Abstract:
The invention relates to a method and to a device for producing a boat-type body ( 10 ) of a water sport device. According to the invention, a rotating frame ( 12 ), which is pre-formed about an access opening of the boat-like body ( 10 ), is arranged on an inner side of a negative mould. The outer shape of the boat-type body ( 10 ) is predetermined, essentially, by the innerside of the negative mould. The boat-like body ( 10 ) is produced in the inner side of the mould by means of a thermoplastic shaping method. During the shaping process, at least one part of the surface of the rotating frame ( 12 ) is in contact with the boat-like body ( 10 ) which is formed by the thermoplastic shaping method. The invention also relates to a water sport device.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention concerns a method and a device for producing the hull of a piece of water sports equipment. The hull is produced by a thermoplastic molding process. The invention also concerns a piece of water sports equipment. 
   2. Description of the Related Art 
   Numerous plastic products are inexpensively produced from thermoplastics by thermoplastic molding processes such as the blow molding process, the rotational molding process, the twin sheet molding process, or the deep drawing molding process. A blow molding process has the advantage over a rotational molding process, for example, that it is less expensive to carry out and can achieve better material properties of the blow molded product. However, especially in the case of boat hulls, openings and areas around openings cannot be molded as desired, and therefore specific requirements cannot always be satisfactorily met. 
   In addition, there is the problem that, due to the essentially uniform wall thickness of thermoplastically molded boat hulls, it is not possible to construct areas in the hull that have any desired degree of stability. For example, areas in which a relatively large force is introduced into the hull are finished by subsequently welding additional material onto the hull in these areas or by mounting additional elements. Examples of areas of this description include especially grips provided on the hull or holes provided in the hull for fastening a line. In other areas in which instability generally does not lead directly to destruction of the hull, this instability is often accepted for cost reasons. 
   In the prior art, in the hull of a piece of water sports equipment, e.g., the hull of a canoe, grip projections and bilge plug formations are subsequently reinforced by the application of additional material. Especially in kayaks, coaming is provided around the cockpit opening, and a spray cover can then be attached to the coaming. This coaming is either reinforced by installing stiffening ribs or is intentionally left unstable. However, if the coaming is unstable, the spray cover cannot be reliably prevented from slipping off. Furthermore, additional molded parts must be subsequently mounted and fastened for the installation of a back support and to realize leg supports. 
   SUMMARY OF THE INVENTION 
   The objective of the invention is to specify a method and a device by which the hull of a piece of water sports equipment can be more or less completely produced by a thermoplastic molding process, so that only a relatively small amount of finishing work is necessary to complete the hull. 
   In accordance with a first aspect of the invention, this objective is achieved by a method with the features of claim  1 . Advantageous modifications of the invention are specified in the dependent claims. 
   The method of the invention for producing the hull of a piece of water sports equipment makes it possible to reinforce the opening area around the cockpit opening of the thermoplastically molded hull by the frame in a simple way and/or to realize projections that cannot be produced solely by the thermoplastic molding process. This makes it possible to improve the range of applications and the quality of the hull produced in this way, and finishing work to finish the complete boat is reduced by means of premolded frames. Moreover, a hull of this type can be produced inexpensively. 
   A second aspect or the invention concerns a device for producing the hull of a piece of water sports equipment. This device comprises a negative mold, on the inner surface of which a peripheral frame is arranged, such that the inner surface of the negative mold essentially predetermines the outer shape of the hull. The device also includes an arrangement which forms the hull on the inner surface of the mold by means of a thermoplastic molding process, so that the hull is at least in partial contact with the peripheral frame, thereby causing the hull and the peripheral frame to be joined in such a way that the frame, which is joined with the hull, extends around the cockpit opening of the hull. 
   A device of this type in accordance with the invention makes it possible to produce a reliable and very durable connection at the point of contact between the hull and the frame. A device of this type eliminates the need for subsequent joining of the hull with stiffening ribs. Hulls that are reinforced and/or stiffened by the frame can be produced in a simple way with the use of this device. Furthermore, almost any desired projections of the area around the cockpit opening can be easily produced, and other functional elements can be realized in this way. With the use of this device, hulls of this type can be produced simply and inexpensively when a mold is used in which the frame can be easily arranged and fixed in the correct position. This simplifies the handling of the mold and the frame. 
