DK202170165A1 - Trawldoor with moveable hydrofoil sections - Google Patents

Abstract

The present invention discloses an inventive spreading device for trawl fishing, seismic survey operations or other water activities where it is desirable to keep distance between two sides of a towed device, said spreading device having at least one part, which at least one part comprises two or more foils, where each foil has a front surface and a rear surface, said surfaces each being defined by two edges and two side limitations, in use being front and rear edges, an upper and lower side limitations where said upper and lower side limitations of the two or more foils are connected to respective upper and lower frames, where at least one foil is stationary and where one or more sections of another foil is pivotably connected to said another foil, such that the section may be moved from a position where the surface of the section is flush with the surface of said another foil, to a position where the surface is out of plane with the surface of said another foil.

Description

DK 2021 70165 A1 1 [Trawl door with moveable hydrofoil sections] Field of the Invention The present invention is directed to a spreading device for trawl fishing, seismic survey operations or other water activities where it is desirable to keep distance between two sides of a towed device. In connection with trawl fishing the two sides shall be under- stood as the two lateral connection points for the trawl in order to maintain the trawl mouth open in order to catch fish. For seismic use it is important to spread for example an array of sensors/microphones as much as possible in order to monitor an as large an area as possible.

In the following, spreading device will often be referred to as “trawl door”, however it shall be understood that trawl door is a spreading device, and that the inventive concept of the present invention is applicable on other devices.

This desire to provide spreading force shall also be evaluated in view of the drag/re- sistance and speed through the water the spreading device exerts on the ship pulling the towed device.

A number of parameters determine the mode of operation and capability of a trawl door when being towed through the water.

The spreading force, which is the lateral force (lift force) exerted by a trawl door for spreading the mouth of the trawl net, is greater the larger the area of the trawl door as seen from the side. There are examples of trawl doors where the area of the trawl door can be adjusted manually. GB 1 405 076 discloses a flat trawl door where the length is greater than the width, and where a displaceable plate element can be made to expose and cover, respectively, an opening at the centre of the trawl door. Another example is seen in SU 1 746 970 Al, disclosing a cambered, but not V-shaped trawl door where two openings in upper and lower half, respectively, of the door can be exposed or cov- ered by a displaceable plate element. A similar feature is shown in WO 86/02525 in a trawl door which is V-shaped but not cambered, and where the length is greater than the width.

DK 2021 70165 A1 2 The position in the water of trawl doors also determines how deep the trawl net is situ- ated in the water body. In order to catch schools of fish at different depths in the water body, it is thus necessary for the trawl doors to assume different depths in the water.

This adjustment of the course of the trawl doors in water can be provided by fastening the towing wires and chains for trawler and trawl net, respectively, in various ways on the trawl doors.

Background of the Invention WO 2010/019049 A1 discloses a cambered trawl door with an H:B ratio greater than I and which is formed symmetrically about a centre plane, which is horizontal in situation of use, as an upper part and a lower part of the trawl door extend in opposite directions from the centre plane. The upper and lower parts are each provided with an opening close to the upper and lower edges of the trawl door, and at some distance from the leading edge and trailing edge of the trawl door. Respective plate elements are arranged at the openings such that the plate elements can cover or expose openings by vertical displacement towards and away from the centre plane, respectively. The upper and lower parts are connected by a longitudinal central tube section that contains a drive mechanism. The plate elements are individually displaced by screw spindles that are mechanically connected to the drive mechanism. By the individual displacement of the plate elements, the active hydrodynamic area of the upper and lower parts, respectively, be adjusted, causing the vertical position of the trawl door in water to be changed. Use of a central mechanical drive mechanism in a tube section as a connecting constructional part means that the design is somewhat heavier than other known trawl doors with the same main features, a fact influencing the capability of the trawl door in a disadvanta- geous way.

Various devices and arrangements for remotely controlling the lateral positions of trawl doors or deflectors are known. Examples of the prior art are disclosed in WO 98/24685, WO 2005/055708, WO 2004/086092 and WO 2010/019049.

