An installation; a monopile suitable for the installation and a method of establishing an installation

Abstract

An installation comprising a buoyant and guyed monopile (BGM), the BGM monopile and a method for installing the BGM monopile. The monopile is upright and comprises an upper section and a lower section comprising a tip section defining a bottom end which is at least partially supported by the water floor. The lower section has an average lower section outer diameter which is less than the average monopile outer diameter. The monopile comprises a primary compartment and an opening arrangement into the primary compartment located at least partially in the lower section. The monopile comprises at least one buoyancy compartment located at least partially in the upper section. The installation comprises a plurality of attachment fairleads attached to the monopile and at least three mooring lines arranged to anchoring the monopile to water floor anchors via the plurality of fairleads.

Description

[0001] AN INSTALLATION; A MONOPILE SUITABLE FOR THE INSTALLATION AND A

[0002] METHOD OF ESTABLISHING AN INSTALLATION

[0003] TECHNICAL FIELD

[0004] The present invention relates to an installation, such as an offshore installation or a lake installation, a monopile suitable for the installation as well as a method of establishing an installation. The installation is advantageously supporting or adapted for supporting a wind turbine.

[0005] BACKGROUND

[0006] In recent years there have been an intensive development of offshore installations suitable for forming foundations for wind turbine support structures, such as fixed bottom offshore installations and floating offshore installations. Over the years the size of the wind turbines and wind blades thereof have increased resulting in an increased demand on the offshore installation for supporting such wind turbines. The loads acting on the offshore installation forming the foundation or the supporting structure for wind turbines are generally very high and of dynamic nature due to the varying wind speeds or even storms inducing loads and vibrations in the entire installation. To withstand such high loads, a high level of stability of the offshore installation is required. A well-known concept for establishing a monopile type offshore installation involves driving a pile section of the monopile deep into the seabed, which is both costly in particular when the water depth is great, such as 60 m deep or more, and may result in reduced lifetime of the offshore installation due to induced fatigue (driving fatigue) caused by the applied loads and the hammering carried out during installation. This method for installing a monopile may create significant noise which may be harmful for underwater wildlife and to the environment in general.

[0007] Several attempts for providing alternative monopile based offshore installations have been provided. EP4098868 discloses an offshore installation which comprises a monopile penetrating in a seabed, and further supported by a jacket structure, to provide that the offshore installation may be used even at relatively high water depths.

[0008] ES2322664 discloses a method for installing and maintaining a monolithic floating structure for supporting a wind turbine in a maritime area which is very deep and far from the coast, wherein the installation consists in the anchoring of the structure from a horizontal transport position to a vertical position by means of the controlled flooding of the interior thereof, in such a way that the section emerging above the sea surface is minimal, in order to perform the installation of the wind turbine be carried out by means of a catamaran-style ship. The maintenance comprises the replacement or removal of the wind turbine and other elements supported by the floating structure by causing a vertical descent of the floating structure until a maximum height above the average sea level of 20 m is attained, by means of the controlled flooding of the interior thereof, and carrying out a process of causing the floating structure to emerge by means of removing the water from the interior thereof.

[0009] WO2022 / 223471 discloses an offshore installation comprising an installed foundation pile, wherein the pile comprises a tapered section arranged in an upper half of the part of the foundation pile embedded in the seabed, thereby material for the foundation pile may be saved while the taper has a particularly minor impact on stability.

[0010] US2022195686 discloses an offshore installation foundation for an offshore structure is disclosed. The foundation includes: a tower having an anchoring section which is anchorable in the seabed and a connection section arranged at the opposite end of the tower. The anchoring section engaging the seabed has one or more anchoring elements which counteract a torsional force about an axis in the longitudinal direction of the tower; wherein in a tilted position of the tower the anchoring section of the tower engaging the seabed is movable in the seabed.

[0011] DISCLOSURE OF INVENTION An objective of the invention is to provide an installation at water location, such as at an ocean site or a lake site and comprising a support structure, such as a foundation suitable for supporting a wind turbine, wherein the stability of the installation against lateral forces becomes relatively high.

[0012] In an embodiment of the invention it is an object to provide an installation that may be established at a relatively low cost.

[0013] In an embodiment of the invention it is an object to provide an installation that has high durability, preferably even where it is installed in relatively deep water.

[0014] In an embodiment of the invention it is an object to provide a monopile that may be installed at a relatively low cost and preferably forms part of the installation.

[0015] In an embodiment of the invention it is an object to provide a method of establishing an installation, which method is very economically attractive and which preferably may be performed without the need for lifting the monopile, such as lifting the entire weight of the monopile or a substantial part of the weight of the monopile during the installation of the monopile at the water location.

[0016] These and other objectives have been solved by the invention as defined in the claims and as described herein below.

[0017] It has been found that the invention and / or embodiments thereof have a number of additional advantages, which will be clear to the skilled person from the following description.

[0018] The inventors of the present invention have found that by providing the installation of the monopile as a buoyant and guyed monopile (BGM) a very strong and stable installation may be obtained and at the same time the installation may be established at a very attractive cost.

[0019] The installation of the invention comprises a buoyant and guyed monopile (BGM), wherein the monopile is upright and has a length from a top end to a bottom end and a wall with an outer surface defining an average monopile outer diameter. The monopile comprises an upper section and a lower section comprising a tip section at least partially supported by the water floor. The lower section has an average lower section outer diameter which is less than the average monopile outer diameter. It has been found that by providing the lower section and especially the tip section with a relatively narrow diameter, this may aid to reduce the lateral moments acting between the tip section and the water floor and thereby increase stability.

[0020] The portion of the lower section above the tip section is also referred to as the lower section body portion.

[0021] The monopile comprises a primary compartment located at least partially in the lower section and an opening arrangement into the primary compartment, which is at least partially in the lower section. In an embodiment the primary compartment is located fully in the lower section body portion. The opening arrangement into the primary compartment may be adapted for adjusting the buoyant force prior to, during or after installation and at the same time it may be applied to reduce the risk of collapse of the portion of the primary chamber that is below water level. The primary compartment is preferably at least partially water filled in the installed condition, such as from water filled from 10 to 90 %, such as from 20 to 80 %, such as from 70 to 30 % of the volume of the primary compartment. Beneficially, the primary chamber is partially filled in the installed condition as it will be explained further below.

[0022] The monopile comprises at least one buoyancy compartment ensuring that the monopile is at least partially buoyant, wherein the buoyancy compartment is located at least partially in the upper section. The phrase "the monopile is buoyant or "partially buoyant" means herein, that the monopile is subjected to buoyancy force sufficient to keep the monopile afloat or partly afloat. As described in more detail below the primary compartment may in an embodiment constitute the buoyancy compartment.

[0023] The installation comprises a plurality of attachment fairleads and at least three mooring lines arranged to support the monopile. The mooring lines may be in the form of guy ropes or cable stays running to and secured to water floor anchors via the plurality of fairleads. The attachment fairleads may be attached to the monopile and / or the attachment fairleads may be attached to an optional superstructure of the installation. In an embodiment, the installation comprises such superstructure, such as a wind turbine, a turbine tower and / or a transition piece, wherein the superstructure is supported by the monopile and wherein one or more of the attachment fairleads are attached to the superstructure.

[0024] The mooring lines may conveniently be arranged to anchor the monopile to water floor anchors via said plurality of fairleads and / or via said superstructure.

[0025] The inventors of the present invention have realised that by providing the lower section and in particular the tip section thereof with a relatively narrow outer diameter and at the same time ensuring a relatively high buoyant force provided by the at least one buoyancy compartment, the stability of the installation against lateral forces becomes relatively high. The mooring lines add additional stability and reduce the required moment capacity at and near the tip section. In addition the desired or required buoyant force may be further adjusted prior to, during or after installation by adjusting the water level in the primary compartment.

[0026] The adjustment of the water level in the primary compartment may preferably involve use of the opening arrangement, which at the same time may ensure a low or reduced risk of collapse of the monopile due to hydrostatic pressure,

[0027] Thanks to the present invention, a very large and valuable contribution to the art has been provided which results in a very strong, durable and cost effective installation.

[0028] Advantageously, the installation is an offshore installation, whereby the water location is an offshore location and the water bed is a seafloor and the raw water is sea (ocean) water.

[0029] Reference made to "some embodiments" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with such embodiment(s) is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases "in some embodiments" or "in an embodiment" in various places throughout the specification are not necessarily referring to the same embodiment(s). Further, the skilled person will understand that particular features, structures, or characteristics may be combined in any suitable manner within the scope of the invention as defined by the claims.

[0030] The term "substantially" should herein be taken to mean that ordinary product variances and tolerances are included. Throughout the description or claims, the singular encompasses the plural unless otherwise specified or required by the context.

[0031] All features of the invention and embodiments of the invention as described herein, including ranges and preferred ranges, may be combined in various ways within the scope of the invention, unless there are specific reasons not to combine such features.

[0032] The upper section of the monopile may also be referred to as the top end section. The upper section defines the top end. The lower section may also be referred to as the bottom end section and defines the bottom end. The lower section includes the tip section.

[0033] In an embodiment, the narrowest portion of the monopile is in the form of the tip section or a length portion thereof.

[0034] The monopile may comprise a mid-section located between the upper section and the lower section. The mid-section comprises or is defined by the primary compartment roof divider.

[0035] The monopile suitable for buoyant and guyed installation as well as the installed monopile suitable for or optionally comprising a superstructure supported by the monopile is herein also referred to a buoyant and guyed monopile (BGM) installation. The term "installation" is herein used to designate the BGM monopile and optionally a superstructure supported by the monopile as installed. The installation may also be referred to as a "support structure installation" or an "under water installation" meaning that at least a portion of the installation is located under water. It is preferred that the entire installation is under water except for a top end portion of the upper section.

[0036] The installation may advantageously be an offshore installation. The term "offshore installation" is herein used to mean an installation located at an ocean site. The term "ocean" is herein used to include "sea".

[0037] In an embodiment, the installation is a lake installation or a river installation, i.e. an installation located at a lake site or a river site. In an embodiment, some or all of the upper section and some or all of the midsection and some of the lower section of the installation may be located above water.

[0038] Preferably at least a part of, such as the entire mid-section is located below the water, such as below the waterline. The term "waterline is herein used to mean an average level of the water determined at still water over one month or longer, such as one year.

[0039] The term "water floor" is herein used to mean the floor of the water (ocean, lake or river). Where the installation is an offshore installation, the water floor is the seafloor.

[0040] The term "raw water" is herein used to mean water found in the environment and in particular ocean water, river water and lake water.

[0041] The term "attachment fairlead" means an attachment structure connecting or suitable for connecting at least one of the mooring lines to the monopile or to a superstructure supported by the monopile. The attachment fairlead may for example be connectable or connected directly to the monopile, such as to an outer surface location of the monopile or the attachment fairlead may for example be connectable or connected indirectly to the monopile, such as via an tension adjustment arrangement. The attachment fairlead may for example be in the form of or comprising an attachment point for securing the mooring line directly or indirectly to the monopile. In an embodiment, the attachment fairlead comprises a padeye for connecting to the mooring line, such as a padeye with a connected shackle or rope, such as a pulling bar.

[0042] In an embodiment the attachment fairlead form part of a tension adjustment arrangement as described further below, wherein the tension adjustment arrangement may be connected to and / or located in the monopile and preferably engaged directly or indirectly with the monopile. Sizes and shapes as used herein include what is within production and / or measuring uncertainties.

[0043] Where the monopile is not circular the monopile outer diameter is determined as the characteristic outer diameter, wherein "characteristic outer diameter" means the outer diameter of a circular shape having a periphery identical to the outer periphery of the non-circular monopile.

[0044] Any protruding flanges or ancillary elements are disregarded when determining the monopile outer diameter or the outer diameter of any sections thereof.

[0045] The monopile may be circular, oval or it may comprise one or more edges. Advantageously, the monopile is circular or predominantly circular. For production and cost reasons it is desired that the monopile at least in a portion of its length is circular, such as preferably in at least 50 % of its length, such as at least 70 % or its length, such as at least 90 % of its length, such as in the entire length of the monopile.

[0046] In a preferred embodiment, the monopile is circular in at least 70 % of its length.

[0047] The outer diameter of the upper section as well as the outer diameter of the lower section may vary gradually or stepwise along the length of the monopile.

[0048] The monopile may conveniently comprise one or more length sections of uniform outer diameter and preferably at least one slope section having a narrowing or widening outer diameter along its length. In an embodiment, the monopile comprises from its bottom end upwards a first section having an outer diameter DI, a second section having a widening outer diameter from DI to D2, a third section having an outer diameter D2, a fourth section having a narrowing section and a fifth section having an outer diameter D3, wherein at least the first section forms part of the lower section and at least the fifth section form part of the upper section.

[0049] In an embodiment, the at least one buoyancy compartment comprise a permanent buoyancy compartment.

[0050] The phrase "a permanent buoyancy compartment" is herein used to mean a compartment that is sufficiently watertight at its location or adapted location to prevent water ingress beyond 10 % of its volume, preferably beyond 5 % of its volume, more preferably beyond 1 % of its volume for 1 year or longer. Ideally the permanent buoyancy compartment is watertight.

[0051] The provision of the buoyancy compartment and especially the permanent buoyancy compartment provides security against loss and / or against damage of asset(s) during the monopile transportation and installation phase, which may reduce overall risk and insurance costs, thereby improving the economics of this support structure solution.

[0052] It should be understood that the monopile transportation may be a transportation over many kilometres of open and potentially very turbulent water.

[0053] The term "watertight" is herein used to mean that watertight element (e.g. a compartment, a divider etc.) in undamaged condition is capable of resisting water in liquid condition to pass into or through the watertight element.

[0054] The term "superstructure" is herein used to mean any structure supported by the monopile, preferably at the top end of the monopile, such as supported by a platform connected at the top end of the monopile. The superstructure may preferably be fixed to the monopile optionally via an intermediate structure, e.g. a platform and / or a transition piece, which in itself may be a superstructure. The superstructure may conveniently be a wind turbine, a turbine tower and / or a transition piece.

[0055] The superstructure may be any type of structure supported by the monopile and preferably connected to the monopile, preferably at or via the top end of the monopile.

[0056] The terms "above", "below", "beside", "under" and "over" when used in respect of locations relative to the monopile, is to be interpreted considering the monopile to be in an upright (vertical) orientation when it is installed.

[0057] As indicated above, the at least one buoyancy compartment may form part of the primary compartment. It may be desired to have only one buoyancy compartment and providing it to form part of the primary compartment, especially where the length of the monopile is not too high, e.g. 40 m or less.

[0058] For increasing durability and stability it is in an embodiment desired that at least one buoyancy compartment comprises a separate buoyancy compartment located closer to the top end than the primary compartment. As mentioned, the permanent buoyancy compartment may also result in reduced risk of loss and / or damage of asset(s) and may reduce insurance cost. Preferably, the at least one separate buoyancy compartment is located adjacent and preferably above the primary compartment separated by a compartment divider. The separate buoyancy compartment is preferably a permanent buoyancy compartment wherein the compartment divider is preferably watertight and preferably sufficiently airtight to maintain a pressure difference of 50 Pa for at least 24 hours, such as for one year or longer, preferably the compartment divider is sufficiently airtight to maintain a pressure difference of at least 1 kPa, such as at least 0.1 bar, such as at least 1 bar at for at least 1 hour, such as for 24 hours or longer.

[0059] Where at least one separate buoyancy compartment is located adjacent the primary compartment separated by a compartment divider, the compartment divider is advantageously sufficiently airtight to maintain a pressure difference corresponding to the hydrostatic pressure acting at a level of the opening arrangement.

[0060] The hydrostatic pressure at the level of the opening arrangement inlet is determined as the hydrostatic pressure in an undisturbed water column at a depth corresponding to the average level of an uppermost edge and a lowermost edge of the opening arrangement, for example for a period of at least 1 hour, such as for 24 hours, such as for 1 year.

[0061] The monopile may comprise one or more buoyancy compartments. In an embodiment, the monopile comprises a buoyancy compartment forming part of the primary compartment and a separate and preferably permanent buoyancy compartment located adjacent, preferably above the primary compartment separated by a compartment divider. The skilled person will understand that the monopile may comprise as many buoyancy compartments as desired to ensure a desired buoyant force and a sufficient level of security against loss of buoyancy during the transportation commissioning and decommissioning phases of the BGM.

[0062] Advantageously, at least a portion of the one or more buoyancy compartments is located above the waterline. Advantageously at least a portion of the one or more buoyancy compartments is located below the waterline.

[0063] Generally, it is desired that at least a top end portion of the uppermost of the one or more buoyancy compartment is located above waterline since this has shown to increase stability of the BGM installation. Advantageously, the primary compartment is watertight except for the one or more openings of the opening arrangement as well as optional openings for an optional internal tube and / or an optional gas escape tube and / or other closable openings e.g. for an inspection ROV (remotely operated vehicle), preferably the primary compartment except for said openings of the opening arrangement and when closable openings are closed, is sufficiently airtight to maintain a pressure difference of 50 Pa for at least 24 hours, such as for one year or longer, preferably the compartment divider is sufficiently airtight to maintain a pressure difference of at least 1 kPa, such as at least 0.1 bar, such as at least 1 bar at for at least 1 hour, such as for 24 hours or longer, such as for 1 year.

[0064] This may be determined by closing off the openings of the opening arrangement and applying the pressure difference.

[0065] The portion of the primary compartment between a primary compartment roof divider and the opening arrangement is advantageously sufficiently airtight to maintain a pressure difference 0.5 bar or more such as of 1 bar, which may for example be applied to establish a positive (tensile) hoop stress in the BGM wall. The primary compartment roof divider may conveniently be in the form of or comprising the compartment divider between a separate buoyancy compartment located adjacent to and above the primary compartment and the primary compartment.

[0066] In an embodiment, the portion of the primary compartment between the primary compartment roof divider and a level of the primary compartment located at a distance from the roof divider, which is 20% or more, such as up to 80 % of the distance between the roof divider and primary compartment floor divider, is sufficiently airtight to maintain a pressure difference of 1 bar or more.

[0067] In an embodiment, the primary compartment is defined by the primary compartment roof divider and a primary compartment floor divider, wherein the primary compartment floor divider defines the tip section of the lower section.

[0068] The tip section thereby stretches from the bottom end of the monopile to the primary compartment floor divider. The portion of the lower section above the primary compartment floor divider is designated the lower section body portion. Advantageously, the primary compartment is closed off by the primary compartment roof divider and the primary compartment floor divider, meaning that the primary compartment roof divider defines an upper end termination of the primary compartment and the primary compartment floor divider defines a lower end termination.

[0069] The primary compartment roof divider may in an embodiment serve as or form part of a compartment divider.

[0070] The one or more compartment dividers of the monopile, such as the primary compartment roof divider, the primary compartment floor divider and / or any compartment divider may advantageously be designed to withstand applied pressure differences, such as over-pressure by either a plate bending effect where the compartment divider comprises a plate, such as a rigid plate or a membrane effect where the compartment divider comprises a membrane, such as a diaphragm, or a combination of the two, such that the resulting stresses in the membrane / diaphragm due to this effect may be tensile, or the pressure may be resisted by the action of a compression dome, where the stresses will be compressive in combination with some plate bending, resulting in compressive only forces in this region. The resulting stresses in the diaphragm due to this effect may be tensile or compressive.

[0071] The primary compartment floor divider may preferably comprise or be constituted by a watertight diaphragm, such as a bulge shaped or dome shaped or flat watertight diaphragm. In an embodiment the primary compartment floor divider comprises a watertight diaphragm and a plate located above the watertight diaphragm.

[0072] The opening arrangement may preferably be located above the primary compartment floor divider.

[0073] The opening arrangement in the lower section into the primary compartment advantageously comprises a flooding hole in the wall of the monopile into the primary compartment. It has been found to be beneficial to provide the flooding hole or at least one of the flooding holes where there are several, to be located closer to the primary compartment floor divider, than to the primary compartment roof divider. This may for example be beneficial during installation where the primary compartment is flooded to ballast the monopile to be tilted to an upright orientation and further it may be beneficial for ensuring a desired pressurization of the upper portion of the primary compartment as explained further below. In an embodiment, at least one flooding hole of the opening arrangement is located above the primary compartment floor divider and with a distance from a centre of the flooding hole to the primary compartment floor divider not exceeding 3 m, such as less than 2 m, such as less than 1 m, such as less than 0.5 m.

[0074] In an embodiment, the opening arrangement comprises a gas escape hole adapted for passing of a gas escape tube as described further below. In an embodiment, the flooding hole and the gas escape hole are provided in the form of a common flooding and gas escape hole.

[0075] The term "gas" is herein used to designate any kind of gas, preferably air or another non-flammable gas. Where the term "air" is used, the skilled person will understand that another gas may be applied instead.

[0076] The primary compartment has a height along the monopile length. The height may be defined as the maximal distance between the primary compartment roof divider the primary compartment floor divider. The flooding hole or at least one of the flooding holes is located within a distance of up to 50 % of the primary compartment height from the primary compartment floor divider, such as within a distance of up to 40 %, such as up to 20 %, such as up to 10 %, such as up to 5 % of the primary compartment height from the primary compartment floor divider, such as within a distance of up to 5 m from the primary compartment floor divider.

[0077] The maximal distance between the primary compartment roof divider and the primary compartment floor divider, may conveniently be a distance determined parallel with a centre axis of the monopile.

[0078] The flooding hole may advantageously be located relatively close to the primary compartment floor divider e.g. immediately adjacent to the primary compartment floor divider. The opening arrangement may comprise two or more flooding holes, preferably all located within the mentioned distances to the primary compartment floor divider.

[0079] In an embodiment, the opening arrangement comprises two or more flooding holes located with different distance to the primary compartment floor divider. The one or more flooding holes may beneficially be closable e.g. using a plug, or a valve, which may be beneficial for transporting the monopile for installation as described further below. In an embodiment, where the opening arrangement comprises two or more flooding holes, these two or more flooding holes may advantageously be individually closable.

