Abstract:
An air vent that passes from the deck of a surfboard through to its bottom. The vent may have a wide variety of shapes. The trailing boundary of the vent&#39;s lower portion is preferably inclined forward toward the surfboard&#39;s nose. The inclination serves to prevent water flowing upward. Instead, air is entrained by the water flowing across the vent&#39;s bottom exit and pulled downward. A portion of the entrained air flows rearward out of the bottom exit along the surfboard&#39;s bottom. This entrained air forms an air film between the board&#39;s bottom and the surrounding water, thereby reducing friction.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the field of surfboards. More specifically, the invention comprises a surfboard with vents that transfer air from the deck to the bottom, where a portion of the air becomes entrained in the water flow and creates an air-film beneath the board. 
     2. Description of the Related Art 
     Surfboards were invented by ancient Polynesians. They were originally carved from straight sections of tree trunk and were typically 3-4 meters (10-15 feet) in length and weighed as much as 70 kg (150 pounds). The sport of surfing expanded greatly in the years following World War II. The expansion of the sport was propelled in part by the availability of new materials for constructing surfboards. The widespread availability of fiberglass was a significant factor. 
     Modern surfboards are typically made by bonding a high-strength “skin” material to a low density/low strength “core” material. The core material is often polyurethane or polystyrene foam, but may also be natural materials such as balsa wood. The skin is made by covering the core with a material such as woven fiberglass cloth. The woven cloth is bonded to itself and the core using polyester or epoxy resin. 
       FIG. 1  shows a plan and elevation view for a representative surfboard. Those skilled in the art will now that a virtually endless variety of surfboards are now in common use. Thus, the board shown in  FIG. 1  is properly viewed as one example among many possibilities. However, all surfboards share some common characteristics and these have been labeled in  FIG. 1  in order to benefit the reader&#39;s understanding. 
     The top of the surfboard is known as deck  12 . The forward portion is known as nose  14 , while the aft portion is known as tail  16 . The board&#39;s lateral boundaries are generally referred to as “rails” (left rail  18  and right  20 ). The board&#39;s downward facing surface is known as bottom  24 . 
       FIG. 1  is not labeled as “prior art” because the surfboard depicted includes the present invention (vents  26 ). Its other features are common to prior art boards, however, and thus it is still useful for discussing the background of the invention. It is common for modern surfboards to include one or more skegs  22 . These prevent lateral slipping and aid in turning the board. Other features may be included, such as an attachment point for a “leash” that is used to link the board to one of the surfer&#39;s ankles. 
     The board shown in  FIG. 1  is known for being fairly agile, meaning that it can be quickly turned. It has a fairly broad beam and a relatively short length (in comparison to traditional “long boards”). When a rider is riding the board such as shown in  FIG. 1 , only the aft portion will engage the water. How much of the board is in contact with the water depends on many factors. However, it is common for at least a substantial portion of the board&#39;s forward region to be free of the water. 
     The surface friction generated by the interaction of the board&#39;s bottom with the water is a significant factor in determining the speed the surfer is able to achieve. Surfboards are commonly smoothed and waxed in order to minimize the friction between the board&#39;s bottom and the water. However, smoothing and waxing will only increase the board&#39;s speed to a certain extent. It is desirable to further increase the board&#39;s speed by further reducing friction. The present invention provides such an enhancement. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention comprises one or more an air vents that pass from the deck of a surfboard through to its bottom. The vent may have a wide variety of shapes. The trailing boundary of the vent&#39;s lower portion is preferably inclined forward toward the surfboard&#39;s nose. The inclination serves to prevent water flowing upward. Instead, air is entrained by the water flowing across the vent&#39;s bottom exit and pulled downward. A portion of the entrained air flows rearward out of the bottom exit along the surfboard&#39;s bottom. This entrained air forms an air film between the board&#39;s bottom and the surrounding water, thereby reducing friction. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a plan and elevation view depicting a common type of surfboard with the addition of the present invention. 
         FIG. 2  is a detailed section view, showing a vent made according to the present invention. 
         FIG. 3  is a detailed elevation view, showing the operation of the present invention. 
         FIG. 4  is a detailed elevation view, showing how the orientation of the present invention is significant to its operation. 
         FIG. 5  depicts four different orientations for the present invention. 
         FIG. 6  is a detailed perspective view, showing one method of manufacturing the present invention. 
         FIG. 7  is a detailed perspective view, showing one method of manufacturing the present invention. 
         FIG. 8  is a detailed perspective view, showing one method of manufacturing the present invention. 
         FIG. 9  is a plan view, showing three different embodiments of the present invention. 
         FIG. 10  is a detailed elevation view, showing an alternate embodiment for the present invention. 
     
