Anchor rode dimension.

[thinwater]

Originally Posted by Tonny9

Once again, thanks for the response.

And in must apologize once again that I have been cluttered tremendously around the anchor sizes.
The Right thing is what I started the thread with.
And I can even say that it is because I was spinning between kilo grams and pounds, that English is not my mother tongue…


NOTE:
And sorry, I typed incorrectly earlier in the thread. The Fortress anchor is FX16 and Mantus 15 kg (35 ib).

And for being bi-lingual, you are doing great.


US engineers are brought up on two systems. A typical exam alternates between SI units and what we call, traditional units. Language, not so much.

[Tonny9]

Thanks.


In general, I am probably more interested in anchoring and anchoring technique than the average of sailors here in DK.


And In general, I would say that people have become better at anchoring here in Denmark, but there was also room for improvement.
I would think that this is one of the advantages of the Internet.
It has become much easier to share experiences.

But I can remember many episodes where people simply do not have the basic knowledge, or just “fair”anchorequipment.

But there are still many misunderstandings about anchor types.
Here in DK, most sailors call each plate anchor for a Danforth anchor and any claw anchor for Bruce.

You also got my curiosity.
I just ordered your book from Amazon.

[noelex 77]

Originally Posted by thinwater

Soil around the anchor becomes disturbed and even liquefied, and hold capacity plummets

Yawing will increase the aerodynamic drag so the force will rise. This has a detrimental effect, but I am not convinced by the argument that the anchor is significantly stressed by not just the increase in force, but also by the change in chain angle.

Yawing gives the impression that the chain angle at the anchor has changed significantly, but in reality the change in angle is only slight. Below is a good example. You can see the boat has yawed over 40° and the impression from the bow is that the anchor is subject to considerable side force. The chain angle to the boat will be significant, but the actual angle to the anchor is zero in this example.

If you have a GPS that takes into account heading you will find that the sideways movement at the bow rather than the stern (where GPS aerials are usually located) is not that significant. The very slight alteration in chain angle produced by yawing is dwarfed by the more significant changes in actual wind direction that typically occur in strong winds.

The other factor is reasonable sized anchors only rotate very slowly. Even with a chain angle of 90° the anchor will only very slowly shuffle to the new orientation. If the force is lower the anchor will not move at all. See the photo of my Mantus below. The chain angle is caused by a windshift rather than yawing.

So take steps to reduce yawing, as it will reduce the load on anchor, but don’t be concerned that your anchor is swinging from side to side.

Originally Posted by thinwater

Don't forget the industry standards already include very conservative safety factors.

I am not convinced this is the case with respect to anchor sizing. When the wind picks up, especially in very strong wind, a frighteningly large portion of boats start to drag. I have seen this on many occasions. Some of these are due to poor technique (not enough scope for example) but a worrying and significant percentage have done nothing fundamentally wrong. Their anchor just cannot cope with the conditions.

[Training Wheels]

Originally Posted by Tonny9

Then the decision is made.
The boat is a sailboat of 28 ft and weighs approx. 6200 ib, with a normal windtrap for this size boat.


The appeal system is intended as a storm anchor system for use in Denmark/Scandinavia and with an expected wind strength of maximum 30 meters per second (approx. 60 knots).

It is based on the assumption that it is possible to anchor in relatively protecting water in relation to the waves, that the bottom will consist of sand, mud and a combination of the two and there will in many cases also be sea grass on the bottom.
There is not winless on the boat (which has great significance for my choices).

I have never experienced chafe on the bottom as a problem, but it is after all under more normal conditions in have the experience, so it is quite clear that it is the "weak link" in my anchor system. I have so relatively little chain, but I must be able to handle it without windless, so it must be.
A typical depth to anchor on will be 3 – 5 meters.
So I cannot expect much catenary from the anchor chain, not at all, when it also has to be kept at a minimum weight for the sake of handling without windlass.

I have several options of anchors.
The two that will be relevant in stormy weather is a Fortress FX37 and a Mantus 20 kg.

