Tension leg platform and installation method therefor

Abstract

A tether and tether tensioning system for a tension leg platform. A plurality of elongate tethers 12 are used to secure a tension leg platform hull 20 to a foundation 14 at the ocean floor. Each tether 12 has a lower end secured to the ocean floor foundation 14. The tethers 12 extend upward to a position slightly below the bottom of the hull 20. A tether securing and tensioning system 30 is positioned within the hull 20 for each tether 12. This system includes a tether extender 22 positioned within a shroud 28 in the hull bottom. The tether extender 22 includes a tether latch 24 at its lower end. The tensioning system is adapted to lower the tether extender 22 downward below the hull 20 to permit the tether extender 22 to latch to the tether 12. The securing and tensioning system 30 then raises the tether extender 22 to tension the tether 12. The tether tensioning system of the present invention permits use of a simplified method for installing TLPs. The tethers 12 extend upward to an elevation which, at least initially, is below the maximum draft of the tension leg platform hull 20. This permits the tethers to be installed offshore prior to installation of the hull 20. Following tether installation the hull 20 is floated to a position directly above the tethers 12 and the tether securing and tensioning system is used to lock the hull 20 to the tethers.