NL2014509B1

NL2014509B1 - Overflow system.

Info

Publication number: NL2014509B1
Application number: NL2014509A
Authority: NL
Inventors: Josephus Petrus Marie Koevoets Adrianus; Van Der Horst Arjen
Original assignee: Ihc Holland Ie Bv
Priority date: 2015-03-24
Filing date: 2015-03-24
Publication date: 2017-01-19
Also published as: NL2014509A

Abstract

An overflow system for a hopper dredger comprises an overflow tube to receive flow; and a skimmer with an inlet arranged to sit below a water surface line for taking in head water from the hopper and a collection chamber to receive the head water from the inlet. The skimmer is in fluid connection with the overflow tube to deliver the head water from the skimmer to the overflow tube.

Description

OVERFLOW SYSTEM

BACKGROUND

Trailing suction hopper dredgers (“TSHD”) are vessels which can be used to dredge at sea or in open water. TSHD’s typically use a suction tube, one end of which can be lowered to the seabed and used to suck up solids such as sand, sludge, silt or sediment, mixed with water. The lower end of this suction tube can be provided with a suction head or a drag head. The solid material mixed with water is pumped through the suction tube into a hopper of the dredging vessel. The mixture is reduced in speed when in the hopper, and this speed reduction allows for the settling of components suspended in the mixture. Excess water is then overflowed out of the hopper through an overflow system to allow for more load capacity within the TSHD.

Water from the hopper flows into the overflow through an entry disk or directly into the overflow from the top. This overflow volume is then released via the bottom of the dredging vessel. Due to the flow into the overflow, the generally vertical flow orientation of the overflow, the cross-sectional area of the overflow tube and the velocity; the overflow volume typically mixes with air. This mixture can reduce the specific weight of the mixture, causing the overflow mixture to stick to the ship’s hull and the boundary flow of the underwater vessel. This mixture, which may also contain lighter particles which have not settled, and the interactions between the overflow volume released, the hull, propellers, speed of the vessel and currents; can form a plume in the wake of the dredging process. The settling of this mixture can have an adverse effect on the local environment. The air in the flow also causes a resistance in the overflow, reducing the effective transport capacity of the overflow.

One method to combat this plume caused by suspended particles is disclosed in WO 2013/119107. A passive overflow device is used to drain away head water and flow it through a conduit to an outlet abutting the sea bottom to deliver the head water close to the sea bottom, thereby minimizing the influence on sea life. U.S. Pat. No. 3,975,842 discloses a system which also attempts to minimize the environmental effects by directing the overflow to the suction head to be used as the liquid supply for loosening the soil to be suctioned, thus forming a closed system where the overflow is recycled.

SUMMARY

Such an overflow system can overflow liquid from the hopper with little to no turbidity in the flow, little to no air bubbles and few or no moving parts. The skimmer is able to flow liquid from near the water surface level in the hopper at low speeds and without aspiring air due to the size and position of the inlet. The flow is delivered to the overflow tube through symphonic action, and can be overflowed from the hopper dredger. Such an overflow system can help to reduce or eliminate any plume resulting from the overflow.

According to an embodiment, the overflow system further comprises a float connected to the skimmer to ensure that the skimmer stays at the water surface line with the inlet below the water surface line. Such an arrangement can ensure that the skimmer and the inlet stay properly positioned for letting in head water from the hopper without aspiring air, no matter the water level in the hopper.

According to an embodiment, the overflow system further comprises a flexible tube connecting the skimmer to the overflow tube to allow the head water to flow from the skimmer to the overflow tube. The flexible tube provides a flow-path from the skimmer to the overflow tube, allowing the skimmer to rise or fall with the water level in the hopper and move around the hopper to some degree. Additionally, the flexible tube can transport the head water from the skimmer to the overflow tube in such a way that minimizes or prevents air to enter and mix in with the head water. Such air can result in a plume, as the air bubbles lift particles to the water surface in the wake of the ship. Thus, the use of overflow system can help to reduce or eliminate such a plume by reducing air bubbles in the flow.

According to an embodiment, the inlet comprises a plurality of inlets. The plurality of inlets can be round, rectangular, or another shape.

