An attempt is made to build a knowledge data base to be used a basis for a navigational situation assessment system. The system is based on Bayesian networks. A research experiment will be described, in which simulation tests were carried out to define a relevant data base. This article also presents a model for manoeuvre identification and a simulator application created for simulation tests. It has been proved that automatic identification of ships manoeuvres is possible and, so is the navigational situation assessment in view of navigational safety