Big anchors

[Tranona]

How many do you want? Loads to choose from.

A contradiction with bigger anchors

That is not what you suggested. Nowhere does that say what you claim it says.

See the first sentence in post#153. Lessons in comprehension needed maybe?

 

[Tranona]

But drag they do, back out in the real world. Example above, 40m chain in 6m. Shuffle those feet again......

Will a bigger anchor help?

In case you have forgotten (or ever even known) this thread is about whether a bigger anchor is better.

See post #160. Anecdote and individual experience is of little value unless it is supported by data and analysis. Seem to remember that you are hot on collecting data for analysis.

 

[Neeves]

I recall Vyv reporting, in some detail, accidentally and by mistake, use of a small anchor at short scope. Its not only Dashew.

By definition our anchors are small - 8kg anchors the same size as the steel version of the same design and we have the windage of a Bav 45, we use them all the time and use them with lightweight chain. To us its totally unremarkable.

Jonathan

 

[thinwater]

We are all just a “guy on the internet”. Why should I believe any of the guys on the internet?

Because this is not a political forum?

 

[boomerangben]

There are some very interesting threads within this, well, thread. There is also some misunderstanding/misinterpretation/misreading/mistyping or simply struggling to say what is meant - and I am sure I am about to fail at some or all of the above.

Back to basics. Setting an anchor involves putting it on the seabed and pulling it in the direction that you intend to load it with forecast wind and current. In that process a load vector is placed on the shackle attachment and the interaction between the flukes and the seabed causes it to dig in. The amount by which it digs in is a function of the seabed structure, the anchor geometry and the load applied (angle, magnitude and to a certain extent acceleration). During the digging in, the soil structure causes friction that opposes the penetration of the fluke parallel to the surface of the fluke. It also provides resistance to motion perpendicular to the fluke. Once the anchor is set and there is a period of time without movement, the soil reconsolidates and grips the anchor better. The friction parallel to the flukes increases and the perpendicular force also changes but by perhaps a different proportion. So a set and consolidated anchor should hold more than the force used to set it, without any increase in setting force. A subsequent increase in rode load say by wind action will do one of three things: firstly the extra load is absorbed with in the soil structure and anchor remains set, secondly the perpendicular resistance is high and the anchor tends to slide deeper into the seabed (ie continues to set deeper) or thirdly the parallel friction is high enough to prevent sliding deeper and the soil around the anchor fails and it breaks out. This far I have assumed no yawing/swaying.

It is probable that a bigger anchor will set less deeply than a smaller anchor under the same load (less than ultimate holding of the smaller anchor for that seabed) therefore set more deeply or breakout under a higher load which might leave the smaller anchor stationary since the soil is gripping it more firmly. This is all fine when the seabed is clean sand and or mud. But when inconsistent seabed such as grass/weed/debris/hard pan to mention but a few more difficult seabeds we simply do not know whether we are going to achieve sufficient holding. Similarly since the setting force is governed by the limits of engine/sail/whatever other reactive force we do not know what our anchor will hold should the wind get up. It makes sense to use all available force to set an anchor if it’s going to blow. It makes further sense to set two anchors since you set each anchor to your maximum (say) engine load there by increasing your guaranteed holding capacity by up to 2 times depending on the geometry of your anchor spread.

In answer to the main question is over sizing your anchor is better, the answer is simply this: unless you know your seabed and tested it, no body knows. The really question that needs answering is can you sleep at night with your current anchor system. And the answer to that is highly subjective

 

[Tranona]

The really question that needs answering is can you sleep at night with your current anchor system. And the answer to that is highly subjective

Surely the purpose of gathering as much relevant data as you can related to you and your boat's situation is that it helps one make a more objective decision. Otherwise you are back to such vague statements as "bigger is better" or " have an anchor as big as you can handle" that get bandied around - along with the "sleep at night" assessment criterion.

BTW otherwise a clear and easy to follow description of the process of anchoring.

