What are the preferred rigging options for tyrolean traverse anchors, when set from the tree (using a grapnel/throw line)? While experimenting, I have been using the climbing end of my entry rope (SRT, ground anchored) by making a limb cinch on the far tree (end of rope threaded through a midline butterfly) and then anchoring it with four wraps around the trunk of the first tree, tied off with a rethreaded F8. This seems fairly stable and safe, but I just wonder what other folks prefer. Is this the best way to do it? The only way?

That sounds good, If you're setting it remotely you have to do a cinch so it's just a matter of what cinch technique you prefer. I always include a "pull back" line on the cinch as I'm sending it over so I don't risk hanging my rope on the destination tree if something goes awry. Always need a back out plan for any rope setting procedure.

For the other side any technique that secures the rope in a solid way with secure knots and/or a screwlink is good. Wraps are helpful to make it easier to tighten and distribute force.

If you're not experienced setting SRT traverses I highly recommend testing it all out low first. I'd do a search on "vector forces" and Tyrolean Traverse to get a handle on what kind of load forces are generated with various angles created by the climber on the traverse line. Essentially you don't want to overtighten, but you should do the research if you haven't already to fully understand best practices.
-AJ

Should a traverse line be pretensioned? If so how much?

I like to tension 1:1 with my arms, at least with my arm strength I'm in no danger of over tightening it.

This Tyrolean load simulator is helpful in understanding effects of rope tensioning. Read the fine print, the simulator only shows loads when the climber is centered on the traverse and does not take into account rope stretch or other real world variables like rope construction, diameter, rope condition, etc.

I think when we discussed this in the past we came up with 15° as the shallowest safe angle (with a decent margin of safety) when the climber is in the middle of the traverse. Of course no one is usually carrying a clinometer or protractor to measure angles on traverses, that's why I think it's very smart to test setting rope tension close to the ground to get a feel for how tight to set once you're up high.
-AJ

Here's a photo of Tengu on a traverse at the Colorado 'Vous 2007, the rope angle looks very close to or slightly greater than 15°, that traverse line was tightened by hand 1:1, no MA involved.


You need a progress capture to climb the uphill side of a traverse, an aggressive toothed ascender is not the smartest choice, a microcender or similar non-toothed rope grab is optimal for this use.
-AJ

My next challenge: traverse across three trees without coming down and only one 150' rope.

Strategy:

Isolate entry limb, cinch SRT
Pull up rope, undo anchor
Throw into 2nd tree, F8OAB to screw link cinch anchor
Trunk cinch 1st tree with midline loop and attach rope tail to harness
Traverse across
Undo anchor in 2nd tree, pull rope tail to retrieve cinch in 1st tree
Throw into 3rd tree and repeat.

Is good? I usually leave my traverse somewhat loose and floppy when unweighted like an empty hammock. Do you actually pull yours taut? Even by hand, that seems like it would be too tight, to me.

What you're doing increases your safety. I pull it taut by hand but I don't go nutty trying get it super tight. Rope stretch will get you up into the 15° or greater rope angle range. Like I said test it low to see what rope angle you get when you hand tighten to make it taut.
-AJ

I use something similar but a directional figure 8 instead of a butterfly, just looks so.....well, right.

I concur that 1:1 tensioning with arms only is a good method. The angle of the rope would be better, but the angle would be the angle of the rope with the rope fully loaded - quite an inconvenient way to determine tension.

I don't remember any discussion that concluded that 15° was a safe angle. It's late so I can't guarantee my mind is working right but 15° would produce almost double the climber's weight in the rope and on each anchor.

'The' angle i.e. the one between the ropes (on top), should be no less than 120°, which means the angle of each side of the rope should be no less than 30° from horizontal. That angle produces a loading of exactly the climber's weight in the rope - and on the anchors.

success! i just did a circuit of four trees. one rope. yay me.

so, a 15° traverse is more or less equivalent to SRT climbing with a ground anchor? that still seems pretty safe, considering the climb spec safety factor. i think i got used to making really loose traverses because we often set them up with just truck rope, which isn't as strong.

Well... double is reasonable yes? I think so anyway. As I remember the discussion a while back we were saying 15° is the minimum safe rope angle not the optimal angle.
-AJ

That's why I recommend a climber testing what angle they get when they hand tension 1:1 low, once they get a feel for the tension that gives them a good angle, go ahead and set it high.
-AJ

Nice work. This has been a dream of mine to see how far I can get moving horizontally through the woods solo in one day, no ground help. One of these days.
-AJ

What was the distance between trees?

Congrats - fun wasn't it!


Well, the force on the anchors are double the climber's weight, but in an SRT ground anchor the force in the rope is NOT double the climber's weight. In a traverse with a rope at 15°, the rope and anchors all experience twice the climber's weight.

A traverse at 15° would be like a limb cinch with two climbers on the rope at the same time. However even that is different. Let's say a climber weighs 200 lbs. He is exerting a heavy lateral force against both trees. Sometimes the tree anchor is the strongest link, sometimes it isn't.

Now let's consider safety margin. Let's say you have a 5000 lb rope in a traverse at 15°. That Butterfly knot, age of the rope, etc. could produce a breaking strength of 60% of the unknotted rope or in this case, 3000 lbs. We weight the traverse rope with a 200 lb load and we produce 400 lbs in the rope. That's a safety margin of 7.5:1 - well below the desired 10:1 we hear so much about.

Now lets consider that a 100 lb climber gets stuck or needs assistance and the only recourse is for a 200 lb climber to traverse out to them. Now we have nearly 600 lbs of force in the rope with a safety margin of 5:1. I'm not sure how much lateral load it take to uproot a tree, but that's a lot of force trying to.

If we had used the rescue rule of 120° (30° from horizontal), the safety margin for the 300 lb load would be 10:1.

I'm convinced Ron, 15° was something that I dimly recalled we discussed, I think Oak came up with that. I could be completely imagining that. I don't think 15° is unsafe for me due to factors related to my own configuration variables. However as a general rule 30° (120° total angle) sounds a very good baseline.

My own variables:
1. Probably not more than 140 lbs fully geared up
2. Don't use a rope spec'd less than 5900 lbs for a traverse
4. Have a very high bar for what the condition of the rope that will be used for a single rope traverse, it's going to be in very good condition, I know the history of the rope's use.
5. I don't use an alpine Butterfly, no knots until after the rope is around a limb or trunk. The friction from a single wrap (cinch) or multiple wraps is taking load (variable based on limb/trunk thickness, bark texture etc.) off any knots, I believe there is less than the standard knot strength loss when set up this way.
6. It is not a rescue rigging scenario so deep strength redundancy is not required.
7. When I go across on a traverse I'm smoothing my motion as much as possible to reduce dynamic loading, not using toothed cam ascender.
8. Flex of tree and or limbs is providing providing useful shock/load dispersal, more so than on a vertical SRT ascent, with the horizontal setting you can feel both trees moving. There are situations where there won't be much flex from the tree, not for me on the east coast. To set a traverse remotely I need enough height to work the Dangle effectively, that means for any east coast tree I'm going to be high enough that the tree will be flexing.

All that said it would be good to collect some data on what the actual angles are with rope fully loaded. so far it's all guesses. A second climber with a clinometer could easily calculate the angles from a vantage point level with and at one end of the traverse line. Actually now that I think of it, I could calculate the angels with a clinometer while I'm doing a traverse, If I add a rangefinder I can get angles at different distance points along the traverse. That would be useful.
-AJ