i know, very imaginative name.
another random "invention" brought to you by this episode of "the endless lockdown".
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this is sort of a de-volved softshackle idea i've been playing with. the short version is: i wanted something that's really quick and easy to use (more like a carabinner and less like a shackle), can be made quickly, at the end of any line you might want, and does not require splicing. and is secure, including for cyclic loading (as you would expect when in use on a tarp ridgeline).
the resulting design idea is so simple that i find it hard to believe i'm the first one to come up with it, but i could not find any documented use of anything similar, anywhere, and believe me i looked everywhere i could think of). if somebody knows of any reference i'd be very curious btw.
the anatomy is simple: a trustworthy mid line loop that doesn't mind being loaded in whichever direction, here the wonderfull butterfly loop (ABoK #1053), and a stopper knot, here in use the equally well regarded ashley stopper (ABoK #526). the end of the line, with the stopper knot on its end, is passed through the loop formed by the butterfly, thus creating a capture loop with some very special characteristics.
the loop is twisted on itself to make it impossible to put the stopper in the loop by mistake, instead of putting it between the "standing line" and the loop. this is not strictly necessary, but very desirable i think, as it reduces the fiddle factor to zero, and removes chance of user error or confusion.
because one side of the capture "hole" is of fixed length (the twisted butterfly loop), and sliding on the other part, this means that, if one makes the butterfly loop long enough so it encircles the stopper and then some, easy release is possible even under load, thus allowing for a controlled release and detensioning of the line, and similarly allowing for a tensioned closing of the "shackle".
i've been playing with it and testing it for the past few weeks, if not months, in various applications. it has surprised me how secure it actually is, i even tried some very unreasonable cyclic loading tests, and even with a butterfly loop which is much larger than necessary, it does not release (the shape of the stopper has a significant role in that).
there are so many uses i won't list them all here, but obviously, whenever one would attach a carabiner to the end of a line or an object, one could use this instead.
another interesting use is to attach the tarp to a continuous ridgeline (as in the picture): one end of the shackle forms the blake hitch (which is superior in almost every way to the prusik), and stays there on the ridgeline, the other side is the shackle part. one neat trick is that, if you want to shorten the shackle, or even add some more tension easily, you can just pull the stopper through, back through the object/tarp tieout, and then back into the capture loop.
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by design, this thing is vulnerable to ring loading (it is actually one way of quick release, to grab the line on the stopper side, and pull away from the load); under actual use, i haven't yet seen it fail even under ring loading, but it is clear it can.
the other thing to beware of is that the two legs of the shackle (the one with the stopper and the one without) need to be "balanced" (both need to be loaded), particularly, if something grabs only the end with the stopper, the shackle will open. so the line of the shackle needs to be free to move through the object it is closed onto. (this is true to some extent of all soft shackles, though)
a word of caution: if someone would be interested to make this in dyneema (which i'm not sure would be so useful, but oh well), the only stopper knot we know to be reliable in dyneema is the estar stopper, and that one has a very different shape, which i haven't tested thoroughly yet, so it might behave quite differently.
before posting here, the last step was to do destruction testing on a few samples. this confirmed that the shackle will fail, as one would expect, at the "exit" of the butterfly (so the single line in the picture), so the expected strength is quite high (i'd estimate above 80% line strength depending on the line, as you'd expect with a good knot like the butterfly, but i don't have equipment to give you numbers for now). the failure mode is consistent, it always breaks there, and the stopper never escapes the loop, even after breaking and slingshoting all over the place.
yes, one could even make an "s-binner" type of configuration, using a double butterfly (tried it, it works, i just don't find it that useful so far, maybe somebody else would). it's also possible to make the butterfly loop really small, so that when the line is loaded, there's no way the stopper can pass through; this seems more secure of cyclic loading and such, but it does make releasing under load impossible, and i didn't find cyclic loading to be a vulnerability at all with the "quick release" version in the pics. however, a smaller butterfly loop will make it safer against accidental release by pressing the button knot (for instance when it is resting on an object when in use)
i'm also thinking in dyneema it might be interesting to skip the butterfly, and instead splice that loop onto the host line, to make it cleaner (and avoid the massive drop in strength a butterfly on the line would bring), but i'm honestly not convinced this design makes that much sense in dyneema.
tell me your thoughts. can you see using it for something? can you see ways to improve it or adapt it to other purposes?
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