Abstract:
An apparatus and method of use of a foldable watercraft and method of construction. The device comprises a collapsible boat hull constructed from a lightweight, low maintenance, and inexpensive material. The boat hull is frameless, folded and unfolded quickly, and is easy to transport and store.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to the field of boating and, more particularly, to a lightweight and portable foldable and collapsible kayak and related methods. 
       BACKGROUND OF THE INVENTION 
       [0002]    Boat ownership, and in particular, kayak ownership and use is a popular recreational pastime, but there are many barriers to entry for an average individual to enjoy the benefits of kayak ownership and use. Kayaks are typically relatively expensive to purchase, the cost for maintenance is also often high, and kayaks are generally rather large, so there are difficulties inherent in both the storage and transportation of such vessels. 
         [0003]    Several styles of kayaks are known that address some of these problems. Composite materials and polymer-based kayaks are less difficult and costly to maintain than traditional wood vessels. They are also cheaper to produce. The problems of storage and transport, however, still remain as these kayaks are large, bulky, and relatively heavy, often necessitating multiple individuals to situate a boat into the water or onto and off of transport means. 
         [0004]    Some modern canoes and kayaks are relatively affordable and easy to maintain, and even light enough for a single person to manipulate in and out of the water. The problem of bulk still remains so transportation and storage are still significant hurdles. A vehicle equipped with a roof rack overcomes the transportation issue, and a garage is a solution to the storage problem, but the fact remains that not all individuals possess a vehicle with a roof rack and/or a garage in which storage is possible. 
         [0005]    Collapsible kayaks are known in the art, typically utilizing modern materials such as aluminum and plastic for construction, resulting in high performance vessels capable of collapsing into a relatively small package. These folding kayaks are generally complex in design and relatively slow (15-50 minutes) to assemble and disassemble, for such vessels require numerous parts and connectors. They are also relatively heavy (roughly 25-75 lbs) and bulky due to components such as frames, skins, and tubing. The user must clean, dry, and maintain such vessels thoroughly prior to storage so to avoid corrosion, mold, and mildew. Finally, because of the complexity and number of manufactured parts these folding kayaks are relatively expensive. 
         [0006]    Inflatable kayaks also overcome a number of the disadvantages associated with hard-sided kayaks. These vessels are simple to assemble, sometimes required a single step comprising inflating the hull. They also are relatively compact to store and transport. However, due to the large volume of air needed for inflation, a pump to inflate and deflate the tubes is required. Inflation time can be upwards of 25 minutes, and is also physically challenging in the absence of an automatic air pump. There are a number of disadvantages to inflatable kayaks as well: These vessels are heavy, often weighing over 35 pounds; Require a pump for practical use; hull shapes are generally not conducive to efficient paddling; such vessels are susceptible to puncturing; and due to the complex manufacturing processes and materials needed to craft a seaworthy vessel, are relatively expensive. 
         [0007]    Some companies that produce foldable kayaks include Feathercraft™, Folbot™, and Pakboats™. The Feathercraft kayaks (www.feathercraft.com) take upwards of 30 minutes to assemble weight at least 30 lbs, and cost between $2,900 CAD and $7,200 CAD. The Folbot™ kayaks (www.folbot.com) range from 24 lbs to over 60 lbs, and cost at least $1,295. Additionally, Feathercraft™ and Folbot™ kayaks each comprise dozens of individual pieces. The Pakboats™ Kayak (www.pakboats.com) costs roughly $900 and requires inflation. These kayaks are relatively expensive, assembly is time consuming, and there are many parts, which add to the general complexity of these vessels. 
         [0008]    Accordingly, there is a need for a foldable kayak that is lightweight, portable, relatively resistant to punctures, resistant to corrosion and degradation, simple to maintain, quickly and simply assembled, contains very few parts, while being economical. 
         [0009]    The present invention addresses these issues using a combination of folding construction, folding technique, and materials to create a watercraft that meets all these specifications. 
         [0010]    These and other objects of the present invention are attained by a foldable and collapsible boat hull that is simple and quick to collapse and uncollapse, that is constructed from lightweight and degradation resistant materials, that collapses into an extremely small form factor, yet provides consumers with a low cost, virtually maintenance free kayak. 
         [0011]    One object of the present invention is to provide a foldable and collapsible kayak made of a sturdy, lightweight, water resistant material. 
