Stainless steel anchor chain

[Neeves]

Well, that strengthens my doubt, I reckon: in spite of what you are saying, they still carry around a helluva lot of iron - also relatively speaking, I mean.

I'm not sure if any comparison is useful - by that I mean I have no idea.

I was on a 70,000 GT commercial vessel about 9 months ago. The forecast was for Storm force winds and 12m seas. The decision was made to anchor in a modicum of shelter for 12 hours until conditions improved. The anchor (10t) was deployed with whatever chain, each link is the size of a mans head, I do not recall how many shackles. The anchor held but the concern was that the chain lock (looks very similar to the chain lock you guys use) would not take the load. If the lock failed they would lose all the chain and that anchor (still anchor and chain on other side and a spare anchor on deck.). They lifted the anchor, set a safety zone and motored up and drifted back for 12 hours. When at anchor, wherever - they must have a working crew on board 24/7.

I did think the kit would have been better.

 

[RupertW]

No-one is suggesting using 8mm (for the vessel in question), or not that I am aware. I used 8mm as an example. Small vessels use small chain 6mm, larger vessels use larger chain 13mm. You know how heavy 10mm chain is to manhandle and I can assure you 50m of 8mm is enough for me - so that is what I used in my little experiment. We use 75m x 6mm x G80 (it weighs 75kg), I wouldn't go back to 8mm (NEVER) and 10mm would be plain stupid. Its horses for courses.

I would consider 8mm and smaller if it was the strongest component in the system. All the maths and anybody's personal experience when snorkelling over an anchor is that catenary is a light wind experience. Chafe is the only logical reason for chain over rope or a theoretical super strong piano wire. The weight of chain is an unfortunate side effect of the strength and chafe resistance required to hold a boat to a properly set anchor - the weight is not useful in any way except in the light winds when it doesn't matter anyway.

 

[sarabande]

I'm having reservations about the figure of 80kgf offered to straighten a catenary of 30m of 8mm chain. Just a gut feeling that to lift 44kg (air weight) of chain to an (almost) straight line more than 80kgf will be needed. And I don't understand the reduction to 70kgf offered. What seems critical is the direction of the force applied to lift the chain; it must resolve into a horizontal and vertical component, though it's clear that on a boat the last couple of feet are horizontal.

There are catenary calculators around and I'll do some ferreting.

 

[Portofino]

I'm having reservations about the figure of 80kgf offered to straighten a catenary of 30m of 8mm chain. Just a gut feeling that to lift 44kg (air weight) of chain to an (almost) straight line more than 80kgf will be needed. And I don't understand the reduction to 70kgf offered. What seems critical is the direction of the force applied to lift the chain; it must resolve into a horizontal and vertical component, though it's clear that on a boat the last couple of feet are horizontal.

There are catenary calculators around and I'll do some ferreting.

Post # 113
Here the best one ---agian ---- refers to density of the line relative to water , p -when it's submerged 7/8 th
http://abc-moorings.weebly.com/catenary-calculator.html

 

[Neeves]

I would consider 8mm and smaller if it was the strongest component in the system. All the maths and anybody's personal experience when snorkelling over an anchor is that catenary is a light wind experience. Chafe is the only logical reason for chain over rope or a theoretical super strong piano wire. The weight of chain is an unfortunate side effect of the strength and chafe resistance required to hold a boat to a properly set anchor - the weight is not useful in any way except in the light winds when it doesn't matter anyway.

The 6mm G80, galvanised, is stronger than the 8mm G30 it replaced, I've tested both. The shackles are 3/8th" Grade B, rated at 12t (or 6t if side loaded). I've tested them as well. The Omega links are G100 strength, and galvanised - and yes I tested them as well. The 6mm G80 is the weakest component in the system, bow roller is massively oversized. The windlass is for 8mm chain edit - with a 6mm gypsy close edit.

