Introducing the "Crown Jewels Soft Shackle"

[Wotname]

Originally Posted by Seaworthy Lass

..........

These soft shackles are still very seductive .

You say seductive, I was thinking elegant but whatever

[Wotname]

Originally Posted by mickeyelam

Wotname,

As for determining the total load exerted by your press, you should be able to roughly calculate it if you have a hydraulic pressure gage plumbed into the jack portion of your press; if you take the hydraulic fluid pressure in pounds per square inch (psi) and multiply that value by the area (in inches) of the internal hydraulic piston, you should get a tension value in pounds. Obviously, the hard part of this exercise is determining the piston area. It might be listed on the jack but you'll probably either need to contact the manufacturer or measure the piston area when changing seals. If you already know you internal diameter of the hydraulic cylinder body you can measure the ram diameter and subtract the smaller area from the larger area to get the piston area.

This won't be as accurate as you'd get with a load cell or other more advanced instrumentation, as there are friction loads unaccounted for, but it should be within a reasonable margin of error.

You could also "calibrate" your calculation if you have access to a line (or other material) with a known breaking strength. Just test to breaking and see what your pressure gage measured at the maximum, then reverse your calculations. It probably goes without being said, but obtaining a pressure gage with the ability to retain the maximum hydraulic pressure via a tell-tale needle would simplify this exercise a great deal.

Yes, this was on my thought radar! Currently don't have a pressure gauge in the system (you don't much with cheap Chinese rams) but perhaps when I find some time to think more about it, I will look for something on fleabay etc. I agree a telltale would be helpful!

Thanks for your thoughts

[conachair]

Originally Posted by weavis

Its hard to fathom how 5mm Dyneema can handle these loads. Wow.
How does UV affect the material?

D12 max sk99 is amazing stuff any way you look at it 5mm MBL of 3800Kg. The anti chafe coating seems to work very well so hopefully the anti UV properties listed will be similar. Anyway, it's so strong something else will very probably go bang long before the dyneema even if degraded by 50%.

[Juho]

Just wondering if there would be some slightly asymmetric stopper knots that would work well with this design.

[Pete7]

Originally Posted by weavis

Its hard to fathom how 5mm Dyneema can handle these loads. Wow. How does UV affect the material?

The 4 and 5mm size have started to appear in the UK chandlers albeit at an exorbitant price and the off white or drab grey doesn't really have a bling value so bought one of these instead:

https://www.jimmygreen.co.uk/item/28...-soft-shackles

The bright blue colour fits nicely with the Genoa strip which is far more important than having a bit of scruffy dyneema to join the sheets to the clew.

Pete

[Seaworthy Lass]

Originally Posted by Juho

Just wondering if there would be some slightly asymmetric stopper knots that would work well with this design.

Good thought. Not many stopper knots hold in dyneema though.

The ABOK also has about a hundred button designs (from #909 onwards). The compex weave of these would probably eliminate the risk of slippage. Checking these out has been on my mental "to do" list for a while. After Ashley passed away, his widow apparently kept these buttons on display in a bowl .

[Seaworthy Lass]

I have just made a second one from some scrap dyneema using Diamond stoppers . If nothing else it is an excellent way of using two scraps of dyneema that are too short for anything else .

It is quite possible that even when loaded differently the Diamond will have a similar limitation to original soft shackle designs (most knots in Dyneema just don't perform much better than around 50% of line strength), but I think it is worth testing.

The idea of two stoppers is an intriguing one for me. If not two Diamonds then maybe something else could be used (or a combination). This eliminates the weak point in the current high strength versions. Also, all this may just spark other new ideas for others. The evolution of these soft shackles is fascinating to observe and to be a small part of .

SWL

[Juho]

Some more thoughts on the size and strength of stopper knots.

One could make the soft shackle n times longer and n times thinner than needed, and tie it in n loops when connecting it. The knot will be n times smaller. We will need thin dyneema (or other) rope to do this.

Assuming that the stopper knot is still the weak spot, we could double a short section of the rope at both ends of the shackle to make the knot section as strong as the mid section. The size of the knot could still be quite small. Details for further study.

