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Re: [rgold] Correction:
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rgold
Jun 2, 2007, 2:13 AM
Views: 1090
Registered: Dec 3, 2002
Posts: 1804
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I'm sorry to say that I have misread the article. The analysis part says that McGlynn fell "20 feet out from a bolt, 60 feet off the ground." Earlier it says, 20 feet out from his last bolt and 60 feet off the deck..."
I mistakenly read these (more than once) as saying the bolt was 60 feet off the deck, not 40 feet. So, looking back at my list of errors:
Error #1 is my error. The fall factor is indeed 0.67.
Error #2 is my error. The percentage stretch represented by 15 feet of rope stretch is 25%.
Error #3 still stands, but a new ideal calculation is in order. Assuming an 80 kg climber using a rope with a UIAA rating of 9 kN falling from 20 feet above a bolt with a total of 60 feet of rope out, the ideal model predicts just about 15 feet of stretch.
Error #4 still stands. 15 feet of stretch is even more precisely in the ballpark.
Error #5 Still stands but is no longer egregious. The rope stretch should have deposited the climber on the ground with little or no impact.
I think in view of this, my later statement that "the article gets virtually every aspect of the analysis wrong, including the hypothesis that gives rise to the title." is now out of line. The climber could easily have hit the ground with rope stretch, but shouldn't, in principle, have been killed by that impact.
The situation is now far more marginal, since anything else that puts slack in the system is going to just about guarantee the leader hits the ground. However, many things, like rope slippage, are themselves energy-absorbing and so do not necessarily imply a fatal impact.
(This post was edited by rgold on Jun 2, 2007, 2:31 AM)
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Edit Log:
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Post edited by rgold
() on Jun 2, 2007, 2:31 AM
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