Patent Publication Number: US-2017369138-A1

Title: Propeller Assembly

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This is a non-provisional patent application based on co-pending U.S. Provisional Patent Application Ser. No. 62/354,411 (Attorney Docket No. MK-16-1) previously titled “Propeller Assembly”, filed on Jun. 24, 2016, the priority of which is hereby claimed and the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Field of the Invention 
     The present invention relates to a propulsion system for watercraft. More particularly, the present invention relates to an auxiliary propeller used in an axial arrangement with a standard propeller in the propulsion system. 
     Description of the Related Art 
     Propulsion systems are used to generate thrust to move a watercraft (also referred to herein as boat and defined as any vessel capable of moving through a water way with use of an engine and propeller). across or through water. Most of the watercrafts are propelled by mechanical systems that include an electric motor or an engine which powers a propeller. Boats often have one or two propellers (also called props) attached thereto for speed through the water. The propeller is generally secured to the rear portion of the electric or gas engine. To navigate the watercraft, the propeller is rotated in either a clockwise or counter-clockwise direction. Typically, once the boat is in shallow water, it will have difficulties pulling out to the deeper end. A boat or watercraft will displace water underneath its hull until the weight of the hull and the weight of the water displaced equal. This is typically called hole shot in boating terms since essentially a hole is formed under the boat. Sometimes the hole shot is also referred to as getting skeg out of the sand, acceleration from a standing position, or getting the boat from plane to acceleration. The hole shot is important information for determining proper hull/power combination. The faster a boat is able to achieve plane, the less fuel is consumed. 
     If the boat engine is started and the boater begins to navigate through the waterway at a closed throttle, generally the boat remains in the hole, i.e., the hole simply moves with the boat. The hull remains low, sitting in the water hole that was formed by the displacement of the boats&#39; hull. To get out of the hole, a boater needs to move the boat fast enough so that it can exceed the speed of the hole that is moving under the boat and have enough power and torque to get the boat to climb the hole in a decent amount of time. In boating, a good hole shot is the ability to get up on plane (“getting out of the hole”) and up to speed quickly from a stopped position. A poor hole shot would often be caused by the motor laboring and taking a long time to get up to speed (often because not properly propped for the load, or the boat is underpowered). 
     As an example, a high powered boat may have excellent top speed, but a poor hole shot, i.e., as the boat begins to move, the boats&#39; hole continues to move and even perhaps increase in depth due to the changing angle of the boat. So when the boat begins to climb out of the hole there is less total hull sitting in the water, and the smaller hull, having the same weight will tend to settle deeper into the water. But now as the boat begins to move, the boat will gradually start climbing the steep edge of the hole. As the boat climbs higher, the edge of the hole gets less steep—hence you see the bow of the boat begin to drop lower. Finally as the boat is almost out of the hole, the boat will be near level and the boat will be moving fast enough to plane on top of the water, leaving the hole behind. Now, if you take the same high powered boat with a much lower pitch and possibly larger diameter propeller, the engine will be able to spin the larger diameter propeller more quickly, be able to more quickly accelerate the boat, and will more quickly climb out of the hole. 
     A lower pitched propeller, which may help in removing the boat from a hole shot, has the disadvantage of generally having a lower top speed motor (defined herein as the engine and propeller). This is because the lower pitched propeller cannot navigate (or screw) itself though the water, as easily as a higher pitched propeller. 
     The ability to get the boat on plane quickly is important for safety as much as any other reason. The quicker a boater can get the bow back down, the sooner s/he can see what is in front of them and avoid any unsafe situations, as well as keep themselves and other boat passengers dry. 
     Hole shot-related problems often occur during take-off of a boat, and most often in shallow versus deep water. Existing motors having single propellers typically perform poorly in shallow water since they cannot easily overcome the hole shot caused. To overcome the problems listed above, boaters have experimented with using multiple motors on the boat for increased speed, modifying the shape of the blades of the propeller (also called cupping), modifying the venting arrangement of the exhausts around the propeller to aerate the water surrounding it, or changing or enhancing the rotational speed of the propeller in existing motors. Other avenues considered for this problem were to modify the boat itself, such as in using trim tabs to keep the boat flat when coming out of a hole. 
     It is well known that a watercraft with dual propellers generates a stronger thrust force than the thrust generated by those equipped with a single propeller. Most known dual-propeller watercrafts require dual engines, each of which powers a corresponding propeller. Thus, having a dual propeller system is impractical for small and inexpensive watercrafts. There exists a need for an inexpensive, easy to produce, dual propeller system that uses a single engine to power the two propellers, thus reducing the expense and weight of the watercraft and generating a strong thrust force. 
     Art located includes: 
     U.S. Pat. No. 2,672,115 to Warren discloses a propulsion device with dual propellers.
 
