Load Testing Results

[estarzinger]

Someone sent me a vectran shackle with wood toggle (14mm dia, a hard wood but not sure exactly what type) to test.

The wood toggle broke at 5140 lbs.

Originally Posted by thinwater

I'm not confused any longer.

I wish I could say that . . .

[estarzinger]

And here is another someone sent me - it is apparently a triple loop of 1/4" amsteel (with end for end splice) inside a dacron cover. It "should be" 15,000 lbs breaking strength.

I pulled it to 10k lbs, there was a lot of crackling noise at and above 8,000lbs and the ends around the pins flattened right out, but it did not break.

[Benz]

Thanks Evans,

The wood-toggle shackle was mine. Wood is Cocobolo; I deliberately used a far smaller toggle than I usually do with that line because I wanted it to break below the 10k lb limit and get an idea of the wood's strength. On my boat I use a good deal of similar shackles (with bigger toggles, of course), and none of them ever take a strain even as great as 5,000 lbs. I'd be real keen to see what a 1/2" aluminum toggle would test to, if you happen to have a bit of rod lying around to push though the hole.
Thanks again for the test and the pic.
Ben

[Therapy]

I want to thank those contributing as I am interested in final results on strongest knots to use.
I am of no use because I only know the knots I am used to using and am not a competent splicer either. When I have idle time at anchor (sure ) some day I will practice.

[estarzinger]

Originally Posted by Benz

I'd be real keen to see what a 1/2" aluminum toggle would test to, if you happen to have a bit of rod lying around to push though the hole.

I am pretty sure I would not be able to breK it with 1/2 aluminum rod, but I will put it on the list to try. The vectran was not even breathing hard, and I did not heard any noise from the splices during the pull.

[estarzinger]

Back to sewing . . . .

Here is a sample . . . the sewing (between the two black lines) is 5" long and the webbing is 1" wide. 9 rows of zig zag stitching (3 rows each overlapped 3 times). The thread is V69, which is 10.6lbs tensile, and is considered a 'typical heavy machine sewing thread' (there are heavier, like V138 at 21lbs).


Two samples of this broke at an average of 2835lbs. The minimum standard for jacklines is 4,500lbs. So this is 63% of that strength requirement. 10" of this stitching would do the job. If it were done in V138 thread, this 5" pattern would (probably) be acceptable. My personal lesson here . . .is that it is easy to make something that 'looks strong' but does not meet the 4,500lb standard.

The stitching efficiency here is 115% (eg breaking load was 115% of the pure thread tensile strength). The previous big set of samples I analyzed (from the climber than Allen found) accomplished 125% efficiency (with different/stronger thread and different/stronger webbing). I do not know if the difference is better sewing tension in the 125% testing, or if the efficiency changes depending on thread and material.

In terms of failure mode, it looks like the all stitches broke (rather than a few breaking and the thread pulling out), and all on one side. It does look (to me) like there could be higher stitch tension.

Any comments from you expert sewing people?
Broken side:
Unbroken side:

[DumnMad]

Nice one Evans. Friction is a funny property in that its value depends heavily on surface roughness. Tighter stitching might increase effective roughness as it binds the two fabrics into each other. Once the roughness is partially overcome by sliding the friction value drops - hence the threads all fail more or less together.

[JPA Cate]

FWIW, and I am only an amateur stitcher, the best you can get it is equal bury of the locks of the stitches in the center of the fabric. If the lock is on the top, you increase the bobbin tension; if on the bottom, you increase the top tension.

Do you think the type of webbing you use might have an effect on when the thread breaks? In the sample in the photo, it looks like the thread is too heavy for the fabric. Is that webbing polypropylene? Also is there a difference between nylon webbing and polyester webbing as to the pull strength needed to break the stitches?

[estarzinger]

Ann, that's nylon webbing.

I am guessing the thread is not too heavy, as some other people are getting better efficiency with even heavier thread (V92 and V138). In fact one of my tentative conclusions is that with webbing the stronger the thread the better. That's not true with cloth because you need a bigger needle which makes bigger holes, but that does not seem to be a concern with webbing. This is my current thought but I don't have the data to prove it yet. I am going to need to get some different size and strength thread. In the past I have used V69 for most everything in fabric, but I am guessing it's not best if you want to do the highest strength in webbing.

I am getting some polyester webbing. Its back ordered. That will match the thread in stretch characteristic.

So Soft Shackles . . . I started a basic examination:

First . . . 'aluminum toggle with o - ring' shackles. These should form a ceiling for shackle strength. 3 pulls, average 4905lbs. Always break at the bend radius (where the loop is around itself under the toggle)


Second . . . 'Aluminum toggle with noose' shackles (the 'noose' is the simple tuck thru the middle of the line as used on most soft shackles. 2 pulls (I had one splice failure I threw out) average 4540lbs. Still broke at the bend radius, but I suspect the 'tuck thru' had some effect on the rope lay in that bend radius.