   A third aspect of the invention concerns a method for producing the hull of a piece of water sports equipment in which a preform with at least two layers is produced, such that the first layer consists of a material of a first color, and the second layer consists of a material of a second color. The preform is placed in the mold and molded by a thermoplastic molding process in such a way that at least the outer layer of the upper part of the hull has the first color and at least the outer layer of the lower part of the hull has the second color. 
   This method allows simple production of a two-color hull of a piece of water sports equipment. Operations for joining an upper part of the hull and a separate, lower part of the hull are eliminated. Possible points of leakage are prevented by the elimination of a joint between the upper and lower parts of the hull. Furthermore, a two-color hull can be produced simply, quickly, and inexpensively by the method of the invention. Subsequent coating of the hull to give it a certain colored appearance is no longer absolutely necessary. 
   A fourth aspect of the invention concerns a piece of water sports equipment with an elongated hull, which is joined at least with a frame by a molding operation for molding the hull. A piece of water sports equipment of this type can be systematically stiffened or stabilized by the frame in the area around the cockpit opening. This constitutes a simple means of meeting requirements for greater stability in this area. By joining the frame with the hull during the molding operation, a very strong and durable connection is produced. After the molding operation, the frame is joined with the hull as a single piece. 
   By contrast, connections between the hull and a frame that are produced at a later time are not as strong and not as durable, since, depending on the type of joining, they do not allow joining over a large surface area or a full-surface connection between adjoining areas of the frame and the hull, or they impair the material stability and material properties of the hull or the frame, for example, by separation. Furthermore, when these types of joining are used, problems arise with the clean formation of marginal areas of a frame placed on the hull, since either no joint is present in the marginal areas or a welding seam and protruding joining material are visible between the frame and the hull. 
   The present invention will now be explained in greater detail with reference to the preferred embodiments that are illustrated in the drawings and described on the basis of specific terminology. However, it should be noted that the scope of the invention is not limited to these specific embodiments, since changes and other modifications of the illustrated devices and of the methods and applications of the invention other than those shown here are regarded as standard present or future technical knowledge of one skilled in the art. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings show specific embodiments of the invention, namely: 
       FIG. 1  shows a top view of a hull of a kayak in accordance with the invention. 
       FIG. 2  shows a scaled-down side view of the kayak of  FIG. 1 . 
       FIG. 3  shows an enlarged view of a longitudinal section through the rear end region of the kayak according to  FIG. 2 . 
       FIG. 4  shows a perspective view of the underside of a prefabricated coaming frame for producing a hull according to  FIGS. 1 and 2 . 
       FIG. 5  shows an enlarged view of a segment of the coaming frame according to  FIG. 4 . 
       FIG. 6  shows a cross-sectional view of the coaming frame according to  FIG. 4  or  FIG. 5  along sectional line A-A in  FIG. 5 . 
       FIG. 7  shows a perspective view of the upper side of the coaming frame according to  FIG. 4 . 
       FIG. 8  shows an enlarged view of a section of the coaming frame according to  FIG. 7 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a hull  10  of a kayak in accordance with the invention, which is produced from a thermoplastic by a blow molding process. The hull  10  has a coaming frame  12  with leg support elements  14 ,  16  formed on it, with seat adjustment elements  18 ,  20  formed on it, and with an element  22  for fixing the back support, which is integrated in the coaming frame  12 . In addition, the hull  10  is provided with carrying handles  24 ,  26  and a hole  28  for receiving a bilge plug. The handle  24 , the handle  26 , which is formed as a single part with the bilge plug hole  28 , and the coaming frame  12  are already positioned in the blow mold before the blowing operation. The blow mold preferably has recesses into which the handle  24 , the coaming frame  12 , and the handle  26  with the bilge plug hole  28  are inserted. These elements  12 ,  24 ,  26  inserted in the recesses are preferably fixed in place by suitable means. These inserted elements  12 ,  24 ,  26  are preferably preheated in the blow mold before the blowing operation. A preform is then placed in the blow mold and blown, so that an essentially uniformly thick blow molded plastic layer forms on the inside wall of the blow mold and around the elements  12 ,  24 ,  26  inserted in the blow mold. 
