WO2024138058A1

WO2024138058A1 - Anchoring method and apparatus

Info

Publication number: WO2024138058A1
Application number: PCT/US2023/085548
Authority: WO
Inventors: Thomas Michael FULTON; Thomas Christopher BAUER; Fabian Wilko HIPPE
Original assignee: Intermoor Inc
Current assignee: Intermoor Inc
Priority date: 2022-12-23
Filing date: 2023-12-21
Publication date: 2024-06-27
Anticipated expiration: 2025-06-23
Also published as: KR20250127129A; EP4638258A1; US20240208614A1

Abstract

The present invention relates to apparatus and a method of embedding a plate anchor. The method comprises providing a plurality of embedment modules each of which is suitable for embedding a plate anchor within a different type of soil. The method comprises determining the type of soil of a seabed at a target site and selecting an embedment module based on the type of soil at the target site. The embedment module is removably mounted within a modular follower assembly. The modular follower assembly is deployed from a vessel and the embedment module is actuated to drive the plate anchor into the seabed. The modular follower assembly is then retrieved to the vessel. The modular follower assembly is reconfigured to provide the modular follower assembly with different embedment modules for a subsequent deployment and to embed futher plate anchors within different soil types.

Description

Anchoring Method and Apparatus

FIELD OF THE INVENTION

The present invention relates to a method of embedding a plate anchor and plate anchor embedding apparatus.

BACKGROUND TO THE INVENTION

Floating Offshore Wind Turbines (FOWTs) are envisioned as a viable solution for offshore wind farms in areas with deep coastal waters where fixed structures become uneconomical. A significant cost component of FOWTs is the mooring and anchoring system used to keep the structure in position. A significant portion of mooring costs are the anchors.

The oil and gas industry has used arrays of mooring lines to keep floating structures on station since the 1960s. A typical oil and gas development involves 8 to 12 mooring lines while a full-scale wind farm will involve hundreds of mooring lines and associated anchors. The large quantity of anchors needed for floating wind farms means reductions in anchoring costs provide huge benefits to the overall economics of floating wind farm developments and end cost to the users of the generated power.

Plate anchors are widely understood to be the most efficient anchor in terms of material usage. Typically made of high strength steel, and deeply embedded below the seabed where soil strength is greatest, their holding capacity to weight ratio exceed all other anchor types such as drag anchors and piles. The reduction of material compared to other types translates to savings in material cost and transportation. In addition to the monetary cost benefits, plate anchors provide a reduced carbon emission benefit in the form of less steelmaking and weight and size to transport.

While plate anchors are very efficient once installed, the act of deeply embedding i them can be challenging and time consuming depending on soil conditions. There is a need in the FOWT industry to address the challenges of difficult soil conditions and reduce the time needed to install plate anchors.

In most instances, plate anchors are installed on soft deepwater clays using suction embedment (for example, US 5,992,060 and US 6, 122,847). In stiff clays, silts and sands, the suction embedment technique can be unfeasible. It may be possible to embed small plate anchors by explosive force, impact driving, vibro driving (vibration driving) and jetting in sands. Experience and theory demonstrate that differing soil types are conducive to different embedment means. For example, suction embedment works well in soft to medium clays, vibro driving works well in sands etc.

Many proposed wind farms are located in areas with layered soil strata of differing soil types or changing soil types over the extent of the wind farm. Accordingly, a single embedment technique and apparatus may not be efficient or even possible. In such situations, a number of different types of driving equipment may be supplied in order to provide the different techniques required wherein the driving equipment is retrieved and a different driving equipment is then used for the different layers of soil strata.

It is an aim of the present invention to overcome at least one problem associated with the prior art, whether referred to herein or otherwise.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a method of embedding a plate anchor, the method comprising: providing a plurality of embedment modules each of which is suitable for embedding a plate anchor within a different type of soil; determining the type of soil of a seabed at a target site; selecting an embedment module based on the type of soil at the target site; removably mounting the embedment module within a modular follower assembly; deploying the modular follower assembly from a vessel; actuating the embedment module to drive the plate anchor into the seabed; retrieving the modular follower assembly to the vessel and reconfiguring the modular follower assembly to provide the modular follower assembly with different embedment modules for a subsequent deployment.

Preferably the method comprises securing a first plate anchor within the modular follower assembly and embedding the first plate anchor at a first target site, retrieving the modular follower assembly and reconfiguring the embedment modules within the modular follower assembly, securing a further plate anchor within the modular follower assembly and embedding the further plate anchor at a further target site. Preferably the method comprises embedding a plurality of plate anchors to provide tethering points for a floating structure and preferably for a floating offshore wind turbine.

The method may comprise: deploying the follower assembly on a first deployment to embed one or more plate anchors with the follower assembly in a first configuration; retrieving the follower assembly to the vessel; reconfiguring the follower assembly to provide the follower assembly with different embedment modules; and subsequently deploying the follower assembly to embed one of more further plate anchors.

The method may comprise deploying and retrieving the follower assembly a number of times (more than once) and/or in a first series (or batch) whilst the configuration of the follower assembly is maintained. The method may further comprise reconfiguring the follower assembly to provide the follower assembly with different embedment modules and deploying the follower assembly to embed at least one further plate anchor. The method may further comprise deploying and retrieving the follower assembly a number of times (more than once) and/or in a second series (or batch) whilst the configuration is maintained in a further configuration which is preferably different to the original configuration of the follower assembly used in a first series.

The method may comprise: deploying the follower assembly on a first deployment to embed a first plate anchors with the follower assembly in a first configuration; retrieving the follower assembly to the vessel; reconfiguring the follower assembly to provide the follower assembly with different embedment modules; and subsequently deploying the follower assembly to embed a second plate anchor.

The method may comprise retrieving the follower assembly after the embedment of each plate anchor. The configuration of the embedment modules in the follower assembly may be changed after the embedment of every plate anchor but preferably the embedment modules may be changed only after a number of plate anchors have been embedded.

