Device and Method for Reeling in a Cable from a Source and Temporarily Storing the Cable

Abstract

A device for reeling in a cable and temporarily storing the cable is described. The device comprises first and second storage units, each comprising a cylindrical body for arranging the cable, as well as support means for carrying the cable from the source to cable seizing means of the second storage unit and further to the first storage unit. The second storage unit is rotatable around a rotation axis parallel to the cylinder longitudinal axis in a reeling direction. The storage units are arranged such that the second storage unit when rotating in the reeling direction can simultaneously reel in a part of the seized cable originating from the source and another part of the seized cable originating from the first storage unit. A method for reeling in the cable is also described. The device and method allow storing an increased amount of cable on a cable laying vessel for instance.

Claims

1.-23. (canceled)

24. A vessel for laying cables on or in a sea bed, comprising a device for reeling in a cable from a source and temporarily storing the cable, the device comprising a first and a second storage unit, each comprising a cylindrical body for arranging the cable, wherein a cylinder longitudinal axis of the first storage unit does not coincide with a rotation axis of the second storage unit; support means for carrying the cable from the source to cable seizing means of the second storage unit and further to the first storage unit; wherein the first storage unit is configured to reel in cable from the source; the second storage unit is rotatable around the rotation axis parallel to the cylinder longitudinal axis in a reeling direction, in which the cable is reeled in from the source; and the storage units are arranged such that the second storage unit when rotating in the reeling direction simultaneously reels in a part of the cable originating from the source and another part of the cable originating from the first storage unit, wherein further the cable seizing means of the second storage unit comprise a centrally disposed cylindrical core and are configured to seize the cable such that a rotation of the second storage unit winds the cable around the centrally disposed core from opposite sides of the core, and the centrally disposed core of the cable seizing means is provided with a passage for the cable extending in a cross-direction of the core.

25. The vessel according to claim 24, wherein the cylinder longitudinal axis of the first and/or second storage unit extends in a vertical direction.

26. The vessel according to claim 24, wherein the first storage unit is rotatable around a rotation axis parallel to the cylinder longitudinal axis in a reeling direction in which the cable is reeled in from the source.

27. The vessel according to claim 24, comprising more than two storage units arranged such that a storage unit n+1 when rotating in the reeling direction can simultaneously reel in a part of the cable originating from the source and another part of the cable originating from a storage unit n.

28. The vessel according to claim 24, comprising storage units of different circumferential size.

29. The vessel according to claim 24, wherein the first and/or the second storage unit comprises a top-loading storage device, such as a turntable or a static tank, or a combination of these.

30. The vessel according to claim 24, wherein the vessel has a deck and at least two of the storage units are arranged below the deck.

31. A method for reeling in a cable from a source and temporarily storing the cable on a vessel for laying cables on or in a sea bed, the method comprising providing a first and a second storage unit on the vessel, each comprising a cylindrical body for arranging the cable; carrying the cable on support means from a source to cable seizing means of the second storage unit and further to the first storage unit; reeling in the cable on the first storage unit to a first filling degree; rotating the second storage unit around a rotation axis parallel to the cylinder longitudinal axis in a reeling direction to simultaneously reel in a part of the seized cable originating from the source and another part of the seized cable originating from the first storage unit until a second filling degree of the second storage unit is reached, wherein a cylinder longitudinal axis of the first storage unit does not coincide with the rotation axis of the second storage unit; wherein the cable seizing means of the second storage unit comprise a centrally disposed core and seize the cable such that a rotation of the second storage unit winds the cable around the centrally disposed core from opposite sides of the core; wherein the centrally disposed core of the cable seizing means is provided with a passage extending in a cross-direction of the core and the cable is seized by the seizing means by providing it through the passage.

32. The method according to claim 31, wherein the first and the second filling degree comprises a substantially 100% filling.

33. The method according to claim 31, wherein the first storage unit rotates around a rotation axis parallel to the cylinder longitudinal axis in a reeling direction to reel in the cable.

34. The method according to claim 31, wherein the cable originating from the source is seized by looping it around a cylindrical core of the second storage unit.

35. The method according to claim 31, comprising more than two storage units arranged such that rotating a storage unit n+1 in a reeling direction simultaneously reels in a part of the seized cable originating from the source and another part of the seized cable originating from a storage unit n.

