BACKGROUND OF THE INVENTION

The invention relates to a dredging assembly for reclaiming sand or minerals from the seabed or for excavating a trench in the seabed.

A known dredging assembly for reclaiming sand or minerals comprises a vessel and a suction part. The vessel comprises a storage space for the reclaimed sand or minerals, a pump and several cranes, also called derricks, placed on deck of the vessel. The suction member comprises a suction pipe suspended from the derricks, which pipe when operative, with a first outer end at vessel height is connected to the pump and storage space. The second outer end of the suction pipe that is submerged when operative, is provided with a draghead that drags over the seabed.

The maximum dredging depth possible is defined by combining the maximum distance possible between the draghead and the connection of the suction pipe to the vessel and the maximum allowable steepness of the pipe of approximately sixty degrees. When put out of operation, the suction pipe is placed stretched on deck of the vessel. The deck serves to support the suction pipe as a result of which the length of the suction pipe is limited to the length of the deck. The maximum depth to be dredged will in that way be approximately one hundred and twenty metres. It is an object of the invention to provide a dredging assembly, with which sand or minerals can be reclaimed at great depth.

SUMMARY OF THE INVENTION

According to a first aspect, the invention provides a dredging assembly for reclaiming sand or minerals from a seafloor or for excavating a trench in the seabed, comprising an elongated vessel, a submersible part and hoisting mechanisms placed on the vessel for from a number of hoist cables lowering the submersible part into the water alongside the vessel, wherein the submersible part is provided with an elongated pump part and an elongated suction part which at its front is connected to the rear of the pump part, wherein at its opposite rear the suction part is provided with a suction nozzle which in the submerged condition of the submersible part rests on the seafloor, wherein the dredging assembly is provided with a flexible pipe connecting the vessel and the pump part to each other for pumping reclaimed sand or minerals upwards therethrough. The submersible part is suspended from the hoist cables, such that a dredging depth can be achieved that is only limited by the length of the hoist cables and the length of the flexible pipe.

In one embodiment at its front the elongated suction part is movably connected to the rear of the pump part by means of a swivel coupling. In that way the suction part and the pump part can be suspended from the hoist cables at a deviating angle to each other .

In one embodiment, considered in the forward sailing direction, the pump part extends rearwardly inclined and downwardly inclined from the front of the pump part in the direction of the swivel coupling. The downward direction of the pump part can as a result contribute to the dredging depth to be achieved. Moreover this position of the pump part corresponds with the most natural position when the pump part is dragged along below the vessel in the forward sailing direction .

In one embodiment, considered in the forward sailing direction, the suction part extends rearwardly inclined and downwardly inclined from the swivel coupling in the direction of the suction nozzle. In that way the downward direction of the suction part can contribute to the dredging depth to be achieved. This position of the suction part corresponds with the most natural position when the suction part is dragged along below the vessel in the forward sailing direction.

In one embodiment the pump part and the suction part are at an oblique angle to each other. In that way an advantageous angle is achieved in the suction part for sucking the sand or the minerals upwardly therethrough.

In one embodiment, with its front as considered in the forward sailing direction, the pump part is suspended from a first hoist cable lowered from the vessel, wherein with its rear as considered in forward sailing direction, near the swivel coupling, the pump part is suspended from a second hoist cable lowered from the vessel, wherein with its rear as considered in forward sailing direction, near the suction nozzle, the suction part is suspended from a third hoist cable lowered from the vessel. As a result the weight of the pump part and the suction part is largely borne by the hoist cables.

In one embodiment, in submerged condition of the submersible part, the first hoist cable is shorter than the second hoist cable, wherein in submerged condition of the submersible part the pump part is suspended at an angle of less than fifty degrees to the waterline, preferably less than forty-five degrees to the waterline, preferably less than forty degrees to the waterline. This position of the pump part corresponds with the most natural position when the pump part is dragged along from the hoist cables below the vessel in the forward sailing direction.

In one embodiment, in submerged condition of the submersible part, the second hoist cable is shorter than the third hoist cable, wherein in submerged condition of the submersible part, the suction part is suspended at an angle of less than thirty-five degrees to the waterline, preferably less than thirty degrees to the waterline, preferably less than twenty-five degrees to the waterline. At this angle an optimal head pressure on the suction nozzle can be obtained.