GB 2122562 discloses a spreading device in the form of a paravane or pelagic trawl door with an arrangement for remote control. The angle of attack of the paravane can be changed by moving a bridle head containing the attachment point for the towing line. Three bridle legs connect the bridle head with the body of the paravane. The point where

DK 2021 70165 A1 3 rear bridle leg is connected to the body of the paravane is movable in horizontal direc- tion when operated at sea by a screw spindle of an electric motor. This prior art arrange- ment is only capable of changing the angular position of the paravane about a vertical axis when used as a spreading device, thereby changing the lateral position of the spreading device relative to the direction of movement in the water. Also, the bridle arrangement is cumbersome and vulnerable when handling on a fishing trawler at sea, where the attachment point is provided close to the body of the spreading device, espe- cially in case of trawl doors used for trawl fishing.

In the art it is known to provide trawl doors with a number of foils. In a cross-sectional design the foils are comparable to air foils, and as such will direct the fluid streaming across the surfaces in a determined manner. Also, the foils are able to create lift, thereby increasing the lift force — or spreading force for trawl doors travelling through the water. As there are many parameters influencing the spreading force of a trawl door, it is de- sirable to also be able to adjust the spreading force, and preferably during use. Some of the parameters influencing the spreading force of a given trawl door may be the waters’ temperature, salinity, trawling depth, size of trawl, speed of trawl through the water, side current and many other factors.

Some prior art examples of such control are disclosed in WO2020/254896, WO2018/108222, WO2010/019049, WO2015/055207, WO2013/014507.

These prior art examples all have some drawbacks. Some of them are not foreseen as being remotely controlled whereby it is not possible to adjust the trawl door's charac- teristics during use, whereas others only allow for very simple adjustment.

Object of the Invention Consequently, it is the object of the present invention to provide a much more versatile and easier manner in which to control a trawl door.

Description of the Invention The present invention addresses this by providing a spreading device for trawl fishing, seismic survey operations or other water activities where it is desirable to keep distance

DK 2021 70165 A1 4 between two sides of a towed device, said spreading device having at least one section, which at least one section comprising two or more foils, where each foil has a front surface and a rear surface, said surfaces each being defined by two edges and two side limitations, in use being front and rear edges (leading or trailing edges), an upper and lower side limitations where said upper and lower side limitations of the two or more foils are connected to respective upper and lower frames, where at least one foil is sta- tionary and where a section or sections of another foil is pivotably connected to said another foil, such that the section or sections may be moved from a position where the surface of the section is flush with the surface of said another foil, to a position where the surface is out of plane with the surface of said another foil.

The foils may be equipped or designed with a bulb which in itself improves the spread- ing force — see also applicants own prior patent application WO2018/054443. The particular feature of having one or more sections of a foil being pivotable relative to the remainder of that foil and particularly with respect to an adjacent foil is unique in that it does provide a number of effects to the spreading devices as such.

Whereas with the prior art devices as mentioned above, most of them will change the affected area of a foil.

The present invention changes the water flow impacting the spreading device, and in particular only a section of the spreading device.

Consequently, by moving a section of one foil the remaining part of that particular foil, wherein the section is inte- grated, will have its normal function such as for example stabilizing the entire spreading device, but at the same time the hydrodynamic probabilities of this spreading device have changed.

Depending on the direction in which this section is pivotable relative to the "neutral position” in which the surface of the section is substantially flush with the surface of the surrounding foil, the waterflow characteristics between the two adjacent foils, one of them being stationary the other one having a movable section, will be changed such that the drag resistance may be altered as well as the lift provided by that particular spreading device.

In a further advantageous embodiment of the invention the section is pivotably connected to said another foil along the front edge, the rear edge or a pivot axis arranged between said front and rear edges.

DK 2021 70165 A1

The variation in the position of the pivot axis relative to the front respective rear sides of the spreading device (for example seen in the direction of travel) has a large effect on the impact of the section’s deflection relative to the foil in which the pivotable sec- tion is arranged.

Consequently it is possible to design spreading devices where the de- 5 flection of the foil will have a great impact on one characteristic, for example the hy- drodynamic drag or/and the hydrodynamic lift i.e. the spreading force created by the spreading device.

In a still further advantageous embodiment of the invention, the section may be pivoted out of the plane of the second foil to such a degree that the section comes into contact with an adjacent foil or any deflection there in between.

With this embodiment it be- comes possible to more or less block part of a section for throughflow of water and as such completely change the constitution of the spreading device relative to the charac- teristics had the section been in the position where it is substantially flush with the sur- rounding foil and thereby having no deflection at all.

