Dyneema splicing conundrum

[Breaking Waves]

Originally Posted by catsketcher

The data from the video I posed shows that Brummel doesn't reduce strength, but that tapering is very important.

To identify a 5% strength loss you have to do quite clean 'science'. All samples from the same spool of rope, at least 10 of each design averaged (more if you want to have higher confidence), same pull speed every pull, samples constructed all absolutely carefully identically (except for the feature being tested), etc. etc.

The how-not-to guys are good guys who do interesting work and they usually get the order of magnitude correct. But they do NOT do precise 'science' and their results consistency are at best >+-10% and I guess they never took any statistics.

[Breaking Waves]

Originally Posted by Tupaia

Doesn't Colligo themselves recommend modified Brummel splices?


https://www.colligomarine.com/tech-splicing

Colligo's perspective has been 'we have not had one break yet so we will continue doing what we have been doing'. They overstrength their stays, so +-5% does not make much difference. It is a fine, conservative approach.

[Breaking Waves]

Originally Posted by Leadfree

Colligo isn't necessarily the last or best authority, as I learned by experience wrt their terminator bend radius assertions.

And yeah, honestly, more 'innovative design' than an 'analytical engineering driven approach'. They did misunderstand a basic principle of splice strength in their early days.. . . which I took pains to educate and correct them on . . . and then they threatened to sue me when I mentioned it publically not the best experience.

[Breaking Waves]

Originally Posted by Leadfree

So Brian Toss' assertion of 72x bury (with taper) is old news and it happened that he died before your tests were made? Hell, I'm glad to not use up so much line, ha ha

Brion (note the correct spelling ) and I worked together closely during the development of the stronger series of soft shackles. He was the design brains and I just broke stuff and suggested what part might be made stronger if he could figure out how. A great guy, a big loss.

His early feeling about Burry length was 'more has to be better even if you can't see it in tests'.He did not often 'preload' (to bed in the bury) (to my knowledge he did not have a 'real' loadcell) and did not (at least in the early days) lock-stitch. So, in those cases, longer bury may give you some extra protection from low load slip out - but is hard to test for and I have never seen anything showing better performance for >60x.

For yachting size rope, using a couple extra feet is not so expensive. For the commercial guys a meter of rope can be > $100's and they have very carefully figured out where the 'break points are' (when made to high standards best practice) and as I said they rarely go over 45x.

[Leadfree]

Originally Posted by Breaking Waves

Brion (note the correct spelling )

even funnier... my spellcheck did that change and I didn't catch it... I note your term "Burry" which is capitalized and misspelled, fyi

[s/v Jedi]

Originally Posted by Hartleyg

Thanks, Jedi!

Its nice to know that the easy way works fine

BTW, I've found that the "blunt" needles work a charm for stitching dyneema - you don't split the strands as much, and less risk of jabbing oneself.

Hartley

Here are the mini fids I wrote about: https://www.amazon.com/gp/product/B01AEALJ8M

[Hartleyg]

Thanks Again, Jedi,


I have a couple of those, originally purchased to do paracord stitching, etc. My only beef with them is the mediocre way they have of attaching the cord to them - the threaded end is OK, but not particularly robust unless you are using them for the exact size of paracord they were designed for. A tapered, coarse-threaded opening would be more versatile, but I don't know how much market there is for such things


I bought these: https://www.amazon.com/gp/product/B08NZDQN2T/ and they work a charm for stitching hollow-braid line (I've used them on Dyneema, Polyester and nylon). They also make similar needles in plastic, but they just aren't rugged enough for me


Hartley
S/V Atsa

[ChrisJHC]

Originally Posted by Hartleyg

Thanks Again, Jedi,


I have a couple of those, originally purchased to do paracord stitching, etc. My only beef with them is the mediocre way they have of attaching the cord to them - the threaded end is OK, but not particularly robust unless you are using them for the exact size of paracord they were designed for. A tapered, coarse-threaded opening would be more versatile, but I don't know how much market there is for such things


I bought these: https://www.amazon.com/gp/product/B08NZDQN2T/ and they work a charm for stitching hollow-braid line (I've used them on Dyneema, Polyester and nylon). They also make similar needles in plastic, but they just aren't rugged enough for me


Hartley
S/V Atsa

You could also spend 2 minutes with an angle grinder to round the ends off if that is what you’re looking for.

