Patent Publication Number: US-2015086337-A1

Title: System for mounting a motorized cassette to a watercraft body

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/536,186 filed on Jun. 28, 2012, which claims the benefit of U.S. Provisional Application No. 61/503,417 filed on Jun. 30, 2011, entitled “MOTORIZED WATERCRAFT WITH INTERCHANGEABLE MOTOR MODULE,” which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to motorized watercrafts. 
     2. Description of the Related Art 
     Watercrafts are used around the world for various purposes including, transportation, fishing, recreation, and/or living spaces. Watercrafts can be motorized or non-motorized. Some watercrafts can be fitted with separate motor assemblies, for example, an outboard motor, to provide motorized propulsion capability to an otherwise non-motorized vessel. Other watercrafts can be constructed with one or more in-board motors. Also, some watercrafts, including sailboats, rowboats, kayaks, and canoes, may be used primarily without motors. 
     SUMMARY 
     In one embodiment, a system for a watercraft comprises a mounting assembly configured to couple the system to a watercraft body, motorized cassette, and a tiller. The motorized cassette contains at least one electric motor, at least one impeller, a water inlet, and a water outlet. The water inlet and the water outlet are in a bottom surface of the motorized cassette and the motorized cassette is attached to and offset from the mounting assembly. Manipulation of the tiller causes rotation of the motorized cassette relative to the mounting assembly. The motorized cassette can be coupled to a housing having a receiving space that is defined by a surface having at least one protrusion. The at least one protrusion may be configured to engage the motorized cassette so as to inhibit movement of the motorized cassette relative to the housing in at least one of a longitudinal direction, a transverse direction, and a lateral direction. The housing may comprise a latch configured to releasably secure the cassette relative to the housing. The motorized cassette can include a substantially flat bottom surface and can be coupled to the tiller by a steering column. 
     In another embodiment, a system for propelling a watercraft comprises a mounting assembly, a housing, a tiller, and a motorized cassette. The mounting assembly includes a bracket configured to secure the system to a watercraft body, the housing comprises a receiving space that is offset from the mounting assembly. Manipulation of the tiller causes rotation of the housing relative to the mounting assembly and the motorized cassette is configured to be at least partially inserted and latched into the receiving space. The cassette may comprise at least one motor, for example, at least one motor configured to propel the watercraft in at least a first direction relative to a body of water. The cassette may comprise an impeller, for example, an impeller position in a flow housing and coupled to one portion of a shaft with another portion of the shaft being coupled to the motor through a bellows coupler. The cassette may comprise at least one battery and/or at least one motor controller. The housing may comprise a protrusion, at least a portion of the cassette may comprise an indentation, and at least a portion of the protrusion can be at least partially receiving within the indentation. The cassette may be removably coupled to the housing, for example, the cassette may be fastened to the housing and/or latched to the housing. 
     In another embodiment, a watercraft comprises a motorized assembly coupled to a watercraft body, a motorized cassette, and a tiller. The motorized cassette contains at least one electric motor, at least one impeller, a water inlet, and a water outlet. The water inlet and water outlet are in a bottom surface of the motorized cassette and the motorized cassette is attached to and offset from the mounting assembly. Manipulation of the tiller causes rotation of the motorized cassette relative to the mounting assembly. The motorized cassette can be positioned such that a bottom surface thereof is less than three inches below the waterlines of the watercraft, for example, less than one inch below the waterline of the watercraft. The motorized cassette can rotate to propel the watercraft in any direction over the water surface and the motorized cassette can have a substantially flat bottom. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view of a top shell of a surfboard showing components placed in top shell recesses. 
         FIG. 2  is an exploded view of a bottom shell of a surfboard showing components placed in bottom shell recesses. 
         FIG. 3  is a cutaway view of a surfboard made from top and bottom shells with power components mounted therein in accordance with one embodiment of the invention. 
         FIG. 4  shows a detailed view of a passageway between a motor recess in a top shell and an impeller recess in a bottom shell. 
         FIG. 5  is a perspective view of a flow housing in which the impeller may be inserted. 
         FIG. 6  illustrates the bottom shell attached to the top shell in the region of the surfboard tail with one flow housing attached in one of the bottom shell recesses. 
         FIG. 7  is a block drawing showing one embodiment of a drive control system, which may be used in one embodiment of the motorized surfboard. 
         FIG. 8  is a flow chart illustrating a method for use with one embodiment of the motorized surfboard. 
         FIG. 9  is a flow a top view of one embodiment of a drive control system, which may be used in one embodiment of the motorized surfboard. 
         FIG. 10  is a perspective view of a personal watercraft including a first embodiment of a motorized cassette received in a bottom recess of the personal watercraft. 
         FIG. 11  is an exploded view of the surfboard of  FIG. 10 . 
         FIG. 12  is a perspective view of the personal watercraft of  FIGS. 10 and 11  including a non-motorized cassette received in a bottom recess of the personal watercraft. 
         FIG. 13  is an exploded view of the surfboard of  FIG. 12 . 
         FIG. 14  is a perspective view of a kayak including the first embodiment of a cassette received in a bottom recess of the kayak. 
         FIG. 15  is an exploded view of the kayak of  FIG. 14 . 
         FIG. 16  is a perspective view of a personal watercraft including a second embodiment of a motorized cassette received in a bottom recess of the personal watercraft. 
         FIG. 17  is an exploded view of the surfboard of  FIG. 16 . 
         FIG. 18  is an exploded view of the motorized cassette of  FIGS. 16 and 17 . 
         FIG. 19  is a perspective cutaway view of the motorized cassette of  FIG. 18 . 
         FIG. 20  is a cross-sectional view of a personal watercraft including a curved body section adjacent to the exhaust port of the pump housing. 
