TECHNICAL FIELD

The present disclosure relates generally to trawl doors used for trawl fishing, and more particularly, to trawl doors adapted for stable and efficient operation.

BACKGROUND OF THE INVENTION

Modern trawl fisheries are complicated by an increase in operating costs due primarily to increasingly expensive fuel costs affecting both the catch of as well as the transportation to market of fish and value added fish product. The increase in operating costs in combination with the tendency of regulatory authorities to impose fixed catch quotas in one form or another have combined to force trawl fishing vessel operators to increase the efficiency of their trawl systems. One impact of this demand for increased efficiency of the trawl system is a demand for increased trawl door efficiency, and in particular an ever increasing need for trawl doors that are efficient at shallow depths and high speeds, as modern trawling increasingly requires economic operations at shallow depths and high speeds.

In addition, more and more modern trawling vessels must participate in a variety of different fisheries in order to be economical, and thus must use a variety of different trawls, having different requirements for the opening parameters of their trawl mouths. For example, some fisheries require trawls exhibiting a high vertical opening and a moderate horizontal opening (high opening trawls), meaning that the trawl doors should provide less spread and thus should generate less water resistance, while other fisheries require trawls exhibiting a low vertical opening and a maximal horizontal opening (wide body trawls), meaning maximal spreading forces are needed from the trawl doors.

While a towed trawl door having a particular shape may operate stably throughout a range of angle of attack, when towed through water at a larger angle of attack trawl doors often exhibit instability and/or low efficiency. Moreover, how the towing vessel maneuvers can vary a trawl door's angle of attack.

Trawl doors operating at large angles of attack create enough drag induced directional forces on the trawl doors so as to impart sufficient stability to the trawl door system to thereby maintain the trawl doors in a workable orientation in the presence of a multitude of destabilizing forces routinely imparted to a trawl door during use. Destabilizing forces result from, for example, side currents, imperfections in rigging, and loss of forward through-water speed affecting an inboard trawl door during turning of a trawling vessel. For example, when a towing vessel turns the inboard trawl door can become almost stationary relative to the water. A similar situation can arise when a trawl door experiences a strong side current. Another condition which can cause trawl door instability is when some portion of the trawl contacts the sea floor. As is readily apparent, a trawl contacting the sea floor increases the force applied to the trawl door through the lower towing bridle in comparison with the force applied through the upper towing bridle. Stabilizing trawl doors when they operate under conditions such as those described above usually requires that the trawl doors operate at a larger angle of attack particularly at slower towing speeds.

US 2008271356 discloses a trawl door with an upper, a lower, and a middle frame defining an intermediate frame positioned between the upper and lower frames thereby establishing an upper section. Panels of aerofoil construction are provided, which are placed over each other and connected to the frames in their respective ends. There are no movable and remotely controllable flaps mounted under any of the panels.

WO 2015055207 discloses a trawl door comprising an upper frame, a lower frame, and an intermediate frame. The trawl door has several foils or panels. Moveable flaps are positioned at the trailing edge of one of the foils. Meanwhile, WO 2015055207 does not disclose flaps provided on both the upper and lower surface of the airfoils in order to ensure both vertical and horizontal adjustment of the trawl in the water.

Higher angles of attack are required at slower towing speeds to obtain a sufficiently large drag induced force vector required to stabilize trawl doors at slower towing speeds. Furthermore, when trawl doors lose their ability to spread they may tangle with each other.

There exists a long felt need for a trawl door that is highly efficient at larger angles of attack and can thus be used at slower towing speeds, while not markedly larger in size than existing trawl doors.

Furthermore, there exists a desire in the industry for a highly efficient trawl door that operates well both at faster towing speeds and smaller angles of attack as well as at slower towing speeds and larger angles of attack.

Finally, there is a long felt need for a trawl door which position in the water may be rapidly adjusted.

SUMMARY OF THE INVENTION

The present invention solves the above mentioned problems, and provides a fast responding trawl door as far as its position in the water is concerned.

The trawl door is based upon curved airfoils to give maximum lift force and minimum drag. In order to fully and quickly control the position of the trawl door in the water flaps are provided on both the upper and lower surface of the airfoils. These flaps are remotely an preferably wireless controlled to give the opportunity to increase and reduce the lift force, and thereby increase or decrease the spreading ability of the doors as well by changing the heel angle of the doors, the opportunity to do vertical and horizontal adjustment is possible.

