Patent Publication Number: US-11383812-B1

Title: Watercraft propulsion system and method for inverting a rotation of an impeller driven by a motor of a watercraft

Description:
CROSS-REFERENCE 
     The present application claims priority from U.S. provisional patent application Ser. No. 62/799,533, filed on Jan. 31, 2019, the disclosure of which is incorporated by reference herein. 
    
    
     FIELD OF TECHNOLOGY 
     The present technology relates to a method for inverting a rotation of an impeller driven by a motor and to a watercraft propulsion system. 
     BACKGROUND 
     Water jet propelled watercraft offer high performance, good acceleration and handling, and allow for shallow-water operation. Accordingly, personal watercrafts, which typically employ water jet propulsion systems, have become popular, especially in resort areas. 
     A common problem with jet propulsion systems is that foreign objects such as vegetation (e.g. weeds), rocks, rope and other debris can get drawn into the jet propulsion system and remain lodged therein. For example, foreign objects can get caught on an intake grate, a driveshaft or an impeller of the jet propulsion system. Clogs caused by these foreign objects can in turn adversely affect performance of the system, notably by reducing a thrust generated by the jet propulsion system. In turn, the reduced thrust in combination with high speed rotation of the impeller can form low pressure areas around the blades of the impeller and thus cause cavitation thereof. In addition, the clogs can in some cases block cooling water flow and thus lead to overheating. While the jet propulsion system can be unclogged manually by accessing a bottom of the watercraft&#39;s hull, this can be a difficult and time-consuming task for the operator. 
     To address this issue, it has been proposed to operate a jet propulsion system in reverse such as to propel water towards an inlet thereof (as opposed to a rearward outlet at a steering nozzle of the jet propulsion system) by unlinking an impeller shaft from a motor of the jet propulsion system, and linking again the impeller shaft to the motor to cause the impeller shaft to rotate in a reverse direction. Hence, the generated thrust may be used to clear clogs in the jet propulsion system. However, careless switching between forward and reverse operations of the jet propulsion system could damage mechanical components such as, for example, a gearbox connecting the motor to the impeller shaft. 
     Moreover, a flow of water that is normally present when the jet propulsion system is operating in the forward direction is useful in cooling an exhaust system of the watercraft. However, such flow is absent, or at least less effective in cooling the exhaust system, when the jet propulsion system is operating in the reverse direction. 
     In view of the foregoing, there is a need for a watercraft with a jet propulsion system that can be unclogged without causing damage to components of the jet propulsion system. 
     SUMMARY 
     It is an object of the present technology to ameliorate at least some of the inconveniences present in the prior art. 
     According to one aspect of the present technology, there is provided a method for inverting a rotation of an impeller driven by a motor of a watercraft, the method comprising: sensing that the motor is stopped; and in response to sensing that the motor is stopped: disconnecting a direct linkage between the motor and the impeller, establishing a reverse connection between the motor and the impeller, sensing that the reverse connection is established between the motor and the impeller, and starting the motor in response to sensing that the reverse connection is established between the motor and the impeller. 
     In some embodiments of the present technology, the method further comprises providing a visual or audible fault indication if the reverse connection is not established. 
     In some embodiments of the present technology, the method further comprises, before disconnecting the direct linkage between the motor and the impeller: receiving a user command requesting reverse operation of the impeller; and providing a visual or audible indication when reverse operation of the impeller is not allowed because the motor is not stopped. 
     In some embodiments of the present technology, the motor is an internal combustion engine; the method further comprises sensing an exhaust gas temperature; and establishing the reverse connection between the motor and the impeller is conditional to the sensed exhaust gas temperature being less than a temperature threshold. 
     In some embodiments of the present technology, the method further comprises providing a visual or audible indication when the direct linkage between the motor and the impeller is not disconnected due to the exhaust gas temperature meeting or exceeding the temperature threshold. 
     In some embodiments of the present technology, the method further comprises stopping the internal combustion engine if the exhaust gas temperature increases to meet or exceed the temperature threshold when operating the internal combustion engine with the reverse connection established between the internal combustion engine and the impeller. 
     In some embodiments of the present technology, the method further comprises providing a visual or audible indication when the internal combustion engine is stopped due to the exhaust gas temperature meeting or exceeding the temperature threshold. 
     In some embodiments of the present technology, the method further comprises sensing a speed of the watercraft, establishing the reverse connection between the motor and the impeller being conditional to the speed of the watercraft being less than a maximum speed threshold. 
     In some embodiments of the present technology, the method further comprises providing a visual or audible indication when the direct linkage between the motor and the impeller is not disconnected due to the speed of the watercraft meeting or exceeding the maximum speed threshold. 
     In some embodiments of the present technology, the method further comprises starting a timer when starting the motor in response to sensing that the reverse connection is established; and stopping the motor if the timer reaches a duration threshold when operating the motor with the reverse connection established between the motor and the impeller. 
     In some embodiments of the present technology, the method further comprises providing a visual or audible indication when the motor is stopped due to the timer reaching the duration threshold. 
     In some embodiments of the present technology, sensing that the motor is stopped comprises sensing a rotational speed of the motor. 
     In some embodiments of the present technology, the method further comprises limiting the rotational speed of the motor to be less than a rotational speed threshold when operating the motor with the reverse connection established between the motor and the impeller. 
     In some embodiments of the present technology, the method further comprises providing a visual or audible indication indicating that the rotational speed of the motor is limited by the rotational speed threshold. 
     In some embodiments of the present technology, the method further comprises energizing an actuator to cause a gearbox to disconnect the direct linkage between the motor and the impeller and to establish the reverse connection between the motor and the impeller. 
     In some embodiments of the present technology, the method further comprises causing a shaft of the motor to rotate in a range between 5 and 10 degrees to complete the establishment of the reverse connection between the motor and the impeller. 
     In some embodiments of the present technology, the motor is an internal combustion engine having a crankshaft; and causing the shaft of the motor to rotate comprises providing an impulse command to a starter motor operatively connected to the crankshaft. 
