Title:
REVERSE MECHANISM FOR A JET SYSTEM
Kind Code:
A1


Abstract:
A jet propulsion system includes an inlet receiving a fluid, and a housing defining a discharge nozzle through which fluid is discharged to provide propulsion of a vehicle in a first direction. The jet propulsion system also includes a reverse mechanism movable between a deployed position redirecting fluid from the discharge nozzle toward the first direction and providing propulsion of the vehicle in a second direction substantially opposite the first direction and a non-deployed position allowing fluid to exit the discharge nozzle and provide propulsion of the vehicle in the first direction. The reverse mechanism produces a flow entrainment that enhances forward thrust while the reverse mechanism is in the non-deployed position which results in a net thrust gain over the thrust attributed to the discharge nozzle alone.



Inventors:
Snow, Scott (Commerce, MI, US)
Application Number:
12/367923
Publication Date:
08/13/2009
Filing Date:
02/09/2009
Assignee:
Marine 1, LLC (Commerce, MI, US)
Primary Class:
International Classes:
B63H11/11
View Patent Images:
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Primary Examiner:
OLSON, LARS A
Attorney, Agent or Firm:
DINSMORE & SHOHL LLP (900 Wilshire Drive Suite 300, TROY, MI, 48084, US)
Claims:
I claim:

1. A jet propulsion system comprised of: a housing having a discharge nozzle through which fluid exits and provides propulsion of a vehicle along a first direction; and a reverse mechanism having a diverting assembly pivotally coupled to the housing for movement between a non-deployed position allowing fluid to exit the discharge nozzle and provide propulsion of the vehicle in a first direction and a deployed position forming a substantially hemispherical inner surface for redirecting fluid from the discharge nozzle and providing propulsion of the vehicle in a second direction substantially opposite the first direction.

2. The jet propulsion system as set forth in claim 1, wherein the reverse mechanism includes a ring attached to the housing, the ring having an inner surface spaced apart from an outer surface of the housing forming an annulus through which flow will pass.

3. The jet propulsion system as set forth in claim 2, wherein the reverse mechanism includes a substantially hemispherically shaped diverting assembly coupled to the ring for movement between the deployed and non-deployed positions.

4. The jet propulsion system as set forth in claim 3, wherein the diverting assembly is formed of a fabric material.

5. The jet propulsion system as set forth in claim 4, wherein the fabric material includes a opening formed between two parts of the diverting assembly, the two parts being movable between the deployed position, in which the opening is closed to prevent fluid from passing therethrough, and non-deployed position, in which the opening is open to allow fluid to pass therethrough.

6. The jet propulsion system as set forth in claim 5, wherein the diverting assembly includes a pair of movable support frames supporting the two parts of the diverting assembly along the opening,

7. The jet propulsion system as set forth in claim 6, wherein each support frame is pivotally coupled to the ring and provides movement of the two parts of the diverting assembly between the deployed and non-deployed positions.

8. The jet propulsion system as set forth in claim 6, wherein each support frame has opposite ends pivotally coupled to opposite sides of the housing, each support frame extending generally arcuately between the opposite ends.

9. The jet propulsion system as set forth in claim 5, wherein the two parts of the diverting assembly are movable to a neutral position between the deployed position and the non-deployed position, in which the amount of thrust in the first direction is substantially the same as the amount of thrust in the second direction.

10. The jet propulsion system as set forth in claim 2, wherein the housing includes a fixed portion interconnected to the vehicle and a movable portion movably coupled to the fixed portion, the discharge nozzle being disposed on the movable portion of the housing.

11. The jet propulsion system as set forth in claim 10, wherein movable portion is pivotally coupled to the fixed portion for movement along at least one pivot axis.

12. The jet propulsion system as set forth in claim 10 including a support frame pivotally coupled to the housing for movement along a generally horizontal first axis.

13. The jet propulsion system as set forth in claim 12, wherein the movable portion is coupled to the support frame for movement therewith about the first axis.

