Abstract:
The submarine cable ( 10 ) having on an outer sheath, ( 11 ) a marking provided by at least one longitudinal strip ( 13 ), which stands out with high contrast from the black color of the outer sheath ( 11 ) by a lighter color, in particular yellow, and, as a result, is more easily visible on television pictures.

Description:
BACKGROUND OF THE INVENTION 
     The invention concerns a cable, in particular an underwater cable, with a cable core having at least one conductor, and an outer sheath. 
     PRIOR ART 
     Underwater cables (so-called submarine cables) must be observed during laying, for inspection purposes and for tracing any defects. This takes place under water with remote-controlled cameras. The pictures taken by the cameras under water, in particular at great depths, often allow the underwater cable to be made out only with difficulty, in particular whenever it has a customary black or dark outer sheath. This makes it difficult in particular to locate defective underwater cables. 
     BRIEF SUMMARY OF THE INVENTION 
     Setting out from the above situation, the invention is based on the object of providing a cable, in particular an underwater cable (submarine cable), which can be made out well under water, even at great depths. 
     A cable serving to achieve this object, in particular an underwater cable or submarine cable, has the features of claim  1 . At least one externally visible marking of a different color on the outer sheath makes the cable more easily visible, in particular in the underwater area. The underwater cable according to the invention can be made out more easily on camera pictures, because the marking of a different color provides the outer sheath with greater contrast. 
     The marking can be formed in a wide variety of ways. The marking preferably consists of one or more strips or lines extending continuously in the longitudinal direction of the outer sheath of the cable and preferably extending spirally around the cable. The marking comprising one or more spiral longitudinal strips or longitudinal lines on the outer sheath has the effect that the marking is always visible, irrespective of from which side the cable is viewed. Since submarine cables turn about their longitudinal axis during laying, the longitudinal strips or longitudinal lines likewise running spirally around the longitudinal axis of the submarine cable represent a marking that is virtually always visible. 
     It is alternatively also conceivable to form the marking by transverse strips or transverse lines running in a cross-sectional direction around the cable. These are then virtually endless, colored rings around the outer sheath. They are also always visible, irrespective of any turning of the cable. Like the abovementioned longitudinal lines or longitudinal strips extending spirally around the cable, the peripheral transverse strips or transverse lines have the advantage that turning of the submarine cable during laying does not become visible and as a result does not disturb the viewer. 
     It is likewise conceivable to form the marking from straight longitudinal strips or longitudinal lines. In order that a straight longitudinal strip or longitudinal line is always visible in each case, a corresponding number of longitudinal strips or longitudinal lines are arranged evenly distributed on the circumference of the outer sheath. The longitudinal strips or longitudinal lines or transverse strips or transverse lines can also be produced from at least one series of two-dimensional formations following one another at intervals. The two-dimensional formations may have any desired base areas, and in particular be round, elliptical, square or rectangular. Similarly, the intervals between the two-dimensional formations may be as desired. 
     Finally, it is also conceivable to provide the entire outer sheath with a marking comprising dots of any desired shape. In this case, the dots are arranged in a uniform grid, which preferably extends over the entire circumference of the outer sheath. Such a grid also has the advantage that the marking is always visible and turns of the submarine cable during laying do not become evident and do not in this case detract from the observation of laying. 
     Any type of marking can be formed by a dye sprayed or printed onto the outer sheath after it has been produced. For this purpose, a dye which is permanently resistant to sea water is used. It is also conceivable, after applying the dye forming the marking, to provide the entire outer sheath with a transparent protective layer, which also covers the colored marking. 
     It is also possible to form the marking from a plastic of a different color during the production of the outer sheath. The outer sheath is then made up of differently colored plastic materials. For example, this can be achieved by coextrusion of the outer sheath or by sintering the plastic of a different color onto the surface of the outer sheath. The types of marking mentioned then have virtually the same sea-water resistance as the outer sheath. 
     According to a preferred development of the invention, the respective marking has a lighter color than the outer sheath. It is also advantageous if the lighter color of the marking has fluorescent properties. As a result, the marking of the submarine cable becomes visible even at great depths if searchlights of an underwater camera shine on it. 
     In the case of submarine cables with a usually black outer sheath, a yellow color, in particular a fluorescent yellow color, which offers easily visible contrast together with the black color of the outer sheath, is preferably chosen for the lighter color of the marking. 
     The marking may also be formed by mixing color particles or color pigments in with the raw material of the plastic for forming the outer sheath. Such an outer sheath then has an essentially regular distribution of colored locations, in particular small dots. The embedding of the color particles or color pigments in the plastic material for forming the outer sheath ensures a permanent bonding of the marking to the submarine cable. 