The method may comprise retrieving the follower assembly only after the embedment of a number of plate anchors.

The method may comprise positioning a number of plate anchors on the seabed. The method may comprise securing a plate anchor in the follower assembly whilst the plate anchor and the follower assembly are located subsea. Preferably the method comprises manipulating the plate anchor on the seabed and then securing plate anchor in the follower assembly.

Preferably the method comprises identifying layers and/or strata (for example, layers of different types of soil) within the seabed. The method may comprise mounting one or more embedment modules to the follower assembly to penetrate the identified layers and/or strata within the seabed. The method may comprise mounting a specific embedment module to penetrate a specific layer or strata within the seabed.

The method may comprise mounting a first embedment module for a first layer/stratum and mounting a second embedment module for a second layer stratum.

The method may comprise mounting a combination of embedment modules to the modular follower assembly to penetrate through a number of layers/strata of the seabed. For example, the seabed may comprise layers/strata of soils each of which have different types of soil which may have different characteristics. These types of soil and/or characteristic may require different embedment modules/means.

Preferably the method comprises selecting and mounting one or more embedment modules from the following: a vibro hammer embedment module; an impact hammer embedment module; a suction embedment module; and a jetting module.

The method may comprise removing and/or mounting one or more of the following embedment modules between successive deployments of the modular follower assembly: a vibro hammer embedment module; an impact hammer embedment module; a suction embedment module; and a jetting module.

One embedment module may comprise a vibro hammer embedment module. The vibro hammer embedment module may be arranged, in use, to create vibrations to embed a plate anchor within the seabed.

One embedment module may comprise an impact hammer embedment module. The impact hammer module may be arranged, in use, to create an embedment force to embed a plate anchor within the seabed.

One embedment module may comprise a suction embedment module. The suction embedment module may be arranged, is use, to create a suction force to embed a plate anchor within the seabed.

One embedment module may comprise a jetting module. The jetting module may be arranged, in use, to create a (fluid) jet to embed a plate anchor within the seabed.

The method may comprise providing a clamp module for the modular follower assembly. The method may comprise removably mounting the clamp module within the modular follower assembly. The method may comprise clamping a plate anchor between (two) opposing jaws of the clamp module and preferably comprises releasing the jaws from the plate anchor once the plate anchor is located in the desired position/depth within the seabed.

The modular follower assembly may comprise a slot for retaining a plate anchor therein. The slot may be provided on a first (lower) end of the modular follower assembly. The slot may comprise an open ended slot. The slot may comprise two guidance or docking slots which are offset 180 degrees around a lower end of a housing or (tubular) body of the modular follower assembly. The slot may comprise two or more guidance or docking slots which are offset around a lower end of a housing or (tubular) body of the modular follower assembly.

The method may comprise providing a power supply module may comprise a connector for receiving power from an umbilical and transferring the power to least one embedment module. The power supply module may comprise a self-contained power supply for supplying power to at least one embedment module. The power supply module may supply hydraulic and/or electric power.

The method may comprise providing a power pack module for the modular follower assembly. The method may comprise removably mounting the power pack module to the modular follower assembly. The power pack module may supply hydraulic or electric power to one or more embedment module, for example, an impact hammer module and/or a clamp module and/or a vibro module and/or a clamp module and/or a jet module.

The or each embedment module may comprise a combined embedment and extraction module.

Preferably the method comprises adjusting/changing the length of a (tubular) housing of the modular follower assembly. Preferably the (tubular) housing forms a suction follower housing.

The method may comprise providing a number of (tubular) housing sections which may be removably incorporated into or removed from a (tubular) housing of the modular follower assembly. The method may comprise adjusting/changing a longitudi nal/axial length of the (tubular) housing following the retrieval of the modular follower assembly from a first deployment and prior to a subsequent/later deployment. The method may comprise provide a number of sections which provide a variety of sections having different longitudinal/axial lengths.

Preferably the method comprises tethering a floating offshore wind turbine or other offshore device to the seabed and connecting a plurality of mooring lines extending from the floating offshore wind turbine or other offshore device to a number of embedded plate anchors.

According to a second aspect of the present invention there is provide plate anchor embedment apparatus comprising a modular follower assembly having a housing, the modular follower assembly extending from a first longitudinal end to a second longitudinal end, the follower assembly comprising: a plate anchor engagement module; a lifting and lowering line securement mechanism; a first mounting mechanism for removably mounting a first embedment module thereto; second mounting mechanism for removable mounting a second embedment module thereto; a power supply module for supplying power to at least one embedment module; wherein the follower assembly is reconfigurable on a vessel between subsea deployments to enable embedment modules to be changed for a subsequent deployment and to enable embedment modules mounted to the follower assembly to be removed therefrom or mounted thereto.

The first mounting mechanism may comprise a first mounting means. The first mounting mechanism may comprise an internal flange securement mechanism. The second mounting mechanism may comprise a second mounting means. The second mounting mechanism may comprise an internal flange securement mechanism.

The lifting and lowering line securement mechanism may comprise a lifting and lowering line securement module. The lifting and lowering line securement module may be mounted to the housing and/or may be mounted to another module.

The first embedment module may generate embedment forces for use in efficiently embedding the plate anchor in a first layer/stratum and the second embedment module may generate embedment forces for use in efficiently embedding the plate anchor in a second layer/stratum.

The combination of embedment modules of the modular follower assembly may be arranged to penetrate the plate anchor through a number of (consecutive) layers/strata of the seabed. For example, the seabed may comprise layers/strata of soils each of which have different types of soil which may have different characteristics. These types of soil and/or characteristic may require different embedment modules/means/forces.

Preferably the first and second embedment modules comprise one of the following: a vibro hammer embedment module; an impact hammer embedment module; a suction embedment module; and a jetting module.

One embedment module may comprise a vibro hammer embedment module. The vibro hammer embedment module may be arranged, in use, to create vibrations to embed the plate anchor within the seabed.

