Technical field

The present disclosure relates to the field of maintenance of fish pens.

Background

[0001] Biofouling of fish pens is a major issue in the fish farming industry. Algae and other biological compounds contaminate the nets of fish pens, which causes inter alia reduced health for the fish, reduced oxygen supply to the fish pen, and increased difficulty in inspecting wear of the fish pen. Several approaches have been employed in order to address biofouling related issues, including hoisting and pressure cleaning the nets, as well as the employment of separate underwater remotely operated vehicles (ROVs) that clean the net while submerged.

[0002] NO 20161708 describes an assembly for carrying out a cleaning operation on a net, where the assembly comprises a first unit and a second unit configured to be positioned on opposite sides of the net to be cleaned. The first and second units adhere to one another and to the net to be cleaned by magnetic attraction and move across the net while cleaning the net using a cleaning system, such as a steam unit, an ultrasound unit, a high-pressure washing unit, or a water suction unit. The choice of cleaning system in NO 20161708 is based on a desire to reduce abrasion of the net to be cleaned compared to more commonly used cleaning means such as brushes and rotating discs. The assembly in NO 20161708 is in other words adapted to clean a net with a certain cleaning power by providing the assembly with a suitable cleaning means.

[0003] The assembly of NO 20161708 may, once provided with a type of cleaning means, adjust its cleaning power by adjusting the power of the steam, ultrasound, high-pressure water or suction. The assembly may on the other hand not adjust its cleaning power if provided with other cleaning means with permanent intrinsic cleaning power, such as a brush, friction surface, permanent pressure high-pressure water etc.

[0004] It is an aim of the present disclosure to provide an assembly for cleaning a submerged net of a fish pen that may adjust its cleaning power for a wider variety of cleaning means. Summary of the present disclosure

[0005] A first aspect of the present disclosure provides a subsea assembly for adhering to, driving across and cleaning a submerged net, the subsea assembly comprising a first subsea unit for being positioned on a first side of the net, the first subsea unit comprising a first subsea unit housing, at least two pa rallelly oriented first subsea unit belt assemblies, and a first subsea unit moving means configured to move the at least two pa rallelly oriented first subsea unit belt assemblies relative to the first subsea unit housing, a second subsea unit for being positioned on a second side of the net opposite to the first subsea unit, the second subsea unit comprising a second subsea unit housing, and at least two parallelly oriented second subsea unit belt assemblies, where each belt assembly comprises a track provided with magnets for generating an attractive force between the at least two parallelly oriented first subsea unit belt assemblies and the at least two parallelly oriented second subsea unit belt assemblies such that the subsea assembly adheres to the net when the first subsea unit is positioned on the first side of the net and the second subsea unit is positioned on the second side of the net opposite to the first subsea unit, and where at least one of the first subsea unit and the second subsea unit further comprises a cleaning means for cleaning the net.

[0006] In an embodiment of the disclosure the second subsea unit further comprises a second subsea unit moving means configured to move the at least two parallelly oriented second subsea unit belt assemblies relative to the second subsea unit housing.

[0007] In another embodiment of the disclosure the first subsea unit moving means is configured to move the at least two parallelly oriented first subsea unit belt assemblies in a direction perpendicular to the net when then the subsea assembly adheres to the net.

[0008] In yet another embodiment of the disclosure the second subsea unit moving means is configured to move the at least two parallelly oriented second subsea unit belt assemblies in a direction perpendicular to the net when then the subsea assembly adheres to the net.

[0009] In yet another embodiment of the disclosure at least one of the first subsea unit moving means and the second subsea unit moving means comprises a linear actuator.

[0010] In yet another embodiment of the disclosure the first subsea unit moving means is further configured to move the at least two first subsea unit belt assemblies between a first position and a second position, where the at least two first subsea unit belt assemblies in the first position are arranged such that the ground pad of each track of the at least two parallelly oriented first subsea unit belt assemblies protrude a non-zero distance from a base of the first subsea unit, and where the at least two first subsea unit belt assemblies in the second position are arranged such that the at least two first subsea unit belt assemblies are withdrawn past the base of the first subsea unit

[0011] In yet another embodiment of the disclosure the subsea unit second subsea unit moving means is further configured to move the at least two second subsea unit belt assemblies between a first position and a second position, where the at least two second subsea unit belt assemblies in the first position are arranged such that the ground pad of each track of the at least two parallelly oriented second subsea unit belt assemblies protrude a non-zero distance from a base of the second subsea unit, and where the at least two second subsea unit belt assemblies in the second position are arranged such that the at least two second subsea unit belt assemblies are withdrawn past the base of the second subsea unit.

