Post by gregggagliardi on Dec 10, 2013 15:38:16 GMT -8
Thanks to Jason Martin and Dane Burns for bringing this interesting Petzl video to wider attention.
The video raises interesting issues about ice anchor strength and how this should be tested. I was a bit disappointed that the breaking strength in Kn was not presented in tabular fashion with mean breaking strength for ice screws versus threads for multiple tests. Several commenters on Dane's blog have offered some methodological criticisms of the tests.
The biggest problems with the testing are:
(1) Multiple tests should have been performed and averaged along with a measure of variability, The means should have been compared with an appropriate statistical test (a T-test would have been adequate). Without statistical testing the findings are almost meaningless.
(2) The tests were carried out without a climbing rope in the system. No one climbs ice on steel cables.
(3) The V threads were not constructed adequately. The holes were too close together and they were not deep enough.
(4) Vertical threads (A-Threads) were not tested. Ice fractures in horizontal layers. A-Threads better avoid this natural structural weakness in the ice
(5) No numerical data was presented. If ice screws fail at 11 Kn and threads fail at 10 Kn, what difference does it make?
(6) The tests were pull tests, not drop tests. For a technical discussion. (see ocw.mit.edu/courses/aeronautics-and-astronautics/16-621-experimental-projects-i-spring-2003/projects/bennettw.pdf)
(6) Remember, Petzl sells ice screws; they make no money from your home made threads
Still, this general subject area on F9 best practices is without any threads and the issue of ice anchors seems to be a good way to get the discussion started.
The video raises interesting issues about ice anchor strength and how this should be tested. I was a bit disappointed that the breaking strength in Kn was not presented in tabular fashion with mean breaking strength for ice screws versus threads for multiple tests. Several commenters on Dane's blog have offered some methodological criticisms of the tests.
The biggest problems with the testing are:
(1) Multiple tests should have been performed and averaged along with a measure of variability, The means should have been compared with an appropriate statistical test (a T-test would have been adequate). Without statistical testing the findings are almost meaningless.
(2) The tests were carried out without a climbing rope in the system. No one climbs ice on steel cables.
(3) The V threads were not constructed adequately. The holes were too close together and they were not deep enough.
(4) Vertical threads (A-Threads) were not tested. Ice fractures in horizontal layers. A-Threads better avoid this natural structural weakness in the ice
(5) No numerical data was presented. If ice screws fail at 11 Kn and threads fail at 10 Kn, what difference does it make?
(6) The tests were pull tests, not drop tests. For a technical discussion. (see ocw.mit.edu/courses/aeronautics-and-astronautics/16-621-experimental-projects-i-spring-2003/projects/bennettw.pdf)
(6) Remember, Petzl sells ice screws; they make no money from your home made threads
Still, this general subject area on F9 best practices is without any threads and the issue of ice anchors seems to be a good way to get the discussion started.