International Guild of Knot Tyers Forum

General => Chit Chat => Topic started by: dfred on October 08, 2007, 01:51:59 AM

Title: Constrictor bend?
Post by: dfred on October 08, 2007, 01:51:59 AM
About a year or so ago I was tying a Double Fisherman's bend (#1415) and a
random thought popped into my head...  The DF effectively uses what
are Strangle knots (#1239) around the respective standings parts, right?  So
what would happen if a similar binding knot like the Constrictor was
used instead of the Strangle in a similarly constructed knot?

What resulted initially didn't wow me, mostly due to me not realizing
it needed a slightly modified dressing procedure to take a proper
shape.  But after playing with it a little, I came to think it a very nice
bend which has some unique properties compared to the DF.

I know enough to realize it's very unlikely such a fairly
obvious combo has never been tried before, but in a bit of
searching I haven't been able to find a previous reference to this
bend.  I'll be interested to hear if folks here have seen it before.

However, on the slim chance it's not already known as something else,
I'm tentatively calling it a "Constrictor bend".  Am I right in
thinking that there are no other bends based directly enough on the
constrictor to have already claimed such a name?  (Hard to believe!)
And while more akin to a Double fisherman's, since it is not
based on the Double constrictor, it seemed more reasonable to just use
the unadorned name.

Here are some images that should help people to reproduce this knot:


(http://www.dfred.net/misc/igkt/20071008/dsc_3110.jpg.small.jpg)
Start with two opposing lines, as in a Double fisherman's bend.

(http://www.dfred.net/misc/igkt/20071008/dsc_3111.jpg.small.jpg)
With each end, form a loose constrictor knot around the standing part
of the other line.  The two constrictors should be mirror images of
each other.  The easiest way to assure this is to make the turns of
both constrictors away from the body when tying.

(http://www.dfred.net/misc/igkt/20071008/dsc_3112.jpg.small.jpg)
With the contstrictor knots still somewhat loose, pull gently on the
two standing parts and allow the knots to slide together.  As they do
so they will rotate 180 degrees with respect to each other as they
come together.

(http://www.dfred.net/misc/igkt/20071008/dsc_3114.jpg.small.jpg)
Alternately tighten the standing parts and working ends to tighten the
knot.  Start this process by pulling slightly harder on the standing
parts than the ends.  As slack is worked out of the knot you can start
pulling more forcefully on the working ends which causes the knot to
"lock" in its final position.  This final locking tends to prevent the knot
from tightening much further when load is applied.   Though you really
never need to pull super hard on the working ends or you may overly
distort the knot.

(http://www.dfred.net/misc/igkt/20071008/dsc_3116.jpg.small.jpg)
"Bottom" of tightened knot.

(http://www.dfred.net/misc/igkt/20071008/dsc_3117.jpg.small.jpg)
Side view.  Note how the standing parts mutually trace an "out of phase" sine-wave-like
pattern through the knot.  This seems to give the knot a lot of internal friction and
makes it resistant to overtightening if properly dressed before loading.

(http://www.dfred.net/misc/igkt/20071008/dsc_3119.jpg.small.jpg)
Even after heavy loading, the bend is easily released by prying the
outside turn towards the standing part.  This action completely
frees the working end and allows the knot to loosen.

(http://www.dfred.net/misc/igkt/20071008/dsc_3120.jpg.small.jpg)
Interestingly, when both working ends are un-tucked as in the above step, you
end-up with something akin to a Barrel knot (#1413) -- a knot not known for its
ease of releasing.

Having used this knot for various tasks for the last year or so, I
have a number of observations and comments about it.  But to avoid
overly prejudicing the discussion here, I'll refrain for a bit and see what
people's initial thoughts are.

I am interested to hear from anybody with access to knot testing equipment
regarding this bend's strength.  That's something I haven't been able to
generate any real data on...

David
Title: Re: Constrictor bend?
Post by: knudeNoggin on October 08, 2007, 05:58:18 PM
Idleness is the devil's workshop.

