Device for dredging soil material under water

1. A device for dumping material onto an underwater bottom or installation, such as a pipeline, the device comprising:

a vessel, provided with a fall pipe through which the material is dumped on the underwater bottom;

a steering device adapted to control the motion of the fall pipe relative to the underwater bottom;

first monitoring means adapted to monitor the state of the underwater bottom;

second monitoring means adapted to monitor the position of the steering device relative to the bottom;

further monitoring means adapted to measure the flow rate of the material transmitted through the fall pipe and the velocity of the vessel; and

computing means adapted to compute, on the basis of data obtained from the first, the second and the further monitoring means, control signals for moving the steering device.

2. The device according to claim 1 , wherein the computing means are adapted to compute the control signals for moving the steering device such that an optimum criterion is minimized.

3. The device according to claim 2 , wherein the optimum criterion comprises the difference between the actual state of the bottom as measured by the first monitoring means and a desired state of the bottom.

4. The device according to claim 3 , wherein the desired state of the bottom concerns its depth profile and the first monitoring means are adapted to measure the depth profile of the bottom.

5. The device according to claim 1 , wherein the first monitoring means comprise an ultrasonic and/or an optical camera.

6. The device according to claim 1 , wherein the second monitoring means comprise a global positioning system.

7. The device according to claim 1 , the device comprising an input/output device adapted to transfer the signals from the first and/or the second and/or the further monitoring means to the computing means.

8. The device according to claim 1 , the device comprising display units adapted to display the position of the steering device, the vessel and/or the state of the bottom, in particular its depth profile.

9. The device according to claim 1 , wherein the steering device is provided at the lower end of the fall pipe and comprises driving means.

10. A method for dumping material onto an underwater bottom or installation, such as a pipeline, the method comprising the steps of:

dumping the material on the underwater bottom through a fall pipe of a vessel;

controlling the motion of the fall pipe relative to the underwater bottom by a steering device;

monitoring the state of the underwater bottom and, the position of the steering device relative to the bottom, as well as the flow rate of the material transmitted through the fall pipe and the velocity of the vessel;

computing, on the basis of data obtained from this monitoring, control signals for moving the steering device; and

moving the steering device (and the fall pipe) in accordance with these control signals.

11. The method according to claim 10 , wherein the control signals for moving the steering device are computed such that an optimum criterion is minimized.

12. The method according to claim 11 , wherein the optimum criterion comprises the difference between the actual state of the bottom as measured and a desired state of the bottom.

13. The method according to claim 12 , wherein the desired state of the bottom concerns its depth profile and the depth profile of the underwater bottom is monitored during dumping.

14. The method according to claim 10 , wherein monitoring the state of the underwater bottom is carried out by an ultrasonic and/or an optical camera.

15. The method according to claim 10 , wherein the amount of dumped material per meter of movement of the steering device is kept substantially constant.

16. The method according to claim 15 , wherein the amount of dumped material per meter of movement of the steering device is kept substantially constant by regulating the flow rate of material through the fall pipe relative to the velocity of the vessel.

17. A computer comprising program instructions for carrying out the method according to claim 10 .