In one embodiment, with its front as considered in the forward sailing direction, the pump part is suspended from a pulling cable which considered in the forward sailing direction extends rearwardly inclined and downwardly inclined from the front of the vessel, wherein the first hoist cable, the pulling cable and the part of the elongated vessel in between the first hoist cable and the pulling cable together form a substantially shape-retaining triangular relation. The pulling cable counteracts that the submersible part as a result of external forces, such as the water current or the resistance of the dragging suction nozzle over the seafloor, moves rearward with respect to the forward sailing direction.

In one embodiment at least one of the hoist cables and/or the pulling cable is suspended from a hoisting mechanism which keeps the hoist cables and/or pulling cable at a substantially constant tension. As a result the suction nozzle can continue to drag over the seafloor at a constant head pressure.

In one embodiment in the submerged condition, considered in a horizontal projection transverse to the forward sailing direction, the submersible part is situated straight below the vessel, preferably straight below the rear half of the vessel, preferably in its entirety straight below the vessel. In that case the first, second and third hoist cables are substantially vertical, which is advantageous to the bearing power of the hoist cables.

In one embodiment in the hoisted condition, considered in a horizontal projection transverse to the forward sailing direction, the submersible part is situated straight below the vessel, wherein the pump part and the suction part are in line in each other's extension. In that way the submersible part can easily be hoisted out of the water and be placed above the ship' s deck .

In one embodiment the flexible pipe has a length that exceeds length of the elongated vessel. Due to the length of the flexible pipe a dredging depth can be achieved that exceeds one and a half times the length of the vessel.

In one embodiment the flexible pipe has a length of at least one and a half times the length of the elongated vessel, preferably twice the length of the elongated vessel. Due to the length of the flexible pipe a dredging depth can be achieved that exceeds twice the length of the vessel.

In one embodiment the vessel is provided with a pipe winch that is connected to the flexible pipe for drawing in or dispensing flexible pipe, wherein the flexible pipe in the drawn in condition is borne over substantially its full length by the vessel, and wherein the flexible pipe has one continuous centre line. The flexible pipe can then easily be deployed because the flexible pipe is fully assembled on the vessel and ready to be dispensed.

In one embodiment the depth of the waterline down to and including the suction nozzle resting on the seabed is at least two hundred metres, preferably at least two hundred and fifty metres. According to a second aspect the invention provides a method for by means of a dredging assembly reclaiming sand or minerals from a seafloor or for by means of a dredging assembly excavating a trench in the seabed, wherein the dredging assembly comprises an elongated vessel, a submersible part and hoisting mechanisms placed on the vessel for from a number of hoist cables lowering the submersible part into the water alongside the vessel, wherein the submersible part is provided with an elongated pump part and an elongated suction part which at a front is movably connected to a rear of the pump part by means of a swivel coupling, wherein at the opposite rear the suction part is provided with a suction nozzle which in the submerged condition of the submersible part rests on the seafloor, wherein the dredging assembly is provided with a flexible pipe whic connects the vessel and the pump part to each other for pumping reclaimed sand or minerals upwards therethrough, wherein with its front as considered in the forward sailing direction, the pump part is suspended from a first hoist cable lowered from the vessel, wherein with its rear as considered in forward sailing direction, near the swivel coupling, the pump part is suspended from a second hoist cable lowered from the vessel, wherein with its rear as considered in forward sailing direction, near the suction nozzle, the suction part is suspended from a third hoist cable lowered from the vessel, wherein with its front as considered in the forward sailing direction the pump part is suspended from a pulling cable which considered in the forward sailing direction extends rearwardly inclined and downwardly inclined from the vessel, wherein the method comprises the following steps; from a number of hoist cables lowering the submersible part into the water alongside the vessel; dispensing lengths of the flexible pipe, the hoist cables and the pulling cable, wherein in submerged condition of the submersible part the length of the third hoist cable is longer than the dispensed length of the second hoist cable, wherein considered in the forward sailing direction the suction part extends rearwardly inclined and downwardly inclined from the swivel coupling in the direction of the suction nozzle; by means of the first hoist cable, the pulling cable and the part of the elongated vessel between the first hoist cable and the pulling cable forming a substantially shape-retaining triangular relation, leaving the suction nozzle to rest on the seafloor, moving the vessel in the forward sailing direction, wherein considered in a horizontal projection transverse to the forward sailing direction, the pulling cable keeps the submarine part straight below the vessel; during the movement dragging the suction nozzle over the seafloor. In that way a dredging depth can be achieved that is only limited by the length of the cables and the length of the flexible pipe. Because of the angle at which the suction part is positioned an optimal distribution of forces can be achieved.

