Sling Angle Forces

General Discussion
1

i think to understand forces inside a knot / lacing; we can take a look at rigging. This gives us the same forces; in same materials; only under a helpful; maginified view point.

i think a choke is often quted as 80% strenght of the material it is maid in; because it bends it’s own Standing Part. i think this same prinicipal places an 80% ceiling on most knot effiicinecies/ strengths.

This goes beyond the standard choke is 80% of linear strength and a basket is 200% of linear strength (thereby 2.5x as strong as a choke); and looks at the angles of the basket sling position itself.http://knotbox1.pbwiki.com/f/basket%20angles%20.jpg

2

80% ceiling? Before you make an assertion based on an unproven premise, you’d better have data with lots of different knots in lots of different rope constructions of lots of different rope material in various conditions that actually verifies that ceiling.

I’d love to see your data on the Bimini Twist.

Without endorsing the methods or results of this test:
http://www.hse.gov.uk/RESEARCH/crr_pdf/2001/crr01364.pdf
…here are some excerpts:

“[The Double Figure 10] produced only one test value higher than the figure-of-nine, but averages were higher with variations from 73% to 87%.”

and

“On all the tests, the rope broke before the [Double Fisherman Knot], at forces of
around 40 kN. This is most likely due to the friction created around the pins at each end of the
sling.”

3

Ummmmmm i don’t consider Bimini Twist, Tripple Noose etc. as a category of ‘most knots’; but rather the exceptional extreme to learn lessons from. i think a Bimini Twist maintains a more straight, even flow of force than most lacings; more like a loose splice. The Triple Noose i think comes around to bend it’s own Standing Part; but does more than that, uses the force flow to reinforce that part of the line and even out the stretching/ thinning. Give a Round Turn on host/mount before the Double Round (3)Turn to self to form Anchor to self/ Triple Noose; reduces the force flow around self that serves to stabilize; and the lacing breaks earlier.

i think friction has a lot to do with it as you say; but also, the even stretch all the way to those frictions and curves; that changes suddenly as the tensions are changed by the bend; all forming the weak link per the loading encountered in that area.

But quite fairly all theory; and to the imagery and perception that the rope is just a device like wire or a garden hose; that conducts the forces down it; varying the direction etc.

4

Is a double or a triple fisherman’s knot an exception as well? The friction comment was not my own, but rather that of the test author(s) explaining why a test failed to break the knot.

5

Hi KC and Roo, et al,
Alice said I was to go on line in “read only mode”.. but I could not resist.
Sorry, for rambling on… in advance ::). To me the stress in slings is almost pure math. Slings are mostly unaffected by friction, ambient humidity and other variables. Simply the working load or breaking strength of the material, with factors for angle of attack.
But when a knot is at hand (that is a part of the calculation) then all that class room calculation is next to nothing.
Knots have; shear, compression, internal friction, attack angles, elongation… all of which is why I like to test knots in the material intended and side by side (more often end to end). All testing I do is just for my own use. Factors affecting even the most basic rigging goes out the window when it rains, slimes up with mildew and so on.
I hope we all learned to break twine and such with the method in ABOK so we know that the shear forces under rapid load make the knot that has that configuration or shear useless in shock loading? See ABOK 142 and 143.
Fishing knots are wet (less friction in the knot) often loaded in a hurry, to set the hook (mayhaps less when line is out in the sea way off a boat but much more intense in Salmon fishing on the River). When I “set the line” it is the ABOK 142/143 and when I am looking for land locked trout… no weak knot need apply.
I am enjoying the thread and perhaps Alice was right.. “read only Roy”.
By the way we have several fisherpersons with web links who delight in making fishing knots that deliver 100% of the rated line strength. So I don’t know where the 80% figure came from. Even the Palomar, maybe most of 80 years old, yields about 95% of rated line strength.. of course I am often wrong and Alice did tell me to stay home tonight.
Back again. An additional thought on how difficult it is to predict or evaluate the knots. After I went on about the shear as in the ABOK methods of breaking twine and line in hand I remembered how many knots use that very structure, internally, for a nonslip “nip”. Then I began wondering if thoes knots were more prone to failure unders a snap or jerk. That lead to thinking about a shock cord in the line to force the stress to come on more slowly, which lead too… well you get the picture. I have believed for many years that one of the reasons than nylon is so handy is the elongation before breaking point, which I think reduces the shock load on the knots.
Won’t it be fun when someone comes up with a computer simulation that lets up put in the variables and spits out an answer. I know that several members and guests on the web and several contributors to Knot News and Knotting Matters have access to or have “home built” some fine testing equipment. Envy. But then I’d have to find a way to crunch the numbers and I’m not sure anyone would gain much by that. All of which makes it seem that over building is still the best way to keep everyone safe (or fish coming to the net).

6

It should be with some question that one reads quoted test data
for knots, as figures are all over the place, but detailed information
about testing is hard to find. The 80% figure for slings in a choke
orientation is a rule of thumb I’d expect to differ with the material
and the closing part of the sling–an eye in tape normally or specially
formed, or metal of some sort, or … . Angle is important–what I
sometimes consider the deflection )(from straight) of the part
in question.