36. The method according to claim 31, comprising storage units of different circumferential size.

37. The method according to claim 31, wherein the first and/or the second storage unit comprise a reel, a carousel, a turntable or a static tank, or a combination of these.

38. The method according to claim 31, wherein the vessel has a deck and at least two of the storage units are arranged below the deck.

39. A method for laying a cable on or in an sea bed, wherein a vessel according to claim 24 is provided with a quantity of stored cable, the vessel sails on water and stored cable is unreeled from the first and second storage unit, brought overboard and laid on or in the sea bed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The invention will now be described in more detail by reference to the attached figures, without however being limited thereto. In the figures:

[0028] FIG. 1 schematically shows a perspective view of a rear deck part of a cable laying vessel according to one embodiment of the invention, wherein the deck is made transparent to show the below deck area;

[0029] FIG. 2 schematically shows a perspective view of two storage units according to an embodiment of the invention;

[0030] FIG. 3 schematically shows a number of method steps in accordance with an embodiment of the invention;

[0031] FIG. 4 schematically shows a number of method steps in accordance with another embodiment of the invention;

[0032] FIG. 5 schematically shows a side view of storage units in accordance with several embodiments of the invention;

[0033] FIG. 6 schematically shows an isometric and side view of cylindrical cores of second storage units and possible cable paths according to the invention;

[0034] FIG. 7 shows a graph of the uninterrupted cable length that can be stored in view of the number of storage units used in accordance with several embodiments of the invention; and finally FIG. 8 shows a graph of the uninterrupted total cable capacity that can be stored in view of the ratio of a smallest to largest storage unit used in accordance with several embodiments of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Referring to FIG. 1, a part of the deck 2 of a vessel 1 for laying cables 3 on or in a sea bed is shown. The vessel 1 is at a rear side 20 of the deck 2 provided with a portside chute 10 and a starboard chute 11 for guiding a cable 3. The chutes (10, 11) may be used to reel in a cable 3 from a suitable source, such as an onshore cable rack (not shown), but may also be used to bring out of board cable 3 during a cable laying operation off shore. A cable tensioner 12 may be present to pull the cable 3 along support means in the form of port side and starboard cable trays (13, 14). The cable trays (13, 14) are supported by poles 15 to elevate and hold the trays above work deck level. A cable 3 that is pulled in from shore in the direction 16 is first led along a so-called quadrant 17. This is also shown in FIG. 2. The quadrant structure 17 guides a cable 3 along an arc with a radius that is equal or larger than the minimum bending radius (MBR) of the cable 3, this in order to prevent damaging or even breaking of the cable 3. As shown in FIGS. 1 and 2, the cable 3 is guided further from the quadrant 17 along the starboard cable tray 14 to a deck penetration 18 which offers access to a second storage unit 20 provided in an area below deck 2. Cable 3 surfaces from this deck penetration 18 again (see below) and is then led over the quadrant 17 and back to another deck penetration 19 giving access to a first storage unit 30 provided in an area below deck 2.

[0036] As further shown in FIG. 1, the storage units (20, 30) are arranged below the deck, and each of the storage units (20, 30) comprises a cylindrical body (21, 31) in which the cable 3 can be arranged in a circumferential direction. As shown, the cylinder longitudinal axis 22 of the second storage unit 20 does not coincide with the cylinder longitudinal axis 32 of the first storage unit 30, and both storage units (20, 30) are spaced apart from each other. In the embodiment shown, the cylinder longitudinal axes (22, 32) of the second and first storage unit (20, 30) extend in a direction about perpendicular to the plane of the deck 2. This direction is substantially vertical. Other directions are also possible.

[0037] The second storage unit 20 is rotatable around a rotation axis parallel to the cylinder longitudinal axis 22 in a reeling direction 23, in which the cable 3 is reeled in from the source. Likewise, the first storage unit 30 is rotatable around a rotation axis parallel to the cylinder longitudinal axis 32 in a reeling direction 33 in which the cable 3 is reeled in from the source.

[0038] The second storage unit 20 is further provided with cable seizing means that in the embodiment shown comprises a cylindrical core 24 provided with a passage 24a for the cable 3. The passage 24a extends in a cross-direction 24b of the cylindrical core 24. The first storage unit 30 may also be provided with a cylindrical core 34.

