There are about 2,230 patents related to ship propulsion systems.
Some focus on methods:
Electric ship propulsion systems and control methods
Methods for evaluating the lower confidence limit of the reliability of series structures of ship propulsion systems
A composite material for ship propulsion systems and its preparation method
Some focus on the structure:
Hydrostatic balanced thrust bearings, ship propulsion systems and underwater vehicles
Ship power battery testing equipment and systems
Ship propulsion systems and ships with two bearing shaft systems
See the patent search website for details