System and fabric to be arranged around or integrated in a net bag of a fish cage

Abstract

The invention relates to a system (10) to be arranged around or integrated in a net bag (4) of a fish cage, the system comprises a framework (20) and a fabric (6) both having a circumference to be arranged around the net bag (4) and a length, wherein the framework (20) comprises at least two stiff rings (7a, 7b) arranged to support the circumference of the fabric (6), and a number of stiff bars (9) arranged between the rings (7a, 7b) to support the rings (7a, 7b) in a direction along the length of the fabric (6).

Description

[0001] System and fabric to be arranged around or integrated in a net bag of a fish cage

[0002] The invention relates to a system and a fabric to be integrated or arranged around a net bag of a fish cage, a fish cage having such a system or fabric, and a method to avoid reduction of the volume available to fish in a fish cage having such a system or fabric, according to the preamble of the independent patent claims.

[0003] Background

[0004] The annual production of salmonids in Norway was about 1 .3 million tons in 2012, 99% being Atlantic salmon and trout. The production of salmon is at present mainly based on fish cage aguaculture in the sea, where salmon are cultivated in large net cages. A traditional fish cage comprises a floating collar at the surface of the sea, and a net bag fastened to and hanging down from the collar. The net bag is tensioned and stretched by weights, for instance a sinker tube.

[0005] When fish is growing in the net bag, it will i.a. consume oxygen and produce CO2 and produce waste such as uneaten food and faeces. Therefore, it is necessary to have sufficient water current in and out of the net bag or otherwise replace the water, and in addition remove the waste to keep the water healthy for the fish. This is often solved by designing the net bag in a material having openings being large enough to allow sufficient water to flow through, yet small enough to prevent fish from escaping the net bag, and small enough to prevent predators including jelly fish and larger objects in the water from entering the net bag. Pathogen organisms, microorganisms and algae should also be prevented from entering the net bag as they may cause sickness and / or death to the fish and reduce the fish welfare substantially.

[0006] The preferred size of the openings when considering replacement and supply of water will often be different from the preferred size when considering the need for preventing organisms such as pathogen organisms from entering the net cage. One well known way to meet both the above said needs, is to arrange a fabric having smaller openings around the net bag having larger openings. The fabric is hanging from the floating collar and into the water. The fabric will have a circumference around the fish cage, and a length being the length from the surface of the sea to the desired depth. Such fabrics are also known as skirts, for instance a lice skirt. The size of the openings and the depth of the fabric may vary according to the pathogen or algae to be avoided, and even non-permeable skirt, such as PVC coated fabrics may be used. A well known organism is the parasite is Caligidae, for instance Lepeophtheirus salmonis, known as salmon louse, having a size of 0,7 mm at the development stage where it attacks the fish. To avoid the salmon lice from entering the net cage, the openings should be less than 350 pm, and the depth should typically be 5-30 meters. A net bag having openings in this range may prevent sufficient replacement of water, at least when the net bag becomes fouled or overgrown. Such a fabric is for instance known from Fiizk, Norlense or Selstad. The fabric may be integrated into the material of the net bag.

[0007] The water flow through the material of the net bag, or a fabric being arranged or integrated as a skirt around the net bag as described above, may become insufficient to keep the water conditions optimal for the fish inside the net bag, for instance due to fouling. In such cases, oxygen may be added to the fish cage, for instance by a system from Linde. The same applies if a non-permeable skirt is being used. Another well known way to refresh the water in the net bag is to pump water from a lower part of the fish cage to an upper part, as water at lower parts often are colder and contain more oxygen. Further, by creating such a flow inside the fish cage, reduced pressure will be created at the lower part and more water will be pulled into the net bag through the net. A system for creating such a flow is known from Framo AS under the trade name AquaStream.