     In an alternative development of the submarine cable according to the invention, the marking is formed by a netting applied to the outer sheath. The netting surrounds the entire outer sheath and extends uninterruptedly in the longitudinal direction of the submarine cable. The netting produces on the outside of the outer sheath of the submarine cable peripheral transverse strands and rectilinear longitudinal strands with preferably a round cross section, although other cross sections, for example square, are also conceivable. If the netting is of a different color, the crossing longitudinal and transverse strands form the marking. 
    
    
     BRIEF SUMMARY OF THE DRAWINGS 
     Preferred exemplary embodiments of the cable according to the invention are explained in more detail below with reference to the drawing, in which: 
     FIG. 1 shows a portion of a submarine cable in a side view, 
     FIG. 2 shows a side view of a portion of a submarine cable according to a second exemplary embodiment of the invention, 
     FIG. 3 shows the submarine cable of FIG. 2 in a side view turned through 90°, 
     FIG. 4 shows a side view of a portion of a submarine cable according to a third exemplary embodiment of the invention, 
     FIG. 5 shows a side view of the submarine cable of FIG. 4, turned through 90° with respect to FIG. 4, 
     FIG. 6 shows a portion of a submarine cable according to a fourth exemplary embodiment of the invention, and 
     FIG. 7 shows a portion of a submarine cable according to a fifth exemplary embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The figures show cables for underwater use, namely submarine cables of any desired construction. In particular, the submarine cables may have in the interior a core of any desired construction. For example, the core may have both electrical conductors and optical waveguides or combinations of the two. In addition, the core has at least one armoring or reinforcement for protection against mechanical influences. The core with the reinforcement or armoring is surrounded by a closed outer sheath, which consists essentially of plastic. The outer sheath is usually black. 
     FIG. 1 shows a submarine cable  10 , the outer sheath  11  of which is provided with an externally visible marking. In the exemplary embodiment shown, the marking is formed by a longitudinal strip  13  running spirally around the outer sheath  11  in the longitudinal direction, in other words along the longitudinal centre axis  12  of the submarine cable  10 . The single longitudinal strip  13  in the exemplary embodiment of FIG. 1 has, depending on the diameter of the submarine cable  10 , a width of between 1 and 5 mm. The longitudinal strip  13  preferably has a width which corresponds approximately to one-quarter to one-fifth of the diameter of the submarine cable  10 . In the exemplary embodiment shown, the pitch of the spiral helix of the longitudinal strip  13  around the submarine cable  10  is chosen such that, over a length of the submarine cable  10  which is approximately three to ten times, preferably approximately eight times, the diameter of the said cable, the longitudinal strip  13  has run once around the outer sheath  11  of the submarine cable  10 . 
     FIGS. 2 and 3 show a submarine cable  14  according to a second exemplary embodiment of the invention. The internals of the submarine cable  14 —which may be of any desired construction—are not represented in any more detail in the figures mentioned (or in any of the other figures). Only the outer sheath  15  with markings according to the invention is shown. In the present exemplary embodiment as well, the marking is formed by longitudinal strips running in a serpentine manner around the outer sheath  15  along the longitudinal centre axis  16 , to be precise two longitudinal strips  17  and  18 . For reasons of simple representation, the longitudinal strips  17  and  18  are only indicated by lines. In fact, they have a width which, depending on the diameter of the submarine cable  14 , may be between 1 and 5 mm. It is also conceivable to make the individual longitudinal strips  17  and  18  of different widths. 
     The two longitudinal strips  17  and  18  run in different directions around the outer sheath  15 . While the longitudinal strip  17  snakes clockwise around the outer sheath  15 , the longitudinal strip  18  runs anti-clockwise around the outer sheath  15 . Both longitudinal strips  17  and  18  have the same pitch, which is indicated in FIGS. 2 and 3 by the dimension L. This means that, on a portion L of the submarine cable  14 , the longitudinal strip  17  wraps once right around the submarine cable  14  in one direction and the longitudinal strip  18  wraps once right around the submarine cable  14  in the other direction. 
     The longitudinal strips  17  and  18 , which follow an identical path, cross at common nodes  19 , the intervals of which have half the dimension L of a complete revolution of the respective longitudinal strip  17  and  18  around the outer sheath  15 . 
