SYSTEMS, METHODS, AND EQUIPMENT FOR OFFSHORE ANCHORAGE OPERATIONS

Abstract

The invention relates to a detachable mooring system for offshore floating structures. The system may consist of: a buoy comprising a connector which allows the connection and detachment of such buoy to the floating structure; a detachable configuration in which the buoy is not connected to the floating structure and the buoy supports at least part of a movable vertical duct on the seabed; a connected configuration in which the buoy is connected to the floating structure; and in which the system is configured to allow the towing of the buoy into the connected configuration and the towing of the movable vertical duct into the connected position. Aspects of the invention include the towing sequence, the independent connection of the first and second movable vertical ducts, and the electrical coupling of the movable vertical duct to the floating structure.Other aspects of the invention include those relating to methods and systems for rapid / emergency dismantling, the use of heavy anchor blocks in the installation sequence, connecting structures and configurations of buoys, and wire connectors.

Description

[0001] SYSTEMS, METHODS, AND APPARATUS FOR OFFSHORE MOORING OPERATIONS

[0002] The present invention relates to systems, methods, and apparatus for offshore mooring operations, and in particular to mooring and / or riser connection and disconnection operations associated with floating offshore assets. The invention has particular, but not exclusive, application to the mooring of floating offshore wind installations, and the connection and disconnection of associated risers.

[0003] Background to the invention

[0004] Wind power is an important renewable energy source, and utilising offshore locations for wind turbines has benefits including higher wind energy yields and fewer spatial and planning constraints compared to those located onshore. Floating offshore wind turbines (FOWTs) are now in use to access locations in deeper water and reduce construction costs compared with the jacket or monopile construction systems used in offshore wind generation.

[0005] It can be expected that FOWTs will have to be disconnected at various points in their service life to enable them to be removed from their operating locations for replacement, servicing and / or upgrade. Motion of a FOWT is generally greater than turbines attached to a jacket that is anchored and fixed to the seabed, which complicates in situ repair operations. The increasing size and height of the turbines makes motion at the nacelle level greater than with smaller turbines. Often the water will be too deep for jack-up crane vessels, necessitating the use of floating crane vessels, with the disadvantage of increased motion at the crane tip compared with a jack-up crane.

[0006] A typical FOWT arrangement is on a floating hull with spread moorings. Such spread moorings have multiple mooring lines which connect to anchors on the seabed, with each mooring line individually connected to a corner of the asset, which remains on a fixed heading. A dynamic power cable riser is connected to the FOWT with a suitable profile supported by buoyancies.

[0007] A typical arrangement for pull-in of a mooring line uses a winch wire connected to the end of the hull mooring connector, the wire being disconnected when the mooring connector is and fully engaged. There are a range of types of mooring connectors available as prior art. This arrangement is applicable to semi-submersible floating structure and a range of other moored floating structures and vessels.

[0008] A disadvantage of these arrangements is that to disconnect and re-connect a FOWT offshore is a long and expensive operation since they typically have between three and nine mooring lines plus typically two dynamic power cables. The connection of the mooring lines and power cable system involves locating, surveying, lifting, and connecting the end of each line individually to the FOWT. During this time the FOWT will have to be held in position by towing vessels. The hook-up can be a long and difficult process, especially in deep water or if the area is congested with platforms, vessels or other floating structures and their moorings. The pull-in of the dynamic power cable is performed after the completion of the mooring hook-up and the cable hook-up itself can be of a long duration with attendant risks of damage.

[0009] Other floating vessels such as ships use turret mooring systems that include a single point mooring (SPM) at which the mooring lines come to a central point around which the ship can rotate via a swivel. Turret mooring systems are normally used in harsh environments where the loads on the mooring system can be reduced by allowing the ship to vane or head into the weather.

[0010] WO2016069636 discloses a disconnectable buoy system for FOWTs. In this system, the power cables are supported by a buoy while the mooring lines are connected in the standard spread mooring arrangement, separate from the buoy and individually to each column of a multi-column hull. A disadvantage of this arrangement is that the power cable(s) are required to hold the disconnectable buoy in position when it is disconnected but must resist damage from the buoy movement. In addition, the buoy may become very large in deep water due to the weight of cables and may present a restriction in the marine operations.

[0011] The applicant’s WO2021 / 234148 describes a disconnectable mooring system for offshore floating structures which offers a number of benefits and advantages over previously proposed systems. In the configuration of WO2021 / 234148, mooring chains can be arranged from mooring points around the structure in the same pattern as for a spread mooring, with the advantage that each is also attached to the disconnectable buoy and thus need only be pulled in from a shallow water depth. A principal advantage of the WO2021 / 234148 system is that it provides a disconnectable mooring system for offshore semi-submersible structures which combines the convenience of a ‘turret’ style buoy with a desired fixed heading spread mooring configuration.

[0012] General Description

[0013] It is amongst the aims and objects of the invention to provide a method and / or apparatus for which obviates or mitigates one or more drawbacks or disadvantages of the prior art.

[0014] According to the presently disclosed subject matter, there is provided a disconnectable mooring system for a floating offshore structure. The system may comprise: a buoy comprising a connector which enables connection and disconnection of the buoy from the floating structure; wherein the system has a disconnected configuration in which the buoy is not connected to the floating structure and the buoy at least partially supports a dynamic riser conduit above the seabed; wherein the system has a connected configuration in which the buoy is connected to the floating structure; and wherein the system is configured to enable pull-in of the buoy to the connected configuration and pull-in of the dynamic riser to a connection position.

[0015] Such features will be referred to as a basic structure of a system according to the presently disclosed subject matter. According to one aspect of the presently disclosed subject matter, a system having the above basic structure can further be configured to enable pull-in of the buoy to the connected configuration and pull-in of the dynamic riser conduit to a connection position in a continuous or sequential installation operation.

[0016] According to a further aspect of the presently disclosed subject matter, which can be used in a system having the above basic structure or in a system according to the above aspect of the presently disclosed subject matter, the system can further be configured to enable through connection of the at least one dynamic riser conduit and a second dynamic riser conduit independently from the floating structure.

[0017] According to a further aspect of the presently disclosed subject matter, which can be used in a system having the above basic structure or in a system according to an above aspect of the presently disclosed subject matter, the system can further be configured to support the at least one dynamic riser conduit and a second dynamic riser conduit in a through connected condition independently from the floating structure.

[0018] According to a further aspect of the presently disclosed subject matter, which can be used in a system having the above basic structure or in a system according to an above aspect of the presently disclosed subject matter, the system can further be configured such that the pull-in of the buoy to the connected configuration brings together a coupling between the dynamic riser conduit and a corresponding conduit connection on the floating structure.

[0019] According to a further aspect of the presently disclosed subject matter, which can be used in a system having the above basic structure or in a system according to an above aspect of the presently disclosed subject matter, the system can further be configured to enable rapid disconnection of the buoy and dynamic riser conduit from the connected configuration under the controlled lowering of one or more winch lines.

[0020] According to a further aspect of the presently disclosed subject matter, which can be used in a system having the above basic structure or in a system according to an above aspect of the presently disclosed subject matter, the system can comprise a clump weight attached to buoy via a clump weight line, wherein the clump weight and the clump weight line enable a height position above the seabed of the buoy to be set when the system is in its disconnected configuration.

[0021] According to a further aspect of the presently disclosed subject matter, which can be used in a system having the above basic structure or in a system according to an above aspect of the presently disclosed subject matter, wherein the buoy is shaped such that in the connected configuration the buoy has a defined rotational position about a main axis of the buoy with respect to a buoy compartment of the floating structure.

[0022] According to a further aspect of the presently disclosed subject matter, which can be used in a system having the above basic structure or in a system according to an above aspect of the presently disclosed subject matter, wherein the buoy comprises a substantially circular cross section with one or more cutaway or scalloped surfaces formed therein, the cutaway or scalloped surfaces corresponding to one or more surface profiles of a buoy compartment of the floating structure. According to a further aspect of the presently disclosed subject matter, which can be used in a system having the above basic structure or in a system according to an above aspect of the presently disclosed subject matter, wherein the system has a connected configuration in which the buoy is connected to a compartment of the floating structure; and wherein the compartment may comprise compartment guide surfaces for the alignment of the buoy to a defined rotational position when the system is in its connected condition.

[0023] According to a further aspect of the presently disclosed subject matter, which can be used in a system having the above basic structure or in a system according to an above aspect of the presently disclosed subject matter, wherein the floating structure comprises an I tube conduit mounted to the exterior of a main hull, and is configured to enable the dynamic riser conduit to be pulled in to a connection position through the l-tube conduit.

[0024] Summary of Invention

[0025] BUOY / RISER PULL IN

[0026] According to an aspect of the invention, there is provided a disconnectable mooring system for a floating offshore structure, the system comprising: a buoy comprising a connector which enables connection and disconnection of the buoy from the floating structure; wherein the system has a disconnected configuration in which the buoy is not connected to the floating structure and the buoy at least partially supports a dynamic riser conduit above the seabed; wherein the system has a connected configuration in which the buoy is connected to the floating structure; and wherein the system is configured to enable pull-in of the buoy to the connected configuration and pull-in of the dynamic riser to a connection position in a continuous or sequential installation operation.

[0027] The system may comprise a plurality of mooring lines. Each mooring line may comprise a lower mooring line portion having a first end connected to a seabed anchor. At least one of the plurality of mooring lines may be a buoy mooring line, which may comprise an upper buoy mooring line portion having a second end connected to the buoy, and a mooring connector for the floating structure located between the second end and the lower mooring line portion.

