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bearbreeder
Sep 5, 2013, 5:47 PM
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rocknice2 wrote: I think in your case the speed differential at the top anchor is minimal if you take a standard fall. If the fall is huge or if the climber continues higher placing more pro and then that will increase the speed differential. I think the highest rubbing will occur at T1 not T final The more you place L1 & L2 to the left the more rope drag is created. In that case I wouldn't clip rope L until pro T2 or T3 even. [image]http://www.rockclimbing.com/cgi-bin/forum/gforum.cgi?do=post_attachment;postatt_id=6607;[/image] I don't really see this scenario as a problem
the exact same fall scenario ... they take whippers, they dont die
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verticon
Sep 5, 2013, 8:15 PM
Post #27 of 44
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acorneau wrote: rocknice2 wrote: I also ask if he could do a non official test. Jim Ewing wrote: I’ve been trying to imagine some sort of test set up for this issue in years past but it never seems to become a very high priority, unfortunately. If you have some ideas feel free to share them and I’ll try to determine if it is possible to set up a test. I could imagine a test jig that would be easy to incorporate into a standard drop test tower, something like this... [image]http://www.rockclimbing.com/cgi-bin/forum/gforum.cgi?do=post_attachment;postatt_id=6606;[/image] This should allow the two ropes to stretch at differing speeds/amounts. Any wear would be witnessed where the ropes pass through the top combining "biner".
You're right, this looks like the worst case scenario. At the moment when the rope on the right will reach it's maximum elongation and stop moving, the other one will still be running for a while through the same biner (because it's longer and stretch is proportional to length).
And this is exactly the scenario Curt couldn't envision "where one of the two ropes, upon being separated and then rejoined, would cross the other rope with either of the two ropes being fixed and not moving"
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curt
Sep 5, 2013, 9:48 PM
Post #28 of 44
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verticon wrote: acorneau wrote: rocknice2 wrote: I also ask if he could do a non official test. Jim Ewing wrote: I’ve been trying to imagine some sort of test set up for this issue in years past but it never seems to become a very high priority, unfortunately. If you have some ideas feel free to share them and I’ll try to determine if it is possible to set up a test. I could imagine a test jig that would be easy to incorporate into a standard drop test tower, something like this...  This should allow the two ropes to stretch at differing speeds/amounts. Any wear would be witnessed where the ropes pass through the top combining "biner". You're right, this looks like the worst case scenario. At the moment when the rope on the right will reach it's maximum elongation and stop moving, the other one will still be running for a while through the same biner (because it's longer and stretch is proportional to length). And this is exactly the scenario Curt couldn't envision "where one of the two ropes, upon being separated and then rejoined, would cross the other rope with either of the two ropes being fixed and not moving"
Actually, when the shorter rope reaches its maximum tension, the climber's fall will be fully arrested and the longer rope will also stop running.
Curt
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acorneau
Sep 5, 2013, 10:29 PM
Post #29 of 44
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curt wrote: Actually, when the shorter rope reaches its maximum tension, the climber's fall will be fully arrested and the longer rope will also stop running. Curt
Ah, but at that point the drop-test is ended; friction between the two ropes has happened and they're ready for inspection. Repeat as necessary.
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verticon
Sep 6, 2013, 6:23 AM
Post #30 of 44
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You're right too :)
So, the Mammut guy is also right, it's safe to split and join the double ropes in the same pitch.
(This post was edited by verticon on Sep 6, 2013, 9:43 AM)
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jktinst
Sep 6, 2013, 4:08 PM
Post #31 of 44
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On a Munter the parts of the rope that are rubbing each other are constantly changing, preventing any one spot from overheating. And if they are not changing, they are not rubbing either.
I’m very much on the fence as to whether there might be a potential safety issue with mixing half and twin techniques. I don’t find the assertion of the Mammut product manager (that it’s OK to mix) particularly convincing, especially in light of the other indications that this particular issue has simply not been tested by anyone yet. The argument that we have not seen accidents attributable specifically to this issue does not carry much weight with me either. As has been mentioned, there’s a variety of reasons why mixing is not a particularly widespread approach: the manufacturers’ inclination to make, certify and market ropes for both uses, the rope path/friction considerations, the clearly fairly widespread belief that this is a safety concern, etc. (plus another potential reason below). On the other hand, I have a hard time imagining huge amounts of rope-to-rope friction from two strands running at different speeds through the same biner during a fall.
