Mantus Anchors .... shank strength

Neeves said:
I'm not quite sure why you want to take your anchor off the bow roller
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Various reasons -

Racing rules often prohibit anchors on the bow. Having seen the damage an empty roller alone made in a raking collision, this seems sensible.

Some boats' bow arrangements do not lend themselves to stowing an anchor. On Kindred Spirit, due to the plumb stem and the bowsprit, I would lower the anchor by hand over the starboard bow a foot or so back from the stem, and only transfer the chain onto the roller alongside the gammon iron once the anchor was on the bottom. On raising, again the anchor itself had to be lifted by hand over the gunwale.

A lot of 60s and 70s small cruisers came with a navel pipe for the chain, chocks for a CQR on the foredeck, and a small or non-existent bow-roller. The assumption was that you would handle the anchor on deck. While more modern anchor-handling arrangements could certainly be added, a lot of owners are happy as they are.

Sometimes the shape of the bow just isn't suitable, without building a large overhanging piece of metalwork.

For some people it's an aesthetic thing - they just think anchors on the bow look ugly.

Some don't like the thought of the weight so far forward.

All that said, on Ariam I'm very happy with the anchor on the bow, ready to go by just unclipping the safety strop and opening the windlass brake!

Pete
 
Thanks for the comments.

I don't know whether I could expect support from all manufacturers. In fact, one of the data points I would like to have is which manufacturers provide their product when the testing protocol is described. If they do, it would show confidence in their product. If they don't, it doesn't necessarily mean they lack confidence as it might be an economic decision since they wouldn't be getting the anchor back, at least not without a bent shaft. In that case, the anchor would have to be purchased. I am also mindful of Rocna's old trick of 'tuning' all anchors sent out for testing, so in an ideal world, you'd buy each one off the shelf.

Regarding rode, I imagined using 30' of 1/4" G4 attached to the winch cable, with a very slow, intermittent pull exerted. I am suspicious of tests where I see the anchor being scooted along quickly because that isn't how anchors set, so I'd like to try to simulate real conditions with a tug, a pause, a tug, etc. Regarding scope, after reflection, I think infinite scope is ok. My reasoning is that this is the way most anchors set. I know many people back down on their anchors that increases scope to 3:1 or 7:1 or whatever, but many don't so one result I am looking for is how well the anchors set with just an intermittent steady pull.

I like the idea of measuring burying depth at intervals of pull. An assumption I have is that hoop style anchors create an impediment to burying with an ultimate reduction in maximum holding capacity. Sand/shell isn't necessarily the place to see that effect best, but knowing the degree to which hoopless anchors dive deeper seems like valuable information.

Probably right on including the Spade, especially for the shank strength test. Same with the Boss. Alloy versions would be nice, but cost becomes a factor. And I would want to include the Tern from NZ, since they sent me one for evaluation and it looks like an interesting diving style anchor that appears robust.

On the single sea bed test, I agree it would be nice, but finding the right locations might be an issue. Likely a sound idea to include a grassy area, but one concern I have is making sure each anchor is really dealing with the same conditions, and it seems there is a lot of variability in grassy bottoms. Mud would be no problem to find up here, but again, each testing dimension added multiplies complexity of analyzing the results. My plan would be to average results over three repeats of all but the shank bending test, with any spurious result tossed and replaced. For example, if you get max pull of 770# twice and one of 2000#, the latter is an anomaly. That said, I would want to publish each and every data point collected so that everyone could see exactly what results were obtained.

And my sincere apologies to the OP for highjacking the thread. But to his question, and just my opinion, I am leery of the Mantus for a couple of reasons.

First, the shank is, as Neeves points out, less substantial than competitor's and made out of mild steel. Second, on another forum, they published calculations on shaft strength that were clearly in error, intentional or otherwise. No discussion was allowed on that forum as to the accuracy or lack thereof, so I don't know whether they were doing what other manufacturers have done - make up performance - or whether they just made a mistake. They promised to republish the numbers, but haven't bothered, perhaps because the forum they inhabit doesn't allow anyone to hold their statements up for scrutiny. Beats me, but it looks like a good hoop style anchor, if that is what you want, but I would wait for the stronger shank they have variously said they already have, will have, or would have if people like me or Neeves stopped pestering them with questions. Again, just my opinion.
 