In one embodiment in submerged condition of the submersible part the length of the second hoist cable is longer than the dispensed length of the first hoist cable, wherein considered in the forward sailing direction the pump part extends rearwardly inclined and downwardly inclined from the front of the pump part in the direction of the swivel coupling. Because of the angle at which the pump part is positioned an optimal distribution of forces can be achieved.

In one embodiment the method comprises the step of reclaiming sand or minerals from the seafloor at a depth of at least two hundred metres, preferably at a depth of at least two hundred and fifty metres.

According to a third aspect the invention provides a dredging assembly for reclaiming sand or minerals from a seafloor or for excavating a trench in the seabed, comprising an elongated vessel, a submersible part and hoisting mechanisms placed on the vessel for from a number of hoist cables lowering the submersible part into the water alongside the vessel, wherein the submersible part is provided with an elongated pump part and an elongated suction part which at its front is connected to the rear of the pump part, wherein at its opposite rear the suction part is provided with a suction nozzle which in the submerged condition of the submersible part rests on the seafloor, wherein the pump part is provided with a submarine outlet for submarine ejection of material sucked up by the suction nozzle. The submersible part is suspended from the hoist cables such that a dredging depth can be achieved that is only limited by the length of the hoist cables.

The aspects and measures described in this description and the claims of the application and/or shown in the drawings of this application may where possible also be used individually. Said individual aspects may be the subject of divisional patent applications relating thereto. This particularly applies to the measures and aspects that are described per se in the sub claims.

SHORT DESCRIPTION OF THE DRAWINGS

The invention will be elucidated on the basis of a number of exemplary embodiments shown in the attached drawings, in which:

figure 1 shows a side view of a dredging assembly according to the invention, provided with a deep water part in a submerged condition;

figure 2 shows a side view of the dredging assembly according to figure 1, with the deep water part in a partially hoisted condition; figure 3 shows a side view of the dredging assembly according to figure 1, with the deep water part in a hoisted condition;

figure 4 shows a top view of the dredging assembly according to figure 1, with the deep water part in a hoisted condition;

figure 5 shows a side view of the deep water part according to figure 2;

figure 6 shows a side view of an alternative embodiment of the dredging assembly;

figure 7 shows a top view of an alternative embodiment of the dredging assembly.

DETAILED DESCRIPTION OF THE DRAWINGS

Figures 1-3 show a dredging assembly 1 for reclaiming or dredging sand or minerals from a seabed 9. In addition to obtaining sand or minerals, reclaiming sand or minerals may also have the purpose of excavating a trench in the seabed 9 for arranging a submarine pipeline. The dredging assembly 1 comprises a vessel 2, a deep water part 4 that can be submerged from the vessel 2 in the direction of the seabed 9 and a flexible riser 8 having a length S which connects the vessel 2 and the deep water part 4 to each other.

The vessel 2 is of the "freighter" type, particularly of the "trailing suction hopper dredger" type. The vessel 2 as such comprises an elongated hull 21 having a length P. As shown in figure 4, the hull 21 is provided with a narrow prow 22 tapering into a tip and a wide blunt stern 23. The forward sailing direction is indicated by arrow A. In the elongated hull 21 a loading space 24 is accommodated for storing reclaimed sand or minerals therein.

As shown in figure 4, at the upper side of the hull 21 the vessel 2 is provided with a deck 25. On the deck 25 the vessel 2 is provided with a pipe winch 32 for drawing in and dispensing the flexible riser 8, a pipe rack 34 that navigates the deck 25 and serves to support the flexible riser 8 in the inoperative condition and several pipe guides 33, 38 for guiding the flexible riser 8 over the pipe rack 34 on the deck 25. The riser 8 can be dispensed and drawn in over its full length S without interruption. Preferably the flexible riser 8 is made of one long snake-shaped flexible pipe having a diameter of sixty to one hundred and twenty centimetres. The flexible riser 8 can be built up from several fixedly connected pipe segments having properties comparable to the integral flexible riser 8 described above. The vessel 2 comprises a deckhouse 36 near the stern 23. The deckhouse 36 is provided with a bridge from which the vessel 2 is steered .

