Chain Versus Rope Scope ?

[Bash]

I don't understand the current tendency to undervalue the relative worth of chain. A simple test might be instructive. Stretch 100 meters of chain out on a sand beach, and then stretch an equal length of rope out beside it. Grab one one of the rope, and drag it fifty paces. Now go back and grab the chain, and try to drag it 50 paces.

It is far easier for nylon rode to foul the anchor, or to foul on the boat's underbody, than chain. That alone is ample reason for me to use an all-chain rode.

The bottom line here is that 4:1 scope on chain is the equivalent to 7:1 scope on nylon.

[delmarrey]

Originally Posted by Jim Cate

Look guys, all this nice talk about not anchoring in coral... you don't have to be on a pristine reef, or even a very ordinary one to encounter coral. A great many anchorages here in the South Pacific islands are primarily sand bottoms, nothing too precious, and thus quite reasonable to anchor in. But, sticking up out of that sand, here and there are little bits of coral, mostly dead. It is pretty easy to get your rode foul of one or more of these bits, and they will shred a rope rode in a very short time. And having a composite rode (some chain followed by rope) only helps to a degree, for the rope bit will likely get onto some coral in the fullness of time.

Jim

In Borocay, PI, the local government will not allow anchoring in the coral. The locals have set up floats (water bottles) that are tied off to large dead coral heads that they use (first come, first serve), which are made of a heavy 3 strand floating poly of some sort.

My plan for the S. Pac. is to carry a line with a rubber hose covering about 15' with a loop on one end. With that I can dive down and wrap that around a coral head w/o damaging the coral or the line.

I don't know how these anchor/rode wars get so heated. There are many ways of anchoring. What may be good for one situation may not be good for another. And the type of boat makes a difference as well. Some boats yaw and others pitch or roll. What may work on one boat may not work for another. Get to know your boat before heading out. And that's it!

[Dockhead]

Originally Posted by Bash

I don't understand the current tendency to undervalue the relative worth of chain. A simple test might be instructive. Stretch 100 meters of chain out on a sand beach, and then stretch an equal length of rope out beside it. Grab one one of the rope, and drag it fifty paces. Now go back and grab the chain, and try to drag it 50 paces.

It is far easier for nylon rode to foul the anchor, or to foul on the boat's underbody, than chain. That alone is ample reason for me to use an all-chain rode.

The bottom line here is that 4:1 scope on chain is the equivalent to 7:1 scope on nylon.

I agree with you, and I don't use a rope rode myself. I have all-chain and always have.

But with respect -- 4:1 scope on chain is not at all equivalent to 7:1 scope with rope. 4:1 scope on chain is equivalent to 4:1 scope on rope once the catenary is out. And it is when catenary is no longer doing anything for you that you care. Scope is all about geometry of the pull on the anchor, and once the wind kicks up it doesn't matter whether you chain, rope, or a carbon nanotube rode weighing one gram -- the geometry is all the same.

Here are some good sources:

http://www.bethandevans.com/pdf/dashew-right-rode.pdf

Catenary & Scope In Anchor Rode: Anchor Systems For Small Boats

[jeremiason]

Is not that I don't want to continue the discussion on anchoring.

It is, I think it is easier for you to go on the offensive than it is to let someone state something you do not want to agree with or simply just agree to disagree with...

Your assumption is wrong...I have dove on my chain in 35 knots of wind and no, it was not pulling the anchor at 5 to 1 scope, if it was pulling on the anchor, I would have let out more chain. Furthermore you make another assumption that I don't properly set my anchor by backing down on it... Wrong!

Your statement about allowing a chain rode to pull on the anchor, is both silly and more importantly dangerous, passing it off as fact to the other members of this board.

Contrary to popular belief SIZE isn't everything! Do you really think the difference between a 25 kg and a 35 kg anchor is going to save your bacon without allowing for sufficient scope?

Furthermore, you are also making assumptions that all anchoring conditions are the same.... Based on that, you allow the chain to pull on your oversized anchor instead of letting out additional rode, again a dangerous practice.

For the purpose of this discussion, you have also assumed that your anchor is set in a good holding area; that you have the proper anchor type for the bottom conditions; that there is no significant bottom slope or obstructions; and finally that a bigger anchor will hold in all conditions without dislodging, even if the rode is not only pulling back, but upward, on the shank when the chain is what you refer to as "Bar tight"

So just to be clear... Each of you is in charge and responsible for your individual boat. The infomration here may be accurate... or it might not. I suggest you read it and then make your own desicions based on the situation...

