Watercraft fin plug assembly

The present disclosure describes a fin plug assembly for removably mounting a watercraft fin on a watercraft. In some embodiments the fin plug assembly includes a fin plug, a fin plug finishing insert and in some instances, a shelf-like support that is configured to house the fin plug assembly. Methods of making, methods of installing, and tools for installing the fin plug assembly in a watercraft are also described.

FIELD OF THE INVENTION

This invention relates to watercraft and in particular to assemblies for removably securing fins to the watercraft.

BACKGROUND TO THE INVENTION

A number of watercraft make use of fins that project from the water-facing surface of the craft. On planing craft, such as surfboards, the fins are typically foil-shaped to enhance the directional stability of the craft during high speed planing motion and to facilitate turning.

On watercraft such as surfboards the use of removable fins has become quite commonplace. These fins are removably and interchangeably fitted to the watercraft by means of fin mounting systems embedded in the water-facing surface of the craft, the fin mountings typically having a cavity that is configured to receive the base of the fin. Various securement mechanisms are used to secure the fin base in the mounting system cavity.

In conventional surfboard manufacturing terminology, the fin mounting systems are referred to as fin plugs.

One of the problems encountered with known fin plugs arises from the characteristics of surfboard construction. Surfboards are typically constructed from a relatively low-density foam core enveloped in a glass reinforced polyester resin skin laminated to the core. It will be appreciated that considerable torsional loads are imposed on the fin plug as a result of sideways thrust forces applied to the fin during use of the surfboard. In typical installations, the outer laminate of the surfboard is extended partially over the fin plug, but given the size limitations imposed by the locations where the fin plugs are installed on the surfboard, the laminate contact surface offered by the fin plug is generally insufficient to provide any real support to the fin plug in resisting the torsional loads imposed on the fin plug. The fin plug extends into the foam core of the surfboard and the fin plug is generally attached to the foam core by means of a suitable bonding agent, typically polyester resin which is conventionally used to laminate the surfboard. However, the low-density foam of the core generally does not have sufficient strength to resist the torsional fin plug loads without deformation or weakening of the surrounding foam over time, with consequential reduction in performance of the fin, cracking and shattering of the laminate in the vicinity of the fin plug and eventually delamination of the laminate from the core.

To overcome these problems, fin systems have been proposed that utilise a fin plug with a collar or flange extending about the open end of the fin-receiving cavity. The collar or flange upper surface is intended to stiffen the fin plug against side loads and to provide a bonding surface for the fibreglass laminate covering the fin plug. These fin plugs are typically of injection mouldable plastics, which generally does not bond well to the polyester resin most commonly used to laminate modern watercraft, unless the fin plug is treated, for instance by sanding, to provide some form of mechanical key and even this does little to improve bonding of the plastic to the resin. In addition, it will be appreciated that this introduces a secondary process that increases the cost and complexity of fin system installation.

It is an object of this invention to address these concerns.

The invention will be described with reference to surfboards as examples of watercraft, but it will be appreciated that the invention will find application in any watercraft that makes use of removable, replaceable fins that are mounted in a fin mounting assembly secured within a cavity formed in the water-facing surface of the craft.

Also, the fin mounting assembly is described and referred to as an assembly including a fin plug. In the majority of the examples described herein, the fin plug assembly is a typical surfboard fin plug assembly, but this is not intended to restrict the invention to surfboards and in this regard, the terms “fin plug” and “fin plug assembly” must be given a wider interpretation so as not to restrict the invention to surfboard fin plugs and fin plug assemblies or to the fin plug assembly illustrated in the drawings.

SUMMARY OF THE INVENTION

This invention provides a fin plug assembly for removably mounting a watercraft fin on the watercraft. The fin plug assembly comprises a fin plug, a fin plug finishing insert and, in certain embodiments of the invention, a foam shelf-like support that is configured to house the fin plug assembly. The invention also includes methods and tools for installing the fin plug assembly in a watercraft.

