Patent Publication Number: US-2018029683-A1

Title: Watercraft and exhaust structure of the watercraft

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a watercraft including an engine, and an exhaust system for the watercraft. 
     2. Description of the Related Art 
     A water vehicle disclosed in Japanese Patent Application Publication No. 2008-157217 includes an exhaust device that exhausts gas emitted from an engine to the outside of a watercraft body. The exhaust device includes a first exhaust pipe extending rearward from a side portion of the engine, a water lock having a tank shape connected to a rear end portion of the first exhaust pipe, and a second exhaust pipe which is connected to a rear portion of the water lock and which opens at a lower portion of a rear end of the watercraft body. The interior of the water lock is divided into an upstream area and a downstream area by a partition. A partition pipe penetrates the partition. The rear end portion of the first exhaust pipe includes an inner pipe located at the upstream area in the water lock. An upstream end portion of the second exhaust pipe is located at the downstream area in the water lock. 
     The exhaust gas emitted from the engine flows from an outlet of the inner pipe into the upstream area in the water lock via the first exhaust pipe, passes the partition pipe, and flows into the downstream area in the water lock. The exhaust gas is then exhausted to the outside of the watercraft body via the second exhaust pipe. 
     The outlet of the inner pipe disclosed in Japanese Patent Application Publication No. 2008-157217 is opposed to or faces the partition in a direction along a pipe axis of the inner pipe. Thus, a portion of the exhaust gas flowing into the upstream area in the water lock from the outlet flows straight along the pipe axis and collides with the partition and the partition pipe. Accordingly, there is a possibility that turbulence occurs in the water lock. If turbulence occurs in the water lock, it is difficult for the exhaust gas in the water lock to reach the second exhaust pipe, and the exhaust efficiency to the outside of the watercraft body deteriorates. 
     SUMMARY OF THE INVENTION 
     In order to overcome the previously unrecognized and unsolved challenges described above, a preferred embodiment of the present invention provides a watercraft including a watercraft body, an engine in the watercraft body, an upstream exhaust pipe including an end portion including an outlet, a water lock including an inner space which houses the end portion, a downstream exhaust pipe connected to the water lock, and a flow direction diverter. The upstream exhaust pipe, the water lock, the downstream exhaust pipe, and the flow direction diverter define an exhaust system of the watercraft. The upstream exhaust pipe guides the exhaust gas from the engine to the end portion. The inner space of the water lock receives the exhaust gas from the outlet of the end portion. The downstream exhaust pipe exhausts the exhaust gas from the inner space to an outside of the watercraft body. The flow direction diverter changes a flow direction of the exhaust gas at the outlet to a cross direction which intersects a pipe axis of the end portion. 
     According to this preferred embodiment, the exhaust gas that reaches the end portion of the upstream exhaust pipe from the engine flows into the inner space of the water lock from the outlet of the end portion to the cross direction intersecting the pipe axis of the end portion. The exhaust gas which flows into the inner space of the water lock flows along an inner wall of the water lock. Thus, turbulence in the water lock is significantly reduced or prevented, the exhaust gas in the water lock smoothly reaches the downstream exhaust pipe, and the exhaust gas is exhausted to the outside of the watercraft body. Accordingly, exhaust efficiency is improved. 
     In a preferred embodiment of the present invention, the end portion penetrates an inner wall of the water lock along a pipe axis direction, and the flow direction diverter changes the flow direction of the exhaust gas to a direction along the inner wall. 
     According to this preferred embodiment, the exhaust gas which flows into the inner space of the water lock from the outlet of the end portion of the upstream exhaust pipe flows along the inner wall of the water lock. Flow of the exhaust gas in the inner space of the water lock is accelerated. Thus, turbulence in the water lock is further reduced or prevented, and exhaust efficiency is further improved. 
     In a preferred embodiment of the present invention, the outlet preferably opens radially to the outside of the upstream exhaust pipe at the end portion. According to this preferred embodiment, the exhaust gas flows along the inner wall of the water lock. Flow of the exhaust gas in the inner space of the water lock is accelerated. Thus, turbulence in the water lock is further reduced or prevented, and exhaust efficiency is further improved. 
