G70 chain vs G4

[double u]

“bar tight“ chain does not necessarily mean “no catenary“. Maybe a mathematician could chime in with a chain's catenary at ~80%BL.
Even if the “bar tight“ chain will preclude a further dissipation of force and the last link has been lifted off the bottom the catenary will give a better angle of traction to the anchorshank, even if this is only 5*.

[Dockhead]

Originally Posted by double u

“bar tight“ chain does not necessarily mean “no catenary“. Maybe a mathematician could chime in with a chain's catenary at ~80%BL.
Even if the “bar tight“ chain will preclude a further dissipation of force and the last link has been lifted off the bottom the catenary will give a better angle of traction to the anchorshank, even if this is only 5*.

Significant improvement of angulation on the anchor is lost fairly soon after the last link lifts. Here's a calculator you can play around with: Catenary Calculation - SVRmoorings


The angle you are interested in is "lower angle of incidence of chain with horizontal in degrees".

[noelex 77]

Originally Posted by KRMS

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.

When ordering G7 direct from Maggi there are options to add this larger link to one, or both ends of the chain.

It is usually possible to connect the chain and anchor satisfactorily without the larger link, but it takes some research finding a suitable connection depending on the chain size and anchor attachment point. It is important that the connection between the chain and the anchor is not the weak link even when subject to side loading.

The larger end link allows a greater range of swivels to be utilised if this is what you desire.

The only caution is when having chain made up by the factory in this way, be prepared for a long wait. The wait can extraordinary. We were promised our G7 order would take a few weeks. In the end it took several months. Others have reported similar delays.

[a64pilot]

The Mantus swivel due to the shape of its pin doesn’t require an enlarged link to maintain strength.
The Mantus S2 swivel breaks at 21,000 lbs and 5/16” G70 chain breaks at 14,000 lbs.

However when going to high strength chain, what swivel and or other means to attach to the anchor becomes especially important, you certainly don’t want all that super strong chain to put a weak link on the end of it.
Personally I wouldn’t put anything in my anchoring system that doesn’t specify the ultimate breaking strength, and my goal would be that the chain is the weakest thing in the system.

Having said that, I don’t believe anchors specify at what load the shank will break at, or which component fails first.
However one should logically assume that oversized anchors are stronger than smaller anchors of the identical design and manufacture.

[CAELESTIS]

Back to the original post . . . .

I switched from 3/8 HT to 5/16 G70 a few years ago. I did have to change the Gypsy to 5/16HT and it works fine on my Maxwell 2200. I saved 150 lbs on the bow. Very happy with the setup. This is on Acco chain with an oversized link on one end.

[Dsanduril]

Originally Posted by double u

“bar tight“ chain does not necessarily mean “no catenary“. Maybe a mathematician could chime in with a chain's catenary at ~80%BL.
Even if the “bar tight“ chain will preclude a further dissipation of force and the last link has been lifted off the bottom the catenary will give a better angle of traction to the anchorshank, even if this is only 5*.

Dockhead's link is interesting from the angle perspective, but what it doesn't give you is the effective "shock absorption" of the catenary. If you look at the math(s) there isn't much effective length change once you get to even a moderate load.

Using 10mm G4 chain (3/8") with a 2.3kg/m (1.5lb/ft) weight, a SWL of 15.6kN (~1600kg, 3500lb), and a 10m anchor depth (including height of fairlead):

With 3:1 scope the last link will lift at 900N (200 lb) horizontal pull and the remaining length in the chain is 0.5m (1.5ft)

With 5:1 scope 2700N (600 lb) and 0.33m (1 ft)

With 7:1 5400N (1200 lb) and 0.25m (9")

With 10:1 11000N (2500 lb) 0.17m (6")

at about 12:1 scope the last link lifts pretty close to the SWL.

So, scope can make a big difference in the point at which the chain lifts and the pull angle on the anchor leaves horizontal. Whether that's necessary, well, that seems to be the topic of most of the recent posts on this thread.

In all cases, however, there isn't much chain left for shock absorption. Over that whole range of loads there's about 0.3m (1 ft) horizontal distance available for the boat to move in absorbing shock, and that's not very much. Hence the need for a good, elastic snubber. It just doesn't take very much load to pull most of the length out of a chain catenary and leave no more to absorb shock.

[Training Wheels]

Originally Posted by CAELESTIS

Back to the original post . . . .



