Patent Publication Number: US-8973513-B2

Title: Recovering capsized watercraft incorporating rapid filling and emptying ballast systems

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to craft, in particular water craft, ballast systems and systems for the rapid filling and emptying of ballast systems. 
     2. Description of the Related Art 
     In many water borne activities, water crafts, such as jet boats and rescue craft, are used to move people and/or objects across the water. The agility and power of such smaller vessels make them attractive for water-sports enthusiasts and thrill-seekers, for example. However, they may be generally unsuitable for military use as they may not be adapted for long deployment, nor be adapted to cope with the various weather conditions prevalent at sea. 
     The speed at which smaller craft can travel makes them comparatively less stable than larger craft, such as navy frigates and destroyers, especially in rough water. As a craft increases its velocity, the chance it will capsize can increase. This is particularly the case for jet boats and other forms of speed boat, and the capsized craft can be very difficult to ‘right’—return to an upright position—in order to continue moving. 
     Devices have been designed to improve the stability of the craft in the water, such as canting keels, which comprise a torpedo shaped ballast body at the tip of an aerofoil. The moment of the ballast body on the aerofoil is generally greater than that of the craft, and capsizing is thereby prevented. However, when travelling normally, the ballast is a deadweight which slows the craft, and such designs are generally impractical for use in faster boats, such as jet boats, as they reduce the speed and agility which make those craft attractive to use. Few practical designs are capable of preventing capsizing. 
     It is, therefore, generally desirable to provide a craft that is capable of righting. 
     Furthermore, it is generally desirable to overcome or ameliorate one or more of the abovementioned difficulties, or at least provide a useful alternative. 
     BRIEF SUMMARY 
     In accordance with the invention, there is provided a craft including: 
     a body having a front end, a rear end, two sides running between said ends, and an axis running generally from the rear end to the front end; and 
     a water displacement system operable to displace water to propel the craft across water, and to displace water to cause the craft to rotate about axis. 
     Preferably, the water displacement system includes a drive propulsion system for displacing water to propel the craft across water and a rotate propulsion system for displacing water to cause the craft to rotate about said axis. 
     Preferably, the rotate propulsion system includes a plurality of water propulsion systems arranged to generate rotation of the craft about the axis when actuated simultaneously. 
     The present invention also provides a ballast system for a craft, including a ballast tank capable of being at least partially filled with ballast to change a position of a center of gravity of the craft to assist in rotation of the craft when capsized. 
     Preferably, the ballast tank includes a bottom ballast tank capable, when in use, of being at least partially filled to draw the center of gravity of the craft towards the bottom of the craft to assist in rotation of the craft when capsized. 
     Preferably, when in use, the bottom ballast tank occupies substantially all of the internal volume of the craft. 
     Preferably, the ballast system is adapted to reduce torque required to right fife craft by filling the ballast tank from one end of the craft only. 
     The present invention also provides a rapid filling and emptying system for a ballast system of a craft, which craft includes a water displacement system, wherein said rapid filling and emptying system includes: 
     at least one ballasting intake through which water is passed from the water displacement system into said ballast system; and 
     at least one ballasting outlet through which said water displacement system draws water from the ballast system. 
     Preferably, the rapid filling and emptying system further includes a common orifice and a valve, wherein the ballasting outlet and ballasting inlet are configured to be coupled to the ballast system at the common orifice, and the valve is positionable to close one or both of the ballasting inlet and ballasting outlet. 
     Preferably, the rapid filling and emptying system is capable of filling the ballast system with sufficient ballast to substantially increase the mass of the craft and thereby lower the position of the craft in water, in order to substantially reduce the portion of the craft visible above water. 
     Preferably, the craft includes the ballast and rapid filling and emptying systems, and water drawn from the ballast system is used to propel the craft. 
     Advantageously, preferred embodiments allow a craft to right without assistance. 
     For ease of understanding, the description and Figures provided below will not show the ballast system and/or rapid filling and emptying system in isolation, but will instead show those systems when housed within a craft. However, the ballast system and/or rapid filling and emptying system may be incorporated into existing vessels and water craft as required. In addition, the mass system shown in the drawings forms part of the ballast system, though the purpose of the ballast system and the purpose of the mass system may be served by separate systems as appropriate. 
