Abstract:
A steering system for a waterjet propelled marine vessel is disclosed that incorporates an intelligent control system interfacing a manually steerable control device with a number integrated propulsion systems. The propulsion systems can be controlled by the control system in isolation or in combination with one another in order to propel and steer the marine vessel.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a steering system for a waterjet propelled marine vessel. 
       BACKGROUND TO THE INVENTION 
       [0002]    A waterjet drive unit for a marine vessel comprises a steering deflector or nozzle (herein a deflector) through which water is expelled to propel the vessel, and which may be moved from one side to the other to change the angle of the waterjet to cause the vessel to steer to port or starboard when underway. A vessel propelled by two or more waterjet units, such as a catamaran with a waterjet unit in each hull, comprises a control system arranged to move the steering deflectors of both waterjet units. The steering deflectors are controlled by the helmsperson via a steering control device such as a helm wheel or a joystick which may be either pivoted from side to side or rotated to control the steering deflectors in different embodiments, or another form of steering control device. 
         [0003]    It is an object of the present invention to provide an improved or at least alternative steering system for a marine vessel propelled by two or more waterjet units. 
       SUMMARY OF THE INVENTION 
       [0004]    In a first aspect, the present invention consists in of a steering system for a marine vessel comprising:
       two or more waterjet units for propelling the vessel, each having a steering deflector;   a manually moveable steering control device which is movable to steer the vessel to port or starboard; and   an associated control system arranged to operate the steering deflectors in accordance with movement of the steering control device to cause turning of the vessel and also to lower a reverse duct of an inside (to a turn) waterjet unit when a higher rate of turning of said vessel is commanded by the steering control device.       
 
         [0008]    Preferably, the control system is arranged to cause the inside reverse duct to lower to an increasing extent when an increasing rate of turning is commanded by the steering control device. 
         [0009]    Preferably, the control system is also arranged to alter the thrust generated by the inside and/or outside waterjet unit(s) when a higher rate of turning is commanded by the steering control device. 
         [0010]    Preferably, the control system is also arranged to increase the thrust generated by the inside waterjet unit when a higher rate of tuning is commanded by the steering control device. 
         [0011]    Preferably, the control system is also arranged to increase the thrust generated by the outside waterjet unit when a higher rate of turn is commanded by the steering control device. 
         [0012]    Preferably, the control system is arranged to alter the thrust generated by the inside and/or outside waterjet unit(s) to a first extent when the steering control device is moved to command a first extent of turning and to a greater extent when the steering control device is moved to command a greater extent of turning. 
         [0013]    Preferably, the control system is arranged to cause the inside reverse duct to lower when the steering control device is moved to command a first extent of turn and to increase the thrust generated by the inside and/or outside waterjet unit(s) when the steering control device is moved to command a greater extent of turning. 
         [0014]    Preferably, the control system is arranged to lower the reverse duct to different extent for different forward speeds of the vessel, for an equivalent rate of turn. 
         [0015]    Preferably, the steering control device is operable to steer the vessel at cruise speeds of the vessel wherein the steering control device is a helm wheel. 
         [0016]    Preferably, the steering control device is operable to steer the vessel at cruise speeds of the vessel and the vessel also comprises a separate manually movable control device operable to manoeuvre the vessel at slow speeds. 
         [0017]    Preferably, the steering device is a helm wheel and the manoeuvre control device is movable in multiple axes. 
         [0018]    In a second aspect, the present invention consists in a steering system for a marine vessel comprising:
       two or more waterjet units each having a steering deflector, for propelling the vessel;   a manually moveable steering control device which is movable to steer the vessel to port or starboard; and   an associated control system arranged to activate the steering deflectors of the waterjet units and alter the thrust generated by the inside and/or outside waterjet unit(s) in accordance with movement of the steering control device to cause turning of the vessel.       
 
         [0022]    Preferably, the control system is arranged to operate the steering deflectors with movement of the steering control device to cause turning of the vessel and to also alter the thrust generated by the inside and/or outside waterjet unit(s) when a higher rate of turning of the vessel is commanded. 
         [0023]    Alternatively, the control system is arranged to alter the thrust generated by the inside and/or outside waterjet unit(s) with movement of the steering control device to cause turning of the vessel and to also operate the steering deflectors when a higher rate of turning of the vessel is commanded. 
         [0024]    Preferably, the control system is arranged to increase the thrust generated by the outside waterjet unit when a higher rate of turning is commanded by the steering control device. 
         [0025]    Alternatively, the control system is arranged to decrease the thrust generated by the inside waterjet unit when a higher rate of turning is commanded by the steering control device. 
         [0026]    Alternatively, the control system is arranged to increase the thrust generated by the outside waterjet unit and decrease the thrust generated by the inside waterjet unit when a higher rate of turning is commanded by the steering control device. 
         [0027]    Preferably, the control system is arranged to move the steering deflectors and alter the thrust generated by the inside and/or outside waterjet unit(s) to a first extent when the steering control device is moved to command a first extent of turning and to further move the steering deflectors and alter the thrust generated by the inside and/or outside waterjet unit(s) when the steering control device is moved to command a greater extent of the turning. 
         [0028]    Alternatively, the control system is arranged to alter the thrust of the waterjet unit(s) to a first extent when the steering control device is moved to command a first extent of turn and to a greater extent when the steering control device is moved to command a greater extent of the turn. 
         [0029]    Preferably, the control system is arranged to alter the thrust of the waterjet unit(s) to a different extent for different forward speeds of the vessel. 
         [0030]    Preferably, the control system is also arranged to lower a reverse duct of an inside waterjet unit when a higher rate of turning is commanded by the steering control device. 
         [0031]    Preferably, the steering control device is operable to steer the vessel at cruise speeds of the vessel. 
         [0032]    Preferably, the steering control device is a helm wheel. 
         [0033]    Preferably, the steering control device is operable to steer the vessel at cruise speeds of the vessel and the vessel also comprises a separate manually movable control device operable to manoeuvre the vessel at slow speeds. 
         [0034]    Preferably, the steering device is a helm wheel and the manoeuvre control device is movable in multiple axes. 
         [0035]    In a third aspect, the present invention consists in a steering system for a marine vessel comprising:
       two or more waterjet units each having a steering deflector, for propelling the vessel;   a manually moveable steering control device which is movable to steer the vessel to port or starboard; and   an associated control system arranged to alter the thrust of the inside and/or outside waterjet units in accordance with movement of the steering control device to cause turning of the vessel.       
 
