Strait Bend Testing?

[Dan Lehman]

Originally Posted by rickc

I am interested in any testing results anyone knows of for the Strait Bend (pg 72 of the Apprentice). My specific use for this knot would be to join two 8mm to 11 mm nylon climbing ropes. The joined ropes would be used for rappelling. Typical forces are less than 1000 lbs force but with considerable possible jerking as the line is loaded and unloaded.

Why ask for (often dubious) test results, when you have all the means to do your
own testing --YOUR particular paired ropes, you body mass, and the ability to tie
up a 2-to-1 crude pulley system (using a 'biner) to increase applied force. Indeed,
your own non-pullied mass is approximately itself double the forces to be expected.
And yet it's common for folks to ask for some break test, which is hardly relevant
to the act of abseiling!

cf the discussion of a better analysis of the common abseil-ropes joint, and some
alternatives that are also *offset*, here : http://www.rockclimbing.com/cgi-bin/...set%20fig .9;

I am unhappy with the knot currently being recommended by many in the climbing community and am looking for a knot with a good lead, is relatively easy to untie after loading, is reasonably strong, and is secure under load cycling.
Thanks for your help in advance.
Rick C

Let me guess --you don't say-- that the "knot currently being recommended by many"
is the infamous "EDK", better named "offset water knot" (i.e., a water knot, aka ring bend,
aka --to some-- and (double) overhand knot, loaded in the *offset* manner --both ends on one side).
And it fits the task arguably better than any other : easily/quickly tied (rappelling comes
sometimes at late hours with fatigue, or pressure from approaching weather), compact
and **offset** --making for easy flow over rough surfaces, less prone to snag--, and, to
your particular question, it's an asymmetric knot enabling it to work better with
unequal rope diameters, properly orienting those ropes in the knot.

The [offset water knot] everyone else was using tends to roll, and people would end up leaving ridiculously long tails, or tying another overhand in the tails, to feel safe. I thought it better safety to have a decent bend properly tied.

"Tends to roll"?? To my awareness, there are no reports of failure of this knot, beyond
one of dubious accuracy of some fellow followed by two women. One might consider
the popular and regular usage of the knot for decades to constitute sufficient testing.
Then, again, one can yet wonder if there is some vulnerability awaiting tickling!? But
if you can tie these other suggested knots --none of which is offset, so lacks that benefit--,
you can surely learn to tie the offset water knot to advantage!

The Zeppelin bend is also very good, and will cause your climbing buddies some eye-popping concern.

Firstly, are you entirely comfortable with the comparatively *airy* (i.e., gaps in the knot)
zeppelin being immune to snagging and being pulled open? --no, not in use, but in the
pull-down of rope, which though unlikely (immediately) fatal, would surely be a major
disappointment (leaving one rope untied well up the wall).
As for impressing your partners, while that can have its element of fun, it has obvious
drawbacks, practically (mutiny comes to mind). There is comfort in the familiar.

... these bends seem to be every bit as secure as a Double Sheet Bend, ...

!!
Considering Dave Richards's testing which found this as well as the single sheet bend
AND single fisherman's knot to slip (at relatively high loads --way above what even obese
climbers would generate), I'd not cite it as a model of security; it is i.p. hardly so secure
when slack, esp. in the kermantle ropes at issue here.

it's not exactly true that the Strait Bend is an Alpine B[utterfly] with the loop cut. I think it's more accurate to say that the two knots are structurally analogous, in the same way that the Bowline and Sheet Bend are.

??! That's exactly the relationship between butterfly bend & eyeknot ; whereas, with
the other two, the match is inexact in that the sheet bend is typically recommended
with tails (resp. standing parts) on the same side --not what results from eye cutting.

The interesting thing in this test is that mostly the [butterflyknot didn't break. The line broke at the attachment to the test fixture. This is a pretty good example of the frustration of trying to find good data on the strength of knots. But as they said, the knot is very strong.

Again --to emphasize--, for rappelling, one is NOT NOT NOT concerned with strength
(unless you're using dental floss?)! You cannot make a knot weak enough in normal
abseil ropes to be at all a risk in strength. (But this dubiously got datum nevertheless
captures the imaginations ... .)

The breakage at the bollards cited in the Bushwhackers report sure surprises, but it
can be conjectured to have this basis : the knot was tested as the joint forming a round
sling in one rope; the sling was relatively short (because of test-device stroke), and
the compression of the knot in loading made a significant imbalance between forces
on the two sides --knotted & straight-- of the sling such that the knot was protected
from actual high-as-there-were forces. --something I'd have expected with the
grapevine (dbl.fish.) bend, but that report found the former feeds out more material.

I wonder if the Tucked Sheet Bend, aka Binder Twine Knot, is worth investigating. That's the knot this link http://www.hudson-family.net/knots/knots.html calls the Locking Sheet Bend.
Pros:
- near-perfect lead in one direction, and presents a fairly slim face to any possible snags.
- stronger than the Overhand Bend
...

No, the "lead" isn't so good; you can verify the benefits of an **offset** end-2-end knot
but pulling it around a sharp corner (of a desk, e.g.); non-offset knots can hang up.
And "stronger ..." is in a practical sense false : no knot will be breaking, so = strength.

I question its low-load & when-slack security --thinking that the bight (U-part) is liable
to pull out.

When doing multiple rappels all in a row, the rope you must pull on alternates, so the lead would be alternately fair and foul.

Why ... ? It has been argued to pull the haul line if that is the smaller line conjoined
with the climbing rope (to make the retrievable, twin-strand abseil line), as the end-2-end
joint would be placed to snug against the rap-ring upon *slippage* got by virtue of differing
rates of flow through the abseil device --and one can't pull the knot through the ring.
You retrieve the two tied together : why would you set them up any differently than the
prior time, and want to pull in the opposite manner (?) (There could also be a question
about which rope you would rather have stuck, if that happened, and which in hand.)

--dl*
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