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melekzek
Sep 20, 2003, 3:29 AM
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A related question to this
Ok, here is a question for those physics guys.... What are the forces on the climber in a typical fall using dynamic rope and static ropes? I present you 2 numerical examples:
1) Toprope case: There is only a little slack, the climber falls 1 meters, and there is 20 meter rope in the system, the belayer is at the top.
2) Lead case: Leader is 2 meter above his last piece and falls. Lets say he has climbed 20 meters.
Here is the reason I am asking, one of my friends told me that he used to carry static rope on easy climbs, just for rappel. The reasoning behind that is that it is a lot lighter than dynamic ropes. I suggested that I would always prefer carrying a dynamic rope because I can use it for unexpected lead climbs as well. He than goes ahead and explaines that he had used static rope for unexpected lead climbing for .... err... "physicological" reasons. I told him that he is crazy, and I wouldnt be "physicologically" safe leading with a static rope. I tried to explain that the fall forces would be too much for his body, but unfortunatelly get lost in the equations.....
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alpnclmbr1
Sep 20, 2003, 4:04 AM
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There is a good calculator here:
http://www.stack.nl/~stilgar/calc.php
for the static rope (use 500 for modulus= 11ml static)
10% for the dynamic rope (use these numbers to calculate the rope modulus in the caculator above)
In the real world the numbers will be worse then the calculator shows due to a lot of different factors
case 1
static rope/climber 1597 lbs / anchor 2650
dyn rope/climber 418 / anchor 675
case 2
static rope/climber 2992 lbs/anchor 4950
dyn rope/ climber 553/ anchor 900
don't ever lead with a static rope (these are best case numbers)
ps. for case 1 is assumed the belayer was on the ground in a tr setup
***(edited to correct static numbers)
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melekzek
Sep 20, 2003, 4:54 AM
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In reply to: don't ever lead with a static rope
I agree with you. BTW, this calculator is excellent. But.....
When I put 3% for a static rope it gives the rope modulus as 26.16. And using this gives even a maximum force on the climber as 9.88kN with a factor 2 fall on the static rope. I am sure I wouldnt survive such a fall but it claims that less than 12kN is nonlethal.
What am I missing here ?
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alpnclmbr1
Sep 20, 2003, 5:10 AM
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Scratch the numbers for the static rope
when you punch in 26 for the modulus and use a factor 2 fall the calculator assumes the rope will stretch 33% to give the 9kn impact force. this isn't the case for a static rope.
the calculator only works for dynamic ropes
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alpnclmbr1
Sep 20, 2003, 5:25 AM
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a rope modulus of 500 is about right for a 11ml static rope
this give a loaded stretch of 8% which is aproximately correct (in the output section of the calculator)
I got these numbers from the second chart on this page
http://bstorage.com/speleo/Pubs/rlenergy/Default.htm
Thanks for catching that mistake, I hadn't really used that calculator in reference to a static rope.
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melekzek
Sep 20, 2003, 5:39 AM
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By using the new numbers a factor 0.16 fall on a static rope will kill you....
Which is roughly a 1.2 meter fall on 10 meter climb. Which also means that you should place solid gear at every 50 cm at this point.
And these numbers are on theoretical best conditions....
This is scary....
Thanks for the numbers, these are what I was looking for.
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elvis
Sep 20, 2003, 5:57 AM
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The numbers are all very interesting but all you have to tell this friend of yours is that all rope maunfacturers including the static rope that he is using will strongly advise against leading with a static all climbing guides instruction books magazines websites and climbing schools will all advise against leading with a static. In fact any climber who does (lead with a static) is just plain stupid.
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melekzek
Sep 20, 2003, 7:08 AM
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In reply to: all you have to tell this friend of yours is that all rope maunfacturers including the static rope that he is using will strongly advise against leading with a static
That was the first thing I told him, but he was thinking that the reason was that the rope will break, which he didnt belive for a short fall. I tried to the explain him how much forces his body will receive, but I was lacking some physical numbers.
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squish
Sep 20, 2003, 7:39 AM
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In reply to: I tried to the explain him how much forces his body will receive, but I was lacking some physical numbers.