    
    
     REFERENCE NUMERALS IN THE DRAWINGS 
     
       
         
               
             
               
               
               
               
             
           
               
                   
               
               
                 REFERENCE NUMERALS IN THE DRAWINGS 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 10 
                 surfboard 
                 12 
                 deck 
               
               
                 14 
                 nose 
                 16 
                 tail 
               
               
                 18 
                 left rail 
                 20 
                 right rail 
               
               
                 22 
                 skeg 
                 24 
                 bottom 
               
               
                 26 
                 vent 
                 28 
                 central axis 
               
               
                 30 
                 core 
                 32 
                 deck skin 
               
               
                 34 
                 bottom skin 
                 36 
                 wall skin 
               
               
                 38 
                 air/water boundary 
                 40 
                 entrained air 
               
               
                 42 
                 air film 
                 44 
                 water flow 
               
               
                 46 
                 lifted flow 
                 48 
                 cavity 
               
               
                 50 
                 pipe 
                 52 
                 resin fillet 
               
               
                 54 
                 bottom exit 
                 56 
                 top exit 
               
               
                 58 
                 leading boundary 
                 60 
                 trailing boundary 
               
               
                   
               
             
          
         
       
     
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention involves one or more vents passing through a surfboard from top to bottom. The vents are used to create an air film beneath the trailing portion of the board as it moves through the water. A broad air film is preferably created. In order to create such a film, an array of two or more vents are included in a suitable pattern. The top view of  FIG. 1  shows such an array. Six vents  26  are provided in this embodiment. 
       FIG. 2  depicts a sectional elevation view of one of the vents  26  shown in  FIG. 1 . Vent  26  passes vertically through the surfboard. The board in this example includes a typical construction used for modern surfboards. Core  30  defines the overall shape of the board. Deck skin  32  is made by laying one or more layers of woven cloth (fiberglass, KEVLAR, or other more exotic materials such as carbon fiber) over the upper surface of the core and bonding it using a liquid resin material that transitions to a strong solid. Examples of the resin include polyester and epoxy. 
     The reinforcing cloth and bonding resin surround and bond to core  30  on all sides. Bottom skin  34  is the portion of the bonded reinforcing cloth that lies over the bottom of the board. In this example, vent  26  is simply an inclined cylindrical cavity having central axis  28 . The cylindrical cavity intersects the deck at top exit  56 . It intersects the bottom at bottom exit  54 . 
     It is undesirable to expose any portion of the core material since it has little toughness or abrasion resistance. Thus, it is preferable to provide wall skin  36  around the perimeter of vent  26 . Wall skin  36  may be formed using a variety of techniques. It is preferable for wall skin  36  to be bonded to deck skin  32  and bottom skin  34 . 
     The reader will observe that the nose of the surfboard lies off to the right of the cross section, and the tail lies off to the left. Vent  26  is therefore inclined so that its upper portion lies close to the nose and its lower portion lies closer to the tail. This geometry is significant to the operation of the vent. 
       FIG. 3  shows the same geometry as the surfboard is moved rapidly through the water. The bottom exit region of vent  26  includes leading boundary  58  and trailing boundary  60 . Water flow  44  slides rapidly along bottom  24  in the direction indicated by the arrow. As the water moves aft past leading boundary  58 , air/water boundary  38  moves up into vent  26 . This phenomenon is well known in the field of fluid mechanics and is commonly referrer to as “hydraulic jump.” 
     As the moving water approaches trailing boundary  60 , however, a different phenomenon occurs. The inclined surface of trailing boundary  60  causes some air to be entrained and pulled beneath the board (entrained air  40 ). Once this entrained air is aft of the vent, it cannot easily escape to the surface and must instead travel along the bottom of the board. Air film  42  is thereby created. As is well known to those skilled in the art, the creation of such an air film substantially reduces the sliding friction between the bottom of the surfboard and the water. 
