WO2013029100A1

WO2013029100A1 - Net clearing device

Info

Publication number: WO2013029100A1
Application number: PCT/AU2012/001013
Authority: WO
Inventors: Peter Aran HEARD
Original assignee: Tassal Operations Pty Ltd
Priority date: 2011-08-30
Filing date: 2012-08-29
Publication date: 2013-03-07

Abstract

A net clearing device for clearing objects caught by a net submerged in a body of water. The net clearing device includes a submersible net clearing head, which has a duct with a mouth at one end through which to collect objects, a flow inducing device for inducing a fluid flow through the duct from the mouth, a container in fluid communication with the duct, the duct being configured to direct collected objects into the container; and a propulsion system for moving the head about on a surface of the net.

Description

Net Clearing Device

Field of the invention

The present invention relates to a submersible net clearing head, and a net clearing device for use in aquaculture.

Background

Open-water aquaculture commonly uses nets submerged in a body of water (such as a lake, river, ocean, etc.) to contain and protect a farmed fish species as they are grown to an appropriate harvest size. This system has a number of advantages, including the use of natural conditions, which promotes rapid fish growth. In addition, containing the farmed fish facilitates feeding and prevents the farmed fish intermingling with other species in the environment.

Periodically, farmed fish die inside the nets due to natural causes or attack by other farmed fish. The dead fish (which are also known as "mortalities", or colloquially as "morts") fall to the bottom of the nets. Aquaculture operators traditionally employ divers to remove dead fish and any other objects (such as rubbish and debris) that have been caught inside the nets of the facility. It is important to the health of the surviving population that the dead fish are removed relatively quickly. For this reason, scuba divers often clear the nets of morts and any foreign objects on a daily basis. The inherent risks of scuba diving limit the length of time and number of dives that a single diver can complete in single day. Furthermore, net clearing is a one of a number of activities that must be undertaken routinely. For these reasons, the use of divers for net clearing is a relatively inefficient use of the available dive time.

Summary of the invention

The present invention provides a submersible net clearing head for in-situ clearing of objects caught by a net submerged in a body of water, the submersible head comprising:

a duct with a mouth at one end through which to collect objects;

a flow inducing device for inducing a fluid flow through the duct from the mouth;

a container in fluid communication with the duct, the duct being configured to direct collected objects into the container; and

a propulsion system for moving the head about on a surface of the net. In some embodiments, the flow inducing device comprises an outlet nozzle for discharging fluid into the duct causing a pressure differential across the nozzle that induces a fluid flow through the duct.

The outlet nozzle can include an annular orifice and a generally curved annular surface positioned downstream of the annular orifice, wherein fluid discharged through the orifice flows onto and along the curved annular surface.

The flow inducing device can further comprise a fluid inlet, and an annular chamber surrounding the duct, the chamber receiving fluid via the fluid inlet and distributing fluid around the duct for discharge through the annular orifice.

The generally curved surface may be formed of a series of frustoconical rings of successively decreasing diameter and angle relative to the duct. The smallest frustoconical ring has a smallest internal diameter that is equal to the internal diameter of the duct. The smallest frustoconical ring also has the shallowest angle relative to the duct. In some embodiments, the flow inducing device has two frustoconical rings.

The annular chamber can comprise a plurality of flow directing vanes that extend radially with respect to the duct and are adjacent the annular orifice. The outlet nozzle can also include a ring that extends between duct and the curved annular surface to guide fluid flow from the annular orifice onto the curved annular surface. The flow inducing device can further comprise a fluid displacement device to drive fluid through the fluid inlet of the flow inducing device. The fluid displacement device can be in the form of a propeller driven by a motor. The motor may conveniently be a hydraulic motor. Preferably, the mouth is wide and has a small height. The shape of the cross section of the mouth may be one of: oval,' ellipse, rectangle, rounded rectangle, or stadium. Preferably, the broadest dimension of the duct at the mouth is orientated to be parallel with a bottom edge of the submersible head. More preferably, the mouth is located adjacent the bottom edge of the submersible head.

In some embodiments, the duct has a circular cross section upstream of the outlet nozzle, and the duct includes transition section in which the cross-section varies from the mouth to a circle.

In certain embodiments, the cross sectional area of the duct is substantially constant through the transition section.

Preferably, the width of the mouth is in the range of 2 to 4 times the diameter of the duct. More preferably, the width of the mouth is approximately 3 times the diameter of the duct.

In some embodiments, the container is in the form of a netting bag that is attached to an outlet of the duct.

