WO2010015254A1

WO2010015254A1 - Trawl system and an unmanned, submerged trawl pulling vessel

Info

Publication number: WO2010015254A1
Application number: PCT/DK2009/050172
Authority: WO
Inventors: Thormund Johannesen
Original assignee: P/F Mest
Priority date: 2008-08-04
Filing date: 2009-07-13
Publication date: 2010-02-11

Abstract

A trawl system comprises a trawl (5) which is pulled under the sea surface during fishing, the trawl (5) comprising a front opening and two sides, the system further comprising two vessels (1, 13) connected to respective sides of the trawl (5) for the purpose of pulling it. One vessel is an unmanned, submerged trawl pulling vessel (13), and the other vessel is a surface vessel (1) floating on the sea.

Description

Trawl system and an unmanned submerged trawl pulling vessel

The present invention relates to a trawl system comprising a trawl which is pulled under the sea surface during fishing, the trawl comprising a front opening and two sides,! the system further comprising two vessels connected to respective sides of the trawl for the purpose of pulling it.

It is known in prior art to use a trawl, that is, a large, substantially funnel-shaped net pulled by one or more vessels, for fishing. The trawl may be guided near the bottom as a so-called bottom trawl or in pelagic waters between the surface and the bottom as a so- called pelagic trawl.

In cases where a single vessel is used to pull the trawl, so- called trawl doors are used to keep the opening of the trawl distended in the intended position. These trawl doors imply a large flow resistance and thereby a high energy consumption.

The use of two vessels operating in pairs to pull the trawl may eliminate at least a large part of the flow resistance from the trawl doors, and net energy savings are obtained. However, it is demanding in terms of resources to use two vessels to pull a single trawl. To obtain savings, it is well-known to let a vessel cooperate with two other vessels so that the three vessels work in parallel with two trawls each pulled by two vessels so that a middle vessel pulls the two trawls in cooperation with respective ones of the two other vessels. In this way, only one and a half vessels are used per trawl.

GB-A-2 122 562 describes a trawl door in which a connecting point for fastening the trawl door is shiftable so that the angle of the trawl door relative to, and the force of the trawl door acting on, a trawl can be controlled.

GB-A-695 641 proposes trawl fishing, whereby a mother ship does not pull the trawl, but follows it to pull up the end of the trawl for emptying from time to time. The trawl is pulled by two submerged vessels driven electrically by means of power transmitted through cables from the mother ship. The two submerged vessels are provided with driving devices at their sterns.

DE-A-I 181 484 also describes trawl fishing, whereby a trawl is pulled by two submerged pulling vessels which are, in this case, positioned close to the trawl, possibly on a frame which distends the opening of the trawl. The submerged pulling vessels are provided with driving devices at their sterns.

DE-A-I 941 622 describes the use of a manned mini U-boat to pull a trawl. US-A-4 993 344 describes a torpedo protection device comprising a free, submerged, battery-driven tug pulling an explosive charge. The tug is provided with propellers at the stem, and a pulling cable is fastened at the stern.

Due to the threat of global warming, great attention is currently directed at energy savings and the resulting reduction of CO₂ emissions, as the prevailing driving means for fishing vessels is oil, for which reason fishing from seagoing vessels is directly connected to the emission of CO₂.

The object of the present invention is therefore to obtain further energy savings in trawl fishing.

According to the present invention, this object is obtained by means of a trawl system of the type mentioned in the introduction, which is characterized in that one vessel is an unmanned, submerged trawl pulling vessel, and the other vessel is a surface vessel floating on the sea. Substantial savings are obtained thereby, as the unmanned, submerged trawl pulling vessel need not be of the same size as the surface vessel, which will act as the mother ship and be able to transport the unmanned, submerged trawl pulling vessel when not trawling, for example, during transportation between fishing grounds or between fishing ground and port. The unmanned, submerged trawl pulling vessel needs no manning like an independent surface vessel and requires substantially less energy for its own propulsion than an independent surface vessel. With a surface vessel, a trawl is usually pulled by means of a long cable extending obliquely relative to vertical and horizontal from the surface vessel to the trawl. On surface vessels, the cable is wound up on a so-called trawl winch, from which it is lowered during fishing, and on which it can be wound up for pulling the trawl up to the surface vessel so that the trawl can be emptied of catch and can be taken onboard. During fishing, an even motion of the trawl through the waters is intended, but the surface vessel is moved up and down by the waves on the sea. Therefore, the trawl winch is constantly being worked to compensate for the movement of the surface vessel caused by the waves. This energy-demanding work with a trawl winch is avoided by the unmanned, submerged trawl pulling vessel.

