Abstract:
A mount for an outboard motor is disclosed in which the cylinder block of the motor is within the hull and the gear box and propeller are outside the hull. The drive shaft passes through the mount from the block to the gear box. The mount permits the motor to be swung about a horizontal axis to raise and lower the propeller. It also permits the motor to perform rotary steering oscillations about an inclined axis which passes through the propeller, or close to the propeller. Because the propeller is oscillated about an axis which passes through or close to it, it remains on the boat center line when the motor is turned for steering purposes and moves to a position in which the line of thrust is downwards.

Description:
FIELD OF THE INVENTION 
     THIS INVENTION relates to motor mounting structures for boats. 
     BACKGROUND TO THE INVENTION 
     Small water craft, meaning inflatable boats and rigid hulled boats of up to about eight meters, are usually powered by one (or more) outboard motors attached to a rear transom. The drive shaft of the motor is substantially vertical. At the lower end of the drive shaft there is a gear box through which drive is transmitted to a substantially horizontal propeller shaft. The main advantage of an outboard motor is that the power losses in the drive train between the crank shaft and the propeller shaft are small. The main disadvantages of an outboard motor are that it occupies space at the stern end of the deck thereby reducing available deck space, it is noisy and is unsightly. 
     Inboard motors are rarely found on the smallest boats where outboards are used almost exclusively. Larger boats use almost exclusively inboard engines. However, there is a size range (say from four meters to eight meters) where some boats have outboard motors and others have inboard motors. An inboard motor is entirely concealed within the structure of the hull and the boat is thus more aesthetically pleasing. The main disadvantage of the inboard motor is that the crank shaft of the motor rotates about a horizontal axis and the propeller shaft also rotates about a horizontal axis but at a lower level. Hence two sets of gearing, usually bevel gearing, and an intermediate shaft, are required to form a power train from the crank shaft to the propeller shaft. Power losses are hence substantial. For this reason inboard and outboard motors of the same rated power will provide substantially different powers at the propeller. As much as thirty percent more power can be lost in the drive train of an inboard motor than in the drive train of an outboard motor. 
     An inboard motor is approximately twice the weight of an outboard motor for the same power. 
     Motor mountings have been proposed in which the motor&#39;s block is within the hull of the boat, the drive shaft passing through a transom and there being a gear box and propeller externally of the hull. An example of a motor mounting of this type is found in U.S. Pat. No. 3,382,839. 
     The main object of the present invention is to provide a motor mounting which provides the boat with advantageous handling characteristics. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one aspect of the present invention there is provided, in combination, an outboard motor having a block, a housing extending downwardly from the block, a gear box within a lower part of said housing, a drive shaft extending from the block to said gear box, a propeller shaft extending rearwardly from said gear box and rotatable about an axis, and a propeller comprising a hub and blades protruding from the hub, the propeller being astern of said housing, a hull including an inclined transom, and means mounting said housing, drive shaft, gear box and propeller on said transom for oscillatory steering movements about an inclined axis which intersects, at a point of intersection astern of said housing, said axis about which the propeller rotates. 
     Said point of intersection is preferably between a front end of said hub and a rear end of said hub. 
     According to a further aspect of the present invention there is provided a boat having a hull including an inclined transom, an outboard motor and a mounting structure mounting said motor on said transom for rotary oscillatory steering movements about an inclined axis, a block of the motor being within the hull, a propeller of the motor being outside the hull and a drive shaft of the motor passing through the mounting from said block to drive said propeller, said propeller being mounted for rotation about a drive axis, said mounting structure including means permitting said motor to rotate about a horizontal axis to displace said propeller between a lowered operative position and a raised inoperative position, said inclined axis and said drive axis intersecting to the rear of a vertical line which intersects both said drive axis and said horizontal axis. 
     Said propeller preferably includes a hub having a front end and a rear end, said inclined axis intersecting said drive axis between said front and rear ends. 
     Hydraulic cylinders mounted between said motor and a fixed anchorage can be provided for displacing said motor in propeller lifting and lowering movements about said horizontal axis. 
