Neeves
Well-Known Member
Anchors can be defined in a number of ways, convex/concave, roll bar/non roll bar, hinged or not hinged, aluminium/steel - I am choosing here to simply call them ballasted or non ballasted. Ballasted would include CQR, Delta, Kobra, Spade, Rocna, Supreme, Excel, Vulcan and now Epsilon. Non ballasted includes, Danforth, Fortress, Bugel, Bruce, Jambo, Britany, Knox, SARCA and Mantus. Many of these anchors have been copied, or are copies (in part) of their predecessors. Many ‘copies’ are inaccurate - buy an original (and preferably one that has been tested independently). I’m focussing on non ballasted anchors here as I am defining why I think the Mantus M1 is an inefficient anchor.
I have been commenting that the Mantus M1 anchor has the hold approximately similar to that of a similarly weighted Delta (or half the hold of a similar weighted Rocna). Unlike a Delta and like a Rocna or Excel a Mantus does engage reliably and if tripped will reset. I thought I’d back up my comments with some background data.
To follow this it will be easier to understand what I say if you look at this article first:
An Inquiry into Anchor Angles - Practical Sailor
I direct you to look at the picture of the Mantus anchor, with the yellow shank and sitting alone on a table, and you will note that the ‘long’ of the shank is horizontal.
If you now look at this thread:
Photos of Anchors Setting - Cruisers & Sailing Forums
You will note that virtually all of the pictures of a Mantus in the thread, there are many - choose any at random, are ‘set’ similarly, if not identical, to the mock up - with the long of the shank horizontal.
If the long of the shank is horizontal then the fluke is at 16 degrees to the horizontal which means if the shank is horizontal to the seabed then the fluke is at 16 degrees to the seabed (I’m happy to correct that to 15 or 17 degrees).
If you look at, any, actually all other anchors set underwater, some of which are in the same CF thread, you will find that their fluke seabed angle is around 30 degrees. It does vary - 25 - 35 degrees. If you read through the Practical Sailor article you will find a breakout box where Mantus and Rocna are compared, based on fluke seabed angles of 16 and 30 degrees respectively. The mock up of the Rocna is typical of a Rocna in its ‘set’ position on the seabed of which I do have pictures. I have similar images of Spade, Fortress and Excel set - they too have a seabed fluke angle of 30 degrees.
Non-ballasted fluke anchors have enjoyed a huge amount of research - because that’s the sort of anchor used commercially. Ballasted anchors, or ballasted in the toe, are restricted (as far as I know) to leisure anchors.
As an example have a look at this PhD thesis by Kim ‘Upper bound analysis for drag anchors in soft clay’ which you will find at this link
https://core.ac.uk/download/pdf/147126425.pdf
And on page 169/170 Kim investigates the location of the shank vs the fluke, the location of the crown.
Now note where the crown is on my list of un-ballasted fluke anchors, with only one exception the crown location, as Kim points out, is ‘away’ from the fluke centre - and in all cases is at the heel (treating the fluke like a shoe). The exception of course is the Mantus M1, whose crown is about 1/3rd forward from the heel. Bruce has the crown, almost behind the heel, the shank protrudes ‘aft’.
This unusual location for the crown of the Mantus results in the 16 degree fluke/seabed angle.
Kim is not the only one to document this simple basic research, there are other identical examples. If you want to learn more about anchors then Kim’s thesis makes a good foundation as he also has tested for shank length etc and he has a copious list of references, most of which can be accessed on line.
The impact of fluke/seabed angle has also been investigated by many and an example might be. Alain Puech’s book ‘The use of anchors in offshore petroleum operations’
If you are lucky you can access the whole book on line, try this link:
https://books.google.com.au/books?id=TVRvkg_i78cC&pg=PA49&lpg=PA49&dq=Small+model+testing+of+fluke+anchors+with+different+fluke+angles&source=bl&ots=mABFjVKJ3q&sig=ACfU3U0Dm35b1KW4wUgqNB2K1r8rLrG5uQ&hl=en&sa=X&ved=2ahUKEwjurOnAnZHkAhUq63MBHTDJBFk4ChDoATAFegQICRAB#v=onepage&q=Small model testing of fluke anchors with different fluke angles&f=false
The relevant location is page 40.
