All Chain vs Chain and Line Anchor Rode

[BruceK]

Eric, that`s how the "Anchor Buddy"works. We`ve got one but with the Sarca of course we don`t need it .
You lower the AB weight attached to and down the set rode to the seafloor as at high tide. Idea is the rode then lies horizontal along the seafloor from the AB weight to the anchor, making the pull horizontal rather than upward. Not really a catenary,but similar in effect.

 

[sahockey]

First, any weight on your anchor line nearer your boat or your anchor than the center when under pulling tension, will not keep the forward pull on the anchor as low as the same weight in the middle of the line. It’s just physics.

Second, if you don’t feed your anchor line, feeling the weight lighten as the anchor settles down, its a guessing game at what point your anchor actually touches bottom. The bottom depth can vary a lot from where you are dropping and where you originally got your depth reading. Not to mention a weedy bottom giving a false depth. Plus if you are in a windy and/or one with a strong current, that anchorage is the one that probably matters most that you do everything correctly. If you just push your down button you may end up with a pile of chain on top of your anchor that could foul it or “conversely drag anchor” before it’s even touched ground.

I’m spending the summer here in gorgeous Penobscot Bay up to Mount Dessert Island Maine. I usually try to anchor because then I usually get more privacy compared to a slip or mooring field as well as saving some money I can then use to buy all the toys needed (like a new auto pilot to replace the old broken one) to fully enjoy this trip.

Recommend all of you put this area in your bucket list if you haven’t already. I doubt there is any nicer cruising grounds in the US. It’s beautiful, very challenging, at a reasonable cost, with friendly people, and then of course there are the lobsters.

Stephen

 

[Nomad Willy]

Eric, that`s how the "Anchor Buddy"works. We`ve got one but with the Sarca of course we don`t need it .
You lower the AB weight attached to and down the set rode to the seafloor as at high tide. Idea is the rode then lies horizontal along the seafloor from the AB weight to the anchor, making the pull horizontal rather than upward. Not really a catenary,but similar in effect.

Yes of course.
Run the AB (anchor buddy or kellet or sentential) down close to the anchor and the angle of seafloor to rode close to the anchor will be reduced. Elementary Bruce. Same thing if you have an all line rode and add 10’ of chain. Rode angle near or at the anchor will decrease increasing anchoring performance w the rode more horizontal than w/o the added chain.

But have you ever thought of adding the 10’ length of chain to the top of the rode? From the anchor roller down 10’. Or slide your AB down the rode 5’. Hmmm? Haven’t seen anybody doing that.

And furthermore w the weight added up high on the rode the rode angle would actually increase near the anchor. That is the rode would rise up (a bit) a few feet from the anchor. If the rode was off the seafloor from the bow roller to the anchor (as in anchored in enough wind to to pull it up) any weight high on the rode would increase the rode angle near the anchor decreasing anchor performance attributable to catenary.
So the weight high on the rode w an all chain rode is actually DECREASING anchor performance with enough wind to lift the rode off the bottom in a typical anchoring in windy conditions scenario.
So just substituting line for chain high on the rode will increase anchor performance by decreasing the rode angle at or near the anchor. It would be the same basically as adding the AB (anchor buddy) low down on the rode. The amount would be small. But it shows how the chain on an all chain rode dosn’t do any good catenary wise w the rode suspended off the bottom in a wind.

So the all chain system is inferior (anchor performance wise) in enough wind to lift the rode off the seafloor. Something that would happen in any typical anchoring a recreational trawler situation in wind strong enough to lift the rode off the bottom at the anchor.

 

[Nomad Willy]

sahocky wrote;
“First, any weight on your anchor line nearer your boat or your anchor than the center when under pulling tension, will not keep the forward pull on the anchor as low as the same weight in the middle of the line.”

Not so.
If I added weight 3/4 of the way down the rode from the bow roller (closer to the anchor than the boat) the rode angle at the anchor will decrease increasing the holding power of the anchor if the wind is strong enough to pull the rode up off the bottom. And the maximum holding power of the anchor has not been exceeded.

Would “it’s just physics” apply?

 

[caltexflanc]

However when the chain is vertical there’s no catenary.

