CA2698429A1

CA2698429A1 - Water jet pump for propelling water borne craft

Info

Publication number: CA2698429A1
Application number: CA2698429A
Authority: CA
Inventors: Richard G. Davies
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-04-07
Filing date: 2010-04-06
Publication date: 2010-10-07
Anticipated expiration: 2030-04-06
Also published as: GB201005723D0; CA2698429C

Abstract

A water jet pump for water borne craft that can have an 'outboard' or a 'stern- drive' configuration. The stator-gearbox housing of the jet pump may have an outboard power-head attached to its upper surface or alternatively a right angle drive can be attached thus permitting an inboard engine or 'stern-drive' layout. A further useful feature is the provision of a flexible neck to the jet pump intake that facilitates steerage and trim. The stator-gearbox housing may be manufactured as a single component or comprise three separate components that are bolted together. An important feature of the stator-gearbox drive housing is that water is able to pass through the stator section of the stator-gearbox and a vertically arranged drive shaft without significant frictional losses due to turbulence. This is achieved by passing the shaft through a thickened stator blade that is hydrodynamically matched to the adjacent blades.

Description

WATER JET PUMP FOR PROPELLING WATER BORNE CRAFT
FIELD OF THE INVENTION

This invention generally relates to water jet propulsion systems used for propelling boats and other water borne vehicles.

BACKGROUND OF THE INVENTION

Marine propulsion is currently dominated by two main propulsion systems.
The first being based on exposed propeller drives and the second, water jet pump designs of a centrifugal, mixed or axial flow configuration. The propeller drives fall into three broad classes called stern-drive, inboard/shaft, and outboard with further subclasses relating to more recent innovations.
Propeller systems by far and away out sell those based on the water jet pump in spite of the obvious benefit that most jet pumps offer whereby their installation requires no below-hull projections.

The reasons for this lies in part, with the basic functionality of propeller systems, in that they are relatively quick to install, have compact and easily managed control systems for steering, trim and throttle control and are well integrated with the driving engine. Further a propeller is still in most circumstances more efficient than the jet pump although improved hydrodynamic design is closing this gap, particularly for high speed applications. In respect of the jet pump based propulsion systems, an outboard design, US Patent 3,082,732 (Stallman), is currently manufactured with the pump being of a centrifugal design whereby a vertical shaft drives a horizontally arranged impeller, fixed directly to the end of the vertical shaft.
This design has some inherent deficiencies that make it somewhat hydrodynamically inefficient being by some estimates 20 to 30 % less efficient than axial or mixed flow jet pump designs (Reference - The Jet Boat ....

pp.80). Its major benefit is its simplicity of design and in particular, an ability to attach the pump section of the device to existing outboard power-head stems thereby reducing the overall cost of manufacture.

This jet pump is currently supplied to the world market by most of the major recreational marine manufacturers. Other types of "axial flow outboard jets"
are produced in much smaller numbers but these devices operate such that the pump section is submerged below the bottom hull line of the boat, when the boat is in planing mode.

Significantly the jet plume is therefore exhausted under the water rather than being expelled into the air behind the boat, with a consequent loss in efficiency. Examples of this type of jet pump are shown US patents 3,249,083 and 3,389,558.

For boating applications these devices cannot therefore be used in very shallow water such as might be found in the shallow braided rivers of North America and shallow coastal marine waters. Their usefulness seems primarily

2 aimed at increased user safety because the impeller is enclosed by the pump casing as compared to an exposed outboard propeller.

In US 4,281,996 is shown a simple outboard jet pump design showing a geared assembly inside the flow path where the vertical drive shaft penetrates through to the driving gears downstream of the stator section. This patent fails to address the hydrodynamic losses that arise from the multiple directional changes in the flow path, between the intake and nozzle.

Further, the jet nozzle is significantly elevated above water level when the boat is in planing mode, resulting in excessive head loss.

Also not addressed are the means by which frictional losses are to be avoided as a result of the placement of a vertical drive shaft in the flow path.

This patent also fails to deal with the dimensional requirements needed for such a device, in respect of low loss flow through the pump, and its overall dimensions, particularly its length. If constructed as shown, this device would protrude a considerable distance out from the transom making it commercially unacceptable in the marine propulsion market.

