The 2000 kg holding myth

[Laminar Flow]

I love these discussions that take place in a vacuum.

I do not care whether my anchor's holding power is 2000kg, 1000kg or 500 kg. All I care about, is that it holds me fast in the present conditions or the the ones I am expecting shortly, over the next night. Fortunately I can easily calculate my anchor's present holding power when setting it. If I deem it not sufficient, I relocate or try again.

The formula is: displacement x (velocity while backing in in m/s divided by the time in sec it takes from the time the boat begins to slow down until the rode comes stiff)

If my wife backs in at 2 kts, for that is the division of labour on our fine ship of 8500 kg, and it takes 15 sec for the chain to come tight and the boat to stop up (a fairly conservative assumption for the purpose of this example) , then I know the anchor will hold 566 kg, which is a couple of hundred kg more than the wind load in a F10.


If you are concerned about "dynamic" loads, they can be calculated in the same way.

When calculating windload, simply assume the the frontal profile as a flat rectangle and that the rig represents a rectangle of beam x 40% of rig height. This is accurate enough and, furthermore, allows for a sufficient (safety) margin for increased loads when the boat veers.

 

[AntarcticPilot]

www.sussex.ac.uk/weatherstation/technical/Windforce.html

Thanks.

 

[Neeves]

2,000kg is a nice round number, aka 2 ton.

Most anchor makers today know exactly the seabeds they can choose to produce the maximum hold for their anchor - why else would Fortress choose Chesapeake Bay to test their anchors against all comers.

Most good 15kg anchors that have been tested by Classification Societies and found to hold 2 times the hold of a Delta can achieve 2,000kg in a chosen seabed. The Anchor maker needs to find a seabed in which Delta will hold 1,000 kg and ensure, by prior testing, that his anchor will hold 2,000kg. Having satisfied himself he has a decent margin of error he can invite the CS of his choice to supervise the tests (and pay the exorbitant fee). He also needs to ensure that his anchor is better than another anchor already awarded SHHP. The first anchor awarded SHHP was Supreme and all others have to prove they are equal or better.

Obviously the test is conducted in an ideal seabed.

But having an anchor that will withstand 2,000kg means that in other seabeds it will, largely, be better than Delta and CQR and if its a difficult seabed it will hold, say 1,000kg - where the Delta and CQR will only hold about 500kg.

In tests I have conducted, chosen to be conducted in a seabed not subject to wave action (only wind) I recorded tensions of 650kg - with a 15kg Excel (I was not testing the Excel - was testing for rode tensions). In that specific location I effectively had a 3:1 safety factor - and the anchor was fine, just darned difficult to retreive.

A 650kg tension is very unpleasant. But in our case its not the anchor that failed - but the courage of the owner - I saw no reason to test all the structures of the catamaran, on which the rode relied, to satisfy a magazine article. I could have moved to a different location - with less wind (I chose a location subject to the developing Seabreeze) but that would have defeated the object of the exercise)

When we, any of us, anchor we have no idea of the shear strength of the seabed - but anchorages are usually described as having good holding (or poor holding - in which case its not a storm anchorage). What we need for our anchor is one that has been tested and found to have the best hold in its weight bracket for most seabeds. If our chosen anchor is of little value (has low hold) in soupy mud we either need a different location or a different anchor. So an anchor that can achieve 2,000kg, is comparable with its peers (and none are renowned to be appreciably better (than 2,000kg) we have done all that is possible. In your chosen anchorage the hold, for your anchor might be much less than 2,000kg - but your anchor will be the best that was available.

It does not matter if in a seabed our anchor can only hold 1,000kg as none of its peers will be any better and the maximum tension we are likely to 'meet' will be 650kg.

In our catamaran with engines running at 3/4 full revs, about 3,000rpm each, we could set out anchor to 400kg (I measured it) - if it did not set - we moved (or used a Fortress in soupy mud). The anchor setting and holding with a jerk - was indicative the seabed was good.

Some might argue that we should have a 30kg anchor - but the hold developed by a 30kg anchor will be identical (might be less in a 'difficult' seabed) to the tension in the rode - so a 15kg anchor and a 30kg anchor will both develop a hold of 650kg - if that is the tension in the rode - but the 30kg anchor will be shallow set (and liable to failure in a veering wind (deep set anchors resist veering).