Again, not so. You will typically have more of an "L" shaped rode in that situation. That's what causes so much mud on a long section of rode as you pull it up. In relatively calm conditions, you can be laying to the buried chain, not the anchor. I have directly seen this first hand a few times in clear water, and experienced the effect several more times.

 

[Nomad Willy]

cal,
Catenary is the curve of line, chain or cable ... is it not?
Of course what we're concerned about is the angle of the chain/line to the seafloor at the anchor shank.
Maybe some consider that to be catenary?
As I percieve it the catenary is the curve the flexible line assumes when pulled up off the bottom.

One could tie a rope from a tree high enough so that when it was anchored out some distance with enough tension that it would be off the ground .. the curve would be "catenary". Is that so or not so?
But by that def the catenary would be the curve (in your example) only from the bow roller to the point where the chain came in contact w the bottom.

 

[Codger2]

Catenary is the curve of line, chain or cable ... is it not.. .. the curve would be "catenary". Is that so or not so?

Eric, that has been my understanding as to what "catenary" is.

 

[sahockey]

Cantenary is probably not the correct term to use in an anchoring situation because the ends of the rope or chain are not at the same height. Obviously the bowsprit is higher than the seabed. A more correct term might be brachistochrome or curve of the fastest descent. I’m certainly not a physicist. Yet intuitively since the greatest leverage is achieved at the center of a length of rope tied between two points (boat and anchor) this would seem to me to be the best way to transfer the vectors of force in a parallel direction to the seabed from the anchor.

 

[Nomad Willy]

sahockey,
HaHa I see where you are in this. There’s a problem w that though. The tension on the anchor rode comes from the boat. But part of the weight is not considered in anchoring. That would be from the weight of the chain pulling on the ends. Always the pull (down) on the bow exceeds the pull on the anchor since it is higher. But I’ve never heard of anybody talking about this element of anchoring physics.

The pertinent anchoring forces are the pull on the rode and the angle of the chain relative to the seafloor. I almost wish Codger and I were wrong and the catenary was the seafloor to rode angle. So I need to call it out each time.
“brachistochrome” is that a joke?
And I don’t see how an anchor rode can exert “leverage” on a rode. Are you talking bout tension? And the center of a horizontal rode is the place to exert force to cause equal tension on the ends but anchor rodes are never horizontal.

Try’in to get my head around this but having troubles.

I’m interested in your “curve of the fastest decent”. That does sound interesting but I can’t connect it to anchoring.

Usually they abandon me when I get technical .... at least I’m getting some feedback today. Thanks

 

[timb7734]

Had the same boat, used all SS chain, only had to clean the last 20 feet or so and it cleaned up easily in the water on hoisting the anchor, used a Rocna anchor. Cruised Florida and Bahamas

 

[sahockey]

Nomad,
I don’t know if brachistochrome applies to this or not. Probably not but at a minimum it does seem to show that cantenary isn’t relevant to this discussion because the ends are at different heights.
Leverage I think can probably be changed over to force vectors by knowing the amount of force applied to the center of the anchor rode. I don’t know the formulas but they can be looked up and involve sign and co-sign values which are beyond my interest and current knowledge level. I believe that the mechanical leverage principles when applied to this will be valid whether the line (rode from anchor to boat) is horizontal or even vertical or anything in between. In this case the force would be the weight applied to the center of the rode. But as you state if the line were vertical or anything other than horizontal that force vector wouldn’t be evenly directed in both directions because of gravity. And yet if you have a scope of 5-1 length to height anchor rode I suspect it would have some relevance. Whether it would be more beneficial to have it nearer the anchor or the boat would be up for discussion.
A rather simple experiment should be able to show that the weight (assume the rode weights nothing in this case) should be closer to one end or the other by tying one end to the ground and then running the other end through a pulley at a 5-1 elevation which is the normal scope of an anchor. Attach that pulley end of the rode to a force gauge which could be just a fish scale. First place the weight near the ground end at a certain z distance and pull x amount of force measuring the height off the ground at a certain y distance. Then put the weight near the higher end at a certain z distance again pulling the fish scale to the same x weight and again measuring the height of the ground at this y distance. Whichever is lower is the winner.

