The invention relates to an installation follower for installing plate anchors for floating wind turbines of a wind farm, an anchoring assembly, and a method for installing multiple plate anchors into the seabed in a single anchoring operation using an installation follower.

It is submitted that more and more wind turbines are installed offshore, and more and more of these wind turbines are of the floating type. These floating wind turbines need to be moored to the seabed to keep their position. Therefore, offshore wind farms are provided with arrays of anchor points, to enable the mooring of rows upon rows of floating wind turbines.

It is known to use plate anchors for providing these anchor points. These plate anchors are driven into the seabed using an installation follower. After the plate anchor is in a vertical position driven into the seabed, it is rotated, also referred to as keying, into an anchoring position by pulling a mooring chain attached to the plate anchor via a shank. Once it is in the correct anchoring position, a plate, also referred to as fluke, of the plate anchor is substantially perpendicular to the direction of loading of the mooring line. This increases the soil resistance of the plate anchor, an provides optimal grip for supporting a mooring chain. The plate anchors typically comprise a plate and a shank mounted to the plate, the shank supporting an attachment point for the mooring line. In some cases, the mooring line is used to key the plate anchor. In other cases, a separate key line, the key line not being the mooring line, is connected to the plate anchor for keying the plate anchor.

An installation follower for installing a plate anchor is known from EP1462356, which discloses a plate anchor for embedment in a mooring bed. The plate anchor is attached generally to a mooring line for connection to an object to be restrained by mooring in a body of water over the mooring bed. The plate anchor includes a load application point for the attachment of the mooring line thereto via mooring line attachment means (for example, a shackle) and a fluke member and includes a plane of symmetry containing a first direction in which the surface of the fluke member viewable from the load application point when the anchor is in operation has a maximum projected area and a second (forward) direction (F) in which said surface has a minimum projected area. Correspondingly, in these directions maximum and substantially minimum resistance to movement of the anchor in a mooring bed soil occurs. The anchor fluke tends to advance in the soil along the forward direction (F) of minimum resistance. A direct embedment anchor for example is a marine anchor as described above which has an mooring line attachment means load application point located such that pulling on the attached mooring line causes the anchor to tend to move in the direction of maximum projected area of the fluke member when buried in the mooring bed soil. This causes the embedded anchor to follow a path that rises to and breaks out through the mooring bed surface and so prevents the anchor line and anchor line attachment means from functioning as the embedment means of the anchor. An embedment means is therefore employed which comprises a pushing member, known as a follower, to engage with and push the anchor deep into the mooring bed soil substantially in the forward direction of minimum projected area of the fluke member.

It is generally known to embed plate anchors using suction anchors. These are so called suction-embedded plate anchors, also referred to as SEPLA.

An installation follower for installing a plate anchor is known from US2014079489. In this document an installation follower embodied as a suction follower is disclosed with an anchor docking station for holding a plate anchor provided at a lower end of the suction follower.

It is an object of the invention to provide an alternative installation follower. It is a further object of the invention to provide an installation follower that facilitates convenient and reliable installation of plate anchors for floating wind turbines of a wind farm.

This object is achieved with an installation follower for installing anchor points for floating wind turbines of a wind farm according to claim 1.

The invention provides an installation follower for installing plate anchors for floating wind turbines of a wind farm, wherein each of the plate anchors comprises a plate and a shank for attaching a mooring line, and wherein the installation follower has a hollow elongate body with a top end for driving the installation follower into the seabed, a bottom end for holding multiple plate anchors, and a central axis extending between the top end and the bottom end, wherein the follower is at the bottom end provided with three or more docking stations arranged for holding the plate anchors parallel to the central axis and preferably uniformly distributed along a circumference of the installation follower. The installation follower according to the invention facilitates convenient and reliable installation of plate anchors for floating wind turbines of a wind farm. The docking stations being arranged for holding the plate anchors allow for driving multiple plate anchors into the seabed in a single anchoring operation. This single anchoring operation allows for the mooring of multiple floating wind turbines of a wind farm wherein each of these floating wind turbines is provided with an individual anchor point. Therefore, each plate anchor is positioned to provide optimal anchoring for the corresponding floating wind turbine. Furthermore, because multiple wind turbines do not share a single anchor point, the pulling forces of one floating wind turbine do not act on the anchor of another wind turbine. Thus, it is prevented that the movement of one wind turbine cause the anchor of another wind turbine to be moved out of the optimal anchoring position.

