The invention relates to a dredging device for dredg ^¬ ing by water injection, comprising fluidization means to flu- idize sediment on a bottom of a waterbody which is to be dredged, and means to transport the device along and above the sediment to be dredged. The waterbody may be of any type such as a river or sea, a harbour basin, a reservoir, etc.

Such a device is known from EP-A-0 119 653 and from EP-A-0 243 994. The known device comprises piping with first water jet nozzles to fluidize or dilute sediment on a bottom of a waterbody which is to be dredged, at least a pump to sup- ply the piping with water under pressure, and means to transport the device and its piping with the water jet nozzles along and above the sediment to be dredged. In the known de- vice a vessel is used from which the piping with the downward- ly directed water jet nozzles are lowered by means of a tackle or otherwise. The piping with the nozzles is tracked along the bottom of the river or sea by the moving vessel. Water is sup- plied to the piping from the vessel by appropriate pressure means .

There are a number of disadvantages or problems that associate with this known device.

In the first place it requires a lot of manpower and therefore costs to operate the device.

Secondly dredging with the device of the prior art is sensitive to waves. The waves cause that the level of the pip- ing and the water jet nozzles varies, due to which effective dredging cannot always be guaranteed.

A third problem is that there is a maximum depth at which dredging can be carried out because the dimensions of the construction below the vessel are not without limitations. With larger depths the underwater construction becomes bulkier and heavier, whereas the vessel must accordingly be upscaled. Both factors contribute to increased costs and impose limita- tions on the maximum water depth at which the dredging can be carried out.

A fourth problem is that although dredging by water injection is much more energy-efficient than other known means of dredging, still the operation of the vessel places a high C02 burden on the environment, which problem becomes larger when dredging must be performed under more difficult circum- stances such as larger water depth.

A fifth problem is that the prior art manner of dredging provides hindrance for the other water traffic.

Ά sixth problem is that moored vessels and pontoons prevent effective dredging below such vessels and pontoons.

It is therefore an object of the invention to address or at least alleviate these problems.

WO99/50508 discloses a submersible dredging device for dredging by water injection, comprising fluidization means embodied as jet pumps to fluidize and/or dilute sediment on a bottom of a waterbody which is to be dredged, and means to transport the device along and above the sediment to be dredged.

The submersible dredging device according to WO99/50508 only partly addresses the above-mentioned problems of the prior art. Notably the first problem, the third prob- lem, the fourth problem, the fifth problem and the sixth prob- lem still exist with the submersible dredging device according to WO99/50508.

According to a first aspect of the invention the sub- mersible dredging device is an independently and autonomously movable submersible vehicle equipped with piping with first water jet nozzles and at least a pump to supply the piping and the water jet nozzles with water under pressure to fluidize and/or dilute the sediment on a bottom of a waterbody which is to be dredged, which device comprises means to transport the device along and above the sediment to be dredged, wherein the device has a sensor for measuring a distance of the device to the bottom to be dredged, and wherein the device is computer- controlled with a computer mounted in the device that is pro- vided with an algorithm which is arranged to execute the dredging according to a pre-established scheme, and wherein the algorithm is arranged to manoeuver the device in depend- ence of a signal from the sensor.

The feature that the device has a sensor for measur- ing a distance of the vehicle to the bottom to be dredged, wherein the algorithm is arranged to manoeuver the device in dependence of a signal from the sensor, enables amongst others that an optimum height of the nozzles with respect to the sed- iment to be dredged can be maintained. This improves the effi- ciency of the dredging operation. The sensor may be functional according to several principles, for instance acoustic or oth- erwise.

It is remarked that EP 2 423 102 discloses a submers- ible vehicle equipped with a memory and sensors that in one of the disclosed embodiments is autonomously movable underwater. This vehicle is however an inspection vehicle which may occa- sionally be used for repair of pipelines, and which is there- fore outside the scope of a skilled person looking for im- provement or modification of a submersible dredging device. Accordingly the document is silent on dredging and does not disclose anything that relates to improving the efficiency of the dredging.

The autonomously movable submersible dredging vehicle of the invention provides several further beneficial features; the vehicle being autonomous reduces the amount of manpower involved for its operation, and further the fact that it is submersible and fully autonomously movable means that it can operate independently below the water level and be therefore insensitive to the effect of waves. A further important fea- ture is that it is possible with the device of the invention to perform dredging at larger depths than is possible accord- ing to the prior art.

Beneficially the algorithm is arranged to adapt the pre-established scheme to meet predefined requirements. The scheme therefore needs not to be stationary but can automati- cally adjust to circumstances underwater where the dredging occurs .

