Help with Pulley System

OK - my simple brain has come up with what might be the most simple answer.
Please be kind and tell me what you think...

It will help to look and the pic to better understand what I'm saying (attached)



One end of the rope is in the bag.
One end of the rope is above the 8 located just above the Upper Pulley.

What if the end of the rope exited this 8, went up and over the branch (crotch) down to the trunk of the tree to be secured.

This will get rid of the creeps.
It can still be set up from the ground assuming you had a long enough piece of rope.

OK, hit me with your feedback.

Geof

That will not be the same system that we have been talking about all this time. When you tie to the base of the tree it is a very safe systen comonly used in SRT. So no discussion on the safety of that one system and you do not need any of the extra figure-8 knuts everywhere! or the (FS) friction saver for that matter. You can actualy use a separate rope and hang all the other pulleys and everthing else from the end of the rope going over the branch (TIP)and have a DRT system with a pulley acting as a Friction saver. I have used that one a few tymes myself! It is ilustrated in The Tree Climbers Companion book, I think

Bill, I like the bumblebee story too. I tell it in my classes and derive exactly the same moral from it that you do.

JimW beat me to most of the other things I was planning to say. I think we DO know why the system hasn't given any problems yet: the bark has been strong enough and the friction has been great enough to hold things in place, so far. My worry is simply that there are easy to imagine circumstances where that might not be the case. Situations that would make me especially nervous include: wet bark, platy or flaky bark like on red pines, and wet lichens.

What Geof_K describes will work - it's one of several fairly simple ways to eliminate the flaw. Another approach is to have a separate rigging line (terminated by a figure 8 loop) going over the branch screw-linked to a figure 8 loop in the top of the climbing line (instead of going over the branch, the climbing line dangles from this loop). I'll try to get a sketch posted tomorrow; I don't have a scanner handy at home. Having a separate rigging line also gives extra ways to handle a rescue situation; given that the usual application of this system is helping people with physical difficulties to climb, that would seem to be a nice feature.

Geof, I’m not sure, but I think what you’re saying (looking at the sketch) is to “cut the rope” at the top left figure-8, and then (a) route the part of the rope above the cut down to the ground (and secure it); and (b) connect the part of the rope below the cut to the carabiner (screw link). Yes, that would remove the flaw. Good thinking.

One thing to note is that this would double the load on the branch.

Mark, I’m not sure if you’re suggesting another line that would go from the carabiner (screw link), up and over the branch (to the left), and then down to the ground to be secured. I’ll wait for your sketch.

That method would have the same effect as my suggestion, which is to attach (probably with a friction hitch) an accessory cord line where the top-left figure-8 knot is, and then secure that safety line at ground level.

Following up on Mark’s comment about having the system rigged so provision for rescue is provided, how about having the entire rig supported in such a way that it could be lowered from the ground?

I remember the first time I watched tree workers carefully (about 15 years ago). They hoisted a pulley up to a branch, and the climber used the pulley as we would a CS. Even if the climber became unconscious, the ground crew could lower him.

I’m pleased that we are beyond whether the system has a flaw, and moving toward mitigating it, as Mark had suggested we do.

Mark, you are correct in that we indeed do understand why the system reportedly has not yet failed: There simply has been sufficient friction at the CS. What I had in mind when I said that we did not understand it is that I was surprised that there ever was enough friction to hold the thing in place. I find it hard to accept that there is so much!

My thinking is that if there is enough friction with a leather CS that this system slips only a little ( a few feet in moss’s tests), that says that the 50 or 60 or 70 pounds imbalance applied at the CS cause only a little slip. If that’s the case, those of us who use a leather CS are wasting a heck of a lot of energy just to overcome that friction!

I climbed only once on a RING/ring friction saver, and that was back at the beginning of my RTCing. I was so new to the game that I don’t remember the difference in friction between the two methods. I’m certain there must be a significant amount, though.

I think it would be very educational to use a force gauge to see how much force is required to overcome the static coefficient of friction of a leather sleeve when climbing DdRT. After all the discussion here, it seems that we probably would be dismayed at the answer.

Originally posted by Jim W
Mark, you are correct in that we indeed do understand why the system reportedly has not yet failed: There simply has been sufficient friction at the CS.

I think "failure" has to be more clearly defined here. If the CS moves off the branch the climber does not fall or even descend. At this point the failure that you describe is one of the CS moving only. You have no empirical data to describe what happens if the CS moves off the branch.

I describe failure as uncontrolled or unexpected descent by the climber.

I will also repeat again that the system should NOT be implemented with F8 to the left of the CS (as shown in the drawing). This could cause the CS to move. However if the CS does move it would have the same effect on the climber as if a CS moved in a traditional DdRT setup: none.

