5:1 pulley systems

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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?

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We've used a Prusik, Vt, Valdotain, and several other friction hitches for both the brake and as the attachment hitch to the main line. I don't think any friction hitch could be released under the tension generated by a 3:1, and certainly not by a 5:1, when used as either the brake or the attachment.



Can you explain a "...load releasing hitch..."?
 
i like the Muenter and extra turns, then muled versions best. i try to set the friction hitch by pulling outwards, then the opposite direction of pull, then the direction of pull. New, slick lines are a no-no.

i think a friction hitch must be pretty much unloaded to slide properly; and that takes 2 legs of line (like in our DdRT). 1 leg of line to be static/ non adjusting and temporarily take the load, as the hitch slides on the other leg fairly unloaded. Sliding a hitch on a 5/1 tightened line; is like 3-4 guys sliding down on a single SRT friction hitch.
 
yes, like I said though there are many right ways of doing it it just depends on what you are comfortable with. I would suggest trying diffrent kinds for diffrent applications to see what works the most smooth.
 
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i like the Muenter and extra turns, ...

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Yeah, that BRMRG thing burns up a LOT of material just wrapping to
the clip-off (which even then maybe isn't assured of having enough
slack to easily unclip for release), which doesn't give good help
in release, and would be a bother to unwrap (as for wrapping).

BTW, the correct name/spelling is 'Munter'--no umlaut or poor-man's
equivalent ('ue'). This info from a knotwise guy OverThere (Austria).
(And I think BRMRG is where I just saw the mistake carried to "Prusik",
along with a surplus 's'.)

*kN*
 
Any way i still like the reversible roll and 'poplock'(so over riding force has to reverse configuration and sometimes 'pop' it through krab) of Münter(by any other name...)as a base configuration; that you can go many ways from to add control and/or lock.

On load line pulls with prusik i also like a slipknot under prusik for security. i think some kernmantles aren't too prusik friendly; in that you are trying to grab the load force, and in is inside the kern; and you are grabbing the loose mantle overlay. So, at some points a cam grab that pinches through both kern and mantle seems fit.


Tom, he's picking on me again!!
grin.gif
 
Over here in the sailing world, melted rope is a frequent problem, at least for racers, as surging at speed over belays is a common requirement. To deal with this, we use high-temperature covers, made from things like Teflon, Nomex, Kevlar, Vectran, and the like, mixed to the ropemakers' preferences.
So on the chance that the melted rope was not a consequence of overload or inappropriate procedure, a tough, high-melting-point cover might be the answer.
As I'm sure you guys know, it doesn't take much to heat a rope up to an amazing degree.
Fair leads,
Brion Toss
 
Very true Brion. In fact, I have even melted a dyneema core line over a winch in a tree removal while lowering at very slow speeds. I was only operating on a 7/1 safety factor of the rope, but still was surprised at how much glazing did occur.
 
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i think a friction hitch must be pretty much unloaded to slide properly; and that takes 2 legs of line (like in our DdRT). 1 leg of line to be static/ non adjusting and temporarily take the load, as the hitch slides on the other leg fairly unloaded. Sliding a hitch on a 5/1 tightened line; is like 3-4 guys sliding down on a single SRT friction hitch.

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i'd like to clarify something of my understanding of the model i go by.

If; the 5/1 tightened line is from a piggyback compression jig (pulls purchase from load line to leave it tighter and/or lift load); you should not lower the load with a prussic type hitch through the single support of the load line. You can get by with light loads that the mechanics aren't loaded well enough to make a difference; and or playing with friction (by squishing rope against tree with free hand etc. to allow slide. But, in general the hitch has to be unloaded to slide smoothly 'loaded'.

But, if you still have the jig in place; you can then lower smoothly through the multi legged rig; under moderate tensions on prussik on control leg IMLHO.

i all ways try to offer that a friction hitch in descending slides smoothly in DdRT and not as well under even 1/4th the load in SRT. Because the multi legged line of the DdRT offers a static and dynamic leg under movement, whereby SRT is just a single, no alternative dynamic leg. i see the alternative support/ static support leg as taking the load / unloading the prussic; while the 'dynamic' leg is stretched/ prussik is moved 'down'.