14. The jet propulsion system as set forth in claim 13, wherein the movable portion is pivotally coupled to the support frame for movement about a second axis.

15. The jet propulsion system as set forth in claim 14, wherein the first axis and second axis are substantially orthogonal relative to each other.

16. The jet propulsion system as set forth in claim 3, wherein the diverting assembly includes a plurality of dimensionally stable shells movable between the deployed and non-deployed positions.

17. The jet propulsion system as set forth in claim 16, wherein the shells are movable about a common pivot axis relative to each other.

18. A jet propulsion system comprising: a housing defining a discharge nozzle through which fluid exits and provides propulsion of a vehicle along a first direction; and a reverse mechanism movable between a deployed position redirecting fluid from the discharge nozzle toward the first direction and providing propulsion of the vehicle in a second direction substantially opposite the first direction and a non-deployed position allowing fluid to exit the discharge nozzle and provide propulsion of the vehicle in the first direction, the reverse mechanism enhancing forward thrust while the reverse mechanism is in the non-deployed position by increasing the mass flux and momentum of the flow at the exit of the discharge nozzle through flow entrainment.

19. The jet propulsion system as set forth in claim 18, wherein the reverse mechanism includes a ring securely fixed to the housing, the ring having an inner surface spaced apart from an outer surface of the housing to define an annular channel through which fluid diverted by the reverse mechanism can flow, the annular channel narrowing to accelerate fluid passing therethrough.

20. The jet propulsion system as set forth in claim 18, wherein the reverse mechanism includes a pair of movable support frames pivotally coupled to the housing moveable between the deployed and non-deployed positions an inner surface of the support members spaced apart from an outer surface of the housing in the non-deployed position to define an annular channel through which fluid diverted by the reverse mechanism can flow, the annular channel narrowing to accelerate fluid passing therethrough.

21. The jet propulsion system as set forth in claim 18, wherein the reverse mechanism includes a diverting assembly with a curved inner surface for reversing fluid exiting the discharge nozzle producing reverse thrust.

22. The jet propulsion system as set forth in claim 18, wherein the reverse mechanism is offset relative to a center line of the discharge nozzle.

23. A jet propulsion system comprising: a housing defining a discharge nozzle through which fluid exits and provides propulsion of a vehicle along a first direction; and a reverse mechanism pivotally coupled to the housing, the housing moveable relative to the discharge nozzle in a pitch and steer axis wherein a thrust vector of fluid exiting the discharge nozzle may be manipulated to control damping of an attitude and motion of the vehicle in any of the pitch, roll and yaw axes.

24. The jet propulsion system as set forth in claim 23 wherein the reverse mechanism is movable between a deployed position redirecting fluid from the discharge nozzle toward the first direction and providing propulsion of the vehicle in a second direction substantially opposite the first direction and a non-deployed position allowing fluid to exit the discharge nozzle and provide propulsion of the vehicle in the first direction, the reverse mechanism enhancing forward thrust while the reverse mechanism is in the non-deployed position by increasing the mass flux and momentum of the flow at the exit of the discharge nozzle through flow entrainment.

25. A jet propulsion system attached to a watercraft comprising: a housing defining a discharge nozzle through which fluid exits and provides propulsion of a vehicle along a first direction; and a ring securely fixed to the housing, the ring having an inner surface spaced apart from an outer surface of the housing to define an annular channel through which fluid diverted by the reverse mechanism can flow, the annular channel narrowing to accelerate fluid passing therethrough.

Description:

RELATED APPLICATIONS

This application claims priority of U.S. Provisional Patent Application No. 61/027,240 filed Feb. 8, 2008, the content of which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to the operation of jet propulsion systems. More particularly, this invention incorporates a reverse mechanism into the jet propulsion system utilizing a deflecting surface to redirect the flow from the primary jet exhaust nozzle to produce a reverse thrust.

