DAMEN tugs can be found in nearly any port or terminal around the world. Operating in ports and terminals requires the tugs to be highly efficient in ship handling in order to quickly escort larger vessels. To predict the escort capabilities of a tug, DAMEN has developed the computer program DAMEN TUGSIM. Since the tool is becoming a decisive tool in the design process, DAMEN wants to strengthen their confidence in the simulation tool TUGSIM by gaining more understanding related to the thruster performance. The goal of this study is to quantify and increase understanding into the following regions: Thruster performance in oblique flow; hydrodynamic interaction effects encountered between thrusters; hydrodynamic interaction effects encountered between the thruster and hull. Recently performed model tests of the RSD (Reverse Stern Drive) tug provided the opportunity to gain insight into these topics and to derive prediction models. Mathematical models are developed and finally implemented in TUGSIM. Implementation of the new models in TUGSIM enabled to harvest new insight into escort capabilities of the RSD tug, especially into the braking capabilities.