Passing a knot in single-strand rappel

Interesting situation yesterday in the alpine yesterday. We had brought a 9.5 mm rope and a tag line for the day. Our 9.5 rope was core-shot in by rock fall so we bailed off the route. Our system for rappelling with the two ropes is to use a knot block (see attached picture), rappel off a single strand, and retrieve the ropes using the tagline. We needed to remove the core shot from the system by isolating it with a alpine butterfly meaning there would now a knot in the rappel strand we would potentially have to pass. Luckily, the rappels were short enough we never needed to pass the knot.

The interesting situation here is what happens had we been forced to pass the knot. The system would no longer be retrievable since the rappel anchor would effectively be captured by the rappel strand having now two alpine butterflies tied in it. There is one alpine butterfly tied above the anchor for the knot block and a second alpine butterfly isolating the core shot tied below the anchor. The knot block method no longer works in this situation so far as I can tell. Any ideas on rappelling with a single rope and a tag line in this situation?

---- the star in the image is where you would find the alpine butterfly/core shot.

Any chance of switching it up and rapping off the tag line, and using your core shot rope as the pull line?  

Yes, that is one method that had crossed our mind. Rapping of the 7mm tag line does pose another set of risks/challenges though as well. For one, the ATC is not meant to be used with such a skinny rope and a gri-gri most likely wouldn't work either. Another challenge is tying a third hand that would be effective on such a skinny line. But I believe you could be correct as so far as I can tell, rapping off the tag is the only option. 

Likely you'd need to do a double rope rappel with both the single rope and the tag line and have the tag line threaded through the anchor. You'd still need to pass the rope but I believe a prussik would probably still bite pretty well on the tag line/single line combination.

how long was your rope? how much rope was there from the core shot spot to the long end? how much did you actually need for the rap? 

you could also setup the knot block below the core shot if you were confident in distance... for example, if the core shot was 20 ft from one end like in your picture.

Alec Baker --- I really like the idea of having the first person to rappel secure the lines to the anchor after the first rappel is complete. This not only secures the system, but as you mentioned it also allows you to remove the clove hitched, backup biner from the system as well. I like that because now you don't need to worry about the backup biner getting snagged or creating friction while pulling the line. And yes, the crux of this method seems to be needing to know that your tag line is rated for the load of the rappel.

Curt86iroc --- The rope was 70m long and the core shot was relatively close to the middle. I'd imagine we had 40m-50m of rope left. This was our first time rappelling the route so we weren't sure how long the rappels might be. Best I could gather from MP, it seemed like there was at least one 200ft rappel we would encounter. Luckily, all the rappels were completed using the amount of good rope we had left. And yes, setting up the knot block with the core shot above the anchor would work if you were certain the raps were doable with that amount of rope.

Jesse B wrote:

Yes, that is one method that had crossed our mind. Rapping of the 7mm tag line does pose another set of risks/challenges though as well. For one, the ATC is not meant to be used with such a skinny rope and a gri-gri most likely wouldn't work either. Another challenge is tying a third hand that would be effective on such a skinny line.

Simply rig the 7mm cord in the atc or grigri as normal (ideally extended), then set up a second locking biner with a munter on the brake side of the 7mm line. 

Or if you own a Omega Pacific SBG belay device, you can clip into the middle hole of the tail and wrap the 7mm cord around the base of the tail for additional friction or clip to the end of the tail and wrap the tag line around the stock as pictured below. 

I'd rig it so that you pull the damaged rope.  Sure, you could then rap the 7 mil, but the potential for damaging it against rock edges while it is under tension is unnerving, especially in an alpine context where things are often not so smooth.  So I'd still like to have the big rope, with the core shot tied off, do at least some of the weight-bearing and more particularly be the thing that moves around as the rappeller descends.  The problem is to keep the differential stretch and different amounts of friction in the device from pulling down the big rope while rapping, now that the system is not blocked at the anchor.  I'd tie a stone knot at the anchor for the first person down so that no rope slip at the anchor is possible, and they can rap both strands, passing the knot, for whatever extra friction and security both strands provide. When they get down, they clove the reepschnur line to the next anchor and tension it. The second rappeller removes the stone knot and raps the big strand, passing the knot, with the reepschnur anchored down below. (It is true that at this point, the reepschnur is taking the full rappel load, but although it is under tension, it isn't moving around and so possibly abrading on edges and lips.)

