× We went to Italy in a ship that we boarded in Barcelona.
√ We went to Italy on a ship that we boarded in Barcelona.
In English we say in the car, BUT for other means of transport, we say on the bus, on the train, on a ship, and on a plane.
We say get in the car or get out of the car, BUT get on the bus/train, etc., or get off the bus/train, etc.