Double Dragon Vs. Double Tucked Perfection loop

[Mike]

just wondering if anyone has come to any conclusions as to wich is the stronger knot?
They are both easy to tie. And I could not get either one of them to jam in 1/2" braided poly. So for me it all boils down to wich is stronger.  Personally I think they would have about the same strength, since they are almost identicle in structure.

[Dan_Lehman]

What's a "Double-Tucked Perfection Loop" ?

And where do you think a difference in strength will be realized?!
(It might well depend on how the knots are dressed (and how will
you get guidance on that, for strength?!), and possibly in what
material they're tied.)

I'll vote for the Dbl.D version whose Single D. is unstable,
as it seems (the Dbl. version, i.e.) to put a nice gradual curve
in the line.

--dl*
====

[Mike]

Dan , I think the perfection loop is the same as the angler. you can see the perfection loop on Layhands.com.  only differece I can see is the first  S curve goes around the standing part on the perfection loop.  I'm not even sure why I asked, its not like I use either one on a regular basis. I guess its the Obsessive compulsive comming out in me

[Dan_Lehman]

Dan , I think the perfection loop is the same as the angler.

I know that; the question was re "Double Tucked  Perfection Loop".

 

[Mike]

wrap the end around a second time.

[DerekSmith]

Hi Mike,

You pose yet another interesting question.  At first sight, I thought the difference was going to be purely theoretical, but as it turned out, reality had yet another lesson for me.

As tied, the DD does indeed seem to offer a gentle curve through the knot as Dan remarks.  However, place the knot under load and the working part straightens out and takes a direct line through the heart of the knot until it emerges to a tight 1 dia curve of ca 60 degrees, followed by a 1 diameter turn of 90 degrees at right angles to the first.  So in theory, the DD is going to fail on the outer curve of those two tight bends.

The double wrap Perfection only has three tiny variations in this all important lead in section.

First, the working part comes into the knot from the opposite side that it eventually emerges from.
Second, the WP is braced on both sides by the legs of the outgoing loop and
Thirdly, The WP has to pass under a diagonal wrap from one of the loop legs as it passes through the body of the knot.

When the dbl Perfection is placed under tension, the effect of the third difference, that diagonal back brace, has the effect of curving the WP backwards against that diagonal brace.  Only perhaps 10 degrees or so, but it is a definate oportunity for the WP to transfer load while essentially straight.  This wrapping effect quite effectively grips the WP as it enters the knot, again offering the oportunity for load shedding over a length of ca. two diameters.  Once the WP leaves the body of the knot, it performs in an identical fashion to the DD, so If it did not manage to shed any load within the body of the knot, it should fail in the same place as the DD and by the same mechanism.

I tested pairs tied back to back in three cords - PP braid, two ply laid 'garden hemp' and four ply laid cotton twine.

I tested the knots by pre loading with a static load to ca 60% failure then overloading with a shock load.

Results for the braid and the 'garden hemp' were all consistent - the DD ruptured on the outer radius (the 'hemp' left a long torn tail reaching back into the knot from threads on the inner side of the radius.

The surprise came from the cotton.  100% failed on the dbl Perfection, but the big surprise is where it failed.  Not on the shoulder as predicted, but right at the entry point to the knot where the grip goes on from the diagonal crossing and the two 'side rails' - an absolute clean snap.

It seemed that the other two materials broke under tension, but the cotton seemed to have failed through compression.

I checked this by rigging a piece of the cotton cord to two 1" dia bars with a wrap friction hitch.  Pre loaded as before, but before giving the shock load I tied a constrictor around the cotton cord using 100# Spectra - and Bingo, every test the cotton fractured at the constrictor compression point.

So what did I learn?

First that the Perfection was consistently stronger in my tests than the DD, which is good because I intrinsically prefer the Perfection because of its cleaner symetry.  But of course, I do not know 'how much' stronger.

Second not to trust theory at the expense of having reality bite you on the bum.

And finally - don't squeeze the cotton !!

[squarerigger]

Hi Derek,

I want to congratulate you on a very comprehensive and comprehensible response and to thank you for describing how you tested the situation with different materials and under different loading conditions.  You presented a potentially complex subject very succinctly and, perhaps more importantly, in a manner that could be understood by anyone approaching the subject for the first time.  Thanks so much!!

Lindsey

[Dan_Lehman]

As tied, the DD does indeed seem to offer a gentle curve through the knot as Dan remarks.
However, place the knot under load and the working part straightens out and takes a direct line
through the heart of the knot until it emerges to a tight 1 dia curve of ca 60 degrees, followed by
a 1 diameter turn of 90 degrees at right angles to the first.  So in theory, the DD is going to fail
on the outer curve of those two tight bends.

