Abstract
An arrangement for positioning a fall pipe end (414) during subsea rock installation includes a submersible frame (400) adapted to be lowered towards an underwater structure. The submersible frame has a first (401) frame structure carrying propulsion equipment (415) and a second frame structure (402) carrying survey equipment (406, 407), a channel structure (410), and a rotation system with an actuator (403). The actuator (403) has a first (411) and a second element (412) and being adapted to convert an energy input into a rotation of the second element (412) when holding the first element (411). The second element (412) is connected to the second frame structure (402), such that in suspended condition of the submersible frame (400), the survey equipment (406, 407) can be rotated about a vertical axis (409) by energizing the actuator (403), without using the propulsion equipment (415).
Claims
1. An arrangement suitable for positioning a fall pipe end, during subsea rock installation from a vessel, the arrangement comprising: a submersible frame adapted to be lowered towards an underwater structure, while being suspended from the vessel, the submersible frame comprising: a first and a second frame structure; a channel structure adapted to receive the fall pipe end or to be joined to the fall pipe end; propulsion equipment adapted for moving the submersible frame in a horizontal plane, thereby controlling the position of the submersible frame independently from the vessel, the propulsion equipment being mounted to the first frame structure; survey equipment adapted for subsea sensing or inspection, the survey equipment being mounted to the second frame structure; wherein the arrangement comprises a rotation system operable independently from the propulsion equipment, wherein: the rotation system comprises an actuator, the actuator comprising a first and a second element adapted to mutually engage or interact, and the actuator being adapted to convert an energy input into a rotation of the second element when holding the first element, the rotation being about a vertical axis; the second element of the actuator is connected to the second frame structure carrying the survey equipment, such that in suspended condition of the submersible frame, the survey equipment can be rotated about the vertical axis by energizing the actuator, without using the propulsion equipment.
2. The arrangement according to claim 1, wherein the first element of the actuator is adapted to be connected to the vessel, via a hoisting system for suspending the submersible frame, or due to the first element being fixed directly to the deck of the vessel, thereby allowing for a rotation of the second element relatively to the first element upon energizing the actuator.
3. The arrangement according to claim 1, wherein the first element of the actuator is connected to the vessel via a hoisting system, and the second element of the actuator is connected to the submersible frame, such that during use, the actuator is submerged into the water together with the submersible frame.
4. The arrangement according to claim 3, wherein the first frame structure carrying the propulsion equipment and the second frame structure carrying the survey equipment are joined, such that by energizing the actuator, the survey equipment and propulsion equipment are rotated together about the vertical axis.
5. The arrangement according to claim 3, wherein the second frame structure carrying the survey equipment is mounted rotatably with respect to the first frame structure carrying the propulsion equipment, such that by energizing the actuator, the survey equipment is rotated about the vertical axis without rotating the propulsion equipment.
6. The arrangement according to claim 1, wherein the first element of the actuator is fixed directly to the deck of the vessel, and the second element of the actuator is connected to the submersible frame via a hoisting system, such that during use, the actuator is found at deck level and is not submerged into the water.
7. The arrangement according to claim 1, wherein the second frame structure comprises one or more elongated arms, the survey equipment being mounted to the one or more elongated arms, the one or more elongated arms being rigidly connected to the rest of the second frame structure, or being collapsible with respect to the rest of the second frame structure.
8. The arrangement according to claim 7, wherein the second frame structure comprises a set of two elongated arms, each of the arms mounted at opposite sides of the submersible frame, wherein the two elongated arms are rigidly connected to the rest of the second frame structure and are in line, or the two elongated arms are collapsible with respect to the rest of the second frame structure, and are in line in unfolded condition.
9. The arrangement according to claim 1, wherein the vertical rotation axis corresponds to the central axis of the channel structure, such that the survey equipment can be rotated about the central axis of the channel structure.
10. The arrangement according to claim 1, wherein the first element comprises a ring having a central axis extending in vertical direction, and the actuator is adapted to move the second element along a ring-shaped trajectory coaxially with the ring, such that the second element is rotated about the central axis of the ring, or the second element comprises a ring having a central axis extending in vertical direction, and the actuator is adapted to rotate the ring about its central axis.
