Abstract:
An easily deployable data relay buoy, in some embodiments, has a diesel powered alternator and storage battery, providing long service life. The data relay buoy has mechanical characteristics that allow it to maintain antenna stability in the presence of seas states from at least zero through four and to survive in sea states up to sea state six.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 61/031,551 filed Feb. 26, 2008, which application is incorporated herein by reference in its entirety. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    This invention was made with government support under Contract No. N00039-04-C-0035 awarded by U.S. Navy. The government has certain rights in the invention. 
     
    
     FIELD OF THE INVENTION 
       [0003]    This invention relates generally to deployable ocean systems and, more particularly, to a deployable buoy, which has self-generated power. 
       BACKGROUND OF THE INVENTION 
       [0004]    As is known, there exist numerous types of floating apparatus for use in water, for example, in the ocean. Some portions of the floating apparatus may be underwater and some portions may be on or near the surface of the water. The portion at or near to the surface of the water is often referred to as a buoy. 
         [0005]    Buoys are used in a variety of applications. For example, both relatively large and relatively small buoys are used as ocean markers, to mark water channels or to mark obstructions in the water. Some conventional buoys used as markers are totally passive and may have one or more colors to represent information. Other conventional buoys used as markers have lights, visible to a person on a ship, or audible devices, such as bells or horns, which may be heard by a person on a ship. A conventional buoy used as a marker is generally not free-floating, meaning that the buoy is tethered to an anchor or other fixed object disposed on the ocean bottom. 
         [0006]    More complex systems having buoys are used in conjunction with electronics as measurement platforms, which may, for example, provide measurements of temperatures of the ocean, or measurements of currents in the ocean. Conventional buoys used as measurement platforms may be either free-floating (i.e., without an anchor), or non free-floating (i.e., with an anchor). 
         [0007]    Still more complex systems having buoys are used in conjunction with electronics as detection platforms, which may, for example, be coupled to acoustic sensors in order to detect vessels, for example, submarines, in the ocean. One such detection platform is conventionally referred to as a sonobuoy, of which there are many types. Most sonobuoys employ free-floating buoys, are battery powered, and have an operation lifetime of a few hours. 
         [0008]    Still more complex conventional systems having buoys and used as detection platforms exist. One such system, made by Harris Corporation, Melbourne, Fla., provided a very large diesel powered buoy, anchored to the ocean bottom. This buoy transmitted radio signals to a receiving station. This buoy was large enough for a person to enter. This existing buoy suffered from large size and resulting difficult deployment and overall low power generating efficiency. 
         [0009]    It would be desirable to have a buoy, which is self powered, which is able to generate a large amount of power, which has high overall power generating efficiency and resulting long operational life in the ocean, which is small and easily deployed, and which is mechanically angularly stable at higher seas states despite its small size, resulting is good signal integrity of radio frequency signals received from the buoy. 
       SUMMARY OF THE INVENTION 
       [0010]    In accordance with one aspect of the present invention, a buoy for deployment in the ocean includes an engine and an electric starter motor coupled to the engine. The buoy further includes an electrical alternator coupled to the engine, thee electrical alternator is configured to generate electricity when the engine is running. The buoy further includes a battery coupled to the electrical alternator, the battery having a battery voltage. The electrical alternator is configured to charge the battery with the electricity when the engine is running. The buoy further includes a fuel tank configured as a soft, flexible, and collapsible bladder coupled to the engine, configured to prevent fuel sloshing. The fuel tank is continually surrounded by seawater such that, as the fuel is expended and the fuel tank collapses accordingly, seawater continually fills in around the fuel tank resulting in a displacement of the buoy remaining substantially unchanged. 
         [0011]    The present invention provides a buoy of the present invention that is self powered, is able to generate a large amount of power, has high overall power generating efficiency and resulting long operational life in the ocean, is small and easily deployed, and is mechanically angularly stable at higher seas states despite its small size, resulting is good signal integrity of radio frequency signals received from the buoy. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The foregoing features of the invention, as well as the invention itself may be more fully understood from the following detailed description of the drawings, in which: 
           [0013]      FIG. 1  is a side view of an autonomous data relay buoy; 
           [0014]      FIG. 1A  is a top view of the autonomous data relay buoy of  FIG. 1 ; 
           [0015]      FIG. 1B  is another side view of the autonomous data relay buoy of  FIG. 1  showing a center of buoyancy, a center of mass, a center of drag, and a virtual center of mass; 
           [0016]      FIG. 2  is a pictorial showing the autonomous data relay buoy of  FIG. 1  in a non-free-floating arrangement and experiencing a relatively high speed ocean current; 
           [0017]      FIG. 2A  is a pictorial showing the autonomous data relay buoy of  FIG. 1  in a non-free-floating arrangement and experiencing a relatively low speed ocean current; and 
           [0018]      FIG. 3  is block diagram of electronic circuits that can be within the autonomous data relay buoy of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    Before describing the present invention, some introductory concepts and terminology are explained. As used herein, the term “sea sate” is a numerical value used to describe a condition of the ocean, including a wave height value, and a wave period. It will be understood that the sea state is often also related to a wind speed value. 
         [0020]    A known Pierson—Moskowitz sea state table is provided below as Table I. 
         [0000]    
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
               
