Worth the difference G40 v G70 anchor chain

[noelex]

Indeed so. Last weekend I was presenting my anchors talk at the Cruising Association HQ in London. Someone asked a question about setting my Fortress kedge, which has a rode of 5 metres of 8 mm chain plus Anchorplait . I only ever throw it overboard, either from the dinghy or bow of the boat, and it never fails to set. I believe that Fortress say the chain is unnecessary. It most definitely does not need heavy chain.

I agree that no anchor needs a chain rode. Most will work OK with a rope rode, but the range of substrates where they will set is reduced. Using the Fortress without any chain is a useful option as the overall weight is so light that it is easy to manage in the dinghy. It is even possible to swim the anchor out.

Below is a photo of my Fortress in soft sand managing on all rope rode:



However, I am surprised that you have never had a Fortress fail to set. The Fortress is a great anchor; every cruising boat should have one, but the range of substrates where it works is more limited than most other modern anchors, and this is exacerbated when used with minimal, or no chain. It has fantastic holding ability in softer substrates but struggles to set in hard sand or thicker weed; be particularly cautious of the performance in less favourable substrates when using rope.

Below is a photo of a small Guardian (made by Fortress) showing how it cannot penetrate this harder sand even with some chain:

 

[vyv_cox]

I agree that no anchor needs a chain rode. Most will work OK with a rope rode, but the range of substrates where they will set is reduced. Using the Fortress without any chain is a useful option as the overall weight is so light that it is easy to manage in the dinghy. It is even possible to swim the anchor out.

Below is a photo of my Fortress in soft sand managing on all rope rode:

View attachment 191311

However, I am surprised that you have never had a Fortress fail to set. The Fortress is a great anchor; every cruising boat should have one, but the range of substrates where it works is more limited than most other modern anchors, and this is exacerbated when used with minimal, or no chain. It has fantastic holding ability in softer substrates but struggles to set in hard sand or thicker weed; be particularly cautious of the performance in less favourable substrates when using rope.

Below is a photo of a small Guardian (made by Fortress) showing how it cannot penetrate this harder sand even with some chain:
View attachment 191312View attachment 191313

Most of our experience using the Fortress has been in Greece, where hard sand is unusual. A very different matter from Wales, where even our Delta utterly refused to set on sand where large waves sometimes crashed.

 

[Neeves]

I completely get the overengineering built into anchor rodes and many other aspects of yacht design. A light boat or anchor system is not of itself flimsy or prone to failure.

With chain, looking at WLL rather than breaking load, then 6mm offers 600kg, 8mm offers 1100kg and 10mm offers 1690kg. I just replaced my 10mm chain with the same size rather than 8mm because it was simple (gypsy wheel) and was in the original spec for the boat. My boat (like NormanS) carries about 3000kg more plastic, wood and metal than it technically needs to plus another 1000kg of fuel and water. Plus 8 sails and lots of gear etc. The extra 44kg of 10mm is insignificant in that lot! In view of the weight and respecting WLL rather than breaking load given that these numbers will decrease with wear and corrosion, I "felt" comfortable with 10mm.

If I had a lighter weight monohull or a multihull then I would sail with a different philosophy and less, lighter stuff. Chosen wisely I would not expect failures.

As a corollary, I was aboard my boat afloat in the marina during one of the vicious storms this winter (92mph recorded nearby). The forces generated by wind striking the boat in a sheltered marina were fearsome. This was shortly before I made the chain replacement decision!
View attachment 191307

You do not make it entirely clear, so I might misinterpret, but you seem to suggest your choice of your new rode was on the basis that was what fitted your gypsy and its what was specified, in terms of WLL, for your yacht (decades ago).

Today you have choices that were not available when your yacht was designed - G70 chain is now commonly available. Its not available as a neat 'mathematical' replacement but 8mm G70 has a WLL of 1,370kg vs the chain you bought with a WLL of 1,690kg.

If I ponder reports of chain failure I have never, or not in the last 40 years, read of an anchor chain failing because it was understrength. I have heard of chain failure because of poor manufacture, welds failing, but never heard of chains deforming nor actually failing. This seems to suggest, to me, that the WLL chosen, sometimes represented by chain size, vs the size of yacht errs very much on the side of safety - and that the WLL of 1,690kg is safe - not one report of failure, so maybe - overly safe.

