EP4139205A1

EP4139205A1 - A self-propelled floating structure and method of construction

Info

Publication number: EP4139205A1
Application number: EP21792368.9A
Authority: EP
Inventors: Marco LUCIDO
Original assignee: Windthrust Ltd
Current assignee: Windthrust Ltd
Priority date: 2020-04-22
Filing date: 2021-04-21
Publication date: 2023-03-01
Also published as: WO2021212173A1; AU2021258901A1; EP4139205A4

Abstract

Disclosed is a method of constructing a self-propelled floating structure. The method may comprise coupling a plurality of marine vessels together in a side by side spaced apart manner. At least one of the marine vessels may comprise a propulsion system and each marine vessel comprises a hull. The method may also comprise forming a weather deck that spans the plurality of marine vessels and spaces between the marine vessels.

Description

A SELF-PROPELLED FLOATING STRUCTURE AND METHOD OF CONSTRUCTION

TECHNICAL FIELD

A self-propelled floating structure and method of constructing are disclosed.

BACKGROUND ART

It is known to deploy wind turbine generators (WTGs) at sea to take advantage of the generally stronger wind conditions and unobstructed flow. WindFloat Atlantic is currently the world’s largest floating WTG installation which comprises three wind turbines each having a blade tip height of over 190 m. With all three turbines operating at maximum capacity the output is 25 MW which is able to power approximately 60,000 homes per year.

The construction of very large WTGs for offshore deployment and installation are logistically and technically difficult. Typically, the components for the WTGs are shipped from various countries to a pre-assembly port. The pre-assembly port needs a large area of vacant land and a heavy lift cranes (some of the WTG components are over 6,000 tonnes hook load), to off load the components from the transport vessels, and then load the components onto a typical jack-up offshore installation vessel.

The offshore installation vessel is then sailed to an offshore preselected site. At that site the legs are jacked to the seabed to give a stable support for the topsides carrying the components and a crane. The WTGs is installed by multiple lifting operations, typically five lifts, commissioned and put into operation. The legs can then be jacked up and the installation vessel sailed back to port for reloading.

Consideration of the difficulties in the installation of large offshore WTG including:

• the limited number of ports with sufficient lay down area to receive, preassembly and temporarily accommodate the very large WGTs preassembled component parts;

• the Jack-up installation vessels are limited to operate near shore in water depth of approx. 60 metres. Future very large WTGs need to operate far from the shore in very deep water, i.e. at depths of over 60 meters;

• the jack-up installation vessel can only carry 3 to a maximum of 6 WTGs

• substantial transport costs;

• multiple handling costs and risk; • inability to meet future demands due to lack of available and suitable ports and offshore installation vessels, has provided the stimulus for embodiments of the disclosed self-propelled floating structure and method of construction. However, as will be clear from the following text, embodiments of the disclosed structure and method of construction have very broad application and are not limited to use in relation to construction and/or installation of offshore WTGs.

The above references to the background art do not constitute an admission that the art forms a part of the common general knowledge of a person of ordinary skill in the art.

SUMMARY OF THE DISCLOSURE

In broad and general terms, the idea or concept behind the disclosed self-propelled floating structure and method of construction is to form the floating structure from a plurality of pre constructed, or second hand marine vessels which are coupled together in a spaced apart manner and have a weather deck that covers the marine vessels and the spaces there between. At least one, and indeed in most cases all the marine vessels will have their own propulsion system. Thus, the propulsion system for the floating structure is provided by one or more of the vessels used to construct the floating structure.

By utilising pre-constructed and in particular second hand marine vessels it is believed that substantial cost and time savings may be made in the construction of the floating structure. This is because the marine vessels may be purchased at or near scrap price. In addition, it avoids the need to stick built from scratch substantive portions of the floating structure. Further construction may be conducted without the need for a dry dock.

The floating structure may have many different uses and applications. For example, the floating structure may be used as a base for a floating solar farm, a near shore floating port or dock, a high seas port or dock or island, a floating transhipment vessel, a mobile floating airport, floating accommodation or a construction vessel. In one specific embodiment the floating structure may be configured to facilitate the offshore fabrication and subsequent installation of wind turbine generators. Such floating structure may include one or more heavy lift cranes including but not limited to a gantry crane. The floating structure may also be configured with one or more bays to allow access from multiple sides of a structure such as a wind turbine generator while being constructed in situ. In a first aspect there is disclosed a method of constructing a self-propelled floating structure comprising: coupling a plurality of marine vessels together in a side by side spaced apart manner, wherein at least one of the marine vessels comprises a propulsion system and each marine vessel comprises a hull, a stern, a bow and a centreline; and forming a weather deck that spans the plurality of marine vessels and spaces between the marine vessels.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of the self-propelled floating structure and method as set forth in the Summary, specific embodiments will now be described, by way of example only, with reference to becoming drawings in which:

