NO346671B1

NO346671B1 - System for preventing fouling on cages for aquatic animals in water

Info

Publication number: NO346671B1
Application number: NO20210104A
Authority: NO
Inventors: Petter Birkeli Wiik Pettersen
Original assignee: Cage Ctrl As
Priority date: 2021-01-27
Filing date: 2021-01-27
Publication date: 2022-11-21
Also published as: WO2022164325A1; NO20210104A1

Description

System for preventing fouling on cages for aquatic animals in water.

The present invention relates a cage for farming aquatic animals in water, and use of such a cage according to the preamble of the independent patent claims.

Aquaculture is a major industry, and most of the farmed animals are farmed in net cages at the sea. A traditional net cage comprises a floating collar at the surface of the sea, a net surrounding the farmed organisms and fastened to the collar, and weights to keep the cage dilated and stretched and in such a way that the meshes of the net is open. The mesh size of the net should be adjusted in such a way that the farmed organisms are kept inside the cage, yet allowing water to flow through the mesh, in and out of the cage.

The floating collars are traditionally round or square and comprises two or three circular tubes arranged outside of each other and a handrail in plastic, fastened to each other by steel or plastic brackets. The net cage traditionally comprises a net wall and net bottom, the bottom may be flat or shaped as a cone. The weight may be any suitable weight, such as a sinker tube.

Another well known type of net cage in the water is a rigid frame covered by a net of metal or textile, and attached to buoyancy means, either floating collars as mentioned above, floating barges, or similar means. The net will thus be expanded by the frame, and weights will not be necessary.

There is however a problem with debris and fouling of the net in the net cages, regardless of how the cage is arranged. Especially during summer and in areas with higher water temperature, algae, barnacles, shells and similar attach to the net and grow. The fouling will prevent water from flowing through the net, and thus the water inside the net cage will not be as fresh as desired, which may lead to less growth and reduced fish health. The oxygen level in the fish cage may become reduced when the net is very fouled. Further, fouling and debris will create a hiding place for parasites such as sea lice, irritant hydroids, parasite eggs and larvae, and organisms causing diseases such as amoebic gill disease. Yet another problem with fouling is that cleaning fish, such as wrasses or lumpfish, prefer to feed off the fouling rather than the sea lice on the fish.

Patent publications CH 714301, NO 20130276, GB 2479375, KR 20170052047 and US 2010/0050952 describe solutions to the above said problems, however none of them fully describes a solution suitable for use on a net cage arranged in the sea.

Further, to avoid the fouling, the net may be made of a material preventing fouling, yet withstanding the harsh and corrosive environments at the sea, offering sufficient strength and ensuring the fish welfare. Such materials are however not efficient in preventing fouling over time. Different types of coating have also been used, however, the coating will lose its effect after a short period of time in the sea, and/or it will be washed or torn off. The coatings may comprise poisonous compounds, and further they may dissolve or loosen from the net and leak into the surrounding sea. This may reduce the welfare of the fish in the net cage, and the environment around the net cage.

When fouling appears, the cage has to be cleaned, traditionally by net washing machines or cleaners, which flush the net with water from a number of nozzles, or clean the net with brushes. This wears the net, and any antifouling agent on the net will be reduced or even removed during the cleaning process.

Objects of the present invention

Based on the above, there is a main object to develop an improved system for avoiding fouling of the net. Another object is to develop a system for cleaning the net if fouling has developed, without any of the problems mentioned above. Yet another object is that the system should be easy to use and to install on new and existing aquaculture farms. Finally, there is an object to develop a system for avoiding and/or cleaning the net which may be controlled remotely, for instance from ashore.

Summary of the invention

The objects are met with a system and a net cage according to the characterizing parts of the independent claims.

The invention relates to a system for preventing fouling on cages for aquatic animals in water. The system comprises a net surrounding the aquatic animals, and having a mesh size allowing water to flow through, wherein the net comprises threads of sound conductive material interwoven in a net of non-conductive material, and in that at least one transducer emitting ultrasound is fastened to the.

The net is a net cage enclosing the aquatic animals. It is preferably closed downwards and separates the animals from the surroundings.

In an alternative embodiment, the net may be a skirt hanging down from buoyancy means at the surface of the water. The skirt will be open downwards, and is normally arranged around a net cage.

In another alternative embodiment, the system comprises both a skirt and a net cage as described above, wherein the skirt is arranged around a net cage.

