Big anchors

[thinwater]

But they will drag equally because the constraint is the hold of the substrate NOT the potential of the anchor. That is the point I am making. For any given load the holding power will be the same.

I have no idea what you are saying. I don't think anyone here does.

The holding potential of the anchor in the substrate at hand is the ultimate holding capacity of the anchor on that day. The holding capacity in cement would surely be terrific, but equally irrelevant. If the common substrate in the cruising area is soft mud, then that substrate is the baseline, not good sand.

Holding capacity can only be discussed meaningfully as a family of curves, where substrate, anchor mass, design, rode angle, and yawing are all factors. I think people are trying to say that a large anchor with more potential holding capacity than you need can be less stable, but the challenge is defining how much holding capacity is available with the substrate at hand. We know it can be as much as 10x less than good sand, which makes the whole idea of having just one anchor very challenging. And yet for practical reasons we want just one anchor. It's kind of like (exaggerated) trying to share wings between a plane and a submarine, like they do in the movies. So the makers try to design an anchor that is flexible, and we try to pick a compromise size.

An obvious way to deal with soft bottoms is to adjust the ground tackle. More scope. A snubber. Reduce yawing by one of several means. Reduce windage by removing deck cargo (dinghies on the bow) and lowering reachers. Set the anchor in stages, over time. Basically, do everything you can to reduce the peak load on the anchor and to help it sit still. Such practices can increase security by 2x, based on testing. With good sand, these measures won't often be needed.

Note on Yawing. Photos don't tell us anything unless they are taken on the verge of dragging. Until then, of course the anchor is stable. Obviously. You can't take a photo of someone falling until they start falling.

It's an interesting topic, but not one wherea single answer will emerge.

 

[sailoppopotamus]

Without wanting to take sides on this debate, a number of posters here are arguing that a smaller anchor is likely to set deeper when power set, and thus be less susceptible to tripping/dragging in case of a wind shift. While the reasoning behind this is plausible, is there any experimental evidence to back this up? I'd be very interested to see actual tests that show that there are scenarios where one would be better off along with a smaller anchor rather than a larger one.

 

[Poignard]

...]
Interestingly, the anchor originally specified for my Sadler 34 was a 25 lb CQR copy. This would be considered light in the extreme today but for ten years or so it was considered adequate. I now carry a 15 kg Rocna, previously a 16 kg Delta, both of which outperform the 25blb CQR by a considerable margin.

I don't know if you have seen this (it's from a Lewmar catalogue) but it confirms what you say that a 25lb CQR is too light for a 35' LOA yacht. It also has to be borne in mind that the chart applies to genuine CQRs.

 

[[167227]]

Thanks for the video. It is always helpful to see how anchors perform in the real world.

Just some more real world use. Good sand, 2000rpm set, photo taken after 90 degree windshift. It was a little deeper before shift, and haven't had any wind since. There's meant to be a hard blow tomorrow so it will be interesting to see how it looks after that.

 

[noelex]

Just some more real world use. Good sand, 2000rpm set, photo taken after 90 degree windshift. It was a little deeper before shift, and haven't had any wind since. There's meant to be a hard blow tomorrow so it will be interesting to see how it looks after that.

The Spade looks much happier in sand than in the seagrass of your previous anchorage . A slight list following a change in wind direction is quite common.

The anchor looks secure. It will bury more from this position if the wind pipes up unless there is rock under the sand.

 

[srm]

The anchor looks secure. It will bury more from this position if the wind pipes up unless there is rock under the sand.

have both measured and experienced rock or cobbles under a nice looking sediment.

I regard anchoring as being very much an act of faith. My practice is a second bower weight anchor if winds of F7-8 plus are possible. Even better, a line to a secure rock, bollard, or the base of a tree to windward - a technique learnt cruising in Norway, but unfortunately not applicable in many cruising grounds.