I’ve probably mixed the two techniques at some point in the past through carelessness or not knowing any better but, since I started paying more attention to my rope paths, length of slings and friction, I have not been tempted to intentionally mix. As others, I would tend to avoid it just to minimize friction. If I hit a straight stretch of route after a zig-zaggy one, I would still prefer to just keep clipping the two strands alternately for that reason. If I were facing a long runout section where I might really want both my strands to catch me at the highest possible pro, I would probably try to place two pros or, failing that, use two slings of different lengths on the same pro. One of the many things I like about half-ropes is the fact that one strand acts as a back-up for the other and it seems to me that they can do a better job of that if the two clipping paths are completely separate: less chance that they’ll both rub on that sharp edge that I failed to spot or that a falling flake will cut both of them.
If the two strands are still clipped in the same biner when you fall and both participate in the arrest, the only differential, as discussed above, would apparently come from greater stretching of the strand that follows the longer path. However, this also means that this longer strand will likely have more friction. So on the one hand you’d have a shorter strand whose stretching will be less impeded by friction (ie more able to stretch throughout its whole length) and on the other, a longer but more impeded strand. I’m not sure that there would be all that much difference between the two in how fast they would run through their shared biner(s). In addition, the Munter comparison makes me think that even if the two strands run together at different speeds or run in opposite directions (one strand slipping back down under its own weight while the other catches the fall ?), you’d just get the same kind of distribution of potential damage over different spots that you get with the Munter, ie no damage.
This would suggest that the main risk of rope-to-rope friction damage, would probably come from one strand running fast over/beside/against the same non-moving spot of the other strand. It seems that this situation would occur mainly if the strands are separated after having been clipped together and if, between the last shared clip and the point of the fall, only one of the strands has been clipped. Longer separated paths and longer falls would result in more rubbing and potentially more damage on that one spot. If testing were to be done to find out whether there really is a safety concern, I would suggest mimicking this situation as the potential worst case scenario before looking at other, less stringent conditions.
This could be yet another reason why there has not been a rash of accident reports from mixing the techniques: you’d have to take a whipper on a single strand after having clipped both together, fail to notice the damage on the other strand and then take another fall on that other strand (plus various other, less obvious conditions).
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verticon
Sep 6, 2013, 5:42 PM
Post #32 of 44
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jktinst wrote: This would suggest that the main risk of rope-to-rope friction damage, would probably come from one strand running fast over/beside/against the same non-moving spot of the other strand. It seems that this situation would occur mainly if the strands are separated after having been clipped together and if, between the last shared clip and the point of the fall, only one of the strands has been clipped. Longer separated paths and longer falls would result in more rubbing and potentially more damage on that one spot. If testing were to be done to find out whether there really is a safety concern, I would suggest mimicking this situation as the potential worst case scenario before looking at other, less stringent conditions.
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rgold
Sep 8, 2013, 3:31 AM
Post #34 of 44
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It seems pretty clear to me that no one, including the rope manufacturers and experienced climbers, has a really clear idea about mixing twin and double technique. It also doesn't seem likely that anyone will have any clear idea very soon, because the circumstances that need to be tested are themselves far from evident.
Much of the "reasoning" offered doesn't sound very plausible to me. For example,
The problems is that once you separate the ropes, the amount of rope out for each strand and the amount of drag for each strand is different. Accordingly, when you fall the ropes can move at different speeds, which if allowed to contact each other could result in rope damage.
If the separated ropes are clipped together at the top piece, then the rate they run out is precisely the rate of the falling climber, and both ropes stop when the falling climber stops. The strand that wanders and is longer stretches a smaller percentage of its total length, and therefore absorbs less of the total fall energy than the other strand, but I don't see any issue with uneven speeds or different stop times at the top biner. This means that there is little to worry about in terms of rubbing in this situation, even from a theoretical point of view, other than creating a harder catch (which might be significant). But Hazel Findlay and others notwithstanding, there isn't much reason to clip two separate strands together. If you really don't trust a single strand to do the job, you shouldn't be climbing with half ropes to begin with. The only scenario I can think of offhand for clipping both strands is that there is a solid piece and something you might hit below. Clipping both strands should reduce the rope stretch and might keep you off the obstacle, at the expense of a higher impact to the pro and your body.
There is an issue with clipping separated strands to a single piece that is not the top piece that is worth mentioning: when loaded, this configuration will lift the draw. If the piece (nut or cam) is in a vertical crack, then it is going to move and could be extracted. If the piece is critical to a back-up role, then this would be reason enough to either not to join to strands there or else make sure the piece is secured from lifting. The lifting action of separated strands could potentially zipper a whole line of doubly-clipped pieces in this fashion if the lowest double-clipped pieces isn't held down.
This means that the potential for rubbing comes from the situation posted by jktinst, but even here the slack unloaded strand would have to be somehow pinned behind the running strand in order for there to be much or even anything in the way of damage. Perhaps this could happen if there was an unfortunate rock feature at that top double-clipped biner. A second possibility with this configuration is that the lower strand does become involved in stopping the fall, in which case you have ropes running in opposite directions through the highest double-clipped biner, a situation with the most potential for some kind of rope damage, although with both ropes running I'd guess the worst that could happen would be glazing of the sheath, which, by the way, has happened with the Munter hitch.
