GrantKing
Well-Known Member
A lot of rocnas were drilled through the shank in auckland marina's too without there being any problem.
Hard, very hard drill bits are needed for the manson shanks, just drill slowly.
I hate to do this...but
- Thread starter macd
- Start date
A lot of rocnas were drilled through the shank in auckland marina's too without there being any problem.
Hard, very hard drill bits are needed for the manson shanks, just drill slowly.
Nostrodamus
Well-Known Member
Guess the affected ones were not up to spec
They were up to spec, and approved. They just bent a little
Delfin
Well-Known Member
Since this is a topic of general interest on a vital piece of safety equipment, I’m posting the below to the 4 sites I participate in, not to beat up on Rocna, but because most everyone with a boat needs an anchor, and sometimes one’s boat and the safety of the crew depends on the integrity of the anchor manufacturer. By way of full disclosure, I use a 176# Bruce type Claw on Delfin, and it has served me well, so far. I have zero financial interest in any anchor manufacturer or marine distributor.
I recently purchased a Rocna 22# anchor for testing because it seemed as if there were many opinions on the strength of this anchor, but not enough objective data to make a final conclusion.
To test my Rocna, I took it to NW Laboratories, who have been performing metal testing in the Seattle area since 1896. An initial hardness test was performed, since tensile strength can be correlated to hardness, and on the basis of that test the anchor was submitted to full testing to determine whether the steel used matched the grade of steel advertised by Rocna. By way of background on the importance of steel quality, here is what Rocna has to say about the steel it uses:
"The shank on any anchor is a common failure point, normally bending when a high lateral load is applied (for instance, when the anchor fouls on a submarine obstacle and is jammed). For this reason, the shank on the Rocna is a high tensile quenched and tempered steel, with a grade of around 800 MPa. Its pure resistance to bending is around three times that of mild steel. This adds to the price of the anchor, but compromising this strength is not something we would entertain."- http://www.rocna.com/kb/Anchor_materials
In this, Rocna is stating that their anchors will be more expensive than cheaper anchors because they want to avoid a “common failure point”, which would be the bending of anchor shanks with steel that had an Ultimate Tensile strength less than 800 Mega Pascals (MPa), or 120,000 psi. This type of steel meets the standards set in ASTM A514, has a Yield Tensile strength of 720 MPa and is available from Bisalloy Steel in Australia, as well as other companies worldwide, including sources in China where the Rocna is made.
In discussing why Rocna doesn’t manufacture an aluminum alloy anchor, they expand on the importance of and the reason for using 800 MPa high tensile steel in their anchors:
"For example, an aluminum shank would not be able to possess the same tensile strength as the 800 grade steel we use without being significantly thicker, which would then affect setting performance in hard sea-beds." http://www.rocna.com/kb/Anchor_materials
In other words, without high tensile 800 MPa steel in the shank their anchor would have to be thicker to withstand the loads typically imposed during normal usage, and this would affect the balance of the anchor adversely when it comes to setting ability.
Finally, in the User’s Guide that comes with each Rocna there is a statement that underscores how the Rocna anchor is superior to its competition because it addresses one of the shortcomings of most anchors – weakness in the shank:
"The Rocna was designed to address the limitations shared by all older and most newer anchors available. These designs suffer from ….. "insufficient strength in the shank or other load bearing components."
Clearly, Rocna believes that the unique design of the Rocna anchor requires the very best components, and competitive anchors that do not meet Rocna’s standards are suggested to be inadequate due to inherent “limitations”.
Attached in the first image below is a summary of the test results from NW Labs in the form of a summary comparison of the Rocna 22# I purchased to its closest analog – the Manson 25# Supreme. The test itself is in the second image. I chose the Manson to compare to mine for a number of reasons.
First, Manson says that they use 800 MPa, 120,000 psi steel in their anchor shanks, and have published tests confirming this. The link to those test results for the Manson 25 is here: http://manson-marine.co.nz/SitePage...ds/11-037 Tensile Manson Anchor 18Apr11VB.pdf
The second reason is that the Manson has a similar design to that of the Rocna, and shows equivalent holding power in most tests.
