Patent Publication Number: US-11046406-B1

Title: Watercraft and venturi unit

Description:
CROSS-REFERENCE 
     The present application claims priority from U.S. Provisional Application No. 62/798,790, filed Jan. 30, 2019, the entirety of which is incorporated herein by reference. 
    
    
     FIELD OF TECHNOLOGY 
     The present invention relates to a jet propulsion system of a watercraft. 
     BACKGROUND 
     Water jet propelled watercraft, such as personal watercraft and jet boats, offer high performance, acceleration, handling, and allow for shallow-water operation. 
     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 so as to propel water towards an inlet thereof (as opposed to a rearward outlet at a steering nozzle of the jet propulsion system) and use the generated thrust to clear clogs in the jet propulsion system. However, many water jet propelled watercraft are equipped with a bailer-siphon system that uses the fluid flow through the jet propulsion system to suction water out of the watercraft&#39;s engine compartment, which water may from time to time enter when in use. In at least some cases, such bailer-siphon systems, while being suitable for their intended purposes, are suboptimal for a jet propulsion system operating in reverse. 
     More particularly, when a jet propulsion system is operated in reverse and there is no water proximate the bailer-siphon system&#39;s inlet, water flows in reverse through the venturi unit thereof and may entrain air from the bailer-syphon system into the flow of water through the venturi unit. This may aerate the impeller of the jet propulsion system. In at least some cases, aeration of the impeller reduces its efficiency and reduces debris clearing performance of the jet propulsion system. 
     In view of the foregoing, there is a need for a watercraft with a jet propulsion system that reduces or eliminates aeration of the impeller during reverse operation of the impeller. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to ameliorate at least some of the inconveniences present in the prior art. 
     For the purposes of this document, the term “conduit” refers to a notional fluid connection and is defined by at least one physical line and/or other components that define at least one fluid conduit (such as a peripheral wall of a venturi unit, a fluid inlet, a fluid outlet, a siphon break, a valve, and the like). For example, in some embodiments, a fluid “conduit” that connects points A and B is defined by a single (physical) fluid line, such as a hose, connecting the points A and B. As another example, in some embodiments, the fluid “conduit” is defined by two or more (physical) fluid lines interconnected in series or parallel with a common inlet and/or outlet, in some cases via elements such as a siphon break and a valve, and connecting the points A and B. 
     In turn, for the purposes of this document, the term “line” refers to a physical line for conveying a fluid, such as water and/or air. One example of a fluid line is a rubber hose. Another example of a fluid line is a plastic tube. 
     According to one aspect of the present technology, there is provided a watercraft having: a hull having a bow and a stern opposite the bow, the hull defining at least a part of a motor compartment; a motor supported by the hull and disposed within the motor compartment; and a jet propulsion system. The jet propulston system has: a duct defining a water inlet in a bottom of the hull; a venturi unit defining part of the duct and defining a venturi outlet; an impeller housing defining part of the duct and disposed between the inlet and the venturi unit; and an impeller disposed within the impeller housing, the impeller being operatively connected to the motor, the impeller being rotatable about an impeller rotation axis in (i) a forward direction whereby the impeller propels water from the water inlet rearward and out of the venturi outlet, and (ii) a reverse direction whereby the impeller propels water from the venturi outlet forward and out of the water inlet. The watercraft also has a bailer-siphon system having a fluid conduit, the fluid conduit being defined in part by a valve. The fluid conduit has: a fluid inlet disposed inside the motor compartment for drawing water out of the motor compartment; and a fluid outlet in fluid communication with the venturi outlet at least when the impeller rotates in the forward direction while the watercraft is in use. The valve is operable between an open position in which the valve fluidly connects the fluid inlet to the fluid outlet, and a closed position in which the valve fluidly disconnects the fluid inlet from the fluid outlet. The valve is in the open position when the impeller rotates in the forward direction while the watercraft is in use thereby allowing flow of water through the venturi outlet to move water out of the motor compartment, the water entering the fluid inlet of the fluid conduit and exiting the fluid outlet of the fluid conduit. The valve is in the closed position when the impeller rotates in the reverse direction while the watercraft is in use. 
     In some embodiments, the valve is moved to the open position when the impeller rotates in the forward direction while the watercraft is in use. The valve is moved to the closed position when the impeller rotates in the reverse direction while the watercraft is in use. 
     In some embodiments, the valve is disposed at the venturi unit. 
     In some embodiments, the valve is operated between the open position and the closed position by a direction of flow of water through the duct. 
     In some embodiments, the valve includes an element pivotable about a pivot axis by flow of water generated by the impeller to operate the valve between the open position and the closed position. 
     In some embodiments, the element extends at least in part into the venturi unit such that the element is exposed to flow of water through the venturi conduit. 
     In some embodiments, the element includes a ball portion pivotable about the pivot axis. The ball portion defines an aperture through the ball portion. The aperture defines part of the fluid conduit when the valve is in the open position. An outer surface of the ball portion blocks the fluid conduit when the valve is in the closed position. 
     In some embodiments, the element includes an arm connected to the ball portion to pivot the ball portion about the pivot axis, the arm extending at least in part into the venturi unit. 
     In some embodiments, the element defines the fluid outlet. 
     In some embodiments, the venturi unit includes a peripheral wall; and the element is disposed radially inward of the peripheral wall. 
     In some embodiments, the inner side of the peripheral wall defines a recess. A part of the element is received pivotally in the recess. The venturi unit includes a resilient element that pushes the part of the element into the recess. 
     In some embodiments, the arm is a tube having a free end, the tube being attached to the ball portion to pivot together with the ball portion about the pivot axis to thereby operate the valve between the open position and the closed position. The tube is in fluid communication with the aperture in the ball portion. The free end of the tube is the fluid outlet. 
     In some embodiments, the peripheral wall defines a part of the fluid conduit. 
     In some embodiments, the venturi unit includes a peripheral wall; and the arm is disposed at least in part radially inward of the peripheral wall. 
     In some embodiments, the ball portion is disposed at least in part radially outward of the peripheral wall. 
     In some embodiments, vthe valve is disposed between the fluid inlet and the fluid outlet. 
     In some embodiments, the venturi unit includes a peripheral wall; the fluid outlet is disposed radially outward of the peripheral wall; the valve fluidly connects the fluid outlet to the venturi outlet via a passage through the peripheral wall when the impeller rotates in the forward direction; and the valve fluidly disconnects the fluid outlet from the venturi outlet when the impeller rotates in the reverse direction. 
