prusiks on skinny rope

[DavidG]

I thought this had been debated at length, but I can't seem to find the relevant thread. I would appreciate thoughts and ideas and links on the following matter:

 

I have a trip coming up with sections of moderate, low angle alpine ice (50 to 60 degrees) and cravasse negotiation. My climbing partner just got some funky new ice floss ( http://www.bluewaterropes.com/dynamicropes/DynamicRopes-8.0mm.htm ). Do I need to go out and get new thinner cord (5.5 mm titan? ) for my prusiks or will my old 7 mm perlon prusiks work fine? Will a fourth wrap with the 7mm cord add enough friction?

 

I've been looking on the web for info, but so far am stymied.

 

Thanks

[Fence_Sitter]

DavidG said:

I thought this had been debated at length, but I can't seem to find the relevant thread. I would appreciate thoughts and ideas and links on the following matter:

 

I have a trip coming up with sections of moderate, low angle alpine ice (50 to 60 degrees) and cravasse negotiation. My climbing partner just got some funky new ice floss ( http://www.bluewaterropes.com/dynamicropes/DynamicRopes-8.0mm.htm ). Do I need to go out and get new thinner cord (5.5 mm titan? ) for my prusiks or will my old 7 mm perlon prusiks work fine? Will a fourth wrap with the 7mm cord add enough friction?

 

I've been looking on the web for info, but so far am stymied.

 

Thanks

 

i have a 7.9 or something mammut... and found that 5-6 mill works with 3-4 wraps, though i would try it as i am sure that sheath friction varies greatly from cord to cord and from rope to rope... just hang your rope somewhere and try it out... that is wha i did and i found i had to tinker a lil bit more to get it 'secure'... my $.02

[Fence_Sitter]

dont use titan! (assuming that is the spectra type stuff) waaaaay to slippery for prussiks i have found... peace!

[Sphinx]

Try it. Personally, I wouldn't use 7 mil prussiks on a 7.9 or 8 min rope. I'd go for 4mil cord, just in case.

[DavidG]

dont use titan! (assuming that is the spectra type stuff) waaaaay to slippery for prussiks i have found... peace!

 

Hmm, titan is indeed spectra, but it has a nylon sheath. I figured that would take care of the problems with slipperyness. Well, I guess I'll have to try it and see who is right. So far it seems that the consensus is that it's better to go with 5mm nylon (breaking strength 579 kg) than 7mm nylon (1181 kg) or 5.5mm titan (1818 kg) due to the need to get enough friction on the ultra skinny rope (8 mm). I guess that makes sense from the point of view that the prusiks in a glacier travel situation are not meant to hold a fall per se ; rather, they are meant to hold body weight or at most 2-3 times that (~200kg for me) during the act of hoisting or self rescue. Is that about the gist of it?

 

By the way the numbers are from here ( http://spelean.com.au/BW/TM/BWtechcrd.html )

 

Thanks

[Beck]

prussiks need to be at 2mm smaller than the rope to work effectively,

 

but you're better off learning the kleimheist!!!

[Figger_Eight]

or get a couple of tiblocs.

[Fence_Sitter]

Figger_Eight said:

or get a couple of tiblocs.

 

i think tiblocs are not effective on smaller diameter ropes... tho mabe with a fatter 'biner?

[Beck]

actually, prussiks are standard rescue protoccol in high angle lifts and lowers, a set of prussiks is used in place of any mechanical devices like tiblocs or ascenders.

 

but you need to make sure you prussiks are at least 2mm less than the rope.... 5 mil works just fine on 8 mm cords

 

and stay away from fancy cordage, spectra type cords are innappropiate for prussiks because they do not take or keep knots well, and are not supple enough for prussiks

 

 

[catbirdseat]

6 mm perlon should work fine with three wraps. Whatever you get, test it first and then you'll know for sure. The thing about prussiks is that more wraps is not necessarily better. If you don't get enough friction with three wraps, switch to the kleimheist.

[Dru]

it might be that with an experience level such that one requires to ask about prussik diameters, sustained 50 to 60 degree blue alpine ice will seem more than "moderate" and not entirely "low angle". just a thought...

[Figger_Eight]

actually, prussiks are standard rescue protoccol in high angle lifts and lowers, a set of prussiks is used in place of any mechanical devices like tiblocs or ascenders.

 

Ummm...so what's your point? There are a lot of things done in rescue scenarios that you wouldn't do on your own trips.

 

Tiblocs can also be placed on pieces when simul-climbing - something that a team might do on 50 - 60 degree ice.

[Coopah]

Beck said:

prussiks need to be at 2mm smaller than the rope to work effectively,

 

but you're better off learning the kleimheist!!!

 

Prusik cord should be 60% - 80% the diameter of the host rope for optimum performance. Therefore in the case of 8mm rope, 5mm (60%) or 6 mm (80%) cord works best.

