BACKGROUND AND SUMMARY 
     The present invention relates to methods of measuring coupling ratios. Moreover, the invention also concerns systems and apparatus operable to employ the methods for measuring such coupling ratios. Such coupling ratios concern, for example, marine vessels regarding power coupling from their engines or motors via associated transmissions to corresponding one or more propellers. 
     The present invention relates to methods of measuring coupling ratios. Moreover, the method is especially suitable for measuring coupling ratios in marine vessels. Referring to  FIG. 1 , a contemporary known marine vessel is indicated generally by  10 . The marine vessel  10 , for example a private boat, comprises a hull  20  complemented with an upper deck  30  above which is included a control cabin  40 . The control cabin  40  includes various user-operable controls such as a steering wheel  50  for steering a direction of travel of the vessel  10  in operation, and a speed controller  60  having a control lever  70  which is user-adjustable for controlling in operation speed of travel of the vessel  10  in forward and reverse directions as will be elucidated in more detail later; a user  80  is thereby able to steer and control movement of the vessel  10  in forward or reverse directions by manipulating the steering wheel  50  and the control lever  70 . Within the hull  20 , the vessel  10  comprises an engine or motor  100  having an output shaft  110  which is driven in operation by the engine or motor  100  in a uni-directional rotation manner as denoted by an arrow  120 . The shaft  110  is coupled to a rotary input of a transmission  130 , also known as a “coupling”; the transmission  130  can optionally include one or more of a clutch and a gear. The transmission  130  includes a toothed output drive wheel with a given number of teeth and optionally a rotation sensor operable to provide a signal indicative of a rotation rate of the toothed drive wheel for the purposes of the present invention as will be elucidated later, the number of teeth of the output drive does not need to be known. An output shaft  140  of the transmission  130  coupled to the aforementioned output drive wheel is operable to be driven bi-directionally in both clockwise and anti-clockwise directions as denoted by an arrow  150  in response to user-adjustment of the control lever  70 . The output shaft  140  is further coupled at its remote end to one or more propellers  160  which are also susceptible to being driven bi-directionally as denoted by an arrow  170  is response to user-adjustment of the lever control  70 . The aforementioned control lever  70  is coupled, optionally via a data processor in the speed controller  60 , to the transmission  130  so that adjustment of the control lever  70  is operable to control a degree of coupling of rotary power from the engine or motor  100  through the transmission  130  to the one or more propellers  160 . Moreover, the vessel  10  is designed to float on water  200  with its one or more propellers  160  immersed in the water  200  as illustrated. 
     The control lever  70  and its associated speed controller  60  are illustrated in more detail in plan view in  FIG. 2 . The control lever  70  is pivotally movable within a slot  250  having a central neutral position denoted by a transverse axis  300 . Moreover, the speed controller  60  includes a graduated scale  310  having a central marking  440  corresponding to the aforesaid neutral position of the control lever  70 . In a forward control position denoted by a symbol “F”, the graduated scale  310  has a first series of markings  41 Of,  42 Of,  43 Of,  44 Of as illustrated corresponding to progressively increasing forward speed, namely corresponding to progressively less slippage occurring between coupling plates of the transmission  130  when propelling the vessel  10  in a forward direction. In a similar manner, the graduated scale  310  has a second series of markings  41 Or,  42 Or,  43 Or,  44 Or as illustrated corresponding to progressively less slippage occurring between the coupling plates of the transmission  130  when propelling the vessel  10  in a reverse direction. The aforesaid neutral position  440  for the control lever  70  corresponds, effectively, to complete slippage between the coupling plates of the transmission  130 , namely a state of non-coupling of mechanical power through the transmission  130 . 
     A problem encountered in practice is that the vessel  10  is often customized or is unique in its configuration of motor or engine  100 , its transmission  130 , and its one or more propellers  160  and also speed controller  60 . It is thus desirable that the vessel  10  should be easily configurable so that a position of the control lever  70  relative to the scale  310  is representative, namely visually indicative, of a manner in which the vessel  10  is susceptible to operating in coupling power from the engine or motor  100  to the one or more propellers  160 . In other words, it is desirable that the control lever  70  positioned at the neutral position  440  should correspond to substantially negligible rotary power being transmitted through to the one or more propellers  160 ; in contradistinction, it is also desirable that the control lever  70  adjusted by the user to align to the markings  440   f ,  44 Or should correspond to full coupling of rotary power from the engine or motor  100  to the one or more propellers  160  so that substantially negligible slippage occurs in the transmission  130 . Moreover, it is also desirable that intermediate markings, for example the markings  42 Of,  42 Or should correspond to substantially half coupling of rotary power from the motor or engine  100  to the one or more propellers  160  in forward and reverse directions respectively. 