[0028] In the disconnected configuration, the buoy may at least partially support the buoy mooring line above the seabed.

[0029] In the connected configuration, the buoy may be connected to the floating structure and the mooring connector is connected to a mooring point on the floating structure to tension the buoy mooring line between the anchor and the mooring point.

[0030] The disconnected configuration may be referred to as a first configuration, and the connected configuration may be referred to as a second configuration.

[0031] The system may comprise a plurality of buoy mooring lines. A subset of, or all of, the plurality of mooring lines may be buoy mooring lines.

[0032] Embodiments of this aspect of the invention may comprise preferred or optional features of any other aspects of the invention as described herein, and vice versa.

[0033] According to an aspect of the invention, there is provided a method of connecting a mooring system for a floating offshore structure, the mooring system comprising a buoy at least partially supporting a dynamic riser conduit above the seabed, wherein the method comprises: pulling in the buoy to a connected configuration in which the buoy is connected to the floating structure; pulling in the dynamic riser conduit to a connection location at the floating structure at which the dynamic riser conduit is connectable to a corresponding conduit connection on the floating structure; wherein the pull-in of the buoy and pull-in of the dynamic riser to a connection position is a continuous or sequential installation operation.

[0034] CONTINUOUS CONNECTION According to an aspect of the invention, there is provided a disconnectable mooring system for a floating offshore structure, the system comprising: a buoy comprising a connector which enables connection and disconnection of the buoy from the floating structure; wherein the system has a disconnected configuration in which the buoy is not connected to the floating structure and the buoy at least partially supports a first dynamic riser conduit and a second dynamic riser conduit above the seabed; wherein the system has a connected configuration in which the buoy is connected to the floating structure and the first and second dynamic riser conduits are connected to corresponding conduit connections on the floating structure; and wherein in the disconnected configuration, the system enables through connection of the first and second dynamic riser conduits independently from the floating structure.

[0035] Preferably, in the disconnected configuration, the system supports the first and second dynamic riser conduits in a through connected condition independently from the floating structure. By through connected, it is meant that the first and second dynamic riser conduits are functionally connected to one another.

[0036] The system may comprise a plurality of mooring lines. Each mooring line may comprise a lower mooring line portion having a first end connected to a seabed anchor.

[0037] At least one of the plurality of mooring lines may be a buoy mooring line, which may comprise an upper buoy mooring line portion having a second end connected to the buoy, and a mooring connector for the floating structure located between the second end and the lower mooring line portion.

[0038] In the disconnected configuration, the buoy may at least partially support the buoy mooring line above the seabed.

[0039] The system may have a connected configuration in which the buoy is connected to the floating structure and the mooring connector is connected to a mooring point on the floating structure to tension the buoy mooring line between the anchor and the mooring point. The disconnected configuration may be referred to as a first configuration, and the connected configuration may be referred to as a second configuration.

[0040] The system may comprise a plurality of buoy mooring lines. A subset of, or all of, the plurality of mooring lines may be buoy mooring lines.

[0041] The first and second dynamic riser conduits may be electrical power conduits.

[0042] In the connected configuration, at least one of the first and second dynamic riser conduits may be connected to electrical equipment on the floating structure.

[0043] The system may comprise a crossover assembly for facilitating connection of the first and second dynamic riser conduits to one another. The crossover assembly may be a watertight structure defining a sealed volume configured to accommodate respective ends of the first and second dynamic riser conduits. The crossover assembly may be configured to be supported by the buoy in the disconnected condition.

[0044] The may be configured to enable pull-in of the buoy to the connected configuration and pull-in of the dynamic riser conduit to a connection position. The system may be configured to enable pull-in of the buoy to the connected configuration and pull-in of the dynamic riser conduit to a connection position in a continuous or sequential installation operation. The system may be configured such that the pull-in of the buoy to the connected configuration brings together a coupling between the dynamic riser conduit and a corresponding conduit connection on the floating structure.

[0045] According to an aspect of the invention, there is provided a method of disconnecting a mooring and dynamic riser conduit system from a floating offshore structure, the system comprising a buoy connected to the floating structure, a first dynamic riser conduit, and a second dynamic riser conduit; wherein the method comprises: making up a through connection between the first dynamic riser conduit and the second dynamic riser conduit; disconnecting the buoy from the floating structure to a disconnected configuration; and at least partially supporting the connected first dynamic riser conduit and the second dynamic riser conduit on the buoy independently from the floating structure. The method may comprise making up the through connection between the first dynamic riser conduit and the second dynamic riser conduit on the floating structure.

[0046] The method may comprise at least partially supporting the connected first dynamic riser conduit and the second dynamic riser conduit on the buoy while in a connected configuration.

[0047] The method may comprise making up the through connection between the first dynamic riser conduit and the second dynamic riser conduit in a crossover assembly.

[0048] The crossover assembly may be a watertight structure defining a sealed volume configured to accommodate respective ends of the first and second dynamic riser conduits.

[0049] The method may comprise lowering the buoy and connected first dynamic riser conduit and second dynamic riser conduit into a body of water to a depth below the floating structure.

[0050] The first and second dynamic riser conduits may be electrical power conduits. The floating structure may be a floating offshore wind turbine forming part of an array of floating offshore wind turbines.

[0051] CONDUCTIVE COUPLING

[0052] According to an aspect of the invention, there is provided a disconnectable mooring system for a floating offshore structure, the system comprising: a buoy comprising a connector which enables connection and disconnection of the buoy from the floating structure; wherein the system has a disconnected configuration in which the buoy is not connected to the floating structure and the buoy at least partially supports a dynamic riser conduit above the seabed; wherein the system has a connected configuration in which the buoy is connected to the floating structure; wherein the system is configured to enable pull-in of the buoy to the connected configuration and pull-in of the dynamic riser conduit to a connection position; and wherein the pull-in of the buoy to the connected configuration brings together a coupling between the dynamic riser conduit and a corresponding conduit connection on the floating structure.

[0053] The dynamic riser conduit may be an electrical power conduit, and the coupling may be a conductive coupling that electrically connects the dynamic riser conduit and a corresponding electrical power conduit on the floating structure.

[0054] According to an aspect of the invention, there is provided a method of connecting a mooring system for a floating offshore structure, the mooring system comprising the system comprising a buoy at least partially supporting a dynamic riser conduit above the seabed, wherein the method comprises: pulling in the buoy to a connected configuration in which the buoy is connected to the floating structure; pulling in the dynamic riser conduit to a connection location at the floating structure at which the dynamic riser conduit is connectable to a corresponding conduit connection on the floating structure; wherein the pull-in of the buoy to the connected configuration brings together a coupling between the dynamic riser conduit and a corresponding conduit connection on the floating structure.

[0055] RAPID I EMERGENCY DISCONNECT

[0056] According to an aspect of the invention, there is provided a disconnectable mooring system for a floating offshore structure, the system comprising: a buoy comprising a connector which enables connection and disconnection of the buoy from the floating structure; wherein the system has a disconnected configuration in which the buoy is not connected to the floating structure and the buoy at least partially supports a dynamic riser conduit above the seabed; wherein the system has a connected configuration in which the buoy is connected to the floating structure and the dynamic riser conduit is connected to a corresponding conduit connection on the floating structure; and wherein the system is configured to enable rapid disconnection of the buoy and dynamic riser conduit from the connected configuration under the controlled lowering of one or more winch lines.

[0057] The system may have a connected configuration in which the buoy is connected to the floating structure and the mooring connector is connected to a mooring point on the floating structure to tension the buoy mooring line between the anchor and the mooring point.

[0058] The disconnected configuration may be referred to as a first configuration, and the connected configuration may be referred to as a second configuration.

[0059] The system may comprise a plurality of buoy mooring lines. A subset of, or all of, the plurality of mooring lines may be buoy mooring lines.

[0060] CLUMP WEIGHT

[0061] According to an aspect of the invention, there is provided a disconnectable mooring system for a floating offshore structure, the system comprising: a buoy comprising a connector which enables connection and disconnection of the buoy from the floating structure; a plurality of mooring lines, each mooring line comprising a lower mooring line portion having a first end connected to a seabed anchor; wherein at least one of the plurality of mooring lines is a buoy mooring line, comprising an upper buoy mooring line portion having a second end connected to the buoy, and a mooring connector for the floating structure located between the second end and the lower mooring line portion; wherein the system has a disconnected configuration in which the buoy is not connected to the floating structure and the buoy at least partially supports the buoy mooring line above the seabed; and wherein the system comprises a clump weight attached to buoy via a clump weight line, wherein the clump weight and the clump weight line enable a height position above the seabed of the buoy to be set when the system is in its first configuration. The system may have a connected configuration in which the buoy is connected to the floating structure and the mooring connector is connected to a mooring point on the floating structure to tension the buoy mooring line between the anchor and the mooring point.

[0062] The disconnected configuration may be referred to as a first configuration, and the connected configuration may be referred to as a second configuration.

[0063] The system may comprise a plurality of buoy mooring lines. A subset of, or all of, the plurality of mooring lines may be buoy mooring lines.

[0064] The clump weight may be a variable clump weight. The variable clump weight may comprise a high mass configuration and a low mass configuration. The variable clump weight may comprise a removable weight in the high mass configuration, and may be configurable to the low mass configuration by removal of the removable weight. Alternatively, or in addition, the variable clump weight may comprise variable weight ballast volumes, or may comprise one or more clump chains.

