Foundation structure

A method for controlling the deployment and retrieval of a foundation structure having an object mounted thereon for location on a sea bed or river bed, the foundation structure comprising a plurality of integral buoyancy devices, the plurality of integral buoyancy devices including first and second static ballast tanks, and a third movable ballast tank having a rigid control surface and pivotably mounted on the first static ballast tank and above the second static ballast tank, each of the plurality of integral buoyancy devices having variable buoyancy, the method comprising:

• varying the position of the third movable ballast tank relative to the first and second static ballast tanks to vary the position of the rigid control surface and control the position of a center of buoyancy relative to the position of a center of gravity, the center of buoyancy of the foundation structure being positioned below the center of gravity of the foundation structure when the foundation structure is in a fully surfaced condition wherein the foundation structure floats on a surface of a body of water, and the center of buoyancy of the foundation structure being positioned above the center of gravity of the foundation structure when the foundation structure is in a fully submerged condition, and wherein the first and second static ballast tanks of the foundation structure are adjacent to one another and each of the first and second static ballast tanks are directly in contact with the sea bed or river bed.