AlanLeeKnots pull tests on bowlines

[mcjtom]

Last bit, as a food for thought.  Tom Moyer tested the susceptibility of the Water knot on flat slings to slipping under cyclical loads.  He found that the 'top' tail slips a little at each cycle but doesn't continue slipping at sustained constant loads.  Keeping long tails requires impractical number of cycles for the knot to slip and makes it 'super good enough'.


W.r.t. Scott's vs. Strangle backup, I see it potentially more likely for the Scott's variant to fail by slipping due to this or similar mode of repeated stress, as remote as as this possibility may be (but nobody expects a bear).


https://user.xmission.com/~tmoyer/testing/Water_Knot_Testing.pdf

[mcjtom]

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.).

Is there a reason why the strangle backup shouldn't be tied on the S.Part instead?

[Dan_Lehman]

Czech-no-Slovakia

Thanks, I corrected my text ; call me old-school geography;
also a "to" => "to be".

Still, I'd like to see the Czechs do a thorough testing in the
*pure* way and in the 2-specimens way --which, yes, SHOULD
have a (predictable, I'd think) bias to posting lower values,
since it's the weaker one's break that occurs and is recorded
(one would need both to strong for a strong knot to register,
increasingly less likely moving away from the mean).

I think you are correct:

Gotta be, re difference obtaining; just don't know how
to figure it any more smartly.  In discrete cases, one
has the logical possible A-v-B combinations as
--named in relation to the Mean divide, the chances
equal of picking higher/lower values, if normally
distributed (and not all values lower but for some one
thing miles away high swinging the median... :-)  :

hi-vs-hi
hi-vs-lo
lo-vs-hi
lo-vs-lo.

In only a quarter of these --top case, here-- will
a high value register.
Now, it was also potential physical-effects that were
warned about as tainting the information --the shifting
of forces in one knot having effect on the other.

But, to me, it does no good to bow to stats purity
and no information because of the cost to achieve it;
IMO, some decent information can come by impure
methods, taking that w/grains of salt as needed.

(-;

[agent_smith]

It appears that many of the questions raised by the original poster have been mostly answered?

With regard to Alan Lee testing (as raised in the opening post and elsewhere) - I have stated on previous occasions that it would be preferable (in my view) to test like Vs like... that is Scott's lock Vs Scott's lock (and not mix and match test specimens).
Alan's test rig also had some issues with limited initial stroke by machine, then reverting to hand pumps to further increase load (resulting in a somewhat inconsistent loading rate).
Although I am being critical (and this is a knot geek forum) - I am appreciative of all of Alan's work - but because the test rig setup can introduce some biases, which ought to be eliminated as far as reasonably possible. Unfortunately, being critical can itself draw criticism!

Scott's locked Bowline (of which there are several variants - one of which is 'TIB') has 3 rope diameters inside the nipping loop.
The issue of having 3 such rope diameters inside the nipping loop has not been properly investigated in peer reviewed technical papers - the subject is remains open for debate (and rigorous future testing).
In my view, extra rope diameters inside the nipping loop may be beneficial in dynamic loading events - particular in repetitive dynamic loading (as would occur in a lead climbing situation).
Scott's locked Bowline is easy to untie after 'heavy' loading - much easier than an F8 (particularly in thinner EN892 dynamic ropes - eg Beal 'Opera' rope).

The cited technical paper (once again) is principally focused on pure MBS yield (ie strength) - which (in my view) is not a useful test criteria for knots used in life critical applications.
The cited paper (for example) points to an F9 as being more 'efficient' - (defined as stronger) which is actually a meaningless proposition. In fact, an F9 knot is more vulnerable to jamming than an F8 knot tied in the same rope. The alleged 'weakness' of an F8 relative to an F9 is irrelevant - jam resistance is of greater relevance, and an F9 knot will jam before an F8.

In fact, the whole premise of defining 'efficiency' in terms of MS yield is (in my view) wrong.
Efficiency ought to be defined in terms of metrics such as; resistance to jamming, footprint, amount of rope required to form the knot, security, stability, and range of possible loading profiles.

I would expect to see higher MBS yield values in a Scotts locked Bowline Vs Scotts locked Bowline compared to a control group such as #1010 simple Bowline Vs #1010 simple Bowline. Although the margins may be small - in theory, it ought to be detectable (the experiment would have to be carefully setup to remove as much bias as possible). In the same way, I would expect to see higher MBS yield values for a #1074 Bowline with a bight. Again - this is all speculative, and needs to be carefully tested.
Part of my speculative assumption lies in the notional concept of the first curve of the S.Part as it enters the knot core. It has long been theorized that tighter bend radius of the first curve of the S.Part may lead to a reduction in measured MBS yield values... again I emphasize that this is all speculative.

[Dan_Lehman]

Scott's locked Bowline (of which there are several variants - one of which is 'TIB') has 3 rope diameters inside the nipping loop.
The issue of having 3 such rope diameters inside the nipping loop has not been properly investigated in peer reviewed technical papers - the subject is remains open for debate (and rigorous future testing).
In my view, extra rope diameters inside the nipping loop may be beneficial in dynamic loading events - particular in repetitive dynamic loading (as would occur in a lead climbing situation).

///

I would expect to see higher MBS yield values in a Scotts locked Bowline Vs Scotts locked Bowline
//
Part of my speculative assumption lies in the notional concept of the first curve of the S.Part as it enters the knot core. It has long been theorized that tighter bend radius of the first curve of the S.Part may lead to a reduction in measured MBS yield values... again I emphasize that this is all speculative.

