Due to the violent slamming, small and fast RHIB (Rigid Hull Inflatable Boats) are exposed to high accelerations. One of the challenges when designing a RHIB is to reduce these accelerations. This paper proposes a method to assess the slamming behaviour of a RHIB in the preliminary design stage, i.e. when the hull forms are not yet determined. This method couples a non-linear 6DOF time domain simulation tool to the visual programming language Grasshopper^®. The time domain tool was used to predict the rigid-body dynamics of the RHIB in different sea states; Grasshopper was used to automatically generate a series of parametrized RHIB hull 3D surfaces, by systematically varying the LP/BPX ratio, the average and longitudinal distribution of deadrise. The results of the simulations highlighted the optimal designs that showed the lowest level of slamming accelerations. This approach has the advantage that any geometrical details of the RHIB can be parametrized and tested, without the need to rely on certain hull forms as with systematic series. Moreover, a large number of scenarios and hull characteristics could be simulated at the cost of modest computational resources.