WO2013157944A1

WO2013157944A1 - Cutter suction dredger

Info

Publication number: WO2013157944A1
Application number: PCT/NL2013/050284
Authority: WO
Inventors: Gérard Louis Marie VAN DER SCHRIECK
Original assignee: Van Der Schrieck Dredging Technology B.V.
Priority date: 2012-04-19
Filing date: 2013-04-18
Publication date: 2013-10-24

Abstract

A cutter suction dredger comprises a pontoon (1), a ladder (2) of which one end is suspended from the pontoon, which ladder can be brought into a position which is directed downwards with respect to the pontoon, a cutter head (3) for cutting rock or soil at the other end of the ladder, an extractor system for extracting cut rock or soil and at least one spud pole (4) cooperating with the pontoon for anchoring the pontoon with respect to a bed (24). A connecting means (21) of adjustable length extends between the spud pole and the ladder. Said connecting means (21) is displaceably guided along a guide (39) on the spud pole (4) and extends from the guide towards an anchorage (40) which can be anchored in the bed (24) and which is situated on that side of the spud pole (3) which is turned away from the cutter head (4).

Description

Cutter suction dredger

The invention relates to a cutter suction dredger, comprising a pontoon, a ladder of which one end is suspended from the pontoon, which ladder can be brought into a position which is directed downwards with respect to the pontoon, a cutter head for cutting rock or soil at the other end of the ladder, an extractor system for extracting cut rock or soil and at least one spud pole cooperating with the pontoon for anchoring the pontoon with respect to a bed, wherein a connecting means of adjustable length extends between the spud pole and the ladder. The invention relates in particular to the stabilization of the position of a cutter head of a floating cutter suction dredger in waves. It relates to the position in the horizontal direction of the longitudinal axis of the pontoon with respect to. the floor or bed.

Such a cutter suction dredger is known from US-A-5791074. This known cutter suction dredger has two spud poles, each of which is connected to the ladder by means of a wire. By alternately easing and shortening the wires, it is possible to cause the ladder and thus the cutter head to swing to and fro during cutting of the ground. The position of the cutter head at the end of the ladder with respect to the floor can thus be controlled to a certain degree.

However, during displacement, the relationship between the spud poles and the floor is temporarily cancelled, resulting in a decrease in the stabilizing action of the wires on the cutter head. It is therefore an object of the invention to provide a cutter suction dredger of the above-described type which does not have this drawback. This object is achieved by the fact that the connecting means is displaceably guided along a guide on the spud pole and is connected to and extends from the guide towards an anchorage which can be anchored in the bed and which is situated on that side of the spud pole which is turned away from the cutter head.

The position of the cutter head with respect to the floor during displacement is now also determined by the anchorage, to which the wire extending from the cutter head is connected. This means that displacement of the spud pole can no longer adversely affect control of the position of the cutter head, since, during displacement, the spud pole is situated on the straight line between the anchorage and the cutter head and therefore no longer plays a part in the stabilization of the cutter head. This prevents any uncontrolled forward movement of the cutter head during the time when the spud pole does not cooperate with the ground.

Preferably, a length-adjusting device is provided by means of which the length of the connection between the spud pole and the ladder can be adjusted. The mounting of the connection to spud pole may be positioned at such a low level that the connection cannot touch the upper side of the bed during the rotating movement of the cutter head when it is tensioned. According to a first possibility, it can be provided that the connecting means is configured as a wire, the length and/or prestress of which is adjustable. The wire may be guided over a pulley on the ladder and may be guided from the pulley to a winch.

According to a second possibility, the connecting means may comprise a fiexurally stiff or rigid connecting body, such as a beam, tube and/or truss which is displaceable or extendable with respect to the spud pole. In this case, the guide along the spud pole may be displaceable. In particular, the connecting body may be displaceable by means of a lifting member which can be moved up and down the spud pole. The spud pole is preferably suspended in a spud carriage which is displaceable in the longitudinal direction of the pontoon, in which case said lifting member cooperates with a hoisting device which is provided on the spud carriage. The connecting body may be securable with respect to the guide in its longitudinal direction. Furthermore, the connecting body may be provided with a fork- shaped end into which the spud pole is accommodated.

