What size anchor shackle?

[MissFitz]

Just bought new 6mm chain to replace rotten 8mm chain on our Centaur, but not sure how to shackle it to the anchor. A 6mm shackle is definitely too small, but 8mm won't go through the chain.

Should we a) put the pin part of the shackle through the chain; b) attach an 8mm shackle to a 6mm shackle to the chain; or c) do something else?

All help much appreciated.

 

[lw395]

Options are:
6mm hightensile shackle.
Squeeze the last link of the chain lengthwise in a big vice so 8mm goes through. Maybe hammer a taper such as a centre punch into it to re-shape the link a little.
Is the 6mm shackle too small for the anchor?
The risk in using two shackles is obviously two chances of coming undone, so ensure the shackles are secure. Either mouse the pins well or fix them by other means. Sometimes I replace the shackle pin with a bolt, with an extra nyloc locknut on the end, all torqued up with loctite. Better than having mousing wire around when you have to handle the anchor IMHO.

 

[LORDNELSON]

Look at the web page of Jimmy Green; they sell tested shackles with advice on which shackle to purchase for each chain size.

 

[Poignard]

Not much help now you have bought the chain but if you buy chain from the manufacturers, Griff Chains Ltd, they will fit enlarged links at the end of the chain, if requested. Then you can use a proper size shackle.

Maybe you could get a skilled blacksmith to fit one to your new chain, but it wouldn't be galvanised.

 

[Eygthene]

Option A. Put the shackle itself through the eye on the anchor and the 8mm shackle pin through the 6mm chain. You don't want to use a 6mm shackle because that would be the weakest link.

When you have tightened it up with a spanner, mouse it with wire and tuck the ends of the twisted wire inside the shackle so as to reduce the risk of catching your hand when handling the anchor.

 

[machurley22]

Another vote for tested 6mm shackles. These get part of their strength from a larger pin which will be a snug fit in your 6mm chain and a SWL of 0.5T will be very similar to the chain.

 

[Refueler]

With due respect - the weakest link (!) is not the shackle really but the chain itself usually. So best 6mm shackle you can get in SAME material as anchor and chain - I assume galvanized. You may find it prudent to change the shackle more often than a 8mm would be.

You could always get one of those anchor 'links' that look like a torpedo and are actually two halves that screw together with Allen Key bolts as the end pins ... very smart and strong.

Final comment - if you are anchoring such that you are going to break a shackle .... then I suggest you shouldn't be anchored ? The strain on bow fittings etc. would be to me unnacceptable.

 

[machurley22]

BTW I've just done this with new 6mm chain and a new anchor (a Raya, but no-one should feel they need comment /forums/images/graemlins/smile.gif ) and used two tested 6mm D shackles with pins through anchor and chain. I bought bow shackles as well to see how they would work but liked the snug fit of the D's.

 

[doug748]

Well,
This year I solved this problem to my entire satisfaction. I have never trusted those anchor thingies.
I put a beefy ( just a size up, so as not to foul the bow roller) shackle on the anchor. I attached this to the chain with another shackle, of a pin size that would just go through the last link.
I bought the type that has no "ear" or hole for mousing, so there is nothing to catch in the bow roller. It articulates nicely and so comes aboard like a rat up a drainpipe.
This type of anchor shackle is designed to be peined over in order to secure it: ie tighten up hard with a screwdriver and then attend to the end of the screw with the ball end of an engineers hammer. This must be reacted against a solid block of metal or maybe a heavy vice.
Done with gusto this is 100% reliable.
I can now sleep tight, whatever else happens I know those pins will not come out.

 

[James_Calvert]

A bit off topic, but why did you go down a chain size? Friends I knew with a Pembroke (a fin keel Centaur) went the other way - to improve anchor holding.

 

[machurley22]

Crikey - that's torn it! Several gentlemen will be along shortly to show you the error of your friends' ways. /forums/images/graemlins/grin.gif

 

[James_Calvert]

No, no, noooooh. I didn't say anything about anchors - did I?

 

[machurley22]

I'm very much afraid that you did and specifically, you suggested that increasing chain weight improves anchor holding which, as everyone knows... well, I've said more than enough on this thread already.

 

[James_Calvert]

Shh (maybe they won't notice).

 

[craigsmith]

[ QUOTE ]
Just bought new 6mm chain to replace rotten 8mm chain on our Centaur, but not sure how to shackle it to the anchor. A 6mm shackle is definitely too small, but 8mm won't go through the chain.

Should we a) put the pin part of the shackle through the chain; b) attach an 8mm shackle to a 6mm shackle to the chain; or c) do something else?

All help much appreciated.

[/ QUOTE ]
The pin should go through the chain, and ideally the shackle body through the anchor. A sensible anchor design accepts the body of the shackle - otherwise you will have to use two shackles, not an elegant solution and doubling the chance of shackle failure.

The shackle should in general be sized by choosing the largest, the pin of which will fit the end link of the chain. For 6mm chain, you'll want an 8mm pin, which usually corresponds to a 7mm body on a high-load shackle.

Choose a good quality shackle, they are a common failure point but are not expensive even for the best, so there's no excuse to scrimp.

On the chain size, good that you will be saving a bit of weight by down-sizing. There will be little detriment to the anchor's performance. I trust you have ensured that strength requirements are maintained by whatever you are using.

More on shackles: www.rocna.com/kb/Shackles

And on chain, why not: www.rocna.com/kb/Chain

 

[Refueler]

[ QUOTE ]
Options are:
6mm hightensile shackle.
Squeeze the last link of the chain lengthwise in a big vice so 8mm goes through. Maybe hammer a taper such as a centre punch into it to re-shape the link a little.
Is the 6mm shackle too small for the anchor?
The risk in using two shackles is obviously two chances of coming undone, so ensure the shackles are secure. Either mouse the pins well or fix them by other means. Sometimes I replace the shackle pin with a bolt, with an extra nyloc locknut on the end, all torqued up with loctite. Better than having mousing wire around when you have to handle the anchor IMHO.

[/ QUOTE ]

I have to comment that I personally would not advise any physical deformation of a chain link - this can only create a weakness. If it was properly done by a blacksmith and then re-galvanized after - maybe.

 

[Poignard]

[ QUOTE ]
The shackle should in general be sized by choosing the largest, the pin of which will fit the end link of the chain. For 6mm chain, you'll want an 8mm pin, which usually corresponds to a 7mm body on a high-load shackle.

[/ QUOTE ]

Will the shackle be as strong as the chain?

 

[craigsmith]

That obviously depends on the shackle and the chain. A good quality high-load shackle should give equivalent WLLs, even with higher grade chains, yes.

 

[doug748]

"not an elegant solution and doubling the chance of shackle failure."

Nope, I think A tres elegant solution. The second shackle leads the anchor nicely onto the bow roller hands free. You should try it

Looking at the big game, it rather depends on the assuptions you make. But adding good shackles (properly banged up as described) will not add to the overall chance of failure. Just as, as....well adding links to an anchor chain.

 

[LORDNELSON]

What is their error? Surely as you increase the size of chain the holding will improve. If you increase it enough you have no need of the anchor and thus the problem described at the beginning of this thread disappears!