NO346650B1 - Submersible cage - Google Patents

Description

Field of the invention

The present invention relates to a device for a submersible cage, as well as a method for regulating the buoyancy of such a submersible cage.

The background of the invention.

Cages for breeding marine organisms, such as fish and shellfish, are located in freshwater or seawater. Today's cages are typically located in fjords or bays where the external conditions such as wind and waves are relatively calm. However, there is a need to install breeding cages also offshore, to be able to use new areas for breeding, and also to make the facilities larger. Furthermore, it would be desirable that some facilities could be moved offshore to avoid contamination by pathogenic organisms.

The challenge of locating the cages offshore is that the weather conditions become harsher, for example on the Norwegian coast in many areas you can have waves with a height of up to 30 metres. Cages that can be submerged in the sea have therefore been developed, so-called submersible cages. Below the sea surface, they will be subjected to less external forces from waves and currents.

The applicant's own patent application WO2016/063040 describes such a submersible cage for breeding marine organisms. The cage has walls and a roof, and is arranged floating in the sea. The cage is equipped with a number of floats to keep the cage afloat, and to be able to regulate the buoyancy so that the cage can be lowered into the sea and raised again. These floats have a horizontal extent and are preferably arranged in the upper part of the cage, i.e. at level with or just below the water surface when the cage is in a raised configuration. Furthermore, the cage is equipped with a number of flexible elements (such as chains) which extend from the cage and to another external support point, and the flexible elements hang in steps in an arc from the cage to the external WO0152638 describes a floating cage which can be completely or partially submerged in the water. The cage has sinking elements that are attached to the bottom and floating elements that are attached to the top of the cage. The buoyancy of the floating elements is adjustable.

WO9806254 describes a submersible cage with a flotation collar at the top and a sinking element at the bottom where the buoyancy is regulated by adjusting the amount of air in the flotation collar.

WO08081229 describes a cage that is fully or partially submerged in water. The cage includes a net bag and floats with adjustable flight ability. The buoyancy is regulated by filling or deflating floats with water or air.

US20100319252 describes an automated submersible cultivation facility for marine species with elongated buoyancy elements which are vertical in the water and which have adjustable buoyancy.

NO336739 describes a cage device which can be raised and lowered in water by means of vertical lifting pipes.

Purpose of the present invention.

An object of the present invention is to provide a submersible cage, i.e.

a cage that can be lowered from the surface into the water, with improved options for regulating the cage's buoyancy.

Furthermore, it is an object of the present invention to improve the regulation of the cage's horizontal positioning, especially when the cage is in a submerged

configuration.

method for precise regulation of buoyancy for a submersible cage. It is also sought to establish a solution where the buoyancy can be individually regulated in many buoyancy points arranged scattered on the cage.

Summary of the invention

The present invention relates in one aspect to a submersible cage for farming

of marine organisms, comprehensive

- a cage bag with walls to contain said marine organisms,

- buoyancy elements designed to establish variable buoyancy,

- sinking elements arranged to establish downward forces on the cage, characterized in that at least one of said buoyancy elements is a first buoyancy element, where said buoyancy element has an elongated shape, is attached to the cage and arranged to be positioned vertically in the water in which the cage floats or is submerged in.

In a preferred embodiment, said first buoyancy element is open in a lower part and closed in an upper part.

In a preferred embodiment, said sinking element comprises one or more flexible

element attached to the cage.

In a preferred embodiment, said flexible element is a chain.

In a preferred embodiment, said first buoyancy element comprises an upper part et

buoyancy agent with fixed buoyancy, where said buoyancy agent with fixed buoyancy is either a solid buoyancy element, such as Styrofoam, an air-filled and tight pipe section which is attached to or part of the upper part of the buoyancy element, or that a buoyancy agent, such as air, is supplied in an upper portion of the buoyancy element, in a position at a predetermined distance from the top of the buoyancy element.

In a preferred embodiment, said buoyancy element is arranged to accommodate;

- a first medium A with equal or higher density than surrounding water, and

- a second medium B with a lower density than surrounding water.

In a preferred embodiment, said float includes means for supplying and discharging said first medium.

In a preferred embodiment, the buoyancy in each of said vertically positioned buoyancy elements is regulated by the amount of first medium A in said buoyancy element, and that the buoyancy in each element can be regulated independently of each other.

In a preferred embodiment, said buoyancy element has a plumb line in a lower part of the buoyancy element.