According to the invention, a fin plug assembly is provided for removably mounting a removable watercraft fin on a water-facing surface of a watercraft, the fin plug assembly comprising:a fin plug configured for mounting within a cavity formed in the water-facing surface of the watercraft and a finishing insert that is configured to co-operate with the fin plug;the fin plug comprising a body formed with a fin receiving housing configured to receive a mounting base of the watercraft fin and a collar that extends about the fin receiving housing, the collar extending outwardly from the fin receiving housing and including a surface relief formation; andthe finishing insert being shaped complementally to the fin receiving housing and the collar and configured to mate with the operationally water-facing surface of the fin plug, the finishing insert including an upper, operationally water-facing surface that is configured for co-operation with the water-facing surface of the watercraft and an operationally inwardly facing surface that is configured, by means of a surface relief formation shaped complementally to the surface relief formation of the fin plug collar, to co-operate with the collar when, in use, the fin plug is mounted within the cavity formed in the watercraft and the finishing insert is mounted on the fin plug.

The finishing insert is essentially a cover element that is installed into the cavity formed in the watercraft to cover the fin plug and the finishing insert is bonded to the fin plug and the watercraft. In this way, the finishing insert is configured for co-operation with the water-facing surface of the watercraft—the finishing insert is configured to close the cavity formed in the watercraft and to provide, after installation, a water-facing surface that is co-extensive with the water-facing surface of the watercraft.

The finishing insert may be a finished cover plate that, after installation and without much finishing-off work, closes the cavity and provides a finished, water-facing surface co-extensive with the water-facing surface of the watercraft.

Alternatively, the finishing insert may be unfinished and configured for installation into the cavity after which finishing-off work needs to be done to conform the installed finishing insert to the water-facing surface of the watercraft. This is a form of the invention that finds particular application with foam-cored watercraft such as surfboards and in this form of the invention the finishing insert is preferably made of a foam similar to the foam core, possibly with a higher density. This form of the finishing insert will typically be installed into the cavity after the fin plug has been installed but before the surface laminate is applied to the foam core, a process that will require the finishing insert to be conformed to the foam core shape using conventional foam shaping tools.

The relief formation or formations on the fin plug collar and finishing insert may be any device or design that modifies the complemental, co-operating surface areas of the collar and finishing insert to something other than a flat plane surface, including mating projections and depressions or any other mechanical key devices or formations.

In the preferred form of the invention, the fin plug relief formation is constituted by concave configuration of the collar, the collar extending about and outwardly from the fin receiving housing and terminating in an enlarged perimetral rim that defines a central depression extending between the rim and the fin receiving housing.

The perimetral rim gives the collar of the fin plug a shape that is concave in cross-section, which renders it substantially more resistant to torsional stress than the simple flat collars or flanges of conventional fin plugs.

The perimetral rim may be configured to extend operationally outwardly from the collar surface to define an operationally outwardly facing concavity. However, other configurations would work equally well, including an operationally inwardly facing rim or a rim that extends in both directions—inwardly and outwardly facing from either surface of the collar.

In this regard, the terms “out”, “outwardly”, “outwardly facing” and even “up” or “upwardly” refer to any orientation of a surface or thing that, like the water-facing surface of the watercraft, faces operationally outwardly towards the outside or the water (when the watercraft is in use). Conversely, the terms “in”, “inwardly”, “inwardly facing” and “down” or “downwardly” refer to the opposite, being any orientation of a surface or thing that faces inwardly into the cavity formed in the watercraft.

Besides the inherent strength of a concave collar shape, the raised perimetral rim constitutes a torsion band that extends about the perimeter of the fin plug. The torsion band serves to resist torsional deformation of the fin plug in use. The resistance to torsional stress and the general rigidity of the fin plug assembly is further enhanced by the fin plug finishing insert which, when bonded to the fin plug, provides further torsional resistance.

The collar, in the preferred form of the invention, is pierced by a plurality of apertures formed in the collar material, the collar material remaining between the apertures constituting interstitial webs.

Besides reducing the mass of the fin plug, which is in itself desirable, the interstitial webs and the apertures in the collar provide additional relief formations and mechanical key for subsequent bonding of the fin plug to the watercraft.

