Abstract:
A watercraft includes a hull construction that incorporates several aspects to reduce the operating noise of the watercraft. One structural aspect improves sound insulation about the engine compartment, and includes a seat design that facilitates such improvement. Insulating material is injected between the hull and inner walls and inserts. The seat design also incorporates air pockets to insulate an upper side of an engine compartment and aft compartment in which a water trap is located. The air supply and cooling system of the watercraft also uses resonator chambers to quiet engine and exhaust noise emitted through the ducts of the system. Another aspect involves insulating a portion of the exhaust system within the insulating material. These aspects of the hull construction each reduce the operating noise of the watercraft.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a small watercraft, and more particularly to the layout of engine components within the watercraft and an associated seat design. 
     2. Description of Related Art 
     Personal watercraft have become very popular in recent years. This type of watercraft is quite sporting in nature and carries a rider and possibly one, two or three passengers. A relatively small hull of the personal watercraft commonly defines a riders&#39; area above an engine compartment. An internal combustion engine frequently powers a jet propulsion unit which propels the watercraft. The engine lies within the engine compartment in front of a tunnel formed on the underside of the watercraft hull. The jet propulsion unit is located within the tunnel and is driven by a drive shaft. The drive shaft usually extends between the engine and the jet propulsion device, through a wall of the hull tunnel. 
     Despite their popularity, many areas have begun imposing restrictions on personal watercraft due in part to the high decibel operating noise of such crafts. Prior personal watercraft have attempted to lessen exhaust and engine noise by a variety of ways. Some personal watercraft exhaust into the tunnel, as taught by, e.g., U.S. Pat. No. 4,811,560, as well as include one or more expansion chambers (e.g., U.S. Pat. No. 5,234,364) in the exhaust system in order to reduce exhaust noise. Some prior watercraft have also lined the engine compartment with a sound insolating material. While such approaches have lessened the exhaust and operating noise associated with the personal watercraft, a need exists for additional noise reduction. 
     SUMMARY OF THE INVENTION 
     The present watercraft involves several approaches to reduce the operating noise of the watercraft. One approach involves improved sound insulation about the engine compartment, and includes a seat design that facilitates such improvement. Another approach involves silencing the sound that is emitted from the engine compartment through the air ducts of the watercraft. And a further approach involves insulating a portion of the exhaust system. These approaches, as well as others described below, can be used together or alone within a watercraft in order to lessen operating noises of the watercraft. 
     One aspect of the present invention thus involves a watercraft comprising a hull having a lower hull portion and an upper deck portion. An internal combustion engine is located within the hull and has an output shaft. A propulsion device is carried by the hull and is driven by the engine output shaft to propel the watercraft. The deck portion includes a central elongated pedestal having first and second sections. The firs section is removable attached to the second section and is arranged to form at least a portion of an upper surface of the pedestal. The deck portion also includes a seat with a base. The seat base is removably attached to the pedestal. In a preferred mode, one or more air pockets are defined between the cover and the seat base to provide sound insulation. 
     The engine compartment also can further silenced by insulation layers about the side walls of a seat pedestal in which at least a portion of the engine is located. In some modes, at least a portion of the exhaust system can also be insulated within such insulation layers. 
     Another aspect of the present invention involves a watercraft comprising a hull having a lower hull portion and an upper deck portion. An internal combustion engine is located within the hull and has an output shaft. A propulsion device is carried by the hull and is driven by the engine output shaft to propel the watercraft. The hull also includes at least one air duct with first and second ports. The first port is arranged to communicate ambient air from outside the hull, and the second port opens into the hull. A sub-resonator chamber communicates with the air duct at a portion between the first and second ports. The sub-resonator chamber preferably is tuned (i.e., sized and shaped) to reduce noise emitted through the air duct. 
     In accordance with a further aspect of the present invention, a watercraft is provided comprising a hull having a lower hull portion and an upper deck portion. An engine compartment is formed within the hull and is defined between a fore bulkhead and an aft bulkhead. Each bulkhead includes at least one tube that communicates with the engine compartment. An internal combustion engine is located within the engine compartment and has an output shaft. A propulsion device is carried by the hull and is driven by the engine output shaft to propel the watercraft. With this construction, the bulkheads help silence engine and exhaust noise. 