Neeves said:
The Mantus shank is made from the same steel thickness plate as the similar weight Supreme, Rocna and Excel, so thickness is not an issue. However the Mantus shank width is around 65% of the width (width, looked from the side) of the equivalent weight Rocna, Supreme or Excel and will thus have approximately 65% of the strength of the Supreme and Excel and around 75% strength of the Rocna (please excuse my rounding of data).

The Rocna and Excel shanks seem based largely on the Delta shank which has a strength near that of these 2 anchors - I'm not too sure as I cannot be precise about the steel used in the Delta shank - but independent comment suggests something similar to that of the Rocna and Excel. The Manson shank is slightly different, in fact has a bit 'more' steel.
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Thanks for the clarification. However can ask for help to try to clarify a bit further and get beyond comparisons into "what is necessary for the task ".

From what I have read the major risk of shank bending appears to result from side loads when the blade is well dug in.

The problem seems to be that new SHHP anchors have higher holding power but thinner section shanks than older "forged" anchors like the CQR. However some SHHP anchors now use stronger steels to reduce the risk of bending under side loads.

However in the "fore and aft" plane all the anchors have a much deeper section than in the side plane and hence all can be expected to hold loads several times the load which would cause a bend in side loading.

For example if the shank section is say 4x the thickness then by my logic this ought to be adequate for the sort of loads that will be applied in the fore and aft plane.

Does this make sense to the experts ?

For the record ..I hold no mandate for any of the anchor manufacturer but am simply looking for the best combination of performance, weight and value for a 37ft Cat cruising English Channel, Western France and Med.

Right now the combination that I think should work for me is to go with a 30Kg SHHP anchor, 10m x 10mm chain and 100m x 20mm Octoplat. By my reckoning this gives maximum weight and area for the anchor with a long scope for low weight which should keep me safe in most conditions in depths up to about 13m of water ( in general we seek out shallower anchorages )

All comments welcome
 
Most modern anchor shanks have a profile at the end of the shank, where it starts to turn 'vertical' toward the fluke, of 8:1, width about 8 times thickness of plate. This seems to be adequate in terms of strength if the steel is 700 MPa or stronger. A 4:1 ratio is fine but you would need a thicker shank (thickness of plate) to engender strength, side to side, but thicker shank impedes diving (which is why we have narrow shank sections). There are exceptions, Spade and Ultra - but they have introduced streamlining - and that's expensive. Strength, side to side, is the square of thickness x width x strength all divided by length. You will find that length (excepting the SARCA) is similar across the models - so being a constant (you can ignore it).

A typical modern anchor would be made from 12mm plate and be about 100mm wide.

You will find that the ratio will vary - steel plate does not come in nice sizes (or not necessarily nice for anchor makers to scale up) so the ratio might be slightly different - all anchor makers have the same issues.

Manson Supreme, Anchor Right Excel, Rocna and Delta all work to the 8:1 ratio and 12mm plate for the 15kg model (approximately). Manson's Boss has gone to thinner plate (and the jury is out on whether they might have gone too far). The Kobra has the same 8:1 ratio but its a much lower strength steel - and I'm sceptical - which is a pity, its a good design. Anchor Right's SARCA is a weaker steel but they use a shorter shank length (so shorter lever arm), its welded to the roll bar and the shank is 18mm not 12mm (and they are considering moving to a higher strength steel) - but it passes Proof Load tests as is. Topically the Mantus is about a 5:1 ratio, same 12mm, same length (if anything slightly longer), appalling with mild steel and marginal/questionable with A 514 steel - and well outside the norm (this is not to say that the norm is not overkill).

You are correct a straight line pull, I suspect all shanks are more than strong enough by a number of factors.

I think it was Snoops that made the comment, pull a carbon fibre profile and its as strong as you can imagine, side load it and it will snap (or break). And if you do not have a nice piece of carbon fibre, use a bamboo cane! or even MDF

We have a 38' cat, 50m of 8mm G3 chain and a 15kg SHHP anchor but use 14m x 11mm climbing rope as snubbers. (We have 40m of nylon but have only used it (with another 30m of 8mm chain) to deploy a second anchor). You would be fine with your 30kg SHHP, chain and warp, I hope you have a windlass! We do not use nylon because we have abrasion problems (primarily coral) in Australia.

Jonathan
 
Delfin,

It would be very beneficial if there was a simple and cheap way to measure seabed types. My mud and your mud will be different. It could be a simple test, how far can you push a standard broom stick into the seabed using body weight? Ideas and debate would be valuable. But to define seabed type would allow better comparison of results to other tests done the same way.