To provide even further surface relief, the surfaces of the interstitial webs may be grooved and in a preferred embodiment of this form of the invention, the web edges are rebated.

The finishing insert is preferably configured to mate with the concavity defined in the collar by the perimetral rim, the finishing insert being configured to be inserted and housed within the concavity in the collar.

In these embodiments of the invention, the finishing insert may be formed with surface protrusions shaped complementally to the apertures and webs formed in the fin plug collar.

Where the fin plug collar is pierced, the protrusions formed on the mating surface of the finishing insert may conveniently be configured to match the apertures in the fin plug collar exactly and to protrude into the apertures upon insertion of the finishing insert into the fin plug.

The fin plug assembly is preferably configured for use with a watercraft constructed of an inner core surfaced with a sheet material overlay laminated to the core by means of a bonding agent, the fin plug being configured for mounting under the surface laminate within a cavity pre-formed in the watercraft core, the finishing insert being configured for mounting between the surface laminate and the fin plug and the finishing insert and fin plug being configured for bonding with the bonding agent that is used to bond the surface laminate to the core.

For such watercraft, the finishing insert may conveniently be of a material more compatible with the laminate bonding agent than the material of the fin plug. An example of such a more compatible material is a foam material similar to the foam material of the watercraft core, which is substantially more compatible with the laminate bonding agent than the conventional plastics materials from which the fin plug is manufactured.

When the fin plug assembly is installed within the cavity in the watercraft and the finishing insert is bonded to the outwardly facing surface of the fin plug, the finishing insert becomes (or is finished off to become) co-extensive with the foam core. In the lamination process, the part of the fin plug assembly exposed to the laminate and bonding agent is the outwardly facing surface of the finishing insert. Being made of a more compatible material, the surface laminate will form a substantially stronger bond with the surface of the finishing insert than it will with the plastics material surface of a conventional fin plug.

In certain embodiments of the invention, the fin plug assembly may include an initially discrete, complementally shaped shelf-like support configured to house the fin plug assembly within the cavity pre-formed in the watercraft core, the cavity and shelf-like support being complementally shaped.

The shelf-like support may conveniently also be of a material more compatible with the laminate bonding agent than the material of the fin plug and as indicated above, the complemental shelf-like support may be made from a foam material similar to the foam material of the watercraft core and preferably from a high density foam material.

The invention includes a shelf-like support configured for use within the fin plug assembly of the invention, as described above, the shelf-like support being formed, internally, with a central aperture configured to accept the fin receiving housing and, externally, to fit snugly within a mounting cavity to be formed within the watercraft core when, in use, the shelf-like support is installed, the shelf-like support being dimensioned to form a shelf to support the fin plug collar at the appropriate level relatively to the surface of the watercraft core.

To accommodate and retain the fin plug securely, the shelf-like support might, depending on the complexity of the fin plug shape, require a central aperture with a relatively complex shape in order to complement the shape of the fin plug. In contrast, the external shape of the shelf-like support can be relatively simple to facilitate installation in the core of the watercraft, where a receiving cavity of relatively simple shape can be formed to accommodate the relatively simple external shape of the shelf-like support.

The invention also includes a fin plug finishing insert configured for use within the fin plug assembly of the invention, as described above.

The finishing insert, in embodiments of the invention, is preferably configured for use with a watercraft constructed of an inner core surfaced with a sheet material overlay laminated to the core by means of a bonding agent, the fin plug being configured for mounting under the surface laminate within a cavity pre-formed in the watercraft core, the finishing insert being configured for mounting between the surface laminate and the fin plug and the finishing insert and fin plug being configured for bonding with the bonding agent that is used to bond the surface laminate to the core, the finishing insert being made of a material similar to the watercraft core material.

The invention includes methods of preparing a watercraft for the installation, in the watercraft, of the fin plug assembly of the invention, as well as cavity forming templates for this purpose, the templates essentially being router jigs or templates.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The fin plug assembly300of the invention comprises a number of parts that together constitute a fin mounting device similar to so-called collared or flange-type fin plugs for removably mounting a removable watercraft fin (not shown) on a watercraft. The parts include a fin plug100and foam filler or finishing insert200that is configured to fit within the fin plug100. The entire assembly300is intended for installation, with or without a foam shelf-like support31,32in a complementally shaped cavity formed in the foam core of a watercraft, such as a surfboard (not shown in full in the drawings).

