'galvanised' shackles?

[snowleopard]

\'galvanised\' shackles?

what do they coat so-called galvanised shackles with? i have 2 attached to my anchor which rapidly turned to lumps of rust while the anchor and chain are still a nice shade of grey. is it that the coating is very thin or are they really just plated with something like cadmium?

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[vyv_cox]

Re: \'galvanised\' shackles?

There's galvanising, and then there's galvanising. All use zinc. I doubt if you can buy anything cadmium plated now, it's a nasty poison and its use has been banned for some years. Chains and anchors are usually hot dipped, i.e. in molten zinc, and this is by far the best way to do it. A step down from this is carried out with regular shaped items, like sheet and wire, which is that most of the zinc is wiped off again. Better than the steel item but won't last for ever.

Next down is probably sherardising, which I guess is how some shackles are done. In this process the item to be coated is put in a box with a load of zinc scrap and carbon and heated up. The zinc coats the steel parts, more or less. The same process is used with other metals, like aluminium, copper, etc. Some shackles are hot dipped, though and you can sometimes see the grain structure in the coating to prove it

Even further down there's a range of spraying and plating processes. None of these establishes particularly good adhesion. Good enough for land-based duties but not good in seawater.

I use stainless shackles to connect my anchor to chain. Not a lot more expensive and saves a lot of mess.

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[yoda]

Re: \'galvanised\' shackles?

You will probably find that only good quality tested galvanised shackles will not rust quickly. To be honest these are nearly as expensive as stainless ones. Tested shackles are made in a different way to non-tested ones and as a result you will find that for the same sized shackle the pin is larger in diameter. I buy my stainless shackles from the local nut and bolt shop in Plymouth (Underwoods) who are substantially cheaper than the candlery. Have now stopped useing galvanised.

Yoda

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[VicS]

Re: \'galvanised\' shackles?

Either you spend a lot of time at anchor or they were very poor quality. My anchor has had the same shackle on it for over 20 years.

They dont last long underwater on a mooring I would agree.

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[Guest]

Re: \'galvanised\' shackles?

most likely that the shackles you buy are made in somewhere like Taiwan or India, and certainly they will not be galvanised to the appropriate BS.

agree with viv - use stainless as long as they are in moving oxygenated water ie not buried in mud. in deep mud, even the lack of galve doesnt usually matter too much since there is little oxygen to allow rusting.

oh - and make sure they're over thick. one of the best defences against corrosion is having lots of metal to corrode.

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[mickshep]

Re: \'galvanised\' shackles?

On my old 5 tonner, the rigging is 6mm stainless, but the chainplates are solid bronze, couldn't get more than 3 years before even good galv shackles became rusted solid, assume combination of different metals to blame, would stainless last in contact with good bronze? Have sold her now but interested anyway.

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[snowleopard]

Re: \'galvanised\' shackles?

i've always found in the past that stainless in contact with galv. results in the galvanising vanishing very rapidly through electrolysis. reluctant to risk my anchor and chain that way. i spent over 6 months at anchor in warm water last year.

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[LadyInBed]

Re: \'galvanised\' shackles?

As the equiv stainless shackle is a much smaller diameter would sleaveing it work?

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[yoda]

Re: \'galvanised\' shackles?

In that case try tested shackles which I find last considerably longer. You will probably get them at local plant equipment sales places that sell lifting equipment.

Yoda

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[charles_reed]

Re: \'galvanised\' shackles?

What you're commenting on is probably the difference btween hot-dipped and elctro-galvanising.
The shackle manufacturers are in a catch-22 situation, if they put a nice thick coating of zinc on the shackle, the thread is blocked.
I've given up on galvanised shackles and always now use SS (except on moorings).

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[sparkie]

Re: \'galvanised\' shackles?

Charles-

Why would you not use S/S shackles for mooring? I am in the process of changing all my galv thimbles and shacks for S/S as I'm fed up with them corroding away after approx two seasons. My moorings are in sand incidentally, and just about dry out at lowest tides. Am I wasting my time and money??

Sparkie


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[Guest]

Re: \'galvanised\' shackles?

in my experience, the best thimbles are the plastic ones. wouldnt partic recommend stainless since part of the thimble (the inside of the curved surface) will be in stagnant water

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[vyv_cox]

Re: \'galvanised\' shackles?

Here's my answer, Charles may have his own.

S/S along with many other alloys that rely on a passivated layer for corrosion protection, is extremely prone to crevice corrosion. One of the best crevices that can be imagined is a cut thread on a nut or bolt. So threaded parts in seawater are likely to corrode through whilst the remainder of the shackle is in perfect condition.

This is also the basis of the accusation that stainless steel tarnishes and is not "stainless". What you are seeing is crevice corrosion on a micro scale, at tiny cracks and laps, very common in hard drawn wires.

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[oldsalt]

Re: \'galvanised\' shackles?

For moorings you should never use galvanised shackles as they corrode very quickly. Stainless will also corrode and set up an electro difference with the chain. I always use "black metal" shackles from an agricultural dealer, they are safer and cheaper.

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[Guest]

Re: \'galvanised\' shackles?

Vyv, you're spot on. Many people do not understand the passivation of s/s, let alone what to do about it. Once the surface is no longer passive, it will show rusting quite quickly despite frequent cleaning. Boarding ladders are notorious - look fine for several years, then suddenly can't get through a season without rust stains. The more you clean, the worse it gets.

For a more detailed technical explanation on s/s corrosion see:

http://www.westmarine.com/webapp/wcs/stores/servlet/WestAdvisorDisplayView?advisor=788.htm

To my knowledge Wichinox is the only phosphate-containing s/s cleaner (which will re-passivate s/s) suitable for yachtie use, and it is hard to find. I had to get my chandler to order it through Pro-Boat Marine, the Wichard UK agent. They do not sell direct.

A more general comment - I find the West Marine Advisor an excellent source of yachting information that is for the most part objective and non-commercial. The full list of subjects covered can be found on:

http://www.westmarine.com/webapp/wcs/stores/servlet/WestAdvisorListView

A quick look at this site would answer many of the legitimate questions raised in this forum. A hard copy of the West Advisor is available free as part of the comprehensive West Marine catalog. BTW, I have no connection to West or any other supplier.

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