Prussic cord?

BigJon

BigJon

Location
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I have been playing around quite a bit different brands and braids of cord used to tie various friction hitches for my split tail. I was just wondering what everyone else out there is using and how well it is working for them. I like the ultra tech from Sherill but it is too costly. I found that buying 3\8 ten x is cheap (.41 per ft) and easy to splice but I really don't like using the swabish all that much.
 
Mark turned me on to some double braid line that I get at West Marine. I think that its the 5/16 that has a breaking strenght of 3k#. This line is durable and the flex of the line makes for a nice slip/grab characteristic.

Tom
 
I have tested about 60 samples of prusik cord with just about every hitch you can think of. The project hasn't been published yet, but to put your minds at rest the climbing line normally breaks before the hitch (in the doubled line system that arborists use)!The tests included everything from 6mm polyester double braid, dyneema, ultra tech (aramid fibres)upto 12mm single braid and 3ply. Many hitches and cords stopped the pull test at 3500Kg (max hydraulic force).

The biggest problem for arborists is the amount of wear that the cord receives during repeated descents - Most other rope access industries go pale with dread when they see how we use a friction hitch! Basically, just because a cord has a high strength doesn't mean it bends well or can handle friction heat and sunlight. Aramid fibres that I tested didn't break, but they had about as much flexibility as wire after pulling.

Some hitches performed better with 8mm cord in terms of grip and release. My recommendations are 10mm polyester with a minimum strength of 1600Kg. 8mm Polyester can be used by those responsible enough to discard them before the outer braid has worn through. I didn't feel the high strength modulus fibres were necessary - overkill with some dubious characteristics.

I do have reservations about the service life of hollow braid used as a friction hitch - there is no core strength, the load fibres are external and wear/pick easily after the coating is worn off. Again, if you are responsible enough to discard it before too much wear, then fine.
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I've also had some problem finding a suitable prusik cord. I'm now using Beal's regate which is, as MrPez reccomends, a 10mm polyester with a minimum strength of 1700Kg. Beal says it's made specially for making prussik loops. You can check it at http://professionalropes.com/anglais/corde_pro4.html
I'm very happy with it and since I gave up my mania of having everything spliced, wear isn't a problem any longer. Now I manage to have a VERY short distal (almost touching the pulley) and replacing the cord is so cheap that there is no excuse not to do it very often.

Sergio
 
I'm still searching for that cord that suits me. I've been using tennex with a french prussik but doesn't grip very well. The double braid seems ok but doesn't last very long. the polyester cord seems not to release after using it for awhile. that utra tech stuff failed me twice, once at a tcc in the work climb coming down for a landing the outer cord melted away. I thought it would withstand high temps so I let it have it and it burnt the cord and my thumb. Next while working the splice came undone. first I noticed the whipping come loose then the outercore . tennex is a hollow braid but seems to withstand the abuse the longest. has this been true in any studies?
 
I have found that West Marine carries a great selection of New england braids. I just started trying the some of the Sta Set. The breaking strength for 3\8 is 4400 lbs. Also the the Sta Set X is 4400 lbs. I also got a piece of the T900 that is 7300lbs for
5\16. It is very much like Ultr Tech. The is another braid called HRC wich is heat resistant but the smallest is 10mm with a tensile of 11,500 lbs. I believe the melting point is up around 600+ degrees. It looks to be a soft lay rope.
 
Need to milk out that Ulta tech before you use it. Otherwise it will pooch.the most important thing I find with ultra tech is the length. Thats why i dont have mine braided.If the braids are wrong you cant adjust it to shorten or lengthen. I also run three wraps a lot vs the four, but using a shorter piece also. This allows me to open it up more freely.
I've had good luck with ultra tech, but I'm in the process of trying the new stuff.24 strand. A little firmer lay, we will see.

Greg
 
Greg what is this 24 strand you speak of? I know they changed the cover of ultra tech. Is this what you are talking about? I have a piece but have yet to climb on it.

[ August 13, 2002: Message edited by: BigJon ]

[ August 13, 2002: Message edited by: BigJon ]
 
You're barking up the right tree Sergio - I've tested a lot of that and it gave very favourable results. I'm glad someone else sees it my way over unnecessary splices as well - Too many people hang on to a cord too long because it is expensive to replace with the splices.

For those that are dabbling with high modulus fibres such as kevlar and ultra tech, the heat resistance is in the core, the outer jackets are of polyester. This is a particular concern with dyneema or spectra - they only have a melting point upto 150 degrees. They are covered usually with polyester. You can imagine what will happen if you burn through the jacket half way down - you may hit the ground sooner and harder than you anticipated!

Also, aramid fibres don't respond well to sunlight - nothing too much to worry about if covered in polyester, but what about those splices with no cover?!

Like I've said before - don't put too much emphasis on strength beyond a certain limit, and be vary wary of stiff braids!

I'm currently having success with 10mm polyester tied as a VT with 4 wraps and one braid tied short. It always grips and releases well. The only downside is it gets a little tight on descents. The best performance I have had is with 10mm polyester tied as a helical with 6 wraps - beautiful!
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