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clc
Sep 1, 2010, 6:37 PM
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I was belaying my friend when he took a small pendulum fall. He swung down and across maybe 5 ft. Anyway its was a slow hobble back up the route and trail with a broken heel bone.
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Rudmin
Sep 1, 2010, 7:27 PM
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What the question is now, is where is the transition between a pendulum style fall and a normal fall. Would you actually be safer if your belayer fed out slack, making your fall longer, but lessening the pendulum? Say you are horizontally 8 feet from an anchor in an overhang. If you fell with the rope tight, you would be flying pretty fast in an arc, but suppose your belayer gave you 4 feet of slack. It could turn your pendulum fall into a regular fall and actually make you safer. It all depends on what the terrain is like of course, but it's something to consider.
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jt512
Sep 1, 2010, 7:44 PM
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Rudmin wrote: What the question is now, is where is the transition between a pendulum style fall and a normal fall. Would you actually be safer if your belayer fed out slack, making your fall longer, but lessening the pendulum? Say you are horizontally 8 feet from an anchor in an overhang. If you fell with the rope tight, you would be flying pretty fast in an arc, but suppose your belayer gave you 4 feet of slack. It could turn your pendulum fall into a regular fall and actually make you safer. It all depends on what the terrain is like of course, but it's something to consider.
As a rule, I generally leave extra slack in the rope when the leader is off to the side of his pro to reduce the swing.
Jay
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ensonik
Sep 1, 2010, 7:55 PM
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jt512 wrote: Rudmin wrote: What the question is now, is where is the transition between a pendulum style fall and a normal fall. Would you actually be safer if your belayer fed out slack, making your fall longer, but lessening the pendulum? Say you are horizontally 8 feet from an anchor in an overhang. If you fell with the rope tight, you would be flying pretty fast in an arc, but suppose your belayer gave you 4 feet of slack. It could turn your pendulum fall into a regular fall and actually make you safer. It all depends on what the terrain is like of course, but it's something to consider. As a rule, I generally leave extra slack in the rope when the leader is off to the side of his pro to reduce the swing. Jay
Ok, I just came back on board.
Really? Is this common for others?
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raingod
Sep 1, 2010, 8:12 PM
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ensonik wrote: jt512 wrote: Rudmin wrote: What the question is now, is where is the transition between a pendulum style fall and a normal fall. Would you actually be safer if your belayer fed out slack, making your fall longer, but lessening the pendulum? Say you are horizontally 8 feet from an anchor in an overhang. If you fell with the rope tight, you would be flying pretty fast in an arc, but suppose your belayer gave you 4 feet of slack. It could turn your pendulum fall into a regular fall and actually make you safer. It all depends on what the terrain is like of course, but it's something to consider. As a rule, I generally leave extra slack in the rope when the leader is off to the side of his pro to reduce the swing. Jay Ok, I just came back on board. Really? Is this common for others?
I do that as well
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ptlong2
Sep 1, 2010, 8:15 PM
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Is this the situation where you would add slack?
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ptlong2
Sep 2, 2010, 12:18 AM
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Like this?
About how much slack would you add?
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jt512
Sep 2, 2010, 12:44 AM
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ptlong2 wrote: Like this? About how much slack would you add?
I don't know. My gut reaction would be five feet, maybe six. In addition, I'm going to dynamically belay, which I think will also reduce the swing into the wall.
Edit: Actually, as drawn, it looks like I can't dynamically belay.
Jay
(This post was edited by jt512 on Sep 2, 2010, 12:50 AM)
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brokesomeribs
Sep 2, 2010, 12:50 AM
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ptlong2 wrote: Like this? [img]http://img825.imageshack.us/img825/3360/horizontala.jpg[/img] About how much slack would you add?
I'd like to preemptively comment that this thread has among the highest SNR's of any active thread I've seen here recently. Kudos, RC! But I digress...
The second scenario isn't as "hopeless" as the first scenario, but still "shitty." Adding slack in this situation would depend primarily on the topography of the rock between the belayer and the climber.
My benchmark for adding slack is when the addition of said slack will reduce the arc of the pendulum, but not forseeably add any danger to the climber.
As an example, if there were a ledge approximately 10' below the illustrated roof, I would not add any slack. That would further increase the already high likelihood of decking and shattering ankles.
A scenario where I might add some extra slack would be if there were a large feature/abutment projecting out from the cliff face, located below the "10 feet" text in the image. In that scenario, adding some slack would allow the climber to fall further before beginning the pendulum, hopefully placing him below the abutment, instead of swinging right into it for a side impact.
