boat, ship, vessel
舩 centers on watercraft: a boat, ship, or vessel used for transport on water.
舩 combines 舟 (boat) with 公, which likely contributes a phonetic element. The exact historical development is uncertain, but the structure suggests a phono-semantic compound related to boats.
A boat 舟 with a public 公 purpose: imagine a ferry open to everyone, a vessel for all.
For セン, picture a boat with a cent sign (¢) painted on its side: cent -> セン, and the boat carries valuable cargo.