According to an embodiment, the inlet comprises one or more slots.

According to an embodiment, the skimmer is arranged such that the inlet points in a downward direction in the hopper. Directing the inlet in a downward direction ensures that it stays below the water surface level in the hopper, and can intake head water. This helps to prevent the intake and mixing of air with the overflow liquid.

According to an embodiment, the overflow system further comprises one or more additional skimmers in fluid connection with the overflow tube, the one or more additional skimmers each arranged with an inlet to sit below a water surface line for taking in head water from the hopper and a collection chamber to receive the head water from the inlet. Using one or more additional skimmers can allow for taking in of head water at multiple points in hopper. This can be useful in systems that have a large amount of inflow to hopper, and can help to avoid situations in which the overflow is stopped due to a clogging up of an inlet in one overflow skimmer.

According to an embodiment, the skimmer is cylindrical.

According to an embodiment, the overflow tube has a flow area with a tube cross-section, wherein the inlet of the skimmer has a inlet cross-section, and wherein the inlet cross-section is larger than the tube cross-section. By having an inlet cross-section which is larger than the tube cross-section, the overflow system can avoid the intake of air and subsequent plume that can result from air bubbles in the flowing mixture. The amount of head water taken in by inlet completely fills the overflow tube, leaving no room for additional air in the mixture.

According to an embodiment, the overflow system further comprises a pump in the overflow system to pump water through the skimmer and/or the overflow tube. The pump can help to start, continue and control the flow through overflow system.

According to an embodiment, the system further comprises a valve in the overflow system to control flow through the overflow system. Optionally, the valve can be a gate or another type of valve. The valve can be located in the flexible hose, at the skimmer, at the entrance to the overflow tube or at another location.

According to an embodiment, the overflow system further comprises one or more filters arranged to filter the headwater entering overflow system. Optionally, the one or more filters can be a geotextile cloth or another type of filter. The one or more filters can be located anywhere throughout the overflow system, for example, at the inlet, the entrance to the flexible tube or another location.

According to an embodiment, the overflow skimmer is rigidly connected to the overflow tube. Such a system can work well with a hopper that has a set water level in the hopper, keeping the parts needed for the overflow system to a minimum, and having a short and direct flow path to the overflow tube.

According to an embodiment, the flow enters the overflow tube at a position below a water surface level in the overflow tube. Optionally, this can be a radial entrance into an overflow tube with a standing water level. By entering at a position below a water surface level in the overflow tube, the flow avoids the mixture of additional air as it flows into the overflow tube, thus reducing air bubbles in the flow liquid and associated plume.

According to an embodiment, the overflow system further comprises a tube which enters a top of the overflow tube and flows the head water to a point below a surface water level in the overflow tube. Such a system can allow the overflow system to work with existing overflow tubes and minimize or avoid the chance for air to mix in with the flow through overflow system. The ability to enter an existing overflow tube from a top can reduce the changes and associated costs needed to adapt a past overflow system to work with the current overflow system.

According to an embodiment, a vessel includes such an overflow system. Optionally, the vessel can be a dredger.

According to an embodiment, a method of flowing head water from a hopper to an exit of a vessel comprises flowing head water from the hopper through an inlet in an overflow skimmer into a collection chamber in the overflow skimmer; and flowing the head water from the overflow skimmer to an overflow tube in a manner that does not allow air to enter the flow. Such a method can flow head water from a hopper while minimizing the mixture of air. The overflow skimmer is able to intake head water from the overflow at a low speed and with little to no aspired air and then flow it to the overflow tube in a manner that does not allow air to enter the flow. This can reduce or eliminate the plume exiting a vessel due to reducing the entering and mixing of air bubbles into the flow.

According to an embodiment, the step of flowing the head water from the overflow skimmer to an overflow tube comprises flowing the head water from the overflow skimmer to an overflow tube through a flexible hose. The flow through the flexible hose can allow for the intake of water through overflow skimmer no matter the water level in hopper.

According to an embodiment, the step of flowing the head water from the overflow skimmer to an overflow tube in a manner that does not allow air to enter the flow comprises flowing the head water into the overflow tube at a position below a surface level of liquid in the overflow tube. By flowing the head water into the overflow tube at a position below a surface level of liquid in the overflow tube, the addition and mixture of air into the flow when entering the overflow tube is reduced or eliminated. This helps to reduce or eliminate any plume in the wake of the vessel.

