Abstract:
An improved air-intake system and engine layout for use on a small watercraft provides for a lower temperature, vapor fuel/air charge with less water vapor content. The watercraft includes an engine-air intake system incorporating an air-intake box which inhibits the engine from intaking water present in the engine compartment, especially during high speed maneuvering. An extended flywheel case is also provided that prevents water located in the engine compartment from being sprayed by moving parts directly into the air-intake box. Furthermore, the improved air-intake system of the present invention incorporates external air-intake valves that prevent water from entering the engine and propulsion compartments through the air intakes while the watercraft is in an inverted.

Description:
This application is a Div of Ser. No. 08/920,793 filed Aug. 29, 1997, now Pat. No. 5,957,072. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the field of small watercraft and, more particularly, to an improved air-intake system for use on a small watercraft. 
     2. Description of Related Art 
     Personal watercraft have become increasingly popular in recent years. This type of watercraft is sporting in nature; it turns swiftly, maneuvers easily, and accelerates quickly. A personal watercraft today commonly carries one rider and possibly one or two passengers. 
     A relatively small hull of the personal watercraft, comprising an upper deck and a lower hull, commonly defines a riders&#39; area above an engine compartment. An internal combustion engine frequently powers a jet propulsion unit which is positioned in a tunnel formed on the underside of the watercraft hull. The propulsion unit propels the watercraft. The engine lies within the engine compartment, below the riders&#39; area. An exhaust system extends between the engine and a discharge opening to expel exhaust gases either to the atmosphere or to the water. The exhaust system usually includes a water trap device that inhibits a reverse flow of water through the exhaust system from the discharge opening toward the engine. 
     It has become commonplace for small watercraft, such as for example, personal watercraft, to be operated in virtually any water condition, including ocean surf. Due to the design of the engine-air path, it is often possible for such small watercraft to operate for short periods of time submerged or in a substantially non-vertically oriented position. By drawing its air supply from the internal engine compartment of the small watercraft these small watercraft engines are generally able to avoid periodic interruptions in the engine-air supply occasioned by waves or other rough weather conditions submerging the external air intakes. 
     SUMMARY OF THE INVENTION 
     The present invention includes the recognition that prior layout of the engine and exhaust components in the watercraft&#39;s engine compartment can lead to reduced engine performance under some operating conditions. One such instance is when a significant amount of water fills the engine compartment. Where the small watercraft experiences extremely rough water conditions such as ocean surf or maneuvers sharply at high speeds, a significant amount of water can quickly flow through the air ducts into the engine compartment of the watercraft. This influx of water, combined with the water already present inside the engine compartment of the watercraft, can possibly submerge or splash into the air-intake(s) of the watercraft engine. Furthermore, this trapped water will often contact various moving parts of the engine, such as a coupling between the engine&#39;s crankshaft and the impeller shaft, which will cause further splashing of water in the engine compartment. Where water enters the air-intake(s), this water will become entrained in the fuel/air change delivered to the engine&#39;s cylinders, which can cause the engine to lose power, sputter, stall, or, in extreme conditions, possibly damage the engine components. 
     While it is possible to reduce the amount of water present in the engine compartment through the use of additional bilge pumps or special hull designs, such solutions increase the number and weight of components in the small watercraft and/or may minimize the cooling-air flow through the engine compartment. In addition, it is extremely difficult to remove all water from the engine compartment. A need therefore exists for a device that reduces the possibility of a small watercraft engine intaking water in the engine compartment during rough water conditions and/or high speed maneuvers. 
     In addition, the exhaust system of the engine can become quite hot after extended periods of watercraft operation. The heat from the exhaust system, and in particular, from the water trap, which usually functions also as an expansion chamber or muffler, heats the surrounding air in the engine compartment. When the engine intakes the heated air, a fuel/air ratio of the produced fuel/air charge does not correspond to a desired fuel/air ratio because the heated intake air has less oxygen per given volume than normal. Engine performance consequently suffers. Accordingly, a need exists for inhibiting a flow of air within the engine compartment from the space surrounding the water trap to the engine&#39;s induction system. 
