Mooring chain corrosion

[steve28]

greenpin shackles

Recently new developments with our Green Pin Super Shackles have resulted in improved performance. We have upgraded the Working Load Limit of four sizes of shackles as follows: from 50 to 55, 80 to 85, 110 to 120 and 140 to 150 tons. In order to distinguish the Green Pin Super shackles from the standard Green Pin shackles the new model can be recognized by the Green painted shackle ‘Crown’. Compared to standard Green Pin shackles they have an up to 50% higher WLL with comparable physical weight and dimensions. These shackles are specially designed for applications where shackles weight and/or size are critical. Please find herewith the latest Van Beest product information including details of these Super shackles

Seems to suggest they are for mechanical lifting and maybe not for permanant imersion ?

Steve

 

[oldharry]

I am amazed by your comment as I would have thought - perhaps incorrectly- that most users would have opted for the green pin type shackle simply because they are of proven strength. Am I wrong?

The ultimate strength of a proof stamped shackle is not important, as long as it matches the chain - e.g. one inch chain = at least one inch shackle. I always fit the largest shackle that will pass through the chain link. The key factor on a mooring is the rate at which shackles corrode or wear through. It doesnt matter hwo strong they are to start with, if they corrode quickly (as green pins seem to) they are useless and dangerous. I just replaced the riser on my mooring this year after 6 years use (Chichester harbour). But most of the shackles needed replacing every 2 years although they were heavier than the chain. The swivel is replaced every three years or sooner if it shows signs of wear. They are not expensive, but the result of failure could be!

Putting stainless components in is unwise too as this accelarates electrolytic corrosion , or seems to, even using stainless instead of monel wire for mousing the shackles. I use a rope penant, but always back it with chain, as I have found too often the rope starts chewing through in a spell of bad weather.

I check my mooring at the beginning and end of every season. It helps that it dries at LW! Once or twice had some nasty surprises.

 

[Heckler]

The stories and pictures are typical of wear of iron on moorings in Swan River except perhaps faster here in warmer water.

I disagree re quality of shackles (and chain) the only thing you need is iron. So far better a bigger shackle of unknown origin than a high quality fully tested shackle that is smaller. In a mooring the gear needs to be so big that actual strength is not an issue. You need large size so large amount of wear still leaves a lot of metal.
Some people have reverted to rope for mooring riser here with some success. You need a large diameter rope and the steel thimbles will still wear away. As will any shackles used.

Our mooring authority suply and require the use of a large yellow buoy. Too heavy to lift on board. It comes with a stainless steel rod through the middle with a swivel built in. I think the metal about 16mm diameter.
Originally they expected boats to use the swivel however the stainless rod failed on many occasions. (about 2000 in use) so replacements deleted the swivel so you had to connect under the buoy. Not necessarily better but gets them out of responsibility. Though many people still rely on the built in swivel.

The stainless steel however caused accelerated wear/corrosion of the Galvanised Iron shackle. I have now gone for all stainless with home made swivel and chain. The chain a gift from a friend out of some furnace.
Well it has been stainless now for a few years with no signs of wear. The smallest bolts in the swivel are about 10mm. I do have some GI connecting additional weights/ anchors but this is isolated by sections of rope so no GI to stainless connection.

I did get a shock a few months back when the authority rang to say the buoy was found on the beach. the rod up the middle had failed. There was a nut on the threaded rod with a pin through it to stop the nut coming loose. The rod had failed at the hole and the nut unscrewed. Fortunately I had moved the boat connection to the riser so only the buoy escaped. They gave me a new rod for the buoy now 18mm stainless. That should last better than the original.

As for attachment to the boat. I use a rope to a snap shackle on the winch out eye half way up the bow. This eliminates all chance of chafe. I then have a second line onto the standard cleat on the foredeck. I remove the bottom connection on arrival by dinghy and reconnect before leaving the boat. The top line is used to cast off and piuck up.

So yes even with the best heaviest gear a mooring needs to be inspected every year. In shallow water I check mine visually by diving every few weeks. This may help olewill

How much wear do the crocs cause? Sharp teeth etc?
Stu

 

[Heckler]

In Belfast Lough and Strangford Lough it is prudent to change shackles every year as they seem to corrode very quickly as per the photos shown above in some of the postings.
As for the green pin shackles; my son works in a chandlers and was advised by the traveller from a shackle company that the green pin shackles should never be used under water, they are supposed to be 'high tensile' or very tough, so corrode quickly in sea water.
I know one of the sailing clubs here some years ago bought chain from a coal mine in England which was closing but the chain was 'high tensile' or whatever, thinking they had had a great deal but it lasted less than a year when used for moorings!!!