The installation follower according to the invention allows for installation of the multiple anchor points in a predetermined configuration, e.g. in close proximity of one another and/or at similar or the same depth in the seabed. Therefore, it allows for precise and efficient design of a wind farm having multiple floating wind turbines.

The installation follower according to the invention allows for providing multiple anchor points in a single anchoring operation, i.e. by driving a single installation follower into the seabed. Furthermore, even though the wind turbines are each provided with individual anchor points, i.e. anchors that are not shared with other wind turbines, the plate anchors points are still positioned close together.

Driving the installation follower into the seabed may e.g. be done using suction installation, vibratory installation or hammer installation.

In an embodiment, the docking stations are uniformly distributed along a circumference of the installation follower. This is advantageous as it leads to a balanced single anchoring operation for the multiple plate anchors. That is, across the circumference the installation follower the plate anchors are subjected to similar soil resistance when driving into the seabed. Therefore, the chance of the installation follower tilting while being driven into the seabed is reduced, and a good penetration of the plate anchors into the seabed is promoted.

In an embodiment, the installation follower has a circular cross section and the docking stations are set up uniformly distributed along a circular circumference of the installation follower to carry the plate anchors with their shank points directed radially outwards. This arrangement of the docking stations enables the installation follower to hold the plate anchors in correct orientation with respect to the mooring positions of the floating wind turbines. Thus, the plate anchors, once positioned in the seabed, do not have to be orientated in the radial direction to be correctly aligned relative to the mooring cables extending to the mooring positions.

In a preferred embodiment, the hollow elongated body of the installation follower is a steel cylinder.

The cross-section of the hollow elongate body may e.g. be 5 m or more, for example the cross section may be 7-8 m.

In an embodiment, the installation follower is provided with three docking stations, and the docking stations are configured for holding the plate anchors such that two adjacent plate anchors extend at an angle p, preferably between 40-70 degrees, more preferably of 60 degrees, relative to each other. This leads to a balanced single anchoring operation for the multiple plate anchors. That is, across the circumference the installation follower the plate anchors are subjected to similar soil resistance when driving into the seabed. Alternatively, the installation follower is provided with four docking stations, and the docking stations are configured for holding the plate anchors such that two adjacent plate anchors extend at an angle of 45 degrees, relative to each other.

In embodiments, the installation follower is configured to releasably secure the plate anchors when mounted in the plate anchor docking stations, such that when the installation follower has been driven into the seabed and the plate anchors are embedded in the soil of the seabed, the plate anchors can be released from the docking stations and the installation follower can be retracted. This allows for re-using the installation follower for a further installation of plate anchors.

In embodiments, the docking stations are configured to hold the plate anchors with their respective shanks directed radially outwards. This is an advantageous configuration for the mooring lines and the tensioning thereof. The latter typically leads to rotation, also known as keying, of the embedded plate anchor from the orientation as being parallel to the central axis of the installation follower towards an orientation wherein the plate of the plate anchor is perpendicular to the direction of loading of the mooring line. This increases the soil resistance of the plate anchor. In embodiments, each plate anchor docking station comprises slots for receiving the anchor plates such that, when a plate anchor is received in the docking station, a central part of the plate anchor is received within the installation follower, and outer edges of the plate anchor are located outside the installation follower. The slots allow for reliable holding of the plate anchors in the docking stations.

In an embodiment, the docking station comprises dedicated slots for receiving the plate of the plate anchor and/or the shank of the plate anchor.

