Turret drive mechanism

An offshore system that includes a vessel which has a hull that floats at the sea surface and that can weathervane and which has a turret that has a turret periphery and that is rotatably mounted on said hull about a vertical axis, said turret having a radius as measured from said axis to said turret periphery, wherein the system includes a plurality of chain devices that each extends at a downward incline from substantially said turret to the seafloor, comprising:

• a torque enhancer which has an inner end pivotally connected to said turret at locations that are angularly spaced about said vertical axis, and which has an outer end that can move with upward and downward directional components independently of said hull, said outer end lying further from said axis than said inner end by a distance from said turret periphery that is greater than one-half of said turret radius, with said outer end of said torque enhancer being coupled to a first of said chain devices to transmit to said turret, at least portions of horizontal components of tension forces in said first chain device.

An offshore system that includes a vessel which has a hull that floats at the sea surface and that can weathervane and which has a turret that is rotatably mounted on said hull about a vertical axis, wherein the system includes a plurality of chain devices that each extends at a downward incline from substantially said turret to the seafloor, comprising:

• a pair of tension members that can transmit tension forces but substantially not compression or bending forces, said members each having an inner end pivotally connected about a largely horizontal axis to said turret and having an outer end, said inner ends being angularly spaced about said axis and said outer ends lying further from said axis than said inner ends, with said outer ends of said members being coupled to a first of said chain devices to transmit, through said members to said turret, at least portions of horizontal components of tension forces in said chain device.

An offshore system that includes a vessel which has a hull that floats at the sea surface and that can weathervane and which has a turret that is rotatably mounted on said hull about a vertical axis, wherein the system includes a plurality of chain devices that each extends at a downward incline from substantially said turret to the seafloor, with a first of said chain devices having an inner end connected to said turret, comprising:

• a member that has a member inner end pivotally connected about a largely horizontal axis to said turret and that has an outer end, said first chain device inner end being angularly spaced about said axis from said member inner end and said member having a member outer end lying further from said axis than said member inner end, with said member outer end being coupled to said first chain device to transmit to said turret, at least portions of horizontal components of tension forces in said first chain device.

A method for use with an offshore system that includes a weathervaning vessel that floats at the sea surface and that includes a hull and a turret that is rotatably mounted on said hull about a substantially vertical axis, wherein the system includes a plurality of chain devices extending at downward inclines and different directions to the seafloor and having upper ends coupled to said turret, comprising:

• pivotally connecting an inner end of a torque enhancer to said turret at locations spaced about said turret axis, and coupling an outer end of said torque enhancer to a first of said chain devices so at least horizontal subcomponents of tension forces in said first chain device that do not pass through said vertical axis are transmitted through said torque enhancer to said turret, while allowing said outer end of said torque enhancer to move up and down substantially without restraint from said hull.