Minimum anchors size, what’s the point?

[sailorboy1]

what it all comes down to is ............................ size envy

[Dockhead]

Originally Posted by 2big2small

Not what I said! I said it hardly matters. Let’s go back to the example of the ball shaped anchor and to keep matters simple assume the rode is weightless at a zero angle and there’s not much friction with the bottom and what not and allow me to oversimplify even further than that, even where the physics aren’t totally accurate.

The situation that could be used as an example under those conditions is that your ball weighs 10 pounds and you need windage of 10 pounds on your boat (zero current) before your ball starts dragging. If you have a ball of 20 lb you might need 20 pounds of windage before you start dragging and so forth. Now windage is a square power of wind speed. Which means the weight of your ball would have to be 4 times as heavy each time the wind speed doubles. Which means weight hardly matters.

"Hardly matters" follows as little, as "doesn't matter"! There is no logic in this.


And neither does the example logically support your conclusion. It's not even a correct description of the mechanism. The holding power of a ball resting on something is not a direct function of weight -- it is a function of friction, so you're entirely missing that coefficient. But even that is not enough to describe what is going on with a ball resting on top of some surface -- there is also stiction.



And an anchor embedded in a seabed works on even different principles. Here the mass of the anchor is even less directly involved -- it's the fluke geometry and area in the first place. But these increase, with a larger anchor.



But the main function of weight, in an anchor, is not the direct effect on holding (the very light Fortress holds very well with much less weight), but the effect on SETTING, on penetrating the seabed so that the flukes can grab. A larger, heavier anchor penetrates better, all other things being equal.

Originally Posted by 2big2small

I know, it is super counter-intuitive that weight doesn’t matter much. Yet it is the case.

Except that this is not the case. Heavier anchors hold better than lighter anchors, all other things being equal. In fact, they hold DISPROPORTIONATELY better.



Anyone who's anchored with anchors of different sizes, knows this from experience!

[2big2small]

Originally Posted by noelex 77

A larger anchor (except in very unusual substrates) will have a higher holding ability that an otherwise identical smaller model. A longer scope will give an anchor greater holding ability.

If you put these two facts together it is logical that a larger anchor can have the same holding ability as an otherwise identical model at a longer scope.

This is also how it works in practice. Hence the comments from Dashew who reports routinely using incredibly small scopes with enormous anchors. I would not recommend following his example, but there is no doubt both theory and practice confirm the relationship.

Nope, it doesn’t work like that. What holds your anchor back is the weight of the substrate the flukes push against. Imagine a scope of 1 to 1, where the rode goes down vertically and is at 90 degrees with a flat sea bottom. The anchor is dug in. What keeps your anchor put is just the bit of sand or mud straight above it, just a few lb. Now imagine you let more scope out and your rode ends up at a 45 degree angle. You still have very little substrate between your anchor and the seabed to “weigh on it.” If you have infinite scope your rode lays flat on the bottom and you have infinite substrate to push against.

Scope is all about angles. The smaller the angle between the rode and the sea bottom, the more substrate the anchor pushes against to keep it put.

If you have a larger anchor you have larger flukes and therefore you push against more substrate. This is a square as well (area) therefore a small increase in fluke height and width creates a proportionall larger increase in holding power. However, there still has to be sand to push against at the angle of pull from the rode and as long as the angle between the rode and the bottom is too large that sand or mud simply isn’t there!

[2big2small]

Originally Posted by Dockhead

...
Here the mass of the anchor is even less directly involved -- it's the fluke geometry and area in the first place. ...

But the main function of weight, in an anchor, is not the direct effect on holding (the very light Fortress holds very well with much less weight), but the effect on SETTING, on penetrating the seabed so that the flukes can grab.

So you do wholeheartedly agree with my initial post after all. Read it again.

Originally Posted by Dockhead

Heavier anchors hold better than lighter anchors, all other things being equal. In fact, they hold DISPROPORTIONATELY better.

Yep, larger anchors hold disproportionately better (not heavier ones). Fluke area, like any area, is a square. Explained that in a subsequent post. Also explained that scope compensates very nicely for area. I’m not picking a fight with people who like larger anchors, just saying it’s not necessary for the vast majority of situations.

[jmh2002]

Wow, a whole lot of nonsense in these last posts. No sense to even bother replying to these individual comments.