                   
                   
                   
                 Significant 
                 Average 
                 Average 
               
               
                 Wind 
                 Sea 
                 Significant 
                 Range of 
                 Period 
                 Length of 
               
               
                 Speed (Kts) 
                 State 
                 Wave (Ft) 
                 Periods (Sec) 
                 (Sec) 
                 Waves (FT) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 3 
                 0 
                 &lt;.5 
                 &lt;.5-1   
                 0.5 
                 1.5 
               
               
                 4 
                 0 
                 &lt;.5 
                 .5-1   
                 1 
                 2 
               
               
                 5 
                 1 
                 0.5 
                  1-2.5 
                 1.5 
                 9.5 
               
               
                 7 
                 1 
                 1 
                  1-3.5 
                 2 
                 13 
               
               
                 8 
                 1 
                 1 
                 1-4  
                 2 
                 16 
               
               
                 9 
                 2 
                 1.5 
                 1.5-4   
                 2.5 
                 20 
               
               
                 10 
                 2 
                 2 
                 1.5-5   
                 3 
                 26 
               
               
                 11 
                 2.5 
                 2.5 
                 1.5-5.5  
                 3 
                 33 
               
               
                 13 
                 2.5 
                 3 
                 2-6  
                 3.5 
                 39.5 
               
               
                 14 
                 3 
                 3.5 
                  2-6.5 
                 3.5 
                 46 
               
               
                 15 
                 3 
                 4 
                 2-7  
                 4 
                 52.5 
               
               
                 16 
                 3.5 
                 4.5 
                 2.5-7   
                 4 
                 59 
               
               
                 17 
                 3.5 
                 5 
                 2.5-7.5  
                 4.5 
                 65.5 
               
               
                 18 
                 4 
                 6 
                 2.5-8.5  
                 5 
                 79 
               
               
                 19 
                 4 
                 7 
                 3-9  
                 5 
                 92 
               
               
                 20 
                 4 
                 7.5 
                  3-9.5 
                 5.5 
                 99 
               
               
                 21 
                 5 
                 8 
                 3-10 
                 5.5 
                 105 
               
               
                 22 
                 5 
                 9 
                 3.5-10.5 
                 6 
                 118 
               
               
                 23 
                 5 
                 10 
                 3.5-11   
                 6 
                 131.5 
               
               
                 25 
                 5 
                 12 
                 4-12 
                 7 
                 157.5 
               
               
                 27 
                 6 
                 14 
                 4-13 
                 7.5 
                 184 
               
               
                 29 
                 6 
                 16 
                 4.5-13.5 
                 8 
                 210 
               
               
                 31 
                 6 
                 18 
                 4.5-14.5 
                 8.5 
                 236.5 
               
               
                 33 
                 6 
                 20 
                   5-15.5 
                 9 
                 262.5 
               
               
                 37 
                 7 
                 25 
                 5.5-17   
                 10 
                 328.5 
               
               
                 40 
                 7 
                 30 
                 6-19 
                 11 
                 394 
               
               
                 43 
                 7 
                 35 
                 6.5-21   
                 12 
                 460 
               
               
                 46 
                 7 
                 40 
                 7-22 
                 12.5 
                 525.5 
               
               
                 49 
                 8 
                 45 
                 7.5-23   
                 13 
                 591 
               
               
                 52 
                 8 
                 50 
                 7.5-24   
                 14 
                 566 
               
               
                 54 
                 8 
                 55 
                   8-25.5 
                 14.5 
                 722.5 
               
               
                 57 
                 8 
                 60 
                 8.5-26.5 
                 15 
                 788 
               
               
                 61 
                 9 
                 70 
                   9-28.5 
                 16.5 
                 920 
               
               
                 65 
                 9 
                 80 
                  10-30.5 
                 17.5 
                 1099 
               
               
                 69 
                 9 
                 90 
                 10.5-32.5  
                 18.5 
                 1182 
               
               
                   
               
             
          
         
       
     