The specification for your yacht, decades ago, would have been made - in the absence of a snuubers - and adding an 8mm chain of WLL 1.370kg and a well engineered snubber and your smaller rode would have been as safe, but more comfortable and more versatile than your new 10mm chain. For confirmation of my bald statement - just look at the graph I posted - correctly sized nylon will give you all the snatch load dampening you could ever need - even with a short rode deployed. The nylon will support you - until it fails - but chain has a very finite usefulness window (unless you can carry an inordinate length and have the room to use it).

However I am the first to acknowledge that the cost of a new gypsy would weigh very heavily in favour of keeping what you have.

The time to change chain size and specification is the time when you, simultaneously, need a new windlass (or a new yacht) - and having that combination occurs.....seldom.

Using nylon to soften snatch loads not only makes life on board more comfortable but also supports any inadequacies of the hold of the anchor, should you be anchored in one of this difficult seabeds (of which we hear so much). Constant snatch loading of your anchor will reduce the shear strength of the seabed in which the anchor is buried and an all chain rode, not touching the seabed, will produce those snatches - adding a snubber will allow the snubber to manage the snatches not the anchor/seabed.

Jonathan

 

[Neeves]

I agree that no anchor needs a chain rode. Most will work OK with a rope rode, but the range of substrates where they will set is reduced. Using the Fortress without any chain is a useful option as the overall weight is so light that it is easy to manage in the dinghy. It is even possible to swim the anchor out.

Below is a photo of my Fortress in soft sand managing on all rope rode:

View attachment 191311

However, I am surprised that you have never had a Fortress fail to set. The Fortress is a great anchor; every cruising boat should have one, but the range of substrates where it works is more limited than most other modern anchors, and this is exacerbated when used with minimal, or no chain. It has fantastic holding ability in softer substrates but struggles to set in hard sand or thicker weed; be particularly cautious of the performance in less favourable substrates when using rope.

Below is a photo of a small Guardian (made by Fortress) showing how it cannot penetrate this harder sand even with some chain:
View attachment 191312View attachment 191313

We don't know why this Guardian did not set - any anchor can catch a 'foreign' object in the toe, whether its a lost swim suit or a bit of kelp and a small unseen contaminant is enough to reduce the performance of any anchor. I have been testing anchors for decades and can anticipate the hold an anchor can return. Often during testing an anchor underperforms, factorially, and on investigation find the toe has impaled an oyster shell or piece of water logged wood (the down side of sharp toes) - this is bad luck - but par for the course.

One of the 'almost' unique advantages of Fortress/Guardian and aluminium Spade, Excel and High Tensile Viking is their high hold to low weight ratio - allowing an owner to deploy an anchor for a popularly sized yacht (say upto 50') by hand from a dinghy (as Vyv describes).

All anchors are a compromise - there is not, yet - the perfect anchor - get used to it and accept reality. Criticising a design for an unknown flaw sends the wrong messages.

Jonathan

 

[Dockhead]

This is an old and discredited idea.

You can test that idea out yourself.

Deploy about 30m of chain, say 8mm, in shallow water. Take one end of the chain, pull it, and give it a bit pf grunt and you can pull it over the seabed, just you, single man power - the chain is offering virtually no hold at all.

Now add a decent anchor one designed for a 30'/35' yacht - you will need a decent 4x4 to break its hold - the anchor will hold to about 2,000kg assuming you are dragging chain and anchor over sand.

You can pull the chain - say about 100kg of tension, pulling the chain, and the 4x4 showing the anchor will hold about 2,000kg.

The chain offers no hold - you rely on the anchor. You could use dyneema, instead of chain, chosen to have the same WLL or tensile strength as chain - but effectively no weight. The trouble is the dyneema floats and will be a hazard to your own yacht, (its a yacht - the dyneema will tangled round the sail drive and keel) and be a hazard to passing yachts.

If you deploy 30m of appropriately sized chain and a decent anchor. and the wind gets up - then the chain will not touch the seabed at all - exactly what mechanism is allowing your chain to provide any friction at all. You can deploy more chain - if you have it, if there is room but the friction (as you prove with you pulling the chain) offers minimum of hold.

You can extend the testing a bit further.

Take a steel Spade or a steel Excel and compare the hold of the aluminium models. You will find the steel Excel or Spade, say 15kg models, have the same hold as the 8kg aluminium models. Similarly take a same sized genuine Danforth and compare with a Fortress and the 2 anchors, steel Danforth and aluminium Fortress will develop the same hold.