     The water displacement system will be hereinafter described as having a single “propulsion system”. However, the water displacement system may be provided with separate propulsion systems, being a drive propulsion system and a rotate propulsion system, to respectively propel the craft across water and displace water in a manner which causes the craft to rotate about its axis. Furthermore, the description and Figures only show the water propulsion systems to be located at the rear end of the craft, however, it will be understood that water propulsion systems may also be located at positions intermediate the ends, closer to the center of gravity of the craft, for example. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Preferred embodiments of the present invention are hereafter described, by way of non-limiting example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a plan view of a craft floating on water; 
         FIG. 2  is a perspective view of the craft of  FIG. 1 , when upright; 
         FIG. 3  is a perspective view of the craft of  FIG. 1 , when capsized; 
         FIGS. 4A and 4B  are plan views of a trim nozzle; 
         FIGS. 5A to 5D  are partial plan views of a craft including jet outlet diverters; 
         FIG. 6  is a rear view of a capsized craft in a wave; 
         FIG. 7  is a cross-sectional view of the craft of  FIG. 1 ; 
         FIGS. 8A and 8B  are cross-sectional views of a rotatable cylinder in various positions; 
         FIGS. 9A and 9B  are cross-sectional views of a sprung flap in open and closed positions respectively; 
         FIG. 10  is a cross-sectional view of a craft; 
         FIG. 11  is a cross-sectional view of a craft, showing a ballast system; 
         FIG. 12  is a cross-sectional view of the craft of  FIG. 11 ; and 
         FIG. 13  is a cross-sectional view of a craft partially showing a ballast system. 
     
    
    
     DETAILED DESCRIPTION 
     As used herein, to ‘right’ is to return from a capsized or overturned position to an upright position, without the aid of external devices or other vessels. A similar meaning also applies to related words such as “righting” and “rights”. 
     Like reference numerals will be used herein to refer to similar features depicted in the various drawings. 
     The craft  10  shown in  FIGS. 1 to 3  is used to propel an operator and/or items, such as cargo, across water  12 . The craft  10  includes a body  14  having a front end  16  (the ‘bow’), a rear end  18  (the ‘stern’), and sides  20   a ,  20   b  running between the ends  16 ,  18 . The body  14  is formed by a series of flat panels  30 , coupled in a known manner (i.e., by welding), for minimizing the possibility that the craft  10  will be detected by radar. Similarly, all features of the body  14 , such as the windscreen, should be formed so as to conform with the surface of the body  14  (i.e., not to incorporate distinct surface features). An axis  22 , as shown in  FIGS. 2 and 3 , about which the craft  10  rolls during righting, is defined between the two ends  16 ,  18  and runs generally parallel with the sides  20   a ,  20   b  through the center of gravity (not shown) of the craft  10 . 
     The craft  10  further comprises a water displacement system  23  coupled to said body  14  in a suitable manner, including a propulsion system  24 , for propelling water  12  through the water displacement system  23 , and a water propulsion system  26 . The water propulsion system  26  is operable to displace water  12  to propel the craft  10  across water  12 , and to displace water  12  to cause the craft  10  to rotate about its axis  22 . Though the functions of propelling the craft  10  across water  12  and causing the craft  10  to rotate about its axis  22 , may employ separate water propulsion systems  26 , in the present case, the water propulsion system  26  is moveable between a drive position and a rotate position, as shown in  FIGS. 2 and 3  respectively. The drive position is a normal operating condition in which the displaced water  28  propels the craft  10  across the water  12 . The rotate position is a righting condition, in which the displaced water  28  causes the craft  10  to rotate about the axis  22 . If the craft  10  capsizes, the water propulsion system  26  moves to the rotate position to assist in returning the craft  10  to an upright position. 
     The craft  10 , as shown in  FIG. 2 , includes two water propulsion systems  26   a ,  26   b  each of which is in a drive position and is arranged closer to one side  20   a ,  20   b  than the other. Spacing the water propulsion systems  26   a ,  26   b  as shown provides stability, as the propulsive force is effectively distributed across the stern  18  of the craft. When in a drive position, the craft  10  and propulsive forces act in generally the same manner as for known speedboats and will, therefore, not be described herein in further detail. 
