Minimum anchors size, what’s the point?

[Simi 60]

Originally Posted by hpeer

I’ll suggest a new rule of thumb for figuring (next gen) anchor size:

3kg/ton

.

So for our 65 tonne (71 ton) and plenty of windage you would suggest 213kg?

That's 145kg more than the 68kg supreme we have now.
2 years+ full time live aboard at anchor, never dragged, even in 80+ knots.

[Mr B]

Originally Posted by thinwater

Two simple questions:

• Do you have a 100-pound anchor?
• Why not 200 pounds?

You certainly can tell there is a person standing on the bow of a Gemini. More pitching and the bow is down an inch of more. I would think you would have noticed. You can tell if the person moves to the transom (it drags more).



Not sarcastic. I'm asking for a basis for picking a size. I'm not even saying 100 pounds is wrong. I'm suggesting that I'm pretty sure 25 pounds is too small for a Gemini on poor bottoms, but I'm not sure what is big enough. The only tale of a Gemini ending up on the beach that I know of (Trouser Rollers) resulted from waves, no snubber and a snapped chain.

I now have a 75 Lb new Gen anchor, Untried as yet, But I will test it at the mouth of Westernport Bay for a few tide changes, The tide there runs very strongly,
If it holds there, It will hold any where,
It certainly stops my car dragging it across my yard, With 50 feet of chain on it,

Some one else mentioned the 100 lb anchor above, Most boats would not notice one hundred pounds on the bows,

My Gemini certainly doesnt, I weigh 140 Lbs and my boat does not sink down in the bows when I walk out there,
I would certainly have noticed my transom rising when I stepped off the boat into the dinghy, It dosent,
On a swing mooring for six weeks, its the only way I could get on and off my boat,
Even with me and the outboard motor in my arms, It didnt sink getting out of the dinghy,
On any other smaller motor boat it would have been up and down like a Yo Yo, More than likely needing two people to transfer the motor across, The bottom transom step is very stable,

25 Lb Danforth is not big enough for my boat, It drags, It also gets rocks caught in the cleavis pin and just slides along the bottom, It wont reset,
It also got bent 30 degrees when I got chucked up on the beach as well, Very violent storm coming up the inlet I was hiding in, Port Stephens got levelled that night,
The 25 Lb Claw that came with my boat, Was just totally useless, I had both out that night,
We get very bad weather here at times, Thats what my anchor is for,
This is todays weather here,

Whats a good size of anchor, That will hold in all bad weather, I dont know,But my new one will certainly go a long way to stop it dragging in all conditions that I may encounter, Fingers crossed, I am over dragging Anchors, I want to sleep at night,
I weigh 4.5 tons,
I also have to drag it up by hand, I dont have a windlass, The 75 Lb is a bit of a struggle these days, I will need a rail across the front to lean against, That will make it easy to lift it up,

This is only my opinion for my boat, And comes from my experience with it,
And fifty years of living and boating on Port Phillip Bay, Which is next door to Westernport bay, 20 kays separate them, Both can be very dangerous waters, Both empty out onto Bass Straight,

[jmh2002]

I realise it goes against all thoughts of weight management, but for serious cruising it makes total sense to go significantly up in size and weight in terms of both the anchor and the chain.

Save weight somewhere else or if you are really concerned have the chain come back and go down into a locker around the mast. Many cats are like that already of course purely from a design point of view.

The upside of the piece of mind is great, but the everyday practical benefits are useful too.

A much heavier anchor and chain will provide better holding in a poor bottom, which is often common in many different cruising locations.

It will also enable the use of less scope, which reduces swinging (especially on a multihull or other high windage vessel) which again provides better holding, reduces stress on the boat and gear, is helpful in a crowded anchorage, as well as also just being more comfortable for life onboard.

Undersized, or even just 'at spec' anchoring gear seems a common mistake.

Here is a interesting recent article from the well known Steve Dashew (Offshore Cruising Encyclopedia, etc) with both technical and real world data:
https://www.setsail.com/anchoring-sy...ch/#more-46615

[noelex 77]

Originally Posted by jmh2002

A much heavier anchor and chain will provide better holding in a poor bottom, which is often common in many different cruising locations.

It will also enable the use of less scope, which reduces swinging (especially on a multihull or other high windage vessel) which again provides better holding, reduces stress on the boat and gear, is helpful in a crowded anchorage, as well as also just being more comfortable for life onboard.

Great post

Barely adequate anchoring gear can be made to work, but there will be anchorages where you cannot visit, or perhaps can visit but not stay overnight because of poor holding, poor protection, limited scope or other factors. A larger anchor is not a panacea for anchoring anywhere, but it does extend the possibilities considerably.

