Anchor chain: downsize from 10mm to 8mm?

[Boathook]

Another reason not to downsize, thanks.

I was going to downsize to 6mm chain but was struggling to find galvanised G70 in the UK so stuck with 8mm. I was trying to reduce the weight at the bows as I was going from mixed rode to all chain to make retrieval easier.

 

[Rappey]

I have 75m of 10mm sat in the garden in a bag and have been deliberating for ages about whether to use it or go to 8mm.
With anchor it's around 200kg. 8mm would be some 70kg lighter and easier if I had to manually haul it.
Looking at boats around the marina this past week I've seen many a boat larger than mine using 8mm.
Neeves load test figures also suggested that the maximum pull on a boat does not even get close to the chain breaking strength. I think I'm sold on the idea of 8mm

 

[[2574]]

I have 75m of 10mm sat in the garden in a bag and have been deliberating for ages about whether to use it or go to 8mm.
With anchor it's around 200kg. 8mm would be some 70kg lighter and easier if I had to manually haul it.
Looking at boats around the marina this past week I've seen many a boat larger than mine using 8mm.
Neeves load test figures also suggested that the maximum pull on a boat does not even get close to the chain breaking strength. I think I'm sold on the idea of 8mm

Exactly my thinking. I’ve also downsized anchor from 30kg Bruce to 25kg Vulcan, the latter being the manufacturer’s recommended sizing. All together I’ve added 20m chain length and taken 65kgs of weight out of the bow. No it wasn’t cheap but good anchor kit soon pays for itself with south coast marinas charging in excess of £50/nt.

 

[Badvisor]

You don't want to be downsizing! On the contrary, I'd be really worried with only 10mm chain on a heavy boat like that. Sure you'll get away with it a lot of the time in sheltered conditions, and while the chain is in perfect condition. But once the wind gets up, your catenary will all but disappear. If there's any corrosion in the chain (and don't forget there's invisible corrosion that you won't see) it won't take a lot to snap a link.
I wouldn't sleep comfortably with less than 12mm, preferably 14mm.
You can't be too careful, you know!

 

[Neeves]

I'm inclined to agree. If Gary needs new chain anyway, downsizing would make sense, likewise if he were heaving it up by hand and finding it difficult. Otherwise, while anything that adds lightness is a good thing, if it ain't broke...

I have not heard of a chain failure for around 10 years. G70 is hardly common, but a number of people use it (think Dashew) and others use Cromox which is a G60 and when people use these chains they are invariably downsizing.. If there were stories of premature failure - we would know. Good news does not travel but bad news travels at a speed that even Sir Richard Branson would be envious.

If you have a space issue - then you can carry more smaller chain. If you decide you are going to need a new windlass in the near future, because the existing one is looking unloved then the time to change is when you need new chain - then you can choose the smaller gypsy and smaller chain. The new windlass will need smaller cables and less power.

And the weight savings can be large - would you sail to windward with a retired, and gone to seed, rugby player sitting at the bow - that's the sort of weight savings that can result.

Of course it is daft to down size chain if the current chain is in good nick and your windlass is relatively new. Its also daft to downsize if you don't really care about weight and sailing performance - plenty, most people sail for pleasure - not to break records.

The other requirement is - you do need to use a decent snubber (but you do that anyway - don't you? .


I'm in discussion with a couple sailing round the world who have been using 8mm chain but it has reached its life expectancy or will do before they reach somewhere else where they can easily replace the chain. I managed the production of 2 rodes, 1 x 8mm x 100m to replace 10mm for an Ovni and one 1 x 6mm x 100m for a 50' tri. earlier this year and the circumnavigating couple look to be ready to confirm for 6mm. I simply make sure they get what they need, defining gal coating thickness and strength (I don't have any financial involvement - I do it to satisfy my ego - I am not breaking Forum rules. The 6mm has the strength of 8mm and 8mm the strength of 10mm. The chains come with matching shackles, chain hooks, Boomerangs (that fit and are stronger than the chain) etc.

If anyone were interested (PM me with a email address and) I can send a pdf of how I had ours made, 6mm x 75m + 15m of 6mm for a second spare rode).

Take care, stay safe

Jonathan

 

[noelex]

Gary, you have mentioned the displacement of your vessel (12t) and this is a factor in selecting a suitable strength/size of anchor chain, but other factors such as the length and type of vessel also play a significant role.

