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acorneau


Oct 20, 2008, 2:35 PM
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Purcell Prusik
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A thread in another forum brought this up so I thought I'd post it here:

"An Examination of Purcell Prusiks as Personal Restraint Lanyards"
http://www.marski.org/...gid=74&Itemid=26


majid_sabet


Oct 20, 2008, 9:54 PM
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Re: [acorneau] Purcell Prusik [In reply to]
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jeepnphreak


Oct 21, 2008, 8:17 AM
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I used one of those instead of a daisy chain. I use 7mm dynamic cord to limit the shock load on my system. plus it adjustable.


binrat


Oct 21, 2008, 5:05 PM
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I have been using one for about 10 years now.

binrat


shockabuku


Oct 21, 2008, 9:42 PM
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Interesting article. The concluding comments about not using high performance low stretch materials for a lanyard at the end of the text seemed out of place however. I did see the following data but no analysis of it was presented or even mention made of the data in the article body.


MudBuzz


Apr 28, 2009, 3:27 PM
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Re: [acorneau] Purcell Prusik [In reply to]
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So I notice there's a single loop on one end to connect to harness, and two loops on the other end with one biner to anchor. Can you put a biner on each loop to clip two anchors?


acorneau


Apr 28, 2009, 6:24 PM
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Re: [MudBuzz] Purcell Prusik [In reply to]
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MudBuzz wrote:
So I notice there's a single loop on one end to connect to harness, and two loops on the other end with one biner to anchor. Can you put a biner on each loop to clip two anchors?

Well, you could, but I don't think anyone has tested it that way.

My guess is that if you were off to one side, loading one loop and not the other, that the holding power of the prussic would be severely reduced.

But wait, this is the Lab... Aric, to the Batmobile (I mean, pull tester)!!!


Rudmin


Apr 29, 2009, 8:36 AM
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Re: [majid_sabet] Purcell Prusik [In reply to]
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Is there a good reason not to save a biner and girth hitch the whole thing to the tie in points?


acorneau


Apr 29, 2009, 9:04 AM
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Rudmin wrote:
Is there a good reason not to save a biner and girth hitch the whole thing to the tie in points?

I'd highly recommend a direct girth hitch and not using a biner.

Maybe the people in Majid's picture are using a biner for a particular reason... Majid?


majid_sabet


Apr 29, 2009, 9:36 AM
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Re: [acorneau] Purcell Prusik [In reply to]
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acorneau wrote:
Rudmin wrote:
Is there a good reason not to save a biner and girth hitch the whole thing to the tie in points?

I'd highly recommend a direct girth hitch and not using a biner.

Maybe the people in Majid's picture are using a biner for a particular reason... Majid?

what do you mean direct girth hitch to harness ?


d0nk3yk0n9


Apr 29, 2009, 12:52 PM
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Re: [majid_sabet] Purcell Prusik [In reply to]
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majid_sabet wrote:
acorneau wrote:
Rudmin wrote:
Is there a good reason not to save a biner and girth hitch the whole thing to the tie in points?

I'd highly recommend a direct girth hitch and not using a biner.

Maybe the people in Majid's picture are using a biner for a particular reason... Majid?

what do you mean direct girth hitch to harness ?

I think he means girth hitching the loop created by the figure 8 on a bight directly to your belay loop instead of using a biner to attach this loop to your belay loop.


majid_sabet


Apr 29, 2009, 10:13 PM
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Re: [d0nk3yk0n9] Purcell Prusik [In reply to]
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d0nk3yk0n9 wrote:
majid_sabet wrote:
acorneau wrote:
Rudmin wrote:
Is there a good reason not to save a biner and girth hitch the whole thing to the tie in points?

I'd highly recommend a direct girth hitch and not using a biner.

Maybe the people in Majid's picture are using a biner for a particular reason... Majid?

what do you mean direct girth hitch to harness ?

