AU2004100617A4

AU2004100617A4 - Shellfish Farming

Info

Publication number: AU2004100617A4
Application number: AU2004100617A
Authority: AU
Inventors: Basil Simpson Dow
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-08-01
Filing date: 2004-08-02
Publication date: 2004-09-09
Anticipated expiration: 2012-08-02
Also published as: AU2004100617B4

Description

1 SHfELLFISH

FARMING

Field of the invention THIS INVENTION relates to shellfish farming and is more specifically, but not exclusively concerned with farming oysters. However it should be understood that the invention is wider than just oyster farming as there are other shellfish, such as mussels, which lend themselves to farming and the present invention may be equally applicable to these shellfish also. However for the convenience of the reader the following description will describe the invention in relation to oyster farming but it is to be understood that the invention is also applicable to other shellfish than oysters.

The traditional method of growing oysters on sticks in tidal zones of certain rivers is inefficient. The type of oyster collected on the sticks is mixed with other shellfish and oyster types which are not acceptable for marketing. Shellfish grown on sticks are of irregular shape which makes machine sorting difficult or impossible. Also oysters grown on tidal leases are prone to raiding and destruction by marine predators before they can be harvested. For these and other reasons shellfish farming is regarded as a business reflecting high labour costs and a low profit margin.

Research has shown that there are sufficient nutrients to support oyster cultivation in the upper surface of relatively deep water in many places. Attempts to exploit this have resulted in the development of buoyant trays on which the oysters can be laid durinr- 2 their growing period from single seed oysters to oysters of marketable size. This can take upwards of a year or so. The trays can be protected above and below by mesh so that the sea water can wash through them but predators are discouraged. A disadvantage of this form of cultivation is that it is necessary to dry the oysters in air for a few days every two months in order to kill off marine growths from the surfaces of the oysters and to remove other harmful predators. This involves lifting the trays for prolonged periods or bringing them ashore from the positions in which they are anchored. A large punt equipped with a crane is necessary to lift the trays and bring them ashore as each tray may weigh in the region of forty or more kilograms. This capital cost involved is therefore substantial and beyond the reach of most oystermen.

This form of cultivation has therefore not been widely adopted.

Suggestions have been made to develop a buoyant tray which is provided with a float system capable of holding the tray immersed in one mode of operation, and which will lift the tray with respect to the water surface in a second mode of operation. While this suggestion is interesting there are practical difficulties standing in the way of its adoption and which have prevented the idea from being put into practice. For example, a tray loaded with oysters can be provided at its ends with floats attached by flexible wires or cords to the tray and movable from stations above the tray at which they allow the tray to be suspended between them at the required depth from the floats. The suggestion for raising the tray during the drying out periods involves moving the floats beneath the ends of the tray.

3 However in practice this is not possible because the diameter of each float necessary to give it the required buoyancy to lift the tray clear of the water is considerable and it is simply not possible for an oysterman in a punt to have the physical strength to push the float manually beneath the surface of the water and beneath the end of the tray in order to buoy it up. Also, it has been found that the natural movement of the tray in deep water quickly releases the float from beneath the tray's end so that one or both ends of the tray drop beneath the surface of the water. Experiments have shown that the buoyancy of a float would have to be so small if it was to be manually pushed beneath a loaded oyster tray, that the tray would only rise an inch or so with respect to the water surface and would still be largely immersed. In consequence, the bulk of the oysters in it would remain beneath the water. For these and other reasons this solution to the problem has been found to be unworkable.

Obiect o thle invention An object of this invention is to provide an improved way of farming shellfish.

The i nv ti Apparatus for buoyantly supporting a tray containing shellfish at two stations respectively above and beneath the water line, comprises: rigid arms arranged in pairs with each pair pivoted close to the ends of the tray for movement in planes parallel to the sides of the tray, the free ends of each pair of arms being connected to respective ends of a float which is moveable between a first stable position at which the tray is buoyantly supported beneath the surface of the water by the floats at each end and a second stable position at which the floats are trapped beneath opposite end-portions of 4 the tray so that it is buoyed upwardly by the floats through a distance sufficient to hold shellfish in the tray above the water level.

The floats may actually engage the underside of the tray when in their second stable positions. However it is preferred that the arms actually engage the undersides of the sides of the tray when the floats are in their second stable positions, so that the floats are actually spaced from the tray and do not physically engage its underside.

Preferred features of the invention Preferably the opposite ends of the tray are respectively attached to respective parallel wires which also have the arms attached to them so that the arms pivot around the longitudinal axes of the wires.

Suitably the tray is moved from its submerged position to its above-water position by a first arrangement which travels beneath the tray to progressively lift it while guide surfaces of the arrangement push the floats downwards and towards one another sufficiently for them to pass through lower dead-centre positions and rise upwards to their second stable positions beneath opposite end-portions of the tray.