     In a preferred embodiment of the present invention, the flow direction diverter includes a baffle that blocks the exhaust gas which reaches the end portion to change the flow direction of the exhaust gas. 
     According to this preferred embodiment, the exhaust gas which reaches the end portion of the upstream exhaust pipe cannot flow straight along the pipe axis of the end portion due to the baffle. Thus, the flow direction of the exhaust gas at the outlet of the end portion is changed to the cross direction. 
     In a preferred embodiment of the present invention, the watercraft further includes a fastener that fastens the baffle to the end portion. 
     According to this preferred embodiment, the baffle is stabilized by being fastened to the end portion of the upstream exhaust pipe, and blocks the exhaust gas which reaches the end portion to change the flow direction of the exhaust gas. 
     In a preferred embodiment of the present invention, the fastener includes three or more fasteners. 
     According to this preferred embodiment, the baffle is fastened to the end portion of the upstream exhaust pipe by the three or more fasteners. Thus, the baffle is further stabilized. 
     In a preferred embodiment of the present invention, the watercraft further includes a drain pipe surrounding the end portion. A flow passage is defined between the drain pipe and the end portion, and guides engine cooling water to the inner space. 
     According to this preferred embodiment, cooling water which flows into the inner space of the water lock from the flow passage smoothly reaches the downstream exhaust pipe and is drained to the outside of the watercraft body from the downstream exhaust pipe by being carried by the exhaust gas flowing along the inner wall of the water lock. Thus, both exhaust efficiency and cooling water drainage efficiency is improved, and turbulence in the water lock is significantly reduced or prevented, as discussed above. For example, spray of cooling water stirred by the turbulence in the water lock is significantly reduced or prevented. Thus, spray flowing backward in the upstream exhaust pipe by infiltrating into the upstream exhaust pipe from the outlet is significantly reduced or prevented. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a watercraft according to a preferred embodiment of the present invention. 
         FIG. 2  is a sectional view of an exhaust system of the watercraft cut along a plane extending in the up-down and front-rear directions. 
         FIG. 3  is a perspective view of an end portion of an upstream exhaust pipe of the exhaust system. 
         FIG. 4  is a perspective view of an end portion of an upstream exhaust pipe according to a first modification of a preferred embodiment of the present invention. 
         FIG. 5  is a perspective view of an end portion of an upstream exhaust pipe according to a second modification of a preferred embodiment of the present invention. 
         FIG. 6  is a sectional view of an exhaust system according to a third modification of a preferred embodiment of the present invention cut along a plane extending in the up-down and front-rear directions. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     First Preferred Embodiment 
       FIG. 1  is a schematic view of a watercraft  1  according to a preferred embodiment of the present invention. A right-left direction in  FIG. 1  is defined as the front-rear direction of the watercraft  1 . The left side in  FIG. 1  shows the front of the watercraft  1 . A right-left direction of the watercraft  1  is seen when facing in the traveling direction of the watercraft  1 . Thus, the near side in a direction perpendicular to the sheet of  FIG. 1  corresponds to the left of the watercraft  1 , and the far side in the direction perpendicular to the sheet of  FIG. 1  corresponds to the right of the watercraft  1 . 
     The watercraft  1  includes a watercraft body  2 , and an engine  3  in an interior of the watercraft body  2 . The watercraft body  2  includes a hull  4  that defines a watercraft bottom, and a deck  5  located above the hull  4 . The watercraft body  2  is elongated in the front-rear direction. The engine  3  is located in an engine room between the hull  4  and the deck  5  in an up-down direction. The engine  3  is preferably an internal combustion engine including a crankshaft that rotates about a crank axis extending in the front-rear direction. 
     The watercraft  1  of this preferred embodiment is preferably a jet propelled watercraft, for example, and further includes a seat  6  on which a rider sits, a steering handle  7  that is operated to the right and left by the rider, and a jet pump  8  mounted on a rear portion of the watercraft body  2 . The seat  6  and the steering handle  7  are located on an upper side of the watercraft body  2 . A throttle lever is mounted on a right end portion of the steering handle  7 . A driving force of the engine  3  is adjusted by operation of the throttle lever by the rider. 