Its not weight but design. The aluminium versions may be, or not be, as strong, or of less robust strength - but that's an engineering issue. Excel beefs up its strength by using HT aluminium, the 5075 alloy (costing an eyewaterinw amount) - but the alloy versions develop similar hold to their steel brothers.

Jonathan

This is all very true, Jonathan, but heavier chain gives more effective catenary, which gives a better ride at anchor. The weight is very beneficial, even though it won't increase ultimate holding power -- as catenary is pulled out by then. But in all conditions up to that point, heavier chain is much nicer, especially in deep water.

The downside is weight in the bow is harmful to sailing performance. Much more noticeable, the smaller the boat.

With my setup -- 100m of 12mm chain, 330kg worth -- I don't need a snubber in winds of less than 30 knots, and in deep water with all the chain out -- maybe never.

 

[Dockhead]

I'm sure that your oft repeated graph means something to some people. It is noticeable, however, that it conveniently omits any information regarding depth. It's obvious that if anchoring in shallow water, chain will not give much useful catenary. Conversely, when anchoring in deeper water, the weight of chain gives a very useful catenary. There is good reason for deploying a stretchy snubber in shallow water, but in deeper water, decent sized chain is perfectly adequate, and much simpler.

It depends on how heavy the chain is, and how deep the water, but in general, I agree with you.

 

[Tranona]

This is all very true, Jonathan, but heavier chain gives more effective catenary, which gives a better ride at anchor. The weight is very beneficial, even though it won't increase ultimate holding power -- as catenary is pulled out by then. But in all conditions up to that point, heavier chain is much nicer, especially in deep water.

The downside is weight in the bow is harmful to sailing performance. Much more noticeable, the smaller the boat.

With my setup -- 100m of 12mm chain, 330kg worth -- I don't need a snubber in winds of less than 30 knots, and in deep water with all the chain out -- maybe never.

The issue about size/weight of chain is whether the difference between for example 8 and 10mm on the effect of catenary is noticeable. In other words if 8mm is strong enough for the loads is there any measurable benefit to offset the additional cost and weight.

 

[Neeves]

Catenary in an anchoring environment is about storing and transferring energy. A snubber does exactly the same.

The wind blows, the yacht moves in the direction dictated by wind, the energy of the wind is transferred to the yacht (making the yacht move), the yacht pulls the catenary more strait (or and stretches the snubber). The energy of the moving yacht is transferred to the chain (stretched snubber), the less saggy catenary (the stretched snubber), the wind drops and the energy stored in the chain (snubber) is transferred back to the yacht and allows the yacht to be pulled back toward the anchor.

If you have chain - you rely only on catenary and as the catenary straightens the chain has increasingly less ability to store more energy - see the graph. At 300kg (depends on the yacht but think 30 knots of wind) the graph for the chain is effectively horizontal - no more energy can be accepted. If the catenary is 'strait enough' it will effectively behave like a rigid wire rod - you will endure snatch loads (on the bow roller/windlass and identically on the anchor). 300kg/30 knots is nothing - even a 6mm G30 chain has a WLL of 'about' 600kg (and 8mm about 750kg


If you have a snubber you rely on both catenary and elesticity. The catenary effect is finite but elasticity is effectively linear, until the snubber fails.

A snubber does have a finite ability to stretching - typically it will stretch 40% and then fail. A good WLL is 10%. BUT - snubbers wear, its a function of the number of, and severity of, stretch cycles. You will not know your snubber is worn - it will fail - carry a spare (or keep the stretch within 10% and you will prolong life - but it will still eventually fail.

A significant downside of chain is that finite ability of the catenary, you need catenary - which determines where you can anchor (not up against the beach where its sheltered - no room for the catenary.

The issue about size/weight of chain is whether the difference between for example 8 and 10mm on the effect of catenary is noticeable. In other words if 8mm is strong enough for the loads is there any measurable benefit to offset the additional cost and weight.

None at all if you are using a snubber. The snubber is lighter, cheaper, takes up less room and will work well beyond the limit of the chain - just look at the graph . You could use all snubber - except snubber is prone to abrasion and more so on the seabed.

