Method for maneuvering a buoyant body of a wave power converter, said wave power converter including a mechanical-electric, mechanical-hydraulic or piezo-electric energy converter which is arranged on seafloor under the buoyant body, said buoyant body and mechanical-electric, mechanical-hydraulic or piezo-electric energy converter being connected by a wire fixed at one end to the mechanical-electric, mechanical-hydraulic or piezo-electric energy converter, and arranged to the buoyant body at the other end by a winch arranged in the buoyant body powered by a motor, and said buoyant body is provided with at least one ballast tank for controlling the buoyancy of the buoyant body, wherein the ballast tank comprises a bottom valve for supply and discharge of water, and said buoyant body further comprising a ventilation pipe arranged to the ballast tank via a valve and a compressor arranged to the ballast tank via the valve for supply and discharge of air, characterized in that the method includes: - measuring wire tension by using a wire tension meter arranged in the buoyant body, - measuring filling level/pressure in the ballast tank by using a laser meter or float arranged in connection with the ballast tank, - measuring stroke of the mechanical-electric, mechanical-hydraulic or piezo-electric energy converter by using a pair of end position sensors (42a-b), wherein, based on the measurements, lowering or raising the buoyant body, without removing the wire tension by: - controlling the buoyancy of the buoyant body by supplying/discharging water/air to/from the ballast tank by controlling the bottom valve, valve and compressor, and at the same time adjusting the tension of the wire by operating a winch in the buoyant body; and - adjusting length of the wire by controlling the winch and buoyancy of the buoyant body in relation to measured stroke of the mechanical-electric, mechanical-hydraulic, or piezo-electric energy converter for ensuring use of an entire stroke of the mechanical-electric, mechanical-hydraulic, or piezo-electric energy converter in relation to the wave movements affecting the buoyant body. - measuring wire tension by using a wire tension meter arranged in the buoyant body, - measuring filling level/pressure in the ballast tank by using a laser meter or float arranged in connection with the ballast tank, - measuring stroke of the mechanical-electric, mechanical-hydraulic or piezo-electric energy converter by using a pair of end position sensors (42a-b), wherein, based on the measurements, lowering or raising the buoyant body, without removing the wire tension by: - controlling the buoyancy of the buoyant body by supplying/discharging water/air to/from the ballast tank by controlling the bottom valve, valve and compressor, and at the same time adjusting the tension of the wire by operating a winch in the buoyant body; and - adjusting length of the wire by controlling the winch and buoyancy of the buoyant body in relation to measured stroke of the mechanical-electric, mechanical-hydraulic, or piezo-electric energy converter for ensuring use of an entire stroke of the mechanical-electric, mechanical-hydraulic, or piezo-electric energy converter in relation to the wave movements affecting the buoyant body.