Semi-submersible spar-type offshore fish farm and method of offshore installing a cassette in the same

Abstract

The invention relates to a semi-submersible spar-type offshore fish farm (1) for cultivating fish at open sea that in use comprises a number of cassettes (7) each having an excess positive buoyancy and being a floating stable netted cage structure. A respective cassette can be connected with respective first and second elongated rigid truss structures of a first set of elongated rigid truss structures (9) of said fish farm via respective first and second connection assemblies of a first set of connection assemblies (12) that allow said cassette to float above said first and second truss structures. Said first and second connection assemblies comprise respective elongated connection elements (13) extending between said cassette and said first and second truss structures allowing floating movements of said cassette relative to said first and second truss structures. The invention also relates to a method of offshore installing a cassette in said fish farm.

Description

[0001] SEMI-SUBMERSIBLE SPAR-TYPE OFFSHORE FISH FARM AND METHOD OF OFFSHORE INSTALLING A CASSETTE IN THE SAME

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a semi-submersible spar-type offshore fish farm for cultivating fish at open sea. The invention also relates to a method of offshore installing a cassette in which fish can be cultivated in said fish farm

[0004] BACKGROUND OF THE INVENTION

[0005] Aquaculture is the farming of aquatic organisms including fish, mollusks, crustaceans and aquatic plants. Farming implies some form of intervention in the rearing process to enhance production, such as regular stocking, feeding, protection from predators. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the harvesting of wild fish. Particular kinds of aquaculture include fish farming, shrimp farming, oyster farming, mariculture, algaculture, and the cultivation of ornamental fish. Fish farming using inshore fish farms in freshwater and offshore fish farms in saltwater is well known. An advantage of offshore fish farms is that deep-water cages can be used that have a large harvesting volume. Another advantage is that the deepwater cages can be kept away from coastal pollution areas, and avoid interference with other coastal stakeholders such as tourism and wind power plants. As a result, a good farming environment can be provided which is the basis for harvesting high- quality cultured fish.

[0006] A semi-submersible spar-type offshore fish farm for cultivating fish at open sea is known in the art and typically comprises an elongated body that is centrally arranged within said fish farm, and a semi-submersible netted cage that is coaxially arranged around the elongated body. The netted cage can be submerged during heavy storms or typhoons to prevent or at least reduce damage because while being submersed, the netted cage is less exposed to harsh sea conditions and hence less subjected to physical stress.

[0007] Besides maintenance of the netting material, and at least one of replacement and repair of the netting material due to damage, periodic replacement of the netting material is required due to wear. During the lifetime of the offshore fish farm, replacement of the netting material can occur between three to ten times depending amongst others on the kind of netting material used, the offshore environment the netting material is exposed to, such as water temperature and salinity, and stresses that the netting material is subjected to.

[0008] Replacement of netting material at the fish farm’s offshore location would be advantageous because ceasing farming operations, removing offshore anchors, wettowing of the fish farm to and from a nearest dry dock or port, and reinstalling the offshore anchors upon return of the fish farm at its offshore location would not be necessary. Therefore, replacement of netting material at the fish farm’s offshore location would result in a shorter downtime of the fish farm compared to replacement of netting material after transport of the entire fish farm to a dry dock or port. Disadvantages associated with offshore replacement of the netting material involve amongst others safety issues such as the risk of injuries for the maintenance personnel, such as divers, as a result of working in an offshore environment, and operational issues such as potential weather delays. At present, the above-mentioned disadvantages outweigh the above-mentioned advantages associated with offshore replacement of netting material. Therefore, it is common practice to perform replacement of netting material after transporting the fish farm to a dry dock or port. Based on the above, there is a need for providing a semi-submersible spar-type offshore fish farm that enables improved replacement of netting material whilst continuing farming operations at the fish farm’s offshore location compared to the above-mentioned common practice regarding replacement of netting material and / or offshore replacement of netting material of the cages of semi-submersible spar-type offshore fish farms known in the art.

[0009] SUMMARY OF THE INVENTION

[0010] It is an object of the present invention to provide a semi-submersible spar-type offshore fish farm for cultivating fish at open sea that enables improved replacement of netting material whilst continuing farming operations at the fish farm’s offshore location by pre-empting or at least reducing at least one of the above-mentioned and / or other disadvantages associated with the above-mentioned common practice regarding replacement of netting material and / or offshore replacement of netting material of the cages of semi-submersible spar-type offshore fish farms known in the art.

[0011] It is another object of the present invention to provide a method of offshore installing a cassette in which fish can be cultivated in the semi-submersible spar-type offshore fish farm according to the invention. Aspects of the present invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features from the independent claims as appropriate and not merely as explicitly set out in the claims. Furthermore, all features may be replaced with other technically equivalent features.

[0012] At least one of the abovementioned objects is achieved by a semi-submersible spar-type offshore fish farm for cultivating fish at open sea, comprising: an elongated body that comprises a first end part, a second end part, and a longitudinal center line that is directed from said first end part to said second end part, the longitudinal center line in use of said fish farm being arranged in a direction transverse to sea level, and said first end part being arranged above said second end part; a buoyancy unit that is associated with the elongated body, the buoyancy unit being configured to have an adjustable buoyancy to allow the elongated body to float at different drafts relative to sea level depending on a value of the adjustable buoyancy; a number of cassettes that in use of said fish farm are arranged around the elongated body, each cassette of the number of cassettes having: a semi-rigid or rigid cage structure that is configured to have excess positive buoyancy; and netting material that is associated with the semi-rigid or rigid cage structure to enable fish to be contained within the cassette; a first set of at least two elongated rigid truss structures, each elongated rigid truss structure of said first set of elongated rigid truss structures having a bound end part that is associated with the second end part of the elongated body and a free end part, the elongated rigid truss structures of said first set of elongated rigid truss structures being: arranged transverse to the elongated body; and positioned next to each other and spaced apart in a circumferential direction of the elongated body; and a first set of connection assemblies, each connection assembly of said first set of connection assemblies comprising an elongated connection element, wherein a first connection assembly of said first set of connection assemblies is arranged to connect a respective cassette of the number of cassettes with a first elongated rigid truss structure of said first set of elongated rigid truss structures at a first distance from each other as seen in a direction of the longitudinal center line of the elongated body, and wherein a second connection assembly of said first set of connection assemblies is arranged to connect the respective cassette with a second elongated rigid truss structure of said first set of elongated rigid truss structures at a second distance from each other as seen in the direction of the longitudinal center line of the elongated body, wherein at least a part of a first elongated connection element of said first connection assembly is arranged to extend over at least a part of said first distance, and at least a part of a second elongated connection element of said second connection assembly is arranged to extend over at least a part of said second distance said first elongated connection element and said second elongated connection element being configured to allow floating movements of the respective cassette relative to said first elongated rigid truss structure and said second elongated rigid truss structure.

[0013] As a result of the way in which a respective cassette of the number of cassettes is installed in the above-described embodiment of the fish farm, the fish farm according to the present invention enables improved replacement of the netting material of the cassettes whilst continuing farming operations at the fish farm’s offshore location compared to the common practice regarding replacement of netting material of semisubmersible spar-type offshore fish farms known in the art, i.e. after transporting the entire fish farm from an offshore location to a dry dock or port, and / or the offshore replacement of netting material of the cages of semi-submersible spar-type offshore fish farms known in the art. It is noted that in the context of the present invention, netting material is to be construed as an open-meshed material that can comprise at least one of twine, wire, rope, thread, and any suitable combination thereof. The netting material can comprise any suitable material, for example a metal, such as copper, a polymer, a fiber-reinforced polymer, or any suitable combination of these different materials. The netting material can be resilient or rigid. The netting material can be arranged as an interior lining of the cassette or as an exterior lining of the cassette.

[0014] After installation in the fish farm according to the present invention, the respective cassette floats at the first distance as seen in the direction of the longitudinal center line of the elongated body from the first elongated rigid truss structure of the first set of elongated rigid truss structures and at the second distance as seen in the direction of the longitudinal center line of the elongated body from the second elongated rigid truss structure of the first set of elongated rigid truss structures. The first connection assembly and the second connection assembly of the first set of connection assemblies can be configured such that their respective elongated connection elements can have an adjustable length. In this way, the first distance and the second distance can be any suitable distances that on the one hand allow floating movements of the respective cassette relative to said first elongated rigid truss structure and said second elongated rigid truss structure, and on the other hand prevent collisions between at least one of the respective cassette and the elongated body, and between neighboring cassettes if the number of cassettes arranged in the fish farm is at least two. The first distance can be equal to the second distance. It is also possible that the first distance and the second distance are different.

[0015] Said floating movements of the respective cassette relative to said first elongated rigid truss structure and said second elongated rigid truss structure can be independent floating movements except for heave, pitch and roll movements of the respective cassette that are restricted as a result of the first connection assembly and the second connection assembly of the first set of connection assemblies that connect the excess positive buoyant cassette with said first elongated rigid truss structure and said second elongated rigid truss structure, respectively. In the context of the present invention, excess positive buoyancy is to be construed as more positive buoyancy than the positive buoyancy that would be required in normal floating conditions of the cassette. If free afloat, for example when being wet-towed to and / or from the fish farm’s offshore location, the excess positive buoyancy of the respective cassette can be reduced by ballasting the respective cassette by for example inserting water into at least one interior space of the cage structure of the respective cassette.

[0016] It is noted that by providing a respective cassette with excess positive buoyancy, a floating system can be created that can control the floating movements of said respective cassette. If said respective cassette is fully submerged, then the excess positive buoyancy of said respective cassette does not change. If a force, for example from waves and currents, acts on the fully submerged cassette, this force will result in a movement in a horizontal plane of the cassette, i.e. a plane parallel to sea level. This creates a respective angle between a respective first attachment point at a respective elongated rigid truss structure of the first set of elongated rigid truss structures with which a respective elongated connection element is connected and a respective second attachment point at the respective cassette with which said respective elongated connection element is connected. Said angle results in an opposing force that counteracts the movement of the cassette as a result of the wave and current forces. In this way, floating movements of said fully submerged cassette in a horizontal plane can be controlled.

[0017] It is noted that control of the floating movements of a respective cassette that is at least partially arranged above sea level can be established by a combination of:

[0018] - an increased excess positive buoyancy of said respective cassette that is caused by a horizontal displacement of said respective cassette, i.e. a displacement parallel to sea level, resulting in a vertical displacement of said respective cassette, i.e. a displacement transverse to sea level; and

[0019] - the above-mentioned angle that provides counteracting floating movements in a horizontal plane.

[0020] Because of the above-described controlled floating arrangement of a respective excess positive buoyant cassette in the fish farm according to the invention, the above-mentioned operational issues and safety issues such as the risk of injuries for the maintenance personnel as a result of working in an offshore environment can be reduced. It is possible to install and / or remove a respective cassette using remotely operated vehicles (ROVs) instead of using divers.

[0021] Because of the possibility to individually install and / or remove a respective cassette, it is not necessary to cease farming operations at the fish farm’s offshore location and transport the entire fish farm according to the present invention from its offshore location to a dry dock or port for replacing netting material of the cassette. Instead, an individual cassette of the total number of cassettes can be removed from the fish farm and replaced by a new or refurbished cassette. In this way, the fish farm can remain operational at its offshore location while the netting material of the removed cassette can be replaced in a dry dock or port. Because of its construction and excess positive buoyancy, each cassette of the number of cassettes is an independently free floating stable structure as such that can be wet-towed between the offshore location of the fish farm and the dry dock. As mentioned above, if a respective cassette is to be wet-towed its excess positive buoyancy can be reduced to the amount of positive buoyancy that is sufficient for establishing a desired draft of the cassette.

[0022] It is also possible to remove an individual cassette for replacing its netting material without installing a new or refurbished cassette. While replacing the netting material of the removed cassette in the dry dock or port, the other cassettes of the total number of cassettes remain in the fish farm that can remain operational despite a reduced capacity. It is also possible to remove a first group of cassettes of the total number of cassettes from the fish farm while a second group of cassettes of the total number of cassettes remains in the fish farm that can remain operational despite a reduced capacity. Once replacement of the netting material of the cassettes of the first group of cassettes has been finished, the first group of cassettes can be reinstalled in the fish farm and the second group of cassettes can be removed in order to have their netting material replaced.

