NO349028B1 - A suction anchor installation system and method - Google Patents

Description

A suction anchor installation system and method

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a system for installation of a suction anchor in the seabed. The invention also relates to a corresponding method, as well as to the individual major components of the system that are connectable and dis-connectable during implementation of the installation system and method.

BACKGROUND AND PRIOR ART

Suction anchors, or suction piles, are widely used in the offshore industry as foundation piles for subsea equipment and for tying in and mooring of floating platforms such as, e.g., wind turbines, fish farming cages and structures for other kind of sea based activities. A suction anchor is, generally speaking, a steel cylinder that is lowered to the sea floor and inserted vertically in the bottom material driven by its own weight under assistance from a pressure difference between the surrounding sea and the inner space of the cylinder from where water is pumped out during installation. Soil conditions and load from tied in equipment decides the number of anchors, the dimension and weight of the anchors required for each application. Sizes of suction anchor cylinders vary typically from in the order of 1 meter to 10-15 meter in width, having axial lengths in the order of about 5 to 30 meters, weighing up to 100 metric tons or more.

Production of suction anchors involves welding together a number of steel rings to achieve the desired length (height) of the suction anchor cylinder. Mooring chain attachments are fastened to the cylinder at a distance from an upper and top end of the cylinder. An end wall is attached to the top end of the cylinder, whereas a lower or bottom end of the cylinder is left open for obvious reasons.

In the current practise, the end wall that is attached to the top end of the suction anchor cylinder is formed with a vent hole through which air and water can pass as the suction anchor is submerged into the sea. A vent cap or hatch is provided for closing the vent hole when the suction anchor has landed on the seabed.

US 9,221, 522 B2 and US 9,868,492 B2 are prior examples of vent cap systems for suction piles, the latter disclosing a valve assembly made integral with the suction pile.

US 8,833,287 B2 discloses a subsea anchor wherein the top end of a cylinder has a top plate and a top aperture. A top hatch for closing the top aperture is hinged to a support frame adapted to receive subsea equipment, such as a manifold or a well template.

WO 2023/064447 A1 discloses a system and method for suction anchor deployment using a reusable deployment interface for connection with suction anchors and submersion into the sea as a unit.

US 2023/113664 A1 discloses a suction anchor installation system comprising a suction anchor wherein in a region near the top end of the suction anchor an installation frame is releasably connected to the suction anchor. The system further comprises a hoisting attachment and controllable locking mechanism arranged for releasable engagement with the suction anchor. The installation frame is connectable directly to the suction anchor.

US 4,432,671 A discloses a suction anchor and an improved method of installing the suction anchor in the bottom of a body of water. The suction anchor is lowered from a floating vessel by paying out a hoisting cable. A cap is provided with an outlet and an inlet. Pumping means are connected to the outlet by means of a releasable coupling, which may be a conventional remotely controlled releasable coupling. The pumping means comprise a pump adapted to pump a mixture of bottom particles and water. The pump is driven by a remotely controlled motor.

EP 3012183 A1 discloses a suction anchor for offshore use as a foundation for floating facilities such as buoys or wind turbines. The suction anchor comprises a cylindrical hollow body which is open at the bottom facing the seabed and closed at the top with a cover. The cover has one or more openings. A supply unit is arranged on the cylindrical hollow body in a decoupleable manner. The supply unit comprises a frame and a suction pump fastened to the frame, which is connected via one or more breakaway couplings to one or more automatically closable valves in the cover of the cylindrical hollow body. The automatically closable valves are arranged at the openings in the cover.

SUMMARY OF THE INVENTION

It is a general object for the present invention to reduce weight and costs for material, production, labour and transportation of suction anchor installation components.

It is a specific object for the present invention to provide components of a suction anchor installation system with a coupling interface that offers versatility of operations.

In a first aspect of the present invention, these objects are achieved through the provision of a suction anchor installation system according to the accompanying patent claim 1.

