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Old 15-10-2013, 17:36   #76
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Re: It's True! The Mantus 65-lb. hooks first time, everytime.

For a sideways load on the shank its pretty simple maths, half the width and you half the strength. In terms of plate thickness its the square of the plate thickness. So if you double the thickness of the plate you increase strength (for a sideways load), everything else being equal, by 4 times.

Its interesting Rocna was condemned for using a low strength steel but did upgrade once public pressure became too great to bear. They also offered to replace all or any anchors of questionable quality. Now we have an anchor that is even weaker than a Rocna at its worst - and no-one bats an eyelid. People seem to have short memories and focus their bile.

I never thought I would say this but:

I would rather have the worst of Rocna production as I could take it back to West Marine (if that is who I bought from), no questions asked and it would be replaced with something near the original spec, and at least twice as strong as a Mantus shank. If I had a Mantus the best I could hope for is that if it bend my yacht did not end up on a beach and the replacement shank would be as bad as the original. And at $300 its simply not worth saving the money.

Its a pity - its a great design of its type and for virtually no extra money could have been a real winner.

But if there is one thing I have learnt - most people simply do not think shank strength is critical, in fact, obviously, most people do not actually even think about it at all.

Take care

Jonathan
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Old 15-10-2013, 19:26   #77
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Re: It's True! The Mantus 65-lb. hooks first time, everytime.

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Originally Posted by JonJo View Post

SNIP!

Its interesting Rocna was condemned for using a low strength steel but did upgrade once public pressure became too great to bear. They also offered to replace all or any anchors of questionable quality. Now we have an anchor that is even weaker than a Rocna at its worst - and no-one bats an eyelid. People seem to have short memories and focus their bile.

SNIP!
Minor correction - Rocna started out with Bis-plate (your 750 MPa steel) and made quite a fuss about how important it was. Production moved to China and the steel was changed to 420 MPa steel. Reports of bent shanks came in with significant denial of any problem coming from Rocna. Lots of pointing of fingers, lies, mis-truths and evasion. Then the steel was upgraded to good enough for intended use with 620 MPa steel.

I do not have a short memory. I'm still pissed off that the Rocna I bought and thought to be made of bis-plate was made in fact of 420 MPa steel. Returned it to West Marine and got the other anchor that is made of bis-plate.

The Rocna fit my bow better. Angry and sad to have been screwed by them.
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Old 15-10-2013, 20:56   #78
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Re: It's True! The Mantus 65-lb. hooks first time, everytime.

Sorry evm,

With regard to short memories I was not referring to owners like yourself.

I was thinking that after the brouhaha of the Rocna debacle people (not Rocna owners, once bitten, twice shy) would think of shank strength as a factor to consider. It seems that anyone who considered soon discarded the thought and bought anyway.

I had also thought manufacturers would be very sensitive to the issue (of shank strength, or quality in general) and would be ensuring that their advertising and promotion was accurate and not intended to mislead.

its odd, those self same people who have bought Mantus will happily suggest one buys a G43 chain or a Crosby shackle - I find it all a bit contradictory.

Jonathan
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Old 15-10-2013, 21:07   #79
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Re: It's True! The Mantus 65-lb. hooks first time, everytime.

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Sorry evm,

With regard to short memories I was not referring to owners like yourself.

I was thinking that after the brouhaha of the Rocna debacle people (not Rocna owners, once bitten, twice shy) would think of shank strength as a factor to consider. It seems that anyone who considered soon discarded the thought and bought anyway.

I had also thought manufacturers would be very sensitive to the issue (of shank strength, or quality in general) and would be ensuring that their advertising and promotion was accurate and not intended to mislead.

its odd, those self same people who have bought Mantus will happily suggest one buys a G43 chain or a Crosby shackle - I find it all a bit contradictory.

Jonathan

No offense taken - I have run into a few who missed the whole Rocna debacle as well as those who are willing to accept the current offering. Looks like Rocna's recovery effort was successful. And that we in general have forgotten about shank strength as you point out.

Now we need to be on the lookout for bent Mantus. Hopefully there will be few and if there are some then hopefully Mantus will step up to the place and make it right.

REgards
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Old 18-10-2013, 02:23   #80
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Re: It's True! The Mantus 65-lb. hooks first time, everytime.

If you look at anchor shanks that have bent they have one thing in common – they all exhibit failure as a result of sideways load, the load (to cause bending) was at right angles to the length of the shank. This is not surprising – the shank of an anchor is weakest when loaded ‘sideways’.

