Abstract:
A watercraft, equipped with a jet drive power source, with improved stability is disclosed. The jet drive power source is configured to produce power along a predetermined direction and form a drive line based upon the predetermined direction. The drive line bisects a plane of the keel at a predetermined angle that is less than about 4 degrees. The drive shaft and the output shaft are not substantially parallel.

Description:
This application is a continuation-in-part of U.S. Non-provisional Patent Application Ser. No. 09/635,262, filed on Aug. 9, 2000, now pending, which is incorporated herein by reference. This application also claims the benefit of U.S. Provisional Patent Application Ser. No. 60/168,676, filed Dec. 3, 1999, and Canadian Application No. 2,279,804, filed Aug. 9, 1999, both of which are incorporated herein by reference. The parent application (Ser. No. 09/635,262) relies on these two applications for priority. In addition, this application relies for priority on U.S. Provisional Patent Application Ser. No. 60/308,836, filed on Aug. 1, 2001, the contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to watercraft and more particularly to watercraft with improved stability. 
     DESCRIPTION OF THE RELATED ART 
     Various types of watercraft exist, each being suited for different types of activities. For example, a pontoon-type watercraft is designed for slower speeds and general recreational use and is typically powered by an outboard engine. In contrast, sport boats and personal watercraft are designed for higher speeds and superior handling and are powered typically by inboard jet drive systems, which consist of an inboard engine and a jet propulsion unit. 
     In a conventional sport boat, the engine is mounted above a jet propulsion unit. The intake for the jet propulsion unit is located beneath the watercraft and the exhaust, or jet port, is located at the rear of the watercraft. 
     There are several parameters that are engineered into a sport boat that may affect its performance. One of those parameters is the “drive line angle,” which is the angle measured between the primary drive shaft (attached to the impeller) and the keel line of the watercraft. 
     Due to the physical characteristics of conventional jet drive systems in sport boats in the prior art, the drive line angle is typically about 4 degrees or greater. In a conventional watercraft, the positive angle of the drive line translates into an angle of thrust that is directed slightly upward toward the surface of the water, as illustrated in FIG.  2 . The upward thrust angle has a tendency to push the bow of the watercraft out of the water. In other words, the positive drive line angle tends to lift the bow of the sport boat during operation. 
     U.S. Pat. No. 5,984,740 (the &#39;740 patent) describes and illustrates a personal watercraft  10 , which incorporates a jet propulsion drive configured according to the teachings of the prior art. As illustrated in FIG. 3 of the &#39;740 patent, the impeller shaft 56 is angled upwardly from the keel line. The exact angle α of the impeller shaft 56, however, is not disclosed. The &#39;740 patent only discusses the advantages of a positive angle α for operation of the personal watercraft  10  described. (See. e.g. the &#39;740 patent at col. 5, lines 36-48.) 
     While those skilled in art may appreciate the benefits of a positive drive angle, a phenomenon known as “porpoising” may be detected, at certain speeds, by occupants of certain boats. “Porpoising” refers to a condition where the boat tends to move up and down in the water like the movement of a porpoise when it jumps out of the water. This can create an unpleasant ride for the occupants of the boat. 
     Conventionally, sport boats powered by jet propulsion units have all had positive drive line angles. In fact, conventional wisdom suggests that anything less than a positive drive line angle will so adversely affect vehicle performance that manufacturers of marine engines have specifically discouraged the incorporation of neutral (0°) or negative drive line angles in boats. 
     “Porpoising,” however, remains a problem with certain boat designs. 
     Accordingly, a need exists for a watercraft that utilizes a jet drive system with improved stability and reduced “porpoising” to ensure that the occupants of the boat will experience a more comfortable and enjoyable ride. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a watercraft, which provides the advantages of a jet propulsion system, with increased stability and reduced “porpoising,” by controlling the angle of thrust of the propulsion unit relative to the keel line. 
     One embodiment of the present invention provides a watercraft including a hull with a keel and a jet drive power source. The jet drive power source includes an engine, an engine output shaft, and a jet propulsion unit. The jet propulsion unit includes a water passage, a drive shaft, an impeller, and a jet port. The engine output shaft is operationally connected to the drive shaft. The jet drive power source is configured to produce power along a predetermined direction and form a drive line based upon the predetermined direction. The drive line bisects a plane of the keel at a predetermined, preferably negative, angle. 