According to an embodiment, the method further comprises pumping the flow through overflow system using a pump. Pumping the flow through the overflow system can help to start, continue and control the flow through overflow system, ensuring that it stays at desired flow rates according to the flow into and within hopper, settlement of particles suspended in the head water in hopper, level of liquid in hopper, and other related system factors.

According to an embodiment, the overflow system further comprises controlling the flow through overflow system using a valve. The valve can be used to control the amount of flow and speed of flow through overflow system, thereby helping to control the settling of particles within hopper and turbidity due to entrained particles in the flow through the overflow system.

According to an embodiment, the method further comprises filtering the flow of head water into and/or through overflow system. Filtering the flow of head water into and/or through overflow system can help to ensure that flow through and out of overflow system has fewer particles. This can help to avoid the turbidity associated with overflowing flow with suspended particles.

According to an embodiment, the flowing of head water from the hopper through an inlet in an overflow skimmer into a collection chamber in the overflow skimmer is done just below a surface of the water level in the hopper. By flowing water into the overflow skimmer just below a surface level, the flow rate is low, resulting in reducing or preventing air intake and any resulting plume as well as reducing particles in the overflow liquid and resulting turbidity within system. The inflow is done in such a manner with inlets of proper size that aspiring of air is avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a trailing suction hopper dredger during a dredging operation.

Fig. 2a shows a perspective view of a hopper with an overflow system with an overflow skimmer.

Fig. 2b shows a cross-sectional view of the overflow system and overflow skimmer of Fig. 2a.

Fig. 3a shows a perspective view of a hopper with a second embodiment of an overflow system with an overflow skimmer.

Fig. 3b shows a cross-sectional view of the overflow system and overflow skimmer of Fig. 3a.

Fig. 4 shows an perspective side view of a third embodiment of an overflow system with an overflow skimmer.

Fig. 5 shows a fourth embodiment of an overflow system with an overflow skimmer.

Fig. 6 shows a fifth embodiment of an overflow system.

Fig. 7 shows a perspective view of an overflow skimmer.

Fig. 8 shows a perspective view of a second embodiment of an overflow skimmer.

DETAILED DESCRIPTION FIG. 1 illustrates a trailing suction hopper dredger (“TSHD”) 10 during a dredging operation. Trailing suction hopper dredger 10 is suctioning a mixture of water and solid particles through suction tube 12. This mixture is then transported to a hopper in THSD 10 (not shown). Excess liquid in the hopper is overflowed, and plume 14 forms due to suspended particles in the overflow mixture and the mixing of air with the overflow due to the vertical orientation of the overflow, and the speed and the general flow into and through the overflow system.

Plume 14 can have an adverse impact on local marine biotope, as it reduces the entrance of light into the water body. Additionally, in some cases, the settling particles smother bottom life, and the suspensions can reduce the ability for microorganisms to develop. The bubbles in the flow also cause a resistance in the overflow, reducing the effective transport capacity of the overflow. Forming an overflow which is able to control the flow of head water into and through the overflow can help to reduce turbidity and the mixing of air into the head water, thus reducing or eliminating the plume 14 exiting vessel 10.

Fig. 2a shows a perspective view of a hopper 18 with overflow system 20, and Fig. 2b shows a cross-sectional view of overflow system 20. Overflow system 20 includes overflow skimmer 22 with collection chamber 23, inlet 24, float 26, flexible hose 28, valve 30 and overflow tube 32 with water line 33.

Float 26 connects to overflow skimmer 22 to keep overflow skimmer 22 at or near the surface of water in hopper 18 and positioned for taking in head water from hopper 18. Overflow skimmer 22 and float 26 are connected and positioned such that inlet 24 is held at a position below the water surface in hopper 18, for example, directly down towards the base of hopper 18 and/or just below water surface level. Overflow skimmer can be cylindrical or another shape and can extend across much of hopper 18, for example, 80% of the width or length of hopper. The cross-sectional area of overflow skimmer 22 could be about the same size as the cross-sectional area of overflow tube 32. The distance between the overflow skimmer 22 and the side of hopper 18 could be about twice the diameter of overflow skimmer 22, though this can vary.

