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.
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EDIT: Some typos. Words on Ashley's comment on the unreliability of 1432.