Patent Publication Number: US-6666737-B1

Title: Cooling system for jet propulsion boat

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2001-269428 filed on Sep. 5, 2001 the entire contents thereof is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a cooling system for a jet propulsion boat provided with a jet propulsion unit in a pump chamber in a vessel body that is propelled by driving the jet propulsion unit by an engine wherein the exhaust gas is discharged from the engine into the pump chamber. 
     2. Description of Background Art 
     The jet propulsion boat is a vessel provided with a jet pump mounted at the rear portion of the vessel body. The vessel is propelled by sucking water from the bottom of the vessel by driving the jet pump by the engine and discharging the sucked water rearwardly. The jet propulsion boat is provided with a cooling system for cooling the engine or an exhaust system with water while being propelled. 
     A cooling system for a jet propulsion boat is disclosed in Japanese Utility Model Laid-Open No. 86899/1990 that is entitled “WASHING UNIT FOR VESSEL PROPELLER.” The cooling system for a jet propulsion boat will be described referring FIG. 1 of this publication that is illustrated hereinafter as FIG. 15 which is a side view showing a jet propulsion boat of the related art. 
     A jet propulsion boat  100  is provided with an engine-cooling flow path  102  for cooling an engine  101 . The engine-cooling flow path  102  takes a part of a jet of water into an intake path  103  as cooling water and guides the cooling water to an engine-cooling duct (as an example, a jacket water) through the intake path  103  for cooling the engine  101  by flowing cooling water through the engine-cooling flow path, and discharges the cooling water to the outside through a drainage duct  105 . 
     The intake path  103  is a flow path being capable of taking a part of a jet of water as cooling water by positioning an intake port  103   a  toward a jet pump  107 . The drainage duct  105  is capable of discharging cooling water to the outside of a vessel body  110  by disposing a discharge port  105   a  at a front outer wall  110   a  of the vessel body  110 . 
     The engine-cooling flow path  102  cools the engine  101  with water by providing cooling water during operation of the jet propulsion boat  100 . When washing the jet propulsion boat  100 , the engine-cooling flow path  102  may be washed with tap water by supplying washing water (for example, tap water) to the discharge port  105   a  of the drainage duct  105 . 
     Generally, the jet propulsion boat  100  is provided with an exhaust-system-cooling flow path for cooling the exhaust system in addition to the engine-cooling flow path  102  for cooling the engine  101 . As a means for cooling the exhaust system, the exhaust-system-cooling flow path is constructed to be provided in series with the engine-cooling flow path  102 . In addition, a construction is available wherein the exhaust-system-cooling flow path and the engine-cooling flow path  102  are provided in parallel. 
     According to the construction in which the exhaust-system-cooling flow path is provided in series with the engine-cooling flow path  102 , cooling water used for cooling the engine  101  is also utilized for cooling the exhaust system. 
     Therefore, since cooling water flows through the engine-cooling flow path  102  and subsequently into the exhaust-system-cooling flow path, the temperature of cooling water in the engine-cooling flow path  102  increases to some extent, which makes preferable control of the temperature of the exhaust system difficult. 
     On the other hand, according to the structure in which the exhaust-system-cooling flow path and the engine-cooling flow path  102  are provided in parallel, cooling water flowing in the engine-cooling flow path  102  and cooling water flowing in the exhaust-system-cooling flow path are flow separately, and thus it is easy to control the temperature of the exhaust system preferably. 
     However, when the engine-cooling flow path  102  and the exhaust-system-cooling duct are provided in parallel, washing water has to be diverged and flows simultaneously into both the engine-cooling flow path  102  and the exhaust-system-cooling duct when washing, which results in an increase in the quantity of washing water consumed. 
     The jet propulsion boat  100  in the above mentioned publication discharges cooling water used for cooling the engine-cooling flow path  102  to the outside through the discharge port  105   a  of the drainage duct  105 . However, since the discharge port  105   a  of the drainage duct  105  is disposed on the front outer wall  110   a  of the vessel body  110 , the discharge port  105   a  of the drainage duct  105  can be seen from the outside, which is not preferable in terms of appearance of the jet propulsion boat  100 . 
     SUMMARY AND OBJECTS OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a cooling system for a jet propulsion boat in which the quantity of washing water consumed can be reduced and the appearance of the boat improved. 
     In order to solve the problem, the present invention provides a jet propulsion boat comprising a jet pump chamber provided in the rear portion of a vessel body with a jet propulsion unit provided in the jet pump chamber wherein a jet of water is emitted for propulsion by driving the jet propulsion unit with an engine. A part of the jet of water is taken into an intake path as cooling water. The cooling water taken into the intake path is diverging into the diverging duct and flows into an engine-cooling flow path and an exhaust-system-cooling flow path for cooling the engine and for cooling the exhaust system. A one-way valve is provided that is capable of opening for allowing cooling water to flow from the intake path towards the diverging duct and is capable of closing for preventing washing water from flowing from the diverging duct into the intake path. The one-way valve is provided in the middle of the intake path. 
     The one-way valve for enabling cooling water to flow from the-intake path into the diverging duct and preventing washing water from flowing from the diverging duct into the intake path is provided in the middle of the intake path. 
     As a consequent, when operating the jet propulsion boat, cooling water taken into the intake path can flow into the diverging duct through the one-way valve, and cooling water flowing into the diverging duct can be diverged at the diverging duct and flows into the engine-cooling flow path and the exhaust-system-cooling flow path. 
     On the other hand, when washing the jet propulsion boat, washing water can be prevented from flowing from the diverging duct into the intake path with the one-way valve. Accordingly, it is possible to supply washing water into the engine-cooling flow path for washing the engine-cooling flow path with the supplied washing water and then to supply the used washing water to the exhaust-system-cooling flow path through the one-way valve. 