Inlet 24 in overflow skimmer 22 can be one elongated inlet or a plurality of inlets located below the water surface level in hopper 18 (see Figs. 5-8). Inlet 24 is sized to control flow into overflow skimmer 22 and collection chamber 23. Inlet 24 is typically large in size in comparison to past inlets for past overflow systems, as the past inlets were typically radial inlets around the overflow tube and/or an open top of the overflow tube which functioned as an inlet. The larger size of inlet 24, for example, as large as practically feasible on the overflow skimmer 22, allows for the maximum speed into the overflow skimmer 22 to be as low as possible and so that the speed is as uniform as possible. This can be, for example, a ratio of 2 to 1 between the area of inlet 24 and the cross-sectional area of the overflow skimmer tube 22.

Flexible hose 28 connects between overflow skimmer 22 and overflow tube 32. Overflow tube 32, can for example, be placed in hopper 18 opposite the inlet to hopper 18. Flexible hose 28 can then allow overflow skimmer 22 to reach all or most of hopper 18. Flexible hose 28 also provides flexibility so that overflow skimmer 22 can always sit at or near the surface level of liquid in hopper 18, whether hopper 18 is full or nearly empty. Flexible hose 28 connects to overflow tube 32 radially, at a point below the water level in hopper 18 and in overflow tube 32. Other embodiments could connect to overflow tube 32 at a different location or in a different manner.

Valve 30, in this embodiment of overflow system 20, is a gate located in flexible tube 28. Valve 30 can be selectively set to control flow through overflow system 20, from overflow skimmer 22 to overflow tube 32. Valve 30 can control the flow in overflow system 20 based on the water level in the hopper 18, flow into hopper 18 or other factors. In other embodiments, valve 30 could have a different construction and/or location in overflow system 20, for example, at the entrance or exit of flexible hose 28.

Overflow tube 32 is shown as a standard, regulation overflow tube which is open on the top. Overflow tube 32 can have a standing column of water which prevents the entrance of air into the flow from flexible hose 28 to overflow tube 32, reducing the mixing of air bubbles in the flow through overflow tube. Overflow tube 22 can also be open at the top, allowing for the entrance of liquids through the top in the case of emergency, to ensure that excess water from the hopper 18 can be removed rapidly.

In operation, as discussed above, TSHD suctions a mixture of liquid and fractions, and deposits that mixture into hopper 18. The head water in hopper 18 continues to rise as particles and fractions settle. The larger particles settle to the bottom of hopper 18, and excess liquid can be overflowed through overflow system 20.

Float 26 helps to position skimmer 22 and inlet 24 just below the surface of water level in hopper 18, and flexible tube 28 allows for overflow skimmer 22 to be able to sit at or near the surface no matter the water level in hopper 18. The distance from the surface (of the sea) which inlet 24 is positioned and the size of inlet 24 will determine the flow rate into overflow system 20.

Head water flows into overflow system 20 through inlet 24 in overflow skimmer 22. Flow enters collection chamber 23, where it then flows through flexible hose 28 to overflow tube 32. Gate 30 can be set to help control flow and speed of flow through overflow system 20. Liquid can flow out of overflow tube 32 to the outside of vessel (not shown).

Overflow system 20 is able to overflow head water from hopper 18 with little to no mixed air and turbidity and with few or no moving parts by using overflow skimmer 22 with inlet 24 and flexible hose 28 to control flow into overflow system 20 and deliver that flow to overflow tube 32. The flow into overflow system 20 is controlled by the size and placement of inlet 24. By using a relatively large inlet 24 and overflow skimmer 22, and positioning inlet 24 just below the surface of water in hopper 18, overflow system 20 is able to intake head water at low speeds, just below the water surface line without aspiring air into overflow skimmer 22. Collection chamber 23 and valve 30 can also be used to help control the speed of flow into and through overflow system 20. The connection of flexible hose 28 to overflow tube 32 below water level 33 helps to ensure no air is aspired when head water enters overflow tube 32 from flexible hose 28. Additionally, the cross-sectional area of inlet 24 can be made larger than the cross-sectional area of overflow tube 32 to ensure there is no opportunity for air to enter the flow. The lack of air bubbles mixing in with the flow can reduce or eliminate any plume in the wake of the vessel from the overflow liquid. Additionally, the slow speed can help in allowing more particles to settle in hopper 18, thereby reducing turbidity in flow through overflow system 20.