         [0012]    Another object of the present invention is to provide a foldable and collapsible kayak with predetermined creases providing the user with a guide to easily unfold the boat into the proper form for usage, or to fold it for storage or transport. 
         [0013]    Another object of the present invention is to provide a foldable and collapsible kayak that is not susceptible to damage from corrosive and degradative elements, which decrease the amount of required maintenance. 
         [0014]    Another object of the invention is to provide a foldable and collapsible kayak that is suited for recreational purposes due to the kayak&#39;s lightweight and compact design, yet is also suited for use as an emergency rescue vessel that can be stored on small watercraft or used by rescue personnel. 
         [0015]    Another object of the invention is to provide a foldable and collapsible kayak that, due to its simple design and construction, is inexpensively produced and inexpensive to purchase. 
         [0016]    These and other objects, features, and advantages of the present invention will become more readily apparent from the attached drawings and the detailed description of the preferred embodiments, which follow. 
       SUMMARY OF THE INVENTION 
       [0017]    In view of the foregoing background, it is therefore an object of the present invention to provide a foldable kayak comprising a foldable multichine hull comprising a cockpit, a forward deck, an aft deck, a port hull side, and a starboard hull side. The port hull side and the starboard hull side meet to define a keel. The port hull side meets the forward and aft decks defining a port side gunwale, and the starboard hull side meets the forward and aft decks to define a starboard side gunwale. In one embodiment, a foldable insert of a size and dimension to fit inside the cockpit comprising a floor thwart, seat, seat back, and aft bulkhead is utilized in the kayak design. In one embodiment, the cockpit comprises a cockpit coaming. 
         [0018]    In one embodiment, the kayak further comprises a first V-shaped center crease on the port hull side having a first bisecting crease beginning at the apex of the first V-shaped center crease and ending at the port side gunwale. Additionally, a second V-shaped center crease on the starboard hull side having a second bisecting crease begins at the apex of the second V-shaped center crease and ends at the starboard side gunwale. 
         [0019]    A plurality of fasteners on the exterior side of the port hull side accommodate a first strap, wherein the first strap pulls the first V-shaped center crease closed upon itself. This pinches the port hull side on itself to create a rocker in the keel and aids in the structural integrity of the kayak. A plurality of fasteners on the exterior side of the starboard hull side accommodate a second strap, wherein the second strap pulls the second V-shaped center crease closed upon itself, pinching the starboard hull side on itself to create a rocker in the keel and aiding structural integrity of the kayak. 
         [0020]    In one embodiment of the invention, the foldable hull comprises a single sheet of plastic. This sheet of plastic is comprised of polypropylene twinwall plastic sheet in a preferred embodiment. 
         [0021]    To form a water-tight forward stem seal and foldable hinge, the keel, proximate the bow of the kayak, is heat sealed. To form a water-tight forward stem seal and foldable hinge, the keel, proximate the stern of the kayak, is heat sealed. 
         [0022]    A center crease traverses the long axis of the plastic sheet, and the center crease forms the kayak keel when folded. The plastic sheet comprises a plurality of chine creases that are mirrored on each side of the center crease. The chine creases form the multichine hull sides when folded. The chines creases allow a somewhat smooth hull curvature and prevent accidental and unwanted creasing of the hull material. A bow crease perpendicular to the center crease that is situated between the bow edge of the plastic sheet and the center of the plastic sheet is used to fold the kayak upon itself. A stern crease perpendicular to the center crease is situated between the stern edge of the plastic sheet and the center of the plastic sheet, and is also used to fold the kayak upon itself. 
         [0023]    A plurality of first angled cuts emanate from a forward point on the keel, the first angled cuts having a size and dimension to remove material from the plastic sheet and defining the edges that fold into the forward stem. A plurality of second angled cuts emanate from an aft point on the keel, the second angled cuts having a size and dimension to remove material from the plastic sheet defining the edges that fold into the aft stem. 
         [0024]    The invention also contemplates a method of unfolding a foldable kayak comprising the steps of unclipping a strap that maintains the kayak in a folded state; unfolding the forward end of the kayak along a forward crease; unfolding the aft end of the kayak along a stern crease; and spreading open the cockpit of the kayak. In one embodiment, the method further comprises the step of tightening straps to maintain the kayak in an unfolded state. One embodiment includes the step of inserting a floor panel into the cockpit aperture. The floor panel comprises a seat. 
