Stainless Steel Shackles on Anchors?

[Training Wheels]

I've never been one fond of stainless steel hardware for ground tackle use, but is it really a concern? I'm wondering if Wichard High Resistance D shackles, made of forged 17.4 PH stainless steel, would be okay to use on ground tackle. Would there be a real risk of crevice corrosion? As a person ignorant in metallurgy, your expert opinions please!

[UNCIVILIZED]

From a theoretical ultimate strength perspective, the stuff is great, but... the difference between it’s yield strength (when it deforms), & ultimate strength (when it fails), is relatively low. Which in the real world means that you’re much less likely to notice a problem with a 17-4 PH shackle than you would with a galvanized, or 316 stainless one, before it self-destructs. And it’s much more prone to stress cracking, & crevice corrosion than a lot of other alloys out there.

So for use in things like an anchor shackle, where you rarely inspect the threads, or sometimes even the shackle, it wouldn’t be a good choice. Especially when you consider that the WLL of galvanized shackles is usually only 1/5th of their ultimate strength. Where with stainless shackles the WLL is often half of it’s breaking strength. Thus by the time you notice it deforming it’s been severely loaded, & you’re lucky to have caught it.

This is one of the key reasons why so much deck hardware & rigging is now attached with Spectra. As you can see the wear in it long before it fails, & replace it. Where as it’s common for stainless shackles attaching hardware to give little to no warning prior to failure. And the only way to know that it’s coming would likely be to x-ray them for damage periodically, as is done with some bits of rod rigging.

You can look up the properties of various materials at Online Materials Information Resource - MatWeb
For example here’s one type of 17-4 PH
MatWeb - The Online Materials Information Resource

[Hydra]

I have had a bad experience with a stainless thimble close to carbon steel in seawater. Then, I fear that stainless would hasten corrosion on exposed steel, such as the anchor and chain links.

Alain

[Training Wheels]

How about titanium?

[UNCIVILIZED]

Originally Posted by Training Wheels

How about titanium?

Look up the specific type used, & investigate from there. Since there are a whole spectrum of alloys. Most of which are quite corrosion resistant. However, some steel alloys are stronger, & definitely more wear resistant (abrasion).

[Training Wheels]

Thank you. Trying to find a shackle to fit and match to 1/4" G70 chain. So far, it seems only stainless and possibly titanium.

[UNCIVILIZED]

Here are some options. You could have just asked
D Shackles
Denali Rose: Anchoring and Storm Tackle [Updated Jun-2017]
https://www.practical-sailor.com/iss...I_12096-1.html
US Rigging - Rigging Hardware - Grade 80 Omega Link

It's worth doing some in depth investigating on them prior to trusting them with your life. And I'd strongly suggest you start a thread on the topic of shackles for G70 chain. Which, if you don't, I may.

For example there was a long, informative article on types of stainless steel in Professional Boatbuilder in the early 2000's. And one of the features in it that stands out in memory was the description & explanation of the surprise failure of 17-4 PH stainless in a tip turnbuckle in some discontinuous rod rigging. IIRC it was on an IACC boat, so not exactly a location or application where salt water soakings would be a big factor.
www.ProBoat.com

[Glenn.Brooks]

Iam curious, has anybody ever seen a SS shackle with the remotest hint of crevice corrosion? 45 years commercial fishing in Alaska and sailing, I never have.

Sure, dredge something up off the bottom after 40 or 50 years, it's gonna be corroded. But, really, anchor rode needing a small 1/4" shackle? small craft with such light weight rode is likely never going to be in a position to put such a strain on that size shackle that it will deform. Use either galvanized or SS, it won't matter. You will be safe either way.

[UNCIVILIZED]

Originally Posted by Glenn.Brooks

Iam curious, has anybody ever seen a SS shackle with the remotest hint of crevice corrosion? 45 years commercial fishing in Alaska and sailing, I never have.

Sure, dredge something up off the bottom after 40 or 50 years, it's gonna be corroded. But, really, anchor rode needing a small 1/4" shackle? small craft with such light weight rode is likely never going to be in a position to put such a strain on that size shackle that it will deform. Use either galvanized or SS, it won't matter. You will be safe either way.

Yes, in addition to what's mentioned in my above post, I've seen it quite commonly. And odds are if you walk the docks at a marina, you'll see some stainless steel anchor shackles weeping corrosion in the region of their threads.

Also, in the stainless used in shackles, the amount of load difference between them failing & deforming is quite small as compared to galvanized ones. See my post above. And on matweb.com look up the properties of the metals in question for things like the Izod Notch test. Which tests how much strength a material loses when it cracks (basically). Hardened stainless alloys suck at it.
You might also look up the ductility of the alloys in question, & see how much they stretch prior to failing. The harder & more corrosion resistant the alloy, the worse it is when it comes to this.

Note, & this is key, (generally) galvanized rigging doesn't work harden, while stainless does. Majorly. Even with minimal movement. Including the wind passing over standing rigging of boats which aren't moving.
I've seen a LOT of cracked stainless over the years. Including stainless shackles exploding at profoundly low loads.

