Big anchors

[geem]

Last night we had tropical storm Brett go through. We were well to the North of it so only got the fringes of it. As a precaution, we set a second anchor in a V with our main anchor, a 30kg Spade. The second anchor, a Fortress FX55 was set on 3 metres of 10mm chain and 50 metres of 3/4" nylon, braid on braid. The wind was forcast to come from the NE for a while so the second anchor would load up in the NE wind direction. The boat is a 44ft ketch of about 18.5 tonnes laiden.
The FX55 is a large anchor, designed for boats up to 60ft. It came to me for free so that what we used. It is the first time I have used this aluminium anchor in anger. We normally use a smaller one of 10kg. The Fx55 is 14.5kg. Both are aluminium.
The maximum wind speed we saw was 39kts. Less than the forecast. Most of the wind was only high 20s. I'd set the FX55 by hand in about 4 ft of water. Soft sand, that should be ideal for the Fortress. We did lie to the Fortress for a few hours, with the main anchor doing very little. This morning we recovered the Fortress anchor.
To my surprise, it was no further set than when I buried it by hand. I easily lifted it off the bottom. I did expect, with the load of close to 40kts, to see the anchor well buried.
I know there has been lots of discussion on this forum about oversized anchors not setting but my own experience would confirm this. It wasn't a problem for us as the wind direction was NE to SE. It would be interesting in tidal waters when lying to an oversized anchor, to see if your own chain would trip the anchor as the boat did a 180 turn. Food for thought. I suspect the anchor would have buried if the load had increased but how much wind would it have taken.
Comparing how much fluke was buried in the sand with my smaller aluminium anchor, I would guess the partly buried FX55 flukes area that was buried was equivalent to the full fluke area on my smaller anchor. So I guess it was developing similar hold to the smaller anchor.

 

[RunAgroundHard]

An interesting observation, thanks for sharing.

 

[fredrussell]

Off we go again then…

 

[geem]

Off we go again then…

If you like

 

[Kelpie]

Is it established fact that an anchor can be too big?

When we bought our current boat, for the first couple of cruises we used a Rocna 15kg, and it never let us down, despite being undersized according to Rocna. We sat out some fairly stiff breezes in the mid 30kt range without any problems.

We then upgraded to a 25kg, which is one size above recommended. We rarely manage to truly bury it, even in good holding. And it has let us down a number of times where there has been poor holding combined with sudden wind shifts. Of course we've been living in the hook for most of the last two years so statistically it had to happen at some point.

I wonder how much benefit we are really gaining from the oversized anchor?
Is it possible that with a smaller anchor we would be able to power set it deeper and therefore better?

 

[Tranona]

You have summarised the situation well from your own experience. You simply cannot exploit the additional potential holding power of your 25kg Rocna. You only have to look at the load required to achieve the maximum holding power to realise that your boat would have difficulty in achieving the maximum holding of the 15kgs according to the tests. Geem shows that even in say 30 knots of wind his boat cannot dig the FX55 in any further than setting it by hand

The problem arises for 2 reasons. First "bigger" and "heavier" tend to be used interchangeably whereas it is only true when both the design and material are the same. So a 20 kg Delta has a higher holding power than a 15kg but a 10 kg Rocna has higher holding power than the 15kg Delta. The aluminium Fortress has similar holding power to a steel version twice its weight. The second reason is the nature of the popular test data which focuses on ultimate holding power rather than the holding power that might be achieved by the boats of a size for which the anchor is recommended. I don't think I have ever seen a structured test that compared anchors of different designs and sizes for the same boat.

If you look at the loads required to achieve maximum hold on anchors in the 15-25kg range you will find they way exceed the sorts of loads that have been either calculated or measured for the sizes and types of boat that would use anchors this size. Just to give an idea of scale. In the wind strength geem reports a typical 35' yacht would be applying around 300kgs of load. Enough to straighten a chain rode and bury a 15kg NG anchor. In the YM 2006 tests even in the worst holding the Rocna held at 600kgs, and in the best close to 2000kgs.. Your second sentence confirms this, and would suggest even in extreme conditions (50 knots+) in good holding you would still be fine.

Your second point about the behaviour of your 25kg Rocna pretty much confirms the tests that Neeves has carried out on oversize anchors - both the failure to set and resetting because so much of the anchor is not buried. You will also find that Pete Smith who designed the Rocna makes exactly the same points when he advises against oversizing.

