Is there a real basis for resting a rope by switching ends after a fall?
Think of a climbing rope as a nylon spring. Every time you load it you use up some of its capacity to stretch, increasing the impact force. Load it enough times—no one knows what that number is because it depends on variables—and you’ll use up its “springiness.” Letting a rope rest between falls gives it time to rebound, or regain some of its springiness. But by how much? Kolin Powick, Director of Black Diamond’s Climbing Category, used a UIAA-style drop tower to conduct drop tests, letting the rope rest five minutes, then 30 minutes, then two hours, and finally for 24 hours between falls. He concluded that letting the rope rest only nominally decreased the impact force. The difference between a five-minute and a 24-hour rest for the second drop, for example, was a decrease of only 102 lbf. Of note is that the impact force increased nearly 500 lbf from the first to the sixth drop, with a five-minute rest between falls. Conclusion: Switching ends of the rope is better than falling on the same end even after a rest. Of course, once you’ve fallen on both rope ends the tactic starts to become only slightly better than resting the same end.
This article appeared in Rock and Ice issue 248 (February 2018).
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