One embedment module may comprise an impact hammer embedment module. The impact hammer module may be arranged, in use, to create an embedment force to embed the plate anchor within the seabed.

One embedment module may comprise a suction embedment module. The suction embedment module may be arranged, is use, to create a suction force to embed the plate anchor within the seabed.

One embedment module may comprise a jetting module. The jetting module may be arranged, in use, to create a (fluid) jet to embed the plate anchor within the seabed.

The plate anchor embedment apparatus may comprise a clamp module. The clamp module may be removably mountable within the modular follower assembly. The clamp module may comprise clamping mechanism comprising (two) opposing jaws of the clamp module for clamping a plate anchor therebetween and preferably comprises releasing the jaws from the plate anchor once the plate anchor is located in the desired position/depth within the seabed.

The modular follower assembly may comprise a slot for retaining a plate anchor therein. The slot may be provided on a first (lower) end of the modular follower assembly. The slot may comprise an open ended slot. The slot may comprise two guidance or docking slots which are offset 180 degrees around a lower end of a housing or (tubular) body of the modular follower assembly. The slot may comprise two or more guidance or docking slots which are offset around a lower end of a housing or (tubular) body of the modular follower assembly. The power supply module may comprise a connector for receiving power from an umbilical and transferring the power to least one embedment module. The power supply module may comprise a self-contained power supply for supplying power to at least one embedment module. The power supply module may supply hydraulic and/or electric power.

The power supply module may comprise a power pack module for the modular follower assembly. The power pack may be removably mountable to the modular follower assembly. The power pack module may supply hydraulic and/or electric power to at least one embedment module and may supply hydraulic and/or electric power to an impact hammer module and/or a clamp module.

Preferably the modular follower assembly may comprise a (tubular) housing having an adjustable/changeable (longitudinal/axial) length. The (tubular) housing may form a suction follower housing.

The plate anchor embedment apparatus may comprise a number of (tubular) housing sections which may be removably incorporated into or removed from a (tubular) housing of the modular follower assembly. The plate anchor embedment apparatus may comprise a number of sections which provide a variety of sections having different longitudinal/axial lengths.

Preferably the plate anchor embedment apparatus may be arranged, in use, to embed a plurality of plate anchors in the seabed to tether a floating offshore wind turbine or other offshore device to the seabed with a plurality of mooring lines extending from the floating offshore wind turbine or other offshore device to the embedded plate anchors. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of example only with reference to the accompanying drawings, in which:

Figure 1 is a side view of an installation vessel positioning itself near a target anchor location on the seabed.

Figure 2 is a side view of a plate anchor connected to a mooring line whilst being loaded into a follower assembly on a deck of the installation vessel.

Figure 3 is a side view showing the mooring line being tensioned and the plate anchor being clamped into the follower assembly on the deck of the installation vessel.

Figure 4 is a side view of the combination of the plate anchor, mooring line and follower assembly being lowered through the water column by the installation vessel towards the target anchor location.

Figure 5 is a side view of the plate anchor being embedded through layered and varying soil types by one or more of the embedment modules.

Figure 6 is a side view of the mooring line and plate anchor being released from the follower assembly.

Figure 7 is a side view of the follower assembly being extracted from the seabed using one or more of the embedment/extraction modules.

Figure 8 is a side view of a preferred embodiment of a follower assembly attached to a lifting line. DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to methods and apparatus for installing plate anchors 7 quickly and efficiently in all soil types. In particular, to address problem and needs of the FOWT industry a flexible methodology is provided.

It may be beneficial to use more than one means of embedment to efficiently install foundation piles in locations where differing soil types are found as layered strata. In such instances one type of driving equipment must be recovered and switched for a different type of driving equipment. The switching operation can be time consuming, especially in deeper water and harsh environments where the time to lower and recover equipment is amplified. The present invention provides a method and apparatus that can be configured for multiple embedment means/modules to address layered soil situations without having to recover and reconfigure the driving equipment. This feature eliminates the time-consuming equipment recovery and redeployment steps resulting in reduced installation time. The time reduction translates to reduced installation vessel costs and carbon emissions. The assembly is also suited for embedment in a single soil type if desired.

The present invention comprises a method and apparatus for efficiently installing plate anchors 7 for offshore wind farms comprised of Floating Offshore Wind Turbines (FOWTs). The present invention is also applicable for plate anchors 7 installed for other purposes in the renewable energy industry (current turbines, tidal turbines, etc.), the oil and gas industries (floating drilling units, floating production units, terminals, etc.) and any instance where efficient anchors are needed.

The present invention provides a method for the embedment of plate anchors 7 and all or part of the connected mooring line 8 using a follower assembly 9. These components are assembled, lifted, lowered, operated and recovered by an installation vessel 3.

The follower assembly 9 is comprised of multiple subassemblies (modules 101 , 102, 103, 104, 105, 106, 108) that perform the needed functions. The needed functions are determined by the soil type(s) present, means for handling the mooring line 8 (or mooring line segment) and means for providing power and fluids to the follower assembly 10. Different installation instances will require different functions, thus, the follower assembly 9 may be comprised of any combination of a number of modules.

The modules may comprise: i. a clamp module 101 - for retaining the plate anchor 7 in the follower assembly 9 for instances when a rigid connection between the plate anchor 7 and follower assembly 9 is needed; in the preferred arrangement a rigid clamp is not required during impact hammering. Accordingly, another function of the clamp module is to distribute impact hammer stresses safely into the plate anchor (i.e. spread out the load). Therefore, the clamp module includes a structural shape mechanism for doing this.