The submersible head may further comprise a frame that supports the components of the head, the frame including skid members that extend around the lower periphery of the submersible head and, in use, contact the net.

The skid members include two transverse skid members that are arranged at the front and rear of the submersible head. The skid members can further include two longitudinal skid members that are parallel to one another and are arranged at the sides of the submersible head. Preferably, the transverse and longitudinal skid members are joined to form a rectangular section. The skid members preferably have curved lower surfaces. In addition, the intersections of the transverse and longitudinal skid members are rounded.

In certain embodiments, the longitudinal skid members are bowed allowing the submersible head to rock back and forth when supported on the longitudinal skid members.

In certain embodiments, the mouth extends through the transverse skid member at the front of the submersible head. The propulsion system may include one or more sprockets having teeth to engage the net, each sprocket having a motor to rotate the respective sprocket relative to the submersible head. In certain embodiments, the submersible head has two sprockets that are each driven by a hydraulic motor, and the sprockets are each positioned beside one of the longitudinal skid members. Thus, the sprockets are arranged to alter the yaw of the submersible head.

Each sprocket may be movable between a deployed position, in which at least a segment of the sprocket is below the frame such that teeth can engage the net, and a retracted position. In certain embodiments, each sprocket is supported on one end of a swing arm that is pivotally connected to the frame. ln such embodiments, the submersible head may further comprise one or more hydraulic actuators that each extend between the frame and a respective swing arm to move the respective sprocket between the deployed and retracted positions. The hydraulic actuators may be associated with the hydraulic motor for the flow inducing device such that when the flow inducing device is active, the hydraulic actuators are operated to position the sprockets in the deployed position.

Alternatively or additionally, the propulsion system may include one or more propellers. In certain embodiments, the propulsion system includes two propellers that are each arranged to provide a net thrust to urge the skid members onto the surface of the net. Each propeller can be mounted within a shroud.

The submersible head may further comprise one or more cameras to facilitate a remote operator locating debris caught by the net and/or directing the head's movement about on the surface of a net. In embodiments in which the propulsion system includes one or more propellers, the submersible head can also include means to direct a fluid flow from the or each propeller to at least one of the cameras. The present invention provides a net clearing device for clearing objects caught by a net submerged in a body of water, the net clearing device comprising: a submersible net clearing head as previously described;

a control unit that can be located above the surface of the body of water, from which an operator can remotely control the submersible head; and

an umbilical that connects the submersible head with the control unit to provide consumables and/or other services between the submersible head and the control unit.

Brief description of the drawings

In order that an invention may be more easily understood, an embodiment will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 : is a front perspective view of a submersible net clearing head according to a first embodiment of the present invention;

Figure 2: is a rear perspective view of the submersible head of Figure 1 ; Figure 3: is a front view of the submersible head of Figure 1 ;

Figure 4: is a top view of the submersible head of Figure 1 ;

Figure 5: is a lower perspective view of the submersible head of Figure 1 ; Figure 6: is an enlarged view of the mouth and frame of the submersible head of Figure 1 ;

Figure 7: is a side view of the submersible head of Figure 1 ;

Figure 8: is a vertical cross section of a portion of the flow inducing device of the submersible head of Figure 1 ;

Figure 9: is an enlarged view of region A of Figure 8; and

Figure 10: is a schematic view of a net clearing device according to a second embodiment of the present invention.

Detailed description

Figures 1 to 7 show a submersible net clearing head 10 according to a first embodiment of the present invention, which is to be used for in-situ clearing of objects caught by a net that is submerged in a body of water. In particular, the head 10 is suitable for clearing dead fish (hereinafter referred to as "morts") that have fallen to the bottom of the net.

The head 10 has a duct 12 with a mouth 14 at one end through which to collect objects, such as morts. A flow inducing device 16 is provided to induce a fluid flow through the duct 12 from the mouth 14. The head 10 also has a container, in fluid communication the duct 12. In this embodiment, the container is in the form of a netting bag 18, which is shown in Figure 4, but for clarity is omitted from the remaining Figures. The duct 12 is configured to direct collected morts into the netting bag 18. To this end, in this embodiment the netting bag 18 is fitted to an outlet end of the duct 12 such that each collected mort is discharged from an outlet end 19 of the duct 12 directly into the netting bag 18. The head 10 also has a propulsion system for moving the head about on a surface of the net, which is described in further detail below.

In use, the head 10 is moved about the inside of the net using the propulsion system. The flow inducing device draws in water from a region immediately in front of the mouth 14, including any morts that are in that region. The collected morts then flow through the duct 12 and are stored in the netting bag 18 for subsequent retrieval, conveniently when the head 10 is raised to the surface.