         [0021]    It will also be understood that the sea state is often also related to an ocean current speed value. The ocean speed current value will be understood to include two components, referred to herein as an “average horizontal component” and a “wave-induced component,” also referred to herein as an “oscillating component.” The average horizontal component is a component that has an average speed relative to the earth. The wave-induced component is a rotational component that rotates once each wave period, and which is affected in magnitude by both the wave height and the wave period. As used herein, the term “wave-induced horizontal component,” or “oscillating horizontal component,” refers to a projection of the rotating wave motion of the “wave-induced component” onto a horizontal plane. 
         [0022]    Referring to  FIG. 1 , an exemplary autonomous data relay buoy  10  is shown statically floating in water  34 , without regard to waves or currents, and also without regard to any particular forces upon the exemplary autonomous data relay buoy  10  that may otherwise tend to cause the exemplary autonomous data relay buoy  10  to tilt. Forces and tilt considerations are discussed below in conjunction with  FIG. 1B . 
         [0023]    The autonomous data relay buoy  10  includes a hull  84 , which can be comprised of joined hull portions  84   a ,  84   b ,  84   c ,  84   d . The first and second hull portion  84   a ,  84   b , respectively, can be joined together in a fashion so as to form a dry compartment  28   a . To this end, there may be a seal, for example, an o-ring seal at a joint between the first and second hull portions  84   a ,  84   b.    
         [0024]    The third hull portion  84   c  can form a compartment  28   b . In some arrangements, the compartment  28   b  is sealed from the compartment  28   a , for example, with a solid boundary or floor  56 . In other arrangements, the compartment  28   b  is open to the compartment  28   a . In some arrangements, the compartment  28   b  is a dry compartment and in other arrangements, the compartment  28   b  fills partially with water once the autonomous data relay buoy  10  is deployed in the water  34 . To this end, the compartment  28   b  can include ports, of which ports  73   a ,  73   b  are but two examples. 
         [0025]    The fourth hull portion  84   d  forms a compartment  28   c . The fourth hull portion  84   d  includes ports, of which a ports  72   a ,  72   b  are but two examples, which allows compartment  28   c  to fill with water once the autonomous data relay buoy  10  is deployed in the water  34 . In some arrangements, the third hull portion  84   c  is sealed from the fourth hull portion  84   d , for example, with a solid boundary  64 . 
         [0026]    In some arrangements, the hull  84  can include a sealed hatch  86 , which can be opened for access. 
         [0027]    The autonomous data relay buoy  10  can include a diesel engine  50 . A diesel engine starter motor  50   a  is coupled to the diesel engine  50 . A starter battery  50   b  is coupled to the diesel engine starter motor  50   a . The starter battery  50   b  and the diesel engine starter motor  50   a  are configured to start the diesel engine. 
         [0028]    The autonomous data relay buoy  10  further includes an electrical generator  48  coupled to the diesel engine  50 , which is configured to generate electricity when the diesel engine  50  is running in order to generate electricity to provide a charging current to charge a storage battery  46  and also to charge the starter battery  50   b . In some arrangements, the alternator  46  is capable of providing a charging current of at least four hundred amperes at a voltage of about fifty volts, for a power of at least twenty thousand watts. In some arrangements, the storage battery  46  has a capacity of at least six thousand watt-hours. In some arrangements, the storage battery  46  has a nominal voltage of about forty-eight volts. 
         [0029]    The autonomous data relay buoy  10  further includes an electronic circuit  52  coupled to the storage battery  46  and configured to compare the battery voltage of the storage battery  46  with a battery voltage threshold. The electronic circuit  52  is also coupled to the electric starter motor  50   a  and to the diesel engine  50 . 
         [0030]    In operation, the electronic circuit  52  is configured to start the diesel engine  50  and to run the diesel engine  50  for a period of time when the battery voltage of the storage battery  46  is below the battery voltage threshold. The electronic circuit  52  is also configured to stop the diesel engine after the period of time. The period of time during which the diesel engine  50  is running is determined in accordance with at least one of the battery voltage of the storage battery  46 , the charging current flowing into the storage battery  46 , or a predetermined time value. 
