Technical Field

[0001] The invention relates to a jack-up vessel for installing elongate construction elements offshore, in particular monopile foundations. Furthermore, the invention relates to a method for loading elongate construction elements on a deck of the jack-up vessel and a method for installing the elongate construction elements offshore.

Background Art

[0002] Offshore structures, for instance wind turbines, require a foundation system. Dependent on the local environmental conditions, such as the average water depth, soil conditions, or wave climate, a selection for the type of foundation system is made. For a water depth up to approximately 60m, typically a monopile foundation system is selected. A monopile normally comprises a hollow tubular structure made of steel, which can have a length between 30 and 130m and a weight up to 4000 Metric Tons. Typically, large vessels, such as jack-up vessels, are equipped with tub or mast lifting cranes to transport and install monopile foundations at offshore locations.

[0003] One example of a pile handling facility for such a vessel is described in patent document WO2021/245236 A1. This document discloses a monopile handling facility for tilting a monopile from a horizontal orientation on a deck of a vessel, to an upright orientation outside an outer boundary of the vessel’s hull. Laying down in a substantially horizontal orientation, the monopiles are extending in a direction perpendicular to the sailing direction such that the piles can easily be upended to the starboard side of the vessel, or the port side of the vessel, depending on the positioning of the upending tool. The monopile handling facility comprises a vessel deck suitable for carrying a monopile, a lifting crane fixed to the vessel, an upending tool, and a winch system.

[0004] A disadvantage of this monopile handling facility is that, once the pile is at the outer boundary of the deck, it is difficult to have access to the monopile from all directions, which increases the risk on the construction crew as they are required to work overboard during installation. Another disadvantage is that, due to the size and weight of the monopiles, a large crane and a complex upending and/or gripper tool are required to upend the monopile and to keep the monopile within the required vertical tolerance. This makes the purchase of the handling facility expensive.

[0005] It is an objective of the invention to provide an installation vessel and/or installation method for elongate construction elements such as monopile foundations that increases the safety forthe construction crew during installation of the foundation structure and/or reduces the purchase costs of the installation equipment to provide a more economical solution.

Summary of Invention

[0006] Therefore, according to a first aspect of the invention, there is provided a jack-up vessel for the installation of a wind turbine foundation system offshore. The foundation system includes at least an elongate construction element, and the vessel comprises: a support for supporting the elongate construction element on a deck of the vessel in a longitudinal direction of the vessel; and a crane assembly comprising at least two cranes configured for lifting the elongate construction element, wherein the at least two cranes are arranged to move along a longitudinal direction of the vessel and wherein the at least two cranes are arranged to move with respect to each other along the longitudinal direction of the vessel; the vessel further comprising a gripper tool arranged to hold the elongate construction element during an upending of the elongate construction element at a stern side of the vessel.

[0007] In this context, the term “vessel” is used to indicate both self-propelling vessels and barges that can be tugged using a tugboat. Advantageous to the use of a jack-up self-propelling vessel or jack-up barge is that a good stability of the vessel can be reached during installation of the elongate construction element. As such, the gripper tool that is arranged to hold the elongate construction element during an upending of the elongate construction element at a stern side of the vessel may have a relatively simple design.

[0008] In this context, the crane assembly comprising at least two cranes includes the structure that carries the at least two cranes and the at least two cranes. The at least two cranes are moveably mounted with respect to each other, and free to move along a longitudinal direction of the vessel. The at least two cranes are preferably equipped with a hook, sling, lifting frame of other attachment means to enable engagement of the cranes to the elongate construction element. These attachment means can be moved in a vertical direction, substantially perpendicular to the deck of the vessel, to lift up the elongate construction elements and/or other wind turbine foundation elements and equipment. Typically, the attachment means of the two cranes can be independently operated from each other and moved with respect to each other in a vertical direction perpendicular to the deck of the vessel.

[0009] The crane assembly and the gripper tool are arranged to upend the elongate construction element at a stern side of the vessel. Additional upending equipment may be provided in addition to, or as part of the crane assembly.

[0010] In this context the term “elongate construction element” is used to indicate any element having a length that is at least twice the size of its diameter for construction elements having a circular cross section, or twice the size of its maximum width for construction elements having an arbitrary cross-sectional area. The elongate construction element may for instance be a jacket structure, a monopile, a transition piece for a foundation structure, or a secondary steel element for the monopile foundation system, such as a boat landing, ladder or platform that may be required for the safe access and operation of the wind turbine.

