WTF? Spectra/Dyneema cord as prusik??

[korup]

A friend, (semi-newbie climber) went to a climbing shop in Seattle (and not the big box) and was told by a salesperson that it is A-OK to use skinny Specta/Dyneema runners as prusiks.

 

OK, so before I head in there and go apeshit about melting point and the FACT THAT THEY AREN'T EVEN ROUND, is there any chance there is new info out there I am not aware of?

[G-spotter]

Forget your "not even round" point, you can use flat webbing with Bachmann/Kleimheist knot just fine. Melting point and slipperiness are the main drawbacks.

[woodchips]

I've seen one of my (way more experienced than I) climbing partners do this with one of my 8mm dyneema runners. I let him keep the runner when he was done.

 

Were they talking about dyneema cord (which has a dyneema core and nylon sheath, I think) or solid dyneema runners (like the mammut ones)? I think it might be OK with the cord, as the core is pretty well protected; it's just kind of stiff.

 

 

[underworld]

i don't think you can put a blanket of whether they are ok for prusiks. what's the prusik used for? need to go on a fixed line? is it part of an anchor? etc etc...

 

there are a ton of uses for prusiks. i would be fine using the skinny stuff for some applications and would lean away from it in others.

 

i wouldn't go 'apeshit' up at the local shop quite yet...maybe talk to em about it tho. each might learn something

 

 

[Bill_Simpkins]

I've tried this and they are slick. Bad idea. Cord is so lite anyways and cheaper.

 

If your trying to pull your buddy out of a crack with that and it slips and they get hurt or die, you're going to feel really stupid.

[Figger_Eight]

If it were the only thing I had around I wouldn't have any problem using it as a friction know - but I'd probably set it up as a klemheist because it is slippery. If it were used as a prusik you can mitigate it up by wrapping it 3 or 4 times.

 

It's not the ideal thing and I may retire it as a "full strength" runner once used that way, especially if it was used as a rappel backup.

 

But yeah...cord is the right choice.

[Wastral]

Dyneema line has Nylon sheeth, so your friction for your prussic is based on nylon. Dyneema/Spectra is made from HDPE which does have a lower melting point than nylon.

 

It is stiffer, thus you would need another loop in the prussic arrangement. What is wrong with cheaper 6mm nylon??? You have to have backup prussic loops for rescue situations anyways. If you don't and your partner doesn't have any back up prussic loops you are royally screwed till he can get the calvary there because you need spare prussics to A) tie off and B) rescue your buddy.

 

Why is the temperature point even relevant??? You are not belaying through your prussic loops where you will have continuous friction!!! If you are, something is wrong. Crevasse rescue is also basically a static endeavor, so once again dyneema would be perfect fine there also.

 

In short there is no problem with Dyneema/Spectra line/webbing for prussics and cordage. It is stiffer and harder to work with, but 5x stronger for same diameter/thickness as nylon creating lighter climbing racks.

 

Brian

[korup]

I should restate.

Obviously, in a rescue situation, I would use anything at hand and feel fine about it.

 

However, my friend says he was told that this was the normal and correct way to do it. Dyneema runners are slippery, melt (think of a wet rope with sand/gravel) and are simply not a good choice if other options are available, safer, and ahem, cheaper.

Edited June 17, 2008 by korup

[mkporwit]

In the self-rescue courses that I've been in, it has been perfectly acceptable to use spectra cord for a prusik or kleimheist on a rope as long as the hitch does not move relative to the rope. So something like a spectra cord kleimheist on an ETO would be just fine.

 

If you're keeping the hitch open and letting the rope run through it, like you might do with a tandem prusik belay or an autoblock, then the rope slipping past the same parts of the hitch can lead to damage of the spectra and should be avoided.

[Figger_Eight]

For clarification: anytime you see white, that means it's spectra. The Mammut skinny slings, for example, are almost entirely white because that's what they're almost entirely made out of.

 

 

[billcoe]

If it were the only thing I had around I wouldn't have any problem using it as a friction know - but I'd probably set it up as a klemheist because it is slippery. If it were used as a prusik you can mitigate it up by wrapping it 3 or 4 times.

 

It's not the ideal thing and I may retire it as a "full strength" runner once used that way, especially if it was used as a rappel backup.

 

But yeah...cord is the right choice.

 

Damn, now I have to change my practices and rethink this. I love this site.

 

I rarely use them as prussics, but yeah, couple of extra wraps they work fine and get pressed into service as prussics on occasion. I suppose that I haven't really done this to the real skinny ones, but the wider older ones that typically date to 1992 - 1994 or so and have been retired from lead climbing. I don't use backups on raps, only to get back up the line if I screw up while cleaning, use as a backup descending on a fixed line or just want to climb out solo. It may be an aversion to carrying extra crap like dedicated 6mil prussic cord that I only have to use maybe every 6 months, yet that dangle down all the time to catch on stuff. It may be a practice carried over when tied slings were used for all kinds of things and general use prized and maximized, including prussics. If you already have the over the neck sized slings, then they can get used for all kinds of stuff. Doubled up as draws, tossed over a horn for pro or rapping, as a full length runner, around a tree for rapping...etc etc.

 

The hard question that arises is does the earlier pull testing Joseph conducted that showed frightening decreases of strength in a short time of the real skinny 8mil Mammut dynema linked to these practices at all?

 

Hmmmm. ??!

 

I'm gonna be careful, but may (probably am) be too old to change practices anyway...

[mike1]

I think it's very poor advice from a salesperson. If someone is asking questions like that of a salesperson then they likely aren't very experienced. I say, march in there and let ‘em have it!

[JohnGo]

In the self-rescue courses that I've been in, it has been perfectly acceptable to use spectra cord for a prusik or kleimheist on a rope as long as the hitch does not move relative to the rope. So something like a spectra cord kleimheist on an ETO would be just fine.

 

If you're keeping the hitch open and letting the rope run through it, like you might do with a tandem prusik belay or an autoblock, then the rope slipping past the same parts of the hitch can lead to damage of the spectra and should be avoided.

 

This is a thoughtful sensible answer, and one I personally feel is correct. The distinction between a "fixed" and a "moving" knot is important.

[campwire]

I haven't actually seen dynamic testing with spectra or dynema used as a prussik, so can only speculate. The testing I have seen with nylon showed the failure was due to friction heating up the material and melting it. In the tests I witnessed the friction was caused by not pre-tightening the knot in the webbing loop enough and one side of the webbing loop lengthening as the knot tightend. The webbing failed at the pin, not the knot due to heat generated with friction. Back when I was a kid I would prusik up a rope and then use them to slide back down. I melted more than one prusik that way. I personally would not use materials with lower melting points in friction situations like prusik or percell unless I had no other option.