Skip the physics for a moment and play along...
For visualization, you could tell him it's like falling from that height onto a 4" wide band in the small of the back, and a 4" wide band across the legs. Heck, tell him it's like falling across a couple of 2x4s, that's probably close enough to the real thing. (I'd guess that a pair of 8' long 2x4s should absorb as much as some given length of static rope.)
And your test case is a 4m fall? Using this physics-for-dummies visual method, I would bet on your friend's back being the first thing to break.
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shawkshaw
Sep 20, 2003, 9:39 AM
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these numbers are great but you need to keep two things in mind.
1) this calculater does NOT take into effect a belay device. The equations used assume that the rope is stopped immediately and there is no slippage. realistically atcs, stich plates, fig 8's all have slippage which lowers the potentially forces placed on a climber. grigri's will give higher loads as they don't slip as much but they still increase the stopping time in a fall.
2) UIAA regulations specify that a climbing rope must not allow a load of more than 12kN to develop. so loads over that are not going to occur. That said 12kN is pretty massive and equates to something like 15 G's and is very unlikely.
that is not particularly relevent to the original question but indeed static ropes are more dangerous as they stretch less and stop you quicker thus increasing the load. don't uses them for climbing
steve
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corpse
Sep 20, 2003, 2:47 PM
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Ever walk down stairs or down a step in complete darkness (or in lightness, when you jsut don't see it), you extend your leg all the way, straight, and step forward expecting ground - but the ground is a few inches down cuz of the step. I KNOW my back feels this big jolt, and it's not friendly on the spine either. I can NOT imagine how that would feel on a static rope, even if you are only talking 3-6". Tell your buddy to try that little test, I bet he does it once, and then doesn't want to do it again.
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robmcc
Sep 20, 2003, 4:48 PM
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In reply to: And your test case is a 4m fall? Using this physics-for-dummies visual method, I would bet on your friend's back being the first thing to break.
I wonder about that. I definitely agree that leading on a static rope is a phenominally stupid thing to do, one this guy's likely to stop doing either before or immediately after his first lead fall. I just imagine him taking the fall and the forces on the climber approaching 12kN....as the force on the last pro rise to 20kN. I think there's a decent chance forces would be held in check by ripping gear out of the rock.
That's just theoretical time-wasting, though. Death by super hard fall on a static line or death by impacting the ground after ripping all your pro out of the wall (and being seriously injured by the sequence of high force impacts on the way). Choose dynamic. Everyone else uses them for a reason.
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alpnclmbr1
Sep 20, 2003, 5:41 PM
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Your statements are pretty much correct but I would add the following comments.
In reply to: these numbers are great but you need to keep two things in mind. 1) this calculater does NOT take into effect a belay device. The equations used assume that the rope is stopped immediately and there is no slippage. realistically atcs, stich plates, fig 8's all have slippage which lowers the potentially forces placed on a climber. grigri's will give higher loads as they don't slip as much but they still increase the stopping time in a fall.
With a dynamic rope take about 20% off the numbers for a gri gri. Take about 60% off for a regular belay device. (This involved letting the slip 30 inches) see footnote (1)(2)
Then add an undefinable quantity for friction against intermediate points of protection and the rock.
The "experts " say that the uiaa test drop numbers understate the real world numbers.
In reply to: 2) UIAA regulations specify that a climbing rope must not allow a load of more than 12kN to develop. so loads over that are not going to occur. That said 12kN is pretty massive and equates to something like 15 G's and is very unlikely.
This rule refers to the force felt by the falling climber and it only applies to one fall, multiple falls on a rope can exceed this limitation. Also the rope can produce a "load" of 20kn on your last piece of gear while still maintaining the 12kn limit on the climber
(1) http://www.leeds.ac.uk/sports_science/abstracts/climb99/wnachbauer1.htm
(2)
http://www.somat.com/applications/articles/rei.htm
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mikeehartley
Sep 20, 2003, 6:50 PM
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I'm not advocating leading on a static line but... BlueWater's static ropes will pass one UIAA drop test and meet the impact force numbers. They'll only do it once though. But I find it reassuring to know that if I have to use my static line for leading in a worse case scenario its not like leading on cable. I just might survive.
