Re-tucking simple bends, to get wider first curves

[xarax]

   Re-tucking simple bends, ( so we "feed" the knot s volume and we allow the Standing parts to follow wider, more gentle curves ) is a possible way to improve their strength characteristics. Of course, because this retucking forces the standing parts to follow a different curve inside the knot s nub than before, it may have deteriorating effects in other aspects of the knot... Only detailed experiments can show us exactly where, and when, will the "new" bend break, in relation to the parent bend.
   See the attached pictures for such a bend. The Standing parts turn around gentle, four rope diameters curves. From the few I know and the even fewer I can remember, I have not met it before... Do you recognize it ? Have you seen it somewhere else? If not, how could we possibly name it, with a proper, descriptive name that will have some relation to its parent, un-tucked bend ?

[xarax]

   Better late than never...After some time, I have realized what was this knot, and how it should have been named. It is a X variation of the twisted Hunter s bend - or a twisted variation of the Hunter s X bend (See (1), Variation 2). Now, if the standing parts are twisted twice, at the front AND the back side, and the tails are crossed ( if they pass through the central opening in an X : crossed configuration ), the knot becomes a "twice twisted Hunter s X bend". ( See the attached pictures for the loose form of this knot, where its structure is clearly shown. Notice the wide "orange" first curve, in the side view picture. )
   To tie this knot easily and unambiguously, we just have to following a method similar to the one described in (2) for the interlocked overhand knot bends described there. We have to re-tuck the "base" shown in the fourth attached picture, through the central opening, ( that is, form a C - C knot on this base) and make sure the tails that pass through this opening are crossed. I have named this particular "base" of the two interlinked bights, "base H", because most bends that are formed using it as parent knot, are some stable or unstable variations of the Hunter s bend. The interested reader is advised to explore this fact, tying bends by re-tucking the working ends through various openings.  
   I am glad that the subject of this thread is clarified so quickly, by the first received reply ...
   1) http://igkt.net/sm/index.php?topic=2019.0
   2) http://igkt.net/sm/index.php?topic=3086.msg18494#msg18494
       http://igkt.net/sm/index.php?topic=3086.msg18601#msg18601
 

[xarax]

   More pictures of the same knot, with the tails slightly bent, and shown parallel to the standing ends.

[Bob Thrun]

At the International Tech Rescue Symposium in 2004, three authors from CMC Rescue presented some rope strength tests where a bight of rope was run around round rods of different diameters.  The rope was 11 mm kernantle, but the material was not specified.  CMC makes both nylon and polyester ropes.
http://www.itrsonline.org/PapersFolder/2004/SmithCedric-McKently-Parker2004_ITRSPaper.pdf

[roo]

  The rope was 11 mm kernantle, but the material was not specified.  CMC makes both nylon and polyester ropes.
http://www.itrsonline.org/PapersFolder/2004/SmithCedric-McKently-Parker2004_ITRSPaper.pdf

While it's certainly better than nothing, their sample sizes seem rather small.

see:  http://www.raosoft.com/samplesize.html

Then again, I place breaking strength for knots pretty far down the list of priorities.

[Dan_Lehman]

At the International Tech Rescue Symposium in 2004,
three authors from CMC Rescue presented some rope strength tests
where a bight of rope was run around round rods of different diameters.

The rope was 11 mm kernmantle, but the material was not specified.
CMC makes both nylon and polyester ropes.
www.itrsonline.org/PapersFolder/2004/SmithCedric-McKently-Parker2004_ITRSPaper.pdf

Thanks much for this.
Re material, possibly one can check current CMC ropes data
and get a good idea of the rope, but it's a pretty sad state of
presenting test results that something as fundamental as test
specimen make-up isn't reported!  --this is especially annoying
in the tests of chemicals on rope (DEET & spit chewing tobacco).
Maybe one should presume there that it was a combination
nylon-polyester (PA/PS(PES)) rope?  Acids more likely hurt
PA, alkalis PES --something like this.

It's interesting to see the pulled-bight data:
the "control" data came in pulling a single strand end-2-end
with ends wrapped around 4" bollards; so, one should expect
at most twice this strength for a (2-strands) bight.
But there are higher test results for pulling a bight
starting at the 1.5" bight-pin !
.:.  Perhaps there is a fatigue factor at play?!

For What is different? in the loading of rope around
opppsed bollards (with multi-wraps) and the test specimens
having this for the legs, yes, but in opposition to a bight
around pins (of various sizes)?  --the difference is the bight,
which has but a turn, no wraps!
And this does what?  This reduces the amount of material
feed into the tension zone, and so reaches higher tensions
per time (there being less incremental stretch out of the bight),
whereas the wraps delay these tensions a little.
Perhaps in more rapid loading, the bight would show some
disadvantage?