That end of the connecting body which is turned away from the ladder may carry an anchorage which is securable with respect to the floor. The position of the connecting body with respect to the guide may be varied by the fact that the guide is provided with a first cable which extends towards the ladder and with a second cable which has at least a part which extends away from the ladder, which cables are each connected to an actuator for displacing the connecting body along the guide by means of said cables.

The first cable may be guided over one or more pulleys towards the actuator which is fitted to the ladder. The second cable may be guided over a return pulley on the connecting body and may then be guided to said actuator via a part which extends towards the ladder and then via one or more pulleys. In addition, at least a prestress device, such as a piston/cylinder device may be provided in order to prestress the cables.

The invention also relates to a number of methods for operating the cutter suction dredger. According to a first possibility, the method may comprise the following steps:

- anchoring the spud pole in a bed,

- positioning the cutter head on the bed,

- tensioning the connecting means between the spud pole and the ladder by extending the actuator of the spud carriage in such a way that the pontoon is forced n a forward direction with respect to the spud carriage,

- easing the connecting means and thereby causing a step displacement.

Furthermore, the method may comprise the following steps:

- anchoring the spud pole in a bed,

- positioning the cutter head on the bed,

- tensioning the connecting means between the anchorage and the ladder by actuating the actuator in such a manner that the spud pole is tilted and the pontoon is forced in a forward direction with respect to the anchorage of the spud pole in the floor,

- easing the connecting means and thereby causing a step displacement.

In addition thereto, or alternatively, the method may comprise the following steps:

- anchoring the spud pole in the bed,

- anchoring an auxiliary wire in the bed at a position situated in front of the spud pole, viewed in the direction from the spud pole towards the cutter head,

- tensioning the auxiliary wire by actuating the associated winch in such a way that the pontoon is forced in the forward direction with respect to the spud carriage,

- on account of tensioning the auxiliary wire, tensioning the connecting means between the spud pole and the ladder,

- easing of the connecting means and thereby causing a step displacement.

In addition, the method may comprise the following steps:

- adjusting the distance between the ladder and the spud pole,

- performing slewing movements with the ladder and the cutter head in the transverse direction,

- maintaining the set distance between the ladder and the spud pole while performing the slewing movements, - easing the connecting means and thereby causing a step displacement.

If the connecting means are configured as a flexurally stiff or rigid rod or bar or the like, the method may comprise the following steps:

- lowering the anchorage onto the floor,

- positioning the cutter head on the bed,

- lifting the spud pole,

- displacing the spud pole forwards in the direction of the ladder in the raised position with respect to the pontoon,

- subsequently lowering the spud pole onto the floor,

- then lifting the anchorage from the floor.

In the embodiment where cables are used to influence the position of the rigid connecting body with respect to the spud pole, the method may comprise the steps of shortening the first cable and simultaneously lengthening the second cable while displacing the connecting means with respect to the spud pole and moving the cutter head forwards. In addition, this may also involve shortening or lengthening the first cable or the second cable by extending the actuator.

The invention will now be explained in more detail with respect to the drawings, in which:

Fig. 1 shows a diagrammatic cross section of a known cutter suction dredger. Fig. 2 shows a diagrammatic top view of a known cutter suction dredger.

Figs. 3 a and b show a vertical cross section of examples of ground profiles in a bed which may be cut into using the cutter head.

Fig. 4a shows a definition sketch of the orbital movement of a long surface wave in shallow water.

Fig. 4b shows a definition sketch of the six main movements of a floating cutter suction dredger.

Fig. 5 shows a side view of a first embodiment of a cutter suction dredger according to the invention.

Fig. 6 shows a top view of the cutter suction dredger according to a slightly modified variant of the first embodiment.

Fig. 7 shows a side view of a second embodiment of the cutter suction dredger.

Fig. 8 shows a top view of the cutter suction dredger according to the second embodiment. Fig. 9 shows a front view according to IX-IX from Fig. 7.