 

[[167227]]

I doubt that the weight/displacement makes any difference other than maybe the effect of momentum when yawing. A floating boat has no effective weight. When Prof John Knox was developing his rode loading expression he found that cross sectional area was the critical value but since this pretty much runs in conjunction with length he used that as being easier to measure.

Weight would definitely be a consideration in my experience. We often get catabatic winds that take a nice 10 knots breeze to over 40 knots in a flash, and the boat gets some nice momentum, then comes up hard on the long snubber we have.

 

[[167227]]

I regard anchoring as being very much an act of faith.

LoL, that actually says is perfectly... especially in Ireland where im from, where you can't see the bottom, ever... and its too cold to dive on the anchor. Here in the caribbean, its luxury to be able to view every single set if i want.. except in Antigua... the water was awful there

 

[noelex]

I regard anchoring as being very much an act of faith. My practice is a second bower weight anchor if winds of F7-8 plus are possible.

A second anchor can be sensible for a variety of reasons, but if regularly needed to reinforce the holding power in only F7-8 then a larger primary anchor is perhaps more sensible and much easier than deploying multiple anchors.

The larger anchor will cover those unexpected situations when unforecast strong winds arise in the early hours of the morning.

 

[Tranona]

I have no idea what you are saying. I don't think anyone here does.

Sorry but I thought the question was simple - perhaps too simple because of the fixation with ultimate holding power and size. The tables and graph offered earlier simply show what is obvious - bigger anchors of the same design have higher ultimate holding power and the relationship between size and ultimate holding power is broadly linear. Second that some anchors of the same size have higher holding power than others. Nothing new, but not relevant to my question.

What I am asking for is a demonstration that for a given level of pull in the same substrate the hold of a larger/heavier anchor of the same design is greater. A simple graph with pull on the X axis and hold on the Y axis plotted for say a 15kg and a 20kg anchor of the same design will do.

My argument, based on tests and observations frequently aired here is that the lines will be essentially the same. So if a smaller anchor drags so will the larger if the pull is the same. The suggestion is that if the wind the wind and therefore the pull on the anchors increases the larger one will set or increase hold when the smaller one will not.

I simply do not believe this and have yet to see any evidence to convince me otherwise.

 

[Neeves]

A second anchor can be sensible for a variety of reasons, but if regularly needed to reinforce the holding power in only F7-8 then a larger primary anchor is perhaps more sensible and much easier than deploying multiple anchors.

The larger anchor will cover those unexpected situations when unforecast strong winds arise in the early hours of the morning.

As usual no actual evidence that a bigger anchor is better. Just a repetitious statement.

Thinwater's work on yawing suggests that a well set anchor better resists yawing. It is easier to well set, deeply set, a small anchor. A larger anchor will have a larger portion of the shank exposed. Any yawing will have larger impact, because of the lever arm effect, on the larger anchor. A buried shank also acts as a verticals fluke offering resistance to yawing.

Setting of 2 anchors in a fork has nothing, or not much, to do with increasing the hold of the ground tackle. Setting anchors in a 'V' reduces the impact of yawing (end of story). A yacht that is not yawing will better support the anchor(s). In reality if you set anchors in a 'V' first one anchor takes all the tension, then the other. Both take the tension, successively, in their set direction (thus no yawing effect on the anchor).

The holding capacity of an anchor is based on a simple increase in tension in one direction. The tension at which the anchor moves and continues to move is the holding capacity of that size of anchor in that substrate. If, in real life, the anchor is constantly being tensioned in different directions (waves, gusts of wind) then the shear strength of the substrate in which the anchor is buried will be reduced. A reduction in shear strength will reduce the hold of the anchor below that when tested. An anchor that does not move, due to yawing or chop, will have a higher hold than one that does move. Using a snubber will support your anchor and make it more stable - it will reduce the impact of snatch loads.

If you have one large poorly set anchor it will successively be loaded first in one direction and then the other - thus the shank will be constantly tensioned in a different direction - read Thinwater's work on yawing. If you have evidence that Thinwater's work is rubbish - say so, with evidence. To make it easier for you - here is one of Thinwater's reports

Yawing and Anchor Holding - Practical Sailor

There are other ways to reduce yawing - again Thinwater has summarised them, above, and if use the search function on Practical Sailor you can read chapter and verse.

