Abstract:
A propulsion system for hybrid electric watercraft for personal enjoyment that incorporates human power with electric motor assistance, energy storage and optional solar power to achieve increased watercraft speeds and/or reduced pedaling effort. Control electronics enable operator-adjustable electric motor assistance to the propulsion, thereby providing flexible pedal cadences and efforts and enjoyment for a wide variety of operators. An optional photovoltaic solar panel augments the power generation to extend travel time with motor assistance, and recharges the energy storage system. This invention enables a pleasure watercraft that is simultaneously lightweight, low cost, low maintenance, environmentally friendly with zero pollution, ultra-low noise, and thrilling to operate, while simultaneously providing a means of enjoyable exercise for operators of nearly all abilities.

Description:
FEDERALLY SPONSORED RESEARCH 
       [0001]    Not Applicable 
       SEQUENCE LISTING OR PROGRAM 
       [0002]    Not Applicable 
       BACKGROUND 
       [0003]    1. Field of Invention 
         [0004]    The present invention relates to the general art of watercraft, and to the particular field of hybrid-electric powered watercraft incorporating human (e.g., pedal) power with electric motor power assistance with energy storage in the form of electric battery, capacitor, fuel cell, and/or flywheel energy storage, and/or solar power. 
         [0005]    2. Description of Prior Art 
         [0006]    A multitude of pedal-powered watercraft (also referred to as water bikes, water-bicycles, and watercycles) are commercially available. They are relatively low cost, low maintenance, light weight, and fun. Their main drawback is the relatively low power output capability of the operators. Unlike watercraft propelled by conventional combustion engines, pedal-powered watercraft are severely limited in power capability; typically less than 200 watts (around ¼ hp) per person on a continuous basis. A cyclist in good condition can generate around 200 watts at a preferred cadence of around 90-100 RPM. Many people of lesser abilities may be only capable of generating around 100 watts in a continuous comfortable manner. Thus maximizing the overall efficiency of the watercraft, including its propulsion system, as it travels in water is vitally important to maximize speed and travel distance capabilities. To maximize the speed (and pedaling efficiency), many of the newer watercycles, such as the Seacycle® and Waterbike® manufactured by the Meyers Boat Company, Inc. and the Surfbike, are designed to be as lightweight with efficient long and narrow hulls. 
       OBJECTS AND ADVANTAGES  
       [0007]    The object of the invention is to provide a propulsion system enabling a pleasure watercraft that is simultaneously lightweight, low cost, environmentally friendly with zero pollution, ultra-low noise, and thrilling to operate, while simultaneously providing an optional means of enjoyable exercise for operators of all abilities. A person that routinely pedals a conventional watercycle on a specific lake or river is likely to see only the same limited area each time, due to the severely restricted speed, and hence, travel distance possible within a finite amount of exercise time. This can lead to boredom rapidly. Thus one objective of the present invention is to provide a new type of watercycle employing an electric motor assistance means with energy storage and/or solar power to substantially increase the speed and range of the watercraft. 
         [0008]    With proper hull design and sufficient electric motor assistance, this invention may enable the watercraft to achieving hull planing speeds, that would normally not be possible under human-power only. 
         [0009]    This invention combines human-power and electric-power watercraft technologies into one watercraft, and by adding new innovative controls, the best of both types of watercraft is obtained. With this invention, the fit cyclist that routinely exercises, as well as the occasional rider, can explore a much larger area of a bay, lake or river, in a shorter amount of time, thereby increasing enjoyment considerably. Unlike battery-only electric watercraft, this invention removes the worry of running out of battery power, or solar power on a cloudy day or night. If the batteries become drained, and solar power is not available, the operator can still pedal back to shore, though at reduced power. Diagnostic displays that monitor the usable stored energy of the battery, as well as the generated solar power and pedal power, keep the operator informed, so that the operator can wisely return to shore under full power, if desired, prior to battery depletion. 
         [0010]    It is another objective of the present invention to provide a propulsion system for watercraft comprising electric motor assistance, thereby permitting operators of differing physical abilities and goals to simultaneously operate one or more of the watercraft over the same distance at the same speed, thereby sharing the experience, while still exercising at their individually preferred effort levels. 
         [0011]    It is another objective of the present invention to provide a propulsion system for dual-seated watercraft comprising electric motor assistance, thereby permitting operators of differing physical abilities and goals to simultaneously operate the same watercraft while each independently achieving their desired level of physical exercise, without sacrificing the overall speed or travel distance of the watercraft. 
         [0012]    It is still another objective of the present invention to provide a propulsion system for watercraft comprising operator-selectable pedal torque vs. pedal cadence characteristics, such as simulated rolling hills to add an additional degree of enjoyment and pedaling comfort to the operator. Such flexibility is not possible with pure mechanically-driven systems, such as prior art waterbikes. 
         [0013]    Yet another objective of the present invention is to provide a propulsion system for watercraft employing an electric motor assistance means via energy storage with photovoltaic power to recharge the energy storage, thereby providing a pollution-free watercraft. 
         [0014]    Yet another objective of the present invention is to provide a propulsion system for watercraft employing an electric motor assistance means via energy storage with photovoltaic power to enable increased travel speed and range when the energy storage system is depleted. 
         [0015]    Yet another objective of the present invention is to provide a propulsion system for an electric watercraft that can be optionally operated solely from stored energy or on-board photovoltaic power. 
         [0016]    Yet another objective of the present invention is to provide a propulsion system for a hybrid-electric watercraft with mechanical linkage connecting a pedal mechanism to a propeller such that the watercraft can still be propelled under human power in the event of a failure of an electric or electronic component. 
         [0017]    Yet another objective of the present invention is to provide a propulsion system for a motor-assisted watercycle wherein the pedal mechanism is operated by an operators hands/arms, thereyby significantly increasing the speed and travel range of the watercycle, compared to a watercycle without this invention. 
       SUMMARY 
       [0018]    A propulsion system for watercraft comprising at least one human-powered propulsion means, at least one electric motor-powered propulsion means, the said electric motor-powered propulsion means configured to provide propulsion as a function of the state of the said human-powered propulsion means, whereby the electric motor-powered propulsion assists the human-powered propulsion means. The propulsion system further comprising a sensing means configured to provide a signal indicative of the state of the human-powered propulsion means, and a control means configured to receive the said signal and to control the state of the said electric motor-powered propulsion means according to the said signal. The electric motor-powered propulsion means is further configured to be a function of the said signal and an operator-adjustable motor assistance factor. 
     
