Author Topic: The right handed bowline is safer than the left handed ! (?)  (Read 16037 times)

xarax

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The right handed bowline is safer than the left handed ! (?)
« on: November 17, 2009, 05:15:19 AM »
    A quite provocative title and exclamation mark, but with big question mark at the end...
  
     Trying to discover a better mousetrap, or a better 'bowline-like" end-of-line-loop, I was thinking about what is really the most dangerous thing that can happen in a loaded bowline, and how the bowline itself is trying to prevent it, most of the time with great success.
    May be it is a very naive thought, but what seems to me the greatest danger is the ultimate bowline collapse ; the capsize and deformation of the nipping loop, and the subsequent transformation of this almost two dimensional circular loop to a more open three dimensional spiral, ( or even a one dimensional straight line at the very end...), which of course can not grip anything any more. And this can happen only if the loop is allowed to rotate around a point close to its crossing point, and untwist. What really prevents this from happening all the time ? Nothing else than the two strands of the rope that pass through it, the one that comes from the loop, the eye leg the bight and its extension to the collar, and the one that comes from the collar, with its extension to the tail. We can even argue that this is the main role of them in passing through the loop, to help the loop itself keep its orientation and prevent it from rotating and untwisting.
    Now, from those two strands, I think the main contribution in the prevention of the loop rotating, untwisting and subsequently un-looping, comes from the former, as this is the only strand of the two that is under tension from both sides. In the "right handed" bowline, this strand is located further away from the point around which the loop can rotate, (which is somewhere near the crossing point of the loop), than in the "left handed", so the advantage is greater. Even if the collar is a little loose, the eye leg of the bight is always under tension when the bowline is loaded, so the nipping loop feel some difficulty in twisting and un-looping altogether. And because in the "right handed" bowline the strand that comes from the loop is situated outside the loop, further away from the crossing point, its leverage in the prevention of a catastrophic rotation of the loop is greater.
    Just a naive thought, but the security of the bowline should not be judged by its resistance to ring loading...
« Last Edit: November 17, 2009, 05:20:55 AM by xarax »
This is not a knot.

Dan_Lehman

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Re: The right handed bowline is safer than the left handed ! (?)
« Reply #1 on: November 17, 2009, 07:49:36 AM »
   A quite provocative title and exclamation mark,
... as taught to headline writers everywhere, ...

Quote
... transformation of this almost two dimensional circular loop
to a more open three dimensional spiral,
 ( or even a one dimensional straight line at the very end...),
which of course can not grip anything any more.
And this can happen only if the loop is allowed to rotate around a point close
to its crossing point, and untwist. ...
    Now, from those two strands, I think the main contribution in the prevention
of the loop rotating, untwisting and subsequently un-looping, comes from the ...
strand of the two that is under tension from both sides.
 In the "right handed" bowline, this strand is located fArther away from the point
around which the loop can rotate (which is somewhere near the crossing point
of the loop) than in the "left handed", so the advantage is greater.
...
    Just a naive thought, but the security of the bowline should not be judged
by its resistance to ring loading...

The Bowline can suffer various defeats:  in slick HMPE 12-strand rope,
it can just slip out, or collapse the eye if the tail is stoppered.  Ring-loading
can be a problem in some circumstances (e.g., someone lowering a loaded
knot somehow snags something within the eye (assume an open/wide eye)
and continues to lower, putting now the load on only the eye legs and
not the S.Part.  If these are your risks, they are how you judge the knot.

But re the capsizing described above, your analysis is wrong.  Indeed,
given the rumor of some "Dutch Naval Bowline" being this so-called
"left-handed" one (where the quoted term connotes inferiority, not any
supposed handedness of the cordage), I mused that then their
preference perhaps comes from the knot being more resistant to capsizing,
which might be a problem in hawsers.  For I have seen many a trawler
hawser with a capsized Common Bowline (Ashley's #1010) in it, as well
as some capsized anti-bowlines, including an Eskimo Bowline (!).

One must note that a rope loop is actually a minimal spiral; and it can
be perhaps nudged to become less minimal, especially by action at
the crossing point, where the rope clearly sits in different planes,
showing its *spirality*.  [Goodness, "spirality" escaped red underscore?!]

