Patent Publication Number: US-2006014445-A1

Title: Outboard jet drive marine propulsion system and control lever therefor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This Application is a Non-Provisional of Provisional (35 USC 119(e)) Application No. 60/574,019 filed on May 25, 2004 and Application No. 60/653,652 filed on Feb. 16, 2005. 
    
    
     BACKGROUND OF THE INVENTION  
      This invention relates to outboard jet drive marine propulsion systems. The present invention relates to an outboard jet drive for a boat and especially to an outboard jet drive having an engine and jet drive mounted in a housing, which is removably attached to a boat hull.  
      There have been several proposed types of outboard jet drives for watercraft but most are similar to an outboard motor in which the outboard motor propeller and lower unit have been replaced with a jet drive. The jet drive includes a jet pump in the lower unit that operates to provide propulsion force for a watercraft. There are advantages in employing jet pumps for propulsion units as opposed to propellers. The jet drive permits operation in shallower water, also the propeller is shrouded, and there is less likelihood of injury. There has been a variety of proposed constructions for outboard jet drives for positioning the jet pump in different positions relative to the hull transom and bottom of the transom but in a typical jet drive, the engine and jet drive are located directly in the hull with an opening in the bottom of the hull for capturing water passing under the hull and then utilizing the jet pumps to thrust the water out the rear of the hull to propel the boat. Outboard jet drive units are made similar to typical outboard motors with a motor driving a drive unit, which operates a jet drive unit.  
      Generally, the engine package includes an internal combustion engine mounted in a thin fiberglass hull. The base plate of the hull includes a water inlet scoop for feeding water to the pump and an exhaust port for exhausting the water. The pumps high-pressure water outlet is pointed in the aft direction above the water line to propel the craft by the reaction force resulting from the high velocity water jet. In the F. C. Clark U.S. Pat. No. 3,055,175, a marine propulsion unit takes a conventional outboard motor and replaces the prop unit with a marine jet motor using a pump to issue a jet of water to propel a boat. The Parker U.S. Pat. No. 5,356,319, is for a boat with a removably inboard jet propulsion unit in which the integral jet power unit is encased in a waterproof housing and positioned in a well located in the hull and is mounted to be removed from the hull.  
      A well matched water jet allows a diesel engine nearly ideal working conditions for reliability, fuel economy and performance in any planing boat, up to 50 mph; however until now this has only been demonstrated on larger vessels. This is evidenced by an increasing number of larger vessels seen using diesel jet propulsion while very few diesel jets are seen on smaller vessels. The weight of the diesel engine, gearbox and jet, coupled with the traditional inline installation make it much more difficult to properly match a waterjet with a diesel engine in a small vessel.  
      Many of the shortcomings of the prior art were overcome by Applicant&#39;s U.S. Pat. No. 6,398,600 in which an outboard jet propulsion unit is detachably mounted to a boat so that the main fuel tank and controls are mounted within the hull of a boat while the outboard jet drive unit is mounted away from the boat in a housing with an engine and is removably attached to the transom of the boat. The fuel tank and controls are connected between the hull and outboard drive through quick disconnect couplings. The housing is shaped to support an engine on a platform directly over the jet drive unit for actuating the jet drive unit through a clutch mechanism with the engine and jet drive positioned parallel to each other.  
      Over many years, the reliability of inboard diesel engines (the most reliable method of marine propulsion) in pleasure boat use has been documented. Approximately 30% of engine failure is raw water pump related, 30% is due to water ingression from exhaust risers or engine height, and 30% of failures are installation related. It is very hard to guarantee the reliability of individually fitted engines regardless of how adept or experienced the installer is. Less than 10% of all pleasure boat engine failures are deemed engine or component failure.  
      The outboard jet unit as designed by Applicant was satisfactory, however, it did not fully realize the efficiencies of jet propulsion. Accordingly, an outboard jet propulsion unit, which overcomes the deficiencies of the prior art, is desired.  
     BRIEF SUMMARY OF THE INVENTION  
      An outboard jet drive includes a housing sealed against the intrusion of water, the housing having front and rear sides and a top and bottom. An engine is disposed in the housing, supported generally horizontally within the housing, and a jet drive unit is disposed in said housing. The jet drive housing is shaped so that at least the bottom surface, when submerged in water, creates a high-pressure area along the bottom of the housing.  
      In a preferred embodiment, the jet drive unit includes an exhaust for exhausting a water jet. A bucket mechanism is mounted at the water exhaust, the bucket mechanism includes a housing disposed on said jet drive, which communicates with a water jet exiting said jet drive unit. The housing has a first exhaust and a second exhaust and a bucket member movably attached to the housing to selectively cause the water jet to either exit through the first exhaust or the second exhaust.  
      In yet another embodiment, the housing includes a heat exchange unit, which is vertically disposed within the housing. The heat exchange unit allows automatic draining of water from the heat exchangers.  
      In yet another embodiment of the invention, a stabilizing structure is provided to support a jet drive unit internally of the housing to reduce excessive vibration of the jet unit thereby reducing wear and tear. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Other objects, features, and advantages of the present invention will be apparent from the written description and the drawings in which:  
       FIG. 1  is a sectional view taken through an outboard jet drive as mounted on a boat in accordance with the present invention;  
       FIG. 2  is a sectional view of an outboard jet drive housing having a jet drive unit mounted therein;  
       FIG. 3  is a rear elevation of the jet drive unit of  FIG. 2 ;  
       FIG. 4  is a block diagram of the connected fuel tanks;  
       FIG. 5  is an elevation view of a drive assembly for an outboard jet drive constructed in accordance with the invention;  
       FIG. 6 a  rear elevation view of an outboard jet drive housing constructed without the jet drive housing attached thereto;  
       FIG. 7  is a drive shaft housing constructed in accordance with the invention;  
       FIG. 8  is a perspective view of a jet drive housing constructed in accordance with the invention;  
       FIG. 9  is a perspective view of a drive shaft support assembly mounted within said housing in accordance with the invention;  
       FIG. 10  is a side elevation view of another embodiment of the invention in which a bucket assembly is mounted on the jet drive unit in accordance with the invention;  
       FIG. 11  is a side elevation view of the bucket assembly in the open position;  
       FIG. 12  is a side elevation view of the bucket assembly in the closed position;  
       FIG. 13  is a sectional view of a saddle assembly for supporting the bucket assembly;  
       FIG. 14  is a side elevation view of a control assembly for the bucket in the open position;  
       FIG. 15  is a side elevation view of a control assembly for the bucket in the closed position;  
       FIG. 16  is a top plan view of the bucket assembly;  
       FIG. 17  is a top plan view of a bucket assembly steering a boat to the left;  
       FIG. 18  is a top plan view of a bucket assembly steering a boat to the right;  
       FIG. 19  is a schematic view of the bottom of the housing showing relative water and airflow;  
       FIG. 20  is a schematic diagram showing the relative widths of the jet inlets and convex portion of the housing;  
      FIGS.  21 A-C are schematic drawings of the water and air flow relative to the housing and jet intake;  
       FIG. 22  is a schematic drawing of the water shape as it moves past the housing;  
       FIG. 23  is a side elevation view of the air and water movement relative to the boat and outboard jet unit;  
       FIG. 24  is a perspective view of an outboard jet propulsion unit constructed in accordance with another embodiment of the invention;  
       FIG. 25  is a perspective view of a jet pump constructed in accordance with the invention;  
       FIG. 26  is a top plan view of a stator constructed in accordance with the invention;  
       FIG. 27  is a side elevation view of a stator constructed in accordance with the invention;  
       FIG. 28  is a front elevation view of a housing for a jet drive marine propulsion system constructed in accordance with the invention;  
       FIG. 29  is an edge perspective view of a housing for an outboard jet drive marine propulsion system in accordance with the invention;  
       FIG. 30  is a schematic drawing of the relative profiles of a propulsion system and boat constructed in accordance with the invention;  
       FIG. 31  is a side elevation view of a shift plate constructed in accordance with the invention;  
       FIG. 32  is a side elevation view of a throttle plate constructed in accordance with the invention;  
       FIG. 33  is a partial elevation view of a first side of a lever plate constructed in accordance with the invention;  
       FIG. 34  is a partial elevation view of the reverse side of a lever plate constructed in accordance with the invention;  
       FIG. 35  is a side elevation view of a lever control assembly constructed in accordance with the invention; and  
       FIG. 36  is a schematic view of a turbocharger constructed in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring to  FIGS. 1-3 , an outboard jet drive unit  10  is shown attached to the hull of a boat  11  on the transom  12 . The jet drive unit  17  includes a housing  13  having a platform  14  mounted therein and having a plurality of flexible engine mounts  15  attached to the platform  14 . An internal combustion engine  16  is mounted to the engine mounts  15  on the platform  14 . Engine  15  is preferably a diesel engine having a turbocharger with an intercooler, but may be a gasoline engine as well, and is preferably a conventional car or truck engine. A jet drive unit  17  is mounted beneath the platform  14  of the housing  13  and is attached to the front end  18  of housing  13 . The housing  13  is sealed against the intrusion of water thereto and sealed between the platform  14  and the housing  13  to prevent water intrusion and to prevent oil or engine antifreeze from escaping therefrom.  
