DE68926295T2 - EXCAVATOR - Google Patents

Abstract

A method and apparatus for dredging in flowing waters comprising a support member (3) carrying thrust means (13) so that the thrust means (13) is directed downwardly towards the area to be cleared, the support member (3) being mounted in the water so that in operation it presents a surface towards the flow of water which causes a resultant downward component of force to balance the upward component of force caused by the thrust means (13).

Description

The invention relates to dredgers for removing sand, silt and the like from a river bed or from the bottom of a lake and is used, for example, for clearing wrecks.

For lifting material, the most common device is a suction dredger, where the suction is generated by a motor-pump unit, similar to a vacuum cleaner. However, when clearing wrecks, such devices have the disadvantage that small or light objects are also lifted from the wreck; even if a screen is provided in the suction path, the objects may be small enough to pass through the screen, or they may be damaged when hitting the screen, or it may be difficult to separate them from other objects lifted.

A modified form of the suction method used in tidal dredging is to provide a vertical section of pipe above the area to be cleared, with air under pressure at the lower end of the pipe being forced upwards through the pipe. This creates a vacuum which acts to lift sand, silt and other material and place it in suspension with water, whereupon it is carried away from the area by the pipe. This method is reliable in reducing the risk of small or light objects being lost, but it is time consuming due to the relatively small diameter of the pipe, which is normally about 0.5 m, and is therefore limited to covered areas.

Another method used in relatively shallow tidal waters, for example up to 10 m depth, is to moor a tug, ship or other vessel in a fixed position above the area to be cleaned and to direct the propeller wash downwards using a suitable guide plate. Flushing disturbs the material around the wreck, causing the material to be lifted, placed in suspension and carried away from the site by the tide. In addition to the shallow depth, another disadvantage of this method is that, in the case of a large wreck, the position of the vessel must be changed progressively to cover the entire area of the wreck, which is difficult and time consuming.

US-A-4123858, which reproduces the preambles of claims 1 and 3, describes a dredging device comprising a watertight, vertically elongated rigid hull, of sufficiently small dimensions to be transported across highways, with a removable sluice extending from the top.

According to the invention there is provided a method of dredging in flowing water comprising lowering a support element carrying a thrust member so that the thrust member is directed downwards towards the area to be cleared, characterized in that the orientation of the support element in the water can be adjusted so that it forms a surface relative to the flow which produces a resulting downward vertical force component and by operating the thrust member to direct a surge of water towards said area, the turbulence created causing sand, mud and similar material covering the area to be suspended in the water to be carried away from the area by the water flow, the weight of the support element and the resulting downward force component being dimensioned during operation such that a downward force is produced which is greater than the upward force produced by the thrust member.

The support element is preferably lowered from a ship. Although it can be dynamically held in position by support bearings, or on a frame resting on the lake or river bed, it is normally guided into its correct orientation by the adjustment of, for example, cables, chains or telescopic arms. The vessel may initially be stationed immediately downstream of the area to be cleared, after which the vessel is moved forward to cover the entire area at a controlled speed, this movement acting to increase the resulting downward force component on the support element.

The support element can be designed to operate in opposite directions so that the vessel can turn and re-traverse the area after re-adjusting the orientation of the support element by adjusting the cables.

There is also provided a dredging device for carrying out the above method, comprising a support member carrying a thrust member mounted thereon, means for orienting the support member to hold the thrust member in a downward position, characterized in that the support member forms a surface on which the water flow can act to generate a resulting downward force component, the arrangement being such that the weight of the support member in operation together with the resulting downward force component generated results in a downward force which exceeds the upward force generated by the thrust member.

The means for aligning the support element preferably comprises cables or the like which engage the support element at at least three points spaced apart from one another. These means can be mounted on an associated ship.

The support element is preferably in the form of a wing with a housing containing ballast tanks for adjusting its weight depending on the working depth and the type of material to be cleared, the housing also having at least one closed bore extending between its upper and lower surfaces and in which the thrust member is arranged.

The housing is preferably provided with an angled surface along at least one (leading) edge which, during operation, at least partially generates the resulting downward force component.

According to a modification, the thrust element and the drive can be made reversible so that the device can be used as a suction dredger for more general application.

The thrust member may comprise one or more propellers, each arranged within a closed bore to rotate substantially parallel to the plane of the housing, in which case drives for the propeller(s) are mounted on the housing and driven from a power source on board the vessel by means of a cable, hose or the like.