Your last sentence is correct. With your boat and engine you should be able to apply 300kgs+ power setting - enough to straighten the rode if all chain and fully set the anchor. You won't do that with a 25kg which is for boats twice your displacement, probably 50% greater windage and twice the horsepower.

Putting my money where my mouth is, on my Golden Hind I have downsized from a 35lb CQR copy to a 10kg Epsilon. I shall never anchor in extreme conditions and maybe if I was ever to go ocean voyaging in the way that GHs did 40 odd years ago I might up to a 16kg version. However I am reminded that 40 boats of this design have crossed the pond and many gone all the way round - most with 35lb CQRs!

I am amazed that so few people are prepared to recognise the enormous improvements in anchors and handling gear so still cling to the old "heavier/bigger is better" at the same time anchor designers are striving for (and achieving) higher performance for less size/weight!

We are collectively a conservative bunch.

 

[Neeves]

Assuming that in the same conditions your small anchor would be completely buried, with just the stock still visible, then the whole fluke embedded, I would expect the larger anchor to bury, very roughly, the same area of fluke. So if your small anchor was fully buried I'd expect the larger anchor to bury that same area. Hold is roughly a function of area.

There will be differences - the larger anchor will be made from aluminium that is thicker - and this will resist burial (more than the smaller anchor, made from thinner plate) - but variations in seabed shear strength might mask (or enhance this).

We have a FX 16, FX23 and FX 55 and I marked the fluke of the FX 55 to indicate the area of the FX 16, simple straight line across the 'toe' of the FX 55. I then set the FX 16 to bury it, with the stock lying on the seabed, fluke completely buried and shank lying 'touching' the seabed. I then set the FX 55 alongside to the same tension in the same rode - the flukes buried roughly as expected. Hold is a function of area.

The larger anchor should be easier to trip as the larger anchor has a longer shank and thus offers you greater support of the lever arm effect.

In the conditions you describe I would use the bigger anchor simply because it would be easier to retrieve. You don't know how bad it might get and retrieving a deep set smaller Fortress by hand would be a devil of a job (and might be irretrievable). In the annals of Fortress history anchors lost simply because they cannot be retrieved is not uncommon.

An interesting observation, totally expected.

Hold as a function of area, or a function of weight in the case of a Fortress, should not be a difficult concept to grasp. With 'other' anchors it can be a bit more complex as steel is made to specific thicknesses and when the anchor designer scales up he might want to use, say 8mm plate and if it is unavailable he then has to decide if he will use, say, 6mm or 10mm....Bigger anchors also are deployed using bigger chain and shackles - all of which impede burial (scaled accurately to a greater or lesser effect).

Jonathan

Edit

As long as the smaller anchor still has potential capacity, so its hold could increase if there was more tension (say stronger wind) then the big and small anchor will have the same developed hold. If the wind continues to increase their individual holds will increase, until the small anchor reaches its maximum hold in that seabed. Even for a small Fortress that hold can be huge, more than the tension you are ever likely to impose on the anchor.

The reason the big anchor's hold is 'questionable' is that if the wind veers, or reverses then the larger (longer) lever arm of the shank will allow a sideways pull to cause the anchor to move, laterally - and the hold may then be compromised. This is exacerbated as only part of the fluke is embedded, the section not buried simply increases the lever arm effect. In the same way the lever arm allows an easier retrievals of a deep set anchor it also 'encourages' the anchor to move.(so ease of retrieval does have side effects).

Fortress are listing the ultimate hold of a FX 16 as 5,000lb in hard sand (much less in mud - where size does matter, as does using a Fortress) - I hope no-one reading this ever experiences even 25% of that tension in their rode.