The third reason is that the Manson is available in North America and the U.K. I don’t have the prices of the Manson in the U.K., but in the U.S., they are significantly less expensive than the Rocna.
The final reason is that according to Ned Wood, the manager of Manson “Honestly, I have never seen or had a complaint from a customer about a bent Supreme Shank, ever. Over 12,000 sold and I am fairly sure I would have heard of something but never have heard, nor has anyone here.” Since we have pictures of bent shanks on the Rocna, something is clearly going on, so I thought a careful comparison between the two products should shed some light. I can’t verify whether Mr. Wood’s statement is true, but I did ask him if I could quote him, so I assume it is the truth.
While the test results are self explanatory, here is the punch line, in my opinion. The Manson has about 14% more steel at the mid point of its shank compared to the Rocna. Increases in cross sectional area proportionally increases resistance to lateral bending, so the Manson would be 14% stronger than the Rocna based on this measurement even if they used the same steel. However, the Manson does use 800 MPa steel for its product, so the yield strength of the Manson is about 30% greater than the lesser steel used in the Rocna. Higher yield translates directly into bend resistance, so on the basis of these two data points, the Manson is half again stronger than the Rocna at 2/3 the price.
Because the shank of an anchor represents a lever, it is possible to put high loads on the shank with lateral loading that exceeds the yield strength (bend resistance) of the steel used. The materials used in the Rocna have resulted in bent shanks; of the Manson - not so much. Presumably Rocna well understands this potential failure point and how to avoid it with the right materials. They didn’t use those materials on my anchor, so it is de facto defective and a threat to my boat. Not good.
With anchors available from manufacturers of integrity and great holding power made of appropriate materials, like Fortress, Sarca, Manson and others, it is hard to understand why anyone would pay more for less by purchasing a Rocna, especially since by their own definition, their product is unsafe. Manufacturers of safety equipment should be held to a high standard of honesty, and retailers of those products should take care when promoting products that are known to be defective.
For those who haven’t had enough punishment from this thread yet, I’ll post the details of how the Rocna was tested, as well as other photos of the test subject. I’ll be returning my Rocna to West Marine for a refund based on the simple fact that it doesn’t meet the specs advertised by Rocna. I assume they’ll give me my money back, but we’ll see.
I recently purchased a Rocna 22# anchor for testing because it seemed as if there were many opinions on the strength of this anchor, but not enough objective data to make a final conclusion.
To test my Rocna, I took it to NW Laboratories, who have been performing metal testing in the Seattle area since 1896. An initial hardness test was performed, since tensile strength can be correlated to hardness, and on the basis of that test the anchor was submitted to full testing to determine whether the steel used matched the grade of steel advertised by Rocna. By way of background on the importance of steel quality, here is what Rocna has to say about the steel it uses:
"The shank on any anchor is a common failure point, normally bending when a high lateral load is applied (for instance, when the anchor fouls on a submarine obstacle and is jammed). For this reason, the shank on the Rocna is a high tensile quenched and tempered steel, with a grade of around 800 MPa. Its pure resistance to bending is around three times that of mild steel. This adds to the price of the anchor, but compromising this strength is not something we would entertain."- http://www.rocna.com/kb/Anchor_materials
In this, Rocna is stating that their anchors will be more expensive than cheaper anchors because they want to avoid a “common failure point”, which would be the bending of anchor shanks with steel that had an Ultimate Tensile strength less than 800 Mega Pascals (MPa), or 120,000 psi. This type of steel meets the standards set in ASTM A514, has a Yield Tensile strength of 720 MPa and is available from Bisalloy Steel in Australia, as well as other companies worldwide, including sources in China where the Rocna is made.
In discussing why Rocna doesn’t manufacture an aluminum alloy anchor, they expand on the importance of and the reason for using 800 MPa high tensile steel in their anchors:
"For example, an aluminum shank would not be able to possess the same tensile strength as the 800 grade steel we use without being significantly thicker, which would then affect setting performance in hard sea-beds." http://www.rocna.com/kb/Anchor_materials
In other words, without high tensile 800 MPa steel in the shank their anchor would have to be thicker to withstand the loads typically imposed during normal usage, and this would affect the balance of the anchor adversely when it comes to setting ability.