The flow inducing device 16 of this embodiment is shown in further detail in Figure 7. A portion of the flow inducing device 16 are also shown in further detail in Figures 8 and 9. The device 16 has an outlet nozzle 20 that is. arranged to discharge fluid into the duct 12. The flow of fluid through the outlet nozzle 20 causes a pressure differential across the nozzle 20, which induces the fluid flow through the duct 12.

The outlet nozzle 20 has an annular orifice 22 and a generally curved annular surface 24 downstream of the orifice 22. The curved annular surface 24 is convex with respect to the internal surface of duct 12. In use, fluid is discharged through the orifice 22 and onto the curved annular surface 24, accelerating the fluid flow and lowering the pressure of fluid in the region adjacent the surface 24. The resulting pressure drop entrains fluid in the duct 12 upstream of the nozzle 20, which creates the fluid flow. Thus, the outlet nozzle 20 employs the Coanda^" effect to create the pressure differential across the nozzle 20. This has the distinct advantage of generating a fluid flow through the duct 12 without requiring any moving parts between the mouth 14 and the bag 18. This eliminates the possibility of the morts interfering with moving parts, which could impede or prevent fluid flow through the duct 12.

As is particularly shown in Figure 8, the flow inducing device 16 also has a fluid inlet 26, and an annular chamber 28 that defines an annular region surrounding a portion of the duct 12. The chamber 28 receives fluid via the fluid inlet 26 and distributes fluid into the annular region for discharge through the annular orifice 22. The chamber 28 also includes a flow directing vanes 30 that extend radially with respect to the duct 12 and are adjacent the annular orifice 22. A ring 32 is connected to the duct 12 upstream of the curved annular surface 24, and extends radially outwardly of the duct 12. The ring 32 includes a surface 34 that faces the curved annular surface 24, and guides fluid discharged from the orifice 22 onto the surface 24.

As is shown particularly in Figure 9, the generally curved annular surface 24 of this embodiment is formed of a series of frustoconical rings 36a, 36b of successively decreasing diameter and angle relative to the duct 12 that are joined together. The smallest frustoconical ring 36b has a smallest internal diameter that is equal to the internal diameter of the duct 12. Further, the smallest frustoconical ring 36b has the shallowest angle relative to the duct 12. In this embodiment, the flow inducing device 16 has two frustoconical rings 36a, 36b.

The flow inducing device 16 further has a fluid displacement device to drive fluid through the fluid inlet 26 and into the annular chamber 28. In this particular embodiment, the fluid displacement device is in the form of a propeller and motor 38. The motor may be a hydraulic motor 38. The propeller blades are located inside a shroud 40, which concentrates the flow of fluid into the fluid inlet 26.

As is evident from Figure 8, the cross sectional area of the fluid inlet 26 is larger than the annular orifice 22. Thus, the fluid velocity through the annular orifice 22 is higher than that through the inlet 26. As will be appreciated, fluid leaving the propeller is turbulent. The annular chamber 28 and the flow directing vanes 30 operate to reduce the turbidity of the fluid moving through the flow inducing device 16 such that at the outlet nozzle 20 the flow is substantially laminar. As shown in Figure 3, the mouth 14 is wide and has a small height, which facilitates collecting morts from as wide a region in front of the head 10 as possible. The height of the duct 12 at the mouth 14 is selected to allow easy passage of a mort that is at the maximum harvest size. In this particular embodiment, the cross section of the mouth 14 has the shape of a two-dimensional geometric stadium; that is, with two linear parallel sections joined by two semi-circles. This particular shape facilitates locating the mouth 14 adjacent the bottom edge of the head 10.

The duct 12 has a circular cross section upstream of the outlet nozzle 20. Furthermore, the duct 12 has a transition section 42 in which the cross section varies from the mouth to a circle. Ideally, the cross section of the duct 12 remains substantially constant through the transition section 42.

In this particular embodiment, the width of the mouth 14 is approximately 3 times the diameter of the duct at the downstream end of the transition section 42.

The head 10 includes a frame 44 that supports the other components of the head 10. The frame 44 has skid members that extend around the lower periphery of the head 10 and, in use, contact the net. As shown most clearly in Figures 4 and 5, the skid members include two transverse skid members 46 that are arranged at the front and rear of the head 10. Furthermore, two longitudinal skid members 48 are arranged at the sides of the head 10. The transverse and longitudinal skid members 36, 38 are joined to form a rectangular section. The transverse and longitudinal skid members 46, 48 have curved lower surfaces. Furthermore, the intersections between the transverse and longitudinal skid members 46, 48 are rounded at both the lower and lateral surfaces. These curved surfaces facilitate the frame 44 sliding over the surface of a net.

