Patent Publication Number: US-2011065341-A1

Title: Push Paddle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/224,035 filed Jul. 8, 2009. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISK APPENDIX 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     The present invention relates to poles and paddles used for propelling a boat or other watercraft from a standing position. The invention is especially relevant to stand-up paddleboarding (SUP). 
     Examples of stand-up propulsion methods include long-handled versions of canoe and kayak paddles, punting poles for pushing off the bottom, and various types of ski-poles. The most popular paddle design for stand-up paddleboarding (SUP) is an elongated version of a canoe paddle, e.g. those made by C4 Waterman Inc. Very long kayak paddles have also been used by SUP enthusiasts as well as stand-up kayakers. 
     Paddling with these elongated paddles is tiring and inefficient because the user must tense muscles throughout the legs, buttocks and torso just to resist the torque applied to the paddle. Nearly all the useful work is done by the back and arm muscles, and the motion fails to utilize the power of the larger muscle groups. 
     Punting with a pole is a biomechanically superior motion since the user can apply body weight to the pole and bend at the hips and knees as well as the arms. Very little energy is wasted tensing muscles that do no useful work. The large muscles of the legs and buttocks are successfully employed to raise the center of gravity of the body during the recoil stroke. 
     Improvements have been made to the punting pole to provide better purchase against underwater grass (U.S. Pat. No. 2,787,795 to Snodgrass 1957), or to reduce the tendency to get stuck in mud (U.S. Pat. No. 6,168,480 B1 to Schaller 2001), but these inventions do not address the main problem with punting: the need for shallow water. 
     The idea of a “ski pole” for use on water dates back to Leonardo Da Vinci. His concept appears to involve simple floats attached to the ends of ski poles which would not provide much “traction”. 
     U.S. Pat. No. 2,893,021 to Lundborg (1957) describes a ski-pole anchored to the hand and forearm. On the end of the pole is a round, slightly buoyant paddle bent forward at about 45 degrees. The invention does not appear to be very efficient since the elbow and shoulder move through only a small fraction of their useful range. The device requires large torques on the elbow and shoulder joints, and the large muscles of the body are not employed. 
     U.S. Pat. No. 4,527,984 to Gilbert (1985) describes ski-poles with floats resisting downward force and a shovel-shaped paddles to resist slipping backwards through the water. This invention models the poling motion involved in cross-country skiing, which is reasonably efficient, but control over the poles is limited since each is held by one hand. 
     U.S. patent application Ser. No. 11/470,217 by Wilkinson (2006) describes a variety of buoyant canoe and kayak “safety” paddles. These paddles are intended to be used in the conventional way, and have the same biomechanical inefficiency as conventional SUP paddles. 
     SUMMARY OF THE INVENTION 
     The objectives of the push-paddle invention are as follows:
         Utilize the power of the large muscle groups of the body and minimize the need to tense muscles that do no useful work.   Extract maximum power from the arm, back and shoulder muscles by working the shoulder and elbow joints through a wide range of motion.   Minimize energy lost due to backwards slippage of the paddle through the water.   Minimize energy lost as the paddle engages and disengages the water.   Provide a very lightweight paddle with low inertia.   Provide a paddle that can be manufactured easily.   Allow length adjustment of the paddle to adapt to the body size of the user.   Allow the pole to be shortened for more compact stowage.   Allow the push-block to be removed for more compact stowage.   Minimize wind resistance during the recoil phase.   Allow the paddle to exit quickly from the water at the end of the stroke, with minimum effort.   Minimize suction and entrainment of water (parasitic mass) as the push-block exits the water.   Minimize the height that the hands must be raised in order for the push-block to clear the water on the recoil phase of the stroke.   Minimize the yaw moment on the watercraft when paddling on one side.   Allow the paddle to be used as a balance aid when standing up and when paddling.   Allow the paddle to operate efficiently over a range of effort-level.   Avoid bobbing and shimmy of the paddle during the power stroke.   Provide the ability to turn sharply, accelerate or stop quickly, and to paddle backwards.   Reduce fluid drag on the watercraft by transferring weight to the paddle.   Provide a rugged paddle that is not damaged by hitting rocks or banging against the watercraft.   Avoid cutting or bruising the user, the watercraft or other people.       

