FAIRED TOWING CABLE

Abstract

A faired towing cable employed on a ship for towing a submersible body launched at sea is provided. The cable comprises a core and a fairing joined to the core. The fairing is profiled so as to reduce the hydrodynamic drag of the cable. The fairing comprises several leading edges and several trailing edges joined to the leading edges. One trailing edge is held directly on two adjacent leading edges.

Claims

1. A faired towing cable intended to tow a submersible body, the cable comprising a core and a fairing joined to the core, the fairing being profiled so as to reduce the hydrodynamic drag of the cable, the fairing comprising several leading edges and several trailing edges joined to the leading edges, wherein one trailing edge is held directly on two adjacent leading edges, in that the leading edges and the trailing edges are in one piece and made of homogeneous materials, and in that a Young's modulus of the material forming the leading edges is greater than a Young's modulus of the material forming the trailing edges.

2. The cable as claimed in claim 1, wherein the core extends mainly along an axis, and in that the trailing edges are disposed in a staggered manner with respect to the leading edges along the axis.

3. The cable as claimed in claim 1, wherein the core extends mainly along an axis, in that the leading edges form a shell folded around the core, in that the trailing edges are formed of a profile that ensures the hydrodynamic function of the trailing edge and of two arms that are each disposed inside one of the two adjacent leading edges, in that each arm extends at least in a direction perpendicular to the axis, and in that each arm is held on the corresponding leading edge.

4. The cable as claimed in claim 3, wherein each arm comprises two ends, a first of which is secured to the profile and a second of which is free, and in that each arm is held on the corresponding leading edge at its second end.

5. The cable as claimed in claim 4, wherein each arm is held on the leading edge by a pivot connection.

6. The cable as claimed in claim 5, wherein the pivot connection is disposed at the second, free end of the corresponding arm, and in that each leading edge comprises two stops that can each come into contact with a corresponding one of the arms so as to limit the relative movement of the trailing edge and of the leading edge connected by the pivot connection.

7. The cable as claimed in claim 3, wherein the trailing edge comprises an intermediate arm connecting the two arms.

8. The cable as claimed in claim 1, wherein the core extends mainly along an axis, and in that, for the different leading edges and trailing edges, perpendicularly to the axis of the core, the fairing is located at a distance D with respect to the axis, and in that a distance d at which the leading edges are located is at least equal to half the distance D.

9. The cable as claimed in claim 7, wherein in a plane containing the axis, a projection of the leading edge is substantially rectangular, with one side being limited by the distance d, in that the trailing edge comprises a profile that ensures the hydrodynamic function of the trailing edge, and in that a projection of the profile is substantially rectangular, with one of the sides being limited by the distance d and another of the sides being limited by the distance D.

10. The cable as claimed in claim 8, wherein ends of the side of the leading edge have rounded corners, and in that the profile is configured to follow the rounded corners.

11. The cable as claimed in claim 1, wherein rings fastened to the core are distributed regularly along the core, the leading edges being able to bear on the rings, and in that the rings are disposed between two adjacent leading edges.

12. The cable as claimed in claim 1, wherein the core extends mainly along an axis, in that each leading edge comprises a channel which extends substantially along an axis and wherein the core is disposed, and in that the channel widens on either side of a median section of the leading edge, the median section being perpendicular to the axis of the channel.

Description

[0027] The invention will be understood better and further advantages will become apparent from reading the detailed description of an embodiment given by way of example, this description being illustrated by the appended drawing, in which:

[0028] FIG. 1 shows a ship towing a towed object by means of a faired towing cable according to the invention;

[0029] FIG. 2 shows a portion of the faired cable;

[0030] FIGS. 3a and 3b show perspective views of two faired cable variants subjected to torsion;

[0031] FIGS. 4a and 4b partially show the cable in two perpendicular section planes;

[0032] FIG. 5 shows the cable passing over a pulley;

[0033] FIGS. 6a, 6b, 6c and 6d illustrate a variant of a leading edge of the cable.

[0034] For the sake of clarity, the same elements will bear the same references in the various figures.