      The predominant prior art configuration of inboard jet boats is the inline setup, that is, the engine is connected in line with the jet drive; this has the engine&#39;s flywheel and drive pulley facing the transom (back of the boat) from inside the boat and the jet attached to it. By turning engine  16  and jet drive unit  17  around as compared to the prior art (i.e., 180 degrees) so that they are outside the boat behind the transom, as shown in the  FIG. 1  in accordance with the present invention, the engine gear  120  and jet drive pulley  28  are positioned so that they both face in the same direction toward the transom from outside the boat, i.e., they face in the opposite direction of the inline arrangement. Thus, in this configuration, the drive pulley and engine flywheel are facing the back of the boat, but from outside the boat. Then, by using the drive belt system  27 , the jet is placed substantially directly below the engine.  
      It should be appreciated by those of skill in this field that by turning the engine around 180 degrees from the inline configuration, this will cause the impeller to turn in the opposite direction (backwards) from other impellers in use currently. Thus, the jet drive unit and engine are in essence installed “backwards” causing the impeller in the jet drive unit to rotate in the opposite or reverse or “backwards” direction, as compared to impellers in jet drive units configured inline.  
      Open propeller driven vessels, inboard, outboard, and stern drives create excessive engine loads when “lugging” to get on plane. Product life is reduced in direct proportion to the number of hours accumulated at partial planning speeds. This design does not experience this phenomenon. When the throttle is placed at the desired position, the engine accelerates immediately to engine speed. The jet instantly pumps the required flow for the selected speed and the boat catches up. The engine and the drive train never experience the level of duress that conventional propeller driven vessels experience.  
      In an exemplary, non-limiting embodiment, engine  16  has a belt drive  27  having a clutch mechanism therein for connecting the engine  16  to the drive pulley  28  of the jet drive unit  17 . More particularly, as shown in  FIG. 5 , a drive train is formed between a gear  120  on a flywheel of engine  16  connected on gear  122  (drive pulley  28 ) mounted on drive shaft  124  of jet drive shaft  17 . In a preferred embodiment, belt drive  27  is a Kevlar® belt, preferably teethed to engage gears  120 ,  122  to prevent skipping and slippage.  
      While the parallel position is the most efficient and preferred position for jet drive unit  17  and the internal combustion engine  16  system to be placed relative to each other, it is not the only possible position. In addition, by being positioned in parallel, it allows use of a standard horizontal engine and drive belt drive as illustrated in  FIGS. 1, 2  and  5  and discussed above.  
      While it is preferred for jet drive unit  17  to be positioned below engine, other locations are contemplated by the present invention, such as on top, opposed, or on the side of the internal combustion engine.  
      Although acceptable within the scope of the invention, they are not preferable. By way of example, if jet drive unit  17  is positioned on top or above the engine, it will operate, however, it would require pumping water up to the jet. The higher the water is pumped, the more power is lost to pumping water and the larger the water intake needs to be (the water intake needs to gradually decrease in size throughout the water intake system, to avoid air bubbles from forming and causing cavitation).  
      Also, the best water flow for the jet intake is at the bottom center of the boat, which may create a problem diverting water around the engine. This position would also most likely cause the engine to be lower which creates another problem. That is corrosion and exhaust riser problems. The lowest part of a boat or marine engine compartment invariably gets water in it. Having the engine low puts the engine in the water.  
      If the jet drive unit  17  is positioned on one or both sides of engine  16 , while this positioning is believed to be better positioning than on top, it still has the problems mentioned above, and would require much greater width of the finished unit, it may create a weight distribution problem in that engine  16  is much heavier than jet drive unit  17 , especially if only one jet drive unit is employed. In addition, putting too much weight to one side or the other would most likely create handling problems with the boat.  
      As already indicated, when the jet drive unit is placed on the bottom or underneath the engine, this positioning is by far the most practical and preferred placement. The engine is elevated, reducing problems from corrosion and riser problems. The jet is at the lowest possible position, creating the best water flow into the jet intake. The weight is centered. Further, by putting the, weight of the engine directly over the jet drive unit and the water intake, the water intake is less likely to come out of the water as often happens in the current systems. When the water intake comes out of the water, both power and maneuverability are lost in a jet drive unit.  
      It is also preferential for the water path entering and exiting the jet drive unit to be axial or straight, as opposed to, for example, a circular or bent.  
      Furthermore, it should be understood that the engine could be attached with a chain, or possible with a direct drive system with a series of two or more gears, although the belt is preferable. A clutch may be used but is not required.  
      The advantage of the belt drive system is efficiency. The belt drive in theory transfers 98% of the engine&#39;s power to the jet impeller. Other systems in practice lose approximately 15% of the engines power by the time power is transferred to the propeller or jet impeller.  
      Also, it is believed that this is the most cost effective method for a jet. For the jet to operate at its best efficiency, the jet should be sized appropriately to the horsepower and expected load. Most jet boats in operation today are using jets sized too small for optimum efficiency. This is done because the jet is being run at engine speed. Smaller jets can run at higher speeds (rotations per minute or “RPM”), larger jets must operate at lower speeds (RPM). In order for the jet to operate at a lower RPM than the engine, some sort of gearing reduction is required. Currently, when a reduction is put in place it is done with a transmission. With the belt drive system of the present invention, it is able to operate the jet at a lower RPM by using different sized gears and the gear size is preferably matched to the engine and jet size when installed.  
      Jet drive unit  17  extends through the rear  21  of housing  13  out an opening  20  in the housing  13 . The jet drive unit  17  has a water intake  22  and is positioned to be about level with the bottom  23  of the hull  11 . A water exhaust  24 , providing the exit path for jetted water, extends out the rear of the housing  13 . A jet pump  25  is mounted in the jet drive  17  for drawing the water thereinto through the jet pump and out the water exhaust  24 . The jet drive unit  17  is shown below the water line  26  and is supported on brackets  29  on the front  18  of the housing  13 .  
      Reference is now made to  FIG. 6-9  in which a mounting structure in accordance with the preferred embodiment for the drive jet unit  17  is provided. As discussed above, jet drive unit  17  is mounted to housing  13  in a way to operatively cooperate with engine  16 . Housing  13  is provided at its rear face  21  with an opening  20 . Opening  20  communicates with the interior of housing  13 .  
      Jet pump  25  is a series of jet blades radially affixed about drive shaft  124 . Reference is made to  FIG. 25  in which a perspective view of a jet pump  25 , constructed in accordance with the invention is provided. Helical blades  500  extend from a support member  502  schematically shown in  FIG. 1 . Support member  502  is preferably conical. Because the blades are helical and spaced, water is drawn between the blades in the direction of arrow  0 . Because the jet pump assembly  25  rotates, water is pushed outwardly as well as forwardly. As the rpms of the blade increase, cavitation increases between the blades. As cavitation increases, thrust is lost. Furthermore, water escapes through the path of least resistance. Most goes forward out through water exhaust  24 . However, because of the spacing between blades, some water travels upstream adding to cavitation and loss of power. The greater the cavitation, the less speed and less thrust. The cavitation decreases as a function of the size of the gap between overlying blades. The gap is reduced as a function of 1-((n-x)/n) expressed as a percentage where n is the number of current blades and x is equal to the number of additional blades as compared to the comparison jet pump. By way of example, if the number of blades is increased from 3 to 4, then n=4 and x=1 so that the increase is 1-75%=25%. If the increase is from 2 blades to 4 blades, the gap is closed by 50%, assuming equidistant spacing of the blades. The more blades, the less cavitation; however, while thrust may increase, speed does not.  
      Accordingly, the jet pump is formed from two types of blades, impeller blades  510  and induction blades  512 . Induction blades  512  draw water towards impeller blades  510  to provide a more dense water stream to impeller blades  510  so that impeller blades  510  force a greater mass of water out of exhaust  24 . In effect, induction blades  512  prime the pump.  
