exactly by how much, but it most definately does.
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phaedrus409
Feb 8, 2005, 9:19 PM
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Perhaps I'm missing something, but I'm not seeing the logic. Regardless of whether you are using one or two ropes, you still have to arrest the same fall force. Granted the impulse might be different, based on the difference in the stretch of twin ropes versus a single rope, but I'm betting the difference there would be fairly negligable. Regardless, in the end you have one piece of pro which is absorbing a very similar force whether you are using one rope, two ropes, three, etc... Obviously there are different forces and tensions applied to each rope, but I'm completely missing the logic which explains why there is a greater force exerted on the ice screw.
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glyrocks
Feb 8, 2005, 9:26 PM
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In reply to: In reply to: In reply to: In reply to: This question pertains to steep ice. Is it safe to use double ropes as twins (clipping both ropes into one piece of protection)? Can you alternate by clipping both ropes into one piece of protection then clipping only one rope into the next piece? no, it's not safe. Half ropes (doubles...whatever) were designed to be clipped in seperately. Clipping both into the peice doubles the impact force, amking it much higher then if you were just using one 10 or 11 mil rope. don't do it, if you want more security place two screws. I'm a bit confused... How is the force much higher with two double ropes into one piece, as opposed to a 10 or 11mm rope? I'm not really grasping the physics of it all. the logic is simple, two 8 or 9 mil ropes = more impact foce then 1 10 or 11. I don't know exactly by how much, but it most definately does.
Not trying to be a dick, but you didn't even begin to explain how or why. I'd be interested in hearing a simple breakdown of the physics as well.
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mtnbkrxtrordnair
Feb 8, 2005, 9:33 PM
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If you had a weight attached to a rubber band and dropped it a couple of inches the rubber band would stretch a certain amount. If you tried that with two rubber bands the total distance the two rubber bands stretch would be less than with one band. Since it's all about dissipating the force of the fall, the single rubber band would have a softer catch because it is dissipating the force of the fall over a greater distance/time.
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phaedrus409
Feb 8, 2005, 9:46 PM
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In reply to: If you had a weight attached to a rubber band and dropped it a couple of inches the rubber band would stretch a certain amount. If you tried that with two rubber bands the total distance the two rubber bands stretch would be less than with one band. Since it's all about dissipating the force of the fall, the single rubber band would have a softer catch because it is dissipating the force of the fall over a greater distance/time.
i agree with that logic, but that is assuming the rubber bands are identical in both scenarios. with our climbing rope hypothetical, you are comparing two 8mm ropes with a 10.5mm or an 11mm (or something roughly equivalent). This should have a fairly substantial effect on things.
Perhaps I'm wrong, and if so, please correct me, but I would assume an 8mm rope would stretch a greater distance than an 11mm, in your "weight attached to a rubber band" scenario. Similar to a thinner rubber band versus a thicker. So the true question is actually how much difference is there in stretch, and will two 8mm's stretch an equivalent distance as one 11mm..
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greenmachineman7
Feb 8, 2005, 9:48 PM
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Edited to read: Damn! Phaedrus out-typed me!
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jeremy11
Feb 8, 2005, 10:20 PM
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would it be ok to use two 10.5 ropes in a double rope setup? I know this has a weight disadvantage, it would only be on single pitch trad to practice/learn double rope technique.
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tradklime
Feb 8, 2005, 10:56 PM
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In reply to: Granted the impulse might be different, based on the difference in the stretch of twin ropes versus a single rope, but I'm betting the difference there would be fairly negligable.
It does all come down to rope stretch and impact force. Different 11 ml ropes can have significantly different impact forces, that are not always negligable in certain circumstances. There has been testing done, I just don't remember wehre to find the link, but the bottom line is that generally two doubles clipped together will have a significantly greater impact force than one single. Old style twins used to have this issue, combined they tended to have a greater impact force than one single. That said, improvements have changed this where double ropes are "certified" to be used as twins, and some twin systems will have a lower impact force than most single ropes.
In reply to: Regardless, in the end you have one piece of pro which is absorbing a very similar force whether you are using one rope, two ropes, three, etc... Obviously there are different forces and tensions applied to each rope, but I'm completely missing the logic which explains why there is a greater force exerted on the ice screw.
It all comes down to the impact force(s) of the ropes involved.
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tradklime
Feb 8, 2005, 10:57 PM
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In reply to: would it be ok to use two 10.5 ropes in a double rope setup? I know this has a weight disadvantage, it would only be on single pitch trad to practice/learn double rope technique.
Yes, just don't use them as twins.
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mtnbkrxtrordnair
Feb 8, 2005, 11:00 PM
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here's a comparison of impact force and elongation:
8.1 twin 9.5 kn, 4.2%
8.6 double 5.9 kn, 9.4%
10.2 single 8.2 kn, 6.8%
8.1 twin also rated as double 5.8 kn, 10%
so 8.1 twins used together have a slightly higher impact force and less strech than a 10.2 single, but not by much. a double rope by itself has the softest catch. the twin also rated as a double is even softer but 10% is a lot of stretch. is the second basically soloing for the first 20 ft. of a full rope length pitch?
