G70 chain vs G4

[contrail]

Originally Posted by Jim Cate

I've said it before... chain breakage is a very uncommon event with chain in decent condition. My opinion is that folks worry too much about chain strength... do remember that SWL isn't breaking strength. In the very unlikely event of winds strong enough to generate breaking loads on the chain, it is highly likely that the anchor will have upset long before the chain fails. Of course one does not wish to routinely exceed SWL, but as a one time event, the world won't end if you get somewhere between SWL and breaking loads.

In thirty plus years of full time cruising, I've seen two broken chains. One was so rusty that a Mexican fisherman had condemned it... and a very low bucks French Canadien yottie bought it from him. It failed under very mild conditions. The other was 12 mm chain used during a cyclone by a ferrocement square rigger of enormous displacement. Huge (ex landing craft) Danforth anchor, 100 ft chain, no snubber... BANG!

There are IMO better things to worry about!

Jim

And dealing with the corrosion issues with G70 is a non-starter for me

I have heard of a few cases of chain breaking, but it was almost always in poor shape. However, I have stretched my own chain, in very good shape, and was very glad it stretched and didn't break.

[Dockhead]

Originally Posted by evm1024

Quite simply when someone states that there will always be some catenary in a chain I have to agree with them. Barring an infinite slope chain.

But, BUT often they fail to take into account the forces that head to an asymptotic infinity as the effective curvature of the catenary approaches zero.

What this means is that at first it takes a few pounds or kg to move the end points of the chain further apart.

Then as the chain comes "tight" the forces are measured in thousands of pounds or kg.

Lastly when the chain is "bar" tight it will take hundresd of thousand pounds or kg of force to flatten the chain further and thus extending the distance between the chain end point another 1 mm.

Can you say brick wall?

Of course something broke long before this point. The catenary of the chain has as much give as hitting water from a 200 meter fall. Zilch! Or should I say splat!

Regardless of the degree of catenary in the bar tight chain there is no effective ability to absorb any further forces - that is reality.

Exactly.


There may be some millimeters of catenary even in a big storm, but at a certain point the chain begins to behave like a bar, so the effect of catenary is gone. The larger and longer the chain involved, the more force required to reach the "bar tight" stage, but you will always reach it. In my boat, if all 100 meters of my 12mm chain are deployed, it's about 30 knots of wind, which is about 1 tonne of force according to the respected ABYC table. Half a tonne of force is enough to lift the last link of this 100 meter 12mm chain off the seabed.

[Jim Cate]

Do not forget that besides altering the angle of pull on the anchor shank, catenary also absorbs energy as it is pulled tighter, much as a snubber does. In normal strong weather conditions the loads are variable as the wind gusts and eases. IN the lulls, the weight of the chain pulls the boat forward a bit and the catenary increases. In the gusts, the boat moves astern, the catenary is reduced and this absorbs quite a lot of energy... a useful factor in anchor loads and in comfort. Heavy chain absorbs more energy in lifting and straightening out, and this is useful. If the lulls are still strong enough that the chain never falls much ("bar tight"), this effect is of no further use, and the situation is similar to what the "ain't no catenary" arguments describe... but it has been helpful up to then and reduced loading on the snubber.

I like heavier chain and don't begrudge the weight on the bow (within reason) because in the far more common anchoring situations, it has been beneficial.

Jim

[Dockhead]

Originally Posted by Jim Cate

Do not forget that besides altering the angle of pull on the anchor shank, catenary also absorbs energy as it is pulled tighter, much as a snubber does. In normal strong weather conditions the loads are variable as the wind gusts and eases. IN the lulls, the weight of the chain pulls the boat forward a bit and the catenary increases. In the gusts, the boat moves astern, the catenary is reduced and this absorbs quite a lot of energy... a useful factor in anchor loads and in comfort. Heavy chain absorbs more energy in lifting and straightening out, and this is useful. If the lulls are still strong enough that the chain never falls much ("bar tight"), this effect is of no further use, and the situation is similar to what the "ain't no catenary" arguments describe... but it has been helpful up to then and reduced loading on the snubber.