      Eachblade  500  of induction blades  512  has a length L IN  and a width W IN . Each induction blade  512  has a lead edge and a trail edge. Each induction blade  512  has a non-uniform pitch, i.e. it is bent so that a leading edge  522  of each induction blade  512  has a pitch less than the pitch of the remaining portion. In a preferred, but not limiting example, leading edge  522  has a pitch of about 14° while a trailing portion  524  of induction blade  512  has a pitch of about  170 .  
      Each blade  500  of impeller blades  510  has a length L IM  and a width W IM . The width W IN  is substantially smaller, about 50%-85% than the width W IM  of impeller blades  510 . Furthermore, the length L IM  of impeller blades  510  is substantially greater than the length L IN  of blade  512 . Impeller blades  510  are also of non-uniform pitch having a leading edge  506 , having a lower pitch, than a trailing section  504 . The change in pitch along each of the blades found in impeller blades  510  and induction blades  512  occurs closer to the leading edge than the trailing section.  
      It should be noted that induction blades  512  are shown as a distinct leading section upstream of impeller blades  510 . However, it would still be in accordance with the invention to provide induction blades  512  interspersed or interleaved among impeller blades  510 . By providing an induction blade in cooperation with an impeller blade in the jet pump, preferably upstream of the impeller blades, denser water is carried to the impeller blades providing better thrust and speed. By providing at least four impeller blades, the gap is sufficiently closed between blades to significantly reduce the reverse flow of water. The addition of more blades increases cavitation on acceleration reducing speed. Therefore, the induction blades  512  are provided.  
      As a result of the action of the blades of jet pump  24 , the water exits exhaust  24  in the direction of arrow P ( FIGS. 1, 2 ). However, the water is turbulent and energy is flowing in all directions. Accordingly, a stator  600  as shown in  FIG. 26  is provided at exhaust  24  to collimate water exiting from jet pump  25 . Stator  600  includes a central member  602 . In a preferred embodiment, central member  602  is conical. A plurality of blades  604  extend radially from conical member  602  to a wall of exhaust  24 . In a preferred embodiment, a wall  606  is integrally formed with blade  604  to form a unitary unit which is mounted within water exhaust  24  or blades  604  and conical member  602  can be unitarily formed with a housing structure within water exhaust  24 .  
      As water flows through stator  600 , it is guided to flow in a single direction, but some energy is lost and the flow of water loses speed. In turn, the boat loses speed. However, a volume reduction member  610  extends from conical member  602  into the exhaust portion of water exhaust  24 . In a preferred embodiment, volume reduction member  610  is merely an extension member from conical member  602 . However, any structure which reduces the volume within water exhaust  24  without substantially interfering with the flow path of water exiting through stator  600  may be used. By reducing the volume available to the water in water exhaust  24 , the water speed increases, the pressure of the water column exiting the jet at water exhaust  24  is increased, providing increased thrust and speed to engine  10 .  
      Jet drive unit  17  may be formed as a removable cartridge. In a preferred embodiment, jet drive unit  17  is housed in a removable jet housing  206 . Jet housing  206  supports a driveshaft housing  201  in which drive shaft  124  is disposed. Drive shaft housing  201  is received in opening  20  and extends through opening  20  and forms a watertight seal with housing  13 . In a preferred embodiment, housing  201  is bolted using a bolting plate  202  to a mating bolting plate  204  of housing  13 . Gaskets and seals, as known in the art, are utilized to affix housing unit  201  to housing  13  in a watertight manner.  
      Jet unit  17  is formed as a unit about drive shaft  124 . Therefore, drive shaft  124 , mounted within housing unit  201 , can be easily mounted to housing  13  by simply sliding the entire unit including housing  201  through opening  20 . Drive pulley  28  is affixed to drive shaft  124 , which in turn is attached to drive belt  27 , and the entire jet propulsion unit is affixed to engine housing  13 . As a result, simple assembly is provided while maintaining a separation between the engine structure, which remains away from water to prevent corrosion and the jet unit structure, which must come in contact with water.  
      In one embodiment, drive shaft housing  201  is slidably received within jet unit housing  206 . Jet unit housing  206  is mounted to the rear surface  21  of housing  13  by bolting the housing in the rear. To maintain the overall shape of the outboard propulsion system  10 , engine housing  13  may be formed with a recess  210  for receiving jet unit housing  206 . Housing  206  is provided with a plate  208  for attachment to housing  13 .  
      Vibration along drive shaft  124  results in wear and tear on the drive shaft. This is especially true at each of the ends of the drive shaft  124 . As seen in  FIG. 9 , brackets  212  affix drive shaft housing  201  to the interior of housing  13  at an end of drive shaft  124  adjacent drive pulley  28 . A bracket  212  is provided at either side of drive shaft housing  201  to stabilize drive shaft  124  at its end.  
      In an exemplary embodiment, the brackets can be made from milled steel, aluminum, stainless steel or other materials. Stainless steel provides the best combination of stiffness, corrosion resistance and weight for the marine environment. In the preferred embodiment, brackets  212  need to be attached as close to the end of drive shaft  124  as possible to provide the best support although it is understood and within the scope of the invention, that brackets  212  could be attached to various positions in the engine compartment. Attaching brackets  124  above and on each side of drive shaft  124  provides the best support while keeping the brackets accessible for maintenance and keeping the fittings, bolt holes, bolts and the like as high above the bilge area as possible.  
      By placing bracket  202  substantially midway along the length of drive shaft housing  201 , further support of drive shaft  124  is provided. When attached, flange  202  is disposed between housing  13  and jet unit housing  206 , and is firmly attached to both, further supporting drive shaft  124  along its length. As discussed above, shaft housing  201  slides into the engine housing  13  as well as the jet housing  206 . The three components are attached at flange  202  by welding, bolting or other known means and bolt plate  208  of jet housing  206  is bolted to rear surface  21  of housing  13 . In this way, jet housing  206  is received and positioned within a receiving area  210  on the rear surface  21  of housing  13 .  
      In a preferred embodiment, having flanges close to the middle of the drive shaft housing provides the best support. Other supports at the end of the drive shaft are helpful, but not required. A support system can be made from milled steel, aluminum, stainless steel or other materials. Again, stainless steel provides the best combination of stiffness, corrosion resistance and weight for the marine environment.  
      Outboard propulsion unit  10  utilizes a closed loop cooling system similar to those used in an automobile. In a preferred embodiment, propulsion unit  10  uses a water-to-water heat exchanger to cool engine  16  in a similar fashion to a radiator in an automobile. The water that circulates through the engine, the water-cooled exhaust manifold, and the oil cooler (where applicable) is treated with fresh water just like used in an automobile. However, propulsion unit  10  cannot expose the engine interior to seawater or dirty fresh water it utilizes during operation. Rather, the hot engine water is circulated by the engine water pump through a heat exchanger where it is cooled by the circulating seawater. Sea water is pumped through the heat exchanger by the water jet eliminating the requirement for a separate engine driven sea water pump and eliminating the high maintenance rubber sea water pump impeller.  
      In another advantage, the propulsion unit  10  may be equipped with turbochargers. The marine propulsion unit  10  also includes a stainless steel and cupronickel intercooler to cool the compressed air before it is inserted into the engine&#39;s intake manifold. The process of compressing the inlet air with the turbocharger increases the temperature of the air. Cooling the inlet air with seawater in the intercooler enables the engine to produce more power more economically and reduces the smoke and other pollution from the engine exhaust to meet environmental standards.  
      In another advantage, the marine propulsion unit  10  may be equipped with fuel coolers. It is believed that fuel injected engines deliver more fuel to the engine than the engine requires. The excess fuel is returned to the fuel tank for use later. The returned fuel is heated by the engine and tends to raise the temperature of the fuel in the tank over a period of time. The higher fuel temperature reduces the engine power and performance. The fuel cooler eliminates this problem. The fuel cooler is constructed of stainless steel and cupronickel and uses seawater for cooling.  
      Reference is now made to  FIG. 24  in which yet another embodiment of outboard propulsion unit  10  utilizing a cooling system is provided. Like numerals are used to indicate like structure for ease of description. Propulsion unit  400  includes an engine  16  and a jet unit  17 . A heat exchanger  402  is coupled to jet unit  17  by hosing  404 . Heat exchanger  402  is also coupled to engine  16  by hosing  406 . A second hosing  408  couples heat exchanger  402  to an intercooler  410 . Intercooler  410  is connected by hosing  412  to an exhaust  414  of engine  16 . Furthermore, intercooler  410  is coupled to the fuel line of engine  16  and the turbo charger of engine  16 .  