Figure 1 is a plan view of an embodiment of the disclosed self-propelled floating structure;

Figure 2 is an end view of the embodiment of the structure shown in Figure 1 ;

Figure 3 is a side view of the structure shown in Figure 1 ;

Figure 4 is a plan view of a second embodiment of the disclosed self-propelled floating structure;

Figure 5 is an end view of the second embodiment of the disclosed floating structure shown in Figure 4;

Figure 6 is a representation of the disclosed floating structure at sea with a berthed vessel;

Figure 7 is a representation of a third embodiment of the disclosed floating structure fitted out to form an offshore wind energy farm comprising a plurality of wind turbine generators;

Figure 8 is a plan view of a representation of a fourth embodiment of the disclosed floating structure at sea with a berthed vessel for warehousing of wind turbine components, preassembly and installation of offshore wind turbine generators;

Figure 9 is a perspective view of the fourth embodiment shown Figure 9 but with the addition of prefabricated masts loaded on the deck of the floating structure; Figure 10 is a perspective view of a fifth embodiment of the disclosed floating structure in the process of fabricating and installing an offshore wind turbine generator;

Figure 11 shows a further embodiment of the self-propelled floating structure in the form of an integrated offshore wind turbine generator assembly and installation vessel;

Figures 12-21 depict one possible operating sequence of the vessel shown in Figure 11 for the on-board assembly and offshore installation of a wind turbine generator; and;

Figure 22 is a representation of an offshore wind farm installed using the vessel shown in Figure 11 .

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

With reference to the drawings an embodiment of the disclosed a self-propelled floating structure 10 comprises a plurality of marine vessels 12 fixed together in a side by side spaced apart manner; and a weather deck 14 that spans the plurality of marine vessels and the spaces 16 between the marine vessels 12.

Figure 1 is a side view of a marine vessel 12 from which the structure 10 may be constructed. The vessel 12 in this example is a cape size vessel having a hull 18, a stern 20, a bow 22, beam 24, weather deck 26 and a centreline 28. A bridge 30 from which the vessel 12 can be controlled and piloted sits on a weather deck 26. To give an idea of scale, a typical cape size vessel has a dead weight of at least about 172000 tons, a draft of about 18m an overall length of about 290m and a beam 24 of about 45 meters. However, it should be understood that embodiments of the disclosed self-propelled floating structure 10 and its method of construction are not constrained by the category or class of vessel and may for example the practice by use of for example Supermax, Ultramax or Panamax type vessels.

Embodiments of the self-propelled floating structure 10 and its method of construction are extremely well suited to the use of second-hand vessels which can be purchased at exceptionally low cost, for example at times scrap cost. Therefore, the proposed embodiments enable the provision and construction of a self-propelled floating structure at extremely low cost. Also because of the type and size of vessels 12 the structure 10 is very stable in open sea conditions. In performing an embodiment of the disclosed method of constructing a floating structure 10 as shown in Figures 1-3, the second-hand vessels 12 are purchased. All the vessels 12 are seaworthy and in particular at least one has an operational propulsion system and bridge 30; although it is envisaged that in most instances two or more, including all, purchased second hand vessels 12 have an operational propulsion system.

The method of constructing may be performed in a wet dock of sufficient size to enable a plurality of the vessels 12 to be positioned in a side-by-side and spaced apart arrangement. When constructing the structure 10 it may be desirable to ballast the vessels 12 to increase stability, including ballasting the vessels 12 to rest on the bottom of the dock in addition alternately it may be desirable to tie or otherwise restrain the vessels 12 from moving once positioned.

When the fitting structure comprises an odd number of vessels 12 the bridge 30 is removed from each of the vessels except the vessel which is located about a central line 32 of the structure 10. This vessel is hereinafter termed as the control and accommodation vessel 12C.

In the event it is considered not necessary for the structure 10 to have more than one propulsion system, and the propulsion system for each of vessels 12 other than the control vessel 12C may be either disabled or removed. If removed the propulsion system may be used as a source of spare parts or scrapped.