[0065] According to an aspect of the invention, there is provided a method of mooring an offshore floating structure using the disconnectable mooring system according to the previous aspect of the invention, wherein the buoy has a height position above the seabed set by the clump weight and the clump weight line, the method comprising:

[0066] - connecting the buoy to the floating structure;

[0067] - pulling in the mooring connector of a buoy mooring line to a mooring point on the floating structure to tension the buoy mooring line between the anchor and the mooring point.

[0068] Where the system comprises a plurality of buoy mooring lines, the method may comprise pulling in the respective mooring connector of each buoy mooring line to a respective mooring point to tension the respective buoy mooring line between a respective anchor and the respective mooring point.

[0069] The method may comprise removing the clump weight, or a portion of the clump weight, from attachment to the buoy. According to an aspect of the invention, there is provided a method of disconnecting a mooring of an offshore floating structure using the disconnectable mooring system according to a previous aspect of the invention, the method comprising:

[0070] - disconnecting the mooring connector of a buoy mooring line from a mooring point on the floating structure to reduce tension in the buoy mooring line between the anchor and the mooring point;

[0071] - disconnecting and lowering the buoy from the floating structure to a height position above the seabed set by the clump weight and the clump weight line.

[0072] Where the system comprises a plurality of buoy mooring lines, the method may comprise disconnecting the respective mooring connector of each buoy mooring line from a respective mooring point to reduce tension the respective buoy mooring line between a respective anchor and the respective mooring point.

[0073] The method may comprise attaching the clump weight, or a portion of the clump weight, to the buoy prior to disconnecting the mooring connector or mooring connectors.

[0074] The method may comprise connecting a buoy winch line between a winch and the buoy, and lowering the buoy from the floating structure by paying out the buoy winch line.

[0075] I-TUBE LAYOUT AND BUOY SHAPE

[0076] According to an aspect of the invention, there is provided a disconnectable mooring system for a floating offshore structure, the system comprising: a buoy comprising a connection arrangement which enables connection of the buoy to and disconnection of the buoy from a compartment of the floating structure; a plurality of mooring lines, each mooring line comprising a lower mooring line portion having a first end connected to a seabed anchor; wherein at least one of the plurality of mooring lines is a buoy mooring line, comprising an upper buoy mooring line portion having a second end connected to the buoy, and a mooring connector for the floating structure located between the second end and the lower mooring line portion; wherein the system has a connected configuration in which the buoy is connected to the floating structure; wherein the system has a disconnected configuration in which the buoy is not connected to the floating structure and the buoy at least partially supports the buoy mooring line above the seabed; and wherein the buoy is shaped such that in the connected configuration the buoy has a defined rotational position about a main axis of the buoy with respect to the compartment.

[0077] Preferably the buoy is shaped such that in the connected configuration the buoy has a unique rotational position about a main axis of the buoy with respect to the compartment. However, in alternative embodiments there may be a plurality of discrete, defined rotational positions of the buoy in which the connected configuration may be formed.

[0078] The buoy may comprise a substantially circular cross section with one or more cutaway or scalloped surfaces formed therein. The cutaway or scalloped surfaces may correspond to compartment guide surfaces for the alignment of the buoy to the defined rotational position.

[0079] The substantially circular cross section may be defined by a substantially cylindrical and / or substantially conical body portion of the buoy.

[0080] According to an aspect of the invention, there is provided a disconnectable mooring system for a floating offshore structure, the system comprising: a buoy comprising a connection arrangement which enables connection of the buoy to and disconnection of the buoy from a compartment of the floating structure; a plurality of mooring lines, each mooring line comprising a lower mooring line portion having a first end connected to a seabed anchor; wherein at least one of the plurality of mooring lines is a buoy mooring line, comprising an upper buoy mooring line portion having a second end connected to the buoy, and a mooring connector for the floating structure located between the second end and the lower mooring line portion; wherein the system has a connected configuration in which the buoy is connected to the floating structure; wherein the system has a disconnected configuration in which the buoy is not connected to the floating structure and the buoy at least partially supports the buoy mooring line above the seabed; and wherein the buoy comprises a substantially circular cross section with one or more cutaway or scalloped surfaces formed therein, the cutaway or scalloped surfaces corresponding to one or more surface profiles of the compartment.

[0081] According to an aspect of the invention, there is provided a floating offshore structure configured with a disconnectable mooring system, the structure comprising: a main hull; a compartment which enables connection and disconnection of a mooring buoy from the floating structure; wherein the mooring system has a disconnected configuration in which the buoy is not connected to the floating structure and the buoy at least partially supports a dynamic riser conduit above the seabed; wherein the system has a connected configuration in which the buoy is connected to the compartment of the floating structure; and wherein the compartment may comprise compartment guide surfaces for the alignment of the buoy to a defined rotational position when the system is in its connected condition.

[0082] The defined rotational position may be a unique rotational position.

[0083] According to an aspect of the invention, there is provided a floating offshore structure configured with a disconnectable mooring system, the structure comprising: a main hull; a compartment which enables connection and disconnection of a mooring buoy from the floating structure; wherein the mooring system has a disconnected configuration in which the buoy is not connected to the floating structure and the buoy at least partially supports a dynamic riser conduit above the seabed; wherein the system has a connected configuration in which the buoy is connected to the compartment of the floating structure; and wherein the floating structure comprises an I tube conduit mounted to the exterior of the main hull, and configured to enable the dynamic riser to be pulled in to a connection position through the l-tube conduit. The l-tube conduit may be mounted to a column of the main hull, which may be a turbine column where the floating structure is a FOWT structure. Alternatively, or in addition, the I- tube conduit may be mounted to an upper and / or lower beam or pontoon of the floating structure. Alternatively, or in addition, the l-tube conduit may be mounted adjacent a column of the main hull, in an internal area defined by a pair of adjacent beams or pontoons.

[0084] The compartment may comprise compartment guide surfaces for the alignment of the buoy to a defined rotational position, which may be a unique rotational position.

[0085] The compartment may comprise a substantially circular cross section with one or more surface profiles formed therein, the surface profiles corresponding to one or more cutaway or scalloped surfaces of the buoy.

[0086] ROPE CONNECTOR

[0087] A connector system for a rope mooring line, the system comprising: a connector comprising: a bearing pin having a main axis and a pair of opposing pin ends; a rope guide having a rope guide surface configured to guide a rope mooring line around the bearing pin; and a connector mount comprising a pair of spaced holding members, each holding member comprising a slot for retaining a respective pin end of the connector such that a guided rope mooring line is retained by the connector mount under tension.

[0088] The bearing pin may comprise a part-spherical bearing portion, and may comprise and a pair of diametrically-opposed bearing pin ends extending from the part-spherical portion.

[0089] The rope guide may be oriented in a guide plane and may be disposed on the bearing pin. The rope guide may have a part-spherical bearing surface in contact with the part- spherical bearing portion of the bearing pin. The rope guide and the bearing pin may be joined such that the guide plane may be inclined to a plane normal or perpendicular to the main axis of the bearing pin, up to a maximum angle of inclination. The rope guide may be formed from one or more plates, connected together around the bearing pin.

[0090] The respective holding members may comprise holding plates, which may for example be mounted to the exterior of a buoy, spaced apart to accommodate the connector. The respective slots may be comprise elbow slots, and may comprise a vertical opening and a bearing end. The slots may extend a partway through the plates from their inner, opposing surfaces towards the outside surfaces of respective plates. Outer walls of the plates may laterally restrain the rope connector. The system may comprise one more a bores coaxial with the bearing pin, to enable a locking pin to be inserted through the connector mount and the connector.

[0091] Brief description of the drawings

[0092] There will now be described, by way of example only, various embodiments of the invention with reference to the drawings, of which:

[0093] Figures 1 A and 1 B are schematic representations of a mooring system according to the prior art, in a first disconnected configuration and a second connected configuration respectively;

[0094] Figures 2A to 2D are schematic representations of a mooring system according to an embodiment of the invention, showing respective steps of a run sequence for installing the mooring system;

[0095] Figure 3A, 3B and 3C are respectively upper isometric, lower isometric, and longitudinal section views of a buoy according to an embodiment of the invention;

[0096] Figure 4 is a schematic side view of a buoy pull-in arrangement according to an embodiment of the invention;

[0097] Figures 5A to 5E are schematic representations of a mooring system according to an embodiment of the invention, showing respective steps of a run sequence for installing risers into the mooring system; Figures 6A to 6D are schematic representations of a mooring system according to an embodiment of the invention, showing respective steps of a run sequence for installing the mooring system into a hull of a floating offshore wind turbine;

[0098] Figure 7A is a schematic side view of a buoy pull-in arrangement according to an alternative embodiment of the invention;

[0099] Figures 7B and 7C are schematic side views of a buoy pull-in arrangement according to an alternative embodiment of the invention, generally shown at 390, respectively in disconnected and connected conditions;

[0100] Figures 8A to 8C are schematic representations of a mooring system according to an embodiment of the invention, showing respective steps of a run sequence for disconnecting the mooring system from a hull of a floating offshore wind turbine;

[0101] Figures 9A to 9C are schematic representations of an embodiment of the invention which is equipped for rapid and / or emergency release of the risers and buoy from a connected configuration, and an operating sequence;

[0102] Figures 10A to 10C are schematic representations of a rope connector system that may be used in aspects and embodiments of the invention;

[0103] Figures 11 A and 11 B are schematic representations of an alternative rope connector system that may be used in aspects and embodiments of the invention;

[0104] Figure 12 is a schematic representation of a mooring system according to an embodiment of the invention, having an external l-tube and buoy compartment;

[0105] Figure 13 is a schematic representation of a mooring system according to an alternative embodiment of the invention, having an external l-tube and buoy compartment;

[0106] Figures 14A and 14B are respectively lower plan and lower isometric views of a mooring system according to an alternative embodiment of the invention, having an external l-tube and buoy compartment; Figure 15 is a schematic side view of a buoy compartment according to an alternative embodiment of the invention, configured to receive a buoy from above;

[0107] Figures 16A and 16B are respectively schematic plan and side views of a buoy compartment according to an alternative embodiment of the invention, configured to receive a buoy from a side or lateral position;

[0108] Figure 16C is a schematic side view of a buoy for use with the compartment of Figures 16A and 16B;

[0109] Figures 17A and 17B show schematically a mooring buoy and floating structure according to an embodiment of the invention, in disconnected and connected conditions respectively; and

[0110] Figure 18 shows schematically an alternative arrangement of a disconnectable mooring buoy and floating structure in accordance with an embodiment of the invention.

