Abstract:
A system is provided which automatically calibrates a marine fouling prevention system. It responds to movements between fresh and saltwater bodies of water, detects damage to the hull or other submerged surface, and responds to the use of the fouling prevention system with different sizes of marine vessels.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention is generally related to a system for inhibiting fouling of an underwater surface and, more particularly, to a system which is capable of self-calibration in order to select appropriate voltages and currents for its operation, to determine the type of water in which the surfaces are submerged, and to diagnose faults or damage in the underwater surfaces. 
   2. Description of the Prior Art 
   Many different systems are well known to those skilled in the art of inhibiting the fouling of underwater surfaces. Depending on the type of water in which the surfaces are submerged or partially submerged, the fouling can consist of algae, barnacles, zebra muscles, or other types of underwater organisms that tend to grow on and cling to submerged surfaces. The submerged surfaces can be portions of a hull of a marine vessel or other submerged components, such as grates for underwater conduits. 
   U.S. Pat. No. 948,355, which issued to Tatro et al. on Feb. 8, 1910, describes a system that provides anodes and cathodes on a ship and passes electric current through these two poles. The circuit is completed through seawater near the ship and chlorine is liberated. The chlorine kills the barnacles near the ship and prevents barnacles from fouling the submerged surface of the ship. 
   U.S. Pat. No. 1,021,734, which issued to Delius et al. on Mar. 26, 1912, is intended for use with a ship that has a metallic surface. An electric generator or other source of current is used and a switch is used to periodically change the circuit of an anode and a cathode which is completed through water surrounding the ship. Chlorine is produced and the fouling of the submerged surface of the ship is inhibited. 
   U.S. Pat. No. 3,625,852, which issued to Anderson on Dec. 7, 1971, describes a marine antifouling system. The antifouling system is intended for use with a boat or ship having a keel and sides diverging upwardly therefrom. A pair of laterally spaced elongated anode electrode components are mounted externally on one side of the hull substantially adjacent the keel and lengthwise thereof. An elongated cathode electrode component is mounted externally on the lengthwise of the keel in spaced relationship between the anode electrode components. A source of electric current energizes the anode electrode components with a positive potential and the cathode electrode component with a negative potential to produce various chemicals, such as chlorine, which inhibits fouling of the surface of the ship. 
   U.S. Pat. No. 6,173,669, which issued to Staerzl on Jan. 16, 2001, discloses an apparatus and method for inhibiting fouling of an underwater surface. Current is caused to flow through seawater in which two conductive surfaces are submerged or partially submerged. A monitor measures the current flowing from one of the two surfaces to the other in order to assure that no leakage of current of substantial quantity exists. By alternating current direction between the two surfaces, both surfaces can be provided with sufficient chlorine gas bubbles to prevent marine growth from attaching to the surfaces. 
   U.S. Pat. No. 6,209,472, which issued to Staerzl on Apr. 3, 2001, discloses an apparatus and method for inhibiting fouling of an underwater surface. The system provides an electric current generator which causes an electric current to flow proximate the underwater surface. A source of electric power causes a flow of current which passes from the underwater surface through water surrounding the surface or in contact with the surface. Gas is liberated from seawater and inhibits the growth of barnacles and other microorganisms on the submerged surfaces. 
   U.S. Pat. No. 6,547,952, which issued to Staerzl on Apr. 15, 2003, discloses a system for inhibiting fouling of an underwater surface. Ambient temperature cure glass (ATC glass) provides a covalent bond on an electrically conductive surface, such as nickel-bearing paint. In this way, boat hulls, submerged portions of outboard motors, and submerged portions of sterndrive systems can be protected effectively from the growth of marine organisms, such as barnacles. The protective coating of glass inhibits the migration of metal ions from the electrically conductive surface into the seawater and therefore inhibits corrosive degradation as a result of galvanic action. 
   The patents described above are hereby expressly incorporated by reference in the description of the present invention. 
   As marine surfaces, such as the surfaces of a boat hull, experience different conditions (e.g. a move from saltwater to freshwater or vice versa), it would be significantly beneficial if an automatic system could be provided to make appropriate adjustments in the operation of the antifouling system. In addition, it would be significantly beneficial if an automatic calibration system could be provided for this type of antifouling system. Furthermore, a system that could detect damage to an antifouling surface would provide a significant benefit to a system for preventing marine fouling of that surface. 
   SUMMARY OF THE INVENTION 
   A method for controlling a marine fouling prevention system, in accordance with a preferred embodiment of the present invention, comprises the steps of providing the first and second submerged surfaces and a source of electrical power. It also provides the step of connecting the first and second surfaces to the source of electrical power and causing a magnitude of current to flow between the first and second surfaces for a preselected period of time. It also includes the step of measuring a voltage potential between the first and second surfaces and determining an operating parameter of the marine fouling prevention system as a function of the voltage. 