     In accordance with one aspect of the present invention there is provided an improved intake system for use with a small watercraft engine located within the engine compartment of a small watercraft. The intake system comprises an air-intake box connected to the air-intake pipes of an engine located within the engine compartment of a small watercraft. The air intake box incorporates valves which serve to isolate the air intake box from splashing water in the engine compartment, thereby preventing the small watercraft from intaking a substantial amount of water. This air-intake box also permits the engine to briefly operate while the entire air-intake box is submerged. 
     Another aspect of the present invention involves extending a portion of the flywheel case over the flywheel and crankshaft coupling. This extension will redirect any water spray caused by the moving crankshaft coupling, thereby preventing such spray from entering the air-intake and being ingested by the engine. The extension also acts as a heat insulator, reducing the ambient heat level in the engine compartment near the air-intake system and inhibiting air flow from about this heated exhaust system with trap to the air-intake system. 
     Another aspect of the present invention involves the positioning of the engine in the engine compartment of the small watercraft. In one embodiment, the engine is tilted approximately 10 degrees towards the engine exhaust side of the engine, thereby raising the air-intakes of the engine above the air-exhausts. This orientation allows an air-intake box of the present invention to be attached to a standard small watercraft engine without substantially changing the air-intake/exhaust components and/or hull design. 
     In another aspect of the present invention is provided an improved valve design for use on the external hull of the watercraft, which prevents water from entering the engine and/or propulsion chamber through the intake-air ducts when the watercraft is inverted or in a substantially non-vertical orientation. This is accomplished by providing buoyant closures in air duct valves which are normally open but, when submerged, operate to close the air ducts and prevent water from traveling through the duct. Once the watercraft is returned to its substantially upright position, the buoyant closures reopen the air duct, returning air flow to the engine. 
     Further aspects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiment which follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features of the invention will now be described with reference to the drawings of a preferred embodiment of the present watercraft. The illustrated embodiments intended to illustrate, but not to limit the invention. The drawings contain the following figures: 
     FIG. 1 is a longitudinal cross-sectional side view of a small watercraft in accordance with preferred embodiment of the present invention; 
     FIG. 2 is a sectional, top plan view of the small watercraft of FIG. 1 with portions of the components as an upper deck shown in phantom; 
     FIG. 3 is a lateral cross-sectional view of the small watercraft of FIG. 1; 
     FIG. 4 is a side view of a rubber valve member construed in accordance with a preferred embodiment of the present invention; 
     FIG. 5 is a cross-sectional side view of the rubber valve member of FIG. 4 with the valve illustrated in an open position and phantom lines illustrating a closed position; 
     FIG. 6 is a cross-sectional side view of another embodiment of a rubber valve member constructed in accordance with the present invention; 
     FIG. 7 is a cross-sectional rear view of a small watercraft incorporating another embodiment of the present invention; 
     FIG. 8 is a side, perspective view of an intake merging box constructed in accordance with the present invention; 
     FIG. 9 is a sectional side elevational view of a small watercraft incorporating an additional embodiment of the present invention; 
     FIG. 10 is a sectional top plan view of the small watercraft of FIG.  9  and illustrates several components on the upper deck in phantom; 
     FIG. 11 is a cross-sectional rear view of the small watercraft of FIG. 9; 
     FIG. 12 is a partial sectional side view of a small watercraft incorporating another embodiment of the present invention; 
     FIG. 13 is a partial sectional top plan view of the small watercraft of FIG. 12; 
     FIG. 14 is a cross-sectional rear view of the small watercraft of FIG. 12; 
     FIG. 15 is a cross-sectional rear view of a small watercraft incorporating an additional embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 through 3 illustrate different views of a small watercraft incorporating an air intake box and engine arrangement configured in accordance with a preferred embodiment of the present invention. While the present invention has particular utility with a small watercraft having an engine located within the engine compartment of the small watercraft, some aspects of the present invention have equal utility with watercraft utilizing external-hull air intakes or externally mounted engines. As such, the invention will be described with the small watercraft design in this context; however, it is understood that the present invention may also be employed on other types of watercraft. 
