Bowline slippage

Graeme McMahon

Participating member
Location
Cockatoo
https://fb.watch/v/1fNdHh49a/
Saw an event today that has rocked my confidence. Bowline slippage on a dynema rope about 30mm. We were asking a bit, however... I always considered the bowline reduced in strength but sound.
The rope was compramised so we continued the task. Some of the standard bowlines came undone. Maybe all bowlines need to have a "keeper" knots applied to enable maximum strength retention.

The Shackle coming into shot in the end is the result of the failure of the lifting lug on the 34 ton harvester pulling.
 
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dmonn

Participating member
Location
Mequon
Photo?

There are two ways to tie a bowline. One where the bitter end is on the inside of the loop, and the other it's on the outside of the loop. I always tie mine where the bitter end is on the inside, but have wondered which is stronger--inside or outside, or does it not matter?
 

Brocky

Been here a while
Location
Michigan
Most knots in dyneema slip at less than 50% of the break strength, those that do hold break at the 50% at most. The Estar and Water Bowline will hold until the line breaks.
 
YMMV but HMPE has seemed to be pretty amazingly slippy with knots.
The late Brion Toss shot a couple videos of 5/32" (IIRC) Spectra 12-strand cord tied with a stopped double BWL and one can see the material just feeding out of the knot --the double turn just flowing material from the outgoing eye leg back out into the SPart--, collapsing the eye around the (rather lowish friction steel ring).
www.youtube.com/watch?v=ZFRQcExLA34

www.youtube.com/watch?v=fpt6nxgAOEI
[ Brion's video of botched knot compacting & holding; bottom slipping out ]

I cannot discern what he tied as his claimed "mirror BWL" but it's NOT what I created as that. In any case, my other creation, at the lower end, collapsed sooner. (Would be nice to have seen its full behavior.)

www.youtube.com/watch?v=Fy6Y2Xoo4Ak
[ Brion's video of partial Mirror'd Bwl, which holds to rupture --NO eye slippage.]
The tail, seen sticking upwards, should've made that "rabbit around the tree and back into the hole" collaring maneuver, adding a 3rd diameter through the nipping turn. (Heck, I described ..., even sent photos, but ... .) These tests apparently --surprisingly!-- did not come with force read-outs; Brion opined that he thought the loads weren't great --not near 50%. (And in testing he had done for some Sail magazine article ca. 2004, IIRC his strongest knot was in the 40% range?! In one rare bit of testing of 5/16" NERopes Dyneema 12-strand (w/some coating, blue), of a set of eye knots (each specimen had the same knot at both ends), the ruptures ranged from 37..43% (IIRC) --not what I was hoping for!

EStar (viz., Evans Starzinger) tested my beefed up Ashley's #1452 (beefed up by making the SParts take a full 360deg. turn and so collar the opposed SPart, which end reciprocated; and then the tail being tucked through the central nipped area TWICE!) and claimed that it slipped --mindboggling, IMO, and I'd really like to have seen that!!

And yet then one can read about behavior that is nothing like this, with holding to rupture!?
.:. most puzzling, IMO.

*kN*
 
There are two ways to tie a bowline. One where the bitter end is on the inside of the loop, and the other it's on the outside of the loop. I always tie mine where the bitter end is on the inside, but have wondered which is stronger--inside or outside, or does it not matter?
Cross Post to old thread and discussion of the bowline knot's "nip"

Great illustrations from the Spyder
 
YMMV but HMPE has seemed to be pretty amazingly slippy with knots.
The late Brion Toss shot a couple videos of 5/32" (IIRC) Spectra 12-strand cord tied with a stopped double BWL and one can see the material just feeding out of the knot --the double turn just flowing material from the outgoing eye leg back out into the SPart--, collapsing the eye around the (rather lowish friction steel ring).
www.youtube.com/watch?v=ZFRQcExLA34
...
. (And in testing he had done for some Sail magazine article ca. 2004, IIRC his strongest knot was in the 40% range?! In one rare bit of testing of 5/16" NERopes Dyneema 12-strand (w/some coating, blue), of a set of eye knots (each specimen had the same knot at both ends), the ruptures ranged from 37..43% (IIRC) --not what I was hoping for!

And yet then one can read about behavior that is nothing like this, with holding to rupture!?
.:. most puzzling, IMO.

*kN*
Egadz, in my own msg., "we can read ..." :: indeed, none of my 5? tested eye knots showed much unusual slippage, including the quite brief "Quick8" (tail threads through Fig.8 base, and then --to be serious(!)-- I brought it back around to tuck between the two eye legs, at the SPart's u-turn point; this safety tuck didn't seem much strained) !

