艘
sāo · HSK 7
ship
🚢 舟 (boat radical) on the left = the measure word for counting ships and boats
艘 is a classifier: one 艘 of ship, two 艘 of boats. The left side 舟 means boat, which fixes its job as the counter for watercraft. Sound-alike: sao rhymes with prow, the front of a vessel.
艘 — boat radical 舟 + sōu phonetic 叟
A phono-semantic compound: 舟 (boat) gives the meaning, while 叟 (an old man) supplies the sound sāo/sōu. Originally written to denote a large vessel, 艘 became the standard measure word for counting ships and boats in Chinese.