FIELD OF THE INVENTION

This invention relates to a trimmable steering nozzle for a water jet propelled marine vessel.

BACKGROUND

In a water jet propelled marine vessel, the jet pump unit is provided with an outboard discharge nozzle that is usually used to steer the vessel by rotating the nozzle about a vertical axis, changing the direction of the water flow in a horizontal plane. It is desirable to change the direction of the water flow vertically by rotating the nozzle about a horizontal 'trim' axis to improve acceleration at low speeds, efficiency at high speeds, control roll of the vessel, or simply to trim the vessel. As used herein, trimming of the vessel refers to changing the attitude or pitch of the marine vessel in the water, and trimming of a nozzle refers to changing the angle of the nozzle relative to horizontal, to change the attitude /pitch or roll of the vessel.

To be able to deflect the water flow both horizontally and vertically, the nozzle may be mounted in a gimbal that has two perpendicular axes; a fixed primary axis, and a secondary axis that rotates about the primary axis. When the steering axis is the primary axis, the trim axis rotates with the gimbal as it is steered. Similarly, when the trim axis is the primary axis, the steering axis rotates with the gimbal as it is trimmed. Such dependency makes it difficult to independently actuate rotation of the nozzle about the secondary axis, whether the trim or steering movement is about the secondary axis. Often the horizontal trim axis is the fixed axis, and the steering axis is the secondary axis such that the steering axis rotates about the trim axis with the gimbal and may, for example, be actuated using a cable.

Some marine vessels with V-bottom hulls are provided with more than one jet pump in the same hull, often a pair, mounted symmetrically in the vessel with their steering axes perpendicular to the underside of the hull. In these cases, the steering pivot axis of each unit is at an angle from vertical that is the same as the hull deadrise above horizontal. As a result, the nozzles and therefore the thrust vectors do not remain parallel when steered, causing the vessel to roll, sometimes excessively. To compensate for the deadrise rotation, and therefore reduce roll, the trim action of each jet can be used in conjunction with the steering action. However, it is difficult to synchronize the trim and steering actions manually, and complex electronic controls are generally necessary. The torque required to steer a tubular nozzle is increasingly higher as the nozzle rotates from a central position towards full lock. This is because, as the steering approaches full lock, the water flow entering the nozzle hits the internal side wall of the nozzle at a progressively higher angle of incidence. Although this effect has the advantage that it tends to centralize the nozzle when the actuation forces cease, the torque required at full lock also determines the required capacity of the actuation system. A mechanism for steering a water jet nozzle that provides increasing mechanical advantage as the nozzle approaches full lock would allow the use of lower capacity actuators.

A common method for reversing or keeping a water jet propelled vessel stationary is to deploy a reverse duct downstream of the or each nozzle. To reverse, the deployed reverse duct captures the water exiting the nozzle and deflects it in the generally opposite direction. To keep the vessel stationary, the reverse duct is positioned to partially impinge on the water stream from the nozzle to the extent required to balance the astern and ahead thrusts so as to keep the vessel stationary. This stationary condition is often called zero-speed. For both reverse and zero- speed, a precise positioning of the reverse duct relative to the jet stream exiting the nozzle is crucial. However, it can be difficult to synchronize the position of the nozzle and the reverse duct as when the reverse duct and the nozzle are independently actuated, there are infinite combinations of reverse duct and trim positions that result in the same ahead to astern thrust ratio.

For example, if the nozzle is trimmed when fully reversing, part of the water stream will miss the reverse duct (unless the reverse duct has a very large opening). Conversely, for a particular trim angle of the nozzle, the reverse duct will have to travel through a range of its total travel for the vessel to go through all variations of thrust ratios that exist between full ahead to full reverse. The range of rotation of the reverse duct required to achieve the same result will be different for each nozzle trim angle. To overcome this problem, the trim could be set to an arbitrary angle prior to deploying the reverse duct. However, that would require two actions and it would be particularly complicated using manual controls.

One difficulty in designing outboard systems for water jets, trim and steering outboard systems, and actuating those systems, is marine growth fouling of movable parts in sea water. Outboard components that have sliding surfaces that alternate between exposed and retracted, such as shafts in hydraulic cylinders, sliding journal bearings, cam mechanisms and gears, are particularly prone to failure due to marine growth. Hydraulic oil leaks due to seal damage, wear and jamming of sliding journal bearings and cams are common problems in this field. In water jet systems inboard steering actuators are desirable due to ease of access for

maintenance, for protection from the severe marine environment, and, particularly for hydraulic actuators, to prevent oil spills that are an environmental hazard. To be able to utilize inboard actuators, it is necessary to transmit motion from inboard to outboard through the transom of the vessel. It can be difficult to do this without introducing sliding surfaces, such as in push-pull rods, which are prone to marine fouling as discussed above.