    
     
       DRAWINGS 
       Drawing Figures 
         [0019]      FIG. 1  illustrates a typical human-powered watercraft of the prior art (U.S. Pat. No. 5,672,080). 
           [0020]      FIG. 2  illustrates the propulsion system unit of the human-powered watercraft of the prior art with chain and sprocket drive mechanisms (U.S. Pat. No. 5,672,080). 
           [0021]      FIG. 3  illustrates the power and control system functional block diagram for the preferred embodiment of this invention for a single operator. 
           [0022]      FIG. 4  illustrates the propulsion system unit of the prior art modified with the addition of a pedal-effort (e.g., cadence or speed) sensor in accordance with this invention. 
           [0023]      FIG. 5  illustrates a watercraft utilizing the propulsion system incorporating electric motor assistance. 
           [0024]      FIG. 6  illustrates the power and control system functional block diagram for the preferred embodiment of this invention for two operators. 
           [0025]      FIG. 7  illustrates the propulsion system unit of the prior art modified with the addition of a pedal-effort (e.g., propeller shaft torque) sensor in accordance with this invention. 
           [0026]      FIG. 8  illustrates the operator control and display unit for a single-operator/single-motor embodiment. 
           [0027]      FIG. 9  illustrates the operator control and display unit for a dual-operator/single-motor embodiment. 
       