     In the present invention a cooling water discharge port of the engine-cooling flow path is disposed in the vicinity of the opening at the rear end of the jet pump chamber. 
     With the provision of a cooling water discharge port of the engine-cooling flow path in the vicinity of the opening at the rear end of the jet pump chamber, the cooling water discharge port can be hidden by the jet pump chamber. Accordingly, a construction wherein the cooling water discharge port cannot be viewed is realized. 
     With the provision of the cooling water discharge port in the vicinity of the opening at the rear end of the jet pump chamber, it is possible to insert a hand from the opening at the rear end of the jet pump chamber into the pump chamber and to easily touch the cooling water discharge port with the inserted hand. Therefore, even when tap water is used as washing water, a tap water hose can be attached to the cooling water discharge port relatively easily. 
     In the present invention a one-way valve is provided with a flow path for communicating a small quantity of washing water from the diverging duct into the intake path when closed. 
     When the one-way valve is closed, the flow path for flowing a small quantity of washing water (hereinafter referred to as “fine flow path”) can be kept opened, and thus a small quantity of washing water can flow from the diverging duct toward the intake path through the fine flow path. Therefore, the jet pump can easily be washed with a small quantity of washing water passing through the fine flow path. 
     In addition, by limiting the quantity of washing water to pass through the fine flow path, most parts of washing water used for washing the engine-cooling flow path can flow into the exhaust-system-cooling flow path. Therefore, the exhaust-system-cooling flow path can be washed preferably without taking too much time. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
     FIG. 1 is a side view of a jet propulsion boat provided with a cooling system according to the present invention; 
     FIG. 2 is plan view of the jet propulsion boat provided with the cooling system according to the present invention; 
     FIG. 3 is a block diagram of the cooling system for a jet propulsion boat according to the present invention; 
     FIG. 4 is a plan view of the cooling system for a jet propulsion boat according to the present invention; 
     FIG. 5 is an exploded perspective view of a one-way valve unit constituting the cooling system for a jet propulsion boat according to the present invention; 
     FIGS.  6 ( a ) and  6 ( b ) show explanatory drawings illustrating the one-way valve unit constituting the cooling system for a jet propulsion boat according to the present invention; 
     FIG. 7 is a perspective view of the cooling water discharge port (for cooling the engine) constituting the cooling system for a jet propulsion boat according to the present invention; 
     FIG. 8 is a perspective view of the cooling water discharge port (for cooling the exhaust system) constituting the cooling system for a jet propulsion boat according to the present invention; 
     FIGS.  9 ( a ) and  9 ( b ) are cross-sectional views of the cooling water discharge port (for cooling the exhaust system) constituting the cooling system for a jet propulsion boat according to the present invention; 
     FIGS.  10 ( a ) and  10 ( b ) are first explanatory drawings illustrating an example in which the engine and the exhaust system are cooled by the cooling system for a jet propulsion boat according to the present invention; 
     FIG. 11 is a second explanatory drawing illustrating an example in which the engine and the exhaust system is cooled by the cooling system for a jet propulsion boat according to the present invention; 
     FIG. 12 is a third explanatory drawing illustrating an example in which the engine and the exhaust system are cooled by the cooling system for a jet propulsion boat according to the present invention; 
     FIGS.  13 ( a ) and  13 ( b ) show first explanatory drawings illustrating an example in which the engine-cooling flow path and the exhaust-system-cooling flow path are washed by the cooling system for a jet propulsion boat according to the present invention; 
     FIGS.  14 ( a ) and  14 ( a ) show second explanatory drawings illustrating an example in which the engine-cooling flow path and the exhaust-system-cooling flow path are washed by the cooling system for a jet propulsion boat according to the present invention; and 
     FIG. 15 is a side view showing a jet propulsion boat in the related art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, an embodiment of the present invention will be described below wherein FIG. 1 is a side view of a jet propulsion boat provided with a cooling system according to the present invention. 
     The jet propulsion boat  10  comprises a vessel body  11  including a lower hull  12  having a ship bottom  12   a  and an upper hull  13  superimposed thereon. A fuel tank  14  is mounted on the front portion  11   a  of the vessel body  11 . An engine  15  is provided rearwardly of the fuel tank  14  with a jet pump chamber  16  provided rearwardly of the engine  15 . A jet pump (jet propulsion unit)  20  is provided in the jet pump chamber  16  with a steering handle  28  mounted upwardly of the fuel tank  14 . A saddle-riding type seat  29  is mounted rearwardly of the steering handle  28 . A cooling system for the jet propulsion boat will be described later. 
     The jet pump  20  has a housing  21  extending rearwardly from an opening  12   b  on the ship bottom  12   a  with an impeller  22  rotatably mounted in the housing  21 . The impeller  22  is connected to a drive shaft  23  of the engine  15 . 
     With the jet pump  20 , by driving the engine  15  and thus rotating the impeller  22 , water is sucked through the opening  12   b  on the ship bottom  12   a  and emitted through the housing  21  from a steering pipe (steering nozzle)  25 . 
     With the provision of the steering nozzle  25  at an opening  17  at the rear end of the jet pump chamber  16 , a jet of water emitted from the steering nozzle  25  can be emitted from the opening  17  at the rear end of the jet pump chamber  16  rearwardly of the vessel body  11 . 
     The steering nozzle  25  is a member mounted at the rear end of the housing  21  so as to be capable of being swung freely in the lateral direction. The steering nozzle  25  is a nozzle to be used for steering the direction of the vessel body  11  by being swung in the lateral direction via the steering handle  28 . 
