Anchor weights and connectors

[KellysEye]

>in well over 20 years of cruising, including full time for the past four years, seized an anchor shackle, nor seen the need.

I have to say I think you were lucky, we've seen three boats on the rocks after their shackles came undone.

Out of interest somebody mentioned stainless steel chain. There was a report down here a week or so ago of a boat that was anchored with stainless for seven months, the chain corroded and broke. I assume I'm right in thinking that the stainless used for chain is just normal (above water) marine grade not the stuff used by oil rigs underwater. Does anybody know anything about this or heard of any incidents?

 

[saltwater_gypsy]

Re: Stainless steel chain.
In the March YM p84 there is an interesting article on the subject where the owner of a HR53 found that his 1/2 inch chain was corroding badly at the welds. Nigel Calder comments that the specification of stainless chain may now be nearer the minimum specification than in the past due to "improved"manufacturing techniques.
The basic problem seems to be that Regular steel chain is forged whereas Stainless chain has welds at each link.The welding can locally change the composition and this leads to corrosion.
The grades of "Stainless "steel seem to be:
304 or 18-8, for nuts and bolts and topsides bits.
316 or 316L for more severe applications.
317L for very corrosive environments.
In each case, the welds are the problem area but 316L is the minimum recommended for anchor chain..

 

[vyv_cox]

The difference is in the 'L'! L stands for 'low', as in the carbon content. Any 300 series stainless that is to be welded should be an L grade, such as 304L, 316L. The problem is that the carbon combines with the chromium in the heat affected zone to form chromium carbide. This leaves surrounding areas of steel low in chromium, enabling it to corrode. The best grades of weldable 300 series steel also contain small amounts of some preferential carbide formers, such as titanium, to further protect the chromium.

The weld filler also needs careful choice, to ensure that it has low carbon and also that it does not corrode preferentially due to galvanic effects.

So far as the YM article is concerned, I didn't entirely agree with Nigel Calder's analysis. I thought the chain was just incredibly badly made, all the link joints seemed to have very poor penetration, leaving it wide open to corrosive attack. The description and photos of the failed areas were much more suggestive of poor penetration than of materials problems.

 

[vyv_cox]

I certainly wouldn't do up my anchor shackles at the beginning of the season and expect them to be just the same at the end. I do them up tight, using a decent tool, and check them periodically. With a countersunk Wichard shackle it is simply not possible to seize it. That doesn't alter the fact, IMO, that this is the best shackle to use for this application.

I have now begun to use Loctite since finding that it does not deteriorate under water.

 

[KellysEye]

>316 or 316L for more severe applications.

I'm no expert on this but I thought 316 was 'standard' marine stainless, certainly our pole holders are made of it. I thought there was a below salt water grade something like 321, which presumably should be use for chain but seemingly isn't?