The propulsion of the device of the invention can suitably be performed with a conventional screw propulsion. In a preferred embodiment or desirably in combination with the other features of the device of the invention it is preferable however that the device has second water jet nozzles for providing propulsion to the device. This effectively uses parts of the device that are anyway required for performing dredging by water injection. Apart from being effective this therefore also saves on costs. In case second water jet noz- zles are used for propulsion, these water jet nozzles are preferably aligned approximately horizontally during use.

Beneficially the device has energy storage on board.

The energy storage may for instance be a battery pack, or oth- er suitable means such as a pneumatic storage of compressed air, or a fuel-cell. The energy from the energy storage may be used for driving the water pump which may thus have the water expel from the first water jets for dredging, and -if present- from the second horizontal water jets to provide propulsive forces to the device.

Advantageously in case the device is provided with a battery pack, the above-mentioned algorithm is arranged to re- turn the device to a docking station at water level when the charge level of the battery pack runs low.

It is further preferable that the battery pack is chargeable with photovoltaic cells provided on top of the de- vice and/or forming part of the docking station, or with other suitable sources of green energy at or through the docking station to save on the C02 impact on the environment.

The invention will hereinafter be further elucidated with reference to the drawing of an exemplary embodiment of an apparatus according to the invention that is not limiting as to the appended claims.

In the drawing:

-figure 1 shows a device according to the invention in an isometric view from above; and

-figure 2 shows the device of figure 1 in an isomet- ric view from below.

Whenever in the figures the same reference numerals are applied, these numerals refer to the same parts.

With reference both to figure 1 and figure 2 for clarity purposes a "translucent" principle scheme of a dredg- ing device 1 according to the invention is shown which may be used for dredging by water injection. The device 1 comprises piping 2, wherein figure 2 shows that said piping 2 is provid- ed with first water jet nozzles 3 which may be used to fluid- ize or dilute sediment on a bottom of a waterbody which is to be dredged.

Both figure 1 and figure 2 also show a pump 4 and an electric pump drive 5 to supply the piping 2 with water under pressure to be expelled through the first waterjet nozzles 3. The water is obtained through an inlet (not shown) that is provided on a superficial area of the device 1.

Figure 1 and figure 2 also show means to transport the device 1 and its piping 2 with the water jet nozzles 3 in the form of second water jet nozzles 6 for providing propul- sive forces to the device. It is however within the scope of the invention to provide other means of propulsion to the de- vice, such as a conventional screw propulsion. As the figures show during use the second water jet nozzles 6 are aligned horizontally. The earlier mentioned pump 4 can be used for providing the propulsive energy to the device 1.

As figure 1 and figure 2 show the device 1 is not me- chanically linked to any other device or apparatus, which un- derlines that the device 1 is an autonomous submersible vehi- cle. The device 1 can be remotely operable through a wireless connection, however it is preferred that the device 1 is com- puter-controlled with a computer 8 mounted in the device 1 which is provided with an algorithm that is arranged to exe- cute the dredging according to a pre-established scheme. It is also possible that this pre-established scheme is adaptable to meet certain circumstances underwater where the dredging oc- curs and which are not anticipated by said scheme at the start of the dredging. Figure 2 shows that it has sensors 9 (one sensor can suffice) for measuring a distance of the device 1 to the bottom to be dredged, wherein the algorithm is arranged to manoeuver the device in dependence of a signal from the sensors 9. The sensors 9 which can be used for measuring depth and distance are connected to the on board computer 8.

To support the autonomous character of the device 1 of the invention it has an energy storage, in this embodiment a battery pack 7 on board. The just mentioned algorithm is preferably arranged to return the device 1 to a docking sta- tion (not shown) above water level when the charge level of the battery pack 7 runs low. Preferably the battery pack 7 is chargeable with photovoltaic cells provided on top of the de- vice 1 and/or forming part of the docking station. It is also possible to provide in using green energy which is made avail- able at or through the docking station. The way how this can be implemented is completely clear to the skilled person, so that an explanation with reference to the drawing can be dis- pensed with.

Although the invention has been discussed in the foregoing with reference to an exemplary embodiment of the ap- paratus of the invention, the invention is not restricted to this particular embodiment which can be varied in many ways without departing from the invention. The discussed exemplary embodiment shall therefore not be used to construe the append- ed claims strictly in accordance therewith. On the contrary the embodiment is merely intended to explain the wording of the appended claims without intent to limit the claims to this exemplary embodiment. The scope of protection of the invention shall therefore be construed in accordance with the appended claims only, wherein a possible ambiguity in the wording of the claims shall be resolved using this exemplary embodiment.