[0011] In an embodiment, the elongate construction element is a monopile. Monopiles are conventionally used for the installation of wind turbine foundations offshore and typically have a length between 30 and 130 m, with a hollow circular cross-section with a diameter between 8m and 15m. Nevertheless, it will be understood by the skilled person that the length and width or diameter of the monopile may depend on the environmental conditions at the installation site and the turbine to be installed on the foundation. The monopile may be supported on deck of the vessel by the upending equipment or by a separate support.

[0012] Advantageously, the elongate construction element is supported on deck of the vessel in a longitudinal direction of the vessel during transport. Here a longitudinal direction of the vessel is defined as the direction connecting the stern and bow of the vessel. The transverse direction of the vessel is defined as the direction perpendicular to the longitudinal direction. Advantageous to placing the elongate construction elements in a longitudinal direction on deck of the vessel is that for relatively long construction elements, the construction elements do not extend beyond the hull of the vessel in a transverse direction. Typically, the width of a large offshore vessel is approximately 1/3 of its length and therefore arranging the construction elements in the longitudinal direction enables the arrangement of long construction elements within the boundaries of the hull. On conventional installation vessels such as the one disclosed in patent document WO2021/245236 A1 , the elongate construction elements are typically carried while extending in a transverse direction. As the construction elements are typically longer than the vessel is wide, they extend from both sides of the vessel, increasing the overall width of the vessel. This prevents the vessel’s access to certain harbours where for instance a relatively narrow fairway is present, or where large vessels are simply not allowed because of safety regulations. Hence an advantage of the jack-up vessel according to the invention is that access to certain harbors or parts of a harbor is permitted that are not accessible for installation vessels according to the prior art. It will be understood by the skilled person that the improved accessibility of harbors may in certain projects lead to a significant reduction of installation costs as harbors closer to the installation site may be selected to load the construction elements, minimizing the time spent on transportation of construction elements from the harbor to the installation site.

[0013] In an embodiment, the crane assembly extends beyond the stern of the vessel and at least one of the two cranes is configured to lift the elongate construction element from a position beyond the stern of the vessel. Here the stern of the vessel is defined as the stern of a hull of the vessel. Advantageously, the overhead crane assembly can be used to load the elongate construction elements) and other foundation installation equipment onto the vessel since also an area behind the stern of the vessel is within reach of at least one of the cranes. Known installation vessels are typically loaded using external cranes in the harbor or by crane ships on the water. Alternatively, ships may have their own cranes on the port side and/or starboard side of the ship for loading and unloading the ship to the respective side. It will be understood that using the same crane assembly for both the installation of an elongate construction element as well as loading the elongate elements on deck of the vessel reduces the overall costs of the equipment on the vessel and/or in the harbor. In embodiments, more than one crane is configured to move beyond the stern of the vessel.

[0014] In an embodiment, the crane assembly is an overhead crane assembly. Alternatively, for instance a rail-mounted gantry crane may be used. Advantageous to the use of an overhead crane assembly instead of a gantry crane is that less space on deck of the vessel is required. A railmounted gantry crane requires the trajectory of the rail to be free to enable the gantry crane to move, whereas an overhead crane does not have this restriction and allows for optimal use of the deck space.

[0015] In an embodiment, the overhead crane assembly comprises a first pair of supporting legs provided on a starboard side of the vessel and a first overhead beam supported by the first pair of supporting legs; a second pair of supporting legs provided on a port side of the vessel and a second overhead beam supported by the second pair of supporting legs, the second overhead beam being substantially parallel to the first overhead beam; wherein the at least two cranes are arranged between the first overhead beam and the second overhead beam. Each of the cranes may independently move along the extent of the first overhead beam and second overhead beam in a longitudinal direction of the vessel. In an embodiment wherein the crane assembly extends beyond the stern of the vessel, the first and second overhead beam extend beyond the stern of the vessel. This allows at least one of the cranes to move beyond the stern side of the vessel and load the elongate construction elements on the deck of the vessel.

[0016] In an embodiment, each of the at least two cranes is provided with a crane block with lifting means for lifting the elongate construction elements. Preferably, the blocks are moveably arranged in a transverse direction of the vessel, wherein the transverse direction is perpendicular to the longitudinal direction. This provides more flexibility to carry out operations on the vessel.