     The present invention achieves the above objectives using a wedge-shaped buoyant “push-block” on the end of a pole. The pole is preferably held with both hands on the upper third of the pole, and the paddling motion most closely resembles punting, i.e. pushing down and backwards. Compared with conventional SUP paddles, the bending moment applied to the pole is minimal. 
     The motion is efficient because the user can sink his/her body weight into the pole on the power stroke, and then use the large muscles of the buttocks and legs to stand back up straight. Applying downward force to the pole also reduces the weight on the watercraft which reduces fluid drag. In contrast, a conventional SUP paddle tends to pull the watercraft deeper into the water during the power stroke. 
     The downward component of force applied to the paddle is reacted against the buoyant force and the lift generated as the push-block slips backward through the water. Backwards slippage represents lost power and should be minimized. There are trade-offs here with respect to the width, height and buoyancy of the push-block. A larger bottom face on the push-block with provide higher fluid drag, and less slippage, but will also be heavier and wider which will reduce the stroke rate and make the watercraft more likely to yaw. Increasing the height of the push-block may require the arms to be lifted higher during the recoil phase. 
     While the “frontal area” of the push-block is constrained by the aforementioned trade-offs, it is still possible and desirable to maximize the coefficient of drag. In the present invention, this is achieved is by making the wedge-end of the push-block point down into the water. This causes separation of flow and minimizes the fluid pressure on the top face of the wedge. Additional methods to increase drag include the following:
         relatively sharp edges adjacent to the bottom face of the wedge   making the bottom face concave   angling the sidewalls of the wedge to form an acute angle between the sidewalls and the bottom face   using flanged sidewalls       

     Conventional SUP paddles have a power stroke that starts with the paddle slightly ahead of the handle. The forward angle of the pole relative to the water is typically about 100°. At the end of the power stroke the angle relative to the water is about 60°. In contrast, the push-paddle has a power stroke that starts with the pole approximately vertical (90°) and ends with the pole at about 30° or less. 
     For the push-block to exit the water quickly and cleanly, the top face of the wedge can have an angle of about 135° or more relative to the pole axis. This avoids “snagging” the water on the recoil phase of the stroke. The bottom face of the wedge is the “push” surface. An angle of 105° relative to the pole axis provides good initial “traction” (high drag) and provides lift which reduces the need for buoyancy. The lift effect can be enhanced by rounding the back end of the wedge. This increases the lift effect as the push-block goes underwater, making the push-block stay at or near the surface of the water over a wider range of pole forces. One successful embodiment measures approximately 10.5×12×4 inches and displaces 318 cu-in. 
     In another embodiment, the push-block is shaped like a hydrofoil and is intentionally driven deep underwater in the beginning of the power stroke. Later in the power stroke, the buoyant force causes the push-block to “fly” upwards and forwards, thus producing forward thrust. 
     Additional embodiments are provided which allow the length of the pole and the angle of the pole relative to the push-block, to be adjusted. Another feature is the ability to detach the pole from the push-block and to shorten the pole for more compact stowage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a push-paddle in use, just prior to insertion into the water. 
         FIG. 2  shows a push-paddle in use, in the middle of the power stroke. 
         FIG. 3  shows a push-paddle in use, at the end of the power stroke. 
         FIG. 4  shows a perspective view of a push-paddle in accordance with the invention, including an adjustable length pole and detachable push-block. 
         FIG. 5  shows a perspective view of the push-paddle of  FIG. 4 , with the pole retracted and the push-block detached. 
         FIG. 6  shows an isometric view of a push-block having relatively sharp edges. 
         FIG. 7  shows a bottom-isometric view of the push-block of  FIG. 6 . 
