Stern drive

A drive mechanism for a boat having the motor located inboard. The mechanism disclosed includes a gearbox located outboard of the transom with an input shaft extending toward the inboard motor and an output shaft extending aft toward a propeller shaft. A universal joint coupling is provided to drive the propeller shaft while a gimbal ring is employed to universally mount a propeller shaft housing such that the propeller may be used for steerage as well as forward thrust. The gearbox is disclosed as including a first gear pair capable of being changed to provide different output ratios. A second drive link in the gearbox gives a selection of directions of rotation of the propeller shaft. In a first instance, a gear pair is employed. In a second instance, a chain drive is employed. Access is provided into the gearbox by a plate located between the gearbox and the transom. This plate provides a mounting for the drive links within the gearbox. Another gearbox having a single gear pair is also disclosed for lowering the level of the propeller shaft relative to the boat hull.

BACKGROUND OF THE INVENTION 
The field of the present invention is drive mechanisms for power boats. 
More specifically, the present invention is directed to mechanisms for 
transmitting power from an inboard motor of a power boat to a propeller. 
A variety of mechanisms for providing power to a propeller for driving a 
boat have been employed, both successfully and unsuccessfully, since at 
least the 1800's. Two general categories of such devices employed with 
inboard motors have developed. Early on, fixed propeller shafts were 
developed which generally required a second mechanism, a rudder, for 
steering. More recently, devices known as inboard-outboards or stern 
drives have been developed which employ an articulated propeller shaft 
coupled with an inboard motor. These devices do not generally require 
additional steering mechanisms as the thrust from the propeller or 
propellers may be directed to effect steering much as a conventional 
outboard motor is employed. 
Two mechanisms may be considered representative of the types of stern 
drives presently available. The first is illustrated in the North patent, 
U.S. Pat. No. 3,136,287. This device employs a horizontal input shaft, a 
vertical power transmission shaft, and a horizontal propeller shaft. This 
type of stern drive provides certain advantages of outboard motor 
flexibility and steering control. However, vertical shaft stern drives are 
typically rather inefficient because of the required gearing. The second 
type is represented by the Adams et al. patent, U.S. Pat. No. 3,933,116. 
This patent employs an inclined shaft from the inboard motor to an 
outboard, articulated propeller shaft. For reasons pointed out below, the 
engine disadvantageously must be placed low in the bilge, must be inclined 
and must be forward in the boat, particularly if gearing is required. 
Coincident with the development of power trains for boats, improved 
propeller performance has also been achieved. To date, it is understood to 
be beneficial to run the propeller of high speed, competition type boats 
only about 55% submerged in the water. It is also believed to be 
beneficial to have the axis of the propeller angled downwardly relative to 
the keel line by a maximum of about two to three degrees. Finally, a 
factor affecting the overall performance of the propeller and the hull is 
to have a relatively low center of thrust. Because of these desirable 
factors for high speed performance, the inboard motor of the Adams et al. 
device must be located low, at an angle, and as far forward as possible. 
The North type stern drive is better able to accomplish a desired 
propeller orientation. However, as mentioned above, substantial efficiency 
is lost in the power train. 
SUMMARY OF THE INVENTION 
The present invention is directed to a power train for a boat having an 
inboard motor and a stern drive propeller. The invention includes a gear 
box located exterior to the hull for achieving the proper propeller 
attitude relative to the hull without the inefficiency of circuitous drive 
train lengths. This result accomplished by the present invention is 
achieved through the employment of an outboard gear box having parallel 
shafts each positioned in a generally horizontal orientation and being 
positioned relative to one another in a generally vertical arrangement, 
the lowermost of the shafts being the output shaft. 
The arrangements contemplated by the present invention do not achieve the 
appropriate orientation of the propeller shaft at the expense of inboard 
motor placement. Instead, the present system also improves the placement 
of the inboard motor by allowing it to be positioned as far aft as the 
inboard side of the transom. It is also contemplated that the inboard 
position of the motor will be substantially horizontal relative to the 
hull and may be located up out of the bilge. In spite of this more 
advantageous placement of the inboard motor, the center of thrust is 
located low in the stern and is not tending to force the stern up and bow 
down. 