In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents or such sources of information is not to be construed as an admission that such documents or such sources of information, in any jurisdiction, are prior art or form part of the common general knowledge in the art.

It is an object of at least preferred embodiments of the present invention to provide a mechanism that allows independent actuation of a water jet nozzle for trim and steering, and that goes some way to overcoming the above mentioned problems, and/ or to at least provide the public with a useful alternative.

SUMMARY OF THE INVENTION

A first aspect of the present invention provides a water jet nozzle arrangement for a marine vessel. The arrangement comprises: a gimbal link that is pivotally connectable to a support to pivot about a steering axis; a nozzle that is pivotally connected to the gimbal link about a trim axis and configured so that the nozzle can be steered by rotating the gimbal link about the steering axis; a trim link that is pivotally connectable to the support to pivot about a trim link axis that is at a different orientation to the steering axis; and a link arm that is pivotally connected at or toward a first end thereof to the trim link about a link arm pivot axis, and pivotally connected at or toward a second end thereof to the nozzle about a nozzle link axis. The arrangement is configured such that rotation of the trim link about the trim link axis trims the nozzle about the trim axis, and the resulting angle of nozzle trim is a function of an angle of rotation of the gimbal link about the steering axis and an angle of rotation of the trim link about the trim link axis.

In an embodiment, the steering axis, and the trim link axis are coincident at a point about which the nozzle is rotatable. Preferably, the trim axis, the steering axis, the trim link axis, the link arm pivot axis, and the nozzle link axis are coincident at a point about which the nozzle is rotatable. This allows non-sliding radial bearings to be used in the pivots.

The link arm pivot axis may be perpendicular to the trim link axis, and the nozzle link axis perpendicular to the trim axis. Alternatively, the link arm pivot axis may be at a non- perpendicular angle to the trim link axis. The trim axis is preferably perpendicular to the steering axis and the trim link axis is preferably perpendicular to the steering axis.

In an embodiment, the gimbal link is an annular ring that is pivotally connectable to the support at an upper pivot and an opposite lower pivot, and the trim link is preferably an arcuate member that is pivotally connectable to the support at a first pivot and a second opposite pivot.

The support for the nozzle may be a water jet pump having an orifice or support members connected to a water jet pump, with the nozzle being positionable over the orifice to direct water flowing from the orifice.

In an embodiment, the arrangement further comprises a reverse duct. In an arrangement having a reverse duct, the nozzle defines a water flow path aft of the nozzle and the reverse duct is preferably movable relative to nozzle between a position where at least a major part of the reverse duct is above the water flow path, and a position where at least a major part of the reverse duct intersects the water flow path to define a reversing water flow path.

The reverse duct may be pivotally connectable to the support about a duct axis, and the reverse duct may have lateral arms that are pivotally connectable to the support at the duct axis.

In an embodiment, the reverse duct is operatively connected to the trim link so that rotation of the reverse duct about the duct axis causes trimming of the nozzle. Such an arrangement may further comprise a coupler link, wherein the trim link comprises a lever arm, and the coupler link is pivotally connected at or toward one end to the reverse duct, and at or toward its other end to the trim link lever arm, so that rotation of the reverse duct about the duct axis causes tirimming of the nozzle. In an embodiment the reverse duct is rotatable between: a first position where the nozzle is trimmed up and at least a major part of the reverse duct is above the water flow path; an intermediate position, where the nozzle is trimmed downwards and at least a major part of the reverse duct is above the water flow path; and a lower position, where the nozzle is trimmed up, and at least a major part of the reverse duct is positioned in the water flow path to define a reversing water flow path.

The arrangement may further comprise a trim actuator operatively connected to the trim link. In an arrangement having a reverse duct, a trim actuator may be operatively connected to the reverse duct. The trim actuator may be a linear actuator or a rotary actuator and may be cable(s) or an electric, hydraulic or rotary actuator. In an embodiment, the trim actuator is operatively connected to the trim link or reverse duct by a trim oscillating mechanism, the trim oscillating mechanism comprising: a rotatable trim shaft having a yoke at or toward one end; a trim connection member pivotally connected at a first axis to the trim shaft yoke and at a second perpendicular axis^ to the trim link or reverse duct. The trim actuator is arranged to rotate the trim shaft and thereby rotate the nozzle about the trim axis.

