Suction dredger provided with an improved dredging tube

Abstract

 A suction dredger comprises a dredging tube (3) which at one end carries a suction head (4) and which at the other end is connected to the suction dredger hull (1) through a hull pivot (41) with a pivot axis which is generally transverse with respect to said hull, said dredging tube (3) comprising a tube (6,7) and a frame (8) which carries an upper tube part (7) of the tube (6,7) and which is connected to the hull pivot (41) through a first frame pivot (10) the pivot axis of which is transversely oriented with respect to the hull pivot axis of the hull pivot (41), a lower tube part (6) of the tube (6,7) being connected to the frame (8) through a second frame pivot (11) which is opposite the first frame pivot (10) and the pivot axis of which is transversely oriented with respect to the first frame pivot axis, a motor driven suction pump (31) being provided for transporting dredged material through the tube (6,7), said frame (8) having a cross-sectional contour defined by a height dimension and a transverse dimension. The upper tube part (7) over at least part of its length is positioned fully within the cross-sectional contour (38) of the frame (8).

Description

[0001] The invention is related to a suction dredger, comprising a dredging tube which at one end carries a suction head and which at the other end is connected to the suction dredger hull through a hull pivot with her pivot axis which extends transverse with respect to said hull, said dredging tube comprising a tube and a frame which carries an upper tube part of the tube and which is connected to the hull pivot through a first frame pivot the pivot axis of which is transversely oriented with respect to the hull pivot axis of the hull pivot, a lower tube part of the tube being connected to the frame through a second frame pivot which is opposite the first frame pivot and the pivot axis of which is transversely oriented with respect to the first frame pivot axis, a motor driven suction pump being provided for transporting dredged material through the tube, said frame having a cross-sectional contour defined by a heigth dimension and a transverse dimension.

[0002] Such a section dredger is disclosed in United States patent 4.295.286. The dredging tube thereof comprises a frame formed of longitudinally extending hollow profiles of a rectangular cross-section. Said profiles are interconnected by a series of transversely oriented hollow profiles. The upper tube part comprises a tube section which is mounted at a relatively large distance above said frame, while another tube section is mounted at a smaller distance. Other embodiments of such dredging tubes are known as well. In those embodiments, the complete upper tube part has been mounted at some distance above the frame.

[0003] Although such dredging tubes have performed well in the past, problems arise in those instances wherein the dredging operations are to be carried out in waters having greater depths. Such greater depths may occur in several operations, such as mining operations, for instance in mining minerals which are deposited on the seabed, sand extraction etc. The dredging tubes which are applied in those circumstances have a considerable length, which inevitably leads to increased loadings of the mechanical components such as the frame. In fact, the frame tends to flex somewhat under those loadings, which flexing deformation influences the upper tube part mounted on the frame. Having regard to the fact that the upper tube part is at some distance away from the neutral line of the frame, said upper tube part is subjected to tensile or compression forces, depending on the flexing direction of the frame. Despite the fact that expansion bellows are provided in the upper tube part, such tensile or compression forces can lead to overloadings. During a dredging operation, the upper tube part is completely filled with a relatively stiff column consisting of water and dredged material. Under those conditions, any loading which tends to change the length of the upper tube part, would lead to an acceleration or deceleration of the moving mass of water and dredged material. In fact, the upper tube part with its contents then behaves as a very stiff component, which would lead to appreciable load increases. As a result, the mountings by means of which the upper tube part is mounted onto the frame are heavily loaded as well which in the end can lead to rupture.

[0004] The object of the invention is to provide a suction dredger of the type described before, which is less vulnerable with respect to overloading of the frame and upper tube part. Said object is achieved in that the upper tube part over at least portion of its length is positioned fully within the cross-sectional contour of the frame.

[0005] By having at least a portion, and preferably the largest portion, or all, of the tube part positioned within the frame, the above addressed problems are solved completely or at least to a large extent. The tube part in question is now positioned closely to or at the position of the neutral line of the frame, which means that said tube part will only be subjected to flexing loadings, and not to tensile or compression loadings. As a result, the structure of the dredging tube is less prone to failure; the internal loads can remain limited. Stress concentrations at the mountings between the upper tube part and the frame are prevented.

[0006] A further important advantage of the dredging tube according to the invention is the relatively low weight thereof. A low weight of the dredging tube in turn also influences in a positive way the construction of the cranes and cables, by means of which the dredging tube is positioned outside the vessel hull. As a result of the relatively low weight of the dredging tube, the construction of those elements can be lighter as well, leading to a further load and cost saving.