As shown most clearly in Figure 7, the longitudinal skid members 48 are bowed, which in use allows the head 10 to rock back and forth when supported on the longitudinal skid members 48. This further facilitates moving the head 10 about the surface of a net.

The leading portion 50 of the mouth 14 extends through a portion of the transverse skid member 46 at the front of the head 10. Further, in the leading portion 50 projects beyond the front transverse skid member 46. As shown in Figures 5 and 6, this facilitates bringing the mouth 14 as close to the bottom of the head 10 as possible, which in turn facilitates ingress of a mort into the duct 12. In this embodiment, the propulsion system, in this embodiment, includes a pair of sprockets 52, and a pair of pitch propeller and motors 60. The sprockets 52 have teeth to engage the net and provide a tractive interaction with rotation of the sprockets 52. Each sprocket 52 is positioned adjacent a respective one of the longitudinal skid members 48, with an axis of rotation that is perpendicular to the longitudinal skid members 48. Each sprocket 52 has a dedicated motor 54 to rotate the respective sprocket 52 relative to the frame 44. Each motor 54 can be driven independently, such that the sprockets 52 can be rotated in the same direction and speed to propel the head fore and aft on the net. Alternatively, the sprockets 52 can be rotated with a speed differential and/or in opposing directions to alter the yaw of the head 10.

The sprockets 52 are each movable between a deployed position, in which at least a segment of the sprocket 52 is below the frame 44 such that teeth can engage the net, and a retracted position. In this embodiment, each sprocket 52 is supported on one end of a swing arm 56 that is pivotally connected to the frame 44. Figure 7 shows the sprocket 52 in the deployed position. The head 10 has a pair of hydraulic actuators 58 that each extend between the frame 44 and a respective swing arm 56 to move the respective sprocket 52 between the deployed and retracted positions. Conveniently, the hydraulic actuators 58 can be operatively associated with the hydraulic motor 38 for the propeller of the flow inducing device 16 such that when the flow inducing device 16 is active, the hydraulic actuators 58 are operated to position the sprockets 52 in the deployed position. The pitch propeller and motors 60 are located towards the front and rear of the head 10, respectively. The motor of each pitch propeller can be a hydraulic motor 62. Furthermore, the blades of each pitch propeller and motor 60 are mounted within a respective shroud 64. As shown in the Figures, each pitch propeller and motor 60 is orientated to provide a downward thrust on the head 10. Both pitch propeller and motors 60 can be driven together to provide a net thrust to urge the skid members 46, 48 towards the surface of a net. The net thrust is perpendicular to the transverse and longitudinal skid members 46, 48. Alternatively, the pitch propeller and motors 60 can be operated independently to alter the pitch of the head 10.

The head 10 includes a pair of buoyancy tanks 66 that are mounted above the head's centre of gravity, so that the head 10 is self-righting. In use, the buoyancy tanks 66 can be filled with air and/or vented to adjust the overall buoyancy of the head 10. Typically, when the head 10 is being used to clear a net, the buoyancy is negative, and approximately 50kg. This facilitates the head 10 being supported by the net, which in turn facilitates engagement of the teeth of the sprockets 52 with the net. The buoyancy tanks 66 can be operated statically so that the air pressure within the tanks is set prior to use of the head 10. Alternatively or additionally, the head 10 can be provided with a venting and charging system to facilitate dynamic setting of the head's buoyancy. Figure 10 shows a net clearing device 100 in accordance with a second embodiment of the present invention, which is for use in clearing objects caught by a net N submerged in a body of water W. The net clearing device 100 includes the submersible net clearing head 10 (described in connection with Figures 1 to 9), a control unit (not shown), and an umbilical 102 that connects the submersible head 10 with the control unit to provide consumables and/or other services between the head 10 and the control unit, as discussed in further detail below.

The control unit can conveniently be located in a cabin of a punt 104, from which an operator can remotely control the submersible head 10. In this way, the operator can drive the punt 104 up to a net N, moor the punt, and then undertake net clearing activities, such as removing morts D from the bottom of the net N.