Usually, the two vessels are connected to the trawl through respective cables, and weights are preferably provided at the respective cables to pull down the respective sides of the trawl. A weight at the side of the trawl connected to the surface vessel will contribute towards keeping the trawl down so that the need for trawl doors, or influence from such boards, is eliminated or reduced, and a weight at the side of the trawl connected to the unmanned, submerged trawl pulling vessel implies that the latter can be run higher in the water than the trawl, which reduces the risk that the unmanned, submerged trawl pulling vessel will hit the bottom in the case of a bottom trawl.

The trawl system preferably comprises a connection between the two vessels for transmitting driving power and control signals. In this way, the unmanned, submerged trawl pulling vessel may be provided with driving power, such as electric power, from the surface vessel, and the unmanned, submerged trawl pulling vessel can be controlled from the surface vessel.

Preferably, the unmanned, submerged trawl pulling vessel comprises a closed, elongated hull with a stem and a stern, at least one motor, at least one propulsion device driven by the motor, a connection for the supply of driving power to the motor from an external source, a fastening place for a pulling cable, and a communication connection, the propulsion device being placed at the stem in front of the fastening place.

Arranging the propulsion device at the stem of the hull provides stability of propulsion, as a possible tendency of the stern to swing to a position in front of the fastening place is avoided. In one embodiment, the unmanned, submerged trawl pulling vessel comprises at least one controllably movable point of application of force preferably comprising the said fastening place for a pulling cable and/or a shiftable ballast. In this way, the unmanned, submerged trawl pulling vessel may be steered up and down, for example, as the mutual positions of points of application of force on the unmanned, submerged trawl pulling vessel can be shifted. Such points of application of force generally comprise: centre of gravity, point of buoyancy, fastening place for a pulling cable connected to a trawl, and point of application of a propulsion device.

In a preferred embodiment, the unmanned, submerged trawl pulling vessel comprises two propulsion devices arranged in parallel. In this way, the unmanned, submerged trawl pulling vessel may be steered sideways, for example, by being supplied with different volumes of power to the two propulsion devices arranged in parallel when they are arranged side by side rather than above and below each other.

The trawl system preferably comprises usual monitoring devices, e.g. an underwater video camera, etc., to help control the trawl process.

The object of the present invention is also obtained by means of an unmanned, submerged trawl pulling vessel as mentioned above.

The invention thus comprises an unmanned, submerged trawl pulling vessel comprising a closed, elongated hull with a stem and a stern, at least one motor, at least one propulsion device driven by the motor, a connection for the supply of driving power to the motor from an external source, a fastening place for a pulling cable, and a communication connection, the propulsion device being placed at the stem in front of the fastening place. The invention also comprises an unmanned, submerged trawl pulling vessel comprising a closed, elongated hull with a stem and a stern, at least one motor, at least one propulsion device driven by the motor, a connection for the supply of driving power to the motor from an external source, a fastening place for a pulling cable, and a communication connection, the trawl pulling vessel comprising at least one controllably movable point of application of force preferably comprising said fastening place for a pulling cable and/or a shiftable ballast. Preferably, the unmanned, submerged trawl pulling vessel has a motor power of at least 250 kW, preferably at least 300 kW, and more preferably at least 400 kW.

The invention will now be described in more detail below by means of an example of an embodiment and with reference to the schematic drawing, in which

Fig. 1 is a side view of a trawl system according to the invention during operation,

Fig. 2 is a top view of the trawl system according to Fig. 1,

Fig. 3 is a front view of the trawl system according to Fig. 1, Fig. 4 is a top view of the trawl pulling vessel of Figs. 1 to 3, and

Fig. 5 is a side view of a variant of the trawl pulling vessel of Fig. 1.

