Rocna Anchors acquired by Canada Metal Pacific

[evm1024]

I think the point here is that when a shank bends, the geometry of the anchor changes and it will no longer set. So given the scenario of a change in wind direction, the anchor bends under stress of the twisting, and does not reset to the new find directions - so you are on the rocks perhaps.

And will very likely corkscrew out of the seabed on the next surge load, if not sooner.

I recall that Smith was adamant about the alignment of the shank and blade being within 1 degree. (Now where was that post....)

 

[toad_oftoadhall]

On the issue of "not-as-advertised" versus "unsafe" - I've seen the many pics of the bent shanks on the Rocnas. So I totally understand and agree with the "not-as-advertised" complaint.

But to me that's not necessarily a safety issue. If the shanks/welds are breaking - then crying foul on safety is perfectly valid. But if they're bending, while still keeping the boat off the rocks, then that just seems like a lousy product with great holding power. In other words, it's still performing its basic function. So does bendiness alone really equate to an immediate safety concern across the board?

I doubt that in actual use they even bend more:

Warranty returns cost a fortune so if the number of warranty returns had risen to any large degree it would have been uneconomic to make them out of the softer metal and Rocna would have switched the metal to something that reduced warrenty claims as close to zero as they could.

Plus IIRC the 'dud' 'soft' galvanised Rocna anchors are still stronger than the 'full strength' stainless steel Rocnas, and nobody complained about them.

So if my memory is right in actual use there's clearly been no meaningful difference.

I'd have thought that if anything was going to bend it would be the narrow "pointy tip" (someone remind me what the hell that's called) which I would guess is slender for faster setting at the expense of strength. But all modern anchors have that because they have to win magazine anchor tests.

None of which excuses publishing incorrect spec on Rocnas website and it *certainly* doesn't begin to excuse bribing Rina staff (if that turns out to be true).

Jesus, I've just got involved in an anchor thread. On the one hand I'm grateful to Grant for breaking the Rina story, on the other hand he's got me reading the anchor threads. :-(

PS: All the above is my own opinion. I haven't checked facts to make sure my memory is correct. Nor have aI checked spelling or grammar!

 

[noelex]

I'd have thought that if anything was going to bend it would be the narrow "pointy tip" (someone remind me what the hell that's called) which I would guess is slender for faster setting at the expense of strength. But all modern anchors have that because they have to win magazine anchor tests.

Like this bent Manson Supreme

 

[toad_oftoadhall]

Like this bent Manson Supreme

The internet rocks.

I make a whisky fueled fireside guess, 25 minutes later someone who actually knows what they're talking about confirms it.

Thanks noelex.

(Well confirmed is overstating the case a bit but I'm still chuffed.)

 

[Neeves]

Noelex - its a toe! as in foot or feet if you have 2 or more anchors.

 

[DaveS]

On the only occasion when I have anchored (and dragged) in a hoolie, the pull has been dead in line with the shank. Of course a hoolie can veer or back, but in those circumstances I might well decide to reset, not only to avoid putting a lateral bending strain on the shank, but also to make enough room for all the scope that is necessary.

This is getting a bit off the topic of the R*cna scandal, but I'm curious...

One of my more challenging anchoring experiences involved a well forecast deep depression. I chose a spot with around 7:1 scope at high water, all chain, with good mud holding and ample clearance on all sides. Over 16 hours the wind varied from F8 to F9 with gusts of much more and veered through 270 degrees from E to N - exactly as per text book. Afterwards, recovering the deeply buried anchor (a 16kg Delta) was very difficult and the jaws of the Kong swivel connector were seen to have been splayed by about 2mm. (I now have a few links of chain between connector and anchor to prevent that.)

If I understand you correctly, in these circumstances you would advocate an alternative strategy of following the veer by lifting and re-laying the anchor several times?

Really?

 

[noelex]

If I understand you correctly, in these circumstances you would advocate an alternative strategy of following the veer by lifting and re-laying the anchor several times?

Really?

New generation anchors (with the exception of the Fortress) will remain buried and reset to the new direction.
The Delta resets well.

 

[BrianH]

If I understand you correctly, in these circumstances you would advocate an alternative strategy of following the veer by lifting and re-laying the anchor several times?
Really?

