Author Topic: Dyneema-friendly knots (new to dyneema)  (Read 612 times)

erizo1

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Dyneema-friendly knots (new to dyneema)
« on: November 19, 2020, 07:20:29 PM »
I'm new to dyneema and I'm doing a little research. I know that it's slippery, that the usual knots are not dependable with that material, and that some would say there is no such thing as a dyneema-friendly knot. I've gone through old posts, but hunting among testing posts and various back-and-forth discussions left me without a confident sense of what works and what doesn't.

I'm hoping someone can provide the names of one or more knots (all kinds, but mostly interested in loops and hitches) that hold reasonably well in dyneema under the following parameters:
  • Application is not life critical
  • Loads up to 20% of breaking strength
  • Plain dyneema without a sheath
  • Proven effectiveness (knot has been either tested or used with enough experience to vouch for it)

Thanks!
« Last Edit: November 19, 2020, 09:21:33 PM by erizo1 »

Dan_Lehman

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Re: Dyneema-friendly knots (new to dyneema)
« Reply #1 on: November 19, 2020, 11:51:35 PM »
> loads up to 20% of breaking strength

Whoa, you won't get this close on most tested
any-ol'-ropes!
I had some 5/16" 12-strand, urethane-coated NERopes
Dyneema tested w/a half-dozen eye knots of my
design; strengths were around 40% (more less,
1-2 greater, a little).  Evans Starzinger did some
testing and ... I didn't pay close enough attention
to give a good report on his results; but he did
come up with a hitch that worked okay, and otherwise
was among those building stopper-&-eye "soft shackles"
using a diamond knot stopper.

Meanwhile, there are also the "gel-spun" HMPE lines
for anglers and their sets of knots; IIRC, just putting
a polyester sleeve on an overhand  boosted strength
a lot (?!).

.:.  It's much a mystery to me.

--dl*
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Brocky

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Re: Dyneema-friendly knots (new to dyneema)
« Reply #2 on: November 25, 2020, 02:41:31 AM »
Evan was only able to reach 50% of the line break strength for the few that didn?t slip.

Brocky

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Re: Dyneema-friendly knots (new to dyneema)
« Reply #3 on: November 25, 2020, 01:05:46 PM »
erizo 1, for some reason I?m not allowed to respond to PMs.  I don?t think Evan is involved much in testing, I have had great service from arbsession.com for pull testing.  It?s located in the rope section with the splicing tools on their website.

And for some reason apostrophes turn into question marks, even when edited???
« Last Edit: November 25, 2020, 03:48:03 PM by Brocky »

agent_smith

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Re: Dyneema-friendly knots (new to dyneema)
« Reply #4 on: November 25, 2020, 02:30:14 PM »
Hello erizo1,

Thank you for your post.

I'm assuming that you are referring to knot stability and security (when tied with 'dyneema' type material)?
Knot MBS yield is largely irrelevant - since there is no load that a climber/abseiler/tree climber/caver/canyoner can reach when personally using the knot for suspension in a harness at height.
NOTE: Obviously, if you grab a mechanical force generating machine (eg a lever hoist or winch) - yes - you can reach the MBS yield point of a knot.
Or - if you are using 'dyneema' as winch line to pull your vehicle or others - you could reach the MBS yield point (if a knot was tied to form a connection).
I'm not sure of your exact application?

Also, you do qualify that the 'dyneema' must have no sheath?
This also narrows down your applications...

Apart from having climbed full-time since 1983 - I also do a heck of a lot of white water kayaking.
I use Jackson kayaks (made in USA) - which use cord to draw-up the back rest in the cockpit.
I have been using 5.0mm dyneema cord for the past 2 years in my cockpit - and I tie a simple slip knot to prevent the cord from sliding back through the 'cleat'.
I have been upside down and rolling back up (eskimo roll) in grade 3 rapids while running wild rivers - and the knot always held without 'slipping'.
If the knot slipped - I would lose the support of my back rest in my kayak - and this would cause me to instantly lose control (and potentially get hurt).

So what am I exactly saying?