     An additional aspect of the present invention involves a watercraft comprising a hull having a lower hull portion and an upper deck portion. An engine compartment is formed within the hull and is defined between a fore bulkhead and an aft bulkhead. A fore air duct opens into the hull forward of the fore bulkhead and an aft air duct opens into the hull rearward of the aft bulkhead. An internal combustion engine is located within the engine compartment and has an output shaft that drives a propulsion device to propel the watercraft. The arrangement of the air ducts relative to the engine and bulkheads further assists in noise reduction. 
     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 embodiment of the watercraft is intended to illustrate, but not to limit the invention. The drawings contain the following figures: 
     FIG. 1 is a cross-sectional, side elevational view of a personal watercraft configured in accordance with a preferred embodiment of the present invention; 
     FIG. 2 is a partial sectional, top plan view of the personal watercraft of FIG. 1; 
     FIG. 3 is a cross-sectional view of the watercraft of FIG. 1 taken along line  3 — 3 ; 
     FIG. 4 is a cross-sectional view of the watercraft of FIG. 1 taken along line  4 — 4 ; and 
     FIG. 5 is a cross-sectional view of the watercraft of FIG. 1 taken along line  5 — 5 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 through 5 illustrate a personal watercraft  10  that includes a seat design and associated engine compartment layout configured in accordance with a preferred embodiment of the present invention. Although these features are illustrated in connection with a personal watercraft, they can be used with other types of watercraft as well, such as, for example, but without limitation, small jet boats and the like. 
     The following describes the illustrated watercraft in reference to a coordinate system in order to ease the description of the watercraft. A longitudinal axis extends from bow to stem and a lateral axis extends from port side to starboard side normal to the longitudinal axis. In addition, relative heights are expressed in reference to the undersurface of the watercraft. And in FIG. 1, a label “forward” has been included for reference purposes. 
     With initial reference to FIGS. 1 and 2, the watercraft  10  includes a body  12  formed by a hull  14  and a deck  16 . The hull  14  and the deck  16  are formed from a suitable material such as, for example, a molded fiberglass reinforced resin or SMC. The hull  14  and the deck  16  are fixed to each other around the peripheral edges  18  in any suitable manner. 
     In the illustrated embodiment, a bond flange  18  is defined as the overlapping mating section where the hull  14  and the deck  16  are joined together. The bond flange  18  also identifies the location of a bond line, which is an imaginary line around the watercraft  10  where the hull  14  and the deck  16  are joined together. Accordingly, the deck  16  generally comprises the upper structural body of the watercraft  10 , which is located above and includes the upper bond flange  18 . 
     The hull  14  is designed such that the watercraft  10  planes or rides on a minimum surface area at the aft end of the hull  14  in order to optimize the speed and handling of the watercraft  10  when up on plane. For this purpose, the hull  14  generally has a V-shaped configuration formed by a pair of inclined section that extend outwardly from a keel line of the hull to the hull&#39;s side walls at a dead rise angle. The inclined sections also extend longitudinally from the bow toward the transom of the hull  14 . The side walls are generally flat and straight near the stem of the lower hull and smoothly blend towards the longitudinal center of the watercraft at the bow. The lines of intersection between the inclined section and the corresponding side wall form the outer chines of the lower hull section. 
     Toward the transom of the watercraft, the incline sections of the lower hull  14  extend outwardly from a recessed channel or tunnel  19  that extends upward toward the deck  16 . The tunnel  19  has a generally parallelepiped shape and opens through the rear of the transom of the watercraft  10 , as seen in FIG.  2 . 
     A plurality of internal walls within the hull define a plurality of compartments in which various components of the watercraft are located. In this manner, operating noise from the watercraft can be reduced. In the illustrated embodiment, two bulkheads  20 ,  22  (i.e., a fore bulkhead  20  and an aft bulkhead  22 ) divide the inner space within the hull into three compartments: a fore compartment  24 ; an engine compartment  26 ; and an aft compartment  28 . Each bulkhead  20 ,  22  includes at least one connecting pipe  30  that permits adjacent compartments to communicate with each other. The bulkheads  22 ,  24  also include one or more openings  32  through which cables, wires, fuel lines, etc. pass between the compartments. These openings  32  desirably are generally sealed around the cables, wires, lines, etc. passing through the openings  32 , as appreciated from FIG. 1, so that the connecting pipes  30  function as the primary air passage between adjacent chambers. (The cables, wires, lines, etc., which pass through the opening  32  in the aft bulkhead  22 , have been omitted from FIG. 1 in order to simplify the drawing.) 