     In some embodiments, the valve includes a ball; the ball is pushed away from an inner side of the peripheral wall by flow of water through the duct generated by the impeller rotating in the forward direction to fluidly connect the fluid outlet to the venturi outlet via the inner side of the peripheral wall; and the ball is pulled toward the inner side of the peripheral wall by flow of water through the duct generated by the impeller rotating in the reverse direction to fluidly disconnect the fluid outlet from the venturi outlet at the inner side of the peripheral wall. 
     In some embodiments, the jet propulsion system also has at least one of: a steering nozzle pivotable about a steering axis and about a variable trim system (VTS) axis relative to the venturi; and a reverse gate movable between a stowed position and a fully lowered position. The valve is operatively connected to one of the at least one of the steering nozzle and the reverse gate such that: when the at least one of the steering nozzle and the reverse gate is the steering nozzle, the valve is moved between the open and closed positions by rotation of the steering nozzle about the VTS axis; and when the at least one of the steering nozzle and the reverse gate is the reverse gate, the valve is moved by movement of the reverse gate such that the valve is moved to the closed position when the reverse gate is moved to a predetermined position, the predetermined position being the fully lowered position or a position intermediate the stowed position and the fully lowered position. 
     In some embodiments, at least one of the steering nozzle and the reverse gate includes the steering nozzle and the valve is operatively connected to the steering nozzle. 
     In some embodiments, the steering nozzle is pivotable about the VTS axis between a plurality of trim-up positions and a plurality of trim-down positions. The valve is moved to the closed position when the steering nozzle is pivoted to a predetermined trim-down position of the plurality of trim-down positions. The valve is at least partially open at positions other than the predetermined trim-down position. 
     In some embodiments, a VTS support is pivotable about the VTS axis. The steering nozzle pivots with the VTS support about the VTS axis. The steering nozzle pivots about the steering axis relative to the VTS support. The valve is operatively connected to the VTS support. 
     In some embodiments, a link operatively connects the valve to the VTS support. The link is pivotally connected to the valve. The link is pivotally connected to the VTS support. 
     In some embodiments, the valve is a ball valve. 
     According to another aspect of the present technology, there is provided a venturi unit for a jet propulsion system of a watercraft. The venturi unit has: a venturi conduit having a peripheral wall that defines a venturi inlet and a venturi outlet, the venturi inlet having a greater cross-sectional area than the venturi outlet; and a valve operable between an open position and a closed position and defining a part of a fluid conduit. The fluid conduit has: a fluid inlet fluidly adapted for connection to a bailer-siphon system; and a fluid outlet in fluid communication with the venturi outlet. The valve is in the open position during flow of water through the venturi conduit from the venturi inlet to the venturi outlet. The valve being in the closed position during flow of water through the venturi conduit from the venturi outlet to the venturi inlet. In the open position, the valve fluidly connects the fluid inlet to the fluid outlet. In the closed position, the valve fluidly disconnects the fluid inlet from the fluid outlet. 
     In some embodiments, the valve is operated: to the open position by flow of water through the venturi conduit from the venturi inlet to the venturi outlet, and to the closed position by flow of water through the venturi conduit from the venturi outlet to the venturi inlet. 
     In some embodiments, the valve includes an element pivotable about a pivot axis by flow of water through the venturi conduit to operate the valve between the open position and the closed position, the element including a ball portion pivotable about the pivot axis, the ball portion defining an aperture through the ball portion, the aperture defining part of the fluid conduit when the valve is in the open position, an outer surface of the ball portion blocking the fluid conduit when the valve is in the closed position. 
     In some embodiments, the element includes a tube having a free end, the tube being attached to the ball portion to pivot together with the ball portion about the pivot axis to thereby operate the valve between the open position and the closed position, the tube being in fluid communication with the aperture in the ball portion, the free end of the tube being the fluid outlet. 
     According to another aspect of the present technology, there is provided a watercraft having: a hull having a bow and a stern opposite the bow, the hull defining at least a part of a motor compartment; a motor supported by the hull and disposed within the motor compartment; and a jet propulsion system. The jet propulsion system has: a duct defining a water inlet in a bottom of the hull; a venturi unit defining part of the duct and defining a venturi outlet; at least one of: a steering nozzle pivotable about a steering axis and about a variable trim system (VTS) axis relative to the venturi; and a reverse gate movable between a stowed position and a fully lowered position; an impeller housing defining part of the duct and disposed between the inlet and the venturi unit; and an impeller disposed within the impeller housing, the impeller being operatively connected to the motor. The watercraft also has a bailer-siphon system having a fluid conduit. The fluid conduit is defined in part by a valve. The fluid conduit has: a fluid inlet disposed inside the motor compartment for drawing water out of the motor compartment; and a fluid outlet in fluid communication with the venturi outlet. The valve is operable between an open position in which the valve fluidly connects the fluid inlet to the fluid outlet, and a closed position in which the valve fluidly disconnects the fluid inlet from the fluid outlet. The valve is operatively connected to one of the at least one of the steering nozzle and the reverse gate such that: when the at least one of the steering nozzle and the reverse gate is the steering nozzle, the valve is moved between the open and closed positions by rotation of the steering nozzle about the VTS axis; and when the at least one of the steering nozzle and the reverse gate is the reverse gate, the valve is moved by movement of the reverse gate such that the valve is moved to the closed position when the reverse gate is moved to a predetermined position. The predetermined position is the fully lowered position or a position intermediate the stowed position and the fully lowered position. 
     In some embodiments, the impeller is rotatable about an impeller rotation axis in (i) a forward direction whereby the impeller propels water from the water inlet rearward and out of the venturi outlet, and (ii) a reverse direction whereby the impeller propels water from the venturi outlet forward and out of the water inlet. The valve is in the open position when the impeller rotates in the forward direction while the watercraft is in use thereby allowing flow of water through the venturi outlet to move water out of the motor compartment, the water entering the fluid inlet of the fluid conduit and exiting the fluid outlet of the fluid conduit, and the valve being in the closed position when the impeller rotates in the reverse direction while the watercraft is in use. 
     In some embodiments, at least one of the steering nozzle and the reverse gate includes the steering nozzle and the valve is operatively connected to the steering nozzle. 
