The larger boards will use mass produced construction and agriculture engines (I work for John Deere, so while I can't speak for the company I can tell marine engines are important enough of a market that we consider their needs when designing a new engine).
Most marine engines in that size range are used in either rail, power generating or other stationary applications. The manufacturers aren't idiots. They're gonna get as many sales out of a design as they can.
Regardless, the point is they're not bespoke for your industry.
The largest ships get custom built engines.