Finally, in the User’s Guide that comes with each Rocna there is a statement that underscores how the Rocna anchor is superior to its competition because it addresses one of the shortcomings of most anchors – weakness in the shank:
"The Rocna was designed to address the limitations shared by all older and most newer anchors available. These designs suffer from ….. "insufficient strength in the shank or other load bearing components."
Clearly, Rocna believes that the unique design of the Rocna anchor requires the very best components, and competitive anchors that do not meet Rocna’s standards are suggested to be inadequate due to inherent “limitations”.
Attached in the first image below is a summary of the test results from NW Labs in the form of a summary comparison of the Rocna 22# I purchased to its closest analog – the Manson 25# Supreme. The test itself is in the second image. I chose the Manson to compare to mine for a number of reasons.
First, Manson says that they use 800 MPa, 120,000 psi steel in their anchor shanks, and have published tests confirming this. The link to those test results for the Manson 25 is here: http://manson-marine.co.nz/SitePage...ds/11-037 Tensile Manson Anchor 18Apr11VB.pdf
The second reason is that the Manson has a similar design to that of the Rocna, and shows equivalent holding power in most tests.
The third reason is that the Manson is available in North America and the U.K. I don’t have the prices of the Manson in the U.K., but in the U.S., they are significantly less expensive than the Rocna.
The final reason is that according to Ned Wood, the manager of Manson “Honestly, I have never seen or had a complaint from a customer about a bent Supreme Shank, ever. Over 12,000 sold and I am fairly sure I would have heard of something but never have heard, nor has anyone here.” Since we have pictures of bent shanks on the Rocna, something is clearly going on, so I thought a careful comparison between the two products should shed some light. I can’t verify whether Mr. Wood’s statement is true, but I did ask him if I could quote him, so I assume it is the truth.
While the test results are self explanatory, here is the punch line, in my opinion. The Manson has about 14% more steel at the mid point of its shank compared to the Rocna. Increases in cross sectional area proportionally increases resistance to lateral bending, so the Manson would be 14% stronger than the Rocna based on this measurement even if they used the same steel. However, the Manson does use 800 MPa steel for its product, so the yield strength of the Manson is about 30% greater than the lesser steel used in the Rocna. Higher yield translates directly into bend resistance, so on the basis of these two data points, the Manson is half again stronger than the Rocna at 2/3 the price.
Because the shank of an anchor represents a lever, it is possible to put high loads on the shank with lateral loading that exceeds the yield strength (bend resistance) of the steel used. The materials used in the Rocna have resulted in bent shanks; of the Manson - not so much. Presumably Rocna well understands this potential failure point and how to avoid it with the right materials. They didn’t use those materials on my anchor, so it is de facto defective and a threat to my boat. Not good.
With anchors available from manufacturers of integrity and great holding power made of appropriate materials, like Fortress, Sarca, Manson and others, it is hard to understand why anyone would pay more for less by purchasing a Rocna, especially since by their own definition, their product is unsafe. Manufacturers of safety equipment should be held to a high standard of honesty, and retailers of those products should take care when promoting products that are known to be defective.
For those who haven’t had enough punishment from this thread yet, I’ll post the details of how the Rocna was tested, as well as other photos of the test subject. I’ll be returning my Rocna to West Marine for a refund based on the simple fact that it doesn’t meet the specs advertised by Rocna. I assume they’ll give me my money back, but we’ll see.
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Delfin
Well-Known Member
Testing details
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.
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.
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Rigger Mortice
N/A
You've certainly been thorough there Delfin. Well done!
I'm tempted to say that it doesn't surprise me to see that Rocna have also been selling their below spec products in US too. What would surprise me would be if somebody can find a Rocna that does conform to the quality standards that Rocna has been boasting about for so long.
Do let us know what West Marine say when you take it back for a refund.
Just to remind people what a Rocna might look like when it is hauled up.........
I'm tempted to say that it doesn't surprise me to see that Rocna have also been selling their below spec products in US too. What would surprise me would be if somebody can find a Rocna that does conform to the quality standards that Rocna has been boasting about for so long.