Perhaps you have mentioned your vessel model previously and I missed the post, but clarifying these details would help provide better answers from the forum

 

[Tranona]

You don't want to be downsizing! On the contrary, I'd be really worried with only 10mm chain on a heavy boat like that. Sure you'll get away with it a lot of the time in sheltered conditions, and while the chain is in perfect condition. But once the wind gets up, your catenary will all but disappear. If there's any corrosion in the chain (and don't forget there's invisible corrosion that you won't see) it won't take a lot to snap a link.
I wouldn't sleep comfortably with less than 12mm, preferably 14mm.
You can't be too careful, you know!

I assume this was posted in jest.

There is simply no evidence to support your suggestion. It is not the weight of the boat that is important but the load it can apply to the chain and as Neeves has said (supported by empirical tests) the maximum load such a boat can apply is around 25% of the ultimate load the 8mm chain can withstand and around 60% of the SWL. So absolutely no chance of it breaking. How can there be "hidden corrosion" on a chain where everything is visible? Even then corrosion of the type normally experienced on anchor chain has minimal impact on strength. As to catenary, if one is worried about that (even though it has little impact on the ability of the anchor to hold) then follow the suggestion to use a snubber.

Perhaps you should do some reading of the copious scientific papers - or even the articles in the Yachting press so that you can understand the subject.

 

[Badvisor]

Posted in jest? As if!
Yes, yes, you can quote all the numbers and "experts", but bigger has to be better. Just think how you'd feel watching your boat being smashed to pieces because you'd skimped on chain.
Remember the old rule of thumb - a millimetre of chain for every tonne of boat. So 12mm is about right for a 12 tonne boat. But I'd be happier with 14mm or 16mm. And a big chum.

 

[dom]

You don't make any sense, at all. You say you are in the catenary club and then imply you would buy G70 8mm if it were cheaper.

Make up your mind.

A decent snubber that costs peanuts will replace the absence of catenary.

Most 8mm chain has a UTS or 4t - you will never develop even 25% of that tension in your rode. If your chain is rusty - it will not improve with time, either get it re-galvanised or buy new chain......

For goodness sake, roll it back in Neeves ! You don't even have the full dets of his vessel

8mm would almost certainly be fine, he knows that, I know that, we all know that.

FWIW on my boat - circa 50' - a respected yacht design office confirmed that 8mm would almost certainly be fine but that in a big blow with a bit of a sea, it might be better to stick with 10mm. This is because, taking account of the error bars involved, the maximum strains may well exceed the 4x safety factor you mention.

According to the American Boat and Yacht Council, (ABYC) the max load a 50' yacht will generate in a storm is around 6000lbs (circa 3 tons) in 60kts of wind. That figure is an estimate of the maximum forces including shock loads, which on the face of it makes 8mm chain a safe bet with its SWL of around 8 tons.

These numbers are, however, just estimates with considerable error bars around them depending on precise conditions.

Sufficient to make me - and Gary - pause for thought. Hence his perfectly reasonable and seamanlike question in a yotty chat room.

As for snubbers, great idea but the ABYC advises against sizing for them. Here is what it has to say:

"After comparing this data in this table to work that has been done since we come to the conclusion that the values presented here represent loads expected on the anchor rode if anchored on chain only without the use of the snubbing system. Further using a line rode or and adequately designed snubber you can reduce the loads by a factor of 3, by eliminating the shock loads. This is an argument for why its so important to use a snubber but when sizing anchor rode or your anchor, it is important to consider loads as stated in the table. The reason is that we can not rely on the integrity of a snubber in a storm. Should the snubber fail, the integrity of the rode should be sufficient to handle the loads without the snubber. "​

ABYC Calcs in lbs

 

[Gary Fox]

I have 75m of 10mm sat in the garden in a bag and have been deliberating for ages about whether to use it or go to 8mm.
With anchor it's around 200kg. 8mm would be some 70kg lighter and easier if I had to manually haul it.
Looking at boats around the marina this past week I've seen many a boat larger than mine using 8mm.
Neeves load test figures also suggested that the maximum pull on a boat does not even get close to the chain breaking strength. I think I'm sold on the idea of 8mm

That's what I was thinking as well ! However, part of the enjoyment of sailing is having visibly strong and stout scantlings, rigging, ground tackle etc which give the confidence that nothing will break. This is the vital point which the 'catenary is mythical' fanatics seem to be incapable of grasping; for all their foaming at the mouth with obscure mathematical formulas, we don't sail by breaking loads calculated to the nearest 0.1 kilo, with ground tackle or anything else . That pie-in-the-sky stuff is for Imoca 60's etc, which oddly enough keep breaking bits off when they encounter real-life scenarios which can't be calculated by a computer.
So, I am not sold on going down to 8mil right now. It is certainly tempting, but is it a siren on the rocks?

