noun
ferryboat; ferry; passenger boat
A boat that carries passengers, often on a regular route. The reading のりあいぶね is standard; のりあいせん is also possible but less common for this sense.
島へ渡るには乗り合い船に乗らなければならない。
To cross to the island, you have to take a ferryboat.
noun
shared fishing boat
Only with reading のりあいせん
A fishing boat shared by multiple anglers, typically for a day trip. The reading のりあいせん is especially common for this sense.
週末に乗り合い船で沖釣りに出かけた。
We went offshore fishing on a shared fishing boat over the weekend.