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infinite loop question

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infinite loop question

Postby alpine345 » Sat Feb 25, 2012 9:11 pm

Has anybody used this system? http://pullharder.org/2012/02/22/the-in ... -sheridan/ It looks like it could be adapted for simul-climbing free pitches and not just aid. BTW, his other stuff is pretty interesting , too. Chief? EB? what do you think?
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Re: infinite loop question

Postby Ben Beckerich » Sat Feb 25, 2012 11:46 pm

Very interesting read... thanks for posting. Sharing, presently..
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Re: infinite loop question

Postby ExcitableBoy » Sat Feb 25, 2012 11:48 pm

Never used this, but I think Colin Haley uses something similar for rope soloing pitches, most notably on solo ascents in Patagonia.
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Re: infinite loop question

Postby The Chief » Sun Feb 26, 2012 2:23 am

Nothing new really. Pretty much what I have used and has been the standard over the years for Solo-Aiding stuff.

- Directionally, I do not know how the anchor would respond if the Lead took a whip while the 2nd was in the process of cleaning the prior pitch. I do know that it would a MOFO to untie the Over-Hands attached to the anchor if this actually occurred. As it is tough enough when I have ripped some 40 to 60 feet on these.
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Re: infinite loop question

Postby Ben Beckerich » Mon Feb 27, 2012 9:23 pm

I must be misunderstanding something, or just still too new to realize how not new this technique is...

Leader anchors rope, solos up, sets new anchor while follower, TR soloing, cleans bottom anchor and so on and so forth all the way up the wall... you're saying this can be done un-partnered soloing?

My understanding is that the author has taken a couple of proven concepts and combined them into a method of fixed-belay simul climbing... I certainly haven't seen it all, or even most of it... but I've never seen it all put together like this before. You have, chief?
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Re: infinite loop question

Postby nartreb » Thu Mar 01, 2012 4:08 pm

Very intriguing technique, but I too am a little nervous about the "mini-belay". I don't like the hand-waving implicit in the reassurance that "this anchor is never the only anchor holding the climbing team to the rock."
Sheridan specifies the following invariants:
-Keep at least one mini-belay, and three bomber pieces between the leader and the second
-The Leader should place a new mini-belay and fix the rope every 80ft or so.

Let's assume that the leader has just led an 80-foot mini-pitch with the minimum three good placements, each twenty feet from each other. The follower is just below the first mini-belay; leader has just placed a new mini-belay and is starting to climb above it (after getting gear from the follower, but that's not relevant to the physics problem). In other words, we have the following scenario, drawn with "up" to the right of the diagram:
F -- 3ft -- MB1 --20ft-- g1 --20ft-- g2 --20ft-- g3 --20ft-- MB2 --3ft-- L
(F is follower, L is leader, MB1 and MB2 are "mini-belay" anchors, g1 through g3 are single gear.

Scenario A: while leader continues climbing, follower cleans MB1. Leader gets 20ft above MB2 and falls without having placed any gear. What is the fall factor experienced by the leader? IMPORTANT: recall that the rope is FIXED to MB2. The rope between MB2 and the follower is NOT part of the system unless MB2 fails. If Leader masses 80kg {edited for realism}, what is the force on MB2? (Note this is a downward pull.) If MB2 does fail, what is the force on the next remaining piece (g3)?

Scenario B: Same starting situation, and again Follower removes MB1 and gets no further. This time Leader has placed one piece (g4) ten feet above MB2 and then climbed a further ten feet before falling. Assuming g4 holds, what is the force on MB2? (Note this is an upward pull.)

OK, thinking about it some more, I'm not so worried about scenario B.
If g4 holds, then either
1) MB2 holds, and catches the leader. (What's the upward force on MB2?)
2) MB2 fails. The rope to the follower becomes part of the system (until the knot from MB2 gets stuck at g4). The follower's weight catches the leader. (Some risk of injury to the follower as he may not be ready for an upward pull and may get yanked into the rock or g1).

If g4 doesn't hold, you're back to Scenario A.

The worst case might be where g4 sort-of-holds, just enough to put an upward pull on MB2 (how strong is that pull?) and dislodge it. Tension then returns to the rope (note, sideways pull on g1 through g3); if g4 then fails (what's the force on g4 after MB2 fails?), you're looking at a long fall onto g3. Call that Scenario C. What's the force on g3 then?

