WO2009134153A1

WO2009134153A1 - A water jet propulsion system including a reverse bucket-actuated deflector vane

Info

Publication number: WO2009134153A1
Application number: PCT/NZ2009/000066
Authority: WO
Inventors: John Robert Borrett
Original assignee: Cwf Hamilton & Co Limited
Priority date: 2008-04-30
Filing date: 2009-04-30
Publication date: 2009-11-05

Abstract

A propulsion unit for a marine vessel, comprising a water jet unit including a tail pipe for extending from a stern of a vessel for delivery of a water jet for propelling the vessel and a steering nozzle mounted at the end of the tail pipe for directing the water jet. A reverse bucket is pivotally mounted to either the tail pipe or the steering nozzle for movement between a normally raised position and a lowered position in which the reverse bucket deflects the water jet to provide the vessel with reverse thrust. The water jet unit also including a deflector, such as a trim tab or an interceptor, for pivotal mounting to the stern of the vessel or to the propulsion unit at the stern of the vessel, and at least one actuating linkage between the deflector and the reverse bucket arranged to cause the deflector to move to impinge below a hull of the vessel when the reverse bucket is raised from the normally raised position to a maximally raised position. The deflector is therefore moved by the same actuator as the reverse bucket, thereby eliminating the need for a separate actuator.

Description

"A WATERJET PROPULSION SYSTEM INCLUDING A REVERSE BUCKET- ACTUATED DEFLECTOR VANE"

FIELD OF INVENTION

The invention relates to water jet propulsion systems for marine vessels and in particular to a water _jet propulsion system in which movement of a reverse bucket or buckets is arranged to actuate a deflector such as one or more trim tab(s) or ιnterceptor(s) of the vessel.

BACKGROUND

Marine vessels such as boats, launches, ferries and similar that operate at higher speeds are commonly provided with one or more deflector vanes or trim tabs pivotally mounted at die stern of the vessel and which may be operated to impinge into the water flow beneath the hull of the vessel, typically to trim the vessel. Commonly two (or more) trim tabs are provided, at least one on eidier side of the longitudinal axis of the vessel In a twin hulled vessel one or more trim tabs may be provided on each hull The helmsperson controls the position of the trim tabs via a trim control such as a stick or switch control for example, and typically the trim tabs are moved via one or more hydraulic or electric actuators which operate between the vessel hull and the trim tab. By operating port and starboard trim tabs together, the trim or pitch angle of the vessel is altered, and by operating port and starboard trim tabs differentially, the roll angle of the vessel is altered When a trim tab is not in use it is raised such that it does not impinge into the flow of water beneath the vessel (or does so minimally) When the trim tab is operated to affect the trim of the vessel, the actuator extends to pivot the trim tab downwardly so that it impinges into the water flow beneath the vessel to affect the trim of the vessel to the desired extent

A marine vessel may also or alternatively be equipped with one or more interceptors

(sometimes referred to as "Gurney flaps") movably attached to the transom of the vessel and which can be lowered to pro_ject below the transom to interrupt the water flow at die stern of the vessel on one or either side and produce upward lift, to adjust the trim of die vessel. Commonly two (or more) interceptors are provided, at least one on either side of the longitudinal axis of the vessel, and in a twin hulled vessel one or more interceptors may be provided on each hull. As with a trim tab, the helmsperson controls die position of the interceptors via a trim control such as a stick or switch control for example, and typically the interceptors are moved via one or more hydraulic or electric actuators. When an inteiceptor is not in use it is raised such that it does not impinge into the flow of water beneath the vessel. When the interceptor is operated to affect the trim of the vessel, the actuator operates to move the trim tab vertically, or approximately vertically, downwardly to impinge into the water flow beneath the vessel and produce upward lift.

A water _jet propulsion unit includes a tail pipe which extends from the stern of the vessel, a steering nozzle for directing the water jet for steering the vessel, and a reverse deflector or bucket (herein: bucket) pivotally mounted to the tail pipe or to the steering nozzle, which can be lowered from a raised position, so that the reverse bucket deflects the water jet to provide reverse thrust to the vessel Actuators such as hydraulic or electric actuators operate under control of the helm control and a reverse bucket control, which can be combined with a throttle control, to move the steering nozzle from port to starboard and to raise and lower the reverse bucket respectively. A vessel may comprise a single water _jet propulsion unit or alternatively a twin or quad (or more) jet vessel comprises two or four water _jet propulsion units, each including a steering nozzle and reverse bucket generally as described.

