WO 2004/024242 PCT/AU2003/001191 IMPROVEMENTS 1N SWIM FINS AND METHOD OF MANUFACTURE THEREOF 5 BACKGROUND The present invention relates to improvements in swim fins and flippers and more particularly relates to a swim tin and method of manufacture thereof 10 which includes fin geometry resulting in a more mechanically efficient, economic, flexible, soft, light weight and comfortable fin in comparison to the known fins. The improvements in such fins enable enhanced maneuverability for the swimmer to whose foot or feet the swim fm or fins are attached. The present invention also provides an improved method of fin construction in 15 which layer hardness distribution throughout the fin i more efficient in that there is increased user comfort, improved geometry and more efficient aqua dynamics. PRIOR ART 20 Swimmers such as surfers and body board users commonly attach swim fins to their feet to gain greater maneuverability. This is achieved by kicking which causes the fins to flex and push against the water with greater force than is possible using the feet alone. 25 There are in existence a wide variety of fm designs each having a particular aqua dynamic effect dictated by their flexibility, weight, shape and configuration. Fin flexibility is a function of the particular construction of the fin and the stiffness of the material used. The shape and contour of a swim fin is largely dictated by its function, Thus, 30 long fins are used in such activities as scuba diving and short fins are used in such activities as surfing where less purchase in the water ( or water displacement) is required. The longer the fin, the greater the load on the foot of the wearer but greater the water displacemenut. The shorter the fin the lower the load on the foot of the wearer and lower the displacement. In fin design WO 2004/024242 PCT/AU2003/001191 the objective is to provide a comfortable fin which reduces wearer effort without compromise to efficiency. Efficiency is related to wearer effort versus mechanical advantage. An efficient in propels the wearer with maximum thrust but with a minimum of effort. The differences between fin designs can 5 be subtle but a subtle change in design can result in a more or less efficient fin. Another design criterion is foot comfort. This is predominately a function of material softness disposed in the right places so the foot interacts favorably with the rubber of the fin. Ideally, soft compound rubber will be located in 10 areas of the fin which engage the foot and hard compound rubber will be in those areas which require sufficient stiffness to resist excessive flexure during water displacement. Thus, tin design is a compromise between adequate stiffness for propulsion and sufficient softness for wearer comfort. 15 As an example, a known fln is disclosed in United States Patent 6,354,894 which teaches a spear bladed swim fin which enables divers to propel themselves through the water. Spear-bladed swim fins generally provide a lower surface area to a higher perimeter edge length. By reducing the effective. surface area of the swim fin, more propulsive force is delivered by the fin for 20 each kick of the diver. Such dispersioc of the diver's energy may be particularly advantageous where stationery swimming is required. Additionally, vortices generated during swim kicks may advantageously complement the operation of the swim fin. The spear blade has a large channel through which water can flow to eliminate dead spots on the lee side of the fin. 25 Fork extension stubs present with the foot pocket of the swim fin provide an adjustable means by which the flexing, bowing, and/or geometry of the swim fin blade may be adjusted according to the preferences and/or demands of the diver. Another known fin is disclosed in United States Patent 5,533,918 which 30 teaches a swim fin unit for use on the foot of a swimmer, comprising a body 2 WO 2004/024242 PCT/AU2003/001191 defining a foot receptacle that opens endwise forwardly; a first Bu structure integral with and extending generally rerwardly of the body to be flexed upwardly and downwardly rearwardly of the body by water pressure; and a second fin structure integral with and extending generally vertically rearwardly 5 relative to the body; wherein the said first flu structure defines a first plane and the second ft structure defines a second pTane; the first and second planes intersecting in generally perpendicular relation. With the advancement of scuba diving and snorkeling, swim fins have likewise developed in order to propel the swimmer through the water more efficiently. 10 As with the swimming fins of fish, swim fins for human beings have certain dynamic characteristics, depending upon fin architecture, that provide for different types of propulsion through the water. 'Most swim fins, particularly those often used in conjunction with body surfing 15 and body board surfing, scuba and skin diving, are bladed fins having edges extending outwardly from a foot pocket. Webbing is present in the form of elastic or plastic webbing that forms a blade by which the diver propels him or herself. Such swim fins often resemble the rounded or truncate caudal fins present on fish. Consequently, such swim fins provide strength, but generally 20 not speed. As a result, skin and scuba divers swimming around reefs and trying to cover longer distances in calm waters must generally work harder in order to propel themselves faster. Additionally, such bladed swim fins are not adjustable and the lateral edges and the blade webbing does generally not provide any adjustment with respect to the foot pocket. 