         FIG. 21  is a bottom view of the personal watercraft of  FIG. 20 . 
         FIG. 22  is a perspective view of a pump housing including a flattened exhaust port. 
         FIG. 23  is a top perspective view of one embodiment of a mounting system for mounting a motorized cassette to a watercraft. 
         FIG. 24  is a top perspective view of a motorized watercraft including the mounting system of  FIG. 23  mounted to a cutaway of a watercraft body. 
         FIG. 25  is a bottom perspective view of the motorized watercraft of  FIG. 24 . 
         FIG. 26  is a partially exploded bottom perspective view of the motorized watercraft of  FIG. 25  showing the motorized cassette separate from a corresponding receiving space. 
         FIGS. 27-29  are top perspective views of the motorized watercraft of  FIGS. 24-26  showing the motorized cassette rotated relative to the watercraft body in different configurations. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Traditionally, watercrafts may be motorized by constructing a vessel with one or more in-board motors and/or by fitting a vessel with one or more outboard motors. However, these methods of motorizing a watercraft can add significantly to a watercraft&#39;s weight and cost. Additionally, existing motors typically run on costly petroleum based fuels and emit exhaust into the surrounding water and/or air. Further, the props that are driven by such motors may necessarily extend well below the waterline of an associated watercraft thereby creating a more prolific fluid profile and limiting the bodies of water that the watercraft can safely traverse without grounding. In any case, such watercrafts are generally not easily converted between a motorized configuration and a non-motorized configuration. 
     The general purpose of many embodiments described herein is to provide a system for mounting a motorized cassette to a watercraft to provide motorized propulsion capability to the watercraft. In some advantageous embodiments, the mounting system can be releasably secured to a battery driven motorized cassette that can be easily removed from the system. In this way, the motorized cassette can operate to quietly propel a watercraft without emitting exhaust. In some embodiments, the cassette may house batteries, motors, control electronics, impellers and associated drive hardware. Such systems can be used with a variety of watercrafts. 
       FIGS. 1-6  illustrate suitable power and drive train components for a motorized watercraft such as a surfboard. In these Figures, the components are not placed in a cassette, but these Figures illustrate the components themselves and their relative placement and function. Referring now to  FIGS. 1 ,  2 , and  3 , in some embodiments, a motorized surfboard comprises a top shell  102 , and a bottom shell  202 . This hollow shell construction has been recently utilized for surfboard manufacture, and represents a departure from traditional shaped foam boards. It is one aspect of the invention that this hollow shell design has been adapted to a motorized surfboard in a manner that minimizes manufacturing costs and provides structural integrity and long term reliability. 
     The top shell  102  is illustrated in  FIG. 1 , and the bottom shell  202  is illustrated in  FIG. 2 . In  FIG. 3 , a conceptual cutaway view is provided showing how the shells mate with each other in one embodiment. 
     The top shell  102  has an outer surface  104 , and an inner surface  106 . Similarly, the bottom shell has an outer surface  204 , and an inner surface  206 . To produce the complete surfboard body, the two shells are sealed together along a seam  302  that extends around the periphery of the top and bottom shells. The “outer surface” of the top and bottom shells are the surfaces that are contiguous with the surfaces exposed to the water in use (although not all of the “outer surface” of the shells is actually exposed to water as will be seen further below). The “inner surface” of the top and bottom shells are the surfaces internal to the hollow board after sealing into a hollow surfboard body. The general methods of producing surfboards with this hollow shell technique are known in the art. Currently, Aviso Surfboards (www.avisosurf.com) manufactures surfboards in this manner from carbon fiber top and bottom shells forming a hollow surfboard body. 
     The outer surface  104  of the top shell  102  is formed with one or more recessed portions  112 , where the recessed portions extend generally toward the inner surface  206  of the bottom shell  202  when the shells are sealed together into a hollow body. The recessed portions  112  form compartments for batteries  114 , motor controller boards  116 , and motors  118 . The motors  118  are coupled to shafts  120  that extend out the rear of the motor compartment as will be explained further below. 
     After installation of these components, the recesses can be sealed with a cover  122  that can be secured in place with adhesive such as caulking or other water resistant sealant. If desired, an internally threaded access port  124  can be provided that receives an externally threaded cover  126 . This can provide easier access than removing or cutting the adhesive on the larger cover  122 . In some advantageous embodiments, one or both of the covers  122 ,  126  are clear so that the batteries, motors, and/or other electronics can be seen when they surfboard is sealed up and in use. Another threaded plug  130  can also be provided, which can be used to ensure equal air pressures on the inside and outside of the hollow body. This feature is well known and normally utilized for hollow shell surfboards. 
     Turning now to  FIG. 2 , the outer surface  204  of the bottom shell  202  also includes one or more recessed portions  212 , where the recessed portions extend generally toward the inner surface  106  of the top shell  102  when the shells are sealed together into a hollow surfboard body. The bottom shell  202  may also contain recesses  218  for fin boxes that accept fins  220  in a manner known in the art. The bottom shell recesses  212  are configured to accept pump housings  224 . As shown in  FIG. 3 , the pump housings  224  receive the motor shafts  120 , onto which an impeller  226  is attached. At the rear of the pump housing  224 , a flow straightener  228  may be attached. 
     As shown in  FIG. 3 , the recessed portion  112  in the top shell and the recessed portion  212  in the bottom shell comprise walls  302  in the bottom shell and  304  in the top shell that are proximate to one another. In advantageous embodiments, these proximate walls extend approximately perpendicular to the overall top and bottom surfaces of the surfboard. In these proximate walls are substantially aligned openings, through which the motor shaft  120  extends. Thus, the motor(s)  118 , which reside in a recessed portion of the top shell, are coupled to the impeller(s) that reside in the pump housing(s) that in turn reside in a recessed portion of the bottom shell. 