On the east coast of Oz we have lots of mud anchorages, most of our rivers are mud and many parts of Moreton Bay (Brisbane) are mud - so mud is common. We also have variable sand anchorages, some silica sands, some coral sands, some granite sands etc. The sands can be soft and hard - so there is sand and sand. Weed is another problem as it varies in thickness (as presumably do the roots) in a very small area, like 10m square it can vary from no weed to lots of weed). We have anchorages, now getting complicated, of nice sand (but only 100mm thick) over 50mm stones!

It is cheap and easy for a manufacturer to supply an anchor made in China, slightly more expensive if they are hand made and polished from stainless steel - but maybe this should not matter.

To engender as much credibility as possible tests can be done any way (as long as its sensible) but needs to have independent witnesses (who can be the labour). I'm in the middle of antifouling tests and the paint companies were all invited to watch application and to visit every time we beach, once every 3 months, and many have come along to watch. I also send them images of every paint panel (there are 12 on each hull) so they know of progress. The public can also, obviously watch the beaching progress. So no secrets.

Jonathan
 
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Neeves said:
The Kobra has the same 8:1 ratio but its a much lower strength steel - and I'm sceptical - which is a pity, its a good design.
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8:1 does not sound right for the Kobra even where the shank joins the fluke. I would have expected less. Are you sure? The Kobra does not have a very deep shank, it is certainly much less deep than the Delta, or Rocna shank.

I would also expect the ratio to decrease with an increase in anchor size and with the very different shank profiles. measurement at single point is not a great a means of comparison.

A single measurement that suggests these two shanks have a similar depth I think is flawed.
 
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Most shanks follow a Delta shape, Rocna, Spade, Ultra, Excel and as they scale up the ratio stays fairly constant. They are also very similar to the Delta dimensions, same angles and length of each arm etc. I confess to only have a small Kobra and certainly the drawing you post shows that the width is not very great, which with its low strength steel makes it even more questionable.

There is no single measurement, its where the shank trends from horizontal to vertical. With the Mantus that gives a very long lever arm, exacerbating its weakness (and compounded as they have drilled a hole where the horizontal and vertical meet - which is why its ratio is only 5:1). The Spade has been cleverly designed that it follows the Delta shape, simply smooth out the corners, but it increases in thickness (or the box does) from shackle point to crown which appears to distribute load evenly (as does the Fortress). In terms of the Kobra measure where the shank goes from horizontal to vertical. The Ultra is much more complex as it now incorporates 2 internal webs of steel and the 'box' itself (the plate thickness of which cannot be measured without cutting one up).

If you measure you can make your own estimates of where vertical meets horizontal to measure width and you can be as generous to a specific design as you like - but realistically, Delta, Excel, Rocna are all a stronger (and significantly so) shank than Kobra and Mantus.

No-one says its an exact science:)

Jonathan
 
I know nothing about anchor design nor steel manufacture except i recall the Rocha was made out of rolled Bisplate. I assume by this this they mean a sheet of thick steel is passed between rollers until the desired thickness is achieved.

Is it a lot more expensive to hand forge an anchor stock so that the narrower sections could be thicker. I reliase it would cost more but is is it dramatically more ? I suppose you would be reliant on the skill of the operative. I also do not know if you can then weld the flukes (I prefer rolled to cast) onto the forged stock. I remember in the CQR the flukes were attached by a hollow swivelling joint.

Sorry if this sounds mickey mouse ;)

Edit: thinking about it, it may be possible for Rocna to have a variable thickness stock if they cast it like they now cast the flukes.
 
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Storyline said:
I know nothing about anchor design nor steel manufacture except i recall the Rocha was made out of rolled Bisplate. I assume by this this they mean a sheet of thick steel is passed between rollers until the desired thickness is achieved.

Is it a lot more expensive to hand forge an anchor stock so that the narrower sections could be thicker. I reliase it would cost more but is is it dramatically more ? I suppose you would be reliant on the skill of the operative. I also do not know if you can then weld the flukes (I prefer rolled to cast) onto the forged stock. I remember in the CQR the flukes were attached by a hollow swivelling joint.