     As appreciated from FIGS. 1 through 3, the fore bulkhead  20  also includes a pair of side walls  34  integrally formed with the bulkhead  20 . The side walls  34  extend rearward from the outer lateral sides of the fore bulkhead  20  and lie generally parallel to the longitudinal axis of the watercraft  10 . The aft end of the side walls  34  turn outward in the lateral direction and abut a portion of the deck  16 . A suitable adhesive (e.g., an epoxy) joins the fore bulkhead  20 , and its side walls  34 , to an inner side of the deck  16 . 
     Hull liners  36  overlie at least portions of the inclined surfaces of the hull  14 . In the illustrated embodiment, as best seen in FIGS. 1 and 2, each hull liner  36  extends from a point in the fore compartment  20  and terminate at the transom of the hull  14  in the longitudinal direction. In the lateral direction, as best seen in FIG. 3, each hull liner  36  is attached to a side wall of the hull  14  and to an inner surface of a corresponding inclined surface of the hull  14 . The lower ends fore bulkhead  20  and side walls  34  are also connected to the hull liners, as seen in FIG.  3 . The hull liners  36  include several recesses and platforms upon which several components of the watercraft  10  are mounted, as described below. 
     The hull liners  36 , as well as the bulkheads  20 ,  22  (including the side walls  34 ) desirably are formed of the same material as the deck  16  and the hull  14 . In this manner, these components can be affixed together in a manner well known to those skilled in the art. 
     A foam material  38  fills the spaces between the hull liners  36  and the hull  14 , as well as the spaces between the side walls  34  of the fore bulkhead  20  and the deck  16 . In the illustrated embodiment, the foam  38  comprises an expandable urethane foam that can be injected into the spaces. Alternatively, the foam can be pre-molded and placed within the hull  14  before the hull liners  36  and the bulkhead  20  are attached. The foam desirably includes a plurality of air pockets to provide sound insulation as well as floatation. Accordingly, other types of foams can be used as well for this purpose. 
     With reference to FIG. 1, the deck  16  includes a bow portion  40 , a control mast  42  and a rider&#39;s area  44 , as viewed in the direction from the bow to the stern of the watercraft  10 . The bow portion  40  slopes upwardly toward the control mast  42  and includes at least one air duct  46  through which air can enter and/or exit the hull  14 . A hatch cover  48  desirably extends above an upper port of the air duct  46  to inhibit an influx of water into the hull  14 . 
     The air duct  46  communicates with a sub-chamber  50  as well as with one of the compartments within the hull  14 . In the illustrated embodiment, the air duct  46  communicates with the fore compartment  20  through a lower port and with the sub-chamber  50  through a port  52  formed between the lower port and the upper port. The sub-chamber  50  desirably is sized so as to tune the air system to reduce noise emitted through the air intake and cooling system. That is, the sub-chamber  50  is sized such that pressure pulses within the air duct  46  are dissipated within the sub-chamber  50 , which acts as a pressure reducer, similar to a Helmholtz tuning chamber. This system effectively quiets engine noise emitted through the air duct  46 . 
     The sub-chamber  50  also desirably functions as a storage compartment. For this purpose, the sub-chamber  50  is located beneath the hatch cover and has an open upper end. 
     In the illustrated embodiment, the air duct  46  and the sub-chamber  50  are integrally formed as storage insert  54 . The deck  16  includes an opening which receives the storage insert  54 , which depends into the fore chamber  20 . A seal extends about the upper opening of the sub-chamber  50  and the cover to generally inhibit an influx of water into the sub-chamber  50 . The presence of a grating across the port  52  between the duct  46  and the sub-chamber  50 , and the position of the port  52  relative to the bottom of the sub-chamber  50 , inhibits articles within the sub-chamber  52  from entering the air duct  46 . 
     As seen in FIG. 1, the hatch cover  48  includes a front wall  56  that divides the storage compartment (i.e., sub-chamber  50 ) from the upper port of the air duct  46 . This front wall  56  cooperates with the seal. 