Do let us know what West Marine say when you take it back for a refund.
Just to remind people what a Rocna might look like when it is hauled up.........
Nostrodamus
Well-Known Member
I would lik to say a big thank you to DELFIN on behalf of this forum for doing something a lot of us would like to have done.
The post he made was clear and even I understood it. The Rocna he bought was unsafe.
As he says this has to be made available to all Rocna owners so they are aware of the limitations to their anchor.
Along with the Manson tests it is difficult for Rocna to say this is from a small batch made some time ago.
Again thank you DELFIN as your tests and Mansons test stopped me from buying one and putting me and my family in danger.
The post he made was clear and even I understood it. The Rocna he bought was unsafe.
As he says this has to be made available to all Rocna owners so they are aware of the limitations to their anchor.
Along with the Manson tests it is difficult for Rocna to say this is from a small batch made some time ago.
Again thank you DELFIN as your tests and Mansons test stopped me from buying one and putting me and my family in danger.
GrantKing
Well-Known Member
Who is the lier now?
Ex-SolentBoy
Well-Known Member
Great to see some professional testing.
Can I please just make sure I have properly read the details?
1. You had a test performed on a newly made Rocna 10kg anchor.
2. The anchor was manufactured in China.
3. The shank was shown to be 696 mpa and not the 800 mpa you expected from the marketing stuff.
I just want to be clear before I further my discussions about our own anchor. Rocna have said that the steel problems were restricted to anchors made in a specific period early last year. It is therefore very important to establish the date of manufacture of the anchor you tested. How can you be sure about this?
Thanks.
Can I please just make sure I have properly read the details?
1. You had a test performed on a newly made Rocna 10kg anchor.
2. The anchor was manufactured in China.
3. The shank was shown to be 696 mpa and not the 800 mpa you expected from the marketing stuff.
I just want to be clear before I further my discussions about our own anchor. Rocna have said that the steel problems were restricted to anchors made in a specific period early last year. It is therefore very important to establish the date of manufacture of the anchor you tested. How can you be sure about this?
Thanks.
Delfin
Well-Known Member
I don't have a way of knowing when my anchor was manufactured. However, the 10 kg is one of the most popular sizes, and the Anacortes West Marine store a busy one, so I assume it has not been sitting in a warehouse or the store from last year. This anchor tested stronger than the anchor tested by Manson even though it was still well below the specified quality of steel, so other than these two reference points and reports and pictures of bent Rocnas pinning down a freshness date on any given anchor is probably hopeless.
We know anecdotally that others have used a center punch on a Manson and it was unaffected, while I know of no one who has done a similar test on a Rocna that hasn't shown metal softer than the punch. I suspect the challenge would be to find any Rocna made in China that would test to specification regardless of the period of manufacture, but that is speculation based on the provable fact that Rocna hasn't been honest on certification, holding tests or claims about its competitors so I have no reason to believe they are being honest when they say only one batch of anchors manufactured last year are defective. Might be true, but the odds don't seem likely.
It also seems weird that this one small batch of defective anchors would show up in NZ, Washington State and in the Venice anchor, and either be the ones tested or show up bent.
Your summary of the main points of the test is correct.
vyv_cox
Well-Known Member
Well done, and good luck with getting a refund from West Marine! Isn't there some sort of rider on returns, to do with being undamaged and not interfered with?
The UTS and YS values on the the Rocna are interesting, lying between the specified figure and a basic low-carbon steel. There could be various reasons why this is the case but it does imply a decision based on what might be got away with.
Your investigator clearly knows his stuff, good to see that the tensiles were done parallel with the rolling direction. do you have copies of the microstructures, or even better, did they do any compositional analysis?
The UTS and YS values on the the Rocna are interesting, lying between the specified figure and a basic low-carbon steel. There could be various reasons why this is the case but it does imply a decision based on what might be got away with.
Your investigator clearly knows his stuff, good to see that the tensiles were done parallel with the rolling direction. do you have copies of the microstructures, or even better, did they do any compositional analysis?
Ubergeekian
Well-Known Member
Thank you for those very detailed postings. May I offer just a brief word of correction on the above, though?