         [0039]    Preferably, the control system is arranged to increase the thrust generated by the outside waterjet unit with movement of the steering control device to cause turning of the vessel. 
         [0040]    Alternatively, the control system is arranged to decrease the thrust generated by the inside waterjet unit with movement of the steering control device to cause turning of the vessel. 
         [0041]    Alternatively, the control system is arranged to increase the thrust generated by the outside waterjet unit and decrease the thrust generated by the inside waterjet unit with movement of the steering control device to cause turning of said vessel. 
         [0042]    Preferably, the control system is arranged to alter the thrust generated by the inside and/or outside waterjet unit(s) to a first extent when the steering control device is moved to command a first extent of turn and to further alter the thrust generated by the inside and/or outside waterjet unit(s) when the steering control device is moved to command a greater extent of the turning. 
         [0043]    Preferably, the control system is arranged to alter the thrust of the waterjet unit(s) to a different extent for different forward speeds of the vessel, for an equivalent rate of turn. 
         [0044]    Alternatively, the control system is also arranged to lower a reverse duct of the inside waterjet unit when the steering control device is moved to command a greater extent of the turn. 
         [0045]    Preferably, the control system is also arranged operate the steering deflectors of the waterjet units when the steering control device is moved to command a greater extent of the turn. 
         [0046]    Preferably, the steering control device is operable to steer the vessel at cruise speeds of the vessel. 
         [0047]    Preferably, the steering control device is a helm wheel. 
         [0048]    Preferably, the steering control device is operable to steer the vessel at cruise speeds of the vessel and the vessel also comprises a separate manually movable control device operable to manoeuvre the vessel at slow speeds. 
         [0049]    Preferably, the steering device is a helm wheel and the manoeuvre control device is movable in multiple axes. 
         [0050]    In a fourth aspect, the present invention consists in a steering system for a marine vessel comprising:
       two or more waterjet units each having a steering deflector, for propelling the vessel;   a manually moveable steering control device which is movable to steer the vessel to port or starboard; and   an associated control system arranged to operate the steering deflectors of the waterjet units in accordance with movement of the steering control device to cause turning of the vessel and also to alter the thrust of the inside and/or outside waterjet units in accordance with movement of the steering control device.       
 
         [0054]    Preferably, the control system is arranged to decrease the thrust generated by the inside waterjet unit. 
         [0055]    Alternatively, the control system is arranged to increase the thrust generated by the outside waterjet unit. 
         [0056]    Alternatively, the control system is arranged to increase the thrust generated by the outside waterjet unit and decrease the thrust generated by the inside waterjet unit. 
         [0057]    Preferably, the control system is arranged to alter the thrust of the waterjet unit(s) to a different extent for different forward speeds of the vessel, for an equivalent rate of turn. 
         [0058]    Alternatively, the control system is arranged to alter the thrust of the waterjet unit(s) to an increasing extent when an increasing rate of turn is commanded. 
         [0059]    Alternatively, the control system is also arranged to lower a reverse duct of the inside waterjet unit when the steering control device is moved to command a greater extent of the turn. 
         [0060]    Preferably, the steering control device is operable to steer the vessel at cruise speeds of the vessel. 
         [0061]    Preferably, the steering control device is a helm wheel. 
         [0062]    Preferably, the steering control device is operable to steer the vessel at cruise speeds of the vessel and the vessel also comprises a separate manually movable control device operable to manoeuvre the vessel at slow speeds. 
         [0063]    Preferably, the steering device is a helm wheel and the manoeuvre control device is movable in multiple axes. 
         [0064]    In fifth aspect, the present invention consists in a steering system for a marine vessel comprising:
       two or more waterjet units each having a steering deflector for propelling the vessel;   a manually moveable steering control device which is movable to steer the vessel to port or starboard; and   an associated control system operable to alter the thrust of the waterjet units to lower a reverse duct of an inside (to a turn) waterjet unit in accordance with movement of the steering control device to cause turning of the vessel.       
 