   The method of the present invention can further comprise the step of calculating an operating current for the marine fouling prevention system as a function of the voltage potential, the magnitude of current, and a preselected target operating voltage. The operating current is the operating parameter of the marine fouling prevention system in this type of embodiment. The present invention can further comprise the step of controlling a subsequent operation of the marine fouling prevention system by regulating a current between the first and second surfaces to be generally equal to the operating current which is determined as a function of the measured voltage potential and a desired operating voltage potential. The first surface can be a starboard side of the hull of a marine vessel and the second surface can be the port side of a hull of the marine vessel. The operating parameter can be representative of the type of water in which the marine fouling prevention system is operating. The voltage potential can be indicative of a fault condition related to the marine fouling prevention system. 
   A preferred embodiment of the present invention can further comprise comparing the voltage potential to a threshold voltage potential and then determining that the marine fouling prevention system is damaged if the voltage potential is less than the threshold voltage potential. In certain embodiments of the present invention, it can further comprise the steps of comparing the operating current to a first threshold operating current and replacing the operating current with a first default operating current value when the operating current is less than the first threshold operating current. The present invention can further comprise the step of comparing the operating current to a second threshold operating current and replacing the operating current with a second default operating current when the operating current is greater than the second threshold operating current. 
   The magnitude of current used in a preferred embodiment of the present invention can be between 0.5 amperes and 1.5 amperes and, in a particularly preferred embodiment, is generally equal to 1.0 amperes. The preselected period of time in a preferred embodiment of the present invention can be between five minutes and fifteen minutes and, in a particularly preferred embodiment, is generally equal to ten minutes. Alternatively, the preselected period of time can be actively determined by monitoring the rate of change of the voltage potential while the magnitude of current is flowing between the first and second surfaces during the calibration procedure. In other words, as the rate of change of voltage decreases, the system is becoming polarized and polarization of the system can allow the voltage potential to be measured and used to calculate the operating parameter, such as the operating current, without the need for waiting for a specific period of time to elapse. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more fully and completely understood from a reading of the description of the preferred embodiment in conjunction with the drawings, in which: 
       FIGS. 1 and 2  are schematic representations of two systems that can be used to prevent fouling of a submerged surface; 
       FIG. 3  is a circuit that can be used in conjunction with one embodiment of the present invention; and 
       FIG. 4  is a flowchart of a system used to perform the features of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Throughout the description of the preferred embodiment of the present invention, like components will be identified by like reference numerals. 
     FIG. 1  is a schematic representation of a marine vessel  10  with a first surface  12  and a second surface  14  which are partially submerged below the surface  18  of a body of water. The first and second surfaces,  12  and  14 , can be the port and starboard surfaces of the hull of the marine vessel. These first and second surfaces are electrically conductive, either by manufacturing the hull from electrically conductive materials or providing an electrically conductive coating on the surface of the hull. The first and second surfaces are insulated from each other by a nonconductive keel member  20 . Two electrodes,  22  and  24 , are symbolically illustrated as providing an electrical connection between the first and second surfaces,  12  and  14 , and a controller  30  which is used to control the voltages of the first and second surfaces. The controller  30  is connected to a power source, such as a battery  32 , in order to distribute electric current to the first and second surfaces in a manner which is generally similar to the techniques described in the patents cited above. This type of system is generally similar to the devices described in U.S. Pat. Nos. 6,173,669 and 6,209,472. 
     FIG. 2  illustrates a marine fouling prevention system that is not associated with the hull of a marine vessel  10  such as that described in conjunction with  FIG. 1 . Instead, the controller  30  and battery  32  are associated with a grate  40  and an associated conductive surface  42 . As described in the patents cited above, the submerged surfaces of the grate  40  and the other conductive surface  42  can be used to produce chlorine gas bubbles on the surface of a device which is intended to be protected by the fouling prevention system, such as the grate  40 . 
     FIG. 3  is a schematic representation of a circuit that can be used to perform the processes of a preferred embodiment of the present invention. Various components are identified in  FIG. 3  and described in Table I below. 
   
