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Squamish, British Columbia
Canada
1008 Posts |
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 | Dru
Mountain Grammar Police
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 Sardonic sandbagging scoundrel, Cascade Climbers lobotomized spraymeister, space blanket flyer, new millennium vulgarian betaboy and friend to all squids
Climbing, a mountain
Canada
∞ Posts |
Posted - 03/19/2012 : 8:16 PM
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| Swap out the cord prusiks for Tiblocks. |
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Finally stopping that crazy suffering that is ice, climbing to concentrate on great ski tours!
3505 Posts |
Posted - 03/19/2012 : 8:16 PM
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| Use an ATC to mind the prussik. I'm using the same rig (8mm Rando with 5mm cord) and I'm carrying an ATC for that very reason. |
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Kootenay Bud
2695 Posts |
Posted - 03/19/2012 : 8:30 PM
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| He wants something to reduce friction. Neither an ATC nor Tiblocs will do that. What about the Petzl mini prusik minding pulley that is supposed to do ropes 7 to 11 mm. Alternatively, do more wraps with 6 mm cord, because most people don't use 5 mm cord for that application. |
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Surrey, BC
Canada
1036 Posts |
Posted - 03/19/2012 : 9:05 PM
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Do you want to put up a picture of your set up? I remember this issue came up last spring when we were doing rescue practices with Justin, otherwise I am with Sandy on this one.
Come out and join Justin in his numerous practices.
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Edmonton, Alberta
Canada
797 Posts |
Posted - 03/19/2012 : 9:36 PM
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Glad to hear some other people are using 5mm cord with an 8mm rope. This is my glacier set up too...and have wondered about the strength rating of the 5mil.
I decided to go with it anyway because you shouldn't ever be only relying on the prussik without having it backed up.
Even with multiple wraps of 6mm I couldn't get it to grip (because getting soft supple prussik cord seems impossible). |
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north van, bc
Canada
940 Posts |
Posted - 03/19/2012 : 9:50 PM
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| bachmann hitch with a beiner instead of pussik |
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north van, bc
Canada
940 Posts |
Posted - 03/19/2012 : 10:13 PM
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quote:
Originally posted by booewen
Glad to hear some other people are using 5mm cord with an 8mm rope. This is my glacier set up too...and have wondered about the strength rating of the 5mil.
I decided to go with it anyway because you shouldn't ever be only relying on the prussik without having it backed up.
Even with multiple wraps of 6mm I couldn't get it to grip (because getting soft supple prussik cord seems impossible).
looking at mec 5mm static is 500kg. a loop is going to hold 700kg = (500kg x 2 strands - 30% for knot) this is srong enough to hold a good top rope fall although on the edge and not something I'd try. (would hold 7KN, top rope falls around 6KN) this is more then enough to hold a hanging person. ~1KN (rapping puts about 2KN on an anchor)
add the friction of the snow edge and the 8mm rope on top is holding less then the weight of the person.
looking at the 3:1 picture. I'd say the minding pussik cord is holding body weight (when 8mm not not being pulled), but the traveling pussik cord would be holding 2x the hanging weight since it's on the backside of a 2:1 pulley. under 2KN force on the 7KN rated cord.
you'd want to keep the miding prussik as short as possible. because if the traveling pussik broke, the miding one is backing up the person from droping, but now you're into falling forces on that pussik instead of static ones. and aproaching the limits of a 5mm on a fall. but the traveling one shouldn't be breaking under static loads of the raise.
This is just my rookie observations. feel free to corect me
booewen how would you back up the pussiks? the minding one can be backed up with a figure 8 while building the pulley system, but has to be removed to use the system.
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Edited by - smac on 03/19/2012 10:34 PM |
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Edmonton, Alberta
Canada
797 Posts |
Posted - 03/20/2012 : 07:19 AM
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quote:
Originally posted by smac
booewen how would you back up the pussiks? the minding one can be backed up with a figure 8 while building the pulley system, but has to be removed to use the system.