 

[thinwater]

There are some very interesting threads within this, well, thread. There is also some misunderstanding/misinterpretation/misreading/mistyping or simply struggling to say what is meant - and I am sure I am about to fail at some or all of the above.

Back to basics. Setting an anchor involves putting it on the seabed and pulling it in the direction that you intend to load it with forecast wind and current. In that process a load vector is placed on the shackle attachment and the interaction between the flukes and the seabed causes it to dig in. The amount by which it digs in is a function of the seabed structure, the anchor geometry and the load applied (angle, magnitude and to a certain extent acceleration). During the digging in, the soil structure causes friction that opposes the penetration of the fluke parallel to the surface of the fluke. It also provides resistance to motion perpendicular to the fluke. Once the anchor is set and there is a period of time without movement, the soil reconsolidates and grips the anchor better. The friction parallel to the flukes increases and the perpendicular force also changes but by perhaps a different proportion. So a set and consolidated anchor should hold more than the force used to set it, without any increase in setting force. A subsequent increase in rode load say by wind action will do one of three things: firstly the extra load is absorbed with in the soil structure and anchor remains set, secondly the perpendicular resistance is high and the anchor tends to slide deeper into the seabed (ie continues to set deeper) or thirdly the parallel friction is high enough to prevent sliding deeper and the soil around the anchor fails and it breaks out. This far I have assumed no yawing/swaying.

It is probable that a bigger anchor will set less deeply than a smaller anchor under the same load (less than ultimate holding of the smaller anchor for that seabed) therefore set more deeply or breakout under a higher load which might leave the smaller anchor stationary since the soil is gripping it more firmly. This is all fine when the seabed is clean sand and or mud. But when inconsistent seabed such as grass/weed/debris/hard pan to mention but a few more difficult seabeds we simply do not know whether we are going to achieve sufficient holding. Similarly since the setting force is governed by the limits of engine/sail/whatever other reactive force we do not know what our anchor will hold should the wind get up. It makes sense to use all available force to set an anchor if it’s going to blow. It makes further sense to set two anchors since you set each anchor to your maximum (say) engine load there by increasing your guaranteed holding capacity by up to 2 times depending on the geometry of your anchor spread.

In answer to the main question is over sizing your anchor is better, the answer is simply this: unless you know your seabed and tested it, no body knows. The really question that needs answering is can you sleep at night with your current anchor system. And the answer to that is highly subjective

Nicely written.

If using two anchors, you should assume that if the wind shifts, one anchor will take the full load. It will either drag until the load is shared enough to stop dragging, or it will hold. Without going into the trig, I think it is understood that the angle between the anchors and the relative lengths of the rodes impact this math. Many different situations. But the main impact of using two anchors is less about increasing holding than ...

• Eliminating yawing and/or the need for resetting.
• Buffering dragging of one anchor.

 

[boomerangben]

Surely the purpose of gathering as much relevant data as you can related to you and your boat's situation is that it helps one make a more objective decision. Otherwise you are back to such vague statements as "bigger is better" or " have an anchor as big as you can handle" that get bandied around - along with the "sleep at night" assessment criterion.

BTW otherwise a clear and easy to follow description of the process of anchoring.

I agree that gathering data is key and being objective is the best way to secure a good nights sleep. It would be an interesting exercise to test the hypothesis that started this off

 

[srm]

What is wrong with using regular sound night's sleep as the criteria for successful anchoring?

In around 50 years of owning cruising yachts and many nights of coastal cruising I have only had one serious dragging episode; with a catamaran so no harm done and I was able to pull her off the beach on the next tide. In retrospect this was my fault, not the anchors. I was the only boat in a shallow sheltered pool that normally had a clean sandy bottom. I noticed that the bottom had a covering of dead weed but still anchored, single handed in strong winds. The weed was deeper than expected, clogged the anchor and I was aground before getting the boat back under control.

