Rocna Anchor Failure

[NorthernMac]

Originally Posted by s/v Jedi

I do not like the swivel to anchor connection (side loading) and would choose a different swivel or put a shackle in between.

Do you have a link to a swivel you’d recommend?

[a64pilot]

You weren’t asking me, but take a look at this swivel, if you have 5/16 chain get the S-2.
You don’t want anything weaker than the chain, and a swivel that is stronger than the chain and can’t be side loaded is rare, there are very few
https://www.mantusmarine.com/mantus-...EaAvDsEALw_wcB

[Exile]

Originally Posted by a64pilot

You weren’t asking me, but take a look at this swivel, if you have 5/16 chain get the S-2.
You don’t want anything weaker than the chain, and a swivel that is stronger than the chain and can’t be side loaded is rare, there are very few
https://www.mantusmarine.com/mantus-...EaAvDsEALw_wcB

Informative link, thanks. Seems to be much debate over whether a swivel is even necessary. But if you're going to have one, this Mantus one certainly looks better than others I've seen.

[BlackHeron]

The Mantus is a sweet swivel. Keep an eye on the seizing wire. In daily use the wire will fail in less than a year. I give them a look-see on every retrieval and before every drop. Belt and suspenders. Eventually they will break at the twist. The wire tie twist must get snagged on stuff down there, and bend the twist back and forth until the wire snaps at the spot it bends.

[s/v Jedi]

Originally Posted by NorthernMac

Do you have a link to a swivel you’d recommend?

The Mantus swivel as recommended above does not have the problem so yes that’s the one to get for a stainless setup

[Oceansailor]

Originally Posted by s/v Jedi

The anchor did not fail. It was the missing swivel, the missing 2nd shackle or even the shackle shown has a fractured pin but sprung back in shape after the anchor shank worked out.



Also, like others stated, the wrong type of swivel was used. Use every component galvanized steel or use every component stainless steel, do not mix types.



Also, do not use Wichard HD shackles, not even on stainless chain and anchor. It’s too brittle.

Could you please present technical data that supports your theory that Wichard HD shackles are to brittle?

[chris in SG]

Originally Posted by a64pilot

You weren’t asking me, but take a look at this swivel, if you have 5/16 chain get the S-2.
You don’t want anything weaker than the chain, and a swivel that is stronger than the chain and can’t be side loaded is rare, there are very few
https://www.mantusmarine.com/mantus-...EaAvDsEALw_wcB

Predictably, there has been a wide range of opinions about 'best practice' but only one point has been made consistently without contradiction in this thread - that you should not mix galvanised and SS fittings. And yet, nobody seems concerned that 'modern' swivel manufacturers use only stainless steel. The Mantus product looks like a superb piece of engineering but the brochure says nothing about materials except that it is made from 316 stainless. My guess is that they know that most of their sales will be to boaters who use galvanised anchors and chains. so if members here are really correct to state that that mixing materials is such a no-no, why is nobody concerned about this?

I suspect that the taboo of mixing materials is being over-stated here. After all, we are not talking about corrosion (nobody is suggesting a stainless pin in a galvanized shackle) we are only concerned with 'weak links' in the system. The relative strength of materials is compensated by sizing appropriately.

However, I would defer to the greater experience of others provided that this is real knowledge and not dogma..

[boatpoker]

Originally Posted by chris in SG

I suspect that the taboo of mixing materials is being over-stated here. After all, we are not talking about corrosion (nobody is suggesting a stainless pin in a galvanized shackle) we are only concerned with 'weak links' in the system. The relative strength of materials is compensated by sizing appropriately.

As a Certified Marine Corrosion Analyst I agree. Of course there will be a galvanic reaction between metals with different voltage potential but such reactions are very slow unlike stray current reactions which can be shockingly fast.

The inconsistent electrical contact and slow process means any damage will occur very slowly (possibly years) and normal vigilance would suffice.

That being said I have never experienced a need for a swivel and don't understand the need to introduce another "weak link".

[thinwater]

Originally Posted by boatpoker

As a Certified Marine Corrosion Analyst I agree. Of course there will be a galvanic reaction between metals with different voltage potential but such reactions are very slow unlike stray current reactions which can be shockingly fast.

The inconsistent electrical contact and slow process means any damage will occur very slowly (possibly years) and normal vigilance would suffice.

That being said I have never experienced a need for a swivel and don't understand the need to introduce another "weak link".

^^ What he said (I do API tank corrosion protection evaluations).


There will be slightly increase corrosion. As for the chain, just trim a few links every few years. It's good practice anyway.


I would always separate the swivel from the anchor with a shackle or some chain. That will also protect the anchor from corrosion.


So not much to worry over. But I don't like swivels. I had one and got rid of it.

[s/v Jedi]

Originally Posted by Oceansailor

Could you please present technical data that supports your theory that Wichard HD shackles are to brittle?

I wrote HD (or spelling changed it) but meant H.R. These (17-4 stainless) shackles are much stronger because they are hardened by heat treatment, which makes them more brittle as well. Here’s some data, look at elongation only 8% vs 50% for 316

[NorthernMac]

Originally Posted by chris in SG

Predictably, there has been a wide range of opinions about 'best practice' but only one point has been made consistently without contradiction in this thread - that you should not mix galvanised and SS fittings. And yet, nobody seems concerned that 'modern' swivel manufacturers use only stainless steel. The Mantus product looks like a superb piece of engineering but the brochure says nothing about materials except that it is made from 316 stainless. My guess is that they know that most of their sales will be to boaters who use galvanised anchors and chains. so if members here are really correct to state that that mixing materials is such a no-no, why is nobody concerned about this?

I suspect that the taboo of mixing materials is being over-stated here. After all, we are not talking about corrosion (nobody is suggesting a stainless pin in a galvanized shackle) we are only concerned with 'weak links' in the system. The relative strength of materials is compensated by sizing appropriately.

However, I would defer to the greater experience of others provided that this is real knowledge and not dogma..

Galvanized! Ewwwww




*waiting on new swivel to get in

[Exile]

Originally Posted by NorthernMac

Galvanized! Ewwwww




*waiting on new swivel to get in

Stainless Steel. $$$$$ (and weaker). No matter. Nice looking front end on that boat, and suggests the rest is rather pleasing as well. But then I'm a sucker for traditional looking boats.

Speaking of SS, I heard "around the boatyard" that SS chain is less susceptible to "castling" down in the locker. I've made improvements but this is still a bit of a PITA on my boat (galvanized chain). Is the boatyard banter true?

[thinwater]

Originally Posted by NorthernMac

Galvanized! Ewwwww

*waiting on new swivel to get in

Is that an anchor, or undersized jewelry for a dock queen wannabe?

[NorthernMac]

Originally Posted by thinwater

Is that an anchor, or undersized jewelry for a dock queen wannabe?

Lol, I was actually thinking it was a little oversized

and it’s a little of both!

[noelex 77]

Originally Posted by Exile

Speaking of SS, I heard "around the boatyard" that SS chain is less susceptible to "castling" down in the locker. I've made improvements but this is still a bit of a PITA on my boat (galvanized chain). Is the boatyard banter true?

Yes, stainless steel chain is “slippier”. If you have a problem with the chain piling up in the chain locker and jamming the windlass a switch to stainless steel chain will often solve the problem.

There is some good quality stainless chain available, but they are not easy to find. Many are poor quality despite the cost. Good quality duplex stainless steel chain seems to hold up well from user reports, but it is expensive.