Abstract:
An axial-flow outboard water jet propulsion unit is designed so that it does not extend below the bottom of the boat hull, but rather is disposed directly behind the hull transom. This is achieved by arranging the impeller shaft generally perpendicular to a generally vertical drive shaft, and by installing the impeller in a flow-through duct which, although placed directly behind the transom, has an inlet for taking in water located directly below the impeller shaft. The duct does not extend to a depth lower than the lowest point of the hull bottom. The impeller shaft penetrates the duct wall, while the impeller itself is rotatable inside the duct. The impeller impels water rearward toward a convergent exit nozzle of the duct, sucking in water through the duct intake. The aft opening of the exit nozzle forms the duct discharge outlet.

Description:
FIELD OF THE INVENTION 
     This invention generally relates to water jet propulsion systems for propelling boats or other watercraft. In particular, the invention relates to outboard water jet propulsion units comprising an engine and a ducted impeller driven by the engine. 
     BACKGROUND OF THE INVENTION 
     Jet-powered boats can be categorized in part in accordance with the types of propulsion systems used. The powerhead can be mounted either inside the hull or outside the hull. In the latter case, the powerhead is mounted on the transom portion of the boat hull and is detachable. Another type of system, called stern drive system, and sometimes referred to as an inboard-outboard system, utilizes a powerhead mounted inside the hull of the boat with a portion of the drive unit extending through the transom. These systems create thrust through rotation of a ducted impeller, which draws water from ahead and impels the water rearward to propel the boat forward. 
     To facilitate use of water jet-propelled boats in shallow water, it is known to mount the ducted impeller at an elevation such that the propulsion system does not project below the bottom of the boat hull. This can be accomplished, for example, by installing a duct in the stern of the boat, the duct being arranged to connect one or more inlet holes formed in the bottom of the hull with an outlet hole formed in the transom. The water jet is then installed outside the hull in a position such that the water jet inlet is in fluid communication with the duct outlet at the transom. Alternatively, a water tunnel is formed in the bottom of the hull which is open at the bottom and at the transom. A water jet propulsion system is then mounted to the transom by means of a mounting adapter, the inlet of the propulsion system being in fluid communication with the water tunnel via the adapter. 
     The use of outboard water jet propulsion units is not new to the marine industry. However, the majority of these applications utilize a centrifugal pump, which allows the propulsion unit to be designed so that it does not extend below the hull bottom. An axial-flow pump is disclosed in U.S. Pat. No. 3,842,787. However, the inlet duct of that system extends below the hull bottom. 
     There is a need for an axial-flow outboard water jet propulsion unit which does not extend below the hull bottom. 
     As used herein, the term “axial-flow pump” means a ducted impeller in which the water is impelled in a direction generally parallel to the axis of impeller rotation. This is in contrast to a centrifugal pump, in which water is impelled radially outward in directions perpendicular to the axis of impeller rotation. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an outboard water jet propulsion unit comprising an axial-flow pump. Preferably the water jet propulsion unit is designed so that it does not extend below the bottom of the boat hull, but rather is disposed directly behind the hull transom. This is achieved by arranging the impeller shaft generally perpendicular to a generally vertical drive shaft, and by installing the impeller in a flow-through duct which, although placed directly behind the transom, has an inlet for taking in water located directly below the impeller shaft. In the preferred embodiment of the invention, the duct does not extend to a depth lower than the lowest point of the hull bottom. The impeller shaft penetrates the duct wall, while the impeller itself is rotatable inside the duct. The impeller impels water rearward toward a convergent exit nozzle of the duct, sucking in water through the duct intake. The aft opening of the exit nozzle forms the duct discharge outlet. 
     In accordance with the preferred embodiment of the invention, the propulsion unit comprises: an engine support housing; an engine supported by the engine support housing; a drive shaft having one end coupled to the engine; an inlet housing attached to and located beneath the engine support housing; and an outlet housing attached to the rear of the inlet housing. The inlet housing comprises a flow-through passage having an inlet and an outlet. The outlet housing comprises a flow-through passage in fluid communication with the inlet housing passage. Preferably, the outlet housing passages converges toward an outlet. The inlet and outlet housings form a duct. In addition, the propulsion unit may comprises: an impeller shaft which penetrates a wall of the inlet housing; an impeller mounted to the impeller shaft and rotatable within the inlet housing passage; bearings for rotatably supporting the shafts; and gears for converting rotation of the drive shaft into rotation of the impeller shaft. The impeller shaft is generally perpendicular to the drive shaft, and the inlet of the inlet housing lies underneath the impeller shaft. 
     In accordance with a further feature of the preferred embodiment, the engine support housing, the inlet housing and the outlet housing each comprise a respective exhaust gas passage. These exhaust gas passages are connected in series so that exhaust gas from the engine is discharged below the waterline. 
