Abstract: A dome-shaped atoll structure (12) having a central aperture at its apex is secured to a station-keeping structure (11, or 40, or 52) positioned on the ocean bottom. The atoll structure (12) is moveable through a range of vertical positions relative to the ocean bottom. Sea waves impinging on the atoll structure (12) are refracted as they crest and break, thereby producing spiralling pulses of water that converge toward the central aperture. The central aperture provides entry into a vertical standpipe (14) for the pulses of water, which impart angular momentum to water already present in the standpipe (14). A turbine (31) attached to a shaft (28) in the standpipe (14) converts the rotational energy of the water in the standpipe (14) to rotational energy of the shaft (28), which is coupled to an electrical generator (27).