[0012] In yet another embodiment of the disclosure each belt assembly comprises a track, a rear road wheel, a middle road wheel and a front road wheel, and where each road wheel is provided with a suspension.

[0013] A second aspect of the present disclosure provides of the subsea assembly for cleaning a net or a sheet of a fish pen.

[0014] A third aspect of the present disclosure provides a method for adhering to, driving across and cleaning a submerged net of a fish pen, comprising the steps of: providing a subsea assembly, positioning the first subsea unit on a first side of the net, positioning the second subsea unit on a second side of the net, driving the subsea assembly across the net, adjusting the distance between the first subsea unit housing and the second subsea unit housing, and cleaning the submerged net of a fish pen using the cleaning means of at least one of the first subsea unit and the second subsea unit.

[0015] Other advantageous features will be apparent from the accompanying claims.

Brief description of the drawings

[0016] To make the present disclosure more readily understandable, the description that follows will refer to accompanying drawings, in which : [0017] Figure la is a schematic representation of a subsea assembly according to the present disclosure being provided on a net to be cleaned,

[0018] Figure lb is a schematic representation of the subsea assembly where the first subsea unit housing is illustrated as transparent in order to visualise belt assemblies of the two subsea units adjoining each other,

[0019] Figure 2 is a schematic representation of a belt assembly according to the disclosure, where the belt assembly is connected to a moving means for moving the belt assembly relative to a subsea unit housing,

[0020] Figure 3 is a schematic representation of a subsea unit where the base of the subsea unit housing is illustrated as transparent, and where the subsea unit comprising a moving means configured to move at least two parallelly oriented subsea unit belt assemblies relative to the subsea unit housing,

[0021] Figure 4 is a schematic representation of a subsea unit comprising two belt assemblies that protrude a distance L from the base of said subsea unit, [0022] Figure 5 is a schematic representation of a subsea unit comprising two belt assemblies that are withdrawn past the base of the subsea unit, more specifically withdrawn into the subsea unit housing,

[0023] Figure 6 is a schematic representation of a belt assembly according to the disclosure, where each road wheel and at least one damper wheel are provided with suspension, and where the belt assembly is connected to a moving means for moving the subsea unit belt assembly relative to the subsea unit housing, and [0024] Figure 7 schematically illustrates an example where a subsea unit comprises a moving means in the form of linear actuators coupled to the subsea unit belt assembly.

Detailed description of the present disclosure

[0025] In the following, general embodiments as well as particular exemplary embodiments of the present disclosure will be described. References will be made to the accompanying drawings. It shall be noted, however, that the drawings are exemplary embodiments only, and that other features and embodiments may well be within the scope of the present disclosure as claimed.

[0026] Unless otherwise defined, all terms of art, notations and other scientific terms or terminology used herein are intended to have the meanings commonly understood by those of skill in the art to which this disclosure pertains. Certain terms of art, notations, and other scientific terms or terminology may, however, find a definition in the field of continuous track propulsion systems, or they may be defined specifically as indicated below.

[0027] The present disclosure provides a subsea assembly 100 for adhering to, driving across, and cleaning a submerged net 130, e.g. that of a fish pen. The subsea assembly 100 according to the present disclosure comprises a first subsea unit 110 for being positioned on a first side of the net 130 and a second subsea unit 120 for being positioned on a second side of the net 130, opposite to the first subsea unit 110. The first subsea unit 110 and the second subsea unit 120 are, as schematically illustrated in figure la and lb, each provided with at least two parallelly oriented belt assemblies 150. More specifically, the first subsea unit 110 comprises at least two parallelly oriented first subsea unit belt assemblies, and the second subsea unit 120 comprises at least two parallelly oriented second subsea unit belt assemblies. The terms first subsea unit belt assembly and second subsea unit belt assembly are herein used to specify which belt assembly 150 that is being referred to. It will be appreciated, however, that the more general term belt assembly may be used to refer to a first subsea unit belt assembly or a second subsea unit belt assembly, which one will be apparent from the context.

[0028] The first subsea unit 110 and the second subsea unit 120 may according to any embodiment of the disclosure each be provided with two parallelly oriented belt assemblies 150. The various embodiments of the present disclosure will be described and illustrated for an example where the first subsea unit 110 and the second subsea unit 120 are each provided with two parallelly oriented belt assemblies 150. A person skilled in the art with knowledge of the present disclosure will appreciate, however, that each embodiment of the present disclosure may be generalized such that at least one of the first subsea unit 110 and the second subsea unit 120 is/are provided with more than two parallelly oriented belt assemblies 150.

