Abstract:
A marine propulsion system comprising a push rod activated pins ( 170 ) which engage eccentric shaft ( 174 ) for unlocking a propeller base ( 190 ) so the base ( 190 ) can rotate around a transverse axis. The base ( 190 ) has an inclined surface ( 192 ) which engages with an inclined surface ( 159 ) defining an opening in the propeller&#39;s hub therefore locking the propeller blade ( 34 ) in position. The inclined surfaces ( 159, 192 ) are disengaged by rotation of the eccentric shaft ( 174 ) thus the propeller blades ( 34 ) can be rotated to adjust the pitch and then the inclined surfaces ( 159, 192 ) re-engage to locking the propeller blade ( 34 ) in the pitch adjusted position.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to a propeller for a marine propulsion system and, in particular, to a propulsion system suitable for an outboard motor or stern drive. However, the propeller has application to other drive systems, such as V-drives and direct drives.  
       BACKGROUND ART  
       [0002]     Marine propulsion systems generally comprise outboard motors or stern drive systems which transmit rotary power to a propeller to drive a boat through water. The propeller includes propeller blades which are angled to provide propulsion through the water. The angle or pitch of the blades relative to a radial axis transverse to the drive axis of the propeller is generally fixed and selected to provide maximum efficiency at maximum speed or cruise speed of the boat to which the system is used. The pitch is generally less efficient at take-off when the boat is driven from stationary up to the cruise speed, which inefficiency results in increased fuel consumption and a longer time for the boat to move from the stationary to cruise speed. If the propeller has too large pitch, the power of the engine may not be sufficient to accelerate the boat to planing speed.  
         [0003]     In order to overcome this problem, variable pitch propeller systems have been proposed in which the pitch of the propeller blades can be altered to suit the changing operating conditions of the propulsion system. Our International Application No. PCT/AU99/00276 discloses such a system which is particularly suitable for outboard motor applications.  
         [0004]     Pitch control systems which are used in stern drives generally comprise hydraulic systems for adjusting the propeller pitch and are therefore relatively expensive and complicated. The size of such systems can also be of issue because it is generally desired that the drive system be as small as possible to minimise drag through the water and weight of the system.  
       SUMMARY OF THE INVENTION  
       [0005]     The invention provides a propeller for a marine propulsion system, comprising: 
        a propeller hub having a plurality of openings, and a hub surface surrounding each opening;     a propeller blade having a propeller base mounted in each of the openings, each base having a base surface for engaging the hub surface of the respective opening;     a mechanical unlocking mechanism for disengaging the respective base surface of the base from the respective hub surface of the hub for enabling rotation of the base, and therefore the propeller blade relative to the hub about an axis transverse to a rotation axis of the hub, by a sliding movement of the hub surface with respect to the base surface; and     a pitch adjusting mechanism for rotating each base to thereby adjust the pitch of the propeller blade.        
 
         [0010]     Preferably the propeller further comprises a mechanical re-locking mechanism for allowing re-engagement of the respective base surface of the base with the respective hub surface of the hub to lock the base in the pitch adjusted position.  
         [0011]     Preferably the unlocking mechanism and the re-locking mechanism comprise a common locking and unlocking mechanism.  
         [0012]     Preferably the re-locking mechanism allows re-engagement of the base surface with the hub surface by virtue of centrifugal force during operation of the propeller after the pitch adjusting mechanism has adjusted the pitch of the propeller blades.  
         [0013]     Preferably the common locking and unlocking mechanism comprise a stem on each base, a respective eccentric coupled to each stem, a respective pin mounted to each eccentric, a push rod for moving the pins to in turn rotate the eccentrics so that the eccentrics push the stems, and therefore the bases, radially inwardly with respect to the hub to unlock the base by removing load from the hub surface and base surface, and after the pitch of the propeller blades have been adjusted, re-applies the load to the surfaces to re-engage the respective base surface of the bases with the respective hub surfaces of the openings to re-lock the bases and therefore the propeller blades in the pitch adjusted position.  
         [0014]     Preferably the mechanical unlocking mechanism disengages the respective base surface from the respective hub surface by transferring load from the base surface and hub surface to thereby allow the hub surface and base surface to move relative to one another.  
         [0015]     Preferably the unlocking mechanism comprises an eccentric, at least one engaging element on the eccentric, a slide surface arranged radially inwardly of the respective hub surface and base surface so that when the eccentric is rotated, load is transferred from the respective hub surface and base surface to the at least one element and slide surface so the respective propeller blades can be adjusted after the transfer of load with the at least one element sliding on the slide surface.  
         [0016]     Preferably the slide surface is arranged on a fixed bridge.  
         [0017]     Preferably the element comprises two elements, each element having a slide member and the slide surface being a ceramic slide surface for engaging with the slide members of the elements.  
         [0018]     Preferably the eccentric is coupled to a pin for firstly rotating the eccentric about a first axis to transfer the load and then rotating the eccentric about a second axis transverse to the first axis to rotate the respective propeller blade to adjust the pitch of the propeller blade.  
         [0019]     Preferably wherein the hub surface and the base surface are inclined cone-shaped surfaces.  