    
    
     DETAILED DESCRIPTION 
     Description and Operation 
       [0028]      FIG. 1  illustrates a typical human-powered watercycle (water bicycle)  1  of the prior art (U.S. Pat. No. 5,672,080). The watercycle  1  has an elongated floatation board  3 , a propulsion and seat unit  7 , and a steering unit  9 . The propulsion and seat unit  7  comprises of an operator seat  6  and a human-powered mechanical propulsion unit  12 . The propulsion unit  12  comprises of an upper body  11  and lower body  19 , pedal mechanism  15 , and propeller  21 . An operator pedals the crank pedal mechanism  15 , which turns the propeller  21 , thereby propelling the watercraft forward. 
         [0029]      FIG. 2  illustrates the propulsion system unit  12  of the human-powered watercycle  1  of the prior art in  FIG. 1 . A human operator pedals a crank pedal mechanism  15 , thereby causing a crankshaft  16  to rotate in equivalent manner as pedaling the crank mechanism of a bicycle. The crankshaft contains a crankshaft sprocket  17 . A propeller  21  is mounted on a rotating propeller shaft  42  that also contains a propeller shaft sprocket  25 . Bearings  32  and  33  support the propeller shaft  42 . The crankshaft sprocket  17  and the propeller shaft sprocket  25  are linked by a chain  23 , which transmits the pedaling motion power from the crankshaft  16  to the propeller shaft  42  and propeller  21 , and causing the propeller to rotate, produce thrust, and propel the watercycle. The direction of thrust and resulting watercycle motion is controlled simply by the direction of the pedaling action by the operator. 
         [0030]    The relative sizes of the crankshaft sprocket  17  and propeller shaft sprocket  25  dictate an effective “gear” ratio for the pedaling action. Typical gear ratios range from 1:5 to 1:10 (with propeller rotational speed increased relative to pedal cadence), and are chosen dependent upon the size and pitch of the propeller, and in some cases, the customization of the propulsion system for specific operators. The propulsion system in  FIG. 2  is single-speed, i.e., no gear ratio (sprocket) changing, unlike multiple speed bikes. This is the most common configuration, although multi-speed system are available, however, pedaling in reverse direction is generally not possible. 
         [0031]    The propulsion unit housing  19  is usually molded or cast from a polymer such as nylon, HDPE, or urethane. The propeller  21  is usually molded or cast from a polymer such as nylon or urethane. The propeller shaft  42  is usually fabricated from stainless steel. The chain  23  and sprockets  17  and  25  are usually steel, with a heavy weight oil or grease applied for lubrication and corrosion protection. 
         [0032]      FIG. 3  is a block diagram illustrating the preferred embodiment of a propulsion system  100  for a watercycle that incorporates electric motor propulsion assistance. The propulsion system  100  comprises of a mechanical propulsion unit  13  powered entirely by human power via pedal/crank system  15 , shaft  42  and propeller  21 , the same or similar to the propulsion unit  12  of the prior art as illustrated in  FIG. 2 . In addition, an electric propulsion unit  88  comprises of an electric motor  34  driving a propeller  36  via shaft  99 . The electric propulsion unit  88  is mechanically isolated, and preferably in a separate housing, from the mechanical propulsion unit  13 . An electronic control unit  52  provides controlled power to the electric motor  34  from an energy storage unit  56 , as well as connects to an operator-interface  58 . 
         [0033]    As also illustrated in  FIG. 4 , a pedaling-effort sensor  46  is located within the mechanical propulsion unit  13  and provides pedal mechanism rotation speed (e.g., cadence) and rotation direction information to the electronic control unit  52  of  FIG. 3 . The sensor  46  is preferably a quadrature gear-tooth sensor providing voltage pulses for each passing of the teeth of crankshaft sprocket  17 . The quadrature pulse signals are decoded to obtain rotation speed and direction information. Alternatively, it can provide a signal similar to that of a tachometer, in which a voltage is generated whose magnitude and polarity is proportional to the velocity of the passing teeth of the sprocket  17 . Commercially available sensors and the means to obtain speed and directional information are well established in industry. Alternative mean include, but are not limited to, sensing of the teeth passing of the propeller shaft sprocket  25  or a via tachometer, encoder or resolver directly coupled to the propeller shaft  42  or crankshaft  16 . 
         [0034]      FIG. 5  illustrates a watercraft  14  of the prior art (from  FIG. 1 ) modified to incorporate this invention. The watercraft is fitted with the propulsion unit  13  and the operator control unit  58 , all interconnected via the appropriate power and control wiring (not shown). The energy storage unit  56  is shown to be located attached to the hull  3 . The electric propulsion unit  88  comprising of electric motor  34  and propeller  36  are located in a propulsion motor housing  37  attached to the hull  3 . 
         [0035]    The electric motor  34  may be of any type including brushed DC, brushless DC, permanent magnet (PM) AC synchronous, induction, switched reluctance, and synchronous reluctance. The preferred types are brushless DC and PM AC synchronous because they generally provide the highest power density with the highest efficiency. Furthermore, the motors are inherently rugged and relatively simple to construct. Another advantage is that the stator windings can be effectively cooled from the surrounding water by fabricating the motor housing  37  from aluminum or steel. Anodized aluminum is preferred for the motor housing  37  because it is lightweight, corrosion resistant, easy to machine, and has high thermal conductivity. 
         [0036]    Brushed DC motors are also a favorable motor type due to their inherent low cost and simple controllers. 