[0007] In this connection it is important to note that the upper tube part and the lower tube part are expendable components which from time to time have to be replaced. In particular in cases wherein materials of a highly abrasive character are transported through the tube, the inner wall of the tube wears down which means that after a certain service time, the tube has reached its maximum useful life. With the aim of allowing for the replacement of the upper tube part, which is largely positioned within the frame, the upper tube part may comprise interconnected tube sections, and the frame may comprise at least one access opening the length of which is larger than the length of at least one of the tube sections so as to allow insertion or extraction of such tube section into respectively out of the frame.

[0008] The frame of the dredging tube according to the invention can be carried out in several ways. For instance, the frame can be assembled from plates provided with openings, which open plates are welded together. This means that such frame would not comprise closed chambers, which makes the process of welding the frame less complicated. It should be borne in mind that the prior art frame described before consist of a multitude of closed chambers, which are indeed difficult to manufacture. Moreover, such chambers should be designed with sufficient resistance to withstand the external overpressure which is developed when submerging the frame. Moreover, such closed chambers provided a frame with a buoyant force, which may hamper the proper operation of the dredging tube. All these conditions make the prior art frames with closed chambers expensive.

[0009] According to the invention, a further improvement can be obtained in case the frame comprises at least three longitudinal frame elements which are interconnected through truss members. Such a spatial truss-like structure on the one hand provides a strong and stiff support for the tube, while on the other hand the upper tube part can be fully accommodated within the internal open space of such structure. It is important to note that similar spatial truss-like structures can be obtained in many different ways, at relatively low cost due to their relatively simple production process.

[0010] Preferably, the spatial truss-like structure comprises four longitudinal frame elements which define a cross-sectional contour. This contour may have any suitable shape, such as a rectangular or square shape. Other shapes, e.g. a parallellogram shape, are possible as well... The respective neighbouring pairs of longitudinal frame elements are interconnected through truss members. With the aim of removing or replacing tube sections, at least one of the longitudinal sides of the frame has a side section where truss members are lacking for providing the access opening.

[0011] The spatial truss-like structure can be carried out in several ways, but preferably the lower and transversal sides of the frame are provided with slantingly oriented truss members. The remaining side, which usually is the top side of the frame, is preferably provided with transversely oriented truss members, the access opening being defined between two of said transversely oriented truss members. A proper of support of the upper tube part can be obtained by providing a first bulkhead near the first frame pivot, the upper tube part emanating through said first bulkhead. Furthermore, a second bulkhead can be provided near the second frame pivot, the upper tube part emanating through said second bulkhead as well.

[0012] In a known fashion, the suction pump and the drive train, including motor and transmission, are accommodated in the frame. In this connection, the cross-sectional dimensions of the frame at or near the location of the suction pump and the drive train can be larger than the cross-sectional dimensions of the frame at a distance from said location.

[0013] Depending on the suction head to be used, also a pressure line can be provided for feeding a pressurised fluid towards the suction head, said pressure line being supported by the frame. According to the invention, a further improvement and simplification of the suction tube structure can be obtained in case the frame comprises at least one pipe shaped longitudinal frame element, said pipe shaped frame element forming part of the pressure line. The pressure line, which now forms part of the frame structure itself, despite the fact that it is not near the neutral line of the frame, is not adversely affected by any flexing or our correctional movement of the frame, having regard to the fact that the longitudinal frame elements in question are designed to carry such loads.

[0014] The invention is also related to a dredging tube for a suction dredger as described before, said dredging tube comprising a tube and a frame which carries an upper tube part of the tube, a first frame pivot having a first frame pivot axis, a lower tube part of the tube being connected to the frame through a second frame pivot which is opposite the first frame pivot and the pivot axis of which is transversely oriented with respect to the first frame pivot axis, a motor driven suction pump being provided for transporting dredged material through the tube, said frame having a cross-sectional contour defined by a height dimension and a transverse dimension. According to the invention, the upper tube part over at least part of its length, is positioned fully within the cross-sectional contour of the frame.

[0015] Similarly, the invention is also related to a frame for a dredging tube addressed before, said frame comprising a spatial truss-like structure provided with a first frame pivot having a first frame pivot axis and an opposite second frame pivot having a second frame pivot axis which is transversely oriented with respect to the first frame pivot axis, said spatial truss-like structure comprising at least one access opening the length of which is larger than the length of all the other openings in said structure.

[0016] The invention will now be described further with reference to an embodiment of a dredging vessel with a suction tube according to the invention as shown in the drawings.

Figure 1 shows a side view of a suction dredger.

Figure 2 shows the upper tube part of the suction tube, together with frame according to the invention, in perspective view.

