Patent Publication Number: US-2018027784-A1

Title: Rigging configuration for a commercial fishing trawl

Description:
FIELD OF THE INVENTION 
     The present invention relates to fishing trawls and, in particular, to devices for spreading the mouth opening of the fishing trawl. 
     BACKGROUND 
     Commercial fishing trawls are designed, inter alia, to maximize the cross-sectional area of the mouth opening of the trawl. This is typically achieved through application of floats across the span of the head line, weights across the span of the foot line, and trawl doors to port and starboard sides to spread the mouth opening. The trawl is then connected to the tow vessel by two warp cables, one connected to each trawl door. 
     A conventional pelagic trawl with a mouth perimeter of 400 meters typically requires two conventional trawl doors of about 15 square meters deployed on either side of the trawl, which create drag. The cross sections of typical floats and weights used to spread the mouth opening of the trawl vertically also create drag. Traditional floats and weights apply constant vertical forces, independent of tow speed. Consequently, the mouth opening tends to collapse with increasing tow speeds. 
     Accordingly, there is a need to provide a fishing trawl which maximizes and maintains the cross-sectional area of the mouth opening of the trawl, while decreasing drag, and consequently, the towing force required to tow the trawl through the water behind the tow vessel. 
     SUMMARY OF THE INVENTION 
     A fishing trawl, according to the present invention, has a net with a mouth opening defined by a head line, a foot line, and side lines. A plurality of longitudinally alignable foil segments each having a foil cross-section, a leading edge, a trailing edge, the leading edge and trailing edge defining a chord, a span, and an internal conduit extending along the span positioned rearward of the leading edge of the foil segment. One of the head line, foot line, or side lines pass through the internal conduits of the plurality of foil segments. 
     In another embodiment, a second head line, a second foot line, and second side lines are provided. The foil segments each further comprise a second internal conduit extending along the span positioned forward of the trailing edge of the foil segment and one of the second head line, second foot line, or second side lines pass through the second internal conduits of the plurality of foil segments. 
     In another embodiment, each foil segment has opposing sides which converge rearwardly from the leading edge to give each foil segment a trapezoidal-like shape with a divergent angle between the sides of adjacent foil segments. 
     In another embodiment, an adjustment mechanism varies the length of the second head line, second foot line, or one of the second side lines passing through the second internal conduits of the plurality of foil segments. 
     In another embodiment, the head line, foot line, and side lines are continuous with one another. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the invention may be more clearly understood, embodiments thereof will now be described in detail by way of example, with reference to the accompanying schematic drawings, in which: 
         FIG. 1 a    is front view of a conventional fishing trawl. 
         FIG. 1 b    is a top view of a conventional fishing trawl. 
         FIG. 2  is a front view of one embodiment of a fishing trawl, according to the present invention. 
         FIG. 3 a    is a cross-sectional view of a foil segment. 
         FIG. 3 b    is a cross-sectional view of a foil segment with an internal conduit positioned to one side of the chord. 
         FIG. 4  is a front view of another embodiment of a fishing trawl, according to the present invention. 
         FIG. 5  is a front view of another embodiment of a fishing trawl, according to the present invention. 
         FIG. 6  is a top view of another embodiment of a fishing trawl, according to the present invention. 
         FIG. 7 a    is a side view of a plurality of foil segments. 
         FIG. 7 b    is a side view of a plurality of foil segments, according to one aspect of the present invention. 
         FIG. 8  is a front view of a plurality of foil segments having a curved profile. 
         FIG. 9  is a view of a plurality of foil segments with a bridle. 
         FIG. 10  is a front view of a plurality of foil segments, with a bridle and an angled profile. 
         FIG. 11  is a front view of a plurality of foil segments, with a bridle and a curved profile. 
         FIG. 12  is a schematic side view of an adjuster mechanism connected to a plurality of foil segments. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     A fishing trawl, according to the present invention, has a mouth opening that is spread by a plurality of foil segments. The foil segments may supplement or replace any or all of the head line floats, foot line weights, or trawl doors, which are typically used to spread the mouth opening of a trawl as it is towed through the water behind a tow vessel. 