[0017] In an embodiment, at least one of the at least two cranes is provided with a plurality of crane blocks with lifting means for lifting the elongate construction elements, wherein the plurality of crane blocks are moveable with respect to each other in a transverse direction, the transverse direction being perpendicular to the longitudinal direction of the vessel. Advantageous to a plurality of crane blocks is that multiple actions can be performed simultaneously. This improves the loading speed of construction elements on the deck of the vessel and/or the installation speed of the construction element, thereby reducing the required time and associated costs. Specifically advantageous to an overhead crane assembly is that during the design phase, additional cranes and/or crane blocks can be added at negligibly low costs in comparison to the costs of adding an additional tub or mast crane on a conventional jack-up installation vessels.

[0018] In an embodiment, the first overhead beam and second overhead beam are spaced from the deck of the vessel over a distance between 20m and 60m. The arrangement of the overhead crane assembly must provide enough height to enable the upending of elongate construction elements using the overhead crane assembly. The height of the crane assembly and the distance of the first and second overhead beams with respect to the deck is thereby dependent on the length of the elongate construction element that the vessel is designed the install.

[0019] In an embodiment, the vessel comprises one or more additional supports for supporting one or more additional elongate construction elements on the deck of the vessel. Typically, the vessel is configured to support between two and four elongate construction elements. Nevertheless, in embodiments also only one or more than four elongate construction elements may be supported on deck of the vessel. In embodiments, all elongate construction elements are provided substantially parallel to each other. Alternatively or in addition, and particularly when the elongate construction elements are relatively short in comparison to the length of the vessel, a plurality of construction elements and additional construction elements may also be arranged in line with each other.

[0020] In an embodiment, the vessel is further configured to carry other components of the wind turbine foundation system, for example a transition piece or secondary steel. This enables the installation of a full wind turbine foundation system using the jack-up installation vessel.

[0021] In an embodiment, the cranes are configured to lift an additional elongate construction element of the one or more additional elongate construction elements into the upending equipment. In embodiments wherein two or more elongate construction elements can be supported on deck of the vessel the first lifting means and/or second lifting means are configured to move each of these elongate constructions elements from their respective supports into the upending equipment. In such embodiments, the cranes or crane blocks are typically moveable both along the longitudinal direction of the vessel as well as along the transverse direction.

[0022] In an embodiment, the vessel further comprises an installation bay at a stern side of the vessel configured for installing the elongate construction element, wherein the upending equipment is arranged on the deck of the vessel to upend the elongate construction element in the installation bay. In this context the term “installation bay” is used to indicate an inlet at the stern side of the vessel that is at least partially enclosed by an outer boundary of the vessel’s hull. The installation bay is configured for installing the elongate construction element. This means that the installation bay is at least dimensioned to enable the upending of the elongate construction element within the installation bay. Typically, the installation bay has a width that equals a maximum diameter or width of the elongate construction element, and at least an additional five meters on both sides of the elongate construction element. It will be understood though that this may vary in embodiments. For example, the additional space required in the installation bay may be dependent on the type and size of the equipment used for the upending and installation of the elongate construction element. Moreover, the required space in the installation bay may be dependent on safety regulations. Alternatively, the elongate construction element may be upended beyond the stern side of the vessel. In this context, upending the elongate construction element at a stern side of the vessel refers to both the upending of the elongate construction element in an installation bay at the stern side of the vessel, as well as beyond the stern side of the vessel.

[0023] Advantageous to the crane assembly in combination with the installation bay at the stern side of the vessel is that the elongate construction elements can be easily installed through the installation bay. The cranes may lift the elongate construction element and upend it by rotation around an axis perpendicular to the longitudinal direction of the vessel using the upending equipment. The type of crane suitable for upending the elongate construction element in this way, may be significantly less expensive than the heavy lifting cranes on conventional jack-up installation vessels that upend the construction elements over a board of the vessel. Consequently, the overall purchase costs of the installation equipment, or the vessel including the installation equipment may be significantly reduced.

[0024] In addition, the presence of an installation bay provides a safer working environment for construction crew. Easy access is provided to the circumference of the elongate construction element for any crew member standing on deck of the vessel. In this way, access to the installed elongated construction element and other parts of the foundation system, for instance to the transition piece and secondary steel elements, is provided from at least three sides of the installation bay. This creates a safe environment for the offshore construction crew due to the avoidance of overboard work when completing activities around the foundation structure, such as bolting activities.