     The jet propulsion boat  10  can be propelled by supplying fuel to the engine  15  from the fuel tank  14  for driving the engine  15 , transmitting the driving force of the engine  15  to an impeller  24  through the drive shaft  23 , sucking water through the opening  12   b  of the ship bottom  12   a  by rotating the impeller  24 , and emitting a jet of water from the steering nozzle  25  through the rear end of the housing  21 . 
     FIG. 2 is a plan view of the jet propulsion boat provided with a cooling system according to the present invention, showing a state in which the steering handle  28  is provided on the upper front portion  13   a  of the upper hull  13  with the saddle-riding type seat  29  extending in the fore-and-aft direction rearwardly of the steering handle  28  at the center  13   b  of the upper surface of the upper hull  13  (widthwise center). Footrest decks  18  are provided on the left side and the right side of the saddle-riding type seat  29 . The engine  15  and an exhaust system  30  are provided in the vessel body  11  with the cooling system being provided for cooling the jet propulsion boat (described later) and for cooling the engine  15  and the exhaust system  30 . 
     FIG. 3 is a block diagram of the cooling system for a jet propulsion boat according to the present invention. 
     The cooling system  40  for a jet propulsion boat forces the engine  15  to be cooled and forces the exhaust system  30  to be cooled by taking a part of a jet of water emitted from the jet pump  20  (shown in FIG. 1) into an intake path  41  as cooling water and diverging the cooling water taken into the intake path  41  at a diverging duct  50  in a one-way valve unit  42  for flowing the cooling water into the engine-cooling flow path  60  and the exhaust-system-cooling flow path  70 . 
     The intake path  41   a  is provided with the one-way valve unit  42  at a discharge port  41   a,  and the one-way valve unit  42  is provided with a one-way valve  43  integrated therein at the intake path  41  side. A diverging duct  50  is integrally provided on the opposite side of the intake path  41 . 
     The engine-cooling flow path  60  is connected to a first diverged discharge port  51  diverged by the diverging duct  50 . The exhaust-system-cooling flow path  70  is connected to a second diverged discharge port  52  diverged by the diverging duct  50 . 
     The engine-cooling flow path  60  is constructed in such a manner that the feed port of an oil-cooler-cooling duct (cooling water jacket)  62  is connected to the first diverged discharge port  51  via a first engine-cooling flow path  61 . The discharge port of the oil-cooler-cooling duct  62  is connected to the feed port of a cylinder-block-cooling duct (cooling water jacket)  64  via a second engine-cooling flow path  63 . The discharge port of the cylinder-block-cooling duct  64  is connected to the feed port of a cylinder-head-cooling duct (cooling water jacket)  65 . The discharge port of the cylinder-head-cooling-duct  65  is connected to the intake port of a third engine-cooling flow path  66  with a cooling water discharge port  67  of the third engine-cooling flow path  66  facing towards the interior of the jet pump chamber  16  (See FIG.  1 ). 
     The exhaust-system-cooling flow path  70  is constructed in such a manner that the feed port of an intercooler-cooling duct (cooling water jacket)  72  is connected to a second diverged discharge port  52  via a first exhaust-system-cooling flow path  71 . The discharge port of the intercooler-cooling duct  72  is connected to the feed port of an exhaust-manifold-cooling duct (cooling water jacket)  74  via a second exhaust-system-cooling flow path  73 . The discharge port of the exhaust-manifold-cooling duct  74  is connected to the feed port of a turbocharger-cooling duct (cooling water jacket)  76  via a third exhaust-system-cooling flow path  75  with the discharge port of the turbocharger-cooling duct  76  being connected to an exhaust-pipe-cooling duct (cooling water jacket)  78  via a fourth exhaust-system-cooling flow path  77 . The intake port of a fifth exhaust-system-cooling flow path  79  is connected to the discharge port of the exhaust-pipe-cooling duct  78  and a cooling water drain  80  at the rear end  79   b  of the fifth exhaust-system-cooling flow path  79  is provided on the rear surface  11   b  of the vessel body  11  except for the portion  29   a  immediately behind the saddle-riding type seat  29  shown in FIG.  2 . 
     The portion where the cooling water drain  80  is to be provided is described to be the rear surface  11   b  of the vessel body  11 , more specifically, it corresponds to the portion in the vicinity of the left side wall as shown in FIG.  4 . 
     A by-pass flow path  85  is provided for preferably adjusting the flow rate of cooling water. 
     FIG. 4 is a plan view of the cooling system for a jet propulsion boat according to the present invention, showing a state in which the jet pump chamber  16  is provided in the rear portion  11   c  of the vessel body  11 . The jet pump  20  is provided in the jet pump chamber  16  with the engine  15  being provided forwardly of the jet pump  20 . The drive shaft  23  (shown in FIG. 1) of the engine  15  is connected to the jet pump  20  with the steering nozzle  25  of the jet pump  20  facing towards the opening  17  at the rear end of the jet pump chamber  16 . 
     The jet propulsion boat  10  can be propelled by emitting a jet of water from the steering nozzle  25  by driving the jet pump  20  with the engine  15  and injecting a jet of water from the opening  17  at the rear end of the jet pump chamber  16  rearwardly of the vessel body  11 . 
     The cooling system  40  for a jet propulsion boat can force the engine  15  and the exhaust system  30  to be cooled respectively by taking a part of a jet of water emitted from the jet pump  20  into the intake path  41  as cooling water and diverging the cooling water taken into the intake path  41  at the diverging duct  50  of the one-way valve unit  42  and providing the cooling water into the engine-cooling flow path  60  and the exhaust-system-cooling flow path  70 . 