         [0068]    Preferably, the control system is arranged to alter the thrust generated by the inside and/or outside waterjet unit(s) with movement of the steering control device to cause turning of the vessel and to also lower a reverse duct of an inside waterjet unit when a higher rate of turning is commanded. 
         [0069]    Alternatively, the control system is arranged to lower a reverse duct of an inside waterjet unit with movement of the steering control device to cause turning of the vessel and to also alter the thrust generated by the inside and/or outside waterjet unit(s) when a higher rate of turning is commanded. 
         [0070]    Preferably, the control system is arranged to decrease the thrust generated by the inside waterjet unit. 
         [0071]    Alternatively, the control system is arranged to increase the thrust generated by the outside waterjet unit. 
         [0072]    Alternatively, the control system is arranged to increase the thrust generated by both the outside and inside waterjet units when the inside reverse duct is lowered when a higher rate of turning of said vessel is commanded by the steering control device. 
         [0073]    Preferably, the control system is arranged to alter the thrust and/or lower a reverse duct to different extents for different forward speeds of the vessel. 
         [0074]    Preferably, the control system is arranged to also operate the steering deflectors when a higher rate of turning of is commanded by the steering control device. 
         [0075]    Preferably, the steering control device is operable to steer the vessel at cruise speeds of the vessel. 
         [0076]    Preferably, the steering control device is a helm wheel. 
         [0077]    Preferably, the steering control device is operable to steer the vessel at cruise speeds of the vessel and the vessel also comprises a separate manually movable control device operable to manoeuvre the vessel at slow speeds. 
         [0078]    Preferably, the steering device is a helm wheel and the manoeuvre control device is movable in multiple axes. 
         [0079]    In a sixth aspect, the present invention consists in a steering system for a marine vessel comprising:
       two or more waterjet units each having a steering deflector for propelling the vessel;   a manually moveable steering control device which is movable to steer the vessel to port or starboard; and   an associated control system operable to activate the steering deflectors and lower the reverse duct of an inside (to a turn) waterjet unit in accordance with movement of the steering control device to cause turning of the vessel when turning of the vessel is commanded by the steering control device.       
 
         [0083]    Preferably, the control system is arranged lower the reverse duct of an inside waterjet unit with movement of the steering control device to cause turning of the vessel and to also activate the steering deflectors when a higher rate of turning is commanded. 
         [0084]    Preferably, the control system is arranged to cause the inside reverse duct to lower to a first extent when the steering control device is moved to command a first extent of turn and lower to a greater extent when the steering control device is moved to command a greater extent of the turn. 
         [0085]    Alternatively, the control system is arranged to cause the inside reverse duct to lower to an increasing extent when an increasing rate of turning is commanded by the steering control device. 
         [0086]    Preferably, the control system is also arranged to increase the thrust generated by the inside and/or outside waterjet unit(s) when a higher rate of turning of said vessel is commanded by the steering control device. 
         [0087]    Preferably, the control system is arranged to lower the reverse duct to different extents for different forward speeds of the vessel, for an equivalent rate of turn. 
         [0088]    Preferably, the steering control device is operable to steer the vessel at cruise speeds of the vessel. 
         [0089]    Preferably, the steering control device is a helm wheel. 
         [0090]    Preferably, the steering control device is operable to steer the vessel at cruise speeds of the vessel and the vessel also comprises a separate manually movable control device operable to manoeuvre the vessel at slow speeds. 
         [0091]    Preferably, the steering device is a helm wheel and the manoeuvre control device is movable in multiple axes. 
         [0092]    In a seventh aspect, the present invention consists in a steering system for a marine vessel comprising:
       two or more waterjet units each having a steering deflector for propelling the vessel;   a manually moveable steering control device which is movable to steer the vessel to port or starboard; and   an associated control system operable to lower said reverse duct of an inside (to a turn) waterjet unit in accordance with movement of the steering control device to cause turning of the vessel and also arranged to alter the thrust of the waterjet units when a higher rate of turning of said vessel is commanded by the steering control device.       
 
         [0096]    Preferably, the control system is arranged to cause the inside reverse duct to lower to a first extent when the steering control device is moved to command a first extent of turn and lower to a greater extent when the steering control device is moved to command a greater extent of the turn. 
         [0097]    Alternatively, the control system is arranged to cause the inside reverse duct to lower to an increasing extent when an increasing rate of turning is commanded by the steering control device. 
         [0098]    Preferably, the control system is also arranged to activate the steering deflectors of the waterjet units when said steering control device is moved to command a greater extent of turning. 
         [0099]    Alternatively, the control system is arranged to lower the reverse duct to different extents for different forward speeds of the vessel, for an equivalent rate of turn. 
         [0100]    Preferably, the steering device is operable to steer the vessel at cruise speeds of the vessel. 
         [0101]    Preferably, the steering control device is a helm wheel. 
         [0102]    Preferably, the steering device is operable to steer the vessel at cruise speeds of the vessel and the vessel also comprises a separate manually movable control device operable to manoeuvre the vessel at slow speeds. 
         [0103]    Preferably, the steering device is a helm wheel and the manoeuvre control device is movable in multiple axes. 
         [0104]    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. The term ‘comprising’ as used in this specification and claims means ‘consisting at least in part of’, that is to say when interpreting statements in this specification and claims which include that term, the features, prefaced by that term in each statement, all need to be present but other features can also be present. 
         [0105]    In this specification and the accompanying claims: 
         [0000]    “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 control device of the invention may be suitable for any planing or displacement type vessels, regardless of their size, speed capabilities, and hull type.
 