At the end of the day, the argument is very probably much ado about nothing, but that doesn't mean one can't comment on what seems to be the most rational procedure, understanding that it is very unlikely to matter one way or another. Personally, I'd go with the rope engineer and say that it is best in some abstract sense not to mix techniques. Moreover, there is almost never any good reason to mix techniques anyway. I mentioned one possibility above, other possibilities might arise when two seconds are following and one wants both ropes through a critical anchor, although one could still use slings of different lengths and avoid having both ropes together in a single biner. Meanwhile, I think the lifting issue is potentially far more problematic than any possible rubbing, so think carefully if you join separated strands about how your system will behave under load.
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daveat
Sep 9, 2013, 3:19 PM
Post #35 of 44
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 Kind of new to the forums, semi new to climbing and brand new to Trad... so maybe i'm making some stupid thoughts here.. BUT,
This is an interesting point to me.
rgold wrote: There is an issue with clipping separated strands to a single piece that is not the top piece that is worth mentioning: when loaded, this configuration will lift the draw. If the piece (nut or cam) is in a vertical crack, then it is going to move and could be extracted. If the piece is critical to a back-up role, then this would be reason enough to either not to join to strands there or else make sure the piece is secured from lifting. The lifting action of separated strands could potentially zipper a whole line of doubly-clipped pieces in this fashion if the lowest double-clipped pieces isn't held down.
As that would apply, the piece on the left could/would likely shoot out of its placement.
acorneau wrote: rocknice2 wrote: I also ask if he could do a non official test. Jim Ewing wrote: I’ve been trying to imagine some sort of test set up for this issue in years past but it never seems to become a very high priority, unfortunately. If you have some ideas feel free to share them and I’ll try to determine if it is possible to set up a test. I could imagine a test jig that would be easy to incorporate into a standard drop test tower, something like this... This should allow the two ropes to stretch at differing speeds/amounts. Any wear would be witnessed where the ropes pass through the top combining "biner".
(This post was edited by daveat on Sep 9, 2013, 3:23 PM)
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jktinst
Sep 9, 2013, 5:33 PM
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rgold wrote: ...A second possibility with this configuration is that the lower strand does become involved in stopping the fall, in which case you have ropes running in opposite directions through the highest double-clipped biner, a situation with the most potential for some kind of rope damage, although with both ropes running I'd guess the worst that could happen would be glazing of the sheath, which, by the way, has happened with the Munter hitch...
I still can’t picture ropes running in opposite directions through a double-clipped biner other than if the slack/non-arresting one were to slip down under its own weight, which would probably not happen all that often. If the belayer manages to take up slack, run backwards, etc. during the fall, both ropes will run downwards together for a bit. If they are both involved in arresting the fall, they will both run up to, over and down from their respective arresting biner, no matter how far apart these two biners are.
I’d also like to know more about the glazing of the rope by the Munter if anyone has more info. I searched both this forum and the Internet at large and didn’t find a whole lot. The following statement from "Moutaineering – Freedom of the hills" is probably as authoritative as they come but it's not much: "After a big fall (on the Munter), the outermost layer of the sheath may be glazed – which is only cosmetic; this glazing, which also occurs to some degree with mechanical devices, wears off with use". I’m curious about the frequency and intensity of the glazing from the Munter compared to other devices. I also wonder whether dynamic vs non-dynamic arrests might give different results. Finally, it would be tricky to pry apart the two effects but I wonder how much of a part the heated biner plays in the glazing, compared to the rope-on-rope friction.
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JimTitt
Sep 9, 2013, 7:06 PM
Post #37 of 44
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I´ve seen some slight glazing on the rope when doing pull tests on the HMS/Italian Hitch (wrongly called the Munter by the way) but it is almost certainly from the rope/rope contact since the coeff. of friction at that point is so high. You get a certain amount of glazing with all devices (even though you probably can´t see it with the naked eye) and it is is of no concern anyway in real life. It´s an annoying phenomenon though when your trying to do repeat pull tests as the friction in the plate with ATC/Tuber style devices drops if you use the same length of rope so you either have to take this into account or keep changing the section of rope being tested.