     When the vessel  10  has initially been constructed, or has been subject to modifications or alterations, the control lever  70  will often be non-representative of characteristics of rotary power transmission occurring within the vessel  10 . A conventional approach contemporarily adopted for the vessel  10  is to input various parameters into the speed controller  60 , for example into an electronic data processor thereof (not shown in  FIG. 1 ), so as to result in the position of the control lever  70  relative to the scale  310  being representative of rotary power transmission occurring within the vessel  10 . Such data entry is not only cumbersome and time consuming, but also requires knowledge of specific characteristics of the motor or engine  100 , the transmission  130  and also the one or more propellers  160 . 
     The present invention therefore seeks to address technical problems encountered with the vessel  10  when implemented in substantially conventional form, by providing a more practical and straightforward method of measuring coupling ratios in a rotary transmission chain in the vessel  10 . 
     Various configurations for the transmission  130  are known in earlier literature, although methods of measuring coupling ratios and providing corresponding calibrations of speed controls is not elucidated in such literature. For example, in a Japanese patent application JP 2003-002296, there is described a hydraulic control mechanism for a marine reduction reversing gear. The hydraulic control mechanism is directed at a technical problem of allowing for changes of two ranges of set values of propeller rotating speed control and slip factor control for a marine reduction reversing gear fixed to a rear part of an engine. The control mechanism is operable to change rotation of a propeller for a ship ahead and astern to change speed. Moreover, the control mechanism is capable of accommodating changes in control by increasing and/or decreasing operating oil pressure applied to the hydraulic clutch. 
     Moreover, in a Japanese patent application JP 07-196090, there is described a slip quantity adjuster for ship marine gears. The adjuster is operable to address a technical problem of providing a convenient approach to setting a control range of a dial to a full range whilst permitting a user to input a number of revolutions of a screw shaft, for example the screw shaft being coupled to a propeller. Such adjustment is provided via a solenoid valve hydraulically controlling a clutch of a marine gear. Moreover, the adjuster employs an electronic PID control unit in connection with a PWM circuit. 
     The aforementioned Japanese applications describe approaches to controlling power transmission through clutches of marine engine or motor systems but does not disclose a more convenient approach to measuring coupling ratios within such systems. 
     It is desirable to provide a more practical and straightforward method of measuring coupling ratios in transmission chains of marine vessels. 
     According to a first aspect of the invention, there is provided a method of measuring coupling ratios in a marine vessel, said vessel comprising:
     (a) a source of mechanical power;   (b) a coupling system operatively coupled via a first input shaft to said source of power and operatively coupled via a second output shaft to one or more propellers of said vessel; and   (c) a controller coupled to a user interface and also to the coupling system such that the user interface is operable via the controller to control a degree of power coupling occurring in operation through the coupling system,   said first and second shafts being provided with first and second rotation rate sensors respectively coupled to said controller for generating first and second rotation rate signals indicative in operation of rotation rates of said first and second shafts respectively, wherein said method includes at least one of steps (d) to (e), such steps including:   (d) adjusting the user interface to invoke substantially full engagement of coupling in the coupling system such that substantially full coupling of the source of power to said one or more propellers occurs corresponding to propelling the vessel at substantially full forward speed, and recording corresponding values of said first and second indicative signals in said controller; and   (e) adjusting the user interface to invoke substantially full engagement of coupling in the coupling system such that full coupling of the source of power to said one or more propellers occurs corresponding to propelling the vessel at substantially full reverse speed, and recording corresponding values of said first and second indicative signals in said controller.   

     The invention is of advantage in that the values of the first and second indicative signals recorded in the controller are susceptible to being used to calculate an effective measure of a coupling ratio provided in the vessel. 
     “Full forward speed” corresponds to substantially full coupling employed in the coupling system. 