         [0037]    The design ratings for the electric motor are dependent upon the level of performance desired for the specific product. A typical embodiment rating would be in the range of 250 to 1000 Watts, at a rated speed in the range of 400 to 1500 RPM assuming direct coupling between the propeller  36  and the electric motor rotor  34 . 
         [0038]    The electronic control unit  52  ( FIG. 3 ) includes a system control electronics unit  62  and a propulsion control electronics unit  64 . The systems control electronics unit  62  preferably contains a microcontroller, such as the Zilog ZNEO Z16F, or a DSP, such as the TMS320C24x. The systems control electronics unit  62  interfaces/monitors a user (operator) interface unit  58 . The primary function of the systems control electronics unit  62  is to monitor the state of the mechanical propulsion unit  13  via sensor  46  and provide a corresponding motor command signal. In the preferred embodiment, the sensor  46  provides a signal that is indicative of the rotational speed of the mechanical propulsion unit  13 , and the systems control electronics unit  62 , receives sensor  46  signal, and then creates a motor speed command signal, ω motor *. The relationship between the speed of the mechanical propulsion unit  13  and the motor speed command, ω motor *, is set by a user (operator) setting via the interface unit  58 . 
         [0039]    For example, with the sensor  46  measuring the speed (cadence) of the pedaling effort, ω pedal , the motor speed command is: 
         [0000]      ω motor *=ω prop36   *=K   assist   N   ped     —     36 ω pedal    1 
         [0040]    where ω prop36 * is the rotational speed of propeller  36 , K assist  is a motor assistance factor set by the user, and N ped     —     36  is a fixed speed ratio (constant factor) between the pedal cadence and motor speed that incorporates the effective gear ratio of propulsion unit  13  and the relative sizes of propellers  21  and  36 . 
         [0041]    Note in the preferred embodiment, the propeller  36  is directly coupled to the electric motor  34  (via shaft  99 ), hence ω motor =ω prop36  and ω motor *=ω prop36 *. In alternative embodiments, the propeller can be indirectly coupled to the motor via gearing, sprockets and chains, pulleys and belts, etc., in which case, an additional “gear” ratio would be incorporated into equation 1. 
         [0042]    The factor N ped     —     36  can be considered as comprising of two parts; 
         [0000]      N ped     —     36 =N ped     —     GR N 21     —     36    2 
         [0043]    where N ped     —     GR  is the effective gear ratio between sprockets  17  and  25  of the propulsion unit  13  and N 21     —     36  is the ratio of the rated (or optimal) speeds of the propellers  36  and  21 , respectively. 
         [0044]    Alternatively, if the sensor  46  measures the speed of the propeller  21 , ω prop21 , directly, then simply 
         [0000]      ω motor *=ω prop36   *=K   assist   N   21     —     36 ω prop21    3 
         [0045]    For example, if propellers  21  and  36  are identical, then N 21     —     36 =1. In which case, for a value of K assist =100%, the propellers  21  and  36  would operate at the same speed. Similarly, for a value of K assist =200%, propeller  36  would rotate at twice the speed of propeller  21 . If for example, the rated speed for propeller  36  is twice that of propeller  21 , then N 21     —     36  would be 2. 
         [0046]    The selection of propellers  21  and  36  depends upon many factors that are preferably taken into account during the propulsion system design phase. These factors include the desired motor rating, speed, and motor efficiency, the respective propeller efficiencies, the amount of energy storage desired, the available gear ratio in propulsion unit  13 , and many more. Faster motors tend to be smaller and lower cost than slower motors for the same power ratings. Likewise, smaller propellers tend to run faster than larger propellers for the same power and thrust rating. However, smaller, fast-turning propellers also tend to have lower efficiency than larger, slower-turning propellers. Hence, a fast turning propeller  36  design may result in a lower cost electric propulsion unit  88 , but additional energy storage would be required due to the lower efficiency. Thus an overall system optimization is preferable to determine the lowest cost system while still meeting the desired market demands. Such capabilities are within the skill set of one skilled in the art of electric motor systems and marine propulsion design. 
         [0047]    Note that the motor speed command, ω motor *, may also simply be a motor frequency command if the motor  34  is an AC motor, or a voltage command if the motor is a DC motor. 
         [0048]    Since propeller (and propulsion) power is proportional to the cube of the propeller speed, for a K assist  value of 200%, the propulsion power of propeller  36  would be 2̂3=8 times the pedal power exerted on propeller  21 . The speed of a watercraft is proportional to the cubic root of net propulsion power (from propellers  21 + 36 ), so that the resulting watercraft speed would be roughly directly proportional to the K assist  factor as defined above. 
         [0049]    In general, the propulsion system comprises of a human-powered propulsion means, an electric motor-powered propulsion means, a sensing means configured to provide a signal indicative of the state of the human-powered propulsion means, and a control means configured to receive the signal and to control the state of the electric motor-powered propulsion means according to that signal. The state of the human-powered propulsion means can be any state indicative of the pedaling effort or propeller  21 ; including, but not limited to, a speed value, ω pedal  or ω prop21 , a pedal torque value, a propeller  21  torque value, a pedal power value, or a propeller  21  power value. 
         [0050]    As one alternative embodiment, the K assist  factor can be defined to be applied to the sensed or estimated pedal torque, T pedal , and thereby, yielding a motor torque command, T motor *; e.g., 
         [0000]    
       