BACKGROUND OF THE INVENTION

Jet propulsion is a well-known means of propelling a watercraft through the water. It is also well-known to provide a reverse gate or “bucket” for converting forward thrust into rearward thrust to the propel watercraft in a reverse direction.

U.S. Pat. No. 5,344,344, which issued to Forsstrom on Sep. 6, 1994, describes a steering and reversing system for a marine jet propulsion unit. The system has a stationary nozzle for discharging a waterjet in the rearward direction from the unit and incorporates a pair of steering and reversing members mounted side by side at the rear end of the nozzle and individually pivot in opposite directions about upright axes from a non-deflecting position to first and second deflecting positions. In the non-deflecting position, the steering and reversing members form an extension of the nozzle in the rearward direction, while in the first deflecting position each member diverts a portion of the waterjet laterally outward by means of its front section. In the second deflecting position each member deflects a portion of the waterjet downward and forward by means of scoop-like members at its rear section.

U.S. Pat. No. 3,937,172, which issued to Castoldi on Feb. 10, 1976, discloses a waterjet propelling apparatus for boats. The apparatus forces water by a pump through a nozzle directed a stern of a boat. A curved jet-deflecting surface deflects the water downward and forward and reverses the thrust, and a pair of steerable parallel rudder blades pivot in unison for laterally deflecting the jet. The jet-deflecting surface has symmetrical channel-like side panels which direct water escaping laterally from the clearance between the trailing edges of the rudder blades and the jet-deflecting surface forward towards the bow to enhance the reverse thrust, and a central portion which is shaped with blades for maintaining the clearance with the later constant for various pivotal deviations of the blades.

U.S. Pat. No. 5,551,898, which issued to Matsumoto on Sep. 3, 1996, describes an exhaust nozzle arrangement for a waterjet propulsion unit. A number of embodiments of the steering nozzle and reverse thrust bucket arrangements for jet propelled watercraft are described. The steering nozzle, in addition to being mounted for steering movement about a vertically extending steering axis, is also mounted for trim adjustment about a horizontally extending axis. A cooperating reverse thrust bucket provides reverse thrust operation. The reverse thrust bucket is either mounted on the hull of the watercraft independent of the jet propulsion unit, on the outer housing of the jet propulsion unit independent of the steering nozzle, or on the steering nozzle.

It remains desirable to provide a jet propulsion system with an improved reverse mechanism that provides robust performance when switching between forward, neutral and reverse directions. It also remains desirable to provide an improved reverse mechanism that enhances or at least does not degrade the performance of the jet propulsion system in the forward direction. It is also desirable to provide an improved reverse mechanism that may be manipulated to control damping of the attitude and motion of a vessel in any of the pitch, roll or yaw axes of the vessel.

SUMMARY OF THE INVENTION

According to one aspect, a jet propulsion system includes a housing having a discharge nozzle through which fluid exits and provides propulsion of a vehicle along a first direction. The jet propulsion system also includes a reverse mechanism having a deflecting movable surface coupled to the housing for movement between a non-deployed position allowing fluid to exit the discharge nozzle and provide propulsion of the vehicle in a first direction and a deployed position forming a substantially hemispherical inner surface for redirecting flow from the discharge nozzle and providing propulsion of the vehicle in a second direction substantially opposite the first direction.

According to another aspect, a jet propulsion system includes an inlet receiving a fluid, and a housing defining a discharge nozzle through which fluid is discharged to provide propulsion of a vehicle in a first direction. The jet propulsion system also includes a reverse mechanism movable between a deployed position redirecting fluid from the discharge nozzle toward the first direction and providing propulsion of the vehicle in a second direction substantially opposite the first direction and a non-deployed position allowing fluid to exit the discharge nozzle and provide propulsion of the vehicle in the first direction. The reverse mechanism produces a flow entrainment that enhances forward thrust while the reverse mechanism is in the non-deployed position which results in a net thrust gain over the thrust attributed to the discharge nozzle alone.

