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Old 02-01-2017, 06:55 AM   #21
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"Setting angle is the measurement in degrees between three shank and the plow. Imagine the shank its parallel to the bottom. The shank is zero degrees. The Mantua digs in at 17 degrees the others at 32. In other words the Mantua takes a shallower bite if bottom."

Every anchor company has its own belief/research in the angle of the shank and the fluke in their design. Generally, a narrower angle allows for "cutting into" firmer seabeds and a more wide open angle allows the fluke to present greater surface resistance to softer seabeds. A narrow angle shank/fluke does not bury as deep as one with a more wide open angle (which can or should go very deep). As a result, an anchor that is excellent in softer seabeds may be difficult to set in harder seabed substrates and vice versa. As an example, the Super MAX Anchor Pivoting arm was designed to allow the operator to set the fluke/shank angle at 19 degrees, 32 degrees, or 45 degrees. A couple years later when we found out that some operators either did not trust anchoring in extremely soft seabeds or did not want to change from the middle 32 degree setting, we designed the rigid shank model with the angle set at 24 degrees. This is an angle that works well in harder and medium seabeds but needs some extra precaution/attention to detail in extremely soft seabeds.

There are lots of reasons why an anchor works well or has some challenges in different seabeds. Fluke/shank angle is one.

Steve
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Old 02-01-2017, 08:28 AM   #22
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Good observation on anchors and their various angles. If you are willing to do a little trigonometry, calculate the inverse of the sin of the anchor's angle of attack to a flat sea bed. This yields a minimum scope ratio needed to properly set the anchor in question. If the anchors angle of attack relative to the bottom is anything less than the anchor's designed angle, the anchor will begin to ascend instead of dive. Handy info to know when you want to break it out . It's also why many anchors don't like to set on short scope. In the case of the mantus with a 17 degree angle of attack this equates to 3.4 : 1 scope ratio. A fortress set at 32 degrees is 1.8 : 1 and set at 45 degrees will start to dive at 1.4 : 1. Scope angles shorter than this will start to break the anchor out. Best I could measure our rocna was 15 degrees and results in a 3.8 : 1 ratio. 19 and 24 degrees would yield 3 and 2.45 : 1 respectively.
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Old 02-01-2017, 09:00 AM   #23
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Originally Posted by cafesport View Post
Good observation on anchors and their various angles. If you are willing to do a little trigonometry, calculate the inverse of the sin of the anchor's angle of attack to a flat sea bed. This yields a minimum scope ratio needed to properly set the anchor in question. If the anchors angle of attack relative to the bottom is anything less than the anchor's designed angle, the anchor will begin to ascend instead of dive. Handy info to know when you want to break it out . It's also why many anchors don't like to set on short scope. In the case of the mantus with a 17 degree angle of attack this equates to 3.4 : 1 scope ratio. A fortress set at 32 degrees is 1.8 : 1 and set at 45 degrees will start to dive at 1.4 : 1. Scope angles shorter than this will start to break the anchor out. Best I could measure our rocna was 15 degrees and results in a 3.8 : 1 ratio. 19 and 24 degrees would yield 3 and 2.45 : 1 respectively.
I was told there would be no maths.
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Old 02-01-2017, 09:04 AM   #24
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Excellent observation. The narrower the fluke/shank angle the longer scope required to set in the seabed. The larger the angle the the less scope because the fluke "tips or points" are already pointing down into the seabed.

Additional variables in this calculation is the slope or flatness of the seabed. The calculations assume a flat seabed and no slope or no ridges. Happen to drop on a seabed that is sloping (even slightly) toward your vessel or away from your vessel changes the required scope for fluke tip penetration in setting. Also a variable is a flat but uneven seabed. Happen to drop the anchor, even with a narrow fluke/shank angle just before a "bump up" of seabed and the fluke tip will probably penetrate the seabed with a much shorter scope.

Again, excellent observations and comments. Thanks for sharing.
Steve
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Old 02-01-2017, 09:07 AM   #25
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Regarding flat seabeds, if you anchor say for a hurricane, and you drop the hook in the deepest part of the anchorage when and if the anchor starts to drag it will dig in deeper. The opposite happens say in Alaska.
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Old 02-01-2017, 09:14 AM   #26
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cafesport wrote;
"It's also why many anchors don't like to set on short scope. In the case of the mantus with a 17 degree angle of attack this equates to 3.4 : 1 scope ratio. A fortress set at 32 degrees is 1.8 : 1 and set at 45 degrees will start to dive at 1.4 : 1. Scope angles shorter than this will start to break the anchor out. Best I could measure our rocna was 15 degrees and results in a 3.8 : 1 ratio. 19 and 24 degrees would yield 3 and 2.45 : 1 respectively."

