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rcparadise
Apr 24, 2007, 5:15 AM
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Hi,
I used to climb about 15 years ago and gave it up. Now I'm back, buying new equipment little by little. But I'm focusing not so much on the actual climbing, but on the building of anchors -- I'm reading John Long's new edition of "Climbing Anchors." It's really wonderful. Also focusing on rapelling, which relates to anchors because they've got to be bombproof! Since my days off are during the week I'm doing most of this solo. I've bought 2 , 30 foot lengths of 8 mm. Bluewater static cord and plan on tying them together with a double fisherman's knot and dropping it over a small cliff for a beginner rappel. I'll use a Mammut Fuse belay device for the descent (works with 7.5 - 11mm. ropes), with a prusik tied from 5mm. accessory cord. This should be OK, shouldn't it? You may ask why the 8mm. rope. Well, mainly because it will fit nicely into the small backpack I carry around during the day to work, and which I use to go directly to the climbing area. Also, the cost. Only about $28. Thanks for any input.
Bob
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moose_droppings
Apr 24, 2007, 5:31 AM
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rcparadise wrote: Hi, I used to climb about 15 years ago and gave it up. Now I'm back, buying new equipment little by little. But I'm focusing not so much on the actual climbing, but on the building of anchors -- I'm reading John Long's new edition of "Climbing Anchors." It's really wonderful. Also focusing on rapelling, which relates to anchors because they've got to be bombproof! Since my days off are during the week I'm doing most of this solo. I've bought 2 , 30 foot lengths of 8 mm. Bluewater static cord and plan on tying them together with a double fisherman's knot and dropping it over a small cliff for a beginner rappel. I'll use a Mammut Fuse belay device for the descent (works with 7.5 - 11mm. ropes), with a prusik tied from 5mm. accessory cord. This should be OK, shouldn't it? You may ask why the 8mm. rope. Well, mainly because it will fit nicely into the small backpack I carry around during the day to work, and which I use to go directly to the climbing area. Also, the cost. Only about $28. Thanks for any input. Bob
Do you plan on tying these 2 pieces tied together to an anchor, or you just throwing them off. You don't explain your anchor so I couldn't tell you if its safe. Also, why didn't you just buy 60ft of rope to rap on instead of 2, 30ft'ers? How are you planning on passing the knot while rapping? 8mm static is strong enough for rapping. The fuse device sounds OK. Is the 5mm for a prusick backup below the rappeling device?
Could you explain a little clearer what it is your doing?
(This post was edited by moose_droppings on Apr 24, 2007, 5:35 AM)
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nooyoozer
Apr 24, 2007, 6:27 AM
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so i'm assuming you're talking about an approximate 25 foot rappel, substituting two full-length ropes for two 30 foot pieces?? are you slinging these two short ropes around a tree or what? If properly tied, with plenty of tail, the double-fisherman's isn't really what you need to worry about, rather what is anchoring your ropes above you? Also, as Moose said, ONE longer piece of rope (60 feet, 30x2 feet) would be more ideal and ultimately safer. If it's a tree, use your judgement, trees are strong, even small ones, but check the roots and health of the tree, just be smart. any strong anchor-point will do. I'm not familiar with the belay device you're using but any ATC style device will work. just, for God's sake, don't do any of this unless you're sure about it!
(This post was edited by nooyoozer on Apr 24, 2007, 6:36 AM)
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rcparadise
Apr 24, 2007, 6:41 AM
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thanks for the response
Sorry it wasn't clearer. I'll set up a solid anchor, probably using two or three trees rigged with some sewn slings, and two biners opposite and opposed for the power point. Of course I could just buy 60 feet of rope but the static cord comes packaged in 30 foot lenths. I won't have to pass the knot while rapping, as it will remain at the power point until I'm down. Then I'll see if I can pull the ropes down. I'm trying to simulate what I'd do on a multi-pitch rappel. I'll tie knots at the bottom of each strand, attach a biner to one strand of the rope, connected to my harness with a sling (to prevent rope twisting), and yes, the 5mm *is* for a prusik below the rappelling device.
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moose_droppings
Apr 24, 2007, 6:56 AM
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Much clearer, a 30ft double rope rap, off a bomber multi piont anchor and double biners at the power point over the edge thats been padded.
Yep, sounds safe to me, a double fisherman knot to tie the 2 ropes together for practicing. You could use a EDK with plenty of tails and checked each time if you wish, many people do it to try to prevent the rope from sticking when they pull them.
Have fun.