     When the water propulsion systems  26   a ,  26   b  move into respective rotate positions, as shown in  FIG. 3 , they work in unison to displace water  28  in a manner which provides an anticlockwise rotational force to the craft  10 . The rotational force provided by the water propulsion systems  26   a ,  26   b  may be increased by increasing their flow rate or by positioning them further apart. Although not strictly necessary, the water propulsion systems  26   a ,  26   b  herein described are independently capable of supplying sufficient rotational force to cause rotation of the craft  10  about the axis  22 . 
     To move the water propulsion systems  26   a ,  26   b  from a drive position to a rotate position, each water propulsion system  26   a ,  26   b  may include a trim nozzle  30  which is pivotable between drive and rotate positions, as shown in  FIGS. 4A and 4B  respectively, in order to redirect thrust from the propulsion system  24 . The stability of the craft  10  while rotating, when the water propulsion systems  26   a ,  26   b  are in the rotate position, will depend on the orientation of the trim nozzles  30 . In particular, if the craft  10  is stationary and a trim nozzle  30  directs thrust directly towards the water  12 , it may encourage the rear end  18  of the craft  10  to rotate and lift, which would move the line of action of the center of gravity towards the front end  16  of the craft  10 , thereby forcing the front end  16  of the craft  10  towards/away from the water  12 , hindering rotation and increasing the force required to right the craft  10 . In such circumstances, if the trim nozzle  30  is adjusted so that some forward/reverse thrust is provided whilst rotating, it may cause the front end  16  of the craft  10  to remain level with the rear end  18 , which can reduce the force required to right the craft  10 . Alternatively, the water propulsion systems  26   a ,  26   b  may initially be positioned to provide forward momentum to the craft  10  and be, before that momentum is lost, repositioned to provide the desired rotational force. Alternatively, the outlets (i.e., trim nozzles  30 ) for the propulsion system  24 , when in a rotate condition, may be placed nearer the center of gravity of the craft  10 , thereby providing greater stability during rotation. Various trim nozzles  30  are disclosed in U.S. patent application Ser. No. 11/849,178, the entirety of which is incorporated herein-by reference. Furthermore, trim nozzle control systems are known and will, therefore, not be described herein in further detail. 
     As an alternative to trim nozzles  30 , the water propulsion systems  26   a ,  26   b  may include diverters  32  (also known as “buckets”), as shown in  FIGS. 5A to 5D , which redirect flow from the jet outlets  34 . A traditional diverter  32 , as shown in  FIGS. 5A and 5B , serves to redirect flow from a jet boat outlet nozzle  36  towards the bottom  38  of the craft  10 , to allow the craft  10  to maneuver slowly and reverse. Such diverters  32  operate in a known way and will not be discussed herein in further detail. An altered diverter  40 , as shown in  FIGS. 5C and 5D , serves to direct flow towards the top  42  of the craft  10  (as shown in  FIG. 1 ). If the craft  10  has capsized, the top  42  of the craft  10  will become submerged. Therefore, when the craft  10  has capsized, as shown in  FIG. 5D , the altered diverter  40  will direct flow towards the water  12 , so that the thrust will cause the craft  10  to rotate about the axis  22  (not shown). 
     The altered diverter  40  includes an hydraulic ram  44  coupled between the side of the diverter  40  and the stern  18  of the craft  10 . By coupling the hydraulic ram  44  to the side of the diverter  40 , rather than the top of the diverter  40  as shown in  FIGS. 5A and 5B , the hydraulic ram  44  can move with the diverter  40 , past the jet outlet  34  of the water propulsion system  26 , without interfering with the flow through the jet outlet  34 . Alternatively, the hydraulic ram  44  may be mounted on the inside curve of the diverter  40 , for example, or at any other suitable location. The altered diverter  40  includes a hinge  46 , providing a fixed pivot point between the altered diverter  40  and jet outlet  34 . The hinge  46  allows the positioning of the altered diverter  40  to be set in a position in which the propulsion system  24  delivers optimum rotational force to the craft  10 . 
