Low Friction Ring strop methods survey

[fxykty]

Originally Posted by Breaking Waves

Not sure who is saying this - but not true.



UV very definitely weakens Dyneema rope, by round numbers 50% (I have seen tests with results ranging from 40% to 70% - depends on size/braid and coatings) over 24 months (in semi-tropics).



Attachment 193771



This HAS been tested quite extensively because it is of high interest for the commercial users. It very definitely degrades.

Thanks for the image.

I was told what I wrote by a local rigger who has been working with UHMWPE rope for a long time. The discrepancy may be that he was talking about coated and heat-set UHMWPE ropes (that is, individual strand coating - his example was DM-20). For standing rigging purposes he said no coating needed unless you want additional chafe protection. This is in NZ, which has very high UV. BS by the rigger?

[Breaking Waves]

Originally Posted by fxykty

he was talking about coated and heat-set UHMWPE ropes . . . BS by the rigger?

Well . . . . in any sort of simulated use - heat set does not matter in this regard, in fact if anything it is slightly worse (because the filaments are sort of pre-fatigued) - true for both Dux and NER HTS.

Coatings make it complicated to make blanket statements. There are some coatings which are quite good UV shields, at least when new. I imagine there are some test which show that if you had one of these especially good coatings and the rope had zero abrasion and zero flogging you could see relatively little UV degradation. The question is whether that is a realistic test. Even shrouds get meaningful (enough to rub a coating) abrasion (from mainsail and sheets).

This is a test I conducted - both ropes coated, but one of them was obviously a 'better' coating



Dyneema is rather better than most of the other high modulus fibers on UV. This is a test (with all of the ropes coated, with same coating):



There is a theory I have heard that one (of the few) difference between Dyneema and spectra is that they have different UV resistance because they pull the filaments to different diameters. I'm not sure if I have ever seen conclusive details/tests on that (was a long time ago I remember it being discussed).

Bottom line - I would expect in pretty much any real-world application to see UV degradation, but the coating specifics do make a difference.

Edit: oh, yea, another complication, is that dyneema shrouds are usually way way over strength. They are sized to minimize creep, which makes them super strong vs the loads. So, the UV strength loss is often totally irrelevant.

Edit 2: something I have never seen examined is the windage of large(r) dyneema shrouds. They are usually larger diameter than say rod (because of sizing for creep), on a high-performance boat I am curious if that would be measurable upwind or not, but never seen it detailed.

[Breaking Waves]

Originally Posted by Dockhead

The design unfortunately is no longer on his site.

JFYI -

https://www.youtube.com/watch?v=K0eZz36PRYI

[conachair]

Originally Posted by Breaking Waves

JFYI -

Good find, ta.

[Breaking Waves]

SWL and others - interested in suggestions for “open issues” related to Dyneema testing?

I know we have the cow hitch questions.

Are there others?

[Seaworthy Lass]

Originally Posted by Breaking Waves

SWL and others - interested in suggestions for “open issues” related to Dyneema testing?

I know we have the cow hitch questions.

Are there others?

I don’t know if you want to limit testing to evaluate currently used methods, but in playing with soft shackle design a couple of years ago I made a few to eliminate the noose (the weak spot in the high strength design). If two stoppers are used instead, even the weaker Diamond knot design, the load is not on the base of the knot and the soft shackle may as a result be a lot stronger.

SWL

[thinwater]

Originally Posted by Breaking Waves

Not sure who is saying this - but not true.

UV very definitely weakens Dyneema rope, by round numbers 50% (I have seen tests with results ranging from 40% to 70% - depends on size/braid and coatings) over 24 months (in semi-tropics).

Attachment 193771

This HAS been tested quite extensively because it is of high interest for the commercial users. It very definitely degrades.

I've also done testing of polyester DB, cover vs. core. The damage goes MUCH deeper into the core than you would guess, particularly in lighter colors. In fact, the core is often weakened nearly as much.


As for Dyneema single braids, the reason should be obvious. All of the strands are on the surface at some point, so they will ALL be weakened by UV. Obvious, no? The same thing is true of chafe; widespread chafe weakens Dyneema single braid disproportionately (I did some testing for publication) because ALL of the strands are on the surface at some point. Because the fibers do not stretch and because they are slippery, they do NOT share loads as well as other fibers when damaged. In fact, there are chafe modes where Dyneema is LESS chafe resistant than even nylon (if the weave is different).