It is precisely THIS beside-the-crossing-point leg of the tail-bight
that wants full loading, to stay as much straight as it can be versus
the tug-of-war between the S.Parts here-adjacent parts.  If this bight
leg is the tail, untensioned [<- THAT get a red-mark?!], then as the
S.Part hauls it away from the eye, and the S.Part-eye-leg resists in
holding towards the eye, some slippage of the tail then puts a gap
between the imperfect closing of the "loop" cum spiral, and now
it's a notch less minimal, working towards spirality writ large.

Maybe in dock lines this can be aggravated by some shifting of
the incidence of loading, such that at least momentarily, as there
is friction of eye around pile, the end-side eye-leg can go a bit
slack and give more ground towards capsizing.  SOMEthing is
at work in the trawlers' lines I've seen, for there is just too many
capsized bowlines, IMO.  -- I need to enquire, but not all of those
a-boat afloat seem to have a clue about knots, and "huh?" might
be a common reply to a pointed question.

Attached are some relevant photos, from Knots In The Wild.
The first is a very loose-collared Bowline from the Pride of
Baltimore, just seen on Columbus Day, at Annapolis Sailboat Show.
It was asking to be capsized!  The 2nd photo is of a "left-handed"
Bowline from a dock that seemed to have predominantly these,
and I'll here surmise that the reason is precisely to resist capsizing;
and I'll have to ask about that.  (small dock)

--dl*
====

DerekSmith

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Re: The right handed bowline is safer than the left handed ! (?)
« Reply #2 on: November 17, 2009, 02:00:55 PM »
snip...

SOMEthing is
at work in the trawlers' lines I've seen, for there is just too many
capsized bowlines, IMO.

snip...
--dl*
====

Yes Dan, I totally agree.

That SOMEthing is TWIST and it doesn't matter what handedness of BWL you are using, if the BWL is loose and the right twist is fed up the rope to the knot, it will cause the Round Turn of the collar to open and form the 'flat spiral' you refer to, in prelude to the oft seen transition.

However, getting a right or left handed twist to feed forward into the knot depends on the the lay of the rope (Z or S twist) or if braid, then how it has been fed out of the reel and how that reel was wound.

Even the Eskimo, which is the most resistant to this effect, can be encouraged to 'flat spiral' by a twist fed into a slack knot.

Derek

Dan_Lehman

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Re: The right handed bowline is safer than the left handed ! (?)
« Reply #3 on: November 17, 2009, 07:15:26 PM »
snip...

SOMEthing is
at work in the trawlers' lines I've seen, for there is just too many
capsized bowlines, IMO.

snip...
--dl*
====

Yes Dan, I totally agree.

That SOMEthing is TWIST and it doesn't matter what handedness of BWL you are using, if the BWL is loose and the right twist is fed up the rope to the knot, it will cause the Round Turn of the collar to open and form the 'flat spiral' you refer to, in prelude to the oft seen transition.

However, getting a right or left handed twist to feed forward into the knot . . .

. . . seems beyond the pale of possibility:  what I'm seeing are
trawler dock lines, run bow/stern to pile, boat to boat (they *park*
sometimes five abeam), and I cannot conceive of men handling
lines imparting to such lines torsion sufficient to have this effect
-- especially, as you remark, that one would need to somehow
direct (most of) it into the knot!  (But I'm happy that you're looking
at this from another perspective, and bring this up openly!)

Rather, I think it's more likely some aspect of isolated loading
as I suggested --i.e., where in a boat's movement it can load
one side of the eye disproportionately, and when the end's
side of the eye loose some tension, capsizing effects increase-- ,
and a loosely tied knot.  Now, while the former factor seems
more happenstance and unavoidable/unplannable, the latter
is within control of the tyer --i.e., the knot could be tied
with a snugger collar, but isn't.  Is this loose collar deliberate,
in anticipation of the (partially) capsized form, with that form
somehow perceived as superior (perhaps because it james
a little, with a now quite tightly gripping collar?); or is it
just a consequence of tying without purpose/intent?

In this light, I should remark that I, as an armchair knots
fiddler, have discovered/invented knots that are and are
like the capsized anti-bowline, such that upon seeing them
in these mooring hawsers, I initially didn't think to question
them as having any other state, but presumed them to be
tied in a desired form; only recently did I effectively "un-
capsize" one to realize the equivalence!?  As noted above,
there might be some reliable fellows out east whom I can
ask (and I've much I'd like to discuss w/them).