25 In addition to the shape and configuration, the materials and methods of construction determine whether the fin will be efficient in use and comfortable for the wearer. Fins are typically manufactured from layers of different compound rubbers. A soft compound is normally used for the foot housing to facilitate convenient and comfortable insertion of the foot therein and also to 30 prevent abrasion from hard edges. A hard compound is used for the free 3 WO 2004/024242 PCT/AU2003/001191 trailing end blade as this requires a minimum stiffness to displace water without unwanted excessive flexure or bending. The known fins and particularly surfing fins have undergone many changes in geometry over the years each attempting to achieve maximum efficiency 5 (propulsion) for minimumuser effort, There is always room for improvement in fin design and method of construction to achieve more improvements in geometry, comfort and user efficiency, 10 INVENTION The present invention provides an improved fln which results in a more economic, flexible, sof, light weight and comfortable fin. It is an object of the invention to provide a method of construction of a tn ad 15 a fin produced by that method of construction. It is an object of the invention to provide an improved fn which meets the needs for significantly enhanced maneuverability realized when used by a surfer, swimmer or surf or body board user. It is another object of the invention to provide a more comfortable fin having improved flexibility and without 20 compromise to the economics of manufacture or to aqua dynamic efficiency. According to a method aspect the present invention provides an improved method of construction of a fin in which layers of rubber are preset prior to compression moulding. According to a preferred embodiment, prescribed rubber layers which will form a bottom of a fin are set along with layers for a 25 heel strap region. A foot mould is introduced between those layers and upper layers which will form an upper surface of the fin including the foot pouch. In one broad form the present invention comprises 30 a laminated swim fin formed using two or more rubberized layers each having different hardness; the fin comprising; a) a foot body defining a foot receptacle, that includes an opening to receive the foot of a wearer; 4 WO 2004/024242 PCT/AU2003/001191 b) a first region integral with and extending generally rearwardly of the .body to be flexed upwardly and downwardly and rearwardly of the body, by action of water when the fin is in use; 5 c) the fin including an outer layer of medium hardness rubberized material; d) an inner layer of soft compound rubber forming the foot receptacle; 10 e) a layer of hard rnbbberized material; wherein, the layer of hard material is disposed laterally of the foot receptacle. In another broad form the present invention comprises: 15 a swim fin for use on the foot of aswimner, the fin comprising; a foot body defining a foot receptacle, that includes an opening to receive a foot of a wearer; a fin body integral with and extending from the body of the foot receptacle and which is capable of being flexed upwardly and downwardly during use and 20 responsive to water pressure wherein, the foot receptacle comprises a soft compound rubber and the fin body includes a medium compound rubber; the fin body further comprising lateral hard rubber regions. between the medium and soft compounds wherein the hard rubber regions and medium rubber layer combine to form contoured splay rails which contribute to water 25 displacemetit and propulsion of the user. According to the preferred embodiment the splay rails are symmetrical about a longitudinal axis through the fin. 30 In its broadest for the present invention comprises; a swim fin including a leading end and a trailing end, the leading end including a recess for receiving a foot of a wearer and the trailing end being a free end which displaces water each sweeps through the water; 5 WO 2004/024242 PCT/AU2003/001191 the fin including a laminated construction comprising a first layer of medium hardness rubberized material; a second layer of hard rubberized material and a third layer of soft rubberized material; wherein the -first and second layers envelope said third layer of soft material. in a broadest form of a method aspect the present invention comprises; a method of construction of a swim fin, the method comprising the steps of; providing a first layer of medium compound rubberized material; 10 b)placing a pocket mould in apposition to the first layer to allow formation of a foot pocket in the fin; c)applying a layer soft compound rubber about said foot pocket; d)applying a hard compound rubber between said medium compound rubber and said soft compound rubber; 15 e)forming an envelope with said medium compound rubber to retain said foot pocket and