A SELF-PROPELLED OFFSHORE INSTALLATION VESSEL

Abstract

A self-propelled offshore installation vessel (1) operates at an offshore position and has at least one water pump (27) being operable to pump water from a water inlet opening (22) to a water outlet opening (25) via water conduit pipes (24). The water system can eject water out through the water outlet opening(s), whereby the ejected water interacts with the waves to dampen waves in an affected area (35) of the sea at the self-propelled offshore installation vessel (1).

Claims

1. A self-propelled offshore installation vessel having a hull with an outer side and with a water system, which water system comprises at least one water inlet opening in the hull associated with a controllable inlet valve, water conduit pipes, at least one water outlet opening in the outer side of the hull associated with a controllable outlet valve, and at least one water pump being operable to pump water from the water inlet opening and/or to pump water to the water outlet opening via the water conduit pipes, characterized in that the at least one water outlet opening is provided with a nozzle device and is located at the outer side of the hull at a position of less than 5 meters from the water line at a predetermined draught of the self-propelled offshore installation vessel.

2. A self-propelled offshore installation vessel according to claim 1, wherein the predetermined draught is a draught at which the self-propelled offshore installation vessel is intended to receive a supply vessel, such as a barge with parts to be installed at an offshore installation site.

3. A self-propelled offshore installation vessel according to claim 1, wherein the at least one water outlet opening is a plurality of water outlet openings in the outer side of the hull.

4. A self-propelled offshore installation vessel according to claim 3, wherein at least some of the plurality of water outlet openings are arranged at different heights in the outer side of the hull, preferably arranged with at least one water outlet opening positioned below the water line corresponding to the predetermined draught of the self-propelled offshore installation vessel.

5. A self-propelled offshore installation vessel according to claim 4, wherein several water outlet openings are positioned below said water line.

6. A self-propelled offshore installation vessel according claim 1 wherein the hull has a stern end and a cargo main deck and a side section extending upwards at either longitudinal side of the cargo main deck, that the self-propelled offshore installation vessel has ballast tanks and a ballast pumping system for changing the vessel draught between the predetermined draught, at which the cargo main deck is submerged below sea level, and a second draught, at which the cargo main deck is above sea level.

7. A self-propelled offshore installation vessel according to claim 1 wherein the at least one water pump is comprised by one or more ballast pumps of the self-propelled offshore installation vessel.

8. A self-propelled offshore installation vessel according to claims 1 wherein the at least one water pump has a total water pumping capacity of at least 9000 m.sup.3/h.

9. A self-propelled offshore installation vessel according to claim 1 wherein the at least one water pump is configured as from 2 to 12 water pumps, each having a water pumping capacity in the range of 1000 m.sup.3/h to 5000 m.sup.3/h.

10. A self-propelled offshore installation vessel according to claims 1 comprising two jack-up legs at a starboard side and two jack-up legs at a port side, one of said two jack-up legs being a forward jack-up leg and the other being an aft jack-up leg, and by the least one water outlet opening being a plurality of water outlet openings which are arranged either at the aft jack-up leg on the starboard side and on the port side, or aft of the aft jack-up leg on the starboard side and on the port side, such as at the starboard side and the port side of the stern of the hull.

11. A self-propelled offshore installation vessel according to claim 1 wherein the nozzle device has a cross-sectional area which is smaller than the cross-sectional area of the water conduit pipe connected to the water outlet opening.

12. A self-propelled offshore installation vessel according to claim 1 wherein the nozzle device directs the water in a direction different from the direction normal to the outer side of the hull.

13. A self-propelled offshore installation vessel according to claim 1 wherein the controllable outlet valve is a spade valve.

14. A method of operating a self-propelled offshore installation vessel at an offshore position having a sea state with waves, which self-propelled offshore installation vessel has a hull with an outer side and with a water system, which water system comprises at least one water inlet opening in the hull associated with a controllable inlet valve, water conduit pipes, at least one water outlet opening in the outer side of the hull associated with a controllable outlet valve, and at least one water pump being operable to pump water from the water inlet opening and/or to pump water to the water outlet opening via the water conduit pipes, characterized in that the water system is activated to eject water out through the at least one water outlet opening, which has a nozzle device, whereby the ejected water interacts with the waves to dampen waves in an affected area of the sea at the self-propelled offshore installation vessel.

15. A method of operating according to claim 14, wherein the offshore wind farm installation vessel is positioned with its bow facing in direction of the incoming waves, said affected area of the sea being located at least aft of the stern of the hull, and preferably the water system ejects water simultaneously out through water openings on both the starboard side and the port side of the hull.