[0029] The first subsea unit 110 comprises, as schematically illustrated in figures la and lb, a first subsea unit housing 115, while the second subsea unit 120 comprises a second subsea unit housing 125. At least one of the first subsea unit housing 115 and the second subsea unit housing 125 may according to any embodiment of the disclosure house various components, such as one or more of a battery, motor, control unit, receiver, transmitter, analytic tool, on board computer, etc. Any subsea unit housing 115,125 according to the present disclosure may for example be a watertight housing or comprise a watertight compartment for housing one or more of said various components. The first subsea unit housing 115 and the second subsea unit housing 125 may each be considered to further comprise a base 128, where the base 128 of the first subsea unit housing and the base 129 of the second subsea unit housing are facing the net when the subsea assembly 100 adheres to the net 130. The base 128 of the first subsea unit housing 115 and the base 129 of the second subsea unit housing 125 may consequently be considered as the part of each respective subsea unit housing 115,125 that is closest to the net to be cleaned during operation of the subsea assembly 100. It will be appreciated by a person skilled in the art with knowledge of the present disclosure that at least one of the base 128 of the first subsea unit housing 115 and the base 129 of the second subsea unit housing 125 may be planar, but that many other shapes may be possible.

[0030] A belt assembly 150 may in the context of the present disclosure be understood as the collection of wheels, track 160, bearings, supports, etc. necessary to enable continuous track propulsion of a subsea unit, and hence the subsea assembly 100. Each belt assembly 150 may, as schematically illustrated in figure 2, for example comprise a rear road wheel 170, optionally one or more middle road wheels 180, a front road wheel 190 and a track 160. Additional elements such as bearings, fastening mechanisms etc. may be provided in a variety of ways as will be appreciated by a person skilled in the art with knowledge of the present disclosure. The terms "front", "middle" and "rear" may here be defined relative to the driving direction 230 of the subsea assembly 100. However, as the driving direction 230 may be reversed, said terms are largely used herein to refer to the relative position of the road wheels 170,180,190, meaning in practice that any middle road wheel 180 is placed between a front road wheel 190 and a rear road wheel 170. A belt assembly 150, or more generally a subsea unit 110,120, may further be considered as comprising a driving unit 380 for enabling the belt assembly to provide continuous track propulsion for the subsea unit 110,120 to which it belongs. A driving unit 380 may for example comprise such as a battery, and a conventional motor or a motor in the hub of any one or more wheel of the belt assembly 150.

[0031] Each belt assembly 150 of any subsea unit 110,120 may, as illustrated in figures 1 and 4, be arranged such that the ground pad 165 of the track 160 of the belt assembly 150 protrudes a non-zero distance L from the base 128,129 of the subsea unit housing of said subsea unit. The ground pad 165 of each belt assembly 150 of the first subsea unit 110 may thus in other words be said to protrude a nonzero distance L from the base 128 of the first subsea unit housing, while the ground pad 165 of each belt assembly 150 of the second subsea unit housing 125 may be said to protrude a nonzero distance L from the base 129 of the second subsea unit housing. The distance L may vary between the first subsea unit 110 and the second subsea unit 120. L may typically be chosen to be in the range between 1 cm and 15 cm, although other values for L may be used. A person skilled in the art with knowledge of the present disclosure will appreciate that the ground pad 165 of any belt assembly 150 may be interpreted as the part of a track 160 of said belt assembly 150 that lies between any two road wheels of said belt assembly 150. A ground pad 165 may thus be considered as a part of a track 160. The ground pad 165 of any track 160 may according to the present disclosure be planar, or at least essentially planar, where essentially planar may be interpreted as meaning that the ground pad 165 may be tilted by a < 10 degrees, or be at least in part wavy, e.g. due to the track 160 not being completely tight.