     According to another aspect of the present technology, there is provided a watercraft propulsion system, comprising: a motor; a motor status sensor adapted for indicating whether the motor is running or stopped; an impeller operatively connected to the motor; an impeller housing receiving the impeller therein; a gearbox comprising a direct linkage and a reversing gear set; an actuator operatively connected to the gearbox and adapted for causing the gearbox to selectively establish an operative connection of the impeller to the motor via one of the direct linkage and the reversing gear set; a gearbox position sensor adapted for indicating whether the impeller is connected to the motor via the direct linkage or the via reversing gear set; an electronic control unit (ECU), comprising: a processor communicating with the motor status sensor, with the actuator and with the gearbox position sensor; and a non-transitory computer-readable medium having stored thereon machine executable instructions for performing, when executed by the processor, the method for inverting a rotation of the impeller. 
     In some embodiments of the present technology, the motor status sensor is a motor rotational speed sensor. 
     In some embodiments of the present technology, the motor is an internal combustion engine; the watercraft propulsion system further comprises an exhaust gas temperature sensor communicating with the processor; and the processor is configured to prevent establishing the reverse connection between the internal combustion engine and the impeller if an exhaust gas temperature meets or exceeds a temperature threshold. 
     In some embodiments of the present technology, the processor is configured to stop the internal combustion engine if the exhaust gas temperature increases to meet or exceed the temperature threshold when the reverse connection is established between the engine and the impeller. 
     In some embodiments of the present technology, the watercraft propulsion system further comprises: a timer communicating with the processor; the processor being configured to evaluate a time duration of operation of the motor with the reverse connection established between the motor and the impeller and to stop the motor if the time duration reaches a duration threshold. 
     In some embodiments of the present technology, the gearbox comprises: an input shaft having one end driven by the motor and an opposite end having a first set of dogs; and an output shaft having one end operatively connected to the impeller and an opposite end having a second set of dogs; the direct linkage being established when the first set of dogs comes in contact with the second set of dogs. 
     In some embodiments of the present technology, the reversing gear set comprises: a shifting rod operatively connected to the actuator, the actuator causing the shifting rod to move to a reversing position in response to receiving a reversing command and to move to a normal position in response to receiving a forwarding command; a shifting fork connecting the shifting rod to the output shaft so that the second set of dogs of the output shaft engages the first set of dogs of the input shaft when the shifting rod is in the normal position, the shifting fork causing a displacement of the output shaft away from the input shaft to disengage the first and second sets of dogs when the shifting rod is in the reversing position; and a shifting shaft adapted for being displaced in parallel to the shifting rod, the shifting shaft carrying gears that engage gears mounted on the input and output shafts to cause a rotation of the output shaft in a direction opposite from a rotation of the input shaft when the shifting rod is in the reversing position, the gear carried by the shifting shaft being disengaged from the gears mounted on the input and output shafts when the shifting rod is in the normal position. 
     In some embodiments of the present technology, the gearbox position sensor is adapted for detecting a position of the shifting rod. 
     In some embodiments of the present technology, the watercraft propulsion system further comprises an impeller shaft operatively connecting the gearbox to the impeller. 
     In some embodiments of the present technology, the actuator is an electric actuator. 
     In some embodiments of the present technology, the actuator is a stepper motor. 
     According to a further aspect of the present technology, there is provided a watercraft comprising: a hull having a bow and a stern opposite the bow; a duct having a water inlet on a lower side of the hull and a water outlet; and the watercraft propulsion system; the impeller housing forming a portion of the duct, the impeller being adapted to force water to flow into the duct from the water inlet and to be expelled from the water outlet to propel the watercraft when the watercraft propulsion system operates in the forward direction, the impeller being adapted to force water to flow into the duct from the water outlet and to be expelled from the water inlet when the watercraft propulsion system operates in the reverse direction. 
     In some embodiments of the present technology, the watercraft further comprises: a vehicle speed sensor for sensing a speed of the watercraft, the vehicle speed sensor communicating with the processor; the processor being configured to prevent establishing the reverse connection between the motor and the impeller if the speed of the watercraft meets or exceeds a maximum speed threshold. 
     In some embodiments of the present technology, the watercraft further comprises a display cluster communicating with the ECU and adapted for providing visual or audible indications of statuses of the jet propulsion system. 
     In some embodiments of the present technology, the processor is further configured to stop the motor when the reverse connection between the motor and the impeller is established and the speed of the watercraft meets or exceeds the maximum speed threshold. 
     Embodiments of the present technology each have at least one of the above-mentioned object and/or aspects, but do not necessarily have all of them. It should be understood that some aspects of the present technology that have resulted from attempting to attain the above-mentioned object may not satisfy this object and/or may satisfy other objects not specifically recited herein. 
     Additional and/or alternative features, aspects and advantages of embodiments of the present technology will become apparent from the following description, the accompanying drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present technology, as well as other aspects and further features thereof, reference is made to the following description which is to be used in conjunction with the accompanying drawings, where: 
         FIG. 1  is a left side elevation view of a personal watercraft in accordance with an embodiment of the present technology; 
         FIG. 2  is a top plan view of the watercraft of  FIG. 1 ; 
         FIG. 3  is a front elevation view of the watercraft of  FIG. 1 ; 
         FIG. 4  is a rear elevation view of the watercraft of  FIG. 1 ; 
         FIG. 5  is a bottom plan view of the watercraft of  FIG. 1 ; 
         FIG. 6  is a perspective view of a driveline of the watercraft of  FIG. 1  showing a motor, an impeller shaft and an impeller; 
         FIG. 7  is a cross-section view of the motor of  FIG. 6  and of a gearbox connecting the motor to the impeller shaft; 
         FIG. 8  is a side elevation view of components of the driveline of  FIG. 6 ; 
         FIG. 9  is a top view of the gearbox of  FIG. 7  showing an input shaft connected to an output shaft in a forward direction; 
         FIG. 10  is a top view of the gearbox of  FIG. 9  showing the input shaft connected to the output shaft in a reverse direction; 
         FIG. 11  is a block diagram of a system for inverting a rotation of the impeller of  FIG. 6 ; and 
         FIGS. 12 a , 12 b  and 12 c    are a sequence diagram showing operations of a method for inverting the rotation of the impeller of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION 
     The present technology will be described with respect to a personal watercraft. However, it is contemplated that the present technology could be applied to other marine vehicles equipped with a jet propulsion system or to marine vehicles equipped with other types of watercraft propulsion systems. Application of the present technology is therefore not intended to be limited to its use in personal watercraft or to jet propulsion systems. Additionally, while an intended use of the present technology is to operate the impeller of the personal watercraft in a reverse direction to help unclogging the jet propulsion system, the present technology can also be used for other applications that benefit from reverse operation of the impeller. 
