Author Topic: Constrictor bend?  (Read 16462 times)

DerekSmith

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Re: Constrictor bend?
« Reply #15 on: November 25, 2007, 10:32:32 AM »

SS369

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Re: Constrictor bend?
« Reply #16 on: November 25, 2007, 04:21:30 PM »
Hi Derek,  I am assuming that on the terrific Root site you are indicating the Adjustable Grip Hitch as the same as the sliding grip hitch??
Sorry but I get really messed up with the changeability of knot names.
Perhaps one day we will have the "standard" names logged somewhere or will have adopted some such somewhere.
Maybe that's for another thread,,,,,,, again?
SS

DerekSmith

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Re: Constrictor bend?
« Reply #17 on: November 25, 2007, 08:38:11 PM »
Hi Scott,

I think the confusion is of my making. The knot is indeed called the Adjustable Grip hitch as depicted by Dave Root.

For some reason I just keep calling it the sliding grip hitch, which when you think about it is a really stupid name because it doesn't slide, it grips and it is adjustable.

Rather than trying for name standardisation, it would probably be a better move to ban idiots like me from getting too near to a keyboard !!

Sorry for the confusion, but I hope you enjoy Dave's site.

Derek

dfred

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Re: Constrictor bend?
« Reply #18 on: November 25, 2007, 10:37:02 PM »
Sorry I haven't had a chance to respond here since the discussion
really got underway...

Idleness is the devil's workshop.

But why stop with half (or one quarter!) of the work?

Well, even my idleness has limits. :) The two variations with the
constrictors progressing towards the center of the bend are fairly
obviously not practical; they are even more fiddly to tie and do not
release easily.  I did consider the identically handed variation...
It produces a similar bend, but I thought the symmetry of the mirrored
version made a nicer knot; specifically that the mirrored version
seemed to create more friction within the knot due to the curvier
paths the standing parts take through the center.  But intuition like
that is often wrong, it would be interesting to know if one is notably
stronger than the other...


Well, I have played with this knot for a while before subjecting it to
comparative strength tests and concluded that I did not like it.  It
is a big ugly knot...
[...]
To date, I have not tested any 'practical' bend that is stronger than this.
[...]
Once loaded to almost breaking point, the knots are impossible to break open. 
I will attempt to photograph the survivors so that you can see the final highly
loaded form which shows the straight line transmission very nicely.

Thanks for working through your aesthetic prejudice. :)   When I posted this I
was hoping to entice you to test this knot, however I didn't really expect such
promising initial results.   And thanks to both you and Dan for the strength/testing
analysis and discussion.

I'll forgive you for calling the knot ugly, but I do object to the word big.
While the CB is a long knot, it is not particularly bulky or large in
diameter.  It seems possible that its length may be what gives it some
of its strength by spreading the force over more area as you
suggested.  As far as being difficult to tie, I think like anything
that's a matter of practice.  While the loop method for tying
constrictors is quick and useful, I find myself forced to tie the
constrictor with the end quite often.  Being able to tie it both ways
quickly is worth learning.  But, in any case, I do agree with your
basic assessment that the CB takes a little more fiddling than some
others.

Given my observations of the bend's behavior at "normal" loads (say,
<20% BS) in somewhat larger rope (6-9mm) I had wondered if the
internal friction would make it a strong knot or be its downfall at
breaking loads.  I was especially worried about the shearing forces in
the very center of the knot.  I'll be very interested when/if these
kinds of tests can be repeated in rope sizes used in real-world load
bearing applications.

Regarding the releasing behavior, does the statement above mean all
the knots you test to near-breaking in this line are unreleasable?
Given the size and type of line, this isn't surprising.  Actually,
though, I'd imagine that any rope near it's breaking point within a
knot will start to deform to an extent that will make untying the knot
very difficult, if not impossible.

Just as a side thought, it would be interesting to know if any knots
can break other knots and still be released themselves.  That is,
could the CB break a sheet bend or some comparatively weak knot, and
still be untied.  At the very least it might give a sense how much relative
distortion/damage was occurring inside of various knots.  But "can it
be untied" is a significantly less objective measure than "which knot
broke first", so probably not something to add to the actual
comparative testing procedures...


« Last Edit: November 25, 2007, 10:41:50 PM by dfred »

SS369

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Re: Constrictor bend?
« Reply #19 on: November 25, 2007, 10:54:50 PM »
Hello Derek,

thank you for the clarity.

Dave's site is just one of many truly amazing undertakings that I visit before, after and during these discussions. I did search through my electronic version of ABOK (alas the pdf search function was useless) so a case of near bleeding eyes followed. But I did want to know.

As for the banning of idiots too near a keyboard? Not likely or we would all be banned from time to time. Certainly I would be.
Self deprecating humor complete now.