     
       
             
             
             
           
         
             
                 
                 
             
             
                 
               REFERENCE 
               TYPE 
             
             
                 
                 
             
           
           
             
                 
               R1 
                1000 kΩ 
             
             
                 
               R1A 
                 100 kΩ 
             
             
                 
               R2 
                45.3 kΩ 
             
             
                 
               R3 
                 100 kΩ 
             
             
                 
               R4 
                45.3 kΩ 
             
             
                 
               R5 
                  1 kΩ 
             
             
                 
               R6 
                  1 kΩ 
             
             
                 
               R7 (Sense) 
                0.1 Ω 
             
             
                 
               R8 
                 20 kΩ 
             
             
                 
               R9 
                 10 kΩ 
             
             
                 
               R10 
                1.1 kΩ 
             
             
                 
               R11 
                 100 kΩ 
             
             
                 
               R12 
                45.3 kΩ 
             
             
                 
               R13 
                 100 kΩ 
             
             
                 
               R14 
                 100 kΩ 
             
             
                 
               R15 
                 100 kΩ 
             
             
                 
               R16 
                 100 kΩ 
             
             
                 
               R17 
                 100 kΩ 
             
             
                 
               R18 
                 100 kΩ 
             
             
                 
               R19 
                 100 kΩ 
             
             
                 
               R20 
                 10 kΩ 
             
             
                 
               R21 
                 10 kΩ 
             
             
                 
               R22 
                 10 kΩ 
             
             
                 
               R22-PTC 
               0.011 Ω 
             
             
                 
               C1 
                 10 μF 
             
             
                 
               C2 
                 10 μF 
             
             
                 
               C3 
                 10 μF 
             
             
                 
               C4 
                 10 μF 
             
             
                 
               C5 
                 10 μF 
             
             
                 
               C6 
                 10 μF 
             
             
                 
               C7 
                 10 μF 
             
             
                 
               C8 
               0.001 μF 
             
             
                 
               C9 
               0.001 μF 
             
             
                 
               C10 
               0.001 μF 
             
             
                 
               C11 
               0.001 μF 
             
             
                 
               C12 
               0.001 μF 
             
             
                 
               C13 
               0.001 μF 
             
             
                 
               C14 
               0.001 μF 
             
             
                 
               C1A 
                0.1 μF 
             
             
                 
                 
             
           
        
       
     
