Over the past years tugs are evolving to more compact designs equipped with large power installations. This inherently increases the risk of accidents, demanding a more reliable prediction of the tug’s dynamical behaviour in critical situations. To capture the dynamic behaviour of a tug, a time domain simulation tool has been developed and used to evaluate the tug’s safety in those critical situations. Multiple methods derived from recent studies are combined and used to establish a reliable description of the involved hydrodynamic forces and moments. Besides a sensitivity study is performed to investigate the impact of inaccurate approximations of those forces and moments. Furthermore, the sensitivity to a change in more design and operation related parameters has been investigated. Finally, the research includes a step by step validation and an evaluation of the current regulations.