Can I use 8mm chain on a 40ft boat?

Sailing in the same area as you, I would be happier with the 10mm chain. I reckon weight is as important as strength. Bear in mind that anchor chain is subject to considerable shock loads as the boat veers about in a decent breeze - the extra weight will act as a damper.

35m of 'anything' I would consider inadequate for NW Scotland. I frequently let out 45m+ if the conditions look dodgy.
 
J Neeves said:
Great image, and completely useless :)

You were 2m of water with 8m of chain or 10m of water with 50m of chain? The chain is 6mm and a 60hp engine or 12mm and a 30hp engine?

Jonathan
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It was in 5.3 m of water @ 3:1 scope. From memory, I think it was a 27hp engine on a 34 foot yacht with 8mm chain, nothing unusual.
 
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There should be no shock loads on an anchor chain (ever), that's what snubbers are for. A nylon snubber should be about 10m long and for the OP's yacht 12mm will be adequate, with some 16mm for storm use. But I would agree - 35m of chain looks a bit parsimonious.

I'd be happy with 8mm G30, but make sure you use a rated shackle - little point in using chain with a decent test certificate with a nefarious shackle.

Jonathan
 
noelex said:
It was in 5.3 m of water @ 3:1 scope. From memory, I think it was a 27hp engine on a 34 foot yacht with 8mm chain, nothing unusual.
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And the revs of the engine, 1,000, 2,000, 3,000 - without this no-one has any idea what the image shows.

But to add some of the detail that would have been usefully posted initially, a 30m length of 8mm chain, at a 5:1 scope will have all the chain lifted off the seabed at about a 70kg tension which is about the tension imposed on a 45' yacht in 17 knots. For a 35' yacht the same effect, but slightly higher wind speed. At around 30 knots that chain will appear as straight at a billiard queue. The max tension will be about 300kg during snatches, on a 45' yacht, which is the tension produced by a 30hp engine at near max cruising revs, say 2,750,with a 3 blade folding prop in reverse. With snubbers these snatches will be absorbed by the snubber(s).

Jonathan
 
>Depends where you will anchor and what conditions - I believe that the weight of the chain is important in stopping a boat dragging.......

>>Science and observation tell us otherwise. Dragging is most likely when it is windy. When it is windy the chain all lifts off the bottom. Its weight makes very little difference.

Chain weight and the amount of chain out is the greatest determinant of whether an anchor drags because weight of the catenary holds the boat. If the chain starts to straighten out let more out if you have more or put out a second anchor in a V. A riding sail cuts the swing from 90 degrees to 35 degrees and thus cuts the snatch load and I've never understood why so few boats have one.
 
Kelly's Eye - there is no catenary, or none that can be detected or is of any value, at 30 knots. You can deploy more chain - but most of us have a finite amount of chain.

The greatest determinate of dragging is the anchor and seabed - but we do not need to go there, the OP is interested in chain:)

Jonathan
 
NormanS said:
It would seem fairly obvious that if you are anchored in such shallow water, no chain of any weight or description is going to give a useful catenary. In such shallow water, a little bit of chain next the anchor, and then stretchy nylon would be much better.
Conversely, if you anchor in deeper water, say 10 metres or more, there is a real benefit in the catenary in the chain. It's horses for courses, so ideally, it's better to be prepared for all eventualities, so plenty chain, plenty stretchy rope, and plenty anchors, used appropriately.
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One would find it fairly obvious, in such shallow water with a scope of about 15:1 the catenary would have a lot of chain on the bottom but in fact with a bit of a blow there is enough force involved to make 10mm chain act just as noelex's photo shows. from bow roller to shank in all but a straight stripe.

That's the whole reason one puts out 3,4,5 or more to 1 scope! More chain to pick up and more inertia to overcome thus damping shock loads. We add a snubber to take out the rest.
 
J Neeves said:
Great image, and completely useless :)

You were 2m of water with 8m of chain or 10m of water with 50m of chain? The chain is 6mm and a 60hp engine or 12mm and a 30hp engine?

Jonathan
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Thanks to noelex for preserving identities! This is my anchor, photographed on the south coast of Lipsi last September. A slight correction to the scope if I may, we measure our chain length from the water, whereas Noelex' 'mermaid' may have thought I was counting from the bow roller, so I would say it's closer to 4:1. 8 mm chain, 15 kg Rocna, 2500 rpm on a Yanmar 3GM30F.

