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I'm joining a rock climbing club that requires an evaluation test in order to become a member. (I think this is a great idea.) They have a detailed handout listing exactly what you need to know for the test, including a bunch of knots. Most of them I was familiar with, but one knot they listed was the slip knot, which I've never used for climbing. Googling turns up this page, which says

You might use it to sling a horn ("chicken head") of rock for example.

What would be the right way to do this? After you tie the knot, pulling on one strand (call it strand 1) tends to tighten the loop, but the other strand (2) won't support tension. Presumably you need to do something else to make it safe. Do you tie a stopper knot in strand 1? Tie the two strands into a butterfly? I'm assuming that in this application you wouldn't have tension on either strand yet, and you may only have access to one end.

Is the slip knot the best knot for this purpose? Are there other rock-climbing applications of the slip knot?

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Slippery versions of knots/hitches are very useful in many applications, but have limited use in climbing. But there is one application for which I often use a slippery overhand knot.

In Sport climbing

When I'm cleaning a sport route and need to rappel, I'll tie a slip knot in the rope (before I untie myself from the rope) and clip it to my harness so that I cannot lose the rope when I'm removing my gear and putting the rope through the rappel rings. (Of course I'm off-belay and clipped into the anchors with other gear while doing this.) The slip knot is great because it's quick, I can do it with one hand, and it doesn't have to hold any load for the short amount of time that it's actually tied. Once I've got the rope distributed through both rings and the ends are down at the bottom of the route, the slip knot is no longer needed and comes right out.


In Arborist climbing

Your question was general enough to "climbing" that I decided to add this: In arborist climbing, sometimes putting a slip overhand knot in your trailing rope is useful as a backup to prevent an accidental descent. The slip knot is tied in such a way that if you descend onto it (meaning your hitch/device is butted up against it), it gets tighter and stops you. If tied in reverse, it would simply get pulled loose when descending and your hitch/belay device hits it. When tied properly, the slip-knot is effective and easy to remove when descending.

In my experience, I have primarily used this for beginners for tree climbing as an added backup for them, tying multiple slip knots under them in case they inadvertently descend. When they are actually ready to come down, from the ground I simply pull down on the rope to remove the slip knots and transfer to bottom belay as a backup.

  • Some people also put slip knots in the ends of the rope before throwing them down to start a rappel. I'm generally against it due to increasing the likelihood of a snag, but it's common-ish. – Ryley Aug 18 '14 at 17:50
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    @Ryley: If it snagged, wouldn't you just be able to clear the snag during the rappel? Rapping off the end of the rope is an extremely common cause of climbing accidents, so I would definitely always use knots. – Ben Crowell Aug 23 '14 at 0:45
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    Personally, if I know my rope should reach the ground, I don't tie knots, I visually confirm that both ends are on the ground and re-throw the rope if they aren't. – Ryley Sep 1 '14 at 16:34
  • @manoftheson: +1 for ..can do it with one hand, and it doesn't have to hold any load.. – WedaPashi Nov 26 '14 at 16:09
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Aside from the slip hitch*, you can also use a girth hitch or clove hitch to sling a chicken head (or similar protrusion). The slip hitch will place only a single strand around the object, which may be helpful if space is limited or if you need the additional length. It's very easy to remember and tie, although with practice a clove hitch can also be quickly placed one-handed.

Since you mention the other strand won't support tension, I assume you also figured out that the slip hitch is structurally similar to a Reepschnur rappel; pulling on the wrong strand will cause the slipped strand to pull through and eventually there is no more loop. This is why you should be tying it with a sling rather than the rope itself. (And yes, you can also add an overhand in the sling if you want.)

The slip hitch isn't one that immediately comes to mind when I think of climbing knots, although it might be the first thing to mind if I wanted to quickly hang some gear. (When done, unhook the gear and just pull the strand to undo the knot.)

*Technically any knot can be "slipped" by inserting a bight rather than the end of a rope; pulling the end allows the knot to be undone. The standard shoelace knot is an example of a slipped reef knot (a.k.a. square knot).

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When aiding, you can use a slip knot to tie off a fixed piton close to the rock face (if the eye is broken). You can do the same thing for a chickenhead if its shaped in such a way that the rope must be tighten to stay on. In that case I'd rather use that for body weight, not fall protection.

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