[0080] Advantageously, the monopile comprises a closing arrangement adapted for temporarily restricting or closing off the opening arrangement or at least a part thereof, preferably for restricting and optionally blocking for water passage through openings, such as through the one or more flooding holes of the opening arrangement. The closing arrangement may for example be adapted for temporarily and optionally quickly closing and sealing the flooding hole(s).

[0081] The closing arrangement may be applied for restricting or closing, such as quickly closing and sealing the opening arrangement and especially the one or more flooding holes during the installation, i.e. during the process of establishing the installation, such as during transportation as further described below. In an embodiment, the closing arrangement is adapted for temporarily and individually restricting or closing one or more flooding holes of the opening arrangement which advantageously may assist in the safe establishment of the monopile in the operational configuration.

[0082] The closing arrangement may for example comprise a valve, a plug, a lid or any combinations comprising one or more of these.

[0083] In an embodiment, the closing arrangement is detachable from the monopile.

[0084] The closing arrangement may conveniently comprise a controller adapted for controlling the opening arrangement from being fully open to water flow to being fully closed for water flow. The controller may be adapted for controlling an opening degree of the opening arrangement from being fully open to being fully closed. The controller may for example be adapted for receiving instructions from an operator, optionally via instruction signals that may be transmitted by wire or wireless e.g. via an operator station. The degree of opening may conveniently comprise two or more stages, such as fully closed, partially open and fully open. The degree of opening may in an embodiment comprise opening degrees, in the form of percentages open, such percentages from zero % (fully closed) to 100 % (fully opened) and any percentages of open there in-between. Thereby a highly fine tuning of the opening arrangement for controlling the passage of water through the flooding holes may be provided.

[0085] The closing arrangement may thereby be at least partly controllable from a distance via the controller.

[0086] In an embodiment, the controller is adapted for controlling the opening and closing, such as the opening degree of two or more flooding holes individually.

[0087] Advantageously, the controller is programmed for at least in part adjust the opening degree in dependence of the orientation from a horizontal orientation e.g. during towing and / or tilting to an upright (essentially vertical) orientation.

[0088] To protect the monopile against damage due to the very high hydrostatic forces acting on the monopile below the waterline, especially acting on the lower section of the monopile, it has been found to be very beneficial to provide that an upper portion of the primary compartment comprises pressurized gas (preferably air or nitrogen). Preferably the pressure in the primary chamber along the length of the monopile is sufficiently high to counter act the hydrostatic pressure acting onto the monopile along this length. Advantageously, the pressure at any elevation inside the primary compartment is larger than or equal to the hydrostatic pressure acting at the outer wall of the monopile at the corresponding elevation.

[0089] By pressurizing the primary compartment the risk of damages the monopile caused by hydrostatic pressure may be reduced. In addition, it has been found that in some embodiments the required wall thicknesses may be relatively low compared to the wall thickness of monopiles of prior art installations. This may reduce the cost of the monopile considerably and thereby reduce the cost of the entire installation.

[0090] The pressurizing of the primary compartment may increase the resistance of the monopile to local buckling as it will generate a positive hoop stress, and it may increase the resistance of the monopile to global buckling as it will reduce the amount of axial loading in the walls of the monopile because of the effect of the upwards pointing loading on the primary compartment roof divider which advantageously may be in the form of a biscuit deck as described further below, These effects allow a designer to account for lower stresses in the monopile walls, and reduced tendency to buckle when the monopile is exposed to the in-service loads.

[0091] The deliberate engineering of an internal over-pressure in the primary compartment increases the required axial load applied to the monopile for a given cross-sectional geometry of the monopile, and it reduces the required wall thickness of the monopile for a given diameter, required to resist the applied loads in the monopile structure without buckling. This effect results from the deliberate equalisation of internal and external pressures at the monopile flooding hole(s) and may be used to allow reduction of steel weight and thereby also a reduction of cost.

[0092] To establish and maintain a desired degree of pressurization, the installation advantageously comprises a pressure control arrangement for controlling the pressure in the primary compartment. The pressure control arrangement preferably comprises a pump for supplying pressurized gas to the primary compartment.

[0093] The pressurized gas, such as air, may for example be supplied to primary compartment via a gas control tube, such as a flexible or rigid tube, e.g. a J-tube, an I-tube or similar. The gas control tube may extend inside the monopile from the primary compartment and upwards e.g. to within the upper section or to the top end of the monopile or even beyond the top end if desired.

[0094] The gas control tube may advantageously comprise an air control valve to maintain the pressure at a desired level.

[0095] The pump or other parts of the pressure control arrangement may be located within or on top of the BGM or on a platform attached to the BGM or at an external unit, such as on a supporting vessel with a connecting pressure line.

[0096] In an embodiment, the pressure control arrangement comprises an internal tube, passing through the primary compartment roof divider into the primary compartment and extending from a first internal tube end located at a first location in the primary compartment to a second internal tube end located at a second location above the primary compartment and preferably above the at least one buoyancy compartment. Preferably the first location in the primary compartment is located at a distance to the primary compartment roof divider up to 20 % of the primary compartment height. The second location may conveniently be located above waterline, such as at or above or within 3 m of the top end.

[0097] The internal tube may conveniently also act as, or be combined with, the gas control tube.

[0098] In practice, the gas control tube may be a small diameter pipe, allowing air to escape and may be throttled, as the BGM is ballasted down. Then when the BGM is in place, and a positive internal pressure is to be applied, gas, such as air from a compressor may be driven down this gas control tube into the upper part of the primary chamber, and the water in the primary compartment may be forced down and some of the water may be expelled via the opening arrangement.

[0099] The pressure control arrangement advantageously comprises a closable gas release valve for allowing gas, such as air to escape from the primary compartment. Preferably the gas release valve is a gas release valve of the gas control tube and is located at the upper half part of the primary compartment closest to the top end, such as located in the primary compartment roof divider or in the monopile wall. In an embodiment, the gas release valve is located in the primary compartment roof divider or in the monopile wall at a distance to the primary compartment roof divider up to 20 % of the primary compartment height, such as a distance to the primary compartment roof divider up to 2 m. In an embodiment the gas release valve may be located above the primary compartment roof divider in and / or above the midsection, with an outlet opening from the primary compartment in the primary compartment roof divider.

[0100] The pressure control arrangement may provide or contribute to the option that the installation of the monopile to be secured with the mooring lines of embodiments of the invention may be carried out without the need for a heavy lift vessel. Thereby the installation of the BGM of embodiments of the invention may be performed in a very economic manner, and yet still being able to meet all of the performance requirements for installation of a monopile forming a foundation, even for a relatively large horizontal axis wind turbine.

[0101] In an embodiment, the pressure control arrangement comprises a gas escape tube, wherein the gas escape tube extends from a first gas escape tube end located in the primary compartment through a gas escape hole of the opening arrangement and along the monopile length, preferably upwards, to a second gas escape tube end located outside the monopile. Advantageously, second gas escape tube end is located at a level of or above the upper section of the monopile. Preferably the first gas escape tube end is located at an upper half part of the primary compartment closest to the primary compartment roof divider.

[0102] In an embodiment, the second gas escape tube end is located above an optional water level in the primary compartment. The second gas escape tube end is preferably located above waterline. The gas escape tube preferably comprises a closable gas release valve for allowing gas, such as air to escape from the primary compartment.

[0103] The gas escape tube is especially valuable during the installation of the BGM, wherein after installation, the gas escape tube may optionally be removed. And the gas escape hole may optionally be sealed e.g. by the closing arrangement.

[0104] The desired length of the respective sections of the monopile depend largely on the total length of the monopile as well as the installation depth.

[0105] In an embodiment the installation is a universal water installation, which may be suitable for instalment at practically any depth of water including both shallow water installations and deep water installations. Where the water is relatively deep, such as 60 m or deeper, the universal water installation is preferred or even required. The universal water installation is characterized in that the attachment fairleads are attached to or engaged with the monopile below the waterline (preferably providing the first attachment of the mooring line as the mooring line passes from one of the water floor anchors to the monopile). Thereby, the monopile is anchored by the mooring lines to the floor anchors via the plurality of attachment fairleads located below the water line.

[0106] The universal water installation is also referred to as a universal BGM installation.

[0107] In an embodiment the installation is a shallow water installation, which may be suitable or even preferred for installation in shallow water, such as water of a depth of 70 m or less, such as 50 m or less. The shallow water installation is characterized in that the attachment fairleads are attached to or engaged with the monopile or to a superstructure of the installation supported by the monopile above the waterline. Preferably, the attachment of each respective mooring line to the monopile or to the superstructure is the first attachment of the mooring line directly or indirectly to the monopile or to the superstructure as the mooring line passes from one of the water floor anchors to the monopile or to the superstructure. Thereby the monopile is anchored by the mooring lines to the floor anchors via the attachment fairleads attached to the monopile and located below the water line or via the attachment fairleads attached to the superstructure and located above the water line.

[0108] The shallow water installation is also referred to as a shallow BGM. The monopile may preferably comprise a mid-section located between the upper section and the lower section. The lower section and the mid-section are advantageously located or adapted to be located below or mostly below the waterline.

[0109] The lower section may conveniently have a length of up to 80 % of the monopile length, such as up to 70 %, such as up to 50 %, such as up to 40 % of the monopile length.

[0110] This means in practice that the lower section may have a length of up to 200 m, such as 150 m, such as up to 130 m, such as up to 100 m, such as up to 60 m, such as up to 30 m.

[0111] As mentioned above it may be beneficial that the lower section has a relatively narrow diameter compared to the total average monopile diameter. In an embodiment, the lower section has an average outer diameter of 80 % or less than the average monopile outer diameter, such as 70 % or less, such as 60 % or less, such as 50 % or less than the average monopile outer diameter.

[0112] In an embodiment, the lower section has an average outer diameter of 75 % or less than a maximal monopile outer diameter, such as 50 % or less such as 40 % or less, such as 30 % or less, such as 20 % or less than the maximal monopile outer diameter.

[0113] The lower section may advantageously have an average outer diameter of 7 m or less, such as of 6 m or less, such as of 4 m or less.

[0114] In an embodiment, the lower section extends from the bottom end to the water level in the primary compartment. In an embodiment, the lower section extends from the bottom end to the primary compartment roof divider. In an embodiment, the lower section extends from the bottom end to half the height of the primary compartment.

[0115] Advantageously, the lower section extends from the bottom end to the mid-section.

[0116] In an embodiment, the lower section body portion extends from the tip section to the water level in the primary compartment. In an embodiment, the lower section body portion extends from the tip section to the primary compartment roof divider. In an embodiment, the lower section body portion extends from the tip section to at least half the height of the primary compartment.

[0117] Advantageously, the lower section body portion extends from the tip section to the mid-section.

[0118] The mid-section is preferably defined by the primary compartment roof divider. In an embodiment, the mid-section is defined as the length section of the monopile comprising the primary compartment roof divider, preferably comprising at least the watertight diaphragm, such as a bulge shaped or dome shaped or flat watertight diaphragm. In an embodiment the primary compartment floor divider comprises a watertight diaphragm and a plate located above the watertight diaphragm. The plate may form part of the biscuit deck described below.

[0119] The tip section may advantageously have a length of up to 20 % of the lower section length, such up to 10 m, such as at least 0.5 m, such as at least 1 m, such as from 2 m to 10 m.

[0120] The upper section may advantageously comprise a top end portion comprising the top end and located or adapted to be located above waterline. The upper section may comprise a body portion below the top end portion, wherein the body portion comprises at least a part of the at least one buoyancy compartment. Thereby an effective buoyancy effect may be provided.

[0121] Advantageously, at least a part of the tip section is supported by the water floor by being at least partially embedded in the water floor or in a footing arrangement, wherein the footing arrangement is located at or in at the water floor and preferably anchored in or at the water floor. The footing arrangement may advantageously comprise a footing in the form of a physical object which is placed on and preferably anchored at or in the water floor and which is advantageously capable of supporting the lower section against significant vertical and horizontal translation / movement.

[0122] The footing arrangement advantageously, comprises a footing, wherein at least a part of the tip section is secured to the footing. The securement may for example comprise at least one of a grouted connection, a slip-joint connection, a bearing connection, a bolted connection, a socket connection, a tension restraint, a hinge connection, a pin connection, or any combinations thereof.

[0123] Where the footing arrangement comprises a footing, the footing may conveniently comprise a support recess in which at least a part of the tip section may be resting. The tip section may advantageously be held fixed to the footing by filler material and / or a binder material, such as grout e.g. cementitious grout and / or epoxy, and / or it may be tethered to the footing with a tensile element, such as a cable or rod.

[0124] The maximal diameter of the part of the tip section secured to and / or adapted to be secured in the footing is preferably not exceeding the diameter of any diameter of the remaining of the monopile.

[0125] In an embodiment the monopile may be connected to the footing in a 'pin' connection, wherein at least the portion of the tip section inserted into the support recess is shaped as a pin, preferably having a constant diameter along the length of the pin shaped tip portion. It has been found that this architecture of the footing and the tip section ensures that lateral forces applied from the monopile to the footing arrangement is relatively low.

[0126] In an embodiment, the monopile may be connected to the footing to provide that there is practically no relative movement between the monopile tip and the recess in the footing, because friction, mechanical interference and / or adhesion may prevent any relative movements. The shape of the monopile adjacent to the waterfloor may be such that the stiffness of the monopile cross-section is reduced, compared to the stiffness of the section of the monopile at the biscuit deck, so that the monopile may flex elastically to reduce moments transmitted from the monopile into the footing, resulting in that the footing requires only minimal resistance to moment loading and thereby a very the economical attractive solution is provided. Furthermore, to prevent accumulation of unwanted moments at the waterfloor, the footing may be designed to permit rotation about a horizontal axis, whilst simultaneously maintaining vertical stability, which reduces the required structural support thereby providing an additional economical attractive solution.

[0127] As explained further below, the footing may advantageously be preinstalled prior to installing the monopile e.g. using suction-caisson principle, or gravity-base principle, or a driven pile, or a drilled pile, with or without skirts.

[0128] The at least one, such as all of the plurality of attachment fairleads may preferably be attached to the monopile at respective fixing locations. Advantageously, the fixing locations are located at a common fixing length section of the monopile, such as a common fixing length section having a length of 6 m or less, such as 5 m or less, such as 4 m or less, such as 2 m or less.

[0129] In an alternative embodiment, the attachment fairleads are attached to a superstructure supported by and preferably connected to the monopile. The superstructure may be any type of structure supported by the monopile and preferably connected to the monopile, preferably at or via the top end of the monopile.

[0130] The monopile and / or the superstructure supported by the monopile may comprise one or more support fairleads for providing additional guiding to one or more of the mooring line. A support fairlead is characteristic in that a mooring line from a water floor anchor is first guided by an attachment fairlead and then optionally to one or more support fairleads. The support fairleads may in principle be located at any locations e.g. as known from prior art.

[0131] The monopile may comprise additional elements such as or trunnions or padeyes located at any locations e.g. higher up on the BGM or inside the monopile and / or as known from prior art.

[0132] In an embodiment, the monopile comprises one or more winches, turn-buckles and / or rams, wherein each winch, turn-buckle and / or ram may be arranged to adjust the tension in one or more of the mooring lines.

[0133] The one or more rams may conveniently comprise a hydraulic ram and / or a pneumatic ram. The attachment fairleads at the fixing locations may in an embodiment provide terminating mooring locations of one or more of the respective mooring lines. In an embodiment, the respective mooring lines may independent of each other continue to another point on, at or within the monopile for anchorage e.g. at a winch.

[0134] As indicated above, the monopile may comprise mid-section located between the upper section and the lower section. Advantageously, the common fixing length section form part of the mid-section. This is especially desired where the installation is a universal BGM installation.

[0135] The common fixing length section advantageously constitutes or form part of the mid-section of the monopile. The mid-section, is a length section of the monopile advantageously located between the upper section and the lower section. By providing that the fixing locations are arranged at a common level defined by the length of the common fixing length section, a high stabilisation of the upright BGM may be ensured and simultaneously it may provide a simpler fine tuning of the tension in the mooring lines.

[0136] The plurality of attachment fairleads attached to the monopile may therefore advantageously be located at the same or similar level of the monopile i.e. at fixing locations which have same or similar distance to the top end, wherein "similar" here means within a length portion of the mid-section of the monopile, such as within up to 4 m, such as up to 2 m of the length of the monopile.

[0137] The fixing location of a fairlead may be a location where the fairlead is directly fixed to the monopile.

[0138] Where the fairlead forms part of a tension adjustment arrangement, the fairlead is provided by the structure having or adapted to have a direct connection to the mooring line, wherein the connection is closer to the water floor anchors than any optional additional connection between the mooring line and the tension adjustment arrangement. The fixing location may thereby be outside or inside the monopile and the level of the fixing location relative to the monopile is determined as the horizontal level of the monopile corresponding to the fixing location. This allows for the mooring lines to be secured at a same or similar fixing location on the circumference from 2 or more different anchors, and for reducing the number of required fixing locations for ease of fabrication.

[0139] In an embodiment the plurality of attachment fairleads attached to the monopile may advantageously be located at fixing locations which have different distance to the top end.

[0140] In an embodiment, the common fixing length section of the monopile forms part of or comprises the mid-section.

[0141] In an embodiment, the common fixing length section of the monopile comprises a length section of the upper section of the monopile located above the mid-section and preferably above the waterline. This is especially desired for the shallow BGM installation.

[0142] In an embodiment, the common fixing length section of the monopile, such as the mid-section of the monopile comprises a biscuit deck, wherein the biscuit deck preferably comprises, forms part of or constitutes the primary compartment roof divider.

[0143] The common fixing length section of the monopile, preferably comprises a reinforcement, such as a stiffening arrangement comprising one stiffening ring, two stiffening rings or other stiffening elements. In an embodiment the mid-section of the monopile comprises the reinforcement, such as the stiffening arrangement.

[0144] The stiffening ring or other stiffening arrangement preferably facilitates the transfer of horizontal loading from the monopile into the mooring lines, and facilitates the application of vertical loading from the mooring lines into the monopile without overstress whereby the monopile is securely kept at the intended vertical position attained after installation is complete.

[0145] In an embodiment, the common fixing length section of the monopile, such as the mid-section of the monopile comprises a deck which may advantageously provide a stiffening effect on the monopile, herein referred to as a biscuit deck. The biscuit deck may provide or form part of the stiffening arrangement of the common fixing length section of the monopile. In an embodiment the biscuit deck comprises, forms part of or constitutes the primary compartment roof divider. In an embodiment, the primary compartment roof divider comprises an airtight diaphragm e.g. as described above, which may be integrated with the biscuit deck or be located below the biscuit deck, such as immediately below the biscuit deck, e.g. within a distance not exceeding 5 m, preferably not exceeding 3 m.

[0146] The airtight diaphragm may advantageously be bulge shaped or dome shaped, e.g. to extend over a height along the length of the monopile which is for example up to 4 m, such as from at least 1 m to 3 m.

[0147] The biscuit deck advantageously provides a strong and stiff region of the monopile. Thereby the biscuit deck provides and ensures a desired strong region for the mooring lines connected to the monopile via the fairleads. In addition the biscuit deck may form part of or constitute the primary compartment roof divider optionally in combination with the airtight diaphragm, which also may require a strong and stiff structure.

[0148] It has been found to be very beneficial to provide the monopile such that the midsection contains the biscuit deck, the common fixing length section and other parts that are material requiring and may require intensive fabrication. Thereby these parts are grouped together and may be fabricated by one fabricator in an economic manner. In addition, this leaves much of the upper section and the lower section, without such fabrication intensive features and contributing to the overall economy of the BGM installation.

[0149] However, where the installation is a shallow BGM installation the common fixing length section of the monopile, including the biscuit deck may be located above the mid-section and / or above the waterline e.g. as described above.

[0150] The plurality of attachment fairleads when attached to the monopile may conveniently comprises at least 3 attachment fairleads, wherein each attachment fairlead is attached to the monopile at a fixing location by anchoring the at least one attachment fairlead to the monopile from the outer surface of the monopile or by anchoring the at least one attachment fairlead at least partially at an internal location of the monopile, such as at or above the biscuit deck. The fixing may advantageously comprise a weldment. The mooring lines may be arranged to anchor the monopile to water floor anchors via the plurality of attachment fairleads, wherein each mooring line is attached to the monopile via at least one of the attachment fairleads and at least one of the water floor anchors. In an embodiment, each of one or more of the mooring lines is attached to the monopile via at least one of the attachment fairleads and at least two separate of the water floor anchors, wherein the two separate water floor anchors to which each end of the mooring line is attached, are located with a distance to each other.

[0151] Thereby, each mooring line may be anchored to two different water floor anchor and thus provides two mooring line portions extends from a respective of the attachment fairleads to a respective of the water floor anchors. It has been found that by applying this mooring line configuration it becomes relative simple to adjust the mooring line tension.

[0152] The mooring lines may be arranged in any configurations that ensures a desired guying of the monopile. A desired mooring line configuration may depend largely on the water floor conditions, water current conditions and other environmental conditions. In an embodiment, two or more mooring lines may be attached to a common of the water floor anchors.

[0153] Each of the mooring lines or mooring line portions may independently of each other extends from a respective of the attachment fairleads to a respective of the water floor anchors with a straight line or a non-straight line. The non-straight line may e.g. be caused by a tension adjustment arrangement, such as a restrictor, or a clump weight.

