Author Topic: 4 ends bend. (Another interesting knot problem)  (Read 9544 times)

Dan_Lehman

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Re: 4 ends bend. (Another interesting knot problem)
« Reply #15 on: September 17, 2010, 07:15:23 AM »
Since the topic has shifted from rope to bungee (and eventually eight arms), I had to adapt my response.

You're reading too quickly: the problem was stated in the OP and hasn't shifted,
except in your view of it.  (Xarax explicitly states, e.g., that we are not concerned
with elasticity.)

 And these failings suggest
that the Mid-span Sheet Bend be kept out of the game: recall the
issue of ring-loading and the Bowline (becoming in effect the
inferior Lapp knot orientation).
Wrong.  The Midspan Sheet Bend never assumes a Lapp Knot orientation since the leftover loop is not used.

Again, you're hasty in reading : I responded to the general case of taking
an eye knot into this situation, and so remarked at how this can lead to
trouble, as with the Bowline .  Now, while it's true that the MSSBend
here (but not in the 2-loops-knot & one cut thread) doesn't present
the orientation called "ring-loading", it does present another circumstance
that Bowline challengers like to put forward -- i.e., that of pulling on
the tail to supposedly create a "slip-knot" ... .  I.e., pulling the bight/U-part
apart : and I don't favor using it where that can happen (be so loaded).
YMMV on results.


As for Have I tried the Overhand (both) in shock cord? , no, I hadn't
(for, again, that wasn't specific to the challenge).  But I have done so now,
w/o problem.  MY cord is that from the sea, and so has lost slickness --
enough so that the Overhands can be tightened and hold; in some sense,
then, I convert the elastic material in the knot to relative inelasticity.
(slightly diff. dia.s, too:  I'll guess 1/4" & 3/16" ?  --that sort of difference)

And I've just now tried to bump the structure with one more "line" (I just
folded one cord into a bight, then laid the other parallel and tied the Oh.:
still fine.

AND, I tried Derek's Disaster :  what you said!  (fails readily (yet is a PITA to untie!))
(Derek, how did you get past the obvious, here, to the keyboard??!)


--dl*
====
« Last Edit: October 07, 2010, 05:36:16 PM by Dan_Lehman »

DerekSmith

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Re: 4 ends bend. (Another interesting knot problem)
« Reply #16 on: September 17, 2010, 11:23:17 AM »

Ashley calls it the worst single Carrick bend, and in my bungee, it rolled freely.   At least the overhand knot solution just flipped a few times before jamming.

P.S.  Did you decide to call the ABoK #1445 the "Myrtle".  If so, why?

Likewise, in my bungee it rolled freely, until I set the knot by heavily (fully) extending the bungee on all four cords.  This preshrank the cords and the knot and placed it under 'elastic tension'.  This stopped any hint of rolling within the forces of the bungee cord's normal elasticity and locked up the knot so effectively I had to use as fid to prise it open.

The Myrtle is a single loop knot and was named by Dave Root as he found it holding up a Myrtle tree.  I cited #1445 to clarify the knot structure much as one might cite the sheetbend structure to describe a bowline to someone who was unaware of it (some chance).

'Why?'[was it called Myrtle] - why not?  It is as easy to remember as it is to tie - cast a Constrictor, feed the end into the constrictor, pull the constrictor and let it unfold, taking the end around with it and 'pop' - a Myrtle loop...  or in this case a four legged bungee 'quadrapus'.  But yes, I take your point, it is a rather new name for a knot that has been around for some time, but then we are used to giving new names to things in order to make them more memorable, and in some cases even 'Nicknames' to further improve memorability within small groups.

Personally, I think that when we get too precious about names then we start to squish some of the fun out of knotting - you only have to look at some of the wonderfully descriptive names that JD~TIAT is bringing to the game - although I am not a great exponent of rope 'knitting' I have to credit him with some lovely designs and highly memorable descriptive new names.