As for "two ways to tie a BWL", well, really, in those intended two there are various dressing of where to put that tail. One can tie the so-called "tail-inside" version and dress it so that the tail is outside, which one might do in anticipating the draw of the SPart upon it, which will then pull it around to roughly the point shown for the knot in illustrations --illustrations, I growl, always bassackwards, wrong face shown! (Google BWL, & compare w/sheet bend, which latter shows the proper front face.)
Strength of knots is seldom something approached and thus important, though maybe weaker knots put more *hurt* on ropes in repeated usage; as for the two BWLs, some testing has concluded <nil>.


*kN*
 

TheTreeSpyder

Participating member
Location
Florida>>> USA
on the coEfficient chart of mated materials: radial(link)
teflon/teflon=teflon/steel=.04
dyneema/dyneema is .05-.08
nylon/nylon is .15-.25
nylon/aluminum is .25
nylon/steel is .4
manilla/wood is .5
.
The above frictions are exponential compounding multiplier in arc/capstan formulae.
>>As exponent of ~logarithm of 1 = ~2.72 = Euler's number used to calc compound interest, population growth, disease spread etc. The Mechanics of Friction in Rope Rescue -Dr. Attaway(link)
.
By the numbers, CoF exponentially compounded in Dyneema is based off something almost as slick as Teflon by this scale...(repeat....slick as Teflon!!)
Newer materials, or slicked present could drop even that lower conceivably.
To me this undermines the very math Bowline and other knots depend on..
Just as some knots were left behind when CoF's of synthetics displaced Natural ropes. (coEfficient spreadchet link above)

.
i personally consider 3x180 arcs to be a working class knot in working materials have handled,
This lends more of a 2D clamping power and more compounding frictions than Turn in 1 move of 2 separate considerations.
so would use RT(Round Turn) not Turn for Bowline 'nipping loop', and takes the innie/outie more out of it for tail.
>>actually DBY to 'cleaner' eye form and more security.
>>single Turn Bowline tail outie secures more 1 side of 'collar', but more exactingly squared clamping
>>single Turn Bowline tail innie secures more 2 side of 'collar, but less squarely so in the shared hit
RT for 'nipping loop' wraps completely around, completely engulfing mo'better in anything i think.
But even then, w/3 arcs nylon/nylon shows 4.11-10.55 friction
Dyneema shows at 1.85....(separate from clamping function of turns that now maintain more force thru from input to output of the RT)
Agent_Smith's Bowline paper: collar, nipping loop, innie/outie tail on SheetBend , Bowline etc. and MUCH more in this and other docs(link)
.


(theories)
Only in arcs on radial face (or corners on linear faced) host as deformities; does the Load force DIRECTLY add to the CONTROLS of nip, grip and friction to not only CONNECT (as 1 function) the Load but also CONTROL (another function)the Load. ANY other time, only the deflected byproduct of sideForce gives nominal CONTROLS. i look at the Load inducing the cosine like impulse wave that holds Load in response, but also can have a byproduct of MUCH lesser sine used for nominal CONTROLS. But at DEFORMITY, get cosine + sine = ALL FORCES FROM TENSION that can NOW work in the CONTROL positions against Load, while also still giving the CONNECT utility too. Outside of deformities arc/corner
>>CONNECT utility is powered by cosine part of tension(primary , main force) and
>>CONTROLs utility is powered by sine(much lesser).
IF this were not true of the nonDeformities, linears; rope would simply be too inEfficient for many force transfer uses. In round rope on round hosts, watch the arcs...
.
Stone bridge arc is miracle as tension tolerance only 10% of compression tolerance
>>but stone bridge arc magic is simply can use ALL cosine and sine in compression.
Rope kinda has opposite problem, can't use compression for Load support AT ALL,
>>still arc is cure, as can use ALL cosine and sine in tension as well,
so real geometry is same answer to both problems as works so well, works in either compression or tension direction.
.
Radial deformity of arc is ORGANIC, gradual, Nature's own answer.
corner deformity is unNatural, brash, higher impacting change against rope's constitution, with some controls but harder to plot and control in it's 'instant' of 'momentary' presence of not being a span of deformity as arc.
 

Graeme McMahon

Participating member
Location
Cockatoo
Graeme did.
This is healthy discussion for both the thread origin and interested persons. Knots are part of my every day specialised work. Constant splicing on the job is unrealistic and is not so compatable in a production environment. Mineral fibre rope and a shortener looks to more practical and reliable. I remain interested in the discussion.
 