“thrust” (unless the context indicates otherwise) refers to the thrust output of the propulsion unit(s) or engine(s) of the vessel before any deflection of the waterjet stream of by the steering deflector(s) and/or reverse duct(s); the thrust of one or both (or more) waterjet units is increased or decreased by an increase or decrease in the power output of the engine(s) driving that or those waterjet unit(s), by increasing or decreasing the throttle opening for those engine(s) in the case of an inernal combustion engine for example.
 
“cruise speeds” is intended to mean vessel speeds over 5 knots, more preferably vessel speeds over 8 knots, and most preferably vessel speeds of 10 knots or above.
 
“slow speeds” is intended to mean vessel speeds of up to 5 knots
 
         [0106]    The invention consists in the foregoing and also envisages constructions of which the following gives examples only. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0107]    Various forms of the invention will be described by way of example only and with reference to the drawings, in which: 
           [0108]      FIG. 1  shows a schematic of one example form of the steering system; 
           [0109]      FIG. 2  shows a turning manoeuvre using a steering system of one embodiment of the invention; 
           [0110]      FIG. 3  shows a sharper turning manoeuvre using the steering system of  FIG. 2 ; 
           [0111]      FIG. 4  shows a sharper turning manoeuvre using another embodiment of the invention; 
           [0112]      FIG. 5  shows a sharper turning manoeuvre using a further embodiment of the invention; 
           [0113]      FIG. 6  shows a turning manoeuvre using another embodiment of the invention; 
           [0114]      FIG. 7  shows a sharper turning manoeuvre using the steering system of  FIG. 6 ; 
           [0115]      FIG. 8  shows a turning manoeuvre using another embodiment of the invention; 
           [0116]      FIG. 9  shows a sharper turning manoeuvre using the steering system of  FIG. 8 ; 
           [0117]      FIG. 10  shows a sharper turning manoeuvre using another embodiment of the invention; and 
           [0118]      FIG. 11  shows a sharper turning manoeuvre using another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0119]    The invention is now described with reference to marine vessels that are propelled with two waterjet units at the stem of the vessel (‘twin waterjet vessel’). The systems and methods of the invention may also be used on waterjet vessels propelled by more than two waterjet units, such as three or four waterjet units for example. A marine vessel such as a catamaran for example, may have two waterjet units on each of the port and starboard sides respectively at the stem of the vessel. This type of vessel is referred to as a “quad waterjet vessel.” 
         [0120]    Referring to  FIG. 1 , a schematic arrangement of one embodiment of the steering system of the invention is shown. The system includes a control system  100 , which may be in the form of a microprocessor, microcontroller, programmable logic controller (PLC) or the like. The control system  100  is programmed to receive and process data so as to appropriately steer the vessel, as will be described in detail later. The control system  100  may be a stand-alone or dedicated controller for steering or may be incorporated into existing vessel controllers. In one form, the control system  100  is a plug-in module that is connected to a network, such as a Controller Area Network (CAN), in the waterjet vessel. 
         [0121]    As shown in  FIG. 1 , the control system  100  controls two waterjet units  102 . The two waterjet units  102  are typically placed port and starboard at the stern of the vessel. Where more than two waterjet units are provided as referred to previously, the control system  100  may be adapted to steer at least one port waterjet unit and one starboard waterjet unit. Alternatively, the control system  100  may be adapted to steer two port waterjet units and one starboard waterjet unit if the vessel is turning to starboard for example. Whilst only two operational steering system configurations are detailed for vessels having more than two waterjet units, persons skilled in the art will appreciate that these are examples only and as such should not be considered to be in any way limiting. 
         [0122]    Each waterjet unit  102  includes a pumping unit  104  driven by an engine  106  through a driveshaft  108 . Each waterjet unit also includes a steering deflector  110  and a reverse duct  112 , of known form. In the form illustrated, each reverse duct  112  is of a type that features split passages to improve reverse thrust. The split-passage reverse duct  112  also affects the direction of the reverse thrust to port and starboard and thus the steering of the vessel, when the duct is lowered into the jet stream. The steering deflectors  110  pivot about generally vertical axes  114  while the reverse ducts  112  pivot about generally horizontal axes  116 , independently of the steering deflectors. Activators for the engine throttle, steering deflector and reverse duct of each unit are controlled by control signals from the actuation modules  118  and  120  through control input ports  122 ,  124  and  126  respectively. The actuation modules  118  and  120  are in turn controlled by the control system  100 . 
         [0123]    The control system  100  receives inputs from a manually moveable steering control device  128 , such as a helm wheel, or other steering control device for steering the vessel at speeds which include cruise speeds, such as a cruise-steering joystick. In at least some cases the vessel may also incorporate a separate control device operable to manoeuvre the vessel at slow speeds, such as a (second) multi-axis joystick for example, or other multi-axis manoeuvre control device. The steering control device  128  is used by a helmsperson to manually steer the vessel at least at cruise speeds. 
         [0124]    In the preferred embodiment, the control system  100  is activated as a result of the helmsperson moving the steering control device  128 . This results in the control system  100  generating all control signals to the activators to cause pivoting of the steering deflectors  110  and/or altering the position of the reverse ducts  112  and/or changing the thrust output generated by the vessel&#39;s engines, to improve the steering command(s). Alternatively, there may also be one or more supplementary control devices, such as throttle levers to control the thrust of the waterjet units, that also can provide inputs to the control system  100 . Where suitable or desired, the one or more supplementary control devices may form part of the steering control device  128  as mentioned above. 
         [0125]      FIG. 2  shows the operation of the manually moveable steering control device  128  and the control system  100  to turn a vessel  200  to port, as shown by arrow  202 , in one embodiment of the invention. To make the turn, the helmsperson manually moves the steering control device  128  to port. In the form shown, the steering control device  128  is a helm wheel that has been turned or rotationally displaced from a neutral position, represented by the phantom arrow  128   a , to port by a first range of motion or extent, φ 1 , represented by arrow  128   b . The rotational displacement of the helm wheel results in input signals, which represent the turning demanded by the helmsperson, being sent to the control system of the present invention. The control system then accordingly moves the steering deflectors  204  to port. The jet streams produced by the waterjet units are redirected as a result, which in turn produces force vectors  206 . The combined effect of the force vectors  206  on the port and starboard of the vessel stem is a turning moment to port. This then results in the vessel  200  making the turn demanded by the helmsperson. 