SUMMARY OF INVENTION

In broad terms the invention comprises a propulsion unit for a marine vessel, comprising: at least one water _jet unit including a tail pipe for extending from the stern of a vessel for deliver}' of a water _jet for propelling the vessel, a reverse bucket pivotally mounted to the tail pipe or to the steering nozzle for movement between a raised position and a lowered position in which the reverse bucket deflects the water jet to provide reverse thrust, and a deflector for movable mounting to the stern of the vessel or the propulsion unit at the stern of the vessel, and at least one actuating link between the deflector and the reverse bucket arranged to cause the deflector to move to impinge below the hull of the vessel when the reverse bucket is raised.

In the system of the invention for actuating the deflector via movement of the reverse bucket, when the reverse bucket is moved to or between its lowered or normally raised position, the deflector does not impinge below the hull of the vessel (or does so minimally), but when the reverse bucket is raised to a greater extent the actuating linkage between the reverse bucket and the deflector causes the deflector to move downwardly to impinge into the water flow, so that the deflector operates to affect the trim of the vessel, as desired by the helmsperson. Movement of the reverse bucket is used to actuate the deflector. It is therefore not necessary to provide one or more separate actuators such as hydraulic or electric actuator(s) for the deflector(s).

In one embodiment a deflector referred to as a trim tab is pivotally mountable to the stern of the vessel and the or each actuating link between the deflector vane and the reverse bucket includes a link arm pivotally connected at one end to the deflector vane to one side of a pivot axis of the deflector vane, and at another end of the link arm to a coupling to the reverse bucket on another side of the axis of movement of the reverse bucket to the operative part of the reverse bucket which impinges into the water jet when the reverse bucket is lowered.

In a preferred form of this embodiment the link arm is pivotally connected to the reverse bucket through a coupling which allows relative movement between the end of the link arm and the reverse bucket when the reverse bucket is lowered to provide reverse thrust. Also the actuating link(s) between the deflector vane and the reverse bucket includes a spring mounted around the link arm arranged to bias the deflector vane towards an upper position in which the deflector vane does not impinge into the water flow beneath the hull of the vessel.

In another embodiment a deflector referred to as an interceptor is mountable to the stern of the vessel and an actuating link between the deflector and the reverse bucket includes an extension arm connected directly or indirecdy to the reverse bucket on another side of an axis of movement of the reverse bucket to the operative part of the reverse bucket.

A single deflector may be provided for affecting vessel pitch, or two (or more) deflectors may be provided one on either side of the longitudinal axis of die vessel for effecting both pitch and roll. The invention may be incorporated in each propulsion unit of a multi water jet vessels, of a single or multi-hulled vessel. In a twin water jet vessel a reverse bucket-actuated deflector may be incorporated in each water jet propulsion unit. In a quad water jet vessel reverse bucket-actuated deflectors may be provided on one or both of each of the port and starboard water jet propulsion units.

The propulsion unit may in one embodiment also comprise a steering no2zle for directing the waterjet for steering the vessel, and in another embodiment may not also comprise a steering nozzle. The term "comprising" as used in this specification means "consisting at least in part of When interpreting each statement in this specification that includes the term "comprising", features other than that or those prefaced by the term may also be present. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described with reference to the accompanying drawings which show preferred embodiment propulsion units installed in a vessel, by way of example and without intending to be limiting. In the drawings:

Figure 1 is a view of a water _jet unit as viewed from the stern of the vessel incorporating a propulsion unit of a first embodiment of the invention, showing the tailpipe, steering nozzle, reverse bucket, trim tab and reverse bucket-trim tab actuating linkage thereof, with the reverse bucket in its normal-raised position,

Figure 2 is a view similar to Figure 1 of the first embodiment, with the reverse bucket fully lowered,

Figure 3 is a view similar to Figure 1 , with the reverse bucket maximally raised, to maximally deflect the trim tab below the hull of the vessel, Figure 4 shows the reverse bucket-trim tab actuating linkage and connections of the linkage to the reverse bucket and trim tab, on the starboard side of the propulsion unit, in more detail, with the reverse bucket in its normal-raised position of Figure 1 ,

Figure 5 shows the reverse bucket-trim tab actuating linkage and connections of the linkage to the reverse bucket and trim tab, on the port side of the propulsion unit, in more detail, with the reverse bucket in its normal-raised position of Figure 1 ,

