Patent Publication Number: US-6669516-B1

Title: Weed-resistant outboard motor drive system

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to portable drive systems for shallow bottom boats, especially for such boats intended for operation in weed infested waters and/or in shallow waters with rocky beds. 
     It is well known that excellent fishing areas are often found in waters that may be weed infested and/or have shallow or rocky bottoms. Such conditions are impossible for conventional outboard motor drive systems and even very difficult for shallow draft trolling motor drive systems. In a conventional transportable trolling motor drive system, a small electric motor and propeller are suspended in the water by a steering handle mechanism that is removably supported by means of a bracket attached to the transom of a boat. Because of the drive system size and configuration, Le., the relatively large in-the-water profile of the motor, propeller and vertical support, weeds tend to catch. This drastically affects motor speed and efficiency and requires frequent stops to manually remove weed buildup. Since the diameter of the propeller is greater than the large diameter of the motor, the motor is operated at low rotation to provide proper low trolling speeds. The low motor rotation is not conducive to cutting and churning through weeds. 
     The weight of the motor also presents a problem. Because of the high inertia of the motor in the water, there is an increased possibility of propeller breakage or motor damage should obstacles be encountered. While there are systems described in the prior art for powering shallow draft boats under such conditions, they either involve significant modification of the boat transom or an unusual propulsion arrangement, such as fitting a propeller drive arrangement to an oar. Such systems have not found favor and none are known to be in use. 
     A practical shallow water, weed-resistant boat drive system should ideally: be lightweight; mount directly to a common boat transom; be readily transportable without requiring breakdown into component parts; present a minimal in-the-water profile; be capable of withstanding impacts with submerged articles; and have the ability to either shed, slice or churn through most weeds that are encountered. 
     As discussed above, the prior art systems fail to meet one or more of the above criteria. Drive systems that have the drive motor in the water do not present a minimal in-the-water profile, are ineffective in cutting, slicing or churning through weeds and are very susceptible to damage by impact with objects. Drive systems that have only a propeller in the water are very cumbersome, primarily due to the very long propeller shafts needed to achieve a favorable propulsion angle. None of the drive systems supports the propeller in the ideal position for weed resistance, ie., just beneath the water surface with the propeller axis parallel to the water surface. 
     U.S. Pat. Nos. 4,604,067 and 4,976,637 describe unusual trolling motor drive systems that utilize conventional hand-held, gasoline engine-powered weed cutting machines. The weed cutting machines include a bent tubular housing having a motor at one end and a rotating trimmer line cutting mechanism at the other end, with a flexible shaft, encased by the tubular housing, coupling the motor and the cutting mechanism. The cutting mechanism is replaced with a small propeller, and a clamping device is added to support the drive system from the transom of a boat. The bent tubular shaft, due to its radius of curvature, supports the propeller at an unfavorable propulsion angle in the water. The devices represent low cost trolling motor arrangements and, while exhibiting certain structural similarities, are not concerned with the problems addressed by the present invention and are clearly ineffective in operating in a weedy environment. 
     The present invention provides a motor drive system that meets all of the above described criteria and does so in a very simple, economical manner. It will be appreciated that others, such as hunters who use boats, often encounter similar weedy and shallow and/or rocky water conditions where the invention will be of significant benefit. The invention is also easily adapted for attachment to various inclined surfaces, such as the walls or gussets of a canoe, or for use on the bow of curved hull boat. 
     OBJECTS OF THE INVENTION 
     A principal object of the invention is to provide a novel motor drive system for a boat. 
     Another object of the invention is to provide a motor drive system that is capable of providing continuous operation of a boat in shallow rocky and/or weedy water. 