     In the preferred form said mounting comprises an outer component mounted on said transom for rotary oscillation about said inclined axis and an inner component mounted on said outer component for rotary oscillation with respect to said outer component about said horizontal axis, said motor being carried by said inner component. 
     According to another aspect of the present invention there is provided, in combination, an outboard motor having a block, a propeller below and to the rear of the block in relation to the direction in which the motor travels, a drive shaft extending downwardly from the block to drive said propeller, the propeller being rotatable about a drive axis and having a hub with a front end and a rear end and blades protruding therefrom, and a mounting structure which includes means for permitting said motor to perform rotary oscillations about a horizontal axis to displace said propeller between a lowered operative position and a raised inoperative position, and means for permitting said motor to perform rotary steering oscillations about an inclined axis, said inclined axis intersecting said drive axis rearwardly of a vertical line which intersects said drive axis and said horizontal axis. 
     Said inclined axis preferably intersects said drive axis between said front and rear ends of said hub. 
     In a preferred form said mounting structure includes an outer component for attachment to an inclined transom of a boat, an intermediate component carried by said outer component and free to perform rotary steering oscillations with respect to said outer component about said inclined axis, and an inner component carried by said intermediate component and free to perform rotary oscillations with respect to said intermediate component about said horizontal axis. 
     According to yet another aspect of the present invention there is provided a boat having a hull, an outboard motor passing through an inclined rear transom of the hull with a block of the motor inside the hull and a propeller outside the hull and mounted on the transom for a first movement about a horizontal axis to enable the propeller to be lowered to an operative position and raised to an inoperative condition, and a second steering movement about an inclined axis which passes close to, or through, the propeller so that the propeller turns on itself thereby to minimise movement of the propeller off the centre line of the boat during steering. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: 
     FIG. 1 is a diagrammatic side elevation of an outboard motor and motor mount in accordance with the present invention; 
     FIG. 2 is a plan view, to a larger scale, of part of the motor mount of FIG. 1 
     FIG. 3 is a detail of a mounting ring and associated structure; 
     FIGS. 4 and 5 are diagrammatic side elevations showing a motor and motor mount with the motor in lowered and raised positions respectively; and 
     FIG. 6 is a view of the motor and motor mount of FIGS. 4 and 5 as seen from the rear of the boat. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring firstly to FIG. 1, reference numeral  10  designates the hull of a boat, the hull including a stern portion  12  and a deck  14 . Part of the stern portion  12 , this part being designated  16 , forms a transom and lies at an angle to the horizontal. The preferred angle is between 35° and 45°. 
     An outboard motor designated  18  is mounted on the transom  16 , the engine block  20  being within the hull  10 . The drive shaft  22  of the motor passes through the transom  16 , and the gear box  24  and propeller  26  of the motor are external of the hull  10 . The lowermost part of the shaft  22  and gear box  24  are within a vertically elongate fairing  25  which also houses the propeller shaft  27 . A skeg  29  protrudes downwardly from the fairing  25 . The propeller  26  comprises a hub  31  and blades  33  protruding from the hub  31 . 
     Between the block  20  and the gear box  24  there is a motor mount generally designated  28 . The motor mount comprises a rotatable ring  30 , the inclined axis about which the ring  30  can rotate being shown at X. The ring  30  forms the external component of a gimbal, the internal component of the gimbal being constituted by a structure which is generally designated  32 . 
     The ring  30  is sandwiched between non-rotatable upper and lower rings  34 ,  36  (see FIG.  3 ), there being ball or roller bearings  38  and  40  between the ring  30  and the rings  34  and  36 . 
     Surrounding the rings  30 ,  34  and  36  and the bearings  38  and  40  is a split collar  42 , the two halves of the collar  42  being secured together by means of studs  44 . The split collar has an internal recess  46  which receives the peripheries of the three rings  30 ,  34  and  36 . The collar includes four pairs of lobes  48  and  50  (see FIGS.  2  and  3 ). The lobe  50  of each pair is formed with a threaded bore  52  and the other lobe  48  of each pair is formed with a socket  54  for receiving the Allen head of a bolt  56 . Each bolt  56  passes through the transom  16  of the hull  10 , the head of each bolt  56  being in one of the sockets  54  and the shaft of each bolt  56  being screwed into one of the bores  52 . 