     A personal watercraft  10  in accordance with one embodiment of the present technology is shown in  FIGS. 1 to 5 . The following description relates to one example of a personal watercraft. Those of ordinary skill in the art will recognize that there are other known types of personal watercraft incorporating different designs and that the present technology would encompass these other watercrafts. 
     As will be discussed in greater detail below, the personal watercraft  10  has a jet propulsion system  50  for propelling the watercraft  10 . In accordance with the present technology, the jet propulsion system  50 , including a venturi unit  100  thereof, is configured to reverse a flow of water therein in such a manner as to clear the jet propulsion system  50  of foreign bodies. 
     The watercraft  10  has a hull  12  and a deck  14 . The hull  12  has a bow  42  and a stern  44  opposite the bow  42 . The hull  12  buoyantly supports the watercraft  10  in the water. The deck  14  is designed to accommodate one or multiple riders. The hull  12  and the deck  14  are joined together at a seam  16  that joins the parts in a sealing relationship. A bumper  18  generally covers the seam  16 , which helps to prevent damage to the outer surface of the watercraft  10  when the watercraft  10  is docked, for example. 
     As seen in  FIG. 1 , the deck  14  has a centrally positioned straddle-type seat  28  positioned on top of a pedestal  30  to accommodate multiple riders in a straddling position. The seat  28  includes a front seat portion  32  and a rear, raised seat portion  34 . The seat  28  is preferably made as a cushioned or padded unit, or as interfitting units. The front and rear seat portions  32 ,  34  are removably attached to the pedestal  30 . The seat portions  32 ,  34  can be individually tilted or removed completely. Seat portion  32  covers a motor access opening defined by a top portion of the pedestal  30  to provide access to a motor  22 . Seat portion  34  covers a removable storage bin  26 . A small storage box is provided in front of the seat  28 . 
     The watercraft  10  has a pair of generally upwardly extending walls located on either side of the watercraft  10  known as gunwales or gunnels  36 . The gunnels  36  help to prevent the entry of water in the footrests  38  of the watercraft  10 , provide lateral support for the riders&#39; feet, and also provide buoyancy when turning the watercraft  10 , since the personal watercraft  10  may roll slightly when turning. Towards the rear of the watercraft  10 , the gunnels  36  extend inwardly to act as heel rests  45  ( FIG. 2 ). A passenger riding the watercraft  10  facing towards the rear, to spot a water-skier for example, may place his or her heels on the heel rests  45 , thereby providing a more stable riding position. Heel rests  45  could also be formed separately from the gunnels  36 . 
     Located on both sides of the watercraft  10 , between the pedestal  30  and the gunnels  36 , are the footrests  38 . The footrests  38  are designed to accommodate the riders&#39; feet in various riding positions. The footrests  38  are covered by carpeting made of a rubber-type material, for example, to provide additional comfort and traction for the feet of the riders. 
     A reboarding platform  40  is provided at the rear of the watercraft  10  on the deck  14  to allow the rider or a passenger to easily reboard the watercraft  10  from the water. Carpeting or some other suitable covering may cover the reboarding platform  40 . A retractable ladder (not shown) may be affixed to a transom  47  of the stern  44  to facilitate boarding the watercraft  10  from the water onto the reboarding platform  40 . 
     Referring to the bow  42  of the watercraft  10 , as seen in  FIG. 1 , the watercraft  10  is provided with a hood  46  located forwardly of the seat  28  and a helm assembly  60 . A hinge (not shown) is attached between a forward portion of the hood  46  and the deck  14  to allow the hood  46  to move to an open position to provide access to a front storage bin  24 . A latch (not shown) located at a rearward portion of the hood  46  locks the hood  46  into a closed position. When in the closed position, the hood  46  prevents water from entering the front storage bin  24 . Rearview mirrors  62  are positioned on either side of the hood  46  to allow the rider to see behind the watercraft  10 . A hook  63  is located at the bow  42  of the watercraft  10  ( FIG. 3 ). The hook  63  is used to attach the watercraft  10  to a dock when the watercraft  10  is not in use or to attach to a winch when loading the watercraft  10  on a trailer, for instance. 
     As best seen in  FIG. 1 , the hull  12  is provided with a combination of strakes  66  and chines  68 . A strake  66  is a protruding portion of the hull  12 . A chine  68  is the vertex formed where two surfaces of the hull  12  meet. The combination of strakes  66  and chines  68  provide the watercraft  10  with its riding and handling characteristics. 
     Sponsons  77  ( FIGS. 2 and 3 ) are located on both sides of the hull  12  near the transom  47 . The sponsons  77  have an arcuate undersurface that gives the watercraft  10  both lift while in motion and improved turning characteristics. The sponsons  77  are fixed to the surface of the hull  12  and can be attached to the hull  12  by fasteners or molded therewith. It is contemplated that the position of the sponsons  77  with respect to the hull  12  may be adjustable to change the handling characteristics of the watercraft  10  and accommodate different riding conditions. 
     The hull  12  has a tunnel  94  in which a part of the jet propulsion system  50  is received. The tunnel  94  is defined at the front, sides and top by the hull  12  and is open at the transom  47 . The bottom of the tunnel  94  is closed by a ride plate  96 . The ride plate  96  creates a surface on which the watercraft  10  rides or planes at high speeds. 
