The authors of this paper suggest a mathematical model of a vessel diesel-generator installation meeting in larger extent the specific properties of such system and its application. A distinctive feature of the method under consideration is the use of the synchronous generator itself as a precise multifunctional sensor of the diagnostic information. The paper is also presenting the results of practical measurements of the system. The represented paper is suggesting the results of a long-term monitoring of a vessel diesel-generator. The synchronous generator of the system is used as a precise multifunctional sensor of the diagnostic information that is a special feature of the method. The specific point of this approach is the application of the results of spectral analysis of the output current and voltage of the synchronous generator. The paper contains the presentation of the results of practical measurements.