Patent Application
20050160656
The present invention relates generally to the technical field of trawls used for fishing and, more particularly, to an improved construction for self-spreading mid-water trawls.
In the field of pelagic and semipelagic fisheries a well recognized problem exists that a targeted species is frequently intermingled with one or more untargeted species. Thus, catching a targeted species with currently available pelagic fish nets, such as pelagic trawl nets that are also known as mid-water trawls, inadvertently results in undesired catching of non-targeted species, frequently referred to as “bycatch.
In the North Pacific Pollock fishery, for example, the targeted species is often densely intermingled with other species. However, during many fishing conditions a comparatively thin strata of water is often substantially free of the non-targeted species, while simultaneously possessing an acceptable density of the targeted species. Directly above this comparatively thin strata that holds an acceptable density of the targeted species and is substantially free of the non-targeted species, there tends to exist a much thicker strata of water that is densely occupied both by the non-targeted and the targeted species. Usually there are neither targeted species nor non-targeted species below the comparatively thin strata that holds an acceptable density of the targeted species and is substantially free of the non-targeted species. Consequently, fishing vessels, that can be penalized for catching non-targeted species, want to fish with maximum efficacy in the narrow strata of water that is substantially free of the non-targeted species thereby reducing and, if possible, avoiding bycatch.
Conventional mid-water trawls, i.e. non self-spreading trawls which are in general cone-shaped and are rather long from front to rear, are substantially less effective if their design or use exhibits a wide horizontal mouth opening and a short vertical mouth opening, e.g. an opening that is 75-200% or more wider than tall. One reason such conventional trawls are less effective if they have such a high aspect ratio mouth opening is that the relatively short vertical opening does not transfer vertically oriented opening forces well from the mouth of the trawl far back to the rear sections of the trawl.
For the preceding reason, conventional mid-water trawls which are intended to exhibit a horizontal mouth opening which is at least 2 times greater than the trawl's vertical opening (i.e. 100% greater) are designed with side panels that are intended to be fished with far lower angles of mesh cell opening in an attempt to reduce the compressive force generated by constriction, i.e. loss of width, of diamond trawl meshes under load. The greater the mesh cell opening angle to achieve a certain mesh cell width, the greater potential for compressive forces due to constriction of loaded mesh cells. Such compressive force occurring in the trawl's side panels tend to collapse the trawl's vertical opening in the aft section of the trawl.
In an attempt to address the problem caused by loaded side panel mesh cells having substantial opening angles collapsing a trawl's vertical opening, contemporary conventional trawls designed to exhibit a high aspect ratio have side panels in which the number of similar sized mesh cells in any particular cross-sectional cut across the trawl have far smaller angles of opening compared to mesh cells in the trawl's top or bottom panels. To obtain these smaller angles of mesh cell opening in side panels, the ratio of the width of the top and bottom panels to the width of a side panel in any particular cross-sectional cut across the trawl of a trawl tends not to exceed 1.25:1 (one point two five to one), and more commonly 1:1 (one to one). Nevertheless, trawls with such closely similar panel widths are then fished with a ratio of horizontal to vertical mouth opening that exceeds 1.5:1 (one point five to one), and often as great as 2.5:1 (two and a half to one), and even more. The contemporary thinking tends to be that low angles of mesh cell opening in the side panels reduces compressive forces that constrain the trawls vertical opening, and maximize deflected water impact force which aids in expanding the trawl in the horizontal plane with less compressive force in the vertical plane thereby preventing the trawl's collapse.
In addition to the above mentioned difficulties, such contemporary conventional trawls designs are relatively expensive to manufacture because they require a comparatively large number of mesh cells and material for narrower side panels. Furthermore, since contemporary conventional trawls lack any force which tends to actively maintain vertical opening, the trawls vertical opening tends to be lost under real fishing conditions which frequently collapses the trawl's aft end. Furthermore, such trawls also tend to produce unwarranted bycatch, for example of marine mammals.
Published Patent Cooperation Treaty (“PCT”) International Patent Applications WO 97/13407, WO 98/46070 and WO 99/39572 (“the published PCT patent applications”) describe various structures and construction techniques for assembling mid-water trawls in which mesh bars forming the trawl's mesh cells, when towed through a body of water, actively produce outwardly directed lift, i.e. lift which has a component directed away from the trawl's central axis. As disclosed in the published PCT patent applications, threads, such as twines, cords, braided cords, cables, ropes or straps, may be advantageously twisted, during assembly of mesh bars which form a trawl's mesh cells, into a loose, corkscrew-shaped pitch thereby establishing helical grooves that are deeper and broader than the depressions in conventional tightly or loosely twisted three-strand ropes or cables. When a properly configured trawl having mesh bars which possess such helical grooves is towed through a body of water, cambered sections established by the helical grooves produce outwardly directed lift. The published PCT patent applications are hereby incorporated by reference as though fully set forth here.