[0154] In an embodiment, mooring lines are arranged to anchor the monopile to water floor anchors via the plurality of attachment fairleads, wherein each of the mooring lines or mooring line portions extends from of the attachment fairleads to one of the water floor anchors with a straight line as seen in plan-top-view, wherein the straight line of each of the mooring lines or mooring line portions intersects at an intersection point with the outer surface of the monopile, and with an intersection plane having an angle of 30 degrees or less, such as an angle of 20 degrees or less, such as an angle of 15 degrees or less from a plane tangential to the outer surface of the monopile at that intersection point. It has been found that providing the straight line of each of the mooring lines or mooring line portions to intersect with the outer diameter of the monopile at an angle within 30 degrees or less, such as 20 degrees or less or in particular 15 degrees or less deviation from an exactly tangential line the out-of-plane loading imposed on the monopile wall may be reduced or even minimised, compared to an angle closer to perpendicular to the monopile wall, and thereby assisting with an effective and efficient transfer of forces from the mooring lines into the shell of the monopile.

[0155] Advantageously, the installation comprises at least one tension adjustment arrangement for adjusting and / or tuning the mooring line tension, such as for controlling and / or fine-tuning the mooring line tension and preferably for adjusting the system stiffness. Optionally the tension adjustment arrangement comprises a winch, or a turn-buckle, or a ram, such as a hydraulic ram and / or a pneumatic ram.

[0156] In an embodiment, one or more of the attachment fairleads form parts of the tension adjustment arrangement.

[0157] The tension adjustment arrangement may ensure that the installation comprising the monopile and optional superstructure supported by the BGM may be maintained continuously to operate within a specified lateral and rotational stiffness limits throughout the operational lifetime thereof.

[0158] In an embodiment, the at least one tension adjustment arrangement comprises a length adjustment device adapted for adjusting a free length of one or more of the mooring lines, such as for adjusting the free length of a plurality of the mooring lines. The free length of a mooring line, is herein defined as the length of the mooring line extending the length between the water floor anchor and the monopile.

[0159] In an embodiment, the at least one tension adjustment arrangement comprises a length adjustment device for each of the mooring lines.

[0160] In an embodiment, the at least one tension adjustment arrangement comprises one or more fairleads.

[0161] In an embodiment the installation comprises a structural health monitoring systems in data communication with the tension adjustment arrangement. The structural health monitoring system is adapted for monitoring a system natural frequency of the installation, such as the universal BGM. installation or the shallow BGM installation based on data received from the tension adjustment arrangement and wherein the structural health monitoring systems is adapted for providing instructions to the tension adjustment arrangement for adjusting the tension in at least one of the plurality of the mooring lines, preferably a plurality of the mooring lines to maintain the natural frequency within a pre-defined frequency range. The pre-defined frequency range may preferably be a frequency range acceptable for an installation comprising the monopile and the superstructure supported by and preferably connected to the monopile, such as a frequency range acceptable for a wind turbine supported by the installation and / or for one or more other superstructures in physically contact with the monopile or other structures in contact with the installation, such as an offshore electrical substation.

[0162] In an embodiment the structural health monitoring systems is adapted determining and for providing instructions to the tension adjustment arrangement for pretensioning one or more of the mooring lines prior to installing a superstructure to be connected to and be supported by the monopile.

[0163] The data communication between the structural health monitoring systems and the tension adjustment arrangement may advantageously be wireless.

[0164] In an embodiment, the structural health monitoring system is adapted for measure or calculate the system natural frequency based on the data received from the tension adjustment arrangement.

[0165] In an embodiment, the mooring line tensioning adjustment is performed automatic comprising that the structural health monitoring and the mooring line tensioning adjustment is operating in an automatic mode, comprising that the structural health monitoring system is adapted for transmitting the provided instructions directly to the tension adjustment arrangement for executing the adjustment of the tension in the at least one plurality of the mooring lines.

[0166] In an embodiment the mooring line tensioning adjustment is performed semiautomatic, wherein the structural health monitoring and the mooring line tensioning adjustment is operating in a semi-automatic mode, comprising that the structural health monitoring systems is adapted for transmitting the provided instructions to an operational management system where the instructions may be verified and / or assessed according to a protocol and if passed the provided instructions will be transmitted to the tension adjustment arrangement for executing the adjustment of the tension in the at least one plurality of the mooring lines. This may advantageously be beneficial in a running-in period, such as such as within the first days, e.g. 1-50 days after having installed the superstructure. Thereafter it may be desired to operate in the semi-automatic mode at regular selected control interval to ensure a desired operation of the structural health monitoring and the mooring line tensioning adjustment when operating in the automatic mode. Advantageously, the at least one tension adjustment arrangement is adapted for adjusting a verticality of the monopile.

[0167] The at least one tension adjustment arrangement may conveniently comprise one or more internal or external hydraulic rams, which are adapted for shorten or elongate one or more of the mooring lines.

[0168] In an embodiment, the at least one tension adjustment arrangement comprises one or more threaded bars acting in-line with the mooring line connected to a fairlead of the tension adjustment arrangement, which can be pulled to elongate the mooring line, or released to shorten it.

[0169] Thereby adjusting the tension force in the line with a high degree of accuracy, consistent with the objective of fine-tuning the system verticality and stiffness.

[0170] The at least one tension adjustment arrangement may preferably be at least partly located internally in the monopile, preferably at or above the biscuit deck.

[0171] By locating the tension adjustment arrangement internally in the monopile access for operation and maintenance from one of the existing deck levels may be enabled. In addition the tension adjustment arrangement may be protected against both mechanical and chemical wear internally in the monopile.

[0172] By locating the tension adjustment arrangement internally in the monopile at or above the biscuit deck i.e. in a compartment comprising an upper surface of the biscuit deck as floor an advantageous access to the tension adjustment arrangement may be provided, thereby enabling easy access for operation and maintenance of the tension adjustment arrangement. In an embodiment, a part of the tension adjustment arrangement and / or the mooring line(s) penetrates the monopile wall and wherein a sealing is arranged to seal around the penetrating part and / or mooring line, preferably provided such that it allows penetrating movable parts of the tension adjustment arrangement and / or penetrating mooring line(s) to move freely through the monopile wall.

[0173] The sealing provided may be any kind of seal suitable for use in offshore environments, such as the type of seal used to prevent water ingress into the hull of a ship around the drive shaft, or the kind of seal used around electrical cables or another kind of seal, which is capable of resisting the pressure that may be expected at the sealing location. The sealing is advantageously provided such that it allows a part of the tension adjustment arrangement and or the mooring line that penetrates the monopile wall to move freely and for the adjustment device to remain dry and accessible from within the personnel accessible areas of the upper section. The sealing may e.g. comprise a seal element for example be a Roxtec™ seal, a ship drive shaft stuffing box or similar. In an embodiment, the sealing arrangement is, similar to a propeller shaft seal allowing the drive shaft to pass through a ship hull without letting any water in.

[0174] In an embodiment, the sealing comprises one or more through hole fittings.

[0175] In an embodiment, where a part of the tension adjustment arrangement and / or the mooring line(s) penetrates the monopile wall and wherein a sealing is arranged to seal around the penetrating part, the monopile may comprise a tension adjustment arrangement opening and the tension adjustment arrangement comprises a pulling bar connected to or connectable to the mooring line. The pulling bar thereby comprises the fairlead, such as a pad eye, which is connected to the mooring line. One of the pulling bar and the mooring line penetrates the monopile wall via the tension adjustment arrangement opening. Thereby the mooring line or the pulling bar of the tension adjustment arrangement extends from outside the monopile and through the tension adjustment arrangement opening into an internal compartment of the monopile, such as an internal compartment located above the mid-section, such as above the biscuit deck. Advantageously, the mooring line is connected to the pulling bar outside the monopile and the pulling bar extends from outside the monopile and through the tension adjustment arrangement opening into an internal compartment of the monopile. Thereby the tension adjustment arrangement including the pulling bar and optionally any seal arrangements may be pre-installed in the monopile.

[0176] The installation comprises the seal arrangement, which comprises a tube seal arrangement connected to the monopile adjacent the tension adjustment arrangement opening to form a seal between the mooring line or preferably the pulling bar penetrating the monopile and an outer edge portion of the outer monopile surface along a periphery of the tension adjustment arrangement opening through the monopile wall.

[0177] In an embodiment the tube seal arrangement comprises an eyeball structure comprising a socket with a bearing surface and a hemisphere tube seal arrangement with a hemisphere adjustment arrangement, wherein the hemisphere tube seal arrangement comprises a spherical cap surface arranged to face the bearing surface. Each of the socket and the hemisphere tube seal arrangement comprises a passage for the mooring line or preferably the pulling bar penetrating the monopile. The hemisphere tube seal arrangement is adjustable via the hemisphere adjustment arrangement relative to the bearing surface to provide that the spherical cap surface is adjusted relative to the bearing surface, to provide that the passage of the socket and the passage through the hemisphere tube seal arrangement are in alignment relative to each other, and in alignment with the pulling bar or said mooring line. Thereby the hemisphere tube seal arrangement may be adjusted to ensure that the mooring line and / or the pulling bar penetrating the monopile extend(s) in a relative straight line. As mentioned it is desired that the mooring line is connected to or connectable to the pulling bar outside the monopile and the pulling bar extends from outside the monopile and through the tension hemisphere adjustment arrangement opening, through the passage of the socket and the passage through the hemisphere tube seal arrangement, which may accordingly be pre-installed in the monopile prior to attaching the mooring line.

[0178] The adjustment of the hemisphere tube seal arrangement may preferably be provided prior to fully tensioning the tension hemisphere adjustment arrangement - i.e. the tension hemisphere adjustment arrangement is in an untensioned stage ensuring that the hemisphere tube seal element is adjustable relative to the socket. After the tension hemisphere adjustment arrangement has been fully tensioned the hemisphere tube seal arrangement cap surface will be pressed towards the socket surface whereby the friction between the hemisphere tube seal arrangement cap surface and the bearing surface may prevent further adjustment.

[0179] The adjustment of the hemisphere tube seal arrangement may e.g. be performed at least partially by the hemisphere adjustment arrangement, such as a mechanical adjustment mechanism located in the internal compartment.

[0180] The hemisphere tube seal arrangement may beneficially be shaped as a hemisphere or as a part-hemisphere.

[0181] In an embodiment the tube seal arrangement comprises a flexible covering structure applied against and optionally connected to the outer edge portion along the periphery of the tension hemisphere adjustment arrangement opening. Preferably the tube seal arrangement further comprises and a seal collar arranged to seal between the flexible covering structure and the mooring line or preferably the pulling bar. In an embodiment the flexible covering structure and the seal collar are integrated with each other, such as formed in a single element or fixed to each other e.g. with a glue. The seal arrangement may further comprise a seal ring located in the passage of the hemisphere tube seal arrangement to form a seal between the hemisphere tube seal arrangement and the mooring line or preferably the pulling bar passing through the hemisphere adjustment element.

[0182] In use, the hydrostatic pressure provided by the surrounding water may apply a hydrostatic pressure towards the flexible covering structure and the seal collar which provides a pressure against the socket and the hemisphere adjustment element. Where the socket is at least partially fixed in the flexible covering structure and / or the seal collar, the resulting pressure may result in a reduce contact pressure between the bearing surface and the spherical cap surface of the hemisphere adjustment element, which may ensure allowing the adjustment of the hemisphere tube seal arrangement relative to the bearing surface, preferably to direct the mooring line exactly at the point close to the seabed where the mooring line terminates, before tension is added to the mooring line by the tension hemisphere adjustment arrangement, which then pushes the hemisphere tube seal arrangement bearing surface, whereby friction is increased and further relative movement may be prevented. On the outside of the monopile, the hydrostatic pressure may cause the flexible covering structure to push tight against the monopile opening, and reduce water ingress to a minimum or even prevent water ingress. The seal collar further add to ensure this sealing. The seal ring ensures that where minor amounts of water has passed the flexible covering structure and the seal collar, such minor amount of water may be prevented to pass further into the internal compartment by said seal ring.

[0183] In an embodiment, the tension hemisphere adjustment arrangement comprises a bolt tensioning structure arranged to provide a pressure toward the tube seal arrangement and towards a flat basic surface of the hemisphere tube seal arrangement when the tension hemisphere adjustment arrangement is tensioned. The bolt tensioning structure may for example comprise a set of tensioning rods to provide the pressure toward the flat basic surface of the hemisphere adjustment element. The bolt tensioning structure may comprise a front plate and a back plate, wherein the set of tensioning rods extend from the front plate to the back plate. The Front plate and the back plate comprises openings for the pulling bar, and at least one of the front plate and the back plate, preferably the back plate, comprises a retainer arrangement, which in a closed stage prevents the pulling bar from being pulled in a direction towards the hemisphere adjustment element, but allow the pulling bar from passing in a direction further away from the hemisphere adjustment element, thereby ensuring that the bolt tensioning structure provide a pressure towards the flat basic surface of the hemisphere tube seal arrangement when the tension hemisphere adjustment arrangement is tensioned and when the retainer arrangement is in the closed stage. Preferably the pressure applied by the bolt tensioning structure towards the flat basic surface of the hemisphere tube seal arrangement is applied at least partially via the front plate, wherein the front plate may be applied face-to-face with the flat basic surface of the hemisphere tube seal arrangement to ensure an evenly distributed pressure.

[0184] In an embodiment the tensioning rods of the set of tensioning rods each comprises a threaded bar and passes through a passage of the back plate via a bolt, that is locked to or is lockable to the threaded bar for ensuring locking of the tensioning rods to provide a desired distance between the front plate and the back plate. In an embodiment, the mooring line(s) is carried within the monopile, preferably at least partially inside a support tube, such as inside a J-tubes to a location below the water level. Thereby the mooring line and optionally a part of the tension adjustment arrangement may penetrates the monopile wall at the location below the water level, preferably via a sealing as described above, and a part or all of the tension adjustment arrangement may be located above water level which may provide a very desired accessibility for an operator.

[0185] In an embodiment, the at least one tension adjustment arrangement comprises at least one beam element arranged to cross a monopile axis, and comprising two fairleads located at a fixed distance to each other, wherein the at least one beam element is located at a distance to the monopile below seawater level. Each of the two fairleads of the beam element may comprise a guide ring and / or wheel arranged to encircle the respective adjacent mooring lines or sections of a mooring line extending between an attachment fairlead on the monopile and a water floor anchor. The tension adjustment arrangement may comprise a pulling arrangement adapted for pulling the beam element towards the monopile, thereby increasing the tension in the mooring lines or mooring line sections.

[0186] The at least one beam is advantageously perpendicular ± up to 15 degrees, such as up to 10 degrees, preferably at most 5 degrees to the to the monopile axis.

[0187] In an embodiment, the beam element is in the form of a cable under tension.

[0188] The beam may advantageously have a fixed length and comprising the two fairleads located at either ends thereof. Each of the two fairleads advantageously comprises a ring or wheel at, which encircles the respective mooring lines or mooring line sections.

[0189] The pulling arrangement may conveniently comprise a separate cable located within a plane which also includes both mooring lines. The separate cable may be adapted to pull the beam element towards the monopile. The beam element, of fixed length, may thereby cause the mooring lines to bend about the rings or wheels and have to take a longer line between the attachment fairleads and the water floor anchor and thereby causing the tension in the mooring lines to increase, or to decrease, as the beam is pulled closer to the monopile, or loosened so that it might relax back towards the anchor, respectively. In a variation thereto the beam element may be replaced by a fencing element as illustrated in figure 6b.

[0190] In an embodiment, the monopile has a plurality of sectional modulus along the monopile length, for example, the modulus at one elevation from the water floor differs from the modulus at another elevation from the water floor.

[0191] Advantageously, the monopile has a sectional modulus such as a second moment of area, at an elevation comprising one or more of the plurality of attachment fairleads which is at least 4 times greater than a minimum value of the section modulus of the monopile at an elevation of from 1 to 10 m above the water floor, such at an elevation of from 4 to 6 m above the water floor, such as 5 m above the water floor.

[0192] Advantageously, the monopile has a maximal sectional modulus at any elevation along the length which is at least 5 times greater than the section modulus determined at an elevation up to a distance of 0.5 m above the primary compartment floor divider.

[0193] Thereby it may be ensured that no more than 20% of the maximum bending moment expected in the BGM predominantly generated by the lateral loading of wind and waves on the structure and from the operational loading of the wind turbine, which may be expected in the vicinity of the mid-section, may be transmitted from the BGM into the footing by bending alone.

[0194] The sectional modulus is determined when the when the monopile is in the installed condition, where the sectional modulus may be determined according to the equation:

[0195] Wherein "OD" means outer diameter and "ID" means inner diameter of the wall of the monopile, and wherein any horizontal, domed or near-horizontal diaphragms or pressure decks or platforms are excluded from the calculation. The invention also comprises a monopile suitable for an installation, wherein the monopile advantageously is as described above. The monopile has a length from a top end to a bottom end and a wall with an outer surface defining an average monopile outer diameter, wherein the monopile comprises an upper section and a lower section comprising a tip section adjacent to the bottom end and at least partially supported by the water floor. The lower section advantageously has an average lower section outer diameter which is less than the average monopile outer diameter.

[0196] The monopile comprises a primary compartment and an opening arrangement into the primary compartment located at least partially in the lower section, wherein the monopile comprises at least one buoyancy compartment located at least partially in the upper section.

[0197] The monopile including the primary compartment and the buoyancy compartment may advantageously be as described above in the description of the installation.

[0198] As described above the at least one buoyancy compartment may form part of the primary compartment and / or the at least one buoyancy compartment may comprise a separate compartment located closer to the top end than the primary compartment, preferably the at least one separate buoyancy compartment is located adjacent and preferably above the primary compartment separated by a compartment divider, wherein the compartment divider preferably is watertight and preferably sufficiently airtight to maintain a pressure difference of 50 Pa for at least 24 hours, such as for one year or longer, preferably the compartment divider is sufficiently airtight to maintain a pressure difference of at least 1 kPa, such as at least 0.1 bar, such as at least 1 bar at for at least 1 hour, such as for 24 hours or longer.

[0199] In an embodiment, the primary compartment is watertight except for the opening arrangement, preferably the primary compartment is sufficiently airtight to maintain a pressure difference of up to 50 Pa for one year or longer except for the opening arrangement.

[0200] The opening arrangement may be as described above.

[0201] Where the monopile comprises openings that are adapted to be sealed off when the monopile is installed, such as parts of a pressure control arrangement for controlling the pressure in the primary chamber e.g. a gas control tube or other tubes as described elsewhere herein, such openings should be closed off when determining the airtightness of the primary compartment.

[0202] In an embodiment, the primary compartment may as described above be defined by a primary compartment roof divider and a primary compartment floor divider, wherein the primary compartment floor divider defines the top of the tip section.

[0203] The tip section thereby stretches from the bottom end to the primary compartment floor divider.

[0204] Advantageously, the maximal diameter of the part of the tip section is preferably not exceeding the diameter of any diameter of the remaining of the monopile.

[0205] In an embodiment, the maximal diameter of the part of the tip section secured to and / or adapted to be secured in the footing is preferably not exceeding the diameter of any diameter of the remaining of the monopile. The lower section of the monopile may conveniently comprise or even consist of the tip section and a lower section body portion, wherein the lower section body portion comprises at least a portion of the primary compartment. In an embodiment, the lower section body portion comprises the entire primary compartment. In an embodiment, the lower section body portion extends from the primary compartment roof divider to the primary compartment floor divider. The primary compartment floor divider map be as described above and may e.g. comprise the biscuit deck.

[0206] The primary compartment roof divider may in an embodiment serve as or form part of a compartment divider.

[0207] The primary compartment roof divider may in an embodiment form part of the midsection.

[0208] The one or more dividers of the monopile, such as the primary compartment roof divider, the primary compartment floor divider and / or any compartment divider may advantageously be as described above.

[0209] The primary compartment floor divider may preferably comprise or be constituted by a watertight diaphragm, such as a bulge shaped or dome shaped or flat watertight diaphragm. In an embodiment the primary compartment floor divider comprises a watertight diaphragm and a plate located above the watertight diaphragm. In an embodiment, the opening arrangement in the lower section into the primary compartment comprises a flooding hole or two or more flooding holes in the wall of the monopile into the primary compartment. The flooding hole is preferably located closer to the primary compartment floor divider, than the primary compartment roof divider.

[0210] In an embodiment, at least one flooding hole of the opening arrangement is located above the primary compartment floor divider and with a distance from a centre of the flooding hole to the primary compartment floor divider not exceeding 3 m, such as less than 2 m, such as less than 1 m, such as less than 0.5 m.

[0211] The flooding hole or holes may be as described above.

[0212] In an embodiment, the monopile comprises a closing arrangement adapted for temporarily restricting or closing off the opening arrangement or at least a part thereof, preferably for restricting and optionally blocking for water passage through openings, such as through the one of more flooding holes of the opening arrangement. The closing arrangement is preferably adapted for temporarily closing and sealing the flooding hole(s). The closing arrangement may for example comprise a valve, a plug, a lid or any combinations comprising one or more of these.

[0213] The closing arrangement and / or the degree of opening may be as described above.

[0214] Advantageously, the closing arrangement comprises a controller adapted for controlling the opening degree of the opening arrangement from being fully open to being fully closed. Preferably the controller the controller is adapted for receiving instructions from an operator, optionally via instruction signals that may be transmitted by wire or wireless e.g. via an operator station.

[0215] The controller may be as described above.

[0216] The flooding hole may advantageously be located as described above in respect of the monopile of the installation. The one or more flooding holes may beneficial be closable e.g. using a valve, a plug, a lid or any combinations comprising one or more of these. The fully or partly closing off the opening arrangement may especially be beneficial for transporting the monopile for installation as described further below. The monopile and the sections thereof may advantageously have heights as described above.

[0217] In an embodiment, the monopile comprises a pressure control arrangement for controlling a pressure in the primary chamber, preferably comprising a pump for supplying pressurized gas to the primary chamber.

[0218] The pressure control arrangement may advantageously be as described above.

[0219] In an embodiment, the lower section has an average outer diameter of 75 % or less than a maximal monopile outer diameter, such as 50 % or less, such as 40 % or less, such as 30 % or less, such as 20 % or less than the maximal monopile outer diameter.

