GB2239485A - Pivot for large structures such as a fish-cage - Google Patents

Abstract

A hinge for bulky bodies, e.g. steel pipe floats 20, 21 of a cage for sea fish, comprises at least one compressible spacer member 13 which separates an inner 12 and an outer 11 hinge element of non-circular cross-section so that their mutual pivotal movement can take place only by compressive deformation of the spacer member which by virtue of its compressibility sets a limit to the angular extent of the hinge action. Also disclosed is a fish cage comprising a closed floating framework of interlinked closed pipe lengths for supporting a walkway and a submerged fish net articulated together by hinges of the invention. The hinge makes the use of mild steel pipe lengths as floats economically feasible. <IMAGE>

Description

HINGE FORBULKY BODIES, AND A FISH CASE INCORPORATIONS THE HINGE.

This invention relates, in a first aspect thereof, to a hinge for connecting together bulky bodies which require a limited freedom for mutual pivoting. It relates in particular to a hinge for connecting together unit floats of an extended floating structure which it is desired shall yield in undulant fashion to the surface contour changes imposed on water by waves or sea swell, so as to reduce the consequent mechanical stresses in the structure. The invention relates, in a second aspect, to a fish cage incorporating said hinge.

The invention provides a hinge comprising an inner pivot member located within and spaced apart from a hollow outer pivot member by at least one spacer member of elastic material, the pivot member cross-sections (ie normal to the pivot axis of the hinge) being non-circular and their cross-sectional dimensions so related that pivoting causes compressive deformation of the spacer member(s) and that the possible angular extent of the hinge action is limited by the compressibility of said spacer member(s).

Preferably the pivot members are of metallic construc ti on and the spacer member(s) of high-density natural or artificial rubber, high resilience polyether, polyurethane or the like substance. More preferably the pivot members are of steel and the spacer member(s) are of a polyether urethane material commercially available under the trade name Yibrathanêl; for example in grades designated 8-600, 8-601, 8-602, 8-604, 8-614, 8-615, 8-621, 8-627, 8-628 and B-640.

Preferably the cross-sections of both the inner and the hollow outer pivot members are square, and the outer diagonal dimension of the inner member is smaller than the internal side length of the hollow outer member. A preferred design with square cross-sections has a resting angular position of minimum stress on the spacer members, in which position the diagonals of the cross-section of the inner pivot member, produced, bisect respective pairs of opposite sides of the cross-section of the outer pivot member, and each of the four "free" spaces defined by and lying between said members has the shape of a triangular prism and is occupied co-axially by a respective cylindrical spacer member, the undeformed cross-section of each spacer member being substantially the inscribed circle of the triangular cross-section of the "free" space occupied by said spacer member.

Details and characteristics of the hinge will be described further below with reference to the accompanying drawings.

The invention, as stated above, also relates to a construction of fish cage employing the abovedescribed special hinge. The hinge was in fact invented in the context of fish cages, although it has a wider field of application, as will be seen.

The term fish cage, as used herein, denotes a device for rearing table fish, especially salmon, in open waters such as offshore sea areas. A fish cage typically comprises a floating, closed frame from the entire periphery of which an essentially vertically disposed tubular fish net, closed at the bottom, is suspended under water. A fish cage typically also has an access and service platform or walkway supported along and atop the floating frame. The frame or the platform also carries upright stanchions at intervals, which stanchions constitute the immediate support members for the net, and may also support a safety rail for the walkway.

Fish cages are conventionally constructed in one of two ways: (1) The frame is of tough flexible tubing with an inflatable interior; the platform comprises metal units laid end to end, and is clamped or strapped or lashed on to the frame, as are the stanchions which support the net. The material of the tubing is natural or artificial rubber or a laminate incorporating such rubber.

(2) The frame is a non-buoyant metal platform beneath which are strapped-on the actual float members which are discrete closed steel tanks disposed at intervals; the platform carries the stanchions which support the net. The platform comprises discrete units laid end to end and hitched (roped or strapped) together.

In both construction types flexibility of the closed frame is necessary so that the frame can undulate in response to the waves or the swell of the sea, thereby avoiding stresses which, in a rigid frame, could lead to fracture. The tubing of construction type (1) is inherently flexible. In construction type (2) the float tanks are not in mutual contact so that only the platform needs to be flexible.

Disadvantages of construction type (1) above include the high cost of the flexible tubing and its susceptibility to mechanical damage with consequent leakage of air out and/or water in; the necessity to inflate the tubes and keep them inflated, topping-up from time to time; the need to patch punctures, and the limited lifetime of the assembly.