I think he means girth hitching the loop created by the figure 8 on a bight directly to your belay loop instead of using a biner to attach this loop to your belay loop.


you can go direct to belay loop and that is ok but in many rescue applications we use the Purcell and biner for easy connect/disconnect.






getsomeethics


Apr 30, 2009, 4:13 PM
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Re: [acorneau] Purcell Prusik [In reply to]
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I saw the Pucell Prusik on here somewhere else a couple years ago and have been using it ever since.

I girth hitch it to my harness and have it such a length that when it is fully extended i can still reach the prusik to re-adjust.

Wish i knew about it years ago.


Adk


Apr 30, 2009, 4:29 PM
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I've seen this before but really never gave it any thought.
How much cord might one need to make the purcell?
I'm beginning to like my thoughts here.


acorneau


Apr 30, 2009, 5:22 PM
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Re: [Adk] Purcell Prusik [In reply to]
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Adk wrote:
I've seen this before but really never gave it any thought.
How much cord might one need to make the purcell?
I'm beginning to like my thoughts here.

I want to say about 12' of 6mm cord will be just about right. If you want it longer, then maybe 13' or 14'.


Adk


Apr 30, 2009, 7:53 PM
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Thanks man. It's much appreciated.


acorneau


May 7, 2009, 3:08 PM
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Re: [MudBuzz] Purcell Prusik [In reply to]
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MudBuzz wrote:
So I notice there's a single loop on one end to connect to harness, and two loops on the other end with one biner to anchor. Can you put a biner on each loop to clip two anchors?

So I tried this at the gym yesterday. What I found out is that yes, it seems to hold just fine while clipped to two horizontal hangers and as long as you're in the middle.

However, I tried offsetting one loop (pulling one stand tighter than the other) as if you were hanging to the side of the anchors. When you weight the Purcell it will slip until both loops are weighted equally.

A pull test and/or drop test on the split-loop configuration would be enlightening.


ja1484


May 7, 2009, 3:40 PM
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Re: [acorneau] Purcell Prusik [In reply to]
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Best. Personal. Tether. Ever. Made the switch to 'em two years ago and haven't looked back since.

They really shine on rappel. Being able to lengthen them under load is a huge plus.

Oh, and fuck 'biners or girth hitches, just tie the damn thing direct into your tie-in points - it cuts down on clutter around the tie-ins and requires less cord. Replace as needed.


(This post was edited by ja1484 on May 7, 2009, 7:52 PM)


d0nk3yk0n9


May 7, 2009, 6:12 PM
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acorneau wrote:
Adk wrote:
I've seen this before but really never gave it any thought.
How much cord might one need to make the purcell?
I'm beginning to like my thoughts here.

I want to say about 12' of 6mm cord will be just about right. If you want it longer, then maybe 13' or 14'.

How long of a tether will this make when fully extended?


moose_droppings


May 7, 2009, 6:46 PM
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d0nk3yk0n9 wrote:
acorneau wrote:
Adk wrote:
I've seen this before but really never gave it any thought.
How much cord might one need to make the purcell?
I'm beginning to like my thoughts here.

I want to say about 12' of 6mm cord will be just about right. If you want it longer, then maybe 13' or 14'.

How long of a tether will this make when fully extended?



The one on the right is made up of 12' of 6mm. It's a little under 2', and all the way extended it's a hair over 3'.


acorneau


May 7, 2009, 7:08 PM
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moose_droppings wrote:
d0nk3yk0n9 wrote:
How long of a tether will this make when fully extended?

The one on the right is made up of 12' of 6mm. It's a little under 2', and all the way extended it's a hair over 3'.

That sounds about right. Mine is about the same size as a 24" sling when shortened up and just at the end of my reach when fully extended.


alexoverhere


Jul 15, 2009, 1:00 AM
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Re: [acorneau] Purcell Prusik [In reply to]
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My first climbing mentor showed me this system (girth hitched to harness tie-in points) and I've used it for about 5 years at rappel stations. However, I've always had a bunch of questions related to the purcell prusik that I could not find answers to. Some of these questions might seem completely retarded, so forgive me for them, and I do appreciate your responses.

