Author Topic: Another Bend for Dyneema  (Read 5435 times)

NautiKnots

  • Full Member
  • ***
  • Posts: 93
    • Nauti Knots
Re: Another Bend for Dyneema
« Reply #30 on: August 01, 2017, 04:32:37 PM »
BUT, you loose the pull-together aspect at the ends
of the knot --where SPart enters :: and where your
knot broke.  I.e., I would have put that broken green
overhand on the INside (i.e., towards knot center)
the corresponding red opposite.

Just to be clear, the green line that broke was the standing end.

Nipping the working end with the standing part is critical to knot security with Dyneema.  If you arrange the overhand knots to form 3 water knots instead of the two water knots and two overhands (as shown), then the bend might slip (I had mixed results in my testing).   An overhand knot formed by the working end tied around the standing end does not have opposing pull and will not develop as tight a nip.

Quote
(And one might even wonder if some other knot put
at the knotted extremes (SPart-entry points) by your
scheme
would yield more strength --a fig.8, strangle
(you did try this, in some way), fig.9 ... ?! )

Some other terminating knot (such as a double-overhand or a strangle) might make the knot stronger, but such embellishments defeat the purpose of this bend - which is to be as simple as possible to remember, yet still secure.

Regards,
Eric
« Last Edit: August 01, 2017, 08:52:25 PM by NautiKnots »

knotsaver

  • Sr. Member
  • *****
  • Posts: 281
Re: Another Bend for Dyneema
« Reply #31 on: August 02, 2017, 02:55:52 PM »
3. A loop with intertwined nipping turns, so that a pull on any leg constricts the others.
4.An Overhand Knot with the working end passed through it.
Would anybody like to venture a guess as to how these knots fared when tied in Dyneema?

Hi Eric,
I was just curious about the Myrtle (your intertwined nipping turns n.3) and about the Honda (your n.4) tied as in ABoK #1454. The Honda in that configuration is known as Bend X

(here in a binder version).
You could retuck the ends as in the Blackwall Bend

I'm curious about that too.
Thanks.
Ciao,
s.

NautiKnots

  • Full Member
  • ***
  • Posts: 93
    • Nauti Knots
Re: Another Bend for Dyneema
« Reply #32 on: August 02, 2017, 06:03:32 PM »
I was just curious about the Myrtle (your intertwined nipping turns n.3) and about the Honda (your n.4) tied as in ABoK #1454. The Honda in that configuration is known as Bend X

I haven't tried those knots specifically tied opposite each other (as in ABoK 1454), but I have tied them with intersecting eyes (as in ABoK 1455).  Both slipped.  I don't see any reason why omitting the eyes would improve the security of the bends.  After all, 1455 itself held better than 1454 (but still not reliably).

Regards,
Eric

NautiKnots

  • Full Member
  • ***
  • Posts: 93
    • Nauti Knots
Re: Another Bend for Dyneema
« Reply #33 on: August 03, 2017, 12:00:39 AM »
When I developed the bend described in post 28 (6 nips) and in discussing it, my working hypothesis was that knots hold in Dyneema when they develop very high nip, not because they have multiple crossings. 

Consider the two bends illustrated below. 
  • The top bend consists of three overhand knots tied in each standing end, and the working ends rove through the center of the other line's knots.  This produces a bend where the overhand knots are pulled away from each other.  Tension on the standing ends tightens the overhand knots.  Security depends entirely on the nip that the overhand knots develop.
  • The bottom bend consists of three overhand knots tied in each working end around the other line's standing end.  This produces a bend where the overhand knots are pulled into each other.  Tension on the standing ends does not directly tighten the overhand knots.  Security depends on the overhand knots jamming tight.
According to my hypothesis, the first bend should hold and the second should slip.  Well, I decided to put that hypothesis to the test.  I tied both bends in 3mm Dyneema, and loaded each one to the point of failure.

It turns out that I was wrong.  The first bend pulled apart even though all six overhand knots set up hard.  The second bend held even though the overhand knots did not tighten up evenly.  It broke at the central pair of overhand knots, which were the most constricted.

