Abstract:
A watercraft attitude control system using GPS and other motion inputs in order to predictively control thrust, steering and hull characteristics in ways that will prevent and minimize porpoising motion of a watercraft.

Description:
CLAIM OF PRIORITY TO PRIOR APPLICATION 
     This application claims the benefit of the filing date of U.S. Provisional Application Ser. No. 61/435,106, filed on Jan. 21, 2011, entitled “Counter-Porpoising Watercraft Attitude Control System”, the entire disclosure of which is hereby incorporated by reference into the present disclosure. 
    
    
     NONPUBLICATION REQUESTED 
     Non-Provisional Application 
     This application is a non-provisional application under 37 CFR 1.53(b) and is submitted with an accompanying non-publication request in accordance with 35 U.S.C. §122(b). Accordingly, the subject matter of this application is to be maintained in secrecy until and unless Applicant allows a patent to issue based on this application. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention primarily pertains to the field of watercraft and boating. More particularly, many aspects of the present invention pertaining to controlling the pitch attitude of powered watercraft moving through the water. 
     2. Related Art 
     Watercraft “porpoising” refers to excessive rise-and-fall motion of a boat while motoring across a body of water at otherwise steady velocity. Virtually every recreational boater experiences it from time to time without much bother, but it can be dangerous, especially if it becomes harmonic with a series of waves. To make matters worse, porpoising can increase unexpectedly and uncontrollably even though engine speed and other boat controls are being held constant. 
     Consider a traditional V-shaped hull moving on a straight path through the water. Ideally the boat reaches the intended speed and everything stays smooth and steady. A large body of water, however, is rarely smooth, and the nautical forces acting on a boat are anything but steady. Buoyancy and drag forces vary depending largely on how much of the hull is submerged. Meanwhile, the thrust from the boat&#39;s propulsion system may be fixed relative to the boat, but if a wave changes the boat&#39;s pitch, then the thrust pushes the hull out of or into the water. So, once a sizeable waves changes the boat&#39;s pitch and position relative to the water, the forces on the hull of the boat are dramatically varied. 
     The boat&#39;s pitch begins to oscillate as the boat rises and falls, because fore and aft buoyancy forces against the hull start varying dramatically once the oscillating motion of porpoising has commenced. As the bow moves down into the water, the bow area displacement and the surface area impinged by moving water both increase, and generate upward forces on the bow. When the upward forces from the water overcome the downward force from the propulsive thrust, the bow pitches up. As it does, the bow displacement decreases and the lifting forces decrease, but the propulsive thrust lifting the stern increases. Thereafter, propulsive thrust and inertia drive the bow back into the water below a steady state displacement level. Hence, without intervention, the porpoising cycle continues. 
     Mild to moderate porpoising can adversely affect fuel consumption, steering, passenger comfort, engine wear, and other matters. In severe porpoising, the pitch oscillations may damage equipment and injure passengers and crew. A control system that can reduce or prevent porpoising is desirable to avoid its adverse effects. 
     Modulating the available control mechanisms such as trim tabs or thrust adjustments (i.e., throttle or cruise control interventions) is also difficult to achieve accurately because the resulting forces act on multiple axes that are displaced from the boat&#39;s center of gravity. If trim tabs or buoyancy propels the stern upward from the water, then the bow is forced down. There are multiple factors that affect porpoising including boat speed, hull design, thrust angle, propeller type, boat loading, wind, waves, and more 
     Even assuming that porpoising is already being managed to a minimum, watercraft operators such as those using recreational boats may also wish to control the boat to achieve a particular pitch attitude of their boats. While such needs arise in various circumstances, ski boat operators for instance may want to alter the size of the boat&#39;s wake. In wakeboarding, a large wake allows the wakeboarder to jump higher in the air. However, if the boat creates large wakes while transiting to a wakeboarding area, the wake may damage moored or docked vessels, damage piers and shoreline, or disturb other boaters. A small wake may be desirable when transiting, trolling, water skiing, wakeskating, or performing other activities. A smaller wake contains less energy, and thus carries less risk of damaging impinged structures. Further, for a given speed, a smaller wake indicates less propulsive energy is being diverted into wave-making energy, and thus reflects increased fuel efficiency. Some existing systems and methods enable watercraft operators to vary the craft&#39;s attitude, but each has significant limitations such as cost, weight, inflexibility, slow response, excess operator intervention, unpredictable results, and the like. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a conceptual flowchart for a control system of preferred embodiments, illustrating the conceptual relationship between various input parameters  10  and output parameters  40  that affect the attitude and motion of a watercraft. 