Backed up in the sense of a prussik is never the only point of contact with the anchor (the person in the hole should be tied off on the actual rope to the anchor somewhere...probably on the rope they fell in on).
If your maths is right...it makes me feel a lot better with my skinny prussiks! |
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Kootenay Bud
2695 Posts |
Posted - 03/20/2012 : 07:36 AM
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It's usually the tech cords that are slippery and don't hold prussik, klemheist or similar knots well. Plain old nylon usually works fine. Personally, I wouldn't be using that 5 mm cord for a climbing application unless you have one of the tech cords in a 5 mm. In which case, I still don't think I'd use it as the strength losses due to knots are greater, they melt at lower heat, and break sooner when subject to repeated flex cycles.
MEC's plain old nylon 5 mm cord is only rated to 500 kg, while the tech cord at 5 mm is 2270 kg, but again, you're into all the conundrums of using tech cord not nylon.
I assume by backing up, he means when climbing the rope using prussiks, he is tying a figure 8 knot on the rope behind him and clipping in every so often. Prussik fails, he falls to figure 8 knot instead of all the way back down. |
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Squamish, British Columbia
Canada
1008 Posts |
Posted - 03/20/2012 : 08:48 AM
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quote:
Originally posted by Dru
Swap out the cord prusiks for Tiblocks.
I'll have to get a tiblock to test that system out. I like prusiks as they are simple enough to setup with one hand should I need to build an anchor while arresting a persons who has fallen into a crevasse. It will add another biner into the system though. I'm looking to simplify the system and reduce friction were possible.
Note: This setup is purely for crevasse rescue where the person has already fallen and is being rescued. The 5mm prusik is for holding the static load of someone in a crevasse. Once I've freed myself from the system it would be obviously backed up before I'd undo my figure 8 on a bite.
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Finally stopping that crazy suffering that is ice, climbing to concentrate on great ski tours!
3505 Posts |
Posted - 03/20/2012 : 09:07 AM
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5mm (or any size) static cord should never be used in a dynamic situation, so static load is the only important measure.
The cord is used to unload the rope during the anchor building process. Once the anchor is built, the rope is then tied into the anchor. Don't rely on the prussik to hold the fallen climber during the rescue.
One note about Tiblocs: they're light and work well, but novices should practice using them, as they do have teeth and can damage the rope. No one has shredded a sheath with a prussik. |
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| Dru
Mountain Grammar Police
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Sardonic sandbagging scoundrel, Cascade Climbers lobotomized spraymeister, space blanket flyer, new millennium vulgarian betaboy and friend to all squids
Climbing, a mountain
Canada
∞ Posts |
Posted - 03/20/2012 : 09:57 AM
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quote:
Originally posted by johngenx
No one has shredded a sheath with a prussik.
Heh. I saw a guy once who had been using a prusik on a fixed rope to solo toprope. You should've seen what happened to the prussik, and the rope, when he took a fall on the slack in the prussik. |
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Kootenay Bud
2695 Posts |
Posted - 03/20/2012 : 10:17 AM
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People use cord all the time in dynamic situations to tie together multiple anchor points to create a master point. Which is one reason why lots of people don't use tech cords because they have very little stretch whereas nylon cord has some stretch which reduces forces on anchors, in the event that someone falls directly onto the anchor.
A lot of people like to use a prussik with a munter mule as the brake prussic, because then, if need be, you can at least lower the climber a short distance (length of your cordelette), whereas with a Tibloc, you are not going to be able to do that. You also can't do that with a really short prussik. I'm not a fan of Tiblocs and wouldn't want to be trusting one as the brake in a rescue situation, as multiple people have reported that they don't hold well on icy or wet ropes, or thin ropes, or have shredded their ropes. |
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| Dru
Mountain Grammar Police
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Sardonic sandbagging scoundrel, Cascade Climbers lobotomized spraymeister, space blanket flyer, new millennium vulgarian betaboy and friend to all squids
Climbing, a mountain
Canada
∞ Posts |
Posted - 03/20/2012 : 10:43 AM
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quote:
Originally posted by sandy
multiple people have reported that they don't hold well on icy or wet ropes, or thin ropes, .
