NO346256B1

NO346256B1 - Device for installation at the bottom of a net cage

Info

Publication number: NO346256B1
Application number: NO20200678A
Authority: NO
Inventors: Tore Stenshaug Strand
Original assignee: Scale Aquaculture As
Priority date: 2020-06-08
Filing date: 2020-06-08
Publication date: 2022-05-16
Also published as: NO20200678A1

Description

Device for installation at the bottom of a net cage

The present invention relates to a device for installation at the bottom of a net cage, and a system for removal of waste from the bottom of the net cage while keeping the net cage expanded, according to the preamble of the independent claims.

Background of the invention.

A traditional fish cage for farming fish such as salmon and trout comprises among others a floating collar being on the surface of the ocean, a net cage stretching downwards from the floating collar. When farming fish in a net cage, it is important to keep the net expanded to give the fish sufficient volume to move, to prevent the fish from being injured due to entanglement or pressure, and to maintain the meshes of the net expanded to ensure sufficient replacement of water through the net.

Therefore a number of weights are connected to the lower parts of the wall and/or the bottom of the net cage, such as a sinker tube and/or bottom weights. The weights or sinker tube are fastened to the net cage in a transition between net wall and net bottom, keeping the walls down and as close to vertical as possible. Water current passing through the net will always act on the wall, temporarily displacing it from vertical position.

The bottom of a net cage is normally designed as a cone, having the centre lower than the lower part of the wall. Ropes, normally denoted lifting ropes, run along the wall of the net cage, crossing the transition from wall to bottom, and is referred to cross ropes when being a part of the bottom. At the centre of the bottom of the net cage, the ends of the cross ropes are either fastened to each other, or to a separate item, such as an attachment ring. An attachment ring is normally made of steel or another metal sufficiently strong to withstand the strengths from ropes, and are wellknown to a skilled person. Below the centre of the net cage, a centre bottom weight is normally arranged on the outside of the cage, keeping the bottom of the net cage expanded.

By "floating collar" it is in this patent application meant devices at the surface of the sea, holding the fish cage floating. This is traditionally two or three pipes running in circle, wherein the pipes are floating on the water and arranged side by side, fasten to each other by brackets. On the brackets there are often vertical bars making attachment for a handrail at the upper end. The net cage is fastened to the inner side of the circles, and the floating collar holds the net cage floating.

By "net cage" it is in this patent application meant the net holding the fish inside the fish cage. The net cage is performed as a bag having walls and bottom, and has preferably shape as a circular cylinder with conical bottom. The upper part of the net cage is fastened to the floating collar, while the lower part, preferably lower part of the wall or the transition between wall and bottom, is fastened to weights or a sinker tube. The net cage may also be a bag wherein the walls incline towards each other without a defined bottom. The materials of the net cage and the fish cage a such are chosen according to traditional criteria, with a convenient mesh width.

By "sinker tube" it is in this patent application meant a device being lowered into the sea to hold the net cage expanded. The sinker tube has preferably about the same shape and diameter as one of the rings of the floating collar, and is heavy so that the fish cage is held down and does not float up. The lower part of the net cage wall is fastened to the sinker tube, and the sinker tube will thus also make sure that the lower part of the net cage and the net cage bottom is expanded.

A traditional net cage is shown in Figure 1, having a floating collar 110, net wall 111, sinker tube 112, and a conical net bottom 113 with centre bottom weight 114.

When the net cage is used for farming fish, fish feed will be added and waste i.a. from the feeding, excess feeding and faeces from the fish will occur. The faeces and excess feeding are nutrient rich waste which may disturb the environment on the seabed under the fish cage. During normal farming, some of the fish dies even in healthy and well operated fish plants. Dead fish, faeces, uneaten feed and other waste generated in the fish cage, will fall to the bottom, and gather at the centre of the conical bottom of the net cage. The dead fish and waste should be removed to maintain a healthy environment for the fresh fish and to avoid disturbing the environment of the fish cage. Another problem is that dead fish may attract predators which will attack and possibly damage the net cage to get hold of both healthy and dead fish.

According to Norwegian regulations, the death rate must be checked and dead fish removed at least once a day. Several systems are developed to remove dead fish, and any waste accumulated together with it, such as the system Mortex owned by the patent applicant, or the Liftup system from Lift up AS. A main feature for all these systems are use of an airlift pump close to a collector arranged at the bottom of the net cage. The airlift pump injects compressed air at the discharge pipe close to the collector, and any dead fish and other waste on the collector, will be discharged with flow of water and air. Such a known system is indicated in Figure 1, where a collector is denoted 115, and the discharge pipe is denoted 116. The air supply pipe runs together with the discharge pipe and is not shown in Figure 1. Corresponding systems are also known from CA2638355 and NO342765.

