Abstract:
A highly efficient watercraft propulsion system that relies on a positive displacement pump to generate a water jet. The pump is fully submerged at all times and its inlet is positioned so as to cause water to be forced into the pump as the watercraft moves through the water. The pump is preferably combined with a variable area pump opening which is configured, positioned and oriented so as to maximize the hydraulic reaction between the water jet stream and the surrounding body of water.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. Ser. No. 11/771,035, filed on Jun. 29, 2007, which is a divisional of U.S. Ser. No. 11/103,318 filed on Apr. 11, 2005, now U.S. Pat. No. 7,238,067. 
     
    
     BACKGROUND 
       [0002]    The present invention generally relates to water jet propulsion systems for watercraft and more particularly pertains to the use of a particular type of pump configuration and its adaptation to a watercraft to achieve enhanced efficiency. 
         [0003]    A variety of jet pump configurations have previously been used to propel watercraft. Most such configurations comprise kinetic pumps of one form or another that serve to accelerate water to a high velocity in order to achieve the desired propulsive force. The losses associated with the high velocities, the non-aligned flow and the turbulent flow inherent in the operation of many such pump configurations limits the efficiency that is ultimately attainable. Nonetheless, kinetic pumps, or dynamic pumps as they may also be referred to, are the most commonly used type of pump for marine propulsion applications and typically rely on an impeller to push water through a duct. Positive displacement pumps on the other hand are capable of generating high hydrostatic pressures at essentially zero velocity and could conceivably be able to provide substantial gains in terms of efficiency. However, the positive displacement pump configurations that have been proposed for the propulsion of watercraft and the adaptations of such pumps to watercraft that have been proposed have failed to cause the use of positive displacement pumps to gain wide acceptance for such purpose. 
         [0004]    It is well known that the velocity with which a water jet is discharged from a watercraft relative to the velocity of the watercraft has a direct effect on the efficiency of such a system. Propulsion efficiency, whether measured with respect to fuel consumption or vessel speed, is a function of both water jet discharge velocity and volumetric flow. While the water jet discharge velocity can of course be controlled by pump&#39;s volumetric output, the jet velocity can also be controlled by varying the cross-sectional area of the orifice through which the water is discharged. Accordingly an increase in the cross sectional area of the discharge orifice for a given pump output reduces the water discharge velocity while a decrease of the cross-sectional area serves to increase said velocity. 
         [0005]    It has long been recognized that the ability to vary discharge orifice area can significantly enhance propulsion efficiency over a wide range of operating conditions and thereby reduce fuel consumption. A large variety of configurations that are either cylindrical, conical, hemispherical or combination of same have been suggested for a discharge orifice that is variable in terms of both area and flow path shape along with various mechanisms to control the water discharge velocity as a function of any of various parameters. Even greater efficiency would nonetheless be desirable. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention provides a highly efficient water jet propulsion system for a watercraft by relying on a non-pulsating positive displacement pump to move water through a duct. Moreover, the pump is preferably arranged so as to be fully submerged at all times. It is further preferred to arrange its inlet opening such that water is forced directly into the pump by the movement of the watercraft through the water. It is additionally preferred to combine the pump with a submerged variable area discharge opening so as to allow for the velocity of the discharge jet to be optimized relative to the velocity of the surrounding water. Finally, it is preferred to package the entire propulsion system so as to be attachable to the bottom of a hull or other fully submerged surface of a watercraft. 
         [0007]    A positive displacement pump displaces a preselected volume of water from the input side of the pump to the output side of the pump with each pump cycle or rotation and substantially precludes any return of water from its output side to its input side even when operating at low velocities and/or under high head pressures. Positive displacement pumps add both potential energy as well as kinetic energy to a continually displaced volume of water and the displaced volume per cycle or rotation is independent of cycle or rotation rate. As such, positive displacement pumps are readily distinguishable from kinetic or dynamic pumps that rely on for example impellers or paddle wheels to move water. A positive displacement pump is capable of generating substantial hydrostatic pressures at very low jet velocities. Non-pulsating configurations generate a constant flow throughout each cycle or rotation. This delivery characteristic has unexpectedly been found to further enhance efficiency in propelling a watercraft. The net result is an increase in performance potential, a reduction in fuel consumption and a commensurate reduction in emissions. 