The fin plug100is integrally moulded from injection moulded plastics with a flange-like perimeter or collar1extending about a fin receiving housing or fin box extending about the open end of a fin box constituted by a fin slot8and fin box base7.

The load beam collar1has a rim or lip2extending about the perimeter of the load beam collar1. The raised perimetral rim2defines a central depression within the collar1extending between the perimetral rim2and the fin slot8. The rim2provides torsional stability to the load beam collar1.

The collar1is pierced to define a series of structural webs3pierced by truss apertures4, the webs3maintaining the structural integrity of the load beam collar1while the truss apertures4are intended to reduce weight and dissipate torsional loads from the fin box into the load beam collar1.

A dam plinth5extends about a raised slot dam6that defines the open end of the fin slot8and the wall of which extends downwardly into the fin box base7that completes the fin slot8. In use the base of the watercraft fin is accommodated within the fin slot8and fin box base7, which is dimensioned to allow forward and rearward adjustment of the fin. Grub screws9are used to secure and lock the fin base into the fin slot8.

The fin box base7(as can be seen fromFIGS. 2 and 6) is formed with a central narrowed section that defines a slot bridge10.

The fin plug assembly300includes a load beam finishing insert200that is configured to be inserted and to fit complementally within the load beam collar1, the finishing insert200being shaped complementally to the collar1and the depression formed by the perimetral rim2. The finishing insert200is formed with an internal opening that is configured partially to expose the dam plinth5and to fully expose the slot dam6, the fin slot8and the grub screws9. The outer perimeter13of the load beam finishing insert200is shaped to conform closely to the shape of the load beam collar1and the collar rim2. The inner perimeter14of the finishing insert200is shaped to confirm closely to the shape of the dam plinth5, which is dimensioned to extend above the finishing insert200when the finishing insert is installed in the collar1, the external surface of the finishing insert100being dimensioned to lie flush with the upper surface of the perimetral rim2after installation of the finishing insert200in the collar1. The under surface of the finishing insert200is formed with truss protrusions12that are shaped and configured to fit snugly within the truss apertures4in the load beam collar1.

During assembly of the fin plug assembly300, the load beam finishing insert200is fitted within the load beam collar1to yield the fin plug assembly300(as illustrated inFIGS. 5 and 6, in which the numeral16designates the load beam finishing insert200installed into the fin plug100and the numeral17designates the underside of the truss protrusions12of the load beam finishing insert200extending into the load beam truss apertures4).

The fin plug assembly300illustrated in the drawings is adapted for use with watercraft constructed of an inner core surfaced with a sheet material overlay laminated to the core by means of a suitable adhesive, such as surfboards, which typically are constructed with a low density foam core surfaced with a polyester resin impregnated fibreglass sheet material laminate. The resin is used as an adhesive that adheres the sheet material laminate to the foam core. The fin plug assembly300, like a conventional fin plug, is adapted for mounting under the surface laminate with the fin plug100mounted within a pre-formed cavity in the foam. The laminating resin is used as an adhesive to adhere to the fin plug assembly300in the cavity in the foam core and to the overlying laminate.

Fin plugs, like the fin plug100of the invention, are typically made from injection moulded plastics, which does not bond exceptionally well to polyester resin. The finishing insert200of the invention, on the other hand, can be made of a material that is substantially more compatible with the laminate adhesive (in this case polyester resin). To this end, the finishing insert200may be made from a foam material similar to the foam material of the surfboard core, which is substantially more compatible with polyester resin than the plastics material of the fin plug100. When the fin plug assembly300, with the finishing insert200bonded to the fin plug100, is installed in the watercraft, the surface laminate will form a substantially stronger bond with the more compatible surface of the finishing insert200than it will with the plastics material surface of the fin plug100. With proper design, it is possible to ensure that very little of the fin plug100(preferably the upper surface of the perimetral rim or less) is exposed to the resin.