Disadvantages of construction type (2) above include the high cost of the closed steel tanks, and the need to tie the platform units together so that the frame yields flexibly to passing waves or a sea swell.

Furthermore there is constant metal-to-metal contact during pivotal and other motion, leading to rapid corrosion when it occurs in a salt water environment.

It is an object of the invention to provide a construction of fish cage which overcomes some at least of the above-recited disadvantages. Another object is to provide a fish cage which is more economical to construct than a conventional fish cage of similar size, which undulates with little or no friction and without serious strain in response to waves and swell, which is robust, long-lasting, and highly resistant to impact, to abrasion, to tearing or shearing forces and, in particular, to corrosion.

Mild steel pipe is inexpensive and widely available.

It can be surface coated to give it a long life even in corrosive surroundings. In closed lengths secured end to end in a closed chain it would be a desirable construction for the floating frame of a fish cage, except for the requirement of freedom for undulatory movement. Any pivotal linkage between lengths of such pipe would seem, to a person of ordinary skill in the matter, to require a bearing wherein metal contacts metal in a wet and perhaps salty environment, leading inevitably to rapid corrosion and ultimate mechanical failure of the linkage. For these and similar reasons little attention has been paid to the possible use of mild steel pipe for the purpose mentioned.

In its second aspect, therefore, the invention provides a fish cage comprising a number of elongate floats joined end to end to form a closed chain or framework for supporting an.overhead walkway and a mainly submerged fish net enclosure, each float being a hollow envelope of sheet metal and each joint being a hinge in accordance with the invention, the hinge pivotal axis extending transversely of the long axis of the adjacent floats and, in use, being approximately horizontally disposed.

Preferably the floats are lengths of steel pipe each closed at either end by a respective transverse end plate. Each float preferably has, extending from one of its end plates, brackets for securing an inner pivot member of a hinge of the invention thereto, and has an outer pivot member of a hinge of the invention secured to the transverse end plate at its other end.

Thus a number of floats can be assembled to give an endless or closed chain by engaging the pivot members, secured to said floats, in appropriate pairs, with the aid of a cotter shaft, and inserting the spacer member(s). Any length of such a chain floating at sea and extending transversely to the.oncoming waves or swell will undulate therewith as the spacer member(s) yield elastically permitting small-angle hinge movement. Larger angles of pivot will however be resisted by the spacer member(s) in greater compression. A useful degree of pivotal freedom does not exceed 45" on either side of a rest position, for use in fish cages. Preferably the steel pipe has a diameter of about 500 mm and a wall thickness of 4-6 mm, and is surface treated by known means to give it a long-lasting resistance to corrosion.The platform or walkway of the fish cage is preferably produced in standard lengths each corresponding to the length of one float and attachable thereto.

The invention will be appreciated in greater detail from the following description of a particular embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which Fig 1 is a plan view of a special hinge; Fig 2 is an end elevation of the hinge of Fig 1; Fig 3 is a cross-section of the hinge of Fig 1, taken along the line III-III in that figure and viewed in the direction of the associated arrows; Fig 4 is a simplified central detail of a cross section of the hinge of Fig 1, taken along the line IV-IV of that figure and viewed in the direction of the associated arrows; Fig 5 is a schematic plan view of a fish cage; and Fig 6 is a detail of a section through the fish cage of Fig 5, taken along the line VI-VI in that figure and viewed in the direction of the associated arrows.

Referring now to the drawings, a hinge 10 comprises a hollow elongate outer pivot member 11 of square crosssection, an elongate inner pivot member 12, likewise of square cross-section, four cylindrical resilient spacer members 13, flanges 14a, 14b for securing the outer pivot member 11 to the closed end plate 17 of a first steel pipe float 20, brackets 15a, 15b for securing the inner pivot member 12 to the closed end plate 18 of a second steel pipe float 21, and a square section cotter shaft 6 for rel easably securing said inner pivot member 12 to the brackets 15a, 15b.

The inner pivot member 12 has an open-ended axial tunnel 19 of square cross-section running its full length. The removable square cotter shaft 16 occupies the tunnel 19 and projects at both ends thereof. The pivot members 11, 12 and spacer members 13 are best appreciated from Figs 3 and 4. The ends of the cotter shaft 16 are held in non-rotatable manner by brackets 15a, 15b welded to an end plate 18 of pipe float 21.

They are secured against displacement and abrasive movement by locking bolts 32 which occupy perforations in respective sleeves 22 of the brackets 15a, 15b and pass through bores in the cotter shaft 16. The brackets 15a, 15b bear each a reinforcing rib 15c which also reinforces the respective sleeve 22.