With known cutter suction dredgers as illustrated in Figs. l-4b, the position of the cutter head in the horizontal direction of the longitudinal axis of the pontoon is adjusted by using a spud pole and in the vertical direction by suspending a ladder at an adjustable depth which is hingedly attached to and suspended from the pontoon at the front. It is generally known that when working with this known cutter suction dredger while the water surface is rough, it is possible for the cutter head to move significantly with respect to the fixed floor and that these movements cause great strain on the cutter head. This may lead to damage and/or failure as a result of impossible operating conditions. A possible embodiment and method of this known cutter suction dredger is described below with reference to Figs. 1 and 2.

Fig. 1 shows a diagrammatic cross section of a cutter suction dredger with a floating pontoon 1 which is provided at the front with a ladder 2 which is suspended from the pontoon by means of a hinge 20. Underneath the ladder, a rotating cutter head 3 is fitted on a rotation shaft which runs virtually parallel to the longitudinal axis of the ladder. On the rear of the pontoon, there is a spud pole 4 which is anchored in the solid floor at point 41 with a penetration depth 26 as a result of its own weight. Point 41 is situated in the spud pole and near the underside of the spud pole. The spud pole 4 has a certain flexural stiffness against bending at right angles to its longitudinal axis and is fitted vertically to a spud carriage 9 by two tightly fitting guide rings 42. Spud pole 4 can freely be moved up and down vertically through both guide rings 42 by the lifting device 64 and thus ensures an anchorage of the pontoon to the solid floor 24, which anchoring is horizontally pivotable about a vertical axis. The spud carriage 9 can travel in the direction of the longitudinal axis of the pontoon on wheels 12. The wheels 12 are clamped in the vertical direction between the guide rails 1 1 , so that the spud carriage 9 cannot rotate. The spud carriage 9 can be displaced in the direction of the longitudinal axis of the pontoon by means of the piston/cylinder device 10 and be set at a desired position. The ladder 2 with cutter head 3 is suspended from the top side in hinge 20 on the pontoon 1 and is suspended on the underside by means of a hoisting wire 6 at a desired depth. The horizontal distance R from the front of the cutter head to the axis of the spud pole 4 is determined and fixed by adjusting and fixing the position of the spud pole 4 with respect to the pontoon 1 in the direction of the longitudinal axis of the pontoon using piston/cylinder device 10. In addition, an auxiliary spud pole 63 with lifting device 64 is present at the rear of the pontoon 1.

Cutter head 3 cuts a certain ground profile around the axis of spud pole 4 by means of a horizontal slewing or rotating movement Z (see Fig. 2). Fig. 3 shows examples of ground profiles A to H which can be cut using the cutter head 3. The slewing movement in one of two directions takes place by using two winches 62 to shorten and ease the lateral wires 60 which are anchored to two front lateral anchors 61. The soil which is cut during the slewing movement is sucked up by pump 16 via suction pipe 14 with flexible suction bag 15. The ladder 2 and the pontoon 1 follow the slewing movement of the cutter head 3 by pivoting about the spud pole 4 in the horizontal plane. In this case, the cutter head 3 runs along a circular path Z with a radius R about the axis of spud pole 4. The point of departure (pulley) 47 of the lateral wires from the ladder is situated at the bottom of the ladder 2, as close as possible to the cutter head 3, as the required pulling force in the lateral wires 60 is largely the result of the cutting forces on the cutter head. The position of the cutter head with respect to the ground surface which is cut at the front and at the pulling side has to be controlled in order to achieve a regular and controlled cutting process. In order to achieve this, the easing lateral wire 60 is eased using a certain brake force and a controlled speed while the pulling lateral wire 60 is pulled inwards at a controlled speed and thus provides the required force for the cutting forces and for the brake force in the easing lateral wire 60 and for displacement of the pontoon and the ladder.