     The jet pump  8  is located rearward relative to the engine  3 . The jet pump  8  sucks in water from the watercraft bottom and ejects the water to an outside of the watercraft body  2  by a driving force of the engine  3 . The jet pump  8  generates a thrust to propel the watercraft  1  forward. 
     For example, the jet pump  8  includes an intake  9  into which water outside the watercraft body  2  is sucked, an outlet  10  from which the water sucked in from the intake  9  is ejected rearward, and a flow passage  11  that guides the water sucked into the intake  9  to the outlet  10 . The jet pump  8  further includes a driveshaft  12  extending in the front-rear direction, an impeller  13  and a stator vane  14  that are located in the flow passage  11 , a nozzle  15 , and a deflector  16  that deflects or directs water ejected rearward from the nozzle  15  to the right and left. 
     The intake  9  opens at the watercraft bottom, and the outlet  10  opens rearward at a location farther to the rear than the intake  9 . A front end portion of the driveshaft  12  is located in the watercraft body  2  and coupled to the crankshaft of the engine  3  via a coupling or the like, for example. A rear end portion of the driveshaft  12  is located in the flow passage  11  and coupled to the impeller  13 . The stator vane  14  is located behind the impeller  13 , and the nozzle  15  is located behind the stator vane  14 . The stator vane  14  and the nozzle  15  are fixed with respect to the flow passage  11 . 
     The impeller  13  is rotatable in the flow passage  11  about a central axis of the driveshaft  12 . The impeller  13  is driven by the engine  3  to rotate about the central axis of the driveshaft  12  together with the driveshaft  12 . When the impeller  13  is driven to rotate, water outside the watercraft body  2  is sucked into the flow passage  11  from the intake  9  and is fed from the impeller  13  to the stator vane  14 . A torsional water flow produced by rotation of the impeller  13  is reduced and straightened by the water fed by the impeller  13  and passing through the stator vane  14 . Thus, the flow-straightened water is delivered from the stator vane  14  to the nozzle  15 . The nozzle  15  preferably has a tubular or substantially tubular shape extending in the front-rear direction, and the outlet  10  is defined by a rear end portion of the nozzle  15 . The water fed to the nozzle  15  is thus jetted rearward from the outlet  10  of the rear end portion of the nozzle  15 . 
     The deflector  16  extends rearward from the nozzle  15 . The deflector  16  is coupled to the nozzle  15  and rotates to the right and left about a deflector axis  16 A extending in the up-down direction. The deflector  16  is preferably hollow. The outlet  10  of the nozzle  15  is located in the deflector  16 . The deflector  16  defines an ejection port  17  that opens rearward. The ejection port  17  is located behind the outlet  10 . Water jetted rearward from the outlet  10  penetrates through an interior of the deflector  16  and is ejected rearward from the ejection port  17 . The deflector  16  turns to the right and left according to an operation of the steering handle  7 . The water that is ejected from the jet pump  8  is directed to the right and left by the operation of the steering handle  7  to steer the watercraft  1 . 
     The watercraft  1  further includes an exhaust system  20  that exhausts exhaust gas generated in the engine  3  to the outside of the watercraft body  2 . An exhaust port  2 A is located at a rear of a left surface or a right surface of the watercraft body  2 . The exhaust system  20  includes an upstream exhaust pipe  21 , a water lock  22 , and a downstream exhaust pipe  23 . The exhaust system  20  is located in the watercraft body  2 . 
     The upstream exhaust pipe  21  is connected to an exhaust port of a cylinder of the engine  3 . When there are two or more cylinders, the exhaust port of each cylinder is connected to the upstream exhaust pipe  21  which joins each exhaust port and then extends rearward. The upstream exhaust pipe  21  guides the exhaust gas from the exhaust port of the engine  3  rearward. An end portion  21 A, which is located at a downstream end of the upstream exhaust pipe  21  in a flow direction of the exhaust gas, defines a rear end portion of the upstream exhaust pipe  21 . In a preferred embodiment, at least the upstream exhaust pipe  21  of the exhaust system  20  is made of metal since the exhaust gas emitted from the engine  3  and flowing into the upstream exhaust pipe  21  is relatively hot. 
