Traction device having bridle with actuator

Abstract

A traction device (4a, 4b) for towing an object (6) along a water surface or through a body of water The traction device (4a, 4b) comprises at least one propulsive engine which has a bridle (37) that is attached at a pair of mountings (35, 36). The mountings (35, 36) are arranged at opposite sides of the traction unit (4a, 4b) and the bridle (37) is capable of turning about an axis (34) through the pair of mountings (35, 36). The axis (34) is transverse to the direction of thrust from said propulsive engine. The bridle (37) has an attachment at a distal end from the turn axis to attach a tow line extending to the towed object. At least one rotating actuator (40) is coupled to the bridle (37) at at least one of said mountings (35, 36), to rotate the bridle (37) about the axis (34).

Description

TRACTION DEVICE HAVING BRIDLE WITH ACTUATORTechnical Field

[0001] The present invention relates to a traction device for towing an object along a water surface or through a body of water.Background Art

[0002] Trawling as a fishing technique has existed in its current form since the end of the 19th century. It is based on a bag shaped net that is towed through the water by a boat, i.e., a trawler. To keep the trawl net open, a pair of trawl doors are connected to the trawl some distance in front of the trawl opening. The doors have an angle of attack with respect to the draw direction, so that a horizontal spread is created.

[0003] Over the centuries the trawling technique has developed to include larger and larger trawls. The large trawl creates a substantial drag and hence ever larger trawlers have had to be employed to be able to pull the trawl. The result of this is that the size of the catch has increased, but also that the fuel consumption has increased. The fuel consumption is one of the greatest expenses in trawling. The fuel consumption is largely unrelated to the catch but is substantially depending on the distance the trawl is towed, the speed of the towing and the depth at which the trawl is being towed. The fuel consumption will increase with these factors, but not necessarily the catch.

[0004] One of the above factors, the trawling depth, is highly depending on the type of catch. For catching species, that are close to the bottom, such as flatfish or shrimp, the trawl has to be towed close to the bottom. This means that very long warps, i.e., the trawl wires that connect the trawl doors to the boat, have to be deployed. The length of the warps is several times the depth of the trawl. These warps create a substantial drag, which makes bottom trawling very fuel demanding, and also require the use of high-power engines.

[0005] Bottom trawling has been criticized from an environmental perspective because the trawl doors and weights of the trawl are dragged along the bottom and make long and wide trails, which disrupt and destroy the environment for seabedplants and animals. Consequently, there are restrictions on where and how much bottom trawling is allowed.

[0006] There have been many solutions suggested to improve trawling. Most of these are modifications of the conventional principle of a trawler that tows a trawl net with trawl doors. However, there have been some attempts to deviate from this principle.

[0007] One of these bold attempts is shown in GB 695641 , which shows a trawl net that is being towed by a pair of underwater crafts. The crafts may be electrically driven and are connected to a mother ship by electrical power lines. The mother ship may also control the depth and side steering of the crafts. The mother ship is connected to the cod end of the net by guide lines, which means that the ship trails the trawl net. The guide lines are kept suitably taut during the trawling. The purpose of the guide lines is to pull the cod end up to the ship when the net is full.

[0008] The invention of GB 695641 was made in 1949, at a time when the technology for such underwater crafts was not mature enough to be used efficiently for trawling.

[0009] DE 1181484 also shows a suggested solution that uses underwater crafts for towing the net. In this solution the crafts are connected to each other by a boom or similar that keeps the crafts at a mutual fixed distance. The boom ensures that the net is held open. However, the boom structure will create a substantial extra drag for the trawl.

[0010] WO 2010 / 015254 shows a trawl configuration that uses one underwater craft that tows one side of the trawl net while the trawler tows the other side. As the underwater craft has a fixed length of wire connecting it to the net, there is little possibility of varying the trawling depth and it would not be possible to trawl below a certain depth.