     As schematically represented in FIG. 1, air A flows through the air duct  46  into the fore compartment  20 . (Air A can also flow through the air duct  46  in the opposite direction.) A labyrinth is formed beneath the hatch cover  48  to inhibit an influx of water into the air duct  46 . The labyrinth is formed at least in part by the upper end of the air duct  46  extending above the deck surface and by an aft wall  58  that depends from the cover  48  to a point near the level of the upper port of the air duct  46 . Water is also inhibited from entering the air duct  46  by the rearward facing opening to the space formed beneath the hatch cover  46 . 
     The control mast  42  extends from the bow portion  40  and supports a handlebar assembly  60 . The handlebar assembly  60  controls the steering of the watercraft  10  in a conventional manner. The handlebar assembly  60  also carries a variety of controls of the watercraft  10 , such as, for example, a throttle control, a start switch and a lanyard switch. In the illustrated embodiment, a cowling  62 , which covers the deck  16 , forms a portion of the control mast  42 . The deck  16  supports a steering column to which the handlebar assembly  60  is attached, at a point beneath the cowling  62 . 
     A display panel (not shown) desirably is located in front of the control mast  42  on the bow portion  40  and is orientated to be visible by the rider. The display panel desirably displays a number of performance characteristics of the watercraft such as for example, watercraft speed (via a speedometer), engine speed (via a tachometer), fuel level, oil level, engine temperature, battery charge level and the like. 
     The rider&#39;s area  44  lies behind the control mast  42  and includes a seat assembly  64 . In the illustrated embodiment, the seat assembly  64  has a longitudinally extending straddle-type shape that may be straddled by an operator and by at least one, two or three passengers. 
     As best illustrated in FIG. 1, the seat assembly  64  includes a front seat section  66  and a rear seat section  68 . Each seat section  66 ,  68  includes a cushion covered by a water-resilient material and supported by a seat base  70 . The seat base  70  desirably is formed of a light-weight material. 
     Each seat section  66 ,  68  is attached to a pedestal  72  from on the deck  16 . The pedestal  72  includes a pair of side walls  74  and an upper surface  76 . As best seen in FIG. 2, the inner side walls  34  of the fore bulkhead  20  lie adjacent to the outer side walls  74  of the pedestal  72  with the foam insulation  38  filing the space between the corresponding inner and outer side walls  34 ,  74 . The upper ends of the inner side walls  34  are joined to an underside of the corresponding pedestal side wall  74 , and the lower ends of the inner side walls  34  are joined to an upper side of the corresponding hull liner  36 , as described above. 
     The upper surface  76  defines an access opening  78  that opens into the engine compartment  26  and that is defined by an upper rim  80 . The width of the access opening  78  substantially matches the lateral spacing between the upper ends of the pedestal side walls  74 . The upper surface  76  also includes a second opening  82  that opens into the aft compartment  28  and is located near an aft end of the pedestal  72 . 
     The pedestal  72  also includes a cover  84  that extends over the access opening  80 . The cover  84  includes a side flange projecting downward from a peripheral compression surface  86 . The cover  84  also includes one or more access holes  88  sealed by a plug  90 . The access holes  88  are located above the engine compartment  26 . 
     A seal  92  extends about the access opening  78  and lies between the cover  84  and the upper rim  80 . The seal  92  desirably is affixed either to the rim  80  or to the cover  84  to permit removal and reattachment of the cover  84  without repositioning the seal  92  each time cover  84  is removed. 
     In the illustrated embodiment, a latch assembly  94  secures the cover  84  to the pedestal walls  74  and compresses the seal  92  between the pedestal rim  80  and the cover compression surface  86 . The latch assembly  94  desirably includes a plurality of latches spaced along each side of the cover  84 . Other types of mechanisms, however, can be used as well to secure the cover  84  to the pedestal walls  74  and/or to the upper surface  76  of the pedestal  72 , and to compress the seal  92  between the cover  84  and the pedestal rim  80  or side walls  74 . 
