Fishing – trapping – and vermin destroying – Fishing – Nets
Patent
1999-05-27
2000-10-31
Carone, Michael J.
Fishing, trapping, and vermin destroying
Fishing
Nets
43 96, 43 97, 114255, 114253, A01K 7320
Patent
active
06138397&
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process and an arrangement for operation of a trawl, that is to say to control the movements for a trawl for fishing, as is indicated in the introduction to the following process and arrangement claims, together with an application thereof. The invention has to do with being able to control and optimise the position of the trawl at seas so that fishing is made efficient. The invention especially has to do with the operation of bottom trawls.
A trawl comprises a cornet-shaped bag of a net material open at the front and closed at the rear. The front part of the trawl constitutes a funnel-shaped guide portion which conducts or controls the catch of fish, shrimps and the like backwards and into the rear portion which constitutes the trawl bag per se in which the catch is collected. A number of cables such as wires or chain links connect the trawl with a fishing vessel (a trawler). Each cable comprises extension means such as a trawl door (a paravane) for stretching out the front portion of the trawl, that is to say the entrance portion to the trawl bag. Rearmost the trawl bag can be opened in order to empty out the catch, for example when the trawl is hauled up on the deck of the vessel.
During fishing cables of the trawl are connected to their respective tension force-regulating means, such as a winch, on board the vessel, and are towed through the sea. Thereby the trawl doors feather outwards to their respective sides and the open entrance portion of the trawl is maintained stretched out.
The trawl control systems which are employed to-day control the trawl by maintaining equal tension in the cables which pull the trawl. This is done in practice by maintaining equal tension force on the winch motors.
The background for this is that it is assumed that the tension forces FS1 and FS2 (see the following FIG. 1) in the cables between the respective trawl doors and trawl, are equal if the forces in the trawl wires FW1 and FW2 out from the vessel are equal. With such a regulation there is obtained an automatic adjustment when the vessel changes course (see the FIGS. 4a and 4b) or is steered up against the wind, so that the trawl bag is maintained open. There is also obtained a certain compensation for various sea-current conditions during manoeuvring of the vessel in the sea.
Even if the tension force on the winch motors is equal, there are many conditions which cause the forces which act on the trawl to become unequal, and that leads to the trawl geometry deviating from the optimum. One of these conditions can be the friction conditions in the winches per se, a friction of 10% giving 20% difference in the cable tension when the winches rotate opposite directions. Furthermore the winding up itself of the cable on the spools can have varying quality, and the friction in the cable blocks themselves can vary.
By an optimum trawl geometry is meant that the trawl bag is adjusted approximately symmetrically about a vertical plane through the longitudinal axis of the trawl. When the direction of flow of the water into the opening portion of the trawl is approximately at right angles to a plane at right angles to the longitudinal axis of the trawl it is reckoned that the trawl has an optimum adjustment relative to the direction of flow of the water for the achievement of the most effective fishing. When the trawl geometry during towing deviates from the optimum, the trawl fishes poorer, and it can become unstable. Moreover as regards the term trawl geometry and optimum trawl geometry, the trawls are to be designed differently depending upon what type of fish it shall fish, and by the size of the vessel. The trawl producers indicate what opening the trawl must have (height and breadth), and this is designated as the optimum entrance opening for the trawl.
When the sea bottom is uneven starboard and port side trawl doors can have totally dissimilar bottom contact, and leads to different tension forces FS1 and FS2 in the trawl, even if the tensions FW1 and FW2 respectively in the cables out
REFERENCES:
patent: 4246781 (1981-01-01), Moe
patent: 4305571 (1981-12-01), Hystad
patent: 5099458 (1992-03-01), Takakii
patent: 5347860 (1994-09-01), Rimer
Hammersland Helge
Tvedt Arne
Beitey Daniel J.
Carone Michael J.
Scantrol AS
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