     Other embodiments of the present invention will be discussed in or will be made apparent from the description that follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the present invention. In the figures: 
     FIG. 1 is a cross-sectional side view of the watercraft of the present invention; 
     FIG. 2 is a detailed cross-sectional view of the jet drive system of the prior art; 
     FIG. 3 is a detailed cross-sectional view of one embodiment of the jet drive system of the present invention; and 
     FIG. 4 is a detailed cross-sectional view of an alternate embodiment of the jet drive system of the present invention as illustrated in FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Throughout the description of the several embodiments of the present invention, reference will be made to various elements, the construction of which is readily known to those skilled in the art. Accordingly, an exhaustive description of each and every component is not provided, only a description of those elements required for an understanding of the present invention. 
     FIG. 1 is a side view of a watercraft  10  of the present invention. In the preferred embodiment, the watercraft  10  is a jet boat that includes a hull  20 , with a bow  21 , a stern  22 , and a keel  23 . The watercraft illustrated in FIG. 1 is a sport boat. The details of the sport boat have been omitted because they are not relevant to the present invention. As those of ordinary skill in the art will appreciate after reading the description set forth below, the present invention may be employed on any style jet-propelled boat, regardless of the size, style, or configuration. 
     In the preferred embodiment, the watercraft  10  of the present invention is powered by a jet drive power source  30 . The jet drive power source  30  of the present invention provides for an improved boat ride by comparison with a conventional, propeller-driven watercraft. 
     As shown in general detail in FIG. 1, and in greater detail in FIGS. 3 and 4, the jet drive power source  30  includes an engine  40  with an output shaft  45  and a jet propulsion unit  50 . The engine  40  may be, but is not limited to, a two-stroke or a four-stroke, inboard, internal combustion engine. 
     Referring to FIGS. 3 and 4, the jet propulsion unit  50  comprises a housing  51  with a water passage  52  defined by the housing  51 , an intake  90 , an drive shaft  55 , an impeller  56 , and a jet port  80 . Although the housing  51  can be a separate piece that is mounted to the hull  20 , the housing  51  is preferably integrally formed as part of the hull  20 . 
     The engine  40  is operatively connected to a jet propulsion unit  50  through its output shaft  45 . The output shaft  45  is rotationally connected to the drive shaft  55 , located within the jet propulsion unit  50 , such that the output shaft  45  and the drive shaft  55  are not substantially parallel. That is, an angle  60  is formed between the longitudinal axis of the output shaft  45  and the longitudinal axis of the drive shaft  55  such that the angle  60  is greater than zero. As would be appreciated by those skilled in the art, however, the output shaft  45  and the drive shaft  55  could be disposed so that they are substantially parallel (either coaxial or coplanar) to one another. 
     As defined herein, in the preferred embodiment, the angle  60  formed between the longitudinal axis of the output shaft  45  and the longitudinal axis of the drive shaft  55  will, by definition, be between about 5 degrees to about 175 degrees, no matter the configuration between the engine  40  and the jet propulsion unit  50 . Preferably, the angle  60  will be between about 45 degrees to about 135 degrees. Most preferably, the angle  60  will be about 90 degrees and the output shaft  45  will have a generally vertical orientation. 
     In the embodiments illustrated, the output shaft  45  and the drive shaft  55  are located in the same longitudinal plane that bisects the hull  20  from the bow  21  to the stern  22 . Alternatively, the output shaft  45  and the drive shaft  55  may be located in a plane that is either parallel to, or intersects with the longitudinal plane that bisects the hull  20  from the bow  21  to the stern  22 . 
     Disposed within the jet propulsion unit  50  is a water passage  52 . During normal operation of the watercraft  10 , water enters the passage  52  at an intake  90  located at the bottom of the hull  20 . The water enters the passage  52 , passes by an impeller  56  and exits the passage  52  through a nozzle  78  and then through a jet port  80 . Depending on the speed of the watercraft  10 , the jet port  80  may or may not operate below the waterline  70  of the watercraft  10 . Normally, at slow speeds, the jet port  80  usually operates beneath the waterline  70 . 
     The jet port  80  typically is a steerable nozzle connected, usually via cables, to the helm of the watercraft  10 . As the operator changes the helm direction, so, too; does he/she change the direction of jet port  80 . In this manner, the operator changes the travel direction of the watercraft  10 . 
