IMPROVEMENTS RELATING TO STEERING DEVICES FOR WATER JET PROPULSION

Abstract: A steering system for water craft having jet propulsion. A stator outlet (16a) discharges water into a steering nozzle (12) which is pivotably mounted on a nozzle housing (8). The internal diameters of the stator outlet and the steering nozzle form a tapered passage for efficient water flow. A seal (27) may be incorporated between the steering nozzle and the nozzle housing.

Description: IMPROVEMENTS RELATING TO STEERING DEVICES FOR WATER JET PROPULSION The present invention provides an improved steering device for a water jet propulsion unit and a water jet propulsion unit incorporating such a steering device. BACKGROUND Water jet propulsion systems require a steerage device which is responsive to the operating conditions encountered by the vessel propelled by the propulsion system and will operate without introducing significant inefficiencies. Broadly, the steering devices may be categorised in to three general classes. The first is external deflectors that are pivotally mounted relative to the water flow and can be moved into the part of the water flow to cause deflection. This system is efficient in the non-steering mode, but once the flow is deflected there is a degradation in thrust. Also external deflectors do not always produce a responsive control there being a significant "dead band" at small steering locks where there is no steerage response. The second general class is an angular pivot where the nozzle through which the water flow is discharged is mounted on an elliptical bearing surface relative to the axis of the stator flow. This construction has a limitation because the steering deflection does not move in a horizontal plane thus generating a lateral tipping moment on the hull of the vessel. The third general type of steering nozzle is an internally mounted nozzle which has the advantage of much more responsive control but with known steering devices in this class has a significant degradation of the thrust in all operating modes. PRESENT INVENTION The present invention is concerned with an improved steering device for a water jet propulsion system of the third general type which will achieve responsive control with reduced degradation of thrust. Accordingly in one aspect the invention consists in a steering device for a water jet propulsion unit said steering device comprising: a nozzle housing attachable to the stator of a water jet propulsion unit; nozzle pivots fitted in said nozzle housing to allow rotation generally in a horizontal plane; a steering nozzle mounted within the nozzle housing upon said nozzle pivots; the inner surface of the nozzle housing defining a substantially symmetrical outwardly curved chamber about the nozzle pivots with the entrance to the mounted steering nozzle having a clearance fit within the chamber over the operational steerage arc of the nozzle; a stator extension from the tailpipe of the jet propulsion unit to deliver a flow of water from the tailpipe to a position inside the entrance to the steering nozzle with the discharge end of the stator extension shaped as a non-interference exit periphery relative to the steerage movement of the steering nozzle so that the stator extension carries the water through the chamber and symmetrically directs the water flow into the steering nozzle at substantially the operating head of the propulsion unit and in use retains water about the outer surfaces of the stator extension; and steerage means to move the steering nozzle on the nozzle pivots through the steerage arc. The stator extension preferably carries the water flow from the stator to a position beyond the nozzle pivots inside to the entrance to the steering nozzle. In a second aspect consists in a water jet propulsion unit having an extended tailpipe, a driven impeller operably rotatable within said extended tailpipe, a water inlet duct to deliver a flow of water to the impeller, stator vanes in the tailpipe after the impeller with the stator vanes directing the flow of water through the tailpipe to the outlet, a nozzle housing supported by and extending rearwardly of the tailpipe, nozzle pivots fitted in said nozzle housing to allow rotation generally in a horizontal plane, a steering nozzle mounted within the nozzle housing upon said nozzle pivots, the inner surface of the nozzle housing defining substantially symmetrical outwardly curved chamber about the nozzle pivots with the entrance to the mounted steering nozzle having a clearance fit within the chamber over the operational steerage arc of the nozzle, a stator extension from the tailpipe to deliver a flow of water from the tailpipe to a position inside the entrance to the steering nozzle with the discharge end of the stator extension shaped as a non-interference exit periphery relative to the steerage arc of the steering nozzle and with the stator extension carrying a water flow through the nozzle housing, symmetrically directing the water flow into the steering nozzle at substantially the operating head of the jet propulsion unit and to retain water about the outer surface of the stator extension; and steerage means to move the steering nozzle on the nozzle pivots through the steerage arc. A water jet propulsion system is designed with an operating head established by the smallest exit opening in the water flow of the propulsion system. In the present invention, this exit opening is the nozzle outlet. The stator extension carries and symmetrically directs the water flow into the nozzle, with the exit diameter of the stator extension being slightly greater than the exit diameter of the nozzle. The nozzle is preferably tapered along its length so that the diameter of the nozzle where the water flow enters is made as close as possible to that of the stator extension outlet. The purpose of this is to maintain an uninterrupted acceleration of the water flow from the stator to the nozzle outlet thereby achieving maximum efficiency. Also it