Author Topic: A working hybrid  (Read 2038 times)

DerekSmith

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A working hybrid
« on: February 19, 2014, 11:56:09 AM »
Two minutes into this tree climbing video you will see a friction knot which is a rather sweet hybrid of a four turn friction knot core, finished with two of the garter wraps of the KC hitch, rather splendidly finished with a bina and a pulley.

I have tried this friction 'knot' using the Pinto Pulley and it really is a dleight to use - instant unlatch and latching again the moment the garter scissors open up.  Pull on the belay line through the pulley and the pulley squishes up the scissors and pushes the four turn core up the belay, the moment you let go of the belay end and load the bina, the scissors open and locks movement back along the belay until you put pressure onto the top of the four turn core, then it slides easily back down.

Of course, you don't need the pulley, nor even the bina, a simple OH tied across the two ends is more than enough to stabilise the friction knot.

http://www.youtube.com/watch?v=6X2AvTQjB_I&feature=c4-overview&list=UU7jakWKUvZqiH7q7dNJau6w

DerekSmith

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Re: A working hybrid
« Reply #1 on: February 20, 2014, 04:06:54 PM »
Question for you Scott,

What material do you think that the friction hitch is made out of, it seems very soft?

Derek

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Re: A working hybrid
« Reply #2 on: February 20, 2014, 05:48:03 PM »
Hi Derek.

I think most prusik cord material will work with this arrangement, but the cord in the video looks to be http://www.teufelberger.com/en/products/arboriculture/accessories/ocean-polyester-8-mm-10-mm.html
Composed of a polyester/aramide sheath and a polyester core.

There are so many choices now that contain a slew of material mixes and sheath braid styles and core combinations!

Soft is good on stiff main ropes and stiff is good on soft main ropes. I find this to be true in my usage (soft for static rope when ascending after an abseil and firm when self tending on dynamic) and it is also suggested by many other professionals (arborists, rescue techs, rope manufacturers).

One of the things to look for in a prusik material is heat resistance, as well as abrasion resistance. Invariably there will be slippage from time to time.  ;)

There are a few names for the hitch used in the video, some with more or less coils at the top and more or less crossings at the bottom. Type of cord, length, main line material/construction, man weight and accompanying hardware play in what is used.
The one in the video has good friction-grabbing ability yet releases easily so the tending pulley can advance it.

Also, what they have learned from another and are most familiar with (what works for them) is most likely the champion decision maker.

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Sweeney

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Re: A working hybrid
« Reply #3 on: February 20, 2014, 05:53:50 PM »
There are a few names for the hitch used in the video, some with more or less coils at the top and more or less crossings at the bottom. Type of cord, length, main line material/construction, man weight and accompanying hardware play in what is used.
The one in the video has good friction-grabbing ability yet releases easily so the tending pulley can advance it.

In the video the narrator refers to the knot as a "VT" - meaning a Valdotrain Tresse commonly used by arborists and as Scott says it has good friction-grabbing..

Barry

DerekSmith

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Re: A working hybrid
« Reply #4 on: February 26, 2014, 11:58:21 PM »
Thanks Scott,

Strange writeup on the website for the Ocean Polyester.  The makers state it was designed for hitch cord being abrasion and heat resistant, then they go and add this little gem -

Do not use this product to secure persons or for hoisting purposes, in compliance with the European Directive 2006/42/EC.

??

What do you make of that?

@ Barry,

Do you know anything of the history or development of the VT ?

Thanks both

Derek

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Re: A working hybrid
« Reply #5 on: February 27, 2014, 01:55:00 AM »
Thanks Scott,

Strange writeup on the website for the Ocean Polyester.  The makers state it was designed for hitch cord being abrasion and heat resistant, then they go and add this little gem -

Do not use this product to secure persons or for hoisting purposes, in compliance with the European Directive 2006/42/EC.


I looked at the ED2006/42/EC and my eyes hurt now and I'll pass on the legalese.
I have to imagine that it may be a blanket statement for products below a certain diameter.  So someone does not use it for their climbing main line or lifting a bundle of lumber with it.
Your guess is as good as mine.

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Sweeney

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Re: A working hybrid
« Reply #6 on: February 27, 2014, 11:17:32 AM »
The EC Directive applies mainly to machinery (this may help: http://www.hse.gov.uk/pubns/indg270.pdf. Manufacturers are required to certify a product if it is to be used for lifting people or for hoisting something so that firms can be sure it is safe for employees etc to use. The rope in question may be perfectly safe for eg tree climbing but the manufacturer is not prepared to certify it for such a purpose possibly because to do so would involve expensive testing of a product they do not wish to market as "climbing" rope.

I have come across the VT several times in videos etc for arborists but never seen anything about its development although it seems to have been around for quite a few years.

Barry