Moonpool is a large cylindrical opening to a drillship hull that facilitates direct access to the ocean floor to drop or lift subsea modules in a sheltered environment for offshore exploration, drilling and production activities. Wave induced oscillations within the moonpool can cause operational hazards. Hence, the current study tries to understand the nature and range of wave-induced water column oscillations within a rectangular moonpool. The regular waves are generated around the frequencies of the model and the gap excitation in the moonpool was investigated. Effect of regular wave steepness at values 1/30, 1/45, 1/60 is measured within the moonpool gap. A significant difference between RAO’s for different wave steepness was observed near the resonance period compared to other periods. Different combinations of keel appendages were studied, as the moonpool gap rib width increases, significant reduction in RAO’s near resonance has been observed. The qualitative and quantitative effect velocities and vortices generated by the appendages at the keel of the moonpool gap has been reported using Particle Image Velocimetry and verified with existing literature. Experimental results are used to validate the numerical modelling based on IITM-RANS3D for focused waves having multiple frequencies, so that future parametric study can be carried out using the model.