     As best seen in  FIGS. 3 and 4 , the helm assembly  60  is positioned forwardly of the seat  28 . The helm assembly  60  has a central helm portion  64 , that is padded, and a handlebar  65  having steering handles at its opposite ends. One of the steering handles is provided with a throttle operator  61  ( FIG. 4 ), which allows the rider to control the motor  22 , and therefore the speed of the watercraft  10 . The throttle operator  61  is a thumb-actuated throttle lever. However it is contemplated that the throttle operator  61  could be a finger-actuated throttle lever or a twist grip. The throttle operator  61  is movable between an idle position and multiple actuated positions. In the present embodiment, the throttle operator  61  is biased towards the idle position, such that, should the driver of the watercraft  10  let go of the throttle operator  61 , it will move to the idle position. The other of the steering handles is provided with a reverse gate operator  67  ( FIG. 4 ) used by the driver to actuate a reverse gate  110  ( FIG. 4 ) of the watercraft  10 . The reverse gate operator  67  is a finger-actuated lever. However, it is contemplated that the reverse gate operator  67  could be a thumb-actuated lever or a twist grip. 
     The reverse gate  110  is movable between a stowed position ( FIG. 4 ) where it does not interfere with the jet of water being expelled rearwardly along a duct  52  by the jet propulsion system  50  and a plurality of positions where it redirects the jet of water being expelled rearwardly along the duct  52  by the jet propulsion system  50 . Notably, the reverse gate  110  may be actuated into a neutral position in which thrust generated by the jet propulsion system  50  does not have a horizontal component such that the watercraft  10  will not be accelerated or decelerated by the thrust and will generally stay in position if it was not moving prior to moving the reverse gate  110  in the neutral position. The reverse gate  110  may also be actuated into a reverse position to redirect the jet of water towards the front of the watercraft  10 , thus causing the watercraft  10  to move in a reverse direction. 
     The reverse gate  110  is pivotally connected to the ride plate  96 . It is also contemplated that the reverse gate  110  could be pivotally attached to the sidewalls of the tunnel  94 . Other ways of operatively mounting the reverse gate  110  to the hull  12  or jet propulsion system  50  are also contemplated. 
     A reverse gate actuator (not shown), in the form of an electric motor, is operatively connected to the reverse gate  110  to move the reverse gate  110 . The reverse gate actuator could alternatively be any one of a mechanical, a hydraulic, or another type of electric actuator. One contemplated reverse gate actuator is shown and described in U.S. Pat. No. 7,841,915, issued Nov. 30, 2010, the entirety of which is incorporated herein by reference. 
     The helm assembly  60  is provided with a key receiving post  41  located near a center of the central helm portion  64 . The key receiving post  41  is adapted to receive a key (not shown) that starts the watercraft  10 . The key is typically attached to a safety lanyard (not shown) that may be attached to a safety vest of a rider of the watercraft  10 . It should be noted that the key receiving post  41  may be placed in any suitable location on the watercraft  10 . 
     A display area or cluster  43  is located forwardly of the helm assembly  60 . The display cluster  43  can be of any conventional display type, including a liquid crystal display (LCD), dials or LED (light emitting diodes). The central helm portion  64  has various buttons, which could alternatively be in the form of levers or switches, that allow the driver to modify the display data or mode (speed, motor RPM, time, fuel level, and the like) on the display cluster  43  or to change a condition of the watercraft  10 , such as trim (the pitch of the watercraft  10 ). 
     As shown schematically in  FIG. 1 , the motor  22  is supported by the hull  12  and is enclosed within a motor compartment  20  defined between the hull  12  and the deck  14 . The motor  22  is configured for driving the jet propulsion system  50  (also commonly referred to as a “jet pump drive”) which propels the watercraft  10 . The motor compartment  20  accommodates the motor  22 , as well as a muffler, tuning pipe, gas tank, electrical system (battery, electronic control unit, and the like), air box, storage bins  24 ,  26 , and other elements required or desirable in the watercraft  10 . In this embodiment, the motor  22  is an internal combustion engine  22  and will thus be referred to as the engine  22 . However, it is contemplated that, in alternative embodiments, the motor  22  may be any other suitable type of motor such as an electric motor. As will be understood, in such an embodiment, certain components would be added to or omitted from the watercraft  10  (e.g., no muffler and gas tank, and the like). 
     The jet propulsion system  50  pressurizes water to create thrust. To that end, the jet propulsion system  50  has a duct  52  ( FIG. 1 ) in which water is pressurized and which is defined by various components of the jet propulsion system  50 . Notably, the duct  52  is defined in part by a water inlet defined on a lower side of the hull  12 , an intake ramp  58 , an impeller  122 , an impeller housing  53  receiving the impeller  122  therein, a venturi unit  100  and a steering nozzle  102  of the jet propulsion system  50 . 
     The steering nozzle  102  defines a water outlet of the duct  52  of the jet propulsion system  50 . Notably, the steering nozzle  102  is disposed rearwardly of the venturi unit  100  such that, when the jet propulsion system  50  propels water rearwardly, water flows from the venturi unit  100  into the steering nozzle  102 . 
     The steering nozzle  102  is pivotally attached to the venturi unit  100  so as to pivot about a vertical axis  104  ( FIG. 4 ). The steering nozzle  102  could also be supported at the exit of the tunnel  94  in other ways without a direct connection to the venturi unit  100 . When the jet propulsion system  50  propels water rearwardly along the duct  52 , the steering nozzle  102  selectively directs the thrust generated by the jet propulsion system  50  to effect turning. The steering nozzle  102  can be replaced by a rudder or other diverting mechanism disposed at the exit of the tunnel  94  to selectively direct the thrust generated by the jet propulsion system  50 . 
