Abstract
The paper deals with the topic of monitoring the performances of a vessel in service in order to establish whether fouling of the hull have worsened the hydrodynamic efficiency of the ship. In the paper the aspects of acquisition, treatment and presentation of the data are discussed. Particular focus is given to the topic of obtaining reliable data for the environmental condition where the ship operates. To the contrary to the traditional approach of installing instrumentation on board of ship, the approach adopted here is to use the ship control system for collecting the data and the weather forecast for the environmental conditions. The results that are presented in the paper are relative to one and half years of monitoring of the performances of a ferry operating in a Norwegian fjord.