The fin plug assembly300of the invention addresses both the bonding and strength concerns outlined above with the use of the fin plug100and the complemental, light weight finishing insert200. The perimetral rim2of the collar1, in effect, converts the conventionally flat flange or collar of a typical fin plug into a non-planar load beam. The use of a non-planar structure provides strength without requiring the same mass as a conventional fin plug flange. In the fin plug100of the invention, the mass of the fin plug100is further reduced by the formation of truss apertures4in the collar to define webs3that transfer load to the perimetral rim2, thereby reducing mass without sacrificing rigidity or strength.

The use of a separate load beam finishing insert200provides the opportunity for improving the mechanical strength of the fin plug assembly300by virtue of the fact that a wide choice of finishing insert materials is available. The finishing insert200will most preferably be moulded from polyurethane foam, which will make it compatible with all resin system and the core foam used most commonly in the construction of watercraft such as surf boards. The finishing insert200fills the entire interior of the load beam collar1and extends from the rim2of the load beam collar1to the dam plinth5at the centre of the load beam collar1.

The use of the finishing insert200also permits the use of materials other than foam, either for decorative or structural purposes. For instance the finishing insert200could be of wood such as balsa wood or of other types of foam such as expanded polystyrene. With the use of an overlay laminated to the upper surface of the finishing insert200, the mechanical bonding capacity and structural strength of the finishing insert200can also be improved. Examples of such overlays include carbon fibre, fibreglass wood veneers or the like. The material of the finishing insert will nevertheless at all times be selected for superior bonding capabilities to the resins and laminates used in the construction of the watercraft.

In the preferred form of the invention, the finishing insert200is preferably bonded into the load beam collar1at the factory. It will be appreciated, however, that the use of a separate finishing insert200provides an opportunity for the finishing insert200to be provided separately to a customer, thereby allowing the customer to personalize the watercraft with the use of an finishing insert or overlaid finishing insert different from the standard finishing insert

The finishing insert200also maximizes bonding capacity by providing a large upper surface area. This combines with a substantial bonding surface on the undersurface of the finishing insert, constituted by the truss protrusions12extending through the load beam truss apertures4once the finishing insert200is installed in the load beam collar1. This provides better mechanical key and bonding to the watercraft foam core on the underside of the fin plug assembly300.

The structural integrity of the load beam collar1is improved by the use of the slot bridge10that serves, essentially, to tie the side walls of the fin box base7together, thereby reducing torsional flexibility of the fin box base7and assisting in the dissipation of side loads.

A fin (not shown) placed into the fin slot8is held in place by two grub screws placed either to one side of the slot8(as illustrated in the drawings) or one on either side of the slot8(as would be the case for a centre fin). The grub screws9pass through the fin plug100at an angle to exert both lateral and downward forces on the fin base, firmly locking the fin in the fin box base7. The fin slot8is dimensioned to be slightly longer than the fin base, thereby allowing for forward and backward adjustment of the fin.

FIGS. 7 to 9illustrate a routing system consisting of a series of routing jigs by means of which the watercraft shaper may use a conventional router to form appropriately shaped cavities within the watercraft foam to accommodate the fin plug assembly300.

If the fin plug assembly300is to be installed directly into the foam core of a watercraft, a two-step routing process is followed that produces a stepped cavity in the foam core of the watercraft to accommodate the fin plug assembly300. The cavity includes a central bottom cavity27that is dimensioned to accommodate the fin box base7. A shelf cavity28is then formed about the perimeter of the bottom cavity27, the shelf cavity28being dimensioned to accommodate and support the load beam collar1of the fin plug100.

To produce the cavity ofFIG. 10, a base jig25(FIG. 9) is positioned on the watercraft foam core29. Once positioned, the base jig25is not moved until after routing has been completed.

