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Googling seems to show that the conventional wisdom is that it's not a good idea to chain carabiners together:

Another thing to avoid is chaining carabiners together to lengthen a connection in the system. If subjected to a twisting motion they can unclip themselves. S. Peter Lewis, Toproping

Avoid chaining carabiners in succession, because they can twist, which weakens them and can open a gate. -- Freedom of the Hills, p. 170

Is there any reason not to chain carabiners together if they're locking biners? The specific application I have in mind is extending my ATC for rappelling. The FotH quote says that twisting can weaken the biners, but I don't believe this is realistically anything to worry about in a rappel setup, as opposed to an anchor.

What I've been doing previously is to girth-hitch a dyneema sling through the tie-in points of my harness, and tie a butterfly knot in the sling in order to shorten it a bit. I'm not happy with that technique because (1) I've learned that a girth-hitched dyneema sling fail in lab tests under surprisingly small loads (small fall factors), and (2) it can be a pain to get the butterfly knot out.

I tried replacing the dyneema sling with a nylon one, but the nylon one is too fat to make it practical to tie a knot in order to shorten it.

  • 2
    You may have discovered the reason for those tiny 30cm (1 foot) slings I've seen in the local REI! – requiem Dec 25 '14 at 5:21
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    This is what we are taught to use here:minusestplus.org/uploaded/big/20070726175111.jpg – Dakatine Dec 25 '14 at 10:25
  • @Dakatine: Interesting. But I don't have any reason to carry a daisy chain, since I don't do any aid climbing. (They're no longer considered safe for use as personal anchors.) – Ben Crowell Dec 26 '14 at 15:58
  • @requiem: Interesting. I've never seen those. Are you thinking that they're intended for linking together two carabiners? But I can accomplish that by just winding a shoulder-length sling five times around my hand. That gives me something about 4" long. (It's awkward to try to get it any shorter than that, because of the bar tacks.) – Ben Crowell Dec 26 '14 at 16:03
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    It seems the question about lockers is getting lost in the question about the rappel extension... Perhaps you can edit so there's a single clear question (I could see chaining lockers being used elsewhere). Personally I think it's a bad idea to carry that many locking biners. If the sling doesn't work for you, carry an equivalent length of 7mm cord and tie it into a Purcell Prussik. – Felix Dec 31 '14 at 19:31
5

Carabiners are designed to be strongest in tension. That's why the biner has two limits -- closed (where the forces are distributed lengthwise among two sides of the biner) and open (where the remaining arm is in tension and torsion.

When you twist two biners together, you are putting rotational forces on each biner that they weren't designed to take.

And while you are correct in that rapping doesn't usually put the kinds of dynamic stresses on biners that anchors do, if you lose half your anchor, it may be a different story.

Short answer is it probably will work, but you could just go buy a quickdraw and be done with it.

  • I think you're misunderstanding the question. I'm using this to extend my ATC so that I can fit a Prusik backup underneath it. I'm not talking about using it on the anchor that I'm rappelling off of. – Ben Crowell Dec 24 '14 at 20:37
  • I know. But Usually rap lines are anchored in two places. If you lose one, you get a rotational moment about the second one that might twist the two biners connected to your atc. – gbronner Dec 26 '14 at 6:28
  • I also don't understand the remark "just go buy a quickdraw." I own some quickdraws, but I don't see how that's helpful here. – Ben Crowell Dec 31 '14 at 1:16
  • @BenCrowell You can simply use the quickdraw to extend your ATC, possibly replace one or both of the biners with a locking biner for that specific application. – pmr Jan 5 '15 at 23:34
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The technique I learned through AMGA is to extend your rappel using a full length nylon sling. Girth hitch one end through your hard points, tie an overhand knot halfway through the sling then clip the remaining end back to your belay loop with a carabiner. You can then clip your ATC carabiner through both loops (over the midway overhand knot) and set up the rope. An autoblock or prusik can be attached below the ATC via your belay loop.

See this Mountaineers article for more details on the set up.

Its a pretty slick set-up that I use frequently. You avoid the mess of attaching a third-hand via the leg loop and instead have everything right in front out you. Also very useful when doing multiple rappels because you can unclip the biner from your belay loop and attached it right to an anchor while still being set up in your rappel (since it's redundant).

As far as linking carabiners is concerned, the one time I do this is when I am managing a topside belay and have set up a large lockers as my masterpoint.

  • Thanks for your answer, but this doesn't really address the question. What you're describing is essentially what I used to do. The question explains what I didn't like about that method. – Ben Crowell Dec 31 '14 at 1:18
  • It is a similar method from what you described above. The advantages of doing it this way are: (1) You avoid the Dyneema fall factor issue. (2) You give yourself a redundant system by backing up the sling. (3) You have an easy way to attach a third-hand without the risk of bumping it into the belay plate. You'll still have to deal with untying a tight knot. But it uses gear on hand. Personally I'd always do with this instead of creating a chain of carabiners (more moving parts in the system). Hope that clarifies things, totally your call! – Brian Eagen Dec 31 '14 at 17:32

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