Author Topic: Sheet bend, Left handed sheet bend, Lapp bend  (Read 5000 times)

dmacdd

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Sheet bend, Left handed sheet bend, Lapp bend
« on: June 05, 2011, 01:33:09 AM »
I have spent several hours over the past three days testing three closely related bends: the sheet bend, ABoK 1431, the left handed sheet bend (Ashley's name), AboK 1432, and the Lapp bend, more commonly known as the Lapp knot, see http://davidmdelaney.com/Lapp-knot/Lapp-knot.html. (Has the Lapp bend got an ABoK number?)

I got surprising results. To summarize: (I will describe my test protocol and other relevant facts after the summary.)

In the circumstances and material of my testing,

1) contrary to Ashley, the left handed sheet bend, ABoK 1432, is significantly more secure when subjected to jerk testing than the sheet bend, ABok 1431;

(Ashley makes an overly general comment in 1432 about its reliability, based on his testing reported between 1543 and 1544.  I am referring to this comment in 1432 in 1) above.)

2) the Lapp bend is substantially more secure when subjected to jerk testing than either the sheet bend or the left-handed sheet bend.

I did this testing as part of an investigation of the properties of the three loops formed by bending the working end to its standing part with each of the three bends:
the sheet bend to form the bowline (ABoK 1034),
the left handed sheet bend to form the left handed or cowboy bowline (ABoK 1034-1/2) ,
the Lapp  bend to form the Eskimo bowline.  

The security of the bowline, when ring loaded, depends on the security of the incorrect, extremely unreliable, form of the Lapp bend (knot), which I call the anti-Lapp knot. (See  http://davidmdelaney.com/Lapp-knot/Lapp-knot.html.)

The security of the cowboy (left handed) bowline, when ring loaded, depends on the correct, extremely reliable (under jerk testing) form of the Lapp bend (knot).

The security of the Eskimo bowline, when ring loaded, depends on the security of the only somewhat jerk resistant left-handed sheet bend.

The material: 3/16" (4.8 mm) nylon braided cord. The braid is a sinnit that filled the circular cross section of the cord. The cord does not flatten easily, but is quite flexible.  Some materials, a hollow braid, for example,  might be kinder to these knots in jerk testing, but I believe many stiffer materials would have them coming apart more easily.

The test protocol: I dressed the knots firmly and compactly, finishing each with about a twenty pound steady pull. I tried to leave as close to 2" (60 mm) of material in each working end as I could estimate.   I grasped the two standing parts with the thumb and first two fingers of each hand about a half inch on either side of the knot, and jerked until the knot came apart, or until I had applied about 200 jerks.  Each jerk iteration consisted of a push from both sides toward the knot followed by a sudden jerk apart of the standing parts. On each push, I tried to push the material into the knot. I then jerked my hands apart with a force of about 2(?) lbs.   When the knot slipped, I adjusted my grip to maintain the tips of the fingers of each hand about  1/2 inch (12.7 mm ) from the knot.

Results:

Sheet bend.  The sheet bend disintegrated in every trial somewhere between 30 and 65 jerks, about a dozen trials.  As soon as it got a little loose, it virtually exploded in four or five jerks.

Left handed sheet bend:   In the dozen trials, the earliest disintegration was at 140 jerks. In half the dozen trials, the knot did not slip at all by jerk 200.  In these cases, when I got to two hundred jerks, I shortened up my grip so that the tips of the fingers of each hand were only 1/4 inch ( 6.3 mm) from the knot, increasing the effectiveness of the push phase of each jerk iteration in exerting a loosening effect on the knot. The knot would then rapidly (15 or twenty  jerks start to slip). In half the trials which extended beyond 200 jerks, the SP that formed the U part of the knot would slip until its end was flush with the body of the knot, and then stick, further slippage being prevented by the slight swelling of the end (to about 1.2 diameters) produced by the hot knife with which the cord had been cut to length before the trials.  When this happened, I could not make the knot disintegrate either by further jerking, or by pulling on the SP's with the full strength of my arms.

Lapp bend. I was not able to make the Lapp knot disintegrate using the 1/2" spacing of my fingertips. Every one of the dozen trials went to 200 jerks without the slightest slippage or perceptible loosening of the knot.   I continued on after 200 jerks without changing my grip, in one case to 400 jerks. (As I write this, my fingertips are quite sore).   In every case, I was  unable to produce a disintegration without changing my grip.

-------

EDIT: Some typos. Words on Ashley's comment on the unreliability of 1432.
« Last Edit: June 05, 2011, 01:42:03 PM by dmacdd »

knot4u

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Re: Sheet bend, Left handed sheet bend, Lapp bend
« Reply #1 on: June 05, 2011, 05:43:33 AM »
I find the Lapp Knot to be difficult to untie.  Is there a trick I'm missing?

Dan_Lehman

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Re: Sheet bend, Left handed sheet bend, Lapp bend
« Reply #2 on: June 05, 2011, 06:55:39 AM »
1) contrary to Ashley, the left handed sheet bend, ABoK 1432, is significantly more secure when subjected to jerk testing than the sheet bend, ABok 1431;

Is this really "contrary Ashley", if one speaks of <material-X> so knotted
and doesn't make the mistake usually made in attributing qualities
to a knot en vacuo so to speak --without regard to materials?
The opposite-sides sheet bend seems to *move* more on steady
loading, which is discomforting, at the least.  Richards found the usual
form, though, to slip in nylon kernmantle rope(s) at high loads.

Quote
2) the Lapp bend is substantially more secure when subjected to jerk testing ...