     The intake path  41  is constructed in such a manner that the rear end  41   a  is attached to a front wall  16   a  of the jet pump chamber  16  and the intake port (not shown) at the rear end  16   a  is connected to the jet pump  20  and is arranged so as to extend forward along the left side surface of the jet pump  20  and the left side surface of the engine  15  with the discharge port at the front end  41   b  disposed in the vicinity of the front end of the engine  15 . 
     The one-way valve unit  42  is provided at the front end  41   b  of the intake path  41 . The one-way valve unit  42  is provided with the one-way valve  43  on the side of the intake path  41  and the diverging duct  50  on the opposite side from the intake path  41  integrally formed therewith. 
     The engine-cooling flow path  60  is connected to the first diverged discharge port  51  diverged by the diverging duct  50 , and the exhaust-system-cooling flow path  70  is connected to the second diverged discharge port  52  diverged by the diverging duct  50 . 
     The engine-cooling flow path  60  is constructed in such a manner that the first diverged discharge port  51  is connected to the cooling duct of an oil cooler  19  via the first engine-cooling flow path  61 , the cooling duct of the oil cooler  19  is connected to the cooling duct of a cylinder block  15   a  via the second engine-cooling flow path  63 , the cooling duct of the cylinder head  15   a  is connected to the cooling duct of the cylinder head  15   b,  the cooling duct of the cylinder head  15   b  is connected to the intake port of the third engine-cooling flow path  66 , and the rear end  66   a  of the third engine-cooling flow path  66  is attached to the left side wall  16   b  of the jet pump chamber  16 , so that the cooling water drain  67  at the rear end  66   a  faces towards the interior of the jet pump chamber  16  and is disposed in the vicinity of the opening  17  at the rear end of the jet pump chamber  16 . 
     The exhaust-system-cooling flow path  70  is constructed in such a manner that the cooling duct of an intercooler  31  is connected to the second diverged discharge port  52  via the first exhaust-system-cooling flow path  71 , the cooling duct of the inter cooler  31  is connected to the cooling duct of an exhaust manifold  32  via the second exhaust-system-cooling flow path  73 , the cooling duct of the exhaust manifold  32  is connected to the cooling duct of a turbocharger  33  via the third exhaust-system-cooling flow path  75 , the cooling duct of the turbocharger  33  is connected to the cooling duct of an exhaust pipe  34  via the fourth exhaust-system-cooling flow path  77 , the intake port of the fifth exhaust-system-cooling flow path  79  is connected to the cooling duct of the exhaust pipe  34 , and the cooling water discharge port  80  at the rear end  79   a  of the fifth exhaust-system-cooling flow path  79  is provided on the rear surface  11   b  of the vessel body  11  except for the portion  29   a  immediately behind the saddle-riding type seat  29  (as shown in FIG.  2 ). 
     FIG. 5 is an exploded perspective view of the one-way valve unit constituting the cooling system for a jet propulsion boat according to the present invention. 
     The one-way valve unit  42  comprises a body  48  including a casing  47  for accommodating a valve body  44  of the one-way valve  43  and a diverging duct  50 , the valve body  44  is accommodated in a storage recess  47   b  from an opening  47   a  of the casing  47 , and a cap  49  for covering the opening  47   a  with the valve body  44  stored in the storage recess  47   b.    
     The valve body  44  comprises a core portion  45  formed into the shape of a tapered cone at an extremity  45   a  thereof. The core portion  45  is formed so that the diameter thereof is reduced gradually from the conical extremity  45   a  toward a proximal portion  45   b.  A plurality of (six) blades  46  . . . extend radially from the outer surface of the core portion  45 . The plurality of blades  46  . . . have front end surfaces  46   a  . . . formed into inclined surfaces being flush with the outer periphery of the conical extremity  45   a.    
     FIGS.  6 ( a ) and  6 ( b ) are explanatory drawings illustrating the one-way valve unit constituting the cooling system for a jet propulsion boat according to the present invention. FIG.  6 ( a ) is a cross-sectional view and FIG.  6 ( b ) is a cross-sectional view taken along the line b—b of the FIG.  6 ( a ). 
     The diverging duct  50  provided in the body  48  is intended to divert the intake path  41  into the first diverged discharge port  51  and the second diverged discharge port  52 . The first diverged discharge port  51  is connected to the engine-cooling flow path  60  and the second diverged discharge port  52  is connected to the exhaust-system-cooling flow path  70 . 
     The one-way valve  43  is operated in such a manner that when cooling water flows from the intake path  41  towards the valve body  44 , the valve body  44  is moved away from a valve seat  49   a  by the hydraulic pressure of the cooling water and is retained in a state being away from the valve seat  49   a  (the state shown in the FIG.  6 ( a )). 
     In addition, the one-way valve  43  is further operated in such a manner when washing water is flowing from the first diverged discharge port  51  towards the valve body  44 , the valve body  44  is moved towards the valve seat  49   a  by the hydraulic pressure of washing water and bought into abutment with the valve seat  49   a.    
     Moving the valve body  44  away from the valve seat  49   a  allows cooling water to flow through the spaces  54  . . . between the blade  46  and the blade  46 , and thus cooling water can flow from the intake path  41  towards the diverging duct  50 . 
     On the other hand, bringing the valve body  44  into abutment with the valve seat  49   a  may prevent washing water flowing from the first diverged discharge port  51  into the diverging duct  50  from flowing into the intake path  41 . 
     The inner diameter d 1  of the first diverged discharge port  51  may be 8mm for example, and the inner diameter d 2  of the second diverged discharge port  52  may be 10mm for example. The relation between the inner diameter d 1  and the inner diameter d 2  is d 1 &lt;d 2 . 