      During operation, hosing  404  is coupled to the jet unit  17  and siphons a portion of the jet stream as it travels through jet unit  17  so that water under pressure travels in the direction of arrow M into heat exchanger  402 . Hose  406  communicates with piping (not shown, but known in the art) within heat exchanger  402  which is surrounded by the cool water flowing from hosing  404  into heat exchanger  402 . In this way, engine  16  is isolated from the water passing through jet unit  17 . The pressure provided by the jet stream and gravity cause heated water to exit heat exchanger  402  through hose  408  in the direction of arrow N into intercooler  410 . Intercooler  410  includes piping systems, which communicate with the turbo charger, exhaust  414 , and fuel line of engine  16  cooling the air and fuel within the engine to provide greater efficiency for a turbo charged engine.  
      It should be noted that heat exchanger  402  and intercooler  410  are each preferably oriented vertically relative to the horizontal orientation of engine  16 . In this way, if in fact outboard propulsion system  10  is not running, gravity drains the seawater or clear water from heat exchanger  402  into hose  408  or back into hose  404 . In this way, no seawater remains in the heat exchanger  402  longer than necessary, reducing the corrosion to any piping within heat exchanger  402  or structure within intercooler  410 . Furthermore, heat exchanger  402  is preferably made of stainless steel and cupronickel, both highly corrosion-resistant alloys to help ensure that the interior of engine  16  is never exposed to seawater. Additionally, no engine flushing is required after each boat trip because a closed cooling system is provided, engine  16  should experience a longer and more reliable life.  
      It is understood that because jet drive unit  17  is continuously coupled to engine  16 , a jet stream is flowing as long as the engine is on. Therefore, barring a catastrophic failure of the drive system, there is always ample water for cooling.  
      In a preferred embodiment, turbocharger  420  controls increases in the back pressure when matching the turbo to the engine rather than releasing energy through a waste gate as known in the art. The housing diameter is adjusted to control the exhaust gas volume and speed to optimize turbine speed to provide more pressure on the housing side. Reference is now made to  FIG. 35  where a schematic diagram of a turbo charger constructed in accordance with the invention is provided.  
      It is often required to obtain extra power from an engine. Applicants have determined that it is possible to boost a 150 horsepower engine to a 200 horsepower engine utilizing a turbocharger  420 . Turbocharger  420  includes a first turbine housing  424 . The housing includes an intake  426 , coupled to an exhaust  428  of engine  422 . A turbine  430  is rotatably disposed within turbine housing between input  428  and housing exhaust  432  so that exhaust from engine  422  exiting through engine exhaust  428  drives turbine  430  as it passes through the blades of turbine  430  towards exhaust  432 . Turbine  430  is in the exhaust flow path.  
      A second housing  450  has an intake  456  for receiving atmospheric air and an output  452  providing output to engine  422  into respective cylinder chambers. An air compressor  454  is rotatably housed within housing  450  and is along a flow path between air intake  456  and exhaust  452 . A shaft  460  connects turbine  430  to air compressor  454 . Therefore, as engine  422  produces exhaust, it spins turbine  430 , in turn turning shaft  460  in air compressor  454 . The turning of air compressor  454  creates a vacuum at exhaust  456  drawing atmospheric air into housing  450  through compressor  454  and then forced under positive pressure through exhaust  452  into engine  422 . This provides extra oxygen in the cylinders  422  of the engine creating larger explosions and more energy for driving the pistons.  
      As is known in the art, air will sometimes backflow through housing  450  decreasing efficiency. It is known in the art to provide a waste gate to allow excess pressure as a result of the backflow to vent. By sizing housing  450  to provide the correct volume and velocity of air flow through the housing, the need for the waste gate is eliminated.  
      This engine and associated control is also suitable for use with rigid, inflatable boats (RIB) such as those manufactured by Zodiac® by way of non-limiting example. Furthermore, the use of the current engine provides a novel advantage of a self-maintaining RIB. One shortcoming with RIBs is that the inflatable structures essentially change volume as a function of the atmosphere. Inflatable sections that appear solid when trailered in the sun, lose volume when placed in the cooler water. Furthermore, no matter how air tight, inflated objects do tend to deflate over time at the valve, the seams or leakage through the material. Accordingly, a self-inflating mechanism is desired.  
      As discussed above, there is air under pressure traveling through the engine constructed in accordance with the invention. Generally, air travels through the engine at 25 psi. In the present invention, a tap is provided along the inlet air passage of the engine for siphoning off a portion of the air under pressure. A hose or other type piping or tube couples the tap or a manifold to the structure to be inflated. A regulator may be provided along the line formed by the tubing. The regulator is a pressure-controlled diaphragm that opens when the downstream pressure falls below a predetermined level allowing inflation. Air may be released in the reverse direction if pressure in the inflated structure exceeds a predetermined amount.  
      Reference is now made to  FIGS. 10-18  in which another embodiment of the jet engine is provided. Like numerals are utilized to identify like structure for ease of description. Water exiting jet exit portion  54  ( FIG. 1 ) is what provides the driving force for the outboard jet propulsion engine, and in turn, the boat to which it is attached. Because exhaust portion  54  is fixed to the fixed structure of housing  13  as described above, a mechanism is required to allow reverse operation and steering. As shown in  FIG. 10 , a bucket assembly, generally indicated as  300 , is attached to jet drive unit  17  at exit portion  54  so that water exiting water exhaust  24  is operated upon by bucket assembly  300 .  
      Bucket assembly  300  includes a bucket housing  308 . Bucket housing  308  is supported by a saddle  302  suspended from housing  13  by a suspension arm  35 . Suspension arm  35  is operatively linked to a steering rod  306 . It is understood and within the scope of the invention that any structure for supporting bucket housing  308  may be used so long as bucket housing  308  is supported at water exhaust  24  so as to receive water exiting water exhaust  24 . Bucket housing  308  has an entrance port  309  for receiving water exiting water exhaust  24  and a first exhaust  311  and second exhaust  314  for causing water to exist housing  308 .  
      A bucket  310  is pivotally mounted on housing  308 . A bucket linkage  312  is connected to bucket  310  and a reverse cable  314 , which controls linkage  312  to rotate bucket  310  in the direction of arrow C to a first position in which bucket  310  is open to allow water to pass through exhaust  311  in the direction of arrow A. Linkage  312  also controls bucket  310  to move in the direction of arrow B to close first exhaust  311  ( FIG. 12 ) and redirect the water path through second exhaust  314  of housing  308 . A directional member  316  is provided at exhaust  314  to guide the water in a direction substantially in the direction of arrow D back towards housing  13 .  
      It should be noted that a pivoting bucket shaped member is utilized, but any structure which selectively opens and closes water exhaust  311  may be utilized. In a preferred embodiment, by way of example only, linkage mechanism  312  is a bi-armed structure having a pivot, connecting one arm to the other at a position linked to reverse cable  314  such that movement of reverse cable  314  in the direction of arrow E ( FIG. 13 ) lifts the pivot point of member  312  bringing the two arms together ( FIG. 14 ) shortening the distance, drawing bucket  310  toward saddle  302  and lifting bucket  310  in the direction of arrow C. In this way, water is allowed to pass substantially unimpeded in the direction of arrow A, pushing housing  13  and the boat affixed thereto in the forward direction. However, any control structure for moving bucket  310  may be used.  
      When reverse cable  314  moves in the direction of arrow F ( FIG. 12 ), the arms of member  12  are spread ( FIG. 15 ) rotating bucket  310  in the direction of arrow B closing one end of housing  308  and forcing water to exit in the direction of arrow D back towards the boat. The force of water exiting through opening  314  as guided by guide member  316 , pushes the boat in a reverse direction. Reverse cable  314  is coupled to the controls of the boat by either mechanical or electro controls.  
      In a preferred embodiment, the reverse cable is mounted on a steering nozzle. This gives maximum reverse thrust control with a steering nozzle mounted to maintain normal reversing direction with a reverse bucket using a standard 3-inch stroke cable. In order to keep the cable out of the water, the vertical operation was designed, i.e., the cable structure is mounted to cooperate with housing  308  above jet pack unit  17  substantially away from the water. This keeps the entire cable, except for the stainless push/pull rod of member  312  over the normal water line eliminating the need for boots, seals or rust-proofing. In order to keep the reverse bucket from moving up and down excessively during steering, reverse cable  314  is positioned close to the rotational point of the steering, i.e. near the steering cable  304 ,  306  at steering rod.  