What theory is this?  --a naive one, methinks!
As best I can see from some samples of broken laid rope--where there
is usually a sequence of rupture of the strands, and by that some means to
deduce where the break began--, the rope fails on the compressed concave
side of a bend--not on the outside, as one occasionally sees put forward as
a theory (or stronger!).  The results of some test devices is a paritally broken
rope--device arresting strain upon the sudden loss of tension (or stopped by
operater).  But, as Derek suggests, there might be differences per material
(and maybe per something else--knot, loading, construction?).

I also did some quick testing:  I tested the given pair and found the D.Perfection
loop to survive, the D.Dragon, not (I believe I used the D.Dragon extending the
Tugboat Bwl-A of the Layhands site, where the end exits away from the SPart's
nip, not through it--where the Tugboat form is quite instable).  Then I tested
the "single" versions of the two knots, this time using the Tugboat Bwl form
shown at Layhands as Tugboat-B.  I first marked the mason line so as
to be able to see where the break came (hope, hope).  Again the Perfection
Loops survied, but the Dragon (Flying/Tugboat Bowline) first capsized, and
so resulted in the SPart making a tortured "Z" pass, severely nipped by a
wrap at its entry--which is where it broke.  And the break clearly was of two
of the 3 strands, shown by their extensive recoil back along the 3rd strand,
last to break.
[cf. www.layhands.com/Knots/Knots_SingleLoops.htm#PerfectionLoop ]

I'm not convinced that the small materials used in our tests are good indicators
of behavior of the knots in thicker material.  Also, as my material was laid, there
might be a difference on the handedness of the knots (Perfections both of
opposite handedness (i.e., SPart's initial/main turn is of opp. handedness
from the lay--left-, for right-handed/Z-lay rope).

--dl*
====

[DerekSmith]

snip ....  So in theory, the DD is going to fail
on the outer curve of those two tight bends.

What theory is this?  --a naive one, methinks!
snip....
--dl*
====

As much as I study knots and their performance for myself and read the findings of others, there is one thing of which I remain absolutely certain - that is that there is much much more for me to learn about this fascinating subject.  I am also certain Dan, that there remains much that I can learn from you !!

So you can imagine how that little comment of yours caught my attention - doubtless it was supposed to?

Your students wait with interest to understand why you should think this - will you enlighten us?

Derek

[Dan_Lehman]

As much as I study knots and their performance for myself and read the findings of others,
there is one thing of which I remain absolutely certain - that is that there is much much more for me
to learn about this fascinating subject.

And you should be unfortunately continually frustrated by the lack of information
given by what you've read from test reports (nevermind the stuff that's pure
fancy!), as there is seldom adequate detail given to repeat the test (one of Science's
fundamental principles), and almost never information about where the knot breaks
(e.g., even with the asymmetric Sheet bend:  is it the bight or loop part that, er, parts?!).
Although many sources state "at the entry to the knot" (and sometimes just outside).
So, the investigator by sources has to accumulate a whole lot of such information
and even then go on only some hunch that a pattern might be recognized, that
enough hints that Knot-A is stronger than Knot-B & -C, etc., can yield good
deductions of Why ... .  But you really aren't going to know even the exact
geometry of the tested structure from a knot name and (as we see in other
threads) dubious indications of how the knot should appear when tied.

As noted above, I made a small attempt to learn position of a break by using
a marker--which turned out to be irrelevant, as that broken capsized Tugboat
Bwl held its form to show a break at the tight entry pinch.

Your students wait with interest to understand why you should think this - will you enlighten us?

As I wrote above, I've seen many breaks in laid rope, and as best I can determine
from those, the broken strand(s) has(have) parted on the concave/inner side (even in
one case against a metal hook (less friction)).

Now maybe this is as characteristic more of laid rope than braided, as there is some
chance for the separate strands to individually elongate, and the one stuck in a severely
compressed, high-friction/-heat(!?) point can be run over, as it were, but the other(s)
--from THAT point towards the load away from it, the outer fibres have some chance to
further move/elongate, whereas the inside ones are getting the heck smushed out of
them or are just locked in place.

How to determine this for braided rope?!  --well, in some kernmantle rope breaks,
one reads of an intial mantle rupture, and that could well be incomplete, and so it
should show inner/outer break (I've not read though of anyone noting this).  For
solid braid, hmmm, likely it all goes too quickly to be seen, even by high-speed
photography (one testers did use this, but were only able to improve their guesses
at where the break came in terms of knot parts, not per strand side).

Might a low-friction material (HMPE, aramid?) show a different behavior (though
HMPE is more heat sensitive)?

--dl*
====