But why stop with half (or one quarter!) of the work?
Consider also the Constrictor the other way round, in this bend.
And also with like/opposite handedness:  so, there are four bends revealed.
Or the Picketline hitch, both ways; and the similar "spar" hitch, #1674.
Of course, of many other such hitch knots that might be pulled together.

*knudeNoggin*
Title: Re: Constrictor bend?
Post by: turks head 54 on October 11, 2007, 06:41:19 AM
Hmmm

Very interesting idea. I will ask around and see if anyone has heard of it.

Turks Head 54
Title: Re: Constrictor bend?
Post by: DerekSmith on November 18, 2007, 06:18:55 PM
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 that does not naturally draw itself up - you have to draw up the ends as well as the loaded lines to dress and set the knot - but worst criticism of all, I just cannot remember how to tie it, so I have to copy it to tie it.  I use the Constrictor a lot and tie it by the loop and fold over technique, so it comes as an absolute pain to actually 'tie' the knot.  Its ends are nicely tucked in and held, so it is a good 'secure' knot, I do not think it would be likely to fall open on jiggling like the sheetbend for example.

For strength, I set it against the Sheetbend -- no surprises, it is stronger than the Sheetbend.
Next I set it against my favorite bend, its close cousin the paired strangles, AKA the Fisherman -- big surprise, it is stronger than the Fisherman.
To punish it for being stronger than my favorite, I then set it against one of the top group of very strong knots, the Sliding Grip Hitch (SGH)-- there was a big bang and the test piece went flying out of the test rig.  When I recovered the test piece, even bigger surprise it was stronger than the SGH.

To date, I have not tested any 'practical' bend that is stronger than this.

I then put this knot up against itself to see just where it would fail, in an attempt to rationalise why this 'ugly' knot could perform with such amazing strength.  Using one of the images posted by David, I have superimposed in yellow the zone where the break occurred (obviously, it only broke on one side, I marked both sides so you could see the above and below of the 'weak point').

(http://knotbox1.pbwiki.com/f/constrictordavid%20copy.jpg)

The force has transfered all the way through the knot to the point where the cord takes its first tight bend.  This knot does not 'constrict' like the strangle does, in fact, because it is necessary to tighten this knot by pulling on the free ends, the knot tends not to cramp down on itself, more so it 'bunches up', so the knot fails by a conventional radial failure after first having lost a significant amount of load by passing through a series of tight, but not constricting, loops, while both the Fishermans and the SGH failed by constrictive weakening.

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.

All in all, a very surprising outcome and a lesson learned not to prejudge a knot.

Well done David, and thank you for bringing us another piece in the jigsaw of understanding what makes a knot 'strong'.

Derek
Title: Re: Constrictor bend?
Post by: turks head 54 on November 18, 2007, 09:35:17 PM
So the constrictor bend is stronger than all those knots you tested?  ???
Title: Re: Constrictor bend?
Post by: DerekSmith on November 19, 2007, 11:56:45 AM
So the constrictor bend is stronger than all those knots you tested?  ???

Yes indeed, quite a surprise -- I wonder what the double Constrictor bend or even the Boar bend might deliver??

Derek

Edit..... 20 Nov.

In deference to Dans later post, I must amend this post by adding --  This knot was the strongest of those tested when tied in R20C polyester braid and loaded progressively to breaking point over a period of ca 2mins. and in the total absence of any dynamic or shock loads.

Derek
Title: Re: Constrictor bend?
Post by: DerekSmith on November 19, 2007, 11:59:50 AM
As promised, here is the image of the Constrictor bend survivor.  Note the near straight flow of the loaded parts into and through the knots, lots of load shedding without undue strangulation.

(http://knotbox1.pbwiki.com/f/Constrictorbend%20sml.jpg)

Derek
Title: Re: Constrictor bend?
Post by: Dan_Lehman on November 19, 2007, 09:05:16 PM
Quote
So the constrictor bend is stronger than all those knots you tested?

This is how the story comes out, and it's missing a key component from the start--typical.
Rather, it is the cord you used was strongest in the slow-tension test when joined
with a Constrictor bend?
.  And one consequence of testing done by those with
different methods & materials would be to immediately (often) deny such an over-reaching
statement.

