As the design complexity of modern maritime systems is increasing, the need for advanced and appropriate simulation technologies is higher than ever. Different subsystems such as shipboard power systems and maritime controllers are directly interlinked making system integration and testing a challenging task. Hardware-in-the-Loop (HIL) testing is an advantageous methodology used for the systematic testing of control systems regarding correct functioning, performance and reliability.In this work, we present a HIL testing methodology to verify a ship power management system (PMS). For this, an AC shipboard power system is modelled including all relevant components such as diesel engines, generators, circuit breakers and loads interfaced by the PMS. The model also includes local controllers like speed governors and automatic voltage regulators (AVRs). A functional PMS was developed and implemented emulating the behaviour of a real controller. The models are exported as Functional Mock-up Units (FMUs) which represent stand-alone simulators. As HIL testing testbed the Open Simulation Platform (OSP) environment is used. This standardized and open platform enables co-simulation and also provides HIL testing capabilities. The exported FMUs are connected via the OSP environment. A load-dependent start-stop scenario is carried out to validate the correct functioning of the PMS and the test setup.