Anchors - Bigger is Better ?

[JonJo]

Thanks Noelex,

Encouraging to have a constructive comment.

Have a good Easter

Jonathan

[JonJo]

We have used a bucket, its not the whole answer but its simple and maybe works better on a multi than mono as we can suspend it between the transoms, so from one transom to the other.

Logically the stern is the place to locate it (or any other device to reduce yawing) but it might be a hazard on a mono as it might foul the prop or rudder. If, on a mono, its suspended to high too on the stern it may hit the hull if too low it might entangle. Our bucket is pretty heavy duty, stainless steel (the calibre of an old coal bucket, for those brought up in northern latitudes) and bought cheaply in HK many years ago.

The advantage on a multi is whatever you do - its does not get in the way, you can motor off (all it does is slow you down) and when you remember easy to retrieve.

But it only 'helps' one needs more.

Jonathan

[Andrew Troup]

A few more esoteric ideas to possibly consider in addition to the excellent list above, to reduce what Noelex calls "veering":

These options are available only on a small minority of cruising boats, so they do not belong on any general list:

Retract a lift keel
Raise dagger rudders (probably not a good idea to raise swing rudders unless they come well clear of the water)
Tall dagger rudders, fully retracted, can help a second way, by simulating a small riding sail
Drop a bow centreboard (very rare beasts)
(On a lightweight boat): trim bow-down: move heavy items to bow

I don't pretend to understand multihulls, so I won't contradict JonJo, but I would think that any underwater drag device would be much more effective at preventing what I think of as "yaw" if it were hung under the bow of a monohull, rather than the stern. It is a phenomenon of the bow blowing off, rather than the stern swinging, in my experience, which is why it hardly happens at a light mooring, and not at all to a sailboat on a ship's mooring.

I'd venture it would work even better (the submerged drag device) if it were dangled from a long outrigger ahead of the bow and chain, like a prod, but even I can see that's impracticable.

The above ruses are all designed to move the centre of lateral resistance (of the submerged underbody + appendages) forrard, and I can vouch for all of them as being surprisingly effective.
The stern will remain downwind of the bow more accurately, like a weathercock, with the pivot point forward of the centre of air resistance of the above-water profile.

One thing I particularly like about the "under-forefoot anchor" method is that it doesn't mask the usual first hint of a drag, which is when the boat turns its bow slightly away from the wind in a strong gust. (As I think I've said previously: it's a bit like a horse, hinting that it might refuse the next fence or narrow passage...)

A riding sail can definitely mask this, and I'm thinking the "bridle line from siderail aft to the rode, to bias the boat at a slight angle" also listed by Noelex, may also do so.

I'd be keen to hear from anyone who has dragged when using this latter method, and might be able to comment on whether the characteristic "tell" is masked.

I've found it highly effective and have never dragged when using it, even on other peoples' boats (people who are not BiB adherents!).

Yawing at anchor can be a crucial factor in dragging, even in less-than-storm conditions.
Mirabella V, (world's largest sloop) dragged her 600kg storm anchor in a mere F6-7, sheltered waters, and the two key reasons were found, in the official post mortem, to be: short scope (for which her anchor design is considered well suited) and uncontrolled yawing (which is a challenge, in my opinion, to any anchor - and a key reason why two anchors in a V works so well: it's often said it "doesn't share the load evenly", but what it does do is ensure that the load direction on each anchor is always the same.

The yacht had a 400kg Bruce knockoff as a second anchor, on a massive chain, which could have been dropped under the forefoot at the same time as the scope had been increased (the latter would no doubt had happened in time to avert the drag, had the bridge been receiving the forecasts. The reason it wasn't: the printer had run out of paper)

[Andrew Troup]

Something else to consider if dropping a second anchor vertically under the forefoot to minimise "veering": (which I personally think is a great idea: a smallish anchor, with a big kellet or two right down at the bottom of the chain, is ideal in many situations)

If using a heavier anchor under the forefoot, there's an old salt's trick which can be a good backup, if the main anchor were to drag:

Flake out the rest of the chain for the second anchor, and then the rope rode (but not in that order: arrange the chain on top for obvious reasons), to a decent scope on the foredeck.