[0111] Detailed description of preferred embodiments

[0112] Referring firstly to Figures 1A and 1 B, there is shown a floating structure in the form of a semi-submersible 4 and a mooring system 11 for the floating structure according to WO2021 / 234148. Figure 1A shows the system 11 in a disconnected configuration and Figure 1 B shows the system 11 in a connected configuration. The mooring system 11 comprises a plurality of mooring lines, of which two are shown at 20a and 20b respectively, and a buoy 24. Each mooring line 20a, 20b has a first end connected to a subsea anchor (not shown) and a second end connected to the buoy 24. The mooring lines may comprise one or more of a chain, wire, rope or any other line used for anchoring in mooring systems. Mooring line 20b has a mooring connector 18 for the floating structure a part way along the mooring line between the first and second ends. The mooring connector is a three-way connector which connects two parts of the mooring line, and also has a connection for pull- in of the mooring line to a mooring point on the floating structure 4 via a winch and winch line (not shown). Additional mooring lines similar to 20b are provided with respective seabed anchors and mooring connection points on the floating structure. A buoy pull-in winch 34 and winch line 35 are provided on the floating structure 4. The buoy 24 supports a riser 10, which in this case is a dynamic power cable riser 10 illustrated in a lazy-wave profile with buoyancies 12.

[0113] As shown in Figure 1A, the buoy 24 is lowered beneath the surface of the water to avoid offshore traffic. The mooring line 20b is in catenary and the arrangement is stable in the water, without having to lower the mooring lines or riser to the seabed.

[0114] Figure 1 B shows the system 11 in a connected configuration, in which the buoy 24, is connected into the hull of the semi-submersible 4 at the base of one column, after pull-in by the winch 34 and winch line 35. The mooring line 20b is connected onto the semisubmersible at mooring point 25b, and an upper portion 22b of the mooring line 20b runs from the buoy 24 to the connection point or mooring point 25b. The lower part of the mooring chain 20b will take the environmental loads on the semi-submersible through the connector arrangement 18 / 25b and the upper portion 22b will hang in a slack catenary configuration to the buoy 24.

[0115] The buoy 24 is easily connected / disconnected from the semi-submersible hull and supports the moorings 20 and power cables 10 deeper in the water. The arrangement also avoids the requirement for swivels by controlling the heading of the semi-submersible 4. When the buoy is pulled into the hull of the structure, if the elevation of the top of the buoy is above the water level, or if the internal compartment can be made water-tight, the power cables can be connected to the electrical system without any handling of the dynamic power cable.

[0116] The present invention in its various aspects utilises the principles of the arrangement in Figures 1A and 1 B, and further described in WO2021 / 234148, but includes a number of operational and / or equipment features which are novel and inventive over the disclosure of WO2021 / 234148.

[0117] Referring to Figures 2A to 2D, respective steps of a run sequence of a method of installing the mooring system according to an embodiment of the invention are described. Figure 2A shows a buoy 124 being lowered from a heavy lift vessel 40 on a line 42 from a vessel crane 44. The buoy 124 is configured to be connected and disconnected from a floating structure (not shown), and has various features, for example line lockers 140, to facilitate its connection and disconnection to the floating structure, and to facilitate riser pull-in to the buoy, as will be described below. The buoy also has a plurality of connectors for connecting to mooring lines.

[0118] The buoy 124 is connected to a variable mass clump weight 130 via a clump weight line 132. The clump weight 130 rests on the seabed in a high mass configuration, for example 50t (metric ton), to retain the buoy during installation of other system components. The clump weight line 132 enables the water depth of the buoy 124 to be set to a desired position. The depth of the buoy will typically be set to around 20 metres from the surface of the water to the top of the buoy, although this is adjustable to best suit the riser installation operation and ROV working depths.

[0119] With the buoy in position, an upper buoy mooring line portion 122 is lowered from the vessel crane 44 for connection to the buoy 124. The upper buoy mooring line portion may be a chain, wire, rope or any other line used for anchoring in mooring systems, but is preferably a fibre rope line, for example an HMPE fibre-based mooring line such DYNEEMA® SK78. A connector on the end of an upper buoy mooring line portion 122 is made up with a corresponding connector on the buoy. An example of a suitable connector on the upper buoy mooring line portion 122 is a male stab connector which is lowered into an upward-facing socket on the buoy 124 and locked into position by a connector pin, inserted and locked by an attending ROV. Figure 2B shows the buoy 124 with the upper buoy mooring line portion 122 connected and having been laid away.

[0120] The upper buoy mooring line portion 122 is then connected to a mooring connector 118 and a main mooring line 121 by an ROV. The mooring connector 118 is a three-way connector which connects the upper mooring line portion 122 to the main mooring line 121 , and also has a connection for pull-in of the mooring line to a mooring point on a floating structure.

[0121] A mooring connector pull-in line 119 is attached to the mooring connector 118 by the ROV, as shown in Figure 2C. Optionally, the pull-in line 119 is tied to the upper mooring line portion 122 prior to its deployment.

[0122] The mooring line 120, comprising the upper buoy mooring line portion 122 and main mooring line 12, is then laid away towards a preinstalled suction anchor 50, comprising a mooring chain fairlead 52 and pull-in pennant 54 (shown in Figure 2D). In this example, and typically, the main mooring line 121 comprises an upper portion 121a spliced to a lower portion 121b via a mid-line buoyancy (not shown). With the main mooring line 121 laid towards the suction anchor 50, the free end of the lower portion 121b is attached to a lower mooring chain 123, which is laid towards the anchor 50. An ROV collects the chain pull-in pennant 54 from the fairlead 52 and attaches it to the free end of the lower mooring chain 123. The free end of the pull-in pennant 54 is attached to the vessel crane hook 46, and the pennant and chain are pulled through the fairlead until a minimum of two chain links are visible.

[0123] The sequence is repeated for each mooring line in the system until all of the mooring lines are installed at their respective anchors, and all of the lines are tensioned by the vessel crane 44 according to a pre-tensioning plan. With mooring line tensions established, the clump weight 130 is reconfigured to a low mass configuration, for example 10t. This may be achieved, for example by removing a fixed mass from the clump weight to reduce its mass from 50t to 10t. Alternatively, or in addition, the variable clump weight can be de-ballasted by pumping or ejecting water from ballast chambers in the weight.

[0124] Figures 3A, 3B and 3C are respectively upper isometric, lower isometric, and longitudinal section views of a buoy 224 according to an embodiment of the invention. The buoy 224 may be used in a method of installing a mooring system, for example as described with reference to Figures 2A to 2D, and in subsequent mooring operations. The buoy 224 comprises a main body 226 having a substantially cylindrical outer wall 228 and a substantially cylindrical inner wall 229 defining an annular buoyancy volume 230 and a central axially-oriented opening 240. The outer shape of the buoy 224 is designed to be received into a corresponding compartment in a floating structure, such as an l-tube of a semi-submersible floating offshore wind structure.

[0125] The buoyancy volume 230 is sealed by upper and lower end plates 232, 234, and contains a system of internal support ribs 236. Within the opening 240 are provided a pair of axially oriented buoy conduits 242a configured to receive respective dynamic riser pull-in arrangements, each having a lower J-bend section 242b connected to a flange plate 243. Together the conduit 242a and the J-bend section 242b form a buoy J-tube 242 (J-bend sections 242a are omitted from Figure 3C for clarity). The buoy also comprises a pair of buoy pull-in chain lockers 244, each housing a chain 248. An upper end of the buoy 224 comprises a pull-in beam 250 and a lifting or hang-off eye 252 secured to the beam. The pull-in beam may be held in place by gravity. Alternatively or in addition, the pull-in beam 250 may be provided with a latch which may be released, for example by an ROV, to enable the pull-in beam to be separated from the buoy.

[0126] Upper ends of the buoy pull in chains 248 are supported by the pull-in beam 250, and lower ends of the chains 248 are secured to a lateral beam on the body of the buoy. A lower end of the buoy comprises a plurality of buoy mooring line connectors 260 for makeup with corresponding connectors on the upper end of mooring lines (not shown). In this case, six buoy mooring line connectors 260 are arranged in pairs circumferentially distributed around the body and extending radially outward and axially downward from the outer wall.

[0127] Figure 4 is a schematic side view of a buoy pull-in arrangement according to an embodiment of the invention, which may optionally be used in a method for installing risers into the mooring system. In this case, the risers are dynamic power cable risers for transfer of electrical power to or from offshore structures. The arrangement, generally shown at 270, comprises a buoy assembly 270a and a riser assembly 270b. The buoy assembly 270a comprises a female Diverless Bend Stiffener Connector (DBSC) 272, which is fitted to the buoy 224 by a flange plate 243 at the bottom of a respective buoy J- tube 242. A corresponding male DBSC 274 is provided in the riser assembly 270b around a power cable 276, between a bend stiffener 278 and a cable termination 280. A support portion 282 of the cable termination includes hang-off locking dogs 284, and an upper end of the termination includes a pull-head 286 with a lifting eye 288.