The suction anchor installation system comprises a suction anchor wherein in a region near the top end of the suction anchor coupling means are arranged for releasably connecting an installation frame to the suction anchor, the system further comprising an installation frame comprising a hoisting attachment and controllable locking mechanism arranged for releasable engagement with the coupling means on the suction anchor. The installation frame is optionally connectable directly to a suction anchor or via a transition piece indirectly connectable to a suction anchor by essentially the same coupling interface.

In another aspect of the present invention, the object is achieved through a method for installation of a suction anchor in the seabed according to the accompanying patent claim 26.

The method comprises the steps of:

• providing a suction anchor installation system according to any of the accompanying patent claims 1 to 25, and

• coupling a suction anchor directly to the installation frame of the installation system for submersion into the sea together as a unit, or optionally coupling a suction anchor indirectly to the installation frame by means of a transition piece that is connectable to the installation frame as well as to the suction anchor, by essentially the same coupling interface, for submersion into the sea together as a unit.

In another aspect of the present invention the installation system comprises a suction and pump module arranged on the installation frame, the suction and pump module comprising a 3-way valve combination by which flow can be directed from the inner space of the suction anchor to the surrounding sea, and redirected in the opposite direction.

The installation frame may be arranged for accommodation of one or several units from a range of service equipment modules including, but not limited to:

• suction and pumping module, including valves and interface for ROV operation or remote operation

• power module

• weight module

• vibration module

• tip flushing module

• seal surface flushing module

• alignment module

• video module

• measurement module

• thruster module,

which are installable, supplied and controlled in response to individual requirements on the suction anchor installation site.

Further embodiments of the system, of the method and of some of the individual components of the installation system will be specified and defined hereinafter in the detailed description and in accompanying superior and subordinated claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in detail below with reference made to the schematic drawings. In the drawings,

Fig. 1 is a side elevational view showing the major components, installation frame and suction anchor, of the installation system in assembled state,

Fig. 2 is a side elevation view showing the installation frame of Fig.1 on a larger scale and in a revolved position with respect to its position in Fig.1,

Figs. 3A and 3B are partially broken away isometric projections showing the top and bottom ends, respectively, of the suction anchor of Fig.1,

Fig. 4 is a perspective bottom view showing the installation frame of a first embodiment, locking mechanism in locking position,

Fig. 5 is a perspective bottom view showing the installation frame of the first embodiment, locking mechanism in non-locking position,

Fig. 6 is a perspective bottom view showing the installation frame of a second embodiment, locking mechanism in locking position,

Fig. 7 is a perspective top view showing the installation frame of the first and second embodiments, locking mechanism in non-locking position,

Fig. 8 is a partially broken away isometric projection of the installation frame showing the components of a locking mechanism of a first configuration from below,

Fig. 9 is a partially broken away isometric projection of the installation frame showing positioning guides on the installation frame and on the suction anchor from above,

Fig. 10 is an exploded isometric projection showing the build-up of a weighing down module and a pump- and valve module to be supported on the installation frame,

Figs. 11A and 11B are elevational side views showing alternative flow directions through the pump- and valve module of Fig.10,

Fig. 12 is a perspective top view showing a transition piece and complementary component to the installation frame of the first or second embodiments,

Fig. 13 is a perspective bottom view of the complementary component of Fig.12,

Fig. 14 is an isometric projection showing the installation frame and the complementary component in position for assembly,

Fig. 15 is an isometric projection showing the assembly of installation frame and complementary component in position for connection to a suction anchor,

Fig. 16 is an isometric projection showing the assembly of installation frame and complementary component connected to the suction anchor,

Fig. 17 is a side elevation view showing the assembly of the suction anchor and the installation frame with the complementary component, and

Figs. 18A and 18B are partially broken away sectional views showing an alternative locking mechanism in non-locking and locking positions, respectively.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to Fig.1 the major components of the installation system of the present invention are the suction anchor 1 and the installation frame 2.

