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j_dub
May 26, 2004, 4:52 PM
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I just bought 6mm cordelette for prussik loops. I got 4 foot lengths of cord, tied the double-fisherman's, and (to my dismay) noted that the loops are only 14 inches. This seems a big short. When I tie a prussik in one of them, I have a 6" loop, which won't reach from my harness (especially with a girth hitch in it) to the rope. :evil:
What is the usual length for prussik loops? 24"? Longer? I did a search on this and looked in my climbing books, but didn't find a guideline for prussik loop size (just how to make them and use them).
Any help would be greatly appreciated; I have to go buy more cord today. :?
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vegastradguy
May 26, 2004, 5:09 PM
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mine are about 15" long.
usually, if using prusiks (or bachmann/klemheist), you would clip a carabiner into the loop, then clip your daisy/sling onto that.
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j_dub
May 26, 2004, 5:16 PM
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Ok. Mine are about 14". I'm using them for rappel back up and self-rescue (if needed). I guess I could clip them to a sling if they need to be longer. (*kicks self for not thinking of this*). Obviously I'd do that if I had to ascend a rope.. just didn't occur to me in the context of a back up for rappel.
Those things just seemed so short when I tied them! Thanks. :)
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jorian_nl
May 26, 2004, 5:19 PM
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I recommend twice the length from the ground to your nose.
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vegastradguy
May 26, 2004, 5:22 PM
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for a rappel backup, a 24" nylon sling rigged as an autoblock and clipped to your leg loop without a sling works perfectly. i prefer this to most other methods of rap backup.
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fitzontherocks
May 26, 2004, 5:23 PM
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How long are the tails on your double fisherman's knot? I, too, bought 4' lengths, tied double fisherman's and ended up with about a 15-16" loop, which works fine for me. Also, how many wraps do you take with your Prussik? About three works foe me. You can wrap it more times, but it eats up the length. Like vegastradguy, I clip the loop with a biner, and the length seems perfect. I usually back up above the belay device, so I sometimes extend the prussik with a quickdraw. And the math: a 14" loop = 28" So your fisherman knots and tail are 12", or 6" per end? That's about right.
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dirtineye
May 26, 2004, 5:24 PM
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HEHE you can't girth hitch a prussik to another closed loop!
(you can girth hitch the start of an autoblock, but you still have to clip the end to a biner)
BUT, And I hope you are using 4 wrap prussiks, if you start with 5 feet of cord you should be able to get a two foot loop ( after tying the joining knot) to practice with, and shorten it accordingly to suit your needs.
Now if you want one for a rappel backup, your 14 incher might be fine, just check it out ( thath's where you make a prussik below the device and use a locking biner to connect to your leg loop)
You actually want to have enough slack below the prussik to work with while ascending. ( if that is what you want it for) The same thing is true for escaping a rappel Feckup-- you need ehough room to work. You can always slide a long one up, but you can't do much with a short one right on top of the mess you are trying to fix.
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rockmaninoff
May 26, 2004, 5:25 PM
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I also found 4' to be a bit short for my taste. I tie the double fisherman's with a 4" tail from a 5' length of cord.
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jt512
May 26, 2004, 5:35 PM
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In reply to: I just bought 6mm cordelette for prussik loops. I got 4 foot lengths of cord, tied the double-fisherman's, and (to my dismay) noted that the loops are only 14 inches. This seems a big short. When I tie a prussik in one of them, I have a 6" loop, which won't reach from my harness (especially with a girth hitch in it) to the rope. :evil: What is the usual length for prussik loops? 24"? Longer? I did a search on this and looked in my climbing books, but didn't find a guideline for prussik loop size (just how to make them and use them). Any help would be greatly appreciated; I have to go buy more cord today. :?
The length depends on your height and reach. Sorry, I don't have a formula but, whatever length you choose, be sure to test it. Tie your prussik loop onto a fixed rope using a prussik knot and clip it to your harness as you would to prussik up the rope. Hang from the knot with your full weight, and make sure you can easily reach the knot with some bend still in your elbow. The consequences of being unable to reach and unlock your prussik knot can be serious.