         [0020]     Preferably the hub surface and base surface are substantially horizontal surfaces perpendicular to an axis about which the pitch of the propeller blades is adjusted.  
         [0021]     Preferably the push rod is coupled to a claw which has a respective finger for each of the propeller blades, each finger being mounted to a respective pin by a socket and eye joint.  
         [0022]     Preferably an adjusting mechanism is provided for enabling adjustment of the claw with respect to the push rod.  
         [0023]     Preferably the adjusting mechanism comprises a bush screw threaded on the push rod by co-operating screw threads on the bush and push rod, the bush carrying the claw, and a locking nut for locking the bush and therefore the claw in a desired position relative to the push rod.  
         [0024]     Preferably the pin locates in a recess in the base so that after the pin rotates the shaft, the pin engages the base to thereby rotate the base about the transverse axis to adjust the pitch of the propeller blade.  
         [0025]     Preferably a fixed bridge is located between each base and each eccentric, the bridge having an arcuate slot through which the respective pin passes to accommodate movement of the pin relative to the bridge.  
         [0026]     The invention also provides a marine propulsion system to be driven by a motor, the system comprising: 
        a propeller having a propeller hub and a plurality of propeller blades;     a drive for rotating the propeller about a first axis;     a pitch adjusting mechanism for adjusting the pitch of the propeller blades about respective axes transverse to the first axis;     a blade supporting mechanism for supporting the blades in the hub to allow adjustment of the pitch of the blades about the transverse axes, the supporting mechanism comprising:     an engaging element for movement by the adjusting mechanism to adjust the pitch of the blades;     the engaging element having an arm for each of the blades;     a joint carried by the arm;     a pin mounted in the joint;     an eccentric in engagement with the pin;     a propeller base connected to the eccentric, the propeller base having a base surface;     a base surface on the hub for engagement with the base surface on the base so the base surface of the base engages the base surface of the hub to lock the propeller in a pitch adjusted position; and     wherein when the adjusting mechanism moves the adjusting element, the engagement between the flexible joint and the pin causes the joint and pin to first rotate the eccentric about an eccentric axis to disengage the base surface of the base and the hub surface of the hub, and whereupon further movement of the adjusting mechanism, and therefore the element, rotates the eccentric and the base relative to the hub about the transverse axis to adjust the pitch of the propeller blades.        
 
         [0039]     Preferably the hub surface and base surface are tapered surfaces.  
         [0040]     Preferably a biasing means is provided for biasing the base surface towards the hub wherein the biasing means also assists in biasing the eccentric and pin back towards an equilibrium position.  
         [0041]     Preferably the joint comprises an outer socket and an inner moveable eye in the socket which carries the pin.  
         [0042]     Preferably the eccentric is an eccentric shaft.  
         [0043]     Preferably the base includes a stem which engages the eccentric shaft so that rotation of the eccentric shaft about the eccentric axis moves the base relative to the hub in a radial direction so the tapered surface of the base can disengage from the tapered surface of the hub, and continued movement of the arm rotates the eccentric shaft about the respective transverse axis to thereby adjust the pitch of the blade relative to the hub about the respective transverse axis.  
         [0044]     Preferably the drive comprises: 
        a first drive shaft for receiving rotary power from the motor;     a second drive shaft arranged transverse to the first drive shaft;     a first gear on the first drive shaft;     a second gear on the second drive shaft meshing with the first gear so that drive is transmitted from the first drive shaft via the gears to the second drive shaft; and     the propeller hub being connected to the second drive shaft for rotation with the second drive shaft.        
 
         [0050]     Preferably the pitch adjusting mechanism comprises a push member for moving the engaging element to thereby move the propeller blades and adjust the pitch of the propeller blades, the push member having a screw thread, a nut member having a screw thread and engaging the screw thread of the push member, and a control mechanism for rotating the nut to move the push member because of the engagement of the screw thread of the push member, and the screw thread on the nut, so the push member is moved in a linear manner to move the element to thereby increase the pitch of the propeller blades.  
         [0051]     Preferably the push member comprises a push rod and a bolt provided about the push rod so the push rod can rotate relative to the bolt, the screw thread of the push member being provided on the bolt, the bolt having a chamber for receiving a thrust portion of the push rod so that upon rotation of the nut in one direction, the bolt is moved in a first direction parallel to the first axis and the push rod is moved with the bolt whilst being able to rotate within the bolt because of the engagement of the thrust portion in the chamber, and upon rotation of the nut member in the opposite direction, the bolt and the push rod are moved in a second direction opposite the first direction parallel to the first axis because of the engagement of the thrust portion of the push rod in the chamber.  
         [0052]     Preferably the second drive shaft is hollow and the push rod is arranged in the second drive shaft so that the push rod can rotate with the second drive shaft whilst being moveable in the first and second directions along the first axis.  
         [0053]     Preferably the push rod has a retaining member for retaining the bolt for movement in the direction of the first axis, but preventing rotation of the bolt about the first axis.  
         [0054]     Preferably the chamber is formed by a flange on the bolt and a cover connected to the flange, the thrust portion of the push rod having a pair of thrust surfaces, and thrust bearing disposed between one of the thrust surfaces and the flange, and the other of the thrust surfaces and the cover.  