11. The arrangement according to claim 1, wherein the first or second element respectively is a slewing ring comprising a toothed rack along its circumference, and the second or first element respectively is a pinion adapted to engage with the toothed rack.
12. The arrangement according to claim 3, wherein the first element or the second element respectively comprises a slewing ring having a central axis corresponding to the vertical rotation axis, and the rotation system comprises multiple bearing assemblies distributed over the circumference of the slewing ring, each of the bearing assemblies adapted to retain the slewing ring in vertical direction with respect to the submersible frame, while allowing for a rotation of the slewing ring relatively to the second or first frame structure respectively.
13. The arrangement according to claim 12, wherein each of the bearing assemblies comprises three individual bearings, of which the first bearing engages with the upper surface of the slewing ring, the second bearing engages with the bottom surface of the slewing ring, and the third bearing engages with the side surface of the slewing ring.
14. The arrangement according to claim 1, wherein the propulsion equipment comprises multiple thrusters, distributed along the circumference of the first frame structure.
15. A method for positioning a fall pipe end during subsea rock installation from a vessel, the method comprising: providing a vessel suitable for subsea rock installation; providing a fall pipe; providing an arrangement according to any of the preceding claims; arranging an end portion of the fall pipe in the channel structure, or joining the fall pipe end to the channel structure; lowering the submersible frame into the water, towards an underwater structure, while being suspended from the vessel; operating the rotation system, by energizing the actuator, such that the second element is rotated about the vertical rotation axis relatively to the first element, thereby rotating the survey equipment about the vertical rotation axis.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0068] FIG. 1 illustrates a fall pipe vessel during a rock installation operation, using an ROV for positioning the fall pipe end, according to a prior art solution.
[0069] FIG. 2 illustrates rotation of the ROV by means of thrusters, according to a prior art solution.
[0070] FIG. 3 illustrates rotation of the ROV by means of a rotation system, operatable independently from the thrusters, according to an embodiment of the invention.
[0071] FIG. 4 to FIG. 8 give conceptual drawings, illustrating the concept of the rotation system, according to various different embodiments of the invention. In particular, FIG. 4 illustrates an embodiment 1Aa, FIG. 5 an embodiment 1Ab, FIG. 6 an embodiment 1Ba, FIG. 7 an embodiment 1Bb, and FIG. 8 an embodiment 2A. In this, embodiments 1Aa, 1Ab, 1Ba, and 1Bb are categorized in a first class of embodiments, and embodiment 2A in a second class of embodiments. Within the first class, embodiments 1Aa and 1Ab belong to a group 1A, while embodiments 1Ba and 1Bb belong to a group 1B.
[0072] FIG. 9 to FIG. 16 illustrate a concrete implementation of the concept according to embodiment 1Aa. In particular, FIG. 9 to FIG. 11 show the ROV, wherein FIG. 10 illustrates how the ROV may be used during a rock installation operation. FIG. 12 and FIG. 13 illustrate the actuator of the rotation system, and FIG. 14 to FIG. 16 illustrate the bearing arrangement.
DETAILED DESCRIPTION OF EMBODIMENT(S)
[0073] FIG. 1 illustrates a fall pipe vessel 100 during a rock installation operation. The vessel 100 is equipped with a fall pipe 103. Rock material stored at the deck 110 is loaded into the fall pipe 103, see 109, for deposition onto the seabed 102 or a subsea structure such as a pipeline or power cable. For positioning the fall pipe end 110, a Remotely Operated Vehicle or ROV 104 is used. In FIG. 1, an ROV according to a prior art solution is illustrated, but an ROV according to an embodiment of the invention may be used in a similar way. The ROV 104 is suspended from the vessel 100 by mean of hoisting cables 106. The ROV 104 comprises thrusters 105, for propelling the ROV. For simplicity, only two thrusters 105 are shown in the figure, but typically at least four thrusters are provided on a prior art ROV. The four thrusters are arranged in four different faces, thereby allowing for forward/backward and sideways movement of the ROV, as well as rotation about its own axis. The ROV 104 comprises inspection arms 107, provided with sensors or inspection means 108 directed to the seabed 102. The inspection arms 107 allow to inspect along a straight line, in front of and behind the ROV, during the rock installation operation. In FIG. 1-3, the X-direction corresponds to the longitudinal direction of the vessel 100, and the Y-direction corresponds to the transverse direction of the vessel 100. The Z-direction corresponds to the vertical direction, also referred to as depth direction or height direction. An XY-plane is referred to as a horizontal plane.