If it is believed desirable for the structure 10 to have more than one propulsion system, then method may include installing or fabricating a control system that is able to control of each of the propulsion systems and is operable from the bridge of the control vessel 12C. In any event irrespective of whether or not more than one propulsion system is to be used, the construction of the structure 10 may include tying control of various systems such as but not limited to: ballast systems, bilge pumps, lighting, and electrical systems of the vessels together so that they may be controlled from the bridge 30 of the control vessel 12C.

The vessels 12 of the structure 10 are coupled together using a plurality of elongated structural members 34a, 34b (hereinafter referred to in general as “members 34”) such as but not limited to I-beams, H beams, and box girders. The structural members may be made from various materials including, but not limited to: metal, metal alloy, timber, composites, including fibre composites. The members can be welded, bolted, glued or otherwise fixed between mutually adjacent vessels 12, and/or themselves, dependent on the type of material from which they are made. With reference to Figures 2 and 3, a plurality of structural members 34a are depicted as being connected to and extending between mutually adjacent vessels 12 in a direction perpendicular to the centre line 32. Other structural members 34b extend diagonally with reference to the centre line 32 and may connect to either adjacent members 34a and/or an underside of the deck 26. The plurality of members 34 that connect the mutually adjacent vessels 12 together create the spaces 16 between the vessels 12. In the illustrated embodiment the spaces 16 is in the order of 35.5m.

During construction is envisaged that some of the members 34 will first be connected between mutually adjacent vessels. This provides the structural rigidity between the mutually adjacent vessels 12 to enable commencement of the construction of the weather deck 26. The weather deck may be constructed as required to provide the designed load-bearing strength for its specific application. This may require for example the construction of the weather deck 14 as a boxlike structure comprising a plurality of plates, I-beams, H-beams, cross braces and struts.

The weather deck 26 is formed as a clean flat area having a perimeter which includes a stern line 36 that is aligned with the stern 20 of each of the vessels 12, and a bow line 38 that aligned with the bow of each of the vessels 12. The perimeter of the weather deck 26 is completed by a line/edge 38 that coincides with the port side of one of the vessels 12, and a line/edge 40 the coincides with the starboard side of another of the vessels 12.

Although not shown in Figs 1 -3 footings may be provided within the weather deck or ended within any of the vessels 12 at specified locations to support a predetermined load. An example of this is where the structure 10 may be used as a floating platform for supporting a plurality of wind turbines. In these circumstances footings may be constructed to coincide with the planned location of the wind turbines.

The structure 10 may be provided with a dynamic positioning system (DPS). If DPS is already provided in the vessels 12 used in the construction of the structure 10, then the method of construction includes appropriate wiring to enable control from the bridge 30. On the other hand, if DPS was not ready provided in the vessels 12, then the method may include installing DPS thrusters at various locations on the structure 10 and a control system which can be operable from the bridge 30. This will allow the structure to be firmly positioned in a predetermined location. An embodiment of the structure 10 constructed from three second-hand cape size vessels may have the technical specification is as follows: self-propelled overall length: 300 m beam: 200 m clean weather deck area of 60,000 m² weather deck load strength: 25 tons/m² or higher as specified by user/client ballastable under deck storage capacity of approximately 770,000 m³ about 600 m of berth space accommodation for up to 60 people or more in conventional water can be moored on a single point mooring dynamic positioning may be provided in deep water if required.

The disclosed structure 10 and method are scalable to increase the overall size of the structure 10 by incorporating more vessels 12 into the structure 10. For example, the structure 10 may comprise four or five marine vessels 12 by connecting one or two more vessels 12 into the illustrated design with the additional vessels being located on the port and/or starboard side of the illustrated structure 10. An example of this is shown in Figures 4 and 5 in which an embodiment of the floating structure 10 comprises five marine vessels 12A-12E located side-by-side in a spaced apart manner having a weather deck 14 that spans the plurality of marine vessels and the spaces 16 between the marine vessels 12. As a result of the additional two vessels 12, and with the same spacing between the vessels 12 is in the first embodiment shown in Figures 1-3, the surface area of the weather deck 14 of the structure 10 is increased to 103,000m².

In this way the weather deck area may be substantially increased to meet a specific requirement. For example, embodiments of the structure 10 may be scaled up to form a repositionable and extremely stable floating airport for either domestic or military application; with one or more runways formed on the weather deck 26. Embodiments of the floating airport may include on deck or below deck parking, amenities and the like. In another example, embodiments of the structure 10 may be scaled up to form a repositionable and extremely stable floating accommodation, such as a hotel or resort.

Figure 6 is a schematic representation of an embodiment of the disclosed structure 10 used as a marine port with a vessel 42 docked along one side. Figure 7 is a representation of an embodiment of the disclosed structure 10 incorporated in an offshore wind energy production plant 10w.