U.S. Pat. No. 3,261,229 to Dallas et al. discloses a propulsion system for a boat.
 
U.S. Pat. No. 3,470,961 to Halsmer discloses a clutch for a twin engine aircraft with two propellers that are mounted coaxially on a single shaft.
 
U.S. Pat. No. 3,922,997 to Jameson discloses a marine power transmission system.
 
U.S. Pat. No. 4,865,520 to Robert et al. discloses a marine propeller with an addendum.
 
U.S. Pat. No. 5,074,814 to Alan discloses a self-contained outboard twin propeller adaptor.
 
U.S. Pat. No. 5,494,466 to Stefan discloses transmission of dual propellers driven by an inboard marine engine.
 
U.S. Pat. No. 6,435,923 to Ferguson discloses a two-speed transmission with reverse gearing for watercraft.
 
U.S. Pat. No. 6,899,576 to Reinhold et al. discloses a twin-propeller drive for watercraft.
 
U.S. Pat. No. 8,668,533 to Philip discloses a water jet-based propulsion system that utilizes more than one water jet outlet port to control selective application of power to the water jets, using a splitter gearbox, thereby improving the efficiency of the marine craft at low and high speeds.
 
U.S. Pub. No. 2005/0064772 to Karel et al. discloses a dual propeller drive for a ski boat.
 
U.S. Pub. No. 2015/0047543 to Thomas discloses propulsion arrangement for a marine vessel.
 
DE 2427245 to Rudolf teaches a drive system for a power glider that has twin propellers mounted on arms with belt drives that are foldable into the fuselage.
 
EP 1476352 to Graham discloses a marine counter-rotating shaft drive mechanism.
 
WO 1993/000529 A1 to Richard discloses a power transmission for use in marine inboards.
 
