Help with Pulley System

I am learning a lot about the mathmatics of this system. It still leaves me confused. What is the worse thing that could happen if the CS creeps CW over the branch? I've experienced this and the only "observable" result is that the climber cannot climb as high as if the CS stayed on the branch. Is there a real threat of a "50 foot pratfall?" If so, how?
My rope & equipment is certainly stronger than a banana peel.

I'm a bit confused by people who think that friction is such a complicated thing that anything that depends on friction should be avoided.

I think there is way more friction in this system than people are giving it credit for, due to the cinching effect that moss mentioned. It is a good point to say that you need to watch out for low-friction situations, but I don't think that merits abandoning the system entirely.

Even if it does start slipping, you will descend at 1/2 the speed of slippage, if that is any consolation.

Also, you can only slip 1/2 the distance between you and the TP. If you are on a 100 foot climb, halfway up, you can only slip 25 feet before the pulleys meet. The only time you can hit the ground is when you are less than 1/3 the way up to the TP.

Even when the system starts slipping, there is still going to be a significant amount of friction on the line, because your entire weight is still running over the branch (1/3 on one side, 2/3 on the other side).

I think the naysayers need to rig this system to see what it feels like. Try a low friction scenario like a wet branch or lichen and see what kind of slippage you get. Just make sure you weight the left hand rope (in the diagram) to cinch the screwlink as close to the branch as you can get it.

-Link

The sky is not falling, there is no fall threat in this system. If the cambium saver moves off the branch nothing happens. The climber does not move down. The top pulley moves down (if it happened) and the climber can only go as high as the top pulley. The cambium saver would theoretically only come off the branch if an F8 was put on the left side (1/3 load side) of the system. The discussion of the CS moving is a red herring, this was not the original design of the system. It is best to set up as shown in my photos above and not include the F8 next to the CS.

To all the well intended theoreticians, set the system up as in the photos, test it out ( you can set up a back up). Using it leads to fully understanding the system characteristics and enhances the analysis with real observational data.

By the way, you'll hate it Very slow to climb. Very good for climber's with compromised arm or leg strength or high weight to height ratio or if you want to carry heavy gear into the canopy. The DdRT RAD system will do the same and not scare you as much. Requires more gear to rig. Always a tradeoff, nothing is perfect in tree climbing.
-moss

This is not going to make me any friends, but you guys (and gals) are used to my being willing to be outspoken. I’ve been gentle so far; now it’s time to be blunt.

Mark, thanks for your comments and concerns. I was beginning to believe that I was the only prudent voice out here. If others consider only one point you made, I think it should be, “The point is, these factors are COMPLICATED, and some of them depend on stuff that you can't even see from the ground.”

You said it in another way with, “. . . the forces opposing that slide into instability are tricky to predict, and they don't just involve classical friction.” Finally, “. . . it just seems so hard to predict when there will be a hidden banana peel.”

Geof, when you say, “What is the worse thing that could happen if the CS creeps CW over the branch,” and, “My rope & equipment is certainly stronger than a banana peel,” it tells me that you have not been paying attention and are not heeding the axiom of “Safety First.” Or maybe you’re just being playful; I can’t tell.

Link, sorry to have to say this, but when you say, “I'm a bit confused by people who think that friction is such a complicated thing,” it shows that you do not have a scientific appreciation for what friction really is. I do not for a second pretend to understand its fine points, but I do know that there is a lot that I don’t know, and I know where most of my areas of ignorance lie. Being ignorant of our lack of knowledge---believing that we understand something when we don’t---can be dangerous.

Your comment, “I think the naysayers need to rig this system to see what it feels like,” misses the whole point of my concern about the possible danger of this system.

Moss says, “Safety note!” and then says to remind the new climber to belay properly, etc., yet totally ignores the dangers of the basic system.

Everyone is in agreement that the system is unbalanced---significantly so---and no one has offered any engineering analysis that would even begin to explain why it doesn’t collapse more easily.