     The following description describes several embodiments of the present invention which include unique induction system construction and orientation within the engine compartment. Where appropriate, the same reference numerals have been used between the various embodiments to indicate like components. In addition, various aspects of the different embodiments can be incorporated into the other embodiments, as will be readily apparent to those skilled in the art. 
     With initial reference to FIGS. 1 through 3, a small watercraft, indicated generally by reference numeral  1 , includes a hull  3  formed by a lower hull section  2   a  and upper deck section  4 . These hull sections  2   a,    4  are formed from a suitable material such as, for example, a molded fiberglass reinforced resin. For instance, the deck  4  and the hull  2   a  can be formed using a sheet molding compound (SMC), i.e. a mixed mass of reinforced fiber and thermal setting resin, that is processed in a pressurized, closed mold. The molding process desirably is temperature controlled such that the mold is heated and cooled during the molding process. For this purpose, male and female portions of the mold can include fluid jackets through which steam and cooling water can be run to heat and cool the mold during the manufacturing process. The lower hull section  2   a  and the upper deck section  4  are fixed to each other around the peripheral edges in any suitable manner commonly known to those skilled in the art. 
     As viewed in a direction from the bow to the stern of the watercraft, the upper deck section  4  includes a bow portion  2 , a control mast  7 , a front seat  5  and a rear seat  6 . The bow portion  2  slopes upwardly toward the control mast  7  and includes at least one air duct  25  through which air can enter the hull  3 . 
     The control mast  7  extends upward from the bow portion  2  and supports a handlebar assembly  150 . The handlebar assembly  150  controls the steering of the watercraft in a conventional manner well known to those skilled in the art. The handlebar assembly also carries a variety of the controls of the watercraft such as, for example, a throttle control, a start switch and a lanyard switch. The handlebar assembly  150  is enclosed by a handle cover  155  and is pivotally provided in front of the front seat  5 . 
     A hatch cover  9  is provided in front of the steering handle  7 . The hatch cover  9  is secured to the upper deck  4  by a hinge  9   a,  and is able to open and close freely, thereby exposing the forward section of the interior of the hull  3 . A latch (not shown) is provided to secure the hatch cover  9  in its closed position during operation of the watercraft  1 . A storage box  8  is removably provided in the deck below the hatch cover  9 . This storage box  8  is covered by the hatch cover  9  in a water sealing manner. 
     A forward air opening  160 , located adjacent to the front seat  5 , desirably allows ambient air traveling over the upper deck  4  to travel below the front bottom plate  5   a  of the front seat  5 . This airflow then travels into an air inlet port  25   a,  located below the front seat  5 , and into the air duct  25 . A rearward air opening  175 , located behind the rear seat  6 , desirably allows ambient air to travel through cover  27 , through air inlet port  26   a,  and into the rear-air duct  26 . 
     The front and rear seats  5 ,  6  are desirably straddle-type seats having an elongated shape that extends along the longitudinal axis of the watercraft. These seats are centrally located between the sides of the hull and are mounted on front bottom plate  5   a  and rear bottom plate  6   a,  respectively. In the illustrated embodiment, the rear seat  6  is positioned at an elevated level relative to the front seat  5 . This advantageously positions the riders at different levels. 
     A fuel tank  12  is located within the hull  3 . A fuel supply pipe  12   a  extends from the surface of deck  4  to the fuel tank  12 . Conventional means such as straps (not shown) secure the fuel tank to the lower hull  2   a.  In the illustrated embodiment, a filler cap assembly  165  is secured to the bow portion  2  of the hull upper deck  4 . In this manner, the fuel tank  12  may be filled from outside the hull  3  with the fuel passing through the fuel supply pipe  12   a  into the tank  12 . 
