Abstract: A float includes a substantially prismatic hollow body, which is made of plastic and which is provided at its side walls, preferably adjacent to its side edges, with connectors for use in assembling a plurality of such floats. In order to reduce the manufacturing costs and to ensure a steady floating behavior, the hollow body is open at its bottom and is formed in its walls with at least one vent hole, which is spaced above the bottom level of the hollow body.

Abstract: A baseplate has an upper surface which is formed with a recess that has substantially the configuration of a figure eight. The baseplate is also formed with a hole, which opens into said recess and which has a vertical axis disposed at the center of said recess. Two identical discs are disposed in said recess on opposite sides of said hole. Each of said discs is formed in its periphery with a plurality of recesses having the configuration of arcs of circles differing in radius. The hole has a radius which is equal to the largest radius of said recesses of said discs.