A belief generally exists that self-spreading trawls assembled in accordance with the published PCT patent applications cannot provide a high aspect trawl mouth opening, i.e. a self-spreading trawl in which the top and bottom panels are wider in calculated overall width than the side panels when considering the mesh cell size and the planned percentage opening of the mesh cells. It has been believed that the spreading force of doors included in a trawl system is such that any additional horizontal outwardly directed lift would collapse the already more narrow vertical opening of a self-spreading trawl. Moreover, use of lift generating mesh bars in assembling mesh cells of “wide body” trawls, i.e. trawls in which at any particular cross-sectional cut across the trawl the top and bottom panels are substantially wider than the height of the trawls side panels for equal mesh cell opening angle, has been unanimously deemed a failure by trawl manufacturers.
The published PCT applications disclose many different ways in which threads, such as twines, cords, braided cords, cables or ropes, may be twisted, during assembly of mesh bars which form a trawl's mesh cells, into a loose, corkscrew-shaped pitch with helical grooves. However, of the many different ways in which threads may be twisted into a loose, corkscrew-shaped pitch with helical grooves, for economic reasons only a few of the many different techniques disclosed in the published PCT applications have been used thus far in commercially manufactured mid-water trawls.
One technique used commercially for forming mesh bars which have a loose, corkscrew-shaped pitch with helical grooves is that depicted in
Another technique used commercially for forming mesh bars which have a loose, corkscrew-shaped pitch with helical grooves is that depicted in
BRIDLES relates to lines that intersect the frontropes and attach to the tow lines. For a particular port or starboard tow line, a pair of bridles extend from a common connection point therewith, back to the frontropes.
CELL means a trawl construction unit used in fishing nets or the like and includes both a mesh cell relating to enclosable sides of the mesh of the trawl or net itself, as well as to upper bridle and frontropes used in towing the trawl or net through a water column to gather marine life.
CELL BAR means both the sides of a mesh cell and the elements that make up the upper bridle, frontropes and tow lines.
CODEND or BRAILER BAG is a portion of a trawl positioned at the trailing end thereof and comprises a closed sac-like terminus in which the gathered marine life including fish are trapped.
CATCH PER UNIT EFFORT (“CPUE”) is the total tonnage of fish caught with a trawl divided by the total fuel a vessel consumes while fishing with the trawl.
FRAME is a portion of the larger sized meshes of a net or trawl upon which is overlaid a netting of finer construction.
FRONTROPE(S) is a term that includes all lines located at perimeter edge of the mouth of the trawl, net or the like, such as headrope, footrope (or bottomrope) and breast lines. The frontropes have a number of connections relative to each other and to the bridle lines.
INTERNAL BRAID describes the method of formation of a particular product strand.
INTERNAL LAY OR TWIST is the direction in which synthetic or natural fibers comprising each product strand are wound when such strand is viewed axially and in a receding direction.
LAY is the direction in which the strands or the straps making up mesh bars twist when viewed axially and in a receding direction.
MESH is one of the openings between threads, ropes or cords of a net.
MESH BARS means the sides of a mesh cell, and does not include knots or equivalent couplers unless otherwise specified.
MESH CELL means the sides of a mesh and includes at least three sides and associated knots or equivalent couplers oriented in space. A quadratic mesh cell has four sides with four knots or couplers, and is usually arranged to form a parallelogram (including rectangular and square), with diamond-shaped mesh (trawl mesh) being preferred. A triangular mesh cell has three sides and three knots or couplers. A hexagonal mesh cell has six sides and six knots or couplers.
NET is a meshed arrangement of threads that have been woven or knotted or otherwise coupled together usually at regular intervals or at intervals that vary usually uniformly along the length of the trawl.
PANEL is one of the sections of a trawl and may be made to fit generally within and about frame ropes, including riblines, that are offset from the central axis of the trawl.
PITCH is the amount of advance viewed axially:
For product strands, pitch values are determined with respect to the diameter of the next-to-largest product strand. For straps, pitch values are determined with respect to the width of the strap.
PRODUCT STRAND includes the synthetic or natural fibers or filaments used to form the construction unit of the invention which is preferably, but not necessarily, the product of a conventional manufacturing process. Product strands are preferably made of synthetic fibers or filaments which are preferably, but not necessarily, the product of a conventional manufacturing process, usually made of nylon, polyethylene, polyester, or the like. Such strands can be twisted, plaited, braided or laid parallel to form a sub-unit for further twisting or other use within a mesh bar or a cell bar in accordance with the invention.
RIGHT- AND/OR LEFT-HANDEDNESS IN A RECEDING DIRECTION along a cell bar involves establishing a central axis for the trawl, net or the like to which the mesh cell associated with the cell bar belongs. Then a normalized imaginary giant stick figure, that is depicted in FIGs. of the published PCT patent applications, is positioned so his feet intersect the central axis, are rotatable about the central axis, his body penetrates through the cell bar, and his back is positioned perpendicular to and first intersects the water flow vector for the moving trawl, net or the like. The right- and/or left-handedness of the cell bar is then determined using the location of either his right or his left arm irrespective of the fact that the position of the cell bar is offset from the central axis.
