WO1995015079A1

WO1995015079A1 - Fish lifting device

Info

Publication number: WO1995015079A1
Application number: PCT/CA1993/000512
Authority: WO
Inventors: Roger Colin Coleman; Wayne Douglas Gorrie
Original assignee: P.R.A. Manufacturing Ltd.
Priority date: 1993-11-30
Filing date: 1993-11-30
Publication date: 1995-06-08
Also published as: AU5557494A

Abstract

In prior fish lifting devices which use a rotating helical screw (3), the screw (3) was dewatered using a lattice-work screw entry portion to dewater the screw (3) at the point of entry of the fish, or dewatering slots in the outer shell of the device adjacent the lower opening. The present invention provides a dewatering system which also provides a fish-attracting aerated current flow along the axis (7) of rotation of the device at the entry to the screw (3).

Description

FISH LIFTING DEVICE

BACKGROUND OF THE INVENTION

The invention relates to the field of fish elevators which use a rotating helical screw to raise fish from a body of water to a storage area.

Fish farming operations use fish elevators to remove fish from a body of water for transferring to a vehicle, a temporary storage tank or another body of water. Prior fish elevators, such as that disclosed in the appli¬ cant's United States patent no. 4,932,149 "Fish Lifting Device" issued June 12, 1990, and Canadian patent no. 1,093,400 issued January 13, 1981 to Faivre, a rotating screw is used to raise the fish. For efficient operation of such a device it is important that sufficient dewatering of the lifting screw be provided to avoid carrying too much water up with the fish, and also that the structure of the entry portion be such that fish are not repelled. In Faivre, there are two screw sections rotating on a common shaft - a lifting screw which is a solid helix, and a catching screw which is a lattice-work helix. The fish are transferred from the catching screw to the lifting screw by means of a deflector formed in the cylindrical drum around the lifting screw. The lattice-work screw portion serves to dewater the transported fish. Since fish are attracted by instinct into a current and are frightened by an area of low water pressure, the applicant discovered, as disclosed in United States patent no. 4,932,149, the advantages of providing a device for lifting fish which attracts fish to the entrance of the device using a counterflow current. The device disclosed in the applicant's prior patent comprised a solid auger of constant pitch and diameter for most of its length which flared out to a greater diameter at its lower entry end. The auger was bonded to a solid fibreglass outer cylindrical sheath which turned with the auger as a single unit. The outer cylinder was provided with dewatering slots in the vicinity of the flared end to dewater the auger. Slots were cut in the outer edge of the entry revolution of the auger to create a current away from the entrance to the device.

A problem with prior art fish elevators is that it is necessary to crowd the fish into the opening area of the elevator to force the fish into the device, which causes stress on the fish and may damage the fish. While the applicant ' s prior device was an improvement over the prior art in its ability to attract fish to the entry of the elevator rather than repel them, it still was not the optimal design in that the current flow was dispersed around the outer circumference of the cylinder so it was not a particularly strong current, and fish would be attracted to the outer edge of the cylinder and not necess¬ arily into the entrance to the elevator. The applicant has now discovered that further benefits are obtained by concentrating the flow of water along the axis of the device and that further fish-attracting benefits are obtained if the water is aerated.

SUMMARY OF THE INVENTION

The present invention provides a device for lifting fish which attracts fish to the entrance of the device using a concentrated current of aerated water along the axis of rotation of the elevator. The device comprises a solid auger of constant pitch and diameter for most of its length and which flares out to a greater diameter at its lower entry end. The auger is bonded to a solid fibreglass outer cylindrical sheath which is turned with the auger as a single unit. Along the central axis of the screw at the lower entry end, within the flared end, is provided a cylindrical pipe having a slotted surface to dewater the auger and to allow water to flow out along the central axis of the screw creating an aerated current away from the entrance to the device which serves to effectively attract fish into the entrance to the device. BRIEF DESCRIPTION OF THE DRAWINGS

In drawings which illustrate a preferred embodi¬ ment of the invention:

Fig. 1 is a perspective view of the auger and sheath of the invention;

Fig. 2 is a side view of the invention shown in Figure 1 mounted in its supporting frame in position for operation;

Fig. 3 is a side view of the invention shown in Figure 1 mounted in its supporting frame in position for transportation;

Fig. 4 is a cross-sectional view taken along lines III-III of Fig. 3;

Fig. 5 is a cross-sectional view taken along lines IV-IV of Figure 4;

Fig. 6 is a detail view showing the entry section of the invention;

