impact force please explain
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I'm shopping for ropes and looking at the mammut revelation 9.2mm. It looks nice and light, and currently 29% off. |
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It should actually be LESS. As I recall, the dropped weight the UIAA uses to test ropes as half/double ropes is substantially lower than the weight used for singles. Maybe a typo, and it should be in reverse? |
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I think they have the twin and half rope impact forces reversed. Half rope force is lower than single because they use a lower mass in the drop test (single 80kg, half 55 kg). Twin is higher than both (single and half) because both ropes are tested together (in parallel) with a 80kg mass. |
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Since Revelations are rated for use as Single / Half / Twin ropes the following table contains three figures for various tests. Half rope testing uses a 55kg mass rather than 80kg as is the case for Single and Twin testing, hence the far lower value for Impact Force. |
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I can't really discuss the particular rope, but, boy, can I generalize, or what? |
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amarius, I don't think this is what the op was looking for but there is a more complete discussion of the difference between impact forces from ropes used as twins (parallel) and halfs /singles for the same test here: |
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Xam wrote:amarius, I don't think this is what the op was looking for but there is a more complete discussion of the difference between impact forces from ropes used as twins (parallel) and halfs /singles for the same test here: mountainproject.com/v/doubl… Short answer: in the ideal lossless spring case, the impact force from ropes used as twins should be 1.4 times higher than the same rope used as a single.Yes, you are right. I attempted to give a simple explanation to what happens when two identical springs/ropes get combined in parallel - the resulting system is going to be stiffer, will result in higher impact force. I did not attempt to get the actual factors, not that the math gets any more complicated by a square root, it simply doesn't add to the story. |
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karl kvashay wrote:I'm shopping for ropes and looking at the mammut revelation 9.2mm. It looks nice and light, and currently 29% off. here are the specs Specs: Diameter: 9.2mm Type: Can be used as a single, half, or twin rope; dry-treated Weight: 55g/m Static Elongation: 7.2% Dynamic Elongation: 31% Impact Force: 8.7kN (single), 6.6kN (twin), 10.1kN (half) UIAA Falls: 7-8 (single), ≥ 20 (twin), ≥ 20 (half) Why is the impact force so dramatically higher when used as a half rope? I'm confused, shouldn't it be the same as when used as a single rope?Those numbers are wrong However the half rope impact force may not be realistic since it is tested with a 55 kg weight rather than 80 kg like single/twins as it assumes the second strand will take some of the weight For more on this go here willgadd.com/single-and-hal… ;) |
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bearbreeder wrote: Those numbers are wrong However the half rope impact force may not be realistic since it is tested with a 55 kg weight rather than 80 kg like single/twins as it assumes the second strand will take some of the weight For more on this go here willgadd.com/single-and-hal… ;)Actually my understanding is that they use the lower mass not assuming the other strand takes the weight. Instead they originally required surviving 1 of the same 80kg test as single ropes, however, many/ most of the half ropes would survive exactly 1 drop with the heavier mass and as a tool used to compare different products having them all show up as "1" does not really help so they ended up lowering the mass to get a spread of results. However the initial idea was to make sure that even a single half rope could survive at least 1 of the "worst scenario" test drop and thus your real world fall. |
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NickMartel wrote: Actually my understanding is that they use the lower mass not assuming the other strand takes the weight. Instead they originally required surviving 1 of the same 80kg test as single ropes, however, many/ most of the half ropes would survive exactly 1 drop with the heavier mass and as a tool used to compare different products having them all show up as "1" does not really help so they ended up lowering the mass to get a spread of results. However the initial idea was to make sure that even a single half rope could survive at least 1 of the "worst scenario" test drop and thus your real world fall.Well if you look at the UIAA drop test youll see that if you were to have a second half rope attached to a belay device in their scenario, it would take some of the force ... Theres a gap of 300m from the "belay device" to the first runner alpy4000.cz/soubory/UIAA101… The problem is that unless we are falling off the belay or from closely spaced pieces on each rope, its likely that a single strand will take the majority of the load in a "normal" fall ... Especially on wandering or traversing pitches which is where half ropes have the advantage ;) |
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old post by Erik W with a bit of history from primary sources.
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What? 7% elongation. |