STRAP is a flexible element of synthetic or natural fibers that forms a mesh bar, the strap having a cross-section that is generally rectangular or can be quasi-rectangular with rounded short sides and elongated long sides with or without camber. In operation, the strap acts as a hydrofoil, preferably twisted along its longitudinal axis, wherein the short sides form interchanging leading and trailing edges.
THREADS are composed of synthetic or natural fibers. Firstly, for the present invention a thread can comprise two strands twisted along the longitudinal axis of symmetry in a loose fashion with a pitch in a range of 3d-70d, where d is:
Or secondly, for the present invention a thread can comprise a extruded, woven, braided, or plaited strap that is twisted along its longitudinal axis of symmetry in a loose fashion with a pitch in a range of 3d-70d, where d is the width of the strap.
TRAWL is a large net generally in the shape of a truncated cone trailed through a water column or dragged along a sea bottom to gather marine life including fish.
TRAWL SYSTEM is a term that includes the trawl, net or the like in association with the tow lines therefor as well as the bridles lines.
An object of the present invention is to provide a trawl that reduces bycatch.
Another object of the present invention is to provide a self-spreading trawl which when towed through a body of water has a mouth which exhibits a high aspect ratio.
Another object of the present invention is to provide a self-spreading trawl which when towed through a body of water has a mouth which exhibits a high aspect ratio while concurrently maintaining an open back-end.
Another object of the present invention is to provide a self-spreading trawl which when towed through a body of water has a mouth which exhibits a high aspect ratio while concurrently requiring a lesser amount of weights about a footrope of the trawl.
Another object of the present invention is to provide a self-spreading trawl in which the top panel has a width that is at least twenty percent (20%) greater, and preferably at least forty percent (40%) or more greater, than the width of the trawl's side panels.
Yet another object of the present invention is to provide self-spreading trawls made with unitary mesh bars which are more rugged, and the ends of which may be joined together using strength retaining spliced eyes.
Briefly the present invention in one embodiment is an improved self-spreading trawl which during field operations in a body of water becomes disposed about a central axis. The trawl includes a mouth that is disposed:
An improved self-spreading trawl in accordance with the present invention also includes a first pair of panels which when the trawl is towed through a body of water become separated on opposite sides of the trawl's central axis. Portions of the first pair of panels form portions of the mouth of the trawl. The improved self-spreading trawl also includes a second pair of panels which when the trawl is towed through a body of water become separated on opposite sides of the central axis of the trawl which differ from the sides of the central axis on which the first pair of panels becomes disposed. Portions of the second pair of panels form portions of the mouth of the trawl which differ from the portions of the mouth of the trawl formed by portions of the first pair of panels.
Regions of the second pair of panels in the improved self-spreading trawl are configured to generate more outwardly directed lift that is directed away from the central axis of the trawl than corresponding regions of the first pair of panels. Thus, when the trawl is towed through a body of water:
Another aspect of the present invention is a braided product strand which when towed through a body of water exhibits less drag and vibration. The braided product strand includes at least 3 (three) plaits, at least one of which has a larger cross-sectional area than other plaits included in the product strand. The larger plait(s) has a cross-sectional area that is/are at least 0.9 (nine tenths) times larger than a combined cross-sectional area of all other plaits also included in the product strand.
An advantage exhibited by trawls which practice the present invention is that they may be fabricated with a ratio of width of the top and bottom panels relative to width of the side panels of 1.5:1 (one and a half to one) and may even equal or exceed a ratio of 2.0:1 (two to one). Since when being towed through a body of water mesh cells included in side panels generally exhibit considerably lower angles of mesh opening compared to the angle of mesh openings of mesh cells in the top and bottom panels, the aspect ratio of the mouth opening can considerably exceed the width ratios of the top and bottom panels relative to the side panels. Trawls having such width ratios of top to side panels when configured in accordance with the present invention exhibit surprisingly better vertical opening particularly in the mid-section and back-end together with wide horizontal opening. For such trawls when towed by similarly powered vessels the horizontal mouth opening for a particular vertical mouth opening significantly exceeds that of known trawls. Ratios of horizontal mouth opening compared to vertical mouth opening greater than 3:1 (three to one), 4:1 (four to one), 5:1 (five to one), 6:1 (six to one), 7:1 (seven to one), and even greater than 10:1 (ten to one) have been modeled for a wide range of bollard pull values, including relatively low bollard pull values as are exhibited by comparatively low horsepower vessels. Consequently, assembling trawls in accordance with the present invention permits custom design of trawl opening and fishing parameters to reduce fuel consumption, reduce bycatch, and better operations compared with present conventional trawl constructions and methods. The present invention is most useful if bettering fishing gear's CPUE and reducing bycatch are primary objectives.
These and other features, objects and advantages will be understood or apparent to those of ordinary skill in the art from the following detailed description of the preferred embodiment as illustrated in the various drawing figures.