And what about the ruptured knot--what is left of it to examine?  (--to determine or guess
at the rupture point within it)  The geometry of the knot at high tension doesn't surprise
me, and resembles the general shape of the Dbl.Harness Bend (shown as (one version,
i.e.) the Benson Bend in Rigger's Apprentice, e.g.).  Long ago, an Irish IGKT member
tested some bend I thought to be strong via its few curves of material prior to the ends
making their "u-turn"s; the irony, it seemed to me, was that he had to re-tie it and the
result (perhaps same as otherwise ...) was akin to what one sees here, with SParts
running through knot fairly straight to a hard tight turn on their opposite member;
and the knot though was strongest of those I had tested!  The Reever (& Dble.R.)
Bend is of the general geometry of the Dbl.Harness, too.

This sort of situation seems to be to be a bit of a race condition:  if one SPart can
more quickly tighten around the other (by some imbalance on dressing, say), then
that bias should be aggravated, as the tighter constriction impedes the other's
constriction upon it, further enabling its own increased tightening.
Btw, I think that a surviving SmitHunter's Bend would be similarly tight & untiable.

--dl*
====
Title: Re: Constrictor bend?
Post by: DerekSmith on November 20, 2007, 11:48:08 AM
I nearly missed this.

(http://knotbox1.pbwiki.com/f/Constrictorbend%20sml.jpg)

Notice in this 'after' image, where the loaded lines enter the knot the braid is bunched up and then tapers down as it gets further from the knot.  At this point the core is now shorter than the braided sheath and is holding it 'bunched'.

I cut one of these ends off flush and sure enough the core retracted (or the sheath expanded) back inside the sheath by ca 2mm.

It looks as if the braid expanded more than the core during loading and pulled out of the knot and was then held in place when the load went off.

Has anyone any thoughts as to how this might influence the strength of the cord during loading?

Derek
Title: Re: Constrictor bend?
Post by: DerekSmith on November 20, 2007, 01:07:38 PM
Quote
So the constrictor bend is stronger than all those knots you tested?

This is how the story comes out, and it's missing a key component from the start--typical.
Rather, it is the cord you used was strongest in the slow-tension test when joined
with a Constrictor bend?
.  And one consequence of testing done by those with
different methods & materials would be to immediately (often) deny such an over-reaching
statement.
snip....
--dl*
====

Dan, my apologies.  While I personally am fully aware that the results that come from the testing protocol I used can only be relied upon within the scope of that protocol, I repeatedly forget that others do not think this way and could (and doubtless do) presume that the results are then applicable to all cord and all loading situations.

While a knot which has 'strong' structural characteristics is likely to outperform a knot which has 'weak' characteristics, it would be wrong to imply that this is always the case until we are in the position of being able to understand how all cords and loading environments react to a knots structure.  Clearly we are a long long way off from being able to do that.

It is perhaps worth while making the point that this comparative testing is not being undertaken with the objective of creating 'The Definitive Table of Knot Strength' (such a thing is unlikely to exist), rather, it's goal is to generate information that will allow us to probe the workings of knot structure and performance, such that we can understand which structural parameters cause weakness and how, and beyond that, which cordage parameters (resistance to radial bending, stretch, compression, torsion etc..) interact with those structural aspects and how these in turn influence weakness, then finally, how the mode of loading impacts all of these factors.

Having said that, many people are aware that knots weaken cord and that some knots weaken more than others.  Out of fear of having a knot break on you, it is reasonable that folk will cast around seeking information on which knots are 'strong' and which are notoriously 'weak' in order to make a better choice of knot.  We already have a quantity of 'folklore' relating to knot reliability - vis "Never use the Reef knot to bend different thickness ropes" etc. etc.  That folklore is based on experience, not rigorous testing in all cords and all loading situations, yet we would be foolish to ignore it.  Likewise it is reasonable for people to glean the fragments of knot strength testing results that fly around and utilise them to make assumptions about knot strength in a situation that has never been rigorously tested.

In the absence of any other information, then the results of just one test are gospel.  When contradictory results have been generated, then in the absence of understanding, common sense and individual caution must prevail, but to ignore the results would be foolhardy.

