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drzaous
Nov 25, 2006, 8:08 AM
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I'm looking into buying some new ice/alpine lines, and I really want a rope that is certified for BOTH twin and half(double) techniques. I looked into the PMI Verglas, and the new Monster 7.8mm by metolius. Both look pretty good, but the PMI looks a little flimsy, and i'm looking for a nice, tight sheath. Any experience with ANY twin AND half certified ropes?
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iceisnice
Nov 25, 2006, 2:20 PM
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i'm not sure that i understand the question since ANY rope (single, double, twin) can be used as a twin. the simple answer to your question is just find the thinnest diameter double rope. its "rated" for double rope use (which just means that it was tested that way......not that its impossible to use it any other way) but can be used as a twin and even a single in the right situation.
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notch
Nov 25, 2006, 3:09 PM
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Of course any rope can be used as a twin Devkrev, it's just that the opposite isn't true. It would be obnoxiously heavy to be dragging around a pair of Blue Water 10.5s, but one could do that and they would function just fine as twins. It's just that (for example) the Beal 8.1 doesn't meet the minimum standard for a single, so it has to take the UIAA rating for a half.
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iceisnice
Nov 25, 2006, 3:51 PM
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notch's explaination is much better than mine, thanks.
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reno
Nov 25, 2006, 8:02 PM
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iceisnice wrote: i'm not sure that i understand the question since ANY rope (single, double, twin) can be used as a twin. I thought this had been discussed here before, and the word was that single ropes used as twins was a bad idea. Maybe I'm going senile. FWIW, I used a pair of Blue Water Ice Floss ropes last year for ice, and they were amazing. Smooth, light, and durable. Would buy another set in a New York Minute, if I needed to. Off to search I go... back when I find something.
(This post was edited by reno on Nov 25, 2006, 8:05 PM)
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iceisnice
Nov 25, 2006, 8:13 PM
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two singles can work as a twin...........it'll just be a real heavy twin. unless someone has some info from UIAA or the rope manufacturers themselves.........i have no reason to believe otherwise.
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reno
Nov 25, 2006, 8:20 PM
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iceisnice wrote: two singles can work as a twin...........it'll just be a real heavy twin. unless someone has some info from UIAA or the rope manufacturers themselves.........i have no reason to believe otherwise. I'm still searching (slow day at work,) but IIRC, it's an impact force/elongation issue: Single ropes are designed to absorb a given amount of force over a given period of time. When there are two such ropes used as twins (a.k.a. the scenario you describe), then neither rope is required to stretch to it's normal parameter. This would create a higher impact on the piece of pro, wouldn't it? Shorter elongation and same amount of force = higher impact on the anchor (or cam, screw, stopper, whatever.) Again, I'm going from memory, and by no means do I fancy myself a physics expert. (And I don't mean to imply that you don't know what you're doing or are unsafe or anything like that....)
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iceisnice
Nov 25, 2006, 8:31 PM
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nah, didn't think you were saying that............ was these actual tests performed by one of the agencies? or is it speculation? i definitely understand what you are saying (i.e. raising the impact force) but it intuitively doesn't seem like a significant increase (for most good size falls that is). apologies to the OP as we digress a bit from his original post.................
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drzaous
Nov 25, 2006, 9:24 PM
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Yeah, I would MAYBE use a half rope as a twin, but I would never use a single. Think about it this way: You have two springs with the same spring constant (meaning that with a given weight they both stretch the same amount). First you load a single spring and the force on the anchor point is x kilonewtons. Now put two of the springs in tandem and the load ont eh anchor is 2x kilonewtons. Basically your cutting down the length that the spring (rope) stretches to catch a fall, hence rasing the impact force very high. Unless you had a good dynamic belay...read VERY dynamic belay, your looking at loading you protection pretty high. The onyl reason i say that a half might work, is that they tend to have VERY low impact forces, hence when doubled might still be low enough (<10kn or so....but only with a 55kg weight). I dunno. I was just wodnerign if anyone had any experience with these half/twin ropes, since having the ability to change depending on the pitch in front of you would be pretty nice. 7.8mm sounds really small though, although diameters really don't mean squat anyways. But it is intriguing that the 7.8mm monster rope comes in at the same weight as a beal ice twin.... for twice the versatility, and still retains a (twin rope configuration) sharp edge fall. For full specs on the monster, the Lanex (mytendon) website has some good info, as monster ropes are exactly the same, just made for metolius.