[0035] FIG. 1 shows a ship 10 towing a submersible object 12 by means of a towing cable 14. The submersible object 12 is for example a sonar antenna, often called a towfish, the depth of which may be variable. The invention is not limited to a sonar antenna. It can be implemented for any type of submersible object, such as seismic detectors or fishing gear.

[0036] The submersible object 12 is tethered to the cable 14. The submersible object 12 is put into and removed from the water by means of a winch 16 disposed on a deck 18 of the ship 10. The winch 16 comprises a drum 20 dimensioned to allow the cable 14 to be wound. The cable 14 may be wound onto the drum 20 by passing via a guide device 22, for example a pulley or a fairlead. The drum 20 and the guide device 22 are dimensioned so as to limit the bending of the cable 14. The guide device 22 also makes it possible to limit the lateral deflection of the cable 14 downstream, that is to say on the seaward side, in order to allow the submersible object 12 to be used under heavy sea conditions. The guide device may also be equipped with a reeling device upstream, that is to say on the drum side 20, for stowing the cable 14 on the drum 20.

[0037] The cable 14 may be just a mechanical link between the ship 10 and the submersible object 12. Alternatively, the cable 14 may transmit power and signals between the ship 10 and the submersible object 12. The cable may comprise a sheath formed of a strand of metal threads ensuring a degree of flexibility in particular to allow the cable 14 to bend. Inside the sheath, conductors may ensure the transmission of the signals and power. These conductors may be of any kind: electrical, optical, fluidic, etc. The sheath provides the mechanical protection for the internal conductors.

[0038] The exterior sheath of the cable generally has a circular cross section. The sheath and any internal conductors will be referred to as core 24 in the following text. As specified in the introduction, the core 24 is advantageously faired, in particular in order to limit its hydrodynamic drag. In order to achieve high towing speeds, the fairing is at least partially rigid. To allow the cable to bend, the fairing is segmented.

[0039] FIG. 2 shows a part of the cable 14. The core 24 and its fairing can be distinguished therein. According to the invention, the fairing comprises several leading edges 26 and several trailing edges 28 joined to the leading edges 26.

[0040] A leading edge 26 is understood to be a mechanical part that surrounds the core 24 and is intended to be oriented toward the current prevailing in the water when the cable 14 is submerged. Similarly, the trailing edge is a mechanical part situated downstream of the leading edge with respect to the current. The leading edges 26 and the trailing edges 28 comprise external surfaces for reducing the drag of the cable 14 when the latter is subjected to the current.

[0041] The various leading edges 26 and trailing edges 28 are advantageously identical to make it easier to produce them. The leading edges 26 may slide along the core 24 and, as mentioned above, the core 24 may be equipped with crimped rings (not shown in FIG. 2) for longitudinally blocking the leading edges 26 along the core 24. The rings absorb the forces to which the leading edges 26 are subjected along the longitudinal axis 30 of the core 24. The leading edges 26 intended to come into contact with the rings may be configured differently than the other leading edges. In the configuration shown in FIG. 2, one trailing edge 28 is held directly on two adjacent leading edges 26 without any intermediate mechanical part.

[0042] The holding together of the leading edges 26 and trailing edges 28 makes it possible to ensure continuity of the hydrodynamic profile of the fairing parallel to the axis 30, making it possible to limit the effects of twisting of the cable about the axis 30. The direct holding of one trailing edge 28 on two adjacent leading edges 26 avoids the fitting of intermediate joining parts, often known as splice plates.

[0043] In the segmentation of the fairing, it is possible to dispose a trailing edge 28 facing each leading edge 26. More specifically, along the axis 30, the exterior surfaces of a leading edge 26 and of a trailing edge 28, which ensure their hydrodynamic function, occupy one and the same portion along the axis 30. The holding of one trailing edge 28 on two adjacent leading edges 26 is thus ensured by protuberances of the trailing edge that are linked to two adjacent leading edges on the inside thereof. However, this facing disposition of the leading edges 26 and trailing edges 28 causes, in the event of twisting of the cable 24, the different trailing edges to be disposed in a “stepped” manner. More specifically, the downstream end of the trailing edges 28 forms a discontinuous line, this having a detrimental effect on the hydrodynamics of the cable. This stepped disposition is shown in FIG. 3a.

