The Zeppelin bend...

Re: The Zeppelin bend... SOME THOUGHTS

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Very pretty knot! I think I will test it, and the loop version as well. I am much more likely personally to put a big load on a loop than on a bend, so it will be interesting to see how the loop behaves.

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I musta missed something - what loop version?

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...In general I want heavily loaded knots to be easy to untie,

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Me too! And so far, as seen in my vid, the ZB looks very promising. Of course that's only 200 lb plus some bounce loading, but I'm inclined to load it up to about 440 lbs and see how it behaves and how easy it is to untie.

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...even if, like this one, they aren't that easy to tie...

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??? The ZB is easy to tie. Notice in my video, I tie it while talking - how hard could it be if I can talk and tie it at the same time
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It's just two 'opposite' loops and tuck the tails. Then it's just a matter of dressing. The F8 bend is not easy to tie.
 
Re: The Zeppelin bend... SOME THOUGHTS

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...I musta missed something - what loop version?...

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Any bend will have a "loop version." Just tie the bend with a single piece of rope and you automatically get a loop.

From there it gets more interesting. I think there are three loop versions for the zeppelin but only one of them can be tied the way you tie it. To tie the others you probably need to use a rethreading procedure as with the F8. If the knot weren't so symmetrical, there should be four loop versions. For each loop version you have two choices for which leg to pull; this might technically give us 8 different versions altogether (for an unsymmetrical bend). Of the truly distinct versions for the zeppelin the properties may be very different, or maybe not. I'll see if I can tie them all and post a picture.

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...??? The ZB is easy to tie...

[/ QUOTE ] For you, yes, for me, no. It wants to fall apart when you start to dress it and you really need all four hands to do it gracefully. Maybe I'll get better at it...
 
The zeppelin loops

Here are the 3 zeppelin loops. The first photo shows the bend itself. When tied as Ron ties it, the main line runs north and south and the tails go to the sides.

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The three loops are shown below. All three knots are oriented in exactly the same way, so it is clear the 3 loops are actually different.

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Re: The zeppelin loops

Ahhh, I use the loop shown in the upper right of the pic regularly for prusik loops. I thought you meant like an eye in the end of a rope, and I hadn't seen that.

It is interesting that Dr. Merchant, in his book, life on a Line, says the Zeppelin bend can go unstable if a tail is pulled. Don't know if that applies to the above loops or not, but I know it doesn't apply to the upper right one.
 
Re: The zeppelin loops

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Ahhh,...I thought you meant like an eye in the end of a rope, and I hadn't seen that...

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?? I do mean that. These are about 4 inches from the end; how close do you want?
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Re: The zeppelin loops

Hmmm, I have used it as the knot to close a sling/prusik loop. Haven't seen anything about the Zep as a loop knot, i.e. bowline, F8 loop, etc. The only thing I've seen is the statement from LOAL that the knot goes unstable if a tail is loaded. I'm pretty sure that is in reference to loading the tail of a bend which could be different than a loop.

You done any tests on a ZL?
 
Re: The zeppelin loops

I am pretty sure that the bottom loop will fail to maintain form do to asymmetrical loading.

Dave
 
Break-testing the loops

I broke all three loops on my testing rig. There was no way to pull on the short tails so I had to pull straight across the loops, in each case positioning the knot midway along one leg of the loop.

The loop in the upper right broke at 670 lbs, the upper left at 732 lbs, and the bottom loop at 650 lbs. Since I was unable to pull on a tail, these aren't loop tests at all, but simple knot tests. All 3 orientations of the zeppelin apparently have about the same strength in this very limited test. The north-south version that everyone ties might be marginally weaker than the east-west version.

The cord was 1/8 inch solid braid nylon.
 
Re: Break-testing the loops

Hey southsoundtree,

This was not a break test; I just took loaded it to 450 lbs.

Now in my other Zeppelin bend thread, Pulling a Zeppelin bend to failure... I did break it. Since I don't have a way to break test non-knotted rope, I can only go by the manufacturer's published MBS for 10mm PMI of 6070 lbs. That reduces the strength of the rope to about 63% of the rope's MBS.

Since I couldn't measure the non-knot break strength of the rope, I decided to at least pull an F8 bend for comparison. It broke at about 66% of the ropes MBS.

66% seems a bit low for an F8 bend though. That would suggest that the break strength, 63%, of the ZB may be a bit low too.
 
Re: Break-testing the loops

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...66% seems a bit low for an F8 bend though. That would suggest that the break strength, 63%, of the ZB may be a bit low too.

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I never tested an F8 bend, but I did break some F8's on a bight. The stresses on the rope won't be precisely the same as in the case of the bend, but it is the same knot, and I would expect very similar behavior. In Yale Blaze (5600# nominal strength) the F8 broke at 4388#, or 78% of nominal.
 
Re: The Zeppelin bend... SOME THOUGHTS

I am pleasantly surprised at how many people use the Zeppelin bend - and everyone so far has had very positive experiences with it!
 
Re: Break-testing the loops

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...66% seems a bit low for an F8 bend though. That would suggest that the break strength, 63%, of the ZB may be a bit low too.