The embodiment of the disclosed structure 10 shown in Figure 7 provides a relocatable offshore wind energy generation plant 10w capable of accommodating for example twenty four (24) wind turbines 44 in any desired deep water offshore location, or indeed nearshore provided sufficient draft for the structure 10. A twenty four wind turbine floating structure 10 may produce 150 MW of power. This embodiment incorporates wind turbine generators 44 of two different height, but this is not an essential feature of the plant 10w. The generators 44 may be installed on the structure 10 either at the fabrication site of the structure 10; or in open sea after the structure 10 has been sailed to the desired location for the wind energy generation plant 10w.

Figures 8 and 9 show a further embodiment of the structure 10 configured as an ocean dock and construction vessel. The same reference numbers are used in Figures 8 and 9 to denote the same features as in the previous embodiments. As with all previous embodiments the structure 10 incorporates a plurality of marine vessels 12 located side-by-side in a spaced apart manner having a weather deck 14 that spans the plurality of marine vessels and the spaces between the marine vessels 12. The main differences between this embodiment and the embodiment shown in Figures 1 -6, is the configuring of the weather deck 14 with two bays 48, and the provision of a heavy lift crane 50. Optionally as shown in Figures 8 and 9 there is also provided forty footings 52 for receiving and holding masts 54 for the generators 44. Although other embodiments are envisaged where racks may be provided to store the masts, or mast components horizontally rather than vertically.

The bays 48 allow access from three sides to a generator 44 being constructed and installed on a seabed at open sea. The bays 48 may be conveniently located between the hulls of the respective vessels used to in the construction of the structure 10. The heavy lift crane 50 is located between the bays 48 at a location in vertical alignment with the deck of a middle one of the marine vessels used in the construction of the structure 10. Likewise, the footings 52 are located in the general region also overlying the deck of the middle one of the marine vessels incorporated in the structure 10.

A supply vessel 42 is shown docked at the structure 10 and having on its deck a rack 55 containing a plurality of turbine blades 56. This rack 55 may be transferred from the supply vessel 42 to the structure 10 using the crane 50. Another rack of turbines 56 is illustrated sitting on the weather deck 14 on a side of one of the bays 48 opposite the crane 50. A plurality of nacelles 58 with corresponding rotors is shown sitting on the weather deck 14 on a side of the other one of the bays 48 opposite the crane 50.

One possible method of constructing and installing a wind turbine generator 44 may comprise the following sequence of steps:

• The crane 50 is used to lift a mast 54 and lower it into one of the bays 48 for installation into the seabed. Any suitable installation method may be used including for example with use of suction piles. Alternatively, the mast 54 may be use on a floating wind turbine installation.

• A nacelle 58 is lifted by the crane 50 from the weather deck 14 and installed at a top end of the installed mast 54 and subsequently attached to the mast.

• Next in three separate lifts the crane 50 is used to pick up individual turbine blades 56 from the rack 55 on the weather deck 14 and manoeuvre and hold them in respective sockets of the rotor associated with the previously installed nacelle 58. Each blade 56 is then fixed to the rotor. Once all three blades 56 have been installed and fixed installation of the generator 44 is complete.

• The structure 10 can then be sailed to another to installation site and the above steps repeated to install a further generator 44.

The embodiment of the structure 10 depicted in Figure 10 enables a different construction and installation sequence in which a generator 44 may be constructed on the weather deck 14 and then installed in a single lift of the fully constructed generator 44. The same reference numbers are used in Figure 10 to denote the same features as in the previous embodiments. In this embodiment the structure 10 is of the same general configuration of that shown in Figures 8 and 9 but is fitted out differently and particular is provided with a gantry crane 50 mounted on rails 60 that extend along the port and starboard sides of the floating structure 10. In addition, the structure 10 in this embodiment has fewer, in this specific example only two, and more widely spaced, footings for holding masts 52 in a vertical disposition. A plurality of winches 62 is also attached to the weather deck 14 to provide support for the masts 52 and fully constructed generators 44 during the installation process.