 

[Deleted User YDKXO]

You must not anchor in the same conditions as us. In Caribbean anchorages winds of 30 kts gusting a lot more are common. Anchor chain doesnt touch the bottom in these conditions. Been snorkeling all over my anchor to see whats going on and chain is irrelevant. Its the anchor that does the work when the wind is up to manly status

OK then if you take that to its logical conclusion why bother with chain at all and why bother with laying out so much of it? If, as you say, in windy conditions the chain is bar straight and the anchor is doing all the work then there is no point in having chain at all. And if, as you say, providing the anchor is buried, it can resist any upward component of the load, there is certainly no point in laying out 5x depth or whatever. So the logical conclusion of your statements is that all you need is a short length of cable or rope which is just enough to get the anchor to the seabed and the anchor will do the rest. And all the traditional advice about laying a sufficient scope of chain relative to the depth is just plain bollox? Right?

 

[Neeves]

I'm having reservations about the figure of 80kgf offered to straighten a catenary of 30m of 8mm chain. Just a gut feeling that to lift 44kg (air weight) of chain to an (almost) straight line more than 80kgf will be needed. And I don't understand the reduction to 70kgf offered. What seems critical is the direction of the force applied to lift the chain; it must resolve into a horizontal and vertical component, though it's clear that on a boat the last couple of feet are horizontal.

There are catenary calculators around and I'll do some ferreting.

When you do the calculations note that the catenary described is simply with every link off the ground, in air. The last, or first link is just lifted - as happens in 17 knots of wind.

Difference between 80kg in air and 70kg in water, call it SG - and its an approximation - be picky if you like but I don't think it material.

 

[Neeves]

OK then if you take that to its logical conclusion why bother with chain at all and why bother with laying out so much of it? If, as you say, in windy conditions the chain is bar straight and the anchor is doing all the work then there is no point in having chain at all. And if, as you say, providing the anchor is buried, it can resist any upward component of the load, there is certainly no point in laying out 5x depth or whatever. So the logical conclusion of your statements is that all you need is a short length of cable or rope which is just enough to get the anchor to the seabed and the anchor will do the rest. And all the traditional advice about laying a sufficient scope of chain relative to the depth is just plain bollox? Right?

The logical conclusion to those of us who do not believe in the merits of catenary is to use Kryptonite piano wire - when you find it, let us know. In the meantime we are limited to high tensile chain.

Normal wire is an option but there are safety issues with swages. Dyneema is an option, but if floats and would be something of a hazard to vessels with props - currently we are limited to high tensile chain. Its strong, can be galvanised, is abrasion resistant and light. We still work to the same sort of scopes that you recognise - because anchors are designed to be set that way. No-one designs an anchor to be set at, say 2:1 scope - so no-one does it.

People have been using HT chain, of smaller sizes than recommended for decades, since the 80's maybe 70's - no-one had died yet, no yachts have gone up on beaches.

If heavy chain works for you, great. Most people have never thought of light chain - they have a catenary mind set. Other people embrace new ideas.

Anchoring is a series of compromises.

 

[RupertW]

OK then if you take that to its logical conclusion why bother with chain at all and why bother with laying out so much of it? If, as you say, in windy conditions the chain is bar straight and the anchor is doing all the work then there is no point in having chain at all. And if, as you say, providing the anchor is buried, it can resist any upward component of the load, there is certainly no point in laying out 5x depth or whatever. So the logical conclusion of your statements is that all you need is a short length of cable or rope which is just enough to get the anchor to the seabed and the anchor will do the rest. And all the traditional advice about laying a sufficient scope of chain relative to the depth is just plain bollox? Right?

The pointlessness of catenary is very different to scope I think. Assuming within a few cms of bar taut chain/rope/piano wire then the point of scope is to get the most horizontal angle possible so the pull on the anchor is in the right direction and all anchors are shaped so that they dig in at quite extreme (30-45%) angles so vital to get below that angle for your particular anchor design then a real but diminishing advantage as it gets more horizontal as your scope gets bigger. The graphs I read recently seemed to show 3:1 for a minimum angle, 5:1 for almst perfect angle and 8:1 as the point where the improvement gets so small that it stops being measurable. Note all of this assuming bar taut rode of whatever material.
So - I'm a fan of scope and anchor holding, and a fan of chain for it's chafe resistance, and a fan of elastic snubbers to absorb the shock loads that a catenary can't.

