Patent Description:
When underwater cables, pipes and structures are to be laid in, erected on, or removed from beds of bodies of water, material frequently needs to be removed and/or added to the substrate in dredging or excavation operations. These operations are conducted either by a diver, a remotely operated vehicle (ROV), or directly from a surface vessel.

Dredgers are used to remove material from the seabed by mechanical action and/or suction. The extracted material is then moved either to a nearby area, or transported elsewhere. Surface vessels are often used for dredging operations, but they can lack precision and risk causing significant damage to the natural environment. ROVs and divers can offer increased precision. However, to facilitate this, any equipment needs to be of a suitable size to allow a diver and/or an ROV to efficiently and safely manipulate it during dredging of the seabed (where the term seabed refers to any solid or sedimentary surface lying below a body of water).

Mass-flow excavators also move material on the seabed, but instead of suction, they blow the material out of the way by using a column of moving water to excavate the substrate. Such excavators are often lowered and controlled from a surface vessel and remain tethered to it. Mass-flow excavation is often used for deburial of pipes and cables, or trenching. Modern mass-flow excavators comprise a thruster in a tube which generates a fluid flow directly. The end of the tube is then directed at the seabed where it ejects material from the vicinity. Making such excavation amenable to divers and/or ROVs will also require any equipment to be of a suitable size.

Neither dredging nor mass flow excavation singularly achieves precise removal or addition of material from or to the seabed. Consequently, both tools are usually required to complete a single task, which can involve multiple changes between the tools. Each time a change is made from one tool to another, work on the task at hand is forced to stop for a considerable period, while one tool is removed from the seabed and the other takes its place. It can be a slow and expensive process to change between tools, particularly those submerged at any great depth such as a seabed.

The present invention seeks to address these problems of the prior art.

According to the present invention there is provided an apparatus for underwater dredging comprising: a pipe and a dredging head; wherein the pipe comprises a first aperture and a second aperture each disposed at opposing ends of the pipe, and the pipe further comprises a sidewall, at least one first sidewall aperture and at least one second sidewall aperture; wherein the dredging head is circumferentially arranged on a sidewall of the pipe and comprises at least one input, at least one output and a plenum chamber; wherein the at least one output is in fluid communication with the at least one first sidewall aperture; and further comprising a first obstruction mechanism configured to selectively deter reverse fluid flow into the dredging head, wherein the first obstruction mechanism is configured to be selectively transformable between:-.

characterised in that the apparatus further comprises at least one thruster tube, wherein the at least one thruster tube comprises a first thruster aperture, and a second thruster aperture, and further comprises a thruster disposed between the first thruster aperture and the second thruster aperture, wherein the at least one thruster tube is in fluid communication with the at least one second sidewall aperture.

According to the present invention there is provided a method of underwater dredging, the method comprising the steps of:.

wherein the fluid flow is entering the pipe directed toward the first aperture, promoting fluid flow from the second aperture to the first aperture.

The following statements represent further optional features but the invention is defined in the appended claims.

For the purposes of this invention, reverse flow is fluid flow in the direction from at least one output to at least one input. In this context, fluid flow may also relate to particle suspensions or particles per se.

Optionally, the apparatus for underwater dredging additionally is configured to further provide for mass-flow excavation.

Typically, the at least one thruster tube is affixed to a sidewall of the pipe.

Optionally, the thruster comprises a propeller rotatable by a motor in order to promote selective fluid flow in the thruster tube. Alternatively, the thruster may comprise other suitable means of promoting fluid flow in the thruster tube including other types of suitable rotodynamic pumps and/or any other suitable type of pump including suitable positive displacement pumps.

Optionally, the at least one output is positioned at and surrounds the at least one first sidewall aperture and is configured to promote fluid flow in the pipe from the first aperture to the second aperture.

Optionally, the at least one thruster tube is affixed to a sidewall of the pipe and is configured to promote fluid flow in the pipe from the second aperture to the first aperture.

Optionally, the first obstruction mechanism selectively obstructs the at least one first sidewall aperture.

Optionally, the first obstruction mechanism selectively obstructs a flow channel through the dredging head.

Optionally, the first obstruction mechanism is provided by fluid control valves, for example, non-return valves, shut-off valves, gate valves etc. in order to prevent or reduce reverse fluid flow into the dredging head.

Optionally, the first obstruction mechanism is activated (to obstruct a flow) by translation of at least one component of the dredging head. The translation of at least one component of the dredging head may be relative to the pipe and/or further components of the dredging head. The translation may comprise, for example, a sliding or helical displacement of at least one component of the dredging head.

Optionally, the first obstruction mechanism is activated by rotation of at least one component of the dredging head. The rotation of at least one component of the dredging head may be relative to the pipe and/or further components of the dredging head.

Optionally, when the first obstruction mechanism is activated it may provide that the at least one output of the dredging head is not aligned with the first sidewall aperture; or optionally that the first sidewall aperture is obstructed.

Optionally, when the first obstruction mechanism is activated it may provide that a flow channel though the dredging head is obstructed or misaligned.

Optionally, the apparatus for underwater dredging, comprises a second obstruction mechanism configured to selectively deter fluid flow between the pipe and the thruster tube.

Optionally, the second obstruction mechanism comprises a valve, for example, a shut-off valve, a one-way valve or a gate valve.

Optionally, the second obstruction mechanism is selectively transformable between:-.

Optionally, wherein the thruster is switchably configured to promote fluid flow between the first thruster aperture and the second thruster aperture in either direction.

