Abstract:
A drive for a marine vessel may include a fully wetted propeller with a fixed drive shaft configuring the propeller in a tractor mode wherein the propeller pulls the water rearwardly relative to a bow of the marine vessel when traveling in a forward direction. The propeller is preferably mounted in a range of 10% to 60% of a length of the marine vessel toward the how from a transom and operates cavitation-free.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The preferred embodiments relate to propulsion of marine vessels; and more particularly, propulsion of a marine vessel with a fully wetted, submerged propeller in a tractor mode configuration and powered by a fixed shaft. 
         [0003]    2. Discussion of the Related Art 
         [0004]    Marine vessels are commonly constructed with a propeller facing the rear end or transom in order to “push” it through the water. This is commonly referred to as “pusher configuration”. In a “puller configuration”, also referred to as “tractor configuration” or tractor mode, the propeller faces the bow of the vessel, such that the vessel is “pulled” through the water. 
         [0005]    Tractor configurations are commonly known in the aircraft industry but have not made any significant entry into the marine space. Tractor configurations have been used in pod-style drives for large yachts, typically, 30 feet in length or longer, but are not offered for more traditional drive systems. Pod drives also come with high maintenance, high costs, and more complications than other drives. Due to these factors, pods are not implemented in smaller marine vessels. Pod drives also may extend the propeller lower in the water than other configurations increasing the opportunity to strike ground or other foreign bodies. Should such an impact occur, the damage can be catastrophic to the pod and incur significant costs or a total loss of the vessel. 
         [0006]    Traditional drive systems, such as direct drive systems, are less complicated and have much lower manufacturing costs as well as lower maintenance costs. Such drive systems also do not extend deep into the water and conic with minimal repair costs should the propeller impact ground or another foreign object. 
         [0007]    When using a more traditional drive system, such as an outboard or a direct drive, the marine industry installs propellers in a pusher configuration. This is done not only as a result of tradition, but simply because it works. However, many marine vessel designers also operate under the old belief that pusher configurations simply perform better than tractor configurations. In fact, in the POD space, it has been proven that the tractor configuration gives greater propulsive efficiency. 
         [0008]    What is therefore needed is a marine propulsion design that can take advantage of a propeller disposed in a tractor configuration, while avoiding the high costs and maintenance of known tractor configurations, such as pod drives. 
         [0009]    What is additionally needed is a marine propulsion system that can be used on all sizes of marine vessels, large and small. Furthermore, a marine propulsion system that can combine the benefits of a tractor configured propeller with a traditional drive system such as direct drive was also desired. 
       SUMMARY AND OBJECTS OF THE INVENTION 
       [0010]    A marine vessel includes a hull with an underside. The underside may include a tunnel configured to accept a drive. A propeller may be mounted at least partially within the tunnel in a tractor mode configuration such that the propeller rotates to create a thrust that pulls the marine vessel in a forward direction. 
         [0011]    The propeller may be fully submerged in water, also known as fully wetted, and does not produce vapor cavities when powering the marine vessel at a cruising speed (e.g., 20 knots or more) of up to 50 knots or more, resulting in a completely “clean” inflow condition. In fact, vapor cavities are avoided at speeds of 50 knots or more. The propeller may also include efficiency ratios of over 60% with an overall propulsive coefficient of over 50%. The propeller includes a diameter in the range of 50% to 90% of a diameter for lateral dimension) of the tunnel. The propeller rotates to produce a thrust disc such that both an upper half and a lower half of the propeller produces thrust without turbulent flow characterized by a vortex and cavitation. 
         [0012]    The marine vessel may further include a shaft joined to the propeller with a shaft angle of about 6 degrees to a horizontal plane when the marine vessel is stationary in the water, producing an effective shaft angle of 0 degrees when the marine vessel is in motion at a cruising running angle of attack and does not produce cavitation during operation when powering the marine vessel at a speed of up to 50 knots or more. 
         [0013]    The marine vessel may also include a fixed shaft for transferring power to the propeller. The fixed shaft may be mounted with a positive shaft angle producing lift in a bow region of the marine vessel when moving at cruising speed. 