[0008] Occasionally, especially during spring and autumn, large amounts of fresh water may flow into the sea, and as fresh water is lighter than sea water, there will be a layer of fresh water on top of the sea water surrounding the fish cage. A fish cage having both a fabric arranged as a skirt, and a pump creating an upwards waterflow in the fish cage, will not have a layer of fresh water at the top. A difference in salinity will thus appear inside and outside of the fish cage. This difference in salinity results in forces acting on the fabric, and the fabric will be drawn towards the centre of the net bag. As the upper part of the fabric is fastened to the floating collar, the fabric will be inclining towards the centre of the net bag and may even be at the surface of the water inside the net bag. This will limit the volume of the net bag available to the fish, but of more concern is the fish being lifted to the surface by the skirt, and not being able to return to the water. If the fabric is arranged on the outside of the net bag, it will be drawn towards the net bag and further push the net bag towards the centre. The volume of the net bag being available to the fish will thereby be reduced.

[0009] Further, as the fabric is inclining or floating rather than being vertical, the depth of the fabric, and thereby the effect of preventing organisms from entering the fish cage, will be reduced.

[0010] Based on the above, it is an object of the invention to provide a net bag without the problems mentioned above, yet preventing undesired organism such as salmon lice to enter. Further, it is an object to provide a net bag without the problems of water quality mentioned above. Another object is to provide a net bag which does not reduce the size when freshwater flows into the sea. Yet another object of the invention is to provide a solution which may be arranged on existing fish cages, and which does not affect the regular farming of fish.

[0011] Summary of the invention

[0012] The objects are met by the invention related to a system and a fabric to be integrated or arranged around a net bag of a fish cage, a fish cage having such system or fabric, and a method to avoid reduction of the volume available to fish in a fish cage having such system or fabric, according to the characterizing parts of the independent patent claims.

[0013] In a first aspect, the invention relates to a system to be integrated or arranged around a net bag of a fish cage, the system comprises a framework and a fabric both having a circumference to be arranged around the net bag, and a length.

[0014] The framework comprises at least two stiff rings arranged to support the circumference of the fabric, and at least one stiff bar arranged between the rings to support the rings in a direction along the length of the fabric. The direction of the length of the fabric and the direction of the circumference are perpendicular to each other. The stiff bar arranged to support the fabric along the length of the fabric may be parallel to the length of the fabric. The stiff bar arranged to support the fabric along the length of the fabric may be inclined to the length of the fabric, meaning that the stiff bar is arranged at an angle to the stiff ring.

[0015] By "arranged around the net bag" it should be understood that the fabric may be arranged on the inside of the net bag, on the outside of the net bag, or integrated in the material of the net bag. The at least one stiff ring arranged to support the circumference of the fabric will also be arranged around the net bag, when the fabric is arranged around or integrated into the net bag.

[0016] By "arranged to support" it should be understood that the framework is arranged to support the fabric in such a way that the fabric maintain its shape, and does not contract radially or axially during waves, tides or differences in salinity. By using a system according to the invention, the ring(s) of the framework will support the circumference of the fabric, and prevent radially contraction. The bar(s) arranged to support the ring(s) will prevent the ring(s) from moving in a direction along the length of the fabric, and further prevent the fabric from contracting radially between the rings. Thereby the framework will also prevent axially contraction of the fabric along its length.

[0017] The framework may be free-standing and not fastened to the fabric. In such case the framework may comprise at least two rings, wherein the bars are arranged between the rings. As said above, the bars may be arranged perpendicular or at an angle to the rings. The rings and bar(s) should be fastened to each other and attached to the floating collar of the fish cage. One of the rings may be a part of the floating collar, in which case the stiff bar(s) may be arranged protruding from the other ring, and a free end of the bar(s) is to be fastened to the ring of the floating collar of the fish cage upon installation. Alternatively, the floating collar and the framework may be integrated with each other. Further, when the framework is free-standing, it should be arranged closer to the centre of the net bag than the fabric. This means that when the system is arranged on the inside of the net bag, the fabric must be arranged between the net bag and the framework, and when the system is arranged on the outside of the net bag, the framework must be arranged between the net bag and the fabric. The circumference of the ring(s) may thus correspond to, or be smaller than the circumference of the fabric. By having the framework free-standing, the framework may be integrated into the floating collar and / or installed at any time, and the fabric may be added only when needed. This will make the installation of the fabric easier, and the fabric may be removed or installed quickly.

