NO343420B1

NO343420B1 - Floatable container for fish farming

Info

Publication number: NO343420B1
Application number: NO20171356A
Authority: NO
Inventors: Alf Reidar Sandstad
Original assignee: Spring Innovation As
Priority date: 2017-08-15
Filing date: 2017-08-15
Publication date: 2019-03-04
Also published as: NO20171356A1; WO2019035720A1

Abstract

It is described a floatable container (1) for fish farming, wherein an internal volume of the container (1) is distributed away from a vertical centre axis (6) of the container (1).

Description

FLOATABLE CONTAINER FOR FISH FARMING

The invention relates to a floatable container for fish farming. More specifically, the invention related to a container for fish farming with high initial stability.

A container for fish farming may also be called a sea pen or a fish cage. Similar to all is that they constitute a confined space for breeding of fish. Several types of sea pens that float in water and form an enclosure for fish are known within fish farming. Such sea pens can be of an open type, where the wall of the pen is formed of a net constituting a water permeable wall and bottom. Such open pens can in their bottom be provided with a dense cloth material for collection of faeces and feed. Alternatively, sea pens can be half-open, with a dense wall and a water permeable bottom section, such as a net. Another alternative is closed sea pens, with a dense wall and a dense bottom section. A dense wall may be formed from a cloth-shaped, soft material, or from a stiff material. The wall may be constructed from elements, such as stiff panels.

One advantage with closed sea pens is that it is easier to collect faeces and feed such that the environmental impact is reduced. A closed sea pen can also prevent parasites, e.g. salmon lice, and algae from reaching the fish due to improved control of the water supply. Examples of closed sea pens are known from the patent documents WO2010/016769 and WO2010/099590.

Document WO2010/016769 discloses a hemispherical fish pen made from a rigid material and having an outlet for effluent.

Document WO2010/099590 discloses a solid wall closed containment system. It comprises floatation panels forming a continuous side wall contiguous with a continuous bottom. The bottom is shaped like a cone and tapered down towards a central drain abutment end.

Another example of a closed sea pen is the «Closed Cage» from Aquafarm Equipment AS. The cage is made from glass reinforced plastic (GRP) and has a downwardly sloped bottom cone for collection of waste from the fish.

Patent document NO 175341 discloses a further example of a closed sea pen. It has a cylindrical upper portion and a downwardly pointing, conical lower portion. The pen can be made from steel, concrete or a soft, reinforced plastic fabric. Water is pumped into the pen at the upper portion of the pen, through a horizontal supply pipe. The supply pipe is arranged with a rotatable outlet at its end portion inside the pen to control the water flow in the desired direction, both horizontally and vertically. The conical lower portion has a funnel-shaped outlet in its lower part.

All the examples of sea pens according to the prior art mentioned above have bottom sections that are either shaped as a downwards cone or a downwards hemisphere. The lowest point of the bottom is located in the centre of the pen. The shape is favourable for gathering waste, as the waste will slide towards the lowest point, and be collected via an outlet at the bottom. A challenge with a downward conically or hemispherical shaped bottom is that the displaced volume of the cone/hemisphere is close to the centre axis, resulting in a low or negative initial stability when emptying the tank. This is unfortunate if elevating the pen by emptying it when it is floating in water, such that the freeboard increases. In an elevated position, it can be susceptible to heeling and prone to capsizing.

The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to prior art.

The object is achieved through features, which are specified in the description below and in the claims that follow.

The invention is defined by the independent patent claim. The dependent claims define advantageous embodiments of the invention.

More specifically, the invention relates to a floatable container for fish farming, wherein at least a portion of a bottom of the container is inclined upwards towards a vertical centre axis of the container such that an internal volume of the container is distributed away from the vertical centre axis. The vertical centre axis is an operable condition. The container may be shaped such that the bulk of the internal volume is arranged towards a periphery of the container. In use, the container may contain a level of water, thus a vertical water column at the centre axis can be lower than a vertical water column further away from the centre axis.

