The present invention relates to a trawl door of the type mentioned in the introductory clause of claim 1.

By trawl fishing it is known a.o. from NO-C-127,690 to make use of trawl doors or otter boards with adjustable hatches in order to be able to regulate the active surface area of the trawl doors. The spreading ability of a given trawl door is defined by several conditions, the most important for the resulting outward leading force being the active surface area of the trawl doors together with the angular position in relation to the towing direction. Trawl fishing may take place at very different depths of the ocean and therefore often trawl doors are chosen being in size adapted to the actual largest depth of the ocean, the spreading ability of the trawl doors in this situation being minimal as a result of the lo.ng and heavy towing wires. By fishery at smaller depths of the ocean or by fishery for species demanding a smaller spreading of the trawl mouth the active surface area of the trawl doors can be reduced by opening the adjustable hatches, i.e. readjustment of the fishing tools can take place without necessarily having to put into port.

Known trawl doors with adjustable hatches have, however, been found insufficient as there are worked with rather small hatches, the placings of which more- over not giving the desired adjusting possibility regard¬ ing correct angular position in relation to the bottom of the sea.

The invention has for its purpose to provide a trawl door of the introductorily mentioned type and by means of which a more optimal adjustment of the movement of the trawl door in the water can be obtained.

The trawl door according to the invention is characte¬ rized in the adjustable hatches being placed at opposite sides of a central longitudinal axis of the plate. Hereby

the possibility is obtained for providing the trawl doors with extra large adjustment hatches which by being placed at each side of the horizontal longitudi¬ nal axis furthermore permit the angular adjustment of the inclination angle of the trawl doors in relation to horizontal position or in relation to the bottom of the sea. Preferably the hatches are made as slide gates with closing plates which by the opening of the hatches are displaced to the same side preferably towards the "rear end" of the trawl door. The centre of gravity of the trawl door will consequently be rearwardly displaced, what may be particularly advantageous e.g. when lobster fishery is in the question, where on often very soft bottom there will be worked with completely open hatches, i.e. with minimum spreading.

The trawl door according to the invention can be constituted by a straight plate, but preferably there is worked with an angularly shaped plate, whereby much better possibilities for optimal adjustment of the position of the trawl doors are obtained concerning spreading ability and movement in the water. By reducing the active surface area of the lower part of the trawl door a decreased "upwards leading" component of a force can be obtained, i.e. the trawl door will have a bottom seeking tendency. Conversely the "upward leading" compo¬ nent of a force will be relatively increased by reducing the active surface area of the upper part of the trawl door.

In the following the invention is described in more detail, reference being made to the accompanying drawing, in which:-

Fig. 1 is a perspective view of an embodiment of a trawl door according to the invention.

Fig. 2 a plane view of a trawl door cf. Fig. 1, but laterally reversed, i.e. a left trawl door cf. Fig. 4, Fig. 3 an end view partly in section of the trawl

door shown in Fig. 2,

Fig. 4 shows the employment principle for trawl doors of the said type, while.

Fig. 5 is a section of Fig. 4. 5 The shown trawl door 1 is made of so-called sea aluminium and consists of a preferably rectangular plate 2 which along a central longitudinal axis is bent in an angle of about 140°, as the appearing convex side of the plate 2 constitutes "the front side" of the trawl door 1 ,

10 i.e. the side which in operation cf. Fig. 4 is facing the towing boat. Hereby the plate 2 is divided into an ^• upper portion 4 and a lower portion 6.

Along its lower edge zone the lower portion 6 is provided with a strong wearing bar 8 consisting of

15 solid iron which hereby as well constitutes a ballasting, which takes care of the wearing bar 8 irrespective of the height position of the trawl door in the water always being downwards oriented. A little below the cen¬ tral longitudinal axis the lower portion 6 of the trawl

20 door is provided with a long, narrow opening 9 with a corresponding sliding hatch 10 which at opposite long sides of the opening 9 are positioned in guiding rails 12, so that the sliding hatch 10 can be displaced along the front side of the portion 6 for laying open of the

25 opening 9 to a desired extent. The sliding hatch 10 can be fixed in a desired position by means of a row of holes 14 and a simple clamp bolt 16 extending through as well the sliding hatch 10 as the lower plate portion 6. The upper plate portion 4 is in a corresponding manner pro-

/-\ 30 vided with an opening 16 with a corresponding sliding hatch 18 - this adjustable sliding hatch 18 in the upper portion just having about the double width as the opening 8 in the lower portion 6. Along the upper edge of the upper portion 4 of the trawl door three holes 20 have

35 been cut adapted for use when handling the trawl door - or when catching the trawl door by the hauling in of the

trawl.

At its front side the trawl door is provided with three brackets 22 and 24 for connection of the trawl door with the towing wire 26 via a three-point pull 28 (Fig. 4 and 5) . The "concave" rear side of the trawl door is provided with as well longitudinal as transverse stiffening ribs, the inner sides of which being provided with suitable connection holes for optional arrangement of a single towing connection or a three-point pull for the wire 30 between the trawl doors and the side booms 32 of the trawl.

The trawl door 1 according to the invention is well suited for lobster fishery, as with the hatches 10 and 16 completely open and rearwardly displaced on the plate portions 4 and 6 it can be adjusted to spread the least possible. Because of the hatches 10 and 16 in the actual situation rearwardly shifting the centre of gravity of the trawl door the latter will tend to be tilted in the water with the rearmost corner down in the bottom of the sea. Nevertheless the trawl door moves rather easily across the bottom of the sea, because the lowermost in¬ clined portion 6 of the plate 2 has a relatively larger active surface area than the upper portion 4, where the hatch 16 has about the double size as that of the bracket 10.

The trawl door according to the invention is pre¬ ferably angularly shaped, but it can also be made as a straight plate with an upper stearing fin along the upper side of the rear side of the plate, so that it is easier for the trawl door to be kept upright in the water during the trawling. A straight trawl door accord¬ ing to the invention can with the unequally large by-pass hatches be easily adjusted to spread as required and with the desired angular position as well in relation to the towing direction as in relation to the bottom of the sea.

All things considered the trawl door according to the invention can be used for almost any fishery, i.e. that normally it will be sufficient for any vessel to have a single set of trawl doors according to the invention.