So to be clear, all I am saying is, in my opinion, using my idea of prudent seamanship on my vessel is:

If the winds start to increase beyond what my ground tackle is set for... I don't let the rode pull on the anchor, I let out more chain to increase the scope and thus avoid pulling on the anchor to begin with. This mitigates the possiblity of dislodging my anchor, regardless of anchor size, bottom or sea conditions...

Originally Posted by s/v Jedi

Tom, I do not question your experience. I just think that you never actually dove on your anchor at 35-40 knots of wind or more, because the chain is really going to pull on the anchor then and it is your anchor that is holding your boat, not the chain. Your position that you can prevent pull on the anchor by putting out a 5:1 scope for up to more than 50 knot winds is not really defensible. This is not opinion, this is how it is.

I do understand that you don't want to continue this discussion, which sounds like a good plan to me.

ciao!
Nick.

[DutchTreat]

Originally Posted by Dockhead

But with respect -- 4:1 scope on chain is not at all equivalent to 7:1 scope with rope. 4:1 scope on chain is equivalent to 4:1 scope on rope once the catenary is out. And it is when catenary is no longer doing anything for you that you care. Scope is all about geometry of the pull on the anchor, and once the wind kicks up it doesn't matter whether you chain, rope, or a carbon nanotube rode weighing one gram -- the geometry is all the same.

Dockhead,

Was I wrong in my previous post? I still have to think at least 50% of the weight of the chain will be putting downward pressure on the anchor in the case that the chain is pulled tight. This has to add to the positional strength of the anchor as opposed to, let's say, a nylon rope which would not have much weight in water?

I just have to think in that case an all chain rode still has that advantage.

[cfarrar]

Tom,

I hear what you're saying about all chain, 7:1 ratios, and your 5/16" G4 / 25 Kg Rocna being a good system. I have the same setup on my 42' boat! Certainly no one is telling you to switch to a Rocna 45 and 3/8" Spectra rode : ) Let me illustrate my point with a real-world scenario that applies to both of us:

- We've got a 42'-47' boat with 300' G4 chain and a 25 Kg Rocna
- We use it properly, with 7:1 scope if required
- We like our set up, but we're headed to the Hurricane Archipelago, and we'd feel more comfortable with a little more holding power
- Our boat and windlass can handle more weight, but there are limits to what we'll tolerate on the pointy end, so we're looking for the optimum solution.
What do we do? Upgrade to 3/8" G4 chain? Trade in the Rocna 25 for a Rocna 33?

I think the optimum solution (with respect to holding power) would be the Rocna 33. If we determine that we also need stronger chain, we can get the Rocna 33 and upgrade to 5/16" G70 chain. Why? The anchor provides more resistance than the chain, even if we assume some catenary. Of course, if we come to believe (after considering the evidence) that catenary is negligible in high winds, then all the more reason to go for the bigger anchor, not the heavier chain.

If we allow even more weight on the bow, we can get the Rocna 33 and the heavier 3/8" G4 chain. In that case, however, we can also get the Rocna 40 and 5/16" G70! And so it goes... we can apply this logic as we trade up to a larger boat.

Cheers, Colin

[noelex 77]

Originally Posted by jeremiason

Is not that I don't want to continue the discussion on anchoring.

It is, I think it is easier for you to go on the offensive than it is to let someone state something you do not want to agree with or simply just agree to disagree with...

Your assumption is wrong...I have dove on my chain in 35 knots of wind and no, it was not pulling the anchor at 5 to 1 scope, if it was pulling on the anchor, I would have let out more chain. Furthermore you make another assumption that I don't properly set my anchor by backing down on it... Wrong!

Your statement about allowing a chain rode to pull on the anchor, is both silly and more importantly dangerous, passing it off as fact to the other members of this board.

Contrary to popular belief SIZE isn't everything! Do you really think the difference between a 25 kg and a 35 kg anchor is going to save your bacon without allowing for sufficient scope?

Furthermore, you are also making assumptions that all anchoring conditions are the same.... Based on that, you allow the chain to pull on your oversized anchor instead of letting out additional rode, again a dangerous practice.

For the purpose of this discussion, you have also assumed that your anchor is set in a good holding area; that you have the proper anchor type for the bottom conditions; that there is no significant bottom slope or obstructions; and finally that a bigger anchor will hold in all conditions without dislodging, even if the rode is not only pulling back, but upward, on the shank when the chain is what you refer to as "Bar tight"

So just to be clear... Each of you is in charge and responsible for your individual boat. The infomration here may be accurate... or it might not. I suggest you read it and then make your own desicions based on the situation...

