This article briefly introduces the characteristics of ships' electrical power networks, and an existing system is described as an example. A mathematical model of a selected power system, including generators with a drive and its loads, is presented. The algorithm implementing the author's numerical method, named 'the average step voltages method', is described. The chosen numerical method is notable for its stability and high accuracy, even in combination with a large integration step size. Software and hardware applications of the RT AVR tester are also shown. To check the adequacy of the simulations using the implemented model, experimental measurements were carried out. The measurements, including dynamic states, obtained by the computer tester with the AVR system, as well as the physical model with the AVR system, are summarized. Possibilities for usage in the marine industry in the future are also outlined.