     In accordance with another feature of the preferred embodiment, the gears are housed in a gear housing which is integrally formed with the inlet housing. 
     In addition, a steering nozzle is pivotably mounted to the exit nozzle. The steering nozzle is pivotable about an axis which is generally perpendicular to the impeller shaft. Because the boat can be steered by turning the steering nozzle, the outboard water jet propulsion unit does not need to be pivotable about a vertical axis, thereby simplifying the mounting of the outboard propulsion unit to the boat hull. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic showing an isometric view of an outboard water jet propulsion unit in accordance with the preferred embodiment of the invention. 
     FIG. 2 is a schematic showing an exploded view of a jet pump unit incorporated in the outboard water jet propulsion unit shown in FIG.  1 . 
     FIG. 3 is a schematic showing an exploded view of the outboard water jet propulsion unit shown in FIG. 1, with the axial-flow jet pump unit assembled. 
     FIG. 4 is a schematic showing a partially sectioned view of the outboard water jet propulsion unit in accordance with the preferred embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An outboard water jet propulsion unit  10 , in accordance with the preferred embodiment of the invention, is shown in FIG. 1, mounted to a hull transom  12 . As will be explained in more detail below with reference to exploded and sectional views of the system, the engine (not visible behind motor cover  14  in FIG. 1) is mounted on and supported by an exhaust housing  16 , while the inlet/gear housing  18  is located below and supported by the exhaust housing  16 . The exhaust housing comprises a pair of support arms  30 , by means of which the exhaust housing (and the entire unit) can be hung on the top edge of the hull transom  12 . The water intake is located at the bottom of the inlet/gear housing  18  and is not visible in FIG.  1 . An outlet housing  20  is attached to the rear face of the inlet housing. Preferably the outlet housing comprises a convergent exit nozzle for increasing the pressure of the water discharge. 
     A steering nozzle  22  is pivotably mounted to the exit nozzle by means of a pair of pivot pins  24  (only one of which is visible in FIG. 1) which are coaxial with a vertical axis. This allows the steering nozzle to be pivoted from side to side for directing thrust to one side or the other for the purpose of steering the boat. The water exiting the steering nozzle creates a reaction force which propels the boat forward. The angular position of steering nozzle  22  is controlled by a steering rod  23 , which is pivotably coupled to a clevis at the end of a lateral steering arm  25 . The water flow exiting the steering nozzle  22  can be reversed by activation of a conventional reverse gate  28 , which is actuated by a shift rod not shown. The reverse gate  28  blocks the rearward discharge of water from the steering nozzle outlet and redirects it througth a slot and out a flow-reversing passage  26  with a forward (instead of rearward) velocity component. The steering nozzle  22 , steering arm  25  and flow-reversing passage  26  are preferably formed as one cast metal piece. The levers, rods and tables for actuating the shift and steering rods from a remote location, e.g., the cockpit of the boat, although not shown in FIG. 1, are conventional structures which penetrate the hull transom in well-known manner. 
     Optionally, a rigid U-shaped bar  32  can be fixedly installed to serve as a bumper for preventing objects from impacting or colliding with the steering nozzle and reverse gate. 
     The disassembled axial-flow pump unit is shown in FIG.  2 . The inlet/gear housing  18  comprises a chamber for housing the gear and bearing assemblies, as well as a water tunnel having an inlet (not visible in FIG. 2) formed in the bottom of the housing and an outlet  34  formed in the rear face of the housing. The inlet/gear housing  18  is further provided with an opening  36  in its top face and an opening  38  in its forward face for respectively receiving a bearing head  40  of a vertical drive shaft assembly and a bearing head  42  of a horizontal impeller shaft assembly. In addition, the inlet/gear housing  18  comprises a pair of exhaust gas outlets  44 , formed in the rear face, which communicate with an exhaust gas inlet  46 , formed in the top face. The top face of the inlet/gear housing  18  further comprises a plurality of throughholes for receiving a corresponding plurality of fasteners for attaching the inlet/gear housing to the exhaust housing (not shown in FIG.  2 ). 
     The outlet housing  20  comprises a mounting flange  48  with throughholes for receiving fasteners for attaching the outlet housing to the rear face of the inlet/gear housing. The outlet housing converges in the rearward direction to form an exit nozzle having a discharge outlet  50 . A pair of bosses  52  are integrally formed on the outside of the exit nozzle to provide reinforcement around the holes which respectively receive the steering pivot pins  24 . Also, a pair of exhaust gas passages  54  (only one of which is visible in FIG. 2) are integrally formed as parts of the outlet housing  20 . Each exhaust gas passage  54  has an inlet connected to a respective exhaust gas outlet  44  of the inlet/gear housing  18 , and an outlet  56  (only one of which is visible in FIG.  2 ). 
