The dynamic behaviour of floating structures is studied in this work. These types of structures are normally simplified into spring-mass systems where frequency dependent mass and damping is used to model the hydrodynamics. A method based on using digital filters to simulate the time response is tested in this work. The problem to identify added mass and added damping coefficients from measurement data is also examined. This is done by using the simulation model to generate time data. The predicted added mass and added damping can then be compared with the true coefficients and the identification method can be evaluated. Finally, an experimental system is studied and compared with simulation results.