[0074] FIG. 2 illustrates the misalignment between the vessel 100 and the inspection arms 107 of the ROV 104 when the vessel is positioned head seas. The figure shows that rock material needs to be deposited along a dumping trajectory 202. The vessel 100 is positioned head seas, see 200, and moves parallel to the dumping trajectory 202 during the rock installation operation, see 201. Therefore, initially a misalignment occurs between the inspection arms 203 and the dumping trajectory 202. To obtain a correct orientation of the inspection arms, the ROV 104 is rotated about its vertical axis, thereby obtaining an orientation 204 of the inspection arms, allowing for inspection along the dumping line 202. When using the prior art ROV 104, such rotation is obtained by means of the thrusters 105. As the ROV 104 is rotated as a whole, the points 206 where the hoisting cables 106 are connected to the ROV rotate too, see 205. As a result, the hoisting cables 106 are twisted during rotation of the ROV 104 for correctly orienting the inspection arms.
[0075] FIG. 3 illustrates how a rotation system according to the invention may be used for correctly orienting the inspection arms. Again, the vessel is positioned head seas, 200, and it moves in a direction 201 parallel to a dumping trajectory 202. Initially, the inspection arms 301 of ROV 300 are misaligned with respect to the dumping trajectory 202. By means of the rotation system, which will be further explained below, an outer structure 304 of the ROV 300 is rotated with respect to an inner structure 305. The inspection arms, mounted to the outer structure 304, are rotated too, thereby reaching the correct orientation 302. The figure also shows that the connection points 303 of the hoisting cables 106, being at the inner structure 305, do not rotate, such that the hoisting cables 106 are not twisted while rotating the inspection arms. Rotating the outer structure 304 is done by means of a rotation system, which is operated independently from the thrusters, as will further be explained below. Rotating the inspection arms towards the correct orientation may happen in an initial stage, after lowering the ROV into the water, and may happen during the rock installation operation. Typically, the operation is shortly interrupted when the orientation of the inspection arms needs to be adjusted by means of the rotation system.
[0076] FIG. 4 to FIG. 8 illustrate the concept of the rotation system, according to different embodiments of the invention. The figures are conceptual, and merely serve to illustrate the essential elements and how these may function within a particular concept of the rotation system. In practice, various designs may apply for implementing a particular concept; one such practical design, implementing the concept of FIG. 4, will be discussed in relation to FIGS. 9 to 16. FIGS. 4 to 8 illustrate the arrangement when being used during a rock installation operation, i.e. in suspended condition and with an installed fall pipe. The various concepts may be combined with the vessel 100 of FIG. 1, i.e. the ROV 104 of FIG. 1 may be replaced with one of the arrangements shown in FIGS. 4 to 8.
[0077] FIG. 4 to FIG. 7 illustrate a first class of embodiments, wherein the respective embodiments will be referred to as 1Aa, 1Ab, 1Ba and 1Bb. The concepts within this first class have in common that the actuator, for rotating the inspection arms, is mounted to the submersible frame, and is therefore submerged together with the ROV during the rock installation operation. FIG. 8 illustrates a second class of embodiments, of which the example shown in FIG. 8 is referred to as 2A. The second class comprises embodiments wherein the actuator is not mounted to the submersible frame, but is found at deck level.
[0078] FIG. 4 illustrates a first possible concept, referred to as embodiment 1Aa. The arrangement illustrated in FIG. 4 comprises a self-propelled vehicle 417 and a rotation system. The rotation system comprises an actuator 403; other components of the rotation system such as an energy source at the vessel are not shown in the figure. The self-propelled vehicle 417 may be remotely operated from the deck, and may thus be referred to as Remotely Operated Vehicle or ROV, 417. The ROV 417 is suspended from the vessel 100 by means of suspension means 416, e.g. hoisting cables, and a fall pipe 418 is arranged in a central channel of the ROV 417.
