Abstract:
A propeller guard assembly for watercraft that, in cooperation with a rotating propeller, creates a substantial increase in propulsive thrust and provides improved all around shielding of the latest state of the art propeller configurations such as wider propeller blades and contra rotating dual propeller systems.

Description:
BACKGROUND OF THE INVENTION  
       [0001]    This is a Continuation-In-Part Application of U.S. Ser. No. 09/767,234 filed Jan. 18, 2002. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to fluid propulsion systems. More particularly, the invention concerns a novel thrust enhancing propeller guard assembly for use in connection with outboard motors.  
         DISCUSSION OF THE PRIOR ART  
         [0003]    Rotating propellers are an integral aspect of outboard motors of the character used to propel various types of small watercraft. Unguarded rotating propellers present a substantial hazard to submerged objects and to people in the water being traversed by the watercraft. Therefore, there is a need for propeller guard that not only guards against damage caused by the rotating propellers of an outboard motor, but also preferably enhances the propulsion characteristics of the motor. As will be better understood from the description that follows, the novel propeller guard assembly of the present invention accomplishes both of these desired results. Additionally the unique propeller guard assembly of the present invention increases fuel efficiency, stabilizes boat handling and also functions to protect the propeller from damage caused by submerged objects.  
           [0004]    A number of different types of propeller guards have been suggested in the past. One such apparatus is disclosed in U.S. Pat. No. 4,637,801 issued to Schultz. The propeller guard disclosed in the aforementioned patent comprises a primary cowling mounted on the motor housing coaxially with the axis of rotation of the propeller, at least a portion of the primary cowling extending forward of the propeller and beyond the outboard motor where a secondary cowling coaxially mounted with respect to the primary cowling and spaced therefrom in an overlapping relationship therewith so that the leading edge of the secondary cowling extends over the trailing edge of the primary cowling and the trailing edge of the secondary cowling extends rearwardly beyond the outboard motor propeller. The apparatus also includes a plurality of axial vanes secured to the primary cowling at spaced annular positions around the outer surface of the primary cowling and secured to the inner surface of the secondary cowling to hold the cowlings in spaced coaxial relationship.  
           [0005]    Another prior art propeller guard arrangement is disclosed in U.S. Pat. No. 5,651,707 issued to Lemont. This patent discloses a low-aspect ratio propeller system provided with a multiple ring structure formed with a plurality of circular or noncircular, annular, narrow equivalent Air foil rings which are held by rails in a predetermined relationship with the propeller blades. Still another prior art U.S. Pat. No. 4,957,459 issued to Snyder discloses a propeller shroud comprising a cage around the motor gear case and the propeller that includes a pair of inner spokes extending inwardly and bearing against the junction of the motor or skeg and the torpedo shaped central portion of the motor such that impact force on the cage is transmitted to the junction. The cage has a first portion with the leading edge extending along the front of the skeg and tapering rearwardly and outwardly and a rear generally cylindrical portion around the propeller and extending rearwardly from the front portion.  
         SUMMARY OF THE INVENTION  
         [0006]    It is a primary object of the present invention to provide a propeller guard assembly for water craft that, in cooperation with a rotating propeller, creates a substantial increase in propulsive thrust and provides improved all around shielding of the latest state of the art propeller configurations such as wider propeller blades and contra rotating dual propeller systems with longer axial dimensions.  
           [0007]    Another object of the invention is to provide a propeller guard of the aforementioned character, which can be easily attached to the shaft housing of present-day outboard motors, or to the stem drive of present-day inboard motors.  
           [0008]    Another object of the invention is to provide an improved propeller guard as described in the preceding paragraphs that can be fabricated from inexpensive resilient material.  
           [0009]    It is another object of the invention to provide a two part propeller guard assembly for water craft that comprises a first or front subassembly and a second or rear subassembly. The rear subassembly can be attached to the shaft housing of an outboard motor and, in cooperation with a rotating propeller, functions to create a substantial increase in propulsive thrust while at the same time providing improved shielding of certain prior art propeller configurations. The rear subassembly can readily be interconnected with the front subassembly to provide a propeller guard assembly for use with propeller systems having longer axial dimensions.  