         FIG. 8  shows a perspective view of a push-block with side flanges. 
         FIG. 9  shows a perspective view of a push-block with chamfered edges where the top face of the wedge meets the sidewalls. 
         FIG. 10  shows a perspective top-view of a push-block having angled sidewalls. 
         FIG. 11  shows a perspective view of a push-block having a convex top face and a concave bottom face. 
         FIG. 12  shows a perspective view of a push-block having a rounded back-end, convex top face, and concave bottom face. 
         FIG. 13  shows a top view of the push-block of  FIG. 12 . 
         FIG. 14  shows cross-section A-A of of  FIG. 13 . 
         FIGS. 15-17  show side views of another variation of push-block, in accordance with the invention, at three stages in the stroke cycle: insertion into the water, mid-power stroke, and end of power stroke. 
         FIGS. 18-21  show side views of a push-block having a rounded back-end. Four stages of the power stroke are shown and the force vectors are annotated. 
         FIGS. 22-24  show side views of an embodiment of the invention that relies on the push-block being sunk underwater. 
         FIGS. 25-26  show cut-away side views of a push-block with adjustable pole angle. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1-3  show push-paddle  20  being used to propel a surfboard. Push-paddle  20  comprises pole  50  and push-block  22 . The user holds the upper section of the pole, and the bottom end is attached to the push-block  22 . In  FIG. 1 , the user is about to press the push-block  22  down into the water to start the power stroke. In  FIG. 2 , the push-paddle is in the middle of the power-stroke and the user is applying force mostly in line with the pole axis. In this embodiment of the invention, as shown in  FIG. 2 , the push-block  22  is slightly underwater. In  FIG. 3  the power stroke is complete and the push-block  22  is starting to emerge from the water aided by its buoyancy. 
       FIG. 4  shows a perspective view of push-paddle  20  with additional details. Push-block  22   a  is wedge-shaped. The top face  26  of the wedge, and bottom face  36  (not visible) intersect to form wedge-edge  38 . Sidewalls  28  intersect the bottom face to form side edges  40 , and intersect the top surface  26  to form top edges  44 . Faces  30 ,  32  and  34  form the back-end of the wedge. 
     In this embodiment, pole  50  uses telescoping tubes  52  and  54  to provide adjustable length. Various means can be employed to lock the tubes in the desired position, for example: pushbutton spring detents, a friction collet, or twist-activated expanding cam. These methods are commonly used on vacuum cleaner tubes and telescoping extension poles. These or similar methods can also be used to attach the bottom end of pole  50  to the receptacle tube  24 . 
     Typically, the user will hold the upper third of the pole with the top hand holding grip  56  attached to the free end of upper tube  54 . For adjustable length it is also possible for grip  56  or tube receptacle  24  to be made longer and have pushbutton detents or other means to adjust length and lock position. 
       FIG. 5  shows the push-paddle  20  of  FIG. 4  prepared for stowage. Pole  50  is retracted and push-block  22   a  is detached. 
     The push-block is preferably made of a low-density hydrophobic closed-cell foam such as expanded polystyrene, polypropylene, polyurethane or PVC. In its molten or reactive state the foam can be injected or otherwise introduced to a female mold. Alternatively, foam billets or sheets can be carved and sanded, e.g. using a saw, hot-wire, water jet, laser, and abrasive materials. Ideally, the foam is non-brittle and can survive being struck or dented, but is rigid enough to hold its shape under hydrodynamic forces. The push-block can also have stiffeners such as wood, plastic, metal, or a higher-density/stronger foam. The stiffeners can be bonded in, over-molded, or attached to the outside of the foam. In one example, the stiffener is an injection molded part which mates with pole  50  and has ribs and a flange to spread the load and make a strong connection with the foam block. The push-block  22   a  can also be made of a strong but brittle foam coated with a soft resilient foam such as EVA. 
