Reducing greenhouse gas (GHG) emissions and improving energy efficiency in the maritime industry have become key priorities in the transition toward more sustainable shipping (UNCTAD, 2024). Since ship resistance is directly linked to fuel consumption, accurate prediction methods are essential to support the design of more efficient vessels. Computational Fluid Dynamics (CFD) has become a widely used approach for simulating ship hydrodynamics. In particular, the Reynolds-Averaged Navier-Stokes (RANS) equations allow for modelling of turbulent, incompressible flows by solving time-averaged forms of the Navier-Stokes (NS) equations. This makes them suitable for practical ship resistance simulations. This thesis investigates the accuracy of ship resistance predictions using RANS-CFD simulations performed in STAR-CCM+. The study focuses on model-scale simulations of the Duisburg Test Case (DTC) hull, with resistance results validated against experimental data from towing tank tests at SVA Potsdam and MarinLab, as well as numerical simulations from FineMarine provided by LMG Marin. The FineMarine dataset includes both model- and full-scale cases, with the hull in fixed and free-motion conditions, whereas the STAR-CCM+ simulations are limited to model scale with the hull fixed in all degrees of freedom. A mesh sensitivity study is conducted to ensure sufficient resolution in the wake region. Resistance values from STAR-CCM+ were compared with the reference data at various Froude numbers. The results show that STAR-CCM+ systematically overestimated total calm water resistance. In addition, the wake behind the hull remained more energetic and did not reduce with distance, which may be linked to the sudden speed input and limited simulation time. The effect of hull motion was assessed using the FineMarine results, which showed minor differences between fixed and free conditions at low Froude numbers. The results point to modelling and numerical factors that influence resistance predictions and emphasise the need for further refinement of CFD approaches to improve accuracy in practical applications. Masteroppgave i havteknologi HTEK399 5MAMN-HTEK MAMN-HTEK