Otherwise my use of an oversized anchor on all chain rode has allowed many blissful nights in northern waters being lulled to sleep by the wind in the rigging and natural movement of the boat. Though a shore line has been regularly used for security in Scandinavian waters and a few Scottish anchorages.

 

[thinwater]

What is wrong with using regular sound night's sleep as the criteria for successful anchoring?

In around 50 years of owning cruising yachts and many nights of coastal cruising I have only had one serious dragging episode; with a catamaran so no harm done and I was able to pull her off the beach on the next tide. In retrospect this was my fault, not the anchors. I was the only boat in a shallow sheltered pool that normally had a clean sandy bottom. I noticed that the bottom had a covering of dead weed but still anchored, single handed in strong winds. The weed was deeper than expected, clogged the anchor and I was aground before getting the boat back under control.

Otherwise my use of an oversized anchor on all chain rode has allowed many blissful nights in northern waters being lulled to sleep by the wind in the rigging and natural movement of the boat. Though a shore line has been regularly used for security in Scandinavian waters and a few Scottish anchorages.

Oh no. An exception that will restart the debate!

The anchor was oversized and dragged anyway, because the sand was covered with debris. The dead weed was probably, in fcat, something that had blown in from a storm. I had friends that lost a sister cat to mine when a good sand bottom had become covered with palm fronds and weed in the wake of a tropical storm. Unfortunately, they dragged into a stone breakwater.

A good night's sleep is a poor measure of safety vs. risk, because fear is not a good measure of actually danger. People scream in scary movies because of something in their head, and die in the mountains because they don't recognize actual danger. YouTube is full of them.

In someways, a poor memory and the ability to switch gears is vital to enjoying cruising. The ability to forget past discomforts and put risks (after evaluation) in a box that we lock away.

 

[srm]

I have found a method that has worked for me and the boats that I chose to sail. Perhaps lighter anchors would have been just as effective. I don't know, but as much of my sailing was north of 60 N I would be inclined to continue with what I know has worked in sustained winds of up to 85 knots. But then I started sailing long before anchor testing, spreadsheets, youtube, etc, and had to make my own judgements of risk with little real data.

I do remember seeing an ocean data buoy being assembled on the pier and commenting that it would not last long with that anchoring system. The reply was that the computer said this was what it needed. A month or so later the buoy was washed up on the west coast of Shetland.

 

[geem]

I have found a method that has worked for me and the boats that I chose to sail. Perhaps lighter anchors would have been just as effective. I don't know, but as much of my sailing was north of 60 N I would be inclined to continue with what I know has worked in sustained winds of up to 85 knots.

You can only say you survived. You can't attribute it to a big anchor. You give no detail
I met a guy who survived a hurricane because his anchor hooked an underwater power cable. Doesn't he attribute that to a good anchor?

 

[Tranona]

Those of you who have worked in large organisations have probably been exposed to the work of Fred Herzberg on designing jobs and working environments to motivate employees although you probably did not know his name. He was arguably the most influential person on the subject in the mid 20th century and his ideas are still in use today.

As an experimental psychologist he derived his methods from a huge amount of empirical work with individuals and organisations, but still many questioned how he knew it worked. His answer was that he had a horseshoe over the door to his office. That is even after you have data and evidence there is still an element of belief needed.

 

[RunAgroundHard]

Oh dear! Faith versus fact. The dichotomy of mankind.

 

[Tranona]

Indeed. His point was that even if you had the data he had collected as a basis for his methods it was still about human behaviour so an element of belief was always there.

Not suggesting anchors are human, but the act of anchoring because of all the variables, unknowns and involvement of humans it has similar characteristics.

The debate here I think is whether the availability of more data reduce the level of "belief" required.

 

[Supertramp]

I have found a method that has worked for me and the boats that I chose to sail. Perhaps lighter anchors would have been just as effective. I don't know, but as much of my sailing was north of 60 N I would be inclined to continue with what I know has worked in sustained winds of up to 85 knots. But then I started sailing long before anchor testing, spreadsheets, youtube, etc, and had to make my own judgements of risk with little real data.

