This invention relates to a floating platform for use in off-shore applications. Conventional floating platforms are significantly affected by adverse sea conditions which result in a relatively high degree of motion of the platform, which has operational implications.

According to a first aspect of the present invention, there is provided apparatus comprising a top structure for supporting one or more items, at least one buoyancy device connected to the top structure and a weighted device movable relative to the at least one buoyancy device, wherein the buoyancy device is comprised of a material of a first density and the weighted device is comprised of a material of a second density, the second density being significantly greater than the first density, said buoyancy device including a plurality of buoyancy columns and said top structure being fixedly connected to the plurality of buoyancy columns at an upper end region thereof, and wherein the weighted device includes a plurality of support legs and a primary ballast mass connected to a lower end region of the support legs, each column having a support in relation to which the support legs are moveable, the support of each column being in the form of externally mounted guiding means which guide the movement of the support legs.

According to a second aspect of the present invention, there is provided apparatus comprising a top structure for supporting one or more items, at least one buoyancy device connected to the top structure and a weighted device movable relative to the at least one buoyancy device, wherein the buoyancy device is comprised of a material of a first density and the weighted device is comprised of a material of a second density, the second density being significantly greater than the first density, said buoyancy device including a plurality of buoyancy columns and said top structure being fixedly connected to the plurality of buoyancy columns at an upper end region thereof, and wherein the weighted device includes a plurality of support legs and a primary ballast mass connected to a lower end region of the support legs, each column having a support in relation to which the support legs According to a third aspect of the present invention there is provided apparatus comprising a top structure for supporting one or more items, at least one buoyancy device connected to the top structure and a weighted device movable relative to the at least one buoyancy device, wherein the buoyancy device is comprised of a material of a first density and the weighted device is comprised of a material of a second density, the second density being significantly greater than the first density.

Owing to these aspects of the invention, it is possible to provide a floating platform which is responsive to a multitude of sea states by adjustment of the position of the weighted device relative to the at least one buoyancy device.

In order that the present invention can be clearly and completely disclosed, reference will now be made, by way of example only, to the accompanying drawings, in which:-

Figure 1 shows side views of a floating platform structure with a weighted device in the fully retracted and fully extended position,

Figure 2 is a view similar to Figure 1 , but with the floating platform being semi- submersed,

Figure 3 shows a perspective view of an alternate arrangement of the weighted device,

Figure 4 is a view similar to Figure 3, but of a further alternative to the arrangement of the weighted device, and

Figure 5 shows respective perspective views of an embodiment of the floating platform with the weighted device in the fully retracted and fully extended position.

Referring to Figures 1 and 2, a semi-submersible floating platform structure 2 of a substantially triangular plan-form comprises a deck structure 4 fixedly connected to a plurality of buoyancy columns 6 at an upper end region thereof. At the opposite lower end region of the columns 6, a support structure 8 retains the columns 6 at the required spaced-apart distance. A movable weighted device 12 is movable relative to the buoyancy columns 6 and includes a plurality of support legs 14 which are movable and a primary ballast mass 16 connected to a lower end region of the support legs 14. Preferably each column 6 has some support in relation to which the support legs 14 are moveable, for example, each column 6 may be provided with an internal chamber 10 in which the support legs 14 are moveable. Of course, other arrangements are possible in which an internal chamber is not used. For example, the columns 6 may include externally mounted guiding means 15 which guide the movement of the support legs 14, as shown in Figure 3 or, alternatively, the support legs 14 may be telescopic, as shown in Figure 4. The support structures 8 assist to enable smooth extension and retraction of the weighted device 12 in and out of the columns 6. The buoyancy columns 6 and preferably the deck structure 4 are made from a material having a first density and advantageously made of a lightweight material, such as fibre-reinforced composite materials which are high-performance, lightweight materials that are strong enough to take harsh loading conditions, or aluminium alloys. The weighted device is made from a material of a second density which is substantially greater than the first density, for example, a relatively heavy metallic material such as steel and lead. The combination of the lightweight deck structure and the use of a plurality of buoyancy columns 6 reduce the waterplane area of the platform 2, thereby decreasing the motions caused by perturbations of the surface of the sea.

In a first embodiment of the invention, the platform 2 is utilised for environmental measurement, with, for example, a LIDAR (Light Detection And Ranging) device mounted on the deck structure 4. Conventional environmental measurement techniques for marine environments utilise a so-called offshore met mast, which are large and extremely expensive structures to install. Other known measurement/monitoring devices may also, of course, be mounted to the platform structure 4 or other parts of the floating platform 2. For example, subsea current/wake measurements are a possibility. The deck structure 4 may also have a separate gimballed platform installed (not shown) to further decrease motions to the supported equipment, such as the LIDAR device. The moveable weighted device 12 having the support legs 14 extendable and retractable from inside the buoyancy columns 6, on the base of which the principal ballast mass 16 is attached. In this way, the centre of gravity CG is thus maintained as low as possible in relation to the static centre of buoyancy CB in order to achieve the lowest motion response of the platform 2 in the open sea. Such an arrangement produces an advantageously low motion floating platform 2. The weighted device can be extended and retracted relative to the columns 6 and so be 'tuned' to the specific site of installation to the prevailing sea conditions, such as wave frequency, so that the optimal response of the platform 2 to a multitude of sea states can be achieved. In addition, the movable weighted device 12 enables an option to tension moorings holding the platform 2 in position. In this case, the moorings would be attached with the weighted device 12 in a fully extended position, and subsequent partial retraction of the weighted device 12 would create tension in the moorings, fixing the platform in place. The platform 2 can also be slack moored using gravity base or positive engagement arrangements for ease of deployment and reduction in installation costs and time.

For installation, the platform 2 can be towed into position with the weighted device 12 in a fully retracted position, having a shallow draft in the water, with full extension of the weighted device 12 occurring once on site to create maximum stability. For small scale versions of the platform 2, such as the environmental measurement platform discussed above, the moveable weighted object (when in the fully retracted position) enables road transportation of the platform 2 between launch/recovery and/or construction/storage sites.

A second embodiment of the invention utilises a larger scaled version of the platform 2 for offshore energy extraction. This may comprise mounting one or more wind turbine devices 18 to the deck structure 4 along with any other necessary equipment 20, as shown in Figure 5. The advantage of such an arrangement is that in offshore locations where wind speeds can reach relatively high levels a floating low motion platform 2 can be provided to extract the energy available by way of the turbine devices 18 which remain relatively stable in such conditions.

The platform 2 is of modular design for ease and reduced cost of construction. The triangular nature of the platform 2 is advantageous in view of the requirement for a corresponding 3 point mooring system which is relatively easy to install.