Trailing suction hopper dredger

Abstract

The invention relates to a trailing suction hopper dredger comprising; - a propulsion system for propelling the trailing suction hopper dredger, - a suction system for transporting dredged material from a bottom of a body of water into the trailing suction hopper dredger, and having i. a suction head ii. a suction tube, and a iii. suction tube inlet connection of the trailing suction hopper dredger, - an inboard pump system for driving a flow of dredged material in the suction system, wherein the suction tube is bow pointing from the suction tube inlet connection.

Description

[0001] Trailing suction hopper dredger

[0002] BACKGROUND

[0003] The current disclosure relates to a trailing suction hopper dredger, in short dredger or vessel, comprising; a propulsion system for propelling the trailing suction hopper dredger, a suction system for transporting dredged material from a bottom of a body of water into the trailing suction hopper dredger, and having a suction head and a suction tube inlet connection at a hull of the trailing suction hopper dredger, as well as a pump system for driving a flow of dredged material in the suction system.

[0004] The current disclosure relates as well to a use of such a trailing suction hopper dredger.

[0005] Known trailing suction hopper dredgers, in particular dredgers with a capacity below 4000m3, have a typical lay out with the main deckhouse accommodation at the aft and the dredge pump in the fore ship. This lay-out is a result from, firstly that often the suction tube is approximately half the length of the vessel, and secondly the requirement that the suction tube needs to be stored on deck of the dredger while sailing. The suction tube inlet connection is therefore at the side of the hull at the fore ship to be close to the pump. The conventional dredger advances in one and the same forward direction during both sailing and dredging.

[0006] In Advanced Training in Execution of Hydraulic Engineering Work Dredging work 5b Trailing suction hopper dredgers ISBN 978-90-7677 5-104 of the “Vereniging van Waterbouwers, the specific gear of a Trailing suction hopper dredger (TSHD) is described. The specific gear of a trailing suction hopper dredger includes a suction pipe equipped with a drag head, which is trailed on the bottom during the suction process. The suction pipe is aft pointing from a pipe inlet connection to the drag head. The TSHD has one or more dredge pumps for suction and to transport the mixture to the hopper of the ship. Therefore, the TSHD has transport pipelines, which flow into the cargo hold (the hopper), where the sucked mixture is deposited. The TSHD has one or more overflow(s) for discharging excess water from the hopper to overboard. The TSHD is equipped with hoist cables, gantries and winches for positioning the suction pipe. The suction pipe can be moved between an onboard position and a lowered position wherein the drag head contacts the bottom. An example of a TSHD is shown in EP2034096 wherein the suction dredger comprises a dredging tube which at one end is connected to a suction head and which at the other end is connected to the suction dredger hull by means of a pivot connection having a pivot axis which is horizontally and transversely oriented with respect to said hull, and a suspension device by means of which said dredging tube is displaceable between a horizontal rest position and an inclined dredging position.

[0007] A drawback of the known dredgers is that position of the pump is relatively high when the hopper dredger is empty and therefore as a consequence production is not optimal, especially for small size dredgers with limited draught, like for example dredgers below 4000m3. On the other hand, in case of moving the dredge pump towards the aft in order to lower the position of the pump, the suction tube inlet in the fore ship in combination with the dredge pump at the aft ship requires long inboard piping resulting in additional weight, maintenance, and pipe resistance.

[0008] These small size dredgers are suitable to operate in small ports with one-man operation, which requires good visibility during dredging. The suction tube is relatively long with respect to the vessel length, which results in a forward position of the suction tube inlet connection. For visibility a deckhouse is often placed aft. The consequence is a forward position of the dredge pump to allow access for maintenance. The forward position of the dredge pump is however not optimal for production, especially for the size of dredgers with limited draught.

[0009] SUMMARY

[0010] The object of the current invention is to provide a trailing suction hopper dredger that is more efficient. Efficiency is a wide concept though in this case it can include dredge production per installed power, dredge production per weight of construction, accuracy of dredging etc.

[0011] Another object of the current invention is to provide a trailing suction hopper dredger wherein a known problem is at least partly solved.

[0012] Another object of the current invention is to provide an alternative trailing suction hopper dredger.

[0013] Therefore, the invention provides a trailing suction hopper dredger comprising; a. a propulsion system for propelling the trailing suction hopper dredger, b. a first suction system for transporting dredged material from a bottom of a body of water into the trailing suction hopper dredger, and comprising i. a suction head, ii. a suction tube and a iii. suction tube inlet connection of the trailing suction hopper dredger, c. a pump system for driving a flow of dredged material in the suction system, wherein the suction tube is bow pointing from the suction tube inlet connection.