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rocknice2
Sep 10, 2013, 1:48 PM
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There have been many good points made in this discussion. One of the reasons I brought up this topic is, on a few occasions I've climbed a route where a double crack system converges to a single. In the past I have alternated clipping red/blue. When the ropes are running directly beside each other as in a single crack, I have found that sometimes I clip one around the other. This doesn't happen when the ropes are separated by a few feet or meters as in a double crack. The reason I think is that one rope will run over a knee and the other between the legs or over the other knee. Before anyone says just keep it organised, let me say that I do but in the real world shit just happens and I've been climbing on doubles for over 20 years.
rgold wrote: There is an issue with clipping separated strands to a single piece that is not the top piece that is worth mentioning: when loaded, this configuration will lift the draw. If the piece (nut or cam) is in a vertical crack, then it is going to move and could be extracted. If the piece is critical to a back-up role, then this would be reason enough to either not to join to strands there or else make sure the piece is secured from lifting. The lifting action of separated strands could potentially zipper a whole line of doubly-clipped pieces in this fashion if the lowest double-clipped pieces isn't held down.
I have done some [very, very] rough calculation and made some huge assumptions but it may be good for discussion. Please understand that this drawing is worst case and is not meant to mimic real world.
I made the blue rope shorter because for some stupid reason there is enormous rope drag at the blue triangle. the red triangle is the belayer.
Assuming a 10m fall on 15m of blue rope @ a dynamic elongation of 30% gives me a rope stretch of 4.5m. I divided that 4.5m by the amount of each rope at key points to find the rope travel at each point.
It's clear to see that the highest differential is at the point of convergence. Taking into account what 'rgold' said, the ropes would not be likely to rub there.
(This post was edited by rocknice2 on Sep 10, 2013, 1:56 PM)
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cracklover
Sep 10, 2013, 4:05 PM
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rgold wrote: There is an issue with clipping separated strands to a single piece that is not the top piece that is worth mentioning: when loaded, this configuration will lift the draw. If the piece (nut or cam) is in a vertical crack, then it is going to move and could be extracted. If the piece is critical to a back-up role, then this would be reason enough to either not to join to strands there or else make sure the piece is secured from lifting. The lifting action of separated strands could potentially zipper a whole line of doubly-clipped pieces in this fashion if the lowest double-clipped pieces isn't held down.
Just a point of clarification: I think you meant to say the *highest*, not the lowest doubly-clipped piece. As I'm envisioning it, in this scenario (unlike the normal zippering scenario) the bottom of a string of doubly-clipped pieces will actually be pulled *down*, while the top ones will be pulled up. And then, if the top one rips, the upward force will go to the next one down, etc.
Here's a quick pic to explain:
GO
(This post was edited by cracklover on Sep 10, 2013, 4:05 PM)
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rocknice2
Sep 10, 2013, 5:18 PM
Post #41 of 44
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Lowest twin clip was referring to this pic
(This post was edited by rocknice2 on Sep 10, 2013, 5:18 PM)
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jktinst
Sep 10, 2013, 6:56 PM
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When you posted your earlier diagram, I kind of lumped it with acorneau’s. I saw that you made the point that the greater differential would be at the bottom of the double-clipped chain, not the top, but missed your assumption that the longer rope, because it had more friction, would behave as if it were shorter than the shorter one. I figured that you were simply disregarding the friction and that, as a result, you thought that it would be the longer rope that would run a greater distance through the lower double-clipped biner.
I get it now but I’m wondering if you might not be confusing what would constitute an enormous amount of rope drag for the leader to keep on climbing with what would significantly cut back on the ability of the rope to transmit the load of a fall to the belay. I think that the leader could easily arrive at a point where he cannot climb further, even pulling up slack two-handed before moving and yet, if he were to fall at that point, a few metres above his last pro, his belayer would still feel a reasonable yank.
My own experience and corner of a napkin estimates of how much tension is lost to friction at different bend angles suggest that in order to have the kind of severe friction that would make the longer rope behave as though it was significantly shorter than the other, you would already be in a situation where progress is impossible, never mind considering double-clipping.
(edited for clarity)
(This post was edited by jktinst on Sep 10, 2013, 9:06 PM)
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rocknice2
Sep 10, 2013, 7:55 PM
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Let me clarify.
This drawing depicts what I would consider real world. I'm not discounting amount of each rope out and differing rope speeds. The whole purpose is to reduce friction by splitting up the ropes. I'm just thinking now that it may not be that great a differential. IMO
Now this pic is total fiction or shall I say friction. It's a proposal that I came up with to show an absolute worst case. The blue rope is made shorter by tremendous rope drag. Notice that where the rope speed differential is greatest the strands are least likely to rub against each other.
Again NOT a real world scenario. Then again there will be one noob that will test it.
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anarkhos
Oct 16, 2013, 11:50 PM
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I made the mistake of clipping both doubles into one biner once. Never again. The ropes twisted in the biner and I ended up with horrendous drag. If I need both on one anchor for whatever reason (like a directional), I will use two biners.
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