Field

The present invention relates to trawl doors used in trawl fishing, including shallow water trawl fishing applications, deep water trawl fishing applications, bottom trawl fishing applications as well as at pelagic trawl fishing applications. The invention also relates to seismic surveillance line spreading and spreading of other items towed in water.

Introduction

Due to the constantly increasing costs of operating commercial trawlers, it is important to improve the efficiency of the fishing equipment so as to minimize drag and fuel consumption requirements. A common problem of using convention trawl doors to spread the mouth of a trawl net open is the lack of efficiency. Traditional doors nowadays fish at about 20-40 degree angle of attack. There is a need to provide for more efficient trawl doors, especially those which exhibit better spread of a trawl net during actual trawling operations as well as reduced drag. Furthermore, with traditional trawl doors vortices are formed behind the trawl door which push the doors towards each other. During operation the door must be constantly forced out to increase the space between the doors, which requires additional energy and hence oil consumption. The vortices make traditional doors unstable and wobbly. Thus, there is need in the industry for trawl doors that are more efficient and stable than known trawl doors.

WO 2007/044859 discloses a portion of a trawl door formed from solid synthetic material enclosing a portion of a frame. The frame, being enclosed within the synthetic material includes support members to which connecting members are secured after liquid synthetic material solidifies. The support members receive connecting members having a shape determined by particular positions of accessible portions of the support members. Neither this publication, nor none of the other known art has proposed a trawl door that solves one or more of the above mentioned problems.

Summary

It is an object of the present invention to overcome and/or ameliorate the aforementioned drawbacks of the prior art and to provide an improved and/or alternative and/or additional method or device for connecting trawl doors to a trawl for increased (and easier) spread of the trawl. It is one preferred object of the present invention to provide a trawl door comprising a front surface and a back surface where the front surface further comprises one or more front-strap ears near the trailing edge. Thus, at least one of the preferred objects of the present invention is solved by a trawl door comprising a front surface and a back surface, where the front surface further comprises one or more front-strap ears near the trailing edge towards the middle of the trawl door. In an embodiment of the present invention the trawl door has a V-shape, U-shape, dihedral, tip dihedral or polyhedral shape.

In an embodiment of the present invention the back surface further comprises one or more back-strap ears near the trailing edge.

In an embodiment of the present invention the trawl door further comprises a bracket at the front surface and optionally a bracket stopper.

In an embodiment of the present invention the trawl door further comprises one or more trawl door shoes.

In an embodiment of the present invention the trawl door further comprises one or more spoilers. In an embodiment of the present invention the trawl door further comprises a location sensor, a monitor sensor or a trawl door monitor sensor and sensor holder, which identifies the location of the trawl door.

The object(s) underlying the present invention is (are) particularly solved by the features defined in the independent claims. The dependent claims relate to preferred embodiments of the present invention. Further additional and/or alternative aspects are discussed below.

In the present context the term "water" relates to clear water or sea water (the ocean) as most trawling takes place in the ocean/sea

Brief Description of the Figures Fig 1 shows front-strap ears near the trailing edge of the trawl door.

Fig 2 shows different shapes of the trawl doors of the present invention. Fig 3 shows a trawl door with front- straps and back-strap ears. Fig 4 shows a bracket and bracket stoppers. Fig 5a-b show a trawl door with spoiler. Fig 6a-b illustrates a conventional trawl door and a hollow door with different angle of attack.

Description The present application provides a novel trawl door connection means with improved stability and efficiency. The inventors are able to demonstrate smaller angles of attack using the trawl door of the present invention, which is as little as 7.5 degrees. Traditional doors nowadays do not operate with such a small angle of attack due to the shape of the doors. They are primarily forcing doors, and consume a large amount of oil during towing. Traditional trawl door connections facilitate a forced angle of fishing with much effort angle (about 20 - 40 degrees) with connections of the towing warp wire in the bracket and with connections from backstops to the trawl. On the other hand, due to the new connections, very small vortices are formed behind the door, which provides higher stability and decrease the energy consumption required to maintain the positions of the doors. In a preferred embodiment, the second side panel has one or more front- straps, preferably near the trailing edge and towards the middle of the trawl door as shown in figure 1. The trawl nets are connected to the front-strap ears which are located at the lower surface of the airfoil, which is the the inside of the door at the aft end instead of to back-strap ears in the traditional doors. When connected to the front-strap ears, the new doors automatically spreads outwards constantly and slowly reaching a smaller angle of attack.

The trawl door according to the present inventions may have V-shape, U-shape, dihedral, tip dihedral or polyhedral shape. The trawl door can be divided into sections for straight, V-shaped and U-shaped doors as shown in figure 2.

In a preferred embodiment, the first side panel has one or more back-strap ears near the trailing edge. Figure 3 shows a trawl door with both front-strap ears and back-strap ears. Back-strap connection can be used for bottom fishing, shrimp fishing and pelagic fishing, whereas front-strap connection can be used for all the same fishing, as well as pelagic fishing high up in the water where a very large opening between the trawl doors is needed.

The new trawl door connections provides a trawl door functions like a kite in that it does not require to be forced sideways by towing and connection to the trawl via the back-strap ears. It seeks sideways during towing at smaller angle and connection to the trawl via the front-strap ears. In the new trawl doors forced spread is not required. In a preferred embodiment, the trawl door further comprises a bracket at the lower surface. Towing warp wire is connected to the bracket and the trawl is connected to the back-strap ears or front-strap ears.

Figure 4 shows a bracket and a bracket stopper where the brackets are on hinges. The stopper has the effect that it prevents the bracket to move to less than certain angle, such as not less than 15 degrees. This can be useful when shooting the trawl doors when the front-strap connection is used.

The trawl door according to the present inventions can further comprises one or more spoilers. Use of spoilers are advantageous depending on the fishing methods and needs. Spoilers can be placed at or near the front part of the first side panel such as shown in figure 5a or 5b at or near the back of the first side panel, at or near the trailing edge of the second side panel.

Preferably, the trawl door further comprises one or more trawl door shoes. The shoes are useful in protecting the structure of the trawl door if bottom trawling is intended. In a preferred embodiment, the trawl door further comprises a location sensor, trawl door sensor, monitoring sensor or trawl door monitoring sensor, such as for example a Scanmar or Simrad signal holders. The location sensor may be placed inside the trawl door chambers so they are better protected and will not affect the fishing ability of the trawl doors.

It is not necessary to force the spread for the trawl doors of the present invention. Fishing with conventional trawl door connections requires a 20 to 40 degrees angle of attack with connections to the brackets and to the back-strap ears. Figure 6a shows a conventional trawl door which operates with a 37 degrees angle of attack. This big angle of attack takes on a lot of sea and increases oil consumption. In contrast, the trawl door connection of the present invention, for example the one illustrated in Figure 6b, surprisingly works at as low as 7.5 degrees of angle of attack, Therefore, the present invention allows trawling at much lower angle of attack which further reduces oil consumption.

As the new form allows a less forced spreading of the trawl doors, there is less resistance due to vortices and hence less energy consumption in towing and stablizing the doors.

This novel form of trawl doors works equally well on the bottom of the ocean, just off the bottom in mid water or high up in the water. This has the advantage that bottom fishing does not require any touching or scraping of the bottom at all, making the doors more environmentally friendly.