The introductory part of this thesis briefly explains the basic parts of the mechanical energy transmission system, such as the drive machine, the working machine and the power transmission, and their role in the overall system. The general characteristics of planetary gears are shown after introduction. The definition of planetary gears, their advantages, disadvantages and kinematics are explained. The conditions that planetary gears must meet for proper operation are also explained, and specific design features of planetary gears are presented. The following is a general overview of the role of planetary gears in a ship's propulsion system and examples of some of the manufacturers. Then the project calculation of the first and second gear and the analysis of the control calculation of both gears are shown. The following is a calculation of other structural elements where the calculations of shafts, plain and roller bearings, toothed joints and keyway and a design calculation of the lubrication system are shown.