     Most of the patents mentioned above disclose the use of propulsion systems that run two propellers with a single engine. Chain and sprocket arrangements are used to transfer power from the drive shaft of the engine to twin propeller shafts driving twin propellers. The propellers are arranged axially. However, the problem with most of the prior art systems is that the propellers wear out quickly and hole shot diminishes. Typically, dual propellers, which are coaxially aligned and driven in the same direction, are welded together. The welding of two propellers is time-consuming and labor-intensive and often shrinks the barrel of the propeller. This does not allow a smooth fit between the two propellers. This misalignment causes pulling and eventual burning of the propellers. The problem with welding is that the metals do not attach evenly, since the metal expands and shifts a little, resulting in the components not fitting snugly. Over time, use and vibration, the weld may sustain itself, but the propeller burns out. 
     In light of the foregoing, there exists a need for an easy to prepare, inexpensive, mechanism and/or a propeller to enhance the thrust force of a watercraft engine, improve the hole shot and maintain (or obtain) top speed of the watercraft. 
     SUMMARY 
     Disclosed herein is an easy and inexpensive method to increase power to a boat motor. While the problem to be solved was avoiding hole shot issues for boats in shallow water, the present invention has numerous benefits beyond the remedy for hole shot concerns. Further disclosed is an auxiliary propeller allowing the combining of two propellers in place on any given engine. This is not suitable for counter-rotating systems, but otherwise useful or suitable for all single output shafts. Still further disclosed is a unique coupling system to attach two propellers together without the need for a method of adhesively securing. Herein, adhesively securing is defined as welding, a chemical adhesive suitable for metal or plastic, or screws to hold the propellers in place or the like. Assembly of the dual propellers can be achieved manually or automatively (or by machine). The dual propeller system increases the thrust, and power of the boat. A perfect alignment is formed when the two propellers are combined, minimizing or eliminating the problems caused by welding or securing propellers with screws (problems such as pull of the metal, vibrations weakening the weld or attachment). A barrel or coupling device having a crown (grooves) was developed which fits securely in the interior section of the lead propeller, and allows for the combining of two propellers onto one engine. It was found that the present inventive device was able to move a boat out of shallow water using about half the RPMS (rotations per minute) than would normally be used. For exemplary purposes, most hulls require less than 2500-3000 RPMS to get on plane in shallow water conditions (shallow water defined herein as about 0″-12″ of water, or preferably anything less than 6″) with this device; with existing propeller systems it would require wide open throttle to get out of the hole. 
     An object of the present invention is to provide a method to enhance the power and thrust of an watercraft engine by combining two propellers; one becomes the trailing propeller that is secured and aligned coaxially with an existing or lead propeller. The trailing propeller includes a first cylindrical hub (or barrel with grooves at its end, also referred to as a coupling system), a second cylindrical hub (accepting the barrel with grooves), and a conical profile there between. The first cylindrical hub or barrel includes a plurality of grooves on one end that are described and shown herein as rectangular in shape. While rectangular is a preferred shape, other shapes such as semi-circular, square-like, round over, V-groove, etc. are acceptable provided the groove fit into propeller. The shape allows the figure sliding over the lead propeller. The grooves are to be aligned with preferably 30° increments for timing purposes and are equidistant to each other. The second cylindrical hub includes a cylindrical mount ring that holds a drive sleeve. The cylindrical mount ring is attached to the second cylindrical hub or spline by using a set of radial mount ring flanges. The conical profile formed between the first cylindrical hub or barrel, and the second cylindrical hub allows smooth alignment of the trailing propeller with most if not all of current or existing propellers. The first cylindrical hub having the barrel with grooves is inserted in a hub (or interior portion) of the existing propeller. The outer diameter of the barrel is selected based on the inner diameter of the hub of the existing propeller. The trailing propeller can be effectively and consistently used with propellers made by any existing manufacturer. 
     The present invention comprises a barrel having grooves on one end, and ancillary parts to secure the propellers, all of which form an aligning system. The barrel fits into what becomes the trailing propeller which is coupled and aligned to a leading propeller without adhesively securing or welding. The leading propeller is any existing propeller. Thus, the coupling of the trailing propeller with the leading propeller is not time-consuming and less labor-intensive to combine than existing welding or attaching techniques. The absence of welding eliminates a potential misalignment of the trailing propeller and the leading propeller. Further, the trailing propeller may be attached to an engine irrespective of the engine manufacturer. Moreover, the trailing propeller and leading propeller do not counter-rotate with each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. Embodiments of the present invention will hereinafter be described in conjunction with the appended drawings provided to illustrate and not to limit the scope of the claims, wherein like designations denote like elements, and in which: 
         FIG. 1  shows an isometric view of a dual propeller assembly; 