     The design and arrangement described of the longitudinal strips  17  and  18  on the submarine cable  14  have the effect that, depending on the viewing direction towards the side of the submarine cable  14 , the two oppositely running longitudinal strips  17  and  18  have different paths. It can be seen from the representation in FIG. 2 that both longitudinal strips  17  and  18  are simultaneously visible in the same region of the length of the submarine cable  14 . Between two successive visible portions of the longitudinal strips  17  and  18 , both longitudinal strips  17  and  18  disappear entirely to the invisible rear side of the submarine cable  14 . The length of this invisible region is half the length of one complete revolution of the respective longitudinal strip  17  and  18  around the submarine cable  14 . If the submarine cable  14  represented in FIG. 2 is viewed from below, one of the two longitudinal strips  17  or  18  is always visible. The serpentine or sinusoidal path shown in the figure is thereby obtained. Thus, from certain views of the submarine cable  14 , the two longitudinal strips  17  and  16  extending in opposite directions have the effect that either only a single longitudinal strip  17  or  18  is visible or both longitudinal strips  17 ,  18  are only partially visible. 
     FIGS. 4 and 5 show a third exemplary embodiment of a submarine cable  20 , in which the marking has four longitudinal strips  21  to  24 . The longitudinal strips  21  and  22  correspond to the longitudinal strips  17  and  18  of the exemplary embodiment of FIGS. 2 and 3. The longitudinal strips  21  and  22  become visible in the left-hand half of the dimension L of FIG.  4 . Located invisibly behind them, with the same path, are the longitudinal strips  23  and  24 . In the right-hand half of the dimension L in FIG. 4, the longitudinal strips  21  and  22  disappear invisibly to the rear side of the outer sheath  25  of the submarine cable  20 . In this region, the longitudinal strips  23  and  24  appear visibly on the front side of the outer sheath  25 . Behind the dimension L in FIG. 4, these strips disappear again to the rear side of the outer sheath  25  and the longitudinal strips  21  and  22  visibly reemerge. 
     The longitudinal strips  21  and  22  on the one hand and  23  and  24  on the other hand are all of the same design as one another. The longitudinal strips  21 ,  22 ,  23 ,  24  wrap around the outer sheath  25  in the direction of the longitudinal centre axis  32  of the submarine cable  20 . The only difference that, at the upper (left-hand) node  26  in FIG. 4, the longitudinal strip  21  begins in one direction and the longitudinal strip  23  begins in another direction. Extending from the node  27  lying below it in FIG. 4 are the longitudinal strips  22  and  24 , to be precise in such a way that they wrap around the submarine cable  20  in opposite directions. As a result, there are always two nodes  26  and  27  diametrically opposite one another on the outer sheath  25  of the submarine cable  20 . The nodes  26  and  27  are always offset by the dimension L-quarter in the direction of the longitudinal centre axis  16  of the submarine cable  20  and also always turned through 90°. 
     The four longitudinal strips  21 ,  22 ,  23  and  24 , which are of the same design and are just directed differently, or extend from different nodes  26  to  27 , achieve the effect that the marking of the outer sheath  25  is continuously visible from every side of the submarine cable  20 , to be precise with the same pattern, as clearly illustrated by FIGS. 4 and 5, which show the submarine cable  20  from two viewing directions respectively offset by 90°. 
     The longitudinal strips  21 ,  22 ,  23  and  24 , again shown only as lines in FIGS. 4 and 5 for reasons of simplification, are in fact designed as wider strips, to be precise with a width of preferably 1 to 5 mm. In the case of relatively thick submarine cables  20 , the strips may be even wider. The same also applies to the other exemplary embodiments of the invention. It is conceivable to make the individual longitudinal strips  21 ,  22 ,  23  and  24  of different widths. 
     FIG. 6 shows a fourth exemplary embodiment of a submarine cable  28 . This submarine cable  28  has on an outer sheath  29  a marking comprising a multiplicity of round dots  30 . The dots  30  are distributed uniformly over the entire length of the submarine cable  28  along its longitudinal centre axis  31  over the entire circumference of the outer sheath  29 . For this purpose, in the exemplary embodiment shown, the dots  30  are arranged in a uniform grid. This is made up of a plurality of rows of dots  30 , following one another at uniform intervals, the said rows extending parallel to the longitudinal centre axis  16  and the dots  30  of adjacent rows being offset by half the interval between pairs of dots  30 , in other words are arranged such that they are staggered. The interval between neighbouring dots  30  is slightly greater than the diameter of the same. The dots  30 , which are the same as one another, have in each case a diameter of preferably 1 to 10 mm. The interval between the dots  30  may also be greater than their diameter; preferably, the interval between the dots  30  is five to twenty times as great as their diameter. 
     While the outer sheaths of the submarine cables shown are black, the markings, in other words the longitudinal strips  13 ,  17 ,  18 ,  21 ,  22 ,  23 ,  24 , or the dots  30 , have a lighter color. The longitudinal strips  13 ,  17 ,  18 ,  21 ,  22 ,  23 ,  24  or the dots  30  are made yellow. This may be a shade of yellow, which has fluorescent or retro-reflective properties. 
