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sactownclimber
Feb 11, 2005, 10:01 PM
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Just curious what diameter accessory cord everybody uses for their prusiks, and whether or not a change in diameter effects the effectiveness of the knot.
--J
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tchamber
Feb 11, 2005, 10:08 PM
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I like good old 7mm Perlon. It's light, has a good hand to it, and with a double fisherman, it will hold a fall with no questions.
You could go thicker, but it would be heavier.
You could go thinner, but then you're getting into shady area if you put a lot of stress on the prussik (i.e. fall on it)
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ryan112ryan
Feb 11, 2005, 10:10 PM
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i use 7mm its a good size i like it :) anyone know the fail point (Kn) of the prusix?
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mr-pink
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Feb 11, 2005, 10:13 PM
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7mm
it really makes a differance, the diameter, in strenght and whether it will slide.
i take 2m of 7mm and make dubble fishermans. then i wrap the prussic arround 4 times. works always.
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tchamber
Feb 11, 2005, 10:18 PM
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2m would be a little long for me. I think mine are 3' lengths tied in a loop to make 1.5' prussik loops.
7mm perlon has a tensile strength of ~9kN. But if you double it into a loop (i.e. prussik or cordelette), you are weighting 2 strands at the same time, so theoretical strength of a 7mm perlon runner is ~18kN. At least that's my understanding.
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tchamber
Feb 11, 2005, 10:19 PM
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2m would be a little long for me. I think mine are 3' lengths tied in a loop to make 1.5' prussik loops.
7mm perlon has a tensile strength of ~9kN. But if you double it into a loop (i.e. prussik or cordelette), you are weighting 2 strands at the same time, so theoretical strength of a 7mm perlon runner is ~18kN. At least that's my understanding.
I hope this doesn't double post...
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whatsupdoc
Feb 11, 2005, 10:29 PM
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I use 6 mil perlon. I make 'em the same length as shoulder-length slings, that way they're easy to carry over the shoulder if necessary. They're plenty strong enough for use as ascenders, escaping the belay, rap anchors etc, as these are static loads and not high stress falls. You might want to use 7 mil if you ever wanted them to double as slings in a pinch. Most slings also work fine in a klemheist knot for the same purpose, even spectra ones in my experience. Nylon grips better supposedly, but I've practiced ascending a rope with spectra slings and I had no problem.
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mcumbrae
Feb 11, 2005, 10:36 PM
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I understand that a prussik loop can be made of smaller diameter cord if used as an autoblock... what would be the smallest diameter acceptable for this especific use, below the belay device?
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trad_mike
Feb 11, 2005, 10:52 PM
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Yes the diameter does matter. You need about a 4mm difference between the prussik and the rope diameter for the prussik to bite well. The prussik itself only has to hold body weight. 5 mm works fine for under 10 mm ropes. 6 mm works great up to 11 mm.
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papounet
Feb 11, 2005, 10:55 PM
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the reason to go for a smaller diameter is that the amount of grip of most kind of autoblock knots (prussik , machard, kleimheist) is directly linked to the ratio diameter of cordelette vs. diameter of rope(s).
(because of "turning ratio" or bending capability of cordelette).
If you need some convincing try to do a prussik with your own rope on itself ;-)
for example, one may choose
to do an autoblock on 2x 8.1, a 6mm
to do an autoblock on 2x 9.7, a 7mm
some people go actually for a larger diameter and then make remove one core bundle or slip the sheath ove the core to get softer (ie griper) large diameter
Please go rent and watch the Bond movie when 007 uses his climbing shoes laces to make ascenders prussiks while climbing in the meteors region. that was actually good and proper technique.
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dirtineye
Feb 12, 2005, 1:14 AM
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In reply to: Just curious what diameter accessory cord everybody uses for their prusiks, and whether or not a change in diameter effects the effectiveness of the knot. --J
Yes, it does.
The 4 turn prusik is a better idea than the three turn, there's an article about that somewhere on one of the climbing safety sites.
All these people advising a prusik cord diam without knowing the rope diam you will use the prusik on, I wonder have they ever tried a 7 mm prusik on an 8.1 rope?