In a still further advantageous embodiment of the invention, the spreading device com- prises three or more foils and where foils having a movable section are arranged on either side of a stationary foil.

With this arrangement it becomes possible to substan- tially completely redesign and reconfigure the waterflow passing the stationary hydro- foil in that by having a section on foils on both sides of a stationary middle foil, the dynamics may be changed altogether.

This is particularly outspoken in a further embodiment of the invention, where the sec- tion may be pivoted either above or below said upper surface of said another foil or both above and below said upper surface of said another foil.

With this embodiment it be- comes possible to either deflect the section towards the stationary foil or away from the stationary foil.

As the section at least for a part of the foil into which it is incorporated, determines the hydrodynamic properties of the foil itself and the channel which is cre- ated by the stationary foil and the foil incorporating a section.

The ability of the foil to move in either direction, i.e. below or above set surface of the foil into which it is inte- grated creates possibilities for influencing the hydrodynamic capabilities of the spread- ing device.

For example, in embodiments of the invention where a stationary foil is arranged between two foils having movable sections it is possible to control the sections

DK 2021 70165 A1 6 such that for example one section has a negative deflection and another section inte- grated in a foil opposite to the stationary foil has a positive deflection, whereby both foil sections will come into contact with the central foil.

The other possibility is also that both foils are moved such that they are furthest away from the centrally arranged stationary foil and in this manner the characteristics of a spreading device will be able to be designed for a wide range of applications given a wide range of spreading charac- teristics.

In a further embodiment of the invention it is possible to move the movable sections on a top part of a trawldoor, in a different direction to the movable sections on the bottom part of the trawldoor.

In this manner, the hydrodynamic characteristics of the top part of a trawldoor are changed in relation to the bottom part, thereby facilitating steering.

Preferably, the movable section constitutes between 20% and 80%, more preferred 30% to 60% and most preferred approx. 40% of the surface area of said foil.

Typically sections in the same spreading device will have the same extent in order to assure symmetry such that the hydrodynamic stability of the entire spreading device is assured, but it is also contemplated that in spreading devices having a multitude of foils, the sections may have different extends on different foils.

In this matter it becomes possible to both create variations in the spreading force but also to control the depths, the drag and compensate for unevenness’s, for example in a trawl or side currents etc.

Furthermore, depending on the type of fishing which is taking place, the sections may be small or large, relative to the entire surfaces of the foil integrating the section, such that the adjustment possibilities are designed to that particular type of fishing.

For ex- ample, in waterbodies where there are only small or negligible variations in for example current, salinity etc. the stability of the foils does not need to be adjustable as much as when fishing in waters, where great variations or even layers of different water are pre- sent, whereby it is necessary to control the spreading devices in order to achieve, at all times, the optimum spreading angle in order, for example, for the trawl mouth to be as open as possible.

In order to control the deflection angle of the section, i.e. to control how much the section will be out of plane with the foil in which it is integrated, a further embodiment of the invention provides that the pivot action of the section is controlled by either:

DK 2021 70165 A1 7 a. manually positioning and locking the section into position relative to the upper surface of said another foil before introducing the spreading device into the water, or b. activation of an actuator arranged between the section and an adjacent foil, or c. remotely controlling an actuator arranged between the section and an adjacent foil. In the optional embodiment where the section positions are decided/selected by manual means, it may, for example, be a piston which is manually pumped into a fixed position prior to the spreading device being lowered into the ocean. In many circumstances, the experienced crew or operators will from experience know the optimum deflection angle of the section such that according to the location in which the spreading devices are to be used the sections may be pre-arranged in the optimum position. In other instances, it may be advantageous to activate an actuator, for example by activating an automatic pump in order to move and lock the section(s) in the desired relative position. However, the most desirable embodiment is where it is possible to remotely control the actuator as such that during the fishing operation when or if it is detected that the spreading characteristics of one or both spreading devices need to be altered in order to carry out the optimum fishing procedure, this may be carried out from the vessel towing the spreading device and as such it is not necessary to stop the fishing procedure in order to readjust the deflection angle of the sections of the spreading devices.