         [0055]     Preferably the disengagement of the base surface and the hub surface comprises a transfer of load from the base surface and hub surfaces so the base surface and hub surfaces can rotate relative to one another by a sliding action. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0056]     A preferred embodiment of the invention will be described, by way of example, with reference to the accompanying drawings, in which:  
         [0057]      FIG. 1  is a schematic view of a boat having a stern drive according to the preferred embodiment of the invention;  
         [0058]      FIG. 2  is a partially cross-sectional view through the propulsion system of the stern drive of  FIG. 1 ;  
         [0059]      FIG. 3  is a more detailed view of part of the system shown in  FIG. 2 ;  
         [0060]      FIG. 4  is a perspective view of part of the system of  FIG. 3 ;  
         [0061]      FIG. 5  is a view of the control mechanism of the propulsion system;  
         [0062]      FIG. 6  is a view of an emergency pitch adjuster of the preferred embodiment of the invention;  
         [0063]      FIG. 7  is a partial cross-section and side view of part of the hub of the propulsion system;  
         [0064]      FIG. 7   a  is a view of an alternative embodiment to that shown in  FIG. 7 ;  
         [0065]      FIG. 8  is a cross section of the propeller hub of the propulsion system of the preferred embodiment;  
         [0066]      FIG. 9  is a perspective view from the rear of the hub of  FIG. 7 ;  
         [0067]      FIG. 10  is a view along the line X-X of  FIG. 8 ;  
         [0068]      FIG. 11  is a view similar to  FIG. 10  but in a second operational position;  
         [0069]      FIG. 12  is a view similar to  FIG. 8  but in the second operational position;  
         [0070]      FIG. 13  is a cross-section of a modified hub according to another embodiment of the invention;  
         [0071]      FIG. 14  is a more detailed view of one of the propeller and pitch adjustment arrangements of the hub of  FIG. 13 ;  
         [0072]      FIG. 15  is a perspective view of an eccentric shaft used in the embodiment of  FIG. 13 ;  
         [0073]      FIG. 16  is a view along the line XVI-XVI of  FIG. 14 ;  
         [0074]      FIG. 17  is a partial cross-section perspective view generally along the line XVII-XVII of  FIG. 16 ;  
         [0075]      FIG. 18  is a view along the line XVIII-XVIII of  FIG. 16 ; and  
         [0076]      FIG. 19  is a view of a further embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0077]     With reference to  FIG. 1 , a boat  10  is shown having a stern drive  12 . The stern drive  12  is powered from a motor  14  within the boat via a main drive shaft  16 .  
         [0078]     As is shown in  FIG. 2 , the stern drive  12  has a casing generally shown at  20  which includes a cavitation plate  22 . The cavitation plate  22  is at about water level when the boat is planing and prevents air from being sucked into propeller  24 . A drive shaft  26  receives rotary power from the main drive  16  shown in  FIG. 1  by way of a gear arrangement (not shown) which is conventional and therefore need not be described. The drive shaft  26  carries a bevel gear  28  which in turn meshes with a bevel gear  29  connected to a second drive shaft  30  which is arranged generally perpendicular to the drive shaft  26 . The drive shaft  30  connects to hub  32  of the propeller  24  for rotating the hub  32  and the propeller blades  34  which are coupled to the hub  32 . It should be understood that in  FIG. 2  only one propeller blade  34  is shown in an exploded position. In the embodiment shown, three propeller blades  34  are provided. However, the propeller may have more or less than three blades.  
         [0079]     A control motor  38  is mounted rearwardly of the stern drive  12  and has a drive shaft  40  which drives an output shaft  42  via bevel gear arrangement  43  and  44 . The output shaft  42  carries a gear sprocket  49 . A gear sprocket  45  is arranged at the front of the stern drive  12  having regard to the position the stern drive takes up when powering a boat, and the sprocket gear  45  is connected to a control shaft  46 . A flexible chain drive  47  engages the sprockets  45  and  49  so that drive can be transmitted from the motor  38  to the output shaft  42 , and then to the chain  47  so the chain rotates the sprocket  45  and therefore the control shaft  46 .  
         [0080]     As is best shown in  FIG. 3 , the bevel gear  29  is mounted in bearing  47  and the bevel gear  29  is splined to the second drive shaft  30  so the second drive shaft  30  rotates when the bevel gear  29  is driven by the first drive shaft  26  and the bevel gear  18 .  
         [0081]     The drive shaft  30  is hollow and a push rod  50  is arranged in the drive shaft  30 . As will be described in more detail hereinafter, the push rod  50  is connected to a coupling mechanism in the hub  32  and the push rod  50  rotates with the drive shaft  30  when the drive shaft is driven to propel the boat  10 . The drive shaft  30  has a recess  52  at its end remote from the propeller hub  32 .  
         [0082]     The push rod  50  has an enlarged diameter thrust portion  54  which carries an annular abutment  56  which has a first abutment surface  57  and a second abutment surface  58 .  
