Author Topic: adjustable grip bend  (Read 16248 times)

Tex

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Re: adjustable grip bend
« Reply #75 on: May 13, 2015, 01:55:41 AM »
Mechanical Advantage

I'll try to make it not too long.  This Perfection round turn and two half hitches (PRTHH) does not actually have a 2:1 advantage as a knot rope system unless the low tension side is relatively short.

For equal length linear-spring ropes* without friction you get a 2x force on one side and 1x on the other which after releasing settles to 1.5x on each side.  So you get 50% more final tension than what you pulled with. 

Whatever fraction of work you do on the high tension side comes at a 2:1 advantage but the work done to stretch the low side comes at a 1:1.  So if you're doing work on both both sides like Batman, you have to realize you'll get less than 2:1.  In a normal binder both sides are the same rope, so then we have a paradox to solve.  This is the essay test question and it's not so easy.

I think it's safe to say the KNOT has 2:1 maximum advantage used the right way, but the knot-rope system is lower than that.  I think PRTHH has at least 25% less friction than sliding grip knots too though so that's at least 1.5 / 075 better, still twice as good maybe before factoring in two-hands, whole-body pulling.

*Dynamic and linear are not quite the same.  Steel cable is a very elastic spring, and probably reasonably linear, at least in some range, but I don't think it would be called a dynamic climbing rope because its elastic modulus is too high.  I guess you could have a very non-linear and/or non-conservative rope with an appropriate range of stretch to be called dynamic still. 
« Last Edit: May 15, 2015, 04:56:20 AM by Tex »

Dan_Lehman

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Re: adjustable grip bend
« Reply #76 on: May 14, 2015, 07:40:21 AM »
Hi DL,

Well, I haven't researched it, I'm just trying to go with the best of what I know.  Wikipedia, notable knots, and animated knots all say the same thing (and, I'm afraid, they don't mention you.)
Oh, actually, Grog does --or did. (generally)   ;)
And that Wiki text, goodness, that does have a
particular sound to it (my writing, i.e., or a good
imitation).  I've not seen the Prohaska-published
source, but Thrun might have, and I trust Heinz.
And I trust that it's a publication pretty obscure
and unlikely to have been seen by Blake, though
Nylon Hwy would be closer to home.

Quote
I'm sorry but I can't precisely tell your position on the issue other than that Prohaska is a bit too funny (I don't find it giggly, but I don't know, I meet many people from many places; it's less memorable though.)   
?!  I'll grab poor memory, just to say that
the "giggly" bit is Heinz's original? name "Gestecke Wicklenotten"
or something like that (my poor imitation of German) !

Ahhh, whew, a Search of mail-not-deleted... yields the prize,
chatting w/Bob T. --to wit
Quote
>I have also learned that Heinz Prohaska sent the
>hitch to Charles Warner with the suggested name of "Tucked
>Coil Hitch", which is better than "Gesteckter Wickleknoten"
>for us English speakers.

Well, "gestecker wicklee-note'n' " has a cute ring to it!
(-;

Quote
I meet many people from many places
I recall with a smile a colleague remarking at the
conference name-label seen lying about reading
"Bernt Dinklage" "Oh, that sounds painful!".
When presented with "Lehman8" make "lemonade"?   ;D


My thoughts of incorporating "klamp" as a "clamp"
with German flair(?) stems from what I take to be
a bona fide German word/component "klem", as
the Hedden hitch was named "kruezklem"
for "cross clamp".  (... from memory here ...)
("klemheist" also >> "clamp hoist" could it be?)

Beyond that, though, the knot (that "rose by
any name") peformed well --best-- for the Lyon
Equip. testing, not slipping and strong, tested
in low-elongation kernmantle ropes (and maybe
one dynamic 10mm?).

Quote
From wikipedia:
Quote
The first known presentation of this knot was made by Heinz Prohaska in an Austrian guides periodical in 1981; in 1990, he presented it in a caving journal, Nylon Highway. Separately, Jason Blake discovered the knot for himself and presented it to the arborist community in a letter to Arbor Age in 1994, after which it was enthusiastically adopted by arborists. It has since become well known under the name "Blake's Hitch"."

Of course the word "known" is relative. It seems maybe (not surprisingly I guess)
you know something Wikipedia doesn't.  Of course you can edit it.
:)  Yes, I could.
(Sometimes that can become a repeated process,
for various reasons!  The origin of the "zeppelin" knot
got a hard knock a few years back, leaving us with
loose ends and doubts, and one more mystery.)


--dl*
====