Abstract:
A small watercraft is provided. The small watercraft comprises a hull formed to have a substantially uniform thickness by using reinforced fibers impregnated with resin. The hull includes a curved portion formed by protruding outward and curving a part of the hull, and a filling material filled in a groove portion on an inner side of the hull which is created by forming the curved portion.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a small watercraft and, more particularly to a reinforcement structure of a spray strip portion provided on a hull of the small watercraft, and a manufacturing method thereof. 
       BACKGROUND ART 
       [0002]    Small watercraft (e.g., PWC) are in some cases provided with a spray strip portion at a front portion of a hull or a bow. The spray strip portion is also called a chine or a spray deflector formed to improve sea kindliness. The spray strip portion is typically a protruding portion formed by curving and protruding outward a part of the hull and by extending it in a longitudinal direction of the hull. One to four spray strip portions are provided on both sides of the hull at different vertical positions. 
         [0003]    The spray strip portion is manufactured in such a manner that FRP sheets impregnated with thermosetting resin or the like are stacked to conform in shape to a mold (female mold) of the hull having grooves corresponding to the spray strip portions and are pressed from downward to upward using a roller or the like every time an FRP sheet is stacked, to avoid uneven heating of the spray strip portion in a thermal hardening process. 
         [0004]    In this process, the roller falls into the groove portion of the spray strip portion and reduces the thickness of a bottom region of the groove portion, whereas a region immediately above the thinned region is made to have a larger thickness. This results in a hull cross-sectional shape in which stress concentration is likely to occur on the groove portion. Such stress concentration tends to occur particularly on the spray strip portion located higher whenever a front bottom portion of the hull hits on the water surface while skipping on the water surface, thereby decreasing stiffness of the hull. 
         [0005]    In addition, as described above, non-uniform thickness may cause the spray strip portion to be unevenly heated and may adversely affect a quality of a product if it is directly thermally hardened. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention has been developed under the circumstances, and provides a reinforced spray strip structure of a small watercraft and a manufacturing method thereof. 
         [0007]    According to a first aspect of the present invention, there is provided a small watercraft comprising a hull formed to have a substantially uniform thickness by using reinforced fibers impregnated with resin, the hull including a curved portion formed by protruding outward and curving a part of the hull; and a filling material filled in a groove portion on an inner side of the hull which is created by forming the curved portion. 
         [0008]    In such a construction, the hull which is not substantially susceptible to stress concentration and is stiff can be provided. 
         [0009]    The curved portion may be a spray strip portion formed on a bow of the hull. 
         [0010]    The groove portion filled with the filling material may define a smooth curved line together with an inner surface of the hull around the groove portion. 
         [0011]    The curved portion may include a plurality of curved portions. In this case, the smooth curved line may extend over a plurality of groove portions on the inner side of the hull which are created by forming the plurality of curved portions. 
         [0012]    The smooth curved line may be a circular-arc curved line. 
         [0013]    According to a second aspect of the present invention, there is provided a method of manufacturing a spray strip portion of a small watercraft, comprising: forming a hull to have a substantially uniform thickness by using reinforced fibers impregnated with resin and protruding outward and curving a part of the hull to form the spray strip portion; thermally hardening the hull provided with the spray strip portion; and filling a filling material in a groove portion on an inner side of the hull that is created by forming the spray strip portion. 
         [0014]    In such a construction, the hull which is not substantially susceptible to stress concentration and is stiff can be provided. Further, since the filling material is filled into the groove portion after the spray strip portion is formed, uneven heating of thermosetting resin in a thermal hardening process will not occur, and therefore, a quality of a product will not be degraded. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings, in which the like reference numerals indicate similar elements and in which: 
           [0016]      FIG. 1  is a right side view of a small watercraft according to an embodiment of the present invention; 
           [0017]      FIG. 2  is a plan view of a hull of the small watercraft of  FIG. 1 , showing a state where a deck portion is not mounted to a hull yet; 
           [0018]      FIG. 3  is a perspective view of spray strip portions formed at a front end portion of the hull of  FIG. 2 , as viewed from rightward and backward; 
           [0019]      FIG. 4  is a cross-sectional view taken along line IV-IV of  FIG. 2 , showing a hull portion provided with the spray strip portions; 
           [0020]      FIGS. 5A and 5B  show a manufacturing method of the spray strip portions of  FIG. 4 ; 
           [0021]      FIG. 6  is a flowchart showing the manufacturing method of the spray strip portions of  FIGS. 5A and 5B ; and 
           [0022]      FIG. 7A  shows a stress distribution of a hull cross-section according to a prior art or in step  1  of  FIG. 6 , and  FIG. 7B  shows a stress distribution of the hull cross-section according to an embodiment of the present invention or in step  2  in  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Hereinafter, a small watercraft of the present invention will be described with reference to the accompanying drawings. 
         [0024]      FIG. 1  shows a water-jet propulsion personal watercraft  10  according to an embodiment of the present invention. A body  13  of the personal watercraft  10  includes a hull  11  and a deck  12  covering the hull  11  from above. 
         [0025]    A seat  15  is mounted over a region extending from a center region to a rear region in a longitudinal direction of the deck  12 , and is configured to be straddled by an operator. A bar-type steering handle  16  is attached to a portion of the deck  12  in front of the seat  15 . 
