Single line rappeling question

[Jud]

I've been reading about single line rappelling in a good alpine climbing book (Alpine Climbing: Techniques to Take You Higher; Mountaineers Press). It's pretty clear, but the one thing I don't quite get is the use of the retrieval line and "jammer" knot (butterfly knot in that book) at the anchor.

 

I get how the retrieval line is tied to the end of the climbing rope...the climbing rope goes through the rap anchor. In this book, they show a butterfly knot tied above the knot joining the two ropes...the bight formed by the butterfly (or figure eight on a bight) has a biner clipped through it and to the climbing rope. When you get to the end of the rap, you pull the retrieval line to get the rope back.

 

But...what I don't understand is how the rap rope is secured at the anchor. In a normal rappel, the doubled rope goes around the anchor and you rap on two ropes: the rope is secure around the anchor. In a single rope rappel, is it the butterfuly knot/biner that is key? In other words, it seems that the butterfly knot is critical in that it keeps the single strand of rope, which is weighted, from slipping through the anchor (e.g., rope is threaded through a sling around a rock horn). But what if the sling stretches a bit while the rope is weighted, and the butterfly slips through it?! It seems like all the climber's weight is being held by the butterfly knot --i.e., you're counting on it jamming at the anchor-- while you rappel (while holding the retrieval line in the other hand? Is that what you do?).

 

I've found an illustration of single rope rappelling in the canyoneering context, and the jammer knot (not a butterfly in that case, but an overhand on a bight) jams up against a quick-link clipped to a sling (anchor), which seems very secure and makes sense to me. So, in the end, I guess my question is...when single line rapping, it seems like you need a fool proof way to keep that jammer knot (butterfly or s.t. on a bight) from pulling through while the rope is weighted with the climber?! Here's the canyoneering pic of single rope rapping, with the jammer knto being held at a small quick-link: http://canyonwiki.com/wiki/index.php/'biner_block Surely you don't always use a quick-link/sacrifice biner when single-line rapping?

 

Noob questions galore...look out! Not sure if my question is clear...hard to describe it succinctly in type.

Edited June 5, 2008 by Jud

[counterfeitfake]

Yeah, you can't do it with a sling anchor, really. If the knot comes out you fall to your death. I think the stopper knot idea only works with chain anchors.

 

What you CAN do is clip a biner through whatever the knot is, and then clip the rope back onto itself (around the anchor). Now it just tightens up when weighted, but you can pull the retrieval line to undo it all. Just make sure the whole mess will move properly when you pull the retrieval line.

[Jud]

I think it's making more sense to me now --the biner clipped through whatever the knot is, clipping the rope back onto itself around the anchor is crucial, since, as you say, it just tightens up when weighted.

 

One of those things that I need to actually DO and see to understand fully...I was looking at the description this morning in a book, and I realized how useful single line rapping is...but all those questions popped into my head, since it wasn't clear in "the book". Yup, just gotta go out and simulate it/try it out in a safe context. Thanks for clarifying.

[sweatinoutliquor]

http://canyoneeringusa.com/utah/tech/blocks.php

 

Here's a link to a canyoneering page that demonstrates a few ways to rappel single strand. Just make sure you have a device that can provide enough friction to go slowly when you approach the end of the rope.