[0011] NO320863 shows a more conventional trawling arrangement. It differs from a conventional arrangement in the fact that the trawl doors can be steered to a certain degree, to control the spread and depth of the trawl. However, as conventional trawling arrangements, the doors and the trawl must be towed by the vessel. This means that the vessel will be situated far forward of the trawl (the distance may varydepending on the depth but would be from a couple of hundred meters to more than one kilometer), and hence the echo sonar field of the vessel cannot possibly see the trawl.

[0012] JPH03198731 also relates to such a conventional trawling arrangement with a trawl eye.

[0013] There have also been a few attempts of towing other objects, such as a ship, by an underwater craft.

[0014] US3999499 describes a submarine cargo carrier that is driven and controlled by a surface vessel. A rotating shaft with universal joints provides power from the surface vessel to the submarine carrier. The surface vessel has its own propeller for propulsion.

[0015] US6260500 shows an emergency ship towing system comprising an underwater thrust unit that can be connected to a ship by a flexible towing line. The thrust unit has its own power supply but can be controlled from the ship. The thrust unit will be transported to a ship that is in distress by a helicopter and lowered onto the ship deck. Here one end of the towing line will be attached to the ship and the thrust device will be launched into the sea. The purpose is to tow the ship out of dire straits.

[0016] US3085533 shows a system for transporting oil under water, which includes a large underwater carrier and a smaller surface vessel. The surface vessel provides power to the underwater carrier and is in turn towed by the carrier.

[0017] Some of the prior art underwater units are not suitable for towing an object, such as a trawl or ship, along or through a body of water. Those that can be used for such a purpose are hampered by inefficiency and poor manoeuvrability.

[0018] DE 942490 C shows a traction unit for towing a boat. A bridle connects the tow line to the traction unit. The bridle is pivotable relative to the traction unit about an axis that goes through the centre of gravity of the traction unit.

[0019] US 2009316526 A1 shows a traction unit that is attached to a seismic tow to increase the spread of the tow, i.e. , replace the otter boards of the tow. A bridle is pivotably attached to the traction unit.

[0020] NO329801 B1 shows a trawl equipped with traction units in the form of water jets. The water jets are used to keep the trawl in correct height and at the correct sideways position.

[0021] The present applicant has suggested new ways of towing and controlling a trawl through his previous patent applications WO2017 / 222390 and WO202 1 / 225451.

[0022] WO2017 / 222390 (also published as NO343896 B1 ) show a trawling arrangement, comprising a trawl net with an opening and a cod end, and at least two propelled and steerable traction units that are coupled to the trawl net, one on each lateral side, by sweep lines. The traction units are coupled to a vessel at the surface by least one electrical power cable. The electrical cable is configured to position the vessel so that the opening of the trawl net is within an echo sonar field of the vessel. Also described is a traction device with at least one propeller arranged within a duct. The traction device is equipped with fins within the duct to steer the traction device in the desired direction. The sweep line is attached to the rearward end of the traction device at a single attachment point.

[0023] WO2021 / 225451 show an improved traction device where the single attachment point at the rear end has been replaced by a bridle that is attached at each side of the traction device at a common centre of gravity and centre of buoyancy. The steering of the traction device is done by four rudders arranged at the rear part of the traction device.

[0024] LIS2150272094 shows a trawling arrangement with a steerable foil. This foil provides no traction.Summary of invention

[0025] The object of the present invention is to further improve the traction device and provide a more efficient traction device, which is also easier to control.

[0026] The more efficient traction device means that the same thrust can be achieved with less power. For a propeller driven traction device, it means that, e.g., the blade area can be reduced, resulting in a smaller device.

[0027] The device of the invention will have less drag than the prior art traction devices since fins and rudders are no longer needed, and the drag that these items would create against the pulling force of the propeller will no longer be present.

[0028] The above objects are achieved by a traction device for towing an object along a water surface or through a body of water, the traction device comprising at least one propulsive engine, comprising a bridle that is attached at a pair of mountings, said mountings being arranged at opposite sides of said traction unit and that the bridle is capable of turning about an a axis through said pair of mountings, said axis being transverse to the direction of thrust from said propulsive engine, said bridle having an attachment at a distal end from the turn axis to attach a tow line extending to the towed object. The invention is characterized in that at least one rotating actuator is coupled to said bridle at at least one of said mountings, to rotate said bridle about said axis.