[0014] To put it in other words, a bow pointing suction tube entails that the suction head is behind the suction tube inlet connection in a forward looking direction of the trailing suction hopper dredger. The suction tube inlet connection is therefore closer to or at the aft section of the trailing suction hopper dredger. The suction tube inlet connection being closer to the aft section of the trailing suction hopper dredger enables placement of the dredge pump closer to the aft section of the vessel. This has a number of advantages.

[0015] Firstly, the pump being in the aft part of the backward trimmed vessel provides a lower position of the dredge pump which helps to prevent cavitation and therefore improves efficiency of dredge pumping. In other words, when the dredge pump is in the aft ship at or near the lowest point in the vessel, the dredge pump will be more submerged, which leads to a shorter loading time. The dredge pump in the aft ship is also optimal for discharging. With the dredge pump located at the lowest point, during discharging of the hopper, the dredged mixture in the hopper will flow more easily towards the dredge pump.

[0016] Secondly, the drive system is normally arranged in the aft section of the vessel. In most cases the drive system both drives the pump system and the propulsion system. The placement of the dredge pump closer to the drive system is beneficial since the pump is then closer to the installed power in the vessel.

[0017] Thirdly, this placement of the inboard pump close to a drive system at the stern results in more weight in the aft ship and therefore a larger backward trim in empty condition. An increased draft reduces the risk of pump cavitation and allows to install larger propellers. Both increase the efficiency.

[0018] The term “trim” relates to the draft of a ship. The draft of a ship's hull is the vertical distance between the waterline and the bottom of the hull, also “keel”. The trim of a ship is the difference between the forward and aft drafts relative to the waterline. When the aft draft relative to the waterline is larger, the vessel is deemed to have a backward trim, also referred to as positive trim, or trimmed by the stern. A backward trim is important to provide efficient propulsion for a vessel especially in an unloaded condition.

[0019] The suction head being behind the suction tube inlet connection when seen in a forward direction means in other words that the suction head is most forward and leading. To put it in another way, this opens the possibility of dredging in a backward direction while having a trailing suction head.

[0020] The suction tube being bow pointing from the suction tube inlet connection, means that the suction tube extends towards the bow directly from the suction tube inlet connection. In other words, the suction tube between the suction tube inlet connection and the suction head, is bow pointing.

[0021] Transporting dredged material from a bottom of a body of water into the trailing suction hopper dredger does not strictly require that the dredged material is ultimately stored within the trailing suction hopper dredger. It may be conceivable that the dredged material is further transported to e.g. another vessel.

[0022] In an embodiment of the trailing suction hopper dredger according to the invention, the suction tube inlet connection is arranged at the aft section of the trailing suction hopper dredger. Arranging the suction tube inlet connection at the aft section of the trailing suction hopper dredger enables to use less inboard piping towards an aft positioned dredge pump. Less inboard piping means less inboard wear and less maintenance. In addition, arranging the suction tube inlet connection at the aft section of the trailing suction hopper dredger, and thus closer to the propulsion system, enables to dredge with more precision since most propulsion power is close to the inlet which improves the manoeuvrability of the vessel.

[0023] In an embodiment of the trailing suction hopper dredger according to the invention, the trailing suction hopper dredger comprises a second suction system different from the first suction system, wherein the second suction system comprises a suction tube that is aft pointing from a suction tube inlet connection. In other words, the first suction system comprises the suction tube that is bow pointing, and the second suction system comprises a suction tube that is aft pointing from a suction tube inlet connection of the second suction system. This embodiment of the trailing suction hopper dredger according to the invention enables a choice to position or use a suction tube aft pointing or bow pointing. This enables two directional dredging. This is especially useful in ports or environments with limited space where maneuverability is limited. A suction system can be arranged at a starboard or portside of the trailing suction hopper dredger. In case of two suction system, the suction tubes can be arranged at opposite sides of the dredger, one suction system at a portside and the other of the two at starboard.

[0024] In an embodiment of the trailing suction hopper dredger according to the invention, the dredge pump system comprises at least one inboard dredge pump arranged at the aft section and in fluid connection with the suction tube inlet connection. Mass in the aft of the vessel provides even more backward trim. This all the more assures that the inboard dredge pump is arranged at a lowest possible position which prevents the risk of cavitation and therefore increases the efficiency. The pump system may also contain an underwater pump connected to the suction tube. An underwater pump has also less cavitation.