In an embodiment, the arrangement comprises a steering actuator operatively connected to the gimbal link. The steering actuator may be a linear actuator or a rotary actuator and may be cable(s) or an electric, hydraulic or rotary actuator. In an embodiment, the steering actuator is operatively connected to the gimbal link by a steering oscillating mechanism, the steering oscillating mechanism comprising: a rotatable steering shaft having a yoke at or toward one end; a steering connection member pivotally connected at a first axis to the steering shaft yoke and at a second perpendicular axis to the gimbal link. The steering actuator is arranged to rotate the steering shaft and thereby rotate the nozzle about the steering axis.

The trim link or reverse duct preferably comprises a yoke and the trim connection member is pivoted about its second axis to the trim link or reverse duct yoke. Similarly, the gimbal link preferably comprises a yoke and the steering connection member is pivoted about its second axis to the gimbal yoke.

In an embodiment, the arrangement is configured such that the output torque acting on the nozzle for a fixed input torque applied to the steering shaft increases towards full lock of the nozzle. This provides increasing mechanical advantage as the nozzle rotates away from a central position.

A second aspect of the present invention provides a marine vessel comprising at least one water jet unit for propulsion of the vessel, wherein the water jet unit comprises an arrangement described above in relation to the first aspect of the invention. Preferably the support comprises a water jet pump.

A third aspect of the present invention provides a marine vessel comprising two water jet units mounted to the stern of the vessel for propulsion of the vessel. One of the units is mounted towards a starboard side of the vessel, and the other of the units is mounted towards a port side of the vessel. Each water jet unit comprises an arrangement described above in relation to the first aspect of the invention. In an embodiment, the water jet nozzle arrangements of the marine vessel are orientated so the steering axes are substantially perpendicular to the bottom of the vessel hull, and the nozzle arrangements may be configured such that water flow from the nozzles remains substantially parallel as the nozzles are steered to the same steering angle, without adjusting the trim links. In this specification and the accompanying claims the term "vessel" is intended to include boats such as smaller pleasure runabouts and other boats, larger launches whether mono-hulls or multi-hulls, and larger ships. More generally, the nozzle arrangement of the invention may be suitable for any planing or displacement type vessels, regardless of their size, speed capabilities, and hull type. The marine vessel could have one, two, four or more water jet units, each having the features of the present invention.

The term "comprising" as used in this specification means "consisting at least in part of. When interpreting statements in this specification and claims which include the term "comprising", other features besides the features prefaced by this term in each statement can also be present. Related terms such as "comprise" and "comprised" are to be interpreted in a similar manner.

It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7) and, therefore, all sub-ranges of all ranges expressly disclosed herein are hereby expressly disclosed. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner. To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting. Where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

As used herein the term "(s)" following a noun means the plural and/or singular form of that noun.

As used herein the term "and/ or" means "and" or "or", or where the context allows both.

The invention consists in the foregoing and also envisages constructions of which the following gives examples only.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of example only and with reference to the accompanying drawings in which:

Figure 1 is a perspective view of a water jet unit having a trimmable steering nozzle in accordance with a preferred embodiment of the invention;

Figure 2 is an exploded view of the water jet unit shown in Figure 1;

Figure 3 is a partial side view of the water jet unit shown in Figure 1 of the water jet unit with the nozzle steered;

Figure 4 is section view A -A taken from Figure 3, showing the steering angle oc;

Figure 5 is a partial top view of the water jet unit shown in Figure 1 of the water jet unit with the nozzle trimmed down;

Figure 6 is section view B-B taken from Figure 5, showing the trim angle β; Figure 7 is a partial perspective view of a water jet unit of Figure 1, showing the nozzle steered to starboard and trimmed up;

Figure 8 is a partial perspective view of a water jet unit of Figure 1, showing the nozzle steered to starboard and trimmed down;

Figure 9 is a partial perspective view of a water jet unit of Figure 1, showing the nozzle steered to port and trimmed up;

Figure 10 is a partial perspective view of a water jet unit of Figure 1, showing the nozzle steered to port and trimmed down;

Figure 1 is a perspective view of the trim bar of the trimmable nozzle of Figure 1, showing different configurations for different positions of the vertical pivot;

Figure 12 shows the variation of the angle β as a function of the angle a for a symmetric trim bar having a centrally positioned vertical pivot;

Figure 13 shows the variation of the angle β as a function of the angle a for an asymmetric trim bar having the trim link pivot positioned towards the port side of the trim bar;