The head 10 can include one or more cameras (not shown), and the control unit can have monitors so that the operator is provided with visual information of any objects, such as morts, that are nearby the head 10 and within the field of the view of the camera(s). Lights (also not shown) may also be provided to the head 10 to illuminate the regions that include the field of view of the camera(s). The umbilical 102 may have hydraulic lines to operate any of the five motors and/or hydraulic actuators; a compressed air line to provide air to the buoyancy tanks; and electrical wires for lighting and communication purposes. The umbilical 102 may also include a cable for hoisting/lowering the head 10 into the body of water. The frame 44 can include a lifting point (not shown) to facilitate attachment of the umbilical 102 to the head 0.

Throughout this specification and claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers or steps but not the exclusion of any other integer or group of integers.

Claims

CLAIMS:

1. A submersible net clearing head for in-situ clearing of objects caught by a net submerged in a body of water, the submersible head comprising:

a duct with a mouth at one end through which to collect objects;

a propulsion system for moving the head about on a surface of the net.

2. A submersible net clearing head according to claim 1, wherein the flow inducing device comprises an outlet nozzle for discharging fluid into the duct causing a pressure differential across the nozzle that induces a fluid flow through the duct.

3. A submersible net clearing head according to claim 2, wherein the outlet nozzle includes an annular orifice and a generally curved annular surface positioned downstream of the annular orifice, and wherein fluid discharged through the orifice flows onto and along the curved annular surface.

4. A submersible net clearing head according to claim 3, wherein the flow inducing device further comprises a fluid inlet, and an annular chamber surrounding the duct, the chamber receiving fluid via the fluid inlet and distributing fluid around the duct for discharge through the annular orifice.

5. A submersible net clearing head according to either claim 3 or 4, wherein the generally curved surface is formed of a series of frustoconical rings of successively decreasing diameter and angle relative to the duct.

6. A submersible net clearing head according to either claim 4 or 5, wherein the annular chamber comprises a plurality of flow directing vanes that extend radially with respect to the duct and are adjacent the annular orifice.

7. A submersible net clearing head according to any one of claims 2 to 6, wherein the outlet nozzle further comprises a ring that extends between duct and the curved annular surface to guide fluid flow from the annular orifice onto the curved annular surface.

8. A submersible net clearing head according to any one of claims 1 to 7, wherein the flow inducing device further comprises a fluid displacement device to drive fluid through the fluid inlet of the flow inducing device.

9. A submersible net clearing head according to any one of claims 1 to 8, wherein the mouth is wide and has a small height.

10. A submersible net clearing head according to claim 9, wherein the broadest dimension of the duct at the mouth is orientated to be parallel with a bottom edge of the submersible head.

11. A submersible net clearing head according to claim 10, wherein the width of the mouth is in the range of 2 to 4 times the diameter of the duct.

12. A submersible net clearing head according to any one of claims 1 to 11 , wherein the mouth is located adjacent the bottom edge of the submersible head.

13. A submersible net clearing head according to any one of claims 1 to 12, further comprising a frame that supports the components of the head, the frame including skid members that extend around the lower periphery of the submersible head and, in use, contact the net.

14. A submersible net clearing head according to claim 13, wherein the skid members include:

two transverse skid members that are arranged at the front and rear of the submersible head; and

two longitudinal skid members that are parallel to one another and are arranged at the sides of the submersible head.

15. A submersible net clearing head according to claim 14, wherein the longitudinal skid members are bowed allowing the submersible head to rock back and forth when supported on the longitudinal skid members.

16. A submersible net clearing head according to either claim 14 or 15, wherein the mouth extends through the transverse skid member at the front of the submersible head.

17. A submersible net clearing head according to any one of claims 1 to 16, wherein the propulsion system includes one or more sprockets having teeth to engage the net, each sprocket having a motor to rotate the respective sprocket relative to the submersible head.

18. A submersible net clearing head according to claim 17, wherein each sprocket is movable between a deployed position, in which at least a segment of the sprocket is below the frame such that teeth can engage the net, and a retracted position.

19. A submersible net clearing head according to claim 18, further comprise one or more hydraulic actuators that are arranged to move the respective sprocket between the deployed and retracted positions.

20. A submersible net clearing head according to claim 19, wherein the hydraulic actuators are associated with the hydraulic motor for the flow inducing device such that when the flow inducing device is active, the hydraulic actuators are operated to position the sprockets in the deployed position.

21. A submersible net clearing head according to any one of claims 1 to 20, wherein the propulsion system includes one or more propellers that are each arranged to provide a net thrust to urge the skid members onto the surface of the net.

22. A net clearing device for clearing objects caught by a net submerged in a body of water, the net clearing device comprising:

a submersible net clearing head according to any one of claims 1 to 21 ; a control unit that can be located above the surface of the body of water, from which an operator can remotely control the submersible head; and