Picture a mine headgear in 50m of sea water sat in a strong current, what materials would you use? It must be strong, and last at least 20 years, is this possible at a realistic price.
I would be glad for any thoughts.
Bronze decays at a rate that is infinitely faster than the rate at which gravity fails.
Designing a structure so that it is all in compression is the best bet regardless of the material.
Very few materials like being under tension in seawater.