     As shown in the FIG.  6 ( b ), by determining the maximum width W of the extremity  45   a  of the valve body  44  to be smaller than the inner diameter d 3  of the intake path  41 , parts of the spaces  54  . . . between the blades  46  of the valve body  44  (fine flow paths)  54   a  . . . may be placed in the intake path  41 . The inner diameter d 3  may be 12 mm for example. 
     With the valve body  44  constructed as described above, when the valve body  44  abuts against the valve seat  49   a,  fine flow paths  54   a  . . . may be provided between the valve seat  49   a  and the valve body  44  as flow paths for allowing a small quantity of washing water. 
     Therefore, a small quantity of washing water out of washing water flowing from the first diverged discharge port  51  to the diverged duct  50  may flow through the fine flow paths  54   a  . . . to the side of the intake path  41 . 
     As a consequent, the interior of the jet pump  20  (shown in FIG. 1) can easily be washed with a small quantity of washing water passing through the fine flow paths  54   a  . . . Therefore, the jet propulsion boat  10  (shown in FIG. 1) can be washed effectively without taking too much time and effort. 
     In addition, since the quantity of washing water that passes through the fine flow paths  54   a  . . . is small, most of the cooling water used for cooling the engine-cooling path  60  may be supplied to the exhaust-system-cooling flow path  70 . Therefore, the exhaust-system-cooling flow path  70  may be washed satisfactorily. 
     FIG. 7 is a perspective view of the cooling water discharge port (for cooling engine) constituting the cooling system for a jet propulsion boat according to the present invention. 
     The cooling system  40  for a jet propulsion boat shown in FIG. 4 is provided with the cooling water discharge port  67  of the engine-cooling flow path  60  in the vicinity of the opening  17  at the rear end of the jet pump chamber  16 . 
     The cooling water discharge port  67  of the engine-cooling flow path  60  is a discharge port for discharging cooling water used for cooling the engine-cooling flow path  60  toward the outside, and serves also as a feed port for feeding washing water to the engine-cooling flow path  60  and the exhaust-system-cooling flow path  70 . 
     The cooling water discharge port  67  is attached on the left side wall  16   b  of the jet pump chamber  16  in such a manner that a flange  67   a  is secured in the vicinity of the opening  17  at the rear end of the left side wall  16   b  with bolts  68 ,  68 , and a nozzle  67   b  extends from the flange  67   a  so as to be orthogonal to the left side wall  16   b.    
     When feeding washing water to the cooling water discharge port  67 , a tap water hose  69   a  can be securely attached on the nozzle  67   b  of the cooling water discharge port  67  by fitting the tip  69   b  of the tap water hose  69   a  on the nozzle  67   b  of the cooling water discharge port  67 , and tightening the outer periphery of the tap water hose  69   a  by the lock spring  69   c.    
     Accordingly, since a disconnection of the tap water hose  69   a  from the nozzle  67   b  of the cooling water discharge port  67  may be prevented at the time of flashing (washing), a washing operation can be performed effectively in a short time. 
     By disposing the cooling water discharge port  67  in the vicinity of the opening  17  at the rear end of the jet pump chamber  16 , it is possible to insert a hand into the jet pump chamber  16  through the opening  17  at the rear end of the jet pump chamber  16  and to easily touch the cooling water discharge port  67  with the inserted hand. 
     Therefore, when tap water is used as washing water for example, the tap water hose  69   a  for tap water can be attached to the nozzle  67   b  of the cooling water discharge port  67  relatively easily, and thus the washing operation can be performed easily without taking too much time and effort. 
     In addition, by providing the cooling water discharge port  67  of the engine-cooling flow path  60  in the vicinity of the opening  17  at the rear end of the jet pump chamber  16 , the cooling water discharge port  67  can be hidden by the jet pump chamber  16 . 
     As a consequent, the cooling water discharge port  67  can be hidden so as not to be viewed from the outside, and thus the appearance of the jet propulsion boat  10  can be improved. 
     FIG. 8 is a perspective view of the cooling water discharge port (for cooling the exhaust system) constituting the cooling system for a jet propulsion boat according to the present invention. 
     The cooling water discharge port  80  of the exhaust-system-cooling flow path  70  is a discharge port for discharging cooling water used for cooling the exhaust-system-cooling flow path  70  to the outside, and serves also as a water pilot hole for detecting whether of not the cooling system  40  for a jet propulsion boat functions normally. 
     The cooling water discharge port  80  is provided in the vicinity of the lower side of a joint  27  between the lower hull  12  and the upper hull  13  on the side of the lower hull  12 . 
     FIGS.  9 ( a ) and  9 ( b ) are cross-sectional views illustrating the cooling water discharge port (for cooling the exhaust system) constituting the cooling system for a jet propulsion boat according to the present invention. FIG.  9 ( a ) is a cross-sectional view taken along the line  9   a — 9   a  in FIG. 8, and FIG.  9 ( b ) is a cross-sectional view taken along the line  9   b — 9   b  in FIG.  8 . 
     As shown in FIG.  9 ( a ), the cooling water discharge port  80  of the exhaust-system-cooling flow path  70  is a through hole formed in the rear wall constituting the lower hull  12 . The discharge port  80  is inclined outwardly by the angle of θ 1 . 
     The end of the exhaust-system-cooling flow path  70  can be brought into communication with the cooling water discharge port  80  by securing a flange  81  to the inner side of the rear surface  11   b  of the lower hull  12  with a bolt  83 . An entry portion  82  extends from the flange  81  so as to be orthogonal to the rear surface  11   b.  The end of the exhaust-system-cooling flow path  70  is inserted into the entry portion  82 . 
     As shown in FIG.  9 ( b ), the cooling water discharge port  80  of the exhaust-system-cooling flow path  70  is inclined downward by the angle of θ 2 . 