 

[sahockey]

Nomad,
I also expect this experiment will show the same results for any length of rode as long as you go with the 5-1 scope. In fact you can probably get a formula to find the best placement of this weight from this experiment.
Stephen

 

[caltexflanc]

Had the same boat, used all SS chain, only had to clean the last 20 feet or so and it cleaned up easily in the water on hoisting the anchor, used a Rocna anchor. Cruised Florida and Bahamas

Not much mud found in those parts, and we anchored all over down there.

 

[Nomad Willy]

Stephen,

I’m thinking if you had a boat at anchor in a wind w the rode just off the bottom at the anchor there would be the equal force exerted at each end from the forces of the wind acting on the boat. Fly stuff but the boat end of the rode would have a bit more weight applied from the anchor rode in varying amounts depending on the scope applied.

But what I just wrote has little to do w the anchoring performance. The bias of the weight of the chain in the rode has a greater effect. The only thing that has a fairly profound effect on anchor performance is the angle of the rode to the seafloor. And re what I’ve said above the location of the weight of the chain probably would have a rather great effect on the bottom rode angle. “Bottom rode angle” being the angle tween the rode at the anchor and the seafloor.
If half of the rode was chain the rode BRA (bottom rode angle) would be least if the chain end of the rode was attached to the anchor. If the chain end was attached to the boat the BRA would be greater. And the rode at the anchor would be less horizontal. Less horizontal = lower anchor performance.

That shows that the upper end of the all chain rode has far less effect on the BRA than the lower half of the rode. The weight of the lower part is the dominant force forcing the rode to become as horizontal as possible. The upper part has little effect.

Sorry some of that was repetitive but saying things differently frequently produces clearer comprehension by others. What think?

 

[sahockey]

Nomad,
I’d be willing to bet this is a pretty simple math/physics problem that could be worked out in a formula but there is more than one way to arrive at the correct answer and I believe this is how I will try doing it in a couple of days. Forget the experiment but just keep moving the weight around on the anchor rode until a certain distance from the anchor is the lowest. Of course the anchor rode I will use is a piece of cord about 60’ long. I will attach one end of the cord to the ground 1’ above the ground to allow room for the weight to hang. I’ll suspend a pulley 49’ away from that spot on the ground at 11’ high. Ill run the cord through this pulley attaching a 10 lb weight to it. This will give me a 5-1 scope. Water depth of 5’ plus bowsprit height of 5’ with a rode of 50’. Then I’ll take a 5 lb weight and attach it at different spots on the cord until the cord is at its lowest point 2’ from the anchor attachment point. This will give the best location for weight to be placed on an anchor rope. Who is betting what? Intuitively I’m betting the weight is best placed near the center but closer to the anchor than the boat.
Stephen

 

[sahockey]

Eric,
I agree with your BRA or bottom rode angle which is the same as my distance from the ground near the anchor but your BRA is just a more accurate description. But here is where my mechanical advantage will make the difference I think. (I should have tried my test before opening my mouth so that I would not be wrong.) On a 5-1 scope there is not a lot of angle to be concerned with but if that angle is reduced to zero or less then that gives more of a safety factor for when the winds start pushing the boat harder than 10lbs.. Since if those winds did pick up above those 10 lbs then that positioning is even more important because it would hold that angle longer.
Stephen

 

[Nomad Willy]

Stephen,
Wow ... you’re going to do that. I’m a man of words and thoughts but fall short on action. At least I lean that way.

But for your information it was leaked or uncovered on a TF thread 5 or so years ago that the best place for weight on an anchor rode was roughly 5 to 10% up the rode from the anchor. I had always assumed it to be at the boat end of the anchor shank before that but I’ve bought into that it’s a bit up the rode. Marin Faure was involved in that discussion but unfortunately he’s gone but Peter B may recall. If one applied this to the practical day one would have a heavy chain about 15’ long. There I am think’in out loud.

Something that occurred to me is that this experiment may work better with the right weight proportion of the rode and the weight. A small weight w a heavy chain or a heavy weight w a light rope would likely produce misleading results ... I’m thinking.
Will be a fun experiment. One of the best ever on TF to be discussed for years ... probably. I have a home made Kellet but I see you’re a long way from me .. geographically speaking. Well tell me more .. even think out loud.