I have stated that (in order to hold) Dyneema bends need to have the working ends nipped by the standing ends, but clearly that is not so.  Now, the termination doesn't appear to me to be as important as having an effective central structure that jams and resists rolling.  Just what makes that structure effective is still a mystery to me.  In my previous attempts above, some have worked and others have not.

I speculate that my "6 nips" bend held because the interspersed overhands (that drew up to water knots) added a jamming component to the nipping force I was after.

Regards,
Eric

NautiKnots

  • Full Member
  • ***
  • Posts: 93
    • Nauti Knots
Re: Another Bend for Dyneema
« Reply #34 on: August 03, 2017, 01:17:58 AM »
With my last tests in mind, I decided to find out a couple of things:
  • does the Carrick Bend provide sufficient entanglement to serve as an effective central jamming component, and
  • if the terminations aren't critical, would a Bowline finish work, and might it be possible to untie after loading?
So, I tied the knot shown below in 3mm Amsteel Blue.  It is simply a Carrick Bend (ABoK 1439) with a Bowline (ABoK 1010) on each end.  Think of it as a cross between the Hawser Bend (ABoK 1446) and the Bowline Bend (ABoK 1455).  I've simply substituted Bowlines for the seizings.

I've tried eye-hitched Bowlines in Dyneema before.  They always drew up snug to each other, so I anticipated that this bend would too.  I wasn't disappointed.  Under load, the Bowlines' eyes shrank until they consisted of just the Carrick Bend.  Then the Bend drew tight and held until one of my end loops broke.

At that point, the Bowlines were hard, but - with the aid of a pair of Vise-Grip pliers - I was able to pry the collars back and untie the ends.  I was then able (with Vice-Grips again) to untie the Carrick Bend.

The knot didn't dress-up pretty but it was:
  • symmetric,
  • simple to tie,
  • easy to remember how to tie,
  • easy to inspect for correct topology,
  • self-dressing to a single stable geometry,
  • secure,
  • as strong as previous efforts, and
  • not easy, but possible to untie (unlike previous efforts).
This may be the closest I've come yet to a practical bend for Dyneema.  A lock finish to the Bowlines might even make it stronger.

edit:  Upon further testing, it turns out that the Bowlines can capsize, making them harder to untie and potentially altering the strength and/or security of the bend.  That makes the knot untrustworthy to me so I cannot recommend it (or other bends terminated with Bowlines) for use in Dyneema.  See reply #41 for details.

Regards,
Eric
« Last Edit: August 04, 2017, 09:57:00 PM by NautiKnots »

NautiKnots

  • Full Member
  • ***
  • Posts: 93
    • Nauti Knots
Re: Another Bend for Dyneema
« Reply #35 on: August 03, 2017, 04:45:23 PM »
Below is a variation of my previous bend.  The difference is that the Bowlines are formed by leading each working end to the opposite standing end (rather than to the same line).  That causes the Carrick Bend to rotate 90 degrees with respect to the Bowlines.  This bend is to my last one as ABoK 1454 is to 1455.

Since my earlier trials showed 1454 to be less secure than 1455 in Dyneema, I didn't expect this bend to do as well as the one in my previous post.  In testing, though, the Bowlines did not get drawn as tightly to the central Carrick Bend.  I speculate that either the opposing pull kept the Bowlines farther apart as the Carrick Bend tightened causing it to jam before fully shrinking the "eyes", or the Carrick Bend simply tightens more readily with sideways pull than lengthwise.  The bend broke at one of the Bowlines.  I was able to untie both Bowlines (one of them and what was left of the other) by hand without any tools.  I needed Vice-Grips to untie the Carrick Bend.

I tried again, this time tying a Scott's Locked Bowline on each end.  I hypothesized that because the nipping loop was larger in diameter:
  • it would have less nip and the Bowline eyes would collapse fully, and
  • the bend would be stronger.
I couldn't guess whether the Bowlines would be more secure (because of the additional tail tucks), or less (because of the reduced nip).

When tied in 3mm Amsteel Blue, both my hypotheses were borne out.  The Bowlines drew up to the central Carrick Bend at lower tension, and the knot held up until one of my end eyes broke instead.  One of the Scott-Locked Bowlines capsized into a big slip knot.  The other held its geometry.  The locking tucks seemed to improve security -- very little tail was swallowed as the bend loaded up.  I was able to untie both Bowlines without tools, albeit with more difficulty than the standard Bowlines.  Again, I needed Vice-Grip pliers to untie the Carrick Bend.

