NO20171837A1

NO20171837A1 - System and method for lifting and lowering the net of a net cage, and use of such a system for cleaning a net

Info

Publication number: NO20171837A1
Application number: NO20171837A
Authority: NO
Inventors: Geir Furberg
Original assignee: Aqualine As
Priority date: 2017-11-17
Filing date: 2017-11-17
Publication date: 2019-05-20
Also published as: NO344372B1

Description

System and method for lifting and lowering a net of a net cage and use of such a system for cleaning net.

The present invention relates to a system and a method for lifting and lowering a net of a net cage in the water, according to the preamble of the independent patent claims. The invention also relates to use of such a system for cleaning the net from fouling and debris.

Background

Aquaculture has changed considerably over the years, and is now a major industry. Most of the farmed animals are farmed in traditional net cages at the sea, wherein the net cages comprise a floating collar at the surface of the sea, a net cage fastened to the collar and surrounding all the farmed organisms, and weights to keep the cage dilated and stretched and in such a way that the meshes of the net is open. The floating collar is traditionally round and comprises a double collar tube and 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 net may be reinforced with horizontal and vertical ropes or baselines, where the horizontal lines are often referred to as waistlines. The weight may be any suitable weight, such as a sinker tube.

There is a problem with debris and fouling of the net in the net cages. Especially during summer and in areas with higher water temperature, alga, coelenterates such as hydroids and shells attaches to the threads of 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 of the fouling rather than the sea lice on the fish.

In order to clean the net it has traditionally been used net washing machines or cleaners, which flush the net with water from a number of nozzles, or cleans the net with brushes. This wears the net, and any antifouling agent on the net will be removed at the same time.

The net cages are becoming larger, deeper and heavier than ever before. In line with increased load, there are stricter standards for inspections, maintenance and servicing of the nets. In addition, operational practices including the need for frequent cleaning and handling of the net for instance for sea lice treatment causes more wear on the net cage than previously.

When a net of a net cage should be raised, for instance for inspection, maintenance or upon removing the fish from the cage, one traditionally raises the weight at the bottom by a winding system, such as a winch or crane on a boat, and the net is drawn up by manpower. This is hard and hazardous work as the net is heavy in it self and even heavier when it is coved with fouling and debris. The net has to be lifted at several places around the cage, and one must either use several persons or one person which lifts only a part of the net before he moves to the next place. The procedure is opposite when the net should be set out in the sea again.

There have been several attempts to solve this problem, but until now they all require manpower. Some machines, for instance in JPH02200134 or JPH02221098 lifts the net, but a person needs to grab the net and fasten it to hooks or the similar on the floating collar, in order to prevent the net from falling into the sea again.

Another device is described in NO 336223, but manpower is still needed and one or more persons need to assist the device while lifting the net.

There is an object of the invention to develop an improved system for lifting and lowering the net of a net cage. Further there is an object to develop an improved method for cleaning the net of a net cage, avoiding wear of the net and removal of anti-fouling. Yet another object is that the system should be easy to use and to install on new as well as existing aquaculture farms.

The objects are met by a system and a method according to the characterizing part of the independent patent claims 1 and 9, and use of such a system according to the characterizing part of patent claim 10.

The invention

The invention is related to a system for lifting and lowering a net of a net cage in the water. The net cage comprises a floating means in the surface of the water and a net fastened to the floating means. The net constitutes the net cage surrounding the farmed fish, and the floating means provides buoyancy to the net cage. The system further comprises a number of lifting sites around the floating means, wherein each lifting site comprises at least one guiding member arranged above the surface of the water, and a line running from a winding system, trough the guiding member above the water and further to at least one fastening point of the net, below the surface of the water.

The fastening point of the net may be a reinforced area of the net which makes the net sufficiently strong to withstand the forces acting on the fastening point when the net is attached to the line and raised at this point. The fastening point may also be on the horizontal and/or vertical reinforcement ropes as described above.

The line for lifting and lowering the net may be fastened directly to the net at the fastening point, for instance by stitching, sewing or tying, or indirectly by a guiding member which is fastened to the net and the line is running through the guiding member. When at least one guiding member below the surface of the water is being used, the line will run alternating through the guiding members above and below the surface of the water.

The system and method according to the invention are especially designed to work with net cages having bottom weight or sinker tube to keep the cage stretched and dilated, and preferably round net cages, more preferred round net cages having a traditional construction as stated above.

When the winding system pulls in the line, the line will be pulled through the guiding member, and the net will be lifted simultaneously.

It is an advantage that the line is attached to the net on the inside of the floating means and that the guiding member is arranged above the surface on the inside of the fish cage. By arranging the line and guiding member on the inside of the fish cage, the net will be lifted on the inside on the net cage, and the risk of pulling the net towards the floating means, and thereby harming the net during lifting, is reduced. Further the risk of getting tangled in mooring lines and the similar are less when arranging the system on the inside of the floating means.

