Green-pin shackles for moorings

[jdc]

There has recently been a thread about the best way to contrive a strop from boat to riser, which drifted a little into discussing shackles, their mousings and propensity to fail. This interested me, but I didn't want to hijack that thread, so have made a new one.

I have recently (last spring) replaced the entire riser assembly for my deep water mooring in Plockton. Following the recommendation of GaelForce in Inverness I used hot-dipped Galvanised green-pin shackles from Van Beest (type G4163). These use stainless steel split-pins, through the threaded end rather than conventional mousing through the bolt head.

http://www.vanbeest.com/getattachment/aa492c75-5752-4fe6-84fc-b506b6fe93ab/Chapter01-Shackles.aspx

I was lucky enough to go out on the mooring contractor's boat while he was servicing moorings, and he also recommended them and was using them everywhere, saying they never had any troubles with them and they last a good long time.

Why I raise this here is two-fold:

1. They are high tensile shackles, made of a grade 6 steel (with very high breaking strains like 28.5 tonnes for 19mm wire size). However some mooring experts say that one should be wary of high grade steels under-water as they are prone to corrosion. Does anyone have evidence of that, or the lack of it, with these shackles? I tried unsuccessfully to find any academic papers detailing corrosion rates for different grades of steel. But maybe grade 6 is not so high.

2. The mousing is done, as I said, with a split pin - again any experience good or bad of this as opposed to the more conventional plastic or wire mousing? The split pins are quite meaty, about 6mm dia but 304 grade (not sure 316 is available for split pins).

I must emphasise that I've no cause to doubt what has been supplied and installed, rather the contrary as they seem to be of superb quality, but recent posts on here show that this design of shackle is not that widely used and I wondered why not.

 

[jakeroyd]

Hi jdc,
yes i've been following your observations on the other thread about making fast to the boat.
I am imagining at present hat i will use a ss bow shackle to fix to the swivel on the bouy , a hippo SB2

The green shackles look interesting.

The reason for my post was your question about corrosion of certain high strength steels under water.

Not quite the same thing but when I worked for Land Rover in product design we came upon the issue of propshaft fixings.
Becuse the then new Discovery and RR vehicles put much higher duty cycles through the prop joints we were really struggling to keep them correctly tensioned using conventional steels and conventional tightening.

We ended up with a 12.9 grade fixing tightened to yield.
The steel that this fixing is made from is a specialised ex Honda spec which was the only 12.9 approved for use underfloor IIRC it was a boron steel alloy.

The reason for this was that the road salts a fixing will see can cause embrittlement over time in grades above 10.9

This might be similar to your finding , salts in seawater having a similar effect ?

Just a thought

 

[Daydream believer]

Whilst you may use green pin shackles yo may be over spec'ing for the chain to which it is fixed
We use 18mm long link chain & this lasts 3 years for a 30ft boat & 4 years for smaller boats such as the Squib.
What happens is that the link in the chain can wear against the shackle so needs replacing at this point
We use CE marked galv shackles 19*22 & they last about the same time as the chain.
Sometimes there is a lot of wear in the pin but provided the thread is given a dip in some stockholm tar it is normally OK

 

[pagoda]

Whilst you may use green pin shackles yo may be over spec'ing for the chain to which it is fixed
We use 18mm long link chain & this lasts 3 years for a 30ft boat & 4 years for smaller boats such as the Squib.
What happens is that the link in the chain can wear against the shackle so needs replacing at this point
We use CE marked galv shackles 19*22 & they last about the same time as the chain.
Sometimes there is a lot of wear in the pin but provided the thread is given a dip in some stockholm tar it is normally OK

+1
Unless a fitting is in clean non-salty air, the high tensile attributes are mostly wasted money. Most of the loss of strength in moorings is down to corrosion and friction wear between components exacerbating wear. I would be more tempted to go for beefier fittings before "skinny" higher strength ones?

PS
I had 2 seasons on Kilmelford moorings (not the 15Ton plus variants). The pick up chain was half inch stuff, the riser was considerably bigger (and beyond lifting to find out!). I didn't ask them the chain change timetable ,but felt pretty safe on the heavy tackle. They insist on chain being taken aboard and pinned at the bow fitting. I have no problem with that.