Description

[0029] In the following, illustrative schematic embodiments and schematic examples according to the present invention are described in further detail with reference to the highly schematic drawings, on which

[0030] FIGS. 1 to 3 illustrate in views from above loading of a barge with wind turbine foundations onto a cargo main deck of a self-propelled offshore installation vessel,

[0031] FIG. 4 depicts in a view from above an embodiment of a self-propelled offshore installation vessel according to the present invention,

[0032] FIG. 5 illustrates in a view from above a horizontal section through the vessel of FIG. 1 at a level just below the upper structure of the cargo main deck,

[0033] FIG. 6 illustrates the vessel of FIG. 1 in a view from the aft forwards,

[0034] FIG. 7 illustrates a cross-section through the cargo main deck of the vessel of FIG. 1,

[0035] FIG. 8 illustrates a water system in another embodiment of a self-propelled offshore installation vessel according to the present invention,

[0036] FIG. 9 illustrates the starboard aft end portion of the vessel of FIG. 1, in a side view,

[0037] FIG. 10 illustrates a water system in yet another embodiment of a self-propelled offshore installation vessel according to the present invention,

[0038] FIG. 11 illustrates four water outlet openings in the side of the hull of a self-propelled offshore installation vessel according to the present invention, and

[0039] FIG. 12 illustrates in a view from above the vessel of FIG. 1 with activated water system for receiving a barge with parts.

[0040] The weather plays a role for the possibilities of performing offshore installation operations, such as installing offshore wind turbine farms, or performing maintenance on such farms. It is a well-known experience that installation work must be suspended when the weather is too rough.

[0041] For the four locations Table 1 lists the probability of exceedance (in percent) of significant wave heights given in metres. The percentages given are based on yearly average data. From the Percentage Exceedence Distribution in Table 1 it appears that a significant wave height of 2.0 metres is exceeded during 25% of the year at location A, while a significant wave height of 3.0 metres is exceeded only during about 9% of the year.

[0042] The below Table 1 exemplifies statistically the weather conditions expressed as Significant Wave Height, SWH, at the following four offshore locations:

[0043] A: 52.503 N, 5.524 W Irish Sea

[0044] B: 49.773 N, 4.657 W English Channel

[0045] C: 55.565 N, 2.250 E North Sea

[0046] D: 57.579 N, 8.209 W Hebrides Shelf

TABLE-US-00001 TABLE 1 SWH in m % at A % at B % at C % at D 0.5 89 99 96 100 1.0 61 80 75 96 1.5 41 57 52 82 2.0 25 38 35 66 2.5 15 25 23 52 3.0 9 17 15 40 3.5 5 11 9 31

[0047] The data in Table 1 are from Wind and wave frequency distributions for sites around the British Isles, Offshore Technology Report 2001/030, Southampton Oceanography Centre.

[0048] An embodiment of a self-propelled offshore installation vessel 1 is illustrated in general in FIGS. 4-7 and 9. The embodiment has the following main particulars: Length over all 215 m, breadth 89 m, depth to upper deck 18 m, depth to main cargo deck 8.25 m, draught free sailing 6.25 m, and draught submerged 15 m, which is a predetermined draught in the context of the present invention. The installation vessel has a hull 2 with two cantilevered arms 3 extending on both sides of an unloading space 4 for lowering parts towards the sea bottom. The installation vessel has a plurality of main generators in a forward engine room, and the installation vessel is propelled by four azimuth propellers located in the aft end of the hull and further driven and positioned by four azimuth thruster propellers in the forward end of the hull, and by a transverse bow thruster.

[0049] A cargo main deck 5 has a side section 6 extending upwards at the starboard and port sides of the cargo main deck. The side sections 6 include ballast tanks 7 and several utility rooms. The side sections 6 have a substantially flat inner side facing the cargo main deck, and this side extends upwards into an upper wall-shaped portion 8, which on its top carries a rail structure. Wall-shaped portion 8 and the rail structure extend from the forward end of the cargo main deck to the aft end of cantilevered arms 3. Trolley winches 9 are mounted on the rail structure and they can move along the rail structure driven by a controllable drive. There are two trolley winches 9 on the port side and two trolley winches 9 on the starboard side. Remote operation of the trolley winches can be performed from the bridge in the forward superstructure or from a control station in a cabin located in the aft of the installation vessel.

[0050] The wind farm installation vessel is provided with four jack-up legs 10. Each leg extends vertically through the hull within a jack house, which is integrated in the hull. Two of the jack-up legs are located at a forward end of the cargo main deck, and two jack-up legs are located in side sections 6 at the aft end of the cargo main deck.