     Optionally, the method comprises a further step of:
     (f) calibrating said user interface based on measurements in at least one of steps (d) and (e) so that said user interface when calibrated is operable to provide a user-interpretable indication when full power is being coupled through the coupling system such that intermediate indications of the user interface are indicative of progressively changing degrees of couple of power from the first shaft to the second shaft through the coupling system.   

     Optionally, the method includes further steps of:
     (g) adjusting the user interface to invoke full slippage to occur within the coupling system so that mechanical power is substantially not coupled from the first shaft to the second shaft such that said second rate sensor is operable to measure substantially zero rotation rate of the second shaft; and   (h) calibrating said user interface based on measurements in step (g) so that said user interface when calibrated is operable to provide a user-interpretable indication when substantially zero power is being coupled through the coupling system. Steps (g) and (h) are of benefit in that they enable a neutral central position to be determined for the user interface.   

     Optionally, in the method, the user interface is operable to provide a user indication of an effective coupling ratio provided in the vessel. 
     Optionally, the method is adapted for implementation when the vessel is either on land or floating on water. The method is of benefit that it can be applied when, for example, the vessel is in dry-dock undergoing upgrades or routine repairs. 
     Optionally, the method is adapted for implementation to recalibrate the vessel after said vessel has been subject to reconfiguration. 
     Optionally, in the method, the user interface includes at least one of: a linearly-adjustable control, a rotary-adjustable control, a virtual control presented as a symbol on a display with associated inputs for user-manipulation of said virtual control. Such implementations of the user interface are convenient when the vessel is being used under marine conditions, for example storm conditions or conditions of poor visibility. 
     Optionally, in the method, the coupling system includes coupling plates operable to couple mechanical power thereacross in response to a control signal generated by said controller, said coupling of power across said coupling plates being responsive to a degree of slippage occurring between said plates. 
     According to a second aspect of the invention, there is provided a marine vessel comprising:
     (a) a source of mechanical power;   (b) a coupling system operatively coupled via a first input shaft to said source of power and operatively coupled via a second output shaft to one or more propellers of said vessel; and   (c) a controller coupled to a user interface also to the coupling system such that the user interface is operable via the controller to control a degree of coupling occurring in operation in the coupling system,   said first and second shafts being provided with first and second shaft rotation rate sensors respectively coupled to said controller for generating first and second rotation rate signals indicative in operation of rotation rates of said first and second shafts respectively,
 
said vessel being operable to be calibrated according to the method according to the first aspect of the invention.
   

     According to a third aspect of the invention, there is provided software recorded on a data carrier, said software being executable on computing hardware for implementing the method according to the first aspect of the invention. 
     It will be appreciated that features of the invention are susceptible to being combined in any combination without departing from the scope of the invention as defined by the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       By way of example only, embodiments of the present invention will now be described with reference to the accompanying drawings wherein: 
         FIG. 1  is a schematic illustration of a contemporary marine vessel including a motor or engine coupled via a clutch to one or more propellers; the vessel is provided with a control arrangement for controlling in operation rotary power transmitted through the clutch from the motor or engine to the one or more propellers; 
         FIG. 2  is a schematic illustration of a control lever and associated calibration scale of the vessel of  FIG. 1 , wherein the control lever is user-adjustable to control a degree of rotary power coupling occurring in operation through the clutch; and 
         FIG. 3  is an illustration of the motor or engine, and its associated clutch provided with rotation rate sensors for implementing the present invention in the marine vessel illustrated in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention will be described with reference to the aforementioned  FIGS. 1 to 3  which have been elucidated in the foregoing. The marine vessel  10 , for purposes of the present invention, is implemented as at least one of: a private boat, a yacht, a pilot boat, a fishing boat to mention a few examples. When implementing the present invention, the engine or motor  100 , the transmission  130  and the one or more propellers  160  are supplemented with rotation rate sensors  500 ,  510  associated with the shafts  110 ,  140  respectively as depicted in  FIG. 3 . The sensors  500 ,  510  are operable to generate rotation rate signals  520 ,  530  respectively indicative of rotation rates of the shafts  110 ,  140  respectively. Optionally, the sensors  500 ,  510  are integral with the motor or engine  100  and with the transmission  130  as represented by  550 ,  560  respectively. 
