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Purcell prusik slings as Screamers?


Original Post
SS Minox · · Unknown Hometown · Joined Jun 2015 · Points: 5

Is it absolutely crazy to use Purcells as slings? They are adjustable, and should provide some shock absorption before the prusik bites itself in half. Do you guys know of any tests?

The walls have never been climbed & are all limestone & dolomite with bad rock, mud, shattered stuff etc deep underground

Rick Blair · · Denver · Joined Oct 2007 · Points: 268

Shock loading a friction hitch? What could possibly go wrong?

Nick Sweeney · · Spokane, WA · Joined Jun 2013 · Points: 650

Do not do this. /topic

Rick Blair · · Denver · Joined Oct 2007 · Points: 268

This is what you want. Kong KISA. Maybe

SS Minox · · Unknown Hometown · Joined Jun 2015 · Points: 5

Yes, ok. But are there any tests on the strength of the purcell loop as an adjustable runner? A normal dyneema runner just breaks since it is completely static. I want to know how weak it is. Does it snap at the friction hitch, or at the single strand, or the knot?

I love the idea with that Kong device, had forgotten about those.

Rick Blair · · Denver · Joined Oct 2007 · Points: 268

Best demo ever of artificial textile on textile friction

youtube.com/watch?v=9A1hX2T…

baldclimber · · Ottawa, Ontario, Canada · Joined Jul 2015 · Points: 0
SS Minox wrote:Is it absolutely crazy to use Purcells as slings? They are adjustable, and should provide some shock absorption before the prusik bites itself in half. Do you guys know of any tests?
Here, let me search that for you
mountainproject.com: can-prusiks-be-shock-loaded?
SS Minox · · Unknown Hometown · Joined Jun 2015 · Points: 5

https://m.youtube.com/watch?v=x43El8zzjAM

Found this, which is not the same, but it looks like the Purcell will strip its sheath

Brian L. · · Unknown Hometown · Joined Feb 2016 · Points: 90

You should ask Eric Moss. I hear he's an expert on these kinds of things.

Jerome Penner · · Louisville KY · Joined Feb 2016 · Points: 30

https://www.youtube.com/watch?v=1_xOq3uoQQo

keithconn · · LI, NY · Joined Jan 2015 · Points: 35

"Can I do this?"

"Don't do that!"

"Like this?"

"Seriously, don't do that!"

"No, like this."

"Don't do it ... you know what, do whatever you want."

Joe Manlove · · Sonora, CA · Joined Jan 2009 · Points: 108

I pull tested a few for SAR applications. They fail at about the breaking strength for a single strand of the cord they're made out of. They clutch (slide under load) about half the time. You'd be better off using a sewn daisy chain. At least, that'll make 20kN. (For the record, it's still a terrible idea.)

Never do this.

Chase Bowman · · Baton Rouge/Durango · Joined Jan 2014 · Points: 560

personally I would just use a bungee cord.. screamers start getting expensive if you suck as much as I do.

SS Minox · · Unknown Hometown · Joined Jun 2015 · Points: 5

Dynamic rope loops as runners?

Rick Blair · · Denver · Joined Oct 2007 · Points: 268
SS Minox wrote:Dynamic rope loops as runners?
Impractical but safe.
SS Minox · · Unknown Hometown · Joined Jun 2015 · Points: 5

I found a thread that was putting ~6kn on the top runner, that kind of fall is too close to the 7.5kn the Purcell should hold. The nuts I have are rated at 8.5kn, so that's close, but not good enough.

CornCob · · Sandy, UT · Joined Nov 2012 · Points: 20

Just out of curiosity, what is your reason for wanting a screamer over a standard runner? You state concerns about dyneema runners "just breaking". They do break, but at forces exceeding 22kN (well beyond your 8.5kN nut). Your lead rope will provide enough dynamic stretch to essentially render any individual piece negligible in terms of dynamic vs static.

John Wilder · · Las Vegas, NV · Joined Feb 2004 · Points: 1,530
SS Minox wrote:I found a thread that was putting ~6kn on the top runner, that kind of fall is too close to the 7.5kn the Purcell should hold. The nuts I have are rated at 8.5kn, so that's close, but not good enough.
Perhaps we should ask- what kind of climbing are you doing that you need this kind of thing? 8.5kn stoppers are fine for normal trad falls- I wouldn't be overly concerned about them failing or reducing the load on them.

It's pretty rare to need screamers- that's generally reserved for really marginal gear like RP's and copperheads and such.
SS Minox · · Unknown Hometown · Joined Jun 2015 · Points: 5

I am not sure I can afford the next piece blowing, I had considered using the Purcell only because I have it available. Never heard any actual numbers on it. I am worried about providing a soft catch so as not to blow a single second piece.
So far, I managed to shear off up to 100lb pieces of the wall with cam placements, etc. If something like that ever shears off attached to me, it's going to be a trip.

CornCob · · Sandy, UT · Joined Nov 2012 · Points: 20
SS Minox wrote:So far, I managed to shear off up to 100lb pieces of the wall with cam placements, etc.
Sounds like you need to work on your judgment for gear placements more than using stretchy gear. Did you put a cam behind a small flake or next to a loose block or something?

Edit: Also, the soft catch should be coming from your belay, not your gear.
Em Cos · · Boulder, CO · Joined Apr 2010 · Points: 5

If this is a frequent concern, it sounds like your time would be better spent working on your gear placements. The dynamic rope provides plenty of energy absorption for most of the gear on your rack in most situations, which is why nylon or dyneema runners are standard and screamers are a special purpose piece.

Guideline #1: Don't be a jerk.

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