Referring to
As depicted in
As illustrated in
The trawl 13 also preferably includes both an upper starboard ribline 52us and an upper port ribline 52up, both depicted in
Usually, product strands forming the riblines 52 are 1.0 to 1.5 inches in diameter. The riblines 52 for the forward section 24 of the trawl 13 are preferably made from fibers which exhibit high elasticity. Conversely, the riblines 52 for the back-end 28 are preferably made from a material which exhibits low elasticity. For example, riblines 52 in the aft end of the trawl 13 may be made from a material which elongates less four percent (4%) when the trawl 13 is towed through the body of water 12.
In the plan view of the trawl 13 depicted in
As depicted in
When the trawl 13 is towed through the body of water 12, all of the panels 56 are offset from a central axis 62 of the trawl 13. Consequently, configured in this way the top panel 56T and the bottom panel 56B are separated on opposite sides of the central axis 62, and the side-panels 56S, 56P are also separated on opposite sides of the central axis 62 which differ from the sides on which the top panel 56T and bottom panel 56B are disposed. Furthermore, a forward portion of each of the panels 56 of the forward section 24 form different portions of the mouth 26 of the trawl 13.
As depicted in
One characteristic of the mesh bars 72 depicted in
To increase the lift generating capability of the mesh bar 72 depicted in
For the mesh bar 72 depicted in
Compact twine braided constructions for the helixing product strand 76, i.e. where a core of parallel or twisted filaments (including slightly twisted filaments) is encased by a braided jacket, has surprisingly and unexpectedly been shown to increase lift and to reduce drag, particularly when the filaments are a made from a hydrophobic material including high tenacity and conventional polyethylene. Such compact braided twine constructions demonstrate, surprisingly, more than a 50% increase in lift relative to non-compact braided twine constructions of the same filaments.
Further, in reference to the mesh bar 72 depicted in
To further increase lift, additional product strands, not illustrated in any of the FIGs., of the same or smaller diameter as the product strand 76, may be placed directly adjacent to and parallel to product strand 76. For example, two, three, or more additional product strands 76 helixing about product strand 77 increase hydrofoil characteristics such as useful camber, and provide a mesh bar 72 which provides more lift. A pair of larger and smaller product strands 76, with the mesh bars 72 oriented so that the larger product strand 76 mainly meets the water flow first, also proves to be advantageous.
Since the shape of the trawl 13 varies along the central axis 62 from almost rectangularly or elongated and quasi-rectangularly shaped at the wings 25 to a shape that more nearly approaches a frustum of a cone throughout the forward section 24, mid-section 27 and back-end 28, the longitudinal axis of symmetry 30a of individual mesh cells 30 have varying orientations with respect to the central axis 62 of the trawl 13. Thus, with respect to the central axis 62 of the trawl 13, the longitudinal axes of symmetry 30a of mesh cell 30 may be parallel, non-parallel and non-intersecting, and/or non-parallel and intersecting. However, note that longitudinal axes of symmetry 30a of the mesh cells 30 are always offset from the central axis 62 of the trawl 263.
As depicted in
Furthermore, as described in greater detail below, in accordance with the present invention the mesh cells 30 included in the side-panels 56S, 56P of the trawl 13, which may or may not be separated from the top and/or bottom panel by riblines 52, are preferably assembled from mesh bars 72 or straps 92 having either or several:
Any of the preceding differences between mesh bars 72 or straps 92 of the side-panels 56S, 56P are selected to generate more outwardly directed lift for mesh bars 72 of the side-panels 56S, 56P than similarly directed lift generated by mesh bars 72 or straps 92 of the mesh cells 30 of the top panel 56T and/or bottom panel 56B. Consequently, for areas of the side-panels 56S, 56P having similarly sized mesh cells 30, the side-panels 56S, 56P preferably generate more outwardly directed lift per unit area than the top panel 56T or bottom panel 56B.
The various alternative constructions described above are particularly advantageous when the designed horizontal distance across the trawl 13 in the wings 25 and in the forward section 24 exceeds the designed height thereat. Advantageously the designed horizontal distance across the trawl 13 in the wings 25 and in the forward section 24 exceeds the designed height thereat by a ratio of at least one and fourteen-hundredths to one (1.14:1), by a ratio of one and two-tenths to one (1.2:1), and preferably by a ratio of one and seven-tenths to one (1.7:1) or greater. That is, when the designed maximum width of the top panel 56T and the bottom panel 56B compared to the maximum designed width of the side-panels 56S, 56P equals or exceeds one and fourteen-hundredths to one (1.14:1) or one and two-tenths to one (1.2:1). For such designs, the intended percentage of mesh opening of mesh cells 30 in the panels 56 is preferably less than the intended percentage of mesh opening in mesh cells 30 that are located in corresponding regions of the top panel 56T and/or bottom panel 56B. Generally, it is desirable that mesh cells 30 attached to any of the breastlines 42, the footrope 44 or the headrope 46 open at least twenty-five percent (25%), with mesh cells 30 attached to the footrope 44 or the headrope 46 opening thirty percent (30%).
