As the offshore industry is developing into deeper and deeper waters Dynamic Positioning (DP) techniques are becoming more important to the industry. MARIN’s new multibody time domain simulation program aNySIM is recently extended with a module to simulate DP applications. The model is 6 degrees of freedom and includes a Kalman filter, PID controller and a Lagrange optimized allocation algorithm. Thruster interaction effects are taken into account in the model. The present paper focuses on the methods used in the numerical DP model. A typical case for a DP operated monohull drillship is presented and will be discussed in comparison with model test results.