In this specification, references to the sea bed should be construed broadly, and as such should be deemed to include river beds, lake beds and the like.

There are various applications, motivated by both environmental and commercial considerations where it may be beneficial to excavate an underwater sea oed. For example, diamonds occur in certain rock and sediment formations lying below the surface of the sea bed. This is the case on the southern west coast of Africa, where typically the highest concentrations of diamond deposits lie between approximately 0.3 metres and 0.8 metres below the gravel layer surface. Apparatus is required for extracting the top layer, preferably to a depth of approximately one metre, to allow the diamonds to be mined.

1 Another application lies in the dredging of harbours or 2 ports where the constant use of oil-based fuels to power 3 marine craft leads to the polluting of the sea bed; 4 creating the desire to provide a means for the periodic 5 lifting and filtering or other cleaning of the sea bed 6 material. A yet further application that is envisaged in 7 consequence to growing environmental concerns relates to 8 the extraction of drill cuttings in the vicinity of off- 9 shore drilling sites.

10 11 The present invention is not limited to these 12 applications but finds utility in any situation where it 13 might be advantageous to excavate the sea bed. Usually, 14 this will also involve the raising of the sea bed 15 particles or other matter to the surface where would be 16 positioned a ship or boat housing the means for 17 performing some operation such as cleaning or separating 18 the matter, for example.

19 20 In the art there are provided diverse means for 21 excavating sea beds. One such means that is used in 22 fairly loosely compacted sea beds involves the use of one 23 or more suction units that are dragged by an overhead 24 ship across the sea floor. Suction is provided by 25 pumping apparatus located on the ship. However this 26 technique is associated with a number of disadvantages, 27 including the relative low efficiency of employing 28 suction as a sole means to encourage the dislodging and 29 uplifting of sea bed material. Movement of the suction 30 means in loosely defined linear paths also leads to poor 31 surface coverage of the entire sea bed; there inevitably 32 being gaps between the linear paths and inconsistencies 33 in the depth of penetration of the apparatus. Dragging 34 heavy equipment across the sea bed may also lead to the

inadvertent damage of pipelines or other sub sea structures.

It is an object of the present invention therefore to provide an improvement to this technique, and moreover to offer a systematic method for removing the sediment top layer of a sea bed with improved sea bed coverage at a consistent depth.

According to the present invention there is provided apparatus for use on a sea bed, the apparatus comprising a chamber defining a volume of sea water located above an area to be excavated, wherein the apparatus further comprises agitation means located within the chamber for agitating the sea bed in the said area and one or more suction means for receiving sediment or other sea bed material agitated by said agitation means.

Preferably the chamber is substantially open at a lower part thereof.

Alternatively the chamber is partially closed at a lower part thereof by a flexible membrane and securing means, wherein the flexible membrane defines an enclosed passageway between the chamber and the sea bed.

The suction means may communicate with one or more rigid or flexible delivery risers for conveying the sea bed material to a vessel or platform located on the sea surface. Typically the vessel or platform would be provided with pumping equipment for generating suction in the suction means.

1 The chamber preferably acts as a barrier to contain the 2 agitated material from the sea bed within a volume 3 defined by the chamber. This serves to increase the 4 efficiency of the apparatus in that the disturbed sea bed 5 material is captured in the excavation area such that it 6 is maintained as available for collection by the suction 7 means.

8 9 The agitation means is preferably a device for jetting 10 sea water at the sea bed. It may for example comprise of 11 a hydraulically driven propeller that is adapted to 12 propel sea water within the chamber forcibly toward the 13 sea bed. The propeller would encourage a circular flow 14 of water in a horizontal plane, but other means may also 15 be included, such as vanes, fins, to encourage such 16 circular flow.

17 18 Alternatively, the agitation means comprises mechanical 19 blades or other members adapted to agitate the sea bed by 20 consequence of physically impacting the sea bed. A yet 21 further alternative may be that the agitation means 22 incorporates a sonic or ultrasonic device.

23 24 Preferably the suction means includes one or more inlets 25 for the intake of sea bed material, wherein the or each 26 inlet is disposed toward the perimeter of the chamber.

27 Most preferably, an inlet is provided at each corner of 28 the lower open side of the chamber.

29 30 The chamber may be further provided with a vent to 31 balance the volume of water in the chamber. The vent may 32 be associated with a valve or plug such that the vent is 33 kept open in normal operation, but in the event that the 34 apparatus becomes trapped in the sea bed can be closed 1 enabling the suction process to be reversed thus freeing 2 the apparatus. Reversal of the suction process may 3 involve the use of the agitation means.

4 5 Preferably, the chamber has a skirt at the lower edge of 6 its side walls, the skirt being robust and resilient.

7 8 According to a second aspect of the invention there is 9 provided a method of excavating a sea bed comprising the 10 steps of isolating an area of the sea bed; agitating the 11 sea bed in the said area and sucking the agitated sea bed 12 material to a surface vessel or the like.

13 14 Preferably the area is isolated by a physical barrier.

15 The sea bed may be agitated by inducing high velocity 16 fluid movement inside the isolated area.

17 18 Preferably the said method is conducted for a first 19 period of time and then repeated for successive periods 20 in respect of successive areas to be excavated.

21 22 Most preferably each successive excavation area is 23 adjacent the preceding area such that optimum coverage of 24 the sea bed is performed.