      In a preferred embodiment, the reverse bucket, levers, bearings and bolts are made of stainless steel and could be made of any suitable material such as aluminum, fiberglass, plastic or any rigid material. The stroke of cable  314  is preferably limited to about 3 inches and is to be hand-powered and moved in a maximum amount of reverse direction with a minimum effort which is achieved by putting an additional stationary diverter, or the like, below the exhaust that the reverse bucket comes down to meet in the full reverse position, that, when connected, adds additional reverse rotation to the bucket. The end of cable  314  has a swivel (ball-type) at the saddle  302  to allow the cable to stay stationary while steering is being turned and also allows angle changes on any steering or reverse bucket position. The arms of member  12  provided at the boat are designed to lock in the forward position and in reverse, eliminating kickback on the cable and allowing the use of full thrust in reverse gear without relying on the cable to hold the bucket in place.  
      In another preferred embodiment, a simple control lever which appears to the operator to behave as known in the art propeller engine throttles are preferred. Reference is now made to  FIGS. 31-35  in which a lever assembly, generally indicated as  1000 , for controlling direction and speed of the engine in accordance with the invention is provided. The desired benefit is to provide a single lever, which through a range of motion controls cable  314  to control both the speed at which the boat will travel as well as the direction.  
      Shift assembly  1000  includes a housing. A shift plate  1010 , a throttle plate  1200  and a lever plate  1100  disposed therebetween, and in operative communication with shift plate  1010  and throttle plate  1200 , are mounted within housing  1001 .  
      Shift plate  1010  ( FIG. 31 ) includes a through hole  1012  forming an axis of rotation for the plate as will be discussed later. A first arced channel  1014  has a substantially L-shape along a surface  1016  of shift plate  1010  and extends through shift plate  1010 . A detent  1018  is provided along the path of channel  1014  at one end thereof. An elbow region  1020  is formed along the path of channel  1014  at the other end of channel  1014 . A second substantially L-shaped channel  1030  is formed in shift plate  1010  along surface  1016 . Channel  1030  extends through shift plate  1010 . Channel  1030  includes a detent  1032  and an elbow region  1034 . Detent  1032  and elbow region  1034  are formed at opposite ends of channel  1030 .  
      A third channel  1040  is formed through shift plate  1010  along its surface  1016 . Channel  1040  also includes an elbow region  1042  located at a first end and a detent  1044  located at a second end. Like channels  1014  and  1030 , channel  1040  has one end with a detent and another end with an elbow section.  
      It should be noted that generally channels  1018  and  1013  substantially lie on shift plate  1010  on an opposed side of axis of rotation  1012  from channel  1040 .  
      Cable  314  connects shift plate  1010  to bucket  310 . Cable  314  is connected to plate  1010  at a shift section  1050 . Movement of shift plate  1010  causes movement of bucket  310 .  
      Reference is now made to  FIG. 32  which shows throttle plate  1200 . Throttle plate  1200  includes an axis of rotation hole  1202  extending through throttle plate  1200 . A channel  1204  having a substantially scythe shape extends along a surface  1206  and through throttle plate  1200 . Channel  1204  includes a curved portion  1208  extending into a first flattened portion  1210  across an elbow portion  1212  from curved portion  1208 . At a second opposite end of channel  1204 , is a second substantially straight portion  1214  separated from curved portion  1208  by a detent  1216  formed by the straightening of channel  1204 .  
      A substantially U-shaped channel  1220  is formed through throttle plate  1200  across surface  1206 . A lever shaft receiving channel  1222  is formed through throttle plate  1200  along surface  1206  and disposed substantially within the arms formed by U-shaped channel  1220 .  
      Throttle plate  1200  includes an activation region  1250 . Activation region  1250  is connected to cable  720  which in turn is connected to a throttle of engine  16 . In a simplified embodiment, a connection hole  1252  is provided at a distal end of region  1250  to provide maximum torque for attaching cable  720  thereto. However, any attachment method known in the art such as the use of a coupling, buckle or the like may be used for attaching cable  720  to throttle plate  1200 . As cable  720  is pulled in the direction of arrow Y, the rpms of engine  16  increase in turn increasing rpms of jet drive  26  and pressure and speed of the water flow from exhaust  24 .  
      Reference is now made to  FIGS. 33 and 34  in which a lever plate, generally indicated as  1100 , is provided. An axis of rotation hole  1102  extends through lever plate  1100 . On a first surface, rollers  1104 ,  1106 , and  1108  are disposed on a first surface  1110  of lever plate  1100 . Roller  1104  extends outwardly from face  1110  and is received through channel  1040  of shift plate  1010  when lever assembly is assembled. Similarly, roller  1106  is received within channel  1020 , and roller  1108  is received within channel  1032 .  
      Rollers  1110 ,  1112  are disposed on an opposed side  1116  of lever plate  1100  and are positioned to be received within channels  1214  and  1220  of throttle plate  1200 . Specifically, roller  1110  is received within channel  1220  and roller  1112  is receiving within channel  1214 . As discussed below, each roller is adapted to slide along its respective channel.  
      Lever plate  1100  includes a lever  1120  for actuating lever plate  1100  when lever assembly  1000  is fully assembled. Lever assembly  1000  is disposed in housing  1001 . A first shaft (not shown) extends from housing  1001  through axis of rotation holes  1012  and  1202 . A second shaft extends from housing  1001  through axis of rotation hole  1102  of lever plate  1100 . When each of rollers  1104 ,  1106 ,  1108 ,  1110  and  1112  are positioned within the respective channels in the reverse direction it is shown in solid lines. The locked in forward position is shown in phantom.  
      For this description, as shown in the solid lines, the description begins with the engine locked in the reverse direction at full throttle. As lever plate  1100  is rotated in the direction of arrow W, roller  1104  travels along channel  1040  in the direction of arrow T while roller  1108  travels in the direction of arrow U and roller  1106  travels along channel  1018  in the direction of arrow V. Roller  1104  is maintained in the reverse position by elbow region  1042 . Without an exertion of force, it is difficult for roller  1104  to traverse elbow region  1042 . Similarly, it is difficult for roller  1106  and  1108  to traverse respective detents  1018  and  1030 , maintaining those respective rollers in the reverse direction. As the roller traverse the respective channels, the rollers apply a force on the respective guide channel rotating plate  1010  about axis of rotation  1012  having the effect of carrying lever plate  1100  in its rotation. This raises cable  314  which in turn raises bucket  310  diverting more and more of the water flow from exhaust  314  to exhaust  311 , initially reducing speed in the reverse direction.  
      At the same time, rollers  1110  and  1112  are traveling through their respective channels  1220 ,  1204 . When going from reverse to forward, roller  1110  travels about channel  1220  in the direction of arrow S while roller  1112  travels in the direction of arrow R through channel  1204 . This causes throttle plate  1200  to rotate in the direction of arrow Q. Furthermore, because of the operation of shift plate  1010  as shift plate  1010  rotates with the change of direction, lever plate  1100  is cammed downward relative to throttle plate  1200  its axis of rotation  1102  moves in the direction of arrow X in effect lowering as throttle plate  1200  rotates about axis of rotation  1202  in effect raising throttle plate  1200 . Another way of considering it, plate  1200  rises relative to throttle  12  so that shaft plate  1200  comes in contact with shaft  1122 .  
      During operation, beginning in an idle position, rollers  1104 ,  1106 ,  1108  are disposed somewhere along the guide channels between the respective elbow regions  1042 ,  1020 ,  1034  respectively and detent regions  1040 ,  1030 ,  1018 . To provide forward propulsion, lever  1120  is rotated in the direction of arrow W causing rollers  1104 ,  1106 ,  1108  to move towards the position of the phantom rollers in each respective guide channel. Because the rollers are fixed to lever plate  1100 , as the rollers travel through the respective guide channels, they have the effect of lifting the guide channels and in turn shift plate  1010  about its axis of rotation  1012  and lifting cable  314 , in turn lifting bucket  310 . This lifting occurs until roller  1106  traverses elbow region  1020 , roller  1108  traverses elbow region  1034  and roller  1104  traverses detent region  1034 . In at least one position, during movement between respective elbow regions and detents, without disengaging the engine from the jet drive, engine  16  is substantially idle, bucket  310  is at a position balancing jet pressure through exhausts  310  and  314 .  