They will be connected to the following:
1. 10 meters, 10 mm chain, titanium Grade 43
2. The shackle between the anchor and chain, Green pin shackle, pin 13 mm
3. The Shackle between chain and Nylon rope, green pin shackle, pin 13 mm and green pin shackle, pin 16.
4. 35 meters 16 mm Nylon rode with 2 meters chafe protector on the rope (at the chain).
5. The shackle between the nylon robe and the Bridle, is Green Pin, 12 mm.
6. 15 meters Bridle, 16 mm polyester rope, with the possibility to mount Rubber shock absorber on the rope.2 PCs,chafe protector mounted on the rope itself and 2PCs in the vessels at the end of the train.

I would have preferred 15 meters 8 mm chain,Hi tensile, but chose 10 meters 10 mm chain to be able to use stronger (larger) shackles.

Since I donothave winless (and therefore can only handle a limited chain length) and also have to expect anchors on relatively lowdepths, the effect of catenary will disappear as the wind increases. I am therefore depend on the stretch elsewhere in the anchor system. Therefore, I use 35 meters of Nylon robe to give this stretch. Since the diameter is relatively large on this robe I do not suppose that there will be too much stretch in the system.
The relatively large diameter of the ropes is chosen, so there is "space" for any chafe filing on the rope, without it being fatally immediately.

It is quite proven that it is oversized in relation to the boat, someone will probably say too much.


To reduce chafe filing on the rope that is fastened on the boat, 3. Part of the anchor rope is Polyester robe, which is given itself less and therefore is not so predisposed to become chafe fillet as a similar Nylon robe would be.

There is nothing that has not been thought about and I would like to justify my choice. I also fully respect if others believe that it is a bad choice, or at least a choice that they would not have made Thems elves.

It is always interesting what others have of input.

And then you must apologize with my English, but I think it is better with me in poor English than "you" in poor Danish.

Where did you get your titanium chain?

[thinwater]

Originally Posted by noelex 77

Yawing will increase the aerodynamic drag so the force will rise. This has a detrimental effect, but I am not convinced by the argument that the anchor is significantly stressed by not just the increase in force, but also by the change in chain angle.

Yawing gives the impression that the chain angle at the anchor has changed significantly, but in reality the change in angle is only slight. Below is a good example. You can see the boat has yawed over 40° and the impression from the bow is that the anchor is subject to considerable side force. The chain angle to the boat will be significant, but the actual angle to the anchor is zero in this example.

If you have a GPS that takes into account heading you will find that the sideways movement at the bow rather than the stern (where GPS aerials are usually located) is not that significant. The very slight alteration in chain angle produced by yawing is dwarfed by the more significant changes in actual wind direction that typically occur in strong winds.

The other factor is reasonable sized anchors only rotate very slowly. Even with a chain angle of 90° the anchor will only very slowly shuffle to the new orientation. If the force is lower the anchor will not move at all. See the photo of my Mantus below. The chain angle is caused by a windshift rather than yawing.

So take steps to reduce yawing, as it will reduce the load on anchor, but don’t be concerned that your anchor is swinging from side to side.




I am not convinced this is the case with respect to anchor sizing. When the wind picks up, especially in very strong wind, a frighteningly large portion of boats start to drag. I have seen this on many occasions. Some of these are due to poor technique (not enough scope for example) but a worrying and significant percentage have done nothing fundamentally wrong. Their anchor just cannot cope with the conditions.

Good points.


If you are using heavy chain (which I mentioned) that has a considerable damping effect on anchor rotation. The chain does not easily come around. The OP, on the other hand, was not using much chain. Thus, your experiences and his will be quite different. Me, I've used both rope and chain, and I've sailed an anchor out MANY times when yawing with rope. Most were during testing, but not all.

The rotation effect only happens when the anchor is strained hard. You won't observe this diving in fair to moderate weather. In your picture, the anchor was barely buried with most of the roll bar exposed, indicating light-moderate conditions. The chain was still on the bottom. I would not expect rotation in these conditions, and thus the example photos are not relevant. Nice pictures, but the conditions are too light. Any good anchor would stick.



I should also add that I am not guessing. I have run these tests, repeatedly, with several anchor types (including Mantus), with load cells. Good anchors resist that initial rotation, in part because the wide shank serves as a large vertical fluke. But once the rotation has started, the soil around the shank is all tilled up and it doesn't take much to keep them walking.