There are limits, and I would not recommend anchoring gear that cannot be handled relatively easily by the crew or the boat, but if you stay within these boundaries there are functional advantages for a cruising boat in going over the minimum level.

[Jim Cate]

Originally Posted by noelex 77

Great post

Barely adequate anchoring gear can be made to work, but there will be anchorages where you cannot visit, or perhaps can visit but not stay overnight because of poor holding, poor protection, limited scope or other factors. A larger anchor is not a panacea for anchoring anywhere, but it does extend the possibilities considerably.

There are limits, and I would not recommend anchoring gear that cannot be handled relatively easily by the crew or the boat, but if you stay within these boundaries there are functional advantages for a cruising boat in going over the minimum level.

Agreed... as I think we have both stated in past discussions. Gear that is sufficiently powerful that it works in far less than ideal situations is a great boon to the cruiser who leaves t he beaten path... and actually to any one who often anchors at all!

Jim

[Simi 60]

Originally Posted by jmh2002

I realise it goes against all thoughts of weight management, but for serious cruising it makes total sense to go significantly up in size and weight in terms of both the anchor and the chain.

Save weight somewhere else or if you are really concerned have the chain come back and go down into a locker around the mast. Many cats are like that already of course purely from a design point of view.

The upside of the piece of mind is great, but the everyday practical benefits are useful too.

A much heavier anchor and chain will provide better holding in a poor bottom, which is often common in many different cruising locations.

It will also enable the use of less scope, which reduces swinging (especially on a multihull or other high windage vessel) which again provides better holding, reduces stress on the boat and gear, is helpful in a crowded anchorage, as well as also just being more comfortable for life onboard.

Undersized, or even just 'at spec' anchoring gear seems a common mistake.

Here is a interesting recent article from the well known Steve Dashew (Offshore Cruising Encyclopedia, etc) with both technical and real world data:
https://www.setsail.com/anchoring-sy...ch/#more-46615

And that article shows what i would consider light chain (10 to 13mm on 80ft), short scoped and giant anchor.
They are putting dependence on anchor, not chain weight.

[hpeer]

Originally Posted by Simi 60

So for our 65 tonne (71 ton) and plenty of windage you would suggest 213kg?

That's 145kg more than the 68kg supreme we have now.
2 years+ full time live aboard at anchor, never dragged, even in 80+ knots.

I said it was non-linear, with small boats needing more. Thus bigger boats need less. It’s a rule of thumb for most folks, whereas you have a far, far, far larger boat than most. Proportionally you will need much, much, much less.

[2big2small]

Sorry to say so but you guys have it all wrong.

Whomever talks about anchors in terms of weight (pretty much all of you so far) has been sidetracked by antique traditions that are incomprehensibly still propagated by guilty manufactures. If it were about weight, then anchors would be ball shaped because a sphere would present the least amount of surface to corrosion. But we’d all intuitively agree that for such an anchor there wouldn’t be much difference between a 50 lb or 80 lb ball in terms of holding power, a difference of 30 lb in this example.

So why on earth do you believe an extra 30 lb on a real anchor, be it delta or spade or whatever, would make any difference? The only things that matter in terms of holding power are the surface area and shape of the flukes. People should let this sink in once and for all. So yes, the heavier anchor of the same model will have larger flukes, but the extra weight is hardly helping and is just a byproduct of making the anchor larger.

New generation anchors have an edge in fluke shape, not in area; that would be the danforth types. But thanks to their shapes they are very polyvalent and are holding in more bottom types than older designs.

Which brings us to the next part: the seabed. Imagine a seabed as strong as concrete and you would still be able to wedge in a super strong needle. Then that needle would have infinite holding power with zero fluke area. Now imagine the opposite, a bottom as soft as chocolate mouse (mmmmm). Before any anchor would hold in that it would need a fluke area so large that it would be too unwieldy to bring along on your boat.

Again, in the two examples above, the actual weight of the anchor does not matter at all. I think this can be clearly rationally understood as well as intuitively felt.

The only time where weight comes into play is when you set the anchor. That’s why it is notoriously more difficult to set lightweight aluminum anchors than their steel counterparts. But once set they perform just as well for the same fluke area (and please never compare by weight unless you’re adressing yourself to the racing crowd. And if you do so then compare your holding power by anchor cost for the cruising crowd as well, right? I’m talking to you, Fortress.)

So, so far we have fluke area and shape, and bottom type. Next big one, the only one you do have control over after you’ve reached a given anchorage with a given anchor, is scope. Pretty much any dragging is due to lack of scope, i.e. not letting out enough rode—assuming the anchor was set properly in the first place.

The rode (chain plus rope) has it’s importance too but marginally so compared to the previous three so I’m not expanding about it here.