     In some embodiments, the steering nozzle is pivotable about the VTS axis between a plurality of trim-up positions and a plurality of trim-down positions. The valve is moved to the closed position when the steering nozzle is pivoted to a predetermined trim-down position of the plurality of trim-down positions. The valve is at least partially open at positions other than the predetermined trim-down position. 
     In some embodiments, a VTS support is pivotable about the VTS axis. The steering nozzle pivots with the VTS support about the VTS axis. The steering nozzle pivots about the steering axis relative to the VTS support. The valve is operatively connected to the VTS support. 
     In some embodiments, a link operatively connects the valve to the VTS support. The link is pivotally connected to the valve. The link is pivotally connected to the VTS support. 
     In some embodiments, the valve is a ball valve. 
     Additional and/or alternative features, aspects, and advantages of embodiments of the present invention 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 bottom plan view of the watercraft of  FIG. 1 ; 
         FIG. 3  is a perspective longitudinal section view of a hull of the watercraft of  FIG. 1 , taken from a rear, left side, and showing a jet propulsion system of the watercraft of  FIG. 1  with a steering nozzle, a reverse gate, and other components removed therefrom; 
         FIG. 4  is a perspective view, taken from a rear, right side, of the jet propulsion system of  FIG. 3 ; 
         FIG. 5  is a perspective view, taken from a rear, right side, of components of the jet propulsion system of  FIG. 4 ; 
         FIG. 6  is a perspective view, taken from a front, left side, of the components of the jet propulsion system of  FIG. 5 ; 
         FIG. 7  is a perspective view, taken from a front, bottom, right side, of a venturi unit of the jet propulsion system of  FIG. 3 , with a valve of the venturi unit being in an open position; 
         FIG. 8  is a perspective view, taken from a front, bottom, right side, of the venturi unit of  FIG. 7 , with the valve of the venturi unit being in a closed position; 
         FIG. 9  is a perspective view, taken from a front, top, left side, of the valve of the venturi unit of  FIG. 7 ; 
         FIG. 10  is a front elevation view of the venturi unit of  FIG. 7 ; 
         FIG. 11  is a cross-sectional view of the venturi unit of  FIG. 10 , taken along section line  11 - 11  in  FIG. 10 , with the valve being in the open position; 
         FIG. 12  is a cross-sectional view of the venturi unit of  FIG. 10 , taken along section line  12 - 12  in  FIG. 10 , with the valve being in the open position; 
         FIG. 13  is a cross-sectional view of the venturi unit of  FIG. 10 , taken along section line  12 - 12  in  FIG. 10 , with the valve being in the closed position; 
         FIG. 14  is a cross-sectional view of the venturi unit of  FIG. 10 , taken along section line  11 - 11  in  FIG. 10 , with the valve being in the closed position; 
         FIG. 15  is an exploded view, taken from a rear, left side, of a venturi unit of the jet propulsion system of  FIG. 3 , according to another embodiment; 
         FIG. 16  is an exploded view, taken from a front, bottom, left side, of the venturi unit of  FIG. 15 ; 
         FIG. 17  is a top plan view of the venturi unit of  FIG. 15 ; 
         FIG. 18  is a cross-sectional view of the venturi unit of  FIG. 15 , taken along section line  18 - 18  in  FIG. 17 , with a valve of the venturi unit being in the open position; 
         FIG. 19  is a cross-sectional view of the venturi unit of  FIG. 15 , taken along section line  19 - 19  in  FIG. 17 , with the valve of the venturi unit being in the open position; 
         FIG. 20  is a cross-sectional view of the venturi unit of  FIG. 15 , taken along section line  18 - 18  in  FIG. 17 , with the valve of the venturi unit being in the closed position; 
         FIG. 21  is a cross-sectional view of the venturi unit of  FIG. 15 , taken along section line  19 - 19  in  FIG. 17 , with the valve of the venturi unit being in the closed position; 
         FIG. 22  is a perspective view, taken from a rear, right side, of a venturi unit of the jet propulsion system of  FIG. 3 , according to another embodiment; 
         FIG. 23  is a front elevation view of the venturi unit of  FIG. 22 ; 
         FIG. 24  is a top plan view of the venturi unit of  FIG. 22 ; 
         FIG. 25  is a cross-sectional view of the venturi unit of  FIG. 22 , taken along section line  25 - 25  in  FIG. 24 , with the valve of the venturi unit being in the open position; 
         FIG. 26  is a cross-sectional view of the venturi unit of  FIG. 22 , taken along section line  25 - 25  in  FIG. 24 , with the valve of the venturi unit being in the closed position; 
         FIG. 27  is a perspective view, taken from a rear, right side, of an alternative embodiment of the jet propulsion system of  FIG. 4 ; 
         FIG. 28  is a longitudinal cross-section of components of the jet propulsion system of  FIG. 27 , with a steering nozzle in a trim-up position and a valve on the impeller housing in a partially open position; 
         FIG. 29  is a close-up view of portion  29 - 29  of  FIG. 28 ; 
         FIG. 30  is a longitudinal cross-section of components of the jet propulsion system of  FIG. 27 , with the steering nozzle in a trim-down position and the valve on the impeller housing in a closed position; and 
         FIG. 31  is a close-up view of portion  31  of  FIG. 30 . 
     
    
    
     DETAILED DESCRIPTION 
     A personal watercraft  10  in accordance with one embodiment of the present technology is shown in  FIGS. 1 and 2 . 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 watercraft, as well as other water jet propelled watercraft such as jet boats and the like. 
     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  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 general construction of the personal watercraft  10  will now be described with respect to  FIGS. 1 and 2 . 
     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  ( FIG. 1 ). 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  rolls slightly when turning. 
     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 forward 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 . 
     As best seen in  FIG. 2 , 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  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 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  FIG. 1 , the helm assembly  60  is positioned forward of the seat  28 . The helm assembly  60  has a central helm portion  64 , that is padded, and a pair of steering handles  65 , also referred to as a handlebar. One of the steering handles  65  is provided with a throttle operator which allows the rider to control the motor  22 , and therefore the speed of the watercraft  10 . The throttle operator is a finger-actuated throttle lever. However it is contemplated that the throttle operator could be a thumb-actuated throttle lever, a twist grip or other mechanism. 