[0079] The ROV 417 comprises a submersible frame 400, propulsion equipment 415, and survey equipment 406, 407. The submersible frame 400 comprises a first frame structure 401 carrying the propulsion equipment 415, a second frame structure 402 carrying the survey equipment 406, 407, and a channel structure 410. The channel structure 410 defines a central channel, adapted for arranging the fall pipe end 414. The figure shows that the channel structure 410 makes part of an inner structure of the submersible frame 400. On the other hand, the first frame structure 401 and the second frame structure 402 make part of an outer structure, positioned around the inner structure.
[0080] The propulsion equipment 415 comprises multiple thrusters, distributed over the circumference of the vehicle 417. For simplicity, only two thrusters are shown in the figure. However, typically four thrusters are available; for example, in the implementation of FIG. 10 six thrusters are provided, distributed evenly over the hexagonal frame. The thrusters 415 allow to propel the vehicle 417 according to any direction in a horizontal XY plane. As such, by operating the thrusters 415, the fall pipe end 414 can be positioned at a desired dumping location. Remark that in FIGS. 4 to 9, the X, Y and Z direction are defined with respect to the vehicle 417; during use, these directions substantially correspond with the respective directions indicated in FIG. 1, the latter defined with respect to the vessel 100 and seabed 102.
[0081] The second frame structure 402 comprises two elongated inspection arms 404, 405, mounted at opposing sides of the frame vehicle 417. The inspection arms 404, 405 are provided with survey equipment 406, 407. E.g. a sensor, camera or other inspection means 406, 407, directed towards the seabed, is mounted to the respective arms 404, 405. During use, the inspection arms 404, 405 are in line, thereby allowing inspection along a straight line. The inspection arms 404, 405 may be collapsible or foldable, as e.g. is the case in the implementation of FIG. 9-10.
[0082] The rotation system comprises an actuator 403. The actuator 403 comprises a first element 411, a second element 412, and a drive 413, e.g. a hydraulic motor 413. The fist element 411 is provided as a circular slewing ring, on which a toothed rack is arranged. The second element 412 is provided as a pinion, engaging with the toothed rack of the slewing ring 411. In FIG. 4, the slewing ring 411 and pinion 412 are drawn in a symbolical way; a possible practical design is e.g. shown in FIG. 12-13. The slewing ring 411 has a central axis in vertical direction, corresponding to the central axis of the channel structure 410. The outer structure of the frame 400 is mounted rotatably with respect to the slewing ring 411, due to a bearing arrangement. Although FIG. 4 represents only one bearing assembly 414, multiple of such bearing assemblies 414 are provided over the circumference, as will further be discussed in relation to FIG. 14-16. As the actuator 403 is mounted to the submersible frame 400, it is submerged into the water during a rock installation operation.
[0083] FIG. 4 shows that the first element 411 of the actuator 403, i.e. the slewing ring 411, is connected indirectly to the vessel 100, namely via the hoisting cables 416. The second element 412 of the actuator 403 is connected to the second frame structure 402, the latter carrying the survey equipment 406, 407. In the shown embodiment, the actuator may be energized by suppling a pressurized fluid to the hydraulic motor 413, which will then drive the pinion 412. As the pinion 412 rotates about its own axis, it engages with the slewing ring 411, such that the pinion 412 will move along a circular trajectory around the slewing ring 411. The pinion 412 thus rotates about a vertical rotation axis 409, the latter corresponding to the central axis of the slewing ring 411 and to the central axis of the channel structure 410. As the pinion 412 is connected to the second frame structure 402, the inspection arms 404, 405 and inspection means 406, 407 are rotated about the vertical axis 409 upon energizing the actuator 403, see rotation 408. In this way, the orientation of the inspection arms 404, 405 may be adjusted, without using the thrusters 415.