Given that the collapsed Bowline still held, I suspect that other terminating knots (such as a constrictor) might work as well -- and may well be stronger.  They probably would not untie, though.

I hope that was interesting,
Eric

Dan_Lehman

  • Sr. Member
  • *****
  • Posts: 3768
Re: Another Bend for Dyneema
« Reply #36 on: August 03, 2017, 09:52:51 PM »
Consider the two bends illustrated below. 
  • The top bend consists of three overhand knots tied in each standing end, and the working ends rove through the center of the other line's knots.  This produces a bend where the overhand knots are pulled away from each other.  Tension on the standing ends tightens the overhand knots.  Security depends entirely on the nip that the overhand knots develop.
  • The bottom bend consists of three overhand knots tied in each working end around the other line's standing end.  This produces a bend where the overhand knots are pulled into each other.  Tension on the standing ends does not directly tighten the overhand knots.  Security depends on the overhand knots jamming tight.
According to my hypothesis, the first bend should hold and the second should slip.  Well, I decided to put that hypothesis to the test.  I tied both bends in 3mm Dyneema, and loaded each one to the point of failure.

It turns out that I was wrong.
This doesn't surprise me.  But I'd like to see the ending
result of the one that held --for it's essentially a backed-up
SINGLE fisherman's knot, hardly a candidate for great security
(in tests of trad. kernmantle, e.g., it has shown slippage
and req'd back-ups/stoppers)!

Rather than you first, I'd have done SOMEwhere (center
or ends?) a fisherman's opposition of the overhands
and then had your grip-the-passed-through-line in the
others.  (Once your top knot started slipping, there was
nothing to alter that --given its slippage, i.e., things were
no longer being more tightly nipped.)

I've a general idea of tying some 1408-like knot where
the exiting-adjacent tails are knotted in an overhand to
stopper their being pulled out through the knot (and thereby
make the base knot tighten further).  One could try this, e.g.,
with a same-side-exit blood knot (the blood like the
dbl.harness can be tied with tails either going opposite
or together.

--dl*
====

knotsaver

  • Sr. Member
  • *****
  • Posts: 281
Re: Another Bend for Dyneema
« Reply #37 on: August 03, 2017, 10:28:25 PM »
With my last tests in mind, I decided to find out a couple of things:
  • does the Carrick Bend provides sufficient entanglement to serve as an effective central jamming component, and
  • if the terminations aren't critical, would a Bowline finish work, and might it be possible to untie after loading?

Hi Eric,
did you try replacing the central Carrick bend by a Zeppelin bend and seeing what happens - the result would be similar, in performance, but somewhat less ugly, after heavy loading...
---
With reference to my previous post I will post as soon as I can a picture  of a retucked Honda loop.
---
Ciao,
s.

NautiKnots

  • Full Member
  • ***
  • Posts: 93
    • Nauti Knots
Re: Another Bend for Dyneema
« Reply #38 on: August 03, 2017, 11:53:28 PM »
did you try replacing the central Carrick bend by a Zeppelin bend and seeing what happens - the result would be similar, in performance, but somewhat less ugly, after heavy loading...

Given the Zeppelin Bend's reputation for not jamming, I thought it would be interesting to try as the central structure for this style of knot.  I tested two variations -- one with the working ends tied to their own standing ends, and one with the working ends tied to the opposing standing ends.

Both drew the Bowlines up snug to the central Zeppelin Bend, and both held (after swallowing a fair amount of tail) up to the point where the strands in the Zeppelin started breaking.  You are correct that the dressed knots are more attractive than the Carrick-centered versions.

Things did not, however, go so well when it came to untying.  In each case, both Bowlines capsized while drawing-up, leaving them in a geometry that was not easy to release.  I had to resort to the Vice-Grips on all four to get them undone.  Likewise, the Zeppelin Bends had pulled so tight that Vice-Grips were needed (on both sides) to open the knots up enough to untie them.