The outer pivot member 11 is a hollow open-ended box-like construction with welded-on parallel flanges 14a, 14b which in turn are welded to an end plate 17 of pipe float 20. The flanges 14a, 14b are extended, and adapted in shape, to act as brackets for this purpose. During assembly of the hinge, the inner pivot member 12 is installed, together with the four spacer members 13, in the outer pivot member 11.

Nylon spacers or washers 23 are fitted to prevent contact between the flanges 14a, 14b and the brackets 15a, 15b. The pivot unit with the washers 23 is then fitted between the brackets 15a, 15b, and the hinge is completed by insertion of the cotter shaft 16 through the tunnel 19 so that its stub ends are non-rotatably retained by the sleeves 22 of the respective brackets 15a, 15b. The bolts 32 are then inserted and retaining nuts are applied on them and tightened.

It will be seen that the resting or unstrained position of the inner pivot member 12 within the outer pivot member 11 is one of a 45" rotation away from parallelism of their respective walls. In use, rotation of the inner member 12 is limited below about 45" on either side of the resting position, and leads to compression of the spacer members 13 by respective corners of the member 12. Such rotation ceases when the torque causing it is balanced by the aggregate forces of elastic recovery of the spacer members 13.

It will be appreciated that there is no metal-to-metal contact between the inner pivot member 12 or any of its extensions, on the one hand, and the outer pivot member 11 or any of its extensions on the other.

Turning to Fig 5, a fish cage in accordance with the invention comprises a closed chain of floats, viz closed-ended steel pipe lengths 20, 21 linked together by hinges 10 in accordance with the invention. Floats may be straight (20, 21) or angular (20a) according to the fish cage design required. The cage shown in Fig 5 is hexagonal, but square, rectangular, octagonal etc layouts can be provided. The walkway, stanchions etc are not shown in Fig 5.

Fig 6 shows in section (partly cut away) a typical float 20 of 6 mm mild steel pipe as used in a fish cage according to the invention. Spigots 25 are welded on in pairs along the float carapace to serve as mounting points for a platform 24 which has a steel framework 26 and walkway metal mesh panels 27. The framework 26 has pairs of downwardly projecting spigots 28 complementary to the spigots 23, steel sleeves 29 being used to connect them. A series of welded-on stems 30 with bored annular flanges 31 serves for the support of the stanchions (not shown) which in turn support the fish net and a safety rail for the walkway. W represents the water level in use of the fish cage.

Claims (10)

1. A hinge comprising an inner pivot member located within and spaced apart from a hollow outer pivot member by at least one spacer member of elastic material, the pivot member cross-sections (ie normal to the pivot axis of the hinge) being non-circular and their cross-sectional dimensions so related that pivoting causes compressive deformation of the spacer member(s) and that the possible angular extent of the hinge action is limited by the compressibility of said spacer member(s).

2. A hinge according to claim 1 wherein the pivot members are of steel and the spacer members are of a polyether urethane material.

3. A hinge according to claim 1 or 2, wherein the cross-sections of both the inner pivot member and the hollow outer pivot member are square, the outer diagonal dimension of the inner member being smaller than the internal side length of the hollow outer member.

4. A hinge according to claim 3, wherein in a resting angular position of minimum stress on the spacer members, the diagonals of the cross-section of the inner pivot member, produced, bisect respective pairs of opposite sides of the cross-section of the outer pivot member, whereby each of the four "free" spaces defined by and lying between said members has the shape of a triangular prism.

5. A hinge according to claim 4 wherein each of the spacer members is cylindrical in form, and the undeformed cross-section thereof is substantially the inscribed circle of the triangular cross-section of said prism.

6. A fish cage which comprises a number of elongate floats joined end to end to form a closed chain or framework for supporting an overhead walkway and a mainly submerged fish net enclosure, each float being a hollow envelope of sheet metal and each joint being a hinge according to any of claims 1 to 5, the hinge pivotal axis extending transversely of the axis of the adjacent floats and, in use, being approximately horizontally disposed.

7. A fish cage according to claim 6 wherein the floats are lengths of mild steel pipe each closed at either end by a respective transverse end plate.

8. A fish cage according to claim 6 wherein each float has, extending from one of its ends, brackets for securing an inner pivot member of a hinge of the invention thereto, and has an outer pivot member of a hinge of the invention secured to the transverse end plate at its other end.

9. A hinge substantially as herein described with reference to or as illustrated in the accompanying drawings.

10. A fish cage substantially as herein described with reference to or as illustrated in the accompanying drawings.