In other words, the system is not truly understood by any of us. Yet at least three voices here continue to insist, in ignorance (don’t misunderstand the definition of that word, or my intent in using it), that the system is safe.

Moss says, "I think it's academic at this point as far as safety goes." That's correct. The academics (so far) indicate that it is unsafe. I’ll even give a little on that: It is unknown enough that it is impossible to say that it is safe; there are valid reasons to believe that it is unsafe.

In my previous post, I said to you, moss: “I note that you didn’t respond to any of the questions that I posed in my preceding three posts . . . I suggest that if you take the time to consider the questions and respond to them, that we will reach a resolution sooner.”

You responded: “I can't answer all Jim's questions directly because I don't know the answers.” No responses were given to any of the questions.

Considering that the questions were elementary, and considering that you could not answer them, please tell me how it is that you believe that you have the competency to categorically declare that this system is safe?

Moss, I have high respect for you---I know that you know that. I think we disagreed only one other time, and that one was minor (I don't even remember what it was). I freely acknowledge that you are a better and more-experienced climber than I ever will be.

Please forgive my bluntness, but this has to be said: You are unquestionably quite competent and almost certainly well respected and regarded by others. It is precisely for that reason that those who read this forum are likely to follow your lead. This is why I find your statement, "There is no danger for the climber in this system beyond the usage dangers of any DdRT system" to be not only imprudent, but also unconscionable and irresponsible. You have absolutely no data to back up that statement. You DO have data to put it in question.

When I said that there was an imbalance, I was rebuffed and told that I was wrong. When I said that a model of the system would collapse, I was told that it would not. After much discussion, and then some tests, it was agreed that I was correct on both counts.

Yet despite the agreement that one-third of the weight being supported by this system is applied as a force across the CS, trying to make the system collapse, and despite the agreement that a model of the system indeed will collapse, some of you are still insisting that the system is safe. I am nonplussed that each of you is doing this solely on the observation that no one has reported that it has collapsed in situ YET.

We are adults and allowed to make choices. There still are lots of people who are certain that using tobacco will not cause them to have health problems. There are those who will pooh-pooh global warming even after the South Pole marker is only an ocean buoy. So you may, of course, use the system yourself if you choose.

I do ask, though, that when you facilitate a climb for others, that you perform a "full disclosure" and tell Mr. Prettyheavy (for whom Geof says he uses the system), who loads it with, say, 270 pounds, that there is a force of 90 pounds trying to cause the supporting rope to rotate and cause system to collapse. It's okay to tell him that you are not aware of anyone yet reporting that this has actually happened.

Oh, yes--you also should tell him that that 90 pounds is derived from a legitimate engineering analysis and is well understood, but the reason it *probably* will support him is not at all understood---that is, that all the factors that MIGHT keep him from falling are variable and change according to the diameter of the limb, the CS, the phase of the moon, etc.

Guys, you are playing with fire.

The absolute minimum that should be done when employing this configuration is to attach a line just to the left of the CS and secure that line to a tree trunk or the like---something to guarantee that the system is secure. Accessory cord should be sufficient for this.

It absolutely amazes me that you all probably are conscientious about wearing PPE, checking your equipment before climbing, double-checking that your carabiners are locked, doubly tying in, etc., yet you insist on using a climbing configuration that has a known flaw.

I've said (and repeated) all I can, and all that I plan to do, to dissuade you from setting up someone for an injury or worse.

Geof: I of course don't know, but I would guess that the "OSHA guy" from Sherrill made the same assumption that we all originally did upon seeing this system, namely that it is balanced at the CS. Did you tell him that a force equal to one-third of the supported weight is attempting to make the climber bite the dust?

Tell him that if he has a few days to spare, he should read this thread. Then call him back and ask him if he is still willing to put his credentials and reputation on the line: Ask him if he would be willing for Sherrill to publish the design in their catalog, or to sign off on it as approved for use by professional climbers. I’d be interested in his response; please let us all know.