The embodiment in Figure 10 enables a complete wind turbine generator 44 to be assembled on the weather deck 14 and then lifted as a complete unit for installation in the sea or on the seabed. One possible, but not the only, method of construction and installation of a generator 44 is as follows: a) A nacelle/rotor assembly 58 is attached to an assembly pad 64 located on a stern edge of the weather deck 14. b) Two of the three blades 56 are fitted to the nacelle/rotor assembly 58. c) The nacelle/rotor assembly 58 with the two fitted blades 56 is lifted by the crane 50 onto the top of a mast 54 being held vertically in a footing 52 and stabilised by winches 62. d) The third and final blade 56 is lifted by the crane 50 from a rack 55 on the deck 14 and manoeuvred and supported to enable it to be fitted to the nacelle/rotor assembly 58. This completes the assembly of the generator 44 on the weather deck 14. e) The fully assembled generator 44 is now lifted by the crane 50 and installed on a pre installed jacket 68; the structure 10 being previously manoeuvred so that the jacket 68 resides within one of the bays 48.

The methods of wind turbine generator installation described above with reference to the embodiment shown in Figures 8-10 may provide substantial cost savings over conventional offshore wind power solutions by reason of: no cost for land area required at the port for storage and assembly turbines; no requirement for installation vessels; handing costs reduction; reduction of port fees; lower capital cost to build each turbine; installation costs; maintenance costs; pre-assembly cost, multiple turbines can be fully assembled on board and installed in one single lift;

• no need for the vessel 10 to return to port for resupply/reloading as all WTGs components can arrive directly to the vessel 10.

Figure 11 shows a further embodiment of the self-propelled floating structure in the form of an integrated offshore wind turbine generator assembly and installation vessel 10A. The vessel 10A is arranged so that it can assemble a wind turbine generator including its supporting mast from a number of components either stored on the weather deck, or on service of vessels that can dock at the vessel 10A, and install a pile or other supporting structure in the open sea upon which the fully constructed wind turbine generator and mast can be placed in a single lift. As explained later the vessel 10A represents a paradigm shift in the installation of offshore wind farms and the associated costs and timeframe. The vessel 10A has a same basic form as the floating structure 10 described above and in particular in this embodiment incorporates three vessel 12a, 12b 12c (hereinafter referred to in general as “vessels 12”) which are connected by and support the weather deck 26. The vessel 10A has a bridge 30 and is formed with four bays 48. All these features are substantially the same as described in relation to the earlier embodiments.

A plurality of mast sections 54s are supported on the weather deck 26 together with a plurality of monopiles 57. To provide context each master section 54s may have a length of 35 m a diameter of 8 meters and weigh 285 tonnes; each monopile 57 may for example have a length of 120m, diameter of 12m and weigh 2500 tonnes. A group of nacelles 58 are also carried on the weather deck 26. A racks/cradles 55 are provided for storing a plurality of wind turbine blades 56.

The main differences between the vessel 10A and the previously described embodiments of the structure 10 is a provision of three separate cranes 50a, 50b and 50c each of which can reach any point on the weather deck 26, and a plurality of holes 70a, 70b, 70c, 70d (hereinafter referred to in general as “hole 70” in the singular or “holes 70” in the plural) formed in the weather deck 26.

The purpose of the holes 70 is to receive respective mast sections 54s during the construction of a wind turbine generator. A mast section 54s is lifted by one of the cranes 50 and lower it into a corresponding hole 70. The holes 70 and mast sections 54 are relatively dimensioned so that an upper portion, for example 5-10m of the mast 54s is above the weather deck 26. In one embodiment a completed mast 54 is made up of three end to end connected mast section 54s.

The holes 70 are shown as being located over the hull of a middle vessel 12c. In one embodiment the holes 70 have a length confined to the hull. But in other embodiments it is possible for the holes 70 to either extend through the hull in a manner similar to a moon pool; or to be located in a region of the weather deck 26 between the vessels 12; where in both instances a lower end of the mast or mast section may be in the water. Pipe clamps such as those used in the and gas industry may be used to support or otherwise retain the mast sections 54s in a hole 70 and prevented from falling from the hole 70 into the water. An advantage of the holes 70 on weather deck 26 being in the form of a moon pool is that the assembly of the WTGs take place at deck level (i.e. 10 meters or less in the air) instead of at a significant height up in the air e.g. >100 metres in the air. This may make assembly of the WTGs safer and faster.

Figure 12-20 are representations of the vessel 10A shown in Figure 11 showing some of the 5 steps in an embodiment of a method for constructing and installing offshore wind turbine generators.