said hard compound rubber; f) bonding said soft, medium and bard layers by beat fusion. According to one embodiment of the method aspect, the bonding of layers may 20 be by a combination of heat fusion and compression. In another broad form of a method aspect the present invention comprises: a method of construction of a swim fin using a compression mould, the method comprising the steps of, a) providing at least one layer of rubberized material having a first 25 degree of hardness; b) providing at least one layer of rubberized material having a second degree of hardness and being a harder material that the first degree of hardness layer; c) taking a mould capable of forming a foot cavity int said fm and 30 placing the mould over at least the said at least one layer of rubberized material having a first degree of hardness; 6.
WO 2004/024242 PCT/AU2003/001191 d) laying over the foot mould two rubberized layers of either the same or different hardness, e) compression moulding all said layers about said foot mould such that at least layers adjacent said mould conform to the shape of said 5 mould and form a foot pocket; f) separating mould parts of said compression mould; g) removing said foot mould from a foot pocket in a so formed fin, 10 The method may comprise the further preliminary step of millitig the rubber layers to a predetermined thickness. A preferred ( but non limiting ) layer thickness would be in the region of 10 - 15mm. The layers can be milled to as low as 3m thick by running the layers through a rolling machine. Also, each layer may be of varying thicknesses 15 The fin formed by the process according to the invention has a stiff inner hard layer, a medium outer layer of reduced stiffness and a foot pocket of soft rubber. 20 According to a preferred embodiment the fin comprises a first medium layer of a first colour, a second layer of a soft rubber layer having a second colour and a hard layer of a third colour. Preferably the colours of said layers provide an indication of the hardness or stiffness of the layers which comprise the fins. 25 The method comprises the further step, before laying out said layer of medium compound rubber, of guillotining the layer to a shape according to the geometry of the fin required. 30 7 WO 2004/024242 PCT/AU2003/001191 DETAILED DESCRIPTION 5 The present invention will tow be described according to a preferred but non liiniting embodiment and with reference to the accompanying illustrations, wherein Figure 1 shows a plan view of a typical known fin construcfed in accordance 10 with prior art methodology; Figure 2 shows a cross sectional view of a fin constructed in accordance with the prior art. 1s Figure 3 shows a plan view of a fin constructed in accordance with a preferred embodiment of the invention; and Figure 4 shows s side elevation view of the fin of figure 3 . 20 Figure 5 shows a cross section across a line A-A as shown in figure 3 according to one embodiment Figure 6 shows a cross section across a line A-A as shown in figure 3 25 according to an alternative embodiment. Figure 7 shows a cross section across a line B-B as shown in figure 3 according to one embodiment. 30 Figure 8 shows a schematic arrangement of an assembly for constructing a fin in accordance with the present invention. Referring to figure 1 there is shown a plan view of a typical known fin I 35 constructed in accordance with prior art methodology. Typically a fin of the type of fig I is divided into key regions which relate to functionality of the fin. Accordingly;fin I comprises a foot pocket 2 disposed in a central region of the fin. Fin 1 also includes a retaining strap 3 which defines an opening 4 through which a users foot is inserted . Retaining strap 3 engages a users heel to retain 40 the foot in foot pocket 2. Fin 1 further comprises a distal or trailing end 5 which forms the major area of the overall fin. Trailing or distal end 5 is 8 WO 2004/024242 PCT/AU2003/001191 splayed outwards such that it is widest at edge 6. The broad width at trailing end 5 enable the fin to displace a substantial amount of water wben used by a swimmer. Figure 2 shows a cross sectional view of fbi I of figure 1 taken across a line 5 A-A constructed In accordance with the prior art. As may be seen from figure 2, fin I comprises a first hard rubber compound layer 7 which is heat fused with a second softer rubberized material 8 which forms a inoulded foot pocket 9 which receives and retains a foot of a wearer. This prior art tin is manufactured by fusing the bard layer 7 with the soft layer .1 The result is a 10 ^generally hard fin base and a soft upper wali 8 of foot pocket 9 which is flexible enough to enable a wearer to insert the foot and provide foot comfort during use. Typically the known fins include a leading ( proximal) end and a trailing end. Intermediate the leading ( proximal) end terminating in strap 3 is a foot pocket 2 for receiving and retaining a foot.of a wearer; wherein the 15 trailing end has a relatively stiff free end which displaces water each sweep of fin 1 through water. Figure 3 shows a plan view of a fin 10 constructed in accordance with a preferred embodiment of the invention. Typically a fin of the type of fig 3, as with fin 1 described