     The engine  22  has a crankshaft  126  ( FIG. 7 ) that extends longitudinally. A gearbox  25  is connected to the crankshaft via an input shaft  136  ( FIG. 8 ) and is disposed in the motor compartment  20  rearwardly of the engine  22 . An impeller shaft  55  is connected to an output shaft  138  ( FIG. 8 ) of the gearbox  25  and is connected to the jet propulsion system  50  as will be described further below. The gearbox  25  is operable to selectively change a direction of rotation of the impeller shaft  55 . Notably, the gearbox  25  can selectively rotate the impeller shaft  55  clockwise or counter clockwise by engaging different gearing in the gearbox  25  to drive the impeller shaft  55 . The gearbox  25  will be described in greater detail below. 
     The jet propulsion system  50  can be operated to propel water forwardly or rearwardly along the duct  52 . Notably, when motion of the watercraft  10  is desired, the jet propulsion system  50  is selectively made to propel water rearwardly along the duct  52 . However, as will be explained further below, the jet propulsion system  50  can also be selectively made to propel water forwardly along the duct  52  in order to clear foreign bodies clogging the duct  52 . 
     As best seen in  FIG. 5 , the duct  52  has an inlet  86  positioned under the hull  12 . When the jet propulsion system  50  propels water rearwardly, water is first scooped into the inlet  86 . An inlet grate  54  is positioned adjacent (i.e., at or near to) the inlet  86  and is configured to prevent large rocks, weeds, and other debris from entering the water jet propulsion system  50 , which may damage the system or negatively affect performance. It is contemplated that the inlet grate  54  could be positioned in the inlet  86 . Water flows from the inlet  86  through the water intake ramp  58 . As shown on  FIG. 1 , the intake ramp  58  has a top portion  90  that is formed by the hull  12  and a bottom portion  92 . 
     The impeller housing  53  is positioned rearwardly of the intake ramp  58  such that, when the jet propulsion system  50  propels water rearwardly along the duct  52 , water flows into the impeller housing  53  from the intake ramp  58 . The impeller housing  53  is located in the tunnel  94  of the hull  12 . The impeller housing  53  is fastened to the tunnel  94  of the hull  12  via bolts that engage openings (not shown) in the impeller housing  53  and corresponding openings in the front wall of the tunnel  94 . 
     Referring now to  FIG. 6 , a driveline  120  for the watercraft  10  includes the engine  22 , the gearbox  25 , the impeller shaft  55  and the impeller  122 . A bellow assembly  124  is mounted to the impeller shaft  55  and provides a seal between the duct  52  and the interior of the hull  12  so as to prevent entry of water into the hull  12 . The jet propulsion system  50  is configured to cause the impeller  122  to rotate in a forward direction in normal operation, and in a reverse direction for unclogging the jet propulsion system  50 . In reverse operation, water is propelled forwardly along the duct  52 , water being sucked into the duct  52  via the outlet of the steering nozzle  102 . In most occurrences, this action facilitates the dislodgement of debris or other foreign bodies clogging the duct  52 . 
       FIGS. 7 and 8  provide further details of the driveline  120 . The engine  22  has a crankshaft  126  connected to a flywheel  128 . A starter gear set  130  allows to selectively connect a starter motor  132  to a toothed gear  134  mounted on the flywheel  128  when the starter motor  132  is energized. The gearbox  25  includes an input shaft  136  operatively connected to the crankshaft  126 . The input shaft  136  extends on a side of the flywheel  128  opposite from the crankshaft  126 . In an embodiment, the input shaft  136  is hollow and one end of the crankshaft  126  extending through the flywheel  128  is press-fitted in a matching end of the input shaft  136 . In turn, another end of the input shaft  136  opposite from the crankshaft  126  is operatively connected to an output shaft  138  of the gearbox  25  as will be described below. The gearbox  25  also comprises a direct linkage  140  to selectively connect the input shaft  136  to the output shaft  138  in the forward direction as well as a reversing gear set  142  to selectively connect the input shaft  136  to the output shaft  138  in the reverse direction. The impeller shaft  55  is connected to the output shaft  138  via splines (not shown) located within another bellow assembly  144 . These splines allow some relative longitudinal movement of the output shaft  138  in relation to the impeller shaft  55  while maintaining an engagement of the impeller shaft  55  to the output shaft  138 . A slight angular motion is also allowed between longitudinal axes of the output shaft  138  and of the impeller shaft  55 . 
       FIGS. 9 and 10  provide more details of the gear set  25 . When the gear set  25  operates in the forward direction ( FIG. 9 ), the input shaft  136  is directly connected to the output shaft  138  via the direct linkage  140  that, in the present embodiment, includes a set of dogs  141  on a mating end of the input shaft  136  that engage another set of dogs (not shown) on a mating end of the output shaft  138 . To operate the gearbox  25  in the reverse direction ( FIG. 10 ), the output shaft  138  is moved away from the input shaft  136  to disengage the direct linkage  140 . 
     An electrical actuator  146  operatively connected to the gear set  25  is controlled by commands received from an electronic control unit (ECU)  200  ( FIG. 11 ). In an embodiment, the electrical actuator  146  is a stepper motor adapted to configure the gear set  25  in opposite directions depending on the nature of the command from the ECU  200 . To change the operation of the jet propulsion system  50  from the forward direction to the reverse direction, the ECU  200  sends a reversing command to the electrical actuator  146 . In response to the reversing command, the electrical actuator  146  causes a longitudinal displacement of a shifting rod  148  from a normal position ( FIG. 9 ) to a reversing position ( FIG. 10 ). The shifting rod  148  is displaced in parallel to a longitudinal axis of the input shaft  136  and moves away from the engine  22  as the gearbox  25  is shifted to the reverse direction. A first shifting fork  150  connects the shifting rod  148  to the output shaft  138 . A second shifting fork  151  connects the shifting rod  148  to a shifting shaft  152  of the reversing gear set  142 . The longitudinal displacement of the shifting rod  148  displaces the first shifting fork  150 , in turn causing a parallel longitudinal displacement of the output shaft  138 , away from the input shaft  136 , disengaging the respective sets of dogs that form the direct linkage  140 . In the illustrated embodiment, the longitudinal displacement of the output shaft  136  is of about 10 mm, which is sufficient to disengage the direct linkage  140 . At the same time, the longitudinal displacement of the shifting rod  148  displaces the second shifting fork  151 , in turn causing a parallel longitudinal displacement of the shifting shaft  152 , causing a gear  154  mounted to the shifting shaft  152  to engage a gear  156  of the input shaft  136  while gear a  159  mounted to the shifting shaft  152  engages a gear  160  of the output shaft  138  via a gear  158  rotatably supported by an intermediate rod  161  and meshing with the gear  159 . In an embodiment, the ECU  200  may shortly thereafter send a brief impulse command to the starter motor  132  to cause a slight rotation of the crankshaft  126 , the flywheel  128  and the input shaft  136 . This facilitates alignment of the gears  156 ,  160  of the input and output shafts  136 ,  138  with the gears  154 ,  158  of the reversing gear set  142 . In embodiments using an electric motor instead of the engine  22 , an impulse command may also be applied to cause a slight rotation of a rotor with the same result. 
