Submersible multi-chamber cage for aquaculture

Abstract

The invention relates to a multi-chamber submersible cage for aquaculture, comprising a novel flotation system which permits a uniform and fast sinking and refloating, using pumps which fill the chambers with the same quantity of seawater in each. The filling is carried out quickly due to the small size of each chamber, the number of pumps and the counterweights.

Description

SUBMERSIBLE MULTI-CHAMBER CAGE FOR AQUACULTURE FIELD OF THE INVENTION The present invention relates to a submersible multi-chamber cage system for aquaculture and a process for submerging and re-floating a multi-chamber submersible cage for aquaculture. BACKGROUND OF THE INVENTION AND PRIOR ART Industrial aquaculture is a growing economic worldwide activity that produces thousands of tons of high value fish such as salmon, trout, halibut, tuna, cobia, tilapia, barramundi and many other commercially important species. The most common method of production of these species is floating circular cages, usually located in coastal waters as well as lakes. However, appropriate locations are getting ever scarcer and must contend with ever more adverse environmental conditions such as large waves, low dissolved oxygen, algal blooms, ice and other objects floating adrift, security and opposition from local communities for disturbing the seascape. Current cage technology has been unable to address these issues effectively and better solutions are required. One of the technical solutions explored in the past has been to use submersible cages. This allows the aquafarmer to dodge toxic algal blooms and low oxygen situations which usually occur near the surface. It also allows the aquafarmer to avoid damage by ice, improves security and hardly changes the seascape. Lastly, by submerging the cage it is possible to insulate the cage from the action of large waves. Among several solutions that have been developed under this technique to date we can find the following: a submersible cage that has a flotation system based on tanks (Kim et al., 2012); also a submersible cylindrical cage (WO / 2018 / 009085); others that have movable sections (WO / 2015 / 099540); others that have a bi-conical structure (ES / 2294940); and finally others that have a flotation system based on water and air pumping mechanisms (US / 8371245). Furthermore, different flotation methods have been developed, such as the use of air compressor and bilge pumps to support the hull of a net structure (WO / 2015 / 055867); the use of flexible hoses connected to an inflation air compressor (CN / 1623378); a polygonal structure made of tubes through which air or water is conducted (CN / 103430888); or the use of an air tank inside the structure of a cage (KR / 2017 / 0092417). These systems have different shapes and designs and they all rely on the circulation of air through tubes or hoses within the structures. However, in all the above-mentioned solutions a number of problems remain that have prevented them from being applied in an industrial scale. These problems can be one or more of the following: 1. difficulty in scaling the design to large cages appropriate for industrial aquaculture (over 30m in diameter); 2. higher cost compared to current non-submersible cages (over 50% higher) due to their complex design and need of special moorings; 3. slow submersion and surfacing times (more than 15 min), which means higher operational cost and slower reaction time to emergencies that require quick submersion, for example a sudden low oxygen conditions; 4. significant deformation of the cage during submersion and surfacing, that can lead to cage damage and risk of fish escaping as well as stress and abrasion of the fish in the cage; 5. lack of control of the submersion and surfacing procedures, which is necessary to adapt the cage to different fish species requirements; and 6. impossibility of adapting existing cages and mooring systems to the new technology. SUMMARY OF THE INVENTION In order to overcome the mentioned problems of the prior art an aquaculture cage system is provided wherein the cage can be submerged and refloated in a uniform and controlled manner by effectively controlling its hydrostatic properties. The cage system comprises a cage with a structure made of one or more flotation rings subdivided into multiple flotation chambers, individual water hoses for each flotation chamber, separate water pumps and a manual or automatic control system for controlling the filling or emptying of the chambers with water. It further comprises a fish containment net hanging therefrom, surrounding it and connected to a sinker tube attached to the net's bottom. It may also comprise filters for the sea water that enters the pumps. No special type of mooring is required and it withstands waves of up to eleven meters high. Optionally, the cage system may comprise an air pipe or hose and an air compressor for emergency purposes. However, in operation air is not removed or introduced from / into the chambers in order to respectively submerge or refloat the cage. Instead, air inside the chambers is only compressed or decompressed as a result of the changes in the amount of water within the chambers, thus eliminating the need for air hoses and compressors. As water is incompressible, the control system can control the weight of each flotation chamber by controlling the precise amount of water added into it or removed, without the need of feedback control loops. This precise control of the hydrostatic properties of the cage leads to a uniform submerging and refloating of the same, that is to say, maintaining the horizontality of the cage in the water, as well as being able to adapt the hydrostatic properties of the cage according to the environment, the biology of the fish