With reference also to Figs. 3A and 3B, the suction anchor 1 is a straight cylinder 3 extending from an open top end 4 to an open bottom end 5. The cylinder 3 constitutes a cylinder wall of circular section defined by an outer periphery O and an inside diameter I. The inside diameter I runs continuously from the top to the bottom end of the cylinder 3. A continuous inside diameter does not exclude the provision of service lines and attachments, such as the flushing water lines 6 and 7 indicated in Figs. 3A and B, inside the cylinder 3. In this connection it serves to mention that flushing water lines may alternatively, or in addition, be provided on the exterior of the cylinder 3, if appropriate. In the embodiment of Fig.3B, the flushing water lines 6 and 7 connect to a ring-shaped, multi-nozzle rim flushing member 8 which runs along the circumference and bottom rim 9 of the cylinder 3. The ring of nozzles 8 are effective in operation to dissolve and remove soil from the bottom end of the cylinder, this way assisting in penetration of the seabed.

Attachments 10 for mooring chains (see Fig.1) may be fastened to the exterior of the suction anchor as in current practise.

With reference to Fig.3A, a ring flange 11 is arranged radially protruding from the exterior in a top end region of the cylinder 3. The flange 11 constitutes a coupling means for the installation frame 2 as will be explained below. Positioning seats 12 are formed in the top end of the cylinder, such as on the periphery of the flange 11 as illustrated, for properly positioning of the installation frame 2 in coaxial relation with the suction anchor 1 upon connection.

Referring now to Fig.2, the installation frame 2 is a cage structure defined by upright posts 13 that rises from a circular disc 14 in a lower end of the installation frame. In the upper end of the installation frame 2, the upright posts 13 meet in a hoisting rope or hoisting chain attachment 15. The cage structure of the installation frame houses and protects process equipment such as a pump 16 and associated valve assembly 17, as will be more discussed below.

With reference also to Figs. 4-7 and Fig.8, the installation frame carries locking mechanism in the form of latches 18 which are rotatable from a non-locking position as shown in Figs.5 and 7, to the locking position shown in Figs. 4, 6 and 8 wherein the latches 18 are engaged by gripping under the lower side of the flange 11, see Fig.8 specifically. The latches 18 are carried in the lower ends of rods 19 which are rotatably journaled in the cage structure of the installation frame. In their upper ends, the rods 19 each carry a cog wheel 20 in toothed engagement with a gear ring 21 which is arranged to slide on bearing supports 22 arranged on the upright posts 13. An ROV-operated bucket handle 23, see Fig.7, applies rotation of the gear ring 21 in a first direction for rotation of the latches 18 into locking position, and in the opposite direction for rotation of the latches 18 into the non-locking position.

With reference to Figs. 4-7, the circular disc 14 in the lower end of the installation frame has a diameter D adapted to the outside periphery O or to the inside diameter I of the suction anchor cylinder 3. More precisely, in the embodiment shown in Fig.4, the lower side of the disc 14 is formed with a circular, lowered insert portion 24 which is adapted for insertion in the top end of the cylinder 3 as the installation frame is connected to the suction anchor. A seat for a ring seal 25 may be formed about the circumference of the insert portion 24 for radially sealing towards the inside diameter I of the suction anchor cylinder.

In the embodiment of Figs.5 and 6, the lower side of the circular disc 14 is smoothed for planar contact with the top end of the cylinder. Whereas the previous embodiment provides radial sealing of the top end of the cylinder, the smoothened surface 26 of the latter embodiment is arranged for axially sealing with the top end of the cylinder. For sealing purposes, sealing elements may be installed at the interface between the disc 14 and the top end of the cylinder in the embodiment of Figs.5 and 6.

In both cases, as will be understood from this disclosure, the disc 14 forms a top end wall of the suction anchor cylinder 3 as the installation frame 2 is connected to the suction anchor 1.

For the purpose of positioning the installation frame 2 in coaxial relation with the suction anchor 2 upon connection, see Fig.9 specifically, positioning guide means may be arranged in the form of legs 27 that protrude radially from the circumference of the circular disc 14, the legs 27 fitting with the seats 12 arranged on the flange 11 in the top end of the suction anchor cylinder.

