Abstract:
An induction system for an internal combustion engine of a small watercraft includes an improved construction that directs water away from the induction system. The air induction system includes an air intake box defining a plenum chamber. An upper surface of the air intake box includes at least one surface feature such as a channel, groove, depression, humps, protrusion and/or ramp. The surface features promote drainage of water disposed on top of the air box.

Description:
RELATED APPLICATION  
         [0001]    This application claims priority to Japanese Patent Application No. 2000-212569, filed on Jul. 13, 2000, the entire contents of which are hereby incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to an engine for a personal watercraft. More particularly, an improved air induction system and oil tank cover for an engine for a personal watercraft.  
           [0004]    2. Description of the Related Art  
           [0005]    Personal watercraft have become very popular in recent years. This type of watercraft is designed for recreational as well as rescue purposes and usually is capable of carrying one to three riders. The craft commonly includes a relatively small hull that defines a rider&#39;s area above an engine compartment. The rider&#39;s area normally includes a seat.  
           [0006]    The engine compartment contains an internal combustion engine that powers a jet propulsion unit. The jet propulsion unit, which includes an impeller, is positioned within a tunnel formed on an underside of the hull behind the engine compartment. An impeller shaft, which is driven by the engine, usually extends between the engine and the jet propulsion device through a bulkhead of the hull tunnel.  
           [0007]    Personal watercraft usually include a maintenance opening for inspecting and maintaining the engine. This maintenance opening is exposed when the seat is removed. While the seat is detached, water may enter the engine compartment. For example, a high wave may hit the side of the watercraft while maintenance is being performed, thereby causing water to enter the engine compartment.  
           [0008]    Water within the engine compartment is potentially harmful for several reasons. First, the water decreases the buoyancy of the watercraft. A large enough amount of water within the engine compartment could cause the watercraft to capsize or sink. Second, water may cause damage to the engine. The air intake system is equipped to filter out water before injecting the air into the combustion chambers, but a large amount of moisture could saturate the air induction system, allowing moisture to enter the interior of the engine. Moisture, of course, is not conducive to combustion. A large amount of water in one or more of the combustion chambers could cause the engine to stall. Smaller amounts of water within the engine, while not necessarily causing the engine to stall, could corrode engine parts, shortening the life span of the engine.  
           [0009]    Thus, it is advantageous to drain water from within the engine compartment as quickly as possible. Typically, the engine compartment includes a bilge pump for this purpose. In order for the bilge pump to drain as much water from the engine compartment as possible, the engine compartment is preferably designed to direct water toward an intake pipe of the pump.  
         SUMMARY OF THE INVENTION  
         [0010]    According to one aspect of a preferred embodiment, a watercraft includes a hull defining an engine compartment. An internal combustion engine is positioned within the engine compartment. The engine includes an upper surface configured to direct water away from the upper surface.  
           [0011]    According to another aspect of a preferred embodiment, a watercraft includes a hull defining an engine compartment. An internal combustion engine is positioned within the engine compartment. The engine includes an engine body which defines a combustion chamber. An air induction system is provided including an air intake chamber. The air intake chamber is configured to guide air into the combustion chamber. An upper surface of the intake air chamber is configured to direct water away from the upper surface.  
           [0012]    According to yet another aspect of the preferred embodiment, an air intake chamber for use with an internal combustion engine includes an upper surface. The upper surface is configured to direct water away from the upper surface.  
           [0013]    According to an additional aspect of the preferred embodiment, a watercraft includes a hull defining an engine compartment. An internal combustion engine is positioned within the engine compartment. The engine includes an oil tank comprising a cover. An upper surface of the cover is configured to draw water away from the upper surface.  
           [0014]    In accordance with another aspect of the preferred embodiment, an oil tank for use with an internal combustion engine includes a cover. An upper surface of the cover is configured to direct water away from the upper surface.  