 

[doug748]

"2. The mousing is done, as I said, with a split pin - again any experience good or bad of this as opposed to the more conventional plastic or wire mousing? The split pins are quite meaty, about 6mm dia but 304 grade (not sure 316 is available for split pins)."



Thick mousing wire probably works well enough underwater, on heavy chain which is normally in nominal tension. However I have seen light monel wire frequently torn away from the shackle on the top of my mooring buoy. In this situation there is often vigorous shaking and unfair loading.

A much better solution is your pattern, the through bolted type secured with a nut and split pin. I searched in vain for this type of stainless jaw - jaw swivel before Christmas and had to settle for the usual type.

I have turned down the shoulder of the pin so it protrudes far enough to take a split pin and will be sleeping better for it.

 

[ffiill]

I dont like the green pin because the pin is free to move and therefore it can work the nut loose against the split pin.
I much prefer heavy duty galvanised threaded shackles which I either weld across the ends or replace the pin with a bolt over length which once tight I lock of with a nylock.
Also I still dont understand why the continued use of mooring anchors,ground chain and chain risers given their propensity to rust?
My mooring also at Plockton consists of a concrete block dry weight about 2.5 tons and a pair of multi plait risers bothe attached to seperate
Concreted in one inch chain plus a spare well protected eye for good measure.
The muddy bottom adds to the concrete blocks holding power in that to move it along the ground means it having to break suction and then snow plough through a two foot deep layer of mud.

 

[William_H]

For a mooring chain there is only one answer to long life in iron chain and shackles and that is large size. Strength is not a question because for long life the sizes must be vastly over specced. So cheapest balck iron shackle of the biggest size you can fit is the best way to go. As suggested it is important that the pin in its thread does not move. Any movement will encourage corrosion wear. So if your split pin is a tight fit it should be fine. Usual thing is wire twisted through the pin hole to hold against any undoing.
However I think you should be wary of stainless stell in the split pin. Probably OK as proffessionals use SS wire for mousing apparently without problem.
However my experience is that stainless steel loops on a buoy or SS shackles where they meet black iron shackles or chain is a real rapid wear point. Try to avoid the dissimilar metals.
My 3m deep swing mooring had to be inspected/maintained by proffessionals a year or so back due to a change in regulations. I had maintained it for 30 years myself.
The authority povided a mooring buoy with integral SS swivel. I have of recent years got a chain of some sort of stainless steel. I used stainless steel 10mm shackles for connection. There was a join in the SS cahin and they fitted a large 20mm iron shackle. I note now that after a year that iron shackle has half worn away. I have fitted a SSshackle in parallel for when the iron one gives way.
Anyway assuming you are stuck with iron chain then keep a close check on the wear of the chain. You will most likely fit bigger shackles than the chain so it is the chain that is likely to wear through first. The wear/corrosion is a function of physical friction wear taking off galvanising then the protective rust coating so rusting further. So it is in the contact points of those parts which move most. Galvanising does no good at all.
So IMHO the best chain is the biggest second hand chain you can find with the biggest cheapest shackles you can find. The inspect at least every year.
good luck olewill

 

[Kelpie]

What about using galvanised fence wire for mousing?

 

[J Neeves]

I suspect Van Beest shackles are being used simply because they are the most readily available Rated shackle. The Van Beest Green Pin shackles are grade 6 and are individually Proof Tested and are batch tested for Break Strength. The WLL, size, origin and batch number are embossed into the bow of the shackle. 'Other' shackles, not rated are not tested (sometimes not at all) so rigorously and would not be accepted by most (maybe any) insurance companies.

Grade 6 shackles are not particularly strong - or you can source Grade 8 shackles that are better.

I would recommend anyone to use Grade 6 or better Grade 8 gal shackles to secure their anchor to their chain - they are not particularly expensive. A Grade 6 shackle fitting a 8mm G30 chain, so the shackle would have a 10mm pin, would have a WLL of 1t - comfortably stronger than the WLL of the chain. If it were a G40 chain I might use a Grade 8 shackle.