Conveniently the tray is moved from its above-water position.to its submerged position by a second arrangement which travels beneath the tray and has deflectors which pushes apart the floats beneath opposite ends of the tray and through lower dead-centre positions so that the natural buoyancy of the floats brings them to the surface of the water beyond the ends of the tray which thus descends to its submerged position between the floats.

The first and second arrangements for moving the tray or trays between their two stable positions, may be carried by a punt which is driven along the end or ends of the tray or trays.

Introduction to the drawings The invention will now be described in more detail, by way of example, with reference to the accompanying largely diagrammatic and somewhat simplified drawings, in which:- FIGURE 1 shows a broken-away string of oyster trays connected at their ends to two parallel wires and some of which are submerged while others are held slightly above water level, a diagrammatically illustrated punt being shown travelling alongside the string; FIGURE 2 is an enlarged view of one of the trays diagrammatically illustrated in figure 1 and taken in the arrowed direction A in that figure; FIGURE 3 is a view corresponding to figure 2 and taken in the direction indicated by the arrow B in figure 1; FIGURE 4 is an enlarged view of a cranked arm used to support one end of a float, the arm being arranged to pivot about an axis provided by one of the parallel wires shown in figure 1; FIGURE 5 is a diagrammatic line drawing taken in the direction of the arrow "C" in figure 4 and illustrating the arc of movement of a float through an unstable lower dead-centre position and two stable upper positions, respectively shown in outline and interrupted outline, at one of which it supports the tray beneath the surface of the water, and at the other of which it supports the tray above the surface of the water, the dead-centre position of the float being shown in dotted outline; FIGURES 6 and 7 respectively show in plan and side elevation a first arrangement carried by the punt beneath the water and which is moved beneath the string of trays shown at the left-hand of figure 1, to move their associated floats from the positions shown in figure 2 to the positions shown in figure 3; FIGURE 8 is a vertical section through figure 9 and taken on the line and in the direction indicated by the arrows VII VIl; and, FIGURE 9 is a plan view of a second arrangement which is moved beneath a string of oyster trays to move them from the positions shown in figure 3 to the positions shown in figure 2.

Description of first embodiment of the invention Figure I shows a string of rectangular, parallel, oyster trays I held at their ends in alignment with one another by a pair of parallel wires 2 strung between respective pairs of posts 3 which are provided with resilient devices (not shown) to maintain the wires 2 in tension.

Each of the trays I has at each end a float 4 held between one pair of ends of two cranked arms 5, as shown in figures 2 and 3, which are respectively pivoted to at their other pair of ends to respective wires 2. The floats 4 associated with each tray are moveable from the position indicated in broken outline in the three left-hand trays of figure 1 at which they lie beneath opposite end-portions of the tray I to lift it so that oysters in the tray are held a few inches above the water level, as shown in figure 2.

The floats are moveable with the arms 5 to the positions shown in figure 3 and in full outline on the right of figure 1, to allow the trays 1 to be fully submerged between the floats 4.

Figure 4 shows one of the arms 5 in more detail. It is clamped by bolts 8 and a clamping piece 6 to one of the wires 2. The clamping piece 6 and the arm 5 are provided with part-cylindrical grooves in which the wire 2 fits and thus the wire 2 provides, by twisting about its longitudinal axis, a pivotal axis about which the arm can turn. The arm 5 is of cranked construction as illustrated to enable it to pass around and beneath the adjacent-end portion of the associated tray 1 and preferably engage the underside of its adjacent side to hold the associated float just beneath the underside of the tray. Each tray 1 has at each end attachments 8 for detachably connecting the outside of each end of the tray to the adjacent wire 2.

The line drawing of figure 5 shows one of the arms 5 in dotted outline in its lower deadcentre position at which the associated float 4 is positioned directly beneath the wire 2 to which the associated arm 5 is connected. The float 4 is unstable in this position. If it is moved slightly to the right, the buoyancy of the float 4 causes it to rise up towards the underside of the associated tray 1 as shown approximately in full outline, so that the tray 1 it is raised from a submerged state to a position at which the oysters in the tray are held a few inches above the prevailing water-line, denoted by the interrupted line 7.

Likewise if the float 4 is moved from the dead-centre position, shown in figure towards the left, its inherent buoyancy causes it to swing outwardly and upwardly on the arm 5 and away from the associated end of the tray 1 which therefore submerges until it is once again supported by the float 4 but this time beneath the prevailing water level, now indicated at 9.