When I first began to question the unproven theory that the weight of the chain provided some holding power I was in Sardinia. We sat out a big blow in a sheltered bay (Cala Lupe) that shallowed remarkably slowly. We were able to anchor in sand with less than a metre of water beneath the keel, i.e. 2.2 or so. Over the next few days I swam frequently to observe what was happening, steadily increasing the scope. In the end we had 35 metres of chain out, same chain as now, Delta anchor. The whole length of chain was lifting off the bottom for maybe 50% of the time in winds to around 40 knots.
 
nimbusgb said:
One would find it fairly obvious, in such shallow water with a scope of about 15:1 the catenary would have a lot of chain on the bottom but in fact with a bit of a blow there is enough force involved to make 10mm chain act just as noelex's photo shows. from bow roller to shank in all but a straight stripe.

That's the whole reason one puts out 3,4,5 or more to 1 scope! More chain to pick up and more inertia to overcome thus damping shock loads. We add a snubber to take out the rest.
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Plus, lots of scope improves the angle to the anchor, so less likely to have it lifted out by too much pull in the vertical plane.
 
Ric said:
You don't understand anything about the mathematics of catenaries evidently.
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Probably better than you, because he's certainly anchored considerably more than you.
As soon as I see the old chestnut of catenaries and chain I know it's someone who's not been anchored in high winds.

At F5 there is no chain catenary left on the normal sailboat - those who insist that only chain is good should reflect upon the probability that they're subjecting their anchor to x3 the load it would suffer if they only had some nice springy nylon in the rode.
Despite the superfluity of self-styled anchoring experts, those who do it more than 150 times a year recognise that we've all got a lot to learn on the subject.

Suggest naysayers have a look @ Alain Fraysse's work.
 
A very interesting thread indeed. I read an article some time ago, I'm sorry I cannot remember the name of the author but I do remember he was an American liveaboard world girdler. In the article, which was written before all new technology anchors appeared, he campaigned the idea and his choice was to use an anchor and chain heavier than that specified for the boat, but rather than having all chain, have chain and octoplait cable. His reasoning was that the cable being far more stretchy would absorb shock loads allowing the chain to provide a dead weight of chain I suppose on the sea bed.

I'm quite happy to read this article, I have great respect for Vyv and J Neeves sounds like he knows his stuff, as I have only 20 meters of 10mm chain plus octoplait cable which is never enough chain to anchor without having to man handle the cable until there is enough chain to get it of the gypsy! I might well downsize to 8mm then for our 35ft boat. Oh! For the record the anchor is a 15kg Delta. I'll have to price this up, anyone want to buy a 10mm Lofrans gypsy!
 
Phoenix of Hamble said:
Plus, lots of scope improves the angle to the anchor, so less likely to have it lifted out by too much pull in the vertical plane.
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Briefly

The difference between 5:1 and 8:1 scope is about 6 degrees - if your anchor is this sensitive to setting angle (get a new anchor) and deploying even more chain will have further minimal difference. The idea that scope, beyond 5:1, impacts performance of an anchor by improving the angle is yet another phurphy:)

Moreover its not the angle of the rode at the seabed interface but the angle of the rode on the anchor shank - and the shank should be buried. If you look at Vyv's anchor - the shank end is buried. The angle of the rode at the seabed has no impact, or none that can be measured, on the rode/shank angle and a larger rode (bigger chain) will increase that angle as thicker chain has a greater resistance to being dragged under the surface (and reduces the ability of the anchor to dive). And the more deeply an anchor can dive, below the surface, the great the hold it will develop.

Jonathan

edit - an ideal if it were reliable, would be to have a wire trace as this would provide the minimum of resistance to an anchor dragging it into the seabed and thus engendering the dive of the anchor, another article in Practical Sailor end edit.
 
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J Neeves said:
The idea that scope, beyond 5:1, impacts performance of an anchor by improving the angle is yet another phurphy:)
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Many people imagine the pull must be horizontal to the seabed for the anchor to bury and work. This is not the case. As the photo shows, Vyv's Rocna is doing a great job burying despite a significant lifting of chain.