There are a number of shank shapes, a straight line shank of the Danforth, Fortress and Bugel, the right angled shape of the Bruce and SARCA and the slightly more complex ‘L’ shape of the Delta. They all have one thing in common – a relatively long shank (or a long lever arm). Modern anchors have something else in common, ‘holding capacity’ – set them in a decent holding seabed and they are difficult to ‘unset’. The recommendation is – un-set slowly. We now have tenacious anchors with a long lever arm attached. Try to break the anchor out too aggressively, get caught in a tropical storm with rapidly changing wind direction and you can experience snatch loads – so swift the anchor will not move. All that snatch load is imposed on your rode and the lever arm, sometimes the weakest section fails. It has been suggested that many anchors are bent when lifting, a rogue wave causing snatch loads, or an anchor caught in rocks.

Many anchor shanks are ‘simple’ ‘L’ sections, the short arm of the ‘L’ is welded to the fluke, the long arm of the ‘L’ is attached to the chain. If you draw out many anchors shanks, Delta, Excel, Mantus, Rocna, Spade, Ultra – the shank design is almost identical (use a French curve to join up the Delta ‘dots’ and you have a Spade). Similarly sized, weighed, anchors have essentially the same length of shank. If you consider an anchor shank, that long section of the ‘L’ then the load necessary to achieve bending is a simple calculation:

Force to achieve yield strength, W = 1/30YBD2/L
Where Y = Yield Strength MPa
B = Breadth of bar, mm
D = Thickness of bar, mm (basically this is the thickness of the steel plate).

That's D to the powerr of 2.
L = Length of lever arm, mm
Force W, or the answer, is in Newtons.

The formula is a standard engineering formula used to calculate lever loads.

It is not easily possible to derive a formula to calculate the loads necessary to bend a Spade or Ultra shank and the Ultra is particularly difficult as, unless you cut one up, no-one knows wall thickness.

Not only do the same sized, weighted, anchors have the same shank length they also have the same thickness, thickness of plate. Most 15kg anchors use 12mm plate, most have a lever arm length of about 600mm.

There are 2 variables, what is the width (or breadth) of the lever arm and which steel is used. Unsurprisingly most anchors have the same breadth, Rocna, Excel, Delta have a width/breadth of about 100mm (for a 15kg anchors). The other variable is the steel quality used. Originally Rocna used a steel with a 780 MPa Yield Stress, YS, (as does the Excel now). Rocna, when it was last confirmed were using a steel of about 650 MPa YS but admitted to using another steel of about 450 MPa YS (though some anchors may have used a steel as low as 350 MPa). I have not quoted a Supreme as its shank has a slightly different shape to anything else (and I do not have the dimensions of a 15kg model).

There is another function, seldom discussed, of steel. High tensile steels are described by steel makers as being ‘tough’ – in my terms, springy. It is possible to bend a HT steel say 30 degrees and on releasing the load it simply returns to the original shape. Take a lower strength steel and bend 10 degrees and you find it has a permanent 5 degree bend. High tensile steels have a high ability to absorb load (like a spring, or like a snubber).

A Mantus has a breadth (or width) of 60mm (vs 100mm for Rocna) and uses a steel with a YS of about 550 MPa (vs 650 MPa now and 780 MPa originally for the Rocna).

A simple calculation shows that a Rocna and Excel using a 780 MPa YS steel demands a force to achieve yield of about 427kg (or 941lbs).
The 650 MPa Rocna would bend under a load of about 356 kg
The 450 MPa Rocna would bend, and did, under a load of about 246 kg
A Mantus with its less wide shank and using a 550 MPa YS steel would bend under a load of 180 kg.

Rocna after identifying the use of the 450 MPa YS steel had West Marine issue a Specification Notice offering to replace all models sold during the ‘questionable’ period. A number, no-one has said quite how many, of anchors made from the 450 MPa YS steel are known to have bent. Some were independently tested and steel quality defined. For reference a force of about 180kg is about the same load that 2 relatively fit men can apply.

Is this dangerous, well Rocna thought their 450 YS shanked anchors needed to be recalled (and these 550 YS shanked anchors have 75% of the strength of those that Rocna recalled).

There is nothing wrong with using a 550 MPa YS steel, there is nothing wrong with using a 350 MPa YS steel – as long as the steel plate is thicker and the width of the plate is not trimmed down. YS is important, but so is shank thickness, so is the width of the shank (and if the shank is shorter there is less lever action).

