Introducing the "Crown Jewels Soft Shackle"

[Seaworthy Lass]

I have been playing with soft shackle design and have come up with a new concept.
Currently the strength of well made soft shackles is limited from around 170-230% of line strength, depending on design. Either the base of the stopper or the noose is the weak spot. This new design tries to minimise this.

The Crown Jewels Soft Shackle is not a replacement for conventional designs, but may be an excellent addition to the arsenal . I hope the fresh concept helps the quest for improving soft shackles.




Advantages of the design:
- The stopper is one most people making soft shackles are familiar with. There are no new skills to learn.
- Although this new design utilises the Diamond stopper, the load at base of the stopper is distributed quite differently. I think there is a high possibility that strength may be increased substantially as a result. Twin stoppers mean the usual loop that makes up the noose is eliminated entirely. There is no noose with a loop at the apex.

Drawbacks:
- The connection point needs to be large enough for a stopper to pass through.
- It uses slightly more rope than a conventional shackle using a Diamond knot, but on the other hand it is less than the length needed for current "High Strength" (230% of line strength) versions.
- The design is as yet untested.

The instructions are simple:
- Cut two lengths of dyneema the inner length of soft shackle when open + 2 x 45 x line diameter for the stoppers. The length needed for the stopper depends on your skill making these. You can get away with 35 x line diameter if you are at ease with making these stoppers.
I made the above 200mm long one (100mm when closed) using 1.1 metres of 5mm dyneema.
- Tape the two pieces firmly together so that 45 x line diameter is left free to make one of the stoppers.
- Tie a Diamond stopper.
- Tighten the weave securely using a Marlingspike. Twist the tails around some pliers and pull to tighten these. For the first Diamond knot a vice can also be used, as is usually done.
- Carefully mark the chosen length on both legs (for good load distribution these need to be identical) and 4 x line diameter short of there cleanly create a hole leaving 6 strands on each side of the hole and feed the other leg through.
Edited to add: I have since found it better to make the opening end next to the first stopper, as then you don't need to fuss with getting the opening size perfect (if you place it next to the second stopper it can increase during tightening)
- Tape the two legs securely at the marks you just made.
- Tie another Diamond stopper and tighten up as for the first.
- Pull on one leg below the stopper to open the gap and push the other stopper through.
- Pretension the shackle closed between two winches and leave sitting for 20-30 minutes (as you should with all soft shackles)
- Cut off the tails about a line diameter from the stoppers. I prefer not to make these too short and nor do I melt them.

Keeping the same principle two stoppers, lots of variations in design are possible:
- If one stopper is made a toggle (tails are spliced over it) it could be pushed through a small aperture. Strength is likely to be higher than the current designs made with a toggle, as the base of the Diamond acts as the apex of the noose.
- The central portion could be buried and a "Better" opening created. I would do this without locking either side of the bury though and milk the cover of the bury vigorously before immediately securing it so it doesn't spring back. Getting the load distribution good is difficult though with a long central bury, so strength is likely to suffer.
- A tiny amount of central bury could be made for better handling, as I do for the BB soft shackle.
-Depending on where the weak point is with this design, it may help to make one stopper a Button stopper. The opening still needs to be below a Diamond stopper. Edited to add: the second stopper could be a Button as well if you make the tail bury short.

I can't wait to test the design. It looks very promising .

SWL

[Seaworthy Lass]

I think the Jewel design would be worth testing (the stress points are very different to other soft shackle designs using a single Diamond stopper so this is likely to perform differently) and I have been thinking how to do this.

Allen Edwards on Sailing Anarchy has suggested comparing it to line strength and loop strength. Taking this idea a step further, I think more valuable preliminary information would be gained testing it against the current designs using a noose and either Diamond or Button stopper. I am confident the strength will be greater than 100% line strength and a loop won't give me 200% due to strength being limited as it bends. Using other types of soft shackles for comparison is not an ideal test (a test cell would be better), but it is better than nothing.

Wotname, a while back you very generously offered to break a few designs if needed. Are you still able to do this? What load are you able to apply?

SWL

[Wotname]

Originally Posted by Seaworthy Lass

...........

Wotname, you very generously offered to a while back to break a few designs if needed. Are you still able to do this? What load are you able to apply?

SWL

Well I can break 'em ; I got 40 tons at my disposal

BUT...

