Shortening a shoulder-length sling to half-length?

Question

For trad climbing, I normally carry shoulder-length slings racked on my harness, set up in Alpine draws at 1/3 their full length. When I'm leading and need to extend my protection, I either use them at this length or extend them to their full length.

There are some cases, though, where I find that I want 1/2 the length, not 1/3, and I want something I can securely girth-hitch. Specifically, when I'm extending my ATC for rappelling, 1/2 the length is just right, while 1/3 is too short and doesn't keep my autoblock from getting into my ATC.

What is the best way to shorten a sling to 1/2 length for this purpose? Let's say I want to hitch to my belay loop and connect to a biner on the other end.

1. The simplest thing is to put the sling through the belay loop, which then gives me the two ends of the sling hanging out of either side. If I bring these ends together, I can clip in with a biner. For reasons explained below, I think this is a very poor method.

2. I can tie a butterfly in the sling and adjust it to get the desired length.

3. I can tie an overhand or figure-8 in the middle of the sling and load it at the knot.

Method 1 is lousy, because the strands aren't redundant, and furthermore when I'm taking it apart there is an extreme tendency to drop the sling, which isn't securely girth-hitched to anything. I could fix these problems by tying an overhand in the middle, but that makes the sling much shorter.

Method 3 is what I used to do, but I've seen this criticized because the knot is sitting right on the biner. However, if the knot slips, the system doesn't fail, it just extends.

Method 2 is what I'm doing right now. It seems OK, although it's difficult to properly dress the butterfly when you make it in a dyneema sling, and it can be a little time-consuming to untie. It requires some fiddling to get the bar tacks out of the way before you tie the knot. This method uses the butterfy for its intended purpose and loads it in the intended way. If the butterfly pops undone, you get extension but not failure. An advantage is that you can adjust the length quite a bit.

Answer 1

When I am trad-climbing (actually generally when rock-climbing), I carry 60cm (shoulder length) and 120cm slings. Some 60cm slings set up as alpine draws, the rest over my shoulder. When setting up a belay station, 60cm slings tend to be too short. When using a double boolean as central point, that uses already most of the sling length. Further, when abseiling, I use 120cm slings in the following setup: Girth hitched parallel to the belay loop (alternatively directly into the belay loop), then a knot (eight, butterfly) at about a third of its length. Thus the autoblock cant reach the abseiling device. The remaining loop in front of the knot I use as self belay sling. Thus when I reach the next belay station, I can immediately secure my self. Another small benefit for the forgetful: While abseiling, you can clip the self belay biner into the rope, that you will pull down afterwards.

I do not see, what the problem of loading the sling at the knot should be. Even if you dislike it, you can simply adjust the girth hitch such, that the knot is not at the end. Both eight knots and butterfly knots can handle ring loads. If you are using a dyneema sling, the knot can slip, but very slowly. This means that under constant load the knot may creep upwards, but I never saw this being the case when abseiling. Burning trough is anyway not a problem in this setup, as a slipping knot will not concentrate the friction heat to one point.

Method 1 could be adjusted in the way, that you take your sling in a double loop and girth hitch it to the belay loop.