By forming overflow system 20 with overflow skimmer 22, float 26 and flexible hose 28, overflow system 20 is able to overflow head water from hopper 18 in a way that minimizes or prevents any plume or turbidity, and with no moving parts in direct contact to the mass flow through overflow system 20, thereby resulting in a robust system that can have a long life. The ability to overflow head water from hopper 18 in a way that minimizes air bubbles in flow and turbidity can reduce or eliminate any plume upon exit of the vessel and the subsequent environmental consequences of such a plume. Additionally, overflow system 20 can reduce local erosion and improve the efficiency of the overall dredging process by leaving more dredged particles in hopper 18.

Fig. 3a shows a perspective view of a second embodiment of an overflow system 20 with overflow skimmer 22, and Fig. 3b shows a cross-sectional view of the second embodiment of overflow system 20. Similar parts are labelled with the same numbers. Overflow system 20 includes overflow skimmer 22, with collection chamber 23 and inlet 24, float 26, flexible hose 28, overflow tube 32 with water line 33, and pump 34.

Overflow system 20 of Figs. 3a-3b works in the same manner as described in relation to overflow system 20 shown in Figs. 2a-2b, with inlet 24 taking in head water from hopper 18, flowing that liquid to collection chamber 23, then through flexible hose 28, and finally to overflow tube 32.

In the embodiment shown in Figs. 3a-3b, pump 34 is located in flexible hose 28, and is used to help start and/or continue the pumping through overflow system 20. Overflow system 20 functions by symphonic action, and this action can be enforced with pump 34. Pump 34 can be, for example, a vacuum pump or another type of pump. Pump 34 could also be placed at a different location, for example, at the entrance or exit to flexible hose 28 or in overflow tube 32. Instead of a pump, an alternative means could also be used to help promote flow through overflow system 20, for example, water jets, which could be located in collection chamber 23, flexible hose 28 and/or in overflow tube 32.

Pump 34 (or another mechanism to help promote flow through overflow system 20) helps to ensure that overflow system 20 is able to start and continue overflowing excess head water in hopper 18.

Fig. 4 shows an perspective view of a third embodiment of an overflow system 20 with an overflow skimmer 22, and Fig. 5 shows a fourth embodiment of an overflow system 20 with an overflow skimmer. Figs. 4-5 include similar parts and function in much of the same manner to overflow system 20 of Figs. 2a-2b, but differ in overflow tube 32 and the connection between flexible hose 28 and overflow tube 32.

Fig. 4 shows overflow system 20 in use with a standard overflow, and entering a top of that overflow tube 32. A rigid tube 36 connects flexible hose 28 to overflow tube 32 at a point below the water line in overflow tube 32.

Fig. 5 shows an overflow system 20 which does not connect to a standard overflow tube, and instead flows the overflow liquid from flexible hose 28 to a closed tube 38, which can overflow out of a vessel (not shown).

By flowing overflow liquid through a closed tube to either below a water line in overflow tube 32 or directly out of overflow system 20 and vessel 10, the possibility of air entering into and mixing with the flowing liquid within overflow system 20 (and the resulting plume exiting the vessel) is avoided. Additionally, the system of Fig. 4 is able to be used with a standard overflow tube, with very few modifications. By having overflow liquid delivered from flexible tube 28 through the top of overflow tube 32, overflow system 20 is adaptable for use with existing overflow systems or tubes, thereby providing an economical way of managing air and turbidity in existing overflow tubes and systems.

Fig. 6 shows a side view of a fifth embodiment of an overflow system 20. Overflow system 20 includes two overflow skimmers 22 with inlets 24 and overflow tube 32 with water level 33.

