Two Anchor Swivels

[SailingHarmonie]

Originally Posted by boatpoker

Electrolysis is an induced process found in industry and laboratories in which the anode is positive and the cathode is negative whereas on your boat it’s the anode that is negative and the cathode which is positive. It simply cannot occur on boats. Be wary of corrosion or electrical advice from anyone using the word "electrolysis" on boats.

Kills hair follicles too.

[toddster8]

I recently replaced all of the existing ground tackle on my new boat. Of relevance to the OP, the Rocna manual states (may not be an exact quote) "We do not recommend attaching a swivel directly to the anchor. A swivel may be installed at the end of a short length of chain that is connected to the anchor with a conventional shackle."

FWIW, my new gear has an Anchorlift anchor-turner and swivel combination. It still comes up backward about 25% of the time.

[sailingharry]

Originally Posted by thinwater

As Nolex points out, SS must be thicker, more similar to strong aluminum alloys than high strength steels.

I am a degreed mechanical engineer. Never really used it in my career. So I set out to design a sprit for an asym on my boat. Dusted off bending formulas and such. I was absolutely stunned to find that size for size, T4 aluminum was STRONGER than SS.

This was for deformation, not ultimate strength. Aluminum's weakness is it breaks with just a touch more force than it bends. Stainless will mangle and not break.

[Dockhead]

Originally Posted by noelex 77

One problem with stainless steel anchors is that the yield strength is lower than for the hi tensile steels used to construct galvanised anchor shanks.

This means the shank must be thicker, or weaker. A thicker, heavier shank will significantly reduce the performance.

Ultra and Spade reduce the effect of this limitation by using fabricated shanks. Ultra do not make a galvanised version so no comparison is possible. Spade make both a stainless steel model and a conventional steel model, but the steel used in galvanised anchors has never been disclosed, which probably means it has a low yield strength so in this case the substitution probably has little effect.

Some other manufacturers simply replace the hi tensile steel for 316L. The more responsible manufacturers use Duplex stainless (for example Mantus) or hi tensile stainless steel (for example Rocna). This is better, but the yield strength is still lower. The anchor performance will be worse if the shank thickness has been increased, or the strength will be lower if the same dimensions are used.

True, but different shank designs make different demands on the material.


The hollow shank of the Spade is extremely strong. I read a test of this somewhere -- the strength was off the charts compared to other anchors; only the old forged CQR with the I-beam-shape shank came close. It would be interesting (and expensive) to test them, but I guess the shanks of the stainless Spade -- and the very similar Ultra -- both made from 316 -- are probably still a lot stronger than anchors with shanks cut from flat plate, even if they use high strength steel.


Simple shank cut from flat plate is an economy measure. Something forged and with a shape, like the CQR, or a welded up hollow shape like the Spade, will be greatly stronger. Such shapes might not bury as well, however.

[noelex 77]

Originally Posted by Dockhead

I guess the shanks of the stainless Spade -- and the very similar Ultra -- both made from 316 -- are probably still a lot stronger than anchors with shanks cut from flat plate, even if they use high strength steel.

The Ultra anchor shank is now made from Duplex stainless steel.

They did have some bending problems with their early shanks. They modified the design by adding some internal webs and I think switched from 316 to Duplex and this has solved the issue.

Spade have always been reticent to divulge their construction materials, but given that they don't boast about using Duplex, I suspect it is just 316.

The Ultra and the Spade both use very thin material in the shank. You can just see the thickness of stainless steel used in the Ultra in this photo where someone has rather stupidly drilled a hole in the lovely Ultra shank.

[Pete7]

Originally Posted by toddster8

Of relevance to the OP, the Rocna manual states (may not be an exact quote) "We do not recommend attaching a swivel directly to the anchor. A swivel may be installed at the end of a short length of chain that is connected to the anchor with a conventional shackle."

Ah, I did wonder what was wrong in this photo of an anchor for sale.

Be careful out there, they walk amongst us

Pete

[toddster8]

Yeah... that doesn't look... right, but... I can't speak to that anchor but the Rocna does have several alternate attachment points which I would not have completely figured out without reading the manual. One is for securing the shank on deck. One is for attaching a buoy/retrieval line. One is for attaching rode to a secondary anchor. I almost remember which is which.

[Benz]

Originally Posted by Pete7

Ah, I did wonder what was wrong in this photo of an anchor for sale.

Be careful out there, they walk amongst us

Pete

There is a use mode where you attach the chain as in the picture, then lash it down to the eye at the end of the shank with twine or zip ties. That keeps the pull as it should be, but if the anchor snags under rocks, the chaing being tugged straight up when retrieveing will snap the lashing/zip ties and pull out the anchor.
Never been bold enough to try it, but I know several who swear by it. One guy even takes it out and around the bail of his Rocna for a better lead.