The floater is a steel structure which has primarily been developed to floater at sea with fewest possible motions and to function as a floating platform and storage unit.

Technical equipment can be installed on the deck of the floater if the task requires the floater to be kept stationary above one or more geographical points on the sea floor, apart from in periods of time when the floater is to be moved under its own propulsion and without other assistance from one area of operation to another.

The term "multi-purpose ship" is used primarily to describe a ship with facilities for well drilling, well testing, fluid injection, installation and retrieval of structures on the sea floor, and also having a storage capacity and the capability of operating as a production ship.

The multi-purpose ship may be looked upon as a basic structure where equipment is installed as required on the ship's deck according to the operation that is to be carried out. Thus, drilling equipment, testing equipment, injection equipment or installation equipment, or a combination of one or more of these can be located on the ship's deck.

When the ship is to be used as a platform for one or more drilling rigs, it is designed for drilling for oil/gas at a minimum of 150 m water depth and a minimum of 3,000 m well depth, measured from the sea floor. In addition, it should be possible to test an oil or gas well, store oil produced from a well, and consume or burn off portions of any gas or other products coming from the well. The structure should also be capable of functioning as a platform for a refining/separation/injection plant which has a capacity for production of oil at a minimum of 5,000 barrels a day.

As mentioned, the structure is also intended to be capable of operating as a platform for the installation of equipment which is to be placed on or retrieved from the sea floor.

To obtain a steel structure of the type mentioned by way of introduction, the overall physical dimensions of the structure at any time must be within defined metric measurements and have certain components as an integrated part of the actual structure.

In accordance with the present invention, a floater of the aforementioned type is provided which is characterised in that it includes storage tanks, living quarters in the bow structure, a substantially level deck extending from the living quarters and away from the bow, propulsion and positioning means, and the floater has a block coefficient Cb of a minimum of 0.75.

The term "block coefficient Cb" is used to mean the ratio between the volume of a ship's hull below the water line and the volume of a rectangular block of the same length, breadth and depth. The block coefficient varies from about 0.5 for slim, high- speed ships, to about 0.85 for broad, barge-like vessels.

The floater has a storage capacity of a minimum of 30,000 m3 of fluid. In addition, it has a ballasting capacity of at least 30,000 m3 of water which is kept separate from the produced and stored liquid. Furthermore, the total carrying capacity of the floater on the deck area will be a minimum of 10,000 metric tons.

It is advantageous if the floater is equipped with azimuth thrusters as propulsion and positioning means.

The floater has preferably parallel sides running astern from the bow structure.

Furthermore, it has hull braces designed for supporting equipment on the deck area.

The floater has specific measurements which are within certain ranges, and has a total length of between 150 and 300 m, a total breadth of between 30 and 50 m, and a total depth of between 15 and 30 m.

The hull is advantageously designed as a substantially parallelepipedic body having two ends, where in one end a bow structure is added or constructed. The vertical well may per se be located anywhere at all that might be found expedient, and in one embodiment may be located in front of the centre of-the floater.

It is an advantage if one azimuth thruster is located in the after end, whilst two azimuth thrusters are located in the bow structure.

The structure may have one or more vertical through holes in the steel structure, each of which is a minimum of 25 m2 in area and 375 m3 in volume and a maximum of 600 m2 in area and 18,000 m3 in volume.

The total deck area should be a minimum of4,500 m2 and a maximum of 15,000 m2.

The steel structure may advantageously be constructed of a combination of high tensile steel and low carbon steel.

Furthermore, the floater should have facilities for loading and unloading the fluid for which it must at any time have storage capacity, whilst maintaining at all times the desired draught. Furthermore, the product should be able to move from one geographical area to another at a minimum speed of 8 knots without requiring assistance from other vessels. The floater may advantageously also have overnight accommodation for a minimum of 60 persons, and may in addition to the dynamic positioning system also have anchoring equipment.