Optionally, wherein the thruster tube may be fitted with mesh grills or other means of reducing or preventing the passage of particles, at either or both sides of the thruster and positioned at any point between the first thruster aperture and the second thruster aperture, or adjacent thereto.

Optionally, the thruster tube is affixed to the pipe.

Optionally, the at least one thruster tube is affixed to a sidewall of the pipe and surrounds the at least one second sidewall aperture, wherein the thruster tube is typically affixed at an angle of less than <NUM> degrees, or preferably less than <NUM> degrees, or more preferably less than <NUM> degrees, or even more preferably <NUM> degrees or less, measured between the centreline of the pipe and the centreline of the thruster tube, optionally when taking the smallest such angle.

Optionally, wherein the centreline of the thruster tube is taken from the point where the thruster tube is affixed to the pipe.

Optionally, the intersection point of the centreline of the pipe and the centreline of the thruster tube is positioned between the first aperture and the centreline of the second sidewall aperture.

Optionally, the thruster tube may comprise a constriction between the thruster and the at least one second sidewall aperture, preferably wherein the constriction is configured to provide the venturi effect when in use.

Optionally, the apparatus for underwater dredging additionally comprises a pump configured for providing fluid to the dredging head.

Optionally, the method of underwater dredging additionally comprises the step of:
f) placing the first aperture of the pipe proximal to the seabed, wherein fluid flow out of the first aperture of the pipe ejects material from the seabed.

Optionally, the dredging operation additionally comprises operating a thruster tube to issue a second flow output of the pipe via at least one second sidewall aperture and typically, the fluid flow is exiting the pipe directed away from the first aperture promoting fluid flow in the pipe from a first aperture to the second aperture,.

Optionally, the dredging operation additionally comprises deterring (i.e. reducing or preventing) fluid flow between the pipe and the thruster tube with a second obstruction mechanism.

Optionally, the mass-flow excavation operation additionally comprises deterring reverse fluid flow into the dredging head with a first obstruction mechanism.

Optionally, fluid may be provided to the dredging head from an external source, e.g. a Remotely Operated Vehicle (ROV), or surface vessel.

Optionally, a pump may be integrated into the apparatus for underwater dredging for providing fluid to the dredging head.

Optionally, the provided fluid may be ambient fluid local to the current location of the apparatus for underwater dredging.

Typically, the at least one input is in fluid communication with the plenum chamber and typically, the plenum chamber is in fluid communication with the at least one output.

Optionally, the at least one output is positioned at the at least one first sidewall aperture and is configured to promote fluid flow in the pipe from the first aperture to the second aperture.

Optionally, the dredging head further comprises at least one venturi.

Optionally, the dredging head may comprise a circular ring comprising a plurality of venturi.

Optionally, the first obstruction mechanism obstructs a flow channel through the dredging head.

Optionally, the first obstruction mechanism is configured to misalign an output of the dredging head with the first aperture.

Optionally, the first obstruction mechanism is configured to misalign a component in a flow channel though the dredging head.

Optionally, the first obstruction mechanism may comprise a fluid control valve, for example, a non-return valve, shut-off valve, gate valve etc..

Optionally, the first obstruction mechanism may be activated by translation of at least one component of the dredging head.

Optionally, the translation of at least one component of the dredging head may be relative to the pipe and/or further components of the dredging head. The translation may comprise, for example, a sliding or helical displacement of at least one component of the dredging head.

Optionally, the first obstruction mechanism may be activated by rotation of at least one component of the dredging head.

Optionally, the rotation of at least one component of the dredging head may be relative to the pipe and/or further components of the dredging head.

Optionally, the second thruster aperture is angled away from the pipe between the second sidewall aperture and the second aperture.

Optionally, a kit of parts for an underwater dredging apparatus may comprise: a dredging head for an underwater dredging apparatus, and a thruster device for an underwater dredging, and at least one pipe reversibly connectable to the dredging head or the thruster device. The dredging head and thruster device are typically selectively connectable such as to be in fluid communication with one another.

Optionally, the kit of parts may contain any additional components disclosed herein.

The various aspects of the present invention can be practiced alone or in combination with one or more of the other aspects, as will be appreciated by those skilled in the relevant arts. The various aspects of the invention can optionally be provided in combination with one or more of the optional features of the other aspects of the invention. Also, optional features described in relation to one aspect can typically be combined alone or together with other features in different aspects of the invention. Any subject matter described in this specification can be combined with any other subject matter in the specification to form a novel combination.

Various aspects of the invention will now be described in detail with reference to the accompanying figures. Still other aspects, features, and advantages of the present invention are readily apparent from the entire description thereof, including the figures, which illustrates a number of exemplary aspects and implementations. The invention is also capable of other and different examples and aspects, and its several details can be modified in various respects, all without departing from the scope of the present invention, as defined by the claims. Accordingly, each example herein should be understood to have broad application, and is meant to illustrate one possible way of carrying out the invention, without intending to suggest that the scope of this disclosure, including the claims, is limited to that example. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. Language such as "including", "comprising", "having", "containing" or "involving" and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term "comprising" is considered synonymous with the terms "including" or "containing" for applicable legal purposes. Thus, throughout the specification and claims unless the context requires otherwise, the word "comprise" or variations thereof such as "comprises" or "comprising" will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Any discussion of documents, acts, materials, devices, articles and the like is included in the specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention.