I'm saying that it is incorrect (for anyone) to suggest that 'all' knots 'fail' when tied in dyneema!
In my case, I have empirical evidence that points to my simple slip knot never failing (if it did - I could potentially lose control of my kayak, get wedged in rocks and drown).

You could state that some knots may exhibit unpredictable behavior under certain types of load conditions.
I also attach my whistle to my PFD (personal flotation device) using #1047 F8 tied in 'dyneema'. This knot has held my whistle for more than 2 years in serious white water and has never came loose.
« Last Edit: November 25, 2020, 02:34:53 PM by agent_smith »

NautiKnots

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Re: Dyneema-friendly knots (new to dyneema)
« Reply #5 on: January 08, 2021, 11:17:52 PM »
A few years back, I went through a couple spools of 3mm Amsteel Blue (a urethane coated Dyneema SK-75 single braid) trying to find knots that held.  I tied every knot I could find that looked promising, including many bowline variants, re-tucked carrick bends, button and knife lanyard knots, fishermans' knots, interlocked buntline hitches, and many other common and invented hitches and loops - including all the recommended (for Dyneema) hitches I could find.  I put them on my bench winch and pulled until the knots either slipped or broke.

None of the recommended knots held 100% of the time.  Some very hopeful candidates slipped at surprisingly low tension.  Even the best EStar hitches only held some of the time.  I evolved several knots, but the only ones that held reliably were derivatives of the Angler's Loop (a.k.a. Perfection Loop) - ABoK 1017.

In fact, I used the Angler's Loop on my test bed to attach the candidate knots to the winch and terminal lines, so I  must have given it hundreds of tries.  The Angler's Loop did sometimes break, but never once did it slip.  Nor did it need extremely careful or hard setting before tensioning.  It swallowed less tail while setting than most any other knot I tried.

I can't say how the Angler's Loop will fare in different diameters, or with different types of HMPE (such as Spectra), or with different coatings.  I don't have a strain gauge so I can't report breaking strength percentages or relative knot strengths (except anecdotally).  I am, however, confident that the Angler's Loop is reliably secure in the cordage I tried. 

The only downside I noted to the Angler's Loop is that it was very difficult to untie after loading, and the line was visibly damaged after high loads.

Given that single-braid HMPE is so easy to splice, and that most of the bends I tried needed practically as much line to tie as a splice would take, I would rather splice than knot single-braid Dyneema when possible. 

HMPE core dependent double-braid should never be knotted - only spliced.

I hope that helps,
Eric

Dan_Lehman

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Re: Dyneema-friendly knots (new to dyneema)
« Reply #6 on: January 09, 2021, 02:21:57 AM »
A few years back, I went through a couple spools of 3mm Amsteel Blue (a urethane coated Dyneema SK-75 single braid) trying to find knots that held.
Brion Toss shows a video of the not-completely-tied
mirrored bowline --a knot like the "water bowline"
with the turns together like a clove hitch (vs. being
broadly spaced, the originally shown knot)--
in which it holds to rupture.  (What he did not do of
that full knot was the final collaring of the eye leg
and tucking then a 3rd diameter through the two
nipping loops.)

And I had 5 knots tied in 5/16" 12-strand NERopes
Amstel blue-like rope and all held sans slippage,
to rupture (nothing to brag about there, sadly).
.:.  There seems to be quite some variation in
behaviors of HMPE cordage !

Somewhere at this site should be my revision of
Ashley's bend #1452 which EStar said he tested
and that it always slipped --dang hard to fathom, IMO !!?
In words, I revised by:
having each SPart turn another 180 degrees and so
then collar the opposing SPart (vs. their own),
AND to make a redundant tucking of the tails
through the center --just an obvious wrap back
for the 2nd tuck.
THIS slips ????   As I said, hard to fathom.
(Esp. considering my "Quick8" eye knot, which
didn't seem to slip w/much force, as I'd tucked
the tail between eye legs and it seemed to hold
a rather UNtightened arc back to the Quick8's
final tuck!?)

Maybe it was the reverse fig.9 eye knot
that was strongest (about 43%)?  (I thought to
*reverse* it for having broader curve vs. any
gripping within... , given how slick HMPE is.)


--dl*
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