A bottom jig (FIG. 8) is then located within the inner perimeter21of the base jig25and the inner perimeter21of the bottom jig24is used to guide the router to produce the bottom cavity27in the watercraft foam29. This is the deepest of the cavities to be routed. The bottom jig24is then removed and the top jig18is placed on the base jig25. This serves to raise the router support surface to correct height and no depth adjustment of the router bit is required to rout the shelf cavity28. The inner perimeter21of the top jig18is then used to guide the router bit to rout the shelf cavity28. The top jig18is provided with a set of end locators26that lock on to the ends of the base jig25to secure the top jig18securely on the base jig25.

All the jigs have shaper's marks on them to help the shaper locate and position the jigs correctly, including a shaper's mark window19, centerline markings20, vertical centerlines22and a cross hatch23. The primary location of the jigs18,24,25is provided by the base jig25and the shaper's marks referred to above are primarily used to ensure that nothing has moved during the routing process.

FIG. 11illustrates a second installation method that makes use of a single cavity30in the watercraft foam core29as opposed to the multi-cavity illustrated inFIG. 10. This method uses the base jig25to rout a single cavity30(FIG. 11). A separate foam SHELF-LIKE SUPPORT31, preferably of high density foam, is located within the routed single cavity30and the bottom jig24, placed within the base jig25, is then used to rout a cavity similar to the bottom cavity27in the foam shelf-like support31. The perimeter of the foam shelf-like support31is pre-cut to the correct shape of the routed single cavity30and the thickness thereof is dimensioned automatically to form a shelf-like supporting shelf, similar to the shelf cavity28of the multi-cavity illustrated inFIG. 10thereby to provide a supporting shelf for the fin plug assembly300.

TheFIG. 11installation method provides a simplified process with fewer steps compared to theFIG. 10method. It also has the advantage of providing an opportunity to use a high density foam for the foam shelf-like support31for installations where the foam core29of the watercraft is of insufficient strength to provide adequate support for the fin plug assembly300.

FIG. 11illustrates the initial routed single cavity30before insertion of the foam shelf-like support31, which is illustrated before formation of a bottom cavity therein.

FIGS. 12 and 13illustrate yet a further foam shelf-like support or foam shelf-like support32that is intended to take the place of the foam shelf-like support31illustrated inFIG. 11.

In this embodiment of the invention, the foam shelf-like support32is pre-moulded, preferably in a high density foam, the shelf-like support32being shaped complementally to the underside of the fin plug assembly300and to receive and shelf-like support the fin plug assembly300. In particular, the shelf-like support32is shaped to conform to the fin box base7and slot bridge10.

To install the foam shelf-like support32, a single cavity similar to the single cavity32ofFIG. 11is routed in the watercraft foam core and the foam shelf-like support32is installed in the single cavity30instead of the foam shelf-like support31, with no need for additional routing.

In all the installation instances described above, the appropriate cavity is routed into the foam core29of the watercraft. The routed cavity is then filled with resin.

Using the first installation method (FIG. 10) the assembled fin plug assembly300is installed directly into the cavity, with the fin box base7being housed within the bottom cavity27and the load beam collar1of the fin plug100supported on the shelf cavity28.

Using the second method illustrated with reference toFIG. 11, the single cavity30is filled with resin and the foam shelf-like support31(with the bottom cavity routed therein) is then pressed into the cavity30. The support shelf and bottom cavity previously formed in the foam shelf-like support31are then filled with resin and the fin plug assembly300is pressed into the foam support cavities until the fin box base7is fully installed within the bottom cavity and the flange of the load beam housing is properly supported on the shelf cavity defined by the upper surface of the foam shelf-like support31.

Using the pre-moulded foam shelf-like support32, a similar installation method is followed. The cavity30is filled with resin, the foam shelf-like support32is pressed into the cavity30such that the upper surface of the foam shelf-like support32provides a shelf cavity similar to the shelf cavity28illustrated inFIG. 10. If necessary, additional resin is poured into the cavity and the fin plug assembly300is pressed into the foam shelf-like support32. In similar fashion to that described above, the fin box base7is pressed into the foam support cavity33to the extent that the shaped underside of the base7fully engages with the complemental shapes in the foam support cavity33and the underside of the collar1of the fin plug100is fully engaged with the shelf cavity defined by the upper surface of the foam shelf-like support32.