         FIG. 2  is a schematic illustration of watercraft  200  of preferred embodiments, illustrating microcontroller  50  in relation to various control systems  60 ,  70 ,  80 ,  90 ,  100  that detect and affect the attitude and motion of watercraft  200 . 
         FIG. 3  provides a relational orientation for reference to watercraft  200 , illustrating the pitch of watercraft  200  as well as the conceptual positional relationship between the watercraft&#39;s center of gravity and various control systems, namely a three-axis accelerometer, thrust and steering systems, and left and right hull tabs. 
         FIG. 4  provides a diagram of the control system of watercraft  200 , illustrating manual controls  80  and microcontroller  50  in relation to inputs  16 ,  17 ,  61 ,  62 , and  70  as well as outputs  41 ,  44  and  100 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Information Incorporated By Reference 
     This description incorporates by reference the entire disclosures of U.S. Pat. No. 7,465,203 dated Dec. 16, 2008, entitled “Watercraft Speed Control Device,” and U.S. Pat. No. 7,494,394 dated Feb. 24, 2009 entitled “Watercraft Speed Control Device.” 
     Various preferred embodiments of the present invention will be implemented in recreational boats, which for these purposes includes all watercraft in the common understanding of ski boats, sport ski boats (also known as “sport/ski” or “sport-ski” boats), tow boats, recreational fishing boats, or any comparable watercraft. Recreational boats include all boats designed and/or used for purposes such as fishing, cruising, patrolling, transport or the like, as well as for towing recreational or competition water skiers, barefooters, kites, wakeboarders, or tubers. It should be recognized that a boat may bear a common classification relating to a particular purpose irrespective of how its owner might choose to use the boat. 
     With reference to  FIG. 1 , watercraft  200  is preferably a recreational boat containing a variety of presently available sensors to sense and transmit various craft operating conditions (sensed conditions) depicted as the input parameters  10 . For example, in the preferred embodiment as depicted in  FIG. 1  the craft  200  has sensors that detect the vertical motion (pitch), horizontal motion (yaw), pitch angle, manual control status, GPS position and motion of the craft  200 , the craft water speed, the craft engine RPM and the hull stress of the craft  200 . A set of corresponding sensors ( 11 ,  12 ,  13 ,  14 ,  15 ,  16 ,  17 ,  18 ) are depicted schematically with minimal specificity on  FIG. 1 . The presently described embodiment of the invention uses a number of presently available components including controls, actuators, sensors, and communication means to provide the input parameters containing information regarding the craft operating conditions. 
     Those skilled in the art will have understanding of the various configurations, combinations, and subcombinations of sensors and input parameters  10  that may not have been specifically disclosed but would fall within the scope of the invention. It should be understood, though, that such sensors come in many forms and may include accelerometers, angle sensors, angle position sensors, encoders, strain gauges, electronic devices, and any other means known to or later discovered by those of skill in the art to detect and report conditions of the corresponding devices and operating and environmental conditions. It should also be understood that many such sensors may be integral with accompanying actuators or other components even though they may be shown discreetly. Also, understand that equivalent sensors may approximate sensing of the intended object by approximating from other indicators or other algorithms. 
     Additionally, such other embodiments may contain a different combination of sensors providing a different combination of measurements of the craft operating conditions. All such sensors communicate their information to a  FIG. 2  microprocessor microcontroller  50 . 