[0128] Referring to Figures 5A to 5E, respective steps of a run sequence of a method of installing risers into the mooring system according to an embodiment of the invention are described. Figure 5A shows a buoy 224 installed at a desired location, with its depth set by a variable clump weight 230 and a clump weight line 232. In this embodiment, the clump weight 230 is a chain clump weight, rather than a clump weight with a fixed high mass configuration and a fixed low mass configuration as previously described. The depth of the buoy will typically be set to around 20 metres from the surface of the water to the top of the buoy, although this is adjustable to best suit the riser installation operation and ROV working depths. For example, the buoy depth can be adjusted at the planning stage to give a straighter or slacker pull-in angle of the riser. Mooring lines have been installed and tensioned according to the method described with reference to Figure 2 on each buoy mooring line connector of the buoy 224. The buoy 224 is pre-configured with the buoy assembly part 270a of the pull-in arrangement 270 of Figure 4, and has been pre-installed with a riser pull in pennant 290 which extends through a buoy J-tube 242. Figure 5A shows a first end of the dynamic riser, preinstalled with the riser assembly part 270b of the pull-in arrangement 270, overboarded from a heavy lift vessel via a vessel crane 44 and crane wire 42, and moved alongside the location of the buoy 224. An attending ROV 292 attaches the pull-in pennant 290 to the eye 288 of the riser pull head.

[0129] In Figure 5B, the crane wire 42 has been paid out to transfer the load of the riser onto the buoy 224 via the pull-in pennant 290, and the crane wire 42 has been disconnected and recovered to surface. The laying of the riser is commenced towards its second end location. Where the riser is an inter-array power cable between floating structures in a daisy-chain arrangement, an identical procedure can be followed to attach the opposite end of the riser to another buoy.

[0130] When the riser is ready to be pulled into the buoy 224, the ROV 292 attaches the upper end of the riser pull-in pennant to the crane wire 42, as shown in Figure 5C. The riser is then pulled up via the pennant 290, such that the pull head and termination is pulled into the J-tube, and the male DSBC 274 engages the female DBSC 272 on the buoy 224 (Figure 5D). The ROV then releases the pull head 286 from the male DBSC and the pull head and cable termination 280 are pulled up into the J-tube to a position at which the latching dogs 284 engage with the J-tube to allow temporary hang-off of the riser on the buoy (Figure 5E). In this position, the riser pull-in pennant 290 is disconnected from the riser and the crane, and the eye of the pull head is connected to the pull-in beam 250 of the buoy.

[0131] The procedure may be repeated to install a second dynamic riser into the second J-tube 242 of the buoy 224. Throughout the installation operations, the installation vessel is free to weathervane as required.

[0132] Variations to the above-described riser installation method are within the scope of the invention. The riser pull-in pennant may be pre-installed in the buoy as described above, or may be lowered into the buoy prior the riser installation campaign. After attaching the first end of the riser to the buoy (as in Figure 5C), the second end of the riser may be attached to a second buoy. The first end may then be pulled-in prior to pull-in of the second end of the riser, or the second end of the riser may be fully pulled in prior to pull-in of the first end. The buoy and installation method are described in the context of the installation of a pair of dynamic power riser ends as part of an array of floating offshore wind structures. However, in other embodiments, similar steps can be used to install different riser types, including fluid production or transport conduits, and / or to install more than two riser ends into a buoy (for example in a conduit hub or manifold application).

[0133] The foregoing text and accompanying drawings describe methods of installing a buoy for supporting mooring lines and risers for a floating structure. Referring now to Figures 6A and 6D, there is described a method of connecting the system to the hull of a floating structure to provide mooring and riser functionality.

[0134] Figures 6A and 6B schematically show a buoy mooring and riser support system 300 and a floating offshore wind turbine (FOWT) structure 304, in a disconnected configuration and a connected configuration respectively. The buoy system 300 comprises a buoy 224 (as described in the foregoing text), a plurality of mooring lines 120, and a pair of dynamic power cable risers (omitted from the drawings for clarity) pulled into and supported by the buoy 224. As shown in Figure 6B, the floating structure is of semi-submersible multi- column hull construction, having a turbine column 308, a plurality of outer columns (of which one is shown at 312) and upper and lower hull brace sections 314 and 316 respectively. The floating structure 304 comprises an l-tube 306 externally mounted on the turbine column 308 of the hull of the structure, with a downward facing compartment 310 for receiving the buoy 224 at the bottom opening of the l-tube 306. Figure 6B also shows in dotted outline at 318 an alternative location for the l-tube and compartment internal to the turbine column 308.

[0135] In Figure 6A, the FOWT structure 304 has been towed out to the buoy mooring location, after an ROV survey of the buoy system has been conducted. The FOWT is moved into position and lined up directly above the buoy with a safe hull clearance distance 320. A hull winch 322 pays out a winch wire 324 via a sheave through the l-tube 306 and compartment 310 to the depth of the buoy, where an attending ROV connects the wire 324 to a buoy lift pennant 326. The buoy lift pennant 326 may be pre-installed on the buoy or directly to a lift beam of the buoy, via an ROV hook or similar connection. The hull winch 322 then pulls the buoy into the compartment 310 located on the hull. The buoy pull-in beam 250 is lifted up through the l-tube 306 and is secured to the deck in the cable termination room 330, as shown in Figure 6B. The pull-in chains 248 are tensioned to secure the buoy into the hull compartment 310, optionally with additional mechanical latching achieved by the use of mechanical latching dogs on the buoy and / or compartment. With the chains 248 in tension, the hull winch wire 324 is released from the pull-in beam 250.

[0136] The buoy mooring system 300 in its disconnected configuration may be set to a sea depth position that is relatively close to the keel of the hull, and therefore the pull-in distance may be relatively short, e.g. 10 to 15 metres, and in any case significantly less than the depth to the seabed. This short pull-in distance means that a wider range of winch types may be used in the pull-in operation, for example relatively low profile, low weight and low cost linear winches. This flexibility in winch choice makes it more viable to use dedicated winches on the hull for the pull-in operations.

[0137] With the buoy in position and tensioned by the chains, a mooring connector pull-in line 332 is lowered from the hull, and the attending ROV attaches it to the mooring connector 118. The mooring connector 118 is then pulled in by the pull-in line 332, which runs behind a turnaround sheave 333 and is attached to a vessel winch wire 334 and a vessel winch (not shown). The mooring connector 118 is pulled in until it automatically latches into a hull mooring connector 325. Tension in the pull-in line 332 is released, the line is removed from the mooring connector and is tied to the hull 304. The mooring connector pull-in line 332 is lowered from the hull again, and the process is repeated to pull-in and connect the mooring connectors on each of the mooring lines 120. With all mooring lines connected, the clump weight (and optionally clump weight line) are removed, and the mooring lines are re-tensioned at the seabed anchors.

[0138] Figures 6C and 6D show subsequent operational steps for pulling in the riser power cables 276a and 276b to the turbine termination room 330. The hull winch wire 324 is lowered through the l-tube 306 and attached to a power cable pull-in line on the buoy. The power cable termination 280 is pulled into the hull and located in a deck plate mating hole, where it is bolted into position. The hull winch wire 324 is released and lowered through l-tube 306, where it is attached to the power cable pull in line of the second cable to repeat the pull in. Figure 6C shows the leftmost power cable 276a after lifting through the l-tube to the termination room 330 and the rightmost cable 276b mid-lift. With the power cables 276a and 276b secured in the termination room, the cable terminations are removed to reveal the cable connectors (Figure 6D). The installed system is tested, and the cable connectors are made up to the turbine switchgear jumpers. Fibre optic and instrumentation lines are also tested, connected, and commissioned in the termination room.

[0139] The foregoing description relates to a process in which the buoy is pulled into and secured to a compartment in the hull, and the power cables are pulled into a termination room above the water line in a subsequent step. Variations to that process are envisaged within the principles of aspects of the invention. For example, in one alternative embodiment, the risers are pulled upwards into the hull in the same step as the buoy pull-in. For example, the power cable terminations 280 may be secured to the buoy pull-in beam 250, so that when the beam 250 is lifted upwards through the l-tube to the position at which it is secured, the power cables are also lifted through the l-tube. Thus the pull-in of the buoy and the power cables may be achieved by the same step or two parts of a continuous lifting process.

[0140] In another variation, the buoy is not secured into the compartment in the hull by a lifting beam, but instead is latched into a secure hang off position using internal or external locking dogs. Power cable terminations may then be pulled into a termination room above the water line in a subsequent, dedicated lifting step.

[0141] Other variations do not require dry make up of cable terminations, and Figure 7A is a schematic side view of a buoy pull-in arrangement according to an alternative embodiment of the invention. Like the arrangement 270, the arrangement 370 includes dynamic power cable risers for transfer of electrical power between offshore structures. The arrangement comprises a buoy assembly 370a and a riser assembly 370b. The buoy assembly 370a is a simple guide cone at the base of a buoy l-tube 342. A corresponding l-tube bung or seal 374 is provided in the riser assembly 370b around a power cable (not shown), between a bend stiffener 378 and a waterproof cable termination housing 380. Rather than incorporating a J-tube bend in the buoy assembly, a J-tube bend is located between the bend stiffener and the cable termination housing 380, and a bend stiffener lock 384 retains the assembly together until released by ROV actuated ball-grab release cables. An upper end of the termination includes a pull-head 386 with a lifting eye 388. The riser assembly 370b is designed to be pulled into a buoy l-tube so that the l-tube bung engages with the guide cone to seal the tube. Release of the bend stiffener lock enables the connector housing termination to move further into the l-tube and expose the cables for connection to switchgear of the FOWT.

