Bob Mehew
Well-known member
Like andrewmc says, it is complicated and frankly I can't explain it even in simple terms. Whilst it is not quite a replica of the drop test, https://www.youtube.com/watch?v=GIkeGBXqWW0 has a number of similarities. The slinky shows you can get variable forces along the length of the slinky since from Newtons 2nd law (F = m * a), some parts of the slinky are accelerating and other parts are not. I suggest our drop test is similar to a speeded up version of the slinky. My expectation is the peak force seen by any part of the set up is the same, it just occurs at slightly different times. (Though the time frame will be different in rope & steel since the speed of sound is different.)
mikem - Would you like to come to the Bradford to witness an experiment where we locate a second load cell within the system?
The use of low stretch (semi static / SRT) ropes in place of dynamic ropes risks giving the climber a bigger peak force. But as I indicated, if the climber is being belayed by another person using the classic belay stance, then that will reduce the peak force seen by the climber. That will be less true if one uses one of the other belay systems.
The report states "Discussions with representatives of Petzl have clarified that the manufacturer does not consider the Petzl STOP to be a belay device of any form. Furthermore, Petzl have never advocated the use of the STOP part threaded. So use of the STOP in this manner would be out with manufacturer?s guidance." BCA have urged "cavers to only use devices ... in line with current manufacturer?s instructions."
mikem - Would you like to come to the Bradford to witness an experiment where we locate a second load cell within the system?
The use of low stretch (semi static / SRT) ropes in place of dynamic ropes risks giving the climber a bigger peak force. But as I indicated, if the climber is being belayed by another person using the classic belay stance, then that will reduce the peak force seen by the climber. That will be less true if one uses one of the other belay systems.
The report states "Discussions with representatives of Petzl have clarified that the manufacturer does not consider the Petzl STOP to be a belay device of any form. Furthermore, Petzl have never advocated the use of the STOP part threaded. So use of the STOP in this manner would be out with manufacturer?s guidance." BCA have urged "cavers to only use devices ... in line with current manufacturer?s instructions."