ship's officer
Refers to a senior crew member on a vessel, such as a captain, first mate, or chief engineer.
He works as an officer on a large tanker.
船員 is a general term for any crew member, while 高級船員 specifically refers to senior officers.
航海士 is a licensed navigation officer, a specific type of 高級船員.
Compound of 高級 (high rank) and 船員 (crew member).