EP2644781B1

EP2644781B1 - Pumping means intended for being trailed by a trailing suction hopper dredger and trailing suction hopper dredger equipped with such pumping means

Info

Publication number: EP2644781B1
Application number: EP12002349.4A
Authority: EP
Inventors: Willy Oscar Blomme; Jan Etienne Diane Fordeyn; Bernard Malherbe
Original assignee: Jan De Nul Nv
Current assignee: Jan De Nul Nv
Priority date: 2012-03-30
Filing date: 2012-03-30
Publication date: 2016-06-29
Anticipated expiration: 2032-03-30
Also published as: PL2644781T3; HUE030692T2; SMT201600346B; DK2644781T3; SI2644781T1; LT2644781T; PT2644781T; EP2644781A1; ES2592282T3; RS55257B1; HRP20160980T1; CY1117979T1

Description

The present invention relates to pumping means intended for being trailed by a trailing suction hopper dredger.
More specifically the present invention relates to pumping means of a type intended for being trailed by a trailing suction hopper dredger, the pumping means comprising at least:

a submergible pump;
a suction tube mounted on an inlet of the submergible pump;
a discharge pipe mounted on an outlet of the submergible pump;
a suction tube mouth at a free end of the suction tube for sucking a mixture of water and seabed material through the suction tube and for discharging it through the discharge pipe; and,
a dredge drag head provided at the suction tube mouth.

