New soft shackle strength question
 

I am trying to come up with a soft shackle variation for attaching eye spliced StaSet jib sheets to a clew ring that is extremely fast but uses line instead of metal. Using a normal soft shackle is not very fast and not suitable to the application I have in mind.

I have thought of two options. Both methods use a the stopper knot loop on the clew so that the soft shackle can be easily opened and closed without having to thread anything through loops and milk it closed around a circle like with a normal soft shackle.

At first I thought I would use a soft shackle with an opening between the crossover and the diamond knot and loop it around the eye spliced sheets like this:


But the way it pulls on the weak diamond knot worries me so I thought of splicing instead of using a diamond knot like this:



But the splice is only 29 diameters on each side to keep the thing from getting too long. It is lock stitched on each side of the corssover so it won't come apart at light loads. Perhaps I could figure out how to do a brummel crossover rather than stitching, not sure.

I know you recommend 72 diameters but my question is, how much is lost when the splice is shorter? In this case, each splice has half the load of a normal eye splice so if I lose 1/2 the strength by having the splice shorter than I am ahead as I lose more than half for sure with the diamond knot approach, perhaps a lot more due to the strange loading on the knot. Losing half the strength at a point where the line has half the load would still leave me with line strength, which is my goal.

I know you have done a lot or work on how long the bury should be and wondered if you can share the strength vs length of bury results.

Allen

Not strength...
 

Hi again,
Another lovely variation, and it might hold promise. But the issue in this case is not strength, but security. The reason for the long bury is that HM fibers are very slick (most knots crawl out of them), so it takes a long bury to generate ultimate friction. I have pulled apart short-buried splices at relatively low loads, in tests, and have heard of them failing in the field.
The Diamond Knot-based soft shackle is weak only relatively; it is still far stronger than a comparably heavy/expensive stainless shackle, as well as being soft. Toggled versions of the soft shackle exist, and they are fast and strong...
Fair leads,
Brion Toss

I did some pull testing of some 5/32 versions. My only calibration is that I cranked on the winch as hard as I could (35 power winch) and that stretched the 7/16 connecting yacht braid 10%. Nothing slipped but the diamond knot version did experience a fair amount of deformation on the underside of the knot, as one would expect. I noticed that the loop tended to compress itself because of the way it is looped around the eye splices. I am sure that gives additional friction to the splice area compared to just pulling on a splice.

Here is an interesting question. If the length of the bury is fixed, would a larger line be stronger or a smaller line. You get more diameters with a smaller line but it is inherently weaker and the larger line gives more surface area in the splice even thought the length is the same. Thinking about that makes my brain hurt.

Allen

I tested a scale version using 1/8 inch Amsteel with a 23 diameter bury. I used a double loop of old 3/8 yacht braid at first to simulate the eye splices but the yacht braid broke in the test. I switched to a single loop of new 1/2 inch 12 strand poly line. I pulled until the stopper loop around the clew broke at the diamond knot. There was no slippage in the buried splice loop. Here is a video of the test. I was going to repeat it with a stronger stopper loop but my jack seems to have failed from the last test.



Allen

Re-examimining
 

Hello again,
Strength vs. security. Bury length vs Diamond weakness. Ring Hitched vs. plain eye. Steadily increasing loads vs what happens in the World. All these factors and more are what went into the establishment of splicing protocols. Sorting them all out and accounting for them in a test can be tricky. Taking another look at the second configuration in your previous post, it appears that bury length is not the primary determinant of strength. By making an eye at the fixed end instead of a Diamond Knot, you open up some interesting possibilities. the Brummel at the point where the bury for the small eye exits contributes to the strength of that end.
A locked Brummel where the Ring Hitch ends go together, or maybe even a multiple version, would provide significant strength to the other end, perhaps to the point where the bury is simply there to dispose of the ends, not to provide strength or security. And the Ring Hitch takes further load off that Brummel. Did you lock-Brummel the Ring Hitch loop? It appears that this structure is stronger than the conventional soft shackle, as that broke first. Had you "set" the Diamond in that before the test?
Fair leads,
Brion Toss

Hi Brion,

Thanks for the reply. I will try and answer your questions regarding what I did.