I switched from 3/8 HT to 5/16 G70 a few years ago. I did have to change the Gypsy to 5/16HT and it works fine on my Maxwell 2200. I saved 150 lbs on the bow. Very happy with the setup. This is on Acco chain with an oversized link on one end.

I switched from 5/16” G40 to 1/4” G70. I didn’t have to change anything on my anchor winch, it gripped it just fine.
[ATTACH]201729

[Dockhead]

Attachment 201743

Originally Posted by Dsanduril

. . . So, scope can make a big difference in the point at which the chain lifts and the pull angle on the anchor leaves horizontal. Whether that's necessary, well, that seems to be the topic of most of the recent posts on this thread.

Yes, and don't forget that scope directly determines the basic angle on the anchor. 1:2.5 gives 22 degrees; 1:3 gives 18 degrees; 1:4 gives 14 degrees; 1:5 gives 11 degrees; 1:6 gives 9.5 degrees; 1:10 gives 6 degrees. That's the basic angle without any effect of catenary; what you would get with a rope rode or with chain in strong enough wind.


A good modern anchor will do pretty well at 3:1 or 18 degrees, with more than half of its maximum holding power. So even in a storm with no effect of catenary, even with rope rode, I'll be getting more holding power out of my oversized Spade on 3:1, than some other guy with standard sized Delta or CQR or whatever, on 10:1.


(From Alain's site)

That's why it is silliness to make a fetish of scope, which is not the only factor which determines whether you will hold or not. And this is an error which could lead to bad decisions like opting to anchor in a poor holding or sloping bottom just to get your 10:1 scope, when you could have had clean level sand in deeper water at 3:1. We even had one guy on here some months ago who argued for anchoring off a lee shore in order to get into water shallow enough to use more scope

Originally Posted by Dsanduril

In all cases, however, there isn't much chain left for shock absorption. Over that whole range of loads there's about 0.3m (1 ft) horizontal distance available for the boat to move in absorbing shock, and that's not very much. Hence the need for a good, elastic snubber. It just doesn't take very much load to pull most of the length out of a chain catenary and leave no more to absorb shock.

Indeed.


Alain wrote about this:


A striking characteristics of this relation is its high non-linearity: a given force variation causes much less drift at high pulling forces than at low ones. When the rode tightens, the pseudo-elasticity due to gravity vanishes, so the force necessary to move the boat back increases asymptotically.





From: Rode - Static Behavior


That's why we need snubbers.

[STELLA31]

Lofrans have a gypsy available for G40 chain in 5/16 for the tigres part number 630994
Lofrans currently manufacture chain for this also.
Best way to check if its a match. Check the inside length of your current 8mm-5/16 chain. Both should be 24mm

[evm1024]

As noted in the past, I run 5/16" Acco G70 chain on an Ideal windlass using their 3/8" BBB gypsy. 5/16" HT (G40) would not run through the gipsy without severe problems.

The measurements I did on the chains showed that 5/16" G70 was within a few percent of the 3/8" BBB link length. The 5/16" HT was 10% or so different in length.

I cannot say that this works for every gypsy but I would suspect that a 3/8" BBB one would work for 5/16" G70 - od course check it out before you buy.

[evm1024]

Originally Posted by Dockhead

Attachment 201743


Yes, and don't forget that scope directly determines the basic angle on the anchor. 1:2.5 gives 22 degrees; 1:3 gives 18 degrees; 1:4 gives 14 degrees; 1:5 gives 11 degrees; 1:6 gives 9.5 degrees; 1:10 gives 6 degrees. That's the basic angle without any effect of catenary; what you would get with a rope rode or with chain in strong enough wind.


A good modern anchor will do pretty well at 3:1 or 18 degrees, with more than half of its maximum holding power. So even in a storm with no effect of catenary, even with rope rode, I'll be getting more holding power out of my oversized Spade on 3:1, than some other guy with standard sized Delta or CQR or whatever, on 10:1.

Attachment 201744
(From Alain's site)

That's why it is silliness to make a fetish of scope, which is not the only factor which determines whether you will hold or not. And this is an error which could lead to bad decisions like opting to anchor in a poor holding or sloping bottom just to get your 10:1 scope, when you could have had clean level sand in deeper water at 3:1. We even had one guy on here some months ago who argued for anchoring off a lee shore in order to get into water shallow enough to use more scope






Indeed.


Alain wrote about this:


A striking characteristics of this relation is its high non-linearity: a given force variation causes much less drift at high pulling forces than at low ones. When the rode tightens, the pseudo-elasticity due to gravity vanishes, so the force necessary to move the boat back increases asymptotically.