[0023] As mentioned above, the cassettes can be installed, removed and replaced while the fish farm remains operational at an offshore location. During prolonged periods of bad weather especially in winter, the cassettes provide the opportunity to continue with harvest operations by removing the cassette with fish inside entirely and bringing them to an in / nearshore environment to do the harvesting.

[0024] The above-mentioned advantages offered by the semi-submersible spar-type fish farm according to the present invention can also result in reduced costs associated with installing and removing of a respective cassette.

[0025] It is noted that the first set of elongated rigid truss structures can be associated with the second end part of the elongated body via the buoyancy unit. It is also possible that the first set of elongated rigid truss structures are connected directly with the second end part of the elongated body. In that case, the buoyancy unit is associated with another portion of the elongated body in such a way that the buoyancy unit allows the elongated body to float at different drafts relative to sea level depending on the value of the adjustable buoyancy of the buoyancy unit.

[0026] Furthermore, it is noted that a connection assembly of the first set of connection assemblies, in addition to an elongated connection element, can comprise at least one of pad-eyes, sheaves and pulleys that are configured to interact with the elongated connection assembly. The pad-eyes, sheaves and pulleys can be associated with the respective cassettes and the elongated rigid truss structures of the first set of elongated rigid truss structures that are to be connected with each other.

[0027] The semi-submersible spar-type offshore fish farm according to the present invention can advantageously be applied in the field of offshore floating wind turbines. Therefore, in accordance with an exemplary embodiment of the semi-submersible spar-type offshore fish farm according to the invention, a wind turbine can be associated with the first end part of the elongated body.

[0028] In an embodiment of the semi-submersible spar-type offshore fish farm according to the invention, at least one cassette of the number of cassettes is provided with at least one attachment system that is configured and arranged to enable establishment of at least two interconnected cassettes. The at least two interconnected cassettes provide a compartmentalized cage segment or a compartmentalized overall cage of the fish farm. It is also possible to establish several groups of interconnected cassettes that provide several compartmentalized cage segments. The number of interconnected cassettes, the number of groups of interconnected cassettes, i.e. the number of compartmentalized cage segments, can be any suitable number depending on for example the specific requirements of the fish farm and / or the size of the elongated rigid truss structures of the first set of elongated rigid truss structures. It is possible that each cassette of the number of cassettes or a selected group of cassettes of the number of cassettes is provided with a respective attachment system or a plurality of respective attachment systems.

[0029] In an embodiment of the semi-submersible spar-type offshore fish farm according to the invention, said fish farm comprises: a second set of at least two elongated rigid truss structures, each elongated rigid truss structure of said second set of elongated rigid truss structures having a bound end part that is associated with the elongated body at a location that is closer to the first end part than to the second end part of the elongated body, and a free end part, the elongated rigid truss structures of said second set of elongated rigid truss structures being: arranged transverse to the elongated body; positioned next to each other and spaced apart in a circumferential direction of the elongated body in alignment with the elongated rigid truss structures of said first set of elongated rigid truss structures; and arranged at a third distance from said first set of elongated rigid truss structures as seen in the direction of the longitudinal center line of the elongated body, the third distance allowing each cassette of the number of cassettes that in use of the fish farm are arranged around the elongated body to be arranged between the elongated rigid truss structures of said first set of elongated rigid truss structures and the elongated rigid truss structures of said second set of elongated rigid truss structures as seen in the direction of the longitudinal center line of the elongated body; and a second set of connection assemblies, each connection assembly of said second set of connection assemblies comprising an elongated connection element, wherein a first connection assembly of said second set of connection assemblies is arranged to connect the respective cassette of the number of cassettes, which is connected with the first elongated rigid truss structure and the second elongated rigid truss structure of said first set of elongated rigid truss structures via said first connection assembly and said second connection assembly of said first set of connection assemblies, with a first elongated rigid truss structure of said second set of elongated rigid truss structures at a fourth distance from each other, and wherein a second connection assembly of said second set of connection assemblies is arranged to connect said respective cassette with a second elongated rigid truss structure of said second set of elongated rigid truss structures at a fifth distance from each other, wherein at least a part of a first elongated connection element of said first connection assembly of said second set of connection assemblies is arranged to extend over at least a part of said fourth distance, and at least a part of a second elongated connection element of said second connection assembly of said second set of connection assemblies is arranged to extend over at least a part of said fifth distance, said first elongated connection element of said first connection assembly of said second set of connection assemblies and said second elongated connection element of said second connection assembly of said second set of connection assemblies being configured to allow floating movements of said respective cassette relative to said first elongated rigid truss structure and said second elongated rigid truss structure of said second set of elongated rigid truss structures.

[0030] In this way, a respective cassette of the number of cassettes is not only connected with a first elongated rigid truss structure of the first set of elongated rigid truss structures via a first connection assembly of the first set of connection assemblies, and a second elongated rigid truss structure of the first set of elongated rigid truss structures via a second connection assembly of the first set of connection assemblies, but also with a first elongated rigid truss structure of the second set of elongated rigid truss structures via a first connection assembly of the second set of connection assemblies, and a second elongated rigid truss structure of the second set of elongated rigid truss structures via a second connection assembly of the second set of connection assemblies. Hence, after installation in the fish farm according to the present invention, the respective cassette floats at:

[0031] - said first distance as seen in the direction of the longitudinal center line of the elongated body with respect to the first elongated rigid truss structure of the first set of elongated rigid truss structures; - said second distance as seen in the direction of the longitudinal center line of the elongated body with respect to the second elongated rigid truss structure of the first set of elongated rigid truss structures;

[0032] - said fourth distance from the first elongated rigid truss structure of the second set of elongated rigid truss structures; and

[0033] - said fifth distance from the second elongated rigid truss structure of the second set of elongated rigid truss structures.

[0034] Said first distance, second distance, fourth distance, and fifth distance can be any suitable distance as long as collisions can be prevented between at least one of:

[0035] - the respective cassette and the elongated body;

[0036] - the respective cassette and the first elongated rigid truss structure and the second elongated rigid truss structure of said second set of elongated rigid truss structures; and

[0037] - neighboring cassettes if the number of cassettes arranged in the fish farm is at least two.

[0038] As mentioned above, said first distance and second distance can be equal but it is also possible that said first distance and second distance are different. Analogously, said fourth distance can be equal to said fifth distance but it is also possible that said fourth distance and fifth distance are different.

[0039] The first elongated connection element of the first connection assembly of the second set of connection assemblies and the second elongated connection element of the second connection assembly of the second set of connection assemblies that are arranged to extend over at least a part of said fourth distance and said fifth distance, respectively allow floating movements of the respective cassette relative to said first elongated rigid truss structure and said second elongated rigid truss structure of said second set of elongated rigid truss structures. The floating movements of the respective cassette relative to said first elongated rigid truss structure and said second elongated rigid truss structure of said first set of elongated rigid truss structures, and said first elongated rigid truss structure and said second elongated rigid truss structure of said second set of elongated rigid truss structures, can be at least one of independent but limited surge, sway and yaw movements. Heave, pitch and roll movements of the respective cassette are restricted as a result of the first connection assembly and the second connection assembly of the first set of connection assemblies that connect the respective cassette with said first elongated rigid truss structure and said second elongated rigid truss structure, respectively of said first set of elongated rigid truss structures, and the first connection assembly and the second connection assembly of the second set of connection assemblies that connect the respective cassette with said first elongated rigid truss structure and said second elongated rigid truss structure, respectively of said second set of elongated frigid truss structures.

[0040] It is noted that a connection assembly of the second set of connection assemblies, in addition to an elongated connection element, can comprise at least one of padeyes, sheaves, roller sheaves, and pulleys that are configured to interact with the elongated connection element. At least one of the pad-eyes, sheaves, roller sheaves, and pulleys can be associated with the respective cassettes and / or the elongated rigid truss structures of the second set of elongated rigid truss structures that are to be connected with each other.

[0041] In an embodiment of the semi-submersible spar-type offshore fish farm according to the invention, each connection assembly of the first set of connection assemblies that is associated with a respective cassette of the number of cassettes is provided with a tensioned elongated connection element comprising at least one of a cable, a chain, a rope, and a rod. A respective elongated connection element of a respective connection assembly of said first set of connection assemblies that is arranged to connect a respective cassette of the number of cassettes with a respective elongated rigid truss structure of said first set of elongated rigid truss structures is tensioned as a result of the excess positive buoyancy of the respective cassette and not as a result of a tensioning system. Therefore, the tensioned elongated connection element can be construed as a passively tensioned elongated connection element.

[0042] An elongated connection element of a connection assembly of said first set of connection assemblies can be a cable, a chain, a rope, a rod or any suitable combination of these elements. Depending on the specific configuration, an elongated connection element of a connection assembly of said first set of connection assemblies can comprise any suitable material such as for example metal, a polymer, a fiber-reinforced polymer, carbon or any suitable combination of these materials.

[0043] In an embodiment of the semi-submersible spar-type offshore fish farm according to the invention, the elongated connection element of a connection assembly of the first set of connection assemblies is a rigid elongated element.

[0044] In this case, a first mechanical connector comprising a first threaded part can be associated with a respective cassette, and a second mechanical connector comprising a second threaded part that can be associated with a respective elongated rigid truss structure of the first set of elongated truss structures. The end parts of the rigid elongated element can be provided with threaded sections comprising threads that are complementary to the threads of said first threaded part and said second threaded part. Upon connecting the respective threaded sections of the rigid elongated element with said first threaded part and said second threaded part, said respective cassette is connected with said respective elongated rigid truss structure of the first set of elongated rigid truss structures.

[0045] Instead of the above-mentioned mechanical connectors, it is possible to use hydraulics-based connectors. A first hydraulics-based connector can be associated with a respective cassette, and a second hydraulics-based connector can be associated with a respective elongated rigid truss structure of the first set of elongated truss structures. The end parts of the rigid elongated element can be configured to cooperate with the first hydraulics-based connector and the second hydraulics-based connector for connecting said respective cassette with said respective elongated rigid truss structure of the first set of elongated rigid truss structures.

[0046] As a result of connecting a respective cassette with a respective elongated rigid truss structure via a rigid elongated connection element, at least one of surge, sway, heave, roll, pitch, and yaw motions of said respective cassette relative to said elongated rigid truss structure of the first set of elongated rigid truss structures can be prevented.

[0047] In an embodiment of the semi-submersible spar-type offshore fish farm according to the invention, a respective connection assembly of the first set of connection assemblies comprises a first damping system that is associated with the elongated connection element of said respective connection assembly. In this way, tension in a respective connection assembly of the first set of connection assemblies that is used to connect a respective cassette of the number of cassettes with a respective elongated rigid truss structure of the first set of elongated rigid truss structures can be damped. As a result, peak stresses and / or sudden impulses on the respective cassette and / or the respective elongated rigid truss structure the respective cassette is connected with can be reduced. The first damping system can comprise a spring and / or a hydraulic piston.

[0048] In an embodiment of the semi-submersible spar-type offshore fish farm according to the invention, a respective connection assembly of the second set of connection assemblies comprises a tensioning system that is configured and arranged to provide the respective connection assembly of the second set of connection assemblies with a tensioned elongated connection element comprising at least one of a cable, a chain, a rope, and a rod. A respective elongated connection element of a respective connection assembly of said second set of connection assemblies that is arranged to connect a respective cassette of the number of cassettes with a respective elongated rigid truss structure of said second set of elongated rigid truss structures that is tensioned by said tensioning system can be construed as an actively tensioned elongated connection element.

