An improved waterjet propulsor that uses differential static pressure from the water flowing through and around the propulsor to provide additional thrust via internal and external vanes. Uniform water velocity is also created by the vanes within the propulsor. A boat trimming system is incorporated as part of the waterjet discharge nozzle.

BACKGROUND OF THE INVENTION
 Waterjet propulsors have been available for many years. Some of their
 obvious advantages over propellers include that they have no exposed
 rotor, have low underwater noise signature, offer even engine loading, and
 offer shallow draft. However, the waterjet's efficiency falls far short of
 the efficiency of an underwater propeller at low boat speeds. The
 propulsive coefficient of a typical underwater propeller at 16 knots is
 about 65 percent while that of a waterjet at the same 16 knots would be
 only about 40 percent. Those numbers given an advantage to the underwater
 propeller of 38 percent at that 16 knot speed. The waterjet becomes more
 competitive at higher speeds where the drag of the underwater propeller's
 appendages including shaft, strut, rudder, etc. causes it to have a severe
 disadvantage. The competition to the waterjet then becomes the surface
 propeller that, in its normal design, operates aft of the transom or a
 step in the boat's bottom. Only the lower half of the surface propeller is
 in the water. As such the surface propeller avoids shaft, thrust, and, in
 some designs, rudder drag. While generally considered to be rather
 inefficient at low boat speeds, the surface propeller is considered the
 favored propulsor at very high boat speeds.
 The Kort Nozzle, first introduced in the 1930's, yields even greater
 performance for a variation of the propeller at low boat speeds. It
 applies a simple ringed nozzle around the periphery of an underwater
 propeller. By use of carefully designed angled airfoil shapes to the
 nozzle ring it is possible for the Kort nozzle to actually gain thrust
 from external forces acting on the nozzle. A well designed Kort nozzle
 shows noticeable performance gains over a standard underwater propeller at
 speeds up to, say, 16-20 knots. Beyond those speeds, the drag of the
 nozzle itself rules out use of the Kort nozzles. As such, Kort nozzles are
 widely applied to tug boats and other low speed mostly work boats. For
 purposes of this application, low speed is defined as boat speeds up to
 and including 20 knots and high speed as boat speeds of over 20 knots.
 In summary, the waterjet propulsor is severely outclassed from efficiency
 standpoints at low to moderate, up to about 25 knot, and very high, over
 60 knot, speeds. The reason for much of its efficiency shortcomings has to
 do with its inlet performance. A well-designed waterjet pump can have a
 rotor efficiency of 93 percent, flow straightening stator vane efficiency
 of 92 percent, and discharge nozzle efficiency of 98 percent. That comes
 to an overall pump efficiency of 84 percent. However, its averaged inlet
 pressure recovery efficiency will probably only be in the 70 percent area.
 Consequently, the best overall efficiency that can be expected from such a
 waterjet propulsor while running at its best performance at hihg boat
 speeds is about 59 percent. The major reason that waterjet inlet
 efficiency or inlet pressure recovery is so poor is because of distortion
 in the inlet flow. The high velocity incoming water in a typical flush
 with the hull waterjet inlet piles up over the lower half of the inlet
 duct. Due to this distorted flow, the rotor generally sees recoveries of
 90 percent or more of boat freestream dynamic head over its lower half and
 as low as 50-60 percent over its upper half.
 The instant invention offers greatly improved thrust values for the
 waterjet at all boat speeds. In its preferred embodiment, it decreases the
 amount of flow distortion that the rotor sees as well as gains thrust
 advantage from an airfoil shaped flow deflector strategically placed in
 the inlet duct. Further, generally airfoil shaping of the lower outside
 portion of the inlet housing so that such housing is submerged adds to
 thrust with little or no increase in external drag.
 In addition to the significant performance gains in waterjet performance to
 be realized by the instant invention, a significant advantage in the form
 of a discharge jet-trimming device is also offered. These features are
 described in detail in the following sections.
 SUMMARY OF THE INVENTION
 With the foregoing in mind, it is the principal object of the preferred
 embodiment of the instant invention to provide a new waterjet propulsor
 that offers efficiencies competitive with or superior to the propeller at
 all boat speeds.
 It is a related object of the invention that thrust enhancements shall be
 provided by specific arrangement and angling of the underside of the inlet
 of the waterjet.
 It is a further object of the invention that a substantially transversely
 oriented divider shall be placed upstream of the rotor inlet to aid in
 directing flow to the rotor to thereby enhance rotor performance.
