Do we need another anchor design?

Robih said:
Jonathan/Vyv,

How do you deploy the second anchor? Carried out and dropped from the dinghy or from the bow of the boat?
Click to expand...

Rob

All our anchor are alloy and weigh about 8kg but are equivalent in size to a 15kg steel version. Alloy make it easier to deploy (Excel, Spade or Fortress).

We store the rode in a milk crate, 40m of 3 ply nylon and 15m of 6mm HT chain (because it 6mm its also light). We coil the rope neatly round the inside of the crate and drop the chain into the hole left after coiling. We keep the ends of the rode 'free', or obvious.

I either take out by dinghy, hence wanting to do it before the wind gets up with the crate on the bow, Josephine deploys the chain as I row (or use the OB). If I do it myself I deploy the anchor and row back deploying as I return. Once I get back to the yacht I take in the 'new' rode until the 2 anchor are roughly deployed with the same length rode, and cleat off the new rode.

We don't deploy from the yacht - but do retrieve from the yacht, its easier.

Once retrieved the mixed rode is then religiously re-coiled.

Jonathan
 
vyv_cox said:
I do think the 3 knot reversal is unrealistic. His video has led to withdrawal of the Rocna as one of Morgans Cloud recommendations, but I have photos and real world experience showing the Rocna survives reversal perfectly well.
Click to expand...

3 knot reversal maybe be uncommon but not completely unrealistic, had it happen with huge gusts coming from everywhere in an bay in La Gomera, friends running a school boat at the quay measured 60Kt gusts. So boat would shoot across the anchorage when the next gust came in from a completely different direction. Not the best sleep that night though the 20Kg rocna seemed to stay very close to where it dropped despite high speed high load 180deg reversals.
 
Neeves said:
My understanding is that Morgan Cloud withdrew support for Rocna (and I think by a association, Supreme) because there were reports of Rocna, more than one, dragging and not re-setting. I believe the anchors did not reset because the fluke was full of mud (or seabed). The removal of support recommendation pre-dates the Panope video by months, maybe years

I did some tests, at considerable personal effort, and found that if you applied a change of tension direction of 180 degrees (think of a thunderstorm cell passing overhead) then concave fluke anchors would not reset if the fluke was filled with mud - until such time the anchor self cleaned by being pulled over the seabed - say by an errant yacht.

I do not subscribe to Morgans Cloud - but others here do - some of whom can be quite vocal - they can confirm the details (hopefully) of the background to MG's removal of support.

https://www.practical-sailor.com/issues/37_26/features/Anchor-Resetting-Tests_10981-1.html

Jonathan
Click to expand...

That sums it up pretty well. John feels that it is a risk that is greater than that with Spade. He does not condemn Rocna, it's just that not his top pick. He is also open about some of the shortcomings of the Spade. There is much we don't know about anchors, so personal opinion becomes a factor. Also remember that is focus is high latitude sailing.

I think his site is worth the subscription fee. An unabashed plug for John.
 
vyv_cox said:
Second anchor in a V. We have used this technique countless times, usually don't bother in winds less than 30 knots but have found it highly successful up to 50 knots. I shot a video two years ago showing yawing reduced from more than 100 degrees to just over 40.
Click to expand...

Yes, a second anchor works very well. Not only dose it reduce yawing, it reduces the direction of pull change on the anchor to zero. I often don't bring that up because it is so unpopular on many forums.

Most often it is a Fortress, and it is easy to set from a kayak, even, once you dial in your method. The one thing to avoid is two all chain rodes led into lockers; if the boat spins the tangle can be epic.
 
Last edited:
Yawing as GHA describes can be pretty aggressive and can occur when bullets are driven down valleys or between gaps in a tree line and would not be uncommon if a storm cell passes over an anchorage. We have found that in such situations shore lines are invaluable.

It was in one such situation, storm, cell, that one of the bendy anchors bent - if the anchor develops good hold and you throw a 6-10t yacht about with, say, even 40knots gusts - something might give. I don't know the wind speed - but the anchor did hold - but the shank was questionable.

If you lave the 2 anchors in a 'V' roughly to cover the average of the 2 extremes of the gusts, or veer, then each anchor in turn becomes the primary and takes the tension in its set direction - so a zero angle. In between times as the yacht is moving from one side to the other the tension reduces, because the yacht moves forward slightly, until it reaches the other extreme.