         [0026]    In this embodiment, the hull  11  includes four spray strip portions  20  ( 20 A,  20 B,  20 D, and  20 D) at a portion forward of the steering handle  16 . The spray strip portions  20  are disposed at different vertical positions, and are arranged in the order of the  20 A,  20 B,  20 C, and  20 D from above. 
         [0027]    As used herein, the term “spray strip portion” is one example of a “curved portion.” The term “curved portion” includes the above mentioned chine, spray deflector, and other portions, and is, of course, applicable to other similar construction of the body of the watercraft. 
         [0028]      FIGS. 2 and 3  are a plan view and a perspective view showing the interior of the hull  11  to which the deck  12  is not mounted yet. As shown in  FIGS. 2 and 3 , in this embodiment, a filling material  22  (see  FIG. 4 ) is applied to the spray strip portions  20 A and  20 B that are located on an upper side and are particularly susceptible to stress concentration as described above. 
         [0029]    It is advantageous that the filling material  22  is made of a material which forms a hull body (e.g., thermosetting FRP) or a similar material, in order to improve stiffness of the entire hull. But, this is merely exemplary and a bond (urethane based bond, bonding agent or other bond), putty, and others may be used. As the bond, the bond used to join the deck  11  and the hull  12  may be used so that the body  13  is manufactured easily. In addition, by using flexible bond, the hardened bond advantageously well conforms to a deformed shape of the hull  12  and does not substantially peel off from the hull body. Furthermore, by using quick-drying putty, a manufacturing time can be reduced. 
         [0030]    As can be seen in  FIG. 4  showing the cross-section of the hull  11 , taken along line IV-IV, the filling material  22  is typically filled over the entire length of inner groove portions  201   a  and  202   a  (see  FIG. 5A ) of the spray strip portions  20 A and  20 B. Preferably, the surface of the filling material  22  is formed into a curved surface continuous with at least an inner surface of the hull body to which the filling material  22  is applied. More preferably, the inner surface of the hull body filled with the filling material  22  is formed in a circular-arc shape with an identical radius R. This makes it difficult to cause stress concentration, and as a result, improves stiffness of the body. 
         [0031]    Next, with reference to  FIGS. 5A ,  5 B, and the flowchart of  FIG. 6 , the manufacturing method of the spray strip portion  20  will be described. In step S 1 , as shown in  FIG. 5A , the FRP sheets impregnated with thermosetting resin are stacked to conform in shape to a mold of the hull (female mold) having groove portions corresponding to the spray strip portions and are typically pressed from downward to upward using a roller or the like every time an FRP sheet is stacked, to avoid uneven heating of the spray strip portions in a thermal hardening process. Thereafter, the FRP sheets are thermally hardened to form the spray strip portions  20 . 
         [0032]    In this embodiment, the hull is manufactured by a hand lay-up method, but may alternatively be manufactured by other methods such as a SMC method or a spray-up method. 
         [0033]    In this process, the roller may in some cases fall into the groove portions  201   a,    202   a,    203   a,  and  204   a  of the spray strip portions  20  and reduce the thickness thereof, while regions located immediately above the thinned regions are made to have a larger thickness. This results in a hull cross-sectional shape in which stress concentration is likely to occur on the groove portion. Accordingly, in step S 2 , as shown in  FIG. 5A , the filling material  22  is applied to the groove portions (herein  201   a  and  202   a  where the stress concentration is most likely to occur), and the inner surface of the hull around the spray strip portions  20  is formed to have a smooth curved line using a scraper, etc. 
         [0034]    At this time, the filling material  22  may be thermally hardened when the thermosetting FRP is used as the filling material  22 . By thus carrying out the thermal hardening process at two stages, the product quality of even the spray strip portions  20  which may have uneven thickness are not degraded, and hence the hull  11  that is stiff and is not substantially deformed can be manufactured. In a case where the bond, adhesive, or the like is used as the filling material  22 , it is dried and hardened directly or after its temperature is increased. 
         [0035]    Alternatively, the FRP sheet may cover the filling material  22  from above and may be hardened together with the filling material  22 . 
         [0036]      FIGS. 7A and 7B  show analysis results of simulation of a stress distribution occurring when the front bottom portion of the hull hits on the water surface while skipping on the water surface, with respect to the spray strip portions  20  shown in  FIGS. 5A and 5B . To be specific,  FIG. 7A  shows the spray strip portions  20  which are not applied with the filling material  22  according to this embodiment or according to the prior art, whereas FIG.  7 B shows the spray strip portions  20  to which the filling material  22  is applied according to this embodiment. In  FIGS. 7A and 7B , each stress distribution is hatched in different ways. 
         [0037]    As shown in  FIG. 7A , the stress concentration occurs in the spray strip portions  20 A and  20 B to which the filling material  22  is not applied. On the other hand, as clearly shown in  FIG. 7B , the stress is well dispersed in the spray strip portions  20 A and  20 B manufactured by filling the filling material  22 . 
         [0038]    Such stress dispersion is effectively achieved by forming the continuous curved surface over the plural spray strip portions  20 . 
         [0039]    Although the present disclosure includes specific embodiments, specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various elements, features, functions, and/or properties disclosed herein. The following claims particularly point out certain combinations and subcombinations regarded as novel and nonobvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of features, functions and elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims and whether broader, narrower, equal, and/or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.