[0142] The arrangement 370 differs from the arrangement 270 in that rather than using unterminated cables, the power cables are pre-terminated with factory fitted connectors. The cables of 370 need not be pulled into a termination room in the hull for termination and connection, but may instead be connected directly to corresponding mating connections within a buoy compartment, for example in a connection plate in the buoy compartment. Alternatively, or in addition, the buoy may comprise a connection plate into which the preterminated cables are connected.

[0143] Figures 7B and 7C are schematic side views of a buoy pull-in arrangement according to an alternative embodiment of the invention, generally shown at 390, respectively in disconnected and connected conditions. Like the arrangements 270 and 370, the arrangement 390 includes dynamic power cable risers for transfer of electrical power between offshore structures. However, in this arrangement, the floating structure includes an upper coupling plate 391a above the buoy compartment 392. The buoy 393 includes a lower coupling plate 391b, located above an upper end of the buoy. The upper and lower coupling plates 391a, 391b together form a conductive coupling arrangement that is brought together on pull-in of the buoy. The lower coupling plate supports termination ends of the dynamic power risers 394b, and the upper coupling plate is pre-installed with the power cables 394a of the floating structure.

[0144] Using the winch line 395, the buoy 393, complete with its coupling plate 391b, is pulled into the buoy compartment, optionally with a damping or soft-landing mechanism to control the forces on the coupling plate and buoy. With the respective coupling plates aligned and in close proximity, a clamp 396 or other mechanical device brings the couplings together to form a conductive coupling between the dynamic risers and the cables of the structure, without requiring further pull-in of the buoy or its power cables to a termination location.

[0145] Figures 7B and 7C show the upper coupling plate 391a at the bottom of an l-tube 397, but it will be appreciated that in alternative embodiments the l-tube may be omitted. The arrangements 370 and 390 may be provided with any of a range of suitable connectors, including dry-mate connectors, subsea dry-connectors, wet-mate connectors, and T-connectors. In the case of wet-mate connectors, the cable connection may be made below the waterline and the cable termination may not be pulled through to a dedicated termination room.

[0146] An important benefit of the invention is that it enables convenient connection and disconnection of a floating offshore structure such as a FOWT from a mooring system, and enables the asset to be removed from its operating locations for replacement, servicing and / or upgrade. With reference to Figures 8A to 8C, there is described how in an embodiment of the invention, a floating offshore structure can be removed from its location while maintaining operational continuity for other assets in a multi-asset array.

[0147] Figures 8A to 8C are schematic representations of a mooring system according to an embodiment of the invention, showing respective steps of a run sequence for disconnecting the mooring system from a hull of a floating offshore wind turbine. Initially, the system is configured according to the method of Figures 6A to 6D, with a buoy pulled into the hull compartment, tensioned moorings connected to the hull, and two power cables 276 connecting to switchgear of the FOWT. When required to remove the FOWT from its location for servicing or maintenance, the cable terminations of the cables 276 are isolated and disconnected from the switchgear of the FOWT. The cables are reconfigured to provide a through connection to one another in a watertight crossover assembly 402, as shown in Figure 8A. With the cables connected and sealed, a pennant 404 connected to a hull winch 406 is attached to the crossover assembly, which is then lifted to allow the cables to be released from their respective hang-offs on the deck of the termination room. The crossover assembly 402 is then lowered in the hull l-tube 306, while carefully monitoring winch pay-out and tension, until the crossover assembly is received in the upper openings of the buoy J-tubes 242.

[0148] When the tension is low, the upper end of the pennant 404 is attached to the buoy pull in beam 250, and the winch 406 is attached to the pull-in beam 450 to take up tension. Operational variations include lowering the lift beam after lowering the cables can crossover assembly, or lowering the lift beam / chains and cables together using the line 404. The clump weight 130 is reattached to the buoy 224 via the clump weight line 132, and a support vessel connects to the first mooring line 120.

[0149] An attending ROV releases the mooring connector 118 from the hull and the vessel winch lowers the mooring connector pull-in line until it is slack. The ROV and vessel repeat the procedure for the other mooring lines. At this point, the line of the hull winch 406 is under tension, and the buoy is ready to be lowered at a controlled constant tension, for example around 31 As the mooring lines continue to be lowered, the buoy 224 lowers into the water column as the tension is transferred from the mooring connectors to the buoy mooring line upper portion 122. When the last mooring line has been lowered, the buoy pull-in beam 250 is lowered onto the buoy 224, and the winch line is released from the buoy by ROV 292 as shown in Figure 8C, or by an acoustic release system. (Note that the clump weight is omitted from Figure 8C for clarity).

[0150] In variations to the above-described method, the buoy pull-in chains may be lowered with the lift beam prior to lowering the buoy from the compartment under the weight of the mooring lines. A mechanical and / or hydraulic-mechanical arrangement may be included to ensure that the buoy releases from the compartment. In one embodiment, a cam mechanism, which is used to lock the buoy in the connected configuration, is also used in reverse to forcibly release the buoy from the compartment.

[0151] When the buoy is disconnected from the floating structure, it supports the mooring lines at a selected depth below the waterline, and supports power cables in a crossover configuration to enable through flow of electrical power to and from adjacent facilities, even in the absence of the local FOWT.

[0152] The method of Figures 8A to 8C represents a carefully planned disconnect procedure, for example for the scheduled removal of an asset from a daisy-chained array. However, there may be operational circumstances in which a faster disconnect procedure is desirable, for example in an emergency situation, or where economic circumstances require it. Figures 9A to 9C show schematically an embodiment of the invention which is equipped for rapid and / or emergency release of the risers and buoy from the connected configuration, and an operating sequence. Figure 9A is a schematic sectional view of a part of a hull 410 of a floating structure, comprising an l-tube 412, with a lower compartment 414 for receiving a mooring buoy 424. The hull, l-tube, and mooring buoy are similar to those described in forgoing embodiments of the invention; and the mooring buoy 424 is secured to the hull and has enabled pull- through of a pair of power cables 476 to the top of the l-tube. The embodiment of Figures 9A to 9C differs from some embodiments in that the power cables are made up with upper cable terminations in a wet mate connector system at a connector plate 426. The connector plate 426 is of split construction comprising an upper half 426a and a lower half 426b, held together by a clamp connector 428, similar to the arrangement 390 of Figures 7B and 7C. A buoy pull-in chain 430 holds the buoy into the hull under tension.

[0153] In a rapid or emergency disconnect situation, the power is isolated from the cables, and the connections are grounded. In response to a disconnect signal from the floating structure’s Distributed Control System (DCS), the clamp connector 428 is opened, and the weight of the lower half of the plate 426b and the lower connector pair is supported by the winch line 432. Controlled pay out of the winch line 432 allows the plate to split into upper and lower halves, and the lower half and the lower connector pair are lowered to the buoy, which remains supported by the buoy pull-in chain 430, as shown in Figure 9B. The winch line 432 is released and the chain 430 is released to the buoy (Figure 9C). Mooring connectors which connect the mooring lines of the buoy to the mooring points of the hull are auto-released using conventional auto-release mechanisms and the buoy takes the tension of the mooring lines. Optionally the buoy has been pre-configured for rapid or emergency release by adding additional mass to the buoy, so that on release the buoyancy is overcome to release the buoy from the hull compartment. In one embodiment, mass is added to a diametrically opposed pair of mooring connectors to facilitate release of the buoy. Optionally such mooring connectors would be released early in the release sequence.

[0154] Embodiments of the invention may be equipped with a lightweight fibre rope connection system to facilitate ROV connection and disconnection operations in free water. An example of such a system is described with reference to Figures 10A to 10C. Figures 10A to 10C are respectively side, longitudinal section, and schematic assembly views of a connection system 450. The system comprises a rope connector 460 and a pair of holding plates 470a, 470b which define slots 472 which receive the rope connector. The holding plates 470 may be mounted to the exterior of a buoy used with aspects and embodiments of the invention, for example to connect an upper buoy mooring line portion to the buoy, and are spaced apart to accommodate the rope connector. The slots 472 are right angle elbow slots with a vertical guided opening 474 and a bearing end 478, and extend a part way through the plates from their inner, opposing surfaces towards the outside surfaces of respective plates. Outer walls of the plates laterally restrain the rope connector.

[0155] The rope connector 460 comprises a bearing pin 462, which comprises a central part- spherical bearing portion 463 and a pair of opposing cylindrical bearing pin ends 464. The pin ends 464 correspond in size to the slots 472, and the bearing pin ends fit between the outer walls of the plates in the slots. A bore 469 extends through and is coaxial with the bearing pin, and corresponding bores in the outer walls of the plates enable a locking pin to be inserted through the plates and the bearing pin to retain it in the plates. Around the central spherical bearing portion is a rope guide 465 formed from a pair of plates 466 with a part spherical bearing surface 467 for the bearing portion 463. A plurality of bolts secures the plates to the bearing pin. Around the circumference of the rope guide is a recess 468 for receiving a length of fibre rope 452 looped around the guide. The recess is part-circular (substantially semi-circular) in cross section and is sized in this example for a 3-inch (approximately 75.6mm) diameter rope. The rope guide is able to rotate on the bearing pin, and pivot with respect to the axis of the bearing pin on the spherical bearing portion.