[0018] The framework may be fastened or integrated in the fabric. In such case an end of the fabric may be attached to a floating collar of the fish cage, and the length of the fabric will correspond to the depth of the fabric when the fish cage is installed in the water. In embodiments wherein the end of the fabric is attached to the fish cage above the surface of the sea, the depth of the fabric will be correspondingly shorter than the length. The framework being fastened or integrated in the fabric may comprise at least two rings, and stiff bars arranged between the rings. The framework being fastened or integrated in the fabric may comprise one ring, and stiff bars are arranged from the ring towards one end of the fabric. As said above, the bars may be arranged perpendicular or at an angle to the rings. The rings and bar(s) may be fastened to each other, or they may be fastened or integrated to the fabric at a distance from each other. In case the framework comprises at least two rings, one of the rings may be a part of the floating collar, in which case the ring may attached to the floating collar of the fish cage upon installation. Alternatively, one end of the fabric is attached to the floating collar, wherein the stiff bars are arranged from the ring towards the end attached to the floating collar.

[0019] The circumference of the fabric and framework may be slightly larger than the net bag when the fabric is to be installed on the outside of the net bag, slightly smaller when the fabric is to be installed on the inside of the net bag or corresponding to the net bag when the fabric is to be integrated in the net bag. By having the framework fastened or integrated in the fabric, only one item needs to be installed / removed, and no modifications are needed to the fish cage. It may be easily installed at a fish cage having fish in the net cage.

[0020] The circumference and length of the framework and fabric may be similar or different. The fabric may be longer than the framework, meaning that the fabric may protrude beyond the ring(s) of the framework. The lower end of the fabric may be connected to a number of weights, a tube filled with weight, often referred to as a sinker tube, or the similar to keep the fabric vertical. The fabric and / or framework may be connected to the net bag or fish cage, or the weights or sinker tube of the net bag. The fabric may be connected to the mooring of the fish cage to keep it vertical after being installed. By using a system according to the invention, comprising a framework having a number of rings and bars, the need for weights to keep the fabric expanded and vertical may be reduced or even eliminated.

[0021] The fabric and framework may have the shape of an open cylinder, wherein the length of the fabric will be in axial direction and the rings will be in radial direction. As said above, the bars may be perpendicular or inclined to the length of the fabric and will maintain the distance between the rings. The cylinder may be a straight cylinder having the same radius along the length, or a conical cylinder, having reduced or increased radius along the length, or a combination having reduced radius along parts of the length. The shape of the fabric and framework may reflect the shape of the net bag. Once the fabric and framework are arranged around or integrated in a net bag of a fish cage installed in the sea, the radial direction will be horizontal and the axial direction will be vertical.

[0022] The fabric may be made of a material being non-permeable or permeable having openings suitable to prevent the undesired organisms from entering the net bag. The fabric may be produced as a cylinder as described above having a circumference and a length, or a rectangular fabric arranged as a cylinder around the net bag, by arranging the ends towards or overlapping each other. The stiff ring(s) and / or the stiff bar(s) may be made of rigid material, such as polymer, fiber-reinforced polymer or metal, preferably with a stiffness similar to the stiffness of a typical floating cage ring of polyethylene (PE) pipes. The rings may be segmented, for example in straight segments coupled together to achieve ring stiffness, for example like a polygon. The expression "ring" should be understood to not be limited to a circle, but also include shapes being segmented such as a pentagon, hexagon or more segments, or a shape being oval, elliptic or egg-shaped.

[0023] Segments of the ring(s) should be interconnected to achieve a stiffness large enough to withstand any radial forces acting on it, while maintaining geometric integrity, and to avoid that excessive forces are transferred to the floating collar. Ring stiffness is achieved when segments are coupled together, the forces acting on one segment are transmitted to adjacent segments, resulting in a balanced distribution of loads throughout the entire ring.

[0024] The cross section of material constituting the ring should preferably be circular in order to avoid tear on the ring. However, the cross section of the ring may have any shape.

[0025] The stiff ring may be made of a pipe, shaped to a ring. The diameter and circumference of the "ring" will be referring to the diameter and circumference of the ring made of the pipe, while the diameter and circumference of the "pipe" will be referring to a cross section of the pipe.