 

[FF]

A kellet is a fine cure for a too small anchor.

The same total weight of anchor and kellet might be better y simply using a bigger anchor? And easirt to set and recover.

Anchors is one area where" Bigger is Better" , is no problem.

 

[Nomad Willy]

FF wrote;
“A kellet is a fine cure for too small an anchor”
But you can’t increase fluke area w a kellet.
It is quite relevant to this thread though.
FF also wrote;
“Anchors is one area where" Bigger is Better" , is no problem.”
One must pul up the anchor and rode before leaving the anchorage. My anchoring would be more assured if I used more chain and/or a bigger/heavier anchor. But I can’t see myself pulling up a 44lb anchor and 100’ of steel chain.
Also if anchoring was made better so easily w a bigger anchor we could choose an anchor that was better at a wider varieties of seafloors. A low performance anchor like a Claw or Navy anchor made considerably bigger becomes high performance. A 65lb Bruce would be a very high performance anchor on my boat.

A Kellet is rarely used because it’s more effort.
Many or most reduce the effort of anchoring to pushing a button from inside the boat. Leaving the helm may put one into an old school category. Or just lazy.

The only people interested are those anchoring by hand. I don’t even do that as I have a capstan. Well .. it’s by powered hand. But it only reduces the effort by half. I like to be on the bow for several reasons. I like to watch the rode as we back down or better yet to reach down and pull up on it. It’s revealing the vibrations one can feel through the nylon line. And as the tension ramps up there’s no doubt about being set. It’s also reassuring.

I made a kellet with lead weights from a commercial fishing bouy. It’s only 12lbs but one of my primary anchors is 12lbs. It may be plenty .. or in another way “worth using”. But I haven’t done so.
I saw the trip line as a good investment. Rigged one up and used it several times in Alaska. But I need to point the lazy finger at myself as I quickly dispensed with the trip line and float. Not much effort .. but too much.
But w all the gear on deck I may just wanted the trip line out of the way.

I look over the bow a lot trying to see what direction and at what angle the rode is streaming away from the boat. It’s amazing how far over I need to lean to see what I want to see.

But just pushing a button has merit much of the time. When we’ve anchored there 20 times and know it’s a walk in the park and the weather is benign. But there are many other scenarios that demand close attention. And close attention cannot be achieved from the helm.

 

[psneeld]

I also believe that every once and a while someone comes up with a better idea than a manufacturer.


However I think those situations are pretty rare depending on who is doing the investigation beyond the manufacturer's scientific experiments.


I'm not a bad backyard mechanic myself and I believe many of the opinions regarding anchoring are way off base.


You can use the word physics and vectors and anything else you want but often in these threads they don't follow the same learnings of physics that I have had.


The vast majority of owners of next-gen anchors have had spectacular results .....modifications to these results may be a slight improvement but for the most part there are many variables that change successful anchoring..... any discussion of physics, of angles, of vectors, or techniques..... anything you want.... I just go by what works for me and what has worked for thousands of other cruisers without all these nitpicky modifications.

 

[sahockey]

I am still committed to doing some experimenting but the more I think about it the more complicated it gets because I want to reduce the impact of many of the variables. I need to rent a car to journey back to upstate NY for an appointment. While I’m there I will do at least some preliminary tests which we can use to decide what additional ones should also be done. I am finding this whole subject to be fascinating. Unlike psneeld I find many of the current ideas may be poorly founded on facts. I hope to be able to provide some facts to add to this discussion. I hope to be able to provide some of those facts by Wednesday

 

[Nomad Willy]

A man of action and resolve. I mean Stephen
Upstate NY sounds like a good place to balance variables. Just thinking about such things often result in new relationships. But the hands on element of experimenting can trump a lot of things.

Have a good trip and bring back revelations.

 

[Datenight]

Thanks. I am sure you are right. North Pacific generally have things well covered. At least that has been my experience so far.


I hope your trip is going well. The weather should be improving this weekend.