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I never tested an F8 bend, but I did break some F8's on a bight. The stresses on the rope won't be precisely the same as in the case of the bend, but it is the same knot, and I would expect very similar behavior. In Yale Blaze (5600# nominal strength) the F8 broke at 4388#, or 78% of nominal.

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That's more in line with what I would expect - around 75% give or take 5%.

If I could have tested the rope itself, I may have found it fails at less that manufacturer's published MBS which would make the percentage of break of the knot higher.

Hence, I'm not so sure that percentage of new rope strength is the best guideline to use. The break point of 3800 lbs I got when testing to failure is absolute and depends on no other unknown(s). So it really doesn't matter what the new rope breaking strength is. The particular sample I used broke at 3800 lbs and that's what I would base any decisions on rather than the percentage.

And that's only for that sample of PMI 10mm EzBend rope.

If I pulled the ZB to failure in Velocity rope, which I almost feel compelled to do, the breaking load may be higher or lower. So again, the percentage thing may not be the best way to evaluate the strength of a knot UNLESS you can actually measure the breaking point of the rope itself - which few of us can because of the required high strength termination required - not to mention the long length of rope required.
 
Re: Break-testing the loops

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...So again, the percentage thing may not be the best way to evaluate the strength of a knot...

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I don't have a problem with percentages so much as any attempt to be terribly precise. Strength is always at the bottom of my list of things to consider when chosing a knot, but when it percolates to the top of the list after the other considerations I have 3 general categories: relatively strong, relatively weak, bad idea.

In the latter category are knots in hollow braids--they seem to be much weaker than the same knots in a solid rope. Knots in hi-tech rope are not such a great idea either.

Most if not all the strong knots I have tested seem to share one property: there is no sharp nip in the rope where it is highly tensioned. The ZB fails this test because the first nip in the tensioned rope is very sharp. But so what? Its other properties matter much more. I can't imagine a plausible real-world scenario where I would reject it for a stronger knot.

The F8 and the DFL do not have a sharp nip in the highly tensioned line and so they end up in the strong category. There are probably exceptions to the pattern. If someone really needs to know if a knot is 60% efficient or 85% efficient there is probably nothing for it but to have it tested in the rope that will be used.
 
A baby experiment

It takes awhile to set up and break down my testing rig, so I like to bundle up experiments whenever I can. A couple of days ago, while the rig was up, I added a couple of quick experiments in braided utility cordage. This cordage is structurally similar to an arborist rope--it has a braided cover and a parallel-stranded core. There were two tests. Each consisted of a single loop of rope with diametrically opposed identical knots. One loop had two double fisherman's bends, and the other had two zeppelin bends.

The idea was to pull each loop to failure. The weakest knot of the pair would fail, and the survivor knot could be evaluated in terms of ease of disassembly.

The DFB loop broke at 422 lbs., and the zeppelin loop broke at 412 lb. The surviving DFB was, as expected, totally locked up. The surviving zeppelin was ridiculously easy to take apart.

I tend to think this sort of experiment in small cordage would scale up to larger rope of similar structure, but I have no evidence for that.
 
Re: A baby experiment

moray
Briefly, mainly because I'm 'time-challenged' today, with regard to both your last posts, I pretty much concur.

When I tested the F8 bend against the ZB, I got 66% and 63% respectfully, in 9mm PMI rope. I don't even consider 3% enough to claim a difference.

The DFB, however, held to a significantly higher loading and I finally ran out of room on the machine before it failed.

I found two things interesting. One, you have to hold the ends of the rope to test a bend, so the terminating knots have to be stronger than the bend. What was interesting about this is that I used F8 loops as terminating knots and both for the F8B and the ZB, the F8 loops were stronger.

The second interesting thing occurred when I tried to shorten the rope in order to pull the DFB to failure. I did a loop around my anchor pin and the F8 loop actually served as a jammed stopper knot against the barrel of the fixture.

I was able to load the DFB heavier, but guess where the failure occurred? Down in the housing the rope that was loaded happened to cross the tail of the F8 loop that was down in the housing. The rope broke right where the tensioned rope crossed the tail!
 
moray said:
Re: The Zeppelin bend... SOME THOUGHTS

Very pretty knot! I think I will test it, and the loop version as well. I am much more likely personally to put a big load on a loop than on a bend, so it will be interesting to see how the loop behaves.

In general I want heavily loaded knots to be easy to untie, even if, like this one, they aren't that easy to tie. For lightly loaded knots all I care about is that they be easy to tie. For a permanent knot or one to be used hundreds of times before untying, securing the tail against creep could be an issue, but I doubt the zeppelin is going to creep.
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I realize this is an OLD thread, and I can start a new one, but the question remains: has anybody done formal testing of the Zeppelin bend, as compared to the double fishermans for example? I am using a Zeppelin (with long tails) for life support and have never had any slippage of the tails. If there are any links to the test results, i would be very interested. I had somebody tell me just today that I can't use Zeppelin for life support... that came from Europe... and somebody in the USA saying I can. Seems like the perfect question for testing. Sure double or triple fishermans are great, but sometimes we do need to untie our life support knots, and the reason why is irrelevant. We do. And fishermans are simply to hard to untie.
 
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