Make off the inboard end of that scope onto the mooring bitts or cleat.

Substitute a light lashing where the chain leaves the bow, so that if the main anchor drags, the lashing will break and the backup anchor will self-set.

I was not confident to judge how light to make the lashing, the one time I tried this, and thought there might well be 'nuisance calls' - ie the second anchor might try to set itself needlessly - so I backed it up with a stronger lashing (long thin nylon for shock absorption) after about three metres more chain would have dived off the bow.

The idea was that the rattling of the chain would alert me and I could dash forward and make a judgement call as to whether we really were dragging, and cut the stronger lashing if need be.

As it happened, neither of these things happened ( I wasn't surprised, as I didn't expect the main to drag; it's just that there was not a lot of leeroom, and I wanted to get familiar with the method in case I needed it in a really nasty spot)

The main advantage over setting two anchors formally: if you need to leave in a hurry, the "anti-veer" anchor can be retrieved in a trice.

[JonJo]

Hi Andrew,

We have found that the yacht yaws for 2 reasons, one it swings (yaws) on its own bow roller but it also yaws (swings) on the anchor. Or put another way, the anchor chain might move through, say, 70 degrees but the yacht will move through, say, 100 degrees. We have found the bucket reduces the yawing round the bow roller - other techniques are better at reducing the swing of the whole chain assembly where the yawing is much more severe (or the forces producing it seem greater). Though if the bucket were all you were to use then deploy from the bow as that is where the greatest movement is.

I agree with you comment and would employ another technique to stop the yacht and chain swinging and the bucket thereafter to stop yacht swinging on the more steady bow roller.

Jonathan

[JonJo]

We have used an antiveer anchor (without your sophisticated alarm) and without the rode quite as well arranged (but attached nonetheless). It works well and is advantageous if all you want to do is restrict movement and have the bucket on the stern.

We used to carry a 12kg, kellet, anchor angel to those in the northern hemisphere, but decided it was more sensible simply to carry an extra, extra, anchor

Jonathan

[Kettlewell]

I posted this in another thread. Don Jordan, designer of the Jordan Series Drogue, wrote this article theorizing that to prevent yawing or veering at anchor one should anchor the boat by the stern instead of the bow. Interesting to think about.

[JonJo]

Someone generously sent me this:

The BIB thesis is that small(er) anchors drag. Much depends on ones definition of 'drag' but I had been thinking of 'breaking out' and allowing the yacht to travel at an increasing speed slowed only by the minimal effect of chain and anchor bouncing across the seabed.

Anchoring Info

It is a loss to us all that he is not here today.

Jonathan

[noelex 77]

Originally Posted by JonJo

Someone generously sent me this:

The BIB thesis is that small(er) anchors drag. Much depends on ones definition of 'drag' but I had been thinking of 'breaking out' and allowing the yacht to travel at an increasing speed slowed only by the minimal effect of chain and anchor bouncing across the seabed.

Anchoring Info

It is a loss to us all that he is not here today.

Jonathan

There are two types of dragging.

The first and most common is when the anchor breaks free of the seabed. Tthe yacht drags very quickly.
The second case is when the anchor remains set, but is gradually pulled backwards.

Both forms of dragging are bad, and can get a boat into trouble.

Some sailors that have not experienced it before, fail to recognise the second form dragging. Some of the usual cues are absent.
Use all the tools at your disposal such as transits and GPS. Having an accurate GPS position of the anchor is particuarly helpful in changing wind directions.

It is sometimes difficult to pick the initial stages of the second form of dragging from movement due to chain straitening out.

The death of Alain Poiraud was a great loss. The Spade was a truly inovative design. I think we will see another leap forward in anchor technology when his patents expire. (Which Andrew pointed out is soon)
At the moment I suspect designers of concave non roll bar anchors are having to come up with less than ideal solutions to avoid patient infringement.