-Jay
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j_dub
May 26, 2004, 5:38 PM
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In reply to: HEHE you can't girth hitch a prussik to another closed loop! (you can girth hitch the start of an autoblock, but you still have to clip the end to a biner) BUT, And I hope you are using 4 wrap prussiks, if you start with 5 feet of cord you should be able to get a two foot loop ( after tying the joining knot) to practice with, and shorten it accordingly to suit your needs. Now if you want one for a rappel backup, your 14 incher might be fine, just check it out ( thath's where you make a prussik below the device and use a locking biner to connect to your leg loop) You actually want to have enough slack below the prussik to work with while ascending. ( if that is what you want it for) The same thing is true for escaping a rappel Feckup-- you need ehough room to work. You can always slide a long one up, but you can't do much with a short one right on top of the mess you are trying to fix.
Thanks - yeah, clearly I'm having a brain fart about rigging a prusik AND a girth hitch on the same loop. :oops: I think I'll get the 5' cord and try that. I'm tying double-fisherman's (so a total of four loops when you look at the whole knot) with 3" tails. I have a 24" sling I could use as an autoblock, too, so I'll have lots of rapping options, I guess.
First time rapping this weekend (can you tell? :oops: ).
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vegastradguy
May 26, 2004, 5:46 PM
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just remember if using a sling for your autoblock, make sure its NYLON. Spectra is not an acceptable material for using as a friction hitch.
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wideguy
May 26, 2004, 5:50 PM
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Have fun rapping. Be safe.
I bought 5' 7MM cord, tied double fishermans and the length works well as my autoblock or for prussiks. Haven't measured the overall finished loop length.
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j_dub
May 26, 2004, 5:53 PM
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Ahhh.. good point. Thankfully, the people taking me climbing would likely halt such death-inviting behavior :shock: - still REALLY good to know.
Jay - thank you for the info about loops being too long. I need to figure out where I could test my loops before we leave for WV (gym is closed and I don't own a rope). Will have to be creative, I think.
24" sounds pretty good.. 20-24, I'm thinking. I'm tall and I have monkey arms (i.e. lonnnnnng arms). :lol:
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rescueman
May 27, 2004, 12:59 AM
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In reply to: I'm using them for rappel back up and self-rescue (if needed).
An above the descender prussik backup is not a good idea for a couple of reasons. If you end up hanging on it, it can be very difficult to break while loaded. And, more importantly, because it almost invariably fails to function in a panic - it is a universal instinct (even highly experienced climbers have died) to grab the prussik in the event of an uncontrolled descent which makes it slide down the rope with you.
As a couple of folk have suggested, use an autoblock below your descender. Not only is it much safer, but it's much easier to break free while loaded (it's holding only the break hand force, not your whole weight). Just make sure that it can't extend up into your descender or it will not grab when needed, and may get caught in the device. Your short loop should be just right.
In reply to: I guess I could clip them to a sling if they need to be longer. Obviously I'd do that if I had to ascend a rope.
You could, but a better method for low-tech ascent is to tie a set of Purcell Prusiks from 6mm - they can be kept in a little ditty bag. Use a frost knot to tie the 8" loop at the top of the leg Purcells.
- Robert
http://www.geocities.com/...l_Sizing_and_Use.jpg
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mustclimb69
May 27, 2004, 1:19 AM
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Ok buy 3 Meters of 6 or 7 mm. then cut them in half and tie with triple fishermans or whatever you want. This legnth closed loop is a bit smaller than a shoulder legnth sling. you can easily tie prussics or "leash" in along with a clove hitch for belay stations.
It racks easily on a locking biner or even across your shoulder.
