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alpnclmbr1
Jul 8, 2003, 7:54 PM
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In reply to: While many of the items you dredged up recently make interesting reading and spawn useful threads, it is odd to me also that you are often citing past references that you clearly don't completely understand.
Why do you think I started this thread?
And personally I am more interested about learning what I can about fall forces in general, as I don’t use screamers and I don’t know much about them.
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alpnclmbr1
Jul 8, 2003, 8:06 PM
Post #27 of 31
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In reply to: Go climb more, and maybe you will understand.
The problem is that until this year all I have done is climb. This is the first time in twenty years that I have gotten into the technical side of climbing. Anyway as far as my misunderstanding, I was confused by Yates calling protection an anchor.
I got your point now, thanks.
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dirtineye
Jul 8, 2003, 8:14 PM
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LJ, I should have said that the data sheet that comes with a screamer talks about series. In series would work better for a normal situation.
For the Osmet situation, I'm sure they knew what they were doing. that is a little different from the simul climbing situation asked about in here. Why take aa 4 kN jolt when you can take a 2 kN jolt instead? Also, in a screamer situation, at least in the ones I've been in (didn't use em though and didn'f fall either hehe) another two feet would not matter.
One major idea of screamers is to lower the force felt by a piece of pro. If you increase the activation force by doubling the screamers, that might not be so good.
I will try to dig up the data sheets for the two kinds of screamers I have.
I'm not going to look at your BP analysis LJ, It's probably good and my own armchair is kind of a mess LOL. OH Darn, well maybe I will, but will you still respect me afterwards? Take two derivatives and call me in the morning :roll:
Oh LJ, if you have not talked to Yates, find a reason! He's great.
I think you should do the PE + KE = Total E for this group. You're still getting paid for that sort of thing hahaha.
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sspssp
Jul 8, 2003, 9:27 PM
Post #29 of 31
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In reply to: Yates suggests puting them in series. Side by side would double the activation force. Think about it a minute and you'll see how that works. YOu guys that think one foot is not enough distance to dissipate force in a meaningful way, have you ever fallen on a crash pad from say 20 feet?
I intentionally put them in side by side (instead of series), because the forces in a simul-fall (where the leader is "sucked" into a piece by the second falling) could be incrediably high. If you put them in series, it is possible they could fully extend before the peak loading. The standard use for screamers is to reduce forces on marginal pieces. I'm trying to reduce forces on good pro in a severe simul-fall. Side by side has an activation of ~1100 ftlbs. This is around 7 gs (I weigh around 150lbs). The body can easily handle 7 gs (especially for a short period). So I'm trying to knock the peak off of a "worst case" scenerio.
Your example of the crash pad is good. As I said before, I'm not doubting Yates.
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dirtineye
Jul 8, 2003, 11:56 PM
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OK, I guess I can sort of see your point.... You want to wait for the 4 kN hit to rip em.
BUT, and maybe I don't understand a simul climbing fall (Hope I'm never in one, A singler 20 foot groundfall is all the "interesting" falling I need for this lifetime), why does it matter when the screamer rips, because reducing the fall is still reducing the fall. If the fall is reduced before the peak, then the peak will be lower.
Maybe you can explain this part to me, or maybe side by side doesn't matter. I have no idea, but it's interesting.
LJ, Maybe, just maybe I am feeling a disturbance in the force about your armchair work.... if I wake up in the middle of the night reaching for classical mech books, you're in trouble!
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nafod
Jul 9, 2003, 1:14 AM
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In reply to: The part that I find so strange: a screamer starts out about a foot long and increases to what? Two feet long (I don't remember exactly). So regardless of what force the screamer activates at, it only happens over a foot of length. Anyway, the conclusion I came to was a fifteen foot simul-fall with the screamer was equivalent to something like a 12 foot fall without it. Just not much difference.
I don't have any reason to doubt Yates' data, but it sure seems puzzling. In a fall over 15 feet or so, you would be traveling so fast that I would think the screamer would extend the full foot in such a short length of time that not much energy would be absorbed.
Screamers can be looked at as having two possible functions. One is to dissipate the energy in a fall. The other is to limit the peak load on an anchor, while letting the dynamic rope dissipate the energy. The second purpose is their real function. The rope absorbs the energy of the fall, the screamer limits the load.
You are right in that a screamer with a static line would extend fully in a not too big fall. A screamer with a 500 lb activation force and a 1 foot extension could only absorb a 150 lb climber falling a little over 3 feet. That's not much, eh?
Here's a shot of a screamer that activates at 10,000 lbs, obviously used for other than climbing.
http://www.personal.psu.edu/...ePix/TailConnect.jpg
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