Attachment 201745


From: Rode - Static Behavior


That's why we need snubbers.

The concept and reality of an asymptote is often lost with only a casual glance. The key word in the definition below is infinity. And, of course, the line referred to is force.

In analytic geometry, an asymptote of a curve is a line such that the distance between the curve and the line approaches zero as one or both of the x or y coordinates tends to infinity.

In terms of the curve shown when there are at least 1 link on the seabed the forces are in the flatter portion of the curve. As the last link lifts off the seabed the catenary chord decreases rapidly as represented by the transition of the curve from flatter to increasingly greater slope. Exactly where on the curve the last link lifts off I cannot say and I suspect is very dependent on a bunch of parameters. Lastly, the transition from the "knee" of the curve to the asymptote is stark and abrupt. The forces experienced by the things at the ends of the chain (i.e. the boat and the anchor) are dramatic. The chain appears bar tight and the shock is profound.

And of course with the last link lifted off the seabed the forces on the anchor are no longer near horizontal.

[chrisr]

only a little bit off topic :

i'm thinking to switch to G70 chain (to save weight), and the chain i'm looking at is "gold passivated" see below

https://www.nobles.com.au/en-au/prod...grade-70-chain

i'm wondering how "gold passivated" compares to galvanised for corrosion resistance ? better or worse ?

obviously i'm going to ask Nobles, but anyone know something about this ?

thanks in advance

cheers,

[Paul L]

Originally Posted by chrisr

only a little bit off topic :

i'm thinking to switch to G70 chain (to save weight), and the chain i'm looking at is "gold passivated" see below

https://www.nobles.com.au/en-au/prod...grade-70-chain

i'm wondering how "gold passivated" compares to galvanised for corrosion resistance ? better or worse ?

obviously i'm going to ask Nobles, but anyone know something about this ?

thanks in advance

cheers,

Far more appropriate for road transport tie down than salt water anchoring. You'll be lucky to get a few months out of this in daily saltwater anchoring.

[wingssail]

Originally Posted by chrisr

only a little bit off topic :

i'm thinking to switch to G70 chain (to save weight), and the chain i'm looking at is "gold passivated" see below

https://www.nobles.com.au/en-au/prod...grade-70-chain

i'm wondering how "gold passivated" compares to galvanised for corrosion resistance ? better or worse ?

obviously i'm going to ask Nobles, but anyone know something about this ?

thanks in advance

cheers,

This was interesting to me since I had not previously heard of "gold passivation".

I am sure you've read the same stuff I now have read about the differences between hot-dip zinc coating and zinc plating. "Gold Passivation" is a color of zinc plating. A common statement I've seen is that zinc-plating is not suitable for outdoor use.

Here is a statement and a list of of differences from a company which does both:

Both processes use zinc coating as protective layer for a substrate/metal

• Galvanized plating produces a metal finish that looks dull and has a rough surface; zinc plating, on the other hand, looks shiny and pretty.
  
  
• Zinc metal plating is preferred for those who also aim for aesthetics; galvanized produces a fairly strong material that prevents corrosion (more protection) in many circumstances.
  
• Zinc plating is also preferred for those who need superficial protection, for indoor use, and in dry environment; galvanized plating is commonly used for outdoors or in a more wet (or hot) environment.
  
• With galvanized plating, a process called hot-dip galvanizing is used, which is a process of coating a substrate by passing the material through a molten bath of zinc at a temperature of about 460 degree Celsius. The resulting finish can be used in a place where the temperature is 200 degree Celsius and below; the zinc coating can peel when the material is exposed to temperature of more than 200 degree Celsius.
  
• With zinc plating, the process involves cleaning the metal surface with an alkaline detergent, then, treating the substrate with acid for rust removal; the protective coating (zinc) is deposited by immersing the substrate in a chemical bath containing dissolved zinc. (See more on zinc metal plating)
  With zinc plating, the coating is only typically 3 microns thick; with galvanized plating, the result is typically 50 microns thick, which therefore provides much more protection against corrosion.
  
• Zinc plating is a popular choice for coating nuts, bolts, washers, metal stampings, automotive parts, fabricated parts for industrial applications, as well as sheet metals; galvanized plating is used in a multitude of materials in the construction industry, including large structural shapes.

[chrisr]

Thanks guys...pretty much my thinking as well

shall come back again once spoken to nobles

cheers,