         [0025]    The invention also contemplates a method of sealing the seams of a kayak made from polypropylene twinwall plastic sheet comprising the steps of: creasing a first sheet having a first side and a second side with a die creating a first crease and first indentation on the first side; creasing a second sheet having a first side and a second side with a die creating a second crease and second indentation on the first side; orienting the first indentation of the first side of the first sheet opposite the second indentation of the first side of the second sheet forming a small substantially symmetrical inter-sheet cavity; clamping against the second side of the first sheet and the second side of the second sheet along the crease lines, creating a crease junction, and causing the inter-sheet cavity to collapse and the sheets to flare outwardly and opposedly deflect; heating the crease junction between the sheets, on the first sides of both sheets, from the direction where the sheets outwardly flare and opposedly deflect, also heating the first side of the first sheet proximate the first crease and the first side of the second sheet proximate the second crease; clamping the heated sheets using a substantially flat clamping surface; and fusing the heated sheets together forming a water-tight junction and hinged seam. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    For a fuller understanding of the invention, reference is made to the following detailed description, taken in connection with the accompanying drawings illustrating various embodiments of the present invention, in which: 
           [0027]      FIG. 1  is a schematic illustration of an isometric view of one embodiment of the invention; 
           [0028]      FIG. 2  is a schematic illustration of a top view of one embodiment of the invention; 
           [0029]      FIG. 3  is a schematic illustration of a top view of one embodiment of the invention; 
           [0030]      FIG. 4  is a schematic illustration of a side view of one embodiment of the invention; 
           [0031]      FIG. 5  is a schematic illustration of an isometric view of one embodiment of the invention; 
           [0032]      FIG. 6  is a schematic illustration of an isometric view of one embodiment of the invention; 
           [0033]      FIG. 7  is a schematic illustration of an isometric view of one embodiment of the invention; 
           [0034]      FIG. 8  is a schematic illustration of an isometric view of one embodiment of the invention; 
           [0035]      FIG. 9  is a schematic of one embodiment of a side view illustrating the method of the invention; 
           [0036]      FIG. 10  is a schematic of one embodiment of a side view illustrating the method of the invention; 
           [0037]      FIG. 11  is a schematic of one embodiment of a side view illustrating the method of the invention; 
           [0038]      FIG. 12  is a schematic of one embodiment of a side view illustrating the method of the invention; 
           [0039]      FIG. 13  is a schematic of one embodiment of a side view illustrating the method of the invention; and 
           [0040]      FIG. 14  is a schematic of one embodiment of a side view illustrating the method of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0041]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and prime notation is used to indicate similar elements in alternate embodiments. 
       Collapsible Boat Hull 
       [0042]    The present invention is generally directed to a collapsible boat hull. In a preferred embodiment, the boat is a kayak, and is made from lightweight materials to promote ease of storage, transportation, and use. Referring initially to  FIG. 1 , an illustrative embodiment of the kayak  100  is shown in the fully open conformation. In this embodiment, the kayak is made of two sheets of material, the first sheet of material substantially forming the hull  101  of the kayak, and the second sheet substantially forming a hull insert  103 . In this conformation, the kayak  100  comprises the basic features of a standard kayak, including a forward deck  105  and aft deck  110 . A port hull side  115  of the kayak  100  meets the port side edge of the forward deck  105  to define the forward port side gunwale  120 . The port hull side  115  of the kayak  100  meets the port side edge of the aft deck  110  to define the aft port side gunwale  125 . A starboard hull side  130 , as is visible in the illustration of  FIG. 2 , of the kayak  100  meets the starboard side edge of the forward deck  105  to define the forward starboard side gunwale  135 . The starboard hull side  130  of the kayak  100  meets the starboard side edge of the aft deck  110  to define the aft starboard side gunwale  140 . The gunwales  120 ,  125 ,  135 ,  140  are formed from creases in the first sheet of material, maintaining a watertight fold. 