species, the net weight and the aquafarmer's changing operational needs. Further, the pumps are able to quickly fill the flotation chambers with the necessary amount of water due to the small size of each chamber, the amount of pumps and the counterweights (mainly sinker tube). Submerging and re-floating of the cage takes little time, in the order of 2 to 10 minutes. The control system in turn controls the flotation characteristics of the cage, the submerged weight as well as the buoyancy when afloat. Filling or emptying of the chambers is done simultaneously with the control system. The chambers are not completely filled or emptied, a variable volume of air and residual water always respectively remaining after each process. The pumps are of the positive displacement type and thus displace the same amount of water, irrespective of the pressure. The pumps are watertight thus preventing seepage when they stop operating. The pumps can handle impurities of up to 18 mm in diameter. The control system allows individual filling of each chamber with precision. Furthermore, the control system enables to limit the weight of the cage to avoid changing the buoys when the cage system of the invention is mounted on an existing mooring system. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a top view of an overall diagram of the multi-chamber submersible cage system for aquaculture according to the invention. It depicts an exemplary model of circular cage system according to the invention with two flotation rings. Figure 2 shows a perspective view of three circular cages that form part of the cage system according to the invention, each comprising a different example of fish containment net. Figure 3 depicts part of the process to submerge and refloat a multi-chamber submersible cage for aquaculture according to the invention. It shows four cross- section views of a segment of the exemplary cage system of Figure 1, each illustrating a step of the process. DETAILED DESCRIPTION OF THE INVENTION An submersible cage system for aquaculture is proposed that can be submerged and refloated by controlling its hydrostatic properties by pumping precise amounts of water to several chambers. It is a simple, low cost and easy to maintain system that can also be installed in most existing floating cages. A description of its constituent parts with reference to the drawings follows below. The cage (J): The first part of the system is the cage itself (J) whose structure is meant to be submerged and refloated. The shape of the structure may be elliptical, circular or any other shape that allows it to be formed by one or more flotation rings (1). In Figure 1 the cage (J) is circular in shape and has two flotation rings with a pre- determined space between each other. These flotation rings are subdivided into flotation chambers (2) formed inside the rings. The flotation rings may be manufactured with any of a variety of appropriate materials, usually high-density polyethylene (HDPE). The size of the cage is within the range of 22 to 90 meters in diameter, with a height or depth of 10 to 60 meters. By having multiple chambers the cage can be submerged or refloated without significant deformation. The amount of chambers will depend on the size of the cage and its hydrodynamic characteristics. The cage (J) further includes a net (4) hanging therefrom and surrounding it. The net can be made from a synthetic textile of polyamide, polyester or polyethylene of ultra- high molecular weight or another high-resistance thermoplastic, wire mesh or any other commonly known net material. Its function is to contain the fish. As shown in Figure 2 the net of the cage can have many shapes but it is generally slightly conical or else cylindrical. Water hoses (3): Individual water hoses are connected at one end to each flotation chamber (2) in the flotation rings (1). The hoses (3) are deployed around the cage in such a way that they can be easily recovered from the surface of the water even when the cage is submerged, and connected to water pumps (5). Figures 1 and 3 depict an example of a deployment of these hoses on a cage with two flotation rings wherein they are connected to each flotation chamber. A chamber comprises a section of the innermost and outermost rings connected as communicating vessels via air and water conduits. Water pumps (5): Positive displacement pumps (5) are used to add or remove precise amounts of water to / from each flotation chamber (2) in the cage (J), through the water hoses (3). The water pumps can be installed on a barge or boat (7) or on land near the cage (J). Ideally the water pumps have associated water filters (6) for the sea water. Control system: The positive displacement pumps (5) use an automatic or manual control system (8) located next to the pumps to control the amount of water added or removed from the flotation chambers and thus the submersion and reflotation of the cage. The control system (8) can comprise a command panel, an electric switchboard, sensors, actuators, valves and other accessories and is located on the same barge or boat (7) or other place where the pumps are installed. The invention also reveals a submersion and reflotation process for a submersible cage for aquaculture (J). To submerge or refloat the cage the water hoses (3) are connected to the water pumps (5) and an operator performs the necessary actions from the command panel of the control system (8) to control the weight of the water in the individual flotation chambers (2), thus altering the hydrostatic properties of the cage (J), allowing it to submerge or refloat with precision. The weight inside each flotation chamber (2) is controlled by varying the amount of water inside each one. This is achieved by adding or removing known and equal amounts of water from each