Derek
Title: Re: Constrictor bend?
Post by: DerekSmith on November 20, 2007, 01:36:43 PM
snip...

And what about the ruptured knot--what is left of it to examine?  (--to determine or guess
at the rupture point within it) snip..
--dl*
====

(http://knotbox1.pbwiki.com/f/Const%20remnant%20sml.jpg)

The part of the knot which failed is left on the line, while the side which did not fail sprang open when the line it held was withdrawn by line tension after the break.

Derek
Title: Re: Constrictor bend?
Post by: Dan_Lehman on November 20, 2007, 06:56:38 PM
Derek, you have the best idea of the elasticity of your cord--I recall you
earlier remarking at that, and maybe having to adjust a test specimen
mid-test to account for elongation.  Looking at the broken remnant,
I see tha the Constrictor component is intact:  in fact, it looks both
recognizable AND relaxed--a far cry from the scrunched material
shown of the knot under high tension!  Given that the rupture point here
(relaxed) lies just outside of the component C., we must deduce that
at the point of failure it was farther removed from this point into the
opposite member.  .:.  The yellow'd highlighted areas you nicely show
over DFred's red-rope image should move more away from their C.
knots into the opposite C. knot--in fact, the yellowing should begin at
the point it currently ends (and maybe shorten its span).

Your results seem to follow those of Stanley Barnes in his ca. 1950
book's (available via Des's Footrope Knots catalogue?) analysis
of ruptures in gut & monofilament line tied with Blood knots--at least
for the nylon:  break came MID knot, where the SParts went around
the tucked ends, not at the endpoints/entrypoints (i.e., neither from
the severe turn at far end or the compression by this turn on entry).

I'm not sure how to interpret the particular fibre-blossom of the rupture.
It seems to show some set of evenly chopped shorter fibres, and a bit
of rougher-hewn longer ones (respectively on left/right as oriented);
this might indicate the initial break (being uniform shorts) coming on
the concave side, then a less orderly tear-off occurring?!

--dl*
====
Title: Re: Constrictor bend?
Post by: Dan_Lehman on November 20, 2007, 07:21:29 PM
Quote
  [testing]'s goal is to generate information that will allow us to probe the workings of knot structure and performance,
 such that we can understand which structural parameters cause weakness and how, and beyond that, which cordage parameters
 (resistance to radial bending, stretch, compression, torsion etc..) interact with those structural aspects and how these in turn influence weakness,
 then finally, how the mode of loading impacts all of these factors.

Amen!  (and, most importantly, what are the best colors)

Quote
Out of fear of having a knot break on you, it is reasonable that folk will cast around seeking information on
which knots are 'strong' and which are notoriously 'weak' in order to make a better choice of knot.

Some might, but in nearly all cases, I think that this is a mis-guided effort:  for starters, the information
just isn't well generated; and no one should be using cordage so near to failure that the knot matters
(and, further, one can wonder at the probability of rupture forces coming in just a small enough increment
to distinguish between knots, rather than in a surge of force that would break any).

Quote
In the absence of any other information, then the results of just one test are gospel.
... to ignore the results would be foolhardy.

 ::)  Oh, come on, now!   That's like saying one should believe whatever an 8yr-old says until
one can get advice from a 15yr-old!  (I'll guess that upwards of 99% of all cordage users are
ignorant of the results at hand here, yet are not provably foolhardy.)

Your testing puts some 2nd point of info on a line (as noted above) determined w/Barnes's
data, and I believe we'll see more results to confirm.  --interesting now to consider the case
of the Grapevine, and to speculate that the Reever/Dbl.Reever will follow suit with the above.
(One testing of the Strangle Noose hitch found rupture in the structure SPart at entry, where
the Strangle SPart so tightly nipped it--and not at the u-turn around the 'biner (in 8mm nylon
kernmantle low-elongation (caving) rope).)