     Microprocessor Microcontroller 
     The microprocessor microcontroller  50  uses one or more presently available computing devices that contain a processor, memory, one or more input means, and one or more output means. The microprocessor microcontroller  50  preferably stores part, or all, of the porpoising detection algorithm  20  and the control countermeasure algorithm  30 . The microprocessor microcontroller  50  receives information on the sensed conditions and detects the presence or absence and degree of porpoising according to the porpoising detection algorithm  20 . When the porpoising detection algorithm  20  indicates the presence of porpoising, the microprocessor microcontroller  50  calculates the most desired control countermeasures according to the control countermeasure algorithm  30 . The microprocessor microcontroller  50  then outputs craft control actions communicating the appropriate output parameters  40  to the appropriate controllers that affect craft  200 . 
     Referring again to  FIG. 1 , preferred embodiments of the present invention will contain a variety of presently available craft controllers to accept the output parameters  40 . For example, in the preferred embodiment as depicted in  FIG. 1  the craft  200  has controllers that can modify the propeller speed  41 , stern rudder angle  42 , trim tabs angle  43 , ballast redistribution  44 , engine RPM  45 , outboard motor angle  46 , manual control override  47 , and keel(s) adjustment ( 48 ). 
     As with the input parameters  10 , those skilled in the art will have understanding of the various configurations, combinations, and subcombinations of controllers and output parameters  40  that may not have been specifically disclosed but would fall within the scope of the invention. It should be understood, though, that such controllers come in many forms. 
     Porpoising Detection Algorithm 
     A porpoising detection algorithm  20  is preferably implemented in the microprocessor microcontroller  50 . The porpoising detection algorithm  20  may include any common or advanced control loop transfer function including, but not limited to, series, parallel, ideal, interacting, noninteracting, analog, classical, and Laplace types. The porpoising detection algorithm  20  calculates absence or presence of porpoising in the craft  200  and if present the degree of porpoising using the input information received by the input parameters  10 . 
     Control Countermeasure Algorithm 
     A control countermeasure algorithm  30  is preferably implemented in the microprocessor microcontroller  50 . The control countermeasure algorithm  30  may include any common or advanced control loop transfer function including, but not limited to, series, parallel, ideal, interacting, noninteracting, analog, classical, and Laplace types. The control countermeasure algorithm  30  receives information on the presence and degree of porpoising from the porpoising detection algorithm  20 . In the presences of porpoising, the control countermeasure algorithm  30  calculates optimal craft control actions to minimize, reduce, or eliminate the porpoising. The control countermeasure algorithm  30  then outputs the correct craft control actions to the appropriate output parameter  40  craft controllers. 
     The control countermeasure algorithm  30  is optimized to achieve accurate modulation of the available control mechanisms such as trim tabs or thrust adjustments (i.e., throttle or cruise control interventions). By using the information from the input parameters  10 , the control countermeasure algorithm  30  can be tuned to calculate the craft control actions that optimize fuel consumption, steering, passenger comfort, engine wear, and other matters. 
     Based on the input information, the control countermeasure algorithm  30  calculates craft control actions for any of the craft controllers implemented in the particular embodiment. For each craft controller it is controlling, the control countermeasure algorithm  30  calculates a desired action and a corresponding craft controller command to achieve as much. The control countermeasure algorithm  30  calculates the desired action based on the sensed conditions. However, because of the inherent limits of the steering system or other craft conditions, the desired action may not be achievable, either instantaneously or at all. A craft controller action limiting function may also be implemented in the control countermeasure algorithm  30  or by some other means, or may not be necessary based on the type of the craft controls for craft  200 . 
     The control countermeasure algorithm  30  preferably includes a comparator function with which the control countermeasure algorithm  30  compares the desired craft control action with the current craft conditions as detected by input parameter sensors. The control countermeasure algorithm  30  produces a series of intermediate craft control actions that achieve the desired craft control actions without exceeding the craft control system&#39;s maximum permissible rate of change or operating limits. Further, the control countermeasure algorithm  30  is adapted to limit the craft control actions to the mechanical limits of watercraft  200 . The control countermeasure algorithm  30  also preferably contains a smoothing function to avoid rapid changes in craft control actions. The smoothing function compensates for noise in sensors or controls and for rapid fluctuations in sensed conditions. 