[0051] A main crane 10 is mounted on a crane structure extending around the aft jack-up leg on the port side. When the main crane is not in use, the boom rests in a supporting structure 12. Two auxiliary cranes 13 are installed on the side sections 6.

[0052] Otherwise, the vessel is equipped in traditional manner with mooring arrangements, life boats, a superstructure suitable for accommodating the needs of the crew and other personnel, fuel oil tanks, fresh water tanks, drain tanks, freshwater systems, heating systems, navigation systems, communications systems etc.

[0053] The self-propelled offshore installation vessel 1 performs many different operations during a complete installation process. One of the most critical operations in view of weather conditions is receiving a supply vessel, such as a barge at the offshore location. With previous installation vessels is was considered possible (however not proven in real operation) to receive a barge when the sea state was 2.0 metres significant wave height, and this was considered the limit of operations. When the sea state was higher than 2.0 metres significant wave height, operations had to be cancelled.

[0054] The process of receiving a barge may be outlined as follows. The ballasting system is activated and ballast taken in until the offshore installation vessel is at the predetermined draught with the cargo main deck submerged below sea level to a depth greater than the draught of a barge to be loaded. The jack-up legs may be activated and lowered onto the sea bottom and loaded with sufficient force to maintain installation vessel 1 in stable state with no movement from the waves. The installation vessel may be positioned with the bow facing the wind and waves so that the hull of the vessel provides a calmer area just aft of the vessel. A barge 14 loaded with parts to be installed has already been towed from port to the offshore site. While one end of the barge is connected to the tug boat 15, the other end of the barge is connected to wires from two trolley winches 9 positioned on the cantilevered arms 3, the connection preferably being in the crossing pattern illustrated in FIG. 1 where the wire from the starboard trolley winch is secured at the forward port corner of barge 14, and where the wire from the port side trolley winch is secured at the forward starboard corner of barge 14. This provides better control over the position of the barge end in relation to the cantilevered arms. The trolley winches are then activated to move in unison in the forward direction along the rail structure. When the trolley winches reach their forward-most position as illustrated in FIG. 3, then the barge has been received completely in a position above the cargo main deck. With the barge in the desired position, the aft end of the barge is moored to vessel 1 and the tug boat is released. The ballast system is activated to pump ballast water out of ballast tanks, until the cargo main deck is above sea level and the barge sits supported on the cargo main deck.

[0055] The hull structure below the cargo main deck 5 includes separate spaces 16 that could be used as tanks, however it is in the embodiment in question more convenient to let these spaces be open to the surroundings via pipes 17 extending through the lower bottom structure 18, see FIG. 7, and open holes 31 are arranged in the deck plating at the top of spaces 16 for ventilation of air. These separate spaces will thus fill with water when the installation vessel increases draught and will empty of water and fill with air when the hull has lower draught or is jacked up by the jack-up legs. The water line at the predetermined draught is denoted 19, and the water line at the draught for free sailing is denoted 20.

[0056] The hull 2 has an outer side 21 which is typically vertical and extends along the circumference of the hull. As illustrated in FIG. 8, the offshore installation vessel has a water system comprising a water inlet opening 22 in the hull associated with a controllable inlet valve 23, water conduit pipes 24, a water outlet opening 25 in the outer side 21 of the hull associated with a controllable outlet valve 26, and a water pump 27 being operable to pump water from the water inlet opening to a tank 28 or to pump water from the tank to the water outlet opening or to pump water from the water inlet opening to the water outlet opening, via the water conduit pipes. Control valves 29 and 30 can be activated between open and closed positions, and when control valve 29 is closed and control valve 30 is open, tank 28 can receive water from water pump 27. When control valve 29 is open and control valve 30 is closed, tank 28 can feed water to water pump 27. When both control valves are closed, water pump 27 can pump water from the water inlet opening directly to the water outlet opening.

[0057] The inlet valve 23 can be a butterfly valve or a spade valve or any other type of valve suitable as sea valve, and the inlet valve can be mounted at a sea chest in the hull. The water inlet opening 22 can be located at the outer side 21 in a position below water line 20, or in the bottom of the hull, or in the wall of separate space 16 in a position below water line 20, provided this separate space 16 is equipped with pipes 17 allowing free flow of water into separate space 16.