     A bulkhead  15  desirably is vertically provided behind the engine  10  and divides the hull  3  into an engine chamber or compartment  13  and a propulsion chamber  14 . Air ducts  25 ,  26 , for guiding air into the engine chamber  13  are provided in the forward/rear parts of the engine chamber  13 . Air inlet ports  25   a,    26   a  of each air duct  25 ,  26  are located in openings formed in the upper deck  4 . Air-outlet ports  25   b,    26   b  of each air duct are respectively opened to the forward and rear sides of the engine  10 . These air outlet ports  25   b,    26   b  are positioned lower than the engine intake-air system (to be described later) so as to prevent water flowing through the air ducts  25 ,  26  from traveling directly into the engine intake-air system. Although air is supplied to the engine compartment  13  though both ducts, a flow of air from the front duct to the rear duct also occurs to air cool the engine and the other components of the watercraft located in the engine compartment  13 . 
     A jet propulsion unit, indicated generally by reference numeral  16 , is provided in the pump chamber  21 . This jet propulsion unit  16  includes an impeller shaft  19  to which an impeller  18  is fixed. The impeller shaft  19  is positioned in the longitudinal directions and extends through a propulsion duct  17  that has a water inlet port  17   a  positioned on the keel of the lower hull section  2   a.  The lower hull section  2   a  includes an opening at the stern  2   b  of the watercraft  1  in which a jet outlet port  17   b  of the propulsion unit  16  is positioned. A front end of the impeller shaft  18  and an output shaft  40  (e.g.,—a crankshaft) of the engine are coupled through a conventional shock-absorbing coupling  41  to transfer power from the crankshaft to the impeller shaft. The propulsion unit  16  generates the propulsive force by applying pressure to water drawn up from the water inlet port  17   a  by means of the rotation of the impeller shaft  18 , and forcing the pressurized water through the jet outlet port  17   b  in a manner well known to those skilled in the art. 
     A nozzle deflector or steering nozzle  20  is connected to the jet outlet port  17   b  of the propulsion unit  16 . The nozzle deflector  20  desirably moves in the left/right and vertical directions via a known gimbal mechanism. The nozzle deflector  20  is connected to the handlebar assembly  150  through a steering mechanism and time mechanism (not shown), whereby the steering and trim angles may be changed by the operation of the handlebar assembly  150  and associated trim controls. 
     The upper deck  4  of the watercraft includes a longitudinally extending pedestal  170 , preferably formed as part of the upper deck  4 . The pedestal  170  supports the front and rear seats  5 ,  6 . Foot areas  40  are formed along side this pedestal  170 , between the pedestal  170  and a pair of raised side gunnels or bulwarks  4   a  that extend along the outer sides of the watercraft  1 . These foot areas  4   b  are sized to accommodate the lower legs and feet of the riders who straddle the front and rear seats  5 ,  6  when seated. In the illustrated embodiment, a deck  4   b ′, formed at the rear of the watercraft behind the pedestal, extends above the propulsion unit  16  and allow ease of entry onto the watercraft  1 , as is well known in the art. 
     A maintenance opening  4   c  is formed on the top surface of the seat pedestal  170  and is desirably positioned below the rear seat  6 . This maintenance opening  4   c  is covered by the rear bottom plate  6   a  in a water-sealing manner. The engine chamber  13  can be accessed through this maintenance opening  4   c  by removing the rear seat  6 . 
     An in-line, three-cylinder, four-cycle engine  10  is mounted in the center of the main body of the watercraft; however, other types of engines also can be used to power the watercraft. For instance, engines which have differing numbers of cylinders, use other cylinder arrangements or operate on other operating principles (e.g., two-stroke) can be used for this purpose. 
     The general construction of the four-stroke engine  10  is well known to those of ordinary skill in the art. As depicted in FIGS. 1 and 3, the engine  10  comprises cylinder block  10   b,  a cylinder head  10   c,  head covers  10   d,  and a crank case  10   a.  Intake valves  43  are disposed in the cylinder head  10   c  for controlling the delivery of a fuel/air mixture to the cylinders of the engine  10 . Exhaust valves  44  are similarly disposed in the cylinder head  10   c  for controlling the expulsion of exhaust gases. Opening and closing of the intake and exhaust valves is regulated by the operation of the camshafts  45 , the sprockets  46 ,  47 , and the timing chain  48 . The timing chain  48  is connected to the drive sprocket  47 , and is enclosed by a cover  49  which protects the timing chain  48  and prevents accidental contact between a rider and the chain during maintenance of the engine  10 . 
