a top - tensioned riser system comprises a substantially vertical riser extending upward from the seafloor ; a conductor surrounding an upper portion of the riser in spaced - apart relation ; a coaxial keel guide surrounding a lower portion of the conductor ; a tensioner attached to the conductor and the riser ; a keel guide support structure attached to the keel guide and connected to the keel of a dry - tree , semi - submersible vessel ; and , a keel joint centralizer attached to the riser proximate the keel guide and sized to prevent radial movement of the riser relative to the conductor . side loads on the riser are reacted from the riser to the conductor via the keel joint centralizer and then to the keel of the vessel via the keel guide .