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diplodocus
Jan 5, 2004, 6:01 AM
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In a pinch, is it safe to use ONE single rope as a double rope (20 meter pitch)? ie.:
1) Climber makes a figure-8 on a bight in the middle of the rope, clips that into his harness
2) Belayer sets up both sides of the same rope as in double-rope belay
3) Climber leads up using double-rope technique
4) Belayer 2nds up with the 2 ends of the rope
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boltdude
Jan 5, 2004, 6:22 AM
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Sure, but it's safest to have the leader tie into the ends and the belayer use a couple lockers on a figure 8 on a bight in the middle of the rope.
In fact, some folks (especially mountaineers) use 100m skinny ropes and do this as a regular practice, since it's far safer on long rappels (you don't have to worry about the knot jamming on double-rope rappels if you don't have a knot).
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ropeburn
Jan 5, 2004, 6:42 AM
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It seems like you'd be in for a harsh "catch". Half the normal dynamic elongation.
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lukeskywalker
Jan 5, 2004, 7:25 AM
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There's no problem with using singles for double rope technique (one strand clipped to each biner), just don't do twin rope technique (both strands clipped to the same biner).. Ropeburn is kind of correct regarding the higher impact force, but only if you clip both strands into the same piece.
Also, you don't have to use lockers or other biners to clip into the middle of the rope.. You can tie in directly to the middle of a rope.. Just tie a big figure 8 on a bight, pass the bight trough the two loops on your harness and then pass the loop over your head and step trough.. If you've done this correctly you would have girth hitched the rope to your harness..
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coldclimb
Jan 5, 2004, 8:29 AM
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If you have effectively turned one rope into two, then you are no longer climbing on only one rope, and therefore it would be just as safe as two full length ropes. Right? ;)
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crushingfinger
Jan 5, 2004, 8:44 AM
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Look at the rope realy hard, somtimes it turns into two. :mrgreen:
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overlord
Jan 5, 2004, 1:02 PM
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its safe, but itll probably be a hrad catch unless you do a proper dynamic belay.
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j_ung
Jan 5, 2004, 2:15 PM
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Double, not twin, right? I don't think the catch will be any harder than the same fall on a single, since it's likely that only one of the two ropes will catch you anyway. Follow boltdude's suggestion to avoid crossloading a biner in a lead fall on a short rope, e.g., lead on the ends, not the middle.
j_ung
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geezergecko
Jan 5, 2004, 2:23 PM
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When you climb using proper double rope technique (as opposed to twin rope technique), a catch is almost always done on one and only one rope. Even if you use 2 carabiners on a piece to clip both ropes, the different length path of the ropes would insure one takes more strain than the other. The second rope is essentially a backup if the piece on the first rope pulls and then you fall on the piece for the second rope. This is good because you get 2 shots at a soft catch. Think of this as a series system not a parallel system.
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diplodocus
Jan 5, 2004, 2:32 PM
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To be clear, it would not be a ‘hard’ catch if I use the “double rope technique†and NOT the “twin rope technique†right? If not, could someone please explain to me why it would be a hard catch.
I get the impression from some of the comments that it would be a hard catch whichever the method.
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esoteric1
Jan 5, 2004, 2:35 PM
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yall ever seen those really long thin chords? ive seen some euros climbing on one of those...120 meeter single line and they double it over, at like 8.5 or something like that, pretty keen idea if ya ask me...
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j_ung
Jan 5, 2004, 9:32 PM
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In reply to: To be clear, it would not be a ‘hard’ catch if I use the “double rope technique” and NOT the “twin rope technique” right? If not, could someone please explain to me why it would be a hard catch. I get the impression from some of the comments that it would be a hard catch whichever the method.
Welllll, sort of.
The more rope length you have in the system, the more stretch you get during a fall, thus a softer catch. Working with only half the rope's total length, as you suggest, means that you'll never get to have more than half the rope in your system. However, the difference isn't going to kill you (unless your protection really sucks).
Some folks, myself included, have cautioned against twin roping (clipping both ropes into every piece) because 2 ropes won't stretch nearly as much as one - that may mean a hard catch, depending on your rope diameter. Instead, most of us seem to think it's OK to use doubles (clipping separate pieces to minimize drag (and a few other reasons)).
Twins = bad
Doubles = AOK
You may, however, encounter other safety concerns. Has your partner belayed on doubles before? It's much trickier. Also how long is the route in total? I ask because with half the rope length, you may have to climb twice as many pitches :( .
But a better question is this: What exactly is the "pinch" that you spoke of in your original post?