         FIG. 2  shows an isometric view of a torsion bushing; 
         FIG. 3  shows an isometric view of a thrust washer; 
         FIG. 4A  shows an isometric view of a leading propeller of the propeller assembly of  FIG. 1 ; 
         FIG. 4B  shows an isometric view of the leading propeller with the torsion bushing and the thrust washer; 
         FIG. 5  shows an isometric view of a drive sleeve (or spline); 
         FIG. 6A  shows an isometric view of a trailing propeller; 
         FIG. 6B  shows a side view of the trailing propeller; 
         FIG. 6C  shows a top view of the trailing propeller; and 
         FIG. 6D  shows an isometric view of the trailing propeller holding the drive sleeve. 
         FIG. 7  shows a lead propeller to receive a trailing propeller. 
         FIG. 8  shows a trailing propeller with a different pitch than shown in  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     As used in the specification and claims, the singular forms “a”, “an” and “the” include plural references, unless the context clearly dictates otherwise. For example, the term “an article” may include a plurality of articles unless the context clearly dictates otherwise. 
     Those with ordinary skill in the art will appreciate that the elements in the figures are illustrated for simplicity and clarity, and are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated, relative to other elements, in order to improve an understanding of the invention. 
     There may be additional components described in the foregoing application that are not depicted in any of the described drawings. In the event such a component is described, but not depicted in a drawing, the absence of such a drawing should not be considered an omission of the design from the specification. 
     Before describing the present invention in detail, it should be observed that it utilizes a combination of system components, which constitutes an axial alignment of two propellers. Accordingly, the components and the method steps have been represented, showing only specific details that are pertinent for an understanding of the present invention, so as not to obscure the disclosure with details that will be readily apparent to those with ordinary skill in the art, having the benefit of the description herein. 
     As required, detailed embodiments of the present invention are disclosed herein. However, it should be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, the specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting, but to provide an understandable description of the invention. 
     The present invention comprises a barrel having grooves and its ancillary parts. The barrel fits into a trailing propeller that is secured and aligned coaxially with a leading propeller to form a dual propeller assembly. In its simplest form, the barrel fits into the trailing propeller with its smooth end, and the grooves are secured into the leading propeller. The propeller assembly facilitates the movement of a watercraft when the propeller shaft of the leading propeller, which is connected to a driver shaft which is in turn connected to an engine of the watercraft, is rotated. For easy understanding, the forthcoming specification first describes various components and assembly of the leading propeller. The assembly can be configured manually without need for tools or welding. Then, the components and assembly of the trailing propeller of the present invention are described, along with the complete propeller assembly of the leading propeller and the trailing propeller. The leading propeller includes an assembly of a cylindrical hub and multiple blades. The trailing propeller includes first and second cylindrical hubs, a conical profile, and multiple blades. 
     Referring now to  FIG. 1 , a propeller assembly  100  that includes a conventional leading propeller  102  and a trailing propeller  104  of the present invention, in accordance with an embodiment of the present invention is shown. The leading propeller  102  includes three blades  106   a ,  106   b , and  106   c . The trailing propeller  104  includes three blades  106   d ,  106   e , and  106   f  ( 106   f  not shown). The trailing propeller  104  is secured and aligned coaxially with the leading propeller  102  to generate an increased thrust force especially useful for a boat in shallow water. A 3-blade prep is shown for exemplary purposes and any number of suitable blades may be used herein provided a coaxial alignment is achieved in the assembly. 
       FIG. 2  illustrates an isometric view of a torsion bushing  202  that protects the engine of the watercraft. The torsion bushing  202  has a cylindrical body which is tapered along its length. The torsion bushing  202  thus has different diameters at the two ends thereof. Further, the torsion bushing  202  has multiple grooves on its inner surface. The torsion bushing  202  axially twists along the longitudinal axis in the event of an impact, such as the collision of the watercraft with an obstacle. To facilitate such axial twisting the torsion bushing  202  is made of a resilient material. An exemplary resilient material for the fabrication of the torsion bushing  202  is an elastomeric polymer, or heavy duty plastic (for example, polyethylene, polypropylene, ABS, and the like) provided it can withstand sheer and temperature forces it will be exposed to. It can also be made of suitable metals such as brass, stainless steel, cast iron, and the like. The torsion bushing can be manufactured, or purchased from a suitable manufacturers such as Evinrude, Mercury, or Honda (or other motor engines manufacturers). The present invention used a bushing from a Mercury engine. 
       FIG. 3  illustrates a thrust washer  302  (also referred to as washer) that prevents movement along the axis of a shaft. The thrust washer  302  is positioned towards the end of the propeller assembly  100  that is attached to the engine, to prevent damage to gears and other operating parts (not shown) of the outboard/inboard motor. The washer has a smooth beveled interior to allow for a secure fit of the components. The washer can be manufactured, or purchased from a suitable manufacturer. The present invention used a washer from the manufacturer Mercury. 