         [0126]      FIG. 3  shows the vessel  200  making a sharper turn  302  to port. The helmsperson moves the helm wheel  128  further to port. In this case, the helm wheel  128  has been turned or rotationally displaced from the neutral position, represented by the phantom arrow  128   a , to port by a second range of motion or extent, φ 2 , represented by arrow  128   c . As compared to the turning manoeuvre demanded in  FIG. 2 , the turning manoeuvre demanded in  FIG. 3  is much sharper, as reflected by the greater rotational displacement of φ 2  of the helm wheel  128  as compared to φ 1 . 
         [0127]    As in  FIG. 2 , the rotational displacement of the helm wheel results in input signals, which represent the turning demanded by the helmsperson, being sent to the control system. As shown in  FIG. 3 , the control system recognises a demand for a sharper turn when the rotational displacement of the helm wheel, or a corresponding movement of other steering control devices, is greater than a first range of motion or extent, and not only moves the steering deflectors  206  to port, but also lowers the reverse duct  304  of an inside (to the turn) waterjet unit. That is, the reverse duct of the side to which the vessel should be turned is lowered 
         [0128]    The effect of also lowering the reverse duct  304  on the inside (to the turn) waterjet unit is that the jet stream produced by the inside waterjet unit is be partially or fully redirected, producing a force vector  306  in the astern direction. The amount of jet stream redirected, and thus the magnitude of the force vector  306 , is dependent on the extent to which the reverse duct is lowered. Force vector  306  in combination with the force vectors  206  produced by the redirection of the jet stream by the steering deflectors  204  results in a greater turning moment being generated. This then causes the vessel  200  to make the sharp turn demanded by the helmsperson. 
         [0129]    The steering system is thus arranged such that the increasing movement of the steering control device to port or starboard, such as increasing the rotational displacement of a helm wheel or of a single axis joystick, from a neutral position, increases the rate of turn of the vessel. When the steering control device  128  is moved to port or starboard over a first range of movement, the steering deflectors  110  of the waterjet units  102  move to cause a turning movement of the vessel  200  to port or starboard. This is shown in  FIG. 2 . When the steering control device  128  is moved to a second range of movement, beyond the first range of movement to port or starboard, the control system  100  causes the inside reverse duct to be lowered so that the reverse duct impinges into the water flow from the inside waterjet and increases the turning moment on the vessel  200 , sharpening the turn of the vessel  200 . This is shown in  FIG. 3 . 
         [0130]    In one form, the control system  100  may be arranged to cause the inside reverse duct to: (i) lower to a first extent as the steering control device  128  is moved to a first extent to commence the turn; (ii) lower to a greater extent as the steering control device  128  is moved to a greater extent to sharpen the turn; and (iii) raise as the steering control device  128  is returned to a central position to complete the turn. 
         [0131]    In another form, the control system  100  may be arranged to cause the inside reverse duct to lower only once a turn has commenced and the steering control device  128  is moved beyond a first extent, so that there is no lowering of the reverse duct as the steering control device  128  is turned to the first extent to commence the turn. Once the steering control device  128  is moved beyond the first extent, the reverse duct lowers in accordance with the movement of the steering control device  128  to increase the rate of turn to meet the turn rate commanded by the steering control device  128 . The reverse duct then raises as the steering control device  128  is returned to a centre point to complete the turn. 
         [0132]    The control system  100  may be programmed with either of the above forms, or alternatively with both of the above forms together with an input for a helmsperson to indicate which of the two forms should be applied. 
         [0133]    The extent and rate at which the reverse duct is lowered is preferably proportional to the forward speed of the vessel  200 . In other words, the inside reverse duct may lower to a lesser extent at a higher forward speed of the vessel than at a lower forward speed to make an equivalent turn. The reverse duct may lower so as to impinge partially into the jet stream from the inside waterjet unit, or to a greater extent into the jet stream from the inside waterjet unit so that there is no net forward thrust from the inside waterjet unit during a part or all of the turn. Alternatively, the reverse duct may lower fully so that a reverse thrust is provided by the inside waterjet unit to maximally increase the rate of turn of the vessel  200 , particularly at slower speeds, at least during part of a turn. This benefits multi-hulled vessels such as catamarans, which have a poor turning capability at planing speed. 
         [0134]    In another embodiment, the steering system of the invention is arranged to generate a higher turning moment by operating the throttles of the waterjet units differentially such that an inside (to the turn) waterjet unit generates less thrust when compared to the outside (to the turn) waterjet unit. This embodiment is described in detail below with reference to  FIG. 4 .  FIG. 4  shows that the helmsperson has displaced the helm wheel  128  to port. The control system recognises the displacement of the helm wheel  128  as a demand for a sharp turn. As before, the control system moves the steering deflectors to port. To generate a greater turning moment, the control system also operates the throttles of the waterjet units such that the thrust generated by the inside (to the turn) waterjet unit is lower than the thrust generated by the outside (to the turn) waterjet unit. In  FIG. 4 , the thrust of the outside (to the turn) waterjet unit is increased, resulting in a force vector  406 . Compared to the force vector of the outside (to the turn) waterjet unit in  FIG. 3 , the force vector  406  has a higher magnitude, represented by the longer arrow of force vector  406 . 
         [0135]    As alternatives to increasing the thrust of the outside (to the turn) waterjet unit, the control system may reduce the thrust of the inside (to the turn) waterjet unit and maintain the thrust of the outside (to the turn) waterjet unit, or reduce the thrust of the inside (to the turn) waterjet unit and increase the thrust of the outside (to the turn) waterjet unit. 
         [0136]    It is possible in a further embodiment to combine the above to generate a higher turning moment to make an even sharper turn. This is described below with reference to  FIG. 5 . The figure shows, with arrow  502 , the turn that is to be made by the vessel  200 . Relative to the arrows  302  and  402 , it is clear that the arrow  502  represents a much sharper turn. The helmsperson has rotationally displaced the helm wheel from the neutral position  128   a  by a third range of motion or extent φ 3  to a position  128   d . In this embodiment, the control system interprets this motion of the helm wheel as a demand for a very sharp turn and causes a combination of using a reverse duct and manipulating the engine thrust to produce differential thrust to effect the sharp turn. 