     The fixed nature of the hinge  46  ensures that the altered diverter  40  only redirects water from the jet outlet  34  towards the top  42  of the craft  10 , and not towards the bottom  38 . Therefore, the hinge  46  prevents the craft  10  from being able to rotate in both clockwise and anticlockwise, in order to right. This can be disadvantageous as conditions which may assist in righting rotation may instead serve to compete against that rotation. For example, as shown in  FIG. 6 , a wave  48  approaching the craft  10  from the side  20   a  (port side) creates a trough  50  on the side  20   b  (starboard side). Therefore, the wave  48  could assist in anticlockwise rotation of the craft  10 . However, the water propulsion systems  26   a ,  26   b  are oriented to cause anticlockwise rotation of the craft  10  and the wave  48  thus competes against the rotational force imparted by the propulsion system  24 . If the water propulsion systems  26   a ,  26   b  were oriented as shown by the broken line, the rotational force imparted by the propulsion system  24  would cooperate with the wave  48  and reduce the force required to right to craft  10 . 
     As an alternative to the hinge  46 , a second hydraulic ram  52  (shown by the broken line) may be used to position the diverter  40 . This can allow the diverter  40  to direct flow towards either the top  42  or bottom  38  of the craft  10 , thereby selectively rotating the craft  10  in either a clockwise or anticlockwise direction. In any event, control systems for trim nozzles  30 , diverters  32 ,  40  and hydraulic rams  44 ,  52  are known and will not be described herein in further detail. 
     The propulsion system  24  will generally be a water jet system and will thus require water intakes  54  as shown in  FIGS. 2 and 3 . The craft  10  has primary water intakes  54  which are used when the craft  10  is upright. However, when the craft  10  capsizes or pitches heavily, these primary intakes  54  may no longer be in contact with the water  12 . Consequently, the propulsion system  24  will not be able to supply thrust. Therefore, the craft  10 , as shown in  FIG. 2 , includes at least one auxiliary intake  56  positioned on a side  20   a ,  20   b  or top  42  of the craft  10 . In the embodiment shown, the craft  10  includes a plurality of auxiliary intakes  56  such that there is always at least one intake  54 ,  56  in contact with the water  12  and a continuous flow can be supplied to the propulsion system  24 . 
     Any of the intakes  54 ,  56  may have, for example, butterfly valves (not shown) mounted at their respective openings so that when a valve is closed (i.e., the respective intake  54 ,  56  is not in use) the surface of the valve remains flush with the surface of the body  14 , thereby minimizing the possibility that the craft  10  will be detected by radar. In circumstances where a capsizing has occurred, or continuous sharp or evasive maneuvering is required, the valves may respond to the change in orientation of the craft  10 , by automatically opening and closing to maintain flow through the propulsion system  24 . This can be achieved by, for example, comparing accelerometer signals, which indicate the pitch of the craft  10 , to the respective positions of the intakes  54 ,  46 , to determine which intakes  54 ,  56  should be in contact with the water  12 . A table listing the intakes which should be open/closed for any particular pitch sensed by the accelerometers, may also be consulted to determine which intakes should be open/closed. Alternatively, a laser sensor (not shown) may be inserted into one or more of the intake pipes  58 , as shown in  FIG. 7 , to optically determine the density of the water in the pipe. As water  12  is more dense than air, the valve may close/open when the signal from the sensor indicates that the density is less/greater than a particular threshold level. Other density measuring instruments, flow meters and detection devices may be used to determine whether a particular valve should be opened/closed, to provide optimum flow to the propulsion system  24 . 
     The intakes  54 ,  56  may all feed into common intake manifolds  60 , or be otherwise connected as appropriate. At these piping joins  62 , undesirable flow disturbances can occur due to changes in inner surface features of the pipes  58 . To minimize these disturbances, further valves can be used to block one pipe and open another. For example, a rotatable cylinder  64 , as shown in  FIGS. 8A and 8B , having channels therethrough, can be installed at the joint of a standard intake pipe  58   a  and an auxiliary intake pipe  58   b . The cylinder  64  is rotatable between a drive position, in which flow from the standard intake pipe  58   a  is delivered to the propulsion system  24 , and a rotate position, in which flow from the auxiliary intake pipe  58   b  is delivered to the propulsion system  24 . 