I measured rode loads, all chain, no snubber, as a seabreeze increased, so I measured when the winds were benign but chickened out when the gusts peaked only at snatch tensions of 650kg. Snatches of 650kg are frightening - its like driving your yacht flat out into a brick wall (and its 150kg less than G30 8mm chain max WLL. Before you get to a snatch of 650kg you will have decided, say at 400kg, to bail out - you will be moving some where more quiet, your crew will have vowed never, ever, to sail with you again - its that bad. You can deploy more chain - if you have more, if you have room - OR you can simply have used a snubber in the first place. If you have down sized chain - the chain will provide the necessary abrasion resistance, use some of its catenary, offer a sensible WLL (similar to the WLL specified for your yacht) but you can rely on elasticity (almost completely).......

.......If your snubber is long enough.

And long snubbers are cheap, light and effective

Jonathan

 

[Neeves]

This is all very true, Jonathan, but heavier chain gives more effective catenary, which gives a better ride at anchor. The weight is very beneficial, even though it won't increase ultimate holding power -- as catenary is pulled out by then. But in all conditions up to that point, heavier chain is much nicer, especially in deep water.

The downside is weight in the bow is harmful to sailing performance. Much more noticeable, the smaller the boat.

With my setup -- 100m of 12mm chain, 330kg worth -- I don't need a snubber in winds of less than 30 knots, and in deep water with all the chain out -- maybe never.

Once you get 'really' big I agree weight in the bow is not such an issue nor are snubbers. But most of us buy smaller AWBs with all the weight factored out and then weight in the bow can be significant - commonly the difference in weight for a rode in 8mm or 10mm would be a man's weight - a man permanently on the bow would. destroy sailing ability - for you - a man on the bow might not be noticed.

You can alter the 'ride' by altering the snubber. In the same way you alter the ride with chain (though you are limited to altering length with chain) you can alter both the length and type of snubber. You can alter diameter, of your snubber, which will impact the amount of elasticity for a give tension, you can alter the fabrication process, 3 ply, braided, kermantle and the ride will also very with age.

With the variables at an owners disposal I doubt you could tell the different in ride of elasticity vs catenary - except for price, space, weight.

Most people who start on the snubber path oversize their snubbers, they have this hang up about strength (they want more) and then they lose elasticity.

We started off with retired dynamic 12/13mm kernmantle which we can source for free in Australia - being free you are more comfortable in experimentation. We transited from 15m snubbers, as a bridle, eventually to 30m each side. We thought we had got it right and then invested in new 12/13mm rope but found it a 'bit' inelastic and decided 10mm dynamic kernmantle , 30m, suited us best.

30m sounds a lot but we had a 12m cat and ran the snubbers from the transom, down the side decks to a turning block on the bow and then to a common chain hook. Normally we simple used that arrangement and kept the spare (about 15m) as one does a sheet - at the transom (in a sheet bag). If the weather became a bit more challenging we had 15m in hand we could further deploy. We could deploy more (or retrieve, from the comfort and safety of the cockpit (retrieving using the sheet winches, we have windlass controls in the cockpit).

Our rode was high tensile 6mm chain and our primary anchors aluminium Spade and Excel (8kg each) but would now use as another option a Odin 40 from Viking (weighing just under 10kg) - its design not weight

We used dynamic kernmantle because it is made to be elastic and has an abrasion resistant outer cover (and for us - was free). We installed the snubbers permenantly running the ropes through 'deck organisers'. I had compared our cat with a mid year 2,000 Bav and we had the same windage as a 48' Bav, though the Bav with its keel was heavier. I'd be happy using 10/12mm for a 48' AWB. I designed and had made my own chain hook.


Reading storm anchoring articles - the fundamental is to keep as many ground tackle controls in the cockpit - the last place you want to be at 2am in 50 knot gusts and rain is at the bow roller. I have seen too many chain hook failures - ours is bullet proof (and available from Viking Anchor (we don't derive any income)


Going back to the thread - I'm of the belief that the rode is a combination of components but should be designed as a whole. 6mm high tensile (downsized) chain is fine - as long as all the other bits a pieces, shackles, anchors, snubbers, chain hooks etc all match and are compatible. No use with downsizing without snubbers.

We also learnt a few tricks along the way - every day is a school day.

Jonathan

 

[Supertramp]

Going back to the thread - I'm of the belief that the rode is a combination of components but should be designed as a whole. 6mm high tensile (downsized) chain is fine - as long as all the other bits a pieces, shackles, anchors, snubbers, chain hooks etc all match and are compatible. No use with downsizing without snubbers.

And there will always be different choices made according to owner philosophy and experience.

I learnt about snubbers from the extensive anchor threads here and now use two. A day to day V-bridle attached at the bow and a long V-bridle for strong winds attached at the midships cleats. Great improvement, even with my 10mm catenary!