Figure 14 is a rear view of the water jet unit of Figure 1, having an asymmetric trim bar, showing the nozzle centred, steered to port (phantom lines) and steered to starboard (phantom lines) as the trim bar is kept stationary;

Figure 15 shows the image of Figure 14, but with the jet pump, gimbal and the trim bar hidden for clarity;

Figure 6 is the rear view of a twin installation of the trimmable steering nozzle of Figure 1 in a V-bottom hull vessel, with both nozzles having asymmetric trim bars and shown steering to port;

Figure 17 is a perspective view of the water jet unit of Figure 1, with a reverse duct connected to the trim bar and shown in the neutral trim position;

Figure 18 is a perspective view of the trim bar of the trimmable steering nozzle of Figure

1, provided with a lateral extension arm;

Figure 9 is a partial side view of the water jet unit of Figure 1 with the nozzle trimmed up and showing details of the four-bar linkage comprising the nozzle, the coupler link, and the reverse duct;

Figure 20 is the view of Figure 19, but with the nozzle in the neutral trim position;

Figure 21 is the view of Figure 19, but with the nozzle trimmed down;

Figure 22 is the view of Figure 20, but with the reverse duct in the zero-speed position; Figure 23 is the view of Figure 19, but with the nozzle and the reverse duct in the reversing position; Figure 24 is a perspective view of a water jet unit with the steering linkage attached;

Figure 25 is an exploded view of the water jet unit shown in Figure 24;

Figure 26 is a partial vertical longitudinal section view of the water jet unit shown in Figure

24;

Figure 27 is a side view of the steering shaft of the steering linkage of Figures 24-26;

Figure 28 is a partial perspective view of the water jet unit shown in Figure 24 with the nozzle steering to starboard;

Figure 29 is a partial perspective view of the water jet unit shown in Figure 24 with the nozzle steering to port;

Figure 30 is a graph showing the output torque T on the nozzle for an unitary input torque on the steering shaft for different angles Φ as the nozzle steering angle a varies from zero to 30 degrees;

Figure 31 shows the water jet unit of Figure 1 with the steering and trim actuating linkages attached;

Figure 32 shows the water jet unit of Figure 1 with the steering actuating linkage attached and with a reverse duct connected to the trim bar and shown in the reversing position;

Figure 33 is a plan view of the trim shaft of the trim actuating mechanism of Figure 31; and

Figure 34 schematically shows a control system for controlling the water jet arrangements of the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Ttimmable steering nozzle

Figure 1 illustrates a water jet unit provided with a variable trim outboard discharge nozzle arrangement or assembly according to an embodiment of the present invention. Typically the water jet unit would be provided at the stern of a water jet propelled marine vessel, and the nozzle used to steer the vessel. One configuration of a preferred embodiment of the water jet unit and nozzle is described with respect to horizontal and vertical orientations, however, it will be understood that the invention is not limited to a nozzle only in the described orientations. The 'horizontal' and 'vertical' orientations could be at an angle to horizontal or vertical without departing from the scope of the invention.

The preferred embodiment shown in Figure 1 and 2 comprises a water jet pump 1 and a nozzle 3. The nozzle 3 is pivotally mounted in an annular gimbal link 5 about a horizontal axis 7. The gimbal link 5 is pivotally mounted to the water jet pump 1 about a vertical axis 9 that is perpendicular to the horizontal axis 7, at mounting brackets 11, so as to provide two rotational degrees of freedom to the nozzle, such that the nozzle is pivotable about both the vertical axis 9 (its primary axis) and the horizontal axis 7 (its secondary axis). The water jet pump 1 acts as a support to which the gimbal link is pivotally mounted. The secondary axis 7 pivots about the primary axis 9 relative to the pump 1, as the gimbal link 5 and thereby the nozzle are turned. The nozzle actively deflects the water flow horizontally to steer the vessel and vertically to trim the vessel. The nozzle 3 is also connected to the water jet pump 1 via a Hnkage comprising a trim link or bar 13 and a link arm 15. The trim bar 13 is preferably an arcuate link pivoted horizontally at each of its ends to the water jet pump 1, via brackets 17 about horizontal trim bar axis 19. The brackets are fixed to the water jet pump 1. The trim link 13 has a generally centrally located protruding arm 13a having a pivot 21 at one end. This arm 13a prevents interference between the gimbal link 5 and the trim link 13 during use. A boss 15a protruding from a first end of the link arm 15 is pivoted to the trim link at pivot 21 where the boss 15a is received in an aperture 21a about a link arm pivot axis 22. An aperture 15b pivotally connects the other end of the link arm 15 to a boss 3a on the nozzle about a nozzle link axis 16, to articulate the nozzle 3 and to connect the nozzle 3 to the trim bar 13. Alternatively, the arrangement of bosses and apertures could be reversed, or the links may be pivotally connected by any other pivoting means, for example via a pin.