         [0083]     A bolt  60  is mounted about the push rod  50  and is accommodated in the recess  52 , as is shown in  FIG. 3 . The bolt  60  carries a flange  62  at its end opposite the recess  52 , and the flange  62  is connected to a generally cup-shaped cover  64 . The cover  64  and flange  62  define an internal chamber  66  in which the enlarged diameter portion  54  and the thrust portion  56  are accommodated so the rod  50  and the portions  54  and  56  can rotate in the chamber  66 . A first thrust bearing  68  is arranged between the surface  58  and the cover  64  and a second thrust bearing  70  is arranged between the surface  57  and the flange  62 . The cover  64  can be fixed to the flange  62  by a circlip or otherwise connected to the flange  62 .  
         [0084]     The bolt  60  carries a screw thread  72  and also has diametrically opposed slots  74  and  75  which are best shown in the perspective view of the bolt  60  shown in  FIG. 4 .  
         [0085]     A nut  78  is provided with an internal screw thread  79  which engages with the screw thread  72 . The nut  78  also has an enlarged recess  80  which accommodates the flange  62  and cover  66  of the bolt  60 . The nut  78  also carries an integral bevel gear  84  which meshes with a bevel gear  86  provided on the end of control shaft  46 . The nut  78  is journalled in bearing  85  and has a peripheral flange  87 .  
         [0086]     A locating plate  90  is provided between the bevel gear  29  and the nut  78  and bearing  91  is located between the flange  87  and the plate  90  for supporting rotation of the nut  78  relative to the plate  90 . The plate  90  is fixed to the housing  20  of the stern drive so the plate  90  cannot move.  
         [0087]     As is best shown in  FIG. 4 , the plate  90  has a central opening  92  through which the bolt  60  can pass and carries a pair of lugs  93  and  94  which locate respectively in the grooves  74  and  75  of the bolt  60 . The lugs  93  and  94  located in the grooves  74  and  75  prevent the bolt  60  from rotating so the bolt  60  is constrained for longitudinal linear movement in the direction of the first axis A of the propulsion system, about which the hub is rotated by the second drive shaft  30 .  
         [0088]     Thus, when the control shaft  46  is rotated, drive is transmitted to the nut  78  by the engagement of the bevel gears  84  and  86  so the nut  78  is rotated within the bearing  85  and the bearing  91 . Rotation of the nut  78  causes the bolt  60  to move in the direction of the longitudinal axis A, either to the left or right in  FIG. 3 , depending on the direction of rotation of the nut  78 . The longitudinal movement of the bolt  60  relative to the plate  90  is accommodated by the lugs  93  and  94  being able to slide in the grooves  74  and  75 . In other words, the grooves  74  and  75  move over the lugs  93  and  94  when the bolt  60  is moved in the longitudinal direction, and at the same time prevent rotation of the bolt  60  so the push rod is constrained for longitudinal movement.  
         [0089]     When the bolt  60  is moved to the left in  FIG. 3 , the flange  62  provides thrust to the annular thrust surface  57  of the thrust portion  56  via bearing  70  so the push rod  50  is pushed to the left in  FIG. 3  whilst the push rod  50  rotates with the drive shaft  30 . As mentioned above, the portion  56  is able to rotate in the chamber  66  with the rotation being supported by the thrust bearings  68  and  70  which also serve to transmit load from the flange  62  to the portion  56  when the bolt  60  is moved by rotation of the nut  78 . If the nut  78  is rotated in the opposite direction, the bolt  60  is moved to the right in  FIG. 3 , and the cover  64  pushes against the thrust surface  58  of the portion  56  via the thrust bearing  68  so the push rod  50  is moved to the right in  FIG. 3 , whilst the push rod  50  rotates with the drive shaft  30 .  
         [0090]     The threads  75  and  79  are self-jamming and therefore prevent axial forces from the propeller blades being fed back into the control shaft  46 . The thrust bearings  68  and  70  act in respective opposite directions when the push rod is pushed to the left or the right in  FIG. 3 , thereby absorbing the forces exerted by the push rod during movement, which is applied back to the push rod by the load applied to the propeller blades  34  when the propulsion system is in operation, and particularly when the pitch of the propeller blades is being adjusted whilst the hub  32  is rotating.  
         [0091]     As is best shown in  FIG. 2  and  FIG. 5 , the sprockets  45  and  49  and the chain  47  are external of the housing  20  of the stern drive  12 . As is shown in  FIG. 5 , the sprocket  45  is mounted in a casing  100  which is connected to the housing  20  of the stern drive  12  via bolts  102 . The control shaft  46  is supported in a bearing  104 . The casing  100  connects with a hollow stem  105  to which a rubber boot  107  is connected. The boot  107  is also connected to a stem section  109 . The chain  47  is provided in a plastic tube  48 . A similar boot (not shown) is also arranged on the other side of the chain  47  (ie. the return side if the side shown in  FIG. 5  is the advancing side). The boots  107  enable access to the chain  47  by removing the boots and sliding the tube  48  so that the chain  47  can be adjusted or maintained if necessary. The boots  107  and the stems  109  also provide adjustment of the chain by moving the control motor  38  and its control shaft  42  and gears  43  and  44  and sprocket  49 , so as to tension the chain with the movement being accommodated by expansion or contraction of the boots  107 . The control motor  38 , the output shaft  42  and the gears  43  and  44  and sprocket  49  can then be locked in their adjusted position.  