     The control countermeasure algorithm  30  is based on mathematical models for the resulting forces acting on the multiple axes of the watercraft  200  during porpoising. Formulas to approximate these forces are known in the art. However, numerous complexities affecting these forces also exist such as hull interaction with flow around the rudder (hull wake), rudder physical profile (e.g., hydrofoil shape, chord length, rudder thickness), turbulence of inflow to the rudder, and other factors. These complexities are preferably approximated in the control countermeasure algorithm  30  using constants. The constants of control countermeasure algorithm  30  may be tuned for different types of watercraft  200  through experimentation and testing. 
     Irrespective of the other preferred details in the porpoising detection algorithm  20  and the control countermeasure algorithm  30 , both algorithms monitor a variety of sensed conditions to determine when porpoising is occurring and what craft control actions are needed to reduce or eliminate porpoising. The control countermeasure algorithm  30  also includes internal limitations for other operating and safety considerations. For example, regardless of sensed conditions, the control countermeasure algorithm  30  never commands a craft control action in excess of the mechanical or safety limits of the craft  200  or the specifically controlled subsystem. In case of certain sensor failures, the electronic controller informs the operator a failure has occurred and calculates the optimal craft control actions to minimize, reduce, or eliminate the porpoising taking into account the failure. In case of microprocessor microcontroller  50 , fail-safe means allows the watercraft&#39;s manual steering system to resume unaided control of the craft  200 . 
     Depiction of Input and Output Parameters in Other Embodiments 
       FIG. 2  depicts an example of one possible configuration, combination, or subcombination of input parameters  10  and output parameters  40  of other embodiments of the invention. In  FIG. 2 , a three axis accelerometer  60  provides measurements of the movement of the watercraft  200  in three dimensions to the microprocessor microcontroller  50 . This provides information corresponding to the input parameters  10  vertical motion (pitch)  11 , horizontal motion (yaw)  12 , pitch angle  13 . A GPS  70  provides information regarding the GPS position/motion  15  and the craft water speed  16  to the microprocessor microcontroller  50 . In addition to the input parameters  10  listed above, a sensor detecting the status of the manual controls  80  provides this information to the microprocessor microcontroller  50 . Finally, a sensor relates information about the engine RPM from the motor &amp; steering  90  to the microprocessor microcontroller  50 . 
     With the information provided by the input parameters described above the microprocessor microcontroller  50  continually runs the porpoising detection algorithm  20 . Once the presence of porpoising has been indicated by the porpoising detection algorithm  20 , microprocessor microcontroller  50  runs the control countermeasure algorithm  30 . The control countermeasure algorithm  30  calculates optimal craft control actions to minimize, reduce, or eliminate the porpoising and outputs the correct craft control actions to the appropriate output parameter  40  craft controllers. 
     In this embodiment, the microprocessor microcontroller  50  outputs craft control actions to motor &amp; steering unit  90  and to the mechanisms providing hull adjustments  100 . Such hull adjustments may be accomplished by, for example, an aft rudder. The microprocessor microcontroller  50  may also use the manual controls  80  as a craft control device. In this embodiment, the microprocessor microcontroller  50  outputs control actions adjusting propeller speed  41 , engine RPM  45 , and outboard motor angle  46  to the motor &amp; steering  90  unit. The microprocessor microcontroller  50  also outputs craft control actions adjusting stern rudder angle  42  and trim tabs angle  43  to the hull adjustments  100 . The microprocessor microcontroller  50  can also send manual control override  47  actions to the manual controls  80 . 