Figure 6 shows the propulsion unit and trim tab from below,

Figure 7 is a side view of a propulsion unit of a second embodiment of the invention, showing the tail pipe, steering nozzle, reverse bucket, and interceptor, and an interceptor actuating extension arm thereof, with the reverse bucket fully lowered, Figure 8 is a view similar to Figure 7 of the embodiment of Figure 7 with the reverse bucket in it's normal-raised position, and

Figure 9 is a view similar to Figures 7 and 8, with the reverse bucket maximally raised, to move the interceptor to protrude maximally below the hull of the vessel. DETAILED DESCRIPTION OF PREFERRED FORM

Figures 1 to 7 show a part of the transom, on the starboard side, of a vessel having twin water _jet units, each incorporating a reverse bucket-actuated trim tab. In the drawings only the parts of the propulsion unit external to the hull of the vessel and on the starboard side are shown. The water jet unit on the port side is not shown but is similar to that shown on the starboard side. The transom of the vessel is indicated at 1, the tailpipe of the propulsion unit which extends through the transom at 2, the steering nozzle at 3, the reverse bucket at 4, and the trim tab at 5.

In the embodiment shown each propulsion unit also comprises a steering nozzle 3, mounted at the end of the tailpipe 2, about an upright pivot axis for port-starboard movement to direct the flow of the water jet to steer the vessel. The steering nozzle is moved by a hydraulic actuator the shaft 6 of which extends from the transom of the vessel and connects to the steering nozzle.

The reverse bucket 4 is pivotally mounted to the tailpipe 2 so that the reverse bucket can be lowered into the water jet to deflect the water jet when it is desired to reverse the vessel, as is known. The reverse bucket is mounted for movement about a transverse pivot axis across the water jet unit and the stern of the vessel In the preferred form shown the reverse bucket is of a form known as a split bucket comprising left and right parts 4a and 4b, which deflect water back beneath the vessel when the reverse bucket is lowered (as shown in Figure 2). The reverse bucket is bolted through bushes to the tailpipe 2 on either side as indicated at 7, so that the reverse bucket can lower in the direction of arrow A in Figure 1 and raise in the direction of arrow B. The reverse bucket is moved by a hydraulic actuator forming part of the water jet unit, the shaft 9 of which extends from the stern of the vessel and is pivotally connected to the reverse bucket at 10.

Figure 1 shows the reverse bucket in its normal-raised position, in which the reverse bucket is clear of the water jet (for providing ahead thiust to the vessel) Figure 2 shows the reverse bucket fully lowered, for providing maximum deflection of the water jet to provide reverse thrust In figures 1 and 2 the trim tab 5 is raised, so that it does not impinge below the hull of the vessel. The reverse bucket and trim tab 5 are coupled via an actuating linkage generally indicated at 8 (and which will be described in more detail subsequently) In the preferred form a linkage is provided on either side of the tailpipe. Figure 3 shows the reverse bucket maximally raised, beyond the normal-raised position of the reverse bucket in Figure 1 As the reverse bucket moves above the position of Figure 1, in the direction of arrow B in Figure 1, the pivotally mounted trim tab 5 is caused to move to impinge progressively below the hull of the vessel. Figure 3 shows the reverse bucket in this maximally raised position and the trim tab 5 in its maximally lowered position. Movement of the reverse bucket between its normal-raised and maximally raised position is via the same reverse bucket actuator 9 which moves the reverse bucket normally. At any intermediate position of the reverse bucket between its normal-raised and maximally raised positions shown in Figures 1 and 3, the trim tab 5 will be at an intermediate position between its raised and maximally lowered positions shown in the same figures.

The trim tab 5 provides an operative water deflecting surface on its lower side, and on its upper side is provided spaced lugs 11 by which the trim tab is pivotally mounted to a flange at the stern of the vessel, in the preferred embodiment as shown. Referring particularly to Figures 4 and 5 each actuating linkage 8 in the preferred form comprises a link arm 12 which is pivotally connected to one of the lugs 11 at one end, on one side of the axis about which the trim tab moves The other end of each link arm 12 is connected to an extending part 4c of the reverse bucket, which is duplicated on both sides of the reverse bucket The arrangement is such that as the reverse bucket moves from its normal-raised position shown in Figure 1 towards its maximally raised position shown in Figure 3, each link arm moves in the direction of arrow C in Figure 4, pulling the trim tab downwardly in the direction of arrow D, while lowering of the reverse bucket back towards the normal-raised position of Figure 1 moves link arm in the direction of arrow E, pulling the trim tab up in the direction of arrow F.