The slewing movement is continued up to a maximum slewing angle of approximately 30 to 45 degrees with respect to the longitudinal axis of a trench which may be dug. After this maximum slewing angle has been reached, the pontoon 1 with ladder 2 and cutter head 3 is moved forwards by a step s by means of piston/cylinder device 10. Fig. 3a and Fig. 3b diagrammatically show straight identical profiles having a width s and a height h of the ground profile to be excavated by the cutter head with curved cutter head profile. In reality, the diagrammatically shown straight sections correspond to the curved profile of the cutter head which cuts the soil. Step s results in a new ground profile B which is to be cut into by the cutter head. Subsequently, the slewing movement in the opposite direction starts. After the ground profile A has been dredged, the cutter head can also be lowered to ground profile E by easing hoisting wire 6. Preferably, the ground profiles which are situated behind one another at the same depth, for example A to D, are worked upon in direct succession with a fixed depth of the cutter head and subsequently, the cutter head travels along the length P to start on ground profile E. The maximum horizontal distance which can be cut in a single layer in this manner from a fixed position of the (operating) spud pole 4 equals the maximum stroke length P of the piston/cylinder device 10. In order to be able to dredge the next ground profiles to the right of D and H, the spud pole 4 first has to be moved, the so-called 'displacement'. This is carried out as follows: while dredging the last ground profile D or H or a deeper layer situated further below, the slewing movement is stopped in the middle of the slewing movement on the axis 48 and the (auxiliary) spud pole 63 is lowered. Then, the spud pole 4 is lifted and spud carriage 9 is driven along the length P to its starting position in the direction of the cutter head 3 by means of the piston/cylinder device 10, following which spud pole 4 is lowered again. The spud pole 63 is lifted and the displacement is finished. Subsequently, the slewing movement is continued at the smaller radius R-P. In this way, several sets of ground profiles A to D at a fixed depth can be cut in succession.

It is also possible, after the maximum length R has been reached, to finish the slewing movement with ground profile D to the end and to then completely pull back the piston/cylinder device 10 and to lower the cutter head above ground profile E into ground profile E by easing of hoisting wire 6 and then to cut into ground profiles E to H.

The above-described cutter suction dredger and method are generally known. When operating a cutter suction dredger in rough seas, the pontoon 1 and the ladder 2 with cutter head 3 may be subjected to significant movements as a result of the waves. Such movements are undesirable since they can lead to excessive forces being exerted on the cutter head 3 and the ladder 2 and the spud poles 4 and 63, in particular in cases where the floor is solid, which may result in considerable damage. Since the lateral wires 60 are substantially at right angles to the vertical plane perpendicular to the hauling movement and these wires are eased and pulled in at a controlled speed and at a certain prestress, the movements of the ladder and the cutter head can take place in the vertical plane perpendicular to the hauling movement virtually unimpeded. In addition to undesirable movements and consequently undesirable forces on the cutter head 3 and ladder 2, waves also lead to considerable forces and moments in the spud pole 4 and in its guide rings 42. When working with a cutter suction dredger in rough seas, preventing the abovementioned damage may result in considerable time losses as a result of weather conditions during which it is impossible to carry out any work.

The movements of the cutter head resulting from the waves are caused by the movements of the pontoon with ladder due to the forces on the pontoon and the ladder caused by the orbital movement of the water from the waves. The theory of surface waves in water says that with waves in relatively deep water with a water depth h greater than half the wave length L, the floor has no effect on the orbital movement. In that case, the orbital movement is circular and at its maximum at the water surface. With waves in relatively shallow water with a water depth h which is smaller than half the wavelength L/2, the floor does influence the orbital movement. In this case, the orbital movement has an elliptical shape, the longest axis of symmetry of which runs in the horizontal direction. With a water depth which is smaller than 1/2 part of the wavelength L, this influence is even so great that the horizontal orbital movement directly above the floor is virtually equal to that at the water surface. When operating a cutter suction dredger on a coast in rough seas with a long wave period and a long wavelength, this shallow water wave movement occurs regularly. Fig. 4a shows an example of a shallow water wave of h<l/2L. The associated flat elliptical shape of the orbital movement of the water can clearly be seen. Here as well, the orbital movement at the water surface is at a maximum, with an amplitude w in the vertical direction which equals half the wave height H. The maximum horizontal movement amplitude u is significantly larger here than the vertical movement amplitude w. In particular these large horizontal wave movements resulting from waves having a long period and a long wavelength exert large forces on the pontoon and ladder and thus result in large movements of the pontoon and the ladder and the cutter head. In addition, the frequency of these forces may be in the vicinity of the natural frequencies of the system consisting of pontoon with ladder and spud pole and its suspension, as a result of which the movements of the pontoon and the cutter head may in addition also be reinforced due to amplification.