I do remember seeing an ocean data buoy being assembled on the pier and commenting that it would not last long with that anchoring system. The reply was that the computer said this was what it needed. A month or so later the buoy was washed up on the west coast of Shetland.

Well put. Perhaps it's the experiences of those who have repeated difficulties with anchoring that are of more use? Although it is always difficult to disentangle equipment, technique and fortune. A large anchor and plenty of rode are my experience to which I have added bridles and a range of anchor types.

It always makes me smile when reading anchor threads to remember the old inshore fishing boats riding out gales in the Hebrides by heaving out a large fisherman's anchor, a pile of heavy chain and often rafting up before retiring for a sleep. And then departing in 8 or 12 hours when the wind was down to 6 or so. No computers or calculations there but a heft of experience.

 

[Tranona]

Well put. Perhaps it's the experiences of those who have repeated difficulties with anchoring that are of more use? Although it is always difficult to disentangle equipment, technique and fortune. A large anchor and plenty of rode are my experience to which I have added bridles and a range of anchor types.

It always makes me smile when reading anchor threads to remember the old inshore fishing boats riding out gales in the Hebrides by heaving out a large fisherman's anchor, a pile of heavy chain and often rafting up before retiring for a sleep. And then departing in 8 or 12 hours when the wind was down to 6 or so. No computers or calculations there but a heft of experience.

Maybe something to do with lack of alternatives. Or the alternative was a rock with a bit of wood lashed to it. Fisherman's anchor and chain were at one time state of the art and no doubt resisted by some until they died out.

Every generation experiences this transition when the "Tried and Tested" is challenged and new norms emerge! In anchors for yachts we are maybe in the middle of one of those transition periods.

 

[NormanS]

Well put. Perhaps it's the experiences of those who have repeated difficulties with anchoring that are of more use? Although it is always difficult to disentangle equipment, technique and fortune. A large anchor and plenty of rode are my experience to which I have added bridles and a range of anchor types.

It always makes me smile when reading anchor threads to remember the old inshore fishing boats riding out gales in the Hebrides by heaving out a large fisherman's anchor, a pile of heavy chain and often rafting up before retiring for a sleep. And then departing in 8 or 12 hours when the wind was down to 6 or so. No computers or calculations there but a heft of experience.

I well remember a three day gale 50 years ago, in Canna, when lots of the ringnetters were sheltering. Some of them would raft up in threes, and then would slowly drag right across the bay. This was repeated regularly. I've no idea what they used for anchors, but I do know that on one occasion they fouled my second anchor, breaking the mostly rope rode, and costing me an anchor. Canna is notoriously bad for weed, although with a fishfinder, clear patches can be found. That of course is just one of the many situations where technique, anchor design, and/or local knowledge is far more useful than a whole book of nebulous "data".

 

[Supertramp]

I well remember a three day gale 50 years ago, in Canna, when lots of the ringnetters were sheltering. Some of them would raft up in threes, and then would slowly drag right across the bay. This was repeated regularly. I've no idea what they used for anchors, but I do know that on one occasion they fouled my second anchor, breaking the mostly rope rode, and costing me an anchor. Canna is notoriously bad for weed, although with a fishfinder, clear patches can be found. That of course is just one of the many situations where technique, anchor design, and/or local knowledge is far more useful than a whole book of nebulous "data".

I was probably there! We used to go right up the bay in shallow water, sometimes touching at LW where there was less weed. We had lots of dragging anchors especially in the Outer isles mainly from weed, but we did use a Danforth....

 

[RunAgroundHard]

I well remember … that on one occasion they fouled my second anchor, breaking the mostly rope rode, and costing me an anchor. … with a fishfinder, clear patches can be found. … technique, anchor design, and/or local knowledge is far more useful than a whole book of nebulous "data".

Did you curse them and shake your fist at them, damning their tardiness and your misfortune?

How can you live with yourself, using data to make a decision.