DEVICE TO HOLD A TRAWL NET OPEN AND MAKE IT PRESS AGAINST THE SEA BOTTOM - OTTER BOARD

Abstract: The invention is a device to hold a trawl net open and make it press against the sea bottom. The device consists of a horizontal foot bar (8) to which is attached a vertical wing (10) to create a lateral pulling force on the trawl net. At right angles to the vertical wing (10), a horizontal wing (11) is attached to create a downward vertical force. Both wings are shaped like aircraft wings to utilize hydrodynamic principles for the creation of the above-mentioned forces when the device is being towed in the water. Alternative embodiments may include a device with an aircraft wing profile attached to the vertical wing (10) and a body shaped like a quarter of an egg, the rounded part of which is facing downwards, said body also attached to the vertical wing (10). In the leading edge of the foot bar (8) is a fastening loop (9) for the towing warp (3) coming from the trawler, while in the trailing edge of the foot bar (8) is a bottom warp fastening loop (12), and a top warp fastening loop (13) on the vertical wing. The horizontal wing (11) may be hinged to the vertical wing (10) to allow for vertical movement. A profiled body may also be hinged to the vertical wing (10). The horizontal wing (11) or the egg-shaped body can both be manoeuvred by means of a pneumatic system.

Description: DEVICE TO HOLD A TRAWL NET OPEN AND MAKE IT PRESS AGAINST THE SEA BOTTOM - OTTER BOARD The present invention relates to a device which can hold a trawl net open while the trawl is being towed by the trawler, and which will contribute to the trawl pressing against the sea bottom. The invention has the same function as an otter board. Fishing is effected with passive or with active equipment. Equipment is said to be passive when the fishing equipment remains passive and the fish must play an active role in order to be caught. Examples of passive equipment are the long line and other equipment with hooks where the fish is lured into biting a bait to be caught, or a net which is thrown in the sea while the fish is expected to swim into it in order to be caught. Active fishing equipment is equipment which plays an active role while the fish is caught by the equipment without having played any active part. The trawl is an example of such active equipment. A trawl is a bag-like net towed by its mouth after a boat while the net traps whatever fish is swimming in its way. The trawl sweeps the fish up without the fish playing any active part in order to be caught. The trawl is drawn by two towing warps attached to either side of the boat and to the extremities of the trawl mouth. Between the towing warp and the_place where it is fastened to the trawl mouth, a flat otter board is positioned obliquely to keep the trawl mouth as wide as possible during towing. Figure 1 shows a common type of equipment with an otter board on one side of a trawl net 1, one otter board 2 and a towing warp 3. The latter is attached to the boat and enters the figure at left where it is fastened to a bridle 4', 4" with different leg lengths, the shortest leg being attached to the leading edge of the otter board 2 and the longest leg being fastened to the trailing edge. In this manner, the otter board will lie at a slight angle to the towing direction shown by the arrow 5. Between the otter board 2 and the trawl net 1 a new bridle-like trawl warp 6' , 6" , 6, is attached. Due to the oblique position of the otter board 2 relative to the towing direction of the trawl 1, a force in a direction shown by the arrow 7 will press the otter board sideways and open the trawl mouth wide. The otter boards 2 are hydrodynamically inadequately shaped, with the result that much of the pulling force from the boat to the trawl is wasted in friction which slows the trawl down. The object of this invention is to provide a device to replace otter boards, this device being formed to pull the trawl mouth open and to draw it down towards the sea bottom. The necessary forces are obtained by utilizing hydrodynamic shapes similar to those of wings on an aircraft, to achieve a suction effect on the pressure forces on the correct side of the shaped device, resulting in forces giving the device an outward lateral and downward direction. This is achieved by providing the device with a vertical wing which creates a lateral force holding the trawl mouth open, and a horizontal wing which pulls the trawl downwards. The device is placed on the fishing equipment where ordinary otter boards would normally be attached, i.e. one on each towing warp immediately prior to the trawl mouth. Further details of the invention will appear from the following description of one embodiment of the invention. Figure 1 shows otter boards of the traditional type. Figure 2 is a vertical lateral view of the invention. Figure 3 is a horizontal view of the invention. Figure 4 shows a vertical view different from figure 2, i.e. perpendicular to the direction of figure 2. Figure 2 illustrates the main characteristics of the inventive device. With the use of conventional otter boards as shown in figure 1, the water masses press the otter boards laterally outwards. The present invention follows hydrodynamic principles to obtain a shape offering the least possible resistance to the water, and utilizing hydrodynamic forces to create the necessary directional forces holding the trawl mouth open and the trawl down on the sea bottom. The device consists of a foot bar 8. The bar is not shaped to make use of the hydrodynamic forces in the water, but solely to reduce direct friction resistance. Its leading edge is provided with a fastening loop 9 to attach the towing warp 3 coming from the trawler. Right angled to the foot bar (8) and in a vertical direction, a vertical wing 10 is provided. Its cross-sectional profile is similar to that of a conventional aircraft wing, its convex face facing the direction in which the force will be applied. See figure 4. This implies that the direction of force F h resulting from the vertical wing 10 will be out of the plane of the paper in figure 2. See also figure 4. To create a force which presses the device downwards against the sea bottom, a horizontal wing 11 with its convex face facing downwards is provided. The horizontal wing 11 is attached to the lower part of the vertical wing 10 close to the foot bar 8. The horizontal wing 11 creates a force F v directed towards the sea bottom. In the trailing edge of the foot bar 8, opposite to the position of the fastening loop 9, a bottom warp fastening loop 12 is provided to fasten the trawl's bottom warp. A trawl has four towing warps attached to it. To each side of the trawl are attached a top warp and a bottom warp. In the upper part of the vertical wing's 10 trailing edge is provided a top warp fastening loop 13. The top warp and the bottom warp help keep the trawl net open during fishing. The vertical wing 10 and the horizontal wing 11 can both consist of an internal frame, like conventional aircraft wings, or of an injected foam material. Another solution would be to keep the wings hollow to be able to fill them with a product of high specific weight if need be, in order to make the wings heavy enough to reach the correct depth in the water. Another embodiment of the otter board device, which would provide the necessary downward and lateral suction forces, can be obtained by replacing the horizontal wing 11 with a profiled body resembling a quarter egg, or even more similar to the profile of an aircraft wing. When such an otter board is towed through the water, the force F h exerted by the vertical wing 10 will be directed as shown in figure 4, while the force exerted by the quarter-egg shaped body will be directed at 45° downwards in relation to F h , and thus create a suction effect both downwards and laterally. In some cases, it will be necessary to fold the horizontal wing 11 back against the vertical wing 10, for example to cancel the downward force. This can be achieved by fastening the horizontal wing 11 to the vertical wing 10 with hinged devices which enable the horizontal wing 11 to be lifted or lowered at will during fishing. The necessary power to achieve such manoeuvring of the horizontal wing 11 can be provided by pneumatic cylinders and remote controlled magnetic valves utilizing the pressure difference between the surface of the water and the bottom of the sea. This can be done by means of a pressure tank storing the pressure which develops when the otter board descends to the sea bottom or ascends to the surface. The above-mentioned egg shape for the proposed body in replacement of the horizontal wing 11 can be utilized when the trawl is being drawn up to create a suction force in an upward direction in the water. When this body is hinged along its upper edge to the vertical wing 10, it can be made to swing upwards and create a lateral and upward suction force when the otter board, directed at an angle of 45°, is being pulled. The upward manoeuvre of the body can be achieved by means of the pressure difference and the pneumatic cylinders as mentioned above.