I'm from a racing background originally, so I totally understand the whole 'just barely enough to pass the rules or meet the specs' and/or 'in theory it works, here are the numbers' and that kind of thinking, and I went there and did all that and yes it was appropriate for the situation at the time.

But this is cruisersforum.com and a different logic should be applied, especially when lives, family, children, homes, or just plain simple peace of mind is more important.

Even in the modern era that we have now, with much more helpful technology, in my mind the core ethos to safe cruising should still be prudence.

I replied in the same way in a different thread about advising someone to arrive late, and at last light, in an unfamiliar tropical anchorage, because it makes for any easier day sail.

Even though I have done it of course, both through mistakes and force majeure, there is no way that I would recommend it to others.

The same goes for anchors, chain, and anchoring. Can you get away with less? Of course you can. Will you end up getting caught out at some stage? If you are really cruising, yes almost surely, it is only a matter of time.

At that moment, being a keyboard warrior won't be of any use...

[2big2small]

I do pick a fight though with recreational boaters who claim a heavier anchor has more holding power.

[Dockhead]

Originally Posted by 2big2small

So you do wholeheartedly agree with my initial post after all. Read it again.

No, you missed the point. Anchors need to do two things -- they need to hold, but first they need to set.



Weight (ignoring size, although this is artificial because the two are not unrelated) is a key factor in setting, particularly in complicated bottoms.


As far as holding is concerned -- take two anchors of the same type -- one is 20% heavier than the other. The heavier one will have more than 20% more fluke area. So even this goes up out of proportion to weight, and then on top of that you have the fact that soil mechanics do not scale in a linear way.


All this is why it is actually not controversial, that there is a great benefit to using a larger and heavier anchor. A 20% increase in weight (say) gives you more than 20% increase in holding power, and more than 20% improvement in setting behavior.

Originally Posted by 2big2small

Yep, larger anchors hold disproportionately better (not heavier ones). Fluke area, like any area, is a square. Explained that in a subsequent post. Also explained that scope compensates very nicely for area. I’m not picking a fight with people who like larger anchors, just saying it’s not necessary for the vast majority of situations.

Ok, so how are you going to get larger, without heavier? You're advocating smaller anchors -- saying it "hardly matters" -- but now you admit that if you reduce the weight, you reduce the fluke area DISPROPORTIONATELY. Unless you just don't need the holding power at all, this is a very bad thing.


It is also not true that scope compensates "nicely" for area. What scope does is very complicated -- it depends on the weight of the chain, the depth, the wind force involved, and the geometry of the anchor. Scope can help a lot, but you cannot count on its making up for a large reduction of fluke area you get from even a small reduction in weight, and besides that, scope has nothing at all to do with whether you can get the anchor set in the first place, which is a much bigger challenge in most cases, than holding.




One thing I will agree with you about -- the majority of situations, for the majority of cruisers, don't demand ultimate setting and holding behavior of their ground tackle. It's true that in the majority of situations, any of us could anchor successfully on 25 pound CQR's. But the design task for the anchoring system is not indeed to deal with the average situation, but with the worst that we will encounter. Unless you are a weekend sailor never getting out of the Bay and never anchoring in bad weather, do not undersize your anchor! It might work for months or years at a time, but just at the moment when you really need the anchor to hold, it might not!


Mike's advice was the correct advice -- use the largest anchor which you can handle reasonably well. It will have holding power disproportionate to its weight and will set better. It can be used successfully with less scope if necessary. It matters!

[2big2small]

Originally Posted by jmh2002

The same goes for anchors, chain, and anchoring. Can you get away with less? Of course you can. Will you end up getting caught out at some stage? If you are really cruising, yes almost surely, it is only a matter of time.

The initial question is not about getting away with less, but about needing more than enough. I’m trying to point out that enough is enough. To be clear, I’m not recommending that people follow manufacturer recommendations especially since they’re still all based on weight and since there are huge differences in windage on different types of boats. And I do appologize for being too snotty but at the same time the perpetual misgivings about anchors and their weight are exasperating to me. I should have not jumped into the discussion in the first place and let it be.

[2big2small]

Originally Posted by Dockhead

No, you missed the point. Anchors need to do two things -- they need to hold, but first they need to set.



Weight (ignoring size, although this is artificial because the two are not unrelated) is a key factor in setting, particularly in complicated bottoms.