[0220] In an embodiment, the lower section has an average outer diameter of 7 m or less, such as of 6 m or less, such as of 4 m or less.

[0221] In an embodiment, the monopile comprises a plurality of attachment fairleads attached to the monopile at respective fixing locations, preferably located at a common fixing length section of the monopile as described above.

[0222] In an embodiment, the monopile comprises one or more winches, turn-buckles and / or rams, such as a hydraulic ram and / or a pneumatic ram, wherein each winch, turn-buckle and / or ram may be arranged to adjust the tension in one or more of the mooring lines.

[0223] In an embodiment, monopile comprises a mid-section located between the upper section and the lower section.

[0224] In an embodiment the common fixing length section form part of the mid-section.

[0225] In an embodiment, the common fixing length section of the monopile comprises a length section of the upper section of the monopile located above the mid-section and preferably above the waterline. This is especially desired for the shallow BGM installation.

[0226] The mid-section is preferably defined by the primary compartment roof divider. In an embodiment, the mid-section is defined as the length section of the monopile comprising the primary compartment roof divider, preferably comprising at least the watertight diaphragm, such as a bulge shaped or dome shaped or flat watertight diaphragm. In an embodiment the primary compartment floor divider comprises a watertight diaphragm and a plate located above the watertight diaphragm. The plate may form part of the biscuit deck described below.

[0227] Advantageously, the mid-section of the monopile comprises a reinforcement, such as a stiffening ring.

[0228] The stiffening ring may be located as described above in respect of the monopile of the installation.

[0229] The common fixing length section advantageously constitutes or forms part of the mid-section of the monopile. The mid-section, is a length section of the monopile advantageously located between the upper section and the lower section. By providing that the fixing locations are arranged at a common level defined by the length of the common fixing length section, a high stabilisation of the upright BGM may be ensured and simultaneously it may provide a simpler fine tuning of the tension in the mooring lines.

[0230] Advantageously, the wherein the mid-section of the monopile comprises a biscuit deck, wherein the biscuit deck preferably comprises, form part of or constitute the primary compartment roof divider as described above

[0231] The primary compartment roof divider advantageously comprises an airtight diaphragm as described above.

[0232] Advantageously, the monopile comprises at least one tension adjustment arrangement for adjusting and / or tuning tension of mooring lines attached to the attachment fairleads.

[0233] The tension adjustment arrangement may advantageously be as described above and may advantageously comprise a length adjustment device adapted for a adjusting the free length of one or more mooring lines e.g. as described above.

[0234] The invention also comprises a method of establishing an installation at a water location, wherein the installation comprises a buoyant and guyed monopile (BGM) e.g. as described above.

[0235] The method comprises • providing a monopile, wherein the monopile has a length from a top end to a bottom end and a wall with an outer surface defining an average monopile outer diameter, wherein the monopile comprises a upper section defining the top end and a lower section comprising a tip section defining bottom end and at least partially supported by the water floor, wherein the lower section has an average lower section outer diameter, which is less than the average monopile outer diameter, wherein the monopile comprises a primary compartment and an opening arrangement into the primary compartment located at least partially in the lower section and wherein the monopile comprises at least one buoyancy compartment located at least partially in the upper section,

[0236] • at least 3 mooring lines,

[0237] • a plurality of water floor anchors and

[0238] • a plurality of attachment fairleads.

[0239] The monopile may advantageously be as described above.

[0240] The method comprises providing that the attachment fairlead are fixed to the monopile, preferably a midsection or at the upper section of the monopile; providing the monopile to be horizontally arranged in the raw water; providing raw water to flow through the opening arrangement into the primary compartment to at least partially flood the primary compartment section ballasting the monopile to being tilted to an upright orientation and to be lowered to provide that the tip section is at least partially supported by the water floor and mooring the monopile to the water floor comprising restraining each of the 3 or more mooring lines between one or two of the water floor anchors and one of the at least three attachment fairleads fixed to the monopile.

[0241] The method advantageously comprises establishing the BGM installation as described above.

[0242] In an embodiment, the method comprises wet-towing the monopile while horizontally arranged in the raw water to a site of the water location. To ensure that the monopile is floating it is desired that the method comprises closing of the opening arrangement into the primary compartment prior to the wet-towing. After having reached the site of the water location the method may comprise re-opening the opening arrangement for providing raw water to flow through the opening arrangement into the primary compartment. The opening procedure may e.g. be as described above.

[0243] It has been found to be very economical attractive to transport the monopile to the site of the water location by wet-towing. At the same time the risk of damaging the monopile may be highly reduced and there is no need for a crane or similar for lifting the monopile into the water at the site of the water location.

[0244] When wet-towing the monopile horizontally arranged in the raw water to a site of the water location, it is desired that the method also comprises closing the top end of the monopile prior to the wet-towing followed by re-opening the top end at the site of the water location. The closing of the top end is preferably performed by a closing arrangement comprising at least one of a diaphragm, a bladder, a bung, a watertight or a hatch.

[0245] The closing of the opening arrangement into the primary compartment prior to the wet-towing followed by re-opening the opening the opening arrangement may advantageously be provided by the closing arrangement as described above.

[0246] The re-opening of the closing arrangement may advantageously comprising a gradually and controlled opening to provide that the flooding of the primary compartment is provided in a controlled way. The controlled re-opening may advantageously be at least partly performed by the controller e.g. in response to an instruction received from an operator.

[0247] The opening arrangement advantageously comprises one or more flooding holes as described above.

[0248] In an embodiment, the method comprises controlling the flooding of the primary compartment using a closing arrangement adapted for temporarily restricting or closing off the opening arrangement, the closing arrangement is preferably as described above. In an embodiment, the opening arrangement comprises a gas escape hole adapted for passing of a gas escape tube as described further below. In an embodiment, the flooding hole and the gas escape hole is provided in the form of a common flooding and gas escape hole e.g. as described above.

[0249] To ensure that the gas escape tube does not block for escape of water it is advantageously that the flooding hole(s) and the gas escape hole is located at a distance from each other, e.g. oppositely to each other.

[0250] Advantageously, the closing arrangement is as described above and preferably comprises a controller adapted for controlling the opening degree of the opening arrangement from being fully open to being fully closed. Preferably the method comprises instructing the controller optionally via instruction signals that may be transmitted by wire or wireless e.g. via an operator station.

[0251] The flooding hole may advantageously be located as described above in respect of the monopile of the installation.

[0252] In an embodiment, the monopile comprises a pressure control arrangement for controlling a pressure in the primary chamber, preferably comprising a pump for supplying pressurized gas to the primary chamber.

[0253] Due to the structure of the monopile including the at least one buoyancy compartment as well as the primary compartment and the opening arrangement into the primary compartment the method of the invention may be carried out under high control and without the need for lifting the entire weight of the sub-structure during the upending or positioning processes, as the buoyant structure will carry most of its weight due to hydrostatic pressure.

[0254] At the site of the water location, the method advantageously comprises embedding at least a part of the tip section in the water floor or in a footing arrangement, wherein the footing arrangement is located at or in at the water floor and preferably anchored in or at the water floor.

[0255] The footing arrangement may be as described above.

[0256] Advantageously, the method comprises preinstalling the footing arrangement in the water floor. This may for example be done applying a suction and / or a gravity principle such as suction-caisson principle, or gravity-base principle, with or without skirts.

[0257] In an embodiment the monopile is installed without a footing arrangement and the tip section is installed directly in the water floor e.g. by using by suction-caisson method (applying a suction-caisson technology), wherein the tip section is defined by the primary compartment floor divider forming a bucket shaped tip section for performing the suction-caisson installation.

[0258] It is generally desired that the embedding if the monopile in the water floor does not include driving the monopile into the water floor using mechanical impacting hammering force, since this may cause mechanical damage to or fatigue in the monopile.

[0259] Advantageously, the footing arrangement comprises a footing comprising a support recess, wherein the method comprises securing at least a part of the tip section to the footing by arranging the tip section in the support recess and preferably fixing it by a filler material and / or a binder material, such as epoxy and / or grout e.g. cementitious grout.

[0260] The recess of the footing may conveniently be located centrally in the footing.

[0261] In an embodiment, the footing arrangement comprises a footing, and the method comprises securing at least a part of the tip section to the footing, preferably by at least one of a grouted connection, a slip-joint connection, a bearing connection, a bolted connection or any combinations thereof.

[0262] In a preferred embodiment, the method comprises positioning the tip section in the footing of the footing arrangement comprising pre-installing a guide wire to the tip section of the monopile prior to providing raw water to flow through the opening arrangement into the primary compartment to at least partially flood the primary compartment, ballasting the monopile to being tilted to an upright orientation, and pulling the guide wire to provide that the tip section docks correctly into footing, such as into the recess of the footing. The guide wire may advantageously be pulled through a guide member, such as a fairlead or a hole in the footing, wherein after the tip section has docked correctly into the footing, the guide wire preferably is pulled through a non-return device ensuring to maintain the tip section in the footing. The non-return device may be an anchor in the water floor, where the mooring line e.g. may pass to via one of the water floor anchors.

[0263] In an embodiment, the method comprises providing raw water to flow through the opening arrangement into the primary compartment to at least partially flood the primary compartment while at the same time allowing gas / air to escape from the primary compartment e.g. via the internal tube and / or the gas escape tube; ballasting the monopile to being tilted to an upright orientation; pulling the guide wire through a guide member of or located at the footing; and pulling the guide wire through a non-return device, wherein the pulling of the guide wire through the nonreturn device comprises pulling of the guide wire through the non-return device to a temporarily stage prior to docking the tip section into the footing followed by gradually pulling the guide wire through further through the non-return device until tip section has docked correctly into the footing where the guide wire is pulled through the non-return device to a final stage.

[0264] It has been found that by pulling of the guide wire through the non-return device to a temporarily stage prior to docking the tip section into the footing the docketing process may be performed under high control, since from the moment that the guide wire has been pulled through the non-return device to the temporarily stage the risk that the tip portion of the monopile is pulled or swirled in an uncontrolled way by water waves is highly reduced.

[0265] In an embodiment, the method comprises inserting the guide wire through a nonreturn device, wherein after the tip section has docked correctly, the guide wire is preferably pulled to tensioning in said non-return device ensuring to maintain the tip section in the footing. The inserting the guide wire through the non-return device may be performed prior to or after the tip section has docked correctly.

[0266] In an embodiment, the mooring of the monopile to the water floor comprises mooring the monopile to water floor anchors using up to 8, such as up to 6 mooring lines.

[0267] The mooring of the monopile to the water floor advantageously comprises preinstalling the plurality of water floor anchors. E.g. as described above. The provision that the attachment fairlead are fixed to the monopile may comprise fixing the plurality of attachment fairlead to the monopile prior to transporting the monopile to the site of the water location and / or at the water location.

[0268] The attachment fairlead may be fixed to the monopile by any method, such as the methods known in the art, preferably comprising welding.

[0269] In an embodiment, the provision that the attachment fairlead are fixed to the monopile comprise fixing the plurality of attachment fairlead to the to the monopile at respective fixing locations, wherein the fixing locations are located at a common fixing length section of the monopile, wherein the common fixing length section has a length of 6 m or less, such as 5 m or less, such as 4 m or less, such as 2 m or less.

[0270] The common fixing length section may be as described above.

[0271] Advantageously, the common fixing length section of the monopile is located at a mid-section of the monopile located between the upper section and the lower section.

[0272] In an embodiment, the common fixing length section of the monopile comprises a length section of the upper section of the monopile located above the mid-section and preferably above the waterline. This is especially desired for the shallow BGM installation.

[0273] In an embodiment, the provision that the attachment fairleads are fixed to the monopile comprise fixing the at least one attachment fairlead to the monopile from the outer surface of the monopile e.g. by welding or by fixing the at least one attachment fairlead at least partially at an internal location of the monopile, such as at or above the biscuit deck e.g. in the compartment above the biscuit deck. E.g. as described above.

[0274] The mooring of the monopile to the water floor may be as described above.

[0275] The mooring of the monopile to the water floor may advantageously comprise anchoring the monopile to the water floor anchors via the plurality of attachment fairleads, comprising attaching each mooring line to the monopile via at least one of the attachment fairleads and at least one of the water floor anchors. Advantageously, the method comprises attaching each mooring line to the monopile via at least one of the attachment fairleads and at least two separate of the water floor anchors, wherein the two separate water floor anchors to which each end of a mooring line is attached are located with a distance to each other.

[0276] In an embodiment, the mooring of the monopile to the water floor comprises anchoring the monopile to the water floor anchors via the plurality of attachment fairleads, wherein each of the mooring lines or mooring line portions is arranged to extend from a respective of the attachment fairleads to a respective of the water floor anchors and wherein the mooring lines are fixed to the monopile via the attachment fairleads and by one or more winches, turn-buckles and / or rams, wherein each winch, turn-buckle and / or ram may be arranged to adjust the tension in one or more of the mooring lines.

[0277] In an embodiment, the mooring of the monopile to the water floor comprises anchoring the monopile to the water floor anchors via the plurality of attachment fairleads, wherein each of the mooring lines or mooring line portions is arranged to extend from a respective of the attachment fairleads to a respective of the water floor anchors with an straight line as seen in plan-top-view, wherein the straight line of each of the mooring lines or mooring line portions intersect with the outer diameter of the monopile at an angle within 30 degrees or less, such as an angle of 20 degrees or less, such as an angle of 15 degrees or less deviation from an exactly tangential line to the monopile outer wall surface.

[0278] The method advantageously comprises pre-installing the water floor anchors.

[0279] The method may advantageously comprise tuning the tension in the mooring lines using one or more tension adjustment arrangement, wherein the tension adjustment arrangement(s) optionally comprises one or more winches, turn-buckles and / or rams. The tension adjustment arrangement(s) may be as described above.

[0280] As described above the monopile may comprise a pressure control arrangement for controlling the pressure in the primary chamber or parts thereof installed. In an embodiment, the method comprises installing a pressure control arrangement for controlling the pressure in the primary chamber of finalizing the instalment where the monopile is not fully equipped with the pressure control arrangement. The pressure control arrangement conveniently comprises a pump for supplying pressurized gas to the primary chamber and a closable gas release valve for allowing gas, such as air to escape from the primary compartment.

[0281] The provision of raw water to flow to flow through the opening arrangement into the primary compartment may advantageously comprise providing the opening arrangement and preferably the gas release valve of the pressure control arrangement to be open to allow air to escape from the primary compartment as water is at least partially flood the primary compartment.

[0282] In an embodiment, the pressure control arrangement comprises an internal tube, passing through the primary compartment roof divider into the primary compartment and extending from a first internal tube end located at a first location in the primary compartment to a second internal tube end located at a second location above the primary compartment and preferably above the at least one buoyancy compartment. Preferably the first location in the primary compartment is located at a distance to the primary compartment roof divider up to 20 % of the primary compartment height. The second location may conveniently be located above waterline, such as at or above or within 3 m of the top end.

[0283] Advantageously, the step of ballasting the tip section of the monopile to be supported by the water floor comprises providing that the second internal tube end of the internal tube is located above and preferably at least 2 m, such as at least 5 m above the waterline. Thereby it may be ensured that the second internal tube end cannot allow water to flow out into the buoyancy compartment or other areas of the upper section or mid-section in which the second internal tube end is located.

[0284] In the step of ballasting the gas control tube may be open to allow gas escape from the primary compartment via the gas control tube. The gas control tube may extend inside the monopile from a first gas control tube end located in the primary compartment or preferably in the primary compartment roof divider with an opening into the primary compartment and upwards e.g. to a second gas control tube end located within the upper section or even at or above the top end of the monopile. Advantageously, the second gas control tube end is located at or above the top end.

[0285] In an embodiment, the pressure control arrangement comprises a gas escape tube, wherein the gas escape tube extends from a first gas escape tube end located in the primary compartment through a gas escape hole of the opening arrangement and along the monopile length to a second gas escape tube end located outside the monopile. Advantageously, second gas escape tube end is located at a level of or above the upper section of the monopile. Preferably the first gas escape tube end is located at the upper half part of the primary compartment closest to the top end.

[0286] In an embodiment, the second gas escape tube end is located above an optional water level in the primary compartment. The second gas escape tube end is preferably located above waterline. The gas escape tube preferably comprises a closable gas release valve for allowing gas, such as air to escape from the primary compartment.

[0287] In an embodiment, the step of ballasting the tip section of the monopile to be supported by the water floor comprises providing that the second gas escape tube end of the air control pipe is located above and preferably at least 2 m, such as at least 5 m above the waterline. Initially this may be provided by ensuring that the monopile prior to the ballasting step is located with the second gas escape tube end away from the water, wherein the flooding hole conveniently is located in the water.

[0288] As the water is passing into the primary compartment via the flooding hole, the gas / air may conveniently pass out of the second gas escape tube end of the gas escape tube.

[0289] When a desired amount of water has flooded the primary compartment, the gas escape tube may be closed off or the gas escape tube may be removed.

[0290] In an embodiment, the step of ballasting the tip section of the monopile to be supported by the water floor comprises providing that the second gas escape tube end of the gas escape tube is located above the waterline and preferably opening the closable gas release valve.

[0291] In an embodiment, the method comprises pumping gas, preferably air into the primary compartment to provide that an upper portion of the primary compartment comprises pressurized gas, wherein the gas is preferably pumped into the primary compartment using the pressure control arrangement.

[0292] In an embodiment, the internal tube may be kept open during the ballasting process, to allow gas to escape along the internal tube as well as along the gas control tube, which will serve to speed up the flooding process. Advantageously, the pumping of gas into the primary compartment comprises pressurizing the upper portion of the primary compartment sufficient to provide that a portion of water is pressed out of the primary compartment via the opening arrangement. Thereby the pressure in the pressurized upper portion of the primary compartment can safely be maintained at a desired level in a very simple way, with practically no risk of reaching a too high pressure. Indeed the pressure is determined by the location of the opening arrangement.

[0293] Advantageously, the pumping of gas into the primary compartment comprises pumping air at a selected pressure into the primary compartment below the biscuit deck, providing that the air pumped into the primary compartment is at a pressure greater than the seawater on the outside of the monopile at every level.

[0294] In practice, the air control pipe may be a small diameter pipe, allowing air to escape and may be throttled, as the BGM is ballasted down. Then when the BGM is in place, and a positive internal pressure is to be applied, air from a compressor may be driven down this air control pipe into the upper part of the primary chamber, and the water in the primary compartment may be forced down and some of the water may be expelled via the opening arrangement.

[0295] In an further aspect of the invention, the invention is directed to an installation comprising a buoyant and guyed monopile (BGM), wherein the monopile is upright and has a length from a top end to a bottom end and a wall with an outer surface defining an average monopile outer diameter, wherein the monopile comprises a upper section and a lower section, wherein the monopile comprises a primary compartment and an opening arrangement into the primary compartment located at least partially in the lower section, wherein the primary compartment is at least partially water filled and wherein an upper portion of the primary compartment comprises pressurized gas (preferably air), preferably the pressure in the primary chamber along the length of the monopile is sufficiently high to counter act the hydrostatic pressure acting onto the monopile along the length.

[0296] In an embodiment, the pressure at any elevation inside the primary compartment is larger than or equal to the hydrostatic pressure acting at the outer wall of the monopile at the corresponding elevation. In an embodiment, the pressure in the primary compartment may be adjusted e.g. for temporarily adjusting the buoyance force provided by the primary compartment. For example it may, be desired to reduce the buoyance force ahead of decommissioning in order to sit the BGM more firmly on the footing before remove the mooring lines. The installation may be as described above with the difference that the lower section may have an average lower section outer diameter which is equal to or larger than the average monopile outer diameter. In addition, the buoyancy compartment is also an optional feature.

[0297] The installation and / or the primary chamber may comprise one or more of the above described features, such as the above described primary compartment roof divider and a primary compartment floor divider, the primary compartment height, the closing arrangement etc.

[0298] The installation may have the beneficial effects associated to the primary compartment as described above.

[0299] In an further aspect of the invention, the invention is directed to a monopile suitable for an installation, wherein the monopile has a length from a top end to a bottom end and a wall with an outer surface defining an average monopile outer diameter, wherein the monopile comprises a upper section and a lower section comprising a tip section adjacent to the bottom end and at least partially supported by the water floor, wherein the monopile comprises a primary compartment and an opening arrangement into the primary compartment located at least partially in the lower section, wherein the opening arrangement in the lower section into the primary compartment comprises a flooding hole in the wall of the monopile, wherein the monopile comprises a closing arrangement adapted for temporarily restricting or closing off the opening arrangement.

[0300] The monopile may be as described above with the difference that the lower section may have an average lower section outer diameter which is equal to or larger than the average monopile outer diameter. In addition the buoyancy compartment is also an optional feature. The monopile and / or the primary chamber and / or the closing arrangement may comprise one or more of the above described features, such as the above described primary compartment roof divider and a primary compartment floor divider, the primary compartment height, the closing arrangement controller etc.

[0301] The monopile may have the beneficial effects associated to the primary compartment and the closing arrangement as described above especially for providing that the monopile may be very economically attractive for instalment.

[0302] In a further aspect of the invention, the invention is directed to a method of installing a monopile of claim 102 at a water location,

[0303] • wherein the method comprises

[0304] • providing the monopile to be horizontally arranged in the raw water,

[0305] • wet-towing the monopile horizontally arranged in the raw water to a site of the water location, wherein the method comprises closing of the opening arrangement into the primary compartment prior to the wet-towing

[0306] • at the site of the water location, re-opening the opening the opening arrangement for providing raw water to flow through the opening arrangement into the primary compartment to ballasting the monopile to being tilted to an upright orientation and to be lowered to the water floor and

[0307] • fixing the monopile to or into the water floor.

[0308] The installation method may comprise all the features described above relating to the wet towing and tilting of the monopile at the site of the water location.

