Method of assembling and deploying a floating offshore wind turbine platform

A method of assembling and deploying a floating offshore wind turbine (FOWT) platform comprising:

• floating a hollow outer tank in a floating assembly area of a body of water, the hollow outer tank having transit lines and suspension lines attached thereto;
• assembling a buoyant floater;
• floating a buoyant floater in the floating assembly area of the body of water;
• placing permanent ballast material in the hollow outer tank to define a mass, and sinking the mass to a seabed of the body of water;
• raising free ends of the transit lines and the suspension lines to a surface of the body of water with buoys;
• moving the buoyant floater to a position over the mass;
• attaching the transit lines to a lifting device in the buoyant floater and attaching the suspension lines to a portion of the buoyant floater, the combined buoyant floater and the mass defining a FOWT platform;
• lifting the mass with the lifting device to a point directly under the buoyant floater;
• towing the FOWT platform to an installation site in the body of water;
• attaching mooring lines to anchors in the seabed and to the buoyant floater;
• lowering the mass with the transit lines and the lifting device to a depth wherein the suspension lines are taught, thus suspending the mass with the suspension lines to define a suspended mass;
• and
• one of storing and removing the transit lines from the mass;
• wherein the buoyant floater includes:
• a central hub;
• three or more buoyant pontoons that extend radially outwardly from the central hub, and defining cross-shaped base;
• a central column mounted to the central hub and extending outwardly and perpendicularly to the buoyant pontoons;
• braces connecting distal ends of the buoyant pontoons to an upper portion of the central column;
• and
• a tower supporting a wind turbine on the central column;
• and wherein the method further includes:
• forming and assembling a plurality of the buoyant pontoons, the central hub, the mass, and the braces in an on-shore location;
• assembling a first and a second pontoon to the central hub;
• post-tensioning the assembled first and second pontoons and central hub from a distal end of the first pontoon to a distal end of the second pontoon to define a buoyant floater sub-assembly;
• assembling a third and a fourth pontoon to the central hub of the buoyant floater sub-assembly;
• post-tensioning the assembled third and fourth pontoons and the buoyant floater sub-assembly from a distal end of the third pontoon to a distal end of the fourth pontoon;
• forming sections of the central column;
• assembling the sections of the central column on a first axial end wall of the central hub;
• longitudinally post-tensioning the central column to the central hub;
• attaching the braces between the buoyant pontoons and the central column;
• installing the tower and the wind turbine, thus defining the buoyant floater;
• and
• launching the buoyant floater into the body of water.

A method of assembling and deploying a floating offshore wind turbine (FOWT) platform comprising:

• floating a hollow outer tank in a floating assembly area of a body of water, the hollow outer tank having transit lines and suspension lines attached thereto;
• floating a buoyant floater in the floating assembly area of the body of water;
• placing permanent ballast material in the hollow outer tank to define a mass, and sinking the mass to a seabed of the body of water;
• raising free ends of the transit lines and the suspension lines to a surface of the body of water with buoys;
• moving the buoyant floater to a position over the mass;
• attaching the transit lines to a lifting device in the buoyant floater and attaching the suspension lines to a portion of the buoyant floater, the combined buoyant floater and the mass defining a FOWT platform;
• lifting the mass with the lifting device to a point directly under the buoyant floater;
• towing the FOWT platform to an installation site in the body of water;
• attaching mooring lines to anchors in the seabed and to the buoyant floater;
• lowering the mass with the transit lines and the lifting device to a depth wherein the suspension lines are taught, thus suspending the mass with the suspension lines to define a suspended mass;
• and
• one of storing and removing the transit lines from the mass;
• wherein the buoyant floater includes:
• a central hub;
• three or more buoyant pontoons that extend radially outwardly from the central hub, and defining cross-shaped base;
• a central column mounted to the central hub and extending outwardly and perpendicularly to the buoyant pontoons;
• and
• braces connecting distal ends of the buoyant pontoons to an upper portion of the central column;
• and
• wherein the method further includes:
• forming and assembling a first and a second pontoon within a dry dock;
• assembling the central hub within the dry dock;
• assembling the first and second pontoons to the central hub;
• post-tensioning the assembled first and second pontoons and central hub from a distal end of the first pontoon to a distal end of the second pontoon to define a buoyant floater sub-assembly;
• launching the buoyant floater sub-assembly into a floating assembly area;
• forming and assembling a third and a fourth pontoon within the dry dock;
• temporarily post-tensioning each of the third and the fourth pontoons;
• launching the third and the fourth pontoons into the floating assembly area;
• assembling a third and a fourth pontoon to the central hub of the buoyant floater sub-assembly;
• and
• post-tensioning the assembled third and fourth pontoons and the buoyant floater sub-assembly from a distal end of the third pontoon to a distal end of the fourth pontoon, thus defining the buoyant floater.