Most rated shackles are lifting shackles and the shackle pins, or the part that takes the load, tend to be shorter - and better for securing chain. Van Beest have a very high reputation (and I have tested some of their components and they are excellent). There are other suppliers of decent lifting equipment and Gunnebo, Pewag and Rud come to mind. The best 'retail' source would be someone who deals with lifting equipment or commercial trawlers (and this latter might be a decent chandlers). Crosby is an American source but their shackles are only sold to a 4.5:1 safety factor but Van Beest (Peerless and Campbell) work to 6:1.

Though galvanising is more abrasion resistant than the underlying steel the thickness of gal is so thin, maybe 100 microns, it simply does not last long (maybe 3 months on sand and less for the pin itself). It depends on where the components are used but the major 'wear' location for many moorings are the components that sweep the seabed most, they wear by abrasion and the longest life will be from chunky components (because there is more steel to wear away). HT steels are more abrasion resistant but good HT abrasion resistant steel is expensive and the usual remedy is to use recycled heavy duty chain, but new shackles and swivels. However there is little point in using rated shackles and wimpy swivels - so you need a matching Grade 6 swivel or something well over size.

But you are not looking for strength, it obviously must be adequate but moorings fail through wear not because they are not strong enough in the first place.

Moorings should be checked annually.

I cannot comment on the mechanism to secure the nut at the end of the shackle pin except to suggest that I would be using Loctite (as well as the split pin). The last Loctite I used on a shackle pin was so strong I could only remove the pin after using a blow torch - but I did use the Loctite liberally!

If the components are subject to constant drying, in a tidal mooring, there will be corrosion (rust) as well as abrasion but you talk of a 'deep water' mooring so I suspect you are subject to, primarily, abrasion.

Jonathan

 

[jdc]

Thank you to those who responded.

I agree with ffiill that innovation in moorings has been really slow, old iron seems still to be the mantra just as it was 100 years ago despite the revolution in materials science we have seen since!

My mooring is in a location where the anchors and ground chain sink slowly into anaerobic mud and seem never to decay, but the riser, especially the top few metres, seems to corrode really fast so swivels, shackles and upper riser chain get eaten up. I have noticed this on the boat's anodes as well: 1 month on the mooring in Plockton eats the anode more than 9 months in Falmouth (and on Eriskay it seems even worse: only one night at anchor eat all the galvanising off my anchor chain, tuning it black with iron oxide).

I had expected more spill-over of techniques from fish-farms by now, but apart from use of polysteel (so floating) or polyester (so sinking) lines on a small minority of moorings we are still arguing over how to do do up shackles so they don't undo when it would be absolutely trivial to design one which never undid: I'm amazed how stick-in-the-mud we all seem to be when designing equipment to stick in the mud.

 

[J Neeves]

JDC

There are alternatives to shackles, that do not undo. Look at Van Beests catalogue and look for their Omega links, I think they are in the Grade 8 section or look at their connectors (I think that is what thy call them) also known as hammerlocks (also in the Grade 8 listings). The biggest problem is finding these 'different' connectors that are also galvanised. The best industry is possibly commercial fishing but I'm a bit out of my depth there. You can certainly source hammerlocks in stainless Grade 5 I think, though I do not recall seeing omega links. Jimmy Green have gal Omega links as part of their supply for Maggi chain. And I have seen big gal hammerlocks - in use but have no idea who supplies them. So there are alternatives, they are used in related industries but have not quite swept to popularity in the leisure marine industry

Jonathan

 

[afterpegassus]

JDC

There are alternatives to shackles, that do not undo. Look at Van Beests catalogue and look for their Omega links, I think they are in the Grade 8 section or look at their connectors (I think that is what thy call them) also known as hammerlocks (also in the Grade 8 listings). The biggest problem is finding these 'different' connectors that are also galvanised. The best industry is possibly commercial fishing but I'm a bit out of my depth there. You can certainly source hammerlocks in stainless Grade 5 I think, though I do not recall seeing omega links. Jimmy Green have gal Omega links as part of their supply for Maggi chain. And I have seen big gal hammerlocks - in use but have no idea who supplies them. So there are alternatives, they are used in related industries but have not quite swept to popularity in the leisure marine industry

Jonathan

Hammerlocks are very difficult to install underwater and because of the relatively small diameter of the pin, this tends to wear quite quickly. I would stick to shackles.

