航海
こうかい · koukai · JLPT N3 · noun
voyage
⛵🌊 航海 = navigate (航) + sea (海): to sail across the sea
航 has the ship radical 舟 and means to navigate or sail, as in 航空 (aviation). 海 is sea, with the water radical 氵. Navigating the sea gives you a voyage. Both kanji use on'yomi here: こう + かい.
海 — water radical 氵 + 每 (phonetic)
海 is a phono-semantic compound. The 氵 (water) radical signals the meaning—a vast body of water—while 每 supplies the sound. Originally referring to the sea or ocean, it later extended figuratively to mean 'vast' or 'a great quantity,' as in 人海 (a sea of people).