So how Strong are Soft Shackles?

[estarzinger]

Shackle 3:

4130lbs broke like the first one (one strand at the diamond . . .if we could get both strands truly evenly tensioned we could probably greatly increase the strength)

I will check the line strength tomorrow . . .but Samson's dacron line strengths were spot on so I trust the rated numbers.

[estarzinger]

By the way . . . Soft Shackles 'theoretical' max strength is 4x the line used, because they use two strands in a loop (so four strands between the two load points). The diamond knot then reduces the strength by 50-60%, so I end up at 170% of line strength.

[Jim Cate]

G'Day Evans,

Just wanted to say that I'm finding your efforts most interesting and educational! Thank you for sharing your information with us all... and I gotta say that you sound like a man having a really good time! I (along with a lot of others) await the next loud bang.

Cheers,

Jim

[estarzinger]

Jim,

Excellent. I am having some fun and learning somethings, and am very glad you are also! By the way, I am keeping a spreadsheet up-to-date on our website (on the 'load tests' tab) with full data from all my pulls.

I think of myself as modestly knowledgeable about cordage and knots and did not expect to be 'surprised' so frequently by the results. The fact that I am (being surprised and as a result learning new things) is making it much more fun.

I am slowing increasing my pull loads and am also learning things about the test bench. I found two parts today that I want to make a bit better/stronger before I go to the next level.

[Cotemar]

estarzinger,

This is very impressive and fun to follow along. Great pictures.

I have to ask though. Is your wife cool with you doing these pull test on the new carpet floor.

[Jim Cate]

Evans, how about testing one of the soft shackles that you have been using to attach your snubber... one that has had considerable usage? This would help to soothe the folks who have expressed doubt about the longevity of soft shackles in that application.

I reckon this will have to wait until you ramp up to much higher load levels, but it would be very interesting. An N of one isn't statistically sound, but still, should it survive to a near-new strength, it would inspire some confidence in the system.

Cheers,

Jim

[s/v Jedi]

I am awaiting the YouTube videos in the style of MainSail's testing of through-hull fittings and seacocks

[thinwater]

Is it possible the position of the knot/loop relative to the shackle matters? If the junction straddles the shackle, for example? Bound to happen, with all the flogging.

[Randy]

I haven't scanned this entire thread but have y'all checked out: L-36.com soft shackle testing?

[estarzinger]

Originally Posted by Cotemar

I have to ask thought. Is your wife cool with you doing these pull test on the new carpet floor.

Beth's a very cool girl, just happy that I am having fun!

Originally Posted by Jim Cate

Evans, how about testing one of the soft shackles that you have been using to attach your snubber... one that has had considerable usage? This would help to soothe the folks who have expressed doubt about the longevity of soft shackles in that application.

I reckon this will have to wait until you ramp up to much higher load levels, but it would be very interesting. An N of one isn't statistically sound, but still, should it survive to a near-new strength, it would inspire some confidence in the system.

Can do, but you are right that will be another test level I am not quite ready for. If my 1/8" test scales up . . . My 1/4" soft shackle will break at 15,000lbs! (Bolding this because it is directly on thread)

Originally Posted by thinwater

Is it possible the position of the knot/loop relative to the shackle matters? If the junction straddles the shackle,....

I am told that it may make a difference. I am planning to do a "bend radius" series of tests, and will include that.

Originally Posted by Randy

I haven't scanned this entire thread but have y'all checked out: L-36.com soft shackle testing?

Yes, he and his website are terrific, he and I have and are discussing my tests. We are trying to understand why mine test higher than his did (when he sent them to NER).

[Cotemar]

estarzinger,

What is the limit of your test bench and load cell?

[estarzinger]

The rams can pull 10tons.

The load cell is calibrated to 5tons, but I can put a 2:1 tackle on it to measure to 10tons.

I don't know about the bench itself. I have pulled 2.5 tons and there is very slight deflection in the main beam. I suspect it can go to 5tons as it is now but that it will definitely need some reinforcing (easy to do) to handle 10tons.

[nigel1]

Thanks for the efforts made in testing the shackles.
As to the actual breaking strength, I thought it would be close to double the single line strength. Although most of the shackle consists of a single line doubled up, and twice that when formed into a strop/shackle, the eye and the two legs before the knot are still single, which makes them the two weak points, especially the legs at the knot where it would be difficult to exactly share the load.

[nigel1]

Just thought this through again, as Evans said, in theory, the shackle will have 4 times the BL of a single part.
Pretty impressive figures anyway, I used 10mm 12 strand for the clew strop. Based on these test figures that should be good for close to 20 tonnes.'
Are there any figures for when deformation will occur.
I'm mainly using large wires at work, up to 90mm diameter. We work on trying to avoid going over one third of the BL of the wire. In theory, the wire starts to deform at 50% of its BL, when it no longer recovers it form.
Limiting the working load to one third of the BL allows for snatch loads over this limit, but should be below the 50% limit.

[JonJo]

Nigel,

From what are the wires made?

I'm completely ignorant - I had always thought wire was used to a 4:1 safety factor.

Jonathan