       FIG. 2  is a sectional view of the exhaust system  20  when cut along a plane extending in the up-down and front-rear directions and seen from left. The end portion  21 A preferably has a pipe shape (for example, a circular or substantially circular pipe shape) including a pipe axis A. In a preferred embodiment, a pipe axis direction of the pipe axis A coincides with the front-rear direction of the watercraft  1 . In another preferred embodiment, the end portion  21 A has, for example, a rectangular or substantially rectangular pipe shape having a polygonal cross section, such as a rectangular or substantially rectangular shape, when cut along a plane perpendicular to the pipe axis A. A narrow portion  21 B in the middle of the end portion  21 A in the front-rear direction is one step narrower than the end portion  21 A. A circular or substantially circular opening  21 C is located at a rear end of the end portion  21 A. A plurality of outlets  21 D are disposed on an outer peripheral surface of the end portion  21 A. Each of the outlets  21 D penetrates the end portion  21 A along a radial direction R, with the pipe axis A as a center, and opens to the outside in the radial direction R. In a preferred embodiment, the outlets  21 D include, for example, four or more outlets  21 D aligned in the front-rear direction at equal or substantially equal intervals that define a line. In a preferred embodiment, a plurality of lines are aligned in a circumferential direction S about the pipe axis A on the outer peripheral surface of the end portion  21 A. A plurality of lines are distributed in a circumferential direction S about the pipe axis A on the outer peripheral surface of the end portion  21 A and are located rearward relative to the narrow portion  21 B. In a preferred embodiment, the outlet  21 D includes, for example, a round or substantially round hole or a slit extending in the front-rear direction or the circumferential direction S. The outlet  21 D may include one or more than one outlet  21 D. 
     The exhaust system  20  further includes a baffle  25  serving as a flow direction diverter. In a preferred embodiment, the baffle  25  preferably has a circular or substantially circular plate shape, for example, with a plate thickness direction that coincides with the front-rear direction. The baffle  25  is opposed to or covers the end portion  21 A from the rear and blocks the opening  21 C. The end portion  21 A includes the baffle  25  when the baffle  25  is fastened to the end portion  21 A. In a preferred embodiment, the baffle  25  is fastened to the end portion  21 A by a plurality of bolts  26 , for example, that serve as fasteners. In a preferred embodiment, three bolts  26 , for example, define and function as the fasteners. 
       FIG. 3  is a perspective view of the end portion  21 A to which the baffle  25  is fastened as seen from the rear. The end portion  21 A integrally and unitarily includes a ring-shaped or substantially ring-shaped flange  21 E which overhangs to the outside in the radial direction R from all areas in the circumferential direction S of a rear end of the end portion  21 A, and a bulge  21 F which bulges to the outside in the radial direction R from the outer peripheral surface of the end portion  21 A and which extends forward from the flange  21 E. In a preferred embodiment, the bulge  21 F includes two or more bulges  21 F corresponding to a number of the bolts  26 . For example, in a preferred embodiment, three bulges  21 F are aligned in the circumferential direction S at equal or substantially equal intervals. The outlets  21 D are deviated or offset from the bulge  21 F in the circumferential direction S. For example, the outlets  21 D are disposed between neighboring bulges  21 F. An outer periphery  25 A of the baffle  25  overlaps with the flange  21 E from the rear. 
     A screw portion or thread of each bolt  26  penetrates the outer periphery  25 A and the flange  21 E from the rear and is installed in a screw hole in the corresponding bulge  21 F. The three bolts  26  are aligned in the circumferential direction S at equal or substantially equal intervals. Thus, the baffle  25  is fastened to the end portion  21 A by the three bolts  26 . In this preferred embodiment, the baffle  25  is more stable than when two or less bolts  26  are used. 
