The paper concerns problems of preliminary designing of bucket dredgers’ power plants. This paper presents results of investigations of six bucket dredgers in service. The operational investigations consisted in measuring the parameters which characterize working conditions of two main receivers of mechanical energy: bucket chains and swing winches. In the paper characteristics of disposition of loading of bucket chains and swing winches are presented. They covered average value, standard deviation and coefficient of variance of loading disposition mutability. Examples of load distributions of chains’ and group of swing winches on chosen dredgers during some period of time were given. Conclusions in view to average values of main receivers of mechanical energy and coefficients of variance of loadings spred were formulated. Results of investigations of dependence of average loadings of main receivers on their nominal power were presented. The results of work will be used in creation of random models describing real conditions of operation of power plant elements of dredgers.