Sorry if this sounds mickey mouse ;)
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Bisplate (the name of the product) is a quench and tempered steel, made by Bisalloy. The chemical composition of the steel is specific to the down stream process of the Q&T company (though the variations might be small - do not know). The steel is delivered to this chem spec in plates of various thicknesses and is then heated, quenched (with oil or water) re-heated and then slowly cooled. Its all about getting the crystalinity right The temperatures and timing are controlled and not disclosed They can 'make' anything upto a 1400 MPa steel (armour plating for military vehicles) - maybe higher, they get secretive! The steel plate thickness is not altered in the process - the steel supplier supplies steel plate to the thickness that is eventually sold - 'all' the processor does is make it stronger! Anchor Right and Manson use an 800 MPa steel. Rocna are now, the information is 2-3 years old, using an alloyed high tensile steel around 700 MPa (similar I think to Delta). Alloyed steel uses the alloy to impart strength but I think 700 MPa is about the max for an alloyed steel. Vyv might correct me on all of this:)

There are a number of Q&T suppliers, Tata in the UK, for example - the Knox anchor uses Corus/Tata Q&T steel. You can buy it off the shelf, - though you need to laser or water cut, be careful welding and its difficult to bend.

The CQR shank was drop forged and needed, what is now expensive equipment, and the same strengths, or better, (and lighter) can be made using alloying or Q&T. Drop forging is 100's of years old, Q&T, commercially, is only a few decades old. Equally welding was in its infancy when the CQR and Danforth were developed and are now both cheap, commonplace and technically, compared to say the 1940s - very sophisticated and easy. WWII was the catalyst to much of this. Though as many things - good welding takes practice and skill.

Going back, 100 years ago, there were limited ways to build strength. - now we can do it many ways. Box structures, think Spade, high alloy steels, think Rocna and Delta and Q&T steels and we have welding (anyone can buy a pretty sophisticated welding machine from B&Q - not even a dream for our fathers!)

Basically its easy to buy steel plate to whatever precise thickness you need, to whatever tensile strength you want, take it to a subcontract cutter, precision cut and then bend and weld. (You pay for small pieces but you would expect that) Your investment is a machine to bend and welding. I simplify but one could build with care and knowledge a perfectly acceptable anchor in a garden shed (you could weld instead of bending). Drop forging, casting - much bigger investment (huge) - not for the garden shed.

What has happened is - the investment the anchor maker would have made 10's of years ago (to effect strength) has now been made by the steel processor. The processor makes a much bigger investment but is able to sell that same steel for mining, nuclear submarines, armoured cars, steel reinforced buildings etc.

Once you have the perfect prototype you can then invest in the bending equipment, contracts for bulk steel plate and cutting etc etc.

Spade have gone another route - the complex box section, which is strong - but inordinately expensive (as is the fluke - lots of little pieces, all welded carefully, think expensive). I suspect the shank, box, design was based on knowledge before Q&T became so commonplace and cheap. Why they have not changed (and gone for a cast fluke) beats me.

Excuse me if I have not quite got the process right - Vyv is welcome to correct - but it gives an idea.

Jonathan
 
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An interesting and, for once, civil thread.

I can't help thinking that those in search of the one perfect anchor are due for an interminable search like the Flying Dutchman. That's for one reason, the bottom in which you're anchoring. Neeves touched on that with his little comment on the different types of sand or mud bottoms.

perhaps that's why Vyv hasn't risen to the temptation of designing the perfect anchor.
 
Storyline said:
It does explain the whole process. So an anchor manufacture could specify a higher strength for the stock using the Q&T method. The only restraint is presumably cost.
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Q&T steels are freely available- you could cut them in your garden shed and if you had reasonable welding skills and stuck to the freely accessable guidelines you could satisfactorily weld them. You could not bend in a garden shed (but you could form shapes by welding). I simplify - you would need to be a good welder, but it is possible.


Hi tensile steel is more expensive than mild steel and is more expensive to process (both cutting and welding) but the cost of the steel (or raw material) is not a significant part of the cost of an anchor. Once you get to the cost of the anchor in the chandler the raw material cost is pretty insignificant (though that more expensive Q&T steel adds to the production cost (but not that much of an add on)).


The best example might be a Kobra. To me a good design (I'm not keen on the folding shank - but ignore that) - in its basic form its a good design. Simple and cheap to make. It works well and is sold relatively cheaply (you can correct me if you think it expensive, or not cheap). But it would be so much more commendable if they used a 800 MPa shank (the steel is freely available in China, its made to the same plate thicknesses and tolerances as anywhere else in the world) as the Q&T steel would add little to cost. The shank is not welded (so no cost there) - its simply cut out. As Vyv points out many components on a yacht are assembled in a way not dissimilar to a Kobra shank to the fluke, turnbuckles for example - slots and pins.