TheTreeSpyder

Participating member
Location
Florida>>> USA
...and the splice bury is hella long.
Again, i put that on the low CoF of securing hold from the same position, pressures etc. compared to other ropes of a shorter bury of higher CoF.
.
Also, a smoother taper, for this material seems to take deformity even less well than others too.
.
Even in not knotting dyneema because doesn't take well;
is not removed from the science of a most extreme knotting, outer benchmark
that all the rest are (hopefully) well with inside, this demarcation border.
So becomes a comparative scale defining the rest.
Kinda like weak link defining strength of chain.
 
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Brocky

Been here a while
Location
Michigan
Also, a smoother taper, for this material seems to take deformity even less well than others too.
From some sailing forums, even the very point of the tail has to be reduced to a single fiber if possible for a stronger result. They say what happens before the point, as far as tapering isn’t as critical.
The lock stitching to prevent low load pull out also is done so that the needle only goes between the outside strands, not into them to prevent distortion.
 

colb

Been here a while
Location
Florida
This is healthy discussion for both the thread origin and interested persons. Knots are part of my every day specialised work. Constant splicing on the job is unrealistic and is not so compatable in a production environment. Mineral fibre rope and a shortener looks to more practical and reliable. I remain interested in the discussion.
Respectfully, knotted dyneema should not be part of an everyday specialized workflow, imo. Interestingly, a bury splice is fast to make, if that is the specification for the dyneema rope you're using.

What is "mineral fiber rope and a shortener"? I've never heard of either.
 

TheTreeSpyder

Participating member
Location
Florida>>> USA
From some sailing forums, even the very point of the tail has to be reduced to a single fiber if possible for a stronger result. They say what happens before the point, as far as tapering isn’t as critical.
The lock stitching to prevent low load pull out also is done so that the needle only goes between the outside strands, not into them to prevent distortion.
TY, amazing, memorable, concise, imagery factoid of just how sensitive this is to these things,
very counter-intuitively to this extent. i don't think stiff cable is that bad by comparison..
Just as say each man is his own savant;
Dyneema is amazing, but i think we are hitting at it's Achille's Heels.
.
Lessons hear are not a throw away tho.
As, always good to have limits of range, know highest/lowest and then define all the rest as percentages in that range/scope between the benchmark extremes to better definition of all. Here, dyneema might be giving us that ranging in splice, rope, frictions, knots etc. of how important smooth taper is, frictions etc., and then as bottom limiter, how much that affects other materials etc. in ratio to define them more clearly.
.
Being more sensitive is a weakness,
but on flipside then just as much makes a more sensitive, flagging barometer in yin-yang trade.
>>strong spring impervious to 300# Load, would not make a good bodyweight scale etc.
When coiling wire it is stiffer than rope, so more sensitive to doing errantly,
>>so if polish lessons there, and carry to rope, are super good in rope and really watching laid properly.
Another fave example is coiling 1" flat rope webbing etc.
>>is more sensitive/reveals more of errant coiling, and the wide flat shape keeps/shows the faults more
>>watching much more evidently see the mechanism that DEMANDS proper handling or simply MUST kink etc./not lay flat, as throw the turns one way to coil are also making a turn in rest of uncoiled length.; that doesn't walk out in long , stiff, or especially wide flat lengths that can leverage against it's urgings to flow curls off the end..
>>'unwritten lessons' of experience shown, to carry back to more awareness, feel and relevance to proper coiling basic rope properly, now 'read' more clearly from the more sensitive devices.

.
The loss of friction/CoF of dyneema in Bowline does then allow more force then thru the nipping loop from less friction reduction;
but does not seem to compensate greater nipping loop force, for the loss of friction tho, as a bad tradeoff.
i wouldn't say this rules out all Bowlines from all materials, but rather that Bowline has it's powerband as any other working tool, and should watch the CoF as key, and give more scrutiny in shituations where CoF is low for Bowline use. Bowline already not fave if very stiff line, fishing line etc. as material exception ranges of usage.
Rope seems to say, in this Bowline structure/form, the friction value is more important, at least in this range, than the locking action of the nipping loop tension value. Perhaps other knots, would have other reveals from this point of view, that other ropes simply can't give, can't speak to as dyneema.
>>Now have a tool to dial the friction out of this or that knot (or as low as possible with virtually teflon rope) how does that knot handle by comparison, can it compensate for the loss with other mechanix etc.(as could not do here)?
.
All Bowlines could use a stopper or seizing yes as mechanical stop;
but am confident w/o in 'my' types of ropes and usages
>>and 98% of time doing a DBY for security and cleaner, more open temporary fixed eye,
>>as most like clean, open permanent fixed eye splice.
.
i'm not saying to knot in dyneema in work; but use the science in lab for better view, by doing so to 'play it backwards' /do what would never do; to more truly align to go purer forwards.
Just as when talk about a 'stronger'/more efficient knot, am not just chasing the greatest tensile, but rather to use to take pulse, read what is going on in knot etc., in numerical form and then the implications from there.
Use these things to 'read' what rope has to say at different times.
 
