Abstract: A semi-submersible crane vessel has a chamber (3) which is open to the sea at the bottom. A piston (4) is movable up and down in the chamber by means of hydraulic jacks (5 and 6) acting on piston rod (7). The part (10) of the chamber above the piston contains air, which may be pressurized via air valve (13) to balance the pressure on both sides of the piston. To stabilize the vessel during movement of a load on the crane (2), the piston is moved in the chamber. This alters the underwater volume of the vessel and therefore its buoyancy.

Abstract: A crane vessel (20) has a temporary load support structure (23) on which to support a load (22) in transit. For installation, the load is hooked up to the vessel crane (21) and the temporary support structure is removed to enable the vessel to set down the load on its tower structure (24).

Abstract: A method of stabilizing a floating body comprises applying to the body a vertical force so as to maintain the body in an equilibrium position which is spaced vertically from the normal floating position of the body, in which the vertical force comprises a limited vertical force applying means acting on the body in one vertical direction and a flexible tension member applying tension to the body or the force applying means in the opposite vertical direction, the tension member having a tension less than the said limited vertical force.

Abstract: A method of controlling the vertical position of a body in water, where the body has or is given a positive buoyancy, providing a structure which is of sufficient weight to give the body negative buoyancy, providing a structure which is separate from the body and from which to support the load over the body, and providing a device for lowering the load into engagement with the body.

Abstract: A method of assembly of an offshore tower comprises engaging a column with a sleeve of a support structure by positioning the column so that its longitudinal axis is vertical or nearly vertical, positioning the support structure so that the column-receiving sleeve is uppermost and the axis of the sleeve is vertical or nearly vertical, with the sleeve above the top of the column, and positioning the column in the sleeve by relative longitudinal movement between the column and support structure.

Abstract: A vessel (10) is provided for installing or removing a module (16) on or from a support structure (30) erected in a body of water. The vessel is able to suspend the module over the support structure by cranes (14, 15), enabling installation or removal of the module to be accomplished while the module is being suspended.

Abstract: A tower structure having a central column, three support legs and a base structure which can be anchored to the sea bed by means of piles. The legs and base structure are constructed as an integral preformed base unit with a sleeve attached to the upper ends of the legs.The column is slidingly engaged within the sleeve of the base unit. A rigid connection is made between the column and the sleeve. In the erected structure, the primary load of the column is transmitted through the column and sleeve connection via the base unit to the sea bed.

Abstract: The invention provides a method of constructing an offshore tower structure having a base structure for positioning on the sea bed, a central enclosed tubular column containing services such as conductors and risers and extending from the base structure to above the water level for supporting a service platform which includes positioning the base structure on the seabed, floating the column and legs over the base structure, lowering the column and legs onto the base structure and securing them onto the latter.

Abstract: The invention provides an offshore tower structure comprising a base structure for positioning on the sea bed, a central enclosed tubular column 20 containing services such as conductors and risers and extending from the base structure to above the water level, in use, for supporting a service platform 21 and at least three tubular support legs 22, 23, 24 each extending between the base structure at a point spaced apart from the column and an upper portion of the tubular column, the support legs each being rigidly attachable to the base structure and to the column and the base structure providing means for maintaining the spacing between the support legs and the column, in which each support leg is attached to the column by welding and there is means to provide a water tight compartment around the joint from which water can be removed so that the leg can be welded to the column in dry surroundings.