with reference to figure 1 is divided into three key regions 20 which relate to functionality of the fin. Accordingly, fin 10 comprises a foot pocket 12 disposed iti a central region of the fin. Fin 10 also includes a retaining strap 13 which defines an opening 14 through which a users foot is inserted , Retaining strap 13 engages a users heel to retain the foot in foot pocket 12. Fin 10 further comprises a distal or trailing end region 15 which 25 forms the major area of the overall fin. Trailing or distal end 15 is splayed outwards such that it is widest across edge 16. The broad width at trailing end 15 enables the fin to displace a substantial aniount of water when used by a swimmer. Figure 4 shows a side elevation of the fin of figure 3 with corresponding numbering, 30 Figure 5 shows a cross section taken along a line A-A through tin 10 according to one embodiment and manufactured in accordance with the 9 WO 2004/024242 PCT/AU2003/001191 method aspect of the invention. As shown in figure 5, fin 10 comprises a first medium hardness layer 17 of rubberized material which is heat fused with a second inner layer 18 of softer rubberized material -which forms a moulded foot pocket 19 which receives and retains a foot of a wearer. Fin 10 further 5 comprises a hard compound rubber 20 which is retained between layers 17 and 18. The result is a generally medium hardness outer layer, a soft inner layer l8 for foot comfort and lateral hard regions which reinforce generally stiff but flexible splay rails.19 and 2l. 10 According to one embodiment, the invention provides a swim fin including a leading end and a trailing end, the leading end including recess for receiving a foot of a wearer and the trailing end being a free end which displaces water eacb sweep through the water. Fin 10 is a laminated construction in which soft layer 18 is in apposition with and enveloped by outer layer 17 and hard 15 layer 20. The method of construction of fin 10 according to one embodiment, generally comprises the following steps. A first layer 17 of medium compound rubberized material is provided which is laid out on a platform after it is cut to the required configuration. Next a pocket mould ( not shown ) is placed in apposition to first layer 17 to allow 20 formation thereabout of a foot pocket in the fin formed by soft layer 18. Soft compound rubber layer 18 is disposed about the foot mould ( not shown) to form the foot pocket 19. Hard compound rubber layer 20 is disposed between soft compound rubber 18 and medium compound rubber layer 17 so that the hard compound rubber layer 20 has a boundary with the 2$ soft inner layer 12 and outer medium rubber compound layer 17. The medium layer 17 may be wrapped over the inner soft layer 18 and hard layer 20. Each of layers 17, .18 and 20 are preferably bonded by heat fusion and compression moulding techniques. In a preferred embodiment, the fin 10 includes splay rails 21 and 22 formed on each side, the rails comprising respectively upper 30 edges 23 and 24 and respective recesses 25 and 26, .10 WO 2004/024242 PCT/AU2003/001191 The layers of the fin will typically be specified according to a flow index of the tubberized material layers, The method comprises the further step, before laying out said layer of medium compound rubber, of guillotining the layers so they are cut to size before compression moulding. A process for construction 5 of the fin will be described below with reference to figure 8. The fiu 10 formed by the process according to the embodiment described with reference to figure 5 above has a stiff hard layer, a medium outer layer of reduced stiffness and an inner foot pocket of soft rubber. 10 According to a preferred embodiment the fm comprises a first medium layer of a first colour, a second layer of a soft rubber Iayer having a second colour and a hard layer of a third colour. Preferably the colours of said layers provide an indication of the hardness.or stiffness of the layers whieb comprise the fins. The flu may be constructed of laminated layers of the same color but 15 it has been found convenient to employ layers of different colours to represent layers of different hardness and also to enhance the visual effect of the finish as layers of different colors undergo migration during compression moulding. The foot recess 19 migrates from a wide region tapering to a narrower region 20 at its opposite end wherein the splay rails 23 and 24 are disposed so as to increase the efficiency of travel of the irm through water and the mechanical advantage to the user. The upper edge of the fim is that which is nearest the users ankle and the lower edge is that which is nearest the soles of the users feet. The upper edge extends laterally beyond the lower edge so that contoured 25 recesses 25 and 26 on opposite sides is formed when viewed in cross section. Fin 10 further comprises and inner rails 27 and 28. The rails 21 and 22 and corresponding recesses 25 and 26 contribute to thrust provided by the fin and increase mechanical advantage. 