 It is a directly related object of the invention that such a flow divider
 shall be, at least in part, airfoil shaped.
 It is yet a further related object of the invention that such a flow
 divider shall have forces acting on it that add forward thrust to enhanced
 waterjet propulsor.
 It is a further related object of the invention that said flow divider may
 be separated into two or more parts so that liquid flow can travel between
 upper and lower surfaces of the flow divider.
 It is another object of the invention that a nozzle that has the ability to
 control the trim of the waterjet propulsor driven boat be offered.
 It is a directly related object of the invention that movable nozzle
 elements disposed within a fixed nozzle structure can be used to apply
 trimming forces to the boat.
 It is yet another directly related object of the invention that such
 movable nozzle elements are, at least partially, returned to their neutral
 positions by force of the water discharging from the nozzle.
 It is a further related object of the invention that similar movable nozzle
 elements to those use for trim can be positioned to accomplish steering of
 the waterjet propelled boat.
 It is yet another object of the invention that a steering rudder can be
 positioned aft of or at least partially internal to the fixed nozzle to
 accomplish steering of the boat.

DETAILED DESCRIPTION
 FIG. 1 presents a centerline cross-sectional view of the prior art Kort
 nozzle 33. This is simply a rotor in the form of a propeller 34 in a
 nozzle ring 39 disposed below the hull of a boat (not shown). Also shown
 are the propeller drive shaft 36, inlet water velocity arrows 31,
 discharge jet water velocity arrows 32, external water velocity arrows 30,
 and a horizontal transverse centerline plane 40. The Kort nozzle 33 is
 noted for generating more thrust than an open water propeller at low boat
 speeds. The reasons for this are explained under the discussion of FIG. 2
 that follows.
 FIG. 2 presents and enlarged view of the lower portion of the Kort nozzle
 ring 39 cross-section that was shown in FIG. 1. Note that is nozzle ring
 39 is actually at least partially airfoil shaped and that its outer or
 lower surface A is angled upward from forward to aft in this illustration.
 The water flow, as depicted by inlet water velocity arrow 31, entering the
 inside of the nozzle ring 39 that is being acted upon by the propeller 34
 is obviously traveling at a much greater velocity (VB)--normally about 1.5
 times--than the outside velocity (VA).
 The vector force arrows shown in FIG. 2 are defined as follows: PA-N is the
 external static pressure normal to surface A, PA-V is the external static
 pressure vertical to surface A, and PA-F is the external static pressure
 force in a forward direction acting on surface A. PB-N is the internal
 static pressure force normal to internal surface B, PB-V is the internal
 static pressure force vertical to surface B, and PB-R is the internal
 static force acting rearward. It has been found by test and application of
 Kort nozzles over the years that the favored value for angle .alpha. is
 generally about nine degrees.
 By Bernoulli's equation, neglecting minor elevation considerations, total
 pressure is made up of static pressure and dynamic pressure. Dynamic
 pressure is a function of velocity squared so even minor velocity
 differences make for big changes in dynamic and hence static pressure. As
 such, there is more static pressure on the outer surface (A) than the
 inner surface (B) of the nozzle ring. Since the outer surface (A) is
 angled outward there is a forward force on outer surface (A). This is
 calculated by simply multiplying the external surface area of A by the
 external static pressure forward (PA-F). Importantly, most of the inner
 surface (B) is parallel to the water flow so there is no forward force on
 that parallel portion of surface (B). Therefore, there is a resultant
 positive forward force on the entire nozzle ring 39 that accounts for at
 least most of the higher efficiencies of the Kort nozzle compared to a
 standard open water propeller.
 The positive forward force acting on the Kort nozzle ring 39 makes for
 greatly improved performance compared to an open water propeller up to
 vessel speeds of, say, 18 knots or so. At that speed the drag of the
 nozzle ring exceeds the positive forward force generated by the nozzle
 ring 39 resulting in the open water propeller being favored.
 FIG. 3 presents a centerline cross-sectional view of a typical prior art
 waterjet propulsor 51. Items shown are the shaft 36, rotor 34, stator
 vanes 35, bearings 49, typical boat keel 58, boat transom 59, discharge
 nozzle 45, waterline 44, lower inlet housing 37. Note that the transverse
 centerline plane 40 bisects the housing 52 and therefore bends downward
 going forward from the rotor 34 to the plane of the inlet 53. Note also
 that the boat keel 58 may be located otherwise with either more or less of
 the waterjet either above or below the boat keel 58. Further, various
 portions of the waterjet from virtually none to all of the waterjet may be
 disposed aft of the boat transom 59.
