Abstract:
An inflatable structure that includes continuous longitudinal and axial curves, constructed to form a hydrodynamically designed performance platform for use as a performance water sports board, rescue board, or rescue sled, such as a stand-up paddle board, paddleboard, surfboard, PWC rescue sled, bodyboard, or other floating or dynamic platform. Alternatively, it may be adapted for use with additional structure to provide an inflatable hull and floor for a watercraft, such as a boat, raft, life-raft, rescue craft, or other floating or dynamic platform. Longitudinal stringers welded to opposing panels defining the interior volume of the inflatable structure are joined by welding, gluing, or lashing, and the shape of the stringers and the welding/gluing/lashing schedule can be employed to give the inflatable structure a highly customized curved shape.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 62/277,740, filed Jan. 12, 2016 (Jan. 12, 2016), which application is incorporated in its entirety by reference herein. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       THE NAMES OR PARTIES TO A JOINT RESEARCH AGREEMENT 
       [0003]    Not applicable. 
       INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
       [0004]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0005]    Field of the Invention 
         [0006]    The invention relates most generally to watercraft, and more particularly to floatation structures for watercraft or comprising a sports board, and still more particularly to inflatable watercraft and/or watercraft parts, and methods of manufacturing the same. 
         [0007]    Background Discussion 
         [0008]    All of the known state of the art inflatable high pressure watersports boards are constructed with a drop-stitched PVC fabric. The manufactures number over 20. The drop stitch fabric includes two walls, and is therefore termed a “double wall fabric.” It typically includes opposing and parallel PVC panels connected with thin and dense columns of tens of thousands of interwoven nylon stitches holding the panels in their opposing relationship. The stitching pattern can be varied so as to provide differing degrees of rigidity, but any degree of rigidity using any known pattern requires the introduction of high pressure into the closed volume defined by the panels. Pressures over 30 psi are possible, and pressures of 15-25 psi are common, but more importantly, they are needed to provide the board with any meaningful degree of rigidity, particularly when the article is embodiment as a watercraft such as a stand-up paddle board. 
         [0009]    To call these boards “high performance” boards, however, would be hyperbole; in truth, their very modest performance characteristics warrant classifying them in a dramatically subordinate, stepped down position from the solid boards. This is due both to the lack of shear strength in the boards, making them prone to collapse unless inflated to very high pressures, and to the fact that no meaningful rocker or other performance design characteristics (including various types of rail configurations) can be introduced using the drop stitch construction techniques. Performance design characteristics can only be minimally provided in a drop stitch board, because by the very nature of the fabric employed, the drop stitch resists rocker, and manufacturers must force minimal dimensional gains through side panels, resulting in “boxy” rails very unlike those in performance “hard boards” and the boards made possible by the present invention. 
         [0010]    Accordingly, the very essence of good waterboard performance—namely, bottom rocker—cannot be included in a drop stitch board, let alone complex bottom rocker, such as nose rocker, tail rocker, and mid rocker. Likewise, there cannot be any upper curvature suitable for rider comfort and performance features. Disappointingly, drop stitch boards are flat and tend toward square. The flatness of the board is reflected in the flatness of the performance characteristics. 
         [0011]    The foregoing discussion reflects the current state of the art of which the present inventors are aware. Reference to, and discussion of, the known products and manufacturing methods is intended to aid in discharging Applicants&#39; acknowledged duty of candor in disclosing information that may be relevant to the examination of claims to the present invention. However, it is respectfully submitted that none of the known prior art products disclose, teach, suggest, show, or otherwise render obvious, either singly or when considered in combination, the invention described and claimed herein. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    The present invention represents a radical departure from the above-described commonly accepted materials and means of manufacturing inflatable watercraft, such as stand up paddle boards (SUP boards). Using the inventive materials and inventive fabrication techniques, high performance inflatable boards can be produced that possess the desirable performance characteristics of solid boards, including remarkable rigidity for an inflatable design, plus bottom rocker of all kinds—nose, tail, staged, continuous, and variations thereof, and performance rail designs such as pinched and ballooned rails, as well as others, and even changes in the rail type and thickness along the length of the board or watercraft. Upper deck shape and curvature is also achieved, including domed or dished shapes (i.e., convex or concave about several axes). This is achieved using a novel internal stringer system, constructed using a new inflatable board construction process. The internal stringers provide internal longitudinal sheer resistance that significantly increases rigidity and simultaneously reduces the necessary internal air pressure required for characteristics comparable to the rigid boards on the market. Several other advantages are realized by the present invention: 
         [0013]    Internal (or recessed) fin boxes may be employed, similar to those found in hard boards, which are vastly superior to externally mounted fin bases on currently marketed inflatable boards, which increase drag by obstructing water flow across the bottom of the inflatable board. In an embodiment, the fin boxes are recessed, and in this configuration the fin boxes can be anchored to the opposing side of the board, thereby decreasing fin flex due to hydrodynamic pressures encountered in high performance conditions. 
