Titanium Chain Plates

[Storm]

Brion,
What are your current thoughts on the use of titanium for chain plates? Does your shop fabricate titanium chain plates? If not, any recommendations? How about bolts for the titanium chain plates- is stainless 316 the most economical choice?
Regards

[Brion Toss]

Hello,
It can be argued that stainless is the worst possible material for chainplates; it only corrodes where you can't see it, is vulnerable to several forms of corrosion -- including contact with water, of all things -- and it becomes brittle with age, tending to fail catastrophically. Grade 5 titanium, of proper scantlings, is just about invulnerable to all of these things, as well as being much stronger. And since it doesn't need to be polished, it can compare favorably in price with polished stainless.
So yes, I like it a lot. On the other hand, it requires some skill to work it, and a lot of machinists are yet unfamiliar with how to do so. Learning curve.
Fair leads,
Brion Toss

[Storm]

Brion,
Thanks for the reply. Any recommendations for a shop to fabricate my chain plates. They are straight forward flat bar with holes drilled. Some do have a slight bend.
Regards

[Brion Toss]

Hi again,
My favorite local supplier is Meridian Stainless (Port Townsend), and they can bend. I've also had great experiences with Allied Titanium, but I don't know if they are bending now.
Fair leads,
Brion Toss

[Storm]

Brion,
Thanks for advice. Just one more question. How do you inspect titanium for end of life? Do you look for cracks? Or do you replace say every 20 years?
Regards

[Stumble]

Storm,

So long as the work load is kept below 71ksi for Grade 5 there is no fatigue life. This works out to about 55% of the UTS. Or about 60% of the yield strength. In other words, assuming a safety margin of 2:1 titanium parts don't have a fatigue limit in marine environments.

Practically speaking the only life span restriction is from galling. So anything with threads could be a problem. Anything that is static should last long enough that it doesn't matter (the U.S. Navy figures 5,000 years fyi).

[Storm]

Thanks Stumble

[billknny]

What advantages does Ti have over bronze for most chainplate applications?

It is lighter of course, but for 99.9% of boats the difference can't be significant down low.

It is shiny and stays that way... so I guess if that is important...

But bronze is similar in strength to stainless in the same dimensions. Corrosion is not an issue. And I don't know of any long term fatigue issues.

With a little care, bronze can be worked by pretty much anybody with a bit of knowledge. The overall fabricated cost is similar to stainless. When I have looked at fabricated Ti vs 316 stainless they are NOT that similar in cost.

For the typical cruising boat why Ti? Cache'?

[Storm]

Originally Posted by billknny

What advantages does Ti have over bronze for most chainplate applications?

It is lighter of course, but for 99.9% of boats the difference can't be significant down low.

It is shiny and stays that way... so I guess if that is important...

But bronze is similar in strength to stainless in the same dimensions. Corrosion is not an issue. And I don't know of any long term fatigue issues.

With a little care, bronze can be worked by pretty much anybody with a bit of knowledge. The overall fabricated cost is similar to stainless. When I have looked at fabricated Ti vs 316 stainless they are NOT that similar in cost.

For the typical cruising boat why Ti? Cache'?

I looked at bronze and wanted to go that way. The cost was similar to stainless and I could drill the material myself and no need to polish like stainless. I was planning to go with silicon bronze. The problem I had is that I did not feel comfortable with the material source. A lot of bronze is coming out of China and I did not feel comfortable with the quality control. The other problem I had was with the material, it was bronze but was is rolled sheet, wrought, or cast? I think there are big differences in the strength. Also, I could not find bar for the dimensions I needed. Therefore I need to have the chain plates cut from bronze plate. The cutting opened up another can of worms. I just did not have a good comfort level with bronze, and some of that is due to my lack of knowledge on the types of bronze material out there. the other problem I found is the strength numbers for bronze seem all over the map. If I look up strength for silicon bronze, I can find some similar to 316 stainless and some well below.

[009hnoor]

This works out to about 55% of the UTS. Or about 60% of the yield strength. In other words, assuming a safety margin of 2:1 titanium parts don't have a fatigue limit in marine environments.