Yes, there have been reports of knots testing above 80%, in rope
(TMoyer had Fig.8 loopknots at 92% !! --highest I’ve seen.). (I
forget if Lyon Equip did a good job of figuring actual tensile, but
they have some strong loopknots as well. Also CMC Rope Rescue
Manual, and Dave Richards’s recent testing of kernmantle ropes
got up to just about that mused limit of 80%, though not in the Fig.8!)

But the angle of the SPart into the knot I don’t see as needed to be
as hard as it is for a choke sling.

Roo muses that the Bimini Twist is a good counter example, and KnotNow!
echoes the old quotes of high percentage for anglers knots. But where’s
the data? (And who are these fisher people with WWWeb site claims?)
Here’s some actual data re the Bimini Twist, which is I think raising some
controversy in the angling world:

±-----------12-turn Bimimi Twist (avg. breaks paired per vendor line)
| ±-----20-turn
101 69
96 90
80 81
49 58
71 53
97 66
92 84
102 98
101 100

Now in the above, if I’m reading right, are some mixed types of lines–both
trad. monofilament and newfangled “braid”, which I take as a keywork for
HMPE (Spectra/Dyneema)–also “gel-spun polyethylene”. And there are
more tests with the Bimini tops at 81% & 80%, 88 & 77%, but then as low
as 33&37%, 27&38% (20#, 50# lines; 40-&60-turns per knot). !?

Oh, and here are a few examples of “rated” vs actual strengths of braided lines
(which helps explain how some test results are so high vs. rated strength!):

actual as % of rated: in 16 “20#” lines, ranged from: 117%, 138%, 150%, … to 273% (!!!)

and in “50#” lines: 94%, 110%, 112%, … to 167% (!!!)

(Now, if I can find my way back to the discussion list re this, I might see how
the dust has settled.) Oh, reference: magazine Sport Fishing, 2006-08,
pp.62ff, by Doug Olander.

Meanwhile, we have a tester reporting rockclimbing tape slings “girth hitched”
together breaking at (in both nylon & HMPE) about 50%; and yet elsewhere
similar testing (of each, and of mixed) got 70%–a whopping difference!
–might wonder at the knot tying (I always do). ::slight_smile:

As for breaking twine the Ashley way (which, for those w/o ABOK, is
holding firmly a bight and drawing through the bight the line near to where you
want to break it, and it running around one’s hand to form the bight (so a sort
of Crossing Knot around one’s hand), where would you expect the break to
come? --at the bight which seems to be getting cut through, or in the line
moving through, attempting to cut, this bight? Well, it surprised ME!
(Ashley’s comments about strength there are a bit silly. Also, somewhere
I have a bit of test report on different ways to interlock two bowline eyes,
and there was a difference in results, which shows that for THEM the break
didn’t occur in the bowlines (else it wouldn’t matter how … interlocked).
And breaking “just outside of the bowline”–nahhhhhh. --wonder how he
tied those knots!

–dl*

7

Hi Dan,
Good to see you at forum again. I’ll try to dig up the URL for the fellow who loves fishing knots and really does have some good thoughts on the subject. About a year or so since he and I were in contact.
Sure, if you (as the rope maker) under rate your line then you avoid nasty law action and folks will find knots that work beyond 100%.
Breaking line or twine by the ABOK way: I won some fair amount of bar tab money breaking cord this way. I also was rigging some drafting parallel bars with the old K&E silk/copper cord. These ride up and down the drafting board on cords with ball bearing shivs built into the drafting edge. The cord may be nylon or dacron but I never bothered to look as we called it “silk”. It has a copper core member so it has an awesome stretch ratio. Since it was at the office and since I was in a hurry I’d just break it in hand as per ABOK. One “stand about” was all for being a wiseguy about my task and I ran short on temper. I am ashamed now (40 years too late) that I showed him how to break it and omitted the crossing of the bight. In what ever way the shear action and inertia may play into the task; if there is no bight crossing the cord cuts right to the bone.
As to the double bowline bend; I suspect than under some sort of gentle loading it will break somewhere else but when I was first messing about with it (not knowing too many bends and always getting a runing start at everything) it did seem to break at the shear. In fact that prompted me to learn more bends. At least that is my memory of the events… more than 45 years back. I have a more distinct memory from that era of the hook breaking off 3/8" log chain and the hook with a bit of tail passing through the rear window, past my head and out the windshield of the pickumup. No rope was involved. Of course I moved up to 1/2" log chain as I had learned nothing. I learned the hard way that when rope is involved and the hardware fails and not the rope that the stored power is beyond imagination. Drove a 2’ bit of 1/2" rebar through the back of my SUV and the seat back as well (with the hardware attached). So, when all is said and done… over design, use more powerful line and hardware than you need and try to be safe (no more running starts).
Hope you are having some fun.