I like heavier chain and don't begrudge the weight on the bow (within reason) because in the far more common anchoring situations, it has been beneficial.

Jim

Of course -- and that's why heavy chain is a blessing in moderate weather. In fact a good long piece of really heavy chain is so effective this way that you don't even need a snubber. I don't use a snubber at all below 20 knots of wind.



The problem is that this effect disappears. For lighter and/or shorter chain than my example (100 meters and 12mm, weighing 1/3 of a metric tonne), it disappears faster. On my last boat with 1/4" chain, catenary had almost no effect.

[wingssail]

Originally Posted by Dockhead

Exactly.


There may be some millimeters of catenary even in a big storm, but at a certain point the chain begins to behave like a bar, so the effect of catenary is gone. The larger and longer the chain involved, the more force required to reach the "bar tight" stage, but you will always reach it. In my boat, if all 100 meters of my 12mm chain are deployed, it's about 30 knots of wind, which is about 1 tonne of force according to the respected ABYC table. Half a tonne of force is enough to lift the last link of this 100 meter 12mm chain off the seabed.

Originally Posted by Dockhead

You can calculate how much force is needed to lift the last link from the seabed with Alain Fraysse's calculators:

Rode - Static Behavior

It is true that there is always some catenary, but even with 12mm chain, the catenary is reduced to millimeters and the chain is behaving like a bar ("bar tight") at forces which realistically exist in real life anchoring situations. The catenary no longer influences the angle of pull on the anchor when the last link is lifted from the seabed.

From the previously quoted catenary thread:

Lifting the last link of the bottom does not mean that there is no catenary or that the chain is anywhere near being straight.

It is worthwhile to read Fraysse's document carefully. You'll find that the horizontal forces from wind on an anchored boat are far less than ABYC tables indicate, perhaps by a factor of three, or more.

The numbers shown in the graphs you quoted,

"This graph shows the same 100m of 3.3Kg/m chain in 30m of water (3.3:1 scope) with a horizontal pull of 500, 1000, 2000, 4000 and 8000 Kg horizontal force"

are pretty hard to imagine or reproduce using Fraysse's formulas.

For a much more detailed analysis, for those who are mathematically inclined, the following paper describes the logic and math behind the forces acting on an anchor: http://northpacificresearch.com/down...d_revealed.pdf

The bottom line, from my point of view, is that chain anchor rodes rarely can have enough force on them to become straight, or even very close to straight, regardless of how "bar tight" they seem. And if the wind is that strong, more scope solves the problem.

[Dockhead]

Originally Posted by wingssail

Lifting the last link of the bottom does not mean that there is no catenary or that the chain is anywhere near being straight.

Agreed. However, the last link lifting is when catenary ceases to prevent angulation of the anchor. Soon after that, angulation approaches the basic geometry implied by the scope being used, so catenary has ceased to have any useful effect on angulation. That's why Alain calls the force requird to lift the last link the "critical force".

Originally Posted by wingssail

It is worthwhile to read Fraysse's document carefully. You'll find that the horizontal forces from wind on an anchored boat are far less than ABYC tables indicate, perhaps by a factor of three, or more.

I have read it, and what you say is true, however these are STATIC loads. The ABYC are really good design parameters for anchoring systems, I think universally respected, reflecting likely PEAK dynamic loads.

Originally Posted by wingssail

The numbers shown in the graphs you quoted,

"This graph shows the same 100m of 3.3Kg/m chain in 30m of water (3.3:1 scope) with a horizontal pull of 500, 1000, 2000, 4000 and 8000 Kg horizontal force"

are pretty hard to imagine or reproduce using Fraysse's formulas.

For a much more detailed analysis, for those who are mathematically inclined, the following paper describes the logic and math behind the forces acting on an anchor: http://northpacificresearch.com/down...d_revealed.pdf

The bottom line, from my point of view, is that chain anchor rodes rarely can have enough force on them to become straight, or even very close to straight, regardless of how "bar tight" they seem. And if the wind is that strong, more scope solves the problem.

