Who is Richard Macfarlane? Here is his anchoring advice...

[RichMac]

I am the man in question, and I’m so glad to make people think about anchoring theory, and stir up some interesting discussions.
When I made my video, I never thought that over 300,000 people would watch it! But I guess everyone who has used an anchor has dragged at some stage, so it’s a popular subject. It’s also a subject lacking any serious science, more myths and legends backed up by personal experience.
My overriding theory of anchoring is this:- If you anchor on a wide range of seabed types, with whatever the weather gods throw at you, you will inevitably find conditions where anchoring is difficult. But it’s a percentage game.
If you use light, inadequate gear, you will always feel insecure with frequent anchoring dramas. Use the best possible anchor, oversize (is the extra 10kg that important?), and use the best techniques, and your anchoring problems will be very rare, or maybe never.

[jo_sail]

Hi Rich, thank you very much for the video!

In my opinion the anchor weight and a small angle to the seafloor not only provide for good holding in the first place. Moreover, they provide the best chance for automatic resetting of the anchor, should it start to come loose by an individual peak load event.

From the beginning of your story I learn that many boats started to drag with less than 25 knots. In normal conditions 25 knots should be no problem with „common anchoring practice“ as discussed here.

So the question is: What was special? You talk of swell and waves and I suspect that the forceful vertical jump of the bows lifted the light anchors, which would perfectly match my thinking on the anchoring physics and priority on wave shelter (see my first bullet point above).

Do you have any idea or record an the direction of waves relative to boats and land? Is it so that the anchoring boats lost their protection from the waves / swell and they started to drag, one after on, and certainly dependent on anchor holding and weight?

Cheers Jo

[Mr B]

I was in 6 metre waves and a full blown Gale with well over 40 knots of wind and an Autopilot that fell to bits, The screws fell out of it,
To fix it, It needed the wheel taken off,
Not that I was going to do that in a Gale,
I pulled in behind Gabo Island in Bass Strait on the East side to get out of the Gale coming from the West, ,

I dragged my 40 KG New Gen type hoop anchor around about six times and it just would not catch.,
I have no idea why, It has always worked before,
So I drifted across the Bay and changed my 40 KG anchor to my 24 KG anchor,
Went back and tried to get it too set in the same place,
It grabbed the first time and I stayed hooked in the same place for four days,
Till the gale blew over and I could leave,

I did have to lift the 24 KG anchor again the next day after I found it set well, and changed it to all chain, As I had dropped it with 16 mm Double Braid Polyester rope on it,
Polyester rope Is not good for anchoring as I didnt know what I was anchoring on,
The rope was chaffed on the anchor when I Pulled it up to change to the chain,
Its some sort of reef down there, Maybe rocks,
My 40 KG anchor was may be too big to get a hold between the rocks, Maybe it was weed, I just dont know, It just would not set,
The wind was still screaming even as I was hidden behind the island, And in about a one metre swell,
The 24 KG New Gen type hoop anchor set straight away with the chain on it as well,
So sometimes, Smaller is better for anchoring, It possibly got caught between the rocks,
But it was rock solid in holding, It took a while to get it free to lift it up again,
Both my anchors have a slot in them so I can pull them out backwards,
Im an overkill type for anchoring my Boat, I like to sleep soundly at night,
I am well and truly over dragging smallish anchors, So bigger is better for me,
And all chain rode, I put all I have out, 100 feet of it,

34 foot Cat,

Cheers, Brian,

[RichMac]

Originally Posted by jo_sail

Hi Rich, thank you very much for the video!

From the beginning of your story I learn that many boats started to drag with less than 25 knots. In normal conditions 25 knots should be no problem with „common anchoring practice“ as discussed here.

So the question is: What was special?
Cheers Jo

Hi Jo, there were a number of reasons so many yachts dragged that night. Kata Beach has a bad reputation, more to do with a casual attitude to anchoring, rather than the bay itself.

It’s a very hard sandy bottom, my CQR seemed ok, but pulled out with a hard pull. My Delta was great. If you don’t pull your anchor, you don’t find out!

The keen racing boats would have complied with the racing requirements, minimum size anchors and chain, only suitable for “normal” conditions.

Most of the racing yacht were unattended, their crews ashore after the fabulous parties. The cruising yachts generally had somebody aboard.

It wasn’t that rough offshore, but the waves were vicious in the bay, maybe focussed by its shape. I was in 6m and felt no jerking on the chain. The yachts closer to the beach were really affected by the surf. I always anchor in deeper water now!

Because of the regatta, everyone stayed in the bay, despite the wind turning to the wrong direction. It’s much safer when you are cruising, you can simply move to a safe anchorage to suit the weather.

[MathiasW]

Originally Posted by Chotu

Including the catenary is a mistake.

Catenary is at maximum with RELATIVELY no wind or current.

When you need the anchor to really work, the catenary is almost zero.

Which was the point!!!!

That simply is not true!

Catenary is always there, at least when there is no transient movement of the chain due to gusts or swell and you only view it as a static snap shot. All that happens is that the curve may not start with a horizontal pull at the anchor shank. But it still is a cosh() function...

