I just want to verify the TIPs loads for a traverse/zipline. Is it correct to say that if I am hanging off a pulley while traversing, each side of the rope is bearing half my load? Does the load "shift" depending the distance from the respective TIP?

Here's an interactive graphic that allows you to change climber weight and rope angles to show how load changes at the anchors when the catenary angle changes. The shallower the angle the greater the loads on the anchors. With an extremely tight or "flat" traverse line the loads are magnified to an extreme amount.
-AJ

That page also answers your question "does the load change at the anchors?" as you move across the traverse.

Super complicated math when you include rope stretch but the basic principles explained help understand the variables and forces involved.

I err on the side of making the traverse line less tight (and the angles more forgiving) as opposed to over tightening. Good to include a tethered rope grab so you can climb the uphill side of the traverse.
-AJ

Cool little simulator, moss. When I think of people setting up Tyroleans happily unaware of the math, it scares the hell out of me. Kudos to BKS for asking.

And good point about climbing up to the anchor with a tethered rope grab. Getting off one of these things can definitely be challenging!

Good question, BKS! Thanks for posting the simulator Moss.

I've only done a couple, but I used what might be called the Intuitive Overkill Method. In other words, I anchored both ends to beefy (>18in diameter) trunks at beefy crotches that seemed to have very low probability of failure and assumed/hoped for the best

Just curious, does anyone actually do the calculations for each traverse (or any traverse with their own weight and rope strength etc.)?

There is a useful point of reference that might be helpful in a Tyrolean traverse. If we were to measure the angle of the rope formed by the 'V', at 120° each side of the rope will have tension equal to the climber's weight.

That 120° V translates to each end of the rope being at a 30° angle from horizontal.

When Hunbaku and I were doing a lot of traverses, we found it pretty difficult to hand tighten a rope enough to produce heavy loading. I.e. no pulleys, no mechanical advantage.

As the angle of the V increases from 120°, forces go up in a hurry. E.g. at 150° each side of the rope will have tension equal to twice the climber's weight.

While arborist rope should handle that weight easily, keep in mind that same load is applied to the anchor points and a respective force is trying to 'break' the tree and that force has a lever arm of the height the anchor is above the ground.

Good stuff Ron. On the page with the catenary load calculator they mentioned that 15° (from horizontal) was a good target for the minimum angle. I need to strongly visualize that angle, maybe a drawing on my helmet or a forearm tattoo

Good thing to think about besides catenary angle, rope strength and stretch is that you get a certain amount of flex in the tree which is very helpful. That assumes you've done a good assessment on the trees and anchor points and have determined they are basically sound.

The catch 22 is that you can't really see what the angle will be until there's a climber out in the middle of the traverse This where experience helps, low and slow steps to create single rope traverses, judgement improves with each traverse set up successfully.

And the last part, as Ron pointed out without mechanical advantage I don't believe the line can be set too tight.
-AJ

This sounds like the sort of rule-of-thumb that the non-mathematical among us would seize upon as a safe rule for making traverses and a convenient way of avoiding the math. The other advice about the angles is sound, but this is not.

If if build my traverse from 3/16 in Amsteel Blue, 5400 lbs. test, and hand-tighten it, or better yet, have my muscle-bound neighbor hand-tighten it, he would be fool to launch his 250-lb. bulk out across the void suspended from the traverse. The same line with the 120-degree angles, would be perfectly safe.

And a hand-tightened line made from stretchy nylon, also 5400-lbs. test, probably would be perfectly safe because the stretch of the line would automatically provide safe angles at the anchors. It's all about the angles at the anchors, which is intimately connected to rope stretch.

I should have said any line suitable for setting a traverse can't be overtightened without mechanical advantage. Seriously though, do you think you can set the tension on a 60000 lb. rated 11mm kernmantle polyester line across a 100' span without MA and make it tight enough to make the catenary dangerous?
-AJ

It is a rule of thumb. It is based on the kind of rope climbers do Tyrolean traverses on, arborist rope, and some common sense. That's about as good as we can do as I doubt many climbers, including myself, will have their calculator with them when they set up the traverse, so yes we need a rule of thumb that keeps us on the safe side. That rule of thumb is hand tighen, i.e. no MA, and you don't have to put anywhere near your maximum effort into it.

As moss alluded to, rope stretch, tree flex, and knot compression provides a lot more 'V' than one would think. And perhaps it should be pointed out that shorter traverses might be more stressful on the rope and anchors than longer ones since there is less rope stretch. But even on shorter traverses the simple rule of thumb of not over tightening should be safe with arborist rope.

