5:1 pulley systems

G

gaiatree

Howdy all ~ I'm curious what people are using for a prussik when attaching a 5:1 ratio pulley system to your bull line when pulling over a tree etc.

My concern lyes in that the other day we pulled over a tree with our brand new pulley system... all went well and it worked like a charm, however when I was dissmantling the system I had to peel the prussik from the bull line, as it had melted and fussed directly to it on the first and only time it's been used. I spliced the prussik up myself using 3/8ths tenex and am now afraid to even touch the stuff if that's how it reacts to heat. Naturally, I suppose a Technora based prussik should hold up much better...
Just curious what others preffer.

Also... I have some 3/8th cordage made by Samson for sail rigging which has a polyester cover over a dyneema core: quite strong but I'm not sure how it will take heat. I use it for my lanyard hitch since there is no real heat/friction to speak of there.
 
Sounds to me like you really overloaded the system. The prussic was moving on the bull rope which is not good. Perhaps modifying felling technique might help (bore cut, add wedges, preload, cut tab, drive wedges then pull over) or buy a GRCS
 
You don't say what sort of Prusik you used (how formed--how many turns?).
A friction hitch allows for re-positioning of the attachment point easily,
and if you find one slipping, you should perhaps add a 2nd one.

*knudeNoggin*
 
WOW! How were you tensioning the 5 to 1? The Tenex had to get to 480* to melt. You got lucky that the Tenex didn't break. I use a prusik made from 3/8" Tech 12 (12 strand constructed of technora). Stay away from the Spectra/Dyneema fibers. They have a low melting point of 297*.
I would start with, why did the Tenex melt; was it slipping? Sounds to me like it was. Maybe tie a different hitch onto the bigger rope. The Technora is a slipperyer fiber and will slip easier than polyester.
 
Boy that was close. Prusiks are not ment for hard pulls, as your experience had demonstrated. Though, for taking stretch out and tensioning a line they are the cats meow, but after that's done knot direct to the bulline behind the prussik.
 
something you can also do is run tandem or tripple prussicks to spread the clamping load on the haul line. I do this often when tension Kootenay highlines......three prussik loops, each a little longer than the last, all prussicked onto the highline, spread out about about 3"s apart and set/dressed. You wont slip or glaze them ever, unless you really shockload your system hard (takes an enourmous amount of shockload to glaze a tripple prussik setup.)
 
I agree that it sounds like the system was overloaded, but another thing to consider is that the prussik was new. If the cord has been broken in a little and has a bit of nap (the fuzzies that rope develops with use) it is much less prone to melt as easily.
 
We do the same thing as SRTTech, We run MA all the time for rescues. We made it a standerd that you have to back up all your running lines with a tandem triple wrapped prussik. This way the only way any glazing or breaking will happen with the prussik will be at aprox 4,000- 4,500 lbs. We use 8mm cord.
 
A VT is your best bet - this will retain most strength in the line, and I'd expect a bowline to break first. Prusiks that I tested were deemed safe with typical rigging safety factors applied to the line. So if you're burning prusiks, Its probably a four wrap and/or you are over tensioning a line. If you consider a prusik to fail the line at 50% like a knot, you won't go far wrong.

As for Tenex, I've been unpopular stating before that, as a prusik cord, I consider it unsuitable; it flattens out 'thin' with all the load bearing fibres taking the heat. Once that overheats, there is no back up core. I wouldn't expect anything less than what happened to you with hollow braids like Tenex.

I'd choose some kind of polyester double braid or kernmantle, so as the core is protected.
 
LAZ, are you saying that instead of the traditional 6 finger prusik you opp for the VT?? I have been thinking about testing that out for myself. If you have used it before for a brake how has it preformed under a good load or shock load? Always looking for a new and better way. I hate how if for whatever reasone you have to slack a highline you need a load releasing hitch or MA on it still to do so. The VT the most I could see needing is a micro pulley in front of it to pull back on it. Also has anyone tested that factor, when taking the tension off of the line with a VT how much jump do you get out of it?
 
I would not be too happy to see anyone slacking a tensioned line by bumping the friction hitch. Too easy to loose control and generate shock loads.

Google 'radium hitch' or 'radium load releasing hitch' for more information on a popular configuration.
 
Well dont get me wrong, my method that I use for releasing a load off a tentiond line is a load releasing hitch. But if there is other ways of doing it for certain loads then I am all ears. I am in no way saying that I would use a VT on a highline carrying people for a rescue for example. But if it were to be for something with no threat to life or property then I see no reason to not try it or use it saying works without damage to anything.

For ex. if you are highlining something but the line dont go to the ground and you need to slack it to get whatever down to you. I know I know, just use a port-a-wrap, but not everyone has one and not to mention a prusik is a heck of alot cheaper. It never hurts to know more then one way to solve one problem.
 
Blinky,

Be VERY aware of the loads that a Gibbs will damage rope. Google or the Gibbs homepage will let you know. Then you'll ahve to do the math to determine the loads.
 
[ QUOTE ]
Blinky,

Be VERY aware of the loads that a Gibbs will damage rope. Google or the Gibbs homepage will let you know. Then you'll ahve to do the math to determine the loads.

[/ QUOTE ]

Will a prussic do any better with 2000# loads? I'm pretty certain we were at less than half of that. We operated the 5:1 with one 190# man... mainly to haul on tip tied pieces above a porty. I don't think I've ever used more than 3:1 to pull on a tree for falling.... unless you count the time a guy used his truck to pull down a hung up hackberry with a straight 1:1 through a block for redirection... ruined that rope sure enough, lesson learned... it seemed like a bad idea at the time but wasn't my call to make.
 
when useing a 6 fingered prusik the fail point is at aprox 4000 lbs. For the most part that is the weakist point for most everyones gear. Gibbs are great for small loads though, but anything heavy I dont think I would want to take the chance.
 
[ QUOTE ]
LAZ, are you saying that instead of the traditional 6 finger prusik you opp for the VT?? I have been thinking about testing that out for myself. If you have used it before for a brake how has it preformed under a good load or shock load? Always looking for a new and better way. I hate how if for whatever reasone you have to slack a highline you need a load releasing hitch or MA on it still to do so. The VT the most I could see needing is a micro pulley in front of it to pull back on it. Also has anyone tested that factor, when taking the tension off of the line with a VT how much jump do you get out of it?

[/ QUOTE ]

Hi Fairfield

I never back off a loaded hitch when used this way. I always run up the fiddle blocks to a porty or winged 8. Even a Muenter Hitch. Doesn't have to be expensive and the control is way more than attempting to back off a prusik.
 
Ok, wow I was about to say I think you are the only one to do that... well glad to hear you dont, but still would like to try it out as a test to see what weight will do what ( ONLY AS A TEST).
 
You must log in or register to reply here.

New threads New posts

Back
Top Bottom