       FIG. 4  illustrates in more detail the surfaces  302  and  304  through which the motor shaft  120  extends. Typically, the motor  118  includes an integral shaft  402  of fairly short extent. This short shaft may be coupled to a longer extended motor shaft  120  with a bellows coupler  404 . These couplers  404  are commercially available, from for example, Ruland, as part number MBC-19-6-6-A. The bellows coupling  404  is advantageous because it allows for smooth shaft rotation even in the presence of vibrations and/or small deviations in linearity of the connection. The long shaft  120  then extends through a bearing  408  which has a threaded rear portion. The threaded rear portion of the bearing  408  is threaded into a threaded insert  410  that is positioned on the other side of the openings, in the recessed portion of the bottom shell. When the bearing is tightened into the insert, a water tight seal is created as the walls  302  and  304  are compressed together. It will be appreciated that the walls  302 ,  304  may directly touch, or they may remain separated, with or without additional material between. To further minimize any potential for leakage, it is possible to place washers of rubber, polymer, or the like between the insert  410  and the wall  320 , and/or between the bearing  408  and the wall  304 . 
       FIGS. 5 and 6  illustrate the positioning of the pump housing  224  in the recessed portion  212  of the bottom shell.  FIG. 5  illustrates the underside of the pump housing  224  and  FIG. 6  illustrates a pump housing installed in a recess of the bottom shell. The pump housing  224  is basically a hollow tube for directing water up to the impeller and out the rear of the surfboard. Thus, the pump housing comprises an inlet port  502  and an exhaust port  504 . The pump housing  224  can be secured in the recess  212  in a variety of ways. The embodiment of  FIGS. 5 and 6  includes shafts  508  that are secured to each side of the pump housing. The tip  510  of the shaft  508  extends through an opening  512  in the frontward of the pump housing  224 . Referring now to  FIG. 6 , these exposed tips  510  are placed in holes  602  in the recess to secure the pump housing into the frontward portion of the recess  212 . The rear of the pump housing may comprise a wall with holes that mate with holes  616  in the bottom shell. The holes in the bottom shell may be provided with press fit threaded inserts. Screws  518  can then be used to secure the rear of the pump housing  224  to the rear of the recess  212 . 
     It will be appreciated that the pump housing  224  can be secured in the recess  212  in a variety of ways. For example, instead of having holes in the bottom shell for screws and pins, slots and/or blind recesses can be formed in or adhesively attached to the side surfaces of the recess that engage mating surfaces on the pump housing. Such structures can also be provided with threads for engaging screw connections. As another alternative, adhesive could be used to secure the pump housing in place. 
     Turning now to the power and control electronics and devices illustrated in  FIGS. 1 and 3 , a wide variety of power sources, motor controllers, and motors may be utilized. They can be secured in their respective recesses on metal frames and/or plates (not shown) that are secured in the recesses with adhesive and/or with fasteners such as screws to structures in the recesses integral to the side walls or adhesively secured thereto. Acceptable sources of power include a lithium battery or plurality of lithium batteries. 
     To avoid a hard wired connection to the motor controllers  116  from a throttle control input, the motor controller  116  advantageously include a wireless receiver. This receiver can communicate with a wireless transmitter that is controlled by the surfer in order to control the motor speed. Wireless throttle controls have been used extensively, but using a throttle while surfing poses unique issues in that paddling, standing, and riding waves will interfere with a surfer&#39;s ability to easily manipulate a control mechanism such as a trigger, a dial, or the like. In one embodiment, wireless transmission circuitry can be configured to transmit electromagnetic and/or magnetic signals underwater. Because one or both transmitter and receiver can be under the surface of the ocean during much of the duration of surfing, a transmission system and protocol that is especially reliable in these conditions may be used. For example, wireless circuitry can be implemented in accordance with the systems and methods disclosed in U.S. Pat. No. 7,711,322, which is hereby incorporated by reference in its entirety. As explained in this patent, it can be useful to use a magnetically coupled antenna operating in a near field regime. A low frequency signal, e.g. less than 1 MHz, can further improve underwater transmission reliability. With this type of throttle system, an automatic shut off may be implemented, where if the signal strength between the transmitter and receiver drops below a certain threshold, indicating a certain distance between the two has been exceeded, the receiver shuts off the electric motor. This is useful as an automatic shut off if the surfer falls off the board. 
       FIG. 7  illustrates an alternative control mechanism  680  for controlling a motorized surfboard. Control mechanism  680  has a processor  690  for coordinating the operation of the control mechanism  680 . The processor  690  is coupled to an accelerometer  700 . The accelerometer  700  measures acceleration. These measurements are communicated to processor  690 . Processor  690  may also communicate with accelerometer  700  for the purpose of initializing or calibrating accelerometer  700 . In one embodiment, accelerometer  700  is a 3-axis accelerometer and can measure acceleration in any direction. Processor  690  is also coupled to memory  710 . In one example, memory  710  is used to store patterns or profiles of accelerometer readings which have been associated with particular motor control commands. For example, memory  710  may store a pattern of accelerometer readings which has been previously associated with a command to cause the motor controller to activate the motors. The processor  690  can compare the current accelerometer  700  outputs to the previously stored profiles to determine whether the current outputs should be interpreted as a motor command. Control mechanism  680  also has a radio transmitter  720  coupled to the processor  690 . In one embodiment, radio transmitter  720  transmits information received from processor  690 , such as motor commands, to radio receiver  504 . 
