<b>Marine Auxiliary Engine</b> Several options are available for the electronic on-board power supply, depending on the main drive system: If the main engine consists of a steam turbine with gearbox and fixed propeller, a shaft generator and / or a steam turbine is selected to drive the three-phase generators. Nuclear-powered ships also receive turbo generator sets. If the main drive is a diesel engine, the shaft generator or one or more electric diesel engine systems, also called auxiliary engines, are used here. Gas turbine ships are also equipped with auxiliary engines. As a rule, three to four auxiliary engine systems are installed. Mainly medium-speed (720-900 rpm), rarely high-speed 4-stroke diesel engines (1200-1800 rpm) are used here. The speed results from the selected frequency and number of pole pairs. The three-phase alternating current generated with these generator sets is required to drive motors; lighting, navigation systems, etc. are operated with 230 V single-phase power or as so-called low-voltage systems (12-24 V).