     O-ring seals  58  encircle the rings  34  and  36  and seal between these rings and the split collar  42 . Packings  60  and  62  seal between the split collar  42  and the transom  16  and around the bolts  56  respectively. 
     The structure  32  comprises a disc  35  and a casing designated  64  which is entirely surrounded by the disc  35 . Opposite end parts  64 . 1  of the casing  64  are of part spherical form and the wall parts  64 . 2  which join the wall end parts  64 . 1  are flat (see FIG.  2 ). At two diametrically opposed locations (see FIG. 2) there are tapered bolts  66  which secure the disc  35  to the ring  30 . The heads of the bolts  66  are in recesses in the outer periphery of the ring  30  and the bolts pass radially through the ring and into the blind bores in the disc  38 . This enables the structure  32  to pivot about the axis designated Y. This axis is indicated as a line in FIG.  2  and is shown as a dot in each of FIGS. 1 and 3 as it is at right angles to the plane of the drawing. 
     Internally of the casing  64  the structure  32  comprises a sleeve  70 . Within the sleeve  70  there are longitudinally extending ribs  72  and a tube  74  (only shown in FIG.  2 ). The drive shaft  22  passes through the tube  74 . Upper and lower bearings  76 ,  78  for the shaft  22  are mounted at the upper and lower ends of the tube  74 . The casing  64  and sleeve  70  extend downwardly to the region of the propeller  26 . The space within the sleeve  70  is, at its upper end, connected to the exhaust port of the engine. Thus exhaust gasses from the engine flow downwardly through the vertical passageways bounded by the sleeve  70 , ribs  72  and tube  74  to escape below water level. The exit from these vertical passageways is designated  80  in FIG.  1 . 
     The casing  64  forms a water jacket that encircles the exhaust gasses sleeve  70 . A water pump (not shown) located within the fairing  25  pumps water upwardly through casing  64  (the water inlet to the casing  64  being shown at  82 ) and into the motor for cooling purposes. The water escapes from the motor through the normal outlet ports provided. 
     The disc  35 , casing  64  and sleeve  70  are connected together by means of tapered pivot pins  84  (FIG.  2 ). The pins  84  enter bosses  85  protruding from the sleeve  70 . The casing  64  and sleeve  70  are not only free to rotate about the axis of the shaft  22  but are also able to tilt about the axis Y with respect to the disc  35 . The motor can thus be tilted. 
     An hydraulic cylinder  86  (FIG. 1) is connected between an anchorage  88  on the ring  30  and an anchorage  90  on the structure  32 . In FIG. 1 the hydraulic cylinder  86  is shown in its retracted condition. When extended it pushes the lower part of the structure  32  to the right thereby tilting the motor  18 , the structure  32 , the gear box  24  and the propeller  26  about the axis Y. 
     A steering arm  92  protrudes from the disc  35 . Movement of the steering arm  92  to the left or right as viewed in FIG. 2 turns the motor  18 , gear box  24  and propeller  26  about the axis X. 
     Referring to FIGS. 4 to  6 , reference numeral  110  designates the hull of a boat, the hull including a stern portion  112  and a deck  114 . Part of the stern portion  112 , this part being designated  116  and forming a transom, lies at an angle to the horizontal. The preferred angle is between 35° and 45°. 
     An outboard motor designated  118  is mounted on the transom  116 , the motor&#39;s block  120  being within the hull  110 . The drive shaft  122  of the motor passes through the transom  116 , and the fairing  125 , the propeller  126  and the skeg  129  are external of the hull  110 . The shaft  122  is indicated by means of its centre line only and it will be noted that it is inclined to the vertical at an angle of about 60 degrees. In FIGS. 1 to  3  the drive shaft  22  is vertical and co-axial with the ring  30 . In FIGS. 4 to  6  the drive shaft is offset in the forward direction from the axis of the ring  130 . 