The basic Mantus design is good, what it needs is a stronger shank. How to introduce strength, easy (maybe). Use a better steel, Rocna use a 620 MPa steel, 780 MPa steels are available in China (but they might be in short supply or expensive). The best returns are to increase thickness (because its thickness squared) but a fat shank hinders diving and thus holding capacity. Maybe with the large fluke of the Mantus this is not an issue. A wider shank is also obvious but both a wider and/or thicker shank will be heavier maybe impacting balance. Time will tell.

Note: All the strength values, in MPa, are typical Yield Stress (except for the Mantus – which is an actual value on one sample).

Jonathan
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Old 18-10-2013, 05:55   #81
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Re: It's True! The Mantus 65-lb. hooks first time, everytime.

Thanks for the analysis.

I too just bought a Mantus at the boat show.

We have a 44'. 44,000 lb steel cutter. We bought it with a 45lb CQR. That was clearly inadequate in soft mud. Our sprit design, with a small hole for the shank limited what we could use. The best I could do was a 66lb spade, but damn expensive.

I went north and didn't anchor much. Water is often too deep or free dockage is available.
But one location I did and had a lot of trouble. Some locals came by laughing at me. Apparently I was near the out flow of an old fish plant and it was locally known as a difficult bottom. In some place the Spade just seemed to pull through hardly slowing the boat. That experience may have tainted my decisions.

Over the winter I replaced my sprit, it was badly rusted. I redesigned the whole anchoring system so I could take much bigger anchors. I moved the rollers forward so the flukes would clear the tip of the sprit, and outboard so the anchor would not foul the bob stay. I added fittings at the water line on the bow for my snubber, thus lowering my anchor attachment point to waterline and eliminating bob stay and other chafe. Time for a bigger anchor.

The Mantus has a lot of surface area for the dollar and weight. I believe that when anchoring in soft mud you want a lot of surface area and will develop less angular stress on the shank because the anchor will spin more freely. Also, because of the very reasonable cost I was able to buy a oversized anchor. While not arguing with you analysis, which I feel is correct, I wish to point out that money also comes into the equation.

Dollar for dollar Mantus appears to represent a good value. I got a larger anchor, 125lb, because it was affordable. Being somewhat oversize I hope it is a bit of insurance should I be tired and muck up anchoring. In a storm the size will hold and the shank stand the strain, because it is oversized.If it bends they will replace it, or I can remove it, straighten it, weld on a reinforcement, and go on.

I like flexible solutions and the Mantus seems to fit.

I have not mounted the anchor yet, much less tried it out. So actual performance reports are still pending.
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Old 18-10-2013, 16:06   #82
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Re: It's True! The Mantus 65-lb. hooks first time, everytime.

hpeer,

I'm now moving into conjecture - but most anchormakers scale up the same way, bigger anchor - thicker steel plate for the shank and longer shank etc.

This scaling is fairly simple and Rocna, Excel, Delta have similar scaling. You can check Delta on their website, they have the dimensions of every anchor (as did Rocna - but that might have been removed). Sometimes the scaling goes a 'bit off line' as the plate one might need for scaling is 22mm but the only available grades are 20mm and 24mm - but in general the scaling is a simple straightline graph.

On this basis

A 15kg Excel shank would bend under a load of 430kg
a 55kg Excel shank would bend under a load of about 1,300kg

So increase the weight by 3.6 times and the shank strength increases by 3 times. The difference between 3.6 and 3 is not a major difference as holding capacity is a function of surface area (not weight) and the surface area does not increase by a factor of 3 (its less). The shank of a 100kg Excel, or NZ Rocna, will bend at about 3,000kg. A Delta shank is about the same strength (weight for weight), certainly upto around 50kg, not sure how big they go.

You can do the same calculation for the Mantus but on my calculation a 50/55kg Mantus shank will bend under a load of about 540kg. Recall that the 15kg Excel will bend under a load of 430kg (and for your information a 20kg Excel will bend under a load of 790kg). Your Mantus has the strength of about a 16/17kg Excel or original NZ Rocna of 16/17kg (but the Mantus has a much bigger surface area than the Excel, so potentially bigger load before the fluke moves).

This is conjecture. I have never seen a 50kg Mantus, maybe they use different steel for the shank (you can check, or ask them). maybe they use thicker plate, maybe they use a wider/broader shank.

