Failure of 316 D Shackle

[GaryC]

Really just trying to see if anyone had seen this before. After a few years the webbing on the winch on the trailer wore through so I replaced the hook with a new set up. This was about 2 years ago.

I used the hook that came with a car towing lead. About 3 metres and about 2 tonnes. I then connected the webbing to a D shackle with a clove hitch and 2 round turns. The webbing ended up on the round part of the D shackle. The D shackle then through the towing hook eye. This saw a season of use without any (observable) problems.

Last weekend had the RIB out and when I was about to attach the hook to the RIB I realised that the D shackle had failed and had come apart just under the webbing knot.

I am quite surprised at this as the D shackle should be rated to approx 6 tonnes. I fact I have a feeling that it has been pulling the RIB out whilst broken as it is now slightly deformed.

Is there anything that may have caused this failure that I have missed?

Thanks

Gary

[BogMonster]

How big is the shackle? (pin size)

It's probably just down to a crap shackle, better to replace with galvanised tested/stamped one IMHO. I've never seen one snap like that though!

[Erin]

I'm no metalurgist, but that doesn't look like a clean break. The metal looks very jagged, almost crystaline. I wonder if it was a bad casting.

[Brian]

If I understand this properly..............could it be the metal of the tow hook that wore away/deformed the shackle..........or have I got it wrong again?
Failing that could it be a "Chinese" shackle, by which I mean a v. cheap one?

[GaryC]

Originally Posted by Brian

If I understand this properly..............could it be the metal of the tow hook that wore away/deformed the shackle..........or have I got it wrong again?
Failing that could it be a "Chinese" shackle, by which I mean a v. cheap one?

The failure was under the webbing knot. The hook ended up at the pin end. This was an 8mm thick shackle with a opening of about an inch.

I suspect it was faulty but wondered if anything else could have caused it.

[captnjack]

Since this is the second failure of the winch strap seems like there's quite a load on it, I'm guessing bigger than you imagine. I would upsize the whole lot. (I also think it was a crap casting but not that bad since it did work for a year)

[Nasher]

I agree it looks like a crap shackle as the fracture looks very brittle and as if it all happened at one time rather than any deformation part way across before the brittle failure.

It certainly doesn't look like your method of securing it caused any harm, for example corrosion by trapped salt water under the knot around it.

Nasher

[m chappelow]

looks like a poor quality shackle to me ,normally the better ones will bend a bit before they do that , i suppose a lot depends on the quality of the metal and how it was made ,,forged or cast ,eg,

how about some form of galvanic action perhaps from somewhere on the trailer .

[Searider]

Crevice corrosion?

Stress corrosion cracking?

Stainless steel kept wet in still water (ie not flowing) will corrode very quickly due to depletion of oxygen.

SS requires oxygen to maintain the shiny oxide flim to prevent corrosion.

You might be better with a galvanised one if its going to be under webbing.

[Rogue Wave]

whats the test number of the shaclke

[Pikey Dave]

I doubt very much that an 8mm shackle would take 6tonnes. Unless ANY form of lifting gear is marked with its SWL(Safe Working Load)& accompanied by a current test cert. Then for all intents & purposes it's junk, you pays your money & takes your chance

[chewy]

Originally Posted by Rogue Wave

whats the test number of the shaclke

316 can you not see it.........

[Bigmuz7]

Dont know what the number refers to .. but the break doesnt look right for an overloading fail

and it doesnt look like a 6 tonne shackle either !




Can you post a pic of the bits ligned up so we can get a better idea of the way it failed ?

[BogMonster]

Originally Posted by Pikey Dave

I doubt very much that an 8mm shackle would take 6tonnes. Unless ANY form of lifting gear is marked with its SWL(Safe Working Load)& accompanied by a current test cert. Then for all intents & purposes it's junk, you pays your money & takes your chance

I doubt it as well. The stamped tested galvanised shackles we sell at work for 4x4 recovery are I think 3/4in pin size for 4.75 ton rating (though I think that is a lifting rating so actual breaking strength is much higher).

Looking around on google an 8mm s/s shackle might be rated at half a ton if you are lucky ... breaking strains around 2500kg seem to be quoted and lifting ratings are usually min 5x safety factor.

[m chappelow]

could the shackle have been used without the pin at sometime or perhaps been unscrewed or come undone then been put under load and not been noticed ,
looks to me like the number will be 316 kgs

[Rogue Wave]

Chewy is wrong!

Originally Posted by chewy

316 can you not see it.........

Stupid me and all this time I thought 316 was a type of Stainless (A4?)

My point being is if the shackle was a proper one and had been load tested then it would have a test number stamped on it and there should be some comeback. If I remember correctly then Stainless doesn't have the load capacity of ordinary steel so it looks very small to me also.

Pikey Stu is in total agreement with Pikey Dave

[m chappelow]

perhaps the shackle dident have an even staight pull on it ,even more so if it was wrapped webbing strap,,eg crown to pin and it was loading sideways or at an angle that would lower the load limit ,if it had been pulling on an angle the shackle could have been springing back and forth on its self over time causing it to crack /fracture especially if the pin was not nipped up .

[Poly]

Originally Posted by Rogue Wave

Chewy is wrong!




Stupid me and all this time I thought 316 was a type of Stainless (A4?)

My point being is if the shackle was a proper one and had been load tested then it would have a test number stamped on it and there should be some comeback. If I remember correctly then Stainless doesn't have the load capacity of ordinary steel so it looks very small to me also.

Pikey Stu is in total agreement with Pikey Dave

Stu - are you suggesting that every shackle the leisure boater uses should be tested and certified? This shackle was being used in place of a hook on a trailer winch - not for some lifting operation. The original hook was probably not individually certified, nor I suspect will the bow eye it was connected to.

The OP doesn't seem to be looking for "comeback" he seems to be saying "wow this looked like the beefiest bit of my set up - its surprising that this was the point that failed - can anyone explain it? or suggest what I can do (within a sensible budget) to avoid its replacement going the same way"

[BogMonster]

Originally Posted by m chappelow

perhaps the shackle dident have an even staight pull on it ,even more so if it was wrapped webbing strap,,eg crown to pin and it was loading sideways or at an angle that would lower the load limit ,if it had been pulling on an angle the shackle could have been springing back and forth on its self over time causing it to crack /fracture especially if the pin was not nipped up .

that's probably a plausible explanation - SS is quite hard so I think it would suffer from fatigue failure if there was any flexing - shackles under load often don't sit straight unless the load on the pin is a flat strap so when a rope is pulling on it (or a bow eye...) it will probably sit slightly cock eyed

[Bigmuz7]

Well the leg that has snapped is the 'loose' side certainly, as opposed to the threaded side as it would appear in the pic