Riser support for floating offshore structure

An offshore platform comprising:

• an inner structure tethered to the sea floor comprising
• a riser structure including at least one riser arranged and designed for connection to a sea floor and a buoyant device creating tension on said riser, and
• a support buoy structure slidably coupled to said riser structure by a slidable coupling;
• an outer hull structure moored to the sea floor independently of said inner structure and which circumferentially surrounds said inner structure, and
• a passive, non-disconnectable connection mechanism between said outer hull structure and said support buoy structure which substantially decouples heave, pitch and roll forces which act on said outer hull structure from being transferred to said inner structure.

A method of decoupling motions acting on a riser structure, comprising the steps of:

• centering a floating inner structure which is tethered to the sea floor inside an outer hull structure, wherein said inner structure includes said riser structure, and wherein said riser structure includes at least one riser and at least one buoyant device;
• and
• providing a passive, permanent coupling between said outer hull structure and to said inner structure in a manner which decouples heave, pitch and roll motions acting on said outer hull structure from acting on said inner structure wherein,
• said coupling step is achieved by coupling link arms between said floating inner structure and said outer hull structure via spherical bushings and pivot connections.

A floating offshore platform comprising,

• an inner structure including at least one riser and a support buoy, wherein said support buoy is tethered to a sea floor tether point and supports said at least one riser generally in a vertical condition;
• wherein,
• at least one buoyant device is coupled to said at least one riser, and
• a slidable coupling is positioned between said at least one riser and said support buoy,
• an outer hull structure which circumferentially completely surrounds said support buoy and is moored with respect to the sea floor independently of said inner structure, whereby said inner structure is substantially isolated from wave and wind forces of the sea by the outer hull structure;
• and
• a passive linking mechanism permanently connected between said inner structure and said outer structure, said linking mechanism being designed and arranged to substantially decouple heave, pitch and roll motions acting on said outer hull structure from acting on said inner structure.

A floating offshore platform comprising,

• an inner structure, including at least one riser and a support buoy, with said support buoy tethered to a sea floor tether point by a tether with a tether connection provided along a longitudinal center line of said support buoy, and with said support buoy supporting said at least one riser generally in a vertical orientation,
• an outer hull structure, circumferentially surrounding said support buoy and moored with respect to the sea floor independently of said inner structure, and
• a connection mechanism permanently connected between said inner structure and said outer structure,
• wherein said connection mechanism substantially decouples heave, pitch and roll motions acting on said outer hull from acting on said inner structure, and
• said tether connection allows said inner structure to incline to accommodate relative angles between said inner structure and said sea floor tether point induced by hull, surge or sway excursions, and
• a drilling rig mounted on said support buoy, whereby said drilling rig is substantially isolated from heave, pitch and roll motions of said outer structure.