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-   -   How Much Chain, Really... In Non-Rock and Non-Coral Areas? (https://www.cruisersforum.com/forums/f118/how-much-chain-really-in-non-rock-and-non-coral-areas-237471.html)

thinwater 24-07-2020 16:13

How Much Chain, Really... In Non-Rock and Non-Coral Areas?
 
I'm going to avoid stating a fixed opinion. I've used all-chain and practically all-rope. I've written numerous articles and one book on anchoring, as well as spent a career and an engineer, and so I know the catenary and snubber math very well.

We all understand the case for chain around rock and coral. Done. But many or possibly most sailors will never come across either. The bottom is sand, mud, and weed. That is not to say cutting is impossible. A keel wrap will do it. A shopping cart can do it. I've seen both do some damage.

There is longevity. Chain rusts, nylon weathers and fatigues; chain will last longer for the full-time cruiser and rope will possibly last longer for the sporadic cruiser.

Economy and weight are obviously in favor of rope.

Scope is important with rope. Depending on the amount of chain and the amount of wind it will be more. Sometimes much more.

Yawing is in favor of chain. But there are other ways to stop yawing. For example, this is neutral for must mutihulls, because the bridle solves it.

Handling depends on whether you use a windlass or not.

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So how much chain? Bugger the rules of thumb. I used 100 feet on my last boat, which was the same as all-chain in the shallows of the Chesapeake Bay. The boat came with less, and that worked too. I've used 6-8 feet on several light boats, because they didn't have rollers and breaking out and anchor with chain against the topsides is a non-starter. I never use much chain on a kedge--it's just a pain and serves no purpose, and anchor testing, I've set a LOT of kedge anchors.

The "length of boat" rule makes little sense to me, since it should relate to the depth of the water and the bottom type. What does the length of the boat have to do with anything, other than ease of carriage? Use high strength chain, if that's the thing.

The diameter rules seem thin to me. Too stretchy and too hard to haul by hand. And bigger wears a LOT longer.

Not all harbors are crowded. I seldom anchor anywhere that swing matters. Many posters have said the same. We are not in the Med. This can also be addressed with a kellet.

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Fire away. But please limit the coral and rock cutting discussion. We've heard it, we get it. Catenary is fair game. Let's see who can come up with an original way of looking at it.

sailorboy1 24-07-2020 17:20

Re: How Much Chain, Really... In Non-Rock and Non-Coral Areas?
 
I have 300’ all chain because it is less problem for me.

I fail to see why we need a new anchor chain thread or how a new thought could possibly be written.

Nicholson58 24-07-2020 18:28

Re: How Much Chain, Really... In Non-Rock and Non-Coral Areas?
 
5 Attachment(s)
Depend on where you expect to be anchoring (Bottom and depth), how heavy the boat.

We are in the Caribbean full time as live aboard. Reliability is not compromised. Depth is mostly 10 to 30 feet. Wind is nearly always East 10-20, 35 tops except storms. Bottom is sand or muddy sand most places and occasional coral debris. The boat is 40 tons, anchor 54 kilo, chain 10 mm, swivel is a forged fore runner. With these facts of life, the rode is all chain. It cannot be hauled by hand and a rope-chain combination would be difficult and dangerous to manage. The windlass is 3000# capacity. The chain is long enough to end-for-end when the galvanizing is gone. Minimum 200 feet.

a64pilot 24-07-2020 19:28

Re: How Much Chain, Really... In Non-Rock and Non-Coral Areas?
 
I have 275’ of chain because that’s what a half barrel is, and a half barrel is cheaper than by the foot. My boat doesn’t seem to care about the weight, so why not? I don’t think I have ever had more than 200’ out and likely didn’t need that when I did.
But extra chain is like extra fuel or extra fresh water or extra money.
Chain stows automatically with my windlass and I don’t believe rope would, so it’s much easier to use, just push a button.

thinwater 24-07-2020 20:39

Re: How Much Chain, Really... In Non-Rock and Non-Coral Areas?
 
It's not about you.



It is about other boats, other situations, and imagination. I didn't post on the "how much chain" thread because the conventional answers were piling on and there was some sense in them. I've used all-chain and I get that. But there are other boats and other situations.


Some imagination, please.