   The element that has been blow molded in this way is in contact with at least one region of the surface of the elements  12 ,  24 ,  26  during the molding operation, so that at least this contacting surface region of these elements  12 ,  24 ,  26  is intimately joined, preferably by fusion, with the blow molded part formed in the blow molding process. This fusion process is promoted especially by the preheating of the inserted elements  12 ,  24 ,  26 . The degree of fusion between the blow molded element and the elements  12 ,  24 ,  26  inserted in the blow mold can be adjusted by the preheating temperature. This makes it possible to form elements  12 ,  24 ,  26  on the hull  10 , which could not otherwise be formed at all or could not be produced with the desired characteristics solely by the blow molding operation. 
   The coaming frame  12  is arranged around a cockpit opening  30  of the hull  10  and is provided with a lateral peripheral groove  36 , which is shown in the cross-sectional view of the coaming frame  12  in  FIG. 6 . To seal the cockpit opening  30  against the part of a person&#39;s body that extends out of the cockpit opening  30 , a peripheral spray cover, which is also referred to as a tarpaulin, is inserted and secured in this groove  36 . The tarpaulin is preferably tubular, and one end of the tube is held in the groove  36  by a prestressed rubber ring. At the other end of the tube, another prestressed rubber ring can be provided, which presses this end of the tube against the body extending out of the cockpit opening  30  and thus creates a seal against the body. The shoulder formed above the groove  36  is also known as the coaming. 
   The extruded section of the coaming frame  12  is produced by the so-called extrusion molding process, and the handles  24 ,  26  are produced by an injection molding process. The coaming frame  12  and the elements  24 ,  26  are preferably made of the same thermoplastic material as the hull  10 , for example, a polyethylene material. The coaming frame  12  is preferably formed as a solid profile, which makes it possible to achieve a high degree of stiffness in the area around the cockpit opening  30 . The extrusion molding process and the injection molding process allow a high degree of freedom of design of the elements  12 ,  24 ,  26  produced by these processes. All of the elements of the hull  10  that are subject to or could be subject to large forces are preferably produced by the extrusion molding process, the injection molding process, or some other suitable molding process and are inserted in the blow mold as inserts. In addition, the extrusion molding process makes it possible to form additional elements directly on or in the coaming frame  12 , such as leg support elements  14 ,  16 , seat adjustment elements  18 ,  20 , and the back support fixing element  22 . 
   In the prior art, these elements  14  to  22  must be produced by complicated methods as single parts and then individually mounted on the blow molded hull  10  by relatively complicated production methods. However, the joining of such elements  14  to  22  with the hull is problematic, since especially the hull can be damaged by the placement of joining elements, such as screws or rivets, by the “dissolving” of the hull with adhesive, or by the material changes that occur during subsequent welding of the hull  10  with the additional elements  14  to  22 . By contrast, the method of the invention for producing the hull  10  is much more cost-effective, and the quality of the hull  10  and the useful properties of the complete boat are also significantly improved. 
   A bilge hole must be provided in the hull  10  to allow water that has entered the hull  10  to be removed. The bilge hole  28  is preferably located at one end of the hull  10  and provides a simple means of removing water present in the hull  10 . However, the ends of suitable hull molds are usually poorly accessible, since they taper to a point. As a result, in the prior art, it is relatively difficult and complicated to introduce material in these end regions from the inside to reinforce a blow molded hull for the purpose of constructing a reinforced bilge hole  28  into which an ordinary bilge plug can be inserted to reliably plug the bilge hole  28 . 
   In accordance with the invention, the handle  26  and the bilge hole  28  are produced as a single part by the injection molding process. As has already been mentioned, this part is inserted in the blow mold before the blowing operation, so that this part is also fused and thus welded with the blow molded part during the blowing operation. 
     FIG. 2  shows a side view of the hull  10  in  FIG. 1 . Elements that are the same have the same reference numbers.  FIG. 3  is an enlarged sectional view that shows the detail of the region within the circle in  FIG. 2 . The hull produced in the blow molding process is shown in  FIG. 3  with hatching that runs from upper left to lower right, and the injection molded part with the handle  26  and the bilge hole  28  is shown with hatching that runs from lower left to upper right. The injection molded part has undercut regions  32 ,  34 , which are surrounded by the blow molded part, so that additionally or alternatively to the welding of the blow molded part with the injection molded part, a positive locking connection is produced. 
