Galv vs SS chain.

[Devs Ad]

HI again.


About to put three moorings together for our RIB, Dory and Champ. We've always used 10mm galv chain in the past, but since it all needs replacing I was wondering what an 'equivalent' chain size in SS would be?


SS is a much stronger and harder alloy than mild steel, so I would expect it to wear much less as well as it being resistant to corrosion. It's obviously a lot more costly, tho', but if - say - 6mm chain were a suitable equivalent to the 10mm galv, it wouldn't cost that much more. It would also mean I could use SS links and swivels, with the benefit of not having rusty pins.


Anyone have experience of how they compare? Any other thoughts, please?



Thanks.

[Matt]

Significant part of the usefulness of chain on a mooring is it's weight.
So assuming the original mooring spec was about right, I wouldn't be downsizing it at all, TBH.

[mhill]

With a collection of boats like that sounds like a Sea Cadet unit......

[Salty Pete]

The only benefit of Stainless is, it looks nice.

[GuyC]

Originally Posted by Devs Ad

SS is a much stronger and harder alloy than mild steel...

Stainless chain which is generally 316L stainless has a lower yield strength than mild steel and the ultimate strength of stainless is at the lower end of the range of the ultimate strength of mild steel.

I'm assuming something like LR Grade A or S275JR steel as a mild steel.

Yield is when it starts to deform and ultimate is when it starts to fail.

As other have said it is the weight of the chain that is probably more important than the strength.

[Devs Ad]

Thanks all.

Yes, a SC unit, mhill.

Have to say, I am surprised by the answers :-)

SS is sooo much harder than mild steel, and the factor that requires us to replace our chains is wear as opposed to corrosion. (Although, of course, corrosion exacerbates wear since, where the links make contact, the galv is worn away first, the mild steel material is exposed and surface corrosion forms - which is softer than the steel - and further movement wears away that corrosion and exposes fresh steel).


SS, being much harder, should suffer far less wear.


The much reduced weight of 6mm chain isn't something I'd thought off - good point, and an important factor as this helps to dampen the movement of the boats in choppy conditions.
8mm SS chain, then?! :-)


I'm trying to figure out whether 8mm SS chain over 10mm galv steel would be worth the extra outlay - around 50% more. Having worked with both materials, I suspect SS would outlast MS many times.

[Matt]

It's been a long time since I've thought about moorings, so apologies if I'm not exactly correct, but I think I recall that there are 3 factors when it comes to mooring chain.
* Weight
* Wear
* Galvanic Corrosion

The sailing club I'm a member of has boats break their moorings and hit the nearby bridge with more regularity than you'd hope. Inevitably it is a failure in the submerged section of the mooring.

So either way, always over engineer a mooring such that when a storm blows in, you can sleep easy.

In your case, spec the chain the mooring requires for the boat/depth etc.

Part of the choice of a nice thick link is so that the combination of wear and corrosion don't risk the chain failing between inspection intervals. Plus the damping effect too.

Regarding stainless I think there is potentially a risk that if you have a stainless riser, but a bit of old chain ferry chain (for example) for the ground tackle, you are setting up a battery with the dissimilar metals, that would then corrode the mild steel bit even more quickly! And if you use a stainless ground tackle too, and stainless shackles all the way - then I bet the hoop on the sinker isn't stainless too.........

So, speaking personally, I'd be sticking with galvanised for all submerged elements of the mooring since the galvanising protects all the bits of mild steel in the "circuit", not just the chain it's attached to.

And remember that the ground tackle needs to be long enough and heavy enough that the sinker never sees any snap loads from the boat at all - it's the ground tackle that does almost all of the work, with the sinker (or an anchor sometimes) just making sure the ground tackle doesn't move too far.

Also use galvanised shackles with an eye on the shackle so you can wire lock them closed. And I think I recall people using hot bitumen on the threads too so that it's possible, with some force, to disassemble and service the mooring annually.

[ribber]

How many galv chains are you are going to be replacing in your lifetime? I would stick to galv ones.

[beamishken]

There's probably a good reason that stainless chain isn't used for moorings and I doubt its cost as some of the most valuable assets on the planet are moored with carbon steel chain. Iirc carbon steel chain is far stronger than stainless steel so reducing size is going the wrong way.
I'm not sure on the whole reasoning but there must be a good reason you almost never see stainless mooring chains.
I stick with carbon steel for my mooring & did some research a few years ago re stainless anchor chain for our cruiser & iirc the only advantage was stainless looked better & it flaked into the locker better but in every other respect the opinion was carbon steel was better than stainless

[Nasher]

Same argument as not using stainless bolts on Brake components I assume.

In 90% of cases and uses it will be fine, but has the chance to be catastrophic under specific conditions.

All I know, apart from the alchemy that is Galvanic Corrosion, is SS is more brittle, or less tough, than MS, so is less likely to snap when under a sudden heavy shock loading.
But lets face it, in 99% of cases other than heavy commercial use it will be fine, and it depends on what risk you are prepared to take for less maintenance.

Nasher.

[Limecc]

Just a reminder there are many different grades of stainless, all with different properties.

The two common marine ones are:

316/316L has a higher corrosion resistance due to extra molybdenum but it's less malleable, harder and more prone (than 304) to cracking or sudden failure. A4 nuts and bolts are made out of 316. It has a price disadvantage to 304 because molybdenum is expensive.

304/304L is more easily formed and machined, yet still has good corrosion resistance. When buying fasteners they are known as A2. If you ever wondered why some shiny stainless object develops traces of rust on your boat's nice white gelcoat, it's probably made out of 304/A2.

[Devs Ad]

Thanks everyone.


Cool - arguments well made, and I'm sticking with galv :-)


Even if it were beneficial, I'd have had to go up to 8mm size for weight alone, and that is silly money.



Cheers - appreciated.