Again, it is not ultimate perfect straightness which matters here, but BEHAVIOR. Anchor chain catenary, even large and long chains by recreational boat standards, ceases to have any useful effect already in conditions far short of survival conditions. The two useful effects are energy absorption, and reducing angulation of the anchor. A "bar tight chain", the way this term is used, means an anchor chain which is no longer absorbing energy to a useful degree nor affecting the angulation of the anchor to a useful degree. Adding scope does not indeed always solve the problem. I have 100 meters of 12mm chain, and putting all of that out does not indeed make it possible to do without a snubber in anything over about 20 - 25 knots. Even that massive chain, which weighs 330kg or 1/3 of a metric tonne, is bar-like enough in over 30 knots of wind to rip the bow roller off.



Listen, I was skeptical about this myself, but if you do the math you'll see that Peter Smith and Dashew were right about this. Just graph force on the chain vs. remaining energy absorption capacity (I think we did that on the previous thread, linked above) and you'll see that catenary disappears as a shock absorber quite early in the game.

[Dockhead]

Originally Posted by Jim Cate

Do not forget that besides altering the angle of pull on the anchor shank, catenary also absorbs energy as it is pulled tighter, much as a snubber does. In normal strong weather conditions the loads are variable as the wind gusts and eases. IN the lulls, the weight of the chain pulls the boat forward a bit and the catenary increases. In the gusts, the boat moves astern, the catenary is reduced and this absorbs quite a lot of energy... a useful factor in anchor loads and in comfort. Heavy chain absorbs more energy in lifting and straightening out, and this is useful. If the lulls are still strong enough that the chain never falls much ("bar tight"), this effect is of no further use, and the situation is similar to what the "ain't no catenary" arguments describe... but it has been helpful up to then and reduced loading on the snubber.

I like heavier chain and don't begrudge the weight on the bow (within reason) because in the far more common anchoring situations, it has been beneficial.

Jim

Indeed. There was much discussion on here some years ago about whether the motion of the chain in the water dissipates a lot of energy, adding to the damping effect. IIRC Evans Starzinger showed that the speed of the chain motion is too low to produce much drag, but I can say from subjective experience that a long piece of heavy chain in deep water tremendously smooths out the ride, and it certainly feels like energy is being dissipated, and not just absorbed and released.


As I said I don't use a snubber at all in less than 20 knots of wind, which means most of the time.


And so I have not taken the advice of Dashew and Peter Smith to ditch the heavy chain and go to G70 a size smaller. I don't like the weight in the bow, but I believe that the heavy chain has a lot of benefits. I like the beefy chain links which mean I don't have to worry whether a tiny bit of rust has compromised the strength, too. And which mean that I can easily regalvanize it (which I will do during this winter). Kind of brings us back to the original subject.

[GordMay]

Originally Posted by Dockhead

... I have read it, and what you say is true, however these are STATIC loads. The ABYC are really good design parameters for anchoring systems, I think universally respected, reflecting likely PEAK dynamic loads...

The Tables in ABYC H-40, Anchoring, Mooring and Lifting include:
DESIGN LOADS FOR SIZING DECK HARDWARE include the effects of wind, current and wave action (dynamic loads, NOT static).
WORKING LOAD LIMIT FOR ANCHOR RODES are based on factors of safety, line strength loss due to knots and splices, and additional factors including abrasion and aging.
H-40 ➥ http://www.epcomarineproducts.com/pdfs/H-40.pdf

However, Don Dodds believes that the ABYC tables are overly conservative with respect to static loads, and under conservative with respect to dynamic loads, as he explains (very interesting read):
➥ http://northpacificresearch.com/down...d_revealed.pdf

[thinwater]

Originally Posted by Dockhead

....I have read it, and what you say is true, however these are STATIC loads. The ABYC are really good design parameters for anchoring systems, I think universally respected, reflecting likely PEAK dynamic loads....

If you read the SYNTHISIS worksheet, those include dynamic loads. In fact, I have done a lot of load cell testing, and although it is not as simple as single number, yes, even the dynamic loads are as much as 3 times less than the ABYC tables.