         
           
             
               
                 
                   
                     T 
                     motor 
                     * 
                   
                   = 
                   
                     
                       
                         K 
                         assist 
                       
                       
                         N 
                         ped_GR 
                       
                     
                      
                     
                       T 
                       pedal 
                     
                   
                 
               
               
                 4 
               
             
           
         
       
     
         [0000]    The electric motor  34  would then be torque controlled, rather than speed controlled; both of which are well known in industry. Or, as another alternative, the K assist  factor can be defined to be applied to the sensed or estimated pedal power, P pedal , or propeller  21  power, P prop21 , and yielding a motor power command, P motor *; e.g., 
         [0000]        P   motor   *=K   assist   P   pedal    5 
         [0000]        P   motor   *=K   assist   P   prop21    6 
         [0051]    The systems control electronics unit  62  ( FIG. 3 ) sends the electric motor control commands (e.g., ω motor * or T motor * or P motor *, etc.) to the propulsion control electronics unit  64 . Thus the electric motor propulsion unit  64  will track the actions and/or effort of the pedal-powered propulsion unit  13 ; e.g., when the operator is not pedaling, motor  34  and propeller  36  will also be stopped. When the operator puts forth effort causing propeller  21  to rotate, motor  34  and propeller  36  will also rotate at a speed, torque, or power setting that is a function of the propeller  21  (or pedal) state and the K assist  factor as set by the operator. The electric motor propulsion unit will thus act to amplify the effort of the pedal-powered propulsion unit  13 , resulting in greater watercraft speed for the same pedaling effort. 
         [0052]    For a given propeller  21  size and shape and rotating speed, the pedaling effort required is partially dependent upon the watercraft speed; i.e., the slip speed of the propeller through the water. Thus the electric motor propulsion unit will also provide the benefit of providing some degree of flexibility for the user in setting the amount of pedaling effort he/she wishes to produce for any given cadence. The operator can, in effect, adjust an “effective” gear ratio via adjusting the K assist  factor, and thus pedal at a preferred cadence vs. torque point. 
         [0053]    The propulsion control electronics  64  comprises preferably of a power electronic switching converter consistent with the electric motor  34 ; e.g., for a 3-phase brushless-DC or PM-AC synchronous motor, the converter would typically be a 3-phase MOSFET PWM voltage-source-inverter bridge. If the motor  34  is a brushed-DC motor, then the converter would typically be either a DC chopper circuit with MOSFET PWM switching and reversing contactors, or a full H-bridge circuit, also with MOSFET PWM switching. 
         [0054]    In the preferred embodiment, the electronic control unit  52  is simply a PWM motor drive with a microcontroller (or DSP) with sufficient processing and I/O, PWM, and A/D ports to generate both the system/motor control commands (e.g., speed, torque or power) and the individual PWM gating signals for the motor drive switches, as well as communicate with the user (operator) interface  58 . 
         [0055]    The two units  62  and  64  are preferably integrated into a single printed circuit board, although they can also be designed to be distinct and physically separated. 
         [0056]    An optional solar electric unit  70 , mounted on the watercraft, comprising of at least one solar (photovoltaic) panel  72  and solar charge control electronics unit  74  is shown in  FIG. 3  and  FIG. 5 . The solar electric unit  70  charges the energy storage unit  56 , and also can supply power to the propulsion unit when the watercraft is in operation. 
