The purpose of the article is the model of perception of difficult situations by the navigator where the rules of COLREG are inconsistent. To build these models, a formal analysis of the situations was carried out, which allowed to design a decision-making support system to reduce risks and accidents related to sea transport. The article presents formal approaches that take into account the factors of vessel speed, qualification of a navigator, and the situations that influence the formation of maneuvering strategies. The illustrations show difficulties and ambiguous situations from the point of view of the rules. An important factor for decision-making is the ability of an adequate perception of the situation by a navigator, and the conditions in which this process is considerably difficult are given. The arguments are made in favor of the use of ECDIS and AIS navigation information systems, and the examples that indicate the difficulties of making decisions at the time of a large number of vessels are given. A relationship between the perception of service information by the navigator and the choice of maneuvering strategies is made. The recommendations on the development of a decision-making support system for navigators in difficult navigation situations are given. The approaches to apply a decision-making support system, as well as the formation of data about the navigator are proposed.