Abstract:
A device ( 10 ) for repelling selected aquatic creatures, such as sharks. The device consists of an electromagnetic field generator ( 21, 30 ) for generating an electromagnetic field ( 50 ) that repels sharks and is supported by a buoyant device ( 20 ). This provides a shark-free region about the device ( 10 ). Multiple devices can be connected together to form an array of repelling devices, thereby extending the shark-free region.

Description:
FIELD OF THE INVENTION 
     This invention relates to devices for repelling selected aquatic creatures, in particular sharks. 
     BACKGROUND OF THE INVENTION 
     Ever since humans have ventured into the sea for exploration, hunting and recreation, a constant danger has been the risk of attack by dangerous sea creatures, in particular sharks. Such attacks, while not common, can be fatal and in many cases if not fatal, can result in horrific injuries to the victim which remain for a lifetime. 
     Furthermore, sharks often hinder fishing expeditions as they are attracted to bait used to catch fish, and to the movement of fish being caught. In instances where nets are used, shark attacks may also result in the loss of any fish caught, as well as damage to the nets. 
     DISCUSSION OF PRIOR ART 
     A number of attempts have been made to address one or more of the above problems with varying degrees of success. These attempts range from divers wearing armour-like suits to minimise damage to themselves in the event of an attack, to the distribution of chemicals in the surrounding water to repel sharks. These approaches have had limited success in the past. 
     A more effective approach is based on the recognition that sharks are highly sensitive to certain electromagnetic fields. 
     A number of devices have been developed which can generate electromagnetic fields which create a zone in which sharks are uncomfortable and which sharks accordingly avoid. These devices may be carried by the diver either as a separate hand held device, or as a part of the scuba equipment attached to the back of the diver. 
     An example of such a device is described in Australian Patent No. 669806 to Natal Sharks Board. In the device, an electromagnetic field is created between a first and a second electrode immersed in a body of water, by passing a pulsed electrical current between the electrodes. These and other like devices provide an effective means of repelling sharks from a region about the diver. 
     A disadvantage of such devices however is that these devices may be bulky and, if hand held, will impede the diver&#39;s actions underwater. Furthermore, such devices are not generally used by amateur water users such as beach goers, or by fisherman, who themselves do not enter the water. 
     It would accordingly be advantageous to provide a device and method of repelling sharks which allow swimmers or divers to be unhindered when in the water and to provide a more general shark-free zone. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention, there is provided a device for repelling selected aquatic creatures, the device comprising an electromagnetic field generator for generating an electromagnetic field which repels selected aquatic creatures, and a buoy supporting the electromagnetic field generator within a body of water when in use, being separated from a user. 
     Preferably the buoy includes a first electrode and a second electrode which, in use, make electrical contact with the body of water. 
     Preferably, at least the first electrode is a conductive outer cover of the buoy. 
     Preferably, the second electrode is a drop-down electrode. 
     The buoy may include an on-board power supply or alternatively, may be connectable to an external power supply for providing power to the electric field generator. 
     The buoyancy of the buoy is advantageously variably adjustable. 
     Preferably the buoy will include one or more tether points to allow the buoy to be tethered to an object, including one or more other buoys. 
     According to a second aspect of the present invention, there is provided a repelling array for repelling selected aquatic creatures, the array comprising a plurality of repelling devices according to the first aspect of the present invention, wherein the plurality of repelling devices are tethered together. 
     The repelling array may define a row, plane or a volume. 
     Preferably, the selected aquatic creature is a shark. 
     According to a third aspect of the present invention, there is provided a method of repelling selected aquatic creatures, the method comprising attaching an electromagnetic field generator that generates an electromagnetic field which repels selected aquatic creatures to a buoy, separated from a user for use in a body off water. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment of the present invention will now be described in more detail with reference to the following drawings in which: 
         FIG. 1  shows the device of the present invention in use in a body of water; 
         FIG. 2  shows the interior of the device of  FIG. 1 ; 
         FIG. 3  shows the exterior of the device of  FIG. 1  in more detail; 
         FIG. 4  shows a series of devices according to the present invention, tethered together to form a shark-free path; 
         FIG. 5  shows a series of devices according to the present invention, tethered together to form a shark-free wall or plane; 
         FIG. 6  shows the device of  FIG. 1  being towed in a body of water; 
         FIG. 7  shows an alternative form of the present invention; 
         FIG. 8  shows the interior of the device of  FIG. 7 ; 
         FIG. 9  shows the device of  FIG. 7  in use in a body of water. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows a typical arrangement in which the device  10  of the present invention may be used. The electromagnetic field generator (not shown) is encased in buoy  20 , which in use, floats at the surface of a body of water  40 . A portion of the casing of buoy  20  is electrically conductive, and forms a first electrode  21 . When operational, a drop electrode  30 , extends below buoy  20  to form a second electrode spaced from the first electrode  21 , to create an electromagnetic field, shown generally at  50 , between electrodes  21  and  30  and within the conductive body of water  40 . 
     This generated electromagnetic field repels sharks, thus forming a shark-free region about the device  10 . 
     Turning now to  FIG. 2 , it can be seen that buoy  20  encases any suitable electromagnetic field generator  24  to generate electromagnetic fields which will repel sharks. A generator of choice is that described in Australian Patent No. 669806, to Natal Sharks Board, the contents of which are hereby incorporated by reference. 
     Generator  24  (and any other electrical devices on board) are powered by two 12 volt gel cell batteries  23 , encased in a moulded polyurethane foam support pack  28 . Alternatively, power for generator  24  may be supplied by an external source, connected via access port  22 . Port  22  may also be used to recharge batteries  23 , should rechargeable batteries be used. 
