So if Derek was looking to identify cords, how is it helpful to identify fibres,
It is principally what he is seeking to know. And typically it's not as complicated as
you want to make it, though, yes, it might in the simple tests one can do not come
to the highest level of certainty. E.g., there's not much indication that in the burn
tests additives/finishes will affect all of the results.
things like density testing (in the book), burn tests (in the book) stretching (in the book)
abrasion resistance (in the book) resistance to oils and greases (in the book) should I go on?
Maybe a float test can help separate floaters from non, in cases of multifilament
cordage; then a burn can further the discrimination. Resistance to chemicals, UV,
& abrasion isn't the sort of thing one can easily check (and I think that all of the'
synthetics resist oil/grease; some vendors however have concerns about the
additives to gasoline). But it would take quite some time and some leap of faith
to make much of the book's information about these aspects into a test method
for determining rope type (and we can note that the book in its limited discussion
of such determination doesn't cite these).
In Chapter 9, are you saying it is not useful to know when to retire a piece of line?
What I said was the this chapter had no relevance to determining rope type. period
Rather, it more presumes one knows this, though again it doesn't distinguish on
fibre type (i.e., chem. compoosition) any of its checks, except for the ONE point
about PP ropes and monofilament fibre splintering (which, yes, one could reverse
and presume "if ... splinters, then => PP").
(But it was in your ton of information, at least.)
But, to Derek, you should find the book worthwhile, and might swallow its
steep price; one can pay a lot less for a lot more and still have a LOT less
(many times over). Just mentally allocate the price over the many other
things that will come along for cheap in your mass of literature growth,
etc..
I am more interested in why we need to know ...
It's a natural curiosity, and we might care to see how certain ropes behave,
or figure what was used by someone for an apparent task (as best one
can then assess from the flotsam-jetsam remnant). And maybe such
knowledge plays a role in employing some find in later use (sometimes
a great deal of cordage can come ashore). One won't be using cordage
of unkown origin (and history) in any mission-critical application, but for
something less demanding, it's possible.
Probably some people will be in areas where certain ropes are common,
and so might have some usual ambiguities to resolve–nylon vs. polyester;
PP vs. PE vs. coextruded PP/PE and maybe that cited Karat brand of
coex PP/PES (I’m unaware of another such rope); or in yachting of some
of the hi-mod stuff. Burn/no-burn quickly sets apart HMPE from Vectran
& aramids (maybe scarcity rules out PBO).
Some other aspects which might be nice to know will remain a matter of
guesswork (more so, if you insist)–such as whether the PP rope one
found is well made with stabilization vs. UV (in case you want to use it
to support that sapling or other sunny task (once found one of those
3-strand yellow-yellow-black PP ropes with the yellow strands bleached
clear & disintegrated; the lone black strand held)). I suspect commercial
fishers get to know a vendor for this sort of quality and the word goes
around (lots of PP & coex & polycombo cordage with them).
On a related note, it’s interesting to go around and collect all of the information
(often presented in tabular form) about fibre characteristics (and for that
matter, rope-structure characteristics, too) and look at it all at once. E.g.,
I’ve read that UV has NO affect on HMPE, and elsewhere that HMPE’s
resistance is merely “good” or maybe it was “fair” !? --or (and this was
in Samson literature) that it was “good” (or better), but then needed a
booster application of their proprietary UV-resistance treatment after
3 years (!). I’ve seen mixed versions of which of PA & PES has the
better of, I think, both UV & abrasion resistance!? --most curious!
(We should all beware the trampling of truth at the hands of marketers.)
Actually, this is a good exercise (and I’m abashed to say I’ve more
noted-in-passing than rigorously checked/compared such information).
–dl*
:-*