Derek

Dan_Lehman

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Re: 4 ends bend. (Another interesting knot problem)
« Reply #17 on: September 17, 2010, 04:24:41 PM »
Ashley calls it the worst single Carrick bend, and in my bungee, it rolled freely.   At least the overhand knot solution just flipped a few times before jamming.

Likewise, in my bungee it rolled freely, until I set the knot by heavily (fully) extending the bungee on all four cords.  This preshrank the cords and the knot and placed it under 'elastic tension'.  This stopped any hint of rolling within the forces of the bungee cord's normal elasticity and locked up the knot so effectively I had to use as fid to prise it open.

Well, okay, that's understandable, but little less worrisome : can one
trust the very-tight knot to remain so over time (where the constant
tension is asking for the relief of some loosening) ?  The Overhand
also wants tightening, but I don't think my tightening went to the
extremes that the *Single Carrick* construction requires.  Now,
also over time, the material I think loses some of the slickness that
makes knotting challenging (as perhaps is indicated by the apparent
trouble Roo had w/Overhand (rolling) and lack of that I had (using
some well non-new material).

--dl*
====

Rrok007

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Re: 4 ends bend. (Another interesting knot problem)
« Reply #18 on: September 17, 2010, 07:36:09 PM »


Thank you Prok007,

It's Rrok007, no "P". Which is not a major issue, just making sure.

 I have to say that I disagree with your view that a Star knot solution goes outside the field of required simplicity...
   Simplicity is not judged by the mere number of initial elements, but of the symmetry of the transformations that produce the final, completed form. Simplicity is not a matter of economy in the senses, but in the mind. The Star knot is a very simple knot, one of the simpler knots I know, and just because it is so simple, it is also so beautiful. :)
   Could you please tell us the kind of hitches you would use to tie each individual leg ? Is it possible to present us with a picture of a well dressed a 4 legs star knot? Does a Star knot retain its pure form regardless of which and how many rays/legs are loaded?
   One advantage of your proposed solution is that it can be generalized in any number of legs. One disadvantage is that the individual hitches are not working together, in a central knot nub, so we might say that some rope element is wasted and some nipping force is used not as effectively as it could.

I guess when I think of simplicity, I mean the nuber of overall steps. Figuring 3-5 steps at most for the entire knot. I do agree that, once you know how it's done, the Star knot is quite rather a simple knot to tie. It's the repition all the way around the knot that makes it less than simple in my mind. I was also keeping in mind that it is generally considered a decorative knot, and as such may not initially thought of to have much practical value. For me, I think it's one of my favorite knots to tie.

As for load bearing, I have never really tried it as a means of supporting weight and can't really say without taking the time to test it out. I know that, depending on how complete you tie it, the legs will be coming from either the outer edge of the knot, or from the center of it. I will say that I have a few small knots that I have, from time to time, pulled on the legs and not had the body deform much. The "petals" if you will of the star knot may flex slightly, but not much, if at all. In fact, the tugging on the legs only helps to tighten the knot and keep it firm. I would imagine in your purposes, and weight loaded onto the legs would have a similar effect, essentially making the knot even more secure. I suppose it's possible for the knot to collapse if enough weight were loaded onto it, but I think it would have to be a disproportionate amount, for example, using the vacumn cause by high altitude cabin pressure loss to clean a carpet, when a simple handy vac would have done the job. Indeed, if one is using bungie cords, I would suspect there would be almost as much chance of the legs, or the supportng structure, breaking as there would be the knot collapsing. IE, if I used a star knot with long legs, then drilled a hole in my ceiling to feed the legs down through, and then hung a lead-lined corpse (don't ask) from the legs, I think it would be just as likely that the ceiling would come apart before the knot did.

Another advantage is that the number of legs in the knot can be doubled, simply by tying it close to the center point of each leg. IE, two ropes can make a four-point star; four ropes can make either a four-point, or an eight-point, star knot.