In embodiments, the installation follower comprises a coupling member, preferably an exchangeable coupling member, arranged at the top end of the installation follower, for coupling the installation follower with a drive, e.g. for suction installation, hammer drive installation or vibratory installation of anchoring points, for driving the installation follower and the plate anchors held by the installation follower into the seabed. An exchangeable coupling member allows for using the same installation follower with a multitude of installation techniques.

In an embodiment, the elongate body of the installation follower has a circular cross-section. Alternatively, the cross-section may e.g. be oval or elliptical.

In another embodiment, the elongate body of the installation follower has a rectangular, in particular a square, cross-section. The docking stations for the plate anchors may be arranged at or near the corners of the rectangular, or square, cross-section.

In an embodiment, the installation follower is a suction can.

The invention further relates to an anchoring assembly comprising an installation follower according to the invention, and a plate anchor for each of the docking stations of the installation follower.

In an embodiment of such an assembly, the installation follower is combined with three plate anchors, wherein the plate anchors each comprise an anchor plate, herein also referred to as a fluke, for providing the plate anchor with resistance once driven into the seabed, and an angular plate-like or blade-like shank fixed to the anchor plate, wherein the shank is provided with an attachment point for connecting the anchor plate with a mooring line. In an embodiment, each plate anchor docking station comprises two slots for receiving the anchor plate of a plate anchor. In addition, one or more slots may be provide for receiving the shank. Preferably, in such an embodiment, when the plate anchor is received in the docking station, a central part of the plate anchor is received within the installation follower, and outer edges of the plate anchor and the part of the shank with the attachment point are located outside the installation follower. The slots allow for reliable holding of the plate anchors in the docking stations.

In an embodiment, the anchor plate of the plate anchor has a width in the range of 4-10 meters, for example has a width of 8 meters, and has a height in the range of 3-6 meters, for example has a height of 4 meters.

In an embodiment, the installation follower has a diameter in the range of 3-12 meters, for example has a diameter of 10 meters, and has a height in the range of 25-35 meters, for example has a height of 30 meters.

In an embodiment, the anchor plate has a planar form and the plate anchor is symmetrical about a plane of symmetry X-X perpendicular to the anchor plate and containing the attachment point, e.g. a padeye, in the shank.

The anchor plate of the plate anchor has a forward edge, directed downwards when the plate anchor is received in the docking station, for penetrating the seabed.

In an unassembled state the installation follower and the plate anchors are provided separately. This may be advantageous for transport, e.g. towards or on the deck of a vessel.

In an installation state the plate anchors are received in the respective docking stations, such that the anchoring assembly is ready to be lowered towards and driven into the seabed.

In an embodiment, the anchoring assembly furthermore comprises a plate anchors set up frame for supporting multiple plate anchors in an anchoring arrangement on a surface, e.g. a deck surface. In a pre-assembled state of the anchoring assembly the plate anchors in the anchoring arrangement are positioned relative to each other in the configuration in which they are to be received in the docking stations of the installation follower, to enable the plate anchors to be mounted into the docking stations of the installation follower by lowering the installation follower onto the plate anchors held by the set up frame. This facilitates simple and efficient mounting of the plate anchors to the installation follower e.g. on the deck of a vessel to obtain - from the unassembled state - the anchoring assembly as in the installation state.

The invention further relates to a method for installing multiple plate anchors into the seabed in a single anchoring operation using an installation follower or an anchoring assembly according to invention, for providing anchor points for multiple floating wind turbines of a wind farm, wherein the method comprises the steps of:

- mounting and releasably securing a plate anchor in each of the docking stations of an installation follower;

- driving the installation follower with the plate anchors into the seabed;

- releasing the multiple plate anchors and

- pulling the installation follower out of the seabed.