In Figure 12 the vessel 10A, has in addition to the features shown in Figure 11 , a jacket 72, and a topsides 74. There are also two surface vessels 42a and 42b docked on the starboard 0 and port sides of the vessel 10A supplying monopiles and nacelles. The vessel 10A is stationary and at an installation location. Flere one step in the installation process has already commenced. The jacket 72 has been lifted from the weather deck 26 by the crane 50a and moved to a location where it can be secured to the seabed. The same crane 50a later lifts the topside power station 74 onto the bedded jacket 72, (see also Fig 22) 5

Figure 13 shows a snapshot in the process of installing a monopile in the seabed for supporting a wind turbine generator 44. One of the monopiles 57 is picked up from the weather deck 26 by the crane 50a and is lowered it into the water through a guide 76. The crane 50a also supports a hammer 78 above the monopile 57. Once it has been lowered so 0 that it rests on the seabed the monopile 57 is driven into the seabed by operating the hammer 78.

While a monopole 57 is being installed into the seabed, or indeed after, components of the wind turbine generator are assembled on the weather deck 26. One, but not the only, 5 possible sequence for the assembly and construction of a wind turbine generator is set out in the table below with reference to the accompanying drawings.

From the above it should be recognised that the entire construction and assembly of wind turbine generator 44 including the mast 54 is performed on the vessel 10A. This provides a highly stable base for construction not only due to the massive size and displacement of the vessel 10A but also due to the mast sections being located in a hole 70 during the assembly stage. Stability can of course be increased by increasing the ballast of the vessel 10V. Preliminary motion analysis of the vessel 10V indicates that when the vessel 10V is ballasted to a IOmeter draft the displacement is about 213,000 tonnes, ballasted to 14m draft the displacement is about 328,000 tonnes, and ballasted to 19m draft the displacement is about 452,000 tonnes. The preliminary analysis also indicates that the vessel 10V with a draft between 10m-19m is able to safely operate in 8 metre waves.

The vessel 10V can be resupplied at open sea from supply vessels 42. This means that the vessel 10A does not need to return to a port for reloading. One or more tugs (not shown in the present drawings) can be docked in one of the recesses 48 and used to assist the supply vessels when docking at the vessel 10V.

The benefits of the vessel 10A and the associated method of installation of wind turbine generators include the following:

Zero onshore port costs-no land is required assure for storage and preassembly of wind turbine generators. • Zero costs for onshore equipment (e.g. cranes, forklifts et cetera) for preassembly of wind turbine generators.

• Zero onshore port fees for feeder vessels bringing wind turbine generator components.

• Zero onshore port fees for current windfarm installation vessels; these are not required.

• Zero stevedoring costs at the onshore port front loading feeder vessels bringing in all reloading wind turbine generator components.

• Zero shipping costs for the onshore port to the windfarm and dead-time voyage back to the onshore port for reloading.

• The vessel 10A can safely operate in 8m waves/swell and in any depth of water.

• Minimises footprint in sensitive coastal areas.

• Reduction of handling operations and costs by delivering the wind turbine generator components directly to the vessel 10A at open sea.

• Reduction of the supply chain, time, costs and risks.

• Scalable.

• Can provide more than 50% savings on current costs for like-for-like installations.

Now that an embodiment has been described, it should be appreciated that the self- propelled floating structure 10 and its method of construction maybe embodied in many other forms. While the illustrated embodiment of the structure 10 shows it being made from three marine vessels as previously mentioned, any number of vessels may be used; also, there is no need for the number of vessels to be odd, and even number may be used. The present embodiment depicts the vessels 12 arranged in a side-by-side juxtaposition. However other embodiments are envisaged where the structure 10 includes a plurality of the vessels 12 some of which are arranged side-by-side but others they are arranged end to end, with the weather deck constructed to cover the entire area of all the vessels 12 and the spaces therebetween. For example, an embodiment of the self-propelled floating structure 10 may comprise six marine vessels arranged a first group of three vessels as shown in Figures 2 and 3, a second group of 3 vessels again as shown in Figures 2 and 3, coupling the first group to the second group in an end to end manner, and then constructing the weather deck to cover the entire area of all of the vessels and spaces therebetween. End to end juxtaposed vessels in such an embodiment may also be spaced apart from each other. These structures may be considered as comprising a linear X by Y matrix of marine vessels coupled together in a spaced apart manner and covered by a common weather deck. By spacing the marine vessels 12 apart the area of the weather deck of the structure 10 is of course greater than the sum of the area of the weather deck of each individual vessel 12.

In relation to the above described embodiments used for the installation of offshore wind turbine generators, cranes 50 may be provided with heave compensation systems for the purposes of either trans-shipment of equipment and parts from docked or other vessels 42, or for phases of the installation process where a generator 44 or mast 52 is being supported by the crane 50 and being fixed to the seabed or jacket. In a further variation the bays 48 shown in the embodiments of Figures 8-10 may be dimensioned or otherwise configured to form a dock for a supply vessel 42. In this variation when the structure 10 has a gantry crane 50 then the supply vessel 42 will be located between the legs of the gantry crane 50.

