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single rope doubled - safe?
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dirtineye


Feb 5, 2004, 9:01 AM
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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?

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?


sspssp


Feb 5, 2004, 9:05 AM
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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?).


dirtineye


Feb 5, 2004, 9:12 AM
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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.

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%?


mustclimb69


Feb 5, 2004, 9:15 AM
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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


abalch


Feb 5, 2004, 9:53 AM
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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.


dirtineye


Feb 5, 2004, 10:14 AM
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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.


diplodocus


Feb 8, 2004, 10:16 PM
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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.


dirtineye


Feb 9, 2004, 8:47 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.

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.


ontherocks


Aug 19, 2005, 7:59 AM
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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.

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).


landgolier


Aug 19, 2005, 8:39 AM
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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).


ontherocks


Aug 19, 2005, 8:43 AM
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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.


landgolier


Aug 19, 2005, 9:13 AM
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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.

: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).


dirtineye


Aug 19, 2005, 12:22 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.


Partner rgold


Aug 19, 2005, 9:17 PM
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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 analysis above is based on an ideal model of a rope satisfying Hooke's Law. This model, or an analogous one involving damping forces, have been successfully used to describe and codify climbing rope behavior. In the basic model, if rope tension is graphed versus rope stretch for a fixed length of rope, a straight line results. In reality, the graph is not a straight line, but something "not far" from a straight line, at least within the expected working range of the rope. The Beal engineers have found a construction that emphasizes and then profits from the potential non-linearity of this graph to produce a rope whose impact force when twinned is not 40% higher than its single-strand impact force, but only about 16% higher.

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.


clmbnski


Aug 22, 2005, 12:55 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.


landgolier


Aug 22, 2005, 12:59 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.

Again, it's kind of counterintuitive, but play with 1 rubber band vs. 10 and it's readily apparent.


aikibujin


Aug 22, 2005, 1:45 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.


Partner rgold


Aug 22, 2005, 5:10 PM
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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.

A good double-bolt anchor? Why not clip one strand into each bolt?

But I agree about never say never.


aikibujin


Aug 22, 2005, 6:23 PM
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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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