In a preferred embodiment, the guiding member above the water is arranged above the water, preferably above a handrail of the floating means. By arranging the guiding member a distance above the water, the net will not only be lifted to the surface of the water, but also above the water. By arranging the guiding member above a handrail of the floating means, the guiding member is easily accessible for service and maintenance. Further, in a traditional net cage the net is fastened both to the floating rings of the floating collar and to the hand rail, and by arranging the guiding member above the hand rail the lifted net will be freely accessible.

In a preferred embodiment, the guiding member above the water is attached to a protruding arm of a vertical element fastened to the floating means. The vertical element protrudes vertically upwards while the arm protrudes radially above the net cage. As described above, the arm should protrude towards the centre of the cage, inside the floating means. The distance from the surface of the water to the protruding arm depends on the desired lifting height of the net, and the length of the protruding arm depends on the desired number of guiding members. In case more than one guiding member is used above the surface of the water, these should be attached to the arm at a distance from each other. The preferred distance between the guiding members and the radial distance from the floating means to the first guiding member will depend on the type of net cage and the conical shape of the net cage. This will be obvious to a skilled person.

The height of the vertical element depends on the desired lifting height of the net, and thus the height of the protruding arm. The system and method according to the invention may be used to lift the net in many situations. Some situations only require that the net should be lifted to the surface, for instance when the fish cage should be emptied, or treated with chemicals. Other situations require that the net is lifted above the surface, such as for cleaning, maintenance and inspection as described herein. In an alternative embodiment, the height of the vertical element is adjustable and thereby the lifting height may be adjusted according to reason for lifting the net.

In a preferred embodiment, a number of guiding members are arranged above the surface, and at least one guiding member is arranged below the surface. The line passes the guiding members alternating above the surface and below the surface of the water. This means that the line will run from the first end being attached to a winding system, to the first guiding member being above the surface of the water, down into the water to a second guiding member fastened to the fastening point of the net, up above the surface to a third guiding member, and so on.

The line has two ends, where the first end is attached to the winding system and the second end is either fastened to the net, such as to a fastening point of the net, or to the protruding arm of the vertical element. The line is running from the winding system through all the guiding members both above and below the surface of the water before it is fastened to the net or protruding arm.

In a preferred embodiment, the last fastening point of the net is at the lower part of the net. By "lower part of the net" it is hereby meant the lower end of the net wall in case the net cage has a defined wall and bottom as an Aqualine Midgard® Net or a tapered net, and at a sufficient depth in case of a cone net. Depending on the depth and size of the net cage, it may not be necessary to stretch the whole net above the water surface as described above, yet it may be desirable to lift the whole net in a controlled manner. The line may then run through a number of rings attached to the net after it has passed the last guiding member above the surface of the water and the second end of the line, or a last guiding member is fastened to lower part of the net, such as the lower end of the net wall. When the winding system pulls the line and the net is lifted, the part of the net where the line is running through rings will be compressed, while the bottom is being lifted.

It is preferred that the winding systems at each lifting site are synchronized in such a way that the net will be lifted evenly around the net cage, and pull and tensions of the net is avoided. However, in some occasions it may be desirable to tilt the net, and then the windings systems should not be synchronized, but arranged in an alternative manner.

When the system according to the invention is installed in cages where there is a bottom weight, such as a sinker tube, arranged at the lower part or bottom of the net cage, the systems for lifting the weight should also be synchronized with the winding systems of the present invention, in order to avoid load and stress on the net. If the system for lifting the weight is not synchronized with the winding systems, the weight may be lifted by drag in the net, and the net may not be designed to withstand such load.

Traditionally a net to be used in a net cage has a number of reinforced vertical and horizontal ropes and the guiding members of the system according to the present invention should preferably be fastened to such a rope and even more preferred to areas where the horizontal and vertical ropes cross each other, in order to avoid load directly on the net. If the net is overloaded, it may rupture and cause holes and escape of fish.

By "line" it is herein meant any line, rope or strap being suitable for the intended use which is lifting and lowering the net. A line may be made of natural or synthetic fibres, which are twisted, braided or wowen. The line must be able to pass a guiding member, and withstand sufficient load. This will be obvious to a skilled person.

By "guiding member" it is herein meant any suitable member such as a pulley, pulley block or castor, but a simple ring or a sheave or tackle may also be used. The guiding member must be strong enough to withstand the load while lifting and lowering the net, and to withstand the environments and surroundings of the net cage, such as sea water, sun and wind. The guiding members above and below water may be different or identical.

