Fore and aft mooring chains

[GsyFoxHound]

Hello,

I’m looking to replace my mooring chains as the old are getting to the end of they’re working life. I have the choice of chain but what’s better, galvanised or self colouring? It’s beenput to me that the chain would ware before corrosion kills it so to save a bit of cash and get self colouring. Is this right? Also what’s size and link type is best.

My mooring dries out at half tide and I’m in a fairly sheltered spot with a 29ft

Many thanks for any help!

 

[zoidberg]

I'm given to understand, by the most meticulous moorings contractor in the West Country, that the 'galv' abrades off bottom chain in a few months, if not weeks. Much of what gets used in that role is heavyweight recycled self-coloured stuff from chain ferries and the like.

Riser chain is more often galvanised, for there's a lot of that - often used for anchoring and replaced - available quite cheaply.

Corrosion starts the day the stuff is immersed - especially on shackles' pins and swivels, where mechanical abrasion may be concentrated.

Ever more people are using Polysteel rope as 'risers', for it doesn't corrode as does steel chain, and it is certainly strong enough.

 

[Neeves]

Coincidentally I'm testing chain now and results suggest that some conventional galvanising can wear off within 4 weeks showing the first signs of bare metal. It obviously depends on the amount of movement, the aggressiveness of the seabed, both chemical and abrasion, and the thickness of the gal - and you don't know the answers to any of these Here, on the other side of the world with chain on the seabed and rope risers the chain will last about 3-4 years and will then, if unserviced, have worn to paper thin (at the point most 'affected') and fail - sweeper chains here are 'black', not galvanised around 20mm diameter.

Zoidbergs comments say exactly the same thing and confirm antipodean experience.

I don't know the difference in cost for galvanised chain in the UK, nor know how much movement your chain experiences but if you want to increase longevity I would use bigger chain, rather than galvanised chain. The galvanising might give you a few extra months of life but the extra life will not be measured in years - unless the chain does not move.

If the chain sits in mud - you will enjoy chemical corrosion, anearobic organisms that exude sulphur based compounds that are acid, or become acidic, and the gal will dissolve - whereas raw steel would be much more resistant. Galvanised chain from such environment will be retrieved jet black - overnight (though this is superficial) but indicates the speed or aggressiveness of the seabed cocktail. A combination of chemical and physical abrasion, the chain moves, is not a recipe for a long life.

Hence maximise size - within limits - rather than spend money on gal.

The swivels and shackles at the ends of your assembly, again as Zoidberg mentions, will suffer the most wear - make sure they are as big as is sensible - more steel means longer life. Use G70 or high tensile components if possible (they might not come in the sizes you need - simply do not know) - strong steel is more abrasion resistant because it is harder. So if there is a choice of component go for G70, failing that G40 and finally, the more common, G30.


Just out of interest - how long has the existing chain lasted and what does it look like to cause you to think it needs replaced - I'm interested in the failure mechanism.


Jonathan