25 26 In order to better convey the invention embodiments will 27 now be described by way of example only with reference to 28 the accompanying Figures, in which: 29 30 Fig. l shows a schematic elevation of a subsea 31 diamond mining system; 32 33 Fig. 2 shows in elevation excavation apparatus in 34 accordance with the invention; 1 2 Fig. 3 is a plan view of the excavation apparatus 3 illustrated in Fig. 2; 4 5 Fig. 4 is a computer generated simulation of the 6 movement of sea water and sea bed material inside 7 the chamber of Figs. 2 and 3; 8 9 Fig. 5 is a plan view of an alternative embodiment 10 of the excavation apparatus illustrated in Fig. 2; 11 and 12 13 Fig. 6 shows in elevation an alternative embodiment 14 of the excavation apparatus in accordance with the 15 invention; 16 17 With reference firstly to Fig. 1, a sea going vessel 1 is 18 provided with hoisting equipment 2 for the controlled 19 lowering and raising of excavation apparatus, generally 20 depicted at 3. The vessel may be provided with means for 21 separating diamonds or material including diamonds from 22 other waste material obtained from the sea bed. It 23 should be appreciated that such means are not critical to 24 the present invention; the invention hereto being 25 concerned with the efficient and systematic collection of 26 excavated material from the sea bed.

27 28 The excavation apparatus 3 is more clearly depicted in 29 Figs. 2 and 3. The apparatus 3 includes a chamber 4 30 formed substantially as a cube, but with an open lower 31 side. The lower side 5 is therefore approximately 32 square, and in the example embodiment is dimensioned with 33 sides of 5 metres.

34

A twenty inch diameter lift line 6 feeds into the chamber and divides via a manifold into four arms 7, each arm 7 terminating with an inlet 8. The line 6 provides a suction medium for sucking and conveying sea bed material up to the vessel 1.

Descending through the centre of the chamber is a relatively powerful water driven propeller 9. The propeller 9 is adapted to thrust sea water downwardly and forcibly onto the sea bed. The momentum of the propelled sea water is sufficient to agitate the sea bed to such extent as to cause sediment and other particles tc unsettle and travel around the chamber 4. It will be appreciated that the rotary action of the propeller 9 will cause the sea water and agitated sea bed material tc move in a swirling direction, which will encourage the sea bed material to migrate to the corners of the chamber 4. Accordingly, the suction inlets 8 are ideally located at these corners for the efficient collection of the sea bed material.

This may be more clearly demonstrated by Fig. 4 which illustrates a simulation of the movement of the seabed material in the chamber 4. The velocity of the material is dependent on its location in relation to both the propeller 9 and the suction inlets 8. Accordingly, material located directly under the propeller 9 and towards the centre of the sides of the chamber 4 is affected least, while the material located towards the edges of the propeller 9 and adjacent to the suction inlets 8 is displaced most.

In an alternative embodiment, the chamber 4 may be provided with means to improve the swirling effect of the

propeller 9 to ensure that the seabed within the area of the chamber 4 is efficiently agitated. Figure 5 illustrates such an alternative embodiment where baffles or directing blades 10 positioned below the propeller 9 are used to achieve this effect.

A further embodiment of the chamber 4 may be provided such that a flexible membrane 11 and chain 12 are incorporated on the lower side 5 of the chamber. Such an embodiment is illustrated in Figure 6. The flexible membrane 11 is employed to define a shallow passageway 13 across the sea bed. The propeller 9 is then used to generate a high velocity water flow across the sea bed.

The water flow enters the passageway 13 at the inlet 14 before passing into the suction inlet 8 at the other end.

As the water flow passes through the passageway 13 it carries with it sediment so permitting excavation of the sea bed. The chain 12 is employed to weigh down the flexible membrane 11 and so stop it billowing upwards when the high velocity water flow passes underneath.

As the sea going vessel 1 passes over the area to be excavated, the apparatus 3 is placed such that the chamber 4 is stationary on the seabed. The sediment is then agitated by the action of the propeller 9. The suction arms 7 draw the sediment through the inlets 8 to the vessel 1. Agitation of a single area is typically done for 30-45 seconds depending on the nature of the sea bed to allow an appropriate depth to be excavated.

Once in the vessel 1 the sediment can be filtered to remove the desired material, such as diamonds, and subsequently returned to the sea bed. The apparatus is then translocated to a neighbouring section of the sea

bed and the process is repeated. The design of the apparatus is such that the entire sea bed can be covered improving the overall efficiency of the process.

Although unlikely, it might be possible as a result of the agitation process that the apparatus can sink into the sea bed and can become stuck. Accordingly, the chamber 4 is also provided with a valve (not shown) which is open during normal operation. However, in the event that the apparatus becomes stuck in the sea bed the valve can be closed and the suction process reversed to free the apparatus. Potentially, this may be achieved in two ways, namely: 1) the suction through the lift line 6 may be replaced by downward flow, or 2) the suction through the lift line may be deactivated and the upward reaction force of the propeller 9 be relied upon.

It will be noted from the example embodiments that the agitation of the sea bed is achieved without causing any direct impacting of the agitation device on the sea bed.

This mitigates the possibility of damaging any existing structures that might pre-exist on the sea floor.

A further advantage of the present invention is that there is provided apparatus with improved capacity/efficiency for excavating a sea bed or the like as a result of improved coverage, higher concentration of material entering the suction arms and deeper penetration of the bed.

Further modifications and improvements may be added without departing from the scope of the invention herein intended.