None of the known systems are fastened to the net cage, they are only resting in and supported by the bottom of the net cage. The pump is used to remove dead fish at intervals, and during use, the compressed air and suction creates an upward force acting on the collector, and may, in worst case, lift or displace the whole system. Further, during heavy weather or strong water current, the water may displace the system. Most of the known systems are thus filled with weight in the lower part, such as 800 kg, to keep the system in place. This will of course also help to expand the net.

A general concern related to net cages floating in the sea, is the risk of rupture of the walls or bottom, with subsequent escape of fish. Rupture of the net cage and escape of farmed fish is, of course, an economical loss for the owner, but it is also an environmental problem as the escaped farmed fish interfere with wild fish and may potentially spread parasites and diseases not common among wild fish. Due to these concerns it is a general understanding that the number of heavy equipment arranged close to the net cage, should be reduced or avoided.

In different situations, one may need to lift the net cage, and this is performed by lifting the sinker tube and/or bottom weights. In cases where a system for removal of dead fish is installed, this must be lifted simultaneously or in advance. Lifting may for instance be necessary upon emptying or treatment of disease of the fish in the fish cage, but also upon cleaning and replacement of the net cage. The net cage is lifted by pulling lines attached to the sinker tube and/or bottom weight, and by pulling the net and collecting it at the inside of the fish cage. Lifting of the different parts must be synchronized to avoid risks for stretch and tear of the net. This is time consuming and labour intensive, and the work may also be heavy and dangerous.

Based on the above, an object of the invention is to keep the net cage expanded, yet making the work related to elevation of the net cage easier, faster and less dangerous. Another object is to reduce the danger of rupture of the net cage.

Summary of the invention

The objects above is met by a device and a system according to the characterizing parts of the independent patent claims. Further features are stated in the corresponding dependent claims.

The present invention relates to a device for installation at the bottom of a net cage, on the inside of the net cage. The device comprises a housing with a plate having a surface arranged for collection of waste, the surface is turning upwards when the device is installed in the net cage. The device further comprises connection means configured to connect a system for removal of the waste to the plate, for removal and transport of the waste from the net cage. The housing of the device further comprises a cylindrical part protruding opposite the plate, and a weight.

Several system for removal of the waste is known, and a skilled person would be familiar to choose the most convenient for the given purpose, and install it appropriately. Thus, it is not described any further here. The system should be connected to the plate, meaning that the system should be arranged to remove any waste collected on the plate.

In a preferred embodiment, the plate is flat and any waste falling through the fish cage, or sliding along walls of the cage, will be collected on the plate. In an alternative embodiment, the plate is concave wherein the center is vertically lower than the peripherical edges once the device is installed

The plate may either be the upper part of the housing, or it may be attached to an upper part of the housing. In one embodiment, wherein the plate is the upper end of the cylinder, the diameter of the plate and cylindrical part is the same. In another embodiment, the plate has larger diameter than the cylindrical part, and protrudes thus radially beyond the cylinder. The plate may be connected to the cylindrical part directly, or by an intermediate conical part.

A lower end of cylindrical part, when the device is installed in a fish cage, may be cylindrical, rounded or even conical or frustoconical, wherein a rounded lower part is preferred in order to avoid the device getting stuck or entangled in the bottom of the net cage. Further, a rounded end will more easily be guided into a pocket of the net cage without any risk of rupture of the net.

The housing comprises a weight, and in a preferred embodiment, the weight is inserted or moulded into the housing. In a preferred embodiment, the weight is arranged at the bottom of the housing, in or at the cylindrical part, more preferred in or at a lower end of the cylindrical part. The weight may be granular material filled into the housing, or one solid part inserted or molded into the housing. In a preferred embodiment, the housing and/or cylindrical part is made of a material being sufficiently heavy to constitute the weight.

The device further comprises fastening means, preferably releasable means, for attaching the device to the net cage. The fastening means may be arranged on the housing, at the peripheral edge of the plate, or when the diameter of the plate is larger than the diameter of the cylinder, under the plate, meaning at the surface of the plate from the peripheral edge to the cylinder. Such fastening means are preferably arranged to cooperate with corresponding fastening means on or in the net cage. In an alternative embodiment of the device, the fastening means may be released remotely.

In a preferred embodiment, the device further comprises installation elements to be used when the device is to be installed in the net cage. Such installation elements are preferably arranged to cooperate with corresponding elements in the net cage. The installation elements may either be released from corresponding elements in the net cage, released from the device once the installation is complete, or be used to lift the device at any desired time. In a preferred embodiment, the installation elements of the device are passages or holes in the plate. If the device has fastening means which may be released remotely, the installation elements may also constitute a part of the fastening means.