         [0014]    The use of chemically bonded urethane coatings provides a permanent extra layer of puncture, tear and abrasion resistance that also seals out water from wicking into the scrim at all of the exterior exposed edges of the assembled fabric panels. 
         [0015]    Further, permanent, customized designs (both board shape and applied artwork) can be achieved for every individual board (just like custom shaped surfboard art). 
         [0016]    The most salient improvements are attributable to a customizable internal longitudinal stringer system. Each internal stringer in the stringer system is longitudinally cut down its length and welded or glued to either the upper or lower board panel. It is then coupled to a complementary opposing stringer on the opposing panel, effectively creating a plurality of upper and lower stringers that are joined together. The upper and lower stringers may overlap a predetermined amount and the overlapping portions can be welded or glued together. Alternatively, the opposing upper and lower stringers can be zig-zag lashed together by parachute cord, from a single anchoring point in the nose or bow, and to a permanent anchor, or alternatively, to an individual winch mechanism in the tail or stern that allows a user to expand or decrease the thickness of the board based on user or environmental conditions. A lower profile board can be achieved for use in doing yoga, for instance, or a higher profile can be achieved for use in rough water conditions. 
         [0017]    In an embodiment, the inventive inflatable panels of the present invention may be employed to make an inflatable boat hull, floor, or even an entire boat. The internal stringer system of the present invention is adaptable and suitable for use in producing innovative inflatable hulls and/or floors and/or sides for and of inflatable boats. This can yield a complete inflatable boat or, when fixed to a conventional inflatable boat solid transom, a complete performance inflatable boat. They may be shaped with complex curvature, as described above. 
         [0018]    The foregoing summary broadly sets out the more important features of the present invention so that the detailed description that follows may be better understood, and so that the present contributions to the art may be better appreciated. There are additional features of the invention described in the detailed description of the preferred embodiments of the invention, which follows, below, and which form the subject matter of the claims appended hereto. 
         [0019]    Accordingly, before explaining the preferred embodiment of the disclosure in detail, it is to be understood that the disclosure is not limited in its application to the details of the construction and the arrangements set forth in the following description or illustrated in the drawings. The inventive apparatus described herein is capable of other embodiments and of being practiced and carried out in various ways. 
     
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         [0020]    The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein: 
           [0021]      FIG. 1  is an upper right rear perspective view of a high performance water sport board constructed using the materials and inventive fabrication techniques of the present invention; 
           [0022]      FIG. 2A  is a highly schematic cross-sectional end view in elevation showing an embodiment of the longitudinal internal stringers used to provide shear strength in the present invention, the embodiment comprising a planar base stringers, and this view showing the upper and lower portions of the stringers in their pre-fabrication configuration; 
           [0023]      FIG. 2B  is the same view showing the base portion of each of the upper and lower stringer portions welded to together to form overlapping upper and lower medial flaps; 
           [0024]      FIG. 3A  is the same view showing upper and lower flexible material panels disposed above and below the stringers; 
           [0025]      FIG. 3B  shows the flexible material panels being folded at their sides to form overlapping edge portions; 
           [0026]      FIG. 3C  shows the overlapping edge portions of the fabric panels welded to form a sealed side; 
           [0027]      FIG. 4A  is a highly schematic cross-sectional side view in elevation corresponding to  FIG. 3A ; 
           [0028]      FIG. 4B  is a schematic side view in elevation corresponding to  FIG. 3C , showing the end portions of the flexible fabric panels being folded to form an overlapping portion; 
           [0029]      FIG. 4C , is a schematic side view in elevation showing the overlapping end portions joined in a welded seam; 
           [0030]      FIG. 5  is a top plan view of the board as formed and shown in  FIG. 4C ; 
           [0031]      FIG. 6A  is a highly schematic end view in elevation of upper and lower portions of a split base stringer with the medial flap portions in their pre-fabrication configuration; 
