Abstract:
An insert for use in the fabrication of a watercraft hull to form an inboard/outboard propulsion system passageway. The design of the insert incorporates a semi-rigid body having an inboard surface, an outboard surface, and sidewalls interconnecting the surfaces. The semi-rigid nature of the body facilitates the insert fitting tightly with the build up of laminate layers forming a watercraft hull while maintain dimensional stability during the manufacture of the hull. The insert is further configured to be easily removed from the completed watercraft hull to reveal the finished inboard/outboard propulsion system passageway.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     None. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     Conventional watercraft, such as recreational powerboats and the like, often generate movement using an inboard/outboard (I/O) propulsion system. These I/O propulsion systems incorporate a stern drive component that typically includes a motor (e.g., a combustion engine), tilt components (e.g., gimbal unit and pivot housing) and an outdrive having a propeller. An opening or passageway is formed in the transom of the watercraft hull so that the stern drive component may be extended therethrough and mounted with the watercraft. 
     Complicating the formation of the transom opening is the typical lay-up that forms the watercraft hull. This lay-up includes a number of laminate layers, such as a glass reinforced resin shell and various core materials including plywood, glass reinforced cast composites, and other materials. Cutting and/or drilling through these types of laminate layers to form the transom opening has proven to be quite difficult and time consuming with traditional hand tools; an accurately formed transom opening is therefore hard to achieve. A more precise transom opening outline may sometimes be realized by using automated cutting equipment, but this equipment is often cost prohibitive and requires substantial training to use properly. 
     One proposed solution is to form the transom opening by using a reusable cast metal insert, such as one made of aluminum. In this method, the insert is shaped to form the transom opening as a watercraft hull is molded around the perimeter of the insert. In a first step, the insert is attached to a molding tool such that one face of the insert faces inboard and an opposing face of the insert faces outboard with respect to the watercraft hull being formed thereon. Then, a shell layer of the hull is molded onto the molding tool and surrounding the perimeter of the insert. It would seem intuitive at this point just to build the remaining laminate layers onto the shell layer around the insert perimeter, detach the insert from the molding tool, and demold the laminate layers forming the finished watercraft hull from the molding tool (and the insert from the hull) to reveal the transom opening in the hull. However, the rigidity of the metal insert does not promote a tight fit between the insert and the molding tool surface. This allows gel coat or other coatings applied to the layer surfaces to promote lamination thereof to flow between the molding tool and the insert, thereby encapsulating the insert and making removal of the insert and hull from the tool without damaging the hull (and thus damaging the transom opening) very difficult. Also, the lack of a tight fit between the insert and the molding tool facilitates the formation of air voids when the coatings are applied, which impair the structural soundness of the hull and are difficult to remove. 
     To solve the problems associated with using the cast metal insert, a raised, curved surface made of clay or wax is formed onto the exposed perimeter of the insert once the insert is installed with the moldling tool. This forms a tighter seal between the insert and the molding tool surface such that the coatings do not pass to the lateral edges of the layers when building up the watercraft hull. Additionally, though, a release agent is usually required to be applied to the perimeter of the case metal insert to thereby form a release film, in order to prevent the laminate from sticking to the insert. Release agents, unfortunately, do not perform ideally when applied to an essentially rigid metal insert. Such agents often form a release film with air voids and damaged spots, resulting in the insert bonding to the molding tool surface and thereby impeding the removal of the insert to expose the finished transom opening. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention overcomes the problems of the prior art by providing an improved insert for use in the fabrication of a watercraft hull to form an inboard/outboard propulsion system passageway, or transom opening. The insert is formed of a semi-rigid body having an inboard surface, an outboard surface, and tapering perimeter sidewalls interconnecting the surfaces. The tapering of the sidewalls facilitates the removal of the insert from the built up layers forming the finished watercraft hull. To provide the semi-rigid body with the desired physical properties, the body may be formed from polyurea, polyurethane, a polyurea/polyurethane compound, or similar materials. Alternatively, the semi-rigid body can be formed of a hybrid structure with a central region formed of a more rigid material (e.g., a metal) and a perimeter region, including the sidewalls, formed of a less-rigid material. 
     Before fabrication of a watercraft hull using the insert can begin, a molding tool is manufactured to form the exterior shape of the watercraft hull and the insert is formed with a shape that will define the transom opening to be formed in the hull. In a first step of the process, a release agent is applied to a surface of the tool. The insert is then attached to the transom surface of the molding tool, and the insert and transom surface are coated with a gel that cures into a semi-rigid film that forms the outermost or “painted” surface of the watercraft hull. Subsequently, various layers of laminate material are applied in successive steps on top of one another and over the semi-rigid film (e.g., fiber material in a liquid resin matrix). To form the stiffening structure of the hull, various core layers (e.g., wood, foam, metal, and other materials) may be applied with the layers of laminate material to build the thickness and add strength to the laminate layers. Upon curing of the various laminate layers, the insert is detached from the molding tool transom surface and the finished watercraft hull and insert are demolded from the tool, preferably together. The insert may then be removed from the hull to reveal the transom opening in the hull. 
