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post #19 of Old 04-05-2010
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How do we determine the life of a rope?

Serious question, all jousting aside.

An anchor rope on a smallish boat could easily see a 500-pound yank every 10-30 seconds for the 10 hour duration of a front passage. That is 1800 cycles.

A climbing rope in a gym could see 20 x 500 pound falls in a day, or 1800 cycles in 90 days.

We can adjust the numbers; the point is that the order of magnitude is similar. The gym association - there is one - has set an expiration date based upon a very strict standard because a failure will always mean serious injury or worse, but to my knowledge has not seen a fatigue related failure. Clearly, we are not going to retire an anchor rode after one significant blow, not an epic storm at all. The gym rope has not seen salt or UV. Neither has seen strain beyond the SWL. Presumably neither has significant fraying. How do we decide?

My gut and any engineering approach I can reason suggests that the retirement age of a climbing rope from critical service is only a very small fraction of its useful life in other services. A climber may fall a distance, but weighs 6000/150=40 times less than the boat. That is material.

We don't know.

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