         [0137]    As with the embodiment described in  FIG. 3 , the control system lowers the reverse duct of the inside (to the turn) waterjet unit. Unlike the partial lowering of the reverse duct in  FIG. 3 , indicated with broken lines, the reverse duct in this embodiment is completely lowered. Also, the control system increases the thrust generated by the inside (to the turn) waterjet unit. The combination of these operations results in a higher magnitude force being generated astern, shown as force vector  506 , as compared to the force vector  306  of  FIG. 3 . 
         [0138]    In  FIG. 5 , the thrust generated by the outside (to the turn) waterjet unit remains the same during the turning manoeuvre. If an even higher turning moment is desired, which may be commanded by a further range of motion of the helm wheel, the control system may increase the thrust of the outside (to the turn) waterjet unit. 
         [0139]    For each of the embodiments described above the steering deflectors of the waterjet units are moved to cause a turning movement to port or to starboard due to the movement of the steering control device from a neutral position to port or starboard. 
         [0140]    In further alternative embodiments, the steering system can be arranged such that when the steering control device  128  is moved to port or starboard over a first range of movement shown as arrow  602  in  FIG. 6 , the position of the inside (to a turn) reverse duct  604  is lowered partially or fully to cause a turning movement of the vessel to port or starboard.  FIG. 6  shows the inside reverse duct  604  in the partially lowered position  604 . When the steering control device  128  is moved to a second range of movement, beyond the first range of movement to port or starboard shown as arrow  702  in  FIG. 7 , the control system  100  causes the steering deflectors  706  of the water jet units to move to increase the turning moment on the vessel  200  thereby sharpening the turn to port or starboard. This will result in a force vector  708  as shown in  FIG. 7 . 
         [0141]    The control system  100  may be arranged to cause the inside reverse duct  704  to: (i) lower to a first extent as the steering control device  128  is moved to a first extent to commence the turn; (ii) lower to a greater extent as the steering control device  128  is moved to a greater extent to sharpen the turn; and (iii) raise as the steering control device  128  is returned to a central position to complete the turn. The inside reverse duct  704  may alternatively be arranged such that the control system  100  may be arranged to cause the inside reverse duct  704  to: (i) lower to a first extent as the steering control device  128  is moved to a first extent to commence the turn and remain in that position as the steering control device  128  is moved to a greater extent; and (ii) raise as the steering control device  128  is returned to a central position to complete the turn. As a further alternative, the control system  100  may be arranged to cause the inside reverse duct  704  to be gradually lowered as the steering control device  128  is moved from a first extent through to a greater extent to effect a sharper turn of the vessel  200 . The inside reverse duct  704  will be raised as the steering control device  128  is returned to a central position to complete the turn. 
         [0142]    In other embodiments the steering system of the invention is arranged to generate a turning moment by operating the engine throttles such that an outside (to a turn) waterjet unit generates more or increased ahead thrust compared to the inside (to the turn) waterjet unit. 
         [0143]    When a greater steering control device  128  is moved from a first extent to a greater extent to effect a sharper turn of the vessel  200 , the control system  100  operates the engine throttles of the outside and/or inside waterjet units a second time to effect a sharper turn of the vessel. There are a number of configurations for controlling the ahead and astern thrust output from the outside and/or inside waterjet units. Typical configurations are detailed in Table 1 below. 
         [0144]    Another embodiment is shown with reference to  FIG. 8  that shows the vessel  200  that is to make a turn to port shown as arrow  802 . The helmsperson has displaced the helm wheel or steering control device  128  to port. The control system  100  recognises the displacement of the steering control device  128  as a demand for a turn. The control system  100  lowers the inside (to the turn) reverse duct  804  either partially or fully (shown partially lowered in  FIG. 8 ) and at the same time alters the thrust by operating the engine throttles to control the thrust output from the inside and/or outside waterjet units. To generate a greater turning moment and produce a force vector  806 . The engine throttles of the inside and/or outside waterjet units can again be altered to effect the sharper turn shown as arrow  902  in  FIG. 9 . Alternatively, to generate a greater turning moment, the control system  100  moves the steering deflectors  904  and at the same time operates the engine throttles such that the ahead thrust generated by the outside (to the turn) waterjet unit is greater than the astern thrust generated by the inside (to the turn) waterjet unit. This will result in a force vector  906  as shown in  FIG. 9 . 
         [0145]    As alternatives to increasing the ahead thrust of the outside (to the turn) waterjet unit, the control system  100  may also increase the astern thrust to the inside (to the turn) waterjet unit, or maintain the ahead thrust to the outside waterjet unit and increase the thrust to the inside waterjet unit. 
         [0146]    In other embodiments the steering system can be arranged such that when the steering control device  128  is moved to port or starboard over a first range of movement, the position of the inside (to a turn) reverse duct  1004  is lowered partially or fully to cause a turning movement of the vessel  200  to port or starboard. This is already shown in  FIG. 6 . When the steering control device  128  is moved to a second range of movement, beyond the first range of movement to port or starboard, the control system  100  causes the engine throttles to operate to alter the thrust output of the waterjet units to increase the turning moment on the vessel  200  thereby sharpening the turn to port or starboard shown as arrow  1002  in  FIG. 10 . This will result in a force vector  1006 . 
         [0147]    The control and operation of the inside reverse duct  1004  has already been discussed above with reference to  FIG. 6  and is applicable to this embodiment of the invention. Similarly, the control of the engine throttles to effect an increased turning moment has also been outlined above and is applicable to this embodiment of the invention. 
         [0148]    In other embodiments and with the inside reverse duct  1104  either partially or fully lowered (shown as fully lowered in  FIG. 1 ), the steering system of the invention is arranged to generate a higher turning moment by moving the steering deflectors  1108  of the waterjet units when the steering control device  128  is moved to a second range of movement shown as arrow  1102  in  FIG. 11 . As such, the higher turning moment is generated by operating the engine throttles to alter the thrust output from the waterjet units in tandem with the movement of the steering deflectors  1108 . This will generate a large force vector  1106  as shown in  FIG. 11 . 
         [0149]    The control system  100  may be arranged to operate the marine vessel propulsion systems either in isolation or in combination with each other to cause a turning movement of the vessel  200  in response to movement of the steering control device  128 . Whilst a number of the embodiments have been described in detail above, the table below includes further possible embodiments that can be implemented by the vessel control system  100 . 
         [0000]    
       