     As shown in  FIGS. 1A and 1B , a conventional fishing trawl has a net  1  with a mouth opening  2  spread apart by floats  3  attached along a head line  4 , weights  5  attached along a foot line  6 , and trawl doors  7  at the side lines  8 . Generally, the floats  3  and weights  5  have a cross-section, which results in a high drag coefficient. The trawl doors  7  are generally spaced apart from the side lines  8  and attached thereto by bridle legs  9 . 
     In one embodiment, as shown in  FIG. 2 , vertical tag lines  10  may be installed between the bridle legs  9  of a conventional fishing trawl and foil segments  11  may be attached on or to the tag lines  10  to provide lateral force for spreading the mouth opening  2  of the net  1 . Each foil segment  11  has a span, a chord, a foil cross-section, which may be a standard hydrofoil cross-section, and a forward internal conduit  12  along the span and rearward of the leading edge  13 , as shown in  FIG. 3 a   , by way of example. Different foil cross-sections may be used, such as NACA, Eppler, Gottingen, or any other custom foil cross-section suitable for the desired application. The tag lines  10  are threaded through the forward internal conduit  12  of the foil segments  11 . Preferably, the foil segments  11  are cambered, or otherwise asymmetric, so that the foil assumes a non-zero equilibrium angle of attack as it is towed through the water and thereby generates lift. Alternatively, a symmetric foil cross-section may be used with a forward internal conduit  12  to either side of the chord line, as shown in  FIG. 3 b   . In this embodiment, the foil segments  11  provide lateral force to supplement the spreading force produced by the trawl doors  7 . 
     In another embodiment, as shown in  FIG. 4 , foil segments  11  are threaded on the head line  4 , by passing the head line  4  through the forward internal conduits  12  of each foil segment  11 , to generate lift upwardly and thereby replace the floats  3  used on conventional trawls. Similarly, foil segments are threaded on the foot line  6  and side lines  8  to generate lift downwardly and laterally and thereby replace the weights  5  and trawl doors  7 . In this embodiment, as illustrated in  FIG. 4 , the head line  4 , foot line  6 , and side lines  8  are schematically shown as a single continuous line, defining the mouth opening  2 . In other embodiments, the foil segments  11  may be threaded on separate head lines  4 , foot lines  6 , and side lines  8 . As shown in  FIG. 4 , the mouth opening  2  is elliptical, but the foil segments  11  and lines  4 ,  6 , and  8  may be configured to generate lift forces appropriate for a mouth opening  2  of any desired shape. In this embodiment, the foil segments  11  generate all the spreading forces required to spread the mouth opening  2  of the net  1  as the trawl is towed through the water. 
     In another embodiment, as shown in  FIGS. 5 and 7   a , foil segments  11  are threaded on a foil line  14 , which is attached to the side lines  8  to provide lateral forces to spread the mouth opening  2  of the net  1 . The foil line  14  is independent of the head line  4 , foot line  6 , and side lines  8 , and is threaded through the forward internal conduits  12  of the foil segments  11  and attached at both ends to one of the side lines  8 . The foil line  14  may be a cable, rope, wire, chain, or other type of rigging line that passes through the forward internal conduits  12  of each of the foil segments  11  and may be secured at either end of the foil segments  11 , for example by knotting the cable to prevent egress, as shown in  FIG. 7 a   . Alternatively, the foil line  14  may be attached to one of the side lines  8  by way of bridle lines  15 . 
     The foil segments may also have an aft internal conduit  18  along the span and forward of the trailing edge  19 , as shown in  FIG. 3 a   . When both ends of the foil line  14  are attached to one of the side lines  15 , a second foil line  17  may be threaded through the aft internal conduits  18  of each foil segment  11 , as shown in  FIGS. 7 a , 7 b   , and  8 . In this configuration, the foil segments  11  are longitudinally aligned to form a wing section. The foil lines  14  and  17  permit steering of the foil segments  11  as described in PCT/CA2012/000996 entitled “Steerable Fairing String”. Alternatively, the second foil line  17  may be omitted and the foil segments  11  strung along only the foil line  14 . In embodiments where the second foil line  17  is omitted asymmetric foils are used whereby the foil segments  11  assume a non-zero equilibrium angle of attack and thereby generate lift in the desired direction. 
