EP2927378A1

EP2927378A1 - Vessel with a spud and method for limiting forces that are exerted by the hull of a vessel on a spud

Info

Publication number: EP2927378A1
Application number: EP15000921.5A
Authority: EP
Inventors: Ruben Boudewijn G. De Lille
Original assignee: ONDERNEMINGEN JAN DE NUL NV; Ondernemingen Jan De Nul naamloze vennootchap
Current assignee: Jan De Nul Nv
Priority date: 2014-04-01
Filing date: 2015-03-30
Publication date: 2015-10-07
Anticipated expiration: 2035-03-30
Also published as: PL2927378T3; HRP20181241T1; ES2691486T3; TR201815322T4; DK2927378T3; BE1021821B1; CY1121039T1; EP2927378A8; EP2927378B1; PT2927378T

Abstract

Vessel (1) with a hull (7) and a spud (2), that is provided with positioning means (9, 16, 22) to set the mutual position and/or orientation of the hull (7) and the spud (2), that is provided with a control unit (14) and measuring means (12) for the force or the pressure exerted by the hull (7) on the spud (2), whereby the control unit (14) is arranged to control the positioning means (9, 16, 22), to make a prediction of the future magnitude of the force or the pressure, and to make an adjustment to the said mutual position and/or orientation.

Description

The present invention relates to a vessel with a spud and method for limiting forces that are exerted by the hull of a vessel on a spud.
For a number of activities at sea, a vessel with a spud, also called a 'spud pole', is used. An important such activity is dredging using a cutter-suction dredger, also called a cutter-suction dredge.
The spud, generally fastened to the front of the cutter-suction dredger, is hereby placed firmly in the seabed to be able to exert sufficient force on the cutter head that must be able to be forcefully pushed against the seabed to be able to do its work, and which is fastened more towards the back of the cutter-suction dredger.
The hull of the ship and the spud are hereby linearly movable with respect to one another over a significant distance, approximately 5 to 10 metres, so that with a single placement of the spud, the cutter head can be used over a certain area of the seabed and not just on a single narrow track.
Such a movement is generally obtained by making use of a long hydraulic piston-cylinder combination that is fastened by a first end to the hull and fastened by a second end to a spud carriage in which the spud is suspended, whereby this spud carriage is slidable or rollable along the longitudinal axis of the cutter-suction dredger by the hydraulic cylinder.
When using such a cutter-suction dredger it is of course exposed to the forces that the sea exerts on the vessel. These are generally essentially cyclic forces caused by waves, but can also be forces due to currents.
For the optimum operation of the cutter head it is desirable for the cutter head to be connected as rigidly as possible to the spud via the hull of the cutter-suction dredger. This means among others that preferably there is the least possible freedom of movement between the spud and the hull of the cutter-suction dredger, of course when a position of the spud is set by means of the hydraulic cylinder.
On the other hand, in the event of high waves such forces occur that the spud or its fastening construction can be damaged. For this reason the fastening of the spud to the hull of the cutter-suction dredger must enable a certain movement, or the use of the cutter-suction dredger must be limited to situations with only relatively small waves.
A problem thus arises relating to simultaneously satisfying the conflicting requirements of preventing freedom of movement and allowing freedom of movement.
A possible solution to this problem is already provided by BE 1016375 in which a cutter-suction dredger is described that is provided with a fastening construction for the spud, which provides no significant freedom of movement when limited forces occur, whereby upon the occurrence of forces above a threshold value a relaxation occurs in the fastening construction so that more movement is possible and damage can be avoided.
This has the disadvantage that the operation of the cutter head is greatly reduced when the forces on the spud exceed the threshold value because the cutter head cannot be pushed in the seabed as forcefully.
Moreover, such a system is only responsive to forces already occurring and thereby reacts relatively slowly, such that high forces, sometimes even higher than desired forces, can still occur.
The purpose of the invention is to provide a better solution to the problem described above, and to this end provides a vessel that comprises a hull and a spud, whereby the vessel is provided with positioning means to set the position and/or orientation of the hull with respect to the spud, whereby the vessel is provided with a control unit and measuring means to measure the force exerted by the hull on the spud or to measure a pressure from which this force can be derived and which is arranged to control the positioning means, whereby the control unit is arranged to make a prediction of the time-dependent future magnitude of the force or pressure and to determine the direction of the future force from values measured by the measuring means over a time interval, whereby the control unit is arranged to make an adjustment to the position and/or orientation of the hull with respect to the spud, whereby the direction of the adjustment corresponds to the direction in which the force is exerted.
The proactive movement of the hull prevents the predicted forces, which can be greater than desired for the spud or its fastening construction, from occurring so that the maximum force exerted by the hull on the spud is reduced compared to a rigid spud fastened to the hull.
Moreover, the spud is always rigidly connected to the hull. As a result, a fastening with a freedom of movement is never formed, so that the operation of the cutter head is not significantly negatively affected.
For clarity it is noted here that the positioning means can of course be set to a large number of positions, but that it does not allow any freedom of movement between the hull and the spud in a set position, unless of course it is driven by the control unit.
The invention is for example based on the realisation that the said force, which essentially occurs as a result of waves, has a sinusoidal variation over time, whereby the intensity and frequency can vary over time as a result of differences in wave intensity, such that it is possible to predict the next part of the force variation on the basis of a first part of a force variation over time.
Such a prediction is of course a prediction on the assumption that the setting of the positioning means does not change. The essence of the invention is that this does indeed happen, which prevents the prediction coming true.