With further reference to Figs.4-7, the circular disc 14 is formed with a through passage 28 providing flow communication to the pump and valve assembly 16, 17 via riser pipe 29.

The pump and valve assembly 16, 17 is one member in a line of process or service equipment modules that can be arranged on the installation frame and housed inside its cage structure. The pump and valve assembly comprises a set of three 3-way valves 30, 31 and 32 which are arranged in series. The valves 30-32 are interlinked by a parallel link 33 which simultaneously switches all valves into suction mode, wherein water and possibly soil is drawn out from the interior of the suction anchor as shown by arrows in Fig.11A during deployment of the suction anchor. In the reverse, such as for retrieving the suction anchor, the parallel link can be operated for switching the valves 30-32 into reverse flow wherein water is returned to the interior of the suction anchor, as shown by the arrows of Fig.11B.

The valves 30-32 may be realized as ball valves of L-configuration each comprising three ports. A central valve 31 is thus communicating with the interior of the suction anchor via the riser pipe 29 and with a left valve 30 and a right valve 32 respectively, whereas each of the left and right valves communicate with the central valve 31, the pump 16 and the surrounding sea. In this way, the pump and valve assembly 16, 17 can be operated for pumping water out from the suction anchor upon installation and alternatively operated for pumping water into the suction anchor in a case of lifting and retrieving the suction anchor from the seabed.

Another member in the line of process equipment modules is a weight module 34 illustrated in Fig.10. The weight module 34 comprises a set of weighing down weights 35 having through holes 36 for passing of bolts 37 to be inserted in bolt holes 38 that are formed in the circular disc 14. The weights can be combined to provide added weight to the suction anchor, either at a centrally located point of gravity, or at an offcentre located point of gravity in order to adjust inclination of the suction anchor, if appropriate.

In a similar way, a weight module with weights may optionally be installed on the transition piece that will be described in more detail below.

Vibration can be applied to support insertion of the suction anchor in the seabed.

Vibration can be generated, e.g., by pounding on the weight module 34 by means of a punch or hammer device, designed as an optional process or service module for installation on the installation frame 2. The punch or hammer device can be designed for reciprocating motion by means of compressed air, by jettisized water or by electricity. Alternatively, vibration can be generated directly using the weights 35 by introducing an oscillating force or energy to the weights.

The installation frame 2 can be prepared for installation of a tip flushing module arranged to effect flushing of water into the seabed in order to remove soil from the lower rim region of the suction anchor during deployment, this way supporting the lowering of the suction anchor in the soil. The tip flushing module can include, e.g., a motor pump module with a water inlet and a water outlet in flow connection with the flushing lines and spraying nozzles arranged on the suction anchor.

The installation frame 2 can be prepared for installation of a seal surface flushing module arranged to effect flushing of water onto the sealing interface between the installation frame and the suction anchor at the upper rim region of the suction anchor. The seal surface flushing module can include, e.g., a motor pump module with a water inlet and a water outlet in flow connection with the flushing lines and spraying nozzles arranged on the suction anchor.

The installation frame 2 can be prepared for installation of a motor pump module which can be powered from a surface vessel, or be powered from stored energy onboard the installation frame or from an ROV.

For the purpose of operating the pump and valve assembly 16, 17, as well as for powering of the motor pump module employed in flushing the upper and lower rims of the suction anchor as explained above, a power centre comprising accumulator and associated current and voltage controls and converters can be installed on the installation frame in the form of a power module. The power module can be controlled remotely from a surface vessel via a service and power umbilical, e.g., and can alternatively include ROV interface for operation on the deployment site.

Other service and/or process equipment of a modular build-up can include, e.g., an alignment module comprises instrumentation displaying inclination of the cylinder during installation, optionally comprising passive or active guiding systems; a video module comprising a camera; a measurement module comprising instrumentation designed to monitor the penetration depth of the cylinder; a thruster module comprising a pump and nozzle assembly effective for creating a water jet reaction force acting towards the cylinder. The thruster module may alternatively comprise a motor and propeller assembly effective for creating a propulsion force acting towards the cylinder.