It's also interesting to consider the case of the large-diameter
bight, given how CMC's test device oriented the bight
--i.e., pin cylinder is parallel to bollard, AND bight legs go
to SAME SIDE of bollard.  Exaggerate the pin size to see what
the effect is : the bight leg going from top-side (both legs do)
DOWN to bottom of the pin is well longer than the other leg.
(CMC sh/could've wrapped the bollard differently, legs going
to opposite sides (and either making an X crossing or not!).)


As for the fire-situation exposure, it's not clear to me exactly
what was done, here : e.g., were the ropes merely coiled and
attached to the firefighter and so brought into the stated conditions,
but still (1) in a coil & (2) not tensioned or used in any way?
That I'd think would suggest that rope more exposed, lying
outside of the coils, would suffer more.  Maybe the test specimens
ensured that some such part of the rope was tested.


Finally, re the chewing-tobacco testing, the last specimen is cited
as having "slipped" : huh, what does this mean?  --slipped in the
clamped-onto-bollard attachment?!


--dl*
====

[xarax]

I place breaking strength for knots pretty far down the list of priorities.

   I think that this is a very debatable issue.
   When someone, that does not know anything about ropes and knots, learn for the first time that a knot diminish the strength of the rope to about two thirds of the initial value, he can not but consider it a great disadvantage for knotting. With time, we are getting accustomed with this sad fact of life...like with everything other unavoidable limitation of our existence. And some people, confronted with the unavoidable, pretend they do not care any more. We are all going to die, so, why bother ? 
    However, when we learn that this situation can be improved to a substantial degree, and we can arrive at a better situation, we feel that we are obliged to explore any road that might leads us there. We modify the old knots we use, or choose some new ones, hoping that we can achieve better numbers than this horrible 66%...
    The strength of the knotted rope is the first priority by definition, because that is what a rope is supposed to do : Do not break. Fishermen, who are the people that use more knots than every other category of knot users, know this very well. The problem is that knot tyers do not know much about fishing knots ! And they tend to abandon the battle for knots with greater strength, even before they fire the first bullet...
   The scientists and industrial engineers that design ropes, take great pains in improving their strength. A 5 % improvement might justify a multiplication of the material cost, besides all the research that was devoted searching ways to achieve this. Why a 5% improvement of the strength of a knot is important ? In most critical situations, like rescue, for example, we would consider ourselves very lucky if we could get a 5 %, even if we should pay a high price for this : multiplication of the cost of the material chosen, of the time needed to learn the knot, and of the time needed to tie and dress it. Why ? Because we place life pretty far up the list of our priorities. And life can be lost in a snap.
    Is it the wisest choice ? No. Many other things matter in life, quality is more important than quantity. However, we are but the descenders of living machines that survived enough to breed and multiply their genes, and we can not escape from the past immortalised into them.
   I have discussed another pretty good reason that it pays to search for strong knots. Economy of our knot toolbox size. With so many possible choices, strength considerations can help us get rid of many knots, in favour of a few others.
    I tie the Zeppelin bend almost all of the times. If one teaches me a knot that has a 5% greater strength than the Zeppelin, I am ready to tie it, even if it needs double time to form it, and triple time to dress it. After some time, the tying difficulties will disappear, and I will not bother tying a more complex knot - EVEN IF I NEVER EVER USED more than a tiny fraction of the maximum allowed strength of my ropes. But who knows how much strength would be needed in advance ? You tie something somewhere, and it is OK. Then, there came a rain, a strong blow of wind, an impurity built into the rope you had no idea of...and suddenly the 100% of the rope strength is needed, and then some ! 
   As long as knots will exist, strength of knots would be a high priority, even if there are not much we can do about it.
   "Re-tucking simple bends, to get wider first curves", addresses this fact, explores one of the offered roads. Most people will not bother, that is for sure, and the great majority of them will buy a mechanical fastener, a clip-on tie, a pair if slip-on shoes, or be happy parotting a ready-made recipe for some knots, from roo s web site...   (Just kidding...)

   
   

[xarax]

  Perhaps there is a fatigue factor at play?!

   Fatigue plays a major role with metals, but a tiny one with plastics. ( A possible permanent elognation of the "synthetic" fibres, is not fatigue.)

[roo]

I place breaking strength for knots pretty far down the list of priorities.

I think that this is a very debatable issue.
  

"...but whenever the task is critical, a few percentage points of strength advantage should not make any difference if properly sized rope is employed.  As pointed out on the frequently asked questions page, you shouldn't assume that your knot is the weakest link in your line.  Wear and severe curvature in the rope path will often pose a more significant threat to line strength than your knot, and the working load limit of your rope should provide ample protection from stress concentrators."

from:  http://notableknotindex.webs.com/figure8loop.html

[knot4u]

Rope strength is pretty high on my priority list.  I use ropes extensively in homemade gym equipment in my home and other people's homes.  In fact, rope strength is the first attribute I consider when purchasing rope for my equipment, then size, then material, then price.  In my equipment, I have tied Bull Hitches, Cow Hitches, Zeppelin Bends, Trucker Hitches, Versatackles, Buntlines, Mooring Hitches, Bowlines, Span Loops and others.  I need to consider the relative strengths of all of them.  As Roo mentioned, I also must consider how a sharp bend weakens a rope.