 

[Gary Fox]

Posted in jest? As if!
Yes, yes, you can quote all the numbers and "experts", but bigger has to be better. Just think how you'd feel watching your boat being smashed to pieces because you'd skimped on chain.
Remember the old rule of thumb - a millimetre of chain for every tonne of boat. So 12mm is about right for a 12 tonne boat. But I'd be happier with 14mm or 16mm. And a big chum.

Yes indeed, and nobody has ever been at anchor, wishing their ground tackle was lighter!
I will try and attach some details of my vessel as requested above.

 

[Gary Fox]

I have 75m of 10mm sat in the garden in a bag and have been deliberating for ages about whether to use it or go to 8mm.
With anchor it's around 200kg. 8mm would be some 70kg lighter and easier if I had to manually haul it.
Looking at boats around the marina this past week I've seen many a boat larger than mine using 8mm.
Neeves load test figures also suggested that the maximum pull on a boat does not even get close to the chain breaking strength. I think I'm sold on the idea of 8mm

Rappey your location has slipped my mind, but if you decide to take the plunge down to 8mm, and are within reach of the Solent, I might have a new home for your chain!
I am sticking at 10mm , although I was wavering, I am lucky having a proper boat with a big chain locker which can carry the weight. (Well it wasn't just luck but that's another topic..)
If I had a light boat, things would be different I'm sure.

 

[Tintin]

You're right about catenary and chain size. I think you a being a bit optimistic even at 10mm. You want as much out as possible, and a lot of (dare I say) girth.

Get yerself 150m of 16 or 18mm. You'll never have a sleepless night at anchor again.

What do the "experts" know anyway, and let's face it you can make maths support anything. These guys that promote thin chain ... pah.... what do they know anyway.

 

[[2574]]

You're right about catenary and chain size. I think you a being a bit optimistic even at 10mm. You want as much out as possible, and a lot of (dare I say) girth.

Get yerself 150m of 16 or 18mm. You'll never have a sleepless night at anchor again.

What do the "experts" know anyway, and let's face it you can make maths support anything. These guys that promote thin chain ... pah.... what do they know anyway.

Yep, spot on I reckon. It’ll weigh about 900kgs, add a decent anchor and it’ll be a tonne all in, proper job……

 

[Tranona]

That's what I was thinking as well ! However, part of the enjoyment of sailing is having visibly strong and stout scantlings, rigging, ground tackle etc which give the confidence that nothing will break. This is the vital point which the 'catenary is mythical' fanatics seem to be incapable of grasping; for all their foaming at the mouth with obscure mathematical formulas, we don't sail by breaking loads calculated to the nearest 0.1 kilo, with ground tackle or anything else . That pie-in-the-sky stuff is for Imoca 60's etc, which oddly enough keep breaking bits off when they encounter real-life scenarios which can't be calculated by a computer.
So, I am not sold on going down to 8mil right now. It is certainly tempting, but is it a siren on the rocks?

But it is not to those margins - just read the actual margins - unless you call 4 times "marginal". Neither is it about "obscure mathematical formulae". Vyv's and Neeves tests (and those of the manufacturers and certifying bodies) are carried out using load cells to measure the load when the chain or shackles break. Simple hard facts using the same forces as your boat puts on your chain.

Actually it is not chain that is the potential "problem", but shackles. Suggest you look at the sort of shackle you use and compare its SWL (if you can find it) with that of your chain. Do you use tested shackles. or do you like most just buy a big shackle from the chandler because it looks big and strong. If so it is almost certainly far weaker than your chain and weaker than smaller tested shackles to a higher load.

Your anchoring system is only as weak as the weakest part. First shackle, then the anchor - whether you are using a 20kgs or 25kgs - with a holding power less than than the SWL of 8mm chain, then probably a tossup between the chain and its attachment to your boat.