Fig. 4b shows the possible 6 degrees of freedom for the movement of a floating pontoon. The orbital movement of the waves ensures lateral movements of the pontoon, both a vertical up and down lateral movement w in the Z direction (heaving) and a horizontal to and fro lateral movement u in the X direction (slacking) and lateral movement v in the Y direction (shifting). The vertical movement w is the direct result of the variation of the upwards force in the vertical direction due to the wave movement as a result of the buoyancy of the pontoon. The horizontal movements u and v are caused inter alia by the horizontal thrust force resulting from the thrust and suction pressure against the side walls of the pontoon and the ladder as a consequence of the horizontal component of the orbital speed.

In addition to these 3 lateral movements, the differences in local wave height also cause rotations of the pontoon at different positions along the pontoon in 3 different directions: the rotation at angle φ about the longitudinal axis X of the pontoon, the so- called 'rolling', and the rotation at angle Θ about the transverse axis Y of the pontoon, the so-called 'pitching' and the rotation at angle ψ about the vertical Z axis of the pontoon, the so-called 'yawing'.

Anchoring to the floor takes place, on the one hand, on the rear side of the pontoon at point 41 by means of the spud pole 4 which is fitted in a vertical guide on the rear side of the pontoon with a certain stiffness against rotation in a vertical plane and, on the other hand, to the front of the ladder with the two transversely projecting lateral wires 60. The point of engagement 31 of the resulting forces of the anchorage which is formed by the two wires 60 via the pulleys 47 is situated closer to the cutter head 3 and therefore also close above the floor 24. Both points 31 and 41 are situated under the longitudinal axis of the pontoon. Point 41 of the spud pole acts as an omnidirectional hinge point and the two lateral wires 60 form a virtually

omnidirectional hinge point 31 approximately in the centre between the pulleys 47. In this case, the horizontal movement of the cutter head 3 caused by waves in the Y direction at right angles to the longitudinal axis X of the pontoon is prevented by the lateral wires 60. As the hinge points 41 and 31 are situated in and close above the floor, respectively, it will be possible to perform a lateral movement v at right angles to the longitudinal direction of the pontoon which is situated at a higher position (shifting) and cause a rotation about the longitudinal axis X of the pontoon (rolling). Conversely, a rotation of the pontoon about the longitudinal axis X will cause a transverse movement v (shifting) of the pontoon. When using the hinge points 41 and 31, both movements can take place freely, as described above, without those movements caused by waves resulting in large movements of the cutter head 3. A movement in the form of 'yawing' about the vertical Z axis of the pontoon is prevented by the abovementioned anchorage and will not cause large movements of the cutter head 3 either. It may be inferred that with the above-described method of anchoring the pontoon, in particular the lateral movements w and u, being the 'heaving' and 'slackening', respectively, and the rotation Θ, being the 'pitching', will lead to considerable movements of the cutter head 3 caused by waves.

In addition to the above-described orbital movement of the waves as a direct cause of forces which cause the movement of the pontoon and the cutter head, an additional significant horizontal displacement u of the pontoon in the direction of the longitudinal axis X results when the pontoon performs a pitching movement due to the rotation of the clamped spud pole 4 at angle Θ about the Y axis. This displacement takes place due to the fact that point 41 in the spud pole 4 is anchored in the floor and spud pole 4 is connected to the pontoon with a certain degree of rotational stiffness. During a pitching movement and a clockwise rotation of the pontoon about the Y axis, the pontoon in Fig. 4b will move to the right. Conversely, if the rotation is anticlockwise, the pontoon in Fig. 4b will move to the left. Starting from an infinitely stiff spud pole and an infinitely stiff connection between the spud pole and the pontoon, the cutter head will in theory make a circular movement in the vertical plane about anchor point 41 of spud pole 4. As the cutter head is positioned closely above the vertical level of anchor point 41 , the movement of the cutter head will be directed substantially vertically. In practice, the spud pole itself and its connection to the pontoon are not infinitely stiff and a certain degree of bending of the pole and its suspension will occur. As a result thereof, the cutter head will also undergo a horizontal displacement. This movement may be further reinforced by amplification due to the natural frequencies of the multiple mass spring system consisting of the spud pole 4 with its own mass and stiffness and the flexible connection 42 to the pontoon and the masses of the pontoon and ladder, hingedly connected to the pontoon, with the flexible connection of hoisting wire 6 between pontoon and ladder. The pontoon itself floats flexibly in the water at a certain natural frequency.