In US 6,776,674 the patent attempts to improve on the efficiency of the outboard jet pump concept but is essentially a conventional axial flow jet pump attached by a swivel to the boat transom. This concept lacks the compactness of a conventional outboard propeller system, which incorporates both a trimming and steering function together using a "centralized" pivot system. In this example there is again, a lack of compactness, in particular its longitudinal overall length being excessive because the entire pump, including the intake, is mounted to the transom of the boat. As previously

3 mentioned this leads to considerable market resistance because by default, it significantly increases the overall length of the craft in which it is installed.
Other examples of outboard jet pumps which propose to operate in planing mode are shown in US 5,769,674 and US 6,283,805. US 5,769,674 attempts to show how the lower superstructure of a conventional propeller outboard can be inserted into a pump housing with an attached intake and thus achieve an axial configuration. The excessive approach angles in the intake and the internal structures of the pump housing mean that it has poor efficiency relative to the conventional axial or mixed flow pump designs.
US 6,283,805 attempts to integrate a conventional axial flow pump with an outboard power head where the entire device is mounted on the boat transom.
In respect of its hydrodynamic efficiency this jet pump is certainly more efficient than that shown in US 3,082,732 but again, its excessive length makes it less suitable for commercial or recreational use. The reader will also note that this jet pump retains a 'through the intake' drive shaft. The drawing FIG.2 also fails to show the actual dimensional requirements that such a device will have. That is, the pump portion of this outboard design will be much longer than is represented - if the intake, for example, is to have an efficient geometry. It should be noted that in my drawings FIGS. 1 - 16, that they are scaled correctly whereby the impellers shown are 210 mm in diameter thus giving the reader an idea of the relative proportional dimensions of the various components. My drawings therefore represent a dimensional outcome arising from the hydrodynamic constraints necessary to minimise losses as the water passes through the intake/pump. In FIG. 7, for example, the distance from the transom to the end of the steering nozzle is approximately 500 mm. The

4 entire length of the pump shown as FIG. 7 is 1320mm, were the impeller diameter to be 210 mm. Given a smaller impeller of 160 mm diameter, driving the same sized craft, the pump length would still be in excess of say 900 mm.
So for designs allowing for the entire pump (including the intake housing) to be attached to the stern of, for example, a 5 metre long boat, the pump would extend beyond the transom by at best 900 mm and at worst 1320 mm. These dimensions thus give the reader an indication as to the limitations this imposes on commercial viability and ultimately pump design as it relates to an efficient outcome.

Inherent in all of the above mentioned devices is a failure to isolate and deal with the hydrodynamic losses arising in the intake but more particularly the hydrodynamics involved in the stator-gearbox housing design and how this is applied to, in the end, producing a compact and commercially acceptable jet pump.

The following describes how the short-comings of present jet pumps can be overcome whereby an axial or mixed flow jet pump can be at least as hydrodynamically efficient, in either a stern-drive or outboard configuration, as conventional jet pumps having a through-intake drive shaft design.
SUMMARY OF THE INVENTION

(i) Pump efficiency as it relates to stator/impeller interaction and design.
One important aspect of this invention is the need to provide a hydrodynamically efficient flow through-put such that the impeller and stator interact to provide maximum efficiency whereby frictional losses are minimised and thrust output is maximised. Some geometrical considerations for this are described in the preferred embodiments but do not preclude the use of existing impeller and or stator configurations which allows the invention to operate within the operating efficiency of existing axial or mixed flow jet pumps.

The most important advantage offered by this aspect of the invention is that I show how to obtain hydrodynamic lift in the stator section blading thereby increasing the thrust output and thus the efficiency of the jet pump.

A further important and associated aspect is the need to overcome losses incurred as a result of the penetration of the vertical drive shaft through the jet pump stator housing. The present invention allows for this by the use of a thickened and hydrodynamically shaped stator blade which allows a more or less parallel (to the adjacent stator blades), low loss path, for the impinging flow. The blade may be in two parts such that downstream end of the blade is tapered and forms part of the stator cone casting inside the exhaust nozzle, where it smoothly butts into the downstream end of the upstream portion of the thickened stator blade. Alternatively it can be cast as a single structure being part of the main stator - gearbox housing. In the drawings I show the stator blading, apart from the thickened stator blade, extending to the rear of the stator-gearbox housing but the number of blades may either be increased and/or they may be lengthened so that they pass into the outlet nozzle when more control of plume divergence is desired.

