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Accident and Incident Analysis:
Re: [Rmsyll2] Top-belay accident:
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dugl33
Feb 8, 2011, 3:27 PM
Views: 13304
Registered: Oct 6, 2009
Posts: 740
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Rmsyll2 wrote: D. explained that the problem with the rigging was the direct connection of the rope to A., instead of the rope being put through an master-point at the anchor and then through the device, similar to how it is from the ground.* My understanding of his point is that making a two-strand pulley divides the force on the device in half.
You are confused with regards to the mechanical advantage of "pulleys". Belay devices add friction, that's it. They reduce the force needed by the braking hand in comparison to the pull on the load side. A top redirect may add a little more friction but does not provide a mechanical advantage as far as braking. It does put the belayer in a more comfortable orientation for braking and tends to lift him up toward the redirect, rather than down.
Rmsyll2 wrote: Majid's drawing seems to show two ways to make a redirect belay; but some posters do not use that, doing it as in the first photo. I think now that an ATC is good only for rappelling, however many do use it for belay. A Reverso now seems much better for belay. Both are always a two-strand pulley, so a redirect makes a four-strand pulley?
I think you are still confused. What is shown in Majids drawing on the left is a way to use a standard atc connected directly to the anchor for a lower. The purpose of the redirect biner here is to orient the pull of the brake strand in the standard lock off orientation, otherwise the strands tend toward parallel and the belayer would have to pull up on the brake strand (weak, awkward, poor control) rather than downward (strong, comfortable, in control).
*edit to add context
(This post was edited by dugl33 on Feb 8, 2011, 3:46 PM)
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Edit Log:
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Post edited by dugl33
() on Feb 8, 2011, 3:46 PM
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