The attention is drawn to the fact that in the dredging or mining methods for which the pumping means of the invention are intended, the dredge drag head is dragged or trailed by the dredger vessel over an underwater soil or bedrock for loosening it, whereby the loosened material is sucked through the suction tube mouth, in comparison to known devices as disclosed in JP 02266088 and FR 1553816 which are not towed but are self-propellant.
According to the state of the art pumping means for being trailed by a trailing suction hopper dredger and having a suction tube, the suction mouth of which provided with a dredger drag head, are already known.
The known pumping means of this type can however still be substantially improved, which is the aim of the present invention.
A first disadvantage of the known pumping means of the concerned type is that it is applicable only to a limited depth underwater, while, at present, mankind is searching more and more for marine resources for both commercial minerals and building materials at ever greater water depths.
This search is driven by the ever growing upland scarcity in sand, mine-materials, etc...
Until approximately 1990, maximum dredging-depth achievable by hydraulic dredgers was about 60 to 70m below water-level.
The sizes and the hydraulic capacities of hydraulic dredgers prevented from working at greater depths.
Between 1990 and 2010, the maximum achievable dredging depth reached gradually 155m to 165m, believed to be a physical frontier due to physical restrictions in dredge-pipes, pump-capacities, etc...
The limitations which prevent from dredging with the method under consideration at even still greater depths are related to a combination of factors such as the length of the suction tube, the available storing capacity for the suction tube and the difficulties related to the manipulation of the pumping line.
Other factors of importance are the high pressures at great water depth; limited pumping capacity of the submergible pump, resulting in a limited flow rate at the required pumping head, which is economically not interesting; the lack of sufficient contact of the dredge drag head with the seabed and so on.
In the mining industry a lot of effort has been done for mining at great under water depths.
For example in the marine diamond mining industry in Namibia several types of mining ships are used such as rotary drill ships, stationary airlift dredgers and seabed crawlers up to about 150 m water depth.
Although the techniques used in this industry are applied at greater under water depths and are therefore interesting, these techniques are however not suitable for being applied in large dredging or mining operations by means of a trailing suction hopper dredger during which large volumes of loosened seabed material are mixed with water and the seabed material is transported to the dredger in its entirety.
Indeed, the techniques used in the diamond industry are aimed at the precise and complete excavation of a specific seabed layer.
As a consequence such diamond mining equipment is of a complete other category due to the method used, since it has a capacity which is completely insufficient compared to the capacity required in trailing suction dredging, requiring high volumes, great flow rate, etc...
Between 1969 and 1980, also much research has been done to find a technical solution to mine manganese nodules at more than 5000 m water depth.
All the kind of systems developed for this purpose provide a kind of initial selection or process of the material to be transported to the water surface, i.e. the manganese nodules, and therefore these systems are again not applicable for the purpose of dredging all the seabed material and on a scale and with a capacity as required in trailing suction dredging.
Such a device for ore mining is disclosed in US 4346937 whereby the ore particles are sifted out and lifted to the water surface by means of an air lift system.
So, there is a need for a new technology that has sufficient capacity in order to be suitable for a trailing suction hopper dredger.
It is therefore an objective of this invention to provide a pumping means for a trailing suction hopper dredger the pumping means having a suction tube with a dredge drag head, which has improved characteristics with respect to the known pumping means for this type of dredging, as well as to provide solutions to mentioned as well as possibly not-mentioned problems.
To this end, the present invention relates to pumping means intended for being trailed by a trailing suction hopper dredger according to claim 1.
A big advantage of pumping means in accordance with the present invention is that underwater soil or bedrock can be dredged by trailing suction dredging using a dredge drag head on a suction tube, at much greater depths than with the known pumping means, while the pumping means according to the invention is furthermore suitable for being applied in high seas, ensures large productivities and provides reliability in supply.
The pumping means according to the invention will for example be applicable at under water depths of at least 300 m, more typically at a water depth of around 450 m and preferably at even greater under water depths.
One of the main reasons why pumping means according to the invention can be applied in dredging operations at greater depths than the known pumping means used for trailing suction dredging is that it comprises a combination of a flexible discharge tube which is connected to a submergible pump mounted on a skid structure for being trailed on the seabed floor.
The skid structure hereby provides support for the heavy weight of the submergible pump and other utilities, as will be explained hereafter, while the same weight can be used for providing a good contact of the dredge drag head with the underwater soil.