 

[Neeves]

And there will always be different choices made according to owner philosophy and experience.

I learnt about snubbers from the extensive anchor threads here and now use two. A day to day V-bridle attached at the bow and a long V-bridle for strong winds attached at the midships cleats. Great improvement, even with my 10mm catenary!

Your development/modification allows you to swap to a long storm snubber relatively easily.

There is no one right way.


If you have a snubber and want to add a stronger (less elastic) one or simply want to deploy more chain than the length of the existing snubber imposes a limitation. I therefore wanted a system where the chain hook (which might be a soft shackle (not a hook at all) could be detached easily and comfortably. This means the chain hook needed to be as close to the bow roller as possible, preferably within an easy stretch. One could then retrieve the chain lazy loop (easy - there is no tension on it) and then take in a short length of snubber, sheet winch, or wait for a lull. The hook was close anyway - just at arms length.

Now you can add a new (different) snubber or deploy more rode and re-attach the original snubber.

But if the chain hook is just forward of the bow roller you need a mechanism to still have a long snubber ( a short snubber will not have the elesticity - the actual stretch (think in metres not centimetres).

The is the reason our snubbers terminated at the transom - our snubbers were deck length + the extra 15m we could deploy if necessary.


These are our snubbers. They commence at a sewn eye attached to the bobstay pad eye at the water line at the bow, pass to the bridle plate attached to the chain, return to a turning block at deck level at the bow and run down the outside of the deck to the transom.



This is simply detail of the bridle plate. 10mm kermantle, 6mm high tensile, galvanised, chain. The little shackle simply allows the bridle plate and bridle to be secured at the bow when on passage. I don't need the bridle plate to be within arms length - we can deploy 15m of bridle simply by releasing the bridle in the cockpit and can shorten the bridle using the sheet winches (which we don't seem to use normally when at anchor ).


Jonathan

 

[Dockhead]

Once you get 'really' big I agree weight in the bow is not such an issue nor are snubbers. But most of us buy smaller AWBs with all the weight factored out and then weight in the bow can be significant - commonly the difference in weight for a rode in 8mm or 10mm would be a man's weight - a man permanently on the bow would. destroy sailing ability - for you - a man on the bow might not be noticed.

You can alter the 'ride' by altering the snubber. In the same way you alter the ride with chain (though you are limited to altering length with chain) you can alter both the length and type of snubber. You can alter diameter, of your snubber, which will impact the amount of elasticity for a give tension, you can alter the fabrication process, 3 ply, braided, kermantle and the ride will also very with age.

With the variables at an owners disposal I doubt you could tell the different in ride of elasticity vs catenary - except for price, space, weight.

Most people who start on the snubber path oversize their snubbers, they have this hang up about strength (they want more) and then they lose elasticity.

We started off with retired dynamic 12/13mm kernmantle which we can source for free in Australia - being free you are more comfortable in experimentation. We transited from 15m snubbers, as a bridle, eventually to 30m each side. We thought we had got it right and then invested in new 12/13mm rope but found it a 'bit' inelastic and decided 10mm dynamic kernmantle , 30m, suited us best.

30m sounds a lot but we had a 12m cat and ran the snubbers from the transom, down the side decks to a turning block on the bow and then to a common chain hook. Normally we simple used that arrangement and kept the spare (about 15m) as one does a sheet - at the transom (in a sheet bag). If the weather became a bit more challenging we had 15m in hand we could further deploy. We could deploy more (or retrieve, from the comfort and safety of the cockpit (retrieving using the sheet winches, we have windlass controls in the cockpit).

Our rode was high tensile 6mm chain and our primary anchors aluminium Spade and Excel (8kg each) but would now use as another option a Odin 40 from Viking (weighing just under 10kg) - its design not weight

We used dynamic kernmantle because it is made to be elastic and has an abrasion resistant outer cover (and for us - was free). We installed the snubbers permenantly running the ropes through 'deck organisers'. I had compared our cat with a mid year 2,000 Bav and we had the same windage as a 48' Bav, though the Bav with its keel was heavier. I'd be happy using 10/12mm for a 48' AWB. I designed and had made my own chain hook.