Compared to the Grapevine (and further multiple-Oh pull-together bends), the parallel
SParts of this C. bend (note:  discordant) lie farther APART, and there is thus a significant
curve to reach back to the parallel member; the SParts lie together in the Grapevine, and so
more force then is delivered into the u-turn wrap!?  (And I've wondered if the significantly
lesser friction in HMPE plays any role in making these two cases less distinct--i.e., that
even with the angles, the lower friction allows more load to be delivered farther into the
knot, and ... !?  And the nature of the cordage (firm & round vs. softly flexible/compressible)
could cheat angles, too.)

--dl*
====
Title: Re: Constrictor bend?
Post by: DerekSmith on November 21, 2007, 12:52:25 AM

Quote
In the absence of any other information, then the results of just one test are gospel.
... to ignore the results would be foolhardy.

 ::)  Oh, come on, now!   That's like saying one should believe whatever an 8yr-old says until
one can get advice from a 15yr-old!  (I'll guess that upwards of 99% of all cordage users are
ignorant of the results at hand here, yet are not provably foolhardy.)

--dl*
====

It's not like believing an 8 year old, unless an 8 year old had just run or read out the test results.

If 99% of cordage users were ignorant of the results at hand here, then they would not be ignoring the results, they would simply be living in blissful ignorance and hence could not be regarded as foolhardy for ignoring them.   ::)

Besides, when you do not know about strength, there is always the colour to worry about.

Derek
Title: Re: Constrictor bend?
Post by: myoman on November 25, 2007, 04:35:05 AM
is there anywhere I can find how to tie the sliding grip hitch (SGH) as mentioned above?
Title: Re: Constrictor bend?
Post by: DerekSmith on November 25, 2007, 10:32:32 AM
Try the Dave Root site here http://www.layhands.com/knots/Knots_Hitches.htm (http://www.layhands.com/knots/Knots_Hitches.htm)
Title: Re: Constrictor bend?
Post by: SS369 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
Title: Re: Constrictor bend?
Post by: DerekSmith 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
Title: Re: Constrictor bend?
Post by: dfred 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...


Title: Re: Constrictor bend?
Post by: SS369 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
Title: Re: Constrictor bend?
Post by: DerekSmith 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
Title: Re: Constrictor bend?
Post by: Dan_Lehman 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*
====
Title: Re: Constrictor bend?
Post by: Dan_Lehman 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*
====
Title: Re: Constrictor bend?
Post by: DerekSmith 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
Title: Re: Constrictor bend?
Post by: Dan_Lehman 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.

 :)
Title: Re: Constrictor bend?
Post by: Dan_Lehman 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*
====
Title: Re: Constrictor bend?
Post by: Transminator 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.
Title: Re: Constrictor bend?
Post by: Dan_Lehman 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*
====
Title: Re: Constrictor bend?
Post by: xarax 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. 
Title: Re: Constrictor bend?
Post by: TheTreeSpyder 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

Title: Re: Constrictor bend?
Post by: xarax on June 23, 2011, 03:29:10 AM
...the fig.8 / constrictor forms won't carry as much line tension through their turns, to stabilize and pass force from the one leg of the line to the next, as much as 2 double nooses/barrels

   Quite possible. We just do not know. And we are not going to learn anything by just talking... We need experimental evidence, tests. Knot tyers are in abundance, but knot testers is a rare endangered species nowadays...
Title: Re: Constrictor bend?
Post by: Dan_Lehman on June 25, 2011, 06:19:29 AM
Another likely problem with this end-2-end joiner is that it can
become imbalanced, with one end getting the jump (so to speak)
on the other, achieving straightened, less-force-impeded passage
to it turn & nip of the opposite end, which thereby aggravates
the imbalance (impeding the reciprocal nipping that would
ameliorate its own delivered force to its nip).  With ropes of
the same nature (e.g., tying a single line into a circular sling),
the matter is likely addressable by careful setting; but with
ropes of differing natures, the situation is problematic.

--dl*
====
Title: Re: Constrictor bend?
Post by: xarax on November 09, 2011, 03:29:27 PM
   A lanyard bend, based on the Constrictor. (See the attached picture). The same knot can serve as a midspan, mid-line bend (1).

1)   http://igkt.net/sm/index.php?topic=3020.msg21274#msg21274