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dc
May 27, 2004, 2:10 AM
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In reply to: Ok buy 3 Meters of 6 or 7 mm. then cut them in half
yeah, my local climbing shop sells prussiks in 1.5 meter sections... it seems like a good length to me.. but then again, it all comes down to personal preference...
the thing is, the shop was out of 6mm cord when i was there last, so i got two 7mm prussiks and two 5mm prussiks... which should i use for a back up rappel? the 5mm's are safe right? (cos alot of people only recommend 6mm)
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rescueman
May 27, 2004, 2:35 AM
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I don't use anything smaller than 7mm for 7/16" rope, and I prefer 8mm for prusiks. If you're using a smaller rope, then 5.5 tech cord or 6mm nylon would be sufficient, but make sure you use a triple fisherman's bend.
- Robert
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rockzen
May 27, 2004, 3:25 AM
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I use:
5ft of 6mm for autoblock - just enough for 6 wraps
6ft of 8mm for prusik
6ft of 6mm for foot prusik
This seems to work nicely for me. As others have said, the length depends partly on your reach. You want enough room to work, but you must be able to reach it when you stand up.
Dave...
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j_dub
May 27, 2004, 5:06 AM
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Thank you all for the great feedback! I think the autoblock is the way to go, from what everyone has said. I take it you want a loop just long enough to make a sufficient amount of wraps and clip to your leg loop.. so.. not too long.
And.. really? 8mm for prusiks? I have 6mm. Is that ok for an autoblock? Do you need fatter cord for prusiks than for an autoblock? And with 6mm, do I need to tie a triple fishermans?
Sorry for all the questions - I really love picking all of your brains, and somehow this is really interesting. (*cough cough* addicted to climbing in every way *cough cough* 8^) ) I sat on the couch tonight practicing knots while we all watched the basketball game.. luckily, my roommates already know I'm weird. :wink:
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dirtineye
May 27, 2004, 5:46 AM
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In reply to: Thank you all for the great feedback! I think the autoblock is the way to go, from what everyone has said. I take it you want a loop just long enough to make a sufficient amount of wraps and clip to your leg loop.. so.. not too long.
Right. BUT, your autoblock needs to be wrapped specifically for the size adn age rope you are rapping on. Smaller newer dry coated rope will need more wraps to hold than larger older fuzzier ropes. AND, most important of all, an auto block is worthless until it is set-- if you just wrap it on and jump, the auto block may not block anything. Rule of thumb is, get as many wraps in as you can, set it, test it, and then adjust the number of wraps til you like the result.
In reply to: And.. really? 8mm for prusiks? I have 6mm. Is that ok for an autoblock? Do you need fatter cord for prusiks than for an autoblock? And with 6mm, do I need to tie a triple fishermans?
8mm prussik cord would not work well on 8.5 or 9 mm rope. In general you want about 3 mm less diam on the prussik cord than on the climbing rope you are going to use it on.
In reply to: Sorry for all the questions - I really love picking all of your brains, and somehow this is really interesting.
You'd do better to get with a flesh n blood authority, like a professional guide and take a class on this stuff. Do you really want to trust your life to some idiots on the internet? I might not even have a brain, last time I looked, it was out to lunch, or something.
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climbfrog
May 27, 2004, 8:13 AM
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Your waist prussik should be 1.8 metres long UNTIED. Your leg prussik should be 2.4 metres long.
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kaczoron
May 27, 2004, 8:43 AM
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Hi,
Even though I'm just some idiot in the intarweb without a brain, I'll chuck in 2 cents...
I use 10.5 mm ropes to climb so i have 7mm prussuk cord, A good way to judge the required diameter of cord is 1/2 the rope diameter plus 2mm.
I have 5 prussiks, 2 short 2 long and one thats real short. The short ones are from the end of my fingertips to my armpit (tied) and my long ones reach from my foot to my belly-button (tied). The realy short one as about 25cm long so that it is just the right length to tie a french prussik, this is a top knot,as it is below the device when you weight it, it can easily be unloaded and doesn't hold the whole climbers weight like a friction knott above the device does also it doesnt get out of reach ever.
But like someone already said, dont listen to us get it shown to you by someone you know that knows.
Cheers,
Nick
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