     The water lock  22  is located between the engine  3  and the jet pump  8  in the front-rear direction ( FIG. 1 ). Referring to  FIG. 2 , the water lock  22  preferably has an elongated tank shape, for example, that extends in the front-rear direction. The water lock  22  integrally and unitarily includes a cylindrical or substantially cylindrical portion  22 A (hereinafter, “cylindrical portion  22 A”) which extends in the front-rear direction, a rear baffle  22 C which is connected to a rear end of the cylindrical portion  22 A and blocks an inner space  22 B of the cylindrical portion  22 A from the rear, and a front baffle  22 D which is connected to a front end portion of the cylindrical portion  22 A and blocks the inner space  22 B from the front. Each of the rear baffle  22 C and the front baffle  22 D preferably has a circular or substantially circular plate shape. In a preferred embodiment, the rear baffle  22 C is curved and bulges rearward, and the front baffle  22 D is curved and bulges forward. A protruding portion  22 E protruding forward is integrally and unitarily disposed at a central or substantially central portion of the front baffle  22 D. The protruding portion  22 E preferably has a cylindrical or substantially cylindrical shape having a smaller outer diameter than that of the cylindrical portion  22 A. An inner space  22 F of the protruding portion  22 E communicates with the inner space  22 B of the cylindrical portion  22 A from the front. An entire inner space  22 G of the water lock  22  includes the inner space  22 F and the inner space  22 B. An opening  22 H communicating with the inner space  22 F is disposed at a front end of the protruding portion  22 E. 
     A portion of the end portion  21 A of the upstream exhaust pipe  21  that is located rearward relative to at least the narrow portion  21 B is inserted into the inner space  22 F of the protruding portion  22 E from the opening  22 H. The end portion  21 A is inserted beyond the protruding portion  22 E to a front end portion of the inner space  22 B of the cylindrical portion  22 A. For example, the end portion  21 A penetrates an inner wall  221  of the water lock  22  of the front baffle  22 D along the front-rear direction. At least the outlet  21 D of the end portion  21 A is located in the inner space  22 B of the cylindrical portion  22 A. The end portion  21 A within the inner space  22 B is preferably coaxial with the cylindrical portion  22 A and the protruding portion  22 E. A flow passage  27  is defined between the end portion  21 A and the protruding portion  22 E which surrounds the end portion  21 A. The flow passage  27  is preferably ring-shaped, extends in the front-rear direction between the end portion  21 A and the protruding portion  22 E, and communicates with the inner space  22 B from the front. 
     The downstream exhaust pipe  23  includes an upstream end portion  23 A connected to the water lock  22  by penetrating the cylindrical portion  22 A of the water lock  22  from above, and a downstream end portion  23 B ( FIG. 1 ) connected to the exhaust port  2 A of the watercraft body  2 . The downstream exhaust pipe  23  extends from the upstream end portion  23 A to the downstream end portion  23 B. In order to prevent water from outside the watercraft body  2 , such as seawater, from flowing backward in the downstream exhaust pipe  23 , a midway portion of the downstream exhaust pipe  23  between the upstream end portion  23 A and the downstream end portion  23 B is bent to extend upward and then downward ( FIG. 1 ). 
     The upstream end portion  23 A is located at a rear portion of the inner space  22 B of the cylindrical portion  22 A. An inlet  23 C which opens downward is located at a lower end of the upstream end portion  23 A. When the watercraft  1  is upset or overturned and the up-down direction of the watercraft body  2  and the exhaust system  20  is reversed, the inlet  23 C is located at a higher position than the water surface around the watercraft body  2 . Thus, water outside the watercraft body  2  that may flow backward in the downstream exhaust pipe  23  from the exhaust port  2 A and infiltrate into the water lock  22  from the inlet  23 C is significantly reduced or prevented. The upstream end portion  23 A is preferably at a same or a substantially same position as the end portion  21 A of the upstream exhaust pipe  21  and the baffle  25  in the right-left direction of the watercraft  1  (a direction perpendicular to the sheet of  FIG. 2 ) and is opposed to or overlaps the end portion  21 A and the baffle  25  from the rear in the inner space  22 B. Alternatively, the upstream end portion  23 A may be located at a position deviated from the end portion  21 A and the baffle  25  in the right-left direction. 
     The exhaust system  20  further includes a drain pipe  30  and a cooling pipe  31 . The drain pipe  30  preferably coaxially surrounds the end portion  21 A of the upstream exhaust pipe  21  and defines a flow passage  32  between the drain pipe  30  and the end portion  21 A. The flow passage  32  is preferably ring-shaped and extends in the front-rear direction between an outer circumferential surface of the end portion  21 A and an inner circumferential surface of the drain pipe  30 . A front end portion of the flow passage  32  is closed. The flow passage  32  communicates with the flow passage  27 , which is between the end portion  21 A and the protruding portion  22 E of the water lock  22 , from the front via the opening  22 H of the protruding portion  22 E. 