         
               
               
             
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Throttle control 
               
             
          
           
               
                   
                   
                 To generate 
                 Reverse duct 
                 Inside 
                 Outside 
               
               
                 First extent 
                 Second extent 
                 a higher rate 
                 depth 
                 (to the turn) 
                 (to the turn) 
               
               
                 of turn 
                 of turn 
                 of turn 
                 configurations 
                 waterjet unit 
                 waterjet unit 
               
               
                   
               
               
                 Steering 
                 Inside 
                 Throttle 
                 a. Partially lower 
                 Reverse duct 
                 not operable 
               
               
                 deflectors 
                 (to the turn) 
                 control 
                 b. Fully lower 
                 Maintain 
                 Increase 
               
               
                 moved 
                 reverse duct 
                   
                 c. Gradually lower 
                 Decrease 
                 Maintain 
               
               
                   
                 lowered 
                   
                 during turn 
                 Decrease 
                 Increase 
               
               
                   
                   
                   
                   
                 Reverse duct 
                 operable 
               
               
                   
                   
                   
                   
                 Maintain 
                 Increase 
               
               
                   
                   
                   
                   
                 Increase 
                 Maintain 
               
               
                   
                   
                   
                   
                 Increase 
                 Decrease 
               
               
                   
                   
                   
                   
                 Increase 
                 Increase 
               
               
                 Steering 
                 Throttle 
                 Inside 
                 a. Partially lower 
                 Reverse duct 
                 not operable 
               
               
                 deflectors 
                 control 
                 (to the turn) 
                 b. Fully lower 
                 Maintain 
                 Increase 
               
               
                 moved 
                   
                 reverse duct 
                 c. Gradually lower 
                 Decrease 
                 Maintain 
               
               
                   
                   
                 lowered 
                 during turn 
                 Decrease 
                 Increase 
               
               
                   
                   
                   
                   
                 Reverse duct 
                 operable 
               
               
                   
                   
                   
                   
                 Maintain 
                 Increase 
               
               
                   
                   
                   
                   
                 Increase 
                 Maintain 
               
               
                   
                   
                   
                   
                 Increase 
                 Decrease 
               
               
                   
                   
                   
                   
                 Increase 
                 Increase 
               
               
                 Throttle 
                   
                   
                   
                 Maintain 
                 Increase 
               
               
                 control 
                   
                   
                   
                 Decrease 
                 Maintain 
               
               
                   
                   
                   