In a preferred embodiment, the adjustment is made before the predicted magnitude of the force or pressure is actually reached.
Because the adjustment of the positioning means precedes the predicted situation, this prevents a reaction only occurring if the force has already reached a threshold value, or has perhaps even exceeded it.
As is known the movements of a vessel at sea, and thus also the forces that are coupled with these movements, are traditionally subdivided into six movements, i.e. three translation movements around three axes perpendicular to one another, and three rotary movements around the same axes.
For the present invention it is primarily the translation movements along the longitudinal axis of the ship, also called 'surge', the rotary movement around the longitudinal axis, also called 'roll', and the rotary movement around a transverse axis, also called 'pitch', that are important.
It is thus desirable to resolve the forces that can be exerted on the spud by the hull into these three components, and to make a prediction and take an action for each of these components independently from one another.
In a preferred embodiment the positioning means thus comprise a hydraulically driven first piston-cylinder combination to move the hull with respect to the spud parallel to the longitudinal axis of the hull, whereby the measuring means are arranged to measure a first component of the said force parallel to the longitudinal axis or to measure a pressure from which this first component can be derived, whereby the control unit is arranged to make a prediction, from the values measured by the measuring means, of the time-dependent future magnitude of the first component or the said pressure and to determine the direction of the first component, whereby the control unit is arranged to move the hull with respect to the spud parallel to the longitudinal axis of the hull, before the predicted magnitude of the first component or the said pressure is actually reached, by moving the piston of the first piston-cylinder combination in the cylinder, whereby the direction of the movement of the hull corresponds to the direction in which the first component is exerted.
In a further preferred embodiment the positioning means thus comprise one or more hydraulically driven second piston-cylinder combinations to rotate the hull with respect to the spud around a first axis that is parallel to the longitudinal axis of the vessel, whereby the measuring means are arranged to measure a second component of the said force, whereby the second component is tangential to the first axis, or to measure a pressure from which this second component can be derived, whereby the control unit is arranged to make a prediction, from the values measured by the measuring means, of the time-dependent future magnitude of the second component or the said pressure and to determine the direction of the second component, whereby the control unit is arranged to rotate the hull with respect to the spud around the first axis, before the predicted magnitude of the second component or the said pressure is actually reached, by moving the piston of the one or more second piston-cylinder combinations in the cylinder thereof whereby the direction of the rotation corresponds to the direction in which the second component is exerted.
In a further preferred embodiment the positioning means thus comprise one or more hydraulically driven third piston-cylinder combinations to rotate the hull with respect to the spud around a second axis that is perpendicular to the longitudinal axis of the vessel and which is horizontal, whereby the measuring means are arranged to measure a third component of the said force, whereby the third component is tangential to the second axis, or to measure a pressure from which this third component can be derived, whereby the control unit is arranged to make a prediction, from the values measured by the measuring means, of the time-dependent future magnitude of the third component or the said pressure and to determine the direction of the third component, whereby the control unit is arranged to rotate the hull with respect to the spud around the second axis, before the predicted magnitude of the third component or the said pressure is actually reached, by moving the piston of the one or more third piston-cylinder combinations in the cylinder thereof whereby the direction of the rotation corresponds to the direction in which the third component is exerted.
It is hereby noted that a piston of a hydraulic piston-cylinder combination can in general be moved by pumping hydraulic fluid into or out of the cylinder, as a result of which the piston is moved.
Alternatively this can be done by exerting an external force on the piston and having an open connection between the cylinder and a reservoir of hydraulic fluid, whereby this open connection, after the desired movement has been completed, is closed to lock the position reached.
In the present patent application both methods are considered as an active adjustment of the position of the piston and are considered to be covered by the expression 'moving the piston of a piston-cylinder combination in the cylinder'.
In a further preferred embodiment, the control unit is arranged to only make the said adjustments if the maximum predicted magnitude of the force or the pressure exceeds a threshold value.
This has the advantage that as long as relatively small forces occur, whereby there is no risk of damage, a completely movement-free connection between the hull and the spud can be maintained so that the cutter head can operate to the optimum.
In a further preferred embodiment, the vessel is additionally provided with, or connected with data transfer capability to, measuring means that are arranged to measure the actual movements of the vessel or the movements of the sea, i.e. the sea surface at some distance, typically less than a few hundred metres, from the vessel.
The information thus obtained can help to make a better prediction of the expected pressures or forces on the basis of the measured pressures or forces.
In a further preferred embodiment, the vessel is provided with a spud carriage in which the spud is fastened, whereby the positioning means are arranged to adjust the position and/or orientation of the hull with respect to the spud carriage, whereby, if present, the second piston-cylinder combination or the third piston-cylinder combination are in the spud carriage.
The invention also concerns a method for limiting the forces exerted by the hull of a vessel, in particular a cutter-suction dredger, on a spud as a result of waves, whereby the following steps are taken:

A: the force exerted by the hull on the spud or a pressure that is the result of this is measured over a time interval;
B: from the measured values a prediction is made of the time-dependent future magnitude of the force or the pressure, and the direction in which the future force is exerted is determined;
C: the position and/or orientation of the hull with respect to the spud is adjusted in the said direction before a predicted magnitude of the force or pressure is actually reached.

Hereby the time interval over which the force or pressure is measured to make a prediction therefrom is preferably between 5% and 50% of the period between two waves.
With the intention of better showing the characteristics of the invention, a preferred embodiment of a vessel according to the invention and the use thereof are described hereinafter by way of an example, without any limiting nature, with reference to the accompanying drawings, wherein:

figure 1 schematically shows a side view of a vessel according to the invention;
figure 2 schematically shows on a larger scale a top view of a cross-section according to II-II of a part of the vessel of figure 1 in the rest state;
figure 3 schematically shows a cross-section according III-III of the part of the vessel shown in figure 2;
figure 4 schematically shows a cross-section according to IV-IV of the part of the vessel shown in figure 2;
figure 5 is a similar presentation as figure 2, during the use of the vessel;
figure 6 is a similar presentation as figure 3, during the use of the vessel;
figure 7 is a similar presentation as figure 4, during the use of the vessel;

The cutter-suction dredger shown in figure 1 is a ship 1 that is provided with a spud 2 close to its front and a cutter arm with a cutter head 3.
In the operating state of figure 1 in which the cutter arm is lowered and the cutter head 3 is used for loosening and removing bed material from a hard seabed, there must be a counterforce for the cutter head 3, for which reason the spud 2 is secured in the seabed before the cutter head 3 is engaged.
As shown in figures 2 to 4, the spud 2 is fastened in a spud carriage 4.
The spud carriage 4 is provided with two wheel sets 5 that are arranged such that the spud carriage 4, if not blocked, is rotatable with respect to the hull 7 of the ship 1 around the longitudinal axis L of the ship and around a horizontal transverse axis D perpendicular thereto.
The wheel sets 5 also enable the spud carriage 4 to move in a forward and backward direction, thus parallel to the longitudinal axis L of the ship 1, in a carriage space 8 on rails provided for this purpose.
Such wheel sets 5 are well known to the person skilled in the art, they are schematically shown in the drawings but are not described in further detail.
In order to drive the spud carriage 4 forwards or backwards, a first hydraulic piston-cylinder combination 9 is provided on the hull 7 of the ship 1, with a first cylinder 10 that is filled with hydraulic fluid and a first piston 11 that is connected to the spud carriage 4.
This first piston 11 is provided with a measuring instrument 12 for pressure and position measurement, that measures the pressure in the first cylinder 10 and the position of the first piston 11 in the first cylinder 10.
The first piston-cylinder combination 9 is connected to a first hydraulic set 13 that comprises the necessary reservoirs, pumps and valves to move the first piston 11 in a controlled way.
The measuring instrument 12 is connected with data transfer capability to a central control unit 14. The central control unit 14 is connected controllably to the first hydraulic set 13 in order to thereby be able to set the position of the first piston 11.
Four second hydraulic piston-cylinder combinations 16 are affixed in the spud carriage that are each provided with a second cylinder 17 that is filled with hydraulic fluid and a second piston 18. These second piston-cylinder combinations 16 are arranged to be able to rotate the spud carriage 4 and the hull 7 with respect to one another around the longitudinal axis L of the ship 1.