Because I really do like you guys (seriously), I’ll offer one more thing that might be of benefit to you. I strongly suggest that you employ it. You probably should have your attorney tweak it a bit.

--- Release from Liability ---

The Client hereby acknowledges that s/he has been advised that the Corporation hopes that the configuration of equipment that is to be used for this climbing occasion will be safe.

The Client further acknowledges that s/he has been advised that the Corporation currently knows of no injuries or fatalities resulting from utilizing this system.

The Client understands that the Corporation is aware that an irrefutable engineering analysis of the configuration to be used indicates that one-third of the weight being supported by it is applied toward causing the system to fail, possibly catastrophically, and that there are no other climbing configurations known to the Corporation that are configured in such an unsafe manner. The Corporation adamantly dislikes those findings.

The Client also acknowledges that the Corporation has explained to him/her that they are unaware of any engineering analysis that explains why the system does not regularly fail, nor do they claim to have the competency to understand why it usually does not fail. Further, the Corporation acknowledges that it is unaware of any valid engineering reason that would justify stating that the operation of this system is safe.

The Corporation vigorously asserts that they have very strong faith that the Client probably will be safe, and that although the system regularly goes into a failure mode, it probably will not cause the Client to experience much more than an unexpected descent of more than a few feet (probably less than one meter). The Corporation asserts that it hopes that there is a good chance that such a descent will not be injurious to the Client.

Understanding the above-stated facts, the Client certifies by his/her signature hereunder that s/he completely absolves the Corporation of any responsibility should s/he be in any way injured, even fatally so, as a result of using this equipment.

Oops---just as I was preparing to post this, I see that moss posted, “. . . there is no fall threat in this system. If the cambium saver moves off the branch nothing happens. The climber does not move down.” That is absolutely incorrect. We have repeatedly proven and demonstrated otherwise.

Moss: “To all the well intended theoreticians, set the system up as in the photos, test it out ( you can set up a back up). Using it leads to fully understanding the system characteristics . . . .” I do understand it. That is why I have continued to caution against its use.

Why do I feel like I’m talking to a wall?!

Wait!!! I get it!!! You guys know how passionate I can get, and this is just a set-up to pull my chain!!! You three planned all this and told everyone else to be quiet and sit back and watch me get suckered in!!! You rascals, you.

Wow!

Jim I agree that the MA is unbalanced (thought I already said that). This alone is not enough to make the system unsafe. It only limits the height of the climb if the pulley moves down.

The CS CANNOT come off the branch when weighted by a climber if there is no F8 on the left side of the system (1/3 side). There SHOULD NOT be an F8 tied on the left side of the system. This would be an incorrect implementation. The entire system is a closed loop with the friction hitch closing the loop. The same as any DdRT system. Unless the climber moves the hitch down with their hand, they will not descend. It's very simple.

I wish some of the TCI instructors who use this system on a regular basis would chime in. I don't know how many 100's of climbers have used it. I have heard zero reports of any mishaps involving the system.

As far as safety goes, the analysis is focused so closely on the 1/3 - 2/3 imbalance that the overall view of the security of the rig is not being comprehended. Nothing happens, I repeat, nothing happens to the climber if the upper pulley moves down. At no time is there a fall danger in the use of this system. Citing the system as unstable is only referring to the MA balance, it does not take into account the entirety of the rig behavior and it's redundant safety aspects.

This is a climb facilitator technique. There is no reason to rig this system unless you are facilitating other climbers. If you are facilitating climbers you are taking full responsibility for their safety. It is your responsibility to fully understand all safety aspects of tree climbing including tree assessment, DdRT technique and aerial rescue. Otherwise you should not be putting another climber on a rope. No climber should set the system under discussion up for another climber unless the above conditions are met.