     Power from the crankshaft  40  is transferred to the impeller shaft  19  through the coupling  41 . The crankshaft  40  also carries a flywheel  77  on the rear side of the engine  10 . A starter motor  78  rotates the crankshaft  40  through a ring gear  77   a  formed on the periphery of the flywheel  77 , and operates to start the engine in a manner well known to those of ordinary skill in the art. An alternator  50  is connected to the crankshaft  40 . The alternator  50  coverts the mechanical power created by the rotation of the crankshaft  40  into electrical power for the engine  10  and associated systems in a manner well known to those of ordinary skill in the art. For this purpose, a drive pulley  51  located on the front side of the engine  10  is attached to the crankshaft  40 . A belt interconnects the drive pulley  51  to a pulley on the alternator  50  to drive the alternator in a known manner. 
     The flywheel  77 , located within the flywheel case  79 , is coupled to the crankshaft  40  to ensure smooth and even rotation of the crankshaft  40  during operation of the engine  10 . The flywheel case  79  extends rearwardly, substantially surrounding the flywheel. In addition, this extension of the flywheel case  79  will prevent water in contact with rotating coupling  41  from spraying into the engine intake-air system (to be described later). Furthermore, the flywheel case  79  acts as an insulator between the air in the engine compartment forward of the flywheel case  79  and the air in the engine compartment behind the flywheel case  79 . The case  79  also inhibits the airflow in the engine compartment in the forward direction, thereby limiting the heating of the engine intake-air system and the intake air. 
     On top of the engine  10  is a lubricating oil supply port  56 , through which oil may be added to the engine  10 . An oil cap  57  closes and seals this supply port  56 , thereby preventing a loss of oil from the engine and ensuring that water does not contaminate the oil supply. An oil pan  10   e  is provided in the bottom of the engine  10 . An oil filter  55 , located adjacent to the oil pan  10   e,  is provided to continuously clean the engine oil. A drain plug  42  is provided in the oil pan  10   e  to facilitate removal of engine oil for maintenance. 
     On one side of the engine  10  an exhaust system is provided. In this exhaust system, exhaust runners  60  extend from the side of the engine and downward into an exhaust-air merging box  61 . An exhaust-air merge pipe  61   a,  extending rearwardly from the exhaust-air merging box  61 , connects to a front end of a water lock or trap  63 . The water lock  63  inhibits a reverse flow of water toward the engine. In the rear end of the water lock  63 , a through-hull exhaust pipe  64  is connected. This exhaust pipe  64  extends upwardly and across the hull and over the pump chamber, and is connected to a pump chamber of the watercraft to exhaust at this location. The outlet of the exhaust pipe  64  can also be located on the lower surface of the hull, on the transom of the hull or on the side of the hull. 
     The engine  10  desirably is oriented within the hull  3  to locate a crankshaft  40  of the engine  10  along a longitudinal axis of the main body. The engine  10  is mounted above the lower hull section  2   a  of the watercraft through a damper member or mount  11 . As best depicted in FIG. 3, in one embodiment of the present invention the engine  10  is mounted such that the cylinder block  10   b  is skewed from vertical such that the axes of its cylinders are about by approximately 10 degrees off vertical. This engine orientation places the engine-air intake approximately 2 to 3 inches above the engine-air exhaust. This rotation permits an intake-air merging box  73  (to be described later) to be positioned in the intake air system without requiring substantial redesign of the intake system components, engine design and/or an increase in the cross-sectional width of the seat pedestal. Furthermore, the increased height of the engine-air intake allows the intake-air merging box  73  to be generally equally distanced from the upper deck and the lower deck of the small watercraft, a location that is least subject to water invasion during operation of the small watercraft. 