      Once each respective roller is past the respective elbow or detent in the forward position, shift plate  1010  no longer rotates despite movement of the roller. However, what has happened to throttle plate  1200  is that the rotation of the shift plate along with the lever has cammed the axis of rotation shaft  1122  of lever plate  1100  in the direction of arrow X relatively raising throttle plate  1200 . Further rotation of lever plate  1100  causes movement of roller  1110  in the direction of arrow S and roller  1112  in the direction of arrow R which comes in contact with guide channels  1220  and  1208  respectively, lifting and rotating throttle plate  1200  in the direction of arrow Q so that activation region  1250  moves in the direction of arrow Y causing cable  720  to move in the direction of arrow Y causing the opening of the throttle of engine  10 . As cable  720  moves further in the direction of arrow Y, the engine provides more rotation to the jet drive, causing more water jet to exit from the water exhaust  24  increasing the speed of the boat in the forward direction. At full throttle, the respective rollers  1110 ,  1112  are shown in the position as shown in phantom as are rollers  1104 ,  1106 ,  1108 .  
      As rollers  1110 ,  1112  are moving within their respective guide channels  1220 ,  1204 , roller  1106 , by way of example, is moving between elbow region  1020  and a stop end  1024  of guide channel  1018 . Although traversing that region has no real affect on shift plate  1010 , throttle plate  1200  is experiencing rotation. Similarly, during that same period, roller  1108  traverses a region from elbow region  1034  to a stop wall  1036  of guide channel  1030  and roller  1104  travels from detent  1044  to a stop wall  1046  of guide channel  1040 .  
      To cause reverse thrust of the engine the travel path is reversed.  
      However, it should be noted that although shift plate  1000  will rotate in the reverse direction, as shaft  1122  moves in the reverse direction within channel  1222  it causes throttle plate  1200  to move in the direction of arrow Q a second time as the rollers  1110 ,  1112  reverse direction, but to a lesser extent. In this manner, engine throttle is lower relative to the full open position so that at least a portion of the exiting jet stream is caught by the bucket, and at a lower speed as it is deflected through exhaust  314  at directional member  316 .  
      In a preferred embodiment, the motion of activation region  1250  in the direction of arrow Y moves about 1-¾ inches when in the forward orientation; it moves about ⅝ inch in reverse. It should be noted that in a preferred embodiment for control purposes, bucket  310  is never entirely lowered to prevent an excessively fast or quick reverse movement of the engine in the boat. Furthermore, idling occurs somewhere between a stroke length of ⅝ inch and 1/-¾ inch where the reverse thrust is balanced with the forward thrust.  
      To the user, operation of the lever will be continuous and seamless. As the lever is moved between a first position and second position, shifting of the bucket occurs to reduce the speed in the forward direction as a portion of the jet stream is deflected in the reverse direction through exhaust  314 . Continued shifting from a second direction to a third direction reduces the throttle, increasing the speed in the forward direction. A fourth position, somewhere between the second and third position is that position where the shift plate has been rotated sufficiently to balance the thrust in the forward and reverse directions at the jet drive unit. This idles the boat without disengaging the engine.  
      When operating in the reverse direction, at first the boat is slowed down as shifting occurs between the third and second position and throttle plate  1200  is rotated to reduce the pull on cable  720  from, in a preferred and non-limiting example, 1-¾ inches to 5 inches. Bucket  310  becomes lowered as the lever is shifted from the second to the first position, causing change of direction of the boat. A single lever controls speed and direction.  
      By utilizing an outboard motor, so that exhaust portion  54  of jet drive unit  17  is distanced away from hull  12  of boat  11 , the water jet exiting housing  308  through exhaust opening  314  does not substantially interact with hull  11 . As a result, the hull does not substantially interfere with the exiting jet stream and the efficiency of the jet engine when driving in reverse is greatly increased.  
      Reference is now made to  FIGS. 16-18 . Steering rod  306  is pivotally connected to bucket housing  308 . Steering rod  306  is also coupled to hand controls on boat  11  so that a driver may control steering. Through movement of steering rod  306 , bucket assembly  308  is rotated in the direction of arrow G to produce a left turn or in the direction of arrow H to produce a right turn.  
      Top  30  of housing  13  is removable from the housing main part  31 , as shown in  FIG. 3 . The housing  13  with the engine  16  and the jet drive unit  17  mounted therein may be attached to the transom  12  of the hull  11  with a pair of brackets  32 . Brackets  32  allow the housing  13  to be mounted substantially even with the bottom of the boat hull or higher than the bottom of the boat hull so as to reduce ingression of debris and damage to wildlife.  
      Reference is now made to  FIGS. 19-23  in which a preferred embodiment of the engine housing is discussed. In a preferred embodiment, housing  313  has a convex lower surface  315 . In a preferred embodiment, the lower surface of housing  313  is substantially bowl-shaped. In the preferred, but not limiting embodiment, the convex surface is disposed between 1 inch higher than a bottom of the hull  11 , or 2 inches lower than the bottom of hull  11 . This significantly reduces cavitation in jet drive unit  17 .  
      As hull  11  of a boat passes through the water, air becomes mixed in the water as is noticed in any foaming wake. Air in the water as it passes through jet unit  17  causes cavitation, which reduces the power of outboard propulsion unit  10 . However, by providing a rounded, convex lower surface  315  at a trailing position from hull  11 , a high-pressure force area is provided along the submerged bottom surface  315  of housing  313 . Furthermore, the water assumes a shape, as shown in  FIG. 22 , as it moves across housing  313 . As the water moves relatively in the direction of arrow I, its path is widened around housing  313  and then narrowed as it travels across housing  313 . This is because a high-pressure area is formed along the surface of housing  313  as it moves through the water relative to the surrounding water.  
      Because air is less dense and lighter than the water which contains it, it either escapes in the direction of arrow J ( FIG. 19 ) through a low pressure area K located between hull  11  and trailing housing  313  or moves to the sides of housing  313  as shown in  FIG. 23 . In effect, air bubbles are pushed from the water by the high pressure. Air bubbles  320  seek the low-pressure area at the sides of housing  313 , allowing the remaining water to proceed directly to inlet  22 . The rounded shape of housing  313  also maintains water close to it in the direction of arrow L more efficiently guiding the water from which the bubbles have escaped towards inlet  22 . “Solid” water is what is provided into the inlet, i.e. water from which substantially all air bubbles have been removed, preventing cavitation.  
      It should be noted that the water traveling in the direction of arrow L tends to travel faster than the water away from housing  313  so that it clings to inlet  22 . It also widens in its shape when under pressure as shown in  FIG. 22  providing more squeezing of air bubbles out of the desired water stream. As seen in  FIG. 23 , bubbles  320  seek their own escape as they are squeezed out, allowing a purer stream of water  324  to enter inlet  22  of jet unit  17 .  
      In a preferred embodiment, the width of the convex shape of housing  313  at the width M is greater than a width N of inlet  22 . In this way, it is assured that the water  324  flowing towards inlet  22  is at the center of the high-pressure region, further ensuring the removal of the air bubbles  320  from the water. In a preferred embodiment, the width of a convex portion of housing  313  is about 120% the width of inlet  22 . Again, bottom surface  315  may be positioned, in a preferred, but non-limiting example, from one inch above a bottom  317  of hull  11  to two inches below bottom  317  of hull  11 . As can be seen, when bucket assembly  300  is substantially orthogonal with hull  11 , the boat is driven forward. When bucket assembly  300  forms an angle of less than 90 degrees (on either side) with hull  11 , the boat is turned.  
      However, as shown in  FIG. 20  there is some overhang of the engine housing  313  relative to hull  11 . These overhang regions  370  catch the water and provide drag. In order to maintain the relative width of housing  313 , and reduce drag, a housing  380  is stepped sufficiently ( FIGS. 28-30 ) to maintain the overall width of housing  313  while being narrow at those positions adjacent hull  11  to prevent overhang. Housing  380  includes a first convex portion  382 , having a centerline  384 . Convex portion  382  is curved in a direction extending from the hull of the boat in a direction away from the boat. Furthermore, the pitch of convex section  382  increases away from centerline  384 . The pitch may be as steep as about 26°. The convex portion further aids in keeping air bubbles away from the intake reducing cavitation.  
      Only one side of housing  380  shall be described because in a preferred embodiment, housing  380  is substantially symmetrical about centerline  384 . Extending from centerline  384 , a step portion  386  forms a shelf portion  388 . A pocket  390  is formed as a further step within step portion  386 . Pocket  390  includes a sidewall  393 , a second wall  396 , and a step  384  formed therebetween.  
