Some comments about knots & various of the preceding remarks.
Knot names. Often a problem, esp. in discussions with users from
different application areas--but also often within ,say, rockclimbing.
Let's try to incorporate functional indicators:
"Fig.8 loop" (distinct from Fig.8 stopper, Fig.8 bend)
"Fig.8 double loop" (to keep "double" from inconsistent use,
as in "Double Overhand", "Dbl. Fisherman's", "Dbl.Bowline")
"Munter Hitch": 'Munter' should have no umlaut? over the 'u',
nor the simple-type equivalent 'eu'; but as Swiss Munter was
but a messenger, of a hitch whose belay use was pioneered
or at least first strongly advocated by Italian climbers, who
named it "Mezzo Barcaiolo" (one of whose names has those
same initials "MB"), I'd like to move towards a unifying name
of "Munter Belay Hitch" to also share in the shorthand "MB
hitch"! --a fair goal, IMHO We can all agree with "MB".
"Dbl.Overhand Bend"/"Dbl.Fisherman's Knot/Barrel ...
I think various issues with these names can be avoided by
using "Grapevine Bend" (and "Dbl.Grapevine Bend" for
the "Treble/Triple Fish."--there's a good point in this!).
Traditional nautical naming had "Fish.KNOT" as the bend,
and "Fish.BEND" as a hitch (which, btw, is a different
orientation of a double Overhand structure--i.e., each
can be shifted into the other, topologically equal).
The overwraps of the Grapevine number one (zero in
the (single) Fish.--just a plain overhand), thus in the
Dbl. two, and so on--a nice match of an observable
functional feature with the nomenclature's modifier.
And what one ties as a back-up is clearly NOT this
knot! Here, "Strangle knot" is appropriate.
I prefer the figure nine to a figure 8 as it's stronger in every way and it won't roll of the end of a rope when abnormally loaded.
One might challenge this assertion by pointing out that in the
exhaustive testing of usage the knots (and many others) have
proved of equal strength--i.e., knots typically don't break in use.
I don't think one will prefer to tie a Fig.9 (asymmetric) loop by
"re-threading" ("tracing" might be a better term for this)! Btw,
you might consider the Reverse Fig.9 (asymmetric) loop.
And most will prefer this Fig.9's generally easier untying,
though it can become tight, too.
I write "...(asymmetric)" to indicate that the Fig.9 knot
has a (two, actually, at least) symmetric form, one of which
works rather well for making some knots, including a loopknot
& mid-line stopper/knob.
knots overlap the same function (eg, bowline and fig-8 follow-through)
Though the Bowline is much easier to untie, and can be
tied after the eye/loop is sized--i.e., one need not beforehand
anticipate the point of the knot in the rope and make a Fig.8
there to later be "followed-through".
I'd also agree with Maratt's comments about learning a limited set of useful knots, rather than every one that comes along. For me it is a matter of looking up the supposed strengths ...
And where does one look up the strength? --and how does it matter?
(see above dismissal of this concern, generally) From what I've
seen in various presentation of strength data, far too little
information is given to replicate the testing that supposedly
generated the results. E.g., in each of the trace ("follow-through")
knots of common use (Overhand, Fig.8, Fig.9), there is a choice
of two ends to load; but usually the test data doesn't indicate
which end was loaded, or how exactly the knot was tied; in the
published literature, one can find images of the Fig.8 in various
dressings/orientations, and I don't presume to know which data
might apply to each.
.:. So there are a few problems with looking at strength data
for knots: (1) you don't know what exact knot is tested;
(2) the relevance to use is usually imaginary--one shouldn't
be using cordage anywhere near a knot's break point--;
(3) in some cases the relevant strength value is something
measurable only after much usage, where wear & tear on
a knot has had effect (not much an aspect for SAR/caving/
climbing maybe; more so in commercial fishing).
Does anyone know if there has been any testing on the double loop knots
for strength and more importantly how they behave if one anchor fails?
Vertical seems to suggest they can pull through and whole knot untie.
Strength should be no concern here.
Slippage might, but I doubt that there will be much at all in
the usual materials--the more worn, the less slippage. For
a Bowline in the Bight, e.g., loading either eye in isolation
pretty much gives one a Bowline; the extra material nipped
by the knot's mainline's loop will reduce the friction on the
loaded legs of the eye only slightly--too little to matter, IMO.
A Trucker's Hitch is usually a 3:1 MA - not accounting for inefficiency due to friction, of course.
It's helpful to do a little experiment with these supposed MA
structures to see what actual MA is--use some dead weights,
and I think you'll be surprised at what LITTLE actual MA there is!
Using something like this with much force can also surprise you
with a core shot or lesser wear of the rope at the sheave point.
Of course this "abnormal" loading is really quite normal for the Butterfly Knot
- but hey, I didn't invent the terminology.
No, but you can help stamp it out! "abnormal" has been used for
some presumed "right" loading of common knots which abnormal
loading is better described as "offset"--the main example being the
infamous "EDK"/"
Offset Overhand Bend" used by climbers to
join rappel ropes. The Butterfly isn't like this, and frankly the only
probable loading of it that I can think of to qualify as abnormal
is
ring-loading--i.e., pulling the eye apart so that the knot
is a bend between eye legs with mainline as its ends!
A reef knot tied with exceptionally long tails these tied as a Double Fishermans
AND the remaining tails tied as a SECOND Double Fishermans as the safety knot and
of course forming the loop for clipping into on the knot pass, using UK SRT.