In a preferred embodiment, said buoyancy element has an opening at a given depth for

limit buoyancy.

In a preferred embodiment, said flexible element is attached to the cage and to an external support point.

In a preferred embodiment, the cage also includes a second, horizontally arranged buoyancy element.

In a preferred embodiment, said second horizontally positioned buoyancy element is an annular float (flotation collar).

In a preferred embodiment, said second buoyancy element comprises means for supplying and discharging a medium with a lower density than surrounding water.

In a preferred embodiment, said medium has a lower density than if moving water is a gas, preferably air.

In a preferred embodiment, said second medium is water, i.e. the same medium as the surrounding water.

In a preferred embodiment, said first medium is air.

In a preferred embodiment, the cage also includes one or more horizontal buoyancy elements.

In a preferred embodiment, each of the horizontal buoyancy elements extends along the entire perimeter of the cage, and is either attached to the vertical buoyancy elements or to the cage wall.

In a preferred embodiment, said buoyancy elements are arranged in an upper and/or lower part of the cage or buoyancy elements.

In a second aspect, the present invention relates to a method for regulating the raising and lowering of a submersible cage, characterized in that said submersible cage comprises a cage bag with walls to accommodate said marine organisms, vertical buoyancy elements arranged to establish variable buoyancy and sinking elements arranged for to establish downward forces on the cage, characterized in that said buoyancy elements comprise means designed to establish a fixed buoyancy, and means to establish a variable buoyancy, and that the buoyancy of the buoyancy elements is regulated by adding or removing an agent with a lower density than surrounding water to/from the buoyancy elements.

In a preferred embodiment, said horizontal buoyancy means are filled with air when the cage is brought to the surface with the vertical buoyancy elements, and when the cage is to be lowered, the horizontal buoyancy elements are emptied and the cage then hangs on the buoyancy of the vertical buoyancy elements, and when the air is released from the vertical I a preferred embodiment is that the cage is equipped with a number of buoyancy means, and that the buoyancy in each of these buoyancy means is regulated individually.

Description of figures

Preferred embodiments of the invention will be described in more detail below with reference to the accompanying figures, where:

Figure 1 schematically shows a breeding cage with first and second buoyancy elements, where the cage is in a floating configuration.

Figure 2 schematically shows a breeding cage with first and second buoyancy elements, where the cage is in a sunken configuration.

Figure 3 schematically shows a vertical elongated buoyancy element with a closed top and open bottom, a fixed buoyancy element and an opening to limit buoyancy.

Figure 4 schematically shows how a medium (air) of less density than the surrounding sea can be added to a first float to regulate the buoyancy of the float and the cage it is attached to.

Figure 5 schematically shows how a first float (buoyancy element) is attached via a

flexible member to an external support point, here a floating unit, where the cage to which the float is attached is in a sunken configuration.

Figure 6 schematically shows how a first float (buoyancy element) is attached via a flexible element to an external support point, here a floating unit, where the cage to which the float is attached is in a floating configuration.

Figure 7 shows a cage according to the invention where there are also arranged horizontal Description of preferred embodiments of the invention.

Figure 1 schematically shows a submersible cage 10 for breeding marine organisms. A volume of water, such as fresh water or seawater, is enclosed by the cage 10, and the walls 12 form both the bottom, wall sections and lid/roof of the cage. The invention relates to the arrangement for lowering and raising the cage 10 in a water reservoir, and buoyancy 16, 30 and lowering elements 18 which effect such raising and lowering. The cage 10 is a so-called submersible cage, i.e. it can in one configuration be floating in the waterline, and then it can be lowered from this position to a submerged position at a given, preferably predetermined depth.

The rearing cage 10 can be of any type, i.e. both tight cages 10 can be used, but also water-permeable cages 10, i.e. the wall part 12 of the cage 10 can be tight or water-permeable. Whether the cage 10 is tight or water-permeable will depend on the conditions under which it is to be used.

From the state of the art, submersible cages are known which have a float, or a set

floats fixed in the upper part of the cage. Such floats are often in the form of a floating collar, and this is normally filled with air to ensure buoyancy. The float collar or float on such known systems is arranged horizontally, i.e. the air that is filled in the float has a large horizontal extent, but a limited vertical extent. The typical cross-sectional diameter for a floating collar is 500 mm, and the length is usually 160 m (the circumference of the cage's upper part). The volume for intake of air then becomes 27m<3>, and the vertical extent only 0.6 m. With normally 3 floating collars, this becomes more than 50 m3 of buoyancy on a vertical extent of only 0.6 m.