In this disclosure, whenever a composition, an element or a group of elements is preceded with the transitional phrase "comprising", it is understood that we also contemplate the same composition, element or group of elements with transitional phrases "consisting essentially of", "consisting", "selected from the group of consisting of", "including" or "is" preceding the recitation of the composition, element or group of elements and vice versa. In this disclosure, the words "typically" or "optionally" are to be understood as being intended to indicate optional or non-essential features of the invention which are present in certain examples but which can be omitted in others without departing from the scope of the invention.

All numerical values in this disclosure are understood as being modified by "about". All singular forms of elements, or any other components described herein are understood to include plural forms thereof and vice versa. References to directional and positional descriptions such as upper and lower and directions e.g. "up", "down" etc. are to be interpreted by a skilled reader in the context of the examples described to refer to the orientation of features shown in the drawings and are not to be interpreted as limiting the invention to the literal interpretation of the term, but instead should be as understood by the skilled addressee.

Embodiments of the present invention will now be described, by way of example only and with reference to the accompanying drawings, in which:.

<FIG> illustrates a perspective view of an example apparatus <NUM> for underwater dredging in accordance with the present invention and which can also be used for mass-flow excavation. The illustration shows an upper (in use) end of an optional suction cone <NUM> attached to the lower (in use) end of a pipe <NUM>. In this example, a plurality of jetting heads <NUM> (i.e. jetting nozzles <NUM>) are circumferentially arranged around the in use lower most end of the suction cone <NUM>. The suction cone <NUM> in this example also comprises an air lift connection <NUM>, which is part of an air lift nozzle <NUM>. A dredging head <NUM> is shown circumferentially arranged in line in the pipe <NUM> above (in use) the suction cone <NUM> and comprising a plenum chamber <NUM>. The plenum chamber <NUM> comprises:-.

Plenum alignment keys <NUM> and plenum chamber cylinders <NUM> are also shown and will be detailed subsequently. In this example, the dredging head <NUM> is shown with two laterally provided inputs <NUM>, each with an optional flow control valve <NUM> attached. A flexi hose 49U is shown connected to output of pump <NUM> at its uppermost (in use) end and an input of the flow control valve <NUM> at the other (in use) lowermost end. A second flexi hose <NUM> is shown connecting an output of the flow control valve <NUM> to the plurality of jetting heads <NUM> (i.e. jetting nozzles) which are circumferentially arranged around the lowermost (in use) end of the suction cone <NUM>.

Moving up the pipe <NUM> from the dredging head <NUM>, the thruster device <NUM> is shown. In this example, the thruster device <NUM> comprises two thruster tubes <NUM>, but a single one <NUM> would suffice. Each thruster tube <NUM> comprises a first thruster aperture (<NUM>) at the innermost end of the thruster tube <NUM> and which is affixed to a sidewall of the pipe <NUM> around an aperture therein such that there is a relatively fluid tight seal between the thruster tube <NUM> and its connection with the pipe <NUM>. The thruster tube <NUM> further comprises a second thruster aperture <NUM> provided at its outermost end and a wire mesh grill <NUM> disposed over the internal cross sectional area of the thruster tube <NUM> proximal to the second thruster aperture <NUM>. A further wire mesh grill <NUM> is disposed over the internal cross sectional area (i.e. the first thruster aperture <NUM>) of the thruster tube <NUM> proximal to where it is affixed to the sidewall of the pipe <NUM> (i.e. proximal to where it is connected around the aperture in the sidewall of the pipe <NUM>). The thruster tube <NUM> comprises a thruster <NUM> (not visible in <FIG> but visible in <FIG>) which is disposed between the first thruster aperture <NUM> and the second thruster aperture <NUM>. In this example, the thruster tube <NUM> additionally comprises an optional thruster chamber <NUM> where the thruster <NUM> is disposed.

In this example arrangement the thruster tube <NUM> comprises two different diameters of thruster tube <NUM>, a wider diameter region sometimes referred to as a thruster chamber <NUM> proximal to the second thruster aperture <NUM>, and a narrower diameter tube which forms a constriction. In other examples, the thruster tube <NUM> may have a constant diameter. <FIG> also illustrates a gate valve 35a, as an example of an obstruction mechanism. Gate valve cylinders <NUM> are illustrated as an obstruction mechanism activation means.

<FIG> further illustrates the pipe <NUM> terminating at its (in use) uppermost end where the second aperture <NUM> is located. It is noted that this uppermost (in use) end of the pipe <NUM> may provide for an outlet from the pipe <NUM> during dredging operations, but does not do so during mass-flow excavation operations, as will be described in more detail subsequently. The pipe <NUM> may be angled at its in use uppermost end <NUM> as illustrated, but may also be straight from the first (lowermost) aperture <NUM> to the second (uppermost) aperture <NUM>. <FIG> also illustrates handling/protection frames intended to prevent damage to the apparatus and a control unit <NUM>.

Optionally the underwater dredging apparatus <NUM> further comprises the control unit <NUM>, with which an ROV (not shown) can interface, for example to plug in at least one control line (not shown). Optionally the at least one control line supplies hydraulic power, or optionally the control line supplies electrical power to the control unit <NUM>. Optionally there are at least two control lines and optionally at least one control line supplies hydraulic power and at least one other control line may supply electrical power. Alternatively, both lines supply hydraulic power. Optionally when the at least one control line is securely plugged into the control unit, the underwater dredging apparatus <NUM> may be controlled remotely, typically by an operator on the vessel at the surface via the ROV.

Preferably there are <NUM> control lines, <NUM> of which are hydraulic lines and one electrical control line leading from the ROV to the control unit. The electrical line is preferably an umbilical line providing power, data and/or communications.

