Abstract: Inclined plane protection boards are provided in a manner to cover an inclined plane of an artificial island whereby the inclined plane may be protected from ice force of growing or drifting ice bodies or wind and wave force.

Abstract: A floating offshore structure which is moored at a fixed position on the sea by means of mooring hawsers and anchors connected to the ends thereof respectively for conducting a submarine excavating operation from a deck of the structure. The structure includes a moorage hull part provided with a vertical through-hole formed therein for receiving an excavating drill pipe and the mooring hawsers and a movable hull part connected to the moorage hull part so as to be rotatable within a horizontal plane. The movable hull part is constituted as a hull defining the outer wall of the floating offshore structure and connected with the moorage hull part by inserting it into a moorage hull part receiving hole formed at a position closer to the bow thereof.

Abstract: A floating offshore structure which is moored at a fixed position on the sea by means of mooring hawsers and anchors connected to the ends thereof respectively for conducting a submarine excavating operation from a deck of the structure. The structure includes a moorage hull part provided with a vertical through-hole formed therein for receiving an excavating drill pipe and the mooring hawsers and a movable hull part connected to the moorage hull part so as to be rotatable within a horizontal plane. The movable hull part is constituted as a hull defining the outer wall of the floating offshore structure and connected with the moorage hull part by inserting it into a moorage hull part receiving hole formed at a position closer to the bow thereof.

Abstract: An apparatus for protecting a marine riser extending downwardly from a platform of an offshore station above a sea level toward a sea bottom. A tubular protector is removably mounted on the underside of the platform in surrounding relation to the marine riser in the vicinity of the sea level. According to another embodiment, a tubular protector has an upper portion in the shape of a truncated cone for contact with ice floes and a lower portion shaped as a grid-like truncated cone flaring downwardly for diverting ice floes away from the tubular protector.

Abstract: An artificial island for installing oil drilling equipment in ice covered sea areas, comprising barricades against ice which surround oil drilling equipment installed in ice covered sea-water and whose respective top portions are projected above the surface of the sea-water, means provided at the bottom portions of the barricades so as to fix them to the sea-bottom, and inclined ice breaking walls provided at the outer sides of the barricades.

Abstract: A working platform for oil drilling operations in ice covered sea areas, which essentially comprises oil drillig equipment, an oil drilling pipe connecting the oil drilling equipment to the sea bottom, and a floating frame having a buoyancy and a strength enough to stand the pressure of an ice covering and being movable in accordance with movement of ice covering; the floating frame is disposed surrounding such a surface area of the ice covered sea as lying around the oil drilling pipe, whereby the pipe is protected by the floating frame against action of the pressure of ice covering during oil drilling operations.

Abstract: The invention relates to a floating structure, e.g. an offshore platform adapted for use in exploitation of submerged oil fields and the like purposes at offshore areas. The structure has a platform from which extended downwardly are columns carried by footings having buoyancy large enough to keep the platform afloat. Tension wires are extended through the footings for connection to the sea bottom in a diverging manner. Sinkers are provided at intermediate portions of respective tension wires so that the portions of the laters between the sea bottom and the points at which the sinkers are provided may exhibit sags. The sagged portions of the tension wires are expected to present a buffering effect to diminish the extraordinary large tension in the tension wires attributable to the movement of the platform. The up and downward movement of the platform is prevented by a riser pipe extended from the center of the platform.