The power source may be an electric generator and the drive an electric motor. Alternatively, the power source may be a hydraulic pump on board the vessel and pressurized fluid may be circulated through the drive unit via flexible hoses, the drive unit comprising a hydraulic motor having a gear meshing with a gear on the and the propeller shafts.

The support organ may be equipped with transducers and/or sonors or similar devices directed downwards so that Use electrical signals corresponding to the working distance and work progress can be fed to a suitable display on board the vessel.

In the following, preferred embodiments of the invention will be described with reference to the accompanying drawings.

Figure 1 is a schematic view showing the dredging process.

Figures 2 (a), (b) and (c) are schematic views of the front side or a longitudinal side or from above of a first embodiment of an excavator device according to the invention.

Figure 3 is a side view of the said excavator device in section.

Figure 4 is a view similar to that of Figure 2(a), partly in section.

Figure 5 is a vertical section through an excavator device according to the invention according to a second embodiment.

Figures 6 and 7 are top views and front views, respectively, of the excavator device according to Figure 5.

Figure 8 is a partially sectioned elevational view of a portion of the dredging device of Figure 5. Figure 9 shows a general arrangement of a cable mounting device for mounting the dredging device of Figure 5.

Reference should be made to Figure 1. A carrier vessel 1 moves against the tide over a wreck 2. To facilitate the process, the area to be covered can be provided with buoys on both sides, or possibly in channels if a wide area is involved, to provide a guideway for the vessel. Alternatively, if the area to be swept is small, the support vessel may be stationed over the area by a four-pump mooring or may be dynamically positioned. A weighted support member 3 is suspended at a suitable distance from the wreck by two pairs of cables 4, 5, arranged fore and aft, one cable of each pair extending from each side of the vessel. The cables of each pair may be driven simultaneously to ensure that the support member maintains a laterally horizontal position. However, the pairs of cables may also be driven independently of each other so that the position of the support member 3 with respect to the horizontal can be adjusted in its longitudinal direction (forward and aft).

Referring to Figures 2 and 3, support member 3 is generally in the shape of a wing and is rectangular in plan view. It is designed as a housing with vertical end walls 6 connected by side walls 7 which in turn form angled surfaces 8 to provide a downward vertical force component when deployed at high tide. The upper wall 9 is substantially flat so that it can be raised and stowed below the bottom of support vessel 1 during transport to or from the work area (indicated by dashed lines in Figure 1) and the lower wall 10 is convex to provide a hydrofoil section to the wing and thus an additional downward force component.

As can be seen from Figure 2 (a), the support element is symmetrical about its lateral axis so that it can be used in both directions with respect to the relevant side wall 7. It can also be seen that the two fastening points 11 spaced apart from one another on each end wall 6 are provided for the cables 4 and 5.

In this embodiment, the housing 3 is provided with two closed vertical bores 12 (see Figures 2 (c) and 3) which are laterally offset from one another; each housing has a thrust element in the form of a propeller 13 which is supported on support arm crosses 16 by means of a shaft 14 and support element bearings 15 (see Figure 2 (c)). The propellers 13 are thus supported in such a way that they rotate essentially in the plane of the housing 3 and are driven in opposite directions in order to reduce the effect of centrifugal forces or centripetal forces. They are driven by means of corresponding gear wheels 17 from corresponding drive shafts 18, which in turn are driven by a central hydraulic unit 19, through which pressure medium flows from supply lines and return lines 20, 21 from a source on board the ship 1.

The support housing 3 is provided with a number of ballast tanks 22, so that the face of the housing can be balanced by injecting or ejecting an appropriate ballast medium such as water and/or sand, mud, etc. from the area to be cleared. In order to pick up the smallest object from a wreck, the smallest force necessary is suitably applied to lift the material to be cleared. Thus, it will be understood that weight adjustment of the support housing is necessary depending on the depth at which the work is carried out and on the amount of thrust required to be generated by the propellers, which in turn depends on the type of material to be cleared, for example light or heavy sand, mud, pebbles, etc.

As previously described, the angled guide surface 8 then generates a downward vertical force component when the tide acts on it and/or due to the forward speed of the vessel; this component can be adjusted by adjusting the forward cables 4 with respect to the rear cables 5 are raised in order to incline the housing and thus its upper wall 9 towards the horizontal.

