Abstract: A lightweight drilling structure for use in offshore arctic waters comprising a lower frustoconical section and upper section wherein the lower section is towed to location, ballasted to sink in place on the sea floor and anchored in position by flooding the stability compartments. The upper section containing the drilling rig and equipment is then floated into place over the lower section, ballasted to rest on the lower section and the two sections sealed and fastened together. The assembled structure is firmly anchored in place by dewatering chambers located in the bottom of the lower section to create a suction between the bottom of the lower section and the ocean floor.