So there is a lot of mythology out there re. Dyneema and how great it is. It's good stuff, but it also has new vulnerabilities that are poorly understood. In my experience--testing and things that have failed--you need just as big a safety factor as you do with polyester. The reasons are different, but the result over time is similar weakening.

[Seaworthy Lass]

Originally Posted by Seaworthy Lass

I don’t know if you want to limit testing to evaluate currently used methods, but in playing with soft shackle design a couple of years ago I made a few to eliminate the noose (the weak spot in the high strength design). If two stoppers are used instead, even the weaker Diamond knot design, the load is not on the base of the knot and the soft shackle may as a result be a lot stronger.

SWL

This is a soft shackle made with no noose. The load is taken on the side of the knot, not the base, so the strength may be significantly more compared to using a conventional soft shackle using a diamond knot and maybe even more than the “high strength” version as the weak spot is eliminated.

They are dead easy to make.

[Breaking Waves]

Originally Posted by Seaworthy Lass

This is a soft shackle made with no noose.

I'm a bit skeptical . . . but if I do set up a test bench it would be easy to check.

What I'm trying to decide is if there are enough important open issues to justify setting up a bench.

I 'think' I now know the answer to the cow hitch question, but a systematic test series to confirm would be useful, however, so far that's really the only thing I have identified and I'm not sure it justifies the work (and space) necessary to get started.

I might get back the results from 3rd test series on the LFR's tomorrow, which should put that to bed one way or another (either I will have found the right combination to the next level of higher strength or probably it is not DIYable).

On your soft shackle version - I wonder if there are construction process methods which would help ensure more accurate strand equalization - not sure but like perhaps pinning the two strands together after the weave at exact same length from the noose. I felt that was a little bit trickier than when making a conventional soft shackle because of the ring/weave. Probably not a huge gain opportunity, but perhaps 10 or 15% extra for this for the typical DIYer if it is a bulletproof construction process.

BTW - re some comments on another forum - there are pretty clear standards (ISO and American, which are close but slightly different in detail) on how to pull test, including speed (for which there is a range of speed allowed). My guys in Huston follow them to the letter (on the 'fast' side of the allowed speed range for our small yachting size pulls) and issue a certificate with each pull. EStar also followed them (on the 'slower' side of the allowed range).

[Breaking Waves]

Ok, the final round of results on low friction ring strops.

I carefully made two endless loops (more careful attention to bury taper than before), with tapered whipping (looser than before to allow strand equalization) - and got 19,000lbs (352% of strand strength) and 18,000lbs (333%). They both broke on the 3/4" pin. The whipping did not break nor slide. The stronger broke 24/24 strands on 1st sample and 22/24 in the second (pic below) which shows decent strand equalization.




So lesson learned - Strength here is mostly about good careful splicing (bury, taper, and strand equalization) and not so much about exactly which design is used to capture the LFR - however, the tapered whipping IMHO offers the least complexity to achieving that good splice hygiene (especially the strand equalization). You can almost double the strength by taking great care (I was still using only the tools a DIYer would have, for instance, did not use hydraulics to pre-set/tension/equalize).

But even the 'average care' samples were still greatly strong, strong enough for most yachting applications. I personally would not use the 'cow hitch to ring' design, but all the other main options are perfectly reasonable. My personal favorite is the double loop with tapered whipping - but I sort of like the art of whipping.

Then we pulled three webbing samples - two with Dyneema stitching to capture the ring and one 'loose'/basket style on the ring. They were all extremely consistent 10,000-11,000lbs - interesting the stitching to capture the ring did not affect the strength noticeably. These are dead easy to make (climbing loops where the main/critical joining stitching is already done at the factory), highly reliable, less sensitive to bend radius on like small bail padeyes than using rope. Seems like quite an efficient solution for someone who just wants to get the job done well and is not totally in love with rope work.




Finally, I did two more of the bullseye soft shackles, using extra care to get strand equalization. The diamond version went to 155%, still lower than I can make a diamond soft shackle probably because I still find the strand equalization trickier with the low friction ring in place. And the Button (with bury) was 200% again a bit lower than my usual shackle result. But both are strong (enough for almost all applications) and do offer easier attachment/moving around.