[0309] The invention also comprises a tube gasket arrangement, such as a stern tube gasket, suitable for forming a sealing between an opening in a wall into a chamber, such as a chamber of a ship and an elongate element passing from outside the chamber, through the opening and into the chamber and wherein the tube gasket arrangement allows longitudinal and / or rotational motions of the elongate elements. The tube gasket arrangement comprises a seal arrangement, which comprises a tube seal arrangement connected to the wall adjacent the opening to form a seal between the elongate element and an outer edge portion of wall surface along a periphery of the opening through the wall. The tube gasket arrangement comprises an eyeball structure comprising a socket with a bearing surface and a hemisphere tube seal arrangement comprising a spherical cap surface arranged to face the bearing surface. Each of the socket and the hemisphere tube seal arrangement comprises a passage for the elongate element. The hemisphere tube seal arrangement is adjustable relative to the bearing surface to provide that the spherical cap surface is adjusted relative to the bearing surface, to provide that the passage of the socket and the passage through the hemisphere tube seal arrangement are in alignment relative to each other, and in alignment with the elongate element.

[0310] The adjustment of the hemisphere tube seal arrangement may e.g. be performed at least partially by a hemisphere adjustment arrangement, such as a mechanical adjustment mechanism located in the internal compartment.

[0311] The hemisphere tube seal arrangement may beneficially be shaped as a hemisphere or as a part-hemisphere.

[0312] In an embodiment the tube seal arrangement comprises a flexible covering structure applied against and optionally connected to the outer edge portion along the periphery of the opening. Preferably the tube seal arrangement further comprises and a seal collar arranged to seal between the flexible covering structure and the elongate element. In an embodiment the flexible covering structure and the seal collar are integrated with each other, such as formed in a single element or fixed to each other e.g. with a glue. The seal arrangement may further comprise a seal ring located in the passage of the hemisphere tube seal arrangement to form a seal between the hemisphere tube seal arrangement and the mooring line or preferably the pulling bar passing through the hemisphere adjustment element.

[0313] In use where the chamber form part of a structure at least partially embedded in water, such as sea water and where at least the wall comprising the opening is embedded in the water, hydrostatic pressure provided by the surrounding water may apply a hydrostatic pressure towards the flexible covering structure and the seal collar which provides a pressure against the socket and the hemisphere adjustment element. Where the socket is at least partially fixed in the flexible covering structure and / or the seal collar, the resulting pressure may result in a reduce contact pressure between the bearing surface and the spherical cap surface of the hemisphere adjustment element, which may ensure allowing the adjustment of the hemisphere tube seal arrangement relative to the bearing surface.

[0314] In addition, the hydrostatic pressure will cause the flexible covering structure to push tight against the opening, and reduce water ingress to a minimum or even prevent water ingress. The seal collar further add to ensure this sealing. The seal ring ensures that where amounts of water minor has passed the flexible covering structure and the seal collar, such minor amount of water will be prevented to pass further into the chamber by the seal ring.

[0315] BRIEF DESCRIPTION OF THE EXAMPLES AND DRAWING

[0316] The invention is being illustrated further below in connection with illustrative embodiments and with reference to the figures. The figures are schematic and may not be drawn to scale.

[0317] Figure 1 is a schematic and perspective illustration of an embodiment of the installation of the invention.

[0318] Figure 2a is a schematic and partially exploded side view of an embodiment of the installation of the invention wherein the installation is a universal BGM installation.

[0319] Figure 2b is a schematic and partially exploded side view of an embodiment of the installation of the invention wherein the installation is a shallow BGM installation.

[0320] Figure 3a is a schematic side view of a portion of an embodiment of the invention.

[0321] Figure 3b is a schematic side view of a portion of a variation of the embodiment of figure 3a.

[0322] Figure 3c is a schematic side view of a portion of a variation of the embodiment of figure 3b.

[0323] Figure 4 is a schematic top view of an embodiment of the installation of the invention.

[0324] Figure 5a is a schematic cross-sectional side view of a portion of a common fixing length of a monopile of an embodiment of the invention. Figure 5b is a schematic cross-sectional side view of a portion of a fixing length section of a monopile of an embodiment of the invention, such as of a mid-section of a monopile of an embodiment of the invention, schematically illustrating a mooring line attached to a portion of a tension adjustment arrangement.

[0325] Figure 5c and figure 5c' are schematic cross-sectional side view of a portion of a fixing length section of a monopile of an embodiment of the invention, schematically illustrating a portion of a tension adjustment arrangement and sealing arrangement.

[0326] Figure 5d is a schematic cross-sectional side view of a portion of a fixing length section of a monopile of an embodiment of the invention, illustrating a portion of a tension adjustment arrangement and sealing arrangement in more details.

[0327] Figures 6a and 6b are schematic top views of an embodiment of the installation of the invention comprising a tension adjustment arrangement in a first stage and a second stage respectively.

[0328] Figure 7 is a schematic top view of an embodiment of the installation of the invention comprising a tension adjustment arrangement.

[0329] Figure 8a is schematic and perspective views of a footing.

[0330] Figure 8b is schematic and perspective views of a water floor anchor.

[0331] Figure 9 is a schematic side view of an embodiment of a monopile of the invention.

[0332] Figures lOa-lOe are schematic illustrations of an embodiment of the method of establishing an installation.

[0333] Figures lla-llb are schematic cross-sectional side view of details of a tension adjustment arrangement of embodiments of installations of the invention or of tension adjustment arrangements of the invention comprising an attachment fairlead of an eyeball type located to adjust tensioning in a mooring line.

[0334] Figures 12a-12c and figures 13a and 13b are schematic illustrations of details of the tension adjustment arrangement of figure lla-llc and variations thereof.

[0335] The installation shown in figure 1 comprises a monopile 1, also called a BGM or a BGM monopile. The BGM comprises a lower section LS, a mid-section MS and an upper section UP, The lower section comprises a tip section TS docked into a footing 3. The footing may advantageously be a footing with suction caisson option. In an embodiment, the footing may be or comprise a pin pile, or a bearing pad, or a gravity base or any other means for holding the tip section laterally immobilized. The BGM comprises an upper section US, the mid-section comprises a number of attachment fairleads. In this embodiment six mooring lines are arranged to anchor the BGM to water floor anchors 6 via the mooring lines 5.

[0336] The mooring lines are held in tension in a not shown tensioning arrangement located inside or outside the BGM. The tensioning arrangement in the BGM is located in the periphery of a not shown biscuit deck compartment of the mid-section MS, where the biscuit deck forms a part such as a floor.

[0337] The tensioning arrangement located in the BGM comprises one or more winches turn-buckles and / or rams, such as one or more hydraulic rams and / or one or more pneumatic rams.

[0338] The mooring lines 5 are arranged in three mooring line pairs of two mooring lines, wherein each mooring line pairs are anchored to one of three water floor anchors, 6, here suction anchors, located with somewhat even distances around the BGM 1.

[0339] The mooring lines 5 are arranged to the respective water floor anchors, 6, via in-line tensioners 6a located at the respective water floor anchors 6.

[0340] At the upper section US, more precisely at the top end, the BGM comprises a support structure 2a and a ladder, 2b leading downwards from the support structure 2a.

[0341] As it can be seen the lower section LS has an average lower section outer diameter which is less than the average monopile outer diameter.

[0342] To ensure that the BGM is held upright and with a high stability in the footing, the BGM comprises a primary compartment and an opening arrangement into the primary compartment located at least partially in the lower section LS and the BGM comprises at least one buoyancy compartment located at least partially in the upper section. As mentioned above the primary compartment and the buoyancy compartment may be a common primary / buoyancy compartment, wherein the uppermost portion of the common primary / buoyancy compartment constitutes the buoyancy compartment and the remaining lowermost portion constitutes the primary compartment.

[0343] The BGM installation shown in figure 2a is a universal BGM installation and comprises a buoyant and guyed monopile (BGM) 10, a footing 13 and a number of mooring lines 15 attached to attachment fairleads 17 below the waterline, wherein only a part of the mooring lines are shown.

[0344] The BGM is upright and has a length from a top end TE to a bottom end BE and has a lower section LS comprising a lower section portion LS' above a tip section TS, a mid-section MS and an upper section US. The lower section LS of the BGM comprises the tip section TS. The tip section TS has a relatively narrow diameter relative to the average diameter of the BGM. The tip section TS is shown in exploded view relative to the footing 13. The footing comprises an anchor portion 13a, which here is anchored to the water floor and a receptor portion 13b comprising a recess for receiving the tip section TS. The anchor portion 13a may e.g. be similar to the water floor anchors. In alternative embodiments the footing may take many forms, which is highly beneficial since this ensures a high flexibility and enables that the BGM may be deployable in all types of ground conditions. Thus the anchor portion 13a may be selected to ensure a safe anchoring at a selected water floor and the receptor portion 13b is shaped in dependence of the tip section TS.

[0345] The BGM comprises a primary compartment 12 extending from a primary compartment floor divider 12a to a primary compartment roof divider, wherein the primary compartment roof divider in this embodiment comprises a biscuit deck 18a which is relatively strong and with a thickness t. The compartment roof divider also comprises an airtight diaphragm 18b below the biscuit deck 18a. The primary compartment roof divider is located to form the mid-section MS of the BGM.

[0346] As described above, the primary compartment 12 may be partially water filled via a flooding hole 14 of an opening arrangement. In addition, the primary compartment 12 is pressurized in it's upper portion above the flooding hole 14. The pressurization may be established as described above e.g. due to the water flooding via the flooding hole 14 and / or by gas, such as air that has been pumped into the upper portion of the primary compartment 12 by a pressure control arrangement. The biscuit deck 18a provides a strong and stiff region of the BGM. As it can be seen, the attachment fairleads 17 for connecting the mooring lines 15 are located at the periphery of the biscuit deck 18a, which provides and ensures a desired strong region for the mooring lines 15. In a variation of the embodiment of figure 2a, the attachment fairleads are located inside the monopile in a compartment above the biscuit deck e.g. forming part of a tension adjustment arrangement. The mooring lines 15 are connected to the water floor anchor via not shown water floor anchors.

[0347] The watertight diaphragm 18b is here bulge shaped, which ensures a very high strength for withstanding stresses in the diaphragm due to the high pressure in the upper portion of the primary compartment 12.

[0348] In the upper section US, the BGM comprises a buoyancy compartment 19. The buoyancy compartment 19 is here located immediately above the biscuit deck 18a.

[0349] In a variation thereof the buoyancy compartment 19 serves as an operators working space and comprises parts of a not shown pressure control arrangement for controlling the pressure in the primary compartment 12 as described above and at least a part of a tension adjustment arrangement e.g. comprising a winch, or a turnbuckle, or a ram, such as a hydraulic ram and / or a pneumatic ram as described above.

[0350] As it can be seen the buoyancy compartment is located at the water line, which adds to ensure a high stability of the BGM.

[0351] The BGM installation shown in figure 2b is a shallow BGM installation and comprises a buoyant and guyed monopile (BGM) 10', a footing 13 and a number of mooring lines 15' attached to attachment fairleads 17' above the waterline, wherein only a part of the mooring lines are shown.

[0352] The BGM installation of figure 2b differs from the BGM installation of figure 2a in that it is a shallow BGM installation with the attachment fairleads located above the waterline

[0353] The BGM comprises a primary compartment 12 extending from a primary compartment floor divider 12a to a primary compartment roof dividerl8b', wherein the primary compartment roof divider 18b' in this embodiment comprises airtight diaphragm 18b. The primary compartment roof divider 18b' is located to form the mid-section MS of the BGM. The portion of the monopile of figure 2b is identical to the corresponding portion of the BGM of figure 2a.

[0354] In this embodiment, the biscuit deck 18a' is located above the water line in the upper section US and provides a strong and stiff region of the BGM. As it can be seen, the attachment fairleads 17' for connecting the mooring lines 15' are located at the periphery of the biscuit deck 18a', which provides and ensures a desired strong region for the mooring lines 15'. In a variation of the embodiment of figure 2a the attachment fairleads are located inside the monopile in a buoyancy compartment 19" above the biscuit deck 18a' e.g. forming part of a tension adjustment arrangement. The mooring lines 15 are connected to the water floor anchor via not shown water floor anchors.

[0355] The watertight diaphragm 18b is as described above for figure 2a here bulge shaped, which ensures a very high strength for withstanding stresses in the diaphragm due to the high pressure in the upper portion of the primary compartment 12.

[0356] The buoyancy compartment 19" is located in the upper section US immediately above the biscuit deck 18a'.

[0357] In a variation thereof the buoyancy compartment 19" also serves as an operators working space and comprises parts of a not shown pressure control arrangement for controlling the pressure in the primary compartment 12 as described above and at least a part of a tension adjustment arrangement e.g. comprising a winch, or a turnbuckle, or a ram, such as a hydraulic ram and / or a pneumatic ram as described above.

[0358] The monopile may comprise an additional buoyancy compartment 19' located between the roof divider 18b' and the biscuit deck 18a'.

[0359] As it can be seen the additional buoyancy compartment 19' is located at the water line, which adds to ensure a high stability of the BGM.

[0360] As mentioned the figures are not drawn to scale and the upper section may be relatively higher than illustrated and e.g. extend further above the biscuit deck than illustrated. Figure 3a shows a portion of a BGM installation wherein the BGM has a top end TE, lower section, a mid-section MS and an upper section US. The lower section has a lower section portion LS' and comprises a tip section TS below the lower section portion LS'. The tip section is embedded in the not shown water floor or docked in a not shown footing.

[0361] TS has a relatively narrow diameter relative to the average diameter of the BGM.

[0362] The BGM comprises a primary compartment 22 marked with the dotted line and extending from a primary compartment floor divider 22a to a primary compartment roof divider, wherein the primary compartment roof divider comprises a biscuit deck 28a and airtight diaphragm 28b below the biscuit deck 28a. The primary compartment roof divider is located in and forms the mid-section MS of the BGM.

[0363] The primary compartment 22 is partially water filled as indicated with the water level line WL. The water is flooded into the primary compartment via a flooding hole 24 of an opening arrangement. In addition, the primary compartment 22 is pressurized in its upper portion above the flooding hole 24. The pressurization is established and / or controlled by a pressure control arrangement 21a, 21b. The pressure control arrangement comprises a gas control tube 21a with an air control valve to maintain the pressure at a desired level. In addition, the pressure control arrangement comprises an internal tube 21b passing through the primary compartment roof divider 28a, 28b into the primary compartment and extending from a first internal tube end 21bf located at a first location in the primary compartment to a second internal tube end 21bs located at a second location above the primary compartment 22 and optionally above a not shown buoyancy compartment.

[0364] The skilled person will understand that the level of the second internal tube end 21bs of the internal tube used for safe conduit of electrical cables, 21bs, beneficially is situated above the level of the Highest Astronomical Tide, HAT, outside of the BGM. The level of the bottom end (first internal tube end 21bf) of the internal tube will be open to the water in the primary compartment 22, so the design of this lower elevation, 21bf, will limit what volume of gas can be safely contained in the primary compartment, so that the internal water level in in the installed situation, will always be above the level of the bottom of this internal tube. In this embodiment, an electrical cable 23 is passed to transport energy between an element above the biscuit deck 28a and a not shown external element. The electrical cable 23 is passed through the wall of the BGM via an electrical cable hole 24a of the opening arrangement into the primary compartment 22 and via the internal tube 21b and upwards.

[0365] The watertight diaphragm 28b is here bulge shaped which ensure a very high strength for withstanding stresses in the diaphragm due to the high pressure in the upper portion of the primary compartment 22.

[0366] In the upper section US, the BGM comprises a buoyancy compartment 29. The buoyancy compartment BC is here located immediately above the biscuit deck 18a.

[0367] The BGM shown in figure 3b is as the BGM shown in figure 3a but where the pressure control arrangement further comprises a gas escape tube 21c. The gas escape tube 21c extends from a first gas escape tube end 21cf located in the primary compartment through a gas escape hole, which is in this embodiments a common flooding and gas escape hole 24a and along the monopile length to a second gas escape tube end 21cs located outside the monopile e.g. attached to the outer surface of the BGM at the upper section, US e.g. to provide that the a second gas escape tube end 21cs is located above the waterline during installation.

[0368] The gas escape 21c tube has the function of providing a controlled escape route for gas during installation when the water is flooding into the primary compartment 22 via the common flooding hole as ballast to facilitate the rotation of the BGM to an upright position.

[0369] In embodiments without such gas escape tube, e.g. as shown in figure 3a, a controlled gas escape route from the primary compartment may be provided and controlled by the gas control tube 21a.

[0370] The BGM shown in figure 3c is as the BGM shown in figure 3b but with the difference that the internal tube 21b' of the pressure control arrangement comprises passes through the primary compartment roof divider 28a, 28b into the primary compartment and extends from a first external tube end 21bf' located at a first location below water and outside the monopile via the electrical cable hole 24b, to a second internal tube end 21bs located at a second location above the primary compartment 22 and optionally above a not shown buoyancy compartment.

[0371] The skilled person will understand that the level of the second internal tube end 21bs of the internal tube used for safe conduit of electrical cables, 21bs, beneficially is situated above the level of the Highest Astronomical Tide, HAT, outside of the BGM. The level of the bottom end (first internal tube end 21bf) of the internal tube will be open to the water in the primary compartment 22, so the design of this lower elevation, 21bf, will not limit what volume of gas can be safely contained in the primary compartment. The internal water level in the installed situation, will always be above the level of the opening arrangement, 24a. Figure 4 shows a BGM installation with very beneficial mooring configuration. The mooring lines 35a-f each extends from a not shown attachment fairlead connected to the outer surface of the BGM 30, preferably at the mid-section thereof to a not shown water floor anchor with a straight line as seen in plan-top-view in figure 4.

[0372] The straight line of each of the mooring lines mooring lines 35a-f intersects at an intersection point 31 with the outer surface of the monopile, and with an intersection vertical plane having an angle a which is relatively low, such described above e.g. an angle of 30 degrees or less from a plane tangential to the outer surface of the monopile at that intersection point 31.

[0373] By this mooring configuration, the out-of-plane loading imposed on the monopile wall may be reduced or even minimised, compared to where the angle is closer to perpendicular to the monopile wall, and thereby this mooring configuration is assisting with an effective and efficient transfer of forces from the mooring lines into the shell of the monopile.

[0374] The mooring lines 35a-f may be moored to the water floor by individual water floor anchors or the mooring lines 35a-f may be moored to the water floor by pairwise mooring comprising that two adjacent mooring lines 35a-b, 35c-d, 35e-f are moored to a common water floor anchor.

[0375] In a variations thereof, the mooring lines are provided in the form of pairwise mooring line sections 35b-c, 35d-e, 35a-f of three mooring lines. Figure 5a shows a tension adjustment arrangement 41 partially internal in the BGM at the mid-section MS and above the not shown biscuit deck. The tension adjustment arrangement 41 comprises a guiding control roller 44 fixed to the outer surface of the BGM wall 40. Internally in the BGM, the tension adjustment arrangement 41 comprises a not shown tension control device, such as a winch, or a turn-buckle, or a ram, such as a hydraulic ram and / or a pneumatic ram for ensuring and a desired and controlled tension in the mooring line 45.

[0376] The mooring line 45 penetrates the BGM wall 40 via a seal element 46 located in the BGM wall 40 and allows the penetrating mooring line 45 to move freely through the monopile wall.

[0377] Thereby limiting the penetration of raw water into the compartment above the biscuit deck comprising the tension control device. The seal element 46 may for example be a Roxtec™ seal, a ship drive shaft stuffing box or similar.

[0378] The skilled person will understand that the purpose of the guiding control roller 44 is to ensure that the mooring line is directed with a desired orientation into the seal element 46 and that the guiding control roller 44 may be replaced by another guiding means such as a fairlead, such as an attachment fairlead or similar.

[0379] Figure 5b illustrates a fixing length section 40a of a monopile of an embodiment of the invention, such as of a buoyancy comportment BC located above a biscuit deck and / or above a mid-section of a monopile of an embodiment of the invention schematically illustrating a mooring line 45a attached to a pulling bar 43 of a tension adjustment arrangement. The buoyancy comportment BC has a diameter D and comprises the tension adjustment arrangement where only a portion of the pulling bar 43 is visible in this figure. The pulling bar 43 is connected to the remaining of the tension adjustment arrangement which may be tighten to provide a desired pulling in the pulling bar 43 for tensioning the mooring line 45a to a desired tensioning force. The mooring line 45a is connected to the pulling bar 43 preferably via a connection, which may conveniently comprise an attachment fairlead 43a e.g. a pad eye of the pulling bar 43. It is preferred that the attachment fairlead 43a is located outside the monopile as in the shown embodiment, such that the mooring line may easily be connected to the pulling bar 43 via the attachment fairlead 43a. This will in addition enable that the tension adjustment arrangement including the pulling bar 43 and optionally any seal arrangements may be pre-installed in the monopile.

[0380] The seal arrangement may also be referred to as a gasket arrangement.

[0381] In the shown embodiment the pulling bar 43 penetrates the monopile wall 40 via a tension adjustment arrangement opening 40b, so that the pulling bar 43 of the tension adjustment arrangement extends from outside the monopile and through the tension adjustment arrangement opening 40b into the buoyancy comportment BS of the monopile. In a variation thereof the attachment fairlead 43a. is located in the buoyancy comportment BC and the mooring line 45a penetrates the monopile wall 40 via a tension adjustment arrangement opening 40b, so that the mooring line 45a extends from outside the monopile and through the tension adjustment arrangement opening 40b into the buoyancy comportment BS of the monopile.

[0382] The dotted square 5c indicates that an embodiment of the sealing arrangement is further illustrated in figure 5c.