<FIG> illustrate the same example apparatus <NUM> for underwater dredging as <FIG>, but in plan and elevation. In <FIG>, the second thruster aperture <NUM> and wire mesh grill <NUM> are more clearly represented than on the perspective view of <FIG>. <FIG> also more clearly illustrates that the thruster tubes <NUM> are angled away from the centreline of pipe <NUM> such that the second thruster aperture <NUM> is disposed some distance away from the pipe <NUM>. In this example, each thruster tube <NUM> is angled away from the pipe <NUM> (typically in the region of <NUM> to <NUM> degrees and more preferably around <NUM> degrees outwardly from their uppermost end compared with the longitudinal axis of the pipe <NUM>) such that fluid drawn into the second thruster aperture <NUM> and accelerated toward the first thruster aperture <NUM> by the thruster <NUM> would enter the pipe <NUM> directed toward the first aperture <NUM>. It is advantageous that said fluid flow enter the pipe <NUM> directed toward the first aperture <NUM> during mass-flow excavation because it promotes additional fluid to flow in the pipe <NUM> from the second aperture <NUM> to the first aperture <NUM> and thereby enhance or increase the mass flow excavation operation. In some embodiments, the thruster tube <NUM> may be other than straight, for example it may be curved.

<FIG> illustrates a closer up/more detailed example end section of the apparatus of <FIG>. The optional suction cone <NUM> is shown which may be advantageous during dredging operations for drawing additional materials into the pipe <NUM>. The circumferentially arranged jetting heads <NUM> can also be advantageous for loosening materials forming the substrate to assist either dredging or mass-flow excavation. The suction cone <NUM> in this example also comprises an airlift connection <NUM> with air lift nozzle <NUM> which can advantageously be used underwater to assist the passage of materials through the pipe <NUM> when the suction cone <NUM> is facing downwards toward the substrate. The dredging head <NUM> is also partly illustrated in <FIG>. In this example, the dredging head <NUM> comprises two laterally arranged inputs <NUM>, but only one is required and more are optional.

The optional plenum alignment key <NUM> and plenum alignment slot 27a are also shown as part of this example, which is advantageous when a first obstruction mechanism is activated (to obstruct a flow) by translation of at least one component of the dredging head <NUM>; e.g. when the translation comprises an axially sliding displacement of the dredging head <NUM> or key components of it, the plenum alignment key <NUM> and plenum alignment slot 27a provide a means for maintaining correct rotational alignment of dredging head output(s) <NUM> and first sidewall aperture(s) <NUM>.

Optional flow control valves <NUM> are also illustrated. The flow control valves <NUM> may direct fluid flow to the jetting heads <NUM> and/or the dredging head <NUM> (the latter via the laterally arranged inputs <NUM>), which supports flexibility of operation. It is also advantageous to use flow control valves <NUM> to allow automation of fluid flow control to facilitate rapid switching between operational modes.

<FIG> illustrates the first example dredging head <NUM> for the underwater dredging apparatus <NUM>. In this first example, the dredging head <NUM> uses translation of a part of the dredging head <NUM> relative to the pipe <NUM> to activate and deactivate an obstruction mechanism <NUM> (not shown). This movement can be controlled by the illustrated plenum chamber cylinders <NUM> which can advantageously be controlled automatically. It can also be advantageous for embodiments using translation of a part of the dredging head <NUM> relative to the pipe <NUM>, to employ an alignment mechanism, e.g. a plenum alignment key <NUM> and slot 27a, to ensure the dredging head <NUM> remains properly aligned (particularly rotationally) during movement and operation. This may be preferable when the dredging head <NUM> comprises the venturi ring <NUM> containing a plurality of venturi <NUM> (not shown in <FIG> but shown in <FIG>) aligned to a plurality of sidewall apertures <NUM> (not shown in <FIG> but shown in <FIG>), where each venturi <NUM> comprises an aperture formed through the venturi ring <NUM> and where the said aperture tapers from a wider diameter end (which is closest to the laterally provided inputs <NUM>) to a narrower diameter end (which is furthest away from the laterally provided inputs <NUM>).

<FIG> illustrates an example thruster device <NUM> as used in the underwater dredging apparatus <NUM> of <FIG>. This figure shows more clearly, an optional wire mesh grill <NUM> over the second thruster aperture <NUM>. It is not required that one or more wire mesh grills be fitted to the thruster tubes, but it is advantageous to protect the thrusters <NUM> from particles, especially large particles, during dredging and/or mass-flow excavation. Other means for protecting the thrusters <NUM> from damage by particles comprised in the fluid flow, e.g. filters of various kinds, may optionally be employed.

It may also be advantageous to protect the thruster <NUM> during dredging operations by employing an obstruction mechanism <NUM> to reduce or prevent fluid flow into the thruster tube <NUM>. It is particularly advantageous to prevent suspensions of particles and especially large particles from entering the thruster tube <NUM> during this mode of operation. Any suitable means to achieve this advantage may be used, one such example is a valve such as a gate valve 35a which is illustrated in <FIG>. The gate valve 35a may be activated (i.e. arranged to block fluid flow between the pipe <NUM> and the thruster tube <NUM>) by hydraulic cylinders <NUM> (shown in part in <FIG> and <FIG>) which can advantageously be used to automatically control the obstruction mechanism and facilitate a rapid change of operating mode. In this example, the gate valve 35a slides in a channel from the inactive position to an active position where it is held over the internal cross section of the thruster tube <NUM> proximal to the first aperture <NUM>. However, the thrusters <NUM> may provide the primary or secondary motive force for dredging and usually provide the primary motive force for mass-flow excavation, all of which require fluid communication between the thruster tube <NUM> and the pipe <NUM>, hence, it is advantageous if the second obstruction mechanism (which in this example are in the form of the gate valves <NUM>) is reversible and can be used in conjunction with the optional wire mesh grill(s) <NUM>. All disclosed thruster devices <NUM> are interchangeable, hence the same reference numerals are used throughout.

