Canada Metals on Rocna: Doublespeak?

[hellosailor]

I don't see how a chain rated at 16,000# can be multiplied enough to put 100,000# on an anchor shank. Which might be why I'm not an engineer, help me grasp this.

If the chain is placed one foot above the base of the shank, and pulled at a 90-degree angle to the anchor, which has been wedged between two boulders or embraced by a giant Kraken, the chain is pulling at a maximum of 16,000 foot pounds before it reches rated failure strength. At two feet above the bend, 32,000#. Four feet, 64000 pounds. So...the chain would have to be some 6+ feet above the bending point to put a 100,000# load on it without snapping the chain first.

And most anchor chains make a dotted line from the bow roller to the anchor--no force multipliers in the way.

Have I gotten the math and physics wrong again, or are the bent anchors proof that giant Kraken have been attempting to mate with Rocna anchors?

[careka]

Do anybody now what steal is used for a Delta anchor. ?
has anyone heard of that one was bent ?
it cost a lot less, so it has to be weaker steal ???

OR ?

[s/v Jedi]

Originally Posted by hellosailor

I don't see how a chain rated at 16,000# can be multiplied enough to put 100,000# on an anchor shank. Which might be why I'm not an engineer, help me grasp this.

If the chain is placed one foot above the base of the shank, and pulled at a 90-degree angle to the anchor, which has been wedged between two boulders or embraced by a giant Kraken, the chain is pulling at a maximum of 16,000 foot pounds before it reches rated failure strength. At two feet above the bend, 32,000#. Four feet, 64000 pounds. So...the chain would have to be some 6+ feet above the bending point to put a 100,000# load on it without snapping the chain first.

And most anchor chains make a dotted line from the bow roller to the anchor--no force multipliers in the way.

Have I gotten the math and physics wrong again, or are the bent anchors proof that giant Kraken have been attempting to mate with Rocna anchors?

You can't translate foot-pounds to pounds. Foot-pounds is a unit of energy, while pounds is weight.

Also, the tensile strength of a material is what it resists before breaking. Bending is not breaking, much less force is needed to bend it.

I hope you're not gonna ask me to calculate it here for you because I am (happy that I am) not a mechanical engineer

cheers,
Nick.

[evm1024]

We are talking about a lever (Lever - Wikipedia, the free encyclopedia) here. Where the shank is the lever. The fulcrum is inside the shank at the point of rotation (near the fluke). The part of the lever opposite the fulcrum is in the shank at right angles to the axis of the shank. One side of the shank is in tension and the other in compression (one is being pulled apart and the other compressed). So the force ratio is the length of the shank to the point of rotation vs half the thickness of the shank. Without measuring we might get 60 cm to 0.5 cm or a ratio of 120 to 1. Quite a force multiplier. (Just think crowbar)

Of course the math and physics are more complex than this but this is a working gross approximation to show how we get the forces needed to exceed yield strength. For one thing the metal is measured in pounds per square inch or the metric equivalent.

If we take the 120 ratio (a wag for sure) and apply 500 pounds through the chain we get (120 x 500) 60,000 pounds force. If the shank cross section at the bending point is 1 sq in then we have 60,000 pounds per sq in.

420 MPa is 60915 pounds per sq in. (Kilopascal [kPa] To Pound Force Per Square Inch [lbf/in2] Converter)

And the shank bends forever.

Like I said what actually happens in the real world is much more complex that what I wrote. But as you can see from this getting 100000 pounds force is actually quite easy with a 120 to 1 lever.

Regards

I don't play a mechanical engineer on TV and a real Mechanical engineer may step in to correct all of the errors and misunderstandings as needed......

[careka]

Originally Posted by evm1024

If we take the 120 ratio (a wag for sure) and apply 500 pounds through the chain we get (120 x 500) 60,000 pounds force. If the shank cross section at the bending point is 1 sq in then we have 60,000 pounds per sq in.

420 MPa is 60915 pounds per sq in. (Kilopascal [kPa] To Pound Force Per Square Inch [lbf/in2] Converter)

And the shank bends forever.

I don't play a mechanical engineer on TV and a real Mechanical engineer may step in to correct all of the errors and misunderstandings as needed......

So then around a 1000p pull, on a stuck rocna (even made out of 800MPa) will bend.

Then i say it has done its jobb, lets get a new one.