 

[J Neeves]

Hammerlocks are very difficult to install underwater and because of the relatively small diameter of the pin, this tends to wear quite quickly. I would stick to shackles.

I would be interested in any first hand knowledge of pin wear in marine environments. it sounds logical but the pins are hardened (so abrasion resistant) but they seem to seldom used it needs verification. Too easy to dismiss - so direct application experience would be useful

Jonathan

 

[afterpegassus]

I used them by the dozen when I had a trawler. Their usefulness was in their strength and neatness (in that they did not foul other parts of the gear). After several months of use the pins would become very slack through wear. Having observed this umpteen times, I would not consider them for any submerged part of my mooring. Remember that the pin in a 6 1/2 ton hammerlock is only about 10mm diameter whereas the pin in a similarly rated shackle will be about 25mm and as has been previously mentioned, it is the amount of material that is available for wear that should be the primary consideration.

 

[J Neeves]

I used them by the dozen when I had a trawler. Their usefulness was in their strength and neatness (in that they did not foul other parts of the gear). After several months of use the pins would become very slack through wear. Having observed this umpteen times, I would not consider them for any submerged part of my mooring. Remember that the pin in a 6 1/2 ton hammerlock is only about 10mm diameter whereas the pin in a similarly rated shackle will be about 25mm and as has been previously mentioned, it is the amount of material that is available for wear that should be the primary consideration.

Afterpagassus - thanks, good to have real feedback as opposed to apocryphal 'my neighbour's neighbour etc'.

Were the hammerlocks you used galvanised - if so, who supplied them (i.e. who made them).

My comment on use of hammerlocks and omega links was really to suggest there were alternatives to shackles (and it seems the commercial fishing industry does use them). Its horses for courses, if you want whatever convenience these alternative items offer then you need to offset those features against some possible downsides. You mention abrasion of the pin but another downside is they are very difficult to undo - I'm guessing that often you need to cut them off. But omega links can be very small, much smaller than a comparable strength shackle. So you could use them, if galvanised, to attach an anchor, instead of a shackle (which is what Maggi are suggesting of Omega links) - but you would need to check them regularly and when questionable cut them off - so not much use if you swap anchors regularly.

Jonathan

 

[PhilW]

Hopefully the pic attached but this is the problem we found at work after putting S/S m6 bolts through shackles. The holes were drilled to take the bolts as snugly as possible the corrosion rate is quite scary really. This was after 6months in the water.

 

[Dipper]

I help with mooring inspection and maintenance in my club where we have over a hundred swinging moorings. We order all our riser chains with a large welded ring in one end. We reeve the other end through the last link of the ground chain and then through the ring and pull up tight. There are no shackles to fail.

Where we have Hippo support buoys, any shackle that is used to attach to the buoy is welded in place.

 

[markhomer]

I used to work in ship repairing , for a starter HT steel was never allowed to be used underwater as I was told it corrodes far quicker than mild steel , similarily with HT chain , in old days mines used to sell off their old chain , as it was HT wasnt suitable underwater although attractive to some as cheaper ,

as for putting ss with steel underwater , recently I was warned not to fasten boats anchor to chain with ss shackle to galv chain due to galvanic action , which would I assume apply to ss pins in steel shackles even worse permantly underwater .

as phils post above clearly shows

 

[J Neeves]

Maybe there is HT steel and HT steel - but all rated shackles are HT steel, though they are galvanised. The fishing industry uses hammerlocks which are HT steels, The Supreme, Knox and Excel anchors use HT steels in their shanks (which again are galvanised). There is some use of gal G70 chain, sold by both Maggi and West Marine, for anchor chain. Though none of these applications are permanently underwater (though I would have thought the environment in which they are stored would be pretty corrosive).

Jonathan

 

[lw395]

View attachment 49329

Hopefully the pic attached but this is the problem we found at work after putting S/S m6 bolts through shackles. The holes were drilled to take the bolts as snugly as possible the corrosion rate is quite scary really. This was after 6months in the water.

I've had much better results using zinc plated steel screws. .
But I did tap the holes and assemble with Loctite.
After a year, not much corrosion, undid with spanner.