The net cages for aquatic animals may both be submerged cages, and cages at the surface of the water, preferably fish cages. The water may be seawater, when the cage is arranged in the sea, or freshwater if the cage is arranged in a lake. The aquatic animals may be any animal suitable for farming, such as shellfish or fish, preferably fish, even more preferred salmonids.

The system comprises a net surrounding the aquatic animals, and when the net is arranged in water, most parts of the net will be submerged. The mesh size of the net is chosen according to the size of the animals, both to prevent the farmed animals escaping from the net, and to avoid any predators or fish from the environment to enter the net. Further, it is important that water may flow through the net to keep the water inside the net cage fresh and with sufficient concentration of oxygen. The optimal mesh size is an obvious choice for a skilled person.

The threads of sound conductive material may be of any suitable material being able to transmit or conduct ultrasound for a distance of at least 3 m. This means that the ultrasound should be transmitted at least 3 m away from the transducer, along the material. When the net cage is arranged in water, it will at least partly be below the surface of the water, and thus the material must be solid and not be dissolvable in the water. Further, the material must withstand the environments of the net, including being submerged in seawater and exposed to water current.

At least one transducer is fastened to the ultrasound transmitting material. The transducer is arranged to transmit ultrasound into the ultrasound transmitting material of the net which then will scatter the ultrasound into the section. When the net is exposed to ultrasound, fouling will be reduced or not take place, and thereby the net will be clean.

The number of transducers needed to cover the whole net or at least parts of the net, and/or the optimal distance between transducers, depends on a number of factors, such as the material and size of the sound conductive threads and the frequency of the ultrasound being transmitted. Water also conducts ultrasound, and the water flow conditions at the location of the cage will thus also influence the number of transducers needed.

The transducers may be any regular transducers suitable to be submerged, and may be wired or battery-operated. In a preferred embodiment the transducers emits ultrasound in the frequency range of 15-100 kHz, preferably in the frequency range 20-60 kHz. The transducers may emit ultrasound constantly or at intervals depending on the amount of fouling.

In a preferred embodiment, the system further comprises a central unit, wherein all the transducers are connected to the unit. The central unit may be used to control and coordinate the frequency and/or interval of the ultrasound emitted by each of the transducers. In a further preferred embodiment, the central unit is arranged to give a signal if there is a break in any of the cables running to the transducers. A break in a cable may simply imply that there is a break in the wire leading to the transducer or in the transducer, but it may also imply that there is a hole in the net.

In another preferred embodiment, the system further comprises a system for wireless and remotely control of the transducers. Such a system will enable remote control and the operator may be in safe environments onshore or in a barge, rather then on the exposed fish cage. Remote control also enables control and adjustment of the system more frequently and in a manner that is independent of the weather conditions. The remote control system is preferably able to switch the transducers on and off, regulate the frequencies, and determine how long the pulses are and often the pulses are emitted (the interval between pulses). The system for remote control preferably further comprises means for transferring data through mobile networks, radio signals, Bluetooth, Wi-Fi and/or underwater modems.

In embodiments wherein the system comprises a central unit, then the system for wireless and remote control may be arranged to communicate with the central unit which then communicates with the transducers.

Reference to an ultrasound transmitting material may be to a material that produces a small damping effect on the ultrasound signal as it passes through the material and along the threads forming the net. For example, a material that, in the case of a 5 kHz signal, will allow ultrasound to travel at least 0.5 m away from the transducer, through the material and along the net before the intensity is reduced to 10% of its initial value. Preferably, the material used will allow the ultrasound to propagate to a distance of at least 1 m, preferably at least 3 m, before the intensity is reduced to 10% of its initial value.

Some metals will produce a relatively small damping effect on the signal (i.e. will not attenuate the ultrasound to any great degree) and are thus suitable for use as the ultrasound transmitting material comprised in the net of the fish cage. Aluminium, cobber and/or brass alloys, for example, or some types of steel, such as stainless steel may be suitable choices. These also will not corrode over time, which will obviously be an advantage when the system is used together with a fish cage.

Traditional materials used to form the net of a fish cage may also transmit ultrasound, at least to a degree, but will not allow the ultrasound to propagate to the distances mentioned above and so cannot be considered an ultrasound transmitting material in the sense referred to herein. The signal may also propagate through the water surrounding the fish, and potentially the body tissues of the fish themselves, however this should not be an issue provided that the no damage or disturbance is caused to the fish. Lower ultrasound frequencies may be preferred for this reason.