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For example, are there crossover points, where chain catenary is far less effective than stretch. For example, in extremely shallow water this is easily demonstrated. In 3 feet of water, 4:1 scope is only 20-30 feet of chain; you can easily pull that off the bottom by just leaning back (catenary lifts at 40 pounds). Catenary is basically useless. You will say, of course, that the example is ridiculous. To you. I've anchored a cruising cat in less. Of course, the bottom was mud, not coral heads.


What is the crossover point where the weight of a bigger anchor is more useful than the weight of chain? I think we can easily show this happens at 10-30 feet, depending on the boat, if we ignore cutting and control yawing. I don't think you want to argue that.


I doubt any of you carry all-chain in your tender. Possible, of course. Do any of you use a new generation anchor in the tender? Probably not. So there is flexibility or at least boundires in the rules.



Other points I made above.

moseriw 25-07-2020 08:57

Re: How Much Chain, Really... In Non-Rock and Non-Coral Areas?
 
Oh man, as much as you have or minimum depth x 5. Daystop in moderate condition depth x 3

Ken Z 25-07-2020 09:31

Re: How Much Chain, Really... In Non-Rock and Non-Coral Areas?
 
I ve used 25í of chain on all anchors for 45 yrs. never chafed line, lost a anchoror had any problems.

rondelais 25-07-2020 09:36

Re: How Much Chain, Really... In Non-Rock and Non-Coral Areas?
 
I think it comes down to total weight. A lot of chain means a lot of weight up forward, and for lighter or smaller boats this matters. So, if you pick a certain weight up forward, you can try to pick the best combination of anchor, chain, and rope. I think there are a few general guidelines:
1. Heavier, shorter chain is better than smaller, longer chain. This is especially true in shallow water. If I have 100 feet of 3/8Ē chain out, thatís 164 pounds vs 118 for 5/16Ē, and itís the total weight that keeps the chain on the bottom. For my boat, the 100 feet of 3/8 keeps the anchor pull horizontal in 20 feet of water up to a wind of 25 kt. The 5/16 chain is only good to 21 kt. So, Iíd rather carry 100 feet of 3/8 than 140 feet of 5/16.
2. A bigger anchor is better than more chain. Once you have 100 - 150 feet of chain, you are better off to use the weight on a bigger anchor.
3. It depends on where you typically anchor. Unless you are regularly in 40 feet plus, 100 feet of chain is generally enough. The total length of chain plus rope ought to be 350 feet or more just in case you are in 40 feet at 60 kt.
4. You need a snubber if you are on all chain. You need a longer snubber in shallow water. (Seems weird, but true. The chain just does not have much catenary in shallow water, so canít absorb much shock.)
Of course, every boat and every anchorage is different, so the best thing to do is go through the calculations for your situation.

waterman46 25-07-2020 09:49

Re: How Much Chain, Really... In Non-Rock and Non-Coral Areas?
 
I'll avoid the all-chain answers so many have given, since that was not your question, and your question is very valid and interesting.

We have a fair amount of anchoring experience on the West Coast, SF Bay to Panama. For short stays we use our rope-chain rode with a Bruce anchor in places where there are no rocks. (There is no coral in shallow water on the W. Coast until you get to Panama, and then it's very isolated and nobody needs to anchor near it). Where there are rocks (SB Channel Islands) of course we use all chain.

In chain, weight is your friend, and even more so with a chain-rope rode. Outside of wear, there is no other reason to use chain. I may be misinformed, but I believe BBB is one of the heaviest chain types. So we use a Bruce anchor with 50' of 3/8 BBB below the 3/4 nylon triple strand. It has always set and held nicely.

Short answer, if you have the recommended size anchor for your boat, then use 50' of the heaviest grade the gypsy will take. I have seen many failed anchoring attempts by folks using much less chain. 20' is not enough, IMHO.
On the stern anchor, only used very occasionally, we have a Fortress aluminum with, again, 50' of chain, although it is a lighter grade chain, and it works very well when deployed from the dinghy.

thinwater 25-07-2020 10:45

Re: How Much Chain, Really... In Non-Rock and Non-Coral Areas?
 
Quote:

Originally Posted by rondelais (Post 3193893)
...1. Heavier, shorter chain is better than smaller, longer chain. This is especially true in shallow water. If I have 100 feet of 3/8Ē chain out, thatís 164 pounds vs 118 for 5/16Ē, and itís the total weight that keeps the chain on the bottom. For my boat, the 100 feet of 3/8 keeps the anchor pull horizontal in 20 feet of water up to a wind of 25 kt. The 5/16 chain is only good to 21 kt. So, Iíd rather carry 100 feet of 3/8 than 140 feet of 5/16....