           [0010]    Another object of the invention is to provide a propeller guard of the aforementioned character, which can be easily attached to the shaft housing of present-day outboard motors, or to the stem drive of present-day inboard motors.  
           [0011]    Another object of the invention is to provide an improved propeller guard as described in the preceding paragraphs that can be fabricated from inexpensive resilient material.  
           [0012]    As will be better understood from the description that follows, the increase in propulsive thrust of the propeller guard assembly of the invention is created primarily by the angle of the attack and hydrofoil cross section of the four guard rings or cowlings of the device. Each guard ring has the same dynamic flow characteristics as a round airfoil wing adopted originally by the kort nozzle.  
           [0013]    As secondary reason for the increase in propulsive thrust of the propeller guard assembly of the invention resides in the fact that the thrust realized is equal to the ratio between the effective projected propeller area and the area of trailing edges of the large primary and secondary guard rings which decreases the tendency of the propeller race to spread, particularly at high propeller slip during acceleration and take off which is advantageous when the pleasure boat is used for water skiing purposes.  
           [0014]    As will be better understood from the description that follows, the increase in propulsive thrust of the propeller guard assembly of the invention is created primarily by the angle of the attack and hydrofoil cross section of the four guard rings or cowlings of the device. Each guard ring has the same dynamic flow characteristics as a round airfoil wing adopted originally by the kort nozzle.  
           [0015]    As secondary reason for the increase in propulsive thrust of the propeller guard assembly of the invention resides in the fact that the thrust realized is equal to the ratio between the effective projected propeller area and the area of trailing edges of the large primary and secondary guard rings which decreases the tendency of the propeller race to spread, particularly at high propeller slip during acceleration and take off which is advantageous when the pleasure boat is used for water skiing purposes. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a generally perspective view of one form of the propeller guard assembly of the invention attached to a conventional outboard motor.  
         [0017]    [0017]FIG. 2 is a side view partly in cross section showing the propeller guard shielding a contra rotating dual propeller system mounted to an outboard motor.  
         [0018]    [0018]FIG. 3 is a rear elevational view of the apparatus shown in FIG. 2.  
         [0019]    [0019]FIG. 4 is a generally schematic view showing a single propeller within the propeller guard assembly of the invention and illustrating the forward thrust enhancement feature of the apparatus.  
         [0020]    [0020]FIG. 5 is a generally perspective, exploded view of one form of the alternate thrust enhancing propeller guard assembly of the invention.  
         [0021]    [0021]FIG. 6 is a generally perspective view of the propeller guard assembly shown in FIG. 5 illustrated in an assembled configuration.  
         [0022]    [0022]FIG. 7 is a generally perspective, exploded view of the forward portion of the propeller guard assembly shown in FIGS. 5 and 6.  
         [0023]    [0023]FIG. 8 is a view taken along lines  8 - 8  of FIG. 9.  
         [0024]    [0024]FIG. 9 is a side-elevational view partly in cross section of the assembled propeller guard construction shown in FIG. 6.  
         [0025]    [0025]FIG. 10 is a view taken along lines  10 - 10  of FIG. 9.  
         [0026]    [0026]FIG. 11 is a cross-sectional view taken along lines  11 - 11  of FIG. 9.  
         [0027]    [0027]FIG. 12 is a cross-sectional view taken along lines  12 - 12  of FIG. 9.  
         [0028]    [0028]FIG. 13 is a cross-sectional view taken along lines  13 - 13  of FIG. 9. 
     
    
     DESCRIPTION OF THE INVENTION  
       [0029]    Referring to the drawings and particularly to FIGS. 1, 2 and  3 , one form of the propeller guard assembly of the invention is there shown and generally designated by the numeral  10 . Assembly  10  is shown in the drawings affixed to a conventional, commercially available outboard motor “M”. Motor “M” includes a housing  12  having a cavitation plate  14 , a generally torpedo shaped central portion  16  and a skeg  18  connected to and extending downwardly from portion  16 . A propeller shaft  20  extends from central portion  16  and carries a pair of contra rotating propellers  22  that rotate about the longitudinal axis  22   a  of shaft  20  (FIG. 2).  