     Mercury brand hubs or boat parts in general (in particular spline or hub system) are relatively universal and fit most to all boats, including Evinrude brand boats. With perhaps slight adapting, Mercury brand parts can be made to work with all or most boat brands. 
       FIGS. 4A and 4B  illustrate the leading propeller  102  of the propeller assembly  100 .  FIG. 4A  illustrates the leading propeller  102  without the thrust washer  302 . The leading propeller  102  includes a cylindrical hub  402 , a cylindrical mount  404 , and radial flanges  406   a - 406   c . The blades  106   a - 106   c  extend from an outer surface of the cylindrical hub barrel  402 . One end of the cylindrical mount  404  has a diameter equal to the larger diameter of the torsion bushing  202 . The leading propeller  102  can be made of either aluminum, stainless steel or other similar materials. Further,  FIG. 4B  illustrates the leading propeller  102  with the thrust washer  302  attached at one end thereof. The thrust washer  302  has an opening that receives the propeller shaft and is tightly fitted in the cylindrical mount  404 . The thrust washer  302  has a conical surface at the bottom thereof, which allows it to rest on the cylindrical mount  404  and top of the end of torsion bushing  202 , which has a smaller diameter. 
       FIG. 5  illustrates a drive sleeve  502  that has a cylindrical body  504 , a circular flange  506  and a cylindrical head  508 . The drive sleeve  502  includes a first set of splines, two of which are shown in the  FIGS. 5-510   a  and  510   b —that extend along the cylindrical body  504 . The circular flange  506  is positioned between the cylindrical body  504  and the cylindrical head  508 . The cylindrical head  508  includes a second set of splines internally that assist the propeller shaft to pass through the drive sleeve  502 . In one embodiment, the drive sleeve  502  is made of bronze but can also be made of stainless steel, iron, aluminum, elastomeric polymer or the like, or other suitable material which results in a solid sleeve. Further, the length of the cylindrical body  504  is more than that of a standard drive sleeve such that the trailing propeller  104  can be easily coupled to the leading propeller  102 . Each groove of the torsion bushing  202  is arranged to receive the corresponding spline of the drive sleeve  502 . The grooves are tapered to enable maximum torsional twisting and distribute stress evenly along the torsion bushing  202  in the event of a significant impact. The drive sleeve can be manufactured, or purchased from a suitable manufacturer such as Mercury. The present invention used a Mercury brand purchased sleeve. 
       FIGS. 6A-6D  illustrate the trailing propeller  104  of the dual propeller assembly  100  of  FIG. 1 . As shown in  FIGS. 6A and 6B , the inventive barrel  602  is installed inside the trailing propeller  104 .  FIG. 6A  includes a first cylindrical hub  602 , a second cylindrical hub  604 , and a conical profile  606  there between. The diameter of the first cylindrical hub  602  is less than that of the second cylindrical hub  604 . The conical profile  606  is formed between the first cylindrical hub  602  and the second cylindrical hub  604 . One end of the first cylindrical hub  602  includes multiple grooves  606 , three of which are identified as  606   a - 606   c . The grooves  606  are equally spaced and are locked onto the radial flanges  406   a - 406   c  of the leading propeller  102  (see  FIG. 4B ). There may be more or less than three grooves on the first cylindrical hub  602 , generally 3-12 grooves on hub  602 , without departing from the scope and spirit of the present invention. 
     The torsion hub holds the trailing propeller in place with a locking nut on the engine shaft. (See  FIG. 6D ). 
     As shown in  FIG. 6C , the trailing propeller  104  includes a cylindrical mount ring  608  with radial mount ring flanges  610   a - 610   c . The radial mount ring flanges  610   a - 610   c  are attached to the internal surface of the second cylindrical hub  604  to affix the cylindrical mount ring  608  to the trailing propeller  104 . The blades  106   d - 106   f  extend from the outer surface of the second cylindrical hub  604 . It will be well understood to a person skilled in the art that the number of blades attached to the trailing propeller  104  may vary. While blades impact thrust, blades are not the primary scope of the present invention. 
     Cylindrical hub  602  fits inside of hub  402  to serve as the alignment system for the dual propeller assembly. The outer diameter of the hub  602  is sized so as to secure to the cylindrical hub barrel  402  of the leading propeller  102 . The diameter can be modified (reduced or expanded) with a lathe to fit different propellers; or increased in diameter with rubber shims. For example in  FIG. 6A , rubber shims may be placed and heat shrunk over the slots to alter the diameter. When the trailing propeller  104  is coupled to the leading propeller  102 , the multiple grooves  606   a - 606   c  of the first cylindrical hub  602  are locked on the corresponding radial flanges  406   a - 406   c  of the leading propeller  102 . The conical profile  606  allows the trailing propeller  104  to align with the tapered end of the leading propeller  102 . 