     Unit  29  controls a strobe light  29   a , which is visible through transparent polycarbonate strobe window  27 . Strobe light  29   a  is used to indicate the position of the device  10  in dark or unclear conditions. Strobe light  29   a  may emit a constant light, or may strobe on and off, as may be desired. The function of strobe light  29   a  is controlled by magnetic switches, activated by slipring  29   b  (see  FIG. 3 ). 
     The outer shell of the base of buoy  20  is made of 316 stainless steel, and forms the first electrode  21 . Of course, any other suitable conductive material may be used in its place. The base of buoy  20  is hollow to accommodate a second electrode  30 . Electrode  30  is a drop electrode, and is connected to buoy  20  via cable  31 . Upon actuation, electrode  30  is released from its chamber in buoy  20  and descends into the body of water  40  to a depth determined by the length of cable  31 . Electrode  30  is retained and released from its housing in buoy  20  via a quick turn release mechanism  32 . Again, any other suitable means may be used, including an automatic release mechanism which may be actuated remotely. 
     A fully covered device  10  of  FIG. 2  is shown in  FIG. 3 , where the transparent polycarbonate strobe window  27  (covering strobe light  29   a ) can be seen. Actuating slip ring element  29   b  is also shown. 
     Buoy  20  is preferably torpedo shaped to facilitate its movement through the water when being towed by a craft such as a boat. Such a scenario is shown in  FIG. 6 . 
     The tip of buoy  20  is an elastomer bump cone  25 , having tether eyelets  26 . This allows device  10  to be tethered to a boat, a stable base, or one or more other devices  10 . 
     An arrangement in which multiple devices  10  are tethered together is shown in  FIGS. 4 and 5 . In  FIG. 4 , there is shown a number of devices  10  tethered together by tether lines  60  in a line across the surface of the body of water. The arrangement shown provides a shark-free zone defining a path parallel to the surface of the water. 
     It is possible to weight device  10  (either externally or internally) to cause device  10  to attain a position below the surface of the water. In this way, a shark-free zone may be created at any desired depth within the water. In  FIG. 5 , there is shown the arrangement of  FIG. 4  plus a similar arrangement located below the first arrangement to form a shark-free zone which defines a wall or plane, perpendicular to the surface of the water. The wall or plane may extend as far as is desired. Such a wall can be utilised to provide a barrier to an area of water used by swimmers. For example, an area of a beach may be cordoned off in this way to prevent sharks from entering the region used by swimmers. A three dimensional “cage” may also be set up to provide a shark free volume, which may be useful for diving expeditions. 
     In commercial fishing, devices of the present invention can be connected to nets which will provide a shark-free region about the net thus preventing sharks from scavenging any fish caught by the nets. 
       FIGS. 7 and 8  illustrate an alternative version of the buoy of the present invention. Like elements have been labelled accordingly with respect to the previous figures. In this version, the buoy is provided as a smaller package which may be carried by an individual at the beach, and set up in-situ in an area where that individual will swim. The size of such a device could conceivably range from an esky-size to a drinks container size. 
     The device  10  is made up of two main parts, buoy  20  and base electrode  30 . These may be locked together for transport, and unlocked when ready to place in the water. 
     The base electrode module  30  is essentially a stainless steel flask fitted with a plastic base  32  that functions as a screw-in retaining lock as well as an access port for the battery pack  23   a . The flask has a small window  14  on the top surface, with a clear flush mounted lens for a battery status LED and a second portion  14   a  (see  FIG. 8 ) located at 180° around the flask with electrical contacts exposed to allow sea water to trigger the main switch on the unit. 
     The flask is constructed with several external circular grooves that form friction ridges on the inside, these in turn act as retainers to hold the fully potted PCB  29  in place. The epoxy-potting compound is poured in-situ when the PCB  29  and ancillaries are in place. This acts as a completely waterproof monolithic mass and adds both weight to the drop electrode and effective insulation and shock protection. 
     A guide and retaining liner is fitting inside the flask to secure the battery packs  23 . These may be  8  cell disposable or  10  cell rechargeable. The battery makes contact with conductive buttons that protrude from the potted section. A stainless steel spring pushes on the base of the battery pack and the spring is tensioned by an ‘O’ ring sealed screw in cap  16 . This also acts as a waterproof seal to the inner chamber. 
     At the top of the flask is a single pin connector  31   a  fitted to a flexible heavy-duty waterproof cable  31  approximately 1.5 meters in length. A screw-on connector is fitted to allow cable replacement in the event of damage. The cable  31  loops over the body of a tubular retainer at the top of the buoy and runs down an access groove  18  moulded into the flat face of one of the hemi formed chambers of the float. It terminates onto a waterproofed lug  19  that is riveted or bolted to a tab  19   a  spot-welded to the electrode  20 . 
     The float is constructed from two identical hemi section forms in a fluorescent colour that may be rotary moulded from a durable plastic such as polypropylene or polyethylene. The two segments are locked in place via the annulus stainless steel top electrode  21  and a tubular two part fastener (not shown) at the top of the unit. A simple braided cord carry handle (not shown) passes through this tubular fastener and is supplied with plastic tips that will screw or clip together. 
       FIG. 9  shows the modified device of  FIGS. 7 and 8  in use in a body of water. 
     The above has been described in the context of a specific embodiment and it will be appreciated by those skilled in the art that many variations and modifications may be made within the general inventive concept of the present invention.