Also note that during my test I was able to cause the pulley to move down considerably when I did not set up properly (ie: snug the screwlink holding the pulley up as high as it could go before I loaded the system). On this climb with the pulley moving down I experienced no unexpected descent. It behaved like a normal DdRT system. I was only limited in how high I could climb.

Sorry I broke my silence I would really like to see JimW and Mark F test the Super System as originally designed and provide input.
-moss

Here's a picture of what I tried to describe last night.



The advantage of this rig is that you can lower the climber to the ground using the rigging rope if need be.

Feedback?

Originally posted by MarkF
Here's a picture of what I tried to describe last night.

That works, need to rig a belay device or ascender on the bottom TIP for rescue. Load is doubled on the branch.
-moss

Originally posted by MarkF
...I think we DO know why the system hasn't given any problems yet: the bark has been strong enough and the friction has been great enough to hold things in place, so far. My worry is simply that there are easy to imagine circumstances where that might not be the case. Situations that would make me especially nervous include: wet bark, platy or flaky bark like on red pines, and wet lichens.

You guys are fixated on this. It doesn't matter if the CS comes off the branch and it won't anyway if the system is rigged correctly (no F8 on left as I 've mentioned a couple of times).

For instance the Super System can be rigged without a CS. If the CS mysteriously vaporized during the climb there would be no change. The only function of the CS is to protect the branch and to lower friction on the rope during installation of the system.

The CS will also protect the branch from any rotational forces that occur if the pulley moves down during the climb (similar to standard DdRT climbing without a cambium saver) so it is nice for the tree.

Can we focus on what happens if the pulley moves down during the climb? The CS is a total non-issue in regards to safety of the system.
-moss

Ok scientists, time to move the discussion to the tree and test. I'm talking about setting it up and climbing on it. I suggest two variations to observe system behavior:

1. Screwlink choked as high as it will go (correct installation).
Load the system with the climber. Try ascending and descending.

2. Send the screwlink up two thirds the height of the system (purposeful incorrect installation).
Load the system with the climber. Try ascending and descending.

Report your results.

Note:
I am requesting that experienced climbers only test. The Super System has been proven safe in real world use by many instructors and facilitators but it must be rigged as specified. I've already posted photos in this thread. PM me directly if you have configuration questions. I'm not posting more photos or diagrams in this thread.

Thank you! Also.. everyone is urged to please send me a check for all the time I'm putting into this thread
-moss

I agree with Moss -- set up the system, try it and report back...!

Moss,

I agree that the rig I've pictured doubles the load on the branch. This is no different from one of the standard ways to rig up an SRT rope.

I also agree that choking the rope around the branch with the screwlink will help. Assuming that classical dry friction applies and that you get, say, 30% more wrap around the branch, you get about 34% more force (the equation for that is described here: http://www.geocities.com/roo_two/friction.html ).

Testing: No time just now; I'm doing these posts in between grading and exam writing. May have time to try some things out in about 2 weeks.

I would not consider testing the "correct" configuration to be conclusive however; just as I would not consider 3000 miles of driving without seat belts and without accidents to be conclusive. The thing that is clear from your experience and what WildBill reports is that the circumstances that cause problems are very unlikely - I have no quarrel with that at all.

I do agree that some handling of the system could lead to an improved "feel" for what is going on. A lot of things guide the proper application of theory to the real world, and "feel" and intuition are some of the critical ones. I respectfully decline, however, to test the system at height.

Back to grading. I'd much rather think about this, and I'd REALLY rather be in a tree about now...

Originally posted by MarkF
Moss,
....I respectfully decline, however, to test the system at height.

Absolutely. For any unfamiliar system climb low and slow. You can always set it on a low branch to fully test as I described. You can also tie in to a DdRT back up with a separate system.

My personal experience is that it is very stable and predictable in behavior and there is nothing to fear.
-moss

Mark,
Thanks for taking the time to make a fine drawing and posting it. I like it. The only differnce between your drawing and my written description is that yours requires 2 ropes and mine only one (but a longer rope) Yours allows for the climber to be lowered in a rescue situation - I like that!
Know that I will be testing it this Sunday at a picnic with a buch of my climbing buddies. I look forward to sharing our conversations with them and getting their feedback.

Thanks again!

Geof

Originally posted by MarkF
I would not consider testing the "correct" configuration to be conclusive however; just as I would not consider 3000 miles of driving without seat belts and without accidents to be conclusive.

I like the car analogy. I think what we need to do is the equivalent of some crash tests without seatbelts to see how bad it can get.

Maybe we're just driving at 2 miles per hour into a wall of jello? It is hard to tell how bad this worst case is without any testing. Of course, you might say that 'worst case' would be the CS replaced by a pulley, but realistically there will always be more friction than that. (Maybe we should still test it though, just for the sake of it. It might not slip!)

Like I said, rig this up on the slickest branch you can find and see what happens, I am curious!

- Link