A wave power apparatus (10) includes a chamber (16) which may be constructed over a coastal gully (12) so that waves (14) cause the water level to rise and fall in the chamber, and so cause air to flow to and fro in a duct (32). A Wells-type biplane turbine (34) in the duct (32) drives a generator (36). The turbine (34) comprises two turbine discs (45) 0.5 m apart, each defining a hub, a plurality of aerofoil section straight blades (80), and an outer ring (56). The ring (56) is sufficiently massive to act as an energy-storage flywheel, and has a greater moment of inertia than the hub and the blades. Each turbine disc (45) might have a kinetic energy of at least 1 MJ when rotating at 1650 rpm.