       FIG. 8  illustrates a method  740  for using control mechanism  680 , consistent with one embodiment of the invention. At step  745 , output is received from the accelerometer. In one embodiment, the output from the accelerometer may be an analog signal representative of the acceleration measured along each axis measured by the accelerometer. In another embodiment, an analog to digital converter may be used to convert the output to a digital representation of the analog signal. Alternatively, the accelerometer may be configured to output digital signals. For example, the accelerometer itself may be configured to output a digital pulse when the acceleration detected on each axis exceeds some threshold amount. 
     After the output from the accelerometer is received, the control mechanism compares the output to pre-determined command profiles as show in step  750 . These command profiles may also be referred to as accelerometer output patterns or simply as patterns. For example, the control mechanism may store a pattern corresponding to a repeated positive and negative acceleration substantially along a particular axis. Another pattern may correspond to an isolated positive acceleration along a particular axis. The patterns of accelerometer outputs may be associated with particular commands for the motor controllers. For example one pattern may correspond to a command to activate a subset of the available motors. Another pattern may correspond to a command to activate one or more available motors with a particular duty cycle or at a particular percentage of maximum operation potential. 
     The comparison of the current accelerometer output to the command profile results in a determination of whether the output matches a particular command profile, as shown in step  755 . In one embodiment, if the current output does not match a command profile, the output from the accelerometer is discarded and the method concludes, leaving the control mechanism to wait for more output from the accelerometer. However, if the current output does match a command profile, the control mechanism transmits the corresponding command to the motor controllers, as shown in step  760 . After the transmission, the command mechanism may again wait for additional output from the accelerometer. 
     In alternative embodiments, the control mechanism may operate without the need for pattern comparison. For example, in one embodiment, the control mechanism may be configured to interpret accelerometer readings as a proxy for throttle control. In one embodiment, the magnitude and duration of the accelerometer output may be directly translated into magnitude and duration signals for the motor controllers. For example, an acceleration reading above a particular threshold may be interpreted as a command to activate the motors. The duration of the command may be a proportional to the duration for which the acceleration reading is received.  FIG. 9  illustrates one possible embodiment for the control mechanism  680 . In this embodiment the control mechanism is encapsulated in a package  790  which is integrated into a glove  780 . It will be appreciated by one of ordinary skill in the art that the term integrated into the glove may comprise being attached to the surface or within the structure of glove  780 . In one embodiment the package  790  is a water tight package. In one embodiment, package  790  comprises a plastic box. In another embodiment, package  790  comprises layers of fabric or other materials. Advantageously this embodiment facilitates control of the motorized surfboard while maintaining the ability of the surfer to use his hands for normal surfing activity. For example, rather than positioning one hand on throttle  620  to control the motorized surfboard, the normal motion of the surfer&#39;s hand, while wearing the glove, may be used to control the motorized surfboard. For example, it may be desirable for the motor controller to activate the motors while the surfer would normally be paddling. This may be when the surfer is paddling out or when the surfer is attempting to position himself to catch a wave. Accordingly, when the control mechanism is embedded in a glove  780 , the control mechanism may be configured to recognize the acceleration experienced by a surfer&#39;s hand during the paddling motion as a command to engage the motors. Thus, the surfer is free to use his hands for normal surfing activity while the control mechanism activates the motors when the surfer&#39;s hand motions indicate that the surfer is performing an activity which would be aided by additional motor support. Alternatively, the control mechanism may be configured to activate the motors in response to patterns which, though not necessarily surfing related, require less effort or distraction than involved in manually manipulating a throttle. For example, while riding a wave, rather than adjusting a throttle, the surfer wearing glove  780  might simply shake his hand to engage or disengage the motor. Accordingly, the surfer is able to control the motors of the surfboard with less effort and coordination than would be required to manipulate the throttle embedded in body of the surfboard. In an alternative embodiment, the packaged control mechanism  790  may also be attached to or integrated into a wrist strap of other clothing or accessory. In another embodiment, a glove  780  or other accessory or clothing may be worn on each hand and each corresponding control mechanism may control a different subset of motors in the motorized surfboard. 
     Turning now to  FIGS. 10 and 11 , a personal watercraft comprising a first embodiment of a motorized cassette  1020  and a watercraft body  1000  is shown. The body  1000  comprises a top side  1004  and a bottom side  1002 . In some embodiments, the body  1000  may comprise a surfboard and in other embodiments the body  1000  may comprise other traditionally non-powered watercrafts including, for example, inflatable watercrafts, dinghies, life rafts, tenders, sail boards, stand up paddle boards (“SUP boards”), kayaks, and canoes. The body  1000  may be constructed by affixing a top shell to a bottom shell as discussed above or may be constructed using other various methods known to those having ordinary skill in the art. The body  1000  may optionally comprise one or more fin boxes  1010  configured to receive one or more fins  1012 . 
     Turning now also to  FIG. 11 , the bottom side  1002  of the body  1000  may comprise a recess  1008  configured to receive a cassette  1020  therein. The recess  1008  may extend from the bottom surface  1002  toward the top surface  1004  and comprise a generally convex shaped depression in the bottom surface  1002  of the body  1000 . In one embodiment, the recess  1008  forms a tear-drop shaped aperture in the bottom surface  1002 . The tear-drop shaped aperture may be complimentary to the shapes of an insert  1014  and/or cassette  1020  such that the insert  1014  and/or cassette  1020  can be oriented and/or positioned in a desired configuration within the recess  1008 . As explained in further detail below, the insert can be useful because it can include desired features such as flanges, threaded holes for fastener engagement, and the like that can be used to, among other things, secure the cassette in the recess of the surfboard. This allows the shell of the surfboard itself to be entirely made with smooth and gently rounded surfaces in and around the recess  1008  and without sharp corners, holes, or other features that require difficult manufacturing processes. This makes the production of the surfboard  1000  itself very easy and requires minimal changes to the process of manufacturing a conventional surfboard. 