There had been a very long discussion on this forum of the mathematics of anchor chains, how long do they really need to be, etc: https://www.cruisersforum.com/forums...pe-235053.html

Perhaps easier to read, but still lengthy, here is my analysis of the minimally required anchor chain length: https://trimaran-san.de/die-kettenku...atiker-ankert/ (also in English)

And, as suggested by the CF, I even created apps for Apple and Android, a description of which can be found here: https://trimaran-san.de/anchor-chain-calculator/

Bottom line: A chain works best in deep water. There it can develop a nice catenary that can absorb very large shock loads (gust and swell). In shallow water, the chain sucks. Even if I pay out an excessive amount of chain, it will be very poor at absorbing shock loads. The only solution then is to use excellent snubbers / bridles. The reason for this is simply that an almost horizontal chain (as is the case in very shallow water) cannot be raised much further, as it is limited by the straight connecting line anchor - bow roller. Thus, its ability to store additional potential energy is very poor.

For these reasons it may well be a better choice to anchor in slightly deeper water where the chain works better. Provided, one has enough chain, and swell is not much worse there.

And yes, water depth has to be always measured from the bow roller!

[MathiasW]

Originally Posted by Lodesman

What boatie said. The anchor and chain work together as a system - one really doesn't work without t'other. But if I had to choose, I'd take chain without the anchor - if I lay out enough it will do the job.

Only chain, without anchor, that would never stand up to a gale storm. Without an anchor, the only force holding the vessel would be the friction of the chain on the seabed, which is usually considerably less than its own weight. So, a gale force can mean a metric ton of wind force for a larger vessel. To hold this, the chain must then weight considerably more than one metric ton. And this for the part that is lying on the seabed, so the chain that is rising up to the vessel adds even more weight.

Clearly, nobody has that much chain in his chain locker!

[Lodesman]

Originally Posted by MathiasW

Only chain, without anchor, that would never stand up to a gale storm. Without an anchor, the only force holding the vessel would be the friction of the chain on the seabed, which is usually considerably less than its own weight. So, a gale force can mean a metric ton of wind force for a larger vessel. To hold this, the chain must then weight considerably more than one metric ton. And this for the part that is lying on the seabed, so the chain that is rising up to the vessel adds even more weight.

Clearly, nobody has that much chain in his chain locker!

It was a cheeky answer - an anchor that is not attached to the boat has zero holding capacity.

As I said (and maintain), chain and anchor work together in a system.
I think you underestimate the "friction" of the chain. When it works itself into the substrate it develops much more "hold" than weight alone. Numerous times I've anchored, and having experienced a large shift in wind/current direction, then witness the chain not re-orientate itself radially from the anchor - effectively being anchored by a section of the chain itself. Granted this was in moderate, not gale conditions, but it illustrates the point. The only time I've dragged was on an admittedly shorter-than-desired scope in marginal conditions - thin layer of sand over hard-pan in a strong reversing current. I didn't reset the anchor, I just paid out another 40 feet of chain, and we stopped dragging. Make of that what you will.

[MathiasW]

Originally Posted by Lodesman

It was a cheeky answer - an anchor that is not attached to the boat has zero holding capacity.

I thought so, , but then again, I have come across more than one person who actually believed that...

Originally Posted by Lodesman

As I said (and maintain), chain and anchor work together in a system.
I think you underestimate the "friction" of the chain. When it works itself into the substrate it develops much more "hold" than weight alone. Numerous times I've anchored, and having experienced a large shift in wind/current direction, then witness the chain not re-orientate itself radially from the anchor - effectively being anchored by a section of the chain itself. Granted this was in moderate, not gale conditions, but it illustrates the point. The only time I've dragged was on an admittedly shorter-than-desired scope in marginal conditions - thin layer of sand over hard-pan in a strong reversing current. I didn't reset the anchor, I just paid out another 40 feet of chain, and we stopped dragging. Make of that what you will.

If the chain digs into the seabed, then yes, its friction will increase quite substantially. But how many metres of chain will actually dig in, I wonder. It would all be the result of the anchor shaft having dug in deeply. I am happy to believe that this can make the chain dig in for a few metres, but not tens of metres. Even if the friction coefficient is much larger than 1, it will not amount to too much: a 10 mm chain weights 2 kp per metre under water. So, 5 metres mean 10 kp. If the coefficient is 5, then this is 50 kp. Enough to hold your boat in a breeze, but not for stronger winds.

There is an easy to do experiment to get clarity: Get a chain of 5 metres to the beach and place it in a trench in the sand then fill up the trench and tread on it. Then pull at one end and measure the force that is required to make it move.

The effect you describe I have often witnessed myself. But only in light winds, really. Remember, the wind force increases quadratically with the wind speed.

[longjonsilver]

Originally Posted by MathiasW

Perhaps easier to read, but still lengthy, here is my analysis of the minimally required anchor chain length: https://trimaran-san.de/die-kettenku...atiker-ankert/ (also in English)

And, as suggested by the CF, I even created apps for Apple and Android, a description of which can be found here: https://trimaran-san.de/anchor-chain-calculator/

Thanks MathiasW. Nice to see a quantitative approach. Reading now, and looking forward to getting the app

jon

[MathiasW]

Thank you Jon!