The above described WTGs are shown as being fixed to the seabed via a monopile. However, the disclosure is not limited to WTGs that are fixed to the seabed with a monopile. Accordingly, in addition to a monopile, the WTGs could be fixed to an ocean floor via a support structure such as gravity base, tripod, tripile, jacket or suction bucket. Optionally, the WTGs could be fixed to a floating structure such as a ballast stabilised spar buoy, mooring line stabilised tension leg platform or buoyancy stabilised barge with catenary mooring lines. The need to use a fixed or floating WTG structure is dependent upon the desired location and ocean characteristics for a WTG windfarm.

In some embodiments the self-propelled floating structure 10 can be provided with additional equipment including a drilling derrick, a submersible ROV, and/or other equipment required for installing jackets or foundations on the seabed.

In an embodiment, electricity generated by the wind energy production plant 10w or offshore wind farm 80 may be used to power a hydrogen and/or ammonia production plant that is positioned on the vessel 10. Hydrogen and/or ammonia storage tanks may be positioned in the under deck storage to store produced hydrogen and/or ammonia. When the vessel 10 is used to produce and optionally store hydrogen and/or ammonia, the vessel 10 may be used as a fuel bunkering vessel.

In an embodiment, production of hydrogen and/or ammonia can be obtained by installing one or more wind turbine generators on board the vessel 10. For example, a 20 MW WTG can be installed at a stern of the vessel 10 or at a similar location that would not imped access to the vessel and/or the weather deck 26. The installed wind turbines can produce the electricity required to generate hydrogen and/or ammonia, such as through electrolysis of water. The hydrogen and/or ammonia that is generated on the vessel 10 can be stored in in under deck space. Given the vessel 10 can have 770,000 m³ of under deck storage, the vessel 10 can store a significant quantity of hydrogen and/or ammonia under deck. The hydrogen and/or ammonia produced on the vessel 10 could be sold to third parties. For example, vessel 10 can acts as a marine port, and a hydrogen and/or ammonia transport vessel can dock along one side of the vessel 10 and a load of hydrogen and/or ammonia can be transferred from the vessel to the hydrogen and/or ammonia transport vessel. Put another way, vessel 10 can act as a renewably powered offshore gas production plant and gas terminal.

In the claims which follow, and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word “comprise” and variations such as “comprises” or “comprising” are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the system and method as disclosed herein.

Claims

1. A method of constructing a self-propelled floating structure comprising: coupling a plurality of marine vessels together in a side by side spaced apart manner, wherein at least one of the marine vessels comprises a propulsion system and each marine vessel comprises a hull; and forming a weather deck that spans the plurality of marine vessels and spaces between the marine vessels.

2. The method according to claim 1 wherein the coupling comprises coupling the mutually adjacent vessels together using a plurality of elongated structural members.

3. The method according to claim 2 comprising coupling the hulls of the mutually adjacent vessels together using the plurality of elongated structural members.

4. The method according to claim 3 comprising supporting or bracing a portion the weather deck that spans a space between two mutually adjacent marine vessels with a plurality of the elongated structural members.

5. The method according to any one of claims 1 -4 wherein the coupling comprises coupling a plurality of second hand marine vessels together.

6. The method according to any one of claims 1 -5 wherein the coupling comprises coupling marine vessels of the same type and size.

7. The method according to any one of claims 1 -5 wherein the coupling comprises coupling together a plurality of second hand (a) Cape size vessels, or (b) Supermax vessels, or (c) Ultramax vessels, or (d) Panamax vessels.

8. The method according to any one of claims 1 -7 comprising uniformly spacing the side- by-side spaced apart marine vessels.

9. The method according to any one of claims 1 -8 wherein coupling a plurality of marine vessels together in a side by side spaced apart manner comprises coupling a first group of marine vessels together in a side-by-side spaced apart manner, coupling a second group of marine vessels together in a side-by-side manner, and coupling the first group to the second group in an end to end manner.

10. The method according to any one of claims 1 -9 comprising removing a bridge from at least one of the plurality of vessels prior to forming the weather deck.

11 . The method according to claim 10 comprising fabricating or installing a control system enabling control of systems and utilities of all the vessels from a single bridge.

12. The method according to any one of claims 1 -11 comprising installing a dynamic positioning system on the self-propelled floating structure.