Ideally you need a quiver of anchors to cater for different seabeds (a Fortress for soupy mud) and a SHHP anchor for most other seabeds - having more than 2 anchor also means if you need to retreat you can drop your primary, buoy it, and go elsewhere and you have a fall back if you loose your primary.

Snubbers are also an option as a long and elastic snubber will tame snatch loads caused by an oscillating wind.


2,000kg hold is not a myth - its the reality and the best a good 15kg anchor, Spade, Excel, Rocna, Supreme, Epsilon, Ultra can achieve, consistently, in a good holding seabed. In a poor holding seabed that 2,000kg maybe reduced to 1,000kg - but the reduction will be similar to all other similar anchors. If you thought that your 15kg anchor could achieve 2,000kg encompassed in every sea bed and and all conditions might be invalidated by poor holding then - your imagination is sorely lacking and you need a reality check.

What is interesting that though the question mark has been raised for the performance of 15kg SHHP anchors with regard to their hold (or 2,000kg) the reports of these same anchor dragging are noticeable, for the last 2 decades, by their absence. For whatever reason that 2,000kg 'ideal' performance has been found to be 'enough' - for most people. You can question the 15kg x 2,000kg - but that benchmark has resulted in no reported dragging. The 15kg SHHP anchors have proven their reliability - it does not matter if in another seabed they only hold 750kg -

They just work.

For the yacht where a 15kg SHHP anchor is recommended (and in fact work where the recommended anchor might be larger (the safety margins are there).

Jonathan

 

[noelex]

But having an anchor that will withstand 2,000kg means that in other seabeds it will, largely, be better than Delta and CQR and if its a difficult seabed it will hold, say 1,000kg - where the Delta and CQR will only hold about 500kg.

Jonathan

How can you say this when results of the large 2006 anchor test shows that even in a good substrate (they did not conduct the test in any poor substrates such as thick weed, very soft mud, cobblestones etc) in one location (out of a total of three locations) the 15 kg Rocna only held 350 kg, the 16 kg steel Spade 220 kg, the 15kg Sarca 340 kg, and the 16 kg Manson Supreme 771 kg.

The results in a poor or difficult substrate would have been much worse than these numbers.

If you want to claim these 15kg anchors can hold 1000 kg in poor or difficult substrates you need to provide supporting evidence. The objective evidence does not support this contention even ignoring the important factors I raised in post #1.

Continually exaggerating the holding power of anchors is not helpful.

 

[Neeves]

How can you say this when results of the large 2006 anchor test shows that even in a good substrate (they did not conduct the test in any poor substrates such as thick weed, very soft mud, cobblestones etc) in one location (out of a total of three locations) the 15 kg Rocna only held 350 kg, the 16 kg steel Spade 220 kg, the 15kg Sarca 340 kg, and the 16 kg Manson Supreme 771 kg.

The results in a poor or difficult substrate would have been much worse than these numbers.

If you want to claim these 15kg anchors can hold 1000 kg in poor or difficult substrates you need to provide supporting evidence. The objective evidence does not support this contention even ignoring the important factors I raised in post #1.

Continually exaggerating the holding power of anchors is not helpful.

Quite easily

Independent Anchor Performance Testing

Just check the holds from independent testing for Rocna.

Every time I mention the 2,000kg hold I mention 'in good holding'. I never say that the anchor holds 2,000kgs in every seabed. You enjoy selective editing . If anyone thinks that my comments of 2,000kg cover every conceivable seabed then my reputation is much higher than I thought - I must be a Guru!!

Poor, difficult, weedy seabeds are meaningless terms - and are usually not terms used to describe good anchorages.

The proof of the high performance of the better anchors is the absence of complaints from owners that they dragged. It does not matter if you want to argue about 2,000kg, or not, (you really must be really bored) these better anchors are reliable. The reality is almost no-one knows the tension in their rode, they have no idea of the shear strength of the seabed, they have no idea of the windage of their yacht - they probably don't care if their anchor is SHHP or not - but the absence of complaint over anchor's dragging has disappeared and most people who anchor frequently are using the correctly sized SHHP anchor which for a 15kg anchor means they need to have the same hold as Rocna, Supreme et al. In many respects it does not matter if when the CS tests the anchors whether they meet that 2,000kg number, it could be (in that seabed) 1,000kg or 500kg - they just have to be better than their peers. It equally does not matter with the 2,000kg I quote - as no-one knows the tension in their rode, the windage of their yacht etc etc.