           [0015]    These and other aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiments disclosed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    These and other features of this invention will now be described with reference to the drawings of a preferred embodiment, which is intended to illustrate and not to limit the invention. The drawings contain the following figures:  
         [0017]    [0017]FIG. 1 is a side elevational view of a personal watercraft of the type powered by an engine configured in accordance with a preferred embodiment of the present invention, certain internal components, such as the engine, are illustrated in phantom;  
         [0018]    [0018]FIG. 2 is a top plan view of the watercraft of FIG. 1;  
         [0019]    [0019]FIG. 3 is a schematic and partial cross-sectional rear view of the watercraft and engine of FIG. 1, including a schematic profile of a hull of the watercraft, an air intake box, an oil tank and an opening of an engine compartment of the hull, which are illustrated partially in section;  
         [0020]    [0020]FIG. 4 is a front, top, and right side perspective view of the engine of FIG. 3, including an oil tank;  
         [0021]    [0021]FIG. 5 is a front, top, and left side perspective view of the engine of FIG. 3;  
         [0022]    [0022]FIG. 6 is a top plan view of a preferred embodiment of an upper surface of the intake box and cover of the oil tank of FIG. 3;  
         [0023]    [0023]FIG. 6 a  is a sectional view of the upper surface of the air box taken along line  6   a - 6   a  of FIG. 6;  
         [0024]    [0024]FIG. 7 is a top plan view of a modification of the upper surface of the intake box and oil tank of FIG. 6;  
         [0025]    [0025]FIG. 7 a  is a sectional view of the upper surface of the air box taken along line  7   a - 7   a  of FIG. 7;  
         [0026]    [0026]FIG. 8 is a top plan view of another modification of an upper surface of the intake box and oil tank of FIG. 6;  
         [0027]    [0027]FIG. 8 a  is a sectional view of the upper surface of the air box taken along line  8   a - 8   a  of FIG. 8;  
         [0028]    [0028]FIG. 9 is a top plan view of yet another modification of the upper surface of the intake box and the oil tank of FIG. 6;  
         [0029]    [0029]FIG. 9 a  is a sectional view of the upper surface of the air box taken along line  9   a - 9   a  of FIG. 9;  
         [0030]    [0030]FIG. 10 is a top plan view of another modification of the upper surface of the intake box and oil tank of FIG. 6; and  
         [0031]    [0031]FIG. 10 a  is a sectional view of the upper surface of the air box taken along line  10   a - 10   a  of FIG. 10; 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]    With reference to FIGS.  1 - 13 , an overall configuration of a personal watercraft  10  is described below. An arrow F, present in several of the figures, indicates a forward direction of the watercraft  10 .  
         [0033]    The personal watercraft  10  includes an engine  12 , a hull  14  formed with a lower hull section  16  and an upper hull section or deck  18 . Both hull sections  16 ,  18  may be constructed of, for example, a molded fiberglass-reinforced resin or a sheet molding compound. The hull sections  16 ,  18  may, however, be constructed from a variety of other materials selected to make the watercraft lightweight and buoyant. The lower hull section  16  and the upper hull section  18  are coupled together to define an internal cavity  20  (FIG. 1). A gunnel  22  defines an intersection of the lower and upper hull sections  16 ,  18 .  
         [0034]    With reference to FIGS. 1 and 2, the hull  14  defines a center plane CP that extends generally vertically from bow to stern. Along the center plane CP, the upper hull section  18  includes a hatch cover  24 , a control mast  26  and a seat  28  arranged from fore to aft.  
         [0035]    In the illustrated embodiment, a bow portion  30  of the upper hull section  18  slopes upwardly and an opening (not shown) is provided through which the rider can access the internal cavity  20 . The hatch cover  24  is detachably affixed (e.g., hinged) to the bow portion  30  so as to cover the opening.  
         [0036]    The control mast  26  extends upwardly to support a handle bar  32 . The handle bar  32  is provided primarily for controlling the direction in which the watercraft  10  travels. Grips are formed at both ends of the bar  32  to aid the rider in controlling the direction of travel, and in maintaining his or her balance upon the watercraft  10 . The handle bar  32  also carries other control units such as, for example, a throttle lever  34  that is used for control of running conditions of the engine  12 .  
         [0037]    The seat  28  extends along the center plane CP to the rear of the bow portion  30 . The seat  28  also generally defines a rider&#39;s area. The seat  28  has a saddle shape, enabling a rider to sit on the seat  28  in a straddle-type fashion. Foot areas  36  are defined on both sides of the seat  28  on the top surface of the upper hull section  18 . The foot areas  36  are generally flat.  
         [0038]    The seat comprises a cushion detachably supported, at least in principal part, by the upper hull section  18 . An opening  38  under the seat  28  allows access to the internal cavity  20 . The opening  38  is accessible by removing the seat  28 . In the illustrated embodiment, the upper hull section  18  also defines a storage box  40  under the seat  28 .  
         [0039]    A fuel tank  42  is disposed in the cavity  20  under the bow portion  30  of the upper hull section  18 . The fuel tank  42  is coupled with a fuel inlet port positioned at a top surface of the upper hull section  18  through a duct (not shown). A cap  44  seals the fuel inlet port. Optionally, the cap  44  can be positioned under the hatch cover  24 .  
         [0040]    The engine  12  is configured in accordance with a preferred embodiment of the present invention. The configurations of the preferred embodiments of the engine  12  have particular utility in combination with a personal watercraft, such as the personal watercraft  10 . Thus, preferred embodiments of the engine  12 , are described in the context of the personal watercraft  10 . These engine configurations, however, can be applied to other types of watercraft as well, such as, for example, small jet boats.  
         [0041]    The engine  12  is disposed in an engine compartment defined in the cavity  20 . The engine compartment is preferably located under the seat  28 , but other locations are also possible (e.g., beneath the control mast  26  or in the bow). The rider can thus access the engine  12  in the illustrated embodiment through the access opening  38  by detaching the seat  28 .  