30 The upper edge rails 21 and 22 are to some extent flexible as a medium compound rubber is used to form the edges. The lower (inner edge rails 27 and 11 WO 2004/024242 PCT/AU2003/001191 28 may flex to some extent laterally as the upper edge flexes substantially vertically. The cup like recess 25 and 26 formed by. the upper and lower edges cause side thrust in conjunction with lateral displacement of water as the fin is maneuvered in an up and down sweep through the water. Due to the unique 5 edge geometry of the fin, the user notices less effort in obtaining thrust in comparison to the known fin configurations. This is in part due to favourable vortices created as the fin undergoes its vertical sweeps through the water and also due to the particular displacement path of the water as the fin sweeps through. The side rails may undergo fine adjustments during manufacture to 10 alter operating parameters such as its flexion, tension, pitch, geometry and/or a combination of each to alter slightly the water flow over the fm and ultimately aqua dynamics of the fin. The rails are preferably U or V shaped and reduce drag on the downward thrust but with lateral stability. Figure 6 shows a cross section taken along a line A-A through a fin according 15 to an alternative embodiment and manufactured in accordance with a method aspect of the invention. Fin 30 comprises a first inner soft layer 31 of. rubberized material which is heat fused with a second layer outer layer 32 of hard rubberized material forming moulded foot pocket 33 which receives and retains a foot of a wearer. The result is a generally hard outer layer 32 and a 20 soft inner layer 31 for foot comfort. Fin 30 further comprises lateral hard splay rails 34 and 35 which provide lateral stiffness and also contribute to improved aqua dynamics of the fin. According to au alternative embodiment, layer 35 maybe substituted with either a medium hardness or soft layer. Thus inner layer 31 is in each 25 embodiment a soft layer . Thus the fin according to two embodiments may be constructed from an inner soft layer and an outer medium hardness layer or from an inner soft layer and an outer hard layer. In the context of the invention, Outer layers will be stiffer and harder than an inner foot pocket layer. A soft layer is preferably within the range of 35 - 40 gerometers. A medium 30 layer is between 41 -60 gerometers and a hard layer is within the range of 61 -75 gerometers. 12 WO 2004/024242 PCT/AU2003/001191 Figure 7 shows a cross section of fin 10 shown in figure 3 taken across line B B with numbering corresponding to parts in figure 6. Line B-B is closer to the wide tapered end 15 of fin 30. 5 Figure 8 shows an exploded view of an assembly 40 for manufacture of a fin in accordance with an embodiment of a method aspect. Assembly 40 comprises upper mould part 41 and lower mould part 42. Mould part 41 includes a moulded recess 43 which has a moulded profile of an upper surface of a flu to 10 be made form the mould. Mould part 42 includes a moulded outstanding profile 44 which has a moulded profile of an upper surface of a fin to be made form the mould. Intermediate mould parts 41 and 42 is a foot mould 45 which allows formation of a foot pocket ( such as foot pocket 12 shown in figure 3) When-a fin is to be formed, layers forming an underside of a fin are disposed 15 underneath foot mould 45 - In figure 8 there are shown two layers 46 and 47 which will form the underside of a fin. Layer 46 is preferably a bard stiff layer and layer 47 is a soft layer as it will form a tread in a foot pocket of the fin. Abutting layer 46 is a layer 50 of a hard material overlain by a layer of soft material 51. Soft layer 51 will during compression moulding of the fin when 20 mould parts 41 and 42 are joined in opposing relationship migrate through channel 53 to form a heel strap of the fin. Layer 48 is a soft layer which forms an inside upper- layer of a foot pocket, Layer 49 is a hard compound layer and forms an outer upper surface ofthe fin. 25 Once each of the aforesaid layers are set in position compression moulding takes place which fuses layers in contact with each other until the fused rubber confonus to the shape of the profiles 43 and 44 and in conjunction with foot mould 45 forms a fin having prescribed parameters. 30 A fin manufactured in accordance with the method of the invention described herein has advantages of stiffhess and flexibility with retention of elasticity, 13 WO 2004/024242 PCT/AU2003/001191 reduced weight increased user comfort and softness and potentially improved manufacturing cycle time . The costs of materials may be reduced due to the use of Iess hard material which is typically more expensive. According to one embodiment of the method aspect, the bonding of layers may be by a 5 .combination of heat fusion and compression. The method of construction may comprise the further preliminary step of milling the rubber layers to a predetermined thickness. A preferred ( but non limiting) layer thickness would be in the region of 10 - 15mm. The layers can 10 be milled to as low as 3mm thick by running the layers through a rolling machine. Also, each layer may be of varying thicknesses It will be recognized by person skilled in the art that numerous variations and 15 modifications may be made to the invention without departing from the overall spirit and scope of the invention broadly described herein. 20 25 30 35 14