The question is what is the impact/elongation of the 8.1 twin/double when used as a twin (not given) or the 8.6 double used as a twin? I don't think it's double the impact and half the elongation. I don't have the physics background but I could PM somebody who might have the answer. I suspect the answer is somwhere in the middle. I guess that a really skinny double used as a twin would have a higher impact force than a single, but not by much, just like the 8.1 twin. a fatter double rope used as a twin would push the force higher but by how much? so If I used it that way I would use screamers. I have been meaning to get screamers for all my screws, not just the first few. Sometimes I climb ice with the 8.1 doubles, sometimes a 10.2 single.
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mtnbkrxtrordnair
Feb 8, 2005, 11:02 PM
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here's a comparison of impact force and elongation:
8.1 twin 9.5 kn, 4.2%
8.6 double 5.9 kn, 9.4%
10.2 single 8.2 kn, 6.8%
8.1 twin also rated as double 5.8 kn, 10%
so 8.1 twins used together have a slightly higher impact force and less strech than a 10.2 single, but not by much. a double rope by itself has the softest catch. the twin also rated as a double is even softer but 10% is a lot of stretch. is the second basically soloing for the first 20 ft. of a full rope length pitch?
The question is what is the impact/elongation of the 8.1 twin/double when used as a twin (not given) or the 8.6 double used as a twin? I don't think it's double the impact and half the elongation. I don't have the physics background but I could PM somebody who might have the answer. I suspect the answer is somwhere in the middle. I guess that a really skinny double used as a twin would have a higher impact force than a single, but not by much, just like the 8.1 twin. a fatter double rope used as a twin would push the force higher but by how much? so If I used it that way I would use screamers. I have been meaning to get screamers for all my screws, not just the first few. Sometimes I climb ice with the 8.1 doubles, sometimes a 10.2 single.
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phaedrus409
Feb 8, 2005, 11:03 PM
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tradklimb, thanks very much for the educated response.. i was unaware of the vast difference in stretch between ropes intended for double use versus ropes intended for twin use. i appreciate the feedback.
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mtnbkrxtrordnair
Feb 8, 2005, 11:15 PM
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here's a comparison of impact force and elongation:
8.1 twin 9.5 kn, 4.2%
8.6 double 5.9 kn, 9.4%
10.2 single 8.2 kn, 6.8%
8.1 twin also rated as double 5.8 kn, 10%
so 8.1 twins used together have a slightly higher impact force and less strech than a 10.2 single, but not by much. a double rope by itself has the softest catch. the twin also rated as a double is even softer but 10% is a lot of stretch. is the second basically soloing for the first 20 ft. of a full rope length pitch?
The question is what is the impact/elongation of the 8.1 twin/double when used as a twin (not given) or the 8.6 double used as a twin? I don't think it's double the impact and half the elongation. I don't have the physics background but I could PM somebody who might have the answer. I suspect the answer is somwhere in the middle. I guess that a really skinny double used as a twin would have a higher impact force than a single, but not by much, just like the 8.1 twin. a fatter double rope used as a twin would push the force higher but by how much? so If I used it that way I would use screamers. I have been meaning to get screamers for all my screws, not just the first few. Sometimes I climb ice with the 8.1 doubles, sometimes a 10.2 single.
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lambone
Feb 8, 2005, 11:18 PM
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The reason I made that claim is because it is what a Sterling rep told me once during a store clinic. But I still think it's logical. T
The impact force of an 8.8 mil on the sterling web site is 6.5kn. A 10.6 is 9.6kn.
So what happens when you have two ropes rated at 6.5kn clipped into once peice. Does it double to 13kn? I don't know, maybe the difference isn't that significant. But I am guessing it is above 9.6kn.
Regardless, it doesn't matter, why would you want to increase the impact force at all by clipping them both in? If that is not how the manufacturer suggests to use the ropes, or how they are tested and approved by the UIAA?
All the numbers don't matter when your on the ice. The only thing that matters is that you don't blow that screw out of the ice and deck. So, when your up there what are you more worried about? Only being clipped in with one rope, or blowing the screw if you fall? For me, I will put the trust in my one rope alot more then some crappy ice.
Use a screamer too.
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sspssp
Feb 9, 2005, 12:18 AM
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There are a couple of different issues going on here. First, as far as the rope manufacturers reported impact forces, I believe that double ropes are usually tested with a lighter weight than twins or singles, so that is going to make comparisons difficult.
Second, the rubber band analogy is a good one. If you drop a weight on two identical rubber bands and then try it on one, the single will stretch farther but it won't be twice as much. The resistance that the rubber band (or rope) has to stretching isn't constant. The more you stretch it, the higher the resistance (or force). So two ropes stretched ten feet will not have the same resistive force as one rope stretched 20 feet. So if one rope will stop your fall in 20 feet, two ropes will take more than ten. So the impact force will be less than doubled.
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