[0084] FIG. 4 shows that in embodiment 1Aa, the first frame structure 401 and the second frame structure 402 are joined, thus making part of an outer structure forming one unity. This implies that upon rotating the second frame structure 402, the first frame structure 401 rotates too. The outer structure comprising the first and second frame structure 401, 402 thus rotates around the inner structure comprising the channel structure 410. Accordingly, upon energizing the actuator 403, the thrusters 415 will rotate together with the inspection arms 404, 405. This has the advantage that acoustic positioning beacons mounted to the outer structure, allow to know the position and orientation of both the thrusters 415 and the inspection arms 404, 405. No additional measurement is thus required for knowing the orientation of the inspection arms 404, 405, thereby avoiding accumulation of measurement faults.
[0085] Apart from the actuator 403, other components, not shown in the figure, may be comprised in the rotation system. For example, the rotation system may additionally comprise a pump and an electrical motor, both mounted at the submersible frame 400, a power supply at the vessel 100, and an umbilical for connecting the power supply to the electrical motor. The electrical motor allows to drive the pump, upon which the pump supplies a pressurized fluid to the hydraulic motor 413, the latter driving the pinion 412. In this case, some components of the rotation system, such as the actuator 403, the electrical motor and the pump are submerged during the operation, while other components such as the power supply are positioned at the vessel 100.
[0086] In embodiment 1Aa, shown in FIG. 4, the complete channel structure 410 is connected to the first element 411 of the actuator 413, such that the channel structure 410 does not rotate upon rotating the inspection arms 404, 405. FIG. 5 shows another embodiment, referred to as 1Ab, wherein a portion 504 of the channel structure 510 rotates upon rotating the inspection arms 404, 405. Indeed, the vehicle 517 comprises a submersible frame 500, the latter comprising a first frame structure 401, a second frame structure 402, and a channel structure 510. The channel structure 510 comprises an upper portion 503, wherein the fall pipe end is arranged, and a lower portion 504. The lower portion 504 defines a channel 505 forming an extension of the fall pipe. The upper portion 503 of the channel structure 510 is connected to the first element 411 of the actuator 413, such that it does not rotate upon rotating the inspection arms 404, 405. The lower portion 504 is connected to the second frame structure 402, and to the second element 412 of the actuator. Accordingly, the lower portion 504 of the channel structure 510 rotates together with the inspection arms 404, 405, see rotation 508. In this case, some part of the inner structure of the frame thus rotates upon energizing the actuator.
[0087] Remark that embodiments 1Aa and 1Ab, shown in FIGS. 4 and 5 respectively, have in common that the first frame structure 401 and second frame structure 402 are connected, such that the survey equipment 406, 407 is rotated together with the propulsion equipment 415 upon energizing the actuator 403. The embodiments of FIG. 4 and FIG. 5 therefore belong to the same group 1A, being a group within the first class of embodiments. Apart from embodiments 1Aa and 1Ab, other embodiments are possible within the group 1A. For example, in an embodiment 1Ac, not shown, the complete channel structure may be connected to the second frame structure 402, such that the complete channel structure rotates upon rotating the survey equipment 406, 407.
[0088] Opposed to group 1A, FIG. 6 and FIG. 7 illustrate another group 1B comprised within the first class of embodiments. In embodiments of group 1B, the second frame structure 602, 702 is not joined to the first frame structure 601, 701, but is mounted rotatably with respect to the first frame structure 601, 701.
[0089] Indeed, FIG. 6, illustrating embodiment 1Ba, shows an ROV 617, comprising a submersible frame 600. The submersible frame 600 comprises a channel structure 610, a first frame structure 601 carrying thrusters 605, and a second frame structure 602 comprising inspection arms 603, 604. The figure shows that the inspection arms 603, 604 are mounted such that they can rotate around the first frame structure 601. The actuator comprises a first element 611, provided as a slewing ring with toothed rack, and a second element 612, provided as a pinion. Upon energizing the actuator, the pinion 612 rotates around the slewing ring 611, thereby rotating the inspection arms 603, 604, see 608, just like in the previous embodiments. However, different from the previous embodiments, upon rotating the inspection arms 603, 604, the first frame structure 601 and thrusters 605 are not rotated. Accordingly, a double rotation option is obtained, wherein the first frame structure 601 may be rotated by means of the thrusters 605, and the inspection arms 603, 604 may be rotated around the first frame structure 601 by means of the actuator. Such an embodiment has the advantage that the design of the ROV, with respect to the first frame structure and channel structure, may remain similar as in a prior art ROV, while the rotation mechanism is added to this existing design.