These second piston-cylinder combinations 16 are each provided with a measuring instrument 12 for pressure and position measurement, that measures the pressure in the second cylinder 17 concerned and the position of the second piston 18 concerned in the second cylinder 17 concerned.
As is especially clear from figure 3, two of the second piston-cylinder combinations 16 are placed above the longitudinal axis L of the ship 1, and two of them are placed below the longitudinal axis L of the ship 1.
Two of the second piston-cylinder combinations 16 are placed on a first side of the spud carriage 4, and two of them are placed on the other side of the spud carriage 4.
The free ends 19 of the second pistons 18 are placed against the walls of the carriage space 8, over which they are slidable forwards and backwards.
The second piston-cylinder combinations 16 are connected to a second hydraulic set 20 that comprises the necessary reservoirs, pumps and valves to move the second pistons 18 in a controlled way.
The said measuring instruments 12 of the second piston-cylinder combinations 16 are connected with data transfer capability to the central control unit 14.
Furthermore, two third hydraulic piston-cylinder combinations 22 are affixed in the spud carriage 4 that are each provided with a third cylinder 23 that is filled with hydraulic fluid and a third piston 24. These third piston-cylinder combinations 22 are arranged to be able to rotate the spud carriage 4 and the hull 7 with respect to one another around the above-mentioned transverse axis D.
To this end a lever 25 is rotatably fastened by its first end 26 to the rear wheel set 5. The third pistons 24 of the third piston-cylinder combinations 22 mounted in mutually opposite directions are fastened to the second end 27 of the lever 25.
The spud carriage 4 is rotatably fastened to the lever 25 at a point 28 between the two ends 26, 27 of the lever 25.
The third piston-cylinder combinations 22 are each provided with a measuring instrument 12 for pressure and position measurement that measures the pressure in the third cylinder 23 concerned and the position of the third piston 24 concerned in the third cylinder 23 concerned.
The third piston-cylinder combinations 22 are connected to the second hydraulic set 20 that comprises the necessary reservoirs, pumps and valves to move the third pistons 24 in a controlled way.
The said measuring instruments 12 of the third piston-cylinder combinations 22 are connected with data transfer capability to the central control unit 14.
The central control unit 14 is connected controllably to the second hydraulic set 20 to thereby be able to set the position of the second pistons 18 and the third pistons 24. Because the first, second and third piston- cylinder combinations 9, 16, 22 can set the mutual position and orientation of the hull 7 and the spud 2, they are considered as positioning means for the mutual position and orientation of the hull 7 and the spud 2.
The operation of the ship 1 is very simple and as follows.
The following three force components of the force exerted by the hull 7 of the ship 1 on the spud carriage 4, and thereby on the spud 2, can hereby be considered separately:

the force component that acts parallel to the longitudinal axis L of the ship 1, hereinafter called the first component and which in general is caused by a surging movement of the ship 1 as a result of waves;
the force component that is tangentially oriented with respect to the longitudinal axis L, hereinafter termed the second component and which in general is caused by a rolling movement of the ship 2 as a result of waves;
the force component that is tangentially oriented with respect to the transverse axis D, hereinafter termed the third component and which in general is caused by a pitching movement of the ship 1 as a result of waves.