         [0014]    The marine vessel may further include a power source within the hull, rearward of the propeller or any desired placement in the hull that delivers power to the fixed shaft and propeller with an angled v-drive also mounted within the hull and rearward of the propeller. The propeller may also be mounted in a range of 10%-50% toward the bow from the transom of the marine vessel. 
         [0015]    An interceptor may be affixed on a trailing edge of the tunnel or a transom of the marine vessel providing the bow with an adjustable positive and a negative lift when moving at cruising speed. Notably, the marine vessel also does not produce a rooster tail when cruising at up to 50 knots or more. 
         [0016]    These and other aspects and objects of the present invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating preferred embodiments of the present invention, is given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    A clear conception of the advantages and features constituting the present invention, and of the construction and operation of typical mechanisms provided with the present invention, will become more readily apparent by referring to the exemplary, and therefore non-limiting, embodiments illustrated in the drawings accompanying and forming a part of this specification, wherein like reference numerals designate the same elements in the several views, and in which: 
           [0018]      FIG. 1  illustrates a perspective view of the bottom of a marine vessel according to the present invention; 
           [0019]      FIG. 2  illustrates a partial cross sectional side view of a marine vessel showing the present invention according to  FIGS. 1 ; and 
           [0020]      FIG. 3  illustrates a close-up, partial cross sectional side view of a marine vessel showing the present invention according to another embodiment. 
       
    
    
       [0021]    In describing the preferred embodiment of the invention which is illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited, to the specific terms so selected and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. For example, the words “connected”, “attached”, or terms similar thereto are often used. They are not limited to direct connection but include connection through other elements where such connection is recognized as being equivalent by those skilled in the art. 
       DETAILED DESCRIPTION OF EMBODIMENTS 
       [0022]    The present invention and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments described in detail in the following description. 
       System Overview 
       [0023]    Generally speaking, tractor mode propulsion of the preferred embodiments includes a fully submerged, fixed shaft drive line in a “pulling” mode. 
         [0024]    More specifically, and referring to the  FIGS. 1 and 2 . the engine of the marine vessel is coupled to a drive by way of a shaft or similar connection, which extends toward the front (bow) of the vessel and which may be accommodated by a “tunnel” or similar structure. The drive shaft is coupled to the drive and configured to rotate about its longitudinal axis for driving the propeller. In particular, the drive shaft extends toward the front of the vessel at a predetermined angle and terminates in the aforementioned tractor propeller, which is configured to pull water rearwardly relative to the bow (i.e., tractor configuration). 
         [0025]    The resulting design provides a propeller location closer to the bow than in known systems. As depicted in  FIG. 2 , the shaft angle is set at about 6 degrees, which gives an effective shaft angle of approximately zero considering the hull&#39;s running angle of attack and water flow angle into the propeller due to the tunnel shape of the boat. 
         [0026]    The invention delivers a number of advantages over conventional designs such as cavitation-free operation at up to 50 knots and greater with a fully wetted, submerged propeller thereby improving propeller efficiencies. Positive shaft angles also provide the vessel with a natural bow-up tendency, which is particularly advantageous at higher speeds such as during trimming out an outdrive. An interceptor may further be provided in the tunnel to provide adjustable transom lift and bow down as required through manual control or automatic computer control. 
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0027]    Marine propulsion systems are designed for a variety of applications. Beginning with  FIG. 1 , a tractor-mode marine propulsion configuration of the preferred embodiments is shown on the bottom side of a marine vessel  10 . Marine vessel  10  shows twin propellers  12 , but the invention may be applied to single-propeller vessels or any number of propellers. Marine vessel  10  includes a hull  44  that forms a bow  24 , a transom  26 , and chine  22 . A rudder  28  allows steering control of vessel  10  and is shown attached to the transom  26 . The rudder may, however, be located anywhere on the vessel  10 . A tunnel(s)  32  forms a recess in the hull  44  of the marine vessel  10  which houses the propeller  12 . The propeller may he located entirely within tunnel  32 , or partially within tunnel  32 . Preferably, at least half of the diameter of propeller  12  is located within the tunnel. A series of interceptors may be used to control the pitch of the marine vessel  10  as it moves through the water. The interceptors  30  may be automatically extended to create lift, thus providing the captain added control. The amount the interceptors extend from the transom may be automatically controlled or manually configured. 