[0383] As seen in figure 5c and the enlarged portion 5c' illustrated in figure 5c', the seal arrangement comprises a tube seal arrangement 42a connected to the monopile adjacent the tension adjustment arrangement opening 40b to form a seal between the pulling bar 43 penetrating the monopile and an edge portion along the periphery of the tension adjustment arrangement opening 40b through the monopile wall. The tube seal arrangement 42a comprises a tube shaped opening 42c through which the pulling bar 43 is passing. A line seal 42b is arranged to seal between the pulling bar 43 and an inner tube face 42a' of the tube seal arrangement 42a in the tube shaped opening 42f. The seal arrangement comprises a socket 49 which may be fully or partly be integrated with the monopile wall 40 and located to form the adjustment arrangement opening 40b, which allows the pulling bar 43 to penetrate into the buoyancy comportment BC of the monopile. In an embodiment, the socket 49 is of the same metal as the remaining of the monopile wall 40, e.g. attached by welding. The socket has a supporting portion 49b extending into the buoyancy comportment BC of the monopile, such that the socket 49 forms a half-shell with the adjustment arrangement opening 40b for the pulling bar 43. The supporting portion 49b is supported by a support structure 49c forming a reinforcement of the socket 49. The socket has an inner surface 49a and the tube seal arrangement 42a has a spherical cap surface 42c arranged to face and seal to the bearing surface. The tube seal arrangement 42a element comprises a hemisphere adjustment arrangement 42e for adjusting the tube seal arrangement 42a relative to the socket to provide that the spherical cap surface 42c is adjusted relative to the bearing surface, such that the passage through the socket and the passage through the tube seal arrangement are in alignment relative to each other, and in alignment with the pulling bar 43. Thereby the tube seal arrangement may be adjusted to ensure that the pulling bar 43 penetrating the monopile extend(s) in a relative straight line. In an embodiment, a hydrostatic pressure is applied towards the socket. The hydrostatic pressure may reduce the sealing force between the inner bearing surface 49a and the spherical cap surface 42c, so assisting relative movement between the surfaces whilst the pulling bar direction is adjusted. In an embodiment, ball bearings embedded within the spherical cap surface, 42c, may be activated to provide low resistance to movement between the concentric surfaces, 49a and 42c, so facilitating adjustment of the pulling bar direction.

[0384] The embodiment shown in figure 5d is a variation of the embodiments of figures 5c and 5c' in that the tube seal arrangement comprises an eyeball structure comprising the socket 49 with a bearing surface 49b (also referred to as the socket inner surface) and a hemisphere tube seal arrangement 47 comprising a spherical cap surface 47c arranged to face the bearing surface 49b. Each of the socket 49 and the hemisphere tube seal arrangement 47 comprises a passage for the pulling bar 43 penetrating the monopile. The hemisphere tube seal arrangement 47 is adjustable relative to the bearing surface 49b to provide that the spherical cap surface 47c is adjusted relative to the bearing surface 49b, to provide that the passage 42f of the socket 49 and the passage through the hemisphere tube seal arrangement 47 are in alignment relative to each other, and in alignment with the pulling bar 43. Thereby the hemisphere tube seal arrangement 47 may be adjusted to ensure that the pulling bar 43 penetrating the monopile wall 40 extends in a relative straight line.

[0385] The adjustment of the hemisphere tube seal arrangement 47 may preferably be provided prior to fully tensioning the tension adjustment arrangement - i.e. the tension adjustment arrangement is in an untensioned stage ensuring that the hemisphere tube seal arrangement is adjustable relative to the socket. The adjustment may be performed using the hemisphere adjustment arrangement 2e. After the tension adjustment arrangement has been fully tensioned the hemisphere tube seal arrangement cap surface 47c will be pressed towards the bearing surface 49b, whereby the friction between the hemisphere tube seal arrangement cap surface and the bearing surface may prevent further adjustment.

[0386] The tensioning state is illustrated with the Max and Min location of the fairlead 43a, where the tension adjustment arrangement is in untensioned state when the location of the fairlead 43a is located at the Min location or further from the tension adjustment arrangement opening 40b and where the tension adjustment arrangement is in tensioned state when the location of the fairlead 43a is located at the Max location or closer to the tension adjustment arrangement opening 40b or even inside the buoyancy comportment BC.

[0387] The hemisphere adjustment arrangement 2e may e.g. be in the form of an at least partially mechanical adjustment mechanism located in the buoyancy comportment BC.

[0388] The hemisphere tube seal arrangement 47 may beneficially be shaped as a hemisphere or as a part-hemisphere.

[0389] In an embodiment the tube seal arrangement comprises a flexible covering structure 48 applied against and optionally connected to the outer edge portion along the periphery of the tension adjustment arrangement opening 40b. Preferably the tube seal arrangement 47 further comprises a seal collar 48a arranged to seal between the flexible covering structure 48 and the pulling bar 43. In a variation of the shown embodiment, the flexible covering structure 48 and the seal collar 48a are integrated with each other, such as formed in a single element or fixed to each other e.g. with a glue. The seal arrangement may further comprise a seal ring 42b located in the passage of the hemisphere tube seal arrangement 47 to form a seal between the hemisphere tube seal arrangement 47 and the pulling bar 43 passing through the hemisphere adjustment element 47.

[0390] In use, the hydrostatic pressure provided by the surrounding water may apply a hydrostatic pressure towards the flexible covering structure 48 and the seal collar 48a which provides a pressure against the socket 49 and the hemisphere tube seal arrangement 47. Where the socket 49 is at least partially fixed to the flexible covering structure 48 and / or the seal collar 48a, the resulting pressure may result in a reduced contact pressure between the bearing surface 49b and the spherical cap surface 47c of the hemisphere adjustment element 47, which may ensure allowing the adjustment of the hemisphere tube seal arrangement relative to the bearing surface, preferably to direct the mooring line exactly at the point close to the seabed where the mooring line terminates, before tension is added to the mooring line by the tension adjustment arrangement 47, which then pushes the hemisphere tube seal arrangement 47 towards the bearing surface 49b, whereby friction is increased and further relative movement may be prevented.

[0391] On the outside of the monopile, the hydrostatic pressure may cause the flexible covering structure 48 to push tight against the monopile opening, and reduce water ingress to a minimum or even prevent water ingress. The seal collar 48a further add to ensure this sealing. The seal ring 42b ensures that where minor amounts of water has passed the flexible covering structure 48 and the seal collar 48a, such minor amount of water may be prevented to pass further into the buoyancy comportment BC by said seal ring 42b.

[0392] As shown in figure 5d, the tension adjustment arrangement may comprise bolt tensioning structure arranged to provide a pressure toward the tube seal arrangement 47 and towards a flat basic surface 47d of the hemisphere tube seal arrangement 47 when the tension adjustment arrangement is tensioned. The bolt tensioning structure may for example comprise a set of tensioning rods 46a to provide the pressure toward the flat basic surface of the hemisphere adjustment element 47d.

[0393] The bolt tensioning structure may comprise a back plate 46b and a not shown front plate having a flat surface lying against the flat basic surface 47d of the hemisphere tube seal arrangement 47 to ensure the apple force to be distributed over at least a portion of the flat basic surface 47d of the hemisphere tube seal arrangement 47.

[0394] The set of tensioning rods 46a extend from the front plate to the back plate. The Front plate comprises openings for the pulling bar 43.

[0395] The back plate or the front plate preferably comprises a not shown retainer arrangement, which in a closed stage prevents the pulling bar from being pulled in a direction towards the hemisphere adjustment element, but allow the pulling bar from passing in a direction further away from the hemisphere adjustment element, thereby ensuring that the bolt tensioning structure provide a pressure towards the flat basic surface of the hemisphere tube seal arrangement when the tension adjustment arrangement is tensioned and when the retainer arrangement is in the closed stage.

[0396] In an embodiment the tensioning rods of the set of tensioning rods each comprises a threaded bar 46 that passes through a passage of the back plate via a bolt, that is locked to or is lockable to the threaded bar for ensuring locking of the tensioning rods to provide a desired distance between the front plate and the back plate.

[0397] Figures 6a illustrates a BGM installation with a mooring configuration where only two mooring lines 55 are shown. It should be understood that the BGM installation may have any number of mooring lines such as 6 as illustrated in figure 4. Each mooring line extends from an water floor anchor 56 to a not shown attachment fairlead connected to the outer surface of the BGM 50 with a straight line as seen in plantop-view in figure 6a.

[0398] Figure 6b show the BGM installation of figure 6a, but with the difference that the BGM installation comprises a tension adjustment arrangement 57 arranged for adjusting and / or tuning the mooring line tension. The tension adjustment arrangement 57 is here in the form of a mooring line restrictor comprising a ring element surrounding the two mooring lines and a not shown pulling arrangement adapted for pulling the beam element towards the monopile, thereby increasing the tension in the mooring lines or mooring line sections. The pulling arrangement may be as described above. A suitable variation of this concept comprises where the radial position of the ring element is fixed, but the length of the ring can be reduced in order to increase tension in the lines, or the ring may be elongated so reducing the tension in the lines.

[0399] Figure 7 shows a BGM installation similar to the BGM installation of figure 6a with a mooring configuration. Also here only two mooring lines 65 of the mooring configuration are shown. It should be understood that the BGM installation may have any number of mooring lines, such as illustrated in figure 4. Each mooring line 65 extends from an water floor anchor 66 to a not shown attachment fairlead connected to the outer surface of the BGM 60 with a straight line as seen in plan-top-view in figure 7.

[0400] A tension adjustment arrangement comprising a beam element 67 is arranged to cross the monopile axis, and comprises two fairleads 67 located at a fixed distance to each other. The tension adjustment arrangement comprises a not shown pulling arrangement adapted for pulling the beam element towards the monopile, thereby increasing the tension in the mooring lines or mooring line sections. This is illustrated with the dotted markings, where the beam 67' has been pulled towards the BGM to a second location by the pulling arrangement, thereby pulling the mooring lines 65 closer to each other at the second location.

[0401] Figure 8a shows a footing 73. As it can be seen, a tip section of a BGM 70 has been docked into the footing 73. The preferred height and diameter of the footing may vary in dependence of the water floor conditions as well as in dependence of the loads to be expected on the BGM once installed.

[0402] Figure 8b shows a water floor anchor 76. The water floor anchor 76 comprises a pair of in-line tensioners 76a which are holding respective mooring lines 75 of a BGM installation in tension.

[0403] The BGM shown in figure 9 comprises a lower section comprising a tip section TS.

[0404] The BGM comprises a primary compartment 82 extending from a primary compartment floor divider 82a to a watertight primary compartment roof divider, wherein the primary compartment roof divider comprises a biscuit deck 88a which is this embodiment is integrated and / or comprises an air tight diaphragm, 88b. The primary compartment roof divider is located at, and forms the mid-section of the BGM.

[0405] As described above, a lower portion 82c may be flooded by water flowing in via a flooding hole 84 of an opening arrangement. In addition, an upper portion 82d of the primary compartment 82 may comprise trapped pressurized gas / air. The pressurization may be established as described above e.g. due to the water flooding via the flooding hole 84 and / or by gas, such as air that has been pumped into the upper portion of the primary compartment 82 via a gas control tube 81a of a pressure control arrangement. Immediately above the tip section TS, the BGM comprises a cable hole 84b for an electrical cable.

[0406] In the upper section the BGM comprises a permanent buoyancy compartment 89. An operator's compartment 89a is located between the biscuit deck 88a and the top end, TE. The operators compartment 89a may for example comprise parts of a not shown pressure control arrangement for controlling the pressure in the primary compartment 82 and / or parts of or all of one or more tension adjustment arrangements e.g. comprising a winch, or a turn-buckle, or a ram, such as a hydraulic ram and / or a pneumatic ram as described above.

[0407] The pressure control arrangement further comprises an internal tube 81b passing through the primary compartment roof divider 88a, 88b into the primary compartment 82 and extending from a first internal tube end 81bf located at a first location in the primary compartment to a second internal tube end 81bs located at a second location above the primary compartment 82 and above, or outside of, the buoyancy compartment 89.

[0408] Close to the end the BGM, comprises an upper water tight deck 83. The upper watertight deck may comprise a winching hatch for access to equipment, such as a not shown cable pulling arrangement. In addition an upper end of the gas control tube 81a is located at the upper water tight deck 83 together with other parts of the pressure control arrangement, such as the air control valve 81c.

[0409] During upending and lowering of the BGM, this valve 81c may be used to control compression of air and ingress of water in the primary compartment.

[0410] The BGM may advantageously comprise one or more internal watertight or non- watertight decks as here illustrated with the non-watertight internal deck 84, which may comprise various equipment and as here located at the level of the second internal tube end 81bs.

[0411] Figures lOa-lOe shows representative steps of the method of establishing an installation. In figure 10a, the BGM 100 has been horizontally arranged in the raw water and the BGM is towed by a first tugboat 97a, to the site of the water location it is to be installed, where it may be held on station by the first tugboat 97a. During the towing the opening arrangement comprising a flooding hole 94 is closed off. The first tugboat 97a is anchored to the BGM 100 via tugger lines fixed to a towing bracket 90 optionally temporarily mounted or fixed to the BGM.

[0412] The BGM is only schematic illustrated and only some details are shown. The BGM 100 comprises a number of fairleads 97 mounted at the level of a biscuit deck that forms part of a primary compartment roof divider 98. Below the primary compartment roof divider 98, the primary compartment 92 is located. At a lower portion of the primary compartment 92, the BGM comprises a flooding hole 94 for partially flooding the primary compartment 92. Below the flooding hole 94 and separated by a not shown primary compartment floor divider the BGM comprises the tip section TS.

[0413] At the bottom end 100a of the BGM, 100, at the tip section TS, a guide wire 90a has been pre-installed. The guide wire 90a is pre-installed to extend from the bottom end 100a of the BGM 100 to a buoy 90b connected to a second tugboat, 97b, or other vessel with a winch, via a tugger line, wherein the guide wire 90a is preinstalled to pass through a guide member, such as a fairlead or a hole in the footing 93, which has been pre-installed at the water floor.

[0414] The footing 93 comprises an anchor portion 93a which here is anchored to the water floor and a receptor portion 93b comprising a recess for receiving the tip section TS, wherein a wall portion of the recess forms or comprises the guide member.

[0415] In figure 10b, the ballasting procedure comprising upending and flooding has been initiated. The first tugboat 97a has released or loosened the tugger line that is fixed to the towing bracket 90. The flooding hole has been opened and the second tugboat 97b has started pulling in the guide wire 90a.

[0416] As it can be seen the BGM 100 has started the tilting processes. The BGM has a pressure control arrangement comprising a gas control tube 91a extending from a first end 92af in the primary compartment 92 to a second end where an air control valve 91c is located at the top end of the BGM 100. The gas control tube 91a is illustrated with dotted lines because it is located internal in the BGM 100.

[0417] By opening the air control valve 91c, the gas / air in the primary compartment 92 may be allowed to escape via the gas control tube 91a to ensure that the flooding is performed in a controlled manner. In figure 10c, the upending and flooding has been completed and the air control valve 91c may be closed off, and the flooding hole 94, may also be closed off.

[0418] The first tugboat 97a has reattached the tugger line that is fixed to the towing bracket 90 to aid in the positioning of the BGM 100 above the footing 93. Also the second tugboat has been attached to the towing bracket 90 with a tugger line 90 to aid in the positioning of the BGM 100 above the footing 93.

[0419] The second tugboat 97b continues the pulling in the guide wire, 90a, to provide that the BGM 100 is positioned above the footing.

[0420] In figure lOd, the second tugboat 97b has pulled the BGM 100 via the guide wire to provide that the BGM 100 is located above the footing and the BGM is lowered and pulled down to provide that the tip section TS docks into the recess of the footing 93.

[0421] In figure lOe, the tip section, TS, has docked correctly into the recess of the footing, 93, and the guide wire has been pulled through a not shown non-return device as described above.

[0422] The mooring line attachment process has been started and the first tugboat 97a supports the BGM in its upright position during the mooring process, while the second tugboat 97b performs the anchoring of the BGM by the mooring lines 95 to water floor anchors 96. As described above, the water floor anchors 96 may conveniently be pre-installed. Each mooring line is fixed to the BGM 100 via a fairlead 97 and is fixed to the water floor anchor 96 via in-line tensioner(s), e.g. a Stevadj uster®, which may be fixed to or form part of the water floor anchor 96.

[0423] The tensioning process may be performed by the second tugboat 97b via a tensioning line connected to a winch on the second tugboat 97b, or it may be performed by another means, such as the tensioning device located at the BGM, 100.

[0424] When all the mooring lines 95 have been installed, the BGM instalment has finally been established.

[0425] The tension adjustment arrangement illustrated in figure 11a is a variation of the tension adjustment arrangement shown in figure 5b-5d. As seen in figure 11a, the tension adjustment arrangement comprises a tube seal arrangement having an eyeball structure comprising a socket 109 with a bearing surface 109a (also referred to as the socket inner surface) and a hemisphere tube seal arrangement 107 comprising a spherical cap surface 107c arranged to face and seal to the bearing surface 109a. Each of the socket 109 and the hemisphere tube seal arrangement 107 comprises a passage for the pulling bar 103 penetrating the monopile 100. The socket 109 may be fully or partly be integrated with the monopile wall 100 and located to form the adjustment arrangement opening 100b, which allows the pulling bar 103 to penetrate into the buoyancy compartementBC of the monopile. The socket 109, may be as the socket 49 described in figures 5b-d.

[0426] The socket has a supporting portion 109b extending into the buoyancy comportment BC of the monopile, such that the socket 109 forms a half-shell with the adjustment arrangement opening 100b for the pulling bar 103.

[0427] The tube seal arrangement 107 comprises a tensioning adjustment arrangement in the form of a hemisphere adjustment arrangement 102e, 106b for adjusting the tube seal arrangement 107 relative to the socket 109 to provide that the spherical cap surface 107c is adjusted relative to the bearing surface 109a, such that the passage through the socket and the passage through the tube seal arrangement are in alignment relative to each other, and in alignment with the pulling bar 103. Thereby the tube seal arrangement may be adjusted to ensure that the pulling bar 103 penetrating the monopile extend(s) in a relative straight line.

[0428] The hemisphere adjustment arrangement 102e, 106b may e.g. be in the form of an at least partially mechanical adjustment mechanism located in the buoyancy comportment BC.

[0429] The hemisphere adjustment arrangement may comprise bolt tensioning structure 106a, 106b arranged to provide an adjustable and / or variable pressure toward the tube seal arrangement 107 and towards a flat basic surface 107a of the hemisphere tube seal arrangement 107 when the hemisphere adjustment screws 106a are tightened or loosened. The bolt tensioning structure 106a, 106b may for example comprise a set of tensioning screws 106a to adjust and thereby vary the pressure toward the flat basic surface of the hemisphere adjustment element 107a. The tensioning screws 106a may pass through elements 106b fixed to a not shown back plate fixed in a fixed distance to the flat basic surface 107a, such that by turning the hemisphere adjustment screws 106a the pressure is applied towards the flat basic surface 107a of the hemisphere tube seal arrangement 107. At the same time the adjustment arrangement 102e, 106b may adjust the tube seal arrangement 107 (hemisphere tube) relative to the socket 109 by adjusting the outstanding length of the respective hemisphere adjustment screws 106a relative to the elements 106b forming part of the hemisphere adjustment arrangement. An adjustment controller 102e of the hemisphere adjustment arrangement is located to control that the adjustments is within a pre-set threshold.

[0430] Figure lib shows a portion lib of figure 11a. Here it can be seen that a number of ball bearings 101 are located to partly embedded within a lower portion 107n of the tube seal arrangement 107 (hemisphere tube) and in contact with the bearing surface 109a thereby assisting in smoothing relative movement between the bearing surface 109a and the spherical cap surface 107c whilst the pulling bar direction is adjusted i.e. while adjusting the tube seal arrangement 107 (hemisphere tube) relative to the socket 109. After the adjustment is done, the ball bearings 101 may be retracted fully into the tube seal arrangement 107 (hemisphere tube)

[0431] Figure 12a shows a cross sectional view of a variation of the embodiment illustrated in figure lib where the ball bearings 101 is permanently located in the lower portion 107n of the tube seal arrangement 107 (hemisphere tube). Each ball bearing is located in a ball recess 107d

[0432] Figure 12b shows a cross sectional view of a variation of the embodiment illustrated in figure 12a, wherein for each ball bearing 101, a pressure unit e.g. in the form of a screw and / or a spring is located to at least temporarily press the ball bearing towards the bearing surface 109a.

[0433] Figure 12c shows a cross sectional view of a variation of the embodiment illustrated in figure 12a, wherein the ball bearings 101 are of or comprises magnetic material and the tube seal arrangement 107 comprises an electrical circuit 102b which may create a magnetic force to puss the ball bearing towards the bearing surface 109a during the adjustment of the tube seal arrangement 107 (hemisphere tube) relative to the socket 109. After the adjustment the power to the electrical circuit 102b may be disconnected. Figure 13a shows the tube seal arrangement 107 (hemisphere tube) seen from the spherical cap surface 107c (without the socket 107). As illustrated the ball bearings 101 may by located along the lines 105. In the centre of the shows the tube seal arrangement 107 the passage 103a for the pulling bar 103 is located. Figure 13b is a perspective view of the tube seal arrangement 107 (hemisphere tube) of figure 13a, wherein a number of the hemisphere adjustment screws 106a are shown.

Claims

PATENT CLAIMS1. An installation comprising a buoyant and guyed monopile (BGM), wherein the monopile is upright and has a length from a top end to a bottom end and a wall with an outer surface defining an average monopile outer diameter, wherein the monopile comprises an upper section defining the top end and a lower section comprising a tip section defining the bottom end and at least partially supported by the water floor, wherein the lower section has an average lower section outer diameter which is less than the average monopile outer diameter, wherein the monopile comprises a primary compartment and an opening arrangement into said primary compartment located at least partially in the lower section, wherein the monopile comprises at least one buoyancy compartment located at least partially in the upper section, wherein the installation comprises a plurality of attachment fairleads and at least three mooring lines arranged to anchor the monopile to water floor anchors via said plurality of fairleads, optionally the installation comprises a superstructure, such as a wind turbine, a turbine tower and / or a transition piece, wherein the superstructure is supported by the monopile.