Regards,
Eric

knotsaver

  • Sr. Member
  • *****
  • Posts: 281
Re: Another Bend for Dyneema
« Reply #39 on: August 04, 2017, 02:08:35 PM »
Things did not, however, go so well when it came to untying....  Likewise, the Zeppelin Bends had pulled so tight that Vice-Grips were needed (on both sides) to open the knots up enough to untie them.


In fact, we shouldn't call that a Zeppelin Bend (Xarax would say that this is NOT a Zeppelin Bend) because both ends are loaded! However, I don't know why I'm more attracted by the #1454 version even if it is to be considered the difficulty of loadbalancing the two legs with an equal pull...so what about two (pseudo-)Zeppelin in a #1454 version?
or what about the use of the #1459-1460 structure with Bowlines instead of seizings?
and #1457? :)
Ciao,
s.

NautiKnots

  • Full Member
  • ***
  • Posts: 93
    • Nauti Knots
Re: Another Bend for Dyneema
« Reply #40 on: August 04, 2017, 03:00:41 PM »
I'm more attracted by the #1454 version even if it is to be considered the difficulty of loadbalancing the two legs with an equal pull

I don't think balancing the legs is a concern in Dyneema.  There's enough slippage during draw-up that they tend to balance themselves.

Quote
...so what about two (pseudo-)Zeppelin in a #1454 version?

The two configurations that I tried were analogous to ABoK 1454 and 1455.  Both fared the same (the Bowlines capsized and all the components needed tools to untie).  For what it's worth, the capsized Bowline appears to be stronger than the normal geometry.

Quote
or what about the use of the #1459-1460 structure with Bowlines instead of seizings?
and #1457? :)

What leads you to think that the round-turns and half-hitches (1457), Whatknot (1459), or Whatknot and half-hitches (1460) would make a better central structure than a reef knot?  In my previous tests, two Bowlines eye-hitched (reef-knotted) together was unreliable.  Sometimes it held and sometimes it slipped.

Regards,
Eric

NautiKnots

  • Full Member
  • ***
  • Posts: 93
    • Nauti Knots
Re: Another Bend for Dyneema
« Reply #41 on: August 04, 2017, 09:47:55 PM »
After speculating that:
  • a Granny Knot might be easier to untie after loading than others, and
  • given that I'm loading the knot on both ends, there's no difference between the Granny and the Whatknot,
I decided to try out a central Granny with Bowlines on each end.

In both forms (like ABoK 1454 and 1455), the Bowlines slipped a little, capsized, and then slipped the rest of the way.  At that point, the bend held.  It was possible, but not easy, to untie the capsized Bowlines and Granny Knots.  Pliers were necessary.

That got me to wondering about why the Bowlines capsized on the Zeppelin and Granny, but not the Reef and Carrick structures.  So, I experimented some more, and discovered that Bowlines can capsize on the other bends too.  The propensity to capsize seems to be related to how close one dresses the knots initially.  If the Bowlines have little distance to migrate, they have less opportunity to capsize.

I do not, however, trust knots whos properties change depending on how closely or snugly you dress them -- especially in high-load applications (like you'd use Dyneema for).  Therefore, I'm no longer enamored of the bends in replies 34 and 35, unless something can be done to prevent the Bowlines from capsizing.

The Overhand and Collar I showed before, and the Angler's Loop do not capsize under load -- but they both jam.  The Overhand and Collar (does it have a name?) can be untied with pliers, but the Angler's Loop defies me.  Is there a Bowline variant that resists capsizing yet remains easy to untie?

Regards,
Eric

Dan_Lehman

  • Sr. Member
  • *****
  • Posts: 3768
Re: Another Bend for Dyneema
« Reply #42 on: August 05, 2017, 05:36:13 PM »
After speculating that:
  • a Granny Knot might be easier to untie after loading than others, and
  • given that I'm loading the knot on both ends, there's no difference between the Granny and the Whatknot,
I decided to try out a central Granny with Bowlines on each end.
Good for you.  I've eyed this structure's appearance
when loaded --i.p., how the apex turn is over space
(between the crossed ends)-- and thought that it should
work well thus!