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ptlong2
Sep 2, 2010, 2:26 AM
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brokesomeribs wrote: I'd like to preemptively comment that this thread has among the highest SNR's of any active thread I've seen here recently.
One person's signal is another's noise. Not everybody thinks geek threads are valuable.
In reply to: Adding slack in this situation would depend primarily on the topography of the rock between the belayer and the climber.
I think it's simpler if this obvious complication is ignored. Pretend there are no ledges below and no obstacles in the way, other than that vertical wall or big corner that the climber could pendulum into.
Is adding slack (how much?) going to reduce the speed that the climber impacts the wall/corner?
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brokesomeribs
Sep 2, 2010, 2:37 AM
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ptlong2 wrote: brokesomeribs wrote: I'd like to preemptively comment that this thread has among the highest SNR's of any active thread I've seen here recently. One person's signal is another's noise. Not everybody thinks geek threads are valuable. In reply to: Adding slack in this situation would depend primarily on the topography of the rock between the belayer and the climber. I think it's simpler if this obvious complication is ignored. Pretend there are no ledges below and no obstacles in the way, other than that vertical wall or big corner that the climber could pendulum into. Is adding slack (how much?) going to reduce the speed that the climber impacts the wall/corner?
I don't think that you can ignore the complication of topography, however I understand you're asking as an exercise in academic thought. And despite the fact that I enjoy participating in geek threads, I'm only an armchair geek at best and I have absolutely no idea how to calculate (or even surmise) an answer to your question. I was a liberal arts major.
Color me stumped.
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ptlong2
Sep 2, 2010, 3:01 AM
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brokesomeribs wrote: I don't think that you can ignore the complication of topography
Not in practice. If you said, "an infinite amount of slack", then you would have had the technically-right answer and forced the issue. But the question, without the obstacles, still has merit. Do you feed some slack (how much?), or not?
In reply to: I'm only an armchair geek at best and I have absolutely no idea how to calculate (or even surmise) an answer to your question.
Computer models are only so good as well. I know what mine says. Anecdotal reports, while suspect, have some value in the absence of solid data. What do climbers do, and how do they perceive that it works (or doesn't)?
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skiclimb
Sep 2, 2010, 3:59 AM
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jt512 wrote: ptlong2 wrote: Like this? [img]http://img825.imageshack.us/img825/3360/horizontala.jpg[/img] About how much slack would you add? I don't know. My gut reaction would be five feet, maybe six. In addition, I'm going to dynamically belay, which I think will also reduce the swing into the wall. Edit: Actually, as drawn, it looks like I can't dynamically belay. Jay
In both cases with pro or with short pro adding slack will increase the speed and therefore impact force ..unless maybe you add the full ropelength of slack in the with pro diagram.. in that case the climber might not hit the wall at all.. but then again..if he does which he probably will anyway....ouch
(This post was edited by skiclimb on Sep 2, 2010, 4:02 AM)
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jt512
Sep 2, 2010, 4:34 AM
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skiclimb wrote: jt512 wrote: ptlong2 wrote: Like this? [img]http://img825.imageshack.us/img825/3360/horizontala.jpg[/img] About how much slack would you add? I don't know. My gut reaction would be five feet, maybe six. In addition, I'm going to dynamically belay, which I think will also reduce the swing into the wall. Edit: Actually, as drawn, it looks like I can't dynamically belay. Jay In both cases with pro or with short pro adding slack will increase the speed and therefore impact force ..unless maybe you add the full ropelength of slack in the with pro diagram..
I doubt it. At least not in the case with pro. Your reasoning does not take into account that as you increase the slack you decrease the angle at which the pendulum starts. By your own admission, there must be an amount of slack that will reduce the impact force into the wall, but I doubt that it really is a whole rope length. My guess is that the impact force against the wall decreases monotonically with the amount of slack. I assume that ptlong2 will eventually run the numbers and give us his solution.
I just had a vague recollection of a similar problem coming up on rec.climbing a long time ago. My memory might be playing tricks on me, but I seem to recall someone claiming that the amount of slack should be greater than the horizontal runout.
Jay
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blondgecko
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Sep 2, 2010, 5:01 AM
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ptlong2 wrote: Like this? About how much slack would you add?
One somewhat unintuitive thing the climber could do in this situation is, if possible, launch himself back towards the belayer as he comes off. The closer to directly underneath the last anchor point he is when tension comes onto the rope, the better off he's going to be.
