Patent Publication Number: US-7223073-B2

Title: Boat propeller

Description:
FIELD OF THE INVENTION 
   The present invention relates to a propeller for a boat, more specifically to a propeller for a higher horsepower motor. 
   BACKGROUND OF THE INVENTION 
   The bushing system design for marine propellers has remained relatively unchanged since the early 1940&#39;s. Typically, a bushing is used to make a connection between the propeller body and the drive hub on the propeller shaft. The conventional bushing generally is formed from a hard rubber and makes the connection using friction. The rubber bushing is bonded to a center hub made of metal or plastic and the rubber is designed to be larger than the hole in which it is to be inserted. An installation funnel is used to compress the diameter of the rubber bushing to enable it to be inserted into the propeller bore. One of the benefits of this conventional design is that it gives both impact protection and harmonic vibration absorption protection. Another benefit of this conventional design is that, under impact, the rubber bushing will slip and, in most cases, reconnect or lock up again and enable the boat to continue to drive, at least under limited power. 
   When the maximum horsepower of boats with outboard motors was 25 hp, this conventional bushing design was ample. However, current horsepower ratings of boats far exceed the design capabilities of such a conventional bushing. With so much torque under impact, the rubber bushing slips and melts. As a result, the bushing does not return to its normal size and becomes unusable in seconds. The damaged conventional bushing remains loose within the propeller bore, leaving the boat drive system useless and the boat undriveable. 
   To correct this problem with higher horsepower motors, manufacturers have placed a hard plastic or metal keyed piece to operatively engage the hub of the propeller. While this method reduces failures akin to the ones mentioned above with the conventional rubber bushings, it does not provide any protection for the drive train under impact, it does not absorb any harmonic vibration from the motor or drive train, and it does not remain sufficiently tight on the propeller shaft. The latter issue induces a rattle in the propeller shaft and produces operating noise. It also promotes wear and tear on all the drive components. 
   There are other designs that have the same and other pitfalls as mentioned herein above. Therefore, what is needed is a propeller bushing that provides the protection of a rubber bushing, while providing the positive lock of a keyed system for higher horsepower motors. 
   SUMMARY 
   The present invention relates to a boat propeller having a longitudinal axis. The propeller comprises an inner hub assembly defining a longitudinally extending bore. The bore extends substantially rearward, concentrically about the longitudinal axis. 
   The propeller also comprises a central hub member. The exterior surface of the central hub member is sized and shaped for disposition within the bore of the inner hub assembly. In one aspect, the exterior surface of the central hub member and the surface of the bore are complementarily keyed. In one aspect, the bore of the inner hub assembly and the exterior surface of the central hub member may be substantially cylindrically shaped, or they may be slightly tapered in a complimentary fashion such that the diameter of the bore gets smaller as the bore extends longitudinally inwardly from its first end to its second end. 
   The central hub may also define a longitudinally extending conduit that extends substantially rearward, concentrically about the longitudinal axis. In this instance, the conduit of the central hub is adapted to mount thereon a rotatable drive shaft such that rotation of the drive shaft about the longitudinal axis imparts rotation of the propeller about its longitudinal axis. 
   The inner hub assembly of the propeller is spaced therefrom the central hub member by a plurality of resilient spacer members. The resilient spacer members are designed to absorb impact forces from the propeller, as well as harmonic vibration from the motor. The cushion provided by the resilient spacer members protects the drive shaft from damage due to the aforementioned impact forces and harmonic vibration. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features of the preferred embodiments of the present invention will become more apparent in the detailed description in which reference is made to the appended drawings wherein: 
       FIG. 1  is an exploded perspective view of one aspect of the present invention for a propeller showing an outer hub assembly, an inner hub assembly, a plurality of resilient spacer members, a plurality of resilient bands, a central hub member, and a rotatable drive shaft. 
       FIG. 2  is a perspective view of the propeller of  FIG. 1 . 
       FIG. 3  is a front cross-sectional view of the propeller of  FIG. 1 , taken along line  3 — 3  of  FIG. 2 . 
       FIG. 4  is a side cross-sectional view of the propeller of  FIG. 1 , taken along line  4 — 4  of  FIG. 3 . 
       FIG. 5  is a partial front cross-section view of the propeller of  FIG. 1 . 
       FIG. 6  is a partial front cross-sectional view of one aspect of the present invention for a propeller showing additional resilient spacer members. 
       FIG. 7  is a partial front cross-sectional view of one aspect of the present invention for a propeller showing the top surface of each rib of the central hub defining a longitudinally extending groove that is adapted for mounting a bottom portion of one resilient spacer member therein. 
