Abstract: A caisson breakwater provided with vertical duct 2?, room 3?, air-duct 4?, self-rectifying turbine 5?. Under the fluctuations of wave pressure on the outer opening 6, the water, alternately, enters and exits, so that the air in room 3?, alternately, is compressed and expands, and an alternate air flow is produced in the air-duct 4?. The vertical duct 2? and the room 3?, form a U-conduit, and the air in the room 3? acts as a spring. The eigenperiod of oscillations in said U-conduit grows as the width of the vertical duct 2? is reduced and/or the length of said vertical duct is increased, and/or the width and height of the room 3? is increased. The eigenperiod is fixed close to the wave period of the waves which convey the largest amount of wave energy in a year, so as to absorb a very large quantity of wave energy.

Abstract: A caisson (1) provided with at least one air pocket (5), and at least one vertical duct or conduit (2) extending transversally along the whole portion of the caisson (1) where the respective air pocket (5) is present. The lower portion of the caisson (1) is filled with water (6), and the vertical duct (2) extends upwards, and communicates with the outside without reaching the sea surface. The height of the air pocket (5), starting from the ceiling of the caisson (1) towards its base, being adjusted so as to obtain the resonance condition, in which the period of the detected pressure fluctuations, at the upper opening (3) of the vertical duct (2), is equal to the period of detected pressure fluctuations of the air pocket (5). Inside the vertical duct (2) turbines may be installed in order to obtain energy conversion.