Heavy loading, in what material ?
What I use to all "heavy", I guess that it should be a significant percentage of the MBS of the knot, or even of the line - say, 25%, 33,3%, or 50%. We have to define what we mean by this term - and it would be great if we could establish some benchmark loading percentages, and test our ropes in all of them.
There are two senses here : that of the proportion to the
tensile strength; and that in proportion to manual strength.
In the first instance, note that the tightness of the structure
can differ widely per strength of the material, even though,
from one perspective, different materials present the same
sort of feel/size --but snap your fingers and magically convert
multifilament polypropylene into HMPE and suddenly that
force that was X% of tensile is now only X/5% or so(!!),
but the tightness is the same.
And otherwise, although Paul Bunyan (a mythical giant)
might find the knot tied in 1" line subjected to normal,
expected loads while mooring the trawler to be easily
untied, a mortal (wo)man might not. YMMV.
My own experience comes from kernmantle ropes, like those used in climbing, canyoning and rescue. I prefer them because they are stiff ( so they do not like sharp turns, and this makes me, too, to tie knots with wide, smooth curves ), they are not very compressible ( so they can not be flattened too much, and fill the voids in between the segments within the knot, turning it into a compact, massive and rigid ball which can not be un-knotted easily ), and they can retain an almost circular cross section ( so the contact area between two adjacent segments is not very extended ). I think that, in such material, the properties of the "knot" itself ( the geometry ) will manifest themselves more clearly, and the properties of the particular rope ( the material ) will play a secondary only role. I also tie knots in marine ropes, but I do not judge them by how they behave there - marine ropes are usually braided, and softer ( and less slippery ) than kernmantle ropes.
Hmmm, I've found that kernmantle ropes --exactly because
the kern (often) comprises individual cords not cohesive themselves,
hence needing the mantle,
are (more) compressible given that these
individual cords can spread out within the mantle. (To me, it makes
sense to define "kernmantle" to be a "rope with a core of separate
cords or fibres not cohesive as a whole themselves", though in the
past of such-named ropes are ones with braided (cohesive) kerns.)
But, yes, often, too, there is a lot of material packed into the
mantle, and the rope doesn't like to bend --notably, e.g., the
PMI caving rope and esp. older, used specimens of that (and
Bluewater II, a like rope)!
To say that "the
properties of the "knot" itself ( the geometry )
will manifest themselves more clearly" is to betray some ideal
of *knot* too biased by a particular material. Who's to say
that sharp turns are any less belonging to knotted material
than stiffly resisted broader ones? Indeed, I can see someone
making just the opposite charge : that stiff ropes defeat allowing
a knot to achieve its truest manifestation (as might come from
some mathematical modeling algorithm, say)!
Which is why I've remarked that we'd do some justice in giving
caution and circumspection to others by referring to not the
qualities of some "*knot*" but to "*<this_material> so knotted*".
--dl*
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