So to get back to the initial, ever recurring question of whether you should pick an anchor one size up or not (notice I don’t say “heavier”) the answer is ultimately a resounding no. What you do have to pick is a normally sized anchor of the right type, which means a new generation anchor with smart fluke shape and larger area compared to the tradional anchors of the same weight.

No anchor is going to hold in a really bad bottom in a howling storm, no matter how much you oversize it. No anchor is going to hold if you use too little scope. No anchor is going to hold down slope in a blow either.

All anchors are going to hold in very light wind, even on the worst bottoms and even with only a 3 to 1 scope.

For anything in between, you have the new generation anchors.

Know on what type of bottom you’re dropping the hook, what the slope is, what the weather forecast says, and always use at least 5 to 1 scope with a new generation anchor and verify it is well set by revving up in reverse on it. Use more scope for a bad weather forecast and seek another anchorage with a better bottom if necessary.

In the majority of conditions, you ultimately don’t need a larger anchor. Just let out more scope on worse bottoms. This amply compensates for the extra fluke area of a larger anchor of the same model. Can you go wrong with buying bigger? Not really as long as you keep it reasonable. But my point is you don’t have to. I’ve slept soundly in over a 1000 different anchorages on 3 continents.

Edit:
In very crowded anchorages with limited swinging room you still don’t need a “heavier” anchor. I’m not expanding this time around but I’ll simply state the obvious that you shouldn’t go in if the weather forecast is bad enough that you can’t let out enough scope and stretch the rode fully without bumping into others.

[Dockhead]

Originally Posted by noelex 77

I think Mike’s recommendation is sensible for a cruising boat.

If an extra 30lb (15 kg) is a big deal on a particular vessel, the question is answered and the anchor is too large.


Is that a bad thing if it can be achieved within Mike’s definition of an “anchor that your boat and crew can reasonably manage”?

I agree with Mike and with Noelex.


In theory, of course, Thinwater is right, at least at the most superficial level. It is true that you can't say, as an engineering matter, that there is "no such thing as overkill".


However, in my opinion, what he says is too simplistic. There is evidence that holding power and reliability of holding goes up disproportionately to weight -- that how well an anchor functions doesn't scale exactly. This is supported by my own experience.



And the task of getting an anchor to hold varies a lot depending on what kind of bottom you have. Any anchor will hold in a simple, flat mud or sand bottom, and a new gen anchor may make you feel invincible in ares with such bottoms, but once you start dealing with something more difficult, then suddenly you need all the help you can get, and a bigger anchor is the single best "all the help" which there is. There is almost nothing, except possibly a sharp fluke, like sheer weight, to get an anchor to penetrate a difficult bottom, and I am talking about sheer weight in absolute terms, NOT indeed as percentage of boat weight.



So I think Mike is absolutely right -- unless you don't contemplate leaving the Chesapeake Bay or some other place without kelp or other conditions which can make it difficult to penetrate the bottom, the bigger the better up to the limit of where it starts to affect trim unacceptably or becomes difficult to handle.



I say even to such an extent, that a major reason not to have a small boat, is that you can't easily carry an anchor of adequate absolute size (not percentage of boat displacement) to deal with bottoms you might have to deal with in some places.



I'm carrying a 100 lb. Spade, myself, downsized from a 121 lb. Rocna which was just a bit too awkward to handle with my boat's particular bow roller and windlass. That's one size, vs. two sizes bigger than recommended. The Spade with its sharp fluke and lead ballast makes the most of this weight, but if you get far enough off the beaten track, you WILL find the limits of your anchoring system, and you WILL be wishing for a bigger anchor (and possibly more chain). I've just spent the summer in a place where many anchorages are 30 meters deep and still sloping away from the land, and with kelp to boot -- a hell of a challenge for the ground tackle, and will take the stuffing right out of anyone's "I can anchor in anything" attitude. I would have been happy to have a much bigger anchor and even more than the 100 meters of 1/2" chain which I have, and would have found it very difficult to manage with less than what I had.





My advice to the OP -- don't settle for the recommended size of anchor, if you can reasonably handle something bigger, unless you are sure that you won't be anchoring in demanding conditions. And pay attention to what Mike wrote (on this and other subjects!).

[Dockhead]

Originally Posted by 2big2small

Sorry to say so but you guys have it all wrong.

Whomever talks about anchors in terms of weight (pretty much all of you so far) has been sidetracked by antique traditions that are incomprehensibly still propagated by guilty manufactures. If it were about weight, then anchors would be ball shaped because a sphere would present the least amount of surface to corrosion. But we’d all intuitively agree that for such an anchor there wouldn’t be much difference between a 50 lb or 80 lb ball in terms of holding power, a difference of 30 lb in this example.