II. a mooring line retention module 104 - for holding the mooring line 8 taut and, in some instances, for holding the plate anchor 7 with mooring line 8 in the follower assembly 9 (i.e. when the clamp module 101 is not needed);

Hi. internal impact hammer module 102 - contains an internal impact hammer 20 for instances when impact hammering is used; iv. length adjustment module 103 - a variable length component used to vary the overall length of the follower assembly 9 in order to control the final depth of the plate anchor 7 and provide a conduit for pressurized water, hydraulics and/or electrical power and signal (as needed); v. suction seal module - provides a top closure and suction pump interface for instances when suction embedment is used; vi. jetting module - provided interface to a water pump or a subsea water pump for instances when jetted embedment is used; vii. vibro hammer/impact hammer interface module 105 - for instances when a commercially available vibro hammer or impact hammer is used; viii. lifting module 107 - an attachment at the upper end for connecting lowering rigging. In some instances, this will be part of the commercially available vibro hammer; and/or ix. subsea hydraulic powerpack module 108 -for instances when the water depth is deep enough that supplying hydraulic pressure from the surface is too inefficient. In some embodiment, the power supply comodule may just transfer power to the relevant embedment module(s) and may or may not have a self-contained power supply source or source (hydraulic/electrical). For example, the power supply module may comprise a connector for receiving power from an umbilical and transferring the power to least one embedment module. The power supply module may comprise a self- contained power supply for supplying power to at least one embedment module. The power supply module may be arranged to supply hydraulic and/or electric power.

The determination of the soil types may be made during a site-specific geotechnical investigation early in the development lifecycle. The information obtained from the geotechnical investigation will determine the types of embedment modules/means that are needed along with power requirements. The combination of modules in the follower assembly 9 may be arranged such that needed modules are present for complete embedment and extraction of the plate anchor 7 through all expected soil layers. Accordingly, the complete embedment and securement of the plate anchor is achieved in a seabed having several different layers/strata 12, 14, 16 of different types of soil without retrieving and changing the embedment mechanism.

The different embedment modules/means are provided to efficiently embed the plate anchors in different soil types (i.e. different materials of the seabed). With some exceptions, all of the embedment module types (vibro, impact, suction and jetting) can theoretically embed in all the generic definitions of soil types (clay, silt, sand). However, the efficiency (i.e. speed) can vary greatly and in some cases be so slow it might as well be considered impossible. The types of soils each embedment module would work best may be considered to be as follows: (1 ) vibro with sands, (2) impact with sands and clays (3), suction with soft clays, and (4) jetting with all soils.

Once the plate anchor 7 is embedded to the desired depth in the seabed 2, the anchor 7 and mooring lone 8 are released and the follower assembly 9 is extracted and recovered for reloading with another plate anchor 7. The soil resistance during extraction is again overcome using one or more of the following means: vibration using a vibro hammer, reverse suction (overpressure) via a suction seal module and/or direct pull from the installation vessel.

The specific example of the present invention depicted in the figures is based on installation with an Anchor Handling Construction Vessel (AHCV) 3 that has a stern roller and crane 17. The method can also be adapted to other vessel types, including crane barges, subsea construction vessels and heavy lift vessels.

As shown in the figures, one end of the mooring line 8 is connected to the plate anchor 7 and the other end is retained on the vessel 3 for subsequent connection to the FOWT. However, the method can be adapted for the use of a short segment of mooring line 8 deployed with a subsea mooring connector. In this instance the connection to the remaining part of the mooring line 8 would occur at a later phase of the operation.

The plate anchor 7 inserted into the follower assembly 9 using the vessel’s crane 17. Other means of lifting, jacking and handling of the plate anchor 7 may be used.

The chain retention mechanism may be hydraulically, electrically, or manually operated.

The present invention may provide for the batch embedment of a number of plate anchors. For example, a number of plate anchors may initially be placed on the seabed adjacent to respective target sites. The follower assembly in a first configuration is deployed (possibly with a first anchor secured therein) and a first batch of anchors are embedded. In this system, each of the anchors may utilise the configuration of embedment modules provided on the follower assembly. The follower assembly could then be retrieved for reconfiguration purposes. The follower assembly could then be redeployed for embedding a second batch of plate anchors. Again, each of the second batch of anchors may utilise this further configuration of the embedment modules provided on the follower assembly. In this system, some time may be saved since the follower assembly is not retrieved between the embedment of each plate anchor. However, this method requires the additional step of separately placing the plate anchors on the seabed and securing the plate anchors within the follower assembly whilst located subsea and on the seabed.

The method may comprise deploying the follower assembly on a first deployment to embed one or more plate anchors with the follower assembly in a first configuration. The follower assembly would then be retrieved to the vessel. Once on the deck of the vessel, the follower assembly should be reconfigured to provide the follower assembly with different embedment modules. The follower assembly could then be subsequently deployed to embed one of more further plate anchors.

The method may comprise deploying and retrieving the follower assembly a number of times (more than once) and/or in a first series (or batch) whilst the configuration of the follower assembly is maintained. The method may further comprise reconfiguring the follower assembly to provide the follower assembly with different embedment modulus/means and deploying the follower assembly to embed at least one further plate anchor. The method may further comprise deploying and retrieving the follower assembly a number of times (more than once) and/or in a second series (or batch) whilst the configuration is maintained in a further configuration which is preferably different to the original configuration of the follower assembly used in a first series.

In this batch embedment method, the method would involve positioning a number of plate anchors on the seabed. The plates anchors are only secured in the follower assembly whilst the plate anchor and the follower assembly are located subsea (although a first plate may be secured in the follower assembly whilst on the vessel).

In some methods, the follower assembly may be retrieved and subsequently deployed for the next plate anchor whilst still maintaining the configuration of embedment modules. For example, the reconfiguration may only be required every so often even though the follower assembly is retrieved to the vessel. In this respect, it is the ability of the follower assembly to be reconfigurable to provide a multifunctional follower assembly.

As shown in Figure 1 , an installation vessel 3 traverses the sea surface 1 and is positioned over or near the target anchor location 4 on the seabed 2. The installation vessel shown is an AHCV 3. However, any type of installation vessel with capable crane 17 and/or winch capacities may be used.