1) The OP's link seems to indicate that some sliding of the prusik occurs during a fall. Is it correct that in a fall, the prusik will slide, thereby reducing the peak force of the fall?

2) What happens if you use a 2-wrap purcell prusik to clip into anchors instead of a 3-wrap? Or a different hitch? (I usually use a hedden hitch for many applications and have tried it instead of my purcell "prusik" too). I understand the hitch would slide at different amounts of force, but how does this affect the peak force the climber encounters? More generally, there is an optimal slipping coefficient that would minimize peak force for a specified cord diameter (e.g. 6mm) and specified maximal slipping length (e.g. 2ft) in a factor 1 or 2 fall?

3) Is it a bad idea to use 5.5mm tech cord as a purcell prusik, and why if so? Would it be bad because sliding/slippage could lead to material failure, or because peak forces would be higher because of the material, etc.?

4) I tie an overhand in my purcell prusik about 1.5 inches away from my harness tie-in point and clip my rappel device into the shelf created by the overhand, so that I can extend my rappel device away from me a bit (which makes it easier to clip backup prusik on my belay loop and onto the rope). Is this a bad idea for any reason? Specifically, does the purcell prusik become weaker to a point where I should be concerned?

5) Are there any hitches one can tie on a single line (instead of a loop of cord) that would be suitable for tying into rap anchors? For example, a tautline hitch (http://en.wikipedia.org/wiki/Taut-line_hitch), tied on two separate cords, each of which is tied off to the harness (***NO*** idea how much force that hitch or the others would hold).

Having an adjustable tether is great, but if there was an clutter-minimal way to be clipped into two bolts, that would be even better. I realize that most people just girth hitch two slings (or worse, daisies) to their harness.. I would like something adjustable. And like someone else mentioned, clipping a carabiner to each of the two loops of the purcell prussik does not work well.


alexoverhere


Jul 15, 2009, 1:03 AM
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And I know this is been posted elsewhere, but I wanted to post it here so people could quickly grab a loop of cord or rope and tie a purcell prusik: http://www.pbase.com/phil_box/purcell_tie_in

makes it so easy to tie one.


acorneau


Jul 15, 2009, 7:57 AM
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Re: [alexoverhere] Purcell Prusik [In reply to]
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Hi Alex,

I'll try to hit your points as best as I can.

alexoverhere wrote:
1) The OP's link seems to indicate that some sliding of the prusik occurs during a fall. Is it correct that in a fall, the prusik will slide, thereby reducing the peak force of the fall?

That is my understanding. If you read the paper I referenced earlier in the thread you can see that all the Purcells slipped a certain amount.

In reply to:
2) What happens if you use a 2-wrap purcell prusik to clip into anchors instead of a 3-wrap?

Just more friction: more wraps = more friction.

In reply to:
I understand the hitch would slide at different amounts of force, but how does this affect the peak force the climber encounters? More generally, there is an optimal slipping coefficient that would minimize peak force for a specified cord diameter (e.g. 6mm) and specified maximal slipping length (e.g. 2ft) in a factor 1 or 2 fall?

That's a pretty complex calculation, one that is beyond me. The problem is that every manufacturer's cord has a different sheath/surface so it would be hard to figure out.

In reply to:
3) Is it a bad idea to use 5.5mm tech cord as a purcell prusik, and why if so? Would it be bad because sliding/slippage could lead to material failure, or because peak forces would be higher because of the material, etc.?

