Author Topic: serial PET loop knots  (Read 2455 times)

erizo1

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serial PET loop knots
« on: August 18, 2015, 05:06:33 PM »
As an intellectual exercise (I'm not a climber), I've been thinking about tie-in knots, especially the security vs. untieability problem with loop knots that end up being put under heavy strain. It occurred to me (others may have been here before me) that as long as the working end leaves a loop knot back along the standing part, one backup knot option is to tie another PET loop knot. The picture shows three Yosemite bowlines in series as an example, but you could combine PET loop knots any way you wanted (figure-8 backed up by a regular bowline, two double dragons, etc.).

I haven't played with the practical results of this in terms of security relative to other setups (either a more robust knot or another way of backing up the original loop knot), and it may be that there really aren't any situations when this kind of arrangement is the best solution, but I thought the concept was interesting. Would this result in dividing the strain between the two knots so that each was loaded less heavily? For example, if you tied two figure-8 knots and then followed the working end back through both of them, would each knot be easier to untie than if only one figure-8 took all the strain? Does putting two knots like a Yosemite bowline in series make each of them more secure, or is there not really an advantage?

Interested to hear what people think about this.

SS369

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Re: serial PET loop knots
« Reply #1 on: August 18, 2015, 05:26:33 PM »
Hi erizo1.

Redundancy can improve security, but at a cost.
What you show can leave places for odd objects to snag or hang the rope for example. Much simpler methods can do the security increase much more easily.

That said, it might be interesting to see if some combination may turn into a truly secure, possible stronger knot. Could even lead to a end to end knot for joining ropes.

Thanks.

SS

xarax

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Re: serial PET loop knots
« Reply #2 on: August 18, 2015, 06:00:36 PM »
  or is there not really an advantage?

  Or, even more, is there a dis-advantage ? ? Because, if we see this series of knots of a rope as a series of links of a chain, it will be as strong as its weakest link - and the more knots / links we add, the probability of adding an even weaker than the already existing knots / links increases.
  In general we should always see the knots as "defaults" of a rope, which hurt its uniform behaviour under load, so more knots mean more hurt. They do not distribute the pain, they increase the wounds.
  Having said that, I believe that, if we take into account rope s lengthwise elasticity, it may be the case that, during peaks of loading, the more vulnerable weak spots are "shielded" from destruction, "protected" behind stronger areas which absorb those peaks before they have the chance to initiate a rupture.
   This is NOT a problem of intellectual exercise, this is something that should be TESTED, by flesh and blood ! Test it ! Measure it. Analyse your results. Tell us.
This is not a knot.

Dan_Lehman

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Re: serial PET loop knots
« Reply #3 on: August 20, 2015, 07:35:57 PM »
As an intellectual exercise (I'm not a climber),
...
 Would this result in dividing the strain between the two knots
so that each was loaded less heavily? For example, if you tied two
figure-8 knots and then followed the working end back through both of them,
would each knot be easier to untie than if only one figure-8 took all the strain?
Continue with that intellectual exercise,
and ask What is the effect on the outermost
(i.e., away from the eye tip) knot?


Quote
Does putting two knots ... in series
make each of them more secure,
or is there not really an advantage?
One can be tempted to (mis)think that it does so,
with the inner knot backing-up the outer, should
the outer come untied.  This is "mis"-thinking to
some degree, missing the question of how that inner
one would be staying tied and ready to serve, immune
to those forces that untied the outer one!  (At least,
I've caught myself mis-thinking such benefits.)

But I do think that there can be some advantage along
these lines, with at least the likelihood that should the
outer knot come untied, there would then be a lot of
loose rope to draw attention to that fact (for a climber
--someone present with the knot, not a knot out of sight).
One might also engage the inner knot to nip the tail from
the outer one.


--dl*
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