Double zeppelin

[Harold Kahl]

I "invented" this knot, then looked it up and found that it was already known, and in fact is mentioned in Wikipedia. That's not surprising, because it is simply a zeppelin bend with the tails wrapped one extra time. All bend knots have a corresponding loop, or eye knot. This is how I tie the bend and eye knots.
https://www.youtube.com/watch?v=4WWTLIRvtgI

The extra wrap on the standing part of the loop knot seems superfluous, at least as far as security of the knot is concerned. Here is how I tie the loop knot with only one wrap of the tail. I'm calling it a semi-double zeppelin loop. I don't know if it already has another name.

https://youtu.be/rUWkAZxewec

The Wikipedia article on the zeppelin bend says of the double zeppelin bend:
"The additional last turn renders the bend even safer both against slippage (already a small danger for Zeppelin bend) and against breakage (due to less curvature strain where it carries most strain), but makes it at the same time considerably less easy to untie, an undesirable side effect; Better to use a slipped and locked version." No citation is given for these assertions.

I did a backyard jamming test to see how the double zeppelin compares to the zeppelin in jamming tendency, and to assess whether the double is much harder to untie, as stated in Wikipedia.

Date of test: 8/19/2018
Rope Tested: Everbilt brand 3/16 inch diamond braid polypropylene, 60 lb working load limit
Procedure: A string of knots was tied including a semi double zeppelin loop, two zeppelin bends, two double zeppelin bends, and a Figure 8 on a bight. This string was then tensioned to 180 lb. The knots were untied completely (except Fig 8 jammed) and time to untie was recorded.
These same knots were then re-tied and test was repeated at 200 lb.

Results:
semi double zeppelin loop, 180 lb, 38 seconds
zeppelin bend, 180 lb, 28 sec.
zeppelin bend, 180 lb, 40 sec.
double zeppelin bend, 180 lb, 31 sec.
double zeppelin bend, 180 lb, 26 sec.
Fig. 8 bight 180 lb, JAMMED
semi double zeppelin loop, 200 lb, 35 seconds
zeppelin bend, 200 lb, 19 sec.
zeppelin bend, 200 lb, JAMMED
double zeppelin bend, 200 lb, 63 sec.
double zeppelin bend, 200 lb, 30 sec.

Conclusions
The double zeppelin bend and semi double zeppelin loop appear to be similar to the zeppelin bend with respect to jamming. The assertion in Wikipedia about the double zeppelin being harder to untie is not confirmed. Differences in time to untie were generally due to the extent that knots were tight, or near jamming. The time to undo the extra wraps on the double zeppelin would only be a few seconds and not a significant factor.

The double zeppelin bend appears to be a good choice if additional security is desired. The semi double zeppelin loop appears to be a potential alternative for a secure and jam resistant eye knot. It is definitely more jam resistant than the Fig. 8.

[jarnos]

Wikipedia (https://en.wikipedia.org/wiki/Zeppelin_bend) does not currently tell about Double Zeppelin Bend but the reference https://notableknotindex.webs.com/Zeppelin.html shows it.

I think it would be worthwhile making some testing video of different variants of Zeppelin bend. Testing their security and ease of untying after serious loading. Preferably using several different types of cords.
Here you can see the weakness of regular Zeppelin Bend on certain stretchy cord:
https://youtu.be/dagg2-If4h8?t=709

Here is another thread about Zeppelin Bend security: https://igkt.net/sm/index.php?topic=1902.0

[Dan_Lehman]

I "invented" this knot, then looked it up and found that it was already known, ...

I feel your pain --moi aussi (ditto #1452, 1408, & Shakehands).

> All bend knots

Make that "all (end-2-end) JOINTS" : let's leave "bend" to its
historical sense, which didn't limit it to end-2-end joints.

> have a corresponding loop, or eye knot.

YMMV, but there are various senses to "corresponding",
including tying one end to a U-fold's two ends, the U-fold
(aka "bight", but I'm abandoning that confused term!)
providing the eye; then just figure how to *fuse* one
U-fold end into the S.Part's end, and ... !  (Which can
be a way of seeing some already familiar EKs as being
essentially familiar ends joints' corresponding EK.)

> The extra wrap on the standing part of the loop knot seems superfluous,
> at least as far as security of the knot is concerned.

But note that it gives the S.Part a full turn of nipping,
and not a pear-shaped nip.

> "The additional last turn renders the bend even safer both against slippage
> (already a small danger for Zeppelin bend) and against breakage
> (due to less curvature strain where it carries most strain), ...

We can acknowledge that the strength claim --both i.p. to Thrun's
Joint (zep), and in general for knots (but a theory some of us hold)--
remains to be tested.  (I'm hoping to see some 3dia BWLs given the
testing.)
But the full (extra) turn should give STABILITY to the knot to counter
the capsizing into opposed BWLesque nipping loops, which then can
themselves capsize into helical twists, as seen in that cited testing,
with the 7mm rope that sure seemed to move a lot, IMO !!
--something your tested PP rope likely was less vulnerable to,
in being maybe firmer cross-sectionally & less stretchy than that 7mm.
(try bungee/shock cord for exaggerating elasticity and seeing any\
vulnerability to that).  (We would suggest that that 7mm knots test
had better set the knot, tightening the tails' pull on the collars,
compressing the opposed S.Part turns more; it would still be "an
easily untied bend" --to quote Bob Thrun's invention-presentation
article.

Thanks,
(-;