   
   Electrical circuits which are suitable for providing a current flow between submerged surfaces are described in the patents cited above. More specifically, U.S. Pat. No. 6,173,669 illustrates such a circuit in its FIG. 10. U.S. Pat. No. 6,209,472 describes another circuit suitable for these purposes in conjunction with its FIG. 9. 
     FIG. 3  shows a circuit that is particularly suited for use in conjunction with a preferred embodiment of the present invention. Components U 2  and U 3  are used in conjunction with components Q 1  and Q 2  to form an H-bridge circuit which can alternate the directions of current flow between two submerged surfaces, such as the port and starboard sides of a marine vessel as identified by reference numerals  12  and  14  in  FIG. 1 . The points in the circuit of  FIG. 3  identified by reference numerals  22  and  24  represent the electrodes that can be connected to those two submerged surfaces. The circuit shown in  FIG. 3  is particularly suited for use in an application of the present invention in conjunction with port and starboard sides of a marine vessel hull. The components identified as R 3 , C 3 , R 4 , C 4 , and D 4  provide a filter for the starboard side of the vessel when the microprocessor U 5  reads the resulting voltage during a calibration procedure. The components identified as C 6 , R 11 , C 7 , R 12 , and D 5  perform a similar filtering function in conjunction with the port side electrode  22 . An amplifier associated with the microprocessor U 5  and used during the measurement of a voltage potential between the first and second surfaces, comprises the component identified as U 4  in  FIG. 3  and the components identified as R 8 , C 5 , R 10 , R 9 , and D 6 . The battery  32  is represented in  FIG. 3  and is associated with a resetable fuse which is identified as R 22 . The microprocessor U 5  controls the current flowing through the water between the first and second surfaces (i.e. between electrodes  22  and  24 ) and also controls messages which are provided on a liquid crystal display  60 . Noise filters are provided for the connections between the liquid crystal display  60  and the microprocessor U 5 . As shown in  FIG. 3 , these filters comprise capacitors C 8 –C 14  and resistors R 13 –R 19 . A five volt voltage supply component U 1  is connected to the LCD  60 . 
   With continued reference to  FIG. 3 , a switch  62  is provided to allow an operator to request certain actions to be performed. A single closure of the switch  62  is recognized by the microprocessor U 5  as a request to reset the system. Three consecutives closures of the switch  62  signifies that the operator wishes to perform a calibration procedure. The components identified as R 20 , R 1 A, and C 1 A assure that a single pulse is received for each closure of the switch  62 . 
   In  FIG. 3 , resistor R 7  is a sense resistor that allows the microprocessor to determine the magnitude of current flowing between the first and second surfaces,  12  and  14 , and regulate to a desired magnitude of current. After the first and second surfaces initially become polarized and the current flow is stabilized, a voltage potential can be measured to determine the voltage associated with that preselected magnitude of current, such as 1.0 amperes. The method of the present invention will be described in greater detail below. 
   In  FIG. 3 , the Schottky diodes, D 4  and D 5 , the Zenor diodes, D 7  and D 8 , and the other known components illustrated in  FIG. 3  perform functions that are well known to those skilled in the art and will not be described in detail herein. Similarly, the high-side drivers, U 2  and U 3 , and the low-side drivers, Q 1  and Q 2 , are well known to those skilled in the art and will not be described in detail herein. The microprocessor U 5  can be one which is available in commercial quantities and identified as PIC16F88 or an equivalent device. Similarly, the liquid crystal display (LCD)  60  can typically be a sixteen-by-two display device or any equivalent component. 
     FIG. 4  shows a flowchart that can be used in conjunction with the present invention. It would typically be performed by a microprocessor such as the one identified as U 5  in  FIG. 3 . Following an initialization step, at functional block  101 , the program determines whether or not a calibration value already exists, at functional block  102 . The calibration value is a magnitude of current that has been determined to require a certain voltage magnitude between the first and second surfaces of the boat hull. If no calibration has been performed, or if a new calibration has been determined to be necessary, the value will be equal to zero. At functional block  103 , the magnitude of this value is interrogated and, if it is higher than zero, the antifouling program described in the cited patents shown above, will be run. This is represented at functional block  104 . However, if the calibration value is equal to zero, a calibration procedure is performed. This begins at functional block  105  by setting a hull current equal to approximately one ampere. This current is maintained for a preselected period of time, such as ten minutes, to allow polarization to occur and then a voltage potential is read between the port and starboard electrodes,  22  and  24 . Functional block  106  illustrates the ten minute time period and functional block  107  represents the step of reading the voltage between the port and starboard surfaces. At this point, the hull current is turned off at functional block  108 . The voltage potential measured between the first and second surfaces,  12  and  14 , is later used to calculate an operating current that will be used as a calibration value for future operation of the fouling prevention system. It has been determined empirically that a voltage of approximately 3.6 volts is desirable for adequate prevention of marine fouling on the surfaces. The operating current is calculated, as described in functional block  109 , by scaling the one ampere calibration current by the ratio of the voltage potential measured during calibration and a preselected magnitude of 3.6 volts. If the operating current is calculated as being less than two amperes, as determined at functional block  110 , the operating current is set to two amperes as described at functional block  111 . If the operating current has been calculated to be greater than five amperes as determined at functional block  112 , the current is set to five amperes as a default value at functional block  113 . In other words, calculated operating currents which are not between two amperes and five amperes are set to default conditions in order to optimize the operation of the fouling prevention system. These values are then stored in the memory of the microprocessor U 5 , as described at functional block  114 . 
   With continued reference to  FIG. 4 , the running of the fouling prevention program at functional block  104  may result in a voltage potential between the electrodes,  22  and  24 , which is less than two volts. If that occurs, as determined at functional block  116 , the calibration procedure is run automatically by beginning at functional block  105 . If the hull voltage potential is not less than two volts, it is interrogated at functional block  117  to determine whether it is less than 2.5 volts. If it is not less than 2.5 volts, the program proceeds to functional block  114 . If it is less than 2.5 volts, an alarm condition is provided to the liquid crystal display  60 , at functional block  118 , which indicates that the gel coat surface on one of the first and second surfaces may be damaged. 
   With continued reference to  FIG. 4 , functional block  111  typically is activated when the hull is calibrated in freshwater. Functional block  113  is typically activated when the hull is either experiencing an electrical shorted condition or the surface area is too large for the controller being used. Currents calculated at functional block  109  which are greater than two amps typically indicate that the calibration has been performed in saltwater conditions. 
   The method of the present invention performs several valuable procedures. First, it allows the system shown in  FIG. 3  to be calibrated automatically for many different sizes of hulls. Since the area of the hull surface can vary significantly from one boat to another and variation in the area will determine the voltage needed to provide a preselected current flow between the first and second surfaces, the automatic calibration provided by the present invention avoids the need for special systems to be devised for use with each boat of varying size. In addition, the calibration automatically accounts for the vessel being operated in freshwater or saltwater. Furthermore, the present invention can determine whether or not damage has occurred to the gel coat surface of the hull. 
   Although it is intended that the present invention be used to calibrate the system shown in  FIG. 3  when first installed on a boat, the calibration can also be run when the boat is moved from saltwater to freshwater or vice versa. Also, as discussed above, the operation of the present invention will detect damage to a hull surface which affects the relationship between the voltage potential between the first and second surfaces and the current flowing through the water between the first and second surfaces. 
   Although the present invention has been described in terms of the port and starboard surfaces of a boat hull, it should be understood that the calibration procedures can be used when an antifouling system is used in conjunction with a submerged surface other than the hull of a boat. The surfaces can be grates on drainage and water conduits or other submerged components.