I would not use it for two reasons:
1. You want the semi-dynamic properties of standard nylon cord (reduces peak force).
2. Tech cord has much less friction so it may not hold on itself as well as standard nylon. (Recommended knot for Tech cord is a triple fisherman's.)
BlueWater Ropes makes a dynamic accessory cord specifically for stuff like this: http://bluewaterropes.com/...Key=&ProdKey=134

In reply to:
4) I tie an overhand in my purcell prusik about 1.5 inches away from my harness tie-in point and clip my rappel device into the shelf created by the overhand, so that I can extend my rappel device away from me a bit (which makes it easier to clip backup prusik on my belay loop and onto the rope). Is this a bad idea for any reason? Specifically, does the purcell prusik become weaker to a point where I should be concerned?

As you know any knot weakens the material, the question becomes does this knot weaken it to the point of concern...

I've got PMI 6mm cord for mine. Breaking strength is 6.8kN single strand, so theoretically 13.6kN in a loop, 40% reduction for an overhand gives you 8.1kN (~1800 lbs.) You have to decide if that's "good enough" for you.

In reply to:
5) Are there any hitches one can tie on a single line (instead of a loop of cord) that would be suitable for tying into rap anchors? For example, a tautline hitch (http://en.wikipedia.org/wiki/Taut-line_hitch), tied on two separate cords, each of which is tied off to the harness (***NO*** idea how much force that hitch or the others would hold).

I have experimented with a single-line Purcell idea, but I don't have any testing data to prove it's viability, so take it as you will. Take the end of your cord, make a bight and use the end to tie a barrel knot on itself, making something like a noose. Use that loop to tie a prussic back on itself. Once in place, work the slack out until the barrel knot is snug against the prussic hitch.

In reply to:
Having an adjustable tether is great, but if there was an clutter-minimal way to be clipped into two bolts, that would be even better. I realize that most people just girth hitch two slings (or worse, daisies) to their harness.. I would like something adjustable. And like someone else mentioned, clipping a carabiner to each of the two loops of the purcell prussik does not work well.

If you figure that one out let me know!


trenchdigger


Jul 15, 2009, 9:09 AM
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Re: [acorneau] Purcell Prusik [In reply to]
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acorneau wrote:
In reply to:
5) Are there any hitches one can tie on a single line (instead of a loop of cord) that would be suitable for tying into rap anchors? For example, a tautline hitch (http://en.wikipedia.org/wiki/Taut-line_hitch), tied on two separate cords, each of which is tied off to the harness (***NO*** idea how much force that hitch or the others would hold).

I have experimented with a single-line Purcell idea, but I don't have any testing data to prove it's viability, so take it as you will. Take the end of your cord, make a bight and use the end to tie a barrel knot on itself, making something like a noose. Use that loop to tie a prussic back on itself. Once in place, work the slack out until the barrel knot is snug against the prussic hitch.

In reply to:
Having an adjustable tether is great, but if there was an clutter-minimal way to be clipped into two bolts, that would be even better. I realize that most people just girth hitch two slings (or worse, daisies) to their harness.. I would like something adjustable. And like someone else mentioned, clipping a carabiner to each of the two loops of the purcell prussik does not work well.

If you figure that one out let me know!

I've experimented with something similar using a Blake's Hitch, but was unsatisfied with the security of it. One option is to take a short (~4ft) segment of 9mm cord and tie it to your tie-in points with a figure 8. Take a relatively short 5mm prusik and either girth hitch it to your harness or tie it into the 9mm cord retraced 8 (preferred), then tie it into a 3/2 prusik onto the 8mm cord. Finish it off with a carabiner tied to the end of the 9mm cord with a double overhand noose. This system gives more adjustability, but doesn't seem to store away as well as a basic purcell, so I've stuck with the purcell as the standard on my harness.

I use a similar setup in a bag with 50' of cord (and a set of fours on the other end of the cord, stored in a pocket in the bag) for edge protection, etc. while doing tech rescue stuff. The setup was adapted from this http://www.rescueresponse.com/...df/aztek_for_rrg.pdf. Works great!

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