     Alternatively, the foil line  14  may be attached to one of the side lines  8  by way of bridle lines  15 , as shown in  FIG. 5 . The lengths of the bridle lines  15  are selected to maintain a vertical and linear, or longitudinally aligned, stack  16  of foil segments  11  when the trawl is being towed through the water. Preferably, the bridle lines  15  are attached at one end to the foil line  14  between each foil segment  11  in the stack  16 . At the other end, the bridle lines  15  are attached to spaced apart locations on one of the side lines  8 . This configuration of a stack  16  of foil segments  11 , attached to one of the side lines  8  by way of bridle lines  15 , is referred to herein as a segmented-foil. Similarly, a second foil line  17  may be threaded through the aft internal conduits  18  of each foil segment  11  to provide additional structural support to the stack  16  and to provide steerability, as will be described hereafter. 
     Alternatively, as shown in  FIG. 6 , the conventional trawl doors may be replaced by a segmented-foil attached to the warp line  20  by way of a generally triangular-like bridle  21 , as described in PCT/CA2015/000593 entitled “Segmented-Foil Divertor”. The bridle  21  is attached at one end to the warp line  20  and at the other end to the stack  16  of foil segments  11 , as shown in  FIG. 9 . Alternatively, rather than attaching the bridle  21  to the warp line  20 , it may be attached at any desired location about the mouth opening  2  of the trawl. 
     The bridle  21  has an apex, sides, and a base, defining its triangular-like shape. The apex is defined by a connection point between the bridle  21  and the warp line  20 . The sides are defined by a number of bridle lines  15 . A first bridle line  15   a  is attached between the connection point and one end, the top end  16   a , of the stack  16  and a second bridle line  15   b  is attached between the connection point and the other end, the bottom end  16   b , of the stack  16 . One or more intermediate bridle lines  15   c  are also attached between the connection point and the stack  16  between the opposing ends of the stack  16 . Optionally, branching bridle lines  15  are used to complete the bridle rigging, as shown in  FIG. 9 . Preferably, the bridle lines  15  attach to the plurality of foil segments  11  by way of attachment to the foil line  14  at each free end of the foil line  14  extending outwardly from each end of the stack  16  and in between each foil segment  11 . Optionally, the free ends of the foil line  14  may be continuous with the bridle lines  15 . Alternatively, the bridle lines  15  may be attached directly to one or more of the plurality of foil segments  11 . 
     The length of the bridle lines  15  are selected to maintain a vertical and linear, or longitudinally aligned, stack  16  of foil segments  11  when the segmented-foil is being towed through the water, as shown in  FIG. 9 . In this embodiment, the sides of the bridle  21  are of equal length. Alternatively, the relative length of the bridle lines  15  on the top half of the stack  16  may be selected to be longer than those on the bottom half of the stack  16  to maintain an angled stack  16 , as shown by the angle θ in  FIG. 10 . In this embodiment, the sides of the bridle  21  are of unequal length. The positive or negative angle θ by which the stack  16  is offset from the vertical, as shown in  FIG. 10 , may be selected to produce a force with a component in the vertical direction. This enables the segmented-foil to be used both as a divertor to position the towed equipment laterally to one side or the other of the towing vessel, and also as a depressor to position the towed equipment at a desired depth. Alternatively, the length of the bridle lines  15  may be selected to maintain a curved stack  16 , as shown in  FIGS. 8 and 11 . Bridle line lengths are thus selected to impart the desired stack shape to the segmented-foil. 
     The foil lines  14  and  17 , threaded through the forward and aft internal conduits  12  and  18  of the foil segments  11 , will assume a curved profile, as shown in  FIGS. 5 and 8 , as they are towed through the water. The length of either of the foil lines  14  and  17  may be selectively varied to control the angle of attack of the foil segments  11 , thereby producing more or less lift. 
