Quote from: knot rigger on May 12, 2015, 07:52:00 PM
[1] start with a single ABK, loop towards you, "front" face up
[2] pass the working bight down through your tie in point
(and the working bight magically turns red ) [--embarrassment ]
and poke it back through the nipping turns, ...
AND THEN ...
[3] tie off the bight end with an overhand stopper
(which you might reasonably have enough rope to do! )
DL you (humorously) point out the main drawback in the doubling method I proposed: passing the whole bight around the climber! This is fairly cumbersome in practice, and would lead to difficulties should the tie-in need to be escaped. I think your stopper knot is an interesting solution, but I find that instinctually I don't trust it enough to fall on it! It doesn't feel "locked" to me, and isn't "bombproof" the Knot may work loose a little while climbing, and then upon falling the stopper may slip through the nipping turns. This seems unlikely, but the slim chance that it might happen would cause me to not trust it.
I first proposed this double ABK method as an interesting solution to the puzzle proposed. It's better than the larks head solution. I've thought about it some more, and you (DL) have inspired an improvement in what I originally proposed: add a carabiner!
The knot must have easy/quick on-off tying capability (that is attaching the rope and also detaching the rope).
The middle climber - third person - on the rope has always presented technical issues to overcome. Most sources advise a Butterfly connective eye knot with dual carabiner clip-in. My contention has always been that carabiners can rotate and/or become misaligned due to cyclic loading / slack shaking. That's why lead climbers always tie the rope directly to their harness - meaning a direct rope-to-harness interface with no connectors. This reduces risk since the knot can withstand multiple loading profiles/angles - and connector misalignment is eliminated.
A_S identifies two needs for this tye in method (1) it must be easy on, easy off and (2) that it should be "bombproof" like the lead climber tying directly in with a re-threaded fig 8 loop. Falling on a loop cliped to your harness with a 'biner isn't as bombproof as tying in directly, but that doesn't mean that one doesn't have any carabiners with them!
So I propose this modification, after [2] (see above) poking the bight through the nipping turns, clip a 'biner through both collars of the ABK,
and the working bight, as shown in [11] (where the working bight is still shown in red, as in the first round of pictures)
now this leaves the gate of the carabiner flapping around to bang into stuff, or possible to turn around such that the gate is loaded by the collars or working bight (rather than the spine of the 'biner as shown) So I've taken the further step of clipping the 'biner through the two tye-in loops, to help dress the overall knot, and keep the kont compact and the biner loaded on the (strong) spine. as shown in [12]
the last picture [13] is of the same knot (DABK locked with 'biner) with 11mm static kernmantle and a 7/16" locking modified D 'biner.
So, last thoughts: I approached this problem as an interesting puzzle, and have now perhaps come up with what could be a real-life solution. ( I'm not a sport climber, but I do ropes access work, which is a similar skill set) I see that this DABK w/ biner lock method
COULD safely improve the middle climber tie in method which A_S is (rightly) dissatisfied with. I think my proposed solution should be tested further by experienced climbers to see if it has merit. One drawback of this method is that it could involve side-loading a carabiner gate, and i've attempted to address the issue with the [12] dressing. I'm not sure if this solution is adequate or successful at addressing the risks of a gate loading event. (this problem of gate loading, or side-loading is what A_S is dissatisfied with in the first place) I have intentionally used locking carabiners, as I think this application warrants it.
PS
Since this butterfly here is intend to the middle climber it will be loaded oftentimes by both side , if we admit that the AB has a "week" (maybe) side, should it be better to begin the double loop with a Figure 8 butterfly?
enhaut, I'm not sure what you mean by "a double loop with a figure 8 butterfly" what's a "figure 8 butterfy"? Also, I'm convinced with 95% certainty that the difference in strength between legs of the ABK loop is less that 6.5% (i just need to make time to update my break testing analysis conclusions with the new data analysis Tex helped me with)