 - - - - - - - - - - - - - - - - -

Xarax, your just not "feeling" this smartly.  The imperfect
"loop" --i.e., our minimal spiral-- wants to open at its crossing
point, pivoting on the opposite point to this (if cross is at
East, opp. is West); and to impede such opening, it is much
surer to have the part that such an opening must distort in
the process be less tensioned in resistance --ergo, it is the
tail and not the tail-side eye-leg.  It can be furthered
in this process if the material is firm and there is some
slippage --so that the S.Part-side eye leg can move more
towards opening with the feed of a bit of tail, and likewise
the S.Part, all pivoting on the loaded led of the tail bight.
The photos are evidence of this effect, or of its prevention.
(But with the complex of factors, including the forces and
possible bias to eye legs, without deliberate testing, this
"evidence" stands as consistent more than compelling.)

In some of the 12(x twin =24?)-strand hollow braid CoEx ropes,
the rope flattens such that it makes a wider spread at the
crossing point, moving the center of forces in the loop's
crossing parts farther apart, without corresponding real
increase in rope diameter --and maybe this aggravates some
of the workings, though the compression of this rope might
lessen other aspects.  It seems to readily go part way, quickly
losing the *Half-hitch*-like geometry; but maybe going further
is then something not so easy for this material!?  [cf photo]

Now, wouldn't it be nice to have some informal survey of
the state of New Bedford's fleet of trawlers' dock lines
-- among others'!?

--dl*
====

Dan_Lehman

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Re: The right handed bowline is safer than the left handed ! (?)
« Reply #4 on: November 18, 2009, 02:32:10 AM »
Hmmm...So what you are telling me is that, in the brink of a bowline collapse,
 the loop wants to open, what I was thinking is that the loop wants to rotate
( around a point near the crossing point). ...

Isn't this obvious?  Put a stick through the loop; load the
loop:  the S.Part pulls the stick side towards it while the
S.Part eye-leg pulls the opposite way, and the stick is set
flying a-twirl.  Now, split the stick into two parts and you'll
see that the part adjacent the crossing point feels this
joint pulling more than the one away from it.

And the compounding factor is the chance for the tail
to slip between these opposed pulls, especially if some
bit of separation comes; in the tail-on-outside ("left-handed")
bowline, the tail is continuously, steadily held, and the
part at the crossingpoint is continous in anchorage
into the eye or collar and will need donations from
either source in order to distort further.

This is a good point at which to remark that the common
bowline has a commonly presented dressing that need not
be seen as set in stone (but can be seen as readily occurring
by common tying methods devoid of much further dressing
beyond perhaps a tug of the tail to snug up the collar a bit).
The draw of the S.Part on the tail could be anticipated by
putting the tail well back around the other leg of the bight,
so that a strong draw would only shift it towards where we
are used to seeing it start!  This also means that the S.Part's
hard (full tension) bite into material would go mostly into
the relatively soft, compressible, tail and not another firm
part (the loaded eye leg), for whatever that might be worth.
(In some cases, I think a worth could come re chafe, where
there might be the difference of parts moving across each
other, or one part moving in sympathy with the other.)

--dl*
====
« Last Edit: November 18, 2009, 06:43:16 AM by Dan_Lehman »

DerekSmith

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Re: The right handed bowline is safer than the left handed ! (?)
« Reply #5 on: November 18, 2009, 01:30:54 PM »
OK Dan, I can buy your rejection of the 'Twist' mechanism, especially having seen your photo.  However, that self same photo immediately suggested to me an alternative mechanism to drive the deformation of these knots.

That mechanism is friction causing a disparity of forces working on a principle weakness of the BWL.

First, the weakness.  It has been described already that the nipping loop is offset.  When load is applied via the loaded line, across the loop and into the exit line (may I call it the primary loop line), then the offset imparts a torque on the loop as demonstrated by your flying stick description.  In normal operation of the knot, this torque is offset by an equal and opposite torque supplied by the return leg of the loop (I will call it the secondary loop line), entering the loop from the opposite side that the 'primary loop line' left by.  The torque on the loop is then balanced by moments from both the primary and secondary loop lines acting to cancel one another and the loop stays in line with the applied load.  The weakness of this knot is that this knot relies on the turning moment from the secondary loop line in order to maintain stability.  In the absence of this moment, the BWL quickly and easily decomposes.

