New Bend?

[Significent]

This is my first post. I am a complete novice at knot tying, but I've come to enjoy spending time at it.

More or less in a vacuum, I've tried to analyze some of the more common knots that are generally described as being strong: around 85% of rope strength. (i.e. Alpine Butterfly Loop, Figure Eight Bend) One of the characteristics I've noted that seems important for good strength is that force be applied to the knot in such a way that the rope bends very obtusely so as not to create a cutting action. In these knots, the primary load-bearing portion of the knot loops around two or three diameters of rope internally, bending gradually in any one direction. With this in mind, I spent a few hours trying to come up with a bend that accentuated that characteristic. After trying multiple approaches, I tied a symmetrical bend in which the load bearing ends symmetrically loop four times around the rope diameter forming, for lack of a better term, a "smooth" circle. As you might expect, the bend is a little bulky, a little difficult to untie, and not especially "pretty", but I'd hypothesize that it's strong. It's not particularly difficult to tie. I haven't been able to find anything quite like it in ABOK although its starting point is a different, common, knot that is generally undesirable.

Now my questions:

1) How does a novice objectively test the strength of a knot to come up with a meaningful measure of strength? From the little reading I've done, there are too many variables to take into consideration. Without buying or building some sort of machine and testing myriad different types of rope, quantifying strength seems a daunting task. Is there a lab somewhere that independently tests knot strength?

2) The bend is simple enough that I can't imagine it's a "new bend". In addition to ABOK, I've Googled, without success, looking for variations of the starting point I used. Is there a place to submit knots for identification?

3) Have I sufficiently embarrassed myself for a "first post"? (Please excuse my lack of proper terminology and naivete?.) By all means, feel free to chuckle.

Thanks for your consideration!

[SS369]

Now my questions:

1) How does a novice objectively test the strength of a knot to come up with a meaningful measure of strength? From the little reading I've done, there are too many variables to take into consideration. Without buying or building some sort of machine and testing myriad different types of rope, quantifying strength seems a daunting task. Is there a lab somewhere that independently tests knot strength?

2) The bend is simple enough that I can't imagine it's a "new bend". In addition to ABOK, I've Googled, without success, looking for variations of the starting point I used. Is there a place to submit knots for identification?

3) Have I sufficiently embarrassed myself for a "first post"? (Please excuse my lack of proper terminology and naivet?.) By all means, feel free to chuckle.

Thanks for your consideration!

Hello Significent and welcome.

1. Testing can be done any number of ways, but doing comparative pull tests could be a simple first step. You could tie your, as yet not presented knot, against another well known knot in a small cord one after the other and see which one survives the tug of war. Done at the rear of a vehicle between it and and an anchor you will have a measure of protection.
Not at all scientific, but then you could know how it stands up to comparables, that have some tested data.
You could seek out a test facility, possibly a technical school, etc. or manufacturer of test equipment (Lyons) and propose a run. Good luck and let us know what you find out.

2. Here in the Forum are a few people who have a number of years studying and discussing matters knotting and so perhaps if you present it here we can be of additional help.
ABoK is a great resource, but as a few of us have found, it is not the end all.

3. We can always use a good chuckle from time to time, but you've left us wanting. ;-)))


Please submit a picture, drawing or verbal description and let's go from there.

SS

[Dan_Lehman]

More or less in a vacuum, I've tried to analyze some of the more common knots
that are generally described as being strong: around 85% of rope strength.
(i.e. [<=e.g., viz.] Alpine Butterfly Loop, Figure Eight Bend)

Hmmm, it should be questioned how these two are
much alike; and how the former meets your stated
criterion re bending.  --could be a question of where
you saw images of these, or how you tied them.
THAT, in fact, has the simple point re the fig.8 end-2-end knot
of asking both for the dressing AND ESP. which *end*
is loaded.

A simple observation : data about knot strength that is
publicly available is without important associated information
and qualification --dubious, IMO!  --and varied !!

You can post images here of your knot, either tied in rope/cord
or in illustration (so that others can try/tie it).

1) How does a novice objectively test the strength of a knot to come up
with a meaningful measure of strength?

I emphasize your closing term, for, in practical circumstances,
the testing that is often done seems beside the point : i.e.,
slow-pull loading might not well represent the sort of loading
a knot in use will receive; there might be more importance
to resistance to wear --such that a lower-strength knot as
indicated by slow-pull testing will, in use, come to endure
higher loads than some knot scoring well on the test bed.
That's my surmise, anyway, with some verification from
Dave Merchant's testing (as he reports, anyway), in which
dynamic loading had greater effect on some "stronger"
knots than on others --presumably because of the amount
of rope movement these more complex knots had.