[0044] Preferably, as shown in FIG. 2 and in FIG. 3b, the trailing edges 28 are disposed in a staggered manner with respect to the leading edges 26 along the axis 30. Thus, when the cable 14 twists, the downstream end of the trailing edges 28 forms a substantially continuous line, as shown in FIG. 3b. During twisting, the downstream end of the trailing edges 28 takes on a continuous helical form. The continuous line is advantageous during the passage of the cable through the guide device 22. Specifically, in the case of significant twisting of the cable 14, the discontinuities that are apparent in FIG. 3a entail the risk of escaping from the guide device 22 or of striking and catching on any imperfections when the winch 16 is in action. More specifically, one trailing edge 28 may come to bear correctly in the guide device 22 and the next one may come out of the guide device 22 on account of the presence of a discontinuity. On coming out of the device, the risk of the fairing breaking is much greater. By contrast, the absence of a discontinuity, as shown in FIG. 3b, allows the different trailing edges 28 to come to bear continuously against the guide device 22, in particular during the passage from one trailing edge 28 to the next. The risk of a trailing edge 28 coming out of the guide device 22 is thus much lower.

[0045] FIG. 4a shows the cable 14 in cross section in a plane perpendicular to the axis 30, and FIG. 4b shows a portion of the cable 14 in cross section in a plane containing the axis 30. The leading edge 26 is in one piece. It is made of a homogeneous material. The leading edge 26 surrounds the core 24. The leading edge 26 comprises a channel 32 in which the core 24 is disposed. A functional clearance is present between the core 24 and the channel 32 in order to allow the leading edge 26 to rotate freely about the core 24. The leading edge 26 is fitted around the core 24 by folding it in order to enclose the channel 32. In other words, the leading edge 26 forms a shell folded around the core 24.

[0046] More specifically, the leading edge 26 comprises two faces 26a and 26b and a connecting part 26c joining the two faces 26a and 26b. The faces 26a and 26b and also the connecting part 26c are substantially in the continuation of one another during the manufacture of the leading edge 26. The leading edge 26 is made for example of molded plastics material. Of course, any other manufacturing process is possible, such as machining or 3D printing.

[0047] After the leading edge 26 has been folded around the core 24, the connecting part 26c forms the surface of the channel 32 and the two faces 26a and 26b come into contact with one another. The two faces 26a and 26b are fastened together, for example by means of screws 34 or rivets.

[0048] The external surfaces of the faces 26a and 26b and of the connecting part 26c ensure the hydrodynamic function of the leading edge 26. During the orientation of the fairing element in the current, the connecting part 26c is positioned farthest upstream.

[0049] The trailing edge 28 comprises a profile 28a that ensures the hydrodynamic function of the trailing edge 28 and of two arms 28b and 28c that are each disposed inside two adjacent leading edges 26.

[0050] Perpendicularly to the axis 30 of the core 24, the fairing formed by the leading edges 26 and the trailing edges 28 is located at a distance D with respect to the axis 30. The distance d at which the leading edge is located is at least equal to half the distance D.

[0051] In a plane containing the axis 30 forming a plane of symmetry of the fairing, the projection of the leading edge 26 is substantially rectangular, with one side 36 being limited by the distance d. The projection of the profile 28a is likewise substantially rectangular. For the profile 28a, one of the sides 38 of the rectangle is limited by the distance d and another side 40 is limited by the distance D.

[0052] The ends of the side 36 may have rounded corners 42, having the form of chamfers or fillets. The profile 28a may follow the rounded corners 42. These shape configurations allow the trailing edges 28 to better follow the relative movements of the leading edges 26 that are caused by bending or twisting of the cable 14.

[0053] The leading edge 26 takes up the largest part of the external surface of the fairing. In other words, the leading edge 26 fulfills the majority of the hydrodynamic function of the fairing.

