Abstract:
An inboard propeller drive system for shallow water boats comprising a stern tunnel and a propeller drive shaft sub-assembly. The tunnel protrudes upwardly from the floor of the boat, and has an S-shaped bottom plate immersed in water. The sub-assembly includes a housed drive shaft, a propeller, a cavitation plate, and a steering mechanism. The forward end of the sub-assembly is pivotally mounted on opposing inner walls of the tunnel. A universal joint connects the forward end of the drive shaft to the output shaft of an inboard engine. A control shaft extends from the forward end of the sub-assembly to the exterior of the tunnel. The control shaft may be rotated by a user-controlled actuator to raise and lower the sub-assembly, thereby pre-determining the depth of the propeller. Encounters with submerged objects may also cause the sub-assembly to rotate upwardly to prevent propeller damage.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to propeller drive systems for boats which are especially adapted for use in shallow and weed-infested water. More specifically, the invention pertains to a pivotally suspended, variable depth, propeller drive system for boats, employing a stern tunnel within the floor of the boat, housing a propeller drive sub-assembly. 
     2. Description of the Prior Art 
     The prior art teaches a variety of different approaches for powering water craft in shallow waters. For example, in U.S. Pat. No. 1,473,832, a tunnel housing a propeller mechanism, is hingeably mounted upon the bottom, stern portion of a boat. When a shoe member, mounted below the tunnel housing, encounters an object, the tunnel housing swings upwardly. RE. 24,451, issued to Daniels, shows a swingable boat propulsion and steering unit, for use in shallow waters. In U.S. Pat. No. 4,089,289, granted to Sauder, a propeller drive assembly, including a pair of universal joints, is pivotally mounted and movable through a vertical plane. U.S. Pat. No. 5,791,954, issued to Johnson, Jr. shows a vertically adjustable propeller and rudder drive. A trimmable marine drive apparatus is disclosed in U.S. Pat. No. 6,482,057, granted to Schoell. A fin assembly for use with power boats, is shown in U.S. Pat. No. 4,088,091. U.S. Pat. No. 3,469,558, granted to Puretic, discloses a marine propulsion unit having a longitudinal tunnel surrounding a hollow tube with a drive shaft passing through. 
     The need exists, however, for a propeller drive system for a boat, which is selectively adjustable to a predetermined operational depth; 
     The need further exists for a propeller drive system having a electric actuator system for selectively determining the propeller&#39;s operational depth; 
     The need also exists for a propeller drive system for a boat which dynamically and automatically adjusts under forward motion of the boat, to an optimum operational depth for the propeller; 
     The need also exists for propeller drive system which is pivotally suspended to avoid damage to the propeller in the event the drive system encounters an underwater object; 
     The need also exists for a propeller drive system which includes a damper in the safety pivoting mounting system to dampen vertical excursions of the drive system; 
     The need also exists for a propeller drive system using either an air cooled or a self-contained water cooled inboard engine, to eliminate an engine cooling system which is susceptible to mud and weed clogging. 
     These and other objects will be described below in the drawings and the detailed description of the preferred embodiment to follow. 
     SUMMARY OF THE INVENTION 
     An inboard propeller drive system for shallow draft boats. The system includes a stern tunnel in the floor of the boat and a propeller drive sub-assembly having its forward end pivotally suspended within the stern tunnel. The stern tunnel protrudes upwardly from the boat&#39;s floor, and includes side walls, a forward end wall, and an upper cover. The bottom portion of the tunnel has an upwardly and rearwardly inclined bottom plate, having a gradual S-shaped configuration. The rear end portion of the tunnel is open, for rearward discharge of the propeller&#39;s wash. A tunnel hood extends rearwardly from the rear end of the stern tunnel. 
     The propeller drive sub-assembly includes a drive shaft housing. A drive shaft extends entirely through the housing, having a forward end connected to a constant velocity joint and a rearward end upon which a propeller is mounted. A deflector skag is located on the lowermost portion of the drive shaft housing, immediately beneath the propeller. The sub-assembly also includes a cavitation plate mounted to the drive shaft housing, and extending above the propeller. Lastly, a steering mechanism is mounted on the rearmost portion of the cavitation plate. The steering mechanism includes a rudder positioned rearwardly from the propeller, and a lever arm interposed between the rudder support shaft and the steering linkage of the boat. 
     An intermediate portion of the drive shaft housing passes through an elongated slot in the bottom plate of the stern tunnel. The slot is sized and configured to accommodate upward and downward excursions of the drive shaft housing through a vertical plane. 
