<p>Numerical simulations on the coupling actions between the free surface oscillation in the moonpool and the heave motion response of hulls with vertical mooring stiffness are carried out in this study, where the influences of edge profiles, including sharp and convex edge profiles, on the coupling actions are considered. Two-peak variations in the free surface oscillations in the moonpool with incident wave frequencies can be observed, which are defined as the first and second peak frequencies. The free surface oscillations and heave motion responses show in-phase and out-of-phase relationships at the first and second peak frequencies, respectively. The convex edge profiles are able to generate effective suppressing actions at the second peak frequencies. However, it is only efficient for large vertical stiffness at the first peak frequency. The relative velocity between the fluid flow along the moonpool bottom and the heave motion of the hulls is the essential reason.</p>