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wivanoff
Dec 27, 2012, 12:56 AM
Post #51 of 63
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jcrew wrote: marc801 wrote: namoclimber wrote: Is this a common practice to not use double rope rap when available. In canyoneering, a double rope rap is almost never used except by the clueless. . guess i'm clueless,......why the hell was he only on 1 wet strand of rope? why is it so cool to rap 1 strand in a canyon?
It's not that it's cool 
One reason is that there's less tangling. Imagine rappelling down a waterfall into a deep plunge pool with a big tangle of excess rope in it. Or tossing two ropes down a waterfall and having them get all tangled up before you start your rappel.
It's much better to lower one end of the rope to the correct length and block it so everyone rappels down that single strand. Once they get into the pool they only have a short length of rope to deal with and they can pull it through their rappel device and swim away. Last person down removes the safety, rappels single stand and either brings the rope bag down with him or tosses it off. Still less cluster than two long ends. AND less rope to pull down because you've set the rope length for the length of the rappel. Also allows for extra rope on top for rescue use if needed.
On longer rappels, you could use a full length of rope and a pull cord to save some bulk/weight. Once again, rappel on one strand and last person down takes care of the pull cord.
This is just one case. In another situation, you might decide to rap on a doubled line like we're used to in climbing.
But, I'm still not clear why you anyone would use a 70m rope AND a 70m pull cord payed out in buckets by the first person down for an 8m drop. Seems like you'd they'd have an awful lot of rope to pull down after rappelling.
Edit: spelling
(This post was edited by wivanoff on Dec 27, 2012, 2:11 PM)
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moose_droppings
Dec 27, 2012, 1:16 AM
Post #52 of 63
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milesenoell wrote: The one time I have actually stopped someone with a fireman's belay was with a BIG guy on a brand new and pretty skinny line so I opted to loop the end under my butt and sit into the loop for tension.
Maybe Curt's foot belay would work in combination with the firemen's belay.
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billl7
Dec 27, 2012, 4:02 AM
Post #53 of 63
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Tried the same setup as the original test with 5 mm Blue Water accessor cord (new, EN564). With same results. Decided to try shortening the loop to shorter stretched out lengths with results shown below (orig tests included).
Edit: * Pre-tensioning the french-prusik allowed it to hold the weight.
With the french prusik, length can matter.  I suspect the shorter lengths force the coils to stay more closely together and so to run in a more compact coil around the rope. This way, more of the cord can act as two fingers do pinching on directly opposite sides of the rope rather than two fingers on opposite sides of the rope but offset up and down the rope from each other.
With the aforementioned prusik & kleimheist, the hitch itself better governs its own compactness in dimension up and down the rope.
I haven't checked out how easily each different configuration can be tended during the rappel (i.e., ease of being pushed down the rope by hand). Might be pretty difficult, especially with the 13 inch loop of cord and four wraps.
Bill L
(This post was edited by billl7 on Dec 27, 2012, 4:39 AM)
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milesenoell
Dec 27, 2012, 6:36 AM
Post #54 of 63
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moose_droppings wrote: milesenoell wrote: The one time I have actually stopped someone with a fireman's belay was with a BIG guy on a brand new and pretty skinny line so I opted to loop the end under my butt and sit into the loop for tension. Maybe Curt's foot belay would work in combination with the firemen's belay.
Classic!
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billl7
Dec 27, 2012, 4:27 PM
Post #55 of 63
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milesenoell wrote: moose_droppings wrote: Maybe Curt's foot belay would work in combination with the firemen's belay. Classic!
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billl7
Dec 27, 2012, 5:18 PM
Post #56 of 63
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After a bit more testing (details below), here are some summary points about using the french-prusik as an autoblock below the rap device:
a) The author of the linked forum contended that clipping forward or aft of the girth made the difference. True - changing the number of wraps by half-a-wrap can indeed make a difference.
b) The length of the loop of cord matters with the french prusik. It affects the compactness of the hitch and so affects ability to grip.
c) Others in this thread have stressed testing the exact config as being important. That is good advice. Variables that can make a significant difference include one-stranded versus two-stranded rappels. The significance of wet versus dry conditions was not tested.
d) In situ testing should not include pre-tensioning the french prusik as this can hide the actual effectiveness in some surprise falls (assuming a surprise fall is what one hopes to back up).
Bill L
P.S. A little more detail from further testing that supports some points stated above ...
After scrutinizing the clearest image of the autoblock in this thread and after a little trial and error, the config chosen to best approximate the accident was a 13" loop with ~3 wraps of 5mm cord with a locking biner that was about 3 3/4" in longest length (BD Positron Screwgate, outside measurement).
Clipping rear-ward of the girth passed the drop test. Clipping front-ward of the girth failed the drop test (removes half a wrap bringing the total to ~2 1/2 wraps). In both cases, pre-tensioning the autoblock held the weight.
Note that all my testing was done dry.
(This post was edited by billl7 on Dec 27, 2012, 5:34 PM)
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marc801
Dec 27, 2012, 5:46 PM
Post #57 of 63
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wivanoff wrote: But, I'm still not clear why you anyone would use a 70m rope AND a 70m pull cord payed out in buckets by the first person down for an 8m drop. Seems like you'd they'd have an awful lot of rope to pull down after rappelling.
