water knot with rope ?

why is the water knot recommended only for tape but not for rope ?

Though I won't make any recommendations on tape/webbing knots, the
tape or webbing type of water knot, (I assume you mean the rethreaded
overhand knot type) will jam if seriously strained in rope.

-roo
http://www.geocities.com/roo_two/knotjam.html

) wrote in message . com...
why is the water knot recommended only for tape but not for rope ?

If you're certain that you'll never need to untie or adjust your knot,
I don't see a big problem with using it. Not that I anticipate any
problems, but just so you get a feel for the security of your knot
with the rope you're using, you might try testing the security of your
knot for yourself:

http://www.geocities.com/roo_two/knotfaq.html

I think Ashley gave it (ring knot/water knot) respectable marks in
that area, if I remember correctly.

I've seen from studies that leaving a knot in a rope for an extended
period can cause a very small permanent reduction of strength. It's
possible that since a jammed knot has strain (stretch) energy stored
up within it, that the reduction of strength may be more pronounced,
but I've haven't seen any study to suggest that this is a significant
concern.

Cheers,
roo


) wrote in message . com...
My application is a permanent knot for a permanent prusik loop with
about 6mm cord. If your jam theory is correct, do you know if this
might be an appropriate knot for this application, and do you know if
the jamming would degrade the strength of the knot for a potential
point of failure ?
-dave

) wrote:
My application is a permanent knot for a permanent prusik loop with
about 6mm cord. If your jam theory is correct, do you know if this
might be an appropriate knot for this application, and do you know if
the jamming would degrade the strength of the knot for a potential
point of failure ?
-dave

A double (or triple) fisherman's knot is commonly used to make a
prusik loop.

Phil

"roo" wrote:

If you're certain that you'll never need to untie or
adjust your knot, I don't see a big problem with using it.

A little hard data from the pen of Tom Moyer:

http://www.xmission.com/~tmoyer/test...ot_Testing.pdf

(NB. This paper examines a failure mode of the water knot in tape/webbing.
This may or may not be applicable to cord: I suspect that it might).

Selected summary:
The water knot (even with overhand stopper safety knots) slips with a cyclic
loading pattern. Single fisherman's doesn't slip anywhere near as much.

Note that Tom's testing method resembles the kind of forces that you will be
putting on your Prussic loops in a real-life situation (e.g., ascending a
fixed rope).

Martin (double fisherman's for me).

That's certainly an interesting test of webbing, however we can't just
apply those results to rope (or even all webbing). I just tested a
water/ring knot with 1/4-in nylon kernmantle rope and after initial
settling of the knot, I saw no slippage after more than 300 cyclical
loads of roughly 200 lbs.

However, I still encourage Dave to test the knot himself in the rope
he intends to use since his line might be stiffer or more slippery,
etc. That way, he can see if the security properties meet his needs.

Since he doesn't care about ever having to untie his knot again, I
agree that many of the angling-type knots are possibilities, such as
the double or triple fisherman's. I assume he's at least aware of
them, so I tried focus my discussion on the knot in question.

As an aside, I have a cord of uncertain composition and coating that
will slither right out of a triple fisherman's. It's a good challenge
to find knots for it. Although no sane person would use such a cord
for critical purposes, I mention this to stress the importance of
testing your knot in the conditions you anticipate.

About 0.8 inches from free end to free end stretched. Nothing drastic.

How much slippage did that "settling" take? (Because if it's two yards....
;-)).

) wrote :

My application is a permanent knot for a permanent prusik loop with
about 6mm cord. If your jam theory is correct, do you know if this
might be an appropriate knot for this application, and do you know if
the jamming would degrade the strength of the knot for a potential
point of failure ?
-dave
why is the water knot recommended only for tape but not for rope ?

First of all, "recommended" by whom?
In the climbing world, which I take to be your area of focus, there
is usually a need to untie knots. However, in your particular application
of forming a "Prusik [CORRECT SPELLING, yea!!] sling", I've not heard of
folks wanting to untie such knots. I.p., I've not heard/read of advice
on what to do with such slings/runners after they've absorbed a fall!?