Figure 3 shows a top view of the upper tube part with frame.

Figure 4 shows a side view of the upper tube part with frame.

Figure 5 shows a cross-section of the upper tube part with frame.

[0017] The suction dredger shown in figure 1 comprises in general a hull 1, onto both sides of which a dredging tube 3 is connected. Only one of these dredging tubes 3 is visible in figure 1. In a manner known per se, said dredging tube 3 has a suction head 4 at one end. At the other end, an elbow 5 has been provided which is connected to an aperture in the hull's side wall so as to be pivotable around an axis 41 which extends transverse with respect to said side wall. Furthermore, the dredging tube 3 comprises a lower tube part 6, and an upper tube part 7 which is carried by a frame 8. Furthermore, an electric motor together with the suction pump unit 9 is carried by a said frame 8.

[0018] Furthermore in a known fashion, the frame 8 is connected to the elbow 5 by means of a pivot 10, the axis of which is perpendicular with respect to the transverse axis by means of which the elbow 5 is connected to the ship's hull. At the other end, by means of a second pivot (cardan joint) 11, the frame 8 is connected to the lower tube part 6. This lower tube part 6 in turn comprises two lower tube sections 12, 13, interconnected through a third pivot (cardan joint) 14. The lower tube part section 12 is connected to the suction head by means of a fixed connection 15. The axes of the second and third pivot 11 and 14 are generally horizontal. Through gantries and cables, not shown, the dredging tube 3 is supported from the hull 1, in such a way that the suction head 4 is positioned on the bed 16 of the water body 17.

[0019] With reference to the figures 2-5, the upper tube part 7 together with frame 8 will be described further. Said frame 8 comprises total number of four longitudinal frame elements 18. At the transversal sides 19, 20, each pair of two neighbouring longitudinal frame elements 18, are mutually connected by means of slantingly oriented truss members 23. Also the lower side 21 of the frame 8 comprises slantingly oriented truss members 24, which interconnect the two lower longitudinal frame elements 18. The upper side 22 of the frame 8 does not comprise such slantingly oriented truss members, but instead a number of transversely oriented truss members 24. It is pointed out that at least two of these transversely oriented truss members 25, enclose a relatively large longitudinal opening 40, the purpose of which will be described below.

[0020] The first pivot 10 it is fork shaped, as is the second pivot 11 the second pivot axis of which is transversely oriented with respect to the first pivot axis of the first pivot 10. At the end near the first pivot 10, a bulkhead 26 has been provided, and at the end near the second pivot 11, and for a bulkhead 27 has been provided. Between these bulkheads 26, 27, the upper tube part 7 extends. Said upper tube part 7 comprises several upper tube part sections 28, which are interconnected inter alia through an expansion bellows 29. The motor and pump unit 9 has been accommodated in said upper tube part 7. Said unit 9 comprises the motor 30, coupled to the centrifugal pump 31. The tangential outlet 32 of said centrifugal pump 31 is connected to the Z-shaped part 33 of the upper tube part 7. Finally, the upper tube part 7 comprises a suction section 34; the combined tube part sections 33 and 28 together form a pressure section.

[0021] With the aim of feeding pressurised liquid to the suction head 4, the dredging tube 3 also carries a pressure line 35. At the location of the frame 3, said pressure line 35 is to a large extent formed by one of the lower longitudinal frame elements 18. Said longitudinal frame elements 18, through said pipe studs 36, 37, is connected to a further parts of the pressure line 35.

[0022] As addressed before, the upperside 20 of the frame 8 has a relatively large opening 40, defined between two transversely oriented truss members 25. The length of this opening 40 is somewhat larger than the length of the largest upper tube part section 28. Thereby, these upper tube part sections 28 can be removed from within the contour 38 of the frame 8, as shown in figure 5. Furthermore, these upper tube part sections 28 can be easily replaced, after they have worn down due to the abrasive character of the materials transported.

[0023] As shown in figures, the frame 8 comprises a prismatic part 39 of a constant cross-section and contour, and also a widened part 41 for accommodating the motor and pump unit 9.

Claims

1. Suction dredger, comprising a dredging tube (3) which at one end carries a suction head (4) and which at the other end is connected to the suction dredger hull (1) through a hull pivot (41) with a pivot axis which is generally transverse with respect to said hull, said dredging tube (3) comprising a tube (6, 7) and a frame (8) which carries an upper tube part (7) of the tube (6, 7) and which is connected to the hull pivot (41) through a first frame pivot (10) the pivot axis of which is transversely oriented with respect to the hull pivot axis of the hull pivot (41), a lower tube part (6) of the tube (6, 7) being connected to the frame (8) through a second frame pivot (11) which is opposite the first frame pivot (10) and the pivot axis of which is transversely oriented with respect to the first frame pivot axis, a motor driven suction pump (31) being provided for transporting dredged material through the tube (6, 7), said frame (8) having a cross-sectional contour defined by a height dimension and a transverse dimension, characterised in that the upper tube part (7) over at least part of its length is positioned fully within the cross-sectional contour (38) of the frame (8).