     To protect the foam from cracking, chipping or abrasion, it can be reinforced with a skin of polymeric or fiber reinforced polymer (FRP) material. In one example, the skin results from a molding process in which the foam cells near the mold walls break and form a higher-density layer. In a second example, the skin is applied by a coating process such as dipping, spraying, brushing, rolling, or powder-coating. StyroSpray by Industrial Polymers Inc. is a good choice for a hard, structural spray-on coating compatible with expanded polystyrene. For a soft, resilient skin, a good choice is TrueKote CS-100, also by Industrial polymers. In a third example, the foam is wrapped with a mat or cloth made of high strength fiber and is impregnated with resin such as polyester or epoxy. 
     Another manufacturing method is to blow-mold the outer shape of the push-block and fill it with a low-density closed-cell foam to improve stiffness and insure buoyancy. The preform used in the blow-mold process can also serve as the attachment point for the pole. For light weight and high strength, a good choice of polymer is PET, but for impact resistance and toughness, Surlyn is preferred. 
     As shown in  FIGS. 4-5 , the push block  22   a  has smooth edges, as may be needed to make the product safer, more rugged or compatible with the chosen manufacturing process. In general, it is desirable, however, for the edges, e.g. edges  40  and  38 , adjacent to bottom face  36  (not visible) to be relatively sharp. This increases the drag coefficient and reduces power loss due to backwards slip through the water. 
       FIGS. 6-7  shows a push-block  22   b  similar to  22   a  in  FIGS. 4-5 , except that the edges are sharp and the receptacle tube  24  is not shown. Hole  25  shows where the receptacle tube  24  or the pole  50  would be attached.  FIG. 6  also shows the critical dimensions of the block: height H, width W and thickness T. In one successful embodiment, H=10.5 in, W=12 in, and T=4 in: The volume in this example is 318 cu-in. Made of foam having 1.6 lb/cu-ft, the weight of foam is 0.29 lb. The buoyant force, i.e. the weight of the water displaced, is 11.5 lb. 
       FIG. 8  shows push-block  22   c  that is essentially the same as push-block  22   b,    FIG. 6-7 , except that it has side flanges  48  to increase the drag coefficient and reduce the tendency to slip backwards. The side flanges  48  may extend in all directions as shown, or can extend from specific faces. Adding side flanges to the bottom face  36  is especially effective. 
       FIG. 9  shows push-block  22   d  where the edges between the top face  26  and the sidewalls  28  have been chamfered, resulting in faces  45 . This is a way to provide a large area of the bottom face while preserving the wedge angle and avoiding excessive buoyancy. 
       FIG. 10  shows push-block  22   e  in which the sidewalls  28 ′ of the block are angled inward toward the pole. This is another way to provide a large area of the bottom face  36  (not visible) without excessive buoyancy. The angled sidewalls also make the side edges  40 ′ more acute which increases drag and reduces backwards slip of the push-block  22   e.    
       FIG. 11  shows push-block  22   f  in which top surface  26 ′ is convex and bottom face  36 ′ (not visible) is concave. This helps increase the drag coefficient as well as providing greater lift to keep the push-block  22   f  from sinking underwater. 
       FIGS. 12-14  show a perspective view, a top view and a cross-sectional view, respectively, of a push-block  22   g  in which the back-end of the wedge is rounded to form surface  33 . This surface replaces the three faces  30 ,  32  and  34 , e.g. of push-block  22   a,    FIG. 4 , and makes the push-block perform like a low-speed, high-lift hydrofoil.  FIGS. 12-14  also show a domed convex top surface  26 ″, and a domed concave bottom face  36 ″. These attributes result in greater lift and drag, thus reacting the downward component of force on the pole more effectively and reducing backward slippage of push-block  22   g  through the water. 