         [0057]    The energy storage unit  56  can be located within or attached to the electric motor propulsion unit housing  37  to provide a compact propulsion system with minimal electrical wiring, connectors, and individual components as seen by the operator. Alternatively, the energy storage unit  56  can be located separate from the propulsion unit housing  37 , but within or attached to watercraft hull or structure, as illustrated in  FIG. 5 . This configuration generally enables a larger amount of energy storage. 
         [0058]    The energy storage unit  56  is preferably a battery such as NiMH, lead-acid, or NiCad. As battery technology improves and costs reduce and safety improves, new battery technologies such as large-format Li-Ion or NaNiCl may become cost effective and safe. Alternative energy storage and conversion means such as fuel-cells, ultra-capacitors, and flywheels may also become cost effective. The preferred rated voltage for the energy storage unit  56  is 24V DC, although 12V, 36V, 42V, and 48V DC are also suitable, as well as values between and above. 
         [0059]    The amount of stored energy is preferably at least sufficient to allow operation with maximum motor assistance for 1-2 hours. The amount of energy storage is therefore dependent upon the maximum ratings of the electric motor  34 . For example, if the motor is rated at 250 Watts, then at least 250-500 Watt-hours of available energy storage capacity is desired. Likewise, if the motor is rated at 1000 Watts, then at least 1000-2000 Watt-hours of available capacity is desired. 
         [0060]    The pedaling-effort sensor  46  may alternatively or additionally provide pedal mechanism torque and torque direction information to the electronic control unit  52 . As illustrated by the propulsion unit  102  in  FIG. 6 , the pedaling-effort sensor  46  may alternatively be a torque and/or speed sensor  55  located near the shaft of the propeller  21  to provide speed and/or torque information of the propeller  21 . 
         [0061]    The electronics control unit  52  is shown in  FIG. 5  to be optionally located below the waterline of the watercraft in the housing  37  to provide cooling of the power electronic components in the propulsion control electronics unit  64 . The MOSFET switching devices are typically connected to the inner surface of an aluminum heatsink or cold plate. The outer surface of the heatsink/cold plate is in direct or at least indirect contact with the water for good thermal heat transfer from the switching devices to the water. The outer edges of the heatsink/cold plate are sealed against the propulsion unit housing  52 . 
         [0062]    An externally located or mounted charging system  82  is used in conjunction, or as an alternative, to the optional solar electric unit  70  to charge the energy (e.g., battery) storage unit  56  when the watercraft is not in operation. The external charging system  82  may be of any type compatible with the voltage rating, storage capacity, and energy storage type, including a conventional lead-acid (or NiMH, Li-Ion, etc.) battery charger connected to the utility grid, a solar electric charging system, or a wind turbine power charging system. If the energy storage unit  56  is a fuel cell, then recharging comprises replenishing the fuel, e.g., hydrogen, etc. 
         [0063]      FIG. 7  illustrates the block diagram of an embodiment  104  designed for two operators, comprising two human (pedal) powered propulsion units  13   a  and  13   b  similar to units  13  in  FIGS. 3 and 4  or  102  in  FIG. 6  or alternative embodiments described prior. A single electric motor propulsion unit  88  is illustrated, but multiple electric motor propulsion units are also readily possible and may also be advantageous to achieve higher watercraft velocities. The system control unit  52  receives pedal-effort signals from sensors  46   a  and  46   b  located on the two pedal-powered propulsion units. In the preferred embodiment, a single motor command, ω motor *, is generated by simply taking the average of the two sensor outputs; e.g., if the sensors  46   a  and  46   b  provide pedal speed signals ω pedal46a * and ω pedal46b *, respectively, then, 
         [0000]    
       