On deck 25 the vessel 2 is provided with a first derrick 26 that can move sideward, transverse to the longitudinal direction of the hull 21, and which is placed on the prow 22, a second derrick 27 that can move sideward, transverse to the longitudinal direction of the hull 21, and a third derrick 28 that can move sideward and which are placed spaced apart from each other between the prow and stern 22, 23 on the rear half of the vessel 2, and a fourth derrick 29 that can move sideward and is placed on the stern 23. As considered in the sailing direction A, the derricks 26- 29 are positioned along the right side of the hull 21, also called starboard. Each derrick 26-29 is provided with a cable winch 30 and two derrick pulleys 31 for lowering cables over them alongside the larboard side of the hull 21. As considered in the sailing direction A, a same arrangement is possible at the left side of the hull 21, also called larboard.

As shown in figure 5, the deep water part 4 comprises a pump section 5, a suction section 6 and a cardan coupling 7 which couples the pump section 5 and the suction section 6 to each other. The pump section 5 comprises an elongated pump frame 51 which at a first outer end 55 is connected to the cardan coupling 7. Elongated in this case means a pump frame 51 that is longer than it is wide, wherein the largest length preferably is twice as large as the largest width or height transverse to the longitudinal direction. Near the cardan coupling 7 the pump section 5 is provided with a centrifugal pump 52 and a jet pump 58 that is accommodated in the pump frame 51. From the centrifugal pump 52 a line 53 connected to the exit of the centrifugal pump 52 extends parallel to the longitudinal direction of the pump frame 51 to a second outer end 56 of the pump frame 51, where the line 53 is provided with a line coupling 54 which couples the line 53 to the flexible riser 8.

The suction section 6 comprises an elongated suction pipe 61 that is connected to the cardan coupling 7 at a first outer end 66. Elongated in this case means a suction pipe 61 that is longer than it is wide, wherein the largest length preferably is twice as large as the largest width or height transverse to the longitudinal direction. At a second, free outer end 67 the suction pipe 61 is provided with a draghead 62. The draghead 62 is provided with a suction nozzle 63 and cutting teeth 64 placed behind the suction nozzle 63. The suction section 6 is provided with a jet line 65 that is connected to the suction nozzle 63. From the suction nozzle 63 the jet line 65 extends parallel to the longitudinal direction of the suction pipe 61 in the direction of the cardan coupling 7, where the suction section 6 is provided with a line transmission 66 that connects the suction pipe 61 and the jet line 65 to the entrance of the centrifugal pump 52 and the entrance of the jet pump 58, respectively, of the pump section 5.

In an alternative embodiment that is not shown, the jet pump 58 is arranged on the vessel 2, wherein from cardan coupling 7 onwards the jet line 65 is continued as a flexible jet line, which is connected to the vessel 2 in a manner comparable to the manner in which the flexible pipe 8 is connected to the vessel 2.

The deep water part 4 is provided with a first hoisting pulley 41 placed at the second outer end 56 of the pump frame 51, a second hoisting pulley 42 placed on the pump frame 51 at a short distance from the first hoisting pulley 41, a third hoisting pulley 43 placed near the cardan coupling 7 on the pump frame 51 and a fourth hoisting pulley 44 placed near the draghead 62 on the suction pipe 61.

As shown in figures 1 and 2, the first derrick 26 is provided with a pulling cable 10 that is turned back around the first hoisting pulley 41 into a loop that couples the pulling cable 10 to the deep water part 4. The first hoisting pulley 41 is bearing mounted in the centre to the pump frame 51 and at that location forms a first point of suspension for the deep water part 4. The pulling cable 10 forms a connection between the first derrick 26 and the first point of suspension in the centre of the first hoisting pulley 41. The loop formed by the pulling cable 10 has an effective length N, measured from the centre of the derrick pulleys 31 of the first derrick 26 to the centre of the first hoisting pulley 41.