The aspects of the operation of the cutter-suction dredger that do not differ from a standard cutter-suction dredger are not dealt with here.
For good understanding, however, it should be stated that when using a standard cutter-suction dredger the spud carriage 4 is movable with respect to the hull 7, but that a completely rigid, fixed fastening of the spud carriage 4 with respect to the hull 7 is maintained between movements.
The control unit 14 is provided with an algorithm to make a prediction of the future time-dependent force variation for each of the said three force components.
To this end the control unit 14 essentially uses the pressures as input data that are measured by the measuring instruments 12.
These pressures, measured by the measuring instruments of the first, second, and third piston- cylinder combinations 9, 16, 22 respectively are proportional to the first, second, and third force components respectively.
During the activities of a cutter-suction dredger the wave movements typically have a period of 5 to 10 seconds. During this period in general a sinusoidal variation of a force component or the pressure proportional to it is observed.
By now analysing a first part of such a sinusoidal variation, i.e. a part that corresponds to the start of a force increase, i.e. approximately the first 25% of a cyclic movement, the further variation of this force can be well predicted, in any case insofar it relates to the same wave movement.
In the case of the first force component, such an analysis is done by the control unit 14 on the basis of the pressures in the first cylinder 10, whereby a prediction of the further course of an increasing pressure is obtained.
If the maximum expected pressure exceeds a threshold value, the control unit 14 will execute a compensatory movement via the first hydraulic set 13.
By prior analysis, this threshold value of the pressure is related to the force at which damage can occur to the spud 2 or other components of the ship 1.
If the maximum expected pressure does not exceed the threshold value, the control unit 14 will not execute a compensatory movement. As a result, at low forces an immovable fastening of the spud carriage 4 with respect to the hull 7 is maintained.
The said compensatory movement consists of the hull 7 being moved with respect to the spud 2 in the direction in which the force acts, thus either forwards or backwards.
This movement is made before the predicted first force component actually reaches its predicted values so that the first force component actually exerted will be less than the predicted first force component.
In practice the said compensatory movement is executed by the first hydraulic set 13, controlled by the control unit 14, pumping hydraulic fluid into or out of the first cylinder 10, and thereby adjusting the position of the first piston 11.
This is illustrated in figure 5, in which a maximum predicted force in the forward direction, indicated by arrow P, is compensated by a forward movement of the hull 7, that is achieved by pumping hydraulic fluid out of the first cylinder 10.
In the case of the second force component, such an analysis is done by the control unit 14 on the basis of the pressures in the second cylinders 17, whereby a prediction of the further course of an increasing pressure is obtained.
Just as with the first force component, if the maximum expected pressure exceeds a threshold value, the control unit 14 executes a compensatory movement, this time via the second hydraulic set 20.
The said compensatory movement consists of the hull 7 being moved with respect to the spud 2 in the direction in which the force acts, thus a rotational movement to the right or left around the longitudinal axis L.
This movement is done before the predicted second force component actually reaches its predicted values so that the second force component actually exerted will be less than the predicted second force component.
In practice the said compensatory movement is executed by the second hydraulic set 20, controlled by the control unit 14, pumping hydraulic fluid into two diagonally opposite second cylinders 17, and hydraulic fluid from the other two second cylinders 17, which thereby adjusts the position of the second pistons 18.
This is illustrated in figure 6, in which a maximum predicted rotational force around the longitudinal axis L, in the clockwise direction when viewed in the direction from the cutter head 3 to the spud 2, indicated by arrow Q, is compensated by a movement of the hull 7 in the same direction, that is achieved by pumping hydraulic fluid 17 into the second cylinders 17 at the top right and bottom left, and pumping hydraulic fluid out of the second cylinders 17 at the bottom right and top left.
In the case of the third force component such an analysis is done by the control unit 14 on the basis of the pressures in the third cylinders 23, whereby a prediction of the further course of an increasing pressure is obtained.
Just as with the first and second force components, if the maximum expected pressure exceeds a threshold value, the control unit 14 executes a compensatory movement, this time via the second hydraulic set 20.
The said compensatory movement consists of the hull 7 being moved with respect to the spud 2 in the direction in which the force acts, thus a rotary movement whereby the front of the ship 1 is moved upwards or downwards around the transverse axis D.
This movement is done before the predicted third force component actually reaches its predicted values so that the third force component actually exerted will be less than the predicted third force component.
The said compensatory movement is in practice executed by the second hydraulic set 20, controlled by the control unit 14, pumping hydraulic fluid into a third cylinder 23 and out of the other third cylinder 23, and thereby adjusting the position of the third pistons 24.
This is illustrated in figure 7, in which a maximum predicted rotary force around the transverse axis D, in the anticlockwise direction in figure 7, indicated by arrow R, is compensated by a movement of the hull 7 in the same direction.
This movement is brought about by pumping hydraulic fluid into the bottom third cylinder 23 and hydraulic fluid out of the top third cylinder 23. As a result the second end 27 of the lever is raised with respect to the fastening point 28 of the spud carriage 4 to the lever 25, such that the first end 26 of the lever 25 is lowered and the hull 7 of the ship 1 is rotated around the transverse axis D.
The magnitude of the various compensatory movements, in the event of the threshold values being exceeded, depend on the maximum magnitude of the predicted forces, of course with a maximum that is determined by the freedom of movement of the spud carriage 4 in the carriage space 10.
The present invention is by no means limited to the embodiment described as an example and shown in the drawings, but a vessel and method according to the invention can be realised in all kinds of forms and variants without departing from the scope of the invention.