According to another aspect, a jet propulsion includes a housing defining a discharge nozzle through which fluid exits and provides propulsion of a vehicle along a first direction. A reverse mechanism is pivotally coupled to the housing. The housing is moveable relative to the discharge nozzle in a pitch and steer axis wherein a thrust vector of fluid exiting the discharge nozzle may be manipulated to control damping of an attitude and motion of the vehicle in any of the pitch, roll and yaw axes.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is perspective view of a portion of a jet propulsion system according to one embodiment of the invention;

FIG. 2 is an exploded perspective view of the jet propulsion system of FIG. 1;

FIG. 3 is an enlarged perspective view of a reverse mechanism for the jet propulsion system shown in a deployed position;

FIG. 4 is an enlarged perspective view of the reverse mechanism for the jet propulsion system shown in a partially deployed position;

FIG. 5 is a cross sectional view of the reversing mechanism for the jet propulsion system shown in a deployed position;

FIG. 6 is a cross sectional view of the reversing mechanism for the jet propulsion system shown in a non-deployed position;

FIG. 7 is a cross sectional view of the reversing mechanism for the jet propulsion system shown in a neutral position between the deployed and non-deployed positions;

FIG. 8 is a cross sectional view of an alternative embodiment of the reversing mechanism for the jet propulsion system shown in the deployed position;

FIG. 9 is a partial cross section view of another alternative of the reversing mechanism for the jet propulsion system shown in the deployed position;

FIG. 10 is a partial perspective view of another alternative embodiment of the reversing mechanism in the deployed position;

FIG. 11 is a partial perspective view of the alternative embodiment of FIG. 10 in the non-deployed position;

FIG. 12 is a partial perspective view of another alternative embodiment of the reversing mechanism in the deployed position;

FIG. 13 is a partial perspective view of the alternative embodiment of FIG. 12 in the non-deployed position;

FIG. 14 is a partial perspective view of another alternative embodiment of the reversing mechanism in the deployed position;

FIG. 15 is a partial perspective view of the alternative embodiment of FIG. 14 in the non-deployed position;

FIG. 16 is a partial perspective view of the alternative embodiment of FIG. 14 in the non-deployed position including the transom and fixed portion of the vessel;

FIG. 17 is a partial perspective view of the alternative embodiment of FIG. 14 in the non-deployed position including the transom and fixed portion of the vessel;

FIG. 18 is a partial perspective view of the alternative embodiment of FIG. 14 in the deployed position including the transom and fixed portion of the vessel;

FIG. 19 is an exploded perspective view of the alternative embodiment of FIG. 14;

FIG. 20 is a perspective view of an alternative embodiment of a nozzle and ring.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1-7, a jet propulsion system according to one embodiment of the invention is generally indicated at 10. The jet propulsion system 10 includes an inlet that receives fluid into the system and an outlet or discharge nozzle 14 through which fluid exits to provide thrust for moving a vehicle 12 in a first direction. Discussed in greater detail below, the jet propulsion system 10 includes a reverse mechanism 20, shown in FIGS. 3 and 4, that reverses the thrust or a portion of the thrust from the discharge nozzle 14 to move the vehicle 12 in a second direction opposite the first direction or to neutralize or hold the vehicle 12 in a generally fixed position relative to the body of fluid in which the vehicle 12 travels. The reverse mechanism 20 is shown illustratively as part of a jet propulsion system 10 for a recreational water vehicle. It should, however, be appreciated that the reverse mechanism 20 may also be used in other jet propulsion systems, where in general an accelerated jet of fluid is expelled to generate thrust, such as turbojets, turbofans, rockets, ramjets, pulse jets, gas turbine engines, and the like.

