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Re: [Carnage] Testing a "Dynamic Belay":
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jt512
Jan 26, 2011, 5:14 PM
Views: 15470
Registered: Apr 12, 2001
Posts: 21904
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Carnage wrote: My assumptions and their backing: Cinch vs grigri: they both lock on the rope quickly, and in most cases don't let the rope slip (i know the cinch slips under high FF, if we want to test that, go for it, i'm trying to minimize the test cases) I think most people thing of the gri-gri and cinch as interchangeable when they're talking about dynamic vs non-dynamic belays
First of all, if most people think that, then most people are wrong. By design, the Cinch is dynamic above a considerably lower force than the Grigri, so the Grigri and Cinch are most certainly not substitutable as the "static" belay device. Secondly, why would you design an experiment based on "what most people think"?
In reply to: "inch or two of slippage" when i catch a fall on an ATC my brake had is typically gripping the rope less than 5-6 inches from the device both before and after a fall. The max distance that my hand would be down the rope is in the 1.5 feet range (again, approx). Given the fact that i dont notice much slippage, and how much rope is in play elsewhere in the fall, i'm hypothesizing that there is very little slippage in a typical fall. I'd like to test this hypothesis as well. I'm sure it will be a function of force, but what would the typical and worst case scenarios be?
In a "typical" fall, if you are using an ATC, and you actually know what you are doing (which is rare), you have the option of allowing as much rope as you like slide through the device to provide as dynamic a belay as you want, including the option of letting no rope slide through the device. That's one reason that Grigris aren't a good idea for trad; you never have the option to provide a dynamic belay.
In a severe fall, with an ATC you have no choice: unless there is a lot of friction in the system, the belay will be dynamic, and a lot more than two inches of rope will pass through the belay device. So, for either type of fall, the assumption implied in your first post that the difference between the devices comes down to one or two inches of rope slipping through the device is wrong.
At any rate, something similar to the test you are proposing has been done, and published. You can probably find it on the Web, and see if it answers your questions. I don't recall the results quantitatively, but qualitatively the impact force was much higher for the grigri than for any other device tested.
Jay
(This post was edited by jt512 on Jan 26, 2011, 5:20 PM)
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Edit Log:
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Post edited by jt512
() on Jan 26, 2011, 5:14 PM
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Post edited by jt512
() on Jan 26, 2011, 5:15 PM
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Post edited by jt512
() on Jan 26, 2011, 5:16 PM
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Post edited by jt512
() on Jan 26, 2011, 5:18 PM
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Post edited by jt512
() on Jan 26, 2011, 5:20 PM
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