[Kettlewell]

I have always had a problem with these tests showing "instability" in certain anchors, when in the real world there are other bottom types where that characteristic is not seen. I have dived on numerous anchors numerous times in bottoms ranging from Massachusetts to the southern Caribbean, and there are many places--probably the vast majority of places within the USA--where the first problem is figuring out where the anchor is because the chain just goes into the bottom and disappears. There is no "instability" except maybe under extreme loads, but my suspicion is that in many of these bottom types with the Fortress or Danforth type anchors something would break before you could pull that anchor free, assuming scope was adequate. They just keep diving down and down and down. I have had the same problem with CQR anchors in the past--after a big blow they can be very deeply buried and difficult to get out even when directly over the anchor winching your bow down. So, I attribute this "instability" problem to not just the anchor design, but to an unfortunate combination of anchor and unsuitable bottom type. I can speculate, and others have too, that there are also bottom types that are not suitable for these supposedly "stable" anchor types, like Spades for example. I have seen a Spade drag and when it was brought up the anchor was fouled with an enormous ball of thick mud and grass, while in that exact same location my Fortress had knifed down through the mud and grass and was holding fine in moderate winds. I suppose "stability" is one thing, but it isn't everything.

[Kettlewell]

This book is interesting, though it pertains to large anchors. One statement on page 82-83 stands out to me with regard to anchor efficiency: "The efficiency always decreases with increasing model size." It goes on to propose a formula for calculating the decrease in efficiency with an increase in size.

[JonJo]

Originally Posted by noelex 77

There are two types of dragging.

The first and most common is when the anchor breaks free of the seabed. Tthe yacht drags very quickly.
The second case is when the anchor remains set, but is gradually pulled backwards.

Both forms of dragging are bad, and can get a boat into trouble.

Some sailors that have not experienced it before, fail to recognise the second form dragging. Some of the usual cues are absent.
Use all the tools at your disposal such as transits and GPS. Having an accurate GPS position of the anchor is particuarly helpful in changing wind directions.

Noelex, Your replies are of considerable intellect and show considerable thought, I might have misunderstood your most recent.

I agree a CQR or Bruce, broken free, is simply a piece of galvanised steel simply ensuring the anchor chain is kept in a straight line as the yacht accelerates across the anchorage.

To look at the final paragraph first.

In strong winds and a well set anchor that might be dragging - the yacht will be moving about, maybe moving through 180 degrees (because there is only one anchor set). It would be very difficult to correlate transits or GPS positions. Look at the Granny Smith vid, take a transit? When? Most people with decent anchors are too busy taking videos

But your idea that this 'well set' anchor dragging is bad - surely you do not really mean what you suggest?

If you set an anchor to, say, 500kg but the wind then loads it to 1,000kg - it will drag. It does not matter whether its a 20kg anchor or a 50kg anchor - it will drag. That drag is not 'bad' its what happens. The anchor will be pulled backward and actually will dive more deeply until it reaches that limit of 1,000kg. Its not bad, its what the anchor was designed to do. Possibly there are anchors you can set to 500kg that then do not move (if you load them further) but they have escaped my notice.

All anchors have a finite limit, the VetV tests, the WM (or Sail, YM) tests all went to around 1,500/2,000 kg on a 15kg anchor - but we do not know if that is the limit for the anchor, or the point when the tested stopped. If you do winch tests from a beach on 10/15kg anchors they dive to 2,000kg load and are still moving - but its really imperceptible (paint dries more quickly, grass grows more quickly). You can take a Boss much further. So, yes, they are dragging but if 10mm every 5 minutes is an issue (considering that rate will decrease) then this is a 'bad'ness that most can live through.

The issue is when the recommended sized anchor will reach its limit and then drag at a steady rate, possibly that's 1mm/ min every time the limit is exceeded, and then what extra 'insurance' the bigger anchor offers.

