The inclusion of a steady flow in a water channel is critical for recreating scaled ocean environments in a laboratory. In this thesis, the effect of flow on the theoretical model and experimental performance of a plunger-type wavemaker has been investigated. Through a variance-based global sensitivity analysis, the influence of the input parameters on the output variance of the wavemaker model was explored. While the flow is less influential compared to the other parameters, it was established that including flow in the model is essential for application to experimental systems. To validate the experimental wavemaker, wave profiles were generated and measured under a variety of test conditions in relation to the sensitivity analysis. It was observed that the difference between the experimental results and the theoretical model increased as both frequency and flow increased. Therefore, a corrected model was suggested, and the operational range of the experimental system was established.