Delfin
Grand Vizier
- Joined
- Jan 20, 2010
- Messages
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Can't.* I still have the back 40 to plant.
*Very good report.Delfin wrote:
*
And for the truly geeky:
First, some term definitions from the above report.* Ultimate Tensile Strength (UTS) is the force required to break a standard sample of the steel being tested.* The first image below shows the shape of the standard sample which was subjected to a pulling force with the maximum force before breaking the sample recorded as the UTS.* Rocna advertises 800 MPa UTS steel, in my anchor, they used 697 MPa.
Yield Tensile Strength (YTS) is the maximum force a sample will absorb and still spring back to its original shape.* This is the measurement that matters to a boater, since resistance to side loading is a function of the YTS of the shank steel.* Rocna advertises 690 MPa YTS steel, in my anchor, they used 626 MPa.
Elongation is the percent the metal stretches before it breaks.
MPa are mega pascals, a metric measurement of force.* The English equivalent is pounds square inch.* 800 MPa equals 120,000 psi.
To test the metal, the lab cut a couple of small pieces out of the shank, embedded them in a bonding media and examined them under the microscope to determine which direction the grain of the metal ran. A picture of this test piece is in the second image.* Steel develops a grain along the direction flat steel plate is rolled.* It will have higher strength when the force applied is in line with this grain, so to ensure that the results we got were the maximum possible for the anchor, the direction of the grain was determined before cutting out the standard sample shown in the first picture.
The reference standard for the metal was what Rocna says they use 800 MPa steel.* This is the same steel that Manson uses, and it meets ASTM A514 standards.* The reference to Bisalloy 80 on the test is because it is 800 MPa, A514 steel and is used by Manson in their manufacture.
To accurately compare the Manson to the Rocna I consulted a friend who is a structural engineer to determine what changes in lateral bending force resulted from differences in the cross sectional area of the two anchors.*
The Rocna and the Manson are designed to have as much of the total anchor weight on the tip as possible.* To achieve this, the shank has to be fairly thin.* Even mild steel (YTS 400+ MPa) would work just fine under pulling conditions only since the chain or rope rode would generally break before the steel reached its YTS.* However, the length of the shank creates a lever that multiplies the lateral pulling in a side load to the point where the shank will easily bend unless it is made out of steel with a relatively high YTS steel.* The Rocna is designed for this higher grade of steel, but for reasons unknown Rocna has elected to advertise one grade and use another.* The result is an unsafe anchor, whose defects will remain hidden until the boater is depending the most on the integrity of the manufacturer.
Since I am not an engineer, I welcome any correction from more knowledgeable forumites on any mistakes in my analysis.
*I assume Peter Smith knows what he's talking about, and reducing shank weight by using higher quality steel ensures effective setting.* If you increased that weight, the anchor presumably wouldn't set as well.*JD wrote:A question I have is. Would someone with a Rocna benefit from having a small*reinforcement plate welded on either side of the shank for it's entire length?
The point being you already own the anchor and it's resale has gone south, would $100 of welding save the anchor.
Or as Eric has said it has*a 15-18% weakness so just live with it and if it bends deal with it then.
*Tom, it only takes about 600# of lateral load to bend the shank of the Rocna 10 I bought because of the lever arm of the moment of force (if I am saying that right).* Any anchor is stronger than the chain if all you are doing is pulling on it.* The problem with the new generation of anchors is that they do set well, so the likelihood of exceeding lateral bend resistance during sudden winds shifts is greater than for an older design.* I think for me, the issue here is paying more for a weaker anchor from a company that doesn't tell the truth about its product.* Even if the Rocna is 'adequate' under most circumstances, I'm still offended by deceptive trade practices.*sunchaser wrote:
During my engineering, construction and metallurgical*career I have seen*and authored considerable *non-destructive testing and weighed the results as to how to relate these findings to the real world.Normally, a safety factor for all non-rotating things made of metal is used after factoring in seismic, vibration, wind loads, snow loads and anticipated corrosion.