[0026] The stiff ring(s) and / or bar(s) may be made of a material which may be pressurized into shape by adding a fluid, being foldable when depressurized, and stiff when pressurized. By "stiff" ring(s) and bar(s) in the context of this application one should also include such ring(s) and bar(s) which are not stiff until they are pressurized. The material may be made as channels to be filled and thereby pressurized, by a fluid such as gas or liquid, or a combination. The rings and / or bars which may be pressurized may be integrated in the fabric. When the ring(s) and bar(s) are made of such material, and fastened or integrated in the fabric, the fabric may be folded during transport and installation, and the ring(s) and bar(s) may be pressurized only when needed. The preferred fluid is water, more preferably water corresponding to the water surrounding the net.

[0027] Further, when the rings and / or bars are made of material which may be pressurized, they may comprise valves, such as check valves or pressure limiting valves for preventing the rings and / or bars to depressurize uncontrolled or being pressurized beyond limits until rupture. The rings and / or bars may comprise several compartments being connected by valves, for instance check valves, to avoid that the whole ring / bar will be depressurized in case of a rupture or puncture. Further, the rings and / or bars may comprise controllable valves, for instance to depressurize the rings and / or bars when needed, or to only pressurize some of the ring(s) and / or bar(s). If the fabric is to be removed, or lifted, the bars may be depressurized before lifting, which makes the fabric more convenient to lift. Each ring may be pressurized by a separate valve, and thereby the number of rings may be controlled. Each bar may be pressurized by a separate valve and thereby the number of bars may be controlled. The rings and / or bars may comprise a pressure sensor, for monitoring the pressure.

[0028] When the framework is fastened or integrated into the fabric, the bars of the framework may be arranged from one end of the fabric to the at least one ring. In this way the system will be stiff from the end of the fabric to the ring, and when the system is installed at the fish cage, the stiffened end of the fabric may be fastened to the floating collar, and thereby the fabric will be supported at the upper end. When the framework comprises more than one ring, the bars may be arranged between the rings, possibly in addition to bars at the end of the fabric. The bar(s) may be connected to the ring(s) for instance in a T-coupling, or the bar(s) may be arranged to stop before interfering directly with the ring(s). In cases where the ring and / or bar is made of material which may be pressurized, the bar may be connected to the ring by a valve, or the bar may constitute a separate channel. The ring(s) and bar(s) may be fastened to the fabric by a number of separate fastening elements, by sewing, or knotting. The fabric may be provided with passages or pockets for receiving the stiff ring(s) and or bar(s), and the rings and bars are fastened to the fabric by inserting the rings / bars in the passages. If the stiff ring(s) and stiff bar(s) are made of a material which may be pressurized as mentioned above, the material may be integrated or sewn into the fabric.

[0029] A fabric according to the invention wherein a framework comprising at least one stiff ring is integrated or fastened to the circumference of the fabric, and at least one stiff bar is integrated and fastened to the fabric along at least a part of the length of the fabric, will be stiffened by the framework. The rings will prevent radial deformation, that is in the horizontal plane once the fabric is arranged around an installed fish cage, and the bars will prevent axial deformation, that is in the vertical plane. The fabric will thus not be moving into the centre of the fish cage, and will not reduce the volume available to the fish in the fish cage or capture fish on the surface of the fabric. As the bars will prevent axial deformation, the depth or length of the fabric will not be reduced, and the risk of getting organisms such as salmon lice into the net bag is reduced.

[0030] The framework comprises at least two stiff rings arranged to support the circumference of the fabric. The rings may be at the middle, an upper and / or lower part of the fabric. The rings may preferably be arranged at a distance from the end of the fabric to be fastened to the floating collar. This will prevent the part lower than the ring to deform and move into the net cage. In another embodiment, a number of stiff rings may be arranged to support the fabric, along the circumference of the fabric. The stiff rings are preferably arranged parallel, for instance one at an upper part the fabric, one at the lower part, and one or more between. The rings will prevent the fabric from moving and / or being deformed in the radial direction. The preferred number of rings may vary and will depend both on the depth of the fabric and the forces acting on the fabric at the given localization. The framework further comprises a number of stiff bars arranged to support the rings in a direction along the length of the fabric. The stiff bars will prevent the rings from moving in axial direction. The bars are preferably arranged from one end of the fabric to the at least one ring, preferably from the end to be attached to the floating collar. If more than one ring is fastened to the fabric, a number of stiff bars may be arranged between the rings, to keep the rings apart.