       FIG. 8  is a partial front cross-sectional view of one aspect of the present invention for a propeller showing the top surface of each rib of the central hub defining a longitudinally extending groove that is adapted for mounting a bottom portion of one resilient spacer member therein. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention is more particularly described in the following exemplary embodiments that are intended as illustrative only since numerous modifications and variations therein will be apparent to those skilled in the art. As used herein, “a,” “an,” or “the” can mean one or more, depending upon the context in which it is used. The preferred embodiments are now described with reference to the figures, in which like reference characters indicate like parts throughout the several views. 
   Ranges may be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. 
   In one aspect of the present invention for a boat propeller  10  having a longitudinal axis, the propeller  10  comprises an inner hub assembly  100  defining a longitudinally extending bore  110 . The bore  110  of the inner hub assembly  100  extends substantially rearward, concentrically about the longitudinal axis. In one aspect, an inner surface  115  of the bore defines at least one longitudinally extending slot  120  having opposed edge surfaces  115 . Exemplarily, the edge surfaces  115  may be curved or substantially straight. In either case, each slot  120  extends outwardly away from the longitudinal axis of the propeller. 
   The propeller  10  also comprises a central hub member  200 . The central hub member  200  has a proximal end  210 , an opposed distal end  220 , and an exterior surface  230 . The exterior surface  230  of the central hub member is sized and shaped for disposition therein the bore  110  of the inner hub assembly  100 . As such, in one aspect, the exterior surface defines at least one longitudinally extending male rib  240  having opposed side surfaces  230 . It is contemplated that the bore  110  of the inner hub assembly and the exterior surface  230  of the central hub member are substantially cylindrically shaped. In another aspect, it is contemplated that the bore of the inner hub assembly and the exterior surface  230  of the central hub member are tapered in a complimentary fashion such that the diameter of the bore gets smaller as the bore extends longitudinally inwardly from the first end  130  of the bore to the second end  132  of the bore. The central hub member  200  is formed from a substantially rigid material suitable for matching the horsepower of the motor used, such as, for example and not meant to be limiting, brass, aluminum, stainless steel, plastic, polypropylene, and the like. 
   In one aspect, in order to compliment the shape of the male rib  240  of the exterior surface  230  of the central hub member  200 , the slot  120  of the inner hub assembly  100  is sized to substantially surround at least a portion of the male rib. Resultantly, a cavity  250  is defined by a portion of each edge surface of the slot of the inner hub assembly that faces and is spaced from a portion of a respective side surface of the rib of the central hub member. In one aspect, the slots  120  may be larger than the ribs  240  and a cavity  250  may be formed on either side of each rib. 
   In another aspect, the propeller  10  further comprises a plurality of resilient spacer members  300  that are constructed and arranged such that at least a portion of one resilient spacer member is adapted to mount therein at least a portion of one formed cavity. In this aspect, the exterior surface of the central hub member  200  is spaced from the inner surface  115  of the bore of the inner hub assembly. When mounted therebetween portions of the central hub member and the inner hub assembly, the resilient spacer members  300  provide a cushion that separates the central hub member  200  and the inner hub assembly  100 . In yet another aspect, as depicted in  FIG. 6 , the cavity  250  may be filled with multiple resilient spacer members  300 . 
   In one aspect, the propeller further comprises an outer hub assembly  400  connected to an outer surface of the inner hub assembly. Here, the exterior surface  420  of the outer hub assembly  400  has a plurality of propeller blades  410  attached to and extending outwardly away from the outer surface. In use, the exterior surface  420  of the outer hub assembly  400  is in contact with the water. 
   In yet another aspect, the outer hub assembly has an interior surface  420  and at least one passageway  430  is defined therebetween the interior surface  420  of the outer hub assembly  400  and the outer surface  117  of the inner hub assembly  100 . This passageway  430  permits the release of exhaust gases from the engine of the watercraft. As can be seen in  FIG. 3 , this aspect of the invention allows for a larger exhaust passageway  430  than is required, which can improve engine performance and allow the fuel-air mixture to burn cleaner on larger motors by lowering the exhaust back-pressure. This design, due to the cleaner fuel burning, also reduces emissions. 
   In one aspect, the central hub member  200  defines a longitudinally extending conduit that extends substantially rearward, concentrically about the longitudinal axis. The drive shaft  500  is sized and shaped for engagement with the conduit of the central hub member, such that rotation of the drive shaft  500  about the longitudinal axis imparts rotation of the propeller about the longitudinal axis. Exemplarily and not meant to be limiting, the exterior surface  510  of the drive shaft  500  comprises a plurality of splines that are sized and shaped for complimentary engagement with the inner surface of the conduit of the central hub member. Of course, it is contemplated that the respective surfaces can be complimentarily shaped for engagement in any conventional fashion. 
