NOVELTY - The invention relates to a method and installation for collecting and converting the wave energy into electricity. According to the invention, for converting both the static and dynamic wave energy, the method consists in using the motion of a hydrostatically balanced flapper oscillating by an optimum angle about its vertical position, automatically adjustable in two versions, being articulated to the bottom of a foundation frame and protected, in case of a breakdown, by launching a front cofferdam gliding between two neighbouring piers of the waterway construction, which is free of the wave action by the position of alternately front disposition of flappers. For applying the method, the installation claimed by the invention consists of an oscillating flap (1) built to be unweighable at the static depth of water, articulated in some bearings (2) to the bottom of a foundation frame (3) and protected, in case of breakdown by launching a cofferdam (4), oscillating under the influence of the waves, about the vertical position, by an optimum angle optim' for which the maximum mechanical energy is extracted from the wave, the flapper causing the movement of double-effect pistons (5) provided with a shock-absorber valve (6) against exceptional waves; the installation for collecting energy further comprises a reflecting display (7) located by means of a device (8) at a convenient distance, the pistons (5) sucking, through two groups of valves (9) in a conduit (10) the liquid from a tank (11) wherein it may be cooled by sea water, through a serpentine (12), and depending on the different action of the wave crest, the pistons generate different pressures: the high pressure P++ in the conduit (13), the average pressure P+ in conduit (14), some hydraulic engines (15) entraining some electric generators (16) being coupled to the high pressure conduit, the pressure-generated oscillations being damped on the high pressure conduit by means of a house water supply plant (17), and on the average pressure conduit by another house water supply plant (18).