Common reasons why people climb on doubles (in no particular order):
1. Minimizes rope drag
2. No extra rope to carry solely for rappelling later
3. No extra slack in the system if you blow a clip
4. Minimizes risk of your only rope being cut in a fall or by rockfall
Is your reason one of those?
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hema
Jan 5, 2004, 10:11 PM
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In reply to: In reply to: yall ever seen those really long thin chords? ive seen some euros climbing on one of those...120 meeter single line and they double it over, at like 8.5 or something like that, pretty keen idea if ya ask me... Cool idea. No knot to get stuck on rappel! :D Can you get it in bi-color so you can still which side is which?
Yeah, you do get them in bi-colors. I got myself 100m bo-colored half-rope and atleast Mammut and Millet(Onesport) do them.
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tedc
Jan 5, 2004, 10:22 PM
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8.5mm x 100m: Cool idea until you find out how tangled you can get it. A 100m line is about 10 times more tangle prone than a 50m and you HAVE to have it flaked perfectly on every pitch or the belayer will end up fighting a knot for half the pitch. The knot is a small price to pay for the flexibility of two ropes. IMHO. BTW the same thing hapens when you double over a 50m. It just takes half as much time to clear the cluster F.
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davidji
Jan 5, 2004, 11:13 PM
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In reply to: There's no problem with using singles for double rope technique (one strand clipped to each biner), just don't do twin rope technique (both strands clipped to the same biner).. Ropeburn is kind of correct regarding the higher impact force, but only if you clip both strands into the same piece.
Why not use one half rope instead of one single? That's how I've done it anyway.
David
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climbaddic
Jan 5, 2004, 11:34 PM
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THIS IS REALLY DANGEROUS.
If you are taking a fall, your Fall Force on the anchor will be too big. You will blow out your anchors from big fall force. Sure you have less chance of cutting your ropes, but your chance goes way up for blowing out anchors.
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diplodocus
Jan 6, 2004, 2:54 AM
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To answer "j_ung"'s question ...
By "pinch", I mean if I come to a new pitch that is about 20-25meters, and because its a winding route and looks safer to use a double rope technique. (but I only have one 30 meter rope with me).
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rgold
Jan 6, 2004, 3:02 PM
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The "hard catch" resulting from clipping both strands can be quantified; the sum of the tensions in both ropes will be the square root of 2 times the tension that would have resulted had only a single strand caught the fall. Since the square root of 2 is approximately 1.4, clipping both strands will result in loads to the system that are 40% higher than the loads imposed by a single strand.
If you've redirected the belay through the belay anchor and the leader falls with the anchor at his feet (fall factor 1), the load on the anchor with both ropes clipped and a static belay would be a bit more than 16 kN or nearly 3700 lbf. (The only way to achieve this would be to belay with two Gri-Gri's.) In order to belay statically, the belayer would have to hold nearly 1500 lbf; of course this is impossible(*) and so the belay will be of the forced dynamic kind. Rope burns are guaranteed (assuming no gloves) and loss of control is quite possible.
Of course, rope burns and possible loss of control are features of the single clip-in too. In the same situation with just one rope clipped to the belay anchor, the load on the anchor for a static belay would be about 12 kN or 2600 lbf and the belayer would be faced with a static load a bit over 1000 lbf.
In any case, as has been said several times already, there is no reason to risk 40% greater loads by clipping both strands when each strand is already a single rope.
(*)Footnote: Maybe it isn't impossible, which is worrisome. I suspect that a belayer can momentarily resist much higher loads than the figures we read for belay devices, which are static holding loads. In other words, rope tension and anchor loads might momentarily build much higher than the figures that result from the static load a belayer can hold.
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esoteric1
Jan 6, 2004, 3:19 PM
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I sure am glad that someone does the math on these things.
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reno
Jan 6, 2004, 3:20 PM
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Why couldn't you take the middle of the rope, tie in with a bowline, and leave the ends for the belayer (akin to the middle person on a three man glacier/snow climb)?? This seems more simple than the "Step through-Girth Hitch" method mentioned on page 1.
Never done either, as I climb on a single 10.5 or doubles.
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j_ung
Jan 6, 2004, 4:26 PM
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In reply to: To answer "j_ung"'s question ... By "pinch", I mean if I come to a new pitch that is about 20-25meters, and because its a winding route and looks safer to use a double rope technique. (but I only have one 30 meter rope with me).
I'm assuming you mean that you have one 60 meter rope with you, correct? In that case you're fine, just be sure to listen to the advice in the thread about impact forces on doubles vs. twin. Seems like a no-brainer, but if a mistake is going to occur, it'll likely be low on the pitch. This is because without much gear placed, you're virtually on twins, not doubles, no matter what you do. Place lots of gear early. You should be doing that anyway!