The invention further relates to a system for expanding a fish cage. The system comprises a device as described above and a net cage having a pocket protruding vertically downwards from the center of the bottom of the net cage, wherein the pocket is configured to accommodate the cylindrical part of the device, and thereby the weight will be expanding the fish cage.

By "pocket" it is in this application meant a small bag that is sewed or inserted into the net cage so that it is open towards the inside of the net cage. The pocket in the net cage is protruding vertically downwards when the net cage is arranged as a fish cage.

The pocket and the housing of the device preferably has a design closely resembling each other, and once the cylindrical part is accommodated in the pocket, the plate of the device will be arranged at the bottom of the net cage. In this way all waste will either directly fall onto the surface of the plate, or slide along the walls and/or bottom and onto the surface.

In a preferred embodiment, the diameter of the plate of the device is larger than the diameter of the housing of the device, and the length of the pocket of the net cage is slightly longer than the cylindrical part of the housing, and the diameter of the pocket is smaller than diameter of the plate. In this way any waste sliding along the net wall and/or bottom of the net cage will be collected on the surface of the plate, and not fall into the pocket.

With such a system, the device according to the invention may replace both a system for removal of waste, and a bottom weight at the center of the net cage to keep the net cage expanded. The bottom weight at the outside of the net cage may thus be removed, and handling of the net cage will be substantially easier.

Further, when using a traditional bottom weight, lines, ropes, chains or the similar is running along the outside of the net cage for lifting the bottom weight and/or sinker tube, and when water current is acting on the net wall, the net may get in touch with these lines with a risk of rupture. When the weight and the corresponding lines are removed, the risk for rupture is also reduced.

In a preferred embodiment, cross lines at the bottom of the net cage is attached to an attachment ring at center. The pocket is also attached to the attachment ring, whereby the opening to the pocket is through the attachment ring.

In a preferred embodiment, the pocket is made of a flexible material, which may be expanded once the cylindrical part of the device is inserted. The retraction of the material will act on the device, and keep the device in place.

In a preferred embodiment, the device has fastening means for fastening the device to the pocket of the net cage, and when the net cage has an attachment ring at the bottom, the attachment ring preferably comprises corresponding fastening means.

The fastening means may for instance be magnetic, threads, or even a cabinet catch, and may be arranged be between the attachment ring and the plate of the device. By having fastening means, the bottom of the net cage may be lifted by lifting the device, which will further reduce the amount of work and the risk of rupture of the net cage. In a more preferred embodiment, the fastening means should be arranged in such a way that they may be remotely fastened and opened.

The system may further comprise installation elements corresponding to installation elements of the device, to ensure that the cylindrical part of the device is led into and accommodated in the pocket of the net. In a preferred embodiment, the installation elements of the net cage is one, or preferably two lines running from the bottom of the net cage to the surface. The lines are preferably attached to the attachment ring at opposite sides of the opening of the pocket. The lines may then be attached to installation elements of the device, and when the device is lowered, the device will be aligned with the pocket, and the cylindrical part will be guided into the pocket. When the installation elements of the net are lines, the preferred installation elements of the device are holes or passages through the plate, configured to accommodate the lines. By using installation elements, any problems relating to guiding the cylindrical part of the device into the pocket are substantially reduced.

In a preferred embodiment of the system, an area surrounding the pocket at the bottom of the net cage, is covered or made by a material having reduced mesh width, more preferably being made of a water tight material, such as tarpaulin. This will assist the installation of the device, as the cylindrical part may slide along the bottom of the net with less danger of rupture, until it is inserted into the pocket.

Further, it will prevent any waste from falling through the bottom of the net cage, and improve the collection of waste at the plate of the device.

Reference throughout the specification to “one embodiment” or “an embodiment”, "one aspect" or "an aspect" means that a particular feature, structure, or characteristic described in connection with an embodiment and/or aspect, is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

The invention will in the following be described with an example given to illustrate the invention, and should not be used to interpret the invention, as it is defined in the enclosed claims, restrictive.

Example

The invention will in the following be described with the help of the enclosed Figures, showing a preferred embodiment of a device and a system. The different parts of the figures are not necessarily to scale in relation to each other, as the figure is merely for illustrating the invention.

The invention will in the following be described with reference to the enclosed Figures, where

Figure 1 shows a fish cage according to prior art,

Figure 2 shows a device according to the invention in perspective from above, Figure 3 shows a cross section of a device installed in a net cage, and

Figure 4 shows a device installed in a net cage in perspective from above.