+1.
That's the whole point, isn't it? I too have been anchored in a 60 knot gale veering after some hours. No way would I have willingly released my grip on the sea bed, especially as a lee shore was very close - the protective bay was small.

That's when loads come onto the shank, as the anchor tries to line up with the new load-line. And just when one doesn't want a 420mpa, thin steel shank .

Maybe it will bend, and hold - vide the Venice example. But if on passage any further use is out of the question.

 

[smackdaddy]

I see your point Barnacle about not being able to use a bent anchor again, even if it did keep you off the rocks in the blow. And this is a safety concern in and of itself.

In the scenario you guys are discussing, any ideas on the additional amount of force that would be required to bend the 800/620 shank vs. the 420?

2X? 3X?

 

[Stork_III]

I see your point Barnacle about not being able to use a bent anchor again, even if it did keep you off the rocks in the blow. And this is a safety concern in and of itself.

In the scenario you guys are discussing, any ideas on the additional amount of force that would be required to bend the 800/620 shank vs. the 420?

2X? 3X?

Basically (620-420)/420 x the 420 force. Ie 48 % more load.

 

[smackdaddy]

Basically (620-420)/420 x the 420 force. Ie 48 % more load.

Cool. Thanks stork. So, basically, though I suck at math...in a hypothetical situation where 1000 pounds of force bends the noodle shank, just 480 pounds of additional force will also bend the "strong" shank?

I assumed there would be more of a difference. Interesting that we don't see more bent shanks across the board.

 

[Twister_Ken]

Interesting that we don't see more bent shanks across the board.

The suspicion is that there were more, but they went back to Rocna and were hushed up. Grant may be able to elucidate.

 

[evm1024]

Actually I think that you should do the calc normalized to BisPlate80 as used in the original design shanks.

Going from Bis80 with 750 MPa typical yield strength to 420 steel is a decrease of 40%. Going up to a 620 steel from 420 gives a shank that has a yield strength about 17% weaker than Bis80.

So what does that mean?

Let's take a 40' sailboat and use some loading figures from the Fortress website. And lets assume that your Bis80 NZ Rocna shank yields (bends) at 3000 pounds side force.

THe fortress site gives 1200 pounds loading for 30 kt. 2400 pounds for 42 kt and 4800 pounds for 60 kt.

With the NZ rocna and a 3000 pound yield shank you are good at 30 kt and 42 kt but would bend the shank with a 60 kt side load wind. This assumes that the anchor will not rotate which is likely of an anchor stuck on something. But if not stuck then the anchor may rotate before a 3000 pound rotational force (torque) is reached. Just how strong is the seabed? This is a key thing.

With CN Rocna with a 420 yield shank we can expect what would have been a 3000 pound shank with bis80 to bend at 1800 pounds side load. So at a 30 kt side wind generating 1200 pounds you are OK but clearly the 2400 pounds from a 42 kt side load is greater than the shanks yield strength. In addition it may be that a well bedded anchor in a firm seabed may resist rotation with a force greater than 1800 pounds. Bent noodles....

With a CN Rocna with a 620 yield shank the results are better. It would bend at 2481 pounds. So with a 30 kt side load wind generating 1200 pounds we are golden and the anchor holds. With the 42 kt wind generating 2400 pounds we can expect the anchor to bend as well, just like the 420 shank would assuming that the seabed held the anchor fixed. Anchor yield 2481, wind 2400. It may be that the "typical" seabed cannot resist a 2400 pound rotational force in which case the anchor changes direction rather than bends.

Now of course these numbers are pulled out of the air and do not come from any specific set of tests. So don't anybody go ripping them apart. They are indications not data.

But the take home point remains.... The shank needs to be engineered so that its strength (yield of steel and size of shank) is greater than the expected resistance to rotation of the anchor in the seabed plus some safety margin. And given the numbers used above even a 620 shank will bend in 42 kt of wind and firm seabed where as a Bis80 shank would not.

Using Bis80 gives a stronger shank for a given size than 620 or 420 steels. When using 620 or 420 the shank size should be increased to retain the original designed shank strength. Using the same size shank decreases the strength which makes noodles.

Playing with number is fun and can only show us the path to understanding.

 

[smackdaddy]

The suspicion is that there were more, but they went back to Rocna and were hushed up. Grant may be able to elucidate.