[0032] The first subsea unit 110 and the second subsea unit 120 may, as schematically illustrated in figure la and lb, be arranged on opposite sides of the net 130 to be cleaned. The first subsea unit 110 and the second subsea unit 120 may be aligned relative to one another such that the at least two pa rallelly oriented first subsea unit belt assemblies are aligned with and adjoins separate belt assemblies 150 of the at least two parallelly oriented second subsea unit belt assemblies. The ground pad 165 of the track 160 of each belt assembly 150 of the at least two parallelly oriented first subsea unit belt assemblies may, as schematically illustrated in figure lb, be positioned such that each said ground pad 165 adjoins the ground pad 165 of the track 130 of separate belt assemblies 150 of the at least two parallelly oriented second subsea unit belt assemblies. Note that in figure lb part of the first subsea unit housing 115 is schematically illustrated as transparent for illustrative purposes. A person skilled in the art with knowledge of the present disclosure will appreciate that a net 130 to be cleaned may be present between any two ground pads 165 described as adjoining in the above context. Figures la and lb illustrates an example where the first subsea unit 110 and second subsea unit 120 are positioned on opposite sides of a net 130 to be cleaned such that the ground pad 165 of the track 160 of each of the at least two parallelly oriented first subsea unit belt assemblies adjoin, via the net 130 to be cleaned, the ground pad 165 of the track 160 of one of the at least two parallelly oriented second subsea unit belt assemblies. [0033] The track 160 of each belt assembly 150 is, as schematically illustrated in figure lb, provided with magnets 210. The magnets 210 are provided in order to generate an attractive force between the at least two pa rallelly oriented first subsea unit belt assemblies and the at least two pa rallelly oriented second subsea unit belt assemblies such that the subsea assembly 100 may adhere to a net 130 to be cleaned. A track 160 of a first subsea unit belt assembly may as a way of example comprise magnets 210 with a first polarity, while a track 160 of a second subsea unit belt assembly may comprise magnets 210 with a second polarity, opposite to the first polarity. When the tracks 160 of said belt assemblies 150 are positioned such that they adjoin, an attractive force will occur between them such that a frictional force will be obtained between each subsea unit 110,120 and the net 130 to be cleaned. The subsea assembly 100 may thus, due to this attractive force, and the resulting frictional force, adhere to the net 130 to be cleaned such that the two subsea units 110,120 may maintain a position on the net 130 relative to one another. A person skilled in the art with knowledge of the present disclosure will appreciate that there are numerous degrees of freedom in the configuration of the magnets 210 in each track 160. The magnets 210 in two adjoining tracks 160 may, as a way of example, be such that all the magnets 210 of the first track 160 have the same polarity, while all the magnets 210 in the second track 160, adjoining the first track 160, have the opposite polarity. Another example is that the magnets 210 in two adjoining tracks 160 may be such that any two adjacent magnets 210 in any one track 160 have opposite polarity, but where the tracks 160 of the two subsea units are adjoining with a shift such that magnets 210 of opposite polarity are adjoining/attracting one another. The latter configuration may be utilized to counteract skidding of the tracks 160.

[0034] The subsea assembly may according to the present disclosure move across a net to be cleaned by means of the at least two parallelly oriented first subsea unit belt assemblies and the at least two parallelly oriented second subsea unit belt assemblies. The adhesion to the net, obtained by the magnetic attraction between adjoining tracks of the two subsea units, will result in a grip for the subsea assembly such that movement is enabled. Said grip may thus be termed a magnetic induced grip. A person skilled in the art with knowledge of the present disclosure will appreciate that each belt assembly of the subsea assembly may operate as a continuous track vehicle propulsion system that is configured to operate under water, i.e. where each belt assembly is provided with or connected to one or more of an engine, a motor, a gear system, watertight gaskets, a power supply, etc. The subsea units may generally be provided with other parts such as a transmitter, receiver, lighting device, battery, etc. At least one of the first subsea unit and the second subsea unit may as a way of example comprise a driving unit, where the driving unit comprises an electric motor and a battery. The electric motor may here be connected to one or more of the wheels of a belt assembly of the first subsea unit or second subsea unit via for example a shaft or another suitable power transfer mechanism. In another example the first subsea unit and the second subsea unit may each comprise a driving unit as described above. A person skilled in the art with knowledge of the present disclosure will appreciate that there are several options for how to drive the belt assemblies of the subsea units.

[0035] The subsea assembly 100 may, as illustrated in figures la and lb be provided with cleaning means 140 for cleaning the net 130. At least one of the first subsea unit 110 and second subsea unit 120 may be provided with cleaning means 140. Cleaning means 140 may according to the present disclosure be any suitable means for cleaning a net 130. As a way of example, the subsea assembly 100 may be provided with one or more brushes, e.g. one or more rotating brushes. The one or more brushes may be provided on only one of the subsea units 110,120 or alternatively be distributed between the two subsea units 110,120. A brush may brush against the net 130 in order to clean the net 130 of unwanted substances such a biofouling. In another example the cleaning means 140 may comprise a water-based cleaning means 140, such as a pressure cleaner. In yet another example the cleaning means 140 may comprise one or more friction surfaces, such as a scrub or stationary brush, suitable for cleaning a net 130 by being moved across the net 130 in contact with the net 130.