I'm always concerned about where the weak link is.  If the weak is NOT the knot, then that's all the better.  It practically always comes down to being an educated guess.  So, I do have to understand the theory.  I calculate forces on a rope and don't want to get anywhere near its breaking point.  Many of my ropes undergo shock loading and support body weights of up to 350 pounds.

If you're wondering, yes, I can over-engineer with a monstrous amount of rope.  However, that's boring and amateurish.  I'm constantly searching for simpler and more elegant ways to make equipment.  That often means using less rope, which requires much more thought.  Also, I have to leave room for error because sometimes my calculations of the forces are erroneous.

Having said all that, if I re-tuck a knot, I won't claim the knot is stronger if I didn't perform tests with a machine.  My equipment literally holds a person's well-being, and so I don't have the luxury of casually making claims that may not be true.  However, I do feel comfortable saying a re-tucked knot is not weaker.

[SS369]

Certainly it is agreed that rope maintaining its integrity is the all important attribute, unless we mean to cause it to break somewhere. So a knot's influence is paramount and we should choose accordingly to the task.

Sometimes circumstances dictate what materials use, what's on hand and an emergency undertaking.
We hope the rating of what we have is beyond expectations. Not always so.

But if there is a way to remove, at least some of the knot's influence to impart damage to the rope, then we should consider all avenues, now, while there are no emergencies.
If the most influential place in the knot is the first curve then that is where the "beefing up" to enlarge the contact patch so to soften the curve (spreading the first force imparted and attained).
If the re-tucking of the ends does this (not in all cases) then I consider that it will be a positive, not to mention in some cases potentially making the end(s) a bit more secure.

If the area of the re-tuck is the location of the highest destructive (to the rope) load then it would seem to me that this bulk would aid in some absorption of the shock loading that can be imparted.
Not all real life situations are slow pull.
Yes, the parent knot's configuration is most likely key, but this additional step won't waste enough material  to justify not using it.

I guess the knot strength is not how strong It is, but how strong the rope is at that particular knot.

SS

[roo]

   All very true, but...
...but, in addition to all those precautions, a knot with a higher strength would do no harm ! 

Unless you had to sacrifice something to achieve that higher strength, such as ease of tying, ease of untying, memorability, ease of error checking, ease of adjustment, economy of rope use, and the like.

I have no qualms with knot strength being the tie-breaker between two knots with otherwise identical properties in all other arenas.

[xarax]

  If the area of the re-tuck is the location of the highest destructive (to the rope) load then it would seem to me that this bulk would aid in some absorption of the shock loading that can be imparted.
Not all real life situations are slow pull.

   Shock absorption of the peaks of dynamic loading is a very good reason re-tucking of bends should be considered.
   Now, I distinguish three broad categories of the core of a re-tucked knot.
   1. Very massive, compact rope tangles, with almost no voids, where the rope strands run parallel to each other, and the standing parts make their first curve going around this massive, compact core. That is the case of the recently published lR-uL bend, for example. Also the Strangle bend (2) and the re-tucked MWalkers 2 strand / re-tucked true lovers bend (3).
   2. Very structured, not-so-compact rope tangles, with some voids, where the rope strands run in right angles to each other, and the standing parts make their first curve stemming out of this structured core. That is the case of the 88 bend, for example (4)
   3. Four or more crossing lines, passing though a central region with many voids, where the standing parts encircle this region around their intersection, forming a curvilinear bight with as great a radius as possible. That is the case of the recently published twice twisted Hunters X bend, for example (5).
   It might well be some other categories of cores that help/force the standing parts to run along wide curved paths, that I have not noticed. The reader who happens to make a relevant observation, is kindly requested to report it here.
   A knot is a static machine dealing with dynamic loadings. As such, it is an engineering solution to two practical problems, how the rope will not slip through, AND how the rope will not break. So, every knot is a compromise, as every engineering solution always is. It might be true that I pay too much attention to knot strength, but this is a means that keeps me searching for modifications of old knots, and learning of new ones. Knotting life would be boring without such motives/excuses, which keep the lights turned on...  

 1) http://igkt.net/sm/index.php?topic=3086.msg18494#msg18494
 2) http://igkt.net/sm/index.php?topic=2154.msg16858#msg16858
 3) http://igkt.net/sm/index.php?topic=1919.msg16706#msg16706
 4) http://igkt.net/sm/index.php?topic=1919.msg13267#msg13267
 5) http://igkt.net/sm/index.php?topic=2894.msg18933#msg18933

[Bob Thrun]

The rope was 11 mm kernantle, but the material was not specified.  CMC makes both nylon and polyester ropes.

I contacted CMC and got a reply from one of the authors.  The rope was 11 mm CMC Rescue Lifeline manufactured by New England.  It is static kernmantle construction with a nylon core and a nylon sheath.  The tests with DEET and tobacco juice were done with 12.5 mm rope.