ensures the chamber about the stator extension is full of water providing balance to facilitate movement of the steering nozzle. The stator extension may project beyond the stator as an extension of the tailpipe or as a separate nozzle insert carried in or through the housing and having the periphery shaped as a non-interference exit periphery relative to the steerage movement of the nozzle entrance. This may mean a shaping of the exit periphery of the stator insert depending upon the particular application. In its most effective form the stator extension is lengthened to a position beyond, and aft of, the nozzle pivots in order to minimise the gap between its exit and the entry to the nozzle. This is a significant factor in the present invention to enhance performance. With this type of steering fitting it is necessary to provide a partially spherical shape in the housing to accommodate steering movement at the nozzle. Previously a significant thrust degradation was evident at all times caused by expansion and subsequent turbulence of the flow within the partially spherical housing chamber prior to entering the nozzle and also by leakage between the entrance periphery of the nozzle and the housing in which the nozzle moves through the steering arc. The stator insert carrying the water flow through the housing minimises this thrust degradation by transporting the flow across the housing chamber prior to entering the nozzle in such a way that little if any expansion or turbulence occurs. In addition there is reduced leakage around the periphery of the nozzle and a larger working clearance can be used in circumstances where this is desirable ie where operating in conditions likely to pick up sand, stones and other particulate material. In its application to large waterjets where maximum efficiency is required peripheral leakage is reduced by means of a seal fitted between the entrance periphery of the nozzle and the housing. The stator extension is also lengthened beyond the nozzle pivots to have minimal gap between its exit and the entry to the nozzle. The present invention has particular application to marine propulsion units where in addition to the steerage, it is also desirable for the steering nozzle to have a trimming capacity. This can be achieved using a set trim, locating the nozzle at a set angle to the horizontal. Another embodiment has a variable trim adjustment. This can be achieved by providing a pivot between the housing and the stator at right angles to the pivots carrying the steering nozzle. This mounting enables the housing to be moved, adjusting the vertical angle at which the steering nozzle has effective operation. A single steering control will be provided allowing both trim control and steering control and this may be a simple tiller steering mechanism with rotational and slide movement to effect the tilt and steering, or it may be a push rod arrangement manually or hydraulically controlled. With a push rod arrangement, there would be separate controls for the steering and the tilt. In the larger units, the steering and trim mechanisms will be regulated by a control through a servo unit which will give an operator a simple operating control, preferably through a single operator control. The trim function on a larger vessel where there are a plurality of water jet propulsion units operating, can also function as stabilisers replacing or complimenting stabiliser fin control. In suitable applications, the trim control could replace trim tabs used to regulate the operating stability of the vessel. The invention also broadly consists in a water jet propulsion unit incorporating a steering device as afore set forth. The invention consists in the foregoing and also envisages constructions of which the following gives examples only. One preferred form of the invention and modifications thereof will now be described with reference to the accompanying drawings in which: Figure 1 is a sectional view through a water jet propulsion system, incorporating a steering device according to the present invention; Figure 2 is a sectional elevation of the steering device according to the present invention with trim fixed in line with jet shaft; Figure 3 is a sectional view of a steering nozzle according to the present invention with a fixed upward trim; Figure 4 is a plan of a steering nozzle according to the present invention incorporating a variable trim capacity; and Figure 5 is an elevation of Figure 4. Figure 6 is a sectional view of a fixed trim steering nozzle incorporating a seal and with lengthened insert for efficiency. Figure 7 is a plan of Figure 6 showing the steering at full helm. Figure 8 is a sectional plan of Figure 7 with the nozzle turned. Figure 9 is a sectional plan view of Figure 7 with the steering nozzle straight and Figure 10 is a graph of test results. Figure 1 1 is a sectional elevation illustrating an alternative seal and Figure 12 is a detail of the seal fixing. One form of a typical water jet propulsion unit 1 is illustrated in Figure 1 having an intake duct 2 to deliver the water flow to an impeller 3 mounted on a rotatable shaft to rotate in an impeller race. A stator carrying stator vanes 4 directs a water flow from the impeller through the tailpipe 5. The power for the impeller is provided through a drive shaft 6 (power unit not illustrated). The steering device 7 for the water jet propulsion unit comprises a means of deflecting the water jet through a steering arc. To this end a housing 8 is provided which is suitably secured to the tailpipe of the water jet propulsion unit 1. This may be achieved by any convenient securing means usually provided through fixing studs and bolts 9 located about the periphery of the housing at appropriate spacing. Located in the housing 8 are pivots 10, 11 designed to pivotally support the steering nozzle 12. " The inner surface 13 of the housing 8 is a part spherical shape with the sphere described about the diameter taken through the pivots 10, 11. The