         [0042]    The engine compartment  20  is substantially sealed so as to prevent water from entering. Water within the engine compartment  20  could damage the engine  12  or other components. The engine compartment is ventilated, however, by a pair of air ducts or ventilation ducts  46  that are provided on both sides of the bow portion  30 . Optionally, the watercraft  10  may also include additional air ducts (not shown) in a rear area of the internal cavity  20 . Ambient air entering the internal cavity  20  through the ducts  46  is used in the combustion reaction inside the engine  12  that powers the watercraft  10 , as described below.  
         [0043]    The engine  12  operates on a four-stroke cycle combustion principle. With reference to FIGS.  3 - 5 , the engine  12  includes a cylinder block  62 . The cylinder block  62  defines four cylinder bores  64  which are spaced from each other in a fore to aft direction along the center plane CP. The engine  12  thus is an L4 (in-line four cylinder) type. The illustrated engine  12 , however, merely exemplifies one type of engine that may include preferred embodiments of the induction system. Engines having other number of cylinders, having other cylinder arrangements, other cylinder orientations (e.g., upright cylinder banks, V-type, and W-type) and operating on other combustion principles (e.g., crankcase compression two-stroke, diesel, and rotary) are all practicable.  
         [0044]    Each cylinder bore  64  has a center axis CA that is oriented at an angle relative to the center plane CP to shorten the engine&#39;s  12  height. All the center axes CA in the illustrated embodiment are inclined at the same angle. Pistons  66  reciprocate within the cylinder bores  64 . A cylinder head member  68  is affixed to the upper end of the cylinder block  62 . The cylinder head member  68  closes the upper ends of the cylinder bores  64  and defines combustion chambers  70  along with the cylinder bores  64  and the pistons  66 .  
         [0045]    A crankcase member  72  is affixed to the lower end of the cylinder block  62  to close the respective lower ends of the cylinder bores  64  and to define a crankcase chamber  74 . A crankshaft  56  is rotatably connected to the pistons  66  through connecting rods  76  and is journaled with the crankcase member  72 . That is, the connecting rods  76  are rotatably coupled with the pistons  66  and with the crankshaft  56 .  
         [0046]    The cylinder block  62 , the cylinder head member  68 , and the crankcase member  72  together define an engine body  78 . The engine body  78  preferably is made of an aluminum based alloy. In the illustrated embodiment, the engine body  78  is oriented in the engine compartment  20  so as to position the crankshaft  56  generally parallel to the central plane CP. Other orientations of the engine body, of course, are also possible (e.g., with a transverse or vertical crankshaft).  
         [0047]    Engine mounts  80  extend from both sides of the engine body  78 . The engine mounts  80  preferably include resilient portions made of, for example, a rubber material so that vibrations from the engine  12  are attenuated. The engine  12  is preferably mounted on a hull liner that forms a part of the lower hull section  16 .  
         [0048]    The engine  12  is lubricated with oil housed in an oil tank  37  mounted aft of the engine  12 . Oil from the tank  37  circulates throughout the engine  12  when the engine  12  is operating. A circulation path of the oil passes through an oil filter  39  that is mounted to a side of the engine. The oil filter  39  removes contaminants from the oil that could harm the engine  12 . An oil dish  41  mounted to the engine  12  just beneath the oil filter  39  captures dripping oil when the oil filter  39  is removed from the engine  12 . Additionally, the oil dish  41  defines a guide which aids users during installation of an original or replacement oil filter  39 .  
         [0049]    The engine  12  preferably includes an air induction system to introduce air into the combustion chambers  70 . In the illustrated embodiment, the air induction system includes at least four air intake ports  82  defined in the cylinder head member  68 . Each intake port  82  communicates with one combustion chamber  70 . Intake valves  84  are provided to selectively open and close the intake ports  82 , thereby selectively connecting and disconnecting the intake ports  82  with the combustion chambers  70 .  
         [0050]    The air induction system also includes an air intake box  86 , which defines a plenum chamber  88  therein. The air intake box  86  smoothes intake air and acts as an intake silencer. The intake box  86  in the illustrated embodiment has a generally rectangular shape. Other shapes for the intake box are, of course, permissible, but it is desirable for the plenum chamber to be as large as possible within the available space in the engine compartment  20 . In the illustrated embodiment, a space is defined between the top of the engine  12  and the bottom of the seat  28  due to the inclined orientation of the engine  12 . The rectangular shape of the intake box  86  conforms to this space.  
         [0051]    With reference to FIGS.  3 - 5 , the intake box  86  comprises an upper chamber member  90  and a lower chamber member  92 . The upper and lower chamber members  90 ,  92  preferably are made of plastic or synthetic resin, although they can be made of metal or other material. Additionally, the intake box  86  can be formed by a different number of members and/or can have a different assembly orientation (e.g., side-by-side).  
         [0052]    With reference to FIG. 2, the engine is disposed beneath the access opening  38  and is thus accessible through the access opening  38 . An upper surface  91  of the air box  86  and an upper surface  35  of the oil tank  37  are also disposed directly beneath the access opening. Thus, the upper surface  91  defines an upper-most surface of the engine  12 .  
