In the early design phase, numerical methods provide an efficient method to predict the motions of a ship. However, it is well known that, due to its underlying resonance principle, the response of an ART is strongly non-linear. This is already known for a long time from observations on board ships (see Watts 1883; Lewison 1975)and is confirmed by numerical studies (see Chu et al. 1968; Verhagen, van Wijngaarden 1965) and experimental campaigns (see van den Bosch, Vugts 1966; Stigter 1966). Therefore, the numerical model that predicts the merits of an ART should take these non-linear effects into account.Time domain seakeeping codes are widely used to study the behaviour of a ship in a seaway when non-linearities, in either the excitation or the reaction forces, are expected. Therefore, a method to include also the effect of an ART in such a simulation seems of great value. The most straightforward approach is to couple such seakeeping code to a CFD model of the ART (see van Daalen et al. 2001; Cercos-Pita et al. 2015). However, CFD calculations of an ART take typically in the order of several hours per hour of simulation on multi-CPU clusters, whereas time domain seakeeping codes usually runs faster than real time on a simple single-core desktop PC.