     An inboard air cooled or self-contained water cooled engine is provided forwardly from the forward end wall of the stern tunnel The engine includes a rearwardly directed output shaft which passes through the end wall and interconnects to the universal joint and the drive shaft. 
     The forward end of the sub-assembly includes a suspension yoke, having a support shaft and a control shaft. Both shafts extend laterally to respective bearings on opposing inner walls of the tunnel, thereby pivotally suspending the sub-assembly within the stern tunnel. 
     The yoke control shaft passes through its bearing to the exterior of the tunnel. A sprocket is located on the exterior end of the control shaft. A chain has one end encircled around a portion of the sprocket. The other end of the chain is connected to the translatable shaft of an electric screw-drive actuator. When the shaft of the actuator is withdrawn, the sprocket and control shaft are rotated counter-clockwise, raising the propeller. When the shaft of the actuator is extended, gravity rotates the propeller drive sub-assembly downwardly, thereby lowering the propeller. In this manner, with the boat at rest, the depth of the propeller in the water may be may be pre-determined by the user to suit the operational conditions. 
     Normally, the propeller drive sub-assembly is maintained in a lowered position when the boat is at rest. However, with the boat underway and gaining speed, hydraulic forces from water flowing upwardly through the stern tunnel impress upward forces upon the cavitation plate. The propeller drive subassembly thereby pivots upwardly to an extent determined by the speed of the boat. A limit stop within the tunnel hood prevents the sub-assembly from raising higher than a pre-determined limit. 
     In the event that the deflector skag encounters either the bottom or an object on the bottom, the upward forces which are generated will pivot the entire sub-assembly upwardly. Once the obstacle has passed, the sub-assembly will pivot downwardly under gravity to its pre-determined depth. A pneumatic or hydraulic damper extends between the sprocket and the tunnel sidewall, to dampen the harshness of vertical excursions of the sub-assembly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a boat fitted with the pivotally suspended, variable depth, propeller drive system present invention; 
     FIG. 2 is a fragmentary, perspective view of the stern tunnel and the rearwardly extending portion of the propeller drive shaft sub-assembly, a section of the drive shaft housing being broken away to reveal the drive shaft; 
     FIG. 3 is a side elevational view of the stern tunnel, showing the sprocket on the exterior end of the control shaft, the screw drive actuator and chain, the damper, and the limit switch assembly; 
     FIG. 4 is a fragmentary, perspective view of the stern of the boat, taken from a low angle, showing the after end of propeller drive shaft sub-assembly in a fully raised position; 
     FIG. 5 is a top plan view of the stern tunnel, with the cover removed, showing the forward end of the propeller drive shaft sub-assembly, the drive shaft, and the yoke including laterally extending shafts with respective bearings; 
     FIG. 6 is a cross-sectional view of the propeller drive shaft, taken on the line  6 — 6  in FIG. 5, showing the spline detail; 
     FIG. 7 is a fragmentary, perspective view of the stern tunnel and the propeller drive shaft sub-assembly; 
     FIG. 8 is a cross-sectional view of the propeller cavitation plate, taken on the line  8 — 8  in FIG. 7; 
     FIG. 9 is a longitudinal, cross-sectional view taken through the stern tunnel, showing the propeller drive shaft sub-assembly in a fully lowered position; 
     FIG. 10 is a detail inset view showing the relationship of the sprocket on the exterior end of the control shaft, the screw actuator chain, and the limit switch assembly, with the propeller drive shaft sub-assembly in a fully lowered position; 
     FIG. 11 is a view as in FIG. 9, but showing the propeller drive shaft sub-assembly in a fully raised position; 
     FIG. 12 is a view as in FIG. 10, but showing the propeller drive shaft sub-assembly in a fully raised position; 
     FIG. 13 is a longitudinal, cross-sectional view taken through the stern tunnel, with the boat at rest in the water, showing the propeller drive shaft sub-assembly in a pre-determined, fully raised position; 
     FIG. 14 is a view as in FIG. 13, but showing the propeller drive shaft sub-assembly after it is allowed to rotate under the force of gravity, into a fully lowered position; 
     FIG. 15 is a view as in FIG. 14, but with the boat underway at a moderate speed, the stern tilting downwardly and the propeller drive shaft sub-assembly free-floating upwardly relative to stern tunnel, into an intermediate position; and 
     FIG. 16 is a view as in FIG. 15, but with the boat underway at a higher speed, the stern tilting farther downwardly and the propeller drive shaft sub-assembly free-floating farther upwardly relative to stern tunnel, into a fully raised position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning now to the drawings, and in particular to FIG. 1, the propeller drive  11  of the present invention is shown installed a boat  12 . The boat shown has a squared-offbow  13 , a stern  14 , and a relatively flat bottom  16 . Such features are typical for a hunting, fishing, or exploration boat, adapted for use in shallow or heavily weeded waters. However, the invention is not limited in application to such boats, and may also be used advantageously with boats having differently configured hulls. Boat  12  is provided with a control console  17 , supporting a steering wheel  18  and housing an air-cooled or self-contained water cooled engine  19 . It is preferred to use either such engine in connection with the invention, as conventional water-cooled engines include external water inlet and cooling plumbing which may become fouled with weeds or clogged with mud. 