It is possible that during use, particularly in an inclined position, vortices may occur at the leading edge 7 of the casing, in which case turbulence is generated which causes the casing to generate shear forces. To prevent this, a spoiler 23 may be fitted along the rear edge 7 (see Figure 1). It may also be difficult to keep the casing constantly on course in the flow during operation, in which case appropriate control vanes 24 may be fitted to the upper wall 9, or small rear-facing propulsion units may be used along the trailing edge 7.

In order to ensure that the housing is correctly positioned at the required distance above the area to be cleared and also to provide a TV display of the work progress, a transducer/sonar arrangement may be provided on board the vessel, comprising a pair of transducers 25 (see Figure 3) to detect the distance present on the lower wall 16 in the area of the leading/trailing edge 7 of the support element housing 3, and for the purpose of TV monitoring a centrally located sonar transmitter/receiver 26 may be provided which rotates and scans 360º around the vertical axis of the housing 3.

In a practical embodiment according to the invention, capable of operating to a depth of about 45 meters of water, the support element casing has dimensions of the order of 9000 x 6000 mm with a weight of up to 20 t. This requires a thrust through the support element casing of up to 4 t. In addition, it has been calculated that with such a casing inclined by 20º to the horizontal, a resulting downward vertical force component of up to 0.77 t is generated, depending on the combined velocity of flow and ship. In order to determine the weight and force components, the propellers must be designed in such a way that a thrust of up to 4.5 t is generated.

It will be appreciated that for wider applications the thrusters (propellers) and the drive required for them can be made reversible so that the device can be used as a suction dredger for general clearing work. In this case the thrusters work directly and actively on the blade housing 3 to generate a force component directed essentially downwards; in this case tilting the housing during operation would not be so important with this mode of operation.

Figures 5 to 9 show an alternative embodiment of the invention. Similar parts have the same reference numerals as in the embodiments of Figures 2 to 4.

As before, the support element 3 is essentially in the shape of a wing and is rectangular in plan view. As can be seen from Figure 5, the support element 3 is constructed from three units, a front unit 3A, a middle unit 3B and a rear unit 3C, which are coupled together so that the support element can be dismantled into three sections to facilitate transport.

Two ribs 51, 52 extend upwardly from the upper wall 9, each of which extends from the region of the leading edge to the region of the trailing edge. Each closed vertical bore 12 extends upwardly through a corresponding rib 51, 52.

In this case, the propellers 13 are driven by corresponding electric motors 53 via a gear 54, which can be seen in detail in Figure 8. Each electric motor 53, each gear 54 and the propellers 13 are six Struts 66 extending to the wall of the corresponding bore 12, one strut 66 carrying an electrical cable 57.

The excavator according to Figures 5 to 8 can be operated and suspended in the same way as in the first embodiment of the invention.

Alternatively, the wing dredger can be suspended in the manner shown in Figure 9 (the support member 3 is shown only schematically). Two cables 58 run down from the support member ship to a corresponding ring 59, and each ring carries a cable loop 61. Each loop 61 runs over a corresponding pair of rollers 62, 63; one roller 62 is located in the area of the leading edge of the dredger, and the other roller 63 is located in the area of the trailing edge of the dredger. Each cable loop 61 also wraps around a corresponding drive 64 in the middle of the dredger. It will be understood that the horizontal position of the excavator can be changed by rotating each roller 64 if the effective length of the cable section between each roller 64 and the corresponding ring 59 via the corresponding roller 62 is changed in relation to the effective length of the cable section between each roller 64 and the corresponding ring 59 via the corresponding roller 63. Each roller 64 can be driven, for example, by means of an electric motor (not shown).

This arrangement simplifies the mounting of the dredger on ship 1.

The dredgers described above have a wide range of uses; for example, they can be used simply for normal dredging purposes, i.e. clearing a channel in a river or sea. A dredger with side dimensions of approximately 9m x 6m can be used to clear a river bed or sea bed of heavy clay in a channel approximately lom wide, Sm deep and loom long in about six hours. This means that around 300 tons of clay could be cleared away within these six hours.

If the riverbed or lakebed consists of sand or mud, a much larger volume of material could of course be cleared away within these six hours.

In addition to dredging, the excavator can be used for salvage, i.e. for clearing mud and silt from wrecks.

A particularly interesting application is to dig a trench into which oil pipelines can be laid and where the trench can be filled again by a similar operation of the excavator.

The excavator can be used to clear away mud, which is referred to as the "Christmas tree" in the oil industry.

The excavator can also be used to level a construction site on which an oil rig is to be installed and it can be used conveniently to remove mud that accumulates around the feet of an oil rig so that the oil rig can be removed.