(This post was edited by moose_droppings on Apr 24, 2007, 7:03 AM)
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coastal_climber
Apr 24, 2007, 3:35 PM
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It's called accessory cord for a reason, get a thicker cord rated to more.
>Cam
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climb_eng
Apr 24, 2007, 7:46 PM
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coastal_climber wrote: It's called accessory cord for a reason, get a thicker cord rated to more. >Cam
Well hold on, what's it rated to??? People use accessory cord for anchors all the time, and those take a very high load.... higher then what you'd expect the loads to be during a rappel.
-JP
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jgailor
Apr 24, 2007, 7:54 PM
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As a rule of thumb (i.e. - check with the brand of accessory cord you use first), the standard ratings are:
6mm - 1200 lbs
7mm - 1500 lbs
8mm - 2200 lbs
I use an 8mm and while it's bulky, equalizing three anchors with gives me 6600 lbs of hold, way more than enough to suffer a nasty factor 2 fall on.
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summerprophet
Apr 24, 2007, 7:57 PM
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In reply to: It's called accessory cord for a reason, get a thicker cord rated to more.
With thicker cord, it would not grasp the 8mm cord as well. 5 mm is fine and plenty strong for prussics. Unless of course you feel that your hold on the brake line is better than 1300 lbf.
(This post was edited by summerprophet on Apr 24, 2007, 7:58 PM)
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trenchdigger
Apr 24, 2007, 8:02 PM
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jgailor wrote: As a rule of thumb (i.e. - check with the brand of accessory cord you use first), the standard ratings are: 6mm - 1200 lbs 7mm - 1500 lbs 8mm - 2200 lbs I use an 8mm and while it's bulky, equalizing three anchors with gives me 6600 lbs of hold, way more than enough to suffer a nasty factor 2 fall on.
That, of course, assumes you always get perfect equalization between three points - something that is impossible even with an equalette setup. You also neglect to consider that the cord will generally be tied into a loop which will, in effect, double the strength of each "branch" of the anchor as the cord will be doubled (minus knot strength).
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jgailor
Apr 24, 2007, 8:11 PM
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trenchdigger wrote: jgailor wrote: As a rule of thumb (i.e. - check with the brand of accessory cord you use first), the standard ratings are: 6mm - 1200 lbs 7mm - 1500 lbs 8mm - 2200 lbs I use an 8mm and while it's bulky, equalizing three anchors with gives me 6600 lbs of hold, way more than enough to suffer a nasty factor 2 fall on. That, of course, assumes you always get perfect equalization between three points - something that is impossible even with an equalette setup. You also neglect to consider that the cord will generally be tied into a loop which will, in effect, double the strength of each "branch" of the anchor as the cord will be doubled (minus knot strength).
Actually, not really. And I'm not really sure what you mean by "doubling". Each loop of the cordellette (sp?) only runs through each biner once, so that's one strand each. You'll lose a little to the knot, but in this case it's fairly negligible given the overall holding power of the system, assuming the anchors you are using are all solid.
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trenchdigger
Apr 24, 2007, 8:20 PM
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jgailor wrote: Actually, not really. And I'm not really sure what you mean by "doubling". Each loop of the cordellette (sp?) only runs through each biner once, so that's one strand each. You'll lose a little to the knot, but in this case it's fairly negligible given the overall holding power of the system, assuming the anchors you are using are all solid.
Cord strengths are quoted end-to-end for a single piece of cord, not as a loop. Tie that cord in a loop, clip two carabiners into the loop and pull on each 'biner, and the load is distributed between two strands of cord. Therefore the strength of a loop of cord is twice the strength of the cord's quoted strength, minus strength loss to the knot.
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jgailor
Apr 24, 2007, 8:25 PM
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trenchdigger wrote: jgailor wrote: Actually, not really. And I'm not really sure what you mean by "doubling". Each loop of the cordellette (sp?) only runs through each biner once, so that's one strand each. You'll lose a little to the knot, but in this case it's fairly negligible given the overall holding power of the system, assuming the anchors you are using are all solid. Cord strengths are quoted end-to-end for a single piece of cord, not as a loop. Tie that cord in a loop, clip two carabiners into the loop and pull on each 'biner, and the load is distributed between two strands of cord. Therefore the strength of a loop of cord is twice the strength of the cord's quoted strength, minus strength loss to the knot.
That's the first time I've heard that. Time to do some research.