         [0092]     Thus, when the control motor  38  is operated, drive is transmitted to the nut  78  as previously mentioned, so that the push rod  50  is pushed either to the left or the right in  FIG. 2  and  FIG. 3  to adjust the pitch of the propeller blades  34 .  
         [0093]     The arrangement of the control motor  38 , the chain  47  and the control shaft  46 , as shown in  FIG. 2 , enables these control mechanisms to be added to an existing stern drive without alteration of the existing operating componentry. In stern drives, the space above the control shaft  46  is occupied by the input power shaft  16  from the motor  14 , an exhaust duct (not shown), and sometimes cooling water channels and mounting and steering components. The space behind the drive shaft  26  is available on stern drives and even outboard motor installations. Thus, by providing the motor  38  in the position shown in  FIG. 2  and connecting it to the control shaft  46  by the chain  47  an inexpensive and small space solution is provided to transmit power from the motor  38  to the control shaft  46 . These components do not require any additional space in the vertical direction, because the chain can be guided around the existing upper leg part  20   a  of the stern drive  12 . Furthermore, by using different gear sprocket diameters at the front and the rear, the overall transmission ratio between the motor  38  and the axial motion of the push rod  50  can be influenced.  
         [0094]      FIG. 6  shows an emergency pitch adjuster for emergency adjustment of the pitch of the propeller blades  34 , should the control motor or chain  47  malfunction. This mechanism allows the boat to still be driven if the other components of the propulsion system are operational to supply power to the drive shaft  30 .  
         [0095]     The emergency pitch adjuster comprises a sprocket gear or ratchet wheel  120  which is mounted on control shaft  46 . A flexible push element  122 , shown in the pushed-in position, is mounted to the housing  100  and passes through a hollow stem  124 . The push element  122  has a button  126  external to the casing  100  on its end, and the external part of the push element  122  and button  126  are closed in a rubber boot  130  which is fixed to the casing  100  to seal the space inside the stern drive  10  from the outside.  
         [0096]     The stem  122  is preferably a tightly wound spring so that the stem  122  is flexible but stiff in its axial direction. The sprocket wheel  120  includes teeth  134 .  
         [0097]     When the button  126  is pushed through the boot  130 , the stem  122  is moved in the direction of arrow B in  FIG. 6  against the bias of a return spring  139  which is arranged between the housing  100  and the button  126 . This movement pushes the spring  122  against one of the teeth  134  to index the sprocket wheel  120  in the direction of arrow C in  FIG. 6  to in turn rotate the control shaft  46  in that direction. When the button  126  is released, the push member  122  is returned to its intermediate position by the spring  139 . Because of the flexible nature of the push member  122 , the push member  122  can bend and simply ride over one of the gear teeth  134 , should a gear teeth be in the way when the push member  122  returns. The button  126  can then be pressed so that the member  122  engages another of the teeth  134  to further index the sprocket wheel and control shaft  46  in the direction of arrow C in  FIG. 6 .  
         [0098]     This continued indexing movement passes all the way through the system to the push rod  50  so the push rod  50  is moved to adjust the pitch of the propellers to a predetermined position, such as a fully forward position so the boat is able to take off and limp home.  
         [0099]     FIGS.  7  to  12  show the coupling mechanism which couples the push rod  50  to the propeller blades  34  to adjust the pitch of the propeller blades relative to the hub  32 .  
         [0100]     As is best shown in  FIG. 9 , an actuator claw  150  is located in the hub and is connected to the push rod  50 . As is best shown in  FIG. 7 , the push rod  50  has a stem  301  which is provided with a screw thread  302 . The claw  150  has a central hole  304  which receives the stem  301  and a nut  305  is screwed onto the screw thread  302  to fix the claw  150  to the push rod  50 . Thus, when the push rod  50  moves along axis A, the claw is also moved with the push rod  50 . As shown in  FIGS. 8 and 9 , the hub  32  is generally hollow and has a central hub  152  which is provided with ribs  154  which connect the central hub  152  to outer hub casing  156  of the hub  32 . The claw  150  has three arms  160 , one for each of the propeller blades  34 . Since the mechanisms which are coupled to the fingers  160  are identical, only one is shown and will be described in  FIGS. 8 and 9 . Each arm  160  carries a finger  162  and a ball joint  164  (such as a rod end joint) is located at the end of each finger  162 . The ball joint  164  is made up of a socket  166  and an eye  168  which is moveable in the socket  166 . The eye  168  (as is best shown in  FIG. 8 ) has a central bore  169  which carries a pin  170 . The pin  170  is a sliding fit in the bore  169 . The pin  170  engages in a bore  172  provided in an eccentric shaft  174 .  
         [0101]     The hub casing  156  is provided with three holes  157 , one for each of the propeller blades  34 . Each of the holes  157  is provided with a hub mount  158  which has a tapered internal surface  159 . The propeller blades  34  have a blade base  190  which are provided with a tapered surface  192  which matches the taper of the surface  159 . The base  190  has a stem  194  which is connected to the eccentric shaft  174 . The central hub  152  is provided with a spring washer  195  for each of the stems  194 . The spring washer  195  is located in a groove or recess  196  in the ribs  154 . The spring washers  195  bear on the bottom surface of the stems  194 . Instead of providing bias by way of the washer  195 , the washer could be replaced by some other biasing mechanism, such as a conventional coil spring, resilient rubber block or the like.  