I'm a big fan (could even say "inventer") of the *double* and higher
forms of this end-2-end knot, but I have little confidence in the base
form; I suspect that your results come with the fine cord you use,
and would not be achieved with e.g. climbing rope (with stiffness,
it's hard to get the knot to set tight at all).


Quote
The security of the Eskimo bowline, when ring loaded, depends on the security of the only somewhat jerk resistant cowboy bowline.

Oops., you lost your parallelism here : you need an end-2-end
not eyeknot in the jerk-testing comparison => opp.-sides sheet bend .


Quote
The test protocol:  ...

Thanks for the details (and re your material)!

Quote
until I had applied about 200 jerks.

And for EACH of some SEVERAL tests PER KNOT!!!
(E.g., "earliest disintegration was at 140 jerks" => 1_700+ jerks!
Even some of the busiest forums don't have that many jerks!)

Holy hyper-dedication, Batman!!

Quote
Each jerk iteration consisted of a push from both sides toward the knot followed by a sudden jerk apart of the standing parts. On each push, I tried to push the material into the knot.

Well, this sure doesn't sound like Ashley's testing, IIRC.

--dl*
====


Dan_Lehman

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Re: Sheet bend, Left handed sheet bend, Lapp bend
« Reply #3 on: June 05, 2011, 06:58:34 AM »
I find the Lapp Knot to be difficult to untie.  Is there a trick I'm missing?

Pull the bight legs apart, to prise out some bit of material
from the hitching line's SPart; then you should be able to
work the knot looser & untied, pulling out some bight leg
material first.

--dl*
====

dmacdd

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Re: Sheet bend, Left handed sheet bend, Lapp bend
« Reply #4 on: June 05, 2011, 01:24:23 PM »
1) contrary to Ashley, the left handed sheet bend, ABoK 1432, is significantly more secure when subjected to jerk testing than the sheet bend, ABok 1431;

Is this really "contrary Ashley", if one speaks of <material-X> so knotted
and doesn't make the mistake usually made in attributing qualities
to a knot en vacuo so to speak --without regard to materials?

As you saw later, I prefaced the results summary with "In the circumstances and material of my testing, ...' , and deferred the details of those.
Quote


Quote
Quote
The security of the Eskimo bowline, when ring loaded, depends on the security of the only somewhat jerk resistant cowboy bowline.

Oops., you lost your parallelism here : you need an end-2-end
not eyeknot in the jerk-testing comparison => opp.-sides sheet bend .

Opps indeed.  I intended " left-handed sheet bend". Thanks.

Quote
Quote
The test protocol:  ...

Thanks for the details (and re your material)!

Quote
until I had applied about 200 jerks.

And for EACH of some SEVERAL tests PER KNOT!!!
(E.g., "earliest disintegration was at 140 jerks" => 1_700+ jerks!
Even some of the busiest forums don't have that many jerks!)

Holy hyper-dedication, Batman!!
My fingers are still sore today!
Quote

Quote
Each jerk iteration consisted of a push from both sides toward the knot followed by a sudden jerk apart of the standing parts. On each push, I tried to push the material into the knot.

Well, this sure doesn't sound like Ashley's testing, IIRC.

Nope. Nothing like.  Ashley's results are often quoted as if applying beyond the circumstances and materials of his tests.  He cites his own results in this over-general way in the article on the left-handed sheet bend, ABoK 1432. It is Ashley's own reference to unreliability of the left handed sheet bend in ABoK 1432 that I am responding to here.  I will insert words to make that clear.

TMCD

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Re: Sheet bend, Left handed sheet bend, Lapp bend
« Reply #5 on: June 05, 2011, 02:16:45 PM »
Interesting results and I can't even imagine tugging thousands of times like you did, my hands would have immediate arthritis. Since we're talking and testing Sheet Bends, I'd be VERY interested in knowing or testing the Double Sheet Bend and Tucked Sheet Bend's strength. I have no trust in the common Sheet Bend and certainly wouldn't tie the cowboy version because of Ashley's negative opinion of it...even though your test results yielded a different conclusion.

I'm utilizing the double sheet bend in a rope I now use for tying down my 24foot ladder on my truck, tying the trucker's hitch with this piece of rope. Can you test the DSB and TSB? Thanks.

dmacdd

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Re: Sheet bend, Left handed sheet bend, Lapp bend
« Reply #6 on: June 05, 2011, 04:45:12 PM »

I'm utilizing the double sheet bend in a rope I now use for tying down my 24foot ladder on my truck, tying the trucker's hitch with this piece of rope. Can you test the DSB and TSB? Thanks.

No!  I doubt the results of these tests would be useful for those bends. And it's too hard on the fingers!

I was not testing these bends primarily as bends but as the operative elements in the ring loading security of the end loops formed by them: each forms the ring loaded elment of one of the others.

 I have become fond of the Lapp bend, http://davidmdelaney.com/Lapp-knot/Lapp-knot.html, for casual, temporary, non-critical use, where I used to tie the sheet bend, because it ties so easily and is more secure generally including under shaking.  But I recommend it only to those able and willing to tie it with conscious care, because it's so easy to tie its evil twin.  I use the butterfly bend, tied by method 4 here: http://davidmdelaney.com/alpine-butterfly-bend/Alpine-butterfly-bend.html for ease of untying after great strain, and excellent all-round security in flexible ropes with good friction, like almost all nylon non-kernmantle ropes. I use the fisherman's or double or triple  fisherman's for very great security -- or for any security at all in stiff or slippery rope.
« Last Edit: June 05, 2011, 05:04:14 PM by dmacdd »