[0025] In an embodiment, the installation bay is provided asymmetrically with respect to a centerline of the vessel. It will be understood that for the distribution of weight on deck of the vessel, the elongate construction elements are preferably placed substantially symmetrical around the centerline of the vessel. Preferably, the installation bay is aligned with one of the elongate construction elements when the construction element is supported in the upending equipment. Hence in embodiments wherein an even number of elongate elements are transported parallel to each other and arranged substantially symmetrically on deck of the vessel, the installation bay is typically provided asymmetrically to a centerline of the vessel. Alignment of an elongate construction element with the installation bay enables the elongate construction element to be upended into the installation bay without moving the elongate construction element first. In embodiments, at least one of the elongate construction elements is supported in the upending equipment or gripper tool during transport.

[0026] Further advantageous to the asymmetric placement of the installation bay is that a large storage space on deck of the vessel adjacent to the installation bay is provided. On large offshore vessels, deck space is typically valuable and providing a large storage space on one side of the installation bay instead of multiple smaller spaces on both sides of a symmetrically arranged installation bay allows for optimal use of the available deck space. The storage space may for instance be used for storing other installation equipment, such as hammering equipment. [0027] In an embodiment, the jack-up vessel further comprises a bridging element configured to selectively open or close the installation bay. The installation bay has an open side at the stern side of the vessel and may be provided with a bridging element to selectively open or close the open side of the installation bay. The bridging element may thereby be used to provide access to the installed elongate instruction element and other parts of the foundation structure from all sides of the installation bay. This further improves the safe environment for the offshore construction crew to carry out completion activities around the foundation structure.

[0028] In an embodiment, the jack-up vessel further comprises hammering equipment for driving the elongate construction element into the sea bed. It will be understood by the skilled person that the necessity for hammering equipment and the selected type of hammering equipment may depend on the specific conditions at the installation site and the associated project-dependent specifics such as the length and type of elongate element. The hammering equipment may be permanently installed on deck of the vessel or may be loaded on deck of the vessel for a specific project. In an embodiment, the hammering equipment is a vibration hammer or an impact hammer and loaded onto the deck of the vessel at the start of a project.

[0029] In an embodiment, the jack-up vessel is configured to transport elongate construction elements having a length of at least 30 m, optionally at least 40 m, or at least 50 m, in a longitudinal direction of the vessel. It will be understood though that the vessel design can be scaled also for other lengths of the elongate construction element. In embodiments, the jack-up vessel may be configured to transport elongate construction elements having a length of at least 60 m, at least 80 m, at least 100m, at least 120m or at least 140m. To that end, in embodiments, the jack-up vessel has a length of between 80 and 190 m. For relatively short elongate construction elements, e.g., construction elements having a length up to 30 m, up to 40 m, up to 50 m, or up to 60 m, a plurality of construction elements may be provided aligned with each other along the longitudinal direction during transportation on deck of the vessel.

[0030] It will be understood by the skilled person that the selected length of an elongate construction element, such as a monopile, is determined by the installation location. In embodiments, the length of the elongate construction element with respect to an average water depth is at least 1 , or 1 .2, or 1 .5.

[0031] In an embodiment, the vessel is configured to support an elongate construction element having a length of at least the width of the vessel, optionally at least 1 .5 times the width of the vessel, or at least twice the width of the vessel. Specifically for elongate construction elements that are longer than the width of the vessel the advantage of transporting the elongate construction elements in a longitudinal direction of the vessel becomes significant.

[0032] According to a second aspect of the invention, and in accordance with the advantages and effects described herein above, there is provided a method for loading an elongate construction element on the deck of a jack-up vessel according to the first aspect of the invention, wherein the method comprises using the crane assembly to arrange an elongate element on deck of the vessel. Advantageously, the elongate construction elements are quickly loaded on deck of the vessel using the same crane assembly that can be used for installing the elongate construction elements offshore. This reduces the overall investment that needs to be made to complete an offshore windfarm installation project.

[0033] In an embodiment, the elongate construction element is provided on a quay side, and the method further comprises maneuvering the vessel with its stern side towards the quay side; arranging the elongate construction element on the quay side within reach of the at least two cranes of the vessel; lifting the elongate construction element from the quay side using the at least two cranes; and operating the crane assembly to arrange the elongate element on deck of the vessel. Typically, the elongate construction elements are provided on a quay side in a harbor.