Proponents of relying on one anchor will be constantly tensioning the rode at 30 degrees each side - something has to give - hopefully the snubber - but often the anchor is subject to constant movement.

If you don't believe any of this, why would you :)

Dive on your anchor, don't bother with photos - do something more useful) and touch any part of the exposed anchor. If the anchor is properly buried and you are keen - take a screw driver to touch any part of the anchor. With the chain off the seabed the anchor constantly twitches. With 2 anchors that twitching is less. Twitching reduces the shear strength of the seabed in direct contact with the anchor - the seabed liquifies and that hold defined in holding capacity tests will be reduced. Twitching is subjective, but it does happen, and others have made the same observation. It would be interesting if twitching could be measured.

So - next time the wind i over about 25 knot get out and try it.

I firmly believe yawing is A primary care of anchor dragging. Buried chain, which will occur if the anchor i buried< will reduce the twitching. Some anchors do not bury and set shallow - Mantus being a prime example. Buried chain reduces anchor twitching.

Jonathan

The US Navy, and possibly others, who have a serious interest in moorings (based on anchors) have done some work on shear strength degradation due to anchor movement.
 
Last edited:
Robih said:
Jonathan/Vyv,

How do you deploy the second anchor? Carried out and dropped from the dinghy or from the bow of the boat?
Click to expand...

I much prefer to launch the Fortress from the dinghy. It is easier to control the angle and the rode length is set by Jill who feeds it out from on deck.

If the dinghy us not inflated I have done it by motoring the boat but it is difficult to estimate where the Rocna is lying. Two years ago the Fortress finished up on a scope of only 3:1, which it coped with in winds to 40 knots extremely well.
 
vyv_cox said:
I much prefer to launch the Fortress from the dinghy. It is easier to control the angle and the rode length is set by Jill who feeds it out from on deck.

If the dinghy us not inflated I have done it by motoring the boat but it is difficult to estimate where the Rocna is lying. Two years ago the Fortress finished up on a scope of only 3:1, which it coped with in winds to 40 knots extremely well.
Click to expand...

I think some tie the anchor on the outside of the transom of the dinghy with a quick release knot and rode laid neatly (so that it does not catch round ankles). I find that 8kg and 6mm chain is manageable by hand - it would be considerably more difficult if the anchor was steel and large, say 20kg and 10mm chain (id then use the 'tie on transom' technique.

The benefit of aluminium really is underlined if you are deploying from a dinghy (or retrieving by hand :) )

Jonathan
 
Neeves said:
if the anchor was steel and large, say 20kg and 10mm chain (id then use the 'tie on transom' technique.
Jonathan
Click to expand...

I recall that Bernard Moitessier was a proponent of the tie on the transom technique.

Do you always buoy your main anchor so that you know precisely where it is? I imagine that dropping one anchor on top of another would lead to an almighty mess.
 
Robih said:
I recall that Bernard Moitessier was a proponent of the tie on the transom technique.

Do you always buoy your main anchor so that you know precisely where it is? I imagine that dropping one anchor on top of another would lead to an almighty mess.
Click to expand...

We never willingly use an anchor buoy, they cause too much trouble. It is usually possible to guess the rough position of the bower, assuming the chain to be about straight. We then try to set up a transit for the second anchor placement but it's a bit hit or miss with the dinghy and a lot worse doing it from the boat.
 
Neeves said:
If you lave the 2 anchors in a 'V' roughly to cover the average of the 2 extremes of the gusts, or veer, then each anchor in turn becomes the primary and takes the tension in its set direction - so a zero angle. In between times as the yacht is moving from one side to the other the tension reduces, because the yacht moves forward slightly, until it reaches the other extreme.

Proponents of relying on one anchor will be constantly tensioning the rode at 30 degrees each side - something has to give - hopefully the snubber - but often the anchor is subject to constant movement.

If you don't believe any of this, why would you :)
Click to expand...

I'm not 'a proponent of relying on one anchor'. I am not arguing against using two anchors. I am trying to clarify the advantages.

I agree that two anchors seems a very good course of action because it will reduce significantly the pulling from side to side of the anchor(s), but I cannot see that it reduces this to zero. (The other advantage of two anchors is that for much of the time the load on the anchor(s) will be lower, as a result of being shared.)