         
           
             
               
                 
                   
                     ω 
                     motor 
                     * 
                   
                   = 
                   
                     
                       ω 
                       
                         prop 
                          
                         
                             
                         
                          
                         36 
                       
                       * 
                     
                     = 
                     
                       
                         K 
                         assist 
                       
                        
                       
                         N 
                         
                           ped_ 
                            
                           36 
                         
                       
                        
                       
                         
                           ( 
                           
                             
                               ω 
                               
                                 pedal 
                                  
                                 
                                     
                                 
                                  
                                 46 
                                  
                                 a 
                               
                             
                             + 
                             
                               ω 
                               
                                 pedal 
                                  
                                 
                                     
                                 
                                  
                                 46 
                                  
                                 
                                     
                                 
                                  
                                 b 
                               
                             
                           
                           ) 
                         
                         2 
                       
                     
                   
                 
               
               
                 7 
               
             
           
         
       
     
         [0000]    Similarly, the motor command may also be in the form of a torque or power command obtained via an average torque or power from the pedaling effort, or any of the alternative embodiments described prior. 
         [0064]    Based upon the above control description, the preferred system embodiment works as follows:
       1.) The operator sets the motor assistance level, K assist .   2.) The operator exerts force on the pedals, which is converted to an effective torque, thereby causing the propulsion unit  13  to achieve some initial propeller  21  speed, ω prop21 , and power, P prop21 .   3.) The controller senses the pedal or propeller speed (or torque or power) from the pedal effort sensor  46 .   4.) From the pedal or propeller speed (or torque or power) and motor assistance level, K assist , the controller calculates and commands the desired motor speed, ω motor * (or torque or power).   5.) The controller  70  sets or regulates the motor voltage and/or frequency (and/or current) to achieve the desired motor speed (or torque or power), and hence propeller  36  speed, ω prop36 , and power, P prop36 .   6.) The total propulsion power of the watercraft increases to P prop21 +P prop36 , thereby increasing the speed of the watercraft; and/or allowing the operator to reduces his/her pedaling effort to a desired comfort/exercise level while still maintaining a high watercraft speed.       
 
         [0071]    In actual practice, the control steps 1-6 outlined above occur nearly simultaneously in a continuous iterative process such the watercraft operation is entirely smooth and pleasant to operate. 
         [0072]    The pedaling through rolling terrain (i.e., “hills” and “valleys”), as with a bicycle on land, can be simulated for the operator, by allowing the motor assistance gain, K assist , to vary in a sinusoidal (or other) manner as a function of time, distance traveled, or revolutions count. The operator would set, for example, the amplitude and period (i.e., wavelength) of the rolling terrain. 
         [0073]    Increased pedaling and vehicle inertia, similar to that experienced while pedaling a bicycle from standstill or coasting from an established speed, can also be simulated by allowing the motor assistance gain, K assist , to vary as a function of watercraft acceleration. For example, when the watercraft and/or pedaling action is accelerating, the K assist  value can be temporarily reduced, and then gradually increased to the operator-set level in an exponential manner, as the acceleration decreases. Likewise, the when the pedaling action is decelerating, the K assist  value can be temporarily increased, and then gradually decreased to the operator-set level in an exponential manner as the deceleration ceases. 
         [0074]      FIG. 8  illustrates the user (operator) interface  58 , comprising of START and STOP switches  83 , UP  82  and DOWN  81  switches to set the K assist  value, and a LCD character (or graphics) module  59  to display various useful information, such as the K assist  value, pedal cadence, pedal power, motor power, and total propulsion power. Other information such as watercraft speed, propeller RPM, pedal torque, battery status, etc. can also be displayed. The switches can be of a low-cost and weather resistant membrane switch type. 
         [0075]      FIG. 9  illustrates an exemplary operator display and interface designed for two operators; Left and Right, in accordance with the dual-operator/single-motor system illustrated in  FIG. 7 . A dual-operator/dual-motor system would utilize a similar operator display and interface, with the option of displaying data status data of either or both propulsion motors. 
         [0076]    Knowledge of the watercraft speed is generally of direct interest to the operator, as well as indirectly. The watercraft speed can be used to calculate distance traveled, available distance to travel with remaining energy storage capacity, etc. Such a method is disclosed in U.S. Pat. No. 6,986,688, and can be incorporated in this invention. The propeller  36  torque is first calculated from the commanded or estimated electric motor torque. Then, if the propeller  36  characteristics are known, the actual watercraft speed can be estimated using an equation; e.g., 
         [0000]    
       