Thank you for your incites (insights) and the testing. It is appreciated.

Could the release ability and strength of the CB bend be addressed favorably with the addition of slipped working ends?

SS

DerekSmith

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Re: Constrictor bend?
« Reply #20 on: December 06, 2007, 10:46:10 AM »


Could the release ability and strength of the CB bend be addressed favorably with the addition of slipped working ends?

SS

Scott,  while it is possible that adding more padding to this knot might help increase its strength, I do not think anything will help its untying.  Once the knot had been loaded to roughly half the line breaking strain, the knot has formed into a rock solid lump.  There is no way a slipped end could be pulled free from such grip.  But having said that, it is important to again reiterate the important issue raised by Dan - that the results are likely to be as much a consequence of the cord as they are of the knot itself.

The cord I use is R20C Polyester cored braid.  While this little 2mm cord can support the weight of a large man before breaking, it will also stretch to nearly double its length under that load.  This characteristic has important consequences for a knot under load, because as the load goes up, so the cord in the knot itself stretches and 'feeds out' of the knot.  So, if I were to take a knot up to say 80kg load, nearly 40% of the cord in that knot would feed out due to tension and depending on the knot another ca 10% to 20% would feed out as the knot itself drew up tight.  When the load is then removed, the knot 'grips itself closed with most of that 80kg tension - the knot is effectively 'pre-stressed' with 80kg tension.  Just because we have removed the load on the cord does not mean that we have also released the load within the knot, it still clamps itself together with the elastic forces stored in its strands.

If we were to tie this knot in a cord with low stretch characteristics, I am confident we would see a totally different set of knot characteristics -- perhaps ease of opening might be one of them and slipped ends might be feasible.

Derek

Dan_Lehman

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Re: Constrictor bend?
« Reply #21 on: December 07, 2007, 10:28:57 PM »
Dave, I find the knot bulky--and in a kind of jagged way, too (pointy
parts protruding), inviting abrasion abuse.

Just loaded a softish double-braid (like a rope within a rope--same structures)
joined with similar-sized climbing kernmantle:  the latter wins the race condition
to which strangles which first, and its SPart runs straighter with the tighter grip on
the softer rope; the two components don't readily slide to abut, but at least
partially take a friction grip (and accent that elongated aspect).  One can
dress & set the knot othewise.  But in either case, I don't see it possible to
completely remove the burden of the later parts (in terms of force transmittal)
of the Constrictor being relatively untensioned bulk bits to be compressed.
Consider, e.g., what the Fisherman's knot would look like in Derick's cord
as one looks at this knot--each end just turning immediately and exiting the
SPart wrap of its opposite.

The stretch Derek's polyester(!) cord is giving is amazing--I'd think that both
the material AND construction worked towards minimizing elongation (which
is usually seen as a negative aspect)!?  Rockclimbing ropes in fact don't
stretch much more than 50% at rupture, I think.

The thinking that adding a slip-tuck for the end enables easy untying is one
of the common bits of nonsense propagated in knots books--often in talking
about the Constrictor (which is given the myth of being impossible to untie
and "must be cut"--parroted rubbish!).  If a knot tightens so much that it's a
pain to loosen, it will similarly be a pain to get the slip-tuck to move, and
given that, to come completely free--the sort of bulb of the very bight-end
being a sort of knob impeding further removal.

--dl*
====
« Last Edit: December 07, 2007, 11:08:09 PM by Dan_Lehman »

Dan_Lehman

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Re: Constrictor bend?
« Reply #22 on: December 07, 2007, 11:07:15 PM »
The two variations with the constrictors progressing towards the center of the bend are fairly
obviously not practical; they are even more fiddly to tie and do not release easily.
I think you've lost me, and maybe vice versa (or I lost myself, earlier).

What is obvious is that with a C. tied around the opposite rope, there are TWO
ends, either of which might be taken qua SPart for this opposed-knots bend;
you chose to take the end that wraps away from the knot center, and I'm
suggesting the other, for consideration.
Now, with the same mis-matched (like dia., diff. firmness...) ropes as I used above,
I've tried this other-way bend (concordant form--likehanded), and it shows less of
the race condition issue, and maybe unties morEasily--certainly those end
collars, now being UNtensioned, pop away w/o trouble, leaving a sort of bulked
up Dbl.Harness Bend to work loose.  Actually, it's not so tough,
and the there is forcible loosening to be had, here.  With a
2nd stressing, the C. components left apart to start, I find signficant
gripping and slow slipping-together.  (I''m putting maybe 200#? on
this roughly 8mm cordage.)