The devices contemplated by the present invention also may enjoy other 
advantages. The outboard location of the gear box removes the gear box 
from the relatively stagnant, heated environment of the engine compartment 
and places it in a position to receive both water and air cooling. The 
gear box housing may be arranged to avoid exposed joints by employing a 
unitary structure with an access plate located between the gear box and 
the transom. When a configuration is selected employing a high location of 
the input to the gear box, an improved inboard motor position and a 
protected access plate, the sealing problems are reduced to the area of 
the output shaft, a problem long overcome in more conventional 
arrangements. 
In the embodiment employing the gearbox having an input shaft, an output 
shaft and an intermediate idler shaft, two selectable features may be 
employed. Between the idler shaft and one of the input and output shafts a 
gear pair selected from a plurality of available gear pairs may be 
employed to select the appropriate stepdown in speed to achieve the 
maximum efficiency of both the engine and the propeller under any given 
conditions. The other link with the idler shaft may be employed as a 
device for selecting direction of rotation of the propeller. To this end, 
either a gear pair or a chain and sprocket arrangement may be selected. 
The gear pair naturally causes counter-rotation of the shafts supporting 
the gear pair while the chain and sprocket arrangement results in shaft 
rotations in the same direction. 
In the context of competitive boating, time considerations can become 
significant. To enhance the ease of gear ratio and direction changes, an 
embodiment of the present invention may employ the access plate referred 
to above as a bearing support for one end of each of the input, idler and 
output shafts. By simply removing the access panel, the gear wheels and 
sprocket wheels are immediately accessible for quick removal and 
replacement. 
Accordingly, it is an object of the present invention to provide an 
improved drive train for a stern drive. Other and further objects and 
advantages will appear hereinafter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Turning in detail to the drawings, FIGS. 1 and 2 illustrate the arrangement 
of a first embodiment of the present invention in association with a hull 
10. The hull 10 includes a transom 12. The hull illustrated in FIG. 1 may 
represent either of two configurations. The first configuration would be 
that of a small boat wherein the drive is positioned centrally in the 
hull. In a second configuration, the portion of the hull illustrated may 
simply be the port side thereof. In such an event, a link, shown in 
phantom as 14, may be employed to control a second stern drive located on 
the starboard side of the hull. 
Located inboard within the hull 10 is an inboard motor 16. Consistent with 
this preferred embodiment of the present invention, the inboard motor 16 
is illustrated as being horizontally disposed relative to the hull 10 and 
positioned well out of the bilge. A hole 17 provides access between the 
motor and the stern drive. 
In the embodiment of FIGS. 1 and 2, a gearbox, generally designated 18, is 
securely positioned to the outboard side of the transom 12. The gearbox 18 
includes a gear box housing 20 which is generally configured in a 
functional manner to enclose the drive train and to provide structural 
support for the articulated propeller shaft housing. The gearbox 18 is 
held to the transom 12 by conventional means such as bolts. The bolts are 
distributed about the gear box housing 20 for optimum support and sealing 
with the transom 12. Where necessary, such as at location 22, clearance is 
made for facile placement of the bolts. The housing 20 generally includes 
a flange 24 which receives the fastening means. 
Turning to the arrangement of the drive train within the gearbox housing 20 
as illustrated in FIG. 4, an input shaft 26 extends forward from the 
gearbox 18 for access through hole 17 to the inboard area of the hull 
where it is coupled to receive power from the inboard motor 16. The actual 
coupling between the motor 16 and the input shaft 26 is via a universal 
joint 28. Any conventional form of attachment may be employed to affix the 
U-joint 28 to both the output shaft of the inboard motor 16 and the input 
shaft 26 of the gearbox 18. In the present embodiment, splines are 
illustrated. The U-joint 28 is held on the splines of the input shaft 26 
by means of a stud and bolt assembly 30. The employment of the U joint 28 
gives certain convenience advantages. The U joint allows the inboard motor 
location and orientation to be less critical. With the use of the U joint 
28, bearing failure from shaft misalignment of the motor 16 is avoided. In 
fact, the inboard motor 16 may be intentionally placed at some angle 
relative to the input shaft 26 where convenient. Furthermore, fore and aft 
placement of the inboard motor 16 is less critical if the splines of the 
drive shaft from the inboard motor 16 are allowed to telescope in and out 
of the U joint 28. Not only is initial placement of the inboard motor 16 
greatly simplified by the U-joint 28, the structural rigidity of the hull 
is not so critical. Naturally, boat hulls are designed to exhibit a 
certain amount of elastic strain. To attempt to design a hull to prevent 
such substantial elastic strain would greatly increase the weight of the 
boat even if such a goal was possible. Consequently, this stern drive must 
experience substantial relative movement between the gear box 18 and the 
inboard motor 16. The U-joint 28 accommodates this elastic strain. 