Second, the mechanism - Friction

In the 'normal' application of the BWL it is expected that the load applied to the knot via the loaded line is shared equally by the two loop lines, i.e. both are under tension to essentially the same degree. 

However, in the situation where the type of rope (hauser) and the anchor point have cause to be subjected to significant friction, and especially where the load is not constant and can vary in its direction, then the situation can develop where the load is applied to the knot from the load line, flows out of the knot through the primary loop line, but does not return to the knot through the secondary loop line, (this would particularly be the case if another Hauser was placed over the top of the first, its loading would clamp the first hausers line tight to the anchor point).

Under this situation, any looseness  in the BWL would allow the unbalanced torque force on the nipping loop to be manifest in the observed 'turning and unwinding' of the out of balance nipping loop.  Couple this with repeated cycling of load and the knot follows the loading imbalance until the transformation occurs. If shifting of the load direction occurs after the knot has transformed, then the knot cannot restructure because it has become a slip noose.

It does not take much to increase the friction around the back of the anchor point to steal all the loading away from the secondary loop line and leave the nipping loop in an unbalanced torque situation.

Given this weakness, I would have to ask why would anyone ever tie up with a BWL?  Would it not be better to simply put two turns around the anchor point, then clove or slip hitch the end to a ring or some suitable static point?  Change of direction, variable load or flogging, none would be an issue and indeed, friction is being put to work instead of working against you.

NB.  One positive observation to come out of this exercise is that if you are going to load one leg rather than the other, then always make sure that it is the secondary loop line (i.e. the bight leg) and safeguard the end in a manner such as the one shown in your photo - this effectively uses the BWL in Sheetbend mode, which does not suffer the risk of unbalanced nipping loop torque from a loaded primary loop line (i.e. nipping loop leg), in fact the opposite, it uses the imbalance to clamp the secondary loop line against the bight legs.

Derek

roo

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Re: The right handed bowline is safer than the left handed ! (?)
« Reply #6 on: November 19, 2009, 05:48:37 PM »
  I think that the nipping loop of the knot in picture B, would collapse easier and earlier than the nipping loop of the knot in picture A,

The differences in capsizing and the much more important aspect of shaking security between a standard Bowline and a Dutch Bowline (if that's what you mean by opposite hand) are, in my experience, very, very minor in the overall security spectrum of loop knots.  

If you are really concerned about security for demanding conditions, you need to leave these two alone.

P.S.  I think you are inadvertently showing identical bowline configurations.

for comparison:
http://upload.wikimedia.org/wikipedia/commons/thumb/e/e1/Standard_bowline_vs_cowboy_bowline.svg/350px-
Standard_bowline_vs_cowboy_bowline.svg.png

UPDATE P.P.S.:  xarax addressed the problem image
« Last Edit: November 20, 2009, 09:37:44 PM by roo »
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roo

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Re: The right handed bowline is safer than the left handed ! (?)
« Reply #7 on: November 19, 2009, 07:22:56 PM »
  I try to understand how these subtle and minor differences could change the behavior of those bowlines....  

If this is an academic pursuit, that's fine, but "eyeball analysis" of knot structure is often deceptive at best.  It's easy to miss certain factors and to improperly emphasize the factors that you do catch.

It may help you form a hypothesis for testing, but eyeball analysis should not be a replacement for objective testing with reproducable results.  Even then, your hypothesis might be right for the wrong reasons.
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roo

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Re: The right handed bowline is safer than the left handed ! (?)
« Reply #8 on: November 19, 2009, 07:49:21 PM »
   I agree, but where are these "experimental facts or computer simulation readings" we need ? I have not seen ANY scientific analysis going beyond crude tests and eyeball analysis ! So what can we do, if we are "trying to discover a better mousetrap, or a better 'bowline-like" end-of-line-loop?"." What is really the most dangerous thing that can happen in a loaded bowline, and how the bowline itself is trying to prevent it ?" We are well into the twenty first century, and the scientific analysis of practical knots is barely out of its prehistory. There are powerful computer simulations available today, in mechanical engineering, cheap, fast, precise, but I have not seen any of them applied on the poor humble king of knots...Till the moment I see one, I have to rely on my own eyeball analysis, what else I can do ?