     In this way, cooling water discharged from the cooling water discharge port  80  can be discharged to the outside of the vessel body  11  by inclining the cooling water discharge port  80  of the exhaust-system-cooling flow path  70  outwardly by the angle of θ 2 . Therefore, the occupant can easily verify that cooling water is discharged from the cooling water discharge port  80 . 
     Since cooling water can be discharged to the lower side of the left and right decks  18 ,  18  (shown in FIG. 8) by inclining the cooling water discharge port  80  of the exhaust-system-cooling flow path  70  downwardly by the angle of θ 2 , it is further ensured that cooling water is prevented from entering to the side of the left and right decks  18 ,  18 . 
     Referring now to FIG. 10 to FIG. 14, the operation of the cooling system for a jet propulsion boat will be described. 
     FIGS.  10 ( a ) and  10 ( b ) are first explanatory drawings illustrating an example in which the engine and the exhaust system are cooled by the cooling system for a jet propulsion boat according to the present invention. 
     When operating the jet propulsion boat  10 , a part of a jet of water emitted from the jet pump  20  is taken into the intake path  41  as cooling water. The cooling water taken into the intake path  41  flows towards the diverging duct  50  through the one-way valve  43  of the one-way valve unit  42 . 
     Cooling water flowing to the diverging duct  50  is diverged into the first diverged discharge port  51  and the second diverged discharge port  52 . Cooling water diverged into the first diverged discharge port  51  flows into the engine-cooling flow path  60 . Further, cooling water diverged into the second diverged discharge port  52  flows into the exhaust-system-cooling flow path  70 . 
     Cooling water flowing into the engine-cooling flow path  60  flows into the feed port of the oil-cooler-cooling duct  62  through the first engine-cooling flow path  61  and then flows from the feed port into the oil-cooler-cooling duct  62  to cool the oil cooler  19 . Cooling water used for cooling the oil cooler  19  flows through the discharge port of the oil-cooler-cooling duct  62  and the second engine-cooling flow path  60  into the feed port of the cylinder-block-cooling duct  64  and then flows from this feed port into the cylinder-block-cooling duct  64  to cool the cylinder block  15   a.    
     Cooling water that was used for cooling the cylinder block  15   a  flows through the discharge port of the cylinder-block-cooling duct  64  to the feed port of the cylinder-head-cooling duct  65  and then flows from the feed port to the cylinder-head-cooling duct  65  to cool the cylinder head  15   b.    
     Cooling water that was used for cooling the cylinder head  15   b  flows from the discharge port of the cylinder-head-cooling duct  65  into the third engine-cooling flow path  66  and then flows out through the third engine-cooling flow path  66  and the cooling water discharge port  67  to the outside. Accordingly the engine  15  is forced to be cooled by cooling water. 
     On the other hand, cooling water flowing into the exhaust-system-cooling flow path  70  flows through the first exhaust-system-cooling flow path  71  to the feed port of the intercooler-cooling duct  72  and then flows from the feed port into the intercooler-cooling duct  72  for cooling the intercooler  31 . 
     Cooling water that was used for cooling the intercooler  31  flows through the discharge port of the intercooler-cooling duct  72  and the second exhaust-system-cooling flow path  73  to the feed port of the exhaust-manifold-cooling duct  74  and then flows from the feed port into the exhaust-manifold-cooling duct  74  for cooling the exhaust manifold  32 . 
     Cooling water that was used for cooling the exhaust manifold  32  flows through the discharge port of the exhaust-manifold-cooling duct  74  and the third exhaust-system-cooling flow path  75  to the feed port of the turbocharger-cooling duct  76  and then flows from the feed port into the turbocharger-cooling duct  76  for cooling the turbocharger  33 . 
     Cooling water that was used for cooling the turbocharger-cooling duct  76  flows through the discharge port of the turbocharger-cooling duct  76  and the fourth exhaust-system-cooling flow path  77  to the feed port of the exhaust-pipe-cooling duct  78  and then flows from the feed port into the exhaust-pipe-cooling duct  78  for cooling the exhaust pipe  34 . 
     Cooling water that is used for cooling the exhaust pipe  34  flows into the discharge port of the exhaust-pipe-cooling duct  78  and the intake port of the fifth exhaust-system-cooling duct  79  and then flows from the intake port through the fifth exhaust-system-cooling flow path  79  and the cooling water discharge port  80  to the outside. Accordingly, the exhaust system  30  is forced to be cooled by cooling water. 
     FIG. 11 is a second explanatory drawing showing an example in which the engine and the exhaust system is cooled by the cooling system for a jet propulsion boat according to the present invention. 
     When cooling water flows from the intake path  41  towards the valve body  44 , the valve body  44  is moved away from the valve seat  49   a  by the hydraulic pressure of cooling water, and is kept in a state of being away from the valve seat  49   a.  By moving the valve body  44  away from the valve seat  49   a,  cooling water flows from the intake path  41  to the diverging duct  50 . 
     Cooling water flowing to the diverging duct  50  is diverged into the first diverged discharge port  51  and the second diverged discharge port  52 . Cooling water diverged into the first diverged discharge port  51  flows into the engine-cooling flow path  60  and cooling water diverged into the second diverged discharge port  52  flows into the exhaust-system-cooling flow path  70 . 
     The inner diameter d 1  of the first diverged discharge port  51  and the inner diameter d 2  of the second diverged discharge port  52  are set to be d 1 &lt;d 2 , cooling water flown into the engine-cooling flow path  60  and cooling water flowing into the exhaust-system-cooling flow path  70  can be diverged into optimal quantities, respectively. 
     The cooling system  40  for a jet propulsion boat is provided at the midsection thereof with a one-way valve  43  for enabling cooling water to flow from the intake path  41  to the diverging duct  50  and preventing washing water from flowing from the diverged duct  50  towards the intake path  41 . 