entrance outer periphery 14 of the steering nozzle 12 has a clearance fit with the spherical surface 13 over the steering arc of the nozzle. The exit nozzle diameter 15 provides the operating head gainst which the water jet propulsion unit operates. A stator/tailpipe extension 16 extends from the tailpipe to a position preferably aft of the nozzle pivots inside the nozzle entrance with the water flow at the effective diameter of the stator extension during operation through the steering arc. The stator extension has the exit periphery 17 shaped and located so that there is no interference with the movement of the steering nozzle. The periphery may also be scalloped away at the sides which has the effect of reducing the operating loads. The effective diameter of the outlet from the stator extension 16 will be slightly greater than the discharge or exit nozzle diameter 15. The inside of the nozzle 15 has been shaped such that at full steering lock it is just clear of the outside of the stator extension while at the point of flow entry it matches the effective diameter of the flow from the stator extension. Because the flow is directed into the nozzle at the effective diameter of the stator extension as described above, and the nozzle diameter at this point of entry is the same, there is little or no degradation in thrust caused by turbulence or expansion within the housing. It is necessary to provide a steering operation of the nozzle and this is through a steering shaft 18 connected to a crank 19 and ball joint 20 allowing rotation and axial movement of the shaft 18 to operate the steering nozzle through the steering arc. The steering shaft is actuated by a steering tiller 21 which is connected to the steering remote control system in the conventional manner. The embodiment of the invention illustrated in Figures 1 and 2 shows the present invention applied to a steering nozzle with trim fixed at 0 degrees. The nozzle according to the present invention may however be preset at a desired trim angle and in Figure 3, there is an illustration of the present invention mounted to achieve a "nozzle up" trim of 8 deg. In Figures 4 and 5 the ability to set the trim is adjustable. In this embodiment, the main housing 22 of the water jet unit 1 has at the tailpipe a housing extension 23 supporting a pivots 24 and 25 which pivotally carry the housing 8 of the steering deflector according to the present invention. The housing 8 carries the pivots 10, 11 that pivotally support the nozzle 12 as previously described. The stator extension 16 also functioning as previously described is fitted by suitable fixing studs 26 to the housing 22. In this embodiment, the steering shaft 18 as illustrated in Figure 5 operates through the crank 19 and ball 20 with a function which allows not only the movement of the steering nozzle through the steering arc, but also by reciprocal motion of the shaft 18 and movement of the housing 8 about the pivots 24, 25 giving a "nozzle up" or "nozzle down" configuration as selected by the operator to give the desired trim setting. The embodiment of the invention illustrated in Figure 6 shows the invention in a form combining a circumferential seal 27 at the entrance periphery of the nozzle 12 which runs against the partially spherical inner surface 13 of the housing 8 to prevent leakage and the stator extension 16a lengthened to reduce the gap to the nozzle entry to a few millimetres only. Steering is operated via a pushrod acting on the steering arm 28 attached to the nozzle 8. In the present invention it is preferable to ensure that the stator extension delivers the water flow symmetrically into the nozzle, ie there is correct alignment of the water flow passing from the stator extension and the entrance to the steering nozzle, otherwise, out of balance forces will be generated with deleterious effect. An alternative flexible sealing arrangement is illustrated in Figures 11, and 12. The molded rubber edge 30 is vulcanized onto an aluminium retainer plate 31 which is then fastened to the inner face of the moveable nozzle 12 using cap screws 32. The mounting holes in the plate are larger than the cap screws so that the rubber lip can be positioned on assembly to close the gap between the nozzle outer periphery and inner spherical surface of the housing. By this means leakage can be reduced. Prototype tests in which the nozzle was filled with sand and then the steering operated showed that the rubber edge reduced the likelihood of jamming. A different type of seal may be energized by the pressure of the water that it is sealing. This consists of a square section plastic seal loosely fitted in a groove around the outer periphery of the nozzle. Water pressure inside the nozzle forces the seal outwards against the spherical housing surface reducing leakage. SUPPORT TESTS A range of tests have been conducted on prototype versions of the jet steering unit to define parameters of the advantages which have been observed in trial tests applying the present steerage invention to jet propulsion units. As a broad outline, in a test to compare the standard deflector type steering with the present invention, a test boat with deflector steering would plane at 2800 rpm but in a moderate turn begin to come off the plane and require an increase in revs to 2900 to 3000 rpm to keep the plane position. With the stator extension and steering according to the present invention fitted the boat would keep on a plane in a moderate turn at essentially the 2800 rpm ie. the same rpm as when travelling in a straight line. In other tests greater efficiencies were observed where a peripheral nozzle seal was fitted, and the short stator extension and the long stator extension were fitted with or without the seal. It was observable that the steerage device according to the present invention represented a significant improvement over a conventional deflector steering device with an advantage achieved by a short stator extension, a greater advantage