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notch
Nov 26, 2006, 7:46 PM
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reno wrote: Single ropes are designed to absorb a given amount of force over a given period of time. When there are two such ropes used as twins (a.k.a. the scenario you describe), then neither rope is required to stretch to it's normal parameter. This would create a higher impact on the piece of pro, wouldn't it? Shorter elongation and same amount of force = higher impact on the anchor (or cam, screw, stopper, whatever.) I'm no expert in physics either, but I don't think what you're describing actually happens. There can be no force multiplication simply by adding a rope. Rather, two ropes share the force, each distributiong 50% via elongation, with the remaining undissipated force being transferred to the anchor. Climbing ropes don't have to stretch a certain distance to dissipate force (i.e. there is no "normal parameter" of stretch as you describe it.), rather they stretch as needed to absorb the force applied. Low force, low stretch; high force, high stretch. One rope stretching a lot or two ropes stretching a little will transfer the same amount of force to the anchor.
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west_coast_climber
Nov 27, 2006, 7:14 PM
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drzaous wrote: Yeah, I would MAYBE use a half rope as a twin, but I would never use a single. Think about it this way: You have two springs with the same spring constant (meaning that with a given weight they both stretch the same amount). First you load a single spring and the force on the anchor point is x kilonewtons. Now put two of the springs in tandem and the load ont eh anchor is 2x kilonewtons. Basically your cutting down the length that the spring (rope) stretches to catch a fall, hence rasing the impact force very high. Unless you had a good dynamic belay...read VERY dynamic belay, your looking at loading you protection pretty high. The onyl reason i say that a half might work, is that they tend to have VERY low impact forces, hence when doubled might still be low enough (<10kn or so....but only with a 55kg weight). I dunno. I was just wodnerign if anyone had any experience with these half/twin ropes, since having the ability to change depending on the pitch in front of you would be pretty nice. 7.8mm sounds really small though, although diameters really don't mean squat anyways. But it is intriguing that the 7.8mm monster rope comes in at the same weight as a beal ice twin.... for twice the versatility, and still retains a (twin rope configuration) sharp edge fall. For full specs on the monster, the Lanex (mytendon) website has some good info, as monster ropes are exactly the same, just made for metolius. i've heard this argument before too. i'm not sure how true it really is however. personally, i'm a little annoyed at the rope companies for not providing very much information regarding the uses of their ropes (i mean, how many discussions have there been regarding how to re-mark the center of the rope?!?!?!?!?)... going through their webpages, you feel like you don't really get a lot of info out of them. i think it's perfectly reasonable to use two single ropes as HALF ropes, although you're just carrying up more weight than necessary. as far as using them as twin ropes.. well, why even bother? just use them as halfs and you're good to go.
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reno
Nov 28, 2006, 4:38 AM
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Well, damn. As of yet, I can not find the evidence to support my earlier statements. For the time being, I will say this: 1. Iceisnice, I have nothing factual to refute your position. 2. I won't use single ropes as doubles, but I can't back up my position with data. 3. I won't tell you to not do it. Each climber must make their own choices. Still searching, though.
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glytch
Nov 28, 2006, 5:18 AM
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Bummer. I just wrote a long physics-y response to Notch's post, and then accidentally hit back. to summarize: Using two single ropes as twin ropes is a BAD idea. A dynamic rope reduces peak force in a fall because it slows a falling climber down over a longer period of time than a rope which does not stretch. The length of time over which a rope slows a person down is (nonlinearly) proportional to the amount that the rope stretches. In other words, make a rope stiffer (by, for instance, using two ropes in parallel) and you increase peak impact force throughout the system. what Notch said here:
In reply to: Climbing ropes don't have to stretch a certain distance to dissipate force (i.e. there is no "normal parameter" of stretch as you describe it.), rather they stretch as needed to absorb the force applied. Low force, low stretch; high force, high stretch. One rope stretching a lot or two ropes stretching a little will transfer the same amount of force to the anchor. runs contrary to F = ma, even without looking at the specific nonlinearities of rope-stretch behavior. I won't pretend to know the precise increase in impact force that is caused by using single ropes as twins, as that question is largely empirical. I can say with certainty, however, that the impact force will be substantially larger than the force of a single rope used as, well, a single.
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drzaous
Nov 28, 2006, 7:48 AM
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Yeah that's pretty much what I was trying to say. I think I've decided to get soem beal ice line 8.1mm. Use them as intended (as half's) and when speed or availability of bomber protection dictates clip em as twins. Plus with the really low impact force the beal has it shouldn;t be too bad in twin mode, but still probably over UIAA specs, but with a dynamic belay and a screamer shoulnd't be too bad, plus, if you fall in the high mountains (as long as you have a screamer on your peice) an extra Kn of impact force is gonna be the last thing on your mind as you grind to a halt after a 70 foot fall.