As will be appreciated from the above, the installation frame 2 is prepared with a modular completion of the installation frame in response to varying conditions and requirements on different installation sites.

In a view of extending the versatility of the system, the present system for installation of a suction anchor in the seabed further includes a transition piece generally assigned reference number 100 in the Figs.12-17. The transition piece 100 bridges a difference in size between the diameter D of the circular disc 14 and the inside diameter or outer periphery of a suction anchor 101 of greater size. The transition piece 100 comprises a circular disc 102, in a top side thereof carrying coupling means 103 arranged for detachably mounting of an installation frame 2 to the transition piece. The coupling means 103 comprises a circular flange 104 protruding radially from a short cylinder piece 105 rising a short length above the top side 106 of the transition piece. The flange 104 is formed with guide seats 107 similar to the guide seats 12 on the suction anchor 1, the guide seats 107 cooperating with the legs 27 on the disc 14 of the installation frame to guide the installation frame 2 upon connection with the transition piece 100. The transition piece 100 is further formed with a through passage 108 providing flow communication to the pump and valve assembly 16, 17 via riser pipe 29 on the installation frame 2.

The circular disc 102 has a diameter D which is adapted either for insertion and radial sealing in the open top end of the suction anchor 101. Alternatively, the disc 102 can have a diameter adapted to the outer periphery of the suction anchor 101 for axially sealing the interface between the suction anchor and the transition piece 100 upon connection. In coupled position, the disc 102 forms a top end wall of the otherwise open top end of the suction anchor 101.

The coupling interface between the transition piece 100 and the suction anchor 101 is essentially the same as the coupling interface between the transition piece 100 and the installation frame 2. A circular flange 109 in the top end of the suction anchor 101 is arranged for engagement from a number of latches 110 that are supported pivotally in a rail 111 that runs about the periphery of the disc 102. The rail 111 is supported in the upper ends of legs 112 that rise from the outer circumference of the disc 102. Inside of the rail 111, a gear ring 113 is rotatably journalled in seats 114 that protrude inwardly from the rail. The gear ring 113 is in geared engagement with cog wheels 115 arranged in the upper ends of rods 116 that suspends the latches 110 below the lower side of the disc 102. An ROV bucket handle 117 is arranged on the rail for rotation of the gear ring 113, thus swinging the latches 110 between the non-locking position shown in Figs. 12-15 and the locking position shown in Figs.16-17.

As will be appreciated, the transition piece 100 forms an adapter that extends the serviceability of the installation frame 2 to use with suction anchors of other size.

Figs. 18A and 18B show a design for a locking mechanism 200 which can be used in alternative for the rotatable latching mechanism described above. The alternative locking mechanism 200 comprises a set of latches 201, each latch 201 suspended on a pivot 202 that is carried in a bracket 203 extending radially from the periphery of the disc 14 or the disc 102. The latch 201 is formed with a hook 204 in its lower end, the hook 204 engaging the lower side of flange 11, 104 or 109, as the case may be, in the locking position shown in Fig.18B. A pusher 205 is journalled for reciprocating linear motion guided in a guide slot 206 formed in the bracket 203. The pusher engages a cam surface which is composed of two mutually angled sections 207 and 208. In a raised and withdrawn position, the pusher 205 engages section 208 to swing the latch 201 into the non-locking position shown in Fig.18A, whereas in its lowered and extended position, the pusher engages section 207 of the cam surface to swing the latch into the locking position wherein the hook 204 engages the lower side of the flange 11, 104 or 109. In Figs.18A and 18B, reference number 209 denotes a sealing element deployed at the interface between a disc 14, 102 and the upper end of the suction anchor 1, 101.

From the foregoing description it will be realized that the suction anchor and installation frame can be interconnected on a surface vessel and lowered to the seabed as a unit. During submersion, an open venting valve 40 on the riser pipe 29 (Fig.11A) provides free passage of water from the inner space of the suction anchor to surrounding sea via the through passage 28 or 108. The venting valve 40 can be ROV operated for closure, whereafter underpressure is created in the inner space of the suction anchor by operation of the pump and valve assembly 16, 17 in a first direction.