The actuators are typically mounted between the sections and the adjacent foil in that although the side limitations in each part may be more stable and stronger, it will se- verely limit the possible position of the section. For practical purposes it is desired to be relatively independent as to the position of the section relative to the entire foil and as such by arranging the actuator between the stationary adjacent foil and the section, the position of the section is completely free in each part.

In modern fishery, spreading devices having a relatively high extent relative to the width in the new situation are usually used. The spreading devices typically comprise two or more parts which are arranged on top of each other and connected by the side limitations or share a common side limitation. Furthermore, by angling two parts relative to each

DK 2021 70165 A1 8 other, a more stable spreading device is obtained, and of course it will be possible to add the advantages of the sections according to the present invention and as discussed above, into a spreading device, thereby achieving the additional advantages of the pre- sent invention.

Description of the Drawing The invention will now be described with reference to the accompanying drawings: Figure 1 illustrates a spreading device in the shape of a trawl door; Figures 2 and 3 illustrate a cross-section through a trawl door, the cross-section depict- ing a position where the movable section is installed; Figure 4 illustrates a trawl door seen from a position where it is clear that the third foil is subdivided such that the section is free to pivot about an axis by activating the actu- ator, Figure 5 illustrates a trawl door having two parts, where each part is limited by a frame; Figure 6 illustrates that the sections may be constructed such that the pivot axis may be on the trailing edge or the leading edge of the trawl door; Figure 7 illustrates an embodiment where the section pivots around an axis provided between the leading and the trailing edges.

Detailed Description of the Invention In Figure 1 is illustrated a spreading device in the shape of a trawl door 10. In the illus- tration, the trawl door 10 is seen from the rear, understood such that in use, the water will exit through the various channels 20, 20” and flow between the foils 12, 14, 16. As illustrated, the trawl door 10 comprises three foils 12, 14, 16 which guide the water as the trawl door 10 is being pulled through the water. During the passage of water in the channels 20, 20’, the foils 12, 14, 16 will be influenced by the passing water and thereby create a spreading force which is used, for example, to keep the trawl mouth open in order to catch fish.

The design of the channels 20, 20° is very important in that it is the design of these channels which decides the properties of the trawl door as it is being pulled through the

DK 2021 70165 A1 9 water. Therefore, by being able to alter the shape of the channels, this will influence the spreading force and the drag force of the trawl door. To this end, the present invention provides a section of a foil which is adjustable such that the characteristics of the entire trawl door may be altered. The section 30 is in this embodiment pivotably mounted on an axis concentric with a leading edge of the third foil 12. An actuator 32 is arranged between the section 30 and the second foil 14 which is stationary, such that by activating the actuator 32, the section 30 may be pivoted about the axis.

Turning to Figures 2 and 3, this movement will be further explained. Figures 2 and 3 illustrate a cross-section through a trawl door 10 in a position where the movable section is installed. In Figure 2 it is clear that the movable section 30 is in a position where the shape of the section 30 is flush with the remaining part of the foil 12 (not shown). The actuator 32 is arranged between the section 30 and the second foil 14. As the second foil 14 is stationary and fixedly mounted to the frames 18, 18” (see Figure 1) arranged in either end of the trawl door 10, the second foil constitutes a fixed, non-movable at- tachment point for the actuator 32. The section, on the other hand, is pivotably mounted on an axis 34, such that when the actuator is in the extended position as illustrated with reference to Figure 2, the section is resting on a bearing 36, whereby the section 30 is flush with the remaining part of the foil 12. As the actuator 32 is activated, as illustrated with reference to Figure 3, the section 30 is pivoted about the axis 34 into a position where the section is not flush with the remaining part of the foil 12. In the illustrated example in Figure 3, the section 30 has been pivoted such that the section 30 is in con- tact with the second foil 14. It is clear that in the example illustrated in Figure 3, the channel 20° has been drastically changed in that the section 30 as illustrated in Figure 3 will block most of the flow of water through the channel in the extent of the section. Turning to Figure 4, the trawl door 10 is seen from a position where it is clear that the third foil 12 is subdivided such that the section 30 is free to pivot about the axis 34 by activating the actuator 32. In the illustrated embodiment, the section 30 is resting on the support 36 such that the position of the section is comparable to the example described above with reference to Figure 2. It is clear that with this configuration, only the section 30 will be pivoted out of its position flush with the remaining foil 12, and as such it will

DK 2021 70165 A1 10 only be the section 30 which has influence on the water flow through the trawl door, whereas the water flowing through the trawl door in the parts of the trawl door having the fixed foils 12 will not be severely influenced.