           [0032]      FIG. 6B  is the same view showing the upper and lower medial portions each welded into upper and lower medial flaps, respectively; 
           [0033]      FIG. 6C  is the same view showing the upper and lower medial flaps welded together to form a unitary stringer; 
           [0034]      FIG. 7A  is a highly schematic end view in elevation of upper and lower portions of a planar base stringer with the medial flap portions in their pre-fabrication configuration; 
           [0035]      FIG. 7B  is the same view showing the upper and lower medial portions each welded into upper and lower medial flaps, respectively; 
           [0036]      FIG. 7C  is the same view showing grommets installed in each of the upper and lower medial flaps and the flaps being lashed together with a lashing so as to form a unitary stringer; 
           [0037]      FIG. 7D  is a side view in elevation showing a portion of the stringer of  FIG. 7C ; 
           [0038]      FIG. 8A  is a highly schematic end view in elevation of upper and lower portions of a split base stringer with the medial flap portions in their pre-fabrication configuration; 
           [0039]      FIG. 8B  is the same view showing the upper and lower medial portions each welded into upper and lower medial flaps, respectively; 
           [0040]      FIG. 8C  is the same view showing grommets installed in each of the upper and lower medial flaps and the flaps being lashed together with a lashing so as to form a unitary stringer; 
           [0041]      FIG. 9A  is a highly schematic end view in elevation of upper and lower portions of a split base stringer with the medial flap portions in their pre-fabrication configuration and cordage disposed in the crotch of each of the upper and lower medial portions; 
           [0042]      FIG. 9B  is the same view showing the upper and lower medial portions each welded into upper and lower medial flaps, respectively, with the cordage secured within the weld at the edges of the upper and lower medial flaps; 
           [0043]      FIG. 9C  is the same view showing the flaps being lashed together with a lashing so as to form a unitary stringer; 
           [0044]      FIG. 9D  is a side view in elevation showing a portion of the stringer of  FIG. 9C ; 
           [0045]      FIG. 10A  is a flow chart showing the method steps employed in the pre-assembly portion of fabricating the inflatable structure of the present invention; 
           [0046]      FIG. 10B  is a flow chart showing the steps involved in the assembly method; 
           [0047]      FIG. 11A  is a top plan view of the inventive apparatus embodiment in a performance surfboard with a planing hull; 
           [0048]      FIG. 11B  is a side view in elevation thereof; 
           [0049]      FIG. 11C  is an end view in elevation thereof; 
           [0050]      FIG. 12A  is a top plan view of the inventive apparatus embodied in a beginner&#39;s surfboard (alternatively, a yoga board) having buoyancy rails; 
           [0051]      FIG. 12B  is a side view in elevation thereof; 
           [0052]      FIG. 12C  is an end view in elevation thereof; 
           [0053]      FIG. 13A  is a top plan view of the inventive apparatus embodied in a performance racing paddleboard or distance ocean board with a displacement hull; 
           [0054]      FIG. 13B  is a side view in elevation thereof; 
           [0055]      FIG. 13C  is an end view in elevation thereof; 
           [0056]      FIG. 14A  is a bottom plan view of performance sports board of the present invention, the view showing a fin and stringer configuration made possible by the fin assembly employed in the present invention; 
           [0057]      FIG. 14B  is a side view in elevation thereof; 
           [0058]      FIG. 15A  is a schematic exploded side view in elevation showing the fin assembly of the present invention disposed between deck and bottom panels; 
           [0059]      FIG. 15B  is a cross-sectional end view in elevation thereof, taken along section lines  15 B- 15 B of  FIG. 15A ; 
           [0060]      FIG. 16A  is a side view in elevation showing the fin assembly installed and secured between the deck and bottom panels; and 
           [0061]      FIG. 16B  is a cross-sectional end view in elevation thereof, taken along section lines  16 B- 16 B of  FIG. 16A . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0062]    Referring initially to  FIG. 1 , we see that in an embodiment, the inflatable structure of the present invention can take the form of a water sport board  10 . The board is shown with evident nose rocker  12  mid-rocker  13 , and tail rocker  14 . Also shown is nose and tail taper as the board thins closer to the ends (refer here to  FIG. 4A ), and rail shape  16 , e.g., a tapered performance rail (referring to  FIG. 3C ). While the rail shape  16  is more subtle, it is clearly seen in  FIG. 3C , and it will be appreciated that there are numerous rail shapes and bottom contours possible, including vee or concave. 
