Help with Pulley System

This is now the most-replied-to post, according to the stats page. Nice!

- Link

Bill and moss, you have suggested a few times that Mark and I (and others) rig this system and try it out.

Sorry, but I missed what specific things we are to be looking for when we do this. What are those things?

Why don't you set it up and try demonstrating that the flaw you keep writing about will actually result in a fall. This would be valuable research for the whole tree-climbing community. I have not been able to make it fall, even when I forced the cambium saver to come off the limb, but maybe I've been going at it the wrong way. Hopefully, when I head up to J-bird's place this summer (and up toward your house too) we can set up several varieties of the system and look at it from different angles.

From moss:
posted on 5-11-07 at 08:40
quote:

---

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.

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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).
---end quote---

Yes, we indeed are “fixated” on this precisely because this is the mechanism (the flaw) by which the top pulley moves down, thus allowing the climber to descend unexpectedly.

Moss, you have commented several times about the CS coming off the branch. Speaking for myself, I don’t recall ever saying anything about that. If I did, it would have been back when we were talking about having a stopper knot on the lhs of the CS.

You are correct in that it wouldn’t make any difference whether the CS slipped off, or the rope slipped through the CS. In either case, this is the flaw allows (causes) the climber to descend. This is what happened back when you said that you had observed “creep” of the TP.

Further to that, if the CS did slip off the branch, the SS actually would be less dangerous than it is in that there would be more friction where the rope passes over the branch (more friction than if the rope passed through the CS). Right?

Bill said:
“Why don't you set it up and try demonstrating that the flaw you keep writing about will actually result in a fall.”

Bill, this would not be of any value. As I said before, it would be analogous to my driving in my car, not having an accident, and then saying that that proved that seat belts were of no value.

It is an indisputable fact that the SS has the flaw that when the rope slips through the CS, the TP goes lower, and the climber goes lower.

Weren’t there some specific parameters of the SS you wanted us to evaluate?

Originally posted by Jim W
Moss, you have commented several times about the CS coming off the branch. Speaking for myself, I don’t recall ever saying anything about that. If I did, it would have been back when we were talking about having a stopper knot on the lhs of the CS.

You are correct in that it wouldn’t make any difference whether the CS slipped off, or the rope slipped through the CS. In either case, this is the flaw allows (causes) the climber to descend. This is what happened back when you said that you had observed “creep” of the TP.

Further to that, if the CS did slip off the branch, the SS actually would be less dangerous than it is in that there would be more friction where the rope passes over the branch (more friction than if the rope passed through the CS). Right?

Correct, thanks for acknowledging that Jim.
-moss

Originally posted by Jim W
Bill and moss, you have suggested a few times that Mark and I (and others) rig this system and try it out.

Sorry, but I missed what specific things we are to be looking for when we do this. What are those things?

Thanks for asking Jim.

1. See whether or not the pulley moves down as the climber ascends when the system is set correctly (screwlink choked/set as high as it will go).

2. Try setting the system with the screwlink/upper pulley incorrectly set. Set screwlink/upper pulley approx. 1/3 the height of the TIP (measuring from the branch). This will cause the upper pulley to move down as the climber ascends. Note whether or not this causes the climber to unexpectedly descend or be unable to ascend. Additionally try climbing until the pulleys meet to see what the behavior is when the pulleys meet. Determine if the climber is able to descend after the pulleys meet. A back up DdRT system can be set to provide backup and easy self-rescue if the test system behaves badly.

I have performed the tests described above (1 and 2) and found no problems occuring in either case. If you could verify same results or find different results for either 1 or 2 please report.

My intent for these tests is not to claim proof of bulletproof safety. I hope the tester will become more familiar with the system and to get a sense of its behavior under two "standard" configuration scenarios. This could provide a basis for further discussion

Thanks!
-moss

How is this for an even cleaner system?
Perhaps you could even get rid of the paw?

- Geof

As a convicted gear addict this system is just way too cool. Up to now I have refrained of posting my thoughts but this last drawing makes me want to go try to lift a Buick.

If I was to rig this I would have to delete the Blakes Hitch as the friction hitch to a Klemheist and connect the lower link to my harness with a web loop runner.

You are going to have to pull three feet of rope to elevate one foot so an easy to slide friction hitch like the KH or the Val. Tress would slide like butter. With the attachment at the lower pulley link would even make it self-advancing- clever ehh?

Using the web loop between your harness and lower link allows a much more length of pull per stroke. All of my climbing systems now have the friction hitch extended as high as I can so when I pull I am pulling in my most powerful zone.

The web loop can be girth hitched to your harness and then secured to the lower pulley link. Once you are ready to decend the loop lenght can be shorten by half by basket hitching both ends to the lower pully link. (of course do not change this connection until you are safely lanyarded in)

So now look at the latest drawing and imagine you attached to the lower link about 24" lower and your down rope is secured with a self-advancing hitch at the lower pulley. You reach up as high as possible to just below the Klemhiest. Pull down as much 42 inches of rope. The hitch advances itself and you have elevated yourself about 14" per stroke.