Resistance to bending doesn't depend linearly on cross sectional area. Elastic deformation depends on EI (Young's Modulus x Second Moment of Area about the bending axis) and yield failure in bending depends on s_y Z_e (yields stress x elastic section modulus).
For the same material properties the dependencies are therefore on I and Z_e and for the same proportions these scale with the fourth and third powers of size, respectively. Since area scales with the second power of size, elastic and yield behaviour in bending scale with area^2 and area^(3/2) respectively, so increasing the shank area by 14% might be expected to reduce the elastic deflection for a given load by 30% and increase the bending moment at yield by 22%.
silver-fox
Well-Known Member
Scotty_Tradewind
Well-Known Member
+1Ubergeekian... you took the words right out of my mouth.........
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Scotty_Tradewind
Well-Known Member
Blimey!
And I'm now wondering how I quickly check my R' as it's not been used yet. Whats the quickest way of getting an idea without a destruction test like Delfins?
Stork_III
Well-Known Member
Centre punch and hammer.Blimey!
And I'm now wondering how I quickly check my R' as it's not been used yet. Whats the quickest way of getting an idea without a destruction test like Delfins?
Rigger Mortice
N/A
Don't bother to check it. Just take it back under their "no questions asked" warranty.
You could always tell them why you're returning it and make it clear that when they can give you a categorical assurance that it's all OK you'll consider buying another.
Delfin
Well-Known Member
I returned my pile of metal to West Marine in Anacortes, Washington, and to their great credit they cheerfully made an instant refund without debate or discussion. Lenore, the manager seemed a little concerned that I might want another anchor in replacement that I would also bring back in pieces, but I assured her that was not the case.
She seemed interested in the test results, noted the gap between the results and what Rocna's specs were and rang up the refund as one for a 'defective' product, which it was.
She seemed interested in the test results, noted the gap between the results and what Rocna's specs were and rang up the refund as one for a 'defective' product, which it was.
Twister_Ken
Well-Known Member
Score. Delfin 1, Rocna 0.
Nostrodamus
Well-Known Member
I would say more of a technical knock out!!!
CONGO
Active Member
Aspecial thanks to all.
Seven years I have endured much slander without a peep; a few months ago I was encouraged by a fellow manufacturer to comment on some dodgy video from C.S. next thing I know I’ve got the forum bug, what a transformation, not saying anything and then saying far too much, I agree with most this forum is for you guy’s to discuss issues regardless of what they may be without manufacturers peddling their products.
But I think the combined effort of everybody good and bad; yes I know I have made some not so very smart post’s myself, all the more reason to now leave and get back to what I do best. I would like to thank the moderators in this effort, Riger , Dubangi, Brian from fortress and Grant king, Delfin you certainly delivered the winning blow and did it decently, professionally, and I thank you.
All manufacturers have won from this episode as the slanderous rubbish against other manufacturers that used to fill C.S. web site is all but gone, this all in effort has also put anchor manufacturers on notice to produce what they say they are marketing.
Delfins findings are a winning blow for all bowties as any would be manufacturer will think twice before he tries to pull a C.S. This means a better quality product.
Rex.
Anchor Right Australia.
Seven years I have endured much slander without a peep; a few months ago I was encouraged by a fellow manufacturer to comment on some dodgy video from C.S. next thing I know I’ve got the forum bug, what a transformation, not saying anything and then saying far too much, I agree with most this forum is for you guy’s to discuss issues regardless of what they may be without manufacturers peddling their products.
But I think the combined effort of everybody good and bad; yes I know I have made some not so very smart post’s myself, all the more reason to now leave and get back to what I do best. I would like to thank the moderators in this effort, Riger , Dubangi, Brian from fortress and Grant king, Delfin you certainly delivered the winning blow and did it decently, professionally, and I thank you.
All manufacturers have won from this episode as the slanderous rubbish against other manufacturers that used to fill C.S. web site is all but gone, this all in effort has also put anchor manufacturers on notice to produce what they say they are marketing.
Delfins findings are a winning blow for all bowties as any would be manufacturer will think twice before he tries to pull a C.S. This means a better quality product.
Rex.
Anchor Right Australia.