Quote
Thanks for working through your aesthetic prejudice. :)   When I posted this I
was hoping to entice you to test this knot, however I didn't really expect such
promising initial results.
With Derek's comparative method, if I'm reading it right, he has a bend on each
side of a loop of cord running around pins.  What can happen is that one knot
can yield more material and so lengthen its side and reduce tension while the
other side remains relatively higher (because of the friction of the pins).  In the
present case, though, I'd think that the Grapevine would give as good as it got?

Quote
Regarding the releasing behavior, does the statement above mean all
the knots you test to near-breaking in this line are unreleasable?
It shouldn't.  Ashley's #1452 & 1425-tied-a-bit-loosely should not jam.  In real
ropes, sometimes bowlines are tested with a loosenable survivor (and some
have reported jammed bowlines in e.g. old climbing rope (stretchy & frictive)).

--dl*
====

DerekSmith

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Re: Constrictor bend?
« Reply #23 on: December 08, 2007, 01:39:18 PM »

With Derek's comparative method, if I'm reading it right, he has a bend on each
side of a loop of cord running around pins.  What can happen is that one knot
can yield more material and so lengthen its side and reduce tension while the
other side remains relatively higher (because of the friction of the pins).  In the
present case, though, I'd think that the Grapevine would give as good as it got?

Quote
Regarding the releasing behavior, does the statement above mean all
the knots you test to near-breaking in this line are unreleasable?
It shouldn't.  Ashley's #1452 & 1425-tied-a-bit-loosely should not jam.  In real
ropes, sometimes bowlines are tested with a loosenable survivor (and some
have reported jammed bowlines in e.g. old climbing rope (stretchy & frictive)).

--dl*
====

The test rig has two 1" dia silver steel bars as the top and bottom 'pins'.  The bottom bar rests on a flat surface and is free to 'roll' on that surface (the bottom of the jack and the axle stand).  The top bar is mounted in roller bearings and is also free to rotate so there should be absolutely minimal difference in the forces in each leg of the test cord.

#1425 and #1452 locked up rock solid in R20C but #1451 with its marked 'hinge' component could always be opened simply by bending the 'hinge', but all these three knots were quite aggressive on the cord and I believe they will come fairly well down the list of comparative strength when the bends are put to test, so the degree of loading they had been subjected to was not a much as the C. bend had sustained.

Derek

Dan_Lehman

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Re: Constrictor bend?
« Reply #24 on: December 08, 2007, 07:13:38 PM »
#1425 and #1452 locked up rock solid in R20C
 but #1451 with its marked 'hinge' component could always be opened simply by bending the 'hinge',

Hmmm, it'll take a photo to understand this.  Esp. #1425--again, esp. if dressed to be a little loose--
shouldn't jam.  (Maybe if set too loose, it deforms somehow into jammable shape?!)

And do consider the other main version of the Opposed-Constrictors bend.  I gave it a harder
loading in heavier ropes (again, diff. natured but similaly sized ropes), and it looks half-decent.
Maybe I'm making too much of its potential for "forcible release", but it so far appears good.

 :)

Dan_Lehman

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Re: Constrictor bend?
« Reply #25 on: December 10, 2007, 10:01:38 PM »
Looking over some old notes, I see that I tied very nearly this bend (and in
discordant version, I might  add) but instead of a Constrictor I made the
intial turn pass under itself (so there is more material between the opposed
SParts at the ends of the knot), the rest being the same.  (1996 record from
something hanging around for a few years, it seems--sometimes it takes a
while, and motivation, to put ink to paper and liberate some play rope.)
My only remark re behavior suggests that I'd hoped it would work like
opposed friction hitches--I note that it slipped in a stress check.

Looking at it again, now, I think it should have more chance of being
loosenable, as the initial, u-turn of the SPart encompasses some of
the end, unable to force it away, and thus doesn't make that Blood-knot-like
tight turn around the opposite SPart.  The course of the SPart through the
knot is a little bent by other parts of it, so must be taking off some load in
the process.  I've just used two different sizes (tied together) of a marine
kernmantle-ish rope (my terms:  core is a collection of *kite-strings*;
mantle is criss-cross of collections of them)--about 7 & 8mm.
The thinner cord tightened more on the other and had a straighter
passage through the knot, and was harder to loosen.

--dl*
====

Transminator

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Re: Constrictor bend?
« Reply #26 on: May 25, 2011, 09:00:29 PM »

The thinking that adding a slip-tuck for the end enables easy untying is one
of the common bits of nonsense propagated in knots books--often in talking
about the Constrictor (which is given the myth of being impossible to untie
and "must be cut"--parroted rubbish!).  If a knot tightens so much that it's a
pain to loosen, it will similarly be a pain to get the slip-tuck to move, and
given that, to come completely free--the sort of bulb of the very bight-end
being a sort of knob impeding further removal.

Well, this is just as dogmatical as the "common bits of nonsense and parroted rubbish" you refer too.