Perhaps this is why The Rocna has fantastic holding power (actually only a bit more than most others) at long scope but less than others at short scope. Several anchor tests have indicated that. But the throat angle (or setting angle) functions differently during setting w anchors that lay on their sides predominantly and anchors like a Danforth or SARCA that set sitting upright. I would think that anchors like the Rocna w a narrow throat angle would set more dependably or consistently but I haven't noticed any other "laying on their side" LOTS anchors having difficulty setting. My own philosophy is that if an anchor sets dependably there's no problem w the throat angle regarding setting. The optimal throat angle for setting may not be optimal for holding when buried. And at each buried depth the optimal throat angle may be different as well. So as Steve Bedford point out the element of compromise weights heavily in anchor design.

And the length of the shank is closely related to the throat angle. I would think a long shank would be detrimental to short scope performance. And a long shank would reduce the buried fluke angle to horizontal angle. But when buried a wider throat angle would be better for holding up to a point where breaking out becomes more likely. Linda like a wing stalling on an aircraft.
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Old 02-01-2017, 09:19 AM   #27
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The opposite happens say in Alaska.
Yes it does (BC too) , and pretty well rules our anchoring experiences. Glacial geology at work as compared to East and Gulf Coast sedimentary deposits.
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Old 02-01-2017, 09:36 AM   #28
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On short scope/penetration...design matters as well.

Mantus anchors may have a shallower angle of attack, but 50% of the anchors weight is at the tip when laying on the sea bed, and because of the roll bar, the Mantus tip is angled downward to get to work right away.
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Old 02-01-2017, 10:12 AM   #29
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Murray I think the roll bar angles the fluke tip up not down once the anchor is buried. Just like a headwind on a boat w a mast will pitch the bow up.
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Old 02-01-2017, 10:56 AM   #30
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Conclusion in practical sailer: "more research is required to determine how significantly a shallow burying angle impacts holding ability... A good anchoring arsenal on a cruising boat will include at least three anchors - two on the bow suited (to) the bottoms you're likely to encounter and a reliable kedge ready to deploy."
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Old 02-01-2017, 11:04 AM   #31
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PS is telling me I need a kedge?

We need a Practical Trawler mag.
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Old 02-01-2017, 11:16 AM   #32
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I can't imagine kedging-off my 50K pound trawler. My former boat, a sailboat with its keel stuck in the mud would be a whole different experience.

On the other hand, unless I run hard aground, I would think my twin 29-inch props and 660 HP of motivation would do a lot to get me off a soft bottom.
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Old 02-01-2017, 01:39 PM   #33
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Gorden J,
I'd say more power to ya but you've got plenty. Plenty more that my 37hp.

I would think a Fortress would be better for kedging off anyway. And at 1/15th the weight.

Eyeshulman,
Thinking of a spare all around anchor the SARCA now being availble in the US would be hard to beat. Many have more holding power but I doubt many would even be close to a do everything anchor. I'll bet the SARCA even does fairly well on weed. Setting upright w that sharp turned down "toe" (as Rex calles it) weeds could be a piece of cake.

But as you say there's so many good top performing anchors l'd be inclined to say choosing which one could be not so important. Choose the cutest one and go.
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Old 02-01-2017, 01:41 PM   #34
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Well... Here we go again!
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Old 02-01-2017, 02:57 PM   #35
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This will be my last post under the name Fortress Anchors, since as per this forum's rules, a commercial name is not allowed and so I will have to make up another name.

Practical Sailor stated in their article: "More research is required to determine how significantly a shallow burying angle impacts holding ability." This comment was referring to their own research, because there has already been extensive research conducted in this area by the US Navy and by anchor manufacturers who design and sell their products to the offshore industry.


It is my understanding that our consultant Bob Taylor, who has spent almost 50 years in anchor design and soil mechanics (most of which with the US Navy), contributed to the story and he was referenced in it.

In addition to the shank / fluke angle, Bob also brought up the importance of the "penetration angle" (also called the "effective fluke angle") which determines how aggressively (or not) the fluke engages and penetrates into a sea bottom.

So even if the ultimate shank / fluke angle (based on extensive research - the Practical Sailor article provides a graph) is 30° for a hard soil and 50° for a soft soil, that does not automatically result in an immediate setting / deeper burying capability. The fluke still has to be designed to attack the sea bottom.


The issue noted with the Mantus and observed in their own videos and in other forum photos was that while the anchor set quickly in dense wet beach sand and other hard bottoms, the anchor never buried very deeply (the roll bar was always visible), which was theorized to be due to a narrower shank / fluke angle, and in turn that cast doubt on its ultimate holding capacity.

Simply stated, it might set quickly, but how well will it hold, and was a trade-off made in the design?


Practical Sailor has only tested a 2 lb Mantus and they looked at the results of the soft mud testing that we did, and so they didn't have a definitive answer, hence the comment: "More research is required....."


To the best of my knowledge, in the pleasure craft industry only the Super Max and Fortress have adjustable fluke angles to insure optimal performance in hard and soft soil conditions.