The preparation and loading of the anchor embedment apparatus is performed on the deck 5 of the installation vessel 3. The follower assembly 9 releasably retains a plate anchor 7 which is subsequently embedded in the seabed 2 and the follower assembly 9 is then retrieved for use with embedding further plate anchors 7. Accordingly, the follower assembly 9 comprises a retaining mechanism for retaining each plate anchor 7 to the follower assembly 9 and, in the preferred embodiment, a clamp mechanism is used, as explained below.

The follower assembly 9 comprises a housing 30 which is a substantially tubular housing extending from a first (lower) longitudinal end 32 to a second (upper) longitudinal end 34. The tubular housing may not be cylindrical and the tubular housing may be another functioning shape but in the preferred embodiment the tubular housing is cylindrical. The housing 30 may form a suction follower housing. The follower assembly 9 includes securement means at or towards the upper end for securing the follower assembly 9 to a lifting and lowering line 6. The securement means comprises one or more brackets 40 having an aperture for securing to a coupling provided on the end of the lifting and lowering line 6. In some embodiments, the securement means may be provided on one of the other modules. The securement means may comprise a bracket or a padeye or a similar securement device.

The retaining mechanism for retaining the plate anchor 7 is provide at the lower end 32 of the follower assembly. In the preferred embodiment, the retaining mechanism comprise a clamp which retains the plate anchor 7 within a slot 50 provided in the lower end of the follower assembly. In particular, the slot 50 consists of two or more docking or guidance slots extending from the lowermost end 32 of the housing 30 wherein each slot is offset around the circumference of the tubular housing 30 and in one embodiment two guidance sots are offset by 180 degrees. The plate anchor 7 extends diametrically across the tubular housing 30 in the retained positon. The slots 50 enables the plate anchor 7 to be constrained within the lower end 32 of the housing 30 and the releasable clamping mechanism 101 may further clamp the plate anchor 7 in position. In some embodiments, the slot 50 may comprise two or more guidance slots which may be provided din the lower end of the housing.

The plate anchor 7 comprises a plate 60 and a shank with means for securing the plate anchor 7 to a mooring line 8, in use. The securement means comprise a shank (bracket) 62 located on a first, upper surface of the plate 60 of the plate anchor 7. The shank 62 comprises a securing aperture for engagement with a coupler associated with a mooring line 8. The mooring line 8 would likely be chain, but other materials used in the mooring line 8 such as wire or synthetic rope may be present.

As shown in Figure 2, the plate anchor 7 may be secured to the mooring line 8 on the deck 5. In addition, for handling purposes, the lifting and lowering line 6 is attached to the securement shank 62 of the plate anchor 7. This enables the plate anchor 7 to be lifted and moved on the vessel 3. In particular, the crane 17 is used to lift and then move the plate anchor 7 in order to load the plate anchor 7 into the follower assembly 9 using the lifting and lowering line 6. This would normally occur on the vessel deck 5. However, the first anchor 7 of a multi-anchor campaign might be pre-loaded at the quayside. In the preferred embodiment described herein, the lifting and lowering line 6 is from the vessel crane 17. The lifting and handling of the plate anchor 7 may also be accomplished by other means such as jacking, winching, robotic arm, etc.

In some arrangements and embodiments, the plate anchor 7 may be secured and held in the follower assembly 9 through a section of tensioned mooring line 8. In such arrangements, the mooring line 8, or at least a section thereof, is tensioned to urge the plate anchor 7 into the slot(s) 50 which thereby holds the plate anchor 7 in the slot(s) 50 sufficiently. However, in some situations a clamping mechanism 101 is required to retain the plate anchor 7 more securely and, in particular, prevents or inhibits movement of the plate anchor 7 about the planar orientation within the follower assembly 9. For example, some embedment modules/means may benefit from the plate anchor 7 being rigidly held in a single plane without allowing significant movement of the plate anchor 7 relatively to the housing 30. Alternatively, some embedment modules/means may benefit from a non-rigid retaining arrangement. This may be provided by the slot(s). For example, with impact hammering the aim may be to distribute the forces rather than to have them concentrated through the clamp mechanism. In this situation, the clamp may be released and the plate anchor retained by the slot(s). A distributing member providing a distribution surface may be provided by the follower assembly for transferring the forces evenly to the plate anchor. These may reduce the stresses particularly in the plate anchor.

As shown in Figure 3, the mooring line 8 is tensioned and the plate anchor 7 is clamped to the follower assembly 9 whilst located on the vessel deck 5. The plate anchor 7 is positioned in the slot(s) 50 provided by the housing 30 of the follower assembly 9. The shank 62 of the plate anchor 7 locates at the entry to the slot(s) 50 with a portion of the plate anchor 7 extending downwardly away from the lower end 32 of the housing 30. This provides a lower end of the plate anchor 7 which will subsequently be directly driven and penetrated into the seabed 2. Once in this position, the clamping mechanism 101 can be actuated. The clamping mechanism 101 comprises at least one jaw and preferably a number of jaws. In the preferred embodiment there is a first clamping member (jaw) 70 and a second clamping member (jaw) 72 between which the plate anchor 7 is clamped. As shown in Figure 3, the two jaw members 70, 72 are driven and urged inwardly towards each other and about opposite faces of the plate anchor 7. The plate anchor 7 is thereby clamped between the two jaw members 70, 72 with a lower portion of the plate anchor 7 extending directly away from the housing 30. In some situations, it is beneficial to provide multiple sets of jaws (i.e. clamps) in order to efficiently transfer vibrations.

The mooring line 8 is tensioned using the mooring line retention mechanism 10. In the preferred embodiment, the retention system is depicted as a hook 80 engaging the mooring line 8 and the hook 80 can be slid lengthwise along the axis of the follower assembly 9 to remove slack in the mooring line 8. For example, a link of the chain of the mooring line 8 is engaged with the hook 80 whilst the hook 80 is in a first, initial position. In this arrangement, the chain of the mooring line 8 is relatively slack and forms a slack section of chain, as shown in Figure 3. The hook 80 is arranged to move translationally along the longitudinal axis of the housing 30. In particular, the hook 80 is arranged to move from the initial position to a second, tensioned positon in which the hook 80 moves away from the first, lower end 32 of the housing 30 and towards the second, upper end 34. Specifically, this movement is away from the shank 62 of the retained plate anchor 7 to which the mooring line 8 is coupled. The translational movement of the hook 80 from the initial position to the tensioned position comprises a sliding action of the hook 80 which may be hydraulically or electrically actuated or manually ratcheted. Other means for tensioning the mooring line 8 could be wire slings and turnbuckles, come-alongs or manual winches.