[0054] The leading edge 26 and the trailing edge 28 may be made of the same material, making it possible to standardize the manufacture of the different mechanical parts that form the fairing. Alternatively, it is possible to configure the relative flexibility of the leading edge 26 and of the trailing edge 28, in particular, by keeping the leading edge 26 with a high level of rigidity and by giving the trailing edge 28 greater flexibility. The various leading edges 26 and the various trailing edges 28 may be in one piece and made of homogeneous materials. The Young's modulus (also known as longitudinal elastic modulus) forming the leading edges 26 is thus greater than the Young's modulus of the material forming the trailing edges 28. This allows the fairing to better follow the movements of the cable 14 in the water, during bending or twisting. In addition, the trailing edges 28 have a smaller cross section than that of the leading edges 26. The trailing edges 28 are therefore more fragile than the leading edges 26. By choosing a more flexible material for the trailing edges 28, the risk of the latter breaking is reduced. By way of example, tests were carried out in-house by the applicant with leading edges 26 produced by molding a plastics material formed of a mixture of polycarbonate (PC) and polybutylene terephthalate (PBT) having a Young's modulus of around 2150 MPa. The trailing edges 28, for their part, were produced by molding a material based on polyurethane having a Young's modulus of around 548 MPa. More generally, as soon as the Young's modulus of the material forming the leading edges 26 is greater than that of the material forming the trailing edges 28, the result is already advantageous. This is because, since the leading edges 26 have thicknesses, defined perpendicularly to the plane of FIG. 4b, that are greater than those of the trailing edges 28, a small difference between the Young's moduli already allows much greater deformation of a trailing edge 28 compared with a leading edge 26 under the same force. With a Young's modulus of the material forming the leading edges 26 at least twice the Young's modulus of the material forming the trailing edges 28, the results are better, and with a Young's modulus of the material forming the leading edges 26 at least four times the Young's modulus of the material forming the trailing edges 28, the results are excellent.

[0055] For plastics materials, the Young's modulus can be determined by referring to the standard ISO 178. In practice, the characterization of the Young's moduli of the materials is relative. It is therefore enough to implement the same measurement conditions to compare the Young's moduli of the materials forming the leading edges 26 and the trailing edges 28.

[0056] The arms 28b and 28c extend at least in a direction perpendicular to the axis 30. Thus, the trailing edge 28 is in the overall shape of a U. More specifically, the profile 28a forms the bottom part of the U shape and the arms 28b and 28c form the legs of the U shape.

[0057] The arms 28b and 28c make it possible to hold the trailing edge 28 on two adjacent leading edges 26. The arms 28b and 28c are anchored in the profile 28a. The arms 28b and 28c do not provide any hydrodynamic function. The arms 28b and 28c are each disposed entirely inside one of the leading edges 26. Thus, the definition of the arms 28b and 28c may be much freer, in particular to adapt the deformation thereof as required and in particular to allow the fairing to withstand bending and twisting of the core 24. The definition of the shapes and dimensions of the arms 28b and 28c is not subject to the constraints of the hydrodynamic functions of the fairing.

[0058] More specifically, each of the arms 28b and 28c comprises two ends, 28b1, 28b2 for the arm 28b and 28c1, 28c2 for the arm 28c. The ends 28b1 and 28c1 are secured to the profile 28a. The ends 28b2 and 28c2 are free and each held on a leading edge 26. An arm 28b or 28c can be held on a leading edge 26 by means of a complete connection. The relative movements of the trailing edge 28 with respect to the two leading edges 26 to which the trailing edge 28 is fastened are ensured by the elasticity of the arms 28b and 28c.

[0059] Alternatively, and as shown in FIGS. 4a and 4b, the free ends 28b2 and 28c2 are each linked to a leading edge 26 by means of a pivot connection 44. This pivot connection 44 allows the elasticity of the arms 28b or 28c to be stressed less during relative movements of the trailing edge 28 with respect to the leading edges 26 to which the trailing edge 28 is linked during twisting or bending of the cable 14.