BTW the designer of your boat was very scientific in the way he designed boats, doing all the calculations long hand - just like most of the really good designers from that era. However one of the reasons why his, and many other boats from that era were heavy was because they did not have reliable data on the properties of the materials they worked with. Even when they did have an idea, because of the natural nature of the material variability was huge, hence the over building, reinforced by the scantling rules which took into account the lack of knowledge about and variability of the materials used. This would of course include chain where although it was possible to calculate breaking strains, and measure them, there were no standards so no way of knowing what the actual properties of a particular type of chain were.

Times have moved on and there is no reason why you cannot take advantage of the improvements in knowledge and products to enhance the performance and safety of your boat - and arguably nowhere is it easier than in anchoring.

 

[Badvisor]

You're right about catenary and chain size. I think you a being a bit optimistic even at 10mm. You want as much out as possible, and a lot of (dare I say) girth.

Get yerself 150m of 16 or 18mm. You'll never have a sleepless night at anchor again.

What do the "experts" know anyway, and let's face it you can make maths support anything. These guys that promote thin chain ... pah.... what do they know anyway.

Good point about length of chain. In a blow you need a good old length out to get a decent catenary. But still want a good length in the anchor locker, as you'll always want spare just in case, plus you'll want the extra weight up there to make the boat steadier at anchor. So yeah, at 10:1 you'll want 100m out if you're anchoring in 10m, plus another 50m in the locker in reserve and steadying the boat. But I'd be happier with a bit more on board for contingency, so maybe go for 200m of chain. As you say, 16 to 18mm would be good. Or maybe 20mm for safety.

I didn't want to go into anchors as it's a contentious subject, but again weight is your friend here.

The thing is, if you're serious about a good night's sleep, then ideally you'll have two anchors out, either in a Vee form, or in a Bahamian moor. So all the above needs to be doubled if you're serious about anchoring.

Listen to your instincts!

 

[Laminar Flow]

Posted in jest? As if!
Yes, yes, you can quote all the numbers and "experts", but bigger has to be better. Just think how you'd feel watching your boat being smashed to pieces because you'd skimped on chain.
Remember the old rule of thumb - a millimetre of chain for every tonne of boat. So 12mm is about right for a 12 tonne boat. But I'd be happier with 14mm or 16mm. And a big chum.

I love the hysteria these threads generate.

16mm on a 12 t, 34 footer, really? And now 20mm and 200m of it?
Such suggestions are beyond any sense of reality and I can only suspect the author(s) "don't get out much".

My last boat was 50' over deck and displaced 30t. We had 80m of 13mm chain which weighed some 350kg (!), if I recall correctly. So, by your suggestion, it should have needed 30mm (????)
Now on 8.5t and 31.5' we have 8mm.

Am I worried? God no! Anyone that fearful or "risk adverse" should perhaps better turn to stamp collecting for a hobby.

 

[CAPTAIN FANTASTIC]

I love the hysteria these threads generate.

16mm on a 12 t, 34 footer, really? And now 20mm and 200m of it?
Such suggestions are beyond any sense of reality and I can only suspect the author(s) "don't get out much".

My last boat was 50' over deck and displaced 30t. We had 80m of 13mm chain which weighed some 350kg (!), if I recall correctly. So, by your suggestion, it should have needed 30mm (????)
Now on 8.5t and 31.5' we have 8mm.

Am I worried? God no! Anyone that fearful or "risk adverse" should perhaps better turn to stamp collecting for a hobby.

I agree; hysteria is an understatement; 200 meters of 20 mm chain????? it must be a joke!!!!

 

[Badvisor]

Now on 8.5t and 31.5' we have 8mm.

Excellent - I'm glad you agree with the rule of thumb 1mm per tonne of displacement!

 

[Rappey]

What is the point of huge chain when the anchor will probably be pulled out way before anywhere close to the breaking point of the chain is achieved?
As for 200m of 20mm, that alone would weigh 1820kg, plus the anchor which surely must be 50kg for that size and the weight of the windlass needed to haul it.. Madness ! Cant see your propellor actually making contact with the water with that weight on the bow !
Many figures people are quoting are calculated
Neeves actually got out there and measured them for real.. they were a lot less than some articles lead you to believe..
The many moorings in portsmouth harbour are either 10mm chain from the buoy to the boat or some form of rope.. Many of these boats sit "at anchor" 365 days a year in winds that sometimes exceed 100 mph yet ropes and chains are not snapping under the load but some seem to think it may snap while occasionally being used in a bay at anchor?? Many failures of moored boats are failures of the deck gear of the boat or a chain that is way beyond its sell by date.