         [0053]    The upper surface  91  of the upper chamber member  90  includes at least one surface feature, such as channels  200 , which is configured to direct water off of the upper surface  91 . Preferably, the surface feature is configured to guide the water toward the rear or aft end of the watercraft  10 . The construction and function of such a surface feature is described in greater detail below.  
         [0054]    With reference to FIG. 3, the lower chamber member  92  preferably is coupled with the engine body  78 . In the illustrated embodiment, several stays  94  extend upwardly from the engine body  78  and a flange portion  96  of the lower chamber member  92  extends generally horizontally. Several fastening members, for example, bolts  98  and nuts  99 , connect the flange portion  96  to respective top surfaces of the stays  94 . The upper chamber member  90  has a flange portion  100  (FIG. 3) that abuts on the flange portion  96  of the lower member  92 . Several coupling or fastening members  102 , which are generally configured as a shape of the letter “C” in section, preferably engage both the flange portions  96 ,  100  so as to couple the upper chamber member  90  with the lower chamber member  92 .  
         [0055]    With reference to FIG. 3, the lower chamber member  92  defines an inlet opening  104  and, preferably, four outlet apertures  106 . Four throttle bodies  108  extend toward the apertures  106  and preferably are fixed to the lower chamber member  92 . Respective bottom ends of the throttle bodies  108  are coupled with the associated intake ports  82 . Preferably, as illustrated in FIG. 3, the position at which the apertures  106  are sealed to the throttle bodies  108  is spaced from the outlet of bottom ends of the throttle bodies  108 . Thus, the lower member  92  is spaced from the engine  12 , thereby attenuating transfer of heat from the engine body  78  to the intake box  86 .  
         [0056]    The throttle bodies  108  slant toward the port side of the watercraft  10 , away from the center axis CA of the cylinder bores  64 . A sleeve  110  extends between the lower chamber member  92  and the cylinder head member  68  and generally surrounds a portion of the throttle bodies  108 . Respective top ends of the throttle bodies  108 , in turn, open upwardly within the plenum chamber  88 . Air in the plenum chamber  88  thus is drawn to the combustion chambers  70  through the throttle bodies  108  and the intake ports  82  when negative pressure is generated in the combustion chambers  70 . Negative pressure is generated when the pistons  66  move toward the bottom dead center from the top dead center.  
         [0057]    Each throttle body  108  includes a throttle valve  112 . A throttle valve shaft  114 , journaled for pivotal movement, links the throttle valves  112 . Pivotal movement of the throttle valve shaft  114  is controlled by the throttle lever  58  on the handle bar  56  through a control cable that is connected to the throttle valve shaft  114 . The rider thus can control the opening and closing of the throttle valves  112  by operating the throttle lever  56 . The degree to which the throttle valves  112  are open determines the amount of air that passes through the throttle bodies  108  and into the respective combustion chambers  70 . The amount of air entering the combustion chambers determines the running condition of the engine  12 . More air generates higher rpm&#39;s, less air generates lower rpm&#39;s.  
         [0058]    With reference to FIG. 3, the air inlet port  104  introduces air into the plenum chamber  88 . In the illustrated embodiment, a filter assembly  116  surrounds the inlet port  104 . The filter assembly  116  comprises an upper plate  118 , a lower plate  120  and a filter element  122  interposed between the upper and lower plates  118 ,  120 . Preferably, the filter element  122  comprises oil resistant and water-repellent elements. The filter assembly  116 , including the lower plate  120 , has a generally rectangular shape in plan view. The filter element  122  extends along a periphery of the rectangular shape so as to define a gap between a peripheral edge of the filter element  122  and an inner wall of the air box  86 .  
         [0059]    The lower plate  120  includes a duct  124  which extends inwardly toward the plenum chamber  88 . The duct  124  is positioned generally above the cylinder head member  68 . An upper end of the duct  124  slants so as to face an inner wall portion of the intake box  86  positioned opposite the throttle bodies  108 . In the illustrated embodiment, the upper or outlet ends of the ducts  124  define a high point proximate to the outlet apertures  106  and a low point distal from the apertures  106 . This is advantageous because water or water mist, if any, is likely to move toward this inner wall portion rather than toward the throttle bodies  108 . If, however, a smooth flow of air is desired rather than water inhibition, the upper end of the ducts  124  may slant toward the throttle bodies  108  as indicated by the phantom line  124   a  of FIG. 3. Optionally, the upper ends of the ducts  124  may be arranged so that some slant away from the throttle bodies  108  and the rest slant toward the throttle bodies  108 .  
         [0060]    In the illustrated embodiment, a guide member  126  is affixed to the lower plate  120  immediately below the duct  124 . The guide member  126  defines a recess  128  that is associated with the duct  124 . The recess  128  opens toward the starboard side of the watercraft  10 . Air traveling from the engine compartment  20  into the plenum chamber  88  thus travels through the recess  128  of the guide member  126 . The duct  124  opens to an interior volume  130  defined by the filter element  122 . The air in this volume  130  thus must pass through the filter element  122  in order to reach the throttle bodies  108 . Foreign substances in the air are removed by the filter element  122  as the air passes through.  