Have fun, man! Figuring out problems like this one is what got me interested in climbing in the first place!
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diplodocus
Jan 10, 2004, 2:31 PM
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opps, yes i meant 60m rope. Tks for the input folks
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diplodocus
Feb 5, 2004, 4:01 PM
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Several people said that it was better to lead using both ends of the rope rather than the middle … is there a reason why it is better?
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scubasnyder
Feb 5, 2004, 4:03 PM
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its safe.......
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dirtineye
Feb 5, 2004, 5:01 PM
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In reply to: Several people said that it was better to lead using both ends of the rope rather than the middle ? is there a reason why it is better?
Well, do you want to trust just one knot or do you want to trust two knots?
If anything happens to the one knot, you are done.
Also, what would happen if the leader, tied in in the middle of the rope, had to do a belay escape?
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sspssp
Feb 5, 2004, 5:05 PM
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As far as trusting the knot, isn't that what you do when you tie into the end of the rope?
If you tie into the middle, you could clip in with a couple of locking biners which make it quick to escape, although this would potentially add additional failure points. You can also tie a loop and "step through it" to tie into with using biners. This knot can be "escaped" although it is a little more awkward to get out of.
In a worse case scenerio, the leader cuts the rope to escape (you do have your knife with you, don't you?).
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dirtineye
Feb 5, 2004, 5:12 PM
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In reply to: The "hard catch" resulting from clipping both strands can be quantified; the sum of the tensions in both ropes will be the square root of 2 times the tension that would have resulted had only a single strand caught the fall. Since the square root of 2 is approximately 1.4, clipping both strands will result in loads to the system that are 40% higher than the loads imposed by a single strand.
I'm probably missing something. I plead rust and extreme laziness, can you show you you got your numbers?
Also, wouldn't the max impact force for the twinned rope be twice that of the single rope, over the same distance, and would this not be perhaps a greater problem than increasing the total load on the system by 40%?
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mustclimb69
Feb 5, 2004, 5:15 PM
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If a single is safe with one strand why wouldnt it be safe with 2???
Yeah I have done this but have the leader tie in with both ends and the follower use a fi8 (or 2 independently) and locking biners
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abalch
Feb 5, 2004, 5:53 PM
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In reply to: If you've redirected the belay through the belay anchor and the leader falls with the anchor at his feet (fall factor 1), the load on the anchor with both ropes clipped and a static belay would be a bit more than 16 kN or nearly 3700 lbf.
What you are ignoring here is one of the primary principles of double rope technique. You NEVER clip both ropes into one piece of gear, if you are doing double rope technique. The reason is, if you have two ropes going through one carabiner, where they also are going through individual pieces, then you will have two different lengths of rope out, and when you fall, the longer length will slide against the shorter length very rapidly, possibly melting the sheath of the ropes. When doing proper double rope technique, unless on a very straight route where it isn't needed, you will almost always have two different lengths of rope out, so if you fall, all the force will be placed on the rope that is in the last piece of gear. If that rope or gear fails, then the second strand will catch (hopefully), with some of the force dissipated, and with less slack then is in the other rope if the gear popped.
So, if leading the second pitch, redirect one rope through the anchor. As soon as possible, place another piece of pro, and clip the other rope to it. You have just eliminated the large forces you spoke of. If that piece with the second rope came out, then you still would face a normal fall on a single rope. If the first piece after the anchor held, you actually have lowered the fall factor.
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dirtineye
Feb 5, 2004, 6:14 PM
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In reply to: In reply to: If you've redirected the belay through the belay anchor and the leader falls with the anchor at his feet (fall factor 1), the load on the anchor with both ropes clipped and a static belay would be a bit more than 16 kN or nearly 3700 lbf. What you are ignoring here is one of the primary principles of double rope technique. You NEVER clip both ropes into one piece of gear, if you are doing double rope technique. The reason is, if you have two ropes going through one carabiner, where they also are going through individual pieces, then you will have two different lengths of rope out, and when you fall, the longer length will slide against the shorter length very rapidly, possibly melting the sheath of the ropes. When doing proper double rope technique, unless on a very straight route where it isn't needed, you will almost always have two different lengths of rope out, so if you fall, all the force will be placed on the rope that is in the last piece of gear. If that rope or gear fails, then the second strand will catch (hopefully), with some of the force dissipated, and with less slack then is in the other rope if the gear popped. So, if leading the second pitch, redirect one rope through the anchor. As soon as possible, place another piece of pro, and clip the other rope to it. You have just eliminated the large forces you spoke of. If that piece with the second rope came out, then you still would face a normal fall on a single rope. If the first piece after the anchor held, you actually have lowered the fall factor.