The above makes clear that as a result of waves in shallow water, a large movement of pontoon 1 and cutter head 3 with respect to the floor is a large movement in the horizontal direction. It also makes clear that the waves may apply a large load on the spud pole 4 in the form of great forces and moments at the location of the connection of the spud pole and the spud carriage 9. Both consequences may result in damage and are therefore restrictive to the workability of the cutter suction dredger. With the cutter suction dredger according to the invention, as illustrated in Figs. 5 and 6, the wire 101 of connecting means 21 runs between the ladder 2 and the spud pole 4 via a guide structure 39 which cooperates with the spud pole 4 to an anchorage 40 with the bed, which anchorage is positioned behind the spud pole 4 on the axis of the cut which the cutter head makes in the floor 24. The tensioning force Fs in the wire 101 is in this case adjusted using piston/cylinder device 10 and is absorbed by the fixed floor via the wire 101 and anchorage 40. During displacement, the axis of the pontoon is on the axis 48 of the cut in the centre of the slewing motion. As a result thereof, the pretensioned wire 101 runs in a straight line from pulley 30 on the ladder to the anchor point 40 and hardly exerts any transverse force on guide structure 39 or any friction force resulting therefrom on spud pole 4. Therefore, the spud pole 4 can be lifted off the floor upon displacement and be displaced horizontally freely sliding along wire 101 by means of guide 39. This has the significant and important advantage that the anchoring of the wire 101 to the fixed floor is also maintained during the displacement and this thus prevents horizontal movement of the cutter head. If desired, auxiliary spud pole 63 may also be designed as, for example, a tilting pole in order to continue to supply the pretensioning force Fs during displacement. In this case, the spud pole 4 can be resiliently suspended, just like the auxiliary spud pole 63, because the connecting means 8, 21 ensures the horizontal position of the cutter head 3. This has the significant and important advantage that the maximum load on the spud pole is limited both during displacement and during slewing. The pretensioning force Fs during displacement can also be supplied by means of a forward bow wire 37 and winch 7 (see Fig. 5).

Alternatively, the pretensioning force Fs can also be supplied by the stern wires 24 and winches 7, as is illustrated in Fig. 6. The slewing movement of the cutter head 3 is produced by means of the wires 60, anchors 61 and winches 62.

In the embodiment from Figs. 7-9, a rigid connecting means in the form of the tube 8 is used between the ladder 2 and the spud pole 4. On the end which is turned away from the ladder 2, the tube 8 has an anchoring means 41 with downwardly directed tips. The anchoring means can be lowered onto the floor by easing the lifting wire 5 using the winch 17, in which case the downwardly directed tips are forced firmly into the floor.

In this position, the spud pole can be lifted and displaced, while the position of the cutter head 3 remains secured by the tube 8 which is fixed with respect to the floor by the anchoring means 65. After the displacement, when the spud pole has been anchored to the floor in the new position, the anchoring means is lifted just sufficiently to raise the downwardly directed tips so that they are clear from the floor.

Subsequently, the slewing movement of the ladder 2 and cutter head 3 can be continued.

The tube 8 has a fork-shaped end 25 whose prongs 18 engage around the spud pole 4, as is illustrated in Fig. 8. The guide 39 is provided around the spud pole 4 and has pulleys 19. A prong 18 is accommodated in between in each case one pair of pulleys. When adjusting the length of the position of the tube 8 with respect to the spud pole 4, these pulleys 19 are in a freely rotatable position. This is the case when a step is being carried out at the furthest corner at the end of the slewing movement.

