Abstract: This invention relates to a structure floating on a body of water and particularly a structure for drilling or producing wells from below the water. Buoyant members support at least a part of the structure above the surface of the water. The structure is connected to anchors or weights in the floor of the body of the water by a series of parallel leg members, usually four in number, forming a rectangular spacing. Each leg member is composed of a plurality of elongated members, such as large-diameter pipe, usually called risers. These risers are parallel. Vertically spaced spacers are provided along the riser of each leg to maintain the risers a fixed distance apart and to change the natural or resonant frequency of the individual riser pipes to be greater than the flutter frequency caused by the motion of the water past the riser. Novel spacers are provided and described which can be set in place without use of divers.