Reading storm anchoring articles - the fundamental is to keep as many ground tackle controls in the cockpit - the last place you want to be at 2am in 50 knot gusts and rain is at the bow roller. I have seen too many chain hook failures - ours is bullet proof (and available from Viking Anchor (we don't derive any income)


Going back to the thread - I'm of the belief that the rode is a combination of components but should be designed as a whole. 6mm high tensile (downsized) chain is fine - as long as all the other bits a pieces, shackles, anchors, snubbers, chain hooks etc all match and are compatible. No use with downsizing without snubbers.

We also learnt a few tricks along the way - every day is a school day.

Jonathan

I guess the chain size matters a lot, in how catenary behaves. Also how much you have out and how deep the water. So experiences vary tremendously between smaller boats with 50m of 8mm chain and bigger ones with 100m of 12mm chain. Ships don't use snubbers, after all.

As a matter of physics, I don't think an elastic snubber behaves "exactly the same" as catenary. I'll ask the physicist in my family and report back.

My guess is snubber is better when approaching the end of the energy absorption range. Snubber will just break if you overload it.

Whereas if you exceed the energy absorption capacity of chain catenary, you hit a brick wall which can break your gear.


But my guess is that lower down in the capacity range, catenary works better with less friction and more resilience.

But we'll see what the physicist says.

 

[Neeves]

This is what one physicist, mathematician says

Anchor Chain Calculator

It may not be exactly what you are looking for - but its part of the story.

The link has been aired previously on YBW, Cruisers Forum and (I suspect) on a number of other sites. The author is a mathematician/physicist and was formally employed as such.

A link to his website:

Catenary Anchor Chain Length - Die Kettenkurve - (In English)

It is in English.

I think there is an App - but though I did a quick search using the obvious key words - I could not find it.

I did find an article on the author and his calculations

http://trimaran-san.de/wp-content/uploads/2021/07/Offshore-Winter-2021-AnchorChainCalculator.pdf

He does warn anyone interested - you need a decent attention span - if you want to assimilate all he offers.


Jonathan

 

[Neeves]

Again returning to the original thread:

Is is worth buying G70 vs G40?........

The life of chain is effectively determined by the life of the galvanising. G40 and G70 galvanised even by the same galvaniser can have different galvanising quality. The major, or most frequent, reason for retiring chain is loss of the galvanised coating. An owner can prolong life by looking after his chain, every time you wash the decks with fresh water - hose down the chain in the bow locker, keep the bow locker (and chain) clear of mud and don't store your chain on top of wet cordage.

If you are buying new chain Vyv Cox has a simple test (bent link test) to check galvanising integrity (how well is the galvanised coating adhering to the chain), and how thick is the coating, this is a bit subjective (but normally more coating = longer life)....see....

Chain

Jonathan

 

[NormanS]

This is what one physicist, mathematician says

Anchor Chain Calculator

It may not be exactly what you are looking for - but its part of the story.

The link has been aired previously on YBW, Cruisers Forum and (I suspect) on a number of other sites. The author is a mathematician/physicist and was formally employed as such.

A link to his website:

Catenary Anchor Chain Length - Die Kettenkurve - (In English)

It is in English.

I think there is an App - but though I did a quick search using the obvious key words - I could not find it.

I did find an article on the author and his calculations

http://trimaran-san.de/wp-content/uploads/2021/07/Offshore-Winter-2021-AnchorChainCalculator.pdf

He does warn anyone interested - you need a decent attention span - if you want to assimilate all he offers.


Jonathan

This is what one physicist, mathematician says

Anchor Chain Calculator

It may not be exactly what you are looking for - but its part of the story.

The link has been aired previously on YBW, Cruisers Forum and (I suspect) on a number of other sites. The author is a mathematician/physicist and was formally employed as such.

A link to his website:

Catenary Anchor Chain Length - Die Kettenkurve - (In English)

It is in English.

I think there is an App - but though I did a quick search using the obvious key words - I could not find it.

I did find an article on the author and his calculations

http://trimaran-san.de/wp-content/uploads/2021/07/Offshore-Winter-2021-AnchorChainCalculator.pdf

He does warn anyone interested - you need a decent attention span - if you want to assimilate all he offers.


Jonathan

This is what one physicist, mathematician says

Anchor Chain Calculator

It may not be exactly what you are looking for - but its part of the story.

The link has been aired previously on YBW, Cruisers Forum and (I suspect) on a number of other sites. The author is a mathematician/physicist and was formally employed as such.

A link to his website:

Catenary Anchor Chain Length - Die Kettenkurve - (In English)

It is in English.

I think there is an App - but though I did a quick search using the obvious key words - I could not find it.