The invention solves the above-mentioned challenges by increasing the initial stability of the container, when the container is floating in water and drained for water internally, as compared to a container where the internal volume is centred around the centre axis. As the container is drained for water, the freeboard will increase. Initial stability can also be defined as metacentric height and is a measure of a floating body’s initial stability against overturning. When a floating body heels, the centre of buoyancy moves laterally towards the heeling side. The intersection between a vertical line through the original centre of buoyancy and a vertical line through the heeled centre of buoyancy, defines the metacentre. The metacentric height (GM) is the distance between the centre of gravity (G) of the body and the metacentre (M). Higher GM means that the floating body is stiffer and quicker to return to its initial position. Thus, the further away from the original centre of buoyancy the heeled centre of buoyancy is located, the higher the initial stability. The invention has a heeled centre of buoyancy which can be further away from the original centre of buoyancy as compared to a sea pen of the known prior art with a downwards-pointing bottom cone.

An inclined bottom can be a favourable way of distributing the internal volume away from the centre axis. It can further guide dropped objects, for example faeces, uneaten feed and dead fish, towards a lowest portion of the bottom of the container, as the waste will slide downwards due to gravity. The lowest point may be near the wall. The lowest portion of the bottom may form a gutter surrounding the centre axis. In one embodiment, the bottom can incline upwards from a peripherical wall towards the vertical centre axis.

In one embodiment, a portion of the bottom is inclined downwards towards the vertical centre axis. Inclining a portion of the bottom downwards can increase the internal volume of the container, thus increasing the capacity to store for example fish. In one embodiment, a portion of the bottom can incline downwards from the peripherical wall and towards the centre axis, before inclining upwards towards the centre axis.

The container may comprise at least two floatable volumes. The floatable volumes may increase the stability of the container when the container is filled with water. The floatable volumes may increase the freeboard of the container without reducing the fluid level in the container. In one embodiment, the floatable volumes may be arranged on an outer part of the container. In one embodiment, the container may comprise four floatable volumes arranged with substantially equal spacing around the container.

In one embodiment, a freeboard of the container may be altered by adjusting a fluid level in the container. To enable adjustment of the fluid level in the container, the container must be watertight. This can be achieved by making the structure, walls and bottom, from a stiff watertight material such as steel, concrete or glass reinforced plastic. In one embodiment, the bottom can be made from a flexible cloth-like material, for example a watertight fabric. Fluid can be supplied into or drained from the container by means of a pump. To ensure that the container is not overfilled and thus run the risk of sinking, it can be arranged with a spillway that drains the water rising above a predetermined level in the container.

The container may comprise at least one outlet for effluent and waste. In one embodiment, the at least one outlet can be arranged at the lowest point in the container. This is favourable as waste such as faeces, uneaten feed and dead fish will sink and slide along the bottom towards the lowest point.

The container may comprise at least one inlet for water supply and/or live fish supply. The water can be supplied from surrounding water, from shore supplies, from recirculated water, or from storage tanks. In one embodiment, the water can be supplied from a sea, from a depth where there is little risk of the water containing for example salmon lice. In one embodiment, at least one inlet can be arranged substantially in the centre of the container. In one embodiment, at least one inlet may be arranged at an elevation between the bottom of the wall and the top of the wall.

In one embodiment, the container may be provided with means for creating a flow of water in the container. A nozzle can direct pumped water into the container to create a circular flow of the water in the container. The pumped water may be supplied from the container and/or surrounding water. If the inlet for fresh water supply is arranged in the centre of the container, the supplied water can start flowing in the same circular direction as the existing water in the container. As more fresh water is supplied, it will displace the existing water outwards, creating a spiral flow out from the centre. The existing water can gradually be drained such that the water is replaced continuously as the container is in use.

A further effect of circulating water is that it will take on a concave surface shape, with a depression towards the rotational axis. This is due to an outward pressure gradient developed from the inertial centrifugal force from rotating the water, where the pressure is higher along the perimeter of the flow than in the centre. This effect may contribute to pulling a bottom made from a flexible material upwards, contributing to keeping it tight.