     As best seen in FIG. 1, a rear end of the front seat section  66  is secured to cover  84  by a seat latch  96 . The seat latch  96  desirably is located beneath the rear seat section  68  and cannot be removed without removing the rear seat section  68  first. The front end of the front seat section  66  includes one or more an planar extensions  98  that fit within a receptacle  100 . The receptacle  100  is formed on the deck  16  between a portion of the deck  16  and a bracket  102  affixed to the deck  16 . The interaction between the extension(s)  98  and the receptacle  100  inhibit lateral and transverse (i.e., vertical) movement of the front seat section front end. 
     As appreciated from FIGS. 1,  3  and  4 , the seat base  70  of the front seat section  66  includes a plurality of recesses  104  that form air pockets between the seat base  70  and the cover  84 . And as seen in FIG. 4, another air pocket is formed between the upper pedestal surface  76  and the cover  84  on the aft side of the access opening  78 . These air pockets provide sound insulation on the upper side of the engine and aft compartments  26 ,  28 . 
     The rear seat section  68  is attached to the upper surface  76  of the seat pedestal  72  by a latch assembly  106 , as seen in FIG. 1, and also includes a plurality of recesses  108 , as seen in FIGS. 1 and 5. These recesses  108  form air pockets between the seat base  70  and the pedestal upper surface  76 , and provide sound insulation on the upper side of aft compartment  28 . The recesses  108  also provide an air flow path beneath the rear seat section  68 . 
     A storage insert  110  is located within the aft opening  82  on the upper surface  76  of the pedestal  72 . Like the front storage insert  54 , the aft storage insert  110  includes a storage compartment  112  and an air duct  114 . The air duct includes an upper port, a lower port, and an opening  116  that communicates with the storage compartment  112 . The opening  116  is located between the upper and lower ports and includes grating to prevent object within the storage compartment  112  from passing into the air duct  114 . 
     The upper port of the air duct  114  is located behind the storage compartment  112  and beneath the second seat section  68 . The air duct  114  communicates with ambient air through its upper port and through one of the recesses  108  formed on the underside of the rear seat section  68 , as described above. Like the front air duct  46 , air A can flow in both directions through the air duct  114  in order to supply ambient air to the engine compartment  26 , as well as provide a flow of air through the engine compartment  26  and through the aft compartment  28  for cooling purposes. The rearward opening direction of the lower port promotes a circulation of air flow through the aft compartment  28 . 
     The storage compartment desirably is sized so as to tune the air system to reduce noise emitted through the air intake and cooling system. That is, the storage compartment  112  is sized such that pressure pulses within the air duct  114  are dissipated within the storage compartment  112 , which acts as a pressure reducer, similar to a Helmholtz tuning chamber. This system thus effectively quiets engine and exhaust system noise emitted through the air duct  114 . 
     The deck  16  of the hull body  12  includes a pair of raised gunnels  116  (FIGS. 2 and 3) positioned on opposite sides of the aft end of the deck  16 . The raised gunnels  116  define a pair of foot areas or wells  118  that extend generally longitudinally and parallel to the sides of the pedestal  72 . In this position, the operator and any passengers sitting on the seat assembly can place their feet in the foot areas  118  with the raised gunnels  116  shielding the feet and lower legs of the riders. A non-slip (e.g., rubber) mat desirably covers the foot areas  118  to provide increased grip and traction for the operator and the passengers. 
     With reference to FIG. 1, a fuel tank  120  is located within the fore compartment  24  of the hull  14  beneath the hatch cover  48 . Conventional means, such as, for example, straps, secure the fuel tank  120  to the lower hull  16 . In addition, as seen in FIG. 1, each hull insert  36  includes a recess  122  that corresponds to the lower shape of the fuel tank  120 . A plurality of mounts support the tank  120  within the recesses  122  of the hull inserts  36 . 
     A fuel filler hose (not shown) extends between a fuel cap assembly and the fuel tank  120 . In the illustrated embodiment, the filler cap assembly (not shown) is secured to the bow portion of the hull upper deck  16  to the side and in front of the control mast. In this manner, the fuel tank  120  can be filled with fuel F from outside the watercraft body  12  with the fuel F passing through the fuel filler hose into the tank  120 . 
     A propulsion system  124  propels the watercraft  10 . The propulsion system  124  comprises an engine  126  that drives a jet pump unit  128 . The engine  126  is located in the engine compartment  26 , while the jet pump unit  128  is mounted within the tunnel  19  formed on the underside of the hull  14  by a plurality of bolt. 