Claims: CLAIMS 1. A device to hold a trawl net open and directed downwards on the sea bottom while trawling takes place characterized by a horizontal friction-reducing foot bar [8] at right angles to which a vertical wing [10] is attached, and perpendicularly on the lower part of said vertical wing, in the vicinity of the foot bar [8] a horizontal wing [11] is provided. 2. The device of claim 1 to hold a trawl net open characterized in that the vertical wing [10] and the horizontal wing [11] each have two large parallel convex faces, the most convex of such faces being that which is closest to the direction of the force created when a fluid flows approximately parallel to the faces. 3. The device of claim 1 to hold a trawl net open characterized by a towing warp fastening loop provided on the leading edge of the foot bar [8], a bottom warp fastening loop [12] provided on the trailing edge of the foot bar [8], and a top waφ fastening loop [13] provided in the upper free extremity of the vertical wing [10]. 4. The device of claim 1 to hold the trawl net open characterized in that the vertical wing [10] is provided with a body shaped approximately like a quarter of an egg and with its convex face facing downwards. 5. The device of claims 2 and 3 to hold the trawl net open characterized in that the horizontal wing [11] is hinged to the vertical wing [10] and can be manoeuvred to alter the angle between said two wings by means of a system powered by pneumatic cylinders which utilizes the pressure difference between the surface of the water and the bottom of the sea. 6. The device of claims 1 and 4 to hold a trawl net open characterized in that the egg-shaped body is hinged to the vertical wing [10] and the convex face of said body can be manoeuvred upwards by means of a system powered by pneumatic cylinders and a pressure tank which utilize the pressure difference between the surface of the water and the bottom of the sea.

Inventors: ANTONSEN TORBJORN, ANTONSEN, TORBJOERN
Applicants: ANTONSEN TORBJORN, ANTONSEN, TORBJOERN
Application year: 1992
Main classification: A01K73
IPC codes: A01K73