Based on very well-established science (and certainly not manufacturer's bluster), there is no question that the performance of fixed-fluke / non-adjustable anchors, which are typically designed and optimized for harder soils, will fall off dramatically in softer bottom conditions.

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Brian
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Old 02-03-2017, 06:03 PM   #36
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I suppose if I am to anchor in a place or boat where there is an abundance of soft mud an adjustable anchor pre set for the soft stuff makes sense. Where I anchor now and even on the East coast where I used to anchor changing fluke angles or exchanging anchors on a 40-50 foot boat is not something I would want to do on a regular basis. My solution is to have a good all around anchor on the bow and carry light aluminum specialty anchors in the bilge that I can deploy from my dinghy when needed. I would then count on two anchors to do the job and probably use the F37 without bothering with the mud angle or the Al spade as the secondary units. Since I don't design or sell anchors and only use them I am not so interested in the nitty gritty of fluke and shaft angle but in the practical field results including the many hundreds of times I have used the metal gizmos.
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Old 02-03-2017, 08:04 PM   #37
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Brian,
Excellent copy as usual.

And eyeshulman sees through the smoke and details. And his post could probably go for most here that probably look at anchor threads but never post on them. I know there's many more of you than "us".

But Brian I am largely in eyeshulman's camp mostly because I usually don't know what the bottom is like. So I deploy an anchor for a typical bottom (if there is one) and hope for the best. However since I hand deploy w initial setting felt in my hands I frequently know more than most. I hold the Brait rode in my hands untill it's too much tension to hang onto. I'll feel nothing but increasing tension in soft mud and gravel feels like I'm pulling a small square chunk of metal on .. well .. gravel. And of course sometimes I see some seafloor on the fluke in the morning while weighing anchor.

However if I was to anchor in soft mud and w increasing wind I noticed drag I could pull up the anchor (night or day) and "set/adjust" it for the then known to be very soft bottom. It's never happened and not having an adjustable anchor I'd just deploy one of me other anchors. Probably one of my several Danforth anchors.

And speaking of mud almost all of the anchorages in the PNW seem to be mud. One would think w all the rocky shores there would be rocky bottoms. There are but not that many. So if you've got a good mud anchor you've just about got it covered. Since I've got so many Dans I probably should modify one of my larger Dans for a 42 to 44 degree fluke/shank angle. HaHa the first time I drag in mud I'll probably do that. But I've not dragged in any bottom yet .. that I know of.
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Old 02-03-2017, 09:19 PM   #38
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Brian,
I sure do hope you make it so we can tell who you are. I hope "Brian" is open or if not perhaps "Brian F". F for Fortress of course.

I made this post on my thread "West Marine Anchor". It has no name that I know about. In the Chesapeke Bay test a West Marine guy is mentioned .. not Bob Taylor but someone else. I think he is the one that designed the WM anchor. I may find his name on the Chesapeke Bay test thread. [I did. It's Chuck Hawley.] Anyway I'd love to ask him about the turned down flange on the LE of the outboard fluke extensions. I made the thread hoping someone would have bought the anchor and used it or perhaps knows more about it.

Steve and 78,
I agree on both counts.
And Steve this was my first thought when I first saw the WM.
Not often does an interesting anchor come onto the market and this one is interesting. I've seen and used more interesting like my XYZ and need I mention the Bulwagga? Even the name is interesting there but it's short scope performance is quite poor and stowing is probably this side of a nightmare.

But the WM is clearly not a rip off of some other design however it would be hard to design an anchor not resembling any other. I suspect I know who designed this anchor and intend to look him up. He has been very involved in anchor testing and West Marine so is a natural suspect.

"I've seen this anchor for some time at the West Marine stores but never seen one elsewhere. This of course leads me to belive few have been sold and that would be a shame if it was a good performer. Probably never been in an an anchor test either. It may do well on Steve's (Panope) high performance reversal test procedure. Could be an opportunity for Steve. Not very expensive either."
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Old 02-03-2017, 10:41 PM   #39
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..... By all measurements, it is not big enough for the Nordic Tug (45 lbs) but the anchor roller won't fit anything bigger without substantial modification. Even undersized I still have confidence in the Mantus as it has held in a good bottom with winds up to 30 knots with a 4:1 scope of 1/4 inch HT chain. When I can build a pulpit to fit the 55 lb Mantus, I will probably upgrade and relegate the 45 lb to spare anchor status as I can break it down.

Tom
By real life testing it would appear that the 'all measurements' thing is probably wrong, so why bother paying for a heavier than necessary, over-sized anchor..?.
Just sayin'
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Old 02-03-2017, 11:01 PM   #40
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I'd be looking for 5/16" chain before a bigger anchor.

Who says a 45lb anchor is'nt big enough?

A 33lb XYZ Extreme has no roll bar and may fit on your boat but fitting wise they Can be dificult. My 18lb XYZ held us in a 50 knot gale without a problem. It was slightly modified though.
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