2. Suction dredger according to claim 1, wherein the upper tube part (7) comprises interconnected tube sections (28, 33), the frame (8) comprising at least one access opening (40) the length of which is larger than the length of at least one of the tube sections (28, 33) so as to allow insertion or extraction of such tube section (28, 23) into respectively out of the frame (8).

3. Suction dredger according to any of the preceding claims, wherein the frame (8) comprises at least three longitudinal frame elements (18) which are interconnected through truss members (23, 24, 25).

4. Suction dredger according to any of the preceding claims, wherein the frame (8) comprises four longitudinal frame elements (18) which define a cross-sectional contour, e.g. having a rectangular or square shape, and the respective neighbouring longitudinal frame elements (18) are interconnected through truss members (23, 24, 25).

5. Suction dredger according to claim 2 and 3 or claim 2 and 4, wherein at least one (22) of the longitudinal sides (19-22) of the frame has a side section where truss members are lacking for providing the access opening (40).

6. Suction dredger according to claim 4 and 5, wherein the lower (21) and transversal sides (19, 20) of the frame (8) are provided with slantingly oriented truss members (23, 24).

7. Suction dredger according to claim 4 and 5, wherein the other side (22) of the frame (8) is provided with transversely oriented truss members (24), the access opening (40) being defined between two of said transversely oriented truss members (24).

7. Suction dredger according to any of the preceding claims, wherein a first bulkhead (26) has been provided near the first frame pivot (10), the upper tube part (7) emanating through said first bulkhead (26).

8. Suction dredger according to any of the preceding claims, wherein a second bulkhead (27) has been provided near the second frame pivot (11), the upper tube part (7) emanating through said second bulkhead (27).

9. Suction dredger according to any of the preceding claims, wherein the suction pump (31) and the drive train, including motor (30) and transmission, are accommodated in the frame (8).

10. Suction dredger according to claim 9, wherein the cross-sectional dimensions of the frame (8) at or near the location of the suction pump (31) and the motor (30) are larger than the cross-sectional dimensions of the frame (8) at a distance from said location.

11. Suction dredger according to claim 10, wherein the frame (8) comprises a prismatic part (39) which borders the first frame pivot (10), and a widening part (41) which is connected to the prismatic part (39).

12. Suction dredger according to any of the preceding claims, wherein the frame pivots (10, 11) are fork shaped.

13. Suction dredger according to any of the preceding claims, wherein a pressure line (35) is provided for feeding a pressurised fluid towards the suction head (4), said pressure line (35) being supported by the frame (8).

14. Suction dredger according to claim 13, wherein the frame (8) comprises at least one pipe shaped longitudinal frame element (18), said pipe shaped frame element (18) forming part of the pressure line (35).

15. Suction dredger according to one of the preceding claims, wherein the second and/or the third frame pivots (11, 14) comprise a cardan joint.

16. Dredging tube (3) for a suction dredger according to any of the preceding claims, said dredging tube (3) comprising a tube (6, 7) and a frame (8) which carries an upper tube part (7) of the tube, a first frame pivot (10) having a first frame pivot axis, a lower tube part (6) of the tube being connected to the frame (8) through a second frame pivot (11) which is opposite the first frame pivot (10) and the pivot axis of which is transversely oriented with respect to the first frame pivot axis, a motor driven suction pump (31) being provided for transporting dredged material through the tube (6, 7), said frame (8) having a cross-sectional contour defined by a height dimension and a transverse dimension, characterised in that the upper tube part (7) over at least part of its length which extends in the longitudinal direction of the frame (8), is positioned fully within the cross-sectional contour of the frame (8).

17. Frame (8) for a dredging tube (3) according to claim 15, said frame (8) comprising a spatial truss-like structure provided with a first frame pivot (10) having a first frame pivot axis and an opposite second frame pivot (11) having a second frame pivot axis which is transversely oriented with respect to the first frame pivot axis, said spatial truss-like structure comprising at least one access opening (40) the length of which is larger than the length of all the other openings in said structure.

18. Frame (8) according to claim 17, wherein the length of the access opening (40) is at least twice the length of all the other openings.

Drawing