[0034] In an embodiment, the elongate structure is provided on the quay side on a transporter, and the step of operating the crane assembly to move the elongate element on deck of the vessel comprises establishing a connection between the first crane of the crane assembly and the elongate construction element; moving the transporter towards an end of the quay side and towards the vessel to push the elongate construction element toward the vessel; establishing a connection between the second crane of the crane assembly and the elongate construction element; and operating the first and second cranes to load the elongate element on deck of the vessel. The transporter is typically a self-propelled modular transporter (SPMT), but may also be a different type of transporter. The connections between the first crane and second crane on the one hand, and the elongate construction element on the other hand, may be obtained by attachment means provided on for instance the end of the construction element, or through external attachment means such as slings or lifting frames that can be connected around or to the construction element.

[0035] In an embodiment, the method further comprises jacking up the vessel on the seabed before loading the elongate construction element on deck of the vessel, and jacking down the vessel after completion of the loading process. Jacking up the vessel provides optimal stability to the vessel during the process of loading of the elongate construction element and/or other equipment onto the deck of the vessel. Moreover, the deck of the jack-up vessel can be levelled with a top surface of the quay side, or another surface carrying the elongate construction elements. This further eases and accelerates the loading process.

[0036] According to a third aspect of the invention, and in accordance with the advantages and effects described herein above, there is provided a method for loading components of an offshore windfarm installation system on deck of a jack-up vessel. The method comprises loading an elongate construction element according to the method of the invention and loading a transition piece, secondary steel and/or hammering equipment on deck of the vessel using the crane assembly.

[0037] According to a fourth aspect of the invention, and in accordance with the advantages and effects described herein above, there is provided a method for installing a wind turbine foundation system offshore. The method comprises providing a jack-up vessel according to the invention, the jack-up vessel supporting an elongate construction element extending in a longitudinal direction of the vessel; upending the elongate construction element at a stern side of the vessel using the gripper tool and the crane assembly; and arranging the elongate construction element into or onto the sea bed. In addition to the gripper tool, other upending equipment may be used for upending the elongate construction element

[0038] In an embodiment, the jack-up vessel comprises an installation bay at a stern side of the vessel, and the method comprises upending the elongate construction element in the installation bay at the stern side of the vessel.

[0039] In an embodiment, the elongate construction element is a monopile. The method further comprises arranging a transition piece on top of the monopile; or connecting a secondary steel to the monopile. The transition piece or secondary steel may be arranged on top of the monopile using the same crane assembly.

[0040] In an embodiment, the method further comprises jacking up the vessel on the seabed before upending the elongate construction element and jacking down the vessel after installing the wind turbine foundation system. By jacking up the vessel on the seabed before upending the elongate construction element, a stable position of the vessel is achieved. In general, a jack-up vessel has a better stability than other types of vessels such as catamaran vessels that actively need to maintain position during the installation of structures, for instance using a dynamic positioning system. This allows for the use of the installation vessel in more challenging environmental conditions.

[0041] According to a further aspect of the invention, and in accordance with the advantages and effects described herein above, there is provided the use of an overhead crane assembly or a gantry crane on a jack-up installation vessel for installing a monopile foundation system. Specifically advantageous is that the same overhead crane assembly or gantry crane may be used for loading elongate construction elements onto the vessel, for upending the elongate construction element, and/or for installing the elongate construction element into the sea bed.

Brief Description of Drawings

[0042] Embodiments will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts. In the drawings, like numerals designate like elements. Multiple instances of an element may each include separate letters appended to the reference number. For example, two instances of a particular element “20” may be labeled as “20a” and “20b”. The reference number may be used without an appended letter (e.g. “20”) to generally refer to an unspecified instance or to all instances of that element, while the reference number will include an appended letter (e.g. “20a”) to refer to a specific instance of the element.

[0043] Figure 1 A schematically shows a top view of a jack-up vessel provided with an installation assembly according to a first embodiment of the invention. [0044] Figure 1 B schematically shows a side view of the jack-up vessel in Fig. 1A.

[0045] Figure 2A-2C schematically illustrate steps of a method of loading monopiles onto the jack-up vessel according to the embodiment in Fig. 1A-1 B.

[0046] Figure 3A-3C schematically illustrate steps of a method of installing a monopile in the sea bed using the jack-up vessel according to the embodiment in Fig. 1 A-1 B.

[0047] The figures are meant for illustrative purposes only, and do not serve as restriction of the scope or the protection as laid down by the claims.