Quote
The propensity to capsize seems to be related to how close one dresses the knots initially.  If the Bowlines have little distance to migrate, they have less opportunity to capsize.

I do not, however, trust knots whose properties change depending on how closely or snugly you dress them
 -- especially in high-load applications (like you'd use Dyneema for).
[Except that unless you can show us actual loads at which
   you're working, here, one might reply that knots don't
   come up to adequate for benefiting from HMPE's strength!]

  Therefore, I'm no longer enamored of the bends in replies 34 and 35, unless something can be done to prevent the Bowlines from capsizing.

The Overhand and Collar I showed before, and the Angler's Loop do not capsize under load -- but they both jam.  The Overhand and Collar (does it have a name?) can be untied with pliers, but the Angler's Loop defies me.  Is there a Bowline variant that resists capsizing yet remains easy to untie?
[/quote]
I'll suggest (a) using the "left-handed" bowline
or (b) putting in a  complementary collar (extend
the common knot by having the tail collar the "outgoing
eye leg" (i.e., the continuation from nipping turn)).
ALSO, one could putting the eye knots close to the
center knot and running the tails through the center
and tucked out through the opposite eye knot's body

(nipping turn) !?  This gives 3 vs 2 diameters in the
nipping loops of the eye knots, and clamps a 2nd time
(opp. eye) and 3rd (center knot) on the tails.
--though sometimes it seems that such stuffing of
a part for further nipping comes with a downside
of lessening the nip effect given the now increased
number of parts nipped there.

--dl*
====

NautiKnots

  • Full Member
  • ***
  • Posts: 93
    • Nauti Knots
Re: Another Bend for Dyneema
« Reply #43 on: August 05, 2017, 10:51:18 PM »
I tried the Cowboy Bowline - ABoK 1034 1/2 (* see note below).  It also capsized.  What about its structure made you think it was resistant to capsizing?

* I generally choose to use Ahsley's names for knots but I dislike the moniker "left-handed bowline".  There are right- and left-handed versions of the actual Bowline (ABoK 1010);  and right- and left-handed versions of the "left-handed bowline" for that matter.  Ashley's name for this knot seems awkward and confusing (dare I say "gauche"?).

Regards,
Eric

NautiKnots

  • Full Member
  • ***
  • Posts: 93
    • Nauti Knots
Re: Another Bend for Dyneema
« Reply #44 on: August 06, 2017, 09:36:50 PM »
Consider the knot in the image below.
 


It is a Reef Knot (tied left-handed) with Bowlines (tied right-handed) on each end; and with the tails tucked through the center of the Reef Knot and then through the nipping turn of the opposite Bowline.  The knot was tied in 3mm Amsteel Blue (Dyneema SK75).

Because each turn in the Reef Knot and the nipping turns in each Bowline now encompass 3 strands instead of 2, I expected that:
  • the bend would be stronger, and
  • the bend would be less secure
than the untucked version I had tried previously.  Given that the previous bend had occasionally slipped, I anticipated that this bend would slip too.

Well, I tried it twice.   The first time, one Bowline drew up tight and the other not quite snug.  When the standing end on the not snug side started to break (strands fracturing) I stopped pulling and inspected the bend.  Both Bowlines had partially capsized.  The nipping turns had migrated into the knots, but had not pulled through the collars and so did not fully invert.  The location of the partial breakage was at the entry to the collar, not at the nipping turn as is the typical failure point for a Bowline.  The central reef knot was not nearly as tight as the untucked version.  I was able to untie both bowlines and the reef knot by hand (no tools) without much difficulty.

On my second try, both Bowlines drew up snug to the Reef Knot.  One of my end loops (an Angler's Loop) broke first.  This photo shows the bend after loading. 



Both Bowlines had partially capsized, just like the first try.  I had left fairly long tails on the bend, but it didn't swallow much of them when tensioned.  Again, I untied the entire bend by hand (no tools needed) without difficulty.

This bend is a bit bulky and complicated, but it did hold and - unlike all previous attempts -  could be readily untied after hard loading.  That is something I began to doubt was possible with Dyneema.

Regards,
Eric

« Last Edit: August 06, 2017, 09:46:52 PM by NautiKnots »