But anchor manufacturers want the benefit of having a 15kg/2000kg anchor (its good marketing) and when they enter CS surveillance they aim for that 2,000kg threshold.

What people do know is that SHHP anchors ..... don't drag.

In our 40 years of sailing we have experienced a cobblestone seabed once (and used it about 10 times), we avoid seabeds with weed and we would not anchor long term in mud (the latter because its not 'nice'). We use muddy seabeds in transit - but never long term. We would not waste our time in weed, you never know what is meant by weed and weedy seabeds are the nursery for young aquatic creatures and anchoring in weed is very environmentally unfriendly. The Admiralty Pilots and Cruising Guides in the waters we have frequented have always offered and described good anchorages with good holding. Give us a sandy seabeds - we can stop longer term.

Maybe we have been lucky and anchoring in Hong Kong, the Phillipines and Australia has not exposed us to the terrors of 'difficult' seabeds.

So I'm a charlatan because I only know one cobblestone seabed, I avoid weed and mud.


What is fascinating is that most people want an anchor with good holding - every if they never express what that means numerically. Most people choosing an anchor now buy one with CS certification (which they may not know, may not influence their choice and possibly don't care) - what they do know is that their choice is good because the anchor sets easily and is reliable. That list again, Rocna, Supreme, Excel, Spade, Ultra, Epsilon (and Fortress).

Interesting that Fortress is an SHHP anchor - as it truly can be a disaster in weed, pebbles and shells - but every, well almost every, yacht has one and when used in anger - people swear by them.

'Anchors are a compromise' - you surely have seen that in posts. I thought I'd coined it originally - but its hardly clever - but I see it quite frequently.

Jonathan

 

[Neeves]

When I've tested anchors I always compare with a known anchor, one off 'that list' as I know how those anchors perform. If I get a result I don't expect, Noelex' 300kg, not the approx 2,000kg I expect - I check and check again. I'm testing usually in quite shallow water and when the tide has retreated I dig the anchors out. I invariably find that the poor performance is due to 'foreign' matter in the seabed (well not foreign - but not conducive to setting an anchor). It might be a bit of water logged wood, an oyster shell - but invariably there is a reason. If you are testing, as YM/WM did using a large vessel and deeper water (not the intertidal zone) you cannot check the anchor, you cannot interrogate the reason - the contaminant falls off as you retrieve the anchor. The modern bunch of anchors are reliable, consistent and a poor result is unusual - there is usually a reason.

Other items found in deeper water in popular anchorages are towels, dinner plates, beer cans, shopping trolleys, gas cylinders, swimming trunks etc etc.

Oyster shells and bits of wood are the reason to power set - but power setting is fool proof. If we power set in reportedly good holding and power setting dragged an anchor - we retrieve and try again - you would be unlucky to catch a contaminant twice.

Jonathan

 

[Neeves]

I love these discussions that take place in a vacuum.

This is not a discussion its Noelex trying to niggle me


For a change of tack. This is a screen shot of all the test results for all of Fortress anchors tested in muds combining Chesapeake Bay and San Francisco. The Chesapeake Bay results are recent and the SF results I think are derived from US Navy tests.

This is a screen shot of the results as the file itself was far too large to post (or being a complete dinosaur I'm incapable of posting such simple data on YBW)

Hopefully this will distract Noelex and he might be encouraged to focus on anchors - again, 'play the ball not the man'. But its his thread - we'll see.

Fortress is an anchor that has been extensively tested, as these results indicate. Its the only anchor I know where the compete spectrum of product sizes has bee tested. Fortress is different (obviously) to most other anchors (excepting Danforth) as the design is primarily fluke and these performances are from fluke area, not weight. The design has both a stock and shank (again obviously) neither component contributes to hold (though the anchor would be a bit sorry without them). I confess I don't know if the plot would look 'better' if surface area of the flukes had been plotted instead of weight - I don't have access to Fortress dimensions.