To further improve the flow path, the inner surface of the internal section of the stator housing, the gearbox casing, is tapered from the upstream end through to the upstream end of the nozzle in order to keep directional changes inside the stator-gearbox/housing/nozzle as smooth flowing as possible.

Another useful feature is that while the stator-gearbox housing would, for commercial purposes, usually be cast as a single unit from a corrosion resistant aluminium, it can also be made in three parts. So I show an inner gearbox component, with attached stator blades, and an outer component comprising two machined and matched, doweled components . The inner gearbox component can thus be located and locked inside the two outer parts, using bolts, not shown, to hold the outer portions together.
Rotation of the statored inner component is prevented because of an extension of the inner gearbox component where the vertical shaft penetrates through into the outer portions thus creating a locking structure. This improvement allows the end user to change both the impeller and the stator geometries, for experimental purposes, thus providing the ability to adjust the pump's performance for a variety of uses or circumstances.

(ii) Improved steering system for large and small water jet propelled craft.
Another aspect of the invention relates to the use of a flexible intake (that is not simply a coupling) which permits articulation of the jet pump in a vertical and right to left direction. This feature allows for both steering and trim functions to be performed without the need for a steering system to be coupled to the jet pump nozzle. A further advantage of this is that the flexible intake neck provides for improved hydrodynamics over that of conventional steering systems and also a reduction in the cost of construction of the intake, as the intake no longer receives the thrust loading form the jet pump - the thrust being transmitted to the rotatable mounts, then to the boat's transom.

(iii) Rigid mount stern-drive jet comparable to a propeller stern-drive system.
Another aspect of the invention is that in a simplified device, the intake may also be a rigid structure whereby the thrust from the jet pump is transmitted to the solid mounted intake. In a further configuration a useful feature is that the stator-gearbox housing, impeller and nozzle section can all be removed as one integrated unit, for maintenance purposes, by simply removing the flange bolts (not shown) attaching the stator-gearbox housing to the impeller housing flange. It should be noted that the impeller housing may be a separately attached housing or be formed as part of the intake housing - that is, a single casting or fabricated component.

(iv) Outboard jet comparable to an outboard propeller system.

In another aspect of the invention I allow for an outboard power head to be attached to both the 'flexible' intake design and also the 'rigid' intake design. This made possible because the stator-gearbox unit is a common or universal component to both the outboard and inboard stern-drive configurations whereby an adapter plate can be provided for either a right angled drive or an outboard power-head/stem assembly to be attached.

(v) Improved engine mounting means and installation.

In this case the invention is directed to the manner in which an inboard located engine may be coupled and securely fixed. The engine may be attached by flexible mounts to a 'shelf attached to the inside of the transom whereby the engine is fixed to the shelf and the transom, in a three point arrangement. Alternatively two of the lower mounts may be provided as part of the intake casting while the third is still attached to the inside of the transom BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 : Isometric view of the stern-drive jet pump.
FIG.2: Part cutaway view of the stern-drive jet pump.
FIG.3: Isometric view of the outboard jet pump.

FIG.4: Isometric view and part cutaway of the outboard unit with a rigid intake housing.

FIG.5: Isometric view and part cut-away of the stern-drive jet pump with a rigid intake housing.

FIG.6: Side view of the outboard unit with a rigid intake housing.

FIG.7: Side view of the stern-drive unit with a rigid intake housing FIG.8: Isometric view of a section of the flexible intake neck (31).
FIG.9: Isometric view of the flexible neck (31) FIG. 10: Sternward looking isometric view from outside the boat showing the stern-drive mounting ring assembly.

FIG.1 1: Isometric view of the pump housing (30) showing separated halves FIG. 12: Upward looking isometric view of the bottom of the boat showing the intake partially withdrawn and the intake neck location hole in the lower side of the engine mount shelf.

FIG. 13: Isometric view of the inside of the boat looking sternwards showing the engine mounting means and access hole to the jet pump unit.
FIG.14: Diagram showing the flow patterns relative to the impeller blades and stator blades FIG.15: Isometric view of the stator and internal view of the pump housing casting and attached impeller.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

FIG. 1 shows a stern-drive configuration with the drive engine (1) attached to the upper right angle drive (2) via a drive shaft (3). The drive shaft (3) comprises a central shaft (4) and two constant velocity joints (5) and (6).
These may also be seen in the part cutaway view, FIG. 2. In FIG. 2 I show a flexible cover (7), which clips to the right angle drive (2) at one end and an oval or elliptical shaped spigot (8), FIG. 10, fixed to the transom (42) at the other end.