I mean with all kinds of anchors, not just Rocna. Why wouldn't we see more evidence of bent shanks with even Fortresses, or Mansons (etc.) if the force difference between a bend and no-bend is "just" 48%?

I assume it's because the 420 started bending in more typical "challenging" anchoring conditions (maybe 20+ knots with a shift?) where bending had not been seen before. But with the scenarios discussed above (anchoring in really heavy conditions), what's the bend point for a Manson? If we took the same ratio, would it be 30+ with a shift?

Or do we start getting into exponents here?

(Just saw the above post. Thanks evm. That helps a lot. So even the topline shanks will bend in roughly 45+ knots.)

 

[evm1024]

I don't have the design specs so I could not say what rotational force the Original Rocna were designed to withstand. I do know that the the designer selected Bis80 so that he could reduce the size of the shanks and still have the resistance to bending that he thought was safe. The shanks were reduced to the minimum safe size so as to keep the weight of the shanks low.

In soft mud any of the shanks (420, 620, 800) would be strong enough to overcome the resistance to resetting without bending. Worst case with the anchor held fixed by the seabed (hard sand?) there will be a point where Bis80 shanks will bend. This was all part of the design tradeoffs. Going to 620 and saying that it is good enough represents a compromise driven only by the desire for more profits rather than an re-engineering.

Regards, Ethan

 

[Neeves]

The whole point of these newer anchors is that they set deeply and have high holding capacity. If you read holding capacity tests on older designs, say the Delta, you will find that they do not pull out when overloaded but simply plough a furrow. It, the Delta, does not bed deeply consequently in a sideways pull it will rotate easily. The newer higher holding capacity anchors achieve their performance by diving, it would not be unusual to see only the top edge of the shank of a well set high holding capacity anchor (the fluke is well buried with the potential under increased load, more wind, to go deeper).

Consequently in a rapidly moving front it would not be unreasonable to consider that with strong gusts the high capacity anchor will be sufficiently well set to resist rotation, or rotate only slowly. Gusts are transitory but almost instantaneous and the shank of a well set anchor could be subject to a lever load.

Why do we not see more bent anchor?

If you find a chandler willing to talk openly they will tell you lots of anchors bend. It is the failure of the anchors that allows anchor companies like Rocna, Manson, Anchor Right, Bainbridge, Lewmar, Fortress, Spade, Plastimo/Navimo - its an endless list, to stay in business. Think of the actual companies selling boats and then think of the number of companies that make anchors (and stay in business). There always seem a large number of anchor makers (and my list does not include the nameless Chinese anchor makers). This is the very reason CMP have taken up the Rocna license - anchors fail (of course they also wanted synergy with their chains - heaven help the gullible or unknowing). We only have Rocna's word that there were only a few failures and their word is as reliable as a 420 shanked anchor, think the claim for Q&T, think of the RINA claim, think of CMP 'words of comfort', think of RocnaONE's promises. RocnaONE carefully isolated all the Rocna owners with a grouch by using PMs. And what proportion of the defined (Rocna owning) population read this thread anyway?

 

[misterg]

Why wouldn't we see more evidence of bent shanks with even Fortresses, or Mansons (etc.) if the force difference between a bend and no-bend is "just" 48%?

Engineering 101:

If the blade of the anchor is held solid on the seabed with a side load on the shank, the situation can be represented as a cantilever beam - look at this drawing sideways and imagine the blob on the left is some sort of transition from the shank to the blade:

'P' is the side load on the anchor from the rode in Newtons, 't' is the thickness of the shank and L is the distance from the rode to the point of max bending stress - roughly the unsupported length of the shank. 'b' is the depth of the shank (top to bottom) where you're measuring L from (not the rode end....)

The formula that matters is:

σ/y = M/I (1)

(σ = stress, y = distance from neutral axis, M = bending moment due to load, I = 2nd moment of area)

Re-arrange (1)

M = (σ x I) / y

(In real life you would work this out along the length of the shank, taking into acount any variations in the section of the shank, but assume it's uniform for now - it won't make a huge difference....)