[0049] The tensioning system, which can for example comprise a chain stopper, can be configured to pre-tension the elongated connection element to control floating motions of said respective cassette relative to said elongated rigid truss structure of the second set of elongated rigid truss structures said cassette is connected with. For example, less tension enables more relative motion, and more tension enables less relative motion. It is noted that the tensioning system can be configured to pre-tension a respective elongated connection element of a respective connection assembly of said second set of connection assemblies in such a way that on the one hand collisions can be prevented between a respective cassette and at least one of a respective elongated rigid truss structure of said second set of elongated rigid truss structure with which the respective cassette is connected with via said respective connection assembly, and a neighboring cassette, if the number of cassettes installed in the fish farm is at least two, and that one the other hand at least one of surge, sway, pitch, roll, and yaw motions of the respective cassette are not completely prevented. By not completely preventing the afore-mentioned floating motions of the respective cassette, a kind of semi-rigid arrangement can be provided that enables avoiding excessive stresses and impulses to be exerted on the respective cassette and the respective elongated rigid truss structure of said second set of elongated rigid truss structures the respective cassette is connected with.

[0050] Similar to an elongated connection element of a connection assembly of said first set of connection assemblies, an elongated connection element of a connection assembly of said second set of connection assemblies can be a cable, a chain, a rope, a rod or any suitable combination of these elements. Depending on the specific configuration, an elongated connection element of a connection assembly of said second set of connection assemblies can comprise any suitable material such as for example metal, a polymer, a fiber-reinforced polymer, carbon or any suitable combination of these materials. In an embodiment of the semi-submersible spar-type offshore fish farm according to the invention, a respective connection assembly of the second set of connection assemblies comprises a second damping system that is associated with the elongated connection element of said respective connection assembly. In this way, tension in a respective connection assembly of the second set of connection assemblies that is used to connect a respective cassette of the number of cassettes with a respective elongated rigid truss structure of the second set of elongated rigid truss structures can be damped. As a result, peak stresses and / or sudden impulses on the respective cassette and / or the respective elongated rigid truss structure the respective cassette is connected with can be reduced. The second damping system can comprise a spring and / or a hydraulic piston.

[0051] In an embodiment of the semi-submersible spar-type offshore fish farm according to the invention, the elongated rigid truss structures of said second set of elongated rigid truss structures have smaller dimensions than the elongated rigid truss structures of said first set of elongated rigid truss structures. This is possible because a respective excess positive buoyant cassette of the number of cassettes that in use of the fish farm is connected with a respective elongated rigid truss structure of said first set of elongated rigid truss structures via a connection assembly of said first set of connection assemblies exerts an upward buoyant force on the respective elongated rigid truss structure of the first set of elongated rigid truss structures, whereas said upward buoyant force is not exerted by the respective excess positive buoyant cassette on a respective elongated rigid truss structure of said second set of elongated rigid truss structures that is connected with said respective excess positive buoyant cassette via a connection assembly of said second set of connection assemblies. Due to this asymmetry between said first set of elongated rigid truss structures and said second set of elongated rigid truss structures, the overall costs of the above-defined embodiment of the fish farm according to the present invention can be reduced relative to an embodiment of the fish farm according to the present invention comprising a first set of elongated rigid truss structures and a second set of elongated rigid truss structures having equal dimensions.

[0052] In an embodiment of the semi-submersible spar-type offshore fish farm according to the invention, the semi-rigid or rigid cage structure of a respective cassette of the number of cassettes comprises elongated tubular members that are configured and arranged to provide a semi-rigid or rigid truss structure, and wherein the netting material is associated with the elongated tubular members for containing fish within the respective cassette. The semi-rigid or rigid truss structure comprises vertically arranged elongated tubular members that are interconnected by horizontally arranged elongated tubular members and diagonally arranged elongated tubular members. The semi-rigid or rigid truss structure can be configured to enclose at least one interior space that is surrounded by netting material that is associated with the elongated tubular members. In this way, fish can be contained within the at least one interior space of the semi-rigid or rigid cage structure of the respective cassette of the fish farm according to the invention.

[0053] In an embodiment of the semi-submersible spar-type offshore fish farm according to the invention, the netting material is configured and arranged to provide at least one cassette of the number of cassettes with at least two segregated compartments for containing fish. In this way, a single cassette can be used for segregating different batches or cohorts of fish and / or for grading fish.

[0054] In an embodiment of the semi-submersible spar-type offshore fish farm according to the invention, at least one cassette of the number of cassettes is provided with a buoyancy adjustment assembly that is associated with at least one elongated tubular member of the at least one cassette, the buoyancy adjustment assembly being configured to adjust the excess positive buoyancy of the at least one cassette. The buoyancy adjustment assembly can comprise at least one controllable valve, and can be associated with a source of compressed air, such as a pressured cylinder or a generator, and a pump, such as a deep well pump. It is possible that at least one respective vertically arranged elongated tubular member of a respective cassette, i.e. an elongated tubular member that is arranged in the direction of the longitudinal center line of the elongated body of said fish farm, is provided with the at least one controllable valve of the buoyancy adjustment assembly. Alternatively or additionally, it is possible that at least one horizontally and / or diagonally arranged elongated tubular member of the respective cassette is provided with at least one controllable valve of respective buoyancy adjustment assemblies. The source of compressed air and the pump can be connected with the respective at least one controllable valve of the respective buoyancy adjustment assemblies. By opening a respective controllable valve of for example a respective vertically arranged elongated tubular member, the respective vertically arranged elongated tubular member can be ballasted with water to adjust the excess positive buoyancy of the respective cassette by decreasing the excess positive buoyancy. If the desired decreased excess positive buoyancy has been established, the respective controllable valve can be closed. The vertically arranged elongated tubular member can be de-ballasted by opening the controllable valve and removing water from the vertically arranged elongated tubular member using compressed air from the compressed air source and / or the pump. In this case, the excess positive buoyancy of the respective cassette is adjusted by increasing the excess positive buoyancy. Upon establishing the desired increased excess positive buoyancy, the respective controllable valve can be closed.

[0055] The buoyancy adjustment assembly can be used to increase the excess positive buoyancy of a fully submerged cassette. In this way, control of the floating movements of a fully submerged cassette can also be established by a combination of an increased excess positive buoyancy of said respective cassette, and the above- mentioned angle that provides counteracting floating movements in a horizontal plane.

[0056] In an embodiment of the semi-submersible spar-type offshore fish farm according to the invention, the elongated body is provided with at least one of a central power supply system, a central air supply system, a central food storage and supply system, and a central waste collection and storage system, and wherein at least one cassette of the number of cassettes is provided with at least one of a local lighting system, a local aeration system, a local food distribution and dispensing system, and a local waste collection and storage system, and a local biomass monitoring system, wherein in use of said fish farm, at least one of said local systems is operatively associated with a functionally corresponding system of said central systems. In this way, a respective cassette can individually be configured depending on the needs of the kind of fish and / or the maturity of the fish that is to be cultivated in said respective cultivating cassette.

[0057] Each one of the afore-mentioned local systems can be provided with at least one first coupling member and each one of the afore-mentioned central systems can be provided with at least one second coupling member. In use of said fish farm, a respective first coupling member of at least one of said local systems of a respective cassette can be operatively connected with a respective second coupling member of a functionally corresponding system of said central systems via at least one elongated flexible connection member that is configured and arranged to accommodate motions of the respective first coupling member and the respective second coupling member relative to each other. The respective first coupling member and the respective second coupling member can be configured as a quick coupling, such as for example a cam lock coupling to enable both easy connecting a respective local system and functionally corresponding central system with each other upon installing a respective cassette in said fish farm, and disconnecting the respective local system and functionally corresponding central system from each other upon removing the respective cassette from said fish farm.

[0058] According to another aspect of the present invention, a method of offshore installing a cassette in a semi-submersible spar-type offshore fish farm according to the invention is provided as defined in claim 14. The method comprises: setting the adjustable buoyancy of the buoyancy unit to a first value to allow the elongated body to float at a first draft relative to sea level, wherein at the first draft the elongated rigid truss structures of the first set of elongated rigid truss structures are located at a first depth relative to sea level; positioning a respective cassette of the number of cassettes, which is arranged to extend at least partially above sea level, opposite said first elongated rigid truss structure and said second elongated rigid truss structure of said first set of elongated rigid truss structures; connecting the respective cassette with: said first elongated rigid truss structure via said first connection assembly of said first set of connection assemblies; and said second elongated rigid truss structure via said second connection assembly of said first set of connection assemblies; adjusting the first value of the adjustable buoyancy of the buoyancy unit to a second value to allow the elongated body to float at a second draft relative to sea level, wherein at the second draft: the elongated rigid truss structures of the first set of elongated rigid truss structures are located at a second depth relative to sea level, the second depth being larger than the first depth; and said respective cassette that extends mainly or completely below sea level is allowed to:

[0059] ■ float at said first distance from said first elongated rigid truss structure and at said second distance from said second elongated rigid truss structure; and

[0060] ■ make floating movements relative to said first elongated rigid truss structure and said second elongated rigid truss structure.

[0061] The above-described method of installing a respective excess positive buoyant cassette in the fish farm according to the present invention at an offshore location provides the possibility to install the first connection assembly and the second connection assembly of the first set of connection assemblies using at least one remotely operated vehicle (ROV) instead of using divers. In this way the method according to the present invention can reduce the risk of injuries for the personnel while installing the respective cassette in the fish farm that is at its offshore location. It is noted that this advantage also applies if the above-described method is executed in reverse order for removing the cassette from the fish farm at its offshore location.

[0062] It is noted that the first depth relative to sea level is smaller than any other depths relative to sea level at which the elongated rigid truss structures of the first set of elongated rigid truss structures are located if the elongated body floats at any other draft. The first depth can be chosen such that the respective excess positive buoyant cassette can float above the first elongated rigid truss structure and the second elongated rigid truss structure of the first set of elongated rigid truss structures when the respective cassette is positioned for installation in the fish farm. It is also possible that the cassette floats between said first elongated rigid truss structure and said second elongated rigid truss structure. The second depth relative to sea level can be any depth larger than the first depth as long as the respective cassette is allowed to float at said first distance from said first elongated rigid truss structure while said first elongated connection element of said first connection assembly of the first set of connection assemblies is tensioned due to the excess positive buoyancy of the cassette, and at said second distance from said second elongated rigid truss structure while said second elongated connection element of said second connection assembly of the first set of connection assemblies is tensioned due to the excess positive buoyancy of the cassette. In addition, said first elongated connection element and said second elongated connection element should allow the respective cassette to make floating movements relative to said first elongated rigid truss structure and said second elongated rigid truss structure if they are at said second depth.

[0063] In an embodiment of the method according to the invention as defined in claim 15, the method comprises: setting the adjustable buoyancy of the buoyancy unit to said second value to allow the elongated body to float at said second draft relative to sea level; and connecting said respective cassette with: said first elongated rigid truss structure of said second set of elongated rigid truss structures via said first connection assembly of said second set of connection assemblies to allow said respective cassette to: ■ be arranged at said fourth distance from said first elongated rigid truss structure of said second set of elongated rigid truss structures; and

[0064] ■ make floating movements relative to said first elongated rigid truss structure of said second set of elongated rigid truss structures; and said second elongated rigid truss structure of said second set of elongated rigid truss structures via said second connection assembly of said second set of connection assemblies to allow said respective cassette to:

[0065] ■ be arranged at said fifth distance from said second elongated rigid truss structure of said second set of elongated truss structures; and

[0066] ■ make floating movements relative to said second elongated rigid truss structure of said second set of elongated rigid truss structures.

[0067] In this way, the respective cassette is connected with two elongated rigid truss structures of said first set of elongated rigid truss structures and with two elongated rigid truss structures of said second set of elongated rigid truss structures while being allowed to float spaced apart from said elongated rigid truss structures and to make floating movements with respect to said elongated rigid truss structures without colliding with any one of them. If there are several cassettes installed in the fish farm, collisions between these cassettes are also prevented as well as collisions between any one of these cassettes and the elongated body of the fish farm. By installing a respective cassette in the fish farm in accordance with the above-described embodiment of the method, control of the floating movements of the respective cassette can be improved.