In the preferred embodiment shown in Figures 1 to 6 the link arm 12 comprises an eye 13 at one end through which a bush 14 loosely passes, in turn through which a bolt passes transversely into the lug 15 At its other end the link arm 12 is connected to the reverse bucket and in particular to extending part 4c of the reverse bucket (which may be integrally formed with the balance of the reverse bucket or separately formed and fixed to die reverse bucket as shown) via a coupling generally indicated at 16. The coupling 16 includes a pin 17 free to rotate about its longitudinal axis and through the centre of which is formed a bore through which the other end of the link aim 12 passes. The link arm is fixed to the pin 17 by a threaded fastener 18 passing into the end of the link arm which captures the end of the link arm in the pin 17, but so that the end of the link arm can slide through the pin in the direction of arrows C and E (Figure 4)

When the reverse bucket is in its normally raised position shown in Figure 1 , the two actuating linkages 8 on either side of the propulsion unit and the trim tab 5 are as shown in Figure 5 When the reverse bucket is raised further, towards the maximally raised position shown in Figure 3, the upward movement of the reverse bucket pulls the linkages in the direction of arrow C, pulling the trim tab downwardly to extend into the water flow below the hull of the vessel. A spring 20 is captive around the link arm 12 between an enlarged intermediate part of the link arm and the pin 17. When the reverse bucket returns from its maximally raised position to its normally raised position, movement of the reverse bucket pushes the linkage in the direction of arrow E, with force acting through the pin 17, the spring 20, and to the link arm 12 to push the trim tab 3 back to its upper position. The spring 20 acts to bias the trim tab towards its upper position out of the water flow below the hull of the vessel (as does water flow or pressure beneath the trim tab when the vessel is moving ahead at any speed).

In the preferred form the length of the link arms 12 can be adjusted to enable adjustment of the mechanism. In particular each link arm 8 comprises a centre part having a threaded bore at one end, into which the eye 13 threads, with a lock nut 21. The length of the link arm may be ad_justed by loosening the lock nut, and rotating the middle part of the link arm to shorten or lengthen the link arm (following which the lock nut 21 is tightened). The tension in the spring 20 may similarly be ad_justed via a nut and lock nut combination 22 threadedly mounted around the other end of the link arm.

The trim tabs 5 may be controlled (through the reverse bucket) by a dedicated trim tab control device, movement of which when the vessel is underway (moving ahead at e.g. above 5 knots) provides a signal to a control system which also receives control signals from the helm device, and throttle control (incorporating forward-reverse), interprets these, and in turn operates the actuators 6 and 9 for the steering nozzle and reverse bucket to cause die reverse bucket to move to operate the trim tabs Movement of the trim control may be mechanically or electronically locked out when the reverse bucket is not raised to at least its normal-raised position. Alternatively the trim tabs may be automatically controlled by a computerised trim system which senses the vessel attitude when underway and automatically operates the reverse bucket actuators 9 to move the trim tabs appropriately to trim the vessel for an optimal attitude or a commanded attitude.

Figures 7 to 9 show a second embodiment, in which movement of the reverse bucket is used to move an interceptor, being a deflector mounted to the stern of the vessel for vertical or substantially vertical movement downwardly to impinge below the hull of the vessel when the reverse bucket is raised maximally. In Figures 7 to 9, as before the transom of the vessel is indicated at 1, the tailpipe of the propulsion unit at 2, the reverse bucket at 4, and the reverse bucket pivot at 7. The hydraulic or electric actuators and their shafts for the steering nozzle and reverse bucket are not shown but are similar to those of the embodiment of Figures 1 to 6

An interceptor 30 is pivotally mounted at or towards the bottom of the transom of the vessel via a pivot 31 along the bottom of the transom. The interceptor has an approximate sideways oriented L-shape as shown, comprising a first part 30a which extends laterally from the pivot 31 and a second part 30b which extends downwardly, and below the hull of the vessel when the interceptor is deployed as will be further described. The interceptor extends laterally across the transom of the vessel beneath the water _jet unit shown or alternatively an interceptor 30 may be provided on either side of the water jet unit.

