marine engineer
A professional who designs, builds, or maintains marine vessels and equipment.
He works as a marine engineer designing large tankers.
To become a marine engineer, you need specialized qualifications.
機関士 is a ship's engineer who operates and maintains the engine room, while 船舶技師 is a broader term for a marine engineer involved in design, construction, or technical management.
Compound of 船舶 (ship, vessel) and 技師 (engineer, technician).