     A further object of the invention is to provide a lightweight, unitary portable weed and impact resistant motor drive system for a boat. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and advantages of the invention will be apparent upon reading the following description in conjunction with the drawings in which: 
     FIG. 1 is a simplified partial view of a prior art motor drive system for trolling with a shallow draft boat; 
     FIG. 2 is a similar simplified view of the motor drive system of the invention applied to such a boat; 
     FIG. 3 illustrates the invention in use on the bow of such a boat; and 
     FIG. 4 depicts a simplified arrangement of the drive system of the invention applied to a canoe. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 discloses a partially illustrated shallow draft boat  10 , having a bottom  12  and a substantially vertical transom  14 , fitted with a prior art trolling motor drive system  20 . Boat  10  draws very little water, and bottom  12  is shown as being just below the water surface or line  17 . In practice, for smooth, quiet and efficient operation of the boat and its trolling motor system, the propeller tips should be at least two inches below the surface of the water. A battery  16  supplies power via electrical leads  18  for energizing motor drive system  20  in a well-known manner. While not essential, the applied power may be modulated, by well-known means (not shown) for controlling the speed of the motor, although for trolling, a slow steady boat speed is generally desired. Motor drive system  20  includes a D.C. motor  22  driving a propeller  24 . A conventional control arrangement  30  (not shown in detail) is coupled to a steering handle  32 , which terminates in a handle grip  34 , and to a vertical portion  36  that is attached to motor  22 . A U-shaped clamping bracket  40  supports a generally T-shaped bearing tube  42  at a pivot  44 . The “T” portion of tube  42  rotatably supports vertical portion  36  and enables horizontal movement of motor  22  for steering. A screw clamp  46  removably secures bracket  40  (and drive system  20 ) to transom  14  of the boat. A skeg  23  is secured to the bottom of motor  22  to help provide impact protection for propeller  24  and includes a leading edge  23  that makes a relatively steep angle “A” with the water line  17 . 
     It will be noted that the in-the-water profile of motor drive system  20  is quite substantial since motor  22  and propeller  24  are large. The part of vertical portion  36  that is in the water, not only presents significant resistance, but the angle of entry “B” of portion  36  to the water surface is 90°, which, as will be discussed in more detail below, is ideal for catching weeds, but of no use in shedding or churning through them. While motor  22  has a streamlined bullet shaped nose, it projects forwardly from vertical portion  36 , thus forming a hook for catching and holding weeds. Propeller  24 , as discussed, is relatively large and necessarily limits the depth of water in which the boat may be operated and increases the likelihood of encountering rocks or the bottom of the water. Similarly, the steep angle “A” of the leading edge  23  of skeg  25  is conducive to catching long stringy type weeds. Clearly, the prior art trolling motor drive system is not weed-resistant. 
     It will be observed that the weight of the prior art drive system is concentrated at a point removed from, and almost directly below, pivot  44 , which results in the drive system having substantial inertia. If the motor or propeller of such a drive system encounters an obstruction or the shallow and/or rocky bottom  19 , significant impact will be experienced and the likelihood of damage to the propeller or motor will be high. Further, the propeller is usually made of a hard plastic, which is readily broken upon impact. Since the propeller diameter is large (to clear the motor body), the motor speed must be low to maintain a desirable slow trolling speed for the boat. Therefore, weeds (especially long, stringy weeds) that are caught on the drive system tend to wrap around the motor and propeller shaft, rather than being cut off or shed, which places a heavy drag on the motor, necessitating frequent stops to manually remove weed buildup. 
     On the contrary, the motor drive system  50  of the invention illustrated in FIG. 2 overcomes these prior art problems. The boat  10 , battery  16  and T shaped bearing tube  42  that is supported by clamping bracket  40  at pivot  44  are the same as in the prior art FIG. 1. A control arrangement  60 , which includes a horizontal handle  62  that terminates in a handle grip  64  is similar in function to the prior art and is not be separately illustrated since it is not germane to this invention. A significant difference between the inventive arrangement and the prior art is a vertically oriented motor  52  that is situated outside the water and above pivot  44 . With this arrangement, the inventive drive system exhibits an inertia that is significantly less than the prior art system. It should be noted that the vertical orientation of motor  52  is not an essential part of the invention, but rather simplifies the construction of the inventive drive system. 