Furthermore, in known solutions, sinking elements attached to the cage are used to exercise

a downward pulling force, i.e. to apply forces acting opposite to the buoyancy effect of the floats. For example, weights can be attached to the cage. Whether the cage is to be in a floating or submerged configuration will in such known solutions be regulated by the amount of air in the horizontal floats. When the floats are filled when the weight of the sinking elements exceeds the buoyancy, i.e. when air is emptied out of the buoyancy elements.

From WO2016/06304, a system is also known in which flexible sinking elements are used. These sinking elements can, for example, be chains, and they are attached at one end to the cage, and at the other end to a fixed support point (for example, a buoy on the water surface). The own weight of the chain means that the chain acts as a sinking element with a downward pulling force. It is preferred that the chain forms an arc between the cage and the support point.

Even with such a cage system with a horizontal float and flexible sinking elements, it has proved challenging to precisely regulate the cage's buoyancy. The present invention provides a solution to this problem, by establishing vertical buoyancy elements 16 where the amount of buoyancy agent in the buoyancy element 16 can be precisely regulated.

A cage 10 is preferably equipped with several such buoyancy elements 16. Preferably

this is a plurality of buoyancy elements 16 arranged in the outer perimeter of the cage, i.e. outside the cage notch 12 or the cage wall 12. In the description and requirements, these buoyancy elements are referred to as first buoyancy elements 16. They are also referred to as vertical buoyancy elements 16. The term "vertical" in connection with these first buoyancy elements 16 should not be interpreted narrowly. It is intended that they have a mainly vertical positioning, but they can also in some cases have a certain inclined position.

The vertical buoyancy elements 16 have an elongated shape, preferably a tube-like shape. They are hollow inside, and tight in an upper part 16b, while they are open in the bottom part 16a. They are equipped with valves for the introduction or discharge of one or more media, preferably two or more media. In the solution shown in Figure 1, it is indicated that a buoyancy element 16 is filled with a liquid which has an equal or greater density than the surrounding water reservoir. This medium is named "A" in the figure. Furthermore, the buoyancy element 16 is filled with a medium, called "B", which has a lower density than the surrounding water reservoir. This medium will cause buoyancy. The medium is often a gas, and most preferably air is used. Two separated phases will thus form in the buoyancy element 16, and the amount of air in the buoyancy element will determine the buoyancy.

Air is supplied to the buoyancy element 16 from a pressurized container (not shown in detail in the figures). As mentioned, a cage 10 can be equipped with a number of buoyancy elements 16. For round cages, or for square cages, 4, 8, 12 or 16 buoyancy elements 16 are appropriate, but any number can in principle be used. Each of the buoyancy elements can be regulated individually, i.e. air can be supplied and removed from each buoyancy element independently of each other.

It is also preferred that the buoyancy elements 16, or some of the buoyancy elements 16, have a buoyancy element of a solid substance in an upper part to establish a fixed non-adjustable buoyancy effect. This can, for example, be Styrofoam or similar light materials, and will ensure a certain buoyancy even if buoyancy agent B were to leak out of the buoyancy element 16.

A cage 10 can be kept afloat, and also lowered to a submerged position, only by using such first vertical buoyancy elements 16 (in combination with sinking elements 18), with the correct dimensioning of the various elements. However, it is preferred that the cage 10 is also equipped with conventional horizontal floats 30, such as a floating collar 30. Such further buoyancy elements 30 are called horizontal or other buoyancy elements 30. One will then be able to use these other buoyancy elements 30 to lower and raise the cage 10 When the buoyancy element 30 is filled with air, the cage 10 has accumulated buoyancy sufficient for the cage 10 to be raised and positioned in a floating configuration (as shown in Figure 1). When air is sucked out of the buoyancy element 30, the cage 10 will sink, and it will suitably sink to a predetermined depth which is determined by the amount of air in the first (vertical) buoyancy elements 16. The vertical buoyancy elements 16 are therefore used to position the cage 10 to a suitable depth, and also to individually regulate the buoyancy of each buoyancy element 16 so that the cage 10 is arranged evenly horizontally in a sunken position (as shown in figure 2).