         [0008]    The preferred pump configuration is a counter-rotating rotor pump which may also be referred to as a counter-rotating lobe pump or external gear pump. Additionally it is preferred that the rotors&#39; lobes follow a helical path along the rotors&#39; rotational axes with a sufficient amount of twist to ensure that there is a continual discharge of fluid as the rotors are rotated. An example of such a pump is described in U.S. Pat. No. 3,164,099 to Hitosi Iyoi which is incorporated herein by reference in its entirety. 
         [0009]    The efficiency provided by the positive displacement pump is further enhanced with its combination with a discharge opening that is continuously variable in terms of its cross-sectional area. Such discharge configuration employs an opening having a cross-sectional shape that is substantially trapezoidal. The sides of the discharge opening transverse to the parallel sides are straight or curved and may be substantially parallel so as to define a rectangle. Additionally, the discharge duct is positioned on the submerged portion of the watercraft hull so that the pump discharge flow is ejected into the surrounding water thereby creating a direct hydraulic coupling to thereby enhance thrust efficiency. 
         [0010]    It is additionally preferred that the inlet be arranged so as to cause water to be forced into the pump as the watercraft moves through water. This inlet ram feature has the benefit of increasing the static pressure head on the suction side of the pump thereby reducing the possibility of rotor cavitation at high pump speeds and therefore allows the pump to operate at higher speeds than have heretofore been possible. Efficiency is further enhanced by arranging the inlet, pump and outlet along a straight line. This not only ensures that the entire propulsion system is fully submerged at all times to preclude any loss of prime but further eliminates any inefficiencies that could otherwise be introduced if the flow of water into, through and out of the pump were forced to change direction. 
         [0011]    On vessels that generally have a flat bottom, the discharge opening of the duct may generally define a horizontally oriented tapered trapezoidal duct. On large vessels, several ducts may be installed at various orientations on the submerged portion of the curved hull. A contoured or generally wedge-shaped control element is movably disposed within the duct such that its narrow end is variably extendible out through the exit of the discharge opening. The control element thereby serves to block off a central portion of the discharge opening to reduce the total cross-sectional area that remains open to the flow of water there through. Its wedge shape serves to block off a progressively larger portion of the discharge opening&#39;s cross-sectional area as the control element is caused to translate out through the discharge opening which in turn results in an increase in the water jet velocity. Conversely, retraction of the control element serves to increase cross-sectional area to thereby reduce water jet velocity. 
         [0012]    The linear position of the wedge-shaped control element may be translated by any number of actuation means including, but not limited to, mechanical, hydraulic, or servo electronic systems or combinations thereof. A variety of different control means may also be relied upon to govern the position to which the control element is actually shifted including, but not limited to, manual selection, direct action of pump output or more sophisticated systems such as for example a microprocessor that considers a plurality of parameters and calculates an optimum setting. A preferred embodiment simply relies on the action of a spring to bias the control member into its retracted position. As the force of the flow of water impinging on the frontal surfaces of the control element is increased by an increase in the volumetric pump output, the bias of the spring is overcome to cause the control element, which is constrained vertically between the upper and lower, parallel surfaces of the discharge duct, to shift linearly towards the discharge opening thereby causing a further increase in flow velocity. 
         [0013]    The location and orientation of the discharge opening serves to further enhance the propulsion efficiency of the water jet discharge system of the present invention. Accordingly, the discharge opening is positioned so as to remain submerged at all times to create a direct hydraulic reaction between the discharge jet and the surrounding body of water. By positioning the discharge opening so as to extend from the bottom of the hull at a location substantially forward of the trailing edge of the hull, the section of hull aft of the discharge opening in the plane of the upper surface of the duct prevents the upward diffusion of the jet. Additionally, an extension of the duct&#39;s bottom surface aft of the discharge opening limits the amount of downward diffusion of the jet in the plane of the lower surface of the duct. By constraining the discharged jet between the hull and the duct extension aft of the discharge opening, a greater portion of the discharge flow is constrained so as to remain substantially parallel to the direction of desired thrust i.e. in-line with the direction of travel. The result is an increase in axial thrust, or vessel driving force, than if the pump discharge is allowed to diffuse freely. 
