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Re: [paulraphael] Proposed Anchor Rigging:
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rgold
May 19, 2007, 7:13 PM
Views: 22675
Registered: Dec 3, 2002
Posts: 1804
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paulraphael wrote: Questions...how efficiently does it distribute the load ... which is pretty academic because I'm sure it does a good enough job. but people might want to know.
Beware of the obvious. "Academic" analyses suggest poor equalization because of friction, and such pull-testing as has been done also suggests the friction in pulley systems could result in unacceptably poor equalization. For example, Craig Connolly says he has pull-tested an Alpine Equalizer and found, in one case, only 6% of the power-point load on one of the arms.
On the other hand, my Geekqualizer has been subjected to drop tests with the outer pair of arms at a 90 degree angle and one of those arms cut 90% through. A drop-test impact at the power point of 11.4 kN did not result in the failure of the rig. Was that outer arm analogous to the one that, in Connolly's test, got only 6% of the load, or did the rig equalize and so keep the load on the cut arm under 4kN? We don't know...
It isn't clear whether the results of pull-testing correspond to the results of drop-testing when friction in a pulley system is a factor. Wootles drop-tests suggesting better equalization for the sliding X over a cordelette are contrasted with some pull tests (I don't have the reference at present) that reached the opposite conclusion.
The Geekqualizer is built on an AE and so has similar potential friction problems (not as bad as PR's system, which will suffer from occurrences of the binding effect already observed for the sliding X in drop-testing). The severity of frictional effects won't be clarified until, as Largo says, we get a bunch of drop tests. Until then, there is the possibility that pulley systems, in spite of their hypothetical advantage in the absence of friction, could in reality be no better and perhaps worse than a cordelette when it comes to real-life equalization.
Edit: The issue of money for testing is, of course, critical. The AAC seems to me to be the only likely source. I have written Phil Powers twice to advocate for an AAC role in this kind of testing. His replies have been receptive, but of course I'm just a single voice. I would suggest that everyone who thinks it is important to understand anchor loads and rigging methods do two things: (1) join the AAC if you haven't, and (2) inundate the president with requests for a testing program.
(This post was edited by rgold on May 19, 2007, 7:21 PM)
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Post edited by rgold
() on May 19, 2007, 7:21 PM
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