Figure 6 and 7 shows a first arrangement in the form of a wedging box 10 which can be carried beneath the string of trays by a punt 11, driven alongside the string of trays 1 as shown diagrammatically in figure 1. The box 10 is provided with two convergent side surfaces 12 and 13 which simultaneously engage the floats 4 associated with each end of each tray Irespectively and wedge them apart so that they move from the position shown in full outline in figure 5 through the lower dead-centre position shown in dotted outline and beneath the wire 2. The buoyancy of the floats then propels them to the positions shown in broken outline in figure 5, so that the associated tray 1 moves from the position shown in figure 2 to the submerged position shown in figure 3.

In order to move the trays 1 from the submerged position to a position at which oysters on the tray are held above the surface of the water, the seemed arrangement shown in figures 8 and 9 is substituted for the first arrangement on one side of the punt 20 and is passed in turn beneath successive trays in the line of trays 1 shown figure 1.

The second arrangement of figure 8 comprises a pair of inclined parallel endless belts 22 and 23 passing around pulleys 24 and 25 and having cross-bars 26 attached to them.

The undersides of the trays 1 are provided with cross-pieces (not shown) which can be engaged by the cross-bars 26 of the belts 22, 23 to progressively lift each of the trays in turn above the level of the surface of the water level as a result of it being carried up the incline by the belts 22, 23. The pulleys 24, 25 carried may be driven from the punt and are mounted in a box structure 19.

The effect of lifting the intermediate portion of each tray up the incline during its movement up the box structure 19, is to cause the two floats 4 respectively beneath opposite end portions of the tray 1 to move from a first stable position shown in broken outline in figure 5, towards the dead-centre position shown in dotted outline in that figure. The floats 4 are guided during this movement by sliding along plates 36 at each side of the box structure 19. Each guide plate 36 has a triangular side face 27 which converges inwardly towards the box structure 10 to urge a float 4, travelling along it, inwardly towards and through the lower dead-centre position directly beneath the wire 3. The guide plate 36 also has a triangular deflector plate 28 which extends inwardly towards the box 20 from the top edge of each side face 27. The guide plates 36 act to push the floats 4 towards one another and downwardly beneath the associated tray 1.

Thus, as the arrangement shown in figures 8 and 9 moves from beneath the underside of one tray 1 towards the underside of the next tray, the guide plates 36 cause the floats 4 to pass through their lower dead-centre positions and rise up beneath the associated tray 1 to the second stable positions shown in figure 2. The tray 1 is then supported above the level of the water surface as a result of the floats 4 locating beneath the undersides of its opposite-end portions.

The above described arrangement of moving the trays between their submerged positions and positions at which the oysters lying within them are held above the water line, has the advantage that it is extremely difficult for anyone to raise the trays individually and steal the oysters, without using the equipment attached to the punt of the oysterman. Thefts of oysters from oyster leases are thereby lessened, and the arrangement allows the oysters on the trays to be quickly and easily raised above the water line for a day or so, to allow natural cleaning of parasites from them to occur by their exposure to the air. The trays may then be returned to their submerged positions.

Claims

1. Apparatus for buoyantly supporting a tray containing shellfish at two stations respectively above and beneath the water line, comprising rigid arms arranged in pairs with each pair pivoted close to the ends of the tray for movement in planes parallel to the sides of the tray, the free ends of each pair of arms being connected to respective ends of a float which is moveable between a first stable position at which the tray is buoyantly supported beneath the surface of the water by the floats at each end and a second stable position at which the floats are trapped beneath opposite end-portions of the tray so that it is buoyed upwardly by the floats through a distance sufficient to hold shellfish in the tray above the water level.

2. Apparatus as claimed in claim 1, in which the opposite ends of the tray are respectively attached to respective parallel wires which also have the arms attached to them so that the arms pivot around the longitudinal axes of the wires, the arms being cranked so that the floats are held spaced from the underside of the tray when in their second stable positions which are determined by the engagement of the arms with the undersides of the sides of the tray.

3. Apparatus as claimed in claim 1 or claim 2, the tray is moved from its submerged position to its above-water position by an arrangement which travels beneath the tray to progressively lift it while guide surfaces of the arrangement push the floats downwards and towards one another sufficiently for them to pass through lower 12 dead-centre positions and rise upwards to engage beneath opposite end-portions of the tray.

4. Apparatus as claimed in any one of the preceding claims, in which the tray is moved from its above-water position to its submerged position by another arrangement which travels beneath the tray and has deflectors which push the floats apart beneath opposite ends of the tray and through lower dead-centre positions so that their natural buoyancy brings the floats to the surface of the water beyond the ends of the tray causing it to descend to its submerged position betweenthe floats. Apparatus arranged and adapted to operate substantially as above described with reference to the accompanying drawings. Dated: this .77' day of July 2004. ASILDMo Pn o (Applicant's Patent Attorney)