     Because of the semi-rigid nature of the materials forming the insert body—more specifically, the semi-rigid perimeter of the insert body which contacts the laminate layers of the watercraft hull—the insert facilitates an effective seal between the molding tool surface and the insert to prevent gel coat or other coatings from damaging the watercraft hull as the insert is being removed from the transom opening in the hull. The taper of the insert sidewalls also makes for easy insertion and removal of the insert, so that the insert may be reused over and over to form an accurately dimensioned transom opening. Furthermore, the design of the present invention obviates the need to use a release agent, further simplifying the watercraft hull fabrication process. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  is an exploded view showing a finished watercraft hull having a transom opening formed by an insert mounted with a molding tool; 
         FIG. 2  is a perspective view of the insert of  FIG. 1 ; 
         FIG. 3  is a top plan view of the insert of  FIG. 1 ; 
         FIG. 4  is a bottom plan view of the insert of  FIG. 1 ; 
         FIG. 5  is a cross-sectional view of the insert of  FIG. 1  taken along line  5 — 5 ; and 
         FIG. 6  is a cross-sectional view of the insert of  FIG. 1  taken along line  6 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention improves upon previous methods of forming transom openings in watercraft hulls through which stern drive components are mounted. This invention employs a reusable insert design comprised of a semi-rigid body around which the hull can be fabricated. The semi-rigid nature of the body allows for ease of removal of the insert from the finished watercraft hull with the built up laminate layers of the hull surrounding the perimeter of the insert.  FIG. 1  shows the insert  10  mounted with molding tool  200  that forms the profile of a watercraft hull  100 . The insert  10  is configured to define the shape of the inboard/outboard propulsion system passageway, in this case, an opening  102  in a transom  104  of the watercraft hull  100 . As the laminate layers of the watercraft hull  100  are applied in successive steps onto a molding tool surface  202  of the tool  200 , the insert extends through the layers in the shape of the transom opening  102 . Upon curing of the laminate layers, the insert  10  is preferably detached from the molding tool  200 , and then the insert  10  and finished watercraft hull  100  are simultaneously demolded from the tool. Finally, the insert  10  is removed from the hull  100  to reveal the finished transom opening  102 . 
     As seen in detail in  FIGS. 2–6 , the insert  10 , or semi-rigid body, has a base or outboard surface  12 , an inboard surface  14  and a sidewall  16  formed in a perimeter region  17  of the insert and spanning between the surfaces  12 ,  14 . The sidewall  16  preferably has a slight taper in the direction moving from the outboard surface  12  to the inboard surface  14 , as best seen in  FIGS. 5–6 . This taper increases the ease in removing the insert  10  from the hull  100  to reveal the transom opening  102 . A perimeter lip  18  is also formed at the intersection of the outboard surface  12  and the sidewall  16  in the perimeter region  17  of the insert  10 . When the insert  10  is attached to the molding tool  200  for watercraft hull fabrication, the perimeter lip  18  is flush against the molding tool surface  202 . Thus, the combination of the perimeter lip  18  and the generally semi-rigid nature of the insert  10  facilitate the formation of a seal between the watercraft hull  100  and the insert. This seal impedes the flow of any coatings or laminates applied to the layers forming the watercraft hull  100  between the hull and the insert  10 , which could prevent the hull from being damaged upon removal from the transom opening in the hull. Additionally, the seal provides the edges of the laminate layers with a contour that minimizes the formation of air voids that can otherwise create weak points in the hull and encourage bonding between the insert  10  and the molding tool surface  202 . 
     The outlining shape of the insert defined by the sidewall  16  is dependent upon the desired shape of the transom opening  102  accommodating a stern drive component, as those of skill in the art will appreciate. The exemplary insert  10  shown in  FIGS. 1–4  has a particular shape that yields a transom opening  102  that is particularly well suited for watercraft in the category of recreational power boats and the like. In the configuration shown, the sidewall  16  has a first set  20  of opposed tapered sections and a second set  22  of opposed tapered sections. The first set  20  comprises generally flat, planar walls  24  having base edges  26  adjoining the perimeter lip  18  and parallel with one another and upper edges  28  adjoining the inboard surface  14  and likewise parallel with one another. The second set  22  comprises planar walls  30  that interconnect the planar walls  24  of the first set  20 . In a preferred arrangement facilitating optimal demolding of the insert  10  and watercraft hull  100 , and subsequent removal of the insert  10  from the hull  100 , the taper of the sidewalls  16  from the outboard surface  12  at the perimeter lip  18  to the inboard surface  14  allows for removal of the insert  10  in a direction from an inboard side  108  to an outboard side  100  of the hull  100 . 