<FIG> illustrates the first example dredging head <NUM> using translation means to activate and deactivate a first obstruction mechanism <NUM>. In this figure, the tapered sleeve 29a is omitted in order to allow the venturi ring <NUM> and first sidewall apertures <NUM> to be seen. In this example, each of the venturi <NUM> are preferably axially aligned with a respective first sidewall aperture <NUM> which in <FIG> are unobstructed as illustrated. If the dredging head <NUM> and in particular the plenum chamber <NUM> were positioned such that the plenum alignment keys <NUM> were at the other end of their plenum alignment slots 27a, then the plenum chamber <NUM> would cover the first sidewall apertures <NUM> and reverse flow into the dredging head <NUM> would be prevented. It is advantageous to prevent reverse flow, i.e. fluid flow into the output <NUM> of the dredging head <NUM> from the pipe <NUM>, because particles within the fluid may interfere with operation of the dredging head <NUM>. Hence, it is an object of the first obstruction mechanism <NUM> to protect the dredging head <NUM> from damage and/or operational impairment due to reverse flow.

It is advantageous that the output <NUM> of the dredging head <NUM> is configured to issue a fluid flow therefrom into the pipe <NUM> via the first sidewall aperture <NUM>. It is further advantageous for dredging operations that said fluid flow be directed toward the second aperture <NUM> because this promotes fluid flow in the pipe <NUM> from the first aperture <NUM> to the second aperture <NUM> as explained below. It is advantageous that the first obstruction mechanism <NUM> be reversible such that the dredging head <NUM> is in fluid communication with pipe <NUM> when being used, e.g. during dredging operations, and is protected from reverse flow when not in use, e.g. during mass flow excavation.

<FIG> illustrates the first example of dredging head <NUM> for use in the underwater dredging apparatus <NUM> and which uses the same translation means to activate and deactivate an obstruction mechanism <NUM> as shown in <FIG> and detailed above. In <FIG>, the obstruction mechanism <NUM> is again shown deactivated and the dredging head <NUM> is operational. When in use, an example process may involve a fluid flow being received at an input <NUM> of the dredging head <NUM>. <FIG> illustrates this as being via a flow control valve <NUM>, but this is optional. The fluid flow may come from any source, for example, a locally positioned pump <NUM> as illustrated in <FIG>, an ROV (not shown) or more remote source such as a surface vessel (not shown). The dredging head <NUM> issues a fluid flow into the pipe <NUM> via a first sidewall aperture <NUM>. As indicated by the black arrows in <FIG> the fluid flow enters the pipe <NUM> directed toward the second aperture <NUM>. Fluid would enter the pipe <NUM> with a fluid flow velocity and/or pressure greater than the ambient fluid resting in the pipe <NUM>.

A simple model may be adopted to facilitate understanding of how it works, for example, consider the situation where fluid in the pipe <NUM> is initially stationary and then fluid flowing into the pipe <NUM> (from the laterally arranged input <NUM> through the ventur1 <NUM> and via the first sidewall apertures <NUM>) is directed toward the second aperture <NUM>. The said fluid flow will exert a force on the fluid ahead of it which will propel it toward the second aperture <NUM>. However, as the fluid flow in the pipe <NUM> between the first sidewall aperture <NUM> and the second aperture <NUM> is now flowing away from the stationary fluid in the pipe <NUM> between the first aperture <NUM> and the first sidewall aperture <NUM>, a low pressure zone is created between the incoming fluid and the stationary fluid which will exert a force on the stationary fluid drawing it along the pipe <NUM> from the first aperture <NUM> toward the second aperture <NUM>. Hence, by introducing fluid flow into the pipe <NUM> directed toward the second aperture <NUM>, the dredging head <NUM> is promoting, i.e. motivating, fluid flow in the pipe <NUM> from the first aperture <NUM> to the second aperture <NUM>. The principles behind this simplified explanation are well known in the art and the skilled person will understand how to generalise this approach.

<FIG> shows an orientation to assist in understanding of its basic principles, but in a dredging operation the apparatus <NUM> would ordinarily be oriented more toward the vertical such that the first aperture <NUM> is angled toward the sea bed, a wide range of angles may be applied as the terrain requires, and optionally pipe <NUM> is angled approximately orthogonal to the seabed. When the first aperture <NUM> is positioned close to the seabed, the flow of fluid into aperture <NUM> during a dredging operation draws material from the seabed into aperture <NUM> along with it (illustrated by the hatched arrow). The fluid comprising material from the seabed then travels along pipe <NUM> toward the second aperture <NUM> where optionally it is ejected into the local environment. The pipe <NUM> may optionally be telescopic and allow for its length to be changed in order to facilitate flexibility when dealing with various seabed terrains.

