We have been preparing for Explorer of the Seas out of Ravenna on July 16, returning July 30. We fly into Bologna on July 15, taking the train (Marconi Express) from Bologna Airport (BLQ) to Bologna Centrale and then a train from Bologna Centrale to Ravenna on July 16 and staying overnight in Ravenna. We will then take the bus from Ravenna to the cruise port. We understand the bus station is behind the central train station in Ravenna. Buses will be running between the station and the cruise port. (Information on the buses taken from previous posts above in this thread).
Upon return on Explorer, we will take the bus from the cruise port to the Ravenna train station, and then take the train from Ravenna to Bologna, and stay overnight in Bologna, taking the Marconi Express to Bologna Airport the next morning.
On Trenitalia, there are between 5 and 8 routes from Roma to Ravenna daily, dependent upon the day of the week. Most involve 2 train changes, and some involve 3. Average time is between 6 and 8 hours. (From the Trenitalia webpage). Once in Ravenna, you can take the bus to the cruise ship the day of the cruise departure.
Getting to Venice upon your return is easier, and can be arranged through the Cruise Line via bus, or via train from Ravenna to Venezia. There are many trains daily. In addition, the Cruise Line offers direct transfers via bus to Venice. Also see previous posts in this thread for details.