a boat: any vessel that travels on water, from a fishing boat to a seagoing ship
This is the ordinary word for a watercraft in the New Testament. It covers the whole range in one term, with size and purpose supplied by the setting rather than by the word itself.
Most often it is the working fishing boat of the Sea of Galilee, the kind Peter, James, and John owned and the one Jesus repeatedly steps into to teach, to cross, or to ride out a storm. The same word then names the large cargo and passenger vessels of the open Mediterranean, including the grain freighter that carries Paul toward Rome and is wrecked off Malta. Whether it holds a few fishermen or hundreds of passengers, the Greek does not change.
Because one word stretches across all of this, the choice between "boat" and "ship" in English is the translator's, not the text's. The word simply points to the vessel itself.