         [0028]    The propeller  12  is driven by a fixed propeller shaft  16 . The rotation of the propeller shaft  16  and the blade pitch of the propeller  12  characterize the propulsion system as a tractor mode configuration. In tractor mode, the propeller  12  faces the bow  24  of the vessel, such that water is drawn from the bow  24  of the marine vessel  10  and expelled toward the transom  26  to effectively “pull” the vessel through the water. This is contrary to typical configurations where the propeller is located closer to the transom  26  and “pushes” the vessel  10  through the water. In order to qualify as a tractor mode configuration in the preferred embodiments, the propeller  12  should be located 10%-60% toward the bow  24  from the transom  26 . For example, at 50%, the propeller would be at the midpoint of the length of the vessel  10 . Preferably, the propeller  12  is located 20% toward the bow  24  from the transom  26 . 
         [0029]    The propeller  12  is driven by the propeller shaft  16  that is supported by a propeller shaft strut  14 . The propeller shaft  16  may pass through the hull  44  with a thru hull  18  port and be exposed to water or may be totally enclosed within the hull  44 . In an exposed configuration, as shown in  FIG. 1 , the thru hull port  18  may also he used as a water intake port for cooling the engine or other water intake needs. Preferably, a sleeve  50  connects to the hull  44  and encapsulates the propeller shaft  16  and prevents any contact of the propeller shaft  16  with water, as best shown in  FIG. 3 . 
         [0030]    As shown in  FIGS. 2 and 3 , the tractor-mode orientation of the propeller  12  draws water into the tunnel  32  to create a flow and pull of the vessel  10  through the water. An engine  38  within hull  44  may also be located in close proximity to transom  26  and generate rotational force through an output shaft  42 . The output shaft  42  redirects the rotational force with a gearbox  40  to the propeller shaft  16  and ultimately to propeller  12 . Any known device may be used to redirect the rotational force, such as a u-joint. Preferably, a gearbox  40 , such as a v-drive, may be used. While the gearbox  40  is shown within the hull  44 , it may be located outside of the hull  44  as well. Either of these configurations locates the engine  38  in close proximity to the transom  26  and creates more usable space within the hull  44 . Notably, more traditional drives, such as “pusher” drives, locate the engine  38  farther away from the transom  26  and therefore occupy more space within the hull  44 . 
         [0031]    Tunnel  32  is preferably formed uniquely for each vessel  10 . Different bull  44  designs require different tunnel  32  cross sections in order to perform at optimum levels. In the tunnel design of the preferred embodiment, the flow  34  of water through the tunnel does not create vortexes or turbulence. In other words, water approaching the propeller  12  will have a generally axial flow path, thus increasing the efficiency of the propeller. The inflowing water will also be free of aeration or cavitation, which can otherwise be a problem, especially at speeds of greater than 20 knots. In fact, in the preferred embodiments, problems due to issues like cavitation are dramatically lessened (compared to, for example, known “pusher” drives) at speeds of 50 knots or more. This increases overall efficiency and lowers fuel consumption. 
         [0032]    Preferably, the propeller shaft  16  creates an angle of between 3-12 degrees, and preferably about six (6) degrees or less, with the bottom datum line  46  of the vessel  10  when it is not moving. When the vessel  10  is moving through the water, e.g., at a speed of 20-50 knots or more, an effective shaft angle of 0 degrees is produced as the bow  24  pitches upward. The shaft angle is defined as the angle created between bottom datum line  46  and the propeller shaft  16 . The effective shaft angle may be defined as the angle of the propeller shaft  16  minus the hull running trim angle and minus the water flow angle into the propeller disc. As the vessel&#39;s speed changes, the angle of attack changes and creates a different effective shaft angle. 