This is an interesting point. It seems counter intuitive, but it is correct.



To simplify the math, think about a kellet instead. If the goal is to keep the chain down close to the anchor is better. This is obvious, because the closer it is to the boat, the greater the lifting angle. You can go through the trig to get to this.


If the goal is to absorb energy, closer to the boat is better. The maximum energy the kellet can absorb from the bottom to the surface times its mass. The curves vary (wind speed during which absorption is most effective), but closer to the boat is better. But with a lot of nylon it probably does not matter much.



Abrasion and cutting would favor longer chain. yawing and swing reduction would favor a longer chain.


As a rule, a small amount of chain is NOT going to keep the hook on the bottom in a squall with 50 knots or more. Less than 40 feet will lift in 15-20 knots, depending on scope.



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A rig I have been experimenting with is very short chain (easier to handle) and a chain kellet (~ 10 feet in loops) near the mid point to reduce yawing. The chain loop is very easy to handle. Just playin', but it works well on a light boat.

noelex 77 25-07-2020 11:22

Re: How Much Chain, Really... In Non-Rock and Non-Coral Areas?
 
Quote:

Originally Posted by thinwater;3193449Fire away. But please limit the coral and rock cutting discussion. We've heard it, we get it. Catenary is fair game. Let's see who can come up with an [B
original[/B] way of looking at it.

I think you have outlined the pros and cons well. An all chain rode is not the ideal answer for all boats. However, for the majority of cruising boats, especially long distance cruising boats, it is overwhelmingly the preferable option.

One area of greater research that I would like to see is the effect of rode weight on anchor setting performance.

MathiasW 25-07-2020 11:23

Re: How Much Chain, Really... In Non-Rock and Non-Coral Areas?
 
1 Attachment(s)
We have had a very long thread on anchoring at

https://www.cruisersforum.com/forums...pe-235053.html

where my mathematical / physical model of anchor chain and snubber/bridle was most thoroughly discussed. My full analysis - updated after all the feedback I had received - can be found at

https://trimaran-san.de/die-kettenku...atiker-ankert/

(don't worry, it is not in German, but in English... ;) )

Bottom line is that a chain is working best if it can be used with shortish scopes, whilst still maintaining a horizontal pull at the anchor. In a storm, this is only achieved in deeper water. Have a look at the curve attached. It is the elasticity of the chain - defined as derivative of the chain's potential energy with regards to wind force, and plotted as a function of scope, i.e. chain length L divided by anchor depth Y.

In shallow water, it takes a very large scope of the chain to make sure it is pulling the anchor only horizontally. This is simply because it is very hard to store additional potential energy in an almost horizontal chain, which has both its ends fixed at a given height (anchor, respectively bow). There is simply almost no headroom for the chain to get further lifted to, anymore. With this we are on the far right-hand side in this diagram and the elasticity of the chain really sucks.

On the other hand, in very deep water, I can maintain a rather small scope of the chain whilst still having it pull only horizontally at the anchor, even in a severe storm. Then I am much closer to the peak in the diagram and the chain works well. So, this says, go for deeper water, if you can (and you have enough chain).

Now another observation: The peak in this diagram scales with the anchor depth Y, meaning, if I halve the chain weight per unit length, but double the chain length and anchor depth, I will have the same shape of the chain, just magnified by a factor of 2, and its elasticity has also doubled! So, from this I conclude that I get a better performance of the chain in terms of its ability to absorb shocks when I make it thinner, but longer, so that the total weight in the locker remains the same. Of course, one may have to use higher-grade chain material then, and the 2nd disadvantage is that the swinging circle will also have doubled. Also, at the same water depth, a thinner chain will pass more of the swell energy to the anchor as additional load.

But for me, intending to sail around the world, this result meant I should opt for a thinner but longer chain. With this I can anchor in deeper waters and have a larger range of suitable anchorage sites available to me. I might have issues with swinging circles in densely populated anchorage places, that is the drawback.

As to bridle / snubber (we have a trimaran, so it is a bridle), it is crucial to help absorb shocks in shallow water. In particular swell. Swell causes huge surges in anchor load, which the chain cannot absorb in shallow water, but luckily, this is where the snubber/bridle works best. It has its performance optimum in the opposite corner compared to chain, and thus the combination of both is ideal.

