The invention relates to a cutter suction dredger.

Dredging is an excavation operation performed underwater. The purpose is to collect bottom sediments and transport them to another location. This is often used to keep waterways at required depths, to build new harbors or to replenish the sand on beaches.

If the bottom sediment is already lose it can easily be sucked by a suction dredger. However, if a more rocky bottom is to be excavated, the bottom needs to be cut into pieces, before the bottom pieces can be transported.

It is known to use a cutter suction dredger to loosen the bottom. This is generally done by moving a large rotating head with a plurality of cutting elements over the bottom. After this cutting operation, the loosened parts are sucked up by a suction mouth at the end of the suction tube of the dredger.

Cutter suction dredgers operate by swinging the suction tube with cutter head over the bottom. The swinging action is achieved by using winches and cables.

A disadvantage of cutter suction dredgers is, that the cutting element are subjected to severe wear and need to be replaced often. This requires to lift the cutter head out of the water. Another disadvantage is that the cutter arm has to be constructed as heavy and as stiff as possible. The weight of the cutter arm will help the cutter teeth to loosen the rock. The overall construction and maintenance costs of cutters is very expensive .

Another known technique to loosen the bottom is to drill holes in the bottom and insert explosives. After the explosion, the loose parts can be dredged with a common suction dredger. However, introducing explosive is a time consuming job.

From the offshore industry it is known to use laser beams when drilling an oil well. For example CA 2576756

discloses the use of a laser beam to locally heat the rocks of the bottom. Then the rocks are suddenly cooled by the surrounding water, which causes cracks in the rock and loosens the rock. Afterwards, the loosened rock can be sucked away with a common suction dredger.

A limitation of using a laser beam is that the laser beam needs to be pointed at a single location for a certain time to have the rock heated sufficiently to get a reliable thermo shock effect. This is not a problem when drilling an oil well.

However, when scanning the bottom surface when dredging, this laser beam method from the prior art cannot be used as the laser beam is not kept at a single position long enough to get the desired thermo shock effect.

It is an object of the invention to improve the known cutter suction dredgers.

This object is achieved with a cutter suction dredger comprising a suction tube with a cutter head, wherein the cutter head comprises:

- a continuous track for running the cutter head over a bottom surface;

- at least one laser head arranged at the track for directing a laser beam to the bottom surface.

The continuous track provided for a stable base at the bottom. From this stable base, the laser head can be easily directed at a single point of the bottom in order to heat the specific bottom portion.

As the laser head is arranged at the track, the laser head will be stationary relative to the bottom, as long as the part of the track with the laser head is in contact with the bottom.

With a preferred embodiment of the cutter suction dredger according to the invention a guide rails is arranged near the continuous track, wherein the laser head is pivotably arranged to the continuous track and wherein the laser head is guided in the guide rails to keep the laser beam directed to the bottom surface. With the guide rails it is possible to keep the laser head at all times directed to the bottom, independent of the position of the laser head along the continuous track.

Another preferred embodiment of the cutter suction dredger comprises a vessel to which the suction tube is

arranged, a laser beam generating device arranged at the vessel and a glass fiber for directing the generated laser beam to the laser head at the track.

A laser beam generating device is generally quite expensive especially when a high power laser beam is desired. By arranging the laser beam generating device on the vessel, the device is arranged in an environment which can rather easily be controlled. The generated laser beam is then guided by an optical fiber to the tip of the cutter head to emit the

generated laser beam close to the bottom. Any filtering of the surrounding water is herewith minimized.

In yet another embodiment the continuous track comprises a number of links and the at least one laser head is arranged to a link of the continuous track. A number of laser heads can be arranged at this way to a number of links of the continuous track. When the track runs along the bottom, the bottom is heated at predetermined intervals along the path of the track. In such an arrangement one could also provide an high pressure water jet. Such a water jet will improve the thermo shock on the rock, because after the laser has heated up the rock locally and possible even a small hole was drilled by the laser, the water will be pressed into the hole and cool down the rock very quickly. As a result the rock will crack even quicker. The water will also evaporate due to the heat. The quick expansion from fluid to gas also will improve the cracking of the rocks.

Another advantage of such a water jet is that it will help to protect the laser lens and it will also give the laser a much cleaner laser path as clean water can be supplied through the j et .

In still another embodiment of the cutter suction dredger according to the invention the suction mouth of the suction tube is arranged downstream of the continuous track. When the laser beam or laser beams have provided the heat to the bottom and parts of the bottom have come loose due to the thermo shock, the downstream arranged suction mouth will clean up the loose parts and transport them to a desired location.

In yet another embodiment of the cutter suction dredger of the invention it is also possible to construct a drag head for a hopper dredger provided with the laser cutter head.

Because it is no longer necessary to put force on the cutter head/cutter teeth there is no need for a heavy cutter arm and even a hopper can do the same job as a cutter. Due to the much longer arms of hoppers one can even cutter much deeper as before .

One could also construct a similar laser cutter on a track without a fixed arm and only a flexible hose and flexible cable for the laser connected to a ship, pontoon or another vessel. In such a way one could operate the track from a

distance. Even a similar construction with the a laser cutter track remotely controlled from ashore is a possibility.

Instead of a laser other suitable beams can be used.

These and other features of the invention will be elucidated in conjunction with the accompanying drawings.

Figure 1 shows a perspective view of an embodiment of the cutter suction dredger according to the invention.

Figure 2 shows a schematic cross sectional view of the continuous track and the laser head according to the invention.

Figure 3 shows a second embodiment of a cutter suction hopper dredger.

Figure 4 shows a detail of the dredger of figure 3.

In figure 1 a vessel 1 is shown having a hull 2. The bridge 6 for controlling the vessel 1 is arranged on top of the deck 5.

On the side of the hull 2 a suction tube 7 with a suction mouth 9 is arranged. The suction tub 7 can be lifted up beside the hull 2 for transportation.

The suction tube 7 is used for collecting loose pieces from the bottom.

Stream upward from the suction mouth 9, in the direction of the arrow M, a laser cutter 10 is arranged. This laser cutter 10 has two parallel continuous tracks 11, 12. In between the two tracks 11, 12 laser heads 13 are arranged. These laser heads 13 are provided with a laser beam by a optical fiber cable 14. The laser beam is generated by a laser beam generating device 15, which is placed on the deck of hull 2.

Figure 2 shows a schematic cross sectional view of the laser cutter 10. The continuous track 11 is build out of a number of links 16. At two positions along the track 11, laser heads 13 are arranged. These laser heads 13 are shielded by a shield 17 to minimize influences from outside.

To keep the laser heads 13 directed to the bottom when they are travelling along the continuous track, a guide rail 18 is arranged, shown schematically. A top part of the laser head 13 is guided in this guide rail 18, which keeps the head 13 in the correct position along the whole track 11.

In figure 3 a hopper dredger 20 according to the invention is shown. The dredger 20 is pulled along the bottom 21. The dredger 20 has a continuous track 22 with links 23.

Behind the continuous track 22 a suction mouth 24 is arranged to collect the rock particles.

Figure 4 shows a detail of a link 23 of the continuous track 22 of figure 3. The link 23 has a U-shaped frame in which two nozzles 25 are arranged. Each nozzle 25 has a center channel 26, in which an optic fiber 27 is arranged.

Concentric to the center channel 26 a second channel 28 is arranged, which is supplied with fluid from a main pipe 29. This fluid, preferably water, is pressurized such that a

powerfull jet is created around the laser beam emitted from the optic fiber 27 through the center channel 26.

The advantage of using a hopper dredger is that the arms are substantially longer, such that the cutting action can be performed at lager depths.