As described above, in this preferred embodiment, the plate anchor 7 is held into the follower assembly 9 using the clamping mechanism 101. In particular, the clamping arrangement 101 allows for vibration transfer from a vibro hammer 106, through the follower assembly 9 and into the anchor 7 assisting in breaking friction with the soil during embedment. In some cases, for example where a vibro hammer is not used, the plate anchor 7 may be retained into the follower assembly 9 solely using the mooring line retention mechanism 10. The clamping arrangement 101 also allows for impact/vi bration transfer from an impact hammer module 102, through the follower assembly 9 and into the anchor 7 which assists in breaking friction with the soil during embedment. Foer this embedment task, the plate anchor 7 may be retained into the follower assembly 9 without a rigid clamp arrangement. This may provide of the spreading and/or distribution of the significant forces when impact hammering is used.

As shown in Figure 4, the plate anchor 7, the mooring line 8 and the follower assembly 9 are lowered using the lifting and lowering line 6. As mentioned above, the lifting and lowering line 6 is attached to a securement bracket 40 located at or towards an upper end 34 of the housing 30. The tensioned section of mooring line

8 locates adjacent to the housing 30 and is engaged to the hook 80. The remaining length of the mooring line 8 extends generally upwardly from the hook 80 to the vessel 3.

There are numerous conventional methods for lifting and upending piles and subsea structures from a vessel and this action would be the same for the follower assembly

9 with the plate anchor 7. Likewise concurrent lowering of the items including the mooring line 8 can be done with various combination of cranes and winches depending on the installation vessel 3 capabilities. An umbilical 110 provides electrical power or hydraulics and signal(s) from the surface to the follower assembly 9. The exact needs from the umbilical 1 10 are dependent on what modules are being used in the follower assembly 9. The lifting and lowering line 6 attached at the upper end 34 enables the lower portion of the plate anchor 7 to be lowered down to the target site 4 and to directly penetrate the seabed 2. Purely gravitational forces will be insufficient to enable the plate anchor 7 to penetrate the seabed 2 to a sufficient depth and the embedment modules/means provided by the follower assembly 9 can then be actuated to penetrate the seabed 2 to the required depth. As mentioned above, the follower assembly 9 has the capability of having a number of different embedment modules mounted thereto. This enables the single follower assembly 9 to drive the plate anchors 7 into the seabed 2 through a different number and combination of strata/layers 12, 14, 16 of soil within the seabed. As mentioned previously, different embedment modules/means may be optimised for soil types having different characteristics. Accordingly, the present invention prevents the follower assembly 9 having to be retrieved for different strata/layers 12, 14, 16 within the seabed 2 and the instalment of the plate anchor 7 is achieved in a single deployment of the follower assembly 9.

As shown in Figure 5, the plate anchor 7 and the lower end of the mooring line 8 are embedded into the seabed 2 using the follower assembly 9. In this example, there are three layers of soils 12, 14, 16 and the present invention provides an easy, quick and reliable method for penetrating each layer 12, 14, 16 and different type soil. The follower assembly 9 is configured to have the required embedment equipment to efficiently penetrate the plate anchor 7 into (and through) each soil layer 12, 14, 16. The follower assembly 9 according to the present invention may provide any combination of vibro driving, impact hammering, suction embedment or jetting. Since all needed modules are present or are able to be present, the system can easily switch between driving methods without having to recover and reconfigure the equipment.

Once the plate anchor 7 has reached the desired penetration, the mooring chain 8 and the plate anchor 7 are released. The clamp mechanism 101 is released by moving the jaw members 70, 72 outwardly away from the respective faces of the plate anchor 7. In this position, the plate anchor 7 is no longer gripped within the housing 30 and could be extracted from the slot(s) 50 in the housing 30.

The hook 80 is moved from the tensioned position to a released position by reversing the sliding action of the hook 80. The hook 80 moves translationally relative to the housing 30 and in a direction towards the lower end 32. This movement causes the tensioned section of the mooring line 8 to become slack and also disengages the chain link of the mooring line 8 from the hook 80. In this configuration, the plate anchor 7 is located within the slot(s) 50 of the housing 30 but is no longer engaged within the follower assembly 9 which is separable.

As shown in Figure 7, the extraction of the follower assembly 9 thereby leaves behind the plate anchor 7 and mooring line 8. The extraction of the follower assembly 9 from the seabed 2 is accomplished using one or more of the extraction means which may be provided by one of more of the embedment module(s) (e.g. combined embedment and extraction modules). The extraction modules/means may comprise one or more of vibro extraction, reverse suction and/or pulling force from the installation vessel. Since these functions are already present in the follower assembly 9 and lifting and lowering line 6, an equipment change is not required. The follower assembly 9 is retrieved to the deck 5 of the vessel 3 ready for use with further plate anchors 7. During this step, the modules for embedment and/or extraction can be quickly and easily changed if the next target site comprises a different combination of strata/layers of soil.

A preferred embodiment of the follower assembly 9 is shown in Figure 8. This figure shows a clamp module 101 , a mooring line retention module 104, an internal impact hammer module 102, a length adjustment module 103, a vibro hammer/impact hammer interface module 105, a lifting module 106 and a subsea hydraulic or electric powerpack module 108.