Fig. 7 is a cross-sectional view taken along lines VI-VI of Figure 3; and

Fig. 8 is a cross-sectional view taken along lines VII-VII of Figure 3.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

With reference to the drawings, the fish lifting device (hereinafter referred to as a fish elevator) is designated generally as 1. It consists generally of a screw or auger 3 (Fig. 3) typically formed of fibreglass, and mounted within, and fixed to, a cylindrical sheath 5. The screw and sheath rotate about a central shaft 7. The sheath is also typically made of fibreglass and is trans- lucent in the upper transport region 13 to allow monitoring of the fish. The sheath and screw assembly is mounted in a supporting frame 9 (Fig. 2) .

The screw and sheath assembly consists of two sections, an entry section 11 and a transport region 13. The sheath 5 in the transport region 13 is a cylinder of constant diameter. The entry section 11 flares outwardly, by way of conical surface 16, to a cylindrical portion 15 of greater diameter than the transport section. The screw 3, however, is continuous and of constant pitch as between the entry and transport sections. The diameter of screw 3 decreases from cylindrical portion 15 to the transport section 13 and is constant in diameter through the trans¬ port section 13. Typical dimensions for the device would be a 36" (91.5 cm.) diameter for the transport region, a 60" (152.5 cm.) diameter for the entry section, and a 24" (61 cm.) pitch for the screw. However other sizes are appro¬ priate for different applications. The entry section 11 is painted black using gel coat or the like to make it friend¬ lier to the fish. Extending coaxially around the central shaft 7 in the entry region 11 of the sheath 5 is a hollow cylindrical pipe 19, a portion of the surface of which is provided with an array of slots or perforations to form a water-permeable screen 81. Preferably pipe 19 is aluminum. Pipe 19 com- municates with the surface of screw 3 in the entry region 11 of the sheath 5 to permit water to flow from the screw 3 into the interior of pipe 19 outside shaft 7 and down¬ wardly by gravity out apertures 83 and out of the entry section of the device. A solid cover or baffle 82 (see Fig.6) extending around half of the pipe 19 is provided in the portion of the first revolution of the screw that is within the cylindrical section 15. Baffle 82 thus causes water flowing from the screw 3 through screen 81 in tapered section 16 to flow out the open ends 83 of pipe 19 in the direction of arrows A, rather than back into the first flight of screw 3. The outflow is thereby concentrated along the axis of the device. The pipe 19 is held in place on shaft 7 by one or more ribs 22. The number and sizes of the perforations in pipe 19 are selected to provide a suitable flow of residual water into the transport stage 13 of the device. In the preferred embodiment, the first flight of screw 3 within the entry section 15 is also provided with slots 4 around the periphery thereof to assist in dewate¬ ring in the first flight of the screw.

As shown in Fig. 2 and 3, the preferred embodi- ment of the invention includes a support frame 9 which also serves to transport the device. Frame 9 consists of rigid longitudinal frame elements 41 and 43, cross-piece 45, support elements 47 and 49, and base frame 30. The lower main frame element 41 slides in box sections 35 on either side of support frame 9. Box sections 35 in turn are pivotally secured to base frame 30 at axle 37. Wheels 36 are rotatably attached to box frames 35. A hydraulic cylinder 31, controlled by controls 44, is connected at one end to box frame 35 and at the other end to support element 47, and acts to variably adjust the position of frame 41 in box frame 35.

Frame 32 rotatably supports the entry section 11 of sheath 5. Semi-circular frame element 34 is a fixed guard to protect the nets from chafing. A centre caster 38 is pivotally mounted on the lower surface of support element 47.

Hydraulic motor 42, controlled by hydraulic controls 44, drives a pulley 57 which in turn drives belt 55 which is in frictional contact with high-friction region 56 of sheath 5 to rotate sheath 5 within frame 9. Outlet sluiceway 70 is pivotally supported on frame 74 at axle 72. A chain 76 holds the sluiceway 70 in the desired location relative to the outlet of sheath 5 when the device is in the operating configuration shown in Fig. 1. Sluiceway 70 has a rear outlet 78 and a lower drain 80 covered by a grate which serves to dewater the outlet. As shown in Fig. 2 and 3, the frame 9 converts from a transport position shown in Fig. 3, in which wheels