The second derrick 27 is provided with a first hoist cable 11 that is turned back around the second hoisting pulley 42 into a loop that couples the first hoist cable 11 to the deep water part 4. The second hoisting pulley 42 is bearing mounted in the centre to the pump frame 51 spaced apart from the first hoisting pulley 41 and at that location forms a second point of suspension for the deep water part 4. The first hoist cable 11 forms a connection between the second derrick 27 and the second point of suspension in the centre of the second hoisting pulley 42. The loop formed by the first hoist cable 11 has an effective length LI, measured from the centre of the derrick pulleys 31 of the second derrick 27 to the centre of the second hoisting pulley 42.

The third derrick 28 is provided with a second hoist cable 12 that is turned back around the third hoisting pulley 43 into a loop that couples the second hoist cable 12 to the deep water part 4. The third hoisting pulley 43 is bearing mounted in the centre to the pump frame 51 spaced apart from the second hoisting pulley 42 and at that location forms a third point of suspension for the deep water part 4. The second hoist cable 12 forms a connection between the third derrick 28 and the third point of suspension in the centre of the third hoisting pulley 43. The loop formed by the second hoist cable 12 has an effective length L2, measured from the centre of the derrick pulleys 31 of the third derrick 28 to the centre of the third hoisting pulley 43.

The fourth derrick 29 is provided with a third hoist cable 13 that is turned back around the fourth hoisting pulley 44 into a loop that couples the third hoist cable 13 to the deep water part 4. The fourth hoisting pulley 44 is bearing mounted in the centre to the suction pipe 61 spaced apart from the third hoisting pulley 43 and at that location forms a fourth point of suspension for the deep water part 4. The third hoist cable 13 forms a connection between the fourth derrick 29 and the fourth point of suspension in the centre of the fourth hoisting pulley 44. The loop formed by the third hoist cable 13 has an effective length L3, measured from the centre of the derrick pulleys 31 of the fourth derrick 29 to the centre of the fourth hoisting pulley 44.

The distance B between the second hoisting pulley 42 and the third hoisting pulley 43 is substantially equal to the distance C between the second derrick 27 and the third derrick 28. The distance D between the third hoisting pulley 43 and the fourth hoisting pulley 44 is substantially equal to the distance E between the third derrick 28 and the fourth derrick 29.

Figure 1 shows the dredging assembly 1 with the deep water part 4 in submerged condition. The vessel 2 has moved onwards in the sailing direction A. In a lowered position the deep water part 4 is suspended from the hoist cables 11-13, wherein the draghead 62 has dragged over the seabed 9. The teeth 64 of the draghead 62 have dislodged sand and clay, after which the sand is sucked up through the suction nozzle 63. Sand that is difficult to dislodge can be eroded using highly pressurised water from the jet line 65, after which the sand can be sucked up as yet through the suction nozzle 63. With the outer end facing away from the deep water part 4 the flexible riser 8 is coupled to a fixed deck line of the vessel 2. The sand reclaimed by the draghead 62 is pushed upwards from the deep water part 4 through the flexible riser 8 by means of the centrifugal pump 52, after which at the location of the connection of the flexible riser 8 it is poured on the vessel 2 into the loading space 24. The dredging assembly 1 is provided with an electricity cable that runs parallel to the flexible riser 8 to connect the centrifugal pump 52 and the jet pump 58 to an electric power supply on the vessel 2.

The effective length LI of the loop formed by the first hoist cable 11 in figure 1 is approximately two hundred and fifty metres. The effective length L2 of the loop formed by the second hoist cable 12 is longer than the effective length LI, as a result of which the longitudinal direction of the elongated pump frame 51 is at an angle V of approximately forty degrees to the waterline W. The effective length L3 of the loop formed by the third hoist cable 13 is longer than the effective length L2, as a result of which the longitudinal direction of the suction pipe 61 is at a smaller angle G of approximately twenty-five degrees to the waterline W. The first and second hoist cable 11, 12 exert a hoisting force HI, H2, respectively, on the pump section 5, with which they largely bear the weight of the pump section 5 and a part of the weight of the suction section 6. The third hoist cable 13 exerts a hoisting force H3 on the suction section 6, in which way the remaining part of the weight of the suction section 6 is borne. When the draghead 62 is on the seafloor 9 the hoisting force H3 is a small force that only just suffices to keep the third hoist cable 13 taut. As a result the suction section 6 is tilted about the cardan coupling 7 and as a result of the moment M about the cardan coupling 7 the draghead 62 exerts a head pressure K on the seabed 9. Provisions are present on the derricks 26-29 for keeping the hoist cables 11- 13 and the pulling cable 10 tensioned and at length.

