© 2022, Chinese Ocean Engineering Society and Springer-Verlag GmbH Germany, part of Springer Nature.Trimaran hydrodynamics have been an important research topic in recent years. Trimarans have even been chosen for naval surface combatants. In this case, investigation of a trimaran with different outrigger positions is important and necessary for better hydrodynamic performance. This paper focuses on the numerical investigation of trimaran hydrodynamics. The trimaran model used in this study is a 1/80 scale high-speed displacement frigate-type concept developed by the Center for Innovation in Ship Design (CISD) at Naval Surface Warfare Center, Carderock Division (NSWCCD). The numerical simulations were conducted for different outrigger positions at low and moderate Froude numbers by using commercial CFD software solving URANS equations. A verification and validation study was carried out for the numerical method in one configuration and one ship velocity. The existing experimental results for the trimaran resistance in the literature were used for validation. Five different outrigger positions were analyzed and the form factor of each configuration was calculated by the Prohaska method. The total resistance was decomposed to its components using the form factor. The interference factor was calculated for each configuration in terms of total resistance, residual resistance and wave resistance. Also, wave profiles using the longitudinal wave cuts in different locations were obtained both numerically and experimentally. It was concluded that the outrigger position had different effects on the interference, total resistance and wave profile at different Froude numbers. It was also shown that the CFD results were in good agreement with the experimental data in all configurations. In conclusion, this study presents the results of interference effects for different trimaran configurations in terms of wave resistance in addition to the total resistance and residual resistance. The numerical method was validated not only with the total resistance test data but also the longitudinal wave profiles along the hull.