The input shaft 26 extends through an access plate 32 which, in this 
embodiment, is positioned between the gearbox 18 and the transom 12. In 
this way, the joint between the access plate 32 and the gearbox housing 20 
is protected from the harsh water environment in which the present 
invention is designed to be used. The access plate 32 provides for 
convenient ratio and direction of rotation selection as will be more fully 
discussed below. 
The input shaft 26 is supported by a ball bearing 34 held within the access 
plate 32 by means of a split ring retainer 36. The other end of the input 
shaft 26 is supported in a bearing cavity provided in the gear box housing 
20 by a roller bearing 38. The roller bearing 38 may be conveniently press 
fit into the cavity provided therefor. A seal 40 forms an appropriate 
closure around the input shaft 26. 
Located centrally in the gear box 18 is an idler shaft 42. The idler shaft 
42 is supported at each end by roller bearings 44 and 46. The roller 
bearings 44 and 46 are positioned in the access plate 32 and the gear box 
housing 20 respectively. 
Located in the lower portion of the gearbox 18 is an output shaft 50. The 
output shaft 50 is supported at a first end in the access plate 32 by 
means of a roller bearing 52. At the output end of the output shaft, a 
ball bearing 54 is employed. The ball bearing 54 is held in place by a 
split ring retainer 56 while the output shaft 50 is held relative to the 
ball bearing 54 which, as is true of ball bearing 34, is capable of 
resisting axial loading. Outwardly of the ball bearing 54 are seals 60 and 
62. The output shaft 50 extends aft relative to the hull to provide aft 
access for coupling with the propeller shaft to provide power from the 
inboard motor 16 as driven through the gearbox. 
To provide power through the gear box 18, the input shaft 26 and the idler 
shaft 42 include a first gear pair including gear wheels 64 and 66. The 
gear wheels 64 and 66 may be replaced by other gear pairs to provide gear 
ratio selection. The gear wheel 64 of the ratio selectable gear pair is 
constrained to rotate with the input shaft 26 by means of splines 68. 
Split ring retainers 70 and 72 retain the gear wheel 64 in position on the 
splines 68. The gear wheel 66 is similarly associated with splines 74 on 
the idler shaft 42. A plurality of spacing washers 76 provide axial 
spacing for the gear wheel 66 as well as the idler shaft 42. Coupling the 
idler shaft 42 with the output shaft 50 is a direction selectable drive 
assembly which may be provided either by a chain coupling as illustrated 
in FIG. 4 or a second gear pair as illustrated in FIG. 7. The choice 
between the chain coupling of FIG. 4 and the gear pair of FIG. 7 
determines the direction of rotation of the output shaft 50 but otherwise 
provides little difference in operation. 
To accommodate the chain coupling of FIG. 4, the idler shaft 42 includes an 
extended splined shoulder to couple with a first sprocket wheel 78. A 
second sprocket wheel 80 is located on a splined portion 82 of the output 
shaft 50. The first sprocket wheel 78 is positioned axially by means of 
the spacing washers 76 while the second sprocket wheel 80 is held axially 
from the access plate 32 by means of spacers 84. Coupling the sprocket 
wheels 78 and 80 is a chain 86. The chain coupling provided by the 
sprocket wheel 78 and 80 and the chain 86 causes the idler shaft 42 and 
the output shaft 50 to rotate in the same direction. 