     The vessel  10  implemented with the sensors  500 ,  510  as depicted in  FIG. 3  according to the present invention is susceptible to be assembled from a potentially wide spectrum of component parts, in particular the engine or motor  100 , the transmission  130  and the one or more propellers  160  can potentially derive from several diverse sources. Moreover, the vessel  10  including the sensors  500 ,  510  may also be changed or upgraded from time-to-time with a result that the engine or motor  100 , the transmission  130  and the one or more propellers  160  have characteristics which are changeable with time. When implementing the present invention, it is desirable to circumvent a need to input to the controller  60  various measured characteristics of component parts of the vessel  10  as required in contemporary approaches. 
     Conventionally, an effective drive frequency/of rotation of the shaft  140  is described by Equation 1 
                   f   =     k   ⁢     WRT   60               (     Eq   .           ⁢   1     )               
wherein
 
     W=rotations per minute (RPM) of the output of the motor or engine  100  provided at the shaft  110 ; 
     R=a gearing ratio provided in the transmission  130 ; 
     T=a number of drive-wheel teeth provided in the transmission  130 ; and k=a constant. 
     In conventional practice, one or more of the parameters in Equation 1 (Eq. 1) which are modified when the vessel  10  is altered or updated are fed, for example via a data-entry switch pad and associated screen, into the speed controller  60 . In an event of one or more of the parameters being incorrectly or inaccurately entered, the lever  70  calibration against its associated scale  310  as depicted in  FIG. 2  is incorrect, which can be misleading to the user  80  or, at worst, can represent an operating safety hazard. 
     The inventors of the present invention have appreciated that calibration of the speed controller  60  can be implemented in a more convenient manner without needing to know specific details of the parameters in Equation 1 (Eq. 1). The method of measuring coupling ratios pursuant to the present invention includes following steps to be executed: 
     STEP 1: the control lever  70  is moved to a substantially central position relative to the scale  310 . The speed controller  60  records in its memory a measure of the position of the lever  70 , namely S 0 , and the corresponding signal  530  from the rotation sensor  510  corresponding to the shaft  140  being stationary such that rotary power from the engine or motor  100  is not substantially coupled to the shaft  140 . 
     STEP 2: the lever control  70  is moved to a full-coupling forward setting whereat the coupling plates of the transmission  130  are fully engaged so that the transmission  130  is substantially devoid of slippage occurring therein and operable to propel the vessel  10  in a forward direction. A measure of the position of the control lever  70  to obtain full forward speed together with signals generated by the sensors  500 ,  510 , namely S-f, S 2   f , are recorded in the speed controller  60 . The vessel  10  can either be in open water or suspended in dry dock when executing step 2. 
     STEP 3: the lever control  70  is moved to its full-power reverse setting whereat the coupling plates of the transmission  130  are fully engaged so that the transmission  130  is substantially devoid of slippage occurring therein and operable to propel the vessel  10  in a reverse direction. A measure of the position of the control lever  70  to obtain full reverse speed together with the signals generated by the sensors  500 ,  510 , namely Sir, S 2   n  are recorded in the speed controller  60 . The vessel  10  can either be in open water or suspended in dry dock when executing step 3. 
     It will be appreciated that the steps 1 to 3 can be implemented in any order or sequence. 
     In view of the engine or motor  100 , the transmission  130  and the one or more propellers  160  potentially being changed, the aforementioned full-power reverse and forward settings of the control lever  70  do not necessarily correspond to the positions  44 Of,  44 Or respectively. Similarly, the central position of the lever  70  corresponding to full slippage occurring within the transmission  130  does not necessarily correspond to the position  440  shown in  FIG. 2 . However, it is desirable that the control lever&#39;s position relative to the graduated scale  310  is representative to the user  80  of the vessel  10  of power being delivered from the engine or motor  100  to the one or more propellers  160 , so that the user  80  can ascertain a degree of power being used to propel the vessel when making maneuvers, for example when steering the vessel  10  in a crowded harbor environment wherein considerable slippage of plates in the transmission  130  is utilized. It is conventional practice to operate the motor or engine  100  at relatively constant rotation rate, and hence thermodynamic operating efficiency, and control power transmitted to the one or more propellers  160  by a degree of slippage occurring in the transmission  130 . Such a mode of operation is in contradistinction to, for example, road vehicles wherein clutch slippage is avoided and power matching is achieved by selecting suitable gear ratios. However, on account of marine vessels such as the vessel  10  being for most of their operating time driven at substantially full power, it is conventionally deemed not necessary to implement the transmission  130  with an associated adjustable gear box but simply accept inefficient coupling of power from the motor or engine  100  via the transmission  130  to the one or more propellers  160  when the vessel  10  is being steered in restricted regions of water, for example along narrow canals and in harbor areas. 
