noun
voyager; navigator
Refers to a person who travels by sea, especially on a long voyage, or one who navigates a ship.
彼は経験豊富な航海者だ。
He is an experienced voyager.
大航海時代の航海者たちは、未知の海へと旅立った。
The navigators of the Age of Discovery set out into unknown seas.
冒険家 means 'adventurer' and can apply to any kind of adventure, not necessarily sea travel. 航海者 is specifically a sea voyager.
Compound of 航海 (kōkai, 'voyage, navigation') and 者 (sha, 'person'). The word is transparently derived from its components.