Third . . . .'Diamond knot with o-ring'. 3 pulls average 3580lbs. All broke at the diamond.

[Seaworthy Lass]

Originally Posted by estarzinger

In terms of failure mode, it looks

Any comments from you expert sewing people?
Broken side: Attachment 73800
Unbroken side: Attachment 73801

Like Anne, I am only an amateur sewer, but when the stretch of the fabric is greater than that of the thread, in practice I have found that stitching is stronger if made perpendicular to the direction of pull, not parallel as you have sewn.

Regarding tension, again stitching is stronger if the stitches are "buried" when viewed from both top and bottom. If in the example you have given the photos are of the top stitching, then the tension of the top thread (spool) was too loose relative to the bottom. Therefore either tighten the spool tension, or loosen the bobbin tension.

It is easier to adjust the tension of the top thread (spool) rather than the bobbin simple by turning the tension knob. To adjust the bobbin you need to take it out and use a screwdriver on the one and only tiny visible screw. The adjustment is much coarser.

This rough diagram shows how the stitch appearance will vary with tension (same applies to zig zag as well as straight stitches):

[Seaworthy Lass]

PS I forgot to add that I would use a straight not zig zag stitch when stitching perpendicular to the stretch. I want to avoid any of the stitch being anything other than perpendicular to the direction of stretch.

[thinwater]

Originally Posted by estarzinger

Back to sewing . . . .

Any comments from you expert sewing people?
Broken side: Attachment 73800
Unbroken side: Attachment 73801

I'm no expert, but I've learned a few things from hand sewing and breaking things, like you trials.

Does it break with a sharp "bang," like a line failure? That is my normal experience for good patterns. No sharp bang (perhaps less of a bang) and some longer threads generally indicates something pulled through a little. I find pealing failures and can do the later, as can sewing with too strong a thread (over 80 pound doubled seems to be trouble--line damage and distortion) or a poor pattern (too far between stitches, very loose stitching, not enough stitches in a transverse row).

I have not done much testing with other webbing a types. A little, not much difference, but they were all nylon.

[thinwater]

Originally Posted by Seaworthy Lass

PS I forgot to add that I would use a straight not zig zag stitch when stitching perpendicular to the stretch. I want to avoid any of the stitch being anything other than perpendicular to the direction of stretch.

I also agree with this. Everything I have seen points to transverse stitching. Unfortunatly, this is the relm of bar tacking, not standard machine stitch, in part because the machine barely gets rolling across the webbing.

[thinwater]

Originally Posted by thinwater

I'm no expert, but I've learned a few things from hand sewing and breaking things, like you trials.

Does it break with a sharp "bang," like a line failure? That is my normal experience for good patterns. No sharp bang (perhaps less of a bang) and some longer threads generally indicates something pulled through a little. I find pealing failures and can do the later, as can sewing with too strong a thread (over 80 pound doubled seems to be trouble--line damage and distortion) or a poor pattern (too far between stitches, very loose stitching, not enough stitches in a transverse row).

I have not done much testing with other webbing a types. A little, not much difference, but they were all nylon.

Edit (the edit time frame expired). When I mentioned "over 80#" I was thinking about sewing 1/2" rope, not webbing. In fact, for 1/4" to 3/8" rope, doubled #4 is better and gives less load concentration. I have sewn webbing with doubled 80# thread and there was distortion and webbing damage. However, with doubled 40# thread the webbing shows no sign of having been sewn and broken, once the thread bits are picked out. I'm sure machine sewing up to 20# is no concern; webbing is dense stuff.

[estarzinger]

I made up 4 more webbing samples, all with straight stitches, smaller stitches, and more thread tension (same settings on all samples)

What my data indicates is a clear correlation between more stitches and less efficiency. That suggests the key for efficiency (in webbing) is to use the strongest thread (and fewer stitches). This is a consistent correlation for my machine stitching right thru the hand stitching. BUT, I should note, it is not that clear in the other guy's data (that I analyzed above in the thread). But his variability is so high that it may be hidden.

Like the other guy I don't get any correlation on whether the stitch count is more across, or down, the webbing. It just seems to be number of stitches that is the first order effect.

There also seems to be a second order effect that single stitched rows separated from each other are more efficient that the same number of stitches in few rows over stitched several times.

And I continue to be interested how hard it is to get to 4,500lbs, with V69 10.6lb thread (which is typically viewed as moderately heavy thread). I am wondering how many sewn jacklines actually meet the standard.

4 samples in order of efficiency, from least to most:

Sample 4: 81% efficiency - 5 rows down (spread out rather than over each other) plus 6 across
photo 4d.jpg Views: 120 Size: 223.8 KB ID: 73865" style="margin: 2px" />

Sample 1: 81% efficiency - 6 rows down (3 rows tripple stitched) plus 2 across


Sample 3: 95% efficiency - 3 rows down plus 5 across


Sample 2: 109% efficiency - 3 rows down plus 2 across


Comments/suggestions?