The second gear pair illustrated in FIG. 7 may be employed to replace the 
chain coupling of FIG. 4 when rotation of the output shaft in the opposite 
direction is desired. The gear pair of FIG. 7 includes gear wheels 88 and 
90 fixed to the splines 74 and 76 of the idler shaft 42 and output shaft 
50 respectively. Additional spacing to properly locate this second gear 
pair of the direction selectable drive assembly is provided by washers 92 
and 94. Through this gear pair, the idler shaft 42 and the output shaft 50 
rotate in different directions. 
As indicated above, the access plate 32 provides a convenient means for 
changing either the gear ratio of the gearbox 18 or the output direction. 
With the entire stern drive assembly removed, the access plate 32 may be 
disassembled from the gearbox housing 20 by removal of fasteners 96. This 
removal of the access plate 32 exposes the ends of the idler shaft 42 and 
the output shaft 50 and removes the input shaft 26. Quick replacement of 
the couplings between any of the shafts may then be effected. 
The location of the three shafts, the input shaft 26, the idler shaft 42, 
and the output shaft 50, are conveniently arranged in the preferred 
embodiment along parallel, substantially horizontal axes. The parallel 
nature of these shafts avoids the necessary inefficiency associated with 
beveled gears and the like. The substantially horizontal arrangement 
requires only small angles of bending of the U-joints associated with this 
stern drive between the inboard motor 16 and the gearbox 18 and between 
the gearbox 18 and the propeller. Small angles through which the U-joints 
must operate adds to their efficiency and longevity of operation. The 
three shafts are also positioned in a vertical arrangement with the input 
shaft 26 above the idler shaft 42 which is in turn above the output shaft 
50. This vertical arrangement provides for a placement of the inboard 
motor 16 above the bilge of the boat and for the delivery of output power 
about a horizontal shaft very near the keel line of the hull. In fact, in 
the preferred embodiment the output shaft 50 is placed just far enough 
above the inner section of the keel and the transom so that the housing 20 
of the gear box 18 does not extend below the end of the transom to create 
additional drag. 
Located aft of the gearbox 18 is a propeller shaft housing generally 
designated 98. The housing of the embodiment illustrated in FIGS. 1, 2 and 
4 includes a propeller shaft 100 rotatably mounted therein. The propeller 
shaft 100 is mounted at its forward end in a thrust bearing 102. The 
propeller shaft 100 is fixed relative to the thrust bearing 102 by means 
of a split ring retainer 104 and a shoulder 106 on the shaft. The bearing 
102 and the interior of the propeller shaft housing 98 is protected by a 
plurality of seals 108 held in place by a retainer cap 110 and fasteners 
112. At the aft or distal end of the propeller shaft 100, it is rotatably 
mounted in the propeller shaft housing 98 by a roller bearing 114. A 
plurality of seals 116 protect the distal end of the propeller shaft 
housing 98 from water intrusion. A cap 118 and a split ring retainer 120 
retain the seals and bearing in position. A propeller 122 is 
conventionally mounted to the end of the propeller shaft 100. The 
propeller shaft housing 98 is fixed to a mount 124 which, in this 
embodiment, is formed as an integral part of the gear box housing 20. If 
no gear box is employed, the mount 124 may be directly affixed to the 
transom 12. Coupled to the mount 124 is a mounting means for retaining the 
propeller shaft housing 98 yet allowing the housing 98 universal pivotal 
motion such that the propeller shaft housing 98 may be pulled up out of 
the water or extended down further into the water or may be pivoted 
laterally for steering. Appropriate portions of the mount 124 and the 
propeller shaft housing 98 are cut away to provide the necessary clearance 
for such movement. The mounting means includes in this preferred 
embodiment of a gimbal ring 126. Gimbal lugs are formed on each of the 
mount 124 and the propeller shaft housing 98 to receive the gimbal pins 
128 of the gimbal ring 126. The gimbal lugs are split and include lug caps 
130 on both the mount 124 and the propeller shaft housing 98. 