         [0031]    The autonomous data relay buoy  10  also includes a diesel fuel tank  62  coupled to the diesel engine  50  with a fuel tube  88 . The diesel fuel tank  62  is configured to hold a volume of diesel fuel sufficient to run the diesel engine  50  sufficiently to maintain a full battery charge of the storage battery  46  (and of the starter battery  50   b ) for at least thirty days while supplying an average of at least three hundred fifty watts of power from the storage battery  46 . In other arrangements, the diesel fuel tank  62  is configured to hold a volume of diesel fuel sufficient to run the diesel engine  50  sufficiently to maintain a full battery charge of the storage battery  46  (and of the starter battery  50   b ) for at least sixty days while supplying an average of at least three hundred fifty watts of power from the storage battery  46 . 
         [0032]    In some arrangements, the diesel fuel tank  62  is a soft, flexible, and collapsible fuel tank. It will be understood that, for arrangements in which the space surrounding the diesel fuel tank  62  is filled with water, for example, via the ports  73   a ,  73   b , a displacement of the buoy  10  will remain substantially unchanged as diesel fuel within the diesel fuel tank  62  is expended. In other arrangements, the diesel fuel tank  62  is rigid. The diesel fuel tank  62  can be designed to prevent sloshing of diesel fuel. 
         [0033]    In some arrangements, the diesel engine  50 , the electrical alternator  48 , the electronic circuit  52 , and the storage battery  46  are selected to result in an overall efficiency corresponding to less than three hundred grains of diesel fuel per kilowatt-hour. 
         [0034]    In some arrangements, the diesel engine  50  is liquid cooled, but in a sealed (non-seawater cooled) configuration. In these arrangements, the autonomous data relay buoy  10  can include a cooling heat exchanger  70 , which can be coupled to the diesel engine  50  with cooling liquid tubes  90   a ,  90   b . The cooling heat exchanger  70  can be within the chamber  28   c , which is filled with seawater  74 . It will be apparent that the seawater  74  can provide cooling of the cooling heat exchanger  70 . 
         [0035]    In some arrangements, the autonomous data relay buoy  10  can include further electronic circuits  71   a , within a sealed enclosure  71 , which is disposed within the seawater  74 . The sealed enclosure  71  can provide cooling of the electronic circuits  71   a.    
         [0036]    In some arrangements, the diesel engine  50  is coupled to a floor  58  with vibration mounts, e.g., the vibration mount  60 . This arrangement has particular advantages, which will be apparent from discussion below in conjunction with  FIGS. 2 and 2A , when the autonomous data relay buoy  10  is used in clandestine applications, or in which the autonomous data relay buoy  10  is used in conjunction with acoustic sensors in the water  34 . 
         [0037]    The autonomous data relay buoy  10  can include a flotation collar  32  configured to keep the autonomous data relay buoy  10  at a desired depth in the water  34  and also to help maintain the autonomous data relay buoy  10  at a desired attitude in the water  34 . A shape of the flotation collar  32  can be selected to provide a particular drag and/or to provide a particular position of a center of drag, discussed more fully below in conjunction with  FIG. 1B . 
         [0038]    As will be understood, the diesel engine  50  needs air for combustion. To this end, the autonomous data relay buoy  10  can include a mast  18  with an inner air tube  22 . In some embodiments, the mast  18  is made of fiberglass. The air tube  22  can be coupled to a baffle  12  at a distal end of the air tube  22 . The baffle  12  can include air passages, e.g., the air passage  16 . The baffle  12  is configured to keep water out of the air tube  22 , but to allow air to enter the air tube  22 . An air valve  14  can also be disposed at the distal end of the air tube  22 . 
         [0039]    In operation, the air valve  14  can be opened by electrical actuation by the electronic circuit  52  when the diesel engine  50  is running, and the air valve  14  can be closed by electrical actuation by the electronic circuit  52  when the diesel engine  50  is not running. The electronic circuit  52  is described more fully below in conjunction with  FIG. 3 . 
         [0040]    In other arrangements, the air valve  14  is mechanically actuated to open and close, for example, by a vacuum created in the air tube  22 , so as to open when the diesel engine is running and attempting to draw combustion air, and so as to close when there is no vacuum. In other arrangements, there is no air valve  14 . 
         [0041]    At the other end, the proximal end, the air tube  22  can couple to an air-water separator  24  having an air escape passage  26  and a water drain  30 . The air escape passage  26  allows air to enter the chamber  28   a  for use in combustion by the diesel engine  50 . Any water that enters the air tube  22  leaves the chamber  28   a  by way of the water drain  30 . 
         [0042]    The diesel engine  50  can couple to an exhaust assembly  42  having a muffler  38 , two gas valves  40   a ,  40   b , and two baffles  44   a ,  44   b . The two baffles  44   a ,  44   b  can be disposed on opposite sides of the buoy as shown so that one of the baffles will be out of the water no matter which way the buoy  10  tilts. The baffles  44   a ,  44   b  can include gas passages  44   a ,  44   b , respectively. Each one of the baffles  44   a ,  44   b  is configured to keep some water out of the exhaust assembly  42 , but to allow exhaust gas from the diesel engine  50  to escape the exhaust assembly  42 . 