Bending moment for single point load = P x L (2)

Substiture into (1)

P = (σ x I) / (y x L)

Max stress occurs at the surface so y=t/2. For failure in bending σ = σy (yield stress)

Pmax = 2 x (σy x I) / (t x L) (3)

'I' depends on the cross section shape of the shank - there are formulae and tables for derermining it for soild, or hollow parts of various cross sections - for a rectangular cross section:

I = (b x t^3)/12

Substitute into (3)

Pmax = (σy x b x t^2)/(6 x L) Newtons

or

Pmax ~ (σy x b x t^2)/(60 x L) Kg

Example (made up dimensions):

b = 100 mm
t = 10 mm
L = 500 mm
σy = 420 MPa

Pmax (i.e. sideways load at failure) ~ 140 kg.

A check on the arithmetic is always welcome, but this seems reasonable - 2 people standing on the end of a piece of 100mm wide x 10mm thick steel strip, 1/2 metre long should be enough to bend it.

HTH

Andy

 

[smackdaddy]

The whole point of these newer anchors is that they set deeply and have high holding capacity. If you read holding capacity tests on older designs, say the Delta, you will find that they do not pull out when overloaded but simply plough a furrow. It, the Delta, does not bed deeply consequently in a sideways pull it will rotate easily. The newer higher holding capacity anchors achieve their performance by diving, it would not be unusual to see only the top edge of the shank of a well set high holding capacity anchor (the fluke is well buried with the potential under increased load, more wind, to go deeper).

Consequently in a rapidly moving front it would not be unreasonable to consider that with strong gusts the high capacity anchor will be sufficiently well set to resist rotation, or rotate only slowly. Gusts are transitory but almost instantaneous and the shank of a well set anchor could be subject to a lever load.

Why do we not see more bent anchor?

If you find a chandler willing to talk openly they will tell you lots of anchors bend. It is the failure of the anchors that allows anchor companies like Rocna, Manson, Anchor Right, Bainbridge, Lewmar, Fortress, Spade, Plastimo/Navimo - its an endless list, to stay in business.

Very good summary. Thanks. This is kind of what I thought. Bending shanks are not that unusual...just not hyped.

 

[Neeves]

Andy or misterg,

Great piece of maths, stresses on beams.

Anyone using the formula shoud bear in mind, as has been mentioned often, the design spec was for Bisplate 80, typically 830 mpa, but many of the shanks were Q420, typically 445 mpa.

Smackdaddy, I might have implied people only buy replacement anchors because they bend, hopefully this is not correct. Many anchors are lost because the shackle was not secured, some are stolen (especially, one might imagine, those delightful Ultras) and hinged or articulated anchors fail becuase the joint fails. Some people also upgrade, from say a CQR and copies, to say something better (one would not want to mention what for fear of being accused of bias and fudiciary interests!). Consequently bending is but one reason anchors need to be replaced (and its more common that is supposed particularly in anchors that are not made to the original design, copy CQRs, copy Danforths, copy Bruces and of course, more recently, Rocna).

Jonathan

 

[BrianH]

The whole point of these newer anchors is that they set deeply and have high holding capacity. If you read holding capacity tests on older designs, say the Delta, you will find that they do not pull out when overloaded but simply plough a furrow. It, the Delta, does not bed deeply consequently in a sideways pull it will rotate easily. The newer higher holding capacity anchors achieve their performance by diving, it would not be unusual to see only the top edge of the shank of a well set high holding capacity anchor (the fluke is well buried with the potential under increased load, more wind, to go deeper).

Consequently in a rapidly moving front it would not be unreasonable to consider that with strong gusts the high capacity anchor will be sufficiently well set to resist rotation, or rotate only slowly. Gusts are transitory but almost instantaneous and the shank of a well set anchor could be subject to a lever load.

Very good points. Many older tall ships are put at risk by replacing rigging that would originally carry away in a gale, with modern materials that are infinitely stronger and cause them to be hove down and sometimes founder (think Bark Marques). Modern anchors set so well that indeed they could be vulnerable to wind shifts by not turning when well buried.

As an example, I keep thinking of the first publicised case, the Venice lagoon one. Of course there could have been debris restraining the anchor but the Italian lagoons are generally a mixture of sand and mud and almost never rock. I anchor in the area all the time and I know how deeply my 15Kg Rocna buries itself and how difficult sometimes it is to retrieve.