      An exhaust  397  for venting engine  400  is provided within pocket  390 . Because pocket  390  is surrounded on at least two sides, one wall  393  being that portion of pocket  390  closest to centerline  384 , air and gas escaping through exhaust  397  are deflected away from centerline  384  and are deflected towards the side of housing  380  by the step walls  386 ,  393  particularly when moving in a reverse direction. Therefore, the bubbles would not reenter the intake of the jet reducing cavitation.  
      In any event, the width should be sufficient so that the bubbles  320  are diverted sufficiently wide as shown in  FIG. 21   a,  they are deflected away from a sufficient radius of intake  22  so as not to interfere or enter inlet  22 , whether inlet  22  is in line with hull  11 , or during left and right turns ( FIG. 21   b,    21   c ).  
      Fitting the waterjet directly below the engine raises the engine much higher than in traditional installations reducing the need for a riser (or raised exhaust elbow). The exhaust, mixed with a raw water spray, also supplied by pressure from the jet, exits the exhaust manifold and is carried down through a fiberglass exhaust/muffler system and ultimately exits under the water line at the rear of the fiberglass housing of the system. By eliminating the need for a riser system, not only is a high maintenance item eliminated, but the possibility of water being trapped and ingested back into the engine is avoided.  
      Hull  11  has the main fuel tank  33  mounted therein having a fuel tank inlet  34  and a fuel line  35  extending therefrom through the transom  12  and to a quick disconnect  36  where it can be quickly coupled or decoupled from an internal fuel line  37  located inside the housing  13 . The fuel line  37  enters an auxiliary internal fuel tank  38  which has a fuel line  40  connected thereto which is connected to a fuel pump  41  for pumping the fuel from the auxiliary fuel tank  38  and from the main fuel tank  33  and into the fuel line  42  where it is fed directly into the fuel injectors of the engine  16 . A fuel return line  43  is connected to the auxiliary fuel tank  38  and to a de-aerator  44  having a bleed top  45  and having a return fuel line  46  from the engine  16  fuel injectors.  
      A battery  47  is shown mounted within the housing  13  and is connected through a ground line  48  to the jet drive unit  17 . The engine and drive unit are controlled through electrical control lines  50  which are connected through a quick electrical connector  51  which is a waterproof connector mounted through the housing  13  and to the engine  16  and clutch unit  27  to control the operation of the outboard jet drive unit.  
      The rear wall  21  of the housing  13  has a tow bracket  52  attached thereto for attaching a line.  
      As seen in  FIG. 4 , the main fuel tank  33  having the filler cap  34  is connected through the fuel line  35  to the auxiliary tank  38  having an auxiliary tank opening  55  and having the fuel pump  41  connected through the fuel line  40  from the auxiliary tank  38  and through a line  42  to the fuel injectors and back through a de-aerator  44  from the fuel injectors and through the fuel line  43  back to the auxiliary fuel tank  38 . A breather  45  is connected to the dc-aerator unit  44 .  
      In operation, the hull  11  has the fuel tank  33  installed therein along with all the controls and sensors. The controls and sensors are connected through the multi-line electrical conductor  50  while the fuel tank is connected through the fuel line  35  through the transom  12 . The outboard drive unit  10  can then be attached to the brackets  32  on the transom  12  in a position to align the bottom of the unit with the bottom of the hull  23 . In a preferred embodiment, brackets  32  may be shock absorbers to further reduce vibration to engine  16  and jet drive unit  17 . Then, merely attaching the quick connect couplings  36  to the fuel line, connects the fuel lines to the outboard jet drive while connecting the quick coupling  51  connects the electrical controls. If the unit has to be removed for any reason, it can be disconnected from the brackets  32  by disconnecting the quick couplings  36  and  51  to remove the entire unit. The outboard jet drive unit  10  is made by constructing a waterproof housing  13  mounting the jet drive unit  17  therein underneath the platform  14  and mounting the engine  16  to the engine mounts  15  on the platform  14  and then connecting the belt drive clutch mechanism  27  between the engine  16  and the jet drive unit  17  through the pulley  28 .  
      Because in a preferred embodiment engine  16  and jet unit  17  ship as a unit, the jet size to use is known. Smaller boats usually forego the reduction and just use a jet, which is too small, operated at engine speed. For those who wish to use a larger jet and a reduction, a transmission must be used. This is an extra cost an extra layer of complexity and an extra gearing change which robs the engine&#39;s efficiency. Furthermore, although transmissions could be made to match a particular engine to a particular jet, the current volumes of production make this cost prohibitive.  
      Another key advantage of the present invention is that the gear ratio can be changed just by changing one or both gears. As a result, any engine power can be matched to a desired RPM in a single jet design. With four or five different jets, a range of engines from 35 HP to 2000 HP can be covered. Thus, one jet can now be used with engines from 50 HP to 400 HP. This is a huge advantage in that different jets do not need to be designed for different engines.  
      A series of engine parameters were tested. The test boat is a Zodiac ZH630, a 6.71 meter rigid inflatable boat with a 24-degree deadrise. The boat used was setup for an I/O (inboard/outboard) installation and had a full transom. This boat is normally powered with a 200 horsepower I/O. The 150 horsepower diesel jet unit was fitted and tested under varying conditions and loads.  
      The following data was obtained:  
                                                      Engine   150 horsepower diesel           Fuel   10 US gallons fuel           Load   2 persons           Conditions   Calm, lake, good wind                                                 Speed (knots)   Speed (knots)           RPM   Direction 1   Direction 2                       1000   3.7   3.4           1500   5.4   5.0           2000   6.3   6.2           2500   7.2   6.8           3000   19.5   14.8           3500   28.0   26.4           3800 WOT   32.1   31.1                                         Engine   150 horsepower diesel           Fuel   50 US gallons fuel           Load   2 persons           Conditions   Rough water, offshore                                                 Speed (knots)   Speed (knots)           RPM   Direction 1   Direction 2                       1000   2.3   3.6           1500   5.4   5.7           2000   6.4   6.4           2500   7.5   7.4           3000   14.3   13.2           3500   25.4   26.3           3800 WOT   29.8   29.7                                         Engine   150 horsepower diesel           Fuel   50 US gallons fuel           Load   8 persons           Conditions   Rough water, offshore                                                 Speed (knots)   Speed (knots)           RPM   Direction 1   Direction 2                       1000   3.3   2.7           1500   5.3   5.2           2000   6.4   6.3           2500   7.0   6.5           3000   8.1   8.0           3500   18.1   17.2           3800 WOT   25.6   24.6                                         Engine   275 horsepower gas           Fuel   50 US gallons fuel           Load   2 persons           Conditions   Calm, lake, good wind                                                 Speed (knots)   Speed (knots)           RPM   Direction 1   Direction 2                       1000   4.0   3.9           1500   5.6   5.6           2000   6.9   6.8           2500   8.3   8.4           3000   21.5   21.2           3500   32.2   31.3           4000   36.2   36.3           4500   43.0   42.1                                         Engine   275 horsepower gas           Fuel   50 US gallons fuel           Load   11 persons and 1000 lbs of sand           Conditions   Calm, lake, good wind                                         RPM   Speed (knots) Direction 1                       4500   34.0                      
 
      Preferably, housings  13 ,  201 ,  206  are sealed mostly to create buoyancy and to protect the engine from corrosion or damage; however, prevention of oil and anti-freeze leaks to the outside (surrounding water) is a side benefit. The leaks from the engine could be isolated by providing a pan below the engine with separate drainage.  
      Notwithstanding the above, it should be appreciated that, in accordance with the present invention, in certain models, water may enter and exit the heat exchanger and intercooler through holes drilled specifically for that purpose; however, these holes are sealed to prevent water from entering or leaking into the engine compartment. In addition, water may enter into the exhaust ports. However, the engine is far enough above the water line to prevent water from rising high enough to enter the engine or engine compartment. Water also may enter the jet intake and exits the jet nozzle; this water is prevented from entering the engine compartment by sealing the hole around the jet impeller shaft. There may also be air intake vents in the lid in which water may enter. These are made with baffles designed to drain any water, which gets in out through the lid before it gets into the engine compartment.  
      While the bottom of the housing may be mounted in any suitable position, such as about even with or higher than the bottom of the boat hull, any position around or even with the bottom of the boat is workable. In a preferred position, the bottom of the housing is at about an inch below the bottom of the boat hull on boats to ensure or maximize the amount of clean water that enters the water intake of the jet drive unit. In addition, this position will reduce ingression of debris and damage to wildlife. It of course should be understood that this position may very depending upon the configuration of the bottom. of the boat. It is believed that this is the optimum position, because the jet intake is built into the housing. Nevertheless, the bottom center of the boat is the optimum depth position for the water intake in the preferred embodiment.  