The mooring line retention module 104 comprise the attachment means to create tension in a section of the mooring line 8 and also to maintain this section of mooring line in a tensioned state. Specifically, as previously mentioned, the mooring line retention module 104 comprises the movable (axially slidable) hook 80 which moves towards and away from the lower end 32 of the follower assembly 9. The hook 80 is arranged to engage a link of the mooring line 8 whilst a lower portion of the mooring line 8 is coupled to the plate anchor 7 which is engageable in the slot(s) 50 at the lower end 32 of the follower assembly 9. With a specific link engaged with the hook 80, the hook 80 is moved upwardly to thereby increase the axial distance between the engaged plate anchor 7 and the hook 80. This thereby increases the tension in the section of mooring line 8 extending between the plate anchor 7 and the hook 80 located at or towards an upper part of the follower assembly 9. Once the anchor plate 7 has been driven into the seabed 2 to the required position/depth, the link of the mooring line 8 is disengaged from the hook 80 by moving the hook 80 axially downwardly. The mooring line 8 may then extend directly from the plate anchor 7 up towards the structure being tethered. The clamp module 101 comprises two or more jaws or set of jaws (multiple set of jaws) and, in the example shown, the clamp module comprises the first and second jaw members 70, 72 which locate at the lower end 32 of the follower assembly 9 for clamping the plate anchor 7 during deployment and also during the embedment phase. The clamp maintains the plate anchor 7 in a fixed position and orientation which may be especially beneficial with some embedment methods. The lower end 32 of the housing 30 of the follower assembly 9 comprises the guidance slots which may comprise two or more slots and, in the example shown, comprises first and second guidance slots 50. These two slots 50 maintain the plate anchor 7 in the desired orientation relative to the tubular housing 30 of the follower assembly 9. The slots 50 also retain the plate anchor 7 in an orientation and position for clamping.

The follower assembly comprises a mounting assembly or mechanism for mounting an internal impact hammer module 102. The mounting mechanism may comprise internal bolted flanges. In the preferred embodiment, the mounting mechanism locates adjacent to and/or above the clamp module 101 . The impact hammer module 102 comprises a hammer 90 (piston or ram) located above an anvil/block 92 in order to generate the embedment force desired for some soil types. Due to the significant forces created, in the preferred embodiment, the internal impact hammer module 102 locates directly above and adjacent to the clamp module 101.

The follower assembly 9 is adjustable in length. This adjustment functionality optimises the follower assembly 9 for embedding the plate anchor to an adjustable maximum depth. For example, the longitudinal/axial length of the follower assembly 9 is increased for greater seabed depths to allow for greater penetration. The follower assembly 9 comprises a length adjustment module 103. The length adjustment module 103 may comprise a section 36 of the tubular housing 30 the length of which may be selected in order to provide a follower assembly 9 having a desired length. In the preferred embodiment, this section 36 of the housing 30 locates directly above the internal impact hammer module 102 and below the mooring line retention module 104. The user may have a number of differing lengths of housing sections 36 each of which could be used and secured within the follower assembly 9. In some embodiments, more than one housing section 36 may be secured within the follower assembly 9. For example, two or more sections 36 may be secured in an end to end configuration to increase the length of the follower assembly 9. As above, these sections 36 can be removed and inserted on the deck 5 of the vessel 3 and selected for each deployment. Accordingly, the length adjustment module 103 enables the provision of a suction follower of differing lengths and hence different capabilities which may be individualised depending on the task and the target site.

The follower assembly 9 comprises mooring line retention module/means 104 to maintain a lower section of the mooring line 8 adjacent to the housing of the follower assembly 9 during the deployment and embedment phases. This reduces the risk of the mooring line 8 becoming tangled and pulling the plate anchor 7 out of the desired embedment direction and helps to keep the mooring line 8 adjacent to the housing 30 during penetration of the seabed 2. In the preferred embodiment, the mooring line retention module/means 104 comprises the hook located at an upper position of the follower assembly/housing 9/30. As previously described, the hook 80 is slidably moveable from a lower position to an upper position. In use, a link of the chain of the mooring line 8 is engaged with the hook 80 located in the lower positon. The hook 80 is then moved away from the plate anchor 7 to increase the separation distance for the two ends of the section of chain which thereby increases the tension in the section of chain. This tension prevents the section of chain from becoming disengaged and being held against the housing 30 of the follower assembly 9. Once the plate anchor 7 is embedded in the seabed 2 to the required depth, the mooring line retention module/means 104 can be activated again to release the mooring line 8. Specifically, the hook 80 is moved back to the lower position to release the tension in the section of chain and this movement causes the link to disengage from the hook 80. Once disengaged, the mooring line 8 will extend from the lower position fixed to the plate anchor 7 to the upper end of the mooring line 8 which will subsequently connect the structure to the plate anchor 7.

A vibro hammer/impact hammer interface module 105 locates above the mooring line retention module/means 104 and below the vibro hammer 106. The vibro hammer 106 locates on the interface and the vibrational movements for the vibro hammer 106 are transmitted through the interface to the housing of the follower assembly 9.

The follower assembly 9 comprises a subsea powerpack 108. This locates on the upper end 34 of the follower assembly 9 and specifically above the vibro hammer module 106. However, the bracket(s) 40 of the lifting module 107 may extend beyond the upper surface of the power pack 108 to provide easily accessible attachment apertures. The power pack 108 is arranged to supply hydraulic or electric power for the follower assembly 9. For example, the power pack 108 may provide hydraulic or electric power to the impact hammer module 102. This may be beneficial in deepwater whereby the supply of such hydraulic power from the surface may be inefficient.

The follower assembly 9 comprises a lifting module 107 located towards the upper end. This lifting module 107 provide attachment means for attaching a lower end of the lifting and lowering line 6. The attachment means may comprise at least one bracket 40 providing a securement aperture. The follower assembly 9 can then be manually attached and detached whilst on the deck 5 of the vessel 3. Once attached, the follower assembly 9 is suspendable from the lifting and lowering line 6 and the plate anchor 7 can be transferred to the target site 4. In some embodiments, the lifting module may be located on one of the other modules.

Each of the modules may be removably secured within the follower assembly with internal bolted flanges and/or similar devices.