 

For 10mm-10,5mm rope use 6 - 8 mm cord.

Good old reliable nylon cord works best for prusik cord material. Most of the Spectra or Kevlar blends are too stiff to grab much...

[DavidG]

it might be that with an experience level such that one requires to ask about prussik diameters, sustained 50 to 60 degree blue alpine ice will seem more than "moderate" and not entirely "low angle". just a thought...

 

Ha! Good one dru. So what do you do when a partner of yours proposes to bring a piece of equipment you've never used before (8mm rope)? Of course I am going to try it before the trip, but I'd rather not have to go through the trouble of buying several different diameters of cord for prusiks. Again, the whole 2mm less rule of thumb is just that a rule of thumb. First of all more important than the absolute difference in diameters of the two ropes is the relative diameters (think percentages [thanks coopah]). Finally, while I appreciate the thoughtful and helpful replys (not yours), I was hoping someone might actually be able to give me some real-world info.

 

spray on dru spray on.

[Beck]

we didn't just give some real world info??

 

at least 2mm smaller than your rope, and don't use spectra....

 

is the microphone on?

[Attitude]

Beck said:

we didn't just give some real world info??

 

at least 2mm smaller than your rope, and don't use spectra....

 

is the microphone on?

The headphone drivers are too well coupled.

[IceIceBaby]

Figger_Eight said:

or get a couple of tiblocs.

Yep that said it all it workd with any rope down to 7mm in my exp'

[DavidG]

we didn't just give some real world info??

 

at least 2mm smaller than your rope, and don't use spectra....

 

is the microphone on?

 

Actually several people did give real world info and overall this thread has been very helpful. Thanks , although your example is not real world info. Here is an example of real world info: "well once my partner and I got off route on my attempt up challenger in late season and realized we had to either descend 2000 feet to get back on or ascend a 75 foot section of ice. My partner started leading up the ice and I stupidly didn't put in an anchor before belaying him. He slipped before getting in any gear and I stopped us from going over the precipice by self arrest (whew!). My 6mm nylon prusiks on our 7.9 mm rope held just fine." Or: " A partner of mine and I had a real epic on a trip because he tried using titan cord for his prusiks. The snow bridge he was on collapsed and the gumby couldn't ascend the rope because his prusiks wouldn't grip very well. I had to rig a Z-pulley to get him up. I nearly threw my back out."

 

Thanks Coopah, Fence-Sitter especially, iceicebaby, and catbirdseat.

 

here is an example of non-real world info: " My mountie instructors always told me that the cord had to be 2mm skinnier than the rope, and that spectra did not work."

 

 

Get it? Got it? Good!

[ryland_moore]

I have used a 6mm perlon on a friend's 8 mm Ice Floss and had no problems. It was in practice and never had to be used in a rescue, but I could prussik up without any incident.

[mtngrrrl]

Testing is a good idea. Test with a wet rope, too, if you can. That's when I found out my nylon prusiks slipped on a 10.? rope without an extra wrap. I have a loop tied off at the top of the foot prusiks, and squeezing an extra wrap through it was pretty tough. I have not tested my prusiks on my skinny ice lines though, so I'll be interested to hear what you come up with.

 

This site has good photos of the various friction knots:

http://www.chockstone.org/TechTips/prusik.htm

 

[Thinker]

mtngrrrl said:

Testing is a good idea. Test with a wet rope, too, if you can. That's when I found out my nylon prusiks slipped on a 10.? rope without an extra wrap. I have a loop tied off at the top of the foot prusiks, and squeezing an extra wrap through it was pretty tough. I have not tested my prusiks on my skinny ice lines though, so I'll be interested to hear what you come up with.

 

I 2nd that! Test em on WET and ICY ropes before drawing a firm conclusion about the diameter of cord to use on a skinny rope.

[Attitude]

DavidG said:

Thanks Coopah, Fence-Sitter especially, iceicebaby, and catbirdseat.

 

here is an example of non-real world info: " My mountie instructors always told me that the cord had to be 2mm skinnier than the rope, and that spectra did not work."

 

 

Get it? Got it? Good!

Heh, catbirdseat is a mountie instructor.

 

Do you get it now? Good.

 

Do you get it now? Good.

 

Do you get it now? Good.

 

....

[DavidG]

Just so you guys don't start scanning the obituaries, be assured that I will be testing 6 and 5mm nylon cord on the ice floss in wet/ icy conditions prior to risking my life to it.

 

That said, even Attitude should be able to see the essential difference between GETTING advice from a mountie instructor (catbirdseat apparently), and GIVING second hand advice without ever actually having direct experience. Although perhaps I'm being too optimistic.

 

I'll revive this thread when the testing is done..... may take a while.