[0068] The above-described embodiment of the method of installing a respective excess positive buoyant cassette in the fish farm according to the present invention at an offshore location also provides the possibility to install the connection assemblies of said first set of connection assemblies and the connection assemblies of the second set of connection assemblies using at least one remotely operated vehicle (ROV) instead of using divers. Hence, the risk of injuries for the personnel while installing the respective cassette in the fish farm that is at its offshore location can be reduced. It is noted that this advantage also applies if the above-described embodiment of the method is executed in reverse order for removing the cassette from the fish farm at its offshore location. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Further features and advantages of the invention will become apparent from the description of exemplary and non-limiting embodiments of a semi-submersible spartype offshore fish farm according to the present invention, and a method of offshore installing a cassette in which fish can be cultivated in the fish farm according to the present invention.

[0070] The person skilled in the art will appreciate that the described embodiments of the semi-submersible spar-type offshore fish farm and the method are exemplary in nature only and not to be construed as limiting the scope of protection in any way. The person skilled in the art will realize that alternatives and equivalent embodiments of the semi-submersible spar-type offshore fish farm and method can be conceived and reduced to practice without departing from the scope of protection of the present invention.

[0071] Reference will be made to the figures on the accompanying drawing sheets. The figures are schematic in nature and therefore not necessarily drawn to scale. Furthermore, equal reference numerals denote equal or similar parts.

[0072] On the attached drawing sheets, figure 1 shows a schematic side view of a first exemplary, non-limiting embodiment of a semi-submersible spar-type offshore fish farm according to the invention, the fish farm being at a second draft relative to sea level; figure 2 shows a schematic side view of the first exemplary, non-limiting embodiment of the semi-submersible spar-type offshore fish farm shown in figure 1, the fish farm being at a third draft relative to sea level; figure 3 shows a schematic side view of a respective cassette that is connected with two elongated rigid truss structures of the first set of elongated rigid truss structures via two connection assemblies of the first set of connection assemblies in accordance with a first exemplary, non-limiting embodiment of the connection assemblies of the first set of connection assemblies; figure 4 shows a schematic side view of a respective cassette that is connected with two elongated rigid truss structures of the first set of elongated rigid truss structures via two connection assemblies of the first set of connection assemblies in accordance with a second exemplary, non-limiting embodiment of the connection assemblies of the first set of connection assemblies; figure 5 shows a schematic top view of the first set of elongated rigid truss structures, the buoyancy unit, and the elongated body in accordance with the first exemplary, non-limiting embodiment of the semi-submersible spar-type offshore fish farm shown in figure 1 ; figure 6 shows a schematic top view of the first set of elongated rigid truss structures, the buoyancy unit, the elongated body, and a number of cassettes in accordance with the first exemplary, non-limiting embodiment of the semi-submersible spar-type offshore fish farm shown in figure 1; figure 7 shows a detailed schematic top view of two elongated rigid truss structures of the first set of elongated rigid truss structures, the buoyancy unit, the elongated body, and a respective cassette of the number of cassettes that is connected with the two elongated rigid truss structures in accordance with the first exemplary, nonlimiting embodiment of the semi-submersible spar-type offshore fish farm shown in figure 1 ; figure 8 shows a schematic side view of a second exemplary, non-limiting embodiment of the semi-submersible spar-type offshore fish farm according to the invention, the fish farm being at the second draft relative to sea level; figure 9 shows a schematic top view of the second set of elongated rigid truss structures, and the elongated body in accordance with the second exemplary, nonlimiting embodiment of the semi-submersible spar-type offshore fish farm shown in figure 8; figure 10 shows a schematic top view of the second set of elongated rigid truss structures, the elongated body, and a number of cassettes in accordance with the second exemplary, non-limiting embodiment of the semi-submersible spar-type offshore fish farm shown in figure 8; figure 11 shows a detailed schematic top view of two elongated rigid truss structures of the second set of elongated rigid truss structures, the elongated body, and a respective cassette of the number of cassettes that is connected with the two elongated rigid truss structures in accordance with the second exemplary, non-limiting embodiment of the semi-submersible spar-type offshore fish farm shown in figure 8; figure 12 shows a detailed schematic top view of exemplary, non-limiting embodiments of connection assemblies of the second set of connection assemblies arranged at an elongated rigid truss structure of the second set of elongated rigid truss structures shown in figure 11 ; figure 13 shows a detailed schematic side view of an exemplary, non-limiting embodiment of a first connection assembly of the second set of connection assemblies connecting an elongated tubular member of a cassette with a first elongated rigid truss structure of the second set of elongated rigid truss structures; figure 14 shows a detailed schematic front view of an exemplary, non-limiting embodiment of a third connection assembly of the second set of connection assemblies connecting the elongated tubular member of a cassette shown in figure 13 with the first elongated rigid truss structure of the second set of elongated rigid truss structures shown in figure 13; figure 15 shows a schematic perspective view of an exemplary embodiment of a respective cassette that can be installed in the semi-submersible spar-type offshore fish farm according to the invention; figure 16 shows a schematic side view of the first exemplary, non-limiting embodiment of the semi-submersible spar-type offshore fish farm shown in figure 1, the fish farm being at a first draft relative to sea level; and figure 17 shows a schematic side view of a first exemplary, non-limiting embodiment of an assembly comprising the first exemplary, non-limiting embodiment of the semi-submersible spar-type offshore fish farm shown in figure 1 , and a wind turbine.

[0073] DETAILED DESCRIPTION OF EMBODIMENTS

[0074] Figure 1 shows a schematic side view of a first exemplary, non-limiting embodiment of a semi-submersible spar-type offshore fish farm 1 for cultivating fish at open sea according to the invention. The fish farm 1 comprises an elongated body 2 that is centrally arranged in the fish farm. The elongated body 2 comprises a first end part 3, a second end part 4, and a longitudinal center line 5 that is directed from said first end part 3 to said second end part 4. In use of said fish farm, i.e. if said fish farm is operational at an offshore location but also if said fish farm is transported from an offshore location to for example a dry dock, the longitudinal center line 5 is arranged in a direction transverse to sea level 50, and said first end part 3 is arranged above said second end part 4. The fish farm further comprises a buoyancy unit 6. In accordance with the first exemplary, non-limiting embodiment of the fish farm 1 shown in figure 1 , the buoyancy unit 6 is connected with the second end part 4 of the elongated body 2. The buoyancy unit 6 can be configured to have an adjustable buoyancy to allow the elongated body 2 to float at different drafts relative to sea level 50 depending on a value of the adjustable buoyancy. The fish farm 1 also comprises a first set of at least two elongated rigid truss structures 9. Each elongated rigid truss structure 9 of said first set of elongated rigid truss structures has a free end part 11 and a bound end part 10 that is associated with the elongated body 2 via the buoyancy unit 6. It is noted that the first set of elongated rigid truss structures 9 can also be connected directly with the second end part 4 of the elongated body 2. In that case, the buoyancy unit 6 can be associated with another portion of the elongated body 2 in such a way that the buoyancy unit 6 allows the elongated body to float at different drafts relative to sea level 50 depending on the value of the adjustable buoyancy of the buoyancy unit. The elongated rigid truss structures 9 of said first set of elongated rigid truss structures are arranged transverse to the elongated body 2, and positioned next to each other and spaced apart in a circumferential direction of the elongated body 2.

[0075] If the fish farm is operational at an offshore location a number of cassettes 7 can be arranged around the elongated body 2. In the side view shown in figure 1, two cassettes of the number of cassettes are visible. Any suitable number of cassettes starting from one can be installed in the fish farm. Each cassette 7 has a semi-rigid or rigid cage structure that is configured to have excess positive buoyancy, and is provided with netting material 8 that is associated with the semi-rigid or rigid cage structure to enable fish to be contained within the cassette.

[0076] The fish farm 1 further comprises a first set of connection assemblies 12. Each connection assembly 12 of said first set of connection assemblies comprises an elongated connection element 13. As shown in more detail in figure 3, a first connection assembly 12a of said first set of connection assemblies is arranged to connect a cassette 7 with a first elongated rigid truss structure 9a of said first set of elongated rigid truss structures at a first distance, d1, from each other as seen in a direction of the longitudinal center line 5 of the elongated body 2. A second connection assembly 12b of said first set of connection assemblies is arranged to connect the cassette 7 with a second elongated rigid truss structure 9b of said first set of elongated rigid truss structures at a second distance, d2, from each other as seen in the direction of the longitudinal center line 5 of the elongated body 2. At least a part of a first elongated connection element 13a of said first connection assembly 12a is arranged to extend over a part said first distance, d1 , and at least a part of a second elongated connection element 13b of said second connection assembly 12b is arranged to extend over a part of said second distance, d2. Said first connection assembly 12a and said second connection assembly 12b can be configured such that the first elongated connection element 13a and the second elongated connection element 13b can have an adjustable length. This will be described in further detail having regard to figure 2. Because of the adjustable length of said first elongated connection element 13a and said second elongated connection element 13b, the first distance, d1 , and the second distance, d2, can be any suitable distances that on the one hand allow floating movements of the cassette 7 relative to said first elongated rigid truss structure 9a and said second elongated rigid truss structure 9b, and on the other hand prevent collisions between at least one of the cassette 7 and the elongated body 2, and between neighboring cassettes if the number of cassettes arranged in the fish farm is at least two. Said floating movements of the cassette 7 relative to said first elongated rigid truss structure 9a and said second elongated rigid truss structure 9b can be independent floating movements except for heave, pitch and roll movements of the cassette 7 that are restricted as a result of said first connection assembly 12a and said second connection assembly 12b.

[0077] Figure 1 shows the fish farm 1 while being at a second draft relative to sea level 50, i.e. the elongated rigid truss structures 9a, 9b are at a second depth, D2, relative to sea level 50 and the cassettes 7 extend mainly below sea level 50. It is also possible that the cassettes 7 are completely below sea level 50 but close to sea level 50. Figure 16 shows the fish farm 1 while being at a first draft relative to sea level 50, i.e. the elongated rigid truss structures 9a, 9b are at a first depth, D1 , relative to sea level 50 and the cassettes 7 extend mainly above sea level 50. The first depth, D1, can be smaller than any other depths relative to sea level 50 at which the elongated rigid truss structures of the first set of elongated rigid truss structures are located if the elongated body 2 floats at any other drafts. Therefore, the first depth, D1, is smaller than the second depth, D2.

[0078] By way of example only, figure 1 schematically shows that two connection assemblies 12 of the first set of connection assemblies each comprise a first damping system 22 that is associated with the respective elongated connection element 13 of the respective connection assembly. In this way, tension in the respective connection assembly that is used to connect the respective cassette 7 with a respective elongated rigid truss structure 9 of the first set of elongated rigid truss structures can be damped. As a result, peak stresses and / or sudden impulses on the respective cassette 7 and / or the respective elongated rigid truss structure 9 the respective cassette is connected with can be reduced. The first damping systems 22, which in figure 1 are represented in a schematic way only, can comprise a spring and / or a hydraulic piston.

[0079] Figure 2 shows a schematic side view of the first exemplary, non-limiting embodiment of the semi-submersible spar-type offshore fish farm 1 shown in figure 1, the fish farm 1 being at a third draft relative to sea level 50. At the third draft, the elongated rigid truss structures 9 are arranged at a distance, D3, from sea level 50 that is sufficient to reduce and ideally prevent stress on the fully submerged cassettes 7 due to bad weather conditions that cause strong currents at and / or close to sea level 50.

[0080] As mentioned above, the connection assemblies 12 of the first set of connection assemblies can be configured such that their respective elongated connection elements 13 have adjustable lengths. An advantage of the adjustable lengths of the elongated connection elements 13 is that a cassette 7 can individually be brought to sea level 50 to allow harvesting while the other cassettes remain fully submerged. For this purpose, the connection assemblies of the first set of connection assemblies can comprise a chain / sheave / winch system (not shown).