1. Though I do agree with you that a jammed knot clamps down on the slip just as much as on the single end tucked through,
in most situations the knots are not loaded so much as to completely jam and then the slip tuck is very helpful. While you still
try to work a bight into the end you want to pull free,  I have already pulled the slip through and undone the knot.
2. Even if your knot has completely jammed, the slip is still an advantage. First of all you have a long end sticking out that you can pull.
You can wrap it around your hand or use a toggle and a marlinspike hitch to try and jerk it free. You cannot do that with the single tuck.
First you have to work a bight free, which may be next to impossible when dealing e.g. with a constrictor that has been tighten on something
soft that gave in or a convex surface, on which it works best.
If jerking the bight through fails and the slip does not want to move (because of the "bulb" you mentioned) you still have the advantage of already having a bight free for pulling. Insert a hand or toggle into the slip and try to pull the end out the other way.

So how on earth would a slip-tuck not be an advantage?
Maybe not all knotting authors are "merely parroting nonsense" but have put it to the test.
And a distinct feature of the constrictor, which is its merit, is that it jams. Though it may not be impossible to untie, it is certainly hard to undo a tightend constrictor
and in some cases (next to) impossible and that is what most knot books I know state and not a dogmaticall: "must be cut" that you claim they do. But there might be examples of that.

In my personal experience a slip-tuck enables speedier and easier untying in most situations and gives a distinct advantage when trying to undo a jammed knot.

Dan_Lehman

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Re: Constrictor bend?
« Reply #27 on: May 27, 2011, 04:34:40 PM »

The thinking that adding a slip-tuck for the end enables easy untying is one
of the common bits of nonsense propagated in knots books -- ...

Well, this is just as dogmatical as the "common bits of nonsense and parroted rubbish" you refer too.

Though I disagree, at least it would be some *balance*, at that.
 
Quote
1. Though I do agree with you that a jammed knot clamps down on the slip just as much as on the single end tucked through,
in most situations the knots are not loaded so much as to completely jam and then the slip tuck is very helpful. While you still
try to work a bight into the end you want to pull free,  I have already pulled the slip through and undone the knot.

The red doesn't follow necessarily from the orange.
And in the interim --i.e., the knot's duration in use--
there is the concern (possibly) of the slip-bight being
a vulnerability to snagging.  It is of course a different
tying, and consumption of material.  --> misc. factors

Quote
2. Even if your knot has completely jammed, the slip is still an advantage.
 First of all you have a long end sticking out that you can pull.

Tail length isn't defined by *slipping*.  For some knots, one
might anticipate difficulty in untying by leaving a long tail,
but it's not a given for this slipping of a knot.

Quote
You can wrap it around your hand or use a toggle and a marlinspike hitch to try and jerk it free. You cannot do that with the single tuck.

Well, in the case of the constrictor, one can gain by some
hard pulling to develop some loosening of the opposed
end (playing on an aspect of why the c. isn't favored qua
hitch).  One need also care about how much damage is done
to the material.


--dl*
====

xarax

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Re: Constrictor bend?
« Reply #28 on: June 20, 2011, 03:42:42 PM »
   I find very difficult tp predict how this bend is going to behave under extreme loading. The distribution of tensile and compression forces is very complex...It is obviously an interesting, secure bend. It is not "bulky", but elongated. It is easy to remember and tie, although it it takes some more time than similar "long" bends. I think that in the "antisymmetric" form, although it is not as nice as in the original form shown by dfred, it is easier to inspect, because we have to look it from one side only. (See attached pictures) Without any doubt, a bend that deserves to be tested on "Knot Wars", with all the other "new" interesting and potentially practical bends we have. 
This is not a knot.

TheTreeSpyder

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Re: Constrictor bend?
« Reply #29 on: June 23, 2011, 01:24:24 AM »
i predict....

That, the fig.8/constrictor forms won't carry as much line tension thru their turns, to stabilize and pass force from 1 leg of line to the next, as much as 2 double nooses/barrels to each other in a bend.

Many times we seek to add this twist or turn to lessen force to the final nip for best security.  BUT, when the line tension passed can be put to work to not only deform the fully loaded Standing Part with a Turn around it,  but to take another clean Turn around to stabilize the deformity some.  Especially in this mechanic, where by some of the force is taken to the other line by the Turns, not just the jamming of the nooses together to pass force.

If you were just placing noose around small spar; the bend in the Standing Part, would be a deforming.  But a Double/Round-Turn Noose; would lend another Turn around the Standing, buffering down the effective loss.  But, place a Round-Turn around a spar, then to Double Noose, and the stabilizing effect would be lost (so DL pointed out 1 afternoon) so wouldn't take as much loading; because it was applied with less tension IMLHO .

Also, the squaring effect of the Constrictor isn't needed