2. The installation of claim 1, wherein said primary compartment is at least partially water filled, preferably the primary compartment is partially water filled.

3. The installation of claim 1 or claim 2, wherein the at least one buoyancy compartment comprises a permanent buoyancy compartment, preferably located above the primary chamber.

4. The installation of any one of the preceding claims, wherein the at least one buoyancy compartment form part of the primary compartment and / or wherein the at least one buoyancy compartment comprises a separate compartment located closer to the top end than the primary compartment, preferably the at least one separate buoyancy compartment is located adjacent the primary compartmentseparated by a compartment divider, wherein the compartment divider preferably is watertight and preferably sufficiently airtight to maintain a pressure difference of 50 Pa for at least 24 hours, such as for one year or longer, preferably the compartment divider is sufficiently airtight to maintain a pressure difference of at least 1 kPa, such as at least 0.1 bar, such as at least 1 bar at for at least 1 hour, such as for 24 hours or longer.

5. The installation of claim 4, wherein the compartment divider is sufficiently airtight to maintain a pressure difference corresponding to the hydrostatic pressure acting at a level of the opening arrangement for a period of at least 1 hour, such as for 24 hours, such as for 1 year.

6. The installation of any one of the preceding claims, wherein at least an uppermost portion of the one or more buoyancy compartment is located above the waterline.

7. The installation of any one of the preceding claims, wherein the primary compartment is watertight except for said opening arrangement, preferably the primary compartment, except for said opening arrangement is sufficiently airtight to maintain a pressure difference of 50 Pa for at least 24 hours, such as for one year or longer, preferably the compartment divider is sufficiently airtight to maintain a pressure difference of at least 1 kPa, such as at least 0.1 bar, such as at least 1 bar at for at least 1 hour, such as for 24 hours or longer, such as for 1 year.

8. The installation of any one of the preceding claims, wherein the primary compartment is defined by a primary compartment roof divider and a primary compartment floor divider, wherein the primary compartment floor divider defines the tip section in the lower section.

9. The installation of claim 8, wherein the primary compartment roof divider comprises a watertight diaphragm, preferably the primary compartment roof divider comprises a watertight diaphragm and a plate located above the watertight diaphragm.

10. The installation of any one of the preceding claims, wherein said opening arrangement in the lower section into said primary compartment comprises a flooding hole in the wall of the monopile into said primary compartment, whereinsaid flooding hole preferably is located closer to the primary compartment floor divider, than the primary compartment roof divider.

11. The installation of claim 10, wherein the primary compartment has a height along said monopile length, preferably defined as the maximal distance between said primary compartment roof divider said primary compartment floor divider, wherein said flooding hole is located within a distance of up to 50 % of said primary compartment height from said primary compartment floor divider, such as within a distance of up to 40 %, such as up to 20 %, such as up to 10 %, such as up to 5 % of said primary compartment height from said primary compartment floor divider, such as within a distance of up to 5 m from the primary compartment floor divider.

12. The installation of any one of the preceding claims, wherein the monopile comprises a closing arrangement adapted for temporarily restricting or closing off said opening arrangement, said closing arrangement is preferably adapted for temporarily closing and sealing said flooding hole(s).

13. The installation of claim 12, wherein the closing arrangement comprises a controller adapted for controlling the opening degree of the opening arrangement from being fully open to being fully closed, preferably the controller is adapted for receiving instructions from an operator optionally via instruction signals that may be transmitted by wire or wireless e.g. via an operator station.

14. The installation of any one of the preceding claims, wherein an upper portion of the primary compartment comprises pressurized gas (preferably air), preferably the pressure in the primary chamber along the length of the monopile is sufficiently high to counter act the hydrostatic pressure acting onto the monopile along said length, preferably the pressure at any elevation inside the primary compartment is larger than or equal to the hydrostatic pressure acting at the outer wall of the monopile at the corresponding elevation.

15. The installation of any one of the preceding claims, wherein the installation comprises a pressure control arrangement for controlling the pressure in the primary chamber, preferably the control arrangement comprises a gas control tube and / or a pump for supplying pressurized gas to the primary chamber.

16. The installation of claim 15, wherein the pressure control arrangement comprises an internal tube passing through said primary compartment roof divider into the primary compartment and extending from a first internal tube end located at a first location in the primary compartment to a second internal tube end located at a second location above the primary compartment and preferably above the at least one buoyancy compartment, preferably the first location in the primary compartment is located at a distance to the primary compartment roof divider not exceeding 20 % of the primary compartment height, preferably the second location is located above waterline, such as at or above within 3 m of the top end.

17. The installation of claim 15 or claim 16, wherein the pressure control arrangement comprises a closable gas release valve for allowing gas, such as air to escape from the primary compartment, preferably the gas release valve is located at the upper half part of the primary compartment closest to the top end, such as located in the primary compartment roof divider or in the monopile wall, preferably located in the primary compartment roof divider or in the monopile wall at a distance to the primary compartment roof divider not exceeding 20 % of the primary compartment height, such as a distance to the primary compartment roof divider not exceeding 2 m.

18. The installation of any one of claims 15-17, wherein the pressure control arrangement comprises a gas escape tube, wherein the gas escape tube extends from a first gas escape tube end located in the primary compartment through a gas escape hole of the opening arrangement and along the monopile length to a second gas escape tube end located at a level of or above the upper section of the monopile, preferably the first gas escape tube end is located at the upper half part of the primary compartment closest to the primary compartment roof divider, preferably the second gas escape tube end is located above an optional water level in the primary compartment and preferably the second gas escape tube end is located above waterline, the gas escape tube preferably comprises a closable gas release valve for allowing gas, such as air to escape from the primary compartment.

19. The installation of any one of the preceding claims, the lower section has a length of up to 80 % of the monopile length, such as up to 70 %, such as up to 50 %, such as up to 40 % of the monopile length.

20. The installation of any one of the preceding claims, wherein the lower section has a length of up to 200 m, such as up to 150 m, such as up to 130 m, such as up to 100 m, such as up to 60 m.

21. The installation of any one of the preceding claims, wherein the lower section has an average outer diameter of 80 % or less than the average monopile outer diameter, such as 70 % or less, such as 60 % or less, such as 50 % or less than the average monopile outer diameter.

22. The installation of any one of the preceding claims, the lower section has an average outer diameter of 75 % or less than a maximal monopile outer diameter, such as 50 % or less, such as 40 % or less, such as 30 % or less, such as 20 % or less than the maximal monopile outer diameter.

23. The installation of any one of the preceding claims, the lower section has an average outer diameter of 7 m or less, such as of 6 m or less, such as of 4 m or less.

24. The installation of any one of the preceding claims, wherein the tip section has a length of up to 20 % of the lower section length, such up to 10 m, such as at least 1 m, such as from 2 m to 10 m.

25. The installation of any one of the preceding claims, wherein the upper section comprises a top end portion comprising the top end and located or adapted to be located above waterline and a body portion below the top end portion comprising at least a part of said at least one buoyancy compartment, optionally the top end portion comprises a connecting area engaged with or connected to or adapted to be engaged with or connected to a superstructure, such as a wind turbine, a turbine tower and / or a transition piece, wherein the superstructure is supported by the monopile.

26. The installation of any one of the preceding claims, wherein at least a part of the tip section is supported by the water floor by being at least partially embedded in the water floor or in a footing arrangement, wherein the footing arrangement is located at or in at the water floor and preferably secured in or at the water floor.

27. The installation of claim 26, wherein the footing arrangement comprises a footing, wherein at least a part of the tip section is secured to the footing, preferably by at least one of a grouted connection, a slip-joint connection, a bearing connection, a bolted connection, a socket connection, a tension restraint, a hinge connection, a pin connection or any combinations thereof.

28. The installation of claim 26 or claim 27, wherein the footing arrangement comprises a footing, wherein the footing comprises a support recess in which at least a part of the tip section is resting, wherein the tip section is held fixed to the footing by a filler material and / or a binder material, such as grout e.g. cementitious grout and / or epoxy.

29. The installation of any one of the preceding claims, wherein the installation is a universal water installation, and wherein at least one, such as all of the attachment fairleads is / are attached to the monopile below the waterline and wherein the monopile is anchored by the mooring lines to the floor anchors via the plurality of fairleads located below the water line.

30. The installation of any one of the preceding claims 1-28, wherein the installation is a shallow water installation and wherein the attachment fairleads are attached to the monopile or to a superstructure of the installation supported by the monopile above the waterline and wherein the monopile is anchored by the mooring lines to the floor anchors via the attachment fairleads attached to the monopile and located below the water line and / or via the attachment fairleads attached to the superstructure and located below the water line.

31. The installation of any one of the preceding claims, wherein at least one of such as all of the plurality of attachment fairleads are attached to the monopile at respective fixing locations, wherein the fixing locations are located at a common fixing length section of the monopile, wherein the common fixing length section has a length of 6 m or less, such as 5 m or less, such as 4 m or less, such as 2 m or less.32 The installation of any one of the preceding claims, wherein at least one of such as all of the plurality of attachment fairleads are in the form of or comprises an attachment point for securing the mooring line directly or indirectly tothe monopile, wherein the attachment fairlead preferably comprises a connecting structure, such as a padeye with a connected shackle, such as a pulling bar.

33. The installation of any one of the preceding claims, wherein the monopile comprises one or more winches turn-buckles and / or rams, such as one or more hydraulic rams and / or one or more pneumatic rams , wherein each winch, turn-buckle and / or ram may be arranged to adjust the tension in one or more of the mooring lines.

34. The installation of any one of the preceding claims, wherein the monopile comprises a mid-section located between the upper section and the lower section, preferably the mid-section comprises or is defined by the primary compartment roof divider, wherein the primary compartment floor divider preferably comprises a watertight diaphragm optionally a plate located above the watertight diaphragm.

35. The installation of any one of claims 31-34, wherein the common fixing length section of the monopile form part of or comprises said mid-section or wherein the common fixing length section of the monopile comprises a length section of the upper section of the monopile located above the mid-section and preferably above the waterline.

36. The installation of claim any one of claims 31-35, wherein the common fixing length section of the monopile, such as the mid-section of the monopile comprises a reinforcement, such as a stiffening ring.

37. The installation of any one of claims 31-36, wherein the common fixing length section of the monopile, such as the mid-section of the monopile comprises a biscuit deck, wherein the biscuit deck preferably comprises, forms part of or constitutes the primary compartment roof divider.

38. The installation of any one of the preceding claims, wherein the plurality of attachment fairleads when attached to the monopile comprises at least 3 attachment fairleads, wherein each attachment fairlead is attached to the monopile at a fixing location by anchoring the at least one attachment fairlead to the monopile from the outer surface of the monopile or by anchoring the at least one attachmentfairlead at least partially at an internal location of the monopile, such as at or above the biscuit deck.

39. The installation of any one of the preceding claims, wherein the mooring lines are arranged to anchor the monopile to the water floor anchors via said plurality of attachment fairleads, wherein each mooring line is attached to the monopile via at least one of the attachment fairleads and at least one of the water floor anchors, preferably each mooring line is attached to the monopile or the superstructure via at least one of the attachment fairleads and at least two separate of the water floor anchors, wherein said two separate water floor anchors to which each end of a mooring line is attached, are located with a distance to each other.

40. The installation of any one of the preceding claims, wherein the mooring lines are arranged to anchoring the monopile to water floor anchors via said plurality of attachment fairleads, wherein each of the mooring lines or mooring line portions extends from one of the attachment fairleads to one of the water floor anchors with a straight line as seen in plan-top-view, wherein the straight line of each of the mooring lines or mooring line portions intersects at an intersection point with the outer surface of the monopile, and with an intersection plane having an angle of 30 degrees or less, such as an angle of 28 degrees or less, such as an angle of 25 degrees or less from a plane tangential to the outer surface of the monopile at that intersection point.

41. The installation of any one of the preceding claims, wherein the installation comprises at least one tension adjustment arrangement for adjusting and / or tuning the mooring line tension, preferably for controlling and / or fine-tuning the mooring line tension and preferably for adjusting the system stiffness, optionally the tension adjustment arrangement comprises a winch, a turn-buckle and / or a ram such as a hydraulic ram and / or a pneumatic ram.

42. The installation of claim 41, wherein the at least one tension adjustment arrangement comprises a length adjustment device adapted for adjusting a free length of one or more of the mooring lines, such as for adjusting the free length of a plurality of the mooring lines, wherein the free length of a mooring line, is the length of the mooring line extending between the water floor anchor and the monopile.

43. The installation of claim 41 or claim 42, wherein the at least one tension adjustment arrangement comprises a length adjustment device for each of the mooring lines.

44. The installation of any one of claims 43, wherein the installation comprises a structural health monitoring systems in data communication with the tensioning adjustment arrangement, wherein the structural health monitoring systems is adapted for monitoring a system natural frequency of the installation based on data received from the tension adjustment arrangement and wherein the structural health monitoring systems is adapted for providing instructions to the tension adjustment arrangement for adjusting the tension in at least one of the plurality of the mooring lines, preferably for adjusting the tension in a plurality of the mooring lines to maintain the natural frequency within a pre-defined frequency range.

45. The installation of any one of claims 41-44, wherein the at least one tension adjustment arrangement is adapted for adjusting a verticality of the monopile.

46. The installation of any one of claims 41-45, wherein the at least one tension adjustment arrangement comprises one or more internal or external hydraulic and / or pneumatic rams, which are adapted for shorten or elongate one or more of the mooring lines.

47. The installation of any one of claims 41-46, wherein the at least one tension adjustment arrangement comprises one or more threaded bars acting in-line with the mooring line, which can be pulled to elongate the mooring line, or released to shorten it.

48. The installation of any one of claims 41-47, wherein the at least one tension adjustment arrangement is at least partly located internally in the monopile, preferably at or above the biscuit deck.

49. The installation of claim 48, wherein a part of the tension adjustment arrangement and / or the mooring line(s) penetrates the monopile wall and wherein a sealing is arranged to seal around the penetrating part and / or mooring line, preferably provided such that it allows penetrating movable parts of the tensionadjustment arrangement and / or penetrating mooring line(s) to move freely through the monopile wall, such as a sealing comprising a seal element comprising a Roxtec™ seal and / or a ship drive shaft stuffing box.50 The installation of any one of claims 41-49, wherein the monopile comprises a tension adjustment arrangement opening, wherein the tension adjustment arrangement comprises a pulling bar connected to or connectable to the mooring line, wherein one of the pulling bar and the mooring line penetrates the monopile wall via said tension adjustment arrangement opening, wherein the installation comprises a tube seal arrangement connected to the monopile adjacent said tension adjustment arrangement opening to form a seal between said pulling bar or said mooring line penetrating the monopile and an outer edge portion of the outer monopile surface along a periphery of the tension adjustment arrangement opening- through the monopile wall.51 The installation of claim 50, wherein the tube seal arrangement comprises an eyeball structure comprising a socket with a bearing surface and a hemisphere tube seal arrangement comprising a spherical cap surface arranged to face the bearing surface, wherein each of the socket and the hemisphere tube seal arrangement comprises a passage for said pulling bar or said mooring line penetrating the monopile, wherein the hemisphere tube seal arrangement is adjustable relative to said bearing surface to provide that the spherical cap surface is adjusted relative to said bearing surface, such that said passage of said socket and said passage through said hemisphere tube seal arrangement are in alignment relative to each other, and in alignment with said pulling bar or said mooring line at least when said tension adjustment arrangement is in a untensioned stage, wherein said pulling bar or said mooring line preferably is passing through said passage of said socket and said passage through said hemisphere adjustment element.52 The installation of claim 51, wherein the tube seal arrangement comprises a flexible covering structure applied against and optionally connected to the outer edge portion along the periphery of the tension adjustment arrangement opening and a seal collar arranged to seal between the flexible covering structure and said pulling bar or said mooring line, preferably the seal arrangement further comprises a seal ring located in the passage of the hemisphere tube seal arrangement to form a seal between the hemisphere tube seal arrangement andsaid pulling bar or said mooring line passing through the hemisphere adjustment element.53 The installation of any one of claims 50-52, wherein the tension adjustment arrangement comprises a bolt tensioning structure comprising a set of tensioning rods to provide a pressure toward the tube seal arrangement and towards a flat basic surface of the hemisphere adjustment element.

54. The installation of any one of claims 50-53, wherein the tube arrangement comprises ball bearings at least partly embedded within a lower portion of the tube seal arrangement (hemisphere tube) and in contact with the bearing surface.

55. The installation of any one of claims 48-54 or claim, wherein the mooring line(s) is carried within the monopile, preferably at least partially inside a support tube, such as inside a J-tube(s) to a location above the water level, preferably a part of the tension adjustment arrangement and / or the mooring line(s) penetrates the monopile wall at a location below the water level.

56. The installation of any one of claims 41-55, wherein the at least one tension adjustment arrangement comprises at least one beam element arranged perpendicular ± up to 15 degrees, such as up to 10 degrees to the monopile axis, and comprising two fairleads located at a fixed distance to each other, wherein the at least one beam element is located at a distance to the monopile below seawater level, wherein each of the two fairleads of the beam element comprise a guide ring and / or wheel arranged to encircle the respective adjacent mooring lines or sections of a mooring line extending between an attachment fairlead on the monopile and a water floor anchor, and wherein the tension adjustment arrangement comprises a pulling arrangement adapted for pulling the beam element towards the monopile, thereby increasing the tension in the mooring lines or mooring line sections.

57. The installation of any one of the preceding claims, wherein the monopile has a plurality of sectional modulus at respective elevations along the monopile length, wherein the monopile has a sectional modulus at an elevation comprising one or more of the plurality of attachment fairleads which is at least 4 times greater than a minimum value of a section modulus of the monopile lowersection at an elevation of from 1 to 10 m above the water floor such as, from 4 to 6 m above the water floor, such as 5 m above the water floor.

58. The installation of any one of the preceding claims, wherein the monopile has a plurality of sectional modulus along the monopile length, wherein the monopile has a maximal sectional modulus at any elevation along the length which is at least 5 times greater than the section modulus determined at an elevation up to a distance of 0.5 m above the primary compartment floor divider.

59. The installation of any one of the preceding claims, wherein the installation is an offshore installation, whereby the water location is an offshore location and the water bed is a seafloor and the raw water is sea (ocean) water.

60. A monopile suitable for an installation according to any one of the preceding claims, wherein the monopile has a length from a top end to a bottom end and a wall with an outer surface defining an average monopile outer diameter, wherein the monopile comprises an upper section and a lower section comprising a tip section at least partially supported by the water floor, wherein the lower section has an average lower section outer diameter which is less than the average monopile outer diameter, wherein the monopile comprises a primary compartment and an opening arrangement into said primary compartment located at least partially in the lower section, and wherein the monopile comprises at least one buoyancy compartment located at least partially in the upper section.

61. The monopile of claim 60, wherein the at least one buoyancy compartment form part of the primary compartment and / or wherein the at least one buoyancy compartment comprises a separate compartment located closer to the top end than the primary compartment, preferably the at least one separate buoyancy compartment is located adjacent the primary compartment separated by a compartment divider, wherein the compartment divider preferably is watertight and preferably sufficiently airtight to maintain a pressure difference of at least 50 Pa for at least 24 hours, such as for one year or longer, preferably the compartment divider is sufficiently airtight to maintain a pressure difference of at least 1 kPa, such as atleast 0.1 bar, such as at least 1 bar at for at least 1 hour, such as for 24 hours or longer, such as for 1 year.

62. The monopile of claim 60 or claim 61, wherein said primary compartment is watertight except for said opening arrangement, preferably the primary compartment, except for said opening arrangement is sufficiently airtight to maintain a pressure difference of 50 Pa for at least 24 hours, such as for one year or longer, preferably the compartment divider is sufficiently airtight to maintain a pressure difference of at least 1 kPa, such as at least 0.1 bar, such as at least 1 bar at for at least 1 hour, such as for 24 hours or longer, such as for 1 year.

63. The monopile of any one of claims 60-62, wherein said primary compartment is defined by a primary compartment roof divider and a primary compartment floor divider, wherein the primary compartment floor divider defines the top of the tip section.

64. The monopile of claim 63, wherein the primary compartment roof divider comprises a watertight diaphragm, preferably the primary compartment roof divider comprises a watertight diaphragm and a plate located above the watertight diaphragm.

65. The monopile of any one of the claims 60-64, wherein said opening arrangement in the lower section into said primary compartment comprises a flooding hole in the wall of the monopile into said primary compartment, wherein said flooding hole preferably is located closer to the primary compartment floor divider, than the primary compartment roof divider.

66. The monopile of any one of the claims 60-65, wherein the monopile comprises a closing arrangement adapted for temporarily restricting or closing off said opening arrangement, said closing arrangement is preferably adapted for temporarily closing and sealing said flooding hole(s).

67. The monopile of claim 66, wherein the closing arrangement comprises a controller adapted for controlling the opening degree of the opening arrangement from being fully open to being fully closed, preferably the controller the controller is adapted for receiving instructions from an operator optionally via instruction signals that may be transmitted by wire or wireless e.g. via an operator station.

68. The monopile of any one of claim 65-67, wherein the primary compartment has a height along said monopile length, preferably defined as the maximal distance between said primary compartment roof divider and said primary compartment floor divider, wherein said flooding hole is located within a distance of up to 50 % of said primary compartment height from said primary compartment floor divider, such as within a distance of up to 40 %, such as up to 20 %, such as up to 10 %, such as up to 5 % of said primary compartment height from said primary compartment floor divider, such as within a distance of up to 5 m from the primary compartment floor divider.

