Riser support system for use with an offshore platform

A riser support system for use in a body of water comprises a buoyant and ballastable support structure and a plurality of substantially vertical and rigid risers each of which is attached to the inside of the support structure at a location below the center of buoyancy of the support structure and below the surface of the body of water. Usually, each riser passes through the inside of a single tube in the support structure. Typically, the riser support system is used to support a plurality of risers and their surface wellheads inside the hull of an offshore platform, usually in such a manner that the axial movement of the risers and support structure is independent of the axially movement of the hull. By attaching the risers at a location below the center of buoyancy of the riser support structure, riser load adds to instead of decreases inherent stability and therefore the structural payload efficiency of the overall floating platform is improved.