the present invention will now be described according to a preferred but non limiting embodiment and with reference to the accompanying illustrations , wherein fig1 shows a plan view of a typical known fin constructed in accordance with prior art methodology ; fig2 shows a cross sectional view of a fin constructed in accordance with the prior art . fig3 shows a plan view of a fin constructed in accordance with a preferred embodiment of the invention ; and fig4 shows s side elevation view of the fin of fig3 . fig5 shows a cross section across a line a — a as shown in fig3 according to one embodiment . fig6 shows a cross section across a line a — a as shown in fig3 according to an alternative embodiment . fig7 shows a cross section across a line b — b as shown in fig3 according to one embodiment . fig8 shows a schematic arrangement of an assembly for constructing a fin in accordance with the present invention . referring to fig1 there is shown a plan view of a typical known fin 1 constructed in accordance with prior art methodology . typically a fin of the type of fig1 is divided into key regions which relate to functionality of the fin . accordingly , fin 1 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 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 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 when used by a swimmer . fig2 shows a cross sectional view of fin 1 of fig1 taken across a line a — a constructed in accordance with the prior art . as may be seen from fig2 , fin 1 comprises a first hard rubber compound layer 7 which is heat fused with a second softer rubberized material 8 which forms a molded foot pocket 9 which receives and retains a foot of a wearer . this prior art fin is manufactured by fusing the hard layer 7 with the soft layer 8 . the result is a generally hard fin base and a soft upper wall 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 trailing end has a relatively stiff free end which displaces water each sweep of fin 1 through water . fig3 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 fig3 , as with fin 1 described with reference to fig1 is divided into three key regions which relate to functionality of the fin . accordingly , fin 10 comprises a foot pocket 12 disposed in 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 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 amount of water when used by a swimmer . fig4 shows a side elevation of the fin of fig3 with corresponding numbering . fig5 shows a cross section taken along a line a — a through fin 10 according to one embodiment and manufactured in accordance with the method aspect of the invention . as shown in fig5 , 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 molded foot pocket 19 which receives and retains a foot of a wearer . fin 10 further 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 18 for foot comfort and lateral hard regions which reinforce generally stiff but flexible splay rails 19 and 21 . 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 each 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 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 mold ( not shown ) is placed in apposition to first layer 17 to allow formation thereabout of a foot pocket in the fin formed by soft layer 18 . soft compound rubber layer 18 is disposed about the foot mold ( 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 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 molding techniques . in a preferred embodiment , the fin 10 includes splay rails 21 and 22 formed on each side , the rails comprising respectively upper edges 23 and 24 and respective recesses 25 and 26 . the layers of the fin will typically be specified according to a flow index of the rubberized 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 molding . a process for construction of the fin will be described below with reference to fig8 . the fin 10 formed by the process according to the embodiment described with reference to fig5 above has a stiff hard layer , a medium outer layer of reduced stiffness and an inner foot pocket of soft rubber . according to a preferred embodiment the fin comprises a first medium layer of a first color , a second layer of a soft rubber layer having a second color and a hard layer of a third color . preferably the colors of said layers provide an indication of the hardness or stiffness of the layers which comprise the fins . the fin may be constructed of laminated layers of the same color but it has been found convenient to employ layers of different colors 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 molding . the foot recess 19 migrates from a wide region tapering to a narrower region at its opposite end wherein the splay rails 23 and 24 are disposed so as to increase the efficiency of travel of the fin through water and the mechanical advantage to the user . the upper edge of the fin 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 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 . 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 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 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 favorable 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 alter operating parameters such as its flexion , tension , pitch , geometry and / or a combination of each to alter slightly the water flow over the fin 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 . fig6 shows a cross section taken along a line a — a through a fin according 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 molded foot pocket 33 which receives and retains a foot of a wearer . the result is a generally hard outer layer 32 and a 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 an alternative embodiment , layer 35 maybe substituted with either a medium hardness or soft layer . thus inner layer 31 is in each 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 layer is between 41 – 60 gerometers and a hard layer is within the range of 61 – 75 gerometers . fig7 shows a cross section of fin 10 shown in fig3 taken across line b — b with numbering corresponding to parts in fig6 . line b — b is closer to the wide tapered end 15 of fin 30 . fig8 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 mold part 41 and lower mold part 42 . mold part 41 includes a molded recess 43 which has a molded profile of an upper surface of a fin to be made form the mold . mold part 42 includes a molded outstanding profile 44 which has a molded profile of an upper surface of a fin to be made form the mold . intermediate mold parts 41 and 42 is a foot mold 45 which allows formation of a foot pocket ( such as foot pocket 12 shown in fig3 ). when a fin is to be formed , layers forming an underside of a fin are disposed underneath foot mold 45 . in fig8 there are shown two layers 46 and 47 which will form the underside of a fin . layer 46 is preferably a hard 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 molding of the fin when mold 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 of the fin . once each of the aforesaid layers are set in position compression molding takes place which fuses layers in contact with each other until the fused rubber conforms to the shape of the profiles 43 and 44 and in conjunction with foot mold 45 forms a fin having prescribed parameters . a fin manufactured in accordance with the method of the invention described herein has advantages of stiffness and flexibility with retention of elasticity , 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 less hard material which is typically more expensive . according to one embodiment of the method aspect , the bonding of layers may be by a 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 – 15 mm . the layers can be milled to as low as 3 mm 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 modifications may be made to the invention without departing from the overall spirit and scope of the invention broadly described herein .
a swim fin formed from laminated rubberized layers . the fin has a fin body with a foot pocket , which includes an opening to receive the foot of a wearer . a fin body includes a distal trailing region integral with the foot pocket capable of flexure upwardly , downwardly and rearwardly of the body , by action of water when the fin is in use . structure engages a heel of a user to maintain a users foot in the foot pocket . the fin includes at least one outer rubberized layer and at least one inner rubberized layer , the at least one inner layer forming the foot pocket . the fin is produced in a compression mold having first and second mold parts and a foot mold for forming the pocket .