The nozzle 3 is steered by rotating the gimbal link 5 about the primary axis 9, and the nozzle 3 is trimmed by rotating the trim bar 13 about the trim bar axis 19. Actuations for steering and trim are independent from each other and drive directly the gimbal link 5 and the trim bar 13 respectively.

Figures 3 and 4 show the nozzle steered in a neutral trim position. Figures 5 and 6 show the nozzle ttimmed in the neutral steering position. Figures 7 to 10 show the nozzle steered and trimmed in various positions. For example, Figure 7 shows the nozzle steered to starboard and trimmed up, Figure 8 shows the nozzle steered to starboard and trimmed down, Figure 9 shows the nozzle steered to port and trimmed up, and Figure 10 shows the nozzle steered to port and trimmed down. All of the pivots are external to the nozzle 3 so as to not impede water flow through the nozzle. For example, the included angle between pivot axes 16, 22 of the link arm 15 is less than 90 degrees, so the link arm 15 does not interfere with the water jet exiting the nozzle. All of the pivot axes 7, 9, 16, 19, 22 in the gimbal link 5, trim bar 13, link arm 15, and the nozzle 3 intersect at one point X, about which the nozzle rotates for both steering and trimming. This allows the use of plain cylindrical bearings at the pivots.

The orientation of the nozzle can be described in respect of a steering angle a, the angle taken in a horizontal plane between the nozzle axis NA and the nozzle axis centered position NAC, as shown in Figure 4, and a trim angle β, the angle taken in a vertical plane between the nozzle axis NA and the nozzle axis neutral trim position NANT, as shown in Figure 6. The angle of rotation of the gimbal link 5 is the same as the horizontal steering angle of rotation of the nozzle a, regardless of the trim bar position. Although the actuations for steering and trim are independent, the vertical trim angle of rotation β of the nozzle, although driven by the trim bar 13 rotation, varies with the steering angle a. In other words, for any given position of the trim bar, the actual trim angle β of the nozzle 3, depends on the gimbal link 5 position.

The relationship between the steering angle a, and the trim angle β is shown in the chart of Figure 12. The grid on the chart is formed from horizontal curves representing the angular trajectory of the nozzle 3 for several different fixed positions of the trim bar 17, and the vertical lines represent the trajectory of the nozzle 3 for several different fixed angular positions of the gimbal 5.

As well as being related to the steering angle a, the angular trajectory of the nozzle 3 for a given trim bar 13 position, is also determined by the position of the trim link pivot 21 of the trim bar 13, and the angle between the trim link pivot and the nozzle pivot 15b on the link bar 15. In the embodiment represented by the chart of Figure 12, and shown in Figure 11, the trim bar 13 trim link pivot 21 is in a central position (as shown in solid lines) for symmetric trajectories about a vertical plane. That is, the protruding arm 13a extends perpendicularly from a central part of the main body of the trim bar 13, such that the nozzle link axis 16 is perpendicular to the trim axis 7, and the link arm pivot axis 22 is perpendicular to the trim link pivot axis 19.

Alternatively, changing the trim bar design by repositioning the trim link pivot 21 towards one side of the jet pump (for example by having a trim bar protruding arm 3a extending at a non- perpendicular angle from the main body of the trim bar such that the link arm pivot axis 22 is non-perpendicular to the trim link pivot axis 19), offsets the angle β down when the nozzle 3 is steered towards the same side and offsets the angle β up when the nozzle 3 is steered towards the opposite side for any given position of the trim bar. This asymmetric behaviour is accentuated with a greater displacement of the trim link pivot 21 away from a central position.

Alternatively, the protruding arm 13a may be a separate part from the main body of the trim bar 13, and may be adjustably mounted at alternate angles to the main body to adjust the degree of deadrise compensation, and optimise the amount of roll when steering the vessel. This would allow the trim bar to be configured appropriately for no deadrise compensation, or alternatively to overcompensate for deadrise rotation, if that were desired. To have an adjustable trim bar without interfering with the trim angle at neutral steering, the angular length of the link arm 15 and the protruding arm 13a should be the same, and the pivot axis 22 should be coincident with the centre of rotation X. In an embodiment where the angle of the arm 13a is adjustable, once the arm is installed, the angle of the trim arm 13a remains constant during operation.