[0156] Figures 11 A and11 B are respectively side and longitudinal section views of a connection system 480 according to an alternative embodiment of the invention. The system 480 is similar to the system 460 and will be understood from Figures 10A to 10C and the accompanying text. The system 480 comprises a rope connector 490 and a pair of holding plates 491a, 491b which define slots 472 which receive the rope connector. The rope connector 490 differs from the rope connector 460 in that it is also provided with an extended bearing nose 492 to accommodate an ROV handle, and to provide improved rope support.

[0157] An important benefit of the rope connector system of Figures 10 and 11 is that it is of simple construction and very lightweight (of the order of 50 to 60 kg in air) compared to a conventional ROV hook (around 175 kg in air) and therefore can be handled more easily by an ROV, including in free water ROV operations. The system is therefore well-suited to the connection of mooring lines to a mooring buoy as described in embodiments of the invention.

[0158] In the foregoing embodiments of the invention, the mooring buoys are pulled into a connected position on a floating structure at the bottom of an l-tube, which facilitates pull- in and connection of dynamic riser assemblies for termination and / or connection with equipment and switchgear on the floating structure. As shown in Figure 6B, the l-tube (and thus the connection compartment for the buoy) may be externally formed to a main hull of the structure (306) or may be formed internally to the main hull structure (318). An advantageous location for the l-tube is external to the turbine column of the hull, as this is possible without re-engineering the main hull structure, enables retrofitting to an existing column, and minimises cable routing.

[0159] Figure 12 is a schematic representation of an external l-tube 501 and buoy compartment 502 mounted onto a turbine column 503 of a FOWT structure 500. The l-tube is restrained at its top and bottom, and optionally at additional positions part-way between the top and bottom, to resist the high forces from passing waves. Ideally the clearance of the l-tube from the column is small to reduce the size of the restraints 505a, 505b, but the l-tube should remain clear of the lower braces 507 of the FOWT to avoid complicating the fabrication and impacting the fabrication of the hull.

[0160] Figure 13 is a schematic representation of an alternative external l-tube 511 and buoy compartment 512, similar to the arrangement shown in Figure 12, but mounted external to an outer column 513 of a FOWT structure, in the interior angle described by the upper and lower braces.

[0161] A further alternative embodiment of the invention is shown schematically in Figures 14A and 14B, which are respectively lower plan and lower isometric views of a mooring buoy 524 and a buoy compartment 526 for an external l-tube on a turbine column of a FOWT structure 530. This embodiment is similar to the arrangement shown in Figure 12, but in this embodiment the buoy includes scalloped, cutaway surfaces 527a, 527b. includes scalloped, cutaway surfaces 527a, 527b provide asymmetry to the body of the buoy, which in this example is otherwise cylindrical over a lower portion of body, and conical over an upper portion of the body. The compartment 526 has a corresponding shape for receiving and connecting the buoy. The asymmetry in the body of the buoy and compartment has the consequence that the buoy needs to enter the compartment in a specific rotational orientation, and is rotationally keyed within the compartment when connected. This provides advantages in aligning equipment with the upper surface of the buoy, for example for pulling in risers from the buoy. The scalloped surfaces and corresponding compartment surfaces facilitate selfalignment of the buoy in the compartment during pull-in.

[0162] In addition, the cutaway scalloped surfaces of the buoy enables the buoy, compartment and l-tube to be positioned closer to the column of the hull without impacting on the structure of the braces, reducing the size of the upper and lower constraints required.

[0163] Other configurations of buoy connection compartment are shown schematically in Figures 15 to 17. Figure 15 is a schematic side view of a buoy compartment 550 mounted on the exterior of a hull 551 of a floating structure, with a connected buoy 552. The buoy is a mooring buoy with similar functionality to the mooring buoys of previously described embodiments. However, whereas previously described embodiments used compartments that received the buoy from below, beneath the waterline, the compartment 550 is configured to receive a buoy from above, and is located above the waterline. The compartment 550 has an upward facing opening 554, sized and shaped to receive the buoy, and a lateral retaining structure 556, upstanding from support elements 558.

[0164] Retaining structure 560 mounts the compartment to the floating structure. In use, the buoy 552 is lifted from the water by a winch wire (not shown) with mooring lines and risers connected, and manoeuvred over the opening 554. Side openings in the lateral retaining structure provide side-access for the risers and mooring lines, to allow them to be brought into position without being disconnected from the buoy. The buoy is lowered into the compartment 550 by paying out the winch wire, and may be latched or otherwise locked into the compartment by a mechanical and / or hydraulic mechanism (not shown).

[0165] With the buoy in the compartment, as with other embodiments, the buoy and / or risers can be accessed from above to be pulled upwards into the structure for connection of the riser ends to equipment and / or switchgear. Optionally, this is via an l-tube 562 on the exterior of the hull, which has a lower opening 563 spaced a suitable distance from the compartment so as to minimise interference with the connection operation. In variations to this embodiment, the l-tube may be moved into its position above the compartment from a laterally displaced position after the buoy is connected, or the l-tube may be omitted from the arrangement.

[0166] When the buoy is required to be disconnected, as part of a planned disconnect or a rapid / emergency disconnect operation, the support elements can be moved to a release position, for example by pivoting or retraction, allowing the buoy and connected risers and mooring lines to fall under gravity (or under controlled pay out of a winch wire) into the water column below.

[0167] Figures 16A and 16B are respectively schematic plan and side views of a buoy compartment 570 according to an alternative embodiment of the invention, and Figure 16C is a schematic side view of a compatible buoy 574. The compartment is designed to be mounted on the exterior of a hull of a floating structure (not shown) to allow connection of the mooring buoy 574, which has similar functionality to the mooring buoys of previously described embodiments. However, whereas previously described embodiments used compartments that received the buoy from below, beneath the waterline, the compartment 550 is configured to receive a buoy from a side or lateral position, and may be located above or below the waterline. The compartment 570 has a through opening 576, a bearing surface 578, and a lateral retaining structure 580, upstanding from the bearing surface. A side opening 577 enables the buoy to be connected and disconnected from a side of the compartment, and a retaining structure 582 mounts the compartment to the floating structure (not shown).

[0168] The buoy 574 of this embodiment has a substantially conical lower body portion 584, and an upper body portion 586. The upper and lower body portions are separated in the axial direction of the buoy by an annular recess 588. The reduced diameter of the annular recess is sized and shaped to fit through the side opening 577 of the compartment. The upper body portion 586 defines a downward facing shoulder 590, which is wider than the through opening 576 of the compartment and acts as a bearing surface to enable the buoy to hang off on the bearing surface 578 of the compartment. The buoy can therefore be slotted into position by lifting the buoy 574 by a winch wire to a height at which the reduced diameter portion of the annular recess 588 aligns with to the opening 577, and pushing or pulling the buoy laterally into the compartment. The winch wire can then be paid out, and gravity acting on the buoy will lower it until the shoulder 590 bears on the bearing surface 578 of the compartment. The buoy may optionally be latched or otherwise locked into the compartment by a mechanical and / or hydraulic mechanism (not shown).

[0169] With the buoy in the compartment, as with other embodiments, the risers can be accessed from above to be pulled upwards into the structure for connection of the riser ends to equipment and / or switchgear, optionally via an l-tube on the exterior of the hull which has a lower opening spaced a suitable distance from the compartment so as to minimise interference with the connection operation.

[0170] When the buoy is required to be disconnected, as part of a planned disconnect or a rapid / emergency disconnect operation, the latching or locking mechanism is disengaged, and the buoy is lifted by a winch wire until the reduced diameter portion of the annular recess 588 aligns with to the opening 577. The buoy can be pushed or pulled laterally out of the compartment, and the buoy lowered into the water column. Optionally, or in addition, the bearing surface 578 is formed from support elements that can be moved to a release position, for example by pivoting or retraction in a similar manner to the arrangement of Figure 15, allowing the buoy and connected risers and mooring lines to fall under gravity (or under controlled pay out of a winch wire) into the water column below.

[0171] A further alternative embodiment of the invention is described with reference to Figures 17A and 17B, which show schematically a mooring buoy 624 and floating structure 600 in disconnected and connected conditions respectively. Like previous embodiments, the mooring buoy supports mooring lines and dynamic risers (one shown 604) in the disconnected configuration of Figure 17A, and is designed to be received and connected to the floating structure 600 at a compartment 602. However, in this case, the floating structure does not have a dedicated l-tube to facilitate pull-in of the buoy and / or the riser ends. Instead, the buoy is vertically extended compared to previous embodiments, and provides an integrated conduit from a riser connection point to a riser termination location on the floating structure.

[0172] The buoy 624 is similar in structure to the buoy 224 of Figures 3A to 3C, and comprises a main body 626 having a substantially cylindrical outer wall and a substantially cylindrical inner wall defining an annular buoyancy volume and a central axially-oriented opening. The outer shape of the buoy 624 is designed to be received into the compartment 602 in the floating structure 600. The buoyancy volume is sealed by upper and lower end plates and contains a system of internal support ribs. Within the opening are a pair of axially- oriented buoy conduits configured to receive respective dynamic riser pull-in arrangements, each having a lower J-bend section. An upper end of the buoy a lifting or hang-off eye 628. A lower end of the buoy comprises a plurality of buoy mooring line connectors 630 for make-up with corresponding connectors on the upper end of mooring lines 632.