         [0063]    The board is generally symmetrical right and left of its longitudinal axis A, and includes a top (first) flexible material panel (“upper panel” or “deck panel”)  18  and a bottom (second) flexible material panel (“lower panel” or “bottom panel”)  20 . The panels are preferably made from very high quality coated fabric, for instance, a plastic-based polymer, such as the XR MARINER® fabric or other material from Seaman Corporation of Wooster, Ohio or comparably strong, waterproof, bondable polymeric material or composite material. [XR MARINER® is a registered trademark of Seaman Corporation.] A plurality of internal longitudinally oriented stringers  22  made of the same fabric are disposed between and affixed to the interior sides  24 ,  26  of the upper and lower panels, respectively. 
         [0064]    In an embodiment, the stringers are paired inboard stringers  28  and outboard stringers  30  and symmetrically spaced about the longitudinal axis, thus entailing the use of an even number of stringers. Full scale water sports boards preferably have a total of eight (8) stringers disposed alongside the board centerline. The interior stringers (those closest to the centerline) each include an upper portion,  28   a,    30   a,  for the upper portions of the inboard and outboard stringers, respectively, and  28   b,    30   b  for the lower portions of the inboard and outboard stringers, respectively. 
         [0065]    In an embodiment, shown in  FIGS. 2A-2B , wherein the stringers have planar bases and the upper and lower stringers are manufactured from a single panel of flexible material, the panels may be folded into a cross-sectional shape of a “V” or inverted “V”. Using the outboard stringer as an example, it is seen that the stringer thus includes the two stems  30   c  (comparable to stem and arm), a crotch  30   d,  and the flanges or base portions  30   e  (comparable to outwardly extending serifs). In manufacture, the stems ( FIG. 2A ) are first welded together to form a single generally planar panel ( FIG. 2B ); then the base portions of the upper stringers are welded to the upper panel and the base portions of the lower stringers are welded to the lower panel. The stringers are oriented generally parallel to the longitudinal axis of the panels. Once affixed, the upper stringers present a medial flap extending downwardly from the interior side of the upper panel, and the lower stringers present a medial flap extending upwardly from the interior side of the lower panel. The medial flaps may overlap in a side-by-side arrangement or have edges slightly spaced apart, depending on whether the flaps are to be joined with a lashing (when the edges are separated) or a weld (when the flaps overlap). 
         [0066]    As can be seen in  FIGS. 3A-3C , once the upper and lower portions of the stringers are coupled, the outboard stringers have a height less than that of the inboard stringers. Further, and referring now to  FIGS. 3A through 3C  and  FIGS. 4A through 4C , it is seen that the stringers can, and preferably do, have upper and lower contours from the front end  32  to the rear end  34  of the inflatable board  10 . These contours may include a continuous or staged concave upper curvature  36  and a continuous or staged lower curvature  38 . The upper and lower contours can be, and preferably are, different from one another. When the upper and lower panels  18 ,  20  are welded to the flanges (base portions)  28   a / 28   b,    30   a / 30   b  of the upper and lower stringers, because the paired inboard and outboard stringers are identical in their pairings, the panel surfaces are configured allochirally in their conformation to the shape dictated by the upper and lower stringers. Thus, in the exemplary views, the upper panel  18  is configured with a concave surface  40 , and the lower panel  20  is configured with a convex surface  42 . 
         [0067]    Closure of the inflatable structure to form an airtight interior volume involves bending the sides and ends of the upper and lower fabric panels to create a continuous, surrounding seam  44  sealed with a high frequency, solvent, hot air, or ultrasonic weld, or glued with a suitable plastic adhesive. The entire floatation platform may be coated with chemically bonded urethane to increase its durability and provide artistic customization. 
         [0068]    An air inlet/outlet (inflation/deflation) boat valve  50 , such as a Boston or thwart valve, or preferably a C7 valve as manufactured by Leafield Marine, Ltd. of Wiltshire, UK, is inserted in the deck fabric along the longitudinal centerline A proximate the stringer terminations on each side of the centerline, or other locations. Thus, air under pressure can be pumped or fed into the inflatable board (or selectively released, as desired) to achieve high overall rigidity, and access can be provided for adjusting stringer tensions in a lashing embodiment. Working models of watersport boards have been demonstrated to provide high performance characteristics inflated with only low pressures, e.g., not exceeding 5 psi. The internal longitudinal stringers provide such superior shear strength that the board will have an overall rigidity and resistance to collapse around any axis, thus rivalling the structural characteristics of solid boards, and with a shear strength vastly exceeding that of drop stitch inflatable designs. 