If the core shot is relatively close to one end of the rope and if the rappels are not too long, it might work to let the isolating butterfly be the blocking knot and just carry on as usual. If the landing is visible, you could inspect for this possibility (main rope has to reach next stance) before defaulting to the method above,

The reepschnur method is fine until it isn't. Use twins for alpine climbing.

I would just setup two friction hitches (from, e.g. slings), transfer the load to 'em, unrig rappel device, descend a bit on two friction hitches, rig the rapper device below the knot, transfer the load to it, untie both friction hitches, continue to rappel.

If I don't have any material to tie friction hitches with (almost impossible on alpine situation) I would use the very end of the rope and form a huge clove-like hitch, or Blake hitch, or whatever else suitable.

I’m a bit confused, did you only have gri-gris with you?  If so, do you know how to do a biner break rappel?   Why couldn’t you just put both knots on the same side of the system, rap both ropes to the knot, pass the knot, keep rapping and pull?  That seems like a very simple solution.  

Alternatively just rap the 7mm with the 9.5 setup as a pull rope.  Add some friction to whatever type of rap device you have.  I’ve single stranded rapped a 6mm (Esprit personal escape rope) countless times in my life with a gri-gri.  Redirect the break strand through a biner on your leg loop.  You can also just use a prussik if you have appropriate material.  Either method works fine and the system is fine unless there might be a lot of weird pendulums or traversing raps.  If that is the case the 6mm can feel a bit unnerving and best to use the above method.

Rap the tag and add friction to your device or pass the knots as Mikey suggested. Rapping a thin tag is definitely a little hairball feeling

You’re in the alpine and your knowledge is so spare that you don’t know even a couple other methods of rappelling?

Fix both ropes to the top. Rap the damaged line, bypass the butterfly by clipping into a temporary bight  in the pull line. Person at the bottom then fixes both lines at the bottom as a replacement for the bight / butterfly block knot that can now be removed, but leave the joining knot on the side of the damaged rope. Fixing both at the bottom will now keep the rope from moving through the anchor at the top so you now only have one butterfly on the damaged spot. Second can now rap and bypass the butterfly, and you now pull the damaged rope and not the 7mm.

Gotta agree with Mark. BITD we didn't carry belay/rappel devices. We still could do biner brake rappels and numerous other methods, and then there is the gearless Dulphersitz.

I haven't gone free climbing for years but still do a lot of aid. We can carry more options. And having rapped and jug dozens of miles knot passing is second nature.

My choice, BITD even free climbers carried baby angles, so I'd rap both (biner brake or even using baby angles as a brake bar, even a series) pass the knot, and bottom out.

If you climb with biners then you should know all their uses. If you do then you can rig a 7mm single strand confidently if, say, you had accidentally dropped the other rope.

If I had a sawbuck for every core shot I had,..... I'd go buy a new (Bluewater) rope.

Agree with Mikey. To add some more details, rap one or both strands with a friction hitch above your device. When you get to the knot add another friction hitch below the knot. Tie a back up bight to your harness. Remove your belay device and reload below the knot and above the second friction hitch. Remove the top friction hitch and back up bight. Off you go.

How bad was the core shot? I'm not calling your judgement into question, but I have climbed with some folks who lose their sh:t if there's a tiny nick in the sheath through which the core is (slightly) visible. Even an honest-to-goodness, "this rope's a goner" shot probably leaves more intact core than what's in the undamaged 7 mm tag line. So rapping the damaged rope without an isolating butterfly MAY have been an option.

Jesse B wrote:

Interesting situation yesterday in the alpine yesterday. We had brought a 9.5 mm rope and a tag line for the day. Our 9.5 rope was core-shot in by rock fall so we bailed off the route. Our system for rappelling with the two ropes is to use a knot block (see attached picture), rappel off a single strand, and retrieve the ropes using the tagline. We needed to remove the core shot from the system by isolating it with a alpine butterfly meaning there would now a knot in the rappel strand we would potentially have to pass. Luckily, the rappels were short enough we never needed to pass the knot.

The interesting situation here is what happens had we been forced to pass the knot. The system would no longer be retrievable since the rappel anchor would effectively be captured by the rappel strand having now two alpine butterflies tied in it. There is one alpine butterfly tied above the anchor for the knot block and a second alpine butterfly isolating the core shot tied below the anchor. The knot block method no longer works in this situation so far as I can tell. Any ideas on rappelling with a single rope and a tag line in this situation?

---- the star in the image is where you would find the alpine butterfly/core shot.

I am not going to belittle your alpine skills like the rest of the MP cohort.