     As a result of the engagement of the various gears  154 ,  156 ,  158 ,  159  and  160 , the reversing gear set  142  is in condition for transmitting power from the input shaft  136 , which is rotating in the forward direction, to the output shaft  138 , causing the output shaft  138  and the impeller shaft  55  to rotate in the reverse direction. A spring  162  positioned on the intermediate rod  161  applies a pressure on the gear  158  to further facilitate its alignment with the gear  160 . 
     The ECU  200  sends a forwarding command to the electrical actuator  146  to cause the shifting rod  148  to return to its normal position as shown on  FIG. 9  so that the watercraft  10  may be propelled in the forward direction again. At the same time, the shifting fork  150  brings the output shaft  138  toward the input shaft  136  to be connected therewith by the respective sets of dogs of the direct linkage  140 . Also at the same time, the shifting shaft  152  moves in parallel with the shifting rod  148 , causing the gears  154 ,  156 ,  158 ,  159  and  160  to become disengaged. 
     A gearbox position sensor  164  detects any displacement of the shifting rod  148 . The gearbox position sensor  148  may comprise a Hall sensor or another linear sensor. Use of a switch indicating that the shifting rod  148  is positioned to engage the gearbox  25  in the forward or in the reverse position is also contemplated. It is also contemplated that the gearbox position sensor  164  could directly sense the position of the output shaft  138  or the position or another component of the gear set  142 , inasmuch as this component adopts different positions when the gearbox  25  is in the forward and reverse directions. Details of the gearbox  25 , in particular details of the direct linkage  140  and of the reversing gear set  142 , may vary as using various other types of reversible gearboxes to connect the crankshaft  126  to the impeller shaft  55  are contemplated. 
     In an embodiment, the driveline  120  is configured such that the impeller shaft  55  and the impeller  122  rotate whenever the motor  22  is running. In such case, any attempt to disengage the direct linkage  140  of the gearbox  25  while the motor  22  is running could cause damage to the respective sets of dogs on the input shaft  136  and on the output shaft  128 . In the particular example of the gearbox  25  that uses the sets of dogs to establish the direct link  140 , attempting to engage or disengage the direct link  140  while the engine  22  is running or attempting to restart the engine  22  while the sets of dogs  141  of the direct link  140  are not fully engaged might cause noise and might damage the gearbox  25 . 
     Turning now to  FIG. 11 , several components of a watercraft propulsion system of the watercraft  10  are reproduced in block form. On  FIG. 11 , double lines between the various shown elements illustrate mechanical connections between these elements. Single lines illustrate electrical connections, signaling and message exchange between other elements. 
     An electronic control unit (ECU)  200  generally controls the engine  22  and various other functions of the watercraft  10 . The ECU  200  comprises a processor, or a plurality of cooperating processors, as well as one or more memory devices operatively connected to the processor or processors. The one or more memory devices include a non-transitory computer-readable medium that stores machine executable instructions that are executable by the processor or cooperating processors. 
     The ECU  200  is in communication with various sensors and electronic components of the watercraft  10 . The ECU  200  receives signals from the gearbox position sensor  164 , a motor speed sensor  210 , a vehicle speed sensor  212 , and a timer  216 . In an embodiment, the timer  216  may be integrated within the ECU  200 . The motor speed sensor  210  detects a rotational speed of the motor in view of determining whether the motor is currently running, or not. Use of another type of motor status sensor that provides a binary indication that the motor is currently running, or not, is also contemplated. In the particular case where the motor is the engine  22  as illustrated, an exhaust gas temperature sensor  214  may sense a temperature of gases being exhausted by the engine  22  and the motor speed sensor  210  may sense the rotational speed of the crankshaft  126  or a rotational speed of any other component that rotates in synchrony with the crankshaft  126 . Depending on the actual component sensed by the motor speed sensor  210 , the motor speed sensor  210  or the ECU  200  is adapted to account for a speed ratio between that component and the engine crankshaft  126 . When the motor is an electric motor, the motor speed sensor  210  may for example sense a rotational speed of a rotor of the electric motor. 
     The ECU  200  also receives commands from the throttle operator  61  to control a power of the engine  22  and from a reversing switch  220  that the user may actuate to request reverse operation of the impeller  122 . In an embodiments, commands from the reversing switch  220  may be transmitted to the ECU  200  via the display cluster  43 . The reversing switch  220  may comprise a pushbutton, a toggle switch, and the like. The ECU  200  sends information, such as statuses related to operation of the jet propulsion system  50 , for visible or audible display on the display cluster  43 . 
     The ECU  200  is configured to send commands to the electric actuator  146  for selecting, in the gearbox  25 , whether the input shaft  136  and the output shaft  138  are to be connected via the direct linkage  140  or via the reversing gear set  142  based on an input received from the reversing switch  220 . In an embodiment, a reversing command from the ECU  200  energizes the actuator  146  to cause a displacement of the shifting rod  148 , resulting in the selection of the reversing gear set  142 . A forwarding command from the ECU  200  energizes the actuator  146  to cause a displacement of the shifting rod  148  in an opposite direction, resulting in the selection of the direct linkage  140 . 