As far as holding is concerned -- take two anchors of the same type -- one is 20% heavier than the other. The heavier one will have more than 20% more fluke area. So even this goes up out of proportion to weight, and then on top of that you have the fact that soil mechanics do not scale in a linear way.


All this is why it is actually not controversial, that there is a great benefit to using a larger and heavier anchor. A 20% increase in weight (say) gives you more than 20% increase in holding power, and more than 20% improvement in setting behavior.






Ok, so how are you going to get larger, without heavier? You're advocating smaller anchors -- saying it "hardly matters" -- but now you admit that if you reduce the weight, you reduce the fluke area DISPROPORTIONATELY. Unless you just don't need the holding power at all, this is a very bad thing.


It is also not true that scope compensates "nicely" for area. What scope does is very complicated -- it depends on the weight of the chain, the depth, the wind force involved, and the geometry of the anchor. Scope can help a lot, but you cannot count on its making up for a large reduction of fluke area you get from even a small reduction in weight, and besides that, scope has nothing at all to do with whether you can get the anchor set in the first place, which is a much bigger challenge in most cases, than holding.




One thing I will agree with you about -- the majority of situations, for the majority of cruisers, don't demand ultimate setting and holding behavior of their ground tackle. It's true that in the majority of situations, any of us could anchor successfully on 25 pound CQR's. But the design task for the anchoring system is not indeed to deal with the average situation, but with the worst that we will encounter. Unless you are a weekend sailor never getting out of the Bay and never anchoring in bad weather, do not undersize your anchor! It might work for months or years at a time, but just at the moment when you really need the anchor to hold, it might not!


Mike's advice was the correct advice -- use the largest anchor which you can handle reasonably well. It will have holding power disproportionate to its weight and will set better. It can be used successfully with less scope if necessary. It matters!

Alright, I see what’s going on. We’re not catching each other’s drift exactly yet we are mostly saying the same thing.

I said weight helps with setting in my initial post. Just like you do. That’s out of the way.

I’m saying that weight, in itself, pure mass, is hardly helping in terms of holding power.

You’re saying that if you increase the weight you therefore have a larger anchor with larger flukes.

I’m saying larger flukes, and smarter shaped ones, are what increases holding power.

I’m saying there are hardly any benefits in oversizing an anchor and recommend against doing so. I never said anything about undersizing one.

You say there are enough worthwile benefits in oversizing that people should go ahead and do it.

Is that about right?

[Mike OReilly]

Originally Posted by thinwater

You are missing my point entirely. A spindly crew with no windlass might find 25 pounds too much. A sturdy crew with a windlass can make 100 pounds work with ease. I feel like "what the crew can manage" is no answer at all. Honest, I don't know what it means.

It is you who is missing the point, even while answering your own question. YES, my answer leads to one of your boats having a 25# anchor, and the other with a 100#. If that is the BEST they can do, then that is what they should do.

Now, if it were me, I’d be uncomfortable at the 25# level, and would then look to upgrade my anchor system in some way to allow for more. But regardless … you can’t do better than the best, so all your machinations are moot.

You are illustrating the problem with all these anchor testers and sizing charts … they treat anchoring as a theoretical engineering problem, not a real-world challenge.

Originally Posted by laika

A 45# on a 27' is 95% ridiculous. Not ashamed to admit. But for us..

-the cost difference between a 35# and 45# is not great
-the 45# is no more difficult for me to handle
-it fits just as well on the bow
...

THIS is exactly the right thinking (in my mind). If you and your boat can manage a larger anchor/rode, then why would you want something lesser? This doesn’t mean bigger is always better. Once it tips over to being too large to reasonably manage on your boat, then it is too big. Until then, it simply builds additional safety into the anchoring system.

[2big2small]

Originally Posted by Mike OReilly

THIS is exactly the right thinking (in my mind). If you and your boat can manage a larger anchor/rode, then why would you want something lesser? This doesn’t mean bigger is always better. Once it tips over to being too large to reasonably manage on your boat, then it is too big. Until then, it simply builds additional safety into the anchoring system.

I guess there’s bound to be a general difference in perspective based on whether you’re on a smaller or larger boat. On a smaller one it is easier to say to go bigger because a single fit person can still handle the biggest anchor easily. On a larger boat sticking with the “recommended” size might already be too much for a single person to pick up, let alone dangle over a bow roller to install.