         
           
             
               
                 
                   
                     υ 
                     boat_calc 
                   
                   ≅ 
                   
                     
                       K 
                       1 
                     
                     ( 
                     
                       
                         ω 
                         
                           prop 
                            
                           
                               
                           
                            
                           36 
                         
                       
                       - 
                       
                         
                           
                             T 
                             
                               prop 
                                
                               
                                   
                               
                                
                               36 
                                
                               _calc 
                             
                           
                           
                             K 
                             0 
                           
                         
                       
                     
                     ) 
                   
                 
               
               
                 8 
               
             
           
         
       
     
         [0000]    where K 0  and K 1  are known parameters characterizing the propeller  36 . 
         [0077]    To reverse the watercraft, the operator preferably reverses the direction of the pedaling effort. The system control electronics unit  62  detects via sensor  46  that the pedal rotation has reversed (or that the torque signal from optional torque sensor  55  has reversed), and then sends a negative motor speed (or torque or power) command to the propulsion control electronics unit  64 , thereby causing the electric motor torque to reverse also. 
         [0078]    Prior to the start of normal operation, the energy storage unit  56  is preferably to be charged to its full capacity. During normal operation with K assist  values above 0%, the energy stored in the energy storage unit  56  will be continuously depleted at a rated dependent upon the K assist  value chosen by the operator and by the pedaling effort put forth. The system control electronics unit  62  will preferably continue to monitor the charge state of the energy storage unit  56 , and notify the operator of the charge state via the user interface  58  LCD display  59 . 
         [0079]    In embodiments whereby a photovoltaic charge unit  70  is not included with the watercraft, when the charge in the energy storage unit  56  is depleted, or at/below a predetermined lower threshold, the system control electronics unit  62  will preferably set the K assist  value to zero and no longer command a non-zero motor torque. The operator will then be responsible for propelling the watercraft solely from pedaling. 
         [0080]    In embodiments whereby a photovoltaic charge unit  70  is mounted on the watercraft, when the charge in the energy storage unit  56  is depleted, or at/below a predetermined lower threshold, the system control electronics unit  62  will preferably continuously and automatically adjust the maximum K assist  value such that the power transferred to the electric motor is originating from the photovoltaic charge unit  70 , and therefore not further depleting the energy storage unit  56  to a point of irreparable damage. 
         [0081]    A significant advantage of this invention, relative to pure electric pedal watercraft (e.g., U.S. Pat. No. 6,855,016), is that in the event of a motor or controller failure, the operator will still be able to propel the watercraft via pedaling. Conversely, the electric motor propulsion unit can be easily configured to independently propel the watercraft even if the operator chooses not to pedal. With an additional switch in the operator interface  58 , the motor command can be changed in software in the system control electronics using  62  to be equal to, or a direct function of, the assistance factor, K assist ; i.e., 
         [0000]      ω motor *=ω prop36   *=K   assist    9 
         [0000]    The operator then controls the speed of the watercraft by adjusting the value of K assist . 
         [0082]    It should be further understood that the invention can be applied to propulsion systems for watercraft with virtually any type of watercraft hull design and construction, including planing hulls and monohulls, and even hulls with hydrofoils. 
         [0083]    The propellers  21  and  36  should be interpreted as any mechanism designed to produce propelling thrust for a watercraft including paddle wheels, rowing mechanisms, and moving fin mechanisms.