I think that completes the LFR strop survey.

[Breaking Waves]

I got all the tested rings/strops back in the mail.

I was particularly curious to see the last one, since it was a 'full size' ring (eg around the size people are actually using for heavy loaded applications) and we took it up to slightly above 19k lbs.

The first pic is of the tapered whipping after the break. I was quite pleased to see it is still completely intact - I was not sure if slightly more development would be needed but it seems not. For reference on the basics of its construction - I have pointed out the Zeppelin bend with whipped ends where I joined the two colors - you would not need this if just using a basic one color whipping. This mid-point/join was hidden at the top of the ring, with the two sides brought down around the ring and started the whipping under the ring. You can see the square knot which finishes the whipping - I brought the two ends up, under the whipping (using a wire puller fid) and again around to the top of the ring and tied there. So the start and finish both hold the whipping up to the ring to prevent it from sliding down when under load.



I see that this strop broke at the bury cross-over, not too surprising because that is where I used both a semi-locking splice feature and some stitching. You could probably squeeze out a little more strength by eliminating one or both of those 'features', I personally consider using one of those worth a bit of strength for their anti-slip security, but on reflection (seeing that is where the break is) doing both is probably not correct.

Then I was interested in how the ring held up under this sort of loading. The answer is really well. There was some slight flattening of the aluminum, roughly equal amounts on the inside (where shackle was) and on the outside (where strop was) - sorry this is hard to photograph because it is really quite minor. And the overall shape of the ring is unchanged (to the tolerance I can measure).

[Breaking Waves]

Looking at two more of the interesting breaks - both these surprised me a bit in the results.

This is a pic of one of the cow hitched rings - these cow hitched rings were the only ones noticeably deformed. The cow hitch is obviously applying a significant amount of compression to the ring. This may well have implications for cow hitching a line onto a Dyneema line - suggests it can potentially apply meaningful compression on the Dyneema, perhaps enough to cause damage (consistent with Samson's comment about cow hitching puller line onto tow line eye).



This is a pic, after breaking, of two of the 'very tight' eye spliced samples. I had expected this tight a throat to break or at least show some tearing. But they really do not. The weave was distorted while I forced the tight throats in the splice, but then really did not change or show extra damage while loaded to breaking on the pin (circa 8-9k lbs for these). The weave does seem to be able to adapt enough to spread the load among its fibers enough to not make this a super stress riser weak spot.

[thinwater]

Originally Posted by Breaking Waves

Well . . . . in any sort of simulated use - heat set does not matter in this regard, in fact if anything it is slightly worse (because the filaments are sort of pre-fatigued) - true for both Dux and NER HTS....

I did some related testing with heat set line (chafe and fatigue testing) and concluded it was worse for every application other than standing rigging. Even the moving parts of adjustable backstays are better made from non-set Dyneema.

[thinwater]

Strength is mostly important because of how it relates to fatigue and working load. But compression damamge to LFRs is probably irrelevant, because no one would load it that high and it has no bearing on fatigue. There are very few applications on a boat where ultimate strength will be tested if properly designed. They may break, but fatigue was involved.


[Exceptions include tethers and jacklines, lifelines, gear impacted in a wild jibe, and standing rigging in a capsize.]



But interesting.

[Breaking Waves]

Originally Posted by thinwater

But compression damamge to LFRs is probably irrelevant,

yes, agreed . . . . but for connecting two ropes Samson at least believes a cow hitch can create meaningful compression damage - see here - and interestingly that is an application where ultimate strength (of the cow hitch) does not come into play, but simply long term sustained squeezing.

I was initially a bit skeptical about that (I figured, similar to what you say, in that application it was more about friction/chafe/fatigue than compression), and am still not sure how it translates to yachting usage of the cow hitch, but I am more alert to the issue now that I see the sort of compression pressure the cow hitch placed on the ring (compared to all the other solutions).

Mostly I was curious about those two failure modes, because they were different from what I expected/predicted before the test.

Originally Posted by thinwater

I did some related testing with heat set line (chafe and fatigue testing) and concluded it was worse for every application other than standing rigging. Even the moving parts of adjustable backstays are better made from non-set Dyneema.

Yes, I agree.