<FIG> shows an enlarged section of <FIG> illustrating part of an example dredging head <NUM> and pipe <NUM> in cross section. A cross section of a venturi <NUM> forming part of a venturi ring <NUM> and a first sidewall aperture <NUM> are shown with flow arrows indicating the direction of fluid flow when in use during a dredging operation. While a single sidewall aperture <NUM> will achieve the effect of promoting fluid flow in the pipe <NUM> as disclosed above, it has been found to be advantageous to use a plurality of sidewall apertures <NUM> (and preferably a plurality of respective venturi <NUM>) because it can provide a high flow rate into the pipe <NUM> while the dredging head <NUM> remains small. It can also provide a uniform flow within the pipe <NUM> which is advantageous for transporting material from the substrate along the pipe <NUM>. If a plurality of sidewall apertures <NUM> are used, it is preferable to distribute them evenly around the circumference of the pipe <NUM>. e.g. if two sidewall apertures <NUM> are used they would be placed <NUM> degrees apart (i.e. opposite each other), and if <NUM> sidewall apertures <NUM> are used they would be placed <NUM> degrees apart around the circumference of the pipe <NUM>.

Provided the dredging head <NUM> issues a fluid flow into the pipe <NUM> via a first sidewall aperture <NUM> such that the fluid flow enters the pipe <NUM> directed toward the second aperture <NUM>, fluid flow in the pipe <NUM> will be suitable for a dredging operation. It has been found to be advantageous to use venturi <NUM> to increase the flow rate of the fluid prior to it entering the pipe <NUM>. This promotes a high flow rate and the venturi <NUM> can produce a jet of fluid which can pass through the centre of a sidewall aperture <NUM> leading to increased efficiency because losses due to fluid flow impacting the sidewall of pipe <NUM> surrounding the aperture <NUM> are reduced. When a plurality of sidewall apertures <NUM> are used it is advantageous to employ a venturi ring <NUM> comprising venturi <NUM> aligned with each sidewall aperture <NUM> to achieve the above identified efficiencies.

<FIG> shows the same components as <FIG> from a different angle.

<FIG> illustrates the first example dredging head <NUM> of <FIG> but this time is shown in <FIG> with the obstruction mechanism <NUM> activated, i.e. reverse flow into the dredging head <NUM> is prevented. It can be seen that the plenum chamber <NUM> which is circumferentially disposed around the pipe <NUM> is acting as a sleeve in this first example <NUM> such that it (and in particular the innermost circumference of the venture ring <NUM>) is blocking or covering over the sidewall apertures <NUM> in the position shown. Comparison with <FIG> shows the same arrangement with the dredging head <NUM> positioned such that the plenum chamber <NUM> is not obstructing the sidewall apertures <NUM>. In this example the obstruction mechanism <NUM> (and particularly the plenum chamber <NUM> thereof) is activated by translation of the dredging head <NUM> relative to the pipe <NUM>, i.e. the plenum chamber <NUM> (and the venturi ring <NUM> which is secured thereto at the approximate midpoint thereof) slides along the pipe <NUM> guided by the plenum alignment keys <NUM> and plenum alignment slots 27a until the co-axially arranged sleeve portion <NUM> and/or the venturi ring <NUM> cover over the outermost side of the sidewall apertures <NUM> and thereby prevent any further fluid flowing therethrough. Other mechanisms may be employed to provide the blocking action of the obstruction mechanism <NUM> and activate said blocking action, for example, venturi <NUM> could be misaligned with the sidewall apertures <NUM> by a helical, or turning movement of the dredging head <NUM> relative to the pipe <NUM>.

<FIG> illustrates a combination of a jetting and dredging operation, but the dredging head <NUM> is not being used on this occasion, hence the first obstruction mechanism <NUM> is active. Instead, the thrusters <NUM> are being used to draw fluid up the pipe <NUM> from the first aperture <NUM>, toward the second aperture <NUM> and into the thruster tubes <NUM>. Consequently, the second obstruction mechanism <NUM> (see <FIG>) is not active. The flow control valves <NUM> can be configured to.

The latter c) may be facilitated by one flow control valve <NUM> directing fluid flow to the jetting nozzles <NUM> and one flow control valve <NUM> directing fluid flow to the laterally provided inputs <NUM> of the dredging head <NUM>. In this latter c) example, the first obstruction mechanism <NUM> would be inactive.

<FIG> illustrates an example dredging head <NUM> as used in the underwater dredging apparatus <NUM> of <FIG>. It has plenum alignment slots 27a and two inputs <NUM>. However, the number of inputs <NUM> may be chosen to be any suitable number. In this example the dredging head <NUM> is not attached to flow control valves <NUM>, but does have connection elbows. All disclosed dredging heads <NUM>; 2a are interchangeable, hence the same reference numerals for their common components are used throughout.

<FIG> illustrates a second example of a dredging head 2a as used in the underwater dredging apparatus <NUM> of <FIG>. In this example the obstruction mechanism <NUM> comprises a slotted ring 23a which can be rotated to block the venturi <NUM>. <FIG> shows the slotted ring 23a in its active position, i.e. preventing or reducing reverse fluid flow through the venturi <NUM>. <FIG> shows the slotted ring 23a in its inactive position, i.e. not impeding fluid flow.

<FIG> illustrates an example of an optional suction cone <NUM> but which is used in the apparatus <NUM> as shown in <FIG>. In this example, jetting heads (nozzles) <NUM> can be seen circumferentially arranged around the base of the suction cone <NUM>. The suction cone <NUM> may be affixed to a pipe <NUM> if desired, and the length of pipe <NUM> may be chosen to best suit the circumstances. This example also shows optional air lift nozzles <NUM> and connectors <NUM>. When in use, a gaseous fluid is input at the air lift connection <NUM> and is emitted from the air lift nozzle <NUM>. Any suitably available gaseous fluid may be used including air, nitrogen etc. As the apparatus <NUM> is underwater during use, the gaseous fluid will travel upwards away from the bed and toward the surface, as it does so it expands but also creates a low pressure region in its wake which exerts a force on the fluid behind it, drawing the fluid up the pipe <NUM>. When used with an apparatus <NUM> for underwater dredging with the suction cone <NUM> directed toward and proximal to the bed, it has been found to be advantageous in assisting the transport of fluid suspensions through the pipe <NUM> from the first aperture <NUM> to the second aperture <NUM> with greatest effect found when the pipe <NUM> is approximately vertical.

