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How to rappel on a loaded rope?

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Postby Day Hiker » Thu Sep 10, 2009 9:43 am

nartreb wrote:The old chain-of-'biners trick (see bottom photo here: http://climbinglife.com/tech-tips/tech- ... -know.html ) requires smaller bends of the rope than a device like an ATC, so should work better with tension on the rope, especially if you rig it for mimimal friction. (It works just like the brake bar shown in an earlier post.) Back it up with a prussik in case the rope gets unweighted for any reason and you lose that fireman's belay...


I won't claim to be an expert or beyond making an incorrect statement. But I have to respectfully disagree with the idea that one could use the photographed method (below) to descend if there is a bodyweight of tension on the rope from another person below.

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Postby Nikolas_A » Thu Sep 10, 2009 6:41 pm

Day Hiker wrote:I won't claim to be an expert or beyond making an incorrect statement. But I have to respectfully disagree with the idea that one could use the photographed method (below) to descend if there is a bodyweight of tension on the rope from another person below.


I agree. Each and every "normal" belay technique requires a small braking force of, say 5-10kg. 70-80kg worth of unconscious climbing partner is bound to give you a fireman's belay. Prussics (or similar knots) may be the only solution. Other ideas?
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Postby nartreb » Thu Sep 10, 2009 8:07 pm

I'm sure you're right about the basic crossed-biners setup shown above, but there's a variation I'd like to try. Imagine if the 'biners in the photo were twice as long, there'd be a lot less friction and you'd need a lot more braking force. Well you can simulate 'biners of arbitrary length by constructing a chain of 'biners.
Normally, additional 'biners are added to the chain so you can thread the rope through all of them, increasing friction. (You can also increase friction by adding more crossing 'biners.) But it should be possible to thread the rope through, say, half of the "holes", creating the equivalent of the long 'biner described in my second sentence. The danger is that if your'e not careful, you could allow the chain to bend in a way that removes all friction entirely, but I think that can be avoided.
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Postby Day Hiker » Fri Sep 11, 2009 12:27 am

nartreb wrote:I'm sure you're right about the basic crossed-biners setup shown above, but there's a variation I'd like to try. Imagine if the 'biners in the photo were twice as long, there'd be a lot less friction and you'd need a lot more braking force. Well you can simulate 'biners of arbitrary length by constructing a chain of 'biners.
Normally, additional 'biners are added to the chain so you can thread the rope through all of them, increasing friction. (You can also increase friction by adding more crossing 'biners.) But it should be possible to thread the rope through, say, half of the "holes", creating the equivalent of the long 'biner described in my second sentence. The danger is that if your'e not careful, you could allow the chain to bend in a way that removes all friction entirely, but I think that can be avoided.


There is a fundamental problem with trying to rappel with a bodyweight of tension on the rope below the device, as long as the device is dependent on the tension in the rope! Even if you could invent a device that gives you a friction low enough to descend, how are you going to effectively modulate that friction enough to do a safe rappel?

If you have a body weight of tension in the rope below your device, you will have no way to change the angle the rope makes as it leaves the device. The rope is always going to be straight down, unless you can lift your partner's weight with one hand.

But even more importantly, this is going to be a device that allows you to rappel with a bodyweight of tension in the rope below the device. But if 200 pounds of tension in the rope below this theoretical device is just enough to let you rappel at a safe speed, how much tension is it going to take in order for you to stop? 300 pounds? 400 pounds? It's less than safe if you have to add 100 or 200 pounds of tension with your brake hand just to stop. And remember, if your partner's weight is on the rope below, you're not going to be able to wrap it behind your back or around your leg or anything like that to create the friction.

And then what happens when your partner reaches the ground and unloads the rope? Now you're on a device that requires 200 pounds of tension for a safe rappel speed and well over 200 pounds for stopping, and you have only your brake hand and some body-part-wrapping techniques to do that.