     The intake air system comprises fuel/air-intake pipes  70  connected to intake passage of the engine  10  which communicate with the engine&#39;s cylinders through the valve  43 . The fuel/air intake pipes  70  also communicate with at least one charge former. In the illustrated embodiment, the opposite end of each intake pipe  70  is connected to carburetors  71 . The carburetors  71  vaporize and mix fuel with the intake-air and regulate this fuel/air mixture using butterfly-type throttle valves  72  in a manner well known to those skilled in the art. 
     As best illustrated in FIGS. 1 and 3, the carburetors  71  are also connected to air intake pipes  70 , which are in turn connected to an intake-air silencer  73 . The intake-air silencer is connected to an air filter  74 , which is in turn connected to the intake box  75 . A trumpet-shaped air-inlet port  75   a  is disposed on the bottom surface of the intake box  75 , which allows air to be drawn into the intake box  75  at a low velocity while inhibiting entrance of water. The intake box  75  is located on the front side of the engine with its opening facing down. Water entrained in the air flow desirably is separated in the intake box  75  and is drained through the downward opening  75   a.    
     As best seen in FIG. 2, the case  79  of the flywheel  77  lies between the intake silencer  73 , as well as the balance of the components of the induction system, and the watertrap  63  and the exhaust pipe  64 . At this location, the casing  79  generally insulates, at least to some degree, the induction system from the heat radiated by the exhaust system, principally by the water trap  63  and the exhaust pipe  64 . The casing also inhibits air from the rear of the engine compartment toward the intake opening  75   a.  The casing  79 , as mentioned above, also generally shields the intake port  75   a  from water which may be splattered by the rotating coupling  41  and the associated shafts. As a result, the air entering into the intake box  75  generally contains less water vapor and is cooler than the air circulating about the rear end of the engine compartment. 
     FIG. 4 shows a rubber valve member  30  constructed in accordance with one embodiment of the present invention. This type of valve  30  is desirably disposed at the upper end of each axis inlet port  25   a,    26   a  of the front and rear air ducts  25 ,  26 . 
     Rubber valve member  30  is comprised of peripheral walls  30   a  and disc  30   c.  Air windows  30   b  are formed in the walls  30   a.  The lower section of the peripheral walls  30   a  encircles and is secured to an external projection of each air inlet port  25   a,    26   a.  A flange  180 , formed integral with and perpendicular to the air inlet port  25   a,    26   a,  secures the air inlet port to the upper deck  4  of the watercraft  1 . In the preferred embodiment, the peripheral walls  30   a  and disc  30   c  are formed of a buoyant, flexible material such as a low density foam rubber. 
     As shown in FIG. 5, during normal operation, the disc  30   c  of the rubber valve member  30  is supported by the peripheral walls  30   a,  thereby allowing air to travel through the air windows and into the air ducts  25 ,  26 . However, when the watercraft is inverted and the rubber valve member  30  is submerged, the natural buoyant forces acting on the disc  30   c  overcome the strength exerted by the peripheral walls  30   a,  thereby buckling the peripheral walls  30   a  and allowing the disc  30   c  to assume new position  30   c ′, effectively sealing the air ducts  25 ,  26  and preventing further water from entering the watercraft. When the watercraft resumes its normal orientation, this buoyant force on the disc is removed, thereby allowing the spring force exerted by the peripheral walls  30   a  to lift the disc  30   c  into its normal operating position and resuming the flow of air into the air ducts  25 ,  26 . 
     FIG. 6 shows an alternate embodiment of a valve member constructed in accordance with the present invention. Spring valve  185  is comprised of buoyant block  31 , spring valve shaft  190 , spring  32 , shaft support  33 , and stopper pin  34 . A flange  180 , formed integral with and perpendicular to the air inlet port  25   a,    26   a,  secures the air inlet port to the upper deck  4  of the watercraft  1 . The shaft support is disposed within the respective air inlet port  25   a,    26   a.    