         [0102]     When the push rod  50  is moved, the push rod  50  pushes against the claw  150 , which in turn pushes the ball joint  164 . The initial movement of the claw  150  causes the pin  170  to lean or tilt over slightly in the ball joint  164  so that the movement of the pin  170  causes the eccentric shaft  174  to rotate about eccentric axis D shown in  FIG. 8 .  
         [0103]      FIG. 7A  shows an alternative embodiment to that shown in  FIG. 7 . In this embodiment the claw  150  is somewhat more accurate but still has the three fingers  162  (only two of which are shown in the cross-sectional view of  7 A). In this embodiment the arms  160  are curved and merged into the fingers  162 . The central hole  304  which receives the push rod  50  is provided with a bush  410  which is provided with an internal screw thread  411  which screws onto a screw thread  412  provided on the push rod  50 . By rotating the bush  410  the claw  150  can be adjusted in position relative to the push rod  50  to in turn adjust the position of the ball joints  164  to set them in their optimum position for engagement with the eccentric shaft  174  and to locate the pins  170  in the optimum position for movement of the propeller blades about the transverse axis to adjust the pitch of the propeller blades  34 . The claw  150  is fixed in position by the locking nut  305  which is also provided on the screw thread  412 . The bush includes a recessed portion  415  and shoulder  416  for receiving the claw  150  and so the claw  150  can be jammed and locked into position between the locking nut  305  and the shoulder  416  of the bush  410  when the bush  410  is adjusted to in turn move the claw  150 .  
         [0104]     In a still further embodiment (not shown) the screw thread  411  could be formed direct on the claw  150  and the bush  410  omitted.  
         [0105]      FIG. 10  is a cross-sectional view along the line X-X of  FIG. 8  and shows the position of the pin  170  before the push rod  50  is moved.  FIG. 11  is a view similar to  FIG. 10 , but shows the position of the pin  170  after the initial movement of the push rod  50  which causes the pin  170  to lean slightly. The amount of leaning of the pin  170  in  FIG. 11  is exaggerated to more clearly show the nature of the movement. This slightly leaning or tilting movement of the pin  170  causes the eccentric shaft  174  to rotate about the eccentric axis D so that the eccentric part  174   a  of the shaft  174  rotates away from the top dead centre position shown in  FIG. 8  to a position more towards the bottom of the stem  194  which pushes the stem  194  and therefore the base  190  downwardly in  FIG. 8  (and also as illustrated in  FIG. 12 ).  
         [0106]     As is apparent from  FIG. 12 , the inclined or tapered surface  159  defines an opening in which the base  190  locates. The opening defined by the inclined surface  159  increases in size from the radially outermost part (which is the upper part of the mount  158 ) to a radially innermost extremity which is at about the midpoint of the mount  158  shown in  FIG. 12 .  
         [0107]     Thus, because of the eccentric nature of the shaft  174 , this rotational movement pulls the base  190  very slightly downwardly in the direction of arrow E in  FIG. 8  (by an amount of about one tenth of a millimeter) against the bias of the spring washer  195  so the tapered surface  192  is released from the tapered surface  159 . Continued movement of the push rod  50  and the claw  150  will then push the finger  162  and the flexible joint  164  so the flexible joint moves into or out of the plane of the paper in  FIG. 8 , and this will cause the eccentric shaft  174  to rotate about transverse axis B. Because the stem  194  is connected to the shaft  174 , the stem  194 , and therefore the blade base  190  is also rotated about the transverse axis B. This in turn rotates the propeller blade  34  to thereby adjust the pitch of the propeller blade relative to the hub  32 .  
         [0108]     It will be apparent that all of the propeller blades  34  are adjusted in the same manner by this movement of the push rod  50 , because the push rod  50  will engage the claw  150  and cause simultaneous movement of each of the legs  162 .  
         [0109]     When movement of the push rod  50  ceases after the push rod has been moved at a sufficient distance to adjust the pitch of the propellers to the required pitch position, the load is removed from the flexible joint  164  and the bias of the spring washer  195  together with the centrifugal force of the blades and the blade bases will push the stem  194  upwardly, again reengaging the tapered surface  192  with the tapered surface  159 . This movement will also tend to rotate the shaft  174  back to its equilibrium position, and the pin  172  will also return to its equilibrium position (as shown in  FIGS. 8 and 10 ) awaiting the next movement of the push rod  50  for further adjustment of the pitch of the propeller blades  34 .  
         [0110]     When the tapered surface  192  is again against the surface  159 , flutter motion of the blades is prevented even under low loads and fatigue stresses are kept away from the operating parts of the coupling mechanism shown in  FIGS. 7 and 8 . The frictional engagement, and therefore locking of the propeller blade  32  to the hub  156  is accomplished by the force of the washer  195  which pushes the tapered surfaces  192  and  159  together. With increasing propeller speed, this force is further supported by centrifugal force caused by the mass of the rotating blades  32  and the blade bases  190 .  