[0025] In an embodiment, the trailing suction hopper dredger according to the invention comprises a deckhouse facility that is arranged at a bow section of the trailing suction hopper dredger. When dredging backwards the deckhouse facility that is arranged at a bow section of the vessel allows the operator to oversee the vessel and dredging equipment.

[0026] In another embodiment, the trailing suction hopper dredger according to the invention comprises a deckhouse facility that is arranged at the aft section of the trailing suction hopper dredger. When dredging backwards the deckhouse facility that is arranged at an aft section of the vessel, has its benefits when there is a need to have accessibility to the space below deck at the bow part or to influence the trim of the vessel.

[0027] In an embodiment of the trailing suction hopper dredger according to the invention, the drive system comprises a thruster at the stern. This even more enables precise dredging, in particular in combination with the suction tube inlet connection arranged at the rear half of the trailing suction hopper dredger, and thus closer to the thruster of the driving system.

[0028] In an embodiment of the trailing suction hopper dredger according to the invention, the propulsion system comprises one or more of a thruster, an azimuth thruster, a cycloidal propeller and a non-directional propeller. This even more enables precise dredging, in particular in combination with the suction tube inlet connection arranged at the aft section of the trailing suction hopper dredger, and thus closer to the propulsion system. The azimuth thruster is a well-known marine propulsion unit consisting of a propeller mounted on a steerable gondola. In an embodiment of the trailing suction hopper dredger according to the invention, the propulsion system comprises an azimuth thruster that is arranged at the aft section. This even more enables precise dredging. In addition, the plume is not mixed by the propulsion system when dredging in the backward direction.

[0029] In an embodiment of the trailing suction hopper dredger according to the invention, the propulsion system comprises a propeller arrangement at the bow section.

[0030] In an embodiment of the trailing suction hopper dredger according to the invention, the suction tube is moveably connected with one end to the hull and having a free opposite end that is lowerable towards the bottom of the body of water, and wherein a longitudinal axis of the suction tube makes an angle a with the horizontal between 10° and 60° when the tube is lowered. Most dredgers have been designed with a nominal angle a of 25° and with freedom to change the angle when necessary.

[0031] In an embodiment of the trailing suction hopper dredger according to the invention, the suction tube can be moved between a retracted position and a lowered position, and wherein the trailing suction hopper dredger comprises a safety system for preventing lowering of the suction tube from the retracted position towards the lowered position when the trailing suction hopper dredger is sailing ahead. The safety system for preventing lowering of the suction tube towards the lowered position improves safe operations of the trailing suction hopper dredger because the safety system assures to avoid contact between the suction tube and the bottom of the body of water while the trailing suction hopper dredger is sailing in the forward direction with a lowered bow pointing suction tube.

[0032] In both the retracted position and the lowered position of the suction tube, the suction head is behind the suction tube inlet connection in a forward direction of the trailing suction hopper dredger. It will be clear that “behind” is not limited to “right behind”. The suction head and the suction tube inlet connection may have different vertical height positions, as well as different lateral positions.

[0033] In an embodiment, the trailing suction hopper dredger according to the invention comprises an overflow system for discharging excess water to outside the vessel during loading of the vessel, wherein the overflow system comprises a discharge outlet that is arranged ahead of the drive system when seen in a forward direction of the trailing suction hopper dredger. The discharge outlet being arranged ahead of the propulsion system when seen in a forward direction of the trailing suction hopper dredger avoids contact between a propeller and a plume from the discharge outlet. Such a plume contains a fraction of fines of the dredged material, and therefore, the plume may damage the propeller of thruster. Furthermore, the propeller may increase the area of the plume which is negative for the environment and marine life. When dredging in the backward direction, the propulsion system operates during dredging in a clean environment without air or fine particles in the water from the overflow.

[0034] Therefore, the invention provides a use of the trailing suction hopper dredger according to the invention.

[0035] In an embodiment of the use of the trailing suction hopper dredger according to the invention, the use comprises the step of dredging in the backward direction. Dredging in the backward direction enables to sail away from the dredging site in a normal forward direction without the need to turn the trailing suction hopper dredger first. This is especially useful in ports or environments with limited space where manoeuvrability is limited.