     The rotatable cylinder  64  includes two channels  66   a ,  66   b  which lie in a plane generally perpendicular to the axis of rotation of the rotatable cylinder  64 . The first channel  66   a  is substantially straight and has the same diameter as the standard intake pipe  58   a , which is preferably also the diameter of the auxiliary intake pipe  58   b . In the drive position, as shown in  FIG. 8A , the first channel  66   a  effectively replicates a portion of the standard intake pipe  58   a , to join the upstream portion  68   a  of the standard intake pipe  58   a  to the downstream portion  68   b  with minimal flow disturbance. In this condition, the auxiliary intake pipe  58   b  cannot supply water  12  to the propulsion system  24 . When in the rotate position, as shown in  FIG. 8B , the second, curved, channel  66   b  is positioned such that it places the auxiliary intake pipe  58   b  in fluid communication with the downstream portion  68   b . In this condition, the standard intake pipe  66   a  cannot supply water  12  to the propulsion system  24 . 
     The rotatable cylinder  64  can be driven by any known means, such as a small standard motor, to rotate between drive and rotate positions, and the same principle of auxiliary intakes can be used for air supply to the engine. 
     As an alternative to the rotatable cylinder  64 , hinged, sprung flaps  70  as shown in  FIGS. 9A and 9B , for example, may be used to cover the auxiliary intake pipes  58   b . The flap  70  serves to selectively open/close the standard intake pipe  58   a  and auxiliary intake pipe  58   b , thereby allowing a flow through one or other of those pipes  58   a ,  58   b . The flap  70  may be held in position (i.e., closing either the standard intake pipe  58   a  or auxiliary intake pipe  58   b ) by a remotely actuated latch (not shown), or by any suitable coupling, such as an electromagnetic coupling  72 , the current of which could be reversed to quickly force the flap  70  open. In any event, the coupling must be sufficiently strong that, whilst drawing air through an intake  58   a ,  58   b , water  12  is not inadvertently drawn through the other intake  58   a ,  58   b , and vice versa. In many cases, air will be drawn into the propulsion system  24  in preference to water  12  and, in such cases the valving must be sufficiently strong to withstand both the force of water  12  thereagainst and the suction of the propulsion system  24  when drawing in air. In this regard, hermetic seals, butterfly valves, magnetic couplings and other closures for pipes are known, including their control systems and methods for control, and will not be described herein in further detail. 
     The flap  70  is constructed to substantially conform to the surface of the standard intake pipe  58   a  to which it connects, thereby minimizing flow disturbances during normal use of the propulsion system  24 . The flap  70  may also be configured so as to provide efficient flow redirection from the auxiliary intake pipe  58   b  down the standard intake pipe  58   a , though this is less important as the auxiliary intakes  56  should only rarely be used. 
     In some craft  10 , similar intakes  56  will be provided for air. However, in the present case, the auxiliary intakes  56  are used for both water and air. This is achieved by branching the auxiliary intakes  56  into each of the fuel/air mix and water intakes (not shown) of the propulsion system  24 , in a manner similar to that shown in  FIGS. 9A and 9B . As small amounts of air passing through the propulsion system  24  will not cause problems with the propulsion system  24 , the valve timing (i.e., opening and closing of an electromagnetic valve) when switching an auxiliary inlet  56  from the air inlet to the water inlet of the propulsion system  56  will not be critical. However, passing water into the combustion chamber along with the fuel can cause significant damage to the propulsion system  24 . Accordingly, a filter (not shown) can be arranged between the branch from the auxiliary intake  56  and the air/fuel inlet of the propulsion system  24 , or valve timing can be adjusted to account for the possibility of water being present in the intake pipe  58 , as shown in  FIG. 7 . 
     Alternatively, as the event of capsizing should not occur regularly, the craft  10  may not have any auxiliary intakes  56  which supply air to the propulsion system  24 . Instead, the craft  10  may be provided with a tank of compressed air (not shown) coupled to the propulsion system  24 , which is opened if the craft  10  capsizes. The tank supplies air to be mixed with the fuel in order to run the propulsion system  24 . Although the tank may be designed such that it has a specific number of uses, or a specific duration of use at a particular throttle position, it is preferable that the craft  10  be provided with a motor (not shown) that is capable of refilling the tank when the craft  10  is in use. The motor may be separate to the propulsion system  24 , but is preferably driven by the propulsion system  24 . 