However, since weight considerations are more important on a smaller boat and since there aren’t much benefits in oversizing as I have been trying to demonstrate, I would still try to not go beyond what’s necessary even on smaller boats.

I would advocate a danforth type anchor as a secondary one, instead of oversizing the primary. For bottoms where you do need lots of fluke area, which is mostly soft mud, it would perform exemplary (for stays without wind or tidal shifts if you want to play it totally safe with a danforth type.)

[Dockhead]

Originally Posted by 2big2small

Alright, I see what’s going on. We’re not catching each other’s drift exactly yet we are mostly saying the same thing.

I said weight helps with setting in my initial post. Just like you do. That’s out of the way.

I’m saying that weight, in itself, pure mass, is hardly helping in terms of holding power.

You’re saying that if you increase the weight you therefore have a larger anchor with larger flukes.

I’m saying larger flukes, and smarter shaped ones, are what increases holding power.

I’m saying there are hardly any benefits in oversizing an anchor and recommend against doing so. I never said anything about undersizing one.

You say there are enough worthwile benefits in oversizing that people should go ahead and do it.

Is that about right?

I sincerely appreciate the effort at understanding!


That's good, intellectually honest stuff in this post.


I actually now agree with most of what you say, but just one small logical quibble: We can agree that enough is enough, but what is enough? A really important point is that what is enough is essentially unknowable. THAT is the reason why most of us recommend oversizing anchors, within the limits of practicality. Because every 20% (say) you oversize the anchor gives you more than 20% of increased performance, both setting and holding -- something I think we now agree on. It's a good deal! Up until the point where it becomes difficult to handle the anchor. That's all.


If we knew exactly what "sufficient" holding power and setting performance was -- then you could size for that and there would be no need to go any further. But we don't. Setting suddenly gets vastly harder, once you have a rocky, kelpy or gravelly bottom. Holding, too. And if you have to anchor in a sloping bottom, this dramatically decreases holding power. Same thing with scope - you can't always put out more scope, and sometimes you are forced to use much less than you would like -- either lack of swing room, or great depth. I myself spend most of the summer anchored with less than 3:1 scope. So when conditions get bad, the need for more holding power goes up tremendously. That's when you will be very glad, if you didn't forgo oversizing that anchor, even a little bit.



Cheers.

[barnakiel]

Originally Posted by RichMac

There’s a popular idea that anchors should be minimum size, just big enough and no more.

(...)

And where exactly is this particular idea popular?

Where we sail, the idea goes more or less along the lines of "fit the biggest one you can handle".

Looking at VERY conservative Bruce tables, our anchor is two sizes up.

Now back to the MINIMUM size, I believe it is dictated by the fact that 99.99% of all anchoring is done in benign conditions where only some current, not much wave action and winds way below 40 knots are encountered. It makes 99.99% sense to have anchor sized for 99.99% use cases too.

Uh?

Cheers,
barnakiel

[jmh2002]

@2big2small

You are the one perpetuating said misgivings and in my opinion simply wrong or at the very least imprudent statements.

Originally Posted by 2big2small

I do pick a fight though with recreational boaters who claim a heavier anchor has more holding power.

If this is meant as picking a fight with me, then once again you are mistaken regarding your assumptions.

I did try to read a few of your other posts in various threads, and I'm sorry but I don't think that other cruisers should accept your comments about anchors, chain, and anchoring as the voice of wisdom.

I'm sorry, no, I do not agree, as neither do many others that a replying here.

Originally Posted by 2big2small

I should have not jumped into the discussion in the first place and let it be.

Probably the only comment that I can agree with.

[Suijin]

Originally Posted by 2big2small

I said weight helps with setting in my initial post. Just like you do. That’s out of the way.

I’m saying that weight, in itself, pure mass, is hardly helping in terms of holding power.

Given the fact that a poorly set anchor is responsible for the majority of dragging episodes, this makes weight a fairly important quality of the anchor.

As an aside, if your hypotheticals were true then moorings would be large danforths, not 500 lb. mushrooms.

But this is all rather silly. It goes without saying that all other things being equal heavier equals larger when selecting an anchor. The term “heavier” gets used instead of “larger” because weight has more of an impact on handling and now weight and dimensional size is rarely an issue.

NG anchors have multiple design elements that contribute to performance. Weight is one of them. Arguing strenuously against that is irrational.