Abstract: A ballasting block for use as chamber floor loading in a concrete caisson breakwater made up of horizontally-arrayed sections having perforated front walls, or for use as armor capping on rubble mound breakwaters, is of parallelepipedic form with two pairs of sides meeting at right angles, and front and rear end faces of rectilinear outline having openings recessed therein defined by at least one through passage extending the length of the block, serving as flow-guiding channel means. A preferred form for caisson ballasting as one or more layers of closely-spaced blocks, is a cube, or a rectangular prism, molded of concrete of weight from about one tonne to about twenty tonnes, having a single passage of circular, elliptical, or polygonal cross-sectional outline with area from 0.2 m.sup.2 to 1.5 m.sup.2. When used for armor capping each end face is perforated by a number of ducts, the blocks being laid in ordered arrays with close spacing presenting one end face upwardly.