Two embodiments of the trim link having asymmetric trajectories are shown by the phantom lines in Figure 11. The effect on the trajectories of the nozzle 3 of the trim link pivot 21 being positioned towards the starboard side is shown in the graph of Figure 13 and in Figures 14 and 15. From these figures it is noticeable that the trim angles are higher when the nozzle 3 is steered towards the port side P and lower when the nozzle 3 is steered towards the starboard side S. If the trim link pivot 21 is positioned towards the port side, the effect will be the opposite. That is, the trim angles will be higher when the nozzle is steered toward the starboard side S and lower when the nozzle is steered toward the port side P. Figure 14 shows the water jet with the nozzle 3 and link arm 15 in a centred position and, in phantom lines, the nozzle 3 and link arm 15 steered to port P and to starboard S. Figure 15 shows the same view but with all other components omitted for clarity. The degree of the effect is proportional to the displacement of the trim link pivot from the central position. Twin nozzle installation

Embodiments having an un-centred trim link pivot 21 on the trim bar 13 for asymmetric trim characteristic are useful to compensate for different deadrise rotation angles Θ. A twin installation of the water jet nozzle systems on a V-bottom hull marine vessel is shown in Figure 16, and is an example of the utilisation of this feature. The nozzles are arranged so their 'vertical' steering axes 9 are substantially perpendicular to the base of the hull. Figure 16 shows the rotated water jet nozzles with both nozzles 3 parallel and steering to port even though the primary (steering) axes 9 of the gimbal links 5 are not parallel. That is, the nozzle arrangements are offset in opposite directions and configured such that the water flow from the nozzles remains substantially parallel as the nozzles are steered to the same steering angle without adjusting the trim links.

Reverse duct

Figure 17 shows the water jet unit provided with a reverse duct or bucket 23 pivotally mounted to the water jet pump 1 at pivot 24. The reverse duct may be a split-type bucket which splits the rearward flow into two directions, or may be a non-split type bucket. A coupler link 25 is pivotally connected at a first end to the reverse duct 23, and at a second end to a modified trim bar 13'. The modified trim bar 13', shown in Figure 18, is provided with a lateral extension arm 27 fixed to the trim bar, to which the coupler link 25 is pivotally connected at pivot 29. The reverse duct 23, coupler link 25, trim bar lateral extension arm 27 and the water jet pump or support, together form a four-bar mechanism or 'double-rocker', in which the reverse duct 23 acts as the driving link and the extension arm 27 is the driven link. This four -bar linkage can be seen in Figures 19-23 and acts to synchronize the trim movement of the nozzle 3 with the deployment of the reverse duct 23.

The selection of link lengths in the four-bar mechanism determines the reverse duct 23 position relative to the trim bar 13'. By correctly selecting the lengths of the four bars, it is possible to utilize part of the reverse duct rotation to trim the nozzle and the rest of the rotation for reversing or keeping the vessel at zero-speed, as shown in Figures 19-23. The particular four-bar arrangement shown in the drawings causes the nozzle 3 to trim fully up both when the reverse duct is at its highest position (Figure 19), not interfering with the water stream exiting the nozzle in the direction F, and when it is at its lowest position (Figure 23), deflecting the whole stream in the direction FR. Rotation of the trim bar 3' is driven by the four bar linkage so as the reverse duct 23 rotates from an upward position to a downward position through an intermediate position, the nozzle 3 is also trimmed down while the reverse duct remains out of the way of the flow F from the nozzle (Figures 19-21). The nozzle trims fully down when the mechanism reaches a "dead point" or "toggle point" which occurs when the coupler link 25 is in line with the reverse duct arm (Figure 21). In this position, as well as in the neutral trim position shown in Figure 20, the reverse duct does not interfere with the water stream. Further downward rotation of the reverse duct then causes the nozzle to begin ttimming up, so that the reverse duct 23 interferes with water flow from the nozzle 3 (Figures 22 and 23).

Zero-speed is obtained in an intermediate position between the trim down and fully reversed states and is shown in Figure 22. This arrangement allows easier duct positioning relative to the nozzle than in other existing systems, as there is only one degree of freedom, and therefore only one duct position that achieves any given ahead and aft thrust ratio.