In accordance with the present invention the mesh cells 30 in the side-panels 56S, 56P are preferably assembled using mesh bars 72 that generate more lift than mesh bars 72 of the top panel 56T and/or the bottom panel 56B when the ratio of the horizontal opening of the mouth 26 to its vertical opening is to equal or exceeds 2:1, (two to one), and applies as well when the ratio is 2.5:1 (two and one-half to one), 3:1 (three to one), and even 10:1 (ten to one), or greater. However, the greater the desired horizontal opening of the mouth 26 relative to the vertical opening, the more important it becomes to assemble mesh cells 30 of the side-panels 56S, 56P with mesh bars 72 that correspondingly produce more outwardly directed lift than the mesh bars 72 used in assembling the mesh cells 30 of the top panel 56T and/or the bottom panel 56B. Since mesh bars 72 in the mesh cells 30 of the side-panels 56S, 56P generally intersect the water flow vector 86 at a lower angle of attack than mesh bars 72 in the top panel 56T and the bottom panel 56B, the cambered sections 88 of mesh bars 72 in the side-panels 56S, 56P are selected to provide a better lift constant (lift coefficient divided by drag coefficient) at this lower angle of attack.
It will be readily apparent to those skilled in the art that, depending upon design goals for a trawl 13, a wide range of different sizes of mesh bars 72 or, alternatively, different lift generating mesh bars 72 may be used in mesh cells 30 of the side-panels 56S, 56P versus mesh bars 72 used in mesh cells 30 of the top panel 56T and the bottom panel 56B. Thus, a wide range of different diameters and/or combinations of self-spreading mesh bars 72 and sizes of mesh cells 30 in the side-panels 56S, 56P relative to the top panel 56T and/or the bottom panel 56B are intended to be within the scope of the present invention. For example, differences of diameters and/or lift generation exhibited by mesh bars 72 may vary to from 10% to 700%, or greater, in side-panels 56S, 56P verses the top panel 56T and/or the bottom panel 56B. Furthermore, those skilled in the art will also understand that mesh bars 72 which generate different amounts of outwardly directed lift may be used at specific locations within a particular panel 56t, 56P, 56S and/or 56B. For example, it may be desirable to use mesh bars 72 which generate more outwardly directed lift in the wings 25 of the side-panels 56S, 56P while progressively reducing the lift generating characteristic of mesh bars 72 in the side-panels 56S, 56P toward the rear of the trawl 13. Thus in the rear of the forward section 24, for example where mesh cell sizes eight (8) or four (4) meters or less, there may exist no difference in the size and/or lift generating characteristics of the mesh bars 72 forming mesh cells 30 in any of the panels 56. Consequently, when a trawl 13 in accordance with the present invention is towed through the body of water 12 the mid-section 27 and the back-end 28 tend to adopt a more tubular cross-sectional shape than the mouth 26 which tends to adopt a rectangular or elongated oval cross sectional shape.
Furthermore, trawls 13 in accordance with the present invention having a horizontal opening of the mouth 26 which exceeds 2.5 times the vertical opening, that are intended for use in catching pelagic species, may also include riblines 52 that change orientation relative to the mesh cells 30 so that toward the aft end of the trawl 13 the number of mesh cells 30 and the length of the mesh bars 72 in the respective panels 56 differ less than near the mouth 26 of the trawl 13. In accordance with the present invention, toward the aft end of the trawl 13 there may exist no difference in the number of mesh cells 30 or the length of mesh bars 72 across any of the panels 56 that respectively span between the four pairs of riblines 52. For such a trawl 13, the side-panels 56s, 56P taper far less from the front to the back of the trawl 13 than the taper of the top panel 56T and/or the bottom panel 56B. Thus a ratio between the number of mesh cells 30 across the various panels 56 toward the aft end of the trawl 13 may be less than 2:1 (two to one), and may even become 1:1 (one to one).
For one particular trawl 13 constructed in accordance with the present invention when towed by a comparatively low powered vessel 10 and while concurrently maintaining desired vertical dimensions in the aft end of the trawl 13, the horizontal opening of the mouth 26 exceeded seventy (70) fathoms while the vertical opening was twenty (20) fathoms, a ratio of 7:2 (seven to two). Horizontal openings exceeding 10:1 (ten to one) have been modeled without loss of other trawl performance characteristics.
Presently designs for trawls 13 which exhibit an opening at the mouth 26 of a trawl 13 such as 7:2 (seven to two) while retaining other performance characteristics such as large vertical opening in the back-end 28 are unknown, and are therefor available for the first time through use of the present invention. For such trawls 13, at corresponding locations along the length of the trawl 13 and for similarly sized mesh cells 30, lift generating mesh bars 72 of the side-panels 56S, 56P exhibit at least one and one-half times more outwardly directed lift per meter than that generated by mesh bars 72 used in the top panel 56T and/or bottom panel 56B. Preferably, the mesh bars 72 used in assembling similarly sized mesh cells 30 of the side-panels 56S, 56P generate two (2) to eight (8) times more outwardly directed lift per meter than that generated by mesh bars 72 used in the top panel 56T and/or bottom panel 56B. This difference in outwardly directed lift per unit length of mesh bars 72 between the side-panels 56S, 56P and the top panel 56T and bottom panel 56B applies readily to large mesh portions of the trawl 13 such as mesh cells 30 that are eight (8) meters or more in overall length, and preferably for mesh cells 30 that are sixteen (16) meters or more in overall length.