     The throttle operator is movable between an idle position and multiple actuated positions. In the present embodiment, the throttle operator is biased towards the idle position, such that, should the driver of the watercraft  10  let go of the throttle operator, it will move to the idle position. The other of the steering handles  65  is provided with a reverse gate operator  67  used by the driver to actuate a reverse gate  74  ( FIG. 4 ) in a fully lowered position for braking and/or reversing the watercraft  10 . The reverse gate operator  67  ( FIG. 1 ) 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  74  is pivotable about a gate axis  73  between a stowed position (shown in  FIG. 4 ) and a fully lowered position where the reverse gate  74  redirects a jet of water expelled by the jet propulsion system  50 . The reverse gate operator  67  communicates with an actuator  71 , which in the present embodiment is an electric motor, which pivots the reverse gate  74  about the gate axis  73  in response to actuation of the reverse gate operator  67 . 
     The helm assembly  60  is provided with a key receiving post located near a center of the central helm portion  64 . The key receiving post is adapted to receive a key (not shown) that starts the watercraft  10 . As is known, the key is typically attached to a safety lanyard (not shown). It should be noted that the key receiving post may be placed in any suitable location on 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, gas tank, electrical system (battery, electronic control unit, etc.), 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 engine  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, etc.). 
     The engine  22  has a crankshaft (not shown) that extends longitudinally. A gearbox  25  is connected to the crankshaft and is disposed in the motor compartment  20  rearward of the engine  22 . A driveshaft  55  is connected to 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 driveshaft  55 . Notably, the gearbox  25  can selectively rotate the driveshaft  55  clockwise or counter clockwise by engaging different gearing to drive the driveshaft  55 . 
     The watercraft  10  is propelled by the jet propulsion system  50  which pressurizes water to create thrust. To that end, the jet propulsion system  50  has a duct  52  ( FIGS. 1 to 3 ) in which water is pressurized and which is defined by various components of the jet propulsion system  50 . 
     Referring to  FIGS. 2 and 3 , the duct  52  is defined in part by an intake ramp  58 , an impeller housing  70 , a venturi unit  100  and a steering nozzle  102  of the jet propulsion system  50 . As shown in  FIG. 2 , the duct  52  has an inlet  86  positioned under the hull  12 . When the jet propulsion system  50  propels water rearward, water from outside of the watercraft  10  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  and into impeller housing  70 . 
     As shown in  FIG. 3 , the impeller housing  70  is located in the tunnel  94  of the hull  12  and is fastened to the tunnel  94  via bolts that engage openings  39  in the impeller housing  70  and corresponding openings in the front wall of the tunnel  94 . In turn, the venturi unit  100  is connected to the impeller housing  70  and is positioned rearward thereof such that the venturi unit  100  is positioned longitudinally between the impeller housing  70  and the steering nozzle  102  ( FIG. 4 ). To this end, the venturi unit  100  has mounting flanges  104  that are evenly circumferentially spaced around a front end of the venturi unit  100 . Fasteners (e.g., bolts) are inserted into openings provided in the mounting flanges  104  and into corresponding openings in the impeller housing  70  in order to secure the venturi unit  100  to the impeller housing  70 . 
     Referring to  FIG. 6 , the impeller housing  70  houses an impeller  72 . The impeller  72  is mounted to the driveshaft  55  such that the impeller  72  is rotated about an impeller rotation axis  75  defined by the driveshaft  55 . The impeller  72  is thus operatively connected to the engine  22  via the driveshaft  55  and the gearbox  25 . Since the gearbox  25  can selectively rotate the driveshaft  55  clockwise or counter-clockwise about the impeller rotation axis  75 , the impeller  72  can be rotated in a “forward direction” or in a “reverse direction”. The impeller  72  is positioned rearward of the intake ramp  58  such that, when the impeller  72  rotates in the forward direction, the impeller  72  propels water rearward along the duct  52  into the venturi unit  100 . 
     As such, when the impeller  72  rotates in the forward direction it pulls water into the duct  52  via the inlet grate  54  and propels it rearward through the impeller housing  70  and out of the venturi unit  100 , thereby propelling the watercraft  10  forward. The venturi unit  100  is configured to constrict this water flow in order to increase water speed. To this end, and referring to  FIGS. 7 and 8 , the venturi unit  100  forms a venturi conduit  106  which defines the venturi inlet  108  and a venturi outlet  110  opposite the venturi inlet  108 . The venturi conduit  106  also has a plurality of vanes  112 , only a few of which are labeled to maintain clarity. The vanes  112  decrease rotational motion of water flowing through the venturi conduit  106  so that energy given to the water by the impeller  72  is used for thrust, as opposed to swirling the water. 
     In order to constrict water flow, the venturi inlet  108  has a greater cross-sectional area than the venturi outlet  110  such that the venturi conduit  106  is generally frustoconical in shape and has a generally frustoconical peripheral wall  114 . Thus, when the impeller  72  rotates in the forward direction propelling water through the venturi inlet  108  and then out of the venturi outlet  110 , the speed of the water flowing through the venturi conduit  106  increases due to the reduction in diameter of the venturi conduit  106  from the venturi inlet  108  to the venturi outlet  110 . This increases thrust. 
     Referring back to  FIG. 4 , the steering nozzle  102  is disposed rearward of the venturi unit  100  and directs the thrust and provides for steering and trim of the watercraft  10 . More particularly, a variable trim system (VTS) support  103  is pivotally mounted relative to the venturi unit  100  about a VTS axis  105  (shown in the embodiment of  FIG. 28 ). The steering nozzle  102  is pivotally mounted to the to the VTS support  103  so as to pivot about a steering axis  107  (shown in the embodiment of  FIG. 28 ). The steering axis  107  is perpendicular to the VTS axis  105 . The steering nozzle  102  is operatively connected to the helm assembly  60  via a push-pull cable (not shown) such that when the helm assembly  60  is turned, the steering nozzle  102  pivots about the steering axis  107 . 
     Movement of the steering nozzle  102  about the steering axis  107  redirects the pressurized water coming from the venturi outlet  110  and steers the watercraft  10 . Movement of the steering nozzle  102  about the VTS axis  105  together with the VTS support  103  is known as trim and controls the pitch of the watercraft  10 . In the present embodiment, the steering nozzle  102  has a plurality of trim-up positions (i.e. the steering nozzle points up relative to the axis  75 ) and a plurality of trim-down positions (i.e. the steering nozzle  102  points down relative to the axis  75 ). In alternative embodiments, the steering nozzle  102  could be supported at the exit of the tunnel  94  in other ways without a direct connection to the venturi unit  100 . It is also contemplated that the steering nozzle  102  could also 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 . 