         [0043]    In operation, as described above for the air valve, the gas valves  40   a ,  40   b  can be opened by electrical actuation by the electronic circuit  52  when the diesel engine  50  is running, and the gas valves  40   a ,  40   b  can be closed by electrical actuation by the electronic circuit  52  when the diesel engine  50  is not running. In other arrangements, there is but one exhaust baffle  44   a  and but one gas valve  40   a . In other arrangements, there is no gas valve. 
         [0044]    In other arrangements, the gas valves  40   a ,  40   b  are mechanically actuated to open and close, for example, by a pressure created in the exhaust assembly  42 , so as to open when the diesel engine is running and attempting to exhaust combustion gasses, and so as to close when there is no pressure. 
         [0045]    The mast  18  can also include a radio frequency antenna  20  insulated from the hull  84  by an insulator ring  36 . The hull  84  and the water  34  form a ground plane for the antenna  20 . 
         [0046]    The antenna  20  can be coupled to the electronic circuit  52  and/or to the electronic circuit  71   a  as described more fully below in conjunction with  FIG. 3 . 
         [0047]    The autonomous data relay buoy  10  can include a tether assembly  76  having a semi-rigid strain relief section  78  and a flexible section  80 . The flexible section  80  can be, or can otherwise contain, a signal cable, for example, a fiber optic cable or an electrical cable, which can couple to the electronic circuit  52  and/or to the electronic circuit  71   a.    
         [0048]    Floats  82   a - 82   d  can be coupled to the flexible section  80 . It will become apparent from discussion below in conjunction with  FIG. 1B  that the floats  82   a - 82   b  can cause the flexible section  80  to be aligned in a desired way in the water  34 , and therefore, any force along an axis of the flexible section  80  will tend to tilt the autonomous data relay buoy  10  less. 
         [0049]    In some alternate embodiments, the diesel engine  50  can be another type of engine, for example, a gasoline engine and the fuel in the tank  62  can be another type of fuel, for example, gasoline. In some alternate embodiments, the starter battery  50   b  and the storage battery  46  can be the same battery used to both start the engine  50  and power the rest of the buoy  10 . In some alternate embodiments, the chamber  28   b  and the associated fuel tank  62  can be below the virtual mass chamber  28   c.    
         [0050]    Referring now to  FIG. 1A , a top view of the autonomous data relay buoy  10  is indicative of a round hull  84 , a round flotation collar  32 , a round mast  18 , a round baffle  12 , and a round insulator ring  36 . 
         [0051]    Referring now to  FIG. 1B , the autonomous data relay buoy  10  is shown in outline form. The autonomous data relay buoy  10  has a central vertical axis  10   a . A center of buoyancy, CB, a dry center of mass, CM, and a center of water drag, CD, are disposed generally along the central vertical axis  10   a , however, they need not be exactly on the axis  10   a . The autonomous data relay buoy  10  also has a virtual center of mass, CM′, also generally along the central vertical axis  10   a , resulting from the seawater  74  being within the chamber  28   c  once the autonomous data relay buoy  10  is deployed in the water  34 . 
         [0052]    In general, it is desirable that the autonomous data relay buoy  10  maintains an orientation in the water  34  such that the central vertical axis  10   a  of the autonomous data relay buoy  10  maintains a bounded range of angles near to vertical relative to the earth. If the autonomous data relay buoy  10  were to tilt greatly, reception of radio signals generated by the autonomous data relay buoy  10  might be greatly degraded. The degradation can occur due to two effects. 
         [0053]    A first effect is associated with a transmitting beampattern (not shown) of the antenna  20  within the mast  18 . In some arrangements, the transmitting beampattern has a maximum power near to a direction perpendicular to the central vertical axis  10   a  and a null near to a direction upward along the central vertical axis. Dynamic movement of the antenna  20  tends to result in power fluctuations of the received radio signal at a receiving station due to movement of the transmitting beampattern relative to the receiving station. 
         [0054]    A second effect is due to changes in impedance of the antenna  20  as the angle of the antenna  20  changes relative to its associated ground plane. As described above, the ground plane associated with the antenna  20  is comprised of effects from the hull  84  and from the water  34 . Impedance fluctuations may not only cause power fluctuations in the signal transmitted by the antenna  20 , but can also cause impedance mismatches with the electronics circuit  52  ( FIG. 1 ) used to generate the transmitted signal. The impedance mismatches can cause a wide variety of effects, including, but not limited to, changes in fundamental frequency of the transmitted signal, generation of spurious frequencies (spurs) within the transmitted signal, unwanted oscillations of the transmitted signal, and overheating of the electronics circuit  52  and/or  71   a.    