[0031] The number of bars may vary and will depend both on the circumference and depth of the fabric and the forces acting on the fabric at the given localization. If the diameter of the fabric is 60 m, the bars may be arranged 5-10 m apart from each other, that is about 20-40 bars.

[0032] When the framework is free-standing as described above, the ring being a part of the floating collar, or the ring attached to the floating collar, will transfer axial forces acting on the framework to the collar. When the framework is integrated or fastened to the fabric, axial forces may be transferred to the floating collar through the fabric, or the fabric may be lifted until a ring or bar will be in contact with the floating collar, and then the forces acting on the framework will be transferred to the collar through the framework.

[0033] The invention further relates to a fish cage having a system and / or a fabric as described above installed.

[0034] The invention further relates to a method to avoid reduction of the volume available to fish in a fish cage having a system and / or fabric as described above. The system comprises at least two rings that may be pressurized arranged to support the circumference of the fabric, and at least one bar which may be pressurized and arranged to support the rings in a direction along the length of the fabric. The method comprises the following steps:

[0035] - pressurizing the rings

[0036] - pressurizing the bar(s), and maintaining the pressure in the rings and bar. The method further provides steps for depressurizing the rings / bars. It may be advantageous to depressurize the rings / bars for instance when side currents become high to avoid excessive loads on cage / mooring. In the case of extreme weather, the fabric is less critical than the cage itself, and to avoid any risks, it is an advantage to be able to depressurize the rings / bars and pressurize them again after the weather has improved.

[0037] The invention will in the following be described by way of exemplary embodiments and accompanying drawings. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to a system wherein a framework is fastened to a fabric arranged around the inside of a fish cage in the sea. However, it should be appreciated that the fabric may also be integrated in the net cage or arranged on the outside of the net cage.

[0038] The mentioning of different features, structures, or characteristics which the invention may comprise means that the particular feature, structure, or characteristic may be included in at least one embodiment. The different features, structures, or characteristics may be combined in the same or different embodiments, and in any combinations.

[0039] In the description relative terms such as front, top, centre, bottom, side, lower, upper, downward, upward, outward, sideward, vertical, and horizontal etc. are all related to the system, fabric and fish cage when it is installed and during use.

[0040] Detailed description

[0041] Embodiments of the present invention will now be described, with reference to the following schematic figures wherein:

[0042] Fig. 1 shows a part of a fish cage having a fabric according to the invention arranged on the inside of the net bag,

[0043] Fig. 2 shows an enlarged detail of Fig. 1 , and

[0044] Fig 3 shows a free-standing framework having two rings and a number of bars. The same reference numbers in different drawings identify the same or similar elements. The figures are for illustration purposes only, and the different parts may necessarily not be in scale to each other.

[0045] The fish cage shown in the figures comprises a floating collar having three pipes 1 shown as rings, with a walkway 2 and handrail 3. The fish cage further comprises a net bag 4 having walls 4a and a bottom 4b slanting vertically down in a cone 4c. In the middle of the fish cage, it is shown an Aquastream 5 which pumps water from the lower part of the fish cage, to the upper part.

[0046] Further, the Figs shows a system 10 comprising a fabric 6 arranged around the net bag 4 on the inside of the net, to prevent any predators or parasites to enter the net bag. The fabric 6 has a circumference corresponding to the net bag and a length L being the depth of the fabric. In the shown embodiment, the system further comprises a framework 20 fastened to the fabric. The framework comprises two stiff rings 7a, 7b are arranged and fastened to the circumference of the fabric, and a number of stiff bars 8 are arranged and fastened from the upper end of the fabric to the first ring 7a, and a corresponding number of bars 9 are arranged between the rings. The framework 20 is fastened to the inside of the fabric, that is closer to the centre of the net bag and prevents the fabric from moving radially into the net bag.

