Synthetic fibres -- objective performance ratings?
 

Hi,

I find myself totally befuddled by the array of synthetic fibres on the market, particularly with regard to how they perform in practise.

• Manufacturers publish breaking strengths, but even there I wonder if they measure by the same criteria -- for example, what is Samson Average Strength as compared with Samson Min Strength?

• Stretch figures are hard to come by in general, and again, I wonder about consistency of measurement. Ditto for creep.

• UV sensitivity -- total minefield! They all say "superior UV resistance", and so forth, but that's meaningless. I want to know how UV-sensitive the fibres are -- is Vectran better/worse than Dyneema? Does PBO really self-destruct after a few months in the Sun? Do the various coatings the manufacturers use (Samthane, Armourcoat, etc.) make much difference?

• Same for chafe!

So, it seems to me that it would not be hard for someone to run objective tests on all this -- eg. set up a rig to pull ropes with weights on the end back and forth over a length of steel wire with UV lamps on them -- but has this ever been done? Is there any real quantitative objective data on how these ropes perform? Failing that, reliable relative data would be a big help -- eg. Vectran is more/less chafe-prone than Spectra, etc.

Cheers, Ian

Saw something in SAIL last month
 

Yes, comprehensive testing like this would be great.

There was some testing (around knot strength actually) in SAIL last month. I found it interesting that they developed their own baseline breaking strengths -- these were far higher than the published tensiles. I believe most published tensiles are fairly conservative. I also under understand that many tensiles are determined from a spliced sample -- so by definition a proper splice is 100% efficient.

Checkout the Layline site, they have done some elasticity testing on their "punisher".

Bob

Chafe is a bear
 

OK, here's one piece of objective data on "chafe" -- apparently bears can chew through Vectran, but not Spectra!

http://ursack.blogspot.com/

Thanks for the heads-ups, Bob & Deralte (that one re bear nibbles will be a hit with the
rockclimbing set! :) ). But, Bob, I've now checked the on-line Sail TOC's for Jan'07,
Dec & Nov 2006, and don't see a hint of any ropes or knots testing: can you please
provide a link to that? (maybe a copy ... ?)

And, yes, the Layline stretches are good to see--and have several levels of tension.
(They had at one time a video of a rope breaking--oddly over an extended few seconds.)

One should expect that the baseline is tested, not quoted, and be disappointed when it's not.
There was a test of gel-spun HMPE fishlines a few months ago, and the differences
between rated & actual strengths in the lines was HUGE--to 270%*!!! And then there
will be knot testers who presume to determine efficiencies w/o determining the material
strength? --and then such determinations get compared w/each other, and ... .
[* Sport Fishing mag., Aug.2006, pp. 62-68]

I have found it intriguing how, in a table of strengths per size of various ropes, one
might be significantly higher in some sizes, then slowly or even suddenly lose that
lead and even trail, then come back again; and how the proportion of strength per
material might be inconsistent.

The Cordage Institute made some noise about their insisting on spliced strength vs.
ISO (?) or some international standard that uses other methods. But splicing takes
skill, which varies; and, of course, one would like to know of the splice's efficiency.
(Notably pathetic, e.g., was Practical Sailor's testing in which their eye splices pulled
out well under the load ultimately borne by bowlines!!)

As for other characteristics, yes, isn't is amazing at some of the assertions: UV has
NO effect on HMPE; or is it that HMPE is only "good" but not "excellent" in UV resistance;
or "excellent" up until about 3 years when more Samthane (?) coating is needed?!
--ditto on the abrasion resistance, with various anecdotes of toughness and resistance
to cutting, yet often polyester is rated higher!?

(As for PBO, the anecdotes I've heard aren't about rapid deterioration in months, but
nearly HOURS! --and yet that material has appeared (at a price!) as part of a sheath
for frictional heat resistance!?)

.:. Ya gotta wonder!

SAIL Mag piece on Knot Strength
 

The knot story is in the Feb 2007 issue (page 82 by David Schmidt) . The testing was done at New England Ropes.

They tested 1/2" double braid nylon, 1/2" Sta-Set, and 1/2" Endura Braid with a bowline, a clove hitch backed with halfhitches, a round turn and halfhitches, a figure 8 follow though, a double fisherman's knot, and an eye splice. No details were given on the eye splice, but I assume it was to NE spec.

As expected, knots in the Endura Braid were pretty bad, they only retained about 30-40% of the strength of the rope . The tensile was tested at 19300#, I believe published is 19000#. The eyesplice broke at 20594#.

The eyesplices in the other ropes were about 78% and 88% efficient at the measured breaking strength -- the measured breaking strengths were about 20% higher than published numbers. The knots were about 50-60% efficient.

It would be interesting to see a comparison between Endura Braid and Endura12 of the equivalent size. I'd assume the cover helps some -- by adding friction.

I would have expected the knots and eyesplices in the nylon and dacron to fair a bit better. The knots were only about 25% better than the same ones in Endura Braid. I would have expected the eyesplices to be closer to 100% efficient.

Bob

PBO Covers
 

I have seen the PBO covers and inquired about the UV problem. Since the covers are not designed to be load bearing, the strength is not a factor, and apparently the heat and chafe resistance is not impacted by the UV induced strength loss.

Bob

What's weird -- to me -- about PBO, is the number of people selling PBO standing rigging systems (eg. Powerlite, OYS). Case in point: a Swan 80 rigged with PBO. OK, these are all race-oriented tweak-freaks; but even so, if it's as bad in UV as people say, they're going to be re-rigging a lot, aren't they?

Hi Bob,
I'm looking forward to seeing the article, especially to see what variables might account for the odd results (like those very low splice numbers). As it happens, two of our apprentices just got the results back from their destruction tests, and nearly all of the splices appear to have approached 100% efficiency, so I know it can be done.
Fair leads,
Brion Toss

PBO Rigging and SAIL Story
 

I have sold a bit of PBO standing rigging. There is no exposed PBO, the terminals are sortof headed and glued -- most like a Cast Lock. The balance of the PBO is covered with a thick plastic tubing.

Don't expect a lot of splice tech detail in the SAIL story. I can only assume that whoever spliced was better at the core-to-core than with a double braid splice -- maybe variables in core bury, taper, etc.

Bob

Well, Bob, Feb '07 might be "last month" for you, but the way I work
it's at least a half year in the future! (And I recently got a med. bill for
my father from April '05 (oh-five, yes)!!)

Um, again, 100% of WHAT? --note Bob's point that the actual tested strengths were
"about 20% higher" than ratings (yet apparently, at least for the Endura Braid, the
test method didn't get it all--splice topping it!) Factor that in and those "weak" splices
approach 100%, too. (If the splice is breaking, it's not 100% but something shy of it
--otherwise breaks should come arbitrarily elsewhere along the line.)

I've been impressed more than once that some tester might conceive that the test
device would care whether a Fig.8 loopknot was tied in the bight or with the end!!
Did the report show the exact form (dressing, and WHICH END WAS LOADED) of the
knot--or are we gifted with Guessland, as usual? In any case, the values are lower
than what one will find in general belief in the kernmantle world--see e.g. fairly recent
testing by Dave Richards http://www.caves.org/section/vertica.../knotrope.html
--12.5/10.5 bar graphs are of each other's data; tables are correct.

(I'll hope to find this Feb SAIL still on some store shelf, thanks!)

--dl*
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