Claims

Vessel (1) that comprises a hull (7) and a spud (2), whereby the vessel (1) is provided with positioning means (9, 16, 22) to set the position and/or orientation of the hull (7) with respect to the spud (2), characterised in that the vessel (1) is provided with a control unit (14) and measuring means (12) to measure the force exerted by the hull (7) on the spud (2) or to measure a pressure from which this force can be derived, whereby the control unit (14) is arranged to control the positioning means (9, 16, 22), whereby the control unit (14) is arranged to make a prediction of the time-dependent future magnitude of the force or pressure and to determine the direction of the future force from values measured by the measuring means (12) over a time interval, whereby the control unit (14) is arranged to make an adjustment to the position and/or orientation of the hull (7) with respect to the spud (2), whereby the direction of the adjustment corresponds to the direction in which the force is exerted.
Vessel according to claim 1, characterised in that the positioning means comprise a hydraulically driven first piston-cylinder combination (9) to move the hull (7) with respect to the spud (2) parallel to the longitudinal axis of the hull (7), whereby the measuring means (12) are arranged to measure a first component of the said force parallel to the longitudinal axis (L) or to measure a pressure from which this first component can be derived, whereby the control unit (14) is arranged to make a prediction, from the values measured by the measuring means (12), of the time-dependent future magnitude of the first component or the said pressure and to determine the direction of the first component, whereby the control unit (14) is arranged to move the hull (7) with respect to the spud (2) parallel to the longitudinal axis (L) of the hull (7), before the predicted magnitude of the first component or the said pressure is actually reached, by moving the piston (11) of the first piston-cylinder combination (9) in the cylinder (10), whereby the direction of the movement of the hull (7) corresponds to the direction in which the first component is exerted.
Vessel according to claim 2, characterised in that the control unit (14) is connected to measuring means (12) to measure the pressure in the cylinder (10) of the first piston-cylinder combination (9), whereby the control unit (14) is arranged to make a prediction, from measured values of this pressure, of the time-dependent future magnitude of this pressure.
Vessel according to any one of the previous claims, characterised in that the positioning means comprise one or more hydraulically driven second piston-cylinder combinations (16) to rotate the hull (7) with respect to the spud (2) around a first axis that is parallel to the longitudinal axis (L) of the vessel (1), whereby the measuring means (12) are arranged to measure a second component of the said force, whereby the second component is tangential to the first axis, or to measure a pressure from which this second component can be derived, whereby the control unit (14) is arranged to make a prediction, from the values measured by the measuring means (12), of the time-dependent future magnitude of the second component or the said pressure and to determine the direction of the second component, whereby the control unit (14) is arranged to rotate the hull (7) with respect to the spud (2) around the first axis, before the predicted magnitude of the second component or the said pressure is actually reached, by moving the piston (18) of the one or more second piston-cylinder combinations (16) in the cylinder (17) thereof, whereby the direction of the rotation corresponds to the direction in which the second component is exerted.
Vessel according to claim 4, characterised in that the control unit (14) is connected to measuring means (12) to measure the pressure in the cylinder (17) of the one or more second piston-cylinder combinations (16), whereby the control unit (14) is arranged to make a prediction, from measured values of this pressure, of the time-dependent future magnitude of this pressure.