As described above, one method for obtaining the greater lift per unit length of self-spreading mesh bars 72 in the side-panels 56S, 56P than in the top panel 556T of bottom panel 56B is by using larger diameter product strands 76, 77 for the mesh bars 72 in the side-panels 56S, 56P compared with the product strands 76, 77 used in the top panel 56T or bottom panel 56B. Another method described above achieves a high aspect ratio mouth opening using mesh bars 72 having similar diameters in the top panel 56T and side-panels 56S, 56P if, when towed through the body of water 12, the mesh bars 72 in the side-panels 56S, 56P provide greater lift constants (lift coefficient divided by drag coefficient) at designed angles of incidence to the water flow vector 86 in comparison with lift constants of mesh bars 72 in the top panel 56T. Yet another method is using different constructions for the self-spreading mesh bars 72. For example, constructions such as or similar to that shown in
Another method for increasing the amount of outwardly directed lift produced by the side-panels 56S, 56P in comparison with lift produced by the top panel 56T and bottom panel 56B, which also opposes trends in the industry, is concentrating more self-spreading mesh cells 30 in the side-panels 56S, 56P in comparison with the mesh cells 30 in the top panel 56T and bottom panel 56B, while either:
Consequently, due to smaller size mesh cells 30 in the side-panels 56S, 56P and larger size mesh cells 30 in the top panel 56T and bottom panel 56B at corresponding locations along the length of the trawl 13 there exists more length of self-spreading mesh bars 72 in the side-panels 56S, 56P than in the top panel 56T and the bottom panel 56B. The greater length of self-spreading mesh bars 72 in the side-panels 56S, 56P generates more outwardly directed lift than that generated by the mesh bars 72 in the top panel 56T and bottom panel 56B. Contrary to popular belief, vertical opening at the mouth 26 of trawls 13 built in this way do not collapse, and, in fact, showed bettered vertical opening in the aft portions of the trawl 13 for a particular vertical opening at the mouth 26. For example, for a balanced design the size of mesh cells 30 of the top panel 56T and the bottom panel 56B may be forty five (45) meters at a particular location along the length of the trawl 13 while those in the same location in the side-panels 56S, 56P may be twenty-two and one-half (22.5) meters in length, i.e. a two to one (2:1) size relationship.
The preferred embodiments described above may be advantageously adapted for trawling deeper in the body of water 12, e.g. deeper than ninety (90) to one-hundred fifty (150) fathoms, when configured as illustrated in
Configured in this way, when the trawl 13 is towed through the body of water 12 the outwardly directed lift generated by the bottom panel 56B exceeds the outwardly directed lift generated by the top panel 56T. Thus, the greater amount of outwardly directed lift generated by the bottom panel 56B tends to pull the trawl deeper into the body of water 12 with a lesser amount of weights 23. The use of a lesser amount of weight on the trawl 13 permits placing more weight on the doors 19 and/or using heavier doors 19 which increases stability of the doors 19 particularly when being towed through a deep body of water 12 with lengthy main tow lines 18 extending between the vessel 10 and the doors 19. The use of a lesser amount of weights 23 also increases the efficacy of the trawl 13, reduces impact between the trawl 13 and the ocean bottom 14, and also reduces fuel consumption, concurrent pollution and environmental degradation.
If a targeted species occupies a thin strata of the body of water 12 near the surface 11, the preferred embodiment described above may be advantageously adapted for trawling shallow depths, e.g. less than thirty (30) fathoms deep. In configuring the trawl 13 for trawling in shallow depths:
Configured in this way, when the trawl 13 is towed through the body of water 12 the outwardly directed lift generated by the top panel 56T exceeds the outwardly directed lift generated by the bottom panel 56B. A trawl 13 constructed in this way tows nearer the surface 11 without adding floats to the trawl 13, and thereby increases the efficacy of the trawl 13, and also reduces fuel consumption, concurrent pollution and environmental degradation.
As shown in
Spreading forces generated by the side-panels 56S, 56P in the Spread Zone relative to spreading forces generated by the top panel 56T or bottom panel 56B in front of the dashed line 112 are significantly greater for a particular amount of drag. Thus, the spreading forces generated by the side-panels 56S, 56P in the Spread Zone assist the doors 19 in opening the mouth 26 of the trawl 13 horizontally which may permit:
The spreading force generated in the Spread Zone substantially betters horizontal opening of the trawl 13.