Rgold can speak for himsself on this, but just because he said redirected through a belay anchor does not mean double ropes through the same piece with the same length out.
In fact, that part of the discussion was about twinning a single rope.
But anyway, whne using double ropes, you can clip each one into a separate carabiner at the belay anchor, and allow more slack in one than in the other, which is a better idea than what you suggest.
As for the people advocating clipping into the middle of the doubled over lead line with carabiners, SHAME! And as for cutting the 120 meter rope, WHY, when you could have tied into the two ends? I suppose the ones talkign aobut stepping out of a girth hitch think that is somehow easier than untieing a knot at your belay point? One other problem is, that if the leader escapes the rope by any means, if he drops the middle of the rope, it's just gone, but if he has tied in the two ends and drops one, he still has a chance with the other end.
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diplodocus
Feb 9, 2004, 6:16 AM
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Tks for the input dirtineye, especially on the point about still having one end of the rope with you, if you accidentally lose the other end. So simple, but I overlooked it.
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dirtineye
Feb 9, 2004, 4:47 PM
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In reply to: Tks for the input dirtineye, especially on the point about still having one end of the rope with you, if you accidentally lose the other end. So simple, but I overlooked it.
You're welcome!
I've never done that (dropped the rope), but I know a story about a well known southern climber who is famous for getting into epics who did drop a rope in a bad place to do that ( like there is a good place), and just the thought is enough to make me stay tied in or at least if I have to untie to put a bight knot in the rope and clip it BEFORE I untie haha.
IT is the simple stuff that counts, isn't it? I'm lucky to have had a few very experienced ( the good kind of experience) partners from the start. When the chance for a screw up arises, they go into KISS and DDAS (don't do anything stupid) mode, and the first two things that happen at a rap station in the dark is, secure the climbers, secure the rope.
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ontherocks
Aug 19, 2005, 2:59 PM
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In reply to: The "hard catch" resulting from clipping both strands can be quantified; the sum of the tensions in both ropes will be the square root of 2 times the tension that would have resulted had only a single strand caught the fall. Since the square root of 2 is approximately 1.4, clipping both strands will result in loads to the system that are 40% higher than the loads imposed by a single strand.
I think you are forgetting that in that ideal situation each strand of rope would catch half of the load, then half of the force. Therefore considering that you have more rope stretch on the system (more rope for half the load), both the factor and the forces would be lower. You won't be blowing your anchor or burning your belayer's hand due to strange forces. You will be either safer, or in the same situation (if only one rope takes the load, due to slack on the other).
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landgolier
Aug 19, 2005, 3:39 PM
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This thread is older than dirt and got pretty well hashed out, why are you reviving it?
In reply to: In reply to: The "hard catch" resulting from clipping both strands can be quantified; the sum of the tensions in both ropes will be the square root of 2 times the tension that would have resulted had only a single strand caught the fall. Since the square root of 2 is approximately 1.4, clipping both strands will result in loads to the system that are 40% higher than the loads imposed by a single strand. I think you are forgetting that in that ideal situation each strand of rope would catch half of the load, then half of the force. Therefore considering that you have more rope stretch on the system (more rope for half the load), both the factor and the forces would be lower. You won't be blowing your anchor or burning your belayer's hand due to strange forces. You will be either safer, or in the same situation (if only one rope takes the load, due to slack on the other). |
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ontherocks
Aug 19, 2005, 3:43 PM
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Well, the Beal Joker (9.1mm), that is a recent product is single, double and twin. I was looking for info on using singles as doubles, and I found this. It seems that someone gave wrong beta on the physics of the issue.
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landgolier
Aug 19, 2005, 4:13 PM
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In reply to: Well, the Beal Joker (9.1mm), that is a recent product is single, double and twin. I was looking for info on using singles as doubles, and I found this. It seems that someone gave wrong beta on the physics of the issue.
:roll: Here we go again....
If you reread the thread and think about it you will see that rgold is right, you need to remember we are talking about impact force on the anchor or piece, in which case two singles used like a twin are going to increase it outside acceptable parameters, unless you're using some weird noodle like the joker or the new mammut. If you don't believe me, play with some rubber bands, or go put a second set of shocks on your car. I won't get into the physics of it, but more elastic elements running "parallel" = less overall elasticity. You will also notice that twin ropes have a higher impact force than singles (look up the stats on the joker, for one).