 

[Zing]

OK then if you take that to its logical conclusion why bother with chain at all and why bother with laying out so much of it? If, as you say, in windy conditions the chain is bar straight and the anchor is doing all the work then there is no point in having chain at all. And if, as you say, providing the anchor is buried, it can resist any upward component of the load, there is certainly no point in laying out 5x depth or whatever. So the logical conclusion of your statements is that all you need is a short length of cable or rope which is just enough to get the anchor to the seabed and the anchor will do the rest. And all the traditional advice about laying a sufficient scope of chain relative to the depth is just plain bollox? Right?

There is no bollox in having sufficient scope. The more scope the better as the angle of pull on the anchor will be lower.

The point in chain as opposed to rope or wire is to give chafe protection. Chain is the most resistant material to rock damage on the seabed.

When anchoring the chain will alternate between dragging all over the seabed when there is a lull to going bar tight when there is a gust or strong wind, often alternating many times in the night, so the rode has to both protect from rocks and to be at the right scope to allow the anchor to work in a blow.

If you don't mind the weight, having a heavy chain gives an advantage not mentioned so far and that is of damping. The catenary will reduce peak loads just like a snubber. If you have a good snubber and have an anchor good enough to hold in very strong conditions then the damping advantage will be negligible in those strong conditions. That said, if you don't mind the weight and have the biggest and best anchor you can get then heavy chain can only help.

I think all this talk about the importance of catenary is a hangover from times when anchors were really bad. It is only some 25? years or so since the CQR was the dogs bollox and when it arrived it was a major improvement from the anchors around at the time that the lore of catenary was being preached. Since then anchors have got very considerably better and so the role of catenary has now become diminished to insignificance.

 

[RupertW]

There is no bollox in having sufficient scope. The more scope the better as the angle of pull on the anchor will be lower.

The point in chain as opposed to rope or wire is to give chafe protection. Chain is the most resistant material to rock damage on the seabed.

When anchoring the chain will alternate between dragging all over the seabed when there is a lull to going bar tight when there is a gust or strong wind, often alternating many times in the night, so the rode has to both protect from rocks and to be at the right scope to allow the anchor to work in a blow.

If you don't mind the weight, having a heavy chain gives an advantage not mentioned so far and that is of damping. The catenary will reduce peak loads just like a snubber. If you have a good snubber and have an anchor good enough to hold in very strong conditions then the damping advantage will be negligible in those strong conditions. That said, if you don't mind the weight and have the biggest and best anchor you can get then heavy chain can only help.

I think all this talk about the importance of catenary is a hangover from times when anchors were really bad. It is only some 25? years or so since the CQR was the dogs bollox and when it arrived it was a major improvement from the anchors around at the time that the lore of catenary was being preached. Since then anchors have got very considerably better and so the role of catenary has now become diminished to insignificance.

I think we are in almost complete agreement except for one point on damping, so bear with me as I lay out the way that I think it works: The damping from chain is caused entirely by the catenary stretching out to near straight then dropping back again to a curve. So like any catenery is most useful in light to moderate winds in deeper water when you may get a couple of metres of straightening. But once the wind picks up only a tiny curve will be left giving perhaps only a few centimetres straightening available, each of which requires more and more huge forces - thus reducing damping to a couple of centimetres so not really worth it.

So with that in mind that's where I prefer a snubber which consists of a rubber snubber on a long nylon rope. Rubber snubber works in light to moderate and is most useful with just a little nylon out when anchoring off a harbour wall or in a veering anchorage. Once the wind gets up then if free anchoring I let a lot more nylon rope out so the rubber is almost permanently stretched out and the nylon provides the high tensile elasticity. Of course rubber snubber is a bit knackered after a particularly gale-y night or tow but is pretty cheap and sacrificial as well as useful nearly all the rest of the time.

 

[Deleted User YDKXO]

Normal wire is an option but there are safety issues with swages.

Again no. Swaged wire rope is used very commonly in the construction industry for loads far higher than will ever be developed by an anchored boat and wire rope could be handled very easily by a winch drum in the anchor locker. I will agree with you that wire rope is less resistant to abrasion than a chain. But we're going to have to agree to disagree on the merits of heavy chain and the catenary effect

We still work to the same sort of scopes that you recognise - because anchors are designed to be set that way. No-one designs an anchor to be set at, say 2:1 scope - so no-one does it.