All of this depends on how "active" the boat is and the relative sizing of the anchor. It doesn't always happen. But if a boat drags due to yawing, anchor rotation is why.

[Tonny9]

Sorry….
It is not made of titanium.
It is just a galvanized chain

But here's a link to where I bought it anyway.

https://jimmygreen.com/titan-grade-4...d-anchor-chain

[noelex 77]

Originally Posted by thinwater

if a boat drags due to yawing, anchor rotation is why.

I think we will have to agree to disagree. The dragging when yawining is due to the 50-100% increase in force that you yourself have reported. This increase in force is due to higher aerodynamic drag when the boat is not pointing directly into the wind, combined with the fact that the boat will tend yaw when hit by the larger gusts so the yawing coincides with the stronger wind. I don’t think the anchor rotation is a factor.

I do agree that any anchor that is moving when the boat yaws and the peak loads are applied is a very bad sign. Good anchor designs that are large enough and are set appropriately should not move at all other than to bury deeper if the peak load increases above the previous maximium level or the wind shifts significantly in direction. Anchors that are at their maximium limits and are struggling to hold will twitch and move, often slowly moving backwards as the peak loads are applied without burying deeper. This is often followed by breaking out completely and the rapid drag many are familiar with.

You can see this in some of my underwater photos as puffs of sand (see the photo below of the Ultra which is twitching and slowly moving backwards). If you see this behaviour it is a sign that your anchor is seriously struggling. It is not normal behaviour with yawing.

I have dived many times on anchors in very strong wind. I have also watched many anchors rotate around so I am also not guessing.

Anyway, keep up the good research. It is great to see some figures even if we sometimes disagree on the interpretation.

[Pete7]

Why not fit a rope windlass?

Even in moderate wind or a tide running I use the manual windlass which takes the strain out of pulling in the anchor. If its flat calm then the load is quite light and pulled by hand, but a couple of knots of tide or 15 knots of wind makes quite a difference.

Whilst I kind of understand the need to plan for 60 knots of wind, it doesn't happen often and its certainly well forecast in Northern Europe, unlike some areas of the med.

Pete

[thinwater]

We may not so much disagree as have different experience. The sand you show, for example, is loose coral sand, which reacts very differently to stress than firm mud or fine mineral sand. It is often underlain by hardpan or much firmer substrate, frustrating deep burying. Around here, a well buried anchor does not show a rollbar, and Fortress anchors can be more than 3 feet into the mud after a storm. Coral sand has lower holding capacity and is quite prone to dragging of undersized anchors. Very different.

In contrast, I've recorded over 500 pounds with a 2-pound anchor in local fine sand, and about 350 pounds for a variety of 45-pound NG anchors in local soft mud. How could you expect any behavior to be universal? You can't. The best you can do is observe trends.


What is clear is that yawing really tests anchors. I hate anchoring near boats that swing excessively. I can't sleep if my boat is yawing more than 40 degrees or so (not counting periodic wind shifts); I have to fix it. That was the message to the OP and the group.

[billknny]

Originally Posted by thinwater

Don't forget the industry standards already include very conservative safety factors.

I guess it depends on which "industry standards" you are talking about, but by way of counter-example, I would point to the table that Ronca publishes for sizing their anchors.

They are very clear that it is based on a wind speed of 50 knots. That might be good for a weekend cruiser, but for someone who mostly lives on anchor in remote locations, I would argue that that is grossly insufficient and not at all conservative. Most thunderstorm and front lines will have winds stronger than this.

In the case of this "industry standard" I can not call it "very conservative" at all. The manufacturer gives no real guidance for what size anchor you should have for stronger than 50 knots of wind.

Now I DO understand that these numbers are more than a bit "squishy" and they might be "very conservative" with the 50 knot rating, but I need ground tackle that the manufacturer is comfortable with recommending for winds higher than that.

The alternative for most people is to use the table and hope the wind stays below 50 knots, or to just pick a bigger than recommended size, based on gut. Neither is a great solution...

[thinwater]

Originally Posted by billknny

I guess it depends on which "industry standards" you are talking about, but by way of counter-example, I would point to the table that Ronca publishes for sizing their anchors.