If you have the two anchors, as you say, at the average of the two extremes of yawing, there is, by definition, part of the time when the pull is beyond those averages.

Imagine the wind is generally from the NW, with gusts/yawing averaging 45 degrees (for simplicity) either side of this. You lay out one anchor to the N, another to the W.

When the boat is lying to the SE the load will be taken equally, and in a straight line from, each anchor. (Of course, the load on each will be more than half of the force on the boat because of the angle between them.)

When lying exactly to the S, or to the E, the load will be taken on a single anchor, again in a straight line with it.

As soon as the boat lies anywhere W of S, or N of E, then the load will again be on a single anchor, but now the pull will be to one side of the anchor.

You could, of course, set your anchors further apart, at or beyond the extremes of the angle of the gusts/yawing (assuming you knew this figure with any accuracy when you anchored, which you wouldn't). But the further apart they are, the more often you are lying to a single anchor, and the higher the load on each when you are lying to the two, so reducing the advantage of using two anchors in the first place. Therefore I agree that your suggested 'average of the extremes' of gust/yawing angles seems a very good rule of thumb for maximising the advantages, and only disagree that this eliminates any side pull on the anchors whatsoever.

(The other wrinkle, interesting rather than problematic, is that having laid your first anchor (to the NW in the example above) you will initially be pulling it to one side as soon as the load begins to be taken by the second anchor.)

None of the above is an argument against using two anchors, it’s just an attempt to clarify the advantages and avoid erroneous assumptions.
 
Little Sister

To clarify one 'simple' point - you are not benefitting from both anchors taking the load, either one or the other takes, most of, the load. There is, or will be, some sharing but the yacht still veers. If you think of a, roughly, equilateral triangle then as the yacht moves from side to side the tension in one leg of the triangle will slacken and tension is then taken by the other leg. If the wind were constant (no shear) the yacht, and if it were aerodynamically stable, it would not move.

I did some testing measuring tension in the rode, (single rode, no snubber), at different scopes and different wind speeds. The primary focus was on tension and wind speed rather than scope - scope was accidental. Maximum tension and it is factorially greater than the average tension is when the yacht is toward the end of a veer (and at short scope its a bit like hitting a brick wall). If you are unprepared it would knock you over. I was recording snatch loads of 650kg in 35 knots of wind - and I stopped testing as the impacts were, scary.

But in between snatches the loads were simply not remarkable.

Veering can be caused by the aerodynamics of the yacht but it is commonly caused by wind shear. Go to an airport during strong winds and watch aircraft landing - they can land in a straight line - but the aircraft itself is constantly veering and the veer corrected by the autopilot. Your yacht enjoys the same shear and the 2 anchors are laid to accomodate that variation. You have the same effect when sailing, you get a lift (or not) - the average wind direction does not change but the wind direction does vary.

Because the wind direction varies your yacht sails and at the end of its tether, the rode, you get a snatch load.

So the wind is varying in direction.

The wind also varies in intensity - you have gusts (which in open water can be 40% stronger than the average, so maybe lulls 50% weaker). In a gust your yacht, at anchor, moves astern and the (kinetic) energy of the moving yacht is absorbed (transferred) to the catenary or snubber to (potential) energy - in the next lull that potential energy is transferred to the yacht and it moves forward.

The yacht is constantly moving, it sails and is moving back and forth and the tension in the rode is constantly varying

You can add another variable, horsing, due to waves, swell or chop.

Add these factors together and you get a snatch load (other times they cancel)

Back to anchoring in a 'V'.

As the yacht moves one of the rodes set in a 'V pattern take the maximum load in turn.

Because the anchors are set apart you would get one snatch load as each rode becomes the primary - and at that point the tension angle will be 'roughly' zero - and if it is not zero the anchor will swing so that it becomes zero (and will stay there unless the wind characteristics change).

Snatch loads are simply the maximum load as the yacht 'moves' and is brought up 'short' by the rode. They can be benign or catastrophic.

Does this help?

Jonathan
 
LittleSister said:
When lying exactly to the S, or to the E, the load will be taken on a single anchor, again in a straight line with it.
Click to expand...

Multiple anchors do have their uses, but as a means of increasing holding power they are not a great solution. The problem is sharing the load between the two anchors. If the full load is periodically on a single anchor, as you have correctly concluded, each anchor has to have enough holding power on its own. If it does not, the two anchors tend to alternately “walk” backwards.