After insertion of the suction anchor in the seabed, the installation frame can be disconnected from the suction anchor and retrieved to the surface vessel for repeated procedure and deployment of another suction anchor. In a case where the suction anchor is to be recovered, the installation frame can be lowered from the surface vessel to connect with the suction anchor, and water pumped into the inner space of the suction anchor by reversed operation of the pump and valve assembly 16, 17 to create overpressure that supports withdrawal of the suction anchor from the seabed.

Claims (33)

1. A suction anchor installation system comprising:

- a suction anchor (1; 101) wherein in a region near the top end (2) of the suction anchor coupling means (11; 109) are arranged for releasably connecting an installation frame (2) to the suction anchor, the system further comprising:

- a hoisting attachment (15) and controllable locking mechanism (18; 201) arranged on the installation frame (2) for releasable engagement with the coupling means (11; 109) on the suction anchor (1; 101),

- a circular disc (14), having a diameter adapted to one of an inside diameter (I) or an outer periphery (O) of a suction anchor (1), being integrated with the installation frame (2), the disc (14) forming a top end wall of the suction anchor (1) during coupled engagement between the installation frame (2) and the suction anchor (1), characterized by:

- a transition piece (100) that bridges a difference in diameter between the disc (14) and an inside diameter (I) or an outer periphery (O) of another suction anchor (101), the transition piece (100) comprising a complementary circular disc (102) in a top side thereof carrying coupling means (103) arranged for detachably mounting the installation frame (2) to the transition piece (100), the complementary disc (102) in coupled position forming a top end wall of the otherwise open top end of the other suction anchor (101), whereby the installation frame (2) is optionally connectable directly to the suction anchor (1) or via the transition piece (100) indirectly connectable to the other suction anchor (101) using essentially the same coupling interface.

2. The system of claim 1, wherein the coupling means on the suction anchor comprises a radially protruding flange (11; 109), and the locking mechanism on the installation frame comprises latches (18; 201) rotatable between non-locking and locking positions, wherein in locking position the latches engage a lower side of the flange (11; 109).

3. The system of claim 2, wherein the latches (18) are supported in a lower end of a rod (19), respectively, the rod rotationally journalled in the installation frame (2), and wherein an upper end of the rod (19) carries a cogwheel (20) in toothed engagement with a gear ring (21) operated by a drive unit (117) to rotate the rods and latches in one direction for locking and in the opposite direction for unlocking.

4. The system of claim 2, wherein the latches (201) are pivotally supported in a bracket (203) formed with a guide slot (206) for a push rod (205) that is linearly movable and operated to swing the latches (201) about a pivot (202) in one direction for locking and in the opposite direction for unlocking.

5. The system of any previous claim, wherein a pump and valve module (16, 17) is arranged on the installation frame (2), the pump and valve module comprising a 3-way valve combination (30, 31, 32) by which flow can be directed from the inner space of the suction anchor to the surrounding sea, and redirected in the opposite direction.

6. The system of claim 5, wherein the 3-way valve combination (30, 31, 32) comprises a set of valves that are interlinked through a parallel link (34) that switches flow direction through all valves (30, 31, 32) simultaneously.

7. The system of claim 5 or 6, wherein the set of valves (30, 31, 32) comprises three ball valves of L-configuration arranged in series.

8. The system of claim 1, wherein the installation frame (2) is a cage structure comprising upright posts (13) rising from the circular disc (14), the cage protectively housing service equipment of the installation system.

9. The system of claim 8, wherein the installation frame (2) is arranged for accommodation of one or several units from a range of service equipment modules including, but not limited to:

• suction and pumping module, including valves and interface for ROV operation or remote operation

• power module

• weight module (34)

• vibration module

• tip flushing module

• seal surface flushing module

• alignment module

• video module

• measurement module

• thruster module

10. The system of claim 9, wherein the weight module (34) comprises a set of weights (35) combinable to provide added weight at a centrally located point of gravity, or at an off-centre located point of gravity.