The flexible discharge pipe can be wound on a reel on deck or be stored on deck by means of other storage means suitable for flexible pipes, so that it is much easier to deploy and store than rigid tubing, and as a consequence, the length of the flexible discharge pipe can be chosen as desired.
Indeed, the known pumping means suitable for a trailing suction hopper dredger are on the contrary all equipped with a rigid pumping line tubing or as an alternative a semi-rigid pumping line tubing, for example realised by means of cardan or swivel couplings mounted in the suction tube or discharge tube, so that the complete pumping line is quite rigid.
Another disadvantage linked with such rigid pumping line tubing is that it requires a lot of space for being stored, which is not the case with the flexible discharge pipe solution provided by the present invention.
Furthermore, compensating the movements of the dredger vessel is easier with a flexible discharge pipe than with the rigid or semi-rigid tubing of the known pumping means.
A very important difference between pumping means according to the current patent application and the existing pumping means, even those known from other domains, is that it is designed for high volume production and fast coverage of large areas.
As a consequence, the skid structure proposed here is very heavy, the installed power very high and requires very high propulsion power to be pulled forward.
None of the existing pumping means which might resemble the pumping means of the present application have the heavy duty design to make high volume excavation feasible or economical on the scale usually applied with a trailing suction hoper dredging.
The development of a workable skid structure and corresponding system on a dredger for descending and ascending the skid structure from the vessel to the sea bottom and vice versa, as well as a working system for towing the skid structure over the seafloor at 300 m water depth and even at 450 m water depth and deeper, with trailing wires of a trailing suction hopper dredger is clearly not a simple matter.
Also, the dynamic behaviour of the flexible discharge pipe demands another approach than is known in the trailing suction dredging domain according to the state of the art.
The big scale applied in trailing suction hopper dredging makes the development of such a pumping means according to the invention a task for specialists.
The skid structure of the pumping means according to the invention for supporting the submergible pump will for example typically have a length of 20 m or more.
Also the submergible pump of the pumping means according to the invention is typically very powerful, and will for example be a centrifugal pump having a pumping capacity of at least 5000 kW, typically 6500 kW and even higher capacity pumps are not excluded.
One can understand that the practical problems related to the manipulation and positioning of such a huge skid structure, as well as to the provision of power supply to the submergible pump, communication with the skid structure, etc.. are not easily overcome.
The applicant has therefore invested for more than 15 years in research for coming to practical feasible and working embodiments of the proposed solution on the required scale and at the desired water depth of 450 m and more, an example of which will be discussed further.
Other specific problems overcome by the solution provided by the present invention are the following.
By using pumping means according to the invention direct contact with the seabed is ensured and the reaction-forces from the seabed during dredging enable a better stability during trailing and an improved control of the trailing process.
Irregularities and low-bearing capacity environments of the seabed are accommodated by a sliding or rolling skid structure.
By using a suction tube by which the angle of incidence of the dredger drag head can be varied, the dredging process is considerably improved.
The capacity to dredge seabed materials at great water-depths is only limited by the capacity of the submergible pump of the pumping means and the maximum achievable flexible discharge pipe length.
A solution for transferring electric power to great water-depth by means of flexible umbilical wiring has been elaborated an the problem of controlling the positioning and the dredge-production at great water depths during operation has been solved.
The present invention also relates to a trailing suction hopper dredger equipped with pumping means according to the invention as described above.
In particular such a trailing suction hopper dredger according to the invention comprises at least:

a vessel equipped with an onboard discharging system for discharging a mixture of water and seabed material into a hopper and/or with an outboard discharging system for discharging said mixture outboard the vessel;
a discharge pipe of the pumping means which is mounted on the outlet of the submergible pump and which is connected to the onboard or outboard discharging system, the pumping means being intended for sucking a mixture of water and seabed material through a suction mouth of the suction tube and discharge it through the onboard or outboard discharging system;
positioning wiring for descending and ascending the pumping means with respect to the vessel and for trailing the pumping means when dredging; and,
umbilical wiring providing a utility line to the pumping means which comprises at least power supply wiring to the submergible pump; and the skid structure of the pumping means is furthermore provided with connection means for connecting the positioning wiring to the skid structure and