It needs to be a good snubber/bridle, though. A bridle is normally long, anyway, but snubbers I sometimes see rather short. In the diagrams that I have calculated in the various digests for different vessel sizes, I have standardised on two different snubbers / bridles: One which extends by 10 cm in 8 BFT of static wind (no gust, no swell), and another which extends by 25 cm at the same conditions. This may not look much, but in gusts and swell, this can easily become 3-4 times the static value.

Obviously, a very short snubber of perhaps 1 - 2 metres length might not provide such a flexibility, but adding a rubber dog bone will help a lot.

I have recently measured my bridle with a hanging scale: One leg of the bridle extends by 50 cm when pulled at with 100 kg. I have 2 rubber dog bones in each leg of the bridle. So, this is really a lot of elasticity.

When you look at the anchor loads induced by swell (as opposed to static wind) one finds that the same swell generates smaller loads in deeper water. So, all things being equal, and in particular the swell being the same, it may make sense to anchor in deeper water rather than shallow water, if one has the chain available.

So, there is no universal answer to the original question, as it all really depends on your typical anchorage sites. If you know your anchorage sites and the typical anchorage depth, then it makes sense to optimise the chain such that it is as thick as possible but still be sufficiently long for the depth and wind situations that you encounter. This gives you the shortest possible swinging circle. Important for crowded places.

If you are in areas with strong tides, you need to factor that in and the chain is likely to be thinner, to allow anchoring also at larger depths.

And when you are sailing around the world and need to be prepared for anything, then go for the heaviest and most universal anchor you can afford, use the best-grade chain you can afford, as thin as possible, and of this as much as your chain-weight budget at the bow allows. This gives you the largest range of accessible anchorage sites, but at the possible disadvantage of a larger swinging circle.

There was also the question why the chain should depend on the boat length. Very correct irritation that is. I think what happens here is that typical vessels scale in all their dimensions in a similar way, and so when I just specify the length, I am also implicitly specifying its windage area towards the wind. At least to some accuracy. But this is not very precise, of course. What really enters all the equations is the ratio of wind force applied to the vessel (which is related to windage area), and the chain weight per unit length in water. This ratio is quite similar for very small vessels to very large ones, and even ships.

If anybody ventures to my web page, somewhere there are pdfs to be downloaded which are tailored to vessels of different windage areas, ranging from 2 square metres to 30 square metres. If you know your windage area, roughly, you can pick your tailored anchorage digests there... :)

Comments are most welcome!

MathiasW 25-07-2020 11:39

Re: How Much Chain, Really... In Non-Rock and Non-Coral Areas?
 
2 Attachment(s)
Here are two mind maps I had created that helped me structure my thoughts to this topic...

rondelais 25-07-2020 12:17

Re: How Much Chain, Really... In Non-Rock and Non-Coral Areas?
 
So, what MathiasW opts for is thinner (and thus lighter) chain, with the saved weight allowing it to be longer, so that he is on all chain always. Heís thought about this a lot - so is worth listening to. What this means is that for a given wind/depth situation, he is going to be on a longer rode, with a bigger swing radius in most cases than if he used heavier chain. At some point, though, as depth or wind is increased, a chain/rope rode will be even longer (there is almost no catenary to the rope part). But, he keeps it simple. I also like the idea of having chain/rope/chain like Thinwater suggested. Might be fun to try it to see the effect on yaw and in waves. The problem would be to come up with a configuration that would be useful in a variety of situations. Maybe 50 feet chain, 50 feet rope, 50 feet chain, 200 feet rope rather than 100 feet chain and 250 rope. The rope in the middle would give nice elasticity, and maybe you could skip the snubber. Of course, I really often use the snubber just to get the anchor load off the roller unless the weather looks threatening. There might also be a problem in coral/rocks with the rope on the bottom. There are so many tradeoffs, including how you use your boat. We end up on anchor in a different place almost every night, so need a simple, flexible approach.

Ramona 25-07-2020 15:45

Re: How Much Chain, Really... In Non-Rock and Non-Coral Areas?
 
I used to have 10 metres of 10mm chain with a replica 13 kg Ultra anchor. Now have 4 metres and could probably getaway with less. Modern anchors have changed everything. Yacht is 30' 4.5 ton.


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