11. The system of claim 10, wherein the weight module (34) comprises a set of semicircular solid plates (35) formed with through holes (36) for passing of bolts (37) in alignment with bolt holes (38) arranged in a top side of the circular disc (14) integrated with the installation frame (2).

12. The system of claim 10 or 11, wherein the vibration module comprises a power hammer acting on the weight module (34).

13. The system of claim 9, wherein the tip flushing module comprises a fluid pump and valves arranged on the installation frame (2), and at least one flush pipe (6; 7) running along the suction anchor cylinder (3), internally or externally, from the pump and valves to a discharge nozzle ring (8) arranged in a lower end of the cylinder (3).

14. The system of claim 9, wherein the seal surface flushing module comprises a fluid pump and valves arranged on the installation frame (2), and at least one flush pipe running to a discharge nozzle directed towards an upper end of the cylinder (3).

15. The system of claim 9, wherein the alignment module comprises instrumentation displaying inclination of the cylinder (3) during installation.

16. The system of claim 9 or claim 15, wherein the alignment module comprises passive or active guiding systems.

17. The system of claim 9, wherein the video module comprises a camera.

18. The system of claim 9, wherein the measurement module comprises instrumentation to monitor the penetration depth of the cylinder (3).

19. The system of claim 9, wherein the thruster module comprises a pump and nozzle assembly effective for creating a water jet reaction force acting on the cylinder (3).

20. The system of claim 9, wherein the thruster module comprises a motor and propeller assembly effective for creating a propulsion force acting on the cylinder (3).

21. The system of any previous claim, wherein the circular disc (14) integrated with the installation frame (2) or the transition piece (100) is formed with a through passage (28; 108) providing flow communication between the inner cylinder space and surrounding sea.

22. The system of claim 21, wherein a lower side of the disc (14) or the transition piece (100) is formed with a lowered insert portion (24) adapted for insertion in the upper end of the cylinder (3).

23. The system of claim 22, wherein a seat for a ring seal (25) is formed in the circumference of the insert portion (24).

24. The system of claim 21, wherein a lower side of the disc (14) is smoothed for planar contact with the upper end of the cylinder (3).

25. The system of any previous claim, wherein positioning legs (27) are arranged about the circumference of the disc (14), mating with positioning seats (12) formed on the flange (11) in the upper end (2) of the suction anchor cylinder (3).

26. A method for installation of a suction anchor (1; 101) in the seabed, the method comprising:

- providing a suction anchor installation system according to any of claims 1 to 25,

- coupling a suction anchor directly to the installation frame (2) of the installation system for submersion into the sea together as a unit, or optionally coupling a suction anchor indirectly to the installation frame by means of a transition piece (100) that is connectable to the installation frame as well as to the suction anchor, by essentially the same coupling interface, for submersion into the sea together as a unit.

27. The method of claim 26, comprising the step of adding weight to the suction anchor (1; 101) by placing balance weights (35) on a top side of the disc (14).

28. The method of claim 27, comprising the step of controlling a centre of gravity of the suction anchor (1; 101) by unevenly distributing the balance weights (35).

29. The method of claim 27 or 28 comprising the step of causing vibration to the suction anchor (1; 101) using the balance weights (35).

30. The method of claim 26, comprising the step of flushing a lower end of the suction anchor (1; 101) via at least one flush pipe (6; 7) and nozzle assembly arranged to run from a fluid pump and valves arranged on the installation frame (2).

31. The method of claim 26, comprising the step of flushing an upper end of the suction anchor (1; 101) via at least one flush pipe and nozzle assembly arranged to run from a fluid pump and valves arranged on the installation frame (2).

32. The method of claim 26, comprising the step of creating a water jet reaction force to act on the suction anchor (1; 101) by means of a pump and nozzle assembly arranged on the installation frame (2).

33. The method of any of claims 26 to 32, comprising the step of monitoring the inclination and/or the penetration depth of the suction anchor (1; 101) by means of instrumentation and video cameras arranged on the installation frame (2).