[0036] In an embodiment of the use of the trailing suction hopper dredger according to the invention, the use comprises the step of lowering the suction tube when the trailing suction hopper dredger is sailing in a backward direction, or the trailing suction hopper dredger is stationary. The use comprising the step of lowering the suction tube when the trailing suction hopper dredger is sailing backwards, or the trailing suction hopper dredger is stationary all the more improves safe operations of the trailing suction hopper dredger because this assures to avoid contact between the suction tube and the bottom of the body of water while the trailing suction hopper dredger is sailing ahead.

[0037] The various aspects and features described and shown in the specification can be applied, individually, wherever possible. These individual aspects, in particular the aspects and features described in the attached dependent claims, can be made subject of divisional patent applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The invention will be elucidated on the basis of an exemplary embodiment shown in the attached schematic drawings, in which; figure 1 shows a side view of a prior art trailing suction hopper dredger, figure 2 shows a side view of an embodiment of a trailing suction hopper dredger according to the invention, and figure 3 shows a side view of a further embodiment of a trailing suction hopper dredger according to the invention.

[0039] DETAILED DESCRIPTION OF THE INVENTION

[0040] Figure 1 shows a side view of a prior art trailing suction hopper dredger 1 according to the prior art. The trailing suction hopper dredger 1 has a propulsion system 12 for propelling the trailing suction hopper dredger 1 in a forward direction 22. The trailing suction hopper dredger 1 has a suction system 3 for transporting dredged material from a bottom 7 of a body of water into the trailing suction hopper dredger 1. The suction system 3 has a suction head 11 that is in contact with the bottom 7 of a body of water during dredging. The suction system 3 has a suction tube 10 that extends between the bottom 7 of a body of water and the vessel 1.

[0041] The suction system 3 has a suction tube inlet connection 9 of the trailing suction hopper dredger 1. The suction tube 10 extends between the bottom 7 of a body of water and the suction tube inlet connection 9 of the vessel 1. In this case, the suction tube inlet connection 9 is arranged at a portside of the hull of the vessel 1. Here, the suction tube inlet connection 9 is arranged below a waterline 8. The suction tube 10 is moveably coupled to the vessel 1 and can be moved between a retracted position (not shown) and a lowered position as shown. Therefore, the trailing suction hopper dredger 1 is equipped with hoist cables 29, gantries 26, and winch systems (not shown) for positioning the suction tube 10. In the retracted position, the suction tube 10 is arranged on board. In order to move from the retracted position to the lowered position, the suction tube 10 is moved outboard, then brought down towards the tube inlet connection 9 where the suction tube 10 is then coupled to. As a last step, the suction tube is hinged into the lowered position. Therefore, the suction tube 10 is hingeably coupled to the vessel 1 at the suction tube inlet connection 9 of the vessel 1. The trailing suction hopper dredger 1 has an inboard pump system (not shown) for driving a flow of dredged material in the suction system 3. The suction head 11 is ahead the suction tube inlet connection 9 when looking in a forward direction 22 of the trailing suction hopper dredger 1. In other words, the suction tube inlet connection 9 is leading with respect to the suction head 11 in a forward direction 22 of the trailing suction hopper dredger l.In other words, the suction tube 10 is aft pointing. The trailing suction hopper dredger 1 has a deckhouse facility 4 that is arranged at the aft section 5 of the trailing suction hopper dredger. The aft section 5 may also be referred to as “rear part” or “rear half’.

[0042] Now turning to the trailing suction hopper dredger according to the invention. Figure 2 shows a side view of an embodiment of a trailing suction hopper dredger 1 according to the invention. The trailing suction hopper dredger 1 comprises a propulsion system 12. The propulsion system 12 is configured for propelling the trailing suction hopper dredger 1. The propulsion system 12 is configured for propelling the trailing suction hopper dredger 1 in two directions, a forward direction 22 and a backward direction 23. The propulsion system 12 is configured for propelling the trailing suction hopper dredger 1 during dredging. The forward sailing direction 22 is different from the movement direction during dredging. The forward sailing direction 22 is opposite the movement direction during dredging.

[0043] The trailing suction hopper dredger 1 comprises a suction system 3 for transporting dredged material from a bottom 7 of a body of water into the trailing suction hopper dredger 1. The suction system 3 has a suction head 11 that is in contact with the bottom 7 of a body of water during dredging. The suction system 3 has a suction tube 10 that extends between the bottom 7 of a body of water and the vessel 1. In this case, during dredging, the suction tube 10 extends in a forward direction, that is from the aft section 5 of the vessel 1 toward the bow section 6 of the vessel 1. In other words, the suction tube 10 is a bow pointing suction tube 10. The bow section 6 may also be referred to as “front part” or “front half’.