     It should be noted that in this embodiment, the certain of the various input and output parameters may share input parameter signal pathways with the corresponding output parameters craft control action signal pathways. Specifically the motor &amp; steering sensor  90 , the hull adjustments  100 , and the manual controls  80  each potentially shares an input parameter signal transmission pathway with its corresponding output parameter craft control action pathway. 
     Diagram of Input and Output Parameters in Other Embodiments 
       FIG. 4  is a diagram of another embodiment configuration, combination, or subcombination of input parameters  10  and output parameters  40 . In  FIG. 4 , each box corresponds to a discrete sensor box or unit that may be placed in separate locations in the watercraft  200 . This provides information from various locations on the craft  200  to the microprocessor microcontroller  50 . There may also be multiple sensor box units of the same or similar sensor types placed in various locations in the water craft  200  to provide more information about the motions and forces the craft  200  is experiencing to the microprocessor microcontroller  50 . 
     In  FIG. 4 , a multi axis accelerometer  61  provides measurements of the movement of the watercraft  200  in multiple dimensions to the microprocessor microcontroller  50 . Additionally, a gyroscope  62  provides information measuring or maintaining orientation, based on the principles of angular momentum. Note also that the multi axis accelerometer  61  sensor box is shown in dashed-line with the gyroscope  62  indicating that these sensors may be paired as a unit or may be separate. Additional sensors include a water speed  16  sensor, a GPS  70 , a sensor detecting the status of the manual controls  80 , and a sensor relating information about the engine RPM  17  to the microprocessor microcontroller  50 . Also, note that the water speed  17  sensor box is shown in dashed-line because it is less critical, particularly given that we usually depend on GPS to get water speed. 
     As also reflected in  FIG. 4 , the multi axis accelerometer  61  module is shown as one box that is positioned forward (or aft, as an alternative) of the boat&#39;s center of gravity CG. It should be understood, though, that the accelerometer module as well as the gyro may be embodied either together in one housing or as multiple independent accelerometers and gyros spaced around the boat. Although keeping them in one location can be beneficial to cost and ease of installation, the spaced-around alternative allows the processor to take advantage of the fact that different locations will respond more or less dramatically to different hull motions based on where they are located. Irrespective, electronic and algorithmic adjustments will be evident to those skilled in the art in order to help compensate for wherever the various accelerometer and gyro components may be located. 
     As with other embodiments of the invention, the microprocessor microcontroller  50  continually runs the porpoising detection algorithm  20  using the information provided by the input parameters. Once the presence of porpoising has been indicated by the porpoising detection algorithm  20 , microprocessor microcontroller  50  runs the control countermeasure algorithm  30 . The control countermeasure algorithm  30  calculates optimal craft control actions to minimize, reduce, or eliminate the porpoising and outputs the correct craft control actions to the appropriate output parameter  40  craft controllers. 
     In this embodiment the microprocessor microcontroller  50  outputs craft control actions to the propeller speed  41  module, the weigh distribution  44  module (that may control bilge pumps or other appropriate devices), and the hull adjustments  100  module. 
     Alternative Components 
     Even though the foregoing embodiments represent the most preferred at present, those of ordinary skill in the art will recognize many possible alternatives that we have not expressly suggested here. While the foregoing written descriptions enable one of ordinary skill to make and use what is presently considered the best modes of the invention, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The drawings and detailed descriptions herein are illustrative, not exhaustive. They do not limit the invention to the particular forms and examples disclosed. To the contrary, the invention includes any further modifications, changes, rearrangements, substitutions, alternatives, design choices, and embodiments apparent to those of ordinary skill in the art, without departing from the spirit and scope of this invention, as defined by any claims included herewith or later added or amended in an application claiming priority to this present filing. The invention covers all embodiments within the scope and spirit of such claims, irrespective of whether such embodiments have been remotely referenced here or whether all features of such embodiments are known at the time of this filing. Thus, the claims should be interpreted to embrace all further modifications, changes, rearrangements, substitutions, alternatives, design choices, and embodiments that may be evident to those of skill in the art. In any case, all substantially equivalent systems, articles, and methods should be considered within the scope of the present invention.