         [0061]    Because the air inlet openings  104  are formed at the bottom of the intake box  86 , water and/or other foreign substances are unlikely to enter the plenum chamber  88 . The filter element  106  provides a further barrier to the entry of water and foreign particles into the throttle bodies  108 . In addition, part of the openings  104  are defined by the ducts  124  extending into the plenum chamber  88 . Thus, a desirable length for efficient silencing of intake noise is accommodated within the plenum chamber  90 .  
         [0062]    The engine  12  also includes a fuel supply system as illustrated in FIGS. 1 and 3. The fuel supply system includes the fuel tank  42  (FIG. 1) and fuel injectors (not shown) that are affixed to a fuel rail (not shown) and are mounted on the throttle bodies  108 . The fuel rail extends generally horizontally in the longitudinal direction. A fuel inlet port (not shown) is defined at a forward portion of the lower chamber member  92  so that the fuel rail is coupled with an external fuel passage. Because the throttle bodies  108  are disposed within the plenum chamber  88 , the fuel injectors are also desirably positioned within the plenum chamber  88 . However, other types of fuel injectors may be used which are not mounted in the intake box  86 , such as, for example, but without limitation, direct fuel injectors and induction passage fuel injectors connected to the scavenge passages of two-cycle engines. Each fuel injector has an injection nozzle directed toward the intake port  82  associated with each fuel injector.  
         [0063]    When the intake valves  84  open, air from the plenum chamber  88  is drawn through the intake ports  82  and into the combustion chambers  70 . At the same time, the fuel injectors deliver a measured amount of fuel spray, which also travels through the intake ports and into the combustion chambers  70 . The air-fuel mixture is compressed, and then ignited. The resulting combustion reaction generates the power that is harnessed to propel the watercraft  10 .  
         [0064]    With reference to FIGS.  3 - 5 , the engine  12  further includes an exhaust system  138  to discharge the combustion by-products, i.e., exhaust gases, from the combustion chambers  70 . In the illustrated embodiment, with reference to FIG. 3, the exhaust system  138  includes a plurality of exhaust ports  140 , at least one for each combustion chamber  70 . The exhaust ports  140  are defined in the cylinder head member  68  and communicate with the associated combustion chambers  70 . Exhaust valves  142  are provided to selectively connect and disconnect the exhaust ports  140  with the combustion chambers  70 .  
         [0065]    The exhaust system includes an exhaust manifold  144 . In a presently preferred embodiment, the manifold  144  comprises a first manifold  146  and a second manifold  148  (FIG. 4) coupled with the exhaust ports  140  to receive exhaust gases from the respective ports  140 . The first manifold  146  is connected to two of the exhaust ports  140  and the second manifold  148  is connected with the two remaining exhaust ports  140 . In a presently preferred embodiment, the first and second manifolds  146 ,  148  are configured to nest with each other.  
         [0066]    Respective downstream ends of the first and second exhaust manifolds  146 ,  148  are coupled with a first unitary exhaust conduit  150 . As seen, for example, in FIGS. 4 and 5, the first unitary conduit  150  is further coupled with a second unitary exhaust conduit  152 . The second unitary conduit  152  is then coupled with an exhaust pipe  154  on the rear side of the engine body  78 .  
         [0067]    With reference to FIG. 5, the exhaust pipe  154  extends along a side surface of the engine body  78  on the port side of the watercraft  10 . The exhaust pipe  154  is then connected to a water-lock  156  at a forward surface of the water-lock  156 . With reference to FIG. 2, a discharge pipe  158  extends from a top surface of the water-lock  156  and transversely across the center plane CP. The discharge pipe  158  then extends rearwardly and opens at a stern of the lower hull section  36  in a submerged position. The water-lock  156  prevents water in the discharge pipe  158  from entering the exhaust pipe  154 .  
         [0068]    With reference to FIG. 4, the engine  12  preferably includes a secondary air supply system  160  that supplies air from the air induction system to the exhaust system  138 . More specifically, for example, hydro carbon (HC) and carbon monoxide (CO) components of the exhaust gases can be removed by an oxidation reaction with oxygen (O 2 ) that is supplied to the exhaust system  138  from the air induction system.  
         [0069]    With reference to FIG. 3, the engine  12  has a valve cam mechanism for actuating the intake and exhaust valves  84 ,  142 . In the illustrated embodiment, a double overhead camshaft drive is employed. That is, an intake camshaft  162  actuates the intake valves  84  and an exhaust camshaft  164  separately actuates the exhaust valves  142 . The intake camshaft  162  extends generally horizontally over the intake valves  84  from fore to aft generally parallel to the center plane CP, and the exhaust camshaft  164  extends generally horizontally over the exhaust valves  142  from fore to aft also generally parallel to the center plane CP.  