The Puech graphs plot, on page 40, the hold of a model Danforth type anchor, it has a 10cm fluke, with its fluke at different fluke angles, coincidentally from 16 degrees - and up. The graphs show that a fluke/seabed angle of 16 degrees results in a hold approximately 50% of the same anchor with its fluke at 30 degrees, or a hold ratio of approximately 2:1.
The NCEL, Naval Civil Engineering Laboratory (the US Navy research facility, now the Naval Facilities Engineering Service Center) have done the self same work as Puech shows and you can access research papers with similar graphs to Puech’s dating from as early as 1960. I suspect Danforth and Ogg will also have conducted tests but I have never seen any documents. Some of the NCEL work is on model anchors some on full sized anchors. The NCEL simplify the graphs to the Sine of the fluke/seabed angle. Sine 16 and 30 are 0.27 and 0.5 respectively. With similar fluke areas the hold will be a function of the sine of the angle, thus a fluke seabed angle of 16 degrees would have a hold of 0.27 and and that of 30 degrees 0.5 - or 2:1.
There is a wealth of information from a variety of sources and authors providing the same data. Most of the authors are recognised ‘titans’ in the field of anchor research and design and you will find the same names in most research papers on anchor research.
I have tested a 15kg Mantus against the same weight of Excel and the Mantus has a hold of 1,200kg and the Excel a hold of 2,000kg. In the same location (Pittwater, Sydney) at a different time I tested a steel and aluminium Spade and a 15kg Delta and for the Spades similar holds, 2,000kg and the Delta 1,000kgs. The Excel, 2 Spades and Delta had seabed fluke angles of around 30 degrees. I also altered the location of the crown of the Mantus, by drilling new bolt holes, placing the crown further aft and developed a hold of 1,800kg, with a fluke/seabed angle of 26 degrees. If I could have moved the crown further aft I am sure I would have improved the angle and hold (but might have compromised fluke strength). In the same seabed, again a different test, I achieved a hold of 1,650kg for a 10kg Viking. All the tests are conducted the same way, same rode etc, just at different times.
The thread linked above ‘Photos of anchors setting’ ran for almost 4 years and not once was the unique characteristic of the fluke/seabed angle being 16 degrees vs 30 degrees for every other anchor (whether ballasted or unballasted) ever mentioned. This characteristic is not mentioned on the Mantus website - leading to the conclusion that if it was known it was not deemed something to be discussed (suppression comes to mind) - or it was not known at all. Now - the information has been available for some months, the Practical Sailor article linked above - but both Mantus and owners of Mantus anchors appear to be in denial - or don’t think it important. If you don’t think hold is important - you will find this thread a waste of time - bordering on trolling.
There are centres of excellence for anchor research and design. The NCEL is one location, in California, as are Universities in Perth (Australia), Southhampton and Houston (amongst others). Coincidentally Mantus Anchor is centred in Houston where access to virtually all research would be very convenient (I’m envious!).
I think knowing the unique characteristic of the Mantus is important.
It merits note that low fluke/seabed angles are recommended for very hard seabeds (along with sharpening the toe) which is why Mantus does well in the Kappari tests. The lowest seabed angle I have heard of is 22 degrees used because a shallow setting anchor is easy to retrieve (which might merit some consideration from owners - for example at low scope ratios the anchor is more prone to tripping than one set deeply).
There is no suggestion that a Mantus anchor is dangerous, many have used a correctly sized Delta, or Bruce, without complaint - it has not dragged. Hold of these anchors can be enough. Mantus engages quickly and reliably, it does take a long time to ‘lock up’ - compared with a similar sized Rocna - twice the distance. But to consider that Mantus is as good as a Spade or Rocna of the same weight is misleading, shows ignorance and potentially could be dangerous. Perpetuating the idea and promoting the idea that Mantus is as good as a Spade or Rocna ignores the large difference in hold and such rash statements should encourage people to demand supporting data. To suggest Mantus is ‘similar’ to a Rocna simply underlines, common, ignorance - appearances are deceptive. In the absence of data - its ‘fake news’ and in my view shows the dangers of hype over substance.