Fibreglass lamination can now proceed over the top of the assembled, installed fin plug assembly300.

The load beam collar1of this invention provides a torsionally stiff load beam that stiffens the entire structure against the torsional loads imposed by surfboard fins in use. This is a similar role to that performed by the flanges of existing flange-type fin plugs. Unlike conventional fin plugs, however, the fin plug assembly300of the invention includes a load beam collar1that enhances the torsional stability of the fin plug assembly300without adding significantly to the mass of the fin plug assembly300. Due to the fact that the rim2extends upwardly about the perimeter of the load beam collar1, any twisting (torsional stress) of the flange part of the load beam collar1will serve to place the rim2under tension, which the rim will resist, thereby increasing the torsional stability of the load beam collar1.

The finishing insert200co-operates structurally with the load beam collar1when the finishing insert is bonded into the fin plug100. For this reason there is no need for the fin plug assembly300to be as heavily constructed as would typically be the case with flange-type fin plugs, thereby allowing reduced mass and lightweight construction. The collar truss apertures4serve further to reduce the mass of the structure whilst at the same time providing a locating device for the load beam finishing insert truss protrusions12, thereby enhancing structural co-operation between the finishing insert200and the load beam collar1whilst at the same time, providing better mechanical key for resin bonding to the undersurface of the fin plug assembly300.

The load beam finishing insert200serves two primary purposes within the fin plug assembly300—improved mechanical bonding and structural strength.

The primary role of the finishing insert200is to fill out the “cup” created by the collar rim2, thereby providing a large surface for mechanical bonding for the overlying laminate of the watercraft. As a result, the primary bonding surface presented to the overlying laminate is one that is better able to provide a strong mechanical bond as opposed to that presented by conventional injection moulded plastics fin plugs. In this way, the finishing insert200provides a large, flat expanse of superior mechanical bonding surface, with very little plastic (only the upper surface of the rim2) exposed to the overlying laminate, thereby vastly improving mechanical bonding.

In addition, (the truss protrusions12) on the underside of the finishing insert200protrude through the load beam1through the load beam truss apertures4, thereby improving the overall mechanical bonding surface presented to the watercraft foam core29.

Cosmetically, the use of the finishing insert reduces the amount of exposed plastic (which is normally visible through the overlying laminate) which allows the fin plug assembly300to blend more fully into the bottom of the watercraft. As described above, the finishing insert can, in addition, be used as a decorative feature. Most commonly, a polyurethane foam would be used to create the finishing insert200, but there are other materials that could be utilised for different applications. For example, in a wood surfboard, the finishing insert could be of matching wood.

The finishing insert200illustrated in the drawings is of substantially the same perimetral shape as the load beam collar1, with the inner boundary of the upper surface of the finishing insert200being constituted by the dam plinth5and the outer boundary of the finishing insert200being constituted by the upper edge of the collar rim2. This is not a necessary requirement however, since the finishing insert200and the rim2could be dimensioned for the rim2not to extend through the upper surface of the finishing insert, the edges of which could possibly extend beyond the perimeter of the load beam collar1. This might require additional routing in the foam core29of the watercraft. Once this is done, however, the designers' ingenuity is the only limitation to the decorative possibilities presented by the finishing insert200, with materials such as wood, carbon fibre and decorative decals being but some examples.

In order for the slot dam6to “float” above the upper surface of the load beam finishing insert200, it is formed within a raised plinth5that elevates and supports the dam6. In co-operation with the collar rim2, the dam plinth5serves, effectively, as an I-beam.

All lamination systems in which the laminate extends over the top of the system make use of a raised dam that will eventually be sanded down to expose the fin slot8and grub screws9. The dam typically has a 45° slope around the entire outer perimeter to ensure that the laminate lays down flat over the collar1.