The Water knot has been reportedly used by commercial fishermen (lobstermen)
in one part of the Boston area (with another *clan* using instead the single
Fisherman's Knot); they presumably are content to chop knots rather than
untie them, judging by the knotted structures that I see. (E.g., I've seen
such things as Groundline & Rolling hitches chopped at the SPart rather
than somewhere in the knot that would enable the knot to be pulled free
from the longline!)

NB: In tape, the common Water knot, aka Tape Bend, aka Ring Bend
(and damn that "follow-through" jargon: how ELSE can one tie a bend?!),
is ASYMMETRIC; in rope, is (should be)/is symmetric; but the symmetric
form in rope can be loaded in two distinct ways (for some hint of the
practical difference, cf. http://www.hse.gov.uk/research/crr_h...1/crr01364.htm
--though this is re the loopknot, not the bend (and the description is
ambiguous as to what form they're referring to). THERE IS A WAY TO TIE
A SYMMETRIC WATER KNOT IN TAPE, which should avoid the cyclic slipping
found in SOME tapes at certain, low loads.

The testing by Tom Moyer of the knot with tape has NO bearing on how
the knot performs in rope; again, there are--for rope only--two main
forms, too, to consider. The knot should be secure without slippage
in most rope, in either form. What Moyer's testing showed is that
some slippage occurred in 9/16" tubular nylon tape, OF THE EXTERIOR
END (only!), bit by bit under low, cyclical loads. Subsequent testing
has shown this to be the case for same size Spectra (with Nylon?) tape
and 3/4" flat (of some weave--there are various) Nylon tape, but NOT
in new 1" tubular Nylon tape. Be careful re generalizing from this;
the authors of the follow-up testing conjecture that stiffness in
the material makes slippage more likely (and one might muse that
non-new Nylon, as it stiffens, becomes vulnerable!?). [The latter
study/testing was share w/me but w/o statement of why/for-whom the
testing was done, or published, and so I can't say more, in reference.]
In any case, note that rope doesn't have an interior/exterior orientation,
but is symmetric, with one loading reaching to the ends of the knot as
measured by the line of tension, and the other loading beind of parts
that are in the center

But the knot isn't so strong, and the strength of your runner is going
to be twice your knot's strength--take an extra 10% points away in the
knot, and you've lost 20% overall! Hence, for runners the ubiquitous
knot is the Grapevine. You could do as well, maybe a notch better with
a Dble Reever Bend. This is a bit harder to tie, but given that you're
not going to be doing this tying a lot, and typically under quiet, at
ease conditions before using, tying difficulty is a lesser concern.
Form as though for a Grapevine (aka Dble Fisherman's), BUT instead of
tucking one rope's end back through its own wraps, send it the opposite
way, out past the opposite end & through the opposite rope's wraps.
(This suggests that the knot is not good for joining dissimilar ropes,
though YMMV.) (This is a version of what Harry Asher called Vice Versa:
in his knot, he gave the symmetric structure asymmetric loading (he
derived it from the Sheet Bend, and after extending both parts, must've
lost sight of the newly gained symmetry, and was unaware of the older
knot (ca. 1928, Wright & Maggowan).)

In another forum (rec.climbing), I mused about using much the same knot
as the Water but involving all of the runner--and I was focused here on
tape--: doing this would add a diameter of your cordage and so strengthen
the knot (my guess--more material to wrap around means a gentler bend).
In the particular case of tape, it enabled the ends to be BOTH put on
an interior (or central) orientation, instead of the exterior side,
which is the ONE end that slips, cyclically. Such a structure would
limit the useability of the sling; one could position the knot near
one end, so to make it easy to double the sling, but one would always
be loading the same endpoints, a possible wear issue; and it would
likely not work well at all for forming ascending knots, which impart
torsion to the parallel legs on forming ... .

--dl*
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