[0081] Figure 3 shows a schematic side view of a cassette 7 that is connected with two elongated rigid truss structures 9a, 9b of the first set of elongated rigid truss structures via two connection assemblies 12a, 12b of the first set of connection assemblies in accordance with a first exemplary, non-limiting embodiment of the connection assemblies of the first set of connection assemblies. As explained above, because of the excess positive buoyancy of the cassette 7, the elongated connection elements 13a, 13b, are tensioned when the fish farm 1 is at the second draft relative to sea level 50 as shown in figure 1. The elongated connection elements 13a, 13b have first end parts that are connected with pad-eyes that are connected with the cassette 7, and second end parts that are connected with pad-eyes that are connected with so- called strong boxes 41, i.e. reinforced parts, of the elongated rigid truss structures 9a, 9b.

[0082] In accordance with the first embodiment of the connection assemblies of the first set of connection assemblies, the elongated connection elements 13 are resilient if they are not tensioned as a result of the excess positive buoyancy of the cassette with which they are connected. The resilient elongated connection elements 13 can comprise a cable, a chain, a rope, a rod or any suitable combination of these elements. Depending on the specific configuration, the elongated connection element 13 can comprise any suitable material such as for example a metal, a polymer, a fiber-reinforced polymer, carbon or any suitable combination of these materials.

[0083] Figure 4 shows a schematic side view of a cassette 7 that is connected with two elongated rigid truss structures 9a, 9b of the first set of elongated rigid truss structures via two connection assemblies 12a, 12b of the first set of connection assemblies in accordance with a second exemplary, non-limiting embodiment of the connection assemblies of the first set of connection assemblies. In accordance with the second embodiment of the connection assemblies of the first set of connection assemblies, the elongated connection elements 13 are rigid elongated elements. To connect the rigid elongated elements 13a, 13b with the cassette 7 and the two elongated rigid truss structures 9a, 9b, the cassette 7 is provided with respective first mechanical connectors 36a, 36b, each comprising a first threaded part. Each of the elongated rigid truss structures 9a, 9b is provided with a respective second mechanical connector 37a, 37b, each comprising a second threaded part. The end parts of the respective rigid elongated elements 13a, 13b can be provided with threaded sections comprising threads that are complementary to the threads of the threaded parts of the respective first mechanical connector 36a and second mechanical connector 36b. Upon connecting the respective threaded sections of the rigid elongated elements 13a, 13b with the threaded parts of the respective first mechanical connector 36a and second mechanical connector 36b, the cassette 7 is connected with the elongated rigid truss structures 9a, 9b.

[0084] As a result of connecting the cassette 7 with the elongated rigid truss structures 9a, 9b via the rigid elongated connection elements 13, 13b, at least one of surge, sway, heave, roll, pitch, and yaw motions of the cassette 7 relative to the elongated rigid truss structures 9a, 9b can be prevented.

[0085] Figure 5 shows a schematic top view of the first set of elongated rigid truss structures 9, the buoyancy unit 6, and the elongated body 2 in accordance with the first exemplary, non-limiting embodiment of the semi-submersible spar-type offshore fish farm 1 shown in figure 1 . In accordance with this embodiment of the fish farm 1 , an exemplary number of six cassettes 7 in total can be installed. This is shown in figure 6. The total number of cassettes can be any desired and suitable number, i.e. two, three, four, five, six, seven, eight, nine, ten, twelve, twenty, and so on, depending on the size of the fish farm. Figure 6 shows, by way of example only, that one cassette 7 is provided with four attachment systems 14 that and arranged to interconnect three cassettes. The three interconnected cassettes provide a compartmentalized cage segment of the fish farm 1. It is also possible to establish several groups of interconnected cassettes that provide several compartmentalized cage segments. The number of interconnected cassettes, the number of groups of interconnected cassettes, i.e. the number of compartmentalized cage segments, can be any suitable number depending on for example the specific requirements of the fish farm and / or the size of the elongated rigid truss structures 9 of the first set of elongated rigid truss structures. It is possible that each cassette 7 of the number of cassettes or a selected group of cassettes of the number of cassettes is provided with a respective attachment system 14 or a plurality of respective attachment systems 14.

[0086] Figure 7 shows a detailed schematic top view of two elongated rigid truss structures 9a, 9b of the first set of elongated rigid truss structures, the buoyancy unit 6, the elongated body 2, and a cassette 7 of the number of cassettes that is connected with the two elongated rigid truss structures 9a, 9b in accordance with the first exemplary, non-limiting embodiment of the semi-submersible spar-type offshore fish farm shown in figure 1. The cassette 7 is arranged partially above the elongated rigid truss structures 9a, 9b and the buoyancy unit 6. The cassette is connected with the respective so-called strong boxes 41 , i.e. reinforced parts, of the respective elongated rigid truss structures 9a, 9b of the first set of elongated rigid truss structures.

[0087] Figure 8 shows a schematic side view of a second exemplary, non-limiting embodiment of the semi-submersible spar-type offshore fish farm 1 according to the invention. The fish farm 1 is at the second draft relative to sea level 50, i.e. the elongated rigid truss structures 9 of the first set of elongated rigid truss structures are at the second depth, D2, relative to sea level 50 and the cassettes 7 extend mainly below sea level 50. Hence, the elongated connection elements 13 of the connection assemblies 12 of the first set of connection assemblies are tensioned due to the excess positive buoyancy of the cassettes 7 with which they are connected.

[0088] In accordance with the second exemplary, non-limiting embodiment of the semisubmersible spar-type offshore fish farm 1 shown in figure 8, the fish farm 1 comprises elongated rigid truss structures 15 of a second set of at least two elongated rigid truss structures. Each elongated rigid truss structure 15 of said second set of elongated rigid truss structures has a free end part 17, and a bound end part 16 that is connected with the elongated body 2 at a location that is closer to the first end part 3 than to the second end part 4 of the elongated body 2. Figure 9 shows that the elongated rigid truss structures 15 of said second set of elongated rigid truss structures are arranged transverse to the elongated body 2, and that they are positioned next to each other and spaced apart in a circumferential direction of the elongated body 2. Comparison with figure 5 shows that the elongated rigid truss structures 15 of the second set of elongated rigid truss structures are in alignment with the elongated rigid truss structures 9 of the first set of elongated rigid truss structures.

[0089] Figure 8 shows that the elongated rigid truss structures 15 of the second set of elongated rigid truss structures are arranged at a third distance, d3, from said first set of elongated rigid truss structures as seen in the direction of the longitudinal center line 5 of the elongated body 2. The third distance, d3, allows each cassette 7 of the number of cassettes that in use of the fish farm 1 are arranged around the elongated body 2 to be arranged between the elongated rigid truss structures 9 of said first set of elongated rigid truss structures and the elongated rigid truss structures 15 of said second set of elongated rigid truss structures as seen in the direction of the longitudinal center line 5 of the elongated body 2.

[0090] Figures 11-14 show that in accordance with the second exemplary, non-limiting embodiment of the semi-submersible spar-type offshore fish farm 1 shown in figure 8, the fish farm 1 comprises a second set of connection assemblies 18. Each connection assembly 18a, 18b of said second set of connection assemblies comprises a respective elongated connection element 19a, 19b.

[0091] Figure 11 shows that a first connection assembly 18a of said second set of connection assemblies is arranged to connect a cassette 7, which is connected with the first elongated rigid truss structure 9a and the second elongated rigid truss structure 9b of said first set of elongated rigid truss structures via said first connection assembly 12a, and said second connection assembly 12b of said first set of connection assemblies (not explicitly shown but analogous to figure 3), with a first elongated rigid truss structure 15a of said second set of elongated rigid truss structures at a fourth distance, d4, from each other. A second connection assembly 18b of said second set of connection assemblies 18 is arranged to connect said cassette 7 with a second elongated rigid truss structure 15b of said second set of elongated rigid truss structures at a fifth distance, d5, from each other. A part of a first elongated connection element 19a of said first connection assembly 18a of said second set of connection assemblies is arranged to extend over at least a part of said fourth distance, d4, and a part of a second elongated connection element 19b of said second connection assembly 18b of said second set of connection assemblies is arranged to extend over at least a part of said fifth distance, d5. Said first elongated connection element 19a of said first connection assembly 18a of said second set of connection assemblies and said second elongated connection element 19b of said second connection assembly 18b of said second set of connection assemblies being configured to allow floating movements of said cassette 7 relative to said first elongated rigid truss structure 15a and said second elongated rigid truss structure 15b of said second set of elongated rigid truss structures.

[0092] From figures 8-14 it becomes clear that in accordance with the second exemplary, non-limiting embodiment of the semi-submersible spar-type offshore fish farm 1, a respective cassette 7 of the number of cassettes is not only connected with a first elongated rigid truss structure 9a of the first set of elongated rigid truss structures via a first connection assembly 12a of the first set of connection assemblies, and a second elongated rigid truss structure 9b of the first set of elongated rigid truss structures via a second connection assembly 12b of the first set of connection assemblies, but also with a first elongated rigid truss structure 15a of the second set of elongated rigid truss structures via a first connection assembly 18a of the second set of connection assemblies, and a second elongated rigid truss structure 15b of the second set of elongated rigid truss structures via a second connection assembly 18b of the second set of connection assemblies. Hence, after installation in the fish farm 1 according to the present invention, the respective cassette 7 floats at:

[0093] - said first distance, d1, as seen in the direction of the longitudinal center line 5 of the elongated body 2 with respect to the first elongated rigid truss structure 9a of the first set of elongated rigid truss structures;

[0094] - said second distance, d2, as seen in the direction of the longitudinal center line 5 of the elongated body 2 with respect to the second elongated rigid truss structure 9b of the first set of elongated rigid truss structures;

[0095] - said fourth distance, d4, from the first elongated rigid truss structure 15a of the second set of elongated rigid truss structures; and

[0096] - said fifth distance, d5, from the second elongated rigid truss structure 15b of the second set of elongated rigid truss structures.

[0097] Said first distance, d1 , second distance, d2, fourth distance, d4, and fifth distance, d5, can be any suitable distance as long as collisions can be prevented between at least one of the respective cassette 7 and the elongated body 2, between the respective cassette 7 and the first elongated rigid truss structure 15a and the second elongated rigid truss structure 15b of said second set of elongated rigid truss structures, and between neighboring cassettes 7 if the number of cassettes arranged in the fish farm 1 is at least two. As mentioned above, said first distance, d1, and second distance, d2, can be equal but it is also possible that said first distance, d1, and second distance, d2, are different. Analogously, said fourth distance, d4, can be equal to said fifth distance, d5, but it is also possible that said fourth distance, d4, and fifth distance, d5, are different.

[0098] The floating movements of the respective cassette 7 relative to said first elongated rigid truss structure 9a and said second elongated rigid truss structure 9b of said first set of elongated rigid truss structures, and said first elongated rigid truss structure 15a and said second elongated rigid truss structure 15b of said second set of elongated rigid truss structures, can be at least one of independent but limited surge, sway and yaw movements. Heave, pitch and roll movements of the respective cassette 7 are restricted as a result of the first connection assembly 12a and the second connection assembly 12b of the first set of connection assemblies that connect the respective excess positive buoyant cassette 7 with said first elongated rigid truss structure 9a and said second elongated rigid truss structure 9b, respectively of said first set of elongated frigid truss structures, and the first connection assembly 18a and the second connection assembly 18b of the second set of connection assemblies that connect the respective excess positive buoyant cassette 7 with said first elongated rigid truss structure 15a and said second elongated rigid truss structure 15b, respectively of said second set of elongated frigid truss structures.