       Crease and Cut Layout and Geometry 
       [0043]      FIG. 3  illustrates one embodiment of the first sheet of material  305 . The first sheet  305  is made of plastic. In one embodiment, the first sheet  305  is made of a corrugated plastic. In a preferred embodiment, the first sheet  305  is made of polypropylene twinwall plastic sheet. In one embodiment, the first sheet  305  is approximately 84 inches long by approximately 48 inches wide. The first sheet  305  comprises a number of creases that define the lines wherein the hull will bend. In the open conformation, the kayak  100  comprises a plurality of folds that are each one of acute, obtuse, and straight. 
         [0044]    A center crease  310  traverses the long axis of the first sheet  305 , and defines the keel in the open conformation of the kayak  100 . A plurality of mirrored chine creases  311   a,    311   b,    312   a,    312   b,    313   a,    313   b,    314   a,    314   b,    315   a,    315   b  are substantially parallel to the center crease  310 . The number of chine creases is at least two chine creases per hull side to 20 chine creases per hull side. In a preferred embodiment, there are five chine creases per hull side, and each chine crease is equidistantly spaced in relation to adjacent chine creases. In a preferred embodiment, the starboard side chine creases  311   a,    312   a,    313   a,    314   a,    315   a  are spaced roughly three inches from each other and the port side chine creases are spaced roughly three inches from each other. In the open conformation of the kayak  100 , each starboard side chine crease  311   a,    312   a,    313   a,    314   a,    315   a  is bent at an angle to define the multichine hull of the starboard hull side  130  and each port side chine crease  311   b,    312   b,    313   b,    314   b,    315   b  is bent at an angle to define the multichine hull of the port hull side  115 . 
         [0045]    Approximately 30 inches from the bow is a bow crease  317  situated perpendicularly to the center crease  310 , the bow crease traversing the width of the first sheet  305 . The bow crease  317  provides a folding point for the kayak  100  to fold upon itself when in the folded conformation. Approximately 30 inches from the stern is a stern crease  320  situated perpendicularly to the center crease  310 , the stern crease traversing the width of the first sheet  305 . The stern crease  320  provides a folding point for the kayak  100  to fold upon itself when in the folded conformation. 
         [0046]    On approximately the midline of the kayak  100  that is perpendicular to the center crease  310 , a starboard side V-crease  325  extending medially from the starboard hull side of the first sheet  305  to meet at the point of the “V.” A first bisecting crease  330  splits the starboard side V-crease  325  extending medially from the starboard hull side of the first sheet  305  to meet at the point of the “V.” A port side V-crease  335  extending medially from the port hull side of the first sheet  305  to meet at the point of the “V.” A second bisecting crease  340  splits the port side V-crease  325  extending medially from the port hull side of the first sheet  305  to meet at the point of the “V.” The side V-creases  325 ,  335  fold inwardly from the exterior sides  115 ,  130  of the kayak  100  when the kayak  100  is in the open conformation, pinching the exterior sides  115 ,  130  upon themselves to create a rocker in the keel (center crease  310 ), and to cause the kayak  100  to maintain an open conformation. 
         [0047]    Again noting  FIG. 3 , a plurality of cuts is made in the first sheet  305  to impart a final kayak-like shape to the unfolded kayak  100 . In particular, measuring from a construction line perpendicular to the center crease  310  that bisects the most distal forward point on the center crease, a first forward stem cut  355   a  is made in the first sheet  305  comprising an angle from 25° to 60° and a second forward stem cut  355   b  is made in the first sheet  305  comprising an angle from 120° to 155°. In a preferred embodiment, the angles are 36° and 144° respectively. This creates a forward wedge shaped area  345  wherein material is removed from the first sheet  305  at the bow of the kayak, the wedge having an angle between 60° and 130° with a preferred angle of 108°. The same angle constraints for the forward wedge area  345  are mirroredly applied to cuts made at the stern of the kayak  100  defining an aft wedge shaped area  350 , a first aft stem cut  360   a,  and a second aft stem cut  360   b.  The edges of the first sheet  305  that are defined after removing the material of forward wedge area  345  are attached together (method described below) to form the forward stem  415  ( FIG. 4 ). The edges of the first sheet  305  that are defined after removing the material of the aft wedge area  350  are attached together (method described below) to form the aft stem  420  ( FIG. 4 ). 