So why on earth do you believe an extra 30 lb on a real anchor, be it delta or spade or whatever, would make any difference? The only things that matter in terms of holding power are the surface area and shape of the flukes. People should let this sink in once and for all. So yes, the heavier anchor of the same model will have larger flukes, but the extra weight is hardly helping and is just a byproduct of making the anchor larger.

New generation anchors have an edge in fluke shape, not in area; that would be the danforth types. But thanks to their shapes they are very polyvalent and are holding in more bottom types than older designs.

Which brings us to the next part: the seabed. Imagine a seabed as strong as concrete and you would still be able to wedge in a super strong needle. Then that needle would have infinite holding power with zero fluke area. Now imagine the opposite, a bottom as soft as chocolate mouse (mmmmm). Before any anchor would hold in that it would need a fluke area so large that it would be too unwieldy to bring along on your boat.

Again, in the two examples above, the actual weight of the anchor does not matter at all. I think this can be clearly rationally understood as well as intuitively felt.

The only time where weight comes into play is when you set the anchor. That’s why it is notoriously more difficult to set lightweight aluminum anchors than their steel counterparts. But once set they perform just as well for the same fluke area (and please never compare by weight unless you’re adressing yourself to the racing crowd. And if you do so then compare your holding power by anchor cost for the cruising crowd as well, right? I’m talking to you, Fortress.)

So, so far we have fluke area and shape, and bottom type. Next big one, the only one you do have control over after you’ve reached a given anchorage with a given anchor, is scope. Pretty much any dragging is due to lack of scope, i.e. not letting out enough rode—assuming the anchor was set properly in the first place.

The rode (chain plus rope) has it’s importance too but marginally so compared to the previous three so I’m not expanding about it here.

So to get back to the initial, ever recurring question of whether you should pick an anchor one size up or not (notice I don’t say “heavier”) the answer is ultimately a resounding no. What you do have to pick is a normally sized anchor of the right type, which means a new generation anchor with smart fluke shape and larger area compared to the tradional anchors of the same weight.

No anchor is going to hold in a really bad bottom in a howling storm, no matter how much you oversize it. No anchor is going to hold if you use too little scope. No anchor is going to hold down slope in a blow either.

All anchors are going to hold in very light wind, even on the worst bottoms and even with only a 3 to 1 scope.

For anything in between, you have the new generation anchors.

Know on what type of bottom you’re dropping the hook, what the slope is, what the weather forecast says, and always use at least 5 to 1 scope with a new generation anchor and verify it is well set by revving up in reverse on it. Use more scope for a bad weather forecast and seek another anchorage with a better bottom if necessary.

In the majority of conditions, you ultimately don’t need a larger anchor. Just let out more scope on worse bottoms. This amply compensates for the extra fluke area of a larger anchor of the same model. Can you go wrong with buying bigger? Not really as long as you keep it reasonable. But my point is you don’t have to. I’ve slept soundly in over a 1000 different anchorages on 3 continents.

Edit:
In very crowded anchorages with limited swinging room you still don’t need a “heavier” anchor. I’m not expanding this time around but I’ll simply state the obvious that you shouldn’t go in if the weather forecast is bad enough that you can’t let out enough scope and stretch the rode fully without bumping into others.

This whole argument is based on a logical fallacy:


* Weight alone does not determine an anchor's holding power [true!]
* Ergo, the weight of an anchor doesn't matter [false!]




One doesn't follow from the other!

[2big2small]

Just would like to add that buying a larger anchor will NEVER compensate for not using enough scope. To any beginner: do not think one moment that you can get away with letting out less rode because you got a larger anchor. Uphold scope with holy reverence if you want to spend good nights on the hook. Or in other words, there are three things you need to know about anchoring before anything else: scope, scope, and scope.

[2big2small]

Originally Posted by Dockhead

This whole argument is based on a logical fallacy:

* Weight alone does not determine an anchor's holding power [true!]
* Ergo, the weight of an anchor doesn't matter [false!]

One doesn't follow from the other!

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.

[2big2small]

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

[2big2small]

Unrelated to the above example, just to put numbers on it:
If 10 knots of wind moves 10 lb then
You need 40 lb to resist 20 kn
160 lb for 40 kn
640 lb for 80 kn
And so forth.

[noelex 77]

Originally Posted by 2big2small

Just would like to add that buying a larger anchor will NEVER compensate for not using enough scope.

A larger anchor (except in very unusual substrates) will have a higher maximum holding ability that an otherwise identical smaller model. A longer scope will give an anchor greater maximum 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 smaller model that is deployed 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 large anchors. I would not recommend following his example, but there is no doubt both theory and practice confirm the relationship.