Anchor Chain Choices

[Dockhead]

I'm replacing my anchor chain.


Boat is nominally 20 metric tonnes displacement (44,000 pounds), but my boatyard guy tell me, based on the hydraulic pressure readings from the fishing boat lifter that I use to haul out, that it's more like 25 tonnes in reality.


The old chain was 100 meters of 12mm G40, weighing a third of a tonne -- 330kg.



My choices now:


1. 100m of 12mm G40 like I had before
2. 100m of 10mm G70
3. 100m of 10mm G40


The third choice has breaking strength of almost 7000kgf, which is pretty close to the strength of the original 12mm G30 chain (what the boat came with).


I'm tempted by variant 3, which is half the cost of the others. Either 10mm variant saves 100kg in the bow. That's good and bad -- less weight in the chain is better for trim and sailing performance, but means a less plush ride at anchor.



Breaking strength doesn't seem so important -- strength of the chain doesn't seem to be the limiting factor in the system. Therefore, I'm finding it hard to justify the G70 which is double the cost of the 10mm G40. But the 12mm chain has the advantage not only of strength, but that there is more meat on it -- can tolerate more rust and corrosion and generally everything without being compromised.



I'm struggling with this decision and hoping someone will say something clever which I didn't think of, which will make it easier.

[tkeithlu]

I think the 10mm G40 will be fine. I'm running 8mm G40 on a 65,000 pound boat.

Take care of your chain and rust/wear will not be a problem.

[rslifkin]

I'd go by working load. Use one of the more realistic wind load estimation tools out there (not the ABYC tables). If the wind load on the chain in 60 kts is under, say, 80% of the working load rating, I'd say the chain is strong enough (leaving a margin for some wave action or other factors the increase load a bit).

[Anders]

I would keep the 12mm. Can't see any reason to go with lighter chain.

[Dockhead]

Originally Posted by Anders

I would keep the 12mm. Can't see any reason to go with lighter chain.

Well, the reasons are 100kg less weight in the bow, and about half the cost.

[gma4]

Before you make a final choice, be certain that the new chain will fit and work in your windlass. It may be very expensive to purchase a new gypsy, and if it is an older windlass, it may not be available. The manufacturer of an old-line windlass company told me that he has seen where batches of the same size chain from the same manufacturer differ in how well they work. He suggested to obtain a two foot piece to test it, and then to be certain that the final chain you order comes from that batch. One reason to buy a high quality brand US made chain.

Greg

[Dockhead]

Originally Posted by gma4

Before you make a final choice, be certain that the new chain will fit and work in your windlass. It may be very expensive to purchase a new gypsy, and if it is an older windlass, it may not be available. The manufacturer of an old-line windlass company told me that he has seen where batches of the same size chain from the same manufacturer differ in how well they work. He suggested to obtain a two foot piece to test it, and then to be certain that the final chain you order comes from that batch. One reason to buy a high quality brand US made chain.

Greg

I would have to change the gypsy, but I found one -- NOS -- for £112. So it's not actually a problem.

[MicHughV]

chain usually has a very high safety factor...5:1....this gives you your wll....working load limit..
so you have to work backwards, ie estimate the max. load the chain is to handle, then multiply that by 5.....
After that pick a link that fits your windlass...
I don't think the weight should be an easy...a person standing at the bow will be 100kg..

[Jim Cate]

Well, in other threads you have said that you could tell no difference in performance with the lighter chain (IIRC) while sailing, but relish the catenary improvement whilst anchored with the heavier chain. Could you not use the 12 mm for all activities other than your occasional race, and swap in a really light (shorter g70 shot plus fiber rode) for those annual races?

Jim

[noelex 77]

There has been plenty of discussion about chain catenary on this forum, but while this will be a significant change there are some other considerations.

12 mm G30 has an ultimate tensile strength of around 13% more than 10mm G40 chain. Genuine G30 chain is not common these days. Testing shows most G30 chain is closer, or identical to G40 chain so in practice the difference is more.

The other factors to consider is that 10mm chain moves around the seabed considerably more than 12mm chain on the same boat. Thus, galvanising life will be shorter, especially on hard seabeds.

In crowded anchorages it is important that the boat moves around the anchoring circle in response to a change in wind direction in a similar fashion to its neighbours. Specifying thinner chain in relation to boat size and windage will result in the boat moving more rapidly and this can cause conflict.

However, there are very significant weight savings reducing chain size. For 100m chain with a thickness of 10mm it will be about 100kg lighter than 12mm chain. This is a very significant saving. Sailors often stress about adding an extra 10 or 20kg to their anchor weight forgetting that for most cruising yachts the majority of the ground tackle weight is in the chain.

[MicHughV]

Well, here is a test you could conduct.
Note the waterline at the boat when at rest.....preferable tied up to a dock in quiet water.
Use a pen or pencil to make a small tick mark where the water meets the hull.

Now have your average size person stand on deck near the bow, more or less over the chain locker and measure again.

I doubt the difference will be noticeable....

[Joli]

We're 65,000#'s and use 3/8" g43 or 10 mm for the Europeans. It's fine. We're switching to 318l electro polished. Pricy but galvanizing didn't last two years in the Caribbean so we'll give it a try.

[Simi 60]

Originally Posted by tkeithlu

Take care of your chain and rust/wear will not be a problem.

Tell us more?

I guess if you never use it it never gets worn so doesn't rust.

[catsketcher]

Originally Posted by MicHughV

Well, here is a test you could conduct.
Note the waterline at the boat when at rest.....preferable tied up to a dock in quiet water.
Use a pen or pencil to make a small tick mark where the water meets the hull.

Now have your average size person stand on deck near the bow, more or less over the chain locker and measure again.

I doubt the difference will be noticeable....

The static behaviour of a boat is different from its dynamic beahviour. I have a pretty light boat (a 4000kg cat) and even though it can carry weight reasonably well it is very sensitive to weight in the ends. The rotational momentum of a few hundred kilos in the bow of a 20 tonne boat may very significant. Of course the best way to check is to remove the weight and go out in a seaway and observe the accelerations. I find that reducing weight on the ends makes the boat lift or drop more quickly at first, but this does not keep going with subsequent oscillations and the amplitude of the pitching reduces very quickly. The boat sails faster and the motion is fine for me.
For my 4000kg boat, I can feel the difference between our 22kg anchor on the bow roller, or having it back in the locker 4 metres from the bow. I prefer the motion when it is moved aft.
I think the OP should consider pitching in the calculations about weight in the bow. It is one of the advantages of cats, in that it is easier to move the chain aft to nearer the middle of the boat between bunks, whereas it is easier to keep the chain in the bows on a mono.

[wsmurdoch]

These discussions seem to revolve around the ultimate breaking strength of the chain rather than the yield strength. Wouldn't the load that causes the chain to be permanently deformed matter too. (especially for those who have a gypsy and windlass) But, I don't see yield strength listed.