I will cease preaching on the subject and beg our beloved academics to rig it with back up, climb it and report back. The time for talk is done, the time for testing has begun.
-moss

Hey Moss, We had this discussion here and the other Web boards (TCI, Treebuzz, even Ekka's site in Australia) many times and the answers are always the same.
There is not firm conclusion. Some people love it, the theorycians, mathematicians, physicists" will dissect it in infinite ways and talk about its defects, vectors, imbalances and impending doom. The practitioners will implement it and hate it because it is so slooooow going up and the others like you will try it and "forgetaboutit".
You have read some of the musings from "spider monkey in Florida" about this topic, and he even has a web site dedicated to this topic exclusively.
His discussions are similar to this endless wise and he knows quite a bit about MA and pulleys........but too hard to follow his writings......... In a few months someone will bring it back up and we will go over it all over again.

Originally posted by Geof_K

In a pulley system, the mechanical advantage is equal to the number of ropes supporting the movable pulley.

Link: Thank you for that simple & clear answer! Perfect!

--but wrong: simply, the climber's weight is supported by both the lines from
the lower block AND the haul line (= 3:1).

The stoppers on either side of the cambium saver are there to ensure
that it does NOT stay in place upon retrieval, and gets into place on set-up.
But the knots themselves are cambium unfriendly; some offset knot,
such as an Overhand loopknot (whose eye is superfluous but part of its
construction) would move over the limb w/o resistance.

The other Fig.8 stoppers I suspect work well enough; for more easy
removal (were loading heavier), there is a symmetric version of the Fig.9
that could be put in (see Ashley #525 (though his dressing/image of it
is not so good)).

I suppose the friction through the cambium saver is sufficient to redress
the load imbalance on the lines--2/3 of load being upon the side
with the upper block, only 1/3 on the lower block's (in pdf image, left)
side of the limb? I.e., whether the system acts so purely at raising the climber
vs. pulling down the R (upper block) side of the line--in effect
making the limb an upper sheave--depends upon friction to arrest
rope movement at the top.

*kN*

Some of you have made suggestions on other (easier) MA systems to climb on.
This is a Spanish Burton MA system. I rigged it, climbed a few feet, but found it very uncomfortable. Not sure if I'll try it again.

Is this also called the YoYo?

Geof

Geeesh, if my prior post reads as though I missed a page of comments,
well, there's a reason for that! oh, well ...

As Moss notes, the system is closed and so "safe", but potentially ineffective
or limiting. (Consider that a rule of thumb for friction of rope over a 'biner
is <66% efficiency, one might suspect that rope through the CS is worse, and <50%,
so the 1:2 imbalance is compensated for.)

Originally posted by Geof_K
Some of you have made suggestions on other (easier) MA systems to climb on.
This is a Spanish Burton MA system. I rigged it, climbed a few feet, but found it very uncomfortable. Not sure if I'll try it again.

No, that would be a Spanish Burton if the bottom block were fixed (not
a pulley, i.e.). With it being a sheave and with the top sheave (hard to see
in the image, being remote), you have just a circle of rope between pulleys,
and I'm suprised if you get anywhere other than just moving
the rope around! (The Spanish Burton is efficient in MA given the
number of sheaves, but has a serious limitation in terms of movement/range.)

*kN*

knude says:

As Moss notes, the system is closed and so "safe"...

This is not necessarily so.

For example, if a system is closed, yet would let the climber descend while the system remains closed, with all nodes intact, that would not be safe.

That is what can happen with the configuration in question.

BTW, does it have a name?

BTW, does it have a name?

It is known as the Super System (minus the 10'piece below the LP. The LP would clip to the saddle)
Geof

moss, I agree with Jim, the climber can descend if the TP slips. Think of it this way:

The TP comes down 1 foot, lowing the loop (2 ropes) supported by it 1 foot, which produces 2 feet of slack. 1 foot of slack is simultaneously taken up by the TP descending, the remaining foot is distributed to rest of the system, which amounts to a 1/2-foot descent.

As I mentined, this will result in a slower descent, and the pulleys will jam before you hit the ground if you are more that 1/3 of the way to the TP when this starts happening.

