Author Topic: adjustable grip bend  (Read 18606 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*
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TS

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Admiral Hitch vs Adjustable Grip Hitch
« Reply #77 on: January 13, 2021, 09:33:31 PM »
I believe my variant of the "Grapple Hitch", (to which I add an extra turn, and which I call the "Admiral's Hitch"), is superior to the Adjustable Grip Hitch in just about every way, when tied around a single rope to form an adjustable loop.  In fact, it is made almost exactly like the AGH, except that the running end is, finally, tucked UNDER THE STANDING PART, (rather than under itself), in the final step.  This causes the knot to form differently, and ultimately to grip harder.  I'd appreciate any feedback.

I've attached images of

1. A Grapple Hitch (ABOK 1231)
2.  A fully formed Admiral Hitch
3.  A partly formed AGH versus a partly formed Admiral Hitch (GIF)

Dan_Lehman

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Re: Admiral Hitch vs Adjustable Grip Hitch
« Reply #78 on: January 16, 2021, 12:31:56 AM »
I believe my variant of the "Grapple Hitch"
--to which I add an extra turn, and which I call the "Admiral's Hitch"--
is superior to the Adjustable Grip Hitch in just about every way,
when tied around a single rope to form an adjustable loop.
//
I'd appreciate any feedback.
Thanks; your 3rd image --switching between knots--
nicely shows their difference.

I just tried the knots in some parachute(-like) cord,
and then in some 1,200# cable--pulling polyester tape
(which admittedly isn't the sort of thing one would
expect friction hitches to work at all well with; it's
thin, soft-flexible but lubircated (!).
method (NOT "methodology"!)  :: I tied each knot
at ends of the test specimen with the eyes around
marker pens (plastic), and standing on one (sort of,
careful not to bind to ground) gave a good pull.

One knot performed, um, admirably in the cord,
but not so well in the tape --a split decision.

IMO, your knot puts more of a dog-leg/bend in the
hitched-to line, and thereby gained grip in the cord,
but w/o good effect in the tape.   The other hitch
I think gets more out of the turns and this helps
with the tape.
GIVEN what you show, YOUR knot I think stands
to gain more from an extra turn (as the other has
more of that already at work).

Now, I'm not sure what you had in mind for
"in just about every way" ?!


Cheers,
--dl*
====

TS

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Re: adjustable grip bend
« Reply #79 on: January 16, 2021, 09:06:12 PM »
Hi Dan

"In just about every way" was an overly-broad statement, I'll admit, but I was only talking about its use to form an adjustable loop in rope, much as a midshipman's hitch might be used or an AGH.

In paracord and thicker cordage, (I've tested up to half-inch stuff, mainly braided rope), I've found that this hitch can be locked into place tighter than any other hitch I've tried, (you hold the lower, "working" end of the loop with one hand, and pull the tail in the opposite direction, to lock it in place).  Later, the hitch can be loosened by bending its "wings" down, (you know what I mean).  In boat rope, this hitch might serve well as an adjustable bowline, in my opinion.  I don't see it working in hawser, etc, and I agree that it's TERRIBLE for tape, if you want it to lock.  I find that a simple "grapple hitch", (with one LESS turn), actually holds tighter in tape.

TWO Admiral Hitches, tied mutually around a pair of similar ropes you'd like to join, create a situation where each hitch only holds HALF the load, much as TEX has ably demonstrated elsewhere, using the AGH to form a strong bend.  I call my joining an "Admiral Bend", and I believe that it's stronger than the AGH bend.

I'll admit that the Admiral Hitch is NOT meant to be tied around a post or, say, a piling, since the final tuck would be behind the post itself!  The Admiral Hitch is purely a rope-to-rope hitch.

I hope I haven't offended my friend, Dave Root, by this post, but he encouraged me to post the Admiral Hitch here in the first place!
 

JohnC

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Re: adjustable grip bend
« Reply #80 on: February 06, 2021, 06:24:36 AM »
Any chance of two separate images for 1) A partly formed AGH, and 2) A partly formed Admiral Hitch.

I agree the animation shows the difference clearly, but I'm finding it impossible to tie either one with it jumping back and forth - as my eye flicks up to the screen from the cord in my hand, by the time I've registered which knot is depicted it has changed!
John

JohnC

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Re: adjustable grip bend
« Reply #81 on: February 06, 2021, 06:51:40 AM »
Just as an aside, I'm grateful for an introduction to the Prohaska knot/Blake's hitch, which seems to have solved a small problem for me.

I have woody weeds that come up everywhere on my (rural) property. I prefer to pull them out by the roots since they regenerate if cut, but they have very strong root systems and even at 18" high they defeat my two-handed grip and leg strength. Especially when the ground is rock hard.

I've tried various tying methods to lever them out with cord and a length of steel pipe, but so far all attempts have either snapped the stem or stripped the bark and run the knot right off the (now) slippery stem. I suppose I could join the gym and work on my clean and jerk technique, but using knots is more fun.

The Prohaska knot has passed the test this afternoon on a couple of samples that would have been too much for me without mechanical advantage. It does actually strip the bark at first but then grips the gathered mess. It's good enough to actually lift a clod of earth as wide as the roots without breaking the stem. A very satisfying result.

fwiw, the first site google led me to (krok.biz) for a picture of this knot has reference to Dan Lehman's "series of adamant emails insisting that I give Prohaska credit". So the message is getting through.

[Edit: added photo of first two victims]

« Last Edit: February 06, 2021, 07:15:39 AM by JohnC »
John

TS

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Re: adjustable grip bend
« Reply #82 on: February 06, 2021, 09:34:45 PM »
Here are the two images that I used to create the GIF animation of the Admiral hitch vs the AGH.
I hope this helps.

JohnC

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Re: adjustable grip bend
« Reply #83 on: February 09, 2021, 05:19:47 AM »
Thanks, the two illustrations are appreciated.

First impressions are that the Admiral hitch is admira-ble and superior to the other.
John