[0060] The arms 28b and 28c extend at least in a direction perpendicular to the axis 30. More specifically, between their ends, the arms 28b and 28c can extend perpendicularly to the axis 30 or be inclined with respect to a direction perpendicular to the axis 30 as shown in FIG. 4b. It is important, however, to maintain, in the projection of a direction connecting the ends of an arm, a component perpendicular to the axis 30. This component, and more generally the U shape of the trailing edge 28, allows greater flexibility of the link between the trailing edge 28 and the two corresponding leading edges 26 during bending or twisting of the cable 14. More specifically, in the prior art, the splice plates keeping the fairings together extend parallel to the axis 30 and are therefore subjected to tension or compression during bending and even during twisting of the cable. By contrast, in the proposed variant of the invention, the arms 28b and 28c, on account of their orientation, undergo bending, which allows greater deformation than tension, resulting in better flexibility of the proposed links. Furthermore, during twisting of the cable 14, the base of the U, that is to say the profile 28a, undergoes both tension and bending. Thus, the proposed variant improves the flexibility of the fairing during bending of the cable 14, making it easier for the cable 14 to pass through the guide means 22, such as a pulley, this passage tending to bend the cable 14. By contrast, the proposed variant maintains a high level of stiffness with regard to twisting of the cable 14, making it possible to limit this twisting.

[0061] The arms 28b or 28c may be independent of one another. Alternatively, as shown in FIG. 4b, the trailing edge 28 may comprise an intermediate arm 28d connecting the two arms 28b or 28c. The intermediate arm 28d is substantially disposed inside two adjacent leading edges 26. The intermediate arm 28d may be secured to each of the arms 28b or 28c halfway between each of the ends of the arms 28b or 28c. The intermediate arm 28d forms, with the free parts of the arms, which extend as far as the free ends 28b2 and 28c2, a U shape that has the same advantages as those described above. The presence of the intermediate arm 28d makes it possible to adjust the flexibility of the fairing with regard to the effects of bending of the cable 14 and the stiffness thereof with regard to twisting of the cable 14.

[0062] FIG. 5 shows a portion of cable 14, the direction of the axis 30 of which is diverted by a pulley 50 forming an example of a guide device 22. In FIG. 5, the cable 14 is schematically depicted and only the core 24 and the leading edges 26 are shown. The trailing edges 28 are not shown. The cable 14 moves in the direction 52 of the axis 30. Upstream of the pulley 50, the speed of the cable 14 is denoted Vc. More specifically, when the cable 14 is straight, the speed of the core 24 and the speed of the leading edges 26 are the same, namely Vc. By contrast, when the cable 14 bends, in particular on passing around the pulley 50, the axis 30 of the core 24 continues at this same speed Vc but the different areas of the leading edge 26 do not all exhibit the same linear speed, which depends on the distance thereof from the axis of the pulley 50.

[0063] More specifically, it was shown above that the leading edge 26 surrounds the core 24. When the cable 14 is in contact with the pulley 50, in the area in which the axis 30 follows a portion of a circle, the part 26c of the leading edge 26 that is closest to the center of the pulley 50 and is indicated by the arrow 54 has a speed lower than Vc. This lower speed tends to cause the leading edges 26 to slip in the upstream direction of the cable 14. The leading edges 26 are thus pressurized against one another, generating stresses in the leading edge 26 that are oriented along the axis 30. This pressure is absorbed by a ring 56 crimped on the core 24.

[0064] Several rings are distributed along the core 24 in order to periodically absorb the axial forces of the different fairings. It is possible to make an incision in several leading edges 26 at their respective channels, this incision being perpendicular to the axis 30. Thus, a leading edge incorporates a ring. This particular leading edge can thus bear either on one side of the ring or on the other. In other words, a leading edge absorbs the forces in the two directions of the axis 30. However, such a configuration forces a leading edge to absorb axial forces both in tension and in compression.

[0065] It is also possible to do away with the absorption of tensile force in order to limit the risk of creeping of the leading edges 26. To this end, as shown in FIG. 5, the rings 56 are disposed between two adjacent leading edges.

[0066] Furthermore, the part 26c is pressurized by the core 24 against the pulley 50. This pressure against the pulley generates stresses in the leading edge 26 that are oriented radially toward the center of the pulley 50.