     During normal operation of the spring valve  185 , the lower surface of the buoyant block  31  is held above the upper surface of the air inlet ports  25   a,    26   a  by a force exerted by the spring  32 , thus allowing air to travel into the corresponding air duct  25 ,  26 . Vertical motion of the buoyant block is limited by the interaction of stopper pin  34  with the lower surface of the shaft support  33 . When the watercraft is inverted and the spring valve  185  is submerged, however, buoyant forces acting on the buoyant block are greater than the force exerted by the spring, thereby allowing the buoyant block to travel towards and abut the air inlet ports  25   a,    26   a.  This substantially seals the air inlet ports and prevents water from entering the engine compartment of the watercraft. When the watercraft resumes its normal orientation, the buoyant force on the buoyant block is removed, thereby allowing the force exerted by the spring to lift the buoyant block off of the air inlet port  25   a,    26   a,  and resuming the flow of air into the corresponding air duct  25 ,  26 . 
     With reference now to FIGS. 7 and 8, depicted is a small watercraft incorporating another embodiment of an intake-air merging box constructed in accordance with the present invention. The intake-air merging box  73  is comprised of a ceiling wall  73   b,  an inner wall  73   c,  a bottom wall  73   d,  an outer wall  73   e  and two cap walls  73   f  and  73   g,  bonded together to form a watertight box. Disposed in the inner wall are trumpet-shaped intake ports  80 , which allow air to be drawn into the merging box  73  at a low velocity while inhibiting entrance of water. Disposed in the ceiling and bottom walls  73   b,    73   d  are drain holes  81   a,    81   b,  which permit water trapped within the merging box  73  to drain into the engine compartment  13 . While this embodiment of an intake-air merging box  73  is a square or rectangular box, it should be noted that various other shaped boxes may be used with equally utility. 
     As can best be seen from FIG. 7, air-intake pipes  70  connect the carburetors to the intake-air merging box  73 . These air-intake pipes are comprised of upstream parts  70   a,  located adjacent to the carburetors, and expanding parts  70   b,  located within the intake air merging box  73 . The trumpet-shaped design of the expanding parts  70   b  allows air to be drawn into the air-intake pipes at low velocity while inhibiting water from being drawn into the air-intake pipes. 
     FIGS. 9 through 11 depict a small watercraft  100  incorporating an additional embodiment of an air intake system constructed in accordance with the present invention. In this embodiment, the engine  10  utilizes a charge forming device such as a fuel injector  101  (see FIG. 11) for forming the fuel/air mixture utilized in the engine  10 . Air is supplied to the engine through a number of intake pipes  102  connected to the engine  10 . The opposite ends of the intake pipes  102  are connected to an intake-air merging pipe  103 , which is in turn connected to a throttle body  104 . The throttle body  104  is connected to the intake box  106 , and an air filter  105  is disposed within the intake box  106  to clean and filter air passing into the engine  10 . An intake opening  106   a  is located on the bottom surface of the intake box  106 . 
     In operation, the air intake system of the small watercraft of FIGS. 9 through 11 will draw air into the intake opening  106   a,  through the filter  105 , through the throttle body  104 , and into the air merging pipe  103 . Air in the air merging pipe will subsequently be drawn into and through the intake pipes  102  and into the engine  10  where it will be mixed with fuel sprayed from one or more fuel injectors  101 . 
     As seen from FIGS. 9 and 10, the intake box  106  is positioned behind the flywheel casing  79  and to one side of the longitudinal axis opposite the side on which the water trap  63  is located. At this location, the inlet  106   a  of the intake box  106  is located next to the lower end of the rear intake duct  26 . At this location, fresh air can enter the intake box while experiencing minimal heating. In addition, the flywheel casing  79  generally insulates the intake box from the engine so as to reduce the heating effect of the intake air from the intake duct  26  into the intake box  106 , as well as to inhibit air flow from the front intake duct  25  across the engine  10  to the intake box  106 . Consequently, the induction system intakes less air heated by the engine and more flesh air flowing through the rear intake duct  26 . 
     In addition, the coupling between the impeller shaft  19  and the output shaft of the engine  10  is enclosed within the casing  79 . As a result, the rotating components within the engine compartment tend to splatter less water about the engine compartment. 