     As shown in FIG. 2, the steering nozzle  22  comprises a pair of pivot arms  58  which have apertures for penetration by the pivot pins  24  and a lateral steering arm (shown in FIG. 1 only). The steering nozzle can be pivoted about the axis of pins  24  (by pulling and pushing on the lateral steering arm) to produce lateral steering thrust. A pair of bosses  60  are formed on the sides of the exterior of the steering nozzle  22 . The bosses  60  provide reinforcement for threaded holes which respectively receive a pair of reverse pivot pins  62 . The reverse pivot pins  62  are coaxial with a horizontal axis. The reverse gate is pivotable up and down about the reverse pivot pins  62 . 
     The components for the vertical drive shaft assembly and the horizontal impeller shaft assembly are also shown in FIG.  2 . The drive and impeller shaft assemblies (assembled using the components depicted in FIG. 2) are shown in FIG.  4 . The following description of the drive and impeller shaft assemblies should be read with reference to both FIGS. 2 and 4. 
     In accordance with the preferred embodiment of the invention, the vertical drive shaft assembly comprises a generally vertical drive shaft  64  having one end coupled to the output shaft of the engine (not shown) and the other end having a pinion gear  66  coupled thereto. For example, a splined end of the drive shaft  64  may be inserted in a splined recess formed in the pinion gear  66 . The pinion gear  66  is rotatably supported by bearing  68  which is held in bearing head  40 . A thrust bearing  70  is installed between the pinion gear  66  and the bearing head  40 . The bearing head  40  is bolted to the top face of the inlet/gear housing  18  and has a small-diameter portion which sits in the opening  36 . The interface of the small-diameter portion of the bearing head  40  and the edge of the opening  36  is sealed by an O-ring  72 . A pair of lip seals  74  are placed between the drive shaft  64  and the bearing head  40 . 
     Again referring to both FIGS. 2 and 4, the horizontal impeller shaft assembly comprises a generally horizontal impeller shaft  76  having a bevel gear  78  coupled to one end and an impeller  80  coupled near the other end. The hub and blades of the impeller  80  are integrally formed as one cast piece. The impeller  80  rotates in unison with the impeller shaft  76 . The outer surface of the impeller hub forms the radially inner boundary for guiding the flow of water impelled by the impeller. The impeller  80  may be screwed onto a threaded portion of the impeller shaft  76 , while a splined end of the impeller shaft  76  is inserted in a splined recess formed in the bevel gear  78 . The chamber for the gear and bearing assemblies and the water tunnel of the inlet/gear housing  18  share a common interior wall  41  which is penetrated by the impeller shaft  76 . The impeller shaft penetration is sealed by a seal  77 . 
     The bevel gear  78  is rotatably supported by bearing  82  which is held in bearing head  42 . A thrust bearing  86  is installed between the bevel gear  78  and the bearing head  42 . The bearing head  42  is bolted to the front face of the inlet/gear housing  18  and has a small-diameter portion which sits in the opening  38 . The interface of the small-diameter portion of the bearing head  42  and the edge of the opening  38  is sealed by an O-ring  84 . 
     As seen in FIG. 4, typically the outlet housing  48  comprises a plurality of stator vanes  88  extending radially from a stator hub  90  to the outer shell of the housing. The stator hub  90  comprises a bearing housing  92  which houses a sealed bearing  94  for rotatably supporting the end of the impeller shaft  76 . The stator vanes  88  are designed to redirect the swirling flow out of the impeller  80  into non-swirling flow. The straightened flow exits the outlet housing  48  via a convergent thrust nozzle, which increases the water pressure. 
     As seen in FIG. 4, the beveled teeth of bevel gear  66  intermesh with the beveled teeth of bevel gear  78 , thereby coupling the impeller shaft  76  to the drive shaft  64 . This beveled tooth coupling converts the rotation about the axis of the drive shaft into rotation about the axis of the impeller shaft. These axes are preferably generally vertical and generally horizontal respectively so that the water discharge is directed generally horizontally. However, a person skilled in the art will readily appreciate that if, for design reasons, the axis of the impeller shaft deviates from true horizontal, the steering nozzle can be designed to compensate for that by fabricating the water passage of the steering nozzle such that its centerline deviates from perpendicularity with the pivot axis (and deviates from parallelism with the impeller shaft axis) by the same angle of deviation. In that case the centerline axis of the steering nozzle will be horizontal even though the impeller shaft axis is not, ensuring that the water is discharged in a horizontal direction. 