         [0111]     It will be appreciated that when the propeller blades are adjusted in pitch, the pins  170  will travel in an arcuate path around the respective blade axes, and will therefore slightly change their distance from the central axis of the hub  32 . In order to accommodate this, the claw  150  and the push rod  50  can rotate slightly relative to the hub  32  and the drive shaft  30  because the push rod  50  is free of the drive shaft  30  and is able to rotate in the chamber  66  as has been previously described.  
         [0112]     The hub configuration described with reference to FIGS.  7  to  12  provides the advantage that exhaust gases from the engine  14  can be guided through the stern drive and the hub  32 .  
         [0113]     FIGS.  13  to  16  show a modified form of the hub according to FIGS.  7  to  12 . Like references indicate like parts to those described with reference to FIGS.  7  to  12 .  
         [0114]      FIG. 13  is a cross-section (viewed from the front) which shows the three propeller blades, and the three separate mechanisms which adjust the pitch of the three propeller blades.  
         [0115]     One of the mechanisms is shown in more detail in  FIG. 14 . With reference to  FIG. 14 , the blade base  190  is mounted on eccentric shaft  174 , as in the earlier embodiment, by the eccentric shaft passing through an opening in stem  194  of the mount  190 . The spring washer  195  is shown in  FIG. 14 , but the central hub  152  is omitted for ease of illustration. The joint  164  is also only schematically illustrated in FIGS.  13  to  18  for ease of illustration. The pin  170  passes through the eccentric shaft  174 , as in the earlier embodiment, and engages in a groove  201  of plate section  202  of the base  190 . The pin  170  is a loose fit in the groove  201 , as will be explained in more detail hereinafter.  
         [0116]     The shaft  174  is shown in detail in  FIG. 15 . As shown in  FIG. 15 , the shaft  174  has an enlarged head  271  in which bore  172  is provided. The pin  170  (not shown in  FIG. 15 ) passes through the bore  172 . The head  271  is enlarged to provide sufficient strength to the shaft  174  where the pin  170  passes through the bore  172 . The shaft  174  has a stem portion  272  which is provided with two grooves  205 . The grooves  205  have curved end regions  205   a  and flat middle region  205   b . The curvature of the grooves  205  is slightly different to the remainder of the stem  272  to provide the eccentricity of the shaft  174  as will be described in more detail hereinafter. The stem  272  is provided with an elongate hole  273 . The end of the stem  272  opposite the head  271  is provided with a stud  210 .  
         [0117]     As shown in  FIG. 14 , a fixed bridge  203  is mounted between the base  190  and the eccentric shaft  174 . Rotation journaling blocks  207  are mounted in the eccentric grooves  205  and bear on the lower surface  209  of the bridge  203 . A nut  208  is screwed onto stud  210  to prevent the block  207  on the right hand side of  FIG. 14  from slipping off the shaft towards the right in  FIG. 14 . The stem  194  of the base  190  is journaled in bushes or bearings  211  and  212 . As is shown in  FIGS. 14 and 16 , the pin  170  passes through an arcuate slot  213  in the bridge  203 . The slot  213  is also shown in  FIG. 17 . The arcuate slot  213  enables the pin  170  to engage in the groove  201  of the base  190 , and also accommodates rotational movement of the pin  170 , base  190  and blade  34  relative to the fixed bridge  203 .  
         [0118]     As is shown in  FIG. 18 , the slot  213  in the bridge  203  communicates with an entrance slot  275  which merely facilitates assembly of the eccentric shaft  174  and pin  170  by enabling the pin  170  to slide in the direction of arrow Y in  FIG. 18  into the arcuate groove  213 , to in turn enable the eccentric shaft  174  to be positioned through the stem  194 . The bridge  203  is also provided with a slightly raised annular land  276  on which the blocks  205  sit, and which provide a surface for facilitating movement of the blocks  205  when the propeller blade is adjusted. In the embodiments shown, two separate blocks  205  are provided. However, in other embodiments, a singular annular continuous block  205  could be provided which sits on the land  276  and has opposed portions contoured to match the contour of the grooves  205  in the eccentric shaft  174 .  
         [0119]     When the claw  150  is moved to adjust the pitch of the propeller blades  34  in the manner previously described, the arm  162  is moved to the right or left in  FIG. 16 . This in turn causes the pin  170  to tilt in the plane of the paper of  FIG. 16  because of the relatively loose connection of the pin  170  in the socket  166 . The tilting movement of the pin  170  rotates the eccentric  174  about its axis, which pushes the base  190  downwardly in  FIGS. 14 and 16  against the bias of the spring washer  195  to release the bevel surface  192  of the base  190  from the bevel surface  159  of the hub mount  158 . The tilting movement of the pin  170  is into and out of the plane of the paper in  FIG. 14 .  
         [0120]     The eccentricity of shaft  174  in this embodiment is provided by the grooves  205  and the sliding blocks  207  so that rotation of the shaft  174  will tend to force the stem  194  downwardly against the bias of the washer  195 .  
