anchor chain and a bow shackle ?

sarabande

sarabande

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A small question over a bow shackle connecting my 8mm chain and the anchor, so some advice please.


The pin of the shackle fits neatly into the anchor shank and the load is taken across the width of the pin to the lugs. However at the chain, the 'clear' of the shackle only touches the chain over a small area of the link and the shackle.

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Now, that shackle is described as a 6mm shackle so it is possibly undersize, but the principle stands: does the (relatively) large radius of the bow mean that the shackle touches the chain with a small area of contact - perhaps a point even - and thus possibly cause a high loading point and a possible deformation initiator ?

How best to resolve joining 8mm chain to the 12mm dia of the anchor shank ? Possibly a Delta "Maillon Rapide" ?

http://www.peguet.fr/self-certified-maillon-rapide-quick-links/delta-maillon-rapide
 
It would be interesting to see the end of the shank.

I get the impression that the anchor shank has a circular hole, not a slot. Consequently you can only fit the clevis pin into the hole in the shank. This is not a common design and is limited to CQRs, Manson Rays, Guardians (and I guess a few others). Most anchors have slots, Rocna, Excel, Spade, Fortress.

The reason, anchormakers have told me, there is a slot is in order that the eyes, lugs, of a bow shackle fit into the slot and the bow is then in the slot. This then allows the shackle to freely articulate. If the anchor only has a hole it is normally anticipated that a 'D' shackle will be used, clevis pin in the hole and a bow shackle through the end of the 'D' with the clevis pin through the chain. In thos latter case the 'D' shackle will be the largest that fits the hole. Genuine CQRs are, were, supplied this way with the 'D' shackle welded up.

In all cases you are usually aiming to maximise the size, in terms of strength, of the shackles being used,

Shackles if loaded at 45 degrees suffer a reduction in strength of 25% and and if loaded at 90 degrees a reduction in strength of 50%.

A 3/8" Grade A gal shackle, say one of Van Beests Grean Pin shackles has a WLL of 1t, this reduces to 500kg if loaded at 90degrees, much lower than the WLL of an 8mm G30 chain. If you have the pin through the anchor shank it is quite possible to side load the shackle. If the shackle can articulate there is greater chance the load, on the shackle, can be a straight line. A 6mm shackle wouldbe considered far too small, I know you use it as an example. I would source a Crosby Grade B, G209A shackle from Tecni in the UK or a Peerlift Grade B shackle from Starrr in America of 3/8" size and WLL of 2t, but check it fits your chain first.

So forget point loading - try to ensure the shackle can be loaded in a straight line. If you use a Grade B shackle it will be well overstrength and point load will not have any impact.

Jonathan
 
NormanS said:
Why not just use two somewhat larger galvanised shackles back to back?
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I think that does still cause the contact point between the two shackles to be very small. The only way round that is to have the radius of the clear just a big bigger than the dia of the wire from which the shackle is made.
 
When shackles are tested they are retained using high tensile components that a circualr in cross section and the loading is exactly the loading that appears to worry you.

A good 3/8th Grade B gal shackle has a breaking strength of 12t. It is proof loaded to 4t (which is the min break strength of matching G30 chain, 8mm). So it is Proof Tested to the same strength of your chain, under load imposed by point loading. You can buy a Peerlift shackle to this specification from Starrr in American for US$2.95 and they will ship it cheaply to you by American Post. The service is cheap, trackable and is inexpensive. What on earth is it that worries you?

Jonathan

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If you do not like the idea of Starrr then Tecni in the UK will sell you a Crosby Grade B shackle, 3/8th" WLL of 2t but only a 4.5: 1 safety factor so 9t min break strength. I think Starrr might be cheaper and the Peerlift are stronger. Peerlift also have a greater range of Grade B shackles, than anyone else I have found, and offer from 3/16th" Grade Bs in 1/16th" increments upto 3/8th (and then larger increments) - so they should have a shackle to fit most eventuaities. Crosby and Campbell both make Grade B shackles but to a less extensive size range. Van Beest Grade B shackles start at a size too large, for most of us.

But check the clevis fits your chain. The clevis are nominally 7/16th". or 11mm. But the sizes are nominal, as are the apperture sizes of your chain. The standards are not tight. I have found surprising variation in shackles sizes - so check and double check.

If you are worried about point loading why are you even thinking of a stainless shackle.

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When we r-vamped our anchor and chain, 45lb Delta to 3/8" or 10mm HT chain. we discovered that West Marine our local chandlers sold special anchor shackles that had the pin diameter one size up from normal for extra beef. Our new Delta had a standard slot attachment point which allowed the shackle to be passed through and the oversized pin go into the end link of the chain. Had this not been the cae i might have used the heavy duty S/S swivel link I have in stock, bought years ago in Poole UK and I think made locally there but which we never used as it was too big for our needs back then and we had a Kong galvanised one which worked well enough.
 
American, imperial, chain ostensibly similar to metric sizes, so 5/16th" = 8mm etc - have different link dimensions. The hole inside the link is larger, considerably, than a metric link.

An American 3/8th" shackle would normally have a 7/16th" clevis pin (as standard). Which actually fits an Australian metric 8mm chain, but does not fit a Maggi 8mm chain?!

I can only suggest that when you go to buy you take 2 links with you and the anchor, unless the chandler has that specific anchor in stock.

I would not touch a West Marine shackle (based on one I tested) - they have a propensity to deformation and standard gal, rated, lifting shackles from Crosby, Peerless and Campbell (and maybe Columbus McKinnon, I have not tested them) are better and cheaper.

