Not sure there are any easy wins here as steam turbines have fallen out of favor. Most commercial ships use diesel main engines due to lower overall costs (capital, fuel, crew, maintenance). Most new warships employ gas turbines (vs. steam turbines) due to power-to-weight and power-to-size ratios, but these are things that commercial shipping does not need and will not pay for. Steam turbines are still kicking around on older ships (like the Jones Act specials rusting up and down the West Coast) and nuclear-powered stuff, and that's about it.

A lot of time and money was spent learning how to reduce cavitation because it's the significant component of the noise produced.

It feels like more efficient screws (which are incidentally quieter) would be a fairly popular sell to the shipping industry.