Figure 19 shows the reverse duct 23 is at its highest position, keeping the nozzle 3 in the fully trimmed up position. In Figure 20, the reverse duct 23 is rotated slightly downwards, to place the nozzle 3 in the neutral trim position. In Figure 21, the reverse duct is rotated slighdy further downwards, so the nozzle is in the fully trimmed down position, but still keeping the reverse duct 23 out of the way of the water flow F. Figure 22 shows the reverse duct 23 rotated even further downwards causing the nozzle 3 to start trimming up from its fully downwards position. In this position, the water stream is partially deflected towards the hull and laterally by the reverse duct as indicated by the arrow FR while the remaining portion of the water stream F continues flowing aft, resulting in zero net thrust acting on the vessel and therefore keeping the vessel stationary in still water. Figure 23 shows the reverse duct 23 in its lowest position, with the nozzle 3 trimmed up, so the reverse duct 23 fully deflects the water flow FR from the nozzle. One advantage of this arrangement is that only one actuation system is required for both trimming and reversing. The nozzle 3 and reverse duct 23 will also be able to be positioned in any intermediate position between those shown. The nozzle will be able to be steered in any of these positions.

Actuation mechanism

Figure 24 illustrates the water jet unit of Figure 1, having a nozzle 3 mounted aft the discharge orifice on the water jet pump 1, and provided with a steering actuation mechanism that will be described herein. The actuation mechanism comprises a linear actuator 31, which may be a hydraulic actuator with a cylinder and ram for example, and an oscillating mechanism 33 that transmits movement from the actuator to rotation of the nozzle 3. The oscillating mechanism comprises a shaft 35 rotatably mounted in an aperture on the vessel transom 36, operatively connected at an inboard end to the actuator 31, and operatively connected to the gimbal link 5 at an outboard end. In the embodiment shown in Figure 24, the outboard end of the shaft 35 comprises a yoke 37, and a second complementary yoke 38 is fixed to the gimbal link 5. A connector 39 having two perpendicular pivot axes CA, GA connects the shaft yoke 37 about one axis CA to the gimbal yoke 38 about a second axis GA. The shaft yoke 37 is angled relative to the shaft 35 so that the connector member 39 has an axis CA at an angle Φ (shown in Figure 27) from the shaft rotation axis. Figure 25 shows the actuation mechanism in an exploded view for clarity and to show the individual components. The steering shaft 35 transmits movement from inboard to outboard through the aperture in the transom 36 where it is rotatably mounted. The shaft is rotatably mounted to the transom via bearings 41 and a water seal 43, as shown in the partial section view of Figure 26. As for the nozzle arrangement, the actuation mechanism utilises only non-sliding radial bearings. Because the actuation mechanism has no linearly moving components on the outboard side of the vessel, and no linearly moving components through the transom 36, the mechanism is less susceptible to failure due to marine growth.

The operation of the actuation mechanism is shown in Figures 28 and 29. In Figure 28, the ram of the actuator 31 is fully retracted rotating the steering shaft 35 to steer the nozzle 3 starboard. Figure 29 shows the ram of the actuator 31 at full stroke, rotating the steering shaft 35 in the opposite direction, and thereby steering the nozzle 3 towards port. The nozzle steering angle a, and the rotation angle γ of the steering shaft, both shown in Figures 28 and 29, are not proportional as the nozzle rotates, therefore, the torque ratio between these components is not constant. The torque ratio depends on the angle between the shaft 35 rotation axis and the nozzle steering axis 9, which is typically 90 degrees, and the angle Φ between the shaft 35 rotation axis and the pivot axis CA about which the connector member 39 is pivoted to the shaft yoke 37. Figure 30 shows the output torque T acting on the nozzle 3 for a unitary input torque applied to the steering shaft 35 for different angles Φ of the shaft yoke 37, as the nozzle 3 is steered from an angle a of zero to 30 degrees for the embodiment shown where the angle between the rotation axes of the shaft 35 and the nozzle steering axis 9 is 90 degrees.

Typically, the torque required to rotate the nozzle 3 is progressively higher for increasing angles of rotation, but this relationship is not necessarily linear. As shown in the graph of Figure 30, for a fixed input torque applied to the steering shaft 35, the output torque T acting on the nozzle 3 by the oscillating mechanism 33 increases towards full lock of the nozzle, offering increasing output torque or mechanical advantage as the nozzle rotates away from a central position. That is, the oscillating mechanism 33 offers greater mechanical advantage where it is most required and less where it is easier to rotate the nozzle, meaning a smaller actuator can be used.