J

 

[[167227]]

Last night we had tropical storm Brett go through. We were well to the North of it so only got the fringes of it. As a precaution, we set a second anchor in a V with our main anchor, a 30kg Spade. The second anchor, a Fortress FX55 was set on 3 metres of 10mm chain and 50 metres of 3/4" nylon, braid on braid. The wind was forcast to come from the NE for a while so the second anchor would load up in the NE wind direction. The boat is a 44ft ketch of about 18.5 tonnes laiden.
The FX55 is a large anchor, designed for boats up to 60ft. It came to me for free so that what we used. It is the first time I have used this aluminium anchor in anger. We normally use a smaller one of 10kg. The Fx55 is 14.5kg. Both are aluminium.
The maximum wind speed we saw was 39kts. Less than the forecast. Most of the wind was only high 20s. I'd set the FX55 by hand in about 4 ft of water. Soft sand, that should be ideal for the Fortress. We did lie to the Fortress for a few hours, with the main anchor doing very little. This morning we recovered the Fortress anchor.
To my surprise, it was no further set than when I buried it by hand. I easily lifted it off the bottom. I did expect, with the load of close to 40kts, to see the anchor well buried.
I know there has been lots of discussion on this forum about oversized anchors not setting but my own experience would confirm this. It wasn't a problem for us as the wind direction was NE to SE. It would be interesting in tidal waters when lying to an oversized anchor, to see if your own chain would trip the anchor as the boat did a 180 turn. Food for thought. I suspect the anchor would have buried if the load had increased but how much wind would it have taken.
Comparing how much fluke was buried in the sand with my smaller aluminium anchor, I would guess the partly buried FX55 flukes area that was buried was equivalent to the full fluke area on my smaller anchor. So I guess it was developing similar hold to the smaller anchor.

Question re your 30kg spade.

I have a 50hp engine. 14 tonne, 38 foot boat and a 30kg spade. I struggle to get it to set well in hard sand. How has your experience been? I also have a reversing pitch propeller.

Does your boat have similar stats to mine? I've dragged once with the spade in about 30 knots, it was the one time I didn't dive the anchor so I cant speak to why it dragged

 

[geem]

Question re your 30kg spade.

I have a 50hp engine. 14 tonne, 38 foot boat and a 30kg spade. I struggle to get it to set well in hard sand. How has your experience been? I also have a reversing pitch propeller.

Does your boat have similar stats to mine? I've dragged once with the spade in about 30 knots, it was the one time I didn't dive the anchor so I cant speak to why it dragged

How much chain do you deploy when you set it? It should set easily in hard sand. You may be struggling to set with such a large anchor for that size/weight of boat.
We have an 86hp engine, 18t, 44ft boat.

 

[thinwater]

... To my surprise, it was no further set than when I buried it by hand. I easily lifted it off the bottom. I did expect, with the load of close to 40kts, to see the anchor well buried.

In fact the data provide two clear lessons:

1. The Fortress has as lot of holding capacity in sand. 200pounds/pound is not unusual.
2. The oversized Fortress did not bury in a stable manner. You said it was "easily lifted from the bottom." Had it been expsoed to a wind shift, it would have popped right out, just as easily. A small Fortress, well burried, would have been far more secure against a shift.

Since you had multiple anchors deployed stability did not matter. But the lesson was clear, just not the lesson you were looking for.

You peak wind load (40 knots) was perhaps 500-750 pounds (typically 3-5x less than ABYC ground tackle specs), which is only enough to set the tips. Your Fx-55 (32 pounds) could probably hold 8000-10,000 pounds in good sand, so I would not expect it to be more than 1/2 burried.

Not sayin' the FX-55 is the wrong answer. There may come a day when you are anchored in 70 knots with soupy mud. The wind will be more and the anchor will hold less. The wind and hold may both be 1500-2000 pounds. But it was oversized for good sand in those conditions, and if there had been yawing, the chance is good it would have popped out and not reset. I'm pretty sure, based on testing oversized Fortress anchors in good sand in yawing conditions. This is a weakness for them. But they are great to have for soft mud.

 

[geem]

In fact the data provide two clear lessons:

1. The Fortress has as lot of holding capacity in sand. 200pounds/pound is not unusual.
2. The oversized Fortress did not bury in a stable manner. You said it was "easily lifted from the bottom." Had it been expsoed to a wind shift, it would have popped right out, just as easily. A small Fortress, well burried, would have been far more secure against a shift.

Since you had multiple anchors deployed stability did not matter. But the lesson was clear, just not the lesson you were looking for.

You peak wind load (40 knots) was perhaps 500-750 pounds (typically 3-5x less than ABYC ground tackle specs), which is only enough to set the tips. Your Fx-55 (32 pounds) could probably hold 8000-10,000 pounds in good sand, so I would not expect it to be more than 1/2 burried.