     As appreciated in FIG. 2, an intake duct of the jet pump unit  128  defines an inlet opening that opens into a gullet of the intake duct. The intake duct leads to an impeller housing assembly in which the impeller  130  of the jet pump unit  128  operates. An impeller housing assembly also acts as a pressurization chamber and delivers the water flow from the impeller housing to a discharge nozzle  132 . 
     A steering nozzle  134  is supported at the downstream end of the discharge nozzle  132  by a pair of vertically extending pivot pins. In an exemplary embodiment, the steering nozzle has an integral lever on one side that is coupled to the handlebar assembly  60  through, for example, a bowden-wire actuator, as known in the art. In this manner, the operator of the watercraft  10  can move the steering nozzle  134  to effect directional changes of the watercraft  10 . 
     As seen in FIG. 5, a ride plate  136  covers a portion of the tunnel  19  behind the inlet opening to enclose the jet pump unit  128  with the tunnel  19 . In this manner, the lower opening of the tunnel  19  is closed to provide a planing surface for the watercraft  10 . 
     An impeller shaft  138  (FIG. 2) supports the impeller  130  within the impeller housing of the jet pump unit  128 . The aft end of the impeller shaft  138  is suitable supported and journalled within the compression chamber of the jet pump unit  128  in a known manner. The impeller shaft  138  extends in the forward direction through a front wall of the tunnel  19  and through the aft bulkhead  22 . 
     The internal combustion engine  126  of the watercraft  10  powers the impeller shaft  138  to drive the impeller  130  of the jet pump unit  128 . As seen in FIGS. 1 through 3, the engine  126  is positioned within the engine compartment  26  and is mounted behind the control mast  42 , beneath the seat assembly  64 . Vibration-absorbing engine mounts  140  (FIG. 3) secure the engine to bosses on the hull inserts  36 . The engine  126  is mounted in approximately a central position in the watercraft  10 . This construction, in which the engine  126  is mounted onto the foam-insulated hull inserts  36 , thus further decouples the hull  14  from engine vibration and noise. 
     In the illustrated embodiment, the engine  126  includes three in-line cylinders and operates on a two-stroke, crankcase compression principle. The engine is positioned such that the row of cylinders lies parallel to a longitudinal axis of the watercraft  10 , running from bow to stern. The axis of each cylinder is generally parallel relative to a vertical central plane of the watercraft  10 , in which the longitudinal axis lies. In this position, the engine  126  lies completely beneath the access opening  78  to facilitate removal of the engine  126  from the watercraft  10 . That is, the lateral size of the access opening  78  is wider than the lateral width of the engine  126 , as seen in FIG.  3 . This engine type, however, is merely exemplary. Those skilled in the art will readily appreciate that the present seat design and engine component layout can be used with a variety of engine types having other number of cylinders, having other cylinder arrangements (e.g., inclined) and operating on other combustion principles (e.g., four-stroke principle). 
     As best seen in FIG. 3, a cylinder block  142  and a cylinder head assembly  144  desirably form the cylinders of the engine  126  A piston (not shown) reciprocates within each cylinder of the engine  126  and together the pistons drive an output shaft  146 , such as a crankshaft, in a known manner. A connecting rod (not shown) links the corresponding piston to the crankshaft  146 . The corresponding cylinder bore, piston and cylinder head of each cylinder forms a variable-volume chamber, which at a minimum volume defines a combustion chamber. A coupling  148  couples the crankshaft  146  to the impeller shaft  138 , as best seen in FIG.  2 . 
     A plurality of spark plugs are mounted in the cylinder head  144  with each spark plug corresponding to one of the cylinders. As appreciated from FIG. 3, the accessing holes  88  in the cover  84  preferably correspond to the position of the spark plugs to permit replacement of the spark plugs without removal of the cover  84 . 
     The crankshaft  146  desirably is journaled with a crankcase  150 , which in the illustrated embodiment is formed between a crankcase member and a lower end of the cylinder block. Individual crankcase chambers of the engine are formed within the crankcase by dividing walls and sealing disks, and are sealed from one another with each crankcase chamber communicating with a dedicated variable-volume chamber. 