     The vent shown in  FIG. 3  is a simple cylindrical bore drilled through the surfboard (having a diameter “D”). This simple shape produces the desired effect. It is readily apparent that other shapes could produce the desired effect as well. The important element is the inclination of trailing boundary  60 . The inclination of leading boundary  58  is relatively unimportant. This portion may simply be vertical, or may even be inclined in the opposite direction as trailing boundary  60 . 
       FIG. 4  provides air extreme illustration of the importance of properly inclining trailing boundary  60 . In the example of  FIG. 4 , trailing boundary  60  is inclined so that its lower portion is closest to the nose and its upper portion is closest to the tail. Water flow  44  slides along the bottom of the board as for the example of  FIG. 3 , but no air is entrained. Instead, lifted flow  46  is “scooped” up through vent  26  and propelled onto deck  12 . This configuration obviously does not produce the desired effect. It is important to realize that the example of  FIG. 4  is not an embodiment of the present invention. It is not really prior art, however, since the inventor is not aware of a board having this precise configuration (though some prior art boards have incorporated scoops intended to spray water upwards).  FIG. 4  merely serves to illustrate—by way of an extreme example—how the inclination of trailing boundary  60  is important to the operation of the present invention. 
       FIG. 5  shows several examples of vents formed by creating a simple cylindrical cavity having a central axis  28 . In  FIG. 5(A) , central axis  28  is perfectly perpendicular to deck  12 . In  FIG. 5(B) , central axis  28  is tilted forward with respect to deck  12 . The angle between the central axis and the deck in this example is 60 degrees.  FIG. 5(C)  shows an example where the angle is 45 degrees, and  FIG. 5(D)  shows an example where the angle of tilt is 30 degrees. The example of  FIG. 5(A)  entrains some air but is not very effective. The other examples work better, with the preferred embodiment being about 45 to 60 degrees. 
     Although the invention is not limited to any particular construction technique, the reader may wish to know some information regarding the construction of suitable vents in a typical surfboard.  FIGS. 6-8  provide illustrations of one suitable process. 
       FIG. 6  shows a small section of core  30  used to create a surfboard. Only the section immediately surrounding the location of a vent is shown. Cavity  48  is made through core  30 . The cavity may be drilled by passing a drill bit along central axis  28 . Alternatively, the cavity may be cast into the core material at the time the core material itself is cast. 
     As stated previously, it is preferable to provide a wall skin in the cavity. In  FIG. 7 , pipe  50  has been added to the cavity by gluing it in position. The pipe may be a PVC extrusion, a fiberglass composite, or even a piece of metal tube. Once the pipe is in position, deck skin  32  and bottom skin  34  are added. The deck and bottom skins are preferably bonded to the pipe. Resin fillet  52  may be formed when the resin is used to soak and bond the woven reinforcing cloth used to make the deck and bottom skins. 
     In the assembly as shown, a portion of pipe  50  sticks up beyond the deck and a second portion (not shown) protrudes down below the bottom. The protruding portions are cut off and the boundaries are sanded smooth.  FIG. 8  shows the result. Pipe  50  is sanded smooth with deck skin  32  and bottom skin  34 . The resulting vent  26  is thereby bounded within a “wall skin” (the pipe). Additional adhesive and/or filler material may be used to dress the joints. 
     In order to create the desired air film beneath the aft portion of the surfboard, it may be necessary to provide two or more vents in a pattern.  FIG. 9  provides a plan view for three different embodiments. The upper surfboard  10  has a single large vent  26 . The middle board has an array of three staggered vents  26 . The bottom board has a linear array of four vents  26 . The invention is by no means limited to any particular number or configuration of vents. Some embodiments may have ten or more vents in various locations. 
     In the preceding examples a simple cylindrical cavity is used for the vent. This is a very easy shape to create, since it involves simply drilling a hole through the board at a desired angle. It may be desirable in some instances, however, to employ a more complex shape for the vent.  FIG. 10  shows an additional embodiment in which vent  26  has a non-uniform cross section as it proceeds from top to bottom. The reader will observe that leading boundary  58  is simply a vertical wall. Trailing boundary  60  is suitably inclined, but only in proximity to the portion of the vent that actually contacts the water. 
     This embodiment pulls in the entrained air and creates air film  42 . However, it uses a complex blended shape for the vent. In studying this shape, the reader will note that the inclination of the trailing boundary is the feature that makes the device produce the desired result. The shape of the other portions of the vent are not critical, as long as they permit enough air to pass. 
     The preceding description contains significant detail regarding the novel aspects of the present invention. It is should not be construed, however, as limiting the scope of the invention but rather as providing illustrations of the preferred embodiments of the invention. Thus, the scope of the invention should be fixed by the claims presented, rather than by the examples given.