I don't follow this, and maybe it's a problem with knot names.
Strictly interpreting "Dbl.Fish" = "Grapevine Bend", then the quoted formula
you give makes a sort of big '8'--bottom joint is Reef, center & top joints are
Grapevines. And loading the spaces of the '8' will abnormally load the Reef!?
As for using a Sheet Bend, one must ensure to orient that such the
bight part (u-turn part) is made in the lower rope, as loading the
tied-off ends loop will then effectively make a Bowline of the
structure; but doing this upside-down will pull the u-part apart,
risking capsizing the knot!
[the Reef/Square knot] is often tied incorrectly (in that case, it usually manifests itself as a thief knot - quite scary).
No: tying a Thief takes deliberate effort, with unnatural tying steps;
a Reef mis-LOADED is a Thief (loaded catercorner, so to speak); a mis-tied
Reef will be a Granny (loaded catercorner this will be a "Grief"/Whatnot).
And actually, for that structure backed up with Strangle knots sometimes
called the "Square Fisherman's", the Thief is arguably better, as some
slippage will impart tension to the back-ups and thereby more ensure
that they don't loosen; and the Thief is less prone to jamming than the
Reef.
As far as the sheet bend, it is essentially a bowline, a knot which is commonly depended
upon in a rescue situation. The bowline is actually quite a strong knot. Sheet bends have been used
in the shipping industry for years. The large hawser lines of ships would sometimes be tied together
by a sheet bend because they were both strong and easy to untie after loading. It seems if the sheet
bend could withstand forces generated by a large loaded cargo ship, they must not be all that bad ;-).
I think that this is the first time I've heard of hawsers being bent
together by a sheet bend; the Carrick bend is the usual knot cited,
and much of what is shown have ends seized. I'm surprised that Dave
Richards's recently pointed-out testing of kernmantle ropes has not been
better recognized. It is at
http://www.caves.org/section/vertical/nh/50/knotrope.htmlNB: In all GRAPHS, the 10.5/12.5 data is switched (the table's data are correct).
Sheet & even Dbl.Sheet bends show serious slippage problems here, and
this is under tension; there would also be concern about loosening without
tension (a Bowline issue).
The Sheet Bend is not essentially a Bowline: the bend loads only two ends,
whereas the loopknot three--and that makes a significant difference in the
shape of the knots under tension, affecting both strength & security.
(Incidentally, the Reversed Sheet Bend (aka Lapp Bend), with an extra
warp of the non-bight/-U part, might be a good replacement. The extra
wrap is needed for achieving security. The knot can often be loosened
by pulling the bight legs apart, which should draw out some of the mainline
from the non-bight rope. This knot should also be more resistant to
loosening when slack.
Also, here in New Zealand, Kip Mandeno is a huge proponent of the use of the sheet bend
in rigging (including technical rope) as well as many of the other folks at SARINZ (Grant Pratley
and others) who teach technical rope to the rescue folks here.
Then I urge you to refer them to the Richards study, for that shows
serious problems with the Sheet Bend. Maybe they have anticipated
the slippage issue with precautions such as back-up stopper knots.
With the reef knot "enclosed" by a double fishermans knot it may show different
breaking characteristics than a plain reef knot because of the additional loops/strands/etc. involved.
Not because of that, but
maybe because the Strangle knots--if set
snug to the Reef knot--will keep the Reef in its symmetric orientation;
often a tightened Reef has one end slide out of orientation, and maybe
this leads to a weakening?! (Another failing of knot testing is that the
point of rupture isn't specified; e.g., which rope of the (asymmetric)
Sheet Bend has the break--bight or non-bight part?)
What does an Alpine Butterfly knot look like as a bend?
--like an Ashley's #1408 gone wrong! A better choice is #1452, often
named "Ashley's Bend; this knot is very easy to untie, no matter. But
#1425 is more slack-secure.
BTW Vertical suggests this [Reef] is just 10 % of the strength of the rope
Holy Nuts, Batman, who's "Vertical" and what did they smoke?
In traditional cordage the Reef is rated around 45%.
One might try the Reverse Surgeon's Bend, which is a Reef with the
ends given one extra tuck (so one more than mainline parts); draw it
up by loading the ends such that the knot assumes a very nice look
not terribly unlike the Grapevine (loading it then will undo this form).
Beware sources: look for FIRST sources (a research principle).
The Net makes access easy, but it makes posting and echoing
nonsense easy; one stupid statement can be echoed to the point
of being a preponderance of evidence volume! (And popular knot
books are much like this: the research grounds for knot-book
authors is other books, often, and not actual usage! The
plagiarism is sometimes appalling (such as scanning images,
paraphrasing (and botching!) text).
---------
Finally, on the issue of learning a small set of knots or large,
I've some ambivalence: I understand the KISS principle, and
the need to keep a
clean, uncluttered knot-knowledge space
for times of critical use under stress; but OTOH learning knots
should be enhanced by knowledge of many different structures,
provided one really tries to understand them and compare/contrast
them with others (and not merely is able to make a long list of
knots and match them to knot images and tie them).
*knudeNoggin*
. 
it's still basically a reef knot just one that won't untie. AFAIK a knot's strength comes from how gentle the bends the rope is forced to make are so unless you change how tight the bends are it's not going to help as far as I can see.
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