     Each crankcase chamber also communicates with an intake pipe  152  of an induction system of the engine through a check valve (e.g., a reed-type valve). In the illustrated embodiment, the intake pipes  152  are separate from the crankcase and from each other; however, the engine  126  can use an intake manifold equally well, or can integrally form the intake pipes with the crankcase member. 
     A plurality of charge formers  154  (e.g., a carburetor) of the induction system communicate with inlet ends of the corresponding intake pipes  152 . The charge formers  154  receive fuel from the fuel tank  120  and produces the fuel charge which is delivered to the cylinders in a known manner. An air intake silencer or plenum chamber  156  of the induction system is connected to an air inlet end of a throttle passage of each charge former  154 . 
     An exhaust system  158  discharges exhaust byproducts from the engine  126  to the atmosphere and/or to the body of water in which the watercraft  10  is operated. As best seen in FIGS. 1,  2  and  4 , the exhaust system includes the exhaust manifold that is affixed to the side of the cylinder block  142  and which receives exhaust gases from the combustion chambers through exhaust ports in a well-known manner. For this purpose, the exhaust manifold desirably includes a number of runners equal in number to the number of cylinders. Each runner communicates with the exhaust port(s) of the respective cylinder. The runners of the exhaust manifold thence merge together at a merge point to form a common exhaust path that terminates at an outlet end of the manifold. 
     An outlet end of the exhaust manifold communicates with an exhaust expansion chamber  160 . The outlet end of the manifold turns upward to mate with a down-turned inlet end of the expansion chamber  160 . 
     The expansion chamber  160  turns downward and communicates with a connection pipe  162 . As best understood from FIGS. 1,  3  and  4 , the connection pipe  162  extends outward in a lateral direction and then turns aft. In doing so, the connection pipe  162  extends through the near hull insert  36  and lies within the space formed between the hull  14  and the hull insert  36 . Insulation material  38  surrounds at least a portion of the connection pipe  162  to silence exhaust noises from the connection pipe  162 . Such insulation  38  is important because of the close spacing of the connection pipe  162  to the wall of the hull  14 . The insulation  38  also enhances heat resistance at this location of the watercraft hull  14 . 
     The downstream end of the connection pipe  162  communicates with a water trap  164 . The water trap  164  includes a generally cylindrical body  166  that resides within a recess  168  formed within the hull inserts  36 . As best seen in FIG. 5, the hull insert  36  includes a generally semi-cylindrical indentation  168  that forms a cradle. An elastic insulation layer  170  lines the surface of the cradle recess  168  with the water trap body set on top the insulation layer  170 . Desirably, this layer  170  generally thermally and vibrationally decouples the water trap  164  from the hull  14 . Alternatively, standoff mounts can support the water trap body  166  relative to the cradle recess  168 . One or more elastic straps, which are secured to the lower hull portion  14  by bolts  118 , hold the water trap body  166  within the recess cradle  168 . 
     The water trap device  164  has a sufficient volume to retain water and to preclude the back flow of water to the expansion chamber  160  and the engine  126 . Internal baffles within the water trap device  164  help control water flow through the exhaust system  158 . 
     An exhaust discharge pipe  172  extends from an outlet section of the water trap device  164  and wraps over the top of the tunnel  19  to a discharge end  174 . As seen in FIG. 5, an insulation cover surrounds at least a portion of the discharge pipe  172 . The discharge end  174  desirably opens into the tunnel  19  or through the transom of the watercraft  10  at an area that is close to or actually below the water level with the watercraft  10  floating at rest on the body of water. 
     As will be appreciated by one skilled in the art, the various sound insulating techniques described above can be used either alone or together. For instance, seat construction need not be used with in insulation material; however, enhanced noise dampening can be obtained by insulating the sides of the pedestal, the lower hull walls and the lower side of the seat in the manners described above. Thus, the air pockets, foam insulation between the inner and outer walls of the pedestal, and the foam insulation between the hull inserts and the hull surfaces all contribute to improving the sound insulation of the engine compartment and the aft compartment. Additional sound attenuation is achieved by the air supply and cooling system including sub-resonant chambers and by insulating at least a portion of the exhaust system. 
     Although this invention has been described in terms of a certain preferred embodiment, other embodiments apparent to those of ordinary skill in the art are also within the scope of this invention. Accordingly, the scope of the invention is intended to be defined only by the claims that follow.