It's True! The Mantus 65-lb. hooks first time, everytime.

[Panope]

Originally Posted by Delfin

Too shiny? My Ultra is too shiny? Now you've hurt my feelings.....

Na, the shiny anchor is good for you because it matches the rest of your boat

The great thing about debating aesthetics is that everyone gets to be right!

Steve

[noelex 77]

Originally Posted by Panope

Now, if we start talking about non-bow anchors, give me a 4X oversize Mantus (that would be 85lbs. for me) disassembled and in the bilge. Would make a hell of a storm anchor or temporary mooring. I would guess that the shank would be as resistant to bending as my 45 lb Supreme regardless of the grade of steel used.
Steve

It is a excellent point that as you oversize anchors you increase the strength. I don't have figures of the progression of shank thickness and depth, but because the strength goes up as the square of the thickness, my guess is the effect is quite dramatic.

The most common reason for bending an anchor is getting it stuck under a rock during retrieval. The maximum force the boat can exert to unstick the anchor is dependent on the boat characteristics (engine size, displacement and the strength of the bow roller and cleats are probably the biggest factors). It is independent of anchor size. Going for an anchor that is +1 to +2 oversized, like most cruisers do, does not alter this maximum force only increases the anchor strength.

Perhaps someone with access to anchor details would like to calculate the typical improvement in shank strength when we go +1 or +2 oversize (or just supply the thickness and depth and I can do the calculations).

[JonJo]

Noelex,

At your request:

And to keep the thread on track:

I do not know what the current shank material of a Rocna is. It was last quoted as Q620 steel. My calculations are on this basis. I quote Rocna as I have the dimensions of the series: If you want to work out the strength of a Bis 80 shank - it is about 10% stronger, a Q420 shank will be about 30% weaker than the Q620.

Load to bend:

15kg Rocna, 384kg
20kg Rocna 715kg
25kg Rocna 670kg
33kg Rocna 639kg
40kg Rocna 1009kg
55kg Rocna 1153kg

As mentioned when you scale up sometimes the steel plate, for the shank, cannot be scaled up the same way. Steel plate comes in standard thicknesses 8mm, 10mm, 12mm, 16mm, 20mm and 25mm etc. The 20kg Rocnas had (it might have changed) 16mm shanks, which looks too strong for the 20kg model and perhaps not strong enough - to provide a nice scale - for the 33kg model.

However it does illustrate going two sizes bigger does not, necessarily, result in an increase in shank strength - in fact far from it. This is not to say any of the shanks might be 'too' weak - it could be some are 'too' strong.

Another way to look at it is

the 3.6 times increase in weight, between the 15kg model and the 55kg model results in a shank strength increase of 3 times (not far from the anchor weight increase - but it is less) - but its not something, scaling, you can rely on and it would be dangerous to make recommendations on the idea that scaling weight automatically allows scaling of shank strength.

This restriction applied by the availability of steel plate might be addressed differently by different anchor makers. Some might use, say, a 12mm plate for the 20kg model, some might change the shank width slightly and/or shorten the length, slightly - so what works for one design might not work for another.


And on another note; I have never heard that -regalvanising Bis 80 would affect its high tensile properties (though if it was left in the bath for a long time there might be an effect). The major issue would have been acid pickling prior to galvanising - the HT suppliers are paranoid about Hydrogen Embrittlement - though finding evidence of failure, outside HT construction bolts is difficult.

Jonathan

[Factor]

Originally Posted by Cotemar

Delta Knockoffs are just ok, I would never call them the best.

The Sarca Excel = Delta has the "Problem Bend" that causes them to drag slowly and push the seabed to the side, you know "Plow"

Not this again. The excel is not a delta knock off, it is a different anchor and I have owned both. Unfortunately you seem to be unable to understand the difference.

[Factor]

Originally Posted by Cotemar

REALLY. what where you thinking ????

Sounds like you like bendy things also.

The Anchor Right Sarca are just as bendy as all the rest.

Ahem, m,ay have been too technical for you, the SARCA and the EXCEL are two different anchors

[downunder]

Originally Posted by Cotemar

Delta Knockoffs are just ok, I would never call them the best.

The Sarca Excel = Delta has the "Problem Bend" that causes them to drag slowly and push the seabed to the side, you know "Plow"

Here we go again. A moderator who has never seen an anchor for some reason with an axe to grind attempting to side-track a Mantus thread. About time the SARCA thread was reactivated to cover some of their new developments.