[0067] FIGS. 6a and 6d show a particular form of the leading edges 26 that makes it possible to limit the effects of the reduction in speed of the part 26c of the leading edge 26. FIG. 6a shows a leading edge 26 on its own and FIG. 6d shows a portion of cable wound over a pulley 50. The channel 32 extends mainly along an axis 60 of the leading edge 26 that is coincident with the axis 30 of the core 24 when the cable 14 is straight. The channel 32 widens on either side of a median section 62 of the leading edge 26, the section 62 being perpendicular to the axis 60. This makes it possible to better distribute the pressure that the core 24 exerts on the walls of the channel 32 when the cable 14 bends. As a result of the channel 32 widening, the pressure is reduced in the sections farthest away from the section 62. The sections can be defined such that, for a given bend of the cable 14, in particular depending on the diameter of the pulley 50, the core 24 is not in contact with the sections farthest away from the section 62 but only with sections that are closest to the section 62. This makes it possible to limit the risks of creeping of the material forming the leading edge 26 when it is pressurized by the core 24.

[0068] The channel 32 may be formed of circular sections about the axis 30. Alternatively, in order to improve the rigidity of the leading edge 26, the sections of the channel 32 are defined in an asymmetric manner about the axis 60, as shown in FIGS. 6a and 6d. More specifically, in the section 62, shown in cross section in FIG. 6b, the channel 32 has a circular contour, and in the sections 64 that are farthest away from the section 62 and shown in cross section in FIG. 6c, the channel 32 has an elongate contour extending toward the interior of the pulley 50. Between the sections 62 and 64, the walls of the channel 32 follow for example a circular curve of radius r centered on a point belonging to the median section 62. The radius r is defined such that r-e is less than the radius R of the pulley 50, e being the thickness of the part 26a in the median section 62. Thus, even if the core 24 partially squashes the internal surface of the channel 32, the length of contact of the core 24, denoted I in FIG. 6d, remains less than the length L of the leading edge 26, the lengths I and L being defined along the axis 60 of the channel 32.

[0069] When the towing cable 14 bends about a pulley 50, the parts of the leading edges 26 that are farthest away from the center of the pulley 50 tend to move apart. The corresponding trailing edges 28 have to follow this movement apart. The presence of the pivot connection 44 at the free end 28b2 and 28c2 of each of the arms 28b and 28c allows the rotation of the trailing edge 28 with respect to each of the leading edges 26 to which the trailing edge 28 is articulated. The pivot connections 44 are disposed as close as possible to the axis 30 in order to limit the movement of the pivot connections 44 apart from one another. For the trailing edge 28, this movement apart is absorbed by elastic deformation of the arms 28b and 28c. The lower Young's modulus of the trailing edge 28 associated with the shape of the arms 28b and 28c allows this deformation. At the ends 28b1 and 28c1 of the arms 28b and 28c, the relative movement of two leading edges is greater than at the pivot connections 44. In FIG. 4b, the possible movement of the leading edge 26 situated on the right in the figure is represented by dashed lines. In the bottom part of FIG. 4b, the two leading edges 26 come into abutment and move apart at the top. At the ends 28b1 and 28c1, the arms 28b and 28c can slide in the plane of FIG. 4b with respect to the corresponding leading edges 26.

[0070] Other relative movements of the leading edges 26 and of the trailing edges 28 are possible, in particular twisting as shown in FIG. 3b. Twisting may bring about a greater relative movement than bending as shown by dashed lines in FIG. 4b, the coming of the leading edges 26 into abutment then being ineffective. It is advantageous, however, to provide for the relative movement between a leading edge 26 and a trailing edge 28 linked by their pivot connection 44 to be limited. This movement is substantially a rotation about the axis of the pivot connection 44 give or take functional clearances and deformations. To this end, the leading edge may comprise two stops in the form of bosses 70 that are intended each to bear against an arm 28b or 28c. The bosses 70 may be used for the passage of the screws 34, as can be seen in FIG. 4a. The bosses 70 form protuberances that connect the faces 26a and 26b of the leading edge 26. In FIG. 4b, one of the bosses 70 is also shown by dashed lines during bending of the core 24. In this position, the boss 70 is still at a distance from the arm 28c. During a larger relative movement, the boss 70 comes into abutment against the arm 28c. This is illustrated by a point 72 of the boss 70 and a point 74 of the arm 28c coming into contact with one another. These two points 72 and 74 are indicated by solid arrows in FIG. 4b. It is, of course, possible to dispense with a stop between two leading edges 26 and to keep only the stop 70. The position of this stop is defined in particular depending on the diameter of the pulley 50 or that of a drum 20 and more generally on the maximum deformation allowed for the cable 14.