An anchor is no different. So long as*an anchor's tensile, shear and bending moment "strength" can exceed the rode's WL by 150%, I'd not worry. On trawlers, the next size or two up in anchor weight should more than adequately give you the comfort you need - provided you have an acceptable rode and seek adequate shelter. The catch of course is to know what the actual, not claimed, load limits for the anchor are - which Delfin has discussed.
The rub here is Rocna's design works, but their advertising and fabrication claims got called. My senses were alerted to the Rocna BS on this forum a year or more ago when layman were touting the anchor's "strength"**as if it were gospel. Pray tell this would never happen to Manson.
I looked at the Rocna on Sarah Sarah today, and it is a lunker - one of the NZ built units that I would think was built to spec.* I'm guessing a 75 kg or so.* Wonder if they would mind if I came on board with my center punch and hammer for a quick metallurgy test......sunchaser wrote:
Delfin, I agree with the Rocna shank length problem you noted. I looked at a Rocna 45KG and the shank was way too long to sensibly fit in the space I have for my current Bruce - from the anchor roller to the gypsy.*
You may want to look at the anchor setup on Sarah Sarah (Dashew FPB) being shown at Trawlerfest Anacortes. Darn it, I can't make it. I'm curious as to if they used a Rocna and what size.
Eric, that seems to make sense, but not according to Peter Smith, the designer of the Rocna.* He says:nomadwilly wrote:
Carl,
*I would think increasing shank weight on the Rocna would INCREASE the anchors ability to set.
*I have heard from one individual through PM who thinks it grossly unfair to test an anchor and publish the results without giving the other side the opportunity to tell "their side of the story." *As you suggest, Eric, we'd love to hear from them, but they may want to come prepared with specific empirical information that explains the results obtained in anchor tests spanning the globe. *Blaming it all on a rogue employee while touting their QC program probably isn't an adequate response, but I for one would welcome hearing from them, or Suncoast Marine who distributes their product. *I used Suncoast's web form to contact them, asking if there was a way to determine when the anchor I tested had been manufactured as well as offering the test results I obtained. *No response. *Sometimes if you have nothing to say, it is best just to keep your mouth shut. *I'm not sure there is a rebuttal for Rocna, so maybe silence is to be expected, here and on all other forums where this topic is being debated. *Rocna still has a few useful idiots defending the indefensible, so perhaps they're hoping it will all just blow over and they can get back to what they do best. *Talk a good game, deliver less.nomadwilly wrote:
Carl,
We have insulted, denounced and called Smith/Rocna liars and manufacturers of fraudulent products for some time now. Smith is a very competitive, verbose and defensive individual who has always been quick to defend himself and his product. We experienced Smith a while back. He picked up some eggs and tomatoes (some delivered by myself) but don't you think it's strange that the Rocna camp has been silent? As I recall they have our address.
*Yes, and they cheerfully refunded my money, noting that the anchor was "defective" as the reason for the return. *The manager wondered if I wanted to replace it with another type of anchor, and was clearly concerned she would receive another pile of pieces for another return, but I reassured her on that point. *I'll probably pick up a Manson for my stern anchor, as it is less expensive and quite a bit stronger than the Rocna.weebobby wrote:
Carl
Just wonering if you tried to return your test anchor to West Marine yet ?
Bob
agree, thanks to Carl *- and to Grant King and the other that has contributed.bobofthenorth wrote:
We all owe Carl a big thank you for taking the time and money to quantify the fraud they were promoting. *
*Thanks for posting this. As a recent (Feb/11) purchaser of a Rocna anchor, I've been following these posts very closely, and am somewhat comforted by the message from Canada Metal.*Singleprop wrote:
I found this document regarding the Rocna anchor quality:
*
http://www.canmet.com/content/resources/documents/ROCNA MEMO.pdf