So, the single main load line bears full wieght/ no alternative support to temporarily unload prussic to slide on a load. But; adjusting the 5/1(unlike the compression stage; on extension the more pulley/rope friction the better here; can even squish or bend pulley legs around for more friction with gloves and proper care under nominal loadings) with prussic on tail is much more successful. Because it more closely follows the model of having legs you are not adjusting as primarys(only secondary/ responsive/ self adjsutmeants).

This also extends, perhaps is easier to visualize; in a simple (for us) 2:1 directly to the load(no piggyback/extra jig) with a return (that forms a forward or backward "N" depending on what side you are looking at). Sliding the prussik on control end is = sliding it on dynamic leg to load from overhead support(ie. "N" loses return to ground leg & becomes a "V" 2:1) = sliding it on inversion(equal/opposite) of same: our DdRT; on moderate/bodyweight type of loading tensions on their control legs; that are prussic adjusted.
 
In my local, we are always pulling tree's over, around
60-100 a day, 12"-40"dbh, and 1000#-7000# trees, on tranny lines. I have always used a VT for attachment on 5:1 advantages. Never burned it and it has only slipped twice, due to ice and snow on the rope. Overloaded it? probably a time or two, but it has always held. 6-7 wraps seemed to get the job done.

Try the VT maybe the ticket for your needs.
 
The amount the hitch gets loaded = [(force needed to flex hinge thickness/leveraged distance:angle from hinge)/5]. So how high you set line, to how stiff a branch per how thick a hinge you try to force can give one person overloading hitch and another not; in seemingly same setup. Then there is the rope devices themselves to consider...

Less static; is more stretch and thinning of line. More length of rope system is more stretch and thus thinning too. But still construction of rope device itself as main operative...


i think rope construction/ how the rope device conducts force and then the mating textures between mating parts (rope internals and rope to prussik) has a lot to do with slip/melt in pulls(as well as to how well prussik's are reverse set etc.). Comments made previously where more to tending hitch to lower through hitch without other brake device; then i go with the mechanics of a single leg loaded(SRT) or multiple(non-SRT).

Like a kernmantle carries the force on the inside; yet you try to grab it with the outer mantle with prussic system. So, a lot of times pinching through with cam seems better. Double braids carry half force on outside; so you only grab half of it and try to stop etc.

In English as a language; we say one part has leverage over the rest if it is point of less force at same time. So we have 'rolling levers' and lever here in pulley system. But, mechanically (for those types of comparitsons to other leverage examples) i don't know if that is apt. For a pulley system is just a bunch of inline forces , stacked together; with a constant direction. In "other levers"; the force is dependent on sine/cosine of angles from each point (and length at inflexible points); and direction is constantly changing/turning(tourque).

But, if we change a round table from having 1 pedestal leg in center, to having 1 in center and 4 at the outer 'corners'; we don't say we have a 5:1; nor that the single leg has leverage through the rest. We just see the load as divided amongst 5 supporting legs. So, i see a 5/1 pulley rig as same mechanics whether a tension(rope) or compression(table) flow through the legs of support example (covering flexible and inflexible ends of the support spectrum).

i think it is important to segregate such things correctly to see the patterns more clearly; as well as definitions between. L-earn in groups, but correct groups. Now, if each table leg was leaned over 30 degrees, they each would be leveraged. So each leg would be leveraged to higher than it's input force; but seeing as the weight of the table was the preceding force; (and the rest responding forces) we don't have leverage onto the work, but rather the work load leveraging against 'us'. Besides, pulley is really a 1:1 1st class lever; and the calculated leverage changes are due to where that lever is placed in system; not it's angle etc.


orrrrrrrrrrrrr something like that...
 
Even if the prusik didn't slip, internal friction caused by load on the rope (in this case between the rope and the prusik) can cause the rope to melt. An example of this is the tensile strength test performed on climbing ropes. When the rope fails, it doesn't usually snap, it melts apart. On larger ropes you can see smoke come out of the rope before failure and the resulting ends will be melted.
 
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