 The lower portion of a prior art waterjet propulsor 51 inlet housing 37 is
 especially designed to keep water away from the discharge jet, as shown by
 discharge jet velocity arrows 32, and its steering and reversing system
 (not shown to simplicity the drawings). This can be seen by shape of the
 waterline 44. As such, the lower portion of the inlet housing 37, noted
 here as surface A, is not angled and does not extend to the aft end of the
 nozzle as does surface A of the Kort nozzle shown in FIG. 2. Therefore,
 there is little or none of the positive forward external force on surface
 A as is experienced by the Kort nozzle. There is however a forward force
 generated on an upper portion of the housing, depicted by surface E, in
 the waterjet. This is discussed further in the following paragraphs that
 describe FIGS. 4 and 5.
 FIG. 4 is a cross-sectional view, as taken through line 4--4 of FIG. 3,
 that shows approximate equal dynamic pressure areas 42 as seen in a plane
 just upstream of the rotor inlet of the prior art waterjet 51. Note that
 such severely distorted velocity patterns just upstream of the rotor are
 typical in prior art waterjets. This particular illustration shows mostly
 95 percent velocity recovery in the lower half and a majority of recovery
 at 65 percent over the upper half. The reason for this effect is that the
 inlet flow tends to pile up in the lower half--this is especially true at
 higher vehicle speeds. Note that surface B is defined as extending below
 and up to the transverse horizontal plane 40 while surface E extends above
 the transverse horizontal plane 40. Also shown in FIG. 4 is a vertical
 centerline plane 41.
 FIG. 5 shows a partial cross-sectional view, as taken through line 5--5 of
 FIG. 4, that illustrates the typical velocity profiles 42 just upstream of
 the rotor inlet in a prior art waterjet 51. Since the velocity over upper
 surface E is substantially less than the velocity over lower surface B,
 there is a noticeably higher static pressure acting on surface E. This is,
 again, verified by Bernoulli's equation as is noted earlier in the
 discussion about the forces acting on the Kort nozzle under the paragraphs
 about FIG. 2. Referring back to FIG. 3, it is to be noted that surface E
 is not only seeing a higher static pressure but is also larger than
 surface B and is angling downward so that there is a net forward thrust on
 the waterjet housing. The fore and aft forces on surface A are negligible
 or actually may slightly rearward since surface A is substantially
 horizontal or angled downward from front to rear due to trim of the driven
 boat.
 So there is actually a net positive forward force occurring over the inlet
 housing of a prior art waterjet. This has been confirmed by static
 pressure measurements made on the inside surfaces of the housings of a
 large waterjet.
 FIG. 6 is a partial cross-sectional view of a similar prior art waterjet
 propulsor 51 as presented in FIG. 3. This view shows the addition of
 turning vanes 43 set in an inlet grille 54 that are used to direct water
 from outside the hull into a waterjet inlet 53. These prior art turning
 vanes 43 are sometimes applied to waterjets in Personnel WaterCraft (PWC).
 The purpose of the turning vanes 43 is to ram water into the PWC waterjet
 inlet 53 during closed course racing. Such turning vanes are effective in
 ramming water into the waterjet to thereby increase acceleration of the
 PWC around race course buoys. However, the drag of the turning vanes
 actually reduces the top speed of the PWC noticeably. Therefore, these
 turning vanes are not employed in waterjets except for the niche
 application of PWC's used in closed course races.
 FIG. 7 is a cross-sectional view of the preferred embodiment of the instant
 invention enhanced waterjet propulsor 50. Note the aft upward angling
 surface of the lower outside portion of the inlet housing A and the at
 least partially airfoil shaped divider 38 disposed in the housing 52. Both
 are important features that add to the enhanced performance of the instant
 invention.
 The, at least partially airfoil shaped, lower inlet housing 37 acts in a
 similar manner to the lower portion of the nozzle ring of the Kort nozzle
 as was described in the discussion of FIG. 2 earlier. This results in a
 net forward thrust when algebraically adding the forces acting on surface
 A and surface B. However, very importantly, since this is a low drag at
 high speed inlet design there is little or no external drag penalty at
 high boat speeds as is the case with the Kort nozzle ring. The aft rising
 angle .alpha. is generally to be kept at less than 18 degrees with an
 angle of less than 12 degrees preferred. It is intended that surface A, as
 seen here in a transverse plane perpendicular to a centerline of the rotor
 shaft 36, can be curvilinear, flat, V-shaped, or any combination of such
 shapes so long as, on average, it angles upward going aft over its
 longitudinal length.