<FIG> shows cross-sectional elevations of an example thruster device <NUM> as for example used in the underwater dredging apparatus <NUM>. In this example, the thruster device <NUM> comprises an obstruction mechanism <NUM> configured to deter fluid flow between the pipe <NUM> and the thruster tube <NUM>, and the obstruction mechanism comprises a gate valve 35a. In <FIG> the gate valve 35a is inactive, i.e. open, thereby allowing fluid flow between the pipe <NUM> and the thruster tube <NUM> unimpeded. In <FIG> the gate valve 35a is active, i.e. closed, thereby preventing or reducing fluid flow between the pipe <NUM> and the thruster tube <NUM>. In <FIG> the thruster <NUM> is also shown. In this example, the gate valve 35a is contained within guide channels. This is advantageous for smooth operation and to ensure an active gate valve 35a is able to withstand pressures exerted between the pipe10 and thruster tube <NUM> during use. It can also be seen from the figures, that the thruster tube <NUM> is affixed to the pipe <NUM> such that it is surrounding a sidewall aperture <NUM> formed in the pipe <NUM>.

The thrusters <NUM> may be arranged to operate such that they promote (cause) fluid to flow from the thruster tube <NUM> into the pipe <NUM> and/or from the pipe <NUM> into the thruster tube <NUM>. When the thruster <NUM> is promoting fluid flow from the thruster tube <NUM> into the pipe <NUM>, fluid is drawn into the thruster tube <NUM> at the second thruster aperture <NUM> and issued into the pipe <NUM> from the first thruster aperture <NUM>. Because the thruster tube <NUM> is angled such that the second thruster aperture <NUM> is held away from the pipe <NUM>, the fluid flow it issues into the pipe <NUM> will be directed toward the first aperture <NUM>. Consequently, the same simple model as given above regarding promoting fluid flow in the pipe <NUM> for dredging is applicable here by analogy.

Provided the fluid flow is directed toward the first aperture of the pipe <NUM>, mass-flow excavation will be enabled. However, improved results are found when the thruster tube is angled at less than <NUM> degrees from the pipe <NUM>, when measured from the centreline of the pipe <NUM> to the centreline of the thruster tube <NUM>. Indeed as the angle is reduced to <NUM> degrees efficiency improves further, as it does again at <NUM> degrees. The optimum angle is <NUM> degrees, but even <NUM> degrees or less gives good results. As this angle is less than <NUM> degrees, and the thruster tube <NUM> issues fluid flow into the pipe <NUM> directed toward the first aperture <NUM>, then the intersection point of the centreline of the pipe <NUM> and the centreline of the thruster tube <NUM> is positioned between the centreline of the second sidewall aperture <NUM> and the first aperture <NUM>. When measuring the angle, the centreline of the thruster tube <NUM> is taken from the point where the thruster tube <NUM> is affixed to the pipe <NUM> as the angle the fluid flow enters the pipe <NUM> is relevant even when curved thruster tubes <NUM> are used.

In this mode of operation the fluid intake is directly from the ambient environment which may be a particle suspension, may contain dissolved or entrained gasses or even biological materials during operation. Most of these things should not impact significantly on performance of the system or apparatus <NUM>, but large particles can cause damage to thruster <NUM> impellers so wire mesh grills <NUM> may be fitted at either side of the thruster <NUM> to provide protection from large particles within the fluid flow travelling in either direction, other filter means may also be employed. Excessive amounts of particulate matter, large or small can still be damaging to the thrusters <NUM>. This can be mitigated to some extent by angling the thruster tube <NUM>, and specifically the second thruster aperture <NUM>, away from the bed. This greatly reduces the amount or particulate matter, and especially large particles, entering the thruster tubes <NUM>.

When the thruster <NUM> is promoting fluid flow from the pipe <NUM> into the thruster tube <NUM>, it draws fluid into the thruster tube <NUM> from the pipe <NUM> via the second sidewall aperture <NUM> and the first thruster aperture <NUM>. The fluid then passes from the thruster tube <NUM> into the environment via the second thruster aperture <NUM>. This fluid flow may be used in isolation to provide a dredging process or operation, or used in addition to a dredging head <NUM>,2a to provide an improved dredging operation performance. Dredging operations can also introduce large quantities of materials into the pipe <NUM>, and so any potential for damage to thrusters <NUM> because of particles in the fluid in this dredging mode may be mitigated by a wire mesh grill <NUM> or other filtering means, and when thrusters <NUM> are not required to assist the dredging operation, an obstruction mechanism <NUM> (optionally, a gate vale <NUM> in the example of <FIG>) may be used to isolate the thrusters <NUM> from the fluid flow within the pipe <NUM>.