Jim, I think we're in a stalemate here. You and Mark think that friction is complex and under certain circumstances could result in an uncontrolled descent. Now we're just left with deciding the likelihood of this happening. Of course, you argue that we should not use a system that has this property, but I would like to make two points regarding this:
1) As I mentioned before, we depend on friction in many ways, so this is not a special situation
2) I think if we have the super-low friction situation that would be necessary to cause a dangerous situation, it would be quite apparent

If the friction was that low, you wouldn't even get off the ground. It is like a badly tied blake's hitch, it wouldn't support you to begin with. I disagree with the banana peel assertion that the system can suddenly switch from sufficient to drastically insufficient friction.

The complex factors that you have listed would not cause a sudden change in the system: if your CS is on a wet, lichen covered branch, this isn't going to change. If anything, the system will have more friction once it starts to slip, since the rope or CS will cut into the branch. Particularly if you don't use the F8 before the CS, the friction should remain fairly constant.

I know this probably won't change anybody's mind, but that's just how I'm thinking about this. I think the only thing that could change my mind is some full scale experimentation that resulted in a dangerous amount of slippage.

-Link

I like how we seem to be able to argue without it degenerating into a flame war; the tone on this forum is almost always that we're all trying to figure stuff out together. That's far from common on the net in my experience.

I agree with some of Link's points, but remain concerned.

The fact that, judging from what moss has said, the system has been used for a while - reportedly without mishap - shows that most of the time there is enough friction/shear strength to hold things in place. It's also true that under most circumstances a problem with friction at the TIP would be apparent early in the climb, before the stakes are too high. Moreover, continued friction during an unstable descent would probably absorb a fair amount of energy, so I imagine the speeds wouldn't usually get too great.

... OK, you knew there was a "but" coming, right? I wanted to address a couple of points in earlier posts to explain why it still worries me.

A minor point first. The fact that an OSHA guy glanced at the rig and didn't see any problems is sort of reassuring, but not conclusive. Any unfamiliar configuration needs some thought before how it works becomes clear.

I don't think it's true that any problems will inevitably show up early. Bark can break during use, or fail under a dynamic load that wasn't there early in the climb.

A couple of posts have pointed out that we rely on friction in other places in our climbing systems - so how is this any different? There's an answer to that. We rely on friction between pairs of very strong, well understood, highly controlled and engineered materials. The friction is generated within very rigidly defined geometries that have been tested repeatedly. These things are very predictable. The friction and shear forces that can be generated between a friction sleeve and the bark of a branch are much less predictable, as I tried to make clear in my last post.

We're already dealing with the fact that the strength of the branch we're hanging from is an unknown; we use our best care and judgment to minimize that risk and get on with life. But why add another random factor into the mix when we don't have to?

So it seems to come down to a philosophical difference - as Link says, a stalemate. Here's a possible way out, if anyone isn't totally burned out on this: How about putting our collective wisdom to work coming up with a system that does what this system does, but doesn't have an obvious Achilles' heel?

Two scientists at a German cocktail party allegedly determined that, according to the laws of physics and aerodynamics, it was impossible for a bumblebee to fly…! – An urban legend.
“The persistence of the bumblebee myth also highlights a misunderstanding about science, models, and mathematics. The real issue isn’t that sciences can be wrong. The real issue is that there is a crucial difference between a “thing” and a mathematical model of the thing. … It is important to distinguish between getting the mathematics right and getting the problem right. … So, no one proved that a bumblebee couldn’t fly. What was shown was that a certain simple mathematical model was not applicable or appropriate for describing the flight of the bumblebee.” – www.sciencenews.org

---

First, both the Super System and the PACT System work very well and are routinely used by at least four major treeclimbing organizations to help people with physical limitations to reach beyond those limitations and enjoy the beauty of the canopy.

Second, no one has ever reported an accident or negative incident to me that involved either the Super System or the PACT System.