One of the highlights of my work is a better understanding of an anchor chain's elasticity.

By this I mean the following: If wind or swell pull (horizontally) a little more on the chain at the bow, say with 1 kp, how much *more* energy can the chain absorb? Obviously, you would want this value to be high. The enclosed graph is the elasticity of an anchor chain. Now, what does it mean?

Let's take a chain that is long enough so that there is still some chain on the seabed in front of the anchor. Within the framework of my model, you can then calculate the elasticity of the chain - see the attached diagram. On the left is calm, on the right is storm. The horizontal axis is scope, i.e. the ratio of chain length to water depth, whereby only the chain counts that is no longer in contact with the seabed. The vertical axis is elasticity divided by its peak value (which in turn is proportional to water depth).

So, there is an optimal working point for the chain! On either side of it its performance will degrade!

Perhaps this thought experiment will help you understand the graph better: I anchor at 5 metres, measured from the bow roller. There are 100 metres of chain paid out, but they are not being used yet, because there is almost no wind. I am now on the far left of the diagram. The elasticity of the chain is poor, but that doesn't matter because there is hardly any wind. Now the wind starts blowing stronger and stronger and we slowly move to the right in the diagram. When 1.4 x 5 = 7 metres of chain have been lifted from the bottom of the seabed, we are already at the maximum elasticity of the chain. Of course, this is still not a lot of wind - just 7 metres of chain are needed so that it still pulls horizontally at the anchor at a depth of 5 metres. So, now it's blowing more and more and we are moving further to the right, away from the maximum. When the 100 metres chain is completely off the ground, I have reached a scope 100 : 5 and thus the right edge of the graph. So what happens is that although we pay out more and more chain, the chain becomes less and less elastic. In other words, it is less and less able to absorb strong gusts or swells the higher the base wind is. Sure, it can absorb large static forces (provided the anchor still holds), but gusts and swell, no way. Consequently, you need a rather good snubber or bridle to absorb these peak loads. This effect is much more pronounced in shallow water than in deep water, and it is the reason why I tend to anchor in somewhat deeper water than others.

[jo_sail]

Hi Rich and Mathias,
in your post I see two very good arguments for going to the deper water.


1. The hight between bow and anchor adds elasticity to the chain by the potential energy needed to lift the chain (as long as the chain is not very streched all the time).

2. The surf can easily get more severe very close to the beach (if you have swell or waves coming in)


At the same time I get more and more convinced from Richs additional explanation of the situation (thanks!), that in the video indeed the increased surf and powerful vertical movements of the boats was the anchor "killing" issue.



Deeper water and additional elasticity from a nylon rope could then have been a promising attempt to get better holding in that bay and place, when no heavy anchor and chain was available on many boats in this situation.


But, as you said Rich, a more wave protected place would have been the safest option in that night, in order to prevent the powerful vertical movement in principle, and instead of trying to heal a very bad situation at this place during night.



Mathias, I perfectly agree, when it really counts, friction of chain on/in the ground is nearly nil. And it's not the normal conditions that we need to worry about but the level of peak loads on the snubber+chain+anchor+ground system.


Thanks for the exchange, Jo

[MathiasW]

Hi Jo, I think we are d'accord!

Cheers, Mathias

[jo_sail]

Originally Posted by MathiasW

Hi Jo, I think we are d'accord!



Cheers, Mathias

Looking at your App screenshots I wonder how you assess the swell enegy in Joule? Do you have an equation or estimation related to wave hight for this?

Cheers Jo

[MathiasW]

Originally Posted by jo_sail

Looking at your App screenshots I wonder how you assess the swell enegy in Joule? Do you have an equation or estimation related to wave hight for this?

Cheers Jo

No, relating this to wave heights proved too difficult. I decided to estimate the kinetic energy of the vessel that it acquires when a swell hits it. Only relevant for the anchor is the component of the kinetic energy that is pointing away from it. I estimate it by looking at the chart plotter and watch the Speed over Ground, SOG, vector. When it it maximum pointing away from the anchor position, that is the reading I use. In my case, this is usually something like 0.1 to 0.3 knots. (There is a risk of confusing swell effect with gust effect here.)

Using this velocity and the weight of the vessel, I know its kinetic energy.

In the app I usually go this route, but it is possible to enter the swell energy directly. But I rarely do that. It is mostly to be able to compare with other calculators, like the one from Bjarne.

Cheers, Mathias

[aqfishing]

So our new Moorings Leopard 40 has been sitting around waiting to be used for almost a year. It finally arrived in the Seychelles first week Jan. So we have a new yacht we have not yet seen as we cannot get to Seychelles.

This discussion prompted me to take a look at what anchors it was supplied with.

I was pleased to see it came with a 20kg Stainless steel DTX. Looking at the Lewmar website, I see it is one size over spec’d. Well done to Leopard and Moorings. Now I just need to get there and ensure that what was on the contract is what was supplied!