A power unit for air conditioning systems installed on boats, including at least one compressor, of the mass produced type used in the automobile industry, connected to the circuit of the refrigeration device, at least one mechanical pump for circulation of a heat exchange fluid along a circuit and one or more rotating electrical machines. Operation of the power unit is ensured during navigation by an internal combustion engine for marine propulsion, in particular a four stroke gasoline engine, with vertical motor axis, normally used for outboard marine propulsion, mass produced at low costs, while when the boat is in port it is ensured by an electric motor. The fan coils are also of the mass produced type used in the automobile industry.