purcell prusik as TR anchor?
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So I haven't been climbing for super long, but I was at a knot-tying clinic tonight, and learned how to tie a purcell prusik. As I was tying it I realized that on the end with two loops, its really easy to make them different lengths, which made me think that it would be good for quickly equalizing a top-rope anchor (if your prusik is made of, say, 9 mm dynamic rope). |
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Can: I don't think you'd be likely to get yourself killed doing this. Though remember that as you adjust your two strands out to your anchor points, you will no longer have even strands at your master point. One will be shorter than the other and bear all the load. |
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Also your TR anchor would be better made from 9mm static than 9mm dynamic. Better abrasion resistance. |
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it's not a terrible idea, but i don't personally think it to be the best solution. if you do use them, i'd vouch for a locking biner attached to each purcell and the rope clipped through both biners, rather than a single locker with the rope and both prussiks attached. otherwise you're looking at cross loading like in the 3rd biner pictured here: purcell prussiks don't always rack so nicely, and thicker cordage makes that worse. 7mm cordage is plenty strong for top rope anchors, but if you like having something nice and strong holding you sterling power cord is rated to 19kn at only 6mm. bit stiff tying knots in, though: Sterling PowerCord as much as i love purcell prussiks for my PAS, i don't like the idea of them out of sight and reach. messing around with one i have on hand, it does seem to slip and extend itself a couple inches with repeated loading. i don't like that property in my anchors. could slip the locking biners somewhere you didn't want them to be and load them all kinds of wrong: really, a large sling or loop of cordage pulled together and tied with an overhand knot into a master-point doesn't take that much time to equalize properly. twisting the cordage or sling into a ball and clipping both ends into a carabiner makes for really easy and compact racking, too. |
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Try it in your living room and report back. Pictures would be great. In doing that ... |
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One: take an anchor clinic from a trained professional. It takes all the what ifs out of it. |
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There is no (non emergency related) reason to build a TR anchor using a purcell prussic, period. |
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Friction (aka heat) hitch + non redundant nylon is a poor idea. I have seen 5mm prussiks fail at .7kN when they fail to grip. |
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Scott O wrote:Should: No, because there are MUCH better ways to use a 9mm rope to tie a top rope anchor to two anchor points. Clove to each anchor (or 8 to one and clove to length on the other). Equalize with BFK. Done.Just the kind of answer I was looking for. I imagined that there were better alternatives, and this makes sense. What I really need to do it set up a few "hangers" on a wall in my apartment and spend an hour building anchors. On a side note, I've found that I'm really good at tying knots from diagrams, so if anyone knows any good web print resources or Youtube videos on anchor building that'd be great for me to practice. Thanks! And in before "if you have to ask you shouldn't be doing it", I'm not building anchors for anyone just yet. I climb with friends who are a lot more experienced than me and I'm picking up everything that I can. Just led my first climb the other day too, which was awesome! |
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Advanced Rock Climbing Book by Craig Luebben and John Long is really good. It was my jumping off book for anchor building. |
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... if anyone knows any good web print resources or Youtube videos on anchor building that'd be great for me to practice.
Careful - you can start an online war with a request like that. ;-) Also consider Climbing Anchors, 2nd edition, by John Long and Bob Gaines (2006). Personally, though, I'd ignore the equalette despite it's recommendation for folks who are beginners. JL took a lot of flak from the community on that one. Were you also looking for resources about knots? |
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In practice I value simplicity and of course redundancy. Make your anchor visual it weight test and move on with your life. Your partner will appreciate you not making a thesis out of it |
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Bill M wrote:In practice I value simplicity and of course redundancy. Make your anchor visual it weight test and move on with your life. Your partner will appreciate you not making a thesis out of itI agree. over-engineering a top-rope anchor is a waste of time. Hypothesizing about theoretical top-rope anchors isn't an awful idea because analyzing knots and systems is fun and worthwhile, but there's a reason most people use the same 4 or 5 tr-anchor systems. |
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Not necessary |
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Gavin W wrote: Just the kind of answer I was looking for. I imagined that there were better alternatives, and this makes sense. What I really need to do it set up a few "hangers" on a wall in my apartment and spend an hour building anchors. On a side note, I've found that I'm really good at tying knots from diagrams, so if anyone knows any good web print resources or Youtube videos on anchor building that'd be great for me to practice. Thanks! And in before "if you have to ask you shouldn't be doing it", I'm not building anchors for anyone just yet. I climb with friends who are a lot more experienced than me and I'm picking up everything that I can. Just led my first climb the other day too, which was awesome!http://www.animatedknots.com/ |
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Scott O wrote: animatedknots.com/Bookmarked. Thanks! |
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what about if yo use TWO purcell prusiks as individual legs of an anchor, so that they WILL slip (until they equalize) then certainly top rope forces wont make TWO prusiks slip at the same time |
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benlucky13 wrote: it's not a terrible idea, but i don't personally think it to be the best solution. if you do use them, i'd vouch for a locking biner attached to each purcell and the rope clipped through both biners, rather than a single locker with the rope and both prussiks attached. otherwise you're looking at cross loading like in the 3rd biner pictured here: its been shown that if the tri axial loading ANGLE is small (less than 60 degrees) then the carabiner strength still maintains 80%+ of its load bearing capacity (and for TR even 50% load is never going to be reached) |
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Jef Anstey wrote: Please stop with the macrame projects and reinventing the wheel. |
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Marc801 C wrote: Please go away? Please mind your own business? ironically the wheel has been "reinvented" and improved in countless ways since the advent of "wheels" |
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Jef Anstey wrote: You're taking something simple and making it needlessly complex. That's not a good thing to do with anchors. |