GB2142956A - Dredging apparatus - Google Patents

Abstract

Dredging apparatus which is particularly suitable for use in marinas and other relatively confined waterways comprises a pontoon 12 supporting four submersible dredging heads 34. Each dredging head 34 comprises a horizontally extending scoop 50 of approximately C-shaped cross-section, with a helical scroll or auger 66 extending coaxially along it. Material dredged up by the scoop 50 is driven along it to one end by the scroll 66, to enter the inlet of a positive displacement sludge pump 52. The pump 52 pumps the dredged material up to the surface and onto the pontoon 12, for subsequent pumping to a barge 59. <IMAGE>

Description

SPECIFICATION Dredging apparatus This invention relates to dredging apparatus. The invention is more particuiarly, but not exclusively, concerned with dredging apparatus suitable for use in shallow, confined, waterways such as marina.

There are many types of dredging apparatus in current use, examples of which are the cutter suction dredger, the trailer suction dredger, the grab dredger, the bucket dredger and the hydraulic backhoe dredger. However, although these dredgers operate satisfactorily in large scale dredging operations in open water, they are subject to a number of drawbacks if it is desired to use them in relatively confined, shallow, waterways such as marinas.

For example, before grab dredging a marina can begin, it is usually necessary to dismantle and remove all the berthing pontoons, floating walkways and similar structures normally present in the marina. This dismantling, and the subsequent reassembly after the dredging operation, can be extremely expensive, not only because of the work involved, but also in terms of the lost revenue resulting from the inability to use the marina while these structures are removed. Additionally, since the underwater portions of the structures tend to be heavily corroded and/or encrusted, dismantling them involves a considerable risk of damage, and consequent further expense.

Drawbacks involved in the use of suction type dredgers, which are typically used in large, coastal, marinas, include the relatively low solids/water ratio achievable in the dredging process: this in turn increases the difficulty of disposing of the dredged solids at sea. Also, a suction-type dredging operation is not able to control accurately the final dredge level achieved. It will be appreciated that this latter drawback is particularly significant in a marina or like environment.

It is therefore an object of the present invention to provide dredging apparatus in which at least some of the abovementioned drawbacks are significantly alleviated, so that the apparatus is suitable for use in marinas ans other shallow, confined, waterways.

According to the present invention, there is provided dredging apparatus including a submersible dredging head arranged to be moved substantially horizontally at a desired depth below the surface of a waterway to be dredged, said dredging head comprising elongate scoop means adapted to be moved substantially horizontally into, and to collect, the material to be dredged, rotary helical transfer means mounted in the scoop means with its axis of rotation extending longitudinally of the scoop means, drive means for rotating said helical transfer means so that the material dredged from the bottom of the waterway by the scoop means is driven longitudinally of the scoop means by the helical transfer means, and positive displacement pump means arranged to receive the dredged material which has been driven along the scoop means and to pump it to the surface of the waterway for subsequent disposal.

The invention will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a plan view showing how dredging apparatus in accordance with the present invention is used to dredge a marina; Figure 2 is a more detailed plan view of the dredging apparatus of Figure 1; Figure 3 is a side view of the dredging apparatus of Figure 1, in operation; and Figure 4 shows an alternative embodiment of part of the dredging apparatus of Figure 1.

The dredging apparatus shown in the drawings is indicated generally at 10, and comprises a floating support structure in the form of a generally rectargular pontoon 12, typically 12.5 metres by 5 metres.

The pontoon 12 is typically made up of five generaly similar pontoon sections 1 2a to 12e, so that it can be readily disassembled for transportation. The three pontoon sections 1 2a to 1 2c nearest the forward end or bow 13 of the pontoon 12 are typically each 5 metres by 2.5 metres, with their longer dimension extending across the width of the pontoon. The other two pontoon sections 12d and 12e are each typically 5 metres by 1.7 metres, with their larger dimensions extending longitudinally of the pontoon 12, and are spaced apart to define a gap 14 therebetween.

The dredging apparatus 10 its shown in Figure 1 in a typical marina, of the kind having floating walkways 15 disposed between many pairs of fixed piles 16. The waterways of the marina include a plurality of berthing areas 18, and a main waterway 20 by which boats using the marina can enter and leave the berthing areas 18. To permit the dredging apparatus 10 to be moved about the marina, to dredge up silt and like material which may have accumulated in it, the pontoon 12 is provided with winches 22, typically four, which are connected via steel cables to suitable achorage points throughout the marina: these cables are indicated at 23.