1, a standard plastic ring 30 or floating collar 30 is used. As flexible element 18, heavier chains 18 are used between support point 40 (mooring plate under buoy), and floating collar 30 or another point on the cage 10. The chain 18 is used as flexible element 18 and is a compensating weight for the cage 10. Such a chain link 18 has a large stabilizing weight and causes passive stabilization of the cage 10 vertically. In this example, 12 vertical tubes 16 with an inner diameter of 27 cm have been used. The outer diameter can be 30 cm as in a standard PE pipe.

On top of the vertical tube 16 there will preferably be a buoyancy element with a certain fixed buoyancy. This will be in addition to, and independent of, the buoyancy established by buoyancy medium B, which provides variable buoyancy. This fixed buoyancy element ensures a certain buoyancy if the supply pipe for air to the buoyancy element 16 breaks, or if the buoyancy element 16 is damaged and the air flows out of the element. The fixed buoyancy provided by the buoyancy medium B in the pipe 16 will ensure that the system between chain 18 and buoyancy tube 16 must have a negative buoyancy. The solid buoyancy can be provided by a solid buoyancy element, made of a light material with a density lower than the surrounding water, such as Styrofoam, for example. Alternatively, it can be ensured that the supply of air takes place at a distance from the top, so even if this supply were to break and air escapes from the element 16, there will be a buoyancy-generating air pocket in the upper part of the buoyancy element 16.

The technology is based on a compensation system that works with the help of

buoyancy which is established by pumping compressed air into vertical pipes 16 and chain 18 with a specific weight (weight/metre) which corresponds to the buoyancy. The cage 10 can be adjusted up and down in the water column very accurately due to air that is pumped in or released from the vertical pipes 16.

Vertically positioned pipes 16 are used because this provides a unique opportunity to control the amount of air (and thus the buoyancy) in each of the pipes 16.

The cage 10 will be in a stable equilibrium with the correct dimensioning of buoyancy and sinking elements. That is when the cage 10 is adjusted to lie at, for example, 10 m water depth, it will adjust back to this depth even if the cage is raised to 30). The same is the case if the cage 10 was lowered to a water depth of 20 m, it will rise to 10 m again and stabilize there. The amount of air in the buoyancy elements 16 will be able to set the cage 10 at a predetermined depth.

The challenges with a raise/lower technology for submersible breeding cages 10 are many. We mention here the essential ones, and we also want to specify that these challenges are solved with the technology that the present invention provides;

When a cage 10 is lowered into a water reservoir, the volume of air will decrease as a result of the state equation V1 x P1 = V2 x P2. This means that if you lower a buoyancy element which is open at the bottom, and which is filled with some air from the surface down to 10 m, the buoyancy will be halved.

V2 =(V1 x P1)/ P2

V2 = 1/2

The present invention provides a fixed (predetermined) buoyancy at the top of the pipe 16 and a variable buoyancy downwards in the pipe 16, and this makes this problem easier to handle.

In the example above where the cage 10 is on the surface, the pressure in the buoyancy tube 16 will be equal to the water level in the tube which can be at 40 m. When the cage is lowered to 10 metres, the volume of air in the vertical tube will be reduced by:

V2 =(V1 x P1)/ P2

V2 = (1 x 4)/5

V2 = 4/5

This means that the pressure will change considerably less with the vertical buoyancy elements. That is, when you lower the cage, air will be released to make the cage sink at the same time as the pressure in the buoyancy elements increases.

With this method, the stability of the cage 10 will be considerably increased when it is

immersion.

The chain principle (flexible sinking element 18) will prevent the transfer of wave forces from anchor buoy 40 to cage 10. This will be a significant advantage in offshore farming where large waves can be encountered.

Adjusting and monitoring buoyancy in deep vertical pipes 16 will be significantly easier than regulating buoyancy by pumping air into the float collar 30 itself. In a vertical pipe 16, one will be able to pump in, for example, air that gives 57 kg of buoyancy and read off a pressure increase of 0.1 bar. If an equal amount of air is to be pumped into a horizontal buoyancy element 30, it will be very difficult to read any pressure difference, and regulation of the buoyancy is therefore difficult.

Figure 4 shows the principle of how one controls the amount of air in the vertical pipes 16 so that one has full control that the cage 10 lies horizontally. Pressure sensors read the pressure in the air hose 60a which goes together with the feed hose from the raft down to the vertical buoyancy pipe 16.

The air hose 60a will typically be a 1⁄4 hose that is qualified for seawater and air.

