Installation of offshore structures

Offshore support apparatus for use in mounting in or on an offshore foundation an offshore structure including a longitudinally extensive shaft, mast or tower, the offshore structure being operatively carried with the shaft, mast or tower in a substantially upright condition in a frame including an engaging portion configured to engage the shaft, mast or tower, a plurality of legs configured to rest on an underlying supporting surface and a plurality of lifting formations by which the frame may operatively be lifted, the offshore support apparatus comprising attachment means configured operatively to attach the offshore support apparatus to the offshore foundation, a support frame depending from the attachment means and a plurality of supporting formations equal in number to the number of legs of the frame and configured to support respective legs of the frame;

• wherein each leg includes an adjustable foot;
• wherein each foot is moveable between an extended condition and a retracted condition;
• and
• wherein each foot is moveable with respect to its respective leg by a control arrangement operable to control the movement of each foot.

System for mounting, in or on an offshore foundation, an offshore structure including a longitudinally extensive shaft, mast or tower, the system comprising:

• a frame including an engaging portion configured to engage the shaft, mast or tower, a plurality of legs configured to rest on an underlying supporting surface and a plurality of lifting formations by which the frame may operatively be lifted, the frame being configured to support and carry the offshore structure with the shaft, mast or tower in a substantially upright condition;
• an offshore support apparatus comprising attachment means configured operatively to attach the offshore support apparatus to the offshore foundation;
• and
• a support frame depending from the attachment means and a plurality of supporting formations equal in number to the number of legs of the frame and configured to support respective legs of the frame;
• wherein each leg includes an adjustable foot, each foot being moveable between an extended condition and a retracted condition;
• wherein each foot is moveable with respect to its respective leg;
• and
• wherein the frame further comprises a control arrangement operable to control the movement of each foot, the feet of the frame and the supporting formations of the offshore support apparatus being configured so that the feet are supported by the supporting formations when the offshore structure is mounted in its operative position.

A method of mounting an offshore structure including a longitudinally extensive shaft, mast or tower on a transporting vessel, the method comprising:

• providing on land a frame including an engaging portion configured to engage the shaft, mast or tower, a plurality of legs configured to rest on an underlying supporting surface and a plurality of lifting formations by which the frame may operatively be lifted, wherein each leg includes an adjustable foot that is moveable between an extended condition and a retracted condition;
• moving each foot with respect to its respective leg by a control arrangement;
• securing the frame to the offshore structure;
• providing a pair or lifting cranes on the transporting vessel, each crane having a lifting cable;
• connecting the lifting cables to the lifting formations of the frame;
• and
• lifting the frame carrying the offshore structure from the land to the vessel such that at least some of the legs are supported by the deck of the vessel and the offshore structure is retained in a substantially upright condition at least partially by the action of the cranes.

A method of transferring an offshore structure including a longitudinally extensive shaft mast or tower from a transporting vessel to an offshore support foundation, the method comprising

• providing:
• a tower supporting apparatus including a frame arranged on the vessel and supporting the offshore structure, the frame comprising an engaging portion which engages the shaft, mast or tower, a plurality of legs at least some of which are supported on the deck of the vessel and a plurality of lifting formations by which the frame may operatively be lifted, wherein each leg includes an adjustable foot, each foot being moveable between an extended condition and a retracted condition, wherein the frame further comprises a control arrangement operable to control the movement of each foot, and wherein each foot is moveable with respect to its respective leg;
• a pair or lifting cranes on the transporting vessel, each crane having a lifting cable connected to the lifting formations of the frame;
• a spreader beam mounted on the shaft, mast or tower and to which the lifting cables of the cranes are attached, the spreader beam being operatively moveable longitudinally with respect to the shaft, mast or tower;
• an offshore support apparatus comprising attachment means by which the offshore support apparatus is attached to the offshore foundation, a support frame depending from the attachment means and a plurality of supporting formations equal in number to the number of legs of the frame and configured to support respective legs of the frame
• the method comprising:
• lifting the tower supporting apparatus and offshore structure from the vessel with the cranes and retaining the offshore structure with the shaft, mast or tower in a substantially upright configuration;
• moving the tower supporting apparatus carrying the offshore structure to a position above the offshore support foundation and aligning the legs of the frame with the support structures of the offshore support apparatus;
• lowering the offshore structure onto the offshore support base such that the legs are supported by the supporting formations of the offshore support apparatus;
• and
• securing the offshore structure to the offshore support apparatus.