Bronze vs Stainless Chainplates

[boatman61]

Here we go, here we go' here we go........

[seacap]

316 stainless steel:
Ultimate tensile strength, psi 85,000
.2% yield strength, psi 35,000

Aluminum bronze:
Ultimate tensile strength, psi 85,000
.2% yield strength, psi 32,000

Every rigging shop I have ever been to has a display of failed rigging parts. All the parts displayed are always SS. I have never seen any failed bronze parts on display.

A local rigger here told me that Lloyd's will not insure any SS rigging parts over 10 years old. I have not confirmed that. Also I do not know what Lloyd's limit on bronze is.

In 40 years of sailing I have seen many SS failures. I have yet to see a bronze failure.

Why isn't bronze used more? it's not shiny (marketing) and it runs the cost of an already pricey endeavor up.

My .2c

[markpierce]

OK. Fine with me. You can have your bronze. If it is so superior over steel, it must be because it is much more expensive than steel because it's applications are very limited.. Bridges, firearms, automobiles, skyscrapers, knives, etc. are made of steel. Is that because steel is inferior but is used because it is cheap? Again, bronze has failed me, but not steel, yet. (Let's see, if my life depended on it, I'd choose a steel sword over a bronze one.)

I've never seen a bronze chainplate. That's why I've never seen one fail. I've seen a bronze tiller-post connection fail, but not it's steel replacement.

[markpierce]

Originally Posted by seacap

A local rigger here told me that Lloyd's will not insure any SS rigging parts over 10 years old. I have not confirmed that. Also I do not know what Lloyd's limit on bronze is.

So, we have not heard the answer to the question of bronze verses steel from Lloyd's. I'm anxiously waiting.

[nv5l]

My ss chainplates failed, and I'll replace them with bronze. Bronze is not a panacea, it suppose it does sometimes fail, but that has more to do with a manufacturing defect, than to age or corrosion. SS will fail. Bronze might fail. Take your choice. Btw, for a DIY, bronze really won't be that much more expensive, no need for expensive bits, and I can do it all myself.

I respect your decision, please respect mine.

[sneuman]

I checked into the new super strains of stainless lately. They are superior in crevice corrosion, but are very expensive and apparently difficult to mill (thus driving up the cost of finished plates).

[Noname1]

these are the people I was considering to supply material and cut bronze chainjplates.

Farmer's Copper Services, Water-Jet Cutting

Is there a "I have no financial interest" emoticon?
and a "I'm finished with this topic"?

[osirissail]

As with most things in use on modern cruising boats it boils down to cost, access to the material, and maintenance issues.
- - Stainless is somewhat more accessible (find and purchase) than Bronze. Both have corrosion problems but bronze also has electrolysis problems. "Pink" spotted bronze is as dangerous as Intragranular corroded Stainless. Because the riggers have more examples of failed SS is really merely a function of 99% of boats using the stuff versus bronze.
- - The other metals are obviously far superior and if you have a boat budget equal to NASA then you can use the stuff.
- - Access is really the big problem these days - try to find 316SS bolts washers and nuts and you will quickly find out that market is gone. A few places still have the stuff and we keep the list very quiet. Most all the "stainless" you find in hardware and boat stores is not 316SS. And the bolts/screws are pressed from wire into their shape (probably in China like everything else these days). Head failure of brand new SS bolts/screws is quite common as there is NO quality control inspection anymore. Bolt/screw heads fracture off with no warning.
- - So in real life it becomes that much more important to use the stuff available within its service requirements for air/water/electrical restrictions. If you maintain and inspect and install the stuff correctly you will get the maximum life span available with minimal risk or failures. But when it comes to "ordinary" (numb-nuts) use of a cruising boat the industry uses Stainless and sets an average service life to compensate. As with old cars, if you take care of the thing, it will last long after its average lifespan.

[boatman61]

Originally Posted by nv5l

My ss chainplates failed, and I'll replace them with bronze. Bronze is not a panacea, it suppose it does sometimes fail, but that has more to do with a manufacturing defect, than to age or corrosion. SS will fail. Bronze might fail. Take your choice. Btw, for a DIY, bronze really won't be that much more expensive, no need for expensive bits, and I can do it all myself.

I respect your decision, please respect mine.

Damn sight easier to drill...

[GordMay]

Keep your stainless steel clean!
A simplistic example of the effectiveness of cleaning is right in the galley. A stainless kitchen sink can see some of the most hostile chemical attacks, but the stainless stays bright.
Why?
Because the constant flow of fresh water and wiping down removes the harmful chemicals that if left unattended, could attack the stainless' passive film. The more hostile the environment, the more cleaning required. Cleanliness is essential for maximum resistance to corrosion.
Never use abrasive powders or materials on stainless. Always use fresh water & a soft cloth.
Mild detergents and soap can be used, but those containing chloride detergents should be avoided.

[Blue Stocking]

I know we dig up artifacts from the bronze age. Have we dug up anything from the stainless steel age

[osirissail]

Originally Posted by boatman61

Damn sight easier to drill...

Very true in a simplistic way. But with the proper tools SS is not a real problem either.
- - But - before you start making chain plates from bronze or SS be sure to get and study Brian Toss's Riggers Handbook and also the Machinist's Handbook as you cannot just "eyeball" where to drill the hole. There are definite measurements that must be made based on the material so that the hole is properly located. Improperly located holes will deform and cause failure of the chain plate.
- - Just another consideration is what are you going to use for rigging terminals, turnbuckles and clevis pins? Mixing SS and Bronze brings up "hardness" and wear considerations as the pins and stuff grind against each other during movement of the boat. Nobody said it was going to be easy . . .

[nv5l]

My turnbuckles and clevis pins are bronze, it's only the sta-lok eye and fasteners that'll be ss. Also, it seems like the only hole that really makes a difference is the one for the pin -- the rest will go into fiberglass/marine plywood, so that'll be sloppy in comparison anyway.

Does anyone have an issue with bronze turnbuckles and pins?

[roverhi]

If I could find the material and get it machined reasonably, would go with bronze. It doesn't suffer crevice corrosion like the common stainless parts (304, 316). Crevice corrosion, usually where they pass through the deck and can't be inspected, is the cause of almost all SS chainplate failures.


Electrolysis affects stainless just as it does bronze. It's not an inherent failure of the material but bad electricity like a hot marina or improperly installed electrikery in the boat.

Most productrion boats have 304 stainless chain plates, not 316.

I'm getting ready to replace my chainplates. From a cursory initial search, Aluminum Bronze seems to be available in a lot more thicknesses/widths than Silicon Bronze. Both are supposed to be salt water tolerant but all I've ever heard about is Silicon Bronze. Is Aluminum Bronze a viable substitute for Silicon Bronze??

[nv5l]

I looked at the other components and tried to make sure that the new chainplates were at least as strong as the weakest link. My original chainplates were probably 304, so I used it's yield strength and multiplied it by the smallest cross-sectional area -- at the hole for the clevis pin in my case -- to get the current strength, then did the same for the new bronze ones. (I actually did this for all components up to and including the masthead)

I won't go through the calculations, but the old ones where 3/16 x 1 1/4 with a 9/16 hole, and the new ones will be 1/4 x 1 1/2 with a 9/16 hole. I used yield because it's a lot less than the tensile strength, and once you exceeded it, the material will neck and the cross-section will be reduced, which will bring on ultimate failure even quicker next time. My new aluminum bronze ones will be slightly stronger than the original ones, which are also stronger than the turnbuckles.

hth...
don

btw, I'm not a engineer, just took some courses long ago. If I've made an error, I hope someone will alert me to it. I plan to do this repair next month.