I would add that whatever stress is in the rope is also applied to the anchor points, so select robust anchor points.

So again, yes, this is a rule of thumb. We've submitted tables, interactive diagrams, and reference points to supplement/explain/illustrate the rule of thumb.

Lots of people read these threads who never post, and for that matter, never climb a tree and know next to nothing about ropes. Let's say I am one of those people. Let's say I am not a YouTube idiot about to span the Grand Canyon with my first tyrolean, but I would like to set one up in my back yard.

I have been soaking up info from you two (moss, Ron) for the last couple of years, watching the videos, etc. I have been impressed by your conservative approach to safety, the thorough manner in which you test equipment and techniques, your thoughtful analyses, etc. But since I daydreamed my way through highschool math, I can't figure out this tyrolean thing.

Ahh, but my two authorities solve my problem! Just use a climbing rope that you pretension without MA and you'll be fine! Coming from these guys, this is advice I can take to the bank!

OK. I choose 3/8 Sterling HTP for my rope. I may not know math, but I am strong, and I pretension my tyrolean to 100 lbs. Then I launch my 250-lb. bulk out into the void.

No, it doesn't break. But the tension on the rope is 1148 lbs. The advertised tensile strength of the rope is 5980 lbs. Forget about a 10:1 safety factor--we barely manage 5:1, and this is before de-rating the rope because I used simple knots at the anchors and the rope is a used climbing rope given to me by my brother.

For the protection of the math illiterate who would like to make a tyrolean, I would say the following. Some ropes are too stiff to allow pretensioning. Whether you use such a rope or not, make sure the loaded rope has a deep V in the middle--aim for 120 degrees--to avoid dangerous vector magnification of tension. There are many other things to get right as well, but that one issue is the one most likely to catch one unawares.

Excellent post, Moray ... well put.

Sound advice, certainly ... permit me to add another important factor almost always overlooked -- BOUNCE -- almost impossible to calculate and therefore often neglected or even worse celebrated. Traverses are fun and the young and 'bullet-proof' love to bounce & 'bungee' along a traverse. I've seen it ... I've done it. However, bouncing in a traverse can easily stress all the traverse components more than three times the static loads. Further, if a harmonic oscillation is induced in an otherwise well calculated system (a la, Tacoma Narrows Bridge), then the stresses could easily exceed the limits of the system to point of catastrophic failure.

This gets to the heart the problem of discussing technical tree climbing online. There's a disclaimer on the front page of the TCC forum. However I am disheartened by the way some folks take what I post as "expert". I'm not an expert, I'm an avid climber who enjoys solving problems and figuring out how to do things. Anything I say or propose is my opinion and not gospel by any means. In other words what Moray stated hypothetically above applies to just about any technical discussion we have on TCC. I don't know what the answer is (to discuss technique online or not). I do know that if there was no online discussion of tree climbing techniques I wouldn't be a tree climber.
-AJ

I think you, Ron and others have been quite responsible in openly "discussing technical tree climbing online." Your advice, techniques and opinions have helped me and many others greatly to advance as a SAFE climber. Perhaps, EVERY technical discussion needs to include a thorough examination of WHAT-CAN-GO-WRONG. That is, any "RULES-OF-THUMB" and 'HOW-TO's' needs to include an immediate list of 'BUT's', 'HOW-NOT-TO's' and 'WHAT-IF's'. Some of the best advice I've received here were from discussions of my system's short-comings with suggestions of how to make it safer.

My post, as I believe Moray's post, were to impress any reader with the fact that simple rules of thumb and even fancy calculations may not be sufficient - i.e. just something to keep in mind when considering any potentially risky endeavor. Please, by all means, keep the tech talk rolling ... even expand it to the point of being just a little scary so as to heighten the attention to detail that this activity requires. "I do know that if" I want advice on what I could be doing wrong -- I come here, FIRST! ... and THANKS! ... THANKS A LOT FOR BEING HERE!!!

Regarding the TCC technical post sidetrack: I'm one of those guilty of lurking often and posting rarely. I for one really appreciate the input of the folks who post regularly on this forum. I think all of them are quick to point out that they're posting their own opinions and experiences, but I value them since they have a lot more experience than I do. Folks on this forum seem to be pretty, nay VERY responsible in encouraging newbies to seek proper training etc. This issue seems to come up periodically but have there actually been any problems of this sort?