One point I'm now emphasizing re testing is getting some
indication of where/how/why the knotted line breaks,
as this more helpful than merely one more ranking of
knotted lines per *knot*.  Having duplicates tested in
a single test specimen has the appealing aspect of leaving
one near-rupture knot to be examined; even if one were
to tests A-vs-B, there would be a survivor that had been
severely loaded.  Sometimes the changes in *geometry*
of knots upon high loading is surprising, and shows that
it might not be your theory of strength that was mistaken,
but your idea of how the line would be bent in the knot.

2) ... Is there a place to submit knots for identification?

You can do that on the IGKT forum; there is now even a
separate (sub-)forum dedicated to such queries.  Please
post a photo or detailed description (to this thread will do,
or the new-knots forum).


--dl*
====

ps : my post #2222 --four of a kind, what do I win?!   

[Significent]

Thank you for your input. My camera battery needed to be recharged before I could provide a photo (attached).

The bend starts as a granny knot. In the photo, the black, right, end is looped over the load-bearing black line and then up through the center of the granny. The left, yellow, end is looped under the left, load-bearing, yellow line and down through the center of the granny. Dressing the bend requires pulling on both ends as well as the load-bearing lines and is a little awkward.

I like the idea of testing the bend in series with other known bends. I'll have to give that a try. In the meantime, I'd appreciate your thoughts.

[X1]

  This is a re-tucked granny knot ( tails go around the standing ends, to form collars, then through the central opening of the granny knot ).
  Judging from the beautiful colour combination of the ropes and the background, I guess you made a mistake when you took this picture, and let the yellow tail go "under" the black tail ... If it goes "over" it, you would have had a symmetric knot / bend, which would be much better. ( For many reasons, most bends we know and use are symmetric - for some notable exceptions, see (1)).
   Now, the retucking of the granny knot through the central opening has a disadvantage : the tails can not be nipped there very much, because, in a sense, they are "protected" by the surrounding granny knot. With stiff ropes, the tails will almost feel free in this soft, warm hug ! 
   I have seen that, if instead of the intrlocked overhand knots you are using in this bend, you use fig.8 knots, the nipping action of the surrounding knot on the pair of tails that penetrate the central opening would be much more efficient (2).
   Another retucked granny knot is shown at (3). For other similar bends, see (4).

1.  http://igkt.net/sm/index.php?topic=4116
2.  http://igkt.net/sm/index.php?topic=3148.0
3.  http://igkt.net/sm/index.php?topic=3729
4.  http://igkt.net/sm/index.php?topic=2085.0

[Significent]

X1, I moved the tails around trying to be sure the photo clearly displayed their path. Sorry about that. The tails don't actually cross per se. They come out on opposite sides, parallel to each other. Thanks for the links to the other images and threads. I like the looks of the bend in the third post of link #2. It's much better looking than the "re-tucked granny" that I've been playing with and appears as though it the load-bearing loop is large and circular. When I can, I'll have to see the relative strengths of both.

Dan, above I referenced both the Alpine Butterfly and Figure 8 together only because both are generally accepted as being strong, and because the loops providing the load-bearing seem smoothly wrapped around two diameters of rope internally not because of any other similarity. Is there a definitive reference that speaks to relative knot strength for most of the common knots and types of rope? (I'll try searching here.)

Thanks everyone for your help. I can see I have lots to learn. I'll keep experimenting.

[Dan_Lehman]

Dan, above I referenced both the Alpine Butterfly and Figure 8 together
only because both are generally accepted as being strong, and because the loops
providing the load-bearing seem smoothly wrapped around two diameters of rope
internally not because of any other similarity.

You should note that in most/many images presented
for the butterfly/lineman's loop the SPart wraps those
two diameters (the tails, i.e.) in a way that really implies
just a 1-diameter turn --the tails aligned with the axis of
tension rather than perpendicular to it.  There are other
orientations of this knot, in which the curvature looks
to be more even/gradual than this.  (But how the knots
that yielded whatever test data one might encounter
were oriented is usually a missing datum, alas.)

As for the figure 8, I'm coming to believe that a more
significant aspect of that knot for strength is the turning
of the twin bight legs around the SPart --that at that
point, there is some transfer of force thus, lessening
the load at the U-turn point; some testing indicated that
the break came at the point of the collars, too (though
we can wonder how accurate this was, but IIRC it was
made with high-speed video).

Is there a definitive reference that speaks to relative knot strength
for most of the common knots and types of rope?

Hardly.  There is almost never a full presentation of the
test data / circumstances from which to well form a theory
of strength and to corroborate or challenge such.  Hence,
I encourage testers to get images of knots at high load
--in a geometry that is what exists at rupture-- and some
good idea of where the break occurs.  Only after we gather
such data can we make better theories of knot strength.

From what little observations I've been able to make,
the point of rupture occurs on the inside of a turn,
not the outside --a guess of a simplistic theory that posits
greater stretch & loading of exterior fibres.  However, it
might be the case that various factors can trigger the
rupture, and one or another might have greatest effect
in a particular knot and not others.


--dl*
====