The transducers coupled to the net produce sound waves which propagate into and across the ultrasound transmitting material. If the sound waves are at ultrasound frequency then the transducers can be referred to as ultrasound transducers.

Suitable types of transducers for this purpose may include piezoelectric elements which are caused to vibrate in response to an AC signal to produce the sound waves, or metallic or non-metallic diaphragm transducers. Any type of transducer may, however, be used, provided that the signal emitted is in the ultrasound range and can propagate to and along the ultrasound transmitting material of the net.

The frequency of the ultrasound produced can be controlled by adjusting characteristics of the driving signal. The frequency of the driving signal, for example, can be used to adjust the frequency of the ultrasound signal produced. The driving signal can also be controlled to produce a continuous ultrasound signal of constant or changing intensity, constant or changing frequency, or a pulsed signal with constant or changing frequency and/or intensity. A square wave signal can be used as the driving signal for the transducer in some cases.

The control/driving signals may cause the set of transducers to emit ultrasound continuously, and at the same amplitude and frequency. Alternatively, different transducers in the set may be caused to emit ultrasound at different frequencies or intensities. These may depend on the exact distribution of transducers across the net, and may be adjusted. The adjustment may be made in order to account for malfunctioning transducers in some cases. A malfunctioning transducer which no longer produces a signal can be compensated for by adjacent transducers being operated to produce a higher intensity signal, for example. A pulsed signal may be used in place of a continuous signal from one, several, or all of the transducers coupled to the net.

The transducers may be coupled to the net in such a way that the ultrasound signal produced is transferred directly from the transducer (i.e. the moving elements of the transducer) to the ultrasound transmitting material of the net. There may be no intervening material between the two, or air may be present. In any case, there will be little or no loss of signal between the transducer and the ultrasound transmitting material at the location of the transducer.

The intensity and frequency of the ultrasound signal may be selected based on properties of the environment, and of the ultrasound transmitting material that has been chosen to form part of the net. A higher intensity signal may be required if attenuation by the ultrasound transmitting material is higher, for example, to ensure that there is sufficient energy in the ultrasound signal to remove or prevent fouling in regions of the cage which are furthest from the transducers. Similarly, the attenuation will depend on the frequency of the signal and this may need to be adjusted accordingly. A pulsed signal may also be preferable in some cases in order to reduce power consumption.

The transducers may be capable of both receiving and emitting ultrasound. This is simple to achieve with minimal change in transducer configuration. In a detecting mode, movement caused by the received signal (movement of the piezoelectric signals in the transducer, for example) results in an electric signal being produced, rather than the other way around as when the transducer is used to produce a signal. The transducers can therefore also be used to test the performance of the system and/or the condition of the net. In a testing phase, one transducer can be caused to emit an ultrasound signal and the adjacent transducers can be set to detect the signal at their position.

The strength of the detected signal at the positions of the surrounding transducers may be able to be used to detect holes in the net, for example, because of the intensity of the signal at an adjacent transducer where a hole in the net is present will be different. If the received signal intensities at the adjacent transducers is found to be too low in the testing phase, the driving signal for the transducers can be adjusted to increase the intensity of the emitted ultrasound or to adapt the frequency to improve performance of the system. This type of testing mechanism can be employed for groups of transducers in turn, varying those which acts to emit the ultrasound signal and those which act to detect the signal.

Control of the system may be via wireless or wired connection between the control unit and a user device. The user device may be located at a large distance from the control unit, such as on a boat or on land, or may be located above the surface of the water on a structure supporting the fish cage. A control signal can be sent from the user device to the control unit, which causes the desired driving signal to be produced for each of the transducers present in the system. If testing capability is provided, the detected signals at each of the transducers can be sent by the control unit back to the user device for processing, or can be processed at the control unit and a message or alert sent back to allow any necessary adaptions to be made to the system.

Connection between the separate transducers and the control unit may also be via wireless or wired connection. In the former case, the transducers may each be equipped with an antenna, which may be fairly compact. Communication signals must obviously be capable of being sent through water. The transducers can be electrically connected together in some cases. Power for the transducers can be provided through this connection or using batteries within the separate units, which will then need to be replaced periodically. The transducers can potentially include energy harvesting capabilities to reduce energy consumption. They could, for example, be configured to harvest light using photovoltaic cells or energy from water currents.

In another aspect, the invention relates to a net to be used in a system as described above wherein the net has a mesh size allowing water to flow through and wherein the net comprises a solid, ultrasound transmitting material interwoven in nonconductive material.