[0173] The buoy 624 differs from the buoys of previous embodiments in that it is axially elongated to extend from a position at which the moorings and dynamic risers can be safely and securely positioned beneath the waterline 601 and an upper position above the waterline to provide a waterplane area to the buoy. In a connection operation, the buoy 624 is initially pulled into the compartment 602 via a side opening, using a lower winch wire 605 connected to a position partway between the upper and lower ends of the buoy. An upper winch wire 606 can be connected to the upper end of the buoy above the waterline (without an ROV, and pulls in the upper end of the buoy to the position shown in Figure 17B. At this position, the upper end of the buoy extends into the lower part of the termination room 610. The conduit defined by the buoy itself therefore facilitates pull-in of the riser ends to the termination room, without reliance on a dedicated l-tube on the floating structure.

[0174] Optionally, the riser ends are recessed into the body of the buoy to provide protection when in the disconnected configuration, and are pulled up to a higher level in the structure / hull for termination and / or connection to equipment or switchgear on the floating structure. The pull in of the riser ends may be a short distance (for example as little as 1 m), if the riser ends have been pulled up towards the top of the buoy as part of the riser pull-in operation. Alternatively, the extended length of the buoy provides a guide conduit for the pull-in of the riser ends after the buoy as been connected.

[0175] Figure 18 shows schematically an alternative arrangement of a disconnectable mooring 724 buoy and floating structure 700 in accordance with an embodiment of the invention. This embodiment is similar to the arrangement of buoy 624 and floating structure 600, and will be understood from Figures 17A and 17B. However, in this embodiment the buoy 724 is configured to be buoyant in its disconnected configuration below the waterline, and pulled into a compartment 702 that is internal to a column of the floating structure 700 and up to a termination room 710. As with the previous embodiment, the conduit defined by the buoy facilitates pull-in of the riser ends to the termination room, without reliance on a dedicated l-tube on the floating structure.

[0176] In optional variations to the embodiments of Figures 17A, 17B and 18, the body of the buoy may be extended to enable the incorporation of ballast material to further stabilise the buoy.

[0177] The invention provides a disconnectable mooring system for a floating offshore structure. The system may comprise: a buoy comprising a connector which enables connection and disconnection of the buoy from the floating structure. The system has a disconnected configuration in which the buoy is not connected to the floating structure and the buoy at least partially supports a dynamic riser conduit above the seabed. The system has a connected configuration in which the buoy is connected to the floating structure; and wherein the system is configured to enable pull-in of the buoy to the connected configuration and pull-in of the dynamic riser to a connection position. Aspects of the invention include related pull-in sequences, independent through connection of first and second dynamic riser conduits, and conductive coupling of a dynamic riser conduit to a floating structure. Further aspects of the invention include related rapid I emergency disconnect systems and methods, use a clump weight in an installation sequence, connection structures and buoy configurations, and rope connectors.

[0178] Various modifications to the above-described embodiments may be made within the scope of the invention, and the invention extends to combinations of features other than those expressly claimed herein. In particular, although the embodiments are described with reference to FOWT structures and electrical power dynamic risers, the principles of the invention and its embodiments and aspects are applicable to other risers, including those used for the transport of fluids to and from offshore facilities (including hydrocarbons and hydrogen fuel products or precursors).

Claims

CLAIMS1. A disconnectable mooring system for a floating offshore structure, the system comprising: a buoy comprising a connector which enables connection and disconnection of the buoy from the floating structure; wherein the system has a disconnected configuration in which the buoy is not connected to the floating structure and the buoy at least partially supports a first dynamic riser conduit and a second dynamic riser conduit above the seabed; wherein the system has a connected configuration in which the buoy is connected to the floating structure and the first and second dynamic riser conduits are connected to corresponding conduit connections on the floating structure; and wherein in the disconnected configuration, the system enables through connection of the first and second dynamic riser conduits independently from the floating structure.

2. The system according to claim 1 , wherein the buoy at least partially supports the first and second dynamic riser conduits in a through connected condition independently from the floating structure.

3. The system according to claim 1 or claim 2, comprising a plurality of mooring lines, each mooring line comprising a lower mooring line portion having a first end connected to a seabed anchor, and comprising a mooring connector for the floating structure.

4. The system according to claim 3, wherein at least one of the plurality of mooring lines comprises a buoy mooring line, the buoy mooring line comprising an upper buoy mooring line portion having a second end connected to the buoy, and a mooring connector for the floating structure located between the second end and the lower mooring line portion.

5. The system according to claim 4, wherein in the disconnected configuration, the buoy at least partially supports the buoy mooring line above the seabed.

6. The system according to claim 4 or claim 5, wherein in the connected configuration, the buoy is connected to the floating structure and the mooring connector is connected to a mooring point on the floating structure to tension the buoy mooring line between the anchor and the mooring point.

7. The system according to any preceding claim, wherein the first and second dynamic riser conduits are electrical power conduits.

8. The system according to any preceding claim, wherein in the connected configuration, at least one of the first and second dynamic riser conduits is connected to electrical equipment on the floating structure.

9. The system according to any preceding claim, comprising a crossover assembly for facilitating connection of the first and second dynamic riser conduits to one another.

10. The system according to claim 9 wherein the crossover assembly is a watertight structure defining a sealed volume configured to accommodate respective ends of the first and second dynamic riser conduits.

11. The system according to claim 9 or claim 10, wherein the crossover assembly is configured to be supported by the buoy in the disconnected condition.

12. The system according to any preceding claim, wherein the system is configured to enable pull-in of the buoy to the connected configuration and pull-in of the dynamic riser conduit to a connection position.

13. The system according to any preceding claim, wherein the system is configured to enable pull-in of the buoy to the connected configuration and pull-in of the dynamic riser conduit to a connection position in a continuous or sequential installation operation.

14. The system according to any preceding claim, wherein the pull-in of the buoy to the connected configuration brings together a coupling between the dynamic riser conduit and a corresponding conduit connection on the floating structure.

15. A method of disconnecting a mooring and dynamic riser conduit system from a floating offshore structure, the system comprising a buoy connected to the floating structure, a first dynamic riser conduit, and a second dynamic riser conduit; wherein the method comprises: making up a through connection between the first dynamic riser conduit and the second dynamic riser conduit; disconnecting the buoy from the floating structure to a disconnected configuration; and at least partially supporting the connected first dynamic riser conduit and the second dynamic riser conduit on the buoy independently from the floating structure.

16. The method according to claim 15, comprising making up the through connection between the first dynamic riser conduit and the second dynamic riser conduit on the floating structure.

17. The method according to claim 15 or claim 16, comprising at least partially supporting the connected first dynamic riser conduit and the second dynamic riser conduit on the buoy while in a connected configuration.

18. The method according to any of claims 15 to 17, comprising making up the through connection between the first dynamic riser conduit and the second dynamic riser conduit in a crossover assembly.

19. The method according to claim 18, wherein the crossover assembly is a watertight structure defining a sealed volume configured to accommodate respective ends of the first and second dynamic riser conduits.

20. The method according to any of claims 15 to 19, comprising lowering the buoy and connected first dynamic riser conduit and second dynamic riser conduit into a body of water to a depth below the floating structure.

21. The method according to any of claims 15 to 20, wherein the first and second dynamic riser conduits are electrical power conduits.

22. The method according to any of claims 15 to 21 , wherein the floating structure is a floating offshore wind turbine forming part of an array of floating offshore wind turbines.

23. A disconnectable mooring system for a floating offshore structure, the system comprising: a buoy comprising a connector which enables connection and disconnection of the buoy from the floating structure; wherein the system has a disconnected configuration in which the buoy is not connected to the floating structure and the buoy at least partially supports a dynamic riser conduit above the seabed; wherein the system has a connected configuration in which the buoy is connected to the floating structure; and wherein the system is configured to enable pull-in of the buoy to the connected configuration and pull-in of the dynamic riser conduit to a connection position in a continuous or sequential installation operation.

24. A method of connecting a mooring system for a floating offshore structure, the mooring system comprising a buoy at least partially supporting a dynamic riser conduit above the seabed, wherein the method comprises: pulling in the buoy to a connected configuration in which the buoy is connected to the floating structure; pulling in the dynamic riser conduit to a connection location at the floating structure at which the dynamic riser conduit is connectable to a corresponding conduit connection on the floating structure; wherein the pull-in of the buoy and pull-in of the dynamic riser to a connection position is a continuous or sequential installation operation.

25. A disconnectable mooring system for a floating offshore structure, the system comprising: a buoy comprising a connector which enables connection and disconnection of the buoy from the floating structure; wherein the system has a disconnected configuration in which the buoy is not connected to the floating structure and the buoy at least partially supports a dynamic riser conduit above the seabed;wherein the system has a connected configuration in which the buoy is connected to the floating structure; wherein the system is configured to enable pull-in of the buoy to the connected configuration and pull-in of the dynamic riser conduit to a connection position; and wherein the pull-in of the buoy to the connected configuration brings together a coupling between the dynamic riser conduit and a corresponding conduit connection on the floating structure.

26. The system according to claim 25, wherein the dynamic riser conduit comprises an electrical power conduit.

27. A method of connecting a mooring system for a floating offshore structure, the mooring system comprising the system comprising a buoy at least partially supporting a dynamic riser conduit above the seabed, wherein the method comprises: pulling in the buoy to a connected configuration in which the buoy is connected to the floating structure; pulling in the dynamic riser conduit to a connection location at the floating structure at which the dynamic riser conduit is connectable to a corresponding conduit connection on the floating structure; wherein the pull-in of the buoy to the connected configuration brings together a coupling between the dynamic riser conduit and a corresponding conduit connection on the floating structure.

28. The method according to claim 27, wherein the dynamic riser conduit comprises an electrical power conduit.

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