The winding system may preferably be a winch, but manpower should also be included. The line should preferably be winded on a reel in order to avoid knots and tangles on the rope, to reduce possible risk for accidents, and to ease lowering of the net whenever convenient. By winding the line on a reel it is also possible to release the net quickly in case of an emergency, for instance by removing a brake on the reel, and thus the rope will unwind it self at the appropriate rate.

The present invention also relates to a method for lifting the net in a net cage having a bottom weight or sinker tube, by using a system as described above. The method comprises the following steps at desired lifting sites around the floating means;

- pulling the first end of the line attached to the winding system, and thereby pulling the line over the guiding member(s) and lifting the fastening point of the net, and

- lifting the sinker tube or bottom weight at a corresponding rate to the pulling of the line.

The winding of the line should preferably be done with the same speed and at all lifting sites around the floating means of the same net cage, and the lifting of the bottom weight or the sinker tube should be performed at a corresponding speed, in order to avoid stretch and stress to the net cage.

When it is desired to tilt the bottom of the net, the method should only be performed at the lifting sites where lifting is desired. The maximum degree of tilting without risks of damaging the net, depends on the size and construction of the net.

When the net should be lowered, the method is reversed, and the winding systems unwinds the line where after the guiding members will be lowered into the water again. The system for lifting the bottom weight should be reversed simultaneously.

If the system only comprises one guiding member arranged above the surface of the water, then the net will be lifted out of the water and raised above the water until the fastening point is sufficiently close to the guiding member. In a preferred embodiment the depth of the fastening point is the same as the distance from the surface of the water to the guiding member, and thus the net will be stretched above water when it is raised.

If the net comprises a number of guiding members, and the line is arranged alternating between guiding members above and below the water, then the distance between two fastening points of the net should be twice the distance from the surface of the water to the guiding member above the water. In this way, the net between two guiding members being fastened to the net, will be above the water, hanging from the guiding members to the surface of the water and up again, when the net is in raised position.

The system according to the present invention may for instance be used for lifting the net for inspection, maintenance and/or upon removing the fish from the cage. The invention also relates to use of the described system and method, for cleaning a net of a net cage. It is known that debris and fouling will dry and become brittle and easy to remove if the net is exposed to air and dry conditions over a time period. If a fouled net is dried sufficiently, then the contact with the surface of the water, and regular water current in the sea is sufficient to remove the dried debris and fouling. Thus, by lifting the net above the surface of the sea with the described system and method, and let the net hang until the debris and fouling is sufficient dry before the net is set out in the sea again, the net will be cleaned, and water may pass through the net again.

How long it takes until the net is sufficiently dry will vary with a number of factors, such as size of the threads of the net, amount and type of fouling, and the number of layers of net being lifted and left to dry. It will also depend on the weather, as it takes longer time during rain and damp weather. Most nets dry sufficient during 24 to 48 hours. The algae causing AGD as well as Yersiniose do not withstand dehydration and will also die when the net is being dried. This is most likely the case for sea lice and other parasites as well. By lifting the net above the surface, drying the net, and then put it back in the water, both debris, fouling and parasites will be removed. This is referred to as "cleaning" in this application.

Examples

The invention will now be described with the help of the enclosed figures, showing a system for lifting and lowering the net of a fish cage, 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 following description of an exemplary embodiment refers to the drawings, 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.

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

Figure 1 shows a system according to the present invention, arranged on a fish cage, wherein the net is in lowered position,

Figure 2 shows a cross section of a lifting site of the system in Figure 1,

Figure 3 shows a cross section of a part of a lifting site, wherein the net is in partly lifted position,

Figure 4 shows across section of a lifting site, wherein the net is in raised position, and

Figure 5 shows the circle marked A in Figure 4 in detail.

A system for lifting and lowering a net of a net cage according to the invention is arranged on a traditional fish cage having a floating means as floating collar 1, walk way 2, hand rail 3 and net cage as shown in the Figures. The net cage shown in the Figures has a sinker tube 4 arranged at the bottom part of the net cage to stretch the net 5.

In Figure 1 only two of the lifting sites of the system is shown, however a number of corresponding sites is arranged around the floating collar 1. At each lifting site, the system comprises a vertical element such as a davit 6 protruding from the floating collar 1 and fastened to a bracket or handrail pole. The davit 6 has an arm 7 protruding into the net cage, wherein three guiding members shown as pulleys 8 are fastened to the arm 7 at a distance from each other. In order to strengthen the arm, a bar 9 is arranged from the outer end of the arm 7 to the top of the davit 6. The bar 9, the arm 8 and the davit 6 constitutes a triangle.