You can do actual testing with actual ropes of various materials.  That's what I do.  That's what Ashley did in his Book of Knots.  That's what any knot nerd should do.   You can count shakes before failure.  You can built a mechanism if you're really motivated and want a reproducable motion, force, etc.

Forget about computer simulations.  Even high-end software tends to focus on solid structures rather than fiberous rope tied in knots.  And even high-end computer simulators have much difficulty with solid structures pressing against another solid structure.
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Dan_Lehman

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Re: The right handed bowline is safer than the left handed ! (?)
« Reply #9 on: November 19, 2009, 09:36:02 PM »
P.S.  I think you are inadvertantly showing identical bowline configurations.

Perhaps an Edit changed this, for there's an obvious end-inside vs. end-outside
difference in the images now.

 :)

As for "I think that the ..." :  Xarax, you have tied, but have not tried ... ?!

I just did, in much stouter old, laid rope, and the difference showed soon
enough via some pulley force:  as I have said, the end-on-inside (common Bwl)
configuration soon saw the nipping loop widening into a spiral.  Same thing
in my old smooth 11mm dynamic rope, much more quickly.  And the reasoning
I gave should've made this behavior expected and understandable; I really don't
see how you can persist in wrong-headed analysis!

--dl*
====

ps:  Now, back to suffering the needle-&-thread marking work urged upon
(absentee-tooooo-long) Agent_Smith, for some Dyneema headed for break
testing with (gasp) "new" knots.  No doubt such tampering with the pure
material will irritate Derek's sense of proper testing, these foreign threads
impeding movement, but ... .  :D


roo

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Re: The right handed bowline is safer than the left handed ! (?)
« Reply #10 on: November 19, 2009, 10:18:06 PM »
You can do actual testing with actual ropes of various materials.  That's what I do.  That's what Ashley did in his Book of Knots.  That's what any knot nerd should do.  

   So what you propose is simply "go back to the nineteenth century, and stay there !" :)
  

Testing the real thing isn't a second-best or old-fashioned proposition, and it is certainly better than testing a knot by eye and adjectives.  Real life tests are conducted on everything of consequence right now in 2009.

Even if you had a computer program to do what you propose (likely sometime in the distance future), it would not be a replacement for real life testing, as the simulation would be just an approximation based on the quality of the input and software, and kneecapped by any errors or omission.  The typical reason for computer simulations is primarily speed and labor advantage over real-life tests, not accuracy.  
« Last Edit: June 04, 2010, 08:33:08 PM by roo »
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roo

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Re: The right handed bowline is safer than the left handed ! (?)
« Reply #11 on: November 19, 2009, 10:24:23 PM »
P.S.  I think you are inadvertantly showing identical bowline configurations.

Perhaps an Edit changed this, for there's an obvious end-inside vs. end-outside
difference in the images now.

It looks fixed now.
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roo

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Re: The right handed bowline is safer than the left handed ! (?)
« Reply #12 on: November 19, 2009, 11:44:28 PM »
  Yes, the space shuttle is tested on each flight, ( and unfortunately it has failed in some of them, I hope it will not fail again in the ongoing one ), but it would not have been designed as it was designed in the first place without the computer simulation of the complex fluid dynamics around the vehicle during its re entry in the atmosphere.
And wind tunnel tests, and data collection, etc.  Notice that more was done than just hypothesize and adjectivify.

Quote
(The same is true for the meteorological problems, where we can not even think of a large scale experiment that will reveal the true workings of a typhoon, for example).

We test weather all the time with real-life outcomes which are 100% accurate by definition.   More precisely, the weather carries out the test without any help from us.  We don't run simulations and then close our eyes to the real-life outcome.
Quote
The relevant equations have not been sold yet, ( they are one of the greatest unsolved mathematical problems ), so computer simulation is the only thing we can do. These are other cases where computer simulation is something more than merely a " speed and labor advantage " over real life tests.
   Secondly, all real life tests, as well as all experimental data in every field, can not drive us to a deep understanding of what is really happening in a real life situation. " It is the theory that decides what is observable ", and only a theory can offer a deep scientific understanding. If we  have achieved this understanding in the first place, then we can understand our experiments, which, of course, can falsify the theory at the very end, and the game of knowledge continues.
   No matter how many experiments we have, if we do not build a theoretical model, we can not understand the real life thing, or even interpret the experiments. Perform 1 million experiments on the right handed bowline and another 1 million on the left handed bowline, and then tell me that the one is better than the other. I would be grateful to you and your labor, this can change my decision about what bowline I am going to use next time, of course, but...but if I do not have a scientific model, I will remain as ignorant about the causes of this as I was before. And I would not become more capable of inventing a better mousetrap, a more secure bowline, than I was before.        