[estarzinger]

^^ Multiple loops is one of the two key ways to beat the current strength limit. If you make a 'single strand' soft shackle (or alternatively, as you say 'thinner', 1/2 the cross section), twice as long, and wrap it twice, you have halved (actually more than halved because of friction) the load on the weak points, while still using the same about of cordage as a 'regular' double strand soft shackle.

This is simpler, but a bit less elegant than the other way, which is to work on the bend radius, and get them all up to 5:1 (which in itself can be done two ways )

The multiple loop approach has no theoretical limit, but practically speaking gets clumsy (imho beyond 2 wrap) to use, and has some "tension equalization" issues beyond 3 wrap, without some clever design. The bend radius approach does have a theoretical limit, and (imho) should be fully exploited before moving to multi-wraps. You can also combine both approaches.

[StuM]

Originally Posted by Juho

Some more thoughts on the size and strength of stopper knots.

One could make the soft shackle n times longer and n times thinner than needed, and tie it in n loops when connecting it. The knot will be n times smaller. We will need thin dyneema (or other) rope to do this.

That's exactly what I do on the main outhaul and jib clew on the Farr 1/2 ton we race. Didn't make them any longer that normal - just use normal ones as per SWL's dimensions. Looping them keeps the connection as short as possible which means we can flatten the foot of the main a bit more and can get the clew of the jib closer to the traveller block.

[estarzinger]

Btw, regarding load testing . . . . For "yachting size" tests, the breakeven between using an outside shop vs building your own test bench is about 100 pulls. And the cost to build such a "yachting bench" is pretty trivial compared to building say a custom aluminum Dutch boat.

If you want to do really high load tests (I'm doing +100k lbs these days), then the situation is different, and you really have to use an outside shop, because the equipment to safely pull and measure at that level is reasonably expensive.

Early on I got two sets of pulls done at the naval academy (for free), but it is not a super convenient or consistent way to get things done.

As to pull procedure, there are documented standards. There is some wiggle room on speed and such, but my experience is that the "flyers" tend to mostly be because of sloppy rope construction, or a puller who does not know/follow the standards, rather than because of wiggle within the standard. If you use an outside shop, you should really get video of their pulls, so you can see exactly what they do, and double check that it is consistent between tests.

[weavis]

Originally Posted by Pete7

The 4 and 5mm size have started to appear in the UK chandlers albeit at an exorbitant price and the off white or drab grey doesn't really have a bling value so bought one of these instead:

https://www.jimmygreen.co.uk/item/28...-soft-shackles

The bright blue colour fits nicely with the Genoa strip which is far more important than having a bit of scruffy dyneema to join the sheets to the clew.

Pete

You dont want to know what Dyneema costs in Spain.........

[Seaworthy Lass]

Evans, thanks for the information.

Regarding the Diamond stopper, was the 46% limitation in strength tested in a straight line pull? Was the Button stopper also ever tested alone? With the buried tails in the Button I suspect it may reach the 90+% mark.

I plan to play a bit more with the Button in this twin stopper design. Although it looked a bit more awkward than the Diamond, this may end up best.

Fun stuff .

[Dockhead]

Originally Posted by weavis

You dont want to know what Dyneema costs in Spain.........

Or Finland. Or Sweden.

I have my cordage shipped from the UK, or lately, buy it on EBay. I just bought a new mainsheet -- 43 meters of 12mm racing dyneema -- for less than 100 quid. Reel end from a private party.

There is hardly a fathom of polyester cordage left on my boat.

[Perna]

Originally Posted by Perna

I'm missing something here. How can the strength of a soft shackle be 170-230% of the tensile strength of the line?

Firstly what would be the point? and secondly how do you prove it? By definition the rope has long since broken.

Thanks in advance for an explanation.

Ah, I thought we were talking about a shackle on the end of a single length of rope. Obviously with one bit of rope it doesn't matter if the shackle is 170 or 200% of the strength of the rope and I can hardly prove it with the single loaded rope anyway.