     In one embodiment and as shown herein, the grooves  606   a - 606   c  are rectangular in shape and symmetrical to ensure that the trailing propeller  104  is aligned comfortably with the leading propeller  102 . To secure the trailing propeller  104  to the leading propeller  102 , the drive sleeve  502  is inserted through the cylindrical mount ring  608  of the trailing propeller  104  into the leading propeller  102 . The circular flange  506  of the drive sleeve  502  rests on the cylindrical mount ring  608 .  FIG. 6D  illustrates that the trailing propeller  104  holds the drive sleeve  502 . The torsion bushing  202  of the leading propeller  102  receives the cylindrical body  504  of the drive sleeve  502 . The design of the trailing propeller  104  makes it easy to mechanically align it with the leading propeller  102 . The alignment allows the leading and trailing propellers  102  and  104  to work together in sync. The assembly works best when the leading and trailing propellers are aligned. 
     The propeller shaft (not shown) has a tapered section for mating with the thrust washer  302 , and a splined section for mating with the drive sleeve  502 . Further, the propeller shaft includes a threaded section to receive the nut (not shown). To secure the propeller assembly  100  to the propeller shaft, the torsion bushing  202  is inserted into the cylindrical hub barrel  402 . Further, the trailing propeller  104  is aligned with the leading propeller  102  by means of the grooves  606   a - 606   c  and the radial flanges  406   a - 406   c . The drive sleeve  502  is inserted into the leading propeller  102  through the torsion bushing  104 . The propeller assembly  100  is then affixed to the propeller shaft such that the propeller shaft is inserted with the drive sleeve  502 . A washer is then affixed to the propeller shaft. Subsequently, the nut is placed on the propeller shaft so that the washer is tightly secured to the drive sleeve  502 . Thus, propeller assembly  100  is secured to the propeller shaft. 
     When the propeller shaft rotates, the torque, generated as a result of the rotation, is transferred to the drive sleeve  502 , and then to the torsion bushing  202 , followed by to the cylindrical hub barrel  402  of the leading propeller  102 . Consequently, the torque is then transferred from the leading propeller  102  to the trailing propeller  104 . The propeller assembly  100  is intact and ensures that the trailing propeller  104  spins synchronously with the leading propeller  102 . 
     The trailing propeller  104  may be manufactured using either of an investment casting method or a machining method. Further, the trailing propeller  104  can be made of materials such as steel, aluminum, stainless steel, plastic, carbon fiber, all types of carbon, and fiberglass, the most preferred materials being stainless steel and aluminum. The first and second cylindrical hubs  602  and  604  of the trailing propeller  104  can be made of heavy-duty plastic if desired. Plastics such as described above. In another embodiment, the first and second cylindrical hubs  602  and  604  of the trailing propeller  104  can be made of aluminum. 
     The trailing propeller  104  can be constructed in all dimensions to fit leading propellers of 5 horsepower (hp) to 400 hp in size. The trailing propeller  104  works using engines having a power range of about 115 hp to 400 hp. The propeller assembly  100  creates a stronger thrust force than a single propeller assembly. The use of the propeller assembly  100  is recommended for water of less than 12 inches, and has been found to be the most beneficial in extremely shallow water (of about or less than 6″ deep) operations, as the propeller assembly provides a strong thrust. 
     For exemplary purposes, preferred dimensions of the trailing propeller  104  are: the diameter (about 3″ to about 4.25″) and length (about 2.5″ to about 4″) of the first cylindrical hub  602  are preferably about 4.16″ and 3″, respectively. The diameter of the second cylindrical hub  604  is about 3″-5″ and preferably about 4.81″. The length of the trailing propeller  104  is about 7″-10″ with a preference for about 9-10 inches. The inner and outer diameters of the cylindrical mount ring  608  are about 1″-1.75″ with a preference for about 1.65″ to about 1.75″ and 2″-3″ with a preference for about 2.25 inches, respectively. The thickness of the first cylindrical hub  602  is about 0.10″-0.250″ with a preference for a thickness of about 0.20″. 
     The leading and trailing propellers  102  and  104  align axially and spin synchronously. This allows the propeller assembly  100  to maintain contact with the water effectively and hold more water mass on the leading and trailing propellers  102  and  104 . This improves the hole shot. Further, the propeller assembly  100  enhances steering and handling of the watercraft. The trailing propeller  104  works with most if not all types of outboard and inboard motors. Moreover, the design of the trailing propeller  104  adapts to most if not all marine engines available. Experiments were conducted with a trailing propeller ( 104 ) having a standard V6 barrel. The dimensions of the trailing propeller  104  can be adjusted to fit most if not all outboard propellers. 
     It was found that the propeller assembly  100 , with the leading and trailing propellers  102  and  104 , retains water on the blades for twice as long as under normal conditions. This allows the blades to remain in contact with water, even though half of the propeller assembly  100  is outside of the water. The propeller assembly  100  allows outboards to get in very shallow water while doing the least amount of damage possible to the environment. It was also found that the propeller assembly  100  can operate completely above the running surface in a river with one-third to one-half of the blades on the water surface. 
     The alignment technique uses the geometry of the common outboard propeller to align the trailing propeller  104  mechanically. The trailing propeller  104  can be effectively and consistently used with propellers made by other manufacturers and it is accomplished with no loss of speed to the engine. The additional cupping of the blades, changing from 3 to 4 blades or 4 to 3 blades in the case of 4 stroke engines, enables additional rotations per minute (rpm) of the propeller assembly  100 . 