     With continued reference to  FIG. 11 , the insert  1014  may comprise a solid or substantially ring-shaped sheet structure configured to cover at least a portion of the recess  1008 . The insert  1014  may be coupled to the recess  1008  using various coupling means, for example, adhesives, bonding agents, and/or fasteners. In some embodiments, by virtue of the complimentary shapes of the insert  1014  and the recess  1008 , the insert  1014  may be form fitted within the recess  1008  such that the engagement therebetween inhibits longitudinal, lateral, and/or transverse motion of the insert  1014  relative to the recess  1008 . When disposed within the recess  1008 , the insert  1014  can define a receiving space  1016  for receiving the cassette  1020 . In some embodiments, the insert  1014  may comprise one or more relatively small flanges or protrusions (not shown) extending into the receiving space  1016 . The one or more flanges can be configured to engage one or more mating grooves (not shown) disposed in the cassette  1020 . In one embodiment, a flange extends from a forward most portion of the insert  1014  into the receiving space  1016  and the forward most portion of the cassette  1020  includes a corresponding groove. In this way, the cassette  1020  may releasably engage the insert  1014  to align and hold the front of the cassette  1020  relative to the insert  1014  and body  1000 . As shown in  FIG. 10 , the base surface  1022  of the cassette  1020  may be configured to substantially match the adjacent base surface  1002  of the body  1000  to achieve a desired hydrodynamic profile of the personal watercraft. 
     The cassette  1020  may be releasably coupled to the insert  1014  and recess  1008  by one or more fasteners  1060 . In one embodiment, the insert  1014  includes an internally threaded bore  1062  configured to threadably engage a portion of a threaded fastener  1060 , for example, a screw, that passes through a corresponding aperture  1024  formed in the cassette  1020 . In another embodiment, a threaded bore is disposed in the body  1000  and configured to engage a portion of threaded fastener  1060 . In one embodiment, a groove on a first end of the cassette  1020  may releasably receive at least a portion of a corresponding flange extending from the insert  1014  and the second end of the cassette  1020  may be fastened to the insert/body by fastener  1060  to restrict longitudinal, lateral, and/or transverse motion of the cassette  1020  relative to the recess  1008 . As discussed in more detail below, the receiving space  1016  may be configured to releasably receive various different cassettes that are similarly shaped to cassette  1020 . 
     As shown in  FIGS. 10 and 11 , the removable cassette  1020  may comprise a drive system for the personal watercraft. In one embodiment, the drive system components disclosed with reference to  FIGS. 1-6  may be housed within the cassette  1020 . For example, cassette  1020  may comprise one or more exhaust ports  1026 , one or more pump housings  1028 , one or more motor shafts  1030 , one or more motors (not shown), one or more batteries (not shown), and/or one or more impellers (not shown). The orientation and design of these components may be basically the same as described above but housed within cassette  1020 . Thus, cassette  1020  may propel the body  1000  relative to a body of water, for example, to aid in paddling out a surfboard and catching waves. 
       FIGS. 12 and 13  show the personal watercraft comprising a second embodiment of a cassette  1040  received within body  1000 . Cassette  1040  may be similarly shaped to cassette  1020  of  FIGS. 10 and 11  such that both cassettes fit tightly within the receiving space  1016  formed by insert  1014 . Cassette  1040  may be releasably coupled to the body  1000  by one or more threaded fasteners  1060  and/or the engagement between a flange extending from the insert and a groove in the cassette  1040 . As shown, fastener  1060  may pass through an aperture  1034  in the cassette  1040  and be received within threaded bore  1062  in insert  1014 . 
     In contrast to cassette  1020  of  FIGS. 10 and 11 , cassette  1040  may be un-powered or non-motorized. In some embodiments, the cassette  1040  may be hollow and may enclose a storage space configured to store personal items, for example, sun screen, watercraft hardware, keys, mobile phones, etc. In one embodiment, the storage space may be substantially water tight to protect items stored therein from the ingress of water from a body of water, for example, the ocean. In other embodiments, the cassette  1040  may be substantially solid such that the watercraft has generally uniform buoyancy and/or rigidity characteristics from the front end to the back end. 
     The cassette  1020  of  FIGS. 10 and 11  and the cassette  1040  of  FIGS. 12 and 13  may be interchanged to convert the body  1000  between a motorized configuration ( FIGS. 10 and 11 ) and a non-motorized configuration ( FIGS. 12 and 13 ). The body  1000  may come as a kit with one or both of the motorized cassette  1020  and the non-motorized cassette  1040 . A user may switch between cassettes  1020  and  1040  depending on water conditions and/or desired performance characteristics of the personal watercraft. For example, a user may wish to lower the overall mass characteristic of the personal watercraft by opting to place the non-motorized cassette  1040  within the body  1000  or a user may wish to minimize human energy used in a surf session by opting to place the motorized cassette  1020  within the body  1000 . 
       FIGS. 14 and 15  show a kayak including the cassette  1020  and insert  1014  of  FIGS. 10 and 11  received within a recess  1408  of the kayak body  1400 . As shown, a single cassette (e.g., cassette  1020  of  FIGS. 10 and 11  or cassette  1040  of  FIGS. 12 and 13 ) may be placed in different watercraft bodies that have recesses configured to receive the cassette. For example, a motorized cassette  1020  can be configured to fit within a recess in the body of a surfboard and a similarly shaped recess in the body of a kayak such that a user may use the same motorized cassette in multiple watercrafts. In this way, a user may purchase a single motorized cassette to propel different watercrafts. Further, in some implementations, a motorized cassette may be used as a stand alone device to propel a user without a watercraft. For example, a user may hold a motorized cassette  1020  and be propelled through a body of water without a more substantial watercraft (e.g., without a surf board or kayak). 
