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post #511 of 535 Old 05-18-2019
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Re: Not Getting the All-Chain Thing

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Originally Posted by pdqaltair View Post
If I post everything that I have published, the publishers will shoot me. However, a few are useful for learning. (This, along with more, is in Practical Sailor, Nov 2017, and in Rigging Modern Anchors, below).

The brands are not listed because the scatter in the data was so great that the information might unfairly prejudice the reader. It was off the point. The pivoting fluke anchor was Fortress. Also note that the Claw was the only other design that continued to function at very short scope. Also remember that these figures were normalized to equal holding at long scope; the claw does not hold nearly as much at a given weight, and the Fortress holds a great deal more. Finally, notice that the multi-ton stockless design has a similar change with scope. I found that very interesting.

We also tested in fine sand. The curves were a little different, but the pattern was the same.

I thought this would get more feedback.

One more bit of data. The Northill curve is between the scoop and the Fortress curves; it withstands uplift reasonably well, and as a result, can be harder to recover from a good bottom. But nobody uses Northill anymore.

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post #512 of 535 Old 05-18-2019
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Re: Not Getting the All-Chain Thing

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Originally Posted by pdqaltair View Post
I thought this would get more feedback......
If you insist.

The chart seems confusing. The Y axis is defined as the percent of ultimate holding capacity, but how does one know what ultimate holding capacity is for each anchor represented.

Further, doesn't that homogenize varying holding capacities. Just because one anchor type falls off the curve faster, doesn't make clear whether it's remain holding capacity may still be greater than another that started with less capacity and lost less. I'm not saying that's true, but I found the chart less than clear.


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post #513 of 535 Old 05-18-2019
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Re: Not Getting the All-Chain Thing

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Originally Posted by pdqaltair View Post
I thought this would get more feedback.
If you insist

Let me understand lead angle. Is this the angle of the rode on a straight line from the end of the anchor to the bow roller measured against horizontal?

If it is then as I have alluded to in earlier posts, it would be a very severe condition a sailor using any amount of chain finds himself in where all of the rode is lifted off the sea bed. And until that condition occurs the lead angle at the anchor is zero because the chain is pulling horizontally. The start of the lead angle would be the point where the chain leaves the ground and not the end of the anchor.

Yes, I know that test results can’t be tailored to my specific sailing habits or conditions but my habits/conditions are similar to many thousands of sailors, at least they were when I still bothered to read sailing magazines. For me, test results that are based on extremes are less valuable.
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Re: Not Getting the All-Chain Thing

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Originally Posted by Minnewaska View Post
If you insist.

The chart seems confusing. The Y axis is defined as the percent of ultimate holding capacity, but how does one know what ultimate holding capacity is for each anchor represented.

Further, doesn't that homogenize varying holding capacities. Just because one anchor type falls off the curve faster, doesn't make clear whether it's remain holding capacity may still be greater than another that started with less capacity and lost less. I'm not saying that's true, but I found the chart less than clear.
Exactly. You would have to go to a different chart to get baseline holding capacity for each anchor, and there you would learn that the baseline value for each anchor varies with the bottom type, and every test program comes up with different values. It's like herding cats. In fact, most of the scoop types are reasonably similar (without picking a fight), pivoting flukes hold more, and claw-types hold less.

Why was it done this way? To make a single message crystal clear; holding capacity declines with angle at the bottom in a fairly consistent way, for nearly all anchor types, regardless of size or substrate.

Is the ratio of mass to holding capacity the be all and end all of anchors? That is a different debate and I'm not going there.

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post #515 of 535 Old 05-19-2019
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Re: Not Getting the All-Chain Thing

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Originally Posted by Cassidy View Post
If you insist

Let me understand lead angle. Is this the angle of the rode on a straight line from the end of the anchor to the bow roller measured against horizontal?

If it is then as I have alluded to in earlier posts, it would be a very severe condition a sailor using any amount of chain finds himself in where all of the rode is lifted off the sea bed. And until that condition occurs the lead angle at the anchor is zero because the chain is pulling horizontally. The start of the lead angle would be the point where the chain leaves the ground and not the end of the anchor.

Yes, I know that test results can’t be tailored to my specific sailing habits or conditions but my habits/conditions are similar to many thousands of sailors, at least they were when I still bothered to read sailing magazines. For me, test results that are based on extremes are less valuable.
Lead angle is the angle between the rode and the bottom. If you used nylon with no chain at all, it would be the angle between the bottom and the roller, but with chain it will be less than that.

In fact, it takes only 25-30 knots in 10-15 feet, depending on scope and chain grade (low grade chain is heavier for the same strength). In my mind, standard anchoring practice should allow for up to 60 knots, since many thunderstorms can deliver that.



Each person will define "extreme" differently. For me it would be strong winds or bad bottoms. For another it might be shallow water. Certainly the middle range--17 feet with 35-40 knots--would be considered normal and commonplace. For me, 6 feet with 60 knots is commonplace in the summer (though never in an open roadstead... although mistakes can happen, and squalls pop up fast).

