This paper describes the use of a Modelica system model to support the development of a heat management control system for a fossil-free sailing yacht. Due to tight project timelines, the control system was developed and tested virtually, avoiding delays associated with waiting for the physical system to become available. The system model covers key functions such as heat recovery and heat dumping, enabling automated testing of various operational scenarios. This approach not only accelerates development but also reveals early insights into interactions between the control logic and system dynamics. The model is designed to be seamlessly replaced by the real system once it is built. Future comparisons between simulated and real-world performance will guide refinements to improve model accuracy and support model-based tuning of the control system.