When adjusting for an unforeseen situation do not things you are not familiar or comfortable with. in this case, and assuming you know what a friction hitch is, keep your system the same and use friction hitches to pass your belay device to the other side of the knot.

Tradiban wrote:

When adjusting for an unforeseen situation do not things you are not familiar or comfortable with. in this case, and assuming you know what a friction hitch is, keep your system the same and use friction hitches to pass your belay device to the other side of the knot.

I'm pretty sure this will make the ropes un-retrievable as there will be knots on both sides of the anchor.

Mikey Schaefer wrote:

I'm pretty sure this will make the ropes un-retrievable as there will be knots on both sides of the anchor.

That's the point! A couple responders in this thread clearly didn't read all of OP's post.

Mikey Schaefer wrote:

I'm pretty sure this will make the ropes un-retrievable as there will be knots on both sides of the anchor.

Lol, damnit. I knew I should have actually read the post. Thank you for the correction.

In which case just climb on twins/doubles like a normal person. 

Or....in lieu of those ropes do what Mikey said in the first post, careful rapping on two totally different ropes!

Tradiban wrote:

In which case just climb on twins/doubles like a normal person.

rgold wrote:

Use twins for alpine climbing.

OP is asking for suggestions about their specific situation, using a rope system that is very common for this type of a route, and multiple people's "super helpful" advice has been... use different ropes?  Which, even if OP did, wouldn't really have changed his situation that much?

In case people aren't aware, the single+tag method is quite common in the 21st century:

https://www.colinhaley.com/nugget-1-the-petzl-purline/

"For all these reasons, a single rope and a rappel rope is usually my preferred system when alpine climbing with two ropes, and I have used this rope system A LOT, starting around 2002"

Kyle Tarry wrote:

OP is asking for suggestions about their specific situation, using a rope system that is very common for this type of a route, and multiple people's "super helpful" advice has been... use different ropes?  Which, even if OP did, wouldn't really have changed his situation that much?

In case people aren't aware, the single+tag method is quite common in the 21st century:

https://www.colinhaley.com/nugget-1-the-petzl-purline/

"For all these reasons, a single rope and a rappel rope is usually my preferred system when alpine climbing with two ropes, and I have used this rope system A LOT, starting around 2002"

I'm very well aware of all of that.  The comment was an aside after providing a viable procedure. With the tags, I'm expressing a personal opinion (based on considerable personal experience) that tags suck compared to twins.  In Europe, where alpine climbing is commonplace for all ability levels, twins appear to dominate.  

Which is not to say there aren't good arguments for single + tag.  Here is Colin Haley's advantage list.

• It allows for hauling, if so desired.
• 2) It allows for the follower to easily ascend the rope directly, if so desired.
• 3) It allows for the best simul-climbing techniques. The advent of the Petzl Microtraxion has significantly increased the difficulty of terrain that I am comfortable simul-climbing on. Using Microtraxions to safeguard against the follower pulling off the leader works best with a single rope (although it is also possible with twin/double ropes).
• 4) It allows for the use of certain rope devices, like a Grigri, that don’t work with twin/double ropes.
• 5) It makes for less rope-drag. This may sound surprising to some people, because many people advocate the use of double ropes specifically to reduce rope drag. There are specific scenarios where double ropes can result in the least rope drag (pitches that are extremely wandering AND very difficult for the climber), but 90% of the time I find that using a single rope results in the least rope drag.

Haley also found that "Using 6mm accessory cord is very unideal [emphasis is mine] for a number of reasons: It is very supple (and thus tends to get tangled with itself, and caught on the rock), it stretches A LOT, and most of all because it is really not very strong or cut-resistant." He goes on to describe a 16 year journey, experimenting with Maxim 5,5 tech cord (sheath slippage) and then six highly specialized ropes, before settling on the Petzl Purline ($240 for 65m).

So when a lot---maybe most---folks speak of using tag lines, they are speaking about using technology that Haley rejected 16 years ago. They likely aren't considering having the follower jumar, nor are they envisioning lots of simulclimbing, and they might not be thinking about hauling either.  And they aren't sporting a Petzl Purline.  The 21st century may have arrived for Haley, but maybe not for most other people who might be embracing "single + tag" without realizing they aren't using the gear Haley is using nor are they intending to do the things he does.  One might also factor in the fact that Haley is an elite climber pushing the envelope and making choices that might not be appropriate for more ordinary climbers.

At the end of the day, it comes down to YMMV. For the majority of us who are non-elite climbers, I remain comfortable with my original aside.