1. I have some good advice that i shouldn't "snap unload" the hydraulic ram - rises damages to the seals. AFAIK, this not so bad on stretchy lines (nylon etc) but a problem with low stretch lines. So I thinking I should limit it to breaking lines needing 10 tons or less.

2. I still haven't worked out a cheap DIY way of measuring the load applied when the line breaks. So at best, I can only comparative breaks. For instance, knots / bends etc in series etc.

I can easily show how the UUT (unit under test) deforms just prior to breaking and whether it is "undoable" after been loaded to near max.

[Seaworthy Lass]

Originally Posted by Wotname

Well I can break 'em ; I got 40 tons at my disposal

BUT...

1. I have some good advice that i shouldn't "snap unload" the hydraulic ram - rises damages to the seals. AFAIK, this not so bad on stretchy lines (nylon etc) but a problem with low stretch lines. So I thinking I should limit it to breaking lines needing 10 tons or less.

2. I still haven't worked out a cheap DIY way of measuring the load applied when the line breaks. So at best, I can only comparative breaks. For instance, knots / bends etc in series etc.

I can easily show how the UUT (unit under test) deforms just prior to breaking and whether it is "undoable" after been loaded to near max.

Thanks Wottie, that is a very kind offer.
I know that there are companies that will load test, but this becomes costly for the number of tests needed. It is bad enough having to buy the dyneema for this.

I need to mull over what is best. Even preliminary trials will need a considerable number of soft shackles. This means lots of time and expense at my end, let alone at the testing end. It would be more worthwhile if actual loads could be measured.

Regarding likely loads, if you are limited to 10 tons that may be getting close to what is needed. I think testing with smaller line diameters than are currently being used is not worthwhile, as results may not scale up. So 5mm dyneema is about the smallest it would be good to test. 5mm SK75/78 typically has a breaking strain of around 3000-3500 kg. It would be nice to have to capacity to get to three times this, so this takes it very close to your equipment's safe limit for snap loads.

In case anyone is wondering, I have zero commercial interest of any kind. I am simply a cruising sailor who finds rope work enjoyable and I am sharing all findings in the hope it may help the sailing community.

SWL

[Wotname]

Originally Posted by Seaworthy Lass

......

I need to mull over what is best. Even preliminary trials will need a considerable number of soft shackles. This means lots of time and expense at my end, let alone at the testing end. It would be more worthwhile if actual loads could be measured.

Regarding likely loads, if you are limited to 10 tons that may be getting close to what is needed. I think testing with smaller line diameters than are currently being used is not worthwhile, as results may not scale up. So 5mm dyneema is about the smallest it would be good to test. 5mm SK75/78 typically has a breaking strain of around 3000-3500 kg. It would be nice to have to capacity to get to three times this, so this takes it very close to your equipment's safe limit for snap loads.

...

Mulling is always good

The 10 ton number is just an arbitrary figure that I have naively plucked from nowhere so providing we aren't doing hundreds, I am happy to higher...

Worst case is blown seals which while annoying, it isn't a major issue.

As for measuring the applied load, perhaps some smart DIY engineering member has some ideas of a practical way to achieve this.

[Wotname]

Originally Posted by Seaworthy Lass

....

I need to mull over what is best. Even preliminary trials will need a considerable number of soft shackles. This means lots of time and expense at my end, let alone at the testing end. It would be more worthwhile if actual loads could be measured.
...........

I'm not so sure that we would a considerable number just for comparative tests.

Large numbers are important if one trying to establish accurate numbers for publication etc.

[Seaworthy Lass]

Originally Posted by Wotname

I'm not so sure that we would a considerable number just for comparative tests.

Large numbers are important if one trying to establish accurate numbers for publication etc.

The number needed depends of the spread of results. I am not interested in publishing anything (although "Seaworthy Lass" is a lovely pseudonym ), but the figures still need to be looked at with the same rigorous standards including statistical significance, otherwise they are not very meaningful.

Advice from those involved with load testing would be useful. There is no point reinventing the wheel . Allen Edwards and Brion Toss should be able to help. I am corresponding with both, so I will ask them.

I think about 6-10 pulls has been used in the past. I think the number can be minimised if the shackles are made with care and ultra high shock loads are not suddenly applied with the testing gear (although this may occasionally be encountered in real life). There must be an optimum way to increase load. I suspect this should decrease the spread of results significantly.