 The low drag at least partially airfoil shaped divider 38 disposed in the
 housing 52 provides twofold advantage. First, it provides an evening of
 the velocity profiles at the rotor 34 inlet which aids overall efficiency
 and second, it offers a resultant net positive forward force based on the
 algebraic adding of the static pressure forces acting on its lower surface
 C and its upper surface D. It is very important to realize that the
 forward end of the generally airfoil shaped divider 38, while normally
 sloping downward, is actually acting on water flow that is already being
 directed upward as can be seen by examination of the orientation of the
 inlet water velocity arrows 31. As such, it is actually at a zero or
 relatively small angle of attack reference to the incoming water flow. As
 such, there is little or none of the drag forces experienced by the inlet
 turning vanes that were described in the discussion of FIG. 6. Analysis of
 the static pressure forces acting on surfaces C and D takes the same
 general form as the analysis presented in the discussion of FIG. 2 so such
 analysis will not be presented here for sake of brevity. Further, it is a
 stated intent of the preferred embodiment of the instant invention that
 the inlet divider 38 at least in its majority, starts aft of the inlet
 plane 53 and terminates less than one rotor diameter forward of the rotor
 34.
 FIG. 8 is a cross-sectional view, as taken through line 8--8 of FIG. 7,
 that shows areas of approximately equal dynamic pressures in a plane just
 upstream of the rotor inlet for the preferred embodiment of the instant
 invention. Note that the velocity distortions are, on average, noticeably
 less severe than for the prior art waterjet situation presented in FIG. 4.
 This is attributed to the flow-directing vane 38 that, in this preferred
 embodiment, transversely connects the internal sides of the housing.
 FIG. 9 shows a partial cross-sectional view, as taken through line 9--9 of
 FIG. 8, that illustrates the typical velocity profiles 42 just upstream of
 the rotor inlet in an enhanced waterjet to the instant invention. Note
 that there is much more high-energy water arriving at the upper portion of
 the rotor inlet here than for the prior art waterjet situation presented
 in FIG. 5. Due to the lower velocity water adjacent to surfaces A, C, and
 E, such surfaces see higher static pressures than upper surfaces B and D.
 The result is, because of the carefully selected aft upward sloping shapes
 of surfaces A, C, and E, a net forward thrust acting on the surfaces of
 the waterjet when it is propelling a boat forward at any speed. However,
 it is obvious that the forward thrust effect on external surface A will
 decrease with increasing boat speed. For example, the ratio of internal
 velocity over surface B to external velocity over surface A is about 2.5
 at 16 knots and only about 1.4 at 40 knots for a typical waterjet to the
 preferred embodiment of the instant invention.
 FIG. 10 is a partial cross-sectional view, as taken through line 10--10 of
 FIG. 8 that shows an optional preferred divider vane 38 concept. In this
 case separation of forward and aft portions of the divider vane 38 into a
 forward portion 55 and aft portion 56 allows water flowing over the top
 portion to be directed to the lower portion or vice versa. This offers
 advantages by controlling the boundary layer over the top portion of the
 divider vane. Any number of portions of divider vane may, of course, be
 used.
 FIG. 11 presents an isometric view of a trimmable nozzle 45 that can be
 applied to the discharge of any jet. In this preferred embodiment of a
 conical nozzle arrangement, either an upper trim control element 47 or a
 lower trim control element 57 can be actuated to give an up or a down trim
 effect on the driven boat. Major advantages of this inventive approach
 nozzle over a fully articulated nozzle are that: 1) construction is very
 simple, 2) control system and actuators are less complicated, and 3) there
 is little or no back flow leakage. The back flow leakage associated with
 an articulated nozzle results in a loss of efficiency. While not shown in
 FIG. 11, it is possible to also use such control flap like elements on
 either side of a discharge nozzle to act as steering means and/or to use a
 rudder element disposed in the discharge jet as steering means.
 While the invention has been described in connection with a preferred and
 several alternative embodiments, it will be understood that there is no
 intention to thereby limit the invention. On the contrary, there is
 intended to be covered all alternatives, modifications and equivalents as
 may be included within the spirit and scope of the invention as defined by
 appended claims, which are the sole definition of the invention.