       FIGS. 15-17  show side views of a simple wedge-shaped push-block  22   h  in three stages of action: insertion, with the pole angle 90° with respect to the waterline, mid-power stroke, with the pole  50  at 60°, and the end of the power stroke, with the pole  50  at 30°. These three views are roughly analogous to those of  FIG. 1-3 .  FIGS. 15-17  also define the critical angles for of the push-block. In general, the “pole angle” is defined as the forward angle of the “pole axis” with respect to the waterline. Since the pole is not necessarily straight, and its point of attachment to the push-block is not necessarily in the center of the push block, the “pole axis” is hereby defined as a line connecting from the centroid of the handle portion of the pole (e.g. the upper third), to the volume centroid of the push-block. The “catch angle” is the angle of the bottom face  36  relative to the waterline during insertion of the paddle. As shown in  FIG. 15 , the “push angle” is 90° plus the “catch angle”. Typically the push angle will be greater than 90° so that the push-block will “dig in” and catch the water. A push angle of 105° has proven to work well. Larger push angles, e.g. 135° result in hydrodynamic forces pushing the push-block down as it slips backward through the water. This can be avoided by making the push-block more buoyant, but this adds weight and wind resistance, and tends to make the push-block depth more sensitive to the level of effort. For example, paddling at a low level of effort may not sink the push-block very far, resulting in less efficient operation as the push-block slips backward more easily. 
     Another variable is the angle of the push-block wedge as shown in  FIG. 16 , labeled “wedge angle”. This affects the buoyancy of the push-block, and affects the “top angle” which is the forward angle between the pole axis and the top surface  26  of the wedge. The “recoil angle” shown in  FIG. 17 , is the top angle less the “final pole angle” which in this case is 30°. The recoil angle is important since it affects whether the push-block will “snag” the water on the recoil stroke. In theory, the recoil angle could be as small as 90° before fully snagging water on recoil, but in practice, a 30° buffer is desirable, since it allows the push-block to be accelerated forward at the end of the stroke while it is emerging from the water. 
     Based on experimentation, a preferred embodiment of the invention uses a wedge angle of 30° and push angle 105°, resulting in a top angle of 135°. If the push-block is inserted at pole angle 90° and the power stroke ends at 30°, then the catch angle is 15°, and the recoil angle is 120°. 
       FIGS. 18-21  show side views of push-block  22   i  and pole  50  in four phases of the power stroke corresponding to pole angles 90°, 75°, 60° and 30°. This embodiment of the push-block has a rounded back-end  33  forming a low-speed/high-lift hydrofoil. In  FIG. 18 , push-block  22   i  is being inserted into the-water. The direction of velocity is labeled V, and the principal force vectors are labeled “pole force”, “drag”, and “buoyant force”. The length and direction of the vectors correspond to the magnitude and direction of forces acting on the push-block. The vector sum of the forces on the push-block in each of the  FIGS. 18-21  is approximately zero, since the accelerations are small. Placement of the force vectors acting on the push-block is done for readability and is not necessarily correct. The vector labeled “pole force” represents the principal force applied to push-block  22   i  by the pole  50 . The force is not exactly in-line with the pole  50  because there is a small moment applied to the pole  50  by the user. The angle of the pole force relative to the pole axis is labeled “pole force angle”. This angle is much smaller than a conventional SUP paddle which typically has a pole force angle of 75-90°. 
     In  FIG. 18 , the push-block  22   i  has been sunk underwater slightly and is slipping backwards horizontally at speed Vslip. Backwards slippage is undesirable; but also unavoidable. The hydrofoil shape of the push-block  22   i  makes use of slip velocity to produce lift which counteracts the downward component of force on the pole  50 . This reduces the buoyancy required of push-block and results in lighter weight and less wind resistance. Another key benefit is that the lift force tends to increase as the push-block goes underwater. This makes the push-paddle perform well over a wider level of effort. A relatively low pole force is needed to get the push-block into the water. This provides good purchase at a low level of effort. Pushing harder tends to drive the push-block slightly underwater, but this increases lift and tends to keep the push-block near the surface. 
