This invention relates to the farming of fin-fish, especially of sea fish in exposed coastal locations.

It is already known to define an enclosed volume of water, within which fin-fish can be cultivated, by means of a bag net attached to a flexible collar suspended from an endless chain of floats. However, such arrangements are unstable as supports from which working of the fish-farming zone can take place. One proposal which includes a working platform is described in WO 85/03411, in which a fish farming plant comprises elongated hollow floating bodies interconnected in pairs in parallel to each other, respective pairs being interconnected by universal joints to form a closed polygonal configuration from which is suspended a network container to define the fish-farming zone. Handrails and platforms may be attached to the floating units for enabling the farm to be worked.

According to the present invention, a cage collar for suspending a fish-farming net comprises an endless array of flotation units, in which the units are linked by flexible retaining elements, the flotation units having major axes which in use lie substantially parallel with the surface of the water, the retaining elements causing the array of flotation units to be sufficiently laterally stable in use to provide a working platform.

By "lateral stability" is meant that the interconnection between adjacent flotation units should be such that the relative twisting and sagging permitted therebetween should be inhibited so as to

provide an effective walkway to serve as a working platform, while at the same time providing sufficient flexibility that wave motion does not create structurally damaging stresses to occur.

Individual flotation units, which are preferably generally disc-shaped, may be buoyant per se or may be rendered or maintained buoyant by means of buoyancy elements to which they are attached, internally or externally. Conveniently, each flotation unit comprises a vehicle tyre, that is a car, lorry, truck or tractor tyre the tread of which is worn, the tyre therefore no longer being capable of fulfilling its original purpose. There are in fact enormous stocks of such tyres in the world and, since they are difficult to dispose of without creating pollution, they present a considerable environmental problem; the invention therefore provides an economic way of using some of these tyres. To render the tyres buoyant, they preferably contain a buoyant material which may be natural such as cork, but is preferably a synthetic air-trapping material such as a foamed plastics material.

The flotation units may have the net suspended from beneath but preferably the net is supported from posts which are upstanding from the flotation units, whereby the net extends from above the water surface to beneath the same to a depth sufficient to contain the fish.

For the purpose of linking individual flotation units together, each flotation unit may be provided with passageways or conduits through each of which may be passed a flexible retaining element. Preferably, two or three such passageways or conduits are provided in

each flotation unit, arranged substantially in the plane of the major axes thereof and in the same respective direction. This enables each individual flotation unit to be linked with its neighbouring unit by essentially concentric annular retaining elements, in which each retaining element will pass through its designated passageway or conduit in each flotation unit in turn. The ends of the retaining elements may be joined together in another, for example a vertical, conduit preferably at the centre of one of the flotation units. A least one of the retaining elements is tensioned, for example by the incorporation of twist tighteners, in order to provide the required lateral stability. In an alternative arrangement, however, retaining elements may be passed around the outer and/or inner annular periphery of the cage collar, rather than through conduits or passageways, and held in position by cross-tie elements which may pass through conduits or passageways formed radially (with respect to the cage collar) in individual flotation units.

It is preferred to use three in-plane retaining elements, one passing centrally through each flotation unit and the other two passing respectively radially inside and outside the central element.

The flexible retaining le ents may be filamentary or strap-like, for example rope formed from a polyalkylene, or steel cable. Preferably, the elements carry an outer protective sleeve formed for example from a flexible plastics material, to minimize chafing or other physical damage.

Adjacent flotation units may be maintained in

spaced-apart relationship by the use of one or more spacer elements between adjacent flotation units, carried by or threaded on the flexible retaining elements. Spacer elements may comprise discs, spheres,

'ϋ' shaped or wedge shaped structures or the like, are preferably resilient, and may extend partly, wholly or predominantly below the water surface. Conveniently, the spacer elements threaded on the central retaining element comprise segments of cut tyres, giving a 'U' cross-sectional shape. The limbs of the 'U* tend to close together under pressure, and to open again when the pressure is relieved, so giving flexibility to the collar while at the same time resisting excessive flexing. The spacer elements may alternatively comprise rigid resilient discs of rubber or lengths of stiff but flexible pipe, and different types of spacer elements may be used in combination on different retaining elements, to give the required degree of lateral stability with flexibility.