Firstly, it's not the number of dia. within the nipping loop
but their effect upon it.  (I analyzed what we can see above
to conclude that the two S.Parts deflection/bending was pretty
similar, despite the 3 vs. 2 dia. difference.)

We need to consider the bunny ears, 2-eye Fig.8 knots,
whose reported breaking does NOT show benefit of going
form 2 to 4 eye legs within nipping U-turn --that is one
LARGE difference, to my eye, and yet ... not in results!?

I've sought to make nicely bending (decreasing-radius)
S.Parts bearing at least initially against UNloaded (hard)
parts (e.g., the Tail), thinking that "heat sink" aspects
of bearing against something rather limp will be helpful,
as well as having the hard-tensioned part compressing
ITS way into the other --vs. say hard-rubbing hard!?

That high-strength Fig.9 of the Slovak study --and both
the interior- & exterior-loaded versions beat others--
suggests a surrounding of the S.Part and enlarged
contact area at high pressure is of benefit; and that
for the Fig.8, there is benefit to the eye legs' wraps
of the S.Part so that the seemingly pretty hard/shape
U-turn of the S.Part doesn't have bad effect!?


.:. One needs to be cognizant of these things and
deliberate in dressing & setting so as to get to the
answer, IMO.

Oh, and in such limited cases, I think I'll feel better
with single-knot testing :: doing my knot-at-each-end
set-up risks those low values talking too loudly.
(Be nice to have a good understanding --from some
ample testing cases-- of what 2-knot samples can show
us, or hide from us --hoping to benefit from lesser number
of test specimens and machine exercising!)


--dl*
====

[mcjtom]

It appears that many of the questions raised by the original poster have been mostly answered?

Not really - what about the bear?

[mcjtom]

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.).

Is there a reason why the strangle backup shouldn't be tied on the S.Part instead?

The strangle backup for a bowline can be tied on the: near leg of the loop, far leg of the loop, or the standing part.  Dan pointed out that the far leg may be more secure against accidental ring loads than the near leg?  Are there any obvious objections as to strangling the S-Part (the loop is cleaner this way)?

[roo]

  Are there any obvious objections as to strangling the S-Part (the loop is cleaner this way)?

Any time you use such an untensioned backup measure, there is not much to resist flogging forces that would pop things open, especially if the line has some stiffness to it.  This is why these types of backup measures are often the first to fail and then provide little help beyond the extra rope length once they come undone.

[mcjtom]

Would it mean that having a limited choice between the BL with one of the Strangle backups and the Scott's Locked version you would choose the latter for greater (flogging bear) security?

[roo]

Would it mean that having a limited choice between the BL with one of the Strangle backups and the Scott's Locked version you would choose the latter for greater (flogging bear) security?

Since I choose my own knots, I would decline either option.  If someone was asking which had better flogging security, that would be a matter for testing, preferably with the most unruly rope the person anticipates using.  Unfortunately, the initial tightness or looseness of the strangle backups would likely make a significant difference in results.

[mcjtom]

:⁠-⁠) The bear is trained to chew up all the other knots, except the two in question - with which she just fiddles. Not tying a knot at all is verboten and there is no more time for research.

[KnotLikely]

  Are there any obvious objections as to strangling the S-Part (the loop is cleaner this way)?

Any time you use such an untensioned backup measure, there is not much to resist flogging forces that would pop things open, especially if the line has some stiffness to it.  This is why these types of backup measures are often the first to fail and then provide little help beyond the extra rope length once they come undone.

ahem...

https://imgur.com/a/7xF8w1q

3 years of use and counting.   Flogging does nothing to my rock of a knot.  The rock only loosens whenever the bowline collar can move at all (that should be almost always) and with two simple moves (bend collar and pull slack, bend girth hitch loopback and pull slack).  Ring loading does nothing to the knot.  The untensioned backup slippage is a few mm on a 2 KN fall and cyclical loading changes nothing with that.  It is set once it is set.  The end bound through that girth hitch simply isn't moving.

Today, I experimented with a Blake's Hitch (5-2, 5-3, 6-3...man, gym ropes are old and full of skin and metal) with the (super extra long) tail end of my knot as a Blake's Hitch backup and part of an ascender / top-rope-solo system using the top-rope self-belay side "tail" with a Blake's hitch to (either side) of the top rope as the foot step ascender.

---side note, forcing myself to hang on my butterfly emergency stopper and then find a way out forced my (belay side tail of rope on an already unweighted top-rope-solo belay) use of a rope that should not generally be traveling up (ATC Pilot, hold the rope down, please)... self rescue from a pure hanging stance---

To be fair, it took me 10 seconds longer to untie my tie-in than it usually does.  After ring loading my weight on a hold for fun and then loading the tail's Blake's Hitch maybe 20 times, then hanging on it on and off for 30min, it untied as well as I could expect of any knot.  De-loading the collar was the hardest it has ever been, due to the tail pull.  I'll leave the collar looser, next time, to see if the tail locks down on the end bound move earlier when given a little extra collar slack.  I tend to tighten the collar in normal use, and did so, today.  Collar slack should be maintained with my "pseudo"-bowline (and all bowlines) (either actually put it through its paces or leave it alone, Mark) even when the tail needs to be loaded.  It never tensions without tail load, so tightening it has never been an issue.

(please put it through its paces, Mark

mcjtom, the bear doesn't tear this one apart.  If I had to choose?  Neither.  Mine.