[0099] Figure 9 shows a schematic top view of the second set of elongated rigid truss structures 15, and the elongated body 2 in accordance with the second exemplary, non-limiting embodiment of the semi-submersible spar-type offshore fish farm 1 shown in figure 8. Comparing figure 9 with figure 5, which shows the elongated rigid truss structures 9 of the first set of elongated rigid truss structures, it can be concluded that the elongated rigid truss structures 15 of the second set of elongated rigid truss structures have smaller dimensions than the elongated rigid truss structures 9 of the first set of elongated rigid truss structures. This is possible because a respective excess positive buoyant cassette 7 of the number of cassettes that in use of the fish farm 1 is connected with a respective elongated rigid truss structure 9 of said first set of elongated rigid truss structures via a connection assembly 12 of said first set of connection assemblies exerts an upward buoyant force on the respective elongated rigid truss structure 9 of the first set of elongated rigid truss structures, whereas said upward buoyant force is not exerted by the respective excess positive buoyant cassette 7 on a respective elongated rigid truss structure 15 of said second set of elongated rigid truss structures that is connected with said respective excess positive buoyant cassette 7 via a connection assembly 18 of said second set of connection assemblies. Due to this asymmetry between said first set of elongated rigid truss structures 9 and said second set of elongated rigid truss structures 15, the overall costs of the above-defined embodiment of the fish farm 1 according to the present invention can be reduced relative to an embodiment of the fish farm according to the present invention comprising a first set of elongated rigid truss structures and a second set of elongated rigid truss structures having equal dimensions.

[0100] Figure 10 shows a schematic top view of the second set of elongated rigid truss structures 15, the elongated body 2, and a number of cassettes 7 in accordance with the second exemplary, non-limiting embodiment of the semi-submersible spar-type offshore fish farm 1 shown in figure 8.

[0101] Figure 12 shows a detailed schematic top view of exemplary, non-limiting embodiments of connection assemblies 18 of the second set of connection assemblies arranged at an elongated rigid truss structure 15a of the second set of elongated rigid truss structures shown in figure 11. The first connection assembly 18a and the third connection assembly 18c are described in more detail having regard to figures 13 and 14, respectively.

[0102] Figure 13 shows a detailed schematic side view of an exemplary, non-limiting embodiment of the first connection assembly 18a of the second set of connection assemblies connecting an elongated tubular member 25 of a cassette 7 with a first elongated rigid truss structure 15a of the second set of elongated rigid truss structures. It is noted that for the sake of clarity only one vertically arranged elongated tubular member 25 of the cassette 7 is shown. The connections between the other vertically arranged elongated tubular members 25 of the cassette 7 with a respective strong box 41 of the first elongated rigid truss structure 15a are established in a similar fashion.

[0103] The first connection assembly 18a of the second set of connection assemblies comprises first elongated connection element, a first pad-eye 42 that is connected with the vertically arranged elongated tubular member 25 of the cassette 7, a first sheave 43 that is connected with a first side of the first elongated rigid truss structure 15a that is facing away from the cassette 7, a first roller sheave 44 that is connected with a second side of the first elongated rigid truss structure 15a that is arranged to face in an opposite direction of the first side of the first elongated rigid truss structure 15a, and a first chain stopper 45 that is arranged at the first side of the first elongated rigid truss structure 15a. By way of example only, the first elongated connection element is a cable 20 having an end part that is connected with a chain section 21. Starting from the first pad-eye 42 that is connected with the cable 20 and the vertically arranged tubular member 25 of the cassette 7, the cable 20 runs through the first pivoting roller sheave 44 at the second side of the first elongated rigid truss structure 15a to the first sheave 43 at the first side of the first elongated rigid truss structure 15a from where the cable 20 is guided towards the first chain stopper 45 further along the first side of the first elongated rigid truss structure 15a. The chain section 21 is connected with the first chain stopper 45. Alternatively (not shown), the cable 20 can be run from the first pivoting roller sheave 44 directly to the first chain stopper 45.

[0104] The first connection assembly 18a further comprises a tensioning system 23 that is connected with the first chain stopper 45 and configured to tension or pre-tension the cable 20 in such a way that on the one hand collisions can be prevented between the cassette 7 and at least one of the first elongated rigid truss structure 15a, and a neighboring cassette, if the number of cassettes installed in the fish farm is at least two, and that one the other hand at least one of surge, sway, pitch, roll, and yaw motions of the respective cassette are not completely prevented. By not completely preventing the afore-mentioned floating motions of the cassette, a kind of semi-rigid arrangement can be provided that enables avoiding excessive stresses and impulses to be exerted on the cassette and the first elongated rigid truss structure 15a the cassette is connected with. For example, less tension or pre-tension enables more relative motion, and more tension enables less relative motion.

[0105] By way of example only, the tensioning system 23 is presented in figure 13 as comprising a cable having an end part that is provided with a chain section that is connected with the first chain stopper 45. The other end part of the cable of the tensioning system 23 is connected with a pad-eye. It is also possible to apply a tensioning system having a completely different configuration as long as the cable 20 of the first connection assembly 18a can be tensioned and / or pre-tensioned.

[0106] It is noted that each elongated element of each connection assembly 18 of the second set of connection assemblies can be provided with a tensioning system. It is also possible to configure a tensioning system that allows multiple elongated connection elements to be individually tensioned and / or pre-tensioned. Figure 14 shows a detailed schematic front view of an exemplary, non-limiting embodiment of the third connection assembly 18c of the second set of connection assemblies connecting the elongated tubular member 25 of a cassette shown in figure 13 with the first elongated rigid truss structure 15a of the second set of elongated rigid truss structures shown in figure 13. Again, it is noted that for the sake of clarity only one vertically arranged elongated tubular member 25 of the cassette 7 is shown. The connections between the other vertically arranged elongated tubular members 25 of the cassette 7 with a respective strong box 41 of the first elongated rigid truss structure 15a are established in a similar fashion.

[0107] The third connection assembly 18c of the second set of connection assemblies comprises a third elongated connection element, a second pad-eye 42 that is connected with the vertically arranged elongated tubular member 25 of the cassette 7, a second sheave 43 that is connected with the first side of the first elongated rigid truss structure 15a, a second roller sheave 44 that is connected with the second side of the first elongated rigid truss structure 15a, and a second chain stopper 45 that is arranged at the first side of the first elongated rigid truss structure 15a. By way of example only, the third elongated connection element is a cable 20 having an end part that is connected with a chain section 21. Starting from the second pad-eye 42 that is connected with the cable 20 and the vertically arranged tubular member 25 of the cassette 7, the cable 20 runs through the second pivoting roller sheave 44 at the second side of the first elongated rigid truss structure 15a to the second sheave 43 at the first side of the first elongated rigid truss structure 15a from where the cable 20 is guided towards the second chain stopper 45. The chain section 21 is connected with the second chain stopper 45. Alternatively (not shown), the cable 20 can be run from the second pivoting roller sheave 44 directly to the second chain stopper 45.

[0108] The third connection assembly 18c further comprises a second damping system 24 that is associated with the cable 20 and configured to dampen tension in the cable 20 that interconnects the cassette and the first elongated rigid truss structure 15a. As a result, peak stresses and / or sudden impulses exerted on the cassette and / or the first elongated rigid truss structure 15a can be reduced. Although not shown, the second damping system 24 can comprise a spring and / or a hydraulic piston.

[0109] Figure 15 shows a schematic perspective view of an exemplary embodiment of a cassette 7 that can be installed in the semi-submersible spar-type offshore fish farm 1 according to the invention. The cassette 7 comprises vertically arranged elongated tubular members 25 that are interconnected by horizontally arranged elongated tubular members 25 and diagonally arranged elongated tubular members 25 to provide a semi-rigid or rigid truss structure having an excess positive buoyancy. As a result, the cassette 7 is an independently free floating stable structure as such that can be wet-towed between the offshore location of the fish farm and a dry dock.

[0110] The elongated tubular members 25 can have any suitable polygonal cross-section, for example circular or square, and comprise any suitable material, for example steel, glass fiber reinforced plastic (GRP), fiber reinforced plastic (FRP), high-density polyethylene (HDPE) or any suitable combination of these materials. The semi-rigid or rigid cage structure can have any suitable polygonal shape, for example triangular, rectangular, hexagonal, circular. A respective cassette can have a volume of ranging from 10,000m3to 100,000m3.

[0111] Netting material 8 is associated with the elongated tubular members 25 for containing fish within the cassette 7. It is noted that netting material 8 covering the top of the cassette 7 is not shown in order to provide a clearer view on the internal arrangement of the exemplary embodiment of the cassette 7 shown in figure 15.

[0112] The netting material 8 is configured and arranged to provide the semi-rigid or rigid truss structure shown in figure 15 with three segregated compartments 26. In this way, a single cassette 7 can be used for segregating different batches or cohorts of fish and / or for grading fish. It is noted that several types of cassettes, i.e. cassettes having for example different internal arrangements, can be installed together in the fish farm 1.

[0113] In accordance with the exemplary embodiment of the cassette 7 shown in figure 15, the cassette 7 is provided with two buoyancy adjustment assemblies 27 by way of example only and can be internal buoyancy adjustments assemblies as well. The two buoyancy adjustment assemblies 27 are associated with two vertically arranged elongated tubular member 25 of the cassette 7 also by way of example only. The buoyancy adjustment assemblies 27 are configured to adjust the excess positive buoyancy of the cassette 7. Although not explicitly shown, each buoyancy adjustment assembly 27 can comprise at least one controllable valve, and can be associated with a source of compressed air, such as a pressured cylinder or a generator, and a pump, such as a deep well pump. The source of compressed air and the pump can be connected with the respective at least one controllable valve of the respective buoyancy adjustment assemblies 27. By opening at least one of the respective controllable valves, the respective vertically arranged elongated tubular member 25 can be ballasted with water to adjust the excess positive buoyancy of the cassette 7 by decreasing the excess positive buoyancy. If the desired decreased excess positive buoyancy has been established, the respective controllable valve can be closed.

[0114] The vertically arranged elongated tubular member 25 can be de-ballasted by opening the controllable valve and removing water from the vertically arranged elongated tubular member 25 using compressed air from the compressed air source and / or the pump. In this case, the excess positive buoyancy of the respective cassette 7 is adjusted by increasing the excess positive buoyancy. Upon establishing the desired increased excess positive buoyancy, the respective controllable valve can be closed.

[0115] In accordance with the exemplary embodiment of the fish farm shown in figure 16, the elongated body 2 is provided with at least one of a central power supply system 28, a central air supply system 29, a central food storage and supply system 30, and a central waste collection and storage system 31. At least one cassette 7 of the number of cassettes is provided with at least one of a local lighting system 32, a local aeration system 33, a local food distribution and dispensing system 34, a local waste collection and storage system 35, and a local biomass monitoring system 51 , for example a fish monitoring system. It is noted that the afore-mentioned central systems and local systems are only schematically presented in figure 16.

[0116] In use of said fish farm 1 , at least one of said local systems is operatively associated with a functionally corresponding system of said central systems. In this way, a respective cassette can individually be configured depending on the needs of the kind of fish and / or the maturity of the fish that is to be cultivated in said respective cultivating cassette. For example, the central power supply system 28 can provide power for amongst others signaling cables, remotely operated vehicles (ROVs), and at least one of the local systems, i.e. the local lighting system 32, the local aeration system 33, the local food distribution and dispensing system 34, the local waste collection and storage system 35, and the local biomass monitoring system 51. These functions can be combined into one umbilical cord inside the elongated body 2 with a flexible connection to a respective cassette 7. The power can be supplied via flexible connections between a respective cassette and a submersible junction box (not shown) that can be arranged at the elongated body of the fish farm.

[0117] Figure 16 shows that the fish farm 1 is at a first draft relative to sea level 50, i.e. if the elongated rigid truss structures 9 are at the first depth, D1 , relative to sea level 50 and the cassettes 7 extend mainly above sea level 50. To arrange a cassette 7 mainly above sea level 50, for example the vertical tubular members 25 of the cassette 7 can be de-ballasted, i.e. removing water from the vertical tubular members through one or more controllable valves that can be arranged at or near the top of the vertical tubular members 25 using for example compressed air or a pump. A cassette 7 will be at the lowest possible draft, with the largest freeboard, i.e. with the largest part of the cassette 7 being arranged above sea level 50, when the vertical tubular members 25 are de-ballasted. In the context of this invention, this draft of the cassette 7 is referred to as “shallow draft”, and is used to transport a cassette 7 between an offshore location of the fish farm 1 and a dry dock, the shore or a port.