     Turning now to  FIGS. 16 and 17 , a personal watercraft comprising a motorized cassette  1620  and a watercraft body  1600  is shown. The body  1600  comprises a top side  1604  and a bottom side  1602 . In some embodiments, the body  1600  may comprise a surfboard and in other embodiments the body  1600  may comprise other various watercrafts. Similar to the personal watercraft of  FIGS. 10-13 , the body  1600  may be constructed by affixing a top shell to a bottom shell as discussed above or may be constructed using other various methods known to those having ordinary skill in the art. The body  1600  may optionally comprise one or more fin boxes  1610  configured to receive one or more fins  1612 . 
     Turning now to  FIG. 17 , the bottom side  1602  of the body  1600  may comprise a recess  1608  configured to receive a cassette  1620  therein. The recess  1608  may extend from the bottom surface  1602  toward the top surface  1604  and comprise a generally convex shaped depression in the bottom surface  1602  of the body  1600 . In one embodiment, the recess  1608  forms a tear-drop shaped aperture in the bottom surface  1602 . The tear-drop shaped aperture may be complimentary to the shapes of the insert  1614  and/or cassette  1620  such that the insert  1614  and/or cassette  1620  can be oriented and/or positioned in a desired configuration within the recess  1608 . 
     With continued reference to  FIG. 17 , the insert  1614  may comprise a solid or substantially ring-shaped sheet structure configured to cover at least a portion of the recess  1608 . The insert  1614  may be coupled to the recess  1608  using various coupling means, for example, adhesives, bonding agents, and/or fasteners. In some embodiments, by virtue of the complimentary shapes of the insert  1614  and the recess  1608 , the insert  1614  may be form fitted within the recess  1608  such that the engagement therebetween inhibits longitudinal, lateral, and/or transverse motion of the insert  1614  relative to the recess  1608 . When disposed within the recess  1608 , the insert  1614  can define a receiving space  1616  for receiving the cassette  1620 . 
     In some embodiments, the insert  1614  may include one or more protrusions  1651  configured to be inserted into one or more indentations  1659  (shown in  FIG. 18 ) on the cassette  1620 . The protrusions  1651  and indentations  1659  on the cassette  1620  can have complimentary shapes such that the protrusions may be received by the indentations by sliding the cassette  1620  forward longitudinally relative to the insert  1614 . The engagement of the protrusions  1651  and corresponding indentations can result in one or more abutments that act to arrest or inhibit longitudinal, lateral, and/or transverse movement of the cassette  1620  relative to the insert  1614  and body  1600 . 
     The insert  1614  may also include a latch element  1653  that is cantilevered from a latch plate  1655 . The latch element  1653  may catch one or more surfaces within a receptacle  1661  (shown in  FIG. 18 ) on the cassette  1620  when the cassette  1620  is received within the insert  1614  to secure the cassette  1620  in the longitudinal direction relative to the insert  1614 . In this way, the cassette  1620  may be slid forward into the insert  1614  until the latch  1653  releasably engages a notch or other feature on the cassette such that the cassette  1620  is aligned and secured relative to the insert  1614 . To remove the cassette  1620  from the insert  1614 , the latch element  1653  may be depressed by applying a force to the cantilevered end of the latch element  1653  to disengage the latch element from the notch or other feature of the cassette. Disengaging the latch element  1653  then will allow a user to slide the cassette  1620  backward longitudinally relative to the insert  1614  to release the protrusions  1651  from the indentations  1659  and to remove the cassette  1620  from the body  1600 . 
     As shown in  FIG. 16 , the base surface  1622  of the cassette  1620  may be configured to substantially match the adjacent base surface  1602  of the body  1600  to achieve a desired hydrodynamic profile of the personal watercraft. The base surface  1622  may also include a charging port  1631  and/or activation switch  1633 . Thus, the cassette  1620  may be charged when the cassette is coupled to the watercraft body  1600  or when it is separate from the watercraft body. In embodiments when these are provided, the charger port  1631  can be disposed on an opposite side of the cassette  1620  and the activation switch  1633  can be disposed elsewhere as well if desired. 
     As shown in  FIGS. 18 and 19 , the removable cassette  1620  may comprise a drive system including one or more motors  1675 . In one embodiment, the drive system can be at least partially housed between a cassette base  1671  and a cassette cover  1657 . The one or more motors  1675  can be powered by one or more batteries  1665  and can be mounted to the cassette base  1671  by motor mounts  1677 . In some embodiments, each motor  1675  can be coupled to a motor shaft  1690  by a shaft coupler  1679 , shaft bearing  1681 , bearing holder  1683 , and spacer  1685 . Each shaft  1690  can be coupled to an impeller  1699  that is disposed at least partially within a pump housing  1695  and a bearing  1697  can optionally be disposed between each shaft and the impeller  1699 . In this way, the one or more motors  1675  can drive each impeller  1699  to draw water through the pump housing  1695  to propel the cassette relative to a body of water. 
     In some embodiments, each shaft  1690  can be disposed within a shaft housing  1694  that is configured to limit the exposure of the shaft  1690  to objects that are separate from the cassette  1620 . Thus, the shaft housing  1694  can protect a user from inadvertently contacting the shaft  1690  during use and/or can protect the shaft  1690  from contacting other objects, for example, sea grass. Additionally, the shaft housing  1694  can improve performance of the cassette  1620  by isolating each shaft  1690  from the water that passes through the pump housing  1695 . In some embodiments, each shaft  1690  can be protected from exposure to the water by one or more shaft seals  1692 . 