The adjustment of the position of the tube 8 with respect to the spud pole 4 is carried out by means of the wires 38, 46 and the piston/cylinder device 58 which is fitted to the ladder 4. One end of wire 38 is connected to the piston rod of the piston/cylinder device 58 and is guided over the ladder 2 via pulleys and towards the guide 39 on the spud pole 4, to which guide 39 the other end of the wire 38 is connected. Both ends of the other wire 46 are also connected to the piston rod of the piston/cylinder device 58 connected. From there, the two parts of the wire 46 run over the ladder 2 to pulleys on the anchoring means 41, and subsequently to the guide 39. By now lengthening or shortening the piston/cylinder device, the tube 8 protrudes more or less far, respectively, with respect to the spud pole 4.

As soon as the correct position of the tube has been set, the pulleys 19 are blocked in such a manner that the distance between the spud pole 4 and the ladder 2 with cutter head 3 is fixed. The prongs 18 have a length which is such that they can absorb both the stroke which the spud carriage 9 performs and the additional displacement of the tube 8 with respect to the spud pole 4 which occurs when the ladder 2 is lifted.

It is also possible to use a winch or winches instead of the piston/cylinder device 58 to operate the wires 38, 46. List of reference numerals

1. Cutter suction dredger

2. Ladder

3. Cutter head

4. Spud pole

5. Lifting member

6. Hoisting wire

7. Winch

8. Connecting means/tube

9. Spud carriage

10. Piston/cylinder device

11. Horizontal guide

12. Wheel

13. Wheel axis

14. Suction pipe

15. Suction bag

16. Pump

17. Winch

18. Prong

19. Pulley

20. Hinge of ladder

21. Connecting means/wire

22. Winch

24. Floor

25. Fork-shaped end

30. Pulley

37. Auxiliary wire

38. Tensioning cable

39. Guide

40. Anchorage

41. Anchorage

42. Guide ring of spud pole 44. Auxiliary wire

46. Tensioning cable

47. Pulley

48. Axis

58. Piston/cylinder device

59. Piston/cylinder device

60. Lateral wire

61. Anchor

62. Winch

63. Auxiliary spud pole

64. Piston/cylinder device

65. Anchoring means

Claims

1. Cutter suction dredger, comprising a pontoon (1), a ladder (2) of which one end is suspended from the pontoon, which ladder can be brought into a position which is directed downwards with respect to the pontoon, a cutter head (3) for cutting rock or soil at the other end of the ladder, an extractor system for extracting cut rock or soil and at least one spud pole (4) cooperating with the pontoon for anchoring the pontoon with respect to a bed (24), wherein a connecting means (8, 21) of adjustable length extends between the spud pole and the ladder, characterized in that the connecting means (8, 21) is displaceably guided along a guide (39) on the spud pole (4) and is connected to and extends from the guide towards an anchorage (40, 65) which can be anchored in the bed (24) and which is situated on that side of the spud pole (3) which is turned away from the cutter head (4).

2. Cutter suction dredger according to Claim 1 , wherein a tensioning device (10, 38, 46, 59) is provided to prestress the connecting means (8, 21).

3. Cutter suction dredger according to one of the preceding claims, wherein a length-adjusting device (22; 58, 59) is provided for adjusting the length of the connection between the spud pole and the ladder.

4. Cutter suction dredger according to one of the preceding claims, wherein the connecting means (21) comprises a wire (101), the length and/or prestress of which is adjustable.

5. Cutter suction dredger according to Claim 4, wherein the wire (101) is guided over a pulley (30) on the ladder (2) and is guided from the pulley to a winch (22).

6. Cutter suction dredger according to one of the preceding claims, wherein the connecting means (21) comprises a flexurally stiff or rigid connecting body (8), such as a beam, tube and/or truss which is displaceable or extendable with respect to the spud pole (4).

7. Cutter suction dredger according to Claim 6, wherein the guide (39) is displaceable along the spud pole (4).

8. Cutter suction dredger according to Claim 6 or 7, wherein the connecting body

(8) is displaceable by means of a lifting member (5) which can be moved up and down the spud pole (4).

9. Cutter suction dredger according to Claim 8, wherein the spud pole (4) is suspended in a spud carriage (9) which is displaceable in the longitudinal direction of the pontoon and the lifting member (5) cooperates with a hoisting device which is provided on the spud carriage.