[0118] Prior to arrival of the cassette 7 at the fish farm, the fish farm 1 will be brought to said first draft, also referred to as surface draft. Once the cassette 7 is positioned opposite two elongated rigid truss structures 9a, 9b of the first set of elongated rigid truss structures, guidewires or towing ropes from the cassette 7 and support vessels used during transport of the cassette to the fish farm are handed over to the fish farm. The guidewires are connected via sheave blocks that are arranged at the elongated rigid truss structures of the first set of elongate truss structures to a winch. Using the guidewires or towing ropes, the cassette is pulled towards the elongated body 2 of the fish farm. In addition to the guidewires or towing ropes, the support vessels can be used to push the cassette towards the elongated body 2 that is arranged in the center of the fish farm. Once the cassette is in position, the compressed air in the vertical tubular members 25 can be released to ballast the vertical tubular members 25 of the cassette, i.e. allowing water to flow into the vertical tubular members 25. In fully ballasted conditions, all vertical tubular members 25, and possibly also some or all of the horizontal tubular members 25, are filled with water and the cassette is at its deepest possible draft, with the smallest freeboard, i.e. with the smallest part of the cassette above sea level 50. In the context of this invention, this draft of the cassette 7 is referred to as “deep draft”, and is used to connect a cassette 7 with two the elongated rigid truss structures 9 of the first set of elongated rigid truss structures using the connection assemblies of the first set of connection assemblies. Alternatively, once the cassette is positioned opposite the two elongated rigid truss structures of the first set of elongated rigid truss structures as shown in figures 3 or 6, the cassette can be ballasted to deep draft using facilities on the support vessel.

[0119] The elongated connection elements 13 of the connection assemblies 12 of the first set of connection assemblies can be referred to as tendons and can comprise aramid wires. The elongated connection elements 13 can be of fixed length or their length can be adjusted at a service deck of the fish farm and / or at the level of the elongated rigid truss structures of the first set of elongated rigid truss structures. The elongated connection elements 13 can be connected with the cassette 7 and the elongated rigid truss structures 9 of the first set of elongated rigid truss structures using ROVs and / or ROV operated shackles.

[0120] With the cassette 7 in position and connected with the two elongated rigid truss structures 9a, 9b of the first set of elongated rigid truss structures, the fish farm 1 is brought to the second draft, i.e. if the elongated rigid truss structures 9 are at the second depth, D2, relative to sea level 50 and the cassette 7 extends mainly below sea level 50 as shown in figure 1. The elongated connection elements 13 of the connection assemblies 12 of the first set of connection assemblies are then tensioned as a result of the excess positive buoyancy of the cassette 7. To increase the excess positive buoyancy of the cassette 7, the vertical tubular members 25 and / or the horizontal tubular members 25 of the cassette 7 can be de-ballasted. This ensures that the elongated connection elements 13 will remain tensioned during all modes of operation of the fish farm, except maintenance mode, and irrespective of all weather conditions. The fish farm 1 according to the present invention functions as an anchoring platform for each individual cassette 7.

[0121] The tension in the elongated connection elements 13 as result of the excess positive buoyancy of the cassette 7 will exert a positive buoyant upward force on the fish farm while the fish farm will keep the cassette 7 submerged. The excess positive buoyancy of the cassette that exerts a net upward force on the cassette will, under all operating conditions, restrict the heave motion of the cassette. As mentioned above, in addition all elongated connection elements 13 will always be tensioned. The fish farm is configured such that the cassette will exert a net upward force on the fish farm above the center of gravity of the fish farm. As a result, the stability of the fish farm is improved. The upward buoyancy increases the stability of the entire fish farm and improves the motions of the fish farm 1.

[0122] The above-mentioned steps can also be followed for connecting a cassette with the elongated rigid truss structures 9 of the first set of elongated rigid truss structures in the fish farm 1 shown in figure 8. For connecting the cassette with the elongated rigid truss structures 15 of the second set of elongated rigid truss structures, the following steps need to be added: set the adjustable buoyancy of the buoyancy unit 6 to said second value to allow the elongated body 2 to float at said second draft relative to sea level 50 as shown in figure 8; and connect the cassette 7 with: said first elongated rigid truss structure 15a of said second set of elongated rigid truss structures via said first connection assembly 18a of said second set of connection assemblies as shown in figure 11 to allow the cassette 7 to:

[0123] ■ be arranged at said fourth distance, d4, from said first elongated rigid truss structure 15a of said second set of elongated rigid truss structures; and

[0124] ■ make floating movements relative to said first elongated rigid truss structure 15a of said second set of elongated rigid truss structures; and said second elongated rigid truss structure 15b of said second set of elongated rigid truss structures via said second connection assembly 18b of said second set of connection assemblies to allow the cassette 7 to:

[0125] ■ be arranged at said fifth distance, d5, from said second elongated rigid truss structure 15b of said second set of elongated truss structures; and

[0126] ■ make floating movements relative to said second elongated rigid truss structure 15b of said second set of elongated rigid truss structures.

[0127] In this way, the cassette 7 is allowed to float spaced apart from said elongated rigid truss structures 9a, 9b, 15a, 15b and to make floating movements with respect to said elongated rigid truss structures 9a, 9b, 15a, 15b without colliding with any one of them. If there are several cassettes installed in the fish farm, collisions between these cassettes are also prevented as well as collisions between any one of these cassettes and the elongated body 2 of the fish farm 1 .

[0128] The person skilled in the art will appreciate that there are equivalent methods to the method described above for offshore installing an excess positive buoyant cassette in the fish farm according to the present invention falling within the scope of the present invention. These equivalent methods can comprise steps focusing on the ballasting and de-ballasting of the excess positive buoyant cassette instead of the ballasting and de-ballasting of the buoyancy unit 6 of the fish farm for positioning the cassette and the elongated rigid truss structures of the first set of elongated rigid truss structures and / or the elongated rigid truss structures of the second set of elongated rigid truss structures with respect to each other, and for tensioning the elongated connection elements 13 of the connection assemblies 12 of the first set of connection assemblies.

[0129] Figure 17 shows a schematic side view of a first exemplary, non-limiting embodiment of an assembly comprising the first exemplary, non-limiting embodiment of the semi-submersible spar-type offshore fish farm 1 shown in figure 1 , and a wind turbine 40 that is associated with the first end part 3 of the elongated body 2. In this way, the semi-submersible spar-type offshore fish farm 1 according to the present invention can advantageously be applied in the field of offshore floating wind turbines and / or wind power plants.

[0130] The present invention can be summarized as relating to a semi-submersible spartype offshore fish farm 1 for cultivating fish at open sea that in use comprises a number of cassettes 7 each having an excess positive buoyancy and being a floating stable netted cage structure. A respective cassette can be connected with respective first and second elongated rigid truss structures 9 of a first set of elongated rigid truss structures of said fish farm via respective first and second connection assemblies 12 of a first set of connection assemblies of said fish farm that allow said cassette to float above said first and second truss structures. Said first and second connection assemblies comprise respective elongated connection elements 13 extending between said cassette and said first and second truss structures allowing floating movements of said cassette relative to said first and second truss structures. The invention also relates to a method of offshore installing a cassette in said fish farm.

[0131] It will be clear to a person skilled in the art that the scope of the present invention is not limited to the examples discussed in the foregoing but that several amendments and modifications thereof are possible without deviating from the scope of the present invention as defined by the attached claims. In particular, combinations of specific features of various aspects of the invention may be made. An aspect of the invention may be further advantageously enhanced by adding a feature that was described in relation to another aspect of the invention. While the present invention has been illustrated and described in detail in the figures and the description, such illustration and description are to be considered illustrative or exemplary only, and not restrictive.

[0132] The present invention is not limited to the disclosed embodiments. Variations to the disclosed embodiments can be understood and effected by a person skilled in the art in practicing the claimed invention, from a study of the figures, the description and the attached claims. In the claims, the word “comprising” does not exclude other steps or elements, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference numerals in the claims should not be construed as limiting the scope of the present invention.

Claims

CLAIMS1. A semi-submersible spar-type offshore fish farm (1) for cultivating fish at open sea, comprising: an elongated body (2) that comprises a first end part (3), a second end part (4), and a longitudinal center line (5) that is directed from said first end part (3) to said second end part (4), the longitudinal center line (5) in use of said fish farm being arranged in a direction transverse to sea level, and said first end part (3) being arranged above said second end part (4); a buoyancy unit (6) that is associated with the elongated body (2), the buoyancy unit (6) being configured to have an adjustable buoyancy to allow the elongated body (2) to float at different drafts relative to sea level depending on a value of the adjustable buoyancy; a number of cassettes (7) that in use of said fish farm are arranged around the elongated body (2), each cassette (7) of the number of cassettes having: a semi-rigid or rigid cage structure that is configured to have excess positive buoyancy; and netting material (8) that is associated with the semi-rigid or rigid cage structure to enable fish to be contained within the cassette (7); a first set of at least two elongated rigid truss structures (9), each elongated rigid truss structure (9) of said first set of elongated rigid truss structures having a bound end part (10) that is associated with the second end part (4) of the elongated body (2) and a free end part (11), the elongated rigid truss structures(9) of said first set of elongated rigid truss structures being: arranged transverse to the elongated body (2); and positioned next to each other and spaced apart in a circumferential direction of the elongated body (2); and a first set of connection assemblies (12), each connection assembly (12) of said first set of connection assemblies comprising an elongated connection element (13), wherein a first connection assembly (12a) of said first set of connection assemblies (12) is arranged to connect a respective cassette (7) of the number of cassettes with a first elongated rigid truss structure (9a) of said first set of elongated rigid truss structures at a first distance, d1, from each other as seen in a direction of the longitudinal center line (5) of the elongated body (2), and wherein a second connection assembly (12b) of said first set of connection assemblies(12) is arranged to connect the respective cassette (7) with a second elongated rigid truss structure (9b) of said first set of elongated rigid truss structures at a second distance, d2, from each other as seen in the direction of the longitudinal center line (5) of the elongated body (2), wherein at least a part of a first elongated connection element (13a) of said first connection assembly (12a) is arranged to extend over at least a part of said first distance, d1 , and at least a part of a second elongated connection element (13b) of said second connection assembly (12b) is arranged to extend over at least a part of said second distance, d2, said first elongated connection element (13a) and said second elongated connection element (13b) being configured to allow floating movements of the respective cassette (7) relative to said first elongated rigid truss structure (9a) and said second elongated rigid truss structure (9b).

2. The semi-submersible spar-type offshore fish farm (1) according to claim 1, wherein at least one cassette (7) of the number of cassettes is provided with at least one attachment system (14) that is configured and arranged to enable establishment of at least two interconnected cassettes.

3. The semi-submersible spar-type offshore fish farm (1) according to claim 1 or 2, comprising: a second set of at least two elongated rigid truss structures (15), each elongated rigid truss structure (15) of said second set of elongated rigid truss structures having a bound end part (16) that is associated with the elongated body (2) at a location that is closer to the first end part (3) than to the second end part (4) of the elongated body (2), and a free end part (17), the elongated rigid truss structures (15) of said second set of elongated rigid truss structures being: arranged transverse to the elongated body (2); positioned next to each other and spaced apart in a circumferential direction of the elongated body (2) in alignment with the elongated rigid truss structures (9) of said first set of elongated rigid truss structures; and arranged at a third distance, d3, from said first set of elongated rigid truss structures as seen in the direction of the longitudinal center line (5) of the elongated body (2), the third distance, d3, allowing each cassette (7) of the number of cassettes that in use of the fish farm are arranged around theelongated body (2) to be arranged between the elongated rigid truss structures of said first set of elongated rigid truss structures and the elongated rigid truss structures of said second set of elongated rigid truss structures as seen in the direction of the longitudinal center line (5) of the elongated body (2); and a second set of connection assemblies (18), each connection assembly (18) of said second set of connection assemblies comprising an elongated connection element (19), wherein a first connection assembly (18a) of said second set of connection assemblies is arranged to connect the respective cassette (7) of the number of cassettes, which is connected with the first elongated rigid truss structure (9a) and the second elongated rigid truss structure (9b) of said first set of elongated rigid truss structures via said first connection assembly (12a) and said second connection assembly (12b) of said first set of connection assemblies, with a first elongated rigid truss structure (15a) of said second set of elongated rigid truss structures at a fourth distance, d4, from each other, and wherein a second connection assembly (18b) of said second set of connection assemblies (18) is arranged to connect said respective cassette (7) with a second elongated rigid truss structure (15b) of said second set of elongated rigid truss structures at a fifth distance, d5, from each other, wherein at least a part of a first elongated connection element (19a) of said first connection assembly of said second set of connection assemblies is arranged to extend over at least a part of said fourth distance, d4, and at least a part of a second elongated connection element (19b) of said second connection assembly (18b) of said second set of connection assemblies is arranged to extend over at least a part of said fifth distance, d5, said first elongated connection element (19a) of said first connection assembly (18a) of said second set of connection assemblies and said second elongated connection element (19b) of said second connection assembly of said second set of connection assemblies being configured to allow floating movements of said respective cassette (7) relative to said first elongated rigid truss structure (15a) and said second elongated rigid truss structure (15b) of said second set of elongated rigid truss structures.

