The boat radical on the left is itself a pictograph - a hull seen from the side with deck and oars. It marks 艇 as a vessel and indexes it with the boat family: 船 ship, 航 sail, 舱 cabin, 舵 rudder.
廷 supplies the sound tíng → tǐng, just a tone shift. Originally 廷 pictured a court-yard where officials stood - no semantic role here. Same phonetic series: 庭 courtyard, 挺 straight, 蜓 dragonfly, 霆 thunderclap - all tíng/tǐng syllables.
