Abstract: A method for reducing VIV is disclosed for a spar platform having a deck, a cylindrical hull having a buoyant tank assembly, a counterweight and an counterweight spacing structure. The overall aspect ratio of the hull is reduced by providing one or more abrupt changes in hull diameter below the waterline.

Abstract: A spar platform is provided comprising an essentially vertical cylindrical buoyant vessel, and a shroud surrounding the essentially vertical cylindrical vessel wherein the shroud comprises two essentially perpendicular intersecting sets of foam-filled fiberglass elements. In a preferred embodiment, the perpendicular intersecting elements form a grid having openings of 0.05 a dimension of between about 0.05 and about 0.35 vessel diameters and wherein each set of elements contains elements where the centerlines of the elements are separated by about 0.06 to about 0.60 vessel diameters. The shroud is preferably fabricated in panels that can be secured to the vessel using standoffs.