I made versions both with a brummel in the ring and with just the bury and lock stitch. The brummel was difficult as the only way I could figure out how to tie it was with the un-breaid cross over and re-braid I think you reference as from Book 5. In previous tests, I have tested the lock stitch and brummel versions of eye splices and find them both stronger than the line with actually more stability from the lock stitch so that is my preference and what I tested. That said, if there is a way to make a brummel in a loop without the re-braid I would like to know how to make it.

In terms of the diamond knot stopper loop, I lock the diamond knot by putting the tails in a vice and pulling on the loop with a lever so there is a large force. After it is locked, it is hard like a marble.

I think the strength of this shackle should be half the strength of a normal soft shackle as the diamond knot has twice the load that it has in the normal soft shackle. This can be addressed some by using the next size up line to make the stopper loop.

My concern now with this shackle is the constriction force on the sheet eye splices. The Ring Hitch really clamps down hard on the line and I am afraid it would tend to cut them under load. My thought is that it is the action of the ring hitch that gives the shackle its strength with the short bury but it comes with a price. I would love to hear your thoughts on this aspect of the shackle.

My concern as led me to work on variation #4, a double soft shackle and will post when that is tested although I need to deal with the broken hydraulic jack.

Allen

Update on new test of new shackle
 

I pulled on a version of this shackle but this time I pulled on the loop without using a ring hitch. This would stress the spliced area fully as there is no additional force holding it together as there is when it is in the ring hitch. This bury was 23 diameters and was made of 7/64 Amsteel so that I would break it with my winch. It broke at near the maximum force I could put on the winch handle with the 35 power winch. That would be close to line strength plus or minus. What broke was the stopper loop (top of first picture below) that the shackle was attached to.


My next test was to use the ring hitch to attach the shackle to the 7/16 XLS that went to the winch. The eye of the shackle was attached to a 3/16 stopper loop to remove that as the failure. The shackle broke at the eye. The 7/26 XLS was stretched 17% when the shackle failed. My estimate is between 2000 and 3000 pounds, more than the line strength. The loop with the 23 diameter bury did not fail.

Actual tests
 

Hi again,
I so admire your work. It seems like now would be the time to put your configurations to some formal testing; might I see if I can arrange some? The idea is that we can get some accurate numbers, but also that we can address some other variables.
For instance, the short bury is for two legs, evenly loaded. But people learned the hard way (i.e. injuries and fatalities) to bury the core in double-braid splices, because the load sometimes comes on one leg, in the real world. Also, shock loads and cyclic loads might make a big difference. The one thing we don't want is to trumpet some Fabulous New Idea, only to have it fall apart when it matters.
Fair leads,
Brion Toss

I can certainly make some up and send them to you. However, what I have is Amsteel. Perhaps Samson would be interested.

From an engineering standpoint, it would be great to know the strength of the individual parts of the shackle. If the same size line is used, then the diamond stopper loop is the weak point. That can be made stronger by just going to the next size up for the stopper loop. Knowing the strength of a normal soft shackle would give me that as it has the same failure mechanism but I have seen online numbers between 120% of line strength (too low -- I don't believe it) to 180%, closer to what I believe. Next would be the strength of the eye itself. That should be something over line strength but we could probably just call it line strength. Finally, the strength vs. bury length for the main loop. Of course, if it is used as I am assuming and is constricting the yacht braid eye splices, it is going to be stronger.

I am wondering if you already have some of these numbers, the normal soft shackle, the strength vs bury length. I know you did some work in coming up with your 72 diameter number but am not sure if you did anything down to the 21 diameters I am using. Obviously these need to be stitched or they will just slip at low forces.

If these numbers do not exist, then best guess would be to use 3/16 for the shackle and 1/4 for the stopper knot and do some testing. As I said, I am happy to make up some samples.

One final point. I have two designs. One with the eye buried and one with the eye just passed through. I like the one with the eye just passed through as it is shorter and easier to use but I am less confident of the construction. But that is another variable. I also did the design with the diamond knot in the center between two shackle eyes. I don't like that because it is weaker and solves a problem I am unsure even exists.

I hope I am not making this too complicated.

Allen