The winches 22 are typically hydraulically operated, the hydraulic fluid required for their operation being provided by a suitable power unit 24. The power unit 24, which includes a diesel engine arranged to drive an electrical generator and a hydraulic pump (not shown), is mounted in the pontoon section 12c, and its associated fuel oil and lubricating oil tanks 25 are also mounted in this pontoon section. A control cabin 26, containing controls for the power unit 24, the winches 22 and all the other main equipment of the dredging apparatus 10 as will be hereinafter described, is mounted on the pontoon section 12b.

The pontoon section 12a, which, in use, constitutes the forward end or bow 13 of the pontoon 12, is provided in its leading edge with two symmetrically disposed, downwardly sloping cutaway portions 30.

Two similar elongate arms 32, of steel lattice, box section construction, each have one end pivotally secured in a respective one of the cutaway portions 30, so that the arms extend parallel to each other and downwardly from, and forwardly of, the pontoon 12.

Each arm 32 has a respective pair of elongate dredging heads 34 secured to its lower end, such that the dredging heads of each pair extend horizon tally and in opposite directions from their respective arm, with their longitudinal axes aligned.

The arms 32 are independently suspended by steel wires 36 from a rectangular (or goal-post-shaped) frame 38, which extends forwardly from the pontoon section 12a and is secured to the pontoon section 12b by steel wires 39. The wires 36 are individually wound and unwound by a double winch 40 on the pontoon section 12c, the winch 40 being hydraulically driven from the power unit 24. Thus, as the wires 36 are reeled in and out by the winch 40, the arms 32 pivot in the cutaway portions 30, so varying the depth at which the respective pairs of dredging heads 34 are held beneath the pontoon 12.

The dredging heads 34 are shown in more detail in Figures 2 and 3, from which it can be seen that each of them comprises scoop means in the form of an elongate scoop 50, and a hydraulically-driven, positive displacement, sludge pump 52 disposed on the upper face of the lower end of the respective arm 32.

The pump 52 can be a reciprocating (ie piston and cylinder) pump, but is preferably a rotary positive displacement pump of the sliding vane type. The hydraulic fluid for driving the variable-speed hydraulic motors (not shown) which drive the sludge pumps 52 is supplied from the power unit 24 via pipes (not shown) which extend along the insides of the box sections of the arms 32. The inlet of each pump 52 is coupled by a short pipe 53 to the mounting end of its respective scoop 50 (ie the end of the scoop connected to the respective arm 32), while the outlet of each pump is connected up to the pontoon 12 by a flexible pipe 54 also extending along the inside of the box section of its respective arm. The pipes 54 extend along the pontoon 12, and discharge into a large sludge tank 55 supported between the pontoon sections 1 2d and 12e.The bottom of the tank 55 has an outlet which is directly coupled to the inlet of a large electrically driven centrifugal slurry pump 56. Power for driving the pump 56 is derived from a further power unit 57, which comprises a further diesel engine and electrical generator set mounted on the pontoon sections 12d and 12e so as to extend across the gap 14 therebetween. The outlet of the pump 56 is connected via a pipe 58 supported on floatation collars 58a to a barge 59 or other suitable receptacle for the silt and like material dredged up by the dredging heads 34.

Each scoop 50 is generally C-shaped in crosssection, with a substantially flat, forwardly project ing, horizontal base 60. Additionally, each scoop 50 is connected to its arm 32 by a coupling which permits the scoop to turn to a limited extent about its longitudinal axis. Respective hydraulic rams (not shown) control the angular positions of the scoops 50 so as to keep their bases 60 horizontal when the angle of the arms 32 is changed to vary the depth at which dredging is to be effected.

As the dredging apparatus 10 is moved forwardly by means of the winches 22 and the steel cables 23 as described earlier, the leading edge of the base 60 cuts into the silt 62 or other material to be removed from the bottom of the marina (hereinafter referred to simply as silt), and the cut-way silt is scopped up and collected by the scoop 50.

The concave portion of the C-shape of each scoop 50 behind the flat base 60 is approximately simicircular in section, and defines a shroud which half surrounds a rotary helical material transfer device, or scroll, 66 extending substantially the whole length of the scoop. Each scroll 66 tapers (ie reduces in diameter) towards the mounting end of its scoop 50, and is driven by a further hydraulic motor 70 mounted at the other end of the scoop. The direction of rotation of each scroll 66 is such that silt scooped up by its scoop 50 is moved therealong, by a kind of "augering" action, towards the mounting end of the scoop, and thus into the inlet of the respective sludge pump 52.

