Following completion of a new 18 m by 16 m 3D coastal wave basin facility by Queen's University Belfast in 2010, efforts to assess and enhance the performance were undertaken. A combined physical and numerical modelling methodology was employed. Key findings are presented which should benefit others using or developing such facilities. Physical mapping was carried out using a specially developed polychromatic wave packet allowing accurate and efficient mapping of multiple frequencies simultaneously. Numerical modelling was undertaken using a phase resolving coastal wave propagation model to determine causes of observed non-homogeneity in the wave basin and efficiently determine an optimum wave basin design. Lateral absorption implemented along the side walls of the basin as a result of this work has significantly improved the homogeneity of the wave climate with little reduction to the total energy in the main working area. The shape of transition panels provided between the wave paddles and side beaches have been optimised using the wave propagation model. These developments have resulted in a wave basin which is significantly improved in terms of wave climate variability and energy absorption.