So you're somewhat changing your tune on this. What in effect you are saying is that you need a certain scope of chain to set the anchor but once it is set you don't need that scope? Is that correct? In other words once the anchor is set you could shorten the scope to something much less. OK let me ask a question. What in your view is the minimum scope that a 'modern' anchor can work with assuming it is embedded in the seabed? I realise that this will vary with depth but give us some idea

 

[Deleted User YDKXO]

There is no bollox in having sufficient scope. The more scope the better as the angle of pull on the anchor will be lower.

Well no that is not what neeves is saying insofar as I understand him. He seems to be saying that if a modern anchor is embedded in the seabed it can resist the upward pull exerted by a chain that is not lying on the seabed.

If you don't mind the weight, having a heavy chain gives an advantage not mentioned so far and that is of damping. The catenary will reduce peak loads just like a snubber. If you have a good snubber and have an anchor good enough to hold in very strong conditions then the damping advantage will be negligible in those strong conditions. That said, if you don't mind the weight and have the biggest and best anchor you can get then heavy chain can only help.

Well that is what some of us are saying but apparently neeves does not agree with this and is suggesting that the weight of the chain doesn't matter and the catenary effect, whether it be to reduce peak loads or ensure that the pull on the anchor is as horizontal as possible, is a myth

 

[sarabande]

IF a Danforth type or any other NG kit has its flukes set to 32 degrees, AND the anchor is dug in so that the shank is horizontal, AND the wind pipes up so that the chain tightens and the angle between the sea bed and boat is >32 degrees, the anchor is pulling in an upwards direction and cannot dig in any more, though the flukes will initially resist very strongly the upward component of pull, but most probably break free on repeated snubbings.

So an extreme example of 15m depth of water would require only 28m of chain to be veered to achieve the angle of 32 degs. That's getting near the limit that many smaller boats carry, and emphasises the need to have lots of spare chain and warp to keep the chain angle below the 32 of the example anchor


It's basic anchoring trigonometry. You know the length of the chain (the hypotenuse), you know the depth of water (the opposite), so depth divided by length gives you the angle (sin theta).

Other angles are available.

In my mind, the more weight and length you have in the chain, the stronger, very much stronger, the wind will have to be to straighten the chain, and until the chain is constantly tight or supported by a nylon snubber, a long and heavy chain will act as a shock absorber.

 

[Magnum]

In my mind, the more weight and length you have in the chain, the stronger, very much stronger, the wind will have to be to straighten the chain, and until the chain is constantly tight or supported by a nylon snubber, a long and heavy chain will act as a shock absorber.

+1

 

[RupertW]

+1

Well no - as per previous posts - a 12mm chain will lose all but a few of centimetres of catenery in moderate winds so is no better a shock absorber than a 6mm chain when it actually matters. The only thing that will give you shock absorbsion under load is elasticicity - so nylon snubber of sufficient length as the usual way.

 

[Magnum]

Well no - as per previous posts - a 12mm chain will lose all but a few of centimetres of catenery in moderate winds so is no better a shock absorber than a 6mm chain when it actually matters. The only thing that will give you shock absorbsion under load is elasticicity - so nylon snubber of sufficient length as the usual way.

We are dealing with a 70ft+ 40 tonne boat here. Using 6mm chain would be ridiculous.

 

[RupertW]

Well no that is not what neeves is saying insofar as I understand him. He seems to be saying that if a modern anchor is embedded in the seabed it can resist the upward pull exerted by a chain that is not lying on the seabed.




Well that is what some of us are saying but apparently neeves does not agree with this and is suggesting that the weight of the chain doesn't matter and the catenary effect, whether it be to reduce peak loads or ensure that the pull on the anchor is as horizontal as possible, is a myth

The catenary effect is not a myth when under minimal load but at anything above light winds the chain loses almost all its curve even with heavy chain, so the angle from bow to anchor is based on scope as a straight line. That's where the 3:1 ratio means that in post 1930s anchors the stock will ensure the flukes will be digging in rather than being pulled upwards which will work in pretty strong winds. But the flukes are at a much better angle for those extreme moments if you have 5:1 (bar taut, no curve or catenary needed), but after that the gains become more marginal as you let more out until at about 8:1 there is no more measurable gain (depending on anchor design).