In
For the second embodiment of the present invention depicted in
For the trawl 13 in accordance with the present invention, relatively few or none of the permanent weights 23 are positioned along the center portion of the footrope 44, i.e. in the middle, or entire center third of the footrope 44 or even as much as the center eighty percent (80%), or more, thereof. With few or none of the permanent weights 23 located at the center of the footrope 44, progressively greater weight is disposed along the footrope 44 so the weight gradually increases, or increases in steps, from the center of the footrope 44 outward to the ends of the footrope 44 that are located at the wings 25. Configured in this way, the largest amount of the weights 23 occurs along that portion of the footrope 44 immediately adjacent to the wings 25. In addition to this permanent footrope weight, the trawl system 9 may also include readily changeable weights 23 that are located at the wings 25.
It is important that particular weight distributions for trawls 13 of the present invention, such as trawls 13 having panels 56 of the type depicted in
In some instances, a “hanging chain footrope” is suitable for inclusion in the weights 23 in which the footrope 44 is towed near the ocean bottom 14, particularly for reducing damage to the ocean bottom 14 and drag. In a “hanging chain footrope” embodiment, it is helpful if sections of chain incorporated into the hanging chain footrope 44 are longer than the synthetic or natural fiber rope also included in the footrope 44. If sections of chain incorporated into the hanging chain footrope 44 are longer than the rope included therein, the rope may stretch, including creep, without placing any undesirable tension on the chain.
For larger mesh cells 30 in the forward section 24 and mid-section 27 of the trawl 13, e.g. mesh cells 30 which equal or exceed four (4) meters in overall length, trawls 13 in accordance with the present invention are preferably assembled using a “Radial Pattern.” A Radial Pattern trawl 13 progressively reduces the size of mesh cells 30 from front to back of the trawl 13 through progressively shorter mesh bars 72. Thus, within individual mesh cells 30 of a Radial Pattern trawl 13 the two mesh bars 72 nearer the mouth 26 of the trawl 13 are longer than the two mesh bars 72 further from the mouth 26. One characteristic of such a trawl 13 is that despite tapering of the panel 56 the number of mesh cells 30 across a panel 56 remains constant throughout any portion that is assembled using the Radial Pattern. Thus, the portion of a trawl 13 assembled using a Radial Pattern lacks any abrupt change both in mesh bar length, e.g. halving of mesh bar length, or in the number of mesh cells 30 across a panel 56.
For example, in each mesh cell 30 of a Radial Pattern portion of a trawl 13, a ratio of length of mesh bars 72 nearer the mouth 26 of the trawl 13 to length of mesh bars 72 further from the mouth 26 may be 1.25:1 (one and a quarter to one), 1.35:1 (one and thirty-five hundredths to one), 1.1:1 (one and one tenth to one), etc. Preferably the ratio of lengths of mesh bars 72 nearer the mouth 26 of the trawl 13 and those further from the mouth 26 is between 1.15:1 (one and fifteen hundredths to one to one) and 1.2:1 (one and two tenths to one). Ratios exceeding 1.2:1 (one and two tenths to one) up to a 1.4:1 (one point four to one), or larger are less preferred.
To facilitate repair of the trawl 13 if damaged through contact with the ocean bottom 14, the Radial Pattern construction may not be used in the bottom panel 56B, particularly the portion of the bottom panel 56B nearest the footrope 44 at the weights 23 of the trawl 13. This portion of the trawl 13, which is most likely to experience such damage, is preferably assembled using smaller mesh cells 30 having uniform lengths for the mesh bar 72 which facilitates repair.
The constructions depicted in
In the illustration of
The larger cross-sectional area, interwoven plait, i.e. product strand 76, provides the mesh bar 72 with a loose, corkscrew-shaped pitch which establishes deep grooves 82 that are helically-shaped and deeper and broader than the depressions in conventional tightly or loosely twisted three-strand rope or cable. When mesh bars 72 of either type depicted in
Lacking the product strand 76, the mesh bars 72 depicted respectively in
In comparison with the mesh bar 72 depicted in
Similar to the product strand 76 depicted in
The mesh bar 72 depicted in
In general, as disclosed in published PCT patent application WO 98/46070, mesh bars 72 formed from bonded product strands 76, 77 exhibit significantly greater lift, e.g. a 1.3 to 1.7 or more greater lift, than unbonded product strands of identical diameter. Published PCT patent application WO 98/46070 specifically discloses that a densely laid, heat set and bonded product strand is preferred for reducing drag and increasing lift of mesh bars 72.
Subsequently, it has been discovered that, after being impregnated, loosely laid nylon product strands 76, 77 prove even more advantageous for mesh bars 72. Specifically, it has been discovered that impregnating, including bonding, previously soft product strands, i.e. product strands which have a substantially compressible cross section before applying an impregnation material, until they are no longer easily deformable provides mesh bars 72 which exhibit even more lift and even less drag than those disclosed in the published PCT patent applications. Product strands which are not easily deformable retain 80% of their cross-sectional width to height ratio upon application 6f one kilogram (1 kg) of pressure per square centimeter. Such product strands 76, 77 which are not easily deformable preserve the profile and configuration of the mesh bars 72, as well as that of the cambered sections created by the loose, corkscrew-shape during and after assembly of the trawl 13, particularly when tension is applied to the mesh bars 72.
