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Post by gregggagliardi on Dec 7, 2013 16:16:14 GMT -8
Check out this method for middle person tie-in. Clever but is it safe? ((I think so). Also check out the two person rope team set-up. Brake knots can also be used with a three person set-up. The crevasse rescue method of choice for use with the brake knots is the Canadian Drop Loop system ( See Houston and Cosley (2004, pp 289-291)
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Post by jasonmartin on Dec 8, 2013 8:12:06 GMT -8
Well,it probably wouldn't pass AMGA muster. The rule is that a person can never have their life dependent on a single friction hitch.
Jason
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Post by steveglenn on Dec 8, 2013 14:40:20 GMT -8
The Mountaineers taught me to tie in to the middle of a three person rope with a double bowline. It is cumbersome and the lesson did not last long. One of my first climbs after graduation from the Basic course was Mt. Rainier via D/C. As the middle person on the rope, I remember clipping into a figure 8 loop, similar to the above picture on the left. I put individual leg loops above and below the knot (standard practice in the early '70s) and ran the prusiks through the waist belt of my harness and into my pants pockets, to keep them out of the way. Around 0200, near Ingrahm Flats, the party crossed a big hole on a small bridge. At the midpoint of the crossing, I remember looking down into the dark hole, and simultaneously noticing that I had come unclipped. All that was attaching me to the rope was the two prusik slings that ran from the rope and into my pockets. I think that was the last time I ever climbed in the middle of the rope... Since then, though, I have always had the middle person on my ropes back up the clip-locking 'biner with a second non-locking biner, placed so that the gate was opposed to the locking 'biner.
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Post by jasonmartin on Dec 8, 2013 16:32:10 GMT -8
We teach people to tie in for mountaineering style climbs (i.e. no pitching) with either figure-eights on bights or with butterfly knots. We also teach them to have two locking carabiners clipped to the tie in. In part this system was devised with the way that we teach crevasse rescue in mind. Once you come out of your figure-eight in a rescue, it's nice to have two lockers on your belay loop for transitions from different back-up lines...
Jason
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Post by gregggagliardi on Dec 9, 2013 9:13:07 GMT -8
Would offset tandem prussiks pass muster for the middle person tie in? Has anyone (or organization) tested various tie in methods with actual crevasse falls or simulated crevasse falls. Mind you, I am not advocating this method, just researching it.
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Post by gregggagliardi on Dec 9, 2013 14:51:52 GMT -8
Here is a bit of pertinent data.
On a Tom Moyer test using a 7mm 3 wrap prusik on an 11mm rope during a pull test, failure occurred at 2,840 lbs (user.xmiasion.com)
Rigging for Rescue reports that when 3 wrap Purcell Prusiks are used s lanyards they uniformly pass a standard FF1 drop fall test (http://www.riggingforrescue.com/reLanyards2.html)
If the middle person is tied into two 6mm three wrap prusiks on a 9-10 mm rope, is there any situation (in glacier travel ) that could generate a fall as high or higher than a fall factor 1?
Again, I am not advocating this method of tie in ( I use an alpine butterfly for mid rope tie in)
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