In the preferred form the lower surface of the hull is extended beyond the transom 1 in a bottom plate extension 32 as shown. The bottom plate extension 32 is of a length relative to the interceptor 30, that when the interceptor is fully lowered as shown in Figure 9, the interceptor will contact the bottom plate extension 32 This assists in stabilising the interceptor in the water flow beneath the vessel, at speed.

An extension arm 33 extends from the reverse bucket pivot 7, on the other side thereof to the bucket 4 and extends towards the transom 1 of the vessel In the preferred form the extension arm 33 terminates in a roller 34 although this is not essential. Figure 7 shows the interceptor 30 fully raised and Figure 9 shows the interceptor fully lowered A spring 35 is connected to a lug on top of interceptor 30 at one end and to a suitable lug on the jet unit at its other end, which biases the interceptor 30 towards its raised position shown in Figures 7 and 8

Figure 8 shows the reverse bucket 4 in its normal-raised position, in which the reverse bucket is clear of the water _jet (for providing ahead thrust to the vessel).

Figure 9 shows the reverse bucket 4 maximally raised, beyond the position of the reverse bucket in Figure 8 (and in the same position as the reverse bucket of the embodiment of Figures 1 to 6, in Figure 3). In this maximally raised position of the reverse bucket 4, the interceptor 30 is fully lowered as shown. As the reverse bucket moves towards this maximally raised position of Figure 9 from its normal-raised position of Figure 8, the end of the extension arm 33, and in the preferred embodiment the roller 34 thereon, contacts the part 30a of the interceptor, pushing it downwardly so that the part 30b of the interceptor protrudes below the bottom plate extension 32 as shown. Movement of the reverse bucket 4 back towards it's normal-raised position of Figure 9 results in raising of the interceptor as the end of the extension arm 33 elevates and the spring 35 pulls the interceptor up.

Figure 7 shows the reverse bucket down, for providing reverse thrust. In this position the end of the extension arm 33 is clear of the interceptor and the interceptor remains raised, under the influence of spring 35.

As in the embodiment of Figures 1 to 6, the interceptor or interceptors of a vessel may be controlled (through the reverse bucket) by a dedicated interceptor control device, movement of which when the vessel is underway provides a signal to the control system which also receives signals from the helm device, and throttle control (incorporating forward-reverse), interprets these, and in turn operates the actuators for the steering nozzle and reverse bucket to cause the reverse bucket to move to operate the interceptors. Movement of the interceptor control may be mechanically or electronically locked out when the reverse bucket is not raised to at least its normal-raised position. Alternatively the interceptors may be automatically controlled by a computerised trim system as referred to previously.

In propulsion units of the invention it is not necessary to provide separate actuator(s) for the trim tab(s) and/or interceptor(s), and the reverse duct(s). A single actuator operates both the reverse duct and trim tab(s) and/or interceptor(s).

The foregoing describes the invention including a preferred form thereof. Alterations and modifications as would be obvious to those skilled in the art are intended to be incorporated within the scope hereof.

Claims

1 A propulsion unit for a marine vessel, comprising" a water jet unit including a tail pipe for extending from a stern of a vessel for delivery of a water _jet for propelling the vessel, a reverse bucket pivotally mounted to the water _jet unit for movement between a raised position and a lowered position in which the reverse bucket deflects the water jet to provide the vessel with reverse thrust, a deflector for pivotal mounting to the stern of the vessel or to the propulsion unit at the stern of the vessel, and at least one actuating linkage between the deflector and the reverse bucket arranged to cause the deflector to move to impinge below a hull of the vessel when the reverse bucket is raised.

2. A propulsion unit as claimed in claim 1 wherein the deflector is biased towards an upper position in which the deflector does not impinge into water beneath the hull of the vessel.

3 A propulsion unit as claimed in either one of claim 1 or claim 2 wherein the or each actuating linkage is arranged to cause the deflector to progressively move to impinge below the hull when the reverse bucket is progressively raised to a greater extent from a normally raised position to a maximally raised position

4. A propulsion unit according to any one of the preceding claims wherein the or each actuating linkage between the deflector and the reverse bucket includes a link arm pivotally connected at one end to the deflector to one side of a pivot axis of the deflector, and at another end of the link arm via a coupling to the reverse bucket, the coupling being on another side of an axis of movement of the reverse bucket to an operative part of the reverse bucket which impinges into the water _jet when the reverse bucket is lowered, such that as the reverse bucket is raised from the lowered position, the end of the link arm progressively nears and abuts the coupling, and further raising of the bucket causes the deflector to move to impinge below the hull of the vessel.