They are very clear that it is based on a wind speed of 50 knots. That might be good for a weekend cruiser, but for someone who mostly lives on anchor in remote locations, I would argue that that is grossly insufficient and not at all conservative. Most thunderstorm and front lines will have winds stronger than this.

In the case of this "industry standard" I can not call it "very conservative" at all. The manufacturer gives no real guidance for what size anchor you should have for stronger than 50 knots of wind.

Now I DO understand that these numbers are more than a bit "squishy" and they might be "very conservative" with the 50 knot rating, but I need ground tackle that the manufacturer is comfortable with recommending for winds higher than that.

The alternative for most people is to use the table and hope the wind stays below 50 knots, or to just pick a bigger than recommended size, based on gut. Neither is a great solution...

In the default US industry standard for rodes and deck hardware (what I was talking about--anchors and holding ground are way too complex to make such statements) is ABYC H-40. The numbers have been well proven over decades. Many manufacturers quote them, often without citation. Mantus and Fortress have H-40 table 1 on their web sites.

[noelex 77]

Originally Posted by billknny

They are very clear that it is based on a wind speed of 50 knots. That might be good for a weekend cruiser, but for someone who mostly lives on anchor in remote locations, I would argue that that is grossly insufficient and not at all conservative. Most thunderstorm and front lines will have winds stronger than this.

+1.

For example the forecast here for tomorrow is gale 8 to storm 10 with gusts predicted to 58 knots at the nearest town.

Many anchor manufacturers, even respected brands such Fortress, only produce tables assuming 30 knots of wind, which is way too low in my view. Rocna’s table is based on 50 knots, which is better, but winds stronger than this are likely to be encountered if you anchor often.

Anchor tables are not conservative.

[thinwater]

Originally Posted by noelex 77

+1.

For example the forecast here for tomorrow is gale 8 to storm 10 with gusts predicted to 58 knots at the nearest town.

Many anchor manufacturers, even respected brands such Fortress, only produce tables assuming 30 knots of wind, which is way too low in my view. Rocna’s table is based on 50 knots, which is better, but winds stronger than this are likely to be encountered if you anchor often.

Anchor tables are not conservative.

There are two rules of thumb that may help.


Wind force ~ V^2.
Holding capacity ~ anchor weight. This can vary depending on the substrate, with an exponent 0.8-0.9 for sand and mud, and an exponent possibly greater than 1 if the bottom is hard to penetrate.



But yeah, 50 knots aint' much and 30 knots is just getting started.

[billknny]

Originally Posted by thinwater

There are two rules of thumb that may help.


Wind force ~ V^2.
Holding capacity ~ anchor weight. This can vary depending on the substrate, with an exponent 0.8-0.9 for sand and mud, and an exponent possibly greater than 1 if the bottom is hard to penetrate.



But yeah, 50 knots aint' much and 30 knots is just getting started.

This might be the marine equivalent of "how many angels..." but for anchors of the same design, might not a better "rule" be

holding capacity~surface area

It's not a huge difference, but surface area does rise a bit slower than weight.

[Tonny9]

Originally Posted by Pete7

Why not fit a rope windlass?

Even in moderate wind or a tide running I use the manual windlass which takes the strain out of pulling in the anchor. If its flat calm then the load is quite light and pulled by hand, but a couple of knots of tide or 15 knots of wind makes quite a difference.

Whilst I kind of understand the need to plan for 60 knots of wind, it doesn't happen often and its certainly well forecast in Northern Europe, unlike some areas of the med.

Pete

I have considered a windlass only for rode.

But to normal conditions, it works very well with my wife sailing the boat towards the anchor while I take the anker rode in.
I should probably also say that our normal anchor gear is not very difficult to handle.

So, I didn't really think we need it, even though we anchor far more than we are in port.
But I never have to say never.

What I am talking about here is an anchor for extreme situations and it may be used once a year. Some years maybe not at all.
The few times it should be used I can live with that it is a little more troublesome.

You are right that at our latitudes a storm will almost always be advised in good time.
It will probably also get most to hurry in port and I will probably do that if I am near my home port.
If I am not, I would much rather find a protect area and anchor.

Here we are also a little better off than many other places, for the wind direction and the movement is almost known beforehand and typically there is no big wind shift. The wind will typically come from a western direction and turn clockwise while the low pressure passes, but of course, no rule without exceptions.