An umbilical 1 10 may be connected to the follower assembly 9 and may be connected to the subsea power pack 108. The umbilical 110 may supply electrical power (and/or hydraulic power) from the surface to the follower assembly 9. The configuration of the umbilical 1 10 will depend on the modules included within the specific follower assembly 9. The suction module and/or jetting module would most likely replace the impact hammer module and the tubular housing sections 30 and 36. In such a configuration, the clamp module and possibly the vibro/impact adapter module 105 would still be required. The suction module comprises vent valves, and a mounted suction pump or interface for an ROV mounted suction pump. This would contain a jetting pump and have plumbing that interfaces with the clamp module and plate anchor and the actual jet nozzles may be incorporated into the plate anchor.

Claims

1 . A method of embedding a plate anchor, the method comprising: providing a plurality of embedment modules each of which is suitable for embedding a plate anchor within a different type of soil; determining the type of soil of a seabed at a target site; selecting an embedment module based on the type of soil at the target site; removably mounting the embedment module within a modular follower assembly; deploying the modular follower assembly from a vessel; actuating the embedment module to drive the plate anchor into the seabed; retrieving the modular follower assembly to the vessel and reconfiguring the modular follower assembly to provide the modular follower assembly with different embedment modules for a subsequent deployment.

2. A method of embedding a plate anchor according to Claim 1 in which the method comprises securing a first plate anchor within the modular follower assembly and embedding the first plate anchor at a first target site, retrieving the modular follower assembly and reconfiguring the embedment modules within the modular follower assembly, securing a further plate anchor within the modular follower assembly and embedding the further plate anchor at a further target site.

3. A method of embedding a plate anchor according to Claim 2 in which the method comprises embedding a plurality of plate anchors to provide tethering points for a floating offshore wind turbine or other offshore device.

4. A method of embedding a plate anchor according to Claim 1 in which the method comprises identifying layers and/or strata within the seabed and mounting one or more embedment modules to the follower assembly to penetrate the identified layers and/or strata within the seabed.

5. A method of embedding a plate anchor according to Claim 1 in which the method comprises mounting a combination of embedment modules to the modular follower assembly to penetrate through a number of layers/strata of the seabed.

6. A method of embedding a plate anchor according to Claim 1 in which the method comprises selecting and mounting one or more embedment modules from the following: a vibro hammer embedment module; an impact hammer embedment module; a suction embedment module; and a jetting module.

7. A method of embedding a plate anchor according to Claim 1 in which the method comprises providing a clamp module for the modular follower assembly and removably mounting the clamp module within the modular follower assembly and wherein the method comprises clamping the plate anchor between opposing jaws of the clamp module and subsequently releasing the jaws from the plate anchor once the plate anchor is located in the desired position/depth within the seabed.

8. A method of embedding a plate anchor according to Claim 1 in which the method comprises providing a power pack module for the modular follower assembly and removably mounting the power pack module to the modular follower assembly wherein the power pack module supplies hydraulic or electric power to at least one embedment module.

9. A method of embedding a plate anchor according to Claim 1 in which the method comprises adjusting a length of a housing of the modular follower assembly.

10. A method of embedding a plate anchor according to Claim 9 in which the method comprises providing a number of housing sections which can be removably incorporated into or removed from the tubular housing of the modular follower assembly.

1 1. A method of embedding a plate anchor according to Claim 10 in which the method comprises adjusting a longitudinal length of the tubular housing following the retrieval of the modular follower assembly from a first deployment and prior to a later deployment wherein the method comprises providing a number of sections which provide a variety of sections having different longitudinal lengths.

12. A method of embedding a plate anchor according to Claim 1 in which the method comprises tethering a floating offshore wind turbine or other offshore device to the seabed and connecting a plurality of mooring lines extending from the floating offshore wind turbine or other offshore device to a number of embedded plate anchors.

13. Plate anchor embedment apparatus comprising a modular follower assembly having a housing, the modular follower assembly extending from a first longitudinal end to a second longitudinal end, the follower assembly comprising: a plate anchor engagement module; a lifting and lowering line securement mechanism; a first mounting mechanism for removably mounting a first embedment module thereto; a second mounting mechanism for removable mounting a second embedment module thereto; a power supply module for supplying power to at least one embedment module; wherein the follower assembly is reconfigurable on a vessel between subsea deployments to enable embedment modules to be changed for a subsequent deployment and to enable embedment modules mounted to the follower assembly to be removed therefrom or mounted thereto.

14. Plate anchor embedment apparatus according to Claim 13 in which the first embedment module generates embedment forces for use in efficiently embedding the plate anchor in a first layer/stratum and the second embedment module generates embedment forces for use in efficiently embedding the plate anchor in a second layer/stratum.

15. Plate anchor embedment apparatus according to Claim 13 in which a combination of embedment modules of the modular follower assembly is arranged to penetrate the plate anchor through a number of consecutive layers/strata of the seabed.

16. Plate anchor embedment apparatus according to Claim 13 in which the first and second embedment modules comprise one of the following: a vibro hammer embedment module; an impact hammer embedment module; a suction embedment module; and a jetting module.

17. Plate anchor embedment apparatus according to Claim 13 comprising a clamp module which is removably mountable within the modular follower assembly and wherein the clamp module comprises a clamping mechanism comprising opposing jaws for clamping a plate anchor therebetween.

18. Plate anchor embedment apparatus according to Claim 13 in which the power supply module comprises a power pack module removably mountable to the modular follower assembly in which the power pack module is arranged to supply hydraulic and/or electric power.

19. Plate anchor embedment apparatus according to Claim 13 in which the modular follower assembly comprises a housing having an adjustable longitudinal length.

20. Plate anchor embedment apparatus according to Claim 19 in which the plate anchor embedment apparatus comprises a number of housing sections which can be removably incorporated into or removed from the housing of the modular follower assembly and wherein the sections provide a variety of sections having different longitudinal lengths.