The reverse mechanism 20 is movable between non-deployed and deployed positions. In the non-deployed position, the reverse mechanism 20 allows fluid to exit the discharge nozzle 14 to provide propulsion of the vehicle 12 in the first direction or “forward” thrust. In the non-deployed position the reverse mechanism 20 may be supported by a ring 26 outside of the discharge nozzle 14. The ring 26 forms an annulus 31 with a nozzle housing 24. Water passes through the annulus 31 in which the cross sectional area is decreased in the axial direction to accelerate the flow as it passes through the exit plane in the same direction as the flow from the discharge or exhaust nozzle 14. The additional mass flow of the water through the annulus 31 mixes with the flow from the jet discharge or exhaust nozzle 14 resulting in thrust augmentation. The extent of the thrust augmentation achieved is determined by the cross section area and axial length of the annulus 31 and the velocity of the flow from the discharge or exhaust nozzle 14. The flow through the annulus 31 is a flow entrainment effect due to the lower pressure in the higher speed flow from the discharge nozzle 14. In the deployed position, the reverse mechanism 20 redirects the fluid from the discharge nozzle 14 from the first direction and provides propulsion of the vehicle 12 in the second direction producing “rearward” thrust. The reverse mechanism 20 is also movable between the deployed and non-deployed position to provide varying degrees of forward thrust, rearward thrust or neutral.

In one embodiment of the invention, the reverse mechanism 20 utilizes a substantially hemispherical shaped diverting assembly 22 for diverting or “reversing” the thrust from the discharge nozzle 14. More specifically, a ring 26 in FIGS. 3 and 4 is attached to a housing 24 of the jet propulsion system 10. The ring 26 includes an inner surface 28 spaced apart from an outer surface 30 of the housing 24 to define the annulus 31 through which fluid diverted by the diverting assembly 22 can flow. The diverting assembly 22 is coupled to the ring 26 and is movable relative to the ring 26 between the deployed and non-deployed positions.

The diverting assembly 22 may include two movable parts 32, 34 movable between the deployed and non-deployed positions. An opening 36 is formed between the two parts 32, 34 and changes in size due to the movement of the parts 32, 34 between the deployed and non-deployed positions. In the deployed position, shown in FIGS. 2 and 5, the opening 36 is closed to prevent fluid from passing through the diverting assembly 22. In the non-deployed position, shown in FIGS. 1 and 6, the opening 36 is open to allow fluid to pass therethrough. The two parts 32, 34 of the diverting assembly 22 are also movable to a neutral position between the deployed position and the non-deployed position, in which the amount of thrust in the first direction is substantially the same as the amount of thrust in the second direction.

In one embodiment, the diverting assembly 22 may include a fabric material 23. In particular, the diverting assembly 22 may be formed of Vectran or other suitable high tensile strength fabric. In this embodiment, the diverting assembly 22 may include a pair of movable support frames 40, 42 that supports the two parts 32, 34 of the diverting assembly 22 along the opening 36. Each support frame 40, 42 may be pivotally coupled to the ring 26 and provides movement of the two parts 32, 34 of the diverting assembly 22 between the deployed and non-deployed positions. Each support frame 40, 42 may have opposite ends 44, 46 pivotally coupled to opposite sides of the housing 24 for rotation about a common pivot axis 47. Each support frame 40, 42 may extend generally arcuately between the opposite ends 44, 46.

As best shown in FIGS. 4-7, each support frame 40, 42 has a generally L-shaped cross section defined by generally orthogonal back 50 and side 52 walls. The back walls 50 of the support frames 40, 42 extend outwardly from each other in a generally symmetrically opposite manner from respective side walls 52 when the diverting assembly 22 is in the deployed position. Further, the side walls 52 of the support frames 40, 42 are substantially parallel to each other when the diverting assembly 22 is in the deployed position. Each part 32, 34 of the diverting assembly 22 includes a longitudinal pocket 54, shown in FIGS. 5, 6, and 7, that extends along the opening 36 and receives one of the support frames 40, 42 therethrough.