         [0070]    Both the intake and exhaust camshafts  162 ,  164  are journaled by the cylinder head member  68  with a plurality of camshaft caps. The camshaft caps holding the camshafts  162 ,  164  are affixed to the cylinder head member  68 . A cylinder head cover member  166  extends over the camshafts  162 ,  164  and the camshaft caps, and is affixed to the cylinder head member  68  to define a camshaft chamber. The stays  94  and the secondary air supply device  160  are preferably affixed to the cylinder head cover member  166 . Additionally, the secondary air supply device  160  is desirably disposed between the intake air box  86  and the engine body  78 .  
         [0071]    The intake camshaft  162  has cam lobes, each associated with a respective intake valve  84 . The exhaust camshaft  164  also has cam lobes associated with respective exhaust valves  142 . Springs bias the intake and exhaust valves  84 ,  142  to close the intake and exhaust ports  82 ,  140 . When the intake and exhaust camshafts  162 ,  164  rotate, the cam lobes push the respective valves  84 ,  142  to open the respective ports  82 ,  142  by overcoming the biasing forces of the springs. The air thus enters the combustion chambers  70  when the intake valves  84  open, and the exhaust gases exit the combustion chambers  70  when the exhaust valves  142  open.  
         [0072]    The crankshaft  56  preferably drives the intake and exhaust camshafts  162 ,  164 . A driven sprocket is affixed to an end of each camshaft  162 ,  164 . A drive sprocket is affixed to an end of the crankshaft  56 . Each driven sprocket has a diameter that is twice as large as a diameter of the drive sprocket. Preferably, a timing chain or belt is wound around the drive and driven sprockets. When the crankshaft  56  rotates, the drive sprocket drives the driven sprockets via the timing chain, causing the intake and exhaust camshafts  162 ,  164  to rotate. The rotational speeds of the camshafts  162 ,  164  are reduced to half of the rotational speed of the crankshaft  56 , due to the difference in diameters of the drive and driven sprockets.  
         [0073]    A jet pump unit  48  propels the watercraft  10 . The jet pump unit  48  is mounted at least partially in a tunnel  50  formed on the underside of the lower hull section  36 , which is preferably isolated from the engine compartment by a bulkhead (not shown). The tunnel  50  has a downward facing inlet port (not shown) opening toward the body of water. A jet pump housing  52  is disposed within a portion of the tunnel  50  and communicates with the inlet port. An impeller (not shown) is supported within the housing  52 .  
         [0074]    An impeller shaft  54  extends forwardly from the impeller and is coupled to the crankshaft  56  by a coupling member  58 . The crankshaft  56  thus drives the impeller shaft  54 , causing the impeller to rotate.  
         [0075]    The rear end of the housing  52  defines a discharge nozzle  59 . A steering nozzle  60  is affixed to the discharge nozzle  59  for pivotal movement about a steering axis which extends generally vertically. The steering nozzle  60  is connected to the handle bar  32  by a cable so that the rider can pivot the nozzle  60 .  
         [0076]    When the watercraft  10  is operating, ambient air enters the internal cavity  20  defined in the hull  34  through the air ducts  46 . The air then enters the plenum chamber  88 , defined by the intake box  86 , through the air inlet ports  104  and travels into the throttle bodies  108 . The majority of the air in the plenum chamber  88  is supplied to the combustion chambers  70 . The throttle valves  112  in the throttle bodies  108  regulate the amount of air that passes into the combustion chambers  70 . With the throttle lever  58 , the rider controls the opening angles of the throttle valves  112 , and thus the amount of air that flows past the valves. The air flowing past the throttle valves flows into the combustion chambers  70  when the intake valves  84  open. At the same time that the intake valves open, the fuel injectors spray fuel into the intake ports  82  at the direction of an electronic control unit (ECU).  
         [0077]    The air/fuel mixture in the combustion chambers  70  is compressed by the pistons  66 , and then ignited by spark plugs (not shown) under the control of the ECU. The exhaust gases from the combustion explosions are discharged to the body of water surrounding the watercraft  10  through the exhaust system  138 . The secondary air supply system  160  delivers a relatively small amount of air from the plenum chamber  88  to the exhaust system  138 . This secondary air aids in combusting any unoxidized fuel remaining in the exhaust gases.  
         [0078]    The force generated by the combustion explosions causes the pistons  66  to reciprocate. The reciprocating pistons  66  cause the crankshaft  56  to rotate. The rotating crankshaft  56  drives the impeller shaft  54 , and the impeller rotates in the hull tunnel  50 . The rotating impeller draws water into the tunnel  50  through the inlet port and discharges it rearward through the discharge nozzle  59  and through the steering nozzle  60 . The rider controls the direction in which the nozzle  60  discharges water by manipulating the steering handle bar  32 . The watercraft  10  thus moves according to the rider&#39;s direction.  
