HR shackle explodes

[fxykty]

Five years ago we had an HR block and a matching block on our running backstays explode during heavy conditions. Last week we had another HR shackle explode. This time during upwind sailing in short seas - this one was on one of our mainsheet blocks. A very loud bang and the mainsail goes slack. First look was up at the rig and the sail, then with relief saw it was just the block failure.

The take aways are that HR steel is brittle and does not deal gracefully with shock loads above working loads.

[pcmm]

Who is "HR"? Sounds like an "unknown" brand to me

[ozolli]

Originally Posted by pcmm

Who is "HR"? Sounds like an "unknown" brand to me

HR stands for High Resistance (stainless steel). It's in fact 17-4Ph stainless steel or 1.4542.
HR has been in use by Wichard for their shackles.

[GordMay]

Originally Posted by pcmm

Who is "HR"? Sounds like an "unknown" brand to me

High-Resistance (“HR”) shackles are forged in either, marine grade High Resistance ‘17-4PH’ stainless steel, or (sometimes) ‘TA6V’ Titanium.

Both Harken, and Wichard, at least, offer “HR” shackles.
Wichard claims that their HR shackle can be up to 60% more resistant than a shackle in 316L stainless steel.

AISI 316 Stainless Steel vs. S17400 (‘HR’, 17-4PH) Stainless Steel
➥ https://www.makeitfrom.com/compare/A...tainless-Steel


I see ozolli beat me to it.

[pcmm]

So I guess the question remains, who's shackle here failed? The OP used "HR" like it was a brand not a specification... and what size shackle was it on what size boat under what load?

[thinwater]

The threads are not stripped or have the matching part attached. There is no evidence of mousing wire (SS wire could have failed, particularly if over-twisted during installation). Mousing requires regular inspection.



Are you sure this did not just come unthreaded? This is not actually a gear failure. I've tested these to failure, and this is not what a strength or fatigue failure looks like IMO. I've also seen unthreaded failures, and they look like this.

[Mal Reynolds]

I've had an HR shackle blow up when going upwind in 10 knots. Upon inspection it was obviously crevice corrosion. Maybe it's related to oxygen deprivation where metal meets metal.

Yours does look different though. Maybe you just had a defective part.

I replaced mine with another HR shackle for simplicity, but learned to keep an eye on it.

[Tin Tin]

How old was the shackle?

[JPA Cate]

fxykty: your boat can put huge loads on such a shackle, so maybe thinwater's got a point: If it wasn't moused, how can you assume the screw just didn't back out?

Thinwater's done a lot of product testing, and when he says that's not what the shackle would look like, I tend to believe that. We also have broken a main sheet shackle for one of the blocks, but the shackle had distorted considerably prior to failure.

I think you'd be okay to replace like with like, and mouse it, even if you have to drill your own hole in the shackle pin to do it.

Ann

[Breaking Waves]

I dont know enough about the details of this specific breakage to comment . . . but

#1 I do think it is pretty clear that big-ish, high-ish performance, cruising multihulls, sailed hard, put higher dynamic peak loads on their gear than many in the industry who spec that gear think it will be. Especially on gear taking load paths from the masthead. I have three friends who blow stuff up that the industry swore was strong enough.

#2 steel shackles are very 'last year' - should really all be dyneema attachments. But ofc then need different blocks. But dyneema lighter, no fatigue issues, strength can be added as necessary - easy DIY upgrade/replacement.

[fxykty]

Hmm, possible the shackle came undone as the two mainsheet block shackles are moused with zip ties, not wire. They are regularly inspected as they’re ’right there’. But the threads aren’t distorted so coming undone is likely the cause of the shackle overloading. Sigh.

Note that HR shackles don’t deform - they just blow apart. It’s a function of their material properties.

The brand is Harken. 20 year old 8mm shackle on the pin of 75mm 2,500 kg working load Black Magic Air Block. Replaced with a spare 8mm HR shackle. We are gradually replacing all the 75mm blocks and metal hardware on the boat with soft shackles and low friction rings, but in this case it would mean replacing blocks that otherwise work well. LFRs wouldn’t work in this application and equivalent soft loop blocks cost half a USD boat buck each.

[donradcliffe]

Looks like plain old fatigue to me. Had two shackles on my 4 part Lewmar vang let go after taking me halfway round the world. Similar load rating.

[Tupaia]

How are your mainsheet blocks attached to your boom?

Rigid fixings often result in shackles unthreading or breaking whereas flexible attachments, strops or dyneema loops are more able to accommodate shock loads.


For information if mousing with zip ties black ones are far more UV resistant than white or natural coloured ties.

[fxykty]

Originally Posted by Tupaia

How are your mainsheet blocks attached to your boom?

Rigid fixings often result in shackles unthreading or breaking whereas flexible attachments, strops or dyneema loops are more able to accommodate shock loads.


For information if mousing with zip ties black ones are far more UV resistant than white or natural coloured ties.

When we got the boat the blocks were shackled directly to stainless steel bales locked into a track on the underside of the boom. When fully sheeted the boom is nearly 1.7m above the traveller. So we removed the two boom bales with Dyneema strops that go over the boom and come down about 1.1m below the boom. The shackles are shackled through eyes in their respective strops.

And duh, we use black zip ties outside.

It’s night time, so the picture isn’t super clear, sorry. The mainsheet goes from the winch through a block on the traveler and up, around a block shackled to one Dyneema strop, down to the middle block on the traveler, up and around a second block shackled to the other strop, and down through the third traveller block and to a winch on the other side of the cockpit.

[mikereed100]

40 years ago my boat ended up on the beach when the large zip tie I used to mouse the mooring shackle failed in calm conditions and the shackle pin unscrewed itself. Since then I have always used s/s wire and never had a failure. I suspect that not only are nylon wire ties subject to chafe and UV, but that the torque on the pin can overcome the grip of the tie's "clamp".