   The injection molded part with the handle  26  and the bilge plug hole  28  is thus both intimately joined by the welding of the blow molded element with the injection molded element and is joined by a positive locking connection as a result of the engagement of the blow molded element in the undercut regions  32 ,  34 .  FIG. 3  also shows a bilge plug  29 , which is inserted in the bilge plug hole  28  to plug it tightly. 
     FIG. 4  shows a perspective view of the underside of the coaming frame  12 . As mentioned earlier in connection with  FIG. 1 , the coaming frame  12  forms a stable frame around the cockpit opening  30  and stabilizes the hull  10  around the cockpit opening  30 . The back support fixing element  22 , the seat adjustment elements  18 ,  20 , and the leg support elements  14 ,  16  are shown in greater detail in  FIG. 4 . 
     FIG. 5  is a detail drawing of the region of the coaming frame  12  within the circle in  FIG. 4 . In particular,  FIG. 5  shows detail of the formation of the seat adjustment element  18  on the coaming frame  12 , in which recesses are visible which serve as grids for positioning and attaching a seat. 
     FIG. 6  shows a cross-sectional view of the coaming frame  12  in the plane A-A according to  FIG. 5 , which passes through the seat adjustment element  18  formed on the coaming frame. The coaming frame  12  has a lateral peripheral groove  36  in which, as mentioned earlier, a peripheral water of condensation tarpaulin can engage. As an alternative to the aforementioned prestressed rubber ring, the tarpaulin can also be prevented from slipping out of the groove  36  by means of a cord. 
     FIG. 7  shows a perspective view of the upper side of the coaming frame  12 .  FIG. 8  shows an enlarged view of the region of the coaming frame  12  within the circle in  FIG. 7 . This region contains the leg support element  16 . The upper side of the leg support elements  14 ,  16  has reinforcing elements arranged in the form of a grid. Two of these reinforcing elements are labeled  38 ,  40  in the drawing. In addition, other reinforcing elements  42 ,  44  are provided, so that the leg support element  16 , which extends inward from the coaming frame  12  towards the cockpit opening  30 , is prevented from bending, even under the effect of relatively large forces. 
   The blow molded hull  10  is preferably produced from a preform with at least two layers, such that the first layer of the preform contains a material of a first color, and the second layer contains a material of a second color. The document DE 195 45 441 A1 discloses a preform of this type and a device for producing a preform of this type with at least two layers. The specification contained in the cited document regarding the preform and the method and device for producing this type of preform are herewith incorporated in the present specification by reference. 
   The preform with at least two layers is inserted in the blow mold in such a way that, after the blowing operation, at least the outer layer of the upper part of the hull  10  has the first color and at least the outer layer of the lower part of the hull  10  has the second color. This makes it possible to produce hulls  10  with at least two colors in a very simple and cost-effective way. Especially in the case of pieces of water sports equipment, the color design of the boat is a deciding factor in the purchase and popularity of a piece of water sports equipment, so that a two-color design of the hull  10  is very advantageous for creating customer interest and thus for selling the piece of water sports equipment. In addition, it is advantageous to provide the outer layer of the lower part of the hull  10  with a dark color and the upper part of the hull  10  with a light color, because the light color absorbs very little solar radiation. On the other hand, contamination with particles present in the water, which are deposited over a long period of time on the lower part of the hull  10  in contact with the water, is not visible with such high contrast on a dark surface. 
   Alternatively to the blow molding process described in this specific embodiment, other suitable thermoplastic molding processes can be used to form a thermoplastically molded element and at least one additional element, e.g., a rotational molding process, a twin sheet molding process, or a deep drawing molding process. 
   Although the drawings show preferred embodiments and the preceding specification provides a detailed description of these preferred embodiments, these specific embodiments must be understood to be purely exemplary in nature and are not intended to limit the invention in any way. It should be pointed out that only the preferred embodiments are shown and described, and that all variations and modifications that are presently within the scope of the invention or in the future will be within the scope of the invention are also to be protected. 
   LIST OF REFERENCE NUMBERS 
   
       
         10  hull 
         12 ,  14  leg support elements 
         16 ,  18  seat adjustment elements 
         22  back support fixing element 
         24 ,  26  handles 
         28  bilge hole 
         29  bilge plug 
         30  cockpit opening 
         31  bilge plug 
         32 ,  34 ,  36  undercut 
         38 ,  40 ,  42 ,  44  reinforcing elements 
       A-A sectional plane