This work simulates the impact of horizontal motion on the Symphony wave power device. To that end the existing time domain simulation is expanded with a module that simulates horizontal motion in the 2d plane. This extension is coupled with the existing operational modelling. the extension is based on a mathematical motion model based on rigid body dynamics and linear wave theory. Simple cases are compared to analytical solutions in order to test the model. The model is then used to calculate expected motions, mooring loads and differences in energy production between a Symphony that can move freely and a restrained Symphony.