         [0069]      FIGS. 6A through 9D  show alternative stringer configurations, each capable of achieving the above-described advantageous characteristics. Referring now to  FIGS. 6A-6C  there is shown in an end view in elevation, a highly schematic split base stringer  60  having upper and lower portions  62   a / 62   b  with medial flaps  64   a / 64   b  in their pre-fabrication configuration, and showing how two unattached fabric sections  66   a / 66   b  form the arms of a “Y” configuration viewed on end, while the bonded medial flap portions (see  FIG. 6B ) for the stem. The base portions  68   a / 68   b  of the upper and lower portions  62   a / 62   b  are welded or otherwise affixed to the upper and lower panel interior sides, as described above. In assembly they are then welded together to form the unitary longitudinal internal stringer (see  FIG. 6C ). 
         [0070]      FIGS. 7A through 7D  show yet another stringer configuration  70 , this having the structural features of the planar base stringer described above, but having upper and lower portions  72   a / 72   b  with medial flap portions  74   a / 74   b  with troughs or crotches  76   a / 76   b  spaced apart when installed on the fabric panels. Grommets  78   a / 78   b  are installed in rows in the upper and lower medial flaps  74   a / 74   b  and a lashing  75  connects the upper and lower stringer portions by being threaded in a continuous serpentine pattern through the grommets extending from the front end of the stringer to the rear end (see  FIG. 7D ). The lashing is anchored at the front end of the stringer and secured for adjustment at the rear end. 
         [0071]      FIGS. 8A-8C  show yet another stringer configuration  80 , this synthesizing the split base design shown in  FIGS. 6A-6C  with the lashing method of coupling the upper and lower stringer portions, as described in connection with  FIGS. 7A-7D . 
         [0072]      FIGS. 9A-9C  show still another embodiment  90  of the longitudinal stringer of the present invention, this design also constituting a slight variation on the lashing design shown in  FIGS. 7A-7D . Rather than using grommets, a durable cord  92   a / 92   b  (such as parachute cord) is placed in the troughs or crotches  94   a / 94   b  of the upper and lower medial flaps  96   a / 96   b,  and the medial portions are then welded or bonded so as to capture the cordage in a strong terminal line defining the edge of the medial flap. Apertures  98   a / 98   b  are then cut in rows immediately above the cordage so that a lashing  95  can be threaded in a continuous serpertine pattern through the apertures, in the manner described with respect to the use of grommets. 
         [0073]    The method of manufacturing and assembling the inflatable structure of the present invention is also novel, making possible the inventive floatation structures. Referring to  FIGS. 10A-10B , there is shown in flow chart form the essential method steps for preparing the structural elements for assembling and then of assembling the inventive inflatable structures. Referring now to  FIG. 10A , pre-assembly  100  involves preparing the structural elements and begins by laying out the first and second flexible material panels (upper/top and lower/bottom, respectively) and using templates to mark the panels for cuts and bonding surfaces  102 . The templates define whether the panels will be employed for a board, hull, boat bottom, or some other inflatable structure. 
         [0074]    The panels are then cut to shape and further cut with accessory installation patterns  104 , as called for by the final design. The panels are also marked for the bonding steps. If the inflatable structure is a sports board, fin base holes are cut in the bottom panel  106 . A valve reinforcement patch is bonded, either by welding or gluing, to the underside (interior side) of the top panel  108 , and a valve hole is cut into the top panel  110 . 
         [0075]    Again, if the inflatable structure is a sports board, injection molded fin base anchors are bonded to the interior side of the top panel  112 , and injection molded fin bases are bonded in the fin base holes in the bottom panel  114 . If a lashing arrangement is contemplated, D-ring attachments/anchors are then glued or welded to the bottom panel  114  at the front, nose, or bow, as well as the rear, tail, or stern. 
         [0076]    Referring next to  FIG. 10B , assembly  120  then begins by assembling the top and bottom stringers  122  by folding each stringer panel in half along its longitudinal axis, and then bonding the halves together. If the cordage/lashing approach is to be employed for connecting upper and lower stringer portions, the cordage is placed in the crotch of each portion before the medial flap portions are bonded together. The stringer flanges remain untouched to this point. This is repeated for all deck and bottom panel stringers until the stringers are assembled. 
