Patent ID: 8220406

Claim:
An off-shore structure ( 1 ) comprising: a support structure ( 2 ) to support a load; and a buoyancy structure ( 5 ) attached to the support structure ( 2 ), the buoyancy structure ( 5 ) being adapted to be fully submerged below a water surface ( 8 ) and to float above the sea floor ( 10 ), the buoyancy structure ( 5 ) comprising at least one buoyancy tank ( 14 ) with a first chamber ( 15 ) adapted to be filled with a gas under pressure, and a second chamber ( 16 ) being in fluid communication with the first chamber ( 15 ), the first chamber during use being positioned above the second chamber, the second chamber ( 20 ) being adapted to be partially filled with sea water defining a water-gas interface ( 21 ) therein, the volume of the first chamber ( 15 ) being substantially larger than the volume of the second chamber ( 16 ), the horizontal cross-section of the first chamber being larger than the horizontal cross-section of the second chamber, wherein the buoyancy structure ( 5 ) is adapted to be moved from a first depth to a second depth greater than the first depth, and wherein the height of the second chamber ( 16 ) and the position of the water-gas interface ( 21 ) inside the second chamber ( 16 ) at the first depth are adapted such that the water-gas interface ( 21 ) rises inside the second chamber ( 16 ) without entering the first chamber ( 15 ) when the buoyancy structure ( 5 ) is moved from the first depth to the second depth, wherein the support structure ( 2 ) is a truss support structure mounted on top of the buoyancy structure ( 5 ), the truss support structure being adapted to be partially submerged into the water, the truss support structure ( 2 ) being attached to the buoyancy structure ( 5 ) below the water surface ( 8 ).