However, the closer the pull is parallel to the seabed the better the anchor's holding ability.

At 5:1 if the catenary disappears the chain angle is little over 11.5 degrees. Extending the scope to 8:1 will reduce this to 7.2 degrees.

As Jonathan points out the angular difference is small (it is actually only just over 4 degrees), but I believe that this does have a practical effect on an anchor's holding ability.

Chain in the locker does no good and would encourage people to use significantly more than 5:1 in bad conditions if it is practical to do so. (That does not mean you should always use a long scope, consider others using the anchorage)

A couple of manufacturers have produced tables relating the anchors holding ability against scope.
Fortress suggest that at 5:1 the anchor will have 70% of its holding ability and the additional 30% is not reached until the scope is 10:1.
 
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galadriel said:
A very interesting thread indeed. I read an article some time ago, I'm sorry I cannot remember the name of the author but I do remember he was an American liveaboard world girdler. In the article, which was written before all new technology anchors appeared, he campaigned the idea and his choice was to use an anchor and chain heavier than that specified for the boat, but rather than having all chain, have chain and octoplait cable. His reasoning was that the cable being far more stretchy would absorb shock loads allowing the chain to provide a dead weight of chain I suppose on the sea bed.
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Not sure of the author you mean but Alain Poireaud, designer of the Spade and one of the first to produce meaningful graphs of drag v. force, was a strong proponent of mostly rope rodes. I saw photos of his Hylas 47 anchored in Magellan Strait in very strong winds. He said that this was comfortable and secure using only 10 - 20 metres of chain for wear resistance and the rest Anchorplait.

I prefer to use all chain for several reasons - most of all because it makes going stern-to in Greek harbours far easier, as the weight of the chain gives directional stability to my boat's otherwise errant behaviour, also because until recently I did not have a gypsy that would handle rope well and I was not confident of its ability to stow well in the locker. I do use a long snubber though, which for me gives the best of all options.
 
vyv_cox said:
Not sure of the author you mean but Alain Poireaud, designer of the Spade and one of the first to produce meaningful graphs of drag v. force, was a strong proponent of mostly rope rodes. I saw photos of his Hylas 47 anchored in Magellan Strait in very strong winds. He said that this was comfortable and secure using only 10 - 20 metres of chain for wear resistance and the rest Anchorplait.
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Hello Vyv,
it dates even back from Alain. Leaving aside the recent "discoveries" of the advantages of snubbers by the various "anchoring PHds" :) , the first one to give a theoretical explanation of rode elasticity, shock loads, snubbers, effects of gusts, etc was Alain Fraysse in a "Loisirs Nautiques" series of articles appeared December 1997-February 1998, almost twenty years ago. Its later (2003) Excel workbooks draw from those articles. Unfortunately the magazine has since disappeared.

Alain Poireaud asked Fraysse's permission to include the articles at the end of his book, they can be found indeed in Appendix I; the content is very similar to the web site.

regards
 
>As soon as I see the old chestnut of catenaries and chain I know it's someone who's not been anchored in high winds.

I often mention catenaries because they are the key to anchoring as is scope, shallow water should be 20 x depth, 25 metres should be four X times depth, there is no fixed amount such as 5 X depth which is often mentioned. In six and half years away we regularly anchored anchored in gales, particularly in the southern Caribbean. If it looked like going over that we put a second anchor out. We carried 180metres of chain which will handle a gale easily especially with a riding sail plus two 100 metre warps each of which could be attached to two one hundred metres of chain for a second anchor and a monster Fortress for a storm anchor.

The great majority of boats will carry nothing like that because most are weekend and holiday sailors who don't go out when strong winds are forecast. What we carried is not unusual for long distance boats, but can vary subject to boat size and weight, because you have to take what comes along, just as you do when sailing offshore or a thousand miles plus from land. Our boat was a steel ketch with long keel and cutaway forefoot and weighed 14 tons fully loaded, so carrying all that wasn't an issue.
 
KellysEye said:
I often mention catenaries because they are the key to anchoring as is scope, shallow water should be 20 x depth, 25 metres should be four X times depth, there is no fixed amount such as 5 X depth
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20x Wow! You must have big anchorages where you sail ;)
 
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