     In addition, the propulsion system  24  must be supplied with fuel when the craft  10  has capsized. In this case, a standard intake at the bottom of the fuel tank  74  will be insufficient as that intake may be at the highest point of the fuel tank  74  when the craft  10  is in a capsized position. Accordingly, the fuel intake (not shown) from the fuel tank  74  into the propulsion system  24  includes a hose extending into the fuel tank  74 , which is provided with a weight at the end. When the craft  10  is operating in either a normal or capsized condition, the weight will draw the hose to the lowest point in the fuel tank  74 , thereby allowing fuel to be continuously supplied to the propulsion system  24 . The weight may also be substituted for any other appropriate means for providing continuous fuel supply irrespective of tank position. 
     To ensure the craft  10  is balanced while in motion, it is preferable that its center of gravity be both close to the water  12  and equally distributed across the width of the craft  10 —this can be achieved by positioning the fuel tank  74 , munitions  76  and other heavy items near the bottom  38  of the craft  10 , as shown in  FIG. 10A . It is also preferable that the center of gravity be located closer to the rear end  18  of the craft  10  than the front end  16 , as this will allow the front end  16  to rise against oncoming waves  48 . In contrast, however, it is advantageous if the center of gravity of the craft  10  is off-center with respect to the sides  20   a ,  20   b , to facilitate rotation of the craft  10  about its axis  22 . 
     In order to move the center of gravity to an off-center position, the internal volume of the craft  10  includes a ballast system  78 , as shown in  FIG. 11 . The ballast system  78  includes tanks  80  that are able to be at least partially filled to change the position of the center of gravity of the craft  10 . The ballast tanks  80  include a bottom ballast tank  80   a , which when filled draws the center of gravity of the craft  10  towards the bottom  38 , and side ballast tanks  80   b ,  80   c , each of which when filled draws the center of gravity to the side  20   a ,  20   b  on which the respective tank  80   b ,  80   c  is located. The tanks  80  may be secured to the craft  10  by known means and be filled through intakes  82  which can be opened or closed in the same manner as the intake pipes  58  described above. The intakes  82  of the side ballast tanks  80   b  and  80   c  may be in direct fluid communication with the water  12  or, as in the present case, be in fluid communication with the bottom ballast tank  80   a  such that water is drained from the bottom ballast tank  80   a  into the side ballast tanks  80   b ,  80   c.    
     The intakes  56  may in some craft contain additional water displacement devices, such as pumps, impellers, propellers or thrusters which can draw water into the main propulsion system should the main propulsions system be unable to draw water from an un-primed pipe. In some embodiments, these displacement devices may take the place of the main water displacement system  24 , and be sufficiently strongly powered to direct the water to provide a force about the axis to assist in righting the boat, or rapidly fill the ballasting system. 
     In some craft, the ballast tanks may additionally be filled, or partially filled by directly opening an orifice that is submerged below the water. The filling, or partial filling of tanks by this method may advantageously, assist in shifting the center of gravity to one side or end of the boat which would more reliably place an intake  54  or  56  in contact with the water to allow for the powered righting system and/or ballast system to be utilized. 
     The propulsion system  24 , as shown in  FIG. 12 , includes a ballast outlet  84  in at least one of the ballast tanks, for facilitating rapid filling. A ballast pipe  86 , which supplies the ballast outlet  84 , is connected to the outlet pipe  88  of the propulsion system  24 , upstream of the water propulsion system  26 , by appropriate valuing. Therefore, when the ballast pipe  86  is connected downstream of the propulsion system  24 , water  12  that would otherwise be directed out through the water propulsion system  26  is instead directed into the ballast system  78 . In another embodiment of the invention, the water may be directed by means of a pipe, scoop or bucket (not shown) downstream of the water propulsion system  26  into a ballast outlet  84  located near the propulsion system  26  on the outside of the craft. 