In one embodiment, the container may comprise a vent for ventilation of air trapped under the container. During launching, air may be trapped under the container. The air may affect the hydrodynamic properties of the container when it is floating in water. The vent may let the trapped air escape, so it can be displaced by water. The vent may be arranged in the centre of the container. In another embodiment, the vent may be arranged at the highest elevation of the bottom section. The container may comprise at least two support members spanning between the vertical centre axis and the peripherical wall. The support members may strengthen the container against wave, current and mooring generated forces.

In one embodiment, a walkway may be arranged at an upper edge of the peripherical wall. The walkway may enable personnel access around the container for example to carry out maintenance, inspection or feeding.

In one embodiment, at least one walkway may span between the vertical centre axis and the upper edge of the peripherical wall. The at least one walkway may enable personnel access to the centre of the container for example to carry out maintenance, inspection or feeding. It may also be used for relocating equipment for feeding and monitoring, and the bird net.

In one embodiment, the container may comprise means for delivering fish into the container. The means may be positioned such that the fish is delivered from a side of the container. In one embodiment, the means for delivering fish may be operable when the container is being elevated. In another embodiment, the means for delivering fish may be operable when the container is in a elevated position.

In the following is described an example of a preferred embodiment illustrated in the accompanying drawings, wherein:

Fig. 1 shows an isometric view of the semi-submersible container according to one embodiment of the invention;

Fig. 2a shows a vertical cross-section A-A of the container in figure 1, but in a different scale;

Fig. 2b shows a detail A of a means for creating a flow of water in the container according one embodiment of the invention;

Fig. 2c shows a horizontal cross-section C-C through detail A from figure 2b;

Fig. 2d shows a horizontal cross-section B-B through the container in figure 1;

Fig. 3a shows the container floating in water in a submerged operating condition; Fig. 3b shows the container floating in water in an elevated service position.

The figures are depicted in a simplified manner, and details that are not relevant to illustrate what is new with the invention may have been excluded from the figures. The different elements in the figures may necessarily not be shown in the correct scale in relation to each other. Equal reference numbers refer to equal or similar elements. In what follows, the reference numeral 1 indicates a floatable container according to one embodiment of the invention. The floatable container 1 includes a cylindrical wall 4 connected to a bottom 14, the bottom 14 being inclined upwards from the wall 4 towards a vertical centre axis 6.

Figure 1 shows a semi-submersible container 1 in accordance with one embodiment of the invention. The container 1 has a cylindrical peripherical wall 4. The upper edge 2 of the wall 4 is provided with a walkway 3. There are four walkways 5 spanning between the centre axis 6 (see figure 2a) and the upper edge 2 of the container 1. A water inlet 7 is arranged with its longitudinal axis coinciding with the centre axis 6 of the container 1. The water inlet 7 comprises a foraminous vertical pipe 8 for supplying water over a height through the water column in the container 1. The vertical pipe 8 comprises a support member for a proximal end 91 of each of four horizontal support members 9. A distant end 92 of each of the four support members 9 is connected to the wall 4.

Buoyancy members 11 are arranged externally on the container 1. The buoyancy members 11 may increase the freeboard and improve the stability of the container 1. A pair of slots 10 are recessed in the wall 4. There are four pairs of slots 10 evenly distributed around the container 1, i.e. with a 90-degree angular distance between each other. These will be explained in further detail below.

Figure 2a shows a vertical cross-section A-A through the centre of the container 1. The bottom 14 has an upwardly pointing cone shape, with the highest section being in the centre of the container 1. The lowest section 13 of the bottom 14 is near the peripherical wall 4. Four outlets 12 (see figure 2d) are located at the lowest section 13. The shape of the bottom 14 ensures that waste, such as faeces, uneaten feed and dead fish, slide down along the bottom 14 towards the lowest section 13 and to the outlets 12. Figure 2a also shows that the internal volume 110 is distributed away from the centre axis 6, with a larger portion of the volume 110 being closer to the wall 4. The more volume 110 that is shifted away from the centre axis, the higher the initial stability will be.