Assuming the anchor you choose is not ridiculously small then if you set the anchor with engine power then you might set to 15% of its potential hold, 30hp engine 100kg per 10 hp. The hold of a modern 15kg anchor, suitable for a yacht with a 30hp engine, has a hold in clean sand of about 2,000kg. Increasing the tension in the rode in the set direction will simply allow the anchor to dive more deeply. If you have evidence that this is incorrect - say so, with data.

If you know the seabed is suspect - you might need to deploy a different anchor to your primary, the classic case is soupy mud. Your primary anchor in soupy mud will be pretty useless and even a bigger primary of the same design will be pretty useless - change the anchor. For more detail read the most recent Fortress tests in the Cheasapeake.

If you have evidence, lets call it data, that a bigger anchor is better than a smaller one - post it now - repetition does not make anything correct. Simply saying that a bigger anchor must be better suggests you don't know - and if you don't know (and are wrong) then you are perpetuating an error.

Jonathan

 

[Tranona]

I don't know if you have seen this (it's from a Lewmar catalogue) but it confirms what you say that a 25lb CQR is too light for a 35' LOA yacht. It also has to be borne in mind that the chart applies to genuine CQRs.


View attachment 159313

It is indeed because the CQR is a poor anchor. If you look at the similar chart for the latest Epsilon you will see that size boat fits comfortably within the 10kg (22lbs) recommendation

lewmar.com/file/9520

Not surprising as it develops well over twice the holding power of a 25lb CQR. The Delta
is somewhere between the two putting a 34' boat at the top end of 10kg recommendation

This all neatly captures developments in anchors - higher holding power for less size/weight. It is not just hype but real and measurable.

 

[noelex]

As usual no actual evidence that a bigger anchor is better. Just a repetitious statement.

The evidence is in post #29. See the table below. UHC is the ultimate holding capacity in this particular substrate.

It clearly shows a larger anchor of the same design and construction material has a higher ultimate holding capacity in the same substrate than an otherwise identical, but smaller anchor. The difference is substantial.

If you want to claim the opposite that a smaller anchor has a higher ultimate holding capacity then you need to provide evidence of this.

 

[Neeves]

The evidence is in post #29. See the table below. UHC is the ultimate holding capacity in this particular substrate.

It clearly shows a larger anchor of the same design and construction material has a higher ultimate holding capacity in the same substrate than an otherwise identical, but smaller anchor. The difference is substantial.

If you want to claim the opposite that a smaller anchor has a higher ultimate holding capacity then you need to provide evidence of this.

View attachment 159328

I think you misunderstand, completely.

No-one, in any of the posts is denying that a bigger anchor, of the same or even similar design does not have a higher hold than a smaller anchor. It would be really illogical to argue such

What is being stated is that there is no need for the bigger anchor - as even an anchor of the recommended size has a holding capacity greater than the hold you will ever need.

So taking, for example, a 15 kg SHHP anchor (Spade, Rocna, Supreme, Ultra, Excel, Epsilon) they all will hold in good clean sand a tension of 2,000kg. A 30kg anchor from the same group might hold 3,000kg of hold (note it might be twice the weight but it will not (in common with all anchors) have double the hold. However the yacht for which a 15kg SHHP anchor is recommended will never be in a situation where the tension in the rode is anywhere near 2,000kg - so why buy a bigger anchor? I can assure you that long before the tension reaches 2,000kg - say a tension of 1,000kg - your wife will be on the phone to the divorce lawyers - and you will be scared witless. I've experienced a 650kg tension, during testing, and I wimped out.