[0039] The principle of operation of the invented device can best be understood with reference to FIG. 3. The method for reeling in a cable 3 from a source and temporarily storing the cable 3 in a first step comprises (A) providing a first storage unit 30 and a second storage unit 20, each comprising a cylindrical body (31, 21) for arranging the cable 3. In a second step (B) the cable 3 is carried on the cable trays (13, 14) from a source through the passage 24a of the cylindrical core 24 of the second storage unit 20 and further to the first storage unit 30 and the cable is reeled in on the first storage unit 30 to a first filling degree, which in an embodiment is substantially a 100% filling, as shown. Reeling can be done by rotating the first storage unit 30 in the reeling direction 33. In a third step (C) the second storage unit 20 is rotated in its reeling direction 23 and, due to the fact that the cable 3 is caught by running through the passage 24a of its core 24, the second storage unit 20 in step (D) simultaneously reels in a part 3a of the seized cable 3 originating from the source in the direction 16 and another part 3b of the seized cable 3 originating from the first storage unit 30 in a direction 26. The first storage unit 30 in this process may be stationary or may rotate in a direction 36 opposite to its reeling direction 33. The second storage unit 20 is filled from the two sources until a second filling degree is reached, preferably until the second storage unit is filled for substantially 100%. The final filling degree of the first storage unit 30 will be less than 100% since a part 3b of the cable 3 was unreeled from the first storage unit 30 in the process.

[0040] When unreeling the stored cable 3, for instance in order to bring it overboard in a cable laying operation, the sequence of steps (A) to (D) is reversed and carried out in the sequence (D) to (A), as shown by the top arrows in FIG. 3.

[0041] The above sequence can be carried out in any type of storage unit (20, 30). FIG. 4 for instance illustrates the method steps (A) to (D) for two carousels (20, 30) positioned side by side, wherein the first storage unit 30 may be stationary. A first step of the embodiment of the method shown comprises (A) providing a first storage unit 30 and a second storage unit 20, each comprising a cylindrical body (31, 21) for arranging the cable 3. In second steps (B1, B2) the cable 3 is carried on the cable trays (13, 14) from a source through the passage 24a of the cylindrical core 24 of the second storage unit 20 and further to the first storage unit 30 and the cable is reeled in on the first storage unit 30 to a substantially 100% filling. A third step (C) involves rotating the second storage unit 20 in its reeling direction 23 and, due to the fact that the cable 3 is caught by running through the passage 24a of its core 24, the second storage unit 20 in steps (D1, D2) simultaneously reels in a part 3a of the seized cable 3 originating from the source and another part 3b of the seized cable 3 originating from the first storage unit 30. The second storage unit 20 is filled from the two sources until a second filling degree is reached, preferably until the second storage unit is filled for substantially 100%. The final filling degree of the first storage unit 30 will be less than 100% since a part 3b of the cable 3 was unreeled from the first storage unit 30 in the process. Indeed, in the embodiment shown, the first storage unit 30 is now half full only. Therefore the total cable length spooled onto the storage units (20, 30) is 75% of the full capacity of the two storage units (20, 30) together. However, the cable is 150% longer than it could be if both storage units (20, 30) were filled completely, since this would require a cut in the cable 3.

[0042] Step (B) of the method shown in FIG. 4 requires that the cable 3 is fed through the passage 4a of the core 4 of the second storage unit 20. As is more clearly shown in FIG. 6, this may involve some extreme bending of the cable 3, and care should be taken to prevent bending the cable over a radius that is lower than the minimum bending radius (MBR) of the cable 3. The invention however does not require the cable 3 to be fed through the core 4 of the second storage unit 20 (or other storage device). If acceptable from a minimum bending requirement, the cable 3 could also, as schematically shown in FIG. 6, be fed around the core (in case of a reel or carousel for instance) or across the first layer of a turntable. Feeding the cable 3 around the core 4 of a reel or carousel (20, 30) may sacrifice a part of the first layer laid. Bending the cable 3 around the core 24 of a storage unit (20, 30) may involve simultaneous biplanar cable bending, which may need to be prevented. The feasibility of bending the cable 3 around a core 24 may be determined by considering the cable's MBR and the dimensions of the storage unit (20, 30). A preferred storage unit (20, 30) comprises a turntable, described further below.