In accordance with the present invention the inventors refer to the upper flaps as a lift dumper, which is intended to reduce the lift component of a wing or hydrofoil in a controlled way. Most often, spoilers are plates on the top surface of a wing that can be extended upward into the airflow to spoil it. By so doing, the spoiler creates a controlled stall over the portion of the wing behind it, greatly reducing the lift of that wing section. Specifically the present invention provides a trawl door (1), comprising:

an upper frame (2) defining a top edge of the device;

a lower frame (3) defining a bottom edge of the device;

a middle frame (4) defining an intermediate frame positioned between the upper (2) and lower (3) frames thereby establishing an upper and lower section;

a lower proximal panel (5) and lower distal panel (6) provided in the lower section and connected between the lower (3) and middle (4) frames as well as an upper proximal panel (7) and an upper distal panel (8) provided in the upper section and connected between the middle (4) and upper (2) frames, said panels (5, 6, 7, 8) being of aerofoil construction and connected to the frames in their respective ends;

lower flaps (9) mounted under or on the distal panels (6, 8) and connected to driving units, the flaps (9) adapted to be controlled remotely, when the device is in use being towed through the water; and

upper flaps (9') mounted on the proximal or mesial panel (5, 7, 10, 1 1) and connected to driving units, the upper flaps (9') adapted to be controlled remotely, when the device is in use being towed through the water;

wherein the proximal (5, 7) and distal (6, 8) panels are placed over each other, and wherein the lower distal panel (6) and upper distal panel (8) have a distal surface (6', 8') rendering them hollow, wherein the flaps (9) constitute a part of the distal surface.

In a preferred embodiment of the invention the flaps (9) are adapted to move relative to each other. Also preferred, the flaps (9) mounted on the distal panels (6, 8) are integrated in the lower parts (6', 8') of the distal panels (6, 8) but may also placed on other positions, such as the end of the distal panels (6, 8). Likewise, the upper flaps (9') are integrated in the proximal panels (5, 7) or mesial panels (10, 1 1).

A lower mesial panel (10) is preferably imposed between the lower proximal (5) and distal (6) panels. Further, it is preferred that an upper mesial panel (11) is imposed between the upper proximal (7) and distal (8) panels.

In a preferred embodiment of the present invention the chord of the mesial panel (10, 11) is not parallel with the chords of the proximal (5, 7) and distal panels (6, 8). The spreading device may be provided with horizontal flaps (12) provided on the upper, middle, and/or lower frame in order to improve the control of the device in the vertical plane. In this respect the horizontal flaps are adapted to be controlled remotely.

In a preferred embodiment the lower distal panel (6) and upper distal panel (8) have a distal surface (6', 8'), preferably about 2-30 cm remote from the opposing aerofoil surface of the panel thereby rendering them hollow, wherein the flaps (9) constitute a part of the distal surface. The distal surface (6', 8') of each distal panel (6, 8) is preferably concave whereas the opposing surface is convex. In a preferred embodiment fixation means are provided in the device for pulling after a vessel.

Configured in this way, the improved trawl door is improved in comparison with a conventional trawl door. Especially the trawl door of the present invention improves stability when the trawl door is towed through water at a high angle of attack. Further, it produces less door drag.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 shows in perspective a trawl door of the present invention. Figure 2 shows lower cut of the trawl door.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Figure 1 there is shown a trawl door (1) of a preferred embodiment of the present invention. It has an upper frame (2) defining a top edge of the door; a lower frame (3) defining a bottom edge of the door; a middle frame (4) defining an intermediate frame positioned between the upper (2) and lower (3) frames thereby establishing an upper and lower section; a lower proximal panel (5) and lower distal panel (6) provided in the lower section and connected between the lower (3) and middle (4) frames as well as an upper proximal panel (7) and an upper distal panel (8) provided in the upper section and connected between the middle (4) and upper (2) frames, said panels (5, 6, 7, 8) being of aerofoil construction and connected to the frames in their respective ends; and flaps (9) mounted below the distal panels (6, 8) and connected to driving units, the flaps (9) adapted to be controlled remotely, when the device is in use being towed through the water; wherein the proximal (5, 7) and distal (6, 8) panels are superimposed and parallel.

Referring to Figure 2 there is shown another view of the trawl door (1) in order to render visible the upper flaps (9') of the system.