         [0079]    As mentioned above, the upper surface  91  of the upper chamber member  90  includes at least one surface feature, such as a ridge, channel, hump and a ramp. Additionally, a cover  35  of the oil tank  37  preferably also includes similar surface features. These surface features may include a wide variety of shapes and textures. The arrangement and construction of the features illustrated in FIGS.  6 - 10  are merely exemplary, and in no way limit the scope of coverage of the claims below.  
         [0080]    When the seat  28  is removed, the opening  38  is exposed. If the watercraft  10  is floating on a body of water when the seat  28  is removed, the interior cavity  20  is vulnerable to taking on water. For example, if a large wave hits the watercraft  10 , water may enter the interior cavity  20  through the opening  38 . The surface features direct water off of the upper surface  91  and toward a bilge pump (not shown) so that the water can be quickly discharged to the exterior of the watercraft  10 .  
         [0081]    The surface features cooperate with at least one of gravity and intertial forces generated during acceleration upon water to increase the rate at which water present on the upper surface  91  and/or cover  35  flows off of the upper surface  91  and/or cover  35 . In addition to relatively larger quantities of water that can be splashed onto the top of the covers  35  and  36 , small droplets can also collect about the upper surface  91  and/or cover  35 .  
         [0082]    Small droplets of water at rest upon a substantially horizontal surface can tend to stay remain stationary due to surface tension of the droplets. Some inertial and/or gravitational forces acting upon the droplets can be insufficient to overcome the tendency of the droplets to remain in place. However, when smaller droplets merge to form larger droplets thereby increasing the mass of the droplet, the inertial and gravitational forces also become larger, and thus, the droplets can move about the horizontal surface more readily.  
         [0083]    Preferably, the surface feature included on the upper surface  91  and/or cover  35  create varying elevations. Water on these surfaces thus tends to collect at the point or points of lowest elevation under the influence of gravity. Although such a surface feature may not define the lowest point on the entire upper surface  91  or cover  35 , such surface features can define one or a plurality of localized low points. Once a sufficient amount of water has collected at such a low point, the water tends to be influenced by at lease one of the motion of the watercraft  10  or gravity to run toward the peripheral edges of the upper surface  91  and/or cover  35 . Once the water reaches the edges, it drips off the upper surface  91  and/or cover  35  and onto a floor (not shown) of the internal cavity  20 . Once on the floor, the water can be sucked into a bilge pump and expelled from the watercraft  10 .  
         [0084]    One preferred embodiment, illustrated in FIG. 6, includes at least one channel  200  extending in a longitudinal direction from a first side  202  of the upper surface  91  to a second side  204  opposite the first side  202 . The cover  35  preferably includes corresponding channels  200   a  extending in a longitudinal direction from a first side  206  of the cover  35  to a second side  208  opposite the first side  206 . The pictured channels  200 ,  200   a  are substantially U-shaped in cross-section. One of skill in the art will understand, however, that the channels  200  may have other cross-sections, such as V-shaped or square.  
         [0085]    In the illustrated embodiment, three channels  200  are depicted. One of ordinary skill in the art will understand, however, that any number of channels  200  may be included.  
         [0086]    As shown in FIG. 6 a , a surface  210  opposite the upper surface  91  may include ridges  212  corresponding to the channels  200 . A lower surface (not shown) of the cover  35  may include similar ridges. One of ordinary skill in the art will understand, however, that the channels  200  need not include corresponding ridges  212 .  
         [0087]    A modification of the covers  35 ,  90  are depicted in FIGS. 7 and 7 a , and identified generally by the reference numerals  35   a ,  90   a , respectively. The covers  35   a ,  90   a  can be constructed in accordance with the descriptions of the covers  35 ,  90 , except as noted below.  
         [0088]    As shown in FIG. 7, a first depression  214  in the upper surface  91   a  is substantially Y-shaped in plan view. Legs  216  of the Y open towards the aft of the watercraft  10 .  
         [0089]    As shown in FIG. 7 a , the surface  210  opposite the upper surface  91   a  may include a raised shoulder portion  220  corresponding to the first depression  214 . One of ordinary skill in the art, however, will understand that the surface  210  need not include the raised shoulder portion  220 .  
         [0090]    An area between the legs  216  defines a second depression  222  having an elevation lower than an elevation of the first depression  214 . The surface  210  may, but need not, include a hump  224  corresponding to the second depression  224 . The cover  35   a  includes a first depression  214  and second depression  222  positioned as aft extensions of the first depression  214  and second depression  222  in the upper surface  91   a.    
         [0091]    Another modification of the covers  35 ,  90  are depicted in FIGS. 8 and 8 a , and identified generally by the reference numerals  35   b ,  90   b , respectively. The covers  35   b ,  90   b  can be constructed in accordance with the descriptions of the covers  35 ,  90 ,  35   a ,  90   a  except as noted below.  
         [0092]    As shown in FIGS. 8 and 8 a , a longitudinal channel  226  extends from the first edge  202  of the upper surface  91   b  to the second edge  204 . The channel  226  is substantially U-shaped in cross-section, although other cross-sectional shapes may be substituted. The surface  210  preferably includes a hump  228  corresponding to the channel  226 .  