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notch
Nov 29, 2006, 10:18 PM
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glytch wrote: Bummer. I just wrote a long physics-y response to Notch's post, and then accidentally hit back. to summarize: Using two single ropes as twin ropes is a BAD idea. A dynamic rope reduces peak force in a fall because it slows a falling climber down over a longer period of time than a rope which does not stretch. The length of time over which a rope slows a person down is (nonlinearly) proportional to the amount that the rope stretches. In other words, make a rope stiffer (by, for instance, using two ropes in parallel) and you increase peak impact force throughout the system. what Notch said here: In reply to: Climbing ropes don't have to stretch a certain distance to dissipate force (i.e. there is no "normal parameter" of stretch as you describe it.), rather they stretch as needed to absorb the force applied. Low force, low stretch; high force, high stretch. One rope stretching a lot or two ropes stretching a little will transfer the same amount of force to the anchor. runs contrary to F = ma, even without looking at the specific nonlinearities of rope-stretch behavior. I won't pretend to know the precise increase in impact force that is caused by using single ropes as twins, as that question is largely empirical. I can say with certainty, however, that the impact force will be substantially larger than the force of a single rope used as, well, a single. Son of a bitch! I just wrote a nice long response regarding how wrong Glytch was, then just as I was spell checking I realized he was right! In the formula f=ma, with force equalling mass times acceleration, the variable changed by adding a second rope is acceleration (in this instance it is actually deceleration, but in physics they are both represented by "a" if I'm not mistaken). The end result will be an increase in force at the anchor. The benefit of twins or doubles is that they will stretch more given their small diameter. Huh, I learn something new every day!
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rhyang
Nov 29, 2006, 10:23 PM
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Has anyone used the Edelweiss Calanques 8.5's ? (just an item of idle curiosity - I already have the PMI 8.1's for ice climbing)
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stymingersfink
Nov 29, 2006, 10:46 PM
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if you want industry confirmation of your findings, check the specs of Beal's Joker. Different impact forces/#of falls for use in single, double and twin configurations. Purchase the 100M rope (is it still available as such?) for maximum versatility.... you can link 320' of climbing as a single, or 160' as twins/doubles.
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chalkfree
Nov 30, 2006, 12:17 AM
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Problem with all this shit is that the systems by which the UIAA tests ropes has nothing to do with the impact on the pieces or the anchor. Sorry guys, but by passing the single test a rope has automatically passed the double and twin tests. Doesn't make it a good idea to speed up your stop, but it definitely is UIAA passed. Personally I'd rather not use singles as twins, simply because I've taking real falls on static ropes, and I have no desire to repeat the damage to my kidneys. Point of this crap being that I'd buy some thin-medium thin doubles. I like my Mammut genesis, but if I was planning on doing tons of ice I'd probly use Pheonixes.
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acrofobic
Nov 30, 2006, 1:20 AM
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I agree with you. The petzl site has a fall factor calculator and using an 11mm single vs 1 half rope can more than double the force the climber and top anchor will see. also the top 3 anchors ( I chose friends) pulled with the 11 mm rope at a 1.2 factor fall but did not with a half rope. With two halves attached to the system the force on the climber was much higher than only one half again. The reduction in stretch significantly increases force on climber and top anchor. I would not climb on doubled singles.
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chalkfree
Nov 30, 2006, 4:23 AM
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Oops. It seems like they do have a standard for impact force. My bad. 12KN is failing for a single and 8kn for a half rope. Unfortunately we aren't ever given the impact forces for singles with the 55kg weight instead of the 80kg. Some of them certainly pass, for example under the UIAA single weight of 80kg the Beal Booster III 10.2 has an impact force of 7.3kn, so it would certainly pass the half rope test. With the lighter weight it might even be as low as most 8mm half ropes.
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drzaous
Nov 30, 2006, 10:13 AM
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I was reading in the Lab forum that roughly you can say that the specs listed for a half rope (55kg, factor 1.77 fall) correspond to how that same rope will handle under 80 kg and a factor 1 fall. Don't ask me how they calculated this, but it seems pretty plausible. Doesn't really apply to the twin/double issue at hand, but I found it pretty interesting.
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mike_maude
Nov 30, 2006, 5:24 PM
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fwiw, I bought a set of the Beals for those very reasons. Once in use, though, I found the sheaths wore very rapidly and the dry-coat was unimpressive; the ropes were more like sponges from the first use in Canada. I replaced them (for ice) with a set of Mammut Genesis' and been much happier.
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mikew
Dec 1, 2006, 7:58 AM
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I have used Bluewater, Beal and Sterling half ropes and I think the Bluewater's were the better of the three. The Beal (Cobra) was a sponge and also seemed prone to tangles. Might have been me though. The Bluewaters (Excellence) seem to be cut a little longer, has a nice smooth sheath and a good hand. I went through two sets of these ropes and was pleased with their performance. I am on Sterlings (Duetto) now and they seem to be wearing pretty quickly but handle nicely. The dry treatment also seems adequate. YMMV
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