If its an anchorage where the bullets are at 180 degrees then, by definition, its a tight anchorage and I'd be better with a line ashore. If its a strong wind in one constant direction I'd be better with 2 anchors to stop veering, if its a cyclonic storm I'd be better with a web of lines, anchors and shore, holding me steady. All would be better than one big anchor (which might catch an old beer can) and have nothing else in the armoury.

To me the BIB is the marine equivalent of the urban 4X4 (say Range Rover) to collect the kids from the local school or to pick up the groceries at the local supermarket.

Jonathan

[DumnMad]

[QUOTE=JonJo;1201391] If you set an anchor to, say, 500kg but the wind then loads it to 1,000kg - it will drag. It does not matter whether its a 20kg anchor or a 50kg anchor - it will drag. Strange logic.

So, yes, they are dragging but if 10mm every 5 minutes is an issue (considering that rate will decrease) then this is a 'bad'ness that most can live through. Setting deeper is different from dragging

To me the BIB is the marine equivalent of the urban 4X4 (say Range Rover) to collect the kids from the local school or to pick up the groceries at the local supermarket. You are talking about day sailing while the BIB sailers are talking about cruising in locations where their anchorage set up in a 30knot wind can turn out to be a 60knot storm anchorage at 4 times the anchor load before daybreak.
No contest as far as I'm concerned. The BIB team are worth listening to, your comments appear to be for specific site & soil conditions and therefore irrelevant for other conditions.

[JonJo]

DumnMad, of course I'm talking about day sailing, otherwise I would not need to anchor, though sometimes we night sail and anchor day time - is that different. I appreciate ocean sailing has a certain superiority to it, much more superior than a mere day sailor - but there is usually not much need to anchor if you are crossing oceans

The BIB yachtsmen have immense expertise and are definitely worth listening to. That does not mean they, I, or anyone else has all the answers. I appreciate you do not like some of the answers, in the same way that I do not understand some of the answers of the BIB side of the discussion. I had thought the idea was to explore ideas and try to remove each other's misconceptions.

As an example 'Dragging' - we now seem to have two definitions, imperceptible movement (or it will certainly be imperceptible in a 50 knot wind until the yacht has moved many, many, metres, buried well beneath the seabed) and an alternative definition: accelerating movement of an anchor across the top surface of the seabed.

I wonder - on the basis that the 'recommended sized anchor works not much beyond 30 knot what is it that give the bigger anchor such superiority, at 60 knots? Its not design, as a Rocna is a Rocna is a Rocna. Can you define in the bigger anchor - precisely what is it that gives it 4 x the effectiveness, its not weight, because it not even twice the weight (its only 70% heavier and even 70% is not much when its wind speed squared). So what is it that makes it so much better? And if it is weight, we may as well all use dumbbells.

[Snowpetrel]

More maths Jon,

Assuming the anchors hold proportional to weight, which they don't quite, but anyway...

(current anchor wt x desired holding windspeed^2)
current anchor windspeed limit^2

This gives us the rough size of anchor we need to hold us for the wind we select.

Ie for your 45lb? excel if it holds to about 40 knots then lets go we could run the calculation to see what size anchor of the same type you would need to hold in 55 knots in the same bottom.

(45*55^2)/40^2=an 85lb anchor would possibly do the trick in theory if anchor holding power was linear. Not 100% on my maths for the next bit, but to account for the slight loss of efficiency with the bigger anchor up the power for the wind speed to about 2.2 or so (anchor efficiently increases as a power of approx 0.9, inverse equals 1.1 1.1 x 2 = 2.2).

This gives us (45*55^2.2)/40^2.2 = 90 lb anchor should hold in 55 knots, provided the seabed enables the anchor to bury to it's proper depth which is generally deeper for heavier anchors of the same type.

Like all simple back of envelope calculations it is rife with potential errors and exclusions, but it is much better than plucking numbers out of thin air, especially when dealing with non linear things.