     In  FIG. 21 , push-block  22   i  is shown near the end of the power stroke and very little lift is needed to counteract the downward component  62  of pole force. One of the reasons this embodiment is successful is that the lift decreases naturally toward the end of the stroke as the hydrofoil goes into “stall”. 
       FIGS. 22-25  show three side views of another embodiment of the invention. The three views correspond to pole angles 75°, 45°, and 30°. The push-block  22   j  is essentially the same as  22   i,    FIGS. 18-21 , except that the push angle has been increased from 105° to 150°. In this case, the intended method of use is to force the push-block underwater early in the power stroke to store potential energy, then at the end of the stroke, the push-block “flies” back up to the surface providing forward thrust, or at least preventing backwards motion. The advantage of this embodiment is that the user can sink his/her weight into the pole early in the power stroke, bending at the waist and the knees, thus capturing energy from the large muscle groups. During the recoil part of the stroke, the user stands back up straight. Compared with push-block  22   i,    FIGS. 18-21 , push-block  22   j  will need to be more buoyant for the same level of average thrust since the “lift” tends to have a downward component of force. Push block  22   j  also requires a greater pole moment, which is slightly more like the “pull” stroke used in canoeing and kayaking. 
       FIGS. 25-26  show cut-away side views of adjustable push-block  22   k  and adjustable pole receptacle  60  which comprises receptacle tube  62  attached to flange  64 . The flange  64  has holes accepting screws  68  which mount to threaded inserts  70  in the push-block. Redundant thread inserts  72  allow the flange to be mounted in different positions resulting in adjustment of the push angle to suit different users or to engage slightly different muscle groups. In  FIG. 25  the push angle is 105°, and in  FIG. 26 , it is 144°. The adjustment mechanism shown is provided as an example. Those skilled in the art know that there are enumerable other ways to provide angle adjustment, including discrete methods (e.g. mating screws or teeth), and continuous methods (e.g. friction clamp). 
     In the above description, a common feature of the push-block is that it is “wedge-shaped”, meaning that the push-block&#39;s top and bottom faces are generally angled and come together to form an edge. The term “wedge-shaped” is intended to include the cases where the top and bottom faces are non-planar, e.g. these surfaces can be convex, concave or chamfered. The edge formed by the wedge also need not be straight or sharp, e.g. it can be curved, rounded or chamfered. “Wedge-shaped” refers to the wedge-end of the push-block. The back-end need not be flat, e.g. it can be chamfered or rounded. By this definition, a hydrofoil shape qualifies as being wedge-shaped. 
     In addition to being more efficient and therefore less tiring to operate, the present invention has other important advantages. Since the push-block is buoyant, it provides a brace to aid in balancing. This is especially helpful when standing up on a paddleboard when there are waves or swells. The user may also modulate his/her balance during the power stroke by pushing harder or softer. The push-paddle provides superior turning ability since it can be used to push the bow of the watercraft right or left. The push-paddle can be used to go backwards or to stop abruptly. Compared with conventional SUP paddles, the push-paddle allows a paddleboard to track straighter: toward the end of the stroke, the push-block overhangs the end of the paddleboard and can be brought closer to the paddleboard centerline thereby creating a smaller yaw moment. The push-block can also be pushed underwater and driven with the pole very close to the side of a paddleboard, again to minimize the yaw moment. 
     The push-paddle can be made of soft materials and is therefore less prone to damage from banging into rocks or the watercraft. It is also much less likely to damage the watercraft. In congested beaches or surf breaks, the push-paddle is less likely to cause injury. A soft push-paddle can also be used to play water games such as polo, tag, or jousting. 
     In broad embodiment, the push-paddle comprises a wedge-shaped buoyant block attached to a pole which when pressed into the water wedge-end first provides high drag for the user to push against and propel a watercraft using a punting-like motion. At the end of the power stroke, the wedge slips easily and quickly out of the water allowing the user to recoil the paddle through the air. 
     While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The invention should therefore not be limited by the above described embodiment, method, and examples, but by all embodiments and methods within the scope and spirit of the invention.