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Graeme McMahon

Participating member
Location
Cockatoo
Respectfully, knotted dyneema should not be part of an everyday specialized workflow, imo. Interestingly, a bury splice is fast to make, if that is the specification for the dyneema rope you're using.

What is "mineral fiber rope and a shortener"? I've never heard of either.
Thanks for your info. What is a "Bury Splice"?
Mineral fibre, "Steel cable" the "shortener" is a device that has been about for about a hundred years that can grasp the rope at any point.
Regards
 

colb

Been here a while
Location
Florida
A bury splice is when a hollow rope is tucked back into its own hollow for a run. Any rope used for professional application should have an accompanying splicing specification, and in at least some specs for dyneema a bury is called for. I don't use dyneema for anything but slings and throwline, but a cursory review of this video:


seems to indicate that a specification is likely to include two brummels as well - at the union - followed by a bury. Brummels are easy too. Since the guy takes 18 minutes to do the splice, I'm going to retract my earlier statement that implied that splicing would be fast enough to replace knotting. In part, I think it's slower than I thought because he's carefully tapering the buried end, as mentioned in other posts above.

I would also look into a soft shackle as a possibility in your application...

The mineral fibre and shortener both look cool. Kind of interested to know what you use them for...
 

Brocky

Been here a while
Location
Michigan
Don’t have much confidence in that guys logic for using a locked brummel, he claims the twine is holding the splice in a long bury, he forgot that the finger trapping action takes over. If there is room for the 72 diameters, a locked brummel isn’t needed for strength, and lock stitching will hold it under low loads.
Locked brummels decrease strength by 5%, and are only useful where a proper length bury isn’t possible, they prevent the tail from pulling out until there is enough squeezing action to hold.
Most on the sailing forums are moving away from the lock brummels and going with the straight bury, stressing doing a proper lock stitching instead.
 

colb

Been here a while
Location
Florida
Don’t have much confidence in that guys logic for using a locked brummel, he claims the twine is holding the splice in a long bury, he forgot that the finger trapping action takes over. If there is room for the 72 diameters, a locked brummel isn’t needed for strength, and lock stitching will hold it under low loads.
Locked brummels decrease strength by 5%, and are only useful where a proper length bury isn’t possible, they prevent the tail from pulling out until there is enough squeezing action to hold.
Most on the sailing forums are moving away from the lock brummels and going with the straight bury, stressing doing a proper lock stitching instead.
Always deferring to you, @Brocky.
 

TheTreeSpyder

Participating member
Location
Florida>>> USA
Still only 5℅ loss is pretty dang good,
but to purist theory and benchmark, pure inline again rules is witnessed again hear.
.
Logically, to have any bury, must have at least 1strand, and we now have that lower benchmark limit defined in this example, nothing could be 'worse' /less and still qualify as a bury...
.
So turning it upside down, playing it bacwards into inductive logic; Brocky/et all are there lines that bury whittles down to 2 strands in final stage in reality tests?
If not what is next tier of final stage minimal strand bury for premium efficiency retention in similar purists usages?
If made list of few that had different ending counts, would it be in same order as CoF for those lines?, to discernible ratio??
Elasticity seem a factor/to what extent?
.
To me all is rope mechanix, and these more efficient than a knot, but permanent rope structures can give many knot clues.
.
Manufacture data is great, but would think perhaps truer in CoF and elasticity ratings of less fanfare. Gets into macho strength, kinda can get tilts of bragging or too cya conservative reporting. The field advice by fine tuners carries a lot of weight as Brocky presents I think.

" ....
Strength of knots is seldom something approached and thus important, though maybe weaker knots put more *hurt* on ropes in repeated usage; as for the two BWLs, some testing has concluded <nil>." -*kN*
Have always held that working a less efficient knot hard would be as working kinked chain of same material into structure with greater forces for lower tolerance in real and longterm timelines. But less efficient is a 'pulse' beat to realize more of what is going on in system also.
 
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