Abstract:
The disclosure relates to an enclosure for installation in the seabed comprising an elongate container for holding a payload. The container has a plurality of passages extending lengthwise of the container and an impeller at the lower end of the container for drawing water through at least one or said passages to form a slurry with the material of the seabed and for discharging the slurry at the upper end of the container into the surrounding water. The enclosure has inner and outer concentric passageways extending lengthwise thereof and said impeller has a blade or blades extending across the inner and outer passageways. The blade of the impeller has a first portion pitched to draw water down one of the passageways to the lower end of the container and a second portion pitched to discharge slurry up the other of the passageways to the top of the container.

Description:
BRIEF DESCRIPTION OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to enclosures for installation on the seabed to carry communications and/or weapon systems to be deployed from the seabed. 
     SUMMARY OF THE INVENTION 
     2. Description of the Prior Art 
     European Patent Specification No. 0110554 discloses an underwater weapon system comprising an elongate outer container which is buried or partially buried in the seabed in an upright position using self-burying means which are at the bottom end of the container and which preferably comprise both pump means for removing sand or silt and rotary material displacing means, e.g. an auger for boring a hole in the seabed or rotary stirring means. The weapon is a self-propelled device with guidance means and is housed within an inner container which is telescopically arranged within the outer container. 
     U.S. Patent Specification No. 6044745 discloses an enclosure for instalation on the seabed comprising an outer cylindrical container one of the which is more buoyant than the other so that the container lies in a vertical orientation when disposed in the sea and auger devices at the other end of the container for activating sand/silt/shingle on the seabed to create a cavity below the container into which the container can self-bury. The container has a payload compartment within the container for holding weaponry, listening, identification recording and/or communications equipment. The container wall is formed with a plurality of separate passages extending spirally from inlets at the lower end of the container upwardly to outlets at the top of the container through which activated sand/silt/shingle and water generated at the lower end of the container can flow upwardly and freely as the container self-buries in the seabed. 
     According to a first aspect, the invention provides an enclosure for installation in the seabed, comprising an elongate container for holding a payload, the container having a plurality of passages extending lengthwise of the container and impeller means at one end-of the container to be the lower end of the container on installation for drawing water through at least one of said passages from the other end of the container to form a slurry with the material of the seabed and for discharging slurry formed at said one end of the container through at least one other of said passages to said other end of the container for discharge into the surrounding water. 
     Preferably the enclosure has inner and outer concentric passageways extending lengthwise thereof and said impeller has a blade or blades extending across the inner and outer passageways, the blade or blades having a first section pitched to draw water down one of the passageways and a second portion pitched to discharge slurry up the other of the passageways. 
     More specifically the impeller may be rotatable about an axis which is co-axial with the axes of the inner and outer concentric passageways, inner portions of the blade or blades of the impeller being pitched to draw water down the inner passageway and the outer portion of the blade or blades of the impeller being pitched to propel slurry up the outer passageway. 
     In one particular arrangement the outer passageway may have an annular outlet port partway up the container for the discharge of slurry outwardly of the container. 
     In any of the above arrangements the payload may include a motor for driving the impeller and a power supply for the motor. 
     Also in any of the above arrangements the payload may include communication means for receiving/transmitting signals which may be sonar, acoustic or seismic. 
     The payload may also include a weapon system or systems. 
     Turning now to further aspects of the invention, worldwide, there are perhaps some several hundred of Mine Hunting Vessels (MHVs) either in existence or under construction. All are designed to a very high standard, costly to build and loaded with even more expensive equipment. They rely on complex and heavy sweep gear, hull mounted sonars, variable depth sonars (Vds), remotely operated vehicles (ROVs) and unmanned underwater vehicles (UUVs) to act as “eyes” when trying to find, identify, and neutralise targets. MHVs and other ancillary vehicles therefore constitute the “point of the spear head” in any amphibious landing or mine clearance operation. Such assets are not easily replaceable. 
     Currently the only way to find articles such as maritime mines whether moored to or buried in the sea bed is, as indicated, to use various types of sonars. 
     Some sonars may perhaps even be mounted on ROVs or UUVs and which for each of designation, are hereinafter referred to as “scouts”. 