[0090] In embodiment 1Bb, illustrated in FIG. 7, another variant withing group 1B is shown. The ROV 717 comprises a submersible frame 700. The submersible frame 700 comprises a channel structure 710, a first frame structure 701 carrying thrusters 705, and a second frame structure 702 comprising inspection arms 703, 704. The inspection arms 703, 704 are mounted such that they can rotate relatively to the first frame structure 701. The actuator comprises a second element 712, provided as a slewing ring with toothed rack, and a first element 711, provided as a pinion. The slewing ring 712 is connected to the inspection arms 703, 704, while the pinion 711 is connected indirectly to the vessel, via the hoisting cables 708. Thus, different from FIG. 6, upon energizing the actuator, the pinion 711 will drive the slewing ring 712, such that the slewing ring 712 rotates about the vertical rotation axis. As a result, the inspection arms 703, 704 are rotated, while the thrusters 705 are not rotated.
[0091] The embodiments of FIG. 4 to FIG. 7, comprised in group 1A and 1B have in common that the actuator is mounted to the submersible frame. The actuator is thus submerged during the rock installation operation. The embodiments of FIG. 4 to FIG. 7 therefore belong to a first class. Opposed to the first class, a second class of embodiments is possible, wherein the actuator is not submerged, but is installed at deck level. One example embodiment of this second class is illustrated in FIG. 8, showing an embodiment 2A.
[0092] FIG. 8 shows an ROV 817, comprising a submersible frame 800. The submersible frame 800 comprises a channel structure 810, a first frame structure 801 carrying thrusters 805, and a second frame structure 802 comprising inspection arms 803, 804. Different from the previous embodiments, the actuator 803 is not mounted to the submersible frame, but is positioned at the deck 804 of the vessel. The actuator 803 may e.g. comprises a hydraulic motor 813, a first element 811 provided as a pinion, and a second element 812 provided as a slewing ring. The ROV 817 is suspended by means of a hoisting system, wherein the submersible frame 800 is connected to the slewing ring 812. Upon energizing the actuator, the pinon 811 drives the slewing ring 812, such that the latter rotates, see 808. Accordingly, the whole suspension system and ROV 817 are rotated, thereby allowing to adjust the orientation of the inspection arms 803, 804. Remark that in this type of embodiment, all components of the rotation system, i.e. the actuator 803 as well as the chain of components for providing the actuator with energy, are installed at the vessel.
[0093] Apart from embodiment 2A, shown in FIG. 8, other embodiments are possible within the second class. For example in an embodiment 2B, not shown, a turntable may be provided at the deck 804. A complete fall pipe system or tower, comprising the fall pipe and other devices making part of the dumping installation at the deck, may be positioned onto the turntable or connected to the turntable. Moreover, the submerged ROV is connected to the fall pipe. As such, upon energizing the actuator, the whole fall pipe system rotates together with the ROV.
[0094] FIG. 9 to FIG. 16 illustrate a concrete implementation of the concept according to embodiment 1Aa, previously shown in FIG. 4.