10. Cutter suction dredger according to one of Claims 7-9, wherein the connecting body (8) is securable with respect to the spud pole (4) and/or the guide (39) in its longitudinal direction.

11. Cutter suction dredger according to one of Claims 6-10, wherein the connecting body (8) has a fork-shaped end into which the spud pole (4) is

accommodated.

12. Cutter suction dredger according to one of Claims 6-1 1, wherein that end of the connecting body (8) which is turned away from the ladder (2) carries an anchorage (65) which is securable with respect to the floor (24).

13. Cutter suction dredger according to one of Claims 6-12, wherein the guide (39) is connected to a first cable (38) which extends towards the ladder (2) and to a second cable (46) which has a part which extends away from the ladder (2), which cables are each connected to an actuator (58) for shortening or lengthening and vice versa said cables for displacing the connecting body along the guide (39).

14. Cutter suction dredger according to Claim 13, wherein the first cable (38) is guided over a pulley towards the actuator (58) which is fitted to the ladder (2).

15. Cutter suction dredger according to Claim 13 of 14, wherein the second cable (46) is guided over a return pulley on the connecting body towards a part which extends as far as the ladder (2) and is guided over a pulley towards the actuator (58) which is fitted on the ladder (2).

16. Cutter suction dredger according to one of Claims 13-15, wherein at least a prestress device, such as a piston/cylinder device (59), is provided in order to prestress the cables (38, 46).

17. Method of operating the cutter suction dredger according to Claim 4 or 5, comprising the following steps:

- anchoring the spud pole (4) in a bed (24),

- positioning the cutter head (3) on the bed (24),

- tensioning the connecting means (21) between the anchorage (40) and the ladder (2) by extending the actuator (10) of the spud carriage (9) in such a way that the pontoon (1) is forced in a forward direction with respect to the spud carriage (9),

- easing or pulling in the connecting means (21) and thereby causing a forward or backward step displacement.

18. Method of operating the cutter suction dredger according to Claim 17, comprising the following steps:

- anchoring the spud pole in a bed,

- positioning the cutter head on the bed,

- tensioning the connecting means between the spud pole and the ladder by actuating the actuator in such a manner that the spud pole is tilted and the pontoon is forced in a forward direction with respect to the anchorage of the spud pole in the floor.

19. Method of operating the cutter suction dredger according to Claim 17 or 18, comprising the following steps:

- anchoring the spud pole (4) in the bed (24), - anchoring an auxiliary wire (37, 44) in the bed (24) at a position situated in front of the spud pole (4), viewed in the direction from the spud pole (4) towards the cutter head (3),

- tensioning the auxiliary wire (37, 44) by actuating the associated winch (7) in such a way that the pontoon (1) is forced in the forward direction with respect to the spud carriage (9),

- on account of tensioning the auxiliary wire (37, 44), tensioning the connecting means (21) between the spud pole (4) and the ladder (2).

20. Method according to one of Claims 17-19, comprising the steps of:

- adjusting the distance between the ladder (2) and the spud pole (4),

- performing slewing movements with the ladder (2) and the cutter head (3) in the transverse direction,

- maintaining the set distance between the ladder (2) and the spud pole (4) while performing the slewing movements.

21. Method of operating the cutter suction dredger according to one of Claims 13- 16 where dependent on Claim 12, comprising the following steps:

- lowering the anchorage (65) onto the floor (24),

- positioning the cutter head on the bed,

- lifting the spud pole (4),

- displacing the spud hole (4) forwards in the direction of the ladder (2) in the raised position with respect to the pontoon (1),

- subsequently lowering the spud pole (4) onto the floor (24),

- then lifting the anchorage (65) from the floor (24),

- displacing the pontoon (1) forwards.

22. Method of operating the cutter suction dredger according to one of Claims 13- 16, comprising the following steps:

- lengthening the first cable (38) and simultaneously shortening the second cable

(46) while displacing the connecting means (8) with respect to the spud pole (4) and moving the cutter head (3) forwards or moving the cutter head (3) backwards.

23. Method according to Claim 22 of operating the cutter suction dredger according to Claim 15, or 15 and 16, comprising shortening or lengthening the first cable (38) or the second cable (46), respectively, by extending the actuator (58).