     The situation is therefore much as follows. All ships generate signals, even when anchored, dead in the water, or if under way, by various means e.g.: 
     (a) Seismic Signals 
     (b) Noise which may be either 
     (i) Vessel General Signals (“VGS”) 
     (I) Sonar Generated Signals (“SGS”) 
     (c) Pressure changes 
     (d) Anomalous magnetic signals (MAD) 
     Sensors already exist which will register-respond, to any one, a combination, or all four of these signals. 
     Even with the use of “scouts” the useful range at which objects may be detected by sonar is limited, perhaps to say 1,000 to fifteen hundred yards at best, and, without VDS, down to a depth of say 50 fathoms or so. The field of vision or “swathe” is similarly restricted. Clearance rates are therefore slow, and progress is pedestrian. 
     In consequence mine clearance is a difficult task even against old fashioned moored and/or contact mines, particularly when coming up against decoys and/or ship count. The situation is not eased if the MHVs are also subject to airborne and other forms of attack, and/or operating under less than ideal sea conditions. 
     Now, if to all the foregoing hazards is added a self propelled sonar/acoustic signal riding weapon, which is programmed to “Hunt the Hunters” e.g. the subject of EP-B-0844963 and which being “passive” will detect the “active” searching sonar signal, from whatever source, e.g. MHV or Scout, at twice the range at which the weapon of 0844963 itself can be detected, then the task of mine clearance becomes immeasurably more difficult, and the likely costs to even the most determined aggressor, will hopefully be prohibitive. 
     Nevertheless some may try, and the following is a further invention will further deter any that do attempt to overcome the arrangement of EP-B-0844963. 
     Thus according to a further aspect the invention provides an underwater communication device comprising means to detect a signal generated by a vessel in the vicinity of the device and means responsive to receipt of such signal to transmit a decoy sonar signal to the vessel. 
     It is proposed that in order to deter, confuse intruding vessels, a series of units (referred to herein after as “Lorelei”) designed to be buried or partially buried/planted in the sea bed, and which will detect and respond to the various signals which will be generated by intruding vessels should be deployed in and around maritime mine fields. They would be particularly effective when deployed in conjunction with the sea bed unit described and illustrated in EP-B-0844963. 
     Each unit which could be constructed of or coated with non reflective materials, will contain the necessary electronic equipment e.g. receivers, sensors, hydrophones, magnetometers, transducers, transponders, signal generators, aerials, transmitters etc. to enable it not only to accept coded instructions, which might be either seismic or acoustic in origin, but also to ensure that when alerted/activated by the presence of an intruding vessel or decoy, either surface or subsurface, that the signals, particularly such sonar signals emanating from the intruder may: 
     (a) be received copied, analysed, classified modulated or amplified before being re-transmitted, if, or as required, alternatively, 
     (b) spurious synthesised signals purporting to be the reflecting echo of different varieties, types, shapes, of mine could be generated and transmitted, as could that of a submarine or running torpedo in order to confuse-blind the searching vessels. 
     In the same way, such units could also be deployed in the littorals, and/or remote areas, where they could be used as a covert early warning system. They too could be alerted by say: 
     (a) Seismic signals, followed by 
     (b) Acoustic and/or magnetic anomaly signals 
     (c) Pressure generated signals. These signals cannot currently, be synthesised, and would therefore be extremely useful in confirming the class of vessel, submarines for instance have a particularly distinctive pressure pattern signature, and with the units tuned accordingly, would be comparatively easy to plot! 
     Having intercepted the various signals emanating from vessels and confirming say, that it is a submarine, the unit could release a buoyant radio beacon which would: 
     (a) transmit a uniquely coded radio signal, thereby confirming its authenticity, before it would 
     (b) self destruct and release a calcium carbide float, and/or fluorescent coagulate dye which would spread across the surface of the sea, and which would therefore, be visible to the “satellite” tracking systems. Different coloured dyes might be used: 
     (i) to identify different types of vessels, and/or 
     (I) to indicate time of release. 
     In this way the course of a submarine could be charted from the time it leaves its base. The use of “decoy dyes” by vessels would be precluded by the need for the dye release to match with the “unique coded identification signal”. 
     Battery life will be important in such units, therefore the arrangement could be programmed to listen for instructions at pre-determined times, rather than maintain at a constant listening watch. Instructions would be coded and might for instance initiate one of the following pre-programmed modes, e.g.: 
     (a) remain dormant unit . . . or 
     (b) await further instructions which will be issued at pre-determined intervals or 
     (c) become active, for a period, or permanently, or 
     (d) set to anti handling mode, or 
     (e) self destruct if breaking from its mooring, or if so instructed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The following is a description of a specific embodiment of the invention, reference being made to the accompanying drawings in which: 
     FIG. 1 is a diagrammatic view of an enclosure to be installed in the seabed to hold communications or weaponry systems having an impeller system at its lower end and to displace material on the seabed for self-burying of the enclosure. 