         [0055]    Static stability of the autonomous data relay buoy  10  can be considered under two conditions. Under a first static condition, the ocean current  34   a  has both a zero average horizontal component and a zero oscillating component (no wave motion), i.e., there is no current  34   a , and no waves. Under this condition, it will be well recognized that an object floating in water achieves an orientation such that the center of mass is below the center of buoyancy. If the reverse were true, if the center of buoyancy were below the center of mass, the object would flip over. In essence, there is an upward force acting upon the center of buoyancy, CB, and there is a downward force acting upon the center of mass, CM, which tends to keep the center of mass, CM, directly below the center of buoyancy, CB. Any static tilt of the autonomous data relay buoy  10  results in a torque of the two forces, which tends to statically un-tilt the autonomous data relay buoy  10 . It is desirable that the center of mass, CM, and the center of buoyancy, CB, be widely spaced. 
         [0056]    Under a second static condition, when the ocean current  34   a  has a non-zero average horizontal component but a zero oscillating component (no wave motion), a static horizontal force acts upon the center of drag, CD, in addition to the two above-described forces. The force acting upon the center of drag, CD, tends to tilt the autonomous data relay buoy  10  if the center of drag, CD, is not at the position of the center of buoyancy, CB, as is shown. In this case, where the center of drag, CD, is below the center or buoyancy, CB, the ocean current  34   a  would tend to tilt the autonomous data relay buoy  10 , to the right. If the center of drag, CD, were above the center or buoyancy, CB, the ocean current  34   a  would tend to tilt the autonomous data relay buoy  10  to the left. If the center of drag, CD, were coincident with the center of buoyancy, CB, the autonomous data relay buoy  10  would not tilt in the presence of the water drag. In some applications, it is desirable to design the autonomous data relay buoy  10  with a center of drag, CD, coincident with the center of buoyancy, CB. However, the positions of the center of buoyancy, CB, and the center of drag, CD, can also be selected in other ways. 
         [0057]    As described above, a position along the central vertical axis  10   a  of the center of drag, CD, can be influence by a shape of the flotation ring  32 . However, it will be recognized that, when the autonomous data relay buoy  10  tilts in the presence of the drag, the center of drag, CD, tends to move to a new position, a new position that may not be along the central vertical axis  10   a . The center of drag, CD, can move greatly with only a small amount of tilt. Thus, predicting the actual orientation of the autonomous data relay buoy  10  under drag conditions becomes a difficult task. Furthermore, it will be recognized from discussion below in conjunction with  FIGS. 2 and 2A , that an angle relative to the buoy  10  of the force represented by the line  92  can change according to a magnitude of the force (generated by a signal/tether line). Therefore, the point  96  can also move along or about the central vertical axis  10   a . Thus, prediction of the static and dynamic motion of the buoy  10  under a variety of current and wave conditions, and selection of design characteristics, including, but not limited to, static positions of the center of buoyancy, CB, center of drag, CD, center of mass, CM, center of virtual mass, CM′, and the point  96 , in order to achieve a stable buoy can be a difficult problem. 
         [0058]    Computer models exist that can assist in the prediction of buoy behaviors under the static conditions described above, and also under dynamic conditions described above and below. For example, one computer program that can be used is Orcaflex from Orcina, Ltd. 
         [0059]    With regard to dynamic motion of the autonomous data relay buoy  10  in the presence the current  34   a  having both an average horizontal component and an oscillating component, the virtual center of mass. CM′, affects the dynamic motion. Because the chamber  28   c  is below the center of mass, CM, the virtual center of mass, CM′, is below the center of mass, CM. The position of the virtual center of mass, CM′, does not affect the above two case of static stability of the autonomous data relay buoy  10 . However, the virtual center of mass, CM′, can influence dynamic behavior of the autonomous data relay buoy  10  when subjected to oscillating wave motion. In effect, the water  74  within the chamber  28   c  adds inertia to the autonomous data relay buoy  10 , inertia below the center of mass, CM, resulting in the autonomous data relay buoy  10  being less influenced by the oscillating horizontal component of the current  34   a , and therefore, resulting in less tilting back and forth in the presence of waves. 
         [0060]    Dashed lines are used to show hypothetical and separate static forces  92  and  94  acting upon the tether assembly  76  at different times, which may be induced by the tether line  80  ( FIG. 1 ) to which the autonomous data relay buoy  10  is coupled. The dashed line  92  is indicative of a desired force direction, the direction of which is influenced by the floats  82   a - 82   d  of  FIG. 1 . The dashed line  92  intersects the central vertical axis  10   a  at a point  96 . The force  92  acts as a force at the point  96 . The dashed line  94  is indicative of a much less desirable force direction, which is more like a force direction that may be achieved without having the floats  82   a - 82   d  of  FIG. 1 . The force  94  acts as a force at a point  98 . 