     It is also conceivable to provide in particular the submarine cables  14  and  20  with a plurality of longitudinal strips  17 ,  18  or  21 ,  22 ,  23  and  24 , respectively, as shown in FIGS. 1 to  5 . The individual longitudinal strips  17 ,  18 ,  21 ,  22 ,  23  or  24  may also be provided with different colors, which however are to be significantly lighter than the black color of the outer sheaths. The dots  30  on the outer sheath  29  of the submarine cable  28  may also be of different colors. 
     The markings are continuously applied to the outer sheaths of the submarine cables while they are being produced, or are made in the outer sheaths. This may take place during or after the production of the respective outer sheath. 
     After the production of the respective outer sheath, the marking may be printed or sprayed onto the outside of the respective outer sheath in the form of longitudinal strips  13 ,  17 ,  18 ,  21 ,  22 ,  23 ,  24  or dots  30 . In this case, the marking is formed from a coating of a corresponding color or from liquid plastic. The coating or the liquid plastic must be of such a nature that it adheres well to the outer sheaths and is indelible, even in salty sea water. 
     It is also conceivable to produce the marking by sintering onto the respective outer sheath. This also takes place preferably after the production of the outer sheath. In this case, the sintering-on can be performed while the outer sheath has not yet fully cured. 
     The marking may also be produced during the production of the respective outer sheath of the submarine cable, by the respective outer sheath being formed from plastics of different colors. Then the outer sheath is formed, for example by the coextrusion process, simultaneously from the black plastic and the differently colored, for example yellow, plastic for forming the marking, in particular the longitudinal strips  13 ,  17 ,  18 ,  21 ,  22 ,  23 ,  24 . 
     The longitudinal strips  13 ,  17 ,  18 ,  21 ,  22 ,  23 ,  24  shown in FIGS. 1 to  5  extend continuously over the entire length of the respective submarine cable, in other words snake constantly, that is to say repeatedly or many times, around the outer sheath. 
     FIG. 7 shows a submarine cable  33  in which the marking is formed by a netting  34 . The netting  34  surrounds the outer sheath  35  of the submarine cable  33 . In the exemplary embodiment shown, the netting is formed by longitudinal strands  36 , extending in the longitudinal direction of the submarine cable  33 , and transverse strands  37 , directed transversely thereto, which surround the outer sheath  35  uninterruptedly. In the present case, the interval between pairs of neighbouring, parallel longitudinal strands  36  is approximately the same size as the interval between two neighbouring, parallel transverse strands  37 . As a result, rectangular openings  38  are created between the longitudinal strands  36  and transverse strands  37 . It is also possible, however, to choose the intervals between neighbouring longitudinal strands  36  to be less or greater than the intervals between neighbouring transverse strands  37 . Similarly, the longitudinal strands may also extend obliquely with respect to the longitudinal axis of the submarine cable  33  or wrap around it in a serpentine manner. Such longitudinal strands are also joined by transverse strands, which, if appropriate, may extend obliquely with respect to the longitudinal axis of the submarine cable  33  in order that they intersect the longitudinal strips at right angles. 
     The longitudinal strands  36  and transverse strands  37  intersect at nodes  39 . At these nodes  39 , the longitudinal strands  36  are at the same time integrally joined to the transverse strands  37 . The longitudinal strands  36  and the transverse strands  37  preferably have round cross sections of the same size. 
     The netting  34  is applied to the outer sheath  35  after the said sheath has been produced. For this purpose, after extrusion of the outer sheath  35  onto the core of the submarine cable  37 , the netting  34  is extruded onto the outside of the outer sheath  35  in a second extrusion step. 
     The netting  34  and the outer sheath  35  are preferably formed from plastic, in particular an identical plastic. With regard to color, the netting  34  differs from the outer sheath  35 . For example, the netting  34  is of a yellow color, if appropriate with fluorescent properties, while the outer sheath  35  is black. The openings  38  between the longitudinal strands  36  and the transverse strands  37  then appear black, while between neighboring openings  38  there is the yellow marking formed by the longitudinal strands  36  and the transverse strands  37 . 
     As a departure from the exemplary embodiments shown, the markings may take any other desired form. For example, transverse strips, longitudinal strips which extend parallel to the longitudinal centre axis of the submarine cable or dots with square or non-round surface areas may be used. It is also conceivable to form the longitudinal strips or other strips by a row of dots following one another at short intervals or to interrupt the continuous longitudinal or transverse strips occasionally. In addition, it is conceivable to vary the number of longitudinal strips as desired or to combine longitudinal strips and dots with one another.