     In the present embodiment, the reverse gate  74  is operatively connected to the VTS support  103  such that rotation of the reverse gate  74  about the gate axis  73  results in rotation of the VTS support  103 , and the steering nozzle  102 , about the VTS axis  105 . As such, the actuator  71  controls both the position of the reverse gate  74  and the trim position of the steering nozzle  102 . A detailed description of a variable trim system and gate assembly of this type can be found in U.S. Pat. No. 9,376,189, issued Jun. 28, 2016, the entirety of which is incorporated herein by reference. It is contemplated that movement of the reverse gate  74  about the gate axis  73  and movement of the VTS support  103  about the VTS axis  105  could be done independently from one another by different actuators. It is also contemplated that in some embodiments that the reverse gate  74  could be omitted. It is also contemplated that in some embodiments the VTS support  73  could be omitted such that the steering nozzle  102  can only pivot about the steering axis  107  and cannot be trimmed. 
     The jet propulsion system  50  can also be operated in reverse to propel water forward along the duct  52  in order to clear foreign bodies clogging the duct  52 , the inlet grate  54 , or other parts of the jet propulsion system  50 . Rotation of the impeller  72  in the reverse direction about the impeller rotation axis  75  pulls water into the venturi outlet  110  and propels it forward through the venturi inlet  108  and then out of the inlet grate  54 . 
     Referring to  FIGS. 1 and 3 , the jet propulsion system  50  is connected to and operates a bailer-siphon system  41  of the watercraft  10 . In summary, the bailer-siphon system  41  draws water from the motor compartment  20  while the watercraft  10  is propelled by the impeller  72  rotating in the forward direction, by using suction created by water flowing out of the venturi outlet  110 . On the other hand, when the impeller  72  is rotating in the reverse direction, the bailer-siphon system  41  is fluidly disconnected from the venturi unit  100 , thereby reducing or eliminating aeration of the impeller  72  which may have otherwise been caused by the fluid connection to the bailer-siphon system and improving thrust for clearing foreign objects. How this functionality is achieved is described next. 
     Referring to  FIG. 1 , the bailer-siphon system  41  includes two fluid conduits  43  defined by various elements, as described later in this document. The two fluid conduits  43  are similar to each other. To maintain clarity, only one of the two fluid conduits  43  has been schematically shown in  FIG. 1 . It is contemplated that the bailer-siphon system  41  could have a single fluid conduit  43 , or more than the two fluid conduits  43 , with a corresponding number of fluid inlet(s)  45  and fluid outlet(s)  49 . 
     In the present embodiment, each of the two fluid conduits  43  has a fluid inlet  45  and a fluid outlet  49 . The fluid inlets  45 , also referred to as bailer pickups, are positioned at or proximate to a bottom, rear surface of the motor compartment  20  for drawing water out of the motor compartment  20 . The fluid outlets  49  are positioned at the venturi unit  100  and are in fluid communication with the venturi outlet  110  at least when the impeller  72  rotates in the forward direction while the watercraft  10  is in use. 
     Water propelled through the venturi conduit  106  from the venturi inlet  108  toward and out of the venturi outlet  110  creates suction at the fluid outlets  49  of the bailer-siphon system  41  and thereby draws water out the motor compartment  20  via the fluid inlets  45 . Water, and any air, that may be drawn in from the motor compartment  20  is expelled out of the venturi outlet  110  with the main flow of water created by the impeller  72 . Since in this operating condition the flow of water is directed from the impeller  72  toward the venturi outlet  110 , any air introduced into the flow of water at the venturi unit  100  by the bailer-siphon system  41  exits the venturi unit  100  without flowing over the impeller  72 . 
     Referring to  FIG. 3 , each of the fluid conduits  43  is defined in part by a set of rubber hoses  116  extending above the jet propulsion system  50  and being fluidly interconnected by a siphon break  118  which ensures that water from outside of the watercraft  10  is not suctioned into the motor compartment  20 . It is contemplated that any suitable number and/or arrangement of hoses or other elements, such as plastic tubes, could be used to define the fluid conduits  43 . 
     In the present embodiment, and still referring to  FIG. 3 , the hoses  116  extending between the siphon breaks  118  and the impeller housing  70  are fluidly connected at their respective rear ends to respective ones of tubes  124 ,  126  that are defined by a peripheral wall  128  of the impeller housing  70 . In turn, at their rear ends the tubes  124 ,  126  are fluidly connected to respective ones of tubes  130 ,  132  defined by a peripheral wall  134  of the venturi unit  100 . More particularly, in the present embodiment, the tubes  130 ,  132  are defined in a removable portion of the peripheral wall  134  at a top side of the peripheral wall  134 . It is contemplated that the peripheral wall  134  could be made of a single piece of material. 
     Lastly, at their rear ends, the tubes  130 ,  132  of the venturi unit  100  are selectively fluidly connected to a valve  136  that defines the fluid outlets  49  of the bailer-siphon system  41 . Still referring to  FIG. 3 , in the present embodiment the valve  136  is disposed at the venturi unit  100 , radially inward of the peripheral wall  134 . The valve  136  is operable between an open position  138  ( FIGS. 3, 7, and 10-12 ), and a closed position  140  ( FIGS. 8 and 13-14 ). 
     As shown in  FIG. 9 , in this embodiment, the valve  136  includes two ball portions  146  joined by a cylindrical post  148 , and two tubes  150 . The tubes  150  are free at their rear ends and are attached at their front ends to respective ones of the ball portions  146  to pivot together with the ball portions  146 . The free rear ends of the tubes  150  define the fluid outlets  49  of the bailer-siphon system  41 . 
     The ball portions  146  are received in respective portions of a seat  152  ( FIGS. 7, 8 and 10 ) defined by the peripheral wall  134  of the venturi unit  100 . The ball portions  146  define apertures  154  therethrough. The apertures  154  align with the apertures  156  ( FIG. 8 ) in the respective ones of the tubes  150 . When the valve  136  is in the open position  138 , the apertures  154  of the ball portions  146  align with the respective ones of the apertures (not separately labeled) in the tubes  130 ,  132  of the venturi unit  100  and thereby fluidly connect the fluid outlets  49  of the bailer-siphon system  41  to the respective fluid inlets  45  of the bailer-siphon system  41 . In the closed position  140 , an outer surface  164  ( FIG. 9 ) of each of the ball portions  146  blocks a respective one of the tubes  130 ,  132  and thereby fluidly disconnects the fluid outlets  49  from the fluid inlets  45 . 