I did find an article on the author and his calculations

http://trimaran-san.de/wp-content/uploads/2021/07/Offshore-Winter-2021-AnchorChainCalculator.pdf

He does warn anyone interested - you need a decent attention span - if you want to assimilate all he offers.


Jonathan

 

[Dockhead]

This is what one physicist, mathematician says

Anchor Chain Calculator

It may not be exactly what you are looking for - but its part of the story.

The link has been aired previously on YBW, Cruisers Forum and (I suspect) on a number of other sites. The author is a mathematician/physicist and was formally employed as such.

A link to his website:

Catenary Anchor Chain Length - Die Kettenkurve - (In English)

It is in English.

I think there is an App - but though I did a quick search using the obvious key words - I could not find it.

I did find an article on the author and his calculations

http://trimaran-san.de/wp-content/uploads/2021/07/Offshore-Winter-2021-AnchorChainCalculator.pdf

He does warn anyone interested - you need a decent attention span - if you want to assimilate all he offers.


Jonathan

I've followed this guy since he started posting on CF some years ago, and I've corresponded with him. He's made great contributions to mankind's understanding of anchoring.

The app can be found here: Anchor Chain Calculator (incl. rope) app for iOS and Android

His greatest contribution to my own knowledge was finally coming up with the mathematical proof for why you need less scope in deeper water. Something I always thought must be true, but could never figure out why.

 

[MathiasW]

Most of you here know my work on the Anchor Chain Calculator (App) and so I do not want to go into a deep repetition mode here. But in short:

- Chain catenary is always present, even beyond the magical 30 kn boundary. It just becomes less and less the more load is applied. This IS Physics. Peter S. of Rocna is simply wrong here (or could it be that he wanted to sell bigger anchors?). And yes, if you are anchoring in deep enough water, 30 kn is hardly worrying.
- Chain catenary gets stronger the deeper the water is. In extremely shallow water it is negligible, even for not very strong winds. This is because the spring effect the catenary offers is a result of gravity, i.e., of the chain sagging. A chain lying at the beach has no catenary at all.
- Chain catenary depends strongly on the chain's weight. The heavier the chain is per running metre, the more catenary you'll get. Again, because it is a gravity effect. But this comes at a cost, obviously.
- Chain catenary is ONLY needed A) to absorb shock loads resulting from gusts or waves, and B) for having a better pulling angle at the anchor, but the latter is getting less important with modern anchors.
- A good - VERY ELASTIC - snubber is working regardless of water depth and so it is the only choice in very shallow water, if and when shock loads are to be worried about (see the disclaimer below, the last point).
- A very short snubber (anything less than a couple of metres) will help, but not make much of a difference.
- The problem with snubbers is that they need to match the boat, in particular its windage area. To work well, a snubber needs to stretch by 1-2 metres in a very strong gust almost regardless of any other boat characteristics and size (well, within reason), and thus a snubber that works well for a small boat will not work well for a big boat, and vice versa. So, some thoughts have to go into its proper choice. And when it fails, the resulting shock load on the remaining anchor gear can be catastrophic.
- Light-weight (in particular multi-hull) boats need to worry MUCH more about providing sufficient elasticity in the rode than old-style heavy displacement boats. This is because the latter pick up less kinetic energy (relatively speaking) in a severe gust than a light-weight boat does. Owing to their vastly different ratios of windage area to weight, the light-weight boat accelerates much more in a gust and thereby picks up much more kinetic energy that needs to be absorbed by some elasticity means compared to the heavy boat. A good analogy is billiard - when a big, heavy ball (the severe gust) hits a light ball at rest, the latter will dash off like mad, whilst when the same big ball hits an even bigger and heavier ball, the latter hardly notices anything at all. This explains why many "old dogs" in the community simply do not understand this matter, because the need for substantial elasticity is simply not present on their type of boats, and they are just fine with their (often heavy) chain in shallow as well as deep water. This is the root cause of many misunderstandings and even fights in this community.

Some time ago I wrote a lengthy pdf document going into many of these aspects, which can be found here: https://trimaran-san.de/wp-content/uploads/2023/08/AnkerChainCalculatorApp_v12.pdf, or as a link towards the end of my description of the anchor chain calculator app, in case this link gets broken in the future. The links in this document are a bit dated, I just noticed, but they still work. A German version also exists. And apologies for the repeated mentioning of my paid app in this article. Feel free to ignore it.