At best it is a very inefficient system. You now have twice the weight in the anchors, but nothing like the holding power of a single anchor that is twice a big. The performance ratio is even worse if weight is added in the form of chain on the second anchor.

I do not have a concern with skippers who feel their boat is more comfortable with a second anchor, but if the motivation is a fear that sheering may upset your anchor and lead to dragging especially at a relatively modest 30 knots, then I think it is time to rethink the groundtackle. A very slight increase in the anchor size, or quality of the anchor design, will provide more security than faffing about deploying and retrieving multiple anchors. The weight will be much less and the ease of use will be greater.

The KISS approach of good single anchor is much better and easier than a couple of inadequate anchors, in my view. It also removes concern about tangles, conflict with other boats, and best of all, if the wind unexpectedly rises at night you won’t lay awake worrying if conditions have reached the stage where a second anchor should have been deployed. Priceless :).
 
Last edited:
Noelex,

I am fascinated - please show us the numbers.

Please provide any holding capacity data on your anchor. Even better - please provide independently verified data.

Please provide any evidence that doubling size doubles hold. This will be most applicable if of the design you favour (as different anchor do perform differently). A word of warning - there is no data of which I am aware (that stands scrutiny) that any anchor of any design will double hold by doubling weight)

Please provide the evidence that one anchor (weighing the sum of the 2 in a 'V') is better than 2 in a 'V' (you might like to read earlier posts in this thread, before you reply).

Looking forward in anticipation, but without any expectation, to your early reply on all points.


An analysis of the design of your anchor design gives it the hold of a similarly weighted Delta. My tests show it to be a bit better than a similarly weighted Delta but simply no-where near as good as a similarly weighted Rocna (so this explains your need to oversize - I hope others did the same). Related to the poor hold the setting distance of your anchor is excessive. This is what was posted on YBW some time ago, 25kg anchor - same design as yours.

'The Mantus sets in about 3m reverse, digs into any soft substrate and resets easily.'

He, of course, was not spruiking an anchor

Most modern anchors set in a shank length

Jonathan
 
I set two anchors in winds over about 30 knots as posted earlier. Either anchor alone is perfectly adequate to hold the boat in severe conditions. The difference in comfort aboard, and presumably stress on each anchor, is considerable. At almost no time is the load shared equally between the anchors: instead it oscillates from one to the other.
 
Noelex comments are interesting

From memory he has a yacht slightly smaller than 50' (aluminium) and uses a approx 50kg anchor and 10mm chain.

We have a 38' cat weighing at 7t (cruising weight) which has the windage of a 45' Bav (which I think weigh around 12t - maybe 13t cruising weight). We use 8kg aluminium anchors and 6mm chain.

Our anchors are said to be inadequate? Really??

There is a suggestion that Bigger is not Better, Better (design) is Better.

So returning to the thread

Do we need another anchor design? In my opinion if it leads to a better combination of design features offering better performance and/or the same performance at a lower price and/or the same performance at lower weight - yes we need it and should embrace it.

Jonathan
 
Neeves said:
Little Sister . . .

. . . Back to anchoring in a 'V'.

As the yacht moves one of the rodes set in a 'V pattern take the maximum load in turn.

Because the anchors are set apart you would get one snatch load as each rode becomes the primary - and at that point the tension angle will be 'roughly' zero - and if it is not zero the anchor will swing so that it becomes zero (and will stay there unless the wind characteristics change).

Snatch loads are simply the maximum load as the yacht 'moves' and is brought up 'short' by the rode. They can be benign or catastrophic.

Does this help?

Jonathan
Click to expand...

Yes, thanks. The info on loads, and the importance of snatch at the end of the yaw is very interesting and informative.

As per the 'V' arrangement, you have convinced me that:
- the load is on one anchor or the other much of the time, and so there is relatively little advantage in shared loads, but there probably is an advantage in each only receiving around half of the peak loads (e.g. c50% of 'end of yaw' snatches);
- I was correct in saying that the arrangement does not preclude a pull of the anchor to one side or the other; and
- as I agreed from the outset, it does very much reduce side loads on the anchor compared to a single anchor, and this is probably its main advantage.
 
You must log in or register to reply here.

Share this page

Top