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Sometimes when clipping in people who are rappelling, or setting up anchors in some places from above or showing people how to get onto a fixed line, I need an adjustable tether.

I often carry a nylon cordelette for just such a purpose, what knot should I use?

  • 2
    Wow, the purcell prusik looks horribly over-engineered to me. Why not simply use a sewn sling and adjust the length e.g. with a clove hitch? – anderas Aug 16 '18 at 20:38
  • @anderas For my use case, that wouldn't be long enough and the prusik slides really nicely with just one hand to adjust – Charlie Brumbaugh Aug 16 '18 at 20:42
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    Daisy chain and fifi hook? One-handed operation, quick and easy, adjustable to within 5cm typically. – Beanluc Aug 16 '18 at 23:15
  • You can use the rope as one adjustable tether by tieing yourself to the anchor with a clove hitch. You should really have two tie ins though – m4tt1mus Apr 1 at 21:10
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The solution to this is a Purcell Prussik, that looks like this,

Purcell Prussi

It's a cordelette tied into a loop with a double fisherman's, and then looped back with a prussik to itself. See here for how to tie one.

If I need more slack, I reach up and pull the prussik towards myself, if I need to go shorter I push it up towards the anchor.

It is important that the loop with two strands goes to the climber, as otherwise, you won't be able to adjust the knot without climbing back to the anchor when it is fully extended.

The other thing to note is that the double fishermans won't go through the prussik, so you want it as close to the side that goes to the anchor as possible but not directly on it.

Finally, note that this should only be used with a cordelette made out of nylon cord and will not work with a cordelette made from dyspectra/dyneema or webbing as it will likely slip.

If you need to shorten one, you can tie a figure eight on bight on the part of the cordelette that goes to the anchor and clip the bight to the anchor.

Close up of the prusik,

Purcell Prussi

For those doubting this as an acceptable solution,

The testing conducted on Purcell Prusiks was by no means a comprehensive examination. However, the testing conducted certainly suggests that a Purcell Prusik constructed out of 6mm cord with a 3-wrap prusik hitch meets the recommended lanyard performance guidelines of being able to withstand a fall factor 1 event with acceptable levels of MAF and no observable degradation of the lanyard. The testing also demonstrates that the margin over and above that minimum performance criteria is approaching the 50% level at fall factor 1.5.

The Purcell Prusik used as a lanyard can certainly be considered a worthwhile alternative to the traditional daisy chains and other personal restraint lanyards available in the marketplace.

DROP TESTING ON PURCELL PRUSIKS: A CRITICAL EVALUATION OF THEIR CAPABILITIES AS A POSITIONING LANYARD IN RESCUE AND CLIMBING

The same guys did a study on daisy chains as personal anchors and they broke at much lower fall factors.

  • Is there a nice way to attach the Purcell to two anchor bolts without creating an American death triangle? I've always wondered how people who use the Purcell as their personal protection deal with this issue. – Qudit Aug 16 '18 at 18:19
  • @Qudit See the picture at the top, you clip the locking biner to the master point. – Charlie Brumbaugh Aug 16 '18 at 18:21
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    That's fine after the anchor is set up, but what about when cleaning? There is no master point then. – Qudit Aug 16 '18 at 18:22
  • @Qudit I have only ever used it where I expect it to hold my body weight, so clipping to just one anchor bolt is an acceptable risk in my opinion. – Charlie Brumbaugh Aug 16 '18 at 20:03
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    Whats wrong with a good old fashioned over hand? Or just cut the cordette to size? Or double the cordette over? You have no redundancy here. Prusiks are not guaranteed and should only be used as backups (or should have backups installed). I'm not sure where you learned this but I'm 100% sure it's not best practice, certainly not in Europe. At best this is massively over engineered, at worst, it's down right dangerous! Don't do this kids – user2766 Mar 24 at 21:43

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