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jcrew
Dec 27, 2012, 9:22 PM
Post #58 of 63
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wivanoff wrote: jcrew wrote: marc801 wrote: namoclimber wrote: Is this a common practice to not use double rope rap when available. In canyoneering, a double rope rap is almost never used except by the clueless. . guess i'm clueless,......why the hell was he only on 1 wet strand of rope? why is it so cool to rap 1 strand in a canyon? It's not that it's cool One reason is that there's less tangling. Imagine rappelling down a waterfall into a deep plunge pool with a big tangle of excess rope in it. Or tossing two ropes down a waterfall and having them get all tangled up before you start your rappel. It's much better to lower one end of the rope to the correct length and block it so everyone rappels down that single strand. Once they get into the pool they only have a short length of rope to deal with and they can pull it through their rappel device and swim away. Last person down removes the safety, rappels single stand and either brings the rope bag down with him or tosses it off. Still less cluster than two long ends. AND less rope to pull down because you've set the rope length for the length of the rappel. Also allows for extra rope on top for rescue use if needed.
o.k. copy that.....but this beta doesn't seem applicable to this situation. IMO, he would have had a lot more control if he'd threaded both ropes. the friction alone would have probably almost stopped him. it seems they were slavish to the technique, not understanding the reasons for the technique.
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billl7
Dec 27, 2012, 10:20 PM
Post #59 of 63
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jcrew wrote: o.k. copy that.....but this beta doesn't seem applicable to this situation. IMO, he would have had a lot more control if he'd threaded both ropes. the friction alone would have probably almost stopped him. it seems they were slavish to the technique, not understanding the reasons for the technique.
It seems unlikely that rapping on two strands would have "almost stopped him", especially on so short of a rap. I find double 9's on a standard ATC to be 'fast' ... enough so that I'm usually either planning to use a different rap device or doubling up on the ATC's locker. Edit: Some of my lighter climbing partners think an ATC-rap on double 9's is okay but I generally don't hear them complaining of too much friction.
All that said, double strands may have helped with the autoblock engaging (not sure). And, even before that, perhaps he would have felt less pressed to just trust to the autoblock.
And I agree that the primary issue was losing control in the first place; thanks for re-emphasizing that in this thread. It would be wrong to assume the beta from the autoblock analysis addresses what is the primary issue.
Bill L
(This post was edited by billl7 on Dec 27, 2012, 10:27 PM)
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Syd
Dec 28, 2012, 3:29 AM
Post #60 of 63
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billl7 wrote: Right. The explanation in that thread for why the autoblock didn't work was that the final clipping to the leg loop should be "at the block's girth" but was not. It was forward on the leg loop where it then "slid up [along the leg loop] and couldn't cinch". This guide teaches that clipping forward of the girth is fine. In David Fasulo's "Self-Rescue" book (1996 - it was recently revised), several illustrations show clipping rear-ward of the girth. Is it really that critical whether the biner is clipped forward, at, or rear-ward of the girth? Can an autoblock in this application really be that sensitive? Bill L
I've always used a normal French Prusik, that is, with the biner clipped into both ends of the cord, then the biner clipped anywhere to the leg loop. I don't attach the cord directly to the leg loop at shown. It seems to work well.
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healyje
Dec 28, 2012, 11:00 AM
Post #61 of 63
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Rgold wrote: The one thing I disagree with is your statement that the accident has nothing to do with the failure of an autoblock. It is beyond contention that the autoblock failed, probably because it was set up too close to the rap device. If the autoblock had held, there would have been no incident at all. Of course he should never have let go of the brake strand like that to begin with, but once he made that potentially fatal error, the autoblock indeed failed to function.
I wasn't commenting on the autoblock failing or not, but was simply stating my opinion the presence or absence of an autoblock was irrelevant in this incident and, as marc801 is also saying, the direct cause of the accident was a lack of competence, skill, and judgment for the rappel at hand.
Personally, when I've used an autoblock I have never 'relied' on it to compensate for any aspect of my ability to manage a rappel. Any assumption an autoblock or any backup device can compensate for lack of skill, competence, or judgment is beyond erroneous, it's a disaster waiting to happen at any moment (and don't even get me started on the risks of rapping waterfalls for a good time).
As for use of a fireman's belay, it's a belay no different from any other belay and if you as a belayer can't competently manage and execute such belay then you shouldn't be doing it and probably shouldn't be belaying TRs or leads either. It's not as common a belay today as it was BITD, when it's use was fairly routine, but its effect is immediate and excellent for the purpose.
As to the effectiveness of autoblocks on skinny, wet, single ropes (let alone figure-8s) you damn well better tune it all out ahead of time and know what the hell you're dealing with. If I somehow became delusional enough to partake of this activity I'd only do it on a 10mm rope and an Anthron double-stop Descender.
(This post was edited by healyje on Dec 28, 2012, 6:56 PM)
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billl7
Dec 28, 2012, 4:07 PM
Post #62 of 63
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An industrial analogy about backups to human operators ...
Powerful cranes often have mechanically triggered limit stops that are necessarily out of the human operator's eyesight. Without an upper limit stop, the full power of the hoist motor can be used to pull an empty hook into the crane structure, leading to catastrophic failure and so to injury or death of those below by falling crane parts.
A very common procedure after setting down a load is to stow an empty crane hook up and away from ongoing work. A crane operator could a) raise the empty hook until it hits the upper limit stop. Or a trained operator could b) stop raising the hook just before it hits the limit stop.
Unnecessary care-free activation of the last backup to failure is best left to settings outside of normal operations.
Bill L
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DFCLIMB
Jan 19, 2013, 2:43 AM
Post #63 of 63
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It looks as though there were not enough wraps on the friction hitch (although it is hard to see for sure on the video). It is best to have the rappel device extended to better control the descent and to ensure the friction hitch does not touch or interfere with the rappel device.
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