The silt entering the inlet of the sludge pump 52 is pumped by the pump up the flexible pipe 54 to the surface, and discharged into the tank 55. The centrifugal pump 56, which operates as if it were immersed in the tank 55, then pumps the silt to the barge 59 for subsequent disposal at a remote location. If the silt contains significant amounts of sand, water can be added to the tank 55, to facilitate the operation of the pump 56.

In order to prevent the ingress of the kinds of solid objects which are typically found on the bottom in marinas, such as bottles, tyres and the like, which objects could damage or jam the pump 52, the scoop 50 can be provided with closely spaced steel bars (not shown), which extend rearwardly and upwardly from the leading edge of the base 60 to the leading edge of the top of the C-shape of the scoop. These bars have the effect of causing such solid objects to tend to ride upwardly over the bars, and thus over the top of the scoop 50. If desired, a net of wire mesh (not shown) can be attached to the back of the scoop 50, to catch the majority of these solid objects.

The dredging apparatus 10 possesses a number of significant advantages when used in a marina-type environment. As can be seen in Figures 1 and 2, the two furthest-apart dredging heads 34 project laterally beyond the sides of the pontoon 12, and can therefore dredge underneath the floating walkways 15 of the marina. Further, the dredging depth can be continuously and accurately controlled by means of the wires 36 and the winch 40, for example as the water level in the marina changes with the tide.

Additionally, the shape of the scoops 50 tends to produce a relatively flat bottom, which is clearly important in a marina.

The combined action of the scoops 50 and their scrolls 66, together with the use of the positive displacement pumps 52, tend to result in a relatively high solidsiwater ratio, typically 70:30, for the dredged material pumped to the surface by the pumps 52. This in turn reduces the discharge of dirty water back into the marina from the barge.

Figure 4 is a somewhat diagrammatic end view of an alternative way of implementing the scoop means of each of the dredging heads 34 of Figures 1 to 3, for use when the material to be dredged is more compacted and therefore more difficult to scoop up.

The dredging head of Figure 4 is referenced 34a, and its scoop means comprises five axially spaced, coaxially aligned bucket wheels 80: the nearest bucket wheel 80 is viewed in Figure 4 is shown in dotted lines. The bucket wheels 80 are secured together to form a single unit, a respective such unit replacing each of the scoops 50 of Figures 1 to 3.

Each bucket wheel 80 has four equiangularlyspaced buckets or scoops 82 around its periphery, and is angularly displaced by 18 with respect to the next, so that the twenty buckets 82 are spaced at 18 intervals.

The bucket wheels 80 coaxiallysurround and are rotatably supported on an elongate circular-section trough or gutter 84, which is in the form of a horizontal extending cylinder open along its upper side or top 86. A variable-speed hydraulic motor (not shown) drives all five bucket wheels 80 to rotate together in the direction of the arrow A, as the dredging head 34a is moved as described earlier in the direction of the arrow B. The trailing wall 88 of each bucket 82 extends inside its bucket wheel 8û, as shown in dotted lines at 90, to bear on the outside of the trough 84. As a result of this, material cut away and picked up by each bucket 82 is carried round the outside of the trough 84 until it reaches the open top 86, whereupon it drops in.

The trough 84 contains a scroll 66a similar to the scrolls 66 of Figures 1 to 3, although the tapering feature may be omitted. Each of these scrolls 66a augers the dredged material in its trough 84 to the inlet of a positive displacement pump (not shown) substantially identical to the pumps 52 of Figures 1 to 3.

Many modifications can be made to the described embodiments of the invention. For example, the invention can also be implemented as described in co-pending United Kingdom Patent Application No.

8314906, whose priority is claimed in the present application.

Clearly, there need be only one arm 32 and dredging head 34 or 34a, and the scoop 50 or multiple bucket wheel 80 need extend only to one side of its arm.