According to another application, the dredger can be used to remove the upper layer of mud from a river bed or lake bed so that an offshore operation can penetrate to the lower layers of interest.

Although the excavator is shown suspended from a ship, it can of course also be suspended from a crane standing on a quay or from a barge.

Other uses of the dredger include stirring up a riverbed to keep toxic substances in the current so that they do not settle on the riverbed, thus preserving life in the river.

Claims (17)

1. A method of dredging in flowing water, comprising lowering a support element (3) carrying a thrust member (13) so that the thrust member (13) is directed downwards towards the area to be cleared, characterized by adjusting the orientation of the support element (3) in the water so that it forms a surface relative to the current which produces a resulting downward vertical force component, and by operating the thrust member (13) to direct a surge of water towards said area, the turbulence generated causing sand, mud and similar material covering the area to be suspended in the water to be carried away from the area by the water flow, the weight of the support element (3) and the resulting downward force component being dimensioned during operation such that a downward force is generated which is greater than that exerted by the thrust member (13) generated upward force. 2. Method according to claim 1, characterized in that the support element (3) is supported by a ship (1) via flexible support means (4, 5) and brought into its correct orientation by adjusting the flexible support means (4, 5), that the ship (1) is initially stationed immediately downstream of the area to be cleared, whereupon the ship (1) is moved forward to cover the entire area at a controlled speed, and that this movement acts to increase the resulting downward force movement on the support element (3). 3. Excavator device for carrying out the method according to claims 1 or 2, with a support element (3) which has a thrust member (13) mounted thereon, with means (4, 5) for aligning the support element (3) for the purpose of holding the thrust member in a downwardly directed position, characterized in that the support element (3) forms a surface on which the water flow can act in order to produce a resultant downwardly directed force component, and that the arrangement is such that the weight of the support element (3) in operation together with the resultant downwardly directed force component generated result in a downwardly directed force which exceeds the upwardly directed force which in turn was generated by the thrust member (13). 4. Device according to claim 3, characterized in that the supporting element (3) has the shape of a wing comprising a housing (3) having ballast tanks (22) to adjust its weight, and that the housing (3) further comprises at least one closed bore (12) which runs between its upper and lower surfaces and in which the thrust member (13) is arranged. 5. Device according to claim 3 or 4, characterized in that the housing (3) is provided on at least one of its guide edges with an angled surface which at least partially generates the resulting downward force component during operation. 6. Device according to one of claims 3 to 6, characterized in that the thrust member (13) is reversible. 7. Device according to one of claims 3 to 6, characterized in that the thrust member (13) has at least one propeller (13) which is arranged within a closed bore (16) is arranged to rotate substantially parallel to the plane of the support element (3). 8. Device according to claim 7, characterized in that a drive (19) for the propeller or propellers is arranged on the housing (3) and is operated by an external energy source. 9. Device according to claim 8 in combination with a ship (1), characterized in that the external energy source is a hydraulic pump on board the ship (1), and that pressure medium is supplied by the drive (19) via flexible hoses, and that the drive (19) has a toothing (17) which meshes with a toothing on the shaft (14) of the propeller or propellers (13). 10. Device according to claim 7, characterized in that a drive (19) for the propeller or propellers (13) comprises an electric motor (53) which is arranged coaxially to the axis of the propeller or propellers (13). 11. Device according to one of claims 3 to 10, characterized in that the said means (4, 5) for aligning the support element (3) comprise a plurality of flexible support means (4, 5). 12. Device according to claim 11, characterized in that the flexible support means (4, 5) comprise ropes (4, 5). 13. Device according to claim 12 in combination with a ship (1), characterized in that the ropes hang from the ship (1) onto the water surface. 14. Device according to claim 13, characterized in that four flexible support means (4, 5) are provided, one at each corner of the support element (3). 15. Device according to claim 13, characterized in that two flexible support means (58) hang down from the ship (1), that two flexible support means (61) run from the lower end of each of the previously mentioned flexible support means to a front and rear corner of the support element (3) and that means (64) are provided to adjust the relative length of each of the two second-mentioned flexible support means (61). 16. Device according to claim 15, characterized in that the means (64) for adjusting the relative lengths of the two second-mentioned flexible support means comprise a driven drum (64) which is mounted on the support element (3) and can be driven. 17. Device according to one of claims 3 to 15, characterized in that the support element (3) is equipped with transducers (25) and/or sonars or similar devices which are directed downwards in such a way that, during operation, electrical signals are generated to indicate the progress of the work.