         [0014]    The pump, inlet opening and discharge opening are preferably disposed within a housing that is attachable to the bottom of the hull of a watercraft. A transfer box extending upwardly and through the hull is relied upon to transfer rotation from a prime mover to the pump. It is important that the shape of the submerged portion of the pump housing is streamlined in such a way so as to minimize the hydrodynamic impact of its presence in such a critical location. 
         [0015]    These and other advantages of the present invention will become apparent from the following detailed description of preferred embodiments which, taken in conjunction with drawings, illustrate by way of example the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0016]      FIG. 1  is a side view of a watercraft fitted with the propulsion system of the present invention; 
           [0017]      FIG. 2  is a front view of the watercraft shown in  FIG. 1 ; 
           [0018]      FIG. 3  is a rear view of the watercraft shown in  FIG. 1 ; 
           [0019]      FIG. 4  is a perspective view of the submerged portion of the housing that contains the propulsion system of the present invention; 
           [0020]      FIG. 5  is a sectioned perspective view taken along lines V-V of  FIG. 1 ; 
           [0021]      FIG. 5   a  is a perspective view of the helical rotors shown in  FIG. 5 ; 
           [0022]      FIG. 6  is a cross-sectional view of an alternative embodiment of discharge opening configuration of the propulsion system of the present invention shown in its full retracted state; 
           [0023]      FIG. 7  is a cross-sectional view of the discharge opening configuration shown in  FIG. 6  in its fully protracted state; 
           [0024]      FIG. 8  is a cross-sectional view of an alternative embodiment of the propulsion system of the present invention; 
           [0025]      FIG. 9  is a perspective view of a preferred embodiment of the propulsion system of the present invention; and 
           [0026]      FIG. 10  is a cross-sectional view of the propulsion system shown in  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]    The water jet propulsion system of the present invention provides for enhanced efficiency in the propulsion of a watercraft. The figures generally illustrate preferred embodiments of the propulsion system in terms of its pump configuration, its adaptation to and orientation relative to a hull, a mechanism for varying the cross-sectional area of the discharge opening and the packaging of its various components. 
         [0028]      FIG. 1  is a side view of a watercraft  12  showing the propulsion system  14  of the present invention fitted to the bottom of its hull  16 . The system includes a housing  18  that contains a pump (not visible) and has an inlet opening  20  at its forward end and a discharge opening  22  at its aft end. The housing is positioned under the hull so as to ensure that the inlet opening, pump and discharge opening remain fully submerged at all times during all modes of operation. The submersion of the outlet opening even under maximum acceleration from low speeds or at maximum velocity ensures that the hydraulic reaction between the liquid jet stream and the adjacent, relatively static body of water can be maximized at all times. As can be seen in the  FIG. 1 , the discharge opening is positioned well forward of the aft edge  24  of the hull. 
         [0029]      FIG. 2  is a front view of the watercraft  12  showing the propulsion system  14  extending below the hull  16 . The inlet opening  20  is shown centered in the forward end of the housing  18 .  FIG. 3  is a rear view of the watercraft  12  showing the propulsion system  14  extending below the hull  16 . The outlet opening  22  is shown centered in the aft end of the housing  18 .  FIG. 4  is a perspective view of the submerged portion of the housing  18  that contains the propulsion system  14  disposed on the bottom of the hull  16 . 
         [0030]      FIG. 5  is a perspective view of a cross-section of the propulsion system  14  taken along lines V-V of  FIG. 1 . Visible in this view is jet pump  26  that is substantially centrally located within housing  18 . The preferred pump configuration that is shown is a counter-rotating helical rotor pump. In the preferred embodiment shown, each rotor  28 ,  30  includes three lobes  32 , wherein the rotors are positioned such that the lobes from each rotor sealingly intermesh with one another at the center and sealingly engage the seal regions  34  that are formed in each side of the housing. Rotation of the rotors causes a fluid to be positively displaced from one end of the pump to the opposite end of the pump while backflow is precluded. Rotation in the direction indicated by the arrows will cause fluid to be forced from the inlet end  20  to the outlet end  22 . Only one particular such pump configuration is shown while different numbers of lobes and lobe profiles can be used. In the preferred embodiment, the lobes  32  and hence the recess  36  there between describe a helical shape relative to the axis of rotation  38  of each rotor as is most visible in  FIG. 5   a . The number of lobes and recesses will determine the angle that is described by the seal regions  34 . Additionally shown in  FIG. 5  are gussets  42 ,  44  that are position within both the inlet end  20  as well as the outlet end  24  of the housing  18 . The gussets serve not only to align the flow to and from the pump but also serve as structural members to reinforce the housing. 