     FIG. 2 is a diagrammatic view of a similar enclosure having a modified impeller arrangement; 
     FIG. 3 is a plan view of the enclosure of FIG. 2; 
     FIG. 4 is a detailed view of the lower end of the enclosure showing the impeller arrangement at its lower end; 
     FIG. 5 shows a further modified arrangement. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The drawing shows an enclosure indicated generally at  10  for installation at a strategic location on the seabed which is indicated at  11 . The enclosure comprises outer and inner concentric containers  12 ,  13  and an inner payload assembly indicated generally at  14  which will be described in greater detail below. 
     The inner and outer containers define between them an outer annular passageway  12   a  extending between the containers from the top to the lower end of the enclosure. The outer container has a nozzle plate  15  mounted within the end of the container to direct spoil from the surface of the seabed into the outer passageway  12   a  as indicated by the arrows. 
     An inner annular passageway  13   a  is formed between the inner container  13  and the payload assembly extending through the enclosure. Towards the upper end of the enclosure, the inner container  13  is stepped outwardly at  16  to form an enlarged upper end  17  having an open entry indicated at  18  at the top of the enclosure to receive water to flow downwardly through the passageway  13   a  in the direction of the arrows. 
     The outer container  12  terminates at its upper end below the step  16  to provide an annular outlet port  19  for release of slurry passing up the outer passageway  12   a  to the surrounding sea. 
     The payload assembly  14  includes an impeller assembly indicated generally at  20  having a drive shaft  21  mounted co axially with the axis of the inner and outer containers in the lower part  22  of the payload assembly which also contains a battery powered electric motor for rotating the shaft. The impeller has laterally extending blades  23 , each of which has an inner section  24  extending across the lower end of the inner passage  13   a  immediately below the inner container  13  and pitched to draw water down the passage  25  from the inlet end  18  at the top of the enclosure. The water is directed by the blade portions  24  in the direction of the arrows  26  inwardly and downwardly onto the seabed  11  below the payload assembly to fluidise the material of the seabed with water. 
     The outer portions  27  of the blades are pitched to draw the fluidised seabed material upwardly from the central region below the payload assembly in the direction of the arrows  28  into the outer passage l 2   a  between the inner and outer containers and upwardly to the outlet  19 . Thus the single impeller generates a downward flow of water in the inner passage  25  and an upward flow of a slurry of material from the seabed and water in the outer passage  12   a  to excavate the seabed immediately below enclosure  10 . By excavating the seabed below the enclosure, the enclosure is allowed to drop progressively into the seabed thereby burying itself to avoid both detection and damage from equipment or implements being drawn over the seabed. 
     The payload assembly  14  of the enclosure may contain a variety of different communications/weapon systems. By way of example, the assembly may include a signal generator unit  35 , a process unit  36 , an analyser unit  37 , a control unit  38 , vessel generated acoustic signal receivers  39 , sonar generated acoustic signal receivers  40 , transmitter units (sonar, acoustic, seismic)  41 , a buoyancy hydrophone chamber  42 , directional transducer  43 , an acoustic imaging transducer  44  and a pressure detection unit  45 . A variety of other equipment and/or weapons may be carried. 
     FIGS. 2 to  4  show a modified form of the enclosure in which the lower part of the container wall  13  below the payload  14  has an annular slit  50  through which the impeller extends to operate the outer passageway  12 a. Also the lower end of the container  13  has an inwardly curved exit  51  to direct water inwardly as indicated by the arrows. In FIG. 5 the lower end of the container is angled inwardly as indicated at  52  for the same purpose. 
     It is proposed that in order to deter, confuse intruding vessels, a series of units designed to be buried or partially buried/planted in the sea bed, and which will detect and respond to the various signals which will be generated by intruding vessels should be deployed in and around maritime mine fields. They would be particularly effective when deployed in conjunction with the sea bed unit described and illustrated in EP-B-0844963. 