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moose_droppings
Apr 24, 2007, 9:22 PM
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coastal_climber wrote: It's called accessory cord for a reason, get a thicker cord rated to more. >Cam
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majid_sabet
Apr 24, 2007, 10:09 PM
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trenchdigger wrote: jgailor wrote: As a rule of thumb (i.e. - check with the brand of accessory cord you use first), the standard ratings are: 6mm - 1200 lbs 7mm - 1500 lbs 8mm - 2200 lbs I use an 8mm and while it's bulky, equalizing three anchors with gives me 6600 lbs of hold, way more than enough to suffer a nasty factor 2 fall on. That, of course, assumes you always get perfect equalization between three points - something that is impossible even with an equalette setup. You also neglect to consider that the cord will generally be tied into a loop which will, in effect, double the strength of each "branch" of the anchor as the cord will be doubled (minus knot strength).
Professor
Assuming we start pulling the rope from end to end with a fig 8 knot,
Could you tell the audience at what area the knot will fail (breaks apart).
[URL=http://imageshack.us]
you better be right
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trenchdigger
Apr 24, 2007, 11:02 PM
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majid_sabet wrote: Professor Assuming we start pulling the rope from end to end with a fig 8 knot, Could you tell the audience at what area the knot will fail (breaks apart). [URL=http://imageshack.us][IMG]http://img400.imageshack.us/img400/9503/fig8bendhp9.gif[/IMG] you better be right
What on earth does this have to do with this thread?
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yokese
Apr 24, 2007, 11:30 PM
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trenchdigger wrote: majid_sabet wrote: you better be right What on earth does this have to do with this thread?
Not surprisingly, nothing. It has nothing to do with this thread.
Anyways, I'll say at point H or J... no, wait a sec... bah... forget it.
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cintune
Apr 24, 2007, 11:47 PM
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F or i, depending which one is loaded.
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coastal_climber
Apr 24, 2007, 11:48 PM
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climb_eng wrote: coastal_climber wrote: It's called accessory cord for a reason, get a thicker cord rated to more. >Cam Well hold on, what's it rated to??? People use accessory cord for anchors all the time, and those take a very high load.... higher then what you'd expect the loads to be during a rappel. -JP
He asked, and I gave him my personal opinion as well as what I would do.
http://www.mec.ca/Products/product_detail.jsp?PRODUCT%3C%3Eprd_id=845524442094539&FOLDER%3C%3Efolder_id=2534374302691499&bmUID=1177458267924
>Cam
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majid_sabet
Apr 25, 2007, 4:46 AM
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cintune wrote: F or i, depending which one is loaded.
Very good you are 80% correct but
It is "I" at " D" location
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codhands
Apr 25, 2007, 5:31 AM
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have fun
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bluesnpolitics
Apr 25, 2007, 6:43 PM
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Cam, I think Mammut is only covering there legal asses with the "not for climbing" comment. They are probably afraid some goof will buy 6mm cord to go toproping cause it's cheaper. Considering that the rappel lines are 8mm, getting a larger diameter prussik could actually be more dangerous because the ratio between the two ropes would be smaller and less likely to bite.
Also, if the prussik is below the rap/belay device, it will not be taking the full load because a large amount of the force will be taken as friction in the device. IMO the best way to do that is to extend the rap/belay device with a dyneema sling (downside is one more piece that can fail and check connection to belay loop because worst wear will occur at this point) which makes it easier for the prussik to be inline with the rope and device.
If you are saying that the 8mm rappel ropes should be thicker, I think that they should be fine for rappeling. As long as nobody is jumping (static line being the bigger problem than the diameter), there is no reason that 8mm will fail. Most likely your hips and back will fail before the static line will.
I respectfully disagree with your assesment and think that, assuming all knots are dressed correctly and technique is good, the set up should be safe, but everyone makes their own decisions... watch sharp edges. Sketchiest part about rapping with my IceLines (8.1) is the contact with rock edges and roots.
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rcparadise
Apr 26, 2007, 3:29 PM
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Wow, this was my first post and it has generated a lively discussion. I think I've gotten most of the information I need. Drew, you raise a good point about the thin (8mm.) cords being more susceptible to being cut. That is defintely the case, and carries a higher risk for rapelling. The cord itself is rated 3100 pounds tensile strength and even with a knot reducing the strength by say 30%, you'll still have a safety margin. The most force you can expect from a rappell would be around 1000 pounds. If you're lead climbing on double stranded twin or half ropes, it's safer than a single rope, because even if one rope gets cut due to rockfall, you've got a separate tie-in on the other rope. The system is redundant. But the rappell is more risky, because think about it, if the rope gets cut anywhere above the rappell device, the rope is just going to slide down through the power point, and you're history!
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