Fishing – trapping – and vermin destroying – Fishing – Line-attached bodies – hooks and rigs
Patent
1991-08-27
1993-08-03
Rowan, Kurt C.
Fishing, trapping, and vermin destroying
Fishing
Line-attached bodies, hooks and rigs
43 91, A01K 9300
Patent
active
052317889
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a buoyancy body for use at large sea depths, primarily for lifting the upper edge of trawl bags in connection with deep sea fishing.
BACKGROUND OF THE INVENTION
It is here particularly relevant to consider the shrimp fishing in the arctic, where the operation depth is 500-1,000 meters or more. The applied trawl bags should be held open with the use of weight bodies at the lower side of the bag mouth and buoyancy bodies at the top side of the mouth; however, due to the large working depth, there are special demands on the buoyancy bodies because they are subjected to an excessive outer pressure.
Conventionally, these bodies are made as air-filled ball shells of plastic, but it is proved difficult to produce reliable buoyancy bodies of this type because, from resisting the high pressure, the ball shells must be so thick that reasonably small buoyancy balls will exhibit only a limited buoyancy while, with the use of large buoyancy balls, a considerable resistance against the trawl being drawn through the water is created.
Moreover, the buoyancy balls are normally required to have a central through-passage for a rope, and, while the ball shell shape is well suited to resist high outer pressures, it is so very difficult to produce the ball shells inexpensively, which are nevertheless effective and durable with buoyancy balls having such a passage. Buoyancy balls may well initially resist a high pressure, but they become weakened by the considerable pressure variations to which they are exposed by the repeated lowerings and raisings to and from the large depths.
SUMMARY OF THE INVENTION
The present invention is based on the consideration that the basic conditions for achieving a stable buoyancy body that can resist large pressure variations are much better fulfilled by a body produced of a foamed plastic material having closed cells, and, in fact, it is already known to produce small buoyancy bodies in such a material.
The foamed plastic material itself is not very costly but it is both expensive and difficult to produce reasonably large bodies, for example, buoyancy balls having a diameter of 20 cm, in foamed plastic material with a sufficiently homogeneous structure to ensure that the bodies can resist high pressures. During production rather large gas bubbles are created in a central area of the bodies, and, body action of gravity, the distribution of such bubbles will be unsymmetrical, whereby the large bubbles may get close to an outer area, thereby resulting in the pressure resistance of the bodies being weakened. Additionally, the process time for the molding or foaming of a thermoplastic material in the mold is rather long because the foam material has a high heat insulating effect such that it is not easily cooled for rapidly solidifying. Large size buoyancy balls or otherwise shaped bodies, therefore, will be quite expensive if produced with a satisfying quality, and it is hereto be remembered that the pressures to be resisted at the depths mentioned above will be some 50-100 bars or more.
The aim underlying the present invention essentially resides in providing a technique by which it is possible to produce bodies of the aforementioned type in the material described above with a high quality and at reasonable costs.
According to the present invention, each of the bodies is manufactured from a plurality of singular elements, with these elements having an overall relatively small material thickness and being shaped so as to be joinable into an at least substantially compact large size body. Hereby the singular elements will be easy to manufacture with a well controlled quality, and, when the bodies are joined to form the complete final body, the final body has a conventional unbroken shape such as, for example, a ball. The expression "at least substantially compact" is to be understood that it is not really desirable that the entire body be effectively compact, that is, with a complete mutual surface connection between the joined singular el
REFERENCES:
patent: 2166463 (1939-07-01), Cressey
patent: 2566612 (1951-09-01), Hearne
patent: 3392475 (1968-07-01), Vakousky
patent: 3545120 (1970-12-01), Takaoka
patent: 3579893 (1971-05-01), Wolfe
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