[0044] The suction system 3 has a suction tube inlet connection 9 of the trailing suction hopper dredger 1. The suction tube 10 extends between the bottom 7 of a body of water and the suction tube inlet connection 9 of the vessel 1. In this case, the suction tube inlet connection 9 is arranged at the starboard side of the hull of the vessel 1. It will be understood that the vessel 1 can also be equipped with a suction system that is operative on the portside of the vessel. It is also possible that both opposite sides of the vessel 1 are each equipped with a respective suction system. The suction tube inlet connection 9 is arranged at the aft section 5 of the trailing suction hopper dredger 1. Like in figure 1, the suction tube 10 is moveably coupled to the vessel 1 and can be moved between a retracted position (not shown) and a lowered position as shown. Therefore, the trailing suction hopper dredger 1 is equipped with hoist cables 29, gantries 26, and winch systems (not shown) for positioning the suction tube 10. In the lowered position, the suction tube 10 is hingeably coupled to the vessel 1 at the suction tube inlet connection 9 of the vessel 1. The suction tube 10 is hingeable around a hinging axis 21. In the retracted position (not shown), the suction tube 10 is stored on deck.

[0045] The trailing suction hopper dredger 1 comprises a pump system 25 for driving a flow of dredged material in the suction system 3. The pump system 25 comprises an inboard dredge pump 24 arranged at the aft and in fluid connection with the suction tube inlet connection 9. The trailing suction hopper dredger 1 comprises a drive system 2 providing power to the dredger. The drive system 2 is normally arranged in the aft section of the vessel. The drive system 2 both drives the pump system 25 and the propulsion system 12.

[0046] Importantly, the suction head 11 is ahead of the suction tube inlet connection 9 in a forward direction 22 of the trailing suction hopper dredger 1. In other words, the suction head 11 is leading with respect to the suction tube inlet connection 9 in a forward direction 22 of the trailing suction hopper dredger 1.

[0047] The suction head 11 comprises an inlet 18. The inlet 18 is open or openable for taking in dredge. The inlet 18 is at least partly facing towards the stem, that is towards the aft section 5 of the vessel 1. The suction head 11 is coupled to a free end 17 of the suction tube 10. The free end 17 is opposite the suction tube inlet connection 9.

[0048] The trailing suction hopper dredger 1 has a deckhouse facility 4 that is arranged at a bow section 6 of the trailing suction hopper dredger 1. Therefore, the deckhouse facility 4 and suction head 11, in retracted position (not shown), are on the fore ship. This allows easy access to the dredge pump system 25 and drive system 2 on the aft section 5 of the vessel 1 for maintenance.

[0049] The trailing suction hopper dredger comprises an overflow system 14. Heavy particles settle in the hopper 15 of the vessel 1. Excess water with fine particles form an upper layer 20. The overflow system 14 is configured for discharging excess water to outside the vessel during loading of the hopper 15 of the vessel 1. The overflow system 14 comprises a discharge outlet 19. The discharge outlet 19 is arranged ahead of the propulsion system 12 when seen in a forward direction 22 of the trailing suction hopper dredger 1. The discharge outlet 19 being arranged ahead of the propulsion system 12 avoids contact between a propeller of the propulsion system 12 and a plume 27 from the discharge outlet 19, when dredging in the backward sailing direction 23. Figure 3 shows a side view of a further embodiment of a trailing suction hopper dredger according to the invention. Only differences with the embodiment of figure 2 are described. In this case, the trailing suction hopper dredger 1 has a deckhouse facility 4 that is arranged at an aft section 5 of the trailing suction hopper dredger 1. This enables to observe the dredging process by an operator.

[0050] Here, the propulsion system 12 comprises a thruster 28 at the stem. This even more enables precise dredging. In particular, the combination of the suction tube inlet connection 9 being arranged at the aft section 5 of the trailing suction hopper dredger 1, and thus closer to the thruster 28, enables precise dredging. In this case, the thruster 28 is an azimuth thruster. The azimuth thruster even more enables precise dredging because the azimuth thruster is steerable around an azimuth axis 13. The azimuth thruster 28 is steerable around an azimuth axis 13 within an angular range of more than 270°, or even up to full circle, 360°.