     The cooling pipe  31  is connected to the engine  3  and the drain pipe  30 . The watercraft body  2  includes a cooling passage which takes in water from outside the watercraft body  2  and from the watercraft bottom as cooling water and feeds the water to the engine  3 . Cooling water, which passes through the cooling passage and cools the engine  3 , flows into the flow passage  32  via the cooling pipe  31 , passes the flow passage  32  and the flow passage  27 , and then flows into the inner space  22 B of the cylindrical portion  22 A of the water lock  22 . Thus, the flow passage  32  and the flow passage  27  guide the cooling water for the engine  3  from the cooling pipe  31  to the inner space  22 B. At a joint between the drain pipe  30  and the protruding portion  22 E, a rear end portion of the drain pipe  30  is securely connected to an outside surface of the protruding portion  22 E in the radial direction R. Thus, leakage of cooling water from the joint between the drain pipe  30  and the protruding portion  22 E is significantly reduced or prevented. 
     The exhaust gas from the engine  3  flows in the upstream exhaust pipe  21  and is guided to the end portion  21 A. The exhaust gas which reaches the end portion  21 A flows rearward along the pipe axis A in the end portion  21 A, as shown by a broken line arrow Y 1 . 
     The baffle  25  is located beyond the exhaust gas which flows rearward in the end portion  21 A. For example, the exhaust gas in the end portion  21 A is blocked by the baffle  25 . The baffle  25  which is fastened to the end portion  21 A by the bolts  26  blocks the exhaust gas which reaches the end portion  21 A. 
     The exhaust gas in the end portion  21 A cannot flow straight along the pipe axis A because the exhaust gas is blocked by the baffle  25 . Thus, the exhaust gas changes flow direction to a cross direction Y 2 , which intersects the pipe axis A, and passes the outlets  21 D of the end portion  21 A. The baffle  25  changes the flow direction of the exhaust gas in the end portion  21 A to the cross direction Y 2  at the outlets  21 D by blocking the exhaust gas in the end portion  21 A. Thus, the exhaust gas in the end portion  21 A flows into the inner space  22 B of the cylindrical portion  22 A of the water lock  22  by being diffused radially outward in the cross direction Y 2  from the outlets  21 D ( FIG. 3 ). 
     The cross direction Y 2  may be inclined rearward with respect to the pipe axis A. In a preferred embodiment, a portion of an inner wall of the water lock  22  that is parallel or substantially parallel with the pipe axis A, for example, an inner wall  22 J of the cylindrical portion  22 A, is located beyond the exhaust gas which flows into the inner space  22 B from the outlets  21 D. Thus, the exhaust gas which flows into the water lock  22  flows rearward along the inner wall  22 J, as shown by a broken line arrow Y 3 . 
     The cross direction Y 2  is preferably not only inclined with respect to the pipe axis A but also extends along the inner wall  221  of the front baffle  22 D which is perpendicular or substantially perpendicular to the pipe axis A, as shown by a broken line arrow Y 4 . In this preferred embodiment, the exhaust gas which flows into the inner space  22 B flows to the outside in the radial direction R along the inner wall  221 , as shown by the broken line arrow Y 4 . The exhaust gas then flows rearward along the inner wall  22 J of the cylindrical portion  22 A as shown by the broken line arrow Y 3 . 
     The exhaust gas flows rearward along the inner wall  22 J of the cylindrical portion  22 A. Thus, the occurrence of turbulence in the water lock  22  is significantly reduced or prevented. For example, the exhaust gas in the water lock  22  reaches the inlet  23 C of the downstream exhaust pipe  23  without being affected by the turbulence, refer to a broken line arrow Y 5 . The exhaust gas in the water lock  22  reaches the inlet  23 C after flowing rearward along the inner wall  22 J and flowing along an inner wall  22 K of the rear baffle  22 C. Alternatively, the exhaust gas reaches the inlet  23 C while flowing along the inner wall  22 J. The exhaust gas which reaches the inlet  23 C is exhausted to the outside of the watercraft body  2  from the exhaust port  2 A ( FIG. 1 ) after passing the downstream exhaust pipe  23 . 