Other and additional objectives, distinctive features and advantages are set forth in the following description of a, for the time being, preferred embodiment of the invention, which is given for the purposes of description without thereby being limiting, and given in connection with the appended drawings, wherein: Figure 1 is a schematic side view of a floater according to the invention; Figure 2 shows the floater according to Fig. 1, seen from above; Figures 3A - 3C are a schematic lateral view, plan view and cross-sectional view of the floater according to Figs. 1 and 2 with drilling equipment installed above the well running through the hull; and Figures 4A - 4B are a schematic view and a plan view of the floater according to Figs. 1 and 2 with a production riser unit and rotary production tower installed.

Fig. 1 shows a multi-purpose ship or floater 5, in a basic embodiment. The floater S has an elongated hull 1 having double sides 3, double ends 7,7' and a double bottom 4. The hull 1 has a bow structure 8 at one end thereof with living quarters 9 built up above the bow structure 8. In addition, the bow portion may be equipped with a helicopter deck

12. A substantially level deck 2 runs aftward from the bow structure 8 all the way to the stern. In the illustrated embodiment, the hull 1 has a vertical well 6 located slightly in front of the centre of the floater. However, the well can be located anywhere on the deck that is found expedient. It is also possible to have several wells 6. Furthermore, the deck is equipped with several whirley cranes 13 for lifting equipment into place on the ship's deck 2. Below the deck, the ship's hull has a storage capacity in the form of storage tanks 10 designed to be filled with production fluid such as oil. Propulsion and positioning means 11 are also provided in the bottom of the hull 1.

The feature which is especially characteristic of the hull structure is its markedly parallelepipedic form, with a virtually flat bottom and an almost rectangular cross- sectional profile. The bow portion will also be rather blunt and the vessel will be capable of moving from one geographical area to another at a relatively low speed, such as a minimum of 8 knots. Thus, the need for high-speed movement is very moderate, what is important is that the floater is exposed to as few motions as possible in the sea when operating out in the field.

This has been achieved by ensuring that the hull has a block coefficient of a minimum of 0.75 and preferably close to 1.

The total length of the hull will be between 150 m and 300 m, the total breadth between 30 m and 50 m and the total depth between 15 m and 30 m.

The vertical through well 6 in the steel structure should as a minimum have a cross- 2 3<BR> <BR> section of 25 m2 and a volume of 375 m3 and as a maximum have a cross-sectional area<BR> <BR> <BR> 2 3<BR> <BR> of 600 m2 and a volume of 18,000 m3.

2 2 The total deck area should be a minimum of 4,500 m2 and a maximum of 15,000 m2, and the deck should have a total carrying capacity of a minimum of 10,000 metric tons.

Furthermore, the total storage capacity in the hull 1 must be a minimum of 30,000 m3 liquefied fluid. A volume that is at least equally great must be available in the hull to be able to carry out ballasting with water and deballasting. The draught of the vessel can thus be continuously controlled and adjusted in the different use situations of the floater, and also during a particular working operation. The floater may be constructed of a combination of high tensile steel and low carbon steel. The hull 1 has braces which are dimensioned and designed to support equipment on the deck 2, such as well drilling equipment, well testing equipment, well injection equipment and means for installing

structures on the sea floor and for retrieving structures therefrom. From this it will be understood that the floater will be a form of multi-purpose ship which may be used as a drilling ship, testing ship, storage ship, injection ship, installation ship and production ship.

The equipment can be adapted so that it can be placed on the deck 2 or taken off the deck 2 as required, and depending on the demand for space, one or more types of equipment may also be in place on the deck 2 concurrently.

The ship must be capable of operating in all geographical areas of the world and satisfy the public laws and regulations which apply in different parts of the world.

Figs. 3A - 3C show the floater 5 as it will appear when in use as a drilling vessel. A drilling rig 15 is installed on the vessel's deck 2 and the drilling derrick 16 is immediately above the well 6 that runs through the hull so that a drill string can run from the derrick 16, down through the well 6 and on towards the sea floor. In addition to this, reference will only be made to Fig. 3C which shows clearly the previously discussed flat bottom and approximately rectangular cross-sectional shape of the hull.

Figs. 4A - 4B show the floater 5 when it has been prepared for production from the sea floor. In this situation, the floater 5 comprises a rotary production tower 17 and a riser unit 18 which runs inside the well 6. The figure illustrates the floater 5 in a phase when it is used for permanant production and as a temporary transit store.