      In a preferred embodiment, marine propulsion unit  10 &#39;s steering nozzles, exhaust of bucket assembly  300 , are generally about 30 inches or more behind boat transom  12 . This provides excellent steering leverage and, with a large diameter having water jet  313  moving large amounts of water, it provides crisp steering response and solid tracking with very little correction. The steering control pressures of marine propulsion unit  10  are very light and do not require power steering for comfortable boating.  
      Because of bucket assembly  300 , propulsion unit  10  provides the capability of “putting on the brakes”. When propulsion unit  10  is shifted into reverse, all the power of the engine and water jet are applied to stop and reverse the boat. Tests on a 5,000-pound boat equipped with a propulsion unit  10  as described herein show that the boat could be stopped completely within two boat lengths from 30 mph with ease.  
      The recommended procedure to stop outboard propulsion unit  10  is to reduce the engine RPM by about 50 percent and shift into reverse. If desired, the engine RPM can be increased. In an emergency, the boat can be shifted into reverse directly at any power setting, but that may injure the boat passengers.  
      Useable space inside a boat is usually at a premium. The outboard propulsion system, in accordance with the invention, and the traditional outboard engines have a distinct advantage over inboard/outboard and inboard systems that require valuable space inside the boat for engines and essential equipment. Even traditional outboards are at a disadvantage compared to the propulsion unit  10  because they generally require space inside the boat when in the tilted up profile. Also, many outboards require a notch in the transom to achieve the correct propeller depth requiring a second “transom” inside the boat to prevent following seas from swamping the boat. That space is lost boat space.  
      Propulsion unit  10  requires no space inside the boat for any of its components. The increase in space inside the boat is available for any use, e.g., for passengers, bait wells, fish holds, and even for lounging decks.  
      Because engine  16  is mounted on high quality vibration isolators inside the fiber glass shell and housing  13  is mounted on the boat transom using a second system of vibration isolators, an exceptional and unexpected level of quiet and comfort is provided. As a result, the boat ride is more comfortable and less tiring.  
      Internal combustion engines get hot when running. That engine heat is handled several ways in a boat. The engine water-cooling system is designed to remove a considerable amount of that heat, but that system operates at about 160 to 220 degrees Fahrenheit to insure that the engine operates correctly. The balance of the heat is released in convection, radiated into the air in the engine compartment. This heat can make it quite uncomfortable in the area of the engine compartment, especially on a hot day. This problem exists with any inboard or UO drive configuration. Ventilating fans and insulation can reduce the problem to a degree, but it is difficult to eliminate.  
      Outboard marine engines are mounted behind the transom behind the boat. Any heat from these engines that is not carried overboard by the water-cooling system is released into the air behind the boat. This gives all outboard engines a distinct advantage over inboard mounted engines.  
      Propulsion unit  10  has an added advantage because it has the engine mounted in a sealed box and the air inside the box is normally ingested into the engine and goes out the exhaust in the water. It is very unlikely that a passenger will feel any warming of the air in the boat caused by the propulsion unit.  
      As a result of sealing housing  313 , propulsion unit  10  is uniquely designed with self-buoyant capability. Because the housing is sealed, it provides flotation. Indeed, in a preferred embodiment, at approximately 1 foot of draft, it floats about 250 lbs, at approximately 1.5 foot (18 inches) of draft, it floats about 500 lbs, and at approximately 2 feet of draft, it floats about 850.lbs (approximately the total weight of the marine propulsion system). This is a significant feature and advantage to any boat and especially valuable to smaller boats with low freeboard dimensions.  
      Some of the new four-cycle outboards are quite heavy and cannot be used on some existing boats because the extra weight causes the scuppers to be submerged. At least one boat manufacturer had to redesign their boat to accommodate these heavy engines. Inboard/outboard and inboard systems depend solely on the boat to provide their flotation. The weight of the propulsion system, in all of these instances, reduces the boats&#39; cargo and passenger carrying capability.  
      Because of the buoyancy of housing, propulsion unit  10  allows boats to uniquely have more weight carrying capacity and, as a further benefit, more useable space inside the boat is available.  
      Propulsion unit  10  preferably uses a stainless steel water jet impeller to supply the seawater to the heat exchanger for engine cooling. If the impeller is turning, there is water for the cooling function. Even if the stainless steel impeller were severely damaged, there would be enough water flow to move the boat and provide engine cooling.  
      High-speed marine diesel engines are traditionally automotive truck or industrial engines with all the marine components plumbed and attached to the engine itself, These engines are designed for multipurpose marine uses and are generally complete with transmission, raw water pump and accessories not always needed for water jet purposes. As a consequence to the complexity of this arrangement, reliability, serviceability, weight and cost are adversely affected. With this new approach the engine is fitted basically stock with the addition of special engine mounts and a water-cooled exhaust manifold. All of the necessary marine components are fitted and plumbed in the fiberglass housing. Installation problems are significantly reduced due to the higher standards allowed by repetitive factory assembly and quality control procedures practiced on identical machines. As the unit is a self-contained stand alone system, no boat design, speed requirements or specific customer demands affect the quality control of the engine assembly and installation.  
      Traditional water jets are made to adapt to engines forward of the waterjet. Although jets should be fitted with a reduction to be efficient, most are fitted directly to the engine. This means the jet driveshaft has to be higher than ideal because of the engine crankshaft height. If the jet were fitted as close to the bottom of the boat as possible as in accordance with the invention, efficiency would be much higher for these reasons: 
          Frictional losses on the inlet and outlet would be less,     Jet outlet would be lower on the transom and thrust line would therefore be lowered. (A low thrust line is desirable because it moves the active center of gravity aft giving less of a nose down attitude to the boat).     The lower thrust line also makes the boat more stable by cutting down the teeter caused by directional changes of the nozzle and this would reduce wandering at all speeds.     Inlet size would be reduced; this would enhance the efficiency of the boat by reducing the hook effect caused by putting a large hole in the most critical part of the hull.        

      In most cases, the further aft the center of gravity, the faster the boat. This is a major part of the outboard performance advantage (a bracket increases this advantage). Because the engine is completely behind the transom, the passengers are typically located further aft also, further enhancing the performance. Just by moving the engine inboard, as in an inboard/outboard configuration and pushing the passengers forward, the performance per horsepower is drastically reduced. Noise, heat, vibration, fuel use and the need for service are greatly increased due to the engine having to work harder to perform the same work. Further, in a small jet boat, the undesirable combination of a forward center of gravity and high center of thrust line is exasperated by the possibility of air from the continuous bottom entering a high speed jet (because the jet is usually driven at engine speed) and causing cavitations.  
      Internal components and internally stored fuel can be preserved indefinitely by replacing the oxygen in a sealed housing with an inert gas. A simple monitoring system can be installed to easily verify that the housing remains sealed and that oxygen is absent. This virtually assures that the condition of the components will be preserved. When the unit is needed for service, air intake and exhaust ports can be opened with a starting mechanism. This system could be used on ocean going lifeboats, eliminating the need for routine and costly removal and recertification of the complete vessel.  
      Because of the shallow draft and the added buoyancy at the rear of the vessel, launching and retrieving the unit into the surf is an option that can now be considered. The jet is manufactured of stainless steel and is tolerant of sand and small stones. On a shallow beach the unit could be launched with a four wheel drive truck, extending tow hitch and fat tired trailer. This would allow faster rescue deployment in places not covered by traditional land launched rescue lifeboats, at a fraction of the cost. In heavy conditions, this craft could be hard beached at speed and picked up by winching it onto a special trailer, without any significant damage.  
      The elimination of the exposed propeller makes this a preferable system for lifeboat use. Additionally the absence of propellers and any lower unit below the bottom of the boat significantly reduces damage and downtime from collisions with submerged debris and rocks, particularly during critical rescue operations.  
      The large diameter jet has ample thrust to maneuver a lifeboat in tight quarters at low speeds. The test boat exhibited exceptional maneuverability at low speed even in rough water with heavy loads.  
      The simplicity of the design and the elimination of high maintenance components should make this an extremely reliable system for lifeboat use. Further, the portability of the system enables the propulsion package to be quickly exchanged with a spare unit, eliminating the need to take entire boats out of service for recertification.  
      Durability under extreme conditions and service has yet to be proven but the simplicity of the unit and the testing already completed have demonstrated significant advantages over all current systems. Systems specifically designed for lifeboat operation could increase longevity, reliability, simplify service, reduce operational cost and make significant improvements in speed maneuverability and safety.