     The barrel can be configured by adding slots and interior footing. The barrel may be modified to accept interchangeable blades allowing interchangeable pitch. This occurs by switching out the different pitch blades. An embodiment of this interchangeable system is use of polymeric composite materials, or aluminum, or stainless steel. The changing of materials allows for a less costly assembly for customers without a loss of performance. The user can experiment with pitch size for their boat, and or a single blade replacement for the propeller assembly, and determine what works best while the boat is in the water. 
     Another alternate embodiment is having a bevel on the lead barrel which allows a stop point for the trailing blades attached to the trailing barrel. This creates an assembly. 
     Collectively,  FIGS. 7 and 8  illustrate that the invention can be modified for different boating needs of the user. This invention allows for modification of the pitch, blade and blade numbers, slots, and barrel to accurately select a correct configuration for a boating set-up. One of skill in the art will appreciate that the inventive propeller assembly herein, will consider factors such as boat engine, size, and gear ratio to ultimately create stern lift for the boat. The pitch of the blade can be varied, both front and rear, to accommodate different boating applications of the user. As the pitch varies, generally the position of the blade on the barrel will vary. 
     Example 
     A turbo 1 Yamaha brand prop (the leading prop) was employed to align with the inventive trailing propeller. The trailing propeller slides directly over the radial flanges of the leading propeller adjusting evenly so as alignment of the hubs is intact. The propeller assembly was placed on a 21 foot boat and taken to water having 6″ of depth to create a hole shot situation. It was found that the 21′ boat while standing in 6″ of water was able to move out of the water in ½ of the boat length. 
     Comparative: The same boat was in the hole shot with the standard turbo 1 Yamaha brand prop, and no trailing inventive propeller to form the assembly. The boat was not able to get on plane at all, or out of the water, and needed to drive in circles to get itself out of the hole shot. When compared to a high performance engine (hole shot prop) the distance to plane was 4 times as long in the above situation. In about 12″ of water, this depth still considered shallow, the 21′ test boat required more than a boat length to get on plane and needed to drive in circles to get out of the hole. 
     The propeller assembly  100  solves a poor hole shot problem without loss of speed and wears out slowly because of its efficiency. Although all cupping can be removed by wearing out of a propeller, the inventive propeller assembly  100  outperforms most of the modified propellers. It was seen that even though the propeller assembly  100  was completely worn out, it had a better hole shot than other modified propellers. Alternatively, when standard propellers exhibit little performance, it has been found that the present invention does not allow performance to suffer; both propellers can have significant wear and with the inventive prop, still perform better than a new or refurbished (“mint condition”) standard propeller. The ability to couple the leading and trailing propellers  102  and  104  together improves hole shot with minimal to zero loss of speed. Further, the propeller assembly  100  design allows for the wearing out of the leading propeller  102  while protecting the wearing off of the trailing propeller  104 . This allows a user to upgrade the performance of a propulsion system without replacing both the propellers. The propeller assembly  100  allows a boat to move out of shallow water in about a third to half the RPMS of its normal speed. 
     The leading propeller  102  and the trailing propeller  104  are coupled and aligned without welding. The propeller assembly  100  allows coupling of the leading and trailing propellers  102  and  104  in minimum time and eliminates potential misalignment from welding. The propeller assembly  100  can be used with both 4-stroke and 2-stroke motors. The leading and trailing propellers  102  and  104  do not counter-rotate. 
     While not wishing to be bound by theory, hole shot (thrust) is maximized by allowing water to remain on more blade surface (generally twice as many blades). The length of the propeller and number of blades maximizes the working force at hole shot. As speed increases, the turbulence of the leading propeller negates the efficiency of the trailing propeller. As propeller speed increases boat speed, the trailing prop idles along, synchronous to the leading propeller. This allows boats to achieve maximum speeds while delivering superior hole shot. Hole shot is increased between 60% to about 80% by adding, and correctly using, the present invention to an existing propeller. 
     It has been found that the present invention impacts steering of the boat and changes the steering from propeller driven to more jet-boat like driven. The handling and steering change once the inventive propeller assembly is installed and creates a safer operation, in particular a reduced blow-out during turns resulting from propeller ventilation often found on standard propeller systems. The reverse thrust is enhanced with the inventive propeller assembly and results in ease and improved stopping, especially important when the boat is near or around decks or docks. 
     Table 1 outlines the water depth and boat length found to get on plane, also known as moving out of the depth noted of water with a boat having the inventive propeller assembly. This shows the invention is directed to water less than 12″ (inches) deep, or areas where the bottom of the water area is soft mud or clay. The boat reached plane within 3-10 seconds and usually between 3-5 seconds, and in some cases, almost instantaneously. The examples for Table 1 were conducted with a 23 foot Shoal Water Cat Boat. 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Water depth 
                 out of hole shot 
               