SWL

[weavis]

I needed some testing done a few years back.
Contacted local tech college and they pressure tested and load tested the equipment for me..Free... made a teaching lesson out of it..

Just a thought

[Seaworthy Lass]

Originally Posted by weavis

I needed some testing done a few years back.
Contacted local tech college and they pressure tested and load tested the equipment for me..Free... made a teaching lesson out of it..

Just a thought

That is an excellent idea. Thanks .

I have also considered approaching one of the rope manufacturers. They may be happy to lend a hand here.

The manner is which load is best applied still needs some consideration. I will not rush into this, as the shackles are not quick or cheap to produce.

SWL

[Wotname]

Originally Posted by Seaworthy Lass

.....

I think about 6-10 pulls has been used in the past. I think the number can be minimised if the shackles are made with care and ultra high shock loads are not suddenly applied with the testing gear (although this may occasionally be encountered in real life). There must be an optimum way to increase load. I suspect this should decrease the spread of results significantly.

SWL

Dunno if this helps but a long way back in the day when I was assisting with some load testing of stitching on aviation cargo nets, we always did 10 but most of the time, the spread was under 10%. We pretty well knew after the first three, what the rest would be. We needed the ten to "prove" what we sorta knew.

Increasing the load slowly is easy enough, my problem is the release point. The "snap back" shock load of a low stretch line breaking is much higher than that of a stretchy line - or so it is as I understand it from someone who should know.

Proper load testing equipment is usually mechanical rather than hydraulic

[UNCIVILIZED]

I like the suggested testing ideas, & the college option is one which ran through my mind as well. Though I also can't help but wonder if testing them using a load cell, & an inexpensive hydraulic cylinder would work. That or even a strain gauge & a fork lift, or similar. There's no shortage of industrial hydraulic equpiment around construction sites. And were the loads lower, I'd suggest renting a Bobcat for the day. Perhaps the local hardware store, or equipment rental shop has something that would work?

Also, how best might one test them so as to mimic the orientation of the loads which they would be likely to see in service? As having the loads applied by the testing equipment spin the orientation of the shackles around a bit, at random, would surely skew any test results. And create inconsistencies in any conclusions. Has this been sorted out via other load tests on some of the other designs in the past? And if so, how?

Plus, to do a fair comparison to other soft shackle designs, the radius of the bars on the testing equipment will need to be the same when testing all of them. And it would help greatly if the size of the pulling implements were akin to what the shackles might see in the real world. Particularly given that the breaking strength of Spectra drops fairly quickly when it's wrapped around smaller radii. So mimicing what they might be used to secure on a boat could be an important factor as well.

Ah, one other thought. While using a vise to make the knots may be fairly mandatory, it's use may be one of the things which causes some of the "fliers" when testing the strength of the knots/shackles. As some of the fibers of the cordage are probably getting damaged to some degree by being clamped quite firmly in the vise's jaws. Especially if the jaws are unpadded metal. And if this is the case, would lining the jaws with hardwood be an option? It's something that's commonly done in some woodworking & cabinetry shops to prevent marring of that which is being clamped. And in fact the wooden blocks are attached, & integral to the vise's jaws.

Also, to some degree the above may be true in terms of that which is being used to pre-stretch the shackles right after they're made. In that the pre-stretching hardware might be accidentallly creating microtraumas to some of the cordage's fibers. So you'd want to insert a degree of consistency in how this is done as well, & with what. Meaning, using the same amount of load on each to pre-stretch them. And to use the same (gentle) radiused tools to do this with each time, for the bits which the shackles are wrapped around during their being pre-stretched. Along with orienting each shackle exactly the same when it's being pre-stretched.

One other thought is that you might contact Colligo Marine about much of this, including getting them to test the strength of the shackles. As in the past (& probably currently) they do their own testing on the strength & creep of some quite large (diameter wise) pieces of Dyneema (Dux). Since knowing these numbers precisely, along with the breaking strength of the stuff, is critical to their rigging of boats.