13. The method according to any one of claims 1 -12 comprising constructing the weather deck to have a surface area of at least 50,000 m².

14. The method according to any one of claims 1 -13 comprising constructing the weather deck of the surface area of at least 60,000 m².

15. The method according to any one of claims 1 -14 comprising constructing the weather deck to have a load strength of at least 25 tonnes per square metre.

16. The method according to any one of claims 1 -15 comprising forming a plurality of holes in the weather deck for receiving an elongate member and supporting the member so that an upper end of the member extends above the weather deck.

17. A method of providing an offshore renewable energy generation plant comprising installing a plurality of wind turbines on a self-propelled floating structure construct in accordance with the method of any one of claims 1 -16.

18. A self-propelled floating structure when constructed in accordance with any one of claims 1-16.

19. A self-propelled floating structure comprising: a plurality of marine vessels wherein at least one of the marine vessels is provided with a propulsion system, the marine vessels arranged in a side-by-side spaced apart manner; a plurality of elongated structural members coupling mutually adjacent marine vessels together; and a weather deck extending across the marine vessels and the elongated structural members.

20. The structure according to claim 19 wherein each of the marine vessels is a second hand or new marine vessel.

21 . The structure according to claim 19 or 20 wherein each marine vessel is a Cape size vessel, or a Supermax vessel, or an Ultramax vessel or a Panamax vessel.

22. The structure according to any one of claims 19-21 comprising a dynamic positioning system.

23. The structure according to any one of claims 19-22 comprising one or more cranes supported on the weather deck.

24. The structure according to claim 23 wherein one of the cranes is a gantry crane.

25. The structure according to any one of claims 19-24 wherein the weather deck comprises one or more bays.

26. The structure according to any one of claims 19-25 comprising a plurality of holes in the weather deck for receiving an elongate member and supporting the member so that an upper end of the member extends above the weather deck.

27. The structure according to claim 26 wherein the holes are formed to enable a lower end of the member received in the hole to be located below a water plane of a body of water in which the structure floats.

28. An offshore renewable energy generation plant comprising a self-propelled floating structure either (a) when constructed in accordance with any one of claims 1 -16 or (b) in accordance with any one of claims 19-27; and a plurality of wind turbines installed on the weather deck.

29. An offshore airport comprising a self-propelled floating structure either (a) when constructed in accordance with any one of claims 1 -15, or (b) in accordance with any one of claims 19-25; and one or more runways on the weather deck.

30. A method of constructing an offshore wind energy generation plant comprising: transferring separate wind turbine generator components onto the weather deck of a self-propelled floating structure; assembling the components to construct a wind turbine generator; and installing the wind turbine generator from the self-propelled floating structure at an offshore location.

31 . The method according to claim 31 wherein transferring separate wind turbine generator components comprises transferring the components directly from a separate supply vessel.

32. The method according to claim 31 comprising docking the supply vessel at the self- propelled floating structure.

33. The method according to any one of claims 30-32 wherein assembling the components comprises assembling the components on the weather deck of the self- propelled floating structure.

34. The method according to any one of claims 30-33 wherein installing the wind turbine generator comprises lifting the wind turbine generator as a single unit from the weather deck using a crane installed on the weather deck.

35. The method according to any one of claims 30-34 wherein the transferring comprises transferring the wind turbine generator components onto the weather deck of a self- propelled floating structure (a) when constructed in accordance with any one of claims 1 -15, or (b) in accordance with any one of claims 19-27.

36. A method of installing offshore wind turbine generator comprising: sailing a self-propelled vessel to a designated installation location in a body of water; from the vessel: a) installing a foundation structure in strata submerged in the body of water; b) fully fabricating on the vessel a wind turbine generator from at least two separate wind turbine generator components; and c) lifting the fabricated wind turbine generator onto the foundation structure using a crane on the vessel.

37. The method according to claim 36 wherein fully fabricating the wind turbine generator comprises fabricating a mast of the wind turbine generator from at least two separate mast components.

38. The method according to claim 37 comprising lowering one of the mast components into a first hole on the vessel and supporting the one component so that an upper portion of the first component is above the weather deck.

39. The method according to claim 36 wherein fully fabricating the wind turbine generator comprises lifting a mast section into a second hole in the weather deck and subsequently fitting a nacelle to the second mast section.

40. An offshore renewable energy generation plant comprising a self-propelled floating structure either (a) when constructed in accordance with any one of claims 1 -16 or (b) in accordance with any one of claims 19-27; a wind turbine installed on the weather deck; and a hydrogen and/or ammonia production plant.