     Preferably, as shown in  FIG. 7 b   , the sides of the foil segments  11  converge rearwardly, such that the span decreases from the leading edge  13  to the trailing edge  19  to provide each foil segment  11  with a trapezoidal shape and a wedged gap, or divergent angle φ, between foil segments  11 . Preferably, the trapezoidal foil segments  11  are used in combination with bridle lines  15  configured to maintain a curved profile, as shown in  FIG. 11 . In this configuration, the length of the second foil line  17  passing through the aft internal conduits  18  of the stack  16  may be selectively shortened to draw the rear edges of the foil segments  11  together and close the divergent angle φ, shown in  FIG. 7 b   . As the rear edges of the foil segments  1  are drawn together, each foil segment  11  rotates about the foil line  14 , changing its angle of attack as it is towed through the water, as shown in  FIG. 8 . This occurs because the combined length of the leading edges  13  of the foil segments  11  is longer than the combined length of the trailing edges  19 . 
     An adjuster mechanism, as shown in  FIG. 12 , may be connected to the second foil line  17  to operationally and selectively shorten or lengthen the second foil line  17  to adjust the angle of attack of the foil segments  11  in the segmented-foil. The adjuster mechanisms may include a turnbuckle  22  and pulley  23 , installed on the foil line  17  between the foil segments  11  and a pod  24 , which houses the communication and electronic components of the adjuster mechanism. Alternatively, a ratchet winch may be used. For automated adjustment of the foil line  17 , an electric solenoid may be used. Alternatively, a hydraulically or pneumatically controlled ram and piston, an electric winch, or a motor driving a rack and pinion may be used. 
     Adjusting the angle of attack results in more or less force from each foil segment  11 . Maximum force is achieved when the divergent angle φ is completely closed. Accordingly, the overall amount of force produced by the segmented-foil may be controlled selectively by the adjuster mechanism as the segmented-foil is towed through the water. This may be controlled automatically or manually by an operator on the towing vessel, by known methods of remote controlling towed equipment. Alternatively, the length of the second foil line  17  may be set at the time of deployment. 
     Although the embodiments shown in  FIG. 5  are described with reference to the side lines  8 , foil segments  11  threaded on a foil line  14  or a segmented-foil may also be attached to the head line  4  or the foot line  6  to provide lift upwardly or downwardly. In some embodiments, the trawl is thereby provided with steerability in the vertical direction. In addition, the embodiment shown in  FIG. 4  may include two headlines  4 , two foot lines  6 , and two pairs of side lines  8  passing through the forward and aft internal conduits  12  and  18  of each foil segment  11 . The trawl is thereby provided with steerability as described above, by adjusting the relative lengths of the two head lines  4 , two foot lines  6 , or either of the two pairs of side lines  8 . Preferably, a separate adjuster mechanism is engaged with each of the two head lines  4 , two foot lines  6 , and the two pairs of side lines  8 . For example, four such adjuster mechanisms permit steerability of the trawl vertically and laterally through lengthening or shortening of the head lines  4 , foot lines  6 , or side lines  8 . 
     In a conventional trawl configuration, two one-inch (1″) diameter steel cables are used for warp lines  20 , which are deployed from port and starboard reels on the deck of the tow vessel and connected to the port and starboard trawl doors  7 . As shown in  FIG. 6 , the trawl may be towed by a single warp line  20  connected to the tow vessel, rather than the conventional trawl configuration, which is towed by two warp lines  20 , as shown in  FIG. 1B . The warp line  20  is split into two secondary warp lines  20   a  near the end attached to the trawl. Each secondary warp line  20   a  attaches to a segmented-foil on either side of the mouth opening  2 . Alternatively, the secondary warp lines  20   a  may attach directly to the side lines  8  or another point on the rigging about the mouth opening  2  of the net  1 . The use of a single warp line  20 , rather than two warp lines  20 , reduces drag and thereby reduces the force required to spread the mouth opening  2  of the net  1  and the back deck handling equipment required to deploy and retrieve a trawl with two warp lines  20 . 
     In some embodiments, which include steerability, remote control may be provided by way of an adjuster mechanism which communicates with onboard equipment on the tow vessel and controls the relative lengths of the foil lines  14  and  17 , or other lines, passing through the forward and aft internal conduits  12  and  18  of the foil segments  11 . Communication between the vessel and the adjuster mechanism may be provided by known means already in common practice in the commercial fishing industry, for example, Ultra-Short Base Line (USBL) communication with acoustic modems. 
     The scope of the following claims should not be limited by the preferred embodiments set forth herein, but should be given the broadest interpretation consistent with the specification as a whole.