4. The semi-submersible spar-type offshore fish farm (1) according to any one of the claims 1 to 3, wherein each connection assembly (12) of the first set of connection assemblies that is associated with a respective cassette (7) of the number ofcassettes is provided with a tensioned elongated connection element (13) comprising at least one of a cable (20), a chain (21), a rope, and a rod.

5. The semi-submersible spar-type offshore fish farm (1) according to any one of the claims 1 to 3, wherein the elongated connection element (13) of a connection assembly (12) of the first set of connection assemblies is a rigid elongated element.

6. The semi-submersible spar-type offshore fish farm (1) according to any one of the claims 1 to 5, wherein a respective connection assembly (12) of the first set of connection assemblies comprises a first damping system (22) that is associated with the elongated connection element (13) of said respective connection assembly.

7. The semi-submersible spar-type offshore fish farm (1) according to claim 3 or any one of the claims 4 to 6 in their dependency on claim 3, wherein a respective connection assembly (18) of the second set of connection assemblies comprises a tensioning system (23) that is configured and arranged to provide the respective connection assembly (18) of the second set of connection assemblies with a tensioned elongated connection element (19) comprising at least one of a cable, a chain, a rope, and a rod.

8. The semi-submersible spar-type offshore fish farm (1) according to claim 3 or any one of the claims 4 to 7 in their dependency on claim 3, wherein a respective connection assembly (18) of the second set of connection assemblies comprises a second damping system (24) that is associated with the elongated connection element (19) of said respective connection assembly.

9. The semi-submersible spar-type offshore fish farm (1) according to claim 3 or any one of the claims 4 to 8 in their dependency on claim 3, wherein the elongated rigid truss structures (15) of said second set of elongated rigid truss structures have smaller dimensions than the elongated rigid truss structures (9) of said first set of elongated rigid truss structures.

10. The semi-submersible spar-type offshore fish farm (1) according to any one of the claims 1 to 9, wherein the semi-rigid or rigid cage structure of a respective cassette (7) of the number of cassettes comprises elongated tubular members (25) that areconfigured and arranged to provide a semi-rigid or rigid truss structure, and wherein the netting material (8) is associated with the elongated tubular members for containing fish within the respective cassette.

11. The semi-submersible spar-type offshore fish farm (1) according to claim 10, wherein the netting material (8) is configured and arranged to provide at least one cassette (7) of the number of cassettes with at least two segregated compartments(26) for containing fish.

12. The semi-submersible spar-type offshore fish farm (1) according to claim 10 or 11 , wherein at least one cassette (7) of the number of cassettes is provided with a buoyancy adjustment assembly (27) that is associated with at least one elongated tubular member (25) of the at least one cassette, the buoyancy adjustment assembly(27) being configured to adjust the excess positive buoyancy of the at least one cassette.

13. The semi-submersible spar-type offshore fish farm (1) according to any one of the claims 1 to 12, wherein the elongated body (2) is provided with at least one of a central power supply system (28), a central air supply system (29), a central food storage and supply system (30), and a central waste collection and storage system (31), and wherein at least one cassette (7) of the number of cassettes is provided with at least one of a local lighting system (32), a local aeration system (33), a local food distribution and dispensing system (34), a local waste collection and storage system (35), and a local biomass monitoring system (51), wherein in use of said fish farm (1), at least one of said local systems is operatively associated with a functionally corresponding system of said central systems.

14. A method of offshore installing a cassette in a semi-submersible spar-type offshore fish farm (1) for cultivating fish at open sea, said fish farm (1) comprising: an elongated body (2) that comprises a first end part (3), a second end part (4), and a longitudinal center line (5) that is directed from said first end part (3) to said second end part (4), the longitudinal center line (5) in use of said fish farm being arranged in a direction transverse to sea level, and said first end part (3) being arranged above said second end part (4);a buoyancy unit (6) that is associated with the elongated body (2), the buoyancy unit (6) being configured to have an adjustable buoyancy to allow the elongated body (2) to float at different drafts relative to sea level depending on a value of the adjustable buoyancy; a number of cassettes (7) that in use of said fish farm are arranged around the elongated body (2), each cassette (7) of the number of cassettes having: a semi-rigid or rigid cage structure that is configured to have excess positive buoyancy; and netting material (8) that is associated with the semi-rigid or rigid cage structure to enable fish to be contained within the cassette (7); a first set of at least two elongated rigid truss structures (9), each elongated rigid truss structure (9) of said first set of elongated rigid truss structures having a bound end part (10) that is associated with the second end part (4) of the elongated body (2) and a free end part (11), the elongated rigid truss structures (9) of said first set of elongated rigid truss structures being: arranged transverse to the elongated body (2); and positioned next to each other and spaced apart in a circumferential direction of the elongated body (2); and a first set of connection assemblies (12), each connection assembly (12) of said first set of connection assemblies comprising an elongated connection element (13), wherein a first connection assembly (12a) of said first set of connection assemblies (12) is arranged to connect a respective cassette (7) of the number of cassettes with a first elongated rigid truss structure (9a) of said first set of elongated rigid truss structures at a first distance, d1 , from each other as seen in a direction of the longitudinal center line (5) of the elongated body (2), and wherein a second connection assembly (12b) of said first set of connection assemblies (12) is arranged to connect the respective cassette (7) with a second elongated rigid truss structure (9b) of said first set of elongated rigid truss structures at a second distance, d2, from each other as seen in the direction of the longitudinal center line (5) of the elongated body (2), wherein at least a part of a first elongated connection element (13a) of said first connection assembly (12a) is arranged to extend over at least a part of said first distance, d1 , and at least a part of a second elongated connection element (13b) of said second connection assembly (12b) is arranged to extend over at least a part of said second distance, d2, said first elongated connection element (13a) and said second elongated connectionelement (13b) being configured to allow floating movements of the respective cassette (7) relative to said first elongated rigid truss structure (9a) and said second elongated rigid truss structure (9b); the method comprising: setting the adjustable buoyancy of the buoyancy unit (6) to a first value to allow the elongated body (2) to float at a first draft relative to sea level, wherein at the first draft the elongated rigid truss structures (9) of the first set of elongated rigid truss structures are located at a first depth, D1, relative to sea level; positioning a respective cassette (7) of the number of cassettes, which is arranged to extend at least partially above sea level, opposite said first elongated rigid truss structure (9a) and said second elongated rigid truss structure (9b) of said first set of elongated rigid truss structures; connecting the respective cassette (7) with: said first elongated rigid truss structure (9a) via said first connection assembly (12a) of said first set of connection assemblies; and said second elongated rigid truss structure (9b) via said second connection assembly (12b) of said first set of connection assemblies; adjusting the first value of the adjustable buoyancy of the buoyancy unit (6) to a second value to allow the elongated body (2) to float at a second draft relative to sea level, wherein at the second draft: the elongated rigid truss structures (9) of the first set of elongated rigid truss structures are located at a second depth, D2, relative to sea level, the second depth, D2, being larger than the first depth, D1; and said respective cassette (7) that extends mainly or completely below sea level is allowed to:■ float at said first distance, d1 , from said first elongated rigid truss structure (9a) and at said second distance, d2, from said second elongated rigid truss structure (9b); and■ make floating movements relative to said first elongated rigid truss structure (9a) and said second elongated rigid truss structure (9b).

15. The method according to claim 14, wherein the semi-submersible spar-type offshore fish farm (1) comprises:a second set of at least two elongated rigid truss structures (15), each elongated rigid truss structure (15) of said second set of elongated rigid truss structures having a bound end part (16) that is associated with the elongated body (2) at a location that is closer to the first end part (3) than to the second end part (4) of the elongated body (2), and a free end part (17), the elongated rigid truss structures (15) of said second set of elongated rigid truss structures being: arranged transverse to the elongated body (2); positioned next to each other and spaced apart in a circumferential direction of the elongated body (2) in alignment with the elongated rigid truss structures (9) of said first set of elongated rigid truss structures; and arranged at a third distance, d3, from said first set of elongated rigid truss structures as seen in the direction of the longitudinal center line (5) of the elongated body (2), the third distance, d3, allowing each cassette (7) of the number of cassettes that in use of the fish farm are arranged around the elongated body (2) to be arranged between the elongated rigid truss structures (9) of said first set of elongated rigid truss structures and the elongated rigid truss structures (15) of said second set of elongated rigid truss structures as seen in the direction of the longitudinal center line (5) of the elongated body (2); and a second set of connection assemblies (18), each connection assembly (18) of said second set of connection assemblies comprising an elongated connection element (19), wherein a first connection assembly (18a) of said second set of connection assemblies is arranged to connect the respective cassette (7) of the number of cassettes, which is connected with the first elongated rigid truss structure (9a) and the second elongated rigid truss structure (9b) of said first set of elongated rigid truss structures via said first connection assembly (12a) and said second connection assembly (12b) of said first set of connection assemblies, with a first elongated rigid truss structure (15a) of said second set of elongated rigid truss structures at a fourth distance, d4, from each other, and wherein a second connection assembly (18b) of said second set of connection assemblies (18) is arranged to connect said respective cassette (7) with a second elongated rigid truss structure (15b) of said second set of elongated rigid truss structures at a fifth distance, d5, from each other, wherein at least a part of a first elongated connection element (19a) of said first connection assembly of said second set of connection assemblies is arranged to extend over at least a part of said fourthdistance, d4, and at least a part of a second elongated connection element (19b) of said second connection assembly (18b) of said second set of connection assemblies is arranged to extend over at least a part of said fifth distance, d5, said first elongated connection element (19a) of said first connection assembly (18a) of said second set of connection assemblies and said second elongated connection element (19b) of said second connection assembly of said second set of connection assemblies being configured to allow floating movements of said respective cassette (7) relative to said first elongated rigid truss structure (15a) and said second elongated rigid truss structure (15b) of said second set of elongated rigid truss structures; the method comprising: setting the adjustable buoyancy of the buoyancy unit (6) to said second value to allow the elongated body (2) to float at said second draft relative to sea level; and connecting said respective cassette (7) with: said first elongated rigid truss structure (15a) of said second set of elongated rigid truss structures via said first connection assembly (18a) of said second set of connection assemblies to allow said respective cassette (7) to:■ be arranged at said fourth distance, d4, from said first elongated rigid truss structure (15a) of said second set of elongated rigid truss structures; and■ make floating movements relative to said first elongated rigid truss structure (15a) of said second set of elongated rigid truss structures; and said second elongated rigid truss structure (15b) of said second set of elongated rigid truss structures via said second connection assembly (18b) of said second set of connection assemblies to allow said respective cassette (7) to:■ be arranged at said fifth distance, d5, from said second elongated rigid truss structure (15b) of said second set of elongated truss structures; and■ make floating movements relative to said second elongated rigid truss structure (15b) of said second set of elongated rigid truss structures.

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