Anchor chain width versus anchor size

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trinity393

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Is it really necessary to use 10mm chain on your anchor rode for a c. 40ft yacht. My old yacht was set up was 60 metres of 10mm chain (safe working load 2.5 tonnes, breaking load 5 tonnes) attached to a 20kg Spade. I never had any anchoring problems (except mediterranean weed), but the total weight was 160kg (2.35kg per metre) and the rode was sometimes a bit short in extreme conditions and/or very deep anchorages.

Does anyone have any views on if it would be as good to use 60 metres of 8mm chain (safe working load 1.6 tonnes, breaking load 3.2 tonnes) attached to a much bigger anchor (eg 30 kg Spade), for my next yacht. Would the larger anchor make up for the lighter chain? Is the safe working load something to worry about. This would only weigh 117kg - or you could take the rode length up to 90 metres for the same 160kg as the old set up which would give huge flexibility.

I always use a long, stretchy line as a snubber.
 
depends how your boat behaves when at anchor. My cat tends to move around a bit, a characteristic that is controlled to a certain extent by using a heavier chain (30m of 10mm chain ) with a 14mm octoplait warp.
 
Many people recommend to use a short but oversized chain with a long rope to get a large scope (1 to 10) even in deep water.

In your case (12m boat) : 20 to 30m (12mm) chain and 60 to 100m (18 mm) rope .
 
I used all chain, 5/16" (approx 7mm) Hi Test, sometimes called G4 or System 4, on my 41' heavy displacement boat. This has a higher working load (3,900 lbs) than 10mm proof coil (2,650 lbs), but only weighs 110 lbs per 100' as opposed to 155 lbs per 100'. I coupled this with a 45 lb (20kg) CQR and had total confidence in this set up. My second anchor was the same, on 20m of G4 chain backed up by three-strand nylon. I also carried a big Danforth but rarely used it. We anchored out most of the time and never had a problem. Mainly coral sand or mud bottom, sometimes weed.
Sorry about the mixture of imperial and metric, it's what you get for living in England and sailing in the USA!
 
Re: Everything you wanted to know...

Some misconceptions out there:

8mm Grade 30 (L) - break load 3200kg WLL 800kg - 1.4kg per metre
10mm Grade 30 (L) - break 5000kg WLL 1250kg - 2.3 kg per metre

8mm (5/16"= 7.9mm) Grade 40 (M) - break 4100kg (9000lb) WLL 1025kg (2250lb)
10mm Grade 40 (M) - break 6500kg WLL 1625kg

These are industry standard load numbers used worldwide except in the US who work funny ways depending on manufacturer and chain grade. 90% odd all 'regulations and standards' by whatever authorities run this system as well i.e ISO, DIN, EN, Aussie and the like.

Grade L is the new term for G30 and Grade M is the new G40 again US excepted.

All reputable (note the term 'reputable') manufactuers test all chains in the factory and give the following numbers:

Break Load - which is twice
Proof Load - which it is loaded to in the factory hence the term 'Proof Coil'
WLL or SWL - 1/2 the proof load or 1/4 of the break load AND the load at which, or below, the manufactuer will regard as acceptable. If it breaks when being used above this load it is likely they will not support any claim.
Again the US appears to work different (no body can tell us including one of their big manufacturers).

So trinity393 your actual WLL is 1/2 what you think it is but 10mm Grade 30 is fine on a boat your size. Using an 8mm on it, even a grade 40, would be regarded as most as being quite lite unless you are a racer.

The weight of all chains in whatever grade are very very similar size for size.

I sell 200 odd tonnes of chain a year mostly into the marine industry.

Safe sailing all
 
Re: Everything you wanted to know...

Yes, 5/16" is 7.9mm (a typo on my part). In the US the wire size is, for some bizarre reason, 1/32" bigger than the nominal chain size, so my 7.9mm nominal size is actually 8.7mm chain. The WLL on G4 of this size is 3900 lbs (about 1700 kg) according to all US data, but in any case exceeds the actual load required for anchoring a 41' boat. Weight in the ends of a yacht is a significant concern, cruising or racing, so if you want the benefits of all chain rode - strength, wear resistance and self stowing properties - you need to go for the lightest chain that will give the required WLL, which means selecting a higher grade alloy.
 
I would refer you to the official report on Mirabella. The inspectors commented that the chain though strong enough, had been selected in a smaller size to save weight, and that the weight of the chain is an integral part of the anchoring system.
I too, have a 40footer, and changed to a 10mm chain at the beginning of this season.
I find that the motion in a blow is better (less snatching), much reduced dragging, and better nights sleep.
 
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