It might be said, I'm sure it will, that in a difficult seabed the holds will be less - but even a hold of only 30% of 2,000kg is going to scare the pans of you (and your wife). If the hold is that bad - why did you choose that anchorage.....?? or why did you not use an anchor better suited to that questionable seabed (and where are these questionable seabeds). The final question here is - if a 15kg anchor is inadequate why will a 25kg anchor be any better - to be better it has to dive more deeply than the 15kg model - what enables an anchor of the same design the ability to dive more deeply......?? , see post below with the Fortress image.

I'm not actually sure that the bow roller of a yacht for which a 15kg SHHP anchor is recommended has the strength to withstand such a tension. It also merits comment that the chain will probably deform at such tensions, WLL of 8mm G30 chain is 750kg, The shackle would also possibly deform (unless you invested in a decent Crosby G80 shackle). Basically at the point when the anchor might drag - your chain and shackle will already have failed.

You can mitigate the situation if you have an endless supply of chain, or better a snubber and certainly a snubber than you can 'extend' or parallel when the chips are down.

Undoubtedly - when the tension in your rode is nearing the hold limit of your 15kg anchor (2,000kg) it would be better to have had a bigger anchor - but to be safe you should also have ungraded all of your ground tackle to match the higher performance of the bigger anchor - or you are further wasting your money. I doubt that the individuals who have oversized their anchors have upgraded to rest of their ground tackle.

A good example of the success in using a 'small' anchor is, indirectly ...... yourself.

Correct any errors but I think for your yacht Rocna recommend a 33kg anchor. You use a 50kg anchor. The builder of your yacht specifically commented that you required the bow of your yacht to be 're-engineered' to meet the demands of such a large anchor. This implies to me that normally most owners of a yacht like yours uses a smaller anchor. I am sure if the smaller anchor was inadequate the builder would have upgraded the ground tackle - long before your yacht was launched.

You have found your anchor to be adequate, even though it sets shallow (and Thinwater notes that a deep set anchor is more stable and a shallow set anchor less stable. I wonder what shallow setting anchor Thinwater might have used.....??So even though your anchor is, on many counts, inadequate it is adequate - and arguably too big (as you have never mentioned it dragging).

Independent tests on smaller anchors of the same design as yours have half the hold of a similarly weighted SHHP anchor. Thus your anchor has at best the hold of a 33kg Rocna. Your anchor has the hold of a 50kg Delta, and I know which anchor I would choose between a 33kg Rocna or your 50kg anchor. Your anchor has not dragged - so increasing size beyond the recommendation of Rocna is.... unnecessary.

Jonathan

 

[Neeves]

This is a picture of a FX23 and a FX37. The 37 is the bigger anchor . I have chosen a Fortress for this comparison as the design is simple, its 2 dimensional, whereas many other anchors are '3D'.

The black line on the FX37 indicates a comparison of the fluke area of the FX23 superimposed on the FX 37. If you tension the FX23 to bury to the stock the FX 37 will bury to the black line (slightly less, the fluke is made from thicker plate). The 37 will be easier to retrieve as the shank offers more leverage. In difficult seabeds the 23 might dive more easily - it has a smaller width, from either side of the fluke, of section.

As Geem mentioned in his opening post it is quite difficult, even with the help of wind, to bury a big Fortress.

Can someone explain to me why or how I will be able to exploit the full hold performance of the 37. The FX23 was the anchor recommended for our cat, 38', equivalent in windage to a Bav 45.

 

[vyv_cox]

This is a picture of a FX23 and a FX37. The 37 is the bigger anchor . I have chosen a Fortress for this comparison as the design is simple, its 2 dimensional, whereas many other anchors are '3D'.

The black line on the FX37 indicates a comparison of the fluke area of the FX23 superimposed on the FX 37. If you tension the FX23 to bury to the stock the FX 37 will bury to the black line (slightly less, the fluke is made from thicker plate). The 37 will be easier to retrieve as the shank offers more leverage. In difficult seabeds the 23 might dive more easily - it has a smaller width, from either side of the fluke, of section.

As Geem mentioned in his opening post it is quite difficult, even with the help of wind, to bury a big Fortress.