Third, both systems (as Moss stated yesterday) are designed to be used during facilitated climbs when there are one or more instructors/facilitators on the ground to supervise that use. I am personally aware that the Super System has been used to heights nearing 100 feet, while employing a 300-foot rope for the system.

Fourth, I do not believe anyone should belittle either system until she/he has set it up properly and has climbed at least 1,000 feet on it.

Remember, some of your theories may be read by those outside the climbing world who take them as fact and then decide that adventure, research and educational treeclimbing is just too dangerous to try. And some of them may just be the insurance underwriters we desperately need for our sport.

In short, back up your theories with a little practical experience.

knudeNoggin: I didn’t have time to mention it in my previous post, but I have respect for anyone who is familiar with the Spanish Burton---a very clever creation! I ran across it years ago and doffed my hat with admiration. I have even more respect for one who actually remembers how to rig it, or the Double Spanish Burton, and actually understands when to use it. Cool stuff!

Link says: “You and Mark think that friction is complex….” Just to be clear about that, to repeat myself, we *know* that it is. As Mark pointed out, most of the time we are dealing with well understood conditions. The friction/“shear force” (a fictitious force) at the location of the CS for this “Super System” (thanks, Geof, for telling me its name) is not well understood . . . at least not by anyone here.

As for the “stalemate,” there appears to be one only in that some contend that the system is safe despite its (now) clearly understood flaw. Mark suggested that we come up with “a system that does what this system does, but doesn't have an obvious Achilles' heel.” As he said, “why add another random factor into the mix when we don't have to?”

I mentioned in a previous post that the flaw could easily be overcome by the addition of a light line that would guarantee that the main rope would not slip. Moss said that it slipped when he tried it. If it will slip, maybe it will slip a lot.

Link, you say, “I think the only thing that could change my mind is some full scale experimentation that resulted in a dangerous amount of slippage.” Suppose I showed you a container with 1000 M&Ms in it, and told you that one of them was poison. Would you eat one? (I’m assuming that you like M&Ms.) Again, the flaw in the “SS” can easily be remedied. Why take an unnecessary chance? (I’ll head off someone’s comment that we then should stop climbing.)

Mark, it seems that I always agree with your ideas. Maybe it’s the fact that you are an educator who is used to critical thinking. I do want to point out your comment about the “OSHA guy”: As I said earlier, I’d like to know what his reaction would be when he realizes the system’s flaw.

Bill, I’ve thought several times during this interminable thread about the bumblebee; thanks for bringing it up. Thanks for pointing out that no one here has been trying to prove that it can’t fly.

You noted that when the SS is in use at facilitated climbs, there are instructors on the ground to monitor things. The problem is, though, that if the system slips, there’s nothing that someone on the ground can do to stop it.

Why take the chance that the bolt won’t come loose; why not simply take a moment and add the safety wire to it?

Next, no one here is “belittling” the system (at least I’m not). Once more, folks, watch my lips: What I’m saying is:
(a) it has a flaw
(b) the reason(s) the flaw does not allow it to slip regularly is not understood
(c) it is really easy to remedy the flaw.

I haven’t said it before, but I have believed all along (even after discovering the system’s flaw) that its design is very clever. It is a real accomplishment to create a 3:1 system without the necessity for ascenders, etc. It’s very creative! I’m impressed. I congratulate the inventor(s). I have never belittled it.

And it has a flaw. That’s a fact.

Bill says, “In short, back up your theories with a little practical experience.” Oh, my.

Well, Bill, I knew a guy who said that he had been using a chain saw since he was a kid (so he had much more than a “little” practical experience), knew how they acted, and didn’t need chaps. He can’t walk any more.

The chances of having an automobile accident and being injured actually are rather small. Both theory and practice will support that. Is that a good reason not to wear a seat belt? (For those who responded, “Yes,” I don’t want to climb with you.)

Why is it that some people are unwilling to act in a safe manner, particularly when that safe manner is so easy to implement?

Put on your helmet. Put on your safety glasses. Put the safety line on the SS.

Will someone *please* tell me why the remedy should not be applied?