The support frames 40, 42 are actuated between the deployed and non-deployed positions by an actuating mechanism 60. The actuating mechanism 60 may include a set of arms 62, 64 extending outward from the pivot axis 47 of the support frames 40, 42. Each arm 62, 64 is connected to one of the respective support frames 40, 42 such that rotation of the arms 62, 64 about the pivot axis 47 causes corresponding rotation of the support frames 40, 42 about the pivot axis 47. In one embodiment, the arms 62, 64 are connected to support frames 42, 40 on opposite sides of the pivot axis 47 so that pulling the arms 62, 64 toward the vehicle (as indicated by the arrow A shown in FIGS. 1, 3 and 4) results in movement of the support frames 40, 42 toward the deployed position. The arms 62, 64 may be actuated by any suitable rod, cable mechanism and/or by a powered actuating device, such as an electric motor, hydraulic actuator or pneumatic actuator.

The housing 24 may also be movably coupled to the vehicle 12 for steering and/or vertical pitch control. In one aspect, the housing may be moveable to allow for simultaneous steering and pitch control. In the illustrated embodiment, the housing 24 may be pivotally coupled to a frame 70, best seen in FIG. 2, for movement about a first pivot 72 relative to the frame 70. The frame 70 is, in turn, pivotally coupled to a fixed portion 74 of the vessel 12 for movement of the housing 24 and frame 70 together about a second pivot 76 relative to the fixed portion 74 of the vessel 12. Cables 80, 82, best seen in FIG. 1, may be used for controlling the movement of the housing 24 about the first 72 and second pivots 76. In one aspect, the housing 24 may be manipulated to control damping of the attitude and motion of the vehicle 12 in any of the pitch, roll or yaw axes in both the forward and reverse directions. The frame 70 includes a tab extending off of the frame 70 and isolates movement in the steering and pitch axis to prevent control loop problems when controlling movement.

As stated above, the reverse mechanism 20 also provides enhanced thrust while the reverse mechanism 20 is in the non-deployed position resulting in a net thrust gain over an amount of thrust attributable to the discharge nozzle 14 alone. More specifically, the annulus 31 defined between the inner surface 28 of the ring 26 and the outer surface 30 of the housing 24 narrows so as to accelerate the flow of fluid passing therethrough as the vehicle 12 is propelled in the first or forward direction. The accelerated fluid, due to the reduction in cross section area of the annulus 31 in the flow direction mixes with the fluid exiting the discharge or exhaust nozzle 14 as a result of the lower pressure in the higher speed flow from the discharge nozzle 14. This increases the mass flow rate and hence the momentum at the exit of the discharge nozzle 14 and thereby contributes to thrust enhancement.

Referring to FIG. 8, an alternative embodiment of the jet propulsion system 110 is shown, wherein like components or features from the previous embodiment are indicated by numerals offset by 100. In this embodiment, the moving parts of the diverting assembly 122 are dimensionally stable or substantially rigid shells 33, 35 instead of the flexible fabric 23 of the previous embodiment. The shells 33, 35 rotate generally telescopically relative to each other between the deployed and non-deployed positions about the pivot axis 147. It should be appreciated that the movement of the shells 33, 35 is not limited to pivotal movement about the axis 147. The shells 33, 35 may, for example, be slidable or movable along a generally compound curve or path between the deployed and non-deployed positions.

Referring to FIGS. 10 and 11, another alternative embodiment of the jet propulsion system 210 is shown, wherein the diverting member 222 includes support frames 240, 242 that are moveable between the deployed and non-deployed positions. The support frames 240, 242 are similar to those of the previous embodiments but they are sized and shaped to define a diverting surface. 241. The diverting surface 241 corresponds to an inner surface 243 of the support frames 240, 242 when in the deployed position. The support members 240, 242 may have a greater width than the previously described support members to deflect the flow of fluid from the discharge nozzle 14. In the deployed position, the diverting surface 241 intersects with the fluid flow to substantially reverse a portion of the fluid flow and direct the vehicle 12 in the second or reverse direction. The width of the support members 240, 242 may be selected such that a balance of the drag cased by the support members 240, 242 in the forward direction or non-deployed position and the amount of area available to contact the fluid in the deployed position is achieved. For example, one may optimize the contact area in the reverse direction or limit the drag dependent upon the design and performance objectives of the vehicle 12.