[0036] The first subsea unit 110 comprises, as schematically illustrated in figures 2 and 3, a first subsea unit moving means 360 configured to move the at least two para llelly oriented first subsea unit belt assemblies relative to the first subsea unit housing 115. The first subsea unit moving means 360 may for example comprise at least one motor connected to the first subsea unit 110, which is coupled to the at least two parallelly oriented first subsea unit belt assemblies such that the motor may move the at least two parallelly oriented first subsea unit belt assemblies relative to the first subsea unit housing 115. Each of the at least two first subsea unit belt assemblies may be provided with separate first subsea unit moving means 360. As a way of example, the first subsea unit moving means 360 may comprise at least one conventional electric motor, a stepper motor, and/or solenoid motor. In a particular example the first subsea unit moving means 360 comprises at least one linear actuator, e.g. based on a rack and pinion principle. Figures 2 and 3 schematically illustrate a moving means comprising a linear actuator connected to the first subsea unit housing 115 and coupled to one of the at least two first subsea unit belt assemblies via one or more mechanical couplings. The at least two first subsea unit belt assemblies may in light of the above be considered as being connected to the first subsea unit housing 115, or more precisely be considered as being connected to the first subsea unit housing 115 via the first subsea unit moving means 360.

[0037] Enabling movement of the at least two parallelly oriented first subsea unit belt assemblies relative to the first subsea unit housing has been found to improve the ability of the subsea assembly 100 to transverse obstacles on the net to be cleaned. Figure 7 schematically illustrates an example where the first subsea unit comprises a first subsea unit moving means 360 in the form of linear actuators coupled to first subsea unit belt assembly 150. In figure 7-a, a first linear actuator may rise the front wheel 190 of the first subsea unit belt assembly 150, hence easing the engagement between the first subsea unit belt assembly 150 and the obstacle. In figure 7-b, as the subsea assembly 100 has progressed further, the first linear actuator may lower the front wheel 190 of the first subsea unit belt assembly so that the magnetic attraction with a second subsea unit belt assembly may be reinstated, hence keeping the subsea assembly 100 adhering to the net. The subsea assembly 100 may then, as schematically illustrated in figure 7-c and 7-d proceed with completing its traversing of the obstacle.

[0038] In another embodiment of the disclosure the second subsea unit 120 further comprises a second subsea unit moving means 370 configured to move the at least two parallelly oriented second subsea unit belt assemblies relative to the second subsea unit housing 125. The second subsea unit moving means 370 may for example comprise at least one motor connected to the second subsea unit 120, that is coupled to the at least two parallelly oriented second subsea unit belt assemblies such that the motor may move the at least two parallelly oriented second subsea unit belt assemblies relative to the second subsea unit housing 125. In a particular example the second subsea unit moving means 370 comprises at least one conventional electric motor, a stepper motor, and/or solenoid motor. In a particular example the second subsea unit moving means 370 comprises at least one linear actuator, e.g. based on a rack and pinion principle. Figures 2 and 3 schematically illustrate a second subsea unit moving means 370 connected to the second subsea unit housing 125 and coupled to the at least two second subsea unit belt assemblies via a mechanical coupling. The at least two second subsea unit belt assemblies may in light of the above be considered as being connected to the second subsea unit housing 125, or more precisely be considered as being connected to the second subsea unit housing 125 via the second subsea unit moving means 370. Each of the at least two second subsea unit belt assemblies may be provided with separate second subsea unit moving means 370.