The is NOT because ABYC was wrong. In fact, if you anchor in shallow water with long fetch (but not in the breaker zone), with all chain and no snubber, the dynamic loads reach ABYC levels. I've measured them that high. They are about 6 times wind alone. This can happen in a rodestead if the wind direction changes. So they are built on a worst case scenario that most of us will never be in. We hope.


That said, if you are using rope or a snubber, the actual working loads are much lower. If you are in deeper water or have enough catenary the loads are lower. They only get that high if the chain is snatching tight as the waves pass.

[Dockhead]

Originally Posted by thinwater

If you read the SYNTHISIS worksheet, those include dynamic loads. In fact, I have done a lot of load cell testing, and although it is not as simple as single number, yes, even the dynamic loads are as much as 3 times less than the ABYC tables.


The is NOT because ABYC was wrong. In fact, if you anchor in shallow water with long fetch (but not in the breaker zone), with all chain and no snubber, the dynamic loads reach ABYC levels. I've measured them that high. They are about 6 times wind alone. This can happen in a rodestead if the wind direction changes. So they are built on a worst case scenario that most of us will never be in. We hope.


That said, if you are using rope or a snubber, the actual working loads are much lower. If you are in deeper water or have enough catenary the loads are lower. They only get that high if the chain is snatching tight as the waves pass.

That all sounds right and I think it's consistent with what I wrote.


Would you care to weigh in on the catenary discussion? Are you in the Dashew/Peter Smith/Morgan's Cloud camp that believes that catenary is not there when you need it, so you should skip the heavy chain and put the weight into the anchor? Or do you agree with those who say catenary is always there; just let out more chain in a storm?


Did you follow our discussion of this issue some months ago, called "Myth of the Bar-Tight Chain"? We got pretty deep into the question; it was an interesting discussion. I started with the premise that you could never pull all the catenary out of a sufficiently large and long chain, before reaching the breaking strength of the chain, and was definitely proven to have been wrong.


http://www.cruisersforum.com/forums/...in-215250.html

[sailcrazy]

following.

[wingssail]

Originally Posted by Dockhead

That all sounds right and I think it's consistent with what I wrote.

Would you care to weigh in on the catenary discussion? Are you in the Dashew/Peter Smith/Morgan's Cloud camp that believes that catenary is not there when you need it, so you should skip the heavy chain and put the weight into the anchor? Or do you agree with those who say catenary is always there; just let out more chain in a storm?

Did you follow our discussion of this issue some months ago, called "Myth of the Bar-Tight Chain"? We got pretty deep into the question; it was an interesting discussion. I started with the premise that you could never pull all the catenary out of a sufficiently large and long chain, before reaching the breaking strength of the chain, and was definitely proven to have been wrong.


http://www.cruisersforum.com/forums/...in-215250.html

The conclusion I'm coming to after participating in this discussion and reading the linked resources is that my experiences are sufficiently different to other's to have distorted my understanding of the issue, and I'm probably wrong in my understanding even though it seemed correct as it pertains to me. I've based my views on my perception, not math. That was wrong.

In my case I've never experienced shock loading on my anchor chain. The catenary has always absorbed it. Whenever we've been anchored, even in heavy wind and wave conditions, the bow of our boat simply moves up and down with the waves, or yaws from side to side, and usually both actions are present, but at no time do we get a sense of shock loading. I know what shock loading feels like. In fact I'm getting it right now tied to the dock. That particular sudden jerking when the movement of the boat is brought to a sudden stop by the lines which have reached the end of their stretch.

When anchored we have not felt this. When we've decided that we wanted the storm anchor it was due to heavy, but steady, strain on the anchor due to yawing in strong winds. Not due to a jerking shock of any kind. And we've often let out more chain as a precaution, not because of shock loads on the anchoring system.

Maybe my boat is lighter, or has less inertia in the bow, I don't know.

But by now I am convinced that what you all have been saying about "bar tight" and "straight" must be true and applies to many other boats, (but for some reason, whatever, not mine.)