The cage collar will be maintained in an essentially circular configuration by the tension in the flexible retaining elements, causing a keystone effect which tends to return each flotation unit to its equilibrium position after disturbance, so maintaining the essentially circular shape. This may be assisted by the positioning of the spacer elements on the preferred central retaining element, in that wedge shaped spacer elements or 'U' shaped spacer elements placed with their thick or closed ends facing to the exterior side of the central retaining element in the horizontal plane will tend .to form a more spherical shape to the collar. 'U' or wedge shaped spacer units may also be positioned in the vertical plane, when attached to the central retaining element, to help resist collar

flexing in this direction.

Each flotation units may be provided with one or more protective discs, each being attached to a flat side parallel with the plane containing the major axes. The discs will preferably be of a similar diameter as the flotation unit, and will protect the foam filling, especially when on the upper facing side when the flotation units are being used as a working platform. A handrail supported by suitable stanchions may be provided, attached to each selected flotation units, to facilitate use as a working platform.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, of which:

Figure 1 shows one form of a cage collar from plan view and side elevation;

Figure 2 shows an individual flotation unit from the collar of Figure 1, joined to fragments of its neighbours;

Figure 3 shows front and side elevations of a flotation unit including a handrail;

Figure 4 shows a fragmentary plan view of another construction of a cage collar; and

Figure 5 shows a U-shaped spacer unit suitable for use in the collar of Figure 1 or Figure 4.

Referring firstly to Figure 1, an essentially annular array of disc-shaped flotation units 11, constituted in

this embodiment by used truck tyres the inner volume of which is filled with a synthetic foamed plastics material for buoyancy, is held together by three concentric bands 12, 13, 14, made of rope which is rot-resistant in sea-water. Nylon or polypropylene rope is suitable. Each rope passes through each flotation unit via a conduit formed therethrough in the plane of the major axes, as seen more clearly in Figure

2. Spacer units 15 are threaded on each rope between each adjacent pair of flotation units such that, on applying tension to one or more (but preferably the middle) rope, the entire collar is held together with such tension and stability that twisting and sagging between adjacent flotation units is prevented to the extent that the flotation units provide a walkway for working the fish-farming zone, while still permitting sufficient relative movement to float on the surface of the sea without undergoing damaging stresses.

A support post 16 is attached to the inner-facing part of each flotation unit, to act as a support for a bag net 17 which encloses the fish-farming zone 18 in the water.

Referring to Figure 2, it is seen how each rope passes through the flotation units by means of conduits 19. The conduits are lined with corrosion-resistant pipes or tubes to protect the foam buoyancy filling of the tyres from abrasion by the ropes and to facilitate free running of the ropes in order more easily to tension them with even effect around the collar. In this embodiment, U-shaped spacer elements 20 are provided on the middle rope 13 and disc-shaped spacers 21 are provided on the inner rope 12. The outer rope 14 has no spacers between adjacent flotation units.

Referring to Figure 3, flotation units similar to those of Figures 1 and 2 are shown but with the addition of stanchions 22 and a linking member 23 to serve in use as a handrail. The tyres have upper and lower discs 24 attached thereto; the lower ends of the stanchions are inserted through vertical holes formed through the tyre sidewalls and buoyancy filling and through corresponding holes formed in the discs and are tightened by a threaded knot at the lower ends, flanges or washers being provided to bear against the discs 24.

Figure 4 shows a fragment of another for of cage collar in which the inner and outer retaining ropes 25, 26 are external to the tyres and are secured thereto by radial cross-ties 27 which are carried in conduits which intersect the conduits for the middle rope 28.

Figure 5 shows a U-shaped spacer unit 29 which consists of a segment cut f m a vehicle tyre and having co-axial holes 30 formed through the sidewalls thereof to allow passage of a retaining rope.