In the embodiment depicted in FIGS. 10 and 11, a leading edge portion 245 of the support members 240, 242 acts as the ring 26 of the previously described embodiment. The leading edge portion 245 is angled to reduce its size radially in the flow direction of the fluid. More specifically, the annulus 231 is defined between the inner surface of the leading edge portion 245 of the support members 240, 242 and the outer surface 30 of the housing 24 in the non-deployed position and narrows so as to accelerate the flow of fluid passing there through as the vehicle 12 is propelled in the first or forward direction. The accelerated fluid, due to the reduction in cross section area of the annulus 231 in the flow direction mixes with the fluid exiting the discharge or exhaust nozzle 14 as a result of the lower pressure in the higher speed flow from the exhaust nozzle. This increases the mass flow rate and hence the momentum at the exit of the discharge nozzle 14 and thereby contributes to thrust enhancement.

Referring to FIGS. 9, 12 and 13 there is shown another alternative embodiment of the jet propulsion system 210. This embodiment is similar to that described above with reference to FIGS. 10 and 11 except that the diverting members 222 or the support members 240, 242 are positioned so they are not concentric or offset relative to a centerline of the discharge nozzle 14. In the depicted embodiment, the discharge nozzle's position is upwards relative to the support members of the previously described embodiment. In this manner the diverting surface 231 of the support members 240, 242 acts as a scoop to channel the flow of fluid around the curved shape of the diverting surface 231. In the illustrated embodiment of FIG. 9, the offset is extreme such that the reverse thrust is fully diverted below the housing 24. It should be appreciated that any degree of offset of the diverting member 222 relative to the exhaust nozzle 14 may be utilized.

Referring to FIGS. 14-19 there is shown another alternative embodiment of the jet propulsion system 310 attached to a transom 311. This embodiment is similar to that described above in FIGS. 10 and 11 with the addition of a ring 326 attached to the housing 24 and a change in the shape of the support members 340, 342. More specifically, the annulus 331 is defined between the inner surface 328 of the ring 326 and the outer surface 30 of the housing 24. The shape of the ring 326 narrows so as to accelerate the flow of fluid passing through the annulus 331 as the vehicle 12 is propelled in the first or forward direction. The ring 326 may also include a shaped leading edge 332 that reduces drag in the forward direction. The support members 340, 342 no longer include a leading edge portion 245 as the ring 326 defines the annulus 331 with the housing 24. This embodiment may also be offset relative to the discharge nozzle 14, as described above. In other words, the discharge nozzle 14 may be moved upwards relative to the support members 340, 342 in the deployed position, as described above.

Referring to FIG. 20, there is shown an alternative embodiment of a jet propulsion system 410. In the depicted embodiment there is shown a discharge nozzle 14 having a nozzle housing 24 and ring 26. The ring 26 forms an annulus 31 with a nozzle housing 24. Water passes through the annulus 31 in which the cross sectional area is decreased in the axial direction to accelerate the flow as it passes through the exit plane in the same direction as the flow from the discharge or exhaust nozzle 14. The additional mass flow of the water through the annulus 31 mixes with the flow from the jet discharge or exhaust nozzle 14 resulting in thrust augmentation. The extent of the thrust augmentation achieved is determined by the cross section area and axial length of the annulus 31 and the velocity of the flow from the discharge or exhaust nozzle 14.

The invention has been described in an illustrative manner. It is, therefore, to be understood that the terminology used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the invention are possible in light of the above description. Thus, within the scope of the appended claims, the invention may be practiced or applied other than as specifically described.