Cheers

Mathias

 

[NormanS]

OK, so I'm a glutton for punishment, so I put some relevant figures into Neeves's link re Anchor Chain Calculator. When anchoring, I consider the normal things and without engaging anything more complicated than depth, type of seabed, quality of shelter and expected weather, I will aim for a scope of no less than 3:1, and in some extreme conditions, a lot more.
According to the "Calculator", with my boat in 50 knots of wind, and 30 feet of water (if I'm reading correctly) the chain angle at the anchor will be 2.2°, and the chain angle at the bow roller will be 17.8°. I'm very happy with that, and it tells me that there is still a useful catenary. I do not have a lightweight boat that skitters about in every gust, and in windy conditions I rig an anchor riding sail to help to keep the boat head to wind and prevent yawing.

 

[Neeves]

OK, so I'm a glutton for punishment, so I put some relevant figures into Neeves's link re Anchor Chain Calculator. When anchoring, I consider the normal things and without engaging anything more complicated than depth, type of seabed, quality of shelter and expected weather, I will aim for a scope of no less than 3:1, and in some extreme conditions, a lot more.
According to the "Calculator", with my boat in 50 knots of wind, and 30 feet of water (if I'm reading correctly) the chain angle at the anchor will be 2.2°, and the chain angle at the bow roller will be 17.8°. I'm very happy with that, and it tells me that there is still a useful catenary. I do not have a lightweight boat that skitters about in every gust, and in windy conditions I rig an anchor riding sail to help to keep the boat head to wind and prevent yawing.

Well done Norman. Now you know why you don't need a snubber, you have the data and the data reinforces what you have found in practice.

Some of us, most of us, have yachts that skitter about, they are plastic fantastics (though the fantastic part might be debatable) and they don't thank an owner with big heavy chain and certainly not lots of big heavy chain. The owners of these lightweight yachts want comfort at anchor and in the absence of lots of big heavy chain (they have, hopefully, an adequate length) of lighter chain.

and a snubber.

Why do they have lightweight yachts - because that is what is being built and has been built over the last few decades and this forms the bulk of the second hand market. I may be wrong but these lightweight yachts will be a significant section of the yachts owned by members.

The reality for us is that our catamaran did not skitter about - but the wind often did. I know we are not alone as I have read of owners anchored, say in Skye where the wind gusts, the word often used is 'bullets' down different valleys in a most unpredictable way - Skitting their yacht hither and thither - a snubber works well. But an alternative is to deploy two anchors in a 'V' as this tames the skittering.

I came from a different background - we raced our yacht and minimising weight was a fetish and won us trophies. We transferred that fetish to our cat and minimised weight wherever possible, we had a de-salinator instead of carrying lots of water, had 6mm rather than 8mm chain (and a long snubber) and carried aluminium rather than steel anchors. Our fetish was a success and we could average 10 knots over 100nm with a decent beam reach.

But we could not have anchored in comfort without snubbers (the price you pay (in our case) for a minimalist chain).

Now a little trick we learnt


Our bow roller is hidden behind the port hull but you can see the lazy loop of chain disappearing toward the bow roller. The bow roller is about 1.5m above the sea. But our rode is effectively just under the water. When we calculate scope we simply use depth. Our ability to keep the rode (or tension angle) to the seabed low is enhanced by how we arrange our bridle, the blue rope, see Post 51. Like you we found ways to make our rode work to best advantage. Anyone with a bobstay could use the same arrangement and its why we had LFRs in our bridle plate.


Jonathan

 

[Roberto]

But we'll see what the physicist says.

If you are interested, the first analytical approach to leisure anchor rodes was Alain Fraysse's one about 30 years ago, his works appeared in a French sailing magazine; his spreadsheets are still available here.
Forces
More recently, you may have a look at ''Artimon'' anchoring rode calculator (only in French I am afraid)
http://artimon1.free.fr/TableurlignedemouillageArtimonversionV6protegee.zip
Among other things, it offers in depth simulations with variations in values of textile elasticity depending on material and construction, air temperature , etc; as a curiosity the latest version takes also into account chain elasticity (oh yes), he computed it in some way (variations mainly due to thick link chain neutral axis not being in the middle of the metal in the rounded parts) then made mechanical tests with a chain maker which showed excellent agreement with theoretical data, in his own words ''chain elasticity is far from irrelevant''. ''Artimon'' is M. d'Allest, (creator then) head of the ESA Ariane rocket launch site in French Guyane for years, now retired.