I agree, the green pin ones are for strength not corrosion resistance. Hi carbon steel is not very corrosion resistant. The Aquaduct near us is a case in point, made from iron, it is still there, Thomas Telford knew what he was doing! It has carried the canal for how many years now? Suffered bangs and bashes from dozy hire boats etc. It still scares me when I see the hirers using the trough as a "guide" to steer across! Its only about an inch thick!
So I would advocate BIG lo carbon shackles, and that is what I use, they last approx 2 seasons on my pile moorings
Stu

 

[NormanS]

Catalac. -
I take your point about the thread corrosion,obviously because there is no plating on it; but failure more likely to be the non-threaded end where the aperture clearance is often a millimetre or two ,allowing the chain to lever the pin on the non-threaded side. the suggestion of PTFE taping the threads seems counterproductive for a secure pin to the shackle, as are all lubricants. Sikaflex sounds a better option threadwise.

ianat182

Funnily enough, I take an entirely opposite view. I liberally smear all shackle pins, all over, with Coppaslip, which entirely prevents them from thread or shoulder corrosion. I've never had any trouble with them. I do of course, wire them up. Belt and braces, I wire and also cable-tie.

For many years I used to take an ordinary (black) shackle, throw away the pin, and use a bolt, with the correct thread, with a locknut, and then a split pin, behind the locknut. Nowadays, I don't have access to the equpment.

I always drop the riser chain, with messenger line attached, for the winter.

 

[John_Clarke]

I agree with Catalac08 about sealant; I use cheap oil based mastic on the shackle threads and where the pin goes through the eye. This stops all corrosion in these vulnerable areas and makes it fairly easy to unscrew the pin.

I heard that Chichester Harbour Conservancy had stopped using galvanised chain and shackles because they corroded faster than plain steel. I had found the same thing on our mooring in Strangford Lough that the 12 mm galvanised chain was heavily pitted. In some areas chain can suffer from pitting corrosion caused by sulfate reducing bacteria (SRB) which, in anaerobic conditions, converts sufates (fertiliser run off and sewage are large contributors) into acid which pits the steel. You can identify this form of corrosion because the steel in the pits is bright and shiny (without rust) when first rinsed out.

I have had this pitting on chain even where there is still galvanising remaining next to the pits. I now suspect that the galvanising makes the problem worse. The worst affected chain is the section which dips in and out of the mud on each tide.

In 2005 Chichester Harbour Conservancy used the following on moorings in 6’ below chart datum (they call this a deep water mooring): 15’ of 1½” ground chain,1 1/8” shackle, 15’ of 1” riser, shackle with 1” pin and 7/8” body, ¾” chain through buoy, ¾” shackle on top of buoy, cable ties to mouse. They said that they would expect a ¾” riser to last 3-4 years.

I have been using ‘self coloured’ 20 mm chain and large high-tensile shackles for 5 seasons without the need to replace them. They rusts quite evenly without any pitting and a very low corrosion rate; after three seasons the chain links had developed some longitudinal grooves. I have lifted it several times to check it and will probably replace it before launching the boat next time just to be safe even though it looks as if it could last several more years.

Underwater I am using 2 and 3 ton high-tensile shackles on each end of the riser; these are massive and have large heads with large eyes for mousing; they can easily take 4 thick cable ties (300 mm). Galvanised shackles have too small an eye and pit badly. Underwater I use several cable ties on each shackle to avoid different metals together.

The ground chain is 1½” and looks as if it will outlast me!
On top of the Hippo buoy I use galvanised shackles and a stainless steel swivel.

 

[Kelpie]

So about shackle choice... not galv, not ss, and apparently not with a green or any other colour pin. Something like this?
http://www.gaelforcemarine.co.uk/Marine-Hardware/Shackles/Tested-Bow-Shackles-Tested-D-Shackles/

 

[John_Clarke]

Rob

Those D shackles look just like the shackles I use. The 3/4" one at the top of the riser and the 5/8" one to join the riser back on itself after pasing it through the last link of the ground chain. They last very well and have big holes for mousing with cable ties.

 

[daryy]

The yard lifts the mooring, as far as the heavy chain, for inspection every year I think.

 

[J*O*A*M*O*N]

As long as we're talking about moorings...

Greetings all....the other day, while looking for something else I found this article..didn't really investigate too closely till this thread came up. Then all I had to do was find it...one of these days I'll get around to organizing those bookmarks...this guy has invented a rubbery...?? rode that has controlled stretchieness. USCG using some, dosn't appear to be avail, for mass distribution yet, but looks promising. NOT AFFILIATED IN ANY WAY SHAPE OR FORM (unfortunately) lol Just something of interest..
.http://www.proboat-digital.com/proboat/20080203?folio=30
Hope this doesn't violate any rules I'm new here Ed

 

[ianat182]

Joamon.
Thanks for that article reference,stimulates some thinking here;wonder if the idea/product will cross the ocean to the UK and Europe.
Perhaps PBO could cover it with a varied test on mooring types ,and locations,and prices.

ianat182