Preferably, elastic materials, such as nylon including nylon braided product strands that are overbraided by other product strands, have a substantially compressible cross section prior to impregnation. A urethane polymeric material, or material having similar properties is a suitable material for impregnating the product strands. Applying the impregnation material prior to final assembly of the product strand, i.e. prior to final twisting or braiding, for example during stranding or to the core prior to braiding, is preferred for distributing the impregnation material into the interior of the finished product strand. Because lower drag is particularly important in panels 56 of trawls 13 of the present invention, the disclosure of product strands having substantially compressible cross sections prior to impregnation and substantially incompressible cross sections after impregnation is important to obtaining all the advantages of trawls 13 of the present invention.
To further enhance stability, twisted product strands 76, 77 preferably include three (3) primary sub-strands, where each of the sub-strands has a lay direction opposite to the lay direction of the product strands 76, 77. The product strands 76, 77 are preferably made as at least a three (3) stage product strand, and preferably have a soft, readily deformed construction before impregnation (including coating) and/or overbraiding, and a substantially incompressible construction after impregnation and/or overbraiding. Similarly, product strand 77 in the mesh bar construction depicted in
For product strands 76, 77 used in constructing mesh bars 72 illustrated in
For further drag reductions and useful lift enhancements, twisted product strands 76, 77 preferably have a different construction for at least one of the three (3) primary sub-strands. For example, one of the primary substrands may be more or less (preferably more) impregnated than the others, or may be of a denser construction than the others. Similarly, the sub-strands, or plaits, making up the braids of a mesh bar 72 as shown in
Such construction for product strands 76, 77 or for the mesh bar 72 depicted in
Because forming mesh bars 72 which provide cambered sections 88 established by the loose, corkscrew-shaped pitch of deep grooves 82 requires twisting pairs of product strands 76, 77 or straps 92, care must be exercised while assembling trawls 13 to eliminate any tendency for their mesh cells 30 to twist-up or wrap-up. Exercising insufficient care in assembling trawls 13 in accordance with the published PCT patent applications produces mesh cells 30 that twist-up or wrap-up. When towed through the body of water 12, self-spreading trawls 13 having mesh cells 30 that twist-up or wrap-up exhibit smaller opening, high drag, collapsing of the back-end 28, undesired bycatch, and/or increased CPUE. Therefore, commercial use of self-spreading trawls 13 that practice any of the inventions disclosed in the published PCT patent applications and in the present application benefits greatly through the use of manufacturing techniques that reduce or eliminate twisting and/or wrapping of mesh cells 30.
To reduce as much as practicable any tendency for twisting and/or wrapping of mesh cells 30, it is important that the filaments making up product strands 76, 77 or straps 92 be pre-shrunk. That is, before being twisted into a product strands 76 or 77 or being woven into a strap 92, the filaments used for manufacturing product strands 76, 77 or straps 92 should possess non-shrink properties, especially as obtained by preshrinking the filaments. A need to pre-shrink filaments before twisting them into product strands 76 or 77 or weaving them into straps 92 is in addition to any subsequent heat setting of the finished product strands 76 or 77 or strap 92 as disclosed in the published PCT patent applications.
Pre-shrinking is particularly advantageous when the product strands 76 or 77 or the strap 92 includes Nylon filaments, or other filaments which exhibit elastic properties similar to nylon filaments. Such materials are preferred for assembling mesh bars 72 such as those depicted in
After construction of the product strands 76 or 77 or strap 92 from pre-shrunk material, e.g. nylon filaments, as disclosed in the published PCT patent applications industry standard stabilization methods, including heat setting, are applied to the product strands 76 or 77 or to the strap 92. After heat setting, the finished product strands 76 or 77, when measured under tension of at least 10 kg [ten kilograms] and after having absorbed the water, shrinkage must not exceed 2%, and preferably does not exceed one 1%.
For the mesh bar construction depicted in
If product strands 76, 77 are prepared as described above, and if assembly of the trawl 13 scrupulously avoids imparting torque to mesh bars 72 mesh wrapping due to residual torque may be eliminated, or at least reduced to insignificant levels. For example, torque may be imparted to mesh bars 72 by:
Although the present invention has been described in terms of the presently preferred embodiment, it is to be understood that such disclosure is purely illustrative and is not to be interpreted as limiting. Consequently, without departing from the spirit and scope of the invention, various alterations, modifications, and/or alternative applications of the invention will, no doubt, be suggested to those skilled in the art after having read the preceding disclosure. Accordingly, it is intended that the following claims be interpreted as encompassing all alterations, modifications, or alternative applications as fall within-the true spirit and scope of the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US03/10114 | 3/22/2003 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 60367134 | Mar 2002 | US | |
| 60366834 | Mar 2002 | US |
