HR shackles can explode

[NSboatman]

Following with interest. Check out this brand-name, brand new (!) snap shackle that gave way (completely) after 1 month of use. It was on the bottom of my running backs- admittedly much too small- but it was never used! It never saw more than 40-50 lbs of tension, and that was only to keep the running back from slapping in a breeze in its storage position. I was walking down the side deck and stumbled, reaching out to grab the soft tackle on the running back- and it broke suddenly in 3 pieces under that load!

The fracture mechanics seem to be very brittle in nature, and under a magnifying glass it is possible to see the beach marks and possibly the initiation point, which looks to have a slightly different colour. Perhaps a bit of corrosion around an inclusion or casting flaw.

Casting- that was a surprise to me. I thought these units were forged- hot worked. They certainly should be. This one though, is clearly a casting- and a poor one at that!

Whatever- it was horrifying to see on a brand new piece of allegedly quality hardware. The retailer gave me my money back- but that does not put one at ease with other gear made in the same way from the same manufacturer... which is all over my boat...

Freak occurrence? I doubt it. More like a statistical certainty at some point- fabrication mistakes will happen- but how the heck would a buyer be able to tell? I’m a frigging attentive Mech Eng with a metallurgist on staff, with whom I work very closely all the time- and yet I bought this, inspected it, and thankfully didn’t have to rely on it- but it still broke and would have been very inconvenient if it happened in anger.

Caveat emptor I suppose; and oversize your hardware! This I fully agree with.

Thoughts?

[a64pilot]

I’m surprised it’s cast too, and not forged, you sure it isn’t?
But I’ve said this over and over, Stainless isn’t that good a structural material.
I don’t know why you don’t see this kind of thing in Titanium, it’s really not that more expensive, not in truth.

[NSboatman]

Yeah A64- not really sure I suppose- haven’t done a proper forensic review. But if it was forged, it was a bloody poor job.

You can get some fittings like this in Ti, but I’m not sure changing the material helps that much- Ti is still susceptible to fatigue failure; particularly if poorly forged or manufactured...

[NSboatman]

Love Ti though- very cool material!

[Toccata]

A 1 year old Harken block "let go" on my boom vang under full load, engineered/designed for the job, BUT it failed.
Didn't find the pieces.
Thinking about it later, I realised that the fragments could have killed someone.
Lesson for me: Upsize those blocks and shackles that you consider to be within a danger zone of your crew. Weight saving is not worth a serious injury.

[Matt Johnson]

Just a suggested safety back-up that may work for the OP.

One option is to have a safety wire back-up for each high load block to help contain disaster if anyone were in the danger zone when a block or shackle were to explode. It's commonly done at the mast base by looping through the center of all the turning blocks and around the mast- if one of these blocks goes, the rest can then take the strain and keep anything in the crook safe- but you can do something similar for any block with a hollow core. For our high load sheet blocks, we loosely loop a dyneema soft shackle through the center of the hollow sheave (Garhauer) and back to the base (toerail) just incase something like what you had happens to us. It would be a nasty snatch load, but it should at least do some good.

Matt

[Rorzech]

Soft shackles, end of problem.

[NSboatman]

I do exactly this with my main sheet block on my boom as well. Gives me a little reassurance that a failure in the metal bits there won’t result in an uncontrolled boom...

[fxykty]

Originally Posted by Rorzech

Soft shackles, end of problem.

Not all connection points can take a soft shackle or lashings. You must have a rounded surface and no edges.

[fxykty]

Originally Posted by funjohnson

Just a suggested safety back-up that may work for the OP.

One option is to have a safety wire back-up for each high load block to help contain disaster if anyone were in the danger zone when a block or shackle were to explode. It's commonly done at the mast base by looping through the center of all the turning blocks and around the mast- if one of these blocks goes, the rest can then take the strain and keep anything in the crook safe- but you can do something similar for any block with a hollow core. For our high load sheet blocks, we loosely loop a dyneema soft shackle through the center of the hollow sheave (Garhauer) and back to the base (toerail) just incase something like what you had happens to us. It would be a nasty snatch load, but it should at least do some good.

Matt

Yes, that’s been suggested to me by a rigger for all shackles and/or blocks - add a soft shackle or equivalent lashings that exceeds the breaking strength of the metal parts.

However, don’t just loop through the centre of the block if it wasn’t designed for loops/lashings as it won’t have any strength there and you’ll destroy the block as it gets loaded there. Instead, lead the soft lashing through the base of the block where the pin is secured, that’s the strong part of the block. Refer to Harken website for why you should not soft shackle a block designed for a hard shackle and adjust your safety lashing to suit.

[Hesti]

About that Lewmar snap shackle - if you still have the pieces, you might want to send them to Lewmar. They just might be interested ... With it giving as it gave, it just smells a tiny bit of "copy" hardware.


And if you have more from the same source on the boat, you might want to consider replacing it all.

[Matt Johnson]

Originally Posted by fxykty

Yes, that’s been suggested to me by a rigger for all shackles and/or blocks - add a soft shackle or equivalent lashings that exceeds the breaking strength of the metal parts.

However, don’t just loop through the centre of the block if it wasn’t designed for loops/lashings as it won’t have any strength there and you’ll destroy the block as it gets loaded there. Instead, lead the soft lashing through the base of the block where the pin is secured, that’s the strong part of the block. Refer to Harken website for why you should not soft shackle a block designed for a hard shackle and adjust your safety lashing to suit.

If you've ever had the cheeks of a block go, you'll see the base of the block isn't much stronger than the shackle itself. The only way to retain all of the pieces of the block (cheeks, sheave, shackle and stem) is by looping through the sheave..... this isn't for normal loading, but for catastrophic failure.

Matt

[Dockhead]

Originally Posted by Hesti

About that Lewmar snap shackle - if you still have the pieces, you might want to send them to Lewmar. They just might be interested ... With it giving as it gave, it just smells a tiny bit of "copy" hardware.


And if you have more from the same source on the boat, you might want to consider replacing it all.

Dollars to doughnuts -- that shackle is a fake cast copy, not made by Lewmar.



You might save somone's life by calling attention to this and getting the rest of them off the shelves.

[Suricat46]

For parts considered as critical hardware (the failure of which may have serious consequences on human or boat safety) is it common practice to perform or have performed Non Destructive Testing (like Fluorescent Penetrent Inspection, Eddy Current Inspection...) during periodic checks or when a defect is suspected ?
Was this process any successful ?

[LongRange]

Originally Posted by Suricat46

For parts considered as critical hardware (the failure of which may have serious consequences on human or boat safety) is it common practice to perform or have performed Non Destructive Testing (like Fluorescent Penetrent Inspection, Eddy Current Inspection...) during periodic checks or when a defect is suspected ?
Was this process any successful ?

Would it not be considerably cheaper to buy a replacement, especially if time and effort are taken into account? At some point the equipment is sufficiently specialized and stratospherically expensive to warrant exotic testing, but I cannot imagine it would be appropriate for shackles?

No doubt the proximity of a lab that can reliably perform such work is also a big factor.

I'd be interested to hear more about your experience with that type of testing.