The rising cost of fuel, the more and more severe international standards and a growing awareness of the environmental impact of pollutant emissions have led energy efficiency to become a theme of great interest in the marine sector. The strategy for increasing energy efficiency may refer both to the consumption reduction and to the increase of energy recovery systems. This need turns out in monitoring and control strategies for energy processes on board. Monitoring information is recorded and stocked in a database, that needs to be analyzed to find out patterns in large data sets. A huge amount of data, from a RO-PAX ship, has been analyzed in order to gain a further insight into ship performances. Improvements in ship energy performances could be reached with an intense study of the historical data of the vessel attitude.