For anyone considering full time cruising information on anchoring gear, of your most important safety systems is always interesting. The information available on this thread re Mantus has been interesting and it is good that the USA has a committed manufacturer /developer. However its early days and I am yet to be convinced to move away from a bisalloy shaft.

[noelex 77]

Originally Posted by JonJo

Noelex,

At your request:

Thanks Jonathan.

As you say, the results are quite variable. We need to be careful talking about the mean when discussing data with such a high standard deviation, but for what its worth:

+1 gives about a 30% increase in shank strength
+2 gives about a 50% increase in shank strength.

The nice thing about these gains is that they are achieved without effecting the anchors balance or reducing the performance, as would be the case if we achieved the 30%, or 50 % increase by making the shank thicker, or deeper.

The bigger anchor will of course also gain significantly more holding by virtue of its larger size so it's a win win.

[d.taylor]

Originally Posted by JonJo

Greg,

The Fortress shank is slightly more complex than a conventional shank, it tapers in 2 planes and it has a bevel on the leading edges. The overall shank length is not the 'lever length' as the shank will impinge on the mud flaps and crown. So it articulates at 'full length' but its lever length is shorter. I did a quick measure and calculation and came up with a load to bend of over 400kg - which seems to agree with actual tests conducted by someone independent of Fortress. They also mentioned it was very bendy, flexible - it would spring back until it reached the bending load. This srpinginess allows the shank to absorb snatch loads. As far as I am aware side loads will be snatch loads. Conversely a mild steel shank lacks any springyness - it simply bends. Delfin raised the issue of springyness in a post some time back.

Jonathan

JonJo you should actually read Greg's post or is it you are just unfamiliar with CAD and Finite Element Modeling? I realize there are a lot of posts, maybe you only skimmed it.

I'll address all your points below.

The Fortress shank (FX-23) that Greg modeled was indeed a 3-D model. It was fully tapered along length & width. That is the benefit of 3-D modeling - much more accurate representation than a 2-D idealization. Although with a straight shank like the Fortress - the 2-D hand calcs correlate very well. (Much more so than the shaped Rocna shank that JonJo analyzed and published in PS. Ref my earlier posts #167)

Regarding the lever arm, yes indeed that was also explained. Greg fixed the shank at 28.5-in (724 mm) from center of shackle hole. The overall length of the shank is ~35-in. Note where the color changes from green to blue. If you open the model you can see the Yield stress (275 MPa, 40ksi ) corresponds to a yellowish-green. Blue is no load.

Cross-section shown below.



Regarding JonJo's “calculated 400-kg load”.
How was this calculated? Using same equation as in your PS article?
http://www.langleysquadron.com/uploa...chor_loads.pdf

W = 1/30 x Y x B x D2/L
Y = 275 MPa (for 6061-T6)
B = 83 mm
D = 21 mm
L = 724 mm
⇨ W = 463 N which is equivalent to 104 lbf.
But it is already known that that equation is erroneous, so it is not surprising the results doesn’t match anything.

Using the correct equation (see my post #165 for derivation or refer to http://en.wikipedia.org/wiki/Bending):

Sigma = Mc/I which leads to
F = sigma * I / (d*c)
Sigma = 275 MPa or 40,000 psi (for 6061-T6)
c = 0.82/2 in
I = 0.11 in4
d = 28.5-in

This results in a Force, F = 376-lbs (or 1,672 N)
Greg's FEM predicted ~400 lbs, so that is pretty good correlation, but not exactly surprising since like I said the Fortress geometry fits this idealized equation well.

BUT we do have the issue of material properties to address. Greg assumed Al 60601-T6. But I notice in your PS article "Anchor Tests: Bending More Shanks" May 2013 Issue. You mention Fortress uses Al 6060.
"The anchors used were a 17.6-pound Fortress FX23, a Danforth-style anchor fabricated from a 6060 alloy aluminum".

You don't mention the temper, but yield strength for 6060 is closer to 120 MPa (17,500 psi).
It's hard for me to believe that Fortress actually uses 6060. So either this is a mistake is your article or the numbers calculated above are too high. Yield load would be closer to 200 lbs.

So please share what you used for your Y, B, D and L and it will be easy for me to see why the difference in calcs.

Regarding the testing, Fortress references, Brian should send test report or post video. Was this test in a test jig or in-situ? Without knowing exactly how the shank was constrained and how the load was applied, I can not comment on difference in values. The ground testing would include friction & misalignments that are not accounted for in the model, but the results should be relatively close. I suspect if loading is as he stated, the load was not pure lateral. Also it sounds like there was potential for cold-working to be occurring with steady load applied and released. This is fairly easy to do with Al. Of course this is just speculation, without the video or recorded test data.

JonJo, we can't work with just "answers" that you can't explain. Please provide calculations so that we can discuss this on a technical level.

"Springyness" - in the engineering world we call this linear elastic behavior. Look at a stress-strain curve. The first part of the curve is linear before it begins to bend over. As long as loading occurs in the linear range the material never strains or deforms and always returns along that line. Steel also has a linear range. Modulus of Elasticity of Al is about 1/3 that of steel. The big difference is Steel has a distinct yield point, but Al, after exceeding the linear elastic range has a slow knee-ing over effect. Look up the curves a visual is much better.

[JonJo]

D. Taylor

Instead of knocking all and sundry

Please define what is the strength of a Mantus shank.

Please clarify what is the position with regard to the roll bar.

Knocking the competition does not earn you brownie points - it might make you smile (to knock them) - but Fortress have thousands of happy customers - your knocking their favourite anchor does not engender love and respect.

If you have an issue with declaring your shank strength, please advise, but having spent so much time analysing a Fortress why are you so reluctant to quantify your own product?

Jonathan

[Dockhead]

Originally Posted by JonJo

D. Taylor

Instead of knocking all and sundry

Please define what is the strength of a Mantus shank.

Please clarify what is the position with regard to the roll bar.

Knocking the competition does not earn you brownie points - it might make you smile (to knock them) - but Fortress have thousands of happy customers - your knocking their favourite anchor does not engender love and respect.

If you have an issue with declaring your shank strength, please advise, but having spent so much time analysing a Fortress why are you so reluctant to quantify your own product?

Jonathan

In order to improve the tone of this valuable discussion, could we all please be more careful about accusing each other of, for example here, "knocking"?

There is absolutely nothing "knocking" in D. Taylor's extremely factual post. He was answering specific comparisons to Fortresses in a completely factual way.

People, don't spoil this thread by spoiling for a fight. We are really tired of it.

[Fortress]

I think that our late company founder would find it quite satisfying, and maybe even amusing, that our shank is being compared in strength to a steel anchor that is what, 2x or 3x heavier?

[JonJo]

D Taylor,

I must confess to have been slightly cavalier with my measurement of the Fortress shank. I have been slightly more careful - as I note you like accuracy and are sharp!

My original calculations were based on

Lever Length 700mm, width 81mm, thickness 25mm and a Yield of 275 MPa

This calculates at a load to bend of 462kg

However note this is a minimum yield, actuals will be higher.

I checked my measurements and sadly would like to ammend them to:

Lever Length 700mm, width 75mm, thickness 24mm and a yield of 275 MPa

This calculates at a load to bend of 395 kg

An original 15kg Rocna has the following dimensions

600mm length; 100mm widrth, 12mm thickness and a 750 MPa yield (note this is typical Yield not min)

This calculates at a load to bend of 418kg (if we use the min yield of 690 MPa it recalculates to 385kg (just so the Fortress is compared like with like to the Rocna)

Now if I take the 15kg Mantus

Length 650mm, width 65mm, thickness 12mm yield 550 MPa

Load to bend 184kg

Note this is the Yield I had measured by an independent lab.

The steel you specify you are actually using is, I think A36 - which has a min Yield of 250 MPa. If I recalculate with this min (so as to compare with the min yield of both the Fortress and Rocna then

Load to bend is: 84kg

If you move to use a A514 steel, say 750 MPa yield, then the load to bend re-calculates to:

251 kg (or 230kg if we use min yields)

I am not sure why the sample I had has a yield stress as measured of 550 MPa if you are using an A36 steel (which I might guess would have a typical yield of 300 MPa?) Hopefully every anchor you have sold has the same steel as my sample.

I accept there can be differences in interpretation of 'lever length', 'width' and 'thickness' (and this latter makes a real difference). There is also some ambiguity of Yield Stress min vs actuals or typical. I have made these calculations the same way - they maybe 'airy fairy' but they are accurate relative to each other. Possibly you can calculate the load to bend of a Mantus and using that exact same formula calculate Fortress and Rocna - the comparison will not change.

However for anchors ostensibly for the same size yacht both the Fortress and Rocna are 'similar' with a load to bend of 400kg (Noting this understates the Fortress as it is based on a min yield not a typical)

The Mantus if I am charitable has a load to bend of 184kg, but based on your quoted steel - it has a load to bend of 100kg (assuming 300 MPa typical). You will be introducing the A514 shanks which will lift the load to bend to 251kg but this is a long way from the industry norm of 400kg and I question those anchors already sold - 100kg to bend!

Now that I have sat down and written this I understand your focus on Fortress and Formula.

I also continue to question clarification of the roll bar issue.

Jonathan

[Fortress]

I think that "knocking," as stated by JonJo, is when you publicly use your own test data, instead of from an independent source, to state what you believe to be a weakness of another brand.

Rather than present complex formulas regarding shank strengths, may I suggest to Mantus that through the use of videos (which you are very adept at), you put to rest the two key concerns and questions which are repeatedly being raised here about your product.

As an example, you could have your anchors put into a pull / destruction machine (which you may already have) and conduct load tests from varying angles and resistance points to prove the structural strength of the shank and fluke. Sure, this is a type of simulation and is not "real world" so to speak, but at least it is understandable and visual.

Next, take videos which show the anchor being deployed without the roll bar and as it is sinking, it self rights itself and lands fluke down on the sea bottom, and is ready to set. If it doesn't self right without the roll bar, then show how it will with simply a minimal pull.

I understand that such videos are not simple to set up, but I am sure that the end results would prove to be worthwhile to you.

Best of success,
Brian

[Mantus Anchors]

Originally Posted by Fortress

I think that "knocking," as stated by JonJo, is when you publicly use your own test data, instead of from an independent source, to state what you believe to be a weakness of another brand.

Rather than present complex formulas regarding shank strengths, may I suggest to Mantus that through the use of videos (which you are very adept at), you put to rest the two key concerns and questions which are repeatedly being raised here about your product.

As an example, you could have your anchors put into a pull / destruction machine (which you may already have) and conduct load tests from varying angles and resistance points to prove the structural strength of the shank and fluke. Sure, this is a type of simulation and is not "real world" so to speak, but at least it is understandable and visual.

Next, take videos which show the anchor being deployed without the roll bar and as it is sinking, it self rights itself and lands fluke down on the sea bottom, and is ready to set. If it doesn't self right without the roll bar, then show how it will with simply a minimal pull.

I understand that such videos are not simple to set up, but I am sure that the end results would prove to be worthwhile to you.

Best of success,
Brian

Brian,
First, as stated many times, I am not knocking your anchor, I think its an excellent anchor and the shank is plenty strong. I think I said this multiple times... Nor did I ever knock on anyone...
What I am is being, is factual as I suggest everyone here should be...
And I will include Mantus in the Mix as stated...

Brian, remember

I agree, I do not think anything I am currently doing,,,,,is important I would rather be doing dragging videos, showing Mantus setting abilities.... or watching "Breaking BAD"
After, being attacked I realized that there is no real data on the subject of shank strengths and that people writing on the subject bring incomplete and often inaccurate information to the end consumer... and induce unnecessary panic in the eye of the consumer....
But as promised I will tabulate all shank strengths in CAD Fine Element Analysis in the public realm... This is just another Altruistic thing I am doing
and since its in a public domain anyone can look at the data and challenge it......

As far as videos you ask, though lacking from your website (as well as material specs), they are coming... Thank you for the complement on my abilities by the way....
Brian in the end, I am sure you are a nice guy and in fact I wanted to say hi to you in Annapolis...We just got so busy. But remember you are in the thread about Mantus and are throwing punches....
Greg

[Fortress]

Originally Posted by Mantus Anchors

But remember you are in the thread about Mantus and are throwing punches....
Greg

Greg, I appreciate your comments. My intention has not been to throw punches at Mantus, but rather defend what is thrown at us.

No matter, publish whatever you see fit and we will let the court of public opinion decide.

Carry on!

Brian