[0058] The water outlet opening 25 is located at the outer side of the hull in vicinity of the water line 19 corresponding to the predetermined draught at which the water system is to be operated to dampen waves. In an embodiment, there is a single water outlet opening located forward of a landing site on the hull of the installation vessel. A transfer vessel can approach the landing site and transfer personnel. The predetermined draught is in this case the relevant draught at which the personnel has to be transferred, e.g. the draught for free sailing. The self-propelled offshore installation vessel 1 may have water outlet openings located forward of a foundation installation position on the vessel, and water can be ejected to form an affected area of the sea at the area of the foundation installation. The predetermined draught is in this case the relevant draught for the installation of foundations.

[0059] In the embodiment illustrated in FIGS. 9 and 12, there are four water outlet openings 25 located on the starboard side of the hull, and four water outlet openings 25 located on the port side of the hull. The four water outlet openings are on both sides of the hull arranged in the area just aft of the aft jack-up leg 10. One of the water outlet openings is located above water line 19 and three water outlet openings are located below water line 19. Each of the water outlet openings is associated with an arrangement as illustrated in FIG. 8. Each water pump 27 is a centrifugal pump having a pumping capacity of 3000 m.sup.3/h. The eight water pumps are installed in a pump room 37 located in the starboard side of the hull. Naturally it is possible to use more than one pumping room and to locate water pumps in both the starboard side and in the port side of the hull. Water conduit pipes 24 are preferably made of glassfibre reinforced epoxy, or made of polyester or steel. Water outlet opening 25 is provided with a nozzle in form of a reinforcement ring in the outer side 21 of the hull. The reinforcement ring defines the outlet opening and has a smaller diameter than the water conduit pipe connected to the outlet opening. As an example, if the water conduit pipe has a diameter of 0.72 m, the reinforcement ring may have a diameter of 0.70 m, or 0.60 m.

[0060] In another embodiment illustrated in FIG. 10, the water system comprises two water pumps 27 without a tank, and two water pumps 27 associated with a ballast tank 7. Other configurations are of course also possible. Ballast pumps may be utilized as water pumps in the water system, provided the ballast pumps have sufficient pumping capacity.

[0061] In the embodiment illustrated in FIG. 11 four water outlet openings 25 are arranged in the vertical in the outer side of the hull with two water outlet openings above the waterline at the predetermined draught, and two water outlet openings below the waterline. It is also possible to arrange all water outlet openings above or below the waterline.

[0062] FIG. 12 illustrates the self-propelled offshore installation vessel 1 in a position where the dynamic positioning system of the vessel maintains the bow 32 facing in direction of the incoming waves. Arrow 32 indicate the direction in which the waves propagate and the vessel is maintained in position with a bearing that is 180 off the direction of arrow 32. The water system is activated to eject water 34 out through four water outlet openings on the starboard side and out through four water outlet openings on the port side. The ejected water interacts with the waves to dampen waves in an affected area 35 of the sea. Affected area 35 is located at the aft end of hull 2 and extends aft of the hull at a considerable distance corresponding to at least one or two lengths of the installation vessel 1. The affected area 35 has a size allowing a barge 14 with parts to be fully within the affected area together with a tug boat 15 and a supply boat 36 that may assist in positioning the barge precisely with respect to the aft end of the installation vessel 1. Wires from trolley winches 9 are then connected to the barge, and the barge is received on the installation vessel, in the manner illustrated in FIGS. 1 to 3.

[0063] In an embodiment, the self-propelled offshore installation vessel assists another offshore installation vessel, and the water system can then include hoses to be extended to and placed on the other vessel and used to eject water from the other vessel to produce an affected area of the sea at the other vessel while the other vessel performs offshore installation operations.

[0064] The vessel may have other dimensions, and modifications may be made within the scope of the patent claims. The water conduit pipe 24 can on the pressure side of the water pump be branched into several pipes of smaller diameter so that one pump can feed several water outlet openings 25. The water conduit pipe can on the inlet side of the water pump be branched into several pipes connected with several water inlet openings. One water inlet opening may feed several water pumps by branching the water conduit pipe connected to the inlet opening into several pipes connected with the water pumps.

[0065] The water system may include water pumps situated on the deck, such as on the cargo main deck. This can be convenient when the installation vessel is an existing vessel that is modified to include a water system as described in the above. The water pumps may include portable pumps, and the water conduit pipes can then include hoses, such as a first hose having a water inlet opening and extending to the water pump and a second hose extending from the water pump to a water outlet opening at the end of the second hose. As the water pump is located on the deck, the controllable inlet valve and the controllable outlet valve are not required.

[0066] Details in the above-mentioned embodiments and methods may be combined into further embodiments and methods within the scope of the patent claims.