I believe a three mm difference is a good starting point.
All mine are 5mm, cause I climb on 8.1 and 8.5 as well as 10.5 and 11.
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vegastradguy
Feb 12, 2005, 2:04 AM
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i use 5mm as well- because i climb on 8.6 doubles and 7.5 twins for the most part.
i'd use a 6mm cord if i still used my single 10.2....
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lucas_timmer
Feb 12, 2005, 1:40 PM
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I use 7mm accesory cord(8 kN), on a 10,5 mm beal rope
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punk
Feb 13, 2005, 12:59 AM
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in my book 5<7 mm with 6MM best
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scgreene2000
Feb 13, 2005, 1:23 AM
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In reply to: Please go rent and watch the Bond movie when 007 uses his climbing shoes laces to make ascenders prussiks while climbing in the meteors region. that was actually good and proper technique.
What Bond movie is this?
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walrus
Feb 13, 2005, 3:32 AM
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I believe it is the one where he is in Vegas and drives around the moon buggy and has the chick in the red mustang. Connery is Bond.
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pico23
Feb 13, 2005, 3:45 AM
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not really sure why the Kn rating matters with a pussik. It's generally not being shock loaded. Not for autoblocking anyway.
I use 5mm. I typically use nothing thicker than a 10.5 and usually for longer stuff we use eithe a 9.6 or double 8.5mm. In either case 6 or 5mm is much more suitable than 7mm. 3 7mm prussiks (2 shoulder lenght and one foot stirups) would be insanely bulky. My 5mm packs down nice and tight in a ball on my harness.
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dirtineye
Feb 13, 2005, 3:46 AM
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If you are talking about the one where bond is climbing up to the lair on the mountain, the guy that actually did the fall is Rick Sylvester.
He's a nice guy.
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jimdavis
Feb 14, 2005, 4:13 AM
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About the Spectra use, Spectra melts around 200 degrees F. As you should know from using a belay device, friction causes heat.
Spectra is also slippier than Nylon.
If the Spectra slips under tension, and it will (creating friction,) it'll heat up.
I remember hearing from an AMGA certified Rock and Alpine guide that a rope will hot-cut through 1" tubular webbing in less than 30 feet under a normal load. It could have been less than 15 feet. Nylon also has about twice the melting point of Spectra. (It was a long day when i heard that, so my number might be a little off)
So, play it safe and stick to Nylon for friction hitches.
Cheers,
Jim
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harrisha
Feb 14, 2005, 4:24 AM
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In reply to: In reply to: Please go rent and watch the Bond movie when 007 uses his climbing shoes laces to make ascenders prussiks while climbing in the meteors region. that was actually good and proper technique. What Bond movie is this?
It's either Connery or Moore. The plot is that Bond is recovering a device off a sunken British ship off the cost of Greece. The Bond girls parents were killed by the bad guys so she gos after them with a cross bow and thats how she and 007 hook up.
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jimdavis
Feb 14, 2005, 4:41 AM
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Yeah, i thought it was Moore. Was it the spy who loved me?
Jim
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mcumbrae
Feb 15, 2005, 7:59 AM
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So... from all this i get that a prussik made of 8mm cord will not grip properly on a 10.5 rope... am i correct? Even if i´m rapping on both strands of the rope?
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antigrav
Feb 15, 2005, 9:00 AM
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In reply to: ... Strong enough to hold you. Generally you probably won't be falling too far onto a prusik so hopefully you won't be pushing the limits of the prusik's strength. Here's a website I found on the tensile stregnth of cordlettes: http://www.nrsrescue.com/...fid=1844&deptid=1620
If you use the prusik as a backup when rapelling etc., i.e., used to connect yourself to a climbing rope, and not some bolt or similar, remember that the force on the prusik will not exceed the impact force of your rope, i.e., between 8-10 kN most likely. This is irrespective of how far you fall.
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veganboyjosh
Feb 15, 2005, 10:45 AM
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i know from reading elsewhere and from this thread that it's important to have a margn of 4-5 mm between the prussik(s) and the rope. a smaller margin won't work as good.
does anyone know if it's possible to have too high of difference? does it matter on this end?
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