the umbilical wiring being connected between the vessel and the skid structure.
It is clear that the invention refers to pumping means to be operated from a trailing suction hopper dredger with loading capacity in its own hopper or as an alternative in barges alongside that trailing suction hopper dredger and which trailing suction hopper dredger is dedicated to dredge materials from shallow as well as deep waters.
With the intention of better showing the characteristics of the invention, hereafter, as example without any limitative character, a preferred form of embodiment is described of pumping means in accordance with the invention, as well as a trailing suction hopper dredger in accordance with the invention equipped with such pumping means, with reference to the accompanying drawings, wherein:

figure 1 represents a schematic side view on pumping means according to the invention;
figure 2 represents on a smaller scale a side view on a trailing suction hopper dredger according to the invention, equipped with the pumping means of figure 1, indicated by F1;
figure 3 represents on the same smaller scale a top view indicated by arrow F3 on the trailing suction hopper dredger of figure 2; and,
figures 4 to 6 illustrate on a larger scale the stern part of the trailing suction hopper dredger of figures 2 and 3, indicated by F4-F6, during different stages of the process of boarding pumping means according to the invention.

The pumping means 1 represented in figure 1 are intended for being trailed by a trailing suction hopper dredger 2 as represented in figures 2 and 3.
The pumping means 1 comprise a skid structure 3 with a bottom 4 intended for being trailed over an underwater soil or bedrock 5 by means of trailing wires 6 suspending from the trailing suction hopper dredger 2.
In the skid structure 3 a submergible pump 7 is provided having an inlet 8 and an outlet 9.
A suction tube 10 is mounted on the inlet 8 of the submergible pump 7 and a discharge pipe 11 is mounted on the outlet 9 of the submergible pump 7.
The suction tube 10 has a suction tube mouth 12 at a free end 13 of the suction tube 10 for sucking a mixture of water and seabed material 5 through the suction tube 10 and for discharging it via the discharge pipe 11.
A dredge drag head 14 is provided at the suction tube mouth 12.
Preferably, the dredge drag head 14 has an adjustable and controllable visor 15 for controlling the flow of mixture of water and seabed material through the suction tube mouth 12.
The skid structure 3 also contains a water jet pump 16 which is connected to a water jet piping 17 having water jet nozzles in the vicinity of the dredge drag head 14 for loosening seabed material 5 by means of water ejected through the nozzles under pressure created by the water jet pump 16.
The jet pump 16 has typically a capacity of 1500 kW, but other capacities are not excluded.
In other embodiments of pumping means 1 according to the invention the dredge drag head 14 can be provided with other or additional seabed loosening means, which can among others for example be one or more of the following elements or a combination thereof:

a dredging chisel tooth or an array of dredging chisel teeth;
a dredging ripper tooth or an array of dredging ripper teeth;
one or more jet-cutting tools;
one or more cutting devices;
etc....

The suction tube 10 extends from the submergible pump 7 outside a back side 18 of the skid structure 3, which is the side 18 most rearwards of the skid structure 3 considered in the trailing direction.
The suction tube 10 preferably comprises means for varying the dredge drag head inclination with respect to the bottom 4 of the skid structure 3 or in other words with respect to the seabed 5, or for setting the dredge drag head inclination according to a desired inclination angle A.
For this purpose, in the embodiment of pumping means 1 according to the invention, represented in figure 1, between the dredge drag head 14 and the skid structure 3 the suction tube 10 is provided with a cardan coupling 19 with arm piece by which the inclination angle A of the dredge drag head 14 with respect to the bottom 4 of the skid structure 3 can vary and/or be modified and set.
The suction tube 10 is also provided with a turning gland 20 by which the dredge drag head 14 can be turned with respect to the suction tube 10 around the axis of the suction tube 10.
The submergible pump 7 and the water jet pump 16 are driven by an electric motor, respectively electric motor 21 and electric motor 22.
In order to provide a power supply for the electric motors 21 and 22 of the pumps 7 and 16, umbilical wiring 23 is connected to the skid structure 3 at a connection box 24, providing a utility line 23 from the trailing suction hopper dredger 2 to the skid structure 3.
Hereby, in this case the submergible pump 7 is a centrifugal pump 7 having a pumping capacity of at least 5000 kW, typically 6500 kW and even more, while according to the invention the water jet pump 16 has a capacity of at least 1000 kW, typically 1500 kW and even more.
Of course, according to the invention, the umbilical wiring 23 also possibly contains other kinds of utility wiring, such as wiring for process control, other power supply wiring, communication wiring for establishing a communication line between the dredger 2 and the skid structure 3 and so on.
The cardan coupling 19 and the visor 15 of the dredge drag head 14 are typically actuated by hydraulic sets also contained in the skid structure 3, but not represented further in detail in the figures however.
Other utility providers which can also be provided in the skid structure 3 can for example be one or more of the following instruments for ascertaining production and position monitoring and/or control:

for example one or more transducers for determining a position;
one or more pressure, velocity and/or concentration gauges for measuring the dredging mixture;
one or more position control propellers for controlling the position of the skid structure during a descent from the trailing suction hopper dredger 2 to the seabed 5 and during ascent from the seabed 5 to the dredger 2;
one or more depth-measuring sensors;
one or more tilt sensors; and so on.

Another important aspect of pumping means 1 according to the invention is that the discharge pipe 11 is a flexible pipe 11.
On the upper side 25 of the skid structure 3 and near the front side 26 of it, connection means 27 are provided for attaching trailing wires 6 to the skid structure 3.
The connection means 27 are in the embodiment represented in figure 1 a pair of vertical plates 27, each plate 27 of which being welded at a lateral side of the skid structure 3 and provided with an eye 28 for a wire connecting hook or the like.
The physical shape of the skid structure 3 represented in figure 1 can be described as a wedge shaped structure 3, having a bottom 4 and an upper side 25 which are inclined towards one another in the direction of the dredge drag head 17 at the back side 19, with an angle B of inclination corresponding in this case to an angle C of inclination of the suction tube 10 at least at the inlet 8 of the submergible pump 7.
The corner side 29 of the wedge shaped structure 3 between the front sidle 26 and the bottom 4 is provided with a double chamfer 30 in order to allow a good sliding of the skid structure 3 over the seabed 5, without being obstructed by non smooth geological structures such as boulders, etc ...
Furthermore, the skid structure 3 has a length L of 25 m in the represented case, the part of the suction tube 10 with dredge drag head 14 which is extending from the actual skid structure 3 included, and this length L will be in other embodiments at least 20 m as well, which again demonstrates the scale of dredging or mining operations for which the pumping means 1 are intended.
In order to be able to control the pressure of the skid structure 3 on the seabed 5 the skid structure 3 is according to the invention preferably provided with ballast tanks or buoyancy tanks.
Figures 2 and 3 represent a trailing suction hopper dredger 2 according to the invention equipped with pumping means 1 according to the invention.
The trailing suction hopper dredger 2 comprises a vessel 31 having a bow side 32, a stern side 33, a hull 34 and a deck 35.
The vessel 31 is equipped with a so-called launch and recovery system 36 (LARS) on the deck 35 in the vicinity of the stern side 32 of the vessel 31, which is intended for descending the skid structure 3 from an onboard position to an underwater position under the water level 37 and vice versa.
This launch and recovery system (LARS) is represented in more detail in figures 4 to 6 and it comprises first of all a docking-pad 38 for supporting the skid structure 3 on the deck 35 of the vessel 31.
Furthermore, the launch an recovery system (LARS) 36 is provided with a frame 39, often designated as an A-frame, for suspending the skid structure 3.
This frame 39 has a pair of legs 40 and 41 connected to one another by means of an overhead beam 42.
The legs 40 and 41 are mounted on the deck 35 of the vessel 31 at starboard 43 and port-side 44 respectively.
Hereby, the legs 40 and 41 are mounted on the deck 35 in a rotatable manner by means of a hinge 45 in such a way that the frame 39 can rotate from a position perpendicular to the deck 35 of the vessel 31, as is the case in figure 6, into an inclined position wherein the skid structure 3 is suspended from the frame 39 outboard the vessel 31, as is the case in figures 4 and 5.
In order to be able to position the skid structure 3, i.e. positioning it by descending and ascending the skid structure 3 with respect to the vessel 31 for deploying it under water or for storing it on board of the vessel 31, as well as positioning it by trailing the skid structure 3 over the underwater soil 5 when deployed, the launch and recovery system (LARS) 36 is also provided with one or more positioning wiring pulleys 46 for guiding positioning wiring.
This positioning wiring can consist of separate wiring for suspending the skid structure 3 during descent to the underwater soil 5 and ascent to the onboard position, and separate trailing wiring for trailing the skid structure 3 on the seabed 5 during dredging.
In the case represented in the figures however, the positioning wiring only comprises the trailing wiring 6 which is also used for suspending the skid structure 3 during ascent and descent with respect to the vessel 31.
As is clear for example from figure 3, the trailing wiring 6 or positioning wiring 6 consists in the embodiment under discussion of a pair of double reeved trailing wires 47 and 48 provided at star-board 43 and port-side 44 respectively, which are guided over the positioning wiring pulleys 46 on the frame 39 to trailing wire winches 49 and 50 provided respectively at star board 43 and port-side 44 on the deck 35 of the vessel 31 at a certain distance from the docking-pad 38.
On the frame 39 of the launch and recovery system (LARS) 36 also one or more umbilical wiring pulleys 51 are provided for guiding the umbilical wiring 23 to an umbilical wiring reel 52 provided on the deck 35 for winding and unwinding the umbilical wiring 23.
Furthermore, a discharge pipe reel 53 is provided on the deck 35 of the vessel 31 on which the flexible discharge pipe 11 can be wound for storing the flexible pipe 11 onboard and from which it can be unwound for use of the pumping means 1.
According to the invention this discharge pipe reel 53 is preferably provided with a controlling device for adjusting the winding and unwinding speed and the traction on or the tensioning of the flexible discharge pipe 11.
Furthermore, the trailing suction hopper dredger 2 is in this case provided with an onboard discharging system for discharging a mixture of water and seabed material 5 sucked by the pumping means 1 into the hopper of the vessel 31.
However, according to the invention it is not excluded to provide on the vessel 31, as an alternative or additionally, an outboard discharging system for discharging said mixture of water and seabed material 5 outboard the vessel 31.
As already mentioned the discharge pipe 11 of the pumping means 1 is mounted at one end on the outlet 9 of the submergible pump 7.
The other end is at least partly wound on the discharge pipe reel 53 and is connected to the onboard or outboard discharging system for discharging the mixture of water and seabed material 5.
The pumping means 1 according to the invention are suitable for dredging operations at a depth D of 300 m and preferably 450 m and more under the water level 37.
In some cases it might be advantageous or necessary to improve the sliding capacity of the skid structure 3 on the underwater soil 5.
Hereby, for guiding the skid structure 3 during trailing it can for example be mounted on a sledge.
As an alternative the skid structure 3 can also be mounted on wheels or on tracks.
In the case tracks or wheels are used for supporting the skid structure 3, a controllable and adjustable braking or driving system can be integrated in order to control trailing-tracks and seabed-depletion.
According to another aspect of the invention, the skid structure 3 is preferably provided with a position-measurement system for measuring the underwater position of the skid structure 3 with respect to the vessel 31.
Such a position measurement system preferably provides an input to a position controller which controls the position of the skid structure 3 by means of the positioning wiring 6.
In order to avoid implosions or water-hammer in the pumping line, the suction tube 10 and/or the discharge pipe 11 can also be provided with one or more vacuum-relief valves.
In order to avoid blockage, the discharge pipe 11 can be provided with an emergency bypass valve.
According to the invention also one or more of the following additional interesting equipments can be provided in the skid structure 3 or on the trailing suction hopper dredger 2:

a hydraulic power-pack;
a jetwater system;
a quick-release system for remotely releasing wires 6 or 23 and/or tubes 11 connected to the skid structure 3;
a redundant power-supply and control system;
an emergency recovery system; and,
possibly other equipment.

The way such a trailing suction hopper dredger 2 and pumping means 1 are used, will now be illustrated in more detail.
In general terms, the trailing suction hopper dredger 2 or the vessel 31 serves as a platform from which the pumping means are deployed and lowered onto the seabed 5 or close to it.
Similarly, the trailing suction hopper dredger 2 or the vessel 31 serves as a towage-vehicle, as a storage facility, as a transport system of the dredged materials and as a platform for unloading the dredged material into barges or ashore.
Globally, the invention intends to enable the dredging of materials from the seabed 5 in shallow or in deep waters, beyond 450 m, where dredging operations with known trailing suction hopper dredgers, known cutter suction dredgers, known plain suction dredgers cannot be executed.
Starting from the situation in which the skid-structure 3 is docked onto the docking-pad 36 on the vessel 31, the dredging process is as follows.
In this starting situation the discharge pipe 11, the umbilical wiring 23 and the positioning wiring 6 are wound respectively on discharge pipe reel 53, umbilical wiring reel 52 and trailing wiring winches 49 and 50.
First, the trailing suction hopper dredger 2 is sailed to the desired area to be dredged.
Upon positioning of the trailing suction hopper dredger 2, ready for operations, the skid-structure 3 is unlocked from its sea-fastening devices and launched via its launch and recovery system (LARS) 36.
Hereby, the skid-structure 3 is first lifted from its docking-pad 36 by winding the trailing wiring 6, the frame 39 being in the vertical position, as is represented in figure 6.
Then, the frame 39 is rotated towards the outboard and the skid structure 3 is hauled overboard, via the stern 33 of the trailing suction hopper dredger 2 or vessel 31, as is represented in figure 5.
In a next step of a dredging process according to the invention the skid structure 3 is lowered in the sea by unwinding the trailing wires 47 and 48 from their winches 49 and 50.
Simultaneously and synchronistically, also the discharge pipe 11 is unwound from the discharge pipe reel 53, the tension of the discharge pipe 11 being kept within acceptable limits by a pipeline tensioning system.
At the same time also the umbilical wiring 23 is unwound from the umbilical wiring reel 53, synchronistically with the unwinding of the other wiring.
Meanwhile, the trailing wiring winches 47 and 48, the umbilical wiring reel 52 and discharge pipe reel 53 are operated in controlled tensioning mode in order to follow the movements of the skid-structure 3.
Hereby, the suspension of the skid-structure 3 from the frame 39 is realised from a balanced central suspension-point so as to ensure a sub-horizontal position of the skid structure 3 during descent and ascent.
During descent into the seawater, the positioning, tilt and depth of the skid structure 3 are monitored and the sounded depth and available lengths of the positioning wiring 6 of the umbilical 23 and the flexible discharge pipe 11 are compared and verified.
For this purpose, the trailing suction hopper dredger 2 is preferably equipped with a skid-borne sensor-system, a ship-borne monitoring system and/or one or more reference units installed on the seabed 5.
Unwanted spinning of the skid structure 3 during descent, and ascent of course as well, is controlled by electric-driven skid-borne propeller systems.
Furthermore, during descent of the skid structure 3 in the seawater the suction tube 10 and the dredge drag head 14 are kept more or less horizontally by modifying accordingly the inclination angle A with cardan coupling 19, as can be seen in figure 4.
The reason is that in that way it is avoided that the skid structure 3 would first touch the seabed 5 by means of the drag head 14 instead of by means of the bottom 4 of the skid structure 3, as is preferable in order to avoid damage.
In some case it can be interesting to execute a sequence of verifications just before touch-down of the pumping means with the seabed 5, in order to verify whether or not all equipment is properly functioning.
Upon touch-down at the underwater soil 5 by the skid structure 3, the correct positioning of the skid structure 3 onto the seabed 5 is verified with sensors, tilt-meters and depth-measuring sensors and the suction tube 10 and dredge drag head 14 are set to the correct inclination angle A for dredging.
Then, the trailing suction hopper dredger 2 or vessel 31 is moved forward while the positioning wiring 6 is unwound until it extends more or less in a direction XX' making the desired angle E with respect to the seabed 5, which angle E is appropriate for trailing the skid structure 3 in an efficient manner, and until the desired tensioning and stress in the positioning wiring 6 are obtained.
At that moment the submergible pump 7 is started together with the water jet pump 16, as well as hydraulic sets and all other possible equipments needed for a proper functioning of the pumping means 1, whilst the trailing suction hopper dredger 2 is sailing.
According to the invention, the skid structure 3 is preferably also equipped with a jetting array destined to unstuck the skid structure 3 in case the seabed soil 5 consists of cohesive seabed sediments or in case any fluidisation of the supporting seabed soil 5 is requesting such an operation.
Propulsion of the trailing suction hopper dredger 2 or vessel 31 is gradually increased till the optimal trailing speed is attained.
During dredging the inclination angle A of the dredge drag head 14 can be adapted with the turning gland 20 into an inclination angle A suitable for loosening the seabed 5, supported by the pressure coming from water ejected through nozzles 18 of the water jet pipe 17.
If required, the dredge drag-head 14 can be equipped with dredging-teeth, chisels or ripper-teeth, jet-cutting tools or cutting devices in order to achieve the required soil-loosening.
The flow rate through the pumping line, i.e. through the suction tube 10 and discharge pipe 11, as well as the actual water to seabed material ratio can be adapted by adjusting the position of the visor 15 of the dredge drag head 14.
The hydraulic submergible pump 7 has of course the needed power necessary to pump the dredged mixtures up to the sea-surface and through the onboard or outboard discharging system on the trailing suction hopper dredger 2, respectively into the hopper of the dredger 2 or into an outboard disposal facility, such as a separate barge, an onshore disposal area or the like.
The submergible pump 7 on the skid structure 3 is controlled by an in-board power-control system of the trailing suction hopper dredger 2, which is in connection with the skid structure 3 by means of the umbilical wiring 23.
Upon completion of a dredging operation, the suction tube 10 with drag-head 14 is tilted until it is brought again into a sub-horizontal position.
Then the suction tube 10 is flushed, as well as the submergible pump 7, the whole discharge pipe 11 and onboard discharging system and/or outboard discharging system.
After this flushing operation, the submergible pump 7 and water jet pump 16 are stopped and the positioning wiring 6, the umbilical wiring 23 and the flexible discharge pipe 11 wound in a synchronous way on their winches 47 and 48 or reel 52 and 53 respectively.
Upon surfacing of the skid structure 3, a triangulating suspension wire catcher 54 locks the positioning wiring 6 and prevents swinging of the skid structure 3 during the on-board hauling operation, as is represented in figures 5 and 6.
The boarding of the skid structure 3 is realised by a manipulation of the frame 39 combined with a correct winding of the trailing wires 6, the umbilical wiring 23 and the flexible discharge pipe 11 in a sequence opposite to the sequence described above for descending the skid structure 3.
The skid structure 3 is docked onto the docking-pad 38 and locked into a sea-fastened status.
According to the invention, the trailing suction hopper dredger 2 is also provided with tools for recovering pumping equipment in case of rupture of for example the trailing wires 6, the umbilical wiring 23 or the discharge pipe 11.
In case of rupture of the suspension wiring or when the trailing wiring 6 is also used for suspending the skid structure 3 during descent and ascent as is the case in the embodiment represented in the figures, a recovery suspension wiring or trailing wiring will be pulled in with a so-called remotely operated vehicle (ROV) and/or with diver assistance.
The present invention is by no means limited to pumping means 1 according to the invention, nor to a trailing suction hopper dredger 2 according to the invention described as an example and illustrated in the drawings, but such pumping means 1 according to the invention as well as a trailing suction hopper dredger 2 can be realised in all kinds of variants, without departing from the scope of the invention.

