Abstract: A buoyancy device is described as comprising one or more buoyancy members, such as inflatable bags, diaphragms, bladders or chambers, for attachment to a structure to be floated or sunk such as a drilling rig. In one embodiment, the buoyancy member comprises a restriction device, such as a substantially rigid tubular, and an inflatable member located substantially within the restriction device, such that the restriction device restricts inflation of the inflatable member. In another embodiment, the buoyancy member comprises a substantially flexible portion and one or more end portions, where the end portions may be dome shaped, the or each end portion being releasably attached to the flexible portion.

Abstract: A buoyancy device is described comprising a number of buoyancy members (9, 9A, 9B) which are substantially equi-spaced around the circumference of a coupling member (7) and the buoyancy members (9, 9A, 9B) being coupled to the coupling member (7) At least two of the buoyancy members (9, 9A, 9B) are inflatable members (9, 9A, 9B). The inflatable members (9, 9A, 9B) are formed from a substantially flexible material such that an inflatable member (9, 9A, 9B) substantially collapses when deflated. The coupling member (7) is is typically coupled to a structure, which may be a drilling rig (3) which requires to be lifted and subsequently moved, or which may be a large device such as a well head Christmas tree for an oil well which requires to be deployed in deep water.