We replaced the 316 austenitic ss chainplates on BCC 116 (launched in November 2000) in 2015 with plates fabricated from duplex ss (2205 for most of the plates, 2507 for the bobstay plate, the lower backstay plate and the boomkin shroud plates right near the waterline).
We used carriage bolts carved from 2507 duplex (on the basis of going one grade higher for the bolts to ensure against crevice corrosion when using any ss).
We had stress crack corrosion signs on the shroud chainplates. The carriage bolts looked okay.
2205 duplex ss is stronger than 316 austenitic. 2205 and especially 2507 are immune from chloride-induced corrosion.
I think 316 ss is a compromise: low price, but low longevity in an environment that includes warm saltwater. A duplex ss chainplate could be expected to have a longevity of 25 - 30 years or more. 316 austenitic ss is perhaps half that (but if the environment is cool and low in chloride ions, such as on the Great Lakes, it’s a different story for 316 ss).
Bronze is better, but in the small economy of Australia it was easier for me to source 2205 and 2507 duplex ss plate and have it fabricated (and for the cranse iron, the upper and lower backstay plates, and the bobstay plate, welded) than to get a local bronze foundry to make what Zygote needed.
Minor edits for accuracy and completeness and to minimise typos