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Post by gregggagliardi on Jul 29, 2013 11:57:32 GMT -8
Although the Mountaineers generally recommend against a single two-person rope team on a glacier, it is common especially among those taking on technically challening routes and not uncommon for Mountaineers who have completed the intermediate course.
The climbing community at large has offered a number of proposals for two person teams. Traveling in coils on a shortened rope is one common recommendation. Tying knots in the rope every meter between the climbers is another. Learning the ZxC and ZxZ crevasse rescue systems is another.
Lately I have been reviewing these recommendations looking for best practice recommendations. Based on what I have researched and tinkered with here is what appears to be the best set-up.
1. 70 meter rope 2. Each climber carries 80 feet of coiled rope leaving ca 69 feet between the climbers 3. The 69 foot section between climbers is knoted every meter (e.g.,alpine butterfly) 4. The team has mastered and agreed to use the Canadian Drop Loop system for CR: a) The drop loop system permits a theoretical 6:1 system that can be employed regardless of rope entrenchment. (the knots deliberately entrench the rope) b) The knots serve as points of aid (like an etrier) for the fallen climber b) A disabled (still conscious) victim can assist in the raise by pulling on the middle line (part of the dropped pulley, "C" section of the system)
As with all techniques there are some disadvantages to the drop loop system:
1. The short distance between climbers does not work well on glaciers with gigantic, long crevasses 2. Higher mechanical advantage systems multiply force on the anchor, which means that the anchor needs to be particularly bomber.
Comments welcome
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Post by nicklyle on Jul 30, 2013 7:41:55 GMT -8
When teams practice these techniques they can work to determine what the minimum mechanical advantage may be for their particular needs. If 3 to 1 will suffice you combine lower anchor loads, lower friction and increased speed. Gear choices matter here too; without pullies, friction will rob a 6 to 1 tackle of a good portion of the gains due to increased mechanical advantage.
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Post by nicklyle on Jul 30, 2013 7:44:26 GMT -8
Many teams of two will travel on a 30 meter rope. Best practice for this arrangement needs to be covered too.
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Post by gregggagliardi on Jul 30, 2013 12:23:17 GMT -8
One rope team with two persons on a 30 meter rope is asking for trouble, unless there is little or no risk of a fall into a crevasse (e.g., an easy dry glacier), in which case perhaps no rope is needed at all. I don't see a safe way for two to climb on a 30 meter rope on a technical glacier. It would be very difficult to set up a crevasse rescue using most of the available systems. The biggest problem is rope entrenchment. With such a short rope it may not be possible to lower a bite to the fallen climber to set-up a C pull. Almost certainly there would not be enough rope for a Canadian Drop Loop. A Z pulley system would probably not be enough to overcome the rope entrenchment, even after post-fall padding of the section of the lip that is not entrenched. A ZxC would also be of questionable assistance in this circumstance for the same reasons. Forget any of the above if the fallen climber has an expedition size pack, skis or a worse yet is pulling a sled. Possibly a 6x1 haul could be set up with a short block and tackle system on a section of the rescuer's rope that is not entrenched. Mammut has recently developed a commercial system of this type (see attachment). One could in a pinch create the same system with a long cordelette, some pulleys and biners. However given the size, weight and relatively low cost of the Mammut product two person teams would be well advised to consider carrying the Mammut system. Attachments:
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Post by jimnelson on Jul 30, 2013 12:38:05 GMT -8
Gregg, how does a higher mechanical advantage raising system increase the load on the anchor?
Makes me think about the importance of monitoring the person being raised in terms of jamming against something when teaching raising systems. I'm not sure this is discussed in Freedom, and definitely not included in our climbing courses, at least in Seattle.
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Post by gregggagliardi on Jul 31, 2013 8:49:53 GMT -8
Jim: Force multiplication. It's identical to the pulley effect on the top piece of pro. Assuming a 150 lb. climber statically hanging on one anchor, the force necessary to lift him up will need to 150 + lbs. The anchor experiences the weight of the climber plus the force required to lift him. Theoretically a 6:1 system in this scenario would put 900 + lbs of force on the anchor. However, this is likely an underestimate since the climber will have a pack and there will be a fair amount of friction in the system that needs to be overcome. Also there is rope stretch. Also it doesn't take into account shock loading the system if part of it fails during the lift. I am sure that someone has done some actual tests measuring these forces. I will see what I can find.
Re raising the victim into the lip: The recommended procedure is to set the anchor up on the loaded side of the rope with a load releasable hitch (Munter mule with overhand back-up knot is one of many good options). This allows the victim to be lowered. Still, the rescuer(s) need to monitor the victim to avoid raising them into trouble.
Rescuing a fallen middle climber (three person team) poses yet another interesting challenge that we do not address. Adhering to the two rope team minimum for glacier travel is the simplest way to manage these complexities. Of course this isn't much help if the two teams are separated by several kilometers, which happens when a fast team is allowed to get way ahead of a slower team.