[0039] In a particular embodiment of the disclosure the first subsea unit moving means is configured to move the at least two pa rallelly oriented first subsea unit belt assemblies relative to the first subsea unit housing in a direction perpendicular to the net when then the subsea assembly adheres to the net, i.e. while the belt assemblies of the first subsea unit adjoin the second subsea unit belt assemblies. Alternatively, or additionally the second subsea unit moving means is configured to move the at least two parallelly oriented second subsea unit belt assemblies relative to the second subsea unit housing in a direction perpendicular to the net when then the subsea assembly adheres to the net. Movement the least two of the first and/or second subsea unit belt assemblies in a direction perpendicular to the net when the subsea assembly adheres to the net enables the first subsea unit housing to move relative to the second subsea unit housing. The latter consequently allows for the adjustment of the distance between the first subsea unit housing and the second subsea unit housing, and hence the distance between the first subsea unit and the net and/or the distance between the second subsea unit and the net. For example, in an embodiment where the cleaning means comprises at least one brush, control of the distance between the first subsea unit housing and the second subsea unit housing may for example enable the pressure that the at least one brush exerts on the net. In the case of the net being particularly dirty, the pressure that the at least one brush exerts on the net may consequently be increased by moving the first subsea unit housing closer to the second subsea unit housing. It will be appreciated that the cleaning effect of other cleaning means, such as a high-pressure cleaner may also be adjustable by controlling the distance between the first subsea unit housing and the second subsea unit housing. One or more linear actuator(s) may according to this embodiment be particularly suitable as at least one of the first subsea unit moving means and the second subsea unit moving means.

[0040] Adjustment of the distance between the first subsea unit housing and the second subsea unit housing may further also be beneficial for enabling docking of the subsea assembly onto a docking station, for example for charging. As the docking station for example may be a charging plate for inductive charging that is configured to be positioned between the first subsea unit housing and the second subsea unit housing, the ideal distance between the first subsea unit housing and the second subsea unit housing during charging may be different than the ideal distance between the first subsea unit housing and the second subsea unit housing when the subsea assembly is cleaning the net. At least one of the first subsea unit moving means and the second subsea unit moving means may thus be used to adjust the distance between the first subsea unit housing and the second subsea unit housing such that the subsea assembly may dock. At least one of the first subsea unit moving means and the second subsea unit moving means may, as a way of example, be used to lower at least one of the first subsea unit and the second subsea unit onto an inductive charger unit. In the latter example the lowering of at least one of the first subsea unit and the second subsea unit onto an inductive charger unit may be performed such that a direct contact is made between at least one of the first subsea unit and the second subsea unit and the inductive charger unit.

[0041] Figures 4 and 5 schematically illustrate an embodiment of the disclosure where the first subsea unit moving means 360 is further configured to move the first subsea unit belt assemblies between a first position and a second position. In the first position, the at least two first subsea unit belt assemblies are arranged such that the ground pad 165 of each track 160 of the at least two parallelly oriented first subsea unit belt assemblies protrude a non-zero distance L from the base 128 of the first subsea unit housing 115. In the second position the at least two first subsea unit belt assemblies are arranged such that the at least two first subsea unit belt assemblies are withdrawn past the base 128 of the first subsea unit housing 115. The base 128,129 of a subsea unit housing 115,125 may generally according to the disclosure be considered as the side of the subsea unit housing 115,125 facing the net to be cleaned. More specifically, the base 128,129 of the subsea unit housing 115,125 may generally according to the disclosure be considered as the side of the part of the subsea unit housing 115,125 being positioned closest to the net to be cleaned during operation of the subsea assembly 100. A belt assembly 150 of a subsea unit 110,120 may according to the disclosure be considered as being withdrawn past the base 128 of the subsea unit 110,120 if the ground pad 165 of the track 160 of the belt assembly 150 does not protrude from the base 128,129 of the subsea unit 110,120. Withdrawing a belt assembly 150 of a subsea unit 110,120 past the base of said subsea unit 110,120 has been found to be beneficial for aiding separation of the first subsea unit 110 from the second subsea unit 120. As a first subsea unit belt assembly of a first subsea unit 110 is being withdrawn past the base 128 said subsea unit 110, e.g. into the first subsea unit housing 115, the track 160 of the first subsea unit belt assembly will be pulled away from any track of any second belt assembly of a second subsea unit 120 which it adjoins. The latter may be beneficial as it removes the need for manual separation of the first subsea unit 110 from the second subsea unit 120, e.g. during maintenance of the subsea assembly. Figure 5 schematically illustrates a subsea unit 110,120 comprising a base 128,129 with openings 390 into which the belt assemblies may be withdrawn.

[0042] Equivalently as explained above for the first subsea unit moving means, the second subsea unit moving means may further configured to move the second subsea unit belt assemblies between a first position and a second position. The second subsea unit moving mean may in other words be configured in the same manner as the first subsea unit moving means.

[0043] The subsea assembly may according to the present disclosure be dimensioned according to the net to be cleaned. A typical extension of the subsea assembly is between 80 cm and 200 cm. The extension of the subsea assembly is according to a specific embodiment of the present disclosure less than 150 cm.

