Chain size and length

[saltyrob]

Hi Folks,
On inspection of our anchor chain I think its time to replace it. We have a Moody 28 and would like advice on anchor chain diameter and min length . We presently have 30 metres of 8 mm and would like to know if this is about right or could dia be reduced. We are on the east coast so our usual anchorages are relatively shallow.

Many thanks

Rob

 

[VicS]

Hi Folks,
On inspection of our anchor chain I think its time to replace it. We have a Moody 28 and would like advice on anchor chain diameter and min length . We presently have 30 metres of 8 mm and would like to know if this is about right or could dia be reduced. We are on the east coast so our usual anchorages are relatively shallow.

Many thanks

Rob

8mm chain is the correct size.
30metres I would say was the min length even I have 15 fathoms. You could have a length of 12 or 14 mm rope ready to add if necessary.

https://www.jimmygreen.co.uk/products/yacht-ropes---rigging/anchor-warps

 

[LadyInBed]

How often have you deployed it all and wished for more?

 

[Chalker]

VicS
15 fathoms is about 10% less than 30m. Is that what you intended?

 

[sailorman]

we use 20m x 8mm chain + 30m x 18mm anchorplait on the East Coast, boat 37ft 7 tons

 

[VicS]

VicS
15 fathoms is about 10% less than 30m. Is that what you intended?

Yes . My chain is 15 fathoms, They had not invented metres when I fitted out my boat.

 

[Neeves]

Our catamaran that draws 1m but is about 1m from waterline to bow roller was supplied with 30m of chain. Tidal range that we were subjected to was 3m. We found that we too often deployed the whole lot and wished for more and we upgraded to 50m, bought a whole new length. More recently we have replaced the 50m of 8mm G30 with 75m of a high tensile chain. Australia tends to be all chain as most people have ambitions to visit The Reef and coral eats nylon overnight. Many times the need to deploy a lot of chain is not because the anchorage is particularly deep nor that the weather is very taxing - but that the anchorage is full and you need to move to deeper water to gain enough room to anchor.

If you have found that on anchoring you often deploy the lot - then you do need more.

If you have a windlass then changing chain size would need a new gypsy but is a bit of a non starter in Europe as 8mm is the smallest HT chain easily available. You are therefore stuck with 8mm. If you decide to increase chain length then Vyv has some excellent advise on joining chain on his website - but do not buy cheap 'C' link chain joiners! (though you imply you are going to retire the old chain and buy new). Again Vyv on his website has some comments on chain quality.

Adding anchor plait is another option but if you are replacing the chain I would tend to buy extra length at the same time.

Jonathan

 

[Kwik Decision]

Hi Folks,
On inspection of our anchor chain I think its time to replace it. We have a Moody 28 and would like advice on anchor chain diameter and min length . We presently have 30 metres of 8 mm and would like to know if this is about right or could dia be reduced. We are on the east coast so our usual anchorages are relatively shallow.

Many thanks

Rob

Went through exactly the same process 2 yrs ago, on a very similar size boat. I settled on 30 m of 7 mm grade 40 chain, which has more or less the same strength as 8 mm grade 30, but weighs significantly less (1 kg/m vs 1.33 kg/m), together with 50 m of nylon warp for deeper water anchoring. This has been very effective, and is significantly easier to haul up by hand than the old 8 mm chain. The 7 mm grade 40 is easily available from Jimmy Green.

 

[CAPTAIN FANTASTIC]

The dia of 8mm is right; the length of chain is a personal preference. I use 8mm, 20m chain and 60m 20mm rope on a heavy 31ft boat. My rope is too long and I know i will never use the whole length but there is hardly any weight on the rope.

 

[ditchcrawler]

I have a Moody 31 and use 30m of 6mm chain spliced to 20m of 12mm 3 ply rope. I have a 6mm electric windlass which came with the boat.
I had a chat with the people at EYE co (The Gunshed) just round the corner from Levington because I thought the 6mm chain might be a bit light. They said that it was fine and that 8mm would be overkill. They do 6mm chain in grade 40 which is stronger than grade 30.There is a weight saving as well as a cost saving if you want new chain.
Most of my anchoring is east coast (lovely mud) and not in bad conditions.My system works well with a Rocna anchor.
Eye go are also good for warps and tested shackles.

 

[saltyrob]

Hi ,

Many thanks for your advise. I checked our chain link by link and found that isolated links had corroded , one down to approx rusty 4 mm . The chain overall looks ok but glad I had a close look.

Rob

 

[KellysEye]

To get a catenery when the picks up shallow depths need 10x depth deep water 3x depth.

 

[VicS]

To get a catenery when the picks up shallow depths need 10x depth deep water 3x depth.

So that would mean if I anchored in 30ft my 90 ft of chain would be Ok but if I wanted to anchor in only 10ft of water I couldn't because I'd need 100ft of chain but dont have that much.

I does not seem logical to me!