Thanks Dave,

The trip is going great. Just dropped my brother in law off in Friday Harbor. Next stop is Griffin bay then perhaps False Bay on the way to Victoria.

We are on Wand'rin Star a NP 43. If anyone sees us give a call. Would love to meet some of you while here.

Rob

 

[Nomad Willy]

Datenight,
Nice to hear about your brother-in-law, Friday Harbor and Griffin Bay but how much chain do you have?

 

[Bacchus]

I found the following an interesting read - seems to dispell some of the myths, theories, and what some consider "common sense" about chain, rope, rodes, etc...

I'm having difficulty inseritng a link so having to work around it.

Catenary & Scope In Anchor Rode

https://www.petersmith.net.nz/boat-anchors/catenary.php

 

[ranger58sb]

I am still committed to doing some experimenting but the more I think about it the more complicated it gets because I want to reduce the impact of many of the variables.

But basically the whole process is dynamic, with all variables possibly changing all the time. Holding ground is never exactly the same, catenary is never exactly the same and it changes throughout the anchoring period anyway, user technique is all over the map...

Example: if the boat moves forward (toward the anchor) by 3 feet, catenary changes, pull on the anchor (if any, at that point) may change direction and force, etc.

I don't know that it's really possible to reduce the impact of the manay variables. Maybe manage some of the impact...?

-Chris

 

[Nomad Willy]

I found the following an interesting read - seems to dispell some of the myths, theories, and what some consider "common sense" about chain, rope, rodes, etc...

I'm having difficulty inseritng a link so having to work around it.

Catenary & Scope In Anchor Rode

https://www.petersmith.net.nz/boat-anchors/catenary.php

Bacchus,
That’s a Rocna add. By Peter Smith no less..
I don’t read Smith but I’m open to anything 2nd hand.
What are the myths and theories dispelled?
If it’s just selling anchors nix on it.
But if it’s well founded or more importantly interesting I’ll lock right onto it.
But he usually sells anchors by selling himself.

 

[Bacchus]

Bacchus,
That’s a Rocna add. By Peter Smith no less..
I don’t read Smith but I’m open to anything 2nd hand.
What are the myths and theories dispelled?
If it’s just selling anchors nix on it.
But if it’s well founded or more important yet interesting I’ll lock right onto it.
But he usually sells anchors by selling himself.

I just see so many post that...
All chain
Heavier is better
Etc... etc
Are you saying this is all BS marketing?
If so fair enough.
I am not a big / learned anchoring type but always open to learn.
This seemed to say the all chain loses advantages in less than mild conditions and shock absorption is important.
I'm a novice learning afa anchoring so trying to learn,
I just see a lot if conjecture without any data so I'm drawn to data.?

 

[Nomad Willy]

Good point Don.
If you haven’t got the shock absorption of nylon chain all the way up to the anchor roller provides. Just because of it’s weight and catenary. But while it’s not providing it’s a lot of weight and expense to bear.
But he’s not a truly honest salesman. When questioned at a big anchor test about his Rocna’s lackluster short scope performance he admits nothing and submits what he tells his customers, that is to set at 5-1 and shorten up. Like then your anchor will perform w the rest. It won’t. But it’s good advice as a deep set anchor has better holding power.
BS? Maybe and maybe not. Not honest though.

 

[Bacchus]

Good point Don.
If you haven’t got the shock absorption of nylon chain all the way up to the anchor roller provides. Just because of it’s weight and catenary. But while it’s not providing it’s a lot of weight and expense to bear.
But he’s not a truly honest salesman. When questioned at a big anchor test about his Rocna’s lackluster short scope performance he admits nothing and submits what he tells his customers, that is to set at 5-1 and shorten up. Like then your anchor will perform w the rest. It won’t. But it’s good advice as a deep set anchor has better holding power.
BS? Maybe and maybe not. Not honest though.

Fair enough .. I'm certainly no expert and learning from you guys that anchor in way deeper waters than I'd ever consider.
I fo find it interesting about the various theories about chain vs nylon... heavy vs lighter vet chasing etc
I'm an engineer so drawn to data vs conjecture.
Open minded and trying to learn.
But realize conditions vary a lot and have to have some impact.