Stainless Shackles on Galvanized Anchor Chain

[tommays]

I don't tend to believe a SS shackle is going to take out a whole chain but i would sure NOT waste the money on one

Common wisdom is that SS bolts and Aluminum are a bad combo BUT try and buy and outboard motor built other wise except some big Yamaha's that use chrome plated SS bolts to cut down on the cant take it apart problem


NOW and SS swivel is a whole other thing because the parts do trap saltwater in a narrow crevice which would allow it to happen pretty fast


As i repair SS mixers for a living i get to see all kinds of bizarre things happen , on older mixers it was common to use a 316 SS pin to hold a 316 SS blade section in place.

I have seen a LOT of 316 SS pins lose out on that deal and modern mixers are 100% welded and polished for both sanitary and to avoid giving a foothold to corrosion

 

[Al - s/v Persephone]

Re: Stainless Shackles - try Titanium

While pure Ti metal would look no better from its position in the electrochemical activation table, it is very hard to find - as it quickly forms an impervious oxide when exposed to air or water.

For that reason, I substituted Titanium shackles for SS with my 5/16 G40 chain.

http://www.titan-marine-hardware.com/titanium-shackles.htm

They are not cheap, however, but far stronger than SS.

Fair winds,
Al
s/v Persephone

 

[Maine Sail]

Photos..

You guys should know I would have a photo...

2 1/2 years use as a mooring pendant with a stainless shackle. No corrosion on the stainless what so ever and the galvanizing is the only thing really suffering on the shackle.

BUT!

This set up is less than 12" below the surface where there is oxygen for the stainless to not suffer from crevice corrosion.

With an anchor rode you can bring it up and examine it every use so you could at lease see what's going on. With a mooring you don't have that luxury. Crevice corrosion of stainless steel sitting on the bottom is a real concern if you anchor for extended periods.

My main concern with stainless over properly rated galvy shackles, like those made by CM, is the strength issue. For instance a 5/16" Suncor Stainless anchor shackle is rated at 1300 lbs. working load while a CM load rated galvanized shackle has a 1500 lb WL but is designed to a 5:1 safety factor.

The CM shackles meet stringent federal standards. It is very tough to find a stainless shackle that will tell you it is designed at a 5:1 safety margin and instead most just give you a SWL. CM shackles meet requirements of Federal Specification RR-C-271D and have shackle pins forged from alloy steel, heat treated and tempered to give greater strength and the ultimate strength equals 5 times working load limit.

P.S. In many thousands of anchorings I have never once found the need for a swivel.

Oh yeah the photo:

 

[Stu Jackson]

Thimble-leena, thimble-leena, oh little thimble-leena...

 

[RichH]

Although this thread has been well discussed ....
I'd strongly recommend to avoid stainless in ANY underwater 'strength' application for the following reasons:
1. Stainless (300 series) is VERY subject to 'fatigue' (unpredictable and catastrophic 'brittle failure'). The 'fatigue endurance limit' of 300 series stainless - is about 1/3 of the ultimate tensile values - meaning that at constant and repetitive load cycles greater than the nominal 30,000 psi fatigue stress limit (while UTS @ ~90ksi) .... the metal will rapidly become weakened, will begin to radically and progressively crack on a macroscopic basis. Fatigue is 'additive', meaning the microcracks will propagate and weaken the structure hence leaving less 'cross section' to bear load .... a descending spiral. Typically when at or near the 'endurance limit' of 1/3 of Ultimate stress values, 300 series can only withstand ~1M 'load cycles' .... then it is subject to 'shattering'.
This translates to "if you use stainless underwater your need it to be better than THREE TIMES stronger than projected .... MaineSail's application/example is FIVE TIMES stronger and therefore exceeds the 3X requirement for fatigue.

2. The micro cracks in #1 above are the 'nucleation sites' in which 'crevice corrosion' starts and propagates ....

#1 + #2 = VERY rapid failure for underwater application with (unknown) repetetive load cycles.

Moral: dont use stainless under water especially where the 'loading' is cyclical and high.


Sorry but, If the galvanization came off quickly .... then it follows there wasnt much galvanization to start with; the stainless had 'nothing' to do with the galvanization loss.

 

[Hermit Scott]

Rust never sleeps

There is a 2' rusted section near the stainless shackle. Then there is a rusted section in the middle somewhere. The other end that tied to the rope was not rusted even though it had a stainless shackle.
This dude put a shuttle bus cabin on a 40' steel pontoon boat. I thought you may want to see that. My investor owns Midas car repair shops. So I go to know a few car techs. I thought the car techs lead the most pathetic lives possible, with the drugs and going in and out of jail, in and out of court, baby-mama drama etc, etc. I have to say the boat yard crew have got them beat. I actually drove home depressed after to talking to one today.