[Seaworthy Lass]

Originally Posted by UNCIVILIZED

I like the suggested testing ideas, & the college option is one which ran through my mind as well. Though I also can't help but wonder if testing them using a load cell, & an inexpensive hydraulic cylinder would work. That or even a strain gauge & a fork lift, or similar. There's no shortage of industrial hydraulic equpiment around construction sites. And were the loads lower, I'd suggest renting a Bobcat for the day. Perhaps the local hardware store, or equipment rental shop has something that would work?

It would be nice if testing was not restricted to just one day. It would be good to modify design depending on failure points observed, and then retest. A permanently set up lab would be better.

Originally Posted by UNCIVILIZED

Also, how best might one test them so as to mimic the orientation of the loads which they would be likely to see in service? As having the loads applied by the testing equipment spin the orientation of the shackles around a bit, at random, would surely skew any test results. And create inconsistencies in any conclusions. Has this been sorted out via other load tests on some of the other designs in the past? And if so, how?

I think it would be useful to initially reproduce techniques used previously, as it allows a comparision between different designs without me needing to made up 10 of each . Later this could be varied.

Originally Posted by UNCIVILIZED

Plus, to do a fair comparison to other soft shackle designs, the radius of the bars on the testing equipment will need to be the same when testing all of them.

And it would help greatly if the size of the pulling implements were akin to what the shackles might see in the real world. Particularly given that the breaking strength of Spectra drops fairly quickly when it's wrapped around smaller radii. So mimicing what they might be used to secure on a boat could be an important factor as well.

Agreed.
As I understand it, the bend has never been super tight with load testing and so it has never shown up as the weak point. Nor has it been made unusually large. I will look up previous load tests to see what was used. I have not paid much attemtion to test technique before.

Originally Posted by UNCIVILIZED

Ah, one other thought. While using a vise to make the knots may be fairly mandatory, it's use may be one of the things which causes some of the "fliers" when testing the strength of the knots/shackles. As some of the fibers of the cordage are probably getting damaged to some degree by being clamped quite firmly in the vise's jaws. Especially if the jaws are unpadded metal. And if this is the case, would lining the jaws with hardwood be an option? It's something that's commonly done in some woodworking & cabinetry shops to prevent marring of that which is being clamped. And in fact the wooden blocks are attached, & integral to the vise's jaws.

Good thought, but the jaws of the vice should not touch the soft shackle at all. What I do is pop the legs (or tail if tightening the other way) through a big washer. The jaws of the vice are made a bit narrower than the washer. The stopper sits against the washer. The legs/tails are completely free to be pulled.

Originally Posted by UNCIVILIZED

Also, to some degree the above may be true in terms of that which is being used to pre-stretch the shackles right after they're made. So you'd want to insert a degree of consistency in this as well. Meaning, using the same amount of load on each to pre-stretch them. And to use the same (gentle) radiused tools to do this with each time, for the bits which the shackles are wrapped around during their being pre-stretched.

Agreed. I have to be less careful with that aspect, as I have sometimes just used a loop of dyneema to secure to one of the winches. I will be more careful for any test shackles.

Originally Posted by UNCIVILIZED

PS: You might contact Colligo Marine about much of this, including getting them to test the strength of the shackles. As in the past (& probably still) do their own testing on the strength & creep of some quite large (diameter wise) pieces of Dyneema (Dux). Since knowing these numbers precisely, along with the breaking strength of the stuff, is critical to their rigging of boats.

Yes, a rope manufacturer (particularly one that has been involved with the design or making of soft shackles) would be a good choice for testing.

Thanks for all the suggestions . Every little bit helps, even if it just sparks other ideas.

SWL

[Sailmonkey]

"Crown Jewels"

Tehehehe[emoji23]

[Seaworthy Lass]

Originally Posted by Sailmonkey

"Crown Jewels"

Tehehehe[emoji23]

I was purely looking at the twin Diamonds .

You can't take all this rope work too seriously .

[Cu Mor Glas]

Originally Posted by Seaworthy Lass

-Depending on where the weak point is with this design, it may help to make one stopper a Button stopper. The opening still needs to be below a Diamond stopper. Edited to add: the second stopper could be a Button as well if you make the tail bury short.

I can't wait to test the design. It looks very promising .

SWL

I will try this in 4mm when I get out of work and back to the boat. I never really mastered the diamond knot. Using your instructions for the button turned out so much easier and I just quit trying as there seemed no advantage to the diamond. I'll try the short bury at the loop end.