Figure 1 shows a fish cage according to prior art, and is described above. Figure 2 shows a device according to the present invention, having a housing 1 with a plate 2 arranged for collection of waste falling down in the fish cage. The device further comprises connection means, shown as two bars 3 protruding vertically up from the plate. The bars 3 are connected to a suction tube 4 of a system for removal of waste, and the shown bars are telescopic to adjust the distance between the plate 2 and the suction tube 4.

The housing 1 of the shown device has a cylindrical part 5, protruding opposite the plate, that is downwards when the device is installed in a fish cage. In the shown embodiment, the plate has a larger diameter than the cylindrical part, and the plate is attached to the cylindrical part by a conical part 6. The distal end 7, being the lower end when the device is installed, of the cylindrical part is rounded, to ease the installation of the part into a pocket of the fish cage.

The housing shown in Figure 2, is made of plastic, and a weight is either inserted into a hollow interior of the housing, or the weight is molded into the material of the housing.

Figure 3 shows a device installed in a net cage in cross section, and in Figure 4 the installed device is shown in perspective from above, wherein only lower parts of the net is shown for clarity reasons. The fish cage has a number of cross ropes 11, and at the centre of the bottom, the ropes are fastened to an attachment ring 12. Further, at the bottom, preferably at the centre of the bottom, the fish cage has a pocket 8 made of net cage material. The pocket is protruding downwards, and the opening to the pocket is through the attachment ring 12. In Figure 4 the pocket is shown in cross section for clarity reasons. The net cage and the pocket are integrated in such a way that there are no openings or holes in the cage.

Once the cylindrical part 5 of the device is guided into the pocket 8, the device is fastened to the attachment ring 12 by fastening means (not shown). In the shown embodiment, corresponding fastening means are arranged at the underside of the plate 2 and at the attachment ring 12.

The fish cage is further provided with installation elements shown as one rope 9 in Figure 3 and two ropes in Figure 4, fastened to the attachment ring 12 in one end, and at the surface (not shown) in the other end. These ropes 9 may also be used for raising the attachment ring 12, and thereby the net, if desired. The shown device is provided with holes 10 through the plate, and in the shown embodiment the holes are in the part of the plate protruding beyond the cylindrical part 6, in such a way that the holes are open. The ropes 9 are running through the holes 10, and thus the device will be guided into the pocket 8 once the device is lowered.

The housing shown in Figure 3, is made of a metal such as steel, and thus it constitutes the weight.

The examples above are given to illustrate the invention, and should not be used to interpret the following claims in a limited manner. The scope of the invention is not limited by the examples given above, but by the following claims. Modifications and amendments of the invention, being obvious to a skilled person, should also be included in the scope of the invention.

Claims

Patent claims

1. Device for installation at the bottom of a net cage, the devices comprises

- a housing (1) with a plate (2) arranged for collection of waste, the plate (2) is turning upwards when the device is installed in the net cage, and

- connection means (3) configured to connect a system for removal of the waste to the plate,

wherein the housing (1) further comprises a cylindrical part (5) protruding opposite the plate (2), and a weight,

characterized in that the device further comprises fastening means arranged under the plate (2) or at the peripherical edge of the plate (2), for attaching the device to the net cage.

2. Device according to claim 1, wherein the device further comprises installation elements (10).

3. Device according to claim 2, wherein the installation elements are holes or passages (10) through the plate.

4. Device according to any one of the preceding claims, wherein the weight is inserted or moulded into the housing.

5. System for expanding a fish cage, characterized in that the fish cage comprises a net cage having cross ropes (11) attached to an attachment ring (12) at the centre of the cage, and a cylindrical pocket (8) protruding downwards from the attachment ring (12), wherein the pocket (8) is configured to accommodate the cylindrical part (5) of a device according to any one of claims 1 - 4, and wherein the attachment ring (12) comprises fastening means corresponding to the device, which are configured to attach the device to the attachment ring (12).

6. System according to claim 5, wherein the device comprises installation elements (10), the net cage further comprises corresponding installation elements (9), running from the surface to the bottom of the net cage.

7. System according to claim 6, wherein the installation elements (9) are running from the surface to the attachment ring (12) of the net cage.

8. System according to claim 7, wherein the installation elements (9) are ropes, lines, or chains (9) fastened to the attachment ring (12).

9. System according to any one of claims 5-8, wherein a lower part of the net cage, surrounding the pocket (8), is provided with a material having reduced mesh width.

10. System according to claim 9, wherein the material having reduced mesh width is a watertight material, preferably a tarpaulin.