So, no way. The only thing that is going to work is something that does not depend on the amount of tension in the rope or the angle the rope makes as it exits the device. The descenders shown earlier would be an example, I think. But I don't know if those devices are going to be fast enough to justify their use over just rappelling one-at-a-time with a standard device.
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Postby nartreb » Fri Sep 11, 2009 1:53 am

The question I'm trying to answer is, suppose you're leading, you've used up almost all of the rope, and your partner is suddenly knocked unconscious. Actually, assume you've finished leading, so you're anchored, but your partner collapses just after undoing his anchor. Now you've got 200lbs of dead weight on your only rope, and you need to get down to your partner, preferably before he bleeds to death. You don't have any of those specially designed descenders mentioned earlier in this thread. Can you get down using what you've got? (Soloing doesn't count.)

I did some indoor experiments, and the classic crossed-biner technique does seem to work even with tension on the rope. It helps to use a very large 'biner (petzl William) and only one crossbar oval. I'll give it a try outdoors (ie with real weight) when I get a chance. Sadly, my idea of a long chain of 'biners doesn't work without some kind of rigid pole to reinforce it (otherwise the whole system can collapse) and since I don't carry anything like that when I climb, I had to reject it.

I also tried lots of half-baked ideas involving large D-shaped biners being held in a rope-pinching position by smaller 'biners, but none of them worked well. (Some had a tendency to seize up, others were prone to coming completely frictionless.)

However, while casting about for something rigid that might work as the core of a chain-of-biners, I found one implement that has: one hole large enough for one or two strands of rope; another hole you can put a 'biner through. In other words, it works fairly well as one of those old-fashioned belay plates, if the rope is under tension and a very slight bend in the rope is what you want. The implement in question: a Black Diamond nut remover. It has rather sharp edges, but my rope is old anyway, so I'll give it a try.

Also sharing those properties: my Reverso 3, if rigged in a way rather different from what's in the owner's manual. If it works outdoors, I'll provide photos of the setup.

Your concern about additional braking is valid. Simply put, you do not have control of the angle at which the rope leaves the device. (Except to the extent that you can pull the rope up to lift the weight , which will achieve the opposite of braking.) If the friction is too low, you risk catastrophic acceleration. Your only defense is to back up the improvised descender with a prussik or similar knot.

You *could* use this to simul-rappel, but it'd be pretty stupid. When the first guy reaches the bottom, hope your prussik backup works. Then scream at him to give you a fireman's belay the rest of your way down. (Or, switch to an ATC type device, but that defeats the purpose of this scenario by wasting lots of time mid-rappel.)

Edit because there is no intelligence test required for reading the internet: my testing will be over a very short drop and/or backed up with a belay on a separate rope.
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Postby vidclimber » Fri Sep 11, 2009 6:18 am

I do not know what this knot is called but it is uesd to descend weighted ropes. You let go to stop and pinch and pull down the top of the knot to descend. It does twist the rope. And it is rope on rope but I have only used it in wet canyons.

The way it is made is by cutting about 3.5 to 4 feet off a thick (around 10.5 mm) rope and pulling one of the bundles of the core out, to make the rope a little more flexible. Then tie a small loop in each of the ends.

To tie the descending knot; place the middle of the 4 foot rope on the weighted rope and begin to rap it around the weighted rope. One half of the 4 foot rope should be going clock wise and the other should be going counter clock wise making little chris-crosses. When you have rapped them about 4 or 5 times ( depense on how much you weigh), The middle (where you started ) should be at the top and the two loops should be right nest to each other at the bottom. Put your locking Carb. threw both loops and you good to go.

That said I think just to go faster, there are much better ways to take up less time when repelling.

Like first person is belayed down setting the ropes length. Rope is lock off and all but last person goes down the single line. Last person puts rope bag on his back and repels down both ropes ( the single line that everyone else went down and the rope that his pulling out of the rope bag). 30 foot repel, 60 feet of rope. Not all 600 feet of rope. And have two ropes.

That all David
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Postby neghafi » Fri Sep 18, 2009 7:25 pm

Well I'm an engineer and though of a new device. The answer is hidden behind the springs. spring make us sure about enough friction ...
But at this time I've no time to make it. I thought maybe there is a solution.
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Postby atavist » Sat Sep 19, 2009 3:33 am

Gri-gri
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Postby The Chief » Sat Sep 19, 2009 3:37 am

baumann_pat wrote:Gri-gri


Have you ever tried to get one one a "loaded rope"?

Not happening.... TRUST ME!
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Postby peladoboton » Sat Sep 19, 2009 5:18 am

c'mon guys, its all ball bearings these days...
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