         [0061]    If the point  96  were coincident with the center of buoyancy, CB, the force  92  would not tend to tilt the autonomous data relay buoy  10 . However, since the point  96  is below the center of buoyancy, CB, the force  92  tends to tilt the autonomous data relay buoy  10  to the left. If the point  96  were above the center of buoyancy, CB, the force  92  would tend to tilt the autonomous data relay buoy  10  to the right. Thus, in some applications, it is desirable that the force  92  aligns in such a way with the autonomous data relay buoy  10  that the point  96  is coincident with the center of buoyancy, CB. However, the position of the point  96  can be selected in other ways as well. 
         [0062]    In some arrangements, it is possible to design the autonomous data relay buoy  10  such that the center of mass, CM, is not aligned on the central vertical axis  10   a . For example, in  FIG. 1B , the center of mass, CM, can be to the right of the right of the center of buoyancy, CB, which will tend to make the autonomous data relay buoy  10  tilt to the right by a predetermined number of degrees when the autonomous data relay buoy  10  is experiencing the first static conditions, i.e., no water current  32  and no wave motion. For example, in some arrangements, the predetermined number of degrees is about ten degrees. 
         [0063]    In other arrangements, the autonomous data relay buoy  10  is designed such that the center of mass is to the left of the right of the center of buoyancy, CB, which will tend to make the autonomous data relay buoy  10  tilt to the left by a predetermined number of degrees when the autonomous data relay buoy  10  is experiencing the first static conditions. For example, in these arrangements, the predetermined number of degrees is about ten degrees. 
         [0064]    In either case, the predetermined angle that the autonomous data relay buoy  10  is designed to achieve under static conditions can serve to offset a tendency for the autonomous data relay buoy  10  to tilt in the opposite direction when experiencing a force along the line  92 . This arrangement will be descried again in conjunction with  FIGS. 2 and 2A . 
         [0065]    Referring now to  FIG. 2 , the autonomous data relay buoy  10  is shown deployed in water  102  and is coupled as a component of an acoustic system  100 . The autonomous data relay buoy  10  experiences a relatively large current  104  with a relatively high average horizontal component. Waves and oscillating components of the current  104  are not shown for clarity. 
         [0066]    Signals carried to (and in some embodiments, from) the autonomous data relay buoy  10  by the signal cable  80  are carried also via a signal cable  106  through intermediate floats  108   a ,  108   b , and via a rotating coupling  110 , and via a signal cable  114  to an anchor  116 . 
         [0067]    The system  100  can include one or more acoustic arrays, of which arrays  120   a ,  120   b  are but two examples. The arrays  120   a ,  120   b  are shown to be vertical arrays, though in other arrangements, the arrays  120   a ,  120   b  are horizontally disposed on an ocean bottom  128 . 
         [0068]    Each array, for example, the array  120   a , includes a plurality of hydrophones  124 , and for vertical arrangements, a float  122 . The array  120   a  couples to an array cable  118  via a node  126 . The node  126  can include a battery to power the array  120   a , and transmission electronics within the node  126  to communicated hydrophone signals along a cable  118  to the anchor and up the signal cable  114 . 
         [0069]    Under the relatively high current  104 , by design method described above in conjunction with  FIG. 1B , under this particular static condition, the autonomous data relay buoy  10  can achieve an orientation wherein the vertical central axis  10   a  of the autonomous data relay buoy  10  is nearly vertical. This orientation is achieved in the presence of a relatively high tension in the signal cable  106 , and a particular angle achieved by the floats  82   a - 82   d.    
         [0070]    Referring now to  FIG. 2A , the autonomous data relay buoy  10  is again shown deployed in the water  102  and is coupled as a component of the acoustic system  100 . However, in this case, the autonomous data relay buoy  10  experiences a relatively small current  152  with a relatively small average horizontal component. Waves and oscillating components of the current  104  are not shown for clarity. This case is like the first static case considered above. 