         [0048]    Still noting  FIG. 3 , additional cuts are made on the edges of the first sheet  305  to define the forward deck  105  and the aft deck  110  of the final unfolded kayak  100 . In particular, measuring from a construction line perpendicular to the first cut in the first sheet  305  that bisects the most distal point of the first cut on the first sheet  305 , a first forward deck cut  365   a  is made measuring from 0° to 20°, with a preferred angle of approximately 6°. Measuring from a construction line perpendicular to the second cut in the first sheet  305  that bisects the most distal point of the second cut on the first sheet  305 , a second forward deck cut  365   b  is made measuring from 0° to 20°, with a preferred angle of approximately 6°. The same angle constraints for the forward deck cuts  365   a,    365   b  are mirroredly applied to cuts made at the stern of the kayak  100  defining a first aft deck cut  370   a,  and a second aft deck cut  370   b.  The edges of the first sheet  305  that are defined after removing the material of the forward deck cuts  365   a,    365   b  are attached together (method described below) to form the forward deck seal  425  ( FIG. 4 ). The edges of the first sheet  305  that are defined after removing the material of the aft deck cuts  370   a,    370   b  are attached together (method described below) to form the aft deck seal  425  ( FIG. 4 ). 
       The Unfolded Vessel 
       [0049]      FIG. 4  illustrates a side view of one embodiment of the open conformation of the kayak  100 . A plurality of port fasteners  405  is attached to the port hull side  115 . A port side strap  410  engages the port side fasteners  405 . When the port side strap  410  is cinched tight, the port side V-crease  335  is securedly pinched upon itself. A plurality of starboard fasteners  415  is attached to the starboard hull side  130 . A starboard side strap  420  engages the starboard side fasteners  415 . When the starboard side strap  420  is cinched tight, the starboard side V-crease  325  is securedly pinched upon itself. The straps  410 ,  420  are made of at least one of rope, webbing, cloth, plastic, nylon, polypropylene, cotton, rubber, bungee shock cord, and any other material known in the art. The fasteners  405 ,  415  are at least one of slide releases, cam buckles, loops, hooks, D-rings, ratchets, footman loops, double bar buckles, carabineers, cleats and any other fastener known in the art. The fasteners  405 ,  415  are made from plastic, nylon, metal, fabric, and any other material known in the art. 
         [0050]    As  FIG. 5  illustrates, in one embodiment, at least one strap  410 ,  420  is long enough to circumscribe the kayak  100 . A storage fastener  505  engages at least one strap  410 ,  420  so that when the kayak  100  is in the folded conformation, the circumscribing strap  410 ,  420  keeps the kayak  100  in a compact and folded state. The storage fastener  505  is at least one of a slide release, cam buckle, loop, hook, D-ring, ratchet, footman loop, double bar buckle, carabineer, cleat and any other fastener known in the art. It should be noted that the insert  103  folds upon itself and fits inside the folded cockpit  145  of the folded kayak  100  for storage and transport. 
         [0051]    In the open conformation a cavity is created on the interior surface of the kayak  100  that defines the cockpit  145 . The cockpit  145  is where the operator of the kayak  100  sits. In one embodiment, the forward border of the cockpit  145  comprises a coaming  150 . The second sheet of material is formed into an insert  103  having a size and dimension to securedly fit within the cockpit  145 . The insert  103  bolsters the integrity of the kayak  100 , adding a second layer of material as the floor  605  of the kayak  100  and by defining a transverse floor thwart member bolstering the integrity of the kayak  100 , and serving as a platform to distribute a pilot&#39;s weight. Forward folds  610  in the insert  103  aid to conform the insert  103  to the shape of the kayak  100  floor. In one embodiment, a second panel of material  615  is attached to the insert  103 , the second panel  615  having an appropriate size and dimension to fold into a seatback  620 . To aid in removing the insert  103  from the cockpit  145 , a pull tab  625  extends from proximate a central crease  630  in the panel  103 . In one embodiment, an aft bulkhead panel  635  extends from second panel  615 . In one embodiment, the aft bulkhead panel  635  is an extension of the seatback  620 . 