     The cassette  1620  can also include one or more grates  1693  disposed over intake ports of the pump housing  1695 . The grates  1693  can limit access to the impeller  1699  and shaft  1690  to protect these components and/or to prevent a user from inadvertently contacting these components during use. In some embodiments, each pump housing  1695  and/or grate  1693  can be coupled to one or more magnetic switches (not shown) that can deactivate the motors  1675  when the pump housing  1695  and/or grate  1693  are separated from the cassette base  1671 . Therefore, the one or more magnetic switches may prevent the cassette from operating without the optional grate  1693  and/or pump housing in place. 
     With continued reference to  FIGS. 18 and 19 , the drive system may also include one or more motor controllers  1673  for each motor  1675 , one or more relays  1687  configured to connect the one or more batteries  1665  with the one or more motor controllers  1673 , an antenna  1667 , and a transceiver  1669 . The one or more motor controllers  1673 , one or more relays  1687 , one or more batteries  1665 , antenna  1667 , and transceiver  1669 , can be electrically connected to each another by one or more wiring harnesses  1663 . As discussed above, the transceiver  1669  can include or be coupled to wireless transmission circuitry that is configured to transmit electromagnetic and/or magnetic signals underwater. 
       FIGS. 20 and 21  show a personal watercraft  2000  comprising a body  2031  having a curved section  2033  disposed adjacent to and rearward of a pump housing  2020  and pump housing exhaust port  2025 . The curved section  2033  may be shaped to create a Coanda Effect to direct flow from the exhaust port  2025  to follow the curve of the curved section  2033 . The Coanda Effect on the flow that exits the exhaust port  2025  can result in an effective thrust of the expelled fluid in a thrust area  2050  as the expelled fluid enters the surrounding water  2060 . As used herein, the term “Coanda Effect” refers to the tendency of a fluid jet to be attracted to a nearby surface, for example, the curved section  2033  of personal watercraft  2000  body  2031 . The curved section  2033  and the relative positioning of the curved section  2033  and the pump housing  2020  can be incorporated in any of the personal watercraft described herein to create a thrust area between the exhaust port  2025  and the curved section  2033 . 
       FIG. 22  shows an embodiment of a pump housing  2220  having a generally curvilinear cross-sectional shape that tapers to a flattened and oblong exhaust port  2225 . The exhaust port  2225  includes a first flattened side  2221  and a second flattened side  2223  disposed opposite to the first side. The first and second sides  2221 ,  2223  of exhaust port  2225  stabilize the rotational flow of water passing therethrough to create a more uniform flow of expelled water in the thrust area  2250  adjacent to and rearward of the exhaust port  2225 . Pump housing  2220  can optionally include one or more flow straighteners, for example, flow straighteners  228  previously discussed with reference to  FIGS. 2 and 3 . The optional flow straighteners can be configured to stabilize the flow of water passing through the pump housing  2220  and the exhaust port  2225  can be configured to further stabilize the flow of water passing therethrough. The shape of the pump housing  2220  and the exhaust port  2225  can be incorporated in any of the personal watercraft described herein to create a more uniform flow in the thrust area adjacent to the exhaust port  2225 . 
       FIGS. 10-17  show embodiments of personal watercrafts that include a receiving space configured to receive a motorized or non-motorized cassette. As discussed now with reference to  FIGS. 23-29 , in some embodiments, the motorized cassettes disclosed herein can be releasably mounted or otherwise coupled to a watercraft body that does not include a corresponding receiving space. In this way, the motorized cassettes can provide motorized propulsion capability to the watercraft. 
       FIG. 23  is a top perspective view of one embodiment of a mounting system  2300  that can be used to secure, mount, or otherwise couple a motorized cassette to a watercraft body. The mounting system  2300  includes a tiller  2301 , a mounting assembly  2311 , a steering column  2321 , and a housing  2331 . As discussed in further detail below, the housing  2331  can be configured to releasably accept a motorized cassette in a receiving space formed in the bottom side of the housing. The housing  2331  can also include optional solar panels  2351  to directly charge the batteries of the received motorized cassette when sunlight is available. 
     The mounting assembly  2311  can include a u-shaped bracket  2313  and one or more mounting disks  2315  that can be adjusted relative to the bracket. The mounting disks  2315  and bracket  2313  can cooperate to frictionally engage a portion of a watercraft, for example, a bow, stern, sidewall, transom, and/or other portion of a watercraft hull. In this way, the mounting assembly  2311  can be releasably secured relative to a watercraft body at various locations. As shown, the steering column extends downward from the mounting assembly  2311  such that the housing  2331  is offset from the mounting assembly. The length of the steering column  2321  can be adjusted depending on the dimensions of the intended watercraft such that some or all of the housing  2331  lies just below the waterline of the watercraft. Thus, the mounting assembly  2311  can be configured to have a limited fluid profile in a body of water and to allow an associated watercraft to traverse shallow waters with motorized propulsion. In some cases, the bottom of the housing  2331  is less than three inches below the water line, or even less than one inch below the water line. With the water inlet and water outlet positioned in a flat bottom surface, the watercraft can be powered with very little of the housing under the water, much less than is required for propeller based propulsion. 
     With continued reference to  FIG. 23 , the tiller  2301 , steering column  2321 , and housing  2331  can each be coupled to one another and configured to move in concert relative to the mounting assembly  2311 . For example, the tiller  2301  can be manipulated to rotate the steering column and housing  2331  relative to the mounting assembly  2311  to steer a watercraft in different directions. In some embodiments, the housing  2331  can include one or more skegs (not shown) disposed near the front and/or rear of the housing to further facilitate steering. 