         [0093]    Transverse grooves  236  extend from a first edge  228  of the channel  226  to a third edge  230  of the upper surface  91   b , and from a second edge  232  of the channel  226  to a fourth edge  234  of the upper surface. The grooves  236  are substantially perpendicular to the channel  226 . One of skill in the art will understand, however, that the grooves  236  may extend diagonally from the channel  226 . The cover  35   b  may also include transverse grooves  236 , as pictured, and may also include a longitudinal channel (not pictured).  
         [0094]    A further modification of the covers  35 ,  90  are depicted in FIGS. 9 and 9 a , and identified generally by the reference numerals  35   c ,  90   c , respectively. The covers  35   c ,  90   c  can be constructed in accordance with the descriptions of the covers  35 ,  90 ,  35   a ,  90   a ,  35   b ,  90   b  except as noted below.  
         [0095]    As shown in FIGS. 9 and 9 a , a series of narrow longitudinal channels  238  and a central broad longitudinal channel  239  extend from the first edge  202  to the second edge  204  of the upper surface  91   c . The broad channel  239  preferably continues across the cover  35   c . The channels  238  cover approximately half of the upper surface  91   c  from near a central longitudinal axis to near the fourth edge  234 . One of skill in the art will understand, however, that the channels  238  could cover more or less of the upper surface  91   c . One of skill in the art will also understand that the channel  239  may be shifted toward either the third edge  230  or fourth edge  234 , or eliminated entirely. With reference to FIG. 9 a , the surface  210  preferably includes ridges  240  corresponding to the channels  238 .  
         [0096]    A portion of the upper surface  91  bounded by its central longitudinal axis and the third edge  230  includes a plurality of upward protrusions  242 . The protrusions  242  preferably are substantially dome-shaped and elliptical in plan view, having a minor axis oriented in the longitudinal direction. The pictured embodiment includes four protrusions  242 . One of skill in the art will understand, however, that more or less protrusions  242  may be provided, and that the protrusions  242  may be any of a variety of shapes, sizes and orientations. One of skill in the art will also understand that a variety of other relative positions of the protrusions  242  and channels  238  are possible. For example, the relative positions of the features may be reversed, or the protrusions  242  may be centered on the upper surface  91   c  with channels  238  on either side, or the channels  238  may be centered on the upper surface  91   c  with the protrusions  242  on either side.  
         [0097]    Yet another modification of the covers  35 ,  90  are depicted in FIGS. 10 and 10 a , and identified generally by the reference numerals  35   d ,  90   d , respectively. The covers  35   d ,  90   d  can be constructed in accordance with the descriptions of the covers  35 ,  90 ,  35   a ,  90   a ,  35   b ,  90   b ,  35   c ,  90   c  except as noted below.  
         [0098]    As shown in FIG. 10, a series of narrow longitudinal channels  244 , a central broader longitudinal channel  246 , and an isolated narrow longitudinal channel  248  spaced from the channels  244  and the channel  246  are disposed in the upper surface  91   d . Each of the channels  244 ,  246 ,  248  extend from the first edge  202  to the second edge  204  of the upper surface  91   d . The channels  246 ,  248  preferably continue across the cover  35   d . The channels  244  cover a narrow strip of the upper surface  91   d  near the fourth edge  234 . One of skill in the art will understand, however, that the channels  244  could cover more or less of the upper surface  91   d . One of skill in the art will also understand that the channel  246  may be widened, narrowed, shifted toward either the third edge  230  or fourth edge  234 , or eliminated entirely. With reference to FIG. 10 a , the surface  210  preferably includes ridges  250  corresponding to the channels  238 , and a hump  252  corresponding to the channel  246 .  
         [0099]    An area of the upper surface  91   d  near the third edge  230  includes a plurality of ramps  254  shaped substantially as half-ovals in plan view, with a rounded end portion  256  of each oval facing the fourth edge  234 . The pictured embodiment includes four ramps  254 . One of skill in the art will understand, however, that more or less ramps  254  may be provided, and that the ramps  254  may be any of a variety of shapes, sizes and orientations. One of skill in the art will also understand that a variety of other relative positions of the ramps  254  and channels  244 ,  246 ,  248  are possible. For example, the relative positions of the features may be reversed.  
         [0100]    The above presents a description of the best mode contemplated for carrying out the present induction system for personal watercraft, and of the manner and process of making and using it, in such full, clear, concise, and exact terms as to enable any person skilled in the art to which it pertains to make and use this induction system. This induction system is, however, susceptible to modifications and alternate constructions from that discussed above which are fully equivalent. Consequently, it is not the intention to limit this induction system to the particular embodiments disclosed. On the contrary, the intention is to cover all modifications and alternate constructions coming within the spirit and scope of the induction system as generally expressed by the following claims, which particularly point out and distinctly claim the subject matter of the induction system.