     Another significant difference is the provision of a curved tubular housing  58  and an elongated flexible shaft  54  encased therein. The tubular housing has a proximal end  58   a  and a slightly enlarged distal end  58   b . Flexible shaft  54  is coupled to a motor  52  at a proximal end  54   a  and is coupled to the propeller shaft  56   a  of a small propeller  56 , at a distal end  54   b . Tubular housing  58  includes a straight vertical portion  66 , secured in bearing tube  42 , that extends from proximal end  58   a  through a large sweeping arc of 90° to distal end  58   b . The proximal end  58   a  of tubular housing  58  may be secured to motor  52  by a flange  52   a  or any suitable means. The proximal end  54   a  of flexible shaft  54  has a square fitting that nests with a mating fitting (neither of which fitting is shown) on motor  52 . The coupling may be similar to a speedometer drive arrangement and is not illustrated. The distal end  54   b  of flexible shaft  54  is coupled to propeller shaft  56   a  by a pin and slotted shaft arrangement  54   c , which is illustrative only, since the method of attachment is not germane to the invention. The distal end  58   b  of tubular housing  58  terminates in a conventional pressed-in bearing/seal  68  for permitting rotation of propeller shaft  56   a  while keeping water out of tubular housing  58 , which is conventionally filled with grease for flexible shaft  54 . 
     To assemble the arrangement shown, propeller shaft  56   a  is coupled to the distal end  54   b  of flexible shaft  54 , via coupling  54   c  and inserted into the distal end of tubular housing  58 . The bearing/seal  68  is pressed into the distal end of tubular housing  58 , the square proximal end  54   a  of flexible shaft  54  is engaged with the fitting on motor  22 , and flange  52   a  secured to motor  22 . The propeller  56  is then secured to propeller shaft  56   a.    
     An important aspect of the invention is the angle of entry of tubular housing  58  in the water. Experimentation with different types of weeds has shown that the included angle “C”, which is formed by a tangent drawn to the curve of the tubular housing at the water surface or line, should be no greater than 55°, and ideally less than 45°, to provide any significant weed shedding ability. Also, as mentioned previously, propeller  56  has a relatively small diameter which enables it to be operated at much higher rotational speed than prior art systems while still maintaining a desired slow trolling speed for the boat. The propeller  56  is of the so called “weed free” type, the blades of which have a retreating radius, i.e., the leading edges of the blades are drafted back from the direction of rotation of the propeller, which together with the propeller speed, enables efficient cutting and churning through of any weeds presented to it. 
     For proper operation of the propeller in the water, its blade tips should be a distance “E” of at least two inches below the surface of the water. At lesser distances, cavitation and noise result and the system becomes very inefficient, as well as useless for trolling. Further benefit in weed shedding ability, as well as protection for the propeller, is obtained by providing a thin skeg  59  that extends beyond the blade tips of the propeller and that makes an angle “D” with the water line or surface that is no greater than the angle “C”. It has been found that with this configuration, long stringy weeds are directed downwardly along the curved portion of tubular housing  58  and by the angled leading edge of skeg  59  to propeller  56  (which also prevents the weeds from being wound around the propeller) where they are sliced and shed as discussed above. Lastly, the combination of the skeg, placement of the motor above the hinge point (pivot  40 ) and the distance of propeller  56  farther behind the hinge point results in significantly less shock to, and movement of; the motor should underwater obstacles be encountered. 
     FIG. 3 discloses the drive system of the invention in use on the bow of a curved hull boat. Everything is the same as that shown in FIG. 2, except that tubular housing  58  has been rotated  180  so that propeller  56  is under the bow of the boat, rather than being positioned at the stern of the boat. Clamping bracket  40  readily accommodates installation on a non-vertical portion  79  of the bow. Operation of the inventive drive system is the same as that previously described for FIG.  2 . 
     In FIG. 4, the drive system of the invention is shown in use with a canoe that includes a horizontal stern piece or gusset  80 . A modified bearing tube  43  supports a pivoted clamping bracket  82  that engages the top of stem piece  80 . The drive system is removably secured to the canoe by a screw-type clamp arrangement  84 . It will be appreciated that the mounting arrangement is merely illustrative of a typical installation and may be readily changed to suit a desired installation. The remainder of the inventive drive system is identical in use and operation to that previously described. 
     What has been described is a novel portable low speed outboard motor drive system for use with shallow bottom boats, that resists weed buildup, has significant impact resistance and is especially suitable for slow speed boating in weedy and shallow/rocky bottom waters. It is recognized that numerous changes to the described embodiment of the invention will be apparent to those skilled in the art without departing from its true spirit and scope. The invention is to be limited only as defined in the claims.