36 and 38 roll on the supporting surface, to the fish pumping configuration shown in Figure 2. By actuating hydraulic cylinder 31, the weight of the device is balanced to be readily tipped from the position in Fig. 3 to that in Fig. 2, pivoting about axle 37. This raises wheels 36, 38 leaving frame 30 sitting on the dock or other supporting surface. A second hydraulic cylinder 71, controlled by controls 44, acts to tip the device and adjust the vertical angle. The lower end of hydraulic cylinder 71 has a bracket 73 which slides in a slot in frame 30 and can be secured at a given position by a pin or screw or the like. The upper end of hydraulic cylinder 71 is pivotally secured to frame 47. Once in the tipped position in Fig. 3, the lower bracket 73 is pinned in place. Further adjustment of the desired angle of the device to the horizontal is then possible by adjusting hydraulic cylinder 71.

The structure of the supporting elements 47 and

49 is shown in Figures 7 and 8 respectively. The top element 47 has four rollers 51 mounted for rotation in corner pieces 53. The rollers are positioned to bear snugly against the sides of sheath 5, thereby holding it firmly in position while allowing rotation. Drive band 55 is of rubber or the like and extends around sheath 5 and drive pulley 57. The lower support element 49 has two rollers 61 mounted for rotation in corner elements 63 in the two lower corners of the frame. Rollers 61 bear against the sides of sheath 5. Two further rollers 65 are mounted for rotation about axes of rotation perpendicular to shaft 7 in frames 66. An annular collar 67 secured coaxially to the outer surface of sheath 5 bears against the rollers 65 due to the force of gravity and holds the sheath in vertical position while allowing it to rotate.

In operation the sheath and screw assembly is mounted so that the entry end 11 of the device 1 is in¬ serted into a body of water, whether a tank or fish pen, at an acute angle of preferably between 20 and 45 degrees, as shown in Figure 2. The fish are crowded towards the open end of the device and the assembly is rotated about shaft 7 by drive band 55 causing water to be drawn up the upper surface of the screw 3. Some of the water from point of entry will travel the full length of the device, but a certain portion of the water drawn up by the screw 3 is necessarily forced out through the slots in the surface of pipe 19 as the diameter of the screw 3 constricts from entry section 11 into region 13. A certain amount of aeration of the water takes place as it is forced through the slots in pipe 19 due to turbulence and contact with the surrounding air. The water drains through the surface of pipe 19 and drains downwardly due to gravity out of the lower end of pipe 19, causing a concentrated, aerated counter-current outwardly along the axis of rotation of the device as indicated by the arrows A in Fig. 6. As oxygen levels in the vicinity of the fish drop, the fish look for an escape route and this concentrated flow of aerated water attracts fish toward the centre axis of the rotating screw. The fish are then deflected onto the lifting screw and gently lifted to the outlet of the device.

As will be apparent to those skilled in the art, various modifications and adaptations of the structure above described may be made without departing from the spirit of the invention, the scope of which is to be construed in accordance with the accompanying claims .

Claims

We Claim :

1. A device for lifting fish comprising a helical screw fixed in a cylindrical sheath having an open fish- receiving end, and supported for rotation in a frame about a central longitudinal axis, and means for rotating said sheath, characterized in that said device further comprises means for producing an aerated flow of water along said central axis out from said open fish-receiving end.

2. The device of claim 1, wherein said means for produc¬ ing an aerated flow of water along said central axis out from said open fish-receiving end comprises means for permitting water to flow by gravity from said screw downwardly along said central axis adjacent said fish-receiving end.

3. The device of claim 2, wherein said means for produc- ing an aerated flow of water along said central axis out from said open fish-receiving end comprises a hollow pipe mounted coaxially on said central axis adjacent said fish-receiving end.

4. The device of claim 3, wherein said hollow pipe mounted coaxially on said central axis adjacent said fish-receiving end comprises a perforated, water permeable material.

5. The device of claim 4, wherein said hollow pipe further comprises baffle means adjacent said fish- receiving end to prevent flow of water from the interior of said hollow pipe into the lower section of said helical screw.

The device of claim 4 wherein the diameter of said cylindrical sheath adjacent said fish-receiving end of said sheath is greater than the diameter of said sheath distant from said fish-receiving end.

The device of claim 5 wherein a continuous taper is provided between said larger diameter and said smaller diameter portions of said cylindrical sheath.

A method of lifting fish using a helical screw fixed in a cylindrical sheath having an open fish-receiving end which is rotated in a frame about a central longitudinal axis, characterized in that said method further comprises the step of providing an aerated flow of water along said central axis out from said open fish-receiving end.