         [0121]     With reference to  FIG. 16 , as the pin  170  tilts to the right or left to rotate the shaft  174  and remove the surface  159  away from the surface  192 , the shaft will eventually contact side surface  220  or  221  (depending on the direction of movement of the arm  162  and therefore of the tilting movement of the pin  170 ). Continued movement of the arm  162  will therefore rotate the base  190  about axis B shown in  FIG. 14 . It should be noted that the movement of direction of the pin  170  in  FIG. 14  is into and out of the plane of  FIG. 14 . Thus, when the pin contacts the surface  220  or  221 , the base  190  is rotated about the axis B.  
         [0122]     As previously mentioned in relation to the earlier embodiments, the rotation of the eccentric shaft  174  pulls the stem  194  downwardly a very slight amount in the order of one tenth of a millimeter. This movement removes the load from the surfaces  192  and  159  so that the load carrying surfaces on the sliding blocks  207  which run on a smaller radius can take over the load. The movement of the surfaces  159  and  192  are a sliding movement on one another with very little, if any, spacing between the surfaces. This is advantageous because it prevents sand and other small particles from entering the mechanism between the surfaces  192  and  159 . When the stem  194  does move downwardly slightly because of rotation of the eccentric  174 , load is shifted from between the surfaces  192  and  159  to the surface engagement between the eccentric  174  and the inner periphery of the opening in the stem  194  through which the eccentric  174  passes. As the eccentric  174  rotates, the load is transferred to the blocks  205  and  207  and in turn to the surface  209  of the bridge  203 . Thus, the load is transmitted from the larger diameter or radius defined by the surfaces  159  and  192  to a much smaller diameter defined by the blocks  207  and the surface  209  so that continued movement of the push rod can rotate the eccentric  174  and therefore the stem  194  about the transverse axis to adjust the pitch of the propeller blade  34 . When adjustment has completed, centrifugal force acting on the propeller blade  34  and the base  190  tends to push the blade  34  outwardly so that the eccentric  174  and pin  170  can move slightly, allowing the load to be retransferred to the surfaces  192  and  159  to lock the propeller blade in the pitch adjusted position. The spring  195  may facilitate some of the return movement of the eccentric  174  and  170 . However, centrifugal force is primarily responsible for the reengagement of the surfaces  192  and  159  so that the load between those surfaces lock the propeller blade  34  in the pitch adjusted position.  
         [0123]     Thus, whilst the spring washer  195  can be solely responsible for returning the shaft  174  and the pin  170  to the equilibrium position, this may also occur as a result of a slight fluttering of the blade  34  as the blade  34  settles at its adjusted position, and the centrifugal force which is supplied to the blade  34  and the base  190  when the propeller  32  is rotating.  
         [0124]     As is best shown in  FIG. 14 , the base  190  is provided with a screw threaded bore  280  which receives a bolt  281 . The bolt  281  projects into the hole  273  in the shaft  174  to locate the shaft  174  in place and prevent movement of the shaft to the left and right in  FIG. 14  to thereby prevent the shaft moving out of position during adjustment of the pitch of the propeller blades  34  when load is applied to the shaft  174  by the respective arm  162  and pin  170 .  
         [0125]      FIG. 19  shows a still further embodiment of the invention in which like reference numerals indicate like parts to those described with reference to  FIG. 14 . In this embodiment the surfaces  192  and  159  are substantially horizontal surfaces rather than inclined or cone-shaped, as in the previous embodiments, and are generally perpendicular to the axis about which the propeller blade  34  is adjusted.  
         [0126]     In this embodiment the blocks  207  are provided with ceramic surfaces  301  which may be glued to the blocks  207  simply to hold the surfaces  301  in position during assembly. The fixed bridge  203  is provided with an annular recess  302  into which is inserted an annular ceramic ring  303  on which the surface  301  sits. Thus, in this embodiment, when the eccentric  174  is rotated and the load is removed from the surfaces  159  and  192 , the load is transferred to the surfaces  301  and ring  303  and then through the bridge  203  to the mount  158 . Once again, the transfer of the load from the larger diameter or radius defined by the surfaces  159  and  192  to the smaller diameter defined by the blocks  207  and ring  303  makes adjustment of the pitch around the transverse axis possible, as in the embodiment of  FIG. 14 .  
         [0127]     In the embodiment of  FIG. 19  and the earlier embodiments, the base  190  is preferably formed from steel and the mount  158  from brass. The eccentric  174  is formed from brass and the blocks  207  from steel.  
         [0128]     In the embodiments described with reference to FIGS.  7  to  18 , exhaust from the motor  14  passes through the hub  32 . The bridge  203  may be provided with grooves  230  to assist in venting exhaust gas through the hub  32  to atmosphere. However, in other embodiments, the hub  32  could be sealed and the mechanism for adjusting the pitch of the propeller blades immersed in an oil bath, with the exhaust being vented to atmosphere other than through the hub  32 . Furthermore, the mechanism may have a different relative position of the pins  170 , eccentric  174  and the stem  194  to that shown in FIGS.  7  to  16 .  
         [0129]     In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise”, or variations such as “comprises” or “comprising”, is used in an inclusive sense, ie. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.  
         [0130]     Since modifications within the spirit and scope of the invention may readily be effected by persons skilled within the art, it is to be understood that this invention is not limited to the particular embodiment described by way of example hereinabove.