The plot shows a number of factors - I know the tests were conducted in 2 totally different locations but the plot shows some consistency. The spread of the results for each anchor is huge and if only a few 'pulls' had been made then the plot could have looked entirely different. This latter point is the killer - anchor testing is very time consuming, time is money, and the kit needed to test a 70lb anchor whose hold is approximately 3.5 tons is a further expense - and explains why few anchors (only Fortress) are fully documented. I obviously don't know how many results were discarded because the anchor might have been fouled - but I suspect there must have been some really anomalous results that will have been discarded. Fortress and the US Navy would have had some idea of the data they expected and discarding data that is well outside expectation would simply be expected.

Jonathan

 

[Irish Rover]

This is not a discussion its Noelex trying to niggle me

You weren't even in the discussion when @Laminar Flow posted his comment. You seem to think every thread which mentions anchor is about you .

 

[Chiara’s slave]

Re the wind pressure chart. I assume that pertains to flat surfaces, ie motor craft. Those of us with more pointy boats are maybe a little more slippery when head to wind?

 

[Bouba]

Re the wind pressure chart. I assume that pertains to flat surfaces, ie motor craft. Those of us with more pointy boats are maybe a little more slippery when head to wind?

The 15 sqm that I said for a boat with a 15kg anchor…was a loose estimate taking account of wind deflecting surfaces and places where the wind can get caught up as it runs along the deck and rigging from forward to aft….but it was only a guesstimate …I was in port looking at boats as I made a rough mental calculation.
On the other hand I could be off by a factor of thirty

 

[Chiara’s slave]

The 15 sqm that I said for a boat with a 15kg anchor…was a loose estimate taking account of wind deflecting surfaces and places where the wind can get caught up as it runs along the deck and rigging from forward to aft….but it was only a guesstimate …I was in port looking at boats as I made a rough mental calculation.
On the other hand I could be off by a factor of thirty

A factor of 30 seems about right for any anchoring business. We’ll be doing it later today, some substrates it goes straight in, yet 20 metres away it takes 3 or 4 goes and may end in failure. Ours is a decent size Spade, the next size would definitely not fit the locker.

 

[Bouba]

A factor of 30 seems about right for any anchoring business. We’ll be doing it later today, some substrates it goes straight in, yet 20 metres away it takes 3 or 4 goes and may end in failure. Ours is a decent size Spade, the next size would definitely not fit the locker.

I always look for sand…but the sea grass is ever expanding….and a lot of sand is only a couple of inches deep with sheet rock underneath…all anchoring does is sharpen the tip

 

[lustyd]

changes in the direction of pull will significantly reduce the holding power.

This is incorrect. There is no way to pull an anchor at the end of a chain anything other than straight. The holding power remains consistent with bottom type. What does happen is that the anchor will break out and reset after a change in pull direction, but most modern anchors will do this in their own length so it's largely irrelevant.

 

[justanothersailboat]

I've had numbers vary by 70% within feet of each other, dive, and find that there was a soft spot or a rotten limb deflecting the chain.

A rotten limb?

Definitely the Manchester Ship Canal.

 

[Neeves]

A rotten limb?

Definitely the Manchester Ship Canal.

I'm not sure that Thinwater will be that knowledgable of all the 'colours' of Manchester Ship Canal.

Jonathan

 

[Laminar Flow]

You weren't even in the discussion when @Laminar Flow posted his comment. You seem to think every thread which mentions anchor is about you .

I wasn't referring to Neeves, who appears quite diligent in backing up his statements.

From an older publication in German:
Holding power for a plow type (CQR, angle of pull zero degr):

minimum 200 N x anchor weight in kg.
Maximum 700 N x anchor weight
average 500 N x anchor weight

In spite of the fact, that I am pretty sure my current 16 kg anchor of choice delivers better performance than a CQR, I know that even the presumptive, minimum holding power will see me through a F8. Moreover, a fact I can easily verify when setting it.

Last summer we had plenty of opportunity to apply and test all of this, in Norway, Shetland, Orkney and Scotland, regularly and consistently in winds over 40 kts. We never once dragged even an inch.