<FIG> illustrates an example apparatus <NUM> operating in dredging mode. In this example, a fluid flow is provided by optional pumps <NUM> mounted on the apparatus <NUM>. The fluid passes via the pumps <NUM> to the dredging head input <NUM>. The dredging head <NUM> then (via the venture <NUM> and first sidewall apertures <NUM>) issues a fluid flow into the pipe <NUM> directed toward the second aperture <NUM>. This causes fluid to flow in the pipe <NUM> from the first aperture <NUM> to the second aperture <NUM>. When the first aperture <NUM> is placed proximal to the bed, the fluid flowing into it draws in material from the bed, this results in a fluid suspension comprising any manner of particles and entrained gasses etc. The resultant fluid then travels along the pipe <NUM> and is ejected at the second aperture <NUM>. This could, for example, be into another pipe or tube (not shown) to be transported elsewhere or simply ejected into the local environment. The length of pipe <NUM> can be selected to suit the operating environment. Each section of the pipe <NUM> may be selected as required. For example, the length may be selected to improve reach from the dredging head <NUM> into a channel or pile (not shown), to move the waste/spoil from a dredging operation further away from where it was removed, or even to change the distance between the dredging head <NUM> and thruster tubes <NUM>. This flexibility may be particularly helpful when being operated by a diver or ROV in order to have the apparatus <NUM> balanced, or assist reach in difficult to access dredging locations. The flexibility can be further promoted by using telescopic sections of pipe <NUM>.

<FIG> illustrates an example apparatus <NUM> with the thrusters <NUM> being used in dredging mode. This arrangement may be used with only thrusters <NUM> providing the fluid flow to enable dredging operations, or may also be used in combination with a dredging head <NUM>, 2a to provide an improved dredging performance. <FIG> illustrates the thruster <NUM> being used in combination with a dredging head <NUM>, but flow through the dredging head <NUM> has not been illustrated for simplicity.

<FIG> illustrates an example apparatus <NUM> in mass-flow excavation mode. In this example thrusters <NUM> draw fluid into thruster tubes <NUM> from the immediate environment and force fluid to flow into the pipe <NUM> toward the first aperture <NUM>. This also causes fluid to flow from the second aperture <NUM> to the first aperture <NUM>. In the example of <FIG> the fluid then travels through the optional suction cone <NUM>. When the end of the pipe <NUM>, or the suction cone <NUM> is placed proximal to the bed, fluid exits the pipe <NUM> with sufficient force to excavate the substrate material. It can be advantageous during mass-flow excavation to not use a suction cone <NUM>, or even to have a narrowing at the end of pipe <NUM> at the first aperture <NUM> because a reduction in the cross section of the pipe <NUM> will increase velocity of the fluid and cause it to impact with greater force on the substrate for the same flow rate, and be more effective at excavating the substrate. The flexibility of pipe length <NUM> disclosed above is also advantageous for mass-flow excavation.

<FIG> illustrates an example apparatus <NUM> in jetting mode. Jetting can be used with mass-flow excavation operations, e.g. as shown in <FIG>, or with dredging operations, e.g. as shown in <FIG>. Jetting is advantageous for loosening material from the substrate. In this example, optional pumps <NUM> draw in ambient fluid and force it though a plurality of jetting heads/nozzles <NUM> which are circumferentially arranged around the suction cone <NUM>. The fluid flow from the pumps <NUM> is directed to the jetting heads <NUM> by flow control valves <NUM>. The control valves <NUM> could instead, or simultaneously, direct fluid into the dredging head <NUM>.

Both <FIG> show the dredging head <NUM> in a position indicating the first obstruction mechanism is active, i.e. deterring reverse fluid flow, as shown in the example of <FIG>.

<FIG> show the same examples as 15a and 15b, except dredging head 2a is illustrated. The first blocking or obstruction mechanism 23a is active (i.e. preventing or reducing reverse fluid flow into the dredging head 2a), but the dredging head 2a is still in the same position relative to the pipe <NUM>. This example blocking mechanism 23a is advantageous because it does not require movement of a significant part of the dredging head 2a relative to the pipe <NUM> which can affect the connections to inputs <NUM>.

Claim 1:
An apparatus (<NUM>) for underwater dredging comprising:
a pipe (<NUM>); and
a dredging head (<NUM>, 2a);
wherein the pipe (<NUM>) comprises a first aperture (<NUM>) and a second aperture (<NUM>) each disposed at opposing ends of the pipe (<NUM>), and the pipe (<NUM>) further comprises a sidewall, at least one first sidewall aperture (<NUM>) and at least one second sidewall aperture (<NUM>);
wherein the dredging head (<NUM>, 2a) is circumferentially arranged on the sidewall of the pipe (<NUM>) and comprises at least one input (<NUM>), at least one output (<NUM>) and a plenum chamber (<NUM>);
wherein the at least one output (<NUM>) is in fluid communication with the at least one first sidewall aperture (<NUM>); and
further comprising a first obstruction mechanism (<NUM>) configured to selectively deter reverse fluid flow into the dredging head (<NUM>, 2a),
wherein the first obstruction mechanism (<NUM>) is configured to be selectively transformable between:-
i) a first, obstructing, configuration in which at least reverse fluid flow through the dredging head (<NUM>, 2a) is deterred; and
ii) a second, open, configuration in which fluid flow through the dredging head (<NUM>, 2a) is permitted; and
characterised in that the apparatus (<NUM>) further comprises at least one thruster tube (<NUM>),
wherein the at least one thruster tube (<NUM>) comprises a first thruster aperture (<NUM>), and a second thruster aperture (<NUM>), and further comprises a thruster (<NUM>) disposed between the first thruster aperture (<NUM>) and the second thruster aperture (<NUM>), wherein the at least one thruster tube (<NUM>) is in fluid communication with the at least one second sidewall aperture (<NUM>).