What do we believe is normal? Water that is 15 feet deep, 7:1 scope, and wind no stronger than 35 knots? If so, then yes, your chain will stay on the bottom. That is what the data say. In fact, that is the whole point; to help sailors understand the boundries of "extreme," so that they can avoid them.

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post #516 of 535 Old 05-19-2019
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Re: Not Getting the All-Chain Thing

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Originally Posted by pdqaltair View Post
Why was it done this way? To make a single message crystal clear; holding capacity declines with angle at the bottom in a fairly consistent way, for nearly all anchor types, regardless of size or substrate.
It does that, but it still is a confusing presentation, unless it is more of a sidebar addendum to a description about bottom angle effect in anchor design in general.

As a standalone, it sends a different message to people without a lot of experience with graphs and datasets. For example, one anchor could lose 50% of its holding power at a certain angle compared to another anchor. But if that anchor has the same holding power at that higher angle as the other, then the loss of 50% isn't meaningful in comparing the anchors suitability.

This is just feedback based on a single graph, because I haven't read the article and the context in which the data are presented.

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Re: Not Getting the All-Chain Thing

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Originally Posted by pdqaltair View Post
Lead angle is the angle between the rode and the bottom. If you used nylon with no chain at all, it would be the angle between the bottom and the roller, but with chain it will be less than that.

In fact, it takes only 25-30 knots in 10-15 feet, depending on scope and chain grade (low grade chain is heavier for the same strength). In my mind, standard anchoring practice should allow for up to 60 knots, since many thunderstorms can deliver that.



Each person will define "extreme" differently. For me it would be strong winds or bad bottoms. For another it might be shallow water. Certainly the middle range--17 feet with 35-40 knots--would be considered normal and commonplace. For me, 6 feet with 60 knots is commonplace in the summer (though never in an open roadstead... although mistakes can happen, and squalls pop up fast).

What do we believe is normal? Water that is 15 feet deep, 7:1 scope, and wind no stronger than 35 knots? If so, then yes, your chain will stay on the bottom. That is what the data say. In fact, that is the whole point; to help sailors understand the boundries of "extreme," so that they can avoid them.
Again, these are nice data, but cannot stand alone in presentation without more perspective. Taken with your previous graph, it is clear that the rode does not have to be on the bottom to retain much of the holding power of the anchor. So the question becomes, how much rode at which depths is required to maintain an angle at or below that which preserves (say) 80% of the holding power of the anchor.

Again, I suspect the story is more fleshed out in the article context than I am seeing in two graphs.

Mark

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post #518 of 535 Old 05-19-2019
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Re: Not Getting the All-Chain Thing

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Originally Posted by colemj View Post
Again, these are nice data, but cannot stand alone in presentation without more perspective. Taken with your previous graph, it is clear that the rode does not have to be on the bottom to retain much of the holding power of the anchor. So the question becomes, how much rode at which depths is required to maintain an angle at or below that which preserves (say) 80% of the holding power of the anchor.

Again, I suspect the story is more fleshed out in the article context than I am seeing in two graphs.

Mark
Yes, that is a good way of stating the question. For any give set of conditions (wind and bottom type) and depth, how much scope (length) do I need to maintain enough holding capacity? In shallow water, over soft mud, with a less efficient anchor and thunderstorm coming, you probably need 10:1 and a long snubber, even with chain. You only have 70' of chain out, and with 1000 pounds of tension, it's going to get pretty darn straight. In 20 feet, over sticky mud, with just a little blustery weather and an oversized NG anchor, 5:1 and a short snubber is more than enough. The chain might come off the bottom, but probably not, and not enough to matter.

It's not something you describe in a few posts. But if you follow the math, the folks that say all-chain, use conservatively sized anchors, and anchor in deeper water, and the people who say rope can work and use pivoting fluke anchors in good bottoms, are both right. The people that say you need a long snubber are right in some conditions, and the folks that claim 6' is enough are right in some conditions. Obviously, members of both groups have practiced their craft for many years. In fact, my anchoring practices with my trimaran (rope) are quite different from those when I had the cruising cat (all chain). The math is different and both are correct.

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Re: Not Getting the All-Chain Thing

Perhaps the question to explore is what arrangement of rode/anchor and snubber has the widest range of effectiveness over the gamut of anchoring environments typically encountered?

For greater granularity we could include some broad categories such as: known vs unknown areas, differing categories of boats, expected weather extremes. Others?

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Re: Not Getting the All-Chain Thing

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Perhaps the question to explore is what arrangement of rode/anchor and snubber has the widest range of effectiveness over the gamut of anchoring environments typically encountered?

For greater granularity we could include some broad categories such as: known vs unknown areas, differing categories of boats, expected weather extremes. Others?
Oh no!!

Abandon all hope of a usable answer!
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