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dirtineye
Aug 19, 2005, 7:22 PM
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The, "someone", you think gave wrong info on the physics is indeed a professor of mathematics. I seriously doubt that he made an error in the math and physics. But, if you see an error, disprove what was written. Do this is a mathematical way, with equations to show why you are right, and why he is wrong. You don't win an argument in math or physics without proof.
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rgold
Aug 20, 2005, 4:17 AM
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I lost track of this thread until it rose up from the dead...here are some replies.
In reply to: What you are ignoring here is one of the primary principles of double rope technique. You NEVER clip both ropes into one piece of gear, if you are doing double rope technique
Sure. Lots of people referred to the "hard catch" that results if you do clip both strands to the same piece, and all I was doing was describing how hard the "hard catch" would be.
In reply to: ...wouldn't the max impact force for the twinned rope be twice that of the single rope, over the same distance?
In reply to: I think you are forgetting that in that ideal situation each strand of rope would catch half of the load, then half of the force...
Rope tension is proportional to stretch (for a given fixed length of rope) but the energy absorbed is proportional to the square of the stretch, and the maximum impact force is found by computing how much the rope must stretch to account for the faller's loss of potential energy.
Suppose a single strand of a given length must stretch an amount S to absorb the fall energy, and two strands sharing the load equally stretch an amount s (note capital and lower-case s's). Each of the two strands absorbs an amount of energy proportional to s^2, and so (cancelling the constants of proportionality) 2s^2=S^2, s=S/sqrt(2). Since the tension in each strand is proportional to its stretch, the combined tensions of the two strands will be proportional to [2/sqrt(2)]S=sqrt(2)S and so the maximum tension in the combined double strands will be sqrt(2) times the single-strand tension.
In reply to: It seems that someone gave wrong beta on the physics of the issue.
The OP was not speaking of this specialty rope, and for other ropes the 40% increase in load is probably a more reasonable estimate.
Edited to correct a typo in one of the exponents. Thanks to dirtineye for pointing out the error.
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clmbnski
Aug 22, 2005, 7:55 PM
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That is interesting, I wouldnt have expected two ropes sharing a load to have a higher peak tension than just a single rope taking the full load.
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landgolier
Aug 22, 2005, 7:59 PM
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In reply to: That is interesting, I wouldnt have expected two ropes sharing a load to have a higher peak tension than just a single rope taking the full load.
Again, it's kind of counterintuitive, but play with 1 rubber band vs. 10 and it's readily apparent.
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aikibujin
Aug 22, 2005, 8:45 PM
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Back from the dead?
In reply to: What you are ignoring here is one of the primary principles of double rope technique. You NEVER clip both ropes into one piece of gear, if you are doing double rope technique. ... So, if leading the second pitch, redirect one rope through the anchor. As soon as possible, place another piece of pro, and clip the other rope to it.
Never say never. Here's a situation I have actually encountered in real life: three pitches up a climb, two new stainless steel bolts as anchors, a not so great green alien placement in soft sandstone I can reach while still standing at the belay, then 30 feet of runout but easy (5.4ish) climbing to the next possible placement.
Would you still have redirected only one strand of your doubles through the anchor in this situation?
Here are some points to consider:
* a single strand of double rope is UIAA tested with 55kg of weight in a fall factor 1.77 fall.
* I'm pretty skinny, weighing in at 140 lbs. With clothes and gear I'm maybe 155lbs - that's 70kg.
* The bolts were about eye level, so assume my belayer holds the belay device 3 feet lower than the redirect. If I somehow loose my balance and fall while placing gear after the 30 feet runout, I'm taking a (30*2)/(33) = 1.82 fall factor fall.
When I led that pitch, I chose to clip both strand of the doubles through the anchor with two different length slings because I felt that was the best practice for the given situation. But even if a single biner was used for both strands, it's not the end of the world. When the single biner is only three feet away from the belay device, rope on rope movement is minimal, unless one rope starts to slip against the other at the belay device. It may not be the best practice, but the danger of rope on rope friction is less likely to occur than if the strands were clipped to the same biner higher up in a pitch. So if you put this in a risk management matrix, the severity might be "high", but the likelyhood might be "rare".
My point is, there aren't a lot of "never do this" rules in climbing. It is about evaluating each unique situation and managing the risks.
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aikibujin
Aug 23, 2005, 1:23 AM
Post #44 of 44
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Registered: Dec 28, 2003
Posts: 408
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In reply to: A good double-bolt anchor? Why not clip one strand into each bolt?
Certainly another option, and probably the best option given the situation. I would have preferred this, but the rap chains and my biners already on the hanger made clipping directly into the hanger difficult.
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