     An engine drive shaft  21  extends rearwardly from engine  19 . Drive shaft  21  first passes through a bearing  20  in forward end wall  22 . Thereafter, drive shaft  21  continues into the forward, interior portion of an elongated stern tunnel  23 . Stem tunnel  23  protrudes upwardly from the floor  24  of the boat  12 , with its longitudinal axis generally aligned with the fore and aft axis of the boat. In addition to the forward end wall  22 , stern tunnel  23  includes a first side wall  26 , an opposing second side wall  27 , and an upper cover  28 . 
     Making particular reference to FIGS. 4,  7 ,  9  and  11 , the lower portion of stern tunnel  23  includes a bottom plate  29 . The upwardly and rearwardly inclined portion of plate  29  is gradually S-shaped in configuration. An elongated fore and aft slot  31  is provided in the center, rearward portion of bottom plate  29 . As shown particularly in FIG. 1, the stern, or rear-end portion  32  of the tunnel is open. A tunnel hood  33 , having triangular side plates  34 , extends outwardly and rearwardly from the rear end of the stern tunnel. 
     A propeller drive sub-assembly  36  has a forward end  37  which is pivotally suspended within the stern tunnel  23 . The propeller drive sub-assembly  36  includes a fore and aft drive shaft housing  38 . A drive shaft  39  extends entirely through the housing  38 , having a forward end  41  connected to a universal joint  42 , and a rearward end  43  upon which a propeller  44  is mounted. 
     Universal joint  42  has a rear circular plate  46 , provided with a female spline  47 . The forward end  41  of drive shaft  39  includes a male spline portion  48  which fits into female spline  47 . (See, FIGS.  5  and  6 ). This splined coupling between drive shaft  39  and universal joint  42  allows a degree of relative fore and aft movement between these elements while maintaining positive torque drive for the propeller  44 . As shown in FIG. 5, the forward end  49  of universal joint  42  is connected to the engine drive shaft  21 . 
     A deflector skag  51  depends from the lowermost portion of the drive shaft housing  38 . The lower end of skag  51  extends to a region forward from and lower than the lower blade ends of the propeller  44 . As will be discussed in more detail herein, deflector skag is effective both to protect the propeller and to produce upward forces sufficient to rotate the propeller drive sub-assembly upwardly, when rocks or other debris is encountered. 
     The propeller drive sub-assembly also includes an anti-cavitation plate  52 , mounted to the drive shaft housing  38  by means of a pair of vertical support arms  53 . Opposing lateral edges of anti-cavitation plate  52  are provided with edge flares  54 , extending outwardly and inclined downwardly. Edge flares  54  provide a degree of additional containment for the turbulence created by the propeller  44 , thereby reducing propeller-induced cavitation. 
     A steering mechanism  56  is mounted on the rearmost portion of the anti-cavitation plate  52 . The steering mechanism  56  includes a rudder  57  positioned rearwardly from the propeller  44 . The rudder  57  is maintained in vertical relation for rotation about a vertical axis by means of a rudder support shaft  58 . A lever arm  59  has one end attached to the upper end of support shaft  58 . The other end of lever arm  59  is attached to a steering linkage cable  61  of the boat. Although not shown in the drawings, cable  61  extends forwardly to interconnect to steering wheel  18 . 
     An intermediate portion  62  of the drive shaft housing  38  passes through the previously mentioned elongated slot  31 , located in the bottom plate  29  of the stern tunnel. The slot is sized and configured to accommodate upward and downward excursions of the drive shaft housing  38  through a vertical plane. (See, for example, FIGS.  9  and  11 ). 
     The forward end  37  of the propeller drive sub-assembly  36  is provided with a suspension yoke, generally designated by the numeral  63 . Yoke  63  comprises an end plate  64 , opposing and rearwardly extending gussets  66  and  67 , and opposing and forwardly extending shaft plates  68  and  69 . A yoke control shaft  71  extends laterally from plate  68  through a bearing  72  mounted on first side wall  26 . A yoke support shaft  73 , axially coincident with control shaft  71 , extends laterally from plate  69  to a bearing  74  mounted on second side wall  27 . Propeller drive sub-assembly  36  is thereby pivotally suspended within the stern tunnel  23 , for rotation about the common axis of control shaft  71  and support shaft  73 . 