At the top of the buoyancy pipe 16, as mentioned, there is a fixed buoyancy element (not shown in the figures) which will ensure that if all the air leaves the pipes 16, for example when the air hoses break, the mead will sink to a depth determined by how much buoyancy the fixed buoyancy elements have.

To lower the cage, release all air from buoyancy element 30, or alternatively from the buoyancy elements 16 if buoyancy element 30 is not used.

The principle of the raising and lowering mechanism is as follows for the representative example; Chain 18 between mooring plate 30 and cage 10 is 70 m long.

The chain 18 has a specific weight of 20 kg/m in water. The weight of chain 18 which must be held up by buoyancy tube 16 is 20 kg/m x (70/2) = 700 kg. This becomes 700 kg/ 57 kg/m = 12.3 m of air in the vertical pipe 16.

With appropriate calculation of weights and buoyancy elements 16,30, the buoyancy will be calculated accurately.

Buoyancy tube has an ID of 27 cm. This gives a buoyancy of approx. 57 kg/m. The pipe will then

be filled with air at the top down to: 700 kg / 57 kg/m = 12.3 m. Then the system will be in equilibrium. When waves affect the buoy, the mooring plate will move up and down in time with the waves. The large mass in the cage itself will mean that the movements will be minimal.

In the surface position (as shown schematically in figure 4), the entire chain 18 will be lifted by air i

the buoyancy tube. 70 m x 20 kg/m gives approx. 1400 kg.

This gives 1400kg / 57kg/m = 24 m of air in the buoyancy tube.

There may be a separate air line 60a from a control point near the cage 10. This may be a feed raft, or another station.

Many conventional components can be used to assemble a cage 10 according to the invention. Mooring frame (not shown) is installed in the normal way.

Anchoring ring 40b below the buoyancy buoy 40 will conveniently be somewhat lower in the water. It is appropriate that it is placed at the desired submerged depth of the cage 10. The cage 10 will then have the greatest possible ability to compensate for large waves.

The cage 10 installation then starts with a standard plastic ring 30 as buoyancy element 30. The mooring frame 40b will be somewhat larger in spread compared to a traditional plastic ring 30 anchorage. This is because extra length is needed on the chain 18 between the anchoring ring 40b under the buoy 40 and the cage 12. The extra length is necessary because it must compensate for high waves, and in addition the cage 10 must be able to be raised to the surface.

After plastic ring 30 is moored, it will be natural to install groove 12. That is

nevertheless, it is entirely possible to install the groove after the vertical pipes 16 have been installed, in the same way as with a groove change.

After plastic ring 30 is moored and groove 12 is installed, the vertical buoyancy tubes 16 will be installed. In the example given above, the vertical pipes 16 consist of a 40 m long PE pipe. The top 6m of the pipe has an OD of 400mm. Here fixed buoyancy (not shown) is installed inside the pipe 16. At the bottom 16a of the pipe there is a 3 m length with an OD of 400 mm. A lot (not shown) is placed in this section. Between the two sections there are 31 m of PE pipes, OD of 300mm for the absorption of medium named A and B. The pipes 16 are drawn and positioned on the correct side of the chain 18, and lowered.

Correct buoyancy on the pipes 16 is adjusted with compressed air that is pumped in during installation

the lation. This makes it easy to connect the pipes 16 to the cage 10. It will be considered whether the vertical pipes 16 should be connected to the chain 18 or directly to the cage 10, both parts are possible. Buoyancy on the entire pipe 16 in the surface position and in the submerged state will be dimensioned as appropriate, and it seems reasonable to start with allowing the pipe 16 to have a buoyancy in the submerged state that corresponds to the weight of half the chain length 18.

After the vertical pipes 16 are in place, the bottom ring 70 must be installed. The bottom ring 70 can be in 12 parts that are attached to the outside of the vertical pipes 16.

The purpose of the bottom ring 70 is to keep the shape of the vertical tubes 16.

In order to further stabilize the cage 10, especially so as not to get variable buoyancy when one lowers or raises the cage 10, or the cage moves up or down in the water for other reasons (waves or currents), a number of horizontal buoyancy elements are also arranged for the cage 10 50, as shown in Figure 7. There can be from one to many such elements 50, and they preferably have a tubular shape that extends along the entire perimeter of the cage. Preferably, the entire buoyancy element 50 is either filled with water or filled with air, so that the element 50's contribution to the buoyancy of the cage 10 is constant.