     As a consequent, when operating the jet propulsion boat  10 , cooling water taken into the intake path  41  may flow into the diverging duct  50  through the one-way valve  43 . Cooling water flowing into the diverging duct  50  is diverged into parts that flow into the first and second diverging duct discharge ports  51 ,  52 , respectively, by the diverging duct  50 . Cooling water flowing through the first diverging duct discharge port  51  can flow into the engine-cooling flow path  60 , and cooling water flowing thorough the second diverging duct discharge port  52  can flow into the exhaust-system-cooling flow path  70 . 
     Since cooling water can be separated into a part flowing thorough the engine-cooling flow path  60  and a part flowing through the exhaust-system-cooling flow path  70 , the temperature of the engine  15  and of the exhaust system  30  can easily be controlled. 
     In addition, with the provision of the one-way valve  43  in the middle of the intake path  41 , even when the engine  15  (that is, the jet pump  20 ) is stopped, the one-way valve  43  can prevent cooling water from flowing out from the engine-cooling flow path  60  and the exhaust-system-cooling flow path  70 . Therefore, when the engine  15  is stopped, cooling water can remain in the engine-cooling flow path  60  or the exhaust-system-cooling flow path  70  for a certain period of time. 
     As a consequent, heat accumulation (portions at high temperature) in the engine  15  or the exhaust system  30  can be prevented from remaining because cooling water flows quickly out from the engine-cooling flow path  60  or the exhaust-system flow path  70 . 
     FIG. 12 is a third explanatory drawing illustrating the example in which the engine and the exhaust system are cooled by the cooling system for a jet propulsion boat according to the present invention. 
     With the provision of the cooling water discharge port  80  of the exhaust-system-cooling flow path  70  on the rear surface  11   b  of the vessel body  11  except for the portion  29   a  immediately behind the saddle-riding type seat  29 , cooling water discharged from the cooling water discharge port  80  is prevented from flowing into the footrest deck  18  or from splashing toward the footrest deck  18 . 
     Furthermore, the opening of the cooling water discharge port  80  is positioned in the vicinity of the lower side of the joint  27  between the lower hull  12  and the upper hull  13  on the side of the lower hull  12 . Therefore, the opening of the cooling water discharge port  80  is set to a position lower than the height of the footrest deck  18 , and thus cooling water discharged from the cooling water discharge port  80  can reliably be prevented from flowing into the footrest deck  18  or from splashing towards the footrest deck  18 . 
     In addition, with the construction in which the cooling water discharge port  80  of the exhaust-system-cooling flow path  70  is inclined downwardly by the angle of θ 2  (See also FIG.  8 ( b )), cooling water can be discharged out downwardly of the left and right decks  18 ,  18  and thus cooling water is further reliably prevented from flowing into the left and right decks  18 ,  18  or from splashing towards the footrest deck  18 . 
     On the other hand, the cooling water discharge port  80  of the exhaust-system-cooling flow path  70  is provided on the rear surface  11   b  of the vessel body  11 , except for the portion  29   a  immediately behind the saddle-riding type seat  29 , that is, at the portion offset from the portion  29   a  immediately behind the saddle-riding type seat  29 . Therefore, cooling water discharged from the cooling water discharge port  80  can be easily verified by an occupant  90 . 
     Furthermore, cooling water discharged from the cooling water discharge port  80  can be discharged towards the outside of the vessel body  11  by inclining the cooling water discharge port  80  of the exhaust-system-cooling flow path  70  towards the outside by the angle of θ 1  (See also FIG.  8 ). 
     Therefore, the occupant  90  can verify that cooling water is easily discharged from the cooling water discharge port  80  and recognize that the cooling system  40  for a jet propulsion boat is functioning normally. 
     FIGS.  13 ( a ), ( b ) are first explanatory drawings illustrating an example in which the engine-cooling flow path and the exhaust-system-cooling flow path are washed by the cooling system for a jet propulsion boat according to the present invention. 
     The tap water hose  69   a  for supplying tap water (washing water) is attached on the cooling water discharge port  67  and washing water flows from the tap water hose  69   a  through the cooling water discharge port  67  to the third engine-cooling flow path  66 . Washing water flowing through the third engine-cooling flow path  66  flows into the cylinder-head-cooling duct  65  and washes the cylinder-head-cooling duct  65 . 
     Washing water that was used for washing the cylinder-head cooling duct  65  flows into the cylinder-block cooling duct  64  for washing the cylinder-block cooling duct  64 . 
     Washing water that is used for washing the cylinder-block cooling duct  64  flows through the second engine cooling flow path  63  into the oil-cooler-cooling duct  62  for washing the oil-cooler-cooling duct  62 . Washing water that was used for washing the oil-cooler-cooling duct  62  flows into the first engine-cooling flow path  61  and then flows from the first engine-cooling flow path  61  through the first diverged discharge port  51  and reaches the diverging duct  50 . 
     Most of cooling water out of washing water reaching the diverging duct  50  flows through the first exhaust-system-cooling flow path  71  to the feed port of the intercooler-cooling duct  72  and then flows through the intercooler-cooling duct  72  for washing the intercooler-cooling duct  72 . 
     Washing water that was used for washing the intercooler-cooling duct  72  flows through the second exhaust-system-cooling flow path  73  to the exhaust-manifold-cooling duct  74  for washing the exhaust-manifold-cooling duct  74 . 
     Washing water that was used for washing the exhaust-manifold-cooling duct  74  flows through the third exhaust-system-cooling flow path  75  to the turbocharger-cooling duct  76  to wash the turbocharger-cooling duct  76 . Washing water that was used for washing the turbocharger-cooling duct  76  flows through the fourth exhaust-system-cooling flow path  77  to the exhaust-pipe-cooling duct  78  for washing the exhaust-pipe-cooling duct  78 . 