Jonathan
 
Neeves said:
American, imperial, chain ostensibly similar to metric sizes, so 5/16th" = 8mm etc - have different link dimensions. The hole inside the link is larger, considerably, than a metric link.

An American 3/8th" shackle would normally have a 7/16th" clevis pin (as standard). Which actually fits an Australian metric 8mm chain, but does not fit a Maggi 8mm chain?!

I can only suggest that when you go to buy you take 2 links with you and the anchor, unless the chandler has that specific anchor in stock.

I would not touch a West Marine shackle (based on one I tested) - they have a propensity to deformation and standard gal, rated, lifting shackles from Crosby, Peerless and Campbell (and maybe Columbus McKinnon, I have not tested them) are better and cheaper.

Jonathan
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I did my upgrade over a year ago and my Delta was in stock although the chain was ordered in specifically to get it in a complete 150ft length, but they did have some in stock to try the shackle fit on. The shackle I bought was not actually labelled a West own brand one,( and was more expensive than others in that store) just one that I bought there, my comment related to the fact they had two very different places in their store ( a new superstore) for shackles and the anchor section ones had one size bigger dia. pins, I was told 'deliberately'. I"ve confused myself now trying to explain, I hope not you as well!.

Robin
 
I picked up my stuff in one of their flagship stores West Islip (I think that was the name) outside NY, or outside Manhattan. What surprised me most was they had so little chain in stock, all they had was G43, no G30, no BBB and no G70. it was explained that if you wanted the other qualities they would deliver to your yacht (which is actually quite sensible) but you could not size anything. Other than this, what I thought - strange anomaly, the store was quite impressive and had more anchors in one place than I had ever seen, more different designs and more sizes of each design. Racks and racks of anchors. A thought I had was that with so many designs how did anyone decide what they wanted - spoilt for choice came to mind!

The other items on stock were equally impressive - but it was the anchors that struck me as I normally see maybe 10 or 20 total sitting dusty and ignored in a corner - and here were hundreds.

Jonathan
 
We ued to have 2 stores locally including one at our marina but they closed both and opened a new superstore 2-3miles away, not transient friendly but I guess their bean counters liked it. The new store is a bit boutique heavy but you can order anything online and have it delivered free to the store in a day or two. I chose HT chain as they had a short section in store that I tested on my windlass and it was the best fit ( Our boat was built in France not USA although the windlass may well have been fitted by the dealership this side of the pond. AS you say they have lots of anchors in stock, racks of them. We have no other good boatstores except a marine surplus one nearby which has a few anchoes and some chain, mostly stuff bought from bankrupt stores and/or used from boaters. They actually have our original polished S/S Lewmar claw for sale there on commission. I would have kept it as a spare on board but it doesn't fit into any convenient lockers on board. If/when it sells I will buy a newgen type (small enough to fit in a deck lazarette or maybe swap the current fortress FX11 spare/kedge for a bigger FX37(?) one.
 
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Their West Islip store is miles from any water and is part of a large commercial/retail development. You need a car, or in my case a bicycle (and use the train). Carrying 75m of chain would be quite a challenge on a bike!, good thing they deliver. The Charleston store, it was too far to ride at the time (other priorities) is 4 miles from the nearest marina. Odd choice of locations - but they sell a lot of garments (and stuff) maybe that's part of the focus and maybe the itinerant yachtsmen are few and far between (and/or marinas might have courtesy transport)

The FX 37 is quite large, it would suit as a hurricane anchor but its simply too big for much else (on your yacht). I'd hang on to the FX 11, as a kedge/stern anchor and look at the FX 23. With our 2 x 20hp in sand we can almost have the FX 23 disappear, we can usually see the stock and a bit of the crown. If it blew 35 knots I think it would disappear. If it blew 55 knots I think we might have difficulty retrieving. I doubt we could anywhere near bury all the fluke of the FX 37, so I'd worry about ease of tripping in a big windshift. It would also be quite a handful to deploy from a dinghy (its quite large - the weight is not an issue but packing assembled might be a challenge). We have the same dilemma as you, we carry a FX 23 and I'm tossing up whether to supplement with a FX 11 or a FX 16. Later this year I'm scheduled to test exactly how deep we can set a FX37, FX23 and a smaller one - using the same engine power in the same seabed and define what load is necessary to trip at 90 degrees - but it will be Octoberish before we get round to it. I have to decide which small one to buy.

Sorry for the thread drift.

Jonathan
 
I think i confused the issue. I just meant I would use the money from the sale of the dock queen special polished claw to buy something decent as a spare that would still stow somewhere convenient. Our 2 deck lockers ( not the anchor locker) are narrow and deepish. The claw would not jiggle even through the opening and regular danforths would only fit if I sawed a bit off the cross bar each side. A Rocna under 20kg might just go but I need to take a tape measure to West to check and/or agree sale or return, which they are usually quite good about. IN the meantime the 45lb Delta does very good service. If I stopped reading anchor threads and looking at mermaids I could probably carry on regardless.;)
 
Neeves said:
If your wife catches you looking at mermaids she might be upset - stick to anchors, much less contentious, and you can touch anchors :)

Jonathan
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:biggrin-new::biggrin-new::biggrin-new::biggrin-new:

Anything that cost money is contentious in our house Anything bought for the boat also has to be matched by similar spending on whatever takes her fancy. My comment that I save the difference in cost between hers and his haircuts over a year and my refusal to buy makeup/perfumery falls on very deaf ears.
 
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