In my estimation teaching of these complex crevasse rescue techniques is greatly enhanced with video demos and lots of practice. I am working with a couple of buddies in Tacoma to make some videos of these procedures.
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Post by jasonmartin on Aug 1, 2013 15:26:32 GMT -8
Greg and others,
It's pretty unreasonable -- and well outside the norm -- to expect people to carry a 70-meter rope in two person glacier travel. It's also unreasonable to expect people to carry an Aztec Kit (which is a heavy device designed for technical rope rescue) in mountain terrain. And lastly, the more butterfly knots you have in the rope, the harder it will be to get the rope back out of the crevasse lip.
It is reasonable to have people carry coils or excess rope in their packs to help facilitate a rescue. And it's reasonable to carry some extra cordage (which you could rig like an Aztec kit on carabiners if you wanted) to facilitate in a rescue. And finally, it is also reasonable to put two or three knots in the rope between people.
I feel like the systems that were pitched -- while not wrong -- are overly cautious, almost to the point of being unrealistic.
On a two person rope team, I generally have about 40 feet of rope out between people, with two or three butterflies in it. Each of the climbers carries 40 feet of rope in coils or in their packs. Certainly there could be more in there if you're using a sixty-meter rope.
The amount of rope out is dictated by the size of the crevasses on the glacier. The amount of rope in the packs is dictated by the amount of rope out. You should have enough to rappel to your partner if something goes wrong.
You don't need any commercial kits to facilitate the creation of any type of hauling system. You can do pretty much anything with some prusiks and a cordellete.
We teach people to arrest the fall, build an anchor, transition the rope into the anchor by clipping it into the rescuer's foot prusiks, and then to create a haul system (usually a 3:1 or 6:1). The system could be built to directly haul on the line that the person is hanging on, or it could be built using the backside rescue rope. If you have butterfly knots welded into the lip, it's always easier to haul using the backside, though it's more complex to set-up.
Some climbers move across the glacier tied in in a Kiwi Coil as opposed to a mountaineers coil. They do this because it's easier to switch from glacier travel mode to pitching. However, a transition from arresting a crevasse fall to a hauling system is more dangerous in this set-up because if your friction hitch slips while you are uncoiling the rope, you could get strangled. If transitioning from a Kiwi to a anchor and hauling system, it is super important to tie a catastrophe knot behind the prussik hitch before uncoiling the rope...
I assume when you say ZxZ that you mean a 9:1 hauling system? I find that even the smallest people are usually able to haul a climber out at a 6:1, but that's not to say that there isn't value in including a 9:1 system...
Anyway, those are a lot of random and unstructured thoughts on this...
Jason
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Post by jasonmartin on Aug 2, 2013 10:27:36 GMT -8
I did just note that the Mammut kit is not a Aztec Kit, but something made specifically for climbing. However, it looks exactly like the rope rescue kit referred to as an Aztec Kit.
With all that in mind, I still do not believe that this is a kit that should be promoted in something like Freedom. It is a work around to baseline glacier travel knowledge.
Another note on 80 feet between people...that is enough rope for there to be significant stretch in a fall. That stretch would be in addition to the fact that a rope is seldom taut when a person falls in, which could lead to climber getting "corked" or hitting something in a fall...
Jason
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Post by dougsanders on Aug 3, 2013 9:03:39 GMT -8
It is my understanding that the tension on the anchor is not multiplied by the mechanical advantage. Rather, The approximate tension on the anchor = (the mass of climber + edge friction loss + pulley friction loss) x 2.
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Post by gregggagliardi on Aug 6, 2013 9:48:28 GMT -8
I have since done a bit of research on forces on an anchor generated with hauling systems. Unfortunately all that I have found is theoretical estimates based on various mathematical models of the rope and system components. What is lacking are empirical tests of the actual force on real anchors with a real victim in a real crevasse hauled by a real climber(s). Petzl has suggested that for the top piece of pro clipped to the rope with a carabiner, friction reduces the load on the belayer's side of the rope to 66%. However others have criticized this estimate. The truth is that these physical systems are a lot more complicated than we think. There is still a lot that is not known, which in my book suggests a cautious approach.
A technical question for Jason: What methods do you teach for crevasse rescue to manage an entrenched rope with 2 climbers (175 lbs each; each carrying a 40 lb pack) on a 60 meter rope each carrying 40 feet of coils? Even if there is enough rope to rappel to the victim, is there enough free rope to create an effective hauling system when the rope is entrenched?
I am looking forward to testing out a 6:1 system, identical in principle to the Mammut product, that is created with a cordelette, one or two pulleys, friction hitches and carabiners. It would be fun if others interested in these issues would experiment with different small 6:1 systems using only normally carried gear and share their experience.
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