     Turing now to FIGS. 12 through 14, there is depicted a small watercraft or jet boat  110 , incorporating another embodiment of an air intake system constructed in accordance with the present invention. As viewed from the bow to the stern, the hull  112  of the jet boat  110  includes floor  113   a  and a bench-type seat  114  located forward of an aft end  111  of the watercraft. A steering handle is positioned forward of the bench-type seat, and controls the steering of the watercraft in a conventional manner well known to those skilled in the art. A deck section  113  is fixed to the hull  112  around the peripheral edges in a manner well known to those skilled in the art. As can best be seen from FIG. 14, the engines  10  are skewed by approximately 10 degrees from vertical. 
     A maintenance opening  113   b  is provided in the deck section  113  to provide access to the engine chamber  13 . An engine hatch  120 , attached to the deck by a rear hinge  120   a,  closes the maintenance opening  113   b  in a watertight manner. Two storage boxes  121 ,  122  are positioned in the engine chamber. 
     A storage chamber  119 , located underneath the bench-type seat  114 , is formed between front dividing wall  117  and rear dividing wall  118 , and contains a fuel tank  116 . Two storage boxes  121 ,  122 , are located within the engine chamber  13  and are disposed alongside the outer side of each engine  10 . A battery  123  is positioned within one of the storage boxes  121 . Electrical engine control components  124  well known to those skilled in the art, such as computer control circuits, are located in the opposite storage box  122 . 
     On one side of each engine  10  an exhaust system is provided. In this exhaust system, exhaust pipes  130  extend from the side of the engines and downward into an exhaust-air merging pipe  131 . The exhaust-air merging pipe extends rearwardly and connects to a front end of a water lock or trap  63 . The water lock  63  inhibits a reverse flow of water toward the engine. In the rear end of the water lock  63 , a through-hull exhaust pipe  64  is connected. This exhaust pipe  64  extends upwardly and across the hull and over the pump chamber, and is connected to a pump chamber of the watercraft to exhaust at this location. 
     In the embodiment depicted in FIGS. 12 through 14, the engines  10  are cooled by a liquid cooling system comprising water jackets  133 , coolant inlet ports  134 , water ports  135 , coolant hoses  136 , and coolant drain ports  137 . In operation, cooling water is pumped into the water ports  135  and travels through the cooling hoses into coolant inlet ports  134 . This flow of cooling water travels into the water jackets  133 , an comes in contact with the cylinder block  10   b,  the cylinder heads  10   c,  and the engine exhaust pipe  130 . The cooling water than travels into the exhaust pipe, travels through the water lock  63 , and is discharged out of the jet boat through the through-hull exhaust pipe  64 . 
     The intake air system comprises intake pipes  140  connected to air inlets of the engines  10 . The opposite ends of these intake pipes  140  are connected to an intake air merging pipe  141 . The intake air merging pipe extends rearwardly and through the bulkhead  15 , and connects to an intake air port  141   a  which is open to the propulsion chamber  14 . An air inlet port  142  is provided in the upper deck  113  which allows outside air to travel into the propulsion chamber  14 . A cover  143 , located over the air inlet port  142 , prevents water from entering the propulsion chamber. 
     FIG. 15 depicts the jet boat of FIGS. 12 through 14, incorporating an additional embodiment of the present invention. In this embodiment, the engines  10  are positioned such that the cylinders of the engines  10  are skewed by approximately 10 degrees left and right, respectively, from vertical, thus forming a V-shape. This embodiment provides for increased separation between the engines, facilitating maintenance and removal of the engines, if required. The increased spacing between the exhaust system of one engine and the induction system of the other engine will further reduce the temperature of the air used to form the fuel/air charge. 
     Accordingly, although this invention has been described in terms of certain preferred embodiments, other embodiments apparent to those of ordinary skill in the art are also within the scope of this invention. Of course, a watercraft need not include all of these features to appreciate some of the aforementioned advantages associated with the present watercraft. Accordingly, the scope of the invention is intended to be defined only by the claims that follow.