This ensures that a watertight seal exists between the jet pump and the transom (42), FIG. 10 and that the drive shaft (3), FIG. 2, is also sealed off from water intrusion. In FIG. 2 I show the drive train consisting of the engine (1), turning the drive-shaft (3) which in turn is connected to the impeller (9), via spiral bevel gears (10), (1 1), and the lower spiral bevel gears (12) and (13) shown in FIG. 5. The spiral bevel gears (10), (11) are supported by bearings (14) and (15) mounted inside the right angle drive (2), FIG. 2 and inside the nose cap (17), that is bolted (18) to the stator-gearbox housing (22) at (16), seen in FIG. 5. Alternatively but not shown in FIG. 5, the spiral bevel gear (13) may be further supported by locating an additional bearing (not shown) at the down-stream end of the stator-gearbox (22). The jet pump outlet nozzle (19) bolts directly to the end of the stator-gearbox housing (22). The downstream end of the stator- gearbox housing (22) has a cone (20) attached to it, with the downstream end of the thickened stator blade (21) formed into its upper surface. The vertical shaft (23), FIG. 5 and FIG. 15 passes through the upstream section of the thickened stator blade (21) , also seen in FIG. 15.
Where the stator -gearbox housing (22) is not constructed as a single casting (for reasons previously discussed) as shown in FIG. 1 land FIG 1 5, the thickened stator blade (21) has an upper locating boss (25) that serves to locate the gearbox housing (24), FIG. 15, as a separate component inside the outer housing(s), (26) and (27) as seen in FIG.] 1. 0 ring seals, not shown, inserted in grooves, not shown, in the boss (25) prevent water intrusion.

The outer housings (26) and (27) FIG. 11 are dowel bolted together (dowel and bolts not shown) such that they clamp the gearbox housing (24) into place.
The impeller housing (28) seen in FIG. 1 and FIG 2 bolts (bolts not shown) to the stator-gearbox housing (22) via flanges (29) and (30) FIG. 1. On the up stream end of the impeller housing (28) is fixed, by means of a clamp, (not shown) a flexible neck or coupling (31) which in turn attaches to the intake (32) FIG. 1 and FIG 2. The flexible intake neck (31) can be seen more clearly as FIG. 9. The flexible neck (31) consists of a concertina section of high strength plastic or rubber, reinforced with a helically wound steel coil (not shown) cast into it during manufacture. The embedded coil prevents the neck (31) from collapsing when the inside of the intake (32) is operating under vacuum or suction. An alternative construction method is shown for the neck (31) in FIG.
8, where two flexible 'u' sections (33) and (34), seen in cutaway view, are bonded together with a central rigid ring (35) sandwiched between, that also allows a smooth inner surface.

In respect of the rotatable jet pump the upstream end of the impeller housing (28) has a ring (36) cast or fixed to it via lugs (37) and (38), as shown in FIG. 1.
and FIG. 2. Each north and south pole of the ring (36) has a locating swivel pin (39A) and (39B), seen in FIG. 2, (Inner ring (36) not shown in FIG.2) that pass into locater bearings (not shown) in the outer ring (40). The outer ring (40) is also, in turn, located by the swivel bearing block (41 A) seen in FIG. 1 and FIG.
2 and pins (both bearing blocks and pins not shown). The bearing block (41 A) (and its opposing twin (41 B) seen in FIG. 10 are in turn fixed to the transom (42), FIG. 10. The thrust is transferred to the boat hull at this point.
The two rings (36) and (40) pivot approximately about the centre point of the intake neck (31) in order to allow the neck (31) to rotate in a relatively unstressed state. This arrangement thus permits movement of the entire downstream section of the jet pump comprising the impeller housing (28), stator- gearbox housing (22) and the nozzle (19) in both the vertical and horizontal plane. This action thus facilitates steering and trimming of the boat in which the jet pump is installed.