   In another aspect, the interior surface  420  of the outer hub comprises plurality of slots  120 , and the exterior surface  230  of the central hub member  200  comprises a plurality of male ribs  240 . It is contemplated that the respective pluralities of slots and ribs may be spaced substantially equally apart relative to the longitudinal axis of the propeller, or they may be unevenly spaced. Further, in one aspect, the respective pluralities of slots and ribs may extend substantially the entire longitudinal length of the inner hub assembly  100 , or they may only extend a portion therein. The surface area therebetween the adjacent slots and ribs is sized to withstand the torque exerted by the drive shaft. 
   In still another aspect, the edge surfaces  115  of each slot  120  have a curved cross-sectional shape and the side surfaces  230  of each rib  240  have a curved cross-sectional shape. By making the edge surface and the side surface curved in their cross-section, the cavity that is formed therebetween, as is seen in  FIG. 5 , has a substantially circular cross section. In this aspect, at least a portion of each resilient spacer member  300  has a circular cross-sectional shape in order to compliment the shape of the cavity  250 . 
   In one aspect, each resilient spacer member has a diameter that is greater than the height of each rib and the depth of each slot. Thus, the resilient spacer member spaces the inner surface  115  of the bore of the inner hub assembly from the exterior surface of the central hub member. As can be appreciated and as shown in the figures, the resilient spacer member can have practically any cross-sectional shape. For instance, the cross-sectional shape of the resilient spacer member may square, rectangular, round, elliptical, etc. 
   In one aspect, the top surface  242  of each rib  240  defines a longitudinally extending groove  247  that is adapted for mounting a bottom portion  315  of one resilient spacer member  300  therein such that a top portion  310  of the resilient spacer member extends upwardly away from the top surface  242 . In this aspect, as shown in  FIGS. 7 and 8 , the resilient spacer member  300  disposed therein the groove  247  extends above the top surface of the rib substantially the same distance as the resilient spacer member disposed within the cavity  250  formed by the edge surface of the slot and the side surface of the rib. This way, the resilient spacer members  300 , together, space the entire inner surface  115  of the bore of the inner hub assembly from the exterior surface of the central hub member and provide a cushion for protecting the drive shaft in the event of a propeller impact, as well as protecting against harmonic vibration. 
   Alternatively, to achieve the cushion between the inner surface of the bore of the inner hub assembly and the exterior surface  230  of the central hub member  200 , at least one resilient band  320  is provided. Each resilient band  320  overlies a portion of the top surface  242  of each rib  240  and contacts adjacent resilient spacer members  300  disposed in the cavities  250 , as shown in  FIG. 1 . In this aspect, the resilient band is positioned therebetween the inner surface  115  of the bore of the inner hub assembly and the top surface of the rib of the central hub member. 
   In another aspect, the inner hub assembly  100  has a back end, which is adjacent the drive shaft  500 . The back end  145  of the inner hub assembly forms a concentric shoulder  150 , which is adapted to stop the central hub member from being inserted past the back end of the propeller  10  assembly. In use, the central hub member of the propeller is placed on the drive shaft until the threaded end  520  of the drive shaft  500  protrudes from the conduit of the central hub member. Then, a propeller nut  530  is tightened onto the threaded end  520  such that the distal end  220  of the central hub member is compressed against the concentric shoulder  150 , securing the propeller assembly onto the drive shaft  500 . 
   In yet another aspect, a resilient washer member  270  is positioned therebetween the concentric shoulder  150  and the distal end of the central hub member. It provides protection for the end of the central hub member and further cushions against harmonic vibration and propeller impact. This design ensures that there is no direct contact between the exterior surface  230  of the central hub member and the inner surface  115  of the bore of the inner hub assembly. 
   The resilient spacer members and the resilient band can be made from any substantially elastic material known by those skilled in the art. For example and not meant to be limiting, they may be constructed from rubber, polypropylene, nylon, polyurethane, plastic, and the like. The hardness of the material can be determined based upon the horsepower of the motor used. For higher horsepower motors, it is recommended to use a harder material. 
   Although several embodiments of the invention have been disclosed in the foregoing specification, it is understood by those skilled in the art that many modifications and other embodiments of the invention will come to mind to which the invention pertains, having the benefit of the teaching presented in the foregoing description and associated drawings. It is thus understood that the invention is not limited to the specific embodiments disclosed herein above, and that many modifications and other embodiments are intended to be included within the scope of the appended claims. Moreover, although specific terms are employed herein, as well as in the claims which follow, they are used only in a generic and descriptive sense, and not for the purposes of limiting the described invention, nor the claims which follow.