[0044] One or more of the road wheels 170,180,190 of any belt assembly may, as schematically illustrated in figures 2 and 6, be provided with a suspension 200. The suspension 200 may be configured with a suspension travel, from fully extended to the fully compressed condition, of less than 15cm. The suspension travel may shift the position of said road wheel 170,180,190 in a direction at least in part perpendicular to a driving direction 230 of the subsea assembly 100. Compensating idler wheels, may be added to the belt assembly to maintain track tension by means of track adjustment. In the following the compensating idler wheel 220 is named damper wheel. The suspension can be of a linear or nonlinear type. Examples of suspension types are live axle with a Watt's link, sliding pillar, swing axle, double wishbone suspension, MacPherson and swing arm variants.

[0045] In an example the suspension travel is less than 15 centimetres. In another example the suspension travel is specifically between 3 and 7 centimetres. The suspension 200 of the road wheels 170,180,190 aims inter alia to enable the subsea assembly 100 to traverse obstacles of the net to be cleaned, such as ropes, knots or similar. The combination of the road wheel suspension 200 and the presence of three road wheels 170,180,190 means that any two adjoining tracks 160 may retain magnetic attraction even when the subsea assembly 100 is traversing an obstacle. As a way of example one can assume a subsea assembly 100 according to the present disclosure traversing a rope of the net to be cleaned. As the subsea assembly 100 drives across the rope, the front road wheels 190 of each pair of adjoining tracks 160 will be displaced away from one another and the magnetic attraction between the part of the ground pad 165 between the front road wheel 190 and middle road wheel 180 of the pair of adjoining tracks 160 will be strongly reduced. A subsea assembly 100 having only two road wheels would in such an instance likely lose its magnet-induced grip on the net to be cleaned and consequently fall off the net. The subsea assembly 100 according to the present disclosure would, on the contrary, maintain its magnet induced grip on the net, as the part of the ground pad 165 between the middle road wheel 180 and read road wheel 170 would still be adjoining, such that sufficient magnetic attraction may be maintained. Following the same example, the subsea assembly 100 will upon continuing its traversing of said rope move relative to the rope such that the front road wheels 190 once again are brought in contact with each other, but where the middle road wheels 180 subsequently are displaced from their default position using their respective suspension 200. At such a position the subsea assembly 100 according to the present disclosure may maintain its adhesion to the net to be cleaned due to the magnet attraction between the ground pad 165 around the front road wheels 190 and the rear road wheels 170. The subsea assembly 100 will upon continuing its traversing of said rope, move relative to the rope such that the middle road wheels 180 once again are brought in contact with each other, but where the rear road wheels 170 subsequently are displaced from their default position using their respective suspension 200. The latter situation is equivalent to the situation where the front road wheels 190 were displaced. [0046] Figures 2 and 6 schematically illustrate an embodiment of the present disclosure where each belt assembly 150 further comprises a damper wheel 220. Said damper wheel 220 may typically be positioned at a non-zero distance from the ground pad 165 of the belt assembly 150 to which it belongs. The latter location may here be in a direction perpendicular to the driving direction 230 of said belt assembly 150. A damper wheel 220 may be utilized in order to compensate for any strain in a track 160 caused when the subsea assembly 100 traverses an obstacle that causes one of its road wheels 170,180,190 to be displaced from their non-damped position. A road wheel 170,180,190 being displaced as a consequence of the subsea assembly 100 traversing an obstacle will result in the relevant track 160 having to conform to the shape of the object that is being traversed. Instead of the track 160 becoming strained due to the displacement of a road wheel 170,180,190, the damper wheel 220 may instead compensate for the shift in position of the road wheel 170,180,190, i.e. compensate for the resulting strain in the track 160, by being itself displaced. Each damper wheel 220 may thus in other words be provided with a suspension 200 for shifting the position of said damper wheel 220 to compensate for a shift in position of a road wheel 170,180,190. As a way of example, if a road wheel 170,180,190 of a belt assembly 150 is displaced in a direction perpendicular to the driving direction 230 of said belt assembly 150, a damper wheel 220 of that belt assembly may be displaced in the opposite direction of the displaced road wheel 170,180,190 in order to compensate for the increased length requirement on the track 160 due to the belt having to conform to the shape of the object that is being traversed. A typical object that needs to be traversed may as previously mentioned be a rope or a knot, which for example could have a diameter or extension of 3-5 centimetres. Each road wheel 170,180,190 may thus be provided with a suspension 200 with a suspension travel of said road wheel 170,180,190 a distance of at least 3-7 centimetres in a direction at least in part perpendicular to a driving direction 230 of the subsea assembly 100. Each damper wheel 220 may consequently be provided with a suspension 200 for shifting the position of said damper wheel 220 a distance of 3-7 centimetres. In general, any road wheel 170,180,190 may be provided with a suspension 200 with suspension travel of said road wheel 170,180,190 a distance of up to 15 centimetres in a direction at least in part perpendicular to a driving direction 230 of the subsea assembly 100. A suspension 200 may generally be any suitable suspension 200. Examples of suitable suspensions 200 are spring-based suspension and hydraulic suspension. [0047] The subsea assembly may according to any embodiment of the present disclosure be configured to traverse obstacles of a given size. As a way of example, the subsea assembly may be configured to traverse an obstacle such as a rope or a rope knot. In order for the subsea assembly to not loose adhesion to the net to be cleaned upon traversing an obstacle, the road wheels of each belt assembly may be spaced apart depending on the dimension of the obstacle to be traversed. In one embodiment of the present disclosure the road wheels of each individual belt assembly may be separated by a distance of at least 3-5 centimetres. The latter distance is here measured between the surface of two adjacent road wheels. The road wheels of each individual belt assembly may generally be separated by a distance longer than 5 centimetres. It will be appreciated by a person skilled in the art that the upper limit for the spacing between two adjacent road wheels of the same belt assembly is determined by for example the obstacle that it is desirable to traverse, and/or for example the dimension and weight of the subsea assembly. A distance between two adjacent road wheels of at least 3-5 centimetres, alternatively 5 - 10 centimetres, is considered adequate for most fish pens. Such a distance will allow the subsea assembly to traverse ropes and rope knots without having two adjacent road wheels of the same belt assembly being displaced by the rope.