Several decades ago when I didn't know better I traded some gear for a new rope (cheap) from a friend. My old one had just gotten chopped and I was desperate. The sheath sure looked different but otherwise it looked great. I showed it to numerous very knowledgeable climbers and they weren't familiar with the make. The last time I used it I caught numerous trad falls in the 4 meter range with a rather large leader. I sure was aware of how much more than usual I was being picked up off the belay! Shortly thereafter another friend said "I think that's a caving rope. I'm not sure you're supposed to take falls on that". Moral #1. I now know the history of my gear. #2. Blackboard analysis of falls can't begin to take into account the dynamics and give in typical belay situations. You can get away with a hell of a lot (with a minimal safety factor) when you are ignorant!
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slcliffdiver
Sep 20, 2003, 7:34 PM
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In reply to: I'm not advocating leading on a static line but... BlueWater's static ropes will pass one UIAA drop test and meet the impact force numbers. They'll only do it once though. But I find it reassuring to know that if I have to use my static line for leading in a worse case scenario its not like leading on cable. I just might survive.
If I remeber correctly the test it was for a factor 1 fall instead of for 1.78. Also are you sure it keep the loads down to that recomended by the UIAA? I thought it broke on the second fall but I don't remeber the part about keeping the forces lower than IUAA recomendation. I might be getting two test mixed up but I'm fairly certain it didn't both keep both keep below the recommended load and use the factor 1.78 fall all in the same test. Do you have the data I haven't been able to locate it again.
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alpnclmbr1
Sep 20, 2003, 8:00 PM
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According to this site the max survivable (uiaa) fall factor with a 10mm static is 0.7
http://bstorage.com/speleo/Pubs/rlenergy/Default.htm
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piton
Sep 26, 2003, 5:00 PM
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here's a good article that rebourne sent me via email
http://www.losalamos.org/climb/xRopes.pdf
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podunkclimber
Sep 28, 2003, 5:53 PM
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This is an engineering not a physics question, the simple physics explanation is that the static line is not capable of absorbing, and disipating the energy that is converted from potential to kinetic energy in a fall. Since a static line does not stretch in any appreciable amount, the energy has to be absorbed else where. This could be a cross loaded carabiner snapping, the rope its' self could snap, the anchor could pull, and or pelvis could be crushed. Not in that specific order, and in any combination if not all of them. Something has to give, and it will be the weakest point in the system first. You all know not to use a static line for top roping or leading, and whether you chose to or not is up to you. The same thing goes for drunk driving, wreckless driving, elicit drug use. I personally would solo climb before I used a static line to lead, atleast if I feel my death would be quick, and I wouldn't take my partner with me.
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piton
Sep 29, 2003, 12:59 PM
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In reply to: This is an engineering not a physics question,
engineering is physics and physics is everything.
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noshoesnoshirt
Sep 29, 2003, 1:39 PM
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physics is an elegant solution to an ideal situation. engineering is the application of that solution to the real world.
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fear
Sep 29, 2003, 2:48 PM
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In reply to: The reasoning behind that is that it is a lot lighter than dynamic ropes...He than goes ahead and explaines that he had used static rope for unexpected lead climbing for .... err... "physicological" reasons. I told him that he is crazy, and I wouldnt be "physicologically" safe leading with a static rope. I tried to explain that the fall forces would be too much for his body, but unfortunatelly get lost in the equations.....
Duh.... I don't think static weighs in any lighter than dynamic.
For an alpine "backup rope" get a single 8.1 mm Beal Ice Line. Rated as a double but it'd hold a couple falls with just a single strand if you had to. Plus it'd be real dynamic. Super light.
No reason to lead on static. Ever.
That being said, the old guys used to use thick hemp lines. I don't recall hemp ropes stretching much. They died a lot more too......
-Fear
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melekzek
Oct 2, 2003, 12:17 AM
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In reply to: That being said, the old guys used to use thick hemp lines. I don't recall hemp ropes stretching much. They died a lot more too.....
I always wondered how dynamic pre-war ropes were. Not much I guess, hence the saying "leader must not fall". But were they somewhere between current statics and dynamics or were they completely static?
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