So maybe I'm missing something, but over in this thread, there is some discussion about having a prussik or tibloc for emergency rope ascension. I have used both and agree that a tibloc or any machined/mechanical ascender is easier and faster than friction hitches (esp on frozen ropes). But what I don't get is what the plan is if you get stuck hanging on doubled rap lines. If the terrain is low angle enough, you can unweight and yard slack into your rap device, but what about vertical or more type terrain?
You may argue, "well just don't let this happen" but I've seen more than one person miss a rap station and now they have to find some way to get back up to it. I've never tried using two tiblocs together on each rope, so maybe that's the answer, but I'm just curious, what would you tibloc/ropeman/etc users do in this situation? Hypothetical or not, I'm just curious.
+1 for Crag. If you should rap past a station: simply hitch the prussik to both ropes above the rap device, stay on repel, use a couple of chest length slings girth hitched to the prussik as (a) foot step(s), and stand on it(them). Draw in the slack from your repel device and rest on the device. Next move the prussik up the rope and like hauling the pig power step up and repeat. It is called "anti-repelling".
These responses aren't really addressing your question. I would say that there isn't any good way to ascend up a double line with one tibloc. An inelegant way could be to tie one end of the rope off to your self and then use the tibloc on the other strand. It would result in the rope being pulled through what ever your were rapping through but would work. I would say that a tibloc and a prussik has their different advantages and disadvantages. This situation be one of them where a prussik would be better.
By Ryan Williams Administrator From London (sort of) Apr 12, 2011
Jesus I can't believe how long it took for someone to actually answer your question. This place is turning into Rockclimbing.com!
The prussik above your ATC and "anti-rappelling" would work but if you have a prussik then you are probably already using it to back up your rappel. You'd have to take if off, adjust the length of the slings and place it back on the rope, all while holding the brake ropes w/ one hand. You could always wrap the rope around your thigh I guess...
Tim's idea of tying into one strand of the rope would work in theory, but this is not always as easy as it sounds as you are creating a lot of friction, depending on the anchor situation above you.
A tibloc is useful but how often are you actually rapping on a single line? It's nice to have one if you need to set up a 3:1 haul to get someone past a crux but a prussik works just fine as well.
I'm now wondering why I even have a tibloc at all?
I've had this happen to me. I put a tiblock on each strand and put a single foot loop on them. It was a short distance, so I didn't bother re-rigging my atc-guide in guide mode and making a self-haul system, I just pulled in the slack while standing up and held the brake strands while re-setting the tiblocs. I use an autoblock on rappel, so I reset that every few feet to back myself up. Alternatively, I could have tied off, taken off my autobloc and used it as a prussik and done the same thing.
Thanks Tim and Ryan. I wanted to make sure I wasn't missing something. I'm not bashing a tibloc by any means, I know they have their uses, but I was surprised at how many people carried one in their emergency gear. I have mine if I *plan* to ascend a rope, but that makes it non emergency gear.
I'll stick with my two prussiks for emergencies.
Larry, that is good to hear that it does work using a tibloc on each rope to ascend, doesn't sound ideal, but then again, ascending a rope never does...
In regards to your last post, I still don't get how you attempted to answer my question. I've never heard of wrapping a prussik around just one of the strands as a backup or for ascending. And how does wrapping one, single prussik around both strands = reascending with prussiks vs tibloc? I usually agree with you Crag, but I agree with Ryan, you didn't address nor answer my question.
As stated above, you gotta use a prussik on both strands to get up. If you're using a mechanical ascender like the Tibloc, then obviously you'd need two, and to clip both in to a single carabiner to evenly weight both ends of the rope that you're rappelling on.
As to how to begin the process, you should practice tying off. I've got a rather grey idea of it, and I've improvised in the past, but it's easily researched. You pull the break strands around your butt, back up to your locker and weave a knot on a bight through your carabiner that you're rapping from. Once you've got the rope ends up and around your arse, there's much of the friction provided by yer own weight, and tying the kont with a bight is not at all difficult.
Remember, knots on a bight don't tighten as well as single-stranded ones and really need a finishing knot. For bights, this means a carabiner clipped through the loop of tail. Usually just the same carabiner that you're weighting.
I've fixed the rope before rappelling down to find the next anchor before. Not perfect as you have to suspect you might be too short, in the wrong place, etc. However, if that does happen and you just have a Tibloc, you have an easy way up.
In the past I did so on a single strand (knew I was going back up after finding the station), but an overhand on a bight on either side of the anchor, and a locker connecting them would fix the rope, and allow the second to release it easily.
Not sure what caused this thread to re-open after years of dormancy, but Pat - If you're gonna go through all that hassle, why do overhands on both sides? Do it only on one side (see simul-rapping thread for pics) then descend your single line, if all checks out OK, you just pull your rope (pull the other side) if not, go back up.
You can still use a single Tibloc on one of the double strands as some pointed out, simply lock-off the non-tibloc strand. On the "Pro" side you need 1/2 the strength effort due to pulley effect, on the "Con" side you need twice the endurance as you move 1/2 as fast and it is obviously putzy. Tie back-up safety knots often as you proceed.
Best to just use Tibloc's for such things like crevasse rescue...