So I don't understand why you think there is any contradiction between understaning the importance of scope for getting the fluke angle right and understanding that catenary is of negligible use in anchoring.

 

[BartW]

The catenary effect is not a myth when under minimal load but at anything above light winds the chain loses almost all its curve even with heavy chain, so the angle from bow to anchor is based on scope as a straight line. That's where the 3:1 ratio means that in post 1930s anchors the stock will ensure the flukes will be digging in rather than being pulled upwards which will work in pretty strong winds. But the flukes are at a much better angle for those extreme moments if you have 5:1 (bar taut, no curve or catenary needed), but after that the gains become more marginal as you let more out until at about 8:1 there is no more measurable gain (depending on anchor design).

So I don't understand why you think there is any contradiction between understaning the importance of scope for getting the fluke angle right and understanding that catenary is of negligible use in anchoring.

imho and experience,

the scope should be long enough so that there is "alway's" at least several meters of chain on the seabed, in ANY sea condition,
if you don’t, and if the chain can 'lift' or move the stock, there is big risc that the anker doesn't hold.

this means indeed that in very strong wind, you need a lot of scope,
so if you don’t have enough scope in strong wind you need a very attentive watch-out !
and yes I know that a long scope is difficult or dangerous in case the wind turns direction,…

now having “always’s some length of chain on the seabed, means you always’s have some amount of catenary.
I can’t quantize this amount, but I am anyway a NON believer of a rubber snubber on my anker chain.
12mm chain and lots of scope gives me very good catenary in any wind condition.

And indeed, when you don’t have enough scope, and the chain is pulled tight,
AND the anker holds between rocks fe,
You will feel that the chain is pulling with peak loads on the boat,
But then again drop more chain or move the boat to somewhere else

 

[Portofino]

[QUOTE

So I don't understand why you think there is any contradiction between understaning the importance of scope for getting the fluke angle right and understanding that catenary is of negligible use in anchoring.[/QUOTE]

For me coming from the catenary camp from snorkelling and looking at the maths the wieght of chain is important .
The heavier the chain the more lies on the bottom in other words X s shorter on the link I have previously posted .
All chain lying on the bottom is applying zero force on the anchor ,so with enough scope the anchor could be a bottle top -cos the heavey chain can not lift it .
That's the theory .
In practice in the SoF and near islands we anchor off like everybody else .
Recently wanted to change the prop anodes in the water .Forcast was 2-6-2 ,6 being the afternoon ,from the E .
Off we went I found a blue sandy bottom ( so,s if I dropped anything I could at least have a chance of recovering ? )
How ever I way over shot and we had to let more chain out to position the stern over the sandy bit .
We were in 3-4 M but I let out 60 M+ .So scope was 1/15 in calm .Anchor chain went vertually vertical .

10 mins later anodes all changed .

As noon approached on q wind started to rise ,boat started to move ,a bit but more importantly change from E to S -ie 90 degree shift .
It was hot. Loads of boats about anchored up .
It got so choppy I could n,t really paddle board . Out in the bay serious white horses and 2 M or more waves .
So I went snorkelling -yeh @ force 6 -wind 22-27 knots it only lifted ( remember 10mm links @ 15-1. Scope in 4 M tops )
By 1/2 boat lengh say 7 M -infact the rest of say 45 M was still 90 degrees sort of big L shape. Anchor never felt a twinge of force .And I still had 10 M in the locker !
A force 8 is 34-40 gale and there's no way with 5-7 M waves we would sit that out , we would have been off .
So 2-3 M waves did not phase us
This is normal boating in a all up 20 ton boat .
Think about it drop the anchor in Sydney harbour and reverse back to lands end .That anchor is not going to feel the gale -bar tight as you say cos of a scope of (guess) 8000 mile /200 ft .
It's this "bar tight " I cannot understand ,just anchor at a sensible depth and let loads out
10 -15 to 1
So with enough scope the anchor just sits there , in the real world .
Not talking about over nighting in 20M with 60m down flat calm -then it blows up @2am ? -just would not do that
3 to 1 scope .