Description of Embodiments

[0048] The following is a description of certain embodiments of the invention, given by way of example only and with reference to the figures.

[0049] Figures 1A and 1 B show a top view, respectively a side view of a jack-up vessel 1 according to the invention. The vessel 1 has a hull 10 extending along a longitudinal axis X between a bow side 11 and stern side 12. The vessel 1 further has a port side 13 and starboard side 14, spaced from each other along a transverse axis Y perpendicular to the longitudinal axis X. The vessel 1 is further provided with a deck 15 and a plurality of jacking systems 16 with jack-up legs 17 at each of the port side 13 and the starboard side 14 that extend through the hull 10 and the deck 15. The vessel 1 has a length h of approximately 150 m and a width wi of approximately 47m. The jack-up legs 17 each are approximately 90 m long, thereby making the vessel 1 suitable to jack up at locations having a water depth up to approximately 60 m. It will be understood, however, that the vessel 1 is scalable and that these measures are only indicative. The vessel 1 is further provided with a propulsion arrangement (not shown) below the hull 10 to make the vessel 1 self-propelling.

[0050] On the deck 15 of the vessel 1 , a windfarm installation assembly 8 is provided. The installation assembly 8 comprises an overhead crane assembly 3 with a first overhead beam 37a, a second overhead beam 37b, cross-beams 38, a front crane 31 , an aft crane 32, a port side front crane block 33, a starboard side front crane block 34, a port side aft crane block 35, and a starboard side aft crane block 36. The installation assembly 8 further comprises upending equipment 4 with a gripper 41 and a plurality of supports 5a, 5b for holding monopiles and/or other elongate construction elements on the deck 15 during transport. At the stern side 12 of the vessel 1 , an installation bay 2 with a first side 21 , a second side 22, and a front side 23 is provided.

[0051] The plurality of jacking systems 16 with jack-up legs 17 provide the vessel 1 with a selfelevating function and enable anchoring of the vessel 1 to the sea bed 51 on an installation site. The jack up systems 16 allow the vessel 1 to quickly convert itself from a self-propelling vessel 1 to a stable installation site at open sea and vice versa. The jack-up legs 17 are approximately 90 m long and can be extended to lift the vessel 1 above the water level at the installation site. The water level 52 at the installation site may for example be approximately 50 m deep. In the harbor, the water depth may be different and the jack-up legs can be extended to facilitate a preferable height of the deck 15 to load elongate construction elements or other installation equipment onto the vessel 1 . Jack-up vessels are thereby particularly suited for the installation of wind turbine foundation systems in environments with all sorts of wave climates and water depths, unlike smaller vessels such as catamarans that may only be used in a more limited range of situations with moderate wind and wave conditions.

[0052] The installation bay 2 is provided asymmetrically with respect to a centerline of the vessel 1 and leaves sufficient space 6 on the starboard side 14 of the vessel 1 for temporary storage of installation equipment such as the hammering equipment 60. The angles between the first side 21 and second sides 22 of the installation bay 2 with respect to the front side 23 may be right angles of approximately 90 degrees, yet it will be understood that the installation bay 2 may also have a polygon shape as depicted in Fig. 1A, or a circular shape. The width W2 of the installation bay 2, as measured between the first side 21 and second side 22, is approximately 25 m. Consequently, the installation bay 2 has a suitable size for the upending and installation of monopiles with a diameter up to 13 m. The installation bay 2 thereby enables installation of monopiles from the stern side 12 of the vessel 1 , in contrast with conventional vessels where installation takes place over a board of the vessel 1 .

[0053] Advantageously, there is access to the installation bay 2 from three different sides 21 , 22, 23 on the deck 15 of the vessel 1 . This provides a safe and easy access for construction crew to the monopile foundation system, for instance to carry out completion activities of the foundation system installed by the vessel 1 , such as for bolting activities.

[0054] The overhead crane assembly 3 comprises two beams 37a, 37b extending along the port side 13 and starboard side 14 of the vessel 1. Between the beams 37a, 37b, two cross-beams 38 are arranged for the stability of the crane assembly 3. The front crane 31 and aft crane 32 are arranged to move along the longitudinal direction X of the vessel 1 , and between the two crossbeams 38. The front crane 31 is provided with a port side front crane block 33 and a starboard side front crane block 34. Similarly, the aft crane 32 is provided with a port side aft crane block 35 and a starboard side aft crane block 36. The beams 37 extend beyond the stern side 12 of the vessel over a distance h of approximately 25 m, thereby enabling both the aft crane 32 and the front crane 31 to be positioned above the installation bay 2 and beyond the stern side 12 of the vessel 1. Movement of the cranes 31 ,32 above the installation bay 2 provides easy access to the foundation structure from above, for instance to carry out hammering activities. Movement of the cranes 31 ,32 to a position beyond the stern side 12 of the hull 10 eases the loading of construction elements and other windfarm installation equipment on the deck 15 of the vessel 1.