     Washing water that was used for washing the exhaust-pipe-cooling duct  78  flows into the intake port of the fifth exhaust-system-cooling duct  79 , and flows through the fifth exhaust-system-cooling flow path  79  and the cooling water discharge port  80  to the outside. 
     On the other hand, a small quantity of the washing water reaches the diverging duct  50  and flows through the fine flow paths  54   a  . . . of the one-way valve  43  (shown in FIG.  6 ( b )) towards the intake path  41 . Accordingly, the interior of the jet pump  20  can easily be washed with a small quantity of washing water passing through the fine flow paths  54   a  . . . 
     FIGS.  14 ( a ) and  14 ( b ) are second explanatory drawings illustrating an example in which the engine-cooling flow path and the exhaust-system-cooling flow path are washed by the cooling system for a jet propulsion boat according to the present invention. FIG.  14 ( a ) shows a cross section of the one-way valve unit. FIG.  14 ( b ) shows a cross-sectional view taken along the line b—b in FIG.  14 ( a ). 
     When washing water flows from the first diverged discharge port  51  to the diverging duct  50 , the valve body  44  is brought into abutment with the valve seat  49   a  by the hydraulic pressure of washing water. Since most of the intake path  41  can be closed by the valve body  44  by bringing the valve body  44  into abutment with the valve seat  49   a,  most of washing water reaching the diverging duct  50  flows towards the second diverged discharge port  52 . 
     The cooling system  40  for a jet propulsion boat can prevent washing water from flowing from the diverging duct  50  towards the intake path  41  when washing the jet propulsion boat  10 . Accordingly, it is possible to wash the engine-cooling flow path  60  by supplying washing water to the engine-cooling flow path  60  and supply the washing water to the exhaust-system-cooling flow path  70  by the one-way valve  43 . 
     Therefore, since washing water that was used for washing the engine-cooling flow path  60  can be used for washing the exhaust-system-cooling flow path  70  the quantity of washing water consumed can be reduced. 
     Since the fine flow paths  54   a  . . . can be formed between the valve body  44  and the intake path  41  as shown in FIG.  14 ( b ) when the valve body  44  of the one-way valve  43  is brought into abutment against the valve seat  49   a,  a small quantity of washing water out of washing water reaching the diverging duct  50  flows towards the intake path  41  through the fine flow paths  54   a  . . . of the one-way valve  43 . 
     Accordingly, the jet pump  20  can easily be washed by a small quantity of washing water passing through the fine flow paths  54   a  . . . 
     Though an example in which the oil cooler  19 , the cylinder block  15   a,  and the cylinder head  15   b  are cooled in the engine-cooling flow path  60 , and the intercooler  31 , the exhaust manifold  32 , the turbocharger  33 , and the exhaust pipe  34  are cooled in the exhaust-system-cooling flow path  70  has been described in the aforementioned embodiment, the components to be cooled are not limited thereto, and may be determined according to the construction of the jet propulsion boat  10 . 
     The present invention exercises the following effects with the construction described above. 
     According to the present invention, a one-way valve for enabling cooling water to flow from the intake path towards the diverging duct and preventing washing water from flowing from the diverging duct into the intake path is provided in the middle of the intake path. 
     As a consequent, when operating the jet propulsion boat, cooling water taken into the intake path can flow into the diverging duct through the one-way valve, and cooling water flown into the diverging duct can be diverged at the diverging duct and flow into the engine-cooling flow path and the exhaust-system-cooling flow path. 
     Cooling water flowing into the engine-cooling flow path and cooling water flowing into the exhaust-system-cooling flow path may be separated and thus it is easy to provide temperature control for the engine and temperature control for the exhaust system. 
     On the other hand, when washing the jet propulsion boat, washing water can be prevented from flowing from the diverging duct into the intake path with the one-way valve. Accordingly, it is possible to supply washing water into the engine-cooling flow path for washing the engine-cooling flow path with the supplied washing water and then to supply the washing water to the exhaust-system-cooling flow path through the one-way valve. 
     Therefore, washing water that is used for washing the engine-cooling flow path can be used for washing the exhaust-system-cooling flow path and thus the quantity of washing water consumed can be reduced. 
     According to the present invention, since the cooling water discharge port of the engine-cooling flow path is disposed in the vicinity of the opening at the rear end of the jet pump chamber, the cooling water discharge port can be hidden by the jet pump chamber. Accordingly, since the construction in which the cooling water discharge port cannot be viewed from the outside is realized, the appearance of the jet propulsion boat is improved. 
     In addition, with the provision of the cooling water discharge port in the vicinity of the opening at the rear end of the jet pump chamber, it is possible to insert a hand from the opening at the rear end of the jet pump chamber into the pump chamber and to easily touch the cooling water discharge port with the inserted hand. Therefore, even when tap water is used as washing water, a tap water hose can be attached to the cooling water discharge port relatively easily. Thus, the washing operation can be performed easily without taking too much time and effort. 
     According to the present invention, since the fine flow path can be kept opened when the one-way valve is closed, a small quantity of washing water can flow from the diverging duct toward the intake path through the fine flow path. Therefore, the jet pump can easily be washed with a small quantity of washing water passing through the fine flow path. Therefore, the jet propulsion boat can be washed effectively without taking too much time and effort. 
     In addition, since the quantity of washing water that passes through the fine flow paths is small, most part of washing water used for washing the engine-cooling flow path may be supplied to the exhaust-system-cooling flow path. Therefore, it is possible to wash the exhaust-system-cooling flow path effectively without taking too much time. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.