Not sayin' the FX-55 is the wrong answer. There may come a day when you are anchored in 70 knots with soupy mud. The wind will be more and the anchor will hold less. The wind and hold may both be 1500-2000 pounds. But it was oversized for good sand in those conditions, and if there had been yawing, the chance is good it would have popped out and not reset. I'm pretty sure, based on testing oversized Fortress anchors in good sand in yawing conditions. This is a weakness for them. But they are great to have for soft mud.

Good summary.
I had read all the talk in here about oversized anchors. It was good to see first hand what that actual means.

 

[[167227]]

How much chain do you deploy when you set it? It should set easily in hard sand. You may be struggling to set with such a large anchor for that size/weight of boat.
We have an 86hp engine, 18t, 44ft boat.

I usually put out 5:1 minimum. It's more the grassy seabed I struggle with. It only digs in half way and doesn't go any further.

 

[Tranona]

I usually put out 5:1 minimum. It's more the grassy seabed I struggle with. It only digs in half way and doesn't go any further.

That is because your anchor is too big for your boat and you simply cannot apply enough load to bury it. A 20kg anchor would be adequate and you would bury that easily in the same conditions. However if you measure the buried fluke area of each anchor you will find they are roughly the same and the holding power generated similar.

Your experience illustrates the fallacy of buying an anchor that is bigger than that recommended for your boat - just as the makers/designers like Pete Smith (Rocna) advise.

All the recent developments in anchor design have been focused on generating higher holding power and better setting for a given weight of material through fluke design, balance and stronger materials. In general NG anchors potentially develop twice the holding power of old style for a given size so it is illogical to oversize your anchor,

 

[[167227]]

That is because your anchor is too big for your boat and you simply cannot apply enough load to bury it. A 20kg anchor would be adequate and you would bury that easily in the same conditions. However if you measure the buried fluke area of each anchor you will find they are roughly the same and the holding power generated similar.

Your experience illustrates the fallacy of buying an anchor that is bigger than that recommended for your boat - just as the makers/designers like Pete Smith (Rocna) advise.

All the recent developments in anchor design have been focused on generating higher holding power and better setting for a given weight of material through fluke design, balance and stronger materials. In general NG anchors potentially develop twice the holding power of old style for a given size so it is illogical to oversize your anchor,

In my defence, if anchor manufactures aren't upfront with this, how was I supposed to know? The Spade chart recommends a 25kg for my boat and I went one size up. I never would have thought it would be an issue to set a bigger anchor. What a pain in the ass

 

[Neeves]

I usually put out 5:1 minimum. It's more the grassy seabed I struggle with. It only digs in half way and doesn't go any further.

Tranona beat me to it.

Then the anchor is too big or you are not providing enough tension to bury it. My initial thought on reading your earlier post was that it was simply not engaging. Any decent anchor, of which Spade is one, once you engage the anchor, ie it starts to develop hold, then in a consistent seabed increased tension will simply increase the depth of burial. This idea falls apart in a seabed where there is a thin layer of loose sand on a hard pan underneath - but these are not common. Usually shear strength of a seabed does increase with, square of, depth but not so rapidly that you cannot bury your, correctly sized, anchor.

Geem, Thinwater's and Tranona's comments describe what happens with an oversized anchor - its difficult to bury - unless you can increase tension to 'match' the size of the anchor. Both you, Tranona, Thinwater and Geem underline the problem with following the mantra 'bigger is better'. Its not..... better

The issue is that the big anchor will develop exactly the same hold as the smaller anchor - because it is set to the same tension. The big anchor will only be part buried, as Geem mentions, and it will trip with easy if the yacht yaws, the wind yaws or veers.

Again as Thinwater mentions - the only time you want a bigger anchor is in soupy mud - and then a Fortress reigns supreme. Under all other conditions a big anchor was simply a waste of money (a correctly sized smaller one would develop the same hold) and the bigger anchor is at significantly increased risk if the tension direction changes.

The anchor makers make it very clear in the sizing charts what anchor you should use. It is not their role to assume you have bulging pockets and that owners are going to ignore them. But as you say - its not your fault - the forum, many forum, are full of the idea 'buy a bigger anchor' - but there is not a shred of evidence to support the Mantra. The instability of the big anchor has been mentioned - and shouted down.

Just google 'bigger is better' and 'Cruisers Forum' and you will find a robust thread on the topic - mostly rubbish.