[0055] The beams 37 are spaced from the deck at a distance h of approximately 53 m. At this level, the overhead cranes 33, 34, 35, 36 are provided with enough freedom of movement to enable the upending of monopiles having a length up to 130 m. It will be understood by the skilled person that preferably the total height of the windfarm installation assembly 8 is kept as low as possible to improve the stability of the vessel 1 . [0056] The vessel 1 according to the first embodiment has the capacity to carry two monopiles at a time. A first monopile may during transport be arranged in the upending equipment 4 with gripper tool 41 and on one of the supports 5a at the port side 13 of the vessel 1 . A second monopile may be arranged on the other supports 5b at the starboard side 14 of the vessel 1 .

[0057] The windfarm installation assembly 8 is significantly less expensive to purchase than a conventional installation assembly comprising tub or mast lifting cranes for the installation of monopiles. Specifically, an overhead crane assembly 3 is relatively cheap in comparison to the conventionally used types of lifting crane. A further advantage of the vessel 1 is that monopiles and other construction elements may easily be loaded on deck 15 of the vessel 1 using the overhead crane assembly 3. This loading method is schematically illustrated in Fig. 2A-2C. A wind turbine foundation installation method is illustrated afterwards, in Fig. 3A-3C.

[0058] Figures 2A-2C schematically illustrate a first embodiment of a method of loading elongate construction elements such as monopiles 9 onto the vessel 1 according to the embodiment in Fig. 1A-1 B. Fig. 2A shows an empty vessel 1 approaching a quay-side 10. Two monopiles 9, hammering equipment 60 and two transition pieces 43 are provided on the quay side 40, ready to be loaded on the deck 15 of the vessel 1. The monopiles 9 are provided in a horizontal position at the quay side 10, on quay supports 44. In addition, a plurality of self-propelled modular transporters (SPMTs) 42 are present on the quay side 10. These SPMTs 42 can be used to move the monopiles 9 on the quay side 10 and bring them to an optimal position for being loaded on deck 15 of the vessel 1 .

[0059] When the vessel 1 approaches the quay side 10, it maneuvers in a reverse direction to arrange the opening in the installation bay 2 adjacent to the quay side 10, and arranges at least part of the crane assembly 3 arranged above the quay side 10 such that when the cranes 31 , 32 are moved to the stern side 12 of the vessel 1 , the windfarm installation components on the quay side 10 such as the monopiles 9 and transition pieces 43 are within reach of the cranes 31 ,32. Once in position, the vessel 1 may moor by extending the jack-up legs 17 of the respective jacking systems 16 to elevate the deck 15 to match an optimal loading level wherein only a substantially horizontal displacement of the monopiles 9 is required to load them onto the deck 15. This allows the monopiles 9 to be brought onto the deck 15 without having to lift them over large height differences.

[0060] The SPMTs 42 are height adjustable and can reach below the monopiles 9 in between the supports 44 to lift up a monopile 9 from below. One or more SPMTs 42 lift up the monopile 9 and transport it across the quay side 10 until it is within reach of the cranes 31 ,32 to be picked up. [0061] Fig. 2B shows a further step of a method for loading a monopile 9 on the deck 15. The jack-up legs 17 have extended, providing a stable position of the vessel 1 with respect to the quay side 10. In addition, the transition pieces 43 have been loaded on the deck 15 of the vessel 1 using the overhead crane assembly 3. [0062] At the quay side 10, the first monopile 9b has been moved to a loading position by an SPMT 42. The port side front crane block 33 is provided with a hook that has been connected to an attachment means (not shown) near a top end of the first monopile 9b. It will be understood by the skilled person that many ways of establishing such a connection are known.

