General > Practical Knots

AlanLeeKnots pull tests on bowlines

(1/6) > >>

mcjtom:
Alan Lee has several videos of pull tests of various loops.  I'm only interested in regular (#1010) and Scott's bowlines.

e.g. https://youtu.be/FPqvrFKpZrU

There are at least 3 ropes used: blue, white, and yellow.  What is the type/diameter of each and have Allan pulled them to failure without knots, just wrapped on larger bollards at both ends?

What is the unit of the tension force displayed?  I'm pretty sure it's in kilogram-force, but want to double check.

mcjtom:
Alan Lee did a series of 12 pull tests where he tied the regular (#1010) bowline at one end and the Scott's lock bowline at the other end of a length of rope and pulled it to failure (recorded how the knots behaved when stressed and then looked at the remains).

First test:
https://youtu.be/0RViCfR1_GM

I took the info off the videos and did a little prediction magic to guess what the next, similar yet untested rope could do in the next test and what it likely means for either of those bowlines when tied on similar material.

Out of 12 observations in the sample, the rope failed 7 times (58%) at the regular bowline and 5 times (42%) at Scott's bowline. 

Whether the rope broke at one knot or the other, all ropes failed at roughly similar tensions / kN, n = 12:

m = 21.7, sd = 0.63
MIN = 21.0, MED = 21.5, MAX = 22.8

That makes their relative ultimate strength indistinguishable with this sample size (i.e. for all we know, the knots are equally strong).

There is some 8% chance that the next rope tested will fail at less than 21 kN.

There is some 1% chance that the next rope tested will fail at less than about 20 kN and likely less than 0.1% chance that it will fail at less than around 19 kN.  It could break equally likely at either knot.

There is no difference between the ease of untying the surviving knots - all easy.

To me it means that the regular bowline backed up with double overhand may be less compact, use more tail and look uglier but is equally strong and practical and at least as safe as the Scott's bowline. 

It probably also means that the idea that packing more rope strands in the choking loop makes the bowline stronger, safer, or easier to untie may not hold much water.

The tests don't show that Scott's bowline is any stronger or easier to untie than the regular bowline.  As to security, l suspect that the regular bowline backed by double overhand has (even) better chances of surviving accidental ring/cross loads, cyclical loads, or shaking/pulling lose owing to the stability of its backup dbl overhand knot.

I just want to add that I still love Scott's bowline :⁠-⁠)

mcjtom:
And the real question with all these is: if you were to anchor a rope, expecting a drunk bear coming to try to untie it, which of the two would you use? :⁠-⁠)

Dan_Lehman:

--- Quote from: mcjtom on April 09, 2023, 10:40:42 AM ---Allan Lee did a series of 12 pull tests where he tied the regular (#1010) bowline at one end and the Scott's lock bowline at the other end of a length of rope and pulled it to failure (recorded how the knots behaved when stressed and then looked at the remains).

--- End quote ---
?!  Seems a wrong-headed way to go --series of A-vs-B testing,
rather than (six each of) A-vs-A, B-vs-B (or just a single knot vs.
anchorage, 2 B *pure*).  One is assured of six survivors of each,
and six broken specimens (possibly the survivors are injured).

Note that with so short a specimen, it's possible the results
are tainted (or particular to) by uneven tensions in the S.Parts
where with longer runs such uneveness would have chance to
be ameliorated in effect.  --but then one is burning more rope
per test!  <sigh>


--- Quote ---Whether the rope broke at one knot or the other, all ropes failed at roughly similar tensions / kN, n = 12:

--- End quote ---
In some testing of the BWL vs. Fig.8 EK,
EStar (Evans Starzinger) tested two sets of ten
specimen also in A-vs-B (BWL-vs-F8) arrangement.
(didn't ask, but I wonder if after initially thinking
he'd get a range of BWL failures --i.e., presuming
the F8 always to be stronger--, and getting some
early BWL victories, he THEN decided to continue
with the A-v-B set-up?)
Interestingly, in the two sets-of-ten I saw posted,
both were exactly 5:5; and the break forces
for the BWL just slightly lower than for the F8, around
82% (he had at some point tested pure rope, I think,
but had found manufacturer quoted figures to be
pretty accurate).



--- Quote ---To me it means that the regular bowline backed up with [STRANGLE is the knot]
 may be less compact, use more tail and look uglier but is equally strong and practical
and at least as safe as the Scott's bowline.

--- End quote ---
Then you're being too quick & low-resolution.
Scott's Lock might have advantage on keeping
it all *together*, whereas just having tied off
the Tail doesn't ensure that the BWL itself
stays in shape (vs. loosening).  YMMV.
One can tie a dbl.OH in form not of Strangle
but Anchor Bend and orient it so that its Tail
can be tucked back through the BWL's nipping
turn, for a 3rd diameter.


--- Quote ---It probably also means that the idea that packing more rope strands in the choking loop makes the bowline stronger, safer, or easier to untie may not hold much water.

--- End quote ---
I might agree (foolishly) except that that's my theory
you're seeing challenge to !!    )-:< !!
Seriously, the point is there, BUT LOOK AT THE EXACT
GEOMETRY, nevermind merely counting diameters.
(Consider : around the 3 dia of ulility poles aligned vs. 3 in a triangle --> ... vs. .:. )

In both of these knots, the S.Part's turn runs pretty
hard into the Returning Eye Leg.  Whereas it CAN
be made (in some knot variations) to compress hard
into a *limp* part such as the Tail :: better curvature,
perhaps, AND more of a heat sink, maybe?!


--- Quote ---As to security, l suspect that the regular bowline backed by [a Strangle knot]
has (even) better chances of surviving accidental ring/cross loads, cyclical loads,
or shaking/pulling lose owing to the stability of its backup [Strangle] knot.

--- End quote ---
Depends how you put the strangle.  Ring-loading should pull
much S.Part through even though the BWL Tail is Strangle-ing
the Returning Eye Leg; such feed of material could be a concern.
Well, then ditto for Scott's; both stem the bad-Lapp-Bend spill
of U-fold tail (Strangle'd or interwoven as that is, resp.).


--dl*
====

mcjtom:

--- Quote ---Depends how you put the strangle.  Ring-loading should pullmuch S.Part through even though the BWL Tail is Strangle-ing the Returning Eye Leg
--- End quote ---

Which one is 'The Returning Eye Leg'?

I imagine the side of the loop closest (along the rope) to the tail?  Or the same way the HowNot2 fellow has tied it in the knots video?

Navigation

[0] Message Index

[#] Next page

Go to full version