[Training Wheels]

Originally Posted by UNCIVILIZED

Here are some options. You could have just asked
D Shackles
Denali Rose: Anchoring and Storm Tackle [Updated Jun-2017]
https://www.practical-sailor.com/iss...I_12096-1.html
US Rigging - Rigging Hardware - Grade 80 Omega Link

It's worth doing some in depth investigating on them prior to trusting them with your life. And I'd strongly suggest you start a thread on the topic of shackles for G70 chain. Which, if you don't, I may.

For example there was a long, informative article on types of stainless steel in Professional Boatbuilder in the early 2000's. And one of the features in it that stands out in memory was the description & explanation of the surprise failure of 17-4 PH stainless in a tip turnbuckle in some discontinuous rod rigging. IIRC it was on an IACC boat, so not exactly a location or application where salt water soakings would be a big factor.
www.ProBoat.com

Thanks for the info. It seems the only option of those choices would be the omega link. Not galvanized, but I suppose they're cheap enough so you could change them out now and then. Wouldn't galvanizing weaken them, or not enough to be a concern?

I did find some titanium shackles elsewhere that were close in breaking strength, but probably not good if titanium doesn't stand up well to being abused.

[UNCIVILIZED]

Stumble is quite sharp on the properties of titanium. So you might ask him to weigh in on the thread, in addition to researching it yourself. And please post what you find.

[Training Wheels]

Darn, I was hoping for an easy answer, not a homework assignment! [emoji41]

[Glenn.Brooks]

Uncivilized, thanks for the reply. Very interesting stuff. Generally I've used galvanized shackles over the years for anchor rode- although considerably larger than 1/4" mostly. Interesting about work hardening SS. I wonder is that accounts in part for broken stands in SS rigging?

Anyway, I still think the OP would be fine with galvanized shackles in his rode - although I don't remember if he mentioned what size boat he planed on equipping. Might make a big difference re: size of shackle and chain depending on the working load imparted by them size of the vessel.

Just as a side light regarding SS deformation - there is a nice plastic Vertue in one of the local marina's here in the PNW that suffered what amounts to catastrophic failure of a SS Sampson post mounted at the bow. The Sampson post is collapsed to a 30 degree angle pointing foward toward the bow, and the rear of the flat deck mounting plate, welded to vertical tube, deformed upward in a u shape, apparently caused by the bow lines chaffing through during a winter's blow and placing the entire load on the boat for an extended length of time, the remaining lines running from themsampson post to the dock exerting sufficient force to compress and collapse the vertical part of the assembly. The four bolts thru deck hold everything in place, but clearly the load limits of the assembly were exceeded - causing the vertical part to collapse toward the bow. These plastic Vertues are fairly heavy displacement at 4.5 net tons, plus gear. Maybe 12000# deadweight. Fascinating to see.

Glenn

[Snowpetrel]

I used to think stainless fatigues more than steel. Now I am not so sure this is normally the culprit. When you start looking at SN curves and the fatigue or endurance limits for the higher strength steels they seem similar to stainless steels.

http://www.bssa.org.uk/topics.php?article=104

Its all a pretty complex subject

https://www.google.com.au/url?sa=t&s...oVURQxFbs-Qv0Q

This is a simple primer, and don't ask me to explain it, because a lot of it is gobbly gook to me! But there are lots of factors to take into account, and stress risers and surface treatment are play a big part.

But anyway, it seems to me that rigging just isn't normally loaded and cycled enough to suffer from fatigue failures for the most part, prehaps on race boats and in some cruising yacht cases , but it just doesn't explain why conservatively rigged cruisers still have failures.

Prehaps its the stress risers caused by cold working the the swages, rod heading process, or bad alignment. Or maybe poor quality control by the manufacturers.

But I suspect stress corrosion cracking might play a big part. This is something austenitic stainless steels (eg 304 and 316) are subject to in the presence of clorides (eg salt) at very low stress levels, and higher temps. Typically 60+ deg c but as low as 25 deg Celsius can cause it in some cases.

https://www.google.com.au/url?sa=t&s...zZXvjMPL6V7rOQ

https://www.google.com.au/url?sa=t&s...cp7oT2V6wrIBGA

http://www.ssina.com/corrosion/stres...-cracking.html

http://www.bssa.org.uk/topics.php?article=18

Overall given this information about 304 and 316 stainless one has to conclude that it is the wrong material to use in a critical and moderately stressed environment with high salt concentration such as on yachts due to the probability of Stress corrosion cracking.

A mate just lost his mast due to a stainless steel shackle failing. Probably SCC.

[Sandero]

I am curious about these failures. my anchor shackle is quite visible.. and rated much higher than the working loads of the anchor. Also note that several companies offer stainless steel swivels... why?

While theoretically AND practically there would be failures... I have never heard or seen one.

Anyone????