Further, the motors 70 which drive the scrolls 66 can be mounted with those which drive the respective sludge pumps 52, rather than in the positions actually shown in Figure 2, while motors other than hydraulic motors, for example electric motors, can be used to drive some or all of the winches 22 and 40, the sludge pumps 52 or 52a and the scrolls 66 or 66a. Additionally, some or all of these motors can be automatically controlled in response to control sig nals derived from concentration meters responsive to the concentration of solids in material being pumped, and/or from torque sensors responsive to the output torque of the motors, and/or from flow velocity sensors responsive to flow velocity at the outputs of the pumps.

Claims (19)

1. Dredging apparatus including a submersible dredging head arranged to be moved substantially horizontally at a desired depth below the surface of a waterway to be dredged, said dredging head com prising elongate scoop means adapted to be moved substantially horizontally into, and to collect, the material to be dredged, rotary helical transfer means mounted in the scoop means with its axis of rotation extending longitudinally of the scoop means, drive means for rotating said helical transfer means so that the material dredged from the bottom of the waterway by the scoop means is driven longitudinally of the scoop means by the helical transfer means, and positive displacement pump means arranged to receive the dredged material which has been driven along the scoop means and to pump it to the surface of the waterway for subsequent disposal.

2. Dredging apparatus as claimed in claim 1, wherein the scoop means comprises and elongate scoop member arranged to be maintained at a substantially fixed angle to the horizontal.

3. Dredging apparatus as claimed in claim 2, wherein the scoop member is approximately Cshaped in cross-section, with a substantially flat, forwardly projecting, base whose leading edge is moved, in use, substantially horizontally into the material to be dredged, the remainder of the C-shape being approximately semi-circular in section and defining a shroud which partially surrounds the rear of the helical transfer means.

4. Dredging apparatus as claimed in claim 3, wherein the mouth of the scoop member is provided with bars extending from said base to the top of the C-shape, to tend to prevent the entry of solid objects into the scoop member.

5. Dredging apparatus as claimed in claim 3, wherein said bars extend rearwardly and upwardly from the leading edge of said base to the leading edge of the top of the C-shape, whereby said solid objects tend to ride up the bars and over the top of the scoop member as the scoop member is moved forward.

6. Dredging apparatus as claimed in claim 1, wherein the scoop means comprises rotary scoop means in the form of a plurality of axially-spaced, coaxially aligned, bucket wheels secured together to rotate as a single unit, and motor means for rotating said bucket wheels.

7. Dredging apparatus as claimed in claim 6, wherein said bucket wheels coaxially surround and are rotatably supported on an elongate open-topped trough of substantially circular cross-section, said helical transfer means being disposed coaxially within said trough.

8. Dredging apparatus as claimed in claim 7, wherein the buckets of said bucket wheels have trailing walls which extend inside the bucket wheels and slide upon the external surface of said trough, thereby serving to carry material dredged by the buckets around the trough and into its open top.

9. Dredging apparatus as claimed in any preceding claim, wherein the helical transfer means tapers in the direction of material transfer.

10. Dredging apparatus as claimed in any preceding claim, wherein said drive means comprises a hydraulic motor.

11. Dredging apparatus as claimed in any preceding claim, wherein the pump means is a rotary positive displacement pump.

12. Dredging apparatus as claimed in any one of claims 1 to 6, wherein the pump is a reciprocating pump.

13. Dredging apparatus as claimed in any preceding claim, wherein the pump means is driven by a hydraulic motor and/or an electric motor.

14. Dredging apparatus as claimed in any preceding claim, wherein the dredging head is secured beneath floating support structure by means of an elongated arm which projects forwardly and downwardly from the floating support structure, and including means for adjusting the position of said arm with respect to the support structure to vary thedepth of the dredging head.

15. Dredging apparatus as claimed in claim 14, wherein said arm makes a substantially fixed angle with said floating support structure, and is either telescopic or slidably supported on said structure so as to be longitudinally movable to vary the depth of the dredging head.

16. Dredging apparatus as claimed in claim 14, wherein said arm is pivotally connected to said floating support structure to vary the depth of the dredging head.

17. Dredging apparatus as claimed in claim 16 and any one of claims 2 to 5, wherein said scoop member is connected to said arm so as to be angularly adjustable about the longitudinal axis of the scoop member, and control means is provided to angularly adjust said scoop member so as to maintain it at a substantially fixed angle to the horizontal as the depth of said dredging head is varied.

18. Dredging apparatus substantially as herein described with reference to Figures 1 to 3 of the accompanying drawings.

19. Dredging apparatus substantially as herein described with reference to Figures 1 to 3, as modified by Figure 4, of the accompanying drawings.