The propeller shaft housing 98 is gimbaled to the mount 124 concentrically 
about a coupling means for transmitting power from the output shaft 50 to 
the propeller shaft 100. This coupling means accommodates a range of 
colinear and non-collinear orientations of the two shafts and, in the 
present embodiment, is provided by a universal joint generally designated 
132. The universal joint 132 is directly coupled to both the output 50 and 
the propeller shaft 100 in a conventional manner. 
To protect the gimbal 126 and the universal joint 132, it is contemplated 
that a boot (not shown) be positioned in sealed engagement with the mount 
124 and extending into a similar sealed engagement with the propeller 
shaft housing 98. In this way, moisture can be excluded from the area of 
both the mounting and coupling means for the gimbaled propeller shaft. The 
boot, of course, requires substantial flexibility to accommodate the 
gimbaled motion of the propeller shaft housing 98. 
In an alternate embodiment illustrated in FIGS. 3 and 8, a gear box is also 
located within a modified propeller shaft housing 134. The modified 
propeller shaft housing includes an input shaft 135 and an output shaft 
136. Together the input shaft 135 and the output shaft 136 combine to form 
a propeller shaft assembly. A gear pair consisting of gear wheels 138 and 
140 couple the propeller shafts 135 and 136 together. The input propeller 
shaft 135 is mounted at a first end by a ball bearing 142 and at a second 
end by a roller bearing 144. The ball bearing 142 is retained by a 
shoulder 146 and a split ring retainer 148. A spacer 150 and another split 
ring retainer 152 retain the gear wheel 138 in position. The gear wheel 
138 is caused to rotate with the shaft 135 by means of a coupling with 
splines 154. 
The output propeller shaft 136 is rotatably mounted in the propeller shaft 
housing 134 by means of two ball bearings 158 and 160. The gear wheel 140 
is held in place on the shaft 136 by means of a spacer 162 and a split 
ring retainer 164. Splines 166 insure coupled rotation of the gear wheel 
140 with the shaft 136. At the distal end of the output propeller shaft 
136, the same sealing arrangement is employed as was described with regard 
to the device of FIG. 4. 
The gear pair provided by gear wheels 138 and 140 are employed in the 
modified propeller shaft housing 134 to lower the center of thrust of the 
stern drive without inducing further angular offset with the keel line. At 
the location where the gear pair is arranged, less drag is encountered 
than if the gear box 18 were to be positioned such that it extended below 
the bottom of the transom 12. Thus, improved propeller performance is 
achieved with out substantially increasing the drag of the stern drive in 
the water. 
Naturally, the propeller shaft housing 134 is configured as narrow as 
possible about the gear pair located therein. The propeller shaft housing 
134 is split in a plane substantially normal to the axis of the propeller 
drive. Fasteners 168 are employed to retain the two portions of the 
propeller shaft housing 134 together and sealed. 
Applicable to both of the preferred embodiments illustrated are the 
steering and attitude control mechanisms. In each case, a boss 170 is 
provided on the upper side of the propeller shaft housings 98 and 134. A 
control bracket 172 is pivotally mounted on the boss 170 by means of a 
clevis and clevis pin assembly 174. To this control bracket 172 are 
coupled an attitude control hydraulic cylinder 176 and a steering control 
hydraulic cylinder 178. Also link 14 may be coupled with the control 
bracket 172 when a dual stern drive arrangement is employed. The steering 
cylinder 178 is then fixed by means of a conventional mount 180 to the 
transom 12. The attitude cylinder 176 is coupled to a plurality of 
mounting brackets 182 located on the upper portion of the gearbox housing 
20. Thus, the gimbaled propeller may be controlled in all directions by 
conventional hydraulics. 
Also on each of the embodiments of propeller shaft housings 98 and 134 are 
fins available for further control. A dorsal fin 184 extends upwardly to a 
horizontal propeller guard 186. A skeg 188 extends downwardly from the 
main portion of the propeller shaft housing. 
Thus, an improved stern drive arrangement is here disclosed. 
While embodiments and applications of this application have been shown and 
described, it would be apparent to those skilled in the art that many more 
modifications are possible without departing from the inventive concepts 
herein. The invention, therefore, is not to be restricted except by the 
spirit of the appended claims.