purcell prusik as TR anchor?

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).

Anyone know if this is in fact possible? Are there better alternatives that are as easy to tie? The guy leading the clinic had never heard of it being used that way, but said that he didn't know if it could safely be done or not.

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.
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.

Also your TR anchor would be better made from 9mm static than 9mm dynamic. Better abrasion resistance.

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.

Try it in your living room and report back. Pictures would be great. In doing that ...

See how practical / impractical it is to adjust. Do you have to run cord through the prusik in each circumstance to get the unevenness? How easy is that? Does the unevenness cause the loop's knot to get in the way?

Can one readily make a reasonably EARNEST anchor with it: legs Equalized; Angle not too big; no single point of failure - Redundant; if something fails No Extension (maybe not as critical for TR); Strong enough individual parts; Timely?

Then make the equivalent checks with something more commonly in use such as posted above or something else.

One: take an anchor clinic from a trained professional. It takes all the what ifs out of it.
Second, simple is better with anchors.

There is no (non emergency related) reason to build a TR anchor using a purcell prussic, period.

It is not redundant in a lot of ways. With bolt anchors redundancy trumps equalization 999 times out of 1000.

Friction (aka heat) hitch + non redundant nylon is a poor idea. I have seen 5mm prussiks fail at .7kN when they fail to grip.

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!

Advanced Rock Climbing Book by Craig Luebben and John Long is really good. It was my jumping off book for anchor building.

... 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?

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

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 it

I 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.

Not necessary

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/

Scott O wrote: animatedknots.com/

Bookmarked. Thanks!

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

also...making it a 3 or even 4 wrap prusik reduces the chance of slippage while loading/unloading the anchor

could still tie a master point, just like if you had two slings and wanted to tie one (aka the prusik side would be at the bolts (just like when used as a PAS)

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)

Jef Anstey wrote:

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

also...making it a 3 or even 4 wrap prusik reduces the chance of slippage while loading/unloading the anchor

could still tie a master point, just like if you had two slings and wanted to tie one (aka the prusik side would be at the bolts (just like when used as a PAS)

Please stop with the macrame projects and reinventing the wheel.

Marc801 C wrote:

Please stop with the macrame projects and reinventing the wheel.

Please go away?

Please mind your own business?

ironically the wheel has been "reinvented" and improved in countless ways since the advent of "wheels"

Jef Anstey 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"

You're taking something simple and making it needlessly complex. That's not a good thing to do with anchors.