[0063] Subsequently, one of the SPMTs 42a, closest to the water, has released its support to the monopile 9b and was moved away. The second SPMT 42b has moved into the former position of the first SPMT 42a, thereby pushing the monopile 9b partially on board of the vessel 1. The port side aft crane block 35, provided with a lifting frame 27, then lifts up the monopile 9b at a second position along its length. Again, it will be understood by the skilled person that there are other appropriate alternative lifting means available for lifting the monopile 9b using the port side aft crane block 35. After the monopile 9b has been lifted by both cranes 31 ,32, the monopile is moved onto the deck 15 of the vessel 1 and into the upending equipment 4 and one of the supports 5a. Afterwards, the second monopile 9b is brought onto the deck 15, in the other supports 5b, using the same method. As the crane blocks 33, 34, 35, 36 can move in a transverse direction, both the first and second monopile 9a, 9b can be brought on deck 15 using any combination of a front crane block 33,34 and an aft crane block 35,36. Hence the port side crane blocks 33, 35 may also be used to load the second monopile 9a. Afterwards, also the hammering equipment 60 is loaded onto the vessel 1 .

[0064] Fig. 2C shows the vessel 1 after the monopiles 9 and other foundation installation equipment including the transition pieces 43 and hammering equipment 60 has been loaded. The vessel 1 has jacked down by retracting the jack-up legs 17 and has started sailing towards the installation location. Consequent to the arrangement of the monopiles 9 in a longitudinal direction on the deck 15, the overall width of the vessel 1 is comprehensible and limited to the width of the hull 10. This allows the vessel 1 to navigate and access relatively narrow harbors. Advantageously, this means that for certain projects it may be possible to select a harbor closer to the installation site than what would have been possible using a conventional installation vessel wherein the monopiles are transported in a transverse direction, partially extending beyond the width of the vessel. This may significantly reduce the time spent on the transportation of the monopiles 9 from the harbor to the installation site.

[0065] At the installation location, the vessel 1 will perform station keeping by means of a dynamic positioning system and will jack-up. After that, the installation of a wind turbine foundation system as shown in Fig. 3A-3C can start.

[0066] Fig. 3A-3C schematically illustrate a method of installing a foundation system in the sea bed according to an embodiment of the invention.

[0067] Fig. 3A shows the upending of a monopile 9 at the installation site after the vessel 1 has jacked-up. The deck 15 of the vessel 1 extends above the water level 52. The monopile 9 is upended within the installation bay 2 using the front port side crane block 33 and upending equipment 4. [0068] Fig. 3B shows the placement of a monopile 9 on the seabed 52 after upending it. Under its own weight, and being stabilized by the upending equipment 4, the monopile 9 penetrates the sea-bed 52 over an initial penetration depth. It will be understood by the skilled person that this initial penetration depth is both dependent on the composition of the seabed 52, as well as on the weight of the monopile 9. The aft crane 32 simultaneously lifts the hammering equipment 60 (schematically indicated) using both the port side aft crane block 35 and the starboard side aft crane block 36 to arrange the hammering equipment 60 on a top side of the monopile 9 and drive the monopile 9 up to a final penetration depth. The hammering equipment 60 comprises an impact hammer. After the monopile 9 is installed, the hammering equipment 60 is lifted by the aft crane 32 and placed back on deck 15 of the vessel 1 .

[0069] Fig. 3C shows the release of the monopile 9 by the aft crane 32 and the preparation of the installation of a transition piece 43. While the aft crane 32 removes the hammering equipment 60, the front crane 31 is used to lift the transition piece 43 for installation onto the monopile 9. Advantageous to the use of at least two cranes, each having a plurality of crane blocks, is that these steps can be performed simultaneously. One of the front crane blocks 33, 34 may already pick up the transition piece 43 while one of the aft crane blocks 35,56 is still occupied with handling the hammering equipment 60. The skilled person will understand that using the same equipment also a second steel may be arranged on top of the monopile, instead of a transition piece.

[0070] Once the installation of one monopile foundation including a monopile 9 and a transition piece 43 has been completed, the vessel 1 jacks down and sails to the next location to repeat the method and install the second monopile 9b that is provided on the deck 15. The method for installing a foundation system in the seabed is repeated. Prior to upending the monopile 9, the cranes 31 , 32 are operated to lift the second monopile 9 from the supports 5b into the upending equipment 4. Once all monopiles 9 that were originally on the deck 15 have been installed into the sea bed, the vessel 1 may sail back to the quay side 10 to load new foundation elements.

[0071] The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. It will be apparent to the person skilled in the art that alternative and equivalent embodiments of the invention can be conceived and reduced to practice. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.