         [0077]    If grommets will be used for lashing, then grommet holes are punched and grommets installed. If cordage and lashing is to be employed, then apertures are punched above the cordage. 
         [0078]    Next, the upper portions of the stringers are bonded to the bottom side of the deck/top panel  124 . This imparts the deck contour to the top panel. The lower portions of the stringers are bonded to the top side of the bottom panel  126 , and this imparts bottom rocker or bow/stern profile. 
         [0079]    Next, if the upper and lower stringer portions are to be coupled using lashings, at step  127  lashing anchors are attached to the top of the bottom panel adjacent to the ends of the stringers at the tail or stern of the watercraft. 
         [0080]    Then, depending on the method employed to connect the upper and lower stringer portions—lashing or welding—the upper/top stringer portions are either welded or lashed to the bottom stringer portions  128 . 
         [0081]    If the inflatable structure is to be a board, then fin bases are installed in fin base anchors at this point (not shown in the view). 
         [0082]    The perimeter of the top panel is folded over and welded to the perimeter of the bottom panel from one side of the structure (or stern) to the other, leaving the center or end open  130 . The end (e.g., the tail/stern) is then closed by hand gluing or welding  132 . 
         [0083]    If the stringer type involves lashing, then lashing adjustments can be made by accessing the interior of the board through the 2 inch valve hole and resetting the stringer D-ring anchor  134 . 
         [0084]    An air fill valve is then installed in the top panel hole  136 . The structure (e.g., the board) is then inflated  138 , at which point all of the shape, curvature, conformations, and design characteristics are fully expressed. 
         [0085]    The structure may then be coated (though it need not be) with a protective and artistic liquid polyurethane  140 . Fins are then installed  142 . If the structure is a sports board, non-slip traction pads are installed on the deck  144 . The structure is then ready for high performance use. It will be appreciated that fins can be swapped out at any time over the life of the board so as to take advantage of various fin shapes for different applications, and number of fins. 
         [0086]      FIGS. 11A-11C  show the inflatable watercraft structure of the present invention embodiment in a performance surfboard with a planing hull  200 . In this embodiment, the eight stringers  202  on each side of the centerline are spaced generally equidistantly on each side of the board. The upper panel (top deck)  204  is provided with a gentle convex curvature (inverted V) induced by the stringer installation as described above. Rails  206  are soft or pinched for hydrodynamic performance. The bottom panel (bottom deck) contains a predetermined rocker profile for surfing performance of various wave applications and rider skill levels. The tail  208  and nose  210  give this particular board a conventional egg design. Different tail and nose shapes are possible for different surfing applications. 
         [0087]      FIGS. 12A-12C  show the inventive apparatus embodied in a beginner&#39;s surfboard (or yoga board)  300  having buoyancy rails. The additional stability provided by the buoyancy rails  302  enables a user to engage in yoga on the water. The stringer shapes employed in this board enable not only the cylindrical buoyancy rails but a gradual tail rocker  304  and a gradual nose rocker  306  for some maneuverability but high stability. The top panel  308  has a slight concavity to cradle the user on the top. The bottom side  310  may include continuous rocker and/or center rocker, or only nose and tail rocker, as shown. 
         [0088]      FIGS. 13A-13C  show the inventive apparatus embodied in a performance racing paddleboard or distance ocean board  500  with a displacement hull having a V-shape bottom  502  and a generally flat top  504 . In this embodiment, the lowest point of the board in the water  506  is along the longitudinal axis. In an alternative embodiment, longitudinal channels can also be included in the bottom contour to promote speed. 
         [0089]      FIGS. 14A-14B  show a board  600  incorporating the fin assembly of the present invention, which assembly is made possible by the stringer system employed in the present invention. The fins (or skegs)  602  are placed between stringers  604  and can include any of a number of suitable depths, base lengths, rakes (sweeps), and orientations according to user preference and intended use.  FIG. 14A  shows a center fin and two side fins, the alignment dictated by longitudinal lines running through the length of the fin and converging at a point in the nose  606  of the board in a manner known in the art. 