In this embodiment, overflow skimmers 22 are directly and rigidly connected to overflow tube 32. Overflow tube 32 may be able to move up and down to position overflow skimmers 22 and inlets 24 at a desired position based on the water level in hopper 18. Alternatively, hopper 18 may be designed to have a set water level, and overflow tube 32 is also set to a certain level.

Overflow system 20 of Fig. 6 flows head water in from hopper 18 through inlets 24 into collection chamber 23 in overflow skimmer 22. From there, liquid is flowed directly to overflow tube 32 at a location below surface level of liquid 33. Such an overflow system is able to inflow head water without aspiring air, and flow it through and out of overflow system in a way that minimizes or prevents the mixture of air and turbidity in flow.

Fig. 7 shows a perspective view of an overflow skimmer 22, and includes inlets 24. Inlets 24 are a plurality of slots in overflow skimmer 22, which are able to let in head water from hopper 18. Overflow skimmer 22 can be used with any of the embodiments of overflow systems shown in Figs. 2a-6.

As described in relation to Figs. 2a-2b, inlets 24 are positioned with overflow skimmer 22 below the water surface level, for example, directly downward toward hopper 18 bottom. The size and placement of inlets 24 control and allow for a slow flow of headwater into overflow system 20 without aspiring air into the mixture. The cross-sectional area of inlets 24 can be relatively large (compared to the inlet of past overflow systems) due to use of and size of overflow skimmer 22. This inlet size can help to control flow and can be used to ensure that the cross-sectional size of inlets 24 is larger than the cross-sectional size of overflow tube 32, thereby ensuring that little to no air is able to mix in as the mixture flows into overflow tube 32. A slow and steady flow also helps to avoid turbidity while flowing into and through overflow system 20, by helping to ensure that many of the particles in the mixture in hopper 18 are able to settle in hopper 18 and do not remain suspended to flow through overflow system 20. This helps to ensure that the head water entering overflow system 20 is cleaner, thereby assisting in avoiding turbidity and any plume.

Fig. 8 shows a perspective view of a second embodiment of an overflow skimmer 22, and includes inlet 24 and fdter 40. In this embodiment, inlet 24 is one elongated inlet, and collection chamber 23 has filter 40.

Filter 40 can be a geotextile cloth or another type of filter, and can be located, for example, at inlet 24, at the connection to flexible hose 28 or overflow tube 32 or at another location. Filter 40 can be arranged so that flow through inlet 24 must flow through filter 40, which can collect particles still present or suspended in flow. Collecting particles with one or more filters 40 in overflow system 20 can further promote a cleaner flow through and out of overflow system 20, thereby minimizing turbidity in the flow,any plume and resulting undesirable environmental consequences. In some embodiments, jets could be positioned to clean filters 40, and/or dislodge particles collected by filters 40.

In summary, overflow system 20 works to control the flow into and through overflow system to reduce or eliminate air in the flow, and thereby reduce any resulting plume exiting the vessel. Overflow system 20 does this through the use of a relatively large inlet 24 on an overflow skimmer 22 that is located near a surface level of the liquid in hopper 18. The placement and size of inlet 24 and collection chamber 23 receive a slow flow without aspiring air into the flow. This slow flow also allows for particles to settle, and thereby reduces turbidity in the flow. The head water entering inlet 24 and collection chamber 23 can then be flowed to the overflow tube 32 in such a way that no air is able to mix with the flow. This can include flowing through a flexible hose 28 and/or other tube 36 which does not allow for the introduction of air and then flowing into the overflow tube at a level below the surface level 33 in the overflow tube 32. This can also include ensuring that the cross-sectional area of inlet 24 is larger than the available cross-sectional area for flow through overflow tube 32. Additional devices, such as one or more valves 30 and/or pumps 34 can be used to help start, maintain and control flow through overflow system 20. One or more filters 40 can be used to collect more particles, thereby cleaning the flow through overflow system 20. Overflow system 20 can also include a flexible hose 28 connecting overflow skimmer 22 to overflow tube 32, allowing for overflow system 20 to collect and overflow liquid no matter the level of liquid in hopper 18. Overflow system 20 is a simple system with few or no moving parts that can flow liquid out of hopper 18 while minimizing air and particles in the overflow mixture, making for an effective, efficient and durable overflow system 20.