Claims

Pumping means (1) intended for being trailed by a trailing suction hopper dredger (2), the pumping means (1) comprising at least:
- a submergible pump (7);

- a suction tube (10) mounted on an inlet (8) of the submergible pump (7);

- a discharge pipe (11) mounted on an outlet (9) of the submergible pump (7);

- a suction tube mouth (12) at a free end (13) of the suction tube (10) for sucking a mixture of water and seabed material (5) through the suction tube (10);

- a skid structure (3) with a bottom (4) intended for being trailed over an underwater soil (5) or bedrock by means of trailing wires (6,47,48);

- connection means (27) for attaching the trailing wires (6,47,48) to the skid structure (3);

- the submergible pump (7) being installed in or on the skid structure (3),
characterized in that the skid structure (3) with the submergible pump (7) is adapted for being trailed by means of trailing wires (6,47,48) suspending from a trailing suction hopper dredger (2) while in use for sucking the mixture of water and seabed material (5) through the suction tube mouth (12) of the suction tube (10), the suction tube (10) with the suction tube mouth (12) at its free end (13) extending from the submergible pump (7) outside a back side (19) of the skid structure (3), the suction tube mouth (12) being provided with a dredge drag head (14), whereby the discharge pipe (11) is a flexible discharge pipe (11) for discharging the mixture of water and seabed material sucked through the suction tube mouth (12) of the suction tube (10) into the trailing suction hopper dredger (2) or into an outboard disposal facility, such as a separate barge, an onshore disposal area or the like.
Pumping means (1) according to claim 1, characterized in that the suction tube (10) comprises means (19) for varying the dredge drag head inclination with respect to the bottom (4) of the skid structure (3) and for setting the dredge drag head inclination according to a desired inclination angle (A)
Pumping means (1) according to any of the preceding claims, characterized in that the skid structure (3) has a length (L) of 20 m or more.
Pumping means (1) according to any of the preceding claims, characterized in that the submergible pump is a centrifugal pump having a pumping capacity of at least 5000 kW.
Pumping means (1) according to any of the preceding claims, characterized in that the skid structure (3) is wedge shaped, having a bottom (4) and an upper side (27) which are inclined towards one another in the direction of the dredge drag head (14) with an angle of inclination (B) corresponding to an angle of inclination (C) of the suction tube (10) at the submergible pump inlet (8).
Pumping means (1) according to any of the preceding claims, characterized in that between the dredge drag head (14) and the skid structure (3) the suction tube (10) is provided with a cardan coupling (19) by which the inclination angle (A) of the dredge drag head (14) with respect to the bottom (4) of the skid structure (3) can be set.
Pumping means (1) according to any of the preceding claims, characterized in that the skid structure (3) is provided with ballast tanks or buoyancy tanks for controlling the ground pressure on the underwater soil or bedrock (5).
Pumping means (1) according to any of the preceding claims, characterized in that the skid structure (3) is provided with one or more of the following instruments for ascertaining production and position monitoring and/or control:
- a transducer for determining a position;

- a pressure, velocity and/or concentration gauge for measuring the dredging mixture.