     As shown in  FIGS. 11 and 14 , the cylindrical post  148  of the valve  136  is received in a congruently shaped recess  158  defined by the peripheral wall  134  of the venturi unit  100 . The recess  158  is defined in the peripheral wall  134  between the portions of the seat  152  that receive the ball portions  146 . As shown in  FIGS. 5, 11 and 14 , a clip  160  is received through and retained in an aperture defined through the peripheral wall  134  above and rearward of the recess  158 . The clip  160  pushes the cylindrical post  148  into the recess  158 . This construction allows the valve  136  to pivot about a pivot axis  162  ( FIGS. 11-14 ) defined by the cylindrical post  148  between the open position  138  and the closed position  140  while keeping the valve  136  in place. The clip  160  is an example of a resilient member. It is contemplated that a different resilient member and/or a different pivot connection could be used. 
     When the watercraft  10  is in use and is being propelled by thrust generated by the impeller  72  rotating in the forward direction, a rearward flow  141  ( FIGS. 7, 11 and 12 ) of water is generated through the venturi conduit  106  from the venturi inlet  108  toward the venturi outlet  110 . If the valve  136  is at that moment in the closed position  140 , the rearward flow  141  acts on the tubes  150  and thereby pivots the valve  136  from the closed position  140  to the open position  138 . If the valve  136  is already in the open position  138 , the rearward flow  141  ensures that the valve  136  stays in the open position  138 . When the valve  136  is in the open position  138 , the fluid outlets  49  of the bailer-siphon system  41  are fluidly connected to the respective fluid inlets  45  of the bailer-siphon system  41 . In addition, the tubes  150  are oriented such that the fluid outlets  49  open in a direction substantially locally parallel to the rearward flow  141  through the venturi conduit  106 . Accordingly, the rearward flow  141  passing the valve  136  creates suction at the fluid outlets  49  and draws water and/or air out of the motor compartment  20  via the fluid inlets  45  of the bailer-siphon system  41 . This water and/or air is expelled via the valve  136  into the water jet leaving the venturi outlet  110 . 
     A flow of water and/or air from the motor compartment  20  out of the valve  136  is shown with arrows  142  in  FIGS. 7, 11 and 12 . In this mode of operation, any air drawn from the motor compartment  20  via the bailer-siphon system  41  exits the valve  136  and leaves the venturi unit  100  via the venturi outlet  110  with the flow  141  of water and does not aerate the impeller  72 . 
     On the other hand, when the watercraft  10  is in use and the impeller  72  is rotating in the reverse direction for clearing debris out of the jet propulsion system  50 , a forward flow  144  ( FIGS. 8, 13 and 14 ) of water is generated through the venturi conduit  106  from the venturi outlet  110  toward the venturi inlet  108 . If the valve  136  is at that moment in the open position  138 , the forward flow  144  acts on the tubes  150  and thereby pivots the valve  136  about the pivot axis  162  from the open position  138  to the closed position  140 . If the valve  136  is already in the closed position  140 , the forward flow  144  ensures that the valve  138  stays in the closed position. As seen from  FIGS. 11 and 14 , due to the action of the clip  160 , the cylindrical post  148  stays in the recess  158  during the pivoting movement of the valve  136  between the open position  138  and the closed position  140 . 
     In the closed position  140 , the valve  136  fluidly disconnects the tubes  130 ,  132  from the venturi outlet  110 , and therefore disconnects the fluid outlets  49  of the bailer-siphon system  41  from the fluid inlets  45  of the bailer-siphon system  41 . This prevents air from being drawn into the venturi unit  100  via the bailer-siphon system  41  and thus prevents the impeller  72  from being aerated via the bailer-siphon system  41  while the impeller  72  is rotating in the reverse direction. 
     As seen from the above, the tubes  150  are an example of elements used to harvest energy from the flows of water through the venturi conduit  106  in order to operate the valve  136  between the closed position  140  and the open position  138 . It is contemplated that a different type of element could be used. 
     Reference is now made to  FIGS. 15 to 21 , which show a venturi unit  200 . The venturi unit  200  is an alternative embodiment of the venturi unit  100  and operates on a similar principles. Parts of the venturi unit  200  that are similar to corresponding parts of the venturi unit  100  have been labeled with the same corresponding reference numerals and will not be described again in detail. 
     One difference between the venturi unit  200  and the venturi unit  100  is that the venturi unit  200  defines a pair of channels  202 ,  204  that fluidly connect to respective ones of the tubes  124 ,  126  of the impeller housing  70 . The channels  202 ,  204  have respective rear ends  206 ,  208  that are open on the inner side of the peripheral wall  210  of the venturi unit  200 , as best shown in  FIGS. 16 and 18 to 21 . The rear ends  206 ,  208  of the channels  202 ,  204  define the fluid outlets  49  of the bailer-siphon system  41 . 
     As shown in  FIG. 15 , the channels  202 ,  204  define a first part  212  of a seat  215  on a top side of the peripheral wall  210  of the venturi unit  200 . The first part  212  of the seat  215  defines an aperture  214  between the channels  202 ,  204 . The aperture  214  extends through the peripheral wall  210  of the venturi unit  200 , peripherally inward into the venturi conduit  106 . The first part  212  of the seat  215  and the aperture  214  receive a valve  216  of the venturi unit  200 . The valve  216  is thus disposed forward of the fluid outlets  49 , between the fluid inlets  45  and the fluid outlets  49 . 
     The seat  215  is then closed by a top cap  218  bolted to the outer side of the peripheral wall  210  over the channels  202 ,  204 . The top cap  218  defines a second, complementary, part  220  of the seat  215  as shown in  FIG. 16 . The second part  220  of the seat  215  mates with the first part  212  of the seat  215  and encloses the valve  216  in the seat  215 . The top cap  218  thereby keeps the valve  216  in the seat  215  during operation. 
