System for offshore power generation

An offshore power generating system (100), comprising:

• a buoyancy body (110) having a shape of a hull and a length between a bow (112) and an aft end (111);
• an elongated mast (140) extending upwards from the buoyancy body (110) and supported on the buoyancy body (110) in a rotatable arrangement (142) about a horizontal transverse axis (122);
• a rotor supported in one end of the longitudinal mast (140) for rotation about a horizontal axis oriented in the length direction of the buoyancy body (110);
• an arrangement for keeping the buoyancy body (110) in a position with the bow (112) turning up towards the wind and incoming waves, wherein
• a rotational support of the mast (140) comprises a horizontal, transversally orientated rotational axis (122) through a center of gravity of the mast (140), wherein the center of gravity of the mast (140) lies in a center plane (114) of the buoyancy body (110) vertically above the aft end (111) of the buoyancy body (110) when the buoyancy body (110) lies in an operational position in calm sea, and where the rotational axis (122) of the rotational support of the mast (140) is orthogonal to the center plane (114) of the buoyancy body (110), and
• the mast with the rotor maintains approximate operating position (140a) by one or more dampening devices (160) for maneuvering the mast (140) for compensation of the pitch motions of the buoyancy body (110).

A method for on-board loading and commissioning of a mast (140) with a mounted rotor on-board in a buoyancy body (110), comprising the steps of:

• placing the mast (140) with the rotor in a horizontal on-board loading position (140b) on a movable rig (170) on a quay, ashore or on a floating unit on water, the buoyancy body (110) ballasted with water for receiving the mast (140) in which the buoyancy body (110) is positioned adjacent the movable rig (170);
• pumping out water ballast (146) for weight transfer of the mast (140) with the rotor;
• and
• rotating the mast (140) with the rotor, with center of gravity in support, to different positions of the mast selected from a normal operating position (140a), on-board and maintenance position (140b), and survival position (140c).