69. The monopile of any one of the preceding claims 60-68, wherein the monopile comprises a pressure control arrangement for controlling a pressure in the primary chamber, preferably comprises a gas control tube and / or a pump for supplying pressurized gas to the primary chamber.

70. The monopile of claim 69, wherein the pressure control arrangement comprises a internal tube passing through said primary compartment roof divider into the primary compartment and extending from a first internal tube end located at a first location in the primary compartment to a second internal tube end located at a second location above the primary compartment and preferably above the at least one buoyancy compartment, preferably the first location in the primary compartment is located at a distance to the primary compartment roof divider not exceeding 20 % of the primary compartment height, preferably the second location is adapted to be located above waterline, such as at or above or within 3 m of the top end.

71. The monopile of claim 69 or claim 70, wherein the pressure control arrangement comprises a closable gas release valve for allowing gas, such as air to escape from the primary compartment, preferably the gas release valve is located at the upper half part of the primary compartment closest to the top end, such as located in the primary compartment roof divider or in the monopile wall, preferably located in the primary compartment roof divider or in the monopile wall at a distance to the primary compartment roof divider not exceeding 20 % of the primary compartment height, such as a distance to the primary compartment roof divider not exceeding 2 m.

72. The monopile of any one of claims 69-71, wherein the pressure control arrangement comprises a gas escape tube, wherein the gas escape tube extends from a first gas escape end located in the primary compartment through a gas escape hole of the opening arrangement and along the monopile length to a second gas escape tube end located at a level of or above the upper section of the monopile, preferably the first gas escape tube end is located at the upper half part of the primary compartment closest to the primary compartment roof divider, the gas escape tube preferably comprises a closable gas release valve for allowing gas, such as air to escape from the primary compartment.

73. The monopile of any one of claims 60-72, wherein the lower section has a length of up to 80 % of the monopile length, such as up to 70 %, such as up to 50 %, such as up to 40 % of the monopile length.

74. The monopile of any one of claims 60-73, wherein the lower section has a length of up to 200 m, such as up to 150m, such as up to 130 m, such as up to 100 m, such as up to 60 m.

75. The monopile of any one of claims 60-74, wherein the lower section has an average outer diameter of 80 % or less that the average monopile outer diameter, such as 70 % or less, such as 60 % or less, such as 50 % or less that the average monopile outer diameter.

76. The monopile of any one of claims 60-75, wherein the tip section has a length of up to 20 % of the lower section length, such up to 10 m, such as at least 1 m, such as from 2 m to 10 m.

77. The monopile of any one of claims 60-76 wherein the upper section comprises a top end portion comprising the top end and being adapted to be located above waterline and a body portion comprising said at least one buoyancy compartment, preferably the top end portion comprises a connecting area adapted to be engaged with or connected to a superstructure, such as a wind turbine, a turbine tower and / or a transition piece, wherein the superstructure is supported by the monopile.

78. The monopile of any one of claims 60-77, wherein the monopile comprises at least one, preferably a plurality of attachment fairleads attached to themonopile at respective fixing locations, wherein the fixing locations are located at a common fixing length section of the monopile, wherein the common fixing length section has a length of 6 m or less, such as 5 m or less, such as 4 m or less, such as 2 m or less.

79. The monopile of any one of claims 60-78, wherein the monopile comprises one or more winches, turn-buckles and / or rams, wherein each winch, turn-buckle and / or ram may be arranged to adjust the tension in one or more of the mooring lines.

80. The monopile of claim 77 or claim 79, wherein the monopile comprises a mid-section located between the upper section and the lower section and wherein the mid-section comprises or is defined by the primary compartment roof divider, wherein the primary compartment floor divider preferably comprises a watertight diaphragm optionally a plate located above the watertight diaphragm.

81. The installation of any one of claims 77-80 wherein the common fixing length section of the monopile form part of or comprises said mid-section or wherein the common fixing length section of the monopile comprises a length section of the upper section of the monopile located above the mid-section and preferably above the waterline.

82. The monopile of any one of claims 77-81, wherein the common fixing length section of the monopile, such as th lm id-section of the monopile comprises a reinforcement, such as a stiffening ring.

83. The monopile of any one of claims 77-82, wherein the wherein the common fixing length section of the monopile, such as thelmid-section of the monopile comprises a biscuit deck, wherein the biscuit deck preferably comprises, form part of or constitute the primary compartment roof divider.

84. The monopile of any one of claims 77-83, wherein the primary compartment roof divider comprises an airtight diaphragm, which may be integrated with the biscuit deck or be located below the biscuit deck, such as immediately below the biscuit deck, e.g. within a distance not exceeding 2 m, preferably not exceeding 1 m.

85. The monopile of any one of the claims 60-84, wherein the plurality of attachment fairleads attached to the monopile comprises at least 3 attachment fairleads, wherein each attachment fairlead is attached to the monopile at a fixing location by anchoring the at least one attachment fairlead to the monopile from the outer surface of the monopile or by anchoring the at least one attachment fairlead at least partially at an internal location of the monopile, such as at or above the biscuit deck.

86. The monopile of any one of claims 60-85, wherein the monopile comprises at least one tension adjustment arrangement for adjusting and / or tuning tension of mooring lines attached to the attachment fairleads.

87. The monopile of claim 86, wherein the at least one tension adjustment arrangement comprises a length adjustment device adapted for adjusting a free length of one or more of the mooring lines, such as for adjusting the free length of a plurality of the mooring lines.

88. The monopile of claim 86 or claim 87, wherein the at least one tension adjustment arrangement comprises a length adjustment device for each of the mooring lines.

89. The monopile of any one of claims 86-88, wherein the at least one tension adjustment arrangement comprises one or more internal or external hydraulic rams, which are adapted for shorten or elongate one or more of the mooring lines.

90. The monopile of any one of claims 86-89, wherein the at least one tension adjustment arrangement comprises one or more threaded bars acting in-line with the mooring line, which may be pulled to elongate the mooring line, or released to shorten it.

91. The monopile of any one of claims 88-90, wherein the at least one tension adjustment arrangement is at least partly located internally in the monopile, preferably at or above the biscuit deck.

92. The monopile of claim 91, wherein a part of the tension adjustment arrangement and / or the mooring line(s) penetrates the monopile wall and wherein a sealing is arranged to seal around the penetrating part and / or mooring line,preferably provided such that it allows penetrating movable parts of the tension adjustment arrangement and / or penetrating mooring line(s) to move freely through the monopile wall, such as a sealing comprising a seal element comprising a Roxtec™ sea and / or a ship drive shaft stuffing box.

93. The monopile of any one of claims 86-92, wherein the monopile comprises a tension adjustment arrangement opening, wherein the tension adjustment arrangement comprises a pulling bar connected to or connectable to the mooring line, wherein one of the pulling bar and the mooring line penetrates the monopile wall via said tension adjustment arrangement opening, wherein the monopile comprises a tube seal arrangement connected to the monopile adjacent said tension adjustment arrangement opening to form a seal between said pulling bar or said mooring line penetrating the monopile and an outer edge portion of the outer monopile surface along a periphery of the tension adjustment arrangement opening- through the monopile wall.94 The monopile of claim 93, wherein the tube seal arrangement comprises an eyeball structure comprising a socket with a bearing surface and a hemisphere tube seal arrangement comprising a spherical cap surface arranged to face the bearing surface, wherein each of the socket and the hemisphere tube seal arrangement comprises a passage for said pulling bar or said mooring line penetrating the monopile, wherein the hemisphere tube seal arrangement is adjustable relative to said bearing surface to provide that the spherical cap surface is adjusted relative to said bearing surface, such that said passage of said socket and said passage through said hemisphere tube seal arrangement are in alignment relative to each other, and in alignment with said pulling bar or said mooring line at least when said tension adjustment arrangement is in a untensioned stage, wherein said pulling bar or said mooring line preferably is passing through said passage of said socket and said passage through said hemisphere adjustment element.95 The monopile of claim 94, wherein the tube seal arrangement comprises a flexible covering structure applied against and optionally connected to the outer edge portion along the periphery of the tension adjustment arrangement opening and a seal collar arranged to seal between the flexible covering structure and said pulling bar or said mooring line, preferably the seal arrangement further comprises a seal ring located in the passage of the hemisphere tube sealarrangement to form a seal between the hemisphere tube seal arrangement and said pulling bar or said mooring line passing through the hemisphere adjustment element.96 The monopile of any one of claims 93-95, wherein the tension adjustment arrangement comprises a bolt tensioning structure comprising a set of tensioning rods to provide a pressure toward the tube seal arrangement and towards a flat basic surface of the hemisphere adjustment element.

97. The monopile of anyone of claims 91-96, wherein the mooring line(s) is carried within the monopile, preferably at least partially inside a support tube, such as inside a J-tubes to a location above the water level, preferably a part of the tension adjustment arrangement and / or the mooring line(s) penetrates the monopile wall at a location below the water level and.

98. The monopile of any one of claims 60-97, wherein the monopile is shaped to have a plurality of sectional modulus at respective elevations along the monopile length when installed in upright orientation with the tip section resting at the water floor, wherein the monopile has a sectional modulus at an elevation comprising one or more of the plurality of attachment fairleads which is at least 4 times greater than a minimum value of a section modulus of the monopile at an elevation of from 1 to 10 m above the water floor such as from 4 to 6 m above the water floor, such as 5 m above the water floor.

99. A method of establishing an installation at a water location, wherein the installation comprises a buoyant and guyed monopile (BGM), wherein the method comprises• providing a monopile, wherein the monopile has a length from a top end to a bottom end and a wall with an outer surface defining an average monopile outer diameter, wherein the monopile comprises an upper section and a lower section comprising a tip section at least partially supported by the water floor, wherein the lower section has an average lower section outer diameter, which is less than the average monopile outer diameter, wherein the monopile comprises a primary compartment and an opening arrangement into said primary compartment located at least partially in the lower section,wherein the monopile comprises at least one buoyancy compartment located at least partially in the upper section,• at least 3 mooring lines,• a plurality of water floor anchors and• a plurality of attachment fairleads, wherein the method preferably comprises providing that the attachment fairlead are fixed to the monopile, preferably at a mid-section of the monopile or above the lower section of the monopile; providing the monopile to be horizontally arranged in the raw water; providing raw water to flow through the opening arrangement into said primary compartment to at least partially flood said primary compartment section ballasting the monopile to being tilted to an upright orientation and to be lowered to provide that the tip section is at least partially supported by the water floor and mooring the monopile to the water floor comprising restraining each of the 3 or more mooring lines between one or two of the water floor anchors and one of the at least three attachment fairleads fixed to the monopile.

100. The method according to claim 99, wherein the monopile is according to any one of claims 60-98.

101. The method according to claim 99 or claim 78, wherein the method comprises establishing the BGM installation according to anyone of claims 1-59.

102. The method of any one of claims 99-101, wherein the method comprises wet-towing the monopile horizontally arranged in the raw water to a site of the water location, wherein the method comprises closing of the opening arrangement into said primary compartment prior to the wet-towing followed by reopening the opening arrangement for providing raw water to flow through the opening arrangement into said primary compartment.

103. The method of any one of claims 99-102, wherein the method comprises wet-towing the monopile horizontally arranged in the raw water to a site of the water location, wherein the method comprises closing the top end of the monopile prior to the wet-towing followed by re-opening the top end at the site ofthe water location, the closing of the top end is preferably performed by a closing arrangement comprising at least one of a diaphragm, a bladder, a bung, a watertight or a hatch.

104. The method of any one of claims 99-103, wherein the method comprises embedding at least a part of the tip section in the water floor or in a footing arrangement, wherein the footing arrangement is located at or in the water floor and preferably secured in or at the water floor.

105. The method of any one of claims 99-104, wherein the method comprises preinstalling the footing arrangement, preferably comprising applying a suction and / or a gravity principle, such as suction-caisson principle, or gravity-base principle, with or without skirts.

106. The method of claim 104 or claim 105, wherein the footing arrangement comprises a footing comprising a support recess, wherein the method comprises securing at least a part of the tip section to the footing by arranging the tip section in the support recess and preferably fixing it by a filler material and / or a binder material, such as grout e.g. cementitious grout and / or an epoxy, wherein the footing arrangement comprises a footing, and the method comprises securing at least a part of the tip section to the footing, preferably by at least one of a grouted connection, a slip-joint connection, a bearing connection, a bolted connection or any combinations thereof.

107. The method of claims, 99-106, wherein the method comprises positioning the tip section in the footing of the footing arrangement comprising preinstalling a guide wire to the tip section of the monopile prior to providing raw water to flow through the opening arrangement into said primary compartment to at least partially flood said primary compartment for ballasting the monopile to be tilted to an upright orientation, and pulling the guide wire to provide that the tip section docks correctly into the footing, such as into the recess of the footing, preferably the guide wire is pulled through a guide member, such as a fairlead or a hole in the footing, wherein the method further comprises inserting the guide wire through a non-return device, wherein after the tip section has docked correctly, the guide wire is preferably pulled to tensioning in said non-return device ensuring to maintain the tip section in the footing.

108. The method of any one of claims 99-107, wherein the mooring of the monopile to the water floor comprises mooring the monopile to water floor anchors using up to 8, such as up to 6 mooring lines.

109. The method of any one of claims 99-108, wherein the mooring of the monopile to the water floor comprises preinstalling the plurality of water floor anchors.110 The method of any one of claims 99-109, wherein the provision that the attachment fairlead are fixed to the monopile comprise fixing the plurality of attachment fairlead to the monopile prior to transporting the monopile to the site of the water location and / or at the water location.

111. The method of any one of claims 99-110, wherein the provision that the attachment fairlead are fixed to the monopile comprise fixing the plurality of attachment fairlead to the to the monopile at respective fixing locations, wherein the fixing locations are located at a common fixing length section of the monopile, wherein the common fixing length section has a length of 6 m or less, such as 5 m or less, such as 4 m or less, such as 2 m or less.

112. The method of any one of claim 99-111, wherein the mid-section of the monopile is located between the upper section and the lower section, , preferably the mid-section comprises or is defined by the primary compartment roof divider, wherein the primary compartment floor divider preferably comprises a watertight diaphragm optionally a plate located above the watertight diaphragm..

113. The method of claim 111 or claim 112, wherein the common fixing length section of the monopile form part of or comprises said mid-section or wherein the common fixing length section of the monopile comprises a length section of the upper section of the monopile located above the mid-section and preferably above the waterline.

114. The method of any one of claims 111-113, wherein the common fixing length section of the monopile, such as the mid-section of the monopile comprises a reinforcement, such as a stiffening ring and / or a biscuit deck, wherein the biscuit deck preferably comprises, forms part of or constitutes the primary compartment roof divider.

115. The method of any one of claims 99-114, wherein the provision that the attachment fairleads are fixed to the monopile comprise fixing the at least one attachment fairlead to the monopile from the outer surface of the monopile or by fixing the at least one attachment fairlead at least partially at an internal location of the monopile, such as at or above the biscuit deck e.g. in a compartment above the biscuit deck.

116. The method of any one of claims 99-115, wherein the mooring of the monopile to the water floor comprises anchoring the monopile to the water floor anchors via said plurality of attachment fairleads, comprising attaching each mooring line to the monopile via at least one of the attachment fairleads and at least one of the water floor anchors, preferably the method comprises attaching each mooring line to the monopile via at least one of the attachment fairleads and at least two separate of the water floor anchors, wherein said two separate water floor anchors to which each end of a mooring line is attached are located with a distance to each other.

117. The method of any one of claims 99-116, wherein the mooring of the monopile to the water floor comprises anchoring the monopile to the water floor anchors via said plurality of attachment fairleads, wherein each of the mooring lines or mooring line portions is arranged to extend from a respective of the attachment fairleads to a respective of the water floor anchors and wherein the mooring lines are fixed to the monopile via said attachment fairleads and by one or more winches, turn-buckles and / or rams, wherein each winch, turn-buckle and / or ram may be arranged to adjust the tension in one or more of the mooring lines.

118. The method of any one of claims 99-117, wherein the mooring of the monopile to the water floor comprises anchoring the monopile to the water floor anchors via said plurality of attachment fairleads, wherein each of the mooring lines or mooring line portions extends from one of the attachment fairleads to one of the water floor anchors with a straight line as seen in plan-top-view, wherein the straight line of each of the mooring lines or mooring line portions intersects at an intersection point with the outer surface of the monopile, and with an intersection plane having an angle of 30 degrees or less, such as an angle of 20 degrees or less, such as an angle of 15 degrees or less from a plane tangential to the outer surface of the monopile at that intersection point.

119. The method of any one of claims 99-118, wherein the mooring of the monopile to the water floor comprises tuning the tension in the mooring lines using one or more tension adjustment arrangement, wherein the tension adjustment arrangement(s) optionally comprises one or more winches, turn-buckles or rams.

120. The method of any one of claims 99-119, wherein the monopile comprises a pressure control arrangement for controlling the pressure in the primary chamber or the method comprises installing a pressure control arrangement for controlling the pressure in the primary chamber, the pressure control arrangement preferably comprises a gas control tube and / or a pump for supplying pressurized gas to the primary chamber and a closable gas release valve for allowing gas, such as air to escape from the primary compartment121. The method of claim 120, wherein the pressure control arrangement comprises an internal tube passing through said primary compartment roof divider into the primary compartment and extending from a first internal tube end located at a first location in the primary compartment to a second internal tube end located at a second location above the primary compartment and preferably above the at least one buoyancy compartment, preferably the first location in the primary compartment is located at a distance to the primary compartment roof divider not exceeding 20 % of the primary compartment height, preferably the second location is located above waterline, such as at or above 3 m of the top end.

122. The method of claim 120 or claim 121, wherein the gas release valve is located at the upper half part of the primary compartment closest to the top end, such as located in the primary compartment roof divider or in the monopile wall, preferably located in the primary compartment roof divider or in the monopile wall at a distance to the primary compartment roof divider not exceeding 20 % of the primary compartment height, such as a distance to the primary compartment roof divider not exceeding 2 m.

123. The method of any one of claims 120-122, wherein the provision of raw water to flow through the opening arrangement into said primary compartment comprises providing the opening arrangement and preferably the gas release valve of the pressure control arrangement to be open to allow air to escape from the primary compartment and for water to partially flood said primary compartment.

124. The method of any one of claims 120-123 wherein the pressure control arrangement comprises a gas escape tube, wherein the gas escape tube extends from a first gas escape tube end located in the primary compartment through a gas escape hole of the opening arrangement and along the monopile length to a second gas escape tube end located at a level of or above the upper section of the monopile, preferably the first gas escape tube end is located at the upper half part of the primary compartment closest to the top end, preferably the second gas escape tube end is located above waterline, the gas escape tube preferably comprises a closable gas release valve for allowing gas, such as air to escape from the primary compartment.

125. The method of any one of claims 120-124, wherein the step of ballasting the tip section of the monopile to be supported by the water floor comprises providing that the second internal tube end of the pressure control arrangement is located above the waterline, preferably at or above the top end.

126. The method of any one of claims 99-125, wherein the step of ballasting the tip section of the monopile to be supported by the water floor comprises providing that the second gas escape tube end of the gas escape tube is located above the waterline and preferably opening the closable gas release valve.

127. The method of any one of claims 99-126, wherein the method comprises pumping gas, preferably air into the primary compartment to provide that an upper portion of the primary compartment comprises a pressurized gas, or mixture of gasses, such as air, wherein said gas is preferably pumped into said primary compartment using said pressure control arrangement.

128. The method of claim 127, wherein the pumping of gas into said primary compartment comprises pressurizing the upper portion of the primary compartment sufficient to provide that a portion of water is pressed out of the primary compartment via said opening arrangement.

129. The method of claim 127 or claim 128, wherein the pumping of gas into said primary compartment comprises pumping gas, such as air at a selected pressure into the primary compartment below the primary compartment roof divider, providing that the air pumped into the primary compartment is at a pressure greaterthan the water on the outside of the monopile at the free surface elevation within the primary compartment at that point in time.

130. The method of any one of claims 99-129, wherein the installation is an offshore installation, whereby the water location is an offshore location and the water bed is a seafloor and the raw water is sea (ocean) water.

131. An installation comprising a buoyant and guyed monopile (BGM), wherein the monopile is upright and has a length from a top end to a bottom end and a wall with an outer surface defining an average monopile outer diameter, wherein the monopile comprises an upper section and a lower section, wherein the monopile comprises a primary compartment and an opening arrangement into said primary compartment located at least partially in the lower section, wherein said primary compartment is at least partially water filled and wherein an upper portion of the primary compartment comprises pressurized gas (preferably air), preferably the pressure in the primary chamber along the length of the monopile is sufficiently high to counter act the hydrostatic pressure acting onto the monopile along said length, preferably the pressure at any elevation inside the primary compartment is larger than or equal to the hydrostatic pressure acting at the outer wall of the monopile at the corresponding elevation.

132. A monopile suitable for an installation, wherein the monopile has a length from a top end to a bottom end and a wall with an outer surface defining an average monopile outer diameter, wherein the monopile comprises an upper section and a lower section comprising a tip section adjacent to the bottom end and at least partially supported by the water floor, wherein the monopile comprises a primary compartment and an opening arrangement into said primary compartment located at least partially in the lower section, wherein said opening arrangement in the lower section into said primary compartment comprises a flooding hole in the wall of the monopile, wherein the monopile comprises a closing arrangement adapted for temporarily restricting or closing off said opening arrangement.

133. A method of installing a monopile of claim 132 at a water location, wherein the method comprises• providing the monopile to be horizontally arranged in the raw water,• wet-towing the monopile horizontally arranged in the raw water to a site of the water location, wherein the method comprises closing of the opening arrangement into said primary compartment prior to the wet-towing• at the site of the water location, re-opening the opening arrangement for providing raw water to flow through the opening arrangement into said primary compartment to ballast the monopile to tilt to an upright orientation and to descend to the water floor and• fixing the monopile to or into the water floor.

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