Vessel according to any one of the previous claims, characterised in that the positioning means comprise one or more hydraulically driven third piston-cylinder combinations (22) to rotate the hull (7) with respect to the spud (2) around a second axis (D) that is perpendicular to the longitudinal axis (L) of the vessel (1) and which is horizontal, whereby the measuring means (12) are arranged to measure a third component of the said force, whereby the third component is tangential to the second axis (D), or to measure a pressure from which this third component can be derived, whereby the control unit (14) is arranged to make a prediction, from the values measured by the measuring means (12), of the time-dependent future magnitude of the third component or the said pressure and to determine the direction of the third component, whereby the control unit (14) is arranged to rotate the hull (7) with respect to the spud (2) around the second axis (D), before the predicted magnitude of the third component or the said pressure is actually reached, by moving the piston (24) of the one or more third piston-cylinder combinations (22) in the cylinder (23) thereof, whereby the direction of the rotation corresponds to the direction in which the third component is exerted.
Vessel according to claim 6, characterised in that the control unit (14) is connected to measuring means (12) to measure the pressure in the cylinder (23) of the one or more third piston-cylinder combinations (22), whereby the control unit (14) is arranged to make a prediction, from measured values of this pressure, of the time-dependent future magnitude of this pressure.
Vessel according to any one of the previous claims, characterised in that the control unit (14) is arranged such that the greater the maximum predicted magnitude of the force or the pressure, the greater the magnitude of the adjustment, at least over a certain interval of the maximum predicted magnitude of the force or the pressure.
Vessel according to any one of the previous claims, characterised in that it is additionally provided with or connected to measuring means (12) that are arranged to measure the actual movements of the vessel (1) or the movements of the sea at some distance from the vessel (1).
Vessel according to any one of the previous claims, characterised in that it is provided with a spud carriage (4) in which the spud (2) is fastened, whereby the positioning means (9, 16, 22) are arranged to adjust the position and/or orientation of the hull (7) with respect to the spud carriage (4).
Vessel according to claim 10 and claim 4 or 6 respectively, characterised in that the one second piston-cylinder combinations (16) or the one third piston-cylinder combinations (22) respectively are in the spud carriage (4).
Vessel according to claim 10 or 11 and claim 2 or 3 characterised in that the first piston-cylinder combination (9) is outside the spud carriage (4).
Vessel according to any one of the previous claims, characterised in that it is a cutter-suction dredger.
Method for limiting the forces exerted by the hull (7) of a vessel (1) on a spud (2) as a result of waves, whereby the following steps are taken:
A: the force exerted by the hull (7) on the spud (2) or a pressure that is the result of this is measured over a time interval;

B: from the measured values a prediction is made of the time-dependent future magnitude of the force or the pressure, and the direction in which the future force is exerted is determined;

C: the position and/or orientation of the hull (7) with respect to the spud (2) is adjusted in the said direction before a predicted magnitude of the force or pressure is actually reached.
Method according to claim 14, characterised in that a vessel (1) according to any one of the claims 1 to 12 is used.
Method for removing bed material from a seabed, whereby a vessel (1) according to claim 13 is used, and whereby a method according to claim 14 or 15 is applied to limit the force exerted by the hull (7) on the spud (2).