                   
                 Decrease 
                 Increase 
               
               
                 Throttle 
                 Steering 
                 Inside 
                 a. Partially lower 
                 Reverse duct 
                 not operable 
               
               
                 control 
                 deflectors 
                 (to the turn) 
                 b. Fully lower 
                 Maintain 
                 Increase 
               
               
                   
                 moved 
                 reverse duct 
                 c. Gradually lower 
                 Decrease 
                 Maintain 
               
               
                   
                   
                 lowered 
                 during turn 
                 Decrease 
                 Increase 
               
               
                   
                   
                   
                   
                 Reverse duct 
                 operable 
               
               
                   
                   
                   
                   
                 Maintain 
                 Increase 
               
               
                   
                   
                   
                   
                 Increase 
                 Maintain 
               
               
                   
                   
                   
                   
                 Increase 
                 Decrease 
               
               
                   
                   
                   
                   
                 Increase 
                 Increase 
               
               
                 Throttle 
                 Inside 
                 Steering 
                 a. Partially lower 
                 Reverse duct 
                 not operable 
               
               
                 control 
                 (to the turn) 
                 deflectors 
                 b. Fully lower 
                 Maintain 
                 Increase 
               
               
                   
                 reverse duct 
                 moved 
                 c. Gradually lower 
                 Decrease 
                 Maintain 
               
               
                   
                 lowered 
                   
                 during turn 
                 Decrease 
                 Increase 
               
               
                   
                   
                   
                   
                 Reverse duct 
                 operable 
               
               
                   
                   
                   
                   
                 Maintain 
                 Increase 
               
               
                   
                   
                   
                   
                 Increase 
                 Maintain 
               
               
                   
                   
                   
                   
                 Increase 
                 Decrease 
               
               
                   
                   
                   
                   
                 Increase 
                 Increase 
               
               
                 Inside 
                 Steering 
                 Throttle 
                 a. Partially lower 
                 Maintain 
                 Increase 
               
               
                 (to the turn) 
                 deflectors 
                 control 
                 b. Fully lower 
                 Increase 
                 Maintain 
               
               
                 reverse duct 
                 moved 
                   
                 c. Gradually lower 
                 Increase 
                 Decrease 
               
               
                 lowered 
                   
                   
                 during entire turn 
                 Increase 
                 Increase 
               
               
                   
                   
                   
                 movement 
               
               
                 Inside 
                 Throttle 
                 Steering 
                 a. Partially lower 
                 Maintain 
                 Increase 
               
               
                 (to the turn) 
                 control 
                 deflectors 
                 b. Fully lower 
                 Increase 
                 Maintain 
               
               
                 reverse duct 
                   
                 moved 
                 c. Gradually lower 
                 Increase 
                 Decrease 
               
               
                 lowered 
                   
                   
                 during entire turn 
                 Increase 
                 Increase 
               
               
                   
                   
                   
                 movement 
               
               
                   
               
             
          
         
       
     
         [0150]    Whilst the above table outlines a number of steering system operational embodiments during the first and the subsequent extent of a turn, this should not be considered in any way limiting. As an example, a combination of two propulsion systems can be activated to undertake a first extent of a turn and a third propulsion system activated when a higher rate (second extent) of turn is demanded. Alternatively, the three propulsion systems can be activated to undertake an entire turn (first and second extent). In this case, the positioning of the reverse ducts and/or thrust provided by the engine throttles may be varied during the turn for example, to provide the higher rate of turning. 
         [0151]    It is preferable that the forward momentum or speed of the vessel  200  does not change as the vessel  200  undertakes a turning manoeuvre (unless the helmsperson separately commands this by also operating the foreard or reverse thrust control device). If the reverse ducts  112  are lowered for example, under the control of the control system  100 , a drag will be generated that will cause a small decrease in the vessel&#39;s forward speed. The control system  100  of the invention may automatically compensate for potential speed variations by increasing the thrust output by the vessel&#39;s waterjet units. This will cause the forward vessel speed to be maintained throughout the turning manoeuvre. The control system  100  can alternatively be overridden by the helmsperson by manually altering the engine throttle control(s). 
         [0152]    The foregoing describes the invention including preferred forms thereof. Alterations and modifications as will be obvious to those skilled in the art are intended to be incorporated within the scope hereof. For instance, where the vessel  200  is reversing and a sharp turn is required, the reverse duct should be raised rather than lowered. The features described above for lowering the reverse ducts for sharpening a turn during a forward motion are similarly applicable in relation to raising the inside (to a turn) reverse duct for sharpening a turn during a reverse motion. 
         [0153]    Three ranges of motion, φ 1 , φ 2  and φ 3 , have been described for the steering control device. The three ranges of motion may be, for instance, a first range of motion that results in normal steering using just the steering deflectors, a second range of motion that results in steering using the steering deflector as well as the reverse duct either partially or fully lowered that results in increased turning capability compared to the first range, and a third range of motion that results in steering using the steering deflector as well as the reverse duct either partially or fully lowered and in addition by adjusting the throttle(s) and thus the revolutions-per-minute (RPM) of the appropriate waterjet unit(s) and hence increasing the turning capability compared to the second range. 
         [0154]    Persons skilled in the art will appreciate that the results defined for the ranges of motion above are only examples and are non-limiting. Skilled persons will also appreciate that more than three ranges of motion may be defined, where desired or where necessary.