         [0071]    Under the relatively low current  152 , by design method described above in conjunction with  FIG. 1B , under this particular static condition, the autonomous data relay buoy  10  can achieve an orientation wherein the vertical central axis  10   a  of the autonomous data relay buoy  10  is tilted by an angle  154 . This orientation is achieved in the presence of a relatively low (or zero) tension in the signal cable  106 , and a particular angle achieved by the floats  82   a - 82   d  when under this tension. As described above in conjunction with  FIG. 1B , in one particular arrangement, the buoy  10  is designed to achieve an angle  154  of about ten degrees under the indicated first static condition, i.e. when experiencing low or zero current and low or zero wave heights. However, the buoy  10  can be designed to achieve other angles, for example, an angle in a range of about five degrees to about fifteen degrees, under this condition. 
         [0072]    Now taking into account wave motions (not shown) and dynamic behavior of the autonomous data relay buoy  10 , particularly in view of the virtual mass provided by the flooded chamber  28   c  ( FIG. 1B ), the autonomous data relay buoy  10  will tend to stay relatively stable and essential ride the waves, substantially maintaining its static case orientations in the presence of the waves. 
         [0073]    In one particular embodiment, the virtual mass is sized and positioned, and the autonomous data relay buoy  10  is otherwise designed, to maintain an orientation such that the central vertical axis  10   a  is within plus or minus twenty degrees of vertical under sea states of zero through four. 
         [0074]    Referring now to  FIG. 3 , an electronic system  200  includes a battery assembly  210 , which can be the same as or similar to the storage battery  46  of  FIG. 1 . The battery assembly  210  is coupled to an alternator  212 , which can be the same as or similar to the alternator  48  of  FIG. 1 . The alternator  212  is coupled to a diesel engine  226 , which can be the same as or similar to the diesel engine  50  of  FIG. 1 . The diesel engine  226  is coupled to a starter battery  232 , which can be the same as or similar to the starter battery  50   b  of  FIG. 1 . The electronic system  200  includes an air intake valve  222 , which can be the same as or similar to the air valve  14  of  FIG. 1 , and an exhaust valve  224 , which can be the same as or similar to the gas valves  40   a ,  40   b  of  FIG. 1 . The electronic system  200  further includes an antenna  206 , which can be the same as or similar to the antenna  20  of  FIG. 1 , and electronics  218 ,  202 , and  204 , all of which together can be the same as or similar to the electronic circuits  52 ,  71   a  of  FIG. 1 . 
         [0075]    Electronics  218  includes a diesel controller  220 , which is configured to control the air intake vale  222  and the exhaust valve  224 , to close the valves when the diesel engine  226  is not running and to open the valves when the diesel engine  226  is running. 
         [0076]    The diesel controller  220  is also configured to sense a voltage associated with the battery assembly  210 , and if the voltage is too low, i.e., below a battery voltage threshold, the diesel controller  220  is configured to start the diesel engine  226 , thereby causing the alternator  212  to generate AC electricity, which is converted to DC electricity by a rectifier  214  and a filter  216  in order to charge the battery assembly  210  and the starter batter  232 . 
         [0077]    The diesel controller  220  is also configured to stop the diesel engine  226  after a period of time by way of switches  230 . In some embodiments, the period of time can be a predetermined period of time, for example one hour. In other embodiments, the period of time can end when a charging current being fed to the battery assembly  210  reaches a predetermined value. In still other embodiments, the period of time can end when a voltage associated with the battery assembly  210  reaches a predetermined voltage. 
         [0078]    Data  208  is received by the electronic system  200  at an input coupling, which can, in some arrangements be a fiber-optic coupling to receive a fiber-optic cable, for example the cable  80  of  FIG. 1 . A processor  202   a  is coupled to receive the data  208  and to provide the data to a radio  202   b  for transmission by the antenna  206  via a tuning unit  204 . It will be understood that the tuning unit  204  operates to match an output impedance of the radio  202   b  with an impedance of the antenna  206 , and also to electronically isolate the radio  202   b  from the antenna  206 , particularly in the event of variations in the impedance of the antenna  206 . Variations of antenna impedance are described above. 
         [0079]    In some arrangements, the electronics  202  is within the electronics enclosure  71  of  FIG. 1  and receives seawater cooling. 
         [0080]    In some arrangements, the diesel controller  220  is coupled to the battery assembly  210  with a standard electronic interface, for example, an RS-485 interface. In some arrangements, the diesel controller  220  is coupled to the processor  202   a  with a standard electronic interface, for example, an RS-232 and/or Ethernet interface. 
         [0081]    All references cited herein are hereby incorporated herein by reference in their entirety. 
         [0082]    Having described preferred embodiments of the invention, it will now become apparent to one of ordinary skill in the art that other embodiments incorporating their concepts may be used. It is felt therefore that these embodiments should not be limited to disclosed embodiments, but rather should be limited only by the spirit and scope of the appended claims.