     The speed controller  60  is operable, when step 3 has been executed to apply a scaling and offset correction, so that:
     (a) the ratio Sif/S 2   f  is achieved when the control lever  70  is substantially in the position  44 Of as illustrated in  FIG. 2 ;   (B) the ratio S 1   r /S 2   r  is achieved when the control lever  70  is substantially in the position  44 Or as illustrated in  FIG. 2 ; and   (c) the signal S 0  being substantially zero is achieved when the shaft  140  is non-rotating and the control lever is in the position  440 .   

     Moreover, the calibration provided by way of STEPS 1 to 3 is also arranged to ensure that the control lever  70  adjusted by the user  80  to the positions  42 Of,  42 Or corresponds to 50% slippage occurring in the transmission  130  for forward and reverse direction of travel of the vessel  10  respectively. In consequence, the lever  70  being user-adjusted to the positions  410   f ,  43 Of corresponds to 75%, 25% slippage in the transmission  130  respectively when the vessel  10  is in forward motion. Moreover, in consequence, the lever  70  being user-adjusted to the positions  410   r ,  43 Or corresponds to 75%, 25% slippage in the transmission  130  respectively when the vessel  10  is in reverse motion. 
     The present invention is of benefit in that the user  80  does not need to enter complicated data into the speed controller  60 . Moreover, calibration of the control lever  70  can be achieved by a simple procedure, as elucidated in the foregoing regarding steps 1 to 3, which the user  80  can implement merely by briefly operating the motor or engine  100  at full power with negligible slippage in the transmission  130  in forward and reverse directions. It will be appreciated that steps 1, 2 and 3 described in the foregoing can be swapped in sequence if desired without departing from the scope of the invention. The method is thus capable of conveniently coping with upgrades to the marine vessel  10  implemented pursuant to the present invention, for example: 
     (a) replacement of the transmission  130  by a different design of clutch; or 
     (b) replacement of the motor or engine  100  with an alternative power unit operable to provide its nominal output power at a shaft rotation rate different to that of the engine or motor  100 . 
     The present invention is not only capable of being applied during manufacture of the vessel  10 , or similar such marine vessels, but also in subsequent upgrades of the vessel  10  by harbor servicing workshops and similar commercial user-support organizations. 
     Calibration performed according to the present invention is thus of benefit in user-selection of a desired degree of coupling, and thus correct and satisfactory adjustment of the vessel  10 . 
     Modifications to embodiments of the invention described in the foregoing are possible without departing from the scope of the invention as defined by the accompanying claims. 
     For example, although the scale  310  is shown in  FIG. 2  as being a series of position markings adjacent to the slot  250  accommodating the control lever  70 , it will be appreciated that the scale  310  and its associated lever  70  can be implemented in alternative ways; such alternative ways can include rotary controls with radial dials, and push-button controls wherein the dial  310  is actively implemented as a series of lamps or light-emitting-diodes (LED) or a liquid crystal device (LCD) operable to present the user  80  with a virtual position of the control lever  70  represented on the device. 
     Expressions such as “including”, “comprising”, “incorporating”, “consisting of”, “have”, “is” used to describe and claim the present invention are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural. 
     Numerals included within parentheses in the accompanying claims are intended to assist understanding of the claims and should not be construed in any way to limit subject matter claimed by these claims.
There is provided a method of measuring coupling ratios in a marine vessel. The vessel includes: (a) a source of mechanical power; (b) a coupling system operatively coupled via a first input shaft to the source of power and operatively coupled via a second output shaft to one or more propellers of the vessel; and (c) a controller coupled to a user interface and also to the coupling system such that the user interface is operable via the controller to control a degree of power coupling occurring in operation through the coupling system. The first and second shafts are provided with first and second rotation rate sensors respectively coupled to the controller for generating first and second rotation rate signals indicative in operation of rotation rates of the first and second shafts respectively. The method involves measuring a ratio of the first and second signals when the coupling system is in a fully coupled state.