[0048] Any belt assembly 150 may, as illustrated in figures 2 and 6, further comprise any number of drive wheels 320, damping wheels 220, road wheels, idlers and/or tightener wheels 340. As a way of example, any belt assembly may be provided with a driving wheel 320, i.e. a wheel that supplies driving power to the track 160. Any road wheel or damper wheel 220 may in any relevant embodiments of the present disclosure be a driving wheel 320. A person skilled in the art would appreciate that the subsea assembly 100 according to the present disclosure may comprise any number of additional wheels, e.g. dependent on the exact size and shape of the belt assemblies 150. A tightener wheel 340 may for example be provided to form the previously described driving edge 245 or trailing edge 255. In a particular embodiment of the present disclosure, each belt assembly 150 may further comprise an additional middle road wheel 180. An additional middle road wheel 180 may contribute to increase the attraction between two adjoining belt assemblies 150 when the subsea assembly 100 traverses an obstacle. An additional middle road wheel 180 may contribute to ensuring a plane surface of the ground pad 165 of two adjoining tracks 160 being in contact during the traversing of said obstacle. The size of each wheel of the subsea assembly 100 will generally depend on the size of each subsea unit. The size of each wheel may typically be dimensioned according to the type of track used, for example such that the track may run across the wheels without experiencing too great a curvature. In a particular embodiment of the present disclosure each wheel of each belt assembly has a diameter in the range of 60 mm to 120 mm. Such a diameter has been found to be preferable when the track is made from silicone, rubber or plastic. Any wheel of a belt assembly that is positioned farthest to the front or back along the driving direction of a belt assembly will typically inflict the largest curvature on the track. These farthermost wheels may thus have a diameter that is larger than that of any road wheels appurtenant to the same belt assembly, e.g. in the range from 10% - 250% larger, in particularly in the range from 50% - 100 % larger. Any one or both of the farthermost wheels may for example be a driving wheel 320.

[0049] The track of any belt assembly of the subsea assembly may according to any embodiment of the present disclosure be made at least in part from rubber, plastic or silicone. A person skilled in the art will appreciate that the track may be made from other materials than those listed explicitly herein. The track may for example be made from a combination of materials, e.g. a combination of those mentioned above.

[0050] It will be appreciated that the subsea assembly according to any embodiment of the present disclosure is not limited to use for cleaning a net. The subsea assembly may according to any embodiment of the present disclosure alternatively be used in order to clean a seine, net cage, a water permeable sheet, water impermeable sheet or similar. Other examples are watertight tarpaulin, perforated tarpaulin, or similar.

[0051] Other advantageous features will be apparent from the accompanying claims.