By the way, we too do not use a snubber unless there is significant wave action or yawing. Here in Mexico the trend for cruising boats is to use a bridle. It's just about universal. We haven't seen the need for that either.

So, as often happens here on CF. I've learned something. Thank You.

[a64pilot]

Your going to disagree of course, but if your anchor chain has never been bar tight, and you have never had your boat yaw enough to be jerked by the chain enough so that you can feel the jerk in the boat, then you haven’t experienced wind and or waves high enough to do so.

Which is good, there is in my opinion no honor in having rode out a severe storm or it doesn’t make you a “real” sailor etc.
Good argument I think to be made for just the opposite, the smart and or lucky guy never experiences a severe storm, just as the good automobile drivers never experience a severe wreck, and those that have totaled several cars, well I don’t want me or mine to ride with them.

I have been lucky and not experienced a severe storm myself, I will consider myself successful if I never do.

A bridle is I believe usually a Cat thing, it’s nothing but dual snubbers, unless I misunderstand, they are wanting to distribute the load between the hulls, I just want a back up line, it really doesn’t distribute the load even on my mono, one is always tight and the other slack and it will oscillate back and forth as the boat yaws, it doesn’t take much.
I have one out of 5/8” three strand for serious weather but it’s not my usual snubber, that’s much smaller line.

[wingssail]

Originally Posted by a64pilot

Your going to disagree of course, but if your anchor chain has never been bar tight, and you have never had your boat yaw enough to be jerked by the chain enough so that you can feel the jerk in the boat, then you haven’t experienced wind and or waves high enough to do so.

Which is good, there is in my opinion no honor in having rode out a severe storm or it doesn’t make you a “real” sailor etc.
Good argument I think to be made for just the opposite, the smart and or lucky guy never experiences a severe storm, just as the good automobile drivers never experience a severe wreck, and those that have totaled several cars, well I don’t want me or mine to ride with them.

I have been lucky and not experienced a severe storm myself, I will consider myself successful if I never do.

A bridle is I believe usually a Cat thing, it’s nothing but dual snubbers, unless I misunderstand, they are wanting to distribute the load between the hulls, I just want a back up line, it really doesn’t distribute the load even on my mono, one is always tight and the other slack and it will oscillate back and forth as the boat yaws, it doesn’t take much.
I have one out of 5/8” three strand for serious weather but it’s not my usual snubber, that’s much smaller line.

Well, I am very particular about where I anchor. I'd rather be at sea in a storm than in a poor anchorage with poor protection.

Yeah, I get that a bridle is a "cat" thing. But here everyone has them. I think there is a orientation they go through in California on the way down.

[KRMS]

Sorry I haven’t read all the replies as I’m on a poor connection.

I’m replying because I have a similar combination to what you are proposing: Lofrans Cayman windlass* with a 8mm/5/16 gypsy, 80m of 8mm G70 Maggi Catena chain, Rocna 25kg anchor (+ a boat called Mystic Breeze as the previous owner was brought up in Mystic). The chandlers Jimmy Green in the UK sell Lofrans windlasses and the G7 chain. I’m sure they’d advise on the phone (even though obviously you won’t end up buying from them). My system works really well holding and gypsy-wise. The only issue is that the G7 chain doesn’t seem to flow over itself so well as the 9mm (yes 9mm) HT I had before. This means that it stacks up in the chain locker so the pile needs knocking over from time to time when hauling up the anchor. This wouldn’t be a problem if you have a nice deep chain locker.

Note also that the smaller stronger chain has an enlarged link (a separate factory fitted part) to allow a large enough anchor shackle to be used so as not to reduce the overall strength. This means that if you wanted to ‘end to end’ the chain later due to wear or corrosion on the sea bed end you’d have to get this link removed and put on the previously inboard end.

* FYI I wouldn’t recommend end the Lofrans Cayman as the design of the motor cover is poor and allows water ingress (it has a very narrow mating surface on the back of the main body casting and no registration groove/flange and is supplied with a very poor cork gasket). I’ve just had to replace the motor under warranty after just 2.5 years.