 

[NotCook]

Oh yeah the photo:

MS, You aren't suggesting that the photo is of a stainless shackle, are you? That HAS to be a galvanized shackle in the photo.

I wouldn't want to try to undo that shackle without a hacksaw!

 

[Maine Sail]

No..

MS, You aren't suggesting that the photo is of a stainless shackle, are you? That HAS to be a galvanized shackle in the photo.

I wouldn't want to try to undo that shackle without a hacksaw!

No the thimble in the pendant is stainless the shackle is load rated galvanized..

P.S. It unscrewed just fine with a pipe wrench after two and a half years in contact with a stainless thimble..

 

[NotCook]

Help me interpret some of the thread. My understanding is that rust and galvanic corrosion are two entirely different processes, though rust (oxidation), can/will occur in the anode in the process. The way I understand galvanic corrosion to work is that electrons actually transfer through the electrolyte from (the vicinity of) the lower metal (anode) to (the vicinity of) the higher (cathode). But, and here is my real question, rust could certainly occur without the presence of galvanic corrosion, particularly in saltwater, and particularly in poorly galvanized steel, right?

Dog, trying to interpret the chart you provided, I have 2 questions. I've seen similar, though less detailed charts before, but thanks for this one. What I don't see, or at least not obvious, is aluminum itself, and I am interpreting the nickel reference to be what we think of as non-stainless "steel". Is that a proper interpretation?

 

[jibes138]

Cold Working of Stainless

Most people would not intuitively think that stainless steel is weaker than galvanized given the "higher grade" and extra cost. But austenitic stainless is pretty weak material. It has great corrosion resistance but as noted the fatigue properties are pretty poor. The tensile and ultimate strengths are pretty low compared to other grades of steel also. The fatigue is a function of work hardening, I have run studies over the years on cold working of stainless and aluminum and the stainless has extreme work hardening properties.
What makes stainless corrosion resistant is the high chromium and nickel content, in the case of 316 stainless it is 17% chromium and 12% nickel with 2.5% Molybdenum thrown in. This material is tailored to resist corrosion, not to be extremely strong. Seems like for an anchor you want strength first as it will most likely get extracted periodically for inspection. I recently replaced my rode thimble because it was severely corroded and it was galvanized along with a galvanized shackle. The shackle is still in use. I'd be more concerned with the materials constantly sitting wet or damp in the anchor locker and being exposed to oxygen in the form of the atmosphere.
I am ordering up a platinum anchor with a gold chain so I can hide all my money underwater before the government takes it all away to give to people that don't have boats. What is the best way to isolate the gold from the platinum?

 

[Hermit Scott]

The best way would be to have a liberal hold on to the chain with one hand and the anchor with the other. This method works because it's not his money and there is no way he will let go.

 

[sailingdog]

Nickel is just that....nickel metal... as in one of the components of cupronickel alloy.....which is copper and nickel.

Aluminum and steel are both there... pretty far down the list—steel is just below Cast Iron, and Aluminum is just above Uranium.

Dog, trying to interpret the chart you provided, I have 2 questions. I've seen similar, though less detailed charts before, but thanks for this one. What I don't see, or at least not obvious, is aluminum itself, and I am interpreting the nickel reference to be what we think of as non-stainless "steel". Is that a proper interpretation?

 

[NotCook]

What is the best way to isolate the gold from the platinum?

Send the gold chain to me - and keep the platinum. That will assure adequate separation of the two elements. )

 

[Ron20324]

I am ordering up a platinum anchor with a gold chain so I can hide all my money underwater before the government takes it all away to give to people that don't have boats. What is the best way to isolate the gold from the platinum?

Call Mr T . I'm sure he can tell you!

 

[NotCook]

Aluminum and steel are both there... pretty far down the list—steel is just below Cast Iron, and Aluminum is just above Uranium.

Ah, now I see them. The first time I looked, there were 2 lines that threw me off:
Cast iron Steel, and Indium Aluminum Uranium (pure).

I thought that latter must have been some exotic alloy!

If they made masts out of Uranium, we wouldn't need anchor lights...

 

[Hermit Scott]

I am experimenting with a small window unit AC. I am trying to avoid having to vent the exaust by running a tube beside the condenser, pumping seawater through it and sealing them in and possibly filling the area with oil to help the heat transfer. It will be pretty simple to do however I am concerned with the durabilty of the copper. There won't be any other metals in contact with it. It is the kind of copper used in water pipes. What happens to copper in seawater?

 

[jibes138]

copper in sea water

copper is a major constituent of bronze. It was used for a godzillion years as water pipes. It tends to turn green in sea water (ever seen a penney in sea water?)? It might last a week or two.