The complexity of ship controllers has been increasing following the advancements in the control devices and technologies as well as the environmental regulations requiring enhanced energy efficiency. Many vessels are under retrofit to integrate onboard Energy Storage System (ESS), necessitating the redesign of the controllers and developing algorithms to improve the vessel efficiency. Operator Training Simulators (OTS) have been developed and manufactured in several industries and have been used for decades. However, the current OTS development method incurs a lot of cost and time to develop retrofitted OTS for the controller that has changed and applied new technologies and algorithms. To develop an OTS that can be flexibly modified for changing the controller of an existing ship, the controller logic, modeling of the physical system, communication protocol, and GUI-based HMI should be compatible and consist of reusable model building blocks. In this paper, the logic for each part is designed as a subdivided module, and these modules are made into reusable blocks. As a proof of concept, the OTS for the power management system of an existing LNG carrier ship is developed with the model building blocks and the test results of the main functions of the PMS are presented.