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skiclimb
Sep 2, 2010, 5:12 AM
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jt512 wrote: skiclimb wrote: jt512 wrote: ptlong2 wrote: Like this? [img]http://img825.imageshack.us/img825/3360/horizontala.jpg[/img] About how much slack would you add? I don't know. My gut reaction would be five feet, maybe six. In addition, I'm going to dynamically belay, which I think will also reduce the swing into the wall. Edit: Actually, as drawn, it looks like I can't dynamically belay. Jay In both cases with pro or with short pro adding slack will increase the speed and therefore impact force ..unless maybe you add the full ropelength of slack in the with pro diagram.. I doubt it. At least not in the case with pro. Your reasoning does not take into account that as you increase the slack you decrease the angle at which the pendulum starts. By your own admission, there must be an amount of slack that will reduce the impact force into the wall, but I doubt that it really is a whole rope length. My guess is that the impact force against the wall decreases monotonically with the amount of slack. I assume that ptlong2 will eventually run the numbers and give us his solution. I just had a vague recollection of a similar problem coming up on rec.climbing a long time ago. My memory might be playing tricks on me, but I seem to recall someone claiming that the amount of slack should be greater than the horizontal runout. Jay
If i remeber my old physic correctly a pendulem only redirects force it does not mitigate it.
the amount of vertical fall is the sole generater of speed. more slack means more speed = more force at impact.
the reason i meantioned that a full ropelength fall might be safer (but probably not) is that other forces can come into play ..such as glide and air friction may allow a person to hit the rope at a point directly under the pro without hitting the wall first.
then again it could make it worse if the person falls in such a way that they push away from the wall..
they key is the direction of fall in regarding slack..if they fall toward the wall such that they aproach nearly directly below the pro point once the slack runs out then they have a chance to not hit the wall at all.
However if they fall straight down or only slightly towards the pro or worst of all away from the pro then the slack just increases the speed at which they impact the wall.
best case would be an aproximately 30 foot freefall towards and slightly past the pro with moderate slack such that you hit the rope at a point between the wall and the pro perhaps about 1ft past the pro on the wall side.. the resulting pendo would actually take you away from the wall...
However realworld best bet in this case is a tight belay and the old rule.."the leader must not fall" If the leader must fall he should try to use the last couple second or so of control before failure to jump/pushoff towards the pro
(This post was edited by skiclimb on Sep 2, 2010, 5:21 AM)
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curt
Sep 2, 2010, 6:32 AM
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ptlong2 wrote: brokesomeribs wrote: I don't think that you can ignore the complication of topography Not in practice. If you said, "an infinite amount of slack", then you would have had the technically-right answer and forced the issue. But the question, without the obstacles, still has merit. Do you feed some slack (how much?), or not? In reply to: I'm only an armchair geek at best and I have absolutely no idea how to calculate (or even surmise) an answer to your question. Computer models are only so good as well. I know what mine says. Anecdotal reports, while suspect, have some value in the absence of solid data. What do climbers do, and how do they perceive that it works (or doesn't)?
I have little doubt we'll see the "correct" answer posted here in short order:
http://www.theclimbinglab.com
...as soon as the proctor, the advisory board and the dumbass get around to it. 
Curt
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jt512
Sep 2, 2010, 10:20 AM
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skiclimb wrote: jt512 wrote: skiclimb wrote: jt512 wrote: ptlong2 wrote: Like this? [img]http://img825.imageshack.us/img825/3360/horizontala.jpg[/img] About how much slack would you add? I don't know. My gut reaction would be five feet, maybe six. In addition, I'm going to dynamically belay, which I think will also reduce the swing into the wall. Edit: Actually, as drawn, it looks like I can't dynamically belay. Jay In both cases with pro or with short pro adding slack will increase the speed and therefore impact force ..unless maybe you add the full ropelength of slack in the with pro diagram.. I doubt it. At least not in the case with pro. Your reasoning does not take into account that as you increase the slack you decrease the angle at which the pendulum starts. By your own admission, there must be an amount of slack that will reduce the impact force into the wall, but I doubt that it really is a whole rope length. My guess is that the impact force against the wall decreases monotonically with the amount of slack. I assume that ptlong2 will eventually run the numbers and give us his solution. I just had a vague recollection of a similar problem coming up on rec.climbing a long time ago. My memory might be playing tricks on me, but I seem to recall someone claiming that the amount of slack should be greater than the horizontal runout. Jay If i remeber my old physic correctly a pendulem only redirects force it does not mitigate it. the amount of vertical fall is the sole generater of speed. more slack means more speed = more force at impact. the reason i meantioned that a full ropelength fall might be safer (but probably not) is that other forces can come into play ..such as glide and air friction may allow a person to hit the rope at a point directly under the pro without hitting the wall first. then again it could make it worse if the person falls in such a way that they push away from the wall.. they key is the direction of fall in regarding slack..if they fall toward the wall such that they aproach nearly directly below the pro point once the slack runs out then they have a chance to not hit the wall at all. However if they fall straight down or only slightly towards the pro or worst of all away from the pro then the slack just increases the speed at which they impact the wall. best case would be an aproximately 30 foot freefall towards and slightly past the pro with moderate slack such that you hit the rope at a point between the wall and the pro perhaps about 1ft past the pro on the wall side.. the resulting pendo would actually take you away from the wall...