     The insert  10  also has a number of voids, preferably through-holes  32 , such that a tool may be inserted therein to manipulate the position of the insert  10  with respect to the watercraft hull  100  and for mounting of the insert  10  with the molding tool surface  202 . The through-holes  32  extend from the outboard surface  12  to the inboard surface  14 . For example, a tool may have a protrusion that is inserted into one through-hole  32  and frictionally fits therewith, or if inserted on the inboard surface  12  side of the insert  10  clamps onto the outboard surface  14  of the insert. A centrally located cavity  34  is also formed in the insert outboard surface  12  to increase the flexibility of the semi-rigid body for insertion with and removal from the watercraft hull  100 . 
     In one embodiment, the insert  10  is provided with the desired properties for use in watercraft hull fabrication by being formed of a semi-rigid body made from a somewhat pliable composite such as a polyurethane, a polyurea, a polyurethane/polyurea compound, or another substance that exhibits similar physical properties, including having a degree of flexibility and being chemically inert to the materials used in lamination of the layers during watercraft hull fabrication such that bonding to these layers by the insert does not occur. The insert  10  should also have a hardness value of less than about 90 Shore D but greater than about 65 Shore A when using lamination materials and a transom opening shape common for recreational power boats. In this range, it has been found that the insert  10  has sufficient dimensional stability when lamination layers of the hull are being applied around the sidewall  16  of the insert  10  to generate a structurally sound finished transom opening  102 , but also has enough flexibility to be easily removed from within the opening  102  upon completion of watercraft hull  100  fabrication and to prevent unwanted movement of the gel coatings or other laminate coatings between the insert  10  and the molding tool  200 , or between the insert  10  and lateral side edges  106  of the laminate layers forming the hull  100 . If any heat curing is used during the lamination process of the hull layers, the insert  10  should also be configured to withstand this process without compromising the integrity thereof. 
     In another embodiment of the insert  10  semi-rigid body, a metal or other more rigid material (e.g., stiff composite) forms a central region  36  of the insert and the insert perimeter  17 , including the sidewalls  16  and the perimeter lip  18 , is formed of a less rigid material, such as a somewhat pliable composite like a polyurethane, a polyurea, or a polyurethane/polyurea compound or another substance that exhibits similar physical properties. This would aid in providing structural integrity to the insert  10  while ensuring that the sidewalls  16  and perimeter lip  18 , which contact the laminate layers of the watercraft hull  100 , remain flexible enough to facilitate the formation of a seal between the watercraft hull  100  and the insert  10 . 
     In use, the molding tool  200  is formed with the surface  202  having a shape that will dictate the shape of the outer layer of the watercraft hull  100 . A release agent is preferably first applied to the molding tool surface  202  to aid in the demolding of the insert  10  and watercraft hull  100  from the tool  200 . The insert  10  is then positioned relative to the tool  200  to align the transom opening  102  on the finished watercraft hull  100 . When the proper position is determined, the insert  10  is attached to the molding tool surface  202  at that location, and with the outboard surface  12  facing the transom of the tool  200  such that the perimeter lip  18  lies against the tool surface  202 . Prior to lamination steps, the molding tool surface  202  and the inboard surface  14  and sidewall  16  of the insert  10  are preferably coated with a liquid gel coat that, upon curing, forms a semi-rigid film that forms the outer or “painted” surface  112  of the watercraft hull  100 . This painted surface  112  is the mirror image of the shape of the molding tool surface  202  and is exposed upon demolding of the insert  100  and hull  100  from the molding tool  200 . Then, various layers of laminate materials are applied in successive steps on top of one another and over the semi-rigid film layer around the sidewall  16  of the insert  10 . The laminate materials typically include a fiber material in a liquid resin matrix that bonds to the semi-rigid film layer and forms a rigid layer upon curing that possesses the desired physical properties (e.g., strength, flexibility) for a watercraft hull. If the lamination process requires, additional actions (applying additional resins, coatings, or other materials, or heat curing) may be undertaken to ensure proper curing of the laminate layers. Additionally, various core layers, such as wood, foam, metals (e.g., aluminum) and the like, may be applied with the fiber and resin to build thickness and add strength to the laminate layers. Finally, upon curing, the insert  10  is detached from the molding tool  200  and the finished watercraft hull  100 —having the insert  10  fit into the transom opening  102  thereof—is demolded from the tool surface  202 . The insert  10  may then be removed towards the outboard direction of the hull  100  and away from the direction of taper thereof to reveal the finished hull having the transom opening  102  formed into the desired shape. 
     As can be seen, the insert  10  of the present invention for forming a transom opening in a watercraft hull provides a superior design to the aforementioned prior designs. The insert  10  can be formed in any number of shapes depending on the desired passageway geometry in a watercraft hull, and the durable and chemically inert nature of the design facilitates the repeated use of the insert in large run watercraft hull fabrication. Furthermore, since certain changes may be made in the above invention without departing from the scope hereof, it is intended that all matter contained in the above description or shown in the accompanying drawing be interpreted as illustrative and not in a limiting sense. It is also to be understood that the following claims are to cover certain generic and specific features described herein.