In another aspect, the invention relates to a net cage to be used in a system as described above, wherein the net cage have a mesh size allowing water to flow through and wherein threads of sound conductive material is interwoven in a net of non-conductive material.

In yet another aspect, the invention relates to use of a system, net and/or net cage as described above for farming fish in the sea, wherein the net surrounds the fish to be farmed.

Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment 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 following description of an exemplary embodiment refers to the figures, and the following detailed description is not meant or intended to limit the invention. Instead, the scope of the invention is defined by the appended claims.

Description of the figures

The invention will now be described with the help of the enclosed figures, showing the principles of a system according to the present invention. The different parts of the figure are not necessarily in scale to each other, as the figure is merely for illustrating the invention.

The invention is illustrated by

Figure 1 showing a system according to the invention, arranged on a fish cage, Figure 2 showing an alternative embodiment of the invention, and

Figure 3 showing a control unit.

Description of preferred embodiments of the invention

Figure 1 shows a system according to the invention, arranged on a traditional fish cage. The fish cage comprises a floating collar 1 at the surface of the sea, and a hand rail 2 above the surface. A net cage having a cylindrical wall 3, and a conical bottom 4, is attached to the floating collar and protruding down into the sea. A number of fish 5 is enclosed by the net cage.

The whole net cage is made of threads of Nylon or Polyester, having metal threads wound into the net, and thus the whole net cage is made of ultrasound transmitting material and is sound conductive. In the shown embodiment, twelve transducers 6 are attached to the net, one row of transducers at the upper part of the net cage, and one row at the bottom of the cylindrical wall. The pattern of the transducers may be adjusted according to the material of the net cage and local conditions. The transducers may be placed spaced apart so that the maximum distance between adjacent transducers is roughly equal to the distance which ultrasound at the frequency used can travel through the ultrasound transmitting material (or along the threads formed of the ultrasound transmitting material) before it’s intensity or amplitude is reduced to 10% of its initial value. The shown transducers are Piezoelectric transducers.

Figure 2 shows a net according to the invention. The net 10 is made of threads 11 of ultrasound transmitting material, connected to create a net. On the net four transducers 12 are arranged at a distance of 3 m from each other. In this arrangement, ultrasound will be transferred to the whole net, and no fouling will occur. The shown net may be included into a net cage or a skirt as a section, or a whole net cage or skirt may be performed as the shown net.

Figure 3 shows a combined central and control unit to be used with the fish cage shown in Figure or the net shown in Figure 2. The unit comprises ports 13 for power supply and a display 14 for showing system status. In some cases an antenna is integrated into the unit, and information is transferred to a monitoring unit through mobile networks, radio signals, Bluetooth, Wi-Fi and/or underwater modems.

In other other cases a monitoring unit is connected via port 15. The transducers, being a part of the system, are connected to the ports 16 of the unit. For clarity only two ports 16 for transducers are shown, but the number will be adjusted according to the specific use. The unit may be designed in any suitable way, and should be adapted to withstand the harsh environments of a fish cage.

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

Claims

1. System for preventing fouling on cages for aquatic animals in water, wherein the system comprises a net (3) for surrounding the aquatic animals, and having a mesh size allowing water to flow through, characterized in that the net (3) comprises treads of sound-conductive material interwoven in a net of non-sound-conductive material, and in that at least one transducer (6; 12) configured to emit ultrasound is fastened to the net.

2. System according to claim 1, characterized in that the transducers are configured to emit ultrasound constantly.

3. System according to any one of the preceding claims, characterized in that the transducers are configured to emit ultrasound in the frequency range of 15-100 kHz, preferably in the frequency range 20-60 kHz.

4. System according to any one of the preceding claims, characterized by comprising a central unit, and in that the transducers are connected to the central unit, which controls the frequency and/or interval of the emitted ultrasound.

5. System according to any one of the preceding claims, characterized in that the system further comprises a system for wireless and remotely control of the transducers.

6. System according to claim 5, characterized that the control system comprises means for transferring data through mobile networks, radio signals, Bluetooth, Wi-Fi and/or submarine modems.

7. A net to be used in a system according to any one of claims 1-6 above, characterized in that the net have a mesh size allowing water to flow through, and comprises treads of sound-conductive material interwoven in a net of non-soundconductive material.

8. Use of a system according to any one of claims 1-6, and/or a net according to claim 7 for farming fish in the sea,

wherein the net surrounds the fish to be farmed.