I did not say that you could not make hypotheses or theories!  Quite the opposite!  I am encouraging you to test your theories, rather than throwing up your hands and asking, "what else can I do beside theorize?"
« Last Edit: November 19, 2009, 11:59:40 PM by roo »
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DerekSmith

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Re: The right handed bowline is safer than the left handed ! (?)
« Reply #13 on: November 21, 2009, 12:50:24 PM »
 

Pretty little thing isn't it.

Now if I have understood this Left Hand / Right Hand thing correctly, when the red end (sticking out the right in this image), and the bight 'end', are on the same side of the knot (that would be the RHS leg of the bight in this picture), then it is the 'normal' version of the knot, but when they stick out opposite sides of the knot, then this is the supposedly less secure, so called 'Left Hand' version.

Grog shows an example on his animatedknots.com website
  -  the wrap 'end' sticks out to the left while the bight end sticks out to the right.

And again, supposedly the RHS versions are the preferred and more secure versions.

I have read several times that the LHS versions should not be used, but I have never come across any justification for this other than xarax's attempt on this post.

But I think there is a reason to disagree.  While taking on board fully Roo's caution that looks and speculation alone can be a foolhardy exercise, I believe that there is a rationale which supports a counter claim that the Left Hand versions are likely to be the most secure and stable.

Let's start simple and imagine the top picture configured as a sheetbend with a load applied to the bottom red cord.  That load can be taken into either the left hand side white bight end or into the right hand side one.  If the load is taken on the right hand side white bight end then the free ends are on opposite sides of the knot, so this is the 'Left Hand' version of the knot = the reportedly inferior one.

Now have a look at the load path for this 'Left Hand' sheetbend.  It flows up through the red cord and in through the bight eye, deflects slightly to the right and wraps around the back of the loaded white leg.  In this process, it also presses against its own end, pinning it against the equally hard loaded white bight leg.

For the white cord, the path is almost identical.  Its load enters over the red collar, dips to the right trapping the red 'end', then wraps around the loaded red line.  The two loaded lines make an overhand type wrap around each other, then collar one another before the 'ends' are trapped in place.  The flow of force is about as 'inline' as it it possible to get them.

Now look at this exercise but bringing the load in through the left hand white line.  The force has to flow across the knot deforming the knot in order to transfer the force.

Make up the knot and put the two alternatives under tension and see for yourself how the 'Left Hand' version loads up uniformly, while the supposedly better 'Right Hand' version deforms under load in a sort of drawn out 'S' while the 'LH' form draws up straight, tight and tidy.

Given this, why then would the 'RH' version be deemed superior?

The Bowline of course is a bastardisation of this lovely knot, an attempt to create an equally memorable loop knot from a structure ill suited to manage the forces of a loop (with the exception of the well designed Eskimo variant that is).  However, the observations from the sheetbend examination above still pertain essentially to the bowline, even though they are somewhat offset by the load sharing of the second loop leg and the geometry change of the forces now fed in through the red 'wrap end' which has become the loop return.

Given that there is a logic borne out by observation that the LH variant is potentially more optimal, what is the basis for the seemingly universal text book claim that the RH variant is 'Best'.

Derek


DerekSmith

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Re: The right handed bowline is safer than the left handed ! (?)
« Reply #14 on: November 21, 2009, 08:08:47 PM »
Yes indeed,

I contacted Puripant last year when he first announced his work and was still working towards his thesis paper with a view to him making his amazing tool available to the Guild.  Sadly he seemed to have more important things going on in his life and there was no followup.

It is certainly a major step forward.  Perhaps others of the Guild could approach Puripant to see if he is now amenable to bring the tool into the knotting world.

Derek