While overflow skimmer 22 and float 26 are shown as cylindrical, one or both can be other shapes. The size, shape, ratio and placements of overflow skimmer 22, inlet 24, valve 30, pump 34 and filter 40 are for example purposes only, and can be varied in different embodiments.

While the term head water is used for the mixture entering and flowing through overflow system, this could be liquid and/or a combination of liquid and particles which were dredged and remain suspended.

While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

An overflow system for a dredging device operating with a hopper, the overflow system comprising: an overflow pipe for receiving a stream; and a skimmer with an inlet arranged to be below a line of the water surface to receive the upper water from the hopper, and a collection chamber for receiving the upper water from the inlet, the skimmer being in fluid communication with the overflow tube to dispense the upper water from the skimmer to the overflow tube.

An overflow system according to claim 1, and further comprising: a floating element connected to the skimmer and adapted to ensure that the skimmer stays at the line of the water surface with the inlet below the line of the water surface.

An overflow system according to any of the preceding claims, and further comprising: a flexible tube connecting the skimmer to the overflow tube to cause the upper water to flow from the skimmer to the overflow tube.

The overflow system according to any of the preceding claims, wherein the inlet comprises a plurality of inlets.

An overflow system according to any of the preceding claims, wherein the inlet comprises one or more slots.

6. Overflow system according to any of the preceding claims, wherein the skimmer is arranged such that the inlet points in a downward direction in the hopper.

An overflow system according to any of the preceding claims, and further comprising: one or more additional skimmers in fluid communication with the overflow tube, the one or more additional skimmers each being arranged such that an inlet is located below a line of the water surface to take in the upper water from the hopper, and a collection chamber for receiving the upper water from the inlet.

An overflow system according to any of the preceding claims, wherein the skimmer is cylindrical.

An overflow system according to any of the preceding claims, wherein the overflow pipe has a flow area with a pipe cross-section, wherein the inlet of the skimmer has an inlet cross-section, and wherein the inlet cross-section is larger than the pipe cross-section.

An overflow system according to any of the preceding claims, and further comprising a pump in the overflow system to pump water through the skimmer and / or the overflow pipe.

An overflow system according to any of the preceding claims, and further comprising a valve in the overflow system adapted to control the flow through the overflow system.

The overflow system of claim 11, wherein the valve comprises a port in a flexible tube of the overflow system.

An overflow system according to any of the preceding claims, and further comprising one or more filters arranged to filter the upper water entering the overflow system.

The overflow system of claim 1, wherein the overflow skimmer is rigidly connected to the overflow pipe.

An overflow system according to any of the preceding claims, wherein the flow enters the overflow pipe at a position below a level of the water surface in the overflow pipe.

An overflow system according to any of the preceding claims, wherein the overflow system further comprises a tube that enters an upper side of the overflow pipe and causes the upper water to flow to a point below the level of the water surface in the overflow pipe.

A vessel comprising the overflow system according to any of the preceding claims.

A method for flowing the upper water from a hopper to an exit opening of a vessel, the method comprising: flowing the upper water from the hopper through an inlet in an overflow skimmer to a collection chamber in the overflow skimmer; and flowing the upper water from the overflow skimmer to an overflow tube in a manner that does not allow air to enter the stream.

The method of claim 18, wherein the step of flowing the upper water from the overflow skimmer to an overflow tube comprises: flowing the upper water from the overflow skimmer to an overflow tube via a flexible hose.

A method according to any of claims 18-19, wherein the step of flowing the upper water from the overflow skimmer to an overflow tube in a manner that does not allow air to enter the flow comprises: flowing into the overflow tube the upper water at a position below a level of the surface of liquid in the overflow pipe

A method according to any of claims 18-20, and further comprising: pumping the flow flowing through an overflow system using a pump.

The method of any one of claims 18 to 21, and further comprising controlling the flow flowing through the overflow system using a valve.

A method according to any of claims 18-22, and further comprising filtering the flow of the upper water flowing to and / or through an overflow system.

A method according to any of claims 18-23, wherein the upper water flows from the hopper via an inlet in an overflow skimmer to a collection chamber in the overflow skimmer at a small distance below a level of the water surface in the hopper.