     When the exhaust gas flows along the inner wall  22 J of the water lock  22 , even if the exhaust gas is forceful due to high-speed rotation, acceleration, or deceleration of the engine  3 , turbulence in the water lock  22  is significantly reduced or prevented and exhaust efficiency is improved. 
     Cooling water (shown by a dashed line arrow Y 6 ) which flows into the inner space  22 G of the water lock  22  from the flow passages  32  and  27  is carried by the exhaust gas, as shown by the broken line arrows Y 2  and Y 3 , which is diffused in the cross direction Y 2  from the outlets  21 D and flows along the inner wall  22 J of the water lock  22 . For example, the cooling water reaches the downstream exhaust pipe  23 , is mixed with the exhaust gas, and is drained to the outside of the watercraft body  2  from the downstream exhaust pipe  23 . Thus, exhaust noise of the exhaust gas is significantly decreased or minimized compared to when only the exhaust gas is exhausted to the outside of the watercraft body  2 . 
     Not only the exhaust gas, but also the cooling water flows along the inner wall  22 J. Thus, not only exhaust gas exhaust efficiency but also cooling water drainage efficiency are both improved. Moreover, because the turbulence of the exhaust gas in the water lock  22  is significantly reduced or prevented, spray of the cooling water stirred by the turbulence in the water lock  22  is significantly reduced or prevented. Thus, spray reaching the engine  3  by flowing backward in the upstream exhaust pipe  21  after infiltrating into the upstream exhaust pipe  21  from the outlet  21 D of the end portion  21 A is significantly reduced or prevented. Since it is not necessary to account for a backward flow of the cooling water in the upstream exhaust pipe  21 , a length of the upstream exhaust pipe  21  is reduced and a size of the exhaust system  20  and the entire watercraft  1  is thus reduced. 
     Although a first preferred embodiment of the present invention has been described above, the present invention is not restricted to the contents of the first preferred embodiment and various modifications are possible within the scope of the present invention. 
     Other Preferred Embodiments 
       FIG. 4  is a perspective view of the end portion  21 A of the upstream exhaust pipe  21  according to a first modification of a preferred embodiment of the present invention as seen from the rear.  FIG. 5  is a perspective view of the end portion  21 A of the upstream exhaust pipe  21  according to a second modification of a preferred embodiment of the present invention as seen from the rear.  FIG. 6  is a sectional view of the exhaust system  20  according to a third modification of a preferred embodiment of the present invention. Elements that are the same as those described above are identified in  FIGS. 4, 5 and 6  by the same reference numerals, and a description thereof will be omitted. 
     In the first modification shown in  FIG. 4 , the outlets  21 D on the outer peripheral surface of the end portion  21 A are omitted, and the baffle  25  integrally and unitarily includes a cylindrical or substantially cylindrical portion  25 B (hereinafter, “cylindrical portion  25 B”) which extends forward from the outer periphery  25 A. The cylindrical portion  25 B contacts the flange  21 E from the rear. Thus, the baffle  25  is opposed to or covers the opening  21 C of the end portion  21 A at intervals in the front-rear direction. For example, the opening  21 C is not blocked by the baffle  25  and opens rearward. A plurality of notches  25 C aligned in the circumferential direction S are disposed on the cylindrical portion  25 B. Each notch  25 C extends forward from a rear end of the cylindrical portion  25 B and penetrates the cylindrical portion  25 B in the radial direction R. Each notch  25 C is blocked from the front by the flange  21 E and defines and functions as the outlet  21 D. Each notch  25 C communicates with a gap, which is between the baffle  25  and the opening  21 C in the front-rear direction, from the outside in the radial direction R. 
     In the first modification, the exhaust gas, which passes in the upstream exhaust pipe  21  and is guided to the end portion  21 A, flows rearward along the pipe axis A and passes through the opening  21 C. The baffle  25  is located downstream of the opening  21 C. The exhaust gas is blocked by the baffle  25  and changes its flow direction to the cross direction Y 2  which intersects the pipe axis A. The exhaust gas passes through each notch  25 C and flows into the inner space  22 B of the water lock  22  by being diffused outward in the radial direction R. The radially diffused exhaust gas flows rearward along the inner wall  22 J of the water lock  22 , as described above. Thus, the exhaust gas smoothly reaches the downstream exhaust pipe  23  and is exhausted to the outside of the watercraft body  2 . 