What the fuck are you smoking?
In reply to: However realworld best bet in this case is a tight belay...
Please don't ever belay me. Ever.
Jay
(This post was edited by jt512 on Sep 2, 2010, 10:21 AM)
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sbaclimber
Sep 2, 2010, 10:51 AM
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jt512 wrote: In reply to: However realworld best bet in this case is a tight belay... Please don't ever belay me. Ever.
+1
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blondgecko
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Sep 2, 2010, 11:24 AM
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ptlong2 wrote: Like this? About how much slack would you add?
Just another random thought on this picture: what if the draw in the roof was extendable by (say) 3-6 feet, but held in a short configuration by a link set to fail at low force (I'm thinking not much more than bodyweight). The idea is to start the pendulum enough to get some (but not too much) sideways momentum, then trigger a period of freefall as the weak link breaks. If you're moving sideways during that freefall, then by the time the rope pulls tight again, the new vector is far more vertical and so more of the fall energy goes into stretching the rope rather than accelerating you sideways.
Just rambling. Seems to make sense to me though.
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skiclimb
Sep 2, 2010, 2:43 PM
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sbaclimber wrote: jt512 wrote: In reply to: However realworld best bet in this case is a tight belay... Please don't ever belay me. Ever. +1
By tight belay i did not mean tension i meant keeping as much slack as possible out of the rope without interfering with the lead.
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sp00ki
Sep 2, 2010, 5:10 PM
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ensonik wrote: non inconsequential
If only there were a word for that...
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ensonik
Sep 2, 2010, 6:56 PM
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sp00ki wrote: ensonik wrote: non inconsequential If only there were a word for that...
I'd suggest a bit Douglas Adams to brush up on your grammatical sense of humour. It sounds like you may need a bit of help in that department.
You seem to be doing fine on irony though. Carry on.
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Rudmin
Sep 2, 2010, 7:08 PM
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I made up a quick numerical calculator in excel to drop a climber at some distance horizontally from an anchor with a given amount of slack. The surprising thing was that adding slack increased peak horizontal velocity. When I charted out the fall path, it quickly became apparent that as the climber fell the rope (modeled as a spring) would bounce them pretty hard like a spring would.
I figured that the problem was that the rope was acting like a perfect spring, so I added a dampening factor that opposed rate of stretch and then jigged the stiffness and dampening factor to roughly match some UIAA numbers for popular retail ropes. This would allow the rope to bleed energy out of the system. I also added a wind resistance proportional to velocity^2 sufficient to give a terminal velocity of 55 m/s.
After all that, still the same result pretty much.
My final results were for a test with a rope with stretch and dampening to give it approximately similar characteristics to a UIAA approved rope. 80 kg climber 10 metres from protection.
Slack [m]/Peak Tension [kN]/Peak Horizontal Velocity [m/s]
0/2.1/13.0
1/2.0/13.3
2/2.4/13.2
3/2.8/13.0
4/3.1/12.8
6/3.7/12.2
8/4.2/11.6
10/4.7/11.1
20/6.4/9.1
50/9.3/6.3 (climber reaches vertical speed of 100 kmph and wind resistance is dominant energy sink)
What I can conclude, is that pendulum speed doesn't depend so much on rope stiffness or rope length, but on how much energy can be removed by the time that swing occurs. Because my rope is simplified down to two numbers, this model probably doesn't accurately represent reality, but it is probably somewhat close.
If you want to reduce forces on your anchor, don't give slack to a pendulum fall. If you want to reduce pendulum velocity, you need to give out a lot of slack, or think of a smarter way to do things.
Here is what a fall 10 metres out with 6 metres of slack looks like:
(This post was edited by Rudmin on Sep 2, 2010, 7:33 PM)
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