This document includes all the information related to the Marine Vessel Energy Management System (MVEMS) developed under Task 2.3 (D2.3), which is designed to optimize energy usage and reduce emissions on the demonstration vessels DEMO-1 Gunnerus and DEMO-2 Atatürk. A Python-based simulation framework was created to model the onboard electrical systems and evaluate a range of EMS strategies—both rule-based (e.g., Finite State Machines) and optimization-based approaches (e.g., MILP and ECMS). Key components such as batteries, generators, and onshore charging systems were modeled using both synthetic and real operational data. The system incorporates a DC switchboard for centralized, efficient power distribution and a Power Management System (PMS) that communicates with the EMS to monitor, optimize, and ensure efficient, safe, and reliable vessel performance.