Figs. 1 to 3 show a trawler or a mother ship 1 on the sea surface, the trawler 1 being connected to a trawl 5 through a pulling cable in the form of a wire 3. The trawl 5 is of a conventional type comprising a substantially funnel-shaped net with an opening 9 and a trawl bag 11. At one side of the opening 9, the trawl is connected to the wire 3, and at the opposite side of the opening 9 the trawl is connected to a trawl pulling vessel 13 in the form of an unmanned, submerged vessel, which will be described in further detail below with reference to

Fig. 3. The trawl pulling vessel 13 is connected to the trawl 5 through a pulling cable in the form of a second wire 15.

A weight 17 is arranged on the first wire 3 near the opening 9 of the trawl, and a second weight 19 is arranged on the second wire 15 near the opening 9.

A connecting cable 21 for the transmission of energy and control signals extends between the trawl pulling vessel 13 and the trawler 1. It should be noted that even though the connecting cable 21 is shown as extending directly from the trawler 1 to the trawl pulling vessel 13 for the sake of illustration, the connecting cable 21 to the trawl pulling vessel 13 preferably extends from the trawler 1, along the wire 3 to the trawl 5, along its opening 9 to the second wire 15 and along the latter to the trawl pulling vessel 13. In this way, any contribution from the connecting cable 21 to the total water resistance against the motion of the trawl system through the water is eliminated, thereby reducing the energy required for propulsion.

Embodiments of the trawl pulling vessel 13 are shown in more detail in Figs. 4 and 5. In the embodiments shown, it comprises a closed, elongated hull 23 made of a suitable material, for example, steel or carbon fibre reinforced or glass fibre reinforced plastics. On the upper side of the hull 23, a fastening device 25 for a crane hook or the like is arranged. In the embodiments shown, the trawl pulling vessel is provided with a propulsion device comprising two propellers 27 arranged side by side at the stem of the trawl pulling vessel. A nozzle 29 is arranged around each propeller 27. The two propellers 27 are driven individually by respective motors M. The second wire 15 (Fig. 4) is fastened at the stern of the hull 23. In the variant shown in Fig. 5, a swingable arm 31 is mounted at the stern, and by means of power means, not shown, the arm can be controllably swung in the vertical plane about an axis 33. At its end, the arm 31 has an eye 35 for fastening the second wire 15.

Furthermore, inside the hull the trawl pulling vessel 13 is provided with a weight 37, which is controllably shiftable in the longitudinal direction of the hull on a rail 39 by means of power means, not shown.

The trawler 1 is of a type known per se, and on its deck it may suitably be provided with one or two crane and holding devices for one or two trawl pulling vessels 13. The crane and holding devices may be of a construction known from similar devices for lifeboats and the like.

Figs. 1 to 3 show the trawler 1 cooperating with a trawl pulling vessel 13 to pull a trawl 5. It should be understood that the invention may similarly be exercised with a trawler cooperating with two trawl pulling vessels to pull two trawls, one on either side of the trawler.

During sailing between the port and the fishing ground, the trawl pulling vessel 13 will be arranged in the said crane and holding device and thus be transported by the trawler. When the fishing ground has been reached, the trawl 5 and the trawl pulling vessel 13 are launched.

In a manner known per se, the weight 17 ensures that the one side of the trawl 5 connected to the trawler 1 through the wire 3 is kept down in the water. The weight 19 pulls down the other side of the trawl 5, which is connected to the trawl pulling vessel 13 through the second wire 15, and, to keep the two sides of the trawl at the same height or to keep the other side of the trawl at a desired height, the trawl pulling vessel 13 must be run in a higher position than the other side of the trawl to obtain an upward pull to compensate for the downward pull of the weight 19. This ensures, in the case of bottom trawls, that the trawl pulling vessel 13 does not risk collision with the seabed. In the case of pelagic trawls, the weight 19 may possibly be dispensed with.

The trawl pulling vessel is steered vertically and horizontally so that the opening 9 of the trawl is kept suitably distended in a suitable position. The position of the opening 9 is monitored by known means, not shown.

To steer the trawl pulling vessel 13 upwards and downwards, the weight 37 may be shifted backwards or forwards in order to correspondingly shift the point of gravity of the trawl pulling device 13 backwards or forwards. Such shifting of the weight 37 and the centre of gravity will make the trawl pulling vessel 13 tilt about a horizontal axis transverse to the longitudinal direction because the centre of gravity is shifted relative to the point of buoyancy of the trawl pulling vessel 13, which point is not moved at the shifting of the weight 37.