- a position control propeller for controlling the position of the skid structure during a descent from the vessel to the seabed and during ascent from the seabed to the vessel (31);

- a depth-measuring sensor; and,

- a tilt sensor.
Pumping means (1) according to any of the preceding claims, characterized in that the skid structure (3) contains a water jet pump (16) connected to a water jet piping (17) having water jet nozzles (18) in the vicinity of the drag head (14) for loosening seabed material (5) by means of water ejected through the nozzles (18) under pressure created by the water jet pump (16).
Pumping means (1) according to any of the preceding claims, characterized in that the dredge drag head (14) has an adjustable and controllable visor (15).
Pumping means (1) according to any of the preceding claims, characterized in that the dredge drag head (14) is provided with seabed loosening means, comprising one or more of the following elements:
- a dredging chisel tooth;

- a dredging ripper tooth;

- a jet-cutting tool; and,

- a cutting device.
Trailing suction hopper dredger (2) equipped with pumping means according to any of the preceding claims, characterized in that it comprises at least:
- a vessel (31) equipped with an onboard discharging system for discharging a mixture of water and seabed material (5) into a hopper and/or with an outboard discharging system for discharging said mixture outboard the vessel (31);

- a discharge pipe (11) of the pumping means (1) which is mounted on the outlet (9) of the submergible pump (7) and which is connected to the onboard or outboard discharging system, the pumping means (1) being intended for sucking a mixture of water and seabed material (5) through a suction mouth (12) of the suction tube (10) and discharge it through the onboard or outboard discharging system;

- positioning wiring (6) for descending and ascending the pumping means (1) with respect to the vessel (31) and for trailing the pumping (1) means when in use for dredging; and,

- umbilical wiring (23) providing a utility line to the pumping means (1) which comprises at least power supply wiring to the submergible pump (7);,
and the skid structure (3) furthermore being provided with connection means (27) for connecting the positioning wiring (6) to the skid structure (3) and the umbilical wiring (23) being connected between the vessel (31) and the skid structure (3).
Trailing suction hopper dredger (2) according to claim 12, characterized in that the discharge pipe (11) is a flexible discharge pipe (11), a discharge pipe reel (53) being provided on the vessel (31) on which the flexible discharge pipe (11) can be wound for storing the flexible pipe (11) onboard and from which it can be unwound for use of the pumping means (1).
Trailing suction hopper dredger (2) according to claim 13, characterized in that the discharge pipe reel (53) is provided with a controlling device for adjusting the winding and unwinding speed and the traction on or the tensioning of the flexible discharge pipe (11).
Trailing suction hopper dredger (2) according to any of the claims 12 to 14, characterized in that the vessel (31) is provided with a launch and recovery system (LARS) (36) in the vicinity of the stern (33) of the vessel (31), for descending the skid structure (3) from an onboard position to an underwater position and vice versa.
Trailing suction hopper dredger (2) according to claim 15, characterized in that the launch and recovery system (LARS) (36) comprises at least:
- a docking-pad (38) for supporting the skid structure (3) on the deck (35) of the vessel (31);

- a frame (39) for suspending the skid structure (3), having a pair of legs (40,41) connected to one another by means of an overhead beam (42), the legs (40,41) being mounted at starboard (43) and port-side (44) respectively on the deck (35) of the vessel (31) in a rotatable manner by means of a hinge (45) in such a way that the frame (39) can rotate from a position perpendicular to the deck (35) of the vessel (31) into an inclined position wherein the kid structure (3) is suspended on the frame (39) outboard the vessel (31);

- one or more positioning wiring pulleys (46) for guiding the suspension wiring and/or trailing wiring (6) ; and,

- one or more umbilical wiring pulleys (51) for guiding the umbilical wiring (23).
Trailing suction hopper dredger (2) according to any of the claims 12 to 16, characterized in that the skid structure (3) is mounted on a sledge.
Trailing suction hopper dredger (2) according to any of claims 12 to 16, characterized in that the skid structure (3) is mounted on wheels.
Trailing suction hopper dredger (2) according to any of claims 12 to 16, characterized in that the skid structure (3) is mounted on tracks.
Trailing suction hopper dredger (2) according to any of the claims 12 to 19, characterized in that the skid structure (3) is provided with a position-measurement system for measuring the underwater position of the skid structure (3) with respect to the vessel (31), which position measurement system provides an input to a position controller which controls the position of the skid structure (3) by means of the positioning wiring (6).
Trailing suction hopper dredger (2) according to any of the claims 12 to 20, characterized in that the suction tube (10) or discharge pipe (11) is provided with one or more vacuum-relief valves and/or one or more emergency bypass valves.
Trailing suction hopper dredger (2) according to any of the claims 12 to 20, characterized in that the skid structure (3) is provided with one or more of the following additional equipments:
- a hydraulic power-pack;

- a jetwater system;

- a quick-release system for remotely releasing wires or tubes connected to the skid structure;

- a redundant power-supply and control system;and,

- an emergency recovery system.
Trailing suction hopper dredger (2) according to any of the claims 12 to 22, characterized in that the skid structure (3) is equipped with a jetting array destined to unstuck the skid-structure (3) in case the seabed soil(5) consists of cohesive seabed sediments or in case any fluidisation of the supporting seabed soil (5) is requesting such an operation.