     As shown in  FIG. 15 , similar to the valve  136 , the valve  216  includes two ball portions  222  joined by a cylindrical post  224 . One difference between the valve  216  and the valve  136  is that the valve  216  does not have the tubes  150 . Instead, the valve  216  includes an arm  226  that is connected to a mid-portion of the cylindrical post  224  generally orthogonally to the cylindrical post  224 , to pivot together with the ball portions  222 . The arm  226  is received through the aperture  214  in the peripheral wall  210  and extends into the venturi conduit  106  of the venturi unit  200 . The ball portions  222  of the valve  216  are received in and operatively mate with respective portions of the seat  215 . The ball portions  222  are thus disposed at least in part radially outward of the peripheral wall  210 , and are outside of the venturi conduit  106 . 
     The ball portions  222  define apertures  228  therethrough. As shown in  FIGS. 18 and 19 , when the valve  216  is in the open position  230  the apertures  228  align with the respective ones of the channels  202 ,  204  and thereby fluidly connect the fluid outlets  49  of the bailer-siphon system  41  to the respective fluid inlets  45  of the bailer-siphon system  41 . On the other hand, as shown in  FIGS. 20 and 21 , when the valve  216  is in the closed position  232 , an outer surface  234  of each of the ball portions  222  blocks a respective one of the channels  202 ,  204  and thereby fluidly disconnects the fluid outlets  49  from the fluid inlets  45 . 
     As shown in  FIGS. 18 and 19 , when the watercraft  10  is in use, a rearward flow  236  of water from the venturi inlet  108  toward the venturi outlet  110  acts on the arm  226  and pivots the arm  226  and thus the valve  216  from the closed position  232  to the open position  230 . This allows the bailer-siphon system  41  to draw water and/or air out of the motor compartment  20 . As shown in  FIGS. 20 and 21 , when the watercraft  10  is in use, a forward flow  238  of water from the venturi outlet  110  toward the venturi inlet  108  acts on the arm  226  and pivots the arm  226  and thus the valve  216  from the open position  230  to the closed position  232 . This fluidly disconnects the fluid outlets  49  of the bailer-siphon system  41  from the fluid inlets  45  of the bailer-siphon system  41 , and prevents aeration of the impeller  72  via the bailer-siphon system  41 . As seen here, the arm  226  is one example of an element that can be used to harvest energy from flows of water through the venturi conduit  106  in order to operate the valve  216  between the closed position  232  and the open position  230 . It is contemplated that a different element could be used. 
     Reference is now made to  FIGS. 22 to 26 , which show a venturi unit  300 . The venturi unit  300  is another alternative embodiment of the venturi unit  100 . Parts of the venturi unit  300  that are similar to corresponding parts of the venturi unit  100  have been labeled with the same corresponding reference numerals and will not be described again in detail. 
     One difference between the venturi unit  300  and the venturi unit  100  is that the venturi unit  300  includes a ball valve  302  operated by water pressure in the venturi unit  300 . 
     Referring to  FIGS. 23 to 26 , the valve  302  defines a pair of channels  304 ,  306  that at their front ends fluidly connect to respective ones of the tubes  124 ,  126  of the impeller housing  70 . As shown in  FIGS. 25 and 26 , the channels  304 ,  306  at their respective rear ends fluidly connect to respective ones of a pair of angled channels  308 ,  310 , also defined by the valve  302 . The angled channels  308 ,  310  are open at their front ends and define the fluid outlets  49  of the bailer-siphon system  41 . As shown in  FIGS. 25 and 26 , in this embodiment the fluid outlets  49  are disposed outside of the venturi conduit  106 . 
     Also as shown in  FIGS. 25 and 26 , the angled channels  308 ,  310  are larger in diameter than the respective ones of the channels  304 ,  306  at the point of where the angled channels  308 ,  310  fluidly connect to the respective ones of channels  304 ,  306 . The larger diameter serves to create a lower pressure zone during operation of the impeller  72  in the forward direction, as explained below. 
     As shown in  FIGS. 24 to 26 , the valve  302  yet further defines a pair of vertical channels  312 ,  314  ( FIG. 24 ) that fluidly connect to respective ones of the angled channels  308 ,  310 . The vertical channels  312 ,  314  at their bottom ends traverse the peripheral wall  307  of the venturi unit  300  into the venturi conduit  106  and open in a direction substantially locally perpendicular to the flow of water through the venturi conduit  106 . Referring to  FIGS. 25 and 26 , each of the vertical channels  312 ,  314  receives a ball  316  therein and is enclosed at a top end thereof by a cap  318 . The caps  318  are threaded into corresponding threads defined in the top ends of the vertical channels  312 ,  314  and keep the balls  316  from exiting the vertical channels  312 ,  314  in an upward direction. The vertical channels  312 ,  314  at their bottom ends are tapered to diameters that are smaller than the respective ones of the balls  316 . These smaller diameters keep the balls  316  from exiting the vertical channels  312 ,  314  in an downward direction. 
     Similarly, the angled channels  308 ,  310  at their rear ends have diameters that are smaller than the respective ones of the balls  316 . The smaller diameters of the angled channels  308 ,  310  keep the balls  316  from exiting the vertical channels  312 ,  314  via the angled channels  308 ,  310 . The balls  316  are solid and do not define apertures therethrough. 
     As shown in  FIG. 25 , when the watercraft  10  is in use, a rearward flow  320  of water from the venturi inlet  108  toward the venturi outlet  110  pushes the balls  316  upwards away from the peripheral wall  307  toward the respective ones of the caps  318 . This fluidly connects the channels  304 ,  306 ,  308 ,  310  to the venturi conduit  106  and places the valve  302  in its open position  324 . In the open position  324 , some of the rearward flow  320  exits the venturi conduit  106  via the vertical channels  312 ,  314  and then the angled channels  308 ,  310  (fluid outlets  49 ), as shown with arrows  328  in  FIG. 25 . 
     In this flow condition, the larger diameters of the angled channels  308 ,  310  at the point where the angled channels  308 ,  310  fluidly connect to the respective ones of the channels  304 ,  306  create a low pressure zone that draws water and/or air from the motor compartment  20  via the fluid inlets  45  of the bailer-siphon system  41 . The flow of water and/or air from the fluid inlets  45  is shown with arrow  330  in  FIG. 25 . As shown, the flow  330  mixes with the flow  328  and exits via the fluid outlets  49  of the bailer-siphon system  41 . 