From the first derrick 26 on the prow 22 the pulling cable 10 extends downwardly inclined at an angle U to the waterline W to, as considered in the sailing direction A, the first hoisting pulley 41 that is situated rearward. Due to its inclined position the pulling cable 10 exerts both a vertical hoisting force component H4 and a horizontal tensile force component T on the deep water part 4.

The effective length N of the loop of the pulling cable 10 is such that the first hoist cable 11 extends substantially vertically downwards. The first hoist cable 11 and the part of the vessel 2 between the first and the second derrick 26, 27 form the two straight sides of a right-angled triangle and the pulling cable 10 forms the hypotenuse of a substantially right-angled triangle, wherein the triangle is somewhat broadly interpreted in connection with the short distance between the first and the second hoisting pulleys 41, 42. In that way a shape- retaining triangular relation is effected, wherein the horizontal tensile force component T of the pulling cable 10 counteracts that the deep water part 4 will start to move with respect to the vessel 2, for instance under the influence of the water current and/or the sailing speed in sailing direction A and/or the resistance Q of the draghead 62 over the seabed 9 during dragging.

Figure 1 shows the situation in which the vessel 2 has moved in the forward sailing direction A and is still moving onwards. The deep water part 4, as shown in the side view of figure 1, considered in a horizontal projection transverse to the forward sailing direction A, during moving onwards and dragging therefore is situated constantly vertically straight below the vessel 2, preferably below the rear half of the vessel 2 and preferably entirely below the vessel 2.

The length S of the flexible riser 8 is approximately one and a half times as long as the length P of the vessel 2. In that way a dredging depth R can be achieved of approximately two hundred and fifty metres. The length S of the flexible riser 8 can be extended, so that a dredging depth R of more than two hundred and fifty metres, preferably more than five hundred metres becomes possible.

In an alternative embodiment that is not shown the pulling cable 10 is left out and the flexible pipe 8 has the function of the pulling cable 10.

In a further alternative embodiment that is not shown, there is no riser 8. Instead thereof the pump section 5 is provided with a submarine opening connected to the exit of the centrifugal pump 52. The material sucked up by the draghead 62 can be flushed away sideward under water from the submersible part 4 through the submarine opening, as a result of which the sand or the minerals descend beyond the dredged area, for instance when excavating a trench in which the reclamation of material and the storage thereof in the vessel is of minor importance. Figure 2 shows a moment during the hoisting of the deep water part 4 in the direction of the vessel 2. The effective lengths L1-L3 of the loops of the hoist cables 11-13 substantially equal each other, as a result of which the deep water part 4 has come to hang horizontally below the vessel 2. The flexible riser 8 has simultaneously been pulled onto the deck 25 of the vessel 2 by means of the pipe winch 32 and has been guided onto the pipe rack 34 via the pipe guides 33.

Figure 3 shows the inoperative deep water part

4 which has been drawn in to above the deck 25 by the movable derricks 26-29. The flexible riser 8 is uncoupled from the pump section 5 and with its largest part placed on the pipe rack 34.

Figure 6 shows an alternative embodiment of the dredging assembly 1, wherein at its prow 22 the vessel 2 is provided with a bowsprit or spud 15, which extends beyond the prow 22 in the sailing direction A. The pulling cable 10 extends from the outer end of said bowsprit or spud 15 to the first hoisting pulley 41 of the receded deep water part . By placing the fastening of the puling cable 10 as far to the fore and/or down as possible, in this case even beyond the prow 22 of the vessel 2, a more level tensile angle U can be obtained, which is advantageous to the magnitude of the horizontal tensile force component T. Moreover in this embodiment the length of the vessel 2 can be reduced with the length of the projecting bowsprit or spud 15, without this affecting the balance of forces in a negative way.

Figure 7 shows an alternative embodiment of the dredging assembly 1, wherein the pipe rack 134 has been passed from the front of the vessel 2 to behind the deckhouse 36, such that a longer inoperative flexible riser 8 can fully be placed on the pipe rack 134.

The above description is included to illustrate the operation of preferred embodiments of the invention and not to limit the scope of the invention. Starting from the above explanation many variations that fall within the spirit and scope of the present invention will be evident to an expert.