Now - I might be wrong - I’d welcome critical comment and if I am wrong - where am I wrong. I try to be impartial - if I am unwittingly wrong I’m showing bias - there is no intent to troll.
Jonathan
I have been commenting that the Mantus M1 anchor has the hold approximately similar to that of a similarly weighted Delta (or half the hold of a similar weighted Rocna). Unlike a Delta and like a Rocna or Excel a Mantus does engage reliably and if tripped will reset. I thought I’d back up my comments with some background data.
To follow this it will be easier to understand what I say if you look at this article first:
An Inquiry into Anchor Angles - Practical Sailor
I direct you to look at the picture of the Mantus anchor, with the yellow shank and sitting alone on a table, and you will note that the ‘long’ of the shank is horizontal.
If you now look at this thread:
Photos of Anchors Setting - Cruisers & Sailing Forums
You will note that virtually all of the pictures of a Mantus in the thread, there are many - choose any at random, are ‘set’ similarly, if not identical, to the mock up - with the long of the shank horizontal.
If the long of the shank is horizontal then the fluke is at 16 degrees to the horizontal which means if the shank is horizontal to the seabed then the fluke is at 16 degrees to the seabed (I’m happy to correct that to 15 or 17 degrees).
If you look at, any, actually all other anchors set underwater, some of which are in the same CF thread, you will find that their fluke seabed angle is around 30 degrees. It does vary - 25 - 35 degrees. If you read through the Practical Sailor article you will find a breakout box where Mantus and Rocna are compared, based on fluke seabed angles of 16 and 30 degrees respectively. The mock up of the Rocna is typical of a Rocna in its ‘set’ position on the seabed of which I do have pictures. I have similar images of Spade, Fortress and Excel set - they too have a seabed fluke angle of 30 degrees.
Non-ballasted fluke anchors have enjoyed a huge amount of research - because that’s the sort of anchor used commercially. Ballasted anchors, or ballasted in the toe, are restricted (as far as I know) to leisure anchors.
As an example have a look at this PhD thesis by Kim ‘Upper bound analysis for drag anchors in soft clay’ which you will find at this link
https://core.ac.uk/download/pdf/147126425.pdf
And on page 169/170 Kim investigates the location of the shank vs the fluke, the location of the crown.
Now note where the crown is on my list of un-ballasted fluke anchors, with only one exception the crown location, as Kim points out, is ‘away’ from the fluke centre - and in all cases is at the heel (treating the fluke like a shoe). The exception of course is the Mantus M1, whose crown is about 1/3rd forward from the heel. Bruce has the crown, almost behind the heel, the shank protrudes ‘aft’.
This unusual location for the crown of the Mantus results in the 16 degree fluke/seabed angle.
Kim is not the only one to document this simple basic research, there are other identical examples. If you want to learn more about anchors then Kim’s thesis makes a good foundation as he also has tested for shank length etc and he has a copious list of references, most of which can be accessed on line.
The impact of fluke/seabed angle has also been investigated by many and an example might be. Alain Puech’s book ‘The use of anchors in offshore petroleum operations’
If you are lucky you can access the whole book on line, try this link:
https://books.google.com.au/books?id=TVRvkg_i78cC&pg=PA49&lpg=PA49&dq=Small+model+testing+of+fluke+anchors+with+different+fluke+angles&source=bl&ots=mABFjVKJ3q&sig=ACfU3U0Dm35b1KW4wUgqNB2K1r8rLrG5uQ&hl=en&sa=X&ved=2ahUKEwjurOnAnZHkAhUq63MBHTDJBFk4ChDoATAFegQICRAB#v=onepage&q=Small model testing of fluke anchors with different fluke angles&f=false
The relevant location is page 40.
The Puech graphs plot, on page 40, the hold of a model Danforth type anchor, it has a 10cm fluke, with its fluke at different fluke angles, coincidentally from 16 degrees - and up. The graphs show that a fluke/seabed angle of 16 degrees results in a hold approximately 50% of the same anchor with its fluke at 30 degrees, or a hold ratio of approximately 2:1.