So to be clear, all I am saying is, in my opinion, using my idea of prudent seamanship on my vessel is:

If the winds start to increase beyond what my ground tackle is set for... I don't let the rode pull on the anchor, I let out more chain to increase the scope and thus avoid pulling on the anchor to begin with. This mitigates the possiblity of dislodging my anchor, regardless of anchor size, bottom or sea conditions...

I think from your posts you are misunderstanding the role of scope. The principal behind scope is that it keeps the pull on the anchor horizontal or at a shallow angle. This allows the anchor to remain buried. It is not the holding power of the chain (which is slight) but the maintenance of this shallow angle that is the reason behind scope.


As the wind increases the chain will eventually become tight, almost a straight line between the anchor and the boat. If you dive on your anchor in strong wings you will see this. Letting out more scope helps because the angle the straight rode makes at the chain is determined by the length of chain and the depth to the bow roller above the anchor.

In any wind that is going to test a well set good quality anchor the chain will be off the bottom and all the holding is due to the anchor. The anchors holding is dependent an the angle of pull. Letting out more chain helps , not because the chain is holding the boat, but because the shallow angle of pull helps the anchor to work better.

In the 54 knots you mention in an earlier post the boat is held by the anchor not the chain. Try disconecting the anchor and see how quickly you drag, but more scope, rope, or chain helps the anchor hold better.
Past 10-14:1 the angle becomes shallow enough that more scope makes no, or at least, little difference.

[avb3]

142 posts and counting.

I'm certainly glad I asked the question! I even learned something (consider chafe, specifically).

As you! were

[s/v Jedi]

Originally Posted by Dockhead

Here are some good sources:

http://www.bethandevans.com/pdf/dashew-right-rode.pdf

Catenary & Scope In Anchor Rode: Anchor Systems For Small Boats

Just to repeat these sources. It would be helpful to actually read these if not read already



ciao!
Nick.

[s/v Jedi]

Originally Posted by avb3

142 posts and counting.

I'm certainly glad I asked the question! I even learned something (consider chafe, specifically).

As you! were

Yep, we're not done yet I think we've done this same discussion at least 5 times the last couple of years. In the end, we hope to change the world haha

If people do not trust the science behind all this, just look at the techniques in real life. Dashew is one of the big names that started to bring this up for about 20 years now. None of his boats drag. Most boats that follow the old lore anchoring beliefs do drag. That should be enough to make people accept.

I would almost post the 3 phases of Truth again but did that recently in another thread so will restrain myself

ciao!
Nick.

[CAELESTIS]

Originally Posted by s/v Jedi

Just to repeat these sources. It would be helpful to actually read these if not read already



ciao!
Nick.

Looking at the Dashew boat, he has a 250lb anchor with 3/8 G70 chain.

I am thinking about getting rid of my 250' of 3/8 HT and going with 5/16 G70 to get rid of weight in the bow. The breaking strengths are almost the same.

[Dockhead]

Originally Posted by DutchTreat

Dockhead,

Was I wrong in my previous post? I still have to think at least 50% of the weight of the chain will be putting downward pressure on the anchor in the case that the chain is pulled tight. This has to add to the positional strength of the anchor as opposed to, let's say, a nylon rope which would not have much weight in water?

I just have to think in that case an all chain rode still has that advantage.

If the chain is straight, there is no downward force.

[s/v Jedi]

Originally Posted by CAELESTIS

Looking at the Dashew boat, he has a 250lb anchor with 3/8 G70 chain.

I am thinking about getting rid of my 250' of 3/8 HT and going with 5/16 G70 to get rid of weight in the bow. The breaking strengths are almost the same.

Exactly. The Sundeer 64s came with 3/8" G70 and a 176lb Bruce. The Sundeer 56s came with 5/16" G70 and 110lb Bruce.

ciao!
Nick.

[avb3]

Originally Posted by s/v Jedi

Yep, we're not done yet I think we've done this same discussion at least 5 times the last couple of years. In the end, we hope to change the world haha

If people do not trust the science behind all this, just look at the techniques in real life. Dashew is one of the big names that started to bring this up for about 20 years now. None of his boats drag. Most boats that follow the old lore anchoring beliefs do drag. That should be enough to make people accept.

I would almost post the 3 phases of Truth again but did that recently in another thread so will restrain myself

ciao!
Nick.

In all seriousness, being a neophyte, I have appreciated the discussion, and I learned a lot more then just the chafe thing.

I asked the question because I just didn't know; hopefully others have learned something too.

Now, if I only could get out of cold country and put some of the theory into practice!

[DutchTreat]

Originally Posted by Dockhead

If the chain is straight, there is no downward force.

OK, I think I can see why.

Thanks