     Generally speaking, the processor of the ECU  200  executes machine executable instructions stored in the non-transitory computer-readable medium to control the reverse operation of the impeller  122 . To this end, the ECU  200  responds to a command received from the reversing switch  220 , either directly or via the display cluster  43 , to initiate reverse operation of the impeller  122 . The ECU  200  uses information received from the various sensors  210 ,  212 ,  214  and  164  as well as from the timer  216  and from the reversing switch  220  to determine whether the reverse operation of the impeller  122  may be initiated or not. In an embodiment, the reverse operation is not started if the engine  22  is not fully stopped, or if a vehicle speed reported by the vehicle speed sensor  212  is above a maximum speed threshold, or if the exhaust gas temperature sensor  214  reports a temperature of gases exhausted by the engine  22  above a temperature threshold. If the reverse operation is allowed, the ECU  200  sends a command to the electrical actuator  146  to cause reversing of the gearbox  25 . In most cases, the gearbox  25  is reversed by the electrical actuator  146  without delay. In an embodiment, the ECU may read the signal from the gearbox position sensor  164  after a predetermined time deemed sufficient for the reversing of the gearbox  25 . If the gearbox position sensor  164  indicates that the reverse position of the gearbox  25  has not yet been established, the ECU  200  may send an impulse command to the starter motor  132  to cause a slight rotation of the crankshaft  126 , the flywheel  128  and the input shaft  136  for alignment of the various components of the gearbox  25 . A duration of the impulse command to the starter motor  132  may depend on mechanical parameters of the driveline  120 , depending for example on an inertia of the driveline  120 . Without limitation, a 20 to 40 millisecond duration for the impulse command may suffice to properly align the various components of the gearbox  25 . If, after this impulse command, the signal received from the gearbox position sensor  164  still indicates that the reverse position of the gearbox  25  has not been established, the ECU  200  may repeat the impulse command to the starter motor  132 . After a predetermined number of attempts to establish the reverse position of the gearbox  25 , for example five times, the ECU may determine to abort the procedure and send a command to the electrical actuator  146  to return the gearbox  25  to the forward position. 
     In an embodiment, in the course of the reverse operation, the ECU  200  may use an input from the throttle operator  61  to control a speed of the engine  22 . In another embodiment, the ECU  200  may use a continuous input from the reversing switch  220  being held by the user to stop the engine  22 , place the gearbox  25  in reverse mode, restart the engine  22  and control a stable speed of the engine  22  until the user releases the continuous input on the reversing switch  220 . Regardless, the ECU  200  uses information from at least some sensors and from the timer  216  to determine whether reverse operation of the impeller  122  needs to be stopped. The ECU  200  may at all time send messages to the display cluster  43  to request visual or audible display of various statuses of the jet propulsion system  50  related to the reverse operation of the impeller  122 . 
     In particular, where the watercraft  10  is propelled by an internal combustion engine such as the engine  22 , the ECU  200  may prevent starting the engine  22  while the reverse connection is established between the engine  22  and the impeller  122  if an exhaust gas temperature meets or exceeds a temperature threshold. As a non-limiting example, the temperature threshold may be set to 80° C. when measured near the end of a water-cooled exhaust pipe (not shown) where a normal operating temperature may be of about 50° C. Also in this case, the ECU  200  may stop the engine  22  if the exhaust gas temperature increases to meet or exceed the temperature threshold when operating the engine  22  while the reverse connection is established between the engine  22  and the impeller  122 . 
     The ECU  200  may use information from the timer  216  to evaluate a time duration of operation of the engine  22  while the reverse connection is established between the engine  22  and the impeller  122 , and then stop the engine  22  if the time duration reaches a duration threshold, for example 10 seconds in a non-limiting embodiment. 
     The vehicle speed sensor  212  may provide a speed of the watercraft  10  to the ECU  200 . The ECU  200  may prevent establishing the reverse connection between the engine  22  and the impeller  122 , or stop the engine  22 , if the speed of the watercraft  10  meets or exceeds a maximum speed threshold, for example 10 km/h in a non-limiting embodiment. 
     In an embodiment, rather than simply preventing starting of the engine  22 , the ECU  200  may refrain from initiating any action leading to the reverse operation of the impeller  122  if the speed of the watercraft  10  meets or exceeds the maximum speed threshold, if the exhaust gas temperature meets or exceeds the temperature threshold, or if the engine  22  is running when receiving the request for reverse operation of the impeller  122  from the reversing switch  220 . 
     Referring now to  FIGS. 12 a , 12 b  and 12 c   , a sequence  300  comprises a plurality of operations, some of which may be executed in variable order, some of the operations possibly being executed concurrently, some of the operations being optional. At operation  302 , a user command requesting reverse operation of the impeller  122  is received at the ECU  200  from the reversing switch  220 . A test is made at operation  304  to determine that that the engine  22  is stopped. This test may be based on a reading from the engine speed sensor  210 , the ECU  200  determining that the engine  22  is stopped when the rotational speed of the engine  22  is zero (0) RPM. If the engine  22  is not stopped, a visual or audible indication indicating that the sequence cannot be initiated while the engine  22  is not stopped is provided on the display cluster  43  at operation  306  and the sequence  300  ends. It may be noted that, in another embodiment, the ECU  200  may initiate stopping of the engine  22  in response to receiving the user command at operation  302 . 
     If the engine is stopped, another test may be made at operation  308  to evaluate a speed of the watercraft  10 . This evaluation may be made at the ECU  200  based on a reading from the vehicle speed sensor  212 . If the speed of the watercraft  10  is above a speed threshold, a visual or audible indication indicating that the sequence cannot be initiated due to an excessive speed of the watercraft  10  is provided on the display cluster  43  at operation  310  and the sequence  300  ends. 
     If the engine is stopped and if the speed of the watercraft  10  is below the speed threshold, a further test may be made at operation  312  to evaluate an exhaust gas temperature. This evaluation may be made at the ECU  200  based on a reading from the exhaust gas temperature sensor  214 . If the exhaust gas temperature is above a temperature threshold, a visual or audible indication indicating that the sequence cannot be initiated due to an excessive exhaust gas temperature is provided on the display cluster  43  at operation  314  and the sequence  300  ends. 