In FIG. 15 I show the stator blade (43) and the impeller (9) with blades (44) and (45). In FIG. 14 I show a diagram of the impeller blade (44) and stator blade (43) relative to each other, with arrows (46) indicating the direction of hydrodynamic lift at about 45 degrees to the stationary stator blade surface (43). The impeller (9) has two sets of blades (44) and (45). The downstream blades (45) are overlapped into the upstream blades (44) and extend beyond the trailing edge of the upstream blades (45). In FIG. 15 I show the thickened stator blade (21) and the hole (47) through which the vertical shaft (23), as seen in FIG. 5 passes. The thickened blade (21) has been shaped to conform with the adjacent blades as far as is practicable so that turbulence and localised pressure effects at the upstream entry points either side of the blade (21) are minimised.

In FIG 12 and FIG. 13 I show a method of installation. FIG. 13 shows the drive engine mounts (49) and jet pump intake (32). In FIG. 12 I show an inside bottom view of the transom shelf (48) and engine (1) and transom (42). The intake (32) is installed from the outside of the hull (50) so that it can be withdrawn in the manner shown, through the bottom of the boat. Because the intake (32) accepts no thrust from the jet pump it can be made of lighter cheaper materials such as, for example, rotary molded plastics. The sternward looking end of the intake (32) inserts into the shelf via the neck hole (51) and has an internal spigot (not shown). An 0 ring or flexible skirt (both not shown) seals the close fitting surfaces to prevent water intrusion. In FIG. 13 I show the hatchway (52) into the transom shelf (48) recess enabling access to the flexible intake neck (31), seen in FIG. 2. In order to remove debris from the intake (32) the clip (not shown) retaining the flexible neck (31), to the intake (32), can be undone and the flexible neck (31) then be pushed back to allow entry to the internal area of the intake (32). A view of the intake (32) with the flexible neck (31) removed altogether, can be seen in FIG. 10. The top of the transom shelf (48) is designed so that it is above the water line and is closed off by a lid (not shown) since the internal space is open to the rear of the boat, as seen in FIG. 10. Up and down movement of the jet pump, which allows the boat to be trimmed under power, is achieved by remote movement of a rotatable trim lever arm (53), FIG 1, (part view only shown), attached to the outer ring (40). Pulling the arm (53) towards the bow angles the nozzle (19) of the jet pump upwards, whilst in the opposite direction, it moves downwards.
Steering is achieved by pulling and pushing on the control cable/rod (54) via a cable (not shown) attached to the steering wheel (not shown) at the helm. The cable/rod (54) is attached to the top of the impeller housing (28) at (55) with a swivel joint and bolt (57) In FIG. 3, FIG. 4, and FIG.6 I describe an outboard configuration whereby an outboard power-head/drive stem (57) is attached directly to the top of the stator-gearbox (22) , thus removing the need for the right angle drive (2) seen in FIG. 1. Further the jet pump/power-head combination may be rigidly in connection with the intake FIG. 4 or as shown in FIG. 3 having a flexible connection allowing an 'outboard' type mounting system.

In respect of mounting, trimming and steering the outboard jet pump is largely similar to the stern-drive version, however in FIG. 3 I show a mounting frame (58), which incorporates the ring pivot system into one structure. In this design the power-head/drive stem (57), is attached to the vertical pivot shaft (59) via two brackets (60) and (61). Trimming is achieved by means of the rams (62) and (63) and steering by remote activation of the steering arm (64).
FIG. 3 and FIG. 4 show an outboard power-head (57) and extension/adapter plate (65) fixed to the stator-gearbox housing (22).

In FIG. 6 I show a simple means for cleaning debris from the inside the intake (32) where an access port (66) is built into the upper surface of the intake (32).
The access port (66) is sized so that when the boat is stationary the walls of the port (66) extend well above the waterline. A removable access lid (67) is fixed in place and sealed with an '0' ring (not shown) to prevent leakage. To provide continuity of shape of the inner intake (32) wall , a water-tight plug (68) is fixed in place inside the the port (67) cavity. Access is gained by removing the lid (67) and plug (68) allowing safe and easy removal of debris up to the impeller (9). This modification is particularly suited to the outboard version shown as FIG. 4 and FIG. 6.