With a 3:1 Mechanical Advantage for me it is like pulling 60 pounds. Piece of cake.

See you at the top,

Dan House

PS Harv has me demo-ing all of these rigs and tree entry tools at Friday am of the Rockies Rendezvous.

Be there or Be a square knot.

Tree Tramp rocks! See you at the Rendezvous.
-moss

I tested the latest drawing today (2 posts above). It was very smooth - had no problems.

I used one long (140 ft) rope. The bitter end went from the ground through a rescue 8 attached to the tree and back up over the branch to support the pully system below. Simple and clean.

I'll be testing other systems with some buds tomorrow.

Geof_K

PS Harv has me demo-ing all of these rigs and tree entry tools at Friday am of the Rockies Rendezvous.

Tree Tramp - please take some pics and post them. Thanks!

Geof

Ok so I decided that it was time for me to try this system and see how it is suposed to work.
First it rigged it with all the figure 8's and friction saver as on the picture.
Muy observations:(minus the lower loop that does not do anything anyways) I used an extra dynema sling (inspired by Dan ) to increase the distance from the saddle to the bottom pulley that does not change anything critical with the system).
1. The figure 8 knots actually drive the FS over the TIP as the climber ascends slowly. ( crumching up the FS).
2. Since there is twice as much force pulling on the down rope the top pulley creeps down along as the climber goes up slowly.
3. For every foot the climber goes up the top pulley descends approximatelly 2 ft so the two pulleys meet about 1/3 of the way up the climb up and the climber can no longer go up only down. This rig was set up on a TIP about 40 feet from the grown.
4. Dependinging on the type of pulleys used the ropes twist on each other increasing the friction on the way up pretty much loosing all the MA adquired by using the pulleys in the first place reducing the progress of the climber up.
Do not know the reason why this happens but I repeated it three times and the same problem happened.

5. The extra carabiner looped around on the down rope below the TIP does not do anything other than holging the top pulley tied to the end of the rope. It creeps slowly down as the system creeps down. No matter how tight you make it at the start of the climb around the TIP limb). Since there is an extra figure 8 knot behind the top FS, it pushes it over the branch while the climber is on the rope actually almost piling the FS outside plastic cover ( give it try and see).
6. I forgot something here!......
7. There is a significat reduction on the friction (due to the pulleys MA) on the way up at the start of the climb.... but it is soon lost when the ropes twist on each other. Since the ropes meet about 1/3 of the way up the MA is pretty much irrelevant since the climber is only about 10 feet from the ground at that time and the climb is pretty much over.

None of these observations can be noticed until the climber goes up a distance so everything looks fine at the start but the problems compound on each other ( the twisting ropes, the top biner comming down, the FS scrapping over the TIP and finaly the two pulleys meeting and stoping the climb.

FYI. For this climb I was tied to a separate basic climbing system so that I was safe in case some bad happened at high elevation. This extra back up system allowed be to untie from the experimental rigging and reposition the pulley back up against the TP and continue all the way up until reaching my target branch but this can not be done without the back up system.
So the predictions by the mathematicians were pretty much on target with my observations on the field.
This system of pulleys is BUSTED as the TV program says!

Later Note: I just notice the second drawing posted by Geff. That is your basic RAD system that we have used many times but we use the Grigri where he has the Blake's hitch. That system can be set up as an DbRT system instead of the DRT posted there.

Oldtimer, thanks for testing and describing your results. What you experienced is worse than I expected, considering what moss and Bill have described. (I still have not had the time to do a test, myself).

Referring to your findings by the numbers:
1---This must be because of what Mark and I predicted: The shear strength (or friction) between the CS and the bark is low enough that it allowed the CS to slide over the bark. If you had not used the figure-8s, then the rope would have slid through the CS.

2 and 3---Yes. This is the problem (the “flaw”). The top pulley (TP) should stay fixed at the top in order for the system to be effective (and not dangerous).

4---Interesting! I wonder what may have caused that. The rope? Does it twist at all like this when you climb DdRT or SRT?

5---This also is not what I would expect from what moss and Bill say, namely that the carabiner allows the system to “strangle” the branch more tightly, thus giving more friction, thus making the system more secure.

6---(you accidentally typed “8”---not a complaint; just trying to be clear)---Yes, because the flaw in the design of the system caused it to “collapse” (although not catastrophically) and the TP moved toward the ground, you could not ascend to the TIP.

If the system had worked as intended, the TP would have stayed at the top. It will stay at the top if any of the easy modifications to the SS that have been described here by Mark, Geof, or me are made.

Thanks again, Oldtimer, for your tests and for sharing the results.