achieved by a longer stator extension and an enhanced performance for each example where a seal was used in combination with the extensions. Reference is made to figure 10 where test results are recorded of a small commercial jet unit internally identified as a 241 jet. Tests were conducted with no insert and with a short insert or stator extension. The test results are presented in table 1 here below and these test results in graphic form in figure 10. Table 1 241 Jet Test As can be seen, there is an even and consistent gain by using the insert according to the present invention. It is particularly significant to observe that the gain in speed is all the way through the speed range. With another small jet unit designed for the pleasure boat market internally identified as the 212 jet, tests were conducted to establish the relative efficiencies with the unit operating having no stator extension, a short stator extension or a long stator extension. The results achieved a maximum speed with no insert of 41.6 knots, a maximum speed with a short insert with stable extension of 42.4 knots and a maximum speed with a long stable extension of 43.2 knots. These results were plotted against a Savitsky resistance curve for the hull and the three jet thrusts were generated varying only the pump efficiency until the trial results were achieved. As a consequence of this test, it is established that the efficiencies with no insert was 75.2%, with the short insert was 79%, and with the long insert was 82.6%. This represents with a short extension, approximately a 5% improvement and with a longer extension insert, approximately a 10% improvement over a unit without the stator extensions. In all of the tests no adverse effects were noted with the steering remaining light and balanced and a gain in acceleration was also observed when the nozzle inserts either short or long were installed. Testing has confirmed the advantages which can be enhanced where a seal is also used in combination with the stator extensions. One form of complete seal developed for use in larger commercial units for deep water operation functions to increase the sealing activity with the water pressure generated by the steering nozzle and an observed enhanced performance of 2 to 3% was achieved. In other applications where the craft will be used for leisure activities or activities likely to cause particles to pass through the jet unit and possibly cause jamming, a different type of seal has been developed. This seal represents a deformable rubber lip or protuberance which achieves some of the advantages of a seal but still has sufficient flexibility to allow the unit to operate even in conditions where there are small particles that otherwise may be likely to cause jamming. Again these features represent an enhanced performance and although there is some leakage, the performance is nearly as greatly enhanced as with the complete seal.

Claims: CLAIMS: 1. A steering device for a water jet propulsion unit said steering device comprising: a nozzle housing attachable to the stator of a water jet propulsion unit; nozzle pivots fitted in said nozzle housing to allow rotation generally in a horizontal plane; a steering nozzle mounted within the nozzle housing upon said nozzle pivots; the inner surface of the nozzle housing defining a substantially symmetrical outwardly curved chamber about the nozzle pivots with the entrance to the mounted steering nozzle having a clearance fit within the chamber over the operational steerage arc of the nozzle; a stator extension from the tailpipe of the jet propulsion unit to deliver a flow of water from the tailpipe to a position inside the entrance to the steering nozzle with the discharge end of the stator extension shaped as a non-interference exit periphery relative to the steerage movement of the steering nozzle so that the stator extension carries the water through the chamber and symmetrically directs the water flow into the steering nozzle at substantially the operating head of the propulsion unit and in use retains water about the outer surfaces of the stator extension; and steerage means to move the steering nozzle on the nozzle pivots through the steerage arc. 2. A water jet propulsion unit having an extended tailpipe, a driven impeller operably rotatable within said extended tailpipe, a water inlet duct to deliver a flow of water to the impeller, stator vanes in the tailpipe after the impeller with the stator vanes directing the flow of water through the tailpipe to the outlet, a nozzle housing supported by and extending rearwardly of the tailpipe, nozzle pivots fitted in said nozzle housing to allow rotation generally in a horizontal plane, a steering nozzle mounted within the nozzle housing upon said nozzle pivots, the inner surface of the nozzle housing defining substantially symmetrical outwardly curved chamber about the nozzle pivots with the entrance to the mounted steering nozzle having a clearance fit within the chamber over the operational steerage arc of the nozzle, a stator extension from the tailpipe to deliver a flow of water from the tailpipe to a position inside the entrance to the steering nozzle with the discharge end of the stator extension shaped as a non-interference exit periphery relative to the steerage arc of the steering nozzle and with the stator extension carrying a water flow through the nozzle housing, symmetrically directing the water flow into the steering nozzle at substantially the operating head of the jet propulsion unit and to retain water about the outer surface of the stator extension; and steerage means to move the steering nozzle on the nozzle pivots through the steerage arc.

Inventors: HAMILTON MIKE JON, STEFFENS PAUL ALFRED, HAMILTON, MIKE, JON, STEFFENS, PAUL, ALFRED
Applicants: CWF HAMILTON & CO LIMITED, HAMILTON MIKE JON, STEFFENS PAUL ALFRED, CWF HAMILTON & CO. LIMITED, HAMILTON, MIKE, JON, STEFFENS, PAUL, ALFRED
Application year: 1999
Main classification: B63H
IPC codes: B63H11