Claims

What is claimed is:

[Claim 1]

A water jet pump where the the stator-gearbox has a hydrodynamically designed and thickened stator blade that allows a vertically aligned drive shaft to pass through it into the gear-case portion of the stator-gearbox whereby frictional losses are minimised in the applied flow through the stator-gearbox, as the water passes into the outlet nozzle, such that the said drive shaft, to which a spiral bevel gear is connected, can then drive a second meshed spiral bevel gear that is fixed to an axially arranged shaft to which in turn is fixed an impeller at its upstream end.
[Claim 2]

A water jet pump as cited in the above claim 1 where the stator-gearbox has a right angled drive attached to its upper surface that is further fixed to a flexible drive-shaft, that is further fixed to a driving engine located inside or upstream of the boat transom, the drive-shaft penetrating the transom and being sealed by means of a flexible enclosing cover.
[Claim 3]

A water jet pump cited in claim 1 where the intake has a flexible portion that allows the stator-gearbox and nozzle assembly, that is attached to a dual ring assembly, to move side to side and vertically at the same time, thus providing a means of steerage and trim, but also allowing an in-board engine to drive the said stator-gearbox and at the same time this function occurs.
[Claim 4]

A water jet pump as cited in claim 1 where the stator-gearbox has an outboard power-head attached to its upper surface by means of an adapter plate.
[Claim 5]

A water jet pump as cited in claim 4 where the intake has a flexible portion that allows the stator-gearbox, nozzle and outboard power-head assembly, that is further attached to a ram adjusted mounting frame and dual ring assembly, to move side to side and vertically at the same time, thus providing a means of steerage and trim.
[Claim 6]

A water jet pump as cited in claim 1 having a stator-gearbox assembly and impeller housing which are attached by bolts or other means rigidly to the intake housing.
[Claim 7]

A water jet pump as cited in claim 6 having a right angled drive attached to its upper surface.
[Claim 8]

A water jet pump as cited in claim 6 having an outboard power-head attached to its upper surface by means of an adapter plate.
[Claim 9]

A water jet pump as cited in claims 1,7 and 8 whereby the stator and impeller blading can be geometrically arranged such that the flow impinging on the stator blading generates an increased level of hydrodynamic lift thereby increasing the thrust output and thus improving the efficiency of the jet pump.
[Claim 10]

A water jet pump as cited in claim 1,7 and 8 whereby the stator blading has the leading 25 - 35 % of their axial length configured to have a peripheral blade angle of about 45 degrees so that the lift component off this portion of the blade surfaces is maximised to improve the overall efficiency of the pump.
[Claim 11]

A water jet pump as cited in claims 1, 7 and 8 where the stator-gearbox comprises three parts, whereby the three parts comprise an inner gearbox enclosed and located by two outer halves that are bolted together.
[Claim 12]

A water jet pump cited in claim 2 and claim 7 where the driving engine, being located inside the boat transom, is mounted in at three point fashion to a shelf and to the inside of the transom.
[Claim 13]

A water jet pump cited in claim 12 where the driving engine, being located inside the boat transom, is mounted in at three point fashion by two mounting points to the intake and by at least one other to the inside of the transom.
[Claim 14]

A water jet pump as cited in claim 1 where the steering and trim system is activated by remote cables or other means by the movement of either or both of the mounting rings which locate the stator-gearbox and nozzle assembly.
[Claim 15]

A water jet pump as cited in claim 8 where the intake is modified such that a large access port is provided in the upper surface of the intake whereby a fixed lid and and inner liner may be removed so that weed or debris can be removed by hand or other means from inside the intake.
[Claim 16]

A water jet pump as cited in claims 1,7 and 8 where the impeller blades control the flow through the stator blading, as cited in claim 10, such that an increased level of hydrodynamic lift is achieved whereby the efficiency of the jet pump is increased due to greater thrust output.
[Claim 17]

A water jet pump as cited in claim 1 where the impeller/ stator-gearbox housing/right angle drive and nozzle/steering assembly can be detached, as a single unit, from the impeller housing, for maintenance purposes.
[Claim 18]

A water jet pump as cited in claim 7 where the impeller/ stator-gearbox housing/right angle drive and nozzle/steering assembly can be detached, as a single unit, from the impeller housing, for maintenance purposes.
[Claim 19]

A water jet pump as cited in claim 8 where the impeller/ stator-gearbox housing/outboard power-head and nozzle/steering assembly can be detached, as a single unit, from the impeller housing, for maintenance purposes.