5 A propulsion unit according to claim 4 wherein the link arm comprises an eye at the end connected to the deflector through which a bush passes and in turn through which a bolt passes transversely into a lug of the deflector to pivotally connect the link arm to the deflector.

6. A propulsion unit as claimed in either one of claim 4 or claim 5 wherein the link arm at the end connected to the reverse bucket is connected to an extending part of the reverse bucket via the coupling, the coupling consisting of a pin that is free to rotate about a longitudinal axis of the pin, and having a bore through which the end of the link arm passes and is shdably captive by an enlarged end of the link arm.

7. A propulsion unit as claimed in any one of claims 4 to 6 wherein at least one actuating linkage between deflector and the reverse bucket includes a spring mounted around the link arm and arranged to bias the deflector towards an upper position in which the deflector does not impinge into water beneath the hull of the vessel

8. A propulsion unit as claimed in claims 4 to 7 wherein a length of the link arm can be adjusted.

9. A propulsion unit as claimed in any one of claims 4 to 8 wherein the deflector is a trim tab.

10. A propulsion unit according to any one of claims 1 to 3 wherein the or each actuating linkage between the deflector and the reverse bucket includes an extension arm connected direcdy or indirecdy to the reverse bucket on another side of an axis of movement of the reverse bucket to an operative part of the reverse bucket which impinges into the water jet when the reverse bucket is lowered, the extension arm extending from the connection to the reverse bucket away from the operative part of the bucket and terminating in an end proximal to the deflector such that as the bucket is raised, the end is moved towards the deflector to thereby direcdy or indirecdy act on the deflector to cause the deflector to impinge below the hull of the vessel.

11. A propulsion unit as claimed in claim 10 wherein die deflector is an interceptor, the interceptor comprising a first part for pivotal mounting to a transom of a vessel such that it extends laterally from the transom into a second part, the second part extending at an angle to the first part such that as the bucket is raised the end of die extension arm proximal to the deflector is moved towards the first part, to act on the interceptor and cause the second part to impinge below the hull of the vessel.

12. A propulsion unit as claimed in any either one of claim 10 or claim 11 wherein the propulsion unit further comprises a spring coupled at one end to the interceptor and at another end to the water )et unit to bias the deflector towards an upper position in which it does not impinge water flow below the hull of the vessel.

13. A propulsion unit as claimed in any one of claims 10 to 12 wherein the extension arm terminates in a roller at the end above the deflector.

14. A propulsion unit as claimed in any one of the preceding claims wherein the water jet unit further comprises a hydraulic actuator having a shaft extending from the stern of the vessel and pivotally connected to the reverse bucket, for moving the reverse bucket.

15. A propulsion unit as claimed in any one of claims 1 to 14, wherein the reverse bucket is pivotally mounted to the tail pipe.

16. A propulsion unit as claimed in any one of claim 1 to 14 further comprising a moveable steering nozzle mounted at one end of the tail pipe to direct the water jet to steer the vessel.

17 A propulsion unit as claimed in claim 16, wherein the reverse bucket is pivotally mounted to the steering nozzle.

18. A propulsion unit as claimed in any one of the preceding claims wherein an actuating linkage is provided on either side of the tailpipe.

19. A propulsion unit as claimed in any one of the preceding claims wherein the reverse bucket is a split bucket comprising left and right bucket parts.

20. A propulsion unit for a marine vessel, comprising: a water _jet unit including a tail pipe for extending from a stern of a vessel for delivery of a water jet for propelling the vessel, a moveable steering nozzle mounted at one end of the tail pipe to direct the water jet to steer the vessel a reverse bucket pivotally mounted to the tail pipe or to the steering nozzle for movement between a raised position and a lowered position in which the reverse bucket deflects the water jet to provide the vessel with reverse thrust, a deflector for pivotal mounting to the stern of the vessel or to the propulsion unit at the stern of the vessel, and at least one actuating linkage between the deflector and the reverse bucket including a link arm pivotally connected at one end to the deflector to one side of a pivot axis of the deflector and at another end of the link arm via a coupling to the reverse bucket and arranged to cause the deflector to move to progressively impinge below the hull when the reverse bucket is progressively raised to a greater extent from a normally raised position to a maximally raised position.

20. A propulsion unit as claimed in claim 20 wherein the deflector is a trim tab.

21. A propulsion unit as claimed in claim 20 wherein the deflector is an interceptor.