Prime lesson seems to be that your mini-belay must be strong enough on downward pull to resist Scenario A, and simultaneously strong enough on upward pull to hold under Scenario B and thus prevent Scenario C. I haven't done the math, but with only two pieces you might need both pieces to be equalized for both upward and downward pulls and both be multidirectional pieces.




I agree with both Chief and Ben B: the leader is in effect roped soloing at all times; if you didn't have a second you could descend the unused portion of rope after building a second anchor - then switch roles and follow your own lead. In that scenario, tying the rope into a loop doesn't accomplish much (except guarantee you don't use more than half the rope while leading) - there's no time savings. In fact by going only a half-rope at a time you lose time because you have to change between modes (lead, rappel, follow) twice as often. (You do get to carry a lighter rack and not worry about managing a separate tag line.)
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Re: infinite loop question

Postby nartreb » Thu Mar 01, 2012 9:04 pm

I've started playing with the math and learned along the way that the rope's force rating is an important variable in high-factor falls. If the rope is rated to 9kN (for a UIAA factor 1.77 fall), then Scenario A (a factor 2 fall of course) gives you a tension of nearly 10kN which equals the downward pull on MB2 (since the rope is fixed to MB2). That's within the ratings of a single beefy cam correctly set; two good equalized cams should suffice for an anchor. However, I'd be unhappy with a two-piece anchor built with stoppers or small cams: it should hold if well-equalized, but there's no redundancy.
If MB2 does fail in scenario A, you're getting a factor 0.8 fall onto g3 (i.e., scenario C), something in the ballpark of 6.3kN rope tension generating over 10kN effective downward force on g3 (figure downward force is 1.7X tension, to allow for friction) - a little *more* than the force that (hypothetically) popped MB2. You'd better hope g3 really is solid, because if you fall onto g2 you're not going to be happy: it's a factor 1.2 fall and you're approaching the rope's tension limits again, giving a downward force on g2 of nearly 15 kN - higher than a lot of gear is rated. (Dropping onto g3 ... you're approaching 17 kN.)

Bottom line so far: MB2 better be double bomber, your strongest gear only, and well-equalized for downward pull. Also, put in a piece above MB2 as soon as you can! (This creates Scenario B.)

Somebody please check my math so far...

Scenario C is bad, but not the open-and-shut casket I'd first imagined. It's nice to do these mental experiments every few years. Twenty feet between gear is not a scenario where I'd feel very comfortable, but it's nice to know it's survivable assuming you don't hit anything on the way down, the gear is really strong, and you know how to place it.

I'll return later to calculate the upward pull on MB2 in Scenario B.

PS beware of online force calculators. The top-listed result in google used a formula that's just plain wrong.
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Re: infinite loop question

Postby glahhg » Fri Mar 02, 2012 7:41 pm

How about you just not fall on the anchor? Quite standard really. If you think you'll FF2 on the anchor place a piece as soon as you can. If you can't place a piece then man up and don't fall.
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Re: infinite loop question

Postby The Chief » Fri Mar 02, 2012 7:59 pm

glahhg wrote:How about you just not fall on the anchor? Quite standard really. If you think you'll FF2 on the anchor place a piece as soon as you can. If you can't place a piece then man up and don't fall.


Good point. But still does not answer the question which I presented regarding a leader fall AFTER sequential pro has been placed and the 2nd following on the lagging line. Counter tension pressure could create a potential total failure of the anchor.

I would not want to be part of a crew that has that happen to them and find out whether or not the anchor holds such a scenario.
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Re: infinite loop question

Postby divnamite » Fri Mar 02, 2012 8:06 pm

The Chief wrote:Good point. But still does not answer the question which I presented regarding a leader fall AFTER sequential pro has been placed and the 2nd following on the lagging line. Counter tension pressure could create a potential total failure of the anchor.
I would not want to be part of a crew that has that happen to them and find out whether or not the anchor holds such a scenario.


Chief, how is this fall scenario any different than short-fixing?
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Re: infinite loop question

Postby The Chief » Fri Mar 02, 2012 8:47 pm

divnamite wrote:
The Chief wrote:Good point. But still does not answer the question which I presented regarding a leader fall AFTER sequential pro has been placed and the 2nd following on the lagging line. Counter tension pressure could create a potential total failure of the anchor.
I would not want to be part of a crew that has that happen to them and find out whether or not the anchor holds such a scenario.


Chief, how is this fall scenario any different than short-fixing?



The 2nd on counter opposing tension of the anchor if they are either on jugs or they, the 2nd, fall at the same time as the lead does(all it takes is once and that is all she wrote).
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