         [0090]      FIGS. 15A-16B  show the components and placement of the fin assembly  700  employed in the present invention. It is a radical departure from any fin system known for inflatable boards and makes possible a rigid, high-performance fin system for inflatables. As will be appreciated from the views, the fin assembly includes a fin base anchor  702  and fin base  704 , the former affixed/welded to the underside  706  of the deck panel  708 , the latter affixed/welded to the upper side  710  of the bottom panel  712 . 
         [0091]    The fin base anchor includes a generally planar top side  714  and an integral anchor box  716 . The anchor box is fabricated from a slightly resilient polymeric material that readily welds to the deck panel, and it may include a channel into which is disposed an interior anchor box  718  with surface features, such as barbs  720 , which prevent the interior anchor box from being removed from the anchor box  716 . The anchor box alone or interior anchor box includes a fin base channel or socket  722 . 
         [0092]    The fin base  704  includes a flexible foot  724  having a generally planar bottom side  726  which may be affixed/welded to the upper side  710  of bottom panel  712 . Integral with the foot is a block portion  728  which tapers upwardly and then narrows into an elongate bar or male element  730  that fits tightly into the base anchor socket  722 . Similarly to the base anchor, the base may include an interior fin box  732  also captured and retained in the block portion using surface features  734  and is formed to include a channel  736  for insertion of a fin base  738  of a fin  740 . The male element is secured in the fin base anchor by passing bolts  742  through aligned fin base anchor holes  744  and fin base holes  746 . The fin itself is secured in the fin box using grub screws  748 . 
         [0093]    From the foregoing, it will be appreciated that in an embodiment, and in a most essential aspect, the inventive inflatable structure is a hydrodynamically designed performance platform that includes: a first flexible material panel having an interior side, an exterior side, and a longitudinal axis; a second flexible material panel having an interior side, and exterior side, and a longitudinal axis; a plurality of internal stringers disposed between the first flexible material panel and the second flexible material panel, the internal stringers having an upper portion affixed to the interior side of the first flexible material panel, a lower portion affixed to the interior side of the second flexible material panel, and a medial portion defining a plane generally normal to the interior sides of the first and second flexible material panel, the internal stringers oriented generally parallel to the longitudinal axes of the first and second flexible material panels; wherein the internal stringers have a profile as seen in side view in elevation that defines the shape of the first flexible material panel and the second flexible material panel when the inflatable structure is assembled; the first and second flexible material panels joined at their edges to form a sealed interior volume; and a valve for selectively introducing pressurized air into and releasing air from the sealed interior volume. 
         [0094]    It will be further appreciated that the essential inventive method for manufacturing and assembling an inflatable structure includes the following steps: laying out first and second flexible material panels; cutting the first and second flexible material panels to a shape suitable for the particular kind of inflatable structure under construction; marking the first and second flexible material panels for bonding; installing a valve reinforcement patch in the interior side of one of the first and second flexible material panels; cutting a valve hole in the flexible material panel at the valve reinforcement patch; installing a first set of stringer panels on the first flexible material panel; installing an opposing second set of stringer panels on the second flexible material panel such that when the first and second material panels are approximated in assembly, the first set of stinger panels overlap and engage stringer panels in the opposing second set of stringer panels; connecting the stringers on the first flexible material panel to their respective opposing stringers on the second flexible material panel; folding over a portion of the perimeter of the first flexible material panel and welding the folded portion to a perimeter of the second flexible material panel, leaving an end of the inflatable structure open; closing the open end by hand gluing or welding; installing an air fill valve in the valve hole; and inflating the inflatable structure by introducing air into the structure through the air valve. 
         [0095]    Numerous sub-steps and variations on the essential steps may be undertaken either due to the particular kind of inflatable structure under construction or to customize or tailor the apparatus according to user preferences or use requirements. 
         [0096]    The above disclosure is sufficient to enable one of ordinary skill in the art to practice the invention, and provides the best mode of practicing the invention presently contemplated by the inventor. While there is provided herein a full and complete disclosure of the preferred embodiments of this invention, it is not desired to limit the invention to the exact construction, dimensional relationships, and operation shown and described. Various modifications, alternative constructions, changes and equivalents will readily occur to those skilled in the art and may be employed, as suitable, without departing from the true spirit and scope of the invention. Such changes might involve alternative materials, components, structural arrangements, sizes, shapes, the number of stringers employed, forms, functions, operational features or the like. 
         [0097]    Therefore, the above description and illustrations should not be construed as limiting the scope of the invention.