This facilitates convenient and reliable installation of plate anchors for floating wind turbines of a wind farm. The docking stations holding the multiple plate anchors allow for driving multiple plate anchors into the seabed in a single anchoring operation. This single anchoring operation allows for the mooring of multiple floating wind turbines of a wind farm wherein each of these floating wind turbines is provided with an individual anchor point. Therefore, each plate anchor is positioned to provide optimal anchoring for the corresponding floating wind turbine. Furthermore, because multiple wind turbines do not share a single anchor point, the pulling forces of one floating wind turbine do not act on the anchor of another wind turbine. Thus, it is prevented that the movement of one wind turbine cause the anchor of another wind turbine to be moved out of the optimal anchoring position.

The method according to the invention allows for installation of the multiple anchor points in a predetermined configuration, e.g. in close proximity of one another and/or at similar or the same depth in the seabed. Therefore, it allows for precise and efficient design of a wind farm having multiple floating wind turbines.

The method according to the invention allows for providing multiple anchor points in a single anchoring operation, i.e. by driving a single installation follower into the seabed. Furthermore, even though the wind turbines are each provided with individual anchor points, i.e. anchors that are not shared with other wind turbines, the plate anchors points are still positioned close together.

Driving the installation follower into the seabed may e.g. be done using suction installation, vibratory installation or hammer installation. Mounting and releasably securing a plate anchor in each of the multiple plate anchor docking stations of an installation follower allows for reliable retention of the plate anchors in the docking stations, e.g. when lowering the follower to the seabed and/or when driving into the seabed.

Pulling the installation follower out of the seabed allows for re-using the installation follower for a further installation of plate anchors.

In an embodiment, the method further comprises the steps of:

- mounting the mooring lines to each of the plate anchors, preferably prior to driving the installation follower into the ground, e.g. whilst on a vessel prior to installation of the plate anchors and/or in the pre-assembled state;

- tensioning the mooring lines attached to the plate anchors, preferably after pulling the installation follower out of the seabed.

Tensioning of the mooring lines attached to each of the plate anchors typically leads to rotation, also known as keying, of an embedded plate anchor from the orientation as being parallel to the central axis of the installation follower towards an orientation wherein the plate of the plate anchor is perpendicular to the direction of loading of the mooring line. This increases the soil resistance of the plate anchor.

Further objects, embodiments and elaborations of the apparatus and the method according to the invention will be apparent from the following description, in which the invention is further illustrated and elucidated on the basis of a number of exemplary embodiments, with reference to the drawings.

In the drawings:

Fig. 1 shows a simplified side view of an installation follower according to the invention, wherein the installation follower is configured to carry three plate anchors;

Fig. 2 shows a simplified side view of a further embodiment of an installation follower according to the invention;

Fig. 3 shows a simplified side view of an anchoring assembly according to the invention comprising the installation follower of Fig. 1,;

Fig. 4 shows a top view of the installation follower of Fig. 1 ; and Fig. 5 shows a frontal view of a plate anchor in isolation; In Figs. 1 and Figs. 3-4 is shown an installation follower 10 for installing plate anchors for floating wind turbines of a wind farm. The installation follower 10 may be a suction can. The installation follower 10 has a hollow elongate body 11 with a top end 12 for driving the installation follower 10 into the seabed, a bottom end 13 for holding multiple plate anchors, and a central axis A extending between the top end 12 and the bottom end 13.

As shown for the plate anchor 30 in isolation of Fig. 5, each of the plate anchors comprises a plate 31 and a shank 33 having an attachment point (34 for plate anchor 30, 38 for plate anchor 25), shown as a padeye, for attaching a mooring line. The shank 33 is formed by shank legs 33a and 33b and thus has an angular plate-like configuration.

The plate anchor 30 furthermore has a flap 32 that is rotatable about axis B relative to the plate 31 which may be beneficial for reduction of the loss of embedment of the plate anchor 30 during keying of the plate anchor 30. The flap 32 and the plate 31 are provided with ribs 36. The ribs 36 aid in increasing the soil resistance of a plate anchor, and provide good grip for supporting a mooring chain.

The installation follower 10 is at the bottom end 13 provided with three or more docking stations (shown are docking stations 14,15) arranged for holding the plate anchors parallel to the central axis A and preferably uniformly distributed along a circumference of the installation follower 10.