But normally the anchor will turn, and bit again and you are OK:

[evm1024]

Originally Posted by careka

So then around a 1000p pull, on a stuck rocna (even made out of 800MPa) will bend.

Then i say it has done its jobb, lets get a new one.

But normally the anchor will turn, and bit again and you are OK:

Your last line it the key.

With a Bisplate80 shank 99% of the time the anchor will rotate (because what it is stuck in is less strong than the shank).

And with a 420 shank 60% of the time the anchor will rotate.

This means that with the Bis80 you bend 1 out of 100 and with 420 you bend 4 out of 10.

4 out of 10 are much worse odds than 1 out of 100.

Of course these numbers are a wag (Wild Ass Guess) used just to show how Bis 80 can be much much better than 420. If you just use the strength you end up with a factor of 2 difference. But when you use strength vs sea bed resistance you end up with a factor of 40.

Regards

[downunder]

Originally Posted by evm1024

Your last line it the key.

With a Bisplate80 shank 99% of the time the anchor will rotate (because what it is stuck in is less strong than the shank).

And with a 420 shank 60% of the time the anchor will rotate.

This means that with the Bis80 you bend 1 out of 100 and with 420 you bend 4 out of 10.

4 out of 10 are much worse odds than 1 out of 100.

Of course these numbers are a wag (Wild Ass Guess) used just to show how Bis 80 can be much much better than 420. If you just use the strength you end up with a factor of 2 difference. But when you use strength vs sea bed resistance you end up with a factor of 40.

Regards

Very plausable points for us dumb assed non engineers

[Surrymark]

A brief run at Google doesn't show the specs of steels used in other anchors - CQR, Bruce, etc. Anybody have any info? Seems pertinent if a person were going to make a decision based on these Rocna threads.

[downunder]

Originally Posted by Surrymark

A brief run at Google doesn't show the specs of steels used in other anchors - CQR, Bruce, etc. Anybody have any info? Seems pertinent if a person was going to make a decision based on these Rocna threads.

Seems that ROCNA has said specs are now secret when previously they openly advertised the specs of their steel to justify their price premium.

SECRETE

Look to the manufacturers that are open on their specs such as SARCA and Manson and then question their secrecy. In this day of the imformation age if it is not important interlectual property why not be open.

Only reason for lack of openness is not to want to expose the use of lesser quality metals than another manufacturer. In that these are primary Marine safety devices quality and specs are important.

Cheers

[evm1024]

Rocna were designed with Bisplate 800 MPa steel so as to allow a thinner and thus less weight shank for the same strength. The steel is very important here. You recall Smith writing on just how important the steel was. High strength steel allowed less weight which was claimed a requirement for good setting performance.

Other anchors use thicker cross sections in their shank to get the desired rigidity/strength. You can get strength by using shapes (I or H for example) other than flat bar.

Different anchor shanks (metal and shape) are not apples to apples.

If Rocna had increased the shank thickness while going to 420 MPa plate we would not be talking about bent Rocnas. We might be talking about suckie setting instead.

[Dkdoyle]

China's copies and quality problems remind me of when made in Japan meant it might or might not work. Eventually they will figure it out but for now it may look good BUT.....

http://www.youtube.com/watch?v=f1Whr...e_gdata_player

[cat man do]

Originally Posted by Dkdoyle

China's copies and quality problems remind me of when made in Japan meant it might or might not work. Eventually they will figure it out but for now it may look good BUT.....

One example, pfft

At least their failure did not cause the deaths of hundreds of people like this one in America

The Hyatt Regency Skywalk Collapse 1981; The Begining of Urban Heavy Rescue | Command Safety

Or the Space shuttle columbia tragedy due to faulty design
or numerous aircraft failures due to faulty design.

Despite what you think, America is not infallable

[hellosailor]

catman, there have been accidents from design errors (as the Skywalk) all over the world. That's of no relevance when we're discussing business ethics.

Enron and Madoff are relevant. The Hyatt isn't.

[cat man do]

Originally Posted by hellosailor

catman, there have been accidents from design errors (as the Skywalk) all over the world. That's of no relevance when we're discussing business ethics.

Enron and Madoff are relevant. The Hyatt isn't.

You did look at Dkdoyle's video right?

No mention of business ethics in it, he has provided a video showing design failure.

[hellosailor]

You did look at Dkdoyle's video right?

Nope. Got an URL?

His video shows...business ethics? Or what we already know, that the shank can be bent because someone used weaker metal?