With the embodiment described above with reference to particularly Figures 2 and 3, the section has been pivoted, creating a positive deflection angle. It is, however, also foreseen that the section may be pivoted with a negative deflection angle, as will be explained with reference to Figure 5. In Figure 5 is illustrated a trawl door having two parts 102, 104, where each part is limited by a frame 18, 18°, 187”. In this embodiment, the two parts share the middle frame 18’. Each part is identical and comprises three foils 112, 114, 116. In this embodiment, the central foil 114 is stationary in its entire length, whereas the upper and lower foils 116, 112 are provided with movable sections 130,

132. The sections are each pivotably mounted around an axis concentric with the lead- ing edges of the foils 112, 116. The upper section 132 is provided with a negative de- flection angle, whereas the lower section 130 is provided with a positive deflection an- gle. The movement of the sections 130, 132 may be achieved as described above by mounting actuators between the central foil 114 and the movable sections 130, 132 re- spectively.

As illustrated in Figure 6, the sections 130°, 132° may be constructed such that the pivot axis 34 may be on the trailing edge or the leading edge of the trawl door. However, common for all embodiments is the fact that the actuator is mounted on a stationary foil and connected to the section which is pivotably mounted either to the leading or trailing edge or in-between of an adjacent foil.

In fig. 7, for example the sections 152,154 are pivotably mounted on axis 156, substan- tially in the middle of the foil 150, such that when the actuator (not shown) is activated part of the section will be brought above the plane of the foil, while another part will be pivoted below the plane of the foil.

Therefore, by manipulating the actuators, the sections may be moved from positions where the sections are flush with the foil into which they are mounted to a position where the section is not flush with the foil, whereby the section will influence the hy- drodynamic characteristics of the trawl door as described above. For other spreading

DK 2021 70165 A1 11 device constructions having a plurality of foils it is clear that the invention finds use where at least one foil is stationary, in order to form a fixed land for the actuator.

Con- sequently, the actual number of foils is not relevant.

Claims (8)

DK 2021 70165 A1 12 CLAIMS

1. A spreading device for trawl fishing, seismic survey operations or other water activities where it is desirable to keep distance between two sides of a towed device, said spreading device having at least one part, which at least one part comprises two or more foils, where each foil has a front surface and a rear surface, said surfaces each being defined by two edges and two side limitations, in use being front and rear edges (leading or trailing edges), an upper and lower side limitations where said upper and lower side limitations of the two or more foils are connected to respective upper and lower frames, where at least one foil is stationary and where one or more sections of another foil is pivotably connected to said another foil, such that the one or more sec- tions may be moved from a position where the surface of any section is flush with the surface of said another foil, to a position where the surface is out of plane with the surface of said another foil.

2. Spreading device according to claim 1, wherein the one or more section is pivotably connected to said another foil along the front edge, the rear edge or a pivot axis arranged between said front and rear edges.

3. Spreading device according to claim 1 wherein the one or more section may be pivoted out of the plane of the second foil to such a degree that the section or sections comes into contact with an adjacent foil or any deflection there in between.

4. Spreading device according to claim 1 wherein the spreading device comprises three or more foils and where foils having one or more moveable sections are arranged on either side of a stationary foil.

5. Spreading device according to claim 1 wherein the one or more section may be pivoted either above or below said upper surface of said another foil or both above and below said upper surface of said another foil.

6. Spreading device according to claim 1 wherein the section constitutes between 20% and 80%, preferably 30% to 60% and most preferred approx. 40% of the surface area of said foil.

DK 2021 70165 A1 13

7. Spreading device according to claim 1 wherein the pivot action of the one or more sections is controlled by either: a. manually positioning and locking said section into a desired position relative to the upper surface of said another foil before introducing the spreading device into the water, or b. activation of an actuator arranged between the section and an adjacent foil, or C. remotely controlling an actuator arranged between the section and an adjacent foil

8. Spreading device according to any preceding claim where a spreading device comprises more than one part, where two adjacent parts are connected by a common side limitation, and where the parts may optionally be angled relative to each other.