Which way round should the shackle be?

[noelex 77]

Originally Posted by JonJo

A circus performer who falls and loads his 3/8th inch WLL 2t HT alloy shackle to its breaking point (of between 10t and 12t) will cut his body in half or certainly break his back.

I would imagine most of the shackles a circus uses are part of rigging that secures equipment rather than a single individual.

Industries like this (lifting etc) have already developed techniques and equipment based on sound engineering. Their standards are, understandably, higher than ours, but they do provide some guidelines to point us towards best practice.

Sailors are already using shackles like the Crosby 209A which have been developed primarily as lifting shackles not anchoring equipment.

[Andrew Troup]

Originally Posted by JonJo

A circus performer who falls and loads his 3/8th inch WLL 2t HT alloy shackle to its breaking point (of between 10t and 12t) will cut his body in half or certainly break his back.

I seriously doubt they ever become close to even WLL. Even a 1/4 inch HT alloy shackle has a WLL of 0.5t (and will still break his back if he gets near it).

I find it difficult to see the relevance as they will never approach the WLL. Their practice might be right but unless they have elasticity in the system they are a dying breed.

Jonathan

JonJo

The WLL is not a useful indication of the breaking point of a shackle used to arrest a falling load.

And this is NOT because of different ways WLL can be defined:
it's intrinsic to the fact that WLL is a STATIC measure of strength.

It would be easy to find two commercial shackles where one had half the static strength (or WLL) but twice the capacity to arrest a falling load.

Shackles (like anchor chains) do not break when their load limit is exceeded.

They break when their energy limit is exceeded.

I hope to post a convincing explanation soon on the BiB2 thread.
Work (the curse of the cruising class) keeps intervening.

[sabray]

I quit. I stick the friggin pin through the chain. Crosby7/16 shackle 3/8 chain. Rates pretty good. If it breaks u should have gotten the hell out of there. Use a snubber. Digging the soft shackle to chain with nylon and then short dyneema. Not that my old chain hook really failed. That's where I improved balance of load. Good snubber and reduced chafe.


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[JonJo]

If the Circuses are using them as lifting shackles then their demands are no more special than anyone using the same kit for lifting. It does not matter if you are lifting circus gear or steel - the same rules apply.

Ours are used in a dynamic situation, as Andrew promises to explain, and therefore the applicability of the Circus needs (or anyone lifting) are different to ours.

Jonathan

[JonJo]

I think if you want ideas on how to centre the chain on a shackle you can usefully look at this thread.

Pros & Cons of Dee shackles vs Bow Shackles - Page 2

Jonathan

[Andrew Troup]

OK; I've posted the clinching portion of my explanation of why I make the claim

<<Anchor chains do not break when their load limit is exceeded.

They break when their energy limit is exceeded.>>

It's up now on the "Bigger is Better, part 2" thread.

[boatman61]

I'm sure there'll be a book written on this subject soon..

[Andrew Troup]

Originally Posted by JonJo

I think if you want ideas on how to centre the chain on a shackle you can usefully look at this thread.

Pros & Cons of Dee shackles vs Bow Shackles - Page 2

Jonathan

Thanks for that, Jonathan.

Here's an idea, building on that classy cone idea JonJo linked to, for securing a shackle with a countersunk-headed pin so it will NOT unscrew, until (if you're lucky) you want it to:

Make the cones with a sufficient 'land' at the small end (axial face) to butt up against each other and resist the shackle ears being squeezed together

Make their length so they only just assemble into the shackle.

Use high strength retaining compound Loctite, not just on the threads but in the countersunk hole and the mating face of the pin (countersunk screws, snugged up against an immovable face, are NOTORIOUSLY unwilling to unscrew again, even without Loctite)

To disassemble, first heat the Loctited parts with a hot air gun (to at least 165C, 330F)

Holding the body in a smooth-jawed vice (or a vice with protectors) try loosening the pin. It will probably still be immovable.

Now for the old toolmaker's trick, handed down for generations:

Take a short pin punch, the largest size which will fit in the hex recess for the allen key. Support the underside of the ears (on the same side of the shackle as the head of the pin) on something heavy and metal (storm anchor, vice jaws) and use your biggest hammer to firmly thump the pin punch end-on, smacking the countersink against the mating face.

A few decent thumps should do the trick. If not, get the grinder out with one of those 1mm thick cutting disks, and cut through the shackle legs in two places. You can always weld them back together later (just kidding)

[noelex 77]

Originally Posted by boatman61

I'm sure there'll be a book written on this subject soon..

I will wait for the movie