         [0033]    The interceptors  30  may also be deployed/retracted as shown by arrows  36  to achieve a 0 degree effective shaft angle. Propellers  12  in this configuration are fully wetted and experience high efficiency of up to 80% while producing little or no cavitation. As the propeller shaft  16  and propeller shaft strut  16  are behind the propeller  12 , the propeller  12  is fed calm, turbulence-free water which substantially eliminates cavitation. 
         [0034]    The hull  44 , tunnel  32 , and the angle of the propeller shaft  16  all work together to attain an effective 0 degree shaft angle at a cruising running angle of attack. As the speed of a planing hull increases, the trim angle, or angle of attack decreases. The angle of attack is the angle between a reference line on the marine vessel&#39;s hull  44  and the vector representing the relative motion between the hull and the water through which it is moving. In sum, angle of attack is the angle between a reference line on the hull  44  and the oncoming water flow. While the angle of attack has an inverse relationship with hull speed, the hull design, weight distribution, and shaft angle determine what exactly the angle of attack will be at a given speed. Despite the relatively predetermined angle of attack, interceptors  30  may be used to dynamically adjust the angle of attack. In order to produce the most amount of thrust with the least amount of energy expended, a 0 degree shaft angle is optimal. As a result, it is possible to achieve an effective shaft angle of 0 degrees when the marine vessel is in motion at a cruising angle of attack due to the novel weight distribution of the engine  38 , shaft angle, tunnel design, and overall hull design. An interceptor  30  may be used to fine-tune the angle of attack and maintain a 0 degree shaft angle at cruising speed. Additionally, the propeller&#39;s propulsive coefficient, a constant that determines the amount of thrust produced for an amount of input power, may be increased due to the weight distribution of the engine  38 . hull design, effective shaft angle and undisturbed water flow into the propeller disc. 
         [0035]    Cruising speed is a relative term that changes according to hull design, weight distribution, and shaft angle. Cruising speed for a displacement hull may he defined as the speed in which a particular marine vessel experiences rapidly diminishing returns for the amount of power needed for an increase in speed. It is a function of how far astern the wake is forming and how large of a hole in the water between bow wave and wake the boat has to climb out of lit varies depending on the efficiency of the hull but is somewhere near, in knots, the number found by about one and a third times the square root of the waterline length in feet. 
         [0036]    Cruising speed for a planing hull is also related to efficiency but is a bit more dependent on hull bottom shape, engine performance. vibrations, and fuel consumption. As hull bottom design is very relevant once the hull is planing on the water surface, weight distribution of the engine plays a critical role in determining cruising speed. 
         [0037]    The rotating propeller  12  creates what is known as a “propeller disc”. The inventive configuration produces a propeller disc which generates thrust on the upper and lower halves of the propeller  12 . Some known configurations only generate thrust on the lower portion of the propeller disk, further increasing drive efficiency of the preferred embodiments. 
         [0038]    Moving on to  FIG. 3 , another embodiment of the invention is shown. In this embodiment the engine  38  is shown supported by engine mounts  48 . The output shaft  42  transmits rotational force through the gearbox  40  and to the propeller  12  with a propeller shaft  16 . The propeller shaft  16  is kept within the hull  44  of the vessel  10  with the use of a sleeve  50 . The sleeve may be incorporated with the propeller shaft strut  14  as shown, or may be an extension of the material that the hull  44  is formed with, for example, aluminum or fiberglass. Keeping the propeller shaft  16  within the hull may extend the service life of the drive system as it is shielded from the harsh elements found in the water and also eliminates the drag of a rotating shaft in water. The propeller  12 , propeller shaft  16 , sleeve  50 , and propeller shaft strut  14  may also be manufactured independently and installed in the tunnel  32  of various marine vessels  10 . 
         [0039]    Although the best mode contemplated by the inventors of carrying out the present invention is disclosed above, practice of the present invention is not limited thereto. It will be manifest that various additions, modifications and rearrangements of the features of the present invention may be made without deviating from the spirit and scope of the underlying inventive concept.