               
                   
               
             
            
               
                  0″(soft mud) 
                 1 boat length 
               
               
                  4″(soft mud) 
                 1 boat length 
               
               
                  6″ (clay bottom) 
                 ½ boat length 
               
               
                 12″ (clay bottom) 
                 ½ boat length 
               
               
                 14″(hard sand) 
                 difficult to get out of; generally a boater will stay away 
               
               
                   
                 from this condition because the hard sand destroys 
               
               
                   
                 equipment. To get out often requires 180-360 
               
               
                   
                 degree spin of the boat and this is then not using the 
               
               
                   
                 invention. 
               
               
                   
               
            
           
         
       
     
     It has been found that the speed performance is not lost as the inventive propeller assembly wears. Often with traditional propellers speed is impacted, and almost always reduced with use or wear and tear of the propellers. With the inventive assembly, when it was newly placed on the boat, the speed was about 58 miles per hour. It was found after about 200 hours of use, the speed with the inventive propeller assembly was 57 miles per hour. Comparatively, a Bravo 1, 4-blade propeller after about 50 hours of similar use, was running at a reduced maximum speed by 5-10 miles per hour. 
     The present invention can produce hole shot in 12″ and usually 6″ or less of water without a counter rotating propeller. It can be mechanically assembled without the need to weld or cast the unit, the front and trailing propellers can be interchanged, and the unit can be retrofitted on a standard outboard motor. 
     The present invention has been described herein with reference to a particular embodiment for a particular application. Although the selected embodiments have been illustrated and described in detail, it should be understood that various substitutions and alterations are possible. Those with ordinary skill in the art and access to the present teachings may realize that additional various substitutions and alterations are also possible without departing from the spirit and scope of the present invention, and as defined by the following claims.