Rocna Anchor Failure

[Tomaz473]

The shackle is too small for this chain and is mounted incorrectly.
Shackle must always be one size bigger then the chain.
For example 10 mm chain should have 12 mm shackle.
That is why anchor slot is bigger: to accommodate shackle to go though it, not only the pin.
10 mm chain can accept 12 mm pin. You can not thread shackle eye though it, but you do not have to. Just the pin.

Here is a possible scenario about what might have happened (with a lot of speculation from my side, but it is possible):
- Shackle eye wedged inside the anchor slot when the shackle turned slightly sideways. So, the shackle could no longer move in relation to the anchor.
- at lifting the anchor a large shock load occurred at the moment when shackle met the roller. The anchor was still pointing down, while the chain was pulling horizontally. At that moment the big side-load tried to wedge the shackle even more and that was the reason the shaft cracked open a little.
This enabled the shackle to rotate.
- The anchor was pulled on deck.
- As the chain was pulled and the anchor reached its resting position on the roller this created another shock-load, which wedged the shackle pin inside the crack.
- movement of the anchor on the way enabled the pin to travel further through the crack until it cam all the way through and the anchor broke free.

It is my strong believe, that there must have been a material flaw at the anchor shank or the shackle would give up first. But without the anchor we will never know.

[hpeer]

^ Best theory I’ve heard yet.

[Simi 60]

Originally Posted by Tomaz473

The shackle is too small for this chain and is mounted incorrectly.
Shackle must always be one size bigger then the chain.
For example 10 mm chain should have 12 mm shackle.
That is why anchor slot is bigger: to accommodate shackle to go though it, not only the pin.

Might work on some chain but not all.

We run 13mm grade L
Hole in chain is 18mm
Pin size on the 13mm shackle is 16mm
Pin size on the 16mm shackle is 19mm so won't fit.

. 10 mm chain can accept 12 mm pin. You can not thread shackle eye though it, but you do not have to. Just the pin.

But the next size shackle from a 10mm has a 13mm pin.

https://www.nobles.com.au/en-au/prod...n-bow-shackles

[JPA Cate]

Always use galvanized to galvoed. There are dissimilar metal problems when you use s/s to the galvanized anchor. iirc, noelex posted a pic showing one case of that in his thread Pictures Of Anchors Setting. It's a long browse, but interesting.

[osprey877]

If you zoom in on the shackle in the first photo, you will see that the two sides of the shackle don’t appear to join under the chain. Could be an optical illusion or photo effect or?? Also, I am very surprised that the shackle ends would fit through the chain link opening. I spent weeks looking for a shackle with ends small enough and eventually gave up. Most shackles have to be fitted the other way around with only the pin going through the chain link. So here’s my conspiracy theory: Shackle was hacksawed through by theif who stole anchor. OP staged the photo hoping to make warranty claim. Is posting here now to pressure Rocna. My apologies to OP if, like most conspiracy theorists, I have it all wrong. In any event, I can certainly see why Rocna wants to see the anchor.

[double u]

whatever metal failed (or didn't), thr OP's common sense certainly did: to claim warranty without being able to show the product or even a foto imho is totally asinine, if he can't see that...

[Bruce K]

Originally Posted by Simi 60

Looks like a lewmar delta to me.

Please read and understand the OPs posts before posting!!

[Simi 60]

Originally Posted by Bruce K

Please read and understand the OPs posts before posting!!

Please read and understand who I was replying to before commenting!!
I wasn't commenting on the op's post.
I was commenting on this one.

Originally Posted by zboss

The anchor isn’t a rocna and that shackle isn’t the shackle on that anchor. The anchor was tied off to the boat.

[CarlF]

I also like Tomaz473’s theory. A shackle stuck sideways in the attachment hole of the shank could exert tremendous bending pressure. The tip of the shank is relatively weak, having been mostly drilled away for the attachment hole.

The broken shackle pin head also suggests that it too was broken off by the shackle having been heavily loaded while stuck sideways. If a force was sufficient to shear the pin head, it was likely also sufficient to bend the weak end section of the shank.