Claims (14)

Patent claims 1. Submersible cage (10) for rearing marine organisms, comprehensive - a cage bag with walls (12) to accommodate said marine organisms, - buoyancy elements designed to establish variable buoyancy, - sinking elements designed to establish downward forces on the cage (10), characterized in that at least one of said buoyancy elements is a first buoyancy element (16), where said buoyancy element (16) has an elongated shape, is attached to the cage (10) and aligned to be positioned vertically in the water in which the cage (10) floats or is submerged. 2. Submersible cage (10) in accordance with claim 1, characterized in that said first buoyancy element (16) is open in a lower part (16a) and closed in an upper part (16b). 3. Submersible cage (10) in accordance with claim 1, characterized in that said sinking element comprises one or more flexible elements (18) attached to the cage (10), preferably that said flexible element (18) is a chain. 4. Submersible cage (10) in accordance with any of the preceding claims, characterized in that said first buoyancy element (16) in an upper part comprises a buoyancy means (16d) with fixed buoyancy, where said buoyancy means (16d) with fixed buoyancy is either a solid buoyancy element, such as Styrofoam, an air-filled and tight tube section attached to or part of the buoyancy element (16) upper part, or that a buoyancy agent, such as air, is supplied in an upper part of the buoyancy element (16), in a position at a predetermined distance from the top of the buoyancy element (16). 5. Submersible cage 10 in accordance with the requirements of any of the preceding requirements, characterized in that said buoyancy element (16) is designed to accommodate; - a first medium A with equal or higher density than surrounding water, and - a second medium B with a lower density than surrounding water. 6. Submersible cage (10) in accordance with any of the preceding claims, characterized in that said buoyancy element (16) comprises means (16a) for the supply and discharge of a first medium. 7. Submersible cage (10) in accordance with any of the preceding claims, characterized in that the buoyancy in each of said vertically positioned buoyancy elements (16) is regulated by the quantity of a first medium A in said buoyancy element (16), and that the buoyancy in each element (16) can be regulated independently of each other. 8. Submersible cage (10) in accordance with any of the preceding claims, characterized in that said buoyancy element (16) has a plumb line (16e) in a lower part of the buoyancy element (16), or that said buoyancy element (16) has an opening (16c) at a given depth to limit buoyancy, or that said flexible element (18) is attached to the cage (10) and to an external support point (40). 9. Submersible cage (10) in accordance with any of the preceding claims, characterized in that the cage (10) also comprises a second, horizontally arranged buoyancy element (30), and preferably that said second horizontally positioned buoyancy element (30) is an annular float (flotation collar) (30), and preferably that said second buoyancy element (30) comprises means (30a) for supplying and discharging a medium with a lower density than surrounding water. 10. Submersible cage (10) in accordance with claim 5, 6, or 7, characterized in that said medium with a lower density than surrounding water is a gas, preferably air, and that said second medium is water, i.e. the same medium as the surrounding water, and where said first medium is preferably air. 11. Submersible cage (10) in accordance with any of the preceding claims, characterized in that the cage (10) also comprises one or more horizontal buoyancy elements (50), preferably that each of the horizontal buoyancy elements (50) extends along the entire perimeter of the cage , and is either attached to the vertical buoyancy elements (16) or to the cage wall (12), and preferably that said buoyancy elements (50) are arranged in an upper and/or lower part of the cage (10) or buoyancy elements (16). 12. Method for regulating the raising and lowering of a submersible cage (10), characterized in that said submersible cage (10) comprises a cage bag (10) with walls (12) to accommodate said marine organisms, vertical buoyancy elements (16) arranged to establish variable buoyancy and sinking elements designed to establish downward forces on the cage, characterized in that said buoyancy elements comprise means designed to establish a fixed buoyancy, and means to establish a variable buoyancy, and that the buoyancy of the buoyancy elements is regulated by adding or removing an agent with a lower density than surrounding water to /from the buoyancy elements. 13. Method in accordance with claim 12, characterized in that said horizontal buoyancy means (30) are filled with air when the cage (10) has been brought to the surface with the vertical buoyancy elements (16), and when the cage (10) is to be lowered, the horizontal buoyancy elements are emptied (30) and the cage (10) then hangs on the buoyancy in the vertical buoyancy elements (16), and when the air is released from the vertical buoyancy elements (16) the cage (10) will sink downwards. 14. Method in accordance with claim 12, characterized in that the cage is equipped with a number of buoyancy elements (16), and that the buoyancy in each of these buoyancy means 25 (16) is individually regulated.