We are slowly seeing a bit of sanity in the topic Dan trickle of hard independent evidence supporting the idea buy the size recommended.

I might add - we did not follow that advice - and use slightly smaller anchors (all aluminium) than recommended (and small chain) - and have not regretted it. 38' cat with the windage of a 45' AWB, using the equivalent in size anchors to steel 15kg models.

Jonathan

 

[Tranona]

In my defence, if anchor manufactures aren't upfront with this, how was I supposed to know? The Spade chart recommends a 25kg for my boat and I went one size up. I never would have thought it would be an issue to set a bigger anchor. What a pain in the ass

If the manufacturer recommends a 25kg why did you buy a 30kg?

Slightly unfair but the "bigger is better" mantra is so ingrained that many people make this mistake and if you read the endless threads on the subject of anchors and particularly anchor and chain size it is very difficult to get people to see this. Makers are generally conservative with their recommendations for 2 reasons, first they know that buyers generally buy by weight/size and second they do not want to be seen as out of step with their competitors, So you find that they all recommend similar sizes usually based on boat length (which is a lousy individual criterion!) although some do offer more detailed guidance using displacement as well as length and type of boat. The advice to consider going up a size can be valid if a particular boat is at the upper limit of a size and the boat is likely to be used in more extreme conditions. This is a matter of judgement. I have not seen the Spade chart but would guess your boat is positioned toward the lower end of the 25kg range.

I am in exactly this situation with my current boat which is near the upper limit (Epsilon anchor) of the 10kg recommendation and many would tend to go to the 16kg because traditionally this boat had a 16kg CQR from new. Given that all the tests show that the Epsilon has well over twice the ultimate holding power of the CQR and sets instantly I do not see the need for a bigger Epsilon with a further 30%+ increase in holding power that I will never be able to access.. Sets easily with a 30hp engine and a feathering propeller.

 

[[167227]]

If the manufacturer recommends a 25kg why did you buy a 30kg?

Simply down to advice from people I look up to. For example, Morgans Cloud. They recommend minimum 2 sizes up and they use a 55kg! spade....

To be fair, in this sea grass I see all anchors struggle to set on smaller boats, so maybe they also have the bigger is better problem.

Sorry for hijacking thread, OP.

 

[[167227]]

"

Sizing Example​

Let’s look at an example: a Valiant 40-foot (12-meter) 30,000-lb (13.6-metric ton) monohull.

Note that I have been realistic about displacement in that the Valiant specification calls for around 24,000 lb, but I have upped that to a more typical cruising weight.

For this boat I would recommend:

• SPADE: S160, 77 lb (35 kg)
• SARCA Excel: #7, 79 lb (36 kg)"

Taken from morgans cloud website.

 

[[167227]]

Also, a video of how the anchor behaves in Turtle grass. In my world, the anchor isn't set if you can move it.... and if you can see the flukes.

 

[Neeves]

Normally - in a clean seabed - once the anchor engages any increase in tension will drive the anchor more deeply, increasing the tension it will dive further (and further). It is very, and I stress the very, unlikely that you will ever reach the ultimate hold of a correctly sized anchor using wind or engine.

Weed is a different proposition as the weed may clog the shank, of any anchor, and this alone is reason avoid weed. Most people don't know what the weed is like when they anchor and in the real world not many dive on their anchor to find out.

I don't think size of the anchor comes into the equation - if the weed will clog, size will not help. Though the bigger the anchor - the bigger the clot of seabed you may lift when you retrieve.

I would agree an anchor that moves is not set, though if it move because of increased tension AND moves more deeply - then its hold is increasing (the deeper the anchor the higher the shear strength to break it out). If it moves and does not dive more deeply - its probably clogged.

You really cannot expect either of these anchors to offer their best when they have collected this amount of debris.




Morgans Cloud may recommend using a bigger anchor than the manufacturer recommends - but they have no data to support the concept and nor does anyone else. 'Bigger is better' sounds right, its preached by everyone (well almost) and repetition makes it sound more feasible - but that does not make it correct. It will be suggested that bigger anchors work in 'difficult' seabeds - but no-one defines what these seabeds are. Now it is correct in soupy mud - but no anchor other than a Fortress and Danforth works in soupy mud - just check Fortress tests in the Chesapeake - its about a design more sympathetic to the seabed.

Jonathan