The rate of increase of this output torque depends on the shaft yoke angle Φ. Similarly, the torque required to deflect the water flow also increases towards full lock at different rates, with the rate of increase depending on nozzle design. For example, a long tubular nozzle is harder to steer than a short nozzle, but both will require greater forces to steer to greater angles. The torque required also increases with the speed of the water flow. The torque-angle curve is therefore unique to a particular nozzle design. Consequently, the angle Φ can be selected to benefit any given nozzle shape enabling the optimization of the actuation capacity. For example, a short tubular nozzle would utilize a small angle Φ and a long nozzle would require a greater angle Φ.

Actuation of the trimmable nozzle having a reverse duct

Figure 31 shows the trimmable steering nozzle with two independent actuators 31, 31' and oscillating mechanisms 33, 45 coupled to the nozzle 2. One of the oscillating mechanisms 33 is coupled to the steering actuator 31 and the gimbal link 5 to steer the nozzle in the manner described above, and the other oscillating mechanism 45 is coupled to the trim actuator 31' and to the trim bar 13 at the trim bar axis 19, to trim the nozzle by rotating the trim bar. Similar to the steering mechanism, the oscillating mechanism 45 coupled to the trim bar 13 comprises a shaft 35' rotatably mounted in an aperture on the vessel transom 36 (with a suitable bearing and seal as described for shaft 35 above), the outboard end of the shaft 35' comprises a yoke 37', and a second yoke 38' is fixed to the trim bar 13. A connector member 38' having two perpendicular pivot axis connects the shaft yoke 37' about one axis and to the trim bar yoke 38' about a second axis. The operation of the trim actuator mechanism is the same as described for the steering actuator mechanism above. In the same way the torque required to rotate the nozzle 3 is typically progressively higher for increasing angles of steering rotation, the torque required to trim the nozzle 3 is also typically progressively higher for increasing angles of trim. For a fixed input torque applied to the trim shaft 35', the output torque acting on the nozzle 3 by the oscillating mechanism 45 increases towards maximum trim of the nozzle, offering increasing output torque or mechanical advantage as the nozzle is trimmed away from a neutral trim position. That is, the oscillating mechanism 45 offers greater mechanical advantage where it is most required and less where it is easier to trim the nozzle, meaning a smaller actuator 31' can be used. The rate of increase of the output torque with trim angle depends on the angle ' in the trim shaft yoke 37' shown in Figure 33, and the rate of increase depends on nozzle design. The trim shaft yoke angle Φ' can therefore be selected to optimize the actuation capacity for a given nozzle shape. The trim and steering functions may have different ranges of motion and actuation forces. The steering shaft yoke 38 and the trim shaft yoke 38' may therefore each have a different yoke angle that is selected to suit the respective steering or trim function.

This actuation arrangement allows the trim and steering movements of the nozzle to be actuated independently using the inboard actuators 31, 31', without any outboard linearly sliding connections.

Figure 32 shows the trimmable steering nozzle with a steering actuating mechanism 31, 35 coupled to the gimbal link 5 to steer the nozzle. A reverse duct 23 is connected to a modified trim bar 13', also as described above. The nozzle is trimmed by rotation of the reverse duct 23 about pivot 24. This rotation may be actuated using the same actuation mechanism described above, with the second yoke 38' being attached to the reverse duct 32 at pivot 24. Alternatively, the reverse duct 32, and thereby the trimming of the steering nozzle, could be actuated using a different arrangement.

Control system

As shown in Figure 34, the trimmable steering arrangement will typically be mounted to one or more water jet pumps 1 at the stern of a vessel and arranged so the nozzle 3 is positioned over and around the exterior of the orifice of the pump to deflect water flowing out of the water jet pump. The marine vessel could have one or multiple water jet pumps, each having the features of the present invention. The water jet pumps may be controlled in unison or independendy, depending on the required response of the marine vessel

The steering, trim and actuation of the reverse duct may be controlled by a manually operable control device 101a or multiple control devices 101a, 101b, preferably located in the cockpit of the vessel. Movement of the control device(s) 101a, 101b provides a signal to a control system 105, which may also receive control signals from a throttle control 103 and/or other controllers. The control system 105 interprets these signals, and in turn operates the actuators 31 and/or 31' for the steering nozzle 3 and reverse duct 23 to steer and/ or trim the nozzle 3, or to lower or raise the reverse duct 23. Alternatively or additionally, nozzle steering or trim may be automatically controlled by a computerised system which senses the vessel attitude, yaw and/ or heading when underway and automatically trims, steers and/ or moves the reverse duct in the water flow, as appropriate, to optimally position the vessel for a commanded or optimal attitude, yaw and/ or heading. Preferred embodiments of the invention have been described by way of example only and modifications may be made thereto without departing from the scope of the invention.