       Method of Unfolding and Folding the Kayak 
       [0052]    Referring to  FIG. 7 , the method of unfolding the kayak  100  comprises a plurality of steps. In particular, any straps that are secured to hold the kayak  100  in a folded conformation are released. The bow crease  317  and the stern crease  320  are unfolded. The bow and stern of the kayak are extended until the bow crease  317  and the stern crease  320  form substantially 180° angles. The coaming  150  is spread apart to open the cockpit  145 . If no coaming is present on the embodiment of the kayak  100 , the opening in the hull that defines the cockpit  145  is spread apart to open the cockpit  145 . The starboard side strap  420  is tightly cinched to pinch the starboard side V-crease  325  upon itself. The port side strap  410  is tightly cinched to pinch the port side V-crease  335  upon itself. The insert  103  is placed in the cockpit with the seatback  620  towards the aft of the kayak  100 . The insert  103  must be bent at the central crease  630  to fit in the opening of the cockpit  145  and then the insert is extended so that the central crease  630  has an approximate angle of 180°. The kayak  100  is then introduced into a body of water and the user enters and is seated in the cockpit  145 . To remove the insert, a user, from without the kayak  100 , pulls the pull tab  625 , causing the central crease  630  to bend so the insert  103  disengages from the cockpit  145 . The starboard side strap  420  is released from tension so the starboard side V-crease  325  relaxes. The port side strap  410  is released so the port side V-crease  335  relaxes. The kayak  100  is folded along the center crease  310  causing the chine creases  311   a,    312   a,    313   a,    314   a,    315   a,    311   b,    312   b,    313   b,    314   b,    315   b  to relax and the kayak  100  to maintain a relatively flat conformation. The cockpit  145  forms a pocket in this conformation, and can store the folded insert  103 . The bow crease  317  is folded so that the bow section  705  points aft. The stern crease  320  is folded so that the stern section  710  points forward. A strap  410 ,  420  is made to circumscribe the kayak and then fastened, capturing the bow section  705  and the stern section  710  against the sides of the kayak  100  as illustrated in  FIG. 5 . 
         [0053]    Noting  FIG. 8 , to form the sealed edges of the forward stem seal  415 , the aft stem seal  420 , the forward deck seal  425 , the aft deck seal  430 , and the coaming seal  430  are water-tight, yet hingedly flexible junctions  800 . 
         [0054]    The method to seal the seams of polypropylene twinwall plastic sheet are illustrated by  FIGS. 9-14 . 
       Method of Constructing Sealed Seams of the Kayak 
       [0055]      FIG. 9  illustrates the creasing of a first polypropylene twinwall plastic sheet  905  and a second polypropylene twinwall plastic sheet  910 . In one embodiment, a crease  915 ,  920  is formed when a pointed die  925  is pressed onto the plastic sheets  905 ,  910 . The creasing of the plastic sheets  905 ,  910  results in indentations  930 ,  935  that remain in the plastic sheets  905 ,  910  after the die  925  is removed. 
         [0056]      FIG. 10  illustrates orienting the first sheet  905  and the second sheet  910  so that the indentations  930 ,  935  are mirroredly adjacent to form an inter-sheet cavity  940  that is substantially defined by the profiles of the indentations  930 ,  935 . 
         [0057]      FIG. 11  illustrates the clamping of a first clamp  1105  against the mirroredly adjacent plastic sheets  905 ,  910  along the creases  915 ,  920 . The first clamp  1105  is of a size and dimension so that upon exerting clamping pressure by the first clamp  1105  along the creases  915 ,  920 , the inter-sheet cavity  940  collapses causing a first end  1110  of the first sheet  905  to outwardly deflect in a direction opposing a second end  1115  of the second sheet  910 . The outward deflection of the sheet ends  1110 ,  1115  defines a crease junction  1120 . 
         [0058]      FIG. 12  illustrates heating of the crease junction  1120  using a heat source  1205 . The heat source  1205  is at least one of a flame, heated air, heating element, combinations thereof, and any other heat source known in the art. The heat source melts the plastic surfaces of the crease junction  1120 .  FIG. 13  and  FIG. 14  illustrate the step wherein a second clamp  1305  applies clamping pressure to the first end  1110  and the second end  1115  of the sheets. The second clamp  1305  is adjacent to the first clamp  1105 . The second clamp  1305  comprises a substantially flat clamping surface having a size and dimension to clamp the melted sheet ends  1110 ,  1115  together. When the second clamp  1305  clamps its jaws together, clamping the heated first end  1110  and the heated second end  1115  of the sheets together, the sheets are melted together, creating a water-tight hingedly flexible junction  800  as shown in  FIG. 14  and  FIG. 8 . 
         [0059]    Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.