chamber (2). Air inside each flotation chamber is not removed or added at any time but only compressed or expanded as water flows in or out of each flotation chamber, which are designed to resist the pressures generated by the process. Part of the submersion and reflotation process for the submersible cage for aquaculture (J) according to the invention is shown in Figure 3. The first step of the process is connecting each flotation chamber (2) solely to an individual water hose (3) and in turn connecting each water hose to a positive displacement water pump (5). Then the process continues according to the sequence from top to bottom and left to right shown in Figure 3, as follows: 1. with the cage floating, begin to individually add only water into each flotation chamber (2) with the positive displacement pumps (5), through the water hoses (3), to make the cage submerge while at the same time air inside the chambers is compressed with the addition of said water, 2. continue individually adding only water into each flotation chamber (2) until the cage has been submerged at a desired depth, 3. with the cage submerged, start individually removing only water from each flotation chamber (2) with the positive displacement pumps (5), through the water hoses (3), to allow the cage to refloat while at the same time air inside the flotation chambers (2) is decompressed with the removal of said water, and 4. continue individually removing only water from each flotation chamber (2) until the cage is floating with a desired buoyancy. The process ends with the step of disconnecting the water hoses (3) from the positive displacement pumps (5) in order to use the pumps on another cage or for storage purposes. The invention stands out for its simplicity compared to other submersible cages, thus resulting in a considerable decrease in production costs for the user: it requires less labor to operate the system (in fact the system can be operated by only one person), less time to submerge and re-float the cage; and less moving parts of the cage itself, which reduces the amount of down-time. This invention is easily scalable, allowing the manufacture of cages in all sizes used today as well as larger ones in the future without any significant changes in the technology. The fact that only water and not air is used to submerge and refloat the cage is highly advantageous. As water is incompressible, the volume of water pumped by the pumps can be assumed to be equivalent to the volume of water added to the flotation chambers, thus allowing for easy and precise calculation of the weight of each chamber and therefore of the cage, by the control system. This is not possible to achieve in a simple manner when using compressed air as other cage systems do. Pressure sensors would have to be installed in each chamber and complex control feedback loops would be needed to control the submerging and refloating processes. The water pumps and control system of the cage system of the invention can be installed on the deck of a small boat or a platform, or even on shore, and taken out in case of strong waves, worsening of climate conditions or other exceptional circumstances. Moreover the investment cost of the water pumping station is divided between many cages (one water pumping station may serve up to 20 cages), as it is only used for submerging and refloating the cage, which are very fast processes, as it is only necessary to add or remove a small quantity of water to / from each watertight chamber. Lastly, with the ability of the invention to totally control the hydrostatic properties of the cage it allows for precise management of the submersion and refloating process without the risk of deformation and / or breaking of the cage, avoiding damage to the fish and fish to escape. Further, the invention can be adapted to the fish species requirements by controlling the rate at which the cage is submerged or refloated. As both the submerged weight of the cage and its buoyancy when afloat can be controlled, the cage system of the invention is adapted, for example, to strong water currents, thus obtaining a safe and flexible industrial solution to the problems of the prior art in this regard. BIBLIOGRAPHY 1. Tae Ho Kim, Kyu Serk Hwang and Moo Hwan Oh, "Development of an automatic submersible fish cage system", presented at AQUA 2012 - World Aquaculture Society Meeting, Prague, Czech Republic, 2012. 2. Simoes Alves Vieira, A, inventor; Simoes Alves Vieira, A, assignee. Submerged cage for flat fish. International patent WO 2018 009085. 2018 Jan 11. 3. Hammernes, TK, Hammernes, AK, inventors; Ocean Farming AS, assignee. A semisubmersible, cylindrical net cage, closable bulkheads for a net cage and a bottom for the net cage that can be elevated. International patent WO 2015 099540. 2015 Jul 02. 4. Fernandez Masaguer, JA, inventor; Aquafarm 2005 SL, assignee. Submersible and seabed cage for aquaculture use. Spanish patent ES 2294940. 2008 Apr 01. 5. Papadoyianis, ED, Cherch, XT, inventors; Papadoyianis, ED, Cherch, XT, assignees. Aquaculture production system. United States patent US 8,371,245. 2005 Jan 26. 6. Ramirez, A, Santana, A, inventors; Sodac Offshore SL, assignee. Oceanic aquaculture platform. International patent WO 2015 055867. 2013 Oct 17. 7. Huang Bin, Guan Changtao, Lin Defang, inventors; Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, assignees. Pump pressure type method of sinking floating net cage and control device. Chinese patent CN 1623378. 2004 Dec 18. 8. Yu Yuming, inventor; Yu Yuming, assignee. Frame of balance submerged culture net cage with double buoyancy vertical pipes. Chinese patent CN 103430888. 2013 Aug 26. 9. Sung Hyun, inventor; Sung Hyun, assignee. Fish cage apparatus type of buoyancy fluctuation. Korean patent KR 2017 0092417. 2016 Feb 03.