 

[rob2]

That's the trouble with all the "rules" I've ever read about scope v. depth - they imply that there are two conditions, rather than a relationship which approaches those two conditions. In practice, if you have 30m of chain you'll probably deploy most of it right up to the point where you shackle on a rope to extend it. If room is available, then extra scope is always of benefit.

The point of selecting chain size to suit your boat has less to do with the displacement, rather the force you can expect to be exerted by the boat's windage. In benign conditions a lighter chain will be ample to hold the boat, but as the wind gets up (and tide, but less so) the size and therefore weight of the chain is needed to maintain a catenary which absorbs snatch loads and keeps the pull on the anchor close to horizontal.

Rob.

 

[Neeves]

To absorb snatch loads use a snubber. Its cheap, effective and light. Carrying heavy chain to produce a catenary is fine upto 30 knots beyond which you have lost any snubbing effect of the chain. A nylon snubber, maybe 2 of different size - will be effective upto 70 knots if you plan to be in the sort of wind.

You simply cannot carry on most yachts enough chain to cover all eventualities. The locker is too small, the chain too heavy. Catenary might have been effective when there was nothing else - we have nylon - use it.

Jonathan

 

[vyv_cox]

So that would mean if I anchored in 30ft my 90 ft of chain would be Ok but if I wanted to anchor in only 10ft of water I couldn't because I'd need 100ft of chain but dont have that much.

I does not seem logical to me!

It's the outmoded RYA teaching that dates from when it was believed that catenary did anything useful. The thinking was that in shallow water there was insufficient vertical height of chain to provide the necessary weight, so horizontal distance needed to be increased. Nowadays we just use a snubber in stronger winds and shallow depths.

 

[charles_reed]

You don't need 8mm chain for strength, but it's commonly available. You could use 6mm (7mm is uncommon for gypsy sizes) and increase the amount of chain - anchoring in 10 - 12m I'd like 50m of chain - for less weight.
High tensile chain (T60) is available but in your position I'd settle for T40.
To fit the windlass, I use 8mm chain 50m with another 50m of 14mm octoplait.
I always anchor on mixed chain/textile rode - far less shock loadings and my boat lies more comfortably.
I anchor overnight about 180 - 200 times a season, mainly sand, in the Ionian/Aegean..
I'd certainly consider having your existing chain pickled and re-galvanised - providing you can find someone with a decent volume of galvanising on whom to piggy-back.
UK-made chain, of the date about which you're speaking is better made than much of the Italian and Chinese chain sold by chandlers and well worth re-galvanising (the zinc will be x3 than on new-purchased chain).

Two regular anchoring subscribers', whose anchoring expertise I value, are no-elex and Neeves. They do have very differing views of "best practice", but their comments are pithy, informed and accurate.

PS No-one has the full picture on anchoring, though many pontificate about it.

 

[Neeves]

Charles you are too kind and generous. But thank you.

As you mention 7mm chain is scarce. Maxwell have gypsies to suit for both EN and DIN size specifications but Muir have nothing. I have never seen it for sale, though have not really looked, I think an issue might be later on down the track if you want to replace it as 7mm is obviously not common. The nearest to 7mm might be a 1/4" - but then link dimensions would not fit a metric gypsy (but 1/4" gypsies are common place (in America) but all the major windlass makers will have one and could get it for you in the UK.

6mm is much easier to source and most windlass makes offer a 6mm gypsy. An advantage of going smaller, and this is going smaller for any chain size, is the large increase in length you can store in a chain locker when going one size smaller, say from 10mm to 8mm or 8mm to 6mm. Because the smaller chain is, well, smaller, you can retrieve more before towering becomes an issue. Smaller chain is obviously lighter, so your weight in the bow is reduced, or you can carry a longer length.

One major problem is finding rated shackles that fit 6mm chain and if you have gone smaller, maybe because you were on the edge of 6mm or 8mm you might have a big(er) anchor and then matching a shackle that physically fits both chain and anchor is another issue. Its all possible you just need to be persistent - but take a couple of links and your anchor when you go to the chandler to buy the shackle(s).

If you have an older heavier displacement yacht, compared with today's production offerings (which appear to have become lighter and lighter) then heavy chain in the bow locker might not be such an issue - though I would tend to favour more chain (and snubber) rather than heavier chain.

Jonathan

 

[syneraida]

I would agree with most, 8mm seems about the right size. The length is very much more subjective and really depends on the depth of water you regularly anchor in, we've got 75 meters and find we regularly use it, but we also often find ourselves anchoring in 20 metes of water. Almost without exception you are better off with chain than rope, but it's not always practical to have all the chain you need.

So I'd say get enough chain for where you regularly anchor and then use rope occasionally. But I would go along the lines of making up a suitable rope with stainless eye spliced into it then make sure your bitter end is accessible and connect the rope only when you need it. That way it doesn't sit in the bottom of your chain locker getting wet and unused all year. If you need the rope you'll probably know in advance and can dig it out from what ever locker you've stored it in, also it gives you one really nice long mooring line if you need one the rest of the time.

Note of caution with rope, if the wind blows up be very careful of chafe!!