Ridiculous. The little teeth hold better than a cord on wet and icy ropes.
Plus you can use them, or a ropeman, for the simul-belay if you don't mind the sketch factor
http://www.gravsports.com/Ice%20pages%20Folder/Route%20Descriptions/howse_of_cards_1100m.htm
Also you can open a beer with a Tibloc but not with a prusik. |
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Maple Ridge, BC
Canada
344 Posts |
Posted - 03/20/2012 : 12:20 PM
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quote:
Originally posted by Dru
Also you can open a beer with a Tibloc but not with a prusik.
That sounds like a challenge. If people can make bongs out of apples, I bet someone in the amateur chemical engineer crowd would figure it out. |
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Squamish, British Columbia
Canada
1008 Posts |
Posted - 03/20/2012 : 1:09 PM
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Ok I'd like to leave the prusik's in the system. I'm trying to be as real-world with this set up as possible. I will always have prusiks with me as they can have other uses, but I may not always have a tiblock on my rack.
Is there no pulleys that mind 5mm rope?
If getting a different pulley isn't an option can anyone recommend some good 6mm static cord that they know to bite consistently as a prusik on an 8mm rope. Also, if you do use 6mm cord how many wraps are you doing when setting up the prusik. |
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Vancouver, BC
Canada
874 Posts |
Posted - 03/20/2012 : 1:17 PM
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quote:
Originally posted by Cherry Pirate
quote:
Originally posted by Dru
Also you can open a beer with a Tibloc but not with a prusik.
That sounds like a challenge. If people can make bongs out of apples, I bet someone in the amateur chemical engineer crowd would figure it out.
That doesn't sound difficult. Apply grease to the neck of a capped beer bottle and place the prussic around it. Draw the bottle down with sufficient force to pull the cap off.
Now, if you can open a beer bottle with an apple or make a bong out of a prussic, I will be impressed.
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1064 Posts |
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Kootenay Bud
2695 Posts |
Posted - 03/20/2012 : 4:06 PM
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Nylon static cord, not slippery tech cord - do you know which cord you have? It does sound as if you have tech cord which is notoriously slick.
Wrap as many times as need be. Try a klemheist if you like instead of a prussic knot.
My pulleys are not even prussic minding pulleys and they work to mind the prussic even on an 8 mm rope, so I am not clear why your pulley is not working. It almost sounds as if your slippery tech cord is not biting properly. If you use your prussics for other purposes (e.g. anchors), I would be real cautious with that 5 mm cord.
I guess you could just use a garda knot and dispense with the prussic altogether, but those introduce a lot of friction and again you can't lower at all with that system. |
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Squamish, British Columbia
Canada
1008 Posts |
Posted - 03/20/2012 : 7:01 PM
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quote:
Originally posted by sandy
Nylon static cord, not slippery tech cord - do you know which cord you have? It does sound as if you have tech cord which is notoriously slick.
Wrap as many times as need be. Try a klemheist if you like instead of a prussic knot.
My pulleys are not even prussic minding pulleys and they work to mind the prussic even on an 8 mm rope, so I am not clear why your pulley is not working. It almost sounds as if your slippery tech cord is not biting properly. If you use your prussics for other purposes (e.g. anchors), I would be real cautious with that 5 mm cord.
I guess you could just use a garda knot and dispense with the prussic altogether, but those introduce a lot of friction and again you can't lower at all with that system.
I'm using this cord:
http://www.mec.ca/AST/ShopMEC/Climbing/RopesCordage/StaticRopeCord/PRD~0403-048/mammut-5mm-static-cord.jsp
The cord is biting fine, the issue is that my pulley (this one: http://www.mec.ca/AST/ShopMEC/Climbing/UppersDowners/Pulleys/PRD~4015-189/smc-mini-cr-prusik-pulley.jsp) does not mind the prusik. The prusik gets pulled up inside the pulley. |
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Prusik minding pulley for 8mm rope?