Can someone explain to me why or how I will be able to exploit the full hold performance of the 37. The FX23 was the anchor recommended for our cat, 38', equivalent in windage to a Bav 45.

View attachment 159331

Not exactly an answer to your question but on the infamous occasion that I anchored using our FX 16 at a scope of 3:1 (in error) in a full gale I dived on it the following day. In the typical Greek seabed of sand, a little mud and light weed it was nowhere near fully buried. I recovered it with some difficulty, despite not being buried it took some strength to lift it.

 

[Poignard]

It is indeed because the CQR is a poor anchor. If you look at the similar chart for the latest Epsilon you will see that size boat fits comfortably within the 10kg (22lbs) recommendation

lewmar.com/file/9520

Not surprising as it develops well over twice the holding power of a 25lb CQR. The Delta
is somewhere between the two putting a 34' boat at the top end of 10kg recommendation

This all neatly captures developments in anchors - higher holding power for less size/weight. It is not just hype but real and measurable.

Yes, I've heard tell that CQRs are not very good.

Mine always been OK, and I've never felt the need to try a different type but if I ever do, I'll shop around a bit and see what's on offer.

 

[Tranona]

The evidence is in post #29. See the table below. UHC is the ultimate holding capacity in this particular substrate.

It clearly shows a larger anchor of the same design and construction material has a higher ultimate holding capacity in the same substrate than an otherwise identical, but smaller anchor. The difference is substantial.

If you want to claim the opposite that a smaller anchor has a higher ultimate holding capacity then you need to provide evidence of this.

View attachment 159328

You still miss the point. I am not asking about ultimate holding power - how many more times do i have to say it - that is obvious. I am asking for evidence that FOR THE SAME PULL a larger anchor generates greater holding power. That table simply shows a bigger anchor has higher POTENTIAL holding power.

I really cannot see why you have so much difficulty with this question - because you are claiming that it does. If that were the case there would only be one size of anchor on the market when in fact anchors are sized according to the sort of load boats of the recommended size can apply.

 

[Tranona]

Yes, I've heard tell that CQRs are not very good.

Mine always been OK, and I've never felt the need to try a different type but if I ever do, I'll shop around a bit and see what's on offer.

Likewise, I used a 25lb CQR on my Eventide (similar size to your boat) for 30 years with only the odd incident of not setting well. However that worked because the anchorages I used around the channel mostly have good holding in mud or sand. As has been pointed out "normal" anchoring really makes very little demands on the holding capacity of an anchor, whatever the type. The table in post#53 shows very clearly that the CQR is poor, and if you look at just about all the published tests you will see exactly the same pattern. This is also reflected in the Lewmar charts which recommend smaller size anhcors for the better Delta and Epsilon. On the other hand there are many examples of boats riding out extreme weather using CQRs because they have managed to get it well dug in and even though its ultimate holding power is poor compared with others it is still enough to hold the boat securely.

It is only when I started boating in the Med that I realised how useless the CQR was, because of the nature of the seabed and the sometimes extreme (relatively) winds that blow up for short periods in many anchorages and harbours. The Delta replacement was better but still not as reliable as I would have liked.

I am of the view that discussion on anchors is too fixated on ultimate holding power rather than how it performs in "normal" anchoring situations which demand quick and reliable setting, high holding power at low loads, resistance to breakout following changes in angle of load and quick resetting. NG anchors in general are much better in these situations plus have the bonus of higher holding power (if the substrate will take it!) in extreme conditions.

 

[noelex]

No-one, in any of the posts is denying that a bigger anchor, of the same or even similar design does not have a higher hold than a smaller anchor. It would be really illogical to argue such

Thank goodness.

What is being stated is that there is no need for the bigger anchor - as even an anchor of the recommended size has a holding capacity greater than the hold you will ever need.

The ”small is always adequate” argument because you have ”all the holding capacity you need" would not go down well with the boats that dragged (including the boat directly in front of us) during the recent Tropical Storm Bret, which was the catalyst that started this thread.