And this side loading may not have been a one time event. The shackle pin head might have broken earlier and not been noticed. Repeated bending of the shank tip would quickly fatigue the metal allowing it to crack and fatigue. This may not have been obvious without inspecting the anchor shank and may have been developing for some time.

Finally, many will remember that Rocna has had previous problems with the metallurgy of their shanks that lead to a recall. While the company has new ownership, making a shank that is stiff enough not to bend while not being brittle is probably a tricky bit of metal working to get right every time.

[Uncle Bob]

Originally Posted by Tomaz473

The shackle is too small for this chain and is mounted incorrectly.
Shackle must always be one size bigger then the chain.
For example 10 mm chain should have 12 mm shackle.
That is why anchor slot is bigger: to accommodate shackle to go though it, not only the pin.
10 mm chain can accept 12 mm pin. You can not thread shackle eye though it, but you do not have to. Just the pin.

Here is a possible scenario about what might have happened (with a lot of speculation from my side, but it is possible):
- Shackle eye wedged inside the anchor slot when the shackle turned slightly sideways. So, the shackle could no longer move in relation to the anchor.
- at lifting the anchor a large shock load occurred at the moment when shackle met the roller. The anchor was still pointing down, while the chain was pulling horizontally. At that moment the big side-load tried to wedge the shackle even more and that was the reason the shaft cracked open a little.
This enabled the shackle to rotate.
- The anchor was pulled on deck.
- As the chain was pulled and the anchor reached its resting position on the roller this created another shock-load, which wedged the shackle pin inside the crack.
- movement of the anchor on the way enabled the pin to travel further through the crack until it cam all the way through and the anchor broke free.

It is my strong believe, that there must have been a material flaw at the anchor shank or the shackle would give up first. But without the anchor we will never know.

Funny but it has been my understanding that the ideal setup is a bow shackle of the same size as the chain or one size up fitted to the anchor with the pin through the slot and a similarly sized bow shackle fitted to the chain, with its pin through the link, the two shackles providing the best articulation possible for the tackle. As has already been mentioned, all of similar metal.
But then it is always possible that I am misinformed.

[Discovery 15797]

My observations...

There is no signs damage or deep gouges in the fiberglass caused by severe banging by a loose anchor. There are signs of wear (gray) where the chains or anchor or shackles rubbed against the gelcoat and a slight gouge (wear) where the shackle possibly hit near the bow on the port side as the anchor was lowered. But, there is no apparent chipped gel coat or deep scratches.

There is no apparent damage or marks on the front aluminum crossbeam. Especially none that would be caused by a 40 lb steel anchor banging against aluminum.

There is no apparent damage to the bow roller (other than the rust).

The shackle used is stainless. Stainless is a softer metal compared to galvanized steel. It is also unknown if a second shackle was used.

The galvanized shackle on the bridle is moused.

The OP indicates the anchor was a 20 kg. This is undersized for the Lagoon 400 according to the Rocna sizing guide, (and way undersized for this vessel IMHO). (Speculation...could the anchor have been over-stressed while at anchor previously which caused a failure in the anchor shank. Possible, but given the shackle was of softer metal it is more likely that would have failed first.)

The anchor shackle pin appears to have sustained a brittle fracture. Brittle fractures occur without appreciable deformation and are perpendicular to the direction of the applied stress. (Speculation...in the case of a shackle pin...tightening the pin into a misaligned or distorted shackle could have caused a brittle fracture.)

Other than my brief speculation above I will not offer further conjecture. However, I will suggest that things do not seem to be lining up well to support the claim.

[boatpoker]

Originally Posted by Discovery 15797

The shackle used is stainless. Stainless is a softer metal compared to galvanized steel.

I believe you have that backwards

[FlyingScot]

Rocha 20kg definitely too small for this boat. Rocna 33kg is what I upgraded to on my Leopard 40. Also Mantus S2 swivel. Recommend both. Mantus would also be a good choice if it fits.

[thinwater]

Is there a "before" picture?

[Bleemus]

Aside from the mystery that shackle was installed backwards. Rounded end goes on the anchor.