     Between the block  120  and the gear box  124  there is a motor mount generally designated  128 . The motor mount comprises a rotatable ring  130 , the axis about which the ring  130  can rotate being shown at X. The ring  130  forms an external component of a gimbal, an internal component of the gimbal being constituted by a structure generally designated  132 . 
     The ring  130  is sandwiched between non-rotatable upper and lower rings  134 ,  136 , there being ball or roller bearings (not shown) between the ring  130  and the rings  134  and  136 . The rings are mounted on the transom  116  by means of a split collar  142 . 
     The structure  132  includes an outer casing  164  of part spherical form. The structure  132  is mounted on the ring  130  as described above with reference to FIGS. 1 to  3 . 
     Parallel hydraulic cylinders  186  are connected between anchorages  188  on the ring  130  and anchorages  190  on the structure  132 . The cylinders  186  lie on opposite sides of a heel plate  194  forming part of the structure  132 . In FIG. 4 the hydraulic cylinder  186  is shown in its retracted condition. When extended it pushes the lower part of the structure  132  to the right thereby tilting the motor  118 , the casing  132 , the gear box  124  and the propeller  126  about the axis Y from the position shown in FIG. 4 to the position shown in FIG.  5 . 
     Operation of the motor will now be described by way of example with reference to FIGS. 4 to  6 . In normal operation the motor is positioned as shown in FIG. 4, or possibly slightly trimmed down from the position illustrated. The line of thrust is thus horizontal or, if the motor is trimmed down, at a shallow angle to horizontal. In this latter arrangement the thrust pushes the stern of the boat down and lifts the bow. The cylinders  186  shown in FIG. 4 are in their retracted positions and hold the motor  118  in the position shown. Trimming down the motor involves feeding hydraulic fluid to the left hand ends of the cylinders  186  to tilt the motor anti-clockwise through a few degrees. 
     To displace the motor to its raised, inoperative position behind the transom  116  (FIG.  5 ), the hydraulic cylinders  186  are fully extended. The motor  118  and casing  132  pivot about the axis Y whilst moving between the operative and retracted positions. 
     The X axis, the axis about which the ring  130  rotates, as clearly seen in FIG. 4, intersects the axis Q of the propeller shaft at a position just to the rear of the propeller  126 . The position of the point of intersection varies with the transom angle. If the angle is less than that shown, which is about  45  degrees, the point of intersection moves to the left in FIG. 4. A transom angle of about 35 degrees is the minimum that achieves the objects of the invention. At any lesser angle the point of intersection is ahead of the hub  131  on which the propeller blades  133  are mounted and, for the reasons set out below, the advantages which are obtained with a transom angle of above 35 degrees are lost. Preferably the point of intersection is between the front and rear ends of the hub  131 . 
     When the motor  120  is rotated about the axis X to turn the boat, the fact that the propeller is intersected by the axis X means that it turns on itself rather than moving along an arc. Movement of the propeller along an arc would result from the axis X intersecting the axis Q too far forward or too far astern of the propeller. In other words, a transom angle which is too big or too small displaces the point of intersection too far from the propeller. Because the propeller rotates about an axis passing through it, it remains on the boat&#39;s centre line. 
     The fairing  125  which contains the gear box and water pump, and downwardly from which the skeg  129  projects, moves in an arc which lies parallel to the ring  132 . The fairing thus moves to a position which is skewed with respect to the direction in which water flows past the boat. The flowing water impinges on those sides of the fairing  125  and skeg  129  which are presented to it, and the lateral component of the resultant force on the fairing and skeg turns the boat. The turning force is thus exerted on the leading edge of the fairing and skeg rather than on the trailing edge. 
     The fairing and skeg also tilt because the axis about which they have been rotated is inclined. This means that the skeg and fairing surfaces which the water flowing under the boat impinges upon face downwardly and the flowing water thus exerts an upward force on them. There is thus, during turning, an upward force exerted on the rear of the boat. This upward force tends to lift the rear of the boat and push the front down. This inhibits “flipping” of the boat during a tight turn. 
     Because the propeller does not move in an arc, but merely turns about an axis passing through it, torque forces are reduced and experimental work has shown that the propeller is less prone to cavitation.