     In addition, the propulsion system  24  includes a ballast inlet  90  in at least one of the ballast tanks  80 , to allow rapid evacuation of the ballast system  78 . The ballast inlet  90  connects to a ballast inlet pipe  92  which itself is connected to an intake manifold  60 , upstream of the propulsion system  24 . In the embodiment shown, the ballast inlet pipe  92  and ballast outlet pipe  86  form a common connection pipe  94  which includes a valve  96  for selectively opening and closing each ballast outlet  84  and ballast inlet  90 . Advantageously, when water  12  is drawn from the ballast system  78  through the ballast inlet  90 , it can be used to propel the craft  10 . Furthermore, if the propulsion system includes a ballast inlet  90  in communication with the internal volume of the body  14  of the craft, in the event that the body  14  of the craft  10  is breached (i.e., by collision with a solid body or through penetration from projectiles such as bullets), the ballast inlet  90  may act as a rapid bilge pump to keep the craft  10  afloat and preferably at least partially operational. Alternative inlets  90  and outlets  84  may be provided as appropriate, in accordance with known ballasting systems  78 . 
     The decks of the craft  10  may provide a broad, and generally flat surface in generally coplanar contact with the water  12  when upside-down. As such, the craft  10  would be quite stable, and hence difficult to right in this orientation. The ballasting system  78  is advantageously used to move the boat&#39;s  10  central axis away from the plane of the waterline to reduce the amount of torque required to achieve rotation to right the craft  10 . By progressively filling the ballast tanks  80   a ,  80   b ,  80   c  from either the rear  18  or the front  16  of the craft  10 , or partitioning the ballast tanks  80   a ,  80   b ,  80   c  into generally forward or rear sections one of which would be filled first, the craft  10  comes to have its front  16  or rear  18  end lowered substantially in the water  12 , and the other end raised. In doing so, the axis of rotation is brought away from the plane of the water&#39;s surface, and the amount of water  12  that must be displaced in order to rotate the craft  10  about its axis to an upright orientation is reduced, and hence reduce the torque required to achieve such a rotation. 
     To facilitate this, the ballast tanks  80   a ,  80   b , and  80   c  are filled from the rear  18  of craft  10 , by opening a gate or valve (not shown) towards the rear of the tanks  80   a ,  80   b ,  80   c  which is submerged under water  12  when the craft  10  is in an upside-down position. Alternatively, the ballast filling system  78  pumps water into the rear of the tanks  80   a ,  80   b ,  80   c  by positioning the ballast outlet  84  towards the rear of the tanks  80   a ,  80   b ,  80   c . In some embodiments, both of these methods of filling the tanks  80   a ,  80   b ,  80   c  are enacted in quick succession, or simultaneously. 
     In another alternative embodiment, the tanks  80   a ,  80   b ,  80   c  are filled from the front  16  of the craft  10  by opening a valve or gate (not shown) submerged when upside-down towards the front  16  of the craft  10 , or repositioning the ballast outlet  84  towards the front of the tank. 
     Advantageously, the ballast tanks  80   a ,  80   b ,  80   c  would be filled in this fashion prior to the water displacement system  23  being engaged to provide a torque about the axis to rotate the craft  10 . 
     Though the body  14  of the craft  10  may be formed from flat panels, the possibility of radar detection, visual sighting or projectile impact (i.e., bullet spray) of the craft  10  can be reduced by reducing the proportion of the craft that visible above surface of the water  12 . In this regard, the lower the buoyancy, the greater the proportion of the craft  10  that is submerged and the lower the possibility of radar detection. To lower the buoyancy, the volume of the ballast system  78  may be sufficient such that, when filled with ballast, the mass of the craft  10  is substantially increased thereby lowering the position of the craft  10  in the water  12 , in order to substantially reduce the portion of the craft  10  that is visible above the water  12 . In emergency situations, such as military exercises, it will be preferable to increase the mass rapidly. Accordingly, in such circumstances, the propulsion system  26  will displace water  12  into the ballast system  78  in order to increase the relative mass of the craft  10  rapidly. Similarly, when it is desired that the craft  10  once again be capable of fast maneuvering, the propulsion system  26  should extract water  12  from the ballast system  78  in preference to water  12  from outside the craft  10 . 