No matter what type of iron you sink into the brine: all it really boils down to, assuming a modicum of common sense and skill, is location, location, location.

The rest is simply nerves, mostly from folk who do not understand the loads involved or how to mitigate them, what an anchor might/should hold and how to check and make sure that it does.

 

[Irish Rover]

I wasn't referring to Neeves,

Somebody needs to tell that to @Neeves

 

[Tranona]

I wasn't referring to Neeves, who appears quite diligent in backing up his statements.

From an older publication in German:
Holding power for a plow type (CQR, angle of pull zero degr):

minimum 200 N x anchor weight in kg.
Maximum 700 N x anchor weight
average 500 N x anchor weight

In spite of the fact, that I am pretty sure my current 16 kg anchor of choice delivers better performance than a CQR, I know that even the presumptive, minimum holding power will see me through a F8. Moreover, a fact I can easily verify when setting it.

Last summer we had plenty of opportunity to apply and test all of this, in Norway, Shetland, Orkney and Scotland, regularly and consistently in winds over 40 kts. We never once dragged even an inch.

No matter what type of iron you sink into the brine: all it really boils down to, assuming a modicum of common sense and skill, is location, location, location.

The rest is simply nerves, mostly from folk who do not understand the loads involved or how to mitigate them, what an anchor might/should hold and how to check and make sure that it does.

The criticism of the CQR has rarely been about ultimate holding power, which is in practice potentially greater than the loads that a yacht can apply. It is the difficulty of setting and intolerance of a wide range of different kinds of seabeds. It is the explosion of numbers of people sailing outside N Europe in the 1980s that prompted the development of alternative designs. While the CQR was fine in most UK settings for example, particularly if oversize and used with heavy chain its weaknesses elsewhere soon showed themselves.

Now we can choose a lighter, more effective anchor that has potential holding power even greater than the CQR that is easier to set and in most cases more resistant to breaking out. Rather than the absolute holding power being an issue (as the OP suggests) it is the relative holding power in relation to the specific boat and anchoring conditions.

 

[Laminar Flow]

The criticism of the CQR has rarely been about ultimate holding power, which is in practice potentially greater than the loads that a yacht can apply. It is the difficulty of setting and intolerance of a wide range of different kinds of seabeds. It is the explosion of numbers of people sailing outside N Europe in the 1980s that prompted the development of alternative designs. While the CQR was fine in most UK settings for example, particularly if oversize and used with heavy chain its weaknesses elsewhere soon showed themselves.

Now we can choose a lighter, more effective anchor that has potential holding power even greater than the CQR that is easier to set and in most cases more resistant to breaking out. Rather than the absolute holding power being an issue (as the OP suggests) it is the relative holding power in relation to the specific boat and anchoring conditions.

I have used CQRs for some forty years and, yes, worldwide in whatever seabeds I happened to encounter. I am well aware of their idiosyncrasies and limitations. While I understand the the UK is supposedly exceptional in every way, as our former colonizer has always assured us, I just hadn't realized that this specialness extends to their seabeds, even though I have essentially circumnavigated the place, frequently anchored in the process and have many other locations to compare with.

Our current anchor, a Kobra, has in some ways a similar configuration to a CQR, in that it too is a plow. While our new hook weighs the same as the old CQR, it has a considerably larger surface area which should translate to higher holding power. The more aggressive and easier setting characteristic of the Kobra not withstanding, I have little doubt that it has a higher ultimate holding than its predecessor, particularly in marginal seabeds. To get a CQR to stick in gravel, for example, requires something of a miracle, the same goes for soupy mud, where I have towed a 75lbs model for several hundred meters before giving up. But, hey, that was of course in Holland and not on CQR home turf.

 

[Tranona]

Did not suggest that the UK was exceptional - there are a variety of seabeds round our shores. However the most common areas for leisure sailing have "good" anchorages. If you move to the Med like I did, particularly the eastern end you very quickly find the shortcomings of the CQR and its copies.

You may find this useful reading petersmith.net.nz/boat-anchors/catenary.php Although the article is specifically about catenary there are links at the bottom to to articles on the development og NG anchors. Of course he is not an "independent" source being a designer and erstwhile purveyor of NG anchors, but his views on the subject are now largely mainstream.