But in this case I'm not very supportive of the idea that

'Bigger is better'

Under extreme conditions, similar to those you might find as you raise an anchor, 2.75:1 scope, we recorded 600kg snatch loads (max angle 35 degrees) at between 30 and 35 knots on a 6t x 38' cat, which is why I suspect many anchors are bent on retrieval. We did not bend the anchor - we did not continue that part of the investigation!

I think yours is a 20t yacht and the shank will bend under sideways, 90 degree, load of 540kg

Jonathan
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Old 18-10-2013, 16:20   #83
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Johnathan, you made it clear that you have negative feelings about Mantus and shaft strength.

Ad infinitum in fact.

Why don't we wait until they respond, as Greg has said he would once he got back from sailing.

Your questions are legitimate but repeating them over again and over again and again does no good.

We get your point and now lets wait for a response.
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Old 18-10-2013, 16:34   #84
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Re: It's True! The Mantus 65-lb. hooks first time, everytime.

avb3,

I was replying to a specific post of hpeer, maybe I should have sent a PM so as not to upset you - but then no-one else would have realised the relationship.

Long race is it not?

Jonathan
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Old 18-10-2013, 16:39   #85
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avb3,

I was replying to a specific post of hpeer, maybe I should have sent a PM so as not to upset you - but then no-one else would have realised the relationship.

Long race is it not?

Jonathan
I'm not upset at all, I just believe the constant questioning the same thing over and over again is unbecoming of a professional journalist.

As is cattiness.
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Old 18-10-2013, 19:48   #86
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Especially because no one has reported a bent shank yet on a Mantus. I don't discount your math on the first and second pass, but by your 5th post you have lost appearance of objectivity. Do you sell rocnas?
I bought a Mantus because the folks at the boat show were super low key, but excited about many aspects of their product. Where I anchor, lots of soft bottoms, saving weight on the shank and putting it in the fluke makes more sense. The opposite- a bulletproof shank- is on my old Bruce, but it has no holding capacity there.
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Old 19-10-2013, 05:30   #87
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Re: It's True! The Mantus 65-lb. hooks first time, everytime.

Jon is not an anchor seller, he is a sailing journalist specialising in anchor writing and reports
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Old 19-10-2013, 09:26   #88
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Re: It's True! The Mantus 65-lb. hooks first time, everytime.

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i doubt it would cost much more. i should ask my welder how much to cut the steel, and bend it, and drill holes. seriously, he may save $10-40 per anchor. seeing as how his price on the anchors are massively marked up (aren't all marine products) i doubt you would notice a price difference.
Just a reminder all our anchors come with a roll bar included, bc the anchor is modular (comes apart) a customer has an option of the using it without the roll bar,
The point we made that often this is a reasonable approach to use the anchor without the roll bar. All the drops without the hoop we did as the boat was moving, the argument Rex making:"stating that dropping in the current creates a vortex and makes the anchor fall upside down is flawed in principle and in practice..." in each of those drop that boat was moving at 8 knots, the anchor orients itself correctly bc the center of gravity of the anchor is between the front two bolts...
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Old 19-10-2013, 09:48   #89
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Re: It's True! The Mantus 65-lb. hooks first time, everytime.

Our shanks were made of A36 mild steel but we have recently switched to a higher strength ASTM 514 alloy ... We never had a claim for a bent shank yet - the shank is designed to accommodate "violent storm, 60+ kts, loads for its respectively sized boat. In a nominal configuration, shank parallel to rode, the shank does not fail or bend. The most common way to bend a shank is by side loading bc stuck in rocks or something similar. But we listen to our customers and strive to bring the best product available on the market. Any customer who wants his Mantus Shank switched to the new ASTM 514 material shank should only call us...
Greg
On another matter I truly believe that when pictures appeared of bent Rocna shanks on the web it was mostly sabotage, Rocna anchors never offered any danger to the end consumer. The different grade of steel used, surely needed to be disclosed but Rocna still provided a premium product that in its setting ability was superior to anything else on the market and was definitely rugged. The pictures of bent shanks I suspect were mostly staged,,, Anchor shanks bend on occasion but pictures of pretzel shanks that appeared online clearly did not result from in situ use...

Humble opinion, but I play with anchors full time....
may be its worth something
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Old 19-10-2013, 09:54   #90
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Re: It's True! The Mantus 65-lb. hooks first time, everytime.

Again if you ever damage an anchor in anyway simply call us, when you buy a Mantus, we are a part of your adventure and will take care of you!
We will ship the defective part anywhere in the world on our tab.... I think and hope that most customers appreciate it
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