[0029] A particularly compact device is achieved when the at least one actuator is an electric wheel hub motor.

[0030] A better control of the bridle and hence the steering of the traction unit is achieved when a wheel hub motor is arranged in each of said mountings.

[0031] An alternative embodiment is achieved by arranging said actuator inside said traction unit with a shaft extending to the bridle.

[0032] A preferred embodiment of the traction unit has the propulsive engine that comprises at least one propeller that is encircled by a duct in the form of an accelerating nozzle.

[0033] Preferably, the propulsive engine comprises at least two counterrotating propellers.

[0034] A better manoeuvrability with minimum momentum required for turning is achieved when the traction unit it has a common centre of gravity, centre of thrust and centre of buoyancy, and said rotational axis of said extends through said common centre.

[0035] It is an advantage if said bridle is a stiff bow partially surrounding the traction unit.

[0036] Conveniently, said bridle forms an attachment point and guide for a power and control cable extending to the traction device.Detailed description of the invention

[0037] Figure 1 show a trawling arrangement for which the traction device of the present invention is intended to be used.Figure 2 shows a traction unit according to the present invention in isometric view,Figure 3 shows the traction unit according to the present invention in side-elevation view,Figure 4 shows the traction unit according to the present invention in planar view, andFigure 5 shows the traction unit according to the present invention in frontal view.

[0038] Figure 1 shows a trawling arrangement of the present invention in isometric view. The trawl arrangement comprises a boat 1 , which is situated at the sea surface 2. From the boat 1 a pair of cables 3a, 3b extend to a respective traction device (hereinafter also called “pod”) 4a, 4b. From the pods 4a, 4b a sweeps 5a, 5b, 5c, 5d extends to the trawl net 6 and are attached to a respective corner 7a, 7b, 7c, 7d of the net 6.

[0039] The configuration may deviate somewhat from the above, e.g., instead of two sweeps from the pod 4a, b to the comers of the net 6, there may also be one sweep that connects with a bridle of two lines, as is generally known in the field of trawling.

[0040] The net 6 comprises a headline 8 and a footrope 9. Between the headline 8 and the footrope 9 is defined an opening 10 into the net 6. At the trailing end of the net is a narrow part called a cod end 11 .

[0041] When trawling it is important to keep the area of the opening 10 of the net 6 as large as possible and to keep the opening as perpendicular as possible to the direction of travel. This ensures the largest catch as possible. Especially, for bottom trawling it is also important to keep the opening as wide as possible. To ensure this, is conventionally used trawl doors (sometimes also called otter boards) to create asideways force that stretches the corners 7a, 7b, 7c, 7d outwards from the direction of travel.

[0042] In the arrangement shown in figurel , the trawl doors have been replaced by traction units (pods) 4a, 4b.

[0043] The pod 4a, b has a similar design as azimuth propellers that are conventionally used on boats and ships to increase manoeuvrability, such as the azimuth propeller described in EP 2468624. The pod comprises a cylindrical duct 12, which encircles a propeller 13. A preferred embodiment of a pod 4a, 4b is shown in figures 2-5.

[0044] Figures 2-5 shows the traction unit in different views. The unit has a propulsive engine comprising a longitudinal motor housing 21. The propulsive engine further comprises a duct 22 encircling the motor housing 21 . The duct 22 is firmly attached to the motor housing 21 by webs 23.

[0045] The duct 22 has a shape of an accelerating nozzle with a frustoconical outer shape and an inner foil shaped wall. This is a conventional way of shaping a duct around a propeller. This type of duct is often referred to as a Kort nozzle after the inventor who patented this type of duct in 1936 (see US 2030375).

[0046] Two propellers 27, 28 are arranged within the duct 22. The propellers 7, 8 are mounted to rotate in opposite directions but to give a thrust in the same direction. The roll of the unit, i.e. , movement about the propeller axis, may achieved by differential speed of each propeller.