Docking station 14 comprises a slot 14a, and docking station 15 comprises slots 15a and 15b. The slots 14a, 15 a and 15b are for receiving the plate anchor, e.g. plate anchor 30, such that, when the plate anchor is received in the docking station 14, 15, a central part of the plate anchor is received within the installation follower 10, and outer edges of the plate anchor are located outside the installation follower 10.

It can be seen in Fig. 3 that the installation follower 10 is provided with three docking stations 14, 15, 17 comprising slots 14a, 14b, 15, 15b, 17a and 17b respectively. And wherein the docking stations 14, 15, 17are configured for holding the plate anchors 30, 35, 40 such that two adjacent plate anchors extend at an angle p relative to each other. Here angle is 60 degrees, and the same for all plate anchors. Alternatively, the adjacent plate anchors may extend at different angles relative to one another. The slots 14a, 15a and 17a are dedicated slots for receiving the plate of the respective plate anchor 30, 35, 40 and the slots 14b, 15b and 17b are dedicated slots for receiving the shank of the plate anchor 30, 35, 40.

The installation follower 10 is configured to releasably secure the plate anchors 30, 35, 40 when mounted in the docking stations 14, 15, such that when the installation follower 10 has been driven into the seabed and the plate anchors are embedded in the soil of the seabed, the plate anchors can be released from the docking stations 14, 15 and the installation follower 10 can be retracted.

The docking stations 14, 15, 17 of Fig. 1 are configured to hold the plate anchors 30, 35, 40 with their respective shanks, e.g. 33 directed radially outwards.

The installation follower 10 comprises a coupling member 16, preferably an exchangeable coupling member 16, arranged at the top end 12 of the installation follower 10, for coupling the installation follower 10 with a drive, e.g. for suction installation, hammer drive installation or vibratory installation of anchoring points, for driving the installation follower 10 and the plate anchors 30, 35, 40 held by the installation follower 10 into the seabed.

The elongate body 11 of the installation follower 10 has a circular cross-section. Alternatively, the elongate body of the installation follower 10 may have a rectangular, in particular a square, cross-section, or an oval or elliptical cross-section.

In Fig. 2 is shown installation follower 110 for installing plate anchors for floating wind turbines of a wind farm. The installation follower 110 may be a suction can. The installation follower 110 has a hollow elongate body 111 with a top end 112 for driving the installation follower 110 into the seabed, a bottom end 113 for holding multiple plate anchors, and a central axis A extending between the top end 112 and the bottom end 113.

The installation follower 110 is at the bottom end 113 provided with three or more docking stations (shown is docking station 114) arranged for holding the plate anchors parallel to the central axis A and preferably uniformly distributed along a circumference of the installation follower 10.

Docking station 114 comprises a slot 114a for receiving the plate anchor, e.g. plate anchor 30, such that, when the plate anchor is received in the docking station 114 a central part of the plate anchor is received within the installation follower 110, and outer edges of the plate anchor are located outside the installation follower 110. The slot 114a is a dedicated slot for receiving the plate of the respective plate anchor, e.g. plate anchors 30, 35, 40, or the shank of the of the respective plate anchor, e.g. plate anchors 30, 35, 40. In Fig. 3 is shown an anchoring assembly 20 comprising the installation follower 10 and plate anchors (shown are 30, 35) for each of the docking stations (shown are 14, 15) of the installation follower 10.

The anchoring assembly 20 may furthermore comprise a plate anchors set up frame for supporting multiple plate anchors 30, 35, 40 in an anchoring arrangement on a surface, e.g. a deck surface, in which anchoring arrangement the plate anchors 30, 35, 40 are positioned relative to each other in the configuration in which they are to be received in the docking stations of the installation follower, to enable the plate anchors 30, 35, 40 to be mounted into the docking stations of the installation follower by lowering the installation follower onto the plate anchors held by the set up frame.