     The yoke control shaft  71  passes through bearing  72  to the exterior of stern tunnel  23 . A sprocket  76  is located on the exterior end of the control shaft  71 . A chain  77  has one end trained around a lower portion of the sprocket  76 . The other end of the chain is connected to the translatable shaft  78  of an electric screw-drive actuator  79 . When the shaft  78  of the actuator  79  is withdrawn, the sprocket  76  and the control shaft  71  are rotated counter-clockwise, effectively raising the propeller  44 . When the shaft  78  of the actuator  79  is extended, gravity effects rotation of the propeller drive sub-assembly downwardly, thereby lowering the propeller. 
     Electro-mechanical limit stop switches  81  and  82 , are wired-in series with the power circuit feeding actuator  79 . The limit stop switches are normally closed, so power will be provided to the actuator  79  unless one or the other of the switches is tripped. For that purpose, first trip rod  83  and second trip rod  84  are provided. In the event that the propeller  44  is lowered to its lowermost position (See, FIG.  9 ), sprocket  76  is rotated to an extreme clockwise limit, in which second trip rod  84  triggers limit stop switch  82 , disabling actuator  79  (See, FIG.  10 ). And, in the event that propeller  44  is raised to its uppermost position (See, FIG.  11 ), sprocket  76  is rotated to an extreme counter-clockwise position, in which first trip rod  83  triggers limit stop switch  81  (See, FIG.  12 ). 
     A mechanical limit stop  86  is also provided, depending from the underside of tunnel hood  33 . Limit stop  86  is vertically adjustable, and includes a bumper  87  on its lower end. As shown in FIG. 11, when the upper surface of anti-cavitation plate  52  comes into contact with bumper  87 , further upward rotation of propeller drive sub-assembly  36  is prevented. 
     In use, the propeller drive  11  has a number of different operational modes and different dynamic adjustments which can be made within those operational modes. For example, as described above, when the boat is at rest, the depth of the propeller  44  maybe maybe manually pre-determined by the user to any elevation from fully lowered to fully raised, or anywhere in between. This depth adjustment for the propeller is made using the electric screw-drive actuator  79 . Typically, the depth of the propeller will be set anywhere from a low to an intermediate position, when the boat is departing from an at rest condition. It is not desirable to have the propeller in a fully raised position when initially departing, as the propeller is out or nearly out of the water, and will be ineffectual in providing drive to the boat. 
     However, it may be that once underway, the boat encounters quite shallow water where the deflector skag  51  could hit bottom. In that event, the user simply activates the electric screw-drive actuator  79 , retracting the translatable shaft  78 . The sprocket  76  and the control shaft  71  are thereby rotated counter-clockwise, raising the propeller  44  to a safe elevation. While this may reduce the efficiency of the drive-system somewhat, it does enable the boat to continue underway. Then, when the boat returns to deeper water, the user again activates the actuator  79 , but this time in the opposite direction. By translating the shaft  78  to an extended position, gravitational forces act to lower the propeller into the deeper water. 
     It should also be noted that depending upon the speed of the boat and the load of persons and items in the boat, the relative position of the propeller drive sub-assembly  36  within the stern tunnel  23  is variable. For example, FIGS. 9 and 11 represent extreme lowered and raised positions, respectively, for the assembly  36 . With a heavier payload in the boat and a greater forward speed, assembly  36  will have a tendency to move upwardly, to that position shown in FIG.  11 . And, with a lighter payload and a lesser forward speed, assembly  36  will tend to assume a relatively lower position, as shown in FIG.  9 . 
     FIGS. 9 and 11 also illustrate the co-operative relationship between the bottom plate  29  and the anti-cavitation plate  52 . Through experimentation, it has been determined that be extending the trailing end of the bottom plate  29  so that it terminates in the vicinity of the leading edge of the anti-cavitation plate  52 , the best performance of the propeller drive  11  is obtained. It is believed that when underway, the bottom plate  29  delivers a substantial flow of water below the anti-cavitation plate directly into the propeller  44 . This enhanced water flow pattern, coupled with the controlling effects of the anti-cavitation plate  52 , ensures that the propeller will provide positive drive for the boat even under marginal water depth conditions. 
     It is believed, then, that I have disclosed an improved inboard propeller drive system for shallow draft boats, utilizing a pivotally mounted propeller drive sub-assembly within a stern tunnel, which is both manually and dynamically adjustable in depth to accommodate a wide variety of operational conditions.