         [0031]    While the embodiment illustrated in  FIG. 5  has a discharge opening with a fixed cross-sectional area, further efficiencies are gained with the fitment of a mechanism for varying the cross-sectional area of the discharge opening such as is shown in  FIGS. 6 and 7 . A moveable control element  46  is positioned in the discharge opening  22  and is shaped such that a shift in its longitudinal position will cause the discharge area  48  to change. Full retraction of the control member, as is shown in  FIG. 6 , will serve to maximize the cross-sectional area and thereby minimize the velocity of the flow of water while full protrusion, as is shown in  FIG. 7 , will minimize the cross-sectional area and thereby maximize the velocity of the flow of water. Any of a variety of control member configurations can be employed as can any of various mechanisms to alter the position of the control member so as to achieve a desirable ratio of the jet velocity relative to the surrounding water velocity.  FIG. 8  illustrates an alternative preferred embodiment wherein five lobe helical rotors  28   a ,  30   a  force the flow of water past two control elements  46   a ,  46   b . Additionally visible is a bottom lip  50   a  that extends beyond the discharge opening from the bottom surface of the housing to limit downward diffusion of the water jet. 
         [0032]      FIG. 9  is a perspective view of the propulsion system  14  of the present invention. A transfer box  52  extends from the top of the housing  18  for transferring rotation from a prime mover (not shown) via flange  54  to the pump rotors that are disposed within the housing. Both the inlet opening  20  as well as the discharge opening  22  are visible. A flange  56  extends about the periphery of the housing to facilitate its attachment to the bottom of a hull. Any of a variety of prime movers can be relied upon to power the propulsion system including, but not limited to internal combustion engines, electric motors, hydraulic motors, vertical axis wind turbines and even human power. 
         [0033]      FIG. 10  is a cross-sectional view of the embodiment shown in  FIG. 9 . In this particular embodiment, a flow  58  of water into the inlet opening  20 , past rotor  30  and out through discharge opening  22  can describe a substantially horizontal path. The decrease in the height of the outlet conduit and the commensurate decrease in cross-sectional area serves to accelerate the jet before being discharged. In the particular embodiment that is illustrated, a gear set  60 ,  61  serves to transfer rotation from flange  54  to the rotors. 
         [0034]    In operation, reliance on a non-pulsating positive displacement pump in water jet propulsion systems yields substantial gains in efficiency over previously used devices. More specifically, a counter-rotating helical rotor pump is able to provide an aligned continuous flow at the most efficient velocity without turbulence. The non-pulsating flow characteristic eliminates the thrust disruptions inherent in pulsating configurations and the inefficiencies resulting therefrom. Such pump in conjunction with a fully submerged discharge opening having a variable cross-sectional area yields extremely high propulsion efficiency over the entire range of pumping capacity. Adjustment of the cross-sectional area of the discharge opening allows the discharge jet velocity to be set to propel a vessel at its best fuel efficiency or, if desired, to provide maximum driving force over a wide range of vessel operating parameters such as weight, displacement and weather conditions. The submerged variable area discharge opening in combination with the installation location on the hull and a bottom lip serve to limit diffusion of the water jet thereby minimizing the dynamic mixing losses aft of the discharge plane allowing the hydraulic reaction to be maximized. It is contemplated that the propulsion system of the present invention can be sized and adapted to most any watercraft from motorized surfboards and kayaks, to sport and pleasure boats to freighters and tankers. In each such application, overall energy consumption can be significantly reduced as the water discharge velocity leaving the housing can be optimized at any given vessel speed to yield the highest possible propulsion efficiency using the least amount of fuel. Unlike water jet propulsion systems that discharge above the waterline of a vessel, there is no need for complicated diversion systems that direct the flow of water forward to provide reverse thrust. A simple reversing of the rotor rotation provides reverse thrust by causing the water to flow from the submerged discharge end out the submerged inlet. 
         [0035]    While particular forms of the invention have been described and illustrated, it will also be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited except by the appended claims.