[0095] FIGS. 9 to 11 show the ROV 417, wherein FIGS. 9 and 11 show the ROV with folded inspection arms 404, 405, e.g. when the ROV is not in use. FIG. 10 shows the ROV 417 in suspended condition, with installed fall pipe and unfolded inspection arms 404, 405, e.g. as being used during a rock installation operation. Remark that the ROV 417 can also be used with deployed inspection arms, but without a fall pipe being installed, e.g. for doing a visual inspection of the seabed. The submersible frame of the ROV 417 comprises an inner structure 902, and an outer structure 901 arranged around the inner structure 902. The inner structure 902 comprises the channel structure 410, for arranging the fall pipe end. The outer structure 902 comprises the first frame structure 401, carrying thrusters 415, and the second frame structure 402 comprising inspection arms 404, 405. The inspection arms 404, 405 are collapsible: in FIGS. 9 and 11 they are in folded condition, while in FIG. 10 they are in unfolded condition. Inspection means 406, 407 are mounted at the bottom side of the unfolded inspection arms 404, 405. In the shown embodiment, the submersible frame has an hexagonal outer circumference, and one thruster 415 is arranged at each of the six corners. The ROV can be suspended by means of hoisting cables 416, which connect to connection points 900 at the inner structure 902.
[0096] The ROV 417 comprises an actuator, arranged at the inside of the ROV. FIG. 11 indicates the location of the actuator in the ROV, see A. A more detailed view of the actuator is given in FIGS. 12 and 13. The actuator comprises a slewing ring 411 provided with a toothed rack, and a pinion 412. The slewing ring 411 is best visible in FIG. 12, wherein the pinion was taken away. FIG. 12 further shows a drive mounting plate 1200. The operation of the actuator is similar as explained above in relation to FIG. 4: upon receipt of a pressurized fluid by a hydraulic motor, the pinion 412 rotates around the slewing ring 411, thereby rotating the inspection arms 404, 405.
[0097] FIGS. 12 and 13 further show a bearing assembly 414, adapted to retain the slewing ring 411, while allowing for rotation of the outer frame structure with respect to the slewing ring. The bearing assembly 414 is shown in more detail in FIGS. 14 and 15. The bearing assembly 414 comprises three bearings: a first bearing 1501 that engages with the upper surface of the slewing ring 411, a second bearing 1502 that engages with the bottom surface of the slewing ring 411, and a third bearing 1503 that engages with the side surface of the slewing ring 411. FIG. 15 shows that the first bearing 1501 and second bearing 1502 each comprise a sliding interface, while the third bearing 1503 comprises a rolling element.
[0098] FIG. 15 further shows that the bearing assembly 414 comprises two separate portions 1500 and 1504. The second portion 1504 comprises the second bearing 1502. The first and third bearing 1501, 1503 are integrated in a bearing block 1500, corresponding to the first portion 1500 of the bearing assembly 414. The bearing block 1500 is tiltable with respect to the slewing ring 411. Upon tilting, the bearing block 1500 pivots around axis 1400, such that the first and the third bearing 1501, 1503 do not longer engage with the upper surface respectively side surface of the slewing ring 411. Upon tilting the bearing blocks, a passage is created, thereby allowing to mount or remove the slewing ring 411, and allowing for easy maintenance. It also allows to deploy the ROV without fall pipe, e.g. for doing a visual inspection of the seabed.
[0099] FIG. 16 shows that six individual bearing assemblies 414 are arranged around the slewing ring 411, distributed evenly over the circumference. Such a bearing arrangement with multiple separate bearing assemblies, has the advantage over a single circumferential bearing, that it is less prone to underwater conditions, especially due to salt water, thereby allowing for proper rotation when the actuator is submerged in the water.
[0100] Although the present invention has been illustrated by reference to specific embodiments, it will be apparent to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied with various changes and modifications without departing from the scope thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. In other words, it is contemplated to cover any and all modifications, variations or equivalents that fall within the scope of the basic underlying principles and whose essential attributes are claimed in this patent application. It will furthermore be understood by the reader of this patent application that the words comprising or comprise do not exclude other elements or steps, that the words a or an do not exclude a plurality, and that a single element, such as a computer system, a processor, or another integrated unit may fulfil the functions of several means recited in the claims. Any reference signs in the claims shall not be construed as limiting the respective claims concerned. The terms first, second, third, a, b, c, and the like, when used in the description or in the claims are introduced to distinguish between similar elements or steps and are not necessarily describing a sequential or chronological order. Similarly, the terms top, bottom, over, under, and the like are introduced for descriptive purposes and not necessarily to denote relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and embodiments of the invention are capable of operating according to the present invention in other sequences, or in orientations different from the one(s) described or illustrated above.
