Shipping is vital for global trade but also emits significant greenhouse gases. To address this issue, various measures have been proposed, including improved ship design, alternative fuels, and improved operational practices. One such cost-effective operational measure is trim optimisation, which involves operating the ship at the hydrodynamically optimal forward and aft draughts. This study focuses on investigating the trim trends of a RoPax vessel using experimental fluid dynamics (EFD) and computational fluid dynamics (CFD) methods. The trim trends are derived in resistance and self-propelled modes. Multiple CFD methods are examined, along with different extrapolation techniques for experimental results. Uncertainty assessment is conducted for the experimental data, and a verification and validation study is performed. Furthermore, the predictions are compared with real operational data. The findings reveal that determining trim trends solely in towed mode is inadequate due to the profound influence of the operating propeller. Some of the investigated CFD methods demonstrate good agreement with the model test results in self-propelled mode, while others exhibit limitations. By selecting appropriate models and configurations, this study demonstrates that trim trends can be determined with sufficient precision, as evidenced by the comparison between ship operational data and predictions from EFD and CFD methods.