     In the second modification shown in  FIG. 5 , the end portion  21 A with the outlets  21 D and the baffle  25  are integrated by welding and the like, for example. Thus, the bolts  26  ( FIG. 3 ) for fastening the baffle  25  to the end portion  21 A, and the bulge  21 F to which the bolt  26  is installed are omitted. In a preferred embodiment, the outlets  21 D are distributed equally or substantially equally in the circumferential direction S on the outer peripheral surface of the end portion  21 A. The end portion  21 A is fastened by, for example, bolts  35  to a portion of the upstream exhaust pipe  21  that is located upstream of the end portion  21 A. 
     In the third modification shown in  FIG. 6 , the water lock  22  includes a partition  40  and a relay pipe  41 . The partition  40  preferably has a circular or substantially circular plate shape which is similar to the rear baffle  22 C of the water lock  22  and is located at a central or substantially central portion in the front-rear direction of the inner space  22 B of the water lock  22 . The partition  40  divides the inner space  22 B into an upstream space  22 L, which accommodates the end portion  21 A of the upstream exhaust pipe  21 , and a downstream space  22 M which is located rearward relative to the upstream space  22 L and accommodates the upstream end portion  23 A of the downstream exhaust pipe  23 . A drain hole  40 A is located at a lower end of the partition  40  to drain cooling water collected in a lower portion of the upstream space  22 L to the downstream space  22 M. 
     The relay pipe  41  extends in the front-rear direction, is fixed to the partition  40 , and penetrates the partition  40  in the front-rear direction. In a preferred embodiment, the relay pipe  41  includes two or more relay pipes  41 , for example, and the two or more relay pipes  41  are aligned in the up-down direction, as shown in  FIG. 6 . The upstream space  22 L and the downstream space  22 M communicate with each other via an interior of the relay pipes  41 . The exhaust gas which flows into the inner space  22 B of the water lock  22  by being diffused radially outward in the cross direction Y 2  from the outlets  21 D flows rearward along the inner wall  22 J of the water lock  22  in the upstream space  22 L (refer to the broken line arrow Y 3 ). The exhaust gas flows into the downstream space  22 M via the interior of the relay pipes  41  and is exhausted to the outside of the watercraft body  2  via the downstream exhaust pipe  23 . In a preferred embodiment, a taper  41 A, which is enlarged in a forward direction, is located at a front end of the relay pipe  41 . The exhaust gas in the upstream space  22 L enters into the relay pipe  41  smoothly via the taper  41 A. 
     In a preferred embodiment of the present invention, instead of the baffle  25 , the flow direction diverter may include a guide  45 , for example, as shown by a broken line in  FIG. 6 . The guide  45  changes the flow direction of the exhaust gas in the end portion  21 A to the cross direction Y 2 . The guide  45  includes an inclined surface  45 A disposed in the end portion  21 A. The inclined surface  45 A is inclined with respect to the pipe axis A and extends outward in a rearward direction and radial direction R, and includes a tapered surface or a planar surface. The flow direction of the exhaust gas flowing straight along the pipe axis A in the end portion  21 A changes to the cross direction Y 2  due to the inclined surface  45 A, such that the exhaust gas passes through the outlets  21 D of the end portion  21 A. 
     In a preferred embodiment of the present invention, instead of the bolts  26 , the fastener may include a nut, for example, to fasten the baffle  25  to the end portion  21 A. The nut is installed, for example, on a screw shaft protruding rearward from the end portion  21 A and penetrating the baffle  25 . The baffle  25  is thus fastened to the end portion  21 A by the nut. 
     It is to be understood that features of two or more of the various preferred embodiments described above may be combined. 
     The present application claims priority to Japanese Patent Application No. 2016-150144 filed on Jul. 29, 2016 in the Japan Patent Office, and the entire disclosure of which is incorporated herein by reference in its entirety. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, thus, is to be determined solely by the following claims.