The system further comprises a winch10 on the walk way, two pulleys 11 attached to fastening points of the net, one pulley 12 attached to the lower end of the net and a number of rings 13 attached to the net below the surface of the water, and a line 14 being used to lift and lower the net. The first end of the line 14 is attached to the winch, and the second end of the line is attached to the the arm 7 above the surface of the water. The line 14 is running from the winch 10 through the first pulley 8 on the arm 7 of the davit 6, through the rest of the pulleys (11, 8) alternating below and above the water, before it is running through the rings 13 to the last pulley 12 at the bottom of the wall of the net 5, and back to the arm 7 where the end is fastened.

When the winch 10 is winding the line 14, the net 5 will be lifted. In order to avoid stress and load to the net cage, the sinker tube 4 should be lifted at a corresponding speed. The winch may thus have two reels being operated at different speeds.

Alternatively, the system comprises two different winches which may be adjusted to each other. A second line 15 is running from the second reel or winch to the sinker tube 4, in order to lift the sinker tube.

When the winch 10 is winding the line 14 fastened to the net, the uppermost pulley 11 below water will be lifted until the pulley is close to the arm 7, or even between the pulleys 8 arranged on the arm as shown in Figure 5. Since the pulley 11 is attached to the net 4, the net 4 between the fastening of the net to the floating collar 1 and the pulley 11 will be lifted above the water. Once the first pulley 11 under water is lifted sufficiently, the next pulley 11 will start to lift and thus more net 4 will be lifted above the water. This continues until all pulleys 11 below water are lifted close to the arm 7, or even between the pulleys 8 attached to the arm 7 as shown in Figure 5, and the net 4 between the pulleys 11 will curve above the water from the arm 7 to the surface of the water and back up again.

If the net 4 is lifted only for the purpose of cleaning, then the net should be allowed to hang until it is dry. If it is desired to empty the net cage, or the entire net 4 should be lifted for any other reason, then the winch 10 should continue to wind the line 14, until the net is close to or above the surface of the water. This is shown in Figure 4, where all pulleys 11 attached to the net 4 is lying between the pulleys 8 of the arm 7, the rings 13 are stacked on top of each other, and the sinker tube 4 is hanging directly below the walk way 2.

The example above is given to illustrate the invention and should not be used to interpret the following claims limiting. Even if this application is written referring to a net of a fish cage, it may very well be used to lift a net of any other similar cage used for farming other organisms. This will be obvious to a skilled person.

The scope of the invention is not limited by the example give above, but the enclosed 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 lifting and lowering a net of a net cage in the water, the net cage comprises a floating means (1) in the surface of the water and a net (5) fastened to the floating means, the net constitutes the net cage surrounding the farmed fish and the floating means provides buoyancy to the net cage, characterized in that the system comprises a number of lifting sites around the floating means, wherein each lifting site comprises at least one guiding member (8, 11) arranged above the surface of the water, and a line (14) running from a winding system (10), through the guiding member (8) above the water and further to at least one fastening point of the net, below the surface of the water.

2. System according to claim 1, characterized in that the guiding member(s) (8) above the surface of the water, is attached to a protruding arm (7) of a vertical element (6) fastened to the floating means.

3. System according to claim 1, characterized in that a guiding member (11, 12) is fastened to the net at least at one fastening point, and that the line (14) is running alternating through the guiding members (8, 11) above and below the surface of the water.

4. System according to any one of claims 1-3, characterized in that the line (14) is running from the winding systems (10) through a number of guiding members (8, 11) alternating above and below the surface of the water, to the protruding arm (7) where the end of the line (14) is fastened.

5. System according to any one of claims 1-3, characterized in that the end of the line (14) is fastened to the net at a fastening point.

6. System according to any of the preceding claims, characterized in that the line (14) is running through a number of rings (13) fastened to the net after it has passed the last guiding member (8) above the water.

7. System according to any one of the preceding claims, characterized in that the winding systems (10) at each lifting site is synchronized, in such a way that the lines (14) are pulled at the same speed and same time at all lifting sites.

8. System according to any one of the preceding claims, wherein the net cage further comprises a weight (4) at the lower part of the fish cage, characterized by further comprising an elevation system for lifting the weight, and that the winding systems of the net and the elevation systems of the weight are synchronized.

9. Method for lifting a net (5) of a net cage having a bottom weight or sinker tube (4), by using a system according to claim 1, characterized by the following steps at the desired lifting sites around the floating means,

- pulling the line (14) attached to the winding system (10), and thereby pulling the line (14) through the guiding members (8, 11) and lifting the fastening point of the net, and

- lifting the sinker tube (4) or bottom weight at a corresponding rate as winding the line.

10. Use of a system according to 1, for cleaning a net (5) of a net cage, wherein at least parts of the net is lifted above the surface of the water by the method according to claim 9, and left until it the debris and fouling is dry, and then it is lowered again.

11. Use according to claim 10, characterized in that the net is left above the surface of the water for at least 24 hours, preferably for at least 48 hours.