     Each unit which could be constructed of or coated with non reflective materials, will contain the necessary electronic equipment e.g. receivers, sensors, hydrophones, magnetometers, transducers, transponders, signal generators, aerials, transmitters etc. to enable it not only to accept coded instructions, which might be either seismic or acoustic in origin, but also to ensure that when alerted/activated by the presence of an intruding vessel or decoy, either surface or subsurface, that the signals, particularly such sonar signals emanating from the intruder may: 
     (a) be received copied, analysed, classified modulated or amplified before being re-transmitted, if, or as required, alternatively, 
     (b) spurious synthesised signals purporting to be the reflecting echo of different varieties, types, shapes, of mine could be generated and transmitted, as could that of a submarine or running torpedo in order to confuse-blind the searching vessels. 
     In the same way, such units could also be deployed in the littorals, and/or remote areas, where they could be used as a covert early warning system. They too could be alerted by say: 
     (a) Seismic signals, followed by 
     (b) Acoustic and/or magnetic anomaly signals 
     (c) Pressure generated signals. These signals cannot currently, be synthesised, and would therefore be extremely useful in confirming the class of vessel, submarines for instance have a particularly distinctive pressure pattern signature, and with the units tuned accordingly, would be comparatively easy to plot! 
     Having intercepted the various signals emanating from vessels and confirming say, that it is a submarine, the unit could release a buoyant radio beacon which would: 
     (a) transmit a uniquely coded radio signal, thereby confirming its authenticity, before it would 
     (b) self destruct and release a calcium carbide float, and/or fluorescent coagulate dye which would spread across the surface of the sea, and which would therefore, be visible to the “satellite” tracking systems. 
     Different coloured dyes might be used: 
     (i) to identify different types of vessels, and/or 
     (I) to indicate time of release. 
     In this way the course of a submarine could be charted from the time it leaves its base. The use of “decoy dyes” by vessels would be precluded by the need for the dye release to match with the “unique coded identification signal”. 
     Battery life will be important in such units, therefore the arrangement could be programmed to listen for instructions at pre-determined times, rather than maintain at a constant listening watch. Instructions would be coded and might for instance initiate one of the following pre-programmed modes, e.g.: 
     (a) remain dormant unit . . . or 
     (b) await further instructions which will be issued at pre-determined intervals or 
     (c) become active, for a period, or permanently, or 
     (d) set to anti handling mode, or 
     (e) self destruct if breaking from its mooring, or if so instructed. 
     It will be appreciated that if the units are deployed in multiples, then a searching MHV will receive a multiplicity of signals in response to each signal which it has generated and transmitted. 
     Provision is also made to enable the units to automatically tune to any frequency that the searching vessel chooses to use. Alternatively, each Lorelei could be programmed on/to a specific range of frequencies, and a quantity of them could thereby cover the whole of the likely spectrum. 
     When deployed in conjunction with EP-B-0844963, there could be communication between the two, if desired, thus if necessary the transmission of the spurious signals may be delayed sufficiently to allow the system to plot the course of say an MHV, and “lock on” before launching its weapon, thereby avoiding the intentional confusion which is being caused by the multiplicity of spurious signals being transmitted by Lorelei. However and in addition, the system is already programmed to switch from the Sonar Riding mode to tracking by Vessel Generated Noise and this facility could easily be called up in necessary. 
     In consequence whilst the MHV remains effectively blinded by a cloud of “synthetic sonar clutter” and is therefore, at risk of collision with moored mines which now it cannot “see/identify”. It is also open to attack by the hunter type weapon launched from the system of EP-B-0844963. 
     Bearing in mind that without changing the laws of physics it is virtually impossible even now, to locate the weapon of EP-B-0844963 any aggressor will find it both difficult and costly in men and ships when attempting a clearance operation, when confronted by both weapon systems. 
     Equally to be confronted by the present system alone, in a suspected mined area, or even in a conventional moored type minefield, should sensibly induce a degree of caution in the most determined aggressor, and this must be of value to a defender. 
     Recently there have been many “informed” articles on mine counter measures, and how the latest technology will solve the problems associated with finding, identifying, and destroying/neutralising maritime mines. Currently there is significant and ongoing expenditure on M.C.M.Vs and sonars, all of which is of course essential, if the fashionable concept of “Projection of Power from the Sea”, is to become a practical reality. However in view of the existence of having the above weapon systems Capital Ships, Mine Hunting Vessels, and all their associates sonars may be rendered obsolescent, in which case it may be time to “think again” in regard to future naval strategy, this time paying due regard to later technology which is now freely available.