     As shown in  FIG. 26 , when the watercraft  10  is in use, a forward flow  322  of water from the venturi outlet  110  toward the venturi inlet  108  pulls the balls  316  downwards toward the peripheral wall  307  and into the respective ones of the tapered bottom ends of the vertical channels  312 ,  314 . The balls  316  thereby mate with and fluidly block the tapered bottom ends of the vertical channels  312 ,  314 . This fluidly disconnects the channels  304 ,  306 ,  308 ,  310  from the venturi conduit  106  and places the valve  302  in its closed position  326 . The valve  302  thereby prevents water or air from entering the forward flow  322  in the venturi conduit  106  via any of the channels  304 ,  306 ,  308 ,  310 , and thus prevents aeration of the impeller  72  via the bailer-siphon system  41 . 
     It is contemplated that the orientations of the channels  304 ,  306 ,  308 ,  310 ,  312  and  314  could be different than as shown, for example that the channels  308 ,  310  could be oriented to open rearward instead upward and forward. It is contemplated that, rather than being passively operated by the flow and/or pressure of water within the venturi conduit  106 , in alternative embodiments the valves  136 ,  216 ,  302  could be actively operated by an actuator. For instance, in such embodiments, the actuator could be a step motor that selectively pivots the valves  136 ,  216 ,  302  between the open position and the closed position. In other embodiments, the actuator could be a mechanical system operated by the operator of the watercraft  10 . 
     In the present embodiment, the valves  136 ,  216 ,  302  are provided at the respective venturi units  100 ,  200 ,  300 . It is contemplated that the valves  136 ,  216 ,  302  could be remote from the venturi units  100 ,  200 ,  300 , in both passively- and actively-actuated valve embodiments. It is also contemplated that fluid conduit  43  of the bailer-siphon system  41  could be defined by a different number of hoses, tubes, valves and/or other elements. 
     It is further contemplated that the valves  136  and  216  could have a different number of ball portions  146 ,  222  and corresponding channels, including a single ball portion and a single channel. It is further contemplated that the valve  302  could have a different number of corresponding channels  304 ,  306 ,  308 ,  310 ,  312 ,  314  and balls  316 . 
     Moreover, it is contemplated that the venturi unit  100  could be provided separately as an after-market accessory for replacing a conventional venturi unit. 
     Reference is now made to  FIGS. 27 to 31 , which show a jet propulsion system. The jet propulsion system  400  is an alternative embodiment of the jet propulsion system  50 . Parts of the jet propulsion system  400  that are similar to corresponding parts of the jet propulsion system  50  have been labeled with the same corresponding reference numerals and will not be described again in detail. 
     The hoses  116  (reference being made to the embodiment of  FIG. 3 ) extending between the siphon breaks  118  and the impeller housing  70  are fluidly connected at their respective rear ends to tubes  402  that are defined by a peripheral wall  128  of the impeller housing  70 . In turn, at their rear ends the tubes  402  are fluidly connected to tubes  404  defined by a peripheral wall  134  of the venturi unit  406 . Tubular extensions  408  are received in the tubes  404  and extend into the passage defined by the venturi unit  406 . The tubular extensions  408  define the fluid outlets  49  of the bailer-siphon system. 
     A valve  410  is provided in the tubes  402 . In this embodiment, the valve  410  is a ball valve  410  that includes two ball portions  412  (only one of which is shown) joined by a cylindrical post (not shown, but similar to the valve  136  without the tubes  150 ). Each ball portion  412  is received in a corresponding seat  414  defined by the tubes  402 . The ball portions  412  define apertures  416  therethrough. In alternative embodiments, the valve  410  is provided in the tubes  402  and/or the tubular extensions  408 . It is contemplated that the valve  410  could be another type of valve, such as a guillotine valve or a butterfly valve for example. 
     The valve  410  is pivotable between open positions ( FIGS. 28, 29 ) and a closed position ( FIGS. 30, 31 ). It should be understood that when the valve  410  is partially opened as shown in  FIGS. 28, 29 , this is still considered an open position for purposes of the present application. When the valve  410  is in an open position, the apertures  416  of the ball portions  412  fluidly connect with the tubes  402 , as shown in  FIGS. 28, 29 , and thereby fluidly connect the fluid outlets  49  of the bailer-siphon system to the respective fluid inlets of the bailer-siphon system. In the closed position, as shown in  FIGS. 30, 313 , an outer surface of each of the ball portions  412  blocks a respective one of the tubes  402  and thereby fluidly disconnects the fluid outlets  49  from the fluid inlets of the bailer-siphon system. When the valve  410  is in an open position, the impeller  72  can be rotated in the forward direction. When the valve  410  is in the closed position, the impeller  72  can be rotated in the forward or the reverse direction. 
     The valve  410  has a pair of arms  418  between which a shaft  420  extends (see  FIG. 27 ). The arms  418  are connected to the ball portions  412  and rotate therewith. The VTS support  103  has an arm  422  at a top thereof from which a shaft  424  extends (see  FIG. 30 ). A link  426  is connected between the shaft  420  and the shaft  424 . More specifically, the link  426  has a hook  428  at a front thereof that is received between the arms  418  and pivotally engages the shaft  420  and a hook  430  at a rear thereof that pivotally engages the shaft  424 . As such, pivoting the VTS support  103  about the VTS axis  105  causes the link  426  to push or pull on the shaft  420  to open and close the valve  410  by rotating the ball portions  412 . When the VTS support  103 , and therefore the steering nozzle  102 , is in the maximum trim-down position, as shown in  FIG. 30 , the valve  410  is closed. When the VTS support  103 , and therefore the steering nozzle  102 , is in a trim-up position, in a neutral axis (i.e. the central axis of the steering nozzle being aligned with the axis  75 ), and in trim-down positions intermediate the neutral and maximum trim-down positions, the valve  410  is at least partially open. It is contemplated that the valve  410  could be closed at a different position than the one described above, such as a maximum trim-up position for example. 
     It is contemplated that in alternative embodiments, the link  426  could be connected directly to the steering nozzle  102  or to the reverse gate  74 . When the link  426  is connected to the reverse gate  74 , the valve  410  is closed when the reverse gate  74  is at a predetermined position, such as a fully lowered position or a position intermediate the stowed and fully lowered positions, and the valve  410  is opened when the reverse gate  74  is in the stowed position and in positions intermediate the stowed position and the predetermined position. 
     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.