Alternatively, or as a supplement to shifting of the weight 37, the fastening point of the second wire 15 may be moved relative to the hull 23. This may be done by moving the eye 35 for fastening of the third wire 15 by swinging the arm 31 up or down as shown by an arrow 41. If the arm 31 is swung up, the trawl pulling vessel 13 will turn correspondingly upwards, and if the arm is swung downwards, the trawl pulling vessel 13 will turn correspondingly downwards.

Sideways steering of the trawl pulling vessel is preferably carried out by means of the propulsion device. In order to steer the trawl pulling vessel 13 of the embodiments shown to one side, the number of revolutions of the propeller at the opposite side is increased relative to the number of revolutions of the propeller at the side towards which it is desired to steer the trawl pulling vessel. The power supplied to the trawl pulling vessel 13 through the connecting cable 21 is adjusted so that the trawl pulling vessel 13 moves synchronously with the trawler 1.

It should be understood that the trawl pulling vessel may be provided with other supplementary or alternative steering devices than the ones mentioned herein.

Claims

C L A I M S

1. A trawl system comprising a trawl (5) which is pulled under the sea surface during fishing, the trawl (5) comprising a front opening (9) and two sides, the system further comprising two vessels (1, 13) connected to respective sides of the trawl (5) for the purpose of pulling it, c h a ra cte ri zed in that one vessel is an unmanned, submerged trawl pulling vessel (13), and that the other vessel is a surface vessel (1) floating on the sea.

2. A trawl system according to claim 1, c h a ra cte ri z e d in that the two vessels (1, 13) are connected to the trawl (5) through respective cables (3, 15), and that weights (17, 19) are provided at the respective cables (3, 15) to pull down the respective sides of the trawl (5).

3. A trawl system according to claim 1 or 2, ch a ra cte r- i z e d in comprising a connection (21) between the two vessels (1, 13) for transmitting driving power and control signals.

4. A trawl system according to any one of claims 1 to 3, c h a ra cte ri zed in that the unmanned, submerged trawl pulling vessel (13) comprises a closed, elongated hull (23) with a stem and a stern, at least one motor (M), at least one propulsion device (27) driven by the motor, a connection for the supply of driving power to the motor (M) from an external source, a fastening place for a pulling cable (15), and a communication connection, the propulsion device (27) being placed at the stem in front of the fastening place.

5. A trawl system according to any one of claims 1 to 4, c h a ra cte ri zed in that the unmanned, submerged trawl pulling vessel (13) comprises a closed, elongated hull (23) with a stem and a stern, at least one motor (M), at least one propulsion device (27) driven by the motor, a connection for the supply of driving power to the motor (M) from an external source, a fastening place for a pulling cable (15), and a communication connection, and that the unmanned, submerged trawl pulling vessel (13) comprises at least one controllably movable point of application of force (35; 37).

6. A trawl system according to claim 5, c h a ra cte ri ze d in that the controllably shiftable point of application of force comprises the said fastening place (35) for a pulling cable and/or a shiftable ballast (37).

7. A trawl system according to any one of claims 4 to 6, c h a ra cte ri z e d in that the unmanned, submerged trawl pulling vessel (13) comprises two propulsion devices (27) arranged in parallel.

8. An unmanned, submerged trawl pulling vessel comprising a closed, elongated hull (23) with a stem and a stern, at least one motor (M), at least one propulsion device (27) driven by the motor, a connection for the supply of driving power to the motor (M) from an external source, a fastening place for a pulling cable (15), and a communication connection, ch a ra cte riz e d in that the propulsion device (27) is placed at the stem in front of the fastening place.

9. An unmanned, submerged trawl pulling vessel according to claim 8, c h a ra cte ri z ed in comprising at least one controllably movable point of application of force (35; 37).

10. An unmanned, submerged trawl pulling vessel according to claim 9, c h a ra cte ri ze d in that the controllably shiftable point of application of force comprises the said fastening place (35) for a pulling cable and/or a shiftable ballast (37).

11. An unmanned, submerged trawl pulling vessel according to any one of claims 8 to 10, c h a ra cte ri z e d in comprising two propulsion devices (27) arranged in parallel.

12. An unmanned, submerged trawl pulling vessel according to any one of claims 8 to 11, c h a ra cte ri z e d in having a motor power of at least 250 kW, preferably at least 300 kW and more preferably at least 400 kW.