         [0030]    Connected to cavitation plate  14  is a pair of first, oppositely disposed mounting members  24 , the purpose of which will presently be described (FIGS. 1 and 3). Similarly, a pair of second, oppositely disposed mounting members of  26  are mounted on skeg  22 . Attached to mounting members  24  and  26  is the novel propeller guard assembly of the invention. In the present form of the invention this novel propeller guard assembly comprises first, second, third and fourth coaxially aligned, axially staggered, generally ring shaped cowlings  32 ,  34 ,  36  and  38  respectively. First and fourth cowlings  32  and  38  are axially spaced from the propellers and each are of a first diameter. Second and third cowlings  34  and  36  are of a second, larger diameter and circumscribe the propellers in the manner shown in FIG. 3.  
         [0031]    As best seen in FIGS. 1 and 3, each of the cowlings of the apparatus is made up of a pair of semicircular shaped segments, the first or upper extremity of which is connected to first mounting member  24  and the second or lower extremity of which is connected to a second mounting member  26 . Interconnecting each of the semicircular shaped segments of the propeller guard assembly proximate their centers is a longitudinally extending anti-torque bar  40 . Anti-torque bar  40  provides structural rigidity to the assembly and also functions to counteract the torque generated by the propellers  20 .  
         [0032]    As can be seen by referring to FIG. 2, each of the cowlings  32 ,  34 ,  36  and  38  are generally hydrafoil shaped in cross section. Additionally, each of the cowlings has a peripheral portion that is located within a place that extends at an acute angle relative to axis  22   a . Cowlings  34  and  36  are positioned in tandem and have an annular space  42  therebetween. As is indicated in FIG. 4, the cowlings  32 ,  34 ,  36 , and  38  have an equal acute angle of attack “a” creating a forward primary thrust force “T”. Due to the accelerated water flow  45  created by the rotating propeller  20 , the secondary thrust enhancing force is created by the ratio between the effective projector propeller area having a diameter “A” and effective propeller area having a diameter “B” of the trailing edge of nozzles  34  and  36 .  
         [0033]    As previously mentioned, the increase in propulsive thrust of the propeller guard is created primarily by the angle of the attack “a” and the novel hydrofoil cross section of the nozzle rings combined. Further, as illustrated in FIG. 4, the increase in propulsive thrust is equal to the ratio between the effective projected propeller area and the area of trailing edges of the large primary and secondary guard rings which decrease the tendency of the propeller race to spread, particularly at high propeller slip during acceleration and take off.  
         [0034]    In operation, when the propellers are driven by the motor “M”, water will flow between the first and second cowlings  34  and  36 , and, because of their unique shape and their positioning relative to the axis of rotation of the propellers, a venturi effect will be created to further enhance the propulsive thrust.  
         [0035]    Turning now to FIGS. 5 through 13, an alternate form of the propeller guard assembly of the invention is there shown and generally designated by the numeral  46 . This alternate form of the propeller guard assembly of the invention uniquely comprises first and second subassemblies  48  and  50 . When the first and second subassemblies are interconnected together in a manner shown in FIG. 6 the assembly thus formed functions in substantially the same manner as the earlier described assembly  10  and can be easily affixed to a conventional, commercially available outboard motor, such as the earlier identified motor “M”. As before, Motor “M” includes a cavitation plate  14  that includes a pair of first and second mounting members  24  and  26  (see FIG. 3).  
         [0036]    In this alternate form of the invention the first or rear subassembly  48  comprises first, second and third coaxially aligned, axially staggered, generally ring shaped cowlings  52 ,  54  and  56  respectively. First cowling  52  is axially spaced from the propellers and is of a first diameter. Second and third cowlings  54  and  56  are of a second, larger diameter and circumscribe the propellers in the manner previously discussed (see for example FIG. 3).  
         [0037]    As before, each of the cowlings of the apparatus is made up of a pair of semicircular shaped segments, the first or upper extremity of which is connected to first mounting member  60  and the second or lower extremity of which is connected to a second mounting member  62 . Interconnecting each of the semicircular shaped segments of subassembly  48  proximate their centers is a longitudinally extending anti-torque bar  64 . Anti-torque bar  64 , like torque bar  40  provides structural rigidity to the subassembly and also functions to counteract the torque generated by the propellers  20 .  