[0047] The traction unit is built to have a common centre of gravity, centre of buoyancy and centre of thrust, denoted by 33. The common centre is consequently in the middle of the traction unit. Coinciding with an axis 34 through this centre 33 the duct 22 has mountings 35, 36 for a bridle 37 that is rotatably attached to each mounting 35, 36, so that the bridle 37 can turn about the axis 34. The bridle 37 extends rearward of the duct 22. At the rearward end of the bridle 37 there is a line attachment 38. A tow line (not shown) between the towed object and the traction unit will be attached at the attachment 38. The attachment 38 can also function as an attachment point and guide for a power and control cable (not shown) between the towed object and the traction unit. This cable may, however, be attached elsewhereto the traction unit as long as it is prevented from interfering with the propellers and bridle.

[0048] The rotational axis 34 of the bridle 37 need no coincide exactly with the three centres. It can deviate somewhat from this without significant influence on the function. Likewise, the three centres (gravity, buoyancy and thrust) need not be placed at exactly the same point.

[0049] The bridle 37 is conveniently a stiff bow that maintains its shape even if subjected to a large pulling force. It can be made of metal, such as high tensile steel or a composite material, such as a carbon fibre reinforced matrix.

[0050] New to traction unit of the present invention is that an actuator 40 is arranged at the mountings 35, 36, which is capable of turning the bridle about the axis 34.Each mounting 35, 36 may have an actuator 40, or only one of the mountings may have an actuator, while the bridle 37 may be allowed to turn freely at the opposite mounting.

[0051] The actuator may be a wheel hub motor or be a motor arranged with the duct 22 with a shaft extending through the duct, to one or both mountings.

[0052] The duct has a lifting ear 50 at the top thereof. This is arranged in the same plane as the axis 34 and hence the gravity centre of the traction unit. Hence the traction unit will be level when lifted out of and into the water.

[0053] At the opposite side of the ear 50 is a stand 51 enabling placement of the traction unit on the deck of a boat.

[0054] The above-described design of the traction unit enables the traction unit to easily turn about the axis 34 and thereby quickly change the direction of pull. The flow through the duct will no longer be hindered by fins or foils or of the tow line attached to it. The tow line will follow the movement of the traction unit.

[0055] As for the previously known arrangements described in WO2017 / 222390 and WO2021 / 225451 , two or more traction units can be attached to one object to operate in unison to tow an object. Traction units can also pull in different directions to accurately position an object.

[0056] Although not preferred, it is also possible, instead of two oppositely rotating propellers, to use the rudders to counteract rotation of the unit.

[0057] Instead of propellers, it is also conceivable to use other types of propulsive engines, such as a waterjet.

Claims

Claims1 . A traction device for towing an object along a water surface or through a body of water, the traction device comprising at least one propulsive engine, comprising a bridle that is attached at a pair of mountings, said mountings being arranged at opposite sides of said traction unit and that the bridle is capable of turning about an a axis through said pair of mountings, said axis being transverse to the direction of thrust from said propulsive engine, said bridle having an attachment at a distal end from the turn axis to attach a tow line extending to the towed object, characterised in that at least one rotating actuator is coupled to said bridle at at least one of said mountings, to rotate said bridle about said axis.

2. The traction device of claim 1 , characterised in that said at least one actuator is an electric wheel hub motor.

3. The traction device of claim 2, characterised in that said wheel hub motor is arranged in each of said mountings.

4. The traction device of claim 1 , characterised in that said actuator is arranged inside said traction unit with a shaft extending to the bridle.

5. The traction device of claim 1 or 2, characterised in that the propulsive engine comprises at least one propeller that is encircled by a duct in the form of an accelerating nozzle.

6. The traction device of claim 5, characterised in that the propulsive engine comprises at least two counterrotating propellers.

7. The traction device of any of the preceding claims, characterised in that it has a common centre of gravity, centre of thrust and centre of buoyancy, and said rotational axis of said extends through said common centre.

8. The traction device of any of the preceding claims, characterised in that said bridle is a stiff bow partially surrounding the traction unit.

9. The traction device of any of the preceding claims, characterised in that said bridle forms an attachment point and guide for a power and control cable extending to the traction device.

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