The NCEL, Naval Civil Engineering Laboratory (the US Navy research facility, now the Naval Facilities Engineering Service Center) have done the self same work as Puech shows and you can access research papers with similar graphs to Puech’s dating from as early as 1960. I suspect Danforth and Ogg will also have conducted tests but I have never seen any documents. Some of the NCEL work is on model anchors some on full sized anchors. The NCEL simplify the graphs to the Sine of the fluke/seabed angle. Sine 16 and 30 are 0.27 and 0.5 respectively. With similar fluke areas the hold will be a function of the sine of the angle, thus a fluke seabed angle of 16 degrees would have a hold of 0.27 and and that of 30 degrees 0.5 - or 2:1.
There is a wealth of information from a variety of sources and authors providing the same data. Most of the authors are recognised ‘titans’ in the field of anchor research and design and you will find the same names in most research papers on anchor research.
I have tested a 15kg Mantus against the same weight of Excel and the Mantus has a hold of 1,200kg and the Excel a hold of 2,000kg. In the same location (Pittwater, Sydney) at a different time I tested a steel and aluminium Spade and a 15kg Delta and for the Spades similar holds, 2,000kg and the Delta 1,000kgs. The Excel, 2 Spades and Delta had seabed fluke angles of around 30 degrees. I also altered the location of the crown of the Mantus, by drilling new bolt holes, placing the crown further aft and developed a hold of 1,800kg, with a fluke/seabed angle of 26 degrees. If I could have moved the crown further aft I am sure I would have improved the angle and hold (but might have compromised fluke strength). In the same seabed, again a different test, I achieved a hold of 1,650kg for a 10kg Viking. All the tests are conducted the same way, same rode etc, just at different times.
The thread linked above ‘Photos of anchors setting’ ran for almost 4 years and not once was the unique characteristic of the fluke/seabed angle being 16 degrees vs 30 degrees for every other anchor (whether ballasted or unballasted) ever mentioned. This characteristic is not mentioned on the Mantus website - leading to the conclusion that if it was known it was not deemed something to be discussed (suppression comes to mind) - or it was not known at all. Now - the information has been available for some months, the Practical Sailor article linked above - but both Mantus and owners of Mantus anchors appear to be in denial - or don’t think it important. If you don’t think hold is important - you will find this thread a waste of time - bordering on trolling.
There are centres of excellence for anchor research and design. The NCEL is one location, in California, as are Universities in Perth (Australia), Southhampton and Houston (amongst others). Coincidentally Mantus Anchor is centred in Houston where access to virtually all research would be very convenient (I’m envious!).
I think knowing the unique characteristic of the Mantus is important.
It merits note that low fluke/seabed angles are recommended for very hard seabeds (along with sharpening the toe) which is why Mantus does well in the Kappari tests. The lowest seabed angle I have heard of is 22 degrees used because a shallow setting anchor is easy to retrieve (which might merit some consideration from owners - for example at low scope ratios the anchor is more prone to tripping than one set deeply).
There is no suggestion that a Mantus anchor is dangerous, many have used a correctly sized Delta, or Bruce, without complaint - it has not dragged. Hold of these anchors can be enough. Mantus engages quickly and reliably, it does take a long time to ‘lock up’ - compared with a similar sized Rocna - twice the distance. But to consider that Mantus is as good as a Spade or Rocna of the same weight is misleading, shows ignorance and potentially could be dangerous. Perpetuating the idea and promoting the idea that Mantus is as good as a Spade or Rocna ignores the large difference in hold and such rash statements should encourage people to demand supporting data. To suggest Mantus is ‘similar’ to a Rocna simply underlines, common, ignorance - appearances are deceptive. In the absence of data - its ‘fake news’ and in my view shows the dangers of hype over substance.
Now - I might be wrong - I’d welcome critical comment and if I am wrong - where am I wrong. I try to be impartial - if I am unwittingly wrong I’m showing bias - there is no intent to troll.
Jonathan