         [0038]    As can be seen by referring to FIG. 9, each of the cowlings  52 ,  54  and  56  are generally hydrafoil shaped in cross section. Additionally, each of the cowlings has a peripheral portion that is located within a plane that extends at an acute angle relative to axis  67 . Cowlings  54  and  56  are positioned in tandem and have an annular space  70  therebetween. As is indicated in FIG. 9, the cowlings  52 ,  54  and  56  have an equal acute angle of attack “a” creating a forward primary thrust force “T” (see, for example, FIG. 4). As in the earlier described embodiments, due to the accelerated water flow created by the rotating propeller  20 , the secondary thrust enhancing force is created by the ratio between the effective projector propeller area having a diameter “A” and effective propeller area having a diameter “B” of the trailing edge of nozzles  54  and  56  (see FIG. 4).  
         [0039]    In this alternate form of the invention the second or front subassembly  50  comprises a cowling  74  that is axially spaced from the propellers and is of a first diameter substantially equal to the diameter of cowling  52 . As illustrated in figure  7 , cowling  74  is made up of a pair of semicircular shaped segments  74   a  and  74   b . The first or upper extremity of segment  74   a  is connected to a forward mounting member  76  and the second or lower extremity is connected to a forward mounting member  78 . Similarly, the first or upper extremity of segment  74   b  is connected to a forward mounting member  80  and the second or lower extremity is connected to forward mounting member  82 .  
         [0040]    In operation, when the propellers are driven by the motor “M”, water will flow between the first and second cowlings  34  and  36 , and, because of their unique shape and their positioning relative to the axis of rotation of the propellers, a venturi effect will be created to further enhance the propulsive thrust.  
         [0041]    It is to be understood that either the first subassembly  48  or the assembly formed by the interconnection of first and second subassemblies  48  and  50  can be interconnected to the motor “M” which is of a character shown in FIG. 1. More particularly, when the rear subassembly is interconnected with the motor “M”, mounting members  60  are affixed by suitable connectors to the under surface of cavitation plate  14 . Similarly, in the manner previously described, mounting members  62  are interconnected to the skeg  18  by suitable connectors. When so affixed to the motor, cowlings  52 ,  54  and  56  of subassembly  48  circumscribe the motor propeller and, because of their unique shape and positioning relative to the axis of the rotation of the propeller, create a venturi effect that enhances the propulsive thrust of the motor.  
         [0042]    When it is desired to attach the forward subassembly  50  to the rearward subassembly  48  and to the motor “M”, unique connector means, the character of which will presently be described are used to accomplish the structural interconnection.  
         [0043]    In the form of the invention shown in FIGS. 6 through 13, the connector means comprises a generally planar, U-shaped connector plate  84  having a front portion  84   a  and a rearward portion  84   b . Also forming a part of the connector means of the invention is a longitudinally extending connector plate or spanner member  86  having a front portion  86   a  and a rear portion  86   b . The forward portion  84   a  of connector plate  84  is affixed to mounting members  76  and  80  by suitable connectors such as connectors  87 . Similarly, connector element  86  is connected at its forward portion  86   a  to forward mounting members  80  and  82  by a suitable connector  89 . When it is desired to interconnect front assembly  50  with rear assembly  48 , rearward portion of plate  84   b  is superimposed over mounting members  60  in the manner shown in FIG. 6 and secured thereto by suitable connectors such as connectors  91 . In a similar manner, connector element  86  is inserted between forward mounting members  78  and  82  and is secured thereto by a suitable connector  93 .  
         [0044]    When the forward and rearward portions are interconnected in the manner described in the preceding paragraphs and as illustrated in the drawings, the assemblage thus formed can be attached to the cavitation plate  14  and to the skeg  18  as, for example, by a suitable connector  95 .  
         [0045]    Having now described the invention in detail in accordance with the requirements of the patent statutes, those skilled in this art will have no difficulty in making changes and modifications in the individual parts or their relative assembly in order to meet specific requirements or conditions. Such changes and modifications may be made without departing from the scope and spirit of the invention, as set forth in the following claims.