     As illustrated in FIGS. 3 and 4, the nozzle  78  and the jet port  80  for the jet drive power source  30  generate a force along the drive line  85  in a rearward direction  86 . The drive line  85  forms an angle  87  with the keel  23  of the watercraft  10 . In FIGS. 3 and 4, a plane  25  defined by the keel  23  is shown at the keel  23  as a solid line and above the keel  23  (for reference) as a dotted line. The plane  25  is laterally oriented, parallel to the keel  23 . 
     In the illustrated embodiments, the central axes of the drive shaft  55 , the impeller  56 , the nozzle  78 , and the jet port  80  are aligned along a common centerline. So aligned, the centerline, which is an extension of the central axis of the drive shaft  55 , defines the drive line  85  of the jet propulsion unit  50 . 
     In the illustrated embodiments, the nozzle  78  and the jet port  80  are substantially oriented along the same direction. In other words, both are oriented to direct the force of the jet power source  30  along the drive line  85 , which corresponds to the axis of the drive shaft  55 . It is possible, however, that the jet port  80  and the nozzle  78  may be oriented with respect to one another so that they are not substantially oriented along the same direction. Regardless, the combined effect of the nozzle  78  and the jet port  80  will establish a drive line  85  with an angular orientation to the plane  25  defined by the keel  23 . That drive line  85  typically corresponds to the axis of the drive shaft  55 . 
     As shown in FIGS. 3 and 4, the drive line  85  intersects with the plane  25  of the keel  23  at an angle  87 . In the conventional embodiment illustrated in FIG. 2, the drive line  85  forms a positive angle  87  of more than about 4 degrees with the plane  25  of the keel  23 . 
     As discussed above, prior to the present invention, those skilled in the art (in particular the jet drive engine manufacturers) believed that the drive line angle must be positive in order for the watercraft to operate properly, as shown in FIG.  2 . Anything less than about a 4 degree drive line angle  87  was strongly discouraged. 
     In certain watercraft designs, however, the positive drive line angle  87  of 4 degrees may create the “porpoising” effect. This problem is acknowledged in the &#39;740 patent, which is discussed above. The reason for this is believed to be as follows. The positive drive line angle  87  has a tendency to push the bow  21  of the watercraft  10  up out of the water. When the watercraft  10  reaches a sufficient speed, enough of the bow  21  of the watercraft  10  extends above the water that the water cannot support the bow  21 . In other words, the weight of the bow  21  exceeds the upward buoyant force of the water. This causes the bow  21  to fall into the water until the flow of the water pushes the bow  21  up again to the point where it no longer is in equilibrium with the buoyant force of the water. The repetitive rise and fall of the bow  21  results in “porpoising.” 
     To address the problem of “porpoising,” the inventors decided to contravene conventional knowledge and decrease the drive line angle  87  to less than the traditionally-required 4 degrees. After reducing the drive line angle  87  to less than 4 degrees, the inventors discovered that “porpoising” can be reduced significantly or eliminated altogether without affecting the performance of the watercraft  10 . This creates a more stable, less bumpy, boat ride. The present invention is intended to encompass watercraft  10  with an angle  87  of less than 4 degrees. Preferably, the predetermined angle  87  is about −5 degrees to about 2 degrees. More preferably, the predetermined angle  87  is about −3 degrees to about 1 degree. Most preferably, the predetermined angle  87  is about −2 degrees to about 0 degrees. 
     In addition, one skilled in the art would understand that the predetermined angle  87  can be altered in a number of different ways without deviating from the scope of the present invention. 
     The embodiment illustrated in FIG. 4 differs from the embodiment illustrated in FIG. 3 in that the power source  30  is disposed above the drive shaft  55 . In particular, the jet drive power source  30  is positioned above the drive shaft  55  such that a substantial portion of the power source  30  extends over the drive shaft  55  toward the rear of the watercraft  10 . In the embodiment illustrated in FIG. 3, the power source  30  is positioned in front of the drive shaft  55 . In that embodiment, a substantial portion of the power source  30  extends forwardly of the end of the drive shaft  55  (toward the front of the watercraft  10 ). The embodiment illustrated in FIG. 4 permits a more compact construction for the jet propulsion unit  50  than the embodiment illustrated in FIG.  3 . Accordingly, the jet propulsion unit  50  illustrated in FIG. 4 may be employed in a watercraft  10  where space is more of a concern than the watercraft  10  illustrated in FIG.  3 . 
     From the invention just described, it will be obvious that the invention may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the following claims.