     The separate components shown in FIG. 2 are assembled into the pump unit generally designated with the numeral  100  in FIG.  3 . The assembled pump unit  100  is in turn attached to the exhaust housing  16  by fasteners (not shown). The exhaust housing  16  has a vertical passage for the vertical drive shaft  64 , the top of which penetrates an opening  114  in the top face of the exhaust housing. To attach the assembled pump unit  100  to the exhaust housing  16 , vertical drive shaft  64  must be aligned with the opening  114  and then lowered onto the pump unit until the bottom face of the exhaust housing sits on top of the top face of the inlet/gear housing  18 . As seen in FIG. 3, the top face of the inlet/gear housing has four threaded bores  102  which align with corresponding bores  104  in opposing recessed side flanges  106  of the exhaust housing  16 . A pair of recesses  108  formed near the bottom on opposing sides of the exhaust housing (only one of which is visible in FIG. 3) provide clearance for insertion and torquing of bolts (not shown) for attaching the assembled pump unit  100  to the exhaust housing  16 . Similarly, a pair of recesses  110  formed near the top on opposing sides of the exhaust housing (only one of which is visible in FIG. 3) provide clearance for insertion and torquing of bolts (not shown) for attaching the engine (not shown) to the exhaust housing  16 . 
     Referring to FIG. 4, the exhaust housing  16  also has an exhaust gas passage  112  which runs from an opening  116  in the top face of the exhaust housing to an opening  118  in the bottom face of the exhaust housing. The opening  116  in the top face of the exhaust housing is in fluid communication with an exhaust port (not shown) of the engine. The opening  118  in the bottom face of the exhaust housing is aligned with the opening  46  (see FIG. 3) in the top face of the inlet/gear housing  18 . Consequently, the exhaust gas passage  112  is in fluid communication with the exhaust gas passage of the inlet/gear housing  18 . The latter is in turn in fluid communication with the exhaust gas passages  54  on opposing sides of the outlet housing  20 . Thus exhaust gases from the engine flow through the connected exhaust gas passages and out the outlets  56  on the outlet housing  20 . When the boat is in the water, the outlets  56  are below the waterline. 
     The exhaust housing  16  also has a vertical water passage  136  for providing cooling water to the engine. The bottom of the water passage  136  is in flow communication with an opening  138  in the stator housing  20 . Cooling water is forced upward from the water passage in stator housing  20  by the impeller  80  in a well-known manner. 
     After the assembled pump unit  100  has been attached to the exhaust housing  16 , the entire assembly can be mounted to the hull transom of a boat. First, a thrust bracket  120  is bolted on the back of the transom  12 . The thrust bracket  120  comprises a flat mounting plate  122  which lies flat against the transom and a pair of side thrust walls  124  which are generally parallel to each other and perpendicular to the mounting plate  122 . The engine housing  16  has a pair of recesses  126  on opposing sides (only one of which is visible in FIG.  3 ). The side thrust walls  124  fit in the corresponding recesses  126 . The distance separating the opposing surfaces of the side thrust walls  124  is only slightly greater than the width of the exhaust housing  16  as measured across the recessed front portion. 
     After the thrust bracket  120  has been mounted to the transom  12 , a pair of mounting brackets  128  (only one of which is shown in FIG. 3) are bolted to the inner face of the upper portion of the hull transom  12 , as best seen in FIG.  4 . Each mounting bracket  128  comprises a lower portion with holes for bolts and an upper portion with a transverse hole  132  for receiving a respective end of a tilt pivot tube or rod  130 . The mounting brackets  128  are positioned so that the upper portions protrude above the top edge of the hull transom  12 , with the transverse holes  132  being coaxial. The exhaust housing  16  is positioned so that the holes  134  in support arms  30  are aligned with the transverse holes  132  in the mounting brackets  128 . The tilt pivot tube  130  is then passed through aligned holes  132  and  134  and fastened in place by means of threaded nuts (not shown). 
     After the exhaust housing with attached pump unit has been mounted to the hull, the engine can be lowered into place atop the exhaust housing and then bolted in place. The engine crankshaft is coupled to the drive shaft  64  and the engine exhaust port is aligned with the opening  116  of the exhaust gas passage  112 . 
     In accordance with the arrangement shown in FIG. 4, the entire water jet propulsion unit, when not latched in place, can be swiveled upward about the axis of the tilt pivot tube  130 . In the down position, the water jet propulsion unit is laterally restrained by the side thrust walls  124  of the thrust bracket  120 . 
     While the invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation to the teachings of the invention without departing from the essential scope thereof. Therefore it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. 
     As used in the claims, the term “duct” means a fluid flow passage having an inlet and an outlet, the duct being formed by a single housing or a multiplicity of housings connected in series.