[0047] A number of weights (not shown) are attached to the lower end of the fabric to keep the fabric down. As the fabric will be expanded due to the framework, the size and number of weights needed to keep the fabric straight are reduced compared to conventional skirts. The use of weights to keep the fabric expanded is well known to a skilled person.

[0048] Figure 3 shows a free-standing framework 20, comprising two stiff rings 7a and 7b, wherein one of the rings should be fastened to the floating collar of the fish cage during installation. The framework further comprises a number of stiff bars arranged between the rings, some of the bars 9a are arranged perpendicularly to the rings, and some bars 9b are arranged at an angle to the rings. The bars may be inclining to the same direction or as shown in alternating directions.

[0049] In the shown embodiment the rings 7a, 7b and bars 8, 9a, 9b are made of plastic tubes, preferably PE tubes having the same density as the floating collar. The tubes are filled with water. However, the tubes and pipes may also be made of other stiff materials, such as steel or glass fibre.

[0050] In a not shown embodiment, the tubes and pipes may be made of a material which may be pressurized, and the material may be sewn as channels. By adding a fluid to the channel, the material will become stiff. This material may be fastened or integrated to the fabric as shown in the figures.

[0051] By having a system 10 comprising a fabric 6 and a framework 20 as described above, the fabric will be stiffened, meaning that the rings will prevent the fabric from moving into the net bag, and the bars will prevent the rings from moving upwards, and also prevent the fabric from moving into the net bag between the rings.

Claims

Claims1 . System (10) to be arranged around or integrated in a net bag (4) of a fish cage, the system comprises a framework (20) and a fabric (6) both having a circumference to be arranged around the net bag and a length, wherein the framework comprises at least two stiff rings (7a, 7b) arranged to support the circumference of the fabric, and at least one stiff bar (9) arranged between the rings to support the rings in a direction along the length of the fabric.

2. System (10) according to claim 1 , wherein the framework is arranged free-standing.

3. System (10) according to any one of the preceding claims, wherein the framework (20) is fastened or integrated to the fabric (6).

4. System (10) according to any one of the preceding claims, wherein one of the rings (7a, 7b) is a part of a floating collar.

5. System (10) according to any one of the preceding claims, wherein the at least two rings (7a, 7b) and / or the at least one bar (9) is made of a material that is pressurized.

6. System (10) according to claim 5, wherein the rings (7a, 7b) and / or bars (9) are arranged to be pressurized by a gas, liquid or a combination of gas and liquid.

7. Fabric (6) to be arranged around or integrated in a net bag (4) of a fish cage, the fabric has a circumference to be arranged around the net bag and a length, wherein a framework (20) comprising at least two stiff rings (7a, 7b) are arranged and fastened to the circumference of the fabric (6), and at least one stiff bar (9) is arranged and fastened to at least parts of the length of the fabric, between the rings.

8. Fabric (6) according to claim 7, wherein the fabric further comprises a number of stiff bars (9) arranged and fastened along the fabric, from one end of the fabric to the at least two rings (7a, 7b).

9. Fabric (6) according to any one of claims 7-8, wherein one of the rings (7a, 7b) is a part of a floating collar.

10. Fabric (6) according to any one of claims 7-9, wherein at least two rings (7a, 7b) and / or the at least one bar (9) is made of a material that is pressurized.11 . Fabric (6) according to claim 10, wherein the rings (7a, 7b) and / or bars (9) are made as channels in a material that is pressurized, and that the channels are pressurized to constitute a stiff ring (7a, 7b) and / or bar (9).

12. Fabric (6) according to any one of the claims 7-11 , wherein the rings and / or bars are fastened to the fabric, by inserting the rings / bars in passages sewn in the fabric.

13. Fish cage comprising a floating collar arranged on the surface of the water and a net bag fastened to the floating collar hanging into the water, wherein a system according to any one of claims 1-6, or fabric according to any of one of claims 7-12 is arranged around or integrated into the net bag.

14. Method to avoid reduction of the volume available to fish in a fish cage having a system according to any one of claims 5-6 or a fabric according to any one of claims 10-12 arranged around the fish cage, by- pressurizing the at least two rings- pressurizing the at least one bar, and maintaining the pressure in the ring and bar.

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