[s/v Jedi]

Originally Posted by Hartleyg

Thanks Again, Jedi,

I have a couple of those, originally purchased to do paracord stitching, etc. My only beef with them is the mediocre way they have of attaching the cord to them - the threaded end is OK, but not particularly robust unless you are using them for the exact size of paracord they were designed for. A tapered, coarse-threaded opening would be more versatile, but I don't know how much market there is for such things

I bought these: https://www.amazon.com/gp/product/B08NZDQN2T/ and they work a charm for stitching hollow-braid line (I've used them on Dyneema, Polyester and nylon). They also make similar needles in plastic, but they just aren't rugged enough for me

Hartley
S/V Atsa

I stick the paracord needle through, then stick the twine in, then pull out.

[peb]

Originally Posted by Breaking Waves

yea, that's me . . . . and that article is pretty old, generally still correct but a bit dated. We have learned stuff since then.

But I have personally done a lot of the background testing on all this.

Re brummels . . . .

From a test perspective - when done perfectly, compared to a perfect long straight splice, the brummel is around 5% weaker.

If the long straight splice has proper bury length and is properly lock stitched, it will NOT slip.

There are DIY risks with brummels and they can end up with way more strength loss if not perfectly done. . . . . generally if the braid is distorted more than it need be, or the braid is not split equally, or the bury is not correct and the load comes on the brummel rather than the bury (it can end up only 50% strength in this case). I have in fact seen these situations in DIY samples I have tested.

And the brummel is more work.

Basically in pretty much all 'serious' applications outside yachting (like commercial heavy lifting), the Brummel is not used at all. The feeling is why give up strength when you don't need to and why do more labor than you need to, and why take construction error risk when you can do the simpler splice and get better results. When I talk to these guys they think the brummel is for casuals.

My general recommendation is to use the long straight bury with lock stitch in almost all applications. The brummel properly done is acceptable, the strength loss is not terrible. So, if you just want to use it I will not argue strongly against it.

But in the OP's specific situation, getting a properly done brummel on the 2nd end is not all that straightforward and the straight bury with lock stitch is better.

I am not doubting your testing, I just have a couple of questions in order to better understand the theory behind these splices. I had thought, been so long I don't recall where I learned this, that the Brummel, dispute the distortions of the rope, did not weaken the splice because having 2 legs at that point makes up for the distortion. When you do these tests and find it is 5% weaker, is the breaking point at the Brummel? With a splice that sis a simple bury and lick stitch, where is the typical breaking point?

[Breaking Waves]

Originally Posted by peb

When you do these tests and find it is 5% weaker, is the breaking point at the Brummel? With a splice that sis a simple bury and lick stitch, where is the typical breaking point?

Typically a straight long bury splice will break at the tip of the taper. There is a stress riser there. And that is why there is benefit to making that taper very fine (down to one filament as I said above). IF you make the whole splice really perfect, with a really fine and smooth taper, you get very close to 100% rope strength and then it can really break anywhere . . . .but that takes some skill and most break at the tip of the taper.

The 'naked brummel' (eg a brummel without a bury behind it) is only 50% strength. Just as an aside - by stacking 5 brummels back to back you can make it naked to 80%. In the 'bury brummel' you are aiming for the bury to carry the strength and the brummel be just there to prevent low load slipping. It will typically break there at the Brummel - I am speculating, but I guess because of constructional stretch (of the splice) and inevitable small imperfections, some load will come on the Brummel, and that becomes the weak point. As I said in post above . . . . it is a more complicated construction with a wider range of outcomes than the straight bury splice.

My knowledge is really about extensive test results and I can report factually about those. However I am not really any sort of expert on the 'why does it break at this strength or like this' - that would take some sort of textile engineering knowledge which I don't have.

[peb]

Thanks for the info, greatly appreciated.