Mantus rode

[thinwater]

Originally Posted by transmitterdan

...An artist is not a magician. Their skill comes with training and practice, practice, practice.

I used that word to stir things up. In fact, my father is a professional artist and he always, repeatedly, emphasized the importance of work, practice, and learned skill. He taught me much of the skill that goes into painting, so I do know the difference, first hand. I also recognize that he feels something about painting that I never will. There is some magic too. The same can be said of conceptual engineering.



[This is 20 years ago, but at 94 he still paints daily and sells his work. And he will tell you that painting is 90% learned, practiced skill.]

[thinwater]

Originally Posted by Dockhead

Certainly the behavior of anchors at higher angulation depends on the design. It would be really interesting if someone would actually test this....

Some have. I published some of the results in Practical Sailor and some in my book.


a. Really, only pivoting fluke (Fortress etc.) resist uplift well. The obvious corollary is that it is difficult to recover a deeply set Fortress. You can't have easy recovery and good short scope performance. Obvious?



b. Many anchors "seem" to do well at short scope because they set fast, they are over sized (right size?), and because the chain keeps the angle low. And there is nothing wrong with that. It works, so long as you keep the chain down. Most of us don't really want true short scope performance (see a); too hard to raise anchor.



c. A few manufactures have claimed "100% holding at X scope." Press them, and they explain that they rated capacity at that scope, so it is actually a definition, not an advantage.


d. The bottom type is another factor. Is the soil cohesive?



The same truths hold for ship anchors, and the fall off with scope is similar. If the rode is straight at 5:1 you have lost 2/3 of your holding capacity. Neat.

[evm1024]

I bought your book. I'm reading it now. Not to that chapter yet...

A worthwhile addition to the anchor locker.

[Dockhead]

Originally Posted by thinwater

Some have. I published some of the results in Practical Sailor and some in my book.


a. Really, only pivoting fluke (Fortress etc.) resist uplift well. The obvious corollary is that it is difficult to recover a deeply set Fortress. You can't have easy recovery and good short scope performance. Obvious?



b. Many anchors "seem" to do well at short scope because they set fast, they are over sized (right size?), and because the chain keeps the angle low. And there is nothing wrong with that. It works, so long as you keep the chain down. Most of us don't really want true short scope performance (see a); too hard to raise anchor.



c. A few manufactures have claimed "100% holding at X scope." Press them, and they explain that they rated capacity at that scope, so it is actually a definition, not an advantage.


d. The bottom type is another factor. Is the soil cohesive?



The same truths hold for ship anchors, and the fall off with scope is similar. If the rode is straight at 5:1 you have lost 2/3 of your holding capacity. Neat.

I don't understand how you're reading that table.


5:1 is 11.54 degrees. In "shingle/sand" that's approximately 4 units, compared to about 6 2/3 at 0 degrees. That's a loss of 2 2/3 units, which is about 40%, nothing like 2/3. And compared to 10:1 scope, which is 5.74 degrees, or maybe 5 1/3 units of holding, it's a loss of only 1 1/3 which is only 20%.


I think the proportions are the same for "clay".


Or am I reading something wrong?

[thinwater]

Originally Posted by Dockhead

I don't understand how you're reading that table.

5:1 is 11.54 degrees. In "shingle/sand" that's approximately 4 units, compared to about 6 2/3 at 0 degrees. That's a loss of 2 2/3 units, which is about 40%, nothing like 2/3. And compared to 10:1 scope, which is 5.74 degrees, or maybe 5 1/3 units of holding, it's a loss of only 1 1/3 which is only 20%.

I think the proportions are the same for "clay".

Or am I reading something wrong?

My mistake entirely. 5:1 is 11.54 degrees and 40% is correct, which is actually the number I had in my head. You are correct and I was in too much of a hurry.

The proportions are the same in this graph, but there is generally some variability, though as you see, not that much. More interesting, to me, is that from 2 pounds to 10,000 pounds, and from design to design, the curve has a similar shape.

Notice in the graph, below, that the HUGE stockless anchor is right in the middle of much smaller NG anchors, which were mostly 35-45 pounds. There were two trials with 2-pounds anchors that fell in line with their larger cousins.

Also remember that this testing was intentionally done with polyester and Dyneema rode. Chain will change the angle for the better. In most cases, the chain will never leave the bottom ( zero angle).

(The brands were intentionally left off for 2 reasons. I wanted to focus on the point that only pivoting fluke anchors really hold at short scope, and because there is ALWAYS a lot of scatter in anchoring data in mud. In other words, I could not be sure of some of the differences and it seemed unfair to publish data that could be wrong. You can try to guess if you want, but I won't tell.)