     To ensure low buoyancy, the bottom ballast tank  80   a  may simply be formed from the volume defined between the body  14  of the craft  10  and the proportion of the volume of the craft  10  which must remain dry, for example the cabin  98  and electrical cabinet  100 , as shown in  FIG. 13 . The ballast inlet  90  and ballast outlet  84  are then simply in fluid communication with the internal volume of the craft  10 . Similarly, the side ballast tanks  80   b ,  80   c  can be selectively placed into, and out of, fluid communication with the internal volume of the craft  10 . The remaining equipment can be water-proofed, consumables vessels such fuel tanks  74  and/or the ballast tanks  80  can be collapsible (i.e., contract around their contents so that air does not occupy any space therein). 
     Although having been hereinbefore described as being advantageous, the body  14  may not be formed entirely of flat panels but may alternatively be partially, or not at all, formed from flat panels. 
     The axis  22  about which the craft  10  rotates may shift, relative to the craft, whilst it is righting, and may not necessarily be located down the center of the craft  10 . However, as water craft  10  will generally be greater in the length dimension than the width dimension (i.e., longer between the ends  16 ,  18  than between the sides  20   a ,  20   b ), the axis  22  will usually run along the length of the craft  10  as shown, as it generally requires less effort to rotate a body about the longer dimension. 
     The water propulsion systems  26   a ,  26   b  may not act in unison but may, instead, be independently operable to cause the craft  10  to rotate about the axis  22 . In addition, the water propulsion system  26  may include outlets located at some point intermediate the sides  20   a ,  20   b  of the craft  10  (i.e., near the center of gravity of the craft  10 ), providing more stable rotation. 
     Although hydraulic rams  44  have been used in, for example, the control of the position of the trim nozzles  30  or diverters  32 ,  40  of the propulsion system  24 , any suitable position controlling mechanism may be employed. The same applies for any of the other features requiring positional control. 
     Valves, rotatable cylinders  64  and any other suitable flow controlling mechanisms may be used interchangeably in the applications described herein. In addition, the drive mechanisms for valves, rotatable cylinders  64 , hinged, sprung flaps, and other features of the embodiments described herein, may be any suitable mechanism. Electromagnetic couplings  72  may be used though their materials can tend to become corroded, or become unreliable due to disturbances from the water  12 . Small motors and mechanically rotatable mechanisms are preferred as many such mechanisms are known, are efficient, and may only require a small aperture to be formed in the pipe  58 ,  58   a ,  58   b ,  86 ,  88 ,  92  in order to receive the shaft about which a larger component, which remains in the pipe  58 ,  58   a ,  58   b ,  86 ,  88 ,  92  (i.e., the disc of a butterfly valve), rotates. 
     Many combinations, of the features herein described, and modifications to the described embodiments will be apparent to those skilled in the art without departing from the scope of the present invention as hereinbefore described with reference to the accompanying drawings. 
     Throughout this specification and claims which follow, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. 
     The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavor to which this specification relates. 
     PARTS LIST 
     
         
         
           
             craft  10   
             water  12   
             body  14   
             front end (bow)  16   
             rear end (stern)  18   
             sides (of craft)  20   a ,  20   b    
             axis (of rotation of craft when righting)  22   
             water displacement system  23   
             propulsion system  24   
             propulsion device  26 ,  26   a ,  26   b    
             displaced water  28   
             trim nozzle  30   
             diverters  32   
             jet outlets  34   
             jet boat outlet nozzle  36   
             bottom (of craft)  38   
             altered diverter  40   
             top (of craft)  42   
             hydraulic ram  44   
             hinge (of diverter)  46   
             wave  48   
             trough  50   
             second hydraulic ram  52   
             water intakes  54   
             auxiliary intake  56   
             intake pipes  58 , (standard)  58   a , (auxiliary)  58   b    
             intake manifolds  60   
             pipe joins  62   
             rotatable cylinder  64   
             channels  66   a ,  66   b    
             upstream and downstream portions  68   a ,  68   b    
             (standard intake pipe) respectively 
             flap  70   
             electromagnetic coupling  72   
             fuel tank  74   
             munitions  76   
             ballast system  78   
             ballast tanks  80 , (bottom)  80   a , (sides)  80   b ,  80   c    
             ballast tank intakes  82   
             ballast outlet  84   
             ballast outlet pipe  86   
             outlet pipe  88   
             ballast inlet  90   
             ballast inlet pipe  92   
             common connection pipe  94   
             valve (common pipe)  96   
             cabin  98   
             electrical cabinet  100