[0043] The storage units may comprise any structure suitable for temporarily storing a length of cable. As shown in FIG. 5, the storage devices may comprise a reel (FIG. 5B), a carousel (FIG. 5A), a turntable or a static tank (5C), or a combination of these.

[0044] Suitable definitions in the context of the invention are the following:

[0045] Efficiency: the efficiency of cable loading is defined as the actual total uninterrupted cable length spooled onto the total number of storage devices considered divided by the sum of the capacities of each individual storage device considered. When considering two storage units where one is completely full and one is half full, the efficiency is (50%+100%)/(100%+100%)=75%.

[0046] The carousel (20, 30) shown in FIG. 5A has a cylindrical core (24, 34) that is oriented substantially vertical, and carries a top and bottom flange (40a, 40b). A carousel may be driven in a rotation direction during loading and unloading a cable 3. The weight of the cable 3 is evenly distributed into the foundation through the bottom flange 40b.

[0047] Preferably some form of back tension is applied for decent spooling (loss of back-tension may cause an entire wrap or layer to drop down). A carousel is typically filled wrap by wrap, from core to outer diameter.

[0048] The reel (20, 30) shown in FIG. 5B has a horizontally oriented core shaft (24, 34) and two vertically disposed flanges (41a, 41b). A reel may be driven in a rotation direction during loading and unloading a cable 3. The weight of the stored cable 3 is transferred through bearings of the core shaft (24, 34). Preferably, some form of back tension is applied, counter-acting the effects of gravity, and a reel is typically filled layer by layer, from the core to the outer diameter.

[0049] The turntable, or alternatively static tank (20, 30), shown in FIG. 5C has a vertically disposed inner core (24, 34), surrounded by an outer cylindrical retaining wall 43, and a bottom flange 42. A turntable may be driven in a rotation direction during loading and unloading a cable 3, whereas the static tank is not rotated. The weight of the stored cable 3 is evenly distributed over the bottom flange 42 and transferred to a suitable foundation. Back tension is not necessary. A turntable or static tank is typically filled layer by layer, from bottom flange to top.

[0050] Although storage units are preferably cylindrical, they may adopt other shapes, such as oval shapes. They may be provided with specific storage unit properties, such as partitions and core extenders for instance.

[0051] The device according to the invention may comprise more than two storage units arranged such that a storage unit n+1 when rotating in the reeling direction can simultaneously reel in a part of the cable originating from the source and another part of the cable originating from a storage unit n.

[0052] FIG. 7 illustrates the total uninterrupted cable length 50 spooled onto the total number of storage devices (as a percentage of the length for one storage device) and the efficiency 60 versus the number 51 of storage devices used. It can be concluded from this figure that a single storage device has the maximum efficiency of 100% of its capacity. Efficiency is seen to drop to 75% for two devices, 68% for three devices, and further to a limit value of 50% for larger numbers of devices. The total storage length however increases linearly with an increasing number of devices, each additional device adding 50% to the total storage length.

[0053] The device according to the invention may also comprise storage units of different circumferential size, for instance diameter.

[0054] FIG. 8 illustrates the total cable capacity 55 (as a percentage of the largest storage unit's capacity) as a function of the capacity ratio 52 of the smallest over the largest storage device (in percent). It can be concluded from this figure that the larger the capacity differences between two storage devices, the higher the efficiency. Further, two equally-sized storage devices have an efficiency of 75%. When selecting storage devices for a certain required capacity, it is most efficient to choose one storage device as large as possible and selecting the smallest possible device to contain the additionally required capacity.

[0055] A further efficiency increase may be obtained when at least two top-loading storage devices are used, such as turntables or static tanks. In such a configuration, cable is spooled from a first storage device to a second storage device near the core of said second storage device, while cable is also spooled from a source to the second storage device near the outside diameter of said second storage device. This configuration may yield an increased efficiency of 80% (relative to 75%). The efficiency gain may be attributed to the fact that a wrap or layer near the core of a storage device holds less cable length than a wrap or layer near the outer diameter of the storage device.