     As schematically illustrated, the tiller  2301  can optionally include a control mechanism  2353  for controlling a motorized cassette received within the housing  2331 . As discussed above with respect to  FIG. 7 , the control mechanism  2353  can include a processor, an accelerometer, a memory, and a transmitter. In some embodiments, the control mechanism  2353  can directly communicate with a received cassette via a hard wire connection through the mounting system  2300 . In other embodiments, the control mechanism  2353  can communicate wirelessly with a received cassette. Additionally, the control mechanism  2353  can be fixed relative to the tiller  2301  or can be releasably securable to the mounting system  2300 . For example, the control mechanism  2353  can be similar to the control mechanism  680  of  FIG. 9  and can be releasably secured to the tiller  2301 . Alternatively, the mounting system  2300  does not include a control mechanism and a received cassette can be controlled by a separate control mechanism, for example, the control mechanism  680  of  FIG. 9  worn as a glove or watch by an operator. 
     As discussed above, the mounting system  2300  of  FIG. 23  can be secured relative to a watercraft to provide motorized propulsion capability thereto.  FIGS. 24-29  illustrate an embodiment of a watercraft  2400  showing mounting system  2300  of  FIG. 23  and an associated watercraft body  2411 . 
     As shown in  FIG. 24 , the mounting system  2300  can be mounted via the mounting assembly  2311  to the aft or starboard sidewall of the watercraft body  2411 . In some embodiments, the mounting system  2300  can be mounted to a transom along the bow or stern of the watercraft body  2411  to provide front-side or rear-side propulsion, respectively. For illustrative purposes, the watercraft body  2411  of  FIGS. 24-29  is depicted as a partial cutaway of a generic watercraft. However, it will be appreciated by one of ordinary skill in the art that the watercraft body  2411  can comprise various watercraft bodies, including, for example, dinghies, rafts, tenders, rowboats, gondolas, skiffs, barges, inflatable watercrafts, motor boats, sail boats, dories, sharpies, punts, jonsboats, and catamarans. Thus, the mounting system  2300  can be utilized to provide motorized propulsion capability to an otherwise non-powered watercraft or can be utilized to provide motorized propulsion capability to an otherwise powered watercraft. 
     As shown in  FIGS. 25 and 26 , an interchangeable motorized cassette  2341  can be inserted at least partially within a receiving space  2308  formed in the bottom side of the housing  2331 . The receiving space  2308  is defined by a bottom facing surface  2314  of the housing  2331  which includes protrusions  2315 . Similar to the insert  1614  and cassette  1620  of  FIGS. 17 and 18 , the protrusions  2315  are configured to be inserted into one or more indentations (not shown) on the cassette  2341  to arrest or inhibit longitudinal, lateral, and/or transverse movement of the cassette  2341  relative to the housing  2331 . 
     The bottom facing surface  2314  may also include a latch element configured to releasably engage a notch or other feature on the cassette  2341  such that the cassette  2341  is aligned and secured relative to the housing  2331 . In some embodiments, the cassette  2341  may be secured relative to the housing  2331  by other means, for example, one or more mechanical fasteners. In this way, the cassette  2341  may be easily inserted into and removed from the mounting assembly. In some implementations, the housing  2331  may be rotated about the mounting assembly  2311  to remove the housing from the water in order to remove or insert the cassette  2341 . In other implementations, the mounting system  2300  and cassette  2341  may have a low enough weight such that the entire mounting system  2300  may be easily separated from the water craft body  2411  to remove or insert the cassette  2341 . 
     In some embodiments, the motorized cassette  2341  may be substantially similar to the motorized cassette  1620  of  FIGS. 17 and 18  and the surface  2314  of housing  2331  can also be substantially similar to the insert  1614  of  FIGS. 17 and 18 . In such embodiments, a single motorized cassette can be provided for use with a personal watercraft having a receiving space and/or for use with mounting system  2300 . In other embodiments, the motorized cassette  2341  may be differently sized and/or shaped than the motorized cassette  1620  of  FIGS. 17 and 18 . For example, motorized cassette  2341  may be larger than the motorized cassette  1620  to house different batteries, motors, impellers, and/or other drive system components. 
     It is also possible for the motorized cassette to be permanently attached to the housing  2331 , rather than removable as described above. As another alternative, the top of the housing  2331  can form the enclosure of the motorized drive system, such that the housing  2331  forms the motorized cassette itself 
     As shown in  FIGS. 27-29 , once the motorized cassette  2341  has been inserted into the housing  2331  and the mounting system  2300  has been secured relative to the watercraft body  2401 , the tiller  2301  can be manipulated to steer the watercraft  2400  in different directions. For example, the tiller  2301  has been manipulated in  FIG. 27  such that the steering column  2321  and housing  2331  have pointed the front side of the motorized cassette towards the watercraft body  2401 . In such a position, the motorized cassette will steer the watercraft  2400  toward the right as shown if the motorized cassette is nearer to the bow than the stern. It will also be appreciated by one or ordinary skill in the art that if the motorized cassette is disposed nearer to the stern than the bow that the motorized cassette in  FIG. 27  will steer the watercraft  2400  toward the left. 
       FIG. 28  shows another example of steering the watercraft  2400  In  FIG. 28  the tiller  2301  has been manipulated such that the steering column  2321  and housing  2331  have pointed the front side of the motorized cassette away from the watercraft body  2401 . In such a position, the motorized cassette will steer the watercraft  2400  toward the left as indicated if the motorized cassette is nearer to the bow than the stern. However, if the motorized cassette in  FIG. 28  is disposed nearer to the stern than the bow, the motorized cassette will steer the watercraft  2400  toward the right. As shown in  FIG. 29 , the tiller  2301  may be rotated  180  degrees from the position shown in  FIG. 24  such that the front side of the motorized cassette is pointed toward the stern of the watercraft  2400 . In such a position, the motorized cassette will drive the watercraft  2400  in reverse (e.g., with the stern headed first). Thus, the tiller  2301  may be easily manipulated to steer the watercraft  2400  in any direction relative to a body of water.