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Old 03 September 2010, 12:47   #1
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Failure of 316 D Shackle

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
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Old 03 September 2010, 12:55   #2
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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!
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Old 03 September 2010, 12:57   #3
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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.
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Old 04 September 2010, 09:47   #4
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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?
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Old 04 September 2010, 14:21   #5
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Quote:
Originally Posted by Brian View Post
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.
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Old 04 September 2010, 14:49   #6
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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)
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Old 04 September 2010, 16:16   #7
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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
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Old 05 September 2010, 16:35   #8
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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 .
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Old 07 September 2010, 10:15   #9
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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.
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Old 09 September 2010, 17:18   #10
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whats the test number of the shaclke
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