The fin slot8and grub screws9are conventional, but the slot bridge10is not. The lateral forces generated by a watercraft fin in use tend to force the fin slot8and the fin box base7to spread open. The primary role of the collar1is to minimize opening or spreading of the fin slot8under such torsional stresses. This function is enhanced by the slot bridge10which serves to tie the two sides of the fin slot8and the fin box base7together in the centre of the fin box base7. The bridge10is not extended to the top of the fin box base7and slot8, thereby allowing the use of a full length fin base which allows the fin loads to be spread over the greatest slot area.

Like the finishing insert which need not be limited to the shape illustrated in the drawings, the single cavity foam shelf-like support31and foam shelf-like support32illustrated inFIGS. 11, 12 and 13need not necessarily follow the exact perimetral shape of the fin plug assembly300and collar1in particular.

Depending on the application, it might be appropriate to install a foam shelf-like support that is larger and possibly differently shaped to the perimetral outline of the collar1. Examples of such foam shelf-like supports35,34are illustrated inFIGS. 14 and 15.

The foam shelf-like support34requires a cavity to be formed in the watercraft foam core29using the base jig25to rout no more than a single cavity, similar to the cavity30ofFIG. 11. Like the foam shelf-like support32, the shelf-like support34is pre-moulded, preferably in a high density foam, the shelf-like support34being shaped complementally to the underside of the fin plug assembly300and to receive and shelf-like support the fin plug assembly300. The shelf-like support34is also shaped to conform to the fin box base7and slot bridge10.

To install the foam shelf-like support34, a single cavity similar to the single cavity30ofFIG. 11is routed in the watercraft foam core29and the foam shelf-like support34is installed in the single cavity30with no need for additional routing. The foam shelf-like support34is located and installed within the routed single cavity30using resin as described above.

The shelf-like support34is pre-formed with a supporting shelf similar to the shelf cavity28of the multi-cavity illustrated inFIG. 10thereby to provide a supporting shelf for the fin plug assembly300.

The perimeter of the foam shelf-like support34is larger and dimensioned to extend beyond the perimetral outline of the rim2extending about the perimeter of the load beam collar1, with the perimeter of the foam shelf-like support34defining a foam collar extending about the fin plug assembly300, once installed in the shelf-like support34.

To accommodate the fin plug assembly300, the cavity in the foam finishing insert34is pre-formed and configured for the fin plug assembly300to fit snugly within the cavity, with the underside of the fin box base7housed within the bottom cavity formed in the shelf-like support34and the underside of the load beam collar1of the fin plug100supported on the shelf pre-formed in the shelf-like support34.

When fully installed in the foam shelf-like support34, the upper, external surface of the foam shelf-like support34is dimensioned to be flush with the upper surface of the perimetral rim2and the finishing insert200installed therein.

The foam shelf-like support35ofFIG. 14is similar in appearance and use to the foam shelf-like support29ofFIG. 11.

Like the foam shelf-like support34, the shelf-like support35requires a cavity to be formed in the watercraft foam core29using the base jig25to rout no more than a single cavity, similar to the cavity30ofFIG. 11.

The shelf-like support35is pre-moulded, preferably in a high density foam, the shelf-like support35being shaped complementally to the underside of the fin plug assembly300and to receive and support the fin plug assembly300. The bottom cavity in the shelf-like support35is simple and not shaped to conform to the fin box base7and slot bridge10.

The foam shelf-like support35is installed similarly to the shelf-like supports described above.

Like the shelf-like support34, the perimeter of the foam shelf-like support35is larger and dimensioned to extend beyond the perimetral outline of the rim2extending about the perimeter of the load beam collar1, with the perimeter of the foam shelf-like support35defining a foam collar extending about the fin plug assembly300, once installed in the shelf-like support35.

In both cases (34,FIG. 15;35,FIG. 14) the foam shelf-like supports have a depression or cavity formed in the upper surface that will accept and locate the entire fin plug assembly300(fin plug100and finishing insert200) in the depression or cavity formed in the upper surface of the foam shelf-like support34,35.

The fin plug100is located within this depression with the fin plug finishing insert200flush with the upper surface of the foam shelf-like support34,35, which is dimensioned to extend, like a foam collar, beyond the fin plug perimeter or collar1.