     When none of the tests  304 ,  308  and  312  prevent reverse operation of the impeller  122 , the direct linkage  140  between the engine  22  and the impeller  122 , specifically between the input shaft  136  and the output shaft  138  of the gearbox  25 , is disconnected at operation  316 . Operation  318  comprises the establishment of a reverse connection between the engine  22  and the impeller  122  via the reversing gear set  142  of the gearbox  25 . 
     In the embodiment of the gearbox  25  as illustrated in  FIGS. 9 and 10 , operations  316  and  318  are performed concurrently by the ECU  200  energizing the actuator  146  to execute operations  316  and  318 . 
     At operation  320 , the ECU  200  may use a signal from the gearbox position sensor  164  to verify that the reverse connection between the engine  22  and the impeller  122  is properly established. If the reverse connection is not properly established, the ECU  200  may execute operation  322  to briefly energize the starter motor  132  to cause the crankshaft  126  to rotate by a few degrees to complete the establishment of the reverse connection between the engine  22  and the impeller  122 . In a non-limiting example, a 20 to 40 millisecond duration for the impulse command applied by the ECU  200  to the starter motor  132  may cause the crankshaft to rotate by about 5 to 10 degrees. Operation  322  may comprise a predetermined number of repetitions, for example five repetitions, of the brief energization of the starter motor  132  in other attempts to establish the reverse connection between the engine  22  and the impeller  122 . If operation  323  determines that the reverse connection still cannot be established after the predetermined number of repetitions, a fault indication is provided on the display cluster  43  at operation  324  and the sequence  300  continues at operation  346  ( FIG. 12 b   ) where the reverse operation of the impeller is aborted. 
     Following the establishment of the reverse connection between the engine  22  and the impeller  122 , as verified at operation  320  or  323 , the engine  22  is started at operation  326  ( FIG. 12 b   ), causing the impeller  122  to rotate in the reverse direction, which is opposite from its normal operation. Operation  326  may include sub-operations  328 ,  330  and/or  332 . At sub-operation  328 , the ECU  200  sets a maximum rotational speed threshold for the engine  22 , for example 5000 RPM, so that the engine  22  will not exceed this rotational speed threshold while the reverse connection is established between the engine  22  and the impeller  122 , even when a full throttle indication is received from the throttle operator  61 . In the same or another embodiment, operation  326  may be aborted if the engine  22  is not successfully started after five (5) seconds. At sub-operation  330 , a visual or audible indication is provided on the display cluster  43  to indicate that the rotational speed of the engine is limited by the rotational speed threshold. A timer is started at sub-operation  332 . 
     While the engine  22  is running with the reverse connection established between the engine  22  and the impeller  122 , a test is continuously made at operation  334  to verify that the exhaust gas temperature does not rise above the temperature threshold. If the exhaust gas temperature rises above the temperature threshold, a visual or audible indication indicating that the engine  22  is stopped due to an excessive exhaust gas temperature is provided on the display cluster  43  at operation  336  and the engine is stopped at operation  344 . 
     In parallel to operation  334 , another test is made at operation  338  to verify whether the timer has reached a duration threshold. If the timer has exceeded the duration threshold, a visual or audible indication indicating that the engine  22  is stopped due to an excessive duration of the reverse operation of the impeller  122  is provided on the display cluster  43  at operation  336  and the engine is stopped at operation  344 . It is contemplated that further tests may be added to the tests of operations  334  and  338 . For example and without limitation, one test may verify that the vehicle speed reported by the vehicle speed sensor  212  is below the maximum speed threshold, and another test may verify that the gearbox position sensor  164  continuously reports a correct position of the gearbox  20 . Use of a sensor of a rotation of the impeller  122  to detect an eventual blockage of the impeller  122  is also contemplated. 
     A user command requesting an end of the reverse operation of the impeller  122  may be received at the ECU  200  from the reversing switch  220  at operation  342 , following which the engine  22  is stopped at operation  344 . The engine  22  is stopped at operation  344 , either automatically or in response to the user command. After the engine  22  has been stopped, the reverse connection between the engine  22  and the impeller  122  is disconnected at operation  346  and the direct linkage  140  is established between the engine  22  and the impeller  122  at operation  348 . Operations  346  and  348  may also follow a determination that the sequence  300  is aborted due to a failure to establish the reverse connection at operation  323 . 
     At operation  350 , the ECU  200  may use a signal from the gearbox position sensor  164  to verify that the direct linkage  140  is properly established between the engine  22  and the impeller  122 . If so, the sequence  300  ends after operation  350 . If the direct linkage  140  is not properly established, the ECU  200  may execute operation  352  to briefly energize the starter motor  132  to cause the crankshaft  126  to rotate by a few degrees to complete the establishment of direct linkage  140  between the engine  22  and the impeller  122 . In a non-limiting example, a 20 to 40 millisecond duration for the impulse command applied by the ECU  200  to the starter motor  132  may cause the crankshaft to rotate by up to about 20 degrees, this rotation being larger than in operation  322  in order to facilitate an alignment of the sets of dogs of the input and output shafts  136  and  138 . Operation  352  may comprise a predetermined number of repetitions, for example five repetitions, of the brief energization of the starter motor  132  in other attempts to establish the direct linkage  140  between the engine  22  and the impeller  122 . Operation  354  may determine that the direct linkage  140  is properly established and the sequence  300  ends. If operation  354  determines that the direct linkage  140  still cannot be established after the predetermined number of repetitions, a fault indication is provided on the display cluster  43  at operation  356  and the sequence  300  ends. 
     Each of the operations of the sequence  300  may be configured to be processed by one or more processors, the one or more processors being coupled to one or more memory devices, the one or more processors and the one or more memory devices being for example implemented in the ECU  200 . 
     Modifications and improvements to the above-described embodiments of the present technology may become apparent to those skilled in the art. The foregoing description is intended to be exemplary rather than limiting. The scope of the present technology is therefore intended to be limited solely by the scope of the appended claims.