Claims

1. A submersible multichamber cage system for aquaculture, wherein the system comprises: a cage having a structure made of one or more flotation rings subdivided into multiple flotation chambers, the cage further having a fish containment net hanging therefrom and surrounding the structure; and individual water hoses for each of the flotation chambers, positive displacement water pumps and a control system for the positive displacement water pumps, for adding or removing water to / from the flotation chambers to respectively submerge or refloat the cage; wherein the flotation chambers are each solely connected to one of the individual water hoses at one end thereof for submerging or refloating the cage while each of the water hoses are connected at an opposite end thereof to one of the positive displacement water pumps whereby, during operation, only water is added or removed from the flotation chambers through the water hoses using said positive displacement water pumps in order to respectively submerge or refloat the cage while air contained inside the floatation chambers is only compressed or decompressed as a result of the changes in the amount of water inside the chambers.

2. The submersible multichamber cage system in accordance to claim 1, wherein the control system is either manual or automatic and wherein the control system is located next to the positive displacement water pumps.

3. The submersible multichamber cage system in accordance to claim 1, wherein the positive displacement water pumps and the control system are installed on land near the cage, or on a boat or barge.

4. The submersible multichamber cage system in accordance to claim 1, wherein the submersible multichamber cage system uses sea water and further comprises a filter for the sea water entering the positive displacement water pumps.

5. A process for submerging and refloating a submersible multichamber cage for aquaculture, wherein the process comprises the following steps: a) providing a cage having a structure made of one or more flotation rings subdivided into multiple flotation chambers, the cage further having a fish containment net hanging therefrom and surrounding the structure; b) providing individual water hoses, positive displacement water pumps and a control system for the positive displacement water pumps; c) connecting each of the flotation chambers solely to one of the individual water hoses at one end thereof and connecting each of the water hoses at an opposite end thereof to one of the positive displacement water pumps; d) with the cage floating, begin to individually add only water into each of the flotation chambers with the positive displacement pumps, through the water hoses, to make the cage submerge while at the same time air inside the flotation chambers is compressed with the addition of said water; e) continue to individually add only water into each of the flotation chambers until the cage has attained a desired submerged weight; f) with the cage submerged, start to individually remove only water from each of the flotation chambers with the positive displacement pumps, through the water hoses, to allow the cage to refloat while at the same time air inside the flotation chambers is decompressed with the removal of said water; g) continue to individually remove only water from each of the flotation chambers until the cage is floating with a desired buoyancy; and h) disconnect the opposite ends of the water hoses from the positive displacement water pumps.

6. The process for submerging and refloating a submersible multichamber cage for aquaculture according to claim 5, wherein adding and removing water to / from each flotation chamber is done simultaneously.

7. The process for submerging and refloating a submersible multichamber cage for aquaculture according to claim 5, wherein the same quantity of water is added or removed to / from each of the flotation chambers.

8. The process for submerging and refloating a submersible multichamber cage for aquaculture according to claim 5, wherein a volume of compressed air and a volume of residual water are left when the flotation chambers are respectively filled or emptied with water.

9. The process for submerging and refloating a submersible multichamber cage for aquaculture according to claim 5, wherein the control system controls flotation characteristics of the cage, the weight once submerged and the buoyancy when the cage is floating.

10. The process for submerging and refloating a submersible multichamber cage for aquaculture according to claim 5, wherein the control system controls the weight of each of the flotation chambers by controlling the amount of water added or removed from said chambers.