Fig. 2b and 2c show the slots 10 recessed in the wall 4. Water 100a flows into an inlet 10a and is diverted through a pump 101. The water 100a is then pumped through an outlet 10b, and back into the container 1. The outlet 10b directs the water 100a such that it creates a circular flow of water in the container 1. As the outlet 10b has a smaller opening 111b than an opening 111a on the inlet 10a, the speed of the flow 100b increases. Four pairs of recessed slots 10 are distributed around the container 1. The top of the inlet 10a is arranged with a spillway 102. The spillway 102 will ensure that the water level 16 in the container 1 does not exceed a predetermined level. If the water level 16 in the container 1 exceeds the height of the spillway 102, the excessive water will be drained via the spillway 102. The spillway 102 is arranged such that it will always be above the surrounding waterline 15 to avoid flooding the container 1.

The pump 101 is also arranged to drain the container 1. Instead of pumping all the water from the inlet 10a to the outlet 10b, some of it can be pumped out. The drainage is controlled by a valve (not shown), such that some of the water is still diverted to the container 1 to maintain the flow. If the container contains fish, for example salmon, it is important for their well-being to maintain the flow of water in the container during drainage. The pump 101 is arranged such that it will be under water both when the container is in an operable condition and a service position, see figure 3a and 3b.

Fig. 2d shows a horizontal cross-section B-B of the container 1. The water inlet 7 is positioned in the centre of the container 1 and supplies fresh water. The existing water in the container has a circular flow, and the fresh water will start flowing in the same direction. As more fresh water is supplied, it will displace the existing water outwards, creating a spiral flow 100 from the centre and outwards. Some of the existing water will exit via the outlets for effluent 12 on the bottom and some will exit via the spillway 102. Thus, the water in the container 1 will gradually be replaced. The spiral flow 100 may also contribute to getting rid of waste, as it will push the waste away from the centre, towards the outlets 12.

Fig. 3a shows the container 1 in an operating condition. The container 1 is supplied with water such that the waterline 16 inside the container 1 is substantially equal to the waterline 15 outside the container 1. The freeboard can be adjusted by either altering the water level inside the container 1, and/or adding buoyancy elements 11. Buoyancy elements 11 may also increase the stability of the container 1 in the operating condition.

Fig. 3b shows the container 1 in a service position. The container 1 is drained for water such that the freeboard is increased. The container 1 will float stable as a result of its shape. Additional stability can be obtained by arranging buoyancy elements 11 on the wall 4.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

C l a i m s

1. A floatable container (1) for fish farming, c h a r a c t e r i z e d i n that at least a portion of a bottom (14) of the container (1) is inclined upwards towards a vertical centre axis (6) of the container (1) such that an internal volume of the container is distributed away from the vertical centre axis (6).

2. The floatable container (1) according to claim 1, wherein a portion of the bottom (14) is inclined downwards towards the vertical centre axis (6).

3. The floatable container (1) according to claim 1 or 2, wherein the container (1) comprises at least two floatable volumes (11).

4. The floatable container (1) according to any of the preceding claims, wherein a freeboard of the container (1) can be altered by adjusting a fluid level (16) in the container (1).

5. The floatable container (1) according to any of the preceding claims, wherein the container (1) comprises at least one outlet (12) for effluent, waste and live fish.

6. The floatable container (1) according to any of the preceding claims, wherein the container (1) comprises at least one inlet (7) for fresh water supply and live fish supply.

7. The floatable container (1) according to any of the preceding claims, wherein the container (1) has a vent for ventilation of air trapped under the container (1).

8. The floatable container (1) according to any of the preceding claims, wherein the container (1) has a means (10) for creating a flow (100) of water in the container (1).

9. The floatable container (1) according to any for preceding claims, wherein at least two support members (9) span between the vertical centre axis (6) and the peripherical wall (4).

10. The floatable container (1) according to any of the preceding claims, wherein a walkway (3) is arranged at an upper edge (2) of the peripherical wall (4).

11. The floatable container (1) according to any for preceding claims, wherein at least one walkway (5) spans between the vertical centre axis (6) and the upper edge (2) of the peripherical wall (4).