[0051] The trailing suction hopper dredger 1 comprises a safety system 16. The safety system 16 is operative for preventing lowering of the suction tube 10 from the retracted position (not shown) towards the lowered position as shown, when the trailing suction hopper dredger 1 is sailing ahead, that is in the forward direction 22.

[0052] -0-0-0-0-0-0-

[0053] List of reference numerals

[0054] 1. Trailing suction hopper dredger

[0055] 2. Drive system

[0056] 3. Suction system

[0057] 4. Deckhouse facility

[0058] 5. Aft section

[0059] 6. Bow section

[0060] 7. Bottom of a body of water

[0061] 8. Waterline

[0062] 9. Suction tube inlet connection

[0063] 10. Suction tube

[0064] 11. Suction head

[0065] 12. Propulsion system

[0066] 13. Azimuth axis

[0067] 14. Overflow system

[0068] 15. Hopper

[0069] 16. Safety system

[0070] 17. Free opposite end

[0071] 18. Inlet

[0072] 19. Discharge outlet

[0073] 20. Upper layer

[0074] 21. Hinging axis

[0075] 22. Forward direction

[0076] 23. Backward direction

[0077] 24. Inboard dredge pump

[0078] 25. Pump system

[0079] 26. Gantry

[0080] 27. Plume

[0081] 28. Thruster

[0082] 29. Hoist cable

Claims

Claims1. Trailing suction hopper dredger (1) comprising; a propulsion system (2) for propelling the trailing suction hopper dredger, a first suction system (3) for transporting dredged material from a bottom (7) of a body of water into the trailing suction hopper dredger, and comprising; i. a suction head (11), ii. a suction tube (10) and a iii. suction tube inlet connection (9) of the trailing suction hopper dredger, a pump system (25) for driving a flow of dredged material in the suction system, characterised in that the suction tube (10) is bow pointing from the suction tube inlet connection (9).

2. Trailing suction hopper dredger according to claim 1, wherein the suction head is behind the suction tube inlet connection in a forward looking direction of the trailing suction hopper dredger.

3. Trailing suction hopper dredger according to a preceding claim, wherein the suction tube inlet connection is arranged at the aft section (5) of the trailing suction hopper dredger.

4. Trailing suction hopper dredger according to a preceding claim, comprising a second suction system different from the first suction system (3), wherein the second suction system comprises a suction tube that is aft pointing from a suction tube inlet connection.

5. Trailing suction hopper dredger according to a preceding claim, wherein the pump system comprises an inboard dredge pump arranged at the stem aft section and in fluid connection with the suction tube inlet connection.

6. Trailing suction hopper dredger according to a preceding claim, comprising a deckhouse facility (4) that is arranged at a bow section (6) of the trailing suction hopper dredger.

7. Trailing suction hopper dredger according to a preceding claim, wherein the propulsion system comprises one or more of a thruster (28), an azimuth thruster, a cycloidal propellor and a non-directional propeller.

8. Trailing suction hopper dredger according to a preceding claim, wherein the propulsion system comprises an azimuth thruster (28) that is arranged at the aft section.

9. Trailing suction hopper dredger according to a preceding claim, wherein the suction tube is moveably connected with one end to the hull and having a free opposite end (17) that is lowerable towards the bottom of the body of water (7), and wherein a longitudinal axis of the suction tube makes an angle a with the horizontal between 10° and 60° when the tube is lowered.

10. Trailing suction hopper dredger according to a preceding claim, wherein the suction tube can be moved between a retracted position and a lowered position, and wherein the trailing suction hopper dredger comprises a safety system (16) for preventing lowering of the suction tube from the retracted position towards the lowered position when the trailing suction hopper dredger is sailing ahead.

11. Trailing suction hopper dredger according to a preceding claim, comprising an overflow system (14) for discharging excess water from a hopper to outside the vessel during loading of the vessel, wherein the overflow system comprises a discharge outlet (19) that is arranged ahead of the propulsion system when seen in a forward direction of the trailing suction hopper dredger.

12. Use of the trailing suction hopper dredger according to a preceding claim.

13. Use according to claim 12, comprising the step of dredging in the backwards direction.

14. Use according to claim 12 or 13, comprising the step of lowering the suction tube towards the lowered position when the trailing suction hopper dredger is sailing backwards, or the trailing suction hopper dredger is stationary.-0-0-0-0-0-0-

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