Equally the Spade complex shank could be replaced with a simple Q&T steel plate, no complex construction and welding and, I'm guessing, real leap of faith, the Q&T shank would be as strong (I think stronger) as the fabricated shank they make already and add no weight (so the balance would remain the same - the anchor would perform the same way, maybe better as it would not need to be profiled).


But go into your local chandler and you will find lots of anchors, of various design, with no brand name. They are cheap but not necessarily cheerful. They suffice as lunch time anchors and meet regulations where anchors are demanded (anchors are specified but they do not need to work). Their major 'advantage' is they are as cheap as chips. The 'quality' manufacturer is up against these anchors and these cheap anchor form a large part of sales (which is why chandlers are full of them). Consequently there is great pressure to keep costs low.. I sympathise (with the dilemma of the quality manufacturer)

The other issue is that most people are not concerned about 'quality' - most people think if its on sale it must work - so why pay more for a 'Rocna' when you can buy this cheap thing that sits along side it. I sympathise with the buyer - if its on sale (and its a safety item) it ought to work. As an example - no-one questioned the strength of the original Mantus shank - despite the furore over Rocna (short memories?). I do not like/want to rake up Mantus - and like Rocna the problems should now be history, but make interesting lessons.


My views are fairly well known, anchors should work, anchors should be indestructible (even if that means they are slightly over engineered), anchors should be fairly idiot proof , viz drop them and they should set easily (no skill should be required). I appreciate that not everyone would agree with me. My requirements add a cost of a bit more than the cheap, unbranded, anchor in the chandler


Sorry but you got me started and further apologies to the OP who did express fears about starting the thread in the first place:)

Jonathan
 
No, I agree with all you say. If a manufacturer can use a better grade of steel for little additional cost then people in the know have every right (maybe even a duty) to take that manufacturer to task for the benefit of fellow sailors.

Edit: i cannot understand why people buy 'copy' anchors of dubious strength. I understand that cost is a very real issue for everyone, some more than others, but going second hand and buying something better would, imho, be a more sensible option.

Edit2: it could be of course, that some people do not realise that anchors can bend. If you pick up a heavy steel copy anchor it might seem unlikely that you could foresee anything that could bend it.
 
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Storyline said:
No, I agree with all you say. If a manufacturer can use a better grade of steel for little additional cost then people in the know have every right (maybe even a duty) to take that manufacturer to task for the benefit of fellow sailors.

Edit: i cannot understand why people buy 'copy' anchors of dubious strength. I understand that cost is a very real issue for everyone, some more than others, but going second hand and buying something better would, imho, be a more sensible option.

Edit2: it could be of course, that some people do not realise that anchors can bend. If you pick up a heavy steel copy anchor it might seem unlikely that you could foresee anything that could bend it.
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I do think that people honestly and sincerely think that the copy anchor they buy in the chandlers is strong enough - in fact I suspect it never crosses their mind it can bend. But copy anchors tend not to hold very well and the chance of the anchor bending, because its holding capacity is high and it does not lift easily from the seabed is not an issue.


Jonathan
 
charles_reed said:
An interesting and, for once, civil thread.

I can't help thinking that those in search of the one perfect anchor are due for an interminable search like the Flying Dutchman. That's for one reason, the bottom in which you're anchoring. Neeves touched on that with his little comment on the different types of sand or mud bottoms.
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My personal theory is that you are quite right that one anchor design may work better in one bottom type than another, however, that design advantage tends to be leveled out a bit if the anchor not optimum to a given sea bed is heavier than the optimized design. In other words, weight can trump design, which is why I am of the opinion that all things being equal, one should go with the largest anchor they can comfortably and safely handle.
 
Neeves said:
I do think that people honestly and sincerely think that the copy anchor they buy in the chandlers is strong enough - in fact I suspect it never crosses their mind it can bend. But copy anchors tend not to hold very well and the chance of the anchor bending, because its holding capacity is high and it does not lift easily from the seabed is not an issue.


Jonathan
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I'm not so sure people with cheap anchors ever plan on anchoring with them much, outside lunch hook territory. I looked at an 82' Westport yacht today, and I swear the Claw they have can't be more than 66#. This vessel has the windage of a spinnaker, so I assume they have rarely anchored, if at all. I should take a picture of this, as it seems like the most extreme example of "what were you thinking" when it comes to anchor selection I have seen.
 
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