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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?

Charlie Brumbaugh
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    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 01 '19 at 21:10

1 Answers1

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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.

Charlie Brumbaugh
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  • 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 –  Mar 24 '19 at 21:43
  • so clipping to just one anchor bolt is an acceptable risk in my opinion right up to the point where that bolt fails and you take a 30m swan dive... I'm genuinely worried at the advice being peddled on this site around climbing... some really quite dangerous ideas. –  Mar 24 '19 at 21:48
  • @Liam Because those are long enough for what I need it for see picture here https://www.instagram.com/p/5-k52GjSS9/?utm_source=ig_web_copy_link In the unlikely chance that you fall to the end, its a loop and so it's not going anywhere. – Charlie Brumbaugh Mar 24 '19 at 21:48
  • What about your second? So you going to keep a hold of the rope during this "fall"? And what about shock loading when this fails? Can you show some references for where this is advised? –  Mar 24 '19 at 21:50
  • I've just realised too, your prusik is using the same rope. You can't do that! The prusik cord needs to be, at most, 3/4 the diameter of what its gripping or else it slips. Your prusik is the same diameter! –  Mar 24 '19 at 22:01
  • @Liam No it's going round two of its own strands so it's 1/2 the side of the diameter its gripping (by the way that's the defining characteristic of a Purcell prussik so it seems like you are unfamiliar with these.) I have updated the answer with studies that showed these are a better alternative to daisy chains. Plenty of outdoor organizations and search and resue teams use this for tethers http://www.conovers.org/ftp/SAR-Evacs-lowres.pdf – Charlie Brumbaugh Mar 24 '19 at 23:54
  • @qudit you can use a sliding X which is very fast, if you add limiter knots its redudant also. – m4tt1mus Apr 01 '19 at 21:11
  • @m4tt1mus That doesn't solve the problem of safely attaching the Purcell to both bolts while cleaning. – Qudit Apr 01 '19 at 21:17
  • @CharlieBrumbaugh I don't find the comparison between Purcells and daisy chains useful. It's not surprising that they are weak since they're only rated for 2 kN and shouldn't be used as a personal anchor system. – Qudit Apr 01 '19 at 21:22
  • @Qudit you create your own anchor using the procell then tie into it. you can use a quad, sliding x, figure 8, etc – m4tt1mus Apr 01 '19 at 21:23
  • @m4tt1mus You could, but having a second anchor for cleaning seems overly complicated and cumbersome to me. I'd rather just use a PAS. – Qudit Apr 01 '19 at 21:43
  • @Qudit Doesn't a PAS have https://www.rei.com/product/117551/metolius-alpine-personal-anchor-system?sku=1175510001&store=44&cm_mmc=PLA_Google_LIA|404_185485|1175510001|none|e4d1f543-f485-4f15-ba4b-ca4b95e719d1|pla-417281855187&lsft=cm_mmc:PLA_Google_Showcase|404_185485|1175510001|none|e4d1f543-f485-4f15-ba4b-ca4b95e719d1&kclid=e4d1f543-f485-4f15-ba4b-ca4b95e719d1&gclid=EAIaIQobChMI-d-qvO-v4QIVFp7ACh3ACg8UEAQYASABEgJhkfD_BwE have the same issue with you only be attached with a single locking carabiner? Or are you meaning something else? – Charlie Brumbaugh Apr 01 '19 at 21:48
  • @CharlieBrumbaugh No. Since the PAS has loops you can clip one loop into each bolt to provide redundancy. This should be done so that there is a minimal amount of slack so that there is as little shock loading as possible if the first bolt fails. PASes are usually rated to the same standard as a sling, so they are very strong. – Qudit Apr 01 '19 at 21:56
  • @CharlieBrumbaugh No. Since the PAS has loops you can clip one loop into each bolt to provide redundancy. This should be done so that there is as little as possible to minimize shock loading if the first bolt fails. PASes are usually rated to the same standard as a sling, so they are very strong. – Qudit Apr 01 '19 at 21:58
  • @Qudit You could always just clip to the other bolt with another sling – Charlie Brumbaugh Apr 01 '19 at 22:38
  • @CharlieBrumbaugh Yes, you could do that too. – Qudit Apr 01 '19 at 22:42
  • @Qudit i have two passes when i multipitch that i use to tie into anchors/chains. technically you can get by with one but i prefer two. Usually i have one setup much shorter than the other to make it easier to clip anchors. You question was how you can clip in with a Cordellete though